NbCl, reacts with NaBH, and LiCp+ (Cp+ = EtMe,C,) dependent on the stoichiometry and temperature to give Cp+,NbCl, (11, Cp+,Nb,CI,(B,H6) (21, Cp+,NbBH, (3a) and Cp+,Nb,(BzH& (4a). With a large excess of NaBH,, Cp+,NbCl, gives 2 at 25"C, which reacts further with NaBH, to give 4a. The synthesis of the deep violet, very stable 4a can be generalised by using C,Me,Li and 'BuCSH,Li, respectively1 Compounds l-4 are characterised by means of IR, 'H, and heteroatom NMR spectra. An X-ray structure analysis was carried out with 4a. Whereas 1 and 3 are analogous to already known complexes, in 2 and 4a the B,H, dianion (which is not stable in the free state) is present as a bridging ligand, oriented perpendicularly with respect to the Nb-Nb axis. So far, the highest nuclear magnetic 93Nb shielding has been observed for compounds 4, extending the range of known S(93Nb) values by 2500 ppm. The temperature dependence of the linewidths of both the "B and the 93Nb NMR signals of 4c allows evaluation of the magnitude of J(93Nb"B) = 50 f 10 Hz. NbCl, reagiert mit NaBH., und LiCp+ (Cpf = EtMe,C,) in Abhlngigkeit von Stiichiometrie und Reaktionstemperatur zu den Produkten Cp +,NbC12 (11, Cp+,Nb$&(B,H,) (2), Cp+,NbBH, (3a) und CpC,Nb2(B2H,), (4a). c~+~N'bCl, ist mit einem groDen UberschuB NaBH, bei 25°C in 2 iiberfiihrbar, das seinerseits mit weiterem NaBH, zu 4a abreagiert. Die Synthese des tiefvioletten, sehr stabilen Komplexes, 4a Iat sich durch Einsatz von CsMe,Li bzw. 'BuCSH,Li verallgemeinern. l-4
