Binh Dang

Ho

Thèse Dirigée

Jean-Pierre Djukic

Iridium(III) silylene complexes: trapping, reactivity and applications

Acknowledgment

First of all, I would like to express my gratefulness to Dr. Jean-Pierre Djukic who gave me a chance to conduct my thesis in LCSOM. Without your thoughtful guidance, I will definitely not achieve this level. You not only provided intelligent ideas to help me to overcome chemistry problems but also support me endlessly when I lacked confidence and motivation. I express my gratitude to Dr. Michel PFEFFER who always gives me valuable advice in both science and career. I also express my thanks to Dr. Mustapha Hamdaoui, my friend, my colleague, who helped me so kindly since my first day in the lab. My chemistry will be not completed if lacking sophisticated X-Ray characterization executed by Lydia Karmazin and Corinne Bailly as well as modern NMR conducted by Bruno Vincent. Contributing to my English fluency is my friend, my proofreader, and my English teacher, Jenna van Buren, who taught me English since I started my journey. I would like to thank Morgan Whitworth for your unconditional, inexhaustible encouragement that you gave me. My colleagues, Geneviève Stoll, Mélanie Boucher, Christophe Deraedt, Milan Milovanovic, Ali Moussa, Wu Fule play a particularly important role in my achievement. I extend thanks to my best friend Trần Hồ Thanh Vũ, Nguyễn Xuân Vũ, Thi Trịnh Tú Như, Huỳnh Dương Thiện Như, Tô Thúy Anh. I show my appreciation to my parents, Lê Kim Đính, Hồ Đức Bình, my extended family, Trịnh Thanh Nhàn, without your support your heartening I will not be strong, be brave to accomplish this study.

Résumé 1) Introduction

La portée de cette thèse englobe les avancées les plus récentes dans l'étude des liaisons chimiques des complexes iridium-silicium, dans lesquelles un groupe silyle lié à un métal se comporte comme un ligand Z qui maintient une liaison dative avec le centre du métal. Ceci contraste grandement avec le cas où ce groupe se comporte comme un ligand X, c'est-à-dire où ce groupe silyl se lie à Ir par une liaison covalente. Enfin, il est intéressant de noter que les ligands de silylène devraient en principe établir une double liaison avec le centre de l'Ir.

2) Résultats et discussions

Il convient de rappeler la ''méthode de classification par liaison covalente (CBC)'', inventée par Malcolm Green, une méthode ingénieuse pour la classification formelle des composés de coordination. La méthode est basée sur la notion que les atomes d'un ligand directement lié par une liaison primaire au centre métallique sont appelés ''atomes de ligature''. Celles-ci contiennent trois types d'interactions possibles, à savoir la fonction X, la fonction L et la fonction Z. Pour examiner plus avant le caractère de la liaison Ir-Si, plusieurs iridacycles [(C,N) Cp*Ir(III)-Cl] ({C,N} = benzo [h]quinoline, phenyl pyridine, dibenzo[f,h]quinoline) associées à des anions de type BArF-type ont été synthétisés (schéma 1). Ces complexes d'iridium ont constitué un bon point de départ pour explorer de nouvelles applications catalytiques et pour étudier le comportement de silyl ou de silylium.

Schéma 1: Synthèse du métallacycle suivie de l'abstraction de chlorure et remplacement par de l'acétonitrile coordiné Ces complexes cationiques ont démontré une capacité remarquable à catalyser la Odéshydrosilylation des alcools et l'hydrosilylation de composés nitriles par Et3SiH. Des études mécanistiques ont également montré que l'intermédiaire clé était un hydrido-Ir(III)-silylium hautement réactif, dans lequel le fragment Et3Si était lié au centre métallique par une liaison dative et se comportait donc comme un ligand de type Z selon le formalisme de Green (schéma 2). Schéma 2: liaison Si-H activée par Irridacycle L'idée d'évaluer et d'ajuster le caractère électrophile du fragment silyl et de sa ''silylicité" a été explorée de manière expérimentale et théorique 1 . Pour mener à bien cette étude, une large gamme d'adduits métal - silane et d'autres complexes métal - silyl ont été étudiés par calcul des énergies d'interaction métalsilyl afin de définir la relation de liaison existant entre le centre métallique et une entité SiR3. En outre, cette recherche a révélé une séparation nette entre les cas dans lesquels le caractère Z du fragment silyl est la meilleure description, et les cas appartenant à des situations "classiques" dans lesquelles le caractère X domine. De plus, nous avons postulé que pour les adduits métal - silane qui possèdent une faible silylicité intrinsèque, une "silylicité" élevée peut être déclenchée par le remplacement du ligand ou par une modification de la charge du complexe. Tout en travaillant sur ce sujet, nous avons découvert qu'en présence de tétrahydrofurane (THF), les adduits [(Ir-H)→SiRH2] + se convertissent facilement par élimination de H2 à une température sub-ambiante en un nouvel au complexe métallacyclique de ''silylene''stabilisé par une molécule de THF (schéma 3). Ces analogues de silicium de complexes carbèniques ont longtemps attiré l'attention par le passé en tant qu'intermédiaires présumés dans les transformations catalysées par des métaux impliquant des composés organosiliciés. Bien que des complexes métalliques stables de ce type aient été ciblés depuis les années 1960, l'accès à ces espèces reste incertain en raison de leur réactivité élevée.

Schéma 3: Résumé de la route vers les complexes de silylène stabilises L'émergence de complexes silylène-métal via des activations séquentielles de liaison H-Si, suivies de la libération spontanée de H2 décrite dans cette thèse de doctorat, est unique. En effet, les principales méthodes de préparation des silylènes métalliques sont basées sur l'abstraction de substituants anioniques, la migration alpha d'hydrogène, la coordination d'un silylène libre ou l'abstraction de substituants sur un ligand de silyl. L'objectif principal de cette thèse était enfin de caractériser complètement ces complexes a priori insaisissables par des analyses par spectroscopie RMN et par analyse par diffraction des rayons X (schéma 4). Schéma 4: structure aux rayons X de complexes de silylènes stabilises Couplé à la chimie des complexes silylène métalliques mentionnés ci-dessus, l'iridacycle cationique 1b présente une réactivité catalytique intéressante vis-à-vis des nitro-arènes, qui peuvent effectuer la réduction du groupe nitro pour donner des produits dérivés de l'aniline (schéma 5).

Schéma 5: Iridacycle cationique 1b effectuer la réduction nitro Un ensemble d'alkylsilanes a été sondé pour rechercher le plus efficace, tandis que les conditions de réaction catalytique ont été optimisées. Comme on pouvait s'y attendre, les silanes primaires et secondaires capables de former des complexes silylniques d'iridium expriment une réactivité catalytique, contrairement aux silanes tertiaires, qui sont incapables de donner des silylènes. Les résultats suggèrent que des complexes de silylène hautement électrophiles sont impliqués dans le processus catalytique.

Il est raisonnable de supposer que la réactivité catalytique des espèces cationiques d'hydrido-Ir(III)-silylium, est en corrélation significative avec l'étendue de la polarisation de la molécule. Une telle polarisation qui se produit déjà dans le produit d'addition Irsilan l'électropositivité du centre Si. En maintenant l'ossature du ligand principal constante, l'introduction d'un substituant fluoré augmente la polarisation de la même molécule et, par voie de conséquence, impacte sa réactivité catalytique (schéma 7). Schéma 6: En ajoutant un groupe attracteur fort, l'intermédiaire clé F-1a est plus polarisé que 1a On a donc fait réagir AgF2 avec de la 2-phényl-pyridine pour donner lieu à la 2-phénylpyridine fluorée, qui devait servir de point de départ pour la synthèse de complexes solvato cationiques fluorés F-1a. (schéma 7) Schéma 7: Synthèse de complexes solvato cationiques fluorés. Comme on pouvait s'y attendre, F-1a présente également une réactivité catalytique remarquable vis-à-vis d'une réaction de test de référence pouvant être suivie par piézométrie, c'est-à-dire la O-déshydrosilylation d'alcools à la température ambiante avec Et3SiH. Un cristal de l'intermédiaire hydrido-Ir(III)-silylium a également été piégé à la suite d'une réaction avec Et2SiH. (schéma 8) Schéma 8: F-1a a réagi avec Et2SiH2 à partir d'un produit d'addition

3) Conclusion générale

En conclusion, s'appuyant sur la découverte d'une nouvelle propriété chimie des intermédiaires hydrido-Ir(III)-silylium, cette thèse a fait progresser les connaissances sur les complexes de coordination de ligands base par la synthèse et la caractérisation structuralle complète de complexes de silylène métalliques extrêmement réactifs. Des méthodes de calcul théorique ont également été utilisées pour éclaircir le mécanisme de conversion des adduits d'Ir-silane en silylènes, dont un grand nombre ont été piégés par cristallisation réactive et ensuite caractérisés par analyse par diffraction des rayons X.

Introduction 1. The journey to silylene chemistry 1.1. First subject: the concept of hemichelation

Around one hundred years ago, the so-called valence bond theory was proposed by the American chemist Gilbert Lewis 2 . Along with ionic bonding theory, these two theories are of ulmost importance in chemistry. However chemical interactions are much more diverse than that. For instance, hydrogen bonds are the result of electrostatic attraction between hydrogen and other more electronegative atom such as nitrogen, oxygen, or fluorine, etc. Dative bonds (now more generally called donoracceptor bonds) possess both electrons arising from just one atom.

Unveiling the nature of bonding between atoms or compounds has always earned a widespread interest for chemists because insight into bonding helps us not only interpret the reactivity of given compounds but also predict their behavior in chemistry.

The thesis was to aim to fundamentally study the nature of covalent and non-covalent interactions in transition metal complex chemistry as well as to probe complex catalytic systems (multicomponent tandem catalysis reaction, catalysis for the production of small energetic molecules, multicomponent catalysis of C-H, Si-H, B-H, C-F activation).

Our laboratory provided a rational method of synthesis of stable neutral T-shaped 14

electron Pd and Pt complexes [3][4][5] . The ambiphilic tricarbonyl(η 6 -indenyl)chromium anion was used as a hemichelating and heteroditopic ligand, which is capable of chelating a metal center( Pd, Pt) by covalent and noncovalent interaction (scheme 1).

Scheme 1: method of synthesis of stable neutral T-shaped 14 electron Pd and Pt 4

Chromium anion complexes were reacted with several Pd and Pt metallacycles to afford new air-stable and persistent synfacial heterobimetallic complexes.

Along with this line, numerous other metal complexes served as acceptors were investigated, for example, ClAu(THT) (THT = tetrahydrothiophene), [(NBD)RuCl]2, [(COD)RuCl]2 (scheme 2). Those were deprotonated and then treated with tricarbonyl chromium anions as the ambiphilic hemichelating ligand, however, the desired products failed to form.

Scheme 2: General method of synthesis hemichelate complexes

Driving the reaction medium to ligand substitution (departure of COD, NBD, Cl, etc…) instead of the redox decomposition is the biggest challenge of those gold complexes.

Regrettably, that was unachievable because Cr(0) in chromium complexes is easy to be oxidized by Au(I). Therefore, the reaction often ended up with the formation of black particles as the decomposition of the starting molecular and reactant complexes.

As for Ruthenium complexes, despite their behavior different than gold complexes, which did not lead to the decomposition, their lack of reactivity obstructed any attempt to isolate new binuclear hemichelates.

In the last endeavor, we tried to reproduce the chemistry of Pomeroy 6-13 that evidenced the possibility of forming metal based donor-acceptor complexes using 18-electron complexes as donor ligands such as Cp*Ir(CO)2 and indenylIr(CO)2 whose fivecoordinate metal centers are expected to expand their coordination numbers to six readily (scheme 3). [M]

Scheme 3: 18-electron Ir complexes behaving as donor ligands

In addition, third-row neutral transition-metal donors give rise to much stronger dative bonds than their lighter congeners according to Pomeroy et al 6,7,[START_REF] Einstein | Synthesis, structure and fluxional properties of (.eta.5--C5Me5)(OC)2IrW(CO)5. A compound with an iridium--tungsten dative bond[END_REF][START_REF] Einstein | Comparison of dative and covalent metal--metal bonds: structures of the isomers (Me3P)(OC)4OsRe(CO)4(Br) and (Br)(Me3P)(OC)3OsRe(CO)5[END_REF][START_REF] Davis | Complexes with unbridged dative bonds between osmium and a Group 6 element. Structures of (Me3P)(OC)4OsM(CO)5 (M = chromium, tungsten)[END_REF] . Nonetheless, these attempts were not successful, owing to the dominance of redox decomposition that ensued almost in all cases and the lack of reactivity of acceptor complexes.

Due to the failure to get promising results on this project, we have refocused our experimental work on the topic "Exploring the reactivity of silyl groups in metal-silane adducts", the aim of which was to understand the nature of the metal-silicon bond in metal-silane adducts.

The second subject: Investigating the reactivity of Silyl groups in metal-silane adducts.

In this project, we wanted to establish a descriptor of the reactivity of silyl groups in transition metal complexes that would help chemists define the character of the silyl group in new metal-silane adducts. At the same time, the objective was to establish the design of new catalysts and the prediction of their reactivity. This project required the theoretical and experimental investigation of the reactivity of a myriad of known Ir-Si complexes, among which are those synthesized by Maitlis [START_REF] Fernandez | Synthesis, x--ray, and low--temperature neutron--diffraction study of a rhodium(V) complex: dihydridobis(triethylsilyl)(pentamethylcyclopentadienyl)rhodium[END_REF][START_REF] Ricc | Dihydridobis(triethylsilyl)pentamethylcyclopentadienyliridium(V):Neutron diffraction and photoelectron spectroscopic studies[END_REF] and hold the reputation of being Ir(V) complexes (scheme 4). This study involved the investigation on parameter could contribute to changing the character of Ir-Si bonds, among which the nature of the ligands bound to the metal and the charge were the most interesting. Obtained data on this project contributed to our publication in 2017 "Is the R3Si Moiety in Metal-Silyl Complexes a Z ligand? An Answer from the Interaction Energy" [START_REF] Binh | Is the R3Si Moiety in Metal-Silyl Complexes a Z ligand? An Answer from the Interaction Energy[END_REF] .

In this article a broad range of metal-silane adducts and other metal-silyl complexes were investigated by the computation of metal-silyl interaction energies to outline the established tools that rationalize the bonding relationship that exists between the metal center and a SiR3 moiety. Also, has this research unveiled a net/clear separation between cases in which the Z character of the silyl moiety is the best description, and cases that belong to "classical" situations in which the X character dominates. Moreover, we postulated that for metal-silane adducts that possess a low intrinsic silylicity, the high "silylicity" can be switched on by ligand replacement or a change in the oxidation state of the metal.

To follow up the idea of evaluation and tuning silylicity character as mentioned above, the set of iridacycles [(C,N)Cp*Ir III -Cl] ( (C,N)=benzo [h]quinoline, phenyl pyridine, dibenzo[f,h]quinoline) associated with BArF-type anions were synthesized (scheme 5) [START_REF] Hamdaoui | Evidence of a Donor-Acceptor (Ir-H)→SiR3 Interaction in a Trapped Ir(III) Silane Catalytic Intermediate[END_REF][START_REF] Hamdaoui | Iridacycles as Catalysts for the Autotandem Conversion of Nitriles into Amines by Hydrosilylation: Experimental Investigation and Scope[END_REF] , then serving as a good starting point to explore new catalytic applications and to investigate silyl or silylium behavior in Ir-Si complexes.

Scheme 5: Synthesis of metallacycle followed by Chloride abstraction and

replacement by coordinated acetonitrile [START_REF] Hamdaoui | Evidence of a Donor-Acceptor (Ir-H)→SiR3 Interaction in a Trapped Ir(III) Silane Catalytic Intermediate[END_REF][START_REF] Hamdaoui | Iridacycles as Catalysts for the Autotandem Conversion of Nitriles into Amines by Hydrosilylation: Experimental Investigation and Scope[END_REF] These cationic complexes display a remarkable capability to catalyze the Odehydrosilylation of alcohols and hydrosilylation of nitrile compounds by Et3SiH. Mechanistic studies also have shown that the key intermediates are highly reactive hydrido-Ir(III)-silylium species in which the Et3Si moiety behaves as a Z-type ligand according to Green's formalism (scheme 6) [START_REF] Hamdaoui | Evidence of a Donor-Acceptor (Ir-H)→SiR3 Interaction in a Trapped Ir(III) Silane Catalytic Intermediate[END_REF] . Scheme 6: A catalytic process to yield the N,N-disilylamine in the presence of adducts [START_REF] Hamdaoui | Evidence of a Donor-Acceptor (Ir-H)→SiR3 Interaction in a Trapped Ir(III) Silane Catalytic Intermediate[END_REF][START_REF] Hamdaoui | Iridacycles as Catalysts for the Autotandem Conversion of Nitriles into Amines by Hydrosilylation: Experimental Investigation and Scope[END_REF] Even though adducts could not be preparatively isolated and fully characterized analytically, crystals could be trapped and analyzed by X-ray diffraction analysis.

Scheme 7: Si-H bond activated by Irridacycle

The discovery of Silyene Ir III complexes

While working on this topic, we discovered that in the presence of tetrahydrofuran (THF), [(Ir-H)→SiRH2] + adducts readily convert by H2 gas elimination at sub-ambient temperature into new THF-stabilized metallacyclic Ir(III)-"silylene" . The primary goal of this thesis finally is to fully characterize those complexes by NMR spectroscopic analyses and X-ray diffraction analysis (scheme 8) [START_REF] Binh | Entrapment of THF--Stabilized Iridacyclic IrIII Silylenes from Double H-Si Bond Activation and H2 Elimination[END_REF] .

Furthermore, DFT calculation and NMR kinetic research were utilized to demonstrate the essential importance of THF, which facilitated H2 elimination. Catalytic reactivity trials on fluorinated compounds and nitro compounds were also performed.

Scheme 8: Summary of our work from 2016 until the discovery of silylene 18

Problematic.

Given that silylene metal complexes are of interest as possible intermediates in many transition metal-catalyzed reactions, silylene transfer is one of the most interesting utilizations one can imagine, and also the aspect that requires an ample scrutiny of synthesis and reactivity of those complexes.

The very first effort on silylene tranfers was made in 1962 by Volpin and colleagues [START_REF] Volpin | Three--membered heteroaromatic compounds-I[END_REF] to trap bivalent silicon, based on the proposed hypothesis of chemical similarity between carbene and silylene. Those reactive species might be obtained by means of:

(1) The reactions of dimethylchlorosilane and sodium in boiling xylene:

(CH3)2SiCl2 + Na ⟶ (CH3)2Si + 2NaCl
(2) The thermolysis of Si-Si bonds in the polymer [(CH3)2Si]n (with n = 55)

[(CH3)2Si]n (t o )⟶ n(CH3)2Si
They presumed that in both cases, the presence of diphenylacetylene triggered the addition of the intermediate dimethylsilylene to the triple carbon-carbon bond to give rise to a silacyclopropene (Eq. 1) whose composition, molecular weight, infrared and chemical all lived up to their expectation.

Eq. 1 [START_REF] Binh | Entrapment of THF--Stabilized Iridacyclic IrIII Silylenes from Double H-Si Bond Activation and H2 Elimination[END_REF] However, the claim of Volpin and colleagues was soon refuted by the demonstration that the isolated product was not a silacyclopropene but its dimer (Eq. 2) [START_REF] West | The Nature of "Silirene" Compounds[END_REF]22 .

C C + (CH 3 ) 2 Si Si CH 3 CH 3
Eq. 2 20 21 The success of trapping divalent silylene to produce silacyclopropene was replicated and achieved years later by Conlin and Gaspar who reported that dimethylsilylene was generated by thermolysis of 1,2-dimethoxytetramethyldisilane in the addition of 2butyne to give tetramethyl- 1-silacyclopropene (Eq. 3) [START_REF] Conlin | Tetramethylsilacyclopropene[END_REF] .

Eq. 3 22 Those works then have initiated an abundance of research on synthesis of silacyclopropene via silylene transfers. There are three standard methods to trigger the formation of bivalent silicon species: photolysis, thermolysis and metal-catalysis, the latter will be discussed further in this section.

One of the initial works was published by Kumada in 1971 (Eq. 4), in which treatment of pentamethyldisilane with diphenylacetylene catalyzed by a platinum complex gives rise to 1,1,4,4-tetramethyl-1,4- disilacyclohexadiene derivative [24][START_REF] Atwell | Divalent Silicon Intermediates[END_REF][START_REF] Atwell | The thermolysis of methoxypolysilanes[END_REF] .

Eq. 4 23- In that account, the authors believed bivalent silicon species was first released by platinum complex after which disilacyclohexadiene was formed via the dimerization of intermediate silacyclopropane that had trapped free "dimethylsilylene" intermediate followed the below mechanism (Eq. 5).

Eq. 5 [START_REF] Conlin | Tetramethylsilacyclopropene[END_REF][24][START_REF] Atwell | Divalent Silicon Intermediates[END_REF] In 1985, Seyferth et al. assessed the interaction of silirene 1,1-dimethyl-2,3bis(trimethylsilyl)silirene with phenylacetylene in the presence of a catalytic amount of bis(triphenylphosphine)palladium dichloride (Ph3P)2PdCl2 (Eq. 6) [START_REF] Seyferth | Silacyclopropenes. 3. Palladium--catalyzed insertion reactions[END_REF] .

