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  • 1. Duan, Lele
    et al.
    Bozoglian, Fernando
    Mandal, Sukanta
    Stewart, Beverly
    Stockholm University, Faculty of Science, Department of Organic Chemistry.
    Privalov, Timofei
    Stockholm University, Faculty of Science, Department of Organic Chemistry.
    Llobet, Antoni
    Sun, Licheng
    A molecular ruthenium catalyst with water-oxidation activity comparable to that of photosystem II2012In: Nature Chemistry, ISSN 1755-4330, E-ISSN 1755-4349, Vol. 4, no 5, p. 418-423Article in journal (Refereed)
    Abstract [en]

    Across chemical disciplines, an interest in developing artificial water splitting to O-2 and H-2, driven by sunlight, has been motivated by the need for practical and environmentally friendly power generation without the consumption of fossil fuels. The central issue in light-driven water splitting is the efficiency of the water oxidation, which in the best-known catalysts falls short of the desired level by approximately two orders of magnitude. Here, we show that it is possible to close that 'two orders of magnitude' gap with a rationally designed molecular catalyst [Ru(bda)(isoq)(2)] (H(2)bda = 2,2'-bipyridine-6,6'-dicarboxylic acid; isoq = isoquinoline). This speeds up the water oxidation to an unprecedentedly high reaction rate with a turnover frequency of >300 s(-1). This value is, for the first time, moderately comparable with the reaction rate of 100-400 s(-1) of the oxygen-evolving complex of photosystem II in vivo.

  • 2.
    Duan, Lele
    et al.
    Department of Chemistry, Royal Institute of Technology .
    Nyhlén, Jonas
    Stockholm University, Faculty of Science, Department of Organic Chemistry.
    Fischer, Andreas
    Department of Chemistry, Royal Institute of Technology .
    Xu, Yunhua
    Department of Chemistry, Royal Institute of Technology .
    Privalov, Timofei
    Stockholm University, Faculty of Science, Department of Organic Chemistry.
    Sun, Licheng
    Department of Chemistry, Royal Institute of Technology .
    Highly Active Mononuclear Ru Catalysts for Water Oxidation: O-O Bond Formation via Direct Radical CouplingIn: Journal of the American Chemical Society, ISSN 0002-7863, E-ISSN 1520-5126Article in journal (Refereed)
  • 3.
    Heshmat, Mojgan
    et al.
    Stockholm University, Faculty of Science, Department of Organic Chemistry.
    Privalov, Timofei
    Stockholm University, Faculty of Science, Department of Organic Chemistry.
    A Prediction of Proton-Catalyzed Hydrogenation of Ketones in Lewis Basic Solvent through Facile Splitting of Hydrogen Molecules2017In: Chemistry - A European Journal, ISSN 0947-6539, E-ISSN 1521-3765, Vol. 23, no 5, p. 1036-1039Article in journal (Refereed)
    Abstract [en]

    A ketone's carbonyl carbon is electrophilic and harbors a part of the lowest unoccupied molecular orbital of the carbonyl group, resembling a Lewis acidic center; under the right circumstances it exhibits very useful chemical reactivity, although the natural electrophilicity of the ketone's carbonyl carbon is often not strong enough on its own to produce such reactivity. Quantum chemical calculations predict that a proton shared between a ketone and the Lewis basic solvent molecule (dioxane or THF) activates carbonyl carbon to the point of enabling a facile heterolytic splitting of H-2. Proton-catalyzed hydrogenation of a ketone in Lewis basic solvent is the result. The mechanism involves the interaction of H-2 with the enhanced Lewis acidity of a carbonyl carbon and the free Lewis basic solvent molecule polarizes H-2 and enables the hydride-type attack on carbonyl carbon, which is very strongly influenced by the proton shared between a ketone and solvent. The hydride-type attack on carbon is reminiscent of the splitting of H-2 by singlet carbenes except that, in this case, a Lewis base from the surrounding environment (solvent) is necessary for polarization of H-2 and acceptance of the proton resulting from the heterolytic splitting of H-2.

  • 4.
    Heshmat, Mojgan
    et al.
    Stockholm University, Faculty of Science, Department of Organic Chemistry.
    Privalov, Timofei
    Stockholm University, Faculty of Science, Department of Organic Chemistry.
    Carbonyl Activation by Borane Lewis Acid Complexation: Transition States of H-2 Splitting at the Activated Carbonyl Carbon Atom in a Lewis Basic Solvent and the Proton-Transfer Dynamics of the Boroalkoxide Intermediate2017In: Chemistry - A European Journal, ISSN 0947-6539, E-ISSN 1521-3765, Vol. 23, no 38, p. 9098-9113Article in journal (Refereed)
    Abstract [en]

    By using transition-state (TS) calculations, we examined how Lewis acid (LA) complexation activates carbonyl compounds in the context of hydrogenation of carbonyl compounds by H-2 in Lewis basic (ethereal) solvents containing borane LAs of the type (C6F5)(3)B. According to our calculations, LA complexation does not activate a ketone sufficiently enough for the direct addition of H-2 to the O = C unsaturated bond; but, calculations indicate a possibly facile heterolytic cleavage of H-2 at the activated and thus sufficiently Lewis acidic carbonyl carbon atom with the assistance of the Lewis basic solvent (i.e., 1,4-dioxane or THF). For the solvent-assisted H-2 splitting at the carbonyl carbon atom of (C6F5)(3)B adducts with different ketones, a number of TSs are computed and the obtained results are related to insights from experiment. By using the Born-Oppenheimer molecular dynamics with the DFT for electronic structure calculations, the evolution of the (C6F5)(3)B-alkoxide ionic intermediate and the proton transfer to the alkoxide oxygen atom were investigated. The results indicate a plausible hydrogenation mechanism with a LA, that is, (C6F5)(3)B, as a catalyst, namely, 1) the step of H-2 cleavage that involves a Lewis basic solvent molecule plus the carbonyl carbon atom of thermodynamically stable and experimentally identifiable (C6F5)(3)B-ketone adducts in which (C6F5)(3)B is the Lewis acid promoter, 2) the transfer of the solvent-bound proton to the oxygen atom of the (C6F5)(3)B-alkoxide intermediate giving the (C6F5)(3)B-alcohol adduct, and 3) the S(N)2-style displacement of the alcohol by a ketone or a Lewis basic solvent molecule.

