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«Inaugural-Dissertation towards the academic degree Doctor rerum naturalium (Dr. rer. nat.) Submitted to the Department of Biology, Chemistry and ...»

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Fluorinated and Trifluoromethylated

Buckybowls

Inaugural-Dissertation towards the academic degree

Doctor rerum naturalium (Dr. rer. nat.)

Submitted to the Department of Biology, Chemistry and Pharmacy,

Freie Universität Berlin

Bernd M. Schmidt, Berlin

December 2012

In Gedenken an meine Großmutter

Waltraut Vogi (✝28.08.2011)

The present work was carried out under the supervision of Prof. Dr. Dieter Lentz from

October 2009 to December 2012 at the Institute of Chemistry and Biochemistry, at the Freie Universität Berlin.

First Reviewer: Prof. Dr. D. Lentz Second Reviewer: Prof. Dr. H.-U. Reißig Date of Defense: 15.02.2013 Publications Parts of this work have been published prior to submission of this manuscript or are due to be published as described below.

Scientific journals:

B. M. Schmidt, B. Topolinski, S. Higashibayashi, T. Kojima, M. Kawano, D. Lentz, H. Sakurai, The Synthesis of Hexafluorosumanene and its Congeners. Manuscript in preparation.

B. M. Schmidt, S. Seki, B. Topolinski, K. Ohkubo, S. Fukuzumi, H. Sakurai, D. Lentz, Electronic Properties of Trifluoromethylated Corannulenes. Angewandte Chemie International Edition 2012, 51, 11385–11388.

B. M. Schmidt, S. Seki, B. Topolinski, K. Ohkubo, S. Fukuzumi, H. Sakurai, D. Lentz, Elektronische Eigenschaften Trifluormethylierter Corannulene. Angewandte Chemie 2012, 124, 11548-11551.

B. M. Schmidt, B. Topolinski, P. Roesch, D. Lentz, Electronpoor N-substituted Imide-fused Corannulenes. Chemical Communications 2012, 48, 6520-6522.

B. Topolinski, B. M. Schmidt, M. Kathan, S. I. Troyanov, D. Lentz, Corannulenylferrocenes:

Towards a 1D, Non-covalent Metal-organic Nanowire. Chemical Communications 2012, 48, 6298-6300.

S. Mebs, M. Weber, P. Luger, B. M. Schmidt, H. Sakurai, S. Higashibayashi, S. Onogi, D. Lentz, Experimental Electron Density of Sumanene, a Bowl-shaped Fullerene Fragment;

Comparison with the related Corannulene Hydrocarbon. Organic & Biomolecular Chemistry 2012, 10, 2218-2222.

Conference Lectures:

B. M. Schmidt, H. Sakurai, B. Topolinski, S. Seki, S. Higashibayashi, D. Lentz, 15. Deutscher Fluortag, September 2012, Schmitten (Germany).

B. M. Schmidt, H. Sakurai, B. Topolinski, S. Higashibayashi, D. Lentz, 20th International Symposium on Fluorine Chemistry, July 2012, Kyoto (Japan).

B. M. Schmidt, D. Lentz, at the 15th Meeting of the Graduate School "Fluorine as the Key Element", June 2011, Berlin (Germany.)

Conference Posters:

B. M. Schmidt, B. Topolinski, P. Roesch, H. Sakurai, D. Lentz, at the GDCh- Wissenschaftsforum Chemie, September 2011, Bremen (Germany).

B. M. Schmidt, A. K. Meyer, B. Topolinski, D. Lentz, at the 2nd CSI General Meeting of the Center for Supramolecular Interactions, March 2011, Berlin (Germany).

Acknowledgements I want to thank Professor Dr. D. Lentz for the opportunity to conduct this work in his group and for his constant believe in the success of this thesis. The measurements and computations of countless of difficult X-ray analyses are highly appreciated and were a key to the success of this work.

Professor Dr. H.-U. Reissig reviewed this thesis and provided help with the HPLC separation, which was carried out for one compound in his group.

Professor Dr. H. Sakurai supported me since my undergraduate studies, like my doctoral adviser. I want to thank you not only for countless inspiring discussions, but also for the trust and support you gave to two foreign strangers.

I am grateful for all the help, profound knowledge and willingness to guide and support me, which I received from so many people from so many countries around the world. Especially Dr. Shuhei Higashibayashi, Dr. Moritz Kühnel, Dr. Qitao Tan, Dr. Katrin Niedermann, Dr. Ryoji Tsuruoka and Professor Dr. Shu Seki are acknowledged.

