The Ullmann Condensation Reaction of Haloanthraquinone Derivatives with Amines in Aprotic Solvents. VI. The Combination of Cu(I) and Hydroxo or Alkoxo Cu(II) as Effective Catalyst System

Abstract

Abstract The reaction rate of the Ullmann condensation reaction of haloanthraquinone with ethylenediamine (EN) by copper(I) halide catalyst decreased along with the formation of inactive Cu(II) species [Cu(EN)2X2] by one-electron transfer from Cu(I) to haloanthraquinone. However, the combination of Cu(I) and Cu(II) salts, having an OH, OCH3, or OCOR group, enhanced the reaction rate in the following order: CuCl<CuCl–CuCl(OCH3)<CuCl–Cu(OCH3)2<CuCl–Cu(OH)2. In condensation using Cu(OR)2 or CuCl(OCH3) alone, the Cu(II) species was reduced to Cu(I) to form an active catalyst system [Cu(I)+Cu(II)]. On the other hand, CuBr2 or CuCl2 was not reduced and was ineffective for the reaction. These were confirmed by ESR measurements and the presence of a dehalogenation product. Mixed valence species bridged by the alkoxo or hydroxo group was proposed as an active species.