A Vanadium Methylidene.

Examples of stable 3d transition metal methylidene complexes are extremely rare. Here we report an isolable and stable vanadium methylidene complex, [(PNP)V(=NAr)(=CH 2 )] (PNP = N[2-P i Pr 2 -4-methylphenyl] - , Ar = 2,6- i Pr 2 C 6 H 3 ), via H atom transfer (HAT) from [(PNP)V(NHAr)(CH 3 )] or [(PNP)V(=NAr)(CH 3 )] using two or one equivalents of the TEMPO radical (TEMPO = (2,2,6,6-tetramethylpiperidin-1-yl)oxyl), respectively. Alternatively, the vanadium methylidene moiety can also be formed via the treatment of transient [(PNP)V=NAr] with the Wittig reagent, H 2 CPPh 3 . Structural and spectroscopic analysis, including 13 C enriched labeling of the methylidene ligand, unequivocally confirmed the terminal nature of a rare 3d methylidene complex, featuring a V=CH 2 bond distance of 1.908(2) Å and a highly downfield 13 C NMR spectral shift at 298 ppm. In the absence of the ylide, intermediate [(PNP)V=NAr] activates dinitrogen to form an end-on bridging N 2 complex, [(PNP)V(=NAr)] 2 (μ 2 -η 1 :η 1 -N 2 ), having a singlet ground state. Complex [(PNP)V(=NAr)(=CH 2 )] reacts with H 3 COTf to form [(PNP)V(=NAr)(OTf)], accompanied by the release of ethylene as evidenced by 1 H NMR spectroscopy, and reactivity studies suggest a β-hydride elimination pathway.