I am indebted to all the former and present members of the Lentz and Seppelt research group, Stefanie Fritz, Darina Heinrich, Dr. Thomas Hügle, Juliane Krüger, Annika Meyer, Dr.

Matthias Molski, as well as current and former members of the Sakurai group: Dr. Nasir Baig, Dr. Raghu Nath Dhital, Setsiri Haesuwannakij, Yuka Ishida, Patcharin Kaewmati, Noriko Kai, Keita Kataoka, Jinyoung Koo, Dr. Yuki Morita, Sachiko Nakano, Yuki Okabe, Satoru Onogi, Professor Dr. Gautam Panda, Dr. Patcharee Preedasuriyachai, Dr. Tsuyuka Sugiishi and Dr.

Sal Prima Yudha.

Additionally, I want to thank all research students who joined lab U306, Alma Jäger, Michael Kathan, Simon Poremski, Kai Redies, Volker Rohde, Philip Roesch, Antti Senf and Mihoko Yamada, for the time we spent discussing inside and outside of the lab and their contributions.

I want to thank Lena Kaufmann and Dominic Gröger for enjoyable lunch breaks and conversations.

Finally, I am most grateful to my girlfriend Berit and my family & friends for their support and patience.

Contents

–  –  –

1.1 Discovery of bowlshaped polycyclic aromatic hydrocarbons During the last 40 years, the chemistry of carbon rich compounds evolved dramatically. The discovery of fullerenes in 1985[1] and the accompanied discovery of the existence of endohedral metallofullerenes,[2] which encapsulate an (metal) atom into its spherical space inside the carbon cage, gave rise to research and the discovery of various types of carbon nanostructures. A related class of three-dimensional carbon surfaces, carbon nanotubes, were prepared in 1991 by using a reactor similar to the one used for the mass production of C60.[3] Single-walled carbon nanotubes (SWNTs) show favourable properties like high thermal conductivity and other fascinating mechanical[4] and electrical properties.[5] Substructures of SWNTs like cycloparaphenylenes inspired various research groups around the world to synthesize cycloparaphenylenes size-selectively and to study their inherent properties and ring-size effects.[6] The latest groundbreaking discovery was made at the beginning of this century, when Andre Geim and Kostya Novoselov succeeded in extracting single-atom-thick crystallites (graphene) from bulk graphite in 2004.[7] Single layers of graphite were previously grown epitaxially on top of other materials but significant charge transfer between the substrate and the graphene notably altered its properties.[8]

–  –  –





Research, other than on its crystal structure determination[10] has been prohibited because of its very low availability, but has been revived with the afore-mentioned discovery of fullerenes.[1a] The bowlshaped C20 structure can be considered as a fullerene subunit, which is relevant, not only as model compound for fullerenes, but also because of its own chemical and physical properties, that were investigated when the group of Siegel and Scott started to improve its synthesis during the 1990s.

2 Scheme 1.3. Main retrosynthetic approaches.

The group of Professor Scott designed and executed a short synthesis of corannulene starting with acenaphtenequinone.[11] After further improvement in development and by the use of a simple DielsAlder reaction, a 7,10-disubstituted fluoranthene was generated and chemically transformed to the precursor molecule 7,10-bis(1-chlorovinyl)fluoranthene. A high-temperature pyrolysis (FVP, flash vacuum pyrolysis) of this precursor generated corannulene in about 30 % yield (200 mg can be obtained from one pyrolysis).[12]

