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Sökning: WFRF:(Ahlquist Mårten)

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1.
  • Agarwala, Hemlata, et al. (författare)
  • Alternating Metal-Ligand Coordination Improves Electrocatalytic CO2 Reduction by a Mononuclear Ru Catalyst**
  • 2023
  • Ingår i: Angewandte Chemie International Edition. - : Wiley. - 1433-7851 .- 1521-3773. ; 62:17
  • Tidskriftsartikel (refereegranskat)abstract
    • Molecular electrocatalysts for CO2-to-CO conversion often operate at large overpotentials, due to the large barrier for C−O bond cleavage. Illustrated with ruthenium polypyridyl catalysts, we herein propose a mechanistic route that involves one metal center that acts as both Lewis base and Lewis acid at different stages of the catalytic cycle, by density functional theory in corroboration with experimental FTIR. The nucleophilic character of the Ru center manifests itself in the initial attack on CO2 to form [Ru-CO2]0, while its electrophilic character allows for the formation of a 5-membered metallacyclic intermediate, [Ru-CO2CO2]0,c, by addition of a second CO2 molecule and intramolecular cyclization. The calculated activation barrier for C−O bond cleavage via the metallacycle is decreased by 34.9 kcal mol−1 as compared to the non-cyclic adduct in the two electron reduced state of complex 1. Such metallacyclic intermediates in electrocatalytic CO2 reduction offer a new design feature that can be implemented consciously in future catalyst designs.
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2.
  • Agarwala, Hemlata, et al. (författare)
  • An Elusive  Intermediate Uncovered in the Pathway for Electrochemical Carbon Dioxide Reduction by Ruthenium Polypyridyl Catalyst - Combined Spectroscopic and Computational Investigation
  • Annan publikation (övrigt vetenskapligt/konstnärligt)abstract
    • A scrutinous study of the catalytic cycle for electrochemical CO2 reduction by the ruthenium 2,2:6,2-terpyridine (tpy) 2,2-bipyridine (bpy) class of catalysts is presented. An unprecedented 2-(C,O)-carboxycarboxylatoruthenium(II) metalacyclic intermediate, critical for C-O bond dissociation at low overpotentials, so far precluded from mechanistic considerations of polypyridyl transition metal complex catalysts, is unearthed by infra-red spectroscopy coupled to controlled potential electrolysis in corroboration with density functional theory (DFT) investigations. Thermodynamic and kinetic analyses of the intermediate reveal the important role of the structural flexibility of polypyridyl ligands and fine electronic tunability of the metal center, along with kinetic trans effect, in propelling catalysis at lower overpotentials. The choice of metal center, Ru in the present case, points to the fact that the requirement of an additional Lewis acid to enhance C-O bond dissociation, hence increase the catalytic rate or turnover, can be circumvented.
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3.
  • Ahlquist, Mårten, et al. (författare)
  • An experimental and theoretical study of the mechanism of stannylcupration of alpha, beta-acetylenic ketones and esters
  • 2006
  • Ingår i: Chemistry - A European Journal. - : Wiley. - 0947-6539 .- 1521-3765. ; 12:10, s. 2866-2873
  • Tidskriftsartikel (refereegranskat)abstract
    • The title reaction has been investigated by experimental and computational (DFT) techniques, and subsequently compared to the corresponding carbocupration reaction, with particular emphasis oil the stereoselectivity. For stannylcupration of an ynone substrate, only the anti-addition product is observed, whereas for the corresponding ynoate substrate, the stereoselectivity can be affected by the reaction conditions: in the presence of methanol as proton donor, the initial syn-addition product can be trapped, whereas a syn/anti mixture is obtained in a non-protic solvent. This is in sharp contrast to the carbocupration of the same ynone substrate with a cyanocuprate (RCu(CN)Li), which is highly selective for syn-addition. The product selectivities can be understood from a detailed computational characterization of the reaction paths, and in particular from the relative stabilities of the vinyl cuprate and allenolate intermediates. It is suggested that the stereodetermining step is protonation of vinyl cuprate intermediates.
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4.
  • Ahlquist, Mårten, et al. (författare)
  • C-H activation in strongly acidic media. The co-catalytic effect of the reaction medium
  • 2009
  • Ingår i: Chemical Communications. - : Royal Society of Chemistry (RSC). - 1359-7345 .- 1364-548X. ; :17, s. 2373-2375
  • Tidskriftsartikel (refereegranskat)abstract
    • Quantum mechanical (QM) results are used to establish the role of sulfuric acid solvent in facilitating the reaction between Pt(II)(bpym)Cl(2) (bpym = 2,2'-bipyrimidinyl) and methane; coordination of methane to the platinum catalyst is found to be catalyzed by the acidic medium.
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5.
  • Ahlquist, Mårten, et al. (författare)
  • Dispersion and Back-Donation Gives Tetracoordinate [Pd(PPh3)4]
  • 2011
  • Ingår i: Angewandte Chemie International Edition. - : Wiley. - 1433-7851 .- 1521-3773. ; 50:49, s. 11794-11797
  • Tidskriftsartikel (refereegranskat)abstract
    • 18e R.I.P. The apparent compliance of [Pd(PPh3)4] ("tetrakis") with the 18-electron rule is not due to an electronic preference on the central metal. Pd is valence-saturated already by two ligands. Further ligand addition gives a minor energy gain, and is only possible due to strong back-bonding. Dispersion corrections are needed for properly describing the interactions between the ligands.
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6.
  • Ahlquist, Mårten, et al. (författare)
  • Enhanced reactivity of dinuclear Copper(I) acetylides in dipolar cycloadditions
  • 2007
  • Ingår i: Organometallics. - : American Chemical Society (ACS). - 0276-7333 .- 1520-6041. ; 26:18, s. 4389-4391
  • Tidskriftsartikel (refereegranskat)abstract
    • Dinuclear alkynyl copper(I) complexes exhibit superior reactivity toward organic azides compared to their monomeric analogues. DFT studies indicate that the second copper center facilitates the formation of the cupracycle in the rate-determining step and stabilizes the metallacycle intermediate itself. These findings support the experimentally determined rate law and shed light on the origin of high reactivity of the in situ generated copper acetylides.
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7.
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8.
