Ten-electron coordination and reactivity of an arylphosphinidene ligand.

Photochemical decarbonylation of [Mo2Cp2(μ-PR*)(CO)4] (Cp = η5-C5H5; R* = 2,4,6-C6H2tBu3) gives [Mo2Cp2(μ-κ1:κ1,η6-PR*)(CO)2], which shows the first example of a remarkable 10-electron donor arylphosphinidene ligand which bridges two Mo atoms through its phosphorus atom while being π-bonded to one Mo center through the six carbon atoms of the aryl ring. This causes a severe pyramidal distortion of the P-bound C atom. The complex adds CO to give [Mo2Cp2(μ-κ1:κ1,η4-PR*)(CO)3], which has an 8-electron donor PR* ligand, and then the parent complex [Mo2Cp2(μ-PR*)(CO)4]. Protonation of [Mo2Cp2(μ-κ1:κ1,η6-PR*)(CO)2] gives the hydride [Mo2Cp2(H)(μ-κ1:κ1,η6-PR*)(CO)2]+, which undergoes P−C bond cleavage and hydride migration, affording the phosphido cation [Mo2Cp2(μ-P)(η6-R*H)(CO)2]+.