Thierry Tron

Yasmina Mekmouche

Jalila Simaan

J ' Aimerais Aussi Remercier

Wadih Ghattas

Thomas Pino

Minh Huong

Ha Thi

Eric Katell

Amélie Anne Sandra

Anne Giulia

Cyril Et

Khaled

Clémence, Stéphanie Phillip

Yiting, Feng, Benjamin, Jully, Maria, Julien, Tania, Rajaa Antoine Linh

Gabriel Je Continuerai Ma

Axel Asma

Amanda Adama

collaboration entre plusieurs équipes de recherche, j'aimerais donc remercier

SOLEIL). Merci d'avoir accepté de juger ce travail avec bienveillance et pour vos interventions très pertinentes qui m'ont permis de mettre en valeur l'étendue de mes travaux.

Je voudrais adresser particulièrement mes

Abstract

Oxidation of hydrocarbons such as olefin epoxidation and alkane hydroxylation plays an important role in the industry for the production of drugs, materials and energy. These chemical transformations are major challenges because of the inert carbon -carbon bonds (BDE = 80-90 kcal / mol) and carbon -hydrogen bonds (BDE = 80-90 kcal / mol). In current processes, they are often carried out in a harsh and dangerous condition associated to high temperature and high pressure in the presence of a costly catalyst such as metallic salts of palladium and ruthenium which massively produces the polluting wastes. It is therefore urgent to seek a new safe and clean process. Nature shows us that these difficult reactions can be catalyzed in the mild condition thanks to metalloenzyms. These enzymatic catalysts containing an active site based on transition metal are capable of activating the sources of green oxygen atom such as dioxygen and water in order to generate a highly oxidized active metal-oxo species. This active species is an intermediate capable of effectuating the oxidation of hydrocarbons. In the context of sustainable development, cheaper and green methods for these transformations have being developed using a bio-inspired catalyst based on transition metal, in particular iron thanks to its high abundance, and support by sophisticated ligands.

In this manuscript we report the synthesis and characterization of an iron(III) complex supported by a non-innocent hemi-porphyrinic ligand, constructed with a dipyrrin fragment and two pyridine functions. This ligand was designed to combine the structural features of well-known catalyst platforms such as porphyrins and poly-nitrogen ligands. The iron(III) complexes have been prepared and characterized by a variety of spectroscopic techniques, with a focus on their electrochemical behavior and their potential use as catalysts in the activation of green oxygen source such as dioxygen and water for hydrocarbon oxidation. We found that these complexes can catalyze the oxidation of a fair variety of substrates using oxidant agent such as iodosylbenzene. Intriguingly, our gathered results point to a reactivity pattern that stems from a low-oxidation state iron species. Electron Paramagnetic Resonance and Mössbauer analyses support a high spin iron(III) reactive species. Furthermore, data from mass spectrometry and Infra-red spectroscopy supported by DFT calculations helped us to propose the chemical formulation of this chemically generated intermediate where the ligand has been reversibly oxidized . 6 Additionally, these complexes were used as catalysts in a photocatalytic system in aqueous media under aerobic condition using a photosensitizer a reversible electron acceptor to preclude the "evil necessity" of a sacrificial electron donor. [START_REF] Werck-Reichhart | Cytochromes P450 for engineering herbicide tolerance[END_REF] O isotopic labelling experiments were undertaken to confirm that the origin of oxygen atom in oxidized product is dioxygen while Laser Flash Photolysis experiments allow us to understand the reactional mechanism.

Our study provides a new paradigm to perform photoinduced oxygen atom transfer reactions with solely light as energy input and dioxygen as oxygen atom source in aqueous solution.

Résumé

L'oxydation des hydrocarbures telles que l'époxydation de l'oléfine et l'hydroxylation de l'alcane joue un rôle important dans le monde de l'industrie pour la production de Curieusement, nos résultats rassemblés suggèrent un schéma de réactivité qui découle d'une espèce de fer de bas degré d'oxydation. Les analyses de résonance paramagnétique électronique et de Mössbauer confirment l'existence d'une espèce réactive de fer (III) haut spin. De plus, les données de spectrométrie de masse et de spectroscopie infrarouge appuyées par des calculs de DFT nous ont aidés à proposer la formulation chimique de cet intermédiaire généré chimiquement où le ligand a été oxydé de manière réversible.

En outre, ces complexes ont été utilisés comme catalyseurs dans un système photocatalytique pour oxyder styrène à diol et benzadehyde à la condition aérobic dans milieux aqueux en utilisant un photosensibilisateur et un accepteur d'électron réversible permettant d'éviter le recours néfaste à un donneur d'électron sacrificiel. L'étude avec l'oxygène marqué O [START_REF] Werck-Reichhart | Cytochromes P450 for engineering herbicide tolerance[END_REF]

Oxidation reactions involving oxygen atom transfer reaction (thioether oxidation, olefin epoxidation) and hydrogen atom abstraction reaction (alkane hydroxylation) are a challenging transformation in chemical synthesis. Those reactions are often associated to expensive metals (palladium, iridium, rhodium), 1,2 toxic reagents (chromates, permanganates, organic peroxides) and generate a high amount of undesired products (moderate selectivity).

Consequently, the development of "green" and cheaper metal-based systems inspired from natural enzymes capable to catalyze such reactions is becoming more and more important in research. A wide variety of biological systems can make this challenging reaction under mild condition by activating dioxygen and forming highly oxidized active metal-oxo species that react with substrates. Especially, most natural systems contain a green abundant transition metal such as iron. The study of such systems is desirable to understand the details of biological oxygen activation and transfer, and to imitate their reactivity. It is also important to develop more sustainable methodologies.

In this chapter, we will present natural systems based on iron metal and most significant synthetic systems. Common methods used to generate and characterize high active iron-oxo will be also reported.

I.1 Enzymatic systems performing oxidation in nature

Catalytic enzymes performing oxidation reaction can be classified in two groups: hemic proteins for example cytochrome P450, and non-hemic proteins such as soluble methanemonooxygenases and  -ketoglutarate dependent hydroxylases (Table I

Soluble methanemonooxygenases Table I-1 : Selection of metalloenzymes involved in biological oxidation

I.1.1 Cytochrome P-450

Cytochrome P-450s are an important family of heme (iron porphyrin) metalloenzymes that are present in all forms of life such as bacteria, plants, yeasts, insects and mammals. These heme enzymes are mono-oxygenases capable to activate dioxygen and to incorporate oxygen atom in a wide variety of substrates under mild condition. 3 Cytochrome P-450s catalyze aromatic and aliphatic hydroxylation, olefin epoxidation and sulfoxide formation using dioxygen as oxygen source and nicotinamide adenine dinucleotide phosphate (NADPH) as reducing agent. Especially, the reactions catalyzed by cytochrome P-450s intrigue chemists because of their high selectivity. In fact, these enzymes are active enough to hydroxylate inert substrates such as cyclohexane without damaging the relatively fragile enzyme organic superstructure.

The active site of cytochrome P-450s (Figure I-1) is an iron protoporphyrin IX center coordinated to a cysteine thiolate in axial position. The last coordination site is occupied by a labile molecule such as solvent allowing the system to activate dioxygen at this position. The principal features of the mechanism of cytochrome P-450s are illustrated in Scheme I- 1. 4 The catalytic reaction starts with the binding of substrate to the enzyme leading to the release of the labile ligand, sometimes accompanied with a spin state change of the iron center.

Molecular oxygen coordinates to the reduced Fe(II) form of cytochrome P-450s obtained by the first reduction of iron(III) form by reducing agent NADPH. Then, a second one-electron reduction and protonation give the Fe(III)-hydroperoxo species. The high valent active iron(IV)-oxo porphyrin cation radical species called Compound I is obtained by protonation and heterolytic cleavage of the O-O bond. Compound I is identified and characterized in a number of heme enzymes by a variety of spectroscopic analyses such as Mössbauer spectroscopy ( = 0.05-0.14 mm/s; E Q = 0.90-1.33 mm/s characterizing a low spin (S = 1) Fe IV species), EPR spectroscopy (g  2 assigned to radical species) and Raman spectroscopy (750-790 cm -1 attributed to Fe-O vibration). [START_REF] Jung | The mystery of cytochrome P450 Compound I[END_REF] Finally, oxygen atom transfer is realized from this iron-oxo species to the bound substrate to form the oxygenated product. Some calculations suggested that the radical may reside to a greater or lesser extent on the thiolate ligand [START_REF] Green | Evidence for Sulfur-Based Radicals in Thiolate Compound I Intermediates[END_REF] or other protein residues. In any case, the iron(IV)-oxo porphyrin radical intermediate is believed to be the species responsible for the reactivity of cytochrome P-450s according to a variety of spectroscopic studies. [START_REF] Loew | Role of the Heme Active Site and Protein Environment in Structure, Spectra, and Function of the Cytochrome P450s[END_REF] 20 Scheme I-1 : Catalytic cycle for oxygen activation and transfer by cytochrome P-450s. The activation of dioxygen through the oxidative decarboxylation of  -ketoglutarate leads to the generation of the highly active iron(IV)-oxo species that hydroxylates various types of substrates such as methylated nucleotides and lipids. The consensus mechanism of the catalytic reaction shown on Figure I-3 is proposed based on spectroscopic studies of enzymes such as Clavaminate Synthase 2 and Taurine dioxygenase. [START_REF] Harlos | Structural origins of the selectivity of the trifunctional oxygenase clavaminic acid synthase[END_REF][START_REF] Ryle | Stopped-Flow Kinetic Analysis of Escherichia coli Taurine/α-Ketoglutarate Dioxygenase: Interactions with α-Ketoglutarate, Taurine, and Oxygen †[END_REF][START_REF] Zhou | Substrate Binding to the α-Ketoglutarate-Dependent Non-Heme Iron Enzyme Clavaminate Synthase 2: Coupling Mechanism of Oxidative Decarboxylation and Hydroxylation[END_REF] The first concluding spectroscopic evidence for an non-heme high spin (S = 2) iron(IV)-oxo was reported by Bollinger and Krebs in 2003 and detected in the Taurine dioxygenase using Mössbauer spectroscopy. [START_REF] Price | The First Direct Characterization of a High-Valent Iron Intermediate in the Reaction of an α-Ketoglutarate-Dependent Dioxygenase: A High-Spin Fe(IV) Complex in Taurine/α-Ketoglutarate Dioxygenase (TauD) from Escherichia coli †[END_REF] The high oxidation state of iron center was identified by an isomer shift of  = 0.31 mm/s and a quadrupolar slitting of E Q = 0.88 mm/s. Additionally, resonance Raman studies revealed a Fe-O vibration at 821 cm -1 that shifted to 787 cm -1 upon labelling with [START_REF] Werck-Reichhart | Cytochromes P450 for engineering herbicide tolerance[END_REF] O. [START_REF] Proshlyakov | Direct Detection of Oxygen Intermediates in the Non-Heme Fe Enzyme Taurine/α-Ketoglutarate Dioxygenase[END_REF] Figure I-3 : Proposed mechanism of catalytic cycle for  -ketoglutarate dependent hydroxylases.

I.1.3 Soluble methane monooxygenases

Soluble methane monooxygenases (sMMO) [START_REF] Wallar | Dioxygen Activation by Enzymes Containing Binuclear Non-Heme Iron Clusters[END_REF] found in some bacteria, have some analogy with cytochrome P-450s and  -ketoglutarate dependent hydroxylases in their ability to hydroxylate un-activated C-H bonds of methane (BDE C-H = 105kcal/mol) using dioxygen as oxygen source and NADP as reducing agent. sMMO contain dinuclear iron units in the active site, each one in a non-heme environment (Figure I-4). Unlike un mononuclear metalloenzymes, the active form of sMMO is a bis µ-oxo diiron(IV) species with a diamond core structure, which was trapped and spectroscopically characterized in catalytic reaction. [START_REF] Tinberg | Dioxygen Activation in Soluble Methane Monooxygenase[END_REF][START_REF] Banerjee | Structure of the key species in the enzymatic oxidation of methane to methanol[END_REF][START_REF] Lee | A transient intermediate of the methane monooxygenase catalytic cycle containing an FeIVFeIV cluster[END_REF] The main features of the catalytic mechanism are shown on Figure In brief, nature's enzymes can oxygenate hydrocarbon under normal pressure and temperature conditions by activating dioxygen molecule to generate high valent active iron oxo species with the help of the reducing agent (NADP) or co-factor such as  -ketoglutarate. Although natural metalloenzymes are highly efficient and selective in oxidation of hydrocarbons, the isolation of theses enzymes from plants is extremely difficult. Indeed, only in recent years have genes of cytochrome P-450s been isolated. [START_REF] Werck-Reichhart | Cytochromes P450 for engineering herbicide tolerance[END_REF] Consequently, the search for robust model systems mimicking these metalloenzymes may help to overcome the intrinsic difficulties of working with enzymes. Besides, the studies of synthetic systems as models for metalloenzymes have afforded important insights into the nature of enzymatic processes themselves.

I.2 Synthetic iron catalysts for oxidation reaction

Once the metal center chosen, chemists have to select two important parameters that will impact on the reactivity of the catalyst. The ligand permits to modulate the electronic properties and steric environment of the metal center and thereby the activation strategies. Below we will discuss these two factors.

I.2.1 Ligand design

In recent years, the development of efficient synthetic systems for oxidation reaction that mimic the catalytic metalloenzymes has attracted much attention. It is known that the main power of catalytic metalloenzymes comes from the protein environment, in particular from the structural ligand coordinating the metal center. Synthetic ligands can be also classified in two groups: biomimetic ligands and bioinspired ligands depending on their design strategy.

I.2.1.1 Biomimetic approach

A biomimetic ligand is a structural analogue exhibiting spectroscopic features close to the enzyme's factor. For example, Porphyrin, the best-know biomimetic ligand has been developed by copying the ligand core of protoporphyrin IX at the heart of Cytochrome-P450s to mimic a similar electronic density with four nitrogen coordination sites (Figure I-6). Since the first synthetic metalloporphyrin, chloro-5,10,15,20-tetraphenylphorphyriniron(III) (Fe III TPPCl), reported by Groves and co-workers in 1979 to catalyze the alkene epoxidation and alkane hydroxylation using iodosylbenzene as an oxygen donor, [START_REF] Groves | Hydroxylation and epoxidation catalyzed by iron-porphine complexes. Oxygen transfer from iodosylbenzene[END_REF] the use of metalloporphyrin as catalysts has received increasing attention during the past four decades.

Substitutions in meso and  position were operated on the next generations of metalloporphyrins which allowed enhanced efficiency in oxidation reactions (Figure I-6). One example of the influence of these distal substituents on their reactivity will be discussed in the next paragraph. One of the remarkable features of cytochrome P-450s is the presence of a thiolate ligand. This function is believed to have a strong influence on the chemistry of the heme iron complex.

Thus, synthetic models carrying a thiolate RS -moiety were developed to reveal their relative effect. In order to avoid the replacement of the thiolate ligand by any other ligand present in solution, the thiolate ligand was attached at the tetraphenylporphyrin by a "S --bridge" or a "S - -tail" (Figure I-7). [START_REF] Battersby | Model Studies on the Active Site of Cytochrome P-450: an Fell-Porphyrin carrying a Strapped Thiolate Ligand[END_REF][START_REF] Collman | Mercaptan-tail' porphyrins: synthetic analogs for the active site of cytochrome P-450[END_REF] The first iron porphyrin coordinated by an alkylthiolate anion used for catalytic oxidation was reported by Hirobe in 1990. [START_REF] Higuchi | Synthesis of a highly stable iron porphyrin coordinated by alkylthiolate anion as a model for cytochrome P-450 and its catalytic activity in oxygen-oxygen bond cleavage[END_REF] His work demonstrated that the thiolate ligand induces around 100 fold increase of the rate of oxidation of 2,4,6-tri-tert-butylphenol and 1,1-diphenyl-2-picryhydrazine compared to Fe III TPPCl, using alkyl hydroperoxides as oxidant. Indeed, the oxidation mechanism consists of several steps: the formation of an alkyl peroxide iron porphyrin, the O-O bond cleavage leading to the formation of an active ironoxo species and the reaction between iron-oxo and substrate. The oxidation rate was accelerated probably because the large electron donating alkyl thiolate enhances the cleavage of the O-O bond and stabilizes the high-valent iron-oxo. [START_REF] Dawson | Magnetic circular dichroism studies. 43. Oxidized cytochrome P-450. Magnetic circular dichroism evidence for thiolate ligation in the substrate-bound form. Implications for the catalytic mechanism[END_REF] The electron donor effect of thiolate ligand was clearly revealed by the change in the potential of Fe III /Fe II redox couples.

An important negative shift (-200 mV) for the Fe III /Fe II process compared to that of the iron porphyrin without thiolate ligand (Fe III TPPCl) was observed by cyclic voltammetry. [START_REF] Woggon | Metalloporphyrines as Active Site AnaloguesLessons from Enzymes and Enzyme Models[END_REF]

Figure I-7 : Synthetic metalloporphyrins containning a « S--bridge » ligand (left) and « S--tail » ligand (right).

Despite the promising result of Hirobe's group, development of the synthetic heme metalloporphyrins with thiolate ligand was limited by the outstanding difficulty in their synthesis because of the facile oxidation of thiolate ligand to disulfide. The presence of an electron donating thiolate ligand decreases the stability of such synthetic complex in highly oxidizing condition. [START_REF] Hessenauer-Ilicheva | Spectroscopic and Mechanistic Studies on Oxidation Reactions Catalyzed by the Functional Model SR Complex for Cytochrome P450: Influence of Oxidant, Substrate, and Solvent[END_REF] Consequently, these models were not further explored.

Alternatively, electron withdrawing groups (EWGs) were introduced in meso or  position with good improvement in reactivity of the cyclohexene oxidation as shown in Table I-2 and Figure I-8. [START_REF] Porhiel | β-Octafluoro-meso-tetraarylporphyrin iron complexes as catalysts for monooxygenation reactions[END_REF] In fact, EWGs increase the electrophilic property of Fe=O moiety that enhances the reactivity of catalysts in reaction with the electron rich nucleophiles such as alkens. On the other hand, EWGs can make the catalysts more robust against oxidation. Over the last two decades, a number of biomimetic non-heme models of metalloenzymes have been reported in order to generate an iron-oxo species able to catalyze the oxidation reaction. [START_REF] Shan | High-valent nonheme iron-oxo species in biomimetic oxidations[END_REF] In 2003, Que reported a synthetic model for  -ketoglutarate dependent hydroxylases based on a tridentate ligand Tp Ph2 (hydrotris(3,5-diphenylpyrazol-1-yl)borate)

Catalysts

Substrate

(Figure I-9) to mimic the three amino acid ligands, and an  -keto acid as the sacrificial electron donor to provide the two electrons needed to activate dioxygen. [START_REF] Mehn | Oxygen Activation by Nonheme Iron(II) Complexes: α-Keto Carboxylate versus Carboxylate[END_REF] This non-heme model is able to react with dioxygen to undergo an oxidative decarboxylation of  -keto acid and displays a versatile reactivity such as sulfide oxidation, alkene cis-hydroxylation and alkane hydroxylation. [START_REF] Paria | Reactivity of an Iron-Oxygen Oxidant Generated upon Oxidative Decarboxylation of Biomimetic Iron(II) α-Hydroxy Acid Complexes[END_REF] But in absence of any organic substrate, the intramolecular hydroxylation of the phenyl group of Tp Ph2 ligand is also observed, probably because the phenyl group is directly maintained above the iron site. Unfortunately, no intermediates could be trapped or characterized. In brief, by replicating structural aspects of biological system, the biomimetic approach can produce good oxidation catalysts capable of oxygenating alkene and alkane although their catalytic reactivity is rather moderate due to their short life-time in oxidation condition. In fact, reproducing partially some structural features of the enzyme without the complex protein environment necessarily changes the property of the active site. However, the study of biomimetic system is very helpful to understand how catalytic metalloenzymes work in nature and to find out the important aspects contributing to their amazing catalytic reactivity. Thus, the result obtained with biomimetic model provides useful insights for the development of bioinspired oxidation catalysts.

I.2.1.2 Bioinspired approach

In contrast with biomimetic approach, bioinspired strategy aims at discovering and capturing the essential idea that underpins a biological system. High-valent iron-oxo identified to be key oxidized intermediate in the mechanism of iron enzymes for a variety of oxidation reaction, is stabilized by a sophisticated proteinic structure. In chemistry, researchers make use of various coordinating functions to stabilize highly oxidized species. Electron-rich ligand having nitrogen or oxygen binding sites are the most abundantly developed .

One of the best know bioinspired system is based on tetradentate Salen ligand containing two phenol and two iminic bindings groups, leaving two coordination sites on the metal ion available for coordination of exogenous ligand and activation of terminal oxidant. These ligands are dianionic like porphyrins allowing to stabilize high valent metal centers.

Furthermore, their structure and electronic density can be easily modulated by functionalizing the substituents due to their simple preparation. Thus, reactivity and durability of Salen-based catalyst are more and more improved at each new generation. Due to similar planar and tetradentate nature of Salen, a large number of metal centers such as ruthenium, iron, manganese have been used to study the Salen-based catalysts. [START_REF] Katsuki | Some Recent Advances in Metallosalen Chemistry[END_REF][START_REF] Cozzi | Metal-Salen Schiff base complexes in catalysis: practical aspects[END_REF] The most attractive example of Salen-based catalyst is Jacobsen's, a complex with manganese as metal center associated with a chiral Salen ligand able to catalyze asymmetric epoxidation of alkenes. This catalyst is used in industrial synthesis of Indinavir, an HIV protease inhibitor (Figure I-10), [START_REF] Jacobsen | Highly enantioselective epoxidation catalysts derived from 1,2-diaminocyclohexane[END_REF] which shows that oxidation reaction catalyzed by bioinspired systems have a really great potential. Inspired by Salen ligand and the macrocyclic tetraamine ligand reported by Margerum, [START_REF] Hinz | Ligand solvation and the macrocyclic effect. Nickel(II)-tetramine complexes[END_REF] another well-known ligand family based on tetraamido macrocyclic molecule has been developed and continuously improved against oxidative degradation and hydrolysis for over forty years by the group of Collins and then Gupta. [START_REF] Collins | Designing Ligands for Oxidizing Complexes[END_REF][START_REF] Collins | TAML Oxidant Activators: A New Approach to the Activation of Hydrogen Peroxide for Environmentally Significant Problems[END_REF] TAML (TetraAmido Macrocyclic Ligands) are tetraanionic ligands providing a strong electron-donor ligand field to stabilize highly oxidized metal center. TAMLs are quite robust thanks to their geometric cyclic rigidity that prevents an intramolecular isomerization process that could lead to their degradation. [START_REF] Anson | Oxidative and hydrolytic decomposition of a polyanionic chelating ligand[END_REF] Until now, seven generations of TAMLs have been developed. [START_REF] Collins | Targeting of High-Valent Iron-TAML Activators at Hydrocarbons and Beyond[END_REF]

I.2.2 Activation strategies and mechanistic insights

I.2.2.1 Using chemical oxygen donor agents

Over the past decade, several synthetic high valent iron-oxo complexes with a wide range of ligands have been prepared by different methods. The general synthesis is carried out by oxidizing iron complex precursor by oxygen atom donor oxidant, such as iodosylbenzene (PhIO), sodium hypochlorite (NaClO), peracids (m-CPBA) and hydroperoxides (H 2 O 2 , t BuOOH). [START_REF] Que | The Road to Non-Heme Oxoferryls and Beyond †[END_REF] Among these oxidants used to generate active iron-oxo species, the two electron oxidant like PhIO, NaClO, mCPBA oxidize directly iron(II) precursor to iron(IV)-oxo species and iron(III) precursor to iron(V)-oxo or iron(IV)-oxo ligand cation radical species.

Generally, the mechanism occurs by two consecutive steps: the adduct formation followed by Alternatively, iron(IV)-oxo species could also be obtained by the decomposition of Fe III OOH by homolytic O-O bond cleavage, [START_REF] Bukowski | Catalytic Epoxidation and 1,2-Dihydroxylation of Olefins with Bispidine-Iron(II)/H2O2 Systems[END_REF] but a DFT calculation suggested this pathway was not energetically favored. [START_REF] Solomon | Non-heme iron enzymes: Contrasts to heme catalysis[END_REF] On the other hand, Que reported that the stoichiometric reaction of [Fe II (TMC)] 2+ / [Fe II (TMC-py)] 2+ with H 2 O 2 in presence of a base affords the corresponding Fe IV =O species in 90 % yield. [START_REF] Li | Near-Stoichiometric Conversion of H 2 O 2 to Fe IV =O at a Nonheme Iron(II) Center. Insights into the O-O Bond Cleavage Step[END_REF] This high conversion was obtained from only one equivalent of H 2 O 2 probably revealing the formation of iron(II) peroxo precursor followed by an heterolytic O-O bond cleavage (Figure I-16). [START_REF] Eser | Direct Spectroscopic Evidence for a High-Spin Fe(IV) Intermediate in Tyrosine Hydroxylase[END_REF] The iron(II) peroxo species formation can be questioned because iron(II) precursor is also probably oxidized by one-electron by H 2 O 2 to the iron(III) product. Other strategies using mCPBA, NaClO and PhIO as oxidant will be discussed in detail in chapter IV.

