Marc Camats

Daniel Pla
email: pla@lhfa.fr

Montserrat Gomez
email: gomez@chimie.ups-tlse.fr

Montserrat Gómez

Earth-Abundant d-Block Metal Nanocatalysis for Coupling Reactions in Polyols

Keywords: 3d metals, Metal nanoparticles, Catalysis, Couplings, Polyols

published or not. The documents may come

Introduction

AQ2

In the 1990s, a ground-breaking movement concerning the Earth preservation for future generations has appeared. In Chemistry, these actions led to the Green Chemistry concept ("Green Chemistry" by Paul et al. [START_REF] Anastas | Green chemistry[END_REF], Warner et al. [128] articulated through the 12 Green Chemistry Principles [START_REF] Anastas | Green chemistry: principles and practice[END_REF]; shortly after, the Sandestin declaration established the bases of the Green Engineering Principles [START_REF] Anastas | Peer reviewed: design through the 12 principles of green engineering[END_REF]. Without any doubt, catalysis is one of the most important pillars of Green approaches [START_REF] Anastas | Catalysis as a foundational pillar of green chemistry[END_REF]. Analyzing the evolution of metal-based catalysis, involving homogeneous and heterogeneous systems, it is evident to conclude that definitely the twentieth century has been the century of "heavy" metal-based catalysts, i.e., catalytic processes concerning 4d and 5d metals (such as Mo, Ru, Rh, Ir, Pd, Pt, Au …), as internationally acknowledged by the Nobel Prizes in 2005 (Y. Chauvin, R. H. Grubbs and R. R. Schrock) and 2010 (R. F. Heck, E.-i. Negishi and A. Suzuki) for the development of metathesis processes (mainly Mo-and Ru-based catalysts) and Pd-catalyzed couplings in organic synthesis, respectively (www.nobelprize.org/prizes/chemistry/2005/summary; www.nobelprize.org/prizes/chemistry/2010/summary). Nevertheless, nature has exploited earth abundant 3d metals (Fe, Ni, Cu, Zn …), leading to metalloenzymes which exhibit a prominent specificity [START_REF] Beller | Introduction: first row metals and catalysis[END_REF]. In coherence to a sustainable development, researches on the design of manufactured catalysts with first-row transition metals have exponentially grown since the 2000s (see the contributions collected in the special issue "First row metals and catalysis" of Chemical Reviews, 2019) [START_REF] Ai | Hydride Transfer reactions catalyzed by cobalt complexes[END_REF][START_REF] Alig | First-row transition metal (de)hydrogenation catalysis based on functional pincer ligands[END_REF][START_REF] Formenti | Reduction of nitro compounds using 3d-non-noble metal catalysts[END_REF][START_REF] Gandeepan | 3d transition metals for C-H activation[END_REF][START_REF] Irrgang | 3d-metal catalyzed N-and C-alkylation reactions via borrowing hydrogen or hydrogen autotransfer[END_REF][START_REF] Langeslay | Catalytic applications of vanadium: a mechanistic perspective[END_REF]100,123, 129] (Fig. 8.1).

On the other hand, solvents represent one of the major concerns for chemical transformations (employed in synthesis, extractions, purifications, analyses…), in particular volatile organic compounds which are generally toxic showing different levels of harmfulness and danger, submitted to severe regulations. Alternative solvents (water, ionic liquids and deep eutectic solvents, alcohols, supercritical fluids, renewable solvents, combination of different solvents…) and solvent-free chemistry are useful and efficient approaches for many applications, needing investment and effort to adapt the current processes to the new reaction conditions [START_REF] Kerton | Alternative solvents for green chemistry[END_REF]. In the frame of this chapter, we are interested in polyols, largely used in the industrial sector (highlighting the production of polymers such as polyurethanes, polyvinyl alcohol …), because they present lower environmental impact than low-weight and volatile organic compounds, and they are particularly attractive for the synthesis and stabilization of nano-sized metal clusters.

