On the mechanism of acceptorless dehydrogenation of N-heterocycles catalyzed by (t)BuOK: 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 (t)BuOK 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 (t)BuOK plays a catalytic role in the ADH process. Herein, our density functional study reveals that the (t)BuOK 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 (t)BuOK. In addition, the computational results show that the cooperation of a suitable alkali metal ion with the (t)BuO(−) group is so critical that the (t)BuOLi and the isolated (t)BuO(−) are both inferior to (t)BuOK as a dehydrogenation catalyst.