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)₅PH₃ (M = Mo, W), W(CO)₅PD₃, and W(CO)₅PF₃ and the results of X-ray structure analyses of W(CO)₅PH₃ and Mo(CO)₅PCl₃ are reported. Quantum-chemical DFT calculations of the geometries and M-P bond dissociation energies of M(CO)₅PX₃ (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 σ donor and a stronger π(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 σ character (65-75%) than π character (25-35%). The M-P bonds of the halophosphane complexes M(CO)₅PF₃ and M(CO)₅PCl₃ are nearly half covalent and half electrostatic. The π bonding contributes ∼50% to the total orbital interaction.