The reaction of triphenylmethyl halides with triphenylphosphine in cumene and tert-butylbenzene

Abstract

Reactions of triphenylmethyl bromide and chloride with triphenylphosphine at elevated temperatures under argon furnish mixtures of the reductive dehalogenation product triphenylmethane and the tele substitution products 2a or 2b, the ratio of the products depending on the reaction conditions. The formation of triphenylmethane indicates that the reaction is, at least partly, initiated by halophilic attack [eqn. (2)] or by single-electron-transfer (SET) from the phosphine [eqn. (5)]. The resulting triphenylmethanide anions or triphenylmethyl radicals would then be converted into triphenylmethane by proton or hydrogen abstraction [eqns. (4) and (6), respectively] or recombine with their phosphorus containing co-products to yield the tele substitution products [eqns. (3a) and (7), respectively]. The latter could, at least partly, also be formed via eqn. (1a). Exclusive operation of the SET initiated mechanisms of formation of both products has been proved by combination of trapping studies with molecular oxygen and proof of the absence of triphenylmethanide anions from the reaction mixtures.