STUDY OF HALOGEN EXCHANGE IN ALLYLTIN TRIHALIDES BY 2-DIMENSIONAL SN-119 EXSY NMR

(2-Ethoxycarbonyl)crotylbromodichlorostannane (1) and (2-ethoxycarbonyl)allylbromodichlorostannane (2), two compounds with formula RSnCl(2)Br, were shown by 2D phase-sensitive EXSY Sn-119 NMR to undergo halogen exchange, resulting in equilibrium mixtures of RSnCl(3), RSnCl(2)Br, RSnClBr(2) and RSnBr(3). The unidirectional pseudo-first-order rate constants were determined by two different methods, the initial rate and the exchange matrix resolution approaches. The data show that the exchange proceeds by single halogen exchange, probably occurring through an intermediate involving two organotin trihalide moieties, as evidenced from the linear dependence of the pseudo-first-order rate constants on concentration. The mechanism is briefly discussed.