Redox Activity in a Vanadium(V)–o‐Dioxolene Complex Is Modulated by Protonation State As Indicated by 51V Solid‐State NMR Spectroscopy and Density Functional Theory

Abstract

AbstractMost known vanadium(V) complexes with redox‐active o‐dioxolene ligands are non‐innocent. Since the vanadium(V) complex [VO(gsal)(HCat)] is innocent, its properties were investigated by 51V solid‐state NMR spectroscopy and density functional theory (DFT). The innocent ligand behavior manifested itself by the upfield isotropic chemical shift and large negative chemical shift anisotropy observed in the solid state. The electronic structure and NMR spectroscopic parameters of this complex were addressed by DFT calculations and found to be consistent with the NMR spectroscopic observations indicating that the complex is redox‐inactive. The observed increase in the HOMO–LUMO gap for the innocent complex is concomitant with the 51V NMR chemical shift of –460 ppm and consistent with the high redox stability of this molecule. The stabilization was traced to the overall charge of [VO(gsal)(HCat)] facilitated by the coordination of the minus‐one‐charged o‐dioxolene ligand and rendering the overall complex neutral. These studies suggest that protonation may prove to be an effective way in which vanadium(V) complexes with redox‐active ligands can be stabilized.