Mechanistic aspects of bond activation with perfluoroarylboranes

In the mid-1990s, it was discovered that tris(pentafluorophenyl)borane, B(C(6)F(5))(3), was an effective catalyst for hydrosilylation of a variety of carbonyl and imine functions. Mechanistic studies revealed a counterintuitive path in which the function of the borane was to activate the silane rather than the organic substrate. This was the first example of what has come to be known as "frustrated Lewis pair" chemistry utilizing this remarkable class of electrophilic boranes. Subsequent discoveries by the groups of Stephan and Erker showed that this could be extended to the activation of dihydrogen, initiating an intense period of activity in this area in the past 5 years. This article describes the early hydrosilylation chemistry and its subsequent applications to a variety of transformations of importance to organic and inorganic chemists, drawing parallels with the more recent hydrogen activation chemistry. Here, we emphasize the current understanding of the mechanism of this process rather than focusing on the many and emerging applications of hydrogen activation by fluoroarylborane-based frustrated Lewis pair systems.     

Directing group-controlled hydrosilylation: regioselective functionalization of alkyne

Pt(0)-catalyzed hydrosilylation of unsymmetric alkynes proceeds in a highly regioselective manner with a dimethylvinylsilyl (DMVS) group as the directing group. This hydrosilylation affords a single regioisomer of silylalkenes from propargylic and homopropargylic alcohol derivatives. DMVS also has an accelerating effect that allows group-selective hydrosilylation of the DMVS-attached alkyne prior to that of other alkynes. Combined hydrosilylation and transformation reactions of the resulting silylalkenes afford various tri-substituted alkenes and multi-oxy-functionalized compounds with high regioselectivity from unsymmetric alkynes.     

Regioselective Rh(I)-catalyzed sequential hydrosilylation toward the assembly of silicon-based peptidomimetic analogues

A highly regioselective Rh(I)-catalyzed hydrosilylation of enamides is presented. This mild protocol allows access to a wide variety of different arylsilanes with substitution at the β-position of the enamide and functionalization on the alkyl chain tethered to the silane. This protocol is extended to include a sequential one-pot hydrosilylation. Using diphenylsilane as the appendage point, hydrosilylation of a protected allyl alcohol followed by hydrosilylation of an enamide generates a complex organosilane in one step. This highly convergent strategy to synthesize these functionalized systems now provides a way for the rapid assembly of a diverse collection of silane-based peptidomimetic analogues.     

Recent advances and actual challenges in late transition metal catalyzed hydrosilylation of olefins from an industrial point of view

Hydrosilylation of olefins is the key catalytic reaction for the production of industrially important organosilicon compounds such as organofunctional silanes and silicones. Moreover catalytic hydrosilylation is used for crosslinking of silicone polymers to elastomers and silicone-based release coatings, and for coupling of silanes and siloxanes to organic polymers. Industrially relevant aspects of hydrosilylation are dominated by the selectivity, activity (defined by the turnover frequency (TOF)), and stability (defined by the turnover number (TON)) of hydrosilylation catalysts as well as switchable catalyses. Furthermore, the high and volatile price of platinum as the industrially most important catalytic metal is a strong motivation for the reduction of precious metal consumption, such as homogeneous catalyst recycling or increasing the TOF resp. TONs of established hydrosilylation catalysts, or employing lower-priced transition metal catalysts. The selectivity of hydrosilylation determines yield and production costs of functional silanes, e.g. hydrosilylation products of allyl chloride, but is of equal importance for the product quality of silane-modified organic polymers and hybrid polymers. As industrial applications of hydrosilylation curing silicones, such as release coatings and elastomers, continuously move towards higher production speed, this requires catalytic systems capable of very high activity resp. turnover frequencies at temperatures typically above 100 °C, but allowing shelf-stable silicone compositions and therefore requiring suppression of any catalytic activity at ambient conditions prior use. This form of switchable catalysis employs carefully designed catalytic systems, which are activated by heating or photoactivation in a very short period of time, demanding very high standards of industrial hydrosilylation chemistry.     

