Change search
Refine search result
12 1 - 50 of 58
CiteExportLink to result list
Permanent link
Cite
Citation style
  • apa
  • harvard1
  • ieee
  • modern-language-association-8th-edition
  • vancouver
  • Other style
More styles
Language
  • de-DE
  • en-GB
  • en-US
  • fi-FI
  • nn-NO
  • nn-NB
  • sv-SE
  • Other locale
More languages
Output format
  • html
  • text
  • asciidoc
  • rtf
Rows per page
  • 5
  • 10
  • 20
  • 50
  • 100
  • 250
Sort
  • Standard (Relevance)
  • Author A-Ö
  • Author Ö-A
  • Title A-Ö
  • Title Ö-A
  • Publication type A-Ö
  • Publication type Ö-A
  • Issued (Oldest first)
  • Issued (Newest first)
  • Created (Oldest first)
  • Created (Newest first)
  • Last updated (Oldest first)
  • Last updated (Newest first)
  • Disputation date (earliest first)
  • Disputation date (latest first)
  • Standard (Relevance)
  • Author A-Ö
  • Author Ö-A
  • Title A-Ö
  • Title Ö-A
  • Publication type A-Ö
  • Publication type Ö-A
  • Issued (Oldest first)
  • Issued (Newest first)
  • Created (Oldest first)
  • Created (Newest first)
  • Last updated (Oldest first)
  • Last updated (Newest first)
  • Disputation date (earliest first)
  • Disputation date (latest first)
Select
The maximal number of hits you can export is 250. When you want to export more records please use the 'Create feeds' function.
  • 1.
    Ahlquist, Mårten
    et al.
    KTH, School of Biotechnology (BIO), Theoretical Chemistry and Biology.
    Fabrizi, G
    Cacchi, S
    Norrby, Per-Ola
    Technical University of Denmark.
    Palladium(0) alkyne complexes as active species: a DFT investigation2005In: Chemical Communications, ISSN 1359-7345, E-ISSN 1364-548X, no 33, p. 4196-4198Article in journal (Refereed)
    Abstract [en]

    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.

  • 2.
    Ahlquist, Mårten
    et al.
    KTH, School of Biotechnology (BIO), Theoretical Chemistry and Biology.
    Fabrizi, Giancarlo
    Cacchi, Sandro
    Norrby, Per-Ola
    Technical Univeristy of Denmark.
    The mechanism of the phosphine-free palladium-catalyzed hydroarylation of alkynes2006In: Journal of the American Chemical Society, ISSN 0002-7863, E-ISSN 1520-5126, Vol. 128, no 39, p. 12785-12793Article in journal (Refereed)
    Abstract [en]

    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.

  • 3.
    Ahlquist, Mårten
    et al.
    Scripps Research Insititute.
    Fokin, Valery V.
    Enhanced reactivity of dinuclear Copper(I) acetylides in dipolar cycloadditions2007In: Organometallics, ISSN 0276-7333, E-ISSN 1520-6041, Vol. 26, no 18, p. 4389-4391Article in journal (Refereed)
    Abstract [en]

    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.

  • 4.
    Ahlquist, Mårten
    et al.
    Technical University of Denmark.
    Fristrup, P
    Tanner, David
    Technical University of Denmark.
    Norrby, Per-Ola
    Technical Univeristy of Denmark.
    Theoretical evidence for low-ligated palladium(0): [Pd-L] as the active species in oxidative addition reactions2006In: Organometallics, ISSN 0276-7333, E-ISSN 1520-6041, Vol. 25, no 8, p. 2066-2073Article in journal (Refereed)
    Abstract [en]

    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.

  • 5.
    Ahlquist, Mårten
    et al.
    Lund University.
    Gustafsson, Mikaela
    Karlsson, Magnus
    Thaning, Mikkel
    Axelsson, Oskar
    Wendt, Ola F.
    Rhodium(I) hydrogenation in water: Kinetic studies and the detection of an intermediate using C-13{H-1} PHIPNMR spectroscopy2007In: Inorganica Chimica Acta, ISSN 0020-1693, E-ISSN 1873-3255, Vol. 360, no 5, p. 1621-1627Article in journal (Refereed)
    Abstract [en]

    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.

  • 6.
    Ahlquist, Mårten
    et al.
    Technical University of Denmark.
    Kozuch, S
    Shaik, S
    Tanner, David
    Technical University of Denmark.
    Norrby, Per-Ola
    Technical Univeristy of Denmark.
    On the performance of continuum solvation models for the solvation energy of small anions2006In: Organometallics, ISSN 0276-7333, E-ISSN 1520-6041, Vol. 25, no 1, p. 45-47Article in journal (Refereed)
    Abstract [en]

    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.

  • 7.
    Ahlquist, Mårten
    et al.
    Technical University of Denmark.
    Nielsen, Robert J.
    Periana, Roy A.
    Goddard, William A., III
    Product Protection, the Key to Developing High Performance Methane Selective Oxidation Catalysts2009In: Journal of the American Chemical Society, ISSN 0002-7863, E-ISSN 1520-5126, Vol. 131, no 47, p. 17110-17115Article in journal (Refereed)
    Abstract [en]

    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.

  • 8.
    Ahlquist, Mårten
    et al.
    Technical University of Denmark.
    Nielsen, T E
    Le Quement, S
    Tanner, David
    Technical University of Denmark.
    Norrby, Per-Ola
    Technical Univeristy of Denmark.
    An experimental and theoretical study of the mechanism of stannylcupration of alpha, beta-acetylenic ketones and esters2006In: Chemistry - A European Journal, ISSN 0947-6539, E-ISSN 1521-3765, Vol. 12, no 10, p. 2866-2873Article in journal (Refereed)
    Abstract [en]

    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.

  • 9.
    Ahlquist, Mårten
    et al.
    KTH, School of Biotechnology (BIO), Theoretical Chemistry and Biology.
    Norrby, Per-Ola
    Department of Chemistry, University of Gothenburg, Sweden.
    Dispersion and Back-Donation Gives Tetracoordinate [Pd(PPh3)4]2011In: Angewandte Chemie International Edition, ISSN 1433-7851, E-ISSN 1521-3773, Vol. 50, no 49, p. 11794-11797Article in journal (Refereed)
    Abstract [en]

    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.

  • 10.
    Ahlquist, Mårten
    et al.
    Technical University of Denmark.
    Norrby, Per-Ola
    Göteborg University.
    Oxidative addition of aryl chlorides to monoligated palladium(0): A DFT-SCRF study2007In: Organometallics, ISSN 0276-7333, E-ISSN 1520-6041, Vol. 26, no 3, p. 550-553Article in journal (Refereed)
    Abstract [en]

    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.

  • 11.
    Ahlquist, Mårten
    et al.
    California Institute of Technology.
    Periana, Roy A.
    Goddard, William A., III
    C-H activation in strongly acidic media. The co-catalytic effect of the reaction medium2009In: Chemical Communications, ISSN 1359-7345, E-ISSN 1364-548X, no 17, p. 2373-2375Article in journal (Refereed)
    Abstract [en]

    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.

