Copper(ii)-benzotriazole coordination compounds in click chemistry: a diagnostic reactivity study

This diagnostic study aims to shed light on the catalytic activity of a library of Cu(ii) based coordination compounds with benzotriazole-based ligands. We report herein the synthesis and characterization of five new coordination compounds formulated as [Cu-II(L-4)(MeCN)(2)(CF3SO3)(2)] (1), [Cu-II(L-5)(2)(CF3SO3)(2)] (2), [Cu-II(L-6)(2)(MeCN)(CF3SO3)](CF3SO3) (3), [Cu-II(L-6)(2)(H2O)(CF3SO3)](CF3SO3)2(Me2CO) (4), and [CuI4(L-1)(2)(L-1)(2)(CF3SO3)(2)](2)4(CF3SO3)8(Me2CO) (5), derived from similar nitrogen-based ligands. The homogeneous catalytic activity of these compounds along with our previously reported coordination compounds (6-13), derived from similar ligands, is tested against the well-known Cu(i)-catalysed azide-alkyne cycloaddition reaction. The optimal catalyst [Cu-II(L-1)(2)(CF3SO3)(2)] (10) activates the reaction to afford 1,4-disubstituted 1,2,3-triazoles with yields up to 98% and without requiring a reducing agent. Various control experiments are performed to optimize the method and examine parameters such as ligand variation, metal coordination geometry and environment, in order to elucidate the behaviour of the catalytic system.