Phosphorus-Atom Transfer from Phosphaethynolate to an Alkylidyne.

A low-spin and mononuclear vanadium complex, ( nacnac)V(CO)(η -P≡C Bu) (2) ( nacnac =[ArNC(CH )] CH, Ar=2,6- Pr C H ), was prepared upon treatment of the vanadium neopentylidyne complex ( nacnac)V≡C Bu(OTf) (1) with Na(OCP)(diox) (diox=1,4-dioxane), while the isoelectronic ate-complex [Na(15-crown-5)]{([ArNC(CH )]CH[C(CH )NAr])V(CO)(η -P≡C Bu)} (4), was obtained via the reaction of Na(OCP)(diox) and ([ArNC(CH )]CH[C(CH )NAr])V≡C Bu(OEt ) (3) in the presence of crown-ether. Computational studies suggest that the P-atom transfer proceeds by [2+2]-cycloaddition of the P≡C bond across the V≡C Bu moiety, followed by a reductive decarbonylation to form the V-C≡O linkage. The nature of the electronic ground state in diamagnetic complexes, 2 and 4, was further investigated both theoretically and experimentally, using a combination of density functional theory (DFT) calculations, UV/Vis and NMR spectroscopies, cyclic voltammetry, X-ray absorption spectroscopy (XAS) measurements, and comparison of salient bond metrics derived from X-ray single-crystal structural characterization. In combination, these data are consistent with a low-valent vanadium ion in complexes 2 and 4. This study represents the first example of a metathesis reaction between the P-atom of [PCO] and an alkylidyne ligand.