Journal
APPLIED CATALYSIS B-ENVIRONMENTAL
Volume 309, Issue -, Pages -Publisher
ELSEVIER
DOI: 10.1016/j.apcatb.2022.121264
Keywords
Photocatalysis; Cross-coupling; Metal cocatalyst; Imines and secondary amines; Selectivity control
Funding
- National Natural Science Foundation of China (NSFC) [21972100, 52073006, 11874003, 51672018]
- Priority Academic Pro-gram Development of Jiangsu Higher Education Institutions (PAPD) [NH10800120]
- Beijing Natural Sci-ence Foundation [Z180007]
- National Key R&D Program of China [2018YFE0202700]
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This study utilizes metal cocatalysts to activate alcohols in photocatalytic reactions, separating the stepwise dehydrogenative-condensation process to imine and the direct condensation process to secondary amine. The Rh/TiO2 catalyst promotes the photocatalytic dehydrogenation of alcohol into aldehyde, allowing rapid condensation with aniline to yield imine. On the other hand, Fe/TiO2 catalyst activates the alcohol mildly and enables direct dehydrative coupling with aniline to produce secondary amine. Both Rh/TiO2 and Fe/TiO2 photocatalysts show excellent performance in terms of conversion, selectivity, stability, and a wide substrate scope, making this strategy promising for applications.
Cross coupling of aniline and alcohol for the synthesis of imine and secondary amines represents a highly atom efficient processes, yet achieving high selectivity requires specialized catalysts and harsh reaction conditions to avoid over-hydrogenation of as-produced imines and dehydrogenation of secondary amines. Here we employ metal cocatalysts to mediate photocatalytic activation of alcohols, thus separating the stepwise dehydrogenative-condensation process to imine and the direct condensation process to secondary amine. The Rh/TiO2 promotes the photocatalytic dehydrogenation of alcohol into aldehyde and molecular hydrogen, resulting in rapid condensation of aldehyde with aniline to yield imine. In contrast, Fe/TiO2 activates the alcohol mildly without forming aldehyde and hydrogen atoms under irradiation, allowing a direct dehydrative coupling of the activated alcohol with aniline to produce secondary amine. Both Rh/TiO2 and Fe/TiO2 photocatalysts show high performance in terms of conversion, selectivity, stability and a wide substrate scope, rendering the strategy promising for applications.
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