Oxidation of cycloalkanes with molecular oxygen in the presence of salen metallocomplexes in thermomorphic conditions

The oxidation of cycloalkanes with molecular oxygen, catalyzed by two groups of metallosalen complexes, was studied. The first group consisted of salen complexes with different metals such as Mn, Fe, Co, Ni, Cu, Zn, while the second group was composed of manganese salen complexes with different substituents (t-butyl electron-donating substituents and/or electron-withdrawing perfluoroalkyl substituents). Mn, Fe and Co salen complexes are the most active catalysts, while Ni, Cu and Zn salen complexes are far less efficient. The introduction of t-butyl electron-donating substituents into Mnsalen complex increases the catalytic activity and catalysts solubility in the reaction mixture. The introduction of perfluoroalkyl electron-withdrawing substituents enhances the catalytic activity and renders the solubility of the catalyst temperature dependent (thermomorphic behaviour), thus allowing one to recover them easily after the reaction by simply cooling the system to room temperature. The synthesis of two new manganese salen complexes with perfluoroalkyl substituents was elaborated. (C) 2013 Elsevier B.V. All rights reserved.