Synthesis and Electronic Properties of New Organic Materials ––––––––––––––––––––––

Synthesis and electronic properties of new organic materials –––––––––––––––––––––––––––––––– Synthese und elektronische Eigenschaften von neuen organischen Materialien

Der Naturwissenschaftlichen Fakultät der Friedrich-Alexander-Universität Erlangen-Nürnberg

zur Erlangung des Doktorgrades Dr. rer. nat.

vorgelegt von Anna Chiara Sale

aus Bitti

Als Dissertation genehmigt von der Naturwissenschaftlichen Fakultät der Friedrich-Alexander-Universität Erlangen-Nürnberg

Tag der mündlichen Prüfung: 7/05/2015

Vorsitzender des Promotionsorgans: Prof. Dr. Jörn Wilms Gutachter: Prof. Dr. Rik R. Tykwinski Gutachter: Prof. Dr. Norbert Jux

Die vorliegende Arbeit entstand in der Zeit von März 2012 bis Februar 2015 am Institut für Organische Chemie (Lehrstuhl I) der Friedrich-Alexander-Universität (FAU) Erlangen- Nürnberg.

Pro sa vamiglia mea e Giovanni.

Per la mia famiglia e Giovanni.

„La più bella e profonda emozione che possiamo provare è il senso del mistero; sta qui il seme di ogni arte, di ogni vera scienza“

A. Einstein

Zusammenfassung

Diese Arbeit basiert auf des Untersuchung an polyzyklischen aromatischen Kohlenwasserstoffen (PAH). Der erste Teil dieser Arbeit befasst sich mit den elektrochemischen Untersuchungen von PAH: Pentacenderivate sowie verschiedene kationische Triangulene und Heterotriangulene wurden durch Cyclovoltammetrie analysiert. Der zweite Teil dieser Arbeit konzentriert sich auf die Synthese arylsubstituierte, Benzolderivate und ihrer Anwendung in der Diels-Alder Reaktion, um Bausteine für PAH herzuskellen. In diesem Zusammenhang werden Triine mit verschiedenen Endgruppen synthetisiert, in einer Diels-Alder Reaktion mit Tetraphenylcyclopentadienon umgesetzt und anschließend in Desilylierungs und Homokupplungs Reaktionen weiter verwendet. Die Diels-Alder-Cycloadditionen werden entweder unter thermischen Bedingungen oder Mikrowellenbestrahlung durchgeführt. Kapitel 1 der vorliegenden Dissertation gibt einen Einblick in kohlenstoffreichen Materialien mit Schwerpunkt auf PAH. Zudem wird ein Überblick über die Analysemethode Cyclovoltammetrie und ihre Verwendung bei mehreren Klassen von PAH gegeben: Pentacen-Derivate, kationische Triangulene und Heterotriangulene. Abschließend werden allgemeine Synthesevorschiften für Triine im Zusammenhang mit der Reaktivität von Polyinen diskutiert. Kapitel 2 zeigt die Synthese und die elektrochemischen Eigenschaften von arylsubstituierten Pentacenen. Ihre relativen HOMO-LUMO Bandlücken werden im Kontext ähnlicher literaturbekannter Verbindungen untersucht. Kapitel 3 beschreibt die Synthese und die elektrochemischen Eigenschaften der Triangulen- Derivate. Der erste Teil des Kapitels konzentriert sich auf die Cyclovoltammetrie von kationischen Triangulenen und deren Helicen-Vorstufen im Vergleich mit dem aktuellen Literatur. Der zweite Teil des Kapitels beschäftigt sich mit der Cyclovoltammetrie von Heterotriangulen Derivaten. Kapitel 4 beschreibt die Synthesen verschiedener substituierter Triine. Diese werden in einer Diels- Alder-Cycloaddition, sowohl unter konventionellem Heizen als such unter Mikrowellenbestrahlung, durchgeführt. Tetraphenylcyclopentadienon reagiert als Dien mit den entsprechenden Triinen zu Tetraphenyl-substituierten Benzolderivaten. Hieraus sind durch eine Abfolge von Desilylierungs und Homokupplungs Reaktionen Dimere erhalten wurden. Monomere und Dimere sind durch UV- vis Spektroskopie, Cyclovoltammetrie und Röntgenkristallographie charakterisiert wurden. Kapitel 5 beinhaltet die experimentellen Vorschriften und Daten der Vorstufen und der Zielmoleküle. In Kapitel 6 sind die 1H und 13C NMR Spektren zu finden.

Abstract

The work described in this thesis is focused on the investigation of polycyclic aromatic hydrocarbons (PAHs). The first topic concerns the electrochemical investigation of PAHs. Pentacene derivatives as well as various cationic triangulenes and heterotriangulenes are analyzed by cyclic voltammetry. The second topic of the thesis is related to the use of the Diels-Alder reaction to obtain aryl substituted benzene derivatives, which might be utilized as precursors for the assembly of PAH. In this context, different end-capped triynes are synthesized as building blocks that are used in Diels-Alder reactions with tetraphenylcyclopentadienone. The Diels-Alder cycloadditions are performed under either thermal conditions or microwave irradiation. Selected Diels-Alder products are taken on to a sequence of desilylation and homocoupling reactions. Chapter 1 introduces carbon-rich materials with the focus on PAHs. This includes an overview about the cyclic voltammetry analysis of several class of PAHs is then presented: pentacene derivatives, cationic triangulenes, and heterotriangulene. Finally, general protocols to synthesize triynes are discussed, together with some example of polyynes reactivity. Chapter 2 presents the synthesis and electrochemical investigation of aryl substituted pentacenes and the relative HOMO-LUMO gaps are investigated. The results are compared to those obtained for similar compounds reported in literature. Chapter 3 describes the synthesis and electrochemical properties of triangulene derivatives. The first part of the chapter is focused on the cyclic voltammetry of cationic triangulenes and their helicene precursors. The results are compared to those obtained for similar compounds known in literature. The second part of the chapter deals with the cyclic voltammetry of heterotriangulene derivatives, and the results are compared to those reported for similar compounds. Chapter 4 describes the synthesis of different substituted triynes. The resulting triynes are taken on to a Diels-Alder cycloaddition reaction which is performed under conventional heating as well as under microwave irradiation. Tetraphenylcyclopentadienone is used as the diene in the Diels-Alder reactions, and this overall reaction results in the construction of tetraphenyl-substituted benzene derivatives. Selected products of these Diels-Alder reactions are taken on to a sequence of desilylation and homocoupling reactions to provide dimers. Selected monomers and dimers have been analyzed by UV-vis spectroscopy, cyclic voltammetry, and X-ray crystallography.

Chapter 5 includes experimental data of the precursors and target compounds, and a description of instruments and methods is provided. Chapter 6 presents an appendix containing the 1H and 13C NMR spectra of selected compounds.

List of Symbols

Å Angström δ chemical shift (NMR) ε molar extinction coefficient Δ heat

λ wavelength

λmax wavelength of lowest energy absorption μ micro J Coupling constant (NMR)

List of Abbreviations

ACN acetonitrile APPI atmospheric pressure photoionization aq aqueous Ar aryl Bu n-butyl calcd calculated CCDC Cambridge Crystallographic Data Centre cm centimeter(s) cmpd compound CV cyclic voltammetry d doublet (NMR) d day(s) deg degree(s) decomp decomposition DMF N, N-dimethylformamide D-π-A donor-π-acceptor E electrochemical potential E½ electrochemical half-wave potential

EA elemental analysis

Egap, el electrochemical band gap energy ESI electrospray ionization Et ethyl EtOAc ethyl acetate equiv equivalent(s) eV electron volt(s) FBW Fritsch-Buttenberg-Wiechell Fc/Fc+ ferrocene/ferrocenium g gram(s) h hour(s) HOMO highest occupied molecular orbital HRMS high resolution mass spectrometry Hz Hertz i iso IR infrared irrev irreversible L liter(s) LUMO lowest unoccupied molecular orbital m multiplet (NMR) m medium (IR) m meta M formula weight m molar LDI laser desorption ionization Me methyl mg milligram(s) MHz megaHertz Min minute(s) mL milliliter(s) mmol millimole(s) mol mole(s) Mp melting point

MS mass spectrometry mV millivolt(s) mw microwave m/z mass-to-charge ratio n-BuLi n-butyllithium NIR near-infrared nm nanometer(s) NMP n-methyl-2-pyrrolidone NMR nuclear magnetic resonance o ortho o-DCB 1,2-dichlorobenzene OFET organic field effect transistor p para PAH polycyclic aromatic hydrocarbon PCC pyridinium chlorochromate Ph phenyl ppm parts per million Pr propyl q quartet (NMR) quant quantitative

Rf retention factor ref reference rt room temperature s singlet (NMR) s strong (IR) s second(s) satd saturated sev several Sub suberyl t triplet (NMR) t tertiary TBAF tetrabutyl ammonium fluoride TCNE tetracyanoethylene

temp temperature TES triethylisilyl THF tetrahydrofuran TIPS triisopropylsilyl TIPS-pc 6,13-bis(triisopropylsilylethynyl)pentacene TLC thin layer chromatography TMEDA N,N,Nʹ′,Nʹ′-tetramethylethylenediamine TMS trimethylsilyl TOF time-of-flight TPCPD tetraphenylcyclopentadienone Tr* tris(3,5-di-t-butylphenyl)methyl TTF tetrathiafulvalene UV ultraviolet vis visible vw very weak (IR) w weak (IR) V volt

Table of Contents

Chapter 1. Introduction ...... 1

1.1 Carbon-rich compounds and polycylic aromatic hydrocarbons (PAHs) ...... 1

1.2 Acenes and pentacene ...... 3

1.3 Triangulenes as a class of PAH ...... 7

1.3.1 Cationic triangulenes...... 8

1.3.2 Heterotriangulenes ...... 9

1.4 Polyynes and acetylenes as possible start point to assembly PAHs ...... 12

1.4.1 Synthesis of triynes ...... 12

1.4.2 Reactivity of monoynes and polyynes ...... 14

1.5 Conclusion and motivation ...... 17

1.6 References ...... 18

Chapter 2. Electrochemical investigation of new aryl substituted pentacenes ...... 22

2.1 Introduction ...... 22

2.2 Synthesis of aryl substituted pentacenes ...... 24

2.3 Electrochemical investigation of aryl substituted pentacenes ...... 26

2.4 Conclusion ...... 33

2.5 References ...... 33

Chapter 3. Electrochemical investigation of new dyes based on functionalized triangulenes…………………………………………………………………………………..35

3.1 Introduction ...... 35

3.2 Electrochemical investigation of new dyes based on functionalized cationic

triangulenes ……………… ...... 36

3.2.1 Synthesis of cationic triangulenes ...... 36

3.2.2 Electrochemical investigation of new cationic triangulenes and relative

helicene precursors ...... 37

3.3 Electrochemical investigation of push-pull system based on

functionalized heterotriangulenes ...... 43

3.3.1 Synthesis of new functionalized heterotriangulenes ...... 43

3.3.2 Electrochemical investigation of new functionalized heterotriangulenes ...... 44

3.4 Conclusion ...... 50

3.5 References ...... 50

Chapter 4. Diels-Alder cycloaddition of tetraphenylcyclopentadienone and

1,3,5-hexatriynes……………………………………………………………………………...52

4.1 Introduction ...... 52

4.2 Synthesis of triynes……………………………………………………………….....54

4.3 Diels-Alder cycloaddition of tetraphenylcyclopentadienone (TPCPD)

and 1,3,5-hexatriynes under conventional heating………………………………….60

4.4 Diels-Alder cycloaddition of tetraphenylcyclopentadienone (TPCPD)

and 1,3,5-hexatriynes under microwave irradiation……………………………………….63

4.5 Desilylation and homocoupling reaction toward the formation of the dimers ...... 68

4.6 UV-vis spectroscopy, cyclic voltammetry, and X-ray crystallography ...... 71

4.7 Attempts to synthesize PAH derivatives via Scholl cyclodehydrogenation ...... 79

4.8 Conclusion ...... 80

4.9 References ...... 81

Chapter 5. Experimental section ...... 83

5.1 General data ...... 83

5.2 Synthesis of known compounds ...... 84

5.3 Synthesis of new compounds ...... 91

5.4 References ...... 106

Chapter 6. Appendix ...... 108

Chapter 1: Introduction

1.1.1 Carbon-rich compounds and polycyclic aromatic hydrocarbons (PAHs)

In recent years, many efforts have been directed to the investigation of carbon rich- compounds such as graphite, graphene, diamond, fullerenes, carbon nanotubes, and PAHs.1 Carbon rich materials have been incorporated into electronic devices such as OLEDs, FETs, and organic solar cells.1,2,3 Within the general class of carbon-rich compounds, polycyclic aromatic hydrocarbons (PAHs) are member of this class and composed of hydrogen and carbon atoms with multiple aromatic rings. Examples of PAH molecules are shown in Figure 1.1 (1.1−1.6). PAHs have been intensely investigated, especially in the field of organic chemistry, material science, and astronomy because they display interesting mechanical, electronic, and optical properties.4,5 Clar and Scholl are often referred as the pioneers of the synthesis of PAHs.6,7,8

1.1 1.2 1.3 1.4

1.5 1.6

Figure 1.1. Examples of common PAHs: hexa-peri-hexabenzocoronene 1.1, pyrene 1.2, pentacene 1.3, tribenzopentaphene 1.4, phenanthrene 1.5, and ovalene 1.6.

The material graphene can be defined as the homologue of molecular polycyclic aromatic hydrocarbon of quasi-infinite size.9 Since the first reported production in 2004,10 an increasing number of chemical and physical protocols have been developed to produce graphene.3,11,12,13 Graphene shows interesting and unique properties such as high electron mobility,14 thermal 1

Chapter 1: Introduction conductivity,15 optical transmittance, and electrical conductivity.16 Due to these, and other, interesting properties research on graphene has focused on possible applications such as in field effect transistors, sensors, transparent conductive films, and as electrodes for clean energy devices.17 Considering the potential application of PAHs reported in recent years,3,18 research efforts have been focused on the investigation of specific PAH such as acenes19 and triangulenes.20 Acenes describe a class of molecules that contain only linearly fused benzene rings, while triangulenes are defined as alternant polycyclic aromatic hydrocarbons with zigzag edges (triangular structure). As a part of the synthesis of new PAHs, new methodologies have been accomplished based on the use acetylene chemistry.2,21 The alkyne functionality is an attractive entry point to synthesize PAHs due to its high-carbon content and the possibility of modular assembly via the Diels-Alder reaction, cyclodehydrogenation, and cross-coupling chemistry leading to a rapid construction of PAH. Several examples are reported in the literature describing the use of functionalized alkynes to construct PAH moieties via phenyl-substituted benzene derivatives.22 In general, rather detailed knowledge about the electronic properties of conjugated molecules is required in order to consider the compounds for incorporation into devices. Related to this, electrochemical techniques, and especially cyclic voltammetry, can play a significant role for understanding the electronic properties of organic compounds. With cyclic voltammetry, for example, it is possible to investigate the HOMO and LUMO energy levels, as well as the HOMO−LUMO gap, which are both fundamental parameters for evaluating organic compounds in devices. The first goal of the thesis is to investigate the electronic properties of new pentacene and triangulene derivatives by cyclic voltammetry. Thus, the following introduction provides an overview about the use of cyclic voltammetry to study selected classes of PAH including pentacenes and triangulenes. The second goal of the thesis is to synthesize triynes and explore the reactivity of this class of compounds in Diels-Alder reactions with tetraphenylcyclopentadienone to obtain tetraphenylbenzene derivatives that might be used as precursors for PAH. Such aryl- substituted benzene have been used in opto-electronic devices and supramolecular assembly materials.23,24,25 Thus, the introduction section also provides a brief overview of synthetic protocols described in literature for the synthesis of triynes, as well as a general overview of reactivity of monoynes and polyynes that might be used for the formation of PAH.

Chapter 1: Introduction

1.2 Acenes and pentacenes

Acenes are polycyclic aromatic hydrocarbons that contain linearly fused benzene rings (Figure 1.2). Acenes have been often investigated as organic semiconductors.19 Within the class of acenes, pentacene 1.3 has been particularly well studied and shows interesting optoelectronic properties. It has, for example, already been used as p-type material in organic solar cells combined with fullerene as n-type semiconductor.26 Pentacene 1.3 was first synthesized by Clar in 1930 (Figure 1.2).7,27 More recently, the purpose to understand the potential use of 1.3 in organic devices, the opto-electronic properties were analyzed for comparison with the results obtained for other PAH. The electrochemical properties of pentacene 1.3 were investigated using voltammetry experiments. Pentacene 1.3 displays an oxidation event at 0.3 V, and a reduction process at −1.8 V (calculated vs Fc/Fc+ in o- dichlorobenzene). Both processes are reversible and the electrochemical HOMO−LUMO gap of 1.3 is thus 2.1 eV.28

4 5 6 7 8 3 9 2 10 n 1 14 13 12 11 1.3

Figure 1.2. General structure of acenes and unsubstituted pentacene (1.3) with atomic labelling.

Unfortunately, pentacene exhibits poor solubility in common organic solvents and is rather unstable under ambient conditions. The most reactive regions of the pentacene framework are usually the 6- and 13-positions, and these are the preferential location for photo-oxidation and Diels−Alder reactions. In order to tune solubility, stability, electronic, and optical properties of 1.3, research has focused on the synthesis of pentacene derivatives through introducing substituents to the acene framework. Pentacene derivatives also display significant charge-transport ability, strong absorption in UV-vis region, stability under ambient conditions, and processability.29,30 Two main strategies to functionalize pentacenes have been adopted: 1) blocking the 6- and 13-positions with substituents 2) appending electron-withdrawing groups substituents at 2,3,9,10-positions. Pentacenes functionalized in 2,3,9,10-positions of the pentacene core with donor groups such as in 2,3,9,10-tetramethylpentacene 1.7 are also reported. Pentacene 1.7 shows more solubility in common organic solvents compared to 1.3. Concerning the electronic properties, the presence of

Chapter 1: Introduction methyl groups increased slightly the HOMO energy level (−4.41 eV) compared to unsubstituted pentacene 1.3 (−4.49 eV, Figure 1.3).31

1.7

Figure 1.3 Pentacene 1.7 investigated by Meng and coworkers.31

One of the goals of acene research is to change the electronic properties of derivatives of 1.3 through the synthetic design of compounds with smaller HOMO−LUMO gaps, while maintaining stability under ambient conditions. Several relevant studies are provided by Miller and coworkers.32 They have investigated the stability of different aryl substituted pentacene 1.8−1.12 (Figure 1.4), and they have reported on the influence of substituents on the values of the HOMO−LUMO gaps. It has been demonstrated that the steric hinderance associated with aryl substituents marginally affects the electrochemical HOMO−LUMO gap, namely pentacenes with 2,6-dimethyl or 2.6-diethyl substitution (1.9 and 1.8, respectively) are somewhat more difficult to reduce and oxidize than phenylated 1.10 (Figure 1.4) where the HOMO−LUMO gap values are 2.01 eV, 2.04 eV, and 1.92 eV. The aryl substituted pentacenes 1.8−1.12 are only partially conjugated to the pentacene ring because of the orthogonal orientation of the aryl rings. As a result, significant differences in the series of pentacenes 1.8−1.12 are not observed in terms of electronic absorption as demonstrated by the λmax value of 601 nm for 1.8, 604 nm for 1.9, and 605 nm for 1.10. All analyzed compounds (1.8−1.12) show an optical HOMO−LUMO gap in the range of 1.92 to 2.04 eV, which is similar to that defined by the cyclic voltammetry experiments and smaller compared to 1.3 (2.1 eV). With respect to stability, the authors show that the inclusion of electron-withdrawing group at the 2,3,9,10-position as in 1.11 leads to a longer-lived species compared to 1.9. The opposite effect is observed with the inclusion of electron-donating groups, tetra-donor 1.12 is less stable compared to 1.10.

Chapter 1: Introduction

1.8 (2.04 eV) 1.9 (2.01 eV) 1.10 (1.92 eV)

Cl Cl O O

1.11 (1.97 eV) 1.12 (1.94 eV)

Figure 1.4 Aryl substituted pentacenes 1.8−1.12 with their relatives electrochemical HOMO−LUMO gaps shown in parenthesis studied by Miller and coworkers.32

The most relevant contributions to pentacene chemistry have been provided by Anthony and coworkers who synthetized 1.13, so called TIPS-pentacene (TIPS-pc, Figure 1.5).33 Compared to 1.3, TIPS-pc shows excellent solubility in many organic solvents, and it is also reasonably stable under ambient conditions in the presence of air, light, and water. Compound 1.13 has been studied electrochemically by cyclic voltammetry and displays two oxidation (0.39 V and 0.99 V) and one reduction potential (−1.52 V); all three of which are reversible. Thus, 1.13 shows a smaller HOMO- LUMO gap (electrochemical 1.91 eV, optical 1.84 eV) compared to unsubstituted pentacene 1.3 (2.1 eV). The change of the HOMO−LUMO gap is ascribed to a decrease of the LUMO energy value because of extended conjugation from the silylethynyl groups, and to the increased electronegativity of sp-hybridized carbons of the ethynyl moieties.34

Chapter 1: Introduction

Sii-Pr3

Sii-Pr3 1.13

Figure 1.5. Pentacene 1.13 synthesized by Anthony.33

To extend the π-system of 1.13 toward improving device characteristics, a new pentacene derivative with additional donor substituents at the 2,3,9,10-positions (1.14) has been explored. The additional alkyl groups appended to the framework of 1.14 result in a decrease in the oxidation potential to 0.69 V for 1.14 compared to 0.85 V observed for 1.13. Pentacene 1.15 has also been assembled in which ethynyl groups have been inserted at the 2,3,6,9,10,13-positions of the pentacene skeleton (Figure 1.6). Compound 1.15 shows even a smaller HOMO−LUMO gap (1.74 eV) compared to 1.13 (1.91 eV).35,36

SiMe Sii-Pr3 3

Me3Si SiMe3

H17C8 C8H17

H17C8 C8H17 Me3Si SiMe3

SiMe Sii-Pr3 3

1.14 1.15

Figure 1.6. Pentacenes 1.14 studied by Wudl and 1.15 investigated by Neckers.35,36

For incorporating organic compound into devices based on light absorption, such as solar cells, the compound should ideally possess a significant absorption in the range of 350 to 525 nm. While pentacene 1.13 has a reasonably small HOMO−LUMO gap, it is transparent in the region of 350−525 nm. As a result, efforts have been directed on the synthesis of other pentacene derivatives in which the absorption is shifted into the visible region. For example, Tykwinski and coworkers have reported about pentacenes derivatives 1.16a−f with a TIPS ethynyl group attached to the 6- position that helps to maintain the solubility, and with a PAH moiety appended to the 13-position through an ethynyl spacer (Figure 1.7). The result of this substitution pattern is a chromophore with

Chapter 1: Introduction extended conjugation and absorption in the range of 300 to 475 nm.37 The electronic aspects of these derivatives have been examined by CV. Derivatives 1.16a−f show one oxidation and two reduction processes and all three events are reversible. Compounds 1.16c and 1.16f show a second oxidation potentials which is reversible. Both the reduction and oxidation potentials become easier as the size of the pendent PAH increased, and the electrochemical HOMO−LUMO gaps decrease from 1.83 eV for 1.16a to 1.81 eV for 1.16b to 1.71 eV for 1.16c.

