PH-controlled synthesis of an aromatic triazene and its copper(II) complexation accompanied by an unexpected aromatic ring halogenation

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An isomeric triazene (H2L) and an azo dye (D1) were synthesized from the reaction between 2-amino-3-cyano-4-chloro-5-formylthiophene and 2-amino-5-nitrophenol under different pH values. Two Cu(II) complexes of the triazene H2L formulated as {[Cu(L′)(H2O)2]·DMF}n (C1) and [Cu2L2(DMF)2] (C2) were obtained by means of the reactions between deprotonated triazene ligand L2− and different copper salts (CuCl2·2H2O and Cu(OAc)2·H2O) at room temperature. It is noted that a new in situ formed chlorinated ligand L′2- was obtained via the unusual Cu(II) mediated phenyl halogenation of L2− evidenced by the formation of one-dimensional coordination polymer C1 in a high yield of 78%. A control experiment by using Cu(OAc)2·H2O as the metal source reveals the formation of a dinuclear Cu(II) complex C2 of ligand L2− without the occurrence of aromatic ring halogenation. It is suggested that the current study could present an effective approach to achieve the aromatic halogenation under a mild experimental condition with a high yield.