The Experts below are selected from a list of 327 Experts worldwide ranked by ideXlab platform
Jean-luc Parrain - One of the best experts on this subject based on the ideXlab platform.
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Asymmetric Rhodium-Directed anti-Markovnikov Regioselective Boracyclopentannulation
Journal of the American Chemical Society, 2012Co-Authors: Momar Toure, Olivier Chuzel, Jean-luc ParrainAbstract:A Shimoi-type activation of B−H bond of NHC-Boranes by a diphosphane-ligated cationic Rh complex was applied in an unprecedented intramolecular hydroboration reaction of simple olefins. The use of NHCBoranes as hydroborating reagents is still undisclosed due to their nonreactivity toward alkenes which could be explained by the high stability of this complex rendering it unable to provide a "free" borane hydroborating reagent. B−H bond Rh activation of NHC-borane circumvents this limitation, and asymmetric Rh-directed anti-Markovnikov boracyclopentannulation reaction led to a library of enantioenriched cyclic Boranes in high yield (up to 94%) with high regio- (up to 100%) and enantioselectivity (er up to 99.2:0.8). This new activation mode of NHCBoranesn highlights their use in organometallic chemistry and offers a very good approach to access chiral cyclic NHC-Boranes.
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Asymmetric Rhodium-Directed anti-Markovnikov Regioselective Boracyclopentannulation
2012Co-Authors: Momar Toure, Olivier Chuzel, Jean-luc ParrainAbstract:A Shimoi-type activation of B–H bond of NHC-Boranes by a diphosphane-ligated cationic Rh complex was applied in an unprecedented intramolecular hydroboration reaction of simple olefins. The use of NHC-Boranes as hydroborating reagents is still undisclosed due to their nonreactivity toward alkenes which could be explained by the high stability of this complex rendering it unable to provide a “free” borane hydroborating reagent. B–H bond Rh activation of NHC-borane circumvents this limitation, and asymmetric Rh-directed anti-Markovnikov boracyclopentannulation reaction led to a library of enantioenriched cyclic Boranes in high yield (up to 94%) with high regio- (up to 100%) and enantioselectivity (er up to 99.2:0.8). This new activation mode of NHC-Boranes highlights their use in organometallic chemistry and offers a very good approach to access chiral cyclic NHC-Boranes
Jean-fabien Petit - One of the best experts on this subject based on the ideXlab platform.
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Ubiquitous Borane Fuel Electrooxidation on Pd/C and Pt/C Electrocatalysts: Toward Promising Direct Hydrazine–Borane Fuel Cells
ACS Catalysis, 2018Co-Authors: Anicet Zadick, Jean-fabien Petit, Umit B Demirci, Vincent Martin, Laetitia Dubau, Christophe Geantet, Marian ChatenetAbstract:Carbon-supported platinum and palladium nanoparticles were studied toward the oxidation of several Boranes (namely ammonia–borane (AB), dimethylamine–borane (DMAB), hydrazine–borane (HB), and hydrazine–bis-borane (HBB)); only palladium is capable to oxidize directly and efficiently these fuels, as platinum first decomposes the Boranes and then valorizes the evolved H2 and adsorbed Had. Changing the nature of the borane fuel enables modulation of the borane oxidation performances at palladium electrodes; the best compromise is reached with HB (HBB suffers safety issues, and AB and DMAB are poisoned by the “counter-fragment” and/or its electroinactivity for any electrooxidation reaction). As a result, with a Pd/C electrode, HB oxidation is possible at low potential (close to the theoretical value), which holds promise for direct alkaline fuel cell applications. The temperature, HB concentration, and palladium nanoparticle loading on the electrode have remarkable effects, which shows that the “direct” electr...
