Secondary Interactions in Symmetric Double Bond
Formation Catalysed by Molecular Ruthenium Complexes
Oleksandr Kravchenko
Doctoral Thesis
Stockholm 2020
Akademisk avhandling som med tillstånd av Kungliga Tekniska Högskolan i Stockholm framlägges till offentlig granskning för avläggande av doktorsexamen i kemi onsdagen den 14:e oktober kl 13.00 i Kollegiesalen, KTH, Brinellvägen 8, Stockholm. Avhandlingen försvaras på engelska. Opponent är Prof. Roger Alberto, University of Zurich.
I
ISBN 978-91-7873-638-6
TRITA-CBH-FOU-2020:42
© Oleksandr Kravchenko, 2020
Printed by: Universitetsservice US AB, Sweden 2020
II Oleksandr Kravchenko, 2020: “Secondary Interactions in Symmetric Double Bond Formation Catalysed by Molecular Ruthenium Complexes”, School of Engineering Sciences in Chemistry, Biotechnology and Health, KTH – Royal Institute of Technology, SE-100 44 Stockholm, Sweden. Abstract
Chemistry has a tremendous impact on everyone’s life, although society does not always realize its power and ubiquity. In recent years, improved economy and sustainability of chemical processes has become a worldwide priority. Since its discovery, catalysis has been leveraged in industry to decrease energy demands in chemical reactions and reduce their cost. This thesis focuses on two catalytic transformations and various aspects of catalyst design that improve the catalytic efficiency and applicability.
The first chapter contains an introduction of important concepts in catalysis and an overview of weak interactions, often used when designing catalysts. As symmetry plays a big role in chemistry in general and especially in the reactions discussed in this thesis, a brief overview of some symmetry aspects in molecules and reactions is provided.
The second chapter addresses applications of olefin metathesis in dynamic chemistry. The catalysts for establishing equilibria in simple dynamic systems under mild conditions are analysed from a structure-activity relationship perspective. An ability to perform self- and cross-metathesis of functionalized substrates in water is evaluated and used to improve selectivity.
The following chapters focus on water oxidation catalysis, which is an essential part of solar fuel generation and the development of sustainable energy solutions. Therefore, the third chapter focuses on the electronic effects in functionalized catalysts. The influence of substituents and backbone modifications on the properties of the catalysts is discussed. The fourth chapter introduces novel design of axial and equatorial ligands in state-of-the-art water oxidation catalysts for improvements in catalytic activity and stability.
The research presented in this thesis demonstrates the influence of weak intra- and intermolecular interactions on catalysis and the strategies of using these interactions in transition metal complexes to improve catalytic properties.
Keywords: homogeneous catalysis, transition metal catalysis, ruthenium catalyst, olefin metathesis, dynamic covalent chemistry, water oxidation, solar fuels, Ru-bda, secondary interactions, hydrophobic interactions, π-π stacking.
III Sammanfattning på svenska
Kemi har en enorm påverkan på allas liv även om samhället inte inser dess kraft och allmänna utbredning. Under de senaste åren har ekonomi och hållbarhet i kemiska processer blivit en världsomfattande prioritering. Ända sedan dess upptäckt har katalys utnyttjats i industrin för att minska energibehovet i kemiska reaktioner. Den här avhandlingen behandlar två katalytiska transformationer och olika aspekter av katalysatordesign som förbättrar den katalytiska effektiviteten och användbarheten.
Det första kapitlet innehåller en introduktion av viktiga begrepp inom katalys och en översikt över svaga interaktioner som ofta används i katalysatordesign. Eftersom symmetri spelar en stor roll i kemi i allmänhet och särskilt i de reaktioner som diskuteras i den här avhandlingen ges också en kort översikt av vissa symmetriaspekter i molekyler och reaktioner.
Det andra kapitlet behandlar tillämpningar av olefinmetatesen i dynamisk kemi. Katalysatorerna för etablering av jämvikt i enkla dynamiska system under milda förhållanden analyseras i en struktur-aktivitetsförhållande studie. Förmågan att utföra själv- och korsmetates av mycket funktionaliserade substrat i vatten utvärderas och används för att öka selektivitet.
Följande kapitel fokuserar på vattenoxidationskatalys som är en väsentlig del för produktionen av solbränsle och utvecklingen av hållbar energi. Det tredje kapitlet fokuserar på de elektroniska effekterna i funktionaliserade katalysatorer. Påverkan av substituenter och andra modifikationer på katalysatorernas egenskaper diskuteras. Det fjärde kapitlet introducerar ny design av axiella och ekvatoriella ligander i toppmoderna vattenoxidations-katalysatorer och betydande förbättringar av katalytisk aktivitet och stabilitet.
