Copper(I) and copper(II) metallacycles as catalysts for microwave assisted selective oxidation of cyclohexane. (25th September 2017)

• Record Type: Journal Article
• Authors: Galassi, Rossana; Simon, Oumarou Camille; Burini, Alfredo; Tosi, Giorgio; Conti, Carla; Graiff, Claudia; Martins, Nuno M.R.; Guedes da Silva, M. Fátima C.; Pombeiro, Armando J.L.; Martins, Luísa M.D.R.S.
• Is Part Of: Polyhedron. Volume 134(2017)
• Page Start: 143
• Page End: 152
• Publication Date: 2017-09-25
• Subjects: Synthesis -- Alkane oxidation -- MW assisted oxidation catalysis -- Pyrazole -- Copper; Chemistry, Inorganic -- Periodicals; Chimie inorganique -- Périodiques; Organometaalverbindingen; Anorganische chemie; 546.05
• DOI: 10.1016/j.poly.2017.06.020
• Languages: English
• ISSNs: 0277-5387

Abstract

Graphical abstract: Cu(I) and Cu(II) metallocycles were prepared with pyrazolates having CF3 or NO2 groups in the 3 and 5 positions. According to similar reaction routes, they yielded a hydrated hexanuclear metallocycle [(µ-pz)Cu(µ-OH]6 and a dinuclear compound with an N2- Cu2 (PPh3 )2 -N2 boat shaped core, respectively. Both compounds are active as homogenous catalysts for MW assisted neat peroxidation of cycloalkanes by a radical mechanism. Abstract: New copper(I) and copper(II) pyrazolate compounds have been prepared by similar synthesis procedures. For the 3, 5-NO2 -pyrazole ligands, the dinuclear cyclic Cu(I) compound [Cu2 (µ-N, N-3, 5-(NO2 )2 pz)2 (PPh3 )2 ], 1, was the only compound isolated in high yield, while in the case of the 3, 5-bis(trifluoromethyl)-pyrazole ligand a spontaneous rearrangement to the hexanuclear cyclic [trans-Cu6 (µ-OH)6 (µ-3, 5-(CF3 )2 pz)6 ], 2, was observed. The formation of this latter compound ruled out an anion templating mechanism for the synthesis. X-ray diffraction analysis of1 revealed that the copper cation is in a trigonal environment and involved in a six-membered Cu2 N4 core; while the structural analysis of2 showed that the metal adopts a square-planar geometry, forms five-membered Cu2 N2 O rings and ultimately gives rise to a large Cu6 (N2 O)6 crown-type assembly. Compounds1 and2 act as very effective homogeneous catalysts towards the neat microwave (MW) assisted peroxidative (with aq. tert-butyl hydroperoxide, TBHP) oxidation of cyclohexane to cyclohexanol and cyclohexanone (total yield up to 58% in 30 min reaction time) via formation of cyclohexyl hydroperoxide (CyOOH) as the primary product.