Copper(II) complexes with an arylhydrazone of methyl 2-cyanoacetate as effective catalysts in the microwave-assisted oxidation of cyclohexane.

Reaction of sodium (E/Z)-2-(2-(1-cyano-2-methoxy-2-oxoethylidene)hydrazinyl)benzene-sulfonate (NaHL) with copper(II) nitrate hydrate in the presence of imidazole (im) in methanol affords [CuL(im)(H 2 O)] ( 1 ). Complex 1 is characterized by IR spectroscopy and ESI-MS spectrometry, elemental and single crystal X-ray crystal structural analyses. The coordination environment of the central copper(II) is nearly intermediate between ideal square-based pyramidal and trigonal bipyramidal geometry, three sites being occupied by the L 2− ligand, which chelates in the O, N, O fashion, while two other sites are filled with the water and imidazole molecules. Extensive intermolecular hydrogen bonds between the L 2− , water and imidazole ligands lead to a 3D supramolecular network. 1 and known Cu(II) complexes [Cu(H 2 O) 2 L]·H 2 O ( 2 ), [Cu(H 2 O)(py)L]·H 2 O ( 3 ) and [Cu 3 (µ 3 -OH)(NO 3 )(CH 3 OH)(µ 2 -X) 3 (µ 2 -HL)] ( 4 ) act as effective catalysts in the oxidation of cyclohexane to cyclohexanol and cyclohexanone, using low power microwave (MW) irradiation, under mild conditions. Without a promoter, the activity of the catalyst reached a turnover number of 1.44 × 10 3 and a turnover frequency of 1.98 × 10 3  h −1 , after 2 h, at 50 °C. [ABSTRACT FROM AUTHOR]