New polycondensed aromatic compounds for applications in the hydrogen cycle

214 Pages·2011·7.74 MB·French

by  Nicolas Fragnière

Département de Chimie
Université de Fribourg (Suisse)
New polycondensed aromatic compounds
for applications in the hydrogen cycle
Thèse
présentée à la Faculté des Sciences de l’Université
de Fribourg (Suisse) pour l’obtention du grade de
Doctor rerum naturalium
Nicolas Fragnière
de Sâles (FR)
Thèse N° 1724
UniPrint
2011
Acceptée par la Faculté des Sciences de l’Université de Fribourg (Suisse) sur la proposition du
jury composé de:
Prof. Dr. Katharina M. Fromm, Université de Fribourg, présidente du jury,
Prof. Dr. Titus A. Jenny, Université de Fribourg, directeur de thèse, rapporteur,
Prof. Dr. Andreas Kilbinger, Université de Fribourg, corapporteur,
Prof. Dr. Yves Rubin, University of California, Los Angeles, corapporteur.
Fribourg, le 19 septembre 2011
Le directeur de thèse Le doyen
Prof. Dr. Titus A. Jenny Prof. Dr. Rolf Ingold
A mes parents, Madeleine et André,
A mes soeurs, Florence et Anne-Laure,
A Valérie et Charline

«Le génie commence les beaux ouvrages,
mais le travail seul les achève.»
Joseph Joubert

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Acknowledgments
This work has been realized under the guidance of Prof. Dr. Titus A. Jenny in the period of Oc-
tober 2007 until September 2011 at the Department of Chemistry, University of Fribourg (Swit-
zerland).
I would like to express my deep gratitude to Prof. Dr. Titus A. Jenny for accepting me in his
research group and for the possibility to realize this work. His enthusiasm and the numerous
councils he has given me has been really helpful.
I would also like to express my gratefulness to Prof. Dr. Yves Rubin and Prof. Dr. Andreas Kil-
binger for their kind acceptance as experts.
My gratitude goes to Katharina Fromm, the president of the Jury.
I also want to thank Prof. Dr. Norbert Engel and Prof. Dr. Titus A. Jenny to give me the oppor-
tunity to guide the students during their practical works.
Many thanks goes to the analytical service of the University of Fribourg: Freddy Nyddegger
(mass analysis), Felix Fehr (NMR analysis) and Inge Müller (general support) for their help.
A special thank to Nicolas Monney, Julien Ducry and Ramona Staehli, who have participated
to this project.
I also want to thank Xavier Hanselmann, Lucienne Rouiller, Bernadette Khun-Piccand, Noelle
Chassot and Nicolas Hoyler of the central service.
Many thanks to Maja Ivanovic, Emerith Brügger and Verena Schwalm for all the administrative
work.
Michel Piccand is acknowledged for the poster impressions and the IT.
All my gratitude to Anne Schuwey and her team for all the syntheses they have made for me.
I thank all the members of the Jenny group for the work very pleasant environment, Olivier Ae-
ii
bischer, Deborah Gusmeroli, Daniela Bossi, Patrick Tondo, Mauro Schindler and Sofia Martin
Caba.
Many thanks to all my colleagues for all the great moments we had. More than colleagues there
are now some friends.
For the nine years we passed together, I really thank my friends Ursi, Karin and Michael.
Finally a real special thank goes to my family, Papa, Maman, Florence, Anne-Laure, Valérie et
Charline for all the love and joy they give me every day.
This project was supported by the Swiss National Science Foundation
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Summary
This work presents the synthesis of a new perfluorinated sulfonic acid function HBC which car-
ries a sulfonic acid at the end of one perfluorinated side-chain.The aim of the introduction of
this sulfonic acid is its ability to form proton channels which could be used as electrolyte in pro-
ton exchange membranes for fuel cells. The channels would be created by the formation of
stacks of three molecules clusters oriented by the hydrophobic effect of the perfluorinated
chains and hydrophilic effect of the sulfonic acid. The π-π stacking would occur by the well-
known properties of HBCs compounds building columns, and hence protons channels would
be formed.
The synthesis of the compound was achieved by a convergent strategy, coupling a perfluoro-
alkyl tetraphenyl cyclopentadienone and a perfluoroalkyl dissymmetric tolane, thanks to a
Diels-Alder reaction. If no real difficulties were met for the formation of the required cyclopen-
tadienone synthon, the preparation of the dissymmetric tolane was more complicated because
of the presence of the sulfonic acid function, which decreases the reactivity, because of solu-
bility issues. Finally the desired compound was obtained as a brown solid by a cyclodehydro-
genation oxidation of a perfluoroalkyl hexaphenyl benzene sulfonic acid and could be analysed
by MALDI-MS, UV absorption and fluorescence spectroscopy, which all confirmed the pres-
ence of this new HBC. With the deposition of this new material on a water impermeable porous
membrane, this HBC could facilitate the selective proton transfer across the membrane and act
therefore as a proton channel membrane.
For comparison, the synthesis of an alkylated HBC sulfonic acid was also planned, using the
same approach as for the perfluorinated HBC analogue. Even if the synthesis of this HBC was
not totally achieved, much preliminary work was done on the attachment of the sulfonic acid.
The best strategy seems to be a nucleophilic substitution of an alcohol function by bromine fol-
lowed by the exchange with a sulfonate, using sodium sulfite. Because of solubility problems,
to best stage at which this sulfonate formation should be performed has to be found.
Second, for an envisioned application in hydrogen gas storage, the synthesis of a new bowl-
shaped polycondensed aromatic compound based on the oxidation of pentaphenyl cyclopen-
tadiene precursor will be discussed. This newly envisioned material is based on a property of
corannulene, which is known as a potential hydrogen absorber. With a larger surface area than
corannulene, our target compound would allow the storage of a larger quantity of hydrogen. As
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synthetic approaches for corannulene are not applicable for our target molecule, the formation
of a pentaphenyl cyclopentadiene derivative which would then be oxidized under Scholl condi-
tions was planned. Commonly used for the oxidation of flat polycondensed aromatic com-
pounds such as hexabenzocoronenes, the Scholl oxidation is a real challenge in the case of
bowl-shaped molecules, because the carbon atoms are further away from each other and the
reaction would have to overcome considerable strain.
So far, the desired bowl-shaped polyaromatic compound has not been obtained. The numer-
ous oxidation attempts either yielded starting material or some unidentified molecules. Since
complexation by iron could stabilize the desired product, the pentaphenyl cyclopentadienyl de-
rivative was successfully complexed with iron, forming ferrocene-like compounds. Unfortunate-
ly, this complexation did not improve the reactivity of the pentaphenyl cyclopentadiene moiety
towards cyclodehydrogenation. Therefore, this idea remains unachieved.