  • 12.
    Ahlquist, Mårten S. G.
    KTH, School of Biotechnology (BIO), Theoretical Chemistry.
    Iridium catalyzed hydrogenation of CO2 under basic conditions-Mechanistic insight from theory2010In: Journal of Molecular Catalysis A: Chemical, ISSN 1381-1169, E-ISSN 1873-314X, Vol. 324, no 1-2, p. 3-8Article in journal (Refereed)
    Abstract [en]

    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.

  • 13.
    Ahlquist, Mårten S. G.
    et al.
    KTH, School of Biotechnology (BIO), Theoretical Chemistry and Biology.
    Norrby, Per-Ola
    Department of Chemistry, University of Gothenburg, Sweden.
    Dispersion and back-donation gives tetracoordinate Pd(PPh3)(4)2012In: Abstract of Papers of the American Chemical Society, ISSN 0065-7727, Vol. 243Article in journal (Other academic)
  • 14.
    Ahlquist, Mårten S. G.
    et al.
    KTH, School of Biotechnology (BIO), Theoretical Chemistry and Biology.
    Wang, Ying
    KTH, School of Biotechnology (BIO), Theoretical Chemistry and Biology.
    Xue, Liqin
    KTH, School of Biotechnology (BIO), Theoretical Chemistry and Biology.
    Sanchez-de-Armas, Rocio
    KTH, School of Biotechnology (BIO), Theoretical Chemistry and Biology.
    Proton transfers in first row transition metal complexes2013In: Abstract of Papers of the American Chemical Society, ISSN 0065-7727, Vol. 245, p. 1381-INOR-Article in journal (Other academic)
  • 15. Ahlstrand, David A.
    et al.
    Polukeev, Alexey V.
    Marcos, Rocio
    KTH, School of Biotechnology (BIO), Theoretical Chemistry and Biology.
    Ahlquist, Mårten S. G.
    KTH, School of Biotechnology (BIO), Theoretical Chemistry and Biology.
    Wendt, Ola F.
    Csp(3)-H Activation without Chelation Assistance in an Iridium Pincer Complex Forming Cyclometallated Products2017In: Chemistry - A European Journal, ISSN 0947-6539, E-ISSN 1521-3765, Vol. 23, no 8, p. 1748-1751Article in journal (Refereed)
    Abstract [en]

    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.

  • 16. Cheng, Mu-Jeng
    et al.
    Nielsen, Robert J.
    Ahlquist, Mårten
    KTH, School of Biotechnology (BIO), Theoretical Chemistry and Biology.
    Goddard, William A., III
    Carbon-Oxygen Bond Forming Mechanisms in Rhenium Oxo-Alkyl Complexes2010In: Organometallics, ISSN 0276-7333, E-ISSN 1520-6041, Vol. 29, no 9, p. 2026-2033Article in journal (Refereed)
    Abstract [en]

    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.

  • 17.
    Daniel, Quentin
    et al.
    KTH, School of Chemical Science and Engineering (CHE), Chemistry, Organic Chemistry.
    Huang, Ping
    Fan, Ting
    KTH, School of Biotechnology (BIO), Theoretical Chemistry and Biology.
    Wang, Ying
    KTH, School of Biotechnology (BIO), Theoretical Chemistry and Biology.
    Duan, Lele
    KTH, School of Chemical Science and Engineering (CHE), Chemistry.
    Wang, Lei
    KTH, School of Chemical Science and Engineering (CHE), Chemistry.
    Li, Fusheng
    KTH, School of Chemical Science and Engineering (CHE), Chemistry.
    Rinkevicius, Zilvinas
    KTH, School of Biotechnology (BIO), Theoretical Chemistry and Biology.
    Ahlquist, Mårten S. G.
    KTH, School of Biotechnology (BIO), Theoretical Chemistry and Biology.
    Mamedov, Fikret
    Styring, Stenbjörn
    Sun, Licheng
    KTH, School of Chemical Science and Engineering (CHE), Chemistry.
    Rearranging from 6-to 7-coordination initiates the catalytic activity: An EPR study on a Ru-bda water oxidation catalyst2017In: Coordination chemistry reviews, ISSN 0010-8545, E-ISSN 1873-3840, Vol. 346, p. 206-215Article in journal (Refereed)
    Abstract [en]

    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.

  • 18. Ding, Xin
    et al.
    Gao, Yan
    Fan, Ting
    KTH, School of Biotechnology (BIO), Theoretical Chemistry and Biology.
    Ji, Yongfei
    KTH, School of Biotechnology (BIO), Theoretical Chemistry and Biology.
    Zhang, Linlin
    Yu, Ze
    Ahlquist, Mårten S. G.
    KTH, School of Biotechnology (BIO), Theoretical Chemistry and Biology.
    Sun, Licheng
    KTH, School of Chemical Science and Engineering (CHE), Chemistry. Dalian University of Technology (DUT), China.
    Silicon Compound Decorated Photoanode for Performance Enhanced Visible Light Driven Water Splitting2016In: Electrochimica Acta, ISSN 0013-4686, E-ISSN 1873-3859, Vol. 215, p. 682-688Article in journal (Refereed)
    Abstract [en]

    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.

  • 19.
    Duan, Lele
    et al.
    KTH, School of Chemical Science and Engineering (CHE), Chemistry, Organic Chemistry.
    Araujo, Carlos Moyses
    KTH, School of Biotechnology (BIO), Theoretical Chemistry and Biology.
    Ahlquist, Mårten S. G.
    KTH, School of Biotechnology (BIO), Theoretical Chemistry and Biology.
    Sun, Licheng
    KTH, School of Chemical Science and Engineering (CHE), Chemistry, Organic Chemistry.
    Highly efficient and robust molecular ruthenium catalysts for water oxidation2012In: Proceedings of the National Academy of Sciences of the United States of America, ISSN 0027-8424, E-ISSN 1091-6490, Vol. 109, no 39, p. 15584-15588Article in journal (Refereed)
    Abstract [en]

    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.

  • 20.
    Fan, Ting
    et al.
    KTH, School of Biotechnology (BIO), Theoretical Chemistry and Biology.
    Duan, Lele
    KTH, School of Chemical Science and Engineering (CHE), Chemistry.
    Huang, Ping
    Chen, Hong
    KTH, School of Chemical Science and Engineering (CHE), Chemistry.
    Daniel, Quentin
    KTH, School of Chemical Science and Engineering (CHE), Chemistry.
    Ahlquist, Mårten S. G.
    KTH, School of Biotechnology (BIO), Theoretical Chemistry and Biology.
    Sun, Licheng
    KTH, School of Chemical Science and Engineering (CHE), Chemistry.
    The Ru-tpc Water Oxidation Catalyst and Beyond: Water Nucleophilic Attack Pathway versus Radical Coupling Pathway.2017In: ACS Catalysis, ISSN 2155-5435, E-ISSN 2155-5435, Vol. 7, no 4, p. 2956-2966Article in journal (Refereed)
    Abstract [en]

    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.

