A Mixed-Valent and High-Spin Vanadium Phosphide

Accessing high-spin configurations of transition metal phosphides defines a dividing line that prevents common properties of solid-state materials from being replicated within multiple-bonded molecular analogs. Here, we report the synthesis of a V^III phosphaethynolate complex, [(pyrNdipp)₂V(PCO)] (2) in a halide metathesis with Na(OCP). Exposure of 2 to Lewis-basic ligands induces a one-electron reductive elimination of the PCO^- moiety, generating V^II complexes [(pyrNdipp)₂V(L)₂] (L = THF, DMAP; 3^THF, 3^DMAP). When 2 is instead photolyzed, a cascade of reduction, decarbonylation, and multiple-bond formation steps affords a high-spin and mixed-valent vanadium phosphide, [(pyrNdipp)₂V═P═V(pyrNdipp)₂] (4) comprising formal [V₂^III, IV] nodes. Structural characterization coupled with vibrational, UV-visible, and X-ray spectroscopic studies reveals an S₄ symmetrical [V═P═V] centered architecture conforming to a fully delocalized, mixed-valency description. Theoretical studies demonstrate that 4 evades spin-pairing by leveraging the weak ligand-field splitting at the vanadium nodes, leading to a high-spin, S_T = 3/2 ground state of this multiple-bonded, weakly Jahn-Teller distorted system.