Applications of Bis(1-R-imidazol-2-yl)disulfides and Diselenides as Ligands for Main Group and Transition Metals: κ2-NN Coordination S-S Bond Cleavage and S-S/E-E (E = S Se) Bond Metathesis Reactions

摘要

Bis(1-R-imidazol-2-yl)disulfides, (mim^R)2 (R = Ph, Bu^t), and diselenides, (seim^Mes)2, serve as bidentate [N,N]-donor ligands for main group and transition metals. For example, [κ²-(mim^But)2]MCl2 (M = Fe, Co, Ni, Zn), [κ²-(mim^Ph)2]MCl2 (M = Co, Zn), [κ²-(mim^But)2]CuX (X = Cl, I) and [κ²-(seim^Mes)2]MCl2 (M = Fe, Co, Ni) are obtained by treatment of (mim^But)2 or (seim^Mes)2 with the respective metal halide, and have been structurally characterized by X-ray diffraction. On the other hand, the zerovalent nickel complex Ni(PMe3)4 effects cleavage of the disulfide bond of (mim^But)2 to give square planar trans-Ni(PMe3)2(mim^But)₂ in which the (mim^But) ligands coordinate via nitrogen rather than sulfur, a most uncommon coordination mode for this class of ligands. Although [κ²-(mim^R)₂]MCl₂ (M = Fe, Co, Ni, Zn) are not subject to homolytic cleavage of the S-S bond because the tetravalent state is not readily accessible, the observation that [κ²-(mim^Ph)₂]CoCl₂ and [κ²-(mim^But)₂]CoCl₂ form an equilibrium mixture with the asymmetric disulfide [κ²-(mim^Ph)(mim^But)]CoCl₂ indicates that S-S bond cleavage via another mechanism is possible. Likewise, metathesis between disulfide and diselenide ligands is observed in the formation of [κ²-(mim^But)(seim^Mes)]CoCl₂ upon treatment of [κ²-(mim^But)₂]CoCl₂ with [κ²-(seim^Mes)₂]CoCl₂.