  • 21.
    Fan, Ting
    et al.
    KTH, School of Biotechnology (BIO), Theoretical Chemistry and Biology.
    Zhan, Shaoqi
    KTH, School of Biotechnology (BIO), Theoretical Chemistry and Biology.
    Ahlquist, Mårten S. G.
    KTH, School of Biotechnology (BIO), Theoretical Chemistry and Biology.
    Why Is There a Barrier in the Coupling of Two Radicals in the Water Oxidation Reaction?2016In: ACS Catalysis, ISSN 2155-5435, E-ISSN 2155-5435, Vol. 6, no 12, p. 8308-8312Article in journal (Refereed)
    Abstract [en]

    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.

  • 22. Fristrup, Peter
    et al.
    Ahlquist, Mårten
    Department of Chemistry, Technical University of Denmark.
    Tanner, David
    Norrby, Per-Ola
    On the Nature of the Intermediates and the Role of Chloride Ions in Pd-Catalyzed Allylic Alkylations: Added Insight from Density Functional Theory2008In: Journal of Physical Chemistry A, ISSN 1089-5639, E-ISSN 1520-5215, Vol. 112, no 50, p. 12862-12867Article in journal (Refereed)
    Abstract [en]

    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.

  • 23. Hansen, Anders L.
    et al.
    Ebran, Jean-Philippe
    Ahlquist, Mårten
    KTH, School of Biotechnology (BIO), Theoretical Chemistry and Biology.
    Norrby, Per-Ola
    Skrydstrup, Troels
    Heck coupling with nonactivated alkenyl tosylates and phosphates: Examples of effective 1,2-migrations of the alkenyl palladium(II) intermediates2006In: Angewandte Chemie International Edition, ISSN 1433-7851, E-ISSN 1521-3773, Vol. 45, no 20, p. 3349-3353Article in journal (Refereed)
  • 24. Johnson, M T
    et al.
    Johansson, R
    Kondrashov, M V
    Steyl, G
    Ahlquist, Mårten S G
    KTH, School of Biotechnology (BIO), Theoretical Chemistry and Biology.
    Roodt, A
    Wendt, O F
    Mechanisms of the CO2 insertion into palladium allyl and methyl sigma-bonds2011Conference paper (Other academic)
  • 25. Johnson, Magnus T.
    et al.
    Dzolic, Zoran
    Cetina, Mario
    Lahtinen, Manu
    Ahlquist, Marten S. G.
    KTH, School of Biotechnology (BIO), Theoretical Chemistry and Biology.
    Rissanen, Kari
    Ohrstrom, Lars
    Wendt, Ola F.
    Preparation of potentially porous, chiral organometallic materials through spontaneous resolution of pincer palladium conformers2013In: Dalton Transactions, ISSN 1477-9226, E-ISSN 1477-9234, Vol. 42, no 23, p. 8484-8491Article in journal (Refereed)
    Abstract [en]

    Understanding the mechanism by which advanced materials assemble is essential for the design of new materials with desired properties. Here, we report a method to form chiral, potentially porous materials through spontaneous resolution of conformers of a PCP pincer palladium complex ({2,6-bis[(di-t-butyl-phosphino)methyl]phenyl}palladium(II)halide). The crystallisation is controlled by weak hydrogen bonding giving rise to chiral qtz-nets and channel structures, as shown by 16 such crystal structures for X = Cl and Br with various solvents like pentane and bromobutane. The fourth ligand (in addition to the pincer ligand) on palladium plays a crucial role; the chloride and the bromide primarily form hexagonal crystals with large 1D channels, whereas the iodide (presumably due to its inferior hydrogen bonding capacity) forms monoclinic crystals without channels. The hexagonal channels are completely hydrophobic and filled with disordered solvent molecules. Upon heating, loss of the solvent occurs and the hexagonal crystals transform into other non-porous polymorphs. Also by introducing a strong acid, the crystallisation process can be directed to a different course, giving several different non-porous polymorphs. In conclusion, a number of rules can be formulated dictating the formation of hexagonal channel structures based on pincer palladium complexes. Such rules are important for a rational design of future self-assembling materials with applications in storage and molecular recognition.

  • 26. Johnson, Magnus T.
    et al.
    Johansson, Roger
    Kondrashov, Mikhail V.
    Steyl, Gideon
    Ahlquist, Mårten S. G.
    KTH, School of Biotechnology (BIO), Theoretical Chemistry.
    Roodt, Andreas
    Wendt, Ola F.
    Mechanisms of the CO2 Insertion into (PCP) Palladium Allyl and Methyl sigma-Bonds. A Kinetic and Computational Study2010In: Organometallics, ISSN 0276-7333, E-ISSN 1520-6041, Vol. 29, no 16, p. 3521-3529Article in journal (Refereed)
    Abstract [en]

    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.

  • 27. Johnson, Magnus T.
    et al.
    van Rensburg, J. Marthinus Janse
    Axelsson, Martin
    Ahlquist, Mårten S. G.
    KTH, School of Biotechnology (BIO), Theoretical Chemistry and Biology.
    Wendt, Ola F.
    Reactivity of NHC Au(I)-C sigma-bonds with electrophiles. An investigation of their possible involvement in catalytic C-C bond formation2011In: CHEM SCI, ISSN 2041-6520, Vol. 2, no 12, p. 2373-2377Article in journal (Refereed)
    Abstract [en]

    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.

  • 28. Jonasson, Klara J.
    et al.
    Polukeev, Alexey V.
    Marcos, Rocio
    KTH, School of Biotechnology (BIO), Theoretical Chemistry and Biology.
    Ahlquist, Mårten S. G.
    KTH, School of Biotechnology (BIO), Theoretical Chemistry and Biology.
    Wendt, Ola F.
    Reversible -Hydrogen and -Alkyl Elimination in PC(sp(3))P Pincer Complexes of Iridium2015In: Angewandte Chemie International Edition, ISSN 1433-7851, E-ISSN 1521-3773, Vol. 54, no 32, p. 9372-9375Article in journal (Refereed)
    Abstract [en]

    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.

