Metal organic frameworks (MOFs) as catalysts: A combination of Cu2+ and Co2+ MOFs as an efficient catalyst for tetralin oxidation

Two metal–organic frameworks, [Cu(2-pymo)2] and [Co(PhIM)2] (2-pymo = 2-hydroxypyrimidinolate; PhIM = phenylimidazolate), containing respectively Cu2+ and Co2+ ions and anionic diazaheterocyclic ligands (pyrimidinolate and phenylimidazolate) as organic linkers, have been successfully used for the aerobic oxidation of tetralin, yielding α-tetralone (TO) as the main product. Both materials are stable and recyclable under the reaction conditions. Kinetic studies revealed significant differences between the two MOFs, as a consequence of the different catalytic behavior of their central metal ions. [Cu(2-pymo)2] is highly active for the activation of tetralin to produce tetralinhydroperoxide (TOOH), and less efficient in reacting the peroxide. Meanwhile, the use of the cobalt catalyst involves a long induction period for the reaction. However, once TOOH is formed, Co2+ rapidly and efficiently transforms this into TO, with high tetralone-to-tetralol ratio (TO/TOH of ca. 7). The combination of both materials has revealed as a convenient strategy for preparing a highly efficient, selective and reusable catalyst for the liquid phase aerobic oxidation of tetralin.