A Transient Vanadium(III) Neopentylidene Complex. Redox Chemistry and Reactivity of the V=CHtBu Functionality

The vanadium(III) bis(neopentyl) complex (PNP)V((CH2Bu)-Bu-t)(2) (PNP = N[4-Me-2-((PPr2)-Pr-i)C6H3](2)(-)), a complex readily prepared from alkylation of (PNP)VCl2 with 2 equiv of LiCH2'Bu, serves as a precursor to the transient vanadium(III) alkylidene complex (PNP)V=(CHBu)-Bu-t. Two-electron oxidation of the intermediate [(PNP)V=CH'Bu] with chalcogen sources results in formation of the vanadium(V) chalcogenide series (PNP)V=(CHBu)-Bu-t(X) (X = O, S, Se, Te). This family of chalcogenide-alkylidenes has been studied via V-51 NMR spectroscopy in combination with DFr computational methods. The redox chemistry of [(PNP)V=CH'Bu] and the reactivity of the alkylidene ligand are explored with the substrates N3SiMe3, N -(CBu)-Bu-t, N-2, and azobenzene. It was discovered that N=N cleavage of the last substrate can be achieved without oxidation of the metal.