Organometallic Modeling of the Hydrodesulfurization (HDS) Process: Rhenium Carbonyl-promoted C-S Bond Cleavage and Hydrogenation of Thiophenes and Benozothiophenes

Ultraviolet photolysis of Re2(CO)io and excess benzothiophenes (BT*) in hexanes solution (10-15 °C) produced the ring-opened BT* complexes Re2(CO)7(|i-BT*) (la-d) (BT* = benzothiophene (BT) la, 2-methylbenzothiophene (2-MeBT) lb, 3-methylbenzothiophene (3-MeBT) Ic, and 3,5-dimethyIbenzothiophene (3,5-Me2BT) Id). The r|'(S)-bound BT* complexes Re2(CO)9(r|'(S)-BT''') (2a-d) were prepared by two different synthetic routes and were readily converted into la-d in good yields (40-60%) during UV photolysis in hexanes solution (10-15 °C). These results suggest that the r| '(S)-bound complexes 2a-d could be precursors in the formation of la-d. When Re2(CO)io and 3,5-Me2BT were irradiated with UV light under an atmosphere of H2 (10 ''C, 24 h) In decane solution, complex Id and the partially hydrogenated BT* complex Re2(CO)7(n-3,5-Me2BT-H)(^-H) (3d) in which the terminal vinyl carbon of the BT* ligand is protonated, were produced. Furthermore, UV irradiation of complexes Ic and Id under a H2 atmosphere (10°C) in decane solution also afforded the partially hydrogenated BT* complexes Re2(CO)7(^-3-MeBT-H)(^-H) (3c) and 3d. Complexes la-d were not reactive towards electrophiles such as methyl iodide, methyl trifluoromethanesulfonate (MeOTf) and triflic acid, but they did react with nucleophiles such