  • 29. Kagalwala, Husain N.
    et al.
    Tong, Lianpeng
    Zong, Ruifa
    Kohler, Lars
    Ahlquist, Mårten S. G.
    KTH, School of Biotechnology (BIO), Theoretical Chemistry and Biology.
    Fan, Ting
    KTH, School of Biotechnology (BIO), Theoretical Chemistry and Biology.
    Gagnon, Kevin J.
    Thummel, Randolph P.
    Evidence for Oxidative Decay of a Ru-Bound Ligand during Catalyzed Water Oxidation2017In: ACS Catalysis, ISSN 2155-5435, E-ISSN 2155-5435, Vol. 7, no 4, p. 2607-2615Article in journal (Refereed)
    Abstract [en]

    In the evaluation of systems designed for 800 catalytic water oxidation, ceric ammonium nitrate (CAN) is often used as a sacrificial electron acceptor. One of the sources of failure for such systems is oxidative decay of the catalyst in the presence of the strong oxidant CAN (E-ox = +1.71 V). Little progress has been made in understanding the circumstances behind this decay. In this study we show that a 2-(2'-hydroxphenyl) derivative (LH) of 1,10-phenanthroline (phen) in the complex [Ru(L)(tpy)](+) (tpy = 2,2';6',2 ''-terpyridine) can be oxidized by CAN to a 2-carboxy-phen while still bound to the metal. This complex is, in fact, a very active water oxidation catalyst. The incorporation of a methyl substituent on the phenol ring of LH slows down the oxidative decay and consequently slows down the catalytic oxidation. An analogous system based on bpy (2,2'-bipyridine) instead of phen shows much lower activity under the same conditions. Water molecule association to the Ru center of [Ru(L)(tpy)](+) and carboxylate donor dissociation were proposed to occur at the trivalent state. The resulting [Ru-III-OH2] was further oxidized to [Ru-IV=O] via a PCET process.

  • 30.
    Marcos, Rocio
    et al.
    KTH, School of Engineering Sciences in Chemistry, Biotechnology and Health (CBH), Theoretical Chemistry and Biology.
    Bertini, Federica
    CNR, Inst Chim Composti Organometallici ICCOM, Via Madonna Piano 10, I-50019 Florence, Italy..
    Rinkevicius, Zilvinas
    KTH, School of Engineering Sciences in Chemistry, Biotechnology and Health (CBH), Theoretical Chemistry and Biology.
    Peruzzini, Maurizio
    CNR, Inst Chim Composti Organometallici ICCOM, Via Madonna Piano 10, I-50019 Florence, Italy..
    Gonsalvi, Luca
    CNR, Inst Chim Composti Organometallici ICCOM, Via Madonna Piano 10, I-50019 Florence, Italy..
    Ahlquist, Mårten S. G.
    KTH, School of Engineering Sciences in Chemistry, Biotechnology and Health (CBH), Theoretical Chemistry and Biology.
    Mechanistic Studies on NaHCO3 Hydrogenation and HCOOH Dehydrogenation Reactions Catalysed by a Fe-II Linear Tetraphosphine Complex2018In: Chemistry - A European Journal, ISSN 0947-6539, E-ISSN 1521-3765, Vol. 24, no 20, p. 5366-5372Article in journal (Refereed)
    Abstract [en]

    We present a theoretical extension of the previously published bicarbonate hydrogenation to formate and formic acid dehydrogenation catalysed by Fe-II complexes bearing the linear tetraphosphine ligand tetraphos-1. The hydrogenation reaction was found to proceed at the singlet surface with two competing pathways: A)H-2 association to the Fe-H species followed by deprotonation to give a Fe(H)(2) intermediate, which then reacts with CO2 to give formate. B)CO2 insertion into the Fe-H bond, followed by H-2 association and subsequent deprotonation. B was found to be slightly preferred with an activation energy of 22.8kcalmol(-1), compared to 25.3 for A. Further we have reassigned the Fe-H complex, as a Fe(H)(H-2), which undergoes extremely rapid hydrogen exchange.

  • 31.
    Marcos, Rocio
    et al.
    KTH, School of Biotechnology (BIO), Theoretical Chemistry and Biology.
    Xue, Liqin
    KTH, School of Biotechnology (BIO), Theoretical Chemistry and Biology. Angstromlab, Angstrom Lab, Dept Chem, Uppsala, Sweden.
    Sanchez-de-Armas, Rocio
    KTH, School of Biotechnology (BIO), Theoretical Chemistry and Biology. Uppsala Univ, Mat Theory Div, Dept Phys & Astron, Sweden.
    Ahlquist, Mårten S. G.
    KTH, School of Biotechnology (BIO), Theoretical Chemistry and Biology.
    Bicarbonate Hydrogenation Catalyzed by Iron: How the Choice of Solvent Can Reverse the Reaction2016In: ACS Catalysis, ISSN 2155-5435, E-ISSN 2155-5435, Vol. 6, no 5, p. 2923-2929Article in journal (Refereed)
    Abstract [en]

    Here we report a mechanism study of the hydrogenation of bicarbonate by tetradentate phosphines iron-complexes. It is an extension of our recent study on the reverse reaction by the same type of complexes [Chem.-Eur. J. 2013, 19, 11869], with special emphasis herein on the effects of the choice of solvent. By using density functional theory we have located the most plausible mechanism and have found remarkable effects of the solvent on the reversibility of this reaction. We predict that the solvent used in experiment, MeOH, for the hydrogenation of bicarbonate to formate could be replaced to enhance the activity of the system. There is a direct correlation of the solubility of the base to favor or disfavor the hydrogenation of bicarbonate to formate.

  • 32. Martinez-Erro, S.
    et al.
    Sanz-Marco, A.
    Bermejo Gómez, A.
    Vázquez-Romero, A.
    Ahlquist, Mårten S. G.
    KTH, School of Biotechnology (BIO), Theoretical Chemistry and Biology.
    Martín-Matute, B.
    Base-Catalyzed Stereospecific Isomerization of Electron-Deficient Allylic Alcohols and Ethers through Ion-Pairing2016In: Journal of the American Chemical Society, ISSN 0002-7863, E-ISSN 1520-5126, Vol. 138, no 40, p. 13408-13414Article in journal (Refereed)
    Abstract [en]

    A mild base-catalyzed strategy for the isomerization of allylic alcohols and allylic ethers has been developed. Experimental and computational investigations indicate that transition metal catalysts are not required when basic additives are present. As in the case of using transition metals under basic conditions, the isomerization catalyzed solely by base also follows a stereospecific pathway. The reaction is initiated by a rate-limiting deprotonation. Formation of an intimate ion pair between an allylic anion and the conjugate acid of the base results in efficient transfer of chirality. Through this mechanism, stereochemical information contained in the allylic alcohols is transferred to the ketone products. The stereospecific isomerization is also applicable for the first time to allylic ethers, yielding synthetically valuable enantioenriched (up to 97% ee) enol ethers.

