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Transition metal-catalysed hydrogen transfer processes for C-C and C-N bond formation: Synthetic studies and mechanistic investigations
Stockholm University, Faculty of Science, Department of Organic Chemistry.
2012 (English)Doctoral thesis, comprehensive summary (Other academic)
Abstract [en]

This thesis focusses on synthetic studies and mechanistic investigations into reactions involving hydrogen-transfer processes.

In the first part, the development of an efficient method for the synthesis of β-hydroxy ketones (aldols) and β-amino ketones (Mannich products) from allylic alcohols and aldehydes is described. These reactions use  Ru(η5-C5Ph5)(CO)2Cl as the catalyst. The reaction parameters were optimised in order to suppress the formation of undesired by-products. Neutral and mild reaction conditions enabled the synthesis of a variety of aldol products in up to 99% yield, with a good syn/anti ratio. The influence of the stereoelectronic properties of the catalyst on the reaction outcome was also studied. Based on the results obtained, a plausible reaction mechanism has been proposed, involving as the key steps the 1,4-addition of hydride to α,β-unsaturated ketones and the formation of ruthenium (Z)-enolates.

In the second part of this thesis, a ruthenium-catalysed tandem isomerisation/C-H activation reaction is presented. A number of ruthenium complexes, phosphine ligands, and additives were evaluated in order to establish the optimal reaction conditions. It was found that the use of a stable ruthenium catalyst, Ru(PPh3)3Cl2, together with PtBu3 and HCO2Na resulted in an efficient tandem transformation. Using this procedure, a variety of ortho-alkylated ketones were obtained in excellent yields. Moreover, homoallylic alcohols could also be used as starting materials for the reaction, which further expands the substrate scope. Mechanistic investigations into the isomerisation part of the process were carried out.

The last project described in the thesis deals with the design and preparation of novel bifunctional iridium complexes containing an N-(2-hydroxy-isobutyl)-N-Heterocyclic carbene ligand. These complexes were used as catalysts to alkylate amines using alcohols as latent electrophiles. The catalytic system developed here was found to be one of the most active systems reported to date, allowing the reaction to be performed at temperatures as low as 50 °C for the first time. A broad substrate scope was examined. Combined experimental and theoretical studies into the reaction mechanism are consistent with a metal-ligand bifunctional activity of the new catalyst.

Place, publisher, year, edition, pages
Stockholm: Department of Organic Chemistry, Stockholm University , 2012. , 90 p.
Keyword [en]
hydrogen transfer, catalysis, transition metal
National Category
Organic Chemistry
Research subject
Organic Chemistry
Identifiers
URN: urn:nbn:se:su:diva-81596ISBN: 978-91-7447-595-1 (print)OAI: oai:DiVA.org:su-81596DiVA: diva2:562713
Public defence
2012-11-30, Magnélisalen, Kemiska övningslaboratoriet, Svante Arrhenius väg 16 B, Stockholm, 10:00 (English)
Opponent
Supervisors
Available from: 2012-11-08 Created: 2012-10-25 Last updated: 2012-11-06Bibliographically approved
List of papers
1. Synthesis of b-Hydroxy Ketones from Allylic Alcohols via Catalytic Formation of Ruthenium Enolates
Open this publication in new window or tab >>Synthesis of b-Hydroxy Ketones from Allylic Alcohols via Catalytic Formation of Ruthenium Enolates
2008 (English)In: Chemistry - A European Journal, ISSN 0947-6539, E-ISSN 1521-3765, Vol. 14, no 34, 10547-10550 p.Article in journal (Refereed) Published
Abstract [en]

The most efficient Ru-catalyzed isomerization–aldol reaction from allylic alcohols has been achieved by using [η5-(Ph5Cp)Ru(CO)2Cl] as the catalyst. The bulky pentaphenylcyclopentadienyl ligand on the ruthenium atom prevents protonation at the oxygen of the Ru–enolate intermediate and completely suppresses the formation of unwanted ketone byproducts (see scheme). The domino transformation is as good as it can be: aldols are obtained in quantitative yields at ambient temperature.

Keyword
aldol reaction, allylic compounds, CC coupling, isomerization, ruthenium
National Category
Organic Chemistry
Research subject
Organic Chemistry
Identifiers
urn:nbn:se:su:diva-81981 (URN)10.1002/chem.200801690 (DOI)
Available from: 2012-11-06 Created: 2012-11-05 Last updated: 2017-12-07Bibliographically approved
2. Synthesis of β-Hydroxy and β-Amino Ketones from Allylic Alcohols Catalyzed by Ru(η5-C5Ph5)(CO)2Cl
Open this publication in new window or tab >>Synthesis of β-Hydroxy and β-Amino Ketones from Allylic Alcohols Catalyzed by Ru(η5-C5Ph5)(CO)2Cl
Show others...
2012 (English)In: European Journal of Inorganic Chemistry, ISSN 1434-1948, E-ISSN 1099-1948, no 9, 1517-1530 p.Article in journal (Refereed) Published
Abstract [en]

