Synthesis and reactivity of η6-arene derivatives of niobium(II), niobium(I), and niobium(0)

Article abstract of DOI:10.1016/0022-328X(91)80041-H

The primary reduction products in the Al/AlX3/NbX5/arene system, namely Nb(η⁶-arene)(AlX4)2, X = Cl, arene = benzene, hexamethylbenzene; X = Br, arene = hexamethylbenzene, have been isolated.Tetrahydrofuran at room temperature reacts with Nb(η⁶-hexamethylbenzene)(AlBr4)2, to give the aluminium-free complex Nb2(η⁶-hexamethylbenzene)2Br4, whose crystal structure was determined by X-ray diffraction methods.In the presence of tetrahydrofuran or dimethoxyethane, the η⁶-mesitylenetetrahaloaluminato complexes are further reduced by aluminium to bis-mesityleneniobium(0), Nb(mes)2, which undergoes: a) disproportionation with CO to ^+-, b) oxidation by V(CO)6 or (4,4'-dimethyl-2,2'-dipyridyl)(BPh4)2 under carbon monoxide to X, X = ^- or BPh4^-.The structure of BPh4 has been determined by X-ray diffration methods.In the presence of CO, Nb(mes)2 is reduced by CoCp2^* * = η⁵-C5(CH3)5> to ^-, which was isolated as its CoCp2^*+ derivative; it efficiently deoxygenates CO2 to CO in the presence of carbon monoxide acceptors such as the ⁺ cation.