.beta.-Hydride Elimination from Alkyl and Cycloalkyl Groups on a Cu(100) Surface: Ring Strain and Planarity of the Transition State

Teplyakov, Andrew V.; Bent, Brian E.

doi:10.1021/ja00145a019

Cited by 38 publications

(53 citation statements)

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“…Clearly ethane and propane will dissociate more rapidly and result in a more facile formation of alkyl radicals, which are likely precursors to graphene 23–25. In addition, studies involving the adsorption of alkanes on single‐crystal copper show the facile conversion of larger alkanes to alkenes by beta‐hydride elimination 26, 27. This is another possible mechanism by which ethane and propane are converted to alkene precursors on the surface of copper and form the initial layer.…”

Section: Resultsmentioning

confidence: 99%

Chemical Vapor Deposition of Graphene on Copper from Methane, Ethane and Propane: Evidence for Bilayer Selectivity

Wassei

Mecklenburg

Torres

et al. 2012

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To study the effects of hydrocarbon precursor gases, graphene is grown by chemical vapor deposition from methane, ethane, and propane on copper foils. The larger molecules are found to more readily produce bilayer and multilayer graphene, due to a higher carbon concentration and different decomposition processes. Single- and bilayer graphene can be grown with good selectivity in a simple, single-precursor process by varying the pressure of ethane from 250 to 1000 mTorr. The bilayer graphene is AB-stacked as shown by selected area electron diffraction analysis. Additionally propane is found to only produce a combination of single- to few-layer and turbostratic graphene. The percent coverage is investgated using Raman spectroscopy and optical, scanning electron, and transmission electron microscopies. The data are used to discuss a possible mechanism for the second-layer growth of graphene involving the different cracking pathways of the hydrocarbons.

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Section: Resultsmentioning

confidence: 99%

Chemical Vapor Deposition of Graphene on Copper from Methane, Ethane and Propane: Evidence for Bilayer Selectivity

Wassei

Mecklenburg

Torres

et al. 2012

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“…These two reaction channels form products with a net stoichiometry of C 2 H 6 O. [31][32][33] These studies suggest that, in general, group IB metals have the capacity to promote the ␤-hydride elimination step necessary to convert hydroxyethyl groups to acetaldehyde. The products with overall C 2 H 4 O stoichiometry are acetaldehyde (CH 3 CHO) and the adsorbed oxametallacycle ͑-CH 2 CH 2 O-) which decomposes at higher temperatures.…”

Section: Identification and Reaction Of Hydroxyethyl Groups On Ag(mentioning

confidence: 95%

Cyclization and related reactions of iodoethanol on Ag(110)

Jones

Barteau

1997

Journal of Vacuum Science &Amp; Technology A: Vacuum, Surfaces, and Films

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Reactions of maleic anhydride over TiO 2 (001) single crystal surfacesThe adsorption and reaction of 2-iodoethanol ͑IEtOH͒ on a clean Ag͑110͒ surface were studied under ultrahigh vacuum conditions using temperature programmed deposition ͑TPD͒. Under these conditions alcohols are typically unreactive on the clean Ag͑110͒ surface. Replacement of one of the ␤ hydrogens with a weakly bound ͑53 kcal/mol͒ iodine atom, however, opens a channel for IEtOH decomposition by initial carbon-iodine scission. TPD results indicate that there are two major reaction channels at 263 and 340 K for IEtOH decomposition on the clean Ag͑110͒ surface. The reaction intermediates that give rise to these two pathways were deduced based upon the products observed, the overall product stoichiometry, and the desorption temperatures of the products. The 263 K reaction channel has an overall stoichiometry of C 2 H 5 O, corresponding to a hydroxyethyl intermediate. The hydroxyethyl intermediate undergoes a ␤-hydride elimination and C-O scission, ultimately yielding volatile acetaldehyde, ethylene, water, ethanol, and another surface intermediate that decomposes at 340 K. Unlike unsubstituted alkyl groups on clean Ag͑111͒ and Ag͑110͒ which couple to form alkanes, there is no evidence for hydroxyethyl coupling to give butanediol. Thus, the hydroxyethyl cannot be treated simply as a substituted alkyl group; that is probably due to interactions between oxygen and the surface. The stoichiometry of the products released at 340 K, C 2 H 4 O, is suggestive of an oxametallacycle intermediate. The products of this reaction channel are the same as the 263 K channel with the addition of a cyclic ester product, ␥-butyrolactone. This species has not previously been synthesized from a C 2 precursor in ultrahigh vacuum, and its observation suggests that surface oxametallacycle chemistry may be richer than previously recognized.

