Phosphorus-Chalcogen Ring Expansion and Metal Coordination

The reactivity of
4-membered (RPCh)2 rings (Ch = S, Se) that contain phosphorus
in the +3 oxidation state is reported. These compounds undergo ring
expansion to (RPCh)3 with the addition of a Lewis base.
The 6-membered rings were found to be more stable than the 4-membered
precursors, and the mechanism of their formation was investigated
experimentally and by density functional theory calculations. The
computational work identified two plausible mechanisms involving a
phosphinidene chalcogenide intermediate, either as a free species
or stabilized by a suitable base. Both the 4- and 6-membered rings
were found to react with coinage metals, giving the same products:
(RPCh)3 rings bound to the metal center from the phosphorus
atom in tripodal fashion.