Hydrogenation of Esters

Saudan, Lionel

doi:10.1002/9781118354520.ch02

Cited by 16 publications

(10 citation statements)

References 73 publications

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“…Yield: 1.19 g, 78%. 1 H NMR (CDCl 3 ): δ 7.43 (t, 1H, 3 J HH = 7.8 Hz, CH arom ), 7.24 (dd, 1H, 3 J HH = 7.7 Hz, 4 J HH = 1.5 Hz, CH arom ), 7.00 (td, 1H, 3 J HH = 7.9 Hz, J HH = 1. Synthesis of (6-((2-Mesitylamino)phenylamino)pyridin-2ylmethyl)diethylamine (3-Et).…”

Section: ■ Experimental Sectionmentioning

confidence: 99%

“…Although homogeneous catalysts for ester hydrogenation, based primarily on ruthenium, have been known since the early 1980s, 3 progress in the development of highly efficient catalysts has greatly accelerated over the past decade. 4 In 2006, Milstein and co-workers reported a highly active ruthenium PNN-pincer catalyst for ester hydrogenation, which is capable of reversible protonation and deprotonation at the methylene carbon linking the pyridine ring to the di-tert-butylphosphino moiety (Figure 1). 5 This acid/base reactivity at a ligand site has become an important design principle for catalytic hydrogenation of polar bonds via the heterolytic activation of H 2 .…”

Section: ■ Introductionmentioning

confidence: 99%

“…4 Hz, CH arom ), 6.91 (s, 2H, CH arom ), 6.77 (d, 1H, 3 J HH = 7.2 Hz, CH arom ), 6.71 (td, 1H 3 J HH = 7.5 Hz, J HH = 1.4 Hz, CH arom ), 6.42 (d, 1H, 3 J HH = 8.4 Hz, CH arom ), 6.41 (br s, 1H, NH) 6.23 (dd, 1H, 3 J HH = 8.2 Hz, J HH = 1.2…”

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confidence: 99%

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Ester Hydrogenation Catalyzed by CNN-Pincer Complexes of Ruthenium

Kim

Drance

et al. 2016

Organometallics

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Ruthenium complexes supported by two new CNN-pincer ligands were synthesized. Both were tested as catalysts for the hydrogenation of esters under mild conditions (105 °C, 6 bar H2). A striking dependence on ligand structure was observed, as a dimethylamino-substituted ligand gave a nearly inactive catalyst, while a diethylamino-substituted variant gave up to 980 catalytic turnovers for the hydrogenation of benzyl benzoate. This system catalyzes the hydrogenation of various substrates including ethyl, benzyl, and hexyl esters, but is surprisingly unreactive toward methyl esters. Experiments demonstrate that base-catalyzed transesterification is rapid under the reaction conditions and that methyl esters are effectively hydrogenated when benzyl alcohol is added to the reaction mixture. The reverse reaction, dehydrogenation of primary alcohols to give esters, was tested as well; up to 920 catalytic turnovers were observed for the dehydrogenation of 1-hexanol to hexyl hexanoate.

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Section: ■ Experimental Sectionmentioning

confidence: 99%

Section: ■ Introductionmentioning

confidence: 99%

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Ester Hydrogenation Catalyzed by CNN-Pincer Complexes of Ruthenium

Kim

Drance

et al. 2016

Organometallics

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“…Unlike ketones and aldehydes, esters are generally inert toward mild reductants as typified by NaBH 4 and instead require more aggressive reductants such as BH 3 and LiAlH 4 , reagents which can pose significant handling risks and often suffer from poor selectivity in the presence of other reducible functionalities . Catalytic hydrogenation has been explored extensively as a more atom-efficient and selective route to ester reduction; however, the high pressures and temperatures required to achieve satisfactory conversions, typically in excess of 5 bar and 100 °C, pose significant safety concerns and require capital-intensive equipment . The need for safer and more convenient ester reduction methodologies has generated great interest in recent years in catalytic hydrosilylation, leading to a wealth of reports detailing the selective reduction of esters and other carbonyl groups at ambient pressures and moderate temperatures (typically <100 °C) .…”

Section: Introductionmentioning

confidence: 99%

La[N(SiMe₃)₂]₃-Catalyzed Ester Reductions with Pinacolborane: Scope and Mechanism of Ester Cleavage

Barger¹,

Motta

Weidner³

et al. 2019

ACS Catal.