–  –  –

The concepts of masked acetylene by the introduction of the 1-chlorovinyl group as a latent ethynyl group in FVP and other mechanisms have been used successfully for the preparation of numerous other new PAHs, related and unrelated to corannulene.[13] This includes the synthesis of [5,5]fulvalene circulene (C30H12),[14] the hemifullerene (triindenotriphenylene, C30H12)[14a, 15] and finally the first rational synthesis of Buckminster-fullerene C60 in isolable quantities.[16] Although the preparation of corannulene by FVP includes a small number of synthetic steps, this strategy suffers from several drawbacks. A suitable FVP apparatus, which withstands the high temperatures of more than a 1000 °C has to be used, almost no functional groups are tolerated and 3 scaling up of the reaction is very difficult or impossible. Therefore, a new solution phase synthesis of corannulene became an important target. The first published example of a corannulene derivative made by a solution-phase synthesis, only was reported by Siegel and co-workers a few years later[17] and further improvement on the synthesis followed by the group of Siegel[18] and Rabideau and Sygula.[19] Finally in 2012, the kilogram-scale synthesis of corannulene was again reported by the group of Siegel, providing access to commercial production and engineering applications.[20] Scheme 1.5. The current benchmark method for the synthesis of corannulene by Siegel’s group,[20] including refinements made by Rabideau and Sygula.[19] The growing availability of corannulene over the course of time increased its popularity and a variety of studies on corannulene and its derivatives appeared.[21] The large π-system undergoes reductions with different alkali metals up to the tetraanion, which was extensively studied by NMR experiments.[22] Condensed and connected corannulene derivatives were also investigated,[23] including their supramolecular oligomerization[24] and heterodimer formation with fullerenes.[25] Hereinafter corannulene anions were studied in the solid state by single-crystal X-ray diffraction,[26] demonstrating selective endo and exo binding[27] and finally confirming the formation of a sandwichtype supramolecular aggregate for the lithium-coordinated corannulene tetraanion.[28] 4 η6-coordination of the curved carbon surface of corannulene was achieved from corresponding ruthenium[29] and osmium[29d] complexes, accompanied by flattening of the corannulene bowl, so that two ruthenium complex ions can be coordinated.[29c] Other metal complexes include η2coordination (generating 1D infinite chains)[30] and mono-,[31] di-,[31-32] tetra-,[32] and penta-[32] σbonded complexes. These have been obtained from the corresponding halogenated precursors by insertion. Halogenated corannulenes were used to synthesize the whole family of indenocorannulenes by palladium-catalysed cross-coupling reactions[33] and were furthermore studied crystallographically.[34] Wu and Siegel obtained functionalized multiethynylcorannulenes and studied their photophysical properties,[35] in addition to the corannulene conjugates prepared by Sutton.[36] In 2012 the group of Professor Scott pushed the boundaries of organic synthetic methods. Starting from the symmetrical pentachlorocorannulene,[37] a short [5,5]-SWNT has been synthesized by stepwise chemical methods with a final FVP step.[38] Figure 1.1. Molecular structure of the short carbon nanotube (C50H10), as determined by X-ray crystallography in the group of Scott.[38] The physical properties of pristine corannulene have been investigated thoroughly in the last decades. The solid state structure was investigated and shows a bowl depth of 0.87 Å and no columnar π-stacking or edge-to-face interactions.[10, 39] The bowl however is not rigid, a bowl-to-bowl inversion process via a planar transition state occurs.[40] The difference in energy between the curved structure and the transition structure represents the bowl inversion energy ΔG‡inv, which can be measured experimentally by variable-temperature NMR studies of suitable substituted corannulenes.

Consequently, the bowl inversion barrier of corannulene was estimated to 11.5 kcal/mol, which 5 implies that the corannulene system inverts 200,000 times per second at room temperature.[41] Albeit some excerpts,[37, 42] a correlation between rim-substitution, bowl depth and inversion barrier can be established.

In 2003, the group of Sakurai succeeded in synthesizing a missing link,[43] the molecular bowl sumanene (C21H12), which can also be considered as a curved subunit of the fullerene C60. The stability of sumanene was predicted several years ago,[44] but attempts to synthesize it, failed.[45] At last, the key to success was to construct a 3D framework mostly based on tetrahedral sp3 carbons. By oxidative aromatization, the π-conjugated bowl was obtained.

Scheme 1.6. The synthesis of sumanene (C21H12).

The bowl inversion energies of sumanene derivatives were experimentally investigated using 2D-EXSY NMR and a value of 20 kcal/mol was obtained,[46] a much slower inversion compared to that of corannulene. In this regard, the experimental bowl depth observed is 1.11 Å,[47] which is deeper than the bowl depth of corannulene (0.87 Å).[10] The curvature already corresponds to 78 % of that of C60.[47a] 6 Figure 1.2. Space-filling model of the 1D columnar π-stacking in a concave-convex fashion.[47a] The group of Seki and Hirao utilized the perfect columnar staggered stacking along the crystallographic c axis and could show that sumanene is an organic n-type semiconductor. High electron mobility along the molecular stacking axis was measured by time-resolved microwave conductivity methods (TRMC), with an anisotropic difference of 9.2 times (parallel versus perpendicular to the c axis) because of the efficient overlap of the molecules.[48] Further unique features of sumanene are its benzylic positions, which can be used for further functionalization to create new bowl-shaped derivatives, like extended π-bowls[49] and π-extended compounds[50] or which can be oxidized to give sumanenetrione.[51] Other compounds include the C3 symmetric chiral trimethylsumanene, which was obtained by asymmetric synthesis[52] or the chiral triazasumanenes, opening a complete new field of research of nitrogen-doped buckybowls in 2012.[53]

71.2 Organic compounds and fluorine



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