Hydrogenation on NHC-Modified Ru/K-Al2O3 Catalysts
Tunable Heterogeneous Catalysis: N-Heterocyclic Carbenes as Ligands for Supported Heterogeneous Ru/K-Al2O3 Catalysts to Tune Reactivity and Selectivity.
J. Am. Chem. Soc. 2016;
17. November 2016 (online)
Key wordsN-heterocyclic carbenes - ruthenium catalysis - hydrogenation - heterogeneous catalysis - ligands
A surface-modification method was developed for tuning the catalytic performance of ruthenium nanoparticles supported on K-doped alumina (Ru/K-Al2O3) by using N-heterocyclic carbene (NHC) ligands. For example, the hydrogenation of ethynylbenzene (1) under hydrogen in the presence of unmodified Ru/K-Al2O3 gave ethylcyclohexane (3) as the sole product in 95% yield, whereas the use of IMes/Ru/K-Al2O3 or ICy/Ru/ K-Al2O3 (2 mol% ruthenium, NHC-modified Ru/K-Al2O3, 3.0 equiv of the NHC based on surface ruthenium) as a catalyst under similar conditions gave ethylbenzene (2) as the sole product in 89% and 92% yield, respectively.
The catalysts were characterized by means of 13C solid-state NMR, Ru 3p XPS, Ru K-edge EXAFS, and TEM. The particle size of ruthenium (TEM), the oxidation state of ruthenium (XPS), and the Ru–Ru coordination number (EXAFS) remained unchanged after the surface modification. In addition, 13C NMR spectroscopy confirmed that the carbene carbon was directly attached to the ruthenium nanoparticles.