Efficient Conversion of CO₂ and Homopropargylic Amines Promoted by a Stable Noble Metal-Free Cu₂O@MOF Heterogeneous Catalyst

The cyclization reaction of homopropargylic amines and CO2 to access value-added six-membered heterocycles (1,3-oxazinan-2-ones) is highly desirable yet still a great challenge. Noble metal catalysts are often involved for achieving efficient conversion of this reaction. Herein, one robust porous Fe-based metal–organic framework (MOF) 1 was prepared, featuring good thermal and solvent/pH stabilities. By encapsulating Cu2O nanoparticles inside the cages of 1, the resultant non-noble metal catalyst Cu2O@1 can highly catalyze the cyclization of homopropargylic amines and CO2 with the turnover number of 10.9, and it can be recycled at least five times. Moreover, this composite MOF catalyst also exhibits rarely catalytic activity for the dopamine derivative and dehydroabietylamine derivative. The reaction mechanism is proposed by nuclear magnetic resonance, 13C isotope labeling tests, and density functional theory calculations, suggesting that the synergistic catalytic effect between Cu2O and 1,8-diazabicyclo[5.4.0]undec-7-ene promotes this reaction, and the protonation process with the energy barrier of 10.6 kcal/mol was the rate-limiting step. In this work, we successfully realized the heterogeneous conversion of CO2 with homopropargylic amines catalyzed by a noble metal-free catalyst.