After 1h, GLC analysis showed that two products had been formed: Me3SiC≡CSiMe3 in 76% yield and a silacyclopentadiene Sey-6 in 80% yield.

Eq. 6: Sey-1 and Sey-6 [START_REF] Atwell | The thermolysis of methoxypolysilanes[END_REF] The proposed mechanism commenced with the formation of the active catalyst (Ph3P)2Pd Eq. 7: Sey-22 and Sey-6 [START_REF] Atwell | The thermolysis of methoxypolysilanes[END_REF] Scheme 9: The proposed mechanism of Seyferth et al. [START_REF] Krause | A Palladium--Catalyzed Stannole Synthesis[END_REF] Yet the presence of silylene palladium intermediate was not evidenced, another mechanism in which the formation of silylene reactive species was cut off was proposed, which turned out to lead to a similar product. (scheme 10)

Scheme 10: Our proposed mechanism

The idea of the mentioned-above report was drew on in 1997 by Woerpel, nevertheless the confirmation of silylene's involvement appears to be vague. The siliranes Woe-cis-1 and Woe-trans-1 were treated with a variety of terminal acetylenes in a catalytic amount of (Ph3P)2PdCl2 (<3 mol %) to yield siloles Woe-2 (Eq. 8, Table 1) [START_REF] Palmer | Stereospecific Palladium--Catalyzed Reactions of Siliranes with Alkynes[END_REF] .

(Ph Woe-trans-1 was treated with the palladium catalyst without alkyne in C6D6, it slowly rearranged to form the silane Woe-6 over the course of a few days.

Eq. 9: Woe-trans-1 and Woe-6 [START_REF] Palmer | Stereospecific Palladium--Catalyzed Reactions of Siliranes with Alkynes[END_REF] The catalytic cycle shown in Scheme 11 is modified from Seyferth's proposed mechanism (mentioned above). The oxidative addition of in-situ-generated Pd(0) 29 into the C-Si bond of Woe-trans-1 associated with stereospecific retention of configuration at the carbon atom provides palladacyclobutane Woe-trans-7 [START_REF] Krause | A Palladium--Catalyzed Stannole Synthesis[END_REF] .

In the absence of alkyne, the palladasilacyclobutane intermediate Woe-trans-7 was subjected to beta-hydride elimination and reductive elimination to give rise to allylsilane Woe-6.

In the presence of an alkyne, association and migratory insertion [START_REF] Tilley | The Silicon--Heteroatom Bond[END_REF] gives rise to the palladasilacyclohexene Woe-trans-8 [START_REF] Krause | A Palladium--Catalyzed Stannole Synthesis[END_REF] . Then Woe-trans-8 would undergo reductive elimination to form the silacyclopentene Woe-trans-3 with retention of configuration at the carbon stereocenter. [START_REF] Milstein | Mechanism of reductive elimination. Reaction of alkylpalladium(II) complexes with tetraorganotin, organolithium, and Grignard reagents. Evidence for palladium(IV) intermediacy[END_REF] Alternatively, Woe-trans-8 may go through migratory deinsertion to release Woe-trans-2- butene and palladasilacyclobutene Woe-9. These species would form silole Woe-2 after alkyne association, migratory insertion, and reductive elimination (Eq. 11). [START_REF] Ishikawa | Silicon--carbon unsaturated compounds. 22. The formation and reactions of a nickelasilacyclobutene[END_REF] Scheme 11: Reaction mechanism from woe-trans-1 to products [START_REF] Palmer | Stereospecific Palladium--Catalyzed Reactions of Siliranes with Alkynes[END_REF] Coupled with reactions towards carbon-carbon unsaturated bond, silylene transfers also can react to other functional groups.

Woerpel et al, in 2007, reported [START_REF] Calad | Formation of Chiral Quaternary Carbon Stereocenters Using Silylene Transfer Reactions: Enantioselective Synthesis of (+)--5--epi--Acetomycin[END_REF] a method for the diastereoselective construction of quaternary carbon stereocenters (Eq.10), encompassing silylene transfer into α,βunsaturated ester to afford silyl ketene acetal which afterward undergoes a stereospecific Ireland-Claisen rearrangement [START_REF] Ireland | Stereochemical control in the ester enolate Claisen rearrangement. 1. Stereoselectivity in silyl ketene acetal formation[END_REF][START_REF] Chai | New aspects of the Ireland and related Claisen rearrangements[END_REF] to provide silalactone (Eq. 10).

Eq 10: Pel-1 [START_REF] Calad | Formation of Chiral Quaternary Carbon Stereocenters Using Silylene Transfer Reactions: Enantioselective Synthesis of (+)--5--epi--Acetomycin[END_REF] The trapping silylene, catalyzed by AgOCOCF3, by ester Pel-4 leads to formation of a silacarbonyl ylide Pel-5 that afterward was 6π electrocyclized to produce oxasilacyclopentene Pel-6 (Scheme.12). At room temperature, oxasilacyclopentene

Pel-6 underwent an Ireland-Claisen rearrangement via a chairlike transition state (scheme 12) in which the isopropyl substituent adopts an equatorial position [START_REF] Faulkner | A synthesis of trans--trisubstituted olefins using the claisen rearrangement[END_REF] to afford silalactone Pel-7.

Scheme 12: Controlling Quaternary Carbon Stereochemistry 34

Silylene transfer to alpha-keto esters is also utilized as a strategy for the stereoselective, one-flask synthesis of enantiomerically enriched tertiary alphahydroxy acids [START_REF] Howard | Synthesis of Tertiary α--Hydroxy Acids by Silylene Transfer to α--Keto Esters[END_REF] that are common substructures in natural products and serve as important synthetic intermediates [START_REF] Bunte | Formal Total Synthesis of (+)--Zaragozic Acid C through an Ireland-Claisen Rearrangement[END_REF][START_REF] Garry | α--Hydroxy Acids in Enantioselective Syntheses[END_REF] .

Table 2: Optimization of the Silylene Source 38

The treatment of ester Pel-1 with silacyclopropane Pel-4 and 10 mol % of AgOTs in toluene resulted in direct formation of silalactones Pel-2 in 73% yield as determined by NMR spectroscopy. The product was later purified by HF•Pyridine [START_REF] Trost | The di--t--butylsilylene protecting group for diols[END_REF] to afford analytically pure R-hydroxy acid Pel-3.

The proposed mechanism for the synthesis of α-hydroxy acids is described in scheme 13. The silver silylenoid species [START_REF] Driver | Mechanism of Silver--Mediated Di--tert--butylsilylene Transfer from a Silacyclopropane to an Alkene[END_REF] generated by subjecting silacyclopropane Pel-4 to AgOTs accompanied by an attack of the ketone carbonyl oxygen gives rise to silacarbonyl ylide Pel-8, which can then be 6π-electrocyclized to produce silyl ketene acetal Pel-9. Ireland-Claisen rearrangement of silane Pel-9 then took place via a chairlike transition state to produce silalactone Pel-10, which was hydrolyzed eventually to afford alpha-hydroxy acid.

Introduction of silylene metal complexes

Classification.

Silylene complexes have attracted a great deal of chemists' interest as possible intermediates in numerous stoichiometric and catalytic chemical transformations [START_REF] Blom | New Vistas in N--Heterocyclic Silylene (NHSi) Transition--Metal Coordination Chemistry: Syntheses, Structures and Reactivity towards Activation of Small Molecules[END_REF][START_REF] Ogino | Synthesis of Silylene and Silyl(silylene)metal Complexes[END_REF] .

Being convergence of transition metal chemistry with main group chemistry, these complexes can be classified into 5 groups according to their distinct structure. Table 3: Five group of silylene complexes and their examples [START_REF] Blom | New Vistas in N--Heterocyclic Silylene (NHSi) Transition--Metal Coordination Chemistry: Syntheses, Structures and Reactivity towards Activation of Small Molecules[END_REF][START_REF] Ogino | Synthesis of Silylene and Silyl(silylene)metal Complexes[END_REF][START_REF] Fukuda | Synthesis of a Tungsten-Silylyne Complex via Stepwise Proton and Hydride Abstraction from a Hydrido Hydrosilylene Complex[END_REF][START_REF] Sakaba | Reactions of Tungsten Acetylide-Silylene Complexes with Pyridines: Direct Observation of Silylene/Silyl Migration in Tungsten Acetylide and Carbyne/Vinylidene Frameworks[END_REF] .

Group 3: n = 1 or 2;; R = bulky aromatic or aliphatic group. with the electrophilic silicon center. Type 1 and type 2 will be focused on this thesis.

A brief history.

In 1970, Kumada and colleagues presented the monomerization and oligomerization of hydropentamethyldisilane, catalyzed by trans-PtCl2(PEt3)2 (Eq. 12), with the possible presence of platinum silylene complexes in their proposed mechanism.

Eq. 12 [START_REF] Ogino | Synthesis of Silylene and Silyl(silylene)metal Complexes[END_REF][START_REF] Yamamoto | Disproportionation of pentamethyldisilane and sym--tetramethyldisilane catalysed by platinum complexes[END_REF] The reactive species were formed by the oxidative addition of the disilane to the coordinatively unsaturated platinum complex PtCl2(PEt3), accompanied by the reductive elimination of the monosilane. These then underwent the addition of disilane or oligosilanes associated with the reductive elimination of SinMe2n+1H to regenerate the reactive platinum catalyst [START_REF] Yamamoto | Disproportionation of pentamethyldisilane and sym--tetramethyldisilane catalysed by platinum complexes[END_REF] .

Scheme 14. Possible mechanism of monomerization and oligomerization of hydrodisilane by trans-PtCl2(PEt3). [START_REF] Ogino | Synthesis of Silylene and Silyl(silylene)metal Complexes[END_REF][START_REF] Yamamoto | Disproportionation of pentamethyldisilane and sym--tetramethyldisilane catalysed by platinum complexes[END_REF] After that, Ojima et al. also reported the formation of the silyl(silylene) complex as a potential intermediate, which plays an essential role in the scrambling substituents and dehydrogenative silane coupling of dihydrosilane H2SiPhMe in the presence of Wilkinson's catalyst (Eq. 13) [START_REF] Ojima | The action of tris(triphenylphosphine)chlororhodium on polyhydromonosilanes[END_REF] .

Eq. 13

The mechanism presented in scheme 15 shows that the oxidative addition reactions of two molecules of the dihydrosilane to the coordinatively unsaturated complex [Rh] producing a silyl(silylene) complex are crucial. Afterwards, the intermediate could undergo either a 1,3-R-shift in the complex followed by the reductive elimination of a monosilane to form a scrambling of the substituents or 1,2-silyl shift in the complex followed by further reductive elimination to yield the dehydrogenative coupling product (scheme. 15).

Scheme 15 [START_REF] Ogino | Synthesis of Silylene and Silyl(silylene)metal Complexes[END_REF][START_REF] Yamamoto | Disproportionation of pentamethyldisilane and sym--tetramethyldisilane catalysed by platinum complexes[END_REF] : Proposed mechanism of reaction Eq.13

Around ten years later, the first synthesis of silylene metal complex has first come to light by Schmid and Welz 50 (Eq. 14 ). The photolysis of Fe(CO)5, in the presence of HSiMe2(NEt2), generated a base stabilized-silylene complex Wel-2

(OC)4Fe(=SiMe2•NHEt2). Eq 14: Wel-2 [START_REF] Schmid | Base--Stabilized Silyleneiron Complexes[END_REF] The irradiation of Fe(CO)5 produced the 16-electron complex Fe(CO)4 that later reacted with HSiMe2(NEt2) to give rise to the oxidative addition product Intermediate A. Finally, the basicity of diethylamino being stronger than the iron counterpart drove the proton migration from the iron center to the diethylamino group in Intermediate A to provide the final product. However, this complex is too unstable to be structurally characterized by X-ray.

The ground-breaking result arose in 1987 when Zybill and colleagues proposed a synthesis route to silyleneiron complexes (OC)4Fe=Si(O t Bu)2 •base by utilizing a salt elimination method and their X-ray crystallographic structures [START_REF] Ogino | Synthesis of Silylene and Silyl(silylene)metal Complexes[END_REF][START_REF] Zybill | Synthesis and Structure of [(OC)4Fe Si(OtBu)2••HMPT], a Donor--Stabilized Silanediyl[END_REF] .

Eq. 15 [START_REF] Blom | New Vistas in N--Heterocyclic Silylene (NHSi) Transition--Metal Coordination Chemistry: Syntheses, Structures and Reactivity towards Activation of Small Molecules[END_REF][START_REF] Schmid | Base--Stabilized Silyleneiron Complexes[END_REF] Figure 1: X-ray structure of iron silylene complex published by Zybill et al [START_REF] Zybill | Synthesis and Structure of [(OC)4Fe Si(OtBu)2••HMPT], a Donor--Stabilized Silanediyl[END_REF] .

Braunstein and colleagues successfully used almost the same routine to synthesize an analogue of Schmid and Welz's Iron silylene complexes (OC)4Fe=Si(NMe2)2

•NHMe2 that also could be structurally determined by X-ray crystallographic (Eq. 16) [START_REF] Ogino | Synthesis of Silylene and Silyl(silylene)metal Complexes[END_REF][START_REF] Bodensieck | Platinum-Iron Silylene Complexes and Metal--Promoted Substituent Exchange between Si(NMe2)3 and P(OEt)3 Ligands[END_REF] .

Eq. 16

Synthesis of metal silylene complexes

Because of the close positional relationship in the periodic table, the chemical reactivity of carbon and silicon was expected to be similar, so the preliminary research on silicon was carried out with the preconception that the chemical properties of these two elements would resemble each other [START_REF] Kipping | Organic Derivatives of Silicon[END_REF] . The enigma whether silylene complex, heavier analogues of the notorious carbenes complex, exists as stable entities could be raised by theoreticians around in the 1980s. The energy of the M=Si bond for the hypothetical complex [(OC)5Cr=Si(OH)H] was calculated to be only 29.6 kcal/mol while that of the corresponding hypothetical complex [(OC)5Cr=C(OH)H] is 44.4 kcal/mol [START_REF] Braunstein | Bimetallic silicon chemistry: New opportunities in coordination and organometallic chemistry[END_REF][START_REF] Nakatsuji | Does a silylene metal complex exist?[END_REF] .

Therefore, the attainment of stable silylene complexes was deemed achievable.

Although the perusal on silylene complex chemistry shed light on major discoveries, for instance the establishment of the high reactivity of simple hydrosilanes or finding polysilanes with sigma-conjugated backbone and silicone polymer [START_REF] Miller | Polysilane high polymers[END_REF][START_REF] West | The polysilane high polymers[END_REF] , those effort appeared not to be of success due to the inherent instability of silicon compounds.

Although the M=Si double bond in the silylene complexes partly possesses σ-donation/ π-back donation related to carbene complexes, the back donation from the dπ orbital of the metal center to the vacant p orbital of the silylene silicon atom is weaker than in the carbene one. (Figure . 2) [START_REF] Ogino | Synthesis of Silylene and Silyl(silylene)metal Complexes[END_REF][START_REF] Braunstein | Bimetallic silicon chemistry: New opportunities in coordination and organometallic chemistry[END_REF] .

That also explains why the M=Si double bond is strongly polarized toward M (-) =Si (+) resulting in high electron-deficiency on the silicon atom. Therefore, theoretically speaking, in the presence of a base, the base-coordinating constituted from the donation from dπ metal orbital to the σ* orbital of the silicon-based bond will stabilize the silylene system [START_REF] Schmid | Base--Stabilized Silyleneiron Complexes[END_REF][START_REF] Nakatsuji | Does a silylene metal complex exist?[END_REF][START_REF] Cundari | Nature of the transition metal--silicon double bond[END_REF][START_REF] Jacobsen | Trends in Structure and Bonding of Fischer Type Chromium Carbenes and Silylenes. A Density Functional Study[END_REF][START_REF] Marquez | Electronic structure of the transition--metal--carbene-like complexes (CO)5Mo--M'H2 (M' = carbon, silicon, germanium and tin). A theoretical study based on ab initio CASSCF calculations[END_REF][START_REF] Ueno | Silicon--silicon interaction in bis(silylene)iron, disilanyliron, and bis(silyl)iron complexes[END_REF] .

To date, the development of a variety of preparative methods have facilitated the synthesis of transition-metal silylene complexes;; this account will describe several of those findings.

Ligation of Free Silylene to Metal Complexes

The most straightforward method to synthesize silylene complexes was acheived by using coordinative unsaturated metal fragment [M] and a free silylene [START_REF] Ogino | Synthesis of Silylene and Silyl(silylene)metal Complexes[END_REF][START_REF] Okazaki | Reactivity of silylene complexes[END_REF] . (Eq.17) Eq 17 [START_REF] Ogino | Synthesis of Silylene and Silyl(silylene)metal Complexes[END_REF][START_REF] Okazaki | Reactivity of silylene complexes[END_REF] Tilley et al. reported the capturing a thermally unstable silylene by way of irradiation of (Me3Si)2SiMes2 (Mes = mesityl of 2,4,6-Me3C6H2) in the presence of low-valent platinum species L2Pt (L = iPr3P and Cy3P) to form a terminal three-coordinate Ptsilylene complexes L2Pt=SiMes2 (scheme 16) [START_REF] Feldman | Isolation and Characterization of Neutral Platinum Silylene Complexes of the Type (R3P)2PtSiMes2 (Mes = 2,4,6--Trimethylphenyl)[END_REF]64 .

Scheme 16: Coordination of a free silylene [START_REF] Waterman | Synthetic Development and Chemical Reactivity of Transition--Metal Silylene Complexes[END_REF] Denk et al. reported the first silylene complex of nickel as well as the first bis-silylene Eq. 18 [START_REF] Denk | Silylene complexes from a stable silylene and metal carbonyls: synthesis and structure of [Ni{(ButN-CH CH-NBut)Si}2(CO)2], a donor-free bis--silylene complex[END_REF][START_REF] Gehrhus | Silylenenickel(0) or Silyl(silylene)platinum(II) Complexes by Reaction of Si[(NCH2But)2C6H4--1[END_REF] Woo described first donor-stabilized silylene complexes of metalloporphyrin osmium (TTP)Os=SiMe2•THF (TPP = meso-tetra-p-tolylporphyrin). The successful outcome was accomplished by employing the reaction of [Os(TTP)]2 with hexamethylsilacyclopropan serving as a useful reagent for generating transient dimethylsilylene under mild condition [START_REF] Seyferth | Hexamethylsilirane. 3. Dimethylsilylene-transfer chemistry[END_REF][START_REF] Berry | Dimethylsilylene insertion into tantalum--hydride bonds[END_REF] . This idea was founded on the ground that bulky substituents on silicon would increase kinetic stability and an electron-rich, late transition metal would stabilize adjacent electron-deficient silicon atom. [START_REF] Woo | Synthesis, reactivity, and characterization of the first donor--stabilized silylene complexes of osmium meso--tetra--p--tolylporphyrin (TTP)Os:SiR2.cntdot.THF (R = Me, Et, iso--Pr) and the molecular structure of (TTP)Os:SiEt2.cntdot.2THF[END_REF] . (Eq.19)

Eq. 19 70

Metal-Mediated dihydrogen elimination from dihydrosilanes

Corriu et al have established the method using the photolysis of hydrosilanes with metal carbonyl accompanied with the external or internal Lewis base stabilization (Eq. 20) [START_REF] Chauhan | Lewis Base--Stabilized Transition Metal Complexes of Divalent Silicon Species[END_REF][START_REF] Corriu | Base Stabilization of Functionalized Silylene Transition Metal Complexes[END_REF][START_REF] Corriu | Photochemical reaction of 16--e metal species generated from Fe(CO)5, Cr(CO)6, or RCpMn(CO)3 (R = H, Me), with primary and secondary arylsilanes in the presence of internal or external electron donors: formation of functionally stabilized hydrosilanediyl--transition metal complexes[END_REF] .

(HMPA = hexamethylphosphoric triamide)

Eq. 20 [START_REF] Corriu | Photochemical reaction of 16--e metal species generated from Fe(CO)5, Cr(CO)6, or RCpMn(CO)3 (R = H, Me), with primary and secondary arylsilanes in the presence of internal or external electron donors: formation of functionally stabilized hydrosilanediyl--transition metal complexes[END_REF] This method has been extended on an array of transition metal carbonyl complexes as Fe(CO)5, Cr(CO)6, CpCo(CO)2, and RCpMn(CO)3 (R = H, CH3) that could generate 16e metal species by releasing one CO compound under photolytic conditions. For example iron pentacarbonyl.

internal Lewis base stabilization Eq 21 [START_REF] Chauhan | Lewis Base--Stabilized Transition Metal Complexes of Divalent Silicon Species[END_REF][START_REF] Corriu | Base Stabilization of Functionalized Silylene Transition Metal Complexes[END_REF][START_REF] Corriu | Photochemical reaction of 16--e metal species generated from Fe(CO)5, Cr(CO)6, or RCpMn(CO)3 (R = H, Me), with primary and secondary arylsilanes in the presence of internal or external electron donors: formation of functionally stabilized hydrosilanediyl--transition metal complexes[END_REF] 3.3.3. Alpha hydrogen migration. Eq. 22 [START_REF] Waterman | Synthetic Development and Chemical Reactivity of Transition--Metal Silylene Complexes[END_REF] B(C6F5)3 abstracted a methide ion (CH3 -) on platinum complex (dippe)PtMe(Si-HMes2)

to form the three-coordinate cation platinum silyl intermediate [(dippe)Pt(Si-HMes2)] + .

