Secondary Kinetic Isotope Effects in Oxidative Addition of Benzyl Bromide to Dimethylplatinum(II) Complexes

Abstract

The secondary α-deuterium kinetic isotope effects (KIEs), (kH/kD)α, have been determined, at different temperatures and in solvents having different polarities, for reaction of PhCH2Br/PhCD2Br with the dimethylplatinum(II) complexes [PtMe2(NN)], in which the bidentate NN ligand is bpy (=2,2′-bipyridine) or bu2bpy (=4,4′-di-tert-butyl-2,2′-bipyridine). The values obtained for the secondary α-deuterium KIEs in acetone solution are close to 1 and may be normal or inverse, but much larger values are found for the reactions in benzene. An explanation is presented on the basis of solvent dependence of the degree of looseness of the transition state in the SN2 mechanism.