Ligand Structural Effects on Cu2S2 Bonding and Reactivity in Side-On Disulfido-Bridged Dicopper Complexes

摘要

In order to assess supporting ligand effects on S-S bond activation, a series of [Cu2(μ-η²:η²-S2)]²⁺ complexes supported by various β-diketiminate or anilido-imine ligands (L) were synthesized via the reaction of Cu(I) precursors LCu(CH3CN) with S8. For the cases where L = β-diketiminate, the syntheses were complicated by formation of clusters [Cu(SR)]4, where “SR” represents the ligand functionalized by sulfur at the central methine position. The [Cu2(μ-η²:η²-S2)]²⁺ products were characterized by X-ray crystallography and electronic absorption and resonance Raman spectroscopy. Correlations among the Cu-S, Cu-Cu, and S-S distances and the ν(S-S) values were observed and interpreted within the framework of a previously described bonding picture. Comparison of these data to those for other relevant species revealed a remarkable degree of S-S bond activation in the compounds supported by the β-diketiminate and anilido-imine ligands, which through strong electron donation increase backbonding from the copper ions into the S-S σ* orbital and cause S-S bond weakening. Reactions of one of the complexes supported by an anilido-imine ligand with PPh3 and xylyl isocyanide were explored, revealing facile transfer of sulfur to PPh3 but only displacement of sulfur to yield a LCu(I)-CNAr (Ar = xylyl) complex with the isocyanide.