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

Abstract

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°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 H 4Ru 4(CO) 8(PPh 3) 4 when working at 170°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 ( t BuOK) 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(PPh 3) 2 under the same conditions. These data show that this reaction is promoted by the cooperation of several metal atoms in the catalytic intermediates.