By possessing a vacant coordination site on metal center, the reactive species afterward underwent presumptively the 1,2-hydrogen migration from Si to metal center to result in platinum silylene complex (Eq.22).

This method demonstrated its reproducibility by an application on fac-IrH(Me)(SiHMes2)(PMe3)3 to provide the cationic silylene complex [fac-(Me3P)3H2Ir=SiMes2][MeB(C6F5)3] 74 . (Eq. 23) Eq 23 [START_REF] Corriu | Base Stabilization of Functionalized Silylene Transition Metal Complexes[END_REF] Another example is the treatment of Cp*(Me3P)(Br)(H)Os(SiHRR′) (R = H, aryl, or silyl;; R′ = R or aryl) with the anion metathesis reagent LiB(C6F5)4•3Et2O which is able to abstract bromide anion in CD2Cl2 to afford a cationic osmium complex with terminal silylene ligands 75 (eq. 24)

Eq 24 [START_REF] Corriu | Photochemical reaction of 16--e metal species generated from Fe(CO)5, Cr(CO)6, or RCpMn(CO)3 (R = H, Me), with primary and secondary arylsilanes in the presence of internal or external electron donors: formation of functionally stabilized hydrosilanediyl--transition metal complexes[END_REF] 1,2 hydrogen migration from silicon to the metal center also is triggered by a combination of sequence processes including silane Si-H oxidative addition, reductive elimination to expose a coordinative position (figure 3). Eq 25 72

Abstraction substituent on silicon ligand

This method is based on anion metathesis, in which a labile substituent on silicon (halide, triflate, or thiolate) is replaced by a non-coordinating anion to yield cationic silylene complexes. Furthermore, this method can be applied to a variety of silicon substituents of metal complexes from group 8, 9, 10 77 .

Scheme 17: Silicon bound substitute abstraction [START_REF] Peters | Silylene Extrusion from a Silane: Direct Conversion of Mes2SiH2 to an Iridium Silylene Dihydride[END_REF] Those complexes, synthesized by Tilley et al [START_REF] Waterman | Synthetic Development and Chemical Reactivity of Transition--Metal Silylene Complexes[END_REF]75,[START_REF] Mork | Multiple Bonding Between Silicon and Molybdenum: A Transition--Metal Complex with Considerable Silylyne Character[END_REF][START_REF] Fasulo | Structural and mechanistic investigation of a cationic hydrogen--substituted ruthenium silylene catalyst for alkene hydrosilation[END_REF][START_REF] Lipke | Electrophilic Activation of Silicon-Hydrogen Bonds in Catalytic Hydrosilations[END_REF] , shown below are the first examples of isolated base-free silylene species resulted from an abstraction of a triflate group from Cp*(Me3P)2RuSi(SR)2OTf (R = p-tol or Et). Eq 26 [START_REF] Peters | Silylene Extrusion from a Silane: Direct Conversion of Mes2SiH2 to an Iridium Silylene Dihydride[END_REF] .

Another successful application of this method is hydride abstraction resulted from a hydrosilylation complex in the presence of HMPA (Hexamethylphosphoramide), which produced an excellent yield of a cationic silyleneiron complex stabilized by HMPA [START_REF] Ogino | Synthesis of Silylene and Silyl(silylene)metal Complexes[END_REF][START_REF] Kobayashi | Synthesis and Structure of the Cationic External Donor--Stabilized Silyleneiron Complex [Cp(OC)2Fe=Si(p--Tol)2••HMPA]PF6 by Hydride Abstraction from a (Hydrosilyl)iron Complex[END_REF] .

Eq 27 [START_REF] Blom | New Vistas in N--Heterocyclic Silylene (NHSi) Transition--Metal Coordination Chemistry: Syntheses, Structures and Reactivity towards Activation of Small Molecules[END_REF][START_REF] Lipke | Electrophilic Activation of Silicon-Hydrogen Bonds in Catalytic Hydrosilations[END_REF]

Synthesis of silylene group 5

This documented section is dedicated to the synthesis of group 5 silylenes resulting from interaction between M-H bonds and silicon center. Another pathway used a metathesis route in which the sigma donor silane coordination from Mes2SiH2 replaces a weak C-H agostic interaction [START_REF] Kitiachvili | Preparation of Stable Alkyl Complexes of Ni(I) and Their One--Electron Oxidation to Ni(II) Complex Cations[END_REF] , to produce an intermediate that afterward undergoes intramolecular H-abstraction followed by neopentane elimination to give rise to Hil-5.

X-ray crystallography supports hydrogen bridging nickel and silicon (Ni-H) 1.70(7) Å, Si-H) 1.64(7) Å), prompting distorted square-planar coordination geometry at nickel. The Ni-Si distance (2.147(2) Å) is 9% shorter than that in Hil-2 and is close in value reported for Ni silylene complexes (∼2.14 Å) [START_REF] Schmedake | Two Trigonal Ni(silylene)3 Complexes[END_REF] . Tilley et al. presented molybdenum silylene complexes provided by the reaction of the benzyl precursor Cp*(dmpe)Mo(η 3 -CH2Ph) with silanes using the alpha hydrogen migration mentioned above [START_REF] Mork | Multiple Bonding Between Silicon and Molybdenum: A Transition--Metal Complex with Considerable Silylyne Character[END_REF][START_REF] Mork | Silylene Hydride Complexes of Molybdenum with Silicon-Hydrogen Interactions: Neutron Structure of (η5--C5Me5)(Me2PCH2CH2PMe2)Mo(H)(SiEt2)[END_REF] .

Eq 29: Til-4 [START_REF] Mork | Multiple Bonding Between Silicon and Molybdenum: A Transition--Metal Complex with Considerable Silylyne Character[END_REF][START_REF] Mork | Silylene Hydride Complexes of Molybdenum with Silicon-Hydrogen Interactions: Neutron Structure of (η5--C5Me5)(Me2PCH2CH2PMe2)Mo(H)(SiEt2)[END_REF] Til-4 X-ray analysis showed that the H-Mo and H-Si bond lengths of 1.85(Å) and 1.39(Å), respectively, although X-ray diffraction cannot locate exactly hydride positions in the vicinity of a heavy metal, the refined position for the hydride ligand of Til-4 might suggest that in the solid state some H•••Si interaction exists (Figure 5).

Figure 5: proposed H•••Si interaction

Metallacycles

Cyclometalation was discovered in the early 1960s [START_REF] Kleiman | The Preparation of Cyclopentadienyl [o--(Phenylazo)Phenyl]Nickel[END_REF][START_REF] Cope | Formation of Covalent Bonds from Platinum or Palladium to Carbon by Direct Substitution[END_REF] , which later became one of the most popular organometallic reactions, providing a straightforward entry to organometallic compounds featuring a metal-carbon σ bond.

Alongside with the development of cyclometalation as a whole, interest in cycloiridated complexes has been greatly attracted by the findings of exceptional activities of iridacycles in catalysis and for photophysical applications [START_REF] Albrecht | Cyclometalation Using d--Block Transition Metals: Fundamental Aspects and Recent Trends[END_REF] .

Recently our lab has reported on the capability of readily accessible Cp*Ir-based iridacycles to promote the double hydrosilylation of a series of nitrile groups containing organic substrates following a so-called autotandem 93 17, 94 catalyzed process. We have developed the use of such iridacycles as potential catalysts of "one-pot" autotandem [START_REF] Fogg | Tandem catalysis: a taxonomy and illustrative review[END_REF][START_REF] Shindoh | Auto--Tandem Catalysis: A Single Catalyst Activating Mechanistically Distinct Reactions in a Single Reactor[END_REF] reactions applied to the fast room-temperature O-dehydrosilylation of alcohols including benzylic or aliphatic.

The intermediates (R3Si)(H)Ir arising from the reaction of the 18-electron irridacycle cationic with a silane can reasonably be considered as the key catalytic species of aforementioned reactions;; this species was trapped and structurally characterized, and its electronic structure was investigated by state-of-the-art DFT methods.

Scheme 7: Si-H bond activated by Irridacycle [START_REF] Hamdaoui | Evidence of a Donor-Acceptor (Ir-H)→SiR3 Interaction in a Trapped Ir(III) Silane Catalytic Intermediate[END_REF][START_REF] Hamdaoui | Iridacycles as Catalysts for the Autotandem Conversion of Nitriles into Amines by Hydrosilylation: Experimental Investigation and Scope[END_REF] This thesis is based on a strong background of interaction between Ir and ailicon that has established for years in our laboratory.

Is the R3Si Moiety in Metal-Silyl Complexes a Z ligand?

The hydrosilation reactions have riveted chemists' longstanding interest in understanding their mechanical insight due to their efficiency, selectivity, and widerange application from industrial processes to laboratory scale syntheses. Among a variety of catalysts and catalytic cycles available for these reactions, the conventional Chalk- Harrod mechanism [START_REF] Chalk | Homogeneous Catalysis. II. The Mechanism of the Hydrosilation of Olefins Catalyzed by Group VIII Metal Complexes1[END_REF][START_REF] Troegel | Recent advances and actual challenges in late transition metal catalyzed hydrosilylation of olefins from an industrial point of view[END_REF] is well-known, which was utilized first time to interpret platinum catalyst olefin hydrosilation reactions in the 1960's [START_REF] Chalk | Homogeneous Catalysis. II. The Mechanism of the Hydrosilation of Olefins Catalyzed by Group VIII Metal Complexes1[END_REF][START_REF] Randolph | Photochemical reactions of (.eta.5-pentamethylcyclopentadienyl)dicarbonyliron alkyl and silyl complexes: reversible ethylene insertion into an iron--silicon bond and implications for the mechanism of transition--metal-catalyzed hydrosilation of alkenes[END_REF][100][101] and then to apply for rhodium-catalyzed ketone hydrosilations by Ojima in 1975 102, 103 .

This historical Chalk-Harrod mechanism includes oxidative addition processes in which initial reaction of a silane of general formula R3SiH (R = aryl, alkyl, halido and hydrogen) interacts with a metal center, resulting in the formal oxidation of the metal center and the formation of two new M-H and M-SiR3 bonds. The silyl ligand in this case is usually considered as the X-type according to the covalent bond classification formalism (abbr. CBC) 104-107 . However, classifying definitively the H and SiR3 ligands as X-type may be oversimplified owing to the fact that H and Si can be mutually interacting, and the H-Si bonding interaction is unlikely entirely fragmented 105, 108-111 .

Moreover, the inherent polarization of the Si-H bond may engender another scenario [START_REF] Hamdaoui | Evidence of a Donor-Acceptor (Ir-H)→SiR3 Interaction in a Trapped Ir(III) Silane Catalytic Intermediate[END_REF] wherein a formal hydride would transfer to the metal, initiating a concerted or nonconcerted transfer of a formal silylium either to the metal [START_REF] Hamdaoui | Evidence of a Donor-Acceptor (Ir-H)→SiR3 Interaction in a Trapped Ir(III) Silane Catalytic Intermediate[END_REF]112 , to a neighboring group or to the organic substrate (termed ionic activation by Tilley et al.). (scheme 20) Scheme 20: The two main modes of activation of silanes : a) oxidative addition;; b) heterolytic polar "electrophilic" activation of the Si-H bond.

M H SiR 3 M H SiR 3 + M H SiR 3 a) M H SiR 3 + b) Nu M H R 3 Si Nu + δ+ δ+ δ-
Therefore, reckoning metal-bound silyl as a Z ligand 113 (a Lewis type acceptor, namely here [SiR3] + ), as a X ligand or in some cases, even as L ligand 108, 114 predicated on the degree of the interaction between silicon fragment and metal center becomes the fundamental issue. More interestingly, based on that, one can logically deduce a possibility of catalytic reactivity of given catalysis or the electronic structure of the M(H)(SiR3) motif.

In fact, not all metal-silyl compounds are catalytically active or even possess a tendency to release easily the SiR3 moiety by a chemical reaction, nor are the chemical properties and the reactivity of known cases of M-SiR3 complexes comprehensively documented. In addition, reports provide a solid ground that reactive M-H-SiR3 intermediates -or silane-metal adducts- that manifest a crucial role in catalytic events or study reactivity of M(H)(SiR3) motif are scarce because of the baffling issues of isolating [START_REF] Hamdaoui | Evidence of a Donor-Acceptor (Ir-H)→SiR3 Interaction in a Trapped Ir(III) Silane Catalytic Intermediate[END_REF]115 and using them as reactants in stoichiometric reactions. As a result, a lack of experimental information on the actual reactivity of a considered metal-silyl fragment will prevent identifying whether the silyl group holds an X, a L or Z character.

It is of necessity that establishing reliable descriptor of bonding could differentiate electrophilic silyl ligands -or "silyliums"- Z ligands (Figure 6) from other situations and suggest rationally the properties of a given catalyst.

Figure 6. How to best formulate a metal-silyl/silane complex ?

Our main goal was to suggest a simple approach, based on the usefulness of some established tools of the density functional theory in order to assess the "relative intrinsic silylicity" of a metal-silyl complex to provide a formal Lewis acidic silylium [116][117][118] [SiR3] + fragment. By doing that, it could facilitate not only rationalizing Lewis formulations, but also clarifying the mechanisms that metal-silyl complex involved, as well as the

L n' X m' M X ? [ L n X m M SiR 3 ] q L n' X m' M Z ? L n' X m' M X ? [ L n X m M SiR 3 ] q L n' X m' M Z ? H H H
dubious concepts lying behind hydrosilylation reactions in which electrophilic silyls are engaged.

In this study, we made use of interaction energies acquired from the energy decomposition analysis EDA 119 by using the protocol implemented in the SCM-Amsterdam Density Functional suite of its 2016 version 120 . The EDA, according to The EDA requires the formal fragmentation of a molecule into two fragments, the geometries of which are kept identical to those in the molecule under scrutiny: for convenience, those geometries of the fragments are termed "prepared" as they are geometrically prepared to give rise to the final molecule in its relaxed geometry without deformation.

The considered fragmentation scheme entails the disruption of a formal "silylium" fragment and the charged or neutral organometallic counterpart in their unrelaxed geometries (Eq. 31), this notwithstanding the "chemical realisticness" of the fragmentation scheme (Eq. 31)

Eq 31 [START_REF] Binh | Is the R3Si Moiety in Metal-Silyl Complexes a Z ligand? An Answer from the Interaction Energy[END_REF] We previously showed that although the triflate ion is one of the weakest Lewis bases and one of the best nucleofuges 125,126 , it had the ability to capture the Et3Si group of UVAWIZ [START_REF] Hamdaoui | Evidence of a Donor-Acceptor (Ir-H)→SiR3 Interaction in a Trapped Ir(III) Silane Catalytic Intermediate[END_REF][START_REF] Hamdaoui | Iridacycles as Catalysts for the Autotandem Conversion of Nitriles into Amines by Hydrosilylation: Experimental Investigation and Scope[END_REF] (Figure 7), implying that the interaction between the silicon atom and the iridium center was not quite considerable. Silyl group of UVAWIZ clearly behaving like a Z ligand [START_REF] Hamdaoui | Evidence of a Donor-Acceptor (Ir-H)→SiR3 Interaction in a Trapped Ir(III) Silane Catalytic Intermediate[END_REF] can be utilized as a standard to compare to other metal-silyl complexes for the sake of distinguishing situations similar to UVAWIZ.

Figure 7

We define the "relative intrinsic silylicity" Π (the greek letter Π was chosen because it is the initial of the Greek word Π that means "elemental silicon") as the ratio of the inter- fragment interaction energy of the triflate with the "silylium" of TfO-SiR3 and the interaction energy of the metal fragment with the same formal "silylium" in a metal-SiR3 compound (Eq. 30)

Π = [ ΔEint (R3Si-OTf)] / [ΔEint(R3Si-M)]
Eq. 32

The relative intrinsic silylicity Π is a descriptor of the Lewis acidic (electrophilic) character of a given SiR3 moiety, where values <1 characterize low "silylium" releasing ability and values >1 high releasing ability.

To carry out mentioned idea, theoretical and experimental investigation were exerted on the reactivity of known Ir-Si complexes 2, 3, and 4 which hold the reputation of being Ir(V) complexes.

Theoretical work shows that the Π of considered complexes 2, 3, 4 are 0.55, 0.74, and 0.67, respectively, which also means their "silylium" releasing ability is low since it is less than 1. This conclusion then was cemented by a myriad of experimental work.

We considered reactions of 3 with a number of Lewis bases such as DMAP,

[ n Bu4N]OTf, CH3CN in different solvent, even in the presence of CO atmosphere for evaluation the possible "silylium" nature of the silyl groups bound. However, the data clearly showed that the Ir-Si bond is much too strong to be cleaved, meaning that the SiR3 group, in this case, is a typical X-ligand.

Scheme 21: Synthesis of 2, 3, 4

Compound 2, of which chlorido ligand can be modified by using substitution reactions was alternatively investigated to probe the relationship between structure and reactivity. Grignard reagents CH3MgCl, C6H5MgCl were used to substitute chlorido ligand. However, all attempts to isolate any new substitution product failed.

Following the same idea with the previous reaction, AgOTf was combined with Grignard reagents for the purpose of precipitating AgCl which played as the driving force for replacement Cl by Me or Ph. However, issues mentioned above remain unsolved.

The other approach for modulating the structure of the Ir-Si complexes was using that using trityl tetrakis(pentafluophenyl)borate as a hydride abstraction reagent which could afford a cationic complex after reacting to hydrido-metal-sily compounds. Several tests with 7 in various solvents were carried out. Although the desired product and side product were detected by NMR, the new isolation product failed because of its high reactivity.

Cultivating Iridium silane adduct chemistry 2.1. Introduction

Transition metal silylenes whose high reactivity ensues from the extremely electrophilic character of the Si center serve as putative pivotal intermediates in a myriad of essential reactions as hydrosilylation, synthesis of chlorosilanes [START_REF] Fasulo | Structural and mechanistic investigation of a cationic hydrogen--substituted ruthenium silylene catalyst for alkene hydrosilation[END_REF]127,128 . Those complexes also provide attractive stoichiometric reactivity toward small molecules such as chlorinated hydrocarbons 75,129 , epoxides 130 , nitriles 131 , isocyanates 132,133 , and carbonyl compounds [132][133][134] . Although having absorbing chemists' interest for decades, establishing a routine method to synthesize transition metal silylenes remains elusive and problematic.

As mentioned in introduction part, there are several methods [START_REF] Waterman | Synthetic Development and Chemical Reactivity of Transition--Metal Silylene Complexes[END_REF] for preparing metal silylenes for instance anionic-substituent abstraction [START_REF] Fasulo | Structural and mechanistic investigation of a cationic hydrogen--substituted ruthenium silylene catalyst for alkene hydrosilation[END_REF][START_REF] Lipke | Electrophilic Activation of Silicon-Hydrogen Bonds in Catalytic Hydrosilations[END_REF] from a metal hydrosilyl precursor, sequential H-Si activations [START_REF] Chauhan | Lewis Base--Stabilized Transition Metal Complexes of Divalent Silicon Species[END_REF]135,136 in the reaction of an RM precursor (e.g., R= alkyl, aryl) with a hydrosilane 137 , coordination of free silylene [START_REF] Chauhan | Lewis Base--Stabilized Transition Metal Complexes of Divalent Silicon Species[END_REF] or Si-H activation combining with α -hydrogen migration [START_REF] Waterman | Synthetic Development and Chemical Reactivity of Transition--Metal Silylene Complexes[END_REF] . Among those paths, applications of directly forming metal silylenes by double H-Si bond activation 71 72 73 under photolytic conditions associated with the presence of a Lewis base as an exogenous donor ligands bonding to the Si center, which allegedly promotes an increase in the "basicity of the H-Si bond" and thus facilitates H2 elimination.

Eq 33: reaction of Fe(CO)5 with a hydrosilane in the presence of a lewis base [START_REF] Woo | Synthesis, reactivity, and characterization of the first donor--stabilized silylene complexes of osmium meso--tetra--p--tolylporphyrin (TTP)Os:SiR2.cntdot.THF (R = Me, Et, iso--Pr) and the molecular structure of (TTP)Os:SiEt2.cntdot.2THF[END_REF][START_REF] Chauhan | Lewis Base--Stabilized Transition Metal Complexes of Divalent Silicon Species[END_REF][START_REF] Corriu | Base Stabilization of Functionalized Silylene Transition Metal Complexes[END_REF] It was proposed by Tilley et al. [START_REF] Waterman | Synthetic Development and Chemical Reactivity of Transition--Metal Silylene Complexes[END_REF] that conversion of hydrosilanes to silylene complexes by Si-H activation and α-hydrogen migration could be an excellent basis for new catalytic applications. (Eq. 34) Eq 34: Conversion of hydrosilanes to silylene complexes by Si-H activation and αhydrogen migration 64 Based on those observations, we investigated the reactivity of hydrosilanes towards

This work

Our work, 2016,2017 The donor-acceptor complexes (Scheme 7) resulted from concerted transfer of hydride from the silane to the electrophilic Ir III center and captured a labile silylium moiety 17 18 .