I.2.2.2 Using dioxygen as oxygen atom source

Chemical oxidants with a controlled quantity allow to properly generate active iron species in order to characterize these short-lived iron species and study the mechanistic activation in oxidation reaction. However, using environmentally friendly oxygen source is highly desirable. Dioxygen is known to be an abundant and green oxygen source that is identified as a terminal oxidant in many natural oxidation processes catalyzed by heme and non-heme metalloenzymes. Inspired from cytochrome P-450s, synthetic iron precursor can activate dioxygen and convert into an active iron-oxo species with the help of a proton source and a reducing agent such as NADPH, BNAH, cobaltocene, BH 4 -. For instance, Banse and coworkers reported clearly this promising strategy using a well-known [Fe II (TMC-py)] 2+

precursor, BPh 4 -as an electron source and HClO 4 as a proton source. [START_REF] Thibon | Proton-and Reductant-Assisted Dioxygen Activation by a Nonheme Iron(II) Complex to Form an Oxoiron(IV) Intermediate[END_REF] In presence of H + and Murray and coll first introduced the idea of electroactivation of O 2 . [START_REF] Horwitz | Electrocatalytic olefin epoxidation using manganese Schiff-base complexes and dioxygen[END_REF] The group of Dey reported in 2013 the study of dioxygen activation by iron(III) porphyrin by electrolysis coupled to resonance Raman spectroscopy is reported. [START_REF] Sengupta | Direct observation of intermediates formed during steady-state electrocatalytic O2 reduction by iron porphyrins[END_REF] Using 18 O isotopical labelling, these combined techniques allowed to directly identify the corresponding iron(III) peroxo and iron(IV) oxo intermediates involved in Fe II -O 2 adduct reduction at -0.5 V vs Ag/AgCl (Figure I-17). However, their report can also be questioned. According to their study, the Fe-O bond of the Fe IV =O species was identified by the vibration at 780 cm -1 , but the Fe-O vibration of all the heme and nonheme iron-oxo species reported until then was experimentally determined in the range of 800-850 cm -1 , as will be presented in next paragraph. The dioxygen activation can also occur by an autooxidation reaction at a synthetic catalyst.

This approach is attractive because it doesn't require electron donor. The mechanism was elucidated in 1980s. The reaction was shown to proceed through a µ-peroxo diiron(III) species, followed by an homolytic O-O bond cleavage to form an iron(IV)-oxo intermediate. [START_REF] Chin | Role of ferryl (FeO2+) complexes in oxygen atom transfer reactions. Mechanism of iron(II) porphyrin catalyzed oxygenation of triphenylphosphine[END_REF][START_REF] Balch | Oxygenation patterns for iron(II) porphyrins. Peroxo and ferryl (FeIVO) intermediates detected by proton nuclear magnetic resonance spectroscopy during the oxygenation of (tetramesitylporphyrin)iron(II)[END_REF][START_REF] Chin | Formation of porphyrin ferryl (FeO2+) complexes through the addition of nitrogen bases to peroxo-bridged iron(III) porphyrins[END_REF] The µ-peroxo diiron(III) porphyrin was trapped and shown to slowly convert to iron(IV)-oxo species at low temperature (-80 to -30 °C) by 1 H NMR and UVvisible spectroscopy. In presence of 50 eq of triphenylphosphine (PPh 3 ), Fe II TPP is thus workers reported a photoinduced oxidation of sulfides, olefins et alkanes using µ-oxo diiron(III) porphyrin as an active catalyst in aprotic solvent such as benzene and toluene. [START_REF] Pistorio | A Phototriggered Molecular Spring for Aerobic Catalytic Oxidation Reactions[END_REF][START_REF] Rosenthal | Aerobic Catalytic Photooxidation of Olefins by an Electron-Deficient Pacman Bisiron(III) μ-Oxo Porphyrin[END_REF][START_REF] Rosenthal | Photocatalytic Oxidation of Hydrocarbons by a Bis-iron(III)-μ-oxo Pacman Porphyrin Using O 2 and Visible Light[END_REF] Especially, a µ-oxo diiron(III) Pacman porphyrin was found much more reactive than the unbridged analogue probably due to the fact that dioxygen easily meets two iron centers to make µ-peroxo bond thanks to the bridged diporphyrin ligand. However, the mechanism of The nonheme synthetic complex [Fe II (TMC)(OTf) 2 ] can also activate dioxygen to convert iron(IV)-oxo species probably through µ-peroxo diiron(III) intermediate. However, its reactivity is moderate. For example, it converts PPh 3 into O=PPh 3 with a TON = 8, thioanisol into methyl phenyl sulfoxide with TON = 7 and benzyl alcohol to benzaldehyde with TON = 6. The formation of µ-oxo diiron(III) complex might be a deactivation pathway responsible for this low activity although it was never detected. Moreover, Nam and co-workers reported that the high electronic density of these iron(II) complexes exhibiting relatively low Fe III /Fe II redox potential (< -0.1 V vs Fc + /Fc) is an important factor in dioxygen activation to form iron(IV)-oxo species. [START_REF] Kim | Dioxygen Activation and Catalytic Aerobic Oxidation by a Mononuclear Nonheme Iron(II) Complex[END_REF] For this reason, other non-heme iron(II) complexes such as [Fe II (TPA)] 2+ , [Fe II (N4Py)] 2+ , [Fe II (BPMEN)] 2+ do not react with O 2 to generate iron(IV)-oxo.

The µ-oxo diiron(IV) 1-TAML ( first generation of TAML) complex firstly reported in 2004 by Collins and co-workers is also capable of oxygenating substrates. [START_REF] Ghosh | Catalytically Active μ-Oxodiiron(IV) Oxidants from Iron(III) and Dioxygen[END_REF] The formation of the µoxo diiron(IV) 1-TAML complex from iron(III) 1-TAML complex and dioxygen, proceeds probably through µ-peroxo diiron(IV) and iron(V)-oxo intermediates as in the mechanism of formation of µ-oxo diiron(III) complex previously described. This amazing behavior for an iron(III) complex toward dioxygen is probably due to the four strong electron donating amidato nitrogens allowing to stabilize to a great extent the oxidized metal. The structure of the µ-oxo bis iron(IV) was confirmed by X-Ray structure characterization. Its reactivity toward oxidation reaction is believed to come from the decomposition of the µ-oxo diiron(IV)

1-TAML complex into iron(III) and iron(V)-oxo species in presence of the substrate (Figure

I-22)
. The latter was identified and characterized as the active species. [START_REF] Sankaralingam | Selective Oxygenation of Cyclohexene by Dioxygen via an Iron(V)-Oxo Complex-Autocatalyzed Reaction[END_REF][START_REF] Singh | Mechanism of Oxygen Atom Transfer from Fe V (O) to Olefins at Room Temperature[END_REF] Thus, The µ-oxo diiron(IV) 1-TAML complex can catalytically oxidize a variety of substrates in the presence of dioxygen as oxygen atom source. Other photocatlytic strategies using a chromophore and an electron donor to photoactivate O 2 at an iron center will be discussed in detail in chapter III.

I.2.2.3 Using water as oxygen atom source

Like dioxygen, water is known as green supply of oxygen atom that is used to generate of the manganese(V)-oxo species in the natural oxidation process of Photosystem II, the enzyme responsible for water slitting, oxygen evolution and plastoquinone reduction. A number of studies of the oxygen-evolving complex in Photosystem II demonstrated that the Mn V =O species can be formed by two-electron oxidation of a water bound molecule via a protoncoupled electron transfer (PCET) mechanism (Figure I-23). [START_REF] Meyer | The Possible Role of Proton-Coupled Electron Transfer (PCET) in Water Oxidation by Photosystem II[END_REF][START_REF] Mcevoy | Water-Splitting Chemistry of Photosystem II[END_REF] In Photosystem II, the visible light activates a chromophore which in turn successively oxidizes the manganese-aqua complex to manganese-oxo species through a series of proton coupled electron transfer reaction. Various synthetic metallic systems including iron systems were developed to attempt to generate highly oxidized metal-oxo species using water as an oxygen source In similar manner, the iron(V)-oxo species [Fe V =O(TAML)] 1-was generated by oxidation of the corresponding iron(III)-aqua complex [Fe III (OH 2 )(TAML)] 1-by a strong oxidant Cerium(IV), [START_REF] Ellis | Fast Water Oxidation Using Iron[END_REF] or by light-driven activation using [Ru(bpy) 3 ] 2+ as a chromophore and Na 2 S 2 O 4 as a sacrificial electron acceptor. [START_REF] Panda | Homogeneous Photochemical Water Oxidation by Biuret-Modified Fe-TAML: Evidence of Fe V (O) Intermediate[END_REF] Another strategy consists in electroactivating the metalbound water molecule. Stahl and co-workers reported the sequential formation of [Fe IV (OH)(1-TAML)] 1-and [Fe V =O(1-TAML)] 1-species by electrochemically oxidizing [Fe III (OH 2 )(1-TAML)] 1-at increasing potential of 0.34 and 0.79 V vs Fc + /Fc, respectively and their catalytic application in electrochemical oxidation of organic molecules such as alkyl benzene, benzyl alcohol. [START_REF] Das | Electrochemical C-H oxygenation and alcohol dehydrogenation involving Fe-oxo species using water as the oxygen source[END_REF] Similarly, a series of high valent iron(IV)-oxo species based on a number of non-heme polynitrogen ligands were quantitatively generated by bulk electrolysis in acetonitrile with 0.1 to 1 M water as an oxygen source. [START_REF] Wang | Nonheme oxoiron( IV ) complexes of pentadentate N5 ligands: spectroscopy, electrochemistry, and oxidative reactivity[END_REF][START_REF] Collins | Electrochemical Generation of a Nonheme Oxoiron(IV) Complex[END_REF] The redox behavior of these iron(II) precursor studied by cyclic voltammetry in dry acetonitrile, showed only a Fe III Raman resonance spectroscopy is usually used to observe the energy of Fe=O bond vibration.

The structure of iron-oxo species can be deduced from Mass spectroscopy and precisely determined by X-Ray Diffraction although the instability of the highly active high-valent iron-oxo species often prevents their crystallization even at low temperature. The result from EXAFS study is useful to characterize the oxidation state of iron center and the ligand environment such as the Fe-O bond distance. 3, 3.9 and 2.0 resulting from a strong ferromagnetic coupling at J > + 40 cm -1 . [START_REF] Mandon | Models for peroxidase compound I: generation and spectroscopic characterization of new oxoferryl porphyrin .pi. cation radical species[END_REF] The EXAFS study of [Fe IV =O(TMP + )] + indicated a Fe=O distance of 1.6 Å corresponding to a double bond very close to that of Compound I intermediate. [START_REF] Penner-Hahn | Structural characterization of horseradish peroxidase using EXAFS spectroscopy. Evidence for Fe = O ligation in compounds I and II[END_REF] The Fe=O double bond character was confirmed by a vibration at 828 cm -1 observed in Raman study. [START_REF] Hashimoto | Observation of the FeIV=O stretching Raman band for a ferryl porphyrin .pi. cation radical[END_REF] Since then, many iron(IV)-oxo porphyrin cation radical species have been prepared with different substituent at the porphyrin core to modify the electronic properties of the active species. [START_REF] Fujii | Electronic structure and reactivity of high-valent oxo iron porphyrins[END_REF][START_REF] Costas | Selective C-H oxidation catalyzed by metalloporphyrins[END_REF] They were fully characterized and some rationalization were drawn to correlate their structure with their activity. Some of them will be discussed in the next paragraph.

It's interesting to note that a non-heme iron(III) complex based on a tridentate carbazole ligand can also lead upon oxidation by the two-electron oxidant PhIO, to an iron(IV) cation radical species capable of epoxydizing alkenes. [START_REF] Niwa | A Non-Heme Iron(III) Complex with Porphyrin-like Properties That Catalyzes Asymmetric Epoxidation[END_REF] As in porphyrin, the -conjugated system of the carbazole-based tridentate ligand was demonstrated to be essential for the generation of iron(IV) cation radical species and its catalytic reactivity. This iron(IV) cation radical species was proposed to be the active intermediate responsible for oxygenating substrates, based on the detection of an absorption band at 660 nm ( = 1.4  10 4 M -1 .cm -1 ) typically observed for iron(IV)-oxo porphyrin cation radical species, [START_REF] Bell | A Highly Reactive P450 Model Compound I[END_REF][START_REF] Groves | The mechanism of olefin epoxidation by oxoiron porphyrins. Direct observation of an intermediate[END_REF] and a sharp symmetrical EPR signal at g value of 2.0 assigned to a -cation radical in the ligand. However, the electronic structure of an iron(IV) cation radical species can be questioned. Indeed, the EPR signal observed at g = 2 is justified in the report by the absence of coupling between the Fe IV center and the -cation which is in deep constrast with what was observed with porphyrin iron-oxo species previously decribed.

A series of non-heme iron(IV)-oxo species were prepared and characterized over twenty years. The first Fe IV =O species reported in 2000 by Grapperhaus and co-workers was generated by ozonolyzing [Fe III (cyclam-acetato)(CF 3 SO 3 )] + at -80 °C in acetone/water (95/5) mixture. [START_REF] Grapperhaus | Mononuclear (Nitrido)iron(V) and (Oxo)iron(IV) Complexes via Photolysis of [(cyclamacetato)Fe III (N 3 )] + and Ozonolysis of [(cyclam-acetato)Fe III (O 3 SCF 3 )] + in Water/Acetone Mixtures ‡[END_REF] This intermediate is stable for around 30 min at -80 °C and quickly decomposes above -40 °C. The Mössbauer study revealed an iron(IV)-oxo species with S = 1 while the EPR spectrum became silent upon oxidation. However, the instability prevented characterizing the [Fe IV =O(cyclam-acetato)] + by other spectroscopic techniques.

Some years later, by using methyl substituted cyclam (TMC) with increased ligand field compared to cyclam ligand, Que succeeded in generating an iron(IV)-oxo species, stable for at least 1 month at -40 °C, from the reaction of [Fe II (TMC)(CH 3 CN)] 2+ complex with PhIO in acetonitrile. [START_REF] Rohde | Crystallographic and Spectroscopic Characterization of a Nonheme Fe(IV)=O Complex[END_REF] The relative stability of this intermediate allowed to obtain its full characterization especially by X-ray diffraction spectroscopy heme iron(IV)-oxo species were synthesized and spectroscopically characterized. [START_REF] Engelmann | Oxidation Reactions with Bioinspired Mononuclear Non-Heme Metal-Oxo Complexes[END_REF] Probably due to the unstability of iron-oxo species in high oxidation state, a few iron(V)-oxo species were prepared and characterized. Indeed, as explained in the previous literature survey, the formation of a Fe IV =O species was suggested proceeding via the degradation of a short-lived Fe V =O species. Moreover, the high oxidative power of Fe V =O species was supported by high potential value of Fe V =O/Fe IV -OH couple. [START_REF] Das | Electrochemical C-H oxygenation and alcohol dehydrogenation involving Fe-oxo species using water as the oxygen source[END_REF][START_REF] Coggins | Electrocatalytic Water Oxidation by a Monomeric Amidate-Ligated Fe(III)-Aqua Complex[END_REF] Consequently, almost Fe V =O species were generated and characterized at very low temperature (-60 to -80 °C), except [Fe V =O(b-TAML)] 1-(Table I-3). [START_REF] Oloo | Bioinspired Nonheme Iron Catalysts for C-H and C═C Bond Oxidation: Insights into the Nature of the Metal-Based Oxidants[END_REF] The first iron(V)-oxo species using a strong electron donor ligand 1-TAML was reported by

Collins in 2007. [START_REF] De Oliveira | Chemical and Spectroscopic Evidence for an FeV-Oxo Complex[END_REF] The high oxidation state of this species was confirmed by a negative isomer shift ( = -0.46 mm/s) measured by Mössbauer spectroscopy, that is more negative than those of iron(IV)-oxo species reported. The EPR signal, observed at g value of 1.99, 1.97 and 1.74, was assigned to a low spin (S = ½) species. Furthermore, the EXAFS study reavealed a Fe-O bond distance of 1.58 Å that is 0.04 to 0.10 Å shorter than those reported for iron(IV)-oxo species. All these data are consistent with a low spin iron(V)-oxo species. Among the iron(V)oxo species synthetized and characterized until now, there is no the high spin (S =3/2) iron(V)-oxo species yet, probably due to a strong field created by th electron donor ligand used to support the generation of iron(V)-oxo species. Unfortunately, no X-ray crystal structure of iron(V)-oxo species was neither reported, probably because of their high reactivity toward oxidation reaction. Interestingly, in chase the Fe=O species, other revealed that short-lived iron intermediates Fe-O-X (X = Cl, OH, O, OAc), identified as precursors of Fe=O species can be detected and characterized. Some of them, have even been identified as the active species capable of oxygenating substrates. They will be discussed in chapter IV.

I.3 Context and objective

The work presented in this manuscript started in the context of our ANR project MULTIPLET. The aim of this project was to promote clean photooxydation reactions by using a chromophore in combination with an iron catalyst and water as an oxygen source on one side, and a Laccase, an enzyme able to reduce dioxygen in water, as a sustainable electron acceptor on the other side (Scheme I-2). The feasibility of the electron transfer between the [Ru(bpy) 3 ] 2+ chromophore and the Laccase was reported by our group in 2015. [START_REF] Schneider | Visible-Light-Driven Oxidation of Organic Substrates with Dioxygen Mediated by a [Ru(bpy) 3 ] 2+ /Laccase System[END_REF] Scheme I-2 : Proposed mechanism for our clean photooxydation.

This strategy was found to be limited by the efficiency of the electron transfer to the laccase.

Nonetheless, while studying the photoactivation of the iron complex in aerobic conditions, we discovered a new paradigm that allowed us to promote photoinduced OAT reaction using O 2 as an oxygen source in the absence of sacrificial electron donor or acceptor. Meanwhile, we sought to chemically generate potent oxidizing intermediate in order to get insight in the nature of these species and reactivity schemes of this new class of iron complexes.

The system we picked for these studies is based on the previous literature survey that revealed that Fe V =O species, or their isoelectronic Fe IV =O(L  ) analogues are potent active species due to their high oxidizing properties. However, what we know of their chemistry is still limited by the paucity of artificial Fe V =O species characterized by contrast with Fe IV =O species. To bring our piece to this field we chose to use an anionic hemiporphyrinic dipyrrin-dipyridine DPy -ligand recently developed in our lab as an organic platform to coordinate Fe(III)

precursor and contain higher oxidation states.

The synthesis of two new DPy-based monomeric and a dimeric iron complexes are described in Chapter II together with their full characterization using various spectroscopic techniques such as absorption spectroscopy, HRMS, EPR and Mössbauer spectroscopy, and study of their redox properties by electrochemistry.

In Chapter III, we will present the study we led to decipher the mechanism of the photocatalytic system containing a [Ru(bpy) 3 Cl 2 ] chromophore, an iron catalyst and a reversible methylviologen chloride [(MV)Cl 2 ] as a reversible electron relay, that can promote OAT reaction with no need for sacrificial electron acceptor or donor.

Chapter IV will describe the strategies employed to chemically generate and characterize potentially active species from the Fe(III) precursors using different oxidants. The nature of these active species will be investigated and the reversible oxidation of the ligand plateform will be evidenced. We will also present the interesting catalytic activity stemming from this unusual behavior.

51

II.1 Presentation of the DPy Ligand

In the development of oxidation catalysts, we've seen in chapter I that the structure of the ligand has a predominant influence on the reactivity and the stability of the catalyst. Several different types of ligands have been used to successfully form metal-based oxidation catalyst having a promising reactivity towards oxo transfer to nucleophiles (PPh 3 , SR 2 ) and hydrocarbons. Although sometimes limited by their turnover numbers, these systems are helpful to identify and rationalize the important structural factors to develop robust and efficient catalyst. For example, the conjugated system of porphyrin ligand facilitates the modulation of the electronic property of catalyst, the four negative charges of TAML contributes largely to stabilize the highly oxidized metal-oxo intermediate, while neutral polydentate nitrogen containing ligands have been designed mainly to investigate the structure/reactivity pattern. In order to design a new ligand family able to support metal-based oxidation catalysts, the Artificial Photosynthesis Group at ICMMO we reasoned to combine structural features from different families of ligands. We targeted a dipyrrin skeleton with an aryl group in meso position to avoid auto-oxidation and two coordinating groups in -position of each pyrrolic cycle allowing to obtain a tetradentate acyclic ligand. The first ligand synthesized was DPP ligand (pentafluoroDiPyrrinPhenol) which has a pentafluorophenyl group in meso position, as in F 20 -TPP porphyrin, to enhance the stability towards oxidative conditions, and two phenolate groups in -position reminiscing that of the Salen ligand. [START_REF] El Ghachtouli | Dipyrrinphenol-Mn(iii) complex: synthesis, electrochemistry, spectroscopic characterisation and reactivity[END_REF] The manganese complex based on DPP ligand was synthetized. Although X-Ray structure showed a dimeric complex, EPR and HRMS analyses revealed a monomer in solution (Figure II-1). This complex is capable of transferring oxygen atom from PhIO to cyclooctene, but its reactivity was not to our expectations.

The next generation of this family was synthetized by replacing phenolate groups with pyridine, groups usually incorporated in poly-nitrogen ligands, to generate a monoanionic DPy ligand (pentafluoroDiPyrrinPyridine). [START_REF] Ducloiset | Monoanionic Dipyrrin-Pyridine Ligands: Synthesis, Structure and Photophysical Properties: Monoanionic Dipyrrin-Pyridine Ligands[END_REF] The pyridine groups allow to conserve the ligand structure and decrease the negative charge of ligand in order to enhance the reactivity of catalyst.

In my thesis, DPy ligand was used to prepare the corresponding iron complexes in order to investigate their catalytic properties towards oxidation reactions. Iron metal was chosen because it's abundant, non-toxic and the highly oxidized iron-oxo species are known to be an active intermediate to perform hydrocarbon oxidation. Given that iron(IV)-oxo species in octahedral geometry usually exhibit moderated reactivity compared to iron(IV)-oxo species in trigonal bipyramid geometry, [START_REF] Engelmann | Oxidation Reactions with Bioinspired Mononuclear Non-Heme Metal-Oxo Complexes[END_REF] Remarkably, the metalation was realized without the help of base. Probably upon coordination there is spontaneous deprotonation. This complex was isolated in 90% yield by precipitation with diethyl ether. The paramagnetic Fe III DPyCl 2 complex was characterized by UV-vis, ESI-HRMS, EPR & Mössbauer spectroscopies, X-Ray diffraction on single crystals. Its redox behavior was also studied towards electrochemical activation of water.

II.2.2 Characterization of Fe III DPyCl 2 complex

II.2.2.1 UV-visible Absorption spectroscopy

Like the porphyrin chromophore, DPy ligand contains a conjugated system, leading to strong absorption in the visible region. UV-vis spectrum (Figure II-4) of Fe III DPyCl 2 in acetonitrile shows four intense bands (ε = 10100; 21600; 27200 and 27700 M -1 .cm -1 ) at 666; 584; 316 and 295 nm, respectively that probably stem from ligand to ligand (π  π * ) transition given their high molar extinction coefficient. A broad band (ε = 6000 M -1 .cm -1 ) is also observed at round 440 nm that can be attributed to metal to ligand transfer (MLCT) transition. Interestingly Fe III DPyCl 2 complex absorbs differently in methanol a band at 630 nm ( 38600 M -1 cm -1 ) and a shoulder at 585 nm, probably because the axial labile sites are occupied by methanol or methanolate ligand in this case.

II.2.2.1 Structure determination in the solid state by X-Ray diffraction crystallography

Purple mono-crystals suitable for single cystal X-ray diffraction analysis were grown by slow diffusion of diethyl ether into a saturated solution of Fe III DPyCl 2 complex in acetonitrile.

Figure II-5 shows the ORTEP diagrams of the complex and Table 1 displays selected bond lengths and angles for the crystallographically determined structure. The complex contains an iron center situated in a distorted octahedral geometry. The four equatorial coordination sites are occupied by the nitrogen atoms of DPy ligand with iron-nitrogen bond lengths in typical range for a high spin complex (longer than 2.05 Å). [START_REF] Nishida | Crystal structures of low-and high-spin iron(III) complexes with quadridentate Schiff bases[END_REF][START_REF] Zang | Models for Nonheme Iron Intermediates: Structural Basis for Tuning the Spin States of Fe(TPA) Complexes[END_REF] The Fe-N1 (N pyrrol ) distance of 2.050

Å in Fe III DPyCl 2 is comparable to the Fe-N pyrrol distance found in high spin iron (III) porphyrin complexes. [START_REF] Guillemot | X-ray Crystallographic Structure of ( meso -Tetraphenylporphinato)bis(phenylphosphinic methyl ester)iron(III) Perchlorate: A New High-Spin Six-Coordinate Ferric Porphyrin[END_REF][START_REF] Mashiko | Six coordination in high-spin ferric porphyrins. A new structural type and models for aquomethemoglobin[END_REF] The Fe-N2 (N Py ) bond length of 2.235 Å is significantly longer than Fe-N Py (1.97 Å) found in other iron complex based on pyridine containing ligands such as TPA, N4Py.

Bond distances Angles

Fe-N1

Z axis

Table II-1 : Selected Bond Distances (Å) and Angles (°) for Fe III DPyCl 2 complex with estimated standard deviation's in parenthesis.

Of note, the molecules are packed head to tail which might indicate the presence of -stacking interactions in the solid state.

II.2.2.2 ESI-HRMS measurement

The structure of the complex in solid state was revealed by the above X-Ray determination.

