SYNTHESIS AND CHARACTERIZATION OF MONOCYCLOPENTADIENYL DITHIOLATO COMPLEXES OF NIOBIUM AND TANTALUM - CRYSTAL-STRUCTURES OF O)-(MU-ETA(2)ETA(2)-S2C2H4)(ETA(5)-C5H4ME)(2)CL-4] AND A(1)ETA(2)-S2C2H4)(2)-(ETA(5)-C5H4ME)(2)O(S2C2H4)]

Reactions of tetrachloro(cyclopentadienyl)niobium with arenedithiolate s yielded products [NbCp(1,2-S2C6H3R-4)(2)] (Cp = eta(5)-C5H5; R = H 1 or Me 2), characterised primarily by analysis, H-1 NMR and mass spect roscopy. Cyclic voltammetric studies on 1 and 2 showed two consecutive , quasi-reversible, reduction processes; ESR spectra of the initial pr oducts of chemical reduction were typical of those from niobium(IV) sp ecies with an unpaired electron largely centred on the metal and assig ned to the anions [NbCp(1,2-S2C6H3R-4)(2)](-). Similar tantalum deriva tives were less tractable, although properties of the more soluble spe cies [TaCp'(1,2-S2C6H4)(2)] (Cp' = eta(5)-C5H4Me) are reported. Reacti ons of tetrachloro(methylcyclopentadienyl)-niobium or -tantalum with s alts of ethane-1,2-dithiol (H(2)edt) were very susceptible to hydrolys is and the major isolable products of reactions using the sodium reage nt (Na(2)edt) were [M-2(mu-O)(mu-eta(2):eta(2)-edt)Cp-2'Cl-4] (M = Nb 4 or Ta 5), containing oxo and symmetrical dithiolate bridges. Reactio n of [NbCp'Cl-4] with 2 molar equivalents of Tl(2)edt formed the unsym metrical compound [Nb-2(mu-eta(1):eta(2)-edt)(2)Cp-2'O(edt)] 6, contai ning a terminal oxide ligand, one chelating and two unsymmetrically br idging edt groups. Structures of compounds 4 and 6 have been determine d 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.