Controlled Copper-Mediated Chlorination of Phenol Rings under Mild Conditions

Abstract

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 (H3L1) with CuCl2 in acetonitrile leads to either the formation of a tetranuclear copper(II) complex [Cu4(HL3)2(mu-Cl)2Cl2](CH3CN) (1) or a linear trinuclear complex [Cu3(HL1)2Cl2(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 CuII ions for 1 and 2, respectively. The tetranuclear complex 1 is obtained, under dry conditions, through the in situ formation of ligand HL3 (H3L3=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 H3L2) 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 1H NMR and MS, after reaction with sodium sulfide of the complexes formed.

Copper‐Catalyzed Aerobic Oxidative CH Functionalizations: Trends and Mechanistic Insights

“…The facile single-electron oxidation of phenols and other electron-rich arenes and heteroarenes has led to the development of copper-catalyzed halogenation protocols for these substrates. [49] Gusevskaya and co-workers reported a highly selective method for oxidative halogenation of phenols under aerobic copper-catalyzed conditions. [50] Para-chlorinated phenols could be obtained with high selectivity [51] using 12.5 mol % CuCl 2 and 2 equiv LiCl in AcOH under 1 atmosphere of O 2 (Scheme 7 A).…”

C–H bond halogenation catalyzed or mediated by copper: an overview

“…As typical electron-enriched arenes, phenols and analogous arenes tend to undergo a single-electron transfer process [ 46 ], the property of these arenes also resulted in sound attention to their C–H halogenations. In 2006, Gusevskaya and Menini [ 47 – 48 ] reported a highly selective method for C–H chlorination and bromination of various phenols under aerobic, copper-catalyzed conditions.…”

In-situ improved phenol adsorption at ions-enrichment interface of porous adsorbent for simultaneous removal of copper ions and phenol

“…The surplus positive charged had strongly attractive force with the deprotonation of the phenolic oxygen to form CuAO phenolate bond [40,41]. Therefore, the increase of attractive strength between Cu 2+ /carboxylic functionalized PGMA porous monolith and deprotonation of the phenolic oxygen would promote adsorption equilibrium of phenol.…”