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Ubiquitous Borane Fuel Electrooxidation on Pd/C and Pt/C Electrocatalysts: Toward Promising Direct Hydrazine–Borane Fuel Cells
2018Co-Authors: Anicet Zadick, Jean-fabien Petit, Umit B Demirci, Vincent Martin, Laetitia Dubau, Christophe Geantet, Marian ChatenetAbstract:Carbon-supported platinum and palladium nanoparticles were studied toward the oxidation of several Boranes (namely ammonia–borane (AB), dimethylamine–borane (DMAB), hydrazine–borane (HB), and hydrazine–bis-borane (HBB)); only palladium is capable to oxidize directly and efficiently these fuels, as platinum first decomposes the Boranes and then valorizes the evolved H2 and adsorbed Had. Changing the nature of the borane fuel enables modulation of the borane oxidation performances at palladium electrodes; the best compromise is reached with HB (HBB suffers safety issues, and AB and DMAB are poisoned by the “counter-fragment” and/or its electroinactivity for any electrooxidation reaction). As a result, with a Pd/C electrode, HB oxidation is possible at low potential (close to the theoretical value), which holds promise for direct alkaline fuel cell applications. The temperature, HB concentration, and palladium nanoparticle loading on the electrode have remarkable effects, which shows that the “direct” electrooxidation of the borane fuel (BH3OR) or of its adsorbates may compete with its spontaneous catalytic decomposition/hydrolysis into H2 followed by electrooxidation of H2 (HOR). The study also highlights that the reactant time of residence influences the pathway and completion of the reactions. These results demonstrate that, using suitable electrocatalysts, well-structured electrodes, and adequate borane fuel, the BH3OR thermodynamic onset potential value and the theoretical number of electrons per fuel moiety (ne– = 10 in the case of HB, 6 for the borane fragment and 4 for the hydrazine one) can nearly be reached, at reasonably low anode potential, which paves the way toward optimization of direct HB fuel cell systems
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Hydrazine borane-induced destabilization of ammonia borane, and vice versa.
Journal of hazardous materials, 2014Co-Authors: Jean-fabien Petit, Umit B Demirci, Rodica Chiriac, Georges Moussa, François Toche, Philippe MieleAbstract:Abstract In the field of solid-state chemical hydrogen storage, ammonia borane NH3BH3 has been widely studied while hydrazine borane N2H4BH3 can be considered as a “novel” material. In the present work, we investigated the behaviour of these Boranes when mixed together in a mole ratio of 1:1. Hydrazine borane and ammonia borane destabilize each other. Though stable at 20–25 °C, the mixture melts at ∼30 °C and then undergoes significant decomposition, with desorption of hydrogen H2 and hydrazine N2H4 from 67 °C. This is explained by the fact that the presence of hydrazine borane disrupts the Hδ+⋯Hδ− network of ammonia borane, and vice versa; the mixture is then much less stable than the pristine Boranes. The mixture can nevertheless be stabilized (by heat- or vacuum-treatment and thus extraction of evolving hydrogen and hydrazine), making the as-obtained solid a potential chemical hydrogen storage material. Over the range 25–300 °C, it is able to release ca. 11.4 wt% of almost pure H2. Furthermore forms boron nitride as the solid residue, at temperatures as low as 300 °C.
