On the mechanism of acceptorless dehydrogenation of N-heterocycles catalyzed by tBuOK: a computational study

The catalytic acceptorless dehydrogenation (ADH) of saturated N-heterocycles has recently gained considerable attention as a promising strategy for hydrogen release from liquid organic hydrogen carriers (LOHCs). Recently, a simple (BuOK)-Bu-t base-promoted ADH of N-heterocycles was developed by Yu et al. (Adv. Synth. Catal. 2019, 361, 3958). However, it is still open as to how the (BuOK)-Bu-t plays a catalytic role in the ADH process. Herein, our density functional study reveals that the (BuOK)-Bu-t catalyzes the ADH of 1,2,3,4-tetrahydroquinoline (THQ) through a quasi-metal-ligand bifunctional catalytic channel or a base-catalyzed pathway with close energy barriers. The hydride transfer in the first dehydrogenation process is determined to be the rate determining step, and the second dehydrogenation can proceed directly from 34DHQ regulated by the (BuOK)-Bu-t. In addition, the computational results show that the cooperation of a suitable alkali metal ion with the (BuO-)-Bu-t group is so critical that the (BuOLi)-Bu-t and the isolated (BuO-)-Bu-t are both inferior to (BuOK)-Bu-t as a dehydrogenation catalyst.

Automated summary

A simple (BuOK)-Bu-t base-promoted acceptorless dehydrogenation of saturated N-heterocycles has been discovered. This study reveals that the (BuOK)-Bu-t catalyzes the dehydrogenation process of 1,2,3,4-tetrahydroquinoline through a quasi-metal-ligand bifunctional catalytic channel or a base-catalyzed pathway.