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“…The hydride character of the leaving hydrogen atom was proven by following the trends in free energy relationships with respect to the degree of fluorine substitution in adjacent carbon atoms, a way to introduce chargeinductive effects, 133 and the planar nature of the transition state of this reaction was indicated by the significant differences in reaction rates among alkyl rings with different degrees of strain. 134 This beta-hydride elimination step leads to the return of the alkyl intermediate back to an olefin, and it is partially responsible for olefin isomerization and H-D exchange reactions.…”

Section: Formation and Reactivity Of Alkyl Intermediatesmentioning

confidence: 99%

“…Indeed, Bent et al reported changes in betahydride elimination rates (on Cu(100) surfaces) of up to more than seven orders of magnitude depending of the degree of strain of the (cyclic) alkyl surface species. 134 Presumably, hydrogenation of those species should not display such strong dependence of conversion rate on structure, which means that selectivities may vary widely in olefin hydrogenation reactions depending on the structure of the reactant. This has not been proven yet, though.…”

Section: Competing Reactionsmentioning

confidence: 99%

Key unanswered questions about the mechanism of olefin hydrogenation catalysis by transition-metal surfaces: a surface-science perspective

Zaera

2013

Phys. Chem. Chem. Phys.

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A personal perspective is offered on the state of the art of our current understanding of the mechanism of olefin hydrogenations promoted by transition-metal catalysts. Much is known about these reactions, but many key issues remain poorly understood. It is acknowledged that these reactions take place on surfaces covered with strongly adsorbed carbonaceous layers, but the role that those play in the catalysis is still in question. The active adsorption state of olefins that converts to the alkanes has been identified as a pi-bonded external precursor, that is, as an olefin weakly adsorbed on top of a first layer of strongly adsorbed organic fragments, but the specific details of the interaction of those pi-bonded intermediates with the metal and the way they incorporate hydrogen atoms to produce surface alkyl intermediates need to be worked out still. Molecular hydrogen is known to dissociate on the metal to yield the surface atomic hydrogens that participate in the hydrogenation steps, but its adsorption kinetics is affected by the carbonaceous layers in ways not well characterized to date, and the possible the participation of sub-surface or bulk hydrogen species has been advanced but not generally proven. Knowledge of the energetics and dynamics of the formation of the alkyl intermediates, key in these hydrogenations, is still by and large undeveloped, and the competition between the beta-hydride and reductive elimination steps from that species that define reaction selectivities has been barely quantified. Bridging the pressure and materials gap between studies with single-crystals under vacuum and more realistic catalytic conditions has offered additional challenges. Some experiments that may answer these questions are proposed.

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.beta.-Hydride Elimination from Alkyl and Cycloalkyl Groups on a Cu(100) Surface: Ring Strain and Planarity of the Transition State

Cited by 38 publications

References 0 publications

Chemical Vapor Deposition of Graphene on Copper from Methane, Ethane and Propane: Evidence for Bilayer Selectivity

Chemical Vapor Deposition of Graphene on Copper from Methane, Ethane and Propane: Evidence for Bilayer Selectivity

Cyclization and related reactions of iodoethanol on Ag(110)

Key unanswered questions about the mechanism of olefin hydrogenation catalysis by transition-metal surfaces: a surface-science perspective

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