  • 5.
    Heshmat, Mojgan
    et al.
    Stockholm University, Faculty of Science, Department of Organic Chemistry.
    Privalov, Timofei
    Stockholm University, Faculty of Science, Department of Organic Chemistry.
    Computational Elucidation of a Role That Bronsted Acidification of the Lewis Acid-Bound Water Might Play in the Hydrogenation of Carbonyl Compounds with H-2 in Lewis Basic Solvents2017In: Chemistry - A European Journal, ISSN 0947-6539, E-ISSN 1521-3765, Vol. 23, no 48, p. 11489-11493Article in journal (Refereed)
    Abstract [en]

    Bronsted acidification of water by Lewis acid (LA) complexation is one of the fundamental principles in chemistry. Using transition-state calculations (TS), herein we investigate the role that Bronsted acidification of the LA-bound water might play in the mechanism of the hydrogenation of carbonyl compounds in Lewis basic solvents under non-anhydrous conditions. The potential energy scans and TS calculations were carried out with a series of eight borane LAs as well as the commonly known strong LA AlCl3 in 1,4-dioxane or THF as Lewis basic solvents. Our molecular model consists of the dative LA-water adduct with hydrogen bonds to acetone and a solvent molecule plus one additional solvent molecule that participates is the TS structure describing the cleavage of H-2 at acetone's carbonyl carbon atom. In all the molecular models applied here, acetone (O=CMe2) is the archetypical carbonyl substrate. We demonstrate that Bronsted acidification of the LA-bound water can indeed lower the barrier height of the solvent-involving H-2-cleavage at the acetone's carbonyl carbon atom. This is significant because at present it is believed that the mechanism of the herein considered reaction is described by the same mechanism regardless of whether the reaction conditions are strictly anhydrous or non-anhydrous. Our results offer an alternative to this belief that warrants consideration and further study.

  • 6.
    Heshmat, Mojgan
    et al.
    Stockholm University, Faculty of Science, Department of Organic Chemistry.
    Privalov, Timofei
    Stockholm University, Faculty of Science, Department of Organic Chemistry.
    H-2 Cleavage by Frustrated Lewis Pairs Characterized by the Energy Decomposition Analysis of Transition States: An Alternative to the Electron Transfer and Electric Field Models2018In: Journal of Physical Chemistry A, ISSN 1089-5639, E-ISSN 1520-5215, Vol. 122, no 36, p. 7202-7211Article in journal (Refereed)
    Abstract [en]

    Knowing that the Papai's electron transfer (ET) and the Grimme's electric field (EF) models draw attention to somewhat different physical aspects, we are going to systematically (re)examine interactions in the transition states (TSs) of the heterolytic H-2-cleavage by the Frustrated Lewis Pairs (FLPs). Our main vehicle is the quantitative energy decomposition analysis (EDA), a powerful method for elucidation of interactions, plus the analysis of molecular orbitals (MOs). Herein, the Lewis acid (LA) is B(C6F5)(3) and the Lewis bases (LBs) are tBu(3)P, (o-C6H4Me)(3)P, 2,6-lutidine, 2,4,6-lutidine, MeN=C(Ph)Me imine, MeN(H)-C(H)PhMe amine, THF, 1,4-dioxane, and acetone. For a series of the phosphorus-, nitrogen-, and oxygen-bearing LBs plus B(C6F5)(3), we will show that (i) neither the electrostatic nor the orbital interactions dominate but instead both are essential alongside the Pauli repulsion and (ii) the frontier molecular orbitals (FMOs) of a TS can arise not only from the push-pull molecular orbital scheme by Papai et al., which directly involves the occupied sigma and the empty sigma* MOs of H-2, but also from a more intricate but energetically more fitting orbital interactions which have escaped notice thus far.

  • 7.
    Heshmat, Mojgan
    et al.
    Stockholm University, Faculty of Science, Department of Organic Chemistry.
    Privalov, Timofei
    Stockholm University, Faculty of Science, Department of Organic Chemistry.
    Structurally Flexible Oxocarbenium/Borohydride Ion Pair: Dynamics of Hydride Transfer on the Background of Conformational Roaming2018In: Journal of Physical Chemistry A, ISSN 1089-5639, E-ISSN 1520-5215, Vol. 122, no 23, p. 5098-5106Article in journal (Refereed)
    Abstract [en]

    We apply Born-Oppenheimer molecular dynamics to the practically significant [dioxane-H(+)-acetone]-[(C6F5)(3)B-H(-)] and [Et2O-H(+)-OCPr2][(C6F5)(3)B-H(-)] ion pair intermediates. Dynamics of hydride transfer in cation/anion ion pair takes place on the background of large amplitude configurational changes. Geometry of oxocarbenium/borohydride ion pairs is flexible, meaning that we uncover significant actual structural disorder at a finite temperature. Therefore, although the starting structure can be fairly close to the configurational area of the hydride transfer transition state (TS) and despite a low potential energy barrier (ca. 1.5 kcal/mol, according to the literature), already at T approximate to 325 K the system can remain ignorant of the TS region and move round and about (roam) in the configurational space for a period of time in the range between 10 and 100 ps. This indicates structural flexibility of oxocarbenium/borohydride ion pair on apparently a flat potential energy landscape of cation/anion interaction, and this has not been taken into consideration by the free energy estimations in static considerations made thus far. The difference between the dynamics-based representation of the system versus the static representation amounts to the difference between quasi-bimolecular versus unimolecular descriptions of the hydride transfer step.

  • 8.
    Heshmat, Mojgan
    et al.
    Stockholm University, Faculty of Science, Department of Organic Chemistry.
    Privalov, Timofei
    Stockholm University, Faculty of Science, Department of Organic Chemistry.
    Surprisingly Flexible Oxonium/Borohydride Ion Pair Configurations2018In: Journal of Physical Chemistry A, ISSN 1089-5639, E-ISSN 1520-5215, Vol. 122, no 15, p. 3713-3727Article in journal (Refereed)
    Abstract [en]

    We investigate the geometry of oxonium/borohydride ion pairs [ether-H(+) ether] [LA-H(-)] with dioxane, THF, and Et2O as ethers and B(C6F5)(3) as the Lewis acid (LA). The question is about possible location of the disolvated proton [ether -H(+) -ether], with respect to the hydride of the structurally complex [LA -H(-)] anion. Using Born Oppenheimer molecular dynamics and a comparison of the potential and free energies of the optimized configurations, we show that herein considered ion pairs are much more flexible geometrically than previously thought. Conformers with different locations of cations with respect to anions are governed by a flat energy -landscape. We found a novel configuration in which oxonium is below [LA-11((-))], with respect to the direction of borane -> hydride vector, and the proton -hydride distance is ca. 6 A. With calculations of the vibrational spectra of [ether-H(+)-ether][(C6F5)(3)B-H(-)] for dioxane, THF, and Et2O as ethers, we investigate the manifestation of SSLB-type (short, strong, low -barrier) hydrogen bonding in the OHO motif of an oxonium cation.