  • Ahlquist, Mårten, et al. (författare)
  • On the performance of continuum solvation models for the solvation energy of small anions
  • 2006
  • Ingår i: Organometallics. - : American Chemical Society (ACS). - 0276-7333 .- 1520-6041. ; 25:1, s. 45-47
  • Tidskriftsartikel (refereegranskat)abstract
    • The determination of continuum solvation models for the solvation energy of anions, was described. To investigate the reliability of the solvent model, a few explicit THF molecules were incorporated. A set of anions was chosen for which the experimental free energiesof solvation were available for both H 2O and DMSO solutions. A major difference between the water model and the DMSO model is that the latter systematically overestimates the free energy of solvation. The full water model in Jaguar v 4.2, including also nonelectrostatic terms, gives good correlation with experimental values for energy of solvation.
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9.
  • Ahlquist, Mårten, et al. (författare)
  • Oxidative addition of aryl chlorides to monoligated palladium(0): A DFT-SCRF study
  • 2007
  • Ingår i: Organometallics. - : American Chemical Society (ACS). - 0276-7333 .- 1520-6041. ; 26:3, s. 550-553
  • Tidskriftsartikel (refereegranskat)abstract
    • Oxidative addition of aryl chlorides to palladium has been investigated by hybrid density functional theory methods (B3LYP), including a continuum model describing the solvent implicitly. A series of para-substituted aryl chlorides were studied to see the influence of electronic effects on the reaction. It was found that the experimentally observed higher reactivity of the more electron deficient aryl chlorides is due to their ability to accept back-donation from Pd-0 and form reasonably strong pre-reactive complexes. This effect is less pronounced in the transition state; when it is measured from the pre-reactive complex, the barrier to oxidative addition is actually higher for the electron-deficient aryl chlorides, but the overall reaction barrier is still lower than for the electron-rich aryl chlorides.
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10.
  • Ahlquist, Mårten, et al. (författare)
  • Palladium(0) alkyne complexes as active species : a DFT investigation
  • 2005
  • Ingår i: Chemical Communications. - : Royal Society of Chemistry (RSC). - 1359-7345 .- 1364-548X. ; :33, s. 4196-4198
  • Tidskriftsartikel (refereegranskat)abstract
    • Alkynes have been found to be excellent ligands for Pd(0); the stability of a range of alkyne-Pd(0) complexes, and their reactivity in oxidative addition, have been investigated by DFT methods.
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11.
  • Ahlquist, Mårten, et al. (författare)
  • Product Protection, the Key to Developing High Performance Methane Selective Oxidation Catalysts
  • 2009
  • Ingår i: Journal of the American Chemical Society. - : American Chemical Society (ACS). - 0002-7863 .- 1520-5126. ; 131:47, s. 17110-17115
  • Tidskriftsartikel (refereegranskat)abstract
    • Selective, direct conversion of methane to methanol might seem an impossible task since the C-H bond energy of methane is 105 kcal mol(-1) compared to the C-H bond energy for methanol of 94. We show here that the Catalytica catalyst is successful because the methanol is protected as methyl bisulfate, which is substantially less reactive than methanol toward the catalyst. This analysis suggests a limiting performance for systems that operate by this type of protection that is well above the Catalytica system.
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12.
  • Ahlquist, Mårten, et al. (författare)
  • Rhodium(I) hydrogenation in water : Kinetic studies and the detection of an intermediate using C-13{H-1} PHIPNMR spectroscopy
  • 2007
  • Ingår i: Inorganica Chimica Acta. - : Elsevier BV. - 0020-1693 .- 1873-3255. ; 360:5, s. 1621-1627
  • Tidskriftsartikel (refereegranskat)abstract
    • The mechanism for hydrogenation of dimethylmaleate in water using cationic rhodium complexes with water-soluble bi-dentate phosphines has been investigated using kinetics and a novel method for the indirect detection of intermediates in catalytic hydrogenation reactions, whereby a late intermediate was detected. A mechanism is proposed involving fast, irreversible substrate binding followed by a rate-determining reaction with dihydrogen.
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13.
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14.
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15.
  • Ahlquist, Mårten S. G. (författare)
  • Iridium catalyzed hydrogenation of CO2 under basic conditions-Mechanistic insight from theory
  • 2010
  • Ingår i: Journal of Molecular Catalysis A. - : Elsevier BV. - 1381-1169 .- 1873-314X. ; 324:1-2, s. 3-8
  • Tidskriftsartikel (refereegranskat)abstract
    • The iridium(III) catalyzed hydrogenation of carbon dioxide under basic conditions was studied with density functional theory. It was found that the insertion of CO2 into an Ir-H bond proceeds via a two-step mechanism. The rate-limiting step was calculated to be the regeneration of the iridium(III) trihydride intermediate, and the overall barrier for the reaction was calculated to 26.1 kcal mol(-1). The formation of the iridium trihydride proceeds via formation of a cationic Ir(H)(2)(H-2) complex at which the base abstracts a proton from the dihydrogen ligand. (C) 2010 Elsevier B.V. All rights reserved.
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16.
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17.
  • Ahlquist, Mårten, et al. (författare)
  • The mechanism of the phosphine-free palladium-catalyzed hydroarylation of alkynes
  • 2006
  • Ingår i: Journal of the American Chemical Society. - : American Chemical Society (ACS). - 0002-7863 .- 1520-5126. ; 128:39, s. 12785-12793
  • Tidskriftsartikel (refereegranskat)abstract
    • The mechanism of the Pd-catalyzed hydroarylation and hydrovinylation reaction of alkynes has been studied by a combination of experimental and theoretical methods (B3LYP), with an emphasis on the phosphine-free version. The regioselectivity of the hydroarylation and hydrovinylation shows unexpected differences, which could be attributed mainly to the higher steric demand of the cyclohexenyl group as compared to the phenyl group. Hydroarylation of alpha,beta-acetylenic carbonyl substrates yields a very unusual anti-Michael selectivity, which is shown to result from reaction of the nonconjugated double bond, leaving the conjugation intact. In all cases were the regioselectivities reproduced by the calculations.
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18.
  • Ahlquist, Mårten, et al. (författare)
  • Theoretical evidence for low-ligated palladium(0) : [Pd-L] as the active species in oxidative addition reactions
  • 2006
  • Ingår i: Organometallics. - : American Chemical Society (ACS). - 0276-7333 .- 1520-6041. ; 25:8, s. 2066-2073
  • Tidskriftsartikel (refereegranskat)abstract
    • The oxidative addition of PhI to Pd-O has been studied by DFT with a continuum representation of the solvent. It is shown that the preferred number of ligands on palladium is lower than would be expected from "conventional wisdom" and the 18-electron rule. The most favored oxidative addition is obtained when Pd is coordinated by only the aryl iodide and one additional ligand in a linear arrangement. The calculations indicate that p-orbitals on the central metal are not involved in bonding in any of the complexes described herein, in good agreement with classic ligand field theory and also with a recent bonding analysis by Weinhold and Landis, but in apparent violation of the 18-electron rule.
