CATALYTIC-HYDROGENATION OF POLYAROMATICS IN THE PRESENCE OF MU-3-OXO-TRIRHODIUM ACETATE AND ITS SILICA-SUPPORTED ANALOG

Mu3-Oxo-trirhodium(III) acetate has been employed as a catalyst precur sor for the partial hydrogenation of polyaromatic hydrocarbons such as naphthalene, anthracene, quinoline and acridine under relatively mild reaction conditions (< 1 atm H-2 Pressure and 25-80-degrees-C) in dim ethylformamide solvent. It is found that the Rh3O(OCOCH3)6+(OCOCH3)- c atalyst system exhibits high activity and selectivity for production o f 1,2,3,4-tetrahydra derivatives under these conditions. Detailed inve stigations on the interaction of H-2 with the Rh3O(OCOCH3)6+(OCOCH3)- suggests that the active catalyst is HRh3O(OCOCH3)5+(OCOCH3)- (A); and that H-2 is activated by a heterolytic splitting process. The Rh3O(OC OCH3)6+(OCOCH3)- cluster has also been supported on silica (SiO2-Rh3O) in order to facilitate the respective addition and removal of the cat alyst to and from the polyaromatic reaction systems. It is found that SiO2-Rh3O, when treated with H-2 in the presence of a small amount of dimethylformamide in decane, exhibits good activity for the partial hy drogenation of quinoline (< 1 atm H-2 and 50-degrees-C). One additiona l advantage of the silica supported catalyst is that its active form h as a greater air stability than its homogeneous counterpart. Detailed kinetic and spectroscopic studies have been carried out for the hydrog enation of aromatics using Rh3O(OCOCH3)6+(OCOCH3)- and SiO2-Rh3O respe ctively. A mechanism was postulated for the two catalyst systems based on the experimental kinetic results. In addition, the activity and se lectivity of Rh3O(OCOCH3)6+(OCOCH3)- towards hydrogenating different a romatic substrates was also investigated.