Tetradentate diamino bis(thiolate) ligands (l-N2S2(2−)) with saturated linkages between
heteroatoms
support fully reduced [(Cu(l-N2S2))2Cu2] complexes that bear relevance as an entry
point toward molecules featuring the Cu2ICu2II(μ4-S) core composition of nitrous
oxide reductase (N2OR). Tetracopper [(Cu(l-N2(SMe2)2))2Cu2] (l-N2(SMe2H)2=N1,N2-bis(2-methyl-2-mercaptopropane)-N1,N2-dimethylethane-1,2-diamine)
does not support clean S atom oxidative addition but undergoes Cl
atom transfer from PhICl2or Ph3CCl to afford
[(Cu(l-N2(SMe2)2))3(CuCl)5],14. When introduced
to Cu(I) sources, thel-N2(SArH)2ligand (l-N2(SArH)2=N1,N2-bis(2-mercaptophenyl)-N1,N2-dimethylethane-1,2-diamine), made by a newly
devised route fromN1,N2-bis(2-fluorophenyl)-N1,N2-dimethylethane-1,2-diamine,
ultimately yields the mixed-valent pentacopper [(Cu(l-N2SAr2))3Cu2] (19), which has 3-fold rotational symmetry (D3) around a Cu2axis. The single CuIIion of19is ensconced within an equatoriall-N2(SAr)2(2−) ligand, as
shown by14N coupling in its EPR spectrum. Formation of19proceeds from an initial, fully reduced product, [(Cu(l-N2SAr2))3Cu2(Cu(MeCN))] (17), which isC2symmetric and exceedingly air-sensitive. While unreactive
toward chalcogen donors,19supports reversible reduction
to the all-cuprous state; generation of [19]1–and treatment with S atom donors only return19because
structural adjustments necessary for oxidative addition are noncompetitive
with outer-sphere electron transfer. Oxidation of19is
marked by intense darkening, consistent with greater mixed valency,
and by dimerization in the crystalline state to a decacopper species
([20]2+) ofS4symmetry.