Catalysts for Oxygen Production and Utilization Closing the Oxygen Cycle: From Biomimetic Oxidation to Artificial Photosynthesis

This thesis describes the development and study of catalysts for redox reactions, which either utilize oxygen or hydrogen peroxide for the purpose of selectively oxidizing organic substrates, or produce oxygen as the necessary byproduct in the production of hydrogen by artificial photosynthesis. The first chapter gives a general introduction about the use of environmentally friendly oxidants in the field of organic synthesis, and about the field of artificial photosynthesis. The second chapter describes a computational study of the mechanism of palladium-catalyzed oxidative carbohydroxylation of allene-substituted conjugated dienes. The proposed mechanism, which was supported by DFT calculations, involves an unusual water attack on a (π-allyl)palladium complex. The third chapter describes a computational study of the oxidation of unfunctionalized hydrocarbons, ethers and alcohols with hydrogen peroxide, catalyzed by methyltrioxorhenium (MTO). The mechanism was found to proceed via rate-limiting hydride abstraction followed by hydroxide transfer in a single concerted, but highly asynchronous, step as shown by intrinsic reaction coordinate (IRC) scans. The fourth chapter describes the use of a new hybrid (hydroquinone-Schiff base)cobalt catalyst as electron transfer mediator (ETM) in the palladiumcatalyzed aerobic carbocyclization of enallenes. Covalently linking the two ETMs gave a fivefold rate increase compared to the use of separate components. The fifth chapter describes an improved synthetic route to the (hydroquinone-Schiff base)cobalt catalysts. Preparation of the key intermediate 5-(2,5-hydroxyphenyl)salicylaldehyde was improved by optimization of the key Suzuki coupling and change of protecting groups from methyl ethers to easily cleaved THP groups. The catalysts could thus be prepared in good overall yield from inexpensive starting materials. Finally, the sixth chapter describes the preparation and study of two catalysts for water oxidation, both based on ligands containing imidazole groups, analogous to the histidine residues present in the oxygen evolving complex (OEC) and in many other metalloenzymes. The first, ruthenium-based, catalyst was found to catalyze highly efficient water oxidation induced by visible light. The second catalyst is, to the best of our knowledge, the first homogeneous manganese complex to catalyze light-driven water oxidation. List of Publications This thesis is based on the following papers, which are referred to in the text by their roman numerals. I Mechanism of the Palladium-Catalyzed Carbohydroxylation of Allene-Substituted Conjugated Dienes: Rationalization of the Recently Observed Nucleophilic Attack by Water on a (πAllyl)palladium Intermediate Karlsson, E. A.; Bäckvall, J.-E. Chem. Eur. J. 2008, 14, 9175–9180. Copyright 2008 Wiley-VCH Verlag GmbH & Co. KGaA. Reproduced with permission. II Oxidation of Ethers, Alcohols, and Unfunctionalized Hydrocarbons by the Methyltrioxorhenium/H2O2 System: A Computational Study on Catalytic C–H Bond Activation Karlsson, E. A.; Privalov T. Chem. Eur. J. 2009, 15, 1862–1869. Copyright 2009 Wiley-VCH Verlag GmbH & Co. KGaA. Reproduced with permission. III Efficient Reoxidation of Palladium by a Hybrid Catalyst in Aerobic Palladium-Catalyzed Carbocyclization of Enallenes Johnston, E. V.; Karlsson, E. A.; Lindberg, S. A.; Åkermark, B.; Bäckvall, J.-E. Chem. Eur. J. 2009, 15, 6799–6801. Copyright 2009 Wiley-VCH Verlag GmbH & Co. KGaA. Reproduced with permission. IV Efficient Synthesis of Hybrid (Hydroquinone-Schiff base)cobalt Oxidation Catalysts Johnston, E. V.; Karlsson, E. A.; Tran, L.-H.; Åkermark, B.; Bäckvall, J.-E. Eur. J. Org. Chem. 2009, 2009, 3973–3976. Copyright 2009 Wiley-VCH Verlag GmbH & Co. KGaA. Reproduced with permission. V Light-Induced Water Oxidation by a Ru-complex Containing a Bio-Inspired Ligand Kärkäs, M. D.; Johnston, E. V.; Karlsson, E. A.; Lee, B.-L.; Åkermark, T.; Shariatgorji, M.; Ilag, L.; Hansson, Ö.; Bäckvall, J.-E.; Åkermark, B. Accepted for publication in Chem. Eur. J. VI Photosensitized Water Oxidation Using a Bio-Inspired Manganese Catalyst Karlsson, E. A.; Lee, B.-L.; Åkermark, T.; Johnston, E. V.; Kärkäs, M. D.; Sun, J.; Hansson, Ö.; Bäckvall, J.-E.; Åkermark, B. Submitted to Science. Papers not included in this thesis: VII Efficient Aerobic Ruthenium-Catalyzed Oxidation of Secondary Alcohols by the Use of a Hybrid Electron Transfer Catalyst Johnston, E. V.; Karlsson, E. A.; Tran, L.-H.; Åkermark, B.; Bäckvall, J.-E. Eur. J. Org. Chem. 2010, 2010, 1971–1976. VIII Efficient regioselective protection of myo-inositol via facile protecting group migration Nkambule, C. M.; Kwezi, N. W.; Kinfe, H. H.; Nokwequ, M. G.; Gammon, D. W.; Oscarson, S.; Karlsson, E. Tetrahedron 2011, 67, 618–623. IX Tuning of the Electronic Properties of a Cyclopentadienylruthenium Catalyst to Match Racemization of Electron-Rich and Electron-Deficient Alcohols Verho, O.; Johnston, E. V.; Karlsson, E.; Bäckvall, J.-E. Submitted to Chem. Eur. J.