N-Heterocyclic Carbene Functionalized Group 7−9 Transition Metal Phosphinidene Complexes

The N-heterocyclic carbene (NHC) functionalized phosphinidene complexes [(pCy)(IiPr2Me2)RuPMes*] (4), [(pCy)(IiPr2Me2)OsPMes*] (6), and [(Cp*)(IiPr2Me2)RhPMes*] (7) were generated by a double-dehydrohalogenation−ligation sequence of the corresponding primary phosphine complexes with 3 equiv of NHC. The effect of the NHC ligand on the electronic properties of the phosphinidene complexes [(Ring)(NHC)MPH] (8−16), bearing group 7−9 transition metals and cycloheptatrienyl (Cht+), benzene, and cyclopentadienyl (Cp−) as ancillary ligands, was studied by density functional theory. All ligand−M bond energy strengths increase with the order of the transition metal in the periodic table. The metal−carbene bond (M−NHC) is dominated by σ-interaction from the ligand, but the π-interaction is substantial, contributing up to ∼20% of the total orbital interaction arising from metal to ligand π-back-donation. The charged ligands Cht+ and Cp− have notable effects on the total σ- and π-interactions in the M−NHC bond. On going to the right in the periodic table, the structures show an increase in M−NHC bond energy that concurs with the net charge on the phosphorus atom of the MP bond.