Photochemical reaction of benzoyltrimethylsilane with substituted phenylsilanes

Photochemical reaction of benzoyltrimethylsilane (I) with substituted phenylsilanes, XC6H4SiH3 (X = m-CF3, m-Cl, pCl, H, m-Me, p-Me-p-MeO) (II), gave [α-(trimethylsiloxy)benzyl]arylsilanes (III) in excellent yields, the formation of which can be accounted for in terms of the insertion reaction of the siloxycarbene, Me3SiO+C̄Ph (IV), derived by photoisomerization of I into the SiH bond of the arylsilanes (II). Relative rates of m- and p-substituted phenylsilanes toward the attacking species correlated well with Hammett σ values and gave a ϱ of +1.82. The correlation with Taftσ★ values for the aryl group on the central silicon gave a ϱ★ value of +2.34. It was found that hydrogen isotope effect in the reaction if very small (solkHkD = 1.26 ± 0.10). From these results the reaction mechanism is discussed.