Conversion of 2-(aminomethyl) substituted pyridine and quinoline to their dicarbonyldiimides using copper(II) acetate

In air, hydrated ethanolic (95%) solution of 2-(aminomethyl) substituted pyridine and quinoline, on stirring with half equivalent of Cu(OAc)2·H2O, respectively afforded [Cu(bpca)(OAc)(H2O)]·H2O (1) and [Cu(bqca)(OAc)(H2O)] (2) {bpca = bis(2-pyridylcarbonyl)diimide ion and bqca = bis(2-quinolylcarbonyl)diimide ion} in good yields. These reactions involve oxidation of the methylene group and formation of the bond between nitrogen and carbon in N–C(O) through coupling. The complex [Cu(pqca)(OAc)(H2O)]3[Cu2(OAc)4(EtOH)2]1.5 (3) {pqca = (2-pyridylcarbonyl)(2-quinolylcarbonyl)diimide ion} was synthesized by stirring an ethanolic solution of the Schiff base [(2-pyridyl)-N-((2-quinolyl)methylene)methanamine] (L1) and with one equivalent of Cu(OAc)2·H2O. A plausible mechanism for the conversion has been proposed. The free ligands were isolated as crystalline solids from compounds 1–3, by extrusion of Cu2+ ion using EDTA2−. The molecular structures of 1–3 and bqcaH were established by X-ray crystallography and compounds having quinolyl group have π-stacking interactions.

Graphical abstractUnder mild aerobic conditions 2-(aminomethyl) substituted pyridine and quinoline were converted respectively to bis(2-pyridylcarbonyl)diimide and bis(2-quinolylcarbonyl)diimide species by stirring with copper(II) acetate monohydrate in hydrated ethanol.Figure optionsDownload full-size imageDownload as PowerPoint slide