Sii-Pr3

Ar = Ar

1.16a 1.16b 1.16c 1.16d 1.16e 1.16f

Figure 1.7. Pentacenes derivatives 1.16a−f reported by Tykwinski and coworkers.37

1.3 Triangulenes as a class of PAH

Triangulenes are defined as alternant polycyclic aromatic hydrocarbons with zigzag edges that result in a triangular structure (Figure 1.8). All the attempts to synthesize the parent triangulene 1.17 have failed so far because the structure is highly reactive due to the biradical nature in the ground state.20 As a result of the instability, triangulene derivatives such as cationic triangulenes and heterotriangulenes have been investigated.38,39 The functionalization of triangulenes is based on three different key points. Region X is defined by the 4-, 8- and 12-positions and with variation of the structure of this region, the electronic demands can be regulated by insertion of for example O or N atoms (Figure 1.8). Substitution in region Y (radial and flanking) can modify the symmetry of 1.17 while variation at the central Z position can be used to vary the solubility through the incorporation of heteroatoms such as N, B or P.40

Chapter 1: Introduction

Y 2 a) b) or 1 3 X: controls electronic demand, could be O N Y: controls symmetry, could be alkyl or aryl moieties X X or . 12 4 Z: controls solubility, could be N, P B Z 11 5 10 6 X 9 8 7

flanking Y radial Y 1.17

Figure 1.8. Triangulene structure: 1.17 with atoms labeling and with definition of positions X, Y, and Z.

1.3.1 Cationic triangulenes

Cationic triangulenes have attractive absorption and emission properties due to rigid planar structure. They also show good stability, which is often also observed also in strongly basic solutions.41 Cationic triangulenes are also important in the field of biology, and there are examples of the interaction of cationic triangulenes with DNA sequences as intercalating agents.42 The study of cationic triangulenes in basic solutions is particularly interesting because the stability of these compounds could make them potential candidates for the use in phase transfer catalysis.41 The stability of cationic triangulenes in basic solution is related to the resistance to nucleophilic

+ attack of water and the hydroxide anion. This resistance is expressed by the pKR values of these

+ compounds. A pKR is defined by the equilibrium between the cationic species and their corresponding carbinols. HX is an acidity function characteristic for the cation/carbinol equilibrium 41 and the solvent system (Figure 1.9).

+ + R3C + H2O R3COH + H

+ pKR+ = HX + log [R3C ]

[R3COH]

+ Figure 1.9. Definition of pKR .

Cationic triangulenes are also important molecules because of their self-assembly properties, especially aggregation.43,44 It has been demonstrated that the delocalization of the positive charge of a cationic triangulene through the molecule strongly affects the aggregation in the solid state, and also the nature of the negative counterions has a noticeable influence on the photophysical 41 properties in solution and in condensed state. 8

Chapter 1: Introduction

The first triangulenium salt 1.18 was synthesized in 1963 by Martin and Smith (Figure 1.10).38 45 Laursen and Krebs synthesized the triazatriangulenium 1.19a that is considered more

+ thermodynamically stable compared to 1.18 (Figure 1.10). Compound 1.19a displays a pKR value

+ of 23.7 compared to 1.18 that shows pKR = 9.1. As a consequence of the bigger pKR value, 1.19a is more stable than 1.18. Related to the applications of cationic triangulenes as organic electronic materials, investigation of stability and the properties by cyclic voltammetry plays a significant role for understanding this class of compounds. Different atoms or substitution in the X-positions of the triangulene core of 1.17 have been incorporated and the products then explored by cyclic voltammetry, such as in the cationic triangulenes 1.18−1.21 by Lacour and coworkers (Figure 1.10).41 The electrochemical results demonstrated that with increasing of the numbers of N rather than of O-atoms, oxidation is easier and the reduction more difficult in the series 1.18 →1.20 →1.21 →1.19b. Specifically, an oxidation event is not observable for 1.18 and 1.20, while the oxidation potential decreases from 1.40 V for 1.21 to 1.20 V for 1.19b demonstrating the better donor ability of N-atoms compared to O-atoms which stabilizes the positive charge. A reduction process is observed for all the compounds with increasing values from −0.39 V for 1.18, to −0.5 V for 1.20, to −0.85 V for 1.21, and −1.40 for 1.19b.

R CH3 C3H7 O N N N

O O N N O O O N R R C3H7 BF - - BF - - 4 X 4 BF4

- 1.18 1.19a R = CH3, X = PF6 1.20 1.21 = = - 1.19b R C8H17, X BF4

Figure 1.10. Triangulenium salts 1.18−1.21 reported in literature.

1.3.2 Heterotriangulenes

A second class of triangulenes, the so called heterotriangulenes, includes derivatives in which the carbon atom at the central core of triangulene structure is replaced with, boron,46 phosphorous,47 or nitrogen atom.39 Heterotriangulenes are simple and attractive building blocks for functional organic materials such as n-type semiconductors.48 Examples of heterotriangulenes have been also reported in which the framework has been appropriately functionalized to serve as a push-

Chapter 1: Introduction pull dye where the planarity of the heterotriangulene framework can avoid phenomenon of the charge recombination.49 The first nitrogen-doped heterotriangulenes 1.22 and 1.23 have been synthesized by Hellwinkel and Melan (Figure 1.11).39,50,51 Compound 1.22 displays n-type semiconductor behavior52 because of the carbonyl groups that reduce the electron density in the core. Unfortunately, the properties of 1.22 could not be investigated by cyclic voltammetry because of the poor solubility of 1.22 in common organic solvents.53 The dimethylmethylene bridges of 1.23 increase the solubility in comparison to 1.22, but unfortunately, these groups also destroy the intermolecular charge transfer interactions. Compound 1.23 has been analyzed by cyclic voltammetry and shows a reversible oxidation event at 0.34 V vs Fc/Fc+.54

O O

N N

O 1.22 1.23

Figure 1.11. Heterotriangulenes reported by Melan and Hellwinkel.39,50,51

With the purpose to obtain π-expanded heterotriangulenes compared to 1.23, heterotriangulenes with substituents in the X and Y-positions 1.24a,b have been synthesized (Figure 1.12).55 Electrochemical investigations by cyclic voltammetry for 1.24a and 1.24b show a reversible oxidation process at 0.40 V for 1.24a and 0.39 V for 1.24b, as well as irreversible reduction processes that occur at −2.49 V for 1.24a and −2.15 for 1.24b.

C6F5 Ar Ar

Ar Ar N

F5C6 C6F5 Ar Ar 1.24a Ar = Ph 1.24b Ar = 2-naphthyl

Figure 1.12 Heterotriangulenes 1.24a-b reported by Chou and coworkers.55

Several heterotriangulenes with substituents in the Y-positions have been reported (1.25a−d),56 and these molecules are designed in order to expand the π-system of triangulene 1.22 and to increase the solubility compared to 1.21 (Figure 1.13). Compounds 1.25a−d have been investigated by cyclic 10

Chapter 1: Introduction voltammetry, and all derivatives except 1.25b display two reduction processes ascribed to the triangulene core (Figure 1.13). The inclusion of electron-withdrawing groups as substituents in 1.25b, 1.25c, 1.25d facilitate the first electron uptake, and the reduction for 1.25a the reduction is shifted cathodically due the directly linked of the alkyl substituent to the heterotriangulene core. Compound 1.25b shows an irreversible oxidation ascribed to the 3,5−bis(dodecyloxy)phenyl donor moiety.

O O

R R O

1.25a R = C12H25

OC12H25

1.25b R =

OC12H25

1.25c R = C12H25

Sii-Pr 1.25d R = 3

Figure 1.13. Heterotriangulenes 1.25a−d reported in literature.56

Ko and coworkers have reported heterotriangulenes 1.26a−c and their potential use as push-pull dyes where the donor moiety is represented by the heterotriangulene skeleton 1.23 and the acceptor linked to the core by thiophene units (Figure 1.14).49 Cyclic voltammetry measurements show a quasi-reversible couples process for each of the three molecules, with oxidation potentials of 1.07 V (1.26a), 1.00 V (1.26b), and 1.01 V (1.26c). Theoretical calculations have shown to determine the HOMO and LUMO energy levels and have been demonstrated that is possible to effect a photoinduced electronic transfer from 1.26a−c to the conduction band of the device.

Chapter 1: Introduction

R2 R1

1.26a R1 = H 1.26b R1 = OC6H13 R2 = S S 1.26c R1 = OC9H19 CN COOH

Figure 1.14. Heterotriangulenes derivatives 1.26a−c synthesized by Ko and coworkers.49

1.4 Polyynes and acetylenes as possible starting point to assemble PAHs

1.4.1 Synthesis of triynes

Triynes are compounds with series of three alternating of single and triple bonds, and these molecules belong to the class of compounds broadly described as polyynes. Due to their unique array of sp-hybridized carbon atoms, polyynes display interesting optoelectronic properties and are potentially suitable for incorporation into organic electronic devices.57,58 There are a variety of ways to synthesize triynes. Cadiot and Chodkiewicz have reported a cross- coupling reaction to obtain unsymmetrical triynes (Scheme 1.1a) in which the terminal diyne is reacted with a bromoalkyne derivative. This reaction can be complicated by the side reaction that involves that homocoupling reaction of the alkynyl halide, which leads to a mixture of products that can be difficult to separate. A version of this protocol using Pd as a catalyst has also been reported (Scheme 1.1b).59,60

CuCl, NH2OH HCl a) R H + Br R R R

EtNH2, MeOH, N2

PdCl2(PPh3)2, CuI b) R H + Br R R R i-Pr2NH, THF Scheme 1.1. Cadiot-Chodkiewicz cross coupling.59,60

Chapter 1: Introduction

Tobe and coworkers have reported the synthesis of triynes 1.27a,b (Scheme 1.2). Dialkynylmethylenebicyclo-[4.3.1]deca-1,3,5-triene derivatives that is irradiated with UV light (254 nm) to induce an electrocyclic ring closure followed by the [2+1] cheletropic fragmentation. Finally, FBW rearrangement reaction of the intermediate alkylidene carbyne affords triynes 1.27a,b.61

hv (254 nm) R R − R R = R R 1.27a R SiMe3 (43%) 1.27b R = Ph (37%)

Scheme 1.2. Synthesis of polyynes 1.27a−c reported by Tobe and coworkers.61

A synthesis of triynes 1.27a,b and 1.28a,b using a solution spray flash vacuum pyrolysis (SS-VP) has been reported starting from 3-cyclobutene-1,2-diones (Scheme 1.3). The starting material is introduced into a quartz tube under vacuum (1−2 torr) which leads to fragmentation and affords 1.27a,b and 1.28a,b. This technique can be efficient for compound that are thermally stable and non-volatile.62

O O SS-FVP R R 650 °C

R R 1.27a R = SiMe3 (99%) 1.27b R = Ph (97%) 1.28a R = SiMe2t-Bu (99%) = 1.28b R Sii-Pr3 (95%)

62 Scheme 1.3. Synthesis of triynes 1.27a,b and 1.28a,b proposed by Diederich and coworkers.

Tykwinski and coworkers have described a procedure to synthesize symmetrical triynes (Route B) 1.27a, 1.28b, and 1.29a−c as well as unsymmetrical triynes (Route A) 1.30a−e (Scheme 1.4). The steps of this synthetic protocol are based on a sequence involving alcohol formation followed by oxidation and dibromoolefination that leads to the triynes 1.27a, 1.28b, 1.29a−c, 1.30a−e. via FBW rearrangement.63, 64, 65

Chapter 1: Introduction

ROUTE A: R1 ≠ R2 ROUTE B: R1 = R2

1. n-BuLi 1. n-BuLi - OH - Et2O, 78 °C Et2O, 78 °C R1 H R2 H 2. O 2. O R1 R2 H H OEt R2

PCC CH2Cl2 rt

R1 R2

CBr4, PPh3 CH2Cl2 rt

Br Br n-BuLi, hexanes -78 °C R1 R2

R1 R2 1.28b, 1.27a, 1.29a-c 1.30a-e

1 2 1 = 2 = 1.28b R = R Sii-Pr3 70% 1.30a R SiMe3, R Sii-Pr3 61% 1 2 1 = 2 = 1.27a R = R SiMe3 50% 1.30b R 1-naphthyl, R SiMe3 70% 1 2 1 2 1.29a R = R n-Bu 80% 1.30c R = 1-naphthyl, R = Sii-Pr3 62% 1 2 1 = 2 = n 1.29b R = R n-octyl 66% 1.30d R SiMe3, R -Bu 82% 1 2 1.29c R1 = R2 64% 1.30e R = SiMe R = Sii-Pr3 61% 2-thienyl 3,

Scheme 1.4. Synthetic route to obtain triynes 1.28b, 1.27a, 1.29a−c, and 1.30a−e as reported by Tykwinski and coworkers.63,64,65

1.4.2 Reactivity of monoynes and polyynes

Many groups have focused research on the synthesis of long polyynes, but the reactivity of the polyyne products remains an undeveloped area. In one of the most useful examples reported to date Diederich and coworkers describe the reaction of electron rich tetrayne 1.31, with tetracyanoethylene (TCNE) and tetrathiafulvalene (TTF) to obtain a push-pull nonplanar molecule 14

Chapter 1: Introduction

1.32 (Scheme 1.5). In this sequential, but one pot reaction, TCNE is used to generate the acceptor groups and TTF donating units of the product 1.32.66 The selectivity of this reaction is based on pi- electron density resulting from the divergent endgroups.

Me2N

1.31

S S CN CN NC S S CN

CH2Cl2/ACN 50 °C

S S Me2N NC CN S S NC CN

NC CN S S NC CN S S

1.32 (21%)

Scheme 1.5. Reaction of polyyne 1.31 to obtain push-pull chromophore 1.32 as reported by Diederich and coworkers.66

White and coworkers reported a synthetic procedure where the central triple bond of the triyne 1.33 67 reacts with Co2(CO)6L2 (L2 = CO) to afford 1.34 (Scheme 1.7).

PPh3 Ph P Ru 3 PPh3 PPh3 Ru Co2(CO)6L2 Ru Ru Ph P C 3 PPh3 C PPh3 Ph3P MeOH,CH2Cl2 min 30 Co(CO)2L L(OC)2Co

= 1.33 1.34 L2 CO (56%)

Scheme 1.7. Reaction of triyne 1.33 with a cobalt complex to afford 1.34, as reported by White and coworkers.67

Another interesting reactivity pattern of polyynes concern the cycloaddition reaction of an azide, the so called Huisgen reaction. Walton and coworkers have developed a procedure in which the thermal reaction of benzyl azide with a silyl endcapped triyne (1.27a) affords the regioselective formation of the triazole product 1.35 (Scheme 1.8). In this case, the reaction regioselectivity is ascribed to orbital control via π−donation from the alkynyl system to silicon.68

Chapter 1: Introduction

O2N O2N N3 N N Me Si SiMe Me Si 3 3 3 N xylenes, reflux Me3Si

1.27a 1.35 (43%)

Scheme 1.8. Reaction of triyne 1.27a with benzyl azide to afford 1.35 as reported by Walton and coworkers.68

Tykwinski and coworkers have used a copper catalyzed variation of the Huisgen reaction to obtain triazoles using triynes 1.36a−d (Scheme 1.9). It was demonstrated that the reaction is regioselective with the attack of benzylazide at the terminal acetylenic bond (Scheme 1.9)69 to afford 1.37a−d. Others groups have also followed this protocol with polyynes.70,71,72

N3 N N R R H N CuSO4 5H2O ascorbic acid, DMF, rt

1.37a R = Bu 1.36a (71%) 1.37b R = Ph 1.36b ( 68%) 1.36c 1.37c R = OMe 1.36d (82%)

− = t Bu (73%) 1.37d R

Scheme 1.9. Reaction of triynes 1.36a−d using benzylazide to obtain 1.37a−d as reported by Tykwinski and coworkers.69

Müllen and coworkers have utilized a Diels-Alder reaction using aryl acetylene 1.38 as dienophile and tetraphenylcyclopentadienone (TPCPD) as diene to obtain hexaphenylbenzene 1.39 (Scheme 1.10).22 This reaction is versatile and has been used to assembly numerous carbon rich frameworks, often on the way to some of the largest PAHs to be synthesized with a defined structure.73,74

Chapter 1: Introduction

Br Br

Ph2O + 94 h, 250 °C

1.38 TPCBD 1.39 (85%)

Scheme 1.10. Diels−Αlder reaction reported by Müllen and coworkers to obtain 1.39.22

1.5 Conclusion and motivation

In this chapter an overview describing the electrochemical properties of PAH, the synthesis of triynes, and reactivity of poly- and monoyne compounds has been presented. Within the class of PAH, selected pentacene derivatives known in literature have been discussed. Functionalization of pentacene by varying the nature, positions, and type of substituents, allows to change the optoelectronic properties with the purpose to decrease the ΗΟΜΟ−LUΜΟ gap to better apply in organic electronic devices. A second class of PAH molecules that has been presented are the cationic triangulenes. These molecules show strong stability, planarity, and fluorescent properties. Different functionalization with acceptors moieties suggested by Ko and coworkers is a fascinating topic due to the potential use of heterotriangulene in push-pull chromophores where the heterotriangulene functionalized with dimethyl substituents in X-positions is used as donating unit. An overview about the synthesis of triynes that have been reported in literature has been presented. In general for polyynes compounds, research has been focused on the development of synthetic methods, but the reactivity is not fully explored. It is known that polyynes can react with metals such as cobalt and another reactivity pattern concerns the cycloaddition reaction. Trends for these additions, however, are not fully understood. The first goal of this thesis work was the investigation by cyclic voltammetry of the electronic properties and electrochemical HOMO−LUMO gaps of new pentacene derivatives with different substitutions in 6- and 13-positions synthesized by my colleague Andreas Waterloo. These studies further on understanding of the possible use of these new compounds in electronic devices. This topic is going to be discussed in Chapter 2.

Chapter 1: Introduction

A second goal of this thesis work was the investigation of the electrochemical properties by cyclic voltammetry of new cationic triangulenes and their helicene precursors with the purpose to understand the relative changes in terms of electronic properties. The synthesis of these compounds was conducted by Agnes Uhl in the groups of Prof. Dr. Jürgen Schatz. The third goal of the project was to investigate the electronic properties of new heterotriangulene derivatives synthesized by my colleague Ute Meinhardt in the Dr. Milan Kivala group with the final goal to explore the push-pull device behavior of this new compounds. These topics are discussed in Chapter 3. The Diels-Alder reaction with monoyne reported by Müllen (Scheme 1.10) offered a start point to explore the reactivity of triynes in Diels-Alder reactions and this topic is going to be discussed in Chapter 4. The first goal of the project was to synthesize triynes with different end-groups and then investigate the regioselectivity of the Diels-Alder reactions, ascribed to electronic and steric influences resulting from different end-capped triynes. The relative results of these cycloaddition reaction on subsequent optimized under microwave irradiations. With different Diels-Alder adducts in hand, the third focus dimers, that together with the Diels-Alder products, might be used as precursors to make PAHs. The properties of these new compounds were investigated by NMR, IR, UV-vis spectroscopy, MS spectrometry, cyclic voltammetry, and crystallographic analysis.

1.6 References

1. M. M. Haley, R. R Tykwinski Carbon-Rich Compounds: From Molecules to Materials; Wiley-VCH: New York, 2006. 2. F. Diederich, Nature 1994, 369, 199−207. 3. J. Wu. W. Pisula. K. Müllen, Chem. Rev. 2007, 107, 718−747. 4. O. F. Aebischer, A. Aeibischer, B. Donnio, B. Alameddine, M. Dadras, H. U. Güdel, D. Guillon, T. A. Jenny, J. Mater. Chem. 2007, 17, 1262−1267.

5. J. Wu, J. Li, U. Kolb, K. Müllen, Chem. Commun. 2006, 48−50. 6. R. Scholl, C. Seer, R. Weitzenbök, Chem. Ber. 1910, 43, 2202−2209. 7. E. Clar, F. John, Chem. Ber. 1930, 63, 2967–2977. 8 . E. Clar, Polycyclic Hydrocarbons; Academic Press: New York, 1964; Vol I/II. 9. E. Fitzer, K. H Kochling, H. P Boehm, H. Marsh, Pure. Appl. Chem. 1995, 67, 473−506.

Chapter 1: Introduction

10. S. Novoselov, A. K. Geim, S. V. Morozov, D. Jiang, Y. Zhang, S.V. Dubonos, I. V. Grigorieva, A. A. Firsov, Science 2009, 306, 666−669. 11. M. H. Rümmeli, C. G. Rocha, F. Ortmann, I. Ibrahim, H. Sevincli, F. Börrnert, J. Kunstmann, A. Bachmatiuk, M. Pötschke, M. Shiraishi, M. Meyyappan, B. Büchner, S. Roche, G. Cuniberti, Adv. Mater. 2011, 23, 4471−4490.

12. D. Chen, L. Tang, J. Li, Chem. Soc. Rev. 2010, 39, 3157−3180. 13. B. Y. Zhu, S. Murali, W. Cai, X. Li, J. Won Suk, J. R. Potts, R. S. Ruoff, Adv. Mater. 2010, 22, 3906−3924. 14. K. I. Bolotin, K. J. Sikes, Z. Jiang, M. Klima, G. Fudenberg, J. Hone, P. Kim, H. L. Stormer, Solid State Commun. 2008, 146, 351−355. 15. A. A. Baladin, S. Ghosh, W. Z. Bao, I. Calizo, D. Teweldebrhan, F. Miao, C. N. Lau, Nano Lett. 2008, 8, 902−907. 16. W. Cai, Y. Zhu, X. Li, R. D. Piner, R. S. Ruoff, Appl. Phys. Lett. 2009, 95, 123115. 17. B. Y. Zhu, S. Murali, W. Cai, X. Li, J. W. Suk, J. R. Potts, R. S. Ruoff, Adv. Mater. 2010, 22, 3906−3924. 18. X. Feng, W. Pisula, K. Müllen, Pure. Appl. Chem. 2009, 12, 2203−2224.

