Re(2)(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-Me(2)BT) 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-Me(2)BT 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-Me(2)BT-H)(eta-H) (3d). Reactions of 1a with phosphines yield further ring-opened BT-Re complexes of the types Re(2)(CO)(7)(PMe(3))(3)(mu-BT) (4) and Re(2)(CO)(7)(PR(3))(2)(mu-BT) (R = Me (5), (i)Pr (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.