Fully Reduced and Mixed-Valent Multi-Copper Aggregates Supported by Tetradentate Diamino Bis(thiolate) Ligands

Tetradentate diamino bis(thiolate) ligands (l-NS(2-)) with saturated linkages between heteroatoms support fully reduced [(Cu(l-NS))Cu] complexes that bear relevance as an entry point toward molecules featuring the CuCu(μ-S) core composition of nitrous oxide reductase (NOR). Tetracopper [(Cu(l-N(S)))Cu] (l-N(SH) = ,-(2-methyl-2-mercaptopropane)-,-dimethylethane-1,2-diamine) does not support clean S atom oxidative addition but undergoes Cl atom transfer from PhICl or PhCCl to afford [(Cu(l-N(S)))(CuCl)], . When introduced to Cu(I) sources, the l-N(SH) ligand (l-N(SH) = ,-(2-mercaptophenyl)-,-dimethylethane-1,2-diamine), made by a newly devised route from ,-(2-fluorophenyl)-,-dimethylethane-1,2-diamine, ultimately yields the mixed-valent pentacopper [(Cu(l-NS))Cu] (), which has 3-fold rotational symmetry () around a Cu axis. The single Cu ion of is ensconced within an equatorial l-N(S)(2-) ligand, as shown by N coupling in its EPR spectrum. Formation of proceeds from an initial, fully reduced product, [(Cu(l-NS))Cu(Cu(MeCN))] (), which is symmetric and exceedingly air-sensitive. While unreactive toward chalcogen donors, supports reversible reduction to the all-cuprous state; generation of [] and treatment with S atom donors only return because structural adjustments necessary for oxidative addition are noncompetitive with outer-sphere electron transfer. Oxidation of is marked by intense darkening, consistent with greater mixed valency, and by dimerization in the crystalline state to a decacopper species ([]) of symmetry.