Phosphorus-Atom Transfer from Phosphaethynolate to an Alkylidyne

A low-spin and mononuclear vanadium complex, (^Me nacnac)V(CO)(η² -P≡C^t Bu) (2) (^Me nacnac^- =[ArNC(CH₃ )]₂ CH, Ar=2,6-ⁱ Pr₂ C₆ H₃ ), was prepared upon treatment of the vanadium neopentylidyne complex (^Me nacnac)V≡C^t Bu(OTf) (1) with Na(OCP)(diox)_2.5 (diox=1,4-dioxane), while the isoelectronic ate-complex [Na(15-crown-5)]{([ArNC(CH₂ )]CH[C(CH₃ )NAr])V(CO)(η² -P≡C^t Bu)} (4), was obtained via the reaction of Na(OCP)(diox)_2.5 and ([ArNC(CH₂ )]CH[C(CH₃ )NAr])V≡C^t Bu(OEt₂ ) (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^t 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.