However, its structure in solution can be modified, for example solvent molecules can replace Therefore, the structure of complex in acetonitrile was probably not changed compared to its structure in solid state with two axial chloride ligands.

II.2.2.3 EPR spectroscopy

EPR measurement was used to verify the oxidation state of iron center and characterize the ligand field. The X-band spectrum of the complex recorded at 10 K in acetonitrile showed a broad signal. Broad signals can be obtained if the frozen solution does not constitute a good "glass". We reasoned that microcrystals might form in acetonitrile due to  - stacking interactions such as evidenced in the previous section on the X-Ray structure (Figure II-6).

We thus decided to add TBAPF 6 in the acetonitrile solution of Fe III DPyCl 2 to prevent the formation of these chains of complexes by intercalation of the bulky salt and allow the formation of a good "glass". The EPR spectrum in presence of TABPF 6 showed clearly three

II.2.2.4 Mössbauer spectroscopy

The magnetic proprieties of iron complex Fe III DPyCl 2 were also assessed by Mössbauer measurement in collaboration with Dr. Geneviève Blondin from the CEA Grenoble.

Mössbauer spectra of [START_REF] Chin | Role of ferryl (FeO2+) complexes in oxygen atom transfer reactions. Mechanism of iron(II) porphyrin catalyzed oxygenation of triphenylphosphine[END_REF] Fe III DPyCl 2 in solid state (15 mg) under zero magnetic field-applied at 80 K showed a doublet that could be fitted with an isomer shift of δ = 0.46 mm.s -1 and quadrupolar splitting of ∆E Q = 0.7 mm.s -1 . While, Mössbauer spectra of [START_REF] Balch | Oxygenation patterns for iron(II) porphyrins. Peroxo and ferryl (FeIVO) intermediates detected by proton nuclear magnetic resonance spectroscopy during the oxygenation of (tetramesitylporphyrin)iron(II)[END_REF]

II.2.3 Electrochemical study

The electrochemical behavior of Fe III DPyCl 2 complex was evaluated by cyclic voltammetry The shape of this voltammogram led us to investigate more deeply the redox behavior of this complex to reveal its catalytic potential towards reductive and oxidative process.

II.2.3.1 Electroactivity in reduction

The first one-electron reduction process at -0.04 V was assigned to the Fe III /Fe II couple. The iron(II) complex obtained by reducing the Fe III DPyCl 2 complex by one electron at -0.

64

Although the second reduction probably takes place at the ligand, the reversibility of two reduction waves reveals that the Fe III DPyCl 2 complex could be used as an electrocatalyst for proton or carbon dioxide reduction. Indeed, the reduction behavior of Fe III DPyCl 2 was similar to that of the iron porphyrin complex Fe III TPPCl which exhibits an interesting reactivity in dioxide carbon reduction (Figure II-16). Although CO 2 reduction was not the heart of this thesis project, our group is interested in this field. Therefore, we decided to investigate on the ability of Fe III DPyCl 2 to promote electrocatalytic reduction of carbon dioxide. Given the high solubility of CO 2 in DMF, this solvent was chosen for the study. As performed. Optimization of the potential applied during the electrolysis was not explored either, but it can be expected that a better selectivity could be achieved at lower potential. In brief, Fe III DPyCl 2 was able to reduce both proton and carbon dioxide to form dihydrogen and carbon monoxide, respectively. As DPy ligand is an active redox ligand in reduction, our results point that the first reduction was centered at iron center to form [Fe II DPy] + ,while the second and thirst reduction are probably centered at the DPy ligand to form [Fe II (DPy)] 1- species such as suggested in the case of iron porphyrin.

II.2.3.2 Electroactivity upon oxidation

To understand the nature of the two irreversible oxidation waves of Fe III DPyCl 2, the redox ), but as mentioned before, iron coordinated-chloride can also be oxidized at a higher potential due to a decreased electronic density upon coordination. To distinguish between these 2 possibilities, EPR spectroscopy was used to monitor the electrolysis of a Fe III DPyCl 2 solution at 1.45 V. A signal with g value at 4.3 corresponding to a rhombic high spin iron(III) species together with a signal pointing at g value at 2.00 assigned to a probable radical species were detected. Of note the initial EPR signal disappeared (Figure II-20). The radical signal is very broad probably because the organic radical is partially delocalized on the iron center. This signal could also be attributed to an Fe(V) species, that usually exhibits a set of signal around g = 2. [START_REF] De Oliveira | Chemical and Spectroscopic Evidence for an FeV-Oxo Complex[END_REF][START_REF] Lyakin | EPR Spectroscopic Trapping of the Active Species of Nonheme Iron-Catalyzed Oxidation[END_REF][START_REF] Lyakin | 1 H and 2 H NMR, and Reactivity Studies of the Iron-Oxygen Intermediates in Bioinspired Catalyst Systems[END_REF][START_REF] Lyakin | Asymmetric Epoxidations with H 2 O 2 on Fe and Mn Aminopyridine Catalysts: Probing the Nature of Active Species by Combined Electron Paramagnetic Resonance and Enantioselectivity Study[END_REF][START_REF] Lyakin | EPR detection of Fe(V)=O active species in nonheme iron-catalyzed oxidations[END_REF][START_REF] Van Heuvelen | One-electron oxidation of an oxoiron(IV) complex to form an [O═Fe V ═NR] + center[END_REF] Iron IV formation cannot be ruled out since this species would be EPR silent. Oxidation of an Fe-bound chloride into the EPR silent chlorine and a new Fe(III) species can however explain the presence of the signal at 4.3 Consequently, both the ligand, one coordinated-chloride and the iron center could be oxidized The above electrochemical study demonstrated that the Fe III DPyCl 2 complex is based on a non-innocent ligand and the electrochemical oxidation of this complex in absence of oxygen source can generate a mixture of oxidized species. However, a highly oxidized iron-oxo species may be electrochemically generated in presence of water as oxygen source, as explained in paragraph I.2.2.3. [START_REF] Das | Electrochemical C-H oxygenation and alcohol dehydrogenation involving Fe-oxo species using water as the oxygen source[END_REF][START_REF] Wang | Nonheme oxoiron( IV ) complexes of pentadentate N5 ligands: spectroscopy, electrochemistry, and oxidative reactivity[END_REF][START_REF] Collins | Electrochemical Generation of a Nonheme Oxoiron(IV) Complex[END_REF] For this reason, the redox behavior of Fe III DPyCl 2 complex was also studied in acetonitrile in presence of water (Figure II-22). The CV showed a positive-shift of Fe III /Fe II couple attesting partial chloride replacement by aqua ligand occurs at axial coordination sites. Indeed, the iron(III)-aqua complex [Fe III DPy(OH 2 ) 2 ] 2+ with two positive charges would be more easily reduced than the neutral Fe III DPyCl 2 complex. Of note, the reduced wave at -0.72 V was not shifted by addition of water, suggesting that the reduction taking place at the ligand was not affected by change of axial coordination. We also tried to detect highly oxidized species such an Fe V =O by EPR measurement Therefore, we can propose that a highly oxidized iron(V)-oxo species can be electrochemically generated at 1.53 V by activation of a water molecule at the iron complex.

Indeed, this kind of electrocatalytic water oxidation was reported by Meyer using an iron(III) complex based on dpaq ligand (dpaq = 2-[bis(pyridine-2-ylmethyl)]amino-N-quinolin-8-ylacetamido) in propylene carbonate solution upon addition of water. [START_REF] Coggins | Electrocatalytic Water Oxidation by a Monomeric Amidate-Ligated Fe(III)-Aqua Complex[END_REF] The water oxidation mechanism using iron catalyst was proposed on the basis of the mechanism earlier proposed for a series of Ru polypyridyl catalyst, 109,110 and is depicted in Fe III DPyCl 2 complex was synthetized and characterized with various spectroscopic analyses.

Electrochemical study revealed an interesting use of this complex in electrocatalytic reaction.

However, the Fe-Cl bond which is rather stable, probably slow down the formation of Fe-OH 2 and Fe-O 2 species required to activate water or dioxygen for oxidation reaction. We thus decided to replace it with a more labile ligand such as triflate by using ferrous triflate Fe(OTf) 2 as iron salt precursor. Triflate being a weaker electron donor ligand than chloride, it should also enhance the electrophilicity of iron complex.

II.3.1 Synthesis & characterization

II.3.1.2 Structure determination in the solid state by X-Ray diffraction crystallographie

Purple monocrystals previously obtained were analyzed by X-Ray diffraction analysis Resolution of the X-Ray diffraction structure revealed the formation of a µ-oxo diiron(III) dimer instead of a bistriflate monomer. This result was not unexpected and possible mechanism explaining the dimer formation will be discussed in paragraph II. 3

.2. Figure II-30

shows the ORTEP diagrams of complex and Table 2 display selected bond lengths and angles for the crystallographically determined structures. Fe-O1-Fe (-x;-y;-z) 180

electroneutrality. The Fe-N bond lengths and the N-Fe-N angles are rather similar to that of This  - stacking distance between two plans is 3.542 Å that is close the distance of 3.35 Å known for graphite sheets. 111 This interligand  - stacking interaction participate to stabilize the µ-oxo bridged diiron complex, [112][113][114] resulting to the short bridging Fe-O bonds and Fe-Fe distance which probably revealed a strong antiferromagnetic coupling between two iron center predicting a silent EPR spectrum.

II.3.1.3 ESI-HRMS measurement

The ESI-HRMS analysis of a dissolved crystals in acetonitrile confirmed the dimeric nature of the complex in solution. Two peaks were detected; one a peak at m/z = 527. However, this observation revealed the fragility of the Fe-O bond and suggests our diiron complex could be used as a catalyst able to trap and transfer an oxygen atom from dioxygen to a substrate, by generating the active high oxidized iron(IV)-oxo species through an autoactivation or photo-activation strategy such as presented in paragraph I.2.2.2.

II.3.1.4 Electrochemical study

In acetonitrile, the triflate ligands are expected to be displaced by solvent molecule.

Accordingly, the Fe III /Fe II oxidation wave is shifted to a higher potential at 0.7 V compared to In presence of water, the Fe III /Fe II oxidation wave was shifted to 0.38 V while two reduction waves were observed at 0.12 V and -0.

II.3.2 Dimer to monomer interconversion

The mechanism of the formation of µ-oxo dimeric iron complex can be envisioned to proceed as mentioned in the well-developed iron porphyrin literature. 115,116 It would starts with the initial coordination of O 2 to Fe II complex to afford an superoxo Fe III -OO  species. The

81

However, the formation of diiron(III) complex (Fe III DPy) 2 O(OTf) 2 was also observed by using Fe III (OTf) 3 precursor. In this case, the dimerization would probably proceed via the formation of an iron(III) hydroxo complex, due to water traces in solution, then followed by formation of hydroxo-bridged ferric dimer Fe III -(OH)-Fe III that would release a µ-oxo diiron(III) complex upon deprotonation (Figure II-36). 117,118 Alternatively a bis-µ-hydroxo dimer could be formed and lead to the µ-oxo dimer by condensation. 119 These two pathways indicate how the monomer can be converted into a µ-oxo-dimer.

Additionally, HRMS analysis of dimer revealed the Fe-O can be activated under certain conditions such as high temperature. Therefore, the dimer to monomer transformation was studied by using different conditions to understand how to activate Fe-O bond.

II.3.2.1 Dimer to monomer conversion upon ligand exchange

In an attempt to crystallize dimer with triflate axial ligand instead of ethanol, the dimer solution in non-coordinating chloroform was slowly evaporated at 30 °C. Interestingly, the X-Ray diffraction analysis of the single crystals obtained showed a monomer iron(III) complex with two triflates ligands occupying the axial positions instead of a dimer. The Fe-O bond was probably cleaved by heating at 30 °C and the dimer was transformed to a more stable bis(trisflate) monomer form in absence of water or coordinating solvent.

II.3.2.2 Reversible µ-oxo-bridge cleavage by acid and base addition

The µ-oxo-bridge of (Fe III DPy) 2 O(OTf) 2 can be reversibly cleaved with acid (HX) to afford either the corresponding anion-bound (Fe-X) or solvent-bound (Fe-MeCN) product or Fe-OH complex. In the following study, triflic acid was used so as to keep the same counter anion (triflate). Therefore, the monomer obtained could be the Fe-MeCN or Fe-OH complex because triflate is a weak ligand compared to acetonitrile and hydroxy coordinating groups.

Indeed, the electrochemical study of the dimer (Fe III DPy) 2 O(OTf) 2 in acetonitrile revealed that the axial positions on iron coordination were occupied by the solvent molecules and not by triflate ions.

The color change was observed within 10 min by adding 1 eq triflic acid into a solution of the dimeric µ-oxo-bridged complex in acetonitrile at room temperature. This is illustrated in the electronic absorption spectrum shown This dimer-to-monomer transformation was optimal upon addition of 1eq of acid per dimer.

This indicates that the dimer to monomer transformation proceeds via the protonation of the µ-oxo bridged diiron complex followed by water coordination and condensation (Figure

II-36).

II.4 Conclusion

The synthesis of iron(III) complex based on DPy ligand was realized by using two different iron salt precursors. A monomeric Fe III DPyCl 2 complex was obtained with chloride iron salt while using triflate iron salt led to the formation of a dimer, the µ-oxo bridged diiron(III) were electrochemically studied to understand their redox properties before using in catalytic reaction. The EPR analysis of the solutions obtained by oxidizing and reducing complex by electrolysis allowed to characterize the oxidized and reduced species, then to determine if the locus of oxidation and reduction takes place at the iron center or the ligand. The EPR spectra evidenced that the first reduction occurs at the metal center to form iron(II) complex and the second is probably centered at the non-innocent DPy ligand. While, the oxidation processes occurring at very close potentials, probably concerned the DPy ligand but iron center and chloride could also be oxidize. However, iron center seemed be oxidized to a putative iron(V)-oxo species in presence of water as a proton source. In the next chapter, {[{Fe III DPy(EtOH)} 2 O](OTf) 2 } dimer with a fragile Fe-O bond will be used in the study of a photocatalytic oxidation using O 2 as oxygen source. In the following, the well-defined monomer Fe III DPyCl 2 will be used as catalyst to perform oxidation using chemical oxidation.

III.1 State of the art

Dioxygen is an abundant molecule and the true green oxidant which serves as the main supplier of the oxygen atom in the biosynthesis of essential organic molecules. Although the thermodynamics behind these chemical reactions are favorable, kinetic limitation come from the fundamental paramagnetic state of dioxygen. This limitation can be lifted off when dioxygen is partnered with paramagnetic species or excited triplet states that can undergo single electron transfer reactions. Chemists have taken inspiration from biology to develop metal complexes that can bind and activate dioxygen in presence of co-reductants thereby the active metal-oxo species. 120 Photoactivating dioxygen at a metal complex through light-induced electron transfer is an even more desirable target. In 2013, Aukauloo and Mahy reported a synthetic diiron(III) These two classical approaches need a sacrificial electron donor to drive photo-induced reactions. But precluding these necessary "evil" molecules in photocatalytic processes is an urgent issues because they can interfere in the activation pathway and also limit the implementation of these chemical oxidation transformations. 123 In a very different approach, Mühldorf and Wolf more recently reported a dual catalytic system containing riboflavin tetraacetate (RFT) and [Fe II (TPA)(MeCN) 2 ](ClO 4 ) 2 complex that efficiently catalyze photooxygenation of various challenging substrates using dioxygen as oxygen source and with no need for a sacrificial electron donor. 124 RFT, which is a synthetic flavin analogue is known to be a non-toxic photocatalyst in the aerobic oxidation of alkanes and benzyl alcohol through a radical processes generating hydrogen peroxide as a byproduct. 125,126 The latter reacts with iron(II) complex to generate the active iron-oxo species itself capable of substrate oxidation. These tandem reactions are believed to be the key for high efficiency of this bi-catalytic system (Figure III-3). Indeed, in absence of iron catalyst hydrogen peroxide is a major drawback of photocatalytic RFT system because it degrades RFT upon irradiation. In this chapter, we interrogate a counter intuitive approach for the light-driven reductive activation of dioxygen by using [Ru(bpy) 3 ]Cl 2 hereby shorthanded as [Ru II ], as a photosensitizer and MV 2+ a reversible electron acceptor to preclude the use of sacrificial electron donor in aqueous solution. This work has been submitted to publication by our group simultaneously to the writing of this manuscript, therefore some explanations and scheme have been used as a slightly modified in this chapter.

III.2 Photocatalytic systems using iron(III) DPy catalyst

To explore this reactivity, we chose [(Fe III DPy Additionally, its oxidized products can be easily detected and quantified by 1 H NMR (see detail in the experimental section).

The photosensitizer and catalyst were introduced in equimolar amounts (30 µM) while the electron mediate (4 mM) and the substrate (10 mM) were added in excess after testing different condition. Excitation of the photosensitizer  abs (max) = 450 nm was performed with the combination of a white LED ( 1.3 mW.cm -1 ) and a filter (T=0 for  < 415 nm).

III. We then performed a series of control experiments ( That was confirmed by the reaction of sodium styrene-4-sulfonate with excess of potassium superoxide (1000 eq) in B&R buffer pH 4, in which no oxidized product was detected.

III.2.2.2 Study of subsystem [Ru II ] + [MV 2+ ] + O 2

In a subsequent blank experiment (Table III- Interestingly, in a deaerated solution and in presence of the olefin, we found that the recovery of the [Ru II ] is faster than the lifetime of [MV + ] (Figure III-9, blue and green). This observation can be assigned to the oxidation of the alkene by [Ru III ] through an intermolecular electron transfer process to form an alkenyl radical cation (Scheme 5, step 4). [START_REF] Schneider | Visible-Light-Driven Oxidation of Organic Substrates with Dioxygen Mediated by a [Ru(bpy) 3 ] 2+ /Laccase System[END_REF] The bimolecular rates can be obtained from the regeneration time of the [Ru II ] photosensitizer at 450 nm in argon-saturated solution (Scheme 5, k 4 = 8*10 4 M -1 s -1 ). The chemical oxidation of the alkene by [Ru III ] complex was performed and confirmed by the EPR detection of an organic radical (Figure III-10) which brings further support for this reaction pathway. Indeed, the EPR signal observed at g = 2.002 appears as a doublet, the shape of which can be related to a previously described styrenyl radical cation. 142 In this parent intermediate, the highest hyperfine coupling constant (with -hydrogens) was found of 1.1 mT, which is very close to the splitting of 1.5 mT measured in our case, while weaker hyperfine coupling were found with and aromatic protons (0.2 to 0.3 mT) which are probably not well resolved in our case. In presence of O 2 , the electronic absorption signature of the (DPy)Fe II can still be detected

A

Wavelength / nm

III.2.2.4 Proposed mechanism for the full system

Scheme 7 illustrates the different events occurring after excitation of the photosensitizer leading to the formation of the two main oxidized products, which are the diol and benzaldehyde. Importantly, our global photocatalytic cycle is in sharp contrast with the classical photoactivation scheme, inasmuch as there is no intervention of a sacrificial electron donor (SED). Traditionally, the function of the SED serves to aliment the photocatalytic process with electrons for the activation of O 2 . 123 The first photoinduced sequence relies on the oxidative quenching of the photosensitizer to form the highly oxidizing [Ru III ] and the powerful reductant MV + (step 1). Laser Flash Photolysis experiments supported by the redox , that can further reacts with the olefin to form the epoxide product. 156 Furthermore, the minor iron(III)-peroxo species protonated to iron(III)-hydroperoxo species followed by a O-O bond cleavage to form ironoxo species transferring oxygen atom to olefin to form epoxide product that is stable at pH 6 solution (eq. 3 in Scheme 8).

III.2.2.6 Limiting step in the proposed mechanism

Based on our proposed mechanism, oxidation of the substrate by the [Ru III ] (step 4) is probably the limiting step in the light-induced electron transfer processes because its rate is 10000 times slower than the back-electron transfer rate between the oxidized photosensitizer and superoxide (step 7) or iron (II) complex (step 8). Accordingly, the photocatalytic reaction rate can be accelerated by playing with substrate concentration (Table III When the photocatalytic run was realized in presence of a mixture of [START_REF] Werck-Reichhart | Cytochromes P450 for engineering herbicide tolerance[END_REF] O 2 and 16 O 2 in H 2 [START_REF] Banerjee | Structure of the key species in the enzymatic oxidation of methane to methanol[END_REF] O, the cis-diol with two inserted [START_REF] Werck-Reichhart | Cytochromes P450 for engineering herbicide tolerance[END_REF] O atoms was detected in the HRMS together with the [START_REF] Werck-Reichhart | Cytochromes P450 for engineering herbicide tolerance[END_REF] O molecule (Scheme 8, eq. 3). The lack of the cis-diol with two inserted [START_REF] Werck-Reichhart | Cytochromes P450 for engineering herbicide tolerance[END_REF] O atoms in this experimental condition confirmed that the origin of oxygen atom in oxidized product is dioxygen. hacman porphyrin where no sacrificial electron donor was present. [START_REF] Pistorio | A Phototriggered Molecular Spring for Aerobic Catalytic Oxidation Reactions[END_REF]161

III.3 Photosystem using iron(II) catalyst

The above results demonstrated that a reversible electron acceptor, methyl-viologen, can act as electron shuttle to oxidatively quench the photosensitizer, [Ru(bpy) 3 ] 2+ , generating the highly oxidized chromophore and the powerful reductant methyl-viologen radical [MV + ].

[MV + ] can then reduce an iron(III) catalyst to the iron(II) form and concomitantly O 2 to O 2 in an aqueous medium to generate an active iron(III)-(hydro)peroxo species responsible for oxygenating substrates. The formation of reduced iron(II) complex by the reaction of iron(III) complex and MV + is likely the most important step in photoproduction of iron(III)-(hydro)peroxo species. However, we have evidenced that formation of the Fe(II) was in competition with the reduction of O 2 . Therefore, we reasoned to study a photocatalytic system using an already reduced and stable iron(II) complex with another set of ligand, the well characterized in organic solvents. [163][164][165][166] Unfortunately, no characterization of these active species was reported in aqueous media to our knowledge.

III.3.1 Reactivity

The mixture of [Ru II ], S, [L 5 Fe II ] 2+ and O 2 was irradiated in absence of MV 2+ and no oxidized product was detected. As in the case of [(Fe III DPy) 2 O](OTf) 2 complex, the absence of any oxidized products under such condition corroborates with the lack of photocatalytic activity of the [L 5 Fe II ] 2+ complex in aerobic aqueous medium through a dimer µ-peroxo diiron(III)

species Fe III -OO-Fe III obtained by the reaction of [L 5 Fe II ] 2+ complex with O 2 then followed by the homolytic O-O cleavage to form the active Fe IV =O species. [START_REF] Kim | Dioxygen Activation and Catalytic Aerobic Oxidation by a Mononuclear Nonheme Iron(II) Complex[END_REF]115,116 Upon light irradiation of an aqueous mixture of [Ru II ], S, [L 5 Fe II ] 2+ and MV 2+ under aerobic condition two oxidized products were detected. As seen previously, both the diol and the benzaldehyde derivatives were characterized at pH 4 or the benzaldehyde and the epoxide at pH 6. An overall TOF comparable with that of the above photo-system using [(Fe III DPy) 2 O](OTf) 2 complex as catalyst was calculated (Table III

III.3.3 Characterization of the active iron species

To verify this hypothesis, we decided to monitor the reaction of [L 5 Fe II ] 2+ catalyst and 1.5 eq. This experiment, that will be reproduced in presence of 10 % glycerol to avoid the formation of ice, will be helpful to identify the photo-generated iron species. 147 In aqueous medium, the initial [L 5 Fe II ] 3+ is mainly in the Fe II -OH 2 form so the oxidation wave was observed at E P,A = 0.25.

III.4 Conclusion & Perspective

The study we present here provides a new paradigm to perform photoinduced oxygen atom transfer reactions with solely light as energy input and O 2 as oxygen atom source in aqueous solution, without the "evil necessity" of a sacrificial electron donor. An introspection of the photocatalytic cycle points to the crucial role of the reversible charge carrier methyl-viologen to produce O 2 -and reduce an iron(III) complex to iron(II) complex in utilization of [Fe III DPy) 2 O] 2+ dimer as a pre-catalyst. Further reaction between iron(II) complex and O 2

-

generates the activated Fe III -(hydro)peroxo as the archetypal OAT reactive species.

Meanwhile, the oxidized photosensitizer is reset to its resting state through oxidation of the olefin substrate to produce an alkenyl radical cation. The latter and the olefin can react with the active catalytic species to form oxygenated products.

Using [Fe II L 5 ] 2+ complex as a pre-catalyst, the active Fe III -(hydro)peroxo species was generated by reducing the combination of [Fe II L 5 ] 2+ and O 2 with the powerful reductant [MV + ] with two possible mechanisms. Dioxygen is reduced under its free form or at the iron center leading to the generation of the Fe III -(hydro)peroxo species. An important experimental fact comes from the observation that the benzaldehyde product is the main product when the photocatalytic run is performed at pH 6. Since the benzaldehyde product is obtained by reaction of the alkenyl radical cation with the Fe III -peroxo species Fe III -OO -, while the diol product was formed by oxidizing olefin with an Fe V =O species, itself evolving from Fe IIIhydroperoxo species Fe III -OOH. We can propose that at pH 6 the protonation of the Fe IIIperoxo species is less favoured, leading to the selective benzaldehyde formation.

The photocatalytic activity of the [(Fe III DPy) 2 O](OTf) 2 complex through homolytic Fe-O cleavage to form the active Fe IV =O species is probably deactivated in aqueous medium.

