Palladium Single Atom‐supported Covalent Organic Frameworks for Aqueous‐phase Hydrogenative Hydrogenolysis of Aromatic Aldehydes via Hydrogen Heterolysis

Abstract Developing a method for the tandem hydrogenative hydrogenolysis of bio‐based furfuryl aldehydes to methylfurans is crucial for synthesizing sustainable biofuels and chemicals; however, it poses a challenge due to the easy hydrogenation of the C=C bond and difficult cleavage of the C−O bond. Herein, a palladium (Pd) single‐atom‐supported covalent organic framework was fabricated and showed a unique 2,5‐dimethylfuran yield of up to 98.2 % when reacted with 5‐methyl furfuryl aldehyde in an unprecedented water solvent at 30 °C. Furthermore, it exhibited excellent catalytic universality while converting various furfuryl‐, benzyl‐, and heterocyclic aldehydes at room temperature. The analysis of the catalytic mechanism confirmed that H 2 was heterolytically activated on the Pd−N pair and triggered the keto‐enol tautomerism of the covalent organic frameworks (COFs) host, resulting in H − −Pd⋅⋅⋅O−H + sites. These sites served as novel asymmetric hydrogenation sites for the C=O group and hydrogenolysis sites for the C−OH group through a scarce SN 2 mechanism. This study demonstrated remarkable bifunctional catalysis through the H 2 ‐induced keto‐enol tautomerism of COF catalysts for the atypical preparation of methyl aromatics in a water solvent at room temperature.