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

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 H2 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 SN2 mechanism. This study demonstrated remarkable bifunctional catalysis through the H2‐induced keto‐enol tautomerism of COF catalysts for the atypical preparation of methyl aromatics in a water solvent at room temperature.