Phosphorus‐Atom Transfer from Phosphaethynolate to an Alkylidyne

A low-spin and mononuclear vanadium complex, ((Me)nacnac)V(CO)(η(2)–P≡C(t)Bu) (2) ((Me)nacnac(−) = [ArNC(CH(3))](2)CH, Ar = 2,6-(i)Pr(2)C(6)H(3)), 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(CH(2))]CH[C(CH(3))NAr])V(CO)(η(2)–P≡C(t)Bu)} (4), was obtained via the reaction of Na(OCP)(diox)(2.5) and ([ArNC(CH(2))]CH[C(CH(3))NAr])V≡C(t)Bu(OEt(2)) (3) in the presence of crown–ether. Computational studies suggest the P–atom transfer to proceed by [2+2]–cycloaddition of the P≡C bond across the V≡C(t)Bu moiety, followed by a reductive decarbonylation to form 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.