  • 9.
    Heshmat, Mojgan
    et al.
    Stockholm University, Faculty of Science, Department of Organic Chemistry.
    Privalov, Timofei
    Stockholm University, Faculty of Science, Department of Organic Chemistry.
    Theory-Based Extension of the Catalyst Scope in the Base-Catalyzed Hydrogenation of Ketones: RCOOH-Catalyzed Hydrogenation of Carbonyl Compounds with H-2 Involving a Proton Shuttle2017In: Chemistry - A European Journal, ISSN 0947-6539, E-ISSN 1521-3765, Vol. 23, no 72, p. 18193-18202Article in journal (Refereed)
    Abstract [en]

    As an extension of the reaction mechanism describing the base-catalyzed hydrogenation of ketones according to Berkessel et al., we use a standard methodology for transition-state (TS) calculations in order to check the possibility of heterolytic cleavage of H-2 at the ketone's carbonyl carbon atom, yielding one-step hydrogenation path with involvement of carboxylic acid as a catalyst. As an extension of the catalyst scope in the base-catalyzed hydrogenation of ketones, our mechanism involves a molecule with a labile proton and a Lewis basic oxygen atom as a catalyst-for example, R-C(= O) OH carboxylic acids-so that the heterolytic cleavage of H-2 could take place between the Lewis basic oxygen atom of a carboxylic acid and the electrophilic (Lewis acidic) carbonyl carbon of a ketone/aldehyde. According to our TS calculations, protonation of a ketone/aldehyde by a proton shuttle (hydrogen bond) facilitates the hydride-type attack on the ketone's carbonyl carbon atom in the process of the heterolytic cleavage of H-2. Ketones with electron-rich and electron-withdrawing substituents in combination with a few carboxylic and amino acids-in total, 41 substrate-catalyst couples-have been computationally evaluated in this article and the calculated reaction barriers are encouragingly moderate for many of the considered substrate-catalyst couples.

  • 10.
    Heshmat, Mojgan
    et al.
    Stockholm University, Faculty of Science, Department of Organic Chemistry.
    Privalov, Timofei
    Stockholm University, Faculty of Science, Department of Organic Chemistry.
    Water and a Borohydride/Hydronium Intermediate in the Borane-Catalyzed Hydrogenation of Carbonyl Compounds with H-2 in Wet Ether: A Computational Study2018In: Journal of Physical Chemistry B, ISSN 1520-6106, E-ISSN 1520-5207, Vol. 122, no 38, p. 8952-8962Article in journal (Refereed)
    Abstract [en]

    We have computationally evaluated water as an active Lewis base (LB) and introduced the borohydride/hydronium intermediate in the mechanism of B(C6F5)(3)-catalyzed hydrogenation of carbonyl compounds with H-2 in wet/moist ether. Our calculations extend the known frustrated Lewis pair mechanism of this reaction toward the inclusion of water as the active participant in all steps. Although the definition of the zero-energy point interweaves in comparison of the scenarios with and without water, we will be able to show that (i) water (hydrogen bonded to its molecular environment) can, in principle, act as a reasonably viable LB in cooperation with the borane Lewis acid such as B(C6F5)(3) but relatively a strong borane-water complexation can be the hindering factor; (ii) the herein-proposed borohydride/hydronium intermediates with the hydronium cation having three OH center dot center dot center dot ether hydrogen bonds or a combination of the OH center dot center dot center dot ether/OH center dot center dot center dot ketone hydrogen bonds appear to be as valid as the previously considered borohydride/oxonium or borohydride/oxocarbenium intermediates; (iii) the proton-coupled hydride transfer from the borohydride/hydronium to a ketone (acetone) has a reasonably low barrier. Our findings could be useful for better mechanistic understanding and further development of the aforementioned reaction.

  • 11.
    Karlsson, Erik A.
    et al.
    Stockholm University, Faculty of Science, Department of Organic Chemistry.
    Privalov, Timofei
    Stockholm University, Faculty of Science, Department of Organic Chemistry.
    Oxidation of ethers, alcohols, and unfunctionalized hydrocarbons by the methyltrioxorhenium/H2O2 system: a computational study on catalytic C-H bond activation2009In: Abstracts of Papers, 238th ACS National Meeting, Washington, DC, United States, August 16-20, 2009, Washington DC: American Chemical Society , 2009Conference paper (Other academic)
  • 12.
    Karlsson, Erik A.
    et al.
    Stockholm University, Faculty of Science, Department of Organic Chemistry.
    Privalov, Timofei
    Stockholm University, Faculty of Science, Department of Organic Chemistry.
    Oxidation of ethers, alcohols, and unfunctionalized hydrocarbons by the methyltrioxorhenium/H2O2 system: a computational study on catalytic C-H bond activation2009In: Chemistry - A European Journal, ISSN 0947-6539, E-ISSN 1521-3765, Vol. 15, no 8, p. 1862-1869Article in journal (Refereed)
    Abstract [en]

    A concerted mechanism that does not involve an ionic intermediate was revealed by a DFT study on oxidation of ethers, alcohols, and unfunctionalized hydrocarbons by methyltrioxorhenium/H2O2. Instead, CH insertion occurs through hydride transfer and then turns into a hydroxide transfer/rebound in a concerted fashion. The picture shows selected frames from an intrinsic reaction coordinate scan from the transition state to the product for the oxidation of cis-1,2-dimethylcyclohexane.

    The potential-energy surfaces (PESs) of methyltrioxorhenium (MTO)-catalyzed CH insertion reactions in the presence of hydrogen peroxide were studied by accurate DFT methods for a series of substrates including unsaturated hydrocarbons, an ether, and an alcohol. Based on the comprehensive analysis of transition states and intrinsic reaction coordinate (IRC) scans, CH insertion was found to proceed by a concerted mechanism that does not require, as previously thought, a side-on or a butterfly-like transition state. We found that a typical transition state follows requirements of the SN2 reaction instead. Furthermore, by exploring the PESs of several CH insertion reactions, we discovered that no ionic intermediate is formed even in a polar solvent. The latter was modeled within the self-consistent reaction field approach in a polarizable continuum model (PB-SCRF/PCM). According to our study, CH insertion occurs by a concerted but highly asynchronous mechanism that first proceeds by hydride transfer and then turns into hydroxide transfer/rebound. For the oxidation of alcohols, CH bond cleavage occurs without formation of alkoxide intermediates on the dominant pathway. The computed deuterium kinetic isotope effect of 2.9 for the hydride-transfer transition state for alcohol oxidation is in good agreement with the experimental kH/kD ration of 3.2 reported by Zauche and Espenson. As confirmed by IRC and PES scans in different solvents, the OH-rebound phase of the CH insertion pathway demonstrates strong similarities with the rebound mechanism that was previously proposed for cytochrome P450 and metalloporphyrin-catalyzed oxidations.

