Stereoselective hydrogenation of lignin degradation model compounds

Abstract

Di-µ-chloro-bis(η4-1,5-hexadiene)dirhodium(I) in a two-phase hexane–aqueous medium catalyzes the diastereoselective H2-hydrogenation of lignin degradation model compounds 4-propylphenol, 2-methoxy-4-propylphenol, and 2,6-dimethoxy-4-propylphenol. The all-cis diastereomer is obtained selectively when the phenolic hydroxy group is protected as a methyl ether or when a model compound possessing two methoxy substituents adjacent to the phenolic hydroxy group is used. The relative stereochemistries of the hydrogenated products are established by X-ray crystal structure analysis and (or) 1H NMR. Keywords: catalytic hydrogenation, diastereomer, lignin degradation model compounds, stereoselective, X-ray crystal structure.

Carbohydrate‐Derived 1,3‐Diphosphite Ligands as Chiral Nanoparticle Stabilizers: Promising Catalytic Systems for Asymmetric Hydrogenation

“…The white foam obtained was purified by flash column chromatography under nitrogen. 1,[3][4][5] ,74,96;H,9,84. Found: C,74.75;H,10.00. General procedure for the synthesis of Ru nanoparticles…”

“…[4,6] This selectivity is rationalized by a continuous coordination of the substrate to the surface of the catalyst during hydrogenation, leading to the addition of the hydrogen atoms to only one face of the arene. [8,9] The trans-diastereomers (compounds 7 and 10, Scheme 1) can be formed through the roll-over mechanism, in which a partially hydrogenated intermediate dissociates from the catalyst surface and then reassociates through its opposite face before further hydrogenation occurs. [2,10] In the last decade, the use of ligands as chiral stabilizing agents has attracted much interest as it offers the possibility to modulate the environment at the surface of the nanoparticles through electronic and/or steric modifications.…”

Recovery and Utilization of Lignin Monomers as Part of the Biorefinery Approach

“…A di-µ-chlorobis (η 4 -1,5-hexadiene)-dirhodium(I) complex catalyzed the lignin-derived model compounds 4-propelphenol, eugenol, 1,2-dimethoxy-4-propylbenzene, and 2,6-dimethoxy-4-propylphenol. The temperature was 298 K and the medium was two-phase hexane/aqueous [228].…”

Review: Synthesis of organometallics and catalytic hydrogenations in ionic liquids

“…Our own interests are largely concerned with the hydrogenation of aromatic substrates to their corresponding cyclohexanes, a process important for the production of cleaner fuels 48 and prevention of yellowing of paper. 49 4 ] ionic liquid using neat arene substrates without any co-solvent. 42 The turnover frequencies obtained in the ionic liquid are higher than those obtained in the aqueous system, arising from the higher concentration of dissolved hydrogen gas and the arene substrates in the ionic liquid compared with water.…”