  • 33. Mironov, Oleg A.
    et al.
    Bischof, Steven M.
    Konnick, Michael M.
    Hashiguchi, Brian G.
    Ziatdinov, Vadim R.
    Goddard, III, William A.
    Ahlquist, Mårten
    California Institute of Technology, United States.
    Periana, Roy A.
    Using Reduced Catalysts for Oxidation Reactions: Mechanistic Studies of the “Periana-Catalytica” System for CH4 Oxidation2013In: Journal of the American Chemical Society, ISSN 0002-7863, E-ISSN 1520-5126, Vol. 135, no 39, p. 14644-14658Article in journal (Refereed)
    Abstract [en]

    Designing oxidation catalysts based on CH activation with reduced, low oxidation state species is a seeming dilemma given the proclivity for catalyst deactivation by overoxidation. This dilemma has been recognized in the Shilov system where reduced Pt-II is used to catalyze methane functionalization. Thus, it is generally accepted that key to replacing Pt-IV in that system with more practical oxidants is ensuring that the oxidant does not over-oxidize the reduced Pt-II species. The “Periana-Catalytica” system, which utilizes (bpym)-(PtCl2)-Cl-II in concentrated sulfuric acid solvent at 200 degrees C, is a highly stable catalyst for the selective, high yield oxy-functionalization of methane. In lieu of the over-oxidation dilemma, the high stability and observed rapid oxidation of (bpym)(PtCl2)-Cl-II to Pt-IV in the absence of methane would seem to contradict the originally proposed mechanism involving CH activation by a reduced Pt-II species. Mechanistic studies show that the originally proposed mechanism is incomplete and that while CH activation does proceed with Pt-II there is a solution to the over oxidation dilemma. Importantly, contrary to the accepted view to minimize Pt-II overoxidation, these studies also show that increasing that rate could increase the rate of catalysis and catalyst stability. The mechanistic basis for this counterintuitive prediction could help to guide the design of new catalysts for alkane oxidation that operate by CH activation.

  • 34.
    Osadchuk, Irina
    et al.
    KTH, School of Biotechnology (BIO), Theoretical Chemistry and Biology. Tallinn University of Technology, Estonia.
    Tamm, Toomas
    KTH, School of Biotechnology (BIO), Theoretical Chemistry and Biology. Tallinn University of Technology, Estonia.
    Ahlquist, Mårten S. G.
    KTH, School of Biotechnology (BIO), Theoretical Chemistry and Biology.
    Reduced State of Iridium PCP Pincer Complexes in Electrochemical CO2 Hydrogenation2016In: ACS Catalysis, ISSN 2155-5435, E-ISSN 2155-5435, Vol. 6, no 6, p. 3834-3839Article in journal (Refereed)
    Abstract [en]

    We present a computational study on the mechanism for electrochemical reduction of CO2 using a PCP pincer iridium(III) dihydride complex. Our results point toward a mechanism that involves an in situ-generated iridium(I) hydride as the active species for the CO2 to formate reduction. The iridium(III) path can operate in parallel but is associated with higher activation free energies in the reaction between the metal hydride and CO2, compared to the reaction at the in situ-generated iridium(I) species.

  • 35. Osadchuk, Irina
    et al.
    Tamm, Toomas
    Ahlquist, Mårten S. G.
    KTH, School of Biotechnology (BIO), Theoretical Chemistry and Biology.
    Theoretical Investigation of a Parallel Catalytic Cycle in CO2 Hydrogenation by (PNP)IrH32015In: Organometallics, ISSN 0276-7333, E-ISSN 1520-6041, Vol. 34, no 20, p. 4932-4940Article in journal (Refereed)
    Abstract [en]

    The (PNP)IrH3 (2,6-bis(diisopropylphosp-hinomethyl)pyridine iridium trihydride) complex by Nozaki is a highly active and selective catalyst for CO2 hydrogenation to formic acid in aqueous KOH. Previous theoretical investigations found that regeneration of the catalyst is the rate-determining step in this reaction. In the current article we present results from a computational study using density func- theory in order to consider the possibility of sequential insertion of two CO2 molecules in two Ir-H bonds before the reaction with hydrogen. We found that insertion of a second CO2 molecule is indeed possible; moreover, this sequential insertion allows formation of a more electrophilic iridium mono-hydride intermediate, and thereby the process of H-2 cleavage is facilitated. In addition, we considered the influence of ligands coplanar with the PNP ligand on the energy of CO2 insertion into the (PNP)IrH2X complex and found that sigma- and pi-donating ligands promote the reaction.

  • 36. Polukeev, Alexey V.
    et al.
    Marcos, Rocio
    KTH, School of Biotechnology (BIO), Theoretical Chemistry and Biology.
    Ahlquist, Mårten S. G.
    KTH, School of Biotechnology (BIO), Theoretical Chemistry and Biology.
    Wendt, Ola F.
    Formation of a C-C double bond from two aliphatic carbons. Multiple C-H activations in an iridium pincer complex2015In: Chemical Science, ISSN 2041-6520, E-ISSN 2041-6539, Vol. 6, no 3, p. 2060-2067Article in journal (Refereed)
    Abstract [en]

    The search for novel, atom-economic methods for the formation of C-C bonds is of crucial importance in synthetic chemistry. Especially attractive are reactions where C-C bonds are formed through C-H activation, but the coupling of unactivated, alkane-type C-sp3-H bonds remains an unsolved challenge. Here, we report iridium-mediated intramolecular coupling reactions involving up to four unactivated C-sp3-H bonds to give carbon-carbon double bonds under the extrusion of dihydrogen. The reaction described herein is completely reversible and the direction can be controlled by altering the reaction conditions. With a hydrogen acceptor present a C-C double bond is formed, while reacting under dihydrogen pressure leads to the reverse process, with some of the steps representing net C-sp3-C-sp3 bond cleavage. Mechanistic investigations revealed a conceptually-novel overall reactivity pattern where insertion or deinsertion of an Ir carbene moiety, formed via double C-H activation, into an Ir-C bond is responsible for the key C-C bond formation and cleavage steps.

  • 37. Polukeev, Alexey V.
    et al.
    Marcos, Rocio
    KTH, School of Biotechnology (BIO).
    Ahlquist, Mårten S. G.
    KTH, School of Biotechnology (BIO), Theoretical Chemistry and Biology.
    Wendt, Ola F.
    Iridium Hydride Complexes with Cyclohexyl-Based Pincer Ligands: Fluxionality and Deuterium Exchange2016In: Organometallics, ISSN 0276-7333, E-ISSN 1520-6041, Vol. 35, no 16, p. 2600-2608Article in journal (Refereed)
    Abstract [en]

    Two hydride compounds with aliphatic pincer ligands, (PCyP)IrH2 (PCyP = {cis-1,3-bis[(di-tert-butylphosphino)methyl]cyclohexane}(-) (1) and (PCyP)IrH4 (2), have been studied, with emphasis on features where such systems differ from arene-based analogues. Both compounds reveal relatively rapid exchange between alpha-C-H and Ir-H, which can occur via formation of carbene or through demetalation, with nearly equal barriers. This observation is confirmed by deuterium incorporation into the alpha-C-H position. Complex 1 can reversibly add an N-2 molecule, which competes with the alpha-agostic bond for a coordination site at iridium. The hydrogen binding mode in tetrahydride 2 is discussed on the basis of NMR and IR spectra, as well as DFT calculations. While the interpretation of the data is somewhat ambiguous, the best model seems to be a tetrahydride with minor contribution from a dihydrido-dihydrogen complex. In addition, the catalytic activity of 1 in deuterium exchange using benzene-d(6) as a deuterium source is presented.