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19.
  • Ahlstrand, David A., et al. (författare)
  • Csp(3)-H Activation without Chelation Assistance in an Iridium Pincer Complex Forming Cyclometallated Products
  • 2017
  • Ingår i: Chemistry - A European Journal. - : WILEY-V C H VERLAG GMBH. - 0947-6539 .- 1521-3765. ; 23:8, s. 1748-1751
  • Tidskriftsartikel (refereegranskat)abstract
    • Cyclometallation of 8-methylquinoline and 2-(dimethylamino)-pyridine in an iridium-based pincer complex is described. The C-H activation of 2-(dimethylamino) pyridine is not chelation assisted, which has not been described before for Csp(3)-H bonds in cyclometallation reactions. The mechanism of the cyclometallation of 2-(dimethylamino) pyridine was studied by DFT calculations and kinetic measurements.
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20.
  • Biaobiao, Zhang, et al. (författare)
  • Modifying Ru-bda Backbone with Steric Hindrance and Hydrophilicity: Influence of Secondary Coordination Environments on Water-Oxidation Mechanism.
  • Tidskriftsartikel (övrigt vetenskapligt/konstnärligt)abstract
    • Understanding the seven coordination and O−O coupling pathway of the distinguished Ru-bda catalysts is essential for the development of next generation efficient water-oxidation catalysts based on earth-abundant metals. This work reports the synthesis, characterization and catalytic properties of a monomeric ruthenium catalyst Ru-bnda (H2bnda = 2,2'-bi(nicotinic acid)-6,6'-dicarboxylic acid) featuring steric hindrance and enhanced hydrophilicity on the backbone. Combining experimental evidence with systematic density functional theory calculations on the Ru-bnda and related catalysts Ru-bda, Ru-pda and Ru-biqa, we emphasized that seven coordination clearly determines presence of RuV=O with high spin density on the ORuV=O atom, i.e. oxo with radical properties, which is one of the necessary conditions for reacting through the O−O coupling pathway. However, an additional factor to make the condition sufficient is the favorable intermolecular face-to-face interaction for the generation of the pre-reactive [RuV=O···O=RuV], which is significantly influenced by the secondary coordination environments. This work provides a new understanding of the structure-activity relationship of water-oxidation catalysts and their potential to adopt I2M pathway for O−O bond formation.
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21.
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22.
  • Castner, Ashleigh T., et al. (författare)
  • Microscopic Insights into Cation-Coupled Electron HoppingTransport in a Metal-Organic Framework br
  • 2022
  • Ingår i: Journal of the American Chemical Society. - : American Chemical Society (ACS). - 0002-7863 .- 1520-5126. ; 144:13, s. 5910-5920
  • Tidskriftsartikel (refereegranskat)abstract
    • Electron transport through metal-organic frameworks by ahopping mechanism between discrete redox active sites is coupled to diffusion-migration of charge-balancing counter cations. Experimentally determinedapparent diffusion coefficients,Deapp, that characterize this form of chargetransport thus contain contributions from both processes. While this is wellestablished for MOFs, microscopic descriptions of this process are largelylacking. Herein, we systematically lay out different scenarios for cation-coupledelectron transfer processes that are at the heart of charge diffusion throughMOFs. Through systematic variations of solvents and electrolyte cations, it isshown that theDeappfor charge migration through a PIZOF-type MOF,Zr(dcphOH-NDI) that is composed of redox-active naphthalenediimide(NDI) linkers, spans over 2 orders of magnitude. More importantly, however,the microscopic mechanisms for cation-coupled electron propagation arecontingent on differing factors depending on the size of the cation and its propensity to engage in ion pairs with reduced linkers,either non-specifically or in defined structural arrangements. Based on computations and in agreement with experimental results, weshow that ion pairing generally has an adverse effect on cation transport, thereby slowing down charge transport. In Zr(dcphOH-NDI), however, specific cation-linker interactions can open pathways for concerted cation-coupled electron transfer processes thatcan outcompete limitations from reduced cationflux.
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23.
  • Chen, Xiaoyu, et al. (författare)
  • Aggregation and Significant Difference in Reactivity Therein : Blocking the CO2-to-CH3OH Reaction
  • 2021
  • Ingår i: Organometallics. - : American Chemical Society (ACS). - 0276-7333 .- 1520-6041. ; 40:17, s. 3087-3093
  • Tidskriftsartikel (refereegranskat)abstract
    • A CoPc/CNT system has been only recently reported to transform CO2 to methanol via electrochemical reductions, despite the fact that catalyst has been studied extensively since the 1980s. The explanation of high methanol selectivity lies behind the fact that in the new report CoPc exists mainly as a monomer, while in earlier works aggregates dominate. Here, we have studied the reactivity of monomeric and dimeric CoPc by DFT. The mechanism involves rate-limiting CO2 association, with the C-O cleavage step having very similar activation free energy. Once the Co-CO-intermediate is formed, the reaction bifurcates with two possible paths: (1) CO dissociation or (2) one additional reduction follows a protonation to give the Co-CHO-intermediate, which then leads to methanol by further reactions. For the monomeric species at low reduction potentials, CO dissociation is favored, but the formation of Co-CHO-becomes competitive at more negative applied potentials. For the dimer, the CO dissociation is always favored, and the reduction needed to form the C-H bond is negative enough for it not to be observed. The more difficult reduction stems from repulsive interactions between the CoPc units and lower solvent stabilization of the charge in the aggregate.
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24.
  • Chen, Xiaoyu, et al. (författare)
  • Aggregation and the Siginificant Difference in Reactivity therein: Blocking the CO2-to-CH3OH Reaction Pathway
  • Annan publikation (övrigt vetenskapligt/konstnärligt)abstract
    • A CoPc/CNT system was recently reported to transform CO2 to methanol via electrochemical reductions, despite the catalyst has been studied since the 1980s, such observations were not reported earlier. A clue to the high methanol selectivity is that CoPc exist as mainly as monomers in the new report while in earlier works CoPc aggregates dominate. Here we have studied the reactivity of monomeric and dimeric CoPc by DFT. The mechanism involves rate limiting CO2 association, with the C-O cleavage step being having very similar activation free energy. Once the Co-CO- intermediate is formed the reaction bifurcates with two possible paths, CO dissociation or further reduction and protonation to give the Co-CHO- intermediate, which then leads to methanol by further reactions. For the monomeric species at low reduction potentials CO dissociation is favored, but the formation of Co-CHO- becomes competitive at more negative applied potentials. For the dimer the CO dissociation is always favored, and the reduction needed to form the C-H bond is negative enough for it not to be observed. The more difficult reduction stems from repulsive interac- tions between the Co-Pc units and lower solvent stabilization of the charge in the aggregate.