R = n Bu [2d][BArF 24 ] R = Ph [3][BArF 24 ] R = n Bu [4][BArF 24 ] R = n Hex [2e][BArF 24 ] R = n Hex [5][BArF 24 ]

This work

R = Ph [2g][BArF 24 ] R = Et [6][BArF 24 ] R = Ph [7][BArF 24 ]
Scheme 7 [START_REF] Hamdaoui | Evidence of a Donor-Acceptor (Ir-H)→SiR3 Interaction in a Trapped Ir(III) Silane Catalytic Intermediate[END_REF][START_REF] Hamdaoui | Iridacycles as Catalysts for the Autotandem Conversion of Nitriles into Amines by Hydrosilylation: Experimental Investigation and Scope[END_REF]

: Si-H bond activated by Irridacycle [1a] +

This study would investigate a wide range of the reaction of [1b][BArF24] with primary alkyl silane (phenylsilane, n-butylsilane, n-hexylsilane) and secondary alkyl silane (diethyl and diphenyl silanes).

The result revealed that reaction of [1b][BArF24] with primary alkyl silanes in CD2Cl2 gave rise to [(IrH)→SiRH2] + adducts. Afterward, by adding THF, those complexes transformed into highly unstable cationic Ir III silylenes, of which all their crystals were successfully trapped by reactive crystallization.

In addition, reaction of reaction of [1b][BArF24] with secondary alkyl silanes (dietyl and diphenyl silane) also produced [(IrH)→SiR2H] + adducts whose structures then were Xray characterized. Although the transformation from these adducts to silylene failed to be clearly observed by NMR, a minute amount of the latter crystal was successfully isolated for crystallographic characterization.

For the sake of legibility, we will discuss sparely reaction of [1b][BArF24] with primary alkyl silanes and secondary alkyl silanes.

Reactions of [1a,b] + with triethylsilane, phenylsilane and n-butylsilane

The reaction of a solution of The 1 H, [START_REF] Yamashita | Oxidative Addition of the Si--C Bonds of Silacyclobutanes to Pt(PEt3)3 and Highly Selective Platinum(0)--Catalyzed Di--or Polymerization of 1,1--Dimethyl--1--silacyclobutane[END_REF] Si HMQC NMR spectrum of [2c] + (Figure 12) also shows that the [START_REF] Yamashita | Oxidative Addition of the Si--C Bonds of Silacyclobutanes to Pt(PEt3)3 and Highly Selective Platinum(0)--Catalyzed Di--or Polymerization of 1,1--Dimethyl--1--silacyclobutane[END_REF] (figure 15). However only Ir-H of [2g][BArF24] presented a correlation with [START_REF] Yamashita | Oxidative Addition of the Si--C Bonds of Silacyclobutanes to Pt(PEt3)3 and Highly Selective Platinum(0)--Catalyzed Di--or Polymerization of 1,1--Dimethyl--1--silacyclobutane[END_REF] Si in HMQC at δ = 0.00 ppm (figure 16). This "secondary interaction" becomes pertinent if considering the extended transition state natural orbital for chemical valence 151,152 (ETS-NOCV) analysis of the interaction of cation [H2SiPh] + with the neutral hydrido iridium residue in [2c-r1] + (Figure 23).

] R = Ph [2c][BArF 24 ] H H R R = n Bu [2d][BArF 24 ] R = n Hex [2e][BArF 24 ]
] R = Et [2f][BArF 24 ] H R R R = Ph [2g][BArF 24 ]

Entrapment of THF-Stabilized Iridacyclic Ir III Silylenes and

theoretical study of their structure.

Discovery of THF-Stabilized Iridacyclic Ir III Silylenes

While attempting to grow crystals of [2c-h][BArF24], we realized that addition of limited amounts of THF induced the formation of new yellow crystals, XRD analysis of which revealed the structures of THF-bound silylene complexes [3][BArF24], [4][BArF24] and 2.05, and 2.30 ppm (see more in experimental section) as a consequence of coordination of THF to the stereogenic Si center. The Δδ ( 29 Si) shift of about +108 ppm on going from [2c][BArF24] to [3][BArF24] is consistent with substantial depletion of electron density at the Si center [START_REF] Corriu | Base Stabilization of Functionalized Silylene Transition Metal Complexes[END_REF] . (figure 25)

Figure 25: 1 H- [START_REF] Yamashita | Oxidative Addition of the Si--C Bonds of Silacyclobutanes to Pt(PEt3)3 and Highly Selective Platinum(0)--Catalyzed Di--or Polymerization of 1,1--Dimethyl--1--silacyclobutane[END_REF] Si HMQC NMR spectra of [3][BArF24] [START_REF] Yamashita | Oxidative Addition of the Si--C Bonds of Silacyclobutanes to Pt(PEt3)3 and Highly Selective Platinum(0)--Catalyzed Di--or Polymerization of 1,1--Dimethyl--1--silacyclobutane[END_REF] Si HMQC and 1 H NOESY NMR spectra of [5][BArF24]

Following the formation of sillylenes from adduct by 1 H-NMR.

Tracking 1

28: Focused view on typical signals of the 1H NMR spectrum monitoring as a function of time the conversion of a freshly prepared solution of [2c] + (made from [1b] + , see dotted arrow) to [3] + upon addition of THF in CD2Cl2 solution at 25 o C;; spectra were acquired at 3 min time intervals, and t = 0 corresponds to the first spectrum, which was recorded about 3-4 min after introduction of the sealed J. Young NMR sample tube containing the mixture into the spectrometer.

By using electrospray mass spectroscopy (heater temperature: 200 o C) in positive-ion mode to characterize adducts [2c,d] + , analysis of the total ion current represented, in both cases, a main peak corresponding to the [(benzo [h]quinolinyl- κ C,N )IrCp*] + cation at m/z = 506 Da. Nevertheless, minor signals could also be detected and assigned to a new ion resulting from [2c,d] + having gained one oxygen atom. The most illustrative example is that obtained from a fresh CH2Cl2 solution of [2d] + injected directly in the ionization chamber without any preliminary treatment, which showed a reasonable signal-to-noise ratio (Figure 28). The hypothesis is this ion might be an iridium silylene complex having captured or reacted with a molecule of water.

Figure 29: Isotopic signature of one of the minor products of fragmentation of [2d][BArF24], injected as a solution in CH2Cl2 in the ionization chamber of an ESI

(positive-ion mode) spectrometer.

Recrystallisation silylene metal complexes.

Reactive crystallization was utilized to obtain a variety of Ir silylene complexes, including Ir dialkyl silylenes (diethyl and diphenyl), which could not be observed in 1 H NMR. This growing crystals method grounds on a diffusion of a heptane solution of silanes into a solution of [1b] + in CH2Cl2/THF through a buffer layer of dry benzene proved to be the only way to trap crystals of the key Ir silylene complexes.

The structures (Figure 30) reveal that Si-Ir interatomic distances remain somewhat in the range of those reported for exogenous-donor-devoid Ir III silylene complexes Among those complexes differences of Interatomic distances are not considerable, [7] while the tranformation from [2g] into [7] possessing the slightest change 0.112 (Å).

Theoretical investigations of Ir-Si bonding

Probing bond structure in transition metal silylene complexes have been of great attraction to chemists for years [START_REF] Nakatsuji | Does a silylene metal complex exist?[END_REF][START_REF] Cundari | Nature of the transition metal--silicon double bond[END_REF][158][159][160] . Especially, Investigating on the σ-donor/ πacceptor character of silylenes and its tuning by a change of substituents are one of the most interesting aspects there are 161 . Accompanied with that, the effects of the nature of the metal on the dominant electronic configuration and its related effect on the π-accepting properties also have been addressed [START_REF] Cundari | Nature of the transition metal--silicon double bond[END_REF]159,160 . To deal with those issues, ab initio [START_REF] Cundari | Nature of the transition metal--silicon double bond[END_REF][START_REF] Marquez | Electronic structure of the transition--metal--carbene-like complexes (CO)5Mo--M'H2 (M' = carbon, silicon, germanium and tin). A theoretical study based on ab initio CASSCF calculations[END_REF]160 and DFT studies [START_REF] Jacobsen | Trends in Structure and Bonding of Fischer Type Chromium Carbenes and Silylenes. A Density Functional Study[END_REF]162 are often employed, which also showed that metal silylenes of late transition metals generally had a significantly less π-accepting character than the parent (Fischer) carbene ligands. Ziegler et al published a prominent work in this field [START_REF] Jacobsen | Trends in Structure and Bonding of Fischer Type Chromium Carbenes and Silylenes. A Density Functional Study[END_REF]162 , in which they harnessed extensively an energy decomposition analysis (EDA)-derived approach to weight the σ-donating versus πaccepting contributions.

In this thesis, both EDA and a fragment-based method ETS-NOCV 151, 152 analysis, were leveraged to estimate symmetry-wise decomposition of inter-fragment orbital interactions, their energetic contribution to the overall orbital interaction energy, and to project an intuitive visualization of how electron density is redistributed in the wide variety of molecular natural orbitals and bonds of the product.

Presuming the bonding of a neutral :SiRH(THF) moiety (Figure 33) to the cationic iridacyclic residue, molecular-fragment-based ETS-NOCV analysis 151 manifested that, deformation densities Δρ1 in figure 33a In spite of the THF-Si interaction, a considerable π-accepting character (Δρ2 in Figure 33b) resides at the Si center in [3] + (Wiberg 150 Ir-Si bond index wbi = 0.68) and [4] + (wbi = 0.67). This residual π-accepting character is characterized by the metal-to-Si pbackdonation deformation density plot Δρ2 (Figure 33b), which accounts for about 10%

of the total interfragment orbital interaction energy.

Calimano and Tilley 127 reported a pertinent relevant reference in which a cationic Ir III silylene complex with a "bare" Si center was synthesized. ETS-NOCV analysis was replicated accompanied with the assumption of an interaction between a neutral :SiPh2

silylene and a cationic Ir-centered residue. The result shows that Ir-to-Si π-backdonation accounts for only 14% of the total interfragment orbital interaction energy, which is less than for the fictitious THF-devoid [3] + and likely an outcome of the weaker donating properties of the ligand set in the PNP complex (Figure 34).

Gibbs energy profile of formation of the THF-bound IrSi(H2)Ph silylene complex

THF played a pivotal role in the H2 elimination step in the line with the computed reaction-energy profile. The formation of [2c] + is exoergonic at 298 K (Figure 35a). In the absence of THF, the concerted coupling of the hydridic Si-bound HSi atom with the Ir-bound HIr atom demands a prohibitive activation energy ΔG o# of about +30 kcal mol - 1 (via transition state TS-I, Figure 35a), overall process resulting in the THF-free silylene complex is endoergonic (ΔG o ≈ + 11 kcal mol -1). On the contrary, in the presence of one molecule of THF (perfect-gas conditions in vacuum), the formation of van der Waals complex [vdW-2c] + requires about +17 kcalmol -1 .

However, that barrier, evidenced experimentally, is completely overcome by leveraging In view of utilizing natural atomic charges analysis, the coordination of THF not only served as the driving force of this reaction but also triggered variable character of the Ir-bound hydrido ligand, which is capable of behaving as H -in key hydrosilylation steps or as H + , as shown here.

Bonding of THF to the Si center actually give rise to [START_REF] Chauhan | Lewis Base--Stabilized Transition Metal Complexes of Divalent Silicon Species[END_REF] 2) minor donation from the Si-bound THF oxygen atom.

3) crucial transfer of density to HIr, which rebalances the charge density between this hydrogen atom and HSi in the process of H2 formation.

Reduction of nitroarenes

Since the nature of (metalla)silylium's catalytic reactivity was ascertained, there have been endeavors making use of that property on O-dehydrosilylation of alcohols [START_REF] Hamdaoui | Evidence of a Donor-Acceptor (Ir-H)→SiR3 Interaction in a Trapped Ir(III) Silane Catalytic Intermediate[END_REF] , reduction of nitriles through N-silylation [START_REF] Hamdaoui | Iridacycles as Catalysts for the Autotandem Conversion of Nitriles into Amines by Hydrosilylation: Experimental Investigation and Scope[END_REF] or the most recent and appealing dehydrofluorination [START_REF] Binh | Entrapment of THF--Stabilized Iridacyclic IrIII Silylenes from Double H-Si Bond Activation and H2 Elimination[END_REF] . To continue to cultivate that fruitful chemistry, nitroarenes reduction via hydrosilyltion was delved into subsequently.

The synthesis of amine arenes via the reduction of nitroarenes laid in the center of organic chemistry which is frequently utilized in the synthesis of pharmaceuticals, agrochemicals, dye intermediates, and pigments, etc. 164 Conventional methods used for that transformation are Béchamp 165, 166 (Fe/HCl) or sulfide 165 (H2S) reduction are fraught with pitfalls as using grossly excessive of iron powder 167 , disposing of a large amount of waste of toxic substances 167,168 and formation of the mephitic sulfurcontaining side-products 165 . Generally, the industrial-scale reductions of nitro compound are currently conducted by utilizing the heterogeneous catalyst.

Nevertheless, there is a limited number of commercially available catalysts, and rest are altered for the specific substrates. Therefore, leveraging hydrosilylation of nitroarenes that provides a cheaper, safer alternative and carried out under mild condition is of utmost importance. However, the yield is quite low and defining a conversion is unachievable in some cases due to a lingering issue that formation of toxic hydroxyl- amine intermediate and side products such as azo and azoxy, which leads to the color impurities in the reaction products (scheme 30) 165 albeit product mixture treated by dilute acid acetic and extracted in organic phase.

Enhancement catalytic reactivity of adduct by utilizing fluorinated ligand.

Synthesis

Continuing with previous section, it is safe to hypothesize that cationic hydrido-Ir(III)silylium species, whose catalytic reactivity is of significant correlation with the extend of polarization of the molecule [START_REF] Binh | Is the R3Si Moiety in Metal-Silyl Complexes a Z ligand? An Answer from the Interaction Energy[END_REF][START_REF] Hamdaoui | Evidence of a Donor-Acceptor (Ir-H)→SiR3 Interaction in a Trapped Ir(III) Silane Catalytic Intermediate[END_REF][START_REF] Hamdaoui | Iridacycles as Catalysts for the Autotandem Conversion of Nitriles into Amines by Hydrosilylation: Experimental Investigation and Scope[END_REF] therefore enhance the polarization in the key intermediates molecule is also means increase its catalytic reactivity. The polarization occurs already in the Ir-silane adduct stemming from the electropositivity of Si centre will be aggravated by adding an electron withdrawing group in N,C ligand. (figure 38) Figure 41: [START_REF] Binh | Entrapment of THF--Stabilized Iridacyclic IrIII Silylenes from Double H-Si Bond Activation and H2 Elimination[END_REF] F- 1

H NMR of F-1a

As expected, F-1a also displays remarkable catalytic reactivity toward a benchmark test reaction that can be followed by piezometry, i.e. the O-dehydrosilylation of alcohols at room temperature with Et3SiH. A hydrido-Ir(III)-silylium intermediate crystal was trapped as well following on a reaction with Et2SiH.

Eq 37: F-1a reacted with Et2SiH2 to from an adduct adduct and [F-5a] + adduct

F-1a F-5a

2. Comparative piezometric study of hydrosilylation catalysts

Introduction

In continuation with work initiated in 2016-2017 [START_REF] Hamdaoui | Evidence of a Donor-Acceptor (Ir-H)→SiR3 Interaction in a Trapped Ir(III) Silane Catalytic Intermediate[END_REF][START_REF] Hamdaoui | Iridacycles as Catalysts for the Autotandem Conversion of Nitriles into Amines by Hydrosilylation: Experimental Investigation and Scope[END_REF] , this research consists of the evaluation of various catalytic reactivity and potential hydrosilylation catalysts based on their ability to promote a dehydro-O-silylation reaction of alcohols by a silane (Eq 38.). This reaction is capable of producing gaseous dihydrogen which, once the saturation has reached in the liquid phase, will be released into the gas phase. This property is pivotal to profile the indirect kinetic data by measuring the quantities of unleashed gas and to determine the initial speed of the reaction, which is considered as a characteristic of the catalysts. These measurements applied on a variety of catalysts are justified and comparable if a mechanism of the reaction and the release of H2 took place under a constant condition.

Eq. 38: Reaction of deshydro-O-silylation of catalytic alcohol

From metrology to catalysis

In this account, the aim was to exploit a direct method to determine the kinetics of the dehydro-O-silylation reaction of alcohols by silanes (Eq 38). Due to the insoluble gas H2 released, there are two options to collect data: either using an operator to record volume variations counted on the isobaric and isothermal volumetric determination of the quantity of hydrogen liberated as a function of time 179 or employing isochoric and isothermal piezometric based on the measurement of pressure variation inside a closed chamber in which the reaction occurs [START_REF] Hamdaoui | Evidence of a Donor-Acceptor (Ir-H)→SiR3 Interaction in a Trapped Ir(III) Silane Catalytic Intermediate[END_REF] . The latter choice was justified here by the fact that, unlike volumetry, this is a technique that allows a total automation of the capture of pressure variations through a piezoelectric pressure probe of which there are relatively accurate models to translate pressure variations into potential differences that are linearly related to the measured pressure. Connected to an Analog-Logic converter, a piezoelectric pressure probe allows the measurement of relative pressure variations conducted in a few ms time resolution. However, limitations of most probe inherently stem from employed technology;; the sensitivity to pressure variation at low DP, and the electronic latency time causing the delay between the physical variation of pressure and its effective detection by the probe. To avoid these limits, all the experiments were carried out so that the maximum pressure variation reaching between t = 0 and t = end is lower than the upper limit of the probe (relative Pmax = 6.90 bar for a Mykrolis probe P / N A332984-007, voltage = 0.05 <P <5.05 Vcontinuous) and higher than 4 bar to reduce the error on the measurement at low pressures.

According to the manufacturer specifications, the measurement error is indeed crucial at very low pressures, however, it is less than 2% of the voltage measured at 1.37 bar and less than 0.5% at 5.52 bar. The deviation of the measurement of the pressure as a function of the temperature is ±0.02% of the voltage compared to a standard measurement at 20.0°C due to an integrated compensation device covering the temperature range of -20 °C to +60°C.

Catalytic hydrosilylation

The hydrosilylation of unsaturated organic compounds is essentially a reduction reaction carried out by the metallo-promoted addition of the polarized Si(d + )-H(d -) bond of a hydrosilane towards a multiple bond 180 . This reaction has emerged with growing prominence as an alternative to hydrogenation and reduction reactions catalyzed by aluminum and borohydride, which pose many safety concerns in industrial facilities 181 . Although thermochemically "spontaneous", the uncatalyzed hydrosilylation reaction is kinetically discernibly slow, which requires a catalyst to lower its activation barrier 182 .

Calas et al. have described the first hydrosilylation catalyst based on ZnCl2 183 . Due to a great interest in this chemical reaction 184 185 , great efforts have been made to develop more efficient and selective catalysts. For instance, cobalt complexes for the hydrosilylation of nitrile 186 , ruthenium for the hydrosilylation of carbonyl 187 , gold for the hydrosilylation of urea 188 , iron and nickel for the hydrosilylation of the alkene 182 , and iridium-based complexes for double hydrosilylation of nitriles to amines were implemented. Alongside that path, metallacycles in figure 43 (A1, A2, A3) or (1a, F-1a, 1b would be subjects for this report. The hydrosilylation reaction can be carried out under two different mechanisms in the initiation phase leading to a formation of the key catalytic species: the first type [START_REF] Binh | Is the R3Si Moiety in Metal-Silyl Complexes a Z ligand? An Answer from the Interaction Energy[END_REF] is an oxidation mechanism which comprises an oxidative addition of the Si-H bond onto a metal, then followed by a conventional migration of silyl group and hydro ligands to an organic substrate;; the second type [START_REF] Binh | Is the R3Si Moiety in Metal-Silyl Complexes a Z ligand? An Answer from the Interaction Energy[END_REF] involves the electrophilic activation of the hydrosilane by a hydride transfer to a metal center ensuing a formation of a silylium which then can be either captured by the complex to form a donor-acceptor adduct, or by the substrate to generate a hydrosilylated product. A dehydro-O-silylation reaction studied in this work was 1a F-1a 1b Since the polarity of the reaction medium would change from a very polar medium to a non-polar medium, it is illogical to determine an absolute rate constant of a reaction.

Hence, kinetic parameters were measured in the time limit as within the first 10% conversion during the reaction time. In case the initiation phase of a given catalysis is particularly long, it is necessary to readjust the calculation of the rate constants and initial rate constants.

Curves

Triethylsilane concentration was used in the kinetic equations to determine the initial rate of catalysis as well as the initial rate constant.

The pressure released by the dehydro-O-silylation enables a measure of a number of moles of the eliminated hydrogen grounded on the equation of the perfect gas PV = nRT (P: pressure in atm;; V: volume in L = 30.7 × 10 -3 -volume of the solution, n: number of moles in mol, R: constant of the perfect gas = 0.008206 L.atm.mol -1 .K -1 , T: temperature in K ).

From the number of moles of dihydrogen, the concentration of triethylsilane as a function of time would be established (number of moles of triethylsilane at a time t = number of initial moles - number of moles of dihydrogen released).

