Ruthenium Single-Atom Anchored in Polyoxometalate-Ionic Liquids for N-Formylation of Amines with CO2 and H2

In this work, we have developed a Ru single-atom substituted polyoxometalate-based ionic liquid ([TOMA 6 SiW 11 O 39 Ru(dmso)], TOMA = methyltrioctylammonium, named as Ru-POM-IL) and confirmed that the single-atom Ru is anchored into the framework of the POM. The binary ionic liquid (IL) system, composed of the POM-based IL and 1-butyl-3-methyl-imidazolium acetate (BMImOAc), exhibits high efficiency for N-formylation of amines with CO 2 and H 2, leading to formylamides with high yields in toluene-IL biphasic media. The characterization by laser confocal scanning microscopy reveals a specific sponge-like structure of the binary IL, facilitating the efficient contact between the catalytic active sites and the substrate molecules. Detailed investigations elucidate that the reaction proceeds via a pathway with formate intermediates, including CO 2 adsorption and activation by BMImOAc, morpholine-assisted heterolytic splitting of H 2 into Ru–H δ- species and the H δ+ attachment to the morpholine N center; the coupling of CO 2 with Ru–H δ- to afford formate species; and then the dehydration of the formate intermediates to formamides. The catalytic system exhibits offered advantages of high efficiency, robustness, and recyclability in the N-formylation reaction.