Low Activation Barriers in N2Reduction with H2at Ruthenium Pincer Complexes Induced by Ligand Cooperativity: A Computational Study

2014 ◽  
Vol 2014 (35) ◽  
pp. 6126-6133 ◽  
Author(s):  
Markus Hölscher ◽  
Walter Leitner
Keyword(s):  
Computational Study ◽  
Pincer Complexes ◽  
Activation Barriers

COMPUTING NARROW NANOTUBES AND THEIR DERIVATIVES

2002 ◽  
Vol 01 (03n04) ◽  
pp. 303-312 ◽  
Author(s):  
ZDENĚK SLANINA ◽  
FILIP UHLÍK ◽  
LESZEK STOBINSKI ◽  
HONG-MING LIN ◽  
LUDWIK ADAMOWICZ
Keyword(s):  
Computational Study ◽  
Activation Barriers ◽  
Enthalpy Changes ◽  
Oxygen Addition

Very recently, narrow nanotubes have been observed with diameters of 5 or even 4 Å. In this report we survey calculations that have so far been performed on narrow model nanotubes, namely capped by fragments of D2d and D6h C 36 fullerene cages or by fragments of C 32 and C 16quasi-fullerene cages with two four-membered rings, or finally by a fragment of dodecahedral C 20. The computations can reproduce the observed diameters of the narrow nanotubes. The results also indicate that fragments of C 32, used as caps instead of C 36, can lead to quite competitive energetics. Thus, a novel possibility that some of the narrow nanotubes can contain four-membered rings at their tips seems plausible. The present paper also surveys computational study of oxygen additions to the narrow nanotubes, i.e., a problem frequently studied with fullerenes. Both thermodynamic enthalpy changes and kinetic activation barriers for oxygen addition to selected bonds are computed and analyzed. The lowest isomer (thermodynamically the most stable) is never of the 6/6 type, i.e., the thermodynamically most convenient structures are produced by oxygen additions to the nanotube tips. The computations show that narrow nanotubes should be relatively prone to additions of oxygen.

scholarly journals A Computational Study of Direct CO2 Hydrogenation to Methanol on Pd Catalysts

2021 ◽  
Author(s):  
Igor Kowalec ◽  
Lara Kabalan ◽  
Richard Catlow ◽  
Andrew Logsdail
Keyword(s):  
Density Functional ◽  
Negative Charge ◽  
Computational Study ◽  
Adsorbed Species ◽  
Pd Catalysts ◽  
Functional Theory ◽  
Activation Barriers ◽  
Rate Determining Step ◽  
Adsorption Energies ◽  
Insight Into

<p>We investigate the mechanism of direct CO<sub>2</sub> hydrogenation to methanol on Pd (111), (100) and (110) surfaces using density functional theory (DFT), providing insight into the reactivity of CO<sub>2</sub> on Pd-based catalysts. The initial chemisorption of CO<sub>2</sub>, forming a partially charged CO<sub>2</sub><sup>δ-</sup>, is weakly endothermic on a Pd (111) surface, with an adsorption energy of 0.06 eV, and slightly exothermic on Pd (100) and (110) surfaces, with adsorption energies of -0.13 and -0.23 eV, respectively. Based on Mulliken analysis, we attribute the low stability of CO<sub>2</sub><sup>δ-</sup><sub> </sub>on the Pd (111) surface to a negative charge that accumulates on the surface Pd atoms interacting directly with the CO<sub>2</sub><sup>δ-</sup><sub> </sub>adsorbate. For the reaction of the adsorbed species on the Pd surface, HCOOH hydrogenation to H<sub>2</sub>COOH is predicted to be the rate determining step of the conversion to methanol in all cases, with activation barriers of 1.35, 1.26, and 0.92 eV on Pd (111), (100) and (110) surfaces, respectively.<br></p>

scholarly journals Computational Study of Methane C–H Activation by Main Group and Mixed Main Group–Transition Metal Complexes

Molecules ◽  
2020 ◽  
Vol 25 (12) ◽  
pp. 2794
Author(s):  
Carly C. Carter ◽  
Thomas R. Cundari
Keyword(s):  
Transition Metal Complexes ◽  
Active Site ◽  
Density Functional ◽  
Computational Study ◽  
Divalent Metal ◽  
Main Group ◽  
Free Energies ◽  
Functional Theory ◽  
Activation Barriers ◽  
Experimental Values