  • 13.
    Kärkäs, Markus D.
    et al.
    Stockholm University, Faculty of Science, Department of Organic Chemistry.
    Åkermark, Torbjörn
    Stockholm University, Faculty of Science, Department of Organic Chemistry.
    Johnston, Eric V.
    Stockholm University, Faculty of Science, Department of Organic Chemistry.
    Karim, Shams R.
    Stockholm University, Faculty of Science, Department of Organic Chemistry.
    Laine, Tanja M.
    Stockholm University, Faculty of Science, Department of Organic Chemistry.
    Lee, Bao-Lin
    Stockholm University, Faculty of Science, Department of Organic Chemistry.
    Åkermark, Tobias
    Stockholm University, Faculty of Science, Department of Materials and Environmental Chemistry (MMK).
    Privalov, Timofei
    Stockholm University, Faculty of Science, Department of Organic Chemistry.
    Åkermark, Björn
    Stockholm University, Faculty of Science, Department of Organic Chemistry.
    Water Oxidation by Single-Site Ruthenium Complexes: Using Ligands as Redox and Proton Transfer Mediators2012In: Angewandte Chemie International Edition, ISSN 1433-7851, E-ISSN 1521-3773, Vol. 51, no 46, p. 11589-11593Article in journal (Refereed)
  • 14.
    Nyhlén, Jonas
    et al.
    Stockholm University, Faculty of Science, Department of Organic Chemistry.
    Boschloo, Gerrit
    Hagfeldt, Anders
    Kloo, Lars
    Privalov, Timofei
    Stockholm University, Faculty of Science, Department of Organic Chemistry.
    Regeneration of oxidized organic photo-sensitizers in Grätzel solar cells: quantum-chemical portrait of a general mechanism2010In: ChemPhysChem, ISSN 1439-4235, E-ISSN 1439-7641, Vol. 11, no 9, p. 1858-1862Article in journal (Refereed)
  • 15.
    Nyhlén, Jonas
    et al.
    Stockholm University, Faculty of Science, Department of Organic Chemistry.
    Duan, Lele
    Åkermark, Björn
    Stockholm University, Faculty of Science, Department of Organic Chemistry.
    Sun, Licheng
    Privalov, Timofei
    Stockholm University, Faculty of Science, Department of Organic Chemistry.
    Evolution of O2 in a seven-coordinate RuIV dimer complex with a [HOHOH]- bridge: A computational study2010In: Angewandte Chemie International Edition, ISSN 1433-7851, E-ISSN 1521-3773, Vol. 49, no 10, p. 1773-1777Article in journal (Refereed)
  • 16.
    Nyhlén, Jonas
    et al.
    Stockholm University, Faculty of Science, Department of Organic Chemistry.
    Privalov, Timofei
    Stockholm University, Faculty of Science, Department of Organic Chemistry.
    "Frustration" of orbital interactions in Lewis base/Lewis acid adducts: a computational study of H2 uptake by phosphanylboranes R2P=BR'22009In: European Journal of Inorganic Chemistry, ISSN 1434-1948, E-ISSN 1099-1948, no 19, p. 2759-2764Article in journal (Refereed)
    Abstract [en]

    The reaction of mol. hydrogen with phosphanylboranes R2P:BR'2 (1) is systematically studied by d. functional theory calcns. and second order Moller-Plesset perturbation theory. The potential energy barriers and the exothermicity of H2 uptake are reported for a series of phosphanylboranes with different electron-donating and -withdrawing groups bound to phosphorus and boron. Systematic MO anal. reveals that the "frustration" between boron and phosphorus can be increased by modifying the substituents, and thus, AO interactions could be exploited in order to increase the reactivity of 1. Addnl., authors found a correlation between the potential energy barrier for H2 uptake and the energy of the HOMO of the P:B complex, which could be relevant for the prediction of the properties of candidate compds. for H2 activation and therefore useful for the development of such systems. [on SciFinder(R)]

  • 17.
    Nyhlén, Jonas
    et al.
    Stockholm University, Faculty of Science, Department of Organic Chemistry.
    Privalov, Timofei
    Stockholm University, Faculty of Science, Department of Organic Chemistry.
    Hydrogenation of carbon-heteroatom unsaturated bonds: An assessment of consistency of density functional methods2010In: Journal of Molecular Catalysis A: Chemical, ISSN 1381-1169, E-ISSN 1873-314X, Vol. 324, no 1-2, p. 97-103Article in journal (Refereed)
    Abstract [en]

    Hydrogenation of unsaturated carbon-heteroatom bonds, C = X, is the general process for which we assess consistency of quantum chemical calculations in the context of B(C6F5)3-catalyzed reduction of imines with H2. According to the mechanism of the reaction, computational uncertainty of energies of hydrogenation of imines, i.e. the difference between results obtained with different methods, contributes to method related uncertainties of the computed relative energies of key H2-activating species. For this reason, it is desirable to know the magnitude of methodological dependence/uncertainty of energies of hydrogenation. Calculations were performed with a number of different density functionals, such as M05-2X, M06-2X, B3LYP, B3PW91, BH&HLYP, MPW1K, MPW1PW91, HCTH407 and PBE, on a number of relevant imines and ketones/aldehydes. Additionally, second order Møller-Plesset perturbation theory was also evaluated. The results quantitatively reveal the manner in which the form of a method affects the calculated energy change and that there is substantial difference between results obtained with different methods even for structurally simple species.

  • 18.
    Nyhlén, Jonas
    et al.
    Stockholm University, Faculty of Science, Department of Organic Chemistry.
    Privalov, Timofei
    Stockholm University, Faculty of Science, Department of Organic Chemistry.
    On the possibility of catalytic reduction of carbonyl moieties with tris(pentafluorophenyl)borane and H2: a computational study2009In: Dalton Transactions, ISSN 1477-9226, E-ISSN 1477-9234, no 29, p. 5780-5786Article in journal (Refereed)
    Abstract [en]

    The study thoroughly examines the Gibbs free energy surfaces of a new mechanism for redn. of ketones/aldehydes by tris(pentafluorophenyl)borane (1) and H2. Key elements of the proposed mechanism are the proton and the hydride transfer steps similar to Stephan's catalytic redn. of imines by 1. The proton is transferred to the ketone/aldehyde in the process of H2 cleavage by the carbonyl-borane couple and the hydride is transferred in a nucleophilic attack on the carbonyl carbon by the hydridoborate in the ionic pair, [HOCRR']+[HB(C6F5)3]-. The in solvent Gibbs free energy barriers of H2 splitting by adducts of B(C6F5)3 with acetone, acetophenone and benzaldehyde are predicted to be in the range of 24.5 ± 2.5 kcal mol-1, which corresponds to potential energy barriers in the range of 17.0 ± 2.0 kcal mol-1. Significantly lower barrier of H2 activation is predicted in cases of bulky ketones such as 2,2,4,4-tetramethylpentan-3-one. With respect to the hydridoborate intermediate, the nucleophilic attack on the activated carbon is predicted to have a relatively low barrier for the sterically unhindered substrates, while this barrier is considerably higher for the sterically encumbered substrates. Since the formation of the hydridoborate intermediates is found to be endothermic, the transition state of the nucleophilic attack is the highest point of the computed energy profile for all tested substrates. Overall, according to in solvent d. function calcns. the proposed redn. of "compact" ketones/aldehydes by 1 and H2 is allowed both thermodynamically and kinetically at elevated temp., but it is expected to be slower and more substrate specific than the corresponding redn. of imines. [on SciFinder(R)]

