Catalytic activity of Copper(I) and Copper(II) 3,5-dinitro- or 3,5-bis(trifluoromethyl)-pyrazolate derivatives

Catalytic activity of Copper(I) and Copper(II) 3,5-dinitro- or 3,5-bis(trifluoromethyl)-pyrazolate derivatives. Rossana Galassi,a Oumarou Camille Simon,a* Claudia Graiff,b M. Fátima C. Guedes da Silva,c Nuno M. R. Martins,c Luísa M. D. R. S. Martins,c,d Armando J. L. Pombeiroc a School of Science and Technology, Via S. Agostino 1, 62032 Camerino (MC), Italy, *camillesimon.oumarou@unicam.it b Dipartimento di Chimica, Parco Area delle Scienze 17/A, Parma, Italy c Centro de Química Estrutural, Complexo I, Instituto Superior Técnico, Universidade de Lisboa, Portugal. d Chemical Engineering Departament, Instituto Superior de Engenharia de Lisboa, Instituto Politécnico de Lisboa, Portugal. The reaction of [µ-N,N-Cu-(3,5(CF3)2pz]3 (1) with halide sources led to the formation of Cu(II) hexanuclear derivatives such as [(Cu((CF3)2pz)6(OH)6)  X][Bu4N] (2a)(Cl-), (2b) (Br-), (2c) (I-), (2d) (NO2-).[1] If the reaction occurs in the same conditions but without halides, a highly hydrated hexanuclear metallocycle [(Cu((CF3)2pz)6(OH)6)  (H2O)n], (3), was isolated, ruling out the template action of the anions. By replacing the CF3 groups with NO2 groups in the pyrazole, neither the trinuclear nor the hexanuclear copper derivatives were obtained, and the dinuclear [Cu-(3,5-(NO2)2pz)(PPh3)]2 compound, (4), was the only Cu(I) derivative isolated in good yield. Even though CF3 and NO2 are both withdrawing groups, a pronounced different chemical behavior was already revealed in the case of similar pyrazolate silver(I) derivatives.[2] All compounds were characterized by elemental analysis, NMR, IR spectroscopy and ESI-MS spectrometry. In the case of compound 4 its crystal structure has been determined by X Ray diffraction analysis, evidencing its dinuclear nature, build up by two bridging ligands which coordinate two copper atoms through nitrogen donors, forming a six member ring with boat conformation. Compounds (3) and (4) act as catalysts towards the microwave (MW) assisted peroxidative oxidation of cyclohexane to cyclohexanol and cyclohexanone under mild conditions, which is of industrial significance for the synthesis of Nylon-6,6. High yield (up to 51% of oxygenated products) is obtained after 2h of MW irradiation, using a maximum of 0.2% molar ratio of 3 (the best catalyst) relatively to the substrate in the presence of TEMPO. The efficiency of the catalytic systems as well as the influence of various parameters, such as the reaction time, amount of catalyst, temperature and presence of different additives, are discussed. The work was partially supported by the Fundação para a Ciência e a Tecnologia (project UID/QUI/00100/2013) [ ] Galassi, R.; Burini, A.; Ahmed, A. M. Eur. J. Inorg. Chem. 2012, 3257. [2] Galassi, R.; Ricci, S., Burini, A., Macchioni A., Rocchiggiani, L., Marmottini, F., Tekarli, S. M., Nesterov, V. N. Omary M. A. Inorg. Chem., 2013, 52, 14124.