Novel cyano-activated Cu(ii) complexes of arylhydrazones of active methylene nitriles and their catalytic application for azide-alkyne cycloaddition in water and glycerol

The reaction of 2-(2-(dicyanomethylene)hydrazineyl)benzoic acid (H2L1) with copper(II) acetate in the absence or presence of imidazole (im), 4,40-bipyridine (4,4'-bipy) or pyridine (py) leads to the new complexes [Cu-2(CH3OH)(2)(m-L-1a)(2)] (1), [Cu(L-1a)(im)] (2), [Cu(L-1a)(H2O)(4,4'-bipy)]center dot H2O (3) or [Cu(L-1a)(py)] (n) (4), respectively, where (L-1a)(2)center dot = (Z)-1-(2-carboxylatophenyl)-2-(1-cyano-2-imino-2-methoxyethylidene)hydrazin-1-ide. A onepot activation of nitrile groups in the reaction of copper(II) acetate monohydrate with 2-(2-(dicyanomethylene)hydrazineyl)terephthalic acid (H3L2) in the presence of pyridine in methanol affords the trinuclear Cu(II) complex [Cu(py)2{Cu(py)(m-L-2a)}2] (5), where (L-2a)3 center dot = (Z)-2-((1-cyano-2-imino-2-methoxyethylidene)-1(2,5-dicarboxylatophenyl)hydrazin-1-ide). Both arylhydrazone ligands and the auxiliary ligands were used to modulate the nuclearity and design of the supramolecular arrangements of the obtained Cu(II) complexes. The complexes were characterized by elemental analyses, electrospray ionization mass spectrometry (ESI-MS), and FT-IR spectroscopy. Their molecular structures were established using single crystal X-ray diffraction (SCXRD) analysis. The catalytic activity of the complexes was investigated for the microwave assisted 1,3-dipolar azidealkyne cycloaddition reaction using a mixture of water and glycerol as reaction medium. Pre-catalyst 1 was found to be the most efficient one by affording a quantitative conversion to 1,4-disubstituted-1,2,3-triazoles after 30 minutes at 125 1C. The catalytic system proceeds with a broad scope of substrates according to ``Click'' rules.