Role of Alkaline-Earth Metal-Catalyst: A Theoretical Study of Pyridines Hydroboration

Frontiers in Chemistry

Lingbo Qu¹  Yuanyuan Li¹  Meijun Wu³  Jing Zhang⁴  Haohua Chen⁵  Ruopeng Bai⁵  Dongdong Xu⁵  Yu Lan⁵ 

[1] College of Chemistry and Molecular Engineering, ZhengZhou University, ZhengZhou, China;Cooperative Innovation Center of Lipid Resources and Children's Daily Chemicals, Chongqing University of Education, Chongqing, China;Department of Biological and Chemical Engineering, Chongqing University of Education, Chongqing, China;Department of Chemistry and Chemical Engineering, Jining University, Jining, China;School of Chemistry and Chemical Engineering, Chongqing University, Chongqing, China;

关键词: alkaline-earth-metals catalyst;    theoretical study;    hydroboration;    dihydropyridine;    metal hydride complex;   

DOI  :  10.3389/fchem.2019.00149

来源: DOAJ

【 摘 要 】

Density functional theory (DFT) calculations have been performed to investigate the mechanism of alkaline-earth-metal-catalyzed hydroboration of pyridines with borane. In this reaction, the active catalytic species is considered to be an alkaline earth metal hydride complex when the corresponding alkaline earth metal is used as the catalyst. The theoretical results reveal that initiation of the catalytic cycle is hydride transfer to generate a magnesium hydride complex when β-diimine alkylmagnesium is used as a pre-catalyst. The magnesium hydride complex can undergo coordination of the pyridine reactant followed by hydride transfer to form a dearomatized magnesium pyridine intermediate. Coordination of borane and hydride transfer from borohydride to magnesium then give the hydroboration product and regenerate the active magnesium hydride catalyst. The rate-determining step of the catalytic cycle is hydride transfer to pyridine with a free energy barrier of 29.7 kcal/mol. Other alkaline earth metal complexes, including calcium and strontium complexes, were also considered. The DFT calculations show that the corresponding activation free energies for the rate-determining step of this reaction with calcium and strontium catalysts are much lower than with the magnesium catalyst. Therefore, calcium and strontium complexes can be used as the catalyst for the reaction, which could allow mild reaction conditions.

【 授权许可】

Unknown