Focusing on this type of nanomaterials, well-defined metal-based nanoparticles (objects showing dimensions in the range 1-100 nm) have known a huge expansion since the 1980s due to their distinctive properties, both physical and chemical, in comparison to molecular and bulk materials. Actually, this is a consequence of their electronic and structural features, making possible a vast number of applications [110,121,133], in particular in catalysis [START_REF] Adil | Biogenic synthesis of metallic nanoparticles and prospects toward green chemistry[END_REF][START_REF] Chaudhuri | Core/shell nanoparticles: classes, properties, synthesis mechanisms, characterization, and applications[END_REF][START_REF] Martínez-Prieto | Organometallic ruthenium nanoparticles: synthesis, surface chemistry, and insights into ligand coordination[END_REF]110,111]. Even though metal nanoparticles (MNPs) have been largely applied in classical heterogeneous catalysis, with crucial participation in industrial processes mainly those related to oil area [136], nanocatalysis, which concerns MNPs dispersed in a solvent have been only developed since the end of the last century. This exponential growth has benefited of the recent advances in characterization techniques (including operando approaches) which has permitted the design of catalysts at nanometric scale by means of controlling morphology and surface state of nanoobjects [START_REF] An | Colloid chemistry of nanocatalysts: a molecular view[END_REF][START_REF] Astruc | Nanoparticles and catalysis[END_REF][START_REF] Heiz | Nanocatalysis[END_REF][START_REF]Metal Nanoclusters in Catalysis and Materials Science: The Issue of Size Control[END_REF]. Noticeably, reproducible synthetic methodologies are crucial for their further applications [106,122]. The chemical strategies (commonly named bottom-up syntheses) often include solvents, from conventional organic compounds to alternative ones (showing a lower environmental impact), such as water [START_REF] Bulut | Aqueous-phase hydrogenation of alkenes and arenes: the growing role of nanoscale catalysts[END_REF]109], ionic liquids [104], scCO 2 , [START_REF] Dahl | Toward greener nanosynthesis[END_REF][START_REF] Patete | Viable methodologies for the synthesis of high-quality nanostructures[END_REF]134], polyols [START_REF] Chahdoura | Glycerol as suitable solvent for the synthesis of metallic species and catalysis[END_REF][START_REF] Favier | Metal-based nanoparticles dispersed in glycerol: an efficient approach for catalysis[END_REF][START_REF] Fiévet | The polyol process: a unique method for easy access to metal nanoparticles with tailored sizes, shapes and compositions[END_REF]. It is important to mention that solvents may be involved in different aspects, for example, as reducing agents, stabilizers, or medium for trapping nanocatalysts preserving their morphology during the catalytic transformation and thus facilitating their recycling. This is the case when polyols are present. In 1989, the polyol methodology was for the first time reported by Fiévet and coworkers where metal salts were reduced in ethylene glycol, obtaining welldefined MNPs [START_REF] Fievet | Homogeneous and heterogeneous nucleations in the polyol process for the preparation of micron and submicron size metal particles[END_REF][START_REF] Fievet | Preparing monodisperse metal powders in micrometer and submicrometer sizes by the polyol process[END_REF]. In this method, the polyol acts as solvent, reducing agent, and stabilizer when higher polyols are involved (e.g., polyphenols or polysaccharides), which prevents the agglomeration of MNPs in solution [START_REF] Dong | Polyol synthesis of nanoparticles: status and options regarding metals, oxides, chalcogenides, and non-metal elements[END_REF][START_REF] Fiévet | The polyol process: a unique method for easy access to metal nanoparticles with tailored sizes, shapes and compositions[END_REF].

These privileged physicochemical properties favor the preparation of tailor-made first-row transition metal nanocatalysts and derived nanocomposites in a controlled manner. Rational catalyst design is essential for the preparation of well-defined clusters and nanoparticles with optimal properties in terms of redox control, cooperative effects, and increased surface areas, all of them are key factors for catalysis. Beyond the dual catalytic behavior related to both surface and reservoir of molecular species, nanocatalysis brings novel reaction manifolds due to the unique structural properties of MNPs, particularly their differential electronic structure as compared to bulk metals (e.g., facilitating single electron transfer processes via the Fermi level for electrons [START_REF] Favier | Palladium-mediated radical homocoupling reactions: a surface catalytic insight[END_REF]).

U N C O R R E C T E D P R O O F

In the present contribution, we focus on the recent advances in 3d metal nanocatalysts (for a recent review, see: [127]), involving polyols acting as stabilizer and/or reaction medium for coupling reactions, Carbon-Carbon and Carbon-Heteroatom bond formation processes, including multicomponent syntheses.

Carbon-Carbon Bond Formation

C-C cross-coupling reactions have been largely dominated by palladium-based catalyzed processes due to their efficiency and versatility. In particular, the ability of this metal to stabilize different kinds of species (complexes, nanoparticles, extended surfaces) and its relatively high robustness under many different reaction conditions has permitted the elucidation of the corresponding mechanisms [START_REF] Biffis | Pd metal catalysts for cross-couplings and related reactions in the 21st century: a critical review[END_REF]119,124]. From a sustainable chemistry point of view, the use of first-row transition metals is obviously preferred and a huge research has been developed in the last years (for instance, see the contributions published in the Accounts of Chemical Research special issue "Earth Abundant Metals in Homogeneous Catalysis," [START_REF] Chirik | Getting down to earth: the renaissance of catalysis with abundant metals[END_REF]).

