Palladium Single Atom-supported Covalent Organic Frameworks for Aqueous-phase Hydrogenative Hydrogenolysis of
Zhihao Ouyang1, Guan Sheng2, Yao Zhong1
1School of Chemistry and Chemical Engineering, Nanchang University, No. 999 Xuefu Avenue, Nanchang, 330031, P. R. China.
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 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.
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