19. J. E. Anthony, Chem. Rev. 2006, 106, 5028−5048. 20. O. A. Gapurenko, A. G. Starikov, R. M. Minyaev, V. I. Minkin, Russ. Chem. Bull. Int. Ed. 2011, 60, 1517−1524. 21. P. M. Byers, I. V. Alabugin, J. Am. Chem. Soc. 2012, 134 (23), 9609−9614. 22. C. Kubel, S. L. Chen, K. Müllen, Macromolecules 1998, 31, 6014−6021. 23. A. J. Berresheim, M. Müller, K. Müllen, Chem. Rev. 1999, 99, 1747−1786. 24. H. Wang, Y. Liang, H. Xie, L. Feng, H. Lu, S. Feng, J. Mat. Chem, 2014, 2, 5601−5606. 25. M. D. Watson, A. Fechtenkötter, K. Müllen, Chem. Rev. 2001, 101, 1267−1300. 26. S. Yoo, B. Domercq, B. Kippelen, Appl. Phys. Lett. 2004, 85, 5427−5429. 27. E. Clar, F. John, Chem. Ber. 1931, 63, 2194–2200. 28. O. L. Griffith, J. E. Anthony, A. G. Jones, D. L. Lichtenberger, J. Am. Chem. Soc. 2010, 132, 580−586.

29. M. Bendicov, F. Wudl, D. F. Perepichka, Chem. Rev. 2004, 104, 4895−4995. 30. J. E. Anthony, Angew. Chem. Int. Ed. 2008, 47, 452−483.

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31. H. Meng, M. Bendikov, G. Mitchell, R. Helgeson, F. Wudl, Z. Bao, T. Siegrist, C. Kloc, C.H. Chen, Adv. Mater. 2003, 15, 1090−1093. 32. I. Kaur, W. Jia, R. P. Kopreski, S. Selvarasah, M. R . Dokmeci, C. Pramanik, N. E McGruer, G. P. Miller, J. Am. Chem. Soc. 2008, 130, 16274−16286. 33. J. E. Anthony, J. S. Brooks, D. L. Eaton, S. R. Parkin, J. Am. Chem. Soc. 2001, 123, 9482−9483. 34. O. Ostroverkhova, S. Scherbyna, D. G. Cooke, R. F. Egerton, F. A. Hegmann, R. R. Tykwinski, S. R. Parkin, J. E. Anthony, Phys. Rev. B 2005, 98, No. 033701. 35. J. E. Anthony, C. R. Swartz, C. A. Landis, S. R. Parkin. Proc. SPIE. 2005, 5940−5949. 36. J. Jiang, B. R. Kaafarani, D. C. Neckers. J. Org. Chem. 2006, 71, 2155−2158. 37. D. Lehnherr, A. H. Murray, R. McDonald, M. J. Ferguson, R. R. Tykwinski, Chem. Eur. J. 2009, 15, 12580−12584. 38. J. C. Martin, R. G. Smith, J. Am. Chem. Soc. 1964, 86, 2252−2256. 39. D. Hellwinkel, M. Melan, Chem. Ber. 1971, 104, 1001−10016. 40. M. Lotthangen, R. V. Clark, K. K. Baldridge, J. S. Siegel, J. Org. Chem. 1992, 57, 61−69. 41. J. Bosson, J. Gouin, J. Lacour, Chem. Soc. Rev. 2014, 43, 2824−2840. 42. A. Pothukuchy, S. Ellapan, K. R. Gopidas, M. Salazar, Bioorg. Med. Chem. Lett. 2003, 13, 1491−1494. 43. C. Nicolas, J. Lacour, Org. Lett. 2006, 8, 4343−4346. 44. O. Kel, A. Fürstenberg, N. Mehanna, C. Nicolas, B. Laleu, M. Hammarson, B. Albinsson, J. Lacour, E. Vauthey, Chem. Eur. J. 2013, 19, 7173−7180. 45. B. W. Laursen, F. C. Krebs, Angew. Chem. Int. Ed. 2000, 39, 3432−3434. 46. W. Pisula, X. Feng, K. Müllen, Adv. Mater. 2010, 22, 3634−3649. 47. D. Hellwinkel, A. Wiel, G. Sattler, B. Nuber, Angew. Chem. Int. Ed. 1990, 29, 689−692. 48. H. Q. Zhang, S. M. Wang, Y. Q. Li, B. Zhang, C. X. Du, X. J. Wan, Y. S. Chen, Tetrahedron 2009, 65, 4455−4463. 49. K. Do, D. Kim, N. Cho, S. Paek, K. Song, J. Ko, Org. Lett. 2012, 14, 222–225. 50. D. Hellwinkel, M. Melan, Chem. Ber. 1974, 107, 616−626. 51. D. Hellwinkel, G. Aulmich, M. Melan, Chem. Ber. 1981, 114, 86−108 52. J. E. Field, D. Venkataraman, Chem. Mat. 2002, 14, 962−964.

Chapter 1: Introduction

53. J. Field, D. Venkataraman, Chem. Mater. 2002, 14, 962−964. 54. Z. Fang, R. D. Webster, M. Samoc, Y-H. Lai, RSC Adv. 2013, 3, 17914−17917. 55. C. M. Chou, S. Saito, S. Yamaguchi, Org. Lett. 2014, 16, 2868−2871. 56. M. Kivala, W. Pisula, S. Wang, A. Mavrinskiy, J. P. Gisselbrecht, X. Feng, K. Müllen, Chem. Eur. J. 2013, 19, 8117−8128. 57. W. Y. Wong, X. Z, Wangi, A. B, Djurisi, C. Tung, J. Organomet. Chem. 2008, 693, 3603−3612. 58. S. Eisler, A. D. Slepkov, E. Elliott, T. Luu, R. McDonald, F. A. Hegmann, R. R. Tykwinski, J. Am. Chem. Soc. 2005, 127, 2666−2676 59. P. Siemens, R. C. Livingston, F. Diederich, Angew. Chem. Int. Ed. 2000, 39, 2632−2657. 60. S. Kim, T. Lee, H. Ko, D. Kim, Org. Lett. 2004, 6, 3601−3604. 61. Y. Tobe, R. Umeda, N. Iwasa, M. Sonoda, Chem. Eur. J. 2003, 9, 5549−5559. 62. Y. Rubin, S. S. Lin, C. B. Knobler, J. Anthony, A. M. Boldi, F. Diederich, J. Am. Chem. Soc. 1991, 113, 6943−6949. 63. A. L. K. Shun, E. T. Chernick, S. Eisler, R. R. Tykwinski. J. Org. Chem, 2003, 68, 339−1347. 64. S. Eisler, N. Chahal, R. McDonald, R. R. Tykwinski, Chem. Eur. J. 2003, 9, 2542−2550. 65. Y. Morisaki, T. Luu, R.R. Tykwinski, Org. Lett. 2006, 8, 689−692. 66. M. Kivala, F. Diederich, Acc. Chem. Res. 2009, 42, 235−248. 67. M. I. Bruce, B. D, Kelly, B. W, A. H, White, J. Organomet. Chem. 2000, 604, 150−156. 68. R. M. Bettinson, P. B. Hitchcock, D. R. M. Walton, J. Organomet. Chem. 1988, 341, 247−254. 69. T. Luu, R. McDonald, R. R, Tykwinski, Org. Lett. 2006, 8, 6035−6038. 70. K. West, L. N. Hayward, A. S. Batsanov, M. R. Bryce, Eur. J. Org. Chem. 2008, 30, 5093−5098. 71. S. Gauthier, N. Weisbach, N. Bhuvanesh, J. A. Gladysz, Organomet 2009, 28, 5597−5599. 72. C. Ross, K. Scherlach, F. Kloss, C. Hertweck, Angew. Chem. Int. Ed. 2014, 53, 7794−7798. 73. S. Yang, R. E. Bachman, X. Feng, K. Müllen, Acc. Chem. Res. 2013, 46, 116−128. 74. L. Chen, Y. Hernandez, X. Feng, K. Müllen, Angew. Chem. Int. Ed. 2012, 51, 7640−7654.

Chapter 2: Electrochemical investigation of new aryl substituted pentacenes

Chapter 2: Electrochemical investigation of new aryl substituted pentacenes†

2.1 Introduction

Pentacene shows interesting optoelectronic properties and it has been already used, for example, in organic solar cells as p-type semiconductor.1 Unfortunately, unsubstituted pentacene (1.3, Figure 2.1a) shows poor solubility in common organic solvents and is unstable under ambient conditions.2 As a result of the insolubility and instability, efforts have been directed to the functionalization of pentacene, especially at the 6- and 13-positions to change the opto-electronic properties with the final purpose to incorporate pentacene derivatives into devices. Pentacene derivatives have been already utilized in FET devices.3 Miller and coworkers have reported aryl substituted pentacenes (Figure 2.1b) where the aryl moieties were linked directly to the pentacene core at 6- and 13-positions, and they have investigated the electronic properties of these compounds by cyclic voltammetry.4 It has been found that the HOMO−LUMO gap values are not dramatically affected by different aryl substituents appended at the pentacene moiety as a result of the lack of coplanarity between the aryl and the pentacene skeleton that limits the conjugation. Anthony and coworkers have reported the synthesis of 6,13-bis(triisopropylsilylethynyl)pentacene (1.13, Figure 2.1c) in which both solubility and stability are increased compared to unsubstituted pentacene.5 With the purpose to incorporate pentacene derivatives into organic devices based on light absorption such as solar cells, Tykwinski and coworkers have reported the synthesis of pentacene derivatives with a TIPS-ethynyl group attached to 13-position to help maintain the solubility, and with a PAH moiety appended to the 6-position via an ethynyl spacer that extends the conjugation and the absorption in the range of 300 to 475 nm compared to 6,13−bis(triisopropylsilylethynyl)pentacene (Figure 2.1d).6

† A version of this chapter has been published: Andreas R. Waterloo, Anna−Chiara Sale, Dan Lehnherr, Frank Hampel, Rik R. Tykwinski, Beilstein J. Org. Chem. 2014, 10, 1692–1705, doi:10.3762/bjoc.10.178.

Chapter 2: Electrochemical investigation of new aryl substituted pentacenes

Previous work

a) b) c) d)

Sii-Pr3 SiR3

1.3 Ar

Sii-Pr3 Ar 1.13

This work

SiR3

Figure 2.1. a-d) Examples of common pentacenes reported in literature and e) aryl substituted pentacene derivatives explored in this work.

With this knowledge in hand, the goal of the current project was to analyze different pentacene derivatives with silyl ethynyl moieties appended at 6-position and with aryl substituents linked directly to the 13-position of the pentacene moiety (Figure 2.1e). Specifically, the solution state properties of the pentacenes have been explored by analysis of the redox behavior and the influence of different aryl substituents linked to the pentacene core on the HOMO−LUMO gap. The obtained results are compared to those for a selection of similar compounds known in literature.

Chapter 2: Electrochemical investigation of new aryl substituted pentacenes

2.2 Synthesis of aryl substituted pentacenes‡

The synthesis of aryl substituted pentacenes started from the known pentacenequinone derivatives 2.1a and 2.1b, formed via the addition of an acetylide to pentacenequinone (Scheme 2.1).7,8,9,10 With these two ketones in hand (2.1a and 2.1b), a second nucleophilic addition was initiated. Thus, commercially available aryl halides dissolved in dry THF were subjected to lithium halogen exchange at −78 °C using n-BuLi. A substoichiometric amount of n-BuLi was used in each case to ensure complete consumption of the n-BuLi through Li-halogen exchanged and thus avoid the possibility of competitive addition of the nucleophilic butyl anion to the ketone group of either 2.1a or 2.1b. After reaction with the appropriate aryl lithium species, the reaction was quenched with a proton source, and the resulting diol intermediates 2.2a–h were carried on directly to reductive aromatization with SnCl2/H2SO4 without further purification, ultimately yielding pentacene products 2.3a–h While the isolation and characterization of diol products resulting from nucleophilic additions to pentacene quinone can typically be isolated and characterized,11 previous work has shown that aromatized products were more easily purified by column chromatography and recrystallization in the last reaction step. Thus, it was deemed procedurally more efficient to eliminate the intermediate purification step. Once formed, pentacenes 2.3a−h were obtained in moderate yields over two steps, as deep-blue solids.

‡ The synthesis of the compounds 2.3a−k was performed by the Tykwinski group member Andreas Waterloo, but for reasons of clarity and comprehensibility, it is discussed in this chapter. 24

Chapter 2: Electrochemical investigation of new aryl substituted pentacenes

O Ar Ar M OH Ar

M = Li or MgBr SnCl2 2H2O THF, rt, 16−18 h OH H2SO4, THF OH rt, 6 h

R R R

2.1a R = Sii−Pr3 2.2a−i 2.3a−i 2.1b R = SiEt3

O I O O Ar = S

c R = Sii−Pr3 a R = Sii−Pr3 b R = Sii−Pr3 51% e R = Sii−Pr3 f R = Sii−Pr3 g R = Sii−Pr3 h R = Sii−Pr3 i R = Sii−Pr3 51% 25% d R = SiEt3 21% 60% 58% 45% 25% 8%

Scheme 2.1. Synthesis of unsymmetrical pentacenes 2.3a-i by nucleophilic addition reactions.

To expand the π−system in a linear fashion along the short molecular axis of the pentacene core, the general procedure described above was changed slightly, and ketone 2.1a was treated with a solution of biphenyl-magnesium bromide in THF. After workup and isolation of the intermediate diol 2.2i, reductive aromatization gave pentacene 2.3i in moderate yield over the two steps. Elaborating on the general idea of lateral functionalization, iodoaryl pentacene 2.3h offered an opportunity to vary the pendent substituent via a Pd-catalyzed cross-coupling protocol (Scheme 2.2). Thus, pentacene 2.3h was treated under Suzuki-Miyaura coupling conditions with arylboronic acids, and the desired pentacenes 2.3j–k were obtained in yields of 92 and 68%, respectively. Notably, anthracenyl substituted pentacene 2.3k was the least stable of all derivatives 2.3a−k. It slowly decomposed in solution when exposed to ambient laboratory conditions and was unstable toward silica gel chromatography, but it could be purified by recrystallization from a mixture of MeOH and acetone.

Chapter 2: Electrochemical investigation of new aryl substituted pentacenes

I Ar

Ar B(OH)2

Pd(PPh3)2Cl2,Na2CO3

reflux, 2-4 h

Sii-Pr3 Sii-Pr3 2.3h

Ar =

2.3j 92% 2.3k 68%

Scheme 2.2. Functionalization of iodoaryl pentacene 2.3h using the Suzuki cross-coupling reaction.

2.2. Electrochemical investigation of aryl substituted pentacenes

Pentacene derivatives 2.3a−k were analyzed by cyclic voltammetry and the results are summarized in Table 2.1. The corresponding cyclic voltammetry plots of compounds 2.3a−k are shown in Figure 2.2. Aryl substituted pentacenes 2.3a−k each show a one reversible oxidation event in the range of 0.30 to 0.37 V, and a second quasi-reversible oxidation process in the range of 0.80 to 0.99 V. There is, unfortunately, no clear trend observed for the oxidation potentials based on the substitution pattern of the aryl-moieties, although both oxidation events appear somewhat easier for pentacene 2.3g (0.30 V and 0.80 V, Table 2.1, entry 7) as a result of the two electron donating methoxy groups attached to the pendent phenyl ring. Aryl-substituted pentacenes 2.3a−k each show one reversible reduction event in a rather narrow range of –1.59 to –1.68 V. Similar to that observed for the oxidation potentials, there is no obvious trend that can be identified in the reduction potentials based on substitution pattern, aside from the observation that the silyl substituent might have a slight impact on reduction: 2.3d (−1.68 V, Table 2.1, entry 4) is slightly harder to reduce than 2.3c (−1.65 V, Table 2.1, entry 3), and the reduction of thienyl derivative 2.3e (–1.59 V, Table 2.1, entry 5) stands out as lower than the others. The electrochemical HOMO−LUMO gap values range between 1.94−2.02 eV. The thienyl derivative 2.3e displays the smallest HOMO−LUMO gap (1.94 eV, Table 2.1, entry 5) compared to the other pentacene in the series. 26

Chapter 2: Electrochemical investigation of new aryl substituted pentacenes

[a] Table 2.1. Cyclic voltammetry results of aryl-substituted pentacenes 2.3a−k.

[b] Entry Compound R1 R2 E½ox1 [V] E½ox2 [V] E½red1 [V] Egap,el [eV]

1 2.3a Sii-Pr3 0.34 0.87 –1.63 1.97

2 2.3b Sii-Pr3 0.37 0.99 –1.61 1.98

3 2.3c Sii-Pr3 0.36 0.93 –1.65 2.01

4 2.3d SiEt3 0.32 0.91 –1.68 2.00

5 2.3e Sii-Pr3 0.35 0.87 –1.59 1.94 S

O 6 Sii-Pr 0.32 0.87 –1.68 2.00 2.3f 3

7 Sii-Pr O 0.30 0.80 –1.67 1.97 2.3g 3

8 2.3h Sii-Pr3 I 0.34 0.87 –1.65 1.99

9 2.3i Sii-Pr3 0.32 0.87 –1.66 1.98

10 2.3j Sii-Pr3 0.32 0.93 –1.67 1.99

11 2.3k Sii-Pr3 0.35 0.88 –1.67 2.02

[a] Cyclic voltammetry was performed in CH2Cl2 solutions (1.5 mM) containing 0.1 M n-Bu4NPF6 as supporting −1 electrolyte at a scan rate of 0.15 V s . Pt wire was used as counter electrode, Ag/AgNO3 as reference electrode, and Pt working electrode. The potential values (E½) were calculated using the following equation E½ =

(Ered + Eox)/2, where Ered and Eox correspond to the cathodic and anodic peak potentials, respectively. Potentials are referenced to the ferrocene/ferrocenium (Fc/Fc+) couple used as an internal standard. [b] Electrochemical

HOMO−LUMO gaps determined by Egap,el = Eox1 – Ered1.

Chapter 2: Electrochemical investigation of new aryl substituted pentacenes

2.3a 2.3b

2.3c 2.3d

2.3e 2.3f

Chapter 2: Electrochemical investigation of new aryl substituted pentacenes

2.3g 2.3h

2.3i 2.3j

2.3k

Figure 2.2.Cyclic voltammetry plots of 2.3a−k.

Chapter 2: Electrochemical investigation of new aryl substituted pentacenes

The results obtained for pentacenes 2.3a−c are compared to those obtained for similar compounds reported in literature: 1.16a, 1.16b, and 1.16c (Table 2.2, entries 1−3).6 For pentacenes 1.16a−c the pendant aryl groups are linked through an ethynyl spacer at the pentacene core that allows electronic communication between the aryl group and the pentacene skeleton. Compounds 2.3a−c display one reversible and a second quasi-reversible oxidation processes 0.34 V and 0.87 V for 2.3a, 0.37 V and 0.99 V for 2.3b, and 0.36 V and 0.93 V for 2.3c, while 1.16a−c display only one reversible oxidation event that is 0.39 V for 1.16a and 1.16b, and 0.33 V for 1.16f. (Table 2.2, entries 1−3). Compounds 2.3a−c display one reversible reduction process that is −1.63 V for 2.3a, −1.61 V for 2.3b, and −1.65 V for 2.3c, while 1.16a−c display two reversible reduction events: −1.44 V and −1.90 V for 1.16a, −1.42 V and −1.86 V for 1.16b, and −1.38 V and −1.77 V for 1.16c (Table 2.2, entries 1−3). Compounds 1.16a, 1.16b, and 1.16c are easier to reduce compared to the series 2.3a−c. Compounds 2.3a−c show larger HOMO−LUMO gaps in the range of 1.97 to 2.10 eV compared to the compounds 1.16a−c with HOMO−LUMO gaps in the range of 1.71 to 1.83 eV. This behavior can be explained with the incorporation of the ethynyl space in 1.16a−c that allows for electronic communication between the pendant substituents and the pentacene moiety resulting in smaller HOMO−LUMO gaps for 1.16a−c compared to the series 2.3a−c. The cyclic voltammetry results of the series 2.3a−k are also compared to the literature known pentacene 1.135 (Table 2.2, entry 4). Pentacene derivatives 1.13 displays two oxidation processes at 0.39 V and 0.99 V (Table 2.2, entry 4). The first oxidation step is similar to 1.16a−b. Thus, compound 1.13 is slightly harder to oxidize than 2.3a−k where the values range from 0.30 to 0.37 V for the first oxidation process and from 0.80 to 0.99 V for the second one (Table 2.1, entries 1−11). Pentacenes 2.3a−k and 1.13 display one reversible reduction process that for 1.13 (−1.52 V) is easier than for 2.3a−k (−1.59 V to −1.68 V). The HOMO−LUMO gaps is marginally smaller for 1.13 (1.91 eV) compared to the series 2.3a−k where the values range between 1.94 to 2.02 eV (Table 2.1, entries 1−11). The cyclic voltammetry results of the series 2.3a−k are also compared to the literature known pentacene 1.10 where the aryl rings are linked directly to the pentacene skeleton in 6- and 13- positions (Table 2.2, entry 5).4 Compound 1.10 display an oxidation event (0.23 V) and appears to be easier to oxidize than 2.3a−k. Pentacene 1.10 appears to be harder to reduce (−1.85 V) compared to the series 2.3a−k (−1.59 V to −1.68 V, Table 2.1, entries 1−11). The HOMO−LUMO gaps is

Chapter 2: Electrochemical investigation of new aryl substituted pentacenes larger for 1.10 (2.08 eV) compared to the series 2.3a−k where the values range between 1.94 to 2.02 eV (Table 2.1, entries 1−11) as a result of orthogonal orientation of the aryls with the pentacene skeleton that limits the conjugation. The range of oxidation potentials within 1.10, 1.13, 1.16a−c, (Table 2.2, entries 1−4) , and 2.3a−k, is, however, quite narrow, suggesting that the pendent substituent offers little influence on the HOMO level. On the other hand, there is a marked difference in the observed reduction potentials. The reduction of 1.13 falls at approximately a midpoint between the two other classes 2.3a−k and 1.16a,c,f suggesting that the biggest influence of the pendent substituent appears to be related to the energy of the LUMO.

