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 PH 3 (M = Mo, W), W(CO) 5 PD 3, and W(CO) 5 PF 3 and the results of X-ray structure analyses of W(CO) 5 PH 3 and Mo(CO) 5 PCl 3 are reported. Quantum-chemical DFT calculations of the geometries and M−P bond dissociation energies of M(CO) 5 PX 3 (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 PMe 3 ligand forms the strongest and the longest M−P bonds of the phosphane ligands. The analysis of M−PX 3 bonds shows that PCl 3 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 PH 3 and PMe 3 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−PH 3 and M−PMe 3 bonds have more σ character (65−75%) than π character (25−35%). The M−P bonds of the halophosphane complexes M(CO) 5 PF 3 and M(CO) 5 PCl 3 are nearly half covalent and half electrostatic. The π bonding contributes ∼50% to the total orbital interaction.