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25.
  • Chen, Xiaoyu, et al. (författare)
  • Deconstructing the Enhancing Effect on CO2 Activation in the Electric Double Layer with EVB Dynamic Reaction Modeling
  • 2020
  • Ingår i: The Journal of Physical Chemistry C. - : American Chemical Society (ACS). - 1932-7447 .- 1932-7455. ; 124:41, s. 22479-22487
  • Tidskriftsartikel (refereegranskat)abstract
    • The reactivities of the same molecular electrocatalyst under homogeneous and heterogeneous conditions can be dramatically different, highlighting that the reaction environment plays an important role in catalysis. For catalysis on solid electrodes, reactions take place in the electric double layer (EDL), where a strong electric field is experienced. In this work, empirical valence bond molecular dynamics (EVB-MD) was used to explore CO2binding in the EDL. It allows explicit descriptions of the solvent, electrolyte, catalyst–reactant, and the electrode surface material, as well as an unbiased description of the applied electric field. The strong local electric field concentrates cations, which in turn stabilizes the bound CO2. Furthermore, controlled computational experiments suggest that neither the electric field nor the cations alone can produce significant stabilization, but that the combination leads to a dramatic stabilization of the CO2 bound state.
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26.
  • Chen, Xiaoyu, 1993- (författare)
  • Theoretical Studies on CO2 Reduction Electrocatalysts
  • 2020
  • Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
    • The atmospheric CO2 concentration has increased by more than 20% since 1980s and has now reached the highest level than at any point in the past 800 000 years. Electrochemical CO2 reductions are receiving particular in- terest as the apparatus are relatively easy to maintain and cheap to operate. However, the direct reduction of CO2 into CO2 radical requires a very high over-potential, meaning a substantial waste in energy. In order to lower the over-potential required, a large number of catalysts has been synthesised and studied. Among these catalysts, three are studied in this work due to their interesting reactivities. We believe the further understanding gained in our studies will benefit the development of new and better catalysts.Ru(6-Mebpy)(tBu3-tpy) reduces CO2 at its first reduction potential and can therefore lower the over-potential required significantly. This observation is unique for Ru(tpy)(bpy) type of catalysts. Density functional theory (DFT) cal- culations revealed that the steric hindrance provided by the 6-methyl group weakens Ru-solvent interactions and hence allows solvent detachment to take place after only one reduction, which is otherwise not possible. Furthermore, we proposed a new mechanism for CO2 to CO reduction at the first reduc- tion potential and identified a cyclic intermediate by Infra-red spectroscopy in collaboration with experimentalists. Such intermediate was not reported pre- viously for Ru-based electrocatalysts.Co(TPP)/CNTs as a heterogenous catalyst exhibits superior reactivity as compared to in solution. DFT calculations with implicit solvent model ac- counts its enhanced reactivity to the increased proton concentration in water. The inverse-loading effect was studied by potential mean force (PME) sam- pling. Our results suggest that aggregation is triggered by the strong inter- molecular p - p interactions among the catalysts. Flatter nanotubes have better contact with Co(TPP) and hence reduces aggregation tendency. The same cat- alyst was also used as an example to study catalysis at interfaces in an electric field. Our full-explicit EVB -MD (Empirical Valence Bond-Molecular Dynam- ics) model illustrates that the electric double layer concentrates cations, which significantly stabilises polarised CO2 at a higher concentration and hence eases CO2 binding. Furthermore, we have also shown that either the electric field or the cations along provides only a minor, almost negligible stabilisation.In 2019, CoPc/CNTs was reported to be the first early-period transition metal complex that can catalyse CO2-to-CH3OH conversion at a decent yield. Literature search on previous work suggests that the presence of well-dispersed, monomeric CoPc is crucial to further reduce CO into CH3OH. We calculated the reaction profiles for both monomeric CoPc and dimeric CoPc, which is the simplest form of aggregates. Our DFT results demonstrate that after the formation of catalyst-CO- complex, monomers tend to go though further reac- tions to afford CH3OH while dimers tend to dissociate CO as reductions are slightly harder, which in turn, is raised from a less degree of solvation stabili- sation upon reductions.
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27.
  • Chen, Xiaoyu, et al. (författare)
  • Understanding the Enhanced Catalytic CO2 Reduction upon Adhering Cobalt Porphyrin to Carbon Nanotubes and the Inverse Loading Effect
  • 2020
  • Ingår i: Organometallics. - : American Chemical Society (ACS). - 0276-7333 .- 1520-6041. ; 39:9, s. 1634-1641
  • Tidskriftsartikel (refereegranskat)abstract
    • Adhering a cobalt porphyrin (Co(TPP)) catalyst on a carbon nanotube (CNT) supporting material greatly enhances its reactivity and enables catalysis in water, which is otherwise impossible. However, the effect of solvent as well as supporting materials on catalysis is still elusive. On the basis of computational results we found that water as a reaction medium lowers the reductive potential required due to the stabilization of intermediates and transition states, and provides higher availability of protons. To understand the effect of the support materials, we combine computations and experiments and illustrate that the curvature of the nanotubes plays an essential role in aggregation through the competition between the Ï-πinteractions between the porphyrin rings as well as between the Co(TPP) and the nanotube, providing an insight into lessening the degree of aggregation.
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28.
  • Chen, Xiaoyu, et al. (författare)
  • Understanding the Mechanism of CO2 to CO Conversion by Ruthenium Polypyridyl Catalysts
  • Annan publikation (övrigt vetenskapligt/konstnärligt)abstract
    • A detailed mechanistic study of ruthenium 2,2:6,2-terpyridine (tpy) 2,2-bipyridine (bpy) class of catalysts is presented, with all three key stages (i.e. solvent dissociation, C-O bond cleavage and CO dissociation) discussed. DFT calculations together with kinetic studies revealed that the introduction of a methyl substituent on the bipyridine ligand eases solvent dissociation and hence allow catalysis to take place at the first reduction potential as the five coordinated Ru complex is easier to reduce. This highlights the importance of steric effect in catalyst-design. For C-O bond cleavage, DFT calculations suggest that proton acts as a much better oxide accepter compared to CO2, explaining the improved activity when water is added to the system. To further understand how the electronic nature of the ring substitutes affects the reactivity, we designed a hypothetical catalyst with fluorine substitutes and found out electron withdrawing groups lower the reductive potentials at a cost of harder solvent dissociation. For the final CO dissociation, due to the special nature of carbonyl ligands, neither steric nor electronic alternations can ease the step and here is where kinetic trans effect comes into play. In line with a recent experimental work, our DFT calculations showed that when a carbene group is trans to CO, the dissociation rate is increased dramatically.  
