Theoretical tools to distinguish O-ylides from O-ylidic complexes in carbene–solvent interactions

Gómez, Sara; Restrepo, Albeiro; Hadad, C. Z.

doi:10.1039/c5cp04783h

Cited by 19 publications

(10 citation statements)

References 60 publications

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“…We have found that stochastic‐based search of suitable candidate structures for the mutual AB and Au 4 spatial disposition, and their subsequent gradient‐based optimizations, has proven to be a very successful combination of methodologies. Among stochastic‐based methods, ASCEC has demonstrated to be very effective, both for atomic and molecular clusters of diverse nature . ASCEC is a simulated annealing algorithm in which the Metropolis criterion has been modified in such a way that it is possible to ensure exhaustive scans, moving down from high energy areas to areas of the lowest possible energies for the studied adducts.…”

Section: Methodsmentioning

confidence: 99%

Activation and diffusion of ammonia borane hydrogen on gold tetramers

Mejía

Ferraro

Osorio

et al. 2017

Int J of Quantum Chemistry

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One of the most serious candidates for safe storage of high hydrogen densities is ammonia borane, AB. Likewise, one of the most versatile catalysts known is gold in the form of atomic clusters. Taking these elements into account, in this work a density functional theory -based study about initial activation, detachment, and diffusion of ammonia borane hydrogen on gold tetramer, as a catalyst model, is developed. It was found that the total process is exergonic and that the hydrogen diffusion occurs with very low energy barriers. The process has a hydrogen detachment energy barrier lower than the one of the uncatalyzed AB, and that is easily overcome by the energy expelled in the previous stage of formation of the initial activated species. Additionally, all the process is assisted by the fluxionality of the gold cluster, and occurs via a unique catalytically activated initial species, which contains a three-center simultaneous interaction at the catalytically activated zone.ammonia borane, gold cluster catalyst, gold-fluxionality, theoretical study, three-center bonding | I N TR ODU C TI ONResearch about new ways for practical, safe, and economically convenient storage and release of large quantities of hydrogen in small volumes is today a very important issue. [1,2] Hydrogen has an energy content by mass almost three times superior to petroleum, [3] is the most abundant substance in the universe, is source-independent, and its combustion product, water, is environmentally friendly. Additionally, the availability of activated hydrogen is highly relevant for a large number of reactions in the chemical industry, where reduction or hydrogenation are necessary steps. [4,5] Among lightweight hydrogen storage materials, ammonia borane, AB (H 3 BNH 3 ), is a substance that contains large amounts of hydrogen (a total of 19.6 wt.%), [3] which is relatively easy to extract, either by direct or by assisted thermolysis, [6,7] by catalyzed room temperature solvolysis, [3,[8][9][10][11] or by other methods. [12][13][14][15] Additionally, AB can be easily and safely transported, [16] because, on the one hand, is a relatively stable solid at room conditions, [3,6,16] and is a substance soluble in many solvents, such as water, methanol, and tetraglyme. [3,[8][9][10][11][12] It has been found that the use of transition metals as catalysts in the AB dehydrogenation has the advantage of avoiding the expenditure of large amounts of energy, necessary for the hydrogen release. [7,[16][17][18] Even, in some cases, the catalysis has emerged as a solution to diminish the unwanted by-products of hydrogen release. [10,12,18] Transition metals of different nature, both noble and non-noble, as well as binary or tertiary combinations among them, have shown catalytic activity toward the extraction of hydrogen from AB. [3,[8][9][10][11][12]17,18] In the case of nanoparticles, the studies show that although some transition metals are better than others, the decrease in size (within certain limits and conditions [19] ) of the nanoparticles of the ...

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Section: Methodsmentioning

confidence: 99%

Activation and diffusion of ammonia borane hydrogen on gold tetramers

Mejía

Ferraro

Osorio

et al. 2017

Int J of Quantum Chemistry

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“…For example, it has been pointed out that "water interactions with aliphatic chains are puzzling due to their inability to form hydrogen bonding or favorable electrostatic interaction". 7 This argument ignores the contributions from secondary hydrogen interactions (those where the proton in the HB comes from a C-H bond), [32][33][34][35][36][37][38][39][40][41] and more specically, it overlooks stabilizing orbital interactions. [42][43][44][45] Recognizing present limitations, the same authors stated in a recent work 3 "there have been no signicant efforts in using modern quantum chemical methods to derive plausible forces from a true ab initio procedure".…”

Section: Introductionmentioning

confidence: 99%

A molecular twist on hydrophobicity

et al. 2021

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“…The shift in the observed wavenumbers of these bands from computational predictions can be explained by solvent-specific interactions at the carbene centre to form an ylidic complex in which there is partial electron donation from the nucleophile to the vacant p-orbital of the carbene centre. 36 Previous reports have identified similar solvent-dependent shifts in the electronic spectra of singlet carbenes. 37 In cyclohexane, decay of singlet carbene bands should be dominated by the stepwise WR because reaction with solvent is not expected.…”

Section: Singlet Carbenementioning

confidence: 67%

Direct Observation of Ylide and Enol Intermediates Formed in Competition with Wolff Rearrangement of Photoexcited Ethyl Diazoacetoacetate

Phelps

Orr-Ewing

2020

J. Am. Chem. Soc.

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The photoexcitation of α-diazocarbonyl compounds produces ketenes by both concerted and stepwise Wolff rearrangements. The stepwise mechanism proceeds through singlet carbene intermediates which can also participate in bimolecular reactions such as ylide formation with nucleophiles. Here, ultrafast transient infra-red absorption spectroscopy is used to show competitive production of singlet carbene and ketene intermediates from the photoexcitation of ethyl diazoacetoacetate. We provide direct spectroscopic evidence for ylide formation by singlet -carbonyl carbene capture in aprotic nucleophilic solvents (with ylide bands at 1625 cm -1 in acetonitrile, and 1586 cm -1 and 1635 cm -1 in tetrahydrofuran) and report an enol mediated pathway for singlet -carbonyl carbene reaction with alcohols (ethanol or tbutanol) identified by an absorption band at 1694 cm -1 , but find no evidence for a previously proposed ylide pathway. The -carbonyl carbene is monitored using a band with solvent-dependent wavenumber in the range 1627 -1645 cm -1 . A computed two-dimensional cut of the potential energy surface for the reaction of the singlet -carbonyl carbene with methanol shows that the enol forms without a barrier, and that this reaction is promoted by an intermolecular hydrogen bond from methanol to the carbonyl oxygen atom. The corresponding ylide structure lies higher in energy, with a barrierless downhill path to isomerization to the enol.

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Theoretical tools to distinguish O-ylides from O-ylidic complexes in carbene–solvent interactions

Cited by 19 publications

References 60 publications

Activation and diffusion of ammonia borane hydrogen on gold tetramers

Activation and diffusion of ammonia borane hydrogen on gold tetramers

A molecular twist on hydrophobicity

Direct Observation of Ylide and Enol Intermediates Formed in Competition with Wolff Rearrangement of Photoexcited Ethyl Diazoacetoacetate

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