Highly Versatile Catalytic Hydrogenation of Carboxylic and Carbonic Acid Derivatives using a Ru-Triphos Complex: Molecular Control over Selectivity and Substrate Scope

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• 作者：Thorsten vom Stein ; Markus Meuresch ; Dominik Limper ; Marc Schmitz ; Markus H枚lscher ; Jacorien Coetzee ; David J. Cole-Hamilton ; J眉rgen Klankermayer ; Walter Leitner
• 刊名：Journal of the American Chemical Society
• 出版年：2014
• 出版时间：September 24, 2014
• 年：2014
• 卷：136
• 期：38
• 页码：13217-13225
• 全文大小：483K
• ISSN：1520-5126

文摘

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)H₂] or the cationic intermediate [Ru(Triphos)(Solvent)(H)(H₂)]⁺ 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鈺怬 groups and C鈥揙 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)H₂] and [Ru(Triphos)(渭-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 HNTf₂ (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.