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29.
  • Cheng, Mu-Jeng, et al. (författare)
  • Carbon-Oxygen Bond Forming Mechanisms in Rhenium Oxo-Alkyl Complexes
  • 2010
  • Ingår i: Organometallics. - : American Chemical Society (ACS). - 0276-7333 .- 1520-6041. ; 29:9, s. 2026-2033
  • Tidskriftsartikel (refereegranskat)abstract
    • Three C X bond formation mechanisms observed in the oxidation of (HBpz(3))ReO(R)(OTf) [HBpz(3) = hydrotris(1-pyrazolypborate; R = Me, Et, and iPr; OTf = OSO(2)CF(3)] by dimethyl sulfoxide (DMSO) were investigated using quantum mechanics (M06//B3LYP DFT) combined with solvation (using the PBF Poisson Boltzmann polarizable continuum solvent model). For R = Et we find the alkyl group is activated through alpha-hydrogen abstraction by external base OTf(-) with a free energy barrier of only 12.0 kcal/mol, leading to formation of acetaldehyde. Alternatively, ethyl migration across the M=O bond (leading to the formation of acetaldehyde and ethanol) poses a free energy barrier of 22.1 kcal/mol, and the previously proposed alpha-hydrogen transfer to oxo (a 2+2 forbidden reaction) poses a barrier of 44.9 kcal/mol. The rate-determining step to formation of the final product acetaldehyde is an oxygen atom transfer from DMSO to the ethylidene, with a free energy barrier of 15.3 kcal/mol. When R = iPr, the alkyl 1,2-migration pathway becomes the more favorable pathway (both kinetically and thermodynamically), with a free energy barrier (Delta G(double dagger) = 11.8 kcal/mol) lower than alpha-hydrogen abstraction by OTf(-) (Delta G(double dagger) = 13.5 kcal/mol). This suggests the feasibility of utilizing this type of migration to functionalize M-R to M-OR. We also considered the nucleophilic attack of water and ammonia on the Re-ethylidene alpha-carbon as a means of recovering two-electron-oxidized products from an alkane oxidation. Nucleophilic attack (with internal deprotonation of the nucleophile) is exothermic. However, the subsequent protonolysis of the Re alkyl bond (to liberate an alcohol or amine) poses a barrier of 37.0 or 42.4 kcal/mol, respectively. Where comparisons are possible, calculated free energies agree very well with experimental measurements.
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30.
  • Colozza, Noemi, et al. (författare)
  • Insights into Tripodal Tris(pyrazolyl) Compounds as Ionophores for Potentiometric Ammonium Ion Sensing
  • 2022
  • Ingår i: ChemElectroChem. - : Wiley. - 2196-0216. ; 9:18
  • Tidskriftsartikel (refereegranskat)abstract
    • The decentralisation of accurate determination of the ammonium ion (NH4+) is relevant for environmental monitoring (i. e., nitrogen cycle) and certain clinical applications (e. g., kidney and liver diseases). Potentiometric ionophore-based sensors are one alternative for these purposes in terms of versatile implementation, though the potassium ion (K+) is known to be a major source of interference. We herein investigate the use of three different tripodal tris(pyrazolyl) compounds derived from 1,3,5-triethylbenzene as NH4+ ionophores. A complete set of potentiometric experiments together with theoretical simulations reveals suitable analytical performance while demonstrating a suppression of the K+ interference given the formation of an adequate cavity in the ionophore to host NH4+ over K+ in the membrane environment. The results support the use of these electrodes in the analytical detection of NH4+ in a wide range of samples with variable contents.
  •  
31.
  • Daniel, Quentin, et al. (författare)
  • Rearranging from 6-to 7-coordination initiates the catalytic activity : An EPR study on a Ru-bda water oxidation catalyst
  • 2017
  • Ingår i: Coordination chemistry reviews. - : Elsevier. - 0010-8545 .- 1873-3840. ; 346, s. 206-215
  • Tidskriftsartikel (refereegranskat)abstract
    • The coordination of a substrate water molecule on a metal centered catalyst for water oxidation is a crucial step involving the reorganization of the ligand sphere. This process can occur by substituting a coordinated ligand with a water molecule or via a direct coordination of water onto an open site. In 2009, we reported an efficient ruthenium-based molecular catalyst, Ru-bda, for water oxidation. Despite the impressive improvement in catalytic activity of this type of catalyst over the past years, a lack of understanding of the water coordination still remains. Herein, we report our EPR and DFT studies on Ru-bda (triethylammonium 3-pyridine sulfonate)(2) (1) at its Ru-III oxidation state, which is the initial state in the catalytic cycle for the O-O bond formation. Our investigation suggests that at this III-state, there is already a rearrangement in the ligand sphere where the coordination of a water molecule at the 7th position (open site) takes place under acidic conditions (pH = 1.0) to form a rare 7-coordinated Ru-III species.
  •  
32.
  • Daniel, Quentin, et al. (författare)
  • Water Oxidation Initiated by In Situ Dimerization of the Molecular Ru(pdc) Catalyst
  • 2018
  • Ingår i: ACS Catalysis. - : AMER CHEMICAL SOC. - 2155-5435. ; 8:5, s. 4375-4382
  • Tidskriftsartikel (refereegranskat)abstract
    • The mononuclear ruthenium complex [Ru(pdc)L-3] (H(2)pdc = 2,6-pyridinedicarboxylic acid, L = N-heterocycles such as 4-picoline) has previously shown promising catalytic efficiency toward water oxidation, both in homogeneous solutions and anchored on electrode surfaces. However, the detailed water oxidation mechanism catalyzed by this type of complex has remained unclear. In order to deepen understanding of this type of catalyst, in the present study, [Ru(pdc)(py)(3)] (py = pyridine) has been synthesized, and the detailed catalytic mechanism has been studied by electrochemistry, UV-vis, NMR, MS, and X-ray crystallography. Interestingly, it was found that once having reached the Ru-IV state, this complex promptly formed a stable ruthenium dimer [Ru-III(pdc)(py)(2)-O-Ru-IV(pdc)(py)(2)](+). Further investigations suggested that the present dimer, after one pyridine ligand exchange with water to form [Ru-III(pdc)(py)(2)-O-Ru-IV(pdc)(py)(H2O)](+), was the true active species to catalyze water oxidation in homogeneous solutions.
