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Abstract A redox‐neutralS‐nitrosation of thiol has been achieved at a dicopper(I,I) center. Treatment of dicopper (I,I) complex with excess NO^.and thiol generates a dicopper (I,I) di‐S‐nitrosothiol complex [Cu^ICu^I(RSNO)₂]²⁺or dicopper (I,I) mono‐S‐nitrosothiol complex [Cu^ICu^I(RSNO)]²⁺, which readily release RSNO in 88–94 % yield. TheS‐nitrosation proceeds by a mixed‐valence [Cu^IICu^III(μ‐O)(μ‐NO)]²⁺species, which deprotonates RS‐H at the basic μ‐O site and nitrosates RS⁻at the μ‐NO site. The [Cu^IICu^III(μ‐O)(μ‐NO)]²⁺complex is also competent forO‐nitrosation of MeOH. A rare [Cu^IICu^II(μ‐NO)(OMe)]²⁺intermediate was isolated and fully characterized, suggesting theS‐nitrosation may proceed through the intermediary of analogous [Cu^IICu^II(μ‐NO)(SR)]²⁺species. This redox‐ and proton‐neutralS‐nitrosation process is the first functional model of ceruloplasmin in mediatingS‐nitrosation of external thiols, with implications for biological copper sites in the interconversion of NO^./RSNO. 

One-pot reaction of tris(2-aminoethyl)amine (TREN), [Cu I (MeCN) 4 ]PF 6 , and paraformaldehyde affords a mixed-valent [ TREN4 Cu II Cu I Cu I (μ 3 -OH)](PF 6 ) 3 complex. The macrocyclic azacryptand TREN4 contains four TREN motifs, three of which provide a bowl-shape binding pocket for the [Cu 3 (μ 3 -OH)] 3+ core. The fourth TREN caps on top of the tricopper cluster to form a cryptand, imposing conformational constraints and preventing solvent interaction. Contrasting the limited redox capability of synthetic tricopper complexes reported so far, [ TREN4 Cu II Cu I Cu I (μ 3 -OH)](PF 6 ) 3 exhibits several reversible single-electron redox events. The distinct electrochemical behaviors of [ TREN4 Cu II Cu I Cu I (μ 3 -OH)](PF 6 ) 3 and its solvent-exposed analog [ TREN3 Cu II Cu II Cu II (μ 3 -O)](PF 6 ) 4 suggest that isolation of tricopper core in a cryptand enables facile electron transfer, allowing potential application of synthetic tricopper complexes as redox catalysts. Indeed, the fully reduced [ TREN4 Cu I Cu I Cu I (μ 3 -OH)](PF 6 ) 2 can reduce O 2 under acidic conditions. The geometric constraints provided by the cryptand are reminiscent of Nature's multicopper oxidases (MCOs). For the first time, a synthetic tricopper cluster was isolated and fully characterized at Cu I Cu I Cu I ( 4a ), Cu II Cu I Cu I ( 4b ), and Cu II Cu II Cu I ( 4c ) states, providing structural and spectroscopic models for many intermediates in MCOs. Fast electron transfer rates (10 5 to 10 6 M −1 s −1 ) were observed for both Cu I Cu I Cu I /Cu II Cu I Cu I and Cu II Cu I Cu I /Cu II Cu II Cu I redox couples, approaching the rapid electron transfer rates of copper sites in MCO.