Construction of biomass-based amines Ir-mediated -alkylation: kinetic analysis

• Published in: Green chemistry : an international journal and green chemistry resource : GC 2024-04, Vol.26 (7), p.3832-3852
• Main Authors: Liang, Meixiang, Xu, Zhongmou, Zhou, Tianhao, Chen, Limin, Chen, Jinzhu
• Format: Article
• ISSN: 1463-9262; 1463-9270
• DOI: 10.1039/d3gc04747d

Biomass-based secondary amine ( 5a ) was obtained via N -alkylation of tetrahydrofurfurylamine ( 1a ) with furfuryl alcohol ( 2a ) using a heterogeneous catalyst composed of an Ir complex immobilized in covalent triazine frameworks. The mechanistic study suggested a borrowing-hydrogen route via three consecutive/reversible steps: dehydrogenation of 2a to provide furfural ( 3a ), which is converted to imine ( 4a ), and the subsequent hydrogenation of 4a by Ir hydride formed in the first step, finally yielding 5a . Kinetic analysis revealed a rate-determining step of 2a -to- 3a dehydrogenation and the presence of reversible equilibrium in 4a -to- 5a transfer hydrogenation. However, the additionally loaded hydrogen-source of HCOONa can completely shift N -alkylation to the 5a side by significantly reducing activation energy from 55.3 to 46.8 kJ mol −1 in the 4a -to- 5a transfer-hydrogenation stage, which leads to a 15-fold increase in the rate constant for 4a hydrogenation at 140 °C. This research study highlights a kinetic understanding of N -alkylation for the construction of biomass-based amines. Kinetic analysis was performed for the construction of biomass-based amines by N -alkylation using an Ir complex immobilized in covalent triazine frameworks.