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Mechanistic Investigation of the Palladium-Catalyzed Synthesis of Allylic Silanes and Boronates from Allylic Alcohols
Stockholm University, Faculty of Science, Department of Organic Chemistry.
Stockholm University, Faculty of Science, Department of Organic Chemistry.
2013 (English)In: Journal of the American Chemical Society, ISSN 0002-7863, E-ISSN 1520-5126, Vol. 135, no 1, 443-455 p.Article in journal (Refereed) Published
Abstract [en]

The mechanism of the palladium-catalyzed synthesis of allylic silanes and boronates from allylic alcohols was investigated. H-1, Si-29, F-19, and B-11 NMR spectroscopy was used to reveal key intermediates and byproducts of the silylation reaction. The tetrafluoroborate counterion of the palladium catalyst is proposed to play an important role in both catalyst activation as well as the transmetalation step. We propose that BF3 is generated in both processes and is responsible for the activation of the substrate hydroxyl group. An (eta(3)-allyl)palladium complex has been identified as the catalyst resting state, and the formation of (eta(3)-allyl)palladium complexes directly from allylic alcohols has been studied. Kinetic analysis provides evidence that the turnover limiting step is the transmetalation, and insights into notable similarities between the borylation and the silylation reaction mechanisms enabled us to considerably improve the stereoselectivity of the borylation.

Place, publisher, year, edition, pages
2013. Vol. 135, no 1, 443-455 p.
National Category
Chemical Sciences
Identifiers
URN: urn:nbn:se:su:diva-87691DOI: 10.1021/ja309860hISI: 000313143000067OAI: oai:DiVA.org:su-87691DiVA: diva2:605859
Funder
Knut and Alice Wallenberg FoundationSwedish Research Council
Note

AuthorCount:2;

Available from: 2013-02-15 Created: 2013-02-14 Last updated: 2017-12-06Bibliographically approved
In thesis
1. Transition metal-catalyzed allylic and vinylic functionalization: Method development and mechanistic investigations
Open this publication in new window or tab >>Transition metal-catalyzed allylic and vinylic functionalization: Method development and mechanistic investigations
2013 (English)Doctoral thesis, comprehensive summary (Other academic)
Abstract [en]

The use of small molecule building blocks in, for example, pharmaceutical research and new material development, creates a need for new and improved organic synthesis methods. The use of transition metals as mediators and catalysts opens up new reaction pathways that have made the synthesis of completely new compounds possible as well as greatly improved the synthetic routes to known compounds.

Herein, the development of new metal-mediated and catalyzed reactions for construction of vinylic and allylic carbon-carbon and carbon-heteroatom bonds is described.  The use of iodonium salts as coupling partners in Pd-catalyzed Heck type reactions with alkenes is shown to improve the current substrate scope. Results from a mechanistic study indicate that the reaction proceeds via high oxidation state palladium intermediates.

The use of IIII reagents is also believed to facilitate a PdII/PdIV catalytic cycle in allylic silylation of alkenes using (SiMe3)2, which, to the best of our knowledge, is the first method developed for metal-catalyzed allylic C-H silylation.

The same silyl-source, (SiMe3)2, has previously been used in a Pd-catalyzed allylic substitution reaction in which allylic silanes are formed from allylic alcohols. A detailed mechanistic investigation of this reaction is described in which by-products as well as intermediates, including the resting state of the catalyst, are identified using 1H, 11B, 19F and 29Si NMR spectroscopy. Kinetic experiments are performed that give information about the turn-over limiting step and the mechanism of the analogous borylation using B2pin2 is also investigated. Insights from this study further made it possible to improve the stereoselectivity of this reaction.

Additionally, a new method for Cu-mediated trifluoromethylation of allylic halides is presented in which linear products are formed exclusively from both linear and branched allylic substrates at room temperature.  Identification of allylic fluorides as by-products during the reaction also led to the development of a similar Cu-mediated reaction for the fluorination of allylic halides.

Place, publisher, year, edition, pages
Stockholm: Department of Organic Chemistry, Stockholm Univeristy, 2013. 70 p.
Keyword
palladium, copper, catalysis, Heck reaction, C-H functionalization, allylic substitution, silylation, borylation, trifluoromethylation, fluorination, mechanistic study, transition metal, alkene, allylic silane, allylic boronate, allylic fluoride
National Category
Organic Chemistry
Research subject
Organic Chemistry
Identifiers
urn:nbn:se:su:diva-89524 (URN)978-91-7447-668-2 (ISBN)
Public defence
2013-06-14, Magnélisalen, Kemiska övningslaboratoriet, Svante Arrhenius väg 16 B, Stockholm, 13:00 (English)
Opponent
Supervisors
Note

At the time of the doctoral defense, the following paper was unpublished and had a status as follows: Paper 4: Manuscript.

Available from: 2013-05-16 Created: 2013-04-29 Last updated: 2014-03-17Bibliographically approved

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