Ruthenium carbonyls as benzo[b]thiophene hydrodesulfurization catalysts in homogeneous phase

The catalytic activity of mononuclear and polynuclear ruthenium complexes in the benzo[b]thiophene (BT) hydrodesulfurization (HDS) has been tested in the temperature range between 150 and 170 degrees C under 100 bar of hydrogen. The ruthenium complexes tested are shown to be catalytically active in the hydrogenation of BT to 2,3-dihydrobenzo[b]thiophene (DHBT) and 2-ethylthiophenol. The best performance was provided by H4Ru4(CO)(8)(PPh3)(4) when working at 170 degrees C: In these conditions BT is hydrogenated to DHBT with a conversion of 38.2% after 96 h or 81.2% after 384 h. Ethylbenzene (conversion 4.9%) is also formed confirming that a complete HDS of the substrate (even if in a low amount) may be obtained. The addition of a strong base ((BuOK)-Bu-t) as a co-catalyst changes the chemioselectivity of the reaction. The mononuclear complexes are less active than the cluster ones. BT is in fact converted to DHBT up to 19.5% in the presence of Ru(CO)(3)(PPh3)(2) under the same conditions. These data show that this reaction is promoted by the cooperation of several metal atoms in the catalytic intermediates. (C) 1999 Elsevier Science S.A. All rights reserved.