Chapter 2: Electrochemical investigation of new aryl substituted pentacenes

Table 2.2. Cyclic voltammetry results of 1.10, 1.13, 1.16a, 1.16b, and 1.16c.4,5,6

Sii-Pr3 Sii-Pr3

Ar Sii-Pr3 1.13 1.10

1.16a 1.16b Ar = 1.16c

a b c

Entry Compound E½ox1 E½ox2 E½red1 E½red2 Egap,el

[V] [V] [V] [V] [eV][e]

1 1.16a[a] 0.39 – −1.44 −1.90 1.83

2 1.16b[a] 0.39 – −1.42 −1.86 1.81

3 1.16c[a][b] 0.33 – −1.38 −1.77 1.71

4 1.13[c] 0.39 0.99 –1.52 − 1.91

5 1.10[d] 0.23 − −1.85 − 2.08

[a] Cyclic voltammetry was performed in benzene/ACN (3:1 v/v) solutions containing 0.1 M n-Bu4NPF6 as −1 support electrolyte at a scan rate of 0.15 V s . Pt wire was used as counter electrode, Ag/AgCl as reference electrode, and Pt as working electrode. The potential values (E½) were calculated using the following

equation E½ = (Ered + Eox)/2, where Ered and Eox correspond to the cathodic and anodic peak potentials, respectively vs Fc/Fc+. [b] Measurement performed at scan rate of 0.2 V s−1.6 [c] Cyclic voltammetry was

performed in CH2Cl2 solutions (1.5 mM) containing 0.1 M n-Bu4NPF6 as supporting electrolyte at a scan −1 rate of 0.15 V s . Pt wire was used as counter electrode, Ag/AgNO3 as reference electrode, and Pt working electrode. Potentials are referenced to the ferrocene/ferrocenium (Fc/Fc+) couple used as an internal 5 [d] + standard. In the reference E½ values are recorded vs Ag/Ag in CH2Cl2 using n-Bu4NPF6 as support electrolyte. 4 In this table E½ values have been converted vs Fc/Fc+. [e] Electrochemical HOMO−LUMO

gaps determined by Egap,el = Eox1 – Ered1.

Chapter 2: Electrochemical investigation of new aryl substituted pentacenes

2.4 Conclusion

A series of 11 aryl substituted pentacenes with silylethynyl moieties appended at 6- position and with aryl substituents linked directly to the 13-position of the pentacene skeleton have been investigated by cyclic voltammetry. The results obtained reveal that electronic communication between the pentacene core and the different aryl substituents is limited, as a result of the orthogonal orientation of the pentacene backbone and the pendent aryl moieties. Thus, these results show that the nature of the aryl substituent does not change the electronic properties of the pentacene skeleton itself. The range of oxidation potentials suggest that the pendent aryl substituent offers a minimal influence on the HOMO level. Comparing the results with those obtained for similar compounds known in literature it is evident that the biggest influence of the pendent substituent appears to be related to the energy of the LUMO.

2.5 References

1. J. E. Anthony, Chem. Rev. 2006, 106, 5028−5048. 2. A. R. Waterloo, A. C. Sale, D. Lehnherr, F. Hampel, R. R. Tykwinski, Beilstein J. Org Chem. 2014, 10, 1692–1705. 3. H. Meng, M. Bendikov, G. Mitchell, R. Helgeson, F. Wudl, Z. Bao, T. Siegrist, C. Kloc, C.H. Chen, Adv. Mater. 2003, 15, 1090−1093. 4. I. Kaur, W. Jia, R. P. Kopreski, S. Selvarasah, M. R. Dokmeci, C. Pramanik, N. E. McGruer, G. P. Miller, J. Am. Chem. Soc. 2008, 48, 16274−16286. 5. J. E. Anthony, J. S. Brooks, D. L. Eaton, S. R. Parkin, J. Am. Chem. Soc. 2001, 123, 9482−9483. 6. D. Lehnherr, A. H. Murray, R. McDonald, M. J. Ferguson, R. R. Tykwinski, Chem. Eur. J. 2009, 15, 12580−12584. 7. D. Lehnherr, R. McDonald, R. R. Tykwinski, Org. Lett. 2008, 10, 4163−4166.

Chapter 2: Electrochemical investigation of new aryl substituted pentacenes

8. A. R. Waterloo, S. Kunakom, F. Hampel, R. R. Tykwinski, Macromol. Chem. Phys. 2012, 213, 1020–1032. 9. A. Boudebous, E. C. Constable, C. E. Housecroft, M. Neuburger, S. Schaffner, Acta Crystallogr. Sect. C 2006, 62, 243–245. 10. N. Vets, M. Smet, W. Dehaen, Synlett 2005, 217–222. 11. S. Li, L. Zhou, K. Nakajima, K. I. Kanno, T. Takahashi, Chem. Asian J. 2010, 5, 1620−1626.

Chapter 3: Electrochemical investigation of new dyes based on functionalized triangulenes

3.1 Introduction

Triangulene derivatives such as cationic triangulenes and heterotriangulenes have been intensely investigated.1,2,3 Cationic triangulenes display high stability in strongly basic solution making them potential candidates for use in phase transfer catalysis.4 In addition, cationic triangulenes have raised interest due to their function of fluorescent dyes, offering applications as stains to image biological system5 and as sensing events.6 In the solid state, cationic triangulenes display self-assembly properties, and the corresponding potential applications have been investigated in the fields of nano and materials science.7,8 The influence of counterions on the photophysical properties in solution and in the solid state is also an issue of great importance.4 Heterotriangulenes, with nitrogen in the central position of the triangulene structure, have attracted attention for their potential use as n-type semiconductors.9 Ko and coworkers have reported examples of heterotriangulenes as possible candidates for new organic sensitizers, which consist in a D-π-A feature. The planar heterotriangulene with methyl substituents in X-positions is used as donor unit and the electron acceptor moieties are alkyl groups connected at the core in Y-position by a π-conjugated bridge that consist of thiophene units.10 Harima and coworkers reported new organic sensitizers where pyridine ligands represent the acceptors and the anchoring moieties of the D-π-A dye.11 The first goal of this project was to investigate by cyclic voltammetry of different functionalized cationic triangulenes and their helicene precursors with the purpose to understand the influence of substituents and counterions on the electronic properties. The results are also compared to those obtained for similar compounds reported in literature. The second goal of this project was to analyze the electrochemical properties by cyclic voltammetry of new donor-acceptor push-pull dyes where the donor units are represented by heterotriangulenes with dimethylmethylene groups attached to the X-positions of the heterotriangulenes core and the

Chapter 3: Electrochemical investigation of new dyes based on functionalized triangulenes acceptor moieties are pyridine ligands connected to the heterotriangulene core in Y-positions. The results are also compared to those obtained for similar push-pull systems known in literature.

3.2 Electrochemical investigations of new dyes based on functionalized cationic triangulenes

3.2.1 Synthesis of cationic triangulenes†

Compound 3.1 (1 equiv) known in literature12 was diluted in NMP, n-dodecylamine (2.1 equiv) was added and the mixture was stirred at rt for 20 h (Scheme 3.1). After dilution with KPF6 and work up, 3.2 was isolated in 48% yield. Compound 3.3 was synthesized from compound 3.2 that was stirred at 120 °C for 45 min and after work up led to 3.3 in 73%. Compound 3.4 was isolated from compound 3.3 that after stirring at 180 °C for 3 d led to 3.4 in 47% yield. Compound 3.1 (1 equiv) was diluted in NMP, n-octylamine (47 equiv) was added and the mixture was stirred at

110 °C for 3 d. After dilution with KPF6 and work up, 3.5 was isolated in 56% yield. Compound 3.1 (1 equiv) was diluted in NMP, n-hexylamine (47 equiv) was added and the mixture was stirred at

110 °C for 24 h. After dilution with H2O and work up, 3.6 was isolated in 49% yield.

† The synthesis of the compounds was performed by Agnes Uhl from the Prof. Dr. Jürgen Schatz group. The synthetic protocol is mentioned in this thesis for reasons of clarity and comprehension. 36

Chapter 3: Electrochemical investigation of new dyes based on functionalized triangulenes

C12H25 C12H25 NMP O N O O NMP O N O O O H25C12NH2 PF O H25C12NH2 6 BF4 PF6 rt, 20 h 120 °C, 45 min KPF , H O KPF6, H2O 6 2 N O O O O C12H25

3.1 3.2 (48%) 3.3 (73%)

NMP H C NH 8 17 2 NMP 110 °C, 3 d NMP H25C12NH2 H13C6NH2 180 °C, 3 d 180 °C, 24 h KPF6, H2O

H17C8 C8H17 N N PF6

H13C6 C6H13 H C C H N N 25 12 12 25 N N N BF4 PF6 C8H17

3.5 (56%) N N C H 6 13 C12H25

3.6 (49%) 3.4 (47%)

Scheme 3.1. Synthesis of cationic triangulenes 3.2−3.6.

3.2.2 Electrochemical investigation of new cationic triangulenes and relative helicenes precursors

Electrochemical investigation by cyclic voltammetry has been performed for compounds 3.2−3.6 and the results are summarized in Table 3.1. The cyclic voltammetry plots of 3.2−3.6 are shown in Figure 3.1. Compounds 3.2−3.6 show a first reduction event which appears to be reversible for 3.2 (−1.15 V) and 3.3 (−1.30 V). The first reduction wave is irreversible for 3.4 and 3.5 (−1.43 V) and 3.6 (−1.44 V). In addition to the first reduction process, compound 3.4−3.6 display a second reversible reduction event and relevant differences within the potentials are not observed in the series: −1.70 V for 3.4 and as well as 3.5, and −1.69 V for 3.6. The first reduction process becomes more difficult within the series 3.2 (−1.15 V) → 3.3 (−1.30 V) → 3.4 (−1.43 V). This trend can be explained by the replacement of methoxy groups with bridging N-alkyl moieties in the X-position that decrease the electron accepting ability of the cationic ring system and, consequently, makes the

Chapter 3: Electrochemical investigation of new dyes based on functionalized triangulenes compounds more difficult to reduce. Furthermore, triangulene 3.4 is planar and this facilitates stabilization of the cationic ring system via electron donation from the amine substituents compared to the helicene precursors 3.2 and 3.3. Thus, 3.4 is more difficult to reduce (−1.43 V) compared to 3.2 and 3.3. Compounds 3.3−3.6 (Table 3.1, entries 2−5) show a reversible oxidation process at 0.96−0.99 V, while 3.2 (Table 3.1 entry 1) does not displays any oxidation potential. As expected, the oxidation process becomes slightly easier with the introduction of more N-alkyl moieties in x- position that stabilize the positive charge in the heterotriangulenes ring as in the series 3.2 → 3.3 → 3.4. The trend of the oxidation and reduction values observed within the series 3.2−3.4 suggests that the replacement of the methoxy groups with N-alkyl moieties in X-positions of the triangulene ring has a slight impact on the oxidation potential and, thus, on the HOMO energy level, while a marked difference is observed in the reduction potentials that suggests that the biggest influence of the N- alkyl substituents appears to be related to the energy of the LUMO.

Chapter 3: Electrochemical investigation of new dyes based on functionalized triangulenes

Table 3.1. Cyclic voltammetry results of 3.2−3.6[a]

C12H25 H25C12 C12H25 C12H25 O N N O N N O O PF 6 PF6 PF6

N O O N C12H25 C12H25

3.2 3.3 3.4

H17C8 C8H17 H13C6 C6H13 N N N N PF6 BF4

N N

C8H17 C6H13

3.5 3.6

Entry Compound E½ox Ered1 E½red2

[V] [V] [V]

[b] 1 3.2 − −1.15 −

2 3.3 0.99 −1.30[b] −

3 3.4 0.96 −1.43 −1.70

4 3.5 0.97 −1.43 −1.70

5 3.6 0.96 −1.44 −1.69

[a] Cyclic voltammetry was performed in CH2Cl2 solutions (1 mM) containing 0.1 M n-Bu4NPF6 as −1 supporting electrolyte at a scan rate of 0.15 V s . Pt wire was used as counter electrode, Ag/AgNO3 as reference electrode and Pt as working electrode. The potential values (E½) were calculated using the

following equation E½ = (Ered + Eox)/2, where Ered and Eox correspond to the cathodic and anodic peak potentials, respectively. Potentials are referenced to the ferrocene/ferrocenium (Fc/Fc+) couple used as an internal standard. [b] The reduction process is reversible. As a result, the reduction value is determined by the equation previously mentioned to calculate E½.

Chapter 3: Electrochemical investigation of new dyes based on functionalized triangulenes

3.2 3.3

3.4 3.5

3.6

Figure 3.1. Cyclic voltammetry plots of 3.2−3.6.

Chapter 3: Electrochemical investigation of new dyes based on functionalized triangulenes

The electrochemical results of 3.2−3.6 are compared to those obtained for similar compounds known in literature 1.19b, 1.20, 1.21,4,13 and 3.74,14 (Table 3.2, entries 1−4). Comparison of 1.19b and 3.5 where the only difference between the compounds is attributed to the nature of the counterions is observed that for the tetrafluoroborate triangulenium salt 3.5 the reversible oxidation event (0.97 V) is more difficult compared to that for the hexafluorophosphate triangulenium salt 1.19b (0.82 V). Compounds 3.5 shows two reduction events, while 1.19b displays one reversible reduction wave. The reductions events appears to be easier for 3.5 compared to 1.19b: −1.43 V and −1.70 V for 3.5, and −1.78 V for 1.19b. Comparison of 3.3 to the similar compound 3.7 where the difference between the compounds is only attribute to the length of the alkyl moieties attached to N- atom in X-position is observed that 3.3 with dodecyl substituents shows one reversible oxidation process (0.99 V) and one reversible reduction event (−1.30 V). Compound 3.7 with propyl groups displays two oxidation processes: the first is reversible (0.94 V) and the second is irreversible (1.72 V). In addition, 3.7 exhibits also two reduction processes: the first is reversible (−1.16 V) and the second one is irreversible (−2.08 V). In general, it is observed that compound 3.3 is slightly more difficult to oxidize and easier to reduce compared to 3.7. The series of triangulenes 1.19b−1.21 and 3.2−3.4 show the same general trend for potentials values: with the replacement of O-atoms as in the series 1.20 → 1.21 → 1.19b or methoxy groups as in the series 3.2 → 3.3 → 3.4 by more N- alkyl substituents in X-position the oxidation becomes easier and the reduction more difficult. This confirms that N-atoms as well as planarization stabilize the positive charge, and thus the triangulene ring. Beside these considerations, in general small differences within potentials values of 3.2−3.6 (Table 3.1 entries 1−5) and 1.19b, 1.20, 1.21, 1.37 (Table 3.1, entries 1−4) can be also attributed to the different conditions used for the measurements.

Chapter 3: Electrochemical investigation of new dyes based on functionalized triangulenes

Table 3.2. Cyclic voltammetry results of 1.19b, 1.20, 1.21, 1.37.4,13,14[a]

C8H17 CH3 C3H7 N N N OO

N N O O O N N N H C C H17 C H 17 8 8 3 7 H7C3 C3H7 - BF - - BF4 4 BF 4 BF4 1.19b 1.20 1.21 3.7

Entry Compound E½ox1 Eox2 E½red1 Ered2

[V] [V] [V] [V]

1 1.19b 0.82 − −1.78 −

2 1.20 − − −0.88 −

3 1.21 1.02 − −1.23 −

4 3.7 0.94 1.72 −1.16 −2.08

[a] Cyclic voltammetry was performed in ACN solutions containing 0.1 M n-Bu4NBF4 as supporting electrolyte at a scan rate of 0.1 V s−1 vs SCE. 4,13,14 In this table, the potential values have been converted vs Fc/Fc+ as described in ref. 15

Chapter 3: Electrochemical investigation of new dyes based on functionalized triangulenes

3.3 Electrochemical investigation of push-pull systems based on functionalized heterotriangulenes

3.3.1 Synthesis of new functionalized heterotriangulenes‡

The brominated starting material 3.8−3.10 were synthesized according to literature16 and undergoes a palladium-catalyzed Suzuki-Miyaura coupling reaction resulting in the desired dyes 3.11−3.13 (Scheme 3.2). The brominated compound 3.8 and 4-pyridineboronic acid (1 equiv) and

[Pd(PPh3)4] as a catalyst in toluene and methanol was heated under microwave irradiations to 120 °C for 9 h to afford 3.11 in 55% yield.17 Compound 3.12 was synthesized according to the analogous protocol using compound 3.9 and 4-pyridineboronic acid (2 equiv) that after 27 h led to 3.12 in 81% yield. The procedure was applied to synthesize 3.13 from 3.10 and 4-pyridineboronic acid (3 equiv) giving 3.13 after 20 h in 86% yield.

‡ The synthesis of the compounds was performed by Ute Meinhardt from the Dr. Milan Kivala group. The synthetic protocol is mentioned in this thesis for reasons of clarity and comprehension.

Chapter 3: Electrochemical investigation of new dyes based on functionalized triangulenes

[Pd(PPh3)4] 2 M K2CO3 N + N B(OH)2 N toluene/EtOH (2:1) mw 120 °C, 9 h

3.8 3.11 (55%)

[Pd(PPh3)4] 2 M K2CO3 N + 2 N B(OH)2 N toluene/EtOH (2:1) mw 120 °C, 27 h Br Br N N

3.9 3.12 (81%)

[Pd(PPh3)4] 2 M K2CO3 N + 3 N B(OH)2 N toluene/EtOH (2:1) mw 120 °C, 20 h Br Br N N 3.10 3.13 (86%)

Scheme 3.2 Syntheses of heterotriangulenes 3.11−3.13.

3.3.2 Electrochemical investigation of new functionalized heterotriangulenes

Electrochemical investigation by cyclic voltammetry has been performed for compounds 1.23, and 3.11−3.13 and the results are summarized in Table 3.3. All the heterotriangulenes 1.23, 3.11−3.13 display one reversible oxidation process. The oxidation potentials values increase within the series 1.23 (0.36 V) → 3.11 (0.42 V) → 3.12 (0.50 V) → 3.13 (0.56 V). The trend can be explained by the electron withdrawing nature of the pyridyl groups: with the increasing number of pyridyl moieties attached to the heterotriangulene scaffold, the oxidation becomes more difficult. The corresponding HOMO energy level decreases: −5.16 eV for 1.23, −5.22 eV for 3.11, −5.30 eV for 3.12, −5.36 eV for 3.13. The compound analyzed 1.23, 3.11−3.13 show an irreversible reduction event that is not expected. The irreversible reduction process becomes easier in the series 1.23

Chapter 3: Electrochemical investigation of new dyes based on functionalized triangulenes

(−1.80 V) → 3.11 (−1.78 V) → 3.12 (−1.72 V) → 3.13 (−1.58 V). The cyclic voltammetry results known in literature for 1.2318 do not report any reduction wave, and similar compound of 3.11−3.13 do not mention reduction events.19,20 Compounds 1.23, 3.11−3.13 have been analyzed by NMR, MS, EA, and IR that establish compounds high purity except for traces of water. Considering the blank recorded before the analysis, impurities derived from the solvent, ferrocene, and the support electrolyte can be excluded. The first hypothesis considered to explain the unexpected reduction waves was the presence of oxygen, but the solutions were degased before each analysis with nitrogen for 25 min and the flow of the gas was maintained into the cell during the analysis. Furthermore, with the presence of oxygen it is typically observed an anodic peak in the region of −1 V21, which in this case it is not visible. The reduction of water21 could be possible due to the presence of water proven by compounds characterization. Considering also that the reduction waves are much smaller compared to the peaks of the reversible oxidation events shown for all the compounds 1.23 and 3.11−3.13, the most likely hypothesis comes from the interaction of water with each compound. The interaction of water with each compound might shift the reduction event of the water leading to the observed trend of the reduction values for 1.23 and 3.11−3.13.

Chapter 3: Electrochemical investigation of new dyes based on functionalized triangulenes

Table 3.3. Cyclic voltammetry results of compound 1.23, 3.11−3.13

N N

N N N N

N N

1.23 3.11 3.12 3.13

[a] [a] [b] Entry Compound E½ox Ered EHOMO

[V] [V] [eV]

1 1.23 0.36 −1.80 −5.16

2 3.11 0.42 −1.78 −5.22

3 3.12 0.50 −1.72 −5.30

4 3.13 0.56 −1.58 −5.36

[a] Cyclic voltammetry was performed in CH2Cl2 solutions (1.5 mM) containing 0.1 M n- −1 Bu4NPF6 as supporting electrolyte at a scan rate of 0.15 V s . Pt wire was used as counter

electrode, Ag/AgNO3 as reference electrode, and Pt as working electrode. The potential

values (E½) were calculated using the following equation E½ = (Ered + Eox)/2, where

Ered and Eox correspond to the cathodic and anodic peak potentials, respectively. Potentials are referenced to the ferrocene/ferrocenium (Fc/Fc+) couple used as an internal standard. [b] For the HOMO levels valuation the formula EHOMO = −(E½ox + 4.8 eV) is applied as described in ref.22

Chapter 3: Electrochemical investigation of new dyes based on functionalized triangulenes

1.23 3.11

3.12 3.13

Figure 3.2. Cyclic voltammetry plots of compounds 1.23 and 3.11−3.13.

Comparing literature results of heterotriangulenes reported by Ko and coworkers10 1.26a-c (Table 3.4), it is observed that in the heterotriangulenes analyzed 3.11−3.13 (Table 3.3). The oxidation process is easier compared to the series 1.26a−c: 1.07 V for 1.26a, 1.00 V for 1.26b, 1.01 V for 1.26c, while in 3.11−3.13, the oxidation potentials values range from 0.42 to 0.56 V. This is not surprising, given the presence of the strong accepting groups of 1.26a−c. In 1.26a−c, reduction events are not observed, while for the series 3.11−3.13, one irreversible reduction process that range from −1.78 to −1.80 V is found.

Chapter 3: Electrochemical investigation of new dyes based on functionalized triangulenes

Table 3.4. Cyclic voltammetry results of heterotriangulenes 1.26a−c reported by Ko and coworkers.10[a]

R1 R2

1.26a R1 = H 1.26b R1 = OC6H13 R2 = S S 1.26c R1 = OC9H19 CN COOH

Entry Compound E½ox [V]

1 1.26a 1.07

2 1.26b 1.00

3 1.26c 1.01

[a] Redox potential were measured in ACN with 0.1 M (n-C4H9)4NPF6 with a scan rate of 0.05 V s−1 vs Fc/Fc+ as described in ref.10

The compounds 1.23, 3.11−3.13 (Table 3.3) are also compared to the dyes 3.14−3.19 reported in literature (Table 3.5).11 The sensitizers 3.14−3.19 are reported due to common use of the pyridyl groups as acceptor moieties as in 1.23, 3.11−3.13. Compounds 3.11, 3.12, 3.13 display a more difficult oxidation process that range of 0.42 to 0.56 V compared to 3.14−3.19 where the values range of 0.34 to 0.39 V.

Chapter 3: Electrochemical investigation of new dyes based on functionalized triangulenes

Table 3.5. Cyclic voltammetry results of dyes 3.14−3.19 reported by Harima and coworkers.11

N N S N N N N R R

3.14 R = H 3.16 R = H 3.15 R = n-butyl 3.17 R = n-butyl

N S N N N N N

6 6 HOOC HOOC 3.18 3.19

[a] Entry Compound E½ ox[V]

1 3.14 0.34

2 3.15 0.39

3 3.16 0.30

4 3.17 0.34

5 3.18 0.38

6 3.19 0.34

[a] The redox potentials were measured using 0.1 M Bu4NClO4 in + 11 CH2Cl2, FC/FC is used as internal standard as described in ref.

