Niobium trihalides

Niobium pentaoxide undergoes two important types of reactions, one is reduction to niobium metal or to lower oxides, and the other involves conversion of pentoxide to oxide trihalides when treated with halogens or hahdes. These reactions occur mostly at elevated temperatures. Reductions may he carried out hy carhon, hydrogen, niobium carbide, niobium metal, and other reducing agents at elevated temperatures and often in vacuum ... 

Table 42 Neutral Adducts of the Niobium and Tantalum Trihalides with Monodentate Donors...

The development of the chemistry of niobium and tantalum in their lower oxidation states, three or less, has long been precluded by the lack of convenient starting materials. Indeed, stoichiometric trihalides MX3 (X = Cl, Br) are only incidental compositions. They are obtained by reduction of the pentahalides or disproportionation of the tetrahalides, and are polymeric and rather inert. 

A new area in niobium and tantalum chemistry was opened with the discovery that the reduction of MX5, MX4, or their complexes to yield molecular trihalides can be achieved easily... 

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