Enantioselective Hydrosilylation of β,β-Disubstituted Enamides to Construct α-Aminosilanes with Vicinal Stereocenters

Despite the advances in the area of catalytic alkene hydrosilylation, the enantioselective hydrosilylation of alkenes bearing a heteroatom substituent is scarce. Here we report a rhodium-catalyzed hydrosilylation of β,β-disubstituted enamides to directly afford valuable α-aminosilanes in a highly regio-, diastereo-, and enantioselective manner. Stereodivergent synthesis could be achieved by regulating substrate geometry and ligand configuration to generate all the possible stereoisomers in high enantio-purity.     

炭材料负载金属催化剂催化硅氢加成反应进展

炭材料具有比表面积大、孔径可调、取材广泛等优点,以其为载体负载金属活性组分制备硅氢加成催化剂极具发展前景.我们详细总结了近20年不同炭材料如活性炭、石墨与石墨烯、碳纳米管、富勒烯、卡宾等在硅氢加成反应中负载金属催化剂的制备方法、催化性能以及可能的催化机理,并对有望应用到该反应的新型炭材料载体进行了对比与展望.认为未来硅氢加成炭负载型催化剂的研究可聚焦于(1)探寻新型双金属活性组分以进一步提高催化活性;(2)研发更具优势的金属配体,明晰配体与载体、配体与金属之间的相互作用关系以提高催化选择性与稳定性;(3)结合科学可靠的催化机理研究,以期研发出更符合可持续发展要求的炭负载型硅氢加成金属催化剂,可使硅氢加成反应基本实现原子经济性.     

Preparation of styrene–divinyl benzene copolymer-supported platinum complexes and their catalytic properties in hydrosilylation

A new type of catalyst for the hydrosilylation of unsaturated monomers with dichloromethylsilane (DCMS) was prepared, which consisted of thiolmethylene-substituted styrene–divinyl benzene copolymer and platinum. When using DCMS as a hydrosilylation agent, these catalysts showed a high activity in the hydrosilylation of vinyl and acetylene monomers as styrene, alkyl vinyl silanes, acetylene, phenyl acetylene, butyl acrylate. The activities of catalysts were not significantly reduced even after 20 reuse cycles.     

Selective hydrosilylation of styrene using an in situ formed platinum(1,3-dimesityl-dihydroimidazol-2-ylidene) catalyst

A highly active and selective in situ formed platinum(N-heterocyclic carbene) catalyst for the hydrosilylation of styrene with triethylsilane is described, which unlike all other known hydrosilylation catalysts, selectively yields hydrosilylation products, but (almost) no dehydrogenative silylation products.     

External Electric Field—Phenyl interaction boosts hydrosilylation of substituted alkynes to α-vinylsilane

The hydrosilylation of terminal alkyne is the most straightforward and atom-economy method to generate α-vinylsilane. In the present paper, the acetylene and phenylacetylene hydrosilylation reactions were firstly studied by imposing external electric field (EEF) as a catalyst at the level of ωB97XD/TZVP. The results demonstrated that the oriented negative FY direction is the optimal direction, which mostly reduced the reaction barriers. Further computations indicated that the larger the EEF, the lower the barrier. When the EEF was increased to 180 (10⁻⁴) au, the barrier height of acetylene hydrosilylation (path Q) reduced almost 20 kcal/mol. To be surprised, as the phenyl substitute used, the hydrosilylation reaction (path FQ) was largely accelerated with the barrier height lowered to 13.2 kcal/mol, which decreased about 37 kcal/mol. Hopefully, this theoretical study would provide a guide for the experiment of the hydrosilylation of alkyne as much as possible.     

Radical‐Induced Hydrosilylation Reactions for the Functionalization of Two‐Dimensional Hydride Terminated Silicon Nanosheets

Herein we present the functionalization of freestanding silicon nanosheets (SiNSs) by radical‐induced hydrosilylation reactions. An efficient hydrosilylation of Si?H terminated SiNSs can be achieved by thermal initiation or the addition of diazonium salts with a variety of alkene or alkyne derivatives. The radical‐induced hydrosilylation is applicable for a wide variety of substrates with different functionalities, improving the stability and dispersibility of the functional SiNSs in organic solvents and potentially opening up new fields of application for these hybrid materials.     

