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

Abstract

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-2mercaptopropane)-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(2fluorophenyl)-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.