  • 38. Polukeev, Alexey V.
    et al.
    Marcos, Rocio
    KTH, School of Biotechnology (BIO), Theoretical Chemistry and Biology.
    Ahlquist, Mårten S. G.
    KTH, School of Biotechnology (BIO), Theoretical Chemistry and Biology.
    Wendt, Ola F.
    Solvent-Dependent Structure of Iridium Dihydride Complexes: Different Geometries at Low and High Dielectricity of the Medium2016In: Chemistry - A European Journal, ISSN 0947-6539, E-ISSN 1521-3765, Vol. 22, no 12, p. 4078-4086Article in journal (Refereed)
    Abstract [en]

    The hydride iridium pincer complex [(PCyP)IrH2] (PCyP=cis-1,3-bis[(di-tert-butylphosphino)methyl]cyclohexane, 1) reveals remarkably solvent-dependent hydride chemical shifts, isotope chemical shifts, J(HD) and T-1(min), with r(HH) increasing upon moving to more polar medium. The only known example of such behaviour (complex [(POCOP)IrH2], POCOP=2,6-(tBu(2)PO)(2)C6H3) was explained by the coordination of a polar solvent molecule to the iridium (J. Am. Chem. Soc. 2006, 128, 17114). Based on the existence of an agostic bond between -C-H and iridium in 1 in all solvents, we argue that the coordination of solvent can be rejected. DFT calculations revealed that the structures of 1 and [(POCOP)IrH2] depend on the dielectric permittivity of the medium and these compounds adopt trigonal-bipyramidal geometries in non-polar media and square-pyramidal geometries in polar media.

  • 39.
    Sanchez-de-Armas, Rocio
    et al.
    KTH, School of Biotechnology (BIO), Theoretical Chemistry and Biology.
    Ahlquist, Mårten S. G.
    KTH, School of Biotechnology (BIO), Theoretical Chemistry and Biology.
    On the nature of hydrogen bonds to platinum(II): Which interaction can predict their strength?2015In: Physical Chemistry, Chemical Physics - PCCP, ISSN 1463-9076, E-ISSN 1463-9084, Vol. 17, no 2, p. 812-816Article in journal (Refereed)
    Abstract [en]

    The interaction between hydrogen bond donors and platinum has been analysed. Our results point to an interaction that can be entirely predicted from the d(z2) orbital energy of the platinum centre indicating strong charge transfer, with significant dispersion contribution to the bonding, very different from classical hydrogen bonds.

  • 40.
    Sanchez-de-Armas, Rocio
    et al.
    KTH, School of Biotechnology (BIO), Theoretical Chemistry and Biology.
    Xue, Liqin
    KTH, School of Biotechnology (BIO), Theoretical Chemistry and Biology.
    Ahlquist, Mårten S. G.
    KTH, School of Biotechnology (BIO), Theoretical Chemistry and Biology.
    One Site Is Enough: A Theoretical Investigation of Iron-Catalyzed Dehydrogenation of Formic Acid2013In: Chemistry - A European Journal, ISSN 0947-6539, E-ISSN 1521-3765, Vol. 19, no 36, p. 11869-11873Article in journal (Refereed)
    Abstract [en]

    Dehydrogenation of HCO2H: The reaction mechanism for the dehydrogenation of formic acid catalyzed by a highly active and selective iron complex (see figure) has been studied by DFT. The most favorable pathway shows the hydride in Fe-H complexes acting as a spectator ligand throughout the catalytic cycle. This result opens up the Fe complex for modification in order to achieve more efficient and selective catalysts.

  • 41.
    Staehle, Robert
    et al.
    KTH, School of Chemical Science and Engineering (CHE), Chemistry.
    Tong, Lianpeng
    KTH, School of Chemical Science and Engineering (CHE), Chemistry, Organic Chemistry.
    Wang, Lei
    KTH, School of Chemical Science and Engineering (CHE), Chemistry, Organic Chemistry.
    Duan, Lele
    KTH, School of Chemical Science and Engineering (CHE), Chemistry.
    Fischer, Andreas
    KTH, School of Chemical Science and Engineering (CHE), Chemistry, Applied Physical Chemistry.
    Ahlquist, Mårten S. G.
    KTH, School of Biotechnology (BIO), Theoretical Chemistry and Biology.
    Sun, Licheng
    KTH, School of Chemical Science and Engineering (CHE), Chemistry, Organic Chemistry.
    Rau, Sven
    Water oxidation catalyzed by mononuclear ruthenium complexes with a 2,2′-bipyridine-6,6′-dicarboxylate (bda) ligand: How ligand environment influences the catalytic behavior2014In: Inorganic Chemistry, ISSN 0020-1669, E-ISSN 1520-510X, Vol. 53, no 3, p. 1307-1319Article in journal (Refereed)
    Abstract [en]

    A new water oxidation catalyst [RuIII(bda)(mmi)(OH 2)](CF3SO3) (2, H2bda = 2,2′-bipyridine-6,6′-dicarboxylic acid; mmi = 1,3- dimethylimidazolium-2-ylidene) containing an axial N-heterocyclic carbene ligand and one aqua ligand was synthesized and fully characterized. The kinetics of catalytic water oxidation by 2 were measured using stopped-flow technique, and key intermediates in the catalytic cycle were probed by density functional theory calculations. While analogous Ru-bda water oxidation catalysts [Ru(bda)L2] (L = pyridyl ligands) are supposed to catalyze water oxidation through a bimolecular coupling pathway, our study points out that 2, surprisingly, undergoes a single-site water nucleophilic attack (acid-base) pathway. The diversion of catalytic mechanisms is mainly ascribed to the different ligand environments, from nonaqua ligands to an aqua ligand. Findings in this work provide some critical proof for our previous hypothesis about how alternation of ancillary ligands of water oxidation catalysts influences their catalytic efficiency.

  • 42. Tenn, William J., III
    et al.
    Conley, Brian L.
    Hoevelmann, Claas H.
    Ahlquist, Mårten
    Division of Chemistry and Chemical Engineering, California Institute of Technology.
    Nielsen, Robert J.
    Ess, Daniel H.
    Oxgaard, Jonas
    Bischof, Steven M.
    Goddard, William A.
    Periana, Roy A.
    Oxy-Functionalization of Nucleophilic Rhenium(I) Metal Carbon Bonds Catalyzed by Selenium(IV)2009In: Journal of the American Chemical Society, ISSN 0002-7863, E-ISSN 1520-5126, Vol. 131, no 7, p. 2466-2468Article in journal (Refereed)
    Abstract [en]

    We report that SeO(2) catalyzes the facile oxy-functionalization of (CO)(5)Re(I)-Me(delta-) with IO(4)(-) to generate methanol. Mechanistic studies and DFT calculations reveal that catalysis involves methyl group transfer from Re to the electrophilic Se center followed by oxidation and subsequent reductive functionalization of the resulting CH(3)Se(VI) species. Furthermore, (CO)(3)Re(I)(Bpy)-R (R = ethyl, n-propyl, and aryl) complexes show analogous transfer to SeO(2) to generate the primary alcohols. This represents a new strategy for the oxy-functionalization of M-R(delta-) polarized bonds.

