Re2(CO)10-promoted S-binding, C-S bond cleavage, and hydrogenation of benzothiophenes:: Organometallic models for the hydrodesulfurization of thiophenes

In hydrodesulfurization model reactions of dinuclear metal complexes with thiophenes, we observe that ultraviolet photolysis of Re-2(CO)(10) and benzothiophenes (BT*) in hexanes solution produces the ring-opened BT* complexes Re-2(CO)(7) (mu-BT*) (1a-d) (BT* = benzothiophene (BT) 1a, 2-methylbenzothiophene (2-MeBT) 1b, 3-methylbenzothiophene (3-MeBT) 1c, and 3,5-dimethylbenzothiophene (3,5-Me2BT) 1d). The eta(1)(S)-bound BT* complexes Re-2(CO)(9)(eta(1)(S)-BT*) (2a-d), prepared from Re-2(CO)(9)(THF) and BT*, are readily converted into 1a-d in good yields (40-60%) during UV photolysis in hexanes solution, which suggests that the eta(1)(S)-bound complexes 2a-d are precursors to 1a-d in the reactions of Re-2(CO)(10) with BT*. Irradiation of Re-2(CO)(10) and 3,5-Me2BT with UV light in decane solution under an atmosphere of H-2 produces complex 1d and the partially hydrogenated BT* complex Re-2(CO())7(mu-3,5-Me2BT-H)(mu-H) (3d). Reactions of 1a with phosphines yield further ring-opened BT-Re complexes of the types Re-2(CO)(7)(PMe3)(3)-(mu-BT) (4) and Re-2(CO)(7)(PR3)(2) (mu-BT) (R = Me (5), Pr-i (6), Cy (7), and bis(diethylphosphino)ethane (8)). Structures of 1d, 2c, 3d, and 6, which demonstrate various bonding modes of benzothiophene and its C-S cleaved derivatives to two metal centers, were determined by X-ray crystallographic studies.