A molecular orbital rationalization of ligand effects in N-2 activation

Molecular orbital theory has been used to study a series of [(mu-N-2){ML3}(2)] complexes as models for dinitrogen activation, with M=Mo, Th, W, Re and L = NH2, PH2, AsH2, SbH2 and N(BH2)(2). The main aims of this study have been to provide a thorough electronic analysis of the complexes and to extend previous work involving molecular orbital analyses. Molecular orbital diagrams have been used to rationalize why for L=NH2 ligand rotation is important for the singlet state but not the triplet, to confirm the effect of ligand pi donation, and to rationalize the importance of the metal d-electron configuration. The outcomes of this study will assist with a more in-depth understanding of the electronic basis for N-2 activation and allow clearer predictions to be made about the structure and multiplicity of systems involved in transition-metal catalysis.