The Key Role of the Hemiaminal Intermediate in the Iron-Catalyzed Deaminative Hydrogenation of Amides

Suàrez, Lluís Artús; Culakova, Zuzana; Balcells, David; Bernskoetter, Wesley H.; Eisenstein, Odile; Goldberg, Karen I.; Hazari, Nilay; Tilset, Mats; Nova, Ainara

doi:10.1021/acscatal.8b02184

Cited by 57 publications

(29 citation statements)

References 115 publications

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“… 48 This is in agreement with previous DFT calculations from the same group, highlighting the TOF-limiting nature of this step that is facilitated by the employed iron complex or via proton relay by a solvent/reactant molecule. 49 We were thus interested how these observations translate to our system. Again, the test amide seems not to be acidic enough to serve as an efficient proton relay for the generation of the labile zwitterion ( TS3D1 , 43.1 kcal/mol).…”

Section: Resultsmentioning

confidence: 99%

Hydrogenative Depolymerization of Nylons

et al. 2020

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The widespread crisis of plastic pollution demands discovery of new and sustainable approaches to degrade robust plastics such as nylons. Using a green and sustainable approach based on hydrogenation, in the presence of a ruthenium pincer catalyst at 150 °C and 70 bar H 2 , we report here the first example of hydrogenative depolymerization of conventional, widely used nylons and polyamides, in general. Under the same catalytic conditions, we also demonstrate the hydrogenation of a polyurethane to produce diol, diamine, and methanol. Additionally, we demonstrate an example where monomers (and oligomers) obtained from the hydrogenation process can be dehydrogenated back to a poly(oligo)amide of approximately similar molecular weight, thus completing a closed loop cycle for recycling of polyamides. Based on the experimental and density functional theory studies, we propose a catalytic cycle for the process that is facilitated by metal–ligand cooperativity. Overall, this unprecedented transformation, albeit at the proof of concept level, offers a new approach toward a cleaner route to recycling nylons.

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Section: Resultsmentioning

confidence: 99%

Hydrogenative Depolymerization of Nylons

et al. 2020

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“…For case of brevity, the focus will be on processes involving carbon dioxide and dinitrogen as the main substrates of interests, as well as chemical transformations promoting the valorization of biomass-derived molecules. Nevertheless, pincer complexes have achieved remarkable results in the (transfer) hydrogenation of a wide series of substrates such as ketones [385,[457][458][459][460][461][462], esters [40,179,220,386,400,[463][464][465][466][467][468][469][470][471][472][473][474][475][476][477], aldehydes [478][479][480], amides [67,[481][482][483][484][485], and imines [486,487]. After screening a range of amines, Prakash and Olah demonstrated the same concept using Ru-MACHO-BH and dimethylethylenediamine (5.3 wt% H2) which was successfully dehydrogenated in the presence of methanol resulting in a mixture of formamides [455].…”

Section: Hydrogenation Reactionsmentioning

confidence: 99%

Recent Progress with Pincer Transition Metal Catalysts for Sustainability

2020

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Our planet urgently needs sustainable solutions to alleviate the anthropogenic global warming and climate change. Homogeneous catalysis has the potential to play a fundamental role in this process, providing novel, efficient, and at the same time eco-friendly routes for both chemicals and energy production. In particular, pincer-type ligation shows promising properties in terms of long-term stability and selectivity, as well as allowing for mild reaction conditions and low catalyst loading. Indeed, pincer complexes have been applied to a plethora of sustainable chemical processes, such as hydrogen release, CO2 capture and conversion, N2 fixation, and biomass valorization for the synthesis of high-value chemicals and fuels. In this work, we show the main advances of the last five years in the use of pincer transition metal complexes in key catalytic processes aiming for a more sustainable chemical and energy production.

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“…The hydrogenation of formanilide, morpholidine and dimethylformamide (DMF) by an iron Noyori-type catalyst was studied by our group in 2018 (see Fig. 6) [24,27]. In this study, it was found that all transition states were thermally accessible, and that the formation of most intermediates and products was endergonic.…”

Section: Reaction Mechanisms For Amide C=o Hydrogenationmentioning

confidence: 99%

“…Examples of reaction mechanisms for the C=O hydrogenation of different amides with bifunctional Noyori-type catalysts [24,26,27,34]. R = CO for M = Mo and Mn.…”

Section: Figmentioning

confidence: 99%

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Computational Studies on the Mechanisms for Deaminative Amide Hydrogenation by Homogeneous Bifunctional Catalysts

2021

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The deaminative hydrogenation of amides is one of the most convenient pathways for the synthesis of amines and alcohols. The ideal source of reducing equivalents for this reaction is molecular hydrogen, though, in practice, this approach requires high pressures and temperatures, with many catalysts achieving only small turnover numbers and frequencies. Nonetheless, during the last ten years, this field has made major advances towards larger turnovers under milder conditions thanks to the development of bifunctional catalysts. These systems promote the heterolytic cleavage of hydrogen into proton and hydride by combining a basic ligand with an acidic metal centre. The present review focuses on the computational study of the reaction mechanism underlying bifunctional catalysis. This review is structured around the fundamental steps of this mechanism, namely the C=O and C–N hydrogenation of the amide, the C–N protonolysis of the hemiaminal, the C=O hydrogenation of the aldehyde, and the competition between hydrogen activation and catalyst deactivation. In line with the complexity of the mechanism, we also provide a perspective on the use of microkinetic models. Both Noyori- and Milstein-type catalysts are discussed and compared.

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The Key Role of the Hemiaminal Intermediate in the Iron-Catalyzed Deaminative Hydrogenation of Amides

Abstract: The source of hydrogen atoms will determine the reaction hazard, cost, and reaction conditions. Hydrogen sources can be classified into two main groups: hydride or molecular hydrogen sources. [3][4][5][6]

Cited by 57 publications

References 115 publications

Hydrogenative Depolymerization of Nylons

Hydrogenative Depolymerization of Nylons

Recent Progress with Pincer Transition Metal Catalysts for Sustainability

Computational Studies on the Mechanisms for Deaminative Amide Hydrogenation by Homogeneous Bifunctional Catalysts

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