Nature of the metal-ligand bond in M(CO)5PX3 complexes (M = Cr, Mo, W;: X = H, Me, F, Cl):: Synthesis, molecular structure, and quantum-chemical calculations

The syntheses of the phosphane complexes M(CO)(5)PH3 (M = MO, W), W(CO)(5)PD3, and W(CO)(5)PF3 and the results of X-ray structure analyses of W(CO)(5)PH3 and Mo(CO)(5)PCl3 are reported. Quantum-chemical DFT calculations of the geometries and M-P bond dissociation energies of M(CO)(5)PX3 (M = Cr, Mo, W; X = H, Me, F, Cl) have been carried out. There is no correlation between the bond lengths and bond dissociation energies of the M-P bonds. The PMe3 ligand forms the strongest and the longest M-P bonds of the phosphane ligands. The analysis of M-PX3 bonds shows that PCl3 is a poorer sigma donor and a stronger pi(P) acceptor than the other phosphanes. The energy decomposition analysis indicates that the M-P bonds of the PH3 and PMe3 complexes have a higher electrostatic than covalent character. The electrostatic contribution is between 56 and 66% of the total attractive interactions. The orbital interactions in the M-PH3 and M-PMe3 bonds have more sigma character (65-75%) than T character (25-35%). The M-P bonds of the halophosphane complexes M(CO)(5)PF3 and M(CO)(5)PCl3 are nearly half covalent and half electrostatic. The pi bonding contributes similar to50% to the total orbital interaction.