• Caesium Fluoride-Mediated Hydrocarboxylation of Alkenes and Allenes: Scope and Mechanistic Insights 

      Gevorgyan, Ashot; Obst, Marc; Guttormsen, Yngve; Maseras, Feliu; Hopmann, Kathrin Helen; Bayer, Annette (Journal article; Tidsskriftartikkel; Peer reviewed, 2019-09-11)
      A caesium fluoride-mediated hydrocarboxylation of olefins is disclosed that does not rely on precious transition metal catalysts and ligands. The reaction occurs at atmospheric pressures of CO<sub>2</sub> in the presence of 9-BBN as a stoichiometric reductant. Stilbenes, β-substituted styrenes and allenes could be carboxylated in good yields. The developed methodology can be used for preparation of ...
    • Carbon-carbon bonds with CO2: Insights from computational studies 

      Obst, Marc; Pavlovic, Ljiljana; Hopmann, Kathrin Helen (Journal article; Tidsskriftartikkel; Peer reviewed, 2018-02-17)
      In this mini-review, we provide an overview of recent computational studies on homogeneous transition metal-catalyzed carbon-carbon bond formation with CO2. We cover substitution and addition reactions involving different metals (mainly Ni, Rh, Cu) and substrates (alkanes, alkenes, alkynes, arenes) with focus on the mechanistic details. The CO2 insertion step is generally found to be rate-limiting. ...
    • Cobalt-Catalysed Alkene Hydrogenation: A Metallacycle Can Explain the Hydroxyl Activating Effect and the Diastereoselectivity 

      Morello, Glenn Robert; Zhong, Hongyu; Chirik, Paul J.; Hopmann, Kathrin Helen (Journal article; Tidsskriftartikkel; Peer reviewed, 2018-05-04)
      Bis(phosphine)cobalt dialkyl complexes have been reported to be highly active in the hydrogenation of tri-substituted alkenes bearing hydroxyl substituents. Alkene substrates containing ether, ester, or ketone substituents show minimal reactivity, indicating an activating effect of the hydroxyl group. The mechanistic details of bis(phosphine)cobalt-catalysed hydrogenation were recently evaluated ...
    • Cobalt-Catalyzed Asymmetric Hydrogenation of Enamides: Insights into Mechanisms and Solvent Effects 

      Pavlovic, Ljiljana; Mendelsohn, Lauren N.; Zhong, Hongyu; Chirik, Paul J.; Hopmann, Kathrin Helen (Journal article; Tidsskriftartikkel; Peer reviewed, 2022-07-25)
      The mechanistic details of the (<sup>Ph</sup>BPE)Co-catalyzed asymmetric hydrogenation of enamides are investigated using computational and experimental approaches. Four mechanistic possibilities are compared: a direct Co(0)/Co(II) redox path, a metathesis pathway, a nonredox Co(II) mechanism featuring an azametallacycle, and a possible enamide−imine tautomerization pathway. The results indicate ...
    • Comparative study of CO2 insertion into pincer supported palladium alkyl and aryl complexes 

      Deziel, Anthony P.; Gahlawat, Sahil; Hazari, Nilay; Hopmann, Kathrin Helen; Mercado, Brandon Q. (Journal article; Tidsskriftartikkel; Peer reviewed, 2023-07-12)
      The insertion of CO2 into metal alkyl bonds is a crucial elementary step in transition metal-catalyzed processes for CO2 utilization. Here, we synthesize pincer-supported palladium complexes of the type (tBuPBP)Pd(alkyl) (tBuPBP = B(NCH2PtBu2)2C6H4−; alkyl = CH2CH3, CH2CH2CH3, CH2C6H5, and CH2-4-OMe-C6H4) and (tBuPBP)Pd(C6H5) and compare the rates of CO2 insertion into the palladium alkyl bonds to ...
    • Computational and experimental insights into asymmetric Rh‐catalyzed hydrocarboxylation with CO2 

      Pavlovic, Ljiljana; Pettersen, Martin; Gevorgyan, Ashot; Vaitla, Janakiram; Bayer, Annette; Hopmann, Kathrin Helen (Journal article; Tidsskriftartikkel; Peer reviewed, 2020-12-18)
      The asymmetric Rh‐catalyzed hydrocarboxylation of α,β‐unsaturated carbonyl compounds was originally developed by Mikami and co‐workers but gives only moderate enantiomeric excesses. In order to understand the factors controlling the enantioselectivity and to propose novel ligands for this reaction, we have used computational and experimental methods to study the Rh‐catalyzed hydrocarboxylation with ...
    • Computational and experimental insights into asymmetric Rh‐catalyzed hydrocarboxylation with CO2 

