Selectively Deoxygenative Deuteration of Aldehydes by Superwetting Porous Carbon Supported Palladium Catalysts

We present a method of deoxygenative deuteration of aldehydes (DDA) over heterogeneously superwetting porous carbons supported palladium catalyst (Pd/SPC), which is efficient for the synthesis of deuterated aromatic compounds with -CD3 group. Exemplified by the DDA reaction of 2-naphthaldehyde (2-NAL) to 2-methylnaphthalene (2-MNE), the total deuterium incorporation radio in the resultant aromatic hydrocarbons was higher than 95% and the selectivity towards 2-MNE-d3 reached 87%. The impressed catalytic activity was found relevant to the combined effect of surface wettability and the electron-rich properties of Pd species of this kind of heterogeneous Pd/SPC catalyst. Mechanistic studies suggest a successive deuteration pathway, i.e., hydrogen isotope exchange (HIE), deuterium addition, and ultimate deoxygenative deuteration over Pd/SPC in the cost-effective D2O/H2 reaction conditions. The in-situ formed D2 from the first step HIE between H2 and D2O can be readily captured by the electron-rich Pd centers, which then boost the subsequent deuterogenolysis of C-O bonds through deuterated alcohol intermediates towards the formation of 2-MNE-d3. This work provides a design principle of heterogeneous catalysts for targeted deuterium labeling from aldehyde substrates, and may inspire the development of alternative deuterium labeling techniques beyond dominated homogeneous catalysis.