Novel strategies for asymmetric hydrogenation reactions [Elektronische Ressource] / Dianjun Chen

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• Publié par: rheinisch-westfalischen_technischen_hochschule_-rwth-_aachen
• Publié le: 01 janvier 2011
• Nombre de lectures: 88
• Langue: English
• Poids de l'ouvrage: 3 Mo

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Novel Strategies for Asymmetric Hydrogenation
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Von der Fakultät für Mathematik, Informatik und Naturwissenschaften der
RWTH Aachen University
zur Erlangung des akademischen Grades eines Doktors der
Naturwissenschaften genehmigte Dissertation




vorgelegt von



MsSc. Dianjun Chen

aus Hubei, China


Berichter: Universitätsprofessor Dr. rer. nat. Walter Leitner
Juniorprofessor Dr. rer. nat. Jürgen Klankermayer

Tag der mündlichen Prüfung: 14. Februar 2011


Diese Dissertation ist auf den Internetseiten der Hochschulbibliothek online verfügbar Der experimentelle Teil der vorliegenden Arbeit wurde in der Zeit von Oktober 2006
bis Mai 2010 am Institut für Technische und Makromolekulare Chemie der Rheinisch-
Westfaelischen Technischen Hochschule Aachen unter Anleitung von Univ. -Prof.
Dr.Walter Leitner angefertigt.
II






Selected results from this thesis were already published:

(1) Enantioselective catalysis with tropos ligands in chiral ionic liquids
Mike Schmitkamp, Dianjun Chen, Walter Leitner, Jürgen Klankermayer, Giancarlo
Franciò, Chem. Commun. 2007, 39, 4012-4014.

(2) Enantioselective hydrogenation with racemic and enantiopure BINAP in the
presence of a chiral ionic liquid
Dianjun Chen, Mike Schmitkamp, Giancarlo Franciò, Jürgen Klankermayer, Walter
Leitner, Angew. Chem. 2008, 120, 7449-7451; Angew. Chem. Int. Ed. 2008, 47, 7339-
7341.

(3) Metal-free catalytic hydrogenation of imines with tris(perfluorophenyl) borane
Dianjun Chen, Jürgen Klankermayer, Chem. Commun. 2008, 18, 2130-2131.

(4) Asymmetric induction by chiral Borate anions in enantioselective hydrogenation
using a racemic Rh-BINAP catalyst
Dianjun Chen, Basker Sundararaju, Rafael Krause, Jürgen Klankermayer, Pierre H.
Dixneuf, Walter Leitner, ChemCatChem 2010, 2, 55-57.