However preliminary study in aerated acetonitrile for 15 h revealed that the oxidation of PPh 3

to O=PPh 3 was accelerated in presence of [(Fe III DPy) 2 O](OTf) 2 dimer as pre-catalyst upon light irradiation ( > 550 nm)(Table III [Fe III (tpena)(OIPh)] could be inactive and play the role of a labile reservoir for the active iron(V)-oxo species or could be an active oxidant transferring oxygen atom to the substrate in a concerted mechanism. 182 The comparison of the decay time of [Fe III (tpena)(OIPh)] 2+ species in absence and presence of one equivalent of thioanisole as a substrate supports the latter hypothesis that the [Fe III (tpena)(OIPh)] 2+ species is able to oxidize the substrate. 183 The presence of 1 eq. of thioanisole led to a 260-fold acceleration of the decay time of the [Fe III (tpena)(OIPh)] 2+ species, while the substrate oxidation rate increased with thioanisole concentration. The authors propose that given that the Fe V =O species was not detected, then if it were the active species it would have reacted instantaneously Therefore no substrate concentration dependence would be observed. Henceforth, the [Fe III (tpena)(OIPh)] 2+ species was postulated as the active species. One could ask if the nature of the active species can depend on the the nature of the ligand. In fact, in 2014 Nam and co-workers came back on their initial mechanistic proposal in the case of a nonheme ligand. They demonstrated that the reaction rate of oxidation of substrates such as thioanisole, cumene, by [(13-TMC)Fe III -OI C 6 F 5 ] 3+ was not influenced by the addition of C 6 F 5 I. 184 If the iron-oxo species was the only active oxidant capable of oxygenating substrate, then the presence of an excess amount of iodoarene should decrease the oxidation rate.

Therefrom, the iron-iodosylarene adduct was proposed to be as the oxidizing agent. However, this hypothesis was based on the assumption that an equilibrium between the ironiodosylarene porphyrin adduct and the iron-oxo cation radical porphyrin exists although while no evidence for this equilibrium was reported with nonheme iron complex was reported.

Furthermore, when [(13-TMC)Fe II ] 2+ was used in combination with the chiral iodosylarene These degraded products, which were isolated and characterized by X-Ray diffraction analysis were proposed to be the products of the aromatic hydroxylation and the Noxygenation by a Fe V =O moiety. Of note, no observation of the Fe V =O species was reported. The multiple active oxidant mechanism possibly involving the low oxidation state iron species have challenged the hypothesis that the highly oxidized iron-oxo species are the only species responsible for iron-catalyzed OAT reaction. Indeed, the nature of the active species depends on both the ligand set and the oxidant. Therefore, further attempts to understand the nature of active species responsible for substrate oxygenation by a given system is indispensable to enhance the reactivity of synthetic catalysts. In this chapter, we will report the generation and characterization of new active iron species using different oxidant and study their reactivity in organic medium. Because the µ-oxo diiron(III) [(Fe III DPy) 2 O](OTf) 2 probably converts to monomer iron(III) complex before reacting with oxidant agent, 181,183,189 we used the well-defined monomer Fe III DPyCl 2 in this study.

IV.2 Chemical oxidation of Fe III DPyCl 2 and evidence of a reversible ligand oxidation

The oxidation of the iron(III) complex to form active species was studied by using oxygenated chemical oxidants. Three oxidants were tested: iodosylbenzene (PhIO), sodium hypochlorite (NaClO) and meta-chloroperbenzoic acid (mCPBA). These reagents are all known to allow the formation of highly oxidized iron-oxo species or an active low-oxidationstate iron intermediates. Our strategy was first to seek the conditions allowing us to well characterize the oxidized form of [Fe III DPy] 2+ complex and then to evaluate its reactivity.

IV.2.1 Oxidation with m-CPBA

The reaction of Fe III DPyCl 2 with an excess of m-CPBA (10 eq) in acetonitrile at room temperature leads to the disappearance of all absorption bands characterizing Fe III The reactional mixture of Fe III DPyCl 2 and 10 eq m-CPBA was stirred for 1 min and frozen in liquid nitrogen before EPR studied. The X-band EPR spectrum at 10 K showed a signal at g = Similarly, the reaction mixture of Fe III DPy(OMe) 2 complex with 10 eq m-CPBA in MeOH after mixing for 1 min was frozen and analyzed by EPR spectroscopy. The EPR spectrum at 10 K also showed a signal with g value at 4. We then attempted to displace the chloride ligand with less donating triflate ( -OTf) ligands.

As already described in Chapter II, this strategy indeed lead to the formation of a dimeric.

IV.2.2 Oxidation with NaClO

Next, we decided to generate and characterize the oxidized forms of Fe III DPyCl 2 complex using NaClO which is also a two-electron oxidant agent as mCPBA.

IV.2.2.1 Characterization of the generated iron species

IV.2.2.1.1 UV-visible spectroscopy

Upon addition of 2 eq. of NaClO in water to the initial blue solution of Fe III DPyCl 2 precursor, a quick color change to cyan followed by a slow evolution to blue over 30 min was observed.

Accordingly, the UV-vis spectroscopy showed the quick apparition of a new band at 631 nm with an extinction molar coefficient of 30 700 M -1 cm -1 assigned to an active iron species. This . 192,193 Unfortunately, upon addition of [START_REF] Werck-Reichhart | Cytochromes P450 for engineering herbicide tolerance[END_REF] O labelled water, the bands sensitive to [START_REF] Werck-Reichhart | Cytochromes P450 for engineering herbicide tolerance[END_REF] O labelling could not be clearly evidenced due to too many changes in the whole spectrum.

IV.2.2.2 Studying the reactivity of the N-oxide iron(III) species

Upon addition of 2 eq PPh 3 into the solution of the intermediate generated, the UV-vis spectrum of the precursor was recovered, suggesting that the detected iron intermediate is able These experiments were repeated with 4-MePhSMe as a substrate. When added in excess amount, similar results were obtained. When stoichiometric amount was used the reaction was slower but allowed the observation of isosbestic points at 603 and 657 nm (Figure IV-28).

Again, HRMS confirmed the formation of the corresponding sulfoxide.

IV.2.2.3 Catalytic tests

The catalytic activity of Fe III DPyCl 2 was evaluated in presence of 1000 eq. of substrate and 1000 eq NaClO in deuteriated acetonitrile at room temperature. After 5 min, the oxidized products O=PPh 3 and 4-Me(SO)PhMe were respectively quantified by [START_REF] Cozzi | Metal-Salen Schiff base complexes in catalysis: practical aspects[END_REF] Interestingly, this [Fe III (DPyN Py O)Cl 2 ] iron species is able to oxidize substrates such as PPh 3 and thioanisole and allow the initial iron precursor to be recovered after transferring the oxygen atom to the substrates. However, NaClO is a non-innocent oxidant that led to the formation of non-desired iron species such as [Fe III (Cl-DPy)] + and [Fe III (Cl-DPyNO)] + . We thus decided to further investigate the oxidation of the Fe III DPyCl 2 complex with the classical oxidant, Iodosylarene.

IV.2.3 Oxidation with iodosylarenes

Iodosylbenzene (PhIO) is an efficient terminal oxidant for the generation of active metal species such as metal-oxo species and metal-iodosylbenzene adduct. Unlike NaClO is it not basic and does not react alone with modest substrates such as PPh 3 . However, its weak solubility in non protic solvent can prevent a good control of its reactivity.

IV.2.3.1 Characterization of generated iron species

IV.2.

IV.2.3.1.2 EPR spectroscopy

The magnetic properties of the intermediate were also characterized by X-band EPR at 10K.

The initial rhombic signal of the iron(III) precursor was replaced by a broad isotropic signal at irreversible degradation pathway by aromatic hydroxylation has been reported by others, 189,194 and cannot be considered as active for oxygen atom transfer reaction. In order to check this hypothesis, ESI-HRMS analysis was performed on the reactional mixture left to evolve a few hours. To our satisfaction, peaks assigned to the actives species at It is thus difficult to affirm that such a species is quantitatively accumulated under our condition. Meanwhile the Fe-Cl bonds are bent away by 10° from their original axial position. The calculated frequencies associated with this geometry allowed evidencing two vibration modes involving the O atom at 852 and 1233 cm -1 that were isotopically shifted to higher energies).

These results nicely reproduce the trends observed experimentally. The oxidation of DPy ligand to form [Fe III (DPyNO)] 2+ species is not a negative point in catalytic oxidation compared to other systems, as reported by McKenzie. 189 The initial iron(III) precursor could be recovered after transferring oxygen atom to substrate, encouraging for further investigation in improving their catalytic activity. For example, an optimized temperature can accelerate the oxidation rate.

In the context of the ANR project MULTIPLET, this thesis focused on the study of new oxidation catalysts for clean photooxidation transformations. Inspired by the highly oxidized iron-oxo species involved in natural oxidative processes, we sought to generate an active iron(V)-oxo species. To this end, we chose, as a precatalyst, an iron(III) complex based on an anionic hemiporphyrinic dipyrrin-dipyridine DPy ligand, recently developed in our lab (Chapter II). This DPy ligand was designed to combine the structural features of well-known catalyst platforms such as porphyrins and poly-nitrogen ligands. The Fe III DPyCl 2 complex was synthetized and characterized by a variety of spectroscopic techniques. X-Ray diffraction on single crystal revealed that the structure of this complex in the solid state is in a distorted octahedral geometry with four coordinated nitrogen in equatorial position and two chloride in axial position. An identical formula was found in solution as confirmed by HRMS. The EPR and Mössbauer spectroscopy indicated the high spin character of the iron(III) center and suggested that at least two iron(III) complexes with very close geometries coexist. Based on the structural parameters measured by X-ray diffraction and DFT calculation, the hemilability of one pyridine arm is proposed to lead to different conformers of the complex in solution.

The electrochemical study of Fe III DPyCl 2 coupled to EPR analysis revealed that the ligand is redox non-innocent. For instance, the locus of the first reduction is at the iron(III) center while the second concerns the DPy ligand. A preliminary study showed that as hemic catalysts, the Fe III DPyCl 2 complex is capable of reducing CO 2 to CO at -1.7 V vs SCE, albeit with a modest selectivity compared to the competitive proton reduction. Towards oxidation, several processes were found to occur at very close potentials, and we were not able to clearly distinguish them. However, they allow the formation of a highly oxidized species able to promote water oxidation at 1.5 V vs SCE.

To enhance the reactivity of this first complex, we synthetized a second iron(III) complex with triflate as weaker electron donor ligands in place of chloride. However, the formation of a µ-oxo diiron(III) complex was obtained instead of the monomer. As a perspective of this work we could envision to explore the next generation of ligand.

Preliminary study on a ligand bearing methyl benzimidazole groups instead of pyridines groups indeedrevealed a promising reactivity. The reaction of the Fe III BIMCl 2 complex with NaClO led to the formation of an iron intermediate characterized at 670 nm, reminisced to that obtained with the Fe III DPyCl 2 complex. This iron intermediate reacts with the stoichiometric amount of 4-MePhSMe within 3 min compared to 30 min in the case of the Fe III DPyCl 2 complex. Moreover, based on UV-visible spectroscopy, the initial iron(III)

precursor is fully recovered. However, one could ask if the oxygen atom can be inserted in the Fe-N BIM bonds. Such a new reactivity pattern will be further investigated in the group.

Led Lamp used for photocatalytic experiments

High performance gas chromatography

The performance gas chromatography experiments (HPGC) were performed on a GC-2010 system from Shimadzu with a Zebron ZB Semi-Volatiles column (25 m, 0.25 mm, 0.25 mm).

The Shimadzu GC software is used to perform analyses.

Laser Flash Photolysis

Samples were prepared in 1 cm quartz cuvettes. Transient absorption and emission measurements were recorded on an Edinburgh Instruments LP920 flash photolysis spectrometer. Laser excitation pulses were generated from a Continuum Surelite OPO laser (5 ns pulses duration, typical energy 10 mJ per flash) for excitation at 460 nm. The probe source is a pulsed 450 W Xenon lamp and the detectors are either a Hamamatsu photomultiplier tube (PMT) or a water cooled Andor intensified charge coupled device (ICCD) camera.

Infra-Red spectrometry

Infra-red spectra were recorded on an attenuated total reflectance-infrared (ATR-IR) Thermo-Nicolet 6700 FTIR spectrometer, equipped with a mercury-cadmium-telluride (MCT) detector. 5 µL of the sample solution (1 mM) was dropped onto the diamond prism of ATR-IR. The solvent was allowed to evaporate in a stream of nitrogen gas until a dry film is deposited. 200 sample scans were recorded with a resolution of 4 cm -1 , recorded for the range of 4000 cm -1 to 500 cm -1 with a speed of 1.8988 kHz and aperture of 10 mm.

Resonance Raman spectrometry

rRaman spectra were measured on a home-made Raman spectrometer at 532 nm excitation wavelength, the spectrum being acquired with a fiber spectrometer coupled to a CCD camera (IsoPlane SCT 320 mounted with a PIXIS, using a 1800 lines grating; Princeton Inst.). An interferential filter was used to cut the elastic scattering. The spectral resolution was set to 6 cm -1 . The laser power was adjusted to about 1-2 mW on the sample to avoid laser damage.

The sample was deposited onto a quartz plate by dropping the sample solution (4 mM) then evaporate solvent under a stream of nitrogen. and (N-Boc-2-pyrrolyl)boronic acid (5.00 g, 23.6 mmol, 1 equiv.) were added under Argon.

Experimental procedures

The mixture was stirred in 20 min. K 2 CO 3 (10.00 g, 0.24 mol, 10 equiv.) was then added, and the reactional mixture was stirred vigorously and heated at 107 °C for 2 h. After cooling to room temperature, solvents were evaporated. The obtained solid was dissolved in 200 mL ethyl acetate then extracted with 200 mL K 2 CO 3 1 M (3 times). The organic phase was dried with Na 2 SO 4 then filtered and concentrated. 2-(N-Boc-1H-pyrrol-2-yl)pyridine as a yellow oil was purified by column chromatography on silica gel (petroleum ether/ethyl acetate, 9:1) to yield 1 as a yellow oil (3.9 g, 68%). 1 H NMR (CDCl3, 250 MHz): δ = 1.36 (s, 9 H, CH 3 ), 6.25 (t, J = 3.3 Hz, 1 H), 6.42 (dd, J = 3. (MeOH): 624 nm (ɛ = 23000 M -1 .cm -1 ), 588 nm (ɛ = 32000 M -1 .cm -1 ), 317 nm (ɛ = 32000 M - 1 .cm -1 ).

[Ru(bpy) 3 ](PF 6 ) 3 : 195 [Ru(bpy) 3 ]Cl 2 (60 mg, 0.08 mmol, 1.00 eq) was diluted in aq. H 2 SO 4 (3 mL, 7 M) then MnO 2 (9 mg, 0.10 mol, 1.25 eq) was added. The mixture was mixed for 1 hours at room temperature in the dark. A green precipitate was formed after the addition of saturated KPF 6 (2.5 mL). After filtration and washing with cold water, the product was obtained as a green solid (69 mg, 0.07 mmol, 85 %). Unfortunately, they were disordered so badly that it could not be modeled even with The central O1 atom is located at the crystallographic inversion center. The crystal data collection and refinement parameters are given in The crystal data collection and refinement parameters are given in Quantification of photo-oxidized products by 1 NMR 10 % deuterium oxide was added in the samples after irradiation to be used as a reference. Oxidizing the Fe III DPyCl 2 complex by PhIO 10 eq. of solid PhIO (1.1 mg) was added into 10 mL solution of 50 µM Fe III DPyCl 2 complex under air atmosphere and at room temperature. The reaction mixture was sonicated for 10 s, then the insoluble PhIO was filtered by a syringe filter.

  médicament, de matériaux et d'énergie. Ces transformations chimiques sont des grands défis à cause de liaison inerte de carbone -carbone (BDE = 80-90 kcal/mol) et de carbonehydrogene (BDE = 80-90 kcal/mol). Dans les procédés actuels, elles sont souvent réalisées dans une condition dure et dangereuse liée à haute température et haute pression en présense d'un catalyseur coûteux comme des sels métalliques de palladium et ruthénium qui produit massivement le déchet polluant. Il est alors urgent de chercher un nouveau procédé doux et propre. La nature nous montre que ces difficiles réactions peuvent être catalysées à la condition douce grâce aux métalloenzyms. Ces catalyseurs enzymatiques contenant un site actif à base de métal de transition sont capables d'activer les sources d'atome d'oxygène verte comme le dioxygène et l'eau afin de générer une espèce active métal-oxo en de haut degré d'oxydation. Cette espèce est un intermédiaire capable d'effectuer l'oxydation des hydrocarbures. Au contexte de développement durable, des méthodes moins onéreux, moins dangereux et non polluant pour ces transformations sont en cours développées en utilisant d'un catalyseur bio-inspirée à base de métal de transition, en particulière de fer grâce à son abondant, et de support des ligands sophistiqués. Dans ce manuscrit, nous rapportons la synthèse et la caractérisation d'un complexe de fer (III) supporté par un ligand hémi-porphyrinique non innocent, construit avec un fragment dipyrrine et deux fonctions pyridines. Ce ligand est désigné de se combiner les caractères structuraux des familles de ligand connus tels que le porphyrine et le ligand poly-azoté neutre utilisés très courant pour le catalyseur bio-inspiré d'oxydation d'hydrocarbure. Les complexes de fer (III) ont été préparés et caractérisés par plusieurs techniques spectroscopiques, en mettant l'accent sur leur comportement électrochimique et leur utilisation potentielle en tant que catalyseurs pouvant achiver des sources d'oxygène vertes telles que le dioxygène et l'eau en vue d'oxyder des hydrocarbures. Nous avons constaté que ces complexes peuvent catalyser l'oxydation d'une grande variété de substrats en utilisant un agent oxydant tel que l'iodosylbenzène.

Figure I- 1 :

 1 Figure I-1 : Iron protoporphyrin IX active site of cytochromes P-450s, X: labile ligand.

I. 1 . 2 

 12 -ketoglutarate dependent hydroxylases Iron(II)  -ketoglutarate dependent hydroxylases are mononuclear non-heme metalloenzymes capable to catalyze an amazing diversity of hydroxylation reactions using the ketoglutarate co-substrate. These enzymes possess an active site that contains one iron center bound to three water molecules and three amino acid side chains (Figure I-2).

Figure I- 2 :

 2 Figure I-2 : Active site of  -ketoglutarate dependent hydroxylases (left) and  -ketoglutarate (right)

Figure I- 4 :

 4 Figure I-4 : Dinuclear iron active site in sMMO : (left) reduced form, (right) oxidized form.

I- 5 .

 5 Dioxygen is activated by both metals to give a peroxo bridge between two iron(III) centers. Then, homolytic O-O bond cleavage leads to the generation of an active bis-µ-oxo diiron(IV) that can react with methane.

Figure I- 5 :

 5 Figure I-5 : Proposed mechanism for methanol conversion using sMMO.

Figure I- 6 :

 6 Figure I-6 : Porphyrin core used for synthetic porphyrin ligand and formula of metalloporphyrin of the first generation used in model system of Cytochrome P450s.

Figure I- 8 :

 8 Figure I-8 : Structure of iron(III) porphyrins with electron withdrawing group in meso and  position.

Figure I- 9 :

 9 Figure I-9 : Synthetic model for  -ketoglutarate dependent iron enzymes.

Figure I- 10 :

 10 Figure I-10 : Jacobsen'catalyst used for asymmetric epoxidation in Industrial synthesis of Indinavir.

  Figure I-11 : Operationally stable, highly active iron(V)-oxo supported by b-TAML and their reactivity toward cyclohexane oxidation.

Figure I- 12 :

 12 Figure I-12 : Examples of poly-nitrogen neutral ligands.

  oxygen atom transfer triggered by heterolytic O-X bond cleavage (Figure I-14).

Figure I- 14 :

 14 Figure I-14 : Proposed mechanism for the iron-oxo species formation using a two-electron oxidant.

Figure I- 15 :

 15 Figure I-15 : Proposed mechanism for generation of an iron(V)-oxo species from iron(II) precursor using H 2 O 2

Figure I- 16 :

 16 Figure I-16 : Proposed mechanism for the base-catalyzed formation of iron(IV)-oxo from iron(II) precursor and H 2 O 2

BPh 4 -,

 4 dioxygen is reductively activated at iron(II) center, yielding a iron(III) superoxo species that converts into a Fe III OOH intermediate which ultimately decomposes into the iron(IV)-oxo species by O-O bond cleavage (Figure I-17). The O-O cleavage can be an homolytic process or an heterolytic process followed by a fast decomposition to afford iron(IV)-oxo species as previously observed with H 2 O 2 in presence of acid. The [Fe IV =O(TMC-py)] 2+ species generated in the study was fully characterized by a variety of spectroscopic analyses, especially by X-Ray diffraction on single crystal.

Figure I- 17 :

 17 Figure I-17 : Proposed dioxygen activation mechanism using [Fe II (TMC-Py)] 2+ .

Figure I- 18 :

 18 Figure I-18 : Proposed mechanism for electro-reductive dioxygen activation and the Raman bands of each detected species.

Figure I- 19 :

 19 Figure I-19 : Proposed reductive activation mechanism of O 2 at [Fe II (TPEN)] 2+ based on modelisation of experimental CVs.

  capable of transferring oxygen atom to PPh 3 , forming O=PPh 3 in 27 successful turnover numbers (TON) before inactivation occurs (Figure I-20).[START_REF] Chin | Role of ferryl (FeO2+) complexes in oxygen atom transfer reactions. Mechanism of iron(II) porphyrin catalyzed oxygenation of triphenylphosphine[END_REF] The deactivation is caused by the formation of inactive µ-oxo diiron(III) porphyrin identified in solution at the end of catalytic reaction.

Figure I- 20 :

 20 Figure I-20 : Proposed mechanism for dioxygen activation by iron porphyrin complex

  µ-oxo diiron(III) Pacman porphyrin formation from dioxygen and diiron(II) Pacman porphyrin is not clarified yet (Figure I-21).

Figure I- 21 :

 21 Figure I-21 : Photocycle of the catalytic oxidation of substrates by µ-oxo diiron(III) Pacman porphyrin using dioxygen without need for an external coreductant.

Figure I- 22 :

 22 Figure I-22 : Proposed mechanism for the oxygenation of substrates by dioxygen catalyzed by iron(III) TAML complex in the presence of O 2 .

Figure I- 23 :

 23 Figure I-23 : Formation of Mn V =O species in PCET mechanism using water as an oxygen source.

Figure I- 24 :

 24 Figure I-24 : Formation of [Fe IV =O(N 4 Py)] 2+ by water chemical activation using Cerium(IV) (left) as an oxidant or by water photoactivation using a chromophore and a sacrificial electron donor (right).

Figure I- 25 :

 25 Figure I-25 : Structure of selected iron-oxo species with their ORTEP plot of their X-ray diffraction analysis when performed.

Figure II- 1 :

 1 Figure II-1 : X-Ray structure of [Mn III (DPy)] 2 complex.

II. 2 . 1

 21 Figure II-2: Scheme of the synthesis of the iron (III) complex Fe III DPyCl 2 The preparation of DPy ligand was developed by Dr. Clemence Ducloiset in our team. 95 The Fe III DPyCl 2 complex was isolated after metalation of DPy ligand and iron(III) chloride in methanol at room temperature (Figure II-2). The following synthetic tactics was used, a solution of DPy ligand was added dropwise into the solution of iron (III) chloride to avoid two ligands to coordinate on one iron center. Upon mixing, the solution turned immediately blue, revealing that the metalation was effective. The reaction was monitored by UV-visible spectroscopy shown in Figure II-3 to ensure that the complexation was complete.

Figure II- 3 :

 3 Figure II-3 : UV-vis spectral changes during metalation of DPy ligand (black) with FeCl 3 (red) inMeOH.

Figure II- 4 :

 4 Figure II-4 : UV-vis spectrum of Fe III DPyCl 2 in acetonitrile (blue) and in methanol (red).

( 2 .

 2 285 and 2.315 Å). -The considerable lengthening of the Fe-Cl bonds can be ascribed to the mutual trans influence of the chloride ligand. These axial Fe-Cl bonds are deviated from the z axis by about 13.98°. The C-C and C-N bond distances are very homogenous over the ligand backbone which indicates a strong delocalization of the electron density over the whole skeleton.

Figure II- 5 :

 5 Figure II-5 : ORTEP representation of X-Ray structure of Fe III DPyCl 2 complex. Thermal ellipsoids are shown at 30 % level of probability. Hydrogen atoms and solvent molecules are omitted for clarity. Symmetry code: (i) x-y+2/3, -y+4/3, -z+5/6.

Figure II- 6 :

 6 Figure II-6 : Fe III DPyCl 2 chain observed by X-Ray diffraction.

  labile chloride ligands. The ESI-HRMS analysis of a Fe III DPyCl 2 solution in acetonitrile showed a prominent peak at m/z = 553.9995 with charge and isotopic distribution assigned to the monochloride [Fe III DPyCl] + complex (Figure II-7). A second prominent peak at m/z = 611.9583 was attributed to the sodium adduct [(Fe III DPyCl 2 )(Na)] + . No peak corresponding to a complex with coordinated acetonitrile molecule [Fe III DPy(MeCN) 1-2 ] 2+ was observed.

