On the relative stability of side-on and end-on coordination of dinitrogen to nickel (O): ”ab initio“ calculations on the model compounds [NiN 2] and [Ni(PH 3) 2N 2

Abstract

”Ab initio“ calculations have been performed on the systems NiN 2 and Ni(PH 3) 2N 2 to investigate the relative stability of end-on and side-on coordination of dinitrogen to Ni 0. The results indicate that both the π-back-donation and the reduction in the σ repulsion are important factors in the description of the NiN 2 bonding. In NiN 2, it is possible to reduce efficiently the repulsion by 4s polarization and the dinitrogen can come close enough to nickel in order to reach overlap in the π space for end-on coordination: this favors the end-on bonding with respect to the side-on one. When ligands are present on both sides of nickel, 4s polarization is no loger possible and N 2 cannot come close enough to nickel to allow the best overlap: this disfavors mainly the end-on coordination where a shorter r(NiN) is required and explains the preference for side-on coordination in Ni(PH 3) 2N 2.