American Chemical Society
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Hydrocarboxylation of Olefins Catalyzed by Polyoxometalate-Anchored Palladium Single-Atom Catalysts

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journal contribution
posted on 2022-11-11, 16:06 authored by Yuan Ma, Yongjun Jiang, Xinjia Wei, Qingpo Peng, Sheng Dai, Zhenshan Hou
Herein, the Keggin-type polyoxometalate (POM)-anchored palladium single-atom catalysts [(n-C4H9)4N]6[SiW11O39Pd] and [(n-C4H9)4N]5[PW11O39Pd] were constructed and employed in the olefin hydrocarboxylation reaction under two-phase conditions. Both the conversion of styrene and the yield of the carboxylic acids can reach as high as 95% at 110 °C. The characterization by high-angle annular dark-field scanning transmission electron microscopy (HAADF-STEM), electrospray ionization mass spectrometry (ESI-MS), and in situ Fourier-transform infrared (FT-IR) spectra of CO adsorption indicated the incorporation of the isolated Pd atom into the POM structure. The POM-anchored Pd catalysts can be directly stored under an ambient atmosphere and easily recovered in consecutive catalytic recycling. Tetrabutylammonium bromide (TBAB) played a crucial role in stabilizing/dispersing the Pd catalyst. Moreover, the catalytic systems showed a unique “pseudo-liquid-phase” behavior and the reactants were absorbed into the flexible POM anions. The catalysts exhibited a wide substrate suitability and have been applied under phosphine ligand-free conditions. The catalytic mechanism studies involving D2O showed that the hydrocarboxylation reaction proceeds through the “Pd–H” pathway.