  •  
33.
  • Das, Sambit, 1994- (författare)
  • A theoretical perspective on photoinduced reactions - based on quantum chemical models and non-adiabatic molecular dynamics.
  • 2023
  • Licentiatavhandling (övrigt vetenskapligt/konstnärligt)abstract
    • The broad range of applications for photochemical reactions is the result of light-matter interaction at the electronic level. The diverse application of photochemistry in various fields, including photovoltaic materials, molecular switches, and biological systems are due to electronic and structural transformations induced by photoexcitation as well as molecular alteration due to electron and charge transfer. An improved understanding of these photochemical events is dependent on the fundamental theoretical evaluation, to model and analyze the ultrafast processes. The studies discussed in this thesis explore such theoretical implementation in two different frontiers.In the first study, dynamic simulations are performed to model the light-induced bond dissociation of phenyl azide. The surface hopping formalism, implemented under the semiclassical molecular dynamics approach helped in tracing the time evolution of the electronic and structural levels, involved in the photodissociation. In the second study, the time-dependent density functional theory has been applied to generate XA spectra of imidazole solutions. The theoretical assessments support experimental measurements and provide more insight into the core excitations and structural influence on the absorption spectra.   
  •  
34.
  • de Gracia Triviño, Juan Angel, 1989-, et al. (författare)
  • Removing the Barrier in O-O Bond Formation Via the Combination of Intramolecular Radical Coupling and the Oxide Relay Mechanism
  • 2024
  • Ingår i: Journal of Physical Chemistry A. - : American Chemical Society (ACS). - 1089-5639 .- 1520-5215. ; 128:19, s. 3794-3800
  • Tidskriftsartikel (refereegranskat)abstract
    • The Ru(tda) catalyst has been a major milestone in the development of molecular water oxidation catalysts due to its outstanding performance at neutral pH. The role of the noncoordinating carboxylate group is to act as a nucleophile, donating an oxygen atom to the oxo group, thereby acting as an oxide relay (OR) mechanism for O-O bond formation. A substitution of the carboxylates for phosphonate groups has been proposed, resulting in the Ru(tPaO) catalyst, which has shown even more efficient performance in experimental characterization. In this study, we explore the feasibility of the OR mechanism in the newly reported Ru(tPaO) molecular catalyst. We investigated the catalytic cycle using density functional theory and identified a variation of the OR mechanism that involves radical oxygen atoms in O-O bond formation. We have also determined that the subsequent hydroxide nucleophilic attack is the sole rate-limiting step in the catalytic cycle. All activation free energies are very low, with a free-energy barrier of 2.1 kcal/mol for O-O bond formation and 4.2 kcal/mol for OH- nucleophilic attack.
  •  
35.
  • De Gracia Triviño, Juan Angel, et al. (författare)
  • The Role of Counterions in Intermolecular Radical Coupling of Ru-bda Catalysts
  • 2022
  • Ingår i: Topics in catalysis. - : Springer Nature. - 1022-5528 .- 1572-9028. ; 65:1-4, s. 383-391
  • Tidskriftsartikel (refereegranskat)abstract
    • Intermolecular radical coupling (also interaction of two metal centers I2M) is one of the main mechanisms for O-O bond formation in water oxidation catalysts. For Ru(bda)L-2 (H(2)bda = 2,2'-bipyridine-6,6'-dicarboxylate, L = pyridine or similar nitrogen containing heterocyclic ligands) catalysts a significant driving force in water solution is the hydrophobic effects driven by the solvent. The same catalyst has been successfully employed to generate -N2 from ammonia, also via I2M, but here the solvent was acetonitrile where hydrophobic effects are absent. We used a classical force field for the key intermediate [(RuN)-N-VI(bda)(py)(2)](+) to simulate the dimerization free energy by calculation of the potential mean force, in both water and acetonitrile to understand the differences and similarities. In both solvents the complex dimerizes with similar free energy profiles. In water the complexes are essentially free cations with limited ion paring, while in acetonitrile the ion-pairing is much more significant. This ion-pairing leads to significant screening of the charges, making dimerization possible despite lower solvent polarity that could lead to repulsion between the charged complexes. In water the lower ion pairing is compensated by the hydrophobic effect leading to favorable dimerization despite repulsion of the charges. A hypothetical doubly charged [(RuIN)-I-VI(bda)py(2)](2+) was also studied for deeper understanding of the charge effect. Despite the double charge the complexes only dimerized favorably in the lower dielectric solvent acetonitrile, while in water the separated state is more stable. In the doubly charged catalyst the effect of ion-pairing is even more pronounced in acetonitrile where it is fully paired similar to the 1+ complex, while in water the separation of the ions leads to greater repulsion between the two catalysts, which prevents dimerization. 
  •  
36.
  • Ding, Xin, et al. (författare)
  • Silicon Compound Decorated Photoanode for Performance Enhanced Visible Light Driven Water Splitting
  • 2016
  • Ingår i: Electrochimica Acta. - : Elsevier. - 0013-4686 .- 1873-3859. ; 215, s. 682-688
  • Tidskriftsartikel (refereegranskat)abstract
    • An efficient dye (1) sensitized photoelectrochemical cell (DS-PEC) has been assembled with a silicon compound (3-chloropropyl) trimethoxy-silane (Si-Cl) decorated working electrode (WE) TiO2(1 + 2). The introduction of this Si-Cl molecule on photoanode leads to better performances on efficiency than untreated ones for light driven water splitting. The firm Si-O layer formed on TiO2 increased the resistance of the TiO2/catalyst interface which is assumed to decrease charge recombination from TiO2 to the oxidized catalyst 2. The work presented here provides an effective method to improve the performances of DS-PECs.
  •  
37.
  • Duan, Lele, et al. (författare)
  • Highly efficient and robust molecular ruthenium catalysts for water oxidation
  • 2012
  • Ingår i: Proceedings of the National Academy of Sciences of the United States of America. - : Proceedings of the National Academy of Sciences. - 0027-8424 .- 1091-6490. ; 109:39, s. 15584-15588
  • Tidskriftsartikel (refereegranskat)abstract
    • Water oxidation catalysts are essential components of light-driven water splitting systems, which could convert water to H-2 driven by solar radiation (H2O + h nu -> 1/2O(2) + H-2). The oxidation of water (H2O -> 1/2O(2) + 2H(+) + 2e(-)) provides protons and electrons for the production of dihydrogen (2H(+) + 2e(-) -> H-2), a clean-burning and high-capacity energy carrier. One of the obstacles now is the lack of effective and robust water oxidation catalysts. Aiming at developing robust molecular Ru-bda (H(2)bda = 2,2'-bipyridine-6,6'-dicarboxylic acid) water oxidation catalysts, we carried out density functional theory studies, correlated the robustness of catalysts against hydration with the highest occupied molecular orbital levels of a set of ligands, and successfully directed the synthesis of robust Ru-bda water oxidation catalysts. A series of mononuclear ruthenium complexes [Ru(bda)L-2] (L = pyridazine, pyrimidine, and phthalazine) were subsequently synthesized and shown to effectively catalyze Ce-IV-driven [Ce-IV = Ce(NH4)(2()NO3)(6)] water oxidation with high oxygen production rates up to 286 s(-1) and high turnover numbers up to 55,400.