Forskningen som presenteras i den här avhandlingen demonstrerar påverkan av svaga intra- och intermolekylära interaktioner på katalys och sätten att använda dessa interaktioner i övergångsmetallkomplex för att förbättra katalytiska egenskaper.
Nyckelord: homogen katalys, övergångsmetallkatalys, rutheniumkatalysator, olefinmetates, dynamisk kovalent kemi, vattenoxidation, solbränslen, Ru-bda, sekundära interaktioner, hydrofoba interaktioner, π-π stapling.
IV Abbreviations
Ac acetyl bda [2,2'-bipyridine]-6,6'-dicarboxylate biqa [1,1'-biisoquinoline]-3,3'-dicarboxylate Bnd benzylidenyl bpa [2,2'-bipyrazine]-6,6'-dicarboxylate Brisq 6-bromoisoquinoline Bu n-butyl CAAC cyclic (alkyl)(amino)carbene CM cross-metathesis Cy cyclohexyl DFT density functional theory dmbda 4,4'-dimethoxy-[2,2'-bipyridine]-6,6'-dicarboxylate DMF N,N-dimethylformamide DMSO dimethylsulfoxide DNA deoxyribonucleic acid dnbda 4,4'-dinitro-[2,2'-bipyridine]-6,6'-dicarboxylate Et ethyl HMDS hexamethyldisilazide HOMO highest occupied molecular orbital I2M inter/intramolecular coupling of two metal-oxo units Ind 3-phenylindenylidenyl iPr isopropyl Ipy 4-iodopyridine iso-biqa [3,3'-biisoquinoline]-1,1'-dicarboxylate Me methyl MS mass spectrometry NHC N-heterocyclic carbene NHE normal hydrogen electrode NMR nuclear magnetic resonance pda 1,10-phenanthroline-2,9-dicarboxylate PEG pentaethylene glycol Ph phenyl pic 4-picoline pKa negative logarithm of acid dissociation constant ppa 6-(6-carboxylatopyridin-2-yl)pyrazine-2-carboxylate RCM ring-closing metathesis SM self-metathesis Tf trifluoromethanesulfonate TFE 2,2,2-trifluoroethanol TOF turnover frequency TON turnover number WNA water nucleophilic attack
V List of Publications
This thesis is based on the following papers, referred to in the text by their Roman numerals I–VI:
I. Stable CAAC-based Ruthenium Complexes for Dynamic Olefin Metathesis Under Mild Conditions Kravchenko, O., Timmer, B.J.J., Biedermann, M., Inge, A.K. and Ramström, O. Submitted II. Selective Cross-Metathesis of Highly Chelating Substrates in Aqueous Media Timmer, B.J.J., Kravchenko, O. and Ramström, O. ChemistrySelect 2020, 5, 7254–7257 III. Modulation of the First and Second Coordination Sphere Effects by Backbone Substitution in Ru(bda)L2 Water Oxidation Catalysts Kravchenko, O., Timmer, B.J.J., Liu, T., Karalius, A., Zhang, B. and Sun, L. Manuscript in preparation IV. Electronic Influence of the 2,2'-Bipyridine-6,6'-dicarboxylate Ligand in Ru-based Type Water Oxidation Catalysts Timmer, B.J.J., Kravchenko, O., Zhang, B., Liu, T. and Sun, L. Submitted V. Improving the Stability of Ru-bda Molecular Water Oxidation Catalysts via π-System Extension of Backbone Ligand Kravchenko, O., Timmer, B.J.J., Liu, T., Zhang, B. and Sun, L. Submitted VI. Off-set Interactions for Low Concentration Water Splitting Catalysis with Ru(bda)L2 Timmer, B.J.J., Kravchenko, O., Liu, T., Zhang, B. and Sun, L. Submitted
VI Papers not included in this thesis:
I. Effects of Molecular Modifications for Water Splitting Enhancement of BiVO4 Grądzka-Kurzaj, I., Meng, Q., Timmer, B.J.J., Kravchenko, O., Zhang, B., Gierszewski, M. and Ziółek, M. Int. J. Hydrog. Energy 2020, 45, 15129–15141 II. Switching O–O Bond Formation Mechanism between WNA and I2M Pathways by Modifying the Ru-bda Backbone Ligands of Water-Oxidation Catalysts Zhang, B.*, Zhan, S.*, Liu, T., Wang, L., Inge, A.K., Duan, L., Timmer, B.J.J., Kravchenko, O., Li, F., Ahlquist, M.S.G. and Sun, L. J. Energy Chem. 2021, 54, 815–821 III. Formation and Out-of-Equilibrium, High/Low State Switching of a Nitroaldol Dynamer in Neutral Aqueous Media Karalius, A., Zhang, Y., Kravchenko, O., Elofsson, U., Szabó, Z., Yan, M. and Ramström, O. Angew. Chem. Int. Ed. 2020, 59, 3434–3438 IV. A Robotics-Inspired Screening Algorithm for Molecular Caging Prediction Kravchenko, O.*, Varava, A.