A Vanadium Methylidene
Shuruthi Senthil, Dominik Fehn, Michael R. Gau, Alexandra M. Bacon, Patrick J. Carroll, Karsten Meyer, Daniel J. Mindiola
Abstract
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.