Lewis Acid-Catalyzed Coupling Reactions

Heterocyclic motifs are present in a large variety of naturally occurring products along with industrial compounds [START_REF] Eicher | The chemistry of heterocycles: structures, reactions, synthesis, and applications[END_REF][START_REF] Haji | Multicomponent reactions: a simple and efficient route to heterocyclic phosphonates[END_REF][START_REF] Joule | Heterocyclic chemistry[END_REF]101]. Multicomponent reactions represent an environmentally friendly approach to prepare polyfunctional compounds, in particular heterocycle derivatives, via one-pot processes involving three or more reactants, with high atom economy and easy implementation [START_REF] Biggs-Houck | Recent advances in multicomponent reactions for diversity-oriented synthesis[END_REF]130,138]. These transformations are often promoted by Lewis acids, which favor the kinetics directing the reaction pathway and in consequence improving the selectivity [START_REF] Ganem | Strategies for innovation in multicomponent reaction design[END_REF]. In this frame, Khurana and coworkers reported nickel nanoparticles (NiNPs) stabilized by polyethylene glycol (PEG-4000) and prepared by polyol-based methodology using ethylene glycol in the presence of NaBH 4 , which was applied in the synthesis of spiropyrans [START_REF] Khurana | Highly monodispersed PEG-stabilized Ni nanoparticles: proficient catalyst for the synthesis of biologically important spiropyrans[END_REF], interesting materials particularly due to their unique molecular switch triggering structural isomerization under the effect of different external stimuli diol. NiNPs were efficiently reused up to 3 times. Authors postulated that nickel activates carbonyl and nitrile groups.

The same authors previously reported Knoevenagel condensations of barbituric or Meldrum acid and aromatic aldehydes in EG, catalyzed by NiNPs and stabilized by PVP (polyvinylpyrrolidone) [START_REF] Khurana | Nickel nanoparticles catalyzed Knoevenagel condensation of aromatic aldehydes with barbituric acids and 2-thiobarbituric acids[END_REF] and PEG [START_REF] Khurana | Nickel nanoparticles catalyzed chemoselective Knoevenagel condensation of Meldrum's acid and tandem enol lactonizations via cascade cyclization sequence[END_REF], respectively (Scheme 8.2). Maleki and coworkers synthesized Fe 3 O 4 nanoparticles stabilized by the biopolymer chitosan coming from chitin (polymer of N-acetylglucosamine) to be applied in three-component reactions yielding benzodiazepines [START_REF] Maleki | An efficient synthesis of benzodiazepine derivatives via a onepot, three-component reaction accelerated by a chitosan-supported superparamagnetic iron oxide nanocomposite[END_REF] and benzimidazoloquinazolinones [START_REF] Maleki | Synthesis of benzimidazolo[2,3-b]quinazolinone derivatives via a one-pot multicomponent reaction promoted by a chitosan-based composite magnetic nanocatalyst[END_REF] (Scheme 8.3), which present biological and pharmacological activities [START_REF] Chakraborty | A novel transition state analog inhibitor of guanase based on azepinomycin ring structure: synthesis and biochemical assessment of enzyme inhibition[END_REF][START_REF] Grasso | Synthesis and in vitro antitumour activity evaluation of 1-aryl-1H,3H-thiazolo[4,3-b]quinazolines[END_REF]. For both types of reactions, the catalyst was recycled up to four times preserving its catalytic performance, being ethanol the most appropriate solvent for these catalytic reactions. Authors proposed a similar pathway for both transformations.

+ N N O R 2 X R 2 O R 1 CHO X = O, S R 1 = H, F,
In Fig. condensation between the aromatic aldehyde and dimedone; the resulting α,βunsaturated ketone reacts with the 2-aminobenzimidazole or its corresponding thioderivative via a Michael addition, giving an acyclic compound which undergoes a further intramolecular cyclization. Similar catalysts were also applied for the synthesis of 2-amino-4H-chromenes [107] and highly substituted pyridines [START_REF] Maleki | An efficient protocol for the one-pot multicomponent synthesis of polysubstituted pyridines by using a biopolymer-based magnetic nanocomposite[END_REF].

Although the Lewis acid properties of Fe 3 O 4 have proven to be useful for the synthesis of heterocycles, these properties seem to be enhanced in the presence of Cu(II) (Scheme 8.4) [START_REF] Maleki | Multicomponent synthesis of pyrano[2,3-d]pyrimidine derivatives via a direct one-pot strategy executed by novel designed cooperated Fe3O4@polyvinyl alcohol magnetic nanoparticles[END_REF]. This catalytic system was reused 6 times with slight yield loss (first run: 98%; sixth run: 91%).

An interesting variant of this reactivity was reported by Kassanee, showing that chromenylphosphonates could also be prepared in a similar manner in water with high yields and short reaction times (20-30 min), using functionalized magnetite with modified sulfo-chitosan (Scheme 8.5) [START_REF] Mohammadi | Sulfochitosan encapsulated nano-Fe3O4 as an efficient and reusable magnetic catalyst for green synthesis of 2-amino-4H-chromen-4-yl phosphonates[END_REF].

