Cagelike Manganesesilsesquioxane Complexes: Synthesis via an Acetone Approach, Structure, and Catalytic Activity for Toluene Oxidation

Abstract

The study describes a new feature in the self-assembly of cagelike manganese-based phenylsilsesquioxanes consisting of the strong influence of acetone solvates on the formation of a cage structure. By this convenient approach, a series of new tri and tetra manganese-based silsesquioxane complexes with (i) 1,10-phenanthroline, (ii) pyrazine, or (iii) 3,5-dimethylpyrazole (dmpzH) ligands were isolated and characterized. Single-crystal X-ray diffraction studies established the molecular architectures of all of the synthesized products. Several compounds represent extraordinary types of cagelike metallasilsesquioxane (CLMS) molecular architectures. Pyrazine- and dmpzH-based Mn3Na3 compounds exhibit total oxidation of initial Mn(II) ions to the Mn(III) state. They present relatively weak antiferromagnetic interactions between the manganese centers. The catalytic performance of a representative precatalyst Mn-CLMS compound, [(Ph6Si6O12)2Mn3Na3(dmpzH)3(acetone)3(H2O)], was investigated for the microwave-assisted oxidation of toluene to obtain benzaldehyde, benzyl alcohol, and benzoic acid as the main products. The effects of reaction parameters were studied, and under optimized conditions, using the tBuOOH oxidant, the oxygenated products were formed with a total yield of 54%, under microwave irradiation at 100 °C after 6 h, with 70% selectivity toward the formation of benzoic acid.