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Elimination of tellurium from the niobocene complex 1, which contains the novel η2‐Te2H ligand, leads to the title compound 2 under the action of [Cr(CO)5(thf)]. Characteristic for the structure of 2 is the folded four‐membered ring in which all adjacent Cr(CO)5 fragments are in a trans arrangement.

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Layering solutions of P(4)S(3) in CH(2)Cl(2) with solutions of CuCl or CuI in CH(3)CN gives the coordination polymers (P(4)S(3))(3)(CuCl)(7) (1), (P(4)S(3))(2)(CuCl)(3) (2), (P(4)S(3))(CuI) (3) and (P(4)S(3))(CuI)(3) (4), respectively, after slow diffusion. The yellow compounds were characterised by elemental analysis, (31)P magic-angle spinning (MAS) NMR spectroscopy and single-crystal X-ray crystallography. The solid-state structures demonstrate the unexpected ligand versatility of the P(4)S(3) molecule, which interacts through two, three, or even all of the phosphorus atoms with copper according to the nature of the copper halide. Compound 1 has a three-dimensional network in which linear and cylindrical infinite CuCl subunits coexist with diatomic CuCl building blocks. For the first time, all four P atoms of the P(4)S(3) cage are involved in coordination with metal atoms. The 3D structure of 2 contains stacks of P(4)S(3) that are interconnected by slightly undulated and planar [CuCl](n) ribbons. Compound 3 is a one-dimensional polymer composed of alternating (CuI)(2) rings and P(4)S(3) bridges. The structure of 4 consists of undulated [CuI](n) layers in which the P(4)S(3) cage functions as a bridge within the layer, as well as a spacer between the layers. The (31)P MAS NMR spectra obtained are in good agreement with the solid-state structures obtained crystallographically. Thus, analytically pure 3 and 4 show singlet peaks that correspond to uncoordinated P and quartets owing to coupling with (63)Cu and (65)Cu, respectively, whereas that of 1 contains quartets according to all-P coordination. The spectrum of 2 was obtained from a sample that still contained 40 % of 1.

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