Figure II- 7 :

 7 Figure II-7: ESI+-HRMS spectrum of the Fe III DPyCl 2 solution in acetonitrile. Inset: comparison of experimental and theoretical peak for the isotopic distributions.

intense signals at g = 9 . 1 , 5 . 1 , 3 . 7

 915137 and a broad weak signal at g value around 2 which are in good agreement with a d 5 iron center in a rhombic environment (Figure II-8). The effective g value could be described when considering a S = 5/2 high spin with E/D = 0.2 rhombicity. This description predicts g ≈ 5.1, 3.7, 3.4 for the | ± 3/2> doublet excited state and g ≈ 9.1, 59 2.0, 1.2 for the | ± 1/2> doublet ground state. However, a series of EPR spectra recorded at different temperatures revealed that the intensity of the signals at g = 5.1 and 3.7 changed in the same trend with the signal at g = 9.1 (Figure II-9, left), and thus cannot belong to two different Kramers doublets of a same species but rather to 2 different species. We thus attempted to simulate the EPR spectrum on the basis of 2 sets of signals (Figure II-9, right). The effective g values could be fitted with a mixture in ratio 1:1 of two high spin (S = 5/2) iron(III) species in 0.2 rhombicity probably corresponding to our Fe III DPyCl 2 in two different geometries. The first set is characterized by three signals at g = 5.1, 3.7 and 2.0 while the second one is characterized by three signals at g = 9.1, 4.2 and 3.

Figure II- 8 :

 8 Figure II-8 : (Left) EPR spectrum of Fe III DPyCl 2 (1 mM) in acetonitrile in absence (red) and in presence (black) of TBAPF 6 (0.1 mM) at 10 K after subtraction of cavity signal. (Left) Rhombogram for an S = 5/2 system.

Figure II- 9 :

 9 Figure II-9 : (Left) EPR spectrum of Fe III DPyCl 2 (1 mM) in acetonitrile in absence at different temperature after subtraction of cavity signal. (Right) Simulation of EPR spectrum based on the experimental signals.

  Fe III DPyCl 2 in frozen acetonitrile solution (2 mL) showed a single broad doublet that was tentatively fitted with an isomer shift of δ = 0.45 mm.s -1 and quadrupolar splitting of ∆E Q = 0.54 mm.s -1 . These parameters fall within the expected range for a high spin (S = 5/2) iron (III) compound (Figure II-10). The abnormal width of doublet was probably due to the present of different sites of close geometries, as stated before by the formation of complex chains mentioned.

Figure II- 10 :

 10 Figure II-10 : Zero-field Mössbauer spectra at 80 K of 56 Fe III DPyCl 2 in solid state (15 mg) (left) and 57 Fe III DPyCl 2 in a frozen acetonitrile solution (2 mM) (right) with their simulation.

  and differential pulse voltammetry at a glassy carbon electrode in argon-degassed acetonitrile containing 0.1 M of tetra-N-butylammonium hexafluorophosphate as electrolyte using platinum wire as auxiliary electrode and saturated calomel reference electrode. The voltammograms are illustrated in Figure II-11. The cyclic voltammogram (CV) shows two reversible cathodic waves at -0.04 V (E p = 80 mV) and -0.72 V (E p = 80 mV) vs SCE and two irreversible anodic waves at 1.32 V and 1.53 V.

Figure II- 11 :

 11 Figure II-11 : Cyclic voltammetry at v = 100 mV/s (black: reduction direction, red: oxidation direction) of 1 mM Fe III DPyCl 2 in acetonitrile.

  4 V vs SCE was confirmed by the recording of a silent EPR spectrum at 10 K (FigureII-12). The second reduction process occurs at the same potential as the reduction of the free ligand and the d[START_REF] Ryle | Stopped-Flow Kinetic Analysis of Escherichia coli Taurine/α-Ketoglutarate Dioxygenase: Interactions with α-Ketoglutarate, Taurine, and Oxygen †[END_REF] Zn complex, which suggests that in this case, the reduction may take place at the ligand rather than at the metal center (Figure II-13). To investigate on the electronic nature of the doubly reduced form, we performed a second electrolysis at -1.2 V. Unfortunately, attempts to electrochemically reduce Fe III DPyCl 2 at -1.2 V in acetonitrile led to the formation of a dark precipitate. EPR of the suspension only revealed the presence of a weak signal at g = 2.00 (FigureII-12), the intensity of which could be explained by the degradation of the species upon the time-scale of the experiment. A weak signal at g = 4.3 was also observed, corresponding probably to reoxidized iron(III) product upon sample preparation.

Figure II- 12 :

 12 Figure II-12: EPR spectra at 10 K of a Fe III DPyCl 2 solution (black) and after controlled potential electrolysis at -0.4 V (red) and -1.2 V (blue) vs SCE in acetonitrile at 10 K.

Figure II- 13 :

 13 Figure II-13 : Cyclic voltammograms of 1 mM DPy ligand (blue), 1 mM ZnDPyCl (red) and 1 mM Fe III DPyCl 2 (black) measured in acetonitrile.

Figure II- 14 :

 14 Figure II-14 : Proposed mechanism for carbon dioxide reduction electro-catalyzed by Fe III TPPCl.

Fe

  III TPPCl needs to be reduced by three one-electron processes to yield a formally form iron(0) species capable to reduce carbon dioxide by two-electron to form carbon monoxide and water in presence of proton source (Figure II-14). 106,107 The presence of a hydrogen source such as water, methanol, trifluoroethanol (TFE) is highly important to diminish the cost of carbon dioxide reduction (Figure II-15).

Figure II- 15 :

 15 Figure II-15 : Standard electrochemical potentials for CO 2reduction. 108

Figure II- 16 :

 16 Figure II-16 : Cyclic voltammograms of 1 mM Fe III TPPCl (black) and Fe III DPyCl 2 (red) measured in DMF.

Fe

  III TPPCl, Fe III DPyCl 2 presented in its CV a 3 nd reduction wave at a more positive value of -1.4 V vs SCE. Next, TFE (trifluoroethanol) was added as a proton source. The CV of Fe III DPyCl 2 complex in DMF with 4 M TFE under argon atmosphere showed a catalytic wave at -1.8 V that was attributed to hydrogen reduction (Figure II-17). When the CV was performed under CO 2 atmosphere, a catalytic wave at a more positive potential of -1.3 V was detected, indicating CO 2 reduction by the Fe III DPyCl 2 complex. The CO 2 reduction was observed at the 3 nd reduction wave of the Fe III DPyCl 2 complex, supporting the fact that the formally reduced [Fe 0 (DPy)] was responsible for CO 2 reduction.To identify the products obtained from CO 2 reduction, a controlled potential electrolysis was run at -1.6 V in CO 2 saturated solution of 1 mM Fe III DPyCl 2 as catalyst for 2 h with 4 M TFE as proton source. Bubbles were observed at the electrode surface. The gases contained in the headspace were regularly analyzed by HPGC. Carbon monoxide CO was detected to be a product from carbon dioxide reduction especially at the begging of the electrolysis (Figure II-18). However, the main gas detected was dihydrogen. The low Faradaic efficiency around 40 % might indicate that other products may have formed in solution such as formate which cannot be detected by HPGC. No further analysis of soluble reduced forms of CO 2 was

Figure II- 17 :

 17 Figure II-17 : Cyclic voltammograms of 1 mM Fe III DPyCl 2 (black) in presence of TFE (4 mM) in saturated argon solution in DMF (red) and in saturated carbon dioxide solution in DMF (blue).

Figure II- 18 :

 18 Figure II-18 : CO, H 2 evolution traces and the corresponding faradaic efficiency in the bulk electrolysis of a Fe III DPyCl 2 (0.5 mM) solution in DMF containing 0.1M TBAPF 6 at -1.7 V vs SCE under CO 2 atmosphere.

  behavior of DPy ligand complex was studied in acetonitrile. The non-innocent DPy ligand shows two irreversible oxidations at 1.21 V and 1.36 V while the Fe III DPyCl 2 complex shows two irreversible oxidation waves at 1.32 V and1.53 V (Figure II-19). The presence of the metal center decreases the electronic density at the ligand and makes its oxidation more difficult. Thus, the two oxidation waves of the ligand coordinated to the iron center can be positively shifted to 1.32 V and 1.53 V. However, the current amplitude observed by CV for the first oxidation at1.32 V is two times more important that the one observed for the oneelectron reduction of Fe III to Fe II , suggesting that the first oxidation is a multi-electron process(Figure II-11). Additionally, DPV of Fe III DPyCl 2 complex revealed that the current amplitude of oxidation wave at 1.32 was 3 times that at1.53 V (Figure II-19). Therefore, the first oxidation at1.32 V was not only assigned to the one electron of the oxidation ligand but also probably to iron or chloride oxidation. Measuring the cyclic voltammetry of tetra-N-butylammonium ([Bu 4 N]Cl) shows that free chloride ions are oxidized at 1.05 V (Figure II-19

Figure II- 19 :

 19 Figure II-19 : Cyclic voltammetry at v = 100 mV/s of [Bu 4 N]Cl (green), 1 mM DPy ligand (blue), 1 mM Fe III DPyCl2 (red) and Differential pulse voltammetry with step potential of 5 mV and intergration time of 1 s of Fe III DPyCl 2 (black) in acetonitrile.

at 1 .

 1 45 V. A sum up of the different possibilities is given in Figure II-21.

Figure II- 20 :

 20 Figure II-20 : EPR spectra of Fe III DPyCl 2 (black)and oxidized species (red) obtained by oxidizing Fe III DPyCl 2 1.45 V vs SCE in acetonitrile at 10 K.

Figure II- 21 :

 21 Figure II-21 :Proposition of the oxidized species obtained by electrolyzing at 1.45 V.

Figure II- 22

 22 Figure II-22 : (Left) Cyclic voltammograms of 1 mM Fe III DPyCl 2 measured in acetonitrile (black) in presence of 0.5 M (red) and 1 M water (blue), scan towards negative potentials; (Right) Cyclic voltammograms measured in acetonitrile with 1 M water in presence (blue) and in absence (orange)of Fe III DPyCl 2 and CV of Fe III DPyCl 2 in absence of water (black), scan towards positive potentials.

Figure II- 23 :

 23 Figure II-23 : Current evolution during controlled potential electrolysis on a glassy carbon at 1.7 V vs SCE with (black) and without (red) 1 mM Fe III DPyCl 2 complex in acetonitrile in presence of 2 M water.

  . The EPR spectrum of a solution obtained by electrolyzing Fe III DPyCl 2 (1 mM) at 1.6 V in wet acetonitrile showed a broad signal with g value at 2.00 that could probably be attributed, as already mentioned to a low spin Fe V =O or a Fe IV =O(DPy) species (Figure II-24).

Figure II- 24

 24 FigureII-24 : : EPR spectra at 10 K of 1 mM Fe III DPyCl 2 (black) and oxidized species obtained by oxidizing Fe III DPyCl2 at1.6 V vs SCE in wet acetonitrile (blue).

  Figure II-25. In this mechanism, it was found that the rate-limiting step is the O-O bond formation, occurring by reaction of the Fe V =O species with H 2 O. Accordingly, the current amplitude of catalytic wave varies with iron catalyst concentration and water concentration following the rate law given in equation 1 and the expression for the catalytic current (i cat ) expressed in equation 2.

Figure II- 25

 25 Figure II-25 :(Left) Proposed mechanism for electrocatalytic water oxidation using iron(III) catalyst. (Right) the rate low and catalytic current equations.

Figure II- 26 :

 26 Figure II-26 : Cyclic voltammograms of 1 mM Fe III DPyCl 2 measured in acetonitrile (black) in presence of 0.5 M (red), 1 M (blue), 2 M (green) and 3 M (purple) water. Scan towards positive potentials. Inset: Plot of catalytic current at 1.53 V versus water concentration.

Figure II- 27 :

 27 Figure II-27 : Cyclic voltammograms measured in acetonitrile with 2 M water of 0.05 mM (black), 0.1 mM (red), 0.3 mM (blue), 0.5 mM (green), 0.7 mM (purple) and 1 mM (yellow) Fe III DPyCl 2 . Scan towards positive potentials. Inset: Plot of catalytic current at 1.53 V versus the Fe III DPyCl 2 concentration.

  Iron(II) triflate reacted quickly with DPy ligand in methanol under argon in glove box. The instant color change from red to blue confirmed the formation of iron(II) DPy intermediate, which was then oxidized to Fe III complex upon exposure to air as attested by a color change to cyan (Figure II-28). The iron(III) complex was obtained by evaporating methanol and was recrystallized by slowly diffusing pentane into a saturated solution in ethanol (85% yield).

Figure II- 28 :

 28 Figure II-28 : UV-visible spectra of Fe II (DPy)(OTf) under argon (blue) after exposure to air (red).

4 II. 3 . 1 . 1

 4311 Absorption spectroscopyThe new UV-vis spectrum (FigureII-29) shows four intense bands (ε = 23700; 30500; and 34500 M -1 .cm -1 ) at 616; 588; 319 and 295 nm, respectively that correspond probably to π-π * charge transfer transitions within the ligand as in Fe III DPyCl 2 . A broad band (ε = M -1 .cm -1 ) observed at around 420 nm is attributed to metal to ligand charge transfer (MLCT).

Figure II- 29 :

 29 Figure II-29 : UV-vis spectrum of [Fe III (DPy)](OTf) 2 (red) and Fe III DPyCl 2 (black)in acetonitrile.

Figure II- 30 :

 30 Figure II-30 : An ORTEP drawing of compound complex {[Fe III DPy(EtOH)] 2 O}(OTf) 2 . Thermal ellipsoids are shown at the 30% level of probability. (symmetry codes: (i) -x, -y, -z).

Fe

  III DPyCl 2 complex. The bridging Fe-O bond distances (1.77 Å) are within the range of typical diiron µ-oxo distances. The structure of {[Fe III DPy(EtOH)] 2 O}(OTf) 2 is characterized by a linear Fe-O-Fe angle of 180 °. Consequently, two planar ligands are quite parallel to each other, leading to a stong  - stacking interaction between the two parallel rings of ligand.

  0278 which was attributed to [(Fe III DPy) 2 O] 2+ ion and second at m/z = 519.0329 which was assigned to [Fe II DPy] + ion (Figure II-31). No peak corresponding to complex with acetonitrile or triflate adduct was observed.

Figure II- 31 :

 31 Figure II-31 : ESI + -HRMS spectrum of the [(Fe III DPy) 2 O(OTf) 2 ] solution in acetonitrile. Inset: comparing experimental and theoretical peaks for the isotopic distribution.

Figure II- 32 :

 32 Figure II-32 : Formation of iron(II) complex from diiron complex.

Fe

  III DPyCl 2 complex (0 V) while the reduction wave taking place at the ligand at -0.72 V remains (FigureII-33). The two reduction waves observed at 0.57 V and 0.33 V can probably be assigned to reduction of the two iron(III) center in the dimer corresponding to the two Fe III OFe III / Fe II OFe III and Fe II OFe III / Fe II OFe II couples. Finally, we propose that the diiron(II) µ-oxo complex obtained by reducing both iron(III) centers dissociates to two monomer iron(II) complexes, the oxidation wave of which is observed at 0.7 V. The coordination of acceptor ligand such as acetonitrile probably causes the positive-shift of Fe III /Fe II couple compared to Fe III DPyCl 2 complex with -donor chloride ligand. The positive charge of complex when acetonitrile occupies one axial coordination site also participates in increasing the oxidation potential. Finally, the reduction wave was observed at -0.21 V probably corresponds to Fe III /Fe II with triflate on axial coordination site.Cyclic voltammetry of (Fe III DPy) 2 O(OTf) 2 in acetonitrile (Figure II-33) also shows two oxidation waves at 1.32 V and 1.63 V. The intensity of the first one is strongly diminished and probably correspond to the oxidation at the ligand. The second is higher in intensity and might concern the oxidation of the iron center to iron(IV/V) species as discussed above.

Figure II- 33 :

 33 Figure II-33: Cyclic voltammogram of 1 mM (Fe III DPy) 2 O(OTf) 2 (red) and 1 mM Fe III DPyCl 2 (black) measured in acetonitrile.

  15 V. The negative shift of the redox Fe III /Fe II potential probably reveals that acetonitrile molecules were displaced by water molecules (Figure II-34). Moreover, an intense oxidation wave at 1.53 V was again observed and probably corresponds to the electrocatalytic water oxidation by (Fe III DPy) 2 O(OTf) 2 as noticed with the Fe III DPyCl 2 monomer. Here too, a more in-depth study is needed to underpin the ongoing catalytic electrochemical reactions.

Figure II- 34 :

 34 Figure II-34 : Cyclic voltammograms of 1 mM (Fe III DPy) 2 O(OTf) 2 (black) measured in acetonitrile in presence of 3 M water (red).

  reaction of this iron(III) superoxo species with the starting iron(II) complex would afford a peroxide-bridged Fe III -OO-Fe III ferric dimer. The O-O bond cleavage would lead to the highly oxidized iron(IV)-oxo species that would ultimately react with the starting iron(II) complex to generate the µ-oxo-bridge ferric dimer (Figure II-35).

Figure II- 35 :

 35 Figure II-35: Proposed mechanism for formation of diiron(III) porphyrin starting from iron(II) complex.

Figure II- 36 :

 36 Figure II-36 : One proposed mechanism for formation of µ-oxo diiron(III) DPy starting form iron(III) complex.

Figure II- 37 :

 37 Figure II-37 : An ORTEP drawing of compound complex [Fe III DPy(OTf) 2 ]. Thermal ellipsoids are shown at 30% level of probability.

  We also questioned the possibility to prevent the formation of the dimer by adding chloride iron(III). Upon addition of four equivalents of ( t Bu 4 N)Cl in the (Fe III DPy) 2 O(OTf) 2 solution in acetonitrile, the instant color change was immediately observed from cyan to blue. UV-visible spectrum after adding ( t Bu 4 N)Cl showed absorbance at 666 nm and 584 nm characteristic for Fe III DPyCl 2 (Figure II-38), indicating that the µ-oxo structure can be cleaved by introducing chloride ligand at the two axial positions of the iron center.

Figure II- 38 :

 38 Figure II-38 : UV-visible change after adding 4 eq (tBu4N)Cl into a 50 µM (Fe III DPy) 2 O(OTf) 2 solution in acetonitrile.

  Figure II-39. UV-visible spectra showed five isosbestic points at 310, 364, 424, 540 and 610 nm indicating a clean chemical transformation. The new spectrum obtained after complete transformation shows an intense band at 621 nm, a broad band around 490 nm and a weak band around 700 nm, that pertains the reversible conversion to the monomeric form of the complex.

Figure II- 39 :

 39 Figure II-39 : UV-visible spectrum evolution showing the reaction of 1 eq triflic acid with (Fe III DPy) 2 O(OTf) 2 in acetonitrile at room temperature in 10 min.

Figure II- 40 :

 40 Figure II-40 : EPR spectra of (Fe III DPy) 2 O(OTf) 2 before (red) and after (black) adding 1 eq triflic acid.

Adding 1

 1 eq of ( t Bu 4 N)OH to the previous solution led to recovery of the initial dimer as monitored by UV-visible absorption spectroscopy (Figure II-41). Based on absorption band, the monomer was completely converted to the µ-oxo bridged dimer by only one equivalent of base in a few seconds. The transformation mechanism was probably through hydroxo bridged dimer again or by condensation as description in Figure II-36.

Figure II- 41 :

 41 Figure II-41 : UV-visible spectrashowing that the reaction of 1eq ( t Bu 4 N)OH with monomer iron(III) complex obtained above (red) in acetonitrile affords the µ-oxo dimer (blue). Black : UV-visible spectrum of the initial dimer.

  complex {[Fe III DPy(EtOH) 2 O](OTf) 2 }. The chloride ions that act as strong electron donor ligands prevent the formation of dimer but also transform dimer to monomer by occupying two axial positions on iron. Moreover, µ-oxo diiron(III) complex can be transformed to the iron(III) monomer under mild temperature in non-coordinating aprotic solvent or upon addition of acid. The lability of Fe-O bridge revealed that this µ-oxo dimer can be a potential catalyst for oxygen atom transfer reaction. Both iron(III) monomer Fe III DPyCl 2 and diiron(III) dimer {[{Fe III DPy(EtOH)} 2 O](OTf) 2 }

  complex [(N-EtHPTB)Fe III Fe III ] 5+ (N-EtHPTB = N,N,N',N'-tetrakis(N-ethyl-2benzimidazolylmethyl)-2-hydroxy-1,3-diaminopropane) as a model of the MMO enzyme able to activate dioxygen using a ruthenium-polypyridine type complex [Ru II (bpy) 3 ] 2+ (bpy = bispyridine) as a chromophore and triethylamine (TEA) as a sacrificial electron donor (Figure III-1). 121 Upon light irradiation, the excited state of chromophore Ru II* was quenched by TEA to form the powerful reduced Ru I capable of reducing both two iron centers of [(N-EtHPTB)Fe III Fe III ] 5+ dimer to [(N-EtHPTB)Fe II Fe II ] 3+ dimer. The reaction of the photoreduced diiron(II) complex with dioxygen leads to formation of an active µ-peroxo diiron(III) intermediate responsible for transferring oxygen atom to triphenylphosphine (PPh 3 ).

Figure III- 1 :

 1 Figure III-1 : Proposed mechanism for the photoinduced dioxygen activation at a dinuclear iron(III) complex.

Figure III- 2 :

 2 Figure III-2 : Oxygenation of organic substrate by a photosentiziting-precatalyst dyad through lightdriven dioxygen activation.

Figure III- 3 :

 3 Figure III-3 : Proposed mechanism for photooxidation of substratescatalyzed by dual catalyst system.

Figure III- 4 :

 4 Figure III-4 :Proposed mechanism for producing hydrogen peroxide by light-driven reaction.

  photosensitizer tris(bispyridine)ruthenium(II) chloride ([Ru II ]) in presence of methylviologen chloride ([MV 2+ ]) as an electron acceptor and sodium styrene-4-sulfonate (S) as a substrate in a pH = 4 Britton-Robinson B&R buffer aqueous. The aqueous medium was picked because of solubility issues and importantly previous studies have evidenced that methylviologen radical can be quenched by O 2 only in aqueous medium to generate in a first place the superoxide radical. Indeed, such electron transfer process does not happen in organic solvent such as acetonitrile etc… Sodium styrene-4-sulfonate was chosen as a water-soluble substrate.

Figure III- 5 :

 5 Figure III-5 : UV-visible spectra of Ru(bpy) 3 Cl2 (30 µM) in B&R buffer at pH 4 before (black) and after (red) irradiation for 22h.

Scheme 3 :

 3 Scheme 3 : Proposed mechanism for reaction involved in the blank experiment containing only Ru II and substrate upon light irradiation at aerobic atmosphere.

Figure III- 6 :

 6 Figure III-6 : Normalized traces of the kinetics of [Ru II *] emission measured at 610 nm in a B&R pH 4 solution of [Ru(bpy) 3 ]Cl 2 (30 µM) (red) in the absence and (black) presence of sodium styrene-4sulfonate (100 mM).

1 ,

 1 Entry 3), where a mixture of [Ru II ], S and O 2 was irradiated in presence of MV2+ , only trace amounts of oxidized substrate were detected, bringing again unambiguous support that the presence of the iron complex is essential for the observed photocatalytic reaction. The photoexcitation with a laser pulse at 460 nm of an aqueous mixture of [Ru II ] and MV 2+ in presence and absence of O 2 resulted in both cases in the formation of MV + detected by its characteristic absorption maximum around 605 nm (( = 14600 M -1 cm -1 ), 138 and [Ru III ] probed by the bleaching of the metal ligand charge transfer (MLCT) band at 450 nm ( = 14600 M -1 cm -1 ) (FigureIII-7).139 In absence of dioxygen, the charge transfer process between [Ru II *] and [MV 2+ ] to form [Ru III ] and [MV + ] was followed the recombination of [MV + ] and [Ru III ] (back electron transfer) with a bimolecular rate k 9 = 9*10 9 M -1 s -1 (Scheme 4). This rate was determined by fitting the decay time of reduced methyl-viologen MV + at 605 nm under argon atmosphere (Figure III-8, green).

Figure III- 7 : 2 (

 72 Figure III-7: Transient absorption spectrum from a B&R pH 4 buffer solution of [Ru(bpy) 3 ]Cl 2 (30 µM), MV 2+ (4 mM) in air at 1 µs delay after excitation.

Scheme 4 :

 4 Scheme 4 : Proposed mechanism for electron transfer reactions involved in the system containing [Ru II ] and MV 2+ upon light irradiation under argon atmosphere (left) and aerobic atmosphere (right).

Figure III- 10 :

 10 Figure III-10 : (Left) EPR spectrum at 80K of sodium 4-styrenesulfonate radical observed by mixing [Ru(bpy) 3 ](PF 6 ) 3 (1 mM) with sodium 4-styrenesulfonate (10 mM) in B&R pH 4 buffer under argon. (Right) alkenyl radica cation forml.

Figure III- 11 :

 11 Figure III-11 : Normalized traces of the kinetics of [Ru II *] emission measured at 610 nm in a B&R pH 4 solution of [Ru(bpy) 3 ]Cl 2 (30 µM) (red) in the absence and (black) presence of [(Fe III DPy) 2 O](OTf) 2 complex (30 µM).

