The Trivalent Copper Complex of a Conjugated Bis-dithiocarbazate Schiff Base: Stabilization of Cu in Three Different Oxidation States

The new tribasic N2S2 ligand H3ttfasbz has been synthesized by condensation of 4-thenoyl
2,2,2-trifluoroacetone
and S-benzyl dithiocarbazate. On complexation with
copper­(II) acetate, spontaneous oxidation to the CuIII oxidation
state is observed, and the complex [Cu­(ttfasbz)] has been isolated
and characterized structurally. Reduction to the EPR active CuII analogue has been achieved chemically and also electrochemically,
and in both cases, the process is totally reversible. The CuIII/II redox potential of the complex is remarkably low and similar to
that of the ferrocenium/ferrocene couple. Further reduction to the
formally monovalent (d10) dianion [CuI(ttfasbz)]2– may be achieved electrochemically.
Computational chemistry demonstrates that the three redox states [Cu­(ttfasbz)],
[Cu­(ttfasbz)]−, and [Cu­(ttfasbz)]2– are truly CuIII, CuII, and CuI complexes,
respectively, and the potentially noninnocent ligand does not undergo
any redox reactions.