We have developed a Keggin polyoxometalate (POM)‐based ionic‐liquid (IL)‐immobilizing rhodium single‐atom Rh catalyst (MTOA)5[SiW11O39Rh] (MOTA=methyltrioctylammonium cation) that can afford exceptionally high catalytic activity for the hydroformylation of alkenes to produce aldehydes at an ultralow loading of Rh (ca. 3 ppm). For styrene hydroformylation, both the conversion and the yield of the aldehyde can reach almost 99 %, and a TOF as high as 9000 h−1 was obtained without using any phosphine ligand in the reaction process. Further characterization by FTIR, ICP and ESI‐MS analysis revealed that the single Rh atom was incorporated in the lacunary POM anions. In particular, the bulky IL cation can play an additional role in stabilizing Rh species and thus prevent aggregation and leaching of Rh species. The IL catalyst was miscible with n‐hexane at temperatures; this contributed to exceptionally high activity for hydroformylation even at ultra‐low loading of IL catalyst.
A new strategy has been proposed for synthesizing Co@CoO core-shell nanoparticles with a core-shell structure, which involves a facile solvent-thermal process in deep eutectic solvents (DESs). In contrast to irregular...
Herein, the Keggin-type polyoxometalate (POM)a n c h o r e d p a l l a d i u m s i n g l e -a t o m c a t a l y s t s [ ( n -C 4 H 9 ) 4 N] 6 [SiW 11 O 39 Pd] and [(n-C 4 H 9 ) 4 N] 5 [PW 11 O 39 Pd] 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 darkfield 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 D 2 O showed that the hydrocarboxylation reaction proceeds through the "Pd−H" pathway.
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