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The reaction of pyridine with NbBr 5 proceeded by oxidation-reduction to yield the niobium(IV) derivative NbBr 4 (C 5 H 5 N) 2 , and the oxidation products 1-(4-pyridyl) pyridinium bromide (I) and pyridinium bromide. I was identified by comparison of the ultraviolet spectra in acidic and basic solutions with those of its known salts. Reduction of NbC l5 by pyridine was also observed but a different reaction stoichiometry was obtained. The reactions of TaC l5 and TaBr 5 with pyridine afforded only the adducts TaC l5 (C 5 H 5 N) and TaBr 5 (C 5 H 5 N). In contrast to the behavior of NbC l5 and NbBr 5 , both Nbl 5 and Ta l5 dissociated in pyridine to give the adducts M l4 (C 5 H 5 N) 2 , and the pyridine adduct of elemental iodine.In previous studies (6, 7) of the reaction of niobium(V) chloride with ammonia and the three methylamines it was found that aminolysis was the primary mode of reaction. The extent of displacement of chloride in the reactions followed the order NH 2 Me > NH 3 = NHMe 2 > NMe 3 . While the products obtained from the reactions with NH 3 , NH 2 Me, and NHMe 2 were separated and identified, the products of the reaction with NMe 3 could not be separated. However, the over-all molar ratio of Nb:Cl:N of approximately 1:5:2 for the latter product led to the authors' suggestion that the product was a simple adduct or a mixture of tetramethylammonium chloride and tetrachloro (dimethylamido) niobium (V). The possibility of reduction was not considered.Other work (I) has shown that the reaction of titanium(IV) chloride and trimethylamine yielded a mixture which was 90% tetrachloro ( trimethylamine )-titanium(IV) and 10% trichlorobis ( trimethylamine) titanium (III). The oxidation product of the reaction was not identified. However, the authors suggested that the oxidation products could be amine polymers or chloroamine derivatives.Many other workers (2,4,5,15) have reported the reduction of various metal halides with ammonia and amines, but the oxidation products of such reactions have never been positively characterized.Generally the metal must be in the maximum valence state consistent with stability of the metal halide before reduction will take place. Where an acidic 243 Downloaded by IMPERIAL COLLEGE LONDON on February 18, 2015 |

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