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- Niclas, Solin, et al.
(författare)
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Control of the Regioselectivity in Catalytic Transformations Involving Amphiphilic Bis-allylpalladium Intermediates : Mechanism and Synthetic Applications
- 2001
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Ingår i: Journal of Organic Chemistry. - : American Chemical Society (ACS). - 0022-3263 .- 1520-6904. ; 66:5, s. 1686-1693
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Tidskriftsartikel (refereegranskat)abstract
- Various dialkyl-substituted allyl chloride derivatives (2d−i) undergo regioselective palladium-catalyzed coupling reactions with allylstannanes (1a,b) and benzylidenemalonitrile (4), providing functionalized 1,7-octadienes in good yield. The catalytic reaction proceeds through an unsymmetrical amphiphilic bis-allylpalladium intermediate. An introductory electrophilic attack on the terminal position of the unsubstituted allyl moiety is followed by a nucleophilic attack on the alkyl-substituted allyl ligand. A theoretical analysis was performed by applying density functional theory at the B3PW91/DZ+P level to study the substituent effects on the electrophilic attack. According to the theoretical results, the high regioselectivity can be ascribed to the electronic effects of the alkyl substituents: The terminal alkyl groups destabilize the η1,η3-bis-allylpalladium intermediate of the reaction; in addition, the alkyl substitution increases the activation barrier for the electrophilic attack.
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| 2. |
- Niclas, Solin, et al.
(författare)
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Mechanism of the η3-η1-η3 Isomerization in Allylpalladium Complexes : Solvent Coordination, Ligand, and Substituent Effects
- 2001
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Ingår i: Organometallics. - : American Chemical Society (ACS). - 0276-7333 .- 1520-6041. ; 20, s. 5464-5471
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Tidskriftsartikel (refereegranskat)abstract
- 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.
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| 3. |
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| 4. |
- Solin, Niclas, 1971-
(författare)
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Development of Palladium-Catalyzed Transformations Involving η1-Allypalladium Species
- 2004
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- 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.
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| 5. |
- Solin, Niclas, et al.
(författare)
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Palladium-catalyzed Tandem Bis-allylation of Isocyanates
- 2001
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Ingår i: Organic Letters. - : American Chemical Society (ACS). - 1523-7060 .- 1523-7052. ; 3:6, s. 909-912
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Tidskriftsartikel (refereegranskat)abstract
- A tandem bis-allylation of p-toluenesulfonyl isocyanate can be achieved by palladium-catalyzed three-component coupling reaction with allylstannanes and allyl chlorides. A high level of regioselectivity can be obtained by the appropriate choice of the allylic substituents. The reaction mechanism and the regiochemistry of the reaction can be explained by formation of an amphoteric bis-allylpalladium intermediate. This bis-allylpalladium intermediate undergoes an initial electrophilic attack on one of the allyl moieties followed by a nucleophilic attack on the other.
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| 6. |
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