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Ag+-Assisted Hydrosilylation: Complementary Behavior of Rh and Ir Catalysts (Reversal of Enantioselectivity)
KTH, School of Chemical Science and Engineering (CHE), Chemistry, Organic Chemistry.
KTH, School of Chemical Science and Engineering (CHE), Chemistry, Organic Chemistry.ORCID iD: 0000-0002-1743-7650
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).

Place, publisher, year, edition, pages
2007. Vol. 9, no 7, 1371-1374 p.
Keyword [en]
CONTAINING OXAZOLINE LIGANDS; ASYMMETRIC HYDROSILYLATION; ALLYLIC SUBSTITUTION; CHIRAL LIGANDS; HYDROGEN-BONDS; KETONES; COMPLEXES
National Category
Organic Chemistry
Identifiers
URN: urn:nbn:se:kth:diva-7126DOI: 10.1021/ol0702730ISI: 000245084300050Scopus ID: 2-s2.0-34147177030OAI: oai:DiVA.org:kth-7126DiVA: diva2:12043
Note
QC 20100709Available from: 2007-05-16 Created: 2007-05-16 Last updated: 2010-07-09Bibliographically 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
Supervisors
Note
QC 20100709Available from: 2007-05-16 Created: 2007-05-16 Last updated: 2010-07-09Bibliographically approved

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