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OH–Pd(0) Interaction as a Stabilizing Factor in Palladium-Catalyzed Allylic Alkylations
KTH, Superseded Departments, Chemistry.
KTH, Superseded Departments, Chemistry.
KTH, Superseded Departments, Chemistry.
KTH, Superseded Departments, Chemistry.
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2004 (English)In: Proceedings of the National Academy of Sciences of the United States of America, ISSN 0027-8424, E-ISSN 1091-6490, Vol. 101, no 15, 5400-5404 p.Article in journal (Refereed) Published
Abstract [en]

In palladium-catalyzed alkylations of allylic acetates with malonate as nucleophile, catalysts with oxazoline ligands bearing hydroxymethyl substituents in 4-position have been shown by density functional theory computations to undergo a conformational change on nucleophilic attack, which is accompanied by reduction of Pd(II) to Pd(0). The conformations of the Pd(0) complexes were shown to be governed by the presence of a hydrogen bond with the metal center acting as a hydrogen bond acceptor. The conformational change, which is absent in catalysts with O-alkylated analogs, largely affects the enantioselectivity of the catalytic process. This process is a previously uninvestigated example of where this type of weak hydrogen bond has been shown to influence the stereochemistry of a chemical reaction.

Place, publisher, year, edition, pages
2004. Vol. 101, no 15, 5400-5404 p.
Keyword [en]
cetic acid; allyl acetate; allyl compound; hydroxide; ligand; malonic acid; oxazoline derivative; palladium; unclassified drug; alkylation; article; catalyst; chemical reaction; conformation; conformational transition; density functional theory; enantioselectivity; hydrogen bond; priority journal; stereochemistry
National Category
Organic Chemistry
Identifiers
URN: urn:nbn:se:kth:diva-7123DOI: 10.1073/pnas.0307084101ISI: 000220861500019Scopus ID: 2-s2.0-1842862757OAI: oai:DiVA.org:kth-7123DiVA: diva2:12040
Note
QC 20100709Available from: 2007-05-16 Created: 2007-05-16 Last updated: 2012-03-21Bibliographically approved
In thesis
1. Impact of Secondary Interactions in Asymmetric Catalysis
Open this publication in new window or tab >>Impact of Secondary Interactions in Asymmetric Catalysis
2007 (English)Doctoral thesis, comprehensive summary (Other scientific)
Abstract [en]

This thesis deals with secondary interactions in asymmetric catalysis and their impact on the outcome of catalytic reactions.

The first part revolves around the metal-catalyzed asymmetric allylic alkylation reaction and how interactions within the catalyst affect the stereochemistry. An OH–Pd hydrogen bond in Pd(0)–π-olefin complexes of hydroxy-containing oxazoline ligands was identified by density functional theory computations and helped to rationalize the contrasting results obtained employing hydroxy- and methoxy-containing ligands in the catalytic reaction. This type of hydrogen bond was further studied in phenanthroline metal complexes. As expected for a hydrogen bond, the strength of the bond was found to increase with increased electron density at the metal and with increased acidity of the hydroxy protons.

The second part deals with the use of hydroxy- and methoxy-containing phosphinooxazoline ligands in the rhodium- and iridium-catalyzed asymmetric hydrosilylation reaction. The enantioselectivities obtained were profoundly enhanced upon the addition of silver salts. This phenomenon was explained by an oxygen–metal coordination in the catalytic complexes, which was confirmed by NMR studies of an iridium complex. Interestingly, the rhodium and iridium catalysts nearly serve as pseudo-enantiomers giving products with different absolute configurations.

The final part deals with ditopic pyridinobisoxazoline ligands and the application of their metal complexes in asymmetric cyanation reactions. Upon complexation, these ligands provide catalysts with both Lewis acidic and Lewis basic sites, capable of activating both the substrate and the cyanation reagent. Lanthanide and aluminum complexes of these ligands were found to catalyze the addition of the fairly unreactive cyanation reagents ethyl cyanoformate and acetyl cyanide to benzaldehyde, whereas complexes of ligands lacking the Lewis basic coordination sites failed to do so.

Place, publisher, year, edition, pages
Stockholm: KTH, 2007. 60 p.
Series
Trita-CHE-Report, ISSN 1654-1081 ; 2007: 29
Keyword
asymmetric catalysis, secondary interaction, hydrogen bond, chiral ligand, allylic alkylation, hydrosilylation, cyanation, pymox, box, PHOX, pybox, palladium, iridium, rhodium, Lewis acid, Lewis base
National Category
Organic Chemistry
Identifiers
urn:nbn:se:kth:diva-4380 (URN)978-91-7178-676-0 (ISBN)
Public defence
2007-06-01, D3, D, Lindstedtsv. 5, Stockholm, 10:00
Opponent
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Note
QC 20100709Available from: 2007-05-16 Created: 2007-05-16 Last updated: 2010-07-09Bibliographically approved

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Moberg, Christina

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