In the present density functional theory (DFT) research, nine different molecules, each with different combinations of A (triel) and E (divalent metal) elements, were reacted to effect methane C–H activation. The compounds modeled herein incorporated the triels A = B, Al, or Ga and the divalent metals E = Be, Mg, or Zn. The results show that changes in the divalent metal have a much bigger impact on the thermodynamics and methane activation barriers than changes in the triels. The activating molecules that contained beryllium were most likely to have the potential for activating methane, as their free energies of reaction and free energy barriers were close to reasonable experimental values (i.e., ΔG close to thermoneutral, ΔG‡ ~30 kcal/mol). In contrast, the molecules that contained larger elements such as Zn and Ga had much higher ΔG‡. The addition of various substituents to the A–E complexes did not seem to affect thermodynamics but had some effect on the kinetics when substituted closer to the active site.

Combined Experimental/Computational Study of Iridium and Palladium Hydride PP(O)P Pincer Complexes

2014 ◽  
Vol 33 (2) ◽  
pp. 571-577 ◽  
Author(s):  
Carmen Martin ◽  
Sonia Mallet-Ladeira ◽  
Karinne Miqueu ◽  
Ghenwa Bouhadir ◽  
Didier Bourissou
Keyword(s):  
Computational Study ◽  
Pincer Complexes ◽  
Palladium Hydride

A Much-Needed Mechanism and Reaction Rate for the Oxidation of Phenols with ClO2: A Joint Experimental and Computational Study

2013 ◽  
Vol 66 (7) ◽  
pp. 814 ◽  
Author(s):  
Carlos Alberto Huerta Aguilar ◽  
Jayanthi Narayanan ◽  
Mariappan Manoharan ◽  
Narinder Singh ◽  
Pandiyan Thangarasu
Keyword(s):  
Oxidation Rate ◽  
Density Functional ◽  
Reaction Rate ◽  
Computational Study ◽  
Reaction Rate Constant ◽  
Oxidation Products ◽  
Gas Chromatography Mass Spectrometry ◽  
Activation Barriers ◽  
Oxidation Of Phenols ◽  
The Right

The oxidation of phenols with chlorine dioxide, a powerful means to eliminate phenol pollutants from drinking water, is explored. Kinetic experiments reveal that 2,4,6-trichlorophenol exhibits a lower oxidation rate than other phenols because the chlorine atoms (σ = 0.22) at ortho and para-positions decrease the benzene’s electron density, in agreement with the Hammett plot. The oxidation of phenol was found to be second order with respect to phenol and first order with respect to ClO2 and a possible mechanism is proposed. The phenol/ClO2 oxidation was found to be pH-dependent since the reaction rate constant increases with increasing pH. The oxidation rate was also significantly enhanced with an increasing methanol ratio in water. The oxidation products, such as benzoquinones, were analysed and confirmed by liquid chromatography and gas chromatography–mass spectrometry. Density functional theory computations at both the B3LYP/6-311+G(d,p) and M06-2X.6-311+G(d,p) levels with the SCRF-PCM solvation model (i.e. with water) further supported the proposed mechanisms in which activation barriers predicted the right reactivity trend as shown by the kinetic experiments.

Selective C−C vs C−H Bond Activation by Rhodium(I) PCP Pincer Complexes. A Computational Study

2000 ◽  
Vol 122 (29) ◽  
pp. 7095-7104 ◽  
Author(s):  
Andreas Sundermann ◽  
Olivier Uzan ◽  
David Milstein ◽  
Jan M. L. Martin
Keyword(s):  
Bond Activation ◽  
Computational Study ◽  
Pincer Complexes ◽  
Pcp Pincer

CO2 Insertion into Metal-Carbon Bonds: A Computational Study of RhI Pincer Complexes

2011 ◽  
Vol 17 (37) ◽  
pp. 10329-10338 ◽  
Author(s):  
Thomas G. Ostapowicz ◽  
Markus Hölscher ◽  
Walter Leitner
Keyword(s):  
Computational Study ◽  
Pincer Complexes ◽  
Carbon Bonds

scholarly journals A Computational Study of Direct CO2 Hydrogenation to Methanol on Pd Catalysts

