CO, CS, N2, PF3, AND CNCH3 AS SIGMA-DONORS AND PI-ACCEPTORS - THEORETICAL-STUDY BY THE HARTREE-FOCK-SLATER TRANSITION-STATE METHOD

Hartree-Fock-Slater calculations have been carried out on Ni(CO)3L for a number of different ligands (L) in order to investigate the abilities of the ligands to act as σ donors and π acceptors. The order, based on extent of electron transfer, • for σ donation is CS ≃ CO > CNCH3> N2~ PF3and for ir back-bonding is CNCH3> CS > CO > PF3> N2. The contributions to the total bonding energy between Ni(CO)3and L from σ donation and π back-donation are evaluated by the Hartree-Fock-Slater transition-state method, and the same method is used to optimize the Ni-L bond distances. Calculations on the stretching frequency vCo of carbon monoxide complexed to Ni(CO)3showed that vCo is decreased by the 7r back-donation but is increased by the steric interaction energy between Ni(CO)3and CO. Thus the decrease in vCo is not a reliable measure of the extent of π back-bonding in the metal-ligand bond. The calculated influence on ycofrom a donation was negligible. © 1979, American Chemical Society. All rights reserved.