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CO dissociation mechanism in racemization of alcohols by a cyclopentadienyl ruthenium dicarbonyl catalyst
Stockholm University, Faculty of Science, Department of Organic Chemistry.
Stockholm University, Faculty of Science, Department of Organic Chemistry.
Stockholm University, Faculty of Science, Department of Organic Chemistry.
2011 (English)In: Journal of the American Chemical Society, ISSN 0002-7863, E-ISSN 1520-5126, Vol. 133, no 9, 2820-2823 p.Article in journal (Refereed) Published
Abstract [en]

13CO exchange studies of racemization catalyst (η5-Ph5C5)Ru(CO)2Cl and (η5-Ph5C5)Ru(CO)2(Ot-Bu) by 13C NMR spectroscopy are reported. CO exchange for the active catalyst form, (η5-Ph5C5)Ru(CO)2(Ot-Bu) is approximately 20 times faster than that for the precatalyst (η5-Ph5C5)Ru(CO)2Cl. An inhibition on the rate of racemization of (S)-1-phenylethanol was observed on addition of CO. These results support the hypothesis that CO dissociation is a key step in the racemization of sec-alcohols by (η5-Ph5C5)Ru(CO)2Cl, as also predicted by DFT calculations.

Place, publisher, year, edition, pages
2011. Vol. 133, no 9, 2820-2823 p.
National Category
Organic Chemistry
Research subject
Organic Chemistry
Identifiers
URN: urn:nbn:se:su:diva-59869DOI: 10.1021/ja1098066ISI: 000289455200008OAI: oai:DiVA.org:su-59869DiVA: diva2:431551
Funder
Swedish Research CouncilKnut and Alice Wallenberg Foundation
Available from: 2011-07-20 Created: 2011-07-20 Last updated: 2017-12-08Bibliographically approved
In thesis
1. Ruthenium-Catalyzed Hydrogen Transfer Reactions: Mechanistic Studies and Chemoenzymatic Dynamic Kinetic Resolutions
Open this publication in new window or tab >>Ruthenium-Catalyzed Hydrogen Transfer Reactions: Mechanistic Studies and Chemoenzymatic Dynamic Kinetic Resolutions
2013 (English)Doctoral thesis, comprehensive summary (Other academic)
Abstract [en]

The main focus of this thesis lies on transition metal-catalyzed hydrogen transfer reactions. In the first part of the thesis, the mechanism for racemization of sec-alcohols with a ruthenium complex, Ru(CO)2Cl(η5-C5Ph5) was studied.

The reaction between 5-hexen-2-ol and Ru(CO)2(Ot-Bu)(η5-C5Ph5) was studied with the aim to elucidate the origin of the slow racemization observed for this sec-alcohol. Two diastereomers of an alkoxycarbonyl complex, which has the double bond coordinated to ruthenium, were characterized by NMR and in situ FT-IR spectroscopy. The observed inhibition of the rate of racemization for substrates with double bonds provided further confirmation of the importance of a free coordination site on ruthenium for β-hydride elimination. Furthermore, we observed that CO exchange, monitored by 13C NMR using 13CO, occurs with both the precatalyst, Ru(CO)2Cl(η5-C5Ph5), and the active catalytic intermediate, Ru(CO)2(Ot-Bu)(η5-C5Ph5). It was also found that added CO has an inhibitory effect on the rate of racemization of (S)-1-phenylethanol. Both these observations provide strong support for reversible CO dissociation as a key step in the racemization mechanism.

In the second part of this thesis, Ru(CO)2Cl(η5-C5Ph5) was combined with an enzymatic resolution catalyzed by a lipase, leading to several efficient dynamic kinetic resolutions (DKR). DKR of exocyclic allylic alcohols afforded the corresponding acetates in high yields and with excellent enantiomeric excess (ee). The products were utilized as synthetic precursors for α-substituted ketones and lactones. DKR of a wide range of homoallylic alcohols afforded the products in good to high yields and with high ee. The homoallylic acetates were transformed into 5,6-dihydropyran-2-ones in a short reaction sequence. Furthermore, DKR of a wide range of aromatic β-chloroalcohols afforded the products in high yields and with excellent ee. The β-chloro acetates were further transformed into chiral epoxides.

