H<sub>2</sub> Elimination Products from Neutral Zr + Alkene Reactions in the Gas Phase

Wen, Y.; Porembski, Meredith; Ferrett, Tricia A.; Weisshaar, James C.

doi:10.1021/jp9825617

Cited by 36 publications

(54 citation statements)

References 32 publications

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“…Previous studies of reaction rates of diatomic transition metal oxide species with hydrocarbons have probed either the rate of consumption of ZrO, NbO, and MoO species using LIF 31 propylene using 157 nm photoionization. 10 Rate constants for reactions of diatomic transition metal oxide species are comparable in magnitude to the bare metal atom consumption rate constants. 10,31 A thorough search was carried out in the ͗E coll ͘ϭ21.4 kcal/mol data set to determine the contribution of YOϩC 2 H 2 reactions to the YC 2 and YC 2 H product channels.…”

Section: F Potential Contribution Of Yo؉c 2 H 2 Reactionsmentioning

confidence: 97%

“…10 Rate constants for reactions of diatomic transition metal oxide species are comparable in magnitude to the bare metal atom consumption rate constants. 10,31 A thorough search was carried out in the ͗E coll ͘ϭ21.4 kcal/mol data set to determine the contribution of YOϩC 2 H 2 reactions to the YC 2 and YC 2 H product channels. Signal at m/eϭ129 ͑YOC 2 ) and m/eϭ130 ͑YOC 2 H͒ was not observed at any angles near the most probable c.m.…”

Section: F Potential Contribution Of Yo؉c 2 H 2 Reactionsmentioning

confidence: 97%

“…1,6,7 Although there now exists an extensive body of such theoretical data, only relatively recently have experimental studies of neutral transition metal atom reactions with small hydrocarbon molecules been carried out. [10][11][12][13][14][15] The combination of theory and experiment is beginning to provide considerable insight into the most important features underlying neutral transition metal reactivity. 6,7 For insertion reactions involving bare transition metal atoms, barrier heights have been rationalized in terms of the ground state electronic configurations of the metal atoms and the energies of low-lying excited state electronic configurations able to minimize long-range repulsion while favoring formation of two covalent bonds in the insertion intermediate.…”

Section: Introductionmentioning

confidence: 99%

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Competing reaction pathways from Y+C2H2 collisions

Stauffer

Hinrichs

Willis

et al. 1999

The Journal of Chemical Physics

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The crossed molecular beams method with 193 and 157 nm photoionization detection was used to study the competing reaction pathways resulting from collisions of ground state Y atoms with acetylene (C2H2). Three channels, corresponding to nonreactive decay of collision complexes, H2 elimination, and H atom elimination, were studied as a function of collision energy (〈Ecoll〉=6–25 kcal/mol). Production of YC2+H2 and decay of long-lived complexes back to reactants were observed at all collision energies studied. Product translational energy distributions for the H2 elimination channel demonstrate that a substantial fraction of excess energy available to the YC2+H2 products is channeled into relative translational energy. Analogous H2 elimination channels were studied in reactions of Zr and Nb with C2H2 at 〈Ecoll〉=6.0 kcal/mol. For these reactions, the H2 elimination product translational energy distributions were found to peak near zero kinetic energy, in contrast to the behavior observed for the YC2+H2 products. This suggests that a significant potential energy barrier exists in the exit channel of the YC2+H2 elimination step, whereas no exit channel barrier exists in forming ZrC2+H2 and NbC2+H2. The reformation of Y + C2H2 reactants following decay of long-lived collision complexes was found to transfer 40%–50% of the initial relative translational energy into C2H2 internal excitation. The YC2H+H product channel was only observed to occur above a collision energy threshold of 21.5±2.0 kcal/mol. Since YC2H+H production is fully spin-allowed and involves simple Y–H bond fission in the intermediate HYC2H complex, it is unlikely that any significant potential energy barrier is present in excess of the reaction endoergicity. Additional studies of Y+C2D2 reactions confirm that the observed collision energy threshold for the H or D atom loss channel corresponds to the energetic threshold for reaction, allowing determination of D0(Y–CCH)=110.2±2.0 kcal/mol.

