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  • 1. Ambre, Ram B.
    et al.
    Daniel, Quentin
    Fan, Ting
    KTH, School of Biotechnology (BIO), Theoretical Chemistry and Biology.
    Chen, Hong
    Zhang, Biaobiao
    Wang, Lei
    Ahlquist, Marten S. G.
    Duan, Lele
    Sun, Licheng
    Molecular engineering for efficient and selective iron porphyrin catalysts for electrochemical reduction of CO2 to CO2016In: CHEMICAL COMMUNICATIONS, ISSN 1359-7345, Vol. 52, no 100, p. 14478-14481Article in journal (Refereed)
    Abstract [en]

    Iron porphyrins Fe-pE, Fe-mE, and Fe-oE were synthesized and their electrochemical behavior for CO2 reduction to CO has been investigated. The controlled potential electrolysis of Fe-mE gave exclusive 65% Faradaic efficiency (FE) whereas Fe-oE achieved quasi-quantitative 98% FE (2% H-2) for CO production.

  • 2.
    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.

  • 3.
    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.

  • 4. 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.

  • 5.
    Kagalwala, Husain
    et al.
    Univ Houston, Chem, Houston, TX USA..
    Tong, Liangpeng
    Univ Houston, Chem, Houston, TX USA..
    Zong, Ruifa
    Univ Houston, Chem, Houston, TX USA..
    Kohler, Lars
    Univ Houston, Chem, Houston, TX USA..
    Ahlquist, Martin
    Fan, Ting
    KTH.
    Gagnon, Kevin
    Lawrence Berkeley Natl Lab, Adv Light Source, Berkeley, CA USA..
    Thummel, Randolph
    Univ Houston, Chem, Houston, TX USA..
    Oxidative transformation of a Ru-bound ligand during chemically driven water oxidation2017In: Abstract of Papers of the American Chemical Society, ISSN 0065-7727, Vol. 254Article in journal (Other academic)
  • 6. Xie, H.
    et al.
    Fan, Ting
    KTH, School of Biotechnology (BIO), Theoretical Chemistry and Biology.
    Lei, Q.
    Fang, W.
    New progress in theoretical studies on palladium-catalyzed C−C bond-forming reaction mechanisms2016In: Science China Chemistry, ISSN 1674-7291, p. 1-16Article in journal (Refereed)
    Abstract [en]

    This review reports a series of mechanistic studies on Pd-catalyzed C−C cross-coupling reactions via density functional theory (DFT) calculations. A brief introduction of fundamental steps involved in these reactions is given, including oxidative addition, transmetallation and reductive elimination. We aim to provide an important review of recent progress on theoretical studies of palladium-catalyzed carbon–carbon cross-coupling reactions, including the C−C bond formation via C−H bond activation, decarboxylation, Pd(II)/Pd(IV) catalytic cycle and double palladiums catalysis.

  • 7. Xie, Hujun
    et al.
    Wang, Lihong
    Li, Yang
    Kuang, Jian
    Wu, Zunyi
    Fan, Ting
    KTH, School of Biotechnology (BIO), Theoretical Chemistry and Biology.
    Leic, Qunfang
    Fang, Wenjun
    N-Insertion reaction mechanisms of phenyl azides with a hafnium hydride complex: a quantum chemistry calculation2017In: New Journal of Chemistry, ISSN 1144-0546, E-ISSN 1369-9261, Vol. 41, no 12, p. 5007-5011Article in journal (Refereed)
    Abstract [en]

    Density functional theory (DFT) calculations were performed to investigate the detailed mechanisms for the N-insertion reaction of phenyl azides with a hafnium hydride complex. This reaction involves an intermolecular hydride transfer from the hafnium center of complex 1 (Cp2HfH2)-Hf-star to the terminal nitrogen atom of a phenyl azide. Subsequently, a 1,3 hydrogen shift from the N1 atom to the N3 atom takes place, accompanied by cleavage of the N2-N3 bond to provide amido complex 3 (Cp2HfH)-Hf-star(NHPh) and dinitrogen. A further reaction is related to the intermolecular hydride transfer from the hafnium center to the N1' atom of a second phenyl azide, followed by the formation of the final product, bis(amido) complex 9 (Cp2HfH)-Hf-star(NHPh)(2) via the liberation of the second dinitrogen, which is the rate-determining step with an overall barrier of 29.8 kcal mol(-1). Frontier molecular orbital theory analysis shows that phenyl azides are activated by nucleophilic attack by the hydride ligand, which is consistent with our previous studies of N2O activation by other transition-metal hydride complexes.

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