Bis(Biguanide)-Anchored Palladium on Covalent Organic Framework: Highly Stable and Recyclable Catalyst for Suzuki, Heck, and Sonogashira Reactions

The palladium-catalyzed cross-coupling reactions are promising methods for carbon–carbon bond formation. In recent decades, porous nanomaterials such as covalent organic frameworks (COFs) have been developed to address the challenges of homogenous catalysts, particularly rapid deactivation and recycling; however, achieving high catalyst loading with stable catalytic performance remains a significant challenge. In this study, we developed a nitrogen-enriched COF with large channels by using bis(biguanide) (DG) and triphenylbenzene (TPB) as building blocks. The bis(biguanide)s offer multiple binding sites, enabling high binding affinity, resulting in the uniform immobilization of Pd(II) with high loading to form Pd/DG-COF. The intersecting TPB structure provides a large pore size, allowing for improved mass transport for efficient catalysis. Additionally, the inherent physiochemical properties of DG and TPB result in potential cation-π interactions and π-π interactions with benzene-based substrates, which significantly accelerate the catalytic activity, resulting in a good catalytic performance, with turnover frequency (TOF) of approximately 5000 h⁻¹ and broad substrate applicability. Pd/DG-COF maintained stable performance and remarkable recyclability, with no significant loss of activity observed after 10 catalytic cycles. This work highlights the importance of rational COF skeleton design in developing robust catalytic systems and highlights the promising potential of Pd/DG-COF in the field of sustainable catalysis, with minimal loss of noble metal centers.