An efficient method for the synthesis of beta-hydroxy and beta-amino ketones from allylic alcohols catalyzed by Ru(5-C5Ph5)(CO)2Cl is described. The influence of the stereoelectronic properties of the catalyst on the reaction outcome has been studied. Optimization of the reaction conditions supressed the formation of undesired side products such as saturated ketones, benzyl alcohols, and a,beta-unsaturated ketones. Several aromatic and aliphatic allylic alcohols have been reacted with a large variety of aldehydes or imines to produce beta-hydroxy ketones or beta-amino ketones, respectively, in yields up to 99%. Based on experimental data, a mechanism via ruthenium alkoxides and ruthenium aldoxides is proposed. In addition, a C-bound ruthenium enolate has been characterized.

Keyword
Synthetic methods, Homogeneous catalysis, Ruthenium, Isomeri-zation, Allylic alcohols, Amines, Mannich reaction, Aldols, Ketones
National Category
Organic Chemistry
Research subject
Organic Chemistry
Identifiers
urn:nbn:se:su:diva-76270 (URN)10.1002/ejic.201101014 (DOI)000301494500028 ()
Funder
Swedish Research CouncilKnut and Alice Wallenberg FoundationVINNOVABerzelii Centre EXSELENT
Note

5

Available from: 2012-05-21 Created: 2012-05-10 Last updated: 2017-11-13Bibliographically approved
3. Building molecular complexity via tandem Ru-catalyzed isomerization/C-H activation
Open this publication in new window or tab >>Building molecular complexity via tandem Ru-catalyzed isomerization/C-H activation
2009 (English)In: Organic Letters, ISSN 1523-7060, E-ISSN 1523-7052, Vol. 11, no 8, 1749-1752 p.Article in journal (Refereed) Published
Abstract [en]

A tandem isomerization/C-H activation of allylic alcohols was performed using a catalytic amount of RUCl(2)(PPh(3))(3). A variety of ortho alkylated ketones have been obtained in excellent yields. This tandem process relies on an in situ generation of a carbonyl functional group that directs the ortho C-H bond activation.

National Category
Organic Chemistry
Research subject
Organic Chemistry
Identifiers
urn:nbn:se:su:diva-30863 (URN)10.1021/ol900243x (DOI)000265084300020 ()
Available from: 2009-10-29 Created: 2009-10-29 Last updated: 2012-11-06Bibliographically approved
4. A Highly Active Bifunctional Iridium Complex with an Alcohol/Alkoxide-Tethered N-Heterocyclic Carbene for Alkylation of Amines with Alcohols
Open this publication in new window or tab >>A Highly Active Bifunctional Iridium Complex with an Alcohol/Alkoxide-Tethered N-Heterocyclic Carbene for Alkylation of Amines with Alcohols
Show others...
2012 (English)In: Chemistry - A European Journal, ISSN 0947-6539, E-ISSN 1521-3765, Vol. 18, no 45, 14510-14519 p.Article, review/survey (Refereed) Published
Abstract [en]

A series of new iridium(III) complexes containing bidentate N-heterocyclic carbenes (NHC) functionalized with an alcohol or ether group (NHC?OR, R=H, Me) were prepared. The complexes catalyzed the alkylation of anilines with alcohols as latent electrophiles. In particular, biscationic IrIII complexes of the type [Cp*(NHC-OH)Ir(MeCN)]2+2[BF4-] afforded higher-order amine products with very high efficiency; up to >99?% yield using a 1:1 ratio of reactants and 12.5 mol?% of Ir, in short reaction times (216 h) and under base-free conditions. Quantitative yields were also obtained at 50?degrees C, although longer reaction times (4860 h) were needed. A large variety of aromatic amines have been alkylated with primary and secondary alcohols. The reactivity of structurally related iridium(III) complexes was also compared to obtain insights into the mechanism and into the structure of possible catalytic intermediates. The IrIII complexes were stable towards oxygen and moisture, and were characterized by NMR, HRMS, single-crystal X-ray diffraction, and elemental analyses.

Keyword
amines, carbene ligands, iridium, bifunctional catalyst, synthetic methods
National Category
Organic Chemistry
Research subject
Organic Chemistry
Identifiers
urn:nbn:se:su:diva-81977 (URN)10.1002/chem.201201845 (DOI)000310474800036 ()
Funder
Swedish Research CouncilKnut and Alice Wallenberg FoundationVINNOVABerzelii Centre EXSELENT
Available from: 2012-11-06 Created: 2012-11-05 Last updated: 2017-11-10Bibliographically approved

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