A N<sub>3</sub>S<sub>(thioether)</sub>-Ligated Cu<sup>II</sup>-Superoxo with
Enhanced Reactivity
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Abstract
Previous
efforts to synthesize a cupric superoxide complex possessing
a thioether donor have resulted in the formation of an end-on <i>trans</i>-peroxo-dicopper(II) species, [{(Ligand)Cu<sup>II</sup>}<sub>2</sub>(μ-1,2-O<sub>2</sub><sup>2–</sup>)]<sup>2+</sup>. Redesign/modification of previous N<sub>3</sub>S tetradentate
ligands has now allowed for the stabilization of the monomeric, superoxide
product possessing a S<sub>(thioether)</sub> ligation, [(<sup>DMA</sup>N<sub>3</sub>S)Cu<sup>II</sup>(O<sub>2</sub><sup>•–</sup>)]<sup>+</sup> (<b>2</b><sup><b>S</b></sup>), as characterized
by UV–vis and resonance Raman spectroscopies. This complex
mimics the putative Cu<sup>II</sup>(O<sub>2</sub><sup>•–</sup>) active species of the copper monooxygenase PHM and exhibits enhanced
reactivity toward both O–H and C–H substrates in comparison
to close analogues [(L)Cu<sup>II</sup>(O<sub>2</sub><sup>•–</sup>)]<sup>+</sup>, where L contains only nitrogen donor atoms. Also,
comparisons of [(L)Cu<sup>II/I</sup>]<sup>n+</sup> compound reduction
potentials (L = various N<sub>4</sub> vs <sup>DMA</sup>N<sub>3</sub>S ligands) provide evidence that <sup>DMA</sup>N<sub>3</sub>S is
a weaker donor to copper ion than is found for any N<sub>4</sub> ligand-complex
