Reusable Ni-Immobilized MOF Catalyst for Dehydrogenation of N-Heterocycles Under Milder Conditions

Herein, we have demonstrated the design and synthesis of a novel Ni-immobilized MOF as heterogeneous catalyst for the dehydrogenation of N-heterocycles. A series of five and six-membered N-heteroarenes bearing one or more heteroatoms were synthesized in up to 98 % yield (>33 examples). Late stage functionalization to the synthesis of β-glucuronides inhibitor, antimalarial drug quinine, and the nonsteroidal anti-inflammatory drug (NSAID) indomethacin were obtained under milder reactions conditions. A series of mechanistic studies revealed the detection of H₂ and H₂O₂ during the progress of the reactions and suggested the involvement of enamine-imine intermediate species for sequential dehydrogenation. Detailed characterization of the fresh catalyst and reused catalyst were performed using SEM, TEM, BET, PXRD, and EDX elemental mappings. The catalyst could be recycled up to four-times without much loss in catalytic activities. In-situ formed defects, pore size enlargement and additional Lewis acid sites within catalyst nanocrystals assisted in attaining high activity and selectivity to N-heteroarenes.