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^*)(IⁱPr₂Me ₂)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.