The Role of the d Orbitals of the Phosphorus Atom in the Metal-Phosphine Coordination Bond

Abstract Ab initio calculations carried out on PX3 (X = CH3, H and F) ligands and on the (PX3)2Pt complexes have shown that the d orbitals of the phosphorus atom may be important for an improved description of the molecular geometry and stability, since they produce a sizeable shortening of the M–P bond. However, the occupancy of the d orbitals is small, both in free and coordinated ligands, a fact which excludes a significant spd hybridization. The analysis of the electronic wavefunctions determined with and without d functions on the P atoms reveals that the π back-bonding mechanism has an increasing importance along the series CH3, H, F, in agreement with the common chemical expectation. However, the results definitely show that the d functions on P atoms are unimportant in determining the extent of the metal-to-phosphine backbonding.