(5) Enantioselective hydrogenation with chiral frustrated Lewis pairs
Dianjun Chen, Yutian Wang, Jürgen Klankermayer, Angew. Chem. Int. Ed. 2010, 49,
9475-9478.
IIIAbstract
This thesis describes two novel possibilities for asymmetric hydrogenation:
enantioselective hydrogenation using chiral ionic liquid systems and metal-free
hydrogenation with boranes.
In the first part, asymmetric hydrogenation systems using chiral ionic liquids in
combination with racemic rhodium catalyst are presented. Enantioselectivities up to
69 % ee were achieved in homogeneous Rh-catalyzed hydrogenation with tropos ligand
(BIPHEP, sulfonated BIPHEP) in a proline derived cation chiral ionic liquid as the
exclusive source of chiral information. After extraction of product from ionic liquid
phase with scCO , the catalytic system could be reused three times with 70-75 % 2
retention of activity and selectivity. In the same chiral ionic liquid, with atropos but
racemic ligand BINAP, the hydrogenation of dimethyl itaconate resulted in identical
level of enantioselectivity (67 % ee) as that obtained with the enantiopure BINAP under
the conventional conditions. Kinetic and NMR spectroscopic investigations revealed a
chiral poisoning mechanism of this catalytic system. Using racemic BINAP together
with an ionic ligand comprising a chiral borate anion, the Rh-catalyzed hydrogenation
of dimethyl itaconate led to an enantioselectivity up to 57 % ee. The
enantiodifferentiation was attributed to diastereomeric formation of ion-pairs between
cationic catalyst and the chiral borate anion in this case.
In the second part, a novel metal-free catalytic system was developed for the reduction
of imines with H. Simple Lewis acid tris(perfluorophenyl)borane and 2
bis(perfluorophenyl)borane were found to be effective catalysts for hydrogenation of
oimines at relative mild conditions (80 C, 20 bar of H ). A thermal induced imine / 2
borane H -activation mechanism was proposed following the concept of “frustrated 2
Lewis pairs”. This catalytic system could be extended to the asymmetric hydrogenation
by the employment of chiral borane as catalyst. A number of commercially available
and synthesized chiral alkenes were used for the preparation of chiral borane through
hydroboration with bis(perfluorophenyl)borane. With these boranes as catalysts, the
hydrogenation of imines with H led to enantioselectivities up to 57 % ee. Camphor 2
derived chiral boranes could be applied in the hydrogen activation together with tri-tert-
butylphosphine under mild conditions. Significant enantioselectivities up to 83 % ee
IVwere obtained for the first time using the ‘frustrated Lewis pairs’ concept with these
chiral catalytic systems.
VAcknowledgement
I am deeply grateful for the assistance and contributions of many people to the work in
this dissertation, without you, it would not have been possible.
First and foremost, I want to thank my supervisor, Prof. Dr. Walter Leitner, for his
continuous guidance and support during my studies. I feel fortunate to have the
opportunity to work in a strongly international team with outstanding working
conditions.
I would like to thank Prof. Dr. Jürgen Klankermayer for being a great direct supervisor.
He provided me with the freedom to pursue my ideas, at same time, steered me in the
right direction at several critical points. I spent a pleasant time to work with him in the
last few years.
I would like to express my sincere thanks to Dr. Giancarlo Franciò for his invaluable
advices and discussions.
Special thanks to Dipl.-Chem Rafael Krause, Basker Sundararaju and Eva Spieker for
the successful cooperation on the chiral ionic liquids project.
I also thank these people:
Frau Ines Bachmann-Remy for the performance of NMR spectroscopic measurements.
Frau Hannelore Eschmann and Frau Julia Wurlitzer for their help with GC and HPLC
measurements.
Frau Brigitte Pütz for performing MS and HRMS measurements of sensitive
compounds.
Mike Schmitkamp and Sandra Walendy for their generous help in the laboratory.
My lab colleagues: Dr. Valentin Cimpeanu, Dr. Alexander Kraynov, Barthel Engendahl,
for pleasant working atmosphere.
All members of the technical staff of the ITMC for valuable technical assistance.
All members of the Leitner and Liauw group for the great work atmosphere.
Finally, the special thanks are given to my parents, my sister and brother in law for their
encouragement and support.
VITable of Content

ABSTRACT ............................................................................................................................................. IV
ACKNOWLEDGEMENT ...................................................................................................................... VI
1. ENANTIOSELECTIVE HYDROGENATION USING CHIRAL IONIC LIQUID SYSTEMS.....1
1.1 INTRODUCTION ...................................................................................................................................1
1.1.1 Chiral ionic liquids (CILs).........................................................................................................1
1.1.2 Chiral activation and deactivation.............................................................................................8
1.2 OBJECTIVE OF THE PRESENT WORK...................................................................................................14
1.3 RESULT AND DISCUSSION..................................................................................................................15
1.3.1 Enantioselective catalysis with tropos ligands in chiral ionic liquids .....................................15
1.3.2 Enantioselective hydrogenation with racemic and enantiopure BINAP in the presence of
chiral ionic liquids............................................................................................................................21
1.3.3 Asymmetric hydrogenation with chiral borate anions in the enantioselective hydrogenation
using a racemic Rh-BINAP catalyst..................................................................................................28
1.4 CONCLUSIONS AND OUTLOOK ..........................................................................................................34
1.5 EXPERIMENTAL ................................................................................................................................36
1.5.1 General ....................................................................................................................................36
1.5.2 Synthesis...................................................................................................................................37
1.5.2.1 (S)-2-(methoxycarbonyl)pyrrolidinium bis(trifluoromethylsulfonyl)amide (1-37a)......................... 37
1.5.2.2 (S)-2-(ethoxycarbonyl)pyrrolidinium bis(trifluoromethylsulfonyl)amide (1-37b) ........................... 37
1.5.2.3 (S)-2-(isopropoxycarbonyl)pyrrolidinium bis(trifluoromethylsulfonyl)amide (1-37c)..................... 38
1.5.2.4 (S)-2-(tert-butoxycarbonyl) pyrrolidinium bis(trifluoromethylsulfonyl) amide (1-37d)................... 38
1.5.2.5 (S)-2-(methoxycarbonyl)pyrrolidinium nitrate (1-37e).............