2021 ◽  
Author(s):  
Igor Kowalec ◽  
Lara Kabalan ◽  
Richard Catlow ◽  
Andrew Logsdail
Keyword(s):  
Density Functional ◽  
Negative Charge ◽  
Computational Study ◽  
Adsorbed Species ◽  
Pd Catalysts ◽  
Functional Theory ◽  
Activation Barriers ◽  
Rate Determining Step ◽  
Adsorption Energies ◽  
Insight Into

<p>We investigate the mechanism of direct CO<sub>2</sub> hydrogenation to methanol on Pd (111), (100) and (110) surfaces using density functional theory (DFT), providing insight into the reactivity of CO<sub>2</sub> on Pd-based catalysts. The initial chemisorption of CO<sub>2</sub>, forming a partially charged CO<sub>2</sub><sup>δ-</sup>, is weakly endothermic on a Pd (111) surface, with an adsorption energy of 0.06 eV, and slightly exothermic on Pd (100) and (110) surfaces, with adsorption energies of -0.13 and -0.23 eV, respectively. Based on Mulliken analysis, we attribute the low stability of CO<sub>2</sub><sup>δ-</sup><sub> </sub>on the Pd (111) surface to a negative charge that accumulates on the surface Pd atoms interacting directly with the CO<sub>2</sub><sup>δ-</sup><sub> </sub>adsorbate. For the reaction of the adsorbed species on the Pd surface, HCOOH hydrogenation to H<sub>2</sub>COOH is predicted to be the rate determining step of the conversion to methanol in all cases, with activation barriers of 1.35, 1.26, and 0.92 eV on Pd (111), (100) and (110) surfaces, respectively.<br></p>

scholarly journals The Impact of Secondary Coordination Sphere Nucleophiles on Methane Activation: A Computational Study

2019 ◽  
Author(s):  
Mary E. Anderson ◽  
Thomas Cundari
Keyword(s):  
Active Sites ◽  
Density Functional ◽  
Bond Activation ◽  
Computational Study ◽  
Solvent Polarity ◽  
Active Hydrogen ◽  
Functional Theory ◽  
Activation Barriers ◽  
Secondary Coordination Sphere ◽  
The Impact

p.p1 {margin: 0.0px 0.0px 0.0px 0.0px; font: 12.0px 'Helvetica Neue'} <p>Density functional theory and ab initio calculations indicate that nucleophiles can significantly reduce enthalpic barriers to methane C–H bond activation. Different pieces of evidence point to an electrostatic origin for the nucleophile effect such as the sensitivity of the C–H activation barriers to the external nucleophile and to continuum solvent polarity. The data further imply a transition state with significant charge build-up on the active hydrogen of the hydrocarbon substrate. From the present modeling studies, one may propose proteins with hydrophobic active sites, available nucleophiles, and hydrogen bond donors as attractive targets for the engineering of novel methane functionalizing enzymes.</p>

scholarly journals The Impact of Secondary Coordination Sphere Nucleophiles on Methane Activation: A Computational Study

2019 ◽  
Author(s):  
Mary E. Anderson ◽  
Thomas Cundari
Keyword(s):  
Active Sites ◽  
Density Functional ◽  
Bond Activation ◽  
Computational Study ◽  
Solvent Polarity ◽  
Active Hydrogen ◽  
Functional Theory ◽  
Activation Barriers ◽  
Secondary Coordination Sphere ◽  
The Impact

p.p1 {margin: 0.0px 0.0px 0.0px 0.0px; font: 12.0px 'Helvetica Neue'} <p>Density functional theory and ab initio calculations indicate that nucleophiles can significantly reduce enthalpic barriers to methane C–H bond activation. Different pieces of evidence point to an electrostatic origin for the nucleophile effect such as the sensitivity of the C–H activation barriers to the external nucleophile and to continuum solvent polarity. The data further imply a transition state with significant charge build-up on the active hydrogen of the hydrocarbon substrate. From the present modeling studies, one may propose proteins with hydrophobic active sites, available nucleophiles, and hydrogen bond donors as attractive targets for the engineering of novel methane functionalizing enzymes.</p>

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