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Catalysts for Oxygen Production and Utilization: Closing the Oxygen Cycle: From Biomimetic Oxidation to Artificial Photosynthesis
Stockholm University, Faculty of Science, Department of Organic Chemistry. (Jan-Erling Bäckvall)
2011 (English)Doctoral thesis, comprehensive summary (Other academic)
Abstract [en]

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 palladium-catalyzed 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.

Place, publisher, year, edition, pages
Stockholm: Department of Organic Chemistry, Stockholm University , 2011. , 65 p.
Keyword [en]
oxygen, catalytic oxidation, biomimetic oxidation, artificial photosynthesis, water oxidation, DFT calculations
National Category
Organic Chemistry
Research subject
Organic Chemistry
Identifiers
URN: urn:nbn:se:su:diva-56917ISBN: 978-91-7447-289-9OAI: oai:DiVA.org:su-56917DiVA: diva2:413927
Public defence
2011-06-01, Magnélisalen, Kemiska övningslaboratoriet, Svante Arrhenius väg 16 B, Stockholm, 10:00 (Swedish)
Opponent
Supervisors
Note

At the time of the doctoral defense, the following papers were unpublished and had a status as follows: Paper 5: Accepted. Paper 6: Submitted.

Available from: 2011-05-10 Created: 2011-04-29 Last updated: 2012-09-27Bibliographically approved
List of papers
1. Mechanism of the palladium-catalyzed carbohydroxylation of allene-substituted conjugated dienes: rationalization of the recently observed nucleophilic attack by water on a (pi-allyl)palladium intermediate
Open this publication in new window or tab >>Mechanism of the palladium-catalyzed carbohydroxylation of allene-substituted conjugated dienes: rationalization of the recently observed nucleophilic attack by water on a (pi-allyl)palladium intermediate
2008 (English)In: Chemistry - A European Journal, ISSN 0947-6539, E-ISSN 1521-3765, Vol. 14, no 30, 9175-9180 p.Article in journal (Refereed) Published
Abstract [en]

The mechanism of the palladium-catalyzed oxidative carbohydroxylation of allene-substituted 1,3-cyclohexadiene was studied by DFT calculations. All intermediates and transition states of the reaction were identified and their structures were calculated. The calculations confirm the mechanism previously proposed and show that the CC bond-forming step occurs via insertion of one of the double bonds of 1,3-cyclohexadiene into a Pdvinyl bond of a vinylpalladium intermediate. This reaction leads to a (π-allyl)palladium intermediate, and coordination of benzoquinone and a double bond in the molecule to Pd creates a highly reactive cationic π-allyl complex, which is readily attacked by water according to the calculations.

Keyword
density functional calculations, homogeneous catalysis, palladium, water
National Category
Organic Chemistry
Identifiers
urn:nbn:se:su:diva-14706 (URN)10.1002/chem.200801294 (DOI)000260703900013 ()
Available from: 2008-12-03 Created: 2008-12-03 Last updated: 2011-05-04Bibliographically approved
2. Oxidation of ethers, alcohols, and unfunctionalized hydrocarbons by the methyltrioxorhenium/H2O2 system: a computational study on catalytic C-H bond activation
Open this publication in new window or tab >>Oxidation of ethers, alcohols, and unfunctionalized hydrocarbons by the methyltrioxorhenium/H2O2 system: a computational study on catalytic C-H bond activation
2009 (English)In: Chemistry - A European Journal, ISSN 0947-6539, E-ISSN 1521-3765, Vol. 15, no 8, 1862-1869 p.Article in journal (Refereed) Published
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.

