Ligand non-innocence allows isolation of a neutral and terminal niobium nitride

Abstract

Complex (PNP)NbCl2(N[(t)3u]Ar) (1) (PNP- = N [2-(PPr2)-Pr-i-4-methylphenyl](2); Ar = 3,5-Me2C6H3) reacts with one equiv. of NaN 3 to form a mixture of (PNPN)NbCl2(N[Bu-t]Ar) (2) and (PNP)Nb N(N[Bu-t]Ar) (3), both of which have been spectroscopically and crystallographically characterized, including N-15 isotopic labelling studies. Complex 3 represents the first structurally characterized example of a neutral and mononuclear Nb nitride. Independent studies established 3 to form via two-electron reduction of 2, whereas oxidation of 3 by two-electrons reversed the process. Computational studies suggest the transmetallation step to produce the intermediate [(PNP)NbCl2(N-3)(N[Bu-t]Ar)] (A) which extrudes N2 to form the phosphinimide [(PNP)NbCl2(N-3)(N[Bu-t]Ar)] (B) followed by disproportionation to 2 and low-valent [(PNP)Nb(N-3)(N[Bu-t]Ar)] (C). The latter then undergoes intramolecular N-atom transfer to form the nitride moiety in 3.