  • 19.
    Nyhlén, Jonas
    et al.
    Stockholm University, Faculty of Science, Department of Organic Chemistry.
    Privalov, Timofei
    Stockholm University, Faculty of Science, Department of Organic Chemistry.
    Bäckvall, Jan-Erling
    Stockholm University, Faculty of Science, Department of Organic Chemistry.
    Racemization of alcohols catalyzed by [RuCl(CO)25-pentaphenylcyclopentadienyl)] – Mechanistic insights from theoretical modeling2009In: Chemistry - A European Journal, ISSN 0947-6539, E-ISSN 1521-3765, Vol. 15, no 21, p. 5220-5229Article in journal (Refereed)
    Abstract [en]

    Two possible pathways of inner-sphere racemization of sec-alcohols by using the [RuCl(CO)(2)(eta(5)-pentaphenylcyclopentadienyl)] catalyst (1) have been thoroughly investigated by means of density function calculations. To be able to racemize alcohols, catalyst 1 needs to have a free coordination site on the metal. This can be achieved either by a eta(5)-->eta(3) ring slippage or by dissociation of a carbon monoxide (CO) ligand. The eta(5)-->eta(3) ring-slip pathway was found to have a high potential energy barrier, 42 kcal mol(-1), which can be explained by steric congestion in the transition state. On the other hand, CO dissociation to give a 16-electron complex has a barrier of only 22.6 kcal mol(-1). We have computationally discovered a mechanism involving CO participation that does not require eta(5)-->eta(3) ring slippage. The key features of this mechanism are 1) CO-assisted exchange of chloride for alkoxide, 2) alcohol-alkoxide exchange, and 3) generation of an active 16-electron complex through CO dissociation with subsequent beta-hydride elimination as the racemization step. We have found a low-energy pathway for reaction of 1 with potassium tert-butoxide and a pathway for fast alkoxide exchange with interaction between the incoming/leaving alcohol and one of the two CO ligands. We predict that dissociation of a Ru-bound CO ligand does not occur in these exchange reactions. Dissociation of one of the two Ru-bound CO ligands has been found necessary only at a later stage of the reaction. Though this barrier is still quite high, our results indicate that it is not necessary to cross the CO dissociation barrier for the racemization of each new alcohol. Thus, the dissociation of a CO ligand is interpreted as a rate-limiting reaction step in order to create a catalytically active 16-electron complex.

  • 20.
    Privalov, Timofei
    Stockholm University, Faculty of Science, Department of Organic Chemistry.
    Hydrogenation of imines by phosphonium borate zwitterions: a theoretical study2009In: Dalton Transactions, ISSN 1477-9226, E-ISSN 1477-9234, Vol. -, no 8, p. 1321-1327Article in journal (Refereed)
  • 21.
    Privalov, Timofei
    Stockholm University, Faculty of Science, Department of Organic Chemistry.
    On the possibility of conversion of alcohols to ketones and aldehydes by phosphinoboranes R2PBR'R'': a computational study2009In: Chemistry - A European Journal, ISSN 0947-6539, E-ISSN 1521-3765, Vol. 15, no 8, p. 1825-1829Article in journal (Refereed)
  • 22.
    Privalov, Timofei
    Stockholm University, Faculty of Science, Department of Organic Chemistry.
    The role of amine-B(C6F5)3 adducts in the catalytic reduction of imines with H2: a computational study2009In: European Journal of Inorganic Chemistry, ISSN 1434-1948, E-ISSN 1099-1948, no 15, p. 2229-2237Article in journal (Refereed)
  • 23.
    Privalov, Timofei
    et al.
    Stockholm University, Faculty of Science, Department of Organic Chemistry.
    Boschloo, Gerrit
    Hagfeldt, Anders
    Svensson, Per H.
    Kloo, Lars
    A study of the interactions between I-/I3- redox , mediators amd organometallic sensitizing dyes in solar cells2009In: The Journal of Physical Chemistry C, ISSN 1932-7447, E-ISSN 1932-7455, Vol. 113, no 2, p. 783-790Article in journal (Refereed)
  • 24.
    Privalov, Timofei
    et al.
    Stockholm University, Faculty of Science, Department of Organic Chemistry.
    Åkermark, Björn
    Stockholm University, Faculty of Science, Department of Organic Chemistry.
    Sun, Licheng
    The O-O Bonding in Water Oxidation: the Electronic Structure Portrayal of a Concerted Oxygen Atom-Proton Transfer Pathway2011In: Chemistry - A European Journal, ISSN 0947-6539, E-ISSN 1521-3765, Vol. 17, no 30, p. 8313-8317Article in journal (Refereed)
  • 25. Pu, Maoping
    et al.
    Heshmat, Mojgan
    Stockholm University, Faculty of Science, Department of Organic Chemistry.
    Privalov, Timofei
    Stockholm University, Faculty of Science, Department of Organic Chemistry.
    Liberation of H-2 from (o-C6H4Me)(3)P-H(+) + H(-)-B(p-C6F4H)(3) ion-pair: A transition-state in the minimum energy path versus the transient species in Born-Oppenheimer molecular dynamics2017In: Journal of Chemical Physics, ISSN 0021-9606, E-ISSN 1089-7690, Vol. 147, no 1, article id 014303Article in journal (Refereed)
    Abstract [en]

    Using Born-Oppenheimer molecular dynamics (BOMD) with density functional theory, transition-state (TS) calculations, and the quantitative energy decomposition analysis (EDA), we examined the mechanism of H-2-liberation from LB-H(+) + H(-)-LA ion-pair, 1, in which the Lewis base (LB) is (o-C6H4Me)(3)P and the Lewis acid (LA) is B(p-C6F4H)(3). BOMD simulations indicate that the path of H-2 liberation from the ion-pair 1 goes via the short-lived transient species, LB center dot center dot center dot H(2 center dot center dot center dot)LA, which are structurally reminiscent of the TS-structure in the minimum-energy-path describing the reversible reaction between H-2 and (o-C6H4Me)(3)P/B(p-C6F4H)(3) frustrated Lewis pair (FLP). With electronic structure calculations performed on graphics processing units, our BOMD data-set covers more than 1 ns of evolution of the ion-pair 1 at temperature T approximate to 400 K. BOMD simulations produced H-2-recombination events with various durations of H-2 remaining fully recombined as a molecule within a LB/LA attractive pocket-from very short vibrational-time scale to time scales in the range of a few hundred femtoseconds. With the help of perturbational approach to trajectory-propagation over a saddle-area, we directly examined dynamics of H-2-liberation. Using EDA, we elucidated interactions between the cationic and anionic fragments in the ion-pair 1 and between the molecular fragments in the TS-structure. We have also considered a model that qualitatively takes into account the potential energy characteristics of H-H recombination and H-2-release plus inertia of molecular motion of the (o-C6H4Me)(3)P/B(p-C6F4H)(3) FLP.

