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Polynuclear Copper(II) Complexes as Catalysts for the Peroxidative Oxidation of Cyclohexane in a Room‐Temperature Ionic Liquid

2014; Wiley; Volume: 2014; Issue: 27 Linguagem: Inglês

10.1002/ejic.201402352

1099-0682

Raja Jlassi, Ana P. C. Ribeiro, M. Fátima C. Guedes da Silva, Kamran T. Mahmudov⧫, Maximilian N. Kopylovich, Tatiana B. Anisimova, Houcine Naı̈li, Gonçalo A. O. Tiago, Armando J. L. Pombeiro,

Polyoxometalates: Synthesis and Applications

Abstract The reaction of copper(II) nitrate hydrate with sodium 2‐[2‐(2,4‐dioxopentan‐3‐ylidene)hydrazinyl]terephthalate (Na 2 H L 1 ) in the absence or presence of imidazole (im) leads to the new complexes [(H 2 O)Cu 0.5 {(μ‐ L 1 ‐1κ O :2κ 3 N , O′ , O″ )Cu(H 2 O) 2 }] 2 ( 1 ) and [Cu(im)(μ‐H L 1 ‐1κ O :2κ 3 N , O , O′ )] 2 ( 2 ), respectively, whereas the 1D coordination polymer [Cu 2 (H 2 O) 2 (μ‐H 2 L 2 ‐1κ 3 N , O , O′ :2κ O″ )(μ‐ L 2 ‐1κ 3 N , O , O′ :2κ 2 N′ , O″ )] n ( 3 ) is obtained from Cu(NO 3 ) 2 · 2.5H 2 O and sodium 2‐[2‐(4,4‐dimethyl‐2,6‐dioxocyclohexylidene)hydrazinyl]terephthalate (Na 2 H L 2 ). All of the compounds were characterized by ESI‐MS, IR spectroscopy, elemental analysis and X‐ray diffraction analysis. Di‐ or tri‐deprotonated ligands display different coordination modes and lead to distinct nuclearities of the Cu II complexes depending on the conditions used for the syntheses. Complexes 1 – 3 were successfully tested as dual‐role catalysts for cyclohexane oxidation under acid‐free conditions in the ionic liquid [1‐butyl‐3‐methylimidazolium tetrafluoroborate, (bmim)(BF 4 )] as well as in acetonitrile. The application of the ionic liquid (IL) increased the product yield and turnover number and decreased the reaction time, in comparison with those for the use of the conventional acetonitrile solvent. Easy recycling of the catalyst, with preservation of almost the initial activity and selectivity, was also achieved by using the IL medium.