Figure III- 12 :

 12 Figure III-12: Left: Transient absorption spectra from an Ar-saturated B&R buffer solution of [Ru(bpy) 3 ] 2+ (30 µM), MV 2+ (4 mM) and [(Fe III DPy) 2 O](OTf) 2 (30 µM) at the indicated delay times after excitation and (Inset) UV-visible spectrum of (DPy)Fe II in water under argon. Right: Time resolved absorption changes at 390 nm (green), 450 nm (red) and 605 nm (blue) corresponding to the contribution of MV +  , [Ru II ], both MV +  and iron(II) complex, respectively.

Figure III- 13 :

 13 Figure III-13 : : Transient absorption spectra from a B&R pH 4 buffer solution of [Ru(bpy) 3 ]Cl 2 (30 µM), MV 2+ (4 mM) and [(Fe III DPy) 2 O](OTf) 2 complex (30 µM) under aerobic conditions at the indicated delay times after excitation.

(

  DPy)Fe II absorption at 590 nm in absence of O 2 (Figure III-12, left) about 10-20 time more than that in presence of O 2 (Figure III-13).

Scheme 6 :

 6 Scheme 6 : Proposed mechanism for reactions involved in the blank experiment containing [Ru II ], [(Fe III DPy) 2 O](OTf) 2 and MV 2+ upon light irradiation under argon atmosphere (left) and aerobic atmosphere (right).

  Scheme 7).

Scheme 7 :

 7 Scheme 7 : Proposed mechanism of the photocatalytic oxidation of sodium styrene-4-sulfonate by the photosensitizer / iron catalyst / methyl-viologen mixture to form the diol and aldehyde products.

18 O

 18 isotopic labelling experiments, which carried out at pH 4 B&R buffer were undertaken to interrogate the origin and the pattern of the inserted oxygen atoms into oxidized products. The HPLC-HRMS analysis of the corresponding photocatalytic experiments indeed confirmed that the oxygen atom stems from[START_REF] Werck-Reichhart | Cytochromes P450 for engineering herbicide tolerance[END_REF] O 2 (FigureIII-16). The isotope labelling study was examined on the cis-diol product because of the fast oxygen exchange between the carbonyl group and water,157 for the HPLC analysis used as an eluent.

Figure III- 16 : 18 O

 1618 Figure III-16 : ESI--HRMS of diol formed in sodium 4-styrenesulfonate oxygenation under irradiation for 22 hours in B&R pH 4 buffer in presence of [Ru(bpy) 3 Cl 2 ] (30 M), MV 2+ (4 mM), [(Fe III DPy) 2 O](OTf) 2 complex (30 M) and sodium 4-styrenesulfonate (10 mM) with (Top) H 2 O and O 2 , (Middle) H 2 O and 18 O 2 , (Bottom) H 2 18 O and O 2 , (inset) theoretical isotopic distribution for unlabelled diol.

Figure III- 17 :

 17 FigureIII-17 : Proposed mechanism for the active iron species and oxygen atom exchange.

Figure III- 18 :

 18 Figure III-18: The spectral distribution of the emitted light without (red) and with sample (black).

L 5

 5 Fe II (OTf)(PF 6 ) complex where L 5 = N-methyl-N,N',N'-tris(2-pyridylmethyl)ethane-1,2-diamine (Figure III-19). [L 5 Fe II ] 2+ complex was synthetized and characterized in 1990s, 162 and the corresponding oxidizing species such as iron(III)-(hydro)peroxo, iron(IV)-oxo have been

  photoactivation pathways for the observed light driven chemical transformation.

Figure III- 19 :

 19 Figure III-19 : Structure of [Fe II L 5 ] 2+ complex (left) and chromophore-catalyst dyad (right). In presence of [Fe II L 5 ] 2+ in the mixture [Ru II ] photosensitizer and [MV 2+ ], under an inert atmosphere, the oxidative quenching of the photosensitizer and the formation of [MV + ] again prevailed. Laser flash photolysis experiment indeed revealed the characteristic absorption bands of [MV + ] (390 nm and 605 nm) and [Ru II ] (450 nm) shown in Figure III-20, left. However, no oxidation of [L 5 Fe II ] 2+ catalyst by the oxidized photosensitizer was observed under such conditions. Indeed a fast recombination between [MV + ] and [Ru III ] was observed as attested by the simultaneous decay of the absorption band at 450 nm and 605 nm corresponding to [MV + ] and [Ru II ], respectively (comparing red and black in Figure III-20, right).

Figure III- 20 :

 20 Figure III-20 : Left: Transient absorption spectra from an Ar-saturated pH 4 buffer solution of [Ru(bpy) 3 ] 2+ (30 µM), MV 2+ (20 mM) and [Fe II L 5 ] 2+ (100 µM) at the indicated delay times after excitation. Right: Time-resolved absorption changes at 605 nm (red) and 450 nm (black) in argon saturated pH 4 buffer; at 605 nm (blue) and 450 nm (green) in pH 4 buffer under aerobic conditions.

Scheme 9 :

 9 Scheme 9 : Proposed reduction mechanism considered to model experimental CVs for the reaction between O 2 and [L 5 Fe II ] 2+ complex.

Figure III- 21 :

 21 Figure III-21 : Time-resolved absorption changes of the mixture [Ru(bpy) 3 ]Cl 2(30 µM), MV 2+ (20 mM) in air-saturated pH 4 buffer without [Fe II L 5 ] 2+ complex at 605 nm (black) and 450 nm (red); in presence of [Fe II L 5 ] 2+ complex (30 µM) at 605 nm (blue) and 450 nm (green); in presence of [Fe II L 5 ] 2+ complex (100 µM) at 605 nm (purple) and 450 nm (orange).

Figure III- 22 :Figure

 22 Figure III-22 : Two possible pathways of the reduction of O 2 by MV +  in presence of [L 5 Fe II ] 2+ complex.

Figure III- 24 :

 24 Figure III-24 : Transient absorption spectra from a pH 4 buffer solution of [Ru(bpy) 3 ]Cl 2 (30 µM), MV 2+ (20 mM) and [Fe II L 5 ] 2+ complex (100 µM) under aerobic conditions at the indicated delay times after excitation. Inset: zoom.

of H 2 O

 2 2 in pH = 4 buffer at 0 °C monitored by absorption spectroscopy. The UV-visible spectra showed a broad absorption band around 700 nm which quickly disappeared (Figure III-25). By using H 2 O 2 as oxidant in pH 4 buffer, the formation of the deprotonated iron(III)peroxo species [L 5 Fe III -OO] + species can be excluded among the generated species in solution. This absorption band around 700 nm could thus be assigned to a mixture of [L 5 Fe III -OOH] 2+ and probably their evolution species such as [L 5 Fe V =O] 2+ obtained by a heterolytic O-O cleavage. [L 5 Fe IV =O] 2+ species characterized by band at 756 nm in methanol and at 732nm in acetonitrile was also probably generated in the reaction .168,169

Figure III- 25 :

 25 Figure III-25 : UV-visible spectra of [Fe II L 5 ] 2+ in pH 4 buffer (black) upon addition of 1.5 eq H 2 O 2 (red) and after 1 min (blue).

Figure III- 26 :

 26 Figure III-26 : EPR spectrum of a solution containing [Ru II ], [MV 2+ ] and [Fe II L 5 ] 2+ in pH 4 buffer upon light irradiation (  = 450 nm, power = 15 mW.cm -1 ) for 120 s at air atmosphere.

Scheme 10 :

 10 Scheme 10 : Proposed mechanism of the photocatalytic oxidation of sodium styrene-4-sulfonate by the photosensitizer / iron catalyst [Fe II L 5 ] 2+ / methyl-viologen mixture to form the diol and aldehyde products.

Figure III- 28 :

 28 Figure III-28 : Consumption of dioxygen during the photo-oxidation of PPh3 in presence (red) and absence (black) of [(Fe III DPy) 2 O](OTf) 2 dimer as pre-catalyst.

Figure IV- 1 :

 1 Figure IV-1 : L 5 ligand structure and mechanism proposed for the formation of mononuclear L 5 Fe IV =O via the L 5 Fe II -OCl species using NaClO. 10 years later, Brown and Visser reported the reaction of [Fe II (MeN4Py)] 2+ precursor with 2 eq NaClO showing the formation of an Fe III -OCl species and subsequently an Fe IV =O species by homolytic O-Cl cleavage. 175 The Fe III -OCl species was characterized by a absorption band at 480 nm and by an EPR resonance revealing 3 signals with g values at 2.26, 2.15 and 1.97 attributed to a low-spin iron(III) species. The Raman spectrum revealed two strong bands at 653 and 580 cm -1 which were assigned to an Fe-O and an O-Cl stretching modes of the Fe III -OCl species. The need for 2 eq NaClO for the formation of Fe III -OCl species was explained by the following events. First the one-electron oxidation of [Fe II (OH 2 )(MeN4Py)] 2+ into [Fe III (OH)(MeN4Py)] 2+ is occurred by 0.5 eq of the two-electron oxidant NaClO. Second, the reversible hydroxo substitution by a hypochlorite ligand yields Fe III -OCl species that slowly decomposes into the Fe IV =O species by a homolytic O-Cl cleavage.

Figure IV- 2 :

 2 Figure IV-2 : The reaction mechanism for the formation of [Fe III (OCl)(MeN4Py)] 2+ and [Fe IV (O)(MeN4Py)] 2+ proposed on the basis of DFT calculations.

Figure IV- 3 :

 3 Figure IV-3 : [Fe III (OCl) 2 (TPFP)] 1-adduct involved in oxidation reaction.

Figure IV- 5 :

 5 Figure IV-5 : Existence of an equilibrium between iron-oxo porphyrin species and iron-iodosylarene porphyrin adduct.

Figure IV- 6 :

 6 Figure IV-6 : (Right) X-ray structure of [Fe III (tpena)(OIPh)] 2+ ; (Left)Proposed mechanism for oxidation of a substrate (Sub) by iodosylbenzene catalyzed by [{Fe III (tpenaH)} 2 O] 4+ .

(

  c PhIO), chalcone was converted to chalcone oxide as major product with 76 % enantioselectivity (Figure IV-7).185 Because the iron(IV)-oxo or iron(V)-oxo species obtained by homolytic or heterolytic O-I bond cleavage do not possess a chiral center, the reaction of iron-oxo species with chalcone would have led to a racemic mixture product. Nam and coworkers thus propose that the active intermediate responsible for oxidation reaction in these

Figure IV- 8 :

 8 Figure IV-8 : Proposed mechanism for iron(III) porphyrin N-oxide formation in toluene..

Figure IV- 9 :

 9 Figure IV-9: Two ligand-oxygenated iron(III) species reported by McKenzie.

Figure IV- 10

 10 Figure IV-10: X-Ray structure of [Fe III ( 2 -S Me2 O)(S Me2 N 3 (Pr,Pr))] + .

DPyCl 2 complex

 2 in 10 min and without the apparition of new bands that would attest the accumulation of an oxidized species(Figure IV-11). m-CPBA is a two-electron oxidant agent which should oxidize the iron(III) precursor to generate probably an iron(V)-oxo species [Fe V =O(DPy)] 2+ or an iron(IV)-oxo ligand cation radical species [Fe IV =O(DPy  )] 2+ , due to the non-innocent semi hemic DPy ligand. Based on the literature, the synthetic iron(V) and iron(IV) oxo species can be identified by an absorption band around 600-800 nm with a moderate extinction molar coefficient ( = 100-4000 M -1 cm -1 ) corresponding to a d-d transition.190 If such a species was formed it is possible that this characteristic weak absorption band would be hidden by the strong -* absorption band of the Fe III DPyCl 2 precursor at 666 and 584 nm ( = 10118 and 21680 M -1 cm -1 , respectively). The short lifetime of the oxidized iron species at room temperature compared to its slow generation by m-CPBA in 10 min also prevented its detection. The reaction of Fe III DPyCl 2 with m-CPBA at low temperature (-40 °C) was not helpful to observe the characteristic band of the active species, probably because both the formation and the degradation of the oxidized species were slow down.

Figure IV- 11 :

 11 Figure IV-11: UV-visible spectral changes of a Fe III DPyCl 2 (25 µM) solution after addition of 10 eq m-CPBA in acetonitrile at room temperature over 10 min.

4. 3

 3 attributed to a high spin (S = 5/2) iron(III) species in a low symmetry environment, while only traces of the tree signals with g value at 9.0, 5.1 and 3.7 characterizing the Fe III DPyCl 2 precursor were observed (Figure IV-12). This could indicate the rapid formation of an iron(III)-mCPBA adduct in less than 1 min. In addition, a broad signal with g value at 2.0 was also observed. This last signal could correspond to a radical cation ligand coordinated on iron center such as [Fe IV =O(DPy  )] 2+ or a low spin iron(V) species [Fe V =O(DPy)] 2+ obtained by a heterolytic O-O bond cleavage. Remarkably, this EPR matched with the one obtained from the electrolysis of the Fe III DPyCl 2 complex at 1.6 V in wet acetonitrile (Figure IV-12).

Figure IV- 12 :

 12 Figure IV-12: EPR spectra recorded at 10 K of the Fe III DPyCl 2 complex solution (1 mM) (black), upon ocidation with 10 eq m-CPBA (red) or electrolyzing at 1.6 V vs SCE (blue).

Figure IV- 13 :

 13 Figure IV-13 : Influence of anionic axial ligands on the locus of the oxidation of iron porphyrins by m-CPBA.

Figure IV- 14

 14 Figure IV-14 : : UV-visible spectral changes of Fe III DPyCl 2 (50 µM) after addition 10 eq m-CPBA in MeOH at room temperature over 10 min.

  3 attributed to a high spin (S = 5/2) iron(III) species and a non-identified positive broad signal at 2.01 (Figure IV-15). With the strong electron donor methanolate ligand in axial position, similar oxidation and degraded mechanisms thus seem to occur as with chloride ligand in acetonitrile.

Figure IV- 15 :

 15 Figure IV-15 : EPR spectra recorded at 10 K of Fe III DPy(OMe) 2 (1 mM) prepared by dissolving Fe III DPyCl 2 in MeOH (black) and oxidized species obtained by reacting with 10 eq m-CPBA (red).

[

  (Fe III DPy) 2 O](OTf) 2 dimer. Upon addition of 10 eq m-CPBA into [(Fe III DPy) 2 O](OTf) 2 solution in acetonitrile, the absorption bands characterizing [(Fe III DPy) 2 O](OTf) 2 dimer at 616 nm and 588 nm slowly disappeared upon 10 min, and new absorption band at 633 nm was observed after mixing for 1 min then slowly disappeared (Figure IV-16). Two isosbestic points at 346 and 424 nm were observed within 1 min, indicating a clean chemical transformation.

Figure IV- 16 :

 16 Figure IV-16: UV-visible spectral changes of [(Fe III DPy) 2 O](OTf) 2 (100 µM) after addition 10 eq m-CPBA in acetonitrile at room temperature over 1 min (left) and 10 min (right).

Figure IV- 17 :

 17 Figure IV-17 : EPR spectra recorded at 10 K of [Fe III DPy) 2 O](OTf) 2 dimer (1 mM) (black), oxidized species obtained by reacting with 10 eq m-CPBA (red) and zoom at the high field area with 10 scans (inset).

band decayed with a lifetime t 1 /

 1 2 of 15 min to yield a new spectrum different from the initial with a new absorption band at 615 nm, different from the initial band at 666 nm (Figure IV-18). Based on the band intensity, the initial iron(III) precursor [Fe III DPy] 2+ was not fully degraded as in the case of mCPBA. However, an altered species was obtained, which could be a complex with aqua or hydroxo ligand in axial position [Fe III Dpy(H 2 O) n (OH) m ] (2-m)+ due to the presence of water. Indeed, a similar UV-vis spectrum was obtained upon addition of 10 % water into Fe III DPyCl 2 precursor in acetonitrile (Figure IV-19). The formation of µ-oxo diiron(III)complex [(Fe III DPy) 2 O](OTf) 2 showing very close absorption band in acetonitrile may also be envisioned.

Figure IV- 18 :

 18 Figure IV-18 : UV-vis spectra showing the formation and decomposition of active iron species generated by oxidizing Fe III DPyCl 2 (25 µM) with NaClO in acetonitrile/water (v/v = 99/1). Blue: the initial Fe III DPyCl 2 precursor, Green: after adding of 2 eq. of NaClO and Red: evolution after 30 min.

Figure IV- 19 :

 19 Figure IV-19 : UV-vis spectra of Fe III DPyCl 2 (25 µM) in acetonitrile / water (v/v = 9/1) (black) and decomposed species obtained after oxidizing Fe III DPyCl 2 (25 µM) in acetonitrile / water (v/v = 99/1) with 2 eq. of NaClO.

Figure IV- 20 :

 20 Figure IV-20 : EPR spectra in perpendicular mode before (black) and after (red) oxidation of Fe III DPyCl 2 by NaClO. Inset: EPR spectrum in parallel mode.

Figure IV- 23 :

 23 Figure IV-23 : ESI+-HRMS analysis of (Fe III DPyCl 2 + NaClO) solution diluted in MeOH and frozen. Inset: Experimental and simulated isotopic distribution of detected species at m/z = 566.0437.

Figure IV- 24 :

 24 Figure IV-24: Proposed structural assigned for m/z = 587.9612 (left) and603.9560 (right)

Figure IV- 25 :

 25 Figure IV-25 : Infrared spectra of Fe III DPyCl 2 precursor (black), after adding NaClO (red) and previous solution added with H 2 18 O (blue). Although Fe III (DPy)(OCl)Cl adduct and [Fe V =O(DPy)Cl]Cl iron-oxo species were not spectroscopically trapped at room temperature, the formation of Fe III (DPyN Py O)Cl 2 iron(III) N-oxide species probably proceeds via the formation of Fe III (DPy)(OCl)Cl adduct followed by a heterolytic O-Cl bond cleavage to form [Fe V =O(DPy)Cl]Cl iron-oxo species, then followed by an intramolecular interaction to generate Fe III (DPyN Py O)Cl 2 species. Unfortunately, all attempts made to detect the iron-hypochlorite adduct and the iron-oxo species by UV-vis, EPR at low temperature (-40 °C) and stopped-flow absorption spectroscopy were not conclusive, probably due to their highly reactivity. At -40 °C, similar absorption bands than that at room temperature were detected. Notably, the intense band at 631 nm characteristic of the Fe III (DPyN Py O)Cl 2 iron N-oxide species persisted at low temperature (t 1/2  8 h), and the EPR spectrum measured on an aliquot of the reactional mixture taken when maximum intensity of the band at 631 nm at -40 °C reached, showed similarly a broad signal at g = 4.3. We thus propose that the formation of Fe III (DPyN Py O)Cl 2 iron(III) N-oxide species either proceeds via the concerted O-Cl bond, or the Fe-O-N bond

  to oxidize PPh 3 to O=PPh 3 (Figure IV-26). This was confirmed by the HRMS detection of O=PPh 3 . We can propose that the iron intermediate characterized by the absorption band at 631 nm is active in oxygen atom transfer.

Figure IV- 26 :

 26 Figure IV-26 : UV-vis spectral changes during the oxidation of the Fe III DPyCl 2 complex (black) by 2 eq. of NaClO (red) and its reaction with 2 eq. of PPh 3 (blue)

Figure IV- 27 :

 27 Figure IV-27 : Second catalytic oxidation cycle. Blue: regenerated iron(III) precursor after the first cycle, black : oxidation with 2 eq. NaClO, red : after reation with 2 eq. PPh3.

Figure IV- 28 :

 28 Figure IV-28 : UV-visible changes during the reaction of the iron intermediate generated by NaClO with stoechiometric 4-MeSPhMe over 30 min.

Figure IV- 29

 29 Figure IV-29 : (Top) 31 P NMR of catalytic reaction with PPh 3 as substrate and (Bottom) 1 H NMR with 4-MeSPhMe as substrate.

3 . 1 . 1

 311 UV-visible spectroscopyThe reaction of FeIII DPyCl 2 with PhIO in acetonitrile in absence of substrate was monitored by different spectroscopic techniques. Mixing the two reactants at room temperature in ACN resulted in the apparition of a new transition band at 636 nm reminiscing the [Fe III (DPyN Py O)] 2+ iron N-oxide species generated by NaClO. Interestingly the new absorption feature faded slowly in about 15 min and the initial Fe III DPyCl 2 spectrum was recovered this time albeit with slightly lower intensity (Figure IV-30). In the presence of triphenylphosphine, the decay was accelerated by at least a factor of 3 and triphenylphosphine oxide was detected by HRMS suggesting that this intermediate species is capable of transferring an oxygen atom, as in the case of NaClO.

Figure IV- 30 :

 30 Figure IV-30 : UV-vis spectra changes during oxidation of Fe III DPyCl 2 complex (blue) by PhIO (green), its evolution after 15 min in absence of substrate (red) and its reaction with PPh3 (black).Inset: (red)Decay of absorption band at 636 nm with (black) and without PPh 3 over time.

g=4. 3

 3 attributed to a high spin (S = 5/2) iron species as detected with NaClO with an estimated conversion of around 60% (Figure IV-31). No signal was detected in parallel mode.Again, the initial characteristic signals of the iron(III) precursor were slowly recovered in absence of substrate while the recovery was accelerated by adding triphenylphosphine as observed by UV-visible spectroscopy. Like in UV-visible spectroscopy, the EPR signals of iron(III) precursor was not totally regenerated probably due to formation a silent iron species in EPR such as µ-oxo diiron(III) complex especially in absence of substrate.

Figure IV- 31 :

 31 Figure IV-31 : EPR spectra changes during oxidation of Fe III DPyCl 2 complex (blue) by PhIO (green), its evolution at room temperature after 16 h in absence of substrate (red) and a few seconds after adding PPh 3 (black).

  Acetate ligand was found in this experiment because sodium acetate was used for calibration of the HRMS shortly before the experiment (FigureIV-33). These peaks cannot be assigned to high oxidized iron-oxo species [Fe V =O(DPy)Cl] + and [Fe V =O(DPy)(OAc)] + due to results found by EPR and Mössbauer analyses, we thus reason that these peaks can be attributed to iron(III) N-oxide species [Fe III (DPyNO)Cl] + and [Fe III (DPyNO)(OAc)] + . Moreover, a peak at m/z = 503.0879 with charge and isotopic distribution agreeing with [(DPyH) + O + Na] + formula was observed which probably comes from iron(III) N-oxide species demetallation under HRMS condition. Upon addition of 18 O labelled water to the previous sample, two new peaks were detected at 571.9988 and 582.0262 corresponding respectively to [Fe(DPy)Cl + 18 O] + and [Fe(DPy)(OAc) + 18 O] + formula, proving the lability of the metal bound oxygen atom in the detected species (Figure IV-33).Moreover, the formation of an iron(III)-iodosylbenzene adduct was revealed by the detection of a peak at m/z = 773.9389 attributed for [Fe(DPy)Cl(OIPh)] + ion. However, the peak corresponding to [Fe(DPy)Cl( 18 OIPh)] + was not found upon addition of[START_REF] Werck-Reichhart | Cytochromes P450 for engineering herbicide tolerance[END_REF] O labelled water.The existence of iron(III)-iodosylbenzene adduct is reasonable because its formation is believed to be the first step in oxidation reaction with PhIO. As a consequence, one can propose that the oxidized solution contains both iron(III)-iodosylbenzene adduct and iron(III) Other peaks were present in the reaction mixture that we tried to identify. One of the major one at 534.0194 was found to have the charge and the isotopic distribution compatible with a [Fe(DPy) + O-H] + formula. Due to the lability of coordinated pyridine in iron(III) precursor as mentioned in chapter II, one C-H bond of a pyridine could be activated leading by oxygen insertion and deprotonation to the formation of [Fe III (DPyO)] + species (Figure IV-34). This

Figure IV- 34 :

 34 Figure IV-34 : (left) Structure of [Fe III (DPyO)] + ion and (right) isotopic distribution of [Fe III (DPyO)] + .

  569.9954, 580.0242 and 503.0879 were absent, while the initial [Fe III DPy] 2+ precursor was detected by the presence of two peaks at 554.0006 and 564.0299 attributed to two [Fe(DPy)Cl] + and [Fe(DPy)(OAc)] + chemical species, respectively (Figure IV-35). Therefore, the recovery of iron(III) precursor observed by UV-vis, EPR, Mössbauer was also confirmed by HRMS, revealing the iron(III) N-oxide species was also active. However, the peak at 534.0200 was absent. A possibility is that such a species would dimerize after a while as previously observed with the manganese [MnDPy] + (Figure II-1). 94 This degradation pathway might explain why spectral features are not fully recovered after quenching of the active species (Figure IV-30 and Figure IV-31).

Figure IV- 35 : 18 O

 3518 Figure IV-35 : ESI + -HRMS analyses of (Fe III DPyCl 2 + PhIO) sample taken 16 h after mixing.

Figure IV- 37 :

 37 Figure IV-37: : Comparison of the infrared spectra of iron intermediates generated by PhIO (red) and by NaClO (blue).

Figure IV- 38 : 2 IV. 2 . 3 . 1 . 6

 3822316 Figure IV-38: Raman resonance of Fe III DPyCl 2 precursor (black), upon addition of PhIO (red) and then H 2

Figure IV- 39 :

 39 Figure IV-39: DFT optimized structure of two Fe III DPyCl 2 complex Next, the structure of Fe III (DPyNO)Cl 2 and the other possible oxidized species such as [Fe III (DPy)(OCl)] + adduct, [Fe V =O(DPy)(Cl)] + iron(V)-oxo species were investigated (Figure IV-40). The most stable geometry we localized features the insertion of an oxygen atom in one of the N pyridine -Fe bound. The iron center hardly deviates from the N4 plane (d(Fe-N4)=0,22A) while the pyridine-N-oxide ring tilts by 27° from N4 plane to allow the bent N-O-Fe 4e-3center interaction to establish (Fe-O = 2.087 Å , N-O = 1.315 Å , NOFe = 122.9°).

