The Chemistry of Vanadium bis-Phenolate NHC Complexes in Three Oxidation States

Twenty-one vanadium bis-phenolate benzimidazolylidene complexes, spanning three oxidation states, have been investigated. Special emphasis is placed on their salt metathesis reactivity and the accessibility of the +IV oxidation state by reductive or oxidative routes, starting from vanadium(V) or vanadium(III) respectively. While the reductive route is highly dependent on the reducing agent and starting material used, the oxidative route gives clean access to vanadium(IV) dihalide complexes. The low-valent vanadium(III) complexes are excellent precursors for salt metathesis reactions which lead to the isolation of a rare vanadium(III) NHC alkyl complex. All new complexes have been characterized by (paramagnetic) H-1 NMR and V-51 NMR, UV-VIS, IR and EPR spectroscopy as well as elemental analysis. Cyclic voltammetry has been performed in selected cases to study the influence of imido or phenolate supporting ligands towards the redox-potential of the vanadium(V/IV) redox couple compared to the parent oxo-chlorido complex A.