Ligand Effects in Dinitrogen Hydrogenation of Binuclear Zirconium Complexes

In this work,we report a theoretical exploration of the ground-state electronic struc-tures and molecular vibrational properties of a series of binuclear zirconium complexes in the framework of density functional theory(DFT)employing the B3LYP hybrid functional.The calculated results reveal that the electronic structure of the complex (η5-C5Me5)2Zr]2(μ2,η2,η2-N2)is unfavorable for hydrogenation due to the exclusion of side-on dinitrogen in the LUMO+1 molecular orbital as compared with the reactant 1(η5-C5Me4H)2Zr]2(μ2,η2,η2-N2).Besides,the structural feature of the hypothetical intermediate 1',(η5-C5Me4H)2Zr]2(μ2,η2,η2-N2)-H2,clearly implies the possibility of further hydrogenation.In addition,the distinguishing of vibrational modes of experimental intermediate 2,(η5-C5Me4H)2ZrH]2(μ2,η2,η2-N2Hz),indicates that the asymmetric stretching of Zr-N and Zr-H leads to dissociation.Moreover,the vibrational intensity of Zr-H is stronger than that of Zr-N.Therefore,it can be predicted that excess hydrogen atmosphere is necessary to ensure the dissociation of Zr-N bonds.