Figure IV- 40 :

 40 Figure IV-40 : Modelisation of 4 structures that could be obtained upon oxidation of Fe III DPyCl 2 by. Relative thermal free energies at 298 K are given under each structure.

Figure V- 1 :

 1 Figure V-1: (Top) structural drawing of the Fe III BIMCl 2 complex; (Bottom, left) UV-vis spectral changes during the oxidation of the Fe III BIMCl 2 complex (red) by 2 eq. of NaClO (green) and its reaction with 2 eq. of PPh 3 (blue); (Bottom, right) Absorption band at 670 nm with and without substrates.

A

  white LED from METAPHASE TECHNOLOGY (light power = 1.3 mW.cm -1 ) equipped with a Wratten 2E filter (blocking  < 415 nm) was used to irradiated reactional mixtures (Figure 0-1).

Figure 0 - 1 :

 01 Figure 0-1: LED panel used for photocatalytic experiment

Synthesis 2 -

 2 (N-Boc-1H-pyrrol-2-yl)pyridine: 2-bromopyridine (2.26 mL, 23.60 mmol, 1 equiv.) were dissolved in the mixture of dioxane (100 mL), ethanol (50 mL) and water (50 mL). This solution was degased within 1h by Argon. Then [Pd(PPh 3 ) 4 ] (2.73 g, 2.36 mmol, 0.1 equiv.)

Figure 0 - 3 :

 03 Figure 0-3 : Crystal packing displaying space occupied by solvent molecules.

  restraints. Consequently, SQUEEZE 3 (from PLATON) was used to calculate the void space, the electron count and to get a new HKL file. According to the SQUEEZE results and the different experimental evidences a total number 14 CH 3 CN solvent molecules (308 electrons) was considered per unit cell. Without solvent molecules: R1= 0.0848 for 3835 reflections of I > 2(I) and wR2= 0.2502 for all data. With solvent molecules (SQUEEZE): R1= 0.0784 for 3835 reflections of I > 2(I) and wR2= 0.1902 for all data, the volume fraction was calculated to 1203 Å 3 which corresponds to 11% of the unit cell volume, and to 305 electrons per unit cell allocated to solvent molecules. The crystal data collection and refinement parameters are given in

2 Figure 0 - 4 :

 204 Figure 0-4 : An ORTEP drawing of compound complex[{Fe III DPy(EtOH)} 2 O](OTf) 2 . Thermal ellipsoids are shown at the 30% level. (symmetry codes: (i) -x, -y, -z).

200Fe III DPy(OTf) 2 Figure 0 - 5 :

 205 Figure 0-5 : ORTEP representation at 30 % of probability of X-Ray structure of Fe III DPy(OTf) 2 complex.

Figure

  Figure 0-6 : Extracts of the

Figure 0 - 7 :

 07 Figure 0-7 : Extracts of the 1 H-NMR spectra of crude reaction mixtures in H 2 O and 10 % D 2 O obtained upon light irradiation of sodium 4-styrenesulfonate (10 mM) for 22 hours under aerobic conditions. (Blue) with [Ru II ] (30 µM) in B&R pH 4; (Cyan) with [Ru II ] (30 µM) and complex I (30 µM) in B&R pH 4; (Green) with [Ru II ] (30 µM) and MV 2+ (4 mM) in B&R pH 4; (Red) with [Ru II ] (30 µM), FeCl 3 (60 µM), MV 2+ (4 mM) in B&R pH 4; (Black) with [Ru II ] (30 µM), complex I (30 µM), MV 2+ (4 mM) in B&R pH 4; (Purple) with [Ru II ] (30 µM), complex I (30 µM), MV 2+ (4 mM) in B&R pH 6.

  nous permet de confirmer la source d'atome d'oxygène comme provenant le dioxygène tandis que l'expérience de Laser Flash Photolysis clarifie le mécanisme réactionnel et le transfert d'électron entre le photosensibilisateur, l'accepteur d'électron réversible, le dioxygène et le catalyseur dans l'activation du dioxygène. La présence de notre complexe de fer est indispensable d'activer dioxygène et de former une espèce active à base de fer qui est responsable d'oxyder le styrène. Notre étude fournit un nouveau paradigme pour effectuer des

	HPLC LIST OF ABBREVIATIONS High Performance Liquid Chromatography GHz Gigahertz
	 K k i	Kelvin Extinction molar coefficient Rate constant
	 L	Wavelength Liter
	° LED	Degree Light-emitting diode
	°C LMCT	Celsius Degree Ligand to Metal Charge Transfer
	A M	Ampère Mole per liter
	m-	Angstrom Milli
	Abs µ	Absorbance Micro
	BDE m-CPBA	Bond Dissociation Energy Meta-chloroperbenzoïc acid
	bpy MeCN	2,2'-bipyridine Acetonitrile
	C-C min	Bonding between two carbons Minute
	C-H MLCT	Bonding between carbon and oxygen Metal to Ligand Charge Transfer
	C-O MMO	Bonding between carbon and oxygen Methane Mono Oxygenase
	CAN n-	Ceric Ammonium Nitrate Nano
	cm NaClO	Centimeter Sodium hypochlorite
	CV NMR	Cyclic Voltammetry Nuclear Magnetic Resonance
	Cyt OAT	Cytochrome Oxygen Atom Transfer
	DFT OTf	Density Functional Model Triflate (Trifluoromethanesulfonate)
	DPV PCET	Differential pulse voltammetry Proton-Coupled Electron transfer
	DPy Ph	3,5-dipyridine-8-pentafluorophenyldipyrrin Phenyl
	EA pH	Electron Acceptor Hydrogen Potential
	E a PhIO	Anodic potential Iodosylbenzene
	E c s	Cathodic potential Second
	E 1/2 SCE	Half-wave potential Saturated Calomel Electrode (Reference)
	ED T	Electron Donor Temperature
	E p TAML	Peak potential Tetra-amido macrocyclic ligand
	EPR TBAPF 6	Electron Paramagnetic Resonance Tetrabutylammonium hexafluorophosphate
	ESI-MS TOF	Electrospray Ionisation Mass Spectrometry Turnover frequency
	EtOH TON	Ethanol Turnover number
	G Uv-vis	Gauss Ultraviolet Visible Spectroscopy
	g V	gram Volt
	h X-Ray	Hour X-ray diffraction Spectroscopy
	HAA	Hydrogen atom abstraction
	HPGC	High Performance Gaz Chromatography
		14

  -1).

	Catalytic metalloenzyme	Active species	Catalytic reaction
	Cytochrome P450
		-	ketoglutarate
	dependent
	hydroxylases.

Table I -

 I

2 : Cyclohexene epoxidation by PhIO catalyzed by iron porphyrin complex. Cyclohexene/PhIO/catalyst = 100/100/1, solvent: DCM. TON based on PhIO in 2h.

Table I -

 I 3 : Spectroscopic characterizations of Fe V =O species.

  100,101 The dipyrrin-pyridine skeleton is almost planar (N py dihedral angle of 3.86°). Two axial sites are occupied by chloride ligands. The Fe-Cl bonds (2.317 Å) are much longer than that of monochloride iron(III) porphyrin complex ClFeTPP (2.192 Å),102 and much closer to that of trans-dichloride iron(III) such as in oxaporphyrin iron complex (2.302 Å) 103 , (-PPh 3 -TPP)Fe III Cl 2 (2.348 and 2.429 Å)104 and non heme iron(III) complex Fe III (dpa)

Table II

 II

		Bonds lengths		Angles
	Fe-N1	2.213(3)	N1-Fe-N2	76.02(12)
	Fe-N2	2.051(3)	N1-Fe-N3	157.61(11)
	Fe-N3	2.055(3)	N1-Fe-N4	124.53(11)
	Fe-N4	2.203(3)	N2-Fe-N3	82.12(10)
	Fe-O1	1.7710(4)	N2-Fe-N4	157.40(11)
	Fe-O2	2.165(2)	N3-Fe-N4	76.38(10)
			O2-Fe-O1	160.24(7)
		-2 : Selected Bond Distances (Å) and Angles (°) for Fe III DPyCl 2 complex with estimated
	standard deviation's in parenthesis.

Remarkably, the structure of dimer in solid state revealed that triflate ligands have been displaced by ethanol. The coordination sphere of each iron(III) ion is described by the four nitrogen atoms of the DPy ligand in a meridional plane and oxygen atoms from the bridging oxo and one ethanol molecule in apical positions. Two triflate counter anions assure

Table II -

 II 3 : Selected Bond Distances (Å) and Angles (°) for Fe III DPyCl 2 complex.Figure II-37 shows the ORTEP diagram of the complex and Table II-3 displays selected bond lengths and angles for the crystallographically determined structure. The Fe-N bond lengths of [Fe III DPy(OTf) 2 ] complex are slightly shorter than that of Fe III DPyCl 2 monomer and {[Fe III DPy(EtOH)] 2 O}(OTf) 2 dimer probably because triflate is a weaker ligand compared to strong ligand donor such as chloride and ethanol. As a consequence, the two pyridine arms are closer to each other than in the two latter complexes, the N Py -C meso -N Py angle being of ° for this complex versus 47.4 ° for Fe III DPyCl 2 monomer and 46.2 ° for {[Fe III DPy(EtOH)] 2 O}(OTf) 2 dimer.

	44.2
		Bond distances		Angles
	Fe-N1	2.133	N1-Fe-N4	122.88
	Fe-N2	2.020	N1-Fe-N2	77.37
	Fe-N3	2.023	N2-Fe-N3	82.28
	Fe-N4	2.139	O1-Fe-O2	161.03
	Fe-O1	2.046	N1-Fe-O1	87.41
	Fe-O2	2.050	N2-Fe-O2	82.96

  Preliminary electrocatalytic study with monomer Fe III DPyCl 2 demonstrated a promising reactivity in activation of inert molecule such as carbon dioxide and water. It is probable that Fe

III DPyCl 2 could be electro-activated to generate an active iron(V)-oxo species capable of activating water molecules. On the other hand, carbon monoxide was identified as a product in carbon dioxide reduction electrochemically catalyzed by Fe III DPyCl 2 . Moreover, there were probably other reduced products non-detected in carbon dioxide reduction. Although Fe III DPyCl 2 exhibited a moderate selectivity for carbon dioxide reduction compared to hydrogen reduction, its selectivity could be improved either by structural modifications or under optimization of experimental conditions.

  Upon continuous illumination using a LED lamp and under an aerobic H NMR of the reactional mixture revealed the presence of 1.17 mM diol and 1.27 mM of benzaldehyde respectively corresponding to 11.7 % and 12.7 % of oxidation yield based on the substrate with an overall turnover number (TON) of 80 (TableIII-1, entry 1). This TON value falls roughly within the range observed for highly oxidized iron species generated upon reaction of iron complex models with O 2 in presence of electron and proton donors.[128][129][130] While, a mixture of [Ru II ], S and O 2 was irradiated in presence of [MV 2+ ] (TableIII-1, entry 4), only trace amounts of oxidized substrate (benzaldehyde) were detected. Moreover, upon addition of iron(III) salt leads also to only trace of benzaldehyde (TableIII-1, entry 3).Therefore, the presence of [(Fe III DPy) 2 O](OTf) 2 catalyst with the support of exogenous DPy ligand is essential for the observed photocatalytic reaction.

	atmosphere,	two	oxygenated	products	were	detected,	the	4-(1,2-
	dihydroxyethyl)benzenesulfonate (diol) and the 4-formylbenzenesulfonate) (benzaldehyde).
	Entry [Ru(bpy) 3 ]Cl 2		Catalyst	MV 2+	Substrate		Product yield a	TON b
							Diol	Benzaldehyde Epoxyde
	1	30 µM	30 µM [(Fe III DPy) 2 O](OTf) 2	4 mM	10 mM	11.7%	12.7%		traces	81
	3	30 µM		30 µM Fe III Cl 3	4 mM	10 mM	0	traces		0	nd
	4	30 µM		0	4 mM	10 mM	0	traces		0	nd
		2.1 Reactivity
	[(Fe III DPy) 2 O](OTf) 2 (30 µM) was utilized as iron(III) catalyst in a Britton & Robinson pH4

buffer aqueous mixture with the [Ru II ] photosensitizer (30 µM), the [MV 2+ ] reversible electron acceptor (4 mM) and an excess of sodium styrene-4-sulfonate (10 mM) (hereby shorthanded as S).

1

Table III -

 III Of note, the monomer Fe III DPyCl 2 showed a similar reactivity in such condition probably due to its dimerization in aqueous medium.131 As a result, dimer [(Fe III DPy) 2 O](OTf) 2 was utilized in the following studying to clarify the mechanism and active species involved in the reactivity of these systems.III.2.2 Study of the photocatalytic mechanismIII.2.2.1 Study of subsystem [Ru II ] + O2Upon light irradiation of a reactional mixture containing a [Ru II ] photosensitizer, methylviologen [MV 2+ ] and semi-hemic iron(III) catalyst [(Fe III DPy) 2 O] we succeeded to utilize a reversible electron relay to exclude sacrificial electron donor in the photocatalytic oxygen atom transfer to an alkene with dioxygen in water. Our work provides a new paradigm to perform photocatalytic oxidation of substrates using solely light as energy input and dioxygen as oxygen source. Understanding the chemistry of this new paradigm is indispensable for improving their reactivity. We thus performed a series of experiments to understand the mechanism and identify the active species responsible for substrate oxygenation under our condition.In 2000, Vaidyalingam and Dutta reported the accumulation of cis-[Ru(bpy) 2 (OH 2 ) 2 ] 2+ complex from decomposition of the [Ru(bpy) 3 ] 2+ photosensitizer following prolonged irradiation of [Ru(bpy) 3 ] 2+ .132 Cis-[Ru(bpy) 2 (OH 2 ) 2 ] 2+ complex can be oxidized to generate highly active Ru IV =O and Ru VI =O species capable of oxygenating substrates.

1 : Substrate conversion under different conditions. Oxygenation reactions were carried out under irradiation for 22, under aerobic conditions in B&R bufer at pH

4. a

The product yield is based on substrate. b TON: turnover number is calculated over catalyst.

133

However, no photo-degradation of the photosensitizer was observed under our irradiation condition. UVvisble spectrum shown a similar absorption of Ru II photosensitizer at 450 nm before and after irradiation for 22 h (Figure III-5), while cis-[Ru(bpy) 2 (OH 2 ) 2 ] 2+ complex is characterized by a absorption band centered at 488 nm. We can thus exclude the participation of chemically altered intermediate such as cis-[Ru(bpy) 2 (OH 2 ) 2 ] 2+ as potent photooxidation catalyst.

  control experiment, where both [(Fe III DPy) 2 O] catalyst and [MV 2+ ] were excluded, we decided to examine the role of oxygen species formed upon reaction with excited [Ru II *]. It is known that [Ru II *] can react with O 2 to form the singlet dioxygen 1 O 2 or the superoxide

	Entry 1 2 3 4 5 Table III-2 : Substrate conversion under different conditions. Oxygenation reactions were carried out [Ru(bpy) 3 ]Cl 2 [(Fe III DPy) 2 O](OTf) 2 MV 2+ Substrate Product yield a TON b Diol Benzaldehyde Epoxyde 30 µM 30 µM 4 mM 10 mM 11.7% 12.7% traces 81 30 µM 0 0 10 mM 0 0 0 0 30 µM 0 4 mM 10 mM 0 traces 0 nd 0 30 µM 4 mM 10 mM 0 0 0 0 30 µM 30 µM 0 10 mM 0 0 0 0 -by an energy or charge transfer, respectively. Although O 2 -is a highly oxidizing agent (E°( O 2 -/H 2 O 2 = 0.94 V vs NHE) 134 and 1 O 2 is known to reacts with double bond to form epoxide product and aldehyde. 135,136 Uunder our experimental conditions, no oxidized products were detected ruling out this photo driven pathway. (Table III-2, Entry 2). The rapid quenching of the Ru* state by MV 2+ probably inhibits the energy transfer to O 2 to form singlet under irradiation for 22 hours, under aerobic conditions, in B&R buffer at pH 4. radical O 2 O 2 while O 2

Table III-2) combined with the detection of relevant intermediate species by Laser Flash Photolysis (LFP) in order to understand the specific role of each compound in our photocatalytic system. a The product yield is based on substrate. b TON: turnover number is calculated over catalyst.

99

In a first -under such experimental conditions leads to the rapid back-electron transfer (Scheme 3). Moreover, O 2 -itself was not capable of oxygenating sodium styrene-4-sulfonate.

  of O 2 is compatible with the competitive reduction of [(Fe III DPy) 2 O](OTf) 2 vs. O 2 by [MV + ] to generate the (DPy)Fe II and O 2 -species respectively with a branching ratio determined essentially by the relative concentrations of [(Fe III DPy) 2 O](OTf) 2 (30 µM) and O 2 ( around 260 µM in air-equilibrated aqueous solution at 25 °C) due to the similar bimolecular rate of two branches (Scheme 6, k 2 and k 2' ). Consequently, the reaction of [MV + ] with O 2 is about 10-20 times more favorable than the reaction of [MV + ] with [(Fe III DPy) 2 O](OTf) 2 due to concentration of [(Fe III DPy) 2 O](OTf) 2 and O 2 that is in agreement with the amplitude of the

	0.02			Time (µs):
				3
				10
				30
	0.01			300
	A
	0.00
	-0.01
	400	500	600	700	800
		Wavelength / nm

(Figure III-13) albeit with lower intensity than in the absence of O 2 . The lower yield in presence

  [START_REF] Werck-Reichhart | Cytochromes P450 for engineering herbicide tolerance[END_REF] O[START_REF] Banerjee | Structure of the key species in the enzymatic oxidation of methane to methanol[END_REF] O and[START_REF] Banerjee | Structure of the key species in the enzymatic oxidation of methane to methanol[END_REF] O[START_REF] Banerjee | Structure of the key species in the enzymatic oxidation of methane to methanol[END_REF] O labelled diol products (Figure III-16, middle). This experimental finding clearly supports that O 2 is the actual source of oxygen atoms. The presence of mixed oxygen-labelled

	diol derivative can be rationalized through dynamic water exchange between an iron-bound
	hydroxo ligand and bulk water (Figure III-17). 158-160 When, the photocatalytic experiment
	was carried out in H 2	18 O under air atmosphere without 18 O 2 , only 18 O 16 O and 16 O 16 O labelled
	diol products were detected (Figure III-16, bottom). One inserted 18 O probably comes from
	epoxide opening by a H 2

  -5).

	buffer
						Diol	Benzaldehyde Epoxide		(h -1 )
	4	30 µM	30 µM	4 mM	10 mM	0.83	1.27	traces	70	3.2
	6	30 µM	30 µM	4 mM	10 mM	traces	1.17	0.66	61	2.7
	Table III-5 : Substrate conversion under different conditions. Oxygenation reactions were carried out
	under irradiation for 22 under aerobic conditions. a TON: turnover number is calculated over
	catalyst.
	pH	[Ru(bpy) 3 ]Cl 2	[L 5 Fe II ] 2+	MV 2+	Substrate		Product (mM)		TON a	TOF
										118

III.3.2

Photo-generation of the active iron species.

Table III -

 III

	[(Fe III DPy) 2 O](OTf) 2	PPh 3	O=PPh 3	TON	TOF
	25 µM	250 mM	6.3 mM	252	17 h -1
	0	250 mM	2.3 mM	x	x
			-6). Moreover, the consumption of O 2 during the
	photo-reaction with [(Fe III DPy) 2 O](OTf) 2 dimer was also accelerated (Figure III-28).
	Therefore, the preliminary results on photocatalytic activity of [(Fe III DPy) 2 O](OTf) 2 in
	organic media are encouraging for further investigation.

6 : Substrate conversion. Oxygenation reactions were carried out under irradiation for 15 hours (λ > 550 nm), under aerobic conditions. a TON: turnover number is calculated over catalyst.

Table IV -

 IV 1: Substrate conversion. a Yield based on substrate, b TON and TOF are calculated over Fe III DPyCl 2 catalyst.

  In this experiment we did not get the chance to add a substrate to identify the signal associated with an active species. However, given previous experiments followed by UV it is quite reasonable to think that at least the main signal corresponds to an active species that is the [Fe III (DPyNO)] 2+ iron N-oxide intermediate. In a second spectrum, measured on the previous solution let to evolve 2 h at room temperature, the weaker signal had disappeared. Therefore, we can propose that it corresponds to an active species too, possibly an Fe III -OIPh intermediate. As already mentioned such an intermediate has been postulated by Nam and McKenzie and shown to be active too in OAT reactions.

	IV.2.3.1.3 Mössbauer spectroscopy
	The iron(III) species intermediate species generated by reaction with PhIO was also studied
	by Mössbauer analysis of the 57 Fe enriched iron(III) samples. The spectrum revealed a main
	signal (73%) that could be fitted with an isotropic shift () of 0.48 mm.s -1 and a quadrupolar
	splitting (E) of 1.53 mm.s -1 , and a minor signal ( = 0.40 mm.s -1 and E = 0.38 mm.s -1 ),
	both compatible with a high spin iron(III) species (Figure IV-32). No highly oxidized iron
	intermediate was thus detected.

  The evolution of these two active species led after 2 hours under inert atmosphere and room temperature to two new sets of signals. The major signal (72 %) could coincidentally be fitted with close isotropic shift (0.49 mm.s -1 ) and quadrupolar splitting (1.53 mm.s -1 ) to the main signal observed before evolution. Knowing that the main active species has a t 1/2 life-time of 15 min, as demonstrated by absorption band at 636 nm. It thus cannot correspond to the same active species but rather to resting forms for example the initial precursor with a different axial ligand like acetonitrile. Similarly, the minor signal (38 %) that was fitted with an isotropic shift of 0.48 mm.s -1 and a quadrupolar splitting of 0.57 mm.s -1 , probably corresponds to another high spin resting iron(III) species that we have not yet characterized.

IV.2.3.1.4 HRMS ESI-HRMS analyses of oxidized solution with PhIO showed two peaks at m/z = 569.9954 and 580.0242 corresponding respectively to [Fe(DPy)Cl + O] + and [Fe(DPy)(OAc) + O] + formula.

Table IV - 2 :

 IV2 Comparison of the characteristic frequencies attributed to N-O-Fe vibrations in the iron intermediate generated by NaClO and PhIO. IV.2.3.1.5 Resonance Raman spectroscopy Having detected such a possible intermediate by HRMS, we also tried to detect the presence of [Fe III (DPy)(OIPh)] 2+ adduct as a precursor of [Fe III (DPyN Py O)] 2+ species. Very few Fe-OIPh species have been characterized. Interestingly, the groups of Nam and Latour were able to identify such a species by Raman spectroscopy. In their case, a 18 O labelled sensitive transition band was detected at 783 cm -1 . The Raman spectra of our sample recorded in collaboration with Dr. Thomas Pino and Dr. Thi Minh Huong Nguyen from Insitut des Sciences Moléculairesd'Orsay (ISMO), showed two new bands at frequencies of 1218 cm -1 and 790 cm -1 upon excitation at 532 nm. Although the band at 790 cm -1 was compatible with the O-I vibration of the iron cyclam iodosylbenzene adduct [Fe III (13-TMC)(OIPh)] 3+ reported by Nam and Latour, 184 attempt to detect a shift upon addition of 18 O labelling water was hampered by the poor quality of the signal (Figure IV-38).

Table IV -

 IV 3: Comparison of the characteristic frequencies attributed to N-O-Fe vibrations found experimentally and theoretically. Another possibility could be the insertion of an oxygen atom in one of the N pyrrole -Fe bonds. The structure of the Fe III (DPyN Pyrrole O)Cl 2 species was also investigated (Figure IV-40). Indeed form II was found very close in energy to form I by DFT calculation. However, no vibration related to the Fe-O-N Pyrrole bounds were calculated in the range observed experimentally. Accordingly, we can exclude the Fe III (DPyN Pyrrole O)Cl 2 species. With the target to isolate the oxidized DPyN Py O ligand, we used the mixture of acetic acid and chlohydric acid (4/1), as reported by Groves, 188 to demetalliated the [Fe III (DPyN Py O)] 2+ intermediate. The isolation of DPyN Py O was unsuccessful probably due to its short lifetime in concentrated acid solution. However, we obtained a chlorinated product determined by X-Ray diffraction on single crystal, reminiscing the chlorinated product observed by HRMS analysis of the frozen Fe III DPyCl 2 solution in acetonitrile after adding NaClO (Figure IV-22 and Figure IV-24). The structure is not presented here due to low quality of the mono-crystals. IV.3 Conclusion The Fe III DPyCl 2 complex was oxidized by different oxidants agents to generate the active iron intermediate species. The reaction with mCPBA probably led to a mixture of many iron intermediates such as [Fe III (DPy)mCPBA] 2+ adduct, [Fe IV (DPy)O] 2+ and [Fe III (DPyN Py O)] 2+ species but the slow formation of these species compared to their life-times under these conditions prevented the characterization. Moreover, The Fe III DPyCl 2 precursor was completely destroyed with mCPBA over 10 min. While, NaClO and PhIO could oxidize the Fe III DPyCl 2 complex to form an identical iron intermediate. The spectroscopic analyses revealed that one of the two pyridine arms was probably oxidized, leading the formation of the N-oxide high spin (S = 5/2) iron(III) species [Fe III (DPyNO)] 2+ species. It is possible that there is an equilibrium between this [Fe III (DPyNO)] 2+ species and the [Fe III (DPy)(OCl)] + or [Fe III (DPy)OIPh] 2+ adduct in solution respectively, but further experiments would be need to confirm this hypothesis.