  •  
38.
  •  
39.
  • Fan, Ting, et al. (författare)
  • The Ru-tpc Water Oxidation Catalyst and Beyond : Water Nucleophilic Attack Pathway versus Radical Coupling Pathway.
  • 2017
  • Ingår i: ACS Catalysis. - : AMER CHEMICAL SOC. - 2155-5435. ; 7:4, s. 2956-2966
  • Tidskriftsartikel (refereegranskat)abstract
    • Many Ru water oxidation catalysts have been documented in the literature. However, only a few can catalyze the O-O bond formation via the radical coupling pathway, while most go through the water nucleophilic attack pathway. Understanding the electronic effect on the reaction pathway is of importance in design of active water oxidation catalysts. The Ru-bda (bda = 2,2'-bipyridine-6,6'-dicarboxylate) catalyst is one example that catalyzes the 0-0 bond formation via the radical coupling pathway. Herein, we manipulate the equatorial backbone ligand, change the doubly charged bda(2-) ligand to a singly charged tpc- (2,2':6',2 ''-terpyridine-6-carboxylate) ligand, and study the structure activity relationship. Surprisingly, kinetics measurements revealed that the resulting Ru-tpc catalyst catalyzes water oxidation via the water nucleophilic attack pathway, which is different from the Ru-bda catalyst. The O-O bond formation Gibbs free energy of activation (AGO) at T = 298.15 K was 20.2 +/- 1.7 kcal mol(-1). The electronic structures of a series of Ru-v=O species were studied by density function theory calculations, revealing that the spin density of O-Ru=O of Ru-v=O is largely dependent on the surrounding ligands. Seven coordination configuration significantly enhances the radical character of Ru-v=O.
  •  
40.
  • Fan, Ting, et al. (författare)
  • Why Is There a Barrier in the Coupling of Two Radicals in the Water Oxidation Reaction?
  • 2016
  • Ingår i: ACS Catalysis. - : American Chemical Society (ACS). - 2155-5435. ; 6:12, s. 8308-8312
  • Tidskriftsartikel (refereegranskat)abstract
    • Two radicals can form a bond without an energetic barrier. However, the radical coupling mechanism in ruthenium catalyzed water oxidation has been found to be associated with substantial activation energies. Here we have investigated the coupling reaction of [Ru=O(bda)L-2](+) catalysts with different axial L ligands. The interaction between the two oxo radical moieties at the Ru(V) state was found to have a favorable interaction in the transition state in comparison to the prereactive complex. To further understand the existence of the activation energy, the activation energy has been decomposed into distortion energy and interaction energy. No correlation between the experimental rates and the calculated coupling barriers of different axial L was found, showing that more aspects such as solvation, supramolecular properties, and solvent dynamics likely play important roles in the equilibrium between the free Ru-v=0 monomer and the [Ru-v=O center dot center dot center dot O=Ru-v] dimer. On the basis of our findings, we give general guidelines for the design of catalysts that operate by the radical coupling mechanism.
  •  
41.
  • Fristrup, Peter, et al. (författare)
  • On the Nature of the Intermediates and the Role of Chloride Ions in Pd-Catalyzed Allylic Alkylations : Added Insight from Density Functional Theory
  • 2008
  • Ingår i: Journal of Physical Chemistry A. - : American Chemical Society (ACS). - 1089-5639 .- 1520-5215. ; 112:50, s. 12862-12867
  • Tidskriftsartikel (refereegranskat)abstract
    • The reactivity of intermediates in palladium-catalyzed allylic alkylation was investigated using DFT (B3LYP) calculations including a PB-SCRF solvation model. In the presence of both phosphine and chloride ligands, the allyl intermediate is in equilibrium between a cationic eta(3)-allylPd complex with two phosphine ligands, the corresponding neutral complex with one phosphine and one chloride ligand, and a neutral eta(1)-allylPd complex with one chloride and two phosphine ligands. The eta(1)-complex is unreactive toward nucleophiles. The cationic eta(3)-complex is the intermediate most frequently invoked in the title reaction, but in the presence of halides, the neutral, unsymmetrically substituted eta(3)-CoMplex will be formed rapidly from anionic Pd(0) complexes in solution. Since the latter will prefer both leaving group ionization and reaction with nucleophiles in the position trans to phosphorus, it can rationalize the observed "memory effect" (a regioretention) in the title reaction, even in the absence of chiral ligands.
  •  
42.
  • Guo, Yaxiao, et al. (författare)
  • Molybdenum and boron synergistically boosting efficient electrochemical nitrogen fixation
  • 2020
  • Ingår i: Nano Energy. - : Elsevier Ltd. - 2211-2855 .- 2211-3282. ; 78
  • Tidskriftsartikel (refereegranskat)abstract
    • Ammonia production consumes ~2% of the annual worldwide energy supply, therefore strategic alternatives for the energy-intensive ammonia synthesis through the Haber-Bosch process are of great importance to reduce our carbon footprint. Inspired by MoFe-nitrogenase and the energy-efficient and industrially feasible electrocatalytic synthesis of ammonia, we herein establish a catalytic electrode for artificial nitrogen fixation, featuring a carbon fiber cloth fully grafted by boron-doped molybdenum disulfide (B-MoS2/CFC) nanosheets. An excellent ammonia production rate of 44.09 μg h–1 cm–2 is obtained at −0.2 V versus the reversible hydrogen electrode (RHE), whilst maintaining one of the best reported Faradaic efficiency (FE) of 21.72% in acidic aqueous electrolyte (0.1 M HCl). Further applying a more negative potential of −0.25 V renders the best ammonia production rate of 50.51 μg h–1 cm–2. A strong-weak electron polarization (SWEP) pair from the different electron accepting and back-donating capacities of boron and molybdenum (2p shell for boron and 5d shell for molybdenum) is proposed to facilitate greatly the adsorption of non-polar dinitrogen gas via N≡N bond polarization and the first protonation with large driving force. In addition, for the first time a visible light driven photo-electrochemical (PEC) cell for overall production of ammonia, hydrogen and oxygen from water + nitrogen, is demonstrated by coupling a bismuth vanadate BiVO4 photo-anode with the B-MoS2/CFC catalytic cathode.
