A Transient Vanadium(III) Neopentylidene Complex. Redox Chemistry and Reactivity of the VCH^tBu Functionality

The vanadium(III) bis(neopentyl) complex (PNP)V(CH₂^tBu)₂ (PNP = N[4-Me-2-(PⁱPr₂)C₆H₃]₂⁻), a complex readily prepared from alkylation of (PNP)VCl₂ with 2 equiv of LiCH₂^tBu, serves as a precursor to the transient vanadium(III) alkylidene complex “(PNP)VCH^tBu”. Two-electron oxidation of the intermediate [(PNP)VCH^tBu] with chalcogen sources results in formation of the vanadium(V) chalcogenide series (PNP)VCH^tBu(X) (X = O, S, Se, Te). This family of chalcogenide−alkylidenes has been studied via ⁵¹V NMR spectroscopy in combination with DFT computational methods. The redox chemistry of [(PNP)VCH^tBu] and the reactivity of the alkylidene ligand are explored with the substrates N₃SiMe₃, NC^tBu, N₂, and azobenzene. It was discovered that NN cleavage of the last substrate can be achieved without oxidation of the metal.