Quantum-chemical study of organophosphorus ligands coordinated to chromiumand nickel carbonyls

A comparative analysis of the electronic structure of free and coordinated nitrogen- and phosphorus-containing ligands was made. The geometric structu res 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. Repl acement of H atoms in the coordinated NH3 Molecule by organic radicals R de creases the energy of the M-NR3 bond, and replacement of H atoms in PH3 inc reases 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 pi -acceptor power of triph enylphosphine is associated with the population of pi* orbitals of the arom atic system, rather than of phosphorus d orbitals.