A Carbene‐Rich but Carbonyl‐Poor [Ir6(IMe)8(CO)2H14]2+ Polyhydride Cluster as a Deactivation Product from Catalytic Glycerol Dehydrogenation

Campos, Jesús; Sharninghausen, Liam S.; Crabtree, Robert H.; Balcells, David

doi:10.1002/anie.201407997

Cited by 45 publications

(52 citation statements)

References 54 publications

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“…In the case of 6 , for example, the two plausible guesses for the H atom locations optimized to the same final structure . For 6 , we were then able to unambiguously assign the hydride region of the 1 H NMR spectrum by correlation of the NMe/IrH cross‐peaks observed in the 2D NOESY spectrum with short NMe/IrH distances in the DFT structure . Very recently, we obtained a neutron diffraction structure of 9 , which confirmed our previous computational hydride assignment for 9 and supports the validity of the DFT method for the other clusters (Figure ) …”

Section: Deactivationsupporting

confidence: 81%

“…In our study of glycerol DO with precatalysts 1 , 3 , and 4 we observed the formation of one or several iridium hydride species in 1 H NMR spectra of crude reaction mixtures, depending on the precatalyst and conditions used. In reactions using 3 we characterized compound 6 as a catalyst deactivation product (Scheme ) . In addition, clusters 7 – 9 form from 3 under similar conditions and also represent presumed deactivation products ,.…”

Section: Deactivationmentioning

confidence: 99%

“…Crucially, the positioning of the hydrides was carried out using DFT methods by Prof. David Balcells for clusters 6 – 9 (Figure ). In the case of 6 , for example, the two plausible guesses for the H atom locations optimized to the same final structure . For 6 , we were then able to unambiguously assign the hydride region of the 1 H NMR spectrum by correlation of the NMe/IrH cross‐peaks observed in the 2D NOESY spectrum with short NMe/IrH distances in the DFT structure .…”

Section: Deactivationmentioning

confidence: 99%

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Activation, Deactivation and Reversibility in a Series of Homogeneous Iridium Dehydrogenation Catalysts

Sharninghausen

Crabtree

2017

Israel Journal of Chemistry

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Dehydrogenation is a sustainable form of oxidation catalysis, as it avoids any primary oxidant and the waste that would accompany it. Homogeneous catalyst design for this reaction is delicate: the catalyst must have a sufficient H2 affinity to abstract two hydrogen atoms from the substrate but not so much affinity as to fail to release them as free H2. N‐Heterocyclic carbene (NHC) ligands achieve this balancing act in a series of iridium catalysts based on the Ir(IMe)2 motif (IMe=N,N′‐dimethylimidazol‐2‐ylidene). Catalyst design also needs to account for mechanistic points outside of the catalytic cycle itself. To enter the cycle, there is often an initial precatalyst activation process, and elucidating this can lead to optimization of both precatalyst and reaction conditions. To leave the cycle, we can have reversible formation of off‐cycle species as well as an irreversible catalyst deactivation step. In our Cp*Ir(IMe)2Cl precatalyst for dehydrogenative oxidation, Cp* is lost in the activation step. This suggested moving to a catalyst precursor lacking the Cp*, [Ir(IMe)2(CO)2]+. Catalyst deactivation produces a series of unusual cluster cations such as [Ir6(IMe)8(CO)2H14]2+. Among applications, dehydrogenative oxidation can be useful in upgrading of biomass glycerol by conversion to lactate, as a part of hydrogen borrowing chemistry and in reversible hydrogenation/dehydrogenation for H2 storage.