The results obtained for 1.23 have been compared to those reported of triphenylamine (TPA).18 Compound 1.23 shows a reversible oxidation process (0.36 V) that is easier compared to that reported for TPA (0.54 V, vs Fc/Fc+ measured by square wave voltammetry), as a result of the increase of the planarity in 1.23.

Chapter 3: Electrochemical investigation of new dyes based on functionalized triangulenes

3.4 Conclusion

Cyclic voltammetry has been performed for cationic triangulenes and helicene precursors and the results are compared to those obtained for similar compounds reported in literature. In general, it is observed that the cationic triangulenes gain less accepting ability with the replacement of methoxy groups in X-positions by N-alkyl moieties that stabilize the positive charge and by increasing of the planarity. The trend of the oxidation and reduction values observed with the replacement of the methoxy groups with N-alkyl moieties in X-positions of the triangulene ring has a slight impact on the oxidation potential, and thus on the HOMO energy level, while a marked difference is observed within the reduction potentials that suggests that the biggest influence of the N-alkyl substituents appears to be related to the energy of the LUMO. The length of the alkyl substituents attached to N-atoms has only a slight impact on the reduction and oxidation potentials. Comparing the results in literature might be assumed that the nature of the counterions influence the redox properties of the cationic triangulenes: in the tetrafluoroborate triangulenium the oxidation appears to be more difficult while the reduction process is easier compared to the similar hexafluorophospate triangulenium. Electrochemical investigations have been conducted for new heterotriangulenes. The electrochemical results demonstrated that the oxidation potential becomes more difficult by the attachment of more pyridyl groups with subsequent reduction of HOMO energy levels.

3.5 References

1. J. C. Martin, R. G. Smith, J. Am. Chem. Soc. 1964, 86, 2252−2256. 2. D. Hellwinkel, M. Melan, Chem. Ber. 1971, 104, 1001−10016.

3. D. Hellwinkel, A. Wiel, G. Sattler, B. Nuber, Angew. Chem. Int. Ed. 1990, 29, 689−692. 4. J. Bosson, J. Gouin, J. Lacour, Chem. Soc. Rev. 2014, 43, 2824−2840. 5. P. Dedecker, C. Flors, J. I. Hotta, I-H Uji, J. Hofkens, Angew. Chem. Int. Ed. 2007, 46, 8330−8332.

Chapter 3: Electrochemical investigation of new dyes based on functionalized triangulenes

6. M. Amelia, A. Lavie-Cambot, N. D. McClenaghan, A. Credi, Chem. Commun. 2011, 47, 325−327. 7. C. Nicolas, J. Lacour, Org. Lett. 2006, 8, 4343−4346. 8. O. Kel, A. Fürstenberg, N. Mehanna, C. Nicolas, B. Laleu, M. Hammarson, B. Albinsson, J. Lacour, E. Vauthey, Chem. Eur. J. 2013, 19, 7173−7180. 9. H. Q. Zhang, S. M. Wang, Y. Q. Li, B. Zhang, C. X. Du, X. J. Wan, Y. S. Chen, Tetrahedron 2009, 65, 4455−4463. 10. K. Do, D. Kim, N. Cho, S. Paek, K. Song, J. Ko, Org. Lett. 2012, 14, 222–225. 11. Y. Ooyama, T. Nagano, S. Inoue, I. Imae, K. Komaguchi, J. Ohshita, Y. Harima, Chem. Eur. J. 2011, 17, 14837–14843. 12. Bo W. Laursen, F. Krebs, Chem. Eur. J. 2001, 7, 1773−1783. 13. S. Dileesh, K. R. Gopidas, J. Photochem. Photobiol. A. 2004, 162, 115−120. 14. B. W. Laursen, PhD thesis, University of Copenhaghen (Risø), 2001. 15. V. V. Pavlishchuk, A. W. Addison, Inorg. Chim. Acta. 2000, 298, 97−102. 16. Z. Fang, T. L. Teo, L. Cai, Y. H. Lai, A. Samoc, M. Samoc, Org. Lett. 2009, 11, 1−4. 17. L. Arnold, H. Norouzi-Arasi, M. Wagner, V. Enkelmann, K. Müllen, Chem. Commun. 2011, 47, 970–972. 18. J. Pommerehne, H. Vestweber, W. Guss, R. F. Mahrt, H. Bässler, M. Porsch, J. Daub, Adv.

Mater. 1995, 7, 551−554 19. C. Hua, P. Turner, D. M. D’Alessandro, Dalton Trans. 2013, 42, 6310−6313. 20. G. Casalbore-Miceli, A. Degli Espositi, V. Fattori, G. Marconi, C. Sabatini, Phys. Chem. Chem. Phys. 2004, 6, 3092−3096. 21. J. J. Van Benschoten, J. Y. Lewis, W. R. Heineman, D. A. Roston, P. T. Kissinger, J. Chem. Ed. 1983, 60, 772−776

Chapter 4: Diels-Alder cycloaddition of tetraphenylcyclopentadienone and 1,3,5-hexatriynes

Chapter 4: Diels-Alder cycloaddition of tetraphenylcyclopentadienone and 1,3,5- hexatriynes

4.1. Introduction

Polycyclic aromatic hydrocarbons such as hexa-peri-hexabenzocoronene (HBC) and tribenzopentaphene (TBP) derivatives have been intensely investigated especially in the field of organic chemistry and material science because they display interesting electronic and optical properties.1 Many examples are reported in literature where HBC and TBP derivatives are synthesized via the Scholl cyclodehydrogenation reaction from aryl-substituted benzene derivatives. For example, Müllen and coworkers have reported the synthesis of HBC from hexaphenylbenzene,2 and Jenny and coworkers have used the same protocol for the synthesis of TBP from tetraphenylbenzene derivatives as precursors to the Scholl reaction.3 Aryl-substituted benzene derivatives are also interesting for the potential application in opto-electronic devices and supramolecular assembly materials.4,5,6 In this context, alkynes are suitable start point for the preparation of aryl-substituted benzene derivatives via Diels-Alder reaction using tetraphenylcyclopentadienone (TPCPD) as diene.7 Diels-Alder reactions have been intensely studied under conventional heating and since the development of microwave chemistry in 1986, the Diels-Alder reactions have also been optimized under microwave irradiations.8,9,10 Microwave chemistry used for Diels-Alder reaction serves to decrease the reaction time, from weeks to days or from hours to minutes, also providing increased reaction yields.11 Classical heating of a reaction mixture is less efficient than microwave heating because it results in localized “hot spot”, so-called “wall effects” that can lead to the formation of side products because the thermal energy is transferred inward from the surface of the reaction vessel (Figure 4.1). In contrast to conventional thermal conditions, microwave heating is essentially instantaneous, rapid, and uniform throughout the entire sample.

Chapter 4: Diels-Alder cycloaddition of tetraphenylcyclopentadienone and 1,3,5-hexatriynes

Figure 4.1. Distribution of the heating a) under microwave irradiations b) under conventional heating showing the wall effect. Picture adapted with the permission of Pelle Lidstrom (Biotage).

In this chapter, Diels-Alder cycloaddition reactions of tetraphenylcyclopentadienone (TPCPD) with a series of 1,3,5-hexatriynes are described, in order to explore the chemical reactivity of triynes under these cycloaddition reaction. Different end-capped triynes used for the Diels-Alder reactions are synthesized according to the protocols reported by Tykwinski and coworkers.12,13,14,15 The Diels-Alder reactions have been initially conducted under conventional thermal heating and then optimized under microwave irradiation. The tetraphenylbenzene derivatives obtained from Diels- Alder reactions have been analyzed by UV-vis spectroscopy, cyclic voltammetry, and in some cases by X-ray crystallography. Selected Diels-Alder products have been then taken on to a sequence of desilylation and homocoupling reactions, and the obtained dimers have been investigated by UV-vis spectroscopy, and cyclic voltammetry.

Chapter 4: Diels-Alder cycloaddition of tetraphenylcyclopentadienone and 1,3,5-hexatriynes

4.2. Synthesis of triynes

Triyne 1.30a was synthesized according to the procedure reported in literature (Scheme 4.1).13 Reaction of lithiated TMS-acetylene and aldehyde 4.1 resulted in the formation of alcohol 4.2 in 90%. The following reaction was an oxidation using pyridinium chlorochromate to afford the ketone 4.3 in 98% yield, and subsequent dibromoolefination of 4.3 led to 4.4 in 67% yield. A FBW rearrangement reaction of 4.4 afforded triyne 1.30a in 68% yield.

PCC 1. n-BuLi OH - CH2Cl2 O Et2O 78 °C Me Si H 3 rt, 24 h 2. O Me Si Sii-Pr 3 3 Me3Si Sii-Pr3 H 4.2 (90%) 4.3 (98%) 4.1 Sii-Pr3

CBr4, PPh3 CH2Cl2 rt, 24 h

n-BuLi, hexanes Br Br from - 78 °C to -10 °C Me3Si Sii-Pr3 i-Pr 1.30a (68%) Me3Si Si 3

4.4 (67%)

13 Scheme 4.1. Synthesis of triyne 1.30a.

Friedel-Crafts acylation of p-methoxy benzoylchloride with 1,4-bis(trimethylsilyl)buta-1,3-diyne afforded the ketone 4.5 in quantitative yield, after work-up and passing the reaction solution through a plug of silica gel (Scheme 4.2). Dibromoolefination of 4.5 led to 4.6 in 61% yield and a FBW rearrangement resulted in the formation of triyne 4.7 in 87% yield.15

Chapter 4: Diels-Alder cycloaddition of tetraphenylcyclopentadienone and 1,3,5-hexatriynes

AlCl O 3 O SiMe3 SiMe3 Cl 0 °C, CH2Cl2, 2 h MeO MeO SiMe3 4.5 (100%)

CBr4, PPh3 CH2Cl2 rt, 24 h

Br Br n−BuLi, hexanes MeO SiMe3 from − 78 °C to −10 °C MeO SiMe3

4.7 (87%) 4.6 (61%)

Scheme 4.2. Synthesis of triyne 4.7.15

Precursor compounds 4.8a-4.12a were synthesized using routes previously reported.16,17 The crosscoupling reaction of n-butyl-1-bromobenzene and TMS-acetylene under Sonogashira coupling conditions was stirred at 50 °C for 3 d (Scheme 4.3). After cooling the reaction to room temperature, work-up, and purification, compound 4.8a was obtained in 81% yield. Desilylation reaction of 4.8a afforded the terminal acetylene 4.9a in 86% yield. Attempts to synthesize the alcohol 4.10a using n-BuLi to form the correspondent acetylide followed by the addition of ethyl formate were unsuccessful. The reaction to obtain 4.10a from 4.9a using Grignard reagent MeMgBr or EtMgBr instead of n-BuLi to generate the acetylide was successful, and the alcohol 4.10a was obtained in 67% yield after work up and column chromatography. The oxidation of 4.10a using pyridinium chlorochromate afforded ketone 4.11a in 76% yield, and the subsequent dibromoolefination reaction of 4.11a led to 4.12a in 78% yield. FBW rearrangement reaction of 4.12a resulted in the formation of triyne 4.13a in 90% yield.14

Chapter 4: Diels-Alder cycloaddition of tetraphenylcyclopentadienone and 1,3,5-hexatriynes

[Pd(PPh3)2Cl2] HNi-Pr 2, CuI K2CO3 Me3Si H THF/MeOH R X R SiMe3 R H THF rt, 5 h 4.9a 4.8a (81%) (86%) 4.9b 4.8b (100%) (78%)

1. MeMgBr THF, 50 °C a: X = Br, R = Bu 2 O H OEt b: X = I, R = OMe

Br Br PCC OH CBr4, PPh3 O CH Cl CH2Cl2 2 2 rt R R R R R R

4.12a (78%) 4.11a (76%) 4.10a (67%)

4.12b (73%) 4.11b (81%) 4.10b (80%)

n-BuLi, hexanes or toluene from - 78 °C to -10 °C

R R

4.13a (90%) 4.13b

Scheme 4.3. Synthesis of triynes 4.13a and 4.13b.16,17

The crosscoupling reaction of p-iodoanisole and TMS-acetylene under Sonogashira coupling conditions was stirred at rt for 24 h (Scheme 4.3).16 After work-up and purification, compound 4.8b was isolated in quantitative yield. Desilylation of 4.8b afforded the terminal acetylene 4.9b in 78% yield.16 Alcohol 4.10b was isolated from the reaction of 4.9b in 80% yield after work-up and purification. The oxidation of 4.10b using pyridinium chlorochromate afforded ketone 4.11b in 81% yield, and subsequent dibromoolefination of 4.11b led to 4.12b in 73% yield. The FBW rearrangement reaction of 4.12b was performed in toluene to increase the solubility of the precursor 4.12b, which is insoluble in hexanes. Thus, the reaction resulted in the formation of impure triyne 4.13b.

Chapter 4: Diels-Alder cycloaddition of tetraphenylcyclopentadienone and 1,3,5-hexatriynes

After work-up, from FBW rearrangement of 4.12b to obtain 4.13b two fractions were isolated 1 (fraction A and fraction B). In Figure 4.2 the H NMR spectrum of fraction A measured in THF-d8 is shown. The 1H NMR spectrum suggested the existence of triyne 4.13b in both fractions. Fraction

A gave a solid that was insoluble in hexanes and CDCl3, and fraction B showed solubility in hexanes and CDCl3. The spectrum suggests the formation of product 4.13b, but reveals also impurities based on signals in the aromatic region around 8 ppm and in the aliphatic region at 2.6 ppm (red boxes in Figure 4.2) ascribed to unknown impurities. The 13C NMR spectrum measured in

THF-d8 in Figure 4.3 also suggests the formation of the desired product 4.13b based on the acetylenic signals at: 79.8 ppm, 73.9 ppm, and 66.9 ppm (green crosses in Figure 4.3), but revealed also the presence of impurities in the range of 31-35 ppm and in the aromatic region around 124-132 ppm and 135 ppm (signals of impurities are shown in the red boxes in Figure 4.3).

1 Figure 4.2. H NMR spectrum in THF-d8 of fraction A containing product 4.13b and impurities highlighted in red boxes. 57

Chapter 4: Diels-Alder cycloaddition of tetraphenylcyclopentadienone and 1,3,5-hexatriynes

13 Figure 4.3. C NMR spectrum of fraction A in THF-d8 containing 4.13b showing acetylenic signals in the green crosses and impurities highlighted in red boxes.

The 13C NMR spectrum of fraction B shows a mixture of 4.12b and 4.13b (Figure 4.4). The acetylenic signals ascribed to the desired product 4.13b are found at 66.3 ppm, 73.5 ppm, 78.6 ppm (green crosses in Figure 4.4) and the acetylenic signals attributed to the starting material 4.12b are visible at 85.1 ppm and 95.8 ppm (red boxes in Figure 4.4). Signals were also observed attributed to both substrate 4.12b and triyne 4.13b in the aromatic region. The formation of the triyne 4.13b is + also confirmed by APPI HRMS by the signal attributed to 4.13b (m/z calculated for C20H14O2 (M ) 286.09883, found 286.0996, Figure 4.5).

Chapter 4: Diels-Alder cycloaddition of tetraphenylcyclopentadienone and 1,3,5-hexatriynes

13 Figure 4.4. C NMR spectrum of fraction B in CDCl3 containing 4.12b (acetylenic in red boxes signals) and 4.13b (acetylenic green crosses).

Chapter 4: Diels-Alder cycloaddition of tetraphenylcyclopentadienone and 1,3,5-hexatriynes

Figure 4.5. APPI HRMS expansion of the region that can be assigned to (M+) of 4.13b.

4.3. Diels-Alder cycloaddition of tetraphenylcyclopentadienone (TPCPD) and 1,3,5-hexatriynes under conventional heating

The Diels-Alder reactions with TPCPD were performed for triynes 1.27a, 1.28a, 1.30a, and 4.14a (Scheme 4.4) using thermal heating of the reaction mixture. In principal, three different regioisomers A, B, C might be obtained depending on reaction regioselectivity for the bond a, b, or a' of the triyne. The reactions was regioselective leading preferentially to the regioisomer A ascribed to the reaction of TPCPD with the central triple bond β of the triyne. Triyne 4.14a (1 equiv) and TPCPD (1 equiv) were dissolved in dry xylenes, and the mixture was heated to 140 °C for 93 h. Solvent was removed in vacuo, and purification by flash chromatography afforded the pure product 4.15a in 49% yield (Table 4.1, entry 1). Triyne 1.30a (1 equiv) and TPCPD (1 equiv) were dissolved in dry xylenes and the mixture was heated to 140 °C for 95 h. The reaction mixture was cooled to rt, solvent was removed in vacuo, and purification by flash chromatography afforded the pure product 4.15b in 70% yield (Table 4.1, entry 2). Triyne 1.28b (1 equiv) and TPCPD (1 equiv) were dissolved in dry xylenes, and the mixture was heated to 140 °C for 97 h. The solvent was removed in vacuo and purification by flash chromatography afforded the pure product 4.15c in 58% yield (Table 4.1, entry 3). Triyne 1.27a (1 equiv) and TPCPD (1 equiv)

Chapter 4: Diels-Alder cycloaddition of tetraphenylcyclopentadienone and 1,3,5-hexatriynes were dissolved in dry xylenes and the mixture was heated to 140 °C for 67 h. After solvent removal and purification by flash chromatography, the pure products 4.15d was isolated in 78% yield (Table 4.1, entry 4). The formation of regioisomer A and the associated yield can be explained to some extent by steric effects and increased donor nature ascribed to the end group. Considering the triynes substituted with two trialkylsilyl groups 1.27a, 1.28b, and 1.30a; increasing the steric hindrance of the endgroups, the yields decrease in the series 4.15d 78% (Table 4.1, entry 4) → 4.15b 70% (Table 4.1, entry 2) → 4.15c 58% (Table 4.1, entry 3). Compound 4.15a is isolated in the lowest yield, perhaps due to the lack of steric shielding from the phenyl substituents 7 that lead to less selectivity for the central triple bond β. Thus, with conventional thermal heating the Diels-Alder reaction of TPCPD with different end- capped triynes is possible, leading predominantly to a reaction at the central acetylenic bond to give regioisomer A. The required reaction time, however, is long with 67-97 h, and the yields are moderate to good (49-78%).

Chapter 4: Diels-Alder cycloaddition of tetraphenylcyclopentadienone and 1,3,5-hexatriynes

R1 R1 a b a' TPCPD R1 R2 + xylenes R2 − h 140 °C, 67 97 R2

A B

1 2 = 1 2 = 4.14a R = SiEt3, R 4.15a R = SiEt3, R + 1 2 1 2 1.30a R = SiMe3, R = Sii−Pr3 4.15b R = SiMe3, R = Sii−Pr3 1 2 1 2 1.28b R = R = Sii−Pr3 4.15c R = R = Sii−Pr3 1 2 1 2 1.27a R = R = SiMe3 4.15d R = R = SiMe3 R1

Scheme 4.4. Diels-Alder reactions performed under thermal heating to give 4.15a-d.

Table 4.1. Diels-Alder reactions performed under thermal heating afforded 4.15a-d.18[a]

Entry Triyne Product Time (h) Yield

Regioisomer A

1 4.14a[b]† 4.15a 93 49%

2 1.30a 4.15b 95 70%

[b] 3 1.28b 4.15c 97 58%

[c] 4 1.27a 4.15d 67 78%

[a] Reactions were performed with TPCPD (1 equiv) and triyne (1 equiv) in dry xylenes under heating to reflux for individual time. [b] Triyne 4.14a was synthesized from a dibromo-precursor provided by a group member. [c] Triyne 1.27a was synthesized by a group member according to literature procedure.

†This reaction was already investigated. Studies related to the formation of the three regioisomers over the time were conducted. For more details see: Michael Vogl, Bachelorarbeit, Universität Erlangen-Nürnberg, 2010.

Chapter 4: Diels-Alder cycloaddition of tetraphenylcyclopentadienone and 1,3,5-hexatriynes

4.4. Diels-Alder cycloaddition of TPCPD and 1,3,5-hexatriynes under microwave irradiation

After the investigation of the Diels-Alder reactions under thermal conditions, the Diels- Alder reactions were performed under microwave irradiation with two different conditions (Scheme 4.5, Table 4.2). Triyne 4.14a (1 equiv) and TPCPD (1 equiv) were dissolved in dry xylenes. The mixture was heated under microwave irradiation to 210 °C for 1.5 h. After solvent removal and purification by column chromatography, 4.15a was isolated in 61% yield (Table 4.2 entry 1, Condition A). This reaction was repeated under microwave irradiations heating triyne 4.14a (1 equiv) and TPCPD (1 equiv) to 250 °C for 1 h. After solvent removal and purification by column chromatography, 4.15a was isolated in a significantly higher yield of 95% (Table 4.2, entry 1, Condition B). Triyne 1.28b (1 equiv) and TPCPD (1 equiv) in o-dichlorobenzene were then tested toward synthesis of 4.15b and also gave good yields using Condition B (Table 4.2, entry 3) establishing that the slightly higher temperature was indeed beneficial Using Condition B, triyne 1.30a (1 equiv.) and TPCPD (1 equiv.) were dissolved in dry o- dichlorobenzene and were used to synthesize 4.15d which was isolated in 92% yield (table 4.2, entry 4, Condition B). The Diels-Alder reactions to obtain 4.15a, 4.15c, and 4.15d were performed using a Cem microwave and the selected solvent xylenes worked well for both Condition A and B (Table 4.2 entries 1, 3, and 4). When the same reaction condition were utilized to obtain 4.15b using Biotage microwave, the reaction did not reach the desired temperature (250 °C) leading to an explosion of the vial inside the vial cavity. The problem was not related to high pressure, but to a different physical set-up of Biotage microwave compared to Cem microwave including different vial materials, and it was expected that the low absorber power of xylenes also played a role. Considering the better ability of o-dichlorobenzene to absorb microwave irradiations compared to xylenes and furthermore that is a common solvent utilized in Diels-Alder reactions19, Diels-Alder reactions to obtain 4.15b, 4.15e, 4.15f were performed with Biotage microwave using o- dichlorobenzene. (Table 4.2 entries 2, 5, and 6). In general, the ability of the solvent to convert electromagnetic energy into heat at a given frequency and temperature is determined by the following equation:

Chapter 4: Diels-Alder cycloaddition of tetraphenylcyclopentadienone and 1,3,5-hexatriynes

tan δ = ε”/ ε’ where the tan δ (loss tangent, the dissipation factor of how efficiently microwave energy is converted into thermal energy) is a function of ε’’ (dielectric loss factor which represent the amount of input microwave energy that is lost to the sample by being dissipate as heat), and ε’ (dielectric constant or relative permittivity which represents the ability of a dielectric material to store electric potential energy under the influence of an electric field). If tan δ > 0.5, the solvent is classified as a high mw absorber, if 0.1 < tan δ < 0.5, the solvent is considered medium mw absorber (e. g o- dichlorobenzene, tan δ = 0.280), and tan δ < 0.1, the solvent is considered low mw absorber (e. g o- xylene shows tan δ = 0.018) . Triyne 4.7 (1 equiv.) and TPCPD (1 equiv.) were dissolved in dry o-dichlorobenzene and were used to synthesize 4.15e according to Condition B and 4.15e was isolated in 72% yield (Table 4.2, entry 5). Triyne 4.13a (1 equiv.) and TPCPD (1 equiv.) were dissolved in dry o-dichlorobenzene and were used to synthesize 4.15f according to Condition B, and 4.15f was isolated in 57% yield (Table 4.2, entry 6, Procedure B). The Diels-Alder reactions were optimized under microwave irradiation (Table 4.2) decreasing the reaction time from 67-97 h under thermal condition to 1 h under mw irradiation. As for Diels-Alder reactions under thermal heating, reactions under mw irradiation lead preferentially to the regioisomer A derived from the reaction of TPCPD to the central triple bond β. The yields of 4.15a range from 85 to 95% under microwave irradiation using Condition B compared to the thermal heating where the yields values range from 49 to 78%. With the inclusion of more electron-donating ability or decreasing steric hindrance of end-groups, the yield is decreased (72% for 4.15e and 57% for 4.15f) compared to the series 4.15b-d (88%, 85%, and 92%, respectively). The slight decrease of the yield from 72% for 4.15e to 57% for 4.15f might also be explained by the steric hindrance of end-groups in 4.13a compared to 4.7 that lead to less selectivity for the central triple bond β.

