ON THE STRUCTURE OF TRANSITION-METAL NITROGEN COMPLEXES

The structures of linear, bent and side-on coordinated dinitrogen fragments to transition metals have been investigated using the frontier orbital approach. The linear M-N-N structures are discussed on the basis of ReCl2(PR3)3NNR'; the main interactions between the NNR'-fragment and the ReCl2(PR3)3+ fragment are between the antibonding pi-N-N-* orbitals and the metal d(xz) and d(yz) orbitals. The bent structures are discussed on the basis of RhCl(PR3)3NNR'+. The essential difference between the linear and the bent M-N-N complexes is the presence of a two-orbital four-electron interaction in the latter type of complexes, which causes the long M-N bond lengths for the bent complexes compared with the linear ones. Other types of linear and bent complexes are discussed, and also complexes with both a linear and a bent M-N-N functionality are analyzed. The orbital population and atomic charge changes when moving from a linear to a bent M-N-N structure are also discussed. The reactivity of some M-N-N complexes is also presented. The side-on coordinated M(NR-NR2) structures are analyzed for complexes containing either a d0 or a d2 metal.