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

Summary Trisubstituted silanes, HSiR_3-n X _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 (- 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, k ₁, of the oxidative addition (followed spectrophotometrically) at 20°C in benzene solution and the structure of the trisubstituted silane represented by Stereoelectronic parameters , and E' for the SiR_3-n X _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.Dedicated to Professor K. Rühlmann on the occasion of his 65th birthday. Part XXVII in the series Catalysis of Hydrosilylation; for Part XXVI see Polish J. Appl. Chem., 38, 169 (1994).