Copper(I) nitrosyls from reaction of copper(II) thiolates with S-nitrosothiols: mechanism of NO release from RSNOs at Cu.

S-nitrosothiols (RSNOs) serve as ready sources of biological nitric oxide activity, especially in conjunction with copper centers. We report a novel pathway for the generation of NO within the coordination sphere of copper model complexes from reaction of copper(II) thiolates with S-nitrosothiols. Reaction of tris(pyrazolyl)borate copper(II) thiolates iPr2TpCu–SR (R = C6F5 or CPh3) with tBuSNO leads to formation of iPr2TpCu(NO) and the unsymmetrical disulfide RS–StBu. Quantum mechanical investigations with B3LYP-D3/6-311G(d) suggest formation of a κ1-N–RSNO adduct iPr2TpCu(SR)(R′SNO) that precedes release of RSSR′ to deliver iPr2TpCu(NO). This process is reversible; reaction of iPr2TpCu(NO) (but not iPr2TpCu(NCMe)) with C6F5S–SC6F5 forms iPr2TpCu–SC6F5. Coupled with the facile, reversible reaction between iPr2TpCu(NO) and C6F5SNO to give iPr2TpCu–SC6F5 and 2 equiv NO, we outline a new, detailed catalytic cycle for NO generation from RSNOs at Cu.