Place, publisher, year, edition, pages
Stockholm: Department of Organic Chemistry, Stockholm University, 2013. 84 p.
Keyword
Hydrogen transfer, ruthenium catalysis, kinetic resolution, dynamic kinetic resolution, racemization, asymmetric synthesis
National Category
Natural Sciences
Research subject
Organic Chemistry
Identifiers
urn:nbn:se:su:diva-89263 (URN)978-91-7447-706-1 (ISBN)
Public defence
2013-05-24, Magnélisalen, Kemiska Övningslaboratoriet, Svante Arrhenius väg 16 B, Stockholm, 10:00 (English)
Opponent
Supervisors
Note

At the time of the doctoral defense, the following papers were unpublished and had a status as follows: Paper 2: Manuscript. Paper 5: Mansucript.

Available from: 2013-04-18 Created: 2013-04-17 Last updated: 2013-11-06Bibliographically approved
2. Transition Metal-Catalyzed Redox Reactions: A Journey from Homogeneous Ruthenium to Heterogeneous Palladium Catalysis
Open this publication in new window or tab >>Transition Metal-Catalyzed Redox Reactions: A Journey from Homogeneous Ruthenium to Heterogeneous Palladium Catalysis
2013 (English)Doctoral thesis, comprehensive summary (Other academic)
Abstract [en]

The first part of the thesis covers the development and utilization of electronically modified (pentaarylcyclopentadienyl)Ru-complexes in the racemization of secondary alcohols. This study revealed that the electronic properties of the substrate were the main factors dictating whether β-hydride elimination or hydride re-addition becomes the rate-determining step of the racemization process. With this knowledge in hand, it proved to be possible to design more efficient racemization protocols by matching the electronic properties of catalyst and substrate.

The second part describes mechanistic work that aimed at elucidating the role of CO dissociation in the mechanism of secondary alcohol racemization catalyzed by a (pentaarylcyclopentadienyl)Ru-complex. From CO exchange studies, we demonstrated that CO dissociation occurred in the catalytically active tert-BuO-species as well as in the chloride precatalyst. Furthermore, an inhibition study showed that an increase of the partial pressure of CO had a negative influence on the racemization rate. Together, these two observations provide strong support for CO dissociation as a key step in the racemization of secondary alcohols.

The third part concerns the improved synthesis and characterization of a heterogeneous catalyst consisting of Pd nanoparticles immobilized on aminopropyl-functionalized siliceous mesocellular foam. The developed Pd nanocatalyst was found to be a highly efficient and recyclable catalyst for the aerobic oxidation of a wide range of primary and secondary alcohols to the corresponding aldehydes and ketones.

The fourth part deals with the successful application of the Pd nanocatalyst in chemically-induced H2O oxidation, when using either ceric ammonium nitrate or [Ru(bpy)3]3+ as the terminal oxidant. Remarkably, the Pd nanocatalyst proved to catalyze this reaction with high efficiency and the measured TOF was found to greatly exceed those of current state-of-the-art metal oxide catalysts.

The fifth and final part describes the co-immobilization of Pd nanoparticles and the enzyme Candida Antarctica Lipase B into the same cavities of mesocellular foam, to generate a “metalloenzyme-like” hybrid catalyst for the dynamic kinetic resolution of a primary amine. The close proximity of the two catalytic species led to an enhanced cooperativity between them and resulted in an overall more efficient tandem process. 

Place, publisher, year, edition, pages
Stockholm: Department of Organic Chemistry, Stockholm University, 2013. 95 p.
National Category
Organic Chemistry
Research subject
Organic Chemistry
Identifiers
urn:nbn:se:su:diva-96713 (URN)978-91-7447-828-0 (ISBN)
Public defence
2014-01-24, Magnélisalen, Kemiska övningslaboratoriet, Svante Arrhenius väg 16 B, Stockholm, 10:00 (English)
Opponent
Supervisors
Note

At the time of the doctoral defense, the following papers were unpublished and had a status as follows: Paper 4: Manuscript. Paper 5: Epub ahead of print.

Available from: 2014-01-02 Created: 2013-11-26 Last updated: 2014-06-12Bibliographically approved

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