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Section: Deactivationsupporting

confidence: 81%

Section: Deactivationmentioning

confidence: 99%

Section: Deactivationmentioning

confidence: 99%

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Activation, Deactivation and Reversibility in a Series of Homogeneous Iridium Dehydrogenation Catalysts

Sharninghausen

Crabtree

2017

Israel Journal of Chemistry

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“…Against this background, we tried to develop new hypergolic compounds with low ID times and good water stability as replacements for toxic hydrazine‐based fuels. It is known that N‐heterocyclic carbenes (NHCs) have received significant attention in the fields of both organometallic chemistry and catalysis . Due to the lone pair of electrons on the carbon atom in the structure, NHCs are capable of combining the unoccupied orbital of borane (BH 3 ) to form stable NHC‐borane adducts.…”

Section: Introductionmentioning

confidence: 99%

Towards Safer Rocket Fuels: Hypergolic Imidazolylidene‐Borane Compounds as Replacements for Hydrazine Derivatives

Huang

Liu

et al. 2016

Chemistry A European J

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Currently, toxic and volatile hydrazine derivatives are still the main fuel choices for liquid bipropellants, especially in some traditional rocket propulsion systems. Therefore, the search for safer hypergolic fuels as replacements for hydrazine derivatives has been one of the most challenging tasks. In this study, six imidazolylidene-borane compounds with zwitterionic structure have been synthesized and characterized, and their hypergolic reactivity has been studied. As expected, these compounds exhibited fast spontaneous combustion upon contact with white fuming nitric acid (WFNA). Among them, compound 5 showed excellent integrated properties including wide liquid operating range (-70-160 °C), superior loading density (0.99 g cm(-3) ), ultrafast ignition delay times with WFNA (15 ms), and high specific impulse (303.5 s), suggesting promising application potential as safer hypergolic fuels in liquid bipropellant formulations.

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“…Remarkably, C4-C6 sugars can been converted to lactic acid and H 2 by complex 1, although catalyst deactivation prevents from obtaining very high LA yields [64]. A unique carbene-Ir 6 cluster was characterized and identified as major product of deactivation in glycerol dehydrogenation suggesting a minor role of other ancillary ligands in the iridium precatalyst [65]. Finally, complex 1 has been successfully applied to related methanol dehydrogenation reactions such as H 2 production through reforming to formate/ carbonate, transfer hydrogenation of ketones and imines and aniline methylation [ 66].…”

Section: From Glycerol To Lactic Acidmentioning

confidence: 99%

Lactic acid and hydrogen from glycerol via acceptorless dehydrogenation using homogeneous catalysts

Bottari¹,

Barta²

2015

Recyclable Catalysis

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Acceptorless dehydrogenation of alcohols has emerged as a powerful methodology for the valorization of biomass derived platform chemicals and building blocks. In this review we provide a short overview of the advantages and possible product outcomes of this method. The main focus will be devoted to the conversion of glycerol, which is the major waste product of biodiesel production, to lactic acid. While extensive research addresses the development of heterogeneous catalysts, recently new and highly active iridium and ruthenium complexes have also been reported. These novel homogeneous catalysts are even more active than the already reported heterogeneous systems and enable the direct conversion of glycerol into lactic acid and molecular hydrogen. While the product hydrogen might be used either as fuel or as reducing agent for other processes, lactic acid is a platform chemical widely employed by the polymer, pharmaceutical and food industries. The used catalytic methodology is atom-economic, waste-free and is uniquely suited for the efficient conversion of renewable resources.

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A Carbene‐Rich but Carbonyl‐Poor [Ir₆(IMe)₈(CO)₂H₁₄]²⁺ Polyhydride Cluster as a Deactivation Product from Catalytic Glycerol Dehydrogenation

Cited by 45 publications

References 54 publications

Activation, Deactivation and Reversibility in a Series of Homogeneous Iridium Dehydrogenation Catalysts

Activation, Deactivation and Reversibility in a Series of Homogeneous Iridium Dehydrogenation Catalysts

Towards Safer Rocket Fuels: Hypergolic Imidazolylidene‐Borane Compounds as Replacements for Hydrazine Derivatives

Lactic acid and hydrogen from glycerol via acceptorless dehydrogenation using homogeneous catalysts

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