The catalytic dehydrohalogenation of fluoro-, chloro-, bromo-, and iodopentanes to yield pentene is studied in a gas flow reactor under 1 atm of helium or hydrogen. The catalysts used are crushed crystals of molecular Nb, Mo, Ta, and W halide clusters possessing an octahedral metal framework and of a solid state Re chloride cluster possessing a triangular metal framework. All of the former clusters develop catalytic activity for dehydrohalogenation of 1-halogenated pentenes yielding 1-pentene and cis- and trans-2-pentenes in a helium or hydrogen stream when the clusters are preliminarily treated at 300 degreesC. The Re cluster develops catalytic activity for the same reaction in a stream of helium above 175 degreesC, while in a stream of hydrogen at 300 degreesC, it is reduced to metallic Re to catalyze both dehydrohalogenation and hydrodehalogenation (hydrogenolysis) concurrently, yielding pentenes and pentane. Even the C-F bond of 1-fluoropentane is hydrogenolyzed by the Re metal. (C) 2003 Elsevier Science B.V All rights reserved.