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

The N-heterocyclic carbene (NHC) functionalized phosphinidene complexes [(pCy)((IPr2Me2)-Pr-i)Ru=PMes*] (4), [(pCy)((IPr2Me2)-Pr-i)OS=PMeS*] (6), and [(Cp*)((IPr2Me2)-Pr-i)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 sigma-interaction from the ligand, but the pi-interaction is substantial, contributing up to similar to 20% of the total orbital interaction arising from metal to ligand pi-back-donation. The charged ligands Cht(+) and Cp- have notable effects on the total sigma- and pi-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.