Hydrosilylation of α,β-unsaturated nitriles and esters catalyzed by tris (triphenylphosphine)chlororhodium

The hydrosilylation of α,β-unsaturated nitriles and esters such as acrylonitrile, crotononitrile, cinnamonitrile, ethyl and methyl acrylate, ethyl and methyl crotonate and ethyl and methyl methacrylate using tris(triphenylphosphine)chlororhodium as a catalyst is described. The hydrosilylation of α,β-unsaturated nitriles provided α-adduct exclusively in high yield except in the case of trichlorosilane which afforded β-adduct with acrylonitrile. On the other hand, the hydrosilylation of α,β-unsaturated esters gave rather complex results. The selectivity of the reactions was dramatically affected by the substituent of the ester group and that on the β-carbon. Thus, the hydrosilylation of ethyl acrylate with triethylsilane afforded a β-adduct, but, that of ethyl crotonate using the same hydrosilane gave a 1,4-adduct exclusively. Possible mechanisms for these reactions are discussed.     

Visible‐Light‐Mediated Metal‐Free Hydrosilylation of Alkenes through Selective Hydrogen Atom Transfer for Si−H Activation

Although there has been significant progress in the development of transition‐metal‐catalyzed hydrosilylations of alkenes over the past several decades, metal‐free hydrosilylation is still rare and highly desirable. Herein, we report a convenient visible‐light‐driven metal‐free hydrosilylation of both electron‐deficient and electron‐rich alkenes that proceeds through selective hydrogen atom transfer for Si−H activation. The synergistic combination of the organophotoredox catalyst 4CzIPN with quinuclidin‐3‐yl acetate enabled the hydrosilylation of electron‐deficient alkenes by selective Si−H activation while the hydrosilylation of electron‐rich alkenes was achieved by merging photoredox and polarity‐reversal catalysis.     

Cyclization/hydrosilylation of functionalized 1,6-diynes catalyzed by cationic platinum complexes containing bidentate nitrogen ligands

A 1:1 mixture of the platinum dimethyl diimine complex [PhN[double bond]C(Me)C(Me)[double bond]NPh]PtMe(2) (4a) and B(C(6)F(5))(3) catalyzed the cyclization/hydrosilylation of dimethyl dipropargylmalonate (1) and HSiEt(3) to form 1,1-dicarbomethoxy-3-methylene-4-(triethylsilylmethylene)cyclopentane (3) in 82% isolated yield with 26:1 Z:E selectivity. Platinum-catalyzed diyne cyclization/hydrosilylation tolerated a range of functional groups including esters, sulfones, acetals, silyl ethers, amides, and hindered ketones. Diynes that possessed propargylic substitution underwent facile cyclization/hydrosilylation to form silylated 1,2-dialkylidene cyclopentanes as mixtures of regioisomers. Diynes that possessed an electron-deficient internal alkyne underwent cyclization/hydrosilylation in moderate yield to form products resulting from silyl transfer to the less substituted alkyne. The silylated 1,2-dialkylidenecyclopentanes formed via diyne cyclization/hydrosilylation underwent a range of transformations including protodesilylation, Z/E isomerization, and [4 + 2] cycloaddition with dieneophiles.     

Chemical assembling of silica surface using a reaction of catalytic hydrosilylation

Chemical assembling of the silica surface modified by dimethylchlorosilane was performed by the catalytic hydrosilylation of 1,3-divinyl-1,1,3,3-tetramethyldisiloxane, α-methyl styrene, acetophenone, allyl butyl and allyl glycidyl ethers with dimethylchlorosilane. The effect of the nature of complexes of platinum, palladium, rhodium and ruthenium on the parameters of hydrosilylation was studied. It was shown that the maximum rate of hydrosilylation was observed in the reaction with allyl glycidyl ether, and minimum, with α-methylstyrene; the most effective catalyst of hydrosilylation was [Rh(CO)₂(acac)].     

Rhodium-catalysed asymmetric hydrosilylation of ketones using HETPHOX ligands

The HETPHOX ligand class was applied to the rhodium-catalysed asymmetric hydrosilylation of a range of substituted acetophenones. Enantioselective hydrosilylation of acetophenone with the tert-butyl substituted HETPHOX ligand gave (R)-phenylethanol in excellent enantioselectivity (84% ee) and in good conversion (80%). When applied to the hydrosilylation of other ketones conversions up to 93% and enantioselectivities up to 88% were observed.     

