Controlled copper-mediated chlorination of phenol rings under mild conditions

The very unusual case of copper-mediated chlorination of phenol rings under mild conditions at room temperature is reported. Reaction of the ligand 1,7-bis(2-hydroxyphenyl)-2,6-diaza-4-hydroxylheptane (H(3)L1) with CuCl2 in acetonitrile leads to either the formation of a tetranuclear copper(II) complex [Cu-4(HL3)(2)(A-Cl)(2)Cl-2](CH3CN) (1) or a linear trinuclear complex [Cu-3(HL1)(2)Cl-2(CH3CN)(2)](CH3CN)(2) (2), depending on the reaction conditions. Both compounds have been fully characterized, including the determination of their 3D structures by X-ray diffraction. The unprecedented tetranuclear compound 1 is constituted of a dichlorido-bridged dimer of di-mu-phenoxido-dinuclear species, whereas the trinuclear complex 2 presents a linear array of copper(II) ions, held together through di-mu-phenoxido bridges of the central and external ions. The magnetic susceptibility of the two compounds was investigated, revealing either very strong (J < - 500 cm(-1)) or strong (J value around - 370(1) cm(-1)) antiferromagnetic dominant interactions among the Cu-II ions for 1 and 2, respectively. The tetranuclear complex 1 is obtained, under dry conditions, through the in situ formation of ligand HL3 (H(3)L3 = 1,7-bis(2-hydroxy-5-chlorophenyl)-2,6-diaza-4-hydroxylheptane) by oxidative chlorination of (HL1)(2-). In the presence of traces of water, 1 is partially hydroxylated at the ortho position of one of the phenyl rings. The use of trimethylorthoformate as the dehydrating agent prevents the formation of hydroxylated ligands. Several partly chlorinated/hydroxylated products (identified as H(3)L2) have also been obtained through slight variations of the synthetic procedures ( presence or absence of water and/or triethylamine in the reaction mixtures). These partially chlorinated and/or hydroxylated coordination species are mutually isomorphous to either 1 or 2. Several modified ligands have been isolated and characterized by H-1 NMR and MS, after reaction with sodium sulfide of the complexes formed.