Atomic-Level Asymmetric Tuning of the Co<sub>1</sub>–N<sub>3</sub>P<sub>1</sub> Catalyst for Highly Efficient <i>N</i>-Alkylation of Amines with Alcohols
Huan Liu, Luyao Tian, Zhentao Zhang, Ligang Wang, Jialu Li, Xiao Liang, Jiahao Zhuang, Hang Yin, Da Yang, Guofeng Zhao, Fabing Su, Dingsheng Wang, Yadong Li
Abstract
Despite the extensive development of non-noble metals for the N -alkylation of amines with alcohols, the exploitation of catalysts with high selectivity, activity, and stability still faces challenges. The controllable modification of single-atom sites through asymmetric coordination with a second heteroatom offers new opportunities for enhancing the intrinsic activity of transition metal single-atom catalysts. Here, we prepared the asymmetric N/P hybrid coordination of single-atom Co 1 –N 3 P 1 by absorbing the Co–P complex on ZIF-8 using a concise impregnation-pyrolysis process. The catalyst exhibits ultrahigh activity and selectivity in the N -alkylation of aniline and benzyl alcohol, achieving a turnover number (TON) value of 3480 and a turnover frequency (TOF) value of 174 –h . The TON value is 1 order of magnitude higher than the reported catalysts and even 37-fold higher than that of the homogeneous catalyst CoCl 2 (PPh 3 ) 2 . Furthermore, the catalyst maintains its high activity and selectivity even after 6 cycles of usage. Controlling experiments and isotope labeling experiments confirm that in the asymmetric Co 1 –N 3 P 1 system, the N -alkylation of aniline with benzyl alcohol proceeds via a transfer hydrogenation mechanism involving the monohydride route. Theoretical calculations prove that the superior activity of asymmetric Co 1 –N 3 P 1 is attributed to the higher d-band energy level of Co sites, which leads to a more stable four-membered ring transition state and a lower reaction energy barrier compared to symmetrical Co 1 –N 4 .