Palladium-catalyzed asymmetric hydrosilylation of 1,3-dienes

Advances in the palladium-catalyzed asymmetric hydrosilylation of 1,3-dienes are presented according to substrate types and chiral monophosphine ligands. Chiral monodentate phosphine ligands with a binaphthyl moiety have been proven to be the most efficient ligands for cyclic 1,3-dienes, and planar chiral ferrocenylmonophosphine ligands with two ferrocenyl moieties for linear 1,3-dienes. The ferrocenylmonophosphine ligands have expanded the substrate scope to 1,3-enynes in the asymmetric hydrosilylation. Palladium-catalyzed asymmetric hydrosilylation of 1,3-dienes and 1,3-enynes leads to the stereoselective synthesis of allylsilanes and allenylsilanes, respectively.     

Hydrosilylation of alkenes catalyzed by Fe powder

A novel iron-catalyzed hydrosilylation of alkenes process under solvent-free conditions has been reported. The influence of the amount of Fe catalyst, reaction temperature and various alkenes and silanes on the hydrosilylation were investigated. High yields of adduct were obtained in the hydrosilylation of octene with MeCl₂H, Me₂ClSiH and Ph₂SiH₂ by using 10?mol% iron powder as a signal catalyst.     

Platinum oxide (PtO(2)): a potent hydrosilylation catalyst

[reaction: see text] Platinum oxide was found to be a versatile and powerful hydrosilylation catalyst upon a wide variety of functionalized alkenes and especially aminated alkenes. Moreover, highly reproducible results and easy removal make this new catalyst a useful tool for hydrosilylation reaction.     

Probing the catalytic potential of chloro nitrosyl rhenium(I) complexes

The reduction of the mononitrosyl Re(II) salt [NMe(4)](2)[ReCl(5)(NO)] (1) with zinc in acetonitrile afforded the Re(i) dichloride complex [ReCl(2)(NO)(CH(3)CN)(3)] (2). Subsequent ligand substitution reactions with PCy(3), PiPr(3) and P(p-tolyl)(3) afforded the bisphosphine Re(i) complexes [ReCl(2)(NO)(PR(3))(2)(CH(3)CN)] (3, R = Cy a, iPr b, p-tolyl c) in good yields. The acetonitrile ligand in 3 is labile, permitting its replacement with H(2) (1 bar) to afford the dihydrogen Re(I) complexes [ReCl(2)(NO)(PR(3))(2)(η(2)-H(2))] (4, R = Cy a, iPr b). The catalytic activity of 2, 3 and 4 in hydrogen-related catalyses including dehydrocoupling of Me(2)NH·BH(3), dehydrogenative silylation of styrenes, and hydrosilylation of ketones and aryl aldehydes were investigated, with the main focus on phosphine and halide effects. In the dehydrocoupling of Me(2)NH·BH(3), the phosphine-free complex 2 exhibits the same activity as the bisphosphine-substituted systems. In the dehydrogenative silylation of styrenes, 3a and 4a bearing PCy(3) ligands exhibit high catalytic activities. Monochloro Re(I) hydrides [Re(Cl)(H)(NO)(PR(3))(2)(CH(3)CN)] (5, R = Cy a, iPr b) were proven to be formed in the initiation pathway. The phosphine-free complex 2 showed in dehydrogenative silylations even higher activity than the bisphosphine derivatives, which further emphasizes the importance of a facile phosphine dissociation in the catalytic process. In the hydrosilylation of ketones and aryl aldehydes, at least one rhenium-bound phosphine is required to ensure high catalytic activity.     

过渡金属膦配合物在硅氢化反应中的应用研究

过渡金属膦配合物在有机合成和催化反应中的应用非常广泛, 大量含膦杂原子配体被设计合成, 利用其特定的配位能力, 和过渡金属配位成过渡金属膦配合物, 并测试其对特定有机化学反应的催化性能. 硅氢加成反应是有机硅化学中的重要反应, 多种过渡金属包括铂、钯、铑、钌等的膦配合物对于硅氢加成反应均有催化活性. 综述了近几年来过渡金属膦配合物在硅氢加成反应中的应用进展.