  • 26.
    Pu, Maoping
    et al.
    Stockholm University, Faculty of Science, Department of Organic Chemistry.
    Privalov, Timofei
    Stockholm University, Faculty of Science, Department of Organic Chemistry.
    Ab initio dynamics trajectory study of the heterolytic cleavage of H2 by a Lewis acid [B(C6F5)3] and a Lewis base [P(tBu)3]2013In: Journal of Chemical Physics, ISSN 0021-9606, E-ISSN 1089-7690, Vol. 138, no 15, article id 154305Article in journal (Refereed)
    Abstract [en]

    Activation of H-2 by a frustrated Lewis pair (FLP) composed of B(C6F5)(3) and P(tBu)(3) species has been explored with high level direct ab initio molecular dynamics (AIMD) simulations at finite temperature (T = 300 K) in gas phase. The initial geometrical conditions for the AIMD trajectory calculations, i.e., the near attack conformations of FLP + H-2, were devised using the host-guest model in which suitable FLP conformations were obtained from the dynamics of the B(C6F5)(3)/P(tBu)(3) pair in gas phase. AIMD trajectory calculations yielded microscopic insight into effects which originate from nuclear motion in the reacting complex, e. g., the alternating compression/elongation of the boron-phosphorous distance and the change of the pyramidality of boron in B(C6F5)(3). The ensemble averaged trajectory analysis has been compared with the minimum energy path (MEP) description of the reaction. Similar to MEP, AIMD shows that an attack of the acid/base pair on the H-H bond gives rise to the polarization of the H-2 molecule and as a consequence generates a large dipole moment of the reacting complex. The MEP and AIMD portrayals of the reaction are fundamentally different in terms of the magnitude of the motion of nuclei in B(C6F5)(3) and P(tBu)(3) during the H-2 cleavage. In the AIMD trajectory simulations, geometries of B(C6F5)(3) and P(tBu)(3) appear as nearly frozen on the short time scale of the H-2 cleavage. This is contrary to the MEP picture. Several of the concepts which arise from this work, e. g., separation of time scales of nuclear motion and the time-dependence of the donor-acceptor interactions in the reacting complex, are important for the understanding of chemical reactivity and catalysis.

  • 27.
    Pu, Maoping
    et al.
    Stockholm University, Faculty of Science, Department of Organic Chemistry.
    Privalov, Timofei
    Stockholm University, Faculty of Science, Department of Organic Chemistry.
    Ab Initio Molecular Dynamics Study of Hydrogen Cleavage by a Lewis Base [tBu(3)P] and a Lewis Acid [B(C6F5)(3)] at the Mesoscopic Level-Dynamics in the Solute-Solvent Molecular Clusters2014In: ChemPhysChem, ISSN 1439-4235, E-ISSN 1439-7641, Vol. 15, no 17, p. 3714-3719Article in journal (Refereed)
    Abstract [en]

    With the help of state-of-the-art ab initio molecular dynamics methods, we investigated the reaction pathway of the {tBu(3)P + H-2 + B(C6F5)(3)} system at the mesoscopic level. It is shown that: i) the onset of H-2 activation is at much larger boronphosphorus distances than previously thought; ii) the system evolves to the product in a roaming-like fashion because of quasi-periodic nuclear motion along the asymmetric normal mode of PHHB fragment; iii) transient configurations of a certain type are present despite structural interference from the solvent; iv) transient-state configurations with sub-picosecond lifetime have potentially interesting infrared activity in the organic solvent (toluene) as well as in the gas phase. The presented results should be helpful for future experimental and theoretical studies of frustrated Lewis pair (FLP) activity.

  • 28.
    Pu, Maoping
    et al.
    Stockholm University, Faculty of Science, Department of Organic Chemistry.
    Privalov, Timofei
    Stockholm University, Faculty of Science, Department of Organic Chemistry.
    Ab initio molecular dynamics with explicit solvent discovers a two-step pathway in the Frustrated Lewis Pair reactionIn: Chemistry - A European Journal, ISSN 0947-6539, E-ISSN 1521-3765Article in journal (Refereed)
  • 29.
    Pu, Maoping
    et al.
    Stockholm University, Faculty of Science, Department of Organic Chemistry.
    Privalov, Timofei
    Stockholm University, Faculty of Science, Department of Organic Chemistry.
    Ab Initio Molecular Dynamics with Explicit Solvent Reveals a Two-Step Pathway in the Frustrated Lewis Pair Reaction2015In: Chemistry - A European Journal, ISSN 0947-6539, E-ISSN 1521-3765, Vol. 21, no 49, p. 17708-17720Article in journal (Refereed)
    Abstract [en]

    The role solvent plays in reactions involving frustrated Lewis pairs (FLPs)-for example, the stoichiometric mixture of a bulky Lewis acid and a bulky Lewis base-still remains largely unexplored at the molecular level. For a reaction of the phosphorus/boron FLP and dissolved CO2 gas, first principles (Born-Oppenheimer) molecular dynamics with explicit solvent reveals a hitherto unknown two-step reaction pathway-one that complements the concerted (one-step) mechanism known from the minimum-energy-path calculations. The rationalization of the discovered reaction pathway-that is, the stepwise formation of P-C and O-B bonds-is that the environment (typical organic solvents) stabilizes an intermediate which results from nucleophilic attack of the phosphorus Lewis base on CO2. This finding is significant because presently the concerted reaction-path paradigm predominates in the rationalization of FLP reactivity. Herein we point out how to attain experimental proof of our results.

  • 30.
    Pu, Maoping
    et al.
    Stockholm University, Faculty of Science, Department of Organic Chemistry.
    Privalov, Timofei
    Stockholm University, Faculty of Science, Department of Organic Chemistry.
    Binding of CO2 by a Mes(2)PCH(2)CH(2)B(C6F5)(2) Species: An Involvement of the Ground State Species in a Low-Energy Pathway2013In: Chemistry - A European Journal, ISSN 0947-6539, E-ISSN 1521-3765, Vol. 19, no 49, p. 16512-16517Article in journal (Refereed)
  • 31.
    Pu, Maoping
    et al.
    Stockholm University, Faculty of Science, Department of Organic Chemistry.
    Privalov, Timofei
    Stockholm University, Faculty of Science, Department of Organic Chemistry.
    Chemistry of Intermolecular Frustrated Lewis Pairs in Motion: Emerging Perspectives and Prospects2015In: Israel Journal of Chemistry, ISSN 0021-2148, Vol. 55, no 2, p. 179-195Article, review/survey (Refereed)
    Abstract [en]