Chapter 4: Diels-Alder cycloaddition of tetraphenylcyclopentadienone and 1,3,5-hexatriynes

R1 α α β ' Condition A or R1 R2 Condition β

1 = 2 = R1 = 2 = 4.14α R SiEt3, R 4.15α SiEt3, R 1 = 2 = 1 2 4.15β R SiMe3, R Sii-Pr3, 1.30α R = SiMe3, R = Sii-Pr 3, 1 = 2 = 1.28β R1 = R2 = Sii-Pr 4.15c R R Sii-Pr3 3 1 2 1 2 4.15d R = R = SiMe3 1.27α R = R = SiMe3 R1 = SiMe R2 = OMe 1 = 2 = 4.15e 3, 4.7 R SiMe3, R OMe

1 2 4.13α R1 = R2 = Bu 4.15f R = R = Bu

Scheme 4.5. Diels-Alder reactions under microwave irradiation giving 4.15a-f.

Table 4.2. Diels-Alder reactions under microwave irradiation afforded 4.15a-f.

Entry Triyne Products Condition A[a] Condition B[b]

1 4.14[d] 4.15a 61% [e] 95% [e]

2 1.30a 4.15b - 88% [f]

3 1.28b[c] 4.15c 79% [e] 85% [e]

4 1.27[d] 4.15d - 92% [e]

5 4.7 4.15e - 72% [f]

6 4.13a 4.15f - 57% [f]

[a] Condition A: mw 210 °C, 1.5 h. [b] Condition B: mw 250 °C, 1 h. [c]Triyne synthesized from dibromo-precursor provided by a group member. [d]Triyne synthesized by a group member. [e] Reaction was carried out using dry xylenes with Cem microwave.18 [f] Reaction performed using o-DCB using Biotage microwave.

The Diels-Alder reaction of triynes 4.16a,b and TPCPD was also explored under microwave irradiation at 250 °C for 1 h (Scheme 4.6). All reaction resulted in a mixture of regioisomer A,

Chapter 4: Diels-Alder cycloaddition of tetraphenylcyclopentadienone and 1,3,5-hexatriynes regioisomer B, and regioisomer C 4.17a,b, 4.18a,b, and 4.19a,b, respectively. It was not possible to separate the regioisomers, but evidence for formation of regioisomer A, B, and C was provided by mass spectroscopy.

Tr* Tr* a a b ' TPCPD Tr* R + xylenes or o-DCB R 4.16a,b mw, 250 °C, 1 h R

A B

4.17a,b 4.18a,b Tr* = +

a R = Sii-Pr3 b R = CH3

Tr*

C 4.19a,b

Scheme 4.6. Diels-Alder reaction of 4.16a,b.

The ESI HRMS analysis confirmed that the Diels-Alder reaction of 4.16a and TPCPD was successful because a signal that can be ascribed to 4.17a, 4.18a, or 4.19a was observed at m/z + calculated for C86H104NaSi ([M + Na] ) 1187.77568, found 1187.77995.

Chapter 4: Diels-Alder cycloaddition of tetraphenylcyclopentadienone and 1,3,5-hexatriynes

Figure 4.6. Expansion of ESI HRMS signals that can be assigned to 4.17a, 4.18a, and 4.19a ([M + Na]+).

The APPI HRMS analysis confirmed that the Diels-Alder reaction of 4.16b and TPCPD was successful because was observed the signals that can be assigned to Diels-Alder products 4.17b, + 4.18b, or 4.19b at m/z calculated for C78H86 (M ) 1022.67241, found 1022.67240, Figure 4.7.

Figure 4.7. Expansion of APPI HRMS signals that can be assigned to 4.17b, 4.18b, and 4.19b (M+).

Chapter 4: Diels-Alder cycloaddition of tetraphenylcyclopentadienone and 1,3,5-hexatriynes

4.5 Desilylation and homocoupling reactions toward the formation of the dimers.

The desilylation of tetraphenylbenzene derivatives 4.15a-e was explored with two different methods (Table 4.3 entries 1-5). Desilylation of 4.15a using KOH was attempted, but the reaction did not lead to a complete conversion to 4.20a after stirring for 24 h. The reaction led to a mixture of 4.15a and 4.20a that was difficult to separate. As a consequence, compound 4.15a (1 equiv) in dry THF was cooled to 0 °C, and TBAF (4 equiv) was added. The mixture was allowed to reach rt and then stirred for 3 h. After work-up, the resulting solid was purified by a short column chromatography to afford 4.20a in 72% yield (Table 4.3, entry 1). Desilylation of compound 4.15b (1 equiv), however, could be accomplished using KOH (3 equiv) in THF and MeOH (2:1 v/v) at rt for 5 h. After work up, the solid was purified by a short column chromatography to afford 4.20b in 93% yield (Table 4.3, entry 2). Compound 4.15c (1 equiv) was desilylated according to the protocol using TBAF (4 equiv) and after 5 h of stirring and work up, 4.20c was isolated in 61% yield (Table 4.3, entry 3). Reaction to 4.20c was attempted using KOH, but did not lead to a complete conversion after 24 h. Rather, the reaction led to a mixture of 4.15d and the product ascribed to the removal of one TMS group. Desilylation of 4.15d and TBAF (3 equiv) generates 4.20c in 88% yield after work-up and purification (Table 4.3, entry 4). Finally, compound 4.20e was synthesized from 4.15e using KOH (3 equiv) After stirring for 2 h and work up, 4.20e was isolated in quantitative yield (Table 4.3, entry 5).

Chapter 4: Diels-Alder cycloaddition of tetraphenylcyclopentadienone and 1,3,5-hexatriynes

R1 H

R2 R3

1 2 = 3 = 4.15a: R = SiEt3, R 4.20a R : 1 = 2 = 3 4.15b R SiMe3, R Sii-Pr3, 4.20b R = Sii-Pr3 1 2 3 4.15c: R = R = Sii-Pr3 4.20c R = H 1 2 4.15d: R = R = SiMe3 : 1 = 2 = 3 = 4.15e R SiMe3, R OMe 4.20e R OMe

Scheme 4.7. Desilylation reactions of 4.20a-e.a

Table 4.3. Desilylation reactions of 4.20a-e.

Entry Substrate TBAF[a] KOH[b] Time Products Yield

(equiv) (equiv) (h)

1 4.15a20 4 - 3 h 4.20a 72%

2 4.15b - 3 5 h 4.20b 93%

3 4.15c 4 - 5 h 4.20c 61%

4 4.15d 3 - 3 h 4.20c 88%

5 4.15e - 3 2 h 4.20e 100%

[a] Desilylation using: substrate (1 equiv), TBAF and THF at rt for 3-5 h. [b] Desilylation using substrate (1 equiv) with KOH and THF/MeOH (2:1 v/v) ar rt for 2-5 h.

With terminal alkynes 4.20a, 4.20c and 4.20e in hand, Cu-catalyzed reactions were explored. Compound 4.20a was subjected to homocoupling under Hay conditions:21 CuCl (2.5 equiv) and

TMEDA (5 equiv.) in CH2Cl2 were kept in the ultrasonic bath for 20 min (Scheme 4.8). Then,

4.20a (1 equiv) was added. CH2Cl2 was evaporated and replaced by toluene, and the mixture was

Chapter 4: Diels-Alder cycloaddition of tetraphenylcyclopentadienone and 1,3,5-hexatriynes heated to 100 °C for 2 h. After work-up, purification by column chromatography gave 4.21a in 32% as a yellow solid. It was clear, however, that the reaction was not completed and unreacted 4.20a (Table 4.4, entry 1, Procedure A) remained. Due to the low yield of 4.21a utilizing Hay conditions, the homocoupling was repeated using Pd as catalyst:22,23 Specifically, to a mixture of

[PdCl2(PPh3)2] (0.04 equiv), CuI (0.05 equiv), and dry i-Pr2NH (2.4 equiv) was added 4.20a (1 equiv) in dry THF. Ethyl bromoacetate (1 equiv) was added, and the mixture was stirred at rt under

N2 atmosphere for 24 h. After work-up and purification by column chromatography, 4.21a was isolated in 66% yield. (Table 4.4, entry 1, Procedure B). Thus, it appeared that the homocoupling reaction under Pd-catalysis increased the yield. Compound 4.20b under Hay conditions led to 4.21b in 23% yield. The reaction was not complete and unreacted substrate 4.20b (Table 4.4, entry 2, Procedure A) was again observed. As a result of the low yield of 4.21b under Hay conditions, the homocoupling using Pd-catalysis was applied for 4.20b leading to 4.21b in 52% yield (Table 4.4, entry 2, Procedure B). Finally, compound 4.21e was synthesized from 4.20e under Hay conditions, but the reaction failed to proceed to completion. Compound 4.21e was isolated in 45% (Table 4.4, entry 3, Procedure A). Homocoupling using Pd-catalysis gave 4.21e in 85% yield (Table 4.4, entry 2, Procedure B).

Chapter 4: Diels-Alder cycloaddition of tetraphenylcyclopentadienone and 1,3,5-hexatriynes

4.20a R1 = 4.21a R1 =

1 1 4.20b R = Sii-Pr3 4.21b R = Sii-Pr3

4.20e R1 = OMe 4.21e R1 = OMe

Scheme 4.8. Homocoupling condition used to synthesize 4.21a,b,e.

Table 4.4. Homocoupling reactions of 4.20a, 4.20b, and 4.20e to give 4.21a,b,e.

Entry Substrate Product Procedure A [a]20 Procedure B [b]

1 4.20a 4.21a 32% 66%

2 4.20b 4.21b 23% 52%

3 4.20e 4.21e 45% 85%

[a] Terminal acetylene (1 equiv), CuCl (2.5 equiv), TMEDA (5 equiv), toluene, 100 °C, 2 [b] h. Terminal acetylene (1 equiv), [Pd(PPh3)2Cl2] (0.04 equiv), CuI (0.05 equiv), HNi-

Pr2 (2.4 equiv), THF, ethyl bromoacetate (1 equiv) , rt, 24 h.

4.6 UV-vis spectroscopy, cyclic voltammetry, and X-ray crystallography

Figure 4.8a shows the structure of 4.15a-f and 4.20c with the corresponding λmax values summarized in parenthesis and Figure 4.8b shows the corresponding UV-vis spectra of 4.15a-f and

4.20c. In the series of 4.15b-d the λmax values are approximately the same with values of 297 nm for 4.15b and 4.15c and 294 nm for 4.15d. ε values increase in the series 4.15d → 4.15c → 4.15b, and also in the series 4.15e → 4.15a. In comparison to 4.15a, 4.15b-d, and 4.15e-f is shown a red 71

Chapter 4: Diels-Alder cycloaddition of tetraphenylcyclopentadienone and 1,3,5-hexatriynes shift of λmax due to the extended conjugation through the aryl groups. Compound 4.20c shows a λmax of 278 nm which is blue shifted relative to all other derivatives as a result of decreased conjugation and loss of the tri-alkylsilyl groups.

Chapter 4: Diels-Alder cycloaddition of tetraphenylcyclopentadienone and 1,3,5-hexatriynes a)

Sii-Pr Sii-Pr3 3 SiMe3

SiEt3 Sii-Pr SiMe3 3 SiMe3

λ λ λ λ 4.15a ( max = 328 nm) 4.15b ( max = 297 nm) 4.15c ( max = 297 nm) 4.15d ( max = 294 nm)

OMe Bu

SiMe3 H Bu

λ λ λ = 278 4.15e( max = 340 nm) 4.15f ( max = 352 nm) 4.20c ( max nm) b)

Figure 4.8 a) Structures of 4.15a-f and 4.20c with correspondent λmax values in parenthesis. b) UV-vis absorption spectra of 4.15a-f and 4.20c measured in CH2Cl2.

Figure 4.9a shows the structure of 4.15a,b,e and 4.21a,b,e with the correspondent λmax values obtained summarized in parenthesis. Figure 4.9b show the UV-vis spectra of 4.15a,b,e and

4.21a,b,e The λmax values of the dimers 4.21a,b,e are red shifted compared the corresponding precursors 4.15a,b,e and this fact is ascribed to the increasing conjugation in the dimers 4.21a,b,e. 73

Chapter 4: Diels-Alder cycloaddition of tetraphenylcyclopentadienone and 1,3,5-hexatriynes

The red shifts observed from the Diels-Alder precursors to the corresponding dimers are: 58 nm from 4.15a to 4.21a, 70 nm from 4.15b to 4.21b, and 54 nm from 4.15e to 4.21e. ε values decrease in the series 4.21e → 4.21a; the reason of this behaviour is not been investigated yet.

Chapter 4: Diels-Alder cycloaddition of tetraphenylcyclopentadienone and 1,3,5-hexatriynes a)

OMe

Sii-Pr3

SiEt3 SiMe3 SiMe3

λ λ λ 4.15a ( max = 328 nm) 4.15b ( max = 297 nm) 4.15e ( max = 340 nm)

OMe λ 4.21a ( max = 386 nm) Sii-Pr3

i-Pr3Si MeO

λ 4.21b ( max = 367 nm) λ 4.21e ( max = 394 nm) b)

Figure 4.9. a) Structures of 4.15a,b,e and 4.21a,b,e with correspondent λmax values in parenthesis. b) UV-vis absorption spectra of 4.15a,b,e and 4.21a,b,e measured in CH2Cl2.

Chapter 4: Diels-Alder cycloaddition of tetraphenylcyclopentadienone and 1,3,5-hexatriynes

Electrochemical analysis were conducted by cyclic voltammetry for compounds 4.15e-f, 4.20c and 4.21a,b,e, but the compounds do not show any redox event. The redox behavior it is surprising for compounds 4.15e and 4.21e due to the fact that in literature is known a similar compounds 4.22 which exhibit oxidation events (Figure 4.10)24. The reason why the compounds analyzed do not display redox events are not known yet.

OMe OMe

OMe i-Pr3Si

SiMe3 Me3Si

OMe MeO

4.15e 4.22 4.21e Figure 4.10. Molecular structure of 4.15e, 4.21e, and 4.22.24

Aryl substituents in tetraphenylbenzene are not constrained by additional bonding in the plane of the aromatic core, and, thus, the phenyl substituents display a twisted angle with respect to the central benzene core. As a consequence, tetraphenyl-benzene derivatives display complex non planar topologies, 25 and the conjugation between the phenyl moieties and the central benzene ring could be limited.26,27 Compound 4.20c was analyzed by X-ray crystallography and the solid state torsion angles are compared to un-substituted tetraphenylbenzene (TPB) known in literature.5 Single crystals of 4.20c were obtained by slow evaporation of a CDCl3 solution at rt. Considering the structures of 4.20c

(Figure 4.11a) and TPB (Figure 4.11b), TPB displays C2 symmetry, while 4.20c does not. The phenyl substituents in 4.20c are more twisted with respect to the central benzene ring than those in TPB. The torsion angles of 4.20c range from 63.6(4)° to 67.6(5)° (Table 4.5, entries 3-6), while those in TPB range from 68.1(2)° to 68.8(2)° (Table 4.6, entries 1-2).

Chapter 4: Diels-Alder cycloaddition of tetraphenylcyclopentadienone and 1,3,5-hexatriynes

a) b)

Figure 4.11. X-ray crystallographic structure of a) 4.20c. b) TPB.

Table 4.5. Torsion angles of phenyl substituents and the central benzene ring of 4.20c.

Entry Carbon atoms Torsion angle °

1 C12 C13 C21 C22 76.9(4)

2 C14 C13 C21 C26 78.5(4)

3 C13 C14 C31 C32 67.6(5)

4 C15 C14 C31 C36 63.6(4)

5 C14 C15 C41 C42 66.0(5)

6 C16 C15 C41 C46 64.3(4)

7 C15 C16 C61 C62 66.7(4)

8 C11 C16 C61 C66 73.2(4)

Chapter 4: Diels-Alder cycloaddition of tetraphenylcyclopentadienone and 1,3,5-hexatriynes

Table 4.6. Torsion angles of phenyl substituents and the central benzene ring of TPB.

Entry Carbon atoms Torsion angle °

1 C5 C1 C2 C2’ 68.1(2)

2 C9 C1 C2 C4 68.8(2)

3 C6 C3 C4 C2 51.5(5)

4 C11 C3 C4 C7 47.6(2)

A single crystal of 4.15c suitable for X-ray crystallographic analysis was obtained by slow evaporation of a CDCl3 solution at rt. The solid state structure with selected carbon atoms labels of 4.15c is shown in Figure 4.12a. Two unique molecules are found in the unit cell: molecule A and molecule B. Both molecules were analyzed in terms of torsion angles of the phenyl substituents to the central benzene rings. The results for molecule A and B are shown in Table 4.7. The molecules show different torsion angles, but the differences are small. Overall the angles vary from 62.0 ° (C35a-C34A-C51A-C52A) to 81.6 ° (C31A.C36A-C71A-C72A) for molecule B, while the angles vary from 63.9 ° (C35B-C34B-C51B-C52B) to 73.2 ° (C31B.C36B-C71B-C72B) for molecule A.

Figure 4.12. a) X-ray crystallographic structure of 4.15c with selected label atoms.

Chapter 4: Diels-Alder cycloaddition of tetraphenylcyclopentadienone and 1,3,5-hexatriynes

Table 4.7. Torsion angles of aryls substituent with the central benzene rings of 4.15c

Entry Carbon atoms Torsion angle ° Torsion angle °

Molecule A Molecule B

1 C32 C33 C41 C42 68.7 (4) 69.0 (4)

2 C34 C33 C41 C46 68.9 (4) 72.1 (4)

3 C33 C34 C51 C56 66.0 (4) 64.7 (4)

4 C35 C34 C51 C52 63.9 (4) 62.0 (4)

5 C34 C35 C61 C66 67.4 (4) 64.4 (4)

6 C36 C35 C61 C62 68.4 (4) 69.2 (4)

7 C35 C36 C71 C76 70.7 (4) 79.9 (4)

8 C31 C36 C71 C72 73.2 (4) 81.6 (4)

4.7 Attempts to synthesize PAH derivatives via Scholl cyclodehydrogenation

Considering the procedure known in literature to synthesize PAH from phenyl-substituted benzenes via the Scholl reaction,2 the same protocol was applied for compounds 4.15c, 4.21a, and 4.21b, but attempts to obtain the desired products, however, failed (Scheme 4.9). For all three cases, products derived from partial cyclization were observed. For the reaction of 4.21a and 4.21b, remaining starting material was also visible in the 1H NMR spectra. Due to time constraints, other cyclodehydrogenation protocols were not tried.

Chapter 4: Diels-Alder cycloaddition of tetraphenylcyclopentadienone and 1,3,5-hexatriynes

Sii-Pr3 Sii-Pr3 FeCl3, CH3NO2

CH2Cl2 Sii-Pr3 Sii-Pr3

4.15c

R R

FeCl3, CH3NO2

CH2Cl2

R R

4.21a R =

= 4.21b R Sii-Pr3

Scheme 4.9. Attempts to synthesize PAHs via the Scholl reaction.

4.8 Conclusions

The Diels-Alder reaction of TPCPD and different triynes has been investigated. The Diels- Alder reactions shows regioselectivity with the preferential reaction of TBCPD at the central triple bond of the triynes. The Diels-Alder reaction was optimized under microwave irradiation resulting in the decrease of the reaction time and increase of the yield compared to the analogous Diels-Alder reaction conducted under thermal conditions. Selected Diels-Alder products have been taken on to a sequence of desilylation and homocoupling reactions to form dimeric derivatives. The homocoupling reaction has been optimized using Pd(PPh3)2Cl2 as a catalyst and the reaction results in an increase of the yield compared to those obtained with Hay homocoupling using Cu(I). The properties of obtained products have been explored using UV-vis spectroscopy, cyclic voltammetry, and in two cases X-ray crystallography. The dimers show a red shift of λmax compared to the

Chapter 4: Diels-Alder cycloaddition of tetraphenylcyclopentadienone and 1,3,5-hexatriynes corresponding monomeric precursors ascribed to the increasing conjugation in the dimers compared to the precursors.

