Sulfonate-Grafted Metal–Organic Frameworks for Reductive Functionalization of CO<sub>2</sub> to Benzimidazoles and <i>N</i>-Formamides
Zecheng Ye, Jinzhu Chen
Abstract
Metal–organic frameworks (MOFs) with inner salt of 3-(pyridinylium)-1-propanesulfonate (PS) as the organic linkage were developed as catalysts (PS/MOFs) for reductive functionalization of carbon dioxide (CO2) to benzimidazoles and N-formamides. The pendant −SO3– anion in the PS/MOFs acted as an organocatalytic active site for reductive cyclization of CO2 with 1,2-phenylenediamine to afford 1H-benzo[d]imidazole. A linear correlation was observed between the catalytic performance (in terms of turnover frequencies) and the specific surface area of PS/MOFs at a low conversion level of 1,2-phenylenediamine. Our theoretical investigation revealed significantly reduced energy barriers from 2.03 eV under catalyst-free conditions to 0.97 eV in the presence of the catalyst. The developed PS/MOFs can efficiently promote a broad range of benzimidazoles in 88–99% yields through reductive cyclization. Moreover, the PS/MOFs can readily catalyze N-formylation of various monoamines with CO2 as the carbonyl source for quantitative syntheses of N-formamides. The research thus highlights MOF-based catalysts for organocatalytic transformation of CO2 into high value-added chemicals.