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(μ-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.