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The zwitterionic complex [Cp*IrCl{(MeIm)2CHCOO}] (1) efficiently catalyzes the selective hydrosilylation of CO2 to afford the corresponding silylformate. The best reaction performance has been achieved in acetonitrile at 348 K using HSiMe2Ph. The 1‐catalyzed reaction of pyrrolidine with CO2 and HSiMe2Ph strongly depends on the CO2 pressure. At low concentration of CO2 (1 bar) formation of the corresponding silylcarbamate, by insertion of CO2 into the Si−N bond of the in situ generated silylamine was observed, while at higher pressure (3 bar) the formamide derivative was obtained as major reaction product. The unexpected formation of pyrrolidin‐1‐ium formate as intermediate of the reaction the 1‐catalyzed of CO2 with pyrrolidine and HSiMe2Ph has been observed, and its role in the formation of 1‐formylpyrrolidine rationalized. Moreover, a mechanism for the reaction of CO2 with hydrosilanes, in the presence and in the absence of amines, based on theoretical calculations has been proposed. [ABSTRACT FROM AUTHOR]

Graphical abstract This work compiles and discusses the great variety of non-classical transition-metal-catalyzed mechanisms hitherto reported for the reduction of organic molecules with hydrosilanes. Highlights • Non-classical mechanisms for hydrosilane-driven reductions are discussed herein. • Non-classical mechanisms often involve the heterolytic activation of the Si–H bond. • Heterolytic Si–H bond activation requires a Lewis acid metal and a Lewis base. • Non-classical mechanism that need no heterolytic Si–H activation are also discussed. Abstract This article reviews the most recent advances on the study of non-classical mechanisms for the reduction of organic substrates with hydrosilanes catalyzed by transition metals. A wide variety of catalytic cycles that go beyond the classical steps described for Ojima, Chalk-Harrod and modified Chalk-Harrod mechanisms, as representative examples, have been proposed in recent years. In this review, these alternative mechanistic proposals have been analyzed and classified according to the type of substrate, focusing on the reduction/hydrosilylation of carbonyl compounds (ketones and aldehydes), carbon dioxide, silylesters, amides, N -heterocycles, alkyl halides, nitriles, alkenes and alkynes. In spite of the broad diversity of non-classical reaction mechanisms hitherto reported, the catalytic cycles described for each substrate have been arranged in different categories according to their characteristics. The epigraph dedicated to the first type of substrate (carbonyl compounds) comprises most of the mechanisms described in this review for the reduction of polar bonds, which, to some extent, show a relationship to those proposed for non-polar bonds (alkenes and alkynes). Remarkable types of reaction mechanisms that will be dealt with in this work are: ionic mechanisms, ligand-assisted mechanisms, nonhydride mechanisms, NHC-Cu-H mediated mechanisms, and silylene-mediated mechanisms. [ABSTRACT FROM AUTHOR]

During recent years, the catalytic transformation of CO2 using silicon‐hydrides as reductants has emerged as a promising methodology that allows the selective reduction of CO2 to the formate, formaldehyde, methoxide or methane level under mild reaction conditions. Moreover, some catalysts have been employed for the formylation and/or methylation of the N−H bonds of secondary and/or primary amines by their reaction with CO2 and hydrosilanes. This work summarizes the different catalytic systems that have shown to be efficient for the above‐mentioned reactions. Furthermore, a brief description of the reactions performance and the conditions employed in each case is included. From silicon valley to silicon hydrides: Catalytic reduction of CO2 with silicon‐hydrides could be considered as a promising and emerging chemical methodology. [ABSTRACT FROM AUTHOR]

The hydrosilylation of CO2 with different silanes such as HSiEt3, HSiMe2Ph, HSiMePh2, HSiMe(OSiMe3)2, and HSi(OSiMe3)3 in the presence of catalytic ammounts of the iridium(III) complex [Ir(H)(CF3CO2)(NSiN*)(coe)] ( 1; NSiN*= fac-bis-(4-methylpyridine-2-yloxy); coe= cis-cyclooctene) has been comparatively studied. The activity of the hydrosilylation catalytic system based on 1 depends on the nature of the reducing agent, where HSiMe(OSiMe3)2 has proven to be the most active. The aforementioned reactions were found to be highly selective toward the formation of the corresponding silylformate. It has been found that using 1 as catalyst precursor above 328 K decreases the activity through a thermally competitive mechanistic pathway. Indeed, the reduction of the ancillary trifluoroacetate ligand to give the corresponding silylether CF3CH2OSiR3 has been observed. Moreover, mechanistic studies for the 1-catalyzed CO2-hydrosilylation reaction based on experimental and theoretical studies suggest that 1 prefers an inner-sphere mechanism for the CO2 reduction, whereas the closely related [Ir(H)(CF3SO3)(NSiN)(coe)] catalyst, bearing a triflate instead of trifluoroacetate ligand, follows an outer-sphere mechanism. [ABSTRACT FROM AUTHOR]

