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 Re₂(CO)₁₀ and benzothiophenes (BT*) in hexanes solution produces the ring-opened BT* complexes Re₂(CO)₇(μ-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 η¹(S)-bound BT* complexes Re₂(CO)₉(η¹(S)-BT*) (2a−d), prepared from Re₂(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 η¹(S)-bound complexes 2a−d are precursors to 1a−d in the reactions of Re₂(CO)₁₀ with BT*. Irradiation of Re₂(CO)₁₀ and 3,5-Me₂BT with UV light in decane solution under an atmosphere of H₂ produces complex 1d and the partially hydrogenated BT* complex Re₂(CO)₇(μ-3,5-Me₂BT-H)(μ-H) (3d). Reactions of 1a with phosphines yield further ring-opened BT−Re complexes of the types Re₂(CO)₇(PMe₃)₃(μ-BT) (4) and Re₂(CO)₇(PR₃)₂(μ-BT) (R = Me (5), ⁱPr (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.