Catalytic dehydrogenation of aliphatic amines to nitriles, imines, or vinylamines and dealkylation of tertiary aliphatic amines over halide cluster catalysts of group 5 and 6 transition metals

A molybdenum halide cluster, (H3O)(2)[(Mo6Cl8)Cl-6](.)6H(2)O, with an octahedral metal framework was used as a catalyst in a gas-flow reactor under hydrogen or helium. Diethylamine started to react above 300 degreesC, and dehydrogenation to N-ethylideneethylamine proceeded selectively above 350 degreesC. Dibutylamine yielded the corresponding dehydrogenation product, and pyrrolidine and piperidine were dehydrogenated to 1-pyrroline and 2,3,4,5-tetrahydropyridine. Dehydrogenation of primary amines yielded the corresponding nitriles and the condensation product N-alkylidenealkylamine. Tripropylamine and tributylamine were dehydrogenated to yield, for the most part, N-vinyldialkylamines. In contrast, triethylamine was dealkylated to diethylamine. Thus, the halide cluster exhibited a characteristic catalysis for aliphatic amines: nitrogen-bonded hydrogens were removed completely to yield nitrile or imine, and when there was no such hydrogen, a neighboring hydrogen or the nitrogen-bonded alkyl group was removed. Niobium, tantalum, and tungsten chloride clusters of the same metal framework were also active catalysts for dealkylation and dehydrogenation of diethylamine. (C) 2004 Elsevier Inc. All rights reserved.