Thermodynamic calculation

The Eyring-Polanyi equation was applied to calculate the thermodynamic activation parameters of the catalysts (enthalpy, entropy and free enthalpy): Ln(k/T) = -ΔH ‡ /RT + Ln(kB/h) + ΔS ‡ /R (with k: absolute catalyst rate constant, T: thermodynamic temperature, ΔH ‡ = activation enthalpy, R = universal ideal gas constant = 1,987 cal.mol -1 .K -1 , kB = constant of Boltzmann = 1.38064852 × 10 -23 J.K -1 ;; h = Planck constant = 6.62607015 × 10 -34 Js;; ΔS ‡ = entropy of activation) by plotting the line of ln(k / T) as a function of 1 / T the enthalpy and entropy can be deduced.

Comparison catalysts

The purpose of this step was to extract information about catalytic reactivity of given catalysts on dehydro-O-silylation reactions carried out under identical conditions in order to compare results. The catalyst 1a seems to be the least efficient catalyst. For catalyst F-1a, it was found that the amount of liberated dihydrogen increased slowly from the beginning, then an inflection showing an H2 production almost as fast as with 1b. This phenomenon suggested that the catalyst F-1a has an initiation step longer than the other two catalysts at room temperature.

A1 = 1a A2 = F-1a A3 = 1b
Generally, the rate equation of a chemistry reaction is in the form of a differential equation containing the time and the concentrations of the different species presenting To calculate the order of the reaction, several experiments were carried out under [A], [B] as constant, and [cat] variables. After that, one can draw the line of Ln(v) plotted against Ln([Cat]) of which a slope designates an order of the reaction relative to the catalyst Ln(v) = Ln(k') + w.Ln([Cat]).

catalyst 1a:

A mixture of benzyl alcohol (0.5 mL, 5 mmol) and triethylsilane (0.8 mL, 5 mmol) was produced in a double-neck Schlenk type reactor. Catalyst 1a was used in different concentrations at different temperatures. The absolute rate of the initial catalyst of the reaction was determined from the slope of the straight-line tangent to t0. The number of TOF cycles represents the maximum number of molecule conversion per catalytic site, and the number of TOF cycles per unit of time, therefore the higher TOF is, the more active the catalysts are 195,196 . In the case of catalyst 1a, it was found that the TOF decreases following a decline of catalyst concentration.

Concentration (M) T=293 K Time (s) Yield (%) Initiale rate (mol.L -1 .s - 1 ×10 -4 ) TON TOFi (h -1 )
The slope of the line of ln(v) = ln(k')+ w.ln([Cat]) is: According to table 12, the alcohol dehydro-O-silylation reaction is pseudo-secondorder.

T(K)

Catalyst F-1a:

A mixture of benzyl alcohol (0.5 ml, 5 mmol) and triethylsilane (0.8 ml, 5 mmol) is added in a double-neck Schlenk type reactor. Catalyst F-1a was injected on different concentrations at different temperatures. In this situation, an initiation step was observed in the presence of this catalyst, thus it would be kinetically studied separately from the catalysis step. The slope values obtained in these cases were rather different presumably since the catalytic system did not follow the same mechanism involving 1a or F-1a, order of catalyst was considered approximately about 2.

Catalyst 1b:

A mixture of benzyl alcohol (0.5 ml, 5 mmol) and triethylsilane (0. 18, the reaction of dehydro-O-silylation is of pseudo-second order.

The TOFs in the presence of the catalyst 1b were higher than in the presence of the catalysts F-1a and 1a. This shows that catalyst 1b is more effective than catalyst F-1a and more effective than catalyst 1a under the same conditions.

From Tables 12 and16

Determination of the rate constant of a reaction (1):

The rate constant is indispensable to understand a chemical reaction. To calculate that, the kinetic equation corresponding to the order must be exercised. Comparing values of rate constants and thermodynamic energies stemming from the dehydro-O-silylation of isopropanol and benzyl alcohol with triethylsilane shows that the aromatic ring resonance effect was in favor of reaction (1), which also played a part in in stabilizing intermediate compounds and gave rise to a higher Bronsted acidity of benzyl alcohol (pKa = 15.4) than isopropanol (pKa = 16.5).

Determination of the rate constant and the thermodynamic coefficients of the reaction (3)

A mixture of hexafluoroisopropanol (0.6 ml, 5 mmol) and triethylsilane (0.8 ml, 5 mmol)

were added in a double-neck Schlenk type reactor and the same amount of the catalyst A3 was injected at different temperatures.

Temperature (K) Time (s) Yield (%) Initial rate (mol.L -1 .s -1 ×10 -6 ) TON TOFi (h -1 ) k Ordre 1 (L.mol -1 .s -1 ) k Ordre 2 (L.mol -1 .s -

Conclusion

By studying a wide range of known compounds as well as recently synthesized compounds in our laboratory, it was proven that the piezometric method developed during this research allows a determination of characteristics of a catalytic reaction such as TON, TOFi, and more broadly certain extent of activation energies. This also foster establishing of a silanes electrophilic activation mechanism and optimizing catalytic quality.

This study demonstrated that the catalyst 1a has a similar catalytic activity to 1b.

Nevertheless, the induction period was longer, indicating its activation triggered by the departure of acetonitrile was kinetic lock which did not exist in the 1a and 1b cases.

In addition, the dehydro-O-silylation of isopropanol, hexafluoroisopropanol, and benzyl alcohol, is less dependent on the thermodynamic acidity than on its kinetic acidity of alcohol during the key step of deprotonating an intermediate [RF-O(H)-SiEt3] + by a hydro-iridium species [phpy] Cp*Ir-H serving as an iridium hydride (III).

Although a wide range of iridacyclic silylene complexes were isolated and fully characterized, preparative synthesis of those compounds is still a lingering hurdle due to their inherently high reactivity. Using silanes with bulky aromatic substituents affecting considerably on Ir-Si bond and stability of a whole system through conjugation system on the silicon atom could provide a solution.

Transfer divalent silicon species and further utilize those in organic synthesis are worthy being exerted more effort especially applications of silylene transfer in organic chemistry remain sparse.

The scope of this research can be expanded to other transition metals for example, Cobalt, Ruthenium, Rhodium associated with diversifying ligands.

Preliminary result on fluorinated Iridacycle complexes is very promising in term of both synthesis and catalyst. Further attempt will be made to replicate a fruitful result of 1b and hopefully facile isolation and preparative synthesis will be achievable in this case.

Relied on this result, more fluorinated ligand should be made and leveraged not only with Iridium but also Cobalt, Ruthenium, Rhodium.

Bringing variety to stabilizing silicon ligand and trapping free silylene species will be also targeted.

General Methods and Technical Details

Experimental techniques and materials

All experiments were conducted under a dry argon atmosphere using standard H (300, 400, 500, and 600 MHz), [START_REF] Davis | Complexes with unbridged dative bonds between osmium and a Group 6 element. Structures of (Me3P)(OC)4OsM(CO)5 (M = chromium, tungsten)[END_REF] C (75 and 126 MHz), [START_REF] Binh | Entrapment of THF--Stabilized Iridacyclic IrIII Silylenes from Double H-Si Bond Activation and H2 Elimination[END_REF] F (282 MHz), and [START_REF] Yamashita | Oxidative Addition of the Si--C Bonds of Silacyclobutanes to Pt(PEt3)3 and Highly Selective Platinum(0)--Catalyzed Di--or Polymerization of 1,1--Dimethyl--1--silacyclobutane[END_REF] Si (119 MHz) NMR spectra were measured on Bruker DPX 300 and 400, Avance I 500, and Avance III 600 spectrometers. All chemical shifts (d) are expressed in parts per million (ppm). For 1 H and [START_REF] Davis | Complexes with unbridged dative bonds between osmium and a Group 6 element. Structures of (Me3P)(OC)4OsM(CO)5 (M = chromium, tungsten)[END_REF] C NMR, values of d are reported relative to Me4Si as an external reference standard and referenced against peaks of solvents (only partially deuterated solvent is visible in 1 H) as secondary reference standards. For other nuclei, the reported values of d are referenced to external reference standards (CF3C6H5 in CDCl3 for [START_REF] Binh | Entrapment of THF--Stabilized Iridacyclic IrIII Silylenes from Double H-Si Bond Activation and H2 Elimination[END_REF] F, Me4Si in CDCl3 for [START_REF] Yamashita | Oxidative Addition of the Si--C Bonds of Silacyclobutanes to Pt(PEt3)3 and Highly Selective Platinum(0)--Catalyzed Di--or Polymerization of 1,1--Dimethyl--1--silacyclobutane[END_REF] Si).

In situ Generation of [3][BArF 24 ] by Reaction of [1b][BArF 24 ]

with HSiPhH 2 and THF: Procedures, NMR Data, and Spectra Procedure 1 for NMR analysis (indirect;; route 1, Figure 1)

In a glovebox, HSiPhH2 (10.0 μL, 81.0 μmol) was added to a solution of [1b][BArF24] (15 mg, 10.6 μmol) in CD2Cl2 (0.55 mL). The resulting solution was shaken and transferred into a J. Young NMR sample tube which was subsequently tightly sealed for analysis. After 25 minutes of reaction, the NMR tube was frozen at < -60 °C. 1 H NMR analysis (at -60 °C) of the reaction was carried to verify the total and exclusive conversion of [1b][BArF24] to [2c][BArF24]. Addition of THF (10 μL, 123.3 μmol) to the latter mixture resulted in immediate effervescence of the yellow solution that indicated H2 gas evolution. To raise up the temperature from -60 °C to ~ 20 °C, it was found necessary to let the latter solution standing in the glovebox at room temperature for ~1-2 h. 1 H NMR analysis (at -60 °C) indicated complete consumption of [2c][BArF24] and formation of [3][BArF24] as the major Ir species along with H2 (singlet at ca. δ 4.60 ppm) in a respective ca. 1:0.2 ratio (see NMR spectra below). A complex pattern of peaks of low-intensity were also observed in the range spanning δ 5.10-5.15 ppm (integrating roughly for 2H relative to [3][BArF24]);; part of the peaks, i.e., a singlet at δ 5.15 ppm, is assigned to the Sibound hydrogen of an unidentified organosilicon derivative "PhxSiyHz" (on the basis of weak [START_REF] Yamashita | Oxidative Addition of the Si--C Bonds of Silacyclobutanes to Pt(PEt3)3 and Highly Selective Platinum(0)--Catalyzed Di--or Polymerization of 1,1--Dimethyl--1--silacyclobutane[END_REF] Si satellites;; vide infra). This procedure was found to be reproductible over (at least) ≥ 5 experiments. with HSi n BuH 2 and THF: Procedures, NMR Data, and Spectra Procedure 2 for NMR analysis (indirect;; route 1, Figure 1)

Compound [4][BArF24] was generated in solution using the procedure 2 previously described for [3][BArF24] (cf. previous section): HSi n BuH2 (20.0 μL, 77.0 μmol) was added to a solution of [1b][BArF24] (30 mg, 21.2 μmol) in d8-THF (0.45 mL). The resulting solution was shaken and transferred into a J. Young NMR sample tube which was subsequently tightly sealed for analysis at -40 °C. Full conversion was obtained after 2 h of reaction, as verified by 1 H NMR analysis (cf. spectra in the next sub-section). Indeed, the latter 1 H NMR spectrum indicated complete consumption of [1b][BArF24] and selective formation of [4][BArF24] along with H2 (singlet at ca. δ 4.55 ppm) in a respective ca. 1:0.3 ratio. A complex pattern of unresolved and unidentified peaks of low-intensity were also observed in the range spanning δ 4.59-4.66 ppm (integrating roughly for 2H relative to [3][BArF24]).

NMR data 1 H, [START_REF] Davis | Complexes with unbridged dative bonds between osmium and a Group 6 element. Structures of (Me3P)(OC)4OsM(CO)5 (M = chromium, tungsten)[END_REF] C-1 H and 1 H, [START_REF] Yamashita | Oxidative Addition of the Si--C Bonds of Silacyclobutanes to Pt(PEt3)3 and Highly Selective Platinum(0)--Catalyzed Di--or Polymerization of 1,1--Dimethyl--1--silacyclobutane[END_REF] Si HMQC One arbitrary representation of the molecular structure of [4][BArF24] is drawn below for indicating the labelling pattern which was chosen for assigning spin-active nuclei to their corresponding chemical shifts. H nuclei. This method of analysis allowed us to obtain (together with all other NMR analyses) additional strong evidence for the structural assignment that we attribute to compound [4][BArF24] in solution. Also, this further confirms that the molecular structure adopted by [4][BArF24] in the solid-state (X-ray diffraction analysis of single crystals) is also maintained in solution. Most importantly, through-space cross-peak correlations are observed between Ha (i.e. hydrogen bound directly to Si) and nuclei belonging to Cp* (CH3) and n-butyl (Hb-e), as well as between CH3 of Cp* and nuclei belonging to B[h]Q (Hh) and [BArF24] -(Hi);; thus unambiguously establishing the long-range interactions between these groups (through either covalent bonds or noncovalent interactions) and hence the overall molecular cohesion of the ionic Ir-"silylene" metallacycle [4][BArF24].

Synthesis of F-2

A mixture of [Cp*IrCl2]2 (50.0 mg, 0.081mmol), NaOAc (40.0 mg, 0.49 mmol), Fphenyl pyridine (21.4 mg, 0.17 mmol), was stirred vigorously at room temperature (RT) in 20 mL of dichloromethane for 5 days. The mixture was filtered through Celite and evaporated to dryness [START_REF] Binh | Is the R3Si Moiety in Metal-Silyl Complexes a Z ligand? An Answer from the Interaction Energy[END_REF][START_REF] Hamdaoui | Evidence of a Donor-Acceptor (Ir-H)→SiR3 Interaction in a Trapped Ir(III) Silane Catalytic Intermediate[END_REF] . The solid obtained was washed with hexane to remove excess ligand. Cyclometalated compound F-2 was isolated as a red-orange solid (60.0 mg, 80%). In a Schlenk flask an equimolar mixture of F-2 and Na[BArF24], was dissolved in acetonitrile (∼7-10 mL). The resulting mixture was vigorously stirred at room temperature for 2 h. The resulting suspension was filtered through a pad of celite, and the solvent was removed from the filtrate under reduced pressure. The solid was either recrystallized in a mixture of CH2Cl2 and n-hexane or n-pentane or washed with n-hexane or n-pentane [START_REF] Binh | Is the R3Si Moiety in Metal-Silyl Complexes a Z ligand? An Answer from the Interaction Energy[END_REF][START_REF] Hamdaoui | Evidence of a Donor-Acceptor (Ir-H)→SiR3 Interaction in a Trapped Ir(III) Silane Catalytic Intermediate[END_REF] , to afford an analytically pure compound. (90%)

  Scheme 4: Synthesis Mia-3 and Mia-4

Group 4 :

 4 n = 1, 2 or 3;; X = halogen or H;; R = bulky aromatic or aliphatic group Group 5: R, R' = alkyl group Type 1 are analogues of carbene complexes ([LnM = CR2]) without stabilizing-base while type 2 entails a coordinated-base silylene ligand bound to transition metal fragment. Type 3 illustrates NHSi complexes including unsaturated functionalities and/or additional R groups in the ligand skeleton, type 4 are NHSi halide or hydride complexes. Type 5 is silylenes complexes stabilized by the interaction of M-H bonds

Figure 2 :

 2 Figure 2: Schematic diagram of the M=Si bonds of silylene complex (a) and basestabilized silylene complex (b). B denotes a base 45, 54 .

  complex without Lewis base stabilization synthesized from a stable silylene and metal carbonyls Ni(CO)4. It is acutely air- and moisture-sensitive yet quite thermally stable (mp 160 o C, decomp.). Although changing the reaction conditions (inverse addition of Den-1 to an excessive excess of Ni(CO)4 at -80 o C) or on the effort comproportionation of Den-3 with Ni(CO)4, monosubstitution product Den-2 was not detected (Eq. 18) 66, 67 .

Figure 3 :

 3 Figure 3: three sequence processes including silane Si-H oxidative addition, reductive elimination, and 1,2 hydrogen migration 65 .

J. C . 82 Eq 28 :

 C8228 Peters et al in 2006 reported that the [(PhBP iPr 3 )Fe II (H)(h 3 -H2SiR2 )] species formed by the reaction between [(PhBP iPr 3)FeMe] Pet-1 and PhSiH3 (eq. 28) leads to the quantitative formation of a single diamagnetic red product Pet-2,which is the first thoroughly characterized examples of ''arrested'' silane adducts of iron that exhibit an h 3 binding mode (i.e., Fe(h 3 - H2SiR2)) Reaction of Pet-1 with phenylsilane[START_REF] Thomas | An η3--H2SiR2 Adduct of [{PhB(CH2PiPr2)3}FeIIH][END_REF] Due to inevitable uncertainty in accurately locating the positions of hydrogen atoms being adjacent to much heavier atoms by X-ray crystallography, a related complex was produced to facilitate structural assignment. Complex Pet-1 reacts with one equivalent of mesitylsilane (H3SiMes) to generate product Pet-3, analogues of reaction shown in Eq. 28, in quantitative yield.As in the case of Pet-2, two of the three hydrides are located within bonding distance of the silicon atom in each molecule (Si...H5: 1.56 and 1.62 Å;; Si...H6: 1.67 and 1.74 Å), while the third hydride seems to be outside the bonding radius of the Si atom(Si•••H4: 2.14 and 1.97 Å). The Fe•••Si distances in both molecules for Pet-3 (2.131 (Å) and Pet-1 2.141 Å) are substantially identical to Pet-2 (2.1280(7) Å). Despite the inevitable uncertainty in the specific Fe•••H and Si•••H distances, the remarkable similarity between the structures of Pet-2 and Pet-3 justifies the presence of two 3centered Fe-H-Si interactions in the solid state and one Fe-H(hydride) interaction.

Figure 4 :

 4 Figure 4: Solid-state molecular structure of [(PhBP iPr 3)Fe II (H)(H2SiPhMe)] Pet-2 and[(PhBP iPr 3)Fe II (H)(H2SiMesMe)] Pet-3 showing 50 % displacement ellipsoids 82Given the tendency for the [PhBP iPr 3]Fe backbone to be subject to two-electron redox processes, mechanism is bound to undergo an oxidative addition/reductive elimination as shown in the path a. In this route, silane first coordinates to the Fe II center, and then an oxidative addition takes place. Reductive 1,2-methyl migration from iron to silicon finally yields an isomer of Pet-2 (or Pet-3)[START_REF] Betley | A Tetrahedrally Coordinated L3Fe-Nx Platform that Accommodates Terminal Nitride (FeIV⋮N) and Dinitrogen (FeI-N2-FeI) Ligands[END_REF][START_REF] Betley | Dinitrogen Chemistry from Trigonally Coordinated Iron and Cobalt Platforms[END_REF][START_REF] Daida | Considering FeII/IV Redox Processes as Mechanistically Relevant to the Catalytic Hydrogenation of Olefins by [PhBPiPr3]Fe-Hx Species[END_REF] .

  Ziegler and Rauk 119 , produces a dichotomy of the inter-fragment interaction energy partitioned into Pauli repulsion, electrostatic attractive, orbital attractive and, with dispersion corrected functionals, dispersion attractive interaction energy terms. This dichotomy into repulsive and attractive energetic contributions is a very powerful tool for the analysis of the nature of chemical bonds 121-124 (Eq. 30). ΔEint = ΔEp + ΔEc + Δd + ΔEo ΔEp: Pauli repulsion;; ΔEc: attractive electrostatic;; ΔEd: attractive dispersion;; ΔEo: attractive orbital Eq 30

CH 2

 2 Cl 2, -20 °C + THF, + C 6 H 6 Recristallisation 109, 114, 115, 145 nor the products of the oxidative addition of the Si-H bond to the Ir center 144 114 108 105 or any of its arrested states 146-148 , but [(IrH)⟶SiEt3] + .

  Scheme 25: The reaction of a solution of [1b][BArF24] with HSiR3 generating products [2c], [2d], [2e][BArF24].

Figure 8 :

 8 Figure 8: ORTEP at 50% probability of the structure of [2c] + determined by XRD analysis. The [BArF24] -anion and atoms corresponding to occupational disorder are omitted for the sake of clarity. Selected interatomic distances [Å] and angles [ o ] for [2c][BArF24]: Si1-Ir1 2.407(2), Si1-Hi1B 1.17(8), N1-Ir1 2.086(5), Ir1-H1A 1.81(9), Si1-H(Ir1) 2.239(8), Si1-Ir1-H1A 62(3), N1-Ir1-Si1 105.2(1), N1-Ir1-H1A 70(3). ORTEP at 50% probability of the structure of [2e] + determined by XRD analysis. The [BArF24] - anion and atoms corresponding to occupational disorder are omitted for the sake of clarity. Selected interatomic distances [Å] and angles [ o ] for [2e][BArF24]: Si1-Ir1 2.4220(7), Si1-Hi1B 1.39(3), N1-Ir1 2.092(2), Ir1-H1A 1.48(3), Si1-H(Ir1) 1.986(7) ,Si1-Ir1-H1A 55(1), N1-Ir1-Si1 108.07(4), N1-Ir1-H1A 80(1).

