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

[Image: see text] Tetradentate diamino bis(thiolate) ligands (l-N(2)S(2)(2−)) with saturated linkages between heteroatoms support fully reduced [(Cu(l-N(2)S(2)))(2)Cu(2)] complexes that bear relevance as an entry point toward molecules featuring the Cu(2)(I)Cu(2)(II)(μ(4)-S) core composition of nitrous oxide reductase (N(2)OR). Tetracopper [(Cu(l-N(2)(S(Me(2)))(2)))(2)Cu(2)] (l-N(2)(S(Me(2))H)(2) = N(1),N(2)-bis(2-methyl-2-mercaptopropane)-N(1),N(2)-dimethylethane-1,2-diamine) does not support clean S atom oxidative addition but undergoes Cl atom transfer from PhICl(2) or Ph(3)CCl to afford [(Cu(l-N(2)(S(Me(2)))(2)))(3)(CuCl)(5)], 14. When introduced to Cu(I) sources, the l-N(2)(S(Ar)H)(2) ligand (l-N(2)(S(Ar)H)(2) = N(1),N(2)-bis(2-mercaptophenyl)-N(1),N(2)-dimethylethane-1,2-diamine), made by a newly devised route from N(1),N(2)-bis(2-fluorophenyl)-N(1),N(2)-dimethylethane-1,2-diamine, ultimately yields the mixed-valent pentacopper [(Cu(l-N(2)S(Ar)(2)))(3)Cu(2)] (19), which has 3-fold rotational symmetry (D(3)) around a Cu(2) axis. The single Cu(II) ion of 19 is ensconced within an equatorial l-N(2)(S(Ar))(2)(2−) ligand, as shown by (14)N coupling in its EPR spectrum. Formation of 19 proceeds from an initial, fully reduced product, [(Cu(l-N(2)S(Ar)(2)))(3)Cu(2)(Cu(MeCN))] (17), which is C(2) symmetric and exceedingly air-sensitive. While unreactive toward chalcogen donors, 19 supports reversible reduction to the all-cuprous state; generation of [19](1–) and treatment with S atom donors only return 19 because structural adjustments necessary for oxidative addition are noncompetitive with outer-sphere electron transfer. Oxidation of 19 is marked by intense darkening, consistent with greater mixed valency, and by dimerization in the crystalline state to a decacopper species ([20](2+)) of S(4) symmetry.