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Tris[N,N-bis(trimethylsilyl)amido]lanthanum (LaNTMS) is an efficient, highly active, and selective homogeneous catalyst for ester reduction with pinacolborane (HBpin). Alkyl and aryl esters are cleaved to the corresponding alkoxy- and aryloxy-boronic esters which can then be straightforwardly hydrolyzed to alcohols. Ester reduction is achieved with 1 mol % catalyst loading at 25–60 °C, and most substrates are quantitatively reduced in 1 h. Nitro, halide, and amino functional groups are well tolerated, and ester reduction is completely chemoselective over potentially competing intra- or intermolecular alkene or alkyne hydroboration. Kinetic studies, isotopic labeling, and density functional theory calculations with energetic span analysis argue that ester reduction proceeds through a rate-determining hydride-transfer step that is ligand-centered (hydride is transferred directly from bound HBpin to bound ester) and not through a metal hydride-based intermediate that is often observed in organolanthanide catalysis. The active catalyst is proposed to be a La-hemiacetal, [(Me3Si)2N]2La-OCHR(OR)[HBpin], generated in situ from LaNTMS via hydroboronolysis of a single La–N(SiMe3)2 bond. These results add to the growing compendium of selective oxygenate transformations that LaNTMS is competent to catalyze, further underscoring the value and versatility of homoleptic lanthanide complexes in homogeneous catalytic organic synthesis.

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“…In contrast to heterogeneous processes, they can often be conducted at milder reaction conditions, reducing side-product formation . Additionally, (de)hydrogenations use smaller amounts of catalysts and additives than the traditional methods with stoichiometric reagents.…”

Section: Introductionmentioning

confidence: 99%

Ru⁰ or Ru^II: A Study on Stabilizing the “Activated” Form of Ru-PNP Complexes with Additional Phosphine Ligands in Alcohol Dehydrogenation and Ester Hydrogenation

Tindall¹,

Menche

Schelwies

et al. 2020

Inorg. Chem.

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The complex Ru-MACHO has been previously shown to undergo uncontrolled degradation subsequent to base-induced dehydrochlorination in the absence of a substrate. In this study, we report that stabilization of the dehydrochlorinated Ru-MACHO with phosphines furnishes complexes whose structures depend on the phosphines employed: while PMe3 led to the expected octahedral RuII complex, PPh3 provided access to a trigonal-bipyramidal Ru0 complex. Because both complexes proved to be active in base-free (de)hydrogenation reactions, thorough quantum-chemical calculations were employed to understand the reaction mechanism. The calculations show that both complexes lead to the same mechanistic scenario after phosphine dissociation and, therefore, only differ energetically in this step. According to the calculations, the typically proposed metal–ligand cooperation mechanism is not the most viable pathway. Instead, a metal–ligand-assisted pathway is preferred. Finally, experiments show that phosphine addition enhances the catalyst’s performance in comparison to the PR3-free “activated” Ru-MACHO.

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Hydrogenation of Esters

Cited by 16 publications

References 73 publications

Ester Hydrogenation Catalyzed by CNN-Pincer Complexes of Ruthenium

Ester Hydrogenation Catalyzed by CNN-Pincer Complexes of Ruthenium

La[N(SiMe₃)₂]₃-Catalyzed Ester Reductions with Pinacolborane: Scope and Mechanism of Ester Cleavage

Ru⁰ or Ru^II: A Study on Stabilizing the “Activated” Form of Ru-PNP Complexes with Additional Phosphine Ligands in Alcohol Dehydrogenation and Ester Hydrogenation

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Hydrogenation of Esters

Cited by 16 publications

References 73 publications

Ester Hydrogenation Catalyzed by CNN-Pincer Complexes of Ruthenium

Ester Hydrogenation Catalyzed by CNN-Pincer Complexes of Ruthenium

La[N(SiMe3)2]3-Catalyzed Ester Reductions with Pinacolborane: Scope and Mechanism of Ester Cleavage

Ru0 or RuII: A Study on Stabilizing the “Activated” Form of Ru-PNP Complexes with Additional Phosphine Ligands in Alcohol Dehydrogenation and Ester Hydrogenation

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Product

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La[N(SiMe₃)₂]₃-Catalyzed Ester Reductions with Pinacolborane: Scope and Mechanism of Ester Cleavage

Ru⁰ or Ru^II: A Study on Stabilizing the “Activated” Form of Ru-PNP Complexes with Additional Phosphine Ligands in Alcohol Dehydrogenation and Ester Hydrogenation