Alkyl Halide Transfer from Palladium(IV) to Platinum(II) and a Study of Reactivity, Selectivity, and Mechanism in This and Related Reactions

Kinetic studies of the oxidative addition of MeI or PhCH2Br to [MMe2(L2)] (M = Pd or Pt, L2 = 2,2'-bipyridine or 1,lO-phenanthroline) indicate that the reactions occur by the SN2 mechanism, and the reactions occur 7-22 times faster when M = Pt over Pd and 1.2-2.2 times faster when L2 = phen over bpy. Reductive elimination from [PdBrMe2(CH2Ph)(L2)] in the solid state occurs to give both Me-Me and PhCH2Me, and there is a preference for methyl group loss. Thermochemical studies indicate that CH3-CH3 loss gives DH = -108 +/- 4 kJ mol-' but PhCH2-CH3 loss gives DH = -48 +/- 12 kJ mol-', indicating a relatively strong PhCH2-Pd bond. The complexes [PdIMe3(L2)] or [PdBrMe2(CH2Ph)(L2)] react rapidly with [PtMe2(L2)] by alkyl halide transfer. Kinetic studies have shown that the major route involves loss of halide from palladium(IV) in a preequilibrium step, followed by SN2 attack by [PtMe2(L2)] on an alkyl group of [PdMe3(L2)]+ or [PdMe2(CH2Ph)(L2)]+. In the latter case, benzyl group transfer is preferred over methyl group transfer.