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Reactions Catalysed by a Binuclear Copper Complex: Aerobic Cross Dehydrogenative Coupling of N ‐Aryl Tetrahydroisoquinolines
Author(s) -
Liu Yuxia,
Wang Chao,
Xue Dong,
Xiao Miao,
Li Chaoqun,
Xiao Jianliang
Publication year - 2017
Publication title -
chemistry – a european journal
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.687
H-Index - 242
eISSN - 1521-3765
pISSN - 0947-6539
DOI - 10.1002/chem.201604749
Subject(s) - iminium , chemistry , catalysis , copper , nucleophile , chloride , aryl , medicinal chemistry , dimer , oxidative coupling of methane , photochemistry , amine gas treating , inorganic chemistry , organic chemistry , alkyl
Binuclear copper complex [{Cu(Sal) 2 (NCMe)} 2 ] (Sal=salicylate) was found to be an active catalyst for the aerobic oxidation of N ‐aryl tetrahydroisoquinolines to the corresponding iminium ions, which could be trapped by a wide range of nucleophiles to form coupled products. The reactions took place under 1 bar of O 2 at room temperature with 1 mol % of the copper catalyst being sufficient in most cases, and are considerably accelerated by catalytic chloride anions. Mechanistic studies show that the Cu II dimer oxidizes the amine to the iminium ion, and this two‐electron process requires O 2 , whereby the resulting Cu I is concomitantly reoxidised back to Cu II . Various lines of evidence suggest that the oxidative coupling reaction is turnover‐limited by the step of iminium formation, and it is this step that is promoted by the chloride anion. Since it is more efficient than and mechanistically distinct from the well‐studied simple copper salts such as CuBr and CuCl 2 , the binuclear copper catalyst provides a new tool for oxidative coupling reactions.