Figure 10 :

 10 Figure 10: Free CH3CN and Ir-Cp* of [2c], [2e][BArF24]. Complex [2c][BArF24] possessed a typical 1 H NMR Ir-H resonance at δ = -11.5 ppm, for which the 1 H, 29 Si HMQC NMR spectrum shows a weak cross-peak correlation with a 29 Si resonance at δ = -35.6 ppm being about 21 ppm downfield from the value found for "free" H3SiPh δ = -56.7 ppm).

Figure 11 :

 11 Figure 11: cross-peak correlation with a 29 Si of Ir-H of [2c][BArF24]

  Si resonance at δ = -35.6 ppm correlates with several other 1 H resonances of the Ir-bound

Figure 13 : 2 . 3 .

 1323 Figure 13: cross-peak correlation with a 29 Si δ = -31.00 ppm of Ir-SiH2Bu of [2d][BArF24]

Figure 15 :Figure 17 :

 1517 Figure 15: typical Ir-H of [2f] and [2g] [BArF24]

Figure 19 :

 19 Figure 19: ORTEP at 50% probability of the structure of [2f] + determined by XRD analysis. The [BArF24] - anion and atoms corresponding to occupational disorder are omitted for the sake of clarity. Selected interatomic distances [Å] and angles [ o ] for [2f][BArF24]: Si1-Ir1 2.455(2), Si1-Hi1B 1.39(7), N1-Ir1 2.092(4), Ir1-H1A 1.52(6), Si1-H(Ir1) 2.066(6),Si1-Ir1-H1A 57(3), N1-Ir1-Si1 107.0(1), N1-Ir1-H1A 75(3).ORTEP at 50% probability of the structure of [2g] + determined by XRD analysis. The [BArF24] -anion and atoms corresponding to occupational disorder are omitted for the sake of clarity. Selected interatomic distances [Å] and angles [ o ] for [2g][BArF24]: Si1-Ir1 2.435(1), Si1-Hi1B 1.52(7), N1-Ir1 2.083(4), Ir1-H1A 1.449(7), Si1-Ir1-H1A 55.65(9), N1-Ir1-Si1 99.19(9), N1-Ir1-H1A 75.27(9).

Figure 20 : 2 . 4 .Figure 21 :

 202421 Figure 20: Si atom binds to Ir center via a dative bond Ir⟶Si

Figure 22 :

 22 Figure 22: Computed low-lying rotamers of [2c] + and relevant NMR coupling constants compared to [2b] + ;; 18 ΔZPE is the relative energy including zero-point energy contribution;; Ni/N is the Boltzmann weight;; scalar coupling constants were computed by the DFT-based CPL 149 method. The J(Si-HCp*) coupling constants for the 15 1 H nuclei of the Cp* ligand in the static DFT model of [2c-r1] + were estimated to span -0.5 Hz and 0 Hz ;; the significant coupling of the Cp* protons in figure.... is consistent with a time-averaged 4 J scalar coupling.

Figure 23 :

 23 Figure 23: ETS-NOCV analysis of the interaction of silylium cation [SiH2Ph] + with the hydrido iridium group of [2c-r1] + . The deformation density isosurface (0.007 e bohr -3) Δρ1 shows that donation of electron density takes place mainly from a delocalized interaction of the Si center with the Ir, hydridic H, and carbanionic Cipso centers to enhance a quite diffuse four-center interaction in which the Ir-Si component dominates. Red and blue lobes are associated with donating and accepting orbital components, respectively.

[ 5 ] 1 H 1 HFigure 24 : 1 H 1 H

 5112411 Scheme 27: complexes[3,4,5][BArF24] can be obtained sequentially from[1b] + by treatment of[2c,d,e][BArF24] respectively with THF

1 H

 1 NMR analysis (-40 o C, [D8]THF) of [4][BArF24] disclosed a triplet at δ = 4.78 ppm with 1 JH,Si = 95Hz for the Si-bound H atom, as well as the typical signals of Sicoordinated THF (four broad peaks at d = 0.65, 0.83, 2.07, 2.31 ppm). A 1 H, 29 Si HMQC NMR experiment (-40 o C, [D8]THF) showed the presence of a cross-peak correlation between the 1H resonance of the Si-H bond at δ = 4.78 ppm and the 29 Si resonance at δ =71.3ppm. (figure 26)

Figure 26 :

 26 Figure26:1 H-29 Si HMQC NMR spectra of[4][BArF24]

Figure 27 :

 27 Figure 27: 1 H-[START_REF] Yamashita | Oxidative Addition of the Si--C Bonds of Silacyclobutanes to Pt(PEt3)3 and Highly Selective Platinum(0)--Catalyzed Di--or Polymerization of 1,1--Dimethyl--1--silacyclobutane[END_REF] Si HMQC and1 H NOESY NMR spectra of[5][BArF24]

  H NMR of the reaction of [2c][BArF24] (formed in situ by reaction of an 85 mM CD2Cl2 solution of [1b][BArF24] with 5 equiv of H3SiPh at -60 o C) with about 5 equiv of THF at 25 o C in a J. Young sealed tube showed rapid release of H2 gas in solution and full conversion to [3][BArF24] within about 20 min (Figure 28).

Figure

  Figure 28: Focused view on typical signals of the 1H NMR spectrum monitoring as a function of time the conversion of a freshly prepared solution of [2c] + (made from [1b] + , see dotted arrow) to [3] + upon addition of THF in CD2Cl2 solution at 25 o C;; spectra were acquired at 3 min time intervals, and t = 0 corresponds to the first spectrum, which was recorded about 3-4 min after introduction of the sealed J. Young NMR sample tube containing the mixture into the spectrometer.

Figure 30 :

 30 Figure 30: ORTEP at 50% probability of the structure of [3] + determined by XRD analysis. The [BArF24] -anion and atoms corresponding to occupational disorder are omitted for the sake of clarity. Selected interatomic distances [Å] and angles [ o ] for [3][BArF24]: Si1-Ir1 2.278(3), Si1-H1 1.3(2), O1-Si1 1.88(2),N1-Ir1 2.09(3), O1-Si1-Ir1 115.7(5), O1-Si1-H1 100(9), N1-Ir1-Si1 88.7(8), Ir1-Si1-H1 126(9). ORTEP at 50% probability of the structure of [4] + determined by XRD analysis. The [BArF24] -anion and atoms corresponding to occupational disorder are omitted for the sake of clarity. Selected interatomic distances [Å] and angles [ o ] for [4][BArF24]: Si1-Ir1 2.288(1), Si1-H1 1.40(8), O1-Si1 1.825(5), N1-Ir1 2.084(5), O1-Si1-Ir1 115.8(2), O1-Si1-H1 90(3), N1-Ir1-Si1 87.3(1), Ir1-Si1-H1 119(3).

Figure 31 :

 31 Figure 31: ORTEP at 50% probability of the structure of [5] + determined by XRD analysis. The [BArF24] - anion and atoms corresponding to occupational disorder are omitted for the sake of clarity. Selected interatomic distances [Å] and angles [ o ] for [5][BArF24]: Si1-Ir1 2.290(3), Si1-H1 1.45(9), O1-Si1 1.860(8), N1-Ir1 2.073(4), O1-Si1-Ir1 115.2(2), O1-Si1-H1 95(5), N1-Ir1-Si1 87.5(1), Ir1-Si1-H1 124(5). ORTEP at 50% probability of the structure of [6] + determined by XRD analysis. The [BArF24] -anion and atoms corresponding to occupational disorder are omitted for the sake of clarity. Selected interatomic distances [Å] and angles [ o ] for [6][BArF24]: Si1-Ir1 2.317(2), O1-Si1 1.838(6), N1-Ir1 2.082(4), O1-Si1-Ir1 112.1(2), N1-Ir1-Si1 91.5(1), C24-Si1-C26 106.1 (4), C24-Si1-Ir1 116.1(4).

  and b clearly represent the electron-density transfers taking place on buildup of the Si-to-Ir σ bond in accordance with the chosen interaction scheme. The ETS-NOCV 151 analysis of the THF-devoid analogue of [3] + (Figure 33a) confirms the π-accepting property of the :SiPh(H) moiety and consolidation of the Ir-Si bond [wbi(Ir-Si)=0.83], which is represented by deformation density Δρ2. In this case, the metal-Si π-backdonation orbital interaction (Figure 33a) represents about 20% of the interfragment orbital interaction energy.

Figure 33 .

 33 Figure 33. a) Main deformation density isosurface plots (0.005 e bohr -3) resulting from the ETS-NOCV analysis of the interaction of a neutral prepared Si(H)Ph silylene fragment with the cationic iridacyclic group in THF-devoid [3] + .b) Main deformation density isosurface plots (0.005 ebohr -3) resulting from the ETS-NOCV analysis of the interaction of a neutral prepared THF-bound Si(H)Ph(THF) silylene fragment with the cationic iridacyclic group in [3] + .The double arrows show which bond is virtually disrupted in the fragmentation.Red and blue isosurfaces correspond to donating and accepting orbitals, respectively. Orbital interaction energies ΔEk associated with a deformation density isosurface are given underneath each isosurface plot. Selected distances [Å] for the computed

Figure 34 .

 34 Figure34. Main deformation density isosurface plots (0.005 e bohr -3) resulting from the ETS-NOCV analysis of the interaction of a neutral prepared silylene fragment SiPh2 with the cationic Ir III group of an Ir silylene complex reported by Calimano and Tilley127 .The double red arrow suggests which bond is cleaved in the fragmentation mode. Δρ1 corresponds to the establishment of the Si-Ir σ bond. Δρ2 corresponds to Ir-to-Si π backbonding, the associated interaction energy ΔEk of which represents about 14 % of the total interfragment orbital interaction energy. Red and blue isosurfaces correspond to donating and accepting orbitals, respectively. The Wiberg bond index for the Ir-Si interaction is 0.81.

  THF in large excess or as solvent of the reaction, which leading plausibly to intermediate [vdW-2c] + . The conversion of [vdW-2c] + to THF-stabilized silylene complex[3] + has an activation barrier of about +14 kcalmol -1 through TS-I-thf with an exoergonicity ΔG o ([2c] + THF → [3] + ) of -4 kcalmol -1 , which confirms that in pure THF[3] + was formed spontaneously 127 .

  a net increase of the formal natural163 negative charge of the Si-bound H atoms and a 50% increase of the natural charge difference Δq between the HSi1 and HIr atoms in TS-I-thf compared to TS-I (Δq(HIr-HSi)TS-I-thf = 0.26, Δq(HIr-HSi)TS-I = 0.17;; Figure35b). Coulombic interactions between HSi1 and HIr essentially assist the formation of H2. Put differently, the relative "acidity" of the latter Ir-bound hydrido ligand HIr and the hydridic character of HSi1 intensified by the interaction with THF to facilitate H2 release. Corriu and coworkers[START_REF] Chauhan | Lewis Base--Stabilized Transition Metal Complexes of Divalent Silicon Species[END_REF] observed the same phenomenon on Fe complexes.

Figure 35 :

 35 Figure 35: a) Proposed Gibbs energy profile for the THF-assisted formation of [3] + , as computed by DFT (Gibbs enthalpies in kcal mol -1) assuming Coulomb-interaction-supported interaction of H atoms in TS-I-thf;; the Gibbs enthalpy (298.15 K, 1 atm) for the [1b] + →[3] + reaction is about -13 kcal mol -1. b) Detailed description of the Wiberg bond indices (in blue font) and (NPA) natural charges (in red font) at the core motif undergoing bond cleavage in transition states TS-I-thf and TS-I.

Figure 36 .

 36 Figure 36. Plot of deformation density Δρ1 (0.005 e/bohr -3) emerging from the ETS-NOCV analysis of the fictitious interactions of the prepared fragments of H2 and THF-bound Ir-silylene cation conducting to transition state TS-I-thf (the double red arrow indicates which bonds are cleaved in the fragmentation scheme). The red and blue isosurfaces (0.005 e bohr -3) are associated with orbitals donating and accepting electron density, respectively. The interaction of H2 with prepared [3] + suggests strong polarization of the H-H bond and donation to the Ir-HIr and HSi1-Si σ bonds from HIr and Ir centers along with the Si-Ir σ bond. In the reverse transformation, that is H2 release and its dissociation from [3] + , orbitals depleted in electron density are now those colored in blue and the accepting orbitals are colored in red.

Figure 37 represents

 37 Figure 37 represents the electron-density redistribution (red arrows) in the H2-release process based on the ETS-NOCV analysis, which consists of, transformation from a donor-acceptor Ir→Si interaction 17, 18 (wbi ≈ 0.44, silylicity, Π 16 related to the [SiPhH2] + moiety ≈ 1.3) in [2c] + to a reversed dative Ir ←Si or a coordinative Ir-Si bond carrying some Ir→Si π character in [3] + . Related conclusions can be rendered for [2d] + and [4] + (silylicity related to [SinBuH2] Π ≈ 1.3).

Figure 37 .

 37 Figure 37. Extrusion of H2 from TS-I-thf (left-hand side) via redistribution electron density (red arrows)fortifies the Ir-Si bond and leads to[3] + (right-hand side) in such way that the exact nature of the Sicentered ligand remains vague regardless of its significant residual p-acidic character (dashed bond).

Figure 38 :Scheme 31 :

 3831 Figure 38: By adding a strong electron-withdrawing group, the key intermediate F-1ais more polarized than 1a

Figure 39 : 19 F- 1 HClF- 2

 391912 Figure 39: 1H-NMR of F- Phenylpyridine, F- Phenylpyridine Iridacycle, and sovato complexe 19F-1 H NMR of F-2 and F-1a shows that[START_REF] Binh | Entrapment of THF--Stabilized Iridacyclic IrIII Silylenes from Double H-Si Bond Activation and H2 Elimination[END_REF] F S(δ ≈ -58 ppm) corelates with not only adjacent protons but also distant ones. (figure40, 41)

Figure 42 :H

 42 Figure 42: ORTEP at 50% probability of the structure of F-1a determined by XRD analysis. The [BArF24] -anion and atoms corresponding to occupational disorder are omitted for the sake of clarity. Selected interatomic distances [Å] and angles [ o ] for [F-1a][BArF24]: N2-Ir1 2.052(5), N1-Ir1 2.115(6), C11-Ir1 2.051(5), N1-C1-F1 115.2(6), N1-Ir1-N2 84.7(2), C11-Ir1-N1 77.4(2) ORTEP at 50% probability of the structure of F-2a adduct determined by XRD analysis. The [BArF24] -anion and atoms corresponding to occupational disorder are omitted for the sake of clarity. Selected interatomic distances [Å] and angles [ o ] for the product: Si1-Ir1 2.464(1), Si1-H1B 1.49(5), N1-Ir1 2.107(4), Ir1-H1A 1.52(4), Si1-Ir1-H1A 52(2), N1-C11-F1 115.6(4), N1-Ir1-Si1 105.2(1), N1-Ir1-H1A 80(2)

Figure 43 :Figure 44 :

 4344 Figure 43: Structure of catalysts synthesized in our laboratory based on iridium

Figure 45 :

 45 Figure 45: Curves of moles of dihydrogen as a function of time in different types of catalysts at different temperatures: (1) T = 293 K;; (2) T = 288 K;; (3) T = 283 K;; (4) T = 278 K, [Catalyst] 0 = 2.77 × 10 -3 mol / L. According to figure 45, the absolute rate of the catalyst of the dehydro-O-silylation reaction (reaction of benzyl alcohol with triethylsilane) is highest in the presence of the catalyst A3.

  medium and the initial rate constant k 194 . Due to the aforementioned issue (changes of polarity), the constant of initial rate was calculated in the first 10% of conversion as described here: vi =ki[A] n [B] m [cat] w vi: initial rate of the reaction ki: initial rate constant [A], [B], [cat]: concentrations of the compounds A, B and the catalyst n, m and w: partial orders in A, B and the catalyst Our work on these catalysts helped guide the research in which the equation vi = k'[cat]w was utilized to determine the order of the reaction relative to the catalyst with vi: initial rate of the reaction;; k': apparent initial rate constant at which A and B concentration were constant;; [cat]: catalyst concentration in (mol / L);; w: partial order of the catalyst.

5

 5 It was no longer possible to distinguish the initiation phase due to a decrease in the temperature and / or the concentration of the catalyst causing a deactivation of the catalysis

  the slope of the equation ln v = ln k'+ n.ln[Cat] was close to 1 at 278 K which was clearly different from those of other temperatures. Hence, the limitation of this method was evident at this instance.Because of time limitation, the reaction order of triethylsilane could not be determined, for which one could apply the kinetic equation of first order ln [A] = - k't + ln [A] 0 and second order 1/ [A] = 1/[A0] + kt to determine the rate constant where [A] is the concentration of the reagent at a time t;; [A0] is the concentration of the initial reagent;; k': is the apparent speed constant;; t is the time.

  Schlenk and glovebox techniques (unless otherwise indicated). All glassware was oven-dried prior to use. All solvents were distilled over sodium or CaH2 under argon before use. Deuterated solvents (including PhF) were dried over sodium or CaH2, filtered over activated neutral alumina, and stored under argon before use. The following compounds were purchased from the indicated companies and used as such (unless otherwise stated): HSiEt3 (Aldrich, 100 mL, 97%), HSiPhH2 [(Alfa-Aesar, 25 g, 97%), (purified by bulb-to-bulb distillation over CaH2 and stored under argon over MS-3Å)], PMHS (Alfa-Aesar, 100 g), 1-fluoroheptane (1-FH) (Aldrich, 1 g, 98%), fluorocyclohexane (F-Cy) (TCI-Chemicals, 5 g, > 98%). Ligand name abbreviations: Cp*, (1,2,3,4,5-pentamethyl-η 5 -cyclopentadienyl);; PhPy, 2-(2-pyridyl)phenyl, B[h]Q, benzo[h]quinolinyl. [1a,b][BArF24] were prepared following published procedures. 1,2 1

1 HFigure S- 15 1 H 1 H

 11511 Figure S- 2

1 HFigure S- 18 Figure S- 19 1 H

 1181 Figure S- 18

Figure S- 20 1 HFigure S- 21 1 H, 1 H

 111 Figure S- 20

1 H, 1 HFigure 1 H

 111 Figure S- 23

1 H( 1 H

 11 600 MHz, 233 K, d8-THF): δ = 9.01 (d, 1H, HAr B[h]Q, J = 5.4 Hz), 8.49 (d, 1H, HAr B[h]Q, J = 7.9 Hz), 7.98 (d, 1H, HAr B[h]Q, J = 8.7 Hz), 7.82 (d, 1H, HAr B[h]Q, J = 8.7 Hz), 7.86 (m, 8H, Hortho BArF24), 7.76 (d, 1H, HAr B[h]Q, J = 7.8 Hz), 7.66 (m, 4H, Hpara BArF24), 7.60-7.65 (m, 3H, HAr B[h]Q), 4.78 (t, 1H, Ha, 1 JH-Si = 95.4 Hz, 1 JH-H = 2.8 Hz), 2.31 (bs, 2H, Si-thf), 2.07 (bs, 2H, Si-thf), 1.88 (bs, 15H, Cp-Me5), 1.34-1.44 [m, 4H, Si-thf (overlap with Hc,d peaks of free silane)], 0.83 (bs, 2H, Hg or Hg'), 0.75 (broad m, 2H, Hd), 0.60-0.69 [broad m, 4H, (Hg or Hg') + Hc], 0.53 (t, 3H, He, J = 8.7 Hz), -0.1 (m, , 1 H NOESY Below is shown one possible representation of the molecular structure of [4][BArF24](asymmetry at Ir and Si centres makes possible the co-existence of two pairs of epimeric forms with four relative diastereomers), which is drawn here for pointing out the various NOESY through-space correlations observed in the 2D spectrum shown in the spectra section.

1 H

 1 Figure S- 30

Figure S- 32 201 1 H, 1 H

 3211 Figure S- 32

1 H, 29 Figure S- 34 C- 1 H

 129341 Figure S- 34

1 H

 1 NMR (500 MHz, CD2Cl2) δ 7.86 (d, J = 7.0 Hz, 1H), 7.84 - 7.79 (m, 1H), 7.74 (d, J = 6.6 Hz, 2H), 7.25 (t, J = 7.4 Hz, 1H), 7.08 (d, J = 7.1 Hz, 1H), 6.95 (s, 1H), 1.73 (s, 15H).

13 C 19 F

 1319 NMR (500 MHz, CD2Cl2) δ 105.55 (C1), 114.70(C3), 122.05(C5), 124.59(C4), 130.89 (C6), 136.02(C7), 141, 47(C2), 53.23 (Cp*), NMR (500 MHz, CD2Cl2) δ -58.21 ppm

1 H

 1 NMR (500 MHz, CD2Cl2) δ 7.90 - 7.81 (m, 1H), 7.73 - 7.68 (m, 3H), 7.22 (td, J = 7.4, 1.4 Hz, 1H), 7.12 (td, J = 7.5, 1.3 Hz, 1H), 6.93 (dt, J = 8.0, 1.2 Hz, 1H), 2.21 (s, 3H), 1.60 (s, 15H).

