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Mechanism of the η3-η1-η3 Isomerization in Allylpalladium Complexes: Solvent Coordination, Ligand, and Substituent Effects
Stockholm University, Faculty of Science, Department of Organic Chemistry.
Stockholm University, Faculty of Science, Department of Organic Chemistry.
2001 (English)In: Organometallics, ISSN 0276-7333, E-ISSN 1520-6041, Vol. 20, 5464-5471 p.Article in journal (Refereed) Published
Abstract [en]

The mechanism of the η3 → η1 → η3 isomerization of (η3-allyl)palladium complexes occurring as catalytic intermediates in important synthetic transformations has been studied by applying density functional theory at the B3PW91(DZ+P) level. It was found that under catalytic conditions, in the condensed phase, the isomerization process involves tetracoordinated (η1-allyl)palladium intermediates. In these intermediates a solvent molecule or another ancillary ligand coordinates to palladium. The stability of the (η1-allyl)palladium intermediates critically depends on the electronic effects and on the coordination ability of the solvent molecules and the ancillary ligands. The theoretical calculations indicate a dσ → π* type hyperconjugative interaction occurring in the η1-allyl moiety of the intermediary complexes. These hyperconjugative interactions influence the structure of the complexes and the activation barrier to rotation through the C1−C2 bond. Alkyl substitution of the metalated carbon leads to destabilization of the (η1-allyl)palladium complexes, which increases the activation energy of the syn/anti isomerization process. This substituent effect arises from a dual steric and electronic destabilizing interaction between the methyl substituent and the metal atom.

Place, publisher, year, edition, pages
2001. Vol. 20, 5464-5471 p.
Identifiers
URN: urn:nbn:se:su:diva-22713DOI: 10.1021/om010793dOAI: oai:DiVA.org:su-22713DiVA: diva2:189306
Note
Part of urn:nbn:se:su:diva-105Available from: 2004-04-22 Created: 2004-04-22 Last updated: 2017-12-13Bibliographically approved
In thesis
1. Development of Palladium-Catalyzed Transformations Involving η1-Allypalladium Species
Open this publication in new window or tab >>Development of Palladium-Catalyzed Transformations Involving η1-Allypalladium Species
2004 (English)Doctoral thesis, comprehensive summary (Other academic)
Abstract [en]

This thesis is focused on investigation of the structure, reactivity and isomerization reactions of η1-allylpalladium complexes, which are key intermediates in catalytic transformations. The first part of this thesis concerns the structure and reactivity of bis-allylpalladium complexes. We have studied the regioselective palladium-catalyzed coupling reaction of various dialkylsubstituted allyl chlorides with allylstannanes and benzylidenemalonitrile, affording functionalized 1,7-octadienes. We have also found that benzylidenemalonitrile can be replaced by isocyanates providing bis-allylated amides. The second part is a computational study on the η3-η1-η3 isomerization of allylpalladium complexes. The mechanism of the isomerization was studied by DFT. It was found that the isomerization involves tetra-coordinated η1-allylpalladium intermediates. Alkyl substitution of the metalated carbon leads to destabilization of the η1-allylpalladium intermediate, which increases the activation energy of the isomerization process. The last part describes our efforts to extend the synthetic scope of mono-allylpalladium chemistry to include catalytic allylation of imine and aldehyde substrates. We have found that this reactivity can be achieved by the use of strongly coordinating tridentate ligands on palladium. The η1-allylpalladium intermediate has been observed by NMR-spectroscopy, and DFT calculations have been performed to show the feasibility of an electrophilic attack occuring on the allyl moiety.

Place, publisher, year, edition, pages
Stockholm: Institutionen för organisk kemi, 2004. 65 p.
Keyword
Palladium, Homogenous catalysis, Allylation, Electrophilic substitution, Density functional calculations
National Category
Organic Chemistry
Identifiers
urn:nbn:se:su:diva-105 (URN)91-7265-868-1 (ISBN)
Public defence
2004-05-14, Magnélisalen, Kemiska övningslaboratoriet, Svante Arrhenius väg 12 A, Stockholm, 10:00 (English)
Opponent
Supervisors
Available from: 2004-04-22 Created: 2004-04-22 Last updated: 2010-02-11Bibliographically approved

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