Kinetics and mechanism of cleavage of sulphur–silicon, –tin, –germanium, and –lead bonds in aqueous dioxan in some organometallic compounds of bivalent sulphur

Abstract

Rates of cleavage have been measured spectrophotometrically for some PhS–MR3 compounds (M = Si, Ge, Sn, and Pb) in neutral and acidic aqueous dioxan. The reactivity sequences are unrelated to the electronegativity of the metals and the ease of cleavage increases in the order Si < Ge < Sn < Pb. The substituent and solvent isotope effects indicate some differences in the cleavage mechanism of these compounds. This is governed by sulphur–metal bond polarization enhanced in the heavier Sn and Pb derivatives by co-ordination between water and the metal. A dual mechanism which fits the experimental results is proposed.