13 C

 13 NMR (500 MHz, CD2Cl2) δ 144.50 (C2), 135.04 (C3, C4,C7), 132.58 (C5), 124.1(C6), 106.78 (C1).

19 F

 19 Figure S-38 Dr1 shows that most of the donation of electron density operates mainly from a delocalized interaction of the Si centre with the Ir, hydridic H and carbanionic CAr centres to build up a rather delocalized 4 centre interaction where the Ir-Si component dominates. Red and blue lobes are associated to donating and accepting orbitals respectively. Identical interactions are noticed for the low lying rotamer [2c-r2] + .

Figure S- 40

 40 Figure S-40 Dr1 corresponds to the s-bond Ir←Si component of the interaction representing about 70 % of the bonding orbiatl interaction energy, whereas Dr2 materializes the residual p-Ir→Si back bonding interaction, representing about 10% of the orbital interaction energy. Red and blue lobes are associated to donating and accepting orbitals respectively. The red double arrow indicates the broken bond in the fragmentation scheme. ETS-NOCV analysis of [4] + assuming the :Si(H)(nBu) ligand as a closed shell neutral fragment

Figure S- 41

 41 Figure S-41 Dr1 corresponds to the s-bond Ir-Si component of the interaction representing about 85 % of the bonding orbiatl interaction energy, whereas Dr2 materializes the residual p-metal-to-Si back bonding interaction, representing about 7% of the orbital interaction energy. Red and blue lobes are associated to donating and accepting orbitals respectively. The red double arrow indicates the broken bond in the fragmentation scheme.

Table 1 :

 1

The siliranes Woe-cis-1 and Woe-trans-1 were treated with a variety of terminal acetylenes in a catalytic amount Eq 8: Woe-1,2 and 3

[START_REF] Palmer | Stereospecific Palladium--Catalyzed Reactions of Siliranes with Alkynes[END_REF]

Table 4 :

 4 Interatomic distances fluctuate evidently, among which Ir-H and Si-H(Ir) interatomic distances of[2c][BArF24][START_REF] Hamdaoui | Evidence of a Donor-Acceptor (Ir-H)→SiR3 Interaction in a Trapped Ir(III) Silane Catalytic Intermediate[END_REF] are longest (1.81(9) Å and 2.239(8) Å respectively) while those of other complexes only approximate averagely 1.499 Å (Ir-H) and 1.861 Å (Si-These atomic distances (table 4) cement our statement on the formal oxidation state of Ir center in previous research[START_REF] Hamdaoui | Evidence of a Donor-Acceptor (Ir-H)→SiR3 Interaction in a Trapped Ir(III) Silane Catalytic Intermediate[END_REF][START_REF] Hamdaoui | Iridacycles as Catalysts for the Autotandem Conversion of Nitriles into Amines by Hydrosilylation: Experimental Investigation and Scope[END_REF] . In such complexes, Si atom carries a great charge density depletion and binds to Ir center via a dative bond Ir⟶Si (figure20). Hence, the silylium [R1R2R3Si] + is actually isoelectronic to neutral boranes BR3 that are prototypical Z-type ligand according to Green's formalism[104][105][106][107] . As a result, a [ML3X3Z] formation in which formal oxidation state of iridium is III is more reasonable than [ML3X4] + Ir(V).

	H). Ir-Si Interatomic distance of [2c][BArF24] (2.107 Å) is shortest compared to average
	(≈ 2.402 Å) and that of [2h][BArF24] is longest (2.5008(8)).

Interatomic distances of adducts and X-ray structure of [2h][BArF24]

[START_REF] Hamdaoui | Evidence of a Donor-Acceptor (Ir-H)→SiR3 Interaction in a Trapped Ir(III) Silane Catalytic Intermediate[END_REF]

Table 6 :

 6

	[BArF24] possessed the longest Ir-Si bond 2.323(1) Å while distance from
	coordinated-THF to Si center of [3][BArF24] is furthest 1.88(2) Å.
			Interatomic distances (Å)
			Adduct	Silylene
	Adduct	Silyene	Ir-Si	Ir-Si
	[2c][BArF24]	[3][BArF24] 2.407(2) 2.278(3)
	No crystal [4][BArF24]	x	2.288(1)
	[2e][BArF24]	[5][BArF24] 2.4220(7) 2.290(3)
	[2f][BArF24]	[6][BArF24] 2.455(2) 2.317(2)
	[2g][BArF24]	[7][BArF24] 2.435(1) 2.323(1)

Comparing Interatomic distances of Ir-Si bond in crystal of silylene with their precursor adducts

Ir-Si bond is approximately 0.15 (Å) shorter in silylenes compared to their precursor adducts, the widest difference 0.138 (Å) belongs to the tranformation from [2f] + to

[6]

+

Table 7 )

 7 DBATO) in 1973 165, 169 , there has been a series of metals were tested catalytic reactivity for instance: Pd 169-172 , Pt 173 , Re 174 , Sn 175 . Along with this line, Iridacycle 1b has been investigated and represented catalytic reactivity. A set of silanes was perused in the same condition (90 o C, C6H14 solvent) with 4-Nitrotoluene as a model substrate to indicate the most effective one. HexSiH3 was determined to be the best in terms of yields of desired anilines. (Eq. 35,Eq.35

	Silanes	Conversion (%)	Yield (%)
	triethylsilane	no conversion
	di-tert-butylsilane	no conversion
	diethylsilane	100	10
	phenylsilane	no conversion
	butylsilane	no conversion
	hexylsilane	100	40

Since Lipowitz et al. reported initial work of nitroarene reduction under hydrosilylation condition using PMHS as a hydride source catalyzed by bis(dibutylacetoxytin) oxide (

Table 7 :

 7

	More interestingly, mono and dialky silanes (diethyl and hexylsilane) were reactive
	whereas tertiary alkyl silane (triethyl silane) was not, that is supposedly on account of
	the tertiary one lacking a possibility of H2 elimination in accord with our aforementioned
	mechanism. This phenomenon provided a reliable indication that iridium silylene
	species presumably involving in nitro reduction process. (Eq. 36, table 8)

A set of silanes was perused in the same condition (90 o C, C6F14 solvent) with 4-Nitrotoluene as a model substrate to indicate the most effective one

Table 8 :

 8

1b catalyzed reduction of nitroarenes to amines

A set of nitroaromatics were tested with hexylsilane as reductive agent under optimized condition 90 o C, 5h, 10% 1b catalyst. Results were show in a table below. Generally, hexylsilane showed a promising reactivity with 4 substrates were converted 100%.

Table 9 :

 9

	Product	Interatomic distances (Å)
		Ir-H	Ir-Si	Si-H(Ir)
	[2c][BArF24]	1.81(9) 2.407(2) 2.239(8)
	[2e][BArF24]	1.48(3) 2.4220(7) 1.986(7)
	[2f][BArF24]	1.52(6) 2.455(2) 2.066(6)
	[2g][BArF24]	1.449(7) 2.435(1) 1.523(7)
	[2h][BArF24] 17 1.47	2.5008(8) 2.10
	[F-5a] [BArF24]	1.52(4) 2.464(1) 1.950(5)

Interatomic distances (Å) of all 1b-adduct, 1a-triethylsilane [2h][BArF24]

Table 11 :

 11 different slope values of the line of Ln (vi) versus ln [cat] at different temperatures.

		293	288	283	278
	Slope	1.9	1.6	1.8	1

Table 12 :

 12 Catalytic performance of F-1a on the dehydro-O-silylation of alcohols at different temperatures.

	2.77×10 -3	7,5	40	2.8	400	1800000
	2.08×10 -3	10,9	32	1.974	426	639000
	1.38×10 -3	16,6	20	0.83	400	436363
	2.77×10 -4	225	62	0.144	6200 1395000

Table 13 :

 13 Different slope value of the line of ln v according to ln [cat] at different temperatures5.

2.5.2.2. Calculations in the catalysis step after the rate of inflection point

	Concentration	Time	Yield	Initial rate	TON	TOFi
	(M) T=293 K	(s)	(%)	(mol.L -1 .s -1 ×10 -4 )		(h -1 )
	2.77×10 -3	3.1	60	16	600	7200000
	2.08×10 -3	7.1	68	8.88	906	2174400
	1.38×10 -3	14	80	2.85	1600 1152000
	Concentration	Time	Yield	Initial rate	TON	TOFi
	(M) T=288 K	(s)	(%)	(mol.L -1 .s -1 ×10 -4 )		(h -1 )
	2.77×10 -3	5.3	70	8.1	690	4968000
	2.08×10 -3	29.5	68	0.91	920	2365714
	1.38×10 -3	38.8	80	0.73	1240 2029090

Table 14 :

 14 Catalytic performance of F-1a in the dehydro-O-silylation of alcohols at different temperatures.

	The slope of the line of ln(v) = ln(k')+ w.ln([Cat]) is:
	T(K)	293	288
	slope	2.5	3.2

Table 15 :

 15 Different slope value of the line of ln v according to ln[cat] at different temperatures

Table 16 :

 16 8 ml, 5 mmol) is added in a double-neck Schlenk type reactor. Catalyst 1b is injected on different concentrations at different temperatures. Catalytic performance of 1b in the dehydro-O-silylation of alcohols at different temperatures.

	Concentration	Time	Yield	Initiale rate	TON	TOFi
	(M) T=293 K	(s)	(%)	(mol.L -1 .s -1 ×10 -4 )		(h -1 )
	2.77×10 -3	0.74	100	16.7	1000 11612903
	2.08×10 -3	0.77	100	20.6	1333 15480000
	1.38×10 -3	1.4	100	6.86	2000	8000000
	2.77×10 -4	115	74	0.425	7400	2858369
	Concentration	Time	Yield	Initial rate	TON	TOFi
	(M) T=288 K	(s)	(%)	(mol.L -1 .s -1 ×10 -4 )		(h -1 )
	2.77×10 -3	2.4	100	7.73	1000 2278481
	2.08×10 -3	1.6	100	127	1333 3427714
	1.38×10 -3	1.8	100	10.4	2000 7578947
	2.77×10 -4	250	72	0.244	7200 1620000
	Concentration	Time	Yield	Initial rate	TON	TOFi
	(M) T=283 K	(s)	(%)	(mol.L -1 .s -1 ×10 -4 )		(h -1 )
	2.77×10 -3	2.4	100	8.81	1000 1241379
	2.08×10 -3	1.6	100	7.01	1333 1548000
	1.38×10 -3	1.8	100	3.42	2000 1714285
	2.77×10 -4	250	53	0.279	5300 1526400
	Concentration	Time	Yield	Initial rate	TON	TOFi
	(M) T=278 K	(s)	(%)	(mol.L -1 .s -1 ×10 -4 )		(h -1 )
	2.77×10 -3	2.4	100	1.38	1000	923076
	2.08×10 -3	1.6	100	1.51	1333 1499625
	1.38×10 -3	1.8	100	1.21	2000 1565217
	2.77×10 -4	250	51	0.12	5100 1092857
	The slope of the line of ln(v) = ln(k')+ w.ln([Cat]) is:
	T(K)	293	288	283		278
	Slope	1.6	2	1.5		1.1

Table 17 :

 17 different slope value of the line of ln v depending on ln[cat] at different temperatures Arcording to Table

Table 18 :

 18 Rate constants(1) of catalyst 1a at different concentration and different temperatures.

	5.2.5.4.1 Catalyst 1a:
	Temperature	[Catalyst] (mmol/L)	2.77	1.851	1.388	0.277
	(K) Ordre 1
	293 K	k (s -1 )	0.1909 0.0657	0.0447	0.0046
	288 K	k (s -1 )	0.0783 0.0293	0.0166	0.0075
	283 K	k (s -1 )	0.0353 0.0192	0.0173	0.0021
	278 K	k (s -1 )	0.0176 0.0095	0.0062	0.0024
	273 K	k (s -1 )	0.0082 0.0055	0.0119	0.0012
	Temperature	[Catalyst] (mmol/L)	2.77	1.851	1.388	0.277
	(K)
	Ordre 2
	293 K	k (L.mol -1 .s -1 )	0.1012 0.0332	0.0225	0.0022
	288 K	k (L.mol -1 .s -1 )	0.0417 0.0145	0.0082	0.0036
	283 K	k (L.mol -1 .s -1 )	0.0173 0.0097	0.0084	0.0013
	278 K	k (L.mol -1 .s -1 )	0.0087 0.0046	0.0031	0.0011

Table 19 :

 19 Table of reaction rate constants (1) of 1a at different temperatures.

	5.2.5.4.2. Catalyst F-1a
	Temperature (K)	[Catalyst] (mmol/L)	2.77	2.083	1.388	0.277
	Ordre 1
	293 K	k (s -1 )	0.33	0.08	0.063	0.00414
	288 K	k (s -1 )	0.08	0.034	0.052	0.00424
	283 K	k (s -1 )	0.07	0.03	0.024	0.00292
	278 K	k (s -1 )	0.016	0.013	0.007	0.00064

Table 20 :

 20 Table of reaction rate constants (1) of catalyst A2 at different concentration and different temperatures.

	Temperature	[Catalyst] (mmol/L)	2.77	2.083	1.388	0.277
	(K) Ordre 2
	293 K	k (L.mol -1 .s -1 )	0.1884 0.1766	0.1649	0.0024
	288 K	k (L.mol -1 .s -1 )	0.1755 0.0542	0.0685	0.0026
	283 K	k (L.mol -1 .s -1 )	0.1086 0.0538	0.0324	0.0011
	278 K	k (L.mol -1 .s -1 )	0.0255 0.0166	0.0072	0.0004

Table 21 :

 21 Table of reaction rate constants (1) of F-1a at different temperatures.

	5.2.5.4.3. Catalyst 1b
	Temperature (K)	[Catalyst] (mmol/L)	2.77	2.083	1.388	2.773
	Ordre 1
	293 K	k (s -1 )	0.5032 0.1126 1.13063 0.0132
	288 K	k (s -1 )	0.0811 0.0362	0.3915 0.0087
	283 K	k (s -1 )	0.0644 0.0735	0.0415 0.0071
	278 K	k (s -1 )	0.0447 0.0554	0.0313 0.0053

Table 22 :

 22 Table of reaction rate constants (1) of catalyst 1b at different concentration and different temperatures.

	Temperature (K)	[Catalyst] (mmol/L)	2,77	2,083	1,388	0,277
	Ordre 2
	293 K	k (L.mol -1 .s -1 )	0.2661 0.0536	0.7262	0.0065
	288 K	k (L.mol -1 .s -1 )	0.0376 0.019	0.2404	0.0043
	283 K	k (L.mol -1 .s -1 )	0.0284 0.0374	0.0207	0.0034
	278 K	k (L.mol -1 .s -1 )	0.0236 0.0283	0.0161	0.0026

Table 23 :

 23 Table of reaction rate constants (1) of 1b at different temperatures.According toTables 19, 20 and 21, the values of the rate constants, at different temperatures, for the catalyst 1a are smaller than that of catalyst F-1a, and even smaller than that of the catalyst 1b. These values ratify our hypothesis that the catalyst A3 is more efficient than the catalyst F-1a and more effective than the catalyst 1a.

	5.2.5.5. Determination of the thermodynamic activation parameters of the
	reaction (1)
	The thermodynamic activation energies (enthalpy and entropy) are specific and
	characteristic for every chemical system. Based on this information, a determination of
	a free enthalpy of a reaction can be carried out, which represents needed energy to
	overcome the highest activation barrier in the kinetically limiting step. As a result, an
	efficiency of different catalysts can be compared according to free enthalpy. Values of
	the rate constant were leveraged to specify a thermodynamic activation parameter
	extracted from the Eyring-Polanyi equation:
		(Ln(k/T) = -ΔH ‡ /RT + Ln(kB/h) +ΔS ‡ /R).
	5.2.5.5.1 Catalyst 1a
	[Catalyst]0	2.77×10 -3	1.851×10 -3	1.388×10 -3	2.77×10 -4
	(mol/L)
	∆H ‡	24.3 ± 0,8	18.7 ± 1.0	10.8 ± 5.0	11.6 ± 4.3
	(kcal.mol -1 )
	∆S ‡	20.8 ± 2,8	-0.23 ± 3.6	-28.3 ± 17.8	-29.0 ± 15.3
	(cal.mol -1 .K -1 )
	∆G ‡	18.2 ± 0,02	18.8 ± 0.6	19.0 ± 0.21	20.1 ± 0.2
	(kcal.mol -1 )

Table 24 :

 24 Different values of the thermodynamic constants as a function of the concentration of the catalyst 1a according to the order of kinetic equation is 1

	[Catalyst]0	2.77×10 -3	1.85×10 -3	1.39×10 -3	2,77×10 -4
	(mol/L)
	∆H ‡	26.5 ± 0.8	20.3 ± 1.8	15.2 ± 15	10.5 ± 7.6
	(kcal.mol -1 )
	∆S ‡	27.5 ± 2.9	3.9 ± 6.3	-20.1 ± 52.8	-34.1 ± 40.9
	(cal.mol -1 .K -1 )
	∆G ‡	18.4 ± 0.05	19.1 ± 0.05	21.1 ± 0.4	20.5 ± 4.4
	(kcal.mol -1 )

Table 25 :

 25 Different values of the thermodynamic constants as a function of the concentration of the catalyst 1a according to the order of kinetic equation is 2

	5.2.5.5.2 Catalyst F-1a
	[Catalyst] 0	2.77×10 -3	2.083×10 -3	1.388×10 -3	2.77×10 -4
	(mol/L)
	∆H ‡	23.4 ± 1.2	14.8 ± 3.4	15.9 ± 2.6	19.1 ± 7.2
	(kcal.mol -1 )
	∆S ‡	17.6 ± 4.2	-14.2 ± 12.1	-11.2 ± 9.1	-3.6 ± 5.5
	(cal.mol -1 .K -1 )
	∆G ‡	18.2 ± 0.07	18.9 ± 0.2	19.2 ± 0.06	20.1 ± 5.5
	(kcal.mol -1 )
	Table 26: Different values of the thermodynamic constants as a function of the
	concentration of the catalyst F-1a according to the order of kinetic equation is 1
	[Catalyst]0	2.77×10 -3	2.083×10 -3	1.388×10 -3	2.77×10 -4
	(mol/L)
	∆H ‡	20.8 ± 7.3	22.9 ± 5.4	33 ± 3.8	20 ± 6.0
	(kcal.mol -1 )
	∆S ‡	9.99 ± 15.7	16 ± 19.1	50.7 ± 13.5	-1.4 ± 21
	(cal.mol -1 .K -1 )
	∆G ‡	17.8 ± 2.7	18.2 ± 0.2	18.1 ± 0.1	20.4 ± 7.9
	(kcal.mol -1 )

Table 27 :

 27 Different values of the thermodynamic constants as a function of the concentration of the catalyst F-1a according to the order of kinetic equation is 2 5

.2.5.5.3 Catalyst 1b:

	[Catalyst]0	2.77×10 -3	2.083×10 -3	1.388×10 -3	2.77×10 -4
	(mol/L)
	∆H ‡	23.5 ± 8.7	3.9 ± 7.8	41.5 ± 8.4	8.9 ± 1.0
	(kcal.mol -1 )
	∆S ‡	19.45 ± 30.4	-50.1 ± 27.5	83.3 ± 29.5	-36.7 ± 3.5
	(cal.mol -1 .K -1 )
	∆G ‡	17.8 ± 0.2	18.6 ± 0.2	17.09 ± 0.2	19.6 ± 0.02
	(Kcal.mol -1 )

Table 28 :

 28 Different values of the thermodynamic constants as a function of the concentration of the catalyst 1b according to the order of kinetic equation is 1

	[Catalyst]0	2.77×10 -3	2.083×10 -3	1.388×10 -3	2.77×10 -4
	(mol/L)
	∆H ‡	24.4 ± 9.9	1.7 ± 0.5	45.3 ± 9.4	9.3 ± 0,9
	(kcal.mol -1 )
	∆S ‡	21.1 ± 34.9	-58.6 ± 2.1	95.5 ± 33	-36.9 ± 3.2
	(cal.mol -1 .K -1 )
	∆G ‡	18.2 ± 0.3	18.9 ± 0.05	17.3 ± 0.2	20.1 ± 0.04
	(kcal.mol -1 )

Table 29 :

 29 Different values of the thermodynamic constants as a function of the concentration of the catalyst 1b according to the order of kinetic equation is 2The values of free enthalpy showed that by applying the second order kinetic equation, a presence of the catalyst 1a caused reactions needing more energy to form products, which validates our hypothesis that 1a is the least efficient. As for catalysts F-1a and

1b, these free enthalpy values are overlapping. Activation entropy values were compromised by grave errors attributable to an extremely limited temperature range and an insufficient number of measurements. The same type of error on the entropy of activation can be committed as well if kinetic measurements are carried out by NMR within a severely limited range of temperatures. Inadequately spaced measurements also contributed to systematic errors resulted from a limited estimation of the pressure sensor, which is less precise at very low dynamic pressure variations.

5.