  • 43. Tong, Lianpeng
    et al.
    Kopecky, Andrew
    Zong, Ruifa
    Gagnon, Kevin J.
    Ahlquist, Mårten S. G.
    KTH, School of Biotechnology (BIO), Theoretical Chemistry and Biology.
    Thummel, Randolph P.
    Light-Driven Proton Reduction in Aqueous Medium Catalyzed by a Family of Cobalt Complexes with Tetradentate Polypyridine-Type Ligands2015In: Inorganic Chemistry, ISSN 0020-1669, E-ISSN 1520-510X, Vol. 54, no 16, p. 7873-7884Article in journal (Refereed)
    Abstract [en]

    A series of tetradentate 2,2':6',2":6",2"-quaterpyridine-type ligands related to ppq (ppq = 8-(1",10"phenanthrol-2"-y1)-2-(pyrid-2'-yOquinoline) have been synthesized. One ligand replaces the 1,10-phenanthroline (phen) moiety of ppq with 2,2'-bipyridine and the other two ligands have a 3,3'-polymethylene subunit bridging the quinoline and pyridine. The structural result is that both the planarity and flexibility of the ligand are modified. Co (II) complexes are prepared and characterized by ultraviolet-visible light (UVvis) and mass spectroscopy, cyclic voltammetry, and X-ray analysis. The light-driven H-2-evolving activity of these Co complexes was evaluated under homogeneous aqueous conditions using [Ru(bpy)(3)](2) as the photosensitizer, ascorbic acid as a sacrificial electron donor, and a blue light-emitting diode (LED) as the light source. At pH 4.5, all three complexes plus [Co(ppq)Cl-2] showed the fastest rate, with the dimethylene-bridged system giving the highest turnover frequency (2125 h(-1)). Cyclic voltammograms showed a significant catalytic current for H2 production in both aqueous buffer and H2O/DMF medium. Combined experimental and theoretical study suggest a formal Co(L)-hydride species as a key intermediate that triggers H-2 generation. Spin density analysis shows involvement of the tetradentate ligand in the redox sequence from the initial Co(II) state to the Co(II)-hydride intermediate. How the ligand scaffold influences the catalytic activity and stability of catalysts is discussed, in terms of the rigidity and differences in conjugation for this series of ligands.

  • 44.
    Tong, Lianpeng
    et al.
    KTH, School of Chemical Science and Engineering (CHE), Chemistry.
    Wang, Ying
    KTH, School of Biotechnology (BIO), Theoretical Chemistry and Biology.
    Duan, Lele
    KTH, School of Chemical Science and Engineering (CHE), Chemistry, Organic Chemistry.
    Xu, Yunhua
    KTH, School of Chemical Science and Engineering (CHE), Chemistry, Organic Chemistry.
    Cheng, Xiao
    KTH, School of Biotechnology (BIO), Theoretical Chemistry and Biology.
    Fischer, Andreas
    KTH, School of Chemical Science and Engineering (CHE), Chemistry.
    Ahlquist, Mårten S. G.
    KTH, School of Biotechnology (BIO), Theoretical Chemistry and Biology.
    Sun, Licheng
    KTH, School of Chemical Science and Engineering (CHE), Chemistry, Organic Chemistry.
    Water Oxidation Catalysis: Influence of Anionic Ligands upon the Redox Properties and Catalytic Performance of Mononuclear Ruthenium Complexes2012In: Inorganic Chemistry, ISSN 0020-1669, E-ISSN 1520-510X, Vol. 51, no 6, p. 3388-3398Article in journal (Refereed)
    Abstract [en]

    Aiming at highly efficient molecular catalyts for water oxidation, a mononuclear ruthenium complex Ru-II(hqc)(pic)(3) (1; H(2)hqc = 8-hydroxyquinoline-2-carboxylic acid and plc = 4-picoline) containing negatively charged carboxylate and phenolate donor groups has been designed and synthesized. As a comparison, two reference complexes, Ru-II(pdc)(pic)(3) (2; H(2)pdc = 2,6-pyridine-dicarboxylic acid) and Ru-II(tpy)(pic)(3) (3; tpy = 2,2':6',2 ''-terpyridine), have also been prepared. All three complexes are fully characterized by NMR, mass spectrometry (MS), and X-ray crystallography. Complex 1 showed a high efficiency toward catalytic water oxidation either driven by chemical oxidant (Ce-IV in a pH 1 solution) with a initial turnover number of 0.32 s(-1), which is several orders of magnitude higher than that of related mononuclear ruthenium catalysts reported in the literature, or driven by visible light in a three-component system with [Ru(bpy)(3)](2+) types of photosensitizers. Electrospray ionization MS results revealed that at the Rum state complex 1 undergoes ligand exchange of 4-picoline with water, forming the authentic water oxidation catalyst in situ. Density functional theory (DFT) was ernployed to explain how anionic ligands (hqc and pdc) facilitate the 4-picoline dissociation compared with a neutral ligand (tpy). Electrochemical measurements show that complex 1 has a much lower E(Ru-III/Ru-II) than that of reference complex 2 because of the introduction of a phenolate ligand. DFT was further used to study the influence of anionic ligands upon the redox properties of mononuclear aquaruthenium species, which are postulated to be involved in the catalysis cycle of water oxidation.

  • 45.
    Wang, Lei
    et al.
    KTH, School of Chemical Science and Engineering (CHE), Chemistry, Organic Chemistry.
    Duan, Lele
    KTH, School of Chemical Science and Engineering (CHE), Chemistry, Organic Chemistry.
    Wang, Ying
    KTH, School of Biotechnology (BIO), Theoretical Chemistry and Biology.
    Ahlquist, Mårten
    KTH, School of Biotechnology (BIO), Theoretical Chemistry and Biology.
    Sun, Licheng
    KTH, School of Chemical Science and Engineering (CHE), Chemistry, Organic Chemistry. State Key Lab of Fine Chemicals, DUT-KTH Joint Education and Research Center on Molecular Devices, Dalian University of Technology (DUT)Dalian, China .
    Highly efficient and robust molecular water oxidation catalysts based on ruthenium complexes2014In: Chemical Communications, ISSN 1359-7345, E-ISSN 1364-548X, Vol. 50, no 85, p. 12947-12950Article in journal (Refereed)
    Abstract [en]

    Two monomeric ruthenium molecular catalysts for water oxidation have been prepared, and both of them show high activities in pH 1.0 aqueous solutions, with an initial rate of over 1000 turnover s(-1) by complex 1, and a turnover number of more than 100 000 by complex 2.