Authors propose a mechanism catalyzed by hydrogen-heteroatom (nitrogen or oxygen) interactions, where water is not an innocent solvent (Fig. 8.3). Similar behavior has been observed with magnetite functionalized with sulfo-PEG,

Fe 3 O 4 @PEG-SO 3 H [87]. N H NH O O O CN CN O HN N H O CN NH 2 O O R 1 R 1 + + [PVA@Fe 3 O 4 -Cu]

Cross-Coupling Reactions

The upbringing of d-block transition metals in catalyzed cross-coupling reactions is gaining ground against palladium thanks to their larger abundance than noble metals. The Sonogashira-Hagihara cross-coupling reaction enables the formation of a C-C bond between an sp 2 -carbon halide (aryl or vinyl) and a terminal alkyne interesting transformations for the synthesis of propargylic compounds [START_REF] Díez-González | Chapter three-copper(I)-acetylides: access, structure, and relevance in catalysis[END_REF]. The search of catalytic versions is key for exploiting the privileged reactivity of this metal from the point of view of sustainability [START_REF] Evano | Copper-mediated coupling reactions and their applications in natural products and designed biomolecules synthesis[END_REF]. Recent reports on the singular π-activation of alkynes leveraged by zero-valent CuNPs reveal the importance of this coordination in catalysis [START_REF] Dang-Bao | Making copper(0) nanoparticles in glycerol: a straightforward synthesis for a multipurpose catalyst[END_REF][START_REF] Nasrollahzadeh | A review on recent advances in the application of nanocatalysts in A3 coupling reactions[END_REF].

In this context, the cross-coupling of terminal alkynes and acyl chlorides has been reported by Bhosale et al. using a Cu/Cu 2 O catalyst prepared from Cu(OAc) 2 in onestep under microwave irradiation (3 min, 600 W) in 1,3-propanediol. The as-prepared catalytic material exhibited an irregular morphology that combines tubular domains and spherical particles ranging from 70 to 110 nm in size (Fig. 8.4) of a mixture of Cu(0) and Cu 2 O as confirmed by high-resolution XPS analysis [START_REF] Bhosale | A facile and rapid route for the synthesis of Cu/Cu 2 O nanoparticles and their application in the Sonogashira coupling reaction of acyl chlorides with terminal alkynes[END_REF].

Taking into account the paramount importance that metal traces might have in catalysis, it is crucial to determine their contribution and potential cooperative effects. to 1500 ppb were tested, but the catalytic activity of Fe 3 O 4 NPs at 5 mol% loadings proved to be superior [START_REF] Firouzabadi | Magnetite (Fe3O4) nanoparticlescatalyzed sonogashira-hagihara reactions in ethylene glycol under ligand-free conditions[END_REF]. The magnetic properties of Fe 3 O 4 NPs allowed an easy catalyst recycling with only an overall 2% yield decrease after five consecutive runs.

An example of bimetallic nanocatalyst for Sonogashira cross-coupling reaction featuring PdCo NPs supported on graphene has been described by Dabiri et al. [START_REF] Dabiri | PdCo bimetallic nanoparticles supported on threedimensional graphene as a highly active catalyst for sonogashira cross-coupling reaction[END_REF].

The synthesis of this nanocomposite was carried out following the polyol methodology. In particular, the co-reduction of PdCl 2 and CoCl 2 was performed in ethylene glycol, which acted as reducing and stabilizing agent for the immobilization of NPs on the 3D graphene support (Fig. where L is a (di)phosphine and n = 1 or 2), which were successfully applied in Suzuki-Miyaura couplings [START_REF] Handa | Nanonickel-catalyzed Suzuki-Miyaura crosscouplings in water[END_REF]. Simultaneously, Han and coworkers reported Nicatalyzed carbonylative Suzuki-based reactions in PEG (Scheme 8.7) [135], process leading to biaryl ketones, motif present in different types of compounds (drugs, photosensitizers …). They compared the reactivity between preformed and in situ generated NiNPs, evidencing that those formed in situ were more active, probably because the latter are smaller, showing less aggregation that the preformed ones.

Authors carried out control tests (with Hg and CS 2 ) in order to prove the nature of the catalytically active species (in the presence of both additives, the reaction did not work), concluding that the activity observed agrees with a surface-like reactivity.

Preformed NiNPs stabilized by triazole-modified chitosan were active nanocatalysts for Suzuki-Miyaura reactions between aryl halides and phenyl boronic acid derivatives (Scheme 8.8) [START_REF] Hajipour | Novel triazole-modified chitosan@nickel nanoparticles: efficient and recoverable catalysts for Suzuki reaction[END_REF]. This represents an example of molecular-like catalytic reactivity using functionalized nanoparticles as support. For the Heck-type reaction, the catalyst was efficient for the coupling of aryl halides (chloro, bromo, iodo) with styrene or methyl acrylate using PEG as solvent (Scheme 8.10). In contrast to the non-functionalized Fe 3 O 4

NPs, the functionalized ones were more active and could be recycled up to five times preserving their efficiency, without metal leaching. The Sonogashira-type coupling between aryl halides (bromo, iodo) and phenylacetylene derivatives gave moderate yields under harsher conditions than those used for the Heck couplings.