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Section: F Potential Contribution Of Yo؉c 2 H 2 Reactionsmentioning

confidence: 97%

Section: F Potential Contribution Of Yo؉c 2 H 2 Reactionsmentioning

confidence: 97%

Section: Introductionmentioning

confidence: 99%

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Competing reaction pathways from Y+C2H2 collisions

Stauffer

Hinrichs

Willis

et al. 1999

The Journal of Chemical Physics

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“…The activation energy ∆E q is decomposed into the activation strain ∆E q strain of and the stabilizing TS interaction ∆E q int between the reactants in the transition state (∆E q int may be further analyzed). -8.438 -7.435 -6.806 -7.303 -7.142 ∆E q int ) ∆V elst + ∆E Pauli + ∆E oi (6) 5c, which are shown in Figure 4: (i) back-donation from the Pd 4d atomic orbital (AO) into the substrate's LUMO (lowest unoccupied molecular orbital) and (ii) donation of the substrate's HOMO (highest occupied molecular orbital) into the Pd 5s AO. The Pd 5p orbitals do not significantly participate in these interactions.…”

Section: Analysis Of the Activation Barriers For Bond Activationmentioning

confidence: 99%

Activation of H−H, C−H, C−C, and C−Cl Bonds by Pd(0). Insight from the Activation Strain Model

2004

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To achieve more insight into palladium-catalyzed H-H, C-H, C-C, and C-Cl bond activation and the mutual competition between these processes, several mechanistic pathways for oxidative addition of Pd(0) to H 2 (H-H), CH 4 (C-H), C 2 H 6 (C-C and C-H), and CH 3 Cl (C-Cl) were studied uniformly at the ZORA-BP86/TZ(2)P level of relativistic nonlocal density functional theory (DFT). Oxidative addition is overall exothermic for all model reactions studied, with 298 K reaction enthalpies (∆H r,298 ) of -35.7 kcal/mol (C-Cl) through -9.7 kcal/mol (C-H in CH 4 ). The lowest barrier pathway is the direct oxidative insertion of Pd into the C-X or H-H bond (X ) H, CH 3 , Cl), with 298 K activation enthalpies (∆H q 298 ) that increase in the order H-H (-21.7 kcal/mol) < C-Cl (-6.0 kcal/mol) ≈ C-H (-5.0 and -4.1 kcal/mol for CH 4 and C 2 H 6 ) < C-C (9.6 kcal/mol). The "straight" S N 2 substitution resulting in PdCH 3 + + Xor PdH + + His highly endothermic (144-237 kcal/mol) and thus not competitive. Only in the case of Pd + CH 3 Cl is a third pathway found in which S N 2 substitution occurs in concert with a rearrangement of the Clleaving group from C to Pd (S N 2/Cl-ra) leading, in one step, to CH 3 PdCl via an activation barrier ∆H q 298 of 21.2 kcal/mol. The competition between the various bond activation processes is analyzed using the activation strain model in which activation energies (∆E q ) are decomposed into the activation strain (∆E q strain ) of and the stabilizing transition state (TS) interaction (∆E q int ) between the reactants in the activated complex: ∆E q ) ∆E q strain + ∆E q int . Interestingly, the activation strain ∆E q strain adopts characteristic values for each type of bond and reaction mechanism. The trend in TS interaction ∆E q int turns out to be mainly determined by the donoracceptor orbital interactions between occupied Pd 4d atomic orbitals and the empty σ* C-X (or σ* H-H ) acceptor orbital associated with the bond to be activated in the substrate.

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“…Analogous reactions of Zr atoms with alkenes, where barrierless association complex formation is thought to be rate-determining, are 55 ( 16 × 10 -12 cm 3 s -1 , and 135 ( 40 × 10 -12 cm 3 s -1 for ethene and propene, respectively. 31 The comparatively small value of k 1 for Zr-dimethyl ether may be attributable to the pressure dependence of k 1 . For the Al-dimethyl ether association reaction, the high-pressure limit of k 1 lies above 600 Torr (8 × 10 4 Pa).…”

Section: Resultsmentioning

confidence: 99%

Bonding in Transition Metal−Ether Complexes: The Spectroscopy and Reactivity of the Zr Atom−Dimethyl Ether System

