A density functional theory study of dinitrogen bonding in ruthenium complexes

Dinitrogen ruthenium complexes were theoretically studied by means of DFT technique. Several isomers of RuH2(N2)(PH3)2, RuH2(N2)2(PH3)2 and RuH2(H2)(N2)(PH3)2 were studied. Calculations of relative energies, geometrical parameters, vibrational frequencies and natural orbital bond analysis were performed. It is shown that the most stable isomer for each series is characterized by a trans position of the phosphines with the dinitrogen ligand trans to one hydride. As usually observed, the dinitrogen moiety adopts an end-on bonding mode and is weakly elongated from free N2 (generally not >1%). As shown by NBO analysis, such a bonding mode involves σ-donation of about 0.2 electron from the lone pair orbital of the ruthenium-bound nitrogen toward ruthenium and back-donation of roughly 0.2 electron from the 4d occupied orbital of ruthenium to the two πg* dinitrogen orbitals.