Vanadium(V/IV) Oxido Complexes: Potential as Bases in Frustrated Lewis Pairs

Frustrated Lewis Pairs (FLP) have found exciting access in catalysis and small molecule activation. Here, we describe the potential of two vanadium(V) oxido complexes with monoanionic bidentate N,O donors, [VOCl(L^CF3)₂] (1 a), [VOCl(L^H)₂] (1 b) as bases in FLPs. Upon reaction of 1 a with the Lewis acid B(C₆F₅)₃ the FLP [VOCl(L^CF3)₂]/B(C₆F₅)₃ (1 a/B(C₆F₅)₃) was observed. Addition of Ph₃SiH led to the reduction of V^V to V^IV under formation of the adduct [V{OB(C₆F₅)₃}(L^CF3)₂] (2 a) while FLP reactivity was not observed. Dissolving 2 a in CH₃CN leads to the V^IV oxido complex, [VO(L^CF3)₂] (3 a). In contrast, when 1 b was reacted with B(C₆F₅)₃, a V^IV oxido complex [VO(L^H)₂] (3 b) was obtained. Upon addition of B(C₆F₅)₃ to 3 b no reaction leading to the expected adduct such as 2 a could be observed. Only few crystals deriving from a disproportion reaction could be identified as an adduct dimer [V{OB(C₆F₅)₃}L^H(μ-O)]₂. While FLP reactivity could not be found yet with the described systems, the redox labile nature and versatility of the metal complexes are demonstrated.