担持PdあるいはAu-Pd合金ナノ粒子触媒による脱水素芳香環形成反応

抄録

In recent years, dehydrogenative aromatization has emerged as an efficient strategy for the synthesis of important aromatic compounds, such as phenols and anilines, from ubiquitous saturated six-membered carbocyclic compounds. Starting with the report of homogeneously Pd-catalyzed dehydrogenative aromatization of cyclohexanones to phenols using molecular oxygen as the terminal oxidant by Stahl and co-workers, to date numerous homogeneously Pd, Cu, or Ir-catalyzed systems have been developed for the synthesis of phenols, anilines, and aryl ethers. On the other hand, heterogeneous supported metal catalysts have traditionally been utilized to dehydrogenate cyclohexane to benzene under harsh (gas-phase) conditions, but it is rarely known that they can be applied to liquid-phase fine chemicals synthesis under relatively mild conditions. Quite recently, we have successfully developed efficient supported Pd or Au-Pd alloy nanoparticles-catalyzed dehydrogenative aromatization reactions; for example, conversion of cyclohexanols/cyclohexanones to phenols, selective conversion of cyclohexylamines to either primary anilines or diarylamines, and one-pot synthesis of unsymmetrically substituted diarylamines. The metal nanoparticle-support cooperation is the key point for efficiently promoting dehydrogenation and realizing high selectivity to the desired products. The proposed reactions are expected to be novel green synthesis methods for important chemicals such as phenols and anilines because they can use molecular oxygen as the terminal oxidant or even proceed under oxidant-free conditions. The catalyses for these reactions are truly heterogeneous, and the catalysts can be easily retrieved from the reaction mixture and reused several times without significant loss of their high catalytic performance.