Sulfonate-Grafted Metal-Organic Frameworks for Reductive Functionalization of CO2 to Benzimidazoles and N-Formamides

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 functional-ization 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.

Automated summary

This study demonstrates the development of metal-organic frameworks (MOFs) with inner salt of 3-(pyridinylium)-1-propanesulfonate (PS) as catalysts (PS/MOFs) for the reductive functionalization of carbon dioxide (CO2) to benzimidazoles and N-formamides. The PS/MOFs show efficient catalytic activity for the synthesis of benzimidazoles and N-formamides through reductive cyclization. The research highlights the potential of MOF-based catalysts for organocatalytic transformation of CO2 into high value-added chemicals.