Quantum-Chemical Study of Organophosphorus Ligands Coordinated to Chromium and Nickel Carbonyls

A comparative analysis of the electronic structure of free and coordinated nitrogen- and phosphorus-containing ligands was made. The geometric structures of NR3 and PR3 ligands and carbonyl complexes Cr(CO)₅(XR3) and Ni(CO)₃(XR3) (X = N or P) were optimized by quantum-chemical calculations. Replacement of H atoms in the coordinated NH₃ molecule by organic radicals R decreases the energy of the M-NR3 bond, and replacement of H atoms in PH₃ increases the ligand binding energy. A correlation was found between the metal-phosphine bond energy and the extent of the electron density transfer from the ligand. According to the calculations, the -acceptor power of triphenylphosphine is associated with the population of ^* orbitals of the aromatic system, rather than of phosphorus d orbitals.