Iridium–PNP Pincer Complexes for Methanol Dehydrogenation at Low Base Concentration

Prichatz, Christoph; Alberico, Elisabetta; Baumann, Wolfgang; Junge, Henrik; Beller, Matthias

doi:10.1002/cctc.201700015

Cited by 50 publications

(30 citation statements)

References 70 publications

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“…In this work, we focus on homogeneous molecular complexes that can generate three equivalents of hydrogen from aqueous methanol under mild conditions (1 atm, <100 °C) . A number of highly active and selective complexes have been reported in the literature for this transformation . For large scale industrial applications, it will be beneficial to develop highly active, additive‐free and stable catalytic systems based on non‐toxic elements (preferably abundant) that can operate under mild conditions .…”

Section: Introductionmentioning

confidence: 99%

An In‐Depth Mechanistic Study of Ru‐Catalysed Aqueous Methanol Dehydrogenation and Prospects for Future Catalyst Design

Govindarajan

Sinha²,

Trincado

et al. 2020

ChemCatChem

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Herein we provide mechanistic insights into the dehydrogenation of aqueous methanol catalysed by the [Ru(trop2dae)] complex (which is in‐situ generated from [Ru(trop2dad)], trop2dad=1,4‐bis(5H‐dibenzo[a,d]cyclohepten‐5‐yl)‐1,4‐diazabuta‐1,3‐diene), established by density functional theory based molecular dynamics (DFT‐MD) and static DFT calculations incorporating explicit solvent molecules. The aqueous solvent proved to participate actively in various stages of the catalytic cycle including the catalyst activation process, and the key reaction steps involving C−H activation and hydrogen production. The aqueous solvent forms an integral part of the reactive system for the C−H activation steps in the [Ru(trop2dae)] system, with strong hydrogen bond interactions with the anionic oxygen (RO−, R=CH3, CH2OH, HCO) and hydride moieties formed along the reaction pathway. In contrast to the [Ru(trop2dad)] catalyst, C−H activation and hydrogen production does not proceed via a metal‐ligand cooperative pathway for the [Ru(trop2dae)] system. The pKa of the coordinated amine donors in these complexes provides a rationale for the divergent reactivity, and the obtained mechanistic information provides new guidelines for the rational design of active and additive free catalytic systems for aqueous methanol dehydrogenation.

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Section: Introductionmentioning

confidence: 99%

An In‐Depth Mechanistic Study of Ru‐Catalysed Aqueous Methanol Dehydrogenation and Prospects for Future Catalyst Design

Govindarajan

Sinha²,

Trincado

et al. 2020

ChemCatChem

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“…Moreover, mechanistic studies suggest that one of the ligand methylene hydrogens takes part of the catalytic cycle via dearomatization of the central pyridine unit, such as Milstein has previously demonstrated with other AAD systems [22]. Other metal complexes have also been shown to conduct MeOH reforming by AAD, specifically iron [16,24], manganese [25], and iridium [26][27][28]. Several of them are comprised of PNP iPr pincer ligand complexes, such as the iron-based compounds shown in Figure 11.…”

Section: Methanolmentioning

confidence: 88%

“…Recently, Beller employed a PNP iPr pincer ligated iridium complex for MeOH reforming [28]. reached after which gas evolution ceased.…”

Section: Advanced Chemical Kineticsmentioning

confidence: 99%

Catalyst Kinetics and Stability in Homogeneous Alcohol Acceptorless Dehydrogenation

Nielsen¹

2018

Advanced Chemical Kinetics

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The anthropogenic climate changes caused by meeting the energy demands of society by use of fossil fuels render the development of benign alternatives imperative. Probably, the most promising alternative is generating energy by means of power units driven by, e.g., solar, wind, water, etc., and then storing the energy that is not immediately used in battery type devices. Such a device might consist of hydrogen chemically stored as alcohol(s). The advantage of this method is that it allows gaseous hydrogen to be stored much more efficiently when liquefied as an alcohol. Moreover, as will be shown in this review, it is possible to release the hydrogen under mild conditions when employing homogeneous catalysis. This review considers the kinetic aspects of homogeneously catalysed acceptorless alcohol dehydrogenation reactions. For clarity, the sections are divided according to alcohol substrate, and each metal are described and discussed in subsections. Moreover, the kinetic information in the homogeneously catalysed AAD is traditionally provided simply as the turnover frequency, and more in-depth studies on the actual kinetic parameters are to date still largely elusive.

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“…Previous methanol dehydrogenation processes with homogeneous catalysts were always carried out with strong alkalis, such as NaOH, KOH, LiOH, and sodium isopropoxide . In this work, organic and inorganic and strong and weak bases were selected.…”

Section: Figurementioning

confidence: 99%

Second Sphere Ligand Promoted Organoiridium Catalysts for Methanol Dehydrogenation under Mild Conditions

Bai

Ning

et al. 2020

ChemCatChem

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Hydrogen produced from renewable resources is a potential source of clean energy. And Methanol is a liquid at room temperature and has a hydrogen content of up to 12.6 wt%, makes it a promising hydrogen source and can provide great benefits for sustainable hydrogen production. In this work, the modification of the picolinic acid ligand along with changes in the type and substituent position of the groups enhances the activity in iridium‐catalyzed methanol dehydrogenation catalysis. These second sphere ligand modifications are found to be effective for achieving highly active organoiridium catalysts for methanol dehydrogenation reaction under mild conditions, i. e. 1 atm, 78 °C, with a weak base and without using an organic solvent, exhibiting a TOF of 377 h−1. The electronic population analysis of each ligand is theoretically calculated, which shows that catalytic activity is dramatically affected by modifications to the metal's secondary coordination sphere environment, and the high activity originates from appropriate coordination by the picolinic acid ligand and carboxylic acid moiety in addition to the hydroxyl functionality. Moreover, kinetic experiments suggest that the C−H bond of methanol is linked to the iridium core and broken in the rate‐determining step of the reaction. This study will be valuable for catalyst development in the field of methanol dehydrogenation.

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Iridium–PNP Pincer Complexes for Methanol Dehydrogenation at Low Base Concentration

Cited by 50 publications

References 70 publications

An In‐Depth Mechanistic Study of Ru‐Catalysed Aqueous Methanol Dehydrogenation and Prospects for Future Catalyst Design

An In‐Depth Mechanistic Study of Ru‐Catalysed Aqueous Methanol Dehydrogenation and Prospects for Future Catalyst Design

Catalyst Kinetics and Stability in Homogeneous Alcohol Acceptorless Dehydrogenation

Second Sphere Ligand Promoted Organoiridium Catalysts for Methanol Dehydrogenation under Mild Conditions

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