Pedersen¹,

Zgierski²,

Anderson³

et al. 2001

J. Phys. Chem. A

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Access and use of this website and the material on it are subject to the Terms and Conditions set forth at NRC Publications Record / Notice d'Archives des publications de CNRC:http://nparc.cisti-icist.nrc-cnrc.gc.ca/npsi/ctrl?action=rtdoc&an=12327092&lang=en http://nparc.cisti-icist.nrc-cnrc.gc.ca/npsi/ctrl?action=rtdoc&an=12327092&lang=fr READ THESE TERMS AND CONDITIONS CAREFULLY BEFORE USING THIS WEBSITE.http://nparc.cisti-icist.nrc-cnrc.gc.ca/npsi/jsp/nparc_cp.jsp?lang=en Vous avez des questions? Nous pouvons vous aider. Pour communiquer directement avec un auteur, consultez la première page de la revue dans laquelle son article a été publié afin de trouver ses coordonnées. Si vous n'arrivez pas à les repérer, communiquez avec nous à PublicationsArchive-ArchivesPublications@nrc-cnrc.gc.ca. Questions? Contact the NRC Publications Archive team atPublicationsArchive-ArchivesPublications@nrc-cnrc.gc.ca. If you wish to email the authors directly, please see the first page of the publication for their contact information. NRC Publications Archive Archives des publications du CNRCThis publication could be one of several versions: author's original, accepted manuscript or the publisher's version. / La version de cette publication peut être l'une des suivantes : la version prépublication de l'auteur, la version acceptée du manuscrit ou la version de l'éditeur. For the publisher's version, please access the DOI link below./ Pour consulter la version de l'éditeur, utilisez le lien DOI ci-dessous.http://doi.org/10.1021/jp0130158The Journal of Physical Chemistry A, 105, 51, pp. 11462-11469, 2001-11-29 Lexington, Kentucky 40506-0055 ReceiVed: August 3, 2001; In Final Form: October 18, 2001 The reactivity and bonding of neutral Zr metal atoms with dimethyl ether have been thoroughly characterized using flow tube reactor, PFI-ZEKE, and DFT techniques. Between 275 and 371 K, these species form an association complex with the Zr bound to the ether O atom. Using a flow tube reactor, the equilibrium constant for the association reaction has been found to be 6 ( 2 × 10 -14 cm 3 at 361 ( 10 K. From this measure the Zr-dimethyl ether bond energy is estimated to be 80 ( 2k Jm o l -1 . The ZEKE spectrum of the association complex is reproduced very well by DFT calculations. The calculations indicate that the Zr-dimethyl ether complex is bound by dative bonding involving donation of electron density from the highest occupied dimethyl ether orbital of a 1 symmetry to the Zr 4d orbital of σ symmetry directed along the Zr-dimethyl ether bond axis. Dative bonding interactions are much stronger than donor-acceptor bonding as the vacant dimethyl ether antibonding orbital lies too high in energy for back-donation of electron density from Zr to be efficient. This finding is likely a general characteristic of neutral transition metal-ether complexes. To our knowledge, these results constitute the most detailed investigation, to date, of neutral transition metal-ether bonding and reactivity.

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H₂ Elimination Products from Neutral Zr + Alkene Reactions in the Gas Phase

Cited by 36 publications

References 32 publications

Competing reaction pathways from Y+C2H2 collisions

Competing reaction pathways from Y+C2H2 collisions

Activation of H−H, C−H, C−C, and C−Cl Bonds by Pd(0). Insight from the Activation Strain Model

Bonding in Transition Metal−Ether Complexes: The Spectroscopy and Reactivity of the Zr Atom−Dimethyl Ether System

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H2 Elimination Products from Neutral Zr + Alkene Reactions in the Gas Phase

Cited by 36 publications

References 32 publications

Competing reaction pathways from Y+C2H2 collisions

Competing reaction pathways from Y+C2H2 collisions

Activation of H−H, C−H, C−C, and C−Cl Bonds by Pd(0). Insight from the Activation Strain Model

Bonding in Transition Metal−Ether Complexes: The Spectroscopy and Reactivity of the Zr Atom−Dimethyl Ether System

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H₂ Elimination Products from Neutral Zr + Alkene Reactions in the Gas Phase