A series of rhodium-NSiN complexes (NSiN=bis (pyridine-2-yloxy)methylsilyl fac-coordinated) is reported, including the solid-state structures of [Rh(H)(Cl)(NSiN)(PCy3)] (Cy=cyclohexane) and [Rh(H)(CF3SO3)(NSiN)(coe)] (coe= cis-cyclooctene). The [Rh(H)(CF3SO3)(NSiN)(coe)]-catalyzed reaction of acetophenone with silanes performed in an open system was studied. Interestingly, in most of the cases the formation of the corresponding silyl enol ether as major reaction product was observed. However, when the catalytic reactions were performed in closed systems, formation of the corresponding silyl ether was favored. Moreover, theoretical calculations on the reaction of [Rh(H)(CF3SO3)(NSiN)(coe)] with HSiMe3 and acetophenone showed that formation of the silyl enol ether is kinetically favored, while the silyl ether is the thermodynamic product. The dehydrogenative silylation entails heterolytic cleavage of the Si−H bond by a metal-ligand cooperative mechanism as the rate-determining step. Silyl transfer from a coordinated trimethylsilyltriflate molecule to the acetophenone followed by proton transfer from the activated acetophenone to the hydride ligand results in the formation of H2 and the corresponding silyl enol ether. [ABSTRACT FROM AUTHOR]

The iridium(III) complex [Ir(H)(CF 3 SO 3 )(NSiN)(coe)] (NSiN = bis(pyridine-2-yloxy)methylsilyl, coe = cyclooctene) has demonstrated to be an active catalyst for the solvent-free and selective hydrosilylation of CO 2 with HSiMe(OSiMe 3 ) 2 to afford the corresponding silyl formate, namely HC(O)OSiMe(OSiMe 3 ) 2 . The activity of this catalytic system depends on both parameters the reaction temperature and the CO 2 -pressure. This work includes a kinetic study at variable temperature (from 25 °C to 75 °C) and pressure (from 1 bar to 8 bar) together with a kinetic modeling of this catalytic reaction. The best catalytic performances have been achieved at 75 °C and 8 bar of CO 2 . [ABSTRACT FROM AUTHOR]

The complex [Ir(H)(CF3SO3)(NSiN)(coe)] (NSiN=bis(pyridine-2-yloxy)methylsilyl fac-coordinated) (1) is an effective catalyst precursor for the solvent-free synthesis of silyl carbamates from reaction of aliphatic secondary amines with CO2 and HSiMe(OSiMe3)2. The preferential formation of the silyl carbamate instead of the expected formamide or methylamine has proven to be consequence of an iridium-catalyzed dehydrogenative Si-N coupling between the silane and the amine to afford the corresponding silyl amine, which under the reaction conditions reacts with CO2 to give the corresponding silyl carbamate. [ABSTRACT FROM AUTHOR]

The copper(I) complexes [Cu(X){2,6-diisopropylphenyl-NHC-(CH2)3Si(O iPr)3}] (X=Cl ( 2 a); I ( 2 b), NHC=N-heterocyclic carbene) have been synthesized and characterized. Furthermore, the structure of 2 b has been confirmed by X-ray diffraction studies. Complex 2 a has been successfully anchored in MCM-41 to afford 2-MCM-41. The activity of both the homogeneous, 2 a, and heterogeneous, 2-MCM-41, catalysts in acetophenone hydrosilylation with HSiEt3 and [3+2] cycloaddition of benzyl azide and phenylacetylene has been investigated. The heterogeneous catalyst exhibits catalytic activity for the cycloaddition reaction though, unexpectedly, shows no catalytic activity for hydrosilylation. [ABSTRACT FROM AUTHOR]

We describe a bis-N-heterocyclic carbene rhodium(III) complex, featuring two trifluoroacetato ligands, that affords a variety of α-vinylsilanes in good yields by hydrosilylation of terminal alkynes. Selectivities around 7:1 α/β-( E) were reached, while the β-( Z) product was only marginally obtained. This example sharply contrasts with the β-( Z)-selectivity observed for its parent diiodido complex [ABSTRACT FROM AUTHOR]

Breaking ties: Recent reports on iridium and ruthenium homogeneous hydrosilylation catalysis point to a heterolytic activation of SiH bonds promoted by the oxophilicity of the silicon atom and the Lewis acidity of the metal center. This unusual type of mechanism opens the door to a more widespread use of catalysts that operate by an ionic or concerted outer‐sphere mechanism in organic synthesis. [ABSTRACT FROM AUTHOR]

