A New Type of Nitrogen Cation Radical Generated from Copper(II)-Induced Oxidation of the Nine-Membered Macrocycle N,N'–Dimethyltribenzo–1,4,7–triazacyclononatriene

Abstract

Nitrogen-containing, small-ring macrocycles display varied reactivity toward transition metals. In this project copper(II) bromide was used originally in an attempt to form stable Cu(II) complexes. Copper(II) bromide has been previously shown to coordinate with TACN (1,4,7–triazacyclononane).1 Among other N3–macrocycles we investigated N,N'–dimethyltribenzo–1,4,7–triazacyclononatriene as the focus of this work. The simple structure is shown in 1 and the crown conformation appears as 2. We reacted 1 with CuBr2 in a protic solvent methanol (MeOH) and in an aprotic solvent acetonitrile (MeCN). X–ray structure determination on the recrystallized MeOH product confirmed formation of an organic radical cation and copper(I) anion. The radical displays extensive structural rearrangement. Instead of our initial goal of generating Cu2+ complexes, we observed Cu2+ reduction and macrocycle oxidation.