Structure, spectral properties and interconversions of bis-niobocenes and their dianions. The crystal and molecular structure of [(η⁵-C5H4SiMe2OSiMe2-η⁵ : η¹-C⁵H³)²Nb²H²] [Na(OEt2)2]2

Abstract Electron-acceptor properties of bis-niobocenes (η5-C5H4Y)(H) Nb(η 5 : η 1 -C 5 H 3 X) 2 N b(H)(η5-C5H4Y) with X  Y  H and XY  SiMe2OSiMe2have been investigated. Bis-niobocenes are shown to readily add two electrons forming stable salts of the corresponding dianions [(η5-C5H4Y)(H)Nb(η5 : η1- C5H3X)2Nb(H)(η5-C5H4Y)]2-. The surplus electrons can be removed to give quantitative regeneration of initial neutral bis-niobocenes. The crystal and molecular structure of the title compound has been determined; R  0.044, interatomic distance are Nb…Nb 3.93, NbH 1.62, average NbC(π) 2.36, NbC(σ) 2.31 A, other distances correspond to the usually observed values. Unlike the neutral bis-niobocenes, there is no direct metalmetal bond in the dianionic structures. This conclusion is supported by electronic spectra of neutral and dianionic species.