DFT studies of two-electron oxidation, photochemistry, and radical transfer between metal centres in the formation of platinum(iv) and palladium(iv) selenolates from diphenyldiselenide and metal(ii) reactants

Abstract

The oxidant diphenyldiselenide reacts with M^IIMe₂(bipy) (bipy = 2,2′-bipyridine) to form a pre-equilibrium involving weak adducts, from which [MMe₂(bipy)]₂·Ph₂Se₂ undergoes rate-limiting dissociation of phenylselenide preceded by the oxidative addition step to obtain [Me₂(bipy)M-MMe₂(bipy)(SePh)]⁺. Coordination of PhSe⁻ gives the neutral M^III–M^III bonded dimers [MMe₂(bipy)(SePh)]₂. The dimers fragment in the presence of light to give radicals [M^IIIMe₂(bipy)(SePh)]˙. After reorientation in the solvent cage, the radicals interact to form triplet adducts [M^IIIMe₂(bipy)(SePh)·(bipy)M^IIIMe₂(SePh)]˙˙ with π-stacked ‘SePh·bipy’, followed by transformation via a Minimum Energy Crossing Point allowing [SePh]˙ transfer to give M^IIMe₂(bipy) and M^IVMe₂(bipy)(SePh)₂. The regenerated M^II reagent reacts with Ph₂Se₂ through the above sequence, allowing completion of reaction to give the M^IV product only. The reaction of PtMe₂(bipy) with diphenyldisulfide has been studied in an analogous manner to assist with interpretation of DFT results for reactions of diphenyldiselenide. In short, this study shows that photochemical cleavage of metal–metal bonds (Pd, Pt) via excitation to an M–M antibonding orbital facilates disproportionation of the M^III–M^III complex to M^II and M^IV complexes.