Simultaneous Pore Confinement and Sidewall Modification of a N-rich COF with Pd(II): An Efficient and Sustainable Heterogeneous Catalyst for Cross-coupling Reactions

Abstract

Covalent organic frameworks (COFs) are crystalline porous materials bearing well-ordered two- or three-dimensional molecular tectons in their polymeric skeletal framework. COFs are structurally robust as well as physiochemically stable. Recently, these are being developed for their use as “heterogeneous catalysts” for various organic transformations. In particular, research in the use of COFs for catalysis for different C-C cross-coupling reactions is in its infancy. To date, COF catalysts reported for such reactions bear Pd(II) bound to an exclusive coordination environment and have been explored for a particular organic reaction. Herein, we report, for the first time, a COF (Pd@COF-TFP_TzPy) that can anchor Pd(II) units in the polymeric framework in two different coordination environments. Thus, Pd@COF-TFP_TzPy is a porous material with dual confinement environment for Pd(II) units. The precursor COF (COF-TFP_TzPy) was easily synthesized and it features a two-dimensional hexagonal sheet structure, for facile incorporation of Pd(II) ions. Loading of Pd(II) in Pd@COF-TFP_TzPy was low (4.859 wt% of Pd), yet the material exhibited excellent catalytic activity in the diverse C-C cross-coupling reactions with broad substrate scope. Furthermore, Pd@COF-TFP_TzPy is highly stable and recyclable, thereby ensuring sustainable utilization of expensive Pd metal. We anticipate that our approach will stimulate further research into designing and utilizing functional COF materials for catalysis.