2 results
Search Results
Now showing 1 - 2 of 2
- ItemMechanistic Understanding of the Heterogeneous, Rhodium-Cyclic (Alkyl)(Amino)Carbene-Catalyzed (Fluoro-)Arene Hydrogenation(Washington, DC : American Chemical Society, 2020) Moock D.; Wiesenfeldt M.P.; Freitag M.; Muratsugu S.; Ikemoto S.; Knitsch R.; Schneidewind J.; Baumann W.; Schäfer A.H.; Timmer A.; Tada M.; Hansen M.R.; Glorius F.Recently, chemoselective methods for the hydrogenation of fluorinated, silylated, and borylated arenes have been developed providing direct access to previously unattainable, valuable products. Herein, a comprehensive study on the employed rhodium-cyclic (alkyl)(amino)carbene (CAAC) catalyst precursor is disclosed. Mechanistic experiments, kinetic studies, and surface-spectroscopic methods revealed supported rhodium(0) nanoparticles (NP) as the active catalytic species. Further studies suggest that CAAC-derived modifiers play a key role in determining the chemoselectivity of the hydrogenation of fluorinated arenes, thus offering an avenue for further tuning of the catalytic properties. Copyright © 2020 American Chemical Society.
- ItemMulti-nuclear, high-pressure, operando FlowNMR spectroscopic study of Rh/PPh3 – catalysed hydroformylation of 1-hexene(Cambridge [u.a.] : Soc., 2021) Bara-Estaún, Alejandro; Lyall, Catherine L.; Lowe, John P.; Pringle, Paul G.; Kamer, Paul C. J.; Franke, Robert; Hintermair, UlrichThe hydroformylation of 1-hexene with 12 bar of 1 : 1 H2/CO in the presence of the catalytic system [Rh(acac)(CO)2]/PPh3 was successfully studied by real-time multinuclear high-resolution FlowNMR spectroscopy at 50 °C. Quantitative reaction progress curves that yield rates as well as chemo- and regioselectivities have been obtained with varying P/Rh loadings. Dissolved H2 can be monitored in solution to ensure true operando conditions without gas limitation. 31P{1H} and selective excitation 1H pulse sequences have been periodically interleaved with 1H FlowNMR measurements to detect Rh–phosphine intermediates during the catalysis. Stopped-flow experiments in combination with diffusion measurements and 2D heteronuclear correlation experiments showed the known tris-phosphine complex [RhH(CO)(PPh3)3] to generate rapidly exchanging isomers of the bis-phosphine complex [Rh(CO)2(PPh3)2] under CO pressure that directly enter the catalytic cycle. A new mono-phosphine acyl complex has been identified as an in-cycle reaction intermediate.