4.9 References

1. X. Feng, W. Pisula, K. Müllen, Pure Appl. Chem. 2009, 81, 2203-2224. 2. R. Liu, D. Wu, X. Feng, K. Müllen, J. Am. Chem. Soc. 2011, 133, 15221-15223. 3. B. Alameddine, S. M. Caba, M. Schindler, T. A. Jenny, Synthesis 2012, 44, 1928-1934. 4. A. J. Berresheim, M. Müller, K. Müllen, Chem. Rev. 1999, 99, 1747-1786. 5. H. Wang, Y. Liang, H. Xie, L. Feng, H. Lu, S. Feng, J. Mater. Chem. 2014, 2, 5601-5606. 6. M. D. Watson, A. Fechtenkötter, K. Müllen, Chem. Rev. 2001, 101, 1267-1300. 7. C. Kübel, S. L. Chen, K. Müllen, Macromolecules 1998, 31, 6014-6021. 8. R. Gedye, F. Smith, K. Westaway, H. Ali, L. Baldisera, Tetrahedron Lett. 1986, 27, 279-282. 9. R. J. Giguere, T. L. Bray, S. M. Duncan, G. Majetich, Tetrahedron Lett. 1986, 27, 4945-4948. 10. A. Loupy, F. Maurel, A. Sabatié-Gogovà, Tetrahedron 2004, 60, 1683-1691. 11. W. D. Shipe, S. E. Wolkenberg, C. W. Lindsley, Drug Discov. Today Technol. 2005, 2,

155-161. 12. A. L. K. Shi Shun, E. T. Chernick, S. Eisler, R. R. Tykwinski, J. Org. Chem. 2003, 68, 1339-1347. 13. S. Eisler, N. Chahal, R. McDonald, R. R. Tykwinski. Chem. Eur. J. 2003, 9, 2542-2550. 14. Y. Morisaki, T. Luu, R. R. Tykwinski, Org. Lett. 2006, 8, 689-692. 15. T. Luu, E. Elliott, A. D. Slepkov, S. Eisler, R. McDonald, F. A. Hegmann, R. R Tykwinski, Org. Lett. 2005, 7, 51-54. 16. I. Van Overmeire, S. A. Boldin, K. Venkataraman, R. Zisling, S. D. Jonghe, S. Van Calenbergh, D. De Keukeleire, A. H. Futerman, P. Herdewijn, J. Med. Chem. 2000, 43, 4189-4199. 17. A. Auffrant, F. Diederich, Helv. Chim. Acta 2004, 87, 3085-3105.

Chapter 4: Diels-Alder cycloaddition of tetraphenylcyclopentadienone and 1,3,5-hexatriynes

18. Initial reactions were carried out during the master thesis, but all the products were completely characterized during the PhD work. 19. N. Kaval, W. Dehaen, C. O. Kappe, E. Van der Eycken, Org. Biomol. Chem. 2004, 2, 154-156. 20. This reaction was already investigated. For more details see: Michael Vogl, Bachelorarbeit, Universität Erlangen-Nürnberg, 2010. 21. A. S. Hay, J. Org. Chem. 1962, 27, 3320-3321. 22. A. Lei, M. Srivastava, X. Zhang, J. Org. Chem. 2002, 67, 1969-1971. 23. W. A. Chalifoux, M. J. Ferguson, R. R. Tykwinski, Eur. J. Org. Chem. 2007, 1001-1006. 24. J. P. Gisselbrecht, N. N. P. Moonen, C. Boudon, M. B. Nielsen, F. Diederich, M. Gross, Eur. J. Org. Chem. 2004, 2959-2972. 25. E. Gagnon, T. Maris, P. M. Arseneault, K. E. Maly, J. D. Wuest, Cryst. Growth Des. 2009, 10, 648-657. 26. I. Y. Wu, J. T. Lin, Y. T. Tao, E. Balasubramanian, Adv. Mater. 2000, 12, 668-669. 27. R. N. Bera, N. Cumpstey, P. L. Burn, I. D. W. Samuel, Adv. Funct. Mater. 2007, 17, 1149-1152.

Chapter 5: Experimental section

5.1 General data

Reagents were purchased reagent grade from commercial suppliers and used without further purification. THF and Et2O were distilled from sodium/benzophenone, CH2Cl2 was distilled from

CaH2, hexanes, toluene, and xylenes from sodium, and i-Pr2NH was distilled from CaCl2. MgSO4 and Na2SO4 were used as standard drying reagents after aqueous work-up. TLC analyses were carried out on TLC plates from Macherey-Nagel (ALUGRAM® SIL G/UV254) and visualized via UV-light (264/364 nm) or standard coloring reagents. Column chromatography was performed using Silica Gel 60M (Merck). 1H and 13C NMR spectra were recorded on a Bruker Avance 300 operating at 300 MHz (1H NMR) and 75 MHz (13C NMR), a Bruker Avance 400 operating at 400 MHz (1H NMR) and 100 MHz (13C NMR), or a Jeol Alpha 500 operating at 500 MHz (1H NMR) and 126 Hz (13C NMR). NMR spectra 1 13 1 were referenced to the residual solvent signal ( H: CDCl3, 7.24 ppm; C: CDCl3, 77.0 ppm; H: 13 THFD8, 3.58 ppm, 1.73 ppm; C: THDD8, 67.4 ppm, 25.2 ppm) and recorded at ambient probe temperature. Coupling constants are reported as observed (±0.5 Hz). Mass spectra were obtained from a Bruker 9.4T Apex-Qe FTICR (MALDI, Matrix: DCTB), Agilent Technologies 6220 TOF (ESI), Bruker micro TOF II focus, and Bruker maxis 4G (APPI,

ESI, in CH2Cl2) instruments. IR spectra were recorded on a Varian 660-IR spectrometer as solids in ATR-mode. UV-vis spectroscopic measurements were carried out on a Varian Cary 5000 UV-vis-NIR spectrophotometer. Melting points were measured with an Electrothermal 9100 instrument. Crystallographic data for unpublished compounds are available from the X-ray Crystallographic Laboratory, Institute for Organic Chemistry, Universität Erlangen-Nürnberg. Reactions under microwave were performed using a Synthesis Cem microwave or Biotage Initiator microwave. Cyclic voltammetry was performed using BAS CV 50 W VERSION 2 instrument. Three electrodes compartment was used: Pt wire was used as counter electrode, Ag/AgNO3 as reference electrode,

Chapter 5: Experimental section

and Pt as working electrode. The reference electrode Ag/AgNO3 contains a solution of 0.001 M of

AgNO3, 0.1 M of n-Bu4NPF6 in ACN. The reference electrode was stored in a solution containing

0.1 M n-Bu4NPF6 in ACN. n-Bu4NPF6, commercial available in 99% for analytical purpose, it was used as the supporting electrolyte without further purification. Ferrocene was used as internal standard. Before each analysis, the solutions were stirred and degassed with a constant flow of nitrogen for 25 min and during the measurement, the flow of nitrogen was maintain in the cell. The solvent used was fresh distilled CH2Cl2.

5.2 Synthesis of known compounds

H i-Pr Si 3

4.1

1 Compound 4.1. To a solution of triisopropylsilyl acetylene (5.1 g, 6.1 mL, 27 mmol) in dry Et2O (50 mL) at –78 °C was slowly added n-BuLi (2.5 M in hexanes, 11 mL, 27 mmol). The solution was stirred for 30 min, and dry DMF (2.5 g, 2.7 mL, 34 mmol) was added via a syringe. The cooling bath was removed and the reaction was allowed to reach rt. The solution was poured into a mixture of ice (50 mL) and HCl (1.0 M, 50 mL). The layers were separated, and the organic phase was washed sequentially with sat. aq. NaHCO3 (2 x 50 mL), sat. aq. NaCl (2 x 50 mL), dried

(MgSO4), and filtered. The solvent was removed in vacuum, and the crude product was filtered through a short silica gel plug with hexanes. After removal of the solvent, 4.1 (4.1 g, 73%) was obtained as a clear colorless liquid. Spectral and physical data were consistent with those reported.2

Chapter 5: Experimental section

Me Si i-Pr 3 Si 3 4.2

Compound 4.2.3 To a solution of trimethylsilylacetylene (1.95 g, 2.7 mL, 20 mmol) in dry THF (60 mL) at –78 °C was slowly added n-BuLi (2.5 M in hexanes, 7.6 mL, 20.1 mmol). The reaction mixture was stirred for 1 h and the aldehyde 4.1 (4.1 g, 20 mmol), dissolved in dry THF (10 mL), was slowly added over 5 min. The reaction mixture was allowed to warm to rt. After stirring for 3.5 h, sat. aq. NH4Cl (25 mL) and Et2O (25 mL) were added and the layers were separated. The organic layer was washed with sat. aq. NH4Cl (3 x 25 mL), dried (MgSO4), filtered, and the solvent removed in vacuum. The crude product was purified by column chromatography (silica gel, hexanes/ethyl acetate 10:1) and 4.2 (5.1 g, 83%) was obtained as a yellow oil. Spectral and physical data were consistent with those reported.4

Me3Si Sii-Pr3 4.3

Compound 4.3 was synthesized according to literature3 and was isolated in 98% yield (3.9 g). Spectral and physical data were consistent with those reported.5

Br Br

Me3Si Sii-Pr3 4.4

Compound 4.4 was synthesized according to literature3 and was isolated in 67% yield (2.1 g). Spectral and physical data were consistent with those reported.5

Chapter 5: Experimental section

Me3Si Sii-Pr3 1.30a

Compound 1.30a was synthesized according to literature3 and was isolated in 68% yield (2.3 g). Spectral and physical data were consistent with those reported.6

MeO SiMe3 4.5

Compound 4.5 was synthesized according to literature7 and was isolated in 100% (4.14 g) yield. Spectral and physical data were consistent with those reported.7

Br Br

MeO SiMe3

4.6

Compound 4.6 was synthesized according to literature3 and was isolated in 61% (4.1 g) yield. Spectral and physical data were consistent with those reported.3

Chapter 5: Experimental section

MeO SiMe3

4.7

Compound 4.7 was synthesized according to literature8 and was isolated in 87% (0.81 g) yield. Spectral and physical data were consistent with those reported.8

SiMe3

4.8a

9 Compound 4.8. To a solution of 4-bromobutylbenzene (3.8 ml, 6.0 g, 28 mmol) in dry i-Pr2NH

(12 ml) were added PdCl2(PPh3)2 (0.21 g, 0.28 mmol), CuI (0.053 g, 0.28 mmol) and trimethylsilylacetylene (9 mL, 63 mmol). After stirring for two days at 50 °C, the volatiles were removed in vacuum and the residue was dissolved in CH2Cl2 (10 mL). The organic layer was washed with sat aq. solution of NaCl (10 mL), H2O (10 mL), and dried over Na2SO4. The pure product was obtained after a column chromatography using hexanes. The reaction afforded the pure product 4.8a (5.2 g, 81%) as a light yellow oil. Spectral and physical data were consistent with those reported.9

4.9a

Compound 4.9.10 To a solution of 4.8a (1.7 g, 8.3 mmol) in MeOH/ THF (30 mL, 1:5 v/v) was added KOH (2.3 g, 42 mmol). The mixture was stirred at rt overnight, and the solvent was removed 87

Chapter 5: Experimental section

by rotary evaporation. The residue was diluted with EtOAc (15 mL) and sequentially washed with

HCl (aq. 10%, 10 mL) and NaCl (10 mL). The organic layer was dried over MgSO4, concentrated under vacuum and purified by column chromatography (hexanes/CH2Cl2, 9:1) to afford 4.9a (0.7 g, 86%) as a brown-yellow oil. Spectral and physical data were consistent with those reported.10,11

MeO SiMe3

4.8b

12 Compound 4.8b. To a solution of 4-iodoanisole (4.9 g, 21 mmol) in dry i-Pr2NH (55 ml) were added PdCl2(PPh3)2 (0.15 g, 0.21 mmol), CuI (0.040 g, 0.21 mmol) and trimethylsilylacetylene (9.0 mL, 63 mmol). After stirring overnight at room temperature, the volatiles were removed in vacuum and the residue was dissolved in CH2Cl2. The organic layers was washed with sat aq. Solution of

NaCl (15 mL), H2O (15 mL) and dried over Na2SO4. The pure product 4.8b (4.3 g, 100%) was isolated after a column chromatography (hexane/CH2Cl2, 10:1). Spectral and physical data were consistent with those reported.12

MeO H

4.9b

Compound 4.9b.12 To a solution of 4.8b (4.4 g, 21 mmol) in MeOH/THF (42 mL, 1:5 v/v) was added K2CO3 (5.9 g, 43 mmol). The mixture was stirred for 2 h, and the reaction solvent was removed by rotary evaporation. The residue was diluted with EtOAc (15 mL) and sequentially washed with HCl (30%, 15 mL), and NaCl (15 mL). The organic layer was dried over MgSO4, concentrated under vacuum to afford 4.9b (2.2 g, 78%) as a colorless oil. Spectral and physical data were consistent with those reported.12

Chapter 5: Experimental section

MeO OMe

4.10b

Compound 4.10b was synthesized according to literature13 and was isolated in 80% (0.73 g) yield. Spectral and physical data were consistent with those reported.13

MeO OMe

4.11b

13 Compound 4.11b. To a solution of 4.10b (0.73 g, 2.5 mmol) in CH2Cl2 (22 mL) were added PCC (0.78 g, 3.6 mmol), celite (0.74 g), and molecular sieves (4 Å, 0.74 g). After 24 h, the reaction mixture was passed through a plug of silica gel using CH2Cl2 (50 mL) to remove the chromium waste. After solvent removal 4.11b (0.59 g, 81%) was obtained as an orange solid. Spectral and physical data were consistent with those reported.13

Chapter 5: Experimental section

Br Br

MeO OMe

4.12b

13 Compound 4.12b. To a solution of CBr4 (9.5 g, 28 mmol) and PPh3 (15 g, 56 mmol) in dry

CH2Cl2 (24 mL) at rt was slowly added a solution of 4.11b (0.61 g, 21 mmol) in dry CH2Cl2 (3 mL). After stirring for 3 d, the solvent was reduced, and hexanes (10 mL)was added. The inhomogeneous mixture was passed through a plug of silica gel (hexanes, 20 mL). After solvent removal, 4.12b was obtained (0.68 g, 73%) as a yellow solid. Spectral and physical data were consistent with those reported.13

5.3 Synthesis of new compounds

Bu Bu

4.10a

Compound 4.10a. MeMgBr (1 M in THF, 0.95 mL, 2.8 mmol) was added to 4.9a (0.49 g, 2.6 mmol) in dry THF (4 mL) and the mixture was heated to 50 °C for 2 h. After cooling to 0 °C, ethyl formate (0.092 g, 1.2 mmol, 0.10 mL) was added and the solution was stirred at rt for 5 h. The mixture was quenched with sat. aq NH4Cl (2 x 10 mL), and the organic phase was extracted with

Et2O (10 mL), washed with sat. aq. NaCl (10 mL), H2O (10 mL), and dried (MgSO4). After purification by column chromatography (hexanes/CH2Cl2 2:4), 4.10a (0.30 g, 67%) was obtained as a light yellow solid. Rf = 0.56 (hexanes/CH2Cl2 2:4). Mp = 85 °C. IR (ATR) 3372 (w), 3024 (vw), 2958 (w), 2925 (m), 2853 (w), 2229 (w), 1604 (m), 1505 (w), 1455 (w), 1410 (w), 1296 (m). 1H 90

Chapter 5: Experimental section

NMR (300 MHz, CDCl3) δ 7.41 (d, J = 8.2 Hz, 4H), 7.11 (d, J = 8.1 Hz, 4H), 5.61 (s, 1H), 2.86 (bs, 1H), 2.6 (t, J = 7.7 Hz, 4H), 1.61−1.54 (m, 4H), 1.38−1.30 (m, 4H), 0.93 (t, J = 7.3 Hz, 6H). 13C

NMR (75.5 MHz, CDCl3) δ 143.8, 131.7, 128.3, 119.1, 85.5, 84.6, 53.2, 35.5, 33.2, 22.2, 13.8. LDI TOF m/z 344 (M+, 20), 327 ([M − OH]+, 100).

Bu Bu

4.11a

Compound 4.11a. To a solution of 4.10a (0.30 g, 0.86 mmol) in CH2Cl2 (8 mL) was added PCC (0.27 g, 1.3 mmol), celite (0.26 g), and molecular sieves (4 Å, 0.26 g). After 24 h, the reaction mixture was passed through a plug of silica gel using CH2Cl2 (15 mL) to remove the chromium waste. After solvent removal and purification by column chromatography (silica gel, hexanes/CH2Cl2 3:2), 4.11a (0.20 g, 67%) was obtained as a light yellow oil. Rf = 0.52

(hexanes/CH2Cl2 3:2). IR (ATR) 3199 (vw), 3029 (vw), 2951 (m), 2926 (m), 2857 (m), 2206 (s), 1 2179 (s), 1600 (s), 1505 (m), 1302 (s), 1091 (s). H NMR (300 MHz, CDCl3) δ 7.53 (d, J = 8.1 Hz, 4H), 7.19 (d, J = 8.1 Hz, 4H), 2.62 (t, J = 7.7 Hz, 4H), 1.61−1.53 (m, 4H); 1.38−1.24 (m, 4H), 0.64 13 (t, J = 7.3 Hz, 6H). C NMR (75.5 MHz, CDCl3) δ 160.7, 146.8, 133.3, 128.7, 116.5, 92.1, 89.4, 35.7, 33.0, 22.2, 13.8. LDI TOF m/z 343 ([M + H]+).

Chapter 5: Experimental section

Br Br

Bu Bu

4.12a

Compound 4.12a. To a solution of CBr4 (0.11 g, 0.33 mmol) and PPh3 (0.18 g, 0.67 mmol) in dry

CH2Cl2 (4 mL) at rt was slowly added a solution of 4.11a (0.086 g, 0.25 mmol) in dry CH2Cl2 (0.4 mL). After stirring overnight, the solvent was reduced and hexanes added. The inhomogeneous mixture was passed through a plug of silica gel (hexanes, 15 mL). After solvent removal, 4.12a

(0.097 g, 78%) was obtained as a light yellow oil. Rf = 0.7 (hexanes). IR (ATR) 3026 (vw), 2947 (m), 2924 (m), 2854 (m), 2264 (vw), 2195 (s), 1605 (m), 1509 (s), 1458 (m). 1H NMR (300 MHz,

CDCl3) δ 7.46 (d, J = 8.1 Hz, 4H), 7.15 (d, J = 8.1 Hz, 4H), 2.61 (t, J = 7.7 Hz, 4H), 1.62−1.54 (m, 13 4H); 1.39−1.27 (m, 4H), 0.93 (t, J = 7.3 Hz, 6H). C NMR (75.5 MHz, CDCl3) δ 144.4, 131.6, 79 128.5, 119.3, 114.5, 106.8, 96.0, 85.6, 35.7, 33.3, 22.3, 13.9. APPI HRMS m/z calcd for C26H26 Br2 (M+): 496.0396; found: 496.0398.

Bu Bu

4.13a

Compound 4.13a. A solution of 4.12a (95 mg, 0.19 mmol) in hexanes (1 mL) was cooled to –78 °C. n-BuLi (1.6 M in hexane, 0.14 mL, 0.23 mmol) was slowly added over a period of ca. 2 min. After 10 min, the reaction was warmed to approximately –10 °C and was stirred for 2 h. The mixture was quenched via the addition of sat. aq. NH4Cl (1 mL). Et2O (1 mL) was added, the organic layer was separated, washed with sat. aq. NH4Cl (2 × 1 mL), dried (MgSO4), filtered, and the solvent was removed in vacuum. After the crude mixture was passed through a plug of silica gel to remove baseline material, 4.13a (58 mg, 90%) was obtained as a light yellow solid. Rf = 0.2 (hexanes). Mp = 72 °C. IR (ATR) 2956 (m), 2925 (s), 2854 (m), 1457 (m). 1H NMR (300 MHz, 92

Chapter 5: Experimental section

CDCl3) δ 7.41 (d, J = 8.1 Hz, 4H), 7.15 (d, J = 8.1 Hz, 4H), 2.6 (t, J = 7.6 Hz, 4H), 1.62−1.52 (m, 13 4H), 1.39−1.27 (m, 4H), 0.93 (t, J = 7.3 Hz, 6H). C NMR (75.5 MHz, CDCl3) δ 145.1, 132.9, + 128.6, 118.0, 78.8, 73.9, 66.4, 35.7, 33.2, 22.3, 13.9. APPI HRMS m/z calcd for C26H27 ([M + H] ): 339.2107; found: 339.2105.

SiEt3

4.15a

Compound 4.15a. Thermal reaction: Triyne 4.14a (0.48 g, 1.9 mmol) and TPCBD (0.71 g, 1.9 mmol) were dissolved in dry xylenes (10 mL). The mixture was heated to reflux at 140 °C for 97 h.

After solvent removal and purification by column chromatography (silica gel, hexanes/CH2Cl2 5:1), 4.15a (0.56 g, 49%) was obtained as a colorless solid. Microwave at 210 °C: Triyne 4.14a (0.10 g, 0.38 mmol) and TPCBD (0.15 mg, 0.38 mmol) were dissolved in dry xylenes (4 mL). The mixture was heated under microwave irradiation at 210 °C for 1.5 h. After solvent removal and purification by column chromatography (silica gel, hexanes/CH2Cl2 5:1), 4.15a (0.14 g, 61%) was obtained as a colorless solid.

Microwave at 250 °C: Triyne 4.14a (48 mg, 0.18 mmol) and TPCBD (70 mg, 0.18 mmol) were dissolved in dry xylenes (1.7 mL). The mixture was heated under microwave irradiation to 250 °C for 1 h. After solvent removal and purification by column chromatography (silica gel, hexanes/CH2Cl2 5:1), 4.15a (11 mg, 95%) was obtained as a colorless solid. Rf = 0.2

(hexanes/CH2Cl2 5:1). Mp = 206 °C. IR (ATR) 3055 (vw), 2951 (w) , 2872 (w), 2141 (w), 1598 –1 (w), 1491 (w), 1441 (m), 1401 (m) cm . UV-vis (CH2Cl2) λmax (ε) 328 (30500), 312 (36100), 272 1 (71700). H NMR (300 MHz, CDCl3) δ 7.20–7.09 (m, 15H), 6.84–6.73 (m, 10H), 0.81 (t, J = 7.8 13 Hz, 9H), 0.46 (q, J = 7.2 Hz, 6H). C NMR (75.5 MHz, CDCl3) δ 144.2, 143.6, 141.1, 141.0, 140.0, 139.8, 139.4, 131.4, 131.2, 131.0, 130.6, 130.4, 127.9, 127.1, 126.70, 126.68, 126.44, 93

Chapter 5: Experimental section

126.40, 126.0, 125.7, 125.6, 125.3, 124.8, 123.6, 104.2, 100.4, 97.1, 88.8, 7.4, 4.3 (two signals are + coincident or not observed) ESI HRMS m/z calcd for C46H40Si (M ): 620.2894; found: 620.2906, ([M + Na]+): 643.2795; found: 643.2792.

SiMe3

Sii-Pr3

4.15b

Compound 4.15b. Thermal reaction: Triyne 1.30a (0.55 g, 1.8 mmol) and TPCBD (0.70 g, 1.8 mmol) were dissolved in dry xylenes (27 mL). The mixture was heated to reflux at 140 °C for 95 h.

After solvent removal and purification by column chromatography (silica gel, hexanes/CH2Cl2 5:1) 4.15b (0.83 g, 70%) was obtained as a colorless solid.

