Homolytic organometallic reactions. Part XI. The reactions of t-butoxyl radicals and of ketone triplets with organotin compounds

Abstract

Whereas t-butoxyl radicals react with tetra-alkyltins at the α-hydrogen centres, the presence of electronegative ligands X in the compounds R_nSnX_{4 –n}(X = halide or carboxylate; n= 1–3) directs attack to the tin atom [equation (i)]. If the t-butoxyl radical is generated by photolysis of di-t-butyl peroxide, the displaced radical R·, Bu^tO·+ R_nSnX_{4 –n}+ [graphic omitted] Bu^tOSnR_{n– 1}X_{4 –n}+ R·(i) can be observed by e.s.r. spectroscopy. If the t-butoxyl radical is derived from t-butyl hypochlorite, a chain reaction is established with reactions (i) and (ii) as the propagating steps. For tripropyltin chloride, k_i= 10^6·88 exp (-1·130/θ)| mol^–1 s^–1(θ= 2·303RT), and k₁(30°)= 1·1 × 10⁶| mol^–1 s^–1. Ketone triplets similarly bring, R·+ Bu^tOCl → RCl + Bu^tO·(ii) about an S_H2 reaction at the tin centre [equation (iii)]. For tripropyltin chloride and acetophenone, k_iii= 4·0 × 10⁸| mol^–1 s^–1, and for p-methylacetophenone, k_iii= 2·2 × 10⁸| mol^–1 s^–1 at room temperature, both, R₂¹CO^T+ R²_nSnX_{4 –n} [graphic omitted] R₂¹COSnR²_{n– 1}X_{4 –n}+ R²·(iii) with a quantum yield of 0·13.