Nickel catalysts, hydrosilylation using

Numerous complexes of nickel(II) and nickel(O) catalyze the addition of the Si-H bond to olefins. Among such catalysts are nickel-phosphine complexes, e.g., Ni(PR3)2X2 (where X=C1, I, NO3 R=alkyl and aryl), Ni(PPh3)4, and Ni-(CO)2(PPh3)2, as well as bidentate complexes of NiCl2-(chelate) and Ni(acac)2L (I phosphine), and Ni(cod)2(Pr3)2 [1-5]. A characteristic feature of nickel-phosphine-catalyzed olefin hydrosilylation is side reactions such as H/Cl, redistribution at silicon and the formation of substantial amounts of internal adducts in addition to terminal ones [69]. Phosphine complexes of nickel(O) and nickel(II) are used as catalysts in the hydrosilylation of olefins with functional groups, e.g., vinyl acetate, acrylonitrile [1-4], alkynes [70], and butadiynes [71]. 

The use of activated nickel in hydrosilylation reactions was investigated. Addition of trichlorosilane to 1-hexene occurs quantitatively in 40 min. The interest in this result lies in the possibility of using such a cheap catalyst instead... 

Alkenes. Most Group VIII metals, metal salts, and complexes may be used as catalyst in hydrosilylation of alkenes. Platinum and its derivatives show the highest activity. Rhodium, nickel, and palladium complexes, although less active, may exhibit unique selectivities. The addition is exothermic and it is usually performed without a solvent. Transition-metal complexes with chiral ligands may be employed in asymmetric hydrosilylation 406,422... 

Catalytic hydrosilylation of alkenes performed in the presence of a chiral catalyst results in the formation of chiral silanes. Initially platinium catalysts of the type L PtCl2, L = (/ )-benzyl-(methyl)phenylphosphine (BMPP) or (/ )-methyl(phenyl)propylphosphine and 1,1-disubstituted prostereogenic alkenes, such as a-methylstyrene, 2,3-dimethyl-l-butene and 2-methyl-l-butene, were used however, the stereoselectivity was low4,5. A slightly higher stereoselectivity is obtained when dichlorobis[(/ )-benzyl(methyl)phenylphosphine]nickel [Ni(BMPP)2Cl2] is used as the catalyst. Note that two chiral silanes are formed in this reaction, both of which are products of anti-Markovnikov addition. The major product is the expected dichlorosilane 3, while the byproduct is an anomalous chlorosilane 4 both products were separated by fractional distillation and the major product methylated to give the trimethylsilanes 56 7. 

Nickel metal catalysts give mixtures of the corresponding silyl ether and silyl enol ether. The former is produced via hydrosilylation, while the latter is produced via de-hydrogenative silylation. The reaction catalyzed by zinc chloride proceeds under drastic conditions, and the product of aldehydes disproportionates. The reaction of a,jS-unsatu-rated carbonyl compounds with H2PtCl6 proceeds by 1,4-addition, while coupling is also observed on using metallic Ni as catalyst. ... 

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. 

Asymmetric hydrosilylation of prochiral olefins, e.g. 1,1-disubstituted olefins, catalyzed by chiral phosphine complexes of platinum(II) [21], nickel(II) [22], and palladium(II) [23] has been reported. When a platinum complex of the type [L PtCl2]2, where L stands for (/ )-benzylmethylphenylphosphine (BMPP), was used as catalyst, methyldichlorosilane, but not trichlorosilane, reacted satisfactorily- with a-methylstyrene, 2,3-dimethyl-l-butene, and 2-methyl-l-butene to give the corresponding optically active addition products, RMeC HCH2SiMeCl2, R = Ph, /-Pr,... 

A similar trend can be seen in the homogeneous hydrosilylation of carbon-hetero atom multiple bonds, which has not received sufficient attention. Although the catalytic hydrosilylation of carbonyl compounds using zinc chloride [29], nickel metal [30] or chloroplatinic acid [31] as catalyst has so far been studied, the reaction conditions were rather drastic and side reactions were often observed. 

Montgomery and coworkers have also reported the hydrosilylation of ketones using a carbohydrate-derived silane (Figure 13.30) [72]. A nickel(0)-IMes catalyst... 

Regarding the use of well-defined nickel complexes as catalysts for reduction of carbonyl groups, only three examples are described in the literature. In 2009, Guan and coworkers [77] described the efficiency of a nickel PCP-pincer complex performing the hydrosilylation of aldehydes. In the same year, the catalytic hydrosilylation of ketones via a transient Ni-H complex supported by a monoanionic bidentate amidophosphine ligand was reported by Mindiola [78]. Later, Jones investigated well-defined PNP nickel pincer complexes, which catalyzed the hydrosilylation of aldehydes [79] (Fig. 10.16). 

Hydrosilanes undergo addition to carbon-carbon multiple bonds under catalysis by transition metal complexes. Nickel, rhodium, palladium, and platinum were used as catalytically active metals. By incorporating chiral ligands into the metal catalyst, the hydrosilylation can be performed analogously to other addition reactions with double bonds, for example, asymmetric hydrogenation to obtain optically active alkylsilanes. 

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