Kumada-type cross-coupling Kumada-Tamao-Corriu reaction, coupling between a Grignard reagent and an organic halide, was initially reported using Ni-based catalysts [START_REF] Corriu | Activation of grignard reagents by transition-metal complexes. A new and simple synthesis of trans-stilbenes and polyphenyls[END_REF]118]; other efficient systems such as those based on palladium and iron, have proven their efficacy, the main part of them involving molecular catalysts, but more recently copper, nickel, and palladium nanoparticles have been used as well ( [START_REF] Heravi | Advances in Kumada-Tamao-Corriu cross-coupling reaction: an update[END_REF][START_REF] Moglie | Nanosized iron-or coppercatalyzed homocoupling of aryl, heteroaryl, benzyl, and alkenyl grignard reagents[END_REF] and references therein). Iron, representing the second more abundant metal in the Earth's crust, has found interesting applications in C-C couplings [START_REF] Jacobi Von | Iron(0) nanoparticle catalysts in organic synthesis[END_REF][START_REF] Bedford | The development of iron catalysts for cross-coupling reactions[END_REF][START_REF] Nakamura | Iron-catalyzed cross-coupling reactions[END_REF].

The main part of reported works assumes the contribution of molecular intermediate species in the catalytic transformation, but also nanoparticles have been identified

for low oxidation states (zero-valent FeNPs should be more stable under catalytic conditions than organometallic Fe(0) complexes) and it has been postulated that they act as a reservoir of molecular species exhibiting higher oxidation state [START_REF] Bedford | How low does iron go? Chasing the active species in fe-catalyzed crosscoupling reactions[END_REF]. Bedford and coworkers studied the reaction of alkyl halides with aryl Grignard compounds catalyzed by in situ generated FeNPs from FeCl 3 in the presence of PEG-14000 (Scheme 8.11 and Fig. 8.6) [START_REF] Bedford | Iron nanoparticles in the coupling of alkyl halides with aryl Grignard reagents[END_REF]. Authors proved that the Grignard reagent acted as 4640081165587 [START_REF] Bedford | Iron nanoparticles in the coupling of alkyl halides with aryl Grignard reagents[END_REF] reducing agent. Preformed FeNPs/PEG (diameter in the range 7-13 nm, determined by TEM) afforded the same reactivity as those formed in situ.

Carbon-Heteroatom Bond Formation

The

N NH R R N R R K 2 CO 3 NH R R = NH NH N NH R R = N NH N NH N NH [CuNPs] (10 mol%) H N R R X NH 2 + [CuNPs] (10 mol%) K 2 CO 3 , PEG400
95 ºC, 4-12 h Isolated Yield: 60-95% X = I, Br, Cl R = H, 4-OMe, 4-Cl, 4-Br, 4-NO 2 , 2-Me, 2-OMe Scheme 8.12 CuNPs catalyzed C-N cross-couplings of anilines and NH heterocycles with aryl halides in PEG400 [START_REF] Kidwai | Cu nanoparticles in PEG: a new recyclable catalytic system for N-arylation of amines with aryl halides[END_REF] Graphene oxide functionalized with carboxamide groups (f-GO) was an efficient support to coordinate Cu(II) salts and further reducing them to give CuNPs immobilized on the solid. This CuNPs on f-GO were then treated with Fe 3 O 4 nanoparticles leading to a magnetic catalytic material, which enhanced the catalyst recyclability (Fig. 8

.7) [112].
The as-prepared heterogenized nanocatalyst was applied to Ullmann-type coupling for the synthesis of N-aryl amines using a deep eutectic solvent (choline chloride:glycerol = 1:2) (Scheme 8.13). Authors compared the efficiency of this catalytic system with other CuNPs, both supported and unsupported, concluding that their catalyst led to higher yields under smoother conditions. However, the recycling was moderate (up to 3 times without loss of activity).

The work of our group on the preparation of small CuNPs (d mean = 1.7-2.4 nm) in glycerol from the reduction of Cu(II) and Cu(I) precursors with PVP as stabilizer and under low pressure of H 2 (3 bar) avoided the formation of oxidized by-products coming from the solvent (Fig. 8.8). This approach represents the first report toward the synthesis of well-defined and stable CuNPs by a bottom-up strategy thanks to the low solubility of O 2 in this medium, circumventing the formation of oxide shells [START_REF] Dang-Bao | Making copper(0) nanoparticles in glycerol: a straightforward synthesis for a multipurpose catalyst[END_REF].

