Synthesis and characterisation of monocyclopentadienyl dithiolato complexes of niobium and tantalum; crystal structures of [Nb2(µ-O)(µ-η2∶η2-S2C2H4)(η5-C5H4Me)2Cl4] and [Nb2(µ-η1∶η2-S2C2H4)2(η5-C5H4Me)2O(S2C2H4)]†

Abstract

Reactions of tetrachloro(cyclopentadienyl)niobium with arenedithiolates yielded products [NbCp(1,2-S₂C₆H₃R-4)₂] (Cp = η⁵-C₅H₅; R = H 1 or Me 2), characterised primarily by analysis, ¹H NMR and mass spectroscopy. Cyclic voltammetric studies on 1 and 2 showed two consecutive, quasi-reversible, reduction processes; ESR spectra of the initial products of chemical reduction were typical of those from niobium(IV) species with an unpaired electron largely centred on the metal and assigned to the anions [NbCp(1,2-S₂C₆H₃R-4)₂]^–. Similar tantalum derivatives were less tractable, although properties of the more soluble species [TaCp′(1,2-S₂C₆H₄)₂] (Cp′ = η⁵-C₅H₄Me) are reported. Reactions of tetrachloro(methylcyclopentadienyl)-niobium or -tantalum with salts of ethane-1,2-dithiol (H₂edt) were very susceptible to hydrolysis and the major isolable products of reactions using the sodium reagent (Na₂edt) were [M₂(µ-O)(µ-η²∶η²-edt)Cp′₂Cl₄] (M = Nb 4 or Ta 5), containing oxo and symmetrical dithiolate bridges. Reaction of [NbCp′Cl₄] with 2 molar equivalents of Tl₂edt formed the unsymmetrical compound [Nb₂(µ-η¹∶η²-edt)₂Cp′₂O(edt)] 6, containing a terminal oxide ligand, one chelating and two unsymmetrically bridging edt groups. Structures of compounds 4 and 6 have been determined in the solid state by X-ray crystallography; 1- and 2-D NMR spectra of the binuclear products support the retention of these structures in solution.