⁹³Nb NMR Characterization of Nb(V) Perfluoropinacolate Complexes and Their Reactivity

Six new niobium complexes supported by bidentate, dianionic perfluoropinacolate, ({OC(CF3)2}2)2–, denoted as pinF, have been synthesized and fully characterized: [Nb(NMe2)(NHMe2)(pinF)2] (1), (Me2NH2)[Nb(pinF)3] (2), {K(THF)3}[Nb(pinF)3] (3), {K(THF)3}2[Nb2(μ2-O)2(pinF)4] (4), {K(18C6)(THF)2}2[Nb2(μ2-O)2(pinF)4] (5), and {K3(MeCN)7}[Nb2(μ2-O)2(pinF)4] (6). Cyclic voltammetry was used to determine the Nb5+/4+ redox potentials in the all-O-donor environments of 2, 3, 4, and 5. One-electron reduction of the {Nb2(μ2-O)2(pinF)4} dimer formed the mixed-valent complex 6. This reduced {NbOx} compound is unique in having (1) a formal oxidation state lower than 5+ and (2) a coordination number lower than eight. SCXRD, solution UV–Vis spectroscopy and DFT data support the Robin-Day classification of 6 as a Class II dimer. Each of the soluble {Nb5+(pinF)} complexes exhibit solution-state 93Nb NMR resonance features that complement previous 93Nb NMR measurements made with static/MAS methods. The heteroleptic complex 1 was found to selectively dehydrate 2° and 3° alcohols to alkenes, including phenylethanol to styrene.