X N H R 3 R 2 + N R 3 R 2 R 1 R 1
Isolated yields:76-99%

[CuNPs-carboxamide-f-GO@Fe 3 O 4 ] (0.05 mol%)

1:2 choline chloride:glycerol K 2 CO 3 , 110 ºC, 30 min [START_REF] Beletskaya | Copper in cross-coupling reactions: the post-Ullmann chemistry[END_REF] CuNPs immobilized on a magnetic-modified graphene oxide (see Fig. Notably, the cyclization only takes place in an intramolecular fashion and no Cu leaching was detected in the EG reaction medium after catalyst filtration (ICP analyses).

R 1 = H, OMe, NO 2 N H R 3 R 2 = N H O N H N H NH 2 NH 2 NH 2 O 2 N O Scheme 8.
Preformed Cu 2 O nanoparticles (mean diameter: ca. 5 nm, Fig. 8.9) were applied in the coupling between iodoaryl derivatives and different nitrogen-based reagents, such as aryl and alkyl amines, but also aqueous ammonia, in glycerol [START_REF] Chahdoura | Copper(I) oxide nanoparticles in glycerol: a convenient catalyst for cross-coupling and azide-alkyne cycloaddition processes[END_REF]. This nanocatalyst was also efficient for the synthesis of thioethers through C-S couplings.

This nanocatalyst has also been applied for the activation of terminal alkyne groups toward azide-alkyne cycloaddition reaction (CuAAC) in glycerol (Scheme 8.17) [START_REF] Chahdoura | Copper(I) oxide nanoparticles in glycerol: a convenient catalyst for cross-coupling and azide-alkyne cycloaddition processes[END_REF]. of copper oxides as proven by XPS [START_REF] Frindy | Copper nanoparticles stabilized in a porous chitosan aerogel as a heterogeneous catalyst for C-S cross-coupling[END_REF]. This nanocatalyst was applied in the C-S coupling of aryl halides and thiophenol, being more active for iodo than bromo and chloro arenes, for the latter ones they were only active for aryl halides containing electron withdrawing substituents (Scheme 8.19). Authors observed that halide anions released to the medium during the catalytic reaction can act as poison for CuNPs, in addition to promoting metal leaching.

Generally speaking, C-O couplings are more challenging reactions mainly due to the limited functional compatibilities and the need of activated substrates [START_REF] Kunz | Renaissance of Ullmann and Goldberg reactionsprogress in copper catalyzed C-N-C-O-and C-S-coupling[END_REF]117]. Besides, the use of polyol medium adds another difficulty because the solvent can compete with the substrate. In this frame, Biegi and Ghiasbeigi have recently reported the synthesis and full characterization of functionalized magnetite with isonicotinic acid with the aim of coordinating Cu(I) precursors (Fig. 8.10) [START_REF] Ghiasbeigi | Copper immobilized on isonicotinic acid hydrazide functionalized nano-magnetite as a novel recyclable catalyst for direct synthesis of phenols and anilines[END_REF]. The resulting catalytic material was efficiently applied to the synthesis of phenol and aniline derivatives (TOF up to 4494 h -1 ), using a mixture of PEG and water as solvent (PEG:H 2 O = 2:1) (Scheme 8.20). The catalytic phase was recycled up to 5 times with slight loss of yield, although the 30% copper loss reported by the authors after the fourth run was substantial (Cu content of catalyst before use: 57,037.8 ppm; after 4th run: 40,297.3 ppm). in polyol medium has been widely reported (for selected articles, see: [START_REF] Fakhri | Organometallic polymer-functionalized Fe3O4 nanoparticles as a highly efficient and eco-friendly nanocatalyst for C-C bond formation[END_REF][START_REF] Gholinejad | Nitro group reduction and Suzuki reaction catalysed by palladium supported on magnetic nanoparticles modified with carbon quantum dots generated from glycerol and urea[END_REF][START_REF] Ghorbani-Choghamarani | Palladium-S-propyl-2aminobenzothioate immobilized on Fe3O4 magnetic nanoparticles as catalyst for Suzuki and Heck reactions in water or poly(ethylene glycol)[END_REF][START_REF] Liu | A highly water-dispersible and magnetically separable palladium catalyst based on functionalized poly(ethylene glycol)-supported iminophosphine for Suzuki-Miyaura coupling in water[END_REF]126,137]). Other supports based on 3d-transition metals such as TiO 2 [START_REF] Mondal | Palladium nanoparticles embedded on mesoporous TiO2 material (Pd@MTiO2) as an efficient heterogeneous catalyst for Suzuki-Coupling reactions in water medium[END_REF], CuO [START_REF] Chattopadhyay | Shape-dependent catalytic activity of copper oxide-supported Pd(0) nanoparticles for Suzuki and cyanation reactions[END_REF], and ZnO [113] have also been used for the same purpose. This heterogenization strategy efficiently enables the recoverability of the catalytic materials by magnetic separation, and also in some cases, the enhancement of TON is observed due to the synergy between catalyst and support. Furthermore, polymetallic systems merit further studies to exploit the cooperative effects between active metal centers in polyol medium [START_REF] Dang-Bao | Bimetallic nanocatalysts in glycerol for applications in controlled synthesis. a structure-reactivity relationship study[END_REF]. The intrinsic properties of polyols in terms of favoring 3D organization via supramolecular interactions, their suitable oxidation potentials for the reduction of transition metal salts and organometallic complexes, as well as their dispersing abilities via solvation interactions, which often trigger an activity increase, confer them unique properties in nanocatalysis.

