Hydrosilylations chlorotris rhodium

A number of metal complexes catalyze the hydrosilylation of various carbonyl compounds by triethylsilane. Stereoselectivity is observed in the hydrosilylation of ketones as in the reactions of 4-t-butylcyclohexanone and triethylsilane catalyzed by ruthenium, chromium, and rhodium metal complexes (eq 4). Triethylsilane and Chlorotris(triphenylphosphine)rho-dium(I) catalyst effect the regioselective 1,4-hydrosilylation of Q ,/3-unsaturated ketones and aldehydes. Reduction of mesityl oxide in this manner results in a 95% yield of product that consists of 1,4- and 1,2-hydrosilylation isomers in a 99 1 ratio (eq 5). This is an exact complement to the use of phenylsilane, where the ratio of respective isomers is reversed to 1 99. ... 

Catalytic activities of several platinum, palladium, nickel as well as rhodium complexes in hydrosilylation of acetophenone were briefly examined by using methyldichlorosilane, and the platinum(II) complex, [(PhMe2P)PtCl2]2 was found to be the most effective for this particular hydrosilane. Chlorotris(triphenylphos-phine)rhodium(I) (7) has no catalytic activity at all in sharp contrast to the case in which the hydrosilylation is carried out by using alkylhydrosilanes, R SiH4 ( = 1, 2 or 3), as described in the previous Section. 

In Section 4, it is described that chlorotris(triphenylphosphine)rhodium(I) (7) is quite an effective catalyst for the hydrosilylation of carbonyl compounds. For this reason, extensive studies on asymmetric hydrosilylation of prochiral ketones to date have been based on employing rhodium(I) complexes with chiral phosphine ligands. The catalysts all prepared in situ are rhodium(I) complexes of the type, (BMPP>2Rh(S)a (8) [40] and (DIOP)Rh(S)Cl (6) [41], and a cationic rhodium(III) complex, [(BMPP)2lUiH2(S)2] Q04 (5) [42], where S represents a solvent molecule. An interesting polymer-supported rhodium complex (V) [41], and several chiral ferrocenylphosphines [43], recently developed as chiral ligands, have also been employed for asymmetric hydrosilylation of ketones. Included in this section also are selective asymmetric hydrosilylation of a,0-unsaturated carbonyl compounds and of certain keto esters. 

Since the intermediacy of a-siloxyalkyl rhodium complex III (see Scheme 4) is strongly suggested in the hydrosilylation of terpene ketones catalyzed by chlorotris-(triphenylphosphine)rhodium(I) (7), such an intermediate most likely plays a key role in the asymmetric induction of the present system. The fundamental premise is to assume a square-pyramidal structure of the a-siloxyalkyl-rhodium intermediate VI, as shown in equation (18), on the basis of the established structures of dihydrido [46] and of silylhydrido [14, 32c, 47] complexes derived from the Wilkinson s rhodium(I) complex. 

Rh-Catalyzed Hydrosilylation of Alkenes. Treatment of 2-p3Tidyldimethylsilane with 1-alkenes in the presence of a catalytic amount of chlorotris(triphenylphosphine)rhodium gives ter-... 

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