Facile Conversion of Alcohols into Esters and Dihydrogen Catalyzed by New Ruthenium Complexes
13 Jul 2005-Journal of the American Chemical Society (American Chemical Society)-Vol. 127, Iss: 31, pp 10840-10841
TL;DR: In this paper, an efficient, environmentally benign method for the preparation of esters from alcohols under mild, neutral conditions without the need for carboxylic acid derivatives and condensing agents was developed.
Abstract: An efficient, environmentally benign method for the preparation of esters from alcohols under mild, neutral conditions without the need for carboxylic acid derivatives and condensing agents was developed. Catalyst design, based on new Ru(II) hydrido carbonyl complexes incorporating electron-rich PNP and PNN ligands has resulted in the novel complex (I) which is an outstanding catalyst for the dehydrogenation of primary alcohols to esters and H2 under neutral conditions.
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1,325 citations
TL;DR: A reaction in which primary amines are directly acylated by equimolar amounts of alcohols to produce amides and molecular hydrogen in high yields and high turnover numbers is reported.
Abstract: Given the widespread importance of amides in biochemical and chemical systems, an efficient synthesis that avoids wasteful use of stoichiometric coupling reagents or corrosive acidic and basic media is highly desirable. We report a reaction in which primary amines are directly acylated by equimolar amounts of alcohols to produce amides and molecular hydrogen (the only products) in high yields and high turnover numbers. This reaction is catalyzed by a ruthenium complex based on a dearomatized PNN-type ligand [where PNN is 2-(di-tert-butylphosphinomethyl)-6-(diethylaminomethyl)pyridine], and no base or acid promoters are required. Use of primary diamines in the reaction leads to bis-amides, whereas with a mixed primary-secondary amine substrate, chemoselective acylation of the primary amine group takes place. The proposed mechanism involves dehydrogenation of hemiaminal intermediates formed by the reaction of an aldehyde intermediate with the amine.
1,098 citations
TL;DR: Acceptorless dehydrogenation and related dehydrogenative coupling reactions have the potential for redirecting synthetic strategies to the use of sustainable resources, devoid of toxic reagents and deleterious side reactions, with no waste generation.
Abstract: Conventional oxidations of organic compounds formally transfer hydrogen atoms from the substrate to an acceptor molecule such as oxygen, a metal oxide, or a sacrificial olefin. In acceptorless dehydrogenation (AD) reactions, catalytic scission of C-H, N-H, and/or O-H bonds liberates hydrogen gas with no need for a stoichiometric oxidant, thereby providing efficient, nonpolluting activation of substrates. In addition, the hydrogen gas is valuable in itself as a high-energy, clean fuel. Here, we review AD reactions selectively catalyzed by transition metal complexes, as well as related transformations that rely on intermediates derived from reversible dehydrogenation. We delineate the methodologies evolving from this recent concept and highlight the effect of these reactions on chemical synthesis.
1,088 citations
TL;DR: In this paper, the metal catalyst returned the hydrogen to the transformed carbonyl compound, leading to an overall process in which alcohols can be converted into amines, compounds containing CC bonds and β-functionalised alcohols.
Abstract: Alcohols can be temporarily converted into carbonyl compounds by the metal-catalysed removal of hydrogen. The carbonyl compounds are reactive in a wider range of transformations than the precursor alcohols and can react in situ to give imines, alkenes, and α-functionalised carbonyl compounds. The metal catalyst, which had borrowed the hydrogen, then returns it to the transformed carbonyl compound, leading to an overall process in which alcohols can be converted into amines, compounds containing CC bonds and β-functionalised alcohols.
929 citations
TL;DR: A range of novel catalytic reactions that were developed guided by these new modes of metal-ligand cooperation are described, including a unique water splitting process, which involves consecutive thermal liberation of H(2) and light-induced liberation of O(2), using no sacrificial reagents, promoted by a pyridine-based pincer ruthenium complex.
Abstract: In view of global concerns regarding the environment and sustainable energy resources, there is a strong need for the discovery of new, green catalytic reactions. For this purpose, fresh approaches to catalytic design are desirable. In recent years, complexes based on “cooperating” ligands have exhibited remarkable catalytic activity. These ligands cooperate with the metal center by undergoing reversible structural changes in the processes of substrate activation and product formation.We have discovered a new mode of metal–ligand cooperation, involving aromatization–dearomatization of ligands. Pincer-type ligands based on pyridine or acridine exhibit such cooperation, leading to unusual bond activation processes and to novel, environmentally benign catalysis. Bond activation takes place with no formal change in the metal oxidation state, and so far the activation of H–H, C–H (sp2 and sp3), O–H, and N–H bonds has been demonstrated. Using this approach, we have demonstrated a unique water splitting process,...
877 citations
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TL;DR: It is shown that the direct condensation of equimolar amounts of carboxylic acids and alcohols can be achieved with the use of hafnium(IV) salts, such as commercially available ha fnium( IV) chloride and hafnia(IV), which may be suitable for large-scale operations.
Abstract: In order to promote atom efficiency in synthesis and to avoid the generation of environmental waste, the use of stoichiometric amounts of condensing reagents or excess substrates should be avoided. In esterification, excesses of either carboxylic acids or alcohols are normally needed. We show that the direct condensation of equimolar amounts of carboxylic acids and alcohols can be achieved with the use of hafnium(IV) salts, such as commercially available hafnium(IV) chloride and hafnium(IV) tert-butoxide. The present method can be applied to direct polyesterification and may be suitable for large-scale operations.
298 citations
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TL;DR: In this article, the electron-rich, bulky tridentate PNP ligand (2,6-bis-(di-tert-butylphosphinomethyl)pyridine) with Ru(PPh3)3Cl2 at 65 °C resulted in formation of a solution containing the dinitrogen monomeric Ru(II) complex 1a and the N2-bridged dinuclear Ru(2) complex 2, which can be interconverted.
270 citations
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171 citations