Fig. 8 . 1

 81 Fig. 8.1 Published contributions per 5-year period for first-row transition metals used in catalysis (data collected from SciFinder Database since 1975 up to July 2019)

  :18/5/2020 Pages: 32 Layout: T1-Standard

(

  light, mechanical stress, temperature…)[START_REF] Klajn | Spiropyran-based dynamic materials[END_REF][START_REF] Lukyanov | Spiropyrans: synthesis, properties, and application (review)[END_REF] 131]. They were synthesized by a multicomponent reaction, constituted of a tandem Knoevenagel-cyclo-condensation involving ninhydrin (or related cyclic dicarbonyl compounds), malonitrile, and dimedone (or related 1,3-dicarbonyl derivatives) (Scheme 8.1). The role of the nanocatalyst (mean size: ca. 7 nm determined by TEM) was evidenced by different control tests; in the absence of nickel, the reaction was much slower (some hours vs. some minutes) and the use of Ni powder (particle size <150 μm) led to moderate yields after 8 h of reaction. Ethylene glycol was a convenient solvent permitting a straightforward biphasic extraction of products by a biphasic system (using ethyl acetate as immiscible soluble with ethylene glycol), preserving the catalyst dispersed in the 485392_1_En_8_Chapter TYPESET DISK LE CP Disp.:18/5/2020 Pages: 32 Layout: T1-Standard

8 . 2 ,Scheme 8 . 3

 8283 Scheme 8.3 Three-component reactions catalyzed by Fe 3 O 4 nanoparticles stabilized by chitosan[START_REF] Maleki | Synthesis of benzimidazolo[2,3-b]quinazolinone derivatives via a one-pot multicomponent reaction promoted by a chitosan-based composite magnetic nanocatalyst[END_REF][START_REF] Maleki | An efficient synthesis of benzodiazepine derivatives via a onepot, three-component reaction accelerated by a chitosan-supported superparamagnetic iron oxide nanocomposite[END_REF]

Fig. 8 . 2

 82 Fig. 8.2 Proposed mechanism for Fe-based catalyzed synthesis of benzimidazolo[2,3b]quinazolinones. Reprinted from [83] with permission from Elsevier 2015, license no. 4639401066332

Scheme 8 . 4 8 . 5 Fig. 8 . 3

 848583 Scheme 8.4 Synthesis of pyrano[2,3-d]pyrimidines catalyzed by Fe 3 O 4 modified with polyvinyl alcohol (PVA) and doped with Cu(II) salts[START_REF] Maleki | Multicomponent synthesis of pyrano[2,3-d]pyrimidine derivatives via a direct one-pot strategy executed by novel designed cooperated Fe3O4@polyvinyl alcohol magnetic nanoparticles[END_REF]

[

  116]. This transformation was initially described with a Pd(0) catalyst and a Cu(I) co-catalyst, but Cu alone[START_REF] Kotovshchikov | Alkynylation of steroids via Pd-free Sonogashira coupling[END_REF][START_REF] Liori | A sustainable, user-friendly protocol for the Pd-free sonogashira coupling reaction[END_REF] 120] or other transition metals have been reported as efficient catalysts for this transformation (Ni[START_REF] Beletskaya | The nickel-catalyzed Sonogashira-Hagihara reaction[END_REF] 102, 103], Fe [66], Co [115]), fueling the important role of abundant metals in C-C bond forming reactions. Gaining a better understanding on the physicochemical processes leading to the formation of MNPs is key for the design of nanocatalysts with defined morphology[START_REF] Gawande | Cu and Cu-based nanoparticles: synthesis and applications in catalysis[END_REF][START_REF] Nasrollahzadeh | A review on recent advances in the application of nanocatalysts in A3 coupling reactions[END_REF], notably when catalyst heterogenization with solid supports such as zeolites, titania, montmorillonite and carbonaceous materials is required. Robustness and catalytic activity of tailor-made nanostructured catalysts outperform in many cases classical ones[START_REF] Mitrofanov | Formation of C-C, C-S and C-N bonds catalysed by supported copper nanoparticles[END_REF].C(sp)-C(sp 2 ) Sonogashira cross-couplingSince synthesis of copper(I) acetylide, the first organometallic copper complex described in 1859[START_REF] Boettger | Ueber die Einwirkung des Leuchtgases auf verschiedene Salzsolutionen, insbesondere auf eine ammoniakalische Kupferchlorürlösung[END_REF], the reactivity of copper toward the activation of terminal alkyne groups has yielded a number of 485392_1_En_8_Chapter TYPESET DISK LE CP Disp.:18/5/2020 Pages: 32 Layout: T1-Standard

