Copper(I)
Nitrosyls from Reaction of Copper(II) Thiolates
with <i>S</i>‑Nitrosothiols: Mechanism of NO Release
from RSNOs at Cu
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Abstract
<i>S</i>-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 <i>S</i>-nitrosothiols. Reaction
of tris(pyrazolyl)borate copper(II) thiolates <sup>iPr2</sup>TpCu–SR
(R = C<sub>6</sub>F<sub>5</sub> or CPh<sub>3</sub>) with <sup>t</sup>BuSNO leads to formation of <sup>iPr2</sup>TpCu(NO) and the unsymmetrical
disulfide RS–S<sup>t</sup>Bu. Quantum mechanical investigations
with B3LYP-D3/6-311G(d) suggest formation of a κ<sup>1</sup>-N–RSNO adduct <sup>iPr2</sup>TpCu(SR)(R′SNO) that
precedes release of RSSR′ to deliver <sup>iPr2</sup>TpCu(NO).
This process is reversible; reaction of <sup>iPr2</sup>TpCu(NO) (but
not <sup>iPr2</sup>TpCu(NCMe)) with C<sub>6</sub>F<sub>5</sub>S–SC<sub>6</sub>F<sub>5</sub> forms <sup>iPr2</sup>TpCu–SC<sub>6</sub>F<sub>5</sub>. Coupled with the facile, reversible reaction between <sup>iPr2</sup>TpCu(NO) and C<sub>6</sub>F<sub>5</sub>SNO to give <sup>iPr2</sup>TpCu–SC<sub>6</sub>F<sub>5</sub> and 2 equiv NO,
we outline a new, detailed catalytic cycle for NO generation from
RSNOs at Cu