Engineering noble-metal-free metal–organic framework composite catalyst for efficient CO2 conversion under ambient conditions

Abstract

The cyclization of propargylic alcohols and propargylic amines with CO2 are of great significance since the generated O/N-containing cyclic skeletons are extensively employed in pharmaceutical chemistry and industrial production. However, most of the reported catalysts only effectively catalyze propargylic alcohols or propargylic amines with CO2, and often involve noble-metal catalysts, high temperature and CO2 pressure. It is a great challenge that non-noble-metal catalysts catalyzed both propargylic alcohols and propargylic amines with CO2 under ambient conditions. Herein, CuBr@NH2-MIL-101 was successfully synthesized by loading CuBr nanoparticles into zeolite-type NH2-MIL-101 via simple thermal conversion method, and it displayed highly selective CO2 uptake properties. Importantly, CuBr@NH2-MIL-101 featured high catalytic activity for carboxylative cyclization of both propargylic alcohols and propargylic amines with CO2 under ambient conditions (25 °C, 0.1 MPa CO2), respectively. Moreover, CuBr@NH2-MIL-101 can be recycled at least three times without significant decline in catalytic activity. The combination explorations of NMR, FTIR and 13C isotope labeling experiments clearly illustrate the reaction process and mechanism. The density functional theory (DFT) calculations uncover that CuBr and 1,8-diazabicyclo[5.4.0]undec-7-ene (DBU) can synergistically activate substrates, and the proton-demetalation step with the highest energy barrier was the rate-determining step in two catalytic systems. To our knowledge, it is the first report of noble-metal-free catalyst that can simultaneously catalyze CO2 conversion with propargylic alcohols and propargylic amines under room temperature and atmospheric CO2 pressure.