  • 46. Wang, N.
    et al.
    Wang, M.
    Wang, Ying
    KTH, School of Biotechnology (BIO), Theoretical Chemistry and Biology.
    Zheng, D.
    Han, H.
    Ahlquist, Mårten S. G.
    KTH, School of Biotechnology (BIO), Theoretical Chemistry and Biology.
    Sun, Licheng
    KTH, School of Chemical Science and Engineering (CHE), Chemistry, Organic Chemistry. KTH, School of Chemical Science and Engineering (CHE), Centres, Centre of Molecular Devices, CMD.
    Catalytic activation of H2 under mild conditions by an [FeFe]-hydrogenase model via an active μ-hydride species2013In: Journal of the American Chemical Society, ISSN 0002-7863, E-ISSN 1520-5126, Vol. 135, no 37, p. 13688-13691Article in journal (Refereed)
    Abstract [en]

    A [FeFe]-hydrogenase model (1) containing a chelating diphosphine ligand with a pendant amine was readily oxidized by Fc+ (Fc = Cp 2Fe) to a FeIIFeI complex ([1]+), which was isolated at room temperature. The structure of [1]+ with a semibridging CO and a vacant apical site was determined by X-ray crystallography. Complex [1]+ catalytically activates H2 at 1 atm at 25 C in the presence of excess Fc+ and P(o-tol) 3. More interestingly, the catalytic activity of [1]+ for H2 oxidation remains unchanged in the presence of ca. 2% CO. A computational study of the reaction mechanism showed that the most favorable activation free energy involves a rotation of the bridging CO to an apical position followed by activation of H2 with the help of the internal amine to give a bridging hydride intermediate.

  • 47.
    Wang, Ying
    et al.
    KTH, School of Biotechnology (BIO), Theoretical Chemistry and Biology.
    Ahlquist, Mårten
    KTH, School of Biotechnology (BIO), Theoretical Chemistry and Biology.
    Theoretical Evidence for Direct Involvement of a Dissociated Picoline in Catalyst DecayManuscript (preprint) (Other academic)
  • 48.
    Wang, Ying
    et al.
    KTH, School of Biotechnology (BIO), Theoretical Chemistry and Biology.
    Ahlquist, Mårten S. G.
    KTH, School of Biotechnology (BIO), Theoretical Chemistry and Biology.
    A computational study of the mechanism for water oxidation by (bpc)(bpy)(RuOH2)-O-II2014In: Dalton Transactions, ISSN 1477-9226, E-ISSN 1477-9234, Vol. 43, no 36, p. 13776-13782Article in journal (Refereed)
    Abstract [en]

    A mechanistic study on the catalytic cycle water oxidation with 1 [(bpc)(bpy)(RuOH2)-O-II](+) (Hbpc = 2,2'-bipyridine-6-carboxylic acid, bpy = 2,2'-bipyridine) is described in this paper. Stepwise oxidation via proton-coupled electron transfer gives 3 [(bpc)(bpy)Ru-IV=O](+). An active 4 [(bpc)(bpy)Ru-V=O](2+), which is involved in the OO bond formation is generated from further 1e(-) oxidation of 3. Another different possible reaction at 4 was investigated and new destructive paths involving overoxidation of the metal were identified. The most viable path for OO bond formation via a water nucleophilic attack at the oxo of 4 is found to be the rate-determining step in this water oxidation catalytic cycle, and the hydro-peroxo 6 [(bpc)(bpy)-(RuOOH)-O-III](+) is generated accompanied with a proton transfer. The super-oxo 7(side-on) [(bpc)(bpy)(RuOO)-O-IV](+) and 8(side-on) [(bpc)(bpy)(RuOO)-O-V](2+), both low spin species, are generated by further oxidations of 6. Through an intersystem crossing they can transform to their high spin states, 9(end-on) [(bpc)(bpy)(RuOO)-O-IV](+) and 12(end-on) [(bpc)(bpy)(RuOO)-O-V](2+), respectively. Following a dissociative pathway O-2 is readily generated from both 9(end-on) and 12(end-on).

  • 49.
    Wang, Ying
    et al.
    KTH, School of Biotechnology (BIO), Theoretical Chemistry and Biology.
    Ahlquist, Mårten S. G.
    KTH, School of Biotechnology (BIO), Theoretical Chemistry and Biology.
    Mechanistic studies on proton transfer in a [FeFe] hydrogenase mimic complex2013In: Dalton Transactions, ISSN 1477-9226, E-ISSN 1477-9234, Vol. 42, no 21, p. 7816-7822Article in journal (Refereed)
    Abstract [en]

    Four different pathways for deprotonation of [(mu-pdt){Fe(CO)(3)}{Fe(CO)(kappa(2)-Me2PCH2N(Me)CH2PMe2)}] (pdt = propane-1,3-dithiolate) [1H(mu)](1+) were examined, including (1) the "Direct" deprotonation; (2) the "Indirect" deprotonation via the pendant amine N; (3) the "Indirect" deprotonation via the distal metal Fe; and (4) the "Indirect" deprotonation via the dithiolate S. Only deprotonation of the "Indirect" pathway via the pendant amine N is feasible at room temperature. The most favorable migration destination for the bridging hydride in [1H(mu)](1+) is the pendant amine N (activation energy barrier 16.1 kcal mol(-1)). Migrations to the other two possible sites including the distal metal Fe (34.6 kcal mol(-1)) and the S in the dithiolate group (41.5 kcal mol(-1)) were hindered by high proton shuttling barriers. Once the migration barriers of those three "Indirect" pathways are overcome, the following deprotonations from all three positions including the distal atom Fe, the dithiolate S and the pendant amine N, are all feasible. The results also demonstrate a large difference for deprotonation of the hydride from the terminal and bridging sites. The low energy of the virtual orbital associated with the antibonding M-H interaction of [1H(Fe)](1+) implies the high activity for the interaction with aniline.

  • 50.
    Wang, Ying
    et al.
    KTH, School of Biotechnology (BIO), Theoretical Chemistry and Biology.
    Ahlquist, Mårten S. G.
    KTH, School of Biotechnology (BIO), Theoretical Chemistry and Biology.
    Where does the water go?: A computational study on the reactivity of a ruthenium(V) oxo complex (bpc)(bpy)RuVO2014In: Physical Chemistry, Chemical Physics - PCCP, ISSN 1463-9076, E-ISSN 1463-9084, Vol. 16, p. 11182-11185Article in journal (Refereed)
    Abstract [en]

    Two possible reactive sites (the oxo site and the Ru site) for water on a high-valent ruthenium(V) oxo complex were examined. Our results suggest that the reaction on the ruthenium (via a seven coordinate intermediate) has both a lower barrier and a product with a lower free energy than the product of addition at the oxo.

12 1 - 50 of 58
CiteExportLink to result list
Permanent link
Cite
Citation style
  • apa
  • harvard1
  • ieee
  • modern-language-association-8th-edition
  • vancouver
  • Other style
More styles
Language
  • de-DE
  • en-GB
  • en-US
  • fi-FI
  • nn-NO
  • nn-NB
  • sv-SE
  • Other locale
More languages
Output format
  • html
  • text
  • asciidoc
  • rtf