    This feature article describes the chemistry in motion of frustrated Lewis pairs (FLPs). With state-of-the-art ab initio molecular dynamics (AIMD) simulations supplemented by minimum energy path (MEP) and potential energy surface (PES) calculations, we examine the binding of CO2 and the heterolytic cleavage of H-2 by a Lewis base (LB), tBu(3)P, and a Lewis acid (LA), B(C6F5)(3). We strive to uncover and understand mechanistic implications of the physical laws that govern the behavior of a LB and a LA when they react with a third species (e.g., CO2 or H-2) at finite temperature. The approximation that we necessarily must make at present is to forgo the quantization of the movement of atoms in favor of the Born-Oppenheimer molecular dynamics (BOMD), which unfold according to the classical (Newton's) laws of motion. However, strict quantum chemical theory is used to compute all of the forces that govern the dynamics of the macromolecular FLP system. Using physical reasoning and innovative computer simulations, we show that multi-scale motion is the predominant mechanistic aspect in reactions of the tBu(3)P/B(C6F5)(3) FLP, as well as, conceivably, those of other similar intermolecular FLPs. Insight achieved thus far leads to a novel activity model for intermolecular FLPs and specific predictions, which could be useful for future experimental and theoretical studies of FLP and other chemistries.

  • 32.
    Pu, Maoping
    et al.
    Stockholm University, Faculty of Science, Department of Organic Chemistry.
    Privalov, Timofei
    Stockholm University, Faculty of Science, Department of Organic Chemistry.
    How Frustrated Lewis Acid/Base Systems Pass through Transition-State Regions: H-2 Cleavage by [tBu(3)P/B(C6F5)(3)]2014In: ChemPhysChem, ISSN 1439-4235, E-ISSN 1439-7641, Vol. 15, no 14, p. 2936-2944Article in journal (Refereed)
    Abstract [en]

    We investigate the transition-state (TS) region of the potential energy surface (PES) of the reaction tBu(3)P+H-2 +B(C6F5)(3)-> tBu(3)P-H(+)+H(-)-B(C6F5)(3) and the dynamics of the TS passage at room temperature. Owing to the conformational inertia of the phosphane center dot center dot center dot borane pocket involving heavy tBu(3)P and B(C6F5)(3) species and features of the PES E(P center dot center dot center dot H, B center dot center dot center dot H vertical bar B center dot center dot center dot P) as a function of P center dot center dot center dot H, B center dot center dot center dot H, and B center dot center dot center dot P distances, a typical reactive scenario for this reaction is a trajectory that is trapped in the TS region for a period of time (about 350 fs on average across all calculated trajectories) in a quasi-bound state (scattering resonance). The relationship between the timescale of the TS passage and the effective conformational inertia of the phosphane center dot center dot center dot borane pocket leads to a prediction that isotopically heavier Lewis base/Lewis acid pairs and normal counterparts could give measurably different reaction rates. Herein, the predicted quasi-bound state could be verified in molecular collision experiments involving femtosecond spectroscopy.

  • 33.
    Pu, Maoping
    et al.
    Stockholm University, Faculty of Science, Department of Organic Chemistry.
    Privalov, Timofei
    Stockholm University, Faculty of Science, Department of Organic Chemistry.
    Multiple-Pathways of Carbon Dioxide Binding by a Lewis Acid [B(C6F5)(3)] and a Lewis Base [P(tBu)(3)]: The Energy Landscape Perspective2014In: International Journal of Quantum Chemistry, ISSN 0020-7608, E-ISSN 1097-461X, Vol. 114, no 4, p. 289-294Article in journal (Refereed)
    Abstract [en]

    Using the reaction-relevant two-dimensional potential energy surface, an accurate reaction-pathway mapping and ab inito molecular dynamics, it is shown that CO2 capture by P(tBu)(3) and B(C6F5)(3) species has many nearly degenerate reaction-routes to take. The explanation of that is in the topography of the transition state (saddle) area. An ensemble of asynchronous reaction-routes of CO2 binding is described in fine detail.

  • 34.
    Pu, Maoping
    et al.
    Stockholm University, Faculty of Science, Department of Organic Chemistry.
    Privalov, Timofei
    Stockholm University, Faculty of Science, Department of Organic Chemistry.
    Uncovering the Role of Intra- and Intermolecular Motion in Frustrated Lewis Acid/Base Chemistry: Ab Initio Molecular Dynamics Study of CO2 Binding by Phosphorus/Boron Frustrated Lewis Pair [tBu(3)P/B(C6F5)(3)]2014In: Inorganic Chemistry, ISSN 0020-1669, E-ISSN 1520-510X, Vol. 53, no 9, p. 4598-4609Article in journal (Refereed)
    Abstract [en]

    The role of the intra- and intermolecular motion, i.e., molecular vibrations and the relative motion of reactants, remains largely unexplored in the frustrated Lewis acid/base chemistry. Here, we address the issue with the ab initio molecular dynamics (AIMD) study of CO2 binding by a Lewis acid (LA) and a Lewis base (LB), i.e., tBu(3)P + CO2 + B(C6F5)(3) -> tBu(3)P-C(O)O-B(C6F5)(3) ([1]). Reasonably large ensemble of AIMD trajectories propagated at 300 K from structures in the saddle region as well as trajectories propagated directly from the reactants region revealed an effect arising from significant recrossing of the saddle area. The effect is that transient complexes composed of weakly interacting reactants nearly cease to progress along the segment of the minimum energy pathway (MEP) at the saddle region for a (subpicosecond) period of time during which the dominant factor is the light-to-heavy type of relative motion of the vibrating reactants, i.e., the bouncing-like movement of CO2 with respect to much heavier phosphine and borane as main contributor to the mode that is perpendicular to the MEP-direction. In terms of how P...C and B...O distances change with time, the roaming-like patterns of typical AIMD trajectories, reactive and nonreactive alike, extend far beyond the saddle region. In addition to the dynamical portrayal of [1], we provide the energy-landscape perspective that takes into account the hierarchy of time scales. The verifiable implication of the effect found here is that the isotopically substituted (heavier) LB/LA pair should be less reactive that the normal and thus lighter counterpart.