      Pavlovic, Ljiljana; Pettersen, Martin; Gevorgyan, Ashot; Vaitla, Janakiram; Bayer, Annette; Hopmann, Kathrin Helen (Journal article; Tidsskriftartikkel; Peer reviewed, 2020-12-18)
      The asymmetric Rh‐catalyzed hydrocarboxylation of α,β‐unsaturated carbonyl compounds was originally developed by Mikami and co‐workers but gives only moderate enantiomeric excesses. In order to understand the factors controlling the enantioselectivity and to propose novel ligands for this reaction, we have used computational and experimental methods to study the Rh‐catalyzed hydrocarboxylation with ...
    • Conformational tuning improves the stability of spirocyclic nitroxides with long paramagnetic relaxation times 

      Sowinski, Mateusz; Gahlawat, Sahil; Lund, Bjarte Aarmo; Warnke, Anna-Luisa; Hopmann, Kathrin Helen; Lovett, Janet E.; Haugland, Marius Myreng (Journal article; Tidsskriftartikkel; Peer reviewed, 2023-06-05)
      Nitroxides are widely used as probes and polarization transfer agents in spectroscopy and imaging. These applications require high stability towards reducing biological environments, as well as beneficial relaxation properties. While the latter is provided by spirocyclic groups on the nitroxide scaffold, such systems are not in themselves robust under reducing conditions. In this work, we introduce ...
    • A Dihydride Mechanism Can Explain the Intriguing Substrate Selectivity of Iron-PNP-Mediated Hydrogenation 

      Hopmann, Kathrin Helen; Morello, Glenn Robert (Journal article; Tidsskriftartikkel; Peer reviewed, 2017-07-24)
      Iron-PNP pincer complexes are efficient catalysts for the hydrogenation of aldehydes and ketones. A variety of hydrogenation mechanisms have been proposed for these systems, but there appears to be no clear consensus on a preferred pathway. We have employed high-level quantum chemical calculations to evaluate various mechanistic possibilities for iron-PNP catalysts containing either CH2, NCH3, ...
    • Efficient palladium-catalyzed electrocarboxylation enables late-stage carbon isotope labelling 

      Batista, Gabriel M. F.; Ebenbauer, Ruth; Day, Craig S.; Bergare, Jonas; Neumann, Karoline; Hopmann, Kathrin Helen; Elmore, Charles; Rosas-Hernandez, Alonso; Skrydstrup, Troels (Journal article; Tidsskriftartikkel; Peer reviewed, 2024-03-22)
      Carbon isotope labelling of bioactive molecules is essential for accessing the pharmacokinetic and pharmacodynamic properties of new drug entities. Aryl carboxylic acids represent an important class of structural motifs ubiquitous in pharmaceutically active molecules and are ideal targets for the installation of a radioactive tag employing isotopically labelled CO<sub>2</sub>. However, direct isotope ...
    • Enantioselective incorporation of CO2: status and potential 

      Vaitla, Janakiram; Guttormsen, Yngve; Mannisto, Jere K.; Nova, Ainara; Repo, Timo; Bayer, Annette; Hopmann, Kathrin Helen (Journal article; Tidsskriftartikkel; Peer reviewed, 2017-09-09)
      CO<sub>2</sub> is a promising and sustainable carbon feedstock for organic synthesis. New catalytic protocols for efficient incorporation of CO<sub>2</sub>into organic molecules are continuously being reported. However, little progress has been made in the enantioselective conversion of CO<sub>2</sub>to form enantioenriched molecules. In order to allow CO<sub>2</sub>to become a versatile carbon ...
    • Exploration of New Biomass-Derived Solvents: Application to Carboxylation Reactions 

      Gevorgyan, Ashot; Hopmann, Kathrin Helen; Bayer, Annette (Journal article; Tidsskriftartikkel; Peer reviewed, 2020-01-07)
      A range of hitherto unexplored biomass‐derived chemicals have been evaluated as new sustainable solvents for a large variety of CO<sub>2</sub>‐based carboxylation reactions. Known biomass‐derived solvents (biosolvents) are also included in the study and the results are compared with commonly used solvents for the reactions. Biosolvents can be efficiently applied in a variety of carboxylation reactions, ...
    • Formal C-H carboxylation of unactivated arenes with carbon dioxide 

      Gevorgyan, Ashot; Hopmann, Kathrin Helen; Bayer, Annette (Journal article; Tidsskriftartikkel; Peer reviewed, 2020-01-31)
      A formal C−H carboxylation of unactivated arenes using CO<sub>2</sub> in green solvents is described. The present strategy combines a sterically controlled Ir‐catalyzed C−H borylation followed by a Cu‐catalyzed carboxylation of the in situ generated organoboronates. The reaction is highly regioselective for the C−H carboxylation of 1,3‐disubstituted and 1,2,3‐trisubstituted benzenes, 1,2‐ or ...
    • How accurate is DFT for iridium-mediated chemistry? 

