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Impact of Secondary Interactions in Asymmetric Catalysis
KTH, School of Chemical Science and Engineering (CHE), Chemistry, Organic Chemistry.
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 [en]
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: urn:nbn:se:kth:diva-4380ISBN: 978-91-7178-676-0 (print)OAI: oai:DiVA.org:kth-4380DiVA: diva2:12045
Public defence
2007-06-01, D3, D, Lindstedtsv. 5, Stockholm, 10:00
Opponent
Supervisors
Note
QC 20100709Available from: 2007-05-16 Created: 2007-05-16 Last updated: 2010-07-09Bibliographically approved
List of papers
1. OH–Pd(0) Interaction as a Stabilizing Factor in Palladium-Catalyzed Allylic Alkylations
Open this publication in new window or tab >>OH–Pd(0) Interaction as a Stabilizing Factor in Palladium-Catalyzed Allylic Alkylations
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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.

Keyword
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:nbn:se:kth:diva-7123 (URN)10.1073/pnas.0307084101 (DOI)000220861500019 ()2-s2.0-1842862757 (Scopus ID)
Note
QC 20100709Available from: 2007-05-16 Created: 2007-05-16 Last updated: 2017-12-14Bibliographically approved
2. OH–Pd Hydrogen Bonding in Pd(0)–Olefin Complexes Containing Hydroxy-Substituted Ligands
Open this publication in new window or tab >>OH–Pd Hydrogen Bonding in Pd(0)–Olefin Complexes Containing Hydroxy-Substituted Ligands
(English)Manuscript (Other academic)
National Category
Organic Chemistry
Identifiers
urn:nbn:se:kth:diva-7124 (URN)
Note
QC 20100709Available from: 2007-05-16 Created: 2007-05-16 Last updated: 2010-07-09Bibliographically approved
3. Conformational preferences and enantiodiscrimination of phosphino-4-(1-hydroxyalkyl)oxazoline-metal-olefin complexes resulting from an OH-metal hydrogen bond
Open this publication in new window or tab >>Conformational preferences and enantiodiscrimination of phosphino-4-(1-hydroxyalkyl)oxazoline-metal-olefin complexes resulting from an OH-metal hydrogen bond
2005 (English)In: Journal of Organic Chemistry, ISSN 0022-3263, E-ISSN 1520-6904, Vol. 70, no 24, 9882-9891 p.Article in journal (Refereed) Published
Abstract [en]

Phosphinooxazolines carrying (1-hydroxy-1-phenyl)methyl and (1-methoxy-1-phenyl)methyl substituents in the 4 position of the oxazoline ring exhibit contrasting behavior in Pd-and Ir-catalyzed allylic alkylations. Whereas catalysts with the methoxy-containing ligand generally provide products with high ee's, use of catalysts prepared from the hydroxy-containing ligand results in products with low ee's or even racemates. DFT calculations suggest the presence of a hydrogen bond with Pd(0) as the proton acceptor in the hydroxy-containing olefin-Pd(0) complexes, which induces a conformational change in the ligand, leading to different stereoselectivity.

Keyword
Catalyst selectivity; Catalysts; Conformations; Hydrogen bonds; Molecular structure; Olefins; Stereochemistry; Substitution reactions
National Category
Organic Chemistry
Identifiers
urn:nbn:se:kth:diva-7125 (URN)10.1021/jo051610q (DOI)000233539200027 ()2-s2.0-28044432560 (Scopus ID)
Note

QC 20100709

Available from: 2007-05-16 Created: 2007-05-16 Last updated: 2017-12-14Bibliographically approved
4. Ag+-Assisted Hydrosilylation: Complementary Behavior of Rh and Ir Catalysts (Reversal of Enantioselectivity)
Open this publication in new window or tab >>Ag+-Assisted Hydrosilylation: Complementary Behavior of Rh and Ir Catalysts (Reversal of Enantioselectivity)
2007 (English)In: Organic Letters, ISSN 1523-7060, E-ISSN 1523-7052, Vol. 9, no 7, 1371-1374 p.Article in journal (Refereed) Published
Abstract [en]

The presence of a suitably situated hydroxy function in a PHOX ligand leads to an enhancement of the enantioselectivity in Rh-catalyzed hydrosilylations of prochiral ketones in the presence of AgBF4 (95% ee for acetophenone as compared to 75% using i-Pr-phosphinooxazoline (PHOX)). Exchanging Rh for Ir affords the product with the opposite absolute configuration (78% ee).

Keyword
CONTAINING OXAZOLINE LIGANDS; ASYMMETRIC HYDROSILYLATION; ALLYLIC SUBSTITUTION; CHIRAL LIGANDS; HYDROGEN-BONDS; KETONES; COMPLEXES
National Category
Organic Chemistry
Identifiers
urn:nbn:se:kth:diva-7126 (URN)10.1021/ol0702730 (DOI)000245084300050 ()2-s2.0-34147177030 (Scopus ID)
Note
QC 20100709Available from: 2007-05-16 Created: 2007-05-16 Last updated: 2017-12-14Bibliographically approved
5. Bifunctional Pybox Ligands: Application in Cyanations of Benzaldehyde
Open this publication in new window or tab >>Bifunctional Pybox Ligands: Application in Cyanations of Benzaldehyde
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(English)Manuscript (Other academic)
National Category
Organic Chemistry
Identifiers
urn:nbn:se:kth:diva-7127 (URN)
Note
QC 20100709Available from: 2007-05-16 Created: 2007-05-16 Last updated: 2010-07-09Bibliographically approved

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