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

The new tribasic N2S2 ligand H(3)ttfasbz 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 Cu-III oxidation state is observed, and the complex [Cu(ttfasbz)] has been isolated and characterized structurally. Reduction to the EPR active Cu-II analogue has been achieved chemically and also electrochemically, and in both cases, the process is totally reversible. The Cu-III/II redox potential of the complex is remarkably low and similar to that of the ferrocenium/ferrocene couple. Further reduction to the formally monovalent (d(10)) dianion [Cu-I(ttfasbz)](2-) may be achieved electrochemically. Computational chemistry demonstrates that the three redox states [Cu(ttfasbz)], [Cu(ttfasbz)](-), and [Cu(ttfasbz)](2-) are truly Cu-III, Cu-II and Cu-I complexes, respectively, and the potentially noninnocent ligand does not undergo any redox reactions.