Mn–Cu composite oxides derived from MOFs for the efficient and selective oxidation of alkenes to carbonyls under mild conditions

The selective oxidation of alkenes to carbonyls is one of fundamental processes in organic synthesis. The MOFs precursor was obtained by impregnating Cu-BTC MOFs with the manganese chloride solution, and then, Mn–Cu composite oxides were obtained by pyrolysis at 400 °C. The Mn–Cu composite oxides as a heterogeneous catalyst show outstanding catalytic performance on the selective oxidation of aryl alkenes to carbonyls, utilizing oxygen as an environmentally friendly oxidant at room temperature. Under optimized reaction conditions, this catalytic system exhibited a broad scope of substrates and the maximum yield of the products was obtained up to 99%. The catalyst was characterized with various techniques (SEM, HRTEM, BET, XRD, IR, XPS, and ICP-OES). The results demonstrate that Mn–Cu catalyst exhibits a well-defined octahedral morphology and possesses abundant oxygen vacancies. Detailed mechanism experiments indicate that reactive oxygen species (ROS) are involved in this transformation, wherein the superoxide radical (O₂^·−) and singlet oxygen (¹O₂) may be the crucially active oxidants. In addition, the reaction mechanism of aerobic cracking of alkenes was reasonably proposed, and the catalyst could be recycled at least six cycles without significant decrease in catalytic activity. Based on catalyst characterization and mechanism experiments, the synergistic effect between Mn and Cu oxides in Mn–Cu composite oxides and the abundant oxygen vacancies on the surface of the catalyst could play a vital role in the selective oxidation of aryl alkenes to carbonyls.