	IV.2.3.2 Preparation of oxidized DPyN Py O ligand

  The [Fe III (DPy) 2 O](OTf) 2 was characterized by HRMS, UV-vis absorption spectroscopy and X-Ray diffraction on single crystal, confirming the lability of the triflate anion in coordinating solvents. Like the Fe III DPyCl 2 complex, this dimer is able to activate water. Besides, the Fe-O bond in this reaction with MV + to form the Fe III -(hydro)peroxo L 5 species, or, the [L 5 Fe II ] 2+ reacts with , as a product of the reduction of O 2 by MV+ . The LFP experiment revealed the formation of a mixture of iron oxygenated species, that could be [L 5 Fe IV (O)] 2+ , [Fe II (O 2 )L 5 ] 1+ and [L 5 Fe II (OOH)] 1+ , according to the UV-vis spectral observed.In chapter IV, by testing different two-electron oxidants we sought to generate and characterize potent oxidizing species derived from Fe III DPyCl 2 . mCPBA slowly degrades the complex preventing the clear detection of relevant intermediate. NaClO reacts with the Fe III DPyCl 2 complex at room temperature to form an iron active species detected by a new absorption band at 631 nm associated with a life time t 1/2 = 15 min. The EPR analysis revealed that the active species generated by NaClO is a rhombic high spin Fe(III) complex characterized by a broad signal at 4.3 and thus cannot be an Fe(V) oxo species as expected.HRMS analysis indicates that one oxygen atom has yet been added to the iron species. After ruling out a possible Fe III -OCl intermediate, we proposed that the oxygen insertion takes place in a N Pyridine -Fe bond, yielding a [Fe III (DPyNO)] 2+ species, due to the hemilability of the ligand. Our proposition was supported by the vibration energies detected at 855 and 1231 cm - Iodosylbenzene oxidizes the Fe III DPyCl 2 complex to generate an active species which seems identical to the [Fe III (DPyNO)] 2+ generated by NaClO, based on UV-vis absorption, Mass and EPR spectroscopies. Two vibration energies at 840 and 1223 cm -1 , sensitive to[START_REF] Werck-Reichhart | Cytochromes P450 for engineering herbicide tolerance[END_REF] O labelling were also identified. DFT calculation nicely corroborated our experimental results and allowed us to propose a geometry for the [Fe III (DPyNO)] 2 intermediate. Finally, we showed that this intermediate is probably involved in the catalytic oxidation of a variety of substrates, among which the challenging cyclohexane.

	O 2	-

1

by Infrared spectroscopy, which are close to the energies reported for the Fe-O-N vibration in the hexa(pyridine-N-oxide) iron(III) complex. To our satisfaction, this intermediate was found to be a potent oxygen atom transfer agent to triphenylphosphine and thioanisole.

However, we also detected degraded chlorinated complex by HRMS, precluding the application of NaClO as an oxidant in catalysis. PhIO, as a more selective reagent was picked in the next study.

  3, 1.8 Hz, 1 H),7.20 (ddd, J = 12, 4.8, 1.2 Hz, 1 H),7.36- 7.43 (m, 2 H),7.68 (td, J = 7.5,1.8 Hz, 1 H),8.60-8.64 (m, 1 H) ppm.2-(2-Pyrrolyl)pyridine: 2-(N-Boc-1H-pyrrol-2-yl)pyridine (3.9 g,16.05 mmol) was dissolved in CH 2 Cl 2(30 mL), and aqueous HCl 3 M (30 mL) was added. The biphasic mixture was vigorously stirred at room temperature for 60 h. The solution was neutralized by adding the saturated solution of NaHCO 3. and extracted with 100 mL of water (3 times). The organic phase was dried with Na 2 SO4 and filtered. The solution was concentrated to yield 2-(2-Pyrrolyl)pyridine as a white solid (2.28 g, 95 %).1 H NMR (CDCl3, 360 MHz): δ =6.30 (dt, J = 2.6, 3.6 Hz, 1 H),6.7 (m, 1 H), 6.9 (m, 2 H),7.03 (dd, J = 2.0, 5.5 Hz, 1 H),7.54 (d, J = 7.7 Hz, 2 H), 7.62 (td, J = 7.7, 1.6 Hz, 1 H), 8.45 (d, J = 5 Hz, 1 H), 9.8 (br. s, NH) ppm.DPy: p-toluensulfonic acid (4.5 g, 23.7 mmol, 3 equiv.) was dissolved in toluene (50 mL).The Dean stark method was used to eliminate water in the solution. 2-(2-Pyrrolyl)pyridine ( 2.28 g, 15.8 mmol, 2 equiv.), pentafluorobenzaldehye ( 1.55 g, 7.9 mmol, 1 equiv.) and 1,1,2,2-tetrachloroethane (50 mL) were then added. The mixture was heated at 138 °C under argon for 7 day, after which it was basified with aqueous K 2 CO 3 (1 M). The aqueous phase was extracted with chloroform, and the combined organic phases were concentrated and dissolved in dichloromethane (100 mL). The dissolved 2,3-dichloro-5,6-dicyano-1,4benzoquinone (10.5 g, 47.4 mmol, 6 equiv.) in tetrahydrofurane (80 mL) was then added dropwise. The reactional mixture was stirred overnight at room temperature. The solvents were evaporated. The obtained solid was dissolved in 200 mL chloroform , then extracted with 200 mL K 2 CO 3 1 M (3 times). The organic phase was dried with Na 2 SO 4 and filtered then concentrated. DPy (2 g, 54 %) as a brown solid was precipitated in methanol (30 mL) at -20 °C ( freezer).1 H NMR (CDCl3, 250 MHz): δ = 6.59 (d, J = 4.4Hz, 2 H, Hpyrrol), 7.10 (d, J = 4.4 Hz, 2 H, Hpyrrol), 7.29 (m, 2 H), 7.82 (dd, J = 7.8, 1.6 Hz,2 H), 8.20 (d, J = 8.1 Hz, 2 H), 8.72 (d, J = 4.7 Hz, 2 H), 13.70 (br. s, 1 H, NH) ppm. Fe III DPyCl 2 : A solution of DPy ligand (100 mg, 215 µmol, 1 equiv.) in methanol (20 mL) was added dropwise to FeCl 3 .6H 2 O (58,3 mg, 215 µmol, 1 equiv.) in methanol (10 mL) at room temperature then diethyl ether (50 mL) was added to precipitate a solid. The brown residue was filtered and dried under vacuum to give complex Fe III DpyCl 2 (116 mg, 197 µmol, 91%). Single crystals were obtained by diffusing slowly diethyl ether to a saturated solution of complex I in acetonitrile. ESI + -HRMS: calcd. For [C 25 H 12 ClF 5 FeN 4 ] + 554.0015; found 553.9995. UV-vis (CH 3 CN): 668 nm, 589 nm, 320 nm, 298 nm.[{Fe III DPy(EtOH)} 2 O](OTf) 2 : A solution of DPy ligand (100 mg, 215 µmol, 1 eq.) in methanol (20 mL) was added dropwise to Fe(OTf) 2 (89 mg, 215 µmol, 1 eq.) in methanol (5 mL) at room temperature under argon atmosphere in a glove box. The instant color change from red to blue confirmed the formation of Fe II (DPy)(OTf) complex. Then, a cyan solution was obtained by aerating for 1 hour under stirring. A brown residue was obtained by evaporation and dried under vacuum for 8 hours. The complex [{Fe III DPy(EtOH)} 2 O](OTf) 2 was recrystallized by slowly diffusing pentane into a saturated solution in ethanol (132 mg, 85%). ESI + -HRMS: calculation for [C 50 H 24 F 10 N 8 O 1 Fe 2 ] 2+ 527.0301; found 527.0287. UV-vis

Table 0 -1 Compound Fe III DPyCl 2

 0 Empirical Formula C 25 H 12 Cl 2 F 5 Fe N 4 [+ 7/9 (C 2 H 3 N)]

	M r	590.14
	Crystal size, mm 3	0.08 x 0.08 x 0.04
	Crystal system	trigonal
	Space group	R -3 c
	a, Å	22.4084(16)
	b, Å	22.4084(16)
	c, Å	25.9110(19)
	α, °	90
	β, °	90
	γ, °	120
	Cell volume, Å 3	11267.7(18)
	Z ; Z'	18 ; 1/2
	T, K	100 (1)
	Radiation type ; wavelength Å	MoKα; 0.71073
	F 000	5310
	µ, mm -1	0.868
	 range, °	2.623-30.530
	Reflection collected	100 553
	Reflections unique	3 835
	R int	0.1980
	GOF	1.023
	Refl. Obs. (I>2(I))	2 070
	Parameters	170
	wR 2 (all data)	0.1902
	R value (I>2(I))	0.0784
	Largest diff. peak and hole (e-.Å -3 )	0.901 ; -0.511

Table 0 -

 0 1 : Crystallographic data and structure refinement details.

  Table 0-2. 36 F 10 Fe 2 N 8 O 3 , 2(C F 3 O 3 S)

	Compound	[{Fe III DPy(EtOH)} 2 O](OTf) 2
	CCDC		1911145
	Empirical Formula C 54 H M r	1444.75
	Crystal size, mm 3		0.12 x 0.09 x 0.06
	Crystal color		orange
	Crystal system		monoclinic
	Space group		P 2 1 /n
	a, Å		10.6564(9)
	b, Å		21.4716(17)
	c, Å		12.5861(12)
	α, °		90
	β, °		94.915(3)
	γ, °		90
	Cell volume, Å 3		2869.2(4)
	Z ; Z'		2 ; 1/2
	T, K		100 (1)
	Radiation type ; wavelength Å		MoKα; 1.54178
	F 000		1456
	µ, mm -1		0.696
	 range, °		2.405-30.586
	Reflections collected		114 256
	Reflections unique		8 791
	R int		0.0948
	GOF		0.862
	Refl. Obs. (I>2(I))		6 278
	Parameters		427
	wR 2 (all data)		0.1999
	R value (I>2(I))		0.0665
	Largest diff. peak and hole (e-.Å -3 )		1.689 ; -1.286

Table 0 -

 0 2 : Crystallographic data and structure refinement details.

Table 0 -

 0 Table 0-3. 3 : Crystallographic data and structure refinement details.

	Compound	Fe III DPy(OTf) 2
	CCDC	Unpublished-yet
	Empirical Formula	C 27 H 12 F 11 Fe N 4 O 6 S 2
	M r	817.38
	Crystal size, mm 3	0.09 x 0.06 x 0.02
	Crystal system	triclinic
	Space group	P -1
	a, Å	8.2592(5)
	b, Å	12.9292(8)
	c, Å	15.0173(9)
	α, °	87.401(3)
	β, °	75.093(2)
	γ, °	72.263(2)
	Cell volume, Å 3	1475.04(16)
	Z ; Z'	2 ; 1
	T, K	100 (1)
	Radiation type ; wavelength Å	MoKα; 0.71073
	F 000	814
	µ, mm -1	0.774
	 range, °	2.208-31.130
	Reflection collected	90 232
	Reflections unique	9 337
	R int	0.2021
	GOF	0.999
	Refl. Obs. (I>2(I))	4 806
	Parameters	460
	wR 2 (all data)	0.1374
	R value (I>2(I))	0.0587
	Largest diff. peak and hole (e-.Å -3 )	0.890 ; -0.776

Table 0 -

 0 4: HPGC conditions used in the quantification of the oxidized products.

	204

Table 0 -

 0 Photocatalytic experiments in chapter III were carried out in a glassy vial (1.5 mL) containing typically 30 µM [Ru(bpy) 3 ]Cl 2 , 30 µM [(Fe III DPy) 2 O](OTf) 2 , 4 mM MV 2+ and 10 mM 4styrene sulfonate sodium in 0.5 mL Britton & Robinson buffer pH 4.0 at 25 °C. The samples were placed on a white LED (1.3 mW.cm -1 ) equipped a filter (T=0 for  < 415 nm). at room temperature, under air, covered with a black box, and irradiated for 22 h. The products were identified and quantified by1 H NMR (see below).Photocatalytic experiments under[START_REF] Werck-Reichhart | Cytochromes P450 for engineering herbicide tolerance[END_REF] O 2 atmosphere were run in a Schlenk tube. The reaction mixture in 1 mL B&R buffer was subjected to 3 vacuum / argon cycles then 1 vacuum / 18 O 2 oxygenation. After photo-reaction, samples were treated with 1 mL HCl 1M then extracted with 1 mL ethyl acetate (3 times). Ethyl acetate was removed by air flow to avoid product loss then the residue was redissolved in 50 µL water. 30 µL of solution were injected in HPLC.The[START_REF] Werck-Reichhart | Cytochromes P450 for engineering herbicide tolerance[END_REF] O labeling products formed were separated by preparative HPLC in presence of solvent gradient detailed in Table 0-6 -. The retention time for p-styrene sulfonate and the corresponding oxidized products is presented in Table 0-7. Each product was collected separately and analysed by HRMS-ESI -without dilution.

	Time (min)	H 2 O + 0.05 % HCOOH	MeCN + 0.1 % HCOOH
	0	95	5
	2	95	5
	5	90	10
	10	0	100
	15	0	100
	17	95	5
	20	95	5

5: Retention time and constant k of each substrate and the corresponding oxidized products. 205 Photocatalytic procedure

Table 0 -

 0 6:Solvent gradient used for HPLC analysis.

	206

Table 0 -

 0 7: Retention times for sulfonic p-styrene acid and the corresponding oxidized products.

  1 NMR spectra were recorded with a water suppression program. The starting compound and oxidized products were identified by 1 NMR (Styrene sulfonate by doublet at 6.75 ppm, benzaldehyde by singlet at 9.11 ppm, diol by doublet at 7.37 ppm, epoxide by doublet at7.42 ppm) and quantified by the following equations, with I: Peak integration:

	% benzaldehyde = [
	% diol	= [
	% epoxide	= [

s -1 ) and a minor oxidation of olefin by the oxidized photosensitizer ([Ru III ]) (step 4 with

O (blue).

Remerciements

a été réalisé dans le cadre du projet Multiplet, financé par l'Agence Nationale de la Recherche (ANR) et effectué à remerciements à mes encadrants Pr. Ally

III.2.2.3 Role of catalyst

We then assessed the role of [(Fe III DPy) 2 O](OTf) 2 complex. The Fe-O bond of µ-oxo diiron(III) can be photoactivated to implicate the formation of a Fe II complex and an active Fe IV =O complex capable of oxygenating alkene and alkane to release Fe II complex in aprotic solvent as previously described by Nocera. [144][145][146] The photogenerated Fe II complex reacts with dioxygen to form a µ-peroxo diiron(III) intermediate followed by a O-O bond cleavage leading to the formation of an Fe IV =O species. [START_REF] Balch | Oxygenation patterns for iron(II) porphyrins. Peroxo and ferryl (FeIVO) intermediates detected by proton nuclear magnetic resonance spectroscopy during the oxygenation of (tetramesitylporphyrin)iron(II)[END_REF]115,120 However, this photocatalytic activity pathway is probably deactivated in aqueous medium that was confirmed by no oxidized product detected in the blank experiment in presence of [(Fe III DPy) 2 O](OTf) 2 and without

2). Alternatively, the formation of the diol may come from the ring opening of an epoxide formed from the high valent Fe-oxo intermediate (Scheme 8, eq. 3).

III.2.2.5 Influence of the pH media

When the photocatalytic run was realized at pH 6, only the epoxide and the aldehyde were revealed (Table III-3). This subtle reactivity control brings further confirmation that the oxygen atom transfer reactions are guided through activated forms of O 2 at the iron center. iron(V) species. The author proposed that the reactivity towards C-H activation comes from the iron(V)-oxo species. IV. 1.1.3 Fe-OIAr Iodosylarenes are another important class of oxygen atom transfer reagents in organic synthesis, often used in conjunction with transition-metal-based catalyst. 177,178 Oxygen atom transfer from iodosylarenes to iron complex giving the corresponding iron-oxo species was suggested to proceed via the formation of iron-iodosylarene adduct shown in Figure IV-5. The existence of an equilibrium between iron-oxo species and iron-iodosylarene adduct was reported by Nam and co-workers in 2003. 179 They indeed showed that by reaching [(TDCPP)Fe IV =O] + or [(TDFPP)Fe IV =O] + (previously generated using mCPBA as oxidant) with iodobenzene, [(TDCPP)Fe III (OIPh)] + or [(TDFPP)Fe III (OIPh)] + , respectively could be formed and detected spectroscopically. Remarkably, the formation of iron-iodosylarene was not observed with any iron-oxo porphyrin species / iodoarene combination. For example, the formation of iron-iodoarene adduct was not observed in the reaction of PhI and [(TMP)Fe IV =O] + based on an electron-rich porphyrin ligand. Nor, the reaction of [(TDCPP)Fe IV =O] + species and the electron-poor F 5 C 6 I. Interestingly, the iron-iodosylarene adducts [(TDCPP)Fe III (OIPh)] + and [(TDFPP)Fe III (OIPh)] + were immediately converted back into the iron(III) porphyrins [(TDCPP)Fe III ] + and [(TDFPP)Fe III ] + respectively, upon addition of a substrate such as thioanisole and cyclohexene, indicating that these iron-iodoarene adducts seemed to be oxidizing agent. However, the possibility that the small amount of the active iron(IV)-oxo cation radical in equilibrium with the iodoarene adduct could oxidize the substrates, was not excluded. cases is the iron-iodosylarene adduct, not iron-oxo species. However, one can not exclude a minor participation of an iron-oxo species

IV.1.2 Ligand-oxygenated iron(III) species

Iron intermediates where the ligand have undergone self-oxidation were detected in the reaction of an iron precursor with oxidizing agent. In 1986, Groves and Watanabe reported on an iron(III) N-oxide porphyrin species obtained by oxidizing [Fe II (TMP)] + in toluene by 2 eq. of m-CPBA. [186][187][188] The reaction was monitored at -50°C by UV-visible spectroscopy, showing the immediate formation of iron(III)-m-CPBA adduct followed by a relatively slow decomposition to iron(III) porphyrin N-oxide species. The formation of iron(III) porphyrin N-

IV.2.3.3 Catalytic activity study

The catalytic activity of Fe III DPyCl 2 was evaluated in presence of 800 eq. of different substrates and 20 eq. of PhIO in acetonitrile at room temperature. The catalyst and the substrates were dissolved in acetonitrile, then solid PhIO was added portion wise and the suspension was stirred for the time indicated (Figure IV-4). The oxidized products were analyzed and quantified by HPGC using an internal standard. Of note, PhIO cannot oxidize the substrates in this study by itself. Quantitative oxidation of thioanisole was observed within 2 h. Among the three alkenes used as substrate, cyclooctene was oxidized to cyclooctene oxide, affording a conversion of 46 % and 100 % of selectivity for epoxidation. The oxidation of cyclohexene and styrene afforded over 100 % conversion calculated on oxidant with a modest selectivity for epoxidation, suggesting an auto-oxidation process occurring under air atmosphere. [START_REF] Sankaralingam | Selective Oxygenation of Cyclohexene by Dioxygen via an Iron(V)-Oxo Complex-Autocatalyzed Reaction[END_REF] Indeed, the catalytic experiment run under inert atmosphere showed a conversion of 19 % for cyclohexene oxidation with high selectivity towards the epoxide product (Table IV-5).

The conversion for toluene oxidation was not changed under inert atmosphere comparred with that under air atmosphere, suggesting that the alkene hydroxylation was not an auto-oxidation process.

Chapter V : Conclusion & Perspectives

dimer is not inert and can be activated under certain conditions such as temperature, or the presence of acid, suggesting promising application in oxygen atom transfer reaction.

In Chapter III, this promising complex was tested as part of a photocatalytic system to promote the aerobic photooxidation of styrene into diol and benzaldehyde, in a completely new and counter-intuitive approach. Sacrificial electron acceptors are usually needed for the activation of the catalyst by the photosensitizer. But they are an "evil necessicity" since they are non-atom economic and can deactivates the photocatalyst. In an attempt to exclude the use of sacrificial electron acceptor, we found that methyl viologen MV 2+ as a reversible electron acceptor produces superoxide in pH 4 B&R buffer under aerobic condition, which can, by the mediation of our catalyst, transfer oxygen atom to an organic substrate. (hydro)peroxo to form benzaldehyde. On the other side, the olefin is oxidized by the Fe V =O species, generated from Fe III -hydroperoxo species, to form the diol product. When the photocatalytic run was performed at pH 6 the benzaldehyde product was found as the main product, since the protonation of the Fe III -peroxo was disfavored in such condition.

All attempt to chase the Fe III -(hydro)peroxo and Fe V -oxo DPy species were unsuccessful in aqueous medium, probably due to their short lifetime. We decided to generate the active iron DPy species by the reaction of H 2 O 2 and the prepared [Fe II DPy] + complex in MeOH at -40 °.

The formation of an active iron species was observed within few seconds by the detection of a band at 632 nm and an EPR signal at g =4.3 assigned to a rhombic high spin iron(III) species.

To investigate further this new approach, we utilized the [L 5 Fe II ] 2+ complex as catalyst.

Electrospray ionization mass spectrometry

The Thermo Scientific DSQ 2004 model from Thermo Fischer Scientific Company was employed for recording the electrospray ionization mass spectrometry experiments with an ESI + or ESI -method. Samples were prepared in a 100-200 µM solution with methanol or acetonitrile as solvent to directly inject into the spectrometer. For intermediate species, the samples were frozen in liquid nitrogen after preparation, then allowed to melt at room temperature just a few seconds before injection it in the device.

Electronic paramagnetic resonance spectrometry

X-band (9.47 GHz) EPR measurements were measured by using a Bruker Elexsys E 500 spectrometer with an Oxford ESR9 liquid helium (5 K) flow cryostat using a gold-chromel thermocouple directly below the sample position. Sample concentration were typically 1 mM.

The complexes and intermediates were prepared in acetonitrile with 0.1 M TBAPF 6 then transferred to a degassed EPR tube and frozen to 77 K. The presence of solvent molecules could easily be seen by residual peaks located in closed spherical cavities (Figure 0-3).

Catalytic procedure

Catalytic experiments in chapter IV were carried out in a glass vial (3 mL) containing 1 mL acetonitrile solution of 1 mM Fe III DPyCl 2 (1 eq.) and 800 mM substrate. 20 eq. of PhIO was added to solution. After stirring for 2 h at room temperature, 3 µL of internal standard solution (2 mM final) was added to the reactional solution. The resulting solution was filtered through a short silica gel column (on a Pasteur pipette). 1.5 mL MeOH was used to collect all remaining organic product from the silica gel column. The obtained solution was injected into HPGC to detect and quantify the oxidized product.

Quantification of oxidized products by HPGC 2 mM acetophenone was used as an internal standard in the catalytic experiments towards the oxidation of cyclohexane, cyclooctene, diphenylmethane and thioanisole, while 2 mM anisole was used as an internal standard for the oxidation of cyclohexene, toluene and ethylbenzene.

The HPGC conditions is detailed inTable 0-4. Concentration of the oxidized products was calculated by the following equation:

k in this equation is a constant which is obtained from the slope of the calibration curves. The retention time (rt) and k value for the oxidized products was presented in Table 0-5.

Simulation of kinetic traces

Simulation of the kinetics of the substrate (4-styrene sulfonate sodium) photo-oxidation in the presence of typically 30 µM [Ru(bpy) 3 ]Cl 2 and 4 mM MV 2+ in absence of dioxygen, was performed using the KinTek Explorer simulation program. 199,200 A reaction scheme was used including the following reaction sequence: Title : Bioinspired semi-hemic iron(III) complex for chemical and photochemical oxygen atom transfer reactions Keywords : iron complex, dioxygen activation, multielectron transfer, oxygen atom transfer, catalysis, photocatalysis Abstract : Hydrocarbon oxidation is a real challenging chemical transformation both in biology and chemistry. Highly oxidized metal-oxo species are the active intermediates to perform these transformations. In this manuscript we report the synthesis and characterization of an iron(III) complex supported by a non-innocent hemi-porphyrinic ligand, constructed with a dipyrrin fragment and two pyridine functions. The iron(III) complexes have been prepared and characterized, with a focus on their electrochemical behavior and their potential use as catalysts in the activation of green oxygen source such as dioxygen and water for hydrocarbon oxidation. We found that these complexes can catalyze the oxidation of a fair variety of substrates using oxidant agent such as iodosylbenzene.

Intriguingly, our gathered results point to a reactivity pattern that stems from a low-oxidation state iron species. Electron Paramagnetic Resonance and Mössbauer analyses support a high spin iron(III) reactive species. Furthermore, data from mass spectrometry and Infra-red spectroscopy supported by DFT calculations helped us to propose the chemical formulation of this chemically generated intermediate where the ligand has been reversibly oxidized. Additionally, these complexes were used as catalysts in a photocatalytic system using a reversible electron acceptor to preclude the "evil necessity" of a sacrificial electron donor. Our study provides a new paradigm to perform photoinduced oxygen atom transfer reactions with solely light as energy input and O2 as oxygen atom source in aqueous solution.