Activation of atmospheric nitrogen and azobenzene N=N bond cleavage by a transient Nb(III) complex.

Atmospheric N2 is activated by two transient Nb(III) "(PNP)NbCl2" (PNP- = N[2-P(CHMe2)2-4-methylphenyl]2) fragments to form the bridging diimido [(PNP)NbCl2]2(mu-N2) (1). Complex 1 can also be independently synthesized from Nb(IV) and Nb(V) precursors via one-electron and transmetalation reactions, respectively. In the presence of azobenzene, the transient Nb(III) intermediate, prepared from Li(PNP) and NbCl3(DME) (DME = dimethoxyethane) under Ar, cleaves the N=N bond via a metal-ligand cooperative four-electron reduction to form niobium imide and phosphoranimine functionalities. Structural studies are presented and discussed for various Nb systems bearing the pincer-type framework PNP as well as the N2 and azobenzene activated products. Theoretical studies addressing the Nb-N2-Nb core in 1 are also presented.