Post synthesis strategy on Zr -based MOF as tandem catalyst for selective formation imines via alcohol -amine cross -coupling

The pore engineering through post-synthetic modification is a powerful strategy to create catalytically active MOFs and control their catalytic behavior. Controlled thermal and/or chemical treatment to remove a fraction of the organic linkers can indeed result in the generation of large-scale structural defects while the original framework remains largely intact after deligandation. As a result, a high density of open metal centers as Lewis acid sites with high potential to react with the desired analyte is obtained. In addition, the hierarchical pores of micro, meso and macro are achieved, allowing for improved mass transport and diffusion of reactants to the active catalytic sites. In this study, the focus is on demonstrating how the deliberate creation of structural defects on a large scale can yield a defective MOF-۸۰۸. This defective Q-MOF-۸۰۸ serves as a tandem catalyst in a one-pot cross-coupling system for the conversion of derivatives of benzyl alcohol and aniline into the corresponding imine. For this purpose, an innovative, recyclable and robust defective Zr-based MOF-۸۰۸ was developed, enabling highly selective imine formation from substituted benzyl alcohol and aniline in toluene. This reaction could be performed under open air conditions at ۶۰ °C without the need for a base or dehydrating agent. The catalyst can be easily synthesized through a post-synthetically controlled thermal treatment of the parent MOF-۸۰۸ under an air atmosphere at ۳۴۰ °C. The QMOF-۸۰۸ catalyst demonstrates the ability to selectively facilitate the direct synthesis of various derivative imines from substituted benzyl alcohol and aniline, achieving high conversion efficiencies. The porous structures and active sites of Zr(IV) centers played crucial roles in the tandem catalytic process. The Zr(IV) centers within the MOF framework acted as catalytic sites, facilitating the desired chemical transformations and promoting the selective formation of imines. Furthermore, the study on the substitution of various substituents on benzyl alcohol and aniline revealed that the rate-determining step in the tandem imine formation catalyzed by Q-MOF-۸۰۸ is the aerobic conversion of alcohol to aldehyde. Additionally, the catalyst exhibited high activity and stability even after several reuses under the investigated conditions. This study demonstrates the potential of obtaining diverse heterogeneous defective MOFs with a high density of unsaturated active metal centers, such as Lewis acids, through facile approaches of post-synthetic structure modification.

کلیدواژه ها:

Defective Zr -MOF ، Pore engineering ، Imine formation ، Selectivity