Keyword
CH activation, density functional calculations, oxidation, reaction mechanisms, rhenium
National Category
Organic Chemistry
Identifiers
urn:nbn:se:su:diva-29462 (URN)10.1002/chem.200801493 (DOI)000263400200010 ()
Available from: 2009-08-31 Created: 2009-08-31 Last updated: 2011-05-04Bibliographically approved
3. Efficient reoxidation of palladium by a hybrid catalyst in aerobic palladium-catalyzed carbocyclization of enallenes
Open this publication in new window or tab >>Efficient reoxidation of palladium by a hybrid catalyst in aerobic palladium-catalyzed carbocyclization of enallenes
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2009 (English)In: Chemistry - A European Journal, ISSN 0947-6539, E-ISSN 1521-3765, Vol. 15, no 28, 6799-6801 p.Article in journal (Refereed) Published
Keyword
carbocyclization, electron transfer, hybrid catalysts, oxidation, palladium
National Category
Organic Chemistry
Research subject
Organic Chemistry
Identifiers
urn:nbn:se:su:diva-28977 (URN)10.1002/chem.200900980 (DOI)000268286200004 ()
Available from: 2009-07-29 Created: 2009-07-29 Last updated: 2015-09-04Bibliographically approved
4. Efficient synthesis of hybrid (hydroquinone-Schiff base)cobalt oxidation catalysts
Open this publication in new window or tab >>Efficient synthesis of hybrid (hydroquinone-Schiff base)cobalt oxidation catalysts
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2009 (English)In: European Journal of Organic Chemistry, ISSN 1434-193X, E-ISSN 1099-0690, no 23, 3973-3976 p.Article in journal (Refereed) Published
Abstract [en]

Hybrid catalysts A and B have recently been found to efficiently transfer electrons from a metal catalyst to molecular oxygen in biomimetic oxidations. In the present work hybrid catalysts A and B were synthesized in high yield from inexpensive starting materials. The key step is an efficient Suzuki cross-coupling, which allows the use of unprotected aldehyde 5. The new synthesis of the title hybrid catalysts is easy to carry out and can be scaled up.

Keyword
Hybrid catalyst, Oxidation, ­Biomimetic oxidation, Electron transfer, Catalyst synthesis, Cross coupling
National Category
Organic Chemistry
Research subject
Organic Chemistry
Identifiers
urn:nbn:se:su:diva-30437 (URN)10.1002/ejoc.200900312 (DOI)000269103600020 ()
Available from: 2009-10-14 Created: 2009-10-14 Last updated: 2011-12-02Bibliographically approved
5. Light-Induced Water Oxidation by a Ru-complex Containing a Bio-Inspired Ligand
Open this publication in new window or tab >>Light-Induced Water Oxidation by a Ru-complex Containing a Bio-Inspired Ligand
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2011 (English)In: Chemistry - A European Journal, ISSN 0947-6539, E-ISSN 1521-3765, Vol. 17, no 28, 7953-7959 p.Article in journal (Refereed) Published
Abstract [en]

The new Ru-complex 8 containing the bio-inspired ligand 7 was successfully synthesized and characterized. Complex 8 could efficiently catalyze water oxidation using CeIV and RuIII as chemical oxidants. More importantly, this complex has sufficiently low overpotential to utilize ruthenium polypyridyl-type complexes as photosensitizers.

Keyword
homogeneous catalysis, oxidation, photochemistry, ruthenium, water splitting
National Category
Organic Chemistry
Research subject
Organic Chemistry
Identifiers
urn:nbn:se:su:diva-56884 (URN)10.1002/chem.201003702 (DOI)000293383300033 ()
Funder
Knut and Alice Wallenberg Foundation
Available from: 2011-04-28 Created: 2011-04-28 Last updated: 2013-04-15Bibliographically approved
6. Photosensitized water oxidation by use of a bioinspired manganese catalyst
Open this publication in new window or tab >>Photosensitized water oxidation by use of a bioinspired manganese catalyst
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2011 (English)In: Angewandte Chemie International Edition, ISSN 1433-7851, E-ISSN 1521-3773, Vol. 50, no 49, 11715-11718 p.Article in journal (Refereed) Published
Keyword
homogeneous catalysis, manganese, N, O ligands, photocatalysis, water oxidation
National Category
Organic Chemistry
Research subject
Organic Chemistry
Identifiers
urn:nbn:se:su:diva-65534 (URN)10.1002/anie.201104355 (DOI)000298084900028 ()
Funder
Knut and Alice Wallenberg FoundationEU, European Research Council
Available from: 2011-12-12 Created: 2011-12-12 Last updated: 2013-04-15Bibliographically approved

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