Properties of homogeneous and heterogenrous rhenium catalysts in the hydrogenation of nitro compounds

Abstract

The behaviour of soluble rhenium(V) oxohalide complexes with coordinatively bound thiourea, triphenylphosphine and their derivatives has been studied in the hydrogenation of C6-C10 olefins, nitrobenzene and p-nitrotoluene. Under homogeneous conditions rhenium complexes containing a Re-S bond were found to catalyze the reduction of the nitro group selectively, whereas those involving a Re-P bond catalyze the reduction of olefins. Activated rhenium thiourea complexes have been isolated in the solid state from the reaction medium. Their analogs, thio complexes, displaying similar physicochemical properties and catalytic activity, and which work without an induction period under atmospheric pressure have been synthesized. In the hydrogenation of 15 substituted nitrobenzenes, soluble rhenium complexes and solid rhenium heptasulfide were found to possess similar catalytic activities due to having the same catalytic center. The hydrogenation of the nitro group is accelerated by electron-acceptor functional groups and is inhibited by electron-donor ones.