Hydrosilylation of Olefins and Acetylenes

In this section the hydrosilylation of olefins and acetylenes promoted by transition metal catalysts is described and some newer aspects of the reaction are disclosed. 

Although extensive studies on the hydrosilylation of olefins and acetylenes have been performed in the last four decades, that of carbon-heteroatom multiple bonds had... 

The bis-silylation of olefins and acetylenes is a potentially desirable reaction on account of the fact that two C-Si bonds are generated in one step. Intramolecular versions would also be attractive. The reaction is analogous to the tethered hydrosilylation described above but has received less attention. One of the major problems which had to be over-... 

The complex [PtCl2(styrene)2] is a catalyst precursor for the hydrosilylation of terminal olefins and acetylenes, the reduction of carbonyl functions (with pyridine or amines as co-catalysts), and for the formation of RaSiOR from RaSiH and alcohols. During the hydrosilylation the complex is reduced to [Pt(styrene)3], which could not be isolated but was characterized by While... 

Phosphine complexes of nickel are used as catalysts in the hydrosilylation of olefins with functional groups, such as vinyl acetate, acrylonitrile, and methylacrylate, as well as in the hydrosilylation of acetylene derivatives. 

Hydrosilylations are the reactions in which silanes are added to olefins or acetylenes. Hydros lylations are able to proceed at high temperatures and pressures in the absence of catalysts. However, usually the reactions are carried out with catalysts. It is considered that, with UV or y-radiation and a peroxide as the catalysts, radical reactions proceed. On the other hand, with tertiary amines and platinum or palladium compounds as the catalysts, ionic reactions proceed. In particular, platinum catalysts show high reactivities, and the side reaction of olefin polymerization is small [10,12]. The reactions with olefins and acetylenes are shown in eqs. (8.13) and (8.14), respectively. 

Hydrosilylation is formally the addition of the units of R3Si and H (R may be alkyl, alkoxy, or halide) to an unsaturated group such as an olefin, acetylene, or ketone, e.g.,... 

The reaction between olefins or acetylenes with silicon hydrides in the presence of phosphinenickel complexes has been studied for a variety of substituents on the phosphine and on the silane. In many cases two products are obtained, one of them is the expected simple adduct and the other is an adduct, the formation of which has involved an interchange of hydrogen and chlorine on silicon in the course of hydrosilylation (206) Eq. (90). When methyldichlorosilane was added to octene-1 at temperatures in excess of 120°, the two silanes obtained were CgHi7SiMeClH and CgHi7SiMeCl2. The results outlined in Table II... 

According to the first information on the catalysis of hydrosilylation by orga-noactinide complexes Cp 2A Me2 (where A = Th, U), they are efficient for hydrosilylation of terminal alkynes [82]. All catalytic and kinetic examinations of catalysis by early (d°) transition metal complexes (also by metal complexes with non-Cp ligands, e.g., [83]) support the generally accepted mechanism involving rapid olefin (acetylene) insertion into an M-H bond followed by a... 

Familiar combinations include Y = H, X = olefin, acetylene, or diene Y = alkyl, X = CO Y = OH or OR, X = CO or olefin. Such reactions constitute important routes for addition to unsaturated molecules, and thus play a widespread role in catalytic reaction processes such as hydrogenation, hydrosilylation, and hydrocyanation of olefins, car-bonylation, etc. ... 

The hydrosilylation of acetylenic bonds is faster than that of olefinic bonds, and vinylacetylene is chemoselectively hydrosilylated to give l-silylbuta-l,3-diene ... 

Aspects of the rhodium-catalysed hydroformylation of olefins have been reviewed. " Copper(ii) acetate catalyses the highly stereoselective solvolysis of -alkenylpentafluorosilicates to -alkenyl ethers under an atmosphere of air. Since the pentafluorosilicates can be obtained via hydrosilylation of acetylenes, the sequence represents a regio- and stereo-selective transformation of acetylenes into carbonyl precursors in moderate yield. The reaction of vinylmercurials and mercury carboxylates catalysed by palladium(ii) acetate provides a stereospecific route to enol carboxylates, which are valuable precursors of specific enolates. ... 

The examples of hydrometalations are hydroboration [64,72-77], hydrosilylation [78], etc. [78,79] of unsaturated compounds such as olefins, acetylenes, carbonyls and imines. For example, styrene reacts with catecholboran in the presence of a rhodium catalyst to afford stereoselectively the R isomer of 2-phenylethanol as shown in eq. (18.34) [72]. 

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