KINETIC STUDIES OF CHLORO COMPLEXES OF RHODIUM AS HYDROGENATION CATALYSTS

The anionic complexes [RhCl6]3−, [Rh(H2O)Cl5]2−, and [Rh(H2O)2Cl4]− activate molecular hydrogen for the reduction of ferric ion in aqueous acid solution; the catalytic activity increased with increasing number of chloride ligands present. Cationic and neutral chloroaquorhodium(III) complexes did not homogeneously catalyze the reduction of ferric ion, the complexes themselves being reduced to metallic rhodium, a powerful heterogeneous catalyst.Chloro complexes of rhodium(III) and rhodium(I) were not effective catalysts in aqueous solution for the homogeneous hydrogenation of the olefinic bond in maleic acid. Anionic chlororhodate(III) complexes were reduced by hydrogen to the univalent state, this state being stabilized against further reduction to the metal by complexing with the maleic acid present. Preliminary studies indicate that in dimethylacetamide solution rhodium (III) trichloride is an effective homogeneous catalyst for the reduction of maleic acid to succinic acid by hydrogen, the reaction proceeding through a rhodium (I) – maleic acid complex.