Does dinitrogen hydrogenation follow different mechanisms for[[[([eta.sup.5]-[C.sub.5]M[e.sub.4]H).sub.2]Zr].sub.2]([mu.sub.2],[eta.sup.2],[eta.sup.2]-[N.sub.2] and [{[Php(C[H.sub.2]SiM[e.sub.2]NSiM[e.sub.2]C[H.sub.2])PPh]Zr}.sub.2]([mu.sub.2],[eta.sup.2],[eta.sup.2]-[N.sub.2] complexes? A computational study

The detailed computation study of the mechanism of dinitrogen hydrogenation in the Chirik-type complex [[[([eta.sup.5]-[C.sub.5]M[e.sub.4]H).sub.2]Zr].sub.2]([mu.sub.2],[eta.sup.2],[eta.sup.2]-[N.sub.2] and the Fryzuk-type complex [{[Php(C[H.sub.2]SiM[e.sub.2]NSiM[e.sub.2]C[H.sub.2])PPh]Zr}.sub.2]([mu.sub.2],[eta.sup.2],[eta.sup.2]-[N.sub.2] was carried out to observe difference in their reactivity. The observed difference in the reactivity of these dizirconium complexes is caused by the former ligands rigid environment than the latter which results in the addition of the first [H.sub.2] molecule to two different products: a non-H-bridged intermediate for the Chirik-type complex and a H-bridged intermediate for the Fryzuk-type complex.