Cu 6 - and Cu 8 -Based Acetylacetonate/Phenylsilsesquioxane Cages: Synthesis, Structure, and Activity in Oxidative Catalysis

Self-assembly of phenylsiloxanolate/acetylacetonate copper complexes resulted in the solvent-controlled (MeCN/EtOH vs DMF or CH2Cl2) isolation of two types of cage complexes. Depending on (Cu6 or Cu8) nuclearity, molecular architectures differ in the number of acetylacetonate species (two or four), while keeping the same sandwich-type cage structure with a pair of Si5-cyclic ligands. The complexes are active precatalysts in the oxidative amidation (OA) reaction of benzylic alcohols and amine hydrochlorides. The developed catalytic protocol led to amides in good to excellent yields with only 100 ppm of Cu loading. The catalysts were also successfully evaluated in the oxidation of aniline to nitrobenzene with use of tert-butyl hydroperoxide (TBHP).