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

Lishuang Ma; Wenxu Feng; Shidong Zhao; Chuangye Wang; Yanyan Xi; Xufeng Lin

doi:10.1039/d3ra04305c

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

RSC Adv. 2023 Jul 11;13(30):20748-20755. doi: 10.1039/d3ra04305c. eCollection 2023 Jul 7.

Authors

Lishuang Ma¹, Wenxu Feng¹, Shidong Zhao¹, Chuangye Wang¹, Yanyan Xi², Xufeng Lin^{1

2}

Affiliations

¹ College of Chemistry and Chemical Engineering, China University of Petroleum (East China) Qingdao 266580 P. R. China hatrick2009@upc.edu.cn.
² State Key Laboratory of Heavy Oil Processing, China University of Petroleum (East China) Qingdao 266580 P. R. China.

Abstract

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 ^tBuOK 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 ^tBuOK plays a catalytic role in the ADH process. Herein, our density functional study reveals that the ^tBuOK 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 ^tBuOK. In addition, the computational results show that the cooperation of a suitable alkali metal ion with the ^tBuO^- group is so critical that the ^tBuOLi and the isolated ^tBuO^- are both inferior to ^tBuOK as a dehydrogenation catalyst.