Discovery of low energy pathways to metal-mediated BN bond reduction guided by computation and experiment

Heiden, Zachariah M.; Szymczak, Nathaniel K.

doi:10.1039/c5sc02348c

Cited by 6 publications

(3 citation statements)

References 89 publications

(156 reference statements)

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“… 174 Szymczak and Heiden have performed DFT calculations and suggested that coordination of borazine to a transition metal fragment such as M(CO) 3 can decrease the activation energy for the reactivity of borazine toward a hydride source. 175 …”

Section: Hydrogen Economymentioning

confidence: 99%

“…Timoshkin reported that the use of a Lewis acid can significantly decrease the activation energy of hydrogenation . Szymczak and Heiden have performed DFT calculations and suggested that coordination of borazine to a transition metal fragment such as M(CO) 3 can decrease the activation energy for the reactivity of borazine toward a hydride source …”

Section: Hydrogen Economymentioning

confidence: 99%

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Homogeneous Catalysis for Sustainable Energy: Hydrogen and Methanol Economies, Fuels from Biomass, and Related Topics

2021

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As the world pledges to significantly cut carbon emissions, the demand for sustainable and clean energy has now become more important than ever. This includes both production and storage of energy carriers, a majority of which involve catalytic reactions. This article reviews recent developments of homogeneous catalysts in emerging applications of sustainable energy. The most important focus has been on hydrogen storage as several efficient homogeneous catalysts have been reported recently for (de)hydrogenative transformations promising to the hydrogen economy. Another direction that has been extensively covered in this review is that of the methanol economy. Homogeneous catalysts investigated for the production of methanol from CO 2 , CO, and HCOOH have been discussed in detail. Moreover, catalytic processes for the production of conventional fuels (higher alkanes such as diesel, wax) from biomass or lower alkanes have also been discussed. A section has also been dedicated to the production of ethylene glycol from CO and H 2 using homogeneous catalysts. Well-defined transition metal complexes, in particular, pincer complexes, have been discussed in more detail due to their high activity and well-studied mechanisms.

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Section: Hydrogen Economymentioning

confidence: 99%

Section: Hydrogen Economymentioning

confidence: 99%

Homogeneous Catalysis for Sustainable Energy: Hydrogen and Methanol Economies, Fuels from Biomass, and Related Topics

2021

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“…9, 10a, 12, 15 The latter are known to proceed through (or stop at) borazine, N 3 B 3 H 6 , as an intermediate with its subsequent conversion to polyborazylene as a slow step in the overall mechanism of hydrogen evolution. 16 This is problematic because (1) slow borazine derivatization limits H 2 productivity, 12 (2) borazine, which boils at 55 ºC, is poisonous to fuel cells, and (3) borazine is known to coordinate metals 17 and deactivate some AB dehydrogenation catalysts. 16 …”

Section: Introductionmentioning

confidence: 99%

Dehydrogenation of ammonia borane through the third equivalent of hydrogen

2016

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Ammonia Borane (AB) has high hydrogen density (19.6 wt. %), and can, in principle, release up to 3 equivalents of H2 under mild catalytic conditions. A limited number of catalysts are capable of non-hydrolytic dehydrogenation of AB beyond 2 equivalents of H2 under mild conditions, but none of these is shown directly to derivatise borazine, the product formed after 2 equivalents of H2 are released. We present here a high productivity ruthenium-based catalyst for non-hydrolytic AB dehydrogenation that is capable of borazine dehydrogenation, and thus exhibits among the highest H2 productivity reported to date for anhydrous AB dehydrogenation. At 1 mol% loading, (phen)Ru(OAc)2(CO)2 (1) effects AB dehydrogenation through 2.7 equivalents of H2 at 70°C, is robust through multiple charges of AB, and is water and air stable. We further demonstrate that catalyst 1 has the ability both to dehydrogenate borazine in isolation and dehydrogenate AB itself. This is important, both because borazine derivatisation is productivity-limiting in AB dehydrogenation and because borazine is a fuel cell poison that is commonly released in H2 production from this medium.

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Mechanism of B‐H Redistribution during Reduction of Polyborazylene by Hydrazine

2023

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Density functional theory has been used to elucidate the mechanistic underpinnings of the regeneration of ammonia‐borane (H3B−NH3, AB) from polyborazylene (BxNxHx, PBz) in the presence of hydrazine (H2N−NH2, Hz). Herein, borazine (B3N3H6, Bz) is used as the simplest relevant model of PBz for the regeneration process. Digestion of Bz using Hz was found to occur by a string of Lewis acid base adduct (between B atoms of Bz and Hz molecule) formation and Hz assisted proton transfer processes. Later, B−H bonds of HB(NHNH2)2, the Bz digested product, are redistributed to form hydrazine‐borane (H3B−NH2NH2, HzB) and B(NHNH2)3. Redistribution of B−H bonds occurs through hydroboration and concerted proton‐hydride transfer. Another B−H redistributed product, B(NHNH2)3, produces HzB as a result of proton and hydride transfer from cis‐diazene (Dz), the oxidized product of Hz in presence of O2.

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Discovery of low energy pathways to metal-mediated BN bond reduction guided by computation and experiment

Abstract: The reduction of borazine-type heterocycles has been a challenge in the area of chemical hydrogen storage. Coordination to low valent metal carbonyls activates borazine for reduction by both 1 e– and 2 e– pathways.

Cited by 6 publications

References 89 publications

Homogeneous Catalysis for Sustainable Energy: Hydrogen and Methanol Economies, Fuels from Biomass, and Related Topics

Homogeneous Catalysis for Sustainable Energy: Hydrogen and Methanol Economies, Fuels from Biomass, and Related Topics

Dehydrogenation of ammonia borane through the third equivalent of hydrogen

Mechanism of B‐H Redistribution during Reduction of Polyborazylene by Hydrazine

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