Mechanisms of the H2-hydrogenation and transfer hydrogenation of polar bonds catalyzed by ruthenium hydride complexes

Clapham, Sean E.; Hadzovic, Alen; Morris, Robert H.

doi:10.1016/j.ccr.2004.04.007

Cited by 1,256 publications

(738 citation statements)

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“…For example, metal-ligand cooperation (MLC) between an amine ligand and an iron centre is thought to be involved in the catalytic mechanism of the enzyme hydrogenase [4]. MLC involving metal-amido metal-amine transformations (scheme 1) [5,6] takes place in catalytic hydrogenation of polar double bonds [6][7][8][9][10].…”

Section: Introductionmentioning

confidence: 99%

Metal–ligand cooperation by aromatization–dearomatization as a tool in single bond activation

Milstein

2015

Phil. Trans. R. Soc. A.

107

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Metal–ligand cooperation (MLC) plays an important role in bond activation processes, enabling many chemical and biological catalytic reactions. A recent new mode of activation of chemical bonds involves ligand aromatization–dearomatization processes in pyridine-based pincer complexes in which chemical bonds are broken reversibly across the metal centre and the pincer-ligand arm, leading to new bond-making and -breaking processes, and new catalysis. In this short review, such processes are briefly exemplified in the activation of C–H, H–H, O–H, N–H and B–H bonds, and mechanistic insight is provided. This new bond activation mode has led to the development of various catalytic reactions, mainly based on alcohols and amines, and to a stepwise approach to thermal H 2 and light-induced O 2 liberation from water.

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Section: Introductionmentioning

confidence: 99%

Metal–ligand cooperation by aromatization–dearomatization as a tool in single bond activation

Milstein

2015

Phil. Trans. R. Soc. A.

107

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“…[2a-b] Each of these reagents presents a significant challenge: LiAlH4 is pyrophoric and challenging to handle on a large scale, some silanes can generate explosive SiH4 via disproportionation, HI-P is strictly controlled due to its use in illicit methamphetamine synthesis, and Bu3SnH is both toxic and difficult to remove from lipophilic products. [2c-d] Recent developments in transfer hydrogenation catalysis have led to safer conditions for the reduction of esters [3] and ketones [4] , and we wondered whether the same advance could be achieved for alkyl halides. Grubbs, Nolan, and Fort have independently reported transition-metal catalyzed reduction of aryl halides using metal alkoxides/alcohols as bases and hydrogen donors.…”

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confidence: 99%

Catalytic Reduction of Alkyl and Aryl Bromides Using Propan‐2‐ol

2017

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Milstein's complex, (PNN)RuHCl(CO), catalyzes the efficient reduction of aryl and alkyl halides under relatively mild conditions by using propan‐2‐ol and a base. Sterically hindered tertiary and neopentyl substrates are reduced efficiently, as well as more functionalized aryl and alkyl bromides. The reduction process is proposed to occur by radical abstraction/hydrodehalogenation steps at ruthenium. Our research represents a safer and more sustainable alternative to typical silane, lithium aluminium hydride, and tin‐based conditions for these reductions.

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“…organometallic catalysis | reaction intermediates | ruthenium | kinetics C atalytic transfer hydrogenation (CTH) is an efficient method for the enantioselective reduction of multiple bonds (e.g., C═O and C═NR) in chemical and pharmaceutical syntheses (1)(2)(3)(4). Typically, a hydrogen donor such as isopropanol is used as a convenient reducing agent and is oxidized to its corresponding ketone (5). As a catalytic version of the classical MeerweinPondorf-Verley reduction/Oppenaur oxidation (6-10), CTH provides a mild method for both ketone reduction and alcohol oxidation.…”

mentioning

confidence: 99%

Transient Ru-methyl formate intermediates generated with bifunctional transfer hydrogenation catalysts

Perry

Brownell

Chingin

et al. 2012

Proc. Natl. Acad. Sci. U.S.A.

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Desorption electrospray ionization (DESI) coupled to high-resolution Orbitrap mass spectrometry (MS) was used to study the reactivity of a (β-amino alcohol)(arene)RuCl transfer hydrogenation catalytic precursor in methanol (CH 3 OH). By placing ½ðp-cymeneÞ RuCl 2 2 on a surface and spraying a solution of β-amino alcohol in methanol, two unique transient intermediates having lifetimes in the submillisecond to millisecond range were detected. These intermediates were identified as Ru (II) and Ru (IV) complexes incorporating methyl formate (HCOOCH 3 ). The Ru (IV) intermediate is not observed when the DESI spray solution is sparged with Ar gas, indicating that O 2 dissolved in the solvent is necessary for oxidizing Ru (II) to Ru (IV). These proposed intermediates are supported by high-resolution and high mass accuracy measurements and by comparing experimental to calculated isotope profiles. Additionally, analyzing the bulk reaction mixture using gas chromatography-MS and nuclear magnetic resonance spectroscopy confirms the formation of HCOOCH 3 . These results represent an example that species generated from the (β-amino alcohol)(arene)RuCl (II) catalytic precursor can selectively oxidize CH 3 OH to HCOOCH 3 . This observation leads us to propose a pathway that can compete with the hydrogen transfer catalytic cycle. Although bifunctional hydrogen transfer with Ru catalysts has been well-studied, the ability of DESI to intercept intermediates formed in the first few milliseconds of a chemical reaction allowed identification of previously unrecognized intermediates and reaction pathways in this catalytic system. organometallic catalysis | reaction intermediates | ruthenium | kinetics C atalytic transfer hydrogenation (CTH) is an efficient method for the enantioselective reduction of multiple bonds (e.g., C═O and C═NR) in chemical and pharmaceutical syntheses (1-4). Typically, a hydrogen donor such as isopropanol is used as a convenient reducing agent and is oxidized to its corresponding ketone (5). As a catalytic version of the classical MeerweinPondorf-Verley reduction/Oppenaur oxidation (6-10), CTH provides a mild method for both ketone reduction and alcohol oxidation. Previous studies show that methanol (CH 3 OH) can serve as a hydrogen donor for (arene)Ru complexes ligated by β-amino alcohols (11), but the nature of the oxidized products from CH 3 OH has not been previously characterized (12). Additionally, some Pd and Ru (13, 14) catalysts can oxidize CH 3 OH to methyl formate (HCOOCH 3 ), but selective oxidation to methyl formate has not been observed previously for a transfer hydrogenation catalysis. Fig. 1 shows the mechanism proposed by Kenney, Heck, Walgrove, and Wills (15) for CTH when Fig. 1, 1 is treated with β-amino alcohol ligands in the presence of a base. Ligation of the cymene dimer Fig. 1, 1 with ligand Fig. 1, 2 generates the Ru-Cl catalyst precursor Fig. 1, 3, which undergoes dehydrohalogenation to form the Ru-amide Fig. 1, 4. An outer-sphere concerted hydrogen transfer of α-C─H to Ru and ─O─H t...

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Mechanisms of the H2-hydrogenation and transfer hydrogenation of polar bonds catalyzed by ruthenium hydride complexes

Cited by 1,256 publications

References 216 publications

Metal–ligand cooperation by aromatization–dearomatization as a tool in single bond activation

Metal–ligand cooperation by aromatization–dearomatization as a tool in single bond activation

Catalytic Reduction of Alkyl and Aryl Bromides Using Propan‐2‐ol

Transient Ru-methyl formate intermediates generated with bifunctional transfer hydrogenation catalysts

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