Carbon−Phosphorus Bond Cleavage in Allyldiphenylphosphine by a Heterobimetallic NiMo Complex and Formation of an Electronically Unsaturated NiMo₂ μ-Diphenylphosphido Cluster

The unsaturated nickel−molybdenum complex [(η-C5Me5)NiMo(CO)3(η-C5H5)] (NiMo), 1, reacts with allyldiphenylphosphine (ADPP) to give the complex [(η-C5Me5)Ni(μ-CO)2Mo(CO)(κ1(P)-PPh2CH2CHCH2)(η-C5H5)] (Ni−Mo), 2, which is in equilibrium with the starting materials at ambient temperature. Nevertheless, orange crystals of complex 2 could be isolated from the solution, and a single-crystal X-ray diffraction study confirmed that the phosphine ligand is bound to the molybdenum atom via the phosphorus atom alone. Prolonged heating of complex 1 with excess ADPP led to activation of the P−Callyl bond and to the isolation of the unsaturated trinuclear NiMo2 μ-diphenylphosphido cluster [(η-C5Me5)NiMo2(η-C5H5)2(μ3-CO)(μ-PPh2)(CO)2], 3. The structure of this 46-electron cluster was established spectroscopically and by a single-crystal X-ray diffraction study. It is electronically unsaturated and contains a formal MoMo double bond that is spanned by a μ-PPh2 ligand; the molecule exhibits effective mirror plane symmetry in solution, and in the solid state, an approximate mirror plane is also observed.