HYDROGENATION OF PENTYNES WITH Rh4(CO)12 AND Rh2(CO)4Cl2 IN SOLUTION AND ANCHORED ON Al2O3

Article abstract of DOI:10.1016/S0022-328X(00)84591-X

The catalytic activities of Rh4(CO)12 and Rh2(CO)4Cl2 for the homogeneous hydrogenation of pentynes in toluene have been studied and compared with those of these complexes anchored on γ-Al2O3.Rh3(CO)12 and Rh2(CO)4Cl2 interact strongly with γ-Al2O3, and the resulting species give identical IR spectra in the C-O stretching region characterised by absorptions at 2080 cm^-1 and 1997 cm^-1, suggesting that the same carbonylrhodium active centres are formed upon binding of both metal carbonyls.However, Rh4(CO)12/Al2O3 and Rh2(CO)4Cl2/Al2O3 show completely different behaviour as catalysts in the hydrogenation of pentynes; Rh2(CO)4Cl2/Al2O3 is more active than Rh2(CO)4Cl2 in solution, while the activity of Rh4(CO)12 is not substantially altered upon going from the homogeneous to the heterogenised system.Complete hydrogenation to give pentane is favored when Rh2(CO)4Cl2 and Rh4(CO)12 are bound to Al2O3, and occurs much more slowly when the complexes are used as homogeneous catalysts.