*, Pokorny, F.T., Devaurs, D., Kavraki, L.E. and Kragic, D. J. Chem. Inf. Model. 2020, 60, 1302–1316 V. Bio-Inspired Water Oxidation Catalysts Zhang, B., Kravchenko, O. and Sun, L. In: Comprehensive Coordination Chemistry III, Elsevier, 2021 Accepted VI. Recent Progress in Nonprecious Water Oxidation Catalysts for Acidic OER Yang, H., Liu, T., Kravchenko, O., Meng, Q., Li, F. and Sun, L. Submitted VII. Isolated Pseudo Seven-Coordinate RuIII-bda Water Oxidation Catalyst with a “Ready-To-Go” Aqua Ligand Liu, T., Shen, N., Wang, L., Timmer, B.J.J., Li, G., Zhou, S., Ahlquist, M.S.G., Zhang, B., Kravchenko, O., Xu, B. and Sun, L. Submitted
VII VIII. 2D MnOx Composite Catalysts Inspired by Natural OEC for Efficient Catalytic Water Oxidation Fan, L.*, Zhang, B.*, Zhang, F., Timmer, B.J.J., Kravchenko, O., Pan, J. and Sun, L. Submitted IX. Configurational and Constitutional Dynamics of Enamine Molecular Switches Ren, Y., Kravchenko, O. and Ramström, O. Submitted X. Stimuli-Responsive Enaminitrile Molecular Switches as Tunable AIEgens Covering the Chromaticity Space and Acting as Vapor Sensors Ren, Y., Kravchenko, O., Xie, S., Svensson Grape, E., Inge, A.K., Yan, M. and Ramström, O. To be submitted XI. Rapidly Exchanging, Double-Dynamic, Catalyst-Free Nitroaldol-Hemiacetal Systems for Metal-Responsive Reversible Polymerization Karalius, A., Kravchenko, O., Elofsson, U., Szabó, Z., Yan, M. and Ramström, O. To be submitted XII. Control Over Emergent π-π Interactions in Double-Dynamic Coordination Complexes Through a Nature-Inspired Coordination-Triggered System Karalius, A., Svensson Grape, E., Inge, K., Kravchenko, O., Szabó, Z., Yan, M. and Ramström, O. To be submitted
VIII Table of Contents
Abstract ...... III Sammanfattning på svenska ...... IV Abbreviations ...... V List of Publications ...... VI Table of Contents ...... IX 1. Introduction ...... 1 1.1 Catalysis ...... 2 1.1.1 Organometallic catalysis ...... 3 1.2 Secondary interactions ...... 4 1.2.1 Hydrogen bonds ...... 5 1.2.2 Van der Waals forces ...... 5 1.2.3 Pi-interactions ...... 6 1.2.4 Hydrophobic effects ...... 7 1.3 Symmetry in catalysis ...... 7 1.3.1 Symmetry in ligands ...... 7 1.3.2 Symmetry in reactions ...... 8 1.4 Aim of this thesis...... 9 2. Applications of C-C Bond Formation via Olefin Metathesis in Dynamic Chemistry ...... 10 2.1 Olefin metathesis ...... 10 2.1.1 Olefin metathesis catalysts ...... 10 2.1.2 Dynamic olefin metathesis ...... 11 2.1.3 Olefin metathesis in protic solvents ...... 12 2.2 Dynamic olefin metathesis in mild conditions ...... 12 2.2.1 Catalyst synthesis ...... 13 2.2.2 Reactivity in ring-closing metathesis ...... 16 2.2.3 Dynamic systems equilibration ...... 17 2.2.4 Functional group tolerance ...... 19 2.3 Cross-metathesis of functionalized substrates ...... 21 2.3.1 Reactivity in self-metathesis ...... 21 2.3.2 Selective cross-metathesis ...... 22 2.4 Conclusions ...... 24 3. Electronic Effects in the Backbone Ligands of Ru-based Water Oxidation Catalysts ...... 25 3.1 Water oxidation ...... 25 3.1.1 Ru-bda catalysts ...... 26 3.1.2 Substitution effects in water oxidation catalysts ...... 28 3.2 Functionalization of bda-based ligands ...... 29
IX 3.2.1 Ligand synthesis ...... 30 3.2.2 Functionalized catalysts ...... 32 3.2.3 Electrochemical and catalytic properties ...... 33 3.3 Electronic vs. supramolecular effects of the catalyst backbone ...... 35 3.3.1 Ligand design and synthesis ...... 35 3.3.2 Electrochemical properties ...... 36 3.3.3 Water oxidation activity...... 38 3.4 Conclusions ...... 39 4. Efficient O-O Bond Formation via Enhanced Catalytic Stability and Activity ...... 40 4.1 Improving catalyst stability via backbone π-extension ...... 40 4.1.1 Implications of π-system modifications ...... 40 4.1.2 Ligand design and synthesis ...... 41 4.1.3 Catalytic performance ...... 42 4.1.4 Catalyst stability...... 44 4.2 Enhancement of radical coupling ...... 46 4.2.1 Ligand design ...... 46 4.2.2 Catalytic performance ...... 48 4.2.3 Substituent effects ...... 50 4.3 Conclusions ...... 52 5. Concluding remarks ...... 53 Acknowledgements ...... 55 Appendix ...... 58 References ...... 59
