Redox-neutral S-nitrosation Mediated by a Dicopper Center

An unprecedented redox-neutral S-nitrosation of thiol has been achieved at 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. The S-nitrosation reaction proceeds through a mixed-valence [Cu^IICu^III(m-O)(m-NO)]²⁺ species, which deprotonates RS-H at the basic m-O site and nitrosates the RS^- at the m-NO site. The [Cu^IICu^III(m-O)(m-NO)]²⁺ complex is also competent for O-nitrosation of MeOH, which is isoelectronic to thiol. In this case, a rare [Cu^IICu^II(m-NO)(OMe)]²⁺ intermediate has been isolated and fully characterized, suggesting the S-nitrosation proceeds through the intermediary of analogous [Cu^IICu^II(m-NO)(SR)]²⁺ species. The redox- and proton-neutral S-nitrosation process reported here represents the first functional model of ceruloplasmin in mediating S-nitrosation of external thiols, adding further implications for biological copper sites in the interconversion of NO^•/RSNO.