  •  
43.
  •  
44.
  • Hansen, Nicolai S.B., et al. (författare)
  • Development and mechanistic investigation of the dehydrogenation of alcohols with an iron(iii) salen catalyst
  • 2023
  • Ingår i: Organic and biomolecular chemistry. - : Royal Society of Chemistry (RSC). - 1477-0520 .- 1477-0539. ; 21:23, s. 4794-4800
  • Tidskriftsartikel (refereegranskat)abstract
    • The iron(iii) salen complex (R,R)-N,N′-bis(salicylidene)-1,2-cyclohexanediamineiron(iii) chloride has been developed as a catalyst for the acceptorless dehydrogenation of alcohols. The complex catalyzes the direct synthesis of imines in good yields from different primary alcohols and amines with the liberation of hydrogen gas. The mechanism has been investigated experimentally with labelled substrates and theoretically with density functional theory calculations. In contrast to the corresponding manganese(iii) salen-catalyzed dehydrogenation, it has not been possible to identify a homogeneous catalytic pathway with the iron complex. Instead, poisoning experiments with trimethylphosphine and mercury indicated that the catalytically active species are heterogeneous small iron particles.
  •  
45.
  •  
46.
  • Johnson, Magnus, et al. (författare)
  • Mechanisms of the CO2 Insertion into (PCP) Palladium Allyl and Methyl sigma-Bonds. A Kinetic and Computational Study
  • 2010
  • Ingår i: Organometallics. - : American Chemical Society (ACS). - 0276-7333 .- 1520-6041. ; 29:16, s. 3521-3529
  • Tidskriftsartikel (refereegranskat)abstract
    • The reaction of the sigma-bonded (PCP)Pd-Me complex (PCP = 2,6-bis[(di-tert-butylphosphino)methyl]phenyl) with CO2 is first-order in palladium and first-order in CO, with a rate constant k(s) = 8.9 +/- 0.8 M-1 s(-1) at 353 K. Activation parameters are Delta H double dagger = 73 7 kJ/mol and Delta S double dagger = 118 +/- 19 J/K mol. Based on this and theoretical calculations we propose an S(E)2 mechanism where the coordinated methyl group attacks a completely noncoordinated carbon dioxide molecule in a bimolecular reaction. The PCPPd-crotyl complex was synthesized in an 65:35 E:Z mixture, and it was shown to react with CO, to give the complex PCPPd-O(CO)CH(CH3)CHCH2 as a single isomer, where the former gamma-carbon has been carboxylated. Theoretical calculations again suggest an S(E)2 mechanism with a noncoordinated carbon dioxide reacting with the terminal carbon on the allyl group, forming an eta(2)-bonded olefin complex as an intermediate. The rearrangement of this intermediate to the O-bonded product is concluded to be rate determining. The crystal structure of PCPPd-O(CO)C(CH3)(2)CHCH2 is reported and as well as the solubility of carbon dioxide in benzene-d(6) at different pressures and temperatures.
  •  
47.
  • Johnson, Magnus, et al. (författare)
  • Reactivity of NHC Au(I)-C sigma-bonds with electrophiles. An investigation of their possible involvement in catalytic C-C bond formation
  • 2011
  • Ingår i: CHEM SCI. - : Royal Society of Chemistry (RSC). - 2041-6520 .- 2041-6539. ; 2:12, s. 2373-2377
  • Tidskriftsartikel (refereegranskat)abstract
    • The first example of the reaction of an isolated gold(I) complex with an aryl halide to form a C-C bond is reported. The reactivity of (NHC) Au(I)-R complexes towards a wide range of electrophiles was investigated. The Au-C sigma-bond is shown to exhibit low nucleophilicity, but it is reactive towards MeI and MeOTf to form toluene, biphenyl and ethane, most likely through an oxidative mechanism. Carbon dioxide is completely unreactive. The experimental findings are supported by theoretical calculations.
  •  
48.
  •  
49.
  • Jonasson, Klara, et al. (författare)
  • Reversible -Hydrogen and -Alkyl Elimination in PC(sp(3))P Pincer Complexes of Iridium
  • 2015
  • Ingår i: Angewandte Chemie International Edition. - : Wiley. - 1433-7851 .- 1521-3773. ; 54:32, s. 9372-9375
  • Tidskriftsartikel (refereegranskat)abstract
    • Despite significant progress in recent years, the cleavage of unstrained C(sp(3))C(sp(3)) bonds remains challenging. A CC coupling and cleavage reaction in a PC(sp(3))P iridium pincer complex is mechanistically studied; the reaction proceeds via the formation of a carbene intermediate and can be described as a competition between -hydrogen and -alkyl elimination; the latter process was observed experimentally and is an unusual way of C(sp(3))C(sp(3)) bond scission, which has previously not been studied in detail. Mechanistic details that are based upon kinetic studies, activation parameters, and DFT calculations are also discussed. A full characterization of a CC agostic intermediate is presented.
  •  
50.
  • Juan Angel, de Gracia Triviño, 1989-, et al. (författare)
  • Combining intramolecular radical coupling with the Oxide Relay mechanism: Radical Oxide Relay mechanism
  • 2022
  • Annan publikation (populärvet., debatt m.m.)abstract
    • The Ru(tda) catalyst has been a major milestone in the development of molecular water oxidation catalysts due to its outstanding performance at neutral pH. The role of the non-coordinating carboxylate group is to act as a nucleophile, donating an oxygen atom to the oxo group, acting as an oxide relay mechanism the the O-O bond formation. A substitution of the carboxylates for phosphonate groups has been proposed, the Ru(tPaO), and its experimental characterization has shown an even more efficient performance. In this study, we explore the feasibility of the oxide relay mechanism in the newly reported Ru(tPaO) molecular catalyst. We have explored the catalytic cycle using density functional theory and we have identified a variation of the oxide relay mechanism that involves radical oxygen atoms in the O-O bond formation. We have explored the origin of the radical character in this complex and we have identified the hydroxyl nucleophilic attack as the sole rate limiting step in the catalytic cycle. The barriers are very low in all the steps, the O-O bond formation has a free energy barrier of 2.1 kcal/mol and the OH- nucleophilic attack 4.2 kcal/mol.
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