KINETICS AND MECHANISMS OF CLEAVAGE OF ALLYLIC DERIVATIVES OF GROUP IVA ELEMENTS BY MERCURIC SALTS .1. ALLYLSILANES

The kinetics and mechanism of cleavage of trimethylallyl silane and its derivatives by mercuric salts have been investigated in solvent acetonitrile. The reaction was followed by spectrophotometric and gas chromatographic methods. The stoichiometry of the reaction is not that of a simple bimolecular process, and is best represented by the reaction scheme: {A figure is presented} A second molecule of substrate is rapidly attacked by Me3SiX formed in the rate determining step. Separate examination of (2) revealed that reaction occurred in the absence of mercuric salts. Me3SiX was not consumed during the process but acts as a catalyst, resulting in first order kinetic behaviour. Mercuric salts strongly catalyse this step, acting as Lewis acids, and enhancing the already polar nature of Me3SiX. Rate constants were calculated for (1) from chromatographic data, adopting the above reaction scheme. The reaction was found to be first order in both substrate and electrophile. Spectrophotometric studies indicated that (1) proceeded via a π complex, the rate of decomposition of which corresponded with that obtained by chromatographic techniques, thus supporting the proposed mechanism. In addition, evidence is presented which supports an SE2 rather than SF transition state for (1). © 1968.