A theoretical study on the co-ordination of dinitrogen and related molecules to nickel(0): ‘ab initio’ calculations on the model compounds [Ni(PH3)2(N2)], [Ni(PH3)2(N2CH2)], and [Ni(PH3)2(N2H2)]
Abstract
‘Ab initio’ calculations have been performed on the systems Ni(PH3)2L, with L = N2, N2CH2, or N2H2, to investigate the nature and the energetics of the interaction between nickel and dinitrogen or related molecules. The results indicate that the bonding between the fragment Ni(PH3)2 and the unsaturated molecule can be explained by the Chatt–Dewar–Duncanson model, although π back donation is much more relevant than σ donation. Dinitrogen prefers to bind to the fragment Ni(PH3)2 in a side-on fashion rather than in an end-on one, since the former mode implies a more pronounced π back donation than the latter. The most efficient electron transfer from the metal to the dinitrogen, therefore, is achieved by side-on bonding and this point is particularly relevant to nitrogen fixation. Also diazomethane prefers to bind in a side-on mode because of the increased π back donation. This molecule gives rise to a stronger bond than dinitrogen with the fragment Ni(PH3)2 since it is a better π-acceptor ligand. The species N2H2 prefers to bind in a η2-di-imide form rather than in a σ-hydrazido(2–) one and this may account for the hydrogenation of side-on bonded dinitrogen, and provides some information on the problem of nitrogen reduction.