Ionic‐Liquid Hydrogen‐Bonding Promoted Alcohols Amination over Cobalt Catalyst via Dihydrogen Autotransfer Mechanism

Abstract

AbstractHigher amines are important high‐valuable chemicals with wide applications, and amination of alcohols is a green route to them, which however generally suffers from harsh reaction conditions and use of equivalent base. Herein, we report an ionic‐liquid (IL) hydrogen‐bonding promoted dihydrogen autotransfer strategy for amination of alcohols to higher amines over cobalt catalyst under base‐free conditions. Co(BF4)2 ⋅ 6 H2O complexed with triphos and IL (e. g., tetrabutylphosphonium tetrafluoroborate, [P4444][BF4]) shows high performances for the reaction and is tolerant of a wide scope of amines and alcohols, affording higher amines in good to excellent yields. Mechanism investigation indicates that the [BF4]− anion activates the alcohol via hydrogen bonding, promoting transfer of both hydroxyl H and α‐H atoms of alcohol to the cobalt catalyst to form an aldehyde intermediate and cobalt dihydride complex, which are involved in the subsequent reductive amination. This strategy provides a green and effective route for alcohol amination, which may have promising applications in alcohol‐involved alkylation reactions.