Stereoelectronic effects of substituents at silicon on the hydrosilylation of 1-hexene catalysed by [RhCl(cod)(1-hexene)]

Authors:

• Wojciech Duczmal,
• Elzbieta Śliwińska,
• Beata Maciejewska,
• Bogdan Marciniec,
• Hieronim Maciejewski

Abstract

Trisubstituted silanes, HSiR_3-nX_n (R = Me or Et, X = Cl, OEt, or Ph; n = 0-3) oxidatively add to the complex [RhCl(cod)(1-hexene)] (cod = cycloocta-1,5-diene) to yield [RhCl(cod)(1-hexene)(H)(SiR₃)] [(1)]. Subsequent steps of hydrosilylation follow, i.e. cis-insertion of the alkene (π-σ rearrangement) and then reductive elimination of the product, according to the general Chalk and Harrod scheme. A quantitative correlation between the second order rate constant, k₁, of the oxidative addition (followed spectrophotometrically) at 20°C in benzene solution and the structure of the trisubstituted silane represented by Stereoelectronic parameters χ,θ and E′' for the SiR_3-nX_n groups was established. The maximal hydrosilylation rate followed by g.l.c., is strongly retarded by highly electronegative substituents X on silicon and results from the elimination rate of the hydrosilylation product from (1) and the maximal concentration of (1) in solution. © 1995 Chapman & Hall.