J. M. D. Macelroy - One of the best experts on this subject based on the ideXlab platform.
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Towards the design of novel boron- and nitrogen-substituted ammonia-borane and bifunctional arene ruthenium catalysts for hydrogen storage
Journal of computational chemistry, 2014Co-Authors: Sateesh Bandaru, Niall J. English, Andrew D. Phillips, J. M. D. MacelroyAbstract:Electronic-structure density functional theory calculations have been performed to construct the potential energy surface for H2 release from ammonia-borane, with a novel bifunctional cationic ruthenium catalyst based on the sterically bulky β-diketiminato ligand (Schreiber et al., ACS Catal. 2012, 2, 2505). The focus is on identifying both a suitable substitution pattern for ammonia-borane optimized for chemical hydrogen storage and allowing for low-energy dehydrogenation. The interaction of ammonia-borane, and related substituted ammonia-Boranes, with a bifunctional η6-arene ruthenium catalyst and associated variants is investigated for dehydrogenation. Interestingly, in a number of cases, hydride-proton transfer from the substituted ammonia-borane to the catalyst undergoes a barrier-less process in the gas phase, with rapid formation of hydrogenated catalyst in the gas phase. Amongst the catalysts considered, N,N-difluoro ammonia-borane and N-phenyl ammonia-borane systems resulted in negative activation energy barriers. However, these types of ammonia-Boranes are inherently thermodynamically unstable and undergo barrierless decay in the gas phase. Apart from N,N-difluoro ammonia-borane, the interaction between different types of catalyst and ammonia borane was modeled in the solvent phase, revealing free-energy barriers slightly higher than those in the gas phase. Amongst the various potential candidate Ru-complexes screened, few are found to differ in terms of efficiency for the dehydrogenation (rate-limiting) step. To model dehydrogenation more accurately, a selection of explicit protic solvent molecules was considered, with the goal of lowering energy barriers for H-H recombination. It was found that primary (1°), 2°, and 3° alcohols are the most suitable to enhance reaction rate. © 2014 Wiley Periodicals, Inc.
Tamás Veszprémi - One of the best experts on this subject based on the ideXlab platform.
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Differences between amine- and phosphine-Boranes: synthesis, photoelectron spectroscopy, and quantum chemical study of the cyclopropylic derivatives.
Inorganic Chemistry, 2010Co-Authors: Balázs Németh, Brahim Khater, Jean-claude Guillemin, Tamás VeszprémiAbstract:Borane complexes of aziridine, phosphirane, cyclopropylamine, cyclopropylphosphine, cyclopropylmethylamine, and cyclopropylmethylphosphine have been prepared by the reaction at low temperatures of a borane complex or diborane on the free phosphine or amine. The products characterized by NMR spectroscopy and mass spectrometry have then been investigated by photoelectron spectroscopy and B3LYP/aug-cc-pVTZ quantum chemical study. The complexation led to rotamers with structures similar to the ones of the corresponding free systems. The main geometry change with the complexation is the P-C bond elongation and the N-C bond shortening, which can be rationalized by the charge transfer attached to the electron donation. The calculated relative stability order of the conformers changes with the complexation only in the case of cyclopropylamine. The calculated complexation energies are higher for the amines, in accord with the differences observed in the flash vacuum thermolysis of methylamine-, methylphosphine-, and aziridine-borane. The photoelectron spectra indicate essential differences between the amines and phosphines toward borane complexation. The dative bond is more stable in the studied amine-Boranes than in phosphine-Boranes, while the sigma(B-H) orbitals are more stable in the latter compounds. The enthalpy of the hydrogen release reaction of aziridine-borane is almost thermoneutral, indicating the potential of this complex as recyclable hydrogen storage material.
Veeraraghavan P Ramachandran - One of the best experts on this subject based on the ideXlab platform.
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amine Boranes as dual purpose reagents for direct amidation of carboxylic acids
Organic Letters, 2020Co-Authors: Veeraraghavan P Ramachandran, Henry J Hamann, Shivani ChoudharyAbstract:Amine-Boranes serve as dual-purpose reagents for direct amidation, activating aliphatic and aromatic carboxylic acids and, subsequently, delivering amines to provide the corresponding amides in up to 99% yields. Delivery of gaseous or low-boiling amines as their borane complexes provides a major advantage over existing methodologies. Utilizing amine-Boranes containing borane incompatible functionalities allows for the preparation of functionalized amides. An intermolecular mechanism proceeding through a triacyloxyborane-amine complex is proposed.
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nucleophilic displacement of ammonia from ammonia borane for the preparation of alkylamine pyridine and phosphine Boranes
RSC Advances, 2014Co-Authors: Veeraraghavan P Ramachandran, Ameya S. KulkarniAbstract:A near quantitative and safe preparation of a series of aliphatic amine- and phosphine-Boranes from ammonia borane (AB) in refluxing THF has been achieved by exploiting the volatility of ammonia. A one-pot preparation of lithium aminoborohydrides from AB has also been described.