Firouzabadi

  Fig. 8.4 TEM micrographs of Cu/Cu 2 O NPs. Reproduced with permission from Royal Society of Chemistry 2014, license no. 4639380035278

Fig. 8 . 5

 85 Fig. 8.5 Synthesis of PdCo NPs supported on graphene. Reproduced with permission from Ref. [29]. Copyright 2016 Wiley, license no. 4639270206261

Scheme 8 . 7 Scheme 8 . 8 AQ3Scheme 8 . 9

 878889 Scheme 8.[START_REF] Anastas | Catalysis as a foundational pillar of green chemistry[END_REF] In situ generated NiNPs in PEG-400 applied in carbonylative Suzuki coupling reactions[135]

Scheme 8 . 1 R 1 = 4 -Scheme 8 .

 81148 Scheme 8.10 Heck-Mizoroki-type couplings catalyzed by Co(II) supported on functionalized Fe 3 O 4 nanoparticles (see Scheme 8.9)[START_REF] Hajipour | Pd/Cu-free Heck and Sonogashira cross-coupling reaction by Co nanoparticles immobilized on magnetic chitosan as reusable catalyst[END_REF]

  activation of C-halogen bonds has been overwhelmingly used in the functionalization of arenes. Since the discovery of Ullmann's coupling in 1901, copper has been one of the most used earth-abundant metals in both C-C and C-heteroatom couplings (original paper of Ullmann: [125]; recent reviews:[START_REF] Beletskaya | Copper in cross-coupling reactions: the post-Ullmann chemistry[END_REF][START_REF] Mondal | Recent advancement of Ullmann-type coupling reactions in the formation of C-C bond[END_REF] 108]). However, many applications of this reactivity are especially limited due to the use of hazardous solvents such as DMF and DMSO. A lot of interest has been put into transforming this reactivity into greener approaches. In this context, considerable efforts have been recently developed in nanocatalytic systems capable of working in friendly environmental conditions[START_REF] Kaushik | New trends in sustainable nanocatalysis: emerging use of earth abundant metals[END_REF] 127], polyols being alternative solvents of interest[START_REF] Favier | Palladium nanoparticles in polyols: synthesis, catalytic couplings and hydrogenations[END_REF]. This strategy has been successfully applied in a wide range of C-N couplings using many different nitrogen-based reagents. Kidwai and coworkers applied preformed unsupported CuNPs in the N-arylation of aryl halides with anilines using PEG400 as solvent (Scheme 8.12)[START_REF] Kidwai | Cu nanoparticles in PEG: a new recyclable catalytic system for N-arylation of amines with aryl halides[END_REF]. A large scope of aniline derivatives and also NH heterocycles was carried out.

Fig. 8 . 7

 87 Fig. 8.7 Illustration of the synthesis of CuNPs immobilized on f-GO containing Fe 3 O 4 NPs (top) with the application in C-N bond formation processes (bottom). Reprinted from [112], Copyright 2018, with permission from Elsevier, license no. 4640121432056

Fig. 8 . 8

 88 Scheme 8.[START_REF] Beletskaya | Copper in cross-coupling reactions: the post-Ullmann chemistry[END_REF] CuNPs immobilized on a magnetic-modified graphene oxide (see Fig.8.7) catalyzed C-N couplings of secondary amines and anilines[112]

Furthermore,R 1 =Scheme 8 . 14 Scheme 8 . 15 Scheme 8 .Fig. 8 . 9

 1814815889 Scheme 8.14 CuA NPs catalyzed C-N couplings and multicomponent reactions[START_REF] Dang-Bao | Making copper(0) nanoparticles in glycerol: a straightforward synthesis for a multipurpose catalyst[END_REF]

Fig. 8 . 8 . 4

 884 Scheme 8.[START_REF] Boettger | Ueber die Einwirkung des Leuchtgases auf verschiedene Salzsolutionen, insbesondere auf eine ammoniakalische Kupferchlorürlösung[END_REF] CuNPs stabilized by chitosan applied in C-S couplings[START_REF] Frindy | Copper nanoparticles stabilized in a porous chitosan aerogel as a heterogeneous catalyst for C-S cross-coupling[END_REF]

From a structural

  point of view, 3d -metals based-species present several oxidation states, often leading to paramagnetic intermediates of challenging elucidation. Given the specificity developed by nature in biocatalyzed transformations involving 3dtransition metals and the demonstrated efficiency of nanocatalysts discussed herein (e.g., Cu NPs for Sonogashira and C-heteroatom couplings, Ni NPs for Suzuki, Co NPs for Heck-Mizoroki, Fe NPs for Kumada-like couplings …), the fundamental and applied research in this field foresees new reactivities and deep mechanistic insights taking advantage of the cutting-edge in operando techniques available nowadays.

Earth-Abundant D-Block Metal Nanocatalysis for Coupling …

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