Mechanistic investigation and new catalyst design in palladium- and platinum-catalyzed Se-Se bond addition to alkynes

The present study explains the different catalytic activities of platinum and palladium in Se−Se addition reactions with alkynes. Under the catalytic conditions cis-[Pt(SePh)2(PPh3)2] undergoes fast isomerization to the trans isomer, which does not react with alkynes. Palladium complexes maintain their catalytic activity, due to the formation of the dinuclear structure [Pd2(SePh)4(PPh3)2]. It was shown that the palladium intermediate involved in the catalytic cycle can be prepared directly in the reaction mixture starting from the simple [PdCl2(PPh3)2] precursor, thus allowing replacement for the traditional Pd(PPh3)4 catalyst. X-ray analysis shows that the products of Se−Se addition reactions with alkynes possess the necessary geometry parameters for coordination as bidentate ligands.