2.5.6. Determination of the rate constant and the thermodynamic activation energy of the (2) dehydro-O-silylation reaction of isopropanol

	5.2.5.6.1. Catalyst 1a:
	T (K) Time	Yield (%)	Initial rate	TON TOFi	k Ordre 1	k Ordre 2
		(s)		(mol.L -1 .s -1 ×10 -6 )	(h -1 )	(L.mol -1 .s -1 )	(L.mol -1 .s -1 )
	293	928	41	9.5	410 79783	0.0031	0.0014
	288	929	29	6.07	290 65950	0.0014	0.0007
	283	853	23	1.96	230 26095	0.0005	0.0003
	278	723	12	0.61	120 15542	0.0001	0.0001
	Table 30: Catalytic performance of 1a in the dehydro-O-silylation of Isopropanol at
		different temperatures [Catalyst]0 = 2.77 × 10 -3 mol / L.
	[Catalyst]0		∆H ‡	∆S ‡	∆G ‡
		(mol/L)	(kcal.mol -1 )	(cal.mol -1 .K -1 )	(kcal.mol -1 )
	2.77×10 -3 (Ordre 1)	36.9±4.3	56.3±15.1	20.4±0.1
	2.77×10 -3 (Ordre 2)	27.7±1.7	23.2 ± 6.2	20.1 ± 0.1
	A mixture of isopropanol (0.4 ml, 5 mmol) and triethylsilane (0.8 ml, 5 mmol) is added
	in a double-walled Schlenk type reactor. The catalyst is injected at different
	temperatures.

Table 31 :

 31 Values of thermodynamic Constants in the presence of catalyst 1a[Catalyst]0 = 2.77 × 10 -3 mol / L.

	5.2.5.6.2. Catalyst 1b
	T	Time	Yield (%)	Initial rate	TON TOFi	k Ordre 1	k Ordre 2
	(K)	(s)		(mol.L -1 .s -1 ×10 -5 )	(h -1 )	(L.mol -1 .s -1 )	(L.mol -1 .s -1 )
	298 390	80	2.25	800 128000	0.0059	0.0029
	293 689	63	1.03	630 100800	0.0034	0.0016
	288 745	31	0.512	310 65516	0.0016	0.0008
	283 831	26	0.478	260 39945	0.0011	0.0005

Table 32 :

 32 Catalytic performance of 1b in the dehydro-O-silylation of Isopropanol at different temperatures [Catalyst]0 = 2.77 × 10 -3 mol / L.

	[Catalyst]0	∆H ‡	∆S ‡	∆G ‡
	(mol/L)	(kcal.mol -1 )	(cal.mol -1 .K -1 )	(kcal.mol -1 )
	2.77×10 -3 (Ordre 1)	18.6±1.6	-6.4±5.5	20.5±0,01
	2.77×10 -3 (Ordre 2)	19.3±1.1	-5.2 ± 3.8	20.8± 0,01
	Table 33: Values of thermodynamic constants in the presence of Catalyst 1b
		[Catalyst]0 = 2.77 × 10 -3 mol / L.

Table 35 :

 35 Values of thermodynamic constants in the presence of Catalyst 1b[Catalyst]0 = 9.69 × 10 -3 mol / L.

Table 36 :

 36 Catalytic performance of 1b in the dehydro-O-silylation of Hexafluoroisopropanol at different temperatures [Catalyst]0 = 9.69 × 10 -3 mol / L. Kinetic measurements showed, in this case, H2 production, rate constants, TON, TOFi are relatively lower than those of isopropanol. Consequently, the plot Eyring's equation was liberally scattered and not linearly correlated as expected because values would have been tainted by errors. This result is particularly interesting because it indicates that although pKa of hexafluorinated alcohol is 9.2 197 , thermodynamically stronger than both isopropanol and benzyl alcohol, nevertheless, it seemed to possess a lower kinetic acidity under the conditions in which one of the key steps is the deprotonation of the intermediate [RF-O(H)-SiEt3] + by a hydro-iridium [species]phpyCp*Ir-H acting as an iridium hydride (III).

	1 )

Si NMR (600 MHz, CD2Cl2) δ 0.00 ppm

Si NMR (600 MHz, CD2Cl2) δ 0.00 ppm

Scheme 13: Proposed mechanism [START_REF] Howard | Synthesis of Tertiary α--Hydroxy Acids by Silylene Transfer to α--Keto Esters[END_REF] The authors stated that although divalent silicon species have not been detected, the justification of that mechanism remains compelling thanks to the conversion of ethyl pyruvate to a similar silyl ketene acetal under identical silylene transfer conditions (Eq. 11). [START_REF] Heinicke | Zur chemie der silylene: Cycloadditionen von methoxymethylsilylen mit heterodienen[END_REF] Eq. 11 [START_REF] Driver | Mechanism of Silver--Mediated Di--tert--butylsilylene Transfer from a Silacyclopropane to an Alkene[END_REF] However, the method is used to generate silylene is totally different in the two publications, Woerpel used AgOTs whereas that of Gehrhus is thermolysis. Notably, no eloquent proof that divalent silicon species substantially appeared.

By pondering those examples above, it's safe to say that although the application of silylene transfer catalyzed by metal in organic chemistry prevails, is well-established, with some attempts made to prove its existence, the generalization of "silylene metal" intermediate remains to be seen.

Result and discussion

All three complex [2c-e][BArF24] were characterized by a typical 1 H-NMR Ir-H resonance at δ = -11.5 ppm. It is noteworthy that no sign of hydrosilylation [START_REF] Hamdaoui | Evidence of a Donor-Acceptor (Ir-H)→SiR3 Interaction in a Trapped Ir(III) Silane Catalytic Intermediate[END_REF][START_REF] Hamdaoui | Iridacycles as Catalysts for the Autotandem Conversion of Nitriles into Amines by Hydrosilylation: Experimental Investigation and Scope[END_REF] of the released CH3CN (singlet at δ = 1.98 ppm) was evidenced with [2c-d][BArF24] [START_REF] Yamashita | Oxidative Addition of the Si--C Bonds of Silacyclobutanes to Pt(PEt3)3 and Highly Selective Platinum(0)--Catalyzed Di--or Polymerization of 1,1--Dimethyl--1--silacyclobutane[END_REF] Si of Ir-SiH2Ph of [2c][BArF24] 1 H, [START_REF] Yamashita | Oxidative Addition of the Si--C Bonds of Silacyclobutanes to Pt(PEt3)3 and Highly Selective Platinum(0)--Catalyzed Di--or Polymerization of 1,1--Dimethyl--1--silacyclobutane[END_REF] Si HMQC NMR spectrum of [2d] + and [2e] + also shows that the [START_REF] Yamashita | Oxidative Addition of the Si--C Bonds of Silacyclobutanes to Pt(PEt3)3 and Highly Selective Platinum(0)--Catalyzed Di--or Polymerization of 1,1--Dimethyl--1--silacyclobutane[END_REF] Si resonance correlates with 1H resonances of the alkylSi(Hα)(Hα') like in [2c] + case. (Figure 13, 14) Scheme 30: General pathway for nitroarene reduction and intermediates 165 . characteristic of electrophilic catalysts that was subjected to the second type of activation mechanism 189 as shown in scheme below.

Scheme 32: proposed mechanism for the reaction of alcohol dehydro-O-silylation [START_REF] Hamdaoui | Evidence of a Donor-Acceptor (Ir-H)→SiR3 Interaction in a Trapped Ir(III) Silane Catalytic Intermediate[END_REF][START_REF] Hamdaoui | Iridacycles as Catalysts for the Autotandem Conversion of Nitriles into Amines by Hydrosilylation: Experimental Investigation and Scope[END_REF] .

Catalysts used in this study are composed of a cationic organometallic complex of iridium, and a counter anion which can play the least likely role on the reactivity and on the binding affinity of the complexes 190 . Accordingly, chosen counter anions must be non-coordinating and modestly reactive to avoid any potential interactions with other ions or molecules in a medium. Based on these criteria, BArF was the most favored;; other non-coordinating anions like (BF4 -, PF6 -, ClO4 -) have demonstrated a high effect in the targeted reactions 191,192 .

In this work, a dehydro-O-silylation reaction of benzyl alcohol, propan-2-ol and hexafluoropropan-2-ol (Figure 44) were studied in the presence of 3 iridium catalysts synthesized in the laboratory (Figure 43).

PERSPECTIVES

X ray diffraction analysis of [3][BArF24] CCDC 1826970 X-Ray diffraction data collection was carried out on a Bruker APEX II DUO Kappa-CCD diffractometer equipped with an Oxford Cryosystem liquid N2 device, using Cu-Kα radiation (λ = 1.54178 Å). The crystal-detector distance was 40mm. The cell parameters were determined (APEX2 software) 3 from reflections taken from tree sets of 20 frames, each at 10s exposure. The structure was solved by Direct methods using the program SHELXS-2014. 4 The refinement and all further calculations were carried out using SHELXL-2014. 5 The H-atom H1 bound to Si1 was added in calculated position and then refined without the "AFIX" instruction. The other Hatoms were included in calculated positions and treated as riding atoms using SHELXL default parameters. The non-H atoms were refined anisotropically, using weighted full-matrix least-squares on F 2 . A semi-empirical absorption correction was applied using SADABS in APEX2 3 ;; transmission factors: Tmin/Tmax = 0.5294/0.7528.

The benzoquinolinyl ligand is disordered over two positions, the THF molecule and the phenyl group linked to Si1 are disordered over two positions (all in all), the fluorine atoms F4, F5, F6, F14, F15, F19, F20, F21, F22, F23 and F24 from the counter-anion are disordered over two positions. Note : Table S4 and S5 gather acquisition and refinement data for [3][BArf24] and [4][BArF24] (CCDC 1843843)

Computational methods and technical details

Computations were performed with the methods of density functional theory using the SCM-ADF2016.01 package [6][7][8] considering the molecules in the gas phase. The PBE functional [START_REF] Einstein | Synthesis, structure and fluxional properties of (.eta.5--C5Me5)(OC)2IrW(CO)5. A compound with an iridium--tungsten dative bond[END_REF] implemented in the Amsterdam Density Functional package 7 (ADF2016 version) and augmented with Grimme's DFT-D3(BJ) implementation of dispersion with a Becke-Johnson (BJ) damping function was used in all geometry optimizations. [START_REF] Einstein | A cluster compound with an unsupported, dative metal-metal bond: structure and unusual nonrigidity of (Me3P)(OC)4OsOs3(CO)11[END_REF][START_REF] Einstein | Comparison of dative and covalent metal--metal bonds: structures of the isomers (Me3P)(OC)4OsRe(CO)4(Br) and (Br)(Me3P)(OC)3OsRe(CO)5[END_REF] Geometry optimizations by energy gradient minimization were carried out in all cases with integration grid accuracy comprised between 4.5 and 6.5, an energy gradient convergence criterion of 10 -3 au, and a tight to very tight SCF convergence criterion. Counterpoise correction for basis set superposition error (BSSE) was neglected throughout this study. Within the PBE scheme, electron correlation was treated within the local density approximation (LDA) in the PW92 [START_REF] Johnston | Structures of the new binary metal carbonyl Os4(CO)15 and (.eta.5--C5Me5)(OC)IrOs3(CO)11. Clusters with three--center--two-electron metal--metal bonds?[END_REF] parametrization. With ADF2016.01, unless otherwise stated, all computations were carried out using scalar relativistic corrections within the zeroth order regular approximation for relativistic effects [START_REF] Davis | Complexes with unbridged dative bonds between osmium and a Group 6 element. Structures of (Me3P)(OC)4OsM(CO)5 (M = chromium, tungsten)[END_REF][START_REF] Fernandez | Synthesis, x--ray, and low--temperature neutron--diffraction study of a rhodium(V) complex: dihydridobis(triethylsilyl)(pentamethylcyclopentadienyl)rhodium[END_REF][START_REF] Ricc | Dihydridobis(triethylsilyl)pentamethylcyclopentadienyliridium(V):Neutron diffraction and photoelectron spectroscopic studies[END_REF] with ad hoc all-electron (abbreviated ae) single polarization function triple-ζ Slater type basis sets (TZP). Vibrational modes were analytically computed to verify that the optimized geometries were related to energy minima or to transition states. The geometries of [2c], [2d], [3] + , [4] + and all other intermediates, transition states and reactants were computed at the ZORA-PBE-D3(BJ)/ae-TZP level and its minimum energy nature confirmed by the absence of any imaginary mode above 50 icm -1 in its computed vibrational spectrum. Intrinsic interaction energies, ETS-NOCV analyses, Natural population analyses (NPA) as well as Wiberg index determinations were performed with the gas-phase geometry relaxed at the (ZORA) PBE-D3(BJ) level using all-electron TZP basis sets with the GENNBO [START_REF] Binh | Is the R3Si Moiety in Metal-Silyl Complexes a Z ligand? An Answer from the Interaction Energy[END_REF] 6.0 module of ADF. NMR coupling constants were computed with the ADF CPL module at the ZORA-SAOP/all-electron TZP basis sets. Drawings of molecular structures and isosurfaces were produced with ADFview2013.

NMR spectra Therefore, the characterization of [2d][BArF24] was only possible in situ (solution NMR solvent). However, appropriate identification of all 1 H nuclei could not be realized due to the formation of a unidentified side-product [much likely of the

, where X may presumably be a solvent and certainly not NCMe or H)]. Nonetheless, 1 H and [START_REF] Yamashita | Oxidative Addition of the Si--C Bonds of Silacyclobutanes to Pt(PEt3)3 and Highly Selective Platinum(0)--Catalyzed Di--or Polymerization of 1,1--Dimethyl--1--silacyclobutane[END_REF] Si chemical shifts that are diagnostic of the structure of [2d][BArF24] could be unambiguously identified (vide infra). [START_REF] Davis | Complexes with unbridged dative bonds between osmium and a Group 6 element. Structures of (Me3P)(OC)4OsM(CO)5 (M = chromium, tungsten)[END_REF] C nuclei could not be assigned with certainty to the product of interest due to the complex nature of the reaction mixture and of the resulting NMR spectrum. (15 mg, 10.6 μmol) in d8-THF (0.55 mL). The resulting solution was shaken and transferred into a J. Young NMR sample tube which was subsequently tightly sealed for analysis. After 15 minutes of reaction at room-temperature, 1 H NMR analysis showed full consumption of [1b][BArF24], but only partial conversion of [2c][BArF24] to [3][BArF24] (~ 50%;; cf. spectrum 1 in Figure S28). After 1 h, this conversion was estimated to amount ~75% (cf. spectrum 2 in Figure S28). Full conversion was obtained after 2 h of reaction;; cf. spectrum 3 in Figure S28. Indeed, the latter 1 15H, Cp-Me5). Two broad peaks of THF were detected at respectively δ 3.66 and 1.79 ppm, indicating fast-exchange of bulk THF molecules with those coordinated to the Si centre of [3][BArF24] (cf. Figure S16). [START_REF] Davis | Complexes with unbridged dative bonds between osmium and a Group 6 element. Structures of (Me3P)(OC)4OsM(CO)5 (M = chromium, tungsten)[END_REF] C (126 Hz, 298 K, CD2Cl2): δ = 162.3 2 JC-F = 31.9 Hz, 3 JC-F = 2.9 Hz, CAr-CF3 in BArF24), 128.88 [START_REF] Davis | Complexes with unbridged dative bonds between osmium and a Group 6 element. Structures of (Me3P)(OC)4OsM(CO)5 (M = chromium, tungsten)[END_REF] C resonances of IrSiPhH2 could not be assigned with certainty as their corresponding 1 H resonances overlapped with some peaks of the C,N-ligand and those of the BArF24 anion]. [START_REF] Yamashita | Oxidative Addition of the Si--C Bonds of Silacyclobutanes to Pt(PEt3)3 and Highly Selective Platinum(0)--Catalyzed Di--or Polymerization of 1,1--Dimethyl--1--silacyclobutane[END_REF] Si [obtained indirectly by 1 H, [START_REF] Yamashita | Oxidative Addition of the Si--C Bonds of Silacyclobutanes to Pt(PEt3)3 and Highly Selective Platinum(0)--Catalyzed Di--or Polymerization of 1,1--Dimethyl--1--silacyclobutane[END_REF] Si HMQC cross-peak correlation with the 1 2H, Si-THF), 2.07 (bs, 2H, Si-THF), 1.68 (bs, 15H, Cp-Me5), 0.86 (bs, 2H, Si-THF), 0.67 (bs, 2H, Si-THF). The new 1 H NMR spectrum recorded at 213 K allowed the detection of peaks characterizing the Si-coordinated THF. However, some peaks of the C,N-ligand and those of the Ir-bound "PhSiH2" moiety could not be clearly detected in this new experiment (due to overlapping with peaks of [BArF24] -and of the Ph group belonging to excess HPhSiH2). Due to chirality at the Si centre, [3][BArF24] is one of two possible diastereoisomers. Thus, the typical peaks of Sicoordinated THF of the other diastereoisomer (found to be the minor one) were also detected by the 1 H NMR experiment recorded at 213 K (as also confirmed by 1

NMR data

In-situ Generation of [5][BArF 24 ] by Reaction of [1b][BArF 24 ]

with HSi n HexH 2 and THF: Procedures, NMR Data, and Spectra Compound [5][BArF24] was generated in solution using the procedure 2 previously described for [3][BArF24] (cf. previous section): HSi n HexH2 (20.0 μL, 77.0 μmol) was added to a solution of [1b][BArF24] (30 mg, 21.2 μmol) in d8-THF (0.45 mL). The resulting solution was shaken and transferred into a J. Young NMR sample tube which was subsequently tightly sealed for analysis at -40 °C. Full conversion was obtained after 2 h of reaction, as verified by 1 H NMR analysis (cf. spectra in the next sub-section). Indeed, the latter 1 H NMR spectrum indicated complete consumption of [1b][BArF24] and selective formation of [5][BArF24] along with H2 (singlet at ca. δ 4.55 ppm).

NMR data 1 H, [START_REF] Davis | Complexes with unbridged dative bonds between osmium and a Group 6 element. Structures of (Me3P)(OC)4OsM(CO)5 (M = chromium, tungsten)[END_REF] C-1 H and 1 H, [START_REF] Yamashita | Oxidative Addition of the Si--C Bonds of Silacyclobutanes to Pt(PEt3)3 and Highly Selective Platinum(0)--Catalyzed Di--or Polymerization of 1,1--Dimethyl--1--silacyclobutane[END_REF] Si HMQC

Résumé en anglais

The scope of this thesis spans the most recent advances in the investigation of chemical bonds of iridium-silicon complexes, in which a metal-bound silyl group behaves as a Z ligand that maintains a dative bond with the metal centre. This contrasts greatly with the case where this group behaves like an X ligand, that is where this silyl group binds to Ir through a covalent bond. Finally, and most interestingly are silylene ligands that in principle should establish a double bond with the Ir centre. The idea of evaluating and tuning the electrophilic character of the silyl moiety and adjuncts its "silylicity" was probed by experimental and theoretical means. To conduct that scheme, a broad range of metal-silane adducts and other metal-silyl complexes were investigated by the computation of metal-silyl interaction energies to outline the established tools that rationalize the bonding relationship that exists between the metal center and a SiR3 moiety. Also, this research revealed a clear separation between cases in which the Z character of the silyl moiety is the best description, and cases that belong to "classical" situations in which the X character dominates. Moreover, we postulated that for metal-silane adducts that possess a low intrinsic silylicity, a high "silylicity" can be triggered by ligand replacement or by changing in the charge of the complex.While working on this topic, we discovered that in the presence of tetrahydrofuran (THF), [(Ir-H)→SiRH2] + adducts readily convert by H2 gas elimination at sub-ambient temperature into new THF-stabilized metallacyclic Ir(III)-"silylene" complexes. The emergence of metal silylene complexes via sequential H-Si activations followed by the spontaneous release of H2 featured in this thesis is unique. The primary goal of this thesis finally was to fully characterize those elusive complexes by NMR spectroscopy analyses and X-ray diffraction analysis. Furthermore, theoretical investigations (static DFT-D reaction-energy profiling, ETS-NOCV) and NMR kinetic studies were utilized to demonstrate the role of THF which facilitated H2 elimination. Coupled with silylene metal complex chemistry mentioned above, cationic iridacycle 1b is of interesting catalytic reactivity toward nitro arenes, which can perform the nitro reduction in arenes to give aniline type products.In crafting a new development of this chemistry, it is safe to hypothesize that cationic hydrido-Ir(III)-silylium species, whose catalytic reactivity is of significant correlation with the extend of polarization of the molecule can enhance in the key intermediates the molecule polarization, and therefore increase its catalytic reactivity. Such polarization that occurs already in the Irsilane adduct stems from the electropositivity of Si centre. Keeping the main ligand backbone constant, introduction of a fluoro substituent can improve the polarization of the same molecule and by way of consequence increase its catalytic reactivity.As expected, F-1a also displays remarkable catalytic reactivity toward a benchmark test reaction that can be followed by piezometry, i.e. the O-dehydrosilylation of alcohols at room temperature with Et3SiH. A hydrido-Ir(III)-silylium intermediate crystal was trapped as well following on a reaction with Et2SiH. In conclusion, based on the discovery of hydrido-Ir(III)-silylium intermediates associated with a comprehensive study of their reactivity and catalytic performance, this thesis has taken steps to advance knowledge of Ir-silicon complexes by synthesis and the full structural characterization of notoriously elusive metal silylene complexes. Also, sophisticated computational methods have been employed to shed light on the mechanism of conversion of Ir-silane adducts into silylenes of which a great number were trapped by reactive recrystallization and subsequently characterized by X-ray diffraction analysis. Keywords : silyl moiety, Z ligand, X ligand, silylene, silylicity, metallacyclic, metal silylene complexes, H-Si activation, DFT-D, ETS-NOCV