X 1. Introduction
“Chemistry without catalysis would be a sword without a handle, a light without brilliance, a bell without sound.” Alwin Mittasch (1869–1953)
Chemical reactions have a larger occurrence in our everyday lives than it is commonly perceived. The notion of chemical reaction rate is intuitively defined as a measure of how fast the reaction progresses. Common examples may include burning (fast), cooking (medium), rusting (slow). The most essential chemical reactions, however, occur in human bodies. Rates of biological reactions are extremely important, as thousands of reactions are interconnected and thus should work in a concerted fashion.
Large-scale reactions occur in industry, where fuels, materials, fertilizers, and drugs are synthesized. Many of these reactions are naturally slow, and therefore require catalysts to proceed at reasonable rates. Typically, reaction rate decreases exponentially with the increase in the amount of energy required for the reaction to occur. Catalysts effectively reduce this energy, therefore making an exponential impact on the rates. This makes catalyst design essential, as even small changes can lead to a drastic acceleration of the catalysed reaction.
The use of transition metals in catalysis was, to some extent, inspired by the discovery of metalloenzymes in nature. Noble metals, such as Ru, Rh, Pd, albeit inert in bulk, were found to exhibit unique reactivity at the nanoscale, allowing their use in catalysis. In recent years, some of the mechanisms and concepts, developed in noble-metal catalysis, have been adopted to earth-abundant metals, such as Fe, Co, Ni. In light of these successes, detailed mechanistic investigations of known noble metal-catalysed processes are extremely important for transferring acquired knowledge to other metals. Despite recent developments in base metal catalysis, there are many examples of reactions that are much more efficiently catalysed by complexes based on noble metals.
Catalysis is one of important chemical tools for sustainable development, as it reduces costs of valuable materials and offers alternative pathways to inefficient and wasteful industrial processes. The achievement of many sustainability goals, such as the ones outlined by United Nations,1 can therefore benefit from the discovery of new catalysts. The works presented in this thesis do not only address the development of various ruthenium catalysts, but also contribute to the development of sustainable energy in the form of solar fuels.
1 1.1 Catalysis Development of catalysis has made a tremendous impact on chemistry. The concept of a sub-equimolar additive able to accelerate reactions, while remaining unchanged, was an attractive topic since the early days of chemistry.2 Small amounts of a material, required for catalysis, led to the unconscious use of catalysis long before it was discovered – a phenomenon, still occurring in modern chemistry.3, 4 Low loadings also made catalysis particularly useful in industrial applications, where it significantly reduced costs and enabled the access to large amounts of products.5
Generally, catalysts decrease the activation energy (𝐸 ) of a chemical reaction by offering an alternative reaction pathway, where the catalyst is involved in the reaction intermediates but released upon reaction completion (Figure 1).
Figure 1. Schematic energy profiles for non-catalysed and catalysed reactions.
Reaction rate can be linked to the activation energy via various expressions, such as Eyring or Arrhenius equations.6-8 All such equations provide an exponential relationship between the rate constant and activation energy: