CHEMISTRY OF ETA(2)-CS2 NIOBOCENE COMPLEXES - SYNTHESIS AND CHARACTERIZATION OF NEW 1,3-DITHIOL-2-YLIDENE COMPLEXES VIA REACTIONS WITH ACTIVATED ALKYNES

The reaction of CS2 with Cp'Nb-2(H)(eta(2)-CH2=CH2) or Cp'Nb-2(H)(eta( 2)-CH2-CHPh) (Cp' = eta(5)-C(5)H(4)SiMe(3)) affords the alkylniobocene complexes Cp'Nb-2(Et)(eta(2)-CS2-C,S) (2) and Cp'Nb-2(CH(2)CH(2)Ph)(e ta(2)-CS2-C,S) (3), respectively. The interaction of eta(2)-CS2-contai ning complexes Cp'2NbCl(eta(2)-CS2-C,S) with alkynes bearing electron- withdrawing groups gives rise to a new family of 1,3-dithiol-2-ylidene niobocene species, Cp'(2)NbX(=CS(R)C=C(R)S) (6, X = Cl, R = CF3; 7, X = Cl, R = COOMe; 8, X = Cl, R = COO(t)Bu; 9, X = Et, R = COOMe; 10, X = Et, R = COO(t)Bu; 11, X = CH(2)CH(2)Ph, R = COOMe; 12, X = CH(2)CH( 2)Ph, R = COO(t)Bu). In a similar way, with the carboxylate complexes Cp'Nb-2(OC(O)H-O)(eta(2)-CS2-C,S) (4) and Cp'Nb-2(OC(O)CH3-O)(eta(2)-C S2-C,S) (5) as starting materials, other 1,3-dithiol-2-ylidene species have been isolated Cp'Nb-2(OC(O)Y-O)(=CS(R)C=C(R)S) (13, Y = H, R = C OOMe; 14, Y = H, R = COO(t)Bu; 15, Y = CH3, R = COOMe; 16, Y = CH3, R = COO(t)Bu). The structures of all complexes have been determined by s pectroscopic methods. The structure of 2 was established by single-cry stal diffractometry studies. The molecular structure shows a typical b ent-sandwich geometry around the niobium atom with the ethyl and carbo n disulfide ligands arrayed in the plane between the two cyclopentadie nyl rings.