The reaction of Cp+2bBH4 with sulfur gives two isomers of composition Cp+2NbS2H (3, 4) and Cp+2NbS3H (5). The structures of 3-5 have been investigated by IR and H-1 NMR spectroscopic means. X-Ray diffraction analyses have been performed on 3 and 4. These investigations demonstrate that 3 and 4 are niobocene derivatives, in which either a eta2-S-2(2)--ligand and a hydride (3) or a S2- and a SH- ligand (4) are attached to the Nb center. Complex 3 can be transformed thermally into 4 by a S-S bond rupture, followed by the insertion of sulfur into the Nb-H bond. The polynuclear compounds Cp+3Nb3S7 (6) and Cp+3Nb3S12 (7) can be formed by the reaction of 3 with S8. The role of polysulfide intermediates is discussed.