Applications of bis(1-R-imidazol-2-yl)disulfides and diselenides as ligands for main-group and transition metals: kappa2-(N,N) coordination, S-S bond cleavage, and S-S/E-E (E = S, Se) bond metathesis reactions

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, kappa2-(mim(Bu)(t))2]MCl2 (M = Fe, Co, Ni, Zn), kappa2-(mim(Ph))2]MCl2 (M = Co, Zn), kappa2-(mim(Bu)(t))2]CuX (X = Cl, I), and kappa2-(seim(Mes))2]MCl2 (M = Fe, Co, Ni) are obtained by treatment of (mim(Bu)(t))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(Bu)(t))2 to give square-planar trans-Ni(PMe3)2(mim(Bu)(t))2 in which the (mim(Bu)(t)) ligands coordinate via nitrogen rather than sulfur, a most uncommon coordination mode for this class of ligands. Although kappa2-(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 kappa2-(mimPh)2]CoCl2 and kappa2-(mim(Bu)(t))2]CoCl2 form an equilibrium mixture with the asymmetric disulfide kappa2-(mim(Ph))(mim(Bu)(t))]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 kappa2-(mim(Bu)(t))(seim(Mes))]CoCl2 upon treatment of kappa2-(mim(Bu)(t))2]CoCl2 with kappa2-(seim(Mes))2]CoCl2.