Highly versatile catalytic hydrogenation of carboxylic and carbonic acid derivatives using a Ru-triphos complex:molecular control over selectivity and substrate scope

The complex [Ru(Triphos)(TMM)] (Triphos = 1,1,1-tris(diphenylphosphinomethyl)ethane, TMM = trimethylene methane) provides an efficient catalytic system for the hydrogenation of a broad range of challenging functionalities encompassing carboxylic esters, amides, carboxylic acids, carbonates, and urea...

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Bibliographic Details
Published in:Journal of the American Chemical Society
Main Authors: Vom Stein, T., Meuresch, M., Limper, D., Schmitz, M., Hölscher, M., Coetzee, J., Cole-Hamilton, D.J., Klankermayer, J., Leitner, W.
Format: Article in Journal/Newspaper
Language:English
Published: 2014
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Online Access:https://risweb.st-andrews.ac.uk/portal/en/researchoutput/highly-versatile-catalytic-hydrogenation-of-carboxylic-and-carbonic-acid-derivatives-using-a-rutriphos-complex(2f0045ca-064b-4d6f-94c3-d7fdd3696614).html
https://doi.org/10.1021/ja506023f
http://pubs.acs.org/doi/suppl/10.1021/ja506023f
Description
Summary:The complex [Ru(Triphos)(TMM)] (Triphos = 1,1,1-tris(diphenylphosphinomethyl)ethane, TMM = trimethylene methane) provides an efficient catalytic system for the hydrogenation of a broad range of challenging functionalities encompassing carboxylic esters, amides, carboxylic acids, carbonates, and urea derivatives. The key control factor for this unique substrate scope results from selective activation to generate either the neutral species [Ru(Triphos)(Solvent)H 2 ] or the cationic intermediate [Ru(Triphos)(Solvent)(H)(H 2 )] + in the presence of an acid additive. Multinuclear NMR spectroscopic studies demonstrated together with DFT investigations that the neutral species generally provides lower energy pathways for the multistep reduction cascades comprising hydrogen transfer to C═O groups and C–O bond cleavage. Carboxylic esters, lactones, anhydrides, secondary amides, and carboxylic acids were hydrogenated in good to excellent yields under these conditions. The formation of the catalytically inactive complexes [Ru(Triphos)(CO)H 2 ] and [Ru(Triphos)(μ-H)] 2 was identified as major deactivation pathways. The former complex results from substrate-dependent decarbonylation and constitutes a major limitation for the substrate scope under the neutral conditions. The deactivation via the carbonyl complex can be suppressed by addition of catalytic amounts of acids comprising non-coordinating anions such as HNTf 2 (bis(trifluoromethane)sulfonimide). Although the corresponding cationic cycle shows higher overall barriers of activation, it provides a powerful hydrogenation pathway at elevated temperatures, enabling the selective reduction of primary amides, carbonates, and ureas in high yields. Thus, the complex [Ru(Triphos)(TMM)] provides a unique platform for the rational selection of reaction conditions for the selective hydrogenation of challenging functional groups and opens novel synthetic pathways for the utilization of renewable carbon sources.