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 MIIMe2(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 MIII-MIII bonded dimers [MMe2(bipy)(SePh)]2. The dimers fragment in the presence of light to give radicals [MIIIMe2(bipy)(SePh)]˙. After reorientation in the solvent cage, the radicals interact to form triplet adducts [MIIIMe2(bipy)(SePh)·(bipy)MIIIMe2(SePh)]˙˙ with π-stacked 'SePh·bipy', followed by transformation via a Minimum Energy Crossing Point allowing [SePh]˙ transfer to give MIIMe2(bipy) and MIVMe2(bipy)(SePh)2. The regenerated MII reagent reacts with Ph2Se2 through the above sequence, allowing completion of reaction to give the MIV 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 MIII-MIII complex to MII and MIV complexes.