      Hopmann, Kathrin Helen (Journal article; Tidsskriftartikkel; Peer reviewed, 2016-09-27)
      Iridium chemistry is versatile and widespread, with superior performance for reaction types such as enantioselective hydrogenation and C−H activation. In order to gain insight into the mechanistic details of such systems, density functional theory (DFT) studies are often employed. But how accurate is DFT for modeling iridium-mediated transformations in solution? We have evaluated how well DFT ...
    • How To Make Your Computational Paper Interesting and Have It Published 

      Hopmann, Kathrin Helen (Journal article; Tidsskriftartikkel; Peer reviewed, 2019-02-11)
      In 1987, the late German chemist Peter Hofmann of the University of Heidelberg wrote: “We still have a long way to go until a computation will be able to compete with or to substitute a lab experiment... one could then conclude that theoretical work in this field—not being quantitatively reliable anyhow—is rather useless, except for the purpose of keeping theorists busy.” However, Hofmann continued: ...
    • Improved Buchwald–Hartwig Amination by the Use of Lipids and Lipid Impurities 

      Gevorgyan, Ashot; Hopmann, Kathrin Helen; Bayer, Annette (Journal article; Tidsskriftartikkel; Peer reviewed, 2021-10-25)
      The development of green Buchwald–Hartwig aminations has long been considered challenging, due to the high sensitivity of the reaction to the environment. Here we show that food-grade and waste vegetable oils, triglycerides originating from animals, and natural waxes can serve as excellent green solvents for Buchwald–Hartwig amination. We further demonstrate that amphiphiles and trace ingredients ...
    • Iridium-PHOX-mediated alkene hydrogenation: Isomerisation influences the stereochemical outcome 

      Hopmann, Kathrin Helen; Frediani, Luca; Bayer, Annette (Journal article; Tidsskriftartikkel; Peer reviewed, 2014-05-27)
      Recent experimental studies of iridium-phosphinooxazoline-mediated alkene hydrogenation indicated two dihydride species as resting states, with the minor isomer assumed to give rise to the major product enantiomer [Gruber and Pfaltz, Angew. Chem. Int. Ed. 2014, 53, 1896]. B3LYP-D2 calculations confirm the two dihydride intermediates as resting states but show that these species do not give rise to ...
    • Iron/Brønsted Acid Catalyzed Asymmetric Hydrogenation: Mechanism and Selectivity-Determining Interactions 

      Hopmann, Kathrin Helen (Journal article; Tidsskriftartikkel; Peer reviewed, 2015-06-03)
      Hydrogenation catalysts involving abundant base metals such as cobalt or iron are promising alternatives to precious metal systems. Despite rapid progress in this field, base metal catalysts do not yet achieve the activity and selectivity levels of their precious metal counterparts. Rational improvement of base metal complexes is facilitated by detailed knowledge about their mechanisms and ...
    • Iron‐Catalyzed Carbenoid Transfer Reactions of Vinyl Sulfoxonium Ylides: An Experimental and Computational Study 

      Vaitla, Janakiram; Bayer, Annette; Hopmann, Kathrin Helen (Journal article; Tidsskriftartikkel; Peer reviewed, 2018-10-15)
      A method for the generation of unprecedented vinyl carbenoids from sulfoxonium ylides has been developed and applied in the synthesis of a diverse array of heterocycles such as indolizines, pyrroles, 3‐pyrrolin‐2‐ones, and furans. The reactions proceed by FeBr<sub>2</sub> catalysis under mild reaction conditions with a broad substrate scope. A reaction pathway involving iron carbenoids is proposed ...
    • Ligand and solvent effects on CO2 insertion into group 10 metal alkyl bonds 

      Deziel, Anthony P.; Espinosa, Matthew; Pavlovic, Ljiljana; Charboneau, David J.; Hazari, Nilay; Hopmann, Kathrin Helen; Mercado, Brandon Q. (Journal article; Tidsskriftartikkel; Peer reviewed, 2022-02-09)
      The insertion of carbon dioxide into metal element σ-bonds is an important elementary step in many catalytic reactions for carbon dioxide valorization. Here, the insertion of carbon dioxide into a family of group 10 alkyl complexes of the type (<sup>R</sup>PBP)M(CH<sub>3</sub>) (<sup>R</sup>PBP = B(NCH<sub>2</sub>PR<sub>2</sub>)<sub>2</sub>C<sub>6</sub>H<sub>4</sub><sup>−</sup>; R = Cy or <sup>t</sup>Bu; ...