The β- Z selectivity in the hydrosilylation of terminal alkynes has been hitherto explained by introduction of isomerisation steps in classical mechanisms. DFT calculations and experimental observations on the system [M(I)2{κ-C,C,O,O-(bis-NHC)}]BF4 (M=Ir ( 3 a), Rh ( 3 b); bis-NHC=methylenebis( N-2-methoxyethyl)imidazole-2-ylidene) support a new mechanism, alternative to classical postulations, based on an outer-sphere model. Heterolytic splitting of the silane molecule by the metal centre and acetone (solvent) affords a metal hydride and the oxocarbenium ion [R3SiO(CH3)2]+, which reacts with the corresponding alkyne in solution to give the silylation product [R3SiCHCR]+. Thus, acetone acts as a silane shuttle by transferring the silyl moiety from the silane to the alkyne. Finally, nucleophilic attack of the hydrido ligand over [R3SiCHCR]+ affords selectively the β-( Z)-vinylsilane. The β- Z selectivity is explained on the grounds of the steric interaction between the silyl moiety and the ligand system resulting from the geometry of the approach that leads to β-( E)-vinylsilanes. [ABSTRACT FROM AUTHOR]

The preparation of 1-(3-triisopropoxysilylpropyl)-3-(2-methoxyethyl)-imidazolium bromide or chloride salts and their reaction with [Rh(COD)(μ-OMe)]2 (COD=1,5-cyclooctadiene) to afford the corresponding [Rh(COD)(NHC)X] (X=Br, Cl; NHC=1-(3-triisopropoxysilylpropyl)-3-(2-methoxyethyl)-2-ilydene-imidazol) species is described. These new compounds were used as catalyst precursors for acetophenone hydrosilylation. The higher activity of the rhodium-chlorido complex evidences a clear halide effect in the activation of the catalyst. Immobilization of the catalytic precursor [Rh(COD)(NHC)Cl] on mobile crystalline material 41 (MCM-41) allows for the preparation of the corresponding heterogeneous catalyst. Reduction of acetophenone to PhMeCH-O-SiMe(OSiMe3)2 by hydrosilylation with 1,1,1,3,5,5,5-heptamethyltrisiloxane is effectively catalyzed by both the homogeneous and the heterogeneous catalysts, in which the homogeneous system is the more active. Interestingly, the heterogeneous catalyst is reusable. Both homo- and heterogeneous catalysts are also effective for the copolymerization of terephthalaldehyde and 1,1,3,3,5,5-hexamethyltrisiloxane, which affords the corresponding poly(silyl ether). The catalyst yields the heterogeneous system polymers with higher molecular weights ( Mw=94 000 g mol−1) and a narrow molecular weight distribution (PDI=1.5-1.7). [ABSTRACT FROM AUTHOR]

Rhodium‐catalyzed polymerization goes heavyweightThe cover picture shows a neutral rhodium(I) N‐heterocyclic carbene hydrosilylation catalyst immobilized on the surface of MCM‐41. In their Full Paper on p. 1133 ff., F. J. Fernández‐Alvarez, L. A. Oro et al. describe how these rhodium‐containing materials catalyze the preparation of poly(silyl ether)s by hydrosilylation. These results show that the immobilized catalysts provide polymers with higher average molecular weight than those obtained by using the corresponding homogenous systems, which could be attributed to a confinement effect exerted by the channels of MCM‐41. [ABSTRACT FROM AUTHOR]

The reaction of (4-methyl-pyridine-2-iloxy)dimethylsilane (NSiMe–H, 1) with [RhCl(coe) 2 ] 2 gives the rhodium(III) complex [Rh(Cl)(κ 2-NSiMe) 2 ] (2), which reacts with a stoichiometric amount of AgCF 3 CO 2 to afford [Rh(κ 2-CF 3 CO 2)(κ 2-NSiMe) 2 ] (3). Complexes 2 and 3 have been fully characterized by elemental analysis and NMR spectroscopy. The solid-state structure of 3 has been confirmed by X-ray diffraction analysis. Moreover, the activity of complex 3 as catalyst for the reaction of secondary amines with CO 2 (3 bar) and hydrosilanes has been studied. The outcomes of these catalytic studies show that under these conditions complex 3 promotes the selective formation of silylcarbamates. Image 1 • First rhodium complexes with bidentate pyridine-2-iloxy-silyl based ligands. • Rhodium-catalyzed preparation of silylcarbamates from amines, CO 2 and silanes. • Dehydrogenative silylation of in situ generates carbamic acid derivatives. [ABSTRACT FROM AUTHOR]

Rhodium complexes featuring one or two trifluoroacetato ligands catalyze the unusual formation of a variety of α-vinylsilanes in good selectivities by non-directed hydrosilylation of terminal alkynes. [ABSTRACT FROM AUTHOR]

The reaction also works with diphenylmethylsilane and dimethylphenylsilane, respectively. [ABSTRACT FROM AUTHOR]