Niobocene

Yasuda and coworkers51 reported a route to niobocene-allyl compounds by hydrometa-lation of conjugated dienes with niobium hydrido-olefin complexes, NbH(C5H5)2(olefin),... 

The X-ray structure of 83 was in accord with the prediction of Scheme 4 in that the Si-Cl bond lies in the niobocene bisecting plane trans to the hydride and is elongated compared with classical complexes of the type [M(SiR2Cl)L ]. There was, however, no good reference system that would allow for the comparison of the Nb-Si bond lengths. The metal-silyl bond lengths are strongly affected by Bent s... 

The Ti-Ti separation (3.195 A) leaves open the question of how much Ti-Ti interaction is present, and it is significant that the compound is weakly paramagnetic. The presence of a 7r-bonded fulvalene has also been found in other systems, namely, the mixed aluminotitanium hydrides (CpTWHXHsAlEtsXCxoHs) (26) (VII), and [(CgH TiHAlEt,], CjoHg) (26, 27), which are discussed further below, and the niobocene (CpNbH)2(CioH8) (28). In addition the l3C-NMR spectrum of titanocene... 

Compounds of this general formula are known where L = CO (145, 176), various alkenes (146,177) and alkynes (178), and also PEt3 (146, 179). In addition, a tantalum analog of "niobocene has been reported... 

Fig. 10. The structure of a molecule commonly called niobocene , whose actual formula is [HNb(C5Hs)(CsH4)l2 (Ref. 57). Unlike most other metallocenes, niobocene is dimeric...

In these final examples, Otero and coworkers described the reaction of a niobocene hydride (134) with triphenylgermanium hydride to afford niobocene germyl complexes... 

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