N-formylation of amines with CO₂ by using Zr-based metal-organic frameworks: Contribution of defect sites of MOFs to N-formylation

N-formylation of amines (NFAs) like N-methylaniline and morpholine with CO₂ was done under mild condition (0.1 MPa, 30 °C) in the presence of PhSiH₃ as a reductant by using Zr-based MOFs like MOF-808 s (with various defect concentrations), UiO-66, and UiO-67. Preparing useful N-formamides from amines is one of the attractive ways to utilize CO₂. The yield of N-methylformanilide from N-methylaniline linearly increased with increasing the defect concentration of MOF-808. Moreover, the performance of MOF-808(6), with the highest defect sites, decreased with the elimination of defects. Amorphized MOF-808(6), with increased defects, showed an impressive performance in NFAs, although the porosity decreased much upon amorphization. Therefore, defect sites had a dominant role in the NFAs, especially in the adsorption or activation of carbamate-like intermediates and silane. Moreover, defective MOF-808(6), prepared in one step (without any functionalization), might be a competitive/recyclable catalyst for NFAs, especially under mild conditions.