Metal-Organic Framework/Organocatalyst Combinations as Powerful Multicatalytic Systems for Aerobic Oxidations

Aerobic oxidation using molecular oxygen as terminal oxidant represents a sustainable route to access valuable organic compounds. However, achieving high selectivity in such transformations remains challenging. Here, an easily tunable biomimetic multicatalytic system combining robust Metal-Organic Frameworks and simple, commercially available, (hydro)quinone-type molecules as co-catalysts, which mimics the cooperative action of enzyme/coenzyme pairs in a confined environment is reported. A Zr-MOF-808/1,8-dihydroxynaphthalene semiheterogeneous system enables the aerobic oxidation of anilines to azoxybenzenes, products that are typically elusive under aerobic conditions, with excellent yields and selectivity. Electron transfer triggers the formation of active oxidation sites in the MOF/(hydro)quinone interface, able to generate reactive oxygen species from O₂ under mild conditions without the need for light or other external stimuli. The generality of this novel multicatalytic approach is demonstrated by expanding it to different reactions and catalytic systems. In particular, the aerobic oxidation of thiols to disulfides is achieved by changing the organic co-catalyst, whereas benzylamines are aerobically oxidized to their corresponding coupled products by employing a Ti-based MOF (Ti-MIL-125) together with another co-catalyst. Overall, this work highlights the untapped potential of MOF/organocatalyst combinations to drive challenging reactions under environmentally benign conditions.