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

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·Ph₂Se₂undergoes 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^IIIbonded 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 transformationviaa Minimum Energy Crossing Point allowing [SePh]˙ transfer to give M^IIMe₂(bipy) and M^IVMe₂(bipy)(SePh)₂. The regenerated M^IIreagent reacts with Ph₂Se₂through the above sequence, allowing completion of reaction to give the M^IVproduct 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)viaexcitation to an M-M antibonding orbital facilates disproportionation of the M^III-M^IIIcomplex to M^IIand M^IVcomplexes.