Modeling biological copper clusters: synthesis of a tricopper complex, and its chloride- and sulfide-bridged congeners.

The synthesis and characterization of a family of tricopper clusters housed within a tris(β-diketimine) cyclophane ligand (H3L) that bear structural similarities to biological copper clusters are reported. In all complexes, each Cu atom is held within the N2-chelate of a single β-diketiminate arm. Reaction of L(3-) with CuCl affords an anionic complex containing a μ3-chloride donor in the central cavity, whereas there is no evidence for bromide incorporation in the product of the reaction of L(3-) with CuBr (Cu3L). Cu3L reacts with elemental sulfur to generate the corresponding air-stable mixed-valent (μ3-sulfido)tricopper complex, Cu3(μ3-S)L, which represents the first example of a sulfide-bridged copper cluster in which each metal center is both coordinatively unsaturated and held within a N-rich environment. The calculated LUMO is predominantly Cu-S π* in character and delocalized over all three metal centers, which is consistent with the isotropic ten-line absorption (g ∼ 2.095, A ∼ 33 G) observed at room temperature in EPR spectra of the one-electron chemically reduced complex, Cu3(μ3-S)L.