  • 35.
    Stewart, Beverly
    et al.
    Stockholm University, Faculty of Science, Department of Organic Chemistry.
    Nyhlén, Jonas
    Stockholm University, Faculty of Science, Department of Organic Chemistry.
    Martin-Matute, Belén
    Stockholm University, Faculty of Science, Department of Organic Chemistry.
    Bäckvall, Jan-E.
    Stockholm University, Faculty of Science, Department of Organic Chemistry.
    Privalov, Timofei
    Stockholm University, Faculty of Science, Department of Organic Chemistry.
    A computational study of the CO dissociation in cyclopentadienyl ruthenium complexes relevant to the racemization of alcohols2013In: Dalton Transactions, ISSN 1477-9226, E-ISSN 1477-9234, Vol. 42, no 4, p. 927-934Article in journal (Refereed)
    Abstract [en]

    The formation of an active 16-electron ruthenium sec-alkoxide complex via loss of the CO ligand is an important step in the mechanism of the racemization of sec-alcohols by (eta(5)-Ph5C5) Ru(CO)(2)X ruthenium complexes with X = Cl and OtBu. Here we show with accurate DFT calculations the potential energy profile of the CO dissociation pathway for a series of relevant (eta(5)-Ph5C5) Ru(CO) 2X complexes, where X = Cl, OtBu, H and (COOBu)-Bu-t. We have found that the CO dissociation energy increases in the following order: OtBu (lowest), Cl, COOtBu and H (highest). Using the distance between ruthenium and C-CO, r = Ru-C-CO, as a constraint, and by optimizing all other degrees of freedom for a range of Ru-CO distances, we obtained relative energies, Delta E(r) and geometries of a sufficient number of transient structures with the elongated Ru-CO bond up to r = 3.4 angstrom. Our calculations provide a quantitative understanding of the CO ligand dissociation in (eta(5)-Ph5C5) Ru(CO)(2)Cl and (eta(5)-Ph5C5) Ru(CO) 2(OtBu) complexes, which is relevant to the mechanism of their catalytic activity in the racemization of alcohols. We recently reported that exchange of the CO ligand by isotopically labeled (CO)-C-13 in the Ru-(OBu)-Bu-t complex occurs twenty times faster than that in the Ru-Cl complex. This corresponds to a difference of 1.8 kcal mol(-1) in the CO dissociation energy (at room temperature). This is in very good agreement with the calculated difference between the two potential energy curves for Ru-OtBu and Ru-Cl complexes, which is about 1.8-2 kcal mol(-1) around the corresponding transition states of the CO dissociation. The calculated difference in the total energy for CO dissociation in (eta(5)-Ph5C5) Ru(CO)(2)X complexes is related to the stabilization provided by the X group in the final 16-electron complexes, which are formed via product-like transition states. In addition to the calculated transition states of CO dissociation in Ru-OtBu and Ru-Cl complexes, the calculated transient structures with the elongated Ru-CO bond provide insight into how the geometry of the ruthenium complex with a potent heteroatom donor group (X) gradually changes when one of the COs is dissociating.

  • 36. Tong, Lianpeng
    et al.
    Duan, Lele
    Xu, Yunhua
    Privalov, Timofei
    Stockholm University, Faculty of Science, Department of Organic Chemistry.
    Sun, Licheng
    Structural Modifications of Mononuclear Ruthenium Complexes: A Combined Experimental and Theoretical Study on the Kinetics of Ruthenium-Catalyzed Water Oxidation2011In: Angewandte Chemie International Edition, ISSN 1433-7851, E-ISSN 1521-3773, Vol. 50, no 2, p. 445-449Article in journal (Refereed)
  • 37. Wang, Lei
    et al.
    Duan, Lele
    Stewart, Beverly
    Stockholm University, Faculty of Science, Department of Organic Chemistry.
    Pu, Maoping
    Stockholm University, Faculty of Science, Department of Organic Chemistry.
    Liu, Jianhui
    Privalov, Timofei
    Stockholm University, Faculty of Science, Department of Organic Chemistry.
    Sun, Licheng
    Toward Controlling Water Oxidation Catalysis: Tunable Activity of Ruthenium Complexes with Axial Imidazole/DMSO Ligands2012In: Journal of the American Chemical Society, ISSN 0002-7863, E-ISSN 1520-5126, Vol. 134, no 45, p. 18868-18880Article in journal (Refereed)
    Abstract [en]

    Using the combinations of imidazole and dimethyl :sulfoxide (DMSO) as axial ligands and 2,2'-bipyridine-6,6'-dicarboxylate (bda) as the equatorial ligand, we have synthesized six novel ruthenium complexes with noticeably different activity as water oxidation catalysts (WOCs). In four C-s symmetric Ru-II(kappa(3)-bda)(DMSO)L-2 complexes L = imidazole (1), N-methylimidazole (2), 5-methylimidazole (3), and 5-bromo-N-methylimidazole (4). Additionally, in two C-2v symmetric Ru-II(kappa(4)-bda)L-2 complexes L = 5-nitroimidazole (5) and 5-bromo-N-methylimidazole (6), that is, fully equivalent axial imidazoles. A detailed characterization of all complexes and the mechanistic investigation of the catalytic water oxidation have been carried out with a number of experimental techniques, that is, kinetics, electrochemistry and high resolution mass spectrometry (HR-MS), and density functional theory (DFT) calculations. We have observed the in situ formation: of a Ru-II-complex with the accessible seventh coordination position. The measured catalytic activities and kinetics of complex 1-6 revealed details about an important structure activity relation: the connection between the nature of axial ligands in the combination and either the increase or decrease of the catalytic activity. In particular, an axial DMSO group substantially increases the turnover frequency of WOCs reported in article, with the ruthenium-complex having one axial 5-bromo-N-methylimidazole and one axial DMSO: (4), we have obtained a high initial turnover frequency of similar to 180 s(-1). DFT modeling Of the binuclear reaction pathway of the O-O bond formation in catalytic Water oxidation further corroborated the concept of the mechanistic significance of the axial ligands and rationalized the experimentally observed difference in the activity of complexes with imidazole/DMSO and imidazole/imidazole combinations of axial ligands.

  • 38.
    Åberg, Jenny B.
    et al.
    Stockholm University, Faculty of Science, Department of Organic Chemistry.
    Nyhlén, Jonas
    Stockholm University, Faculty of Science, Department of Organic Chemistry.
    Martín-Matute, Belén
    Stockholm University, Faculty of Science, Department of Organic Chemistry.
    Privalov, Timofei
    Stockholm University, Faculty of Science, Department of Organic Chemistry.
    Bäckvall, Jan-Erling
    Stockholm University, Faculty of Science, Department of Organic Chemistry.
    CO Assistance in ligand exchange of a ruthenium racemization catalyst: identification of an acyl intermediate2009In: Journal of the American Chemical Society, ISSN 0002-7863, E-ISSN 1520-5126, Vol. 131, no 27, p. 9500-9501Article in journal (Refereed)
    Abstract [en]

    An acyl intermediate in the activation of eta(5)-(Ph(5)Cp)Ru(CO)(2)Cl by t-BuOK was identified by means of in situ FT-IR measurements and NMR spectroscopy. This strongly supports the conclusion that the ligand exchange takes place via CO assistance, i.e., that the activation occurs via nucleophilic attack by tert-butoxide on one of the CO ligands. The tert-butoxycarbonyl intermediate shows stretching vibrations at 1933 and 1596 cm(-1), corresponding to the CO and COOt-Bu groups, respectively. In the (13)C NMR spectrum, the CO group appears at 209.5 ppm and the COOt-Bu group at 208.7 ppm. The NMR assignments were confirmed by density functional theory calculations. The subsequent alcohol-alkoxide exchange is also thought to take place via CO assistance. However, no intermediate in that step could be detected.

1 - 38 of 38
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