Single-Pore versus Dual-Pore Bipyridine-Based Covalent–Organic Frameworks: An Insight into the Heterogeneous Catalytic Activity for Selective C-H Functionalization

Abstract

Exponential growth in the field of covalent–organic frameworks (COFs) is emanating from the direct correlation between designing principles and desired properties. The comparison of catalytic activity between single-pore and dual-pore COFs is of importance to establish structure–function relationship. Herein, the synthesis of imine-linked dual-pore [(BPyDC)]x%-ETTA COFs (x = 0%, 25%, 50%, 75%, 100%) with controllable bipyridine content is fulfilled by three-component condensation of 4,4′,4″,4′″-(ethene-1,1,2,2-tetrayl)tetraaniline (ETTA), 4,4′-biphenyldialdehyde, and 2,2′-bipyridyl-5,5′-dialdehyde in different stoichiometric ratio. The strong coordination of bipyridine moieties of [(BPyDC)]x%-ETTA COFs with palladium imparts efficient catalytic active sites for selective functionalization of sp2 C-H bond to C-X (X = Br, Cl) or C-O bonds in good yield. To broaden the scope of regioselective C-H functionalization, a wide range of electronically and sterically substituted substrates under optimized catalytic condition are investigated. A comparison of the catalytic activity of palladium decorated dual-pore frameworks with single-pore imine-linked Pd(II) @ Py-2,2′-BPyDC framework is undertaken. The finding of this work provides a sporadic example of chelation-assisted C-H functionalization and disclosed an in-depth comparison of the relationship between superior catalytic activity and core properties of rationally designed imine linked frameworks.