Microwave at 250 °C: Triyne 1.30a (0.10 g, 0.33 mmol) and TPCBD (0.13 g, 0.33 mmol) were dissolved in dry o-dichlorobenzene (3.7 mL). The mixture was heated under microwave irradiation at 250 °C for 1 h. After solvent removal and purification by column chromatography (silica gel, hexanes/CH2Cl2 5:1), 4.15b (0.19 g, 88%) was isolated as a colorless solid. Rf = 0.3

(hexanes/CH2Cl2 5:1). Mp = 174 °C. IR (CDCl3 cast): 3076 (vw), 3055 (vw), 3024 (vw), 2941 (m), –1 1 2862 (m), 2150 (m), 1247 (m) cm . UV-vis (CH2Cl2) λmax (ε) 297 (21300), 260 (54900). H NMR

(300 MHz, CDCl3) δ 7.12–7.05 (m, 10H), 6.83–6.78 (m, 6H), 6.72–6.67 (m, 4H), 1.02−0.92 (m, 13 21H), 0.08 (s, 9H). C NMR (75.5 MHz, CDCl3) δ 144.6, 144.1, 141.3, 141.1, 140.0, 139.9, 139.4, 139.3, 130.9, 130.4, 130.3, 127.2, 127.1, 126.64, 126.62, 126.4, 126.3, 125.6, 125.2, 124.7, 104.5, + 103.5, 102.8, 99.3, 97.3, 18.6, 11.1, –0.4. ESI HRMS m/z calcd for C46H50Si2Na ([M + Na] ): 681.3343; found: 681.3352.

Chapter 5: Experimental section

Sii-Pr3

4.15c

Compound 4.15c. Thermal reaction: Triyne 1.28b (0.20 g, 0.52 mmol) and TPCBD (0.20 g, 0.52 mmol) were dissolved in dry xylenes (7 mL). The mixture was heated to reflux at 140 °C for 97 h.

After solvent removal and purification by column chromatography (silica gel, hexanes/CH2Cl2 5:1) 4.15c (0.22 g, 58%) was obtained as a colorless solid. Microwave at 210 °C: Triyne 1.28b (0.10 g, 0.26 mmol) and TPCBD (0.099 g, 0.26 mmol) were dissolved in dry xylenes (4 mL). The mixture was heated under microwave irradiation at 210 °C for 1.5 h. After solvent removal and purification by column chromatography (silica gel, hexanes/CH2Cl2 5:1), 4.15c (0.15 g, 79%) was obtained as a colorless solid.

Microwave at 250 °C: Triyne 1.28b (0.10 g, 0.26 mmol) and TPCBD (0.10 g, 0.26 mmol) were dissolved in dry xylenes (4.1 mL). The mixture was heated under microwave irradiation at 250 °C for 1 h. After solvent removal and purification by column chromatography (silica gel, hexanes/CH2Cl2 5:1), 4.15c (0.17 mg, 85%) was obtained as a colorless solid. Rf = 0.2

(hexanes/CH2Cl2 5:1). Mp = 235 °C. IR (CDCl3 cast): 3080 (vw), 3057 (vw), 3026 (wv), 2941 (s), –1 2890 (m), 2864 (s), 2145 (w), 1602 (w), 1462 (m) cm . UV-vis (CH2Cl2) λmax (ε) 297 (19000), 260 1 (48300), 227 (20200). H NMR (300 MHz, CDCl3) δ 7.12–7.02 (m, 10H), 6.81–6.76 (m, 6H), 6.68– 13 6.64 (m, 4H), 0.91–0.85 (m, 42H). C NMR (75.5 MHz, CDCl3) δ 144.7, 141.3, 140.1, 139.5, 130.9, 130.4, 127.3, 126.6, 126.4, 125.5, 124.8, 104.6, 99.6, 18.6, 11.3. LDI TOF m/z 766 ([M + Na]+, 100).

Chapter 5: Experimental section

Single crystals suitable for X-ray crystallographic analysis were crystallized from CDCl3. 3 C52H62Si2, Fw = 743.20; crystal dimension 0.5135 x 0.1863 x 0.0598 mm ; triclinic system; space group P-1: a = 13.6637(5) Å, b = 19.1001(5) Å, c = 19.4906(7) Å, α β = 102.853 (3)°, β V = 3 –3 –1 4599.5(3) Å , Z = 4, ρcalcd = 1.073 mg mm ; µ(CuKα) = 0.927 mm ; T = 173.00(10) K; 2θ max =

125.62°; total data collected = 21646; R1 = 0.0776 [11216 independent reflections with [I≥ 2σ(I)]; wR2 = 0.2387 for 13963 data, 1019 variables, and 10 restraints, largest difference, peak and hole = 1.43 and –0.47 e Å–3. The crystal showed disorder that was resolved to the following occupation factors: C15/15’ = 70:30%, C17/C17’/C19/C19’ = 32:68%, C5a/C5a’/C6a/C6a’ = 60:40%, C21/C21’/ C22/C22’ = 33:67 %, C13a/C13 = 50:50%.

SiMe3

4.15d

Compound 4.15d. Thermal reaction: Triyne 1.27a (0.11 g, 0.46 mmol) and TPCBD (0.18 g, 0.46 mmol) were dissolved in dry xylenes (4 mL). The mixture was heated to reflux at 140 °C for 67 h.

After solvent removal and purification by column chromatography (silica gel, hexanes/CH2Cl2 5:1), 4.15d (0.21 g, 78%) was obtained as a colorless solid.

Microwave at 250 °C: Triyne 1.27a (0.11 g, 0.46 mmol) and TPCBD (0.18 g, 0.46 mmol) were dissolved in dry xylenes (3.6 mL). The mixture was heated under microwave irradiation at 250 °C for 1 h. After solvent removal and purification by column chromatography (silica gel, hexanes/CH2Cl2 5:1), 4.15d (0.25 g, 93%) was isolated as a colorless solid. Rf = 0.2

(hexanes/CH2Cl2 5:1). Mp = 235 °C. IR (ATR) 3078 (vw), 3058 (vw) , 3026 (vw), 2959 (m), 2898 (vw), 2158 (w), 1601 (vw), 1497 (vw), 1443 (w), 1404 (m), 1288 (w), 1249 (s), 1072 (w), 1027 (m)

Chapter 5: Experimental section

–1 1 cm . UV-vis (CH2Cl2) λmax (ε) 294 (17000), 259 (42100). H NMR (300 MHz, CDCl3) δ 7.09–6.82 13 (m, 10H), 6.81–6.69 (m, 10H), 0.01 (s, 18H). C NMR (75.5 MHz, CDCl3) δ 144.0, 141.1, 139.7, 139.3, 131.0, 130.4, 127.0, 126.7, 126.3, 125.7, 125.0, 103.0, 102.8, 0.4. ESI HRMS m/z calcd for + C40H38Si2Na ([M + Na] ): 597.2404; found: 597.2423.

OMe

SiMe3

4.15e

Compound 4.15e. Microwave at 250 °C: Triyne 4.7 (30 mg, 0.12 mmol) and TPCBD (46 mg, 0.12 mmol) were dissolved in dry o-dichlorobenzene (3 mL). The mixture was heated under microwave irradiation at 250 °C for 1 h. After solvent removal and purification by column chromatography (silica gel, hexanes/CH2Cl2 8:3), 4.15e (52 mg, 72%) was isolated as a light orange solid. Rf = 0.41 (hexanes/CH2Cl2 8:3). Mp = 168 °C. IR (ATR) 3054 (vw), 3026 (vw) , 2954 (vw), 1603 (m), 1508 (m), 1441 (w), 1288 (w), 1245 (m), 1165 (w), 1027 (m) cm–1. UV-vis 1 (CH2Cl2) λmax (ε) 340 (19200), 322 (23600), 277 (38300), 230 (25800). H NMR (300 MHz, CDCl3) 13 δ 7.19–7.08 (m, 12H), 6.84–6.74 (m, 12H), 3.75 (s, 3H), 0.05 (s, 9H). C NMR (75.5 MHz, CDCl3) δ 159.5, 144.1, 142.9, 141.1, 140.5, 140.0, 139.8, 139.4, 132.9, 131.1, 131.0, 130.7, 130.5, 127.1, 127.0, 126.7, 126.4, 126.3, 125.6, 125.5, 124.5, 115.8, 113.7, 103.5, 102.5, 97.3, 87.5, 55.2, 0.3 (one signal coincident or not observed). LDI TOF m/z 608 (M+, 100). ESI HRMS m/z calcd for + C44H37OSi ([M + H] ): 609.2608; found: 609.2625.

Chapter 5: Experimental section

4.15f

Compound 4.15f. Microwave at 250 °C. Triyne 4.13a (3.1 mg, 0.093 mmol) and TPCBD (3.6 mg, 0.093 mmol) were dissolved in dry o-dichlorobenzene (1 mL). The mixture was heated under microwave irradiation at 250 °C for 1 h. After solvent removal and purification by column chromatography (silica gel, hexanes/CH2Cl2 4:1) 4.15f (3.7 mg, 57%) was obtained as a light orange solid. Rf = 0.48 (hexanes/CH2Cl2 4:1). Mp = 174 °C. IR (ATR) 3059 (w), 3026 (w), 2954 (w), 2925 (m), 2855 (m), 1601 (w), 1510 (m), 1459 (m), 1405 (m), 1071 (m), 1022 (m) cm–1. UV- 1 vis (CH2Cl2) λmax (ε) 352 (16400), 330 (26600), 300 (62700), 277 (32500). H NMR (300 MHz,

CDCl3) δ 7.21–7.00 (m, 18H), 6.86–6.76 (m, 10H), 2.54 (t, J = 7.6 Hz, 4H), 1.58−1.49 (m, 4H); 13 1.36−1.34 (m, 4H), 1.29 (t, J = 7 Hz, 6H). C NMR (75.5 MHz, CDCl3) δ 143.3, 143.2, 140.8, 140.0, 139.5, 131.3, 131.1, 130.71, 127.1, 126.7, 126.4, 125.6, 125.1, 120.8, 97.3, 88.30, 35.6, 33.3, + 22.2, 13.9 (one signal coincident or not observed). APPI HRMS m/z calcd for C54H46 (M ): 694.3594; found: 694.3606.

Chapter 5: Experimental section

4.20a

Compound 4.20a. Compound 4.15a (96 mg, 0.15 mmol) in THF (10 mL) was cooled to 0 °C and TBAF (1 M. 0.16 g, 0.60 mmol, 0.60 mL) was added. The mixture was allowed to reach rt and was stirred for 3 h, diluted with Et2O (10 mL), washed with sat. aq. NH4Cl (2 x 10 mL), sat. aq. NaCl

(10 mL), H2O (10 mL), dried (MgSO4), filtered, and concentrated under vacuum. The resulting solid was purified by passing through a short column (silica gel, hexanes/CH2Cl2 1:1) to afford

4.20a (56 mg, 72%) as a colorless solid. Rf = 0.5 (hexanes/CH2Cl2 1:1). Mp = 201 °C (decomp). IR (ATR) 3288 (m), 3024 (m), 2920 (m), 2851 (m), 2141 (w), 1441 (m), 1441 (m) cm–1. 1H NMR (300 13 MHz, CDCl3) δ 7.24–7.02 (m, 10H), 6.88–6.79 (m, 15H), 3.28 (s, 1H). C NMR (75.5 MHz,

CDCl3) δ 145.0, 143.5, 141.6, 141.2, 139.8, 139.5, 139.2, 131.5, 131.0, 131.0, 130.6, 130.4, 128.2, 128.1, 127.20, 127.15, 126.7, 126.64, 126.57, 126.1, 125.74, 125.70, 123.4, 97.2, 88.5, 84.7, 81.9 (3 signals coincident). LDI TOF m/z 506 (M+, 100).

Chapter 5: Experimental section

Sii-Pr3

4.20b

Compound 4.20b. Compound 4.15b (0.14 g, 0.21 mmol) and KOH (33 mg, 0.63 mmol) were dissolved in THF (2 mL) and MeOH (1 mL). The mixture was stirred at rt for 5 h. Satd. aq. NH4Cl

(3 mL) and CH2Cl2 (3 mL) were added, the organic layer separated, washed with satd. aq. NH4Cl (3 mL), satd. aq. NaCl (3 mL), H2O (3 mL), dried (MgSO4), filtered, and the solvent removed in vacuum. Purification by column chromatography (silica gel, hexanes/CH2Cl2 4:1) afforded 4.20b

(0.11 g, 93%) as a colorless solid. Rf = 0.52 (hexanes/CH2Cl2 4:1). Mp = 172 °C. IR (CDCl3 cast): 3302 (m), 3081 (vw), 3056 (vw), 3025 (vw), 2941 (m), 2889 (w), 2862 (m), 2156 (w), 1601 (w), –1 1 1462 (m), 1442 (m), 1403 (m) 1246 (w) cm . H NMR (300 MHz, CDCl3) δ 7.16–7.07 (m, 10H), 13 6.84–6.73 (m, 6H), 6.72–6.69 (m, 4H), 3.11 (s, 1H), 0.93 (s, 21H). C NMR (75.5 MHz, CDCl3) δ 144.0, 143.9, 141.6, 141.1, 139.7, 139.6, 139.2, 131.1, 130.94, 130.89, 130.6, 130.4,127.3, 127.23, 127.17, 126.70, 126.68, 126.60, 126.5, 126.2, 125.7, 124.3, 104.4, 99.7, 84.8, 82.0, 18.5, 11.1 (two signals are coincident). LDI TOF m/z 609 ([M + Na]+ 30).

100

Chapter 5: Experimental section

4.20c

Compound 4.20c. Compound 4.15d (0.11 g, 0.17 mmol) in THF (10 mL) was cooled to 0 °C and TBAF (1 M, 30 mg, 0.43 mmol, 0.43 mL) was added. The mixture was allowed to reach rt and was stirred for 3 h, diluted with Et2O (10 mL), washed with sat. aq. NH4Cl (2 x 10 mL), sat. aq. NaCl

(10 mL), H2O (10 mL), dried (MgSO4), filtered, and concentrated under vacuum. The resulting solid was purified by passing through a short column (silica gel, hexanes/ CH2Cl2 2:1) to afford

4.20c (66 mg, 88%,) as a colorless solid. Rf = 0.54 (hexanes/CH2Cl2 2:1). Mp = 197 °C. IR (CDCl3 cast): 3289 (m), 3081 (vw), 3056 (w), 3024 (w), 2923 (w), 2852 (w), 2244 (w), 1602 (w), 1496 (m), –1 1 1443 (m), 1072 (m), 1026 (m) cm . UV-vis (CH2Cl2) λmax (ε) 278 (18400), 252 (37500). H NMR 13 (300 MHz, CDCl3) δ 7.14–7,12 (m, 10H), 6.85−6.81 (m, 4H), 6.72–6.69 (m, 4H), 3.20 (s, 2H). C

NMR (75.5 MHz, CDCl3) δ 144.1, 141.7, 139.9, 139.0, 130.9, 130.3, 127.2, 126.8, 126.7, 125.8, + 124.6, 84.8, 81.6. APPI HRMS m/z calcd for C34H22 (M ): 430.1716; found: 430.1719.

Single crystals suitable for X-ray crystallographic analysis were crystallized from CDCl3. C34H22, 3 Fw = 430.52; crystal dimension 0.18 x 0.14 x 0.06 mm ; trigonal system; space group P32, a = 3 11.8722(3) Å, b = 11.8722(3) Å, c = 14.6199(5) Å, V = 1784.57(8) Å , Z = 3, ρcalcd = 1.202 mg mm–3; µ(CuKα) = 0.516 mm–1; T = 173.05(10) K; 2θ max = 140.92°; total data collected = 7175;

R1 = 0.0520 [3876 independent reflections with [I≥ 2σ(I)]; wR2 = 0.1344 for 4392 data, 308 variables, and 1 restraint, largest difference, peak and hole = 0.17 and –0.18 e Å–3.

101

Chapter 5: Experimental section

OMe

4.20e

Compound 4.20e. A mixture of compound 4.15e (83 mg, 0.14 mmol) and KOH (30 mg, 0.41 mmol) in THF (3.1 mL) and MeOH (1.5 mL) was stirred at rt for 2 h. The mixture was diluted with

CH2Cl2, washed with sat. aq. NH4Cl (2 x 4 mL), sat. aq. NaCl (4 mL), H2O (4 mL), dried (MgSO4), filtered, and concentrated under vacuo. The resulting solid was purified by passing through a short column (silica gel, hexanes/ CH2Cl2 2:1) to afford 4.20e (75 mg, 100%,) as a light yellow solid. Rf =

0.5 (hexanes/CH2Cl2 2:1). Mp = 204 °C. IR (ATR) 3284 (w), 3024 (vw), 2928 (vw), 2208 (w), 1 1602 (m), 1507 (m), 1440 (m). H NMR (300 MHz, CDCl3) δ 7.19–7.06 (m, 12H), 6.84–6.73 (m, 13 12H), 3.75 (s, 3H), 3.23 (s, 1H). C NMR (75.5 MHz, CDCl3) δ 159.6, 143.9, 143.1, 142.9, 141.5, 141.1, 140.7, 140.0, 139.6, 139.3, 133.0, 131.1, 131.0, 130.7, 130.4, 127.2, 127.1, 126.7, 126.6, 126.5, 125.72, 125.67, 123.3, 115.6, 113.8, 97.5, 87.4, 84.5, 82.0, 55.2. APPI HRMS m/z calcd for + C41H28O (M ): 536.2135; found: 536.2146.

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4.21a

Compound 4.21a. Homocoupling reaction under Hay condition. CuCl (17 mg, 0.17 mmol) and

TMEDA (50 μL, 39 mg, 0.33 mmol) in CH2Cl2 (1.3 mL) were kept in the ultrasonic bath for 20 min. Then, 4.20a (34 mg, 0.067 mmol) was added. CH2Cl2 was evaporated and replaced by toluene (1.3 mL) and the mixture was heated at 100 °C for 2 h. The reaction mixture was washed with sat. aq. NH4Cl (2 x 2 mL), NaCl (2 mL), dried (MgSO4), and filtered. After solvent removal and purification by column chromatography (silica gel, hexanes/ CH2Cl2 1:1), 4.21a was obtained (11 mg, 32%) as a yellow solid.

Pd homocoupling reaction. To a mixture of [PdCl2(PPh3)2] (1.1 mg, 0.0016 mmol), CuI (0.34 mg,

0.066 mmol), and dry i-Pr2NH (15 μL) was added 4.20a (24 mg, 0.45 mmol) in dry THF (0.57 mL). Ethyl bromoacetate (5.1 μL, 0.46 mmol) was added, and the mixture was stirred at rt under N2 atmosphere for 24 h. H2O (2 mL) was added, and the resulting mixture extracted with CH2Cl2 (2 mL). The organic layer was washed with sat. aq. NaCl (2 x 2 mL), dried (MgSO4), and filtered. The resulting solution was concentrated under vacuum. After purification by column chromatography

(silica gel, hexanes/CH2Cl2 1:1), 4.21a was obtained (15 mg, 66%,) as a yellow solid. Rf = 0.5

(hexanes/CH2Cl2 1:1). Mp = 324 °C. IR (ATR) 3053 (w), 3024 (vw), 2961 (w), 2921 (w), 1489 (m) –1 1 cm . UV-vis (CH2Cl2) λmax (ε) 386 (5600), 356 (10600), 290 (33600), 226 (27400). H NMR (300 13 MHz, CDCl3) δ 7.23–7.06 (m, 30H), 7.05–6.7 (m, 20H). C NMR (75.5 MHz, CDCl3) δ 144.5, 143.5, 142.0, 141.2, 139.8, 139.4, 139.3, 139.2, 131.9, 131.3, 131.2, 130.8, 130.6, 129.5, 128.6, 128.3, 128.2, 127.43, 127.37, 127.0, 126.8, 126.01, 125.97, 125.8, 124.2, 123.3, 98.1, 88.3, 81.7, 81.6. LDI TOF m/z 1010 (M+, 65).

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Sii-Pr3

i-Pr3Si

4.21b

Compound 4.21b. Homocoupling reaction under Hay condition. CuCl (17 mg, 0.17 mmol) and

TMEDA (5.1 μL, 40 mg, 0.35 mmol) in CH2Cl2 (1.8 mL), were kept in the ultrasonic bath for 20 min. Then, 4.20b (41 mg, 0.069 mmol) was added. CH2Cl2 was evaporated and replaced by toluene (1.8 mL) and the mixture was heated at 100 °C for 2 h. The reaction mixture was cooled and washed with sat. aq. NH4Cl (2 x 2 mL), NaCl (2 mL), dried (MgSO4), and filtered. After solvent removal and purification by column chromatography (silica gel, hexanes/CH2Cl2 4:1) 4.21b (9.2 mg, 23%) was obtained as a yellow solid.

Pd homocoupling reaction. To a mixture of [PdCl2(PPh3)2] (2.9 mg, 0.0041 mmol), CuI (11 mg,

0.0046 mmol), and dry i-Pr2NH (36 μL) was added 4.20b (66 mg, 0.11 mmol) in dry THF (1.4 mL). Ethyl bromoacetate (14 μL, 0.12 mmol) was added, and the mixture was stirred at rt under N2 atmosphere for 24 h. H2O (2 mL) was added, and the resulting mixture was extracted with CH2Cl2

(2 mL). The organic layer was washed with sat. aq. NaCl (2 x 2 mL), dried (MgSO4), and filtered.

The resulting solution was concentrated under vacuum. After purification by column chromatography (silica gel, hexanes/CH2Cl2 4:1), 4.21b (34 mg, 52%) was obtained as a yellow solid. Rf = 0.33 (hexanes/CH2Cl2 4:1). Mp = 178 °C. IR (ATR) 3082 (vw), 3056 (vw), 3025 (vw), 2940 (m), 2924 (vw), 2862 (m), 2154 (w), 1601 (m), 1498(m), 1461 (m), 1443 (m), 1388 (m). UV- vis (CH2Cl2) λmax (ε) 367 (5200), 344 (14900), 322 (30500), 307 (38300), 270 (87000), 229 1 (40900). H NMR (300 MHz, CDCl3) δ 7.13–7.02 (m, 20H), 6.83–6.79 (m, 12H), 6.71–6.65 (m, 13 8H), 0.92−0.89 (m, 42H). C NMR (75.5 MHz, CDCl3) δ 144.4, 144.0, 141.6, 141.0, 140.4, 139.6, 139.3, 139.2, 139.0, 138.3, 131.0, 130.9, 130.42, 130.37, 127.2, 127.1, 126.69, 126.65, 126.4,

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126.3, 125.6, 124.5, 104.1, 100.1, 81.7, 81.2, 18.6, 11.1. ESI HRMS m/z calcd for C86H82Si2Na ([M + Na]+): 1193.5847; found: 1193.5829.

OMe

MeO

4.21e

Compound 4.21e. Homocoupling reaction under Hay condition. CuCl (13 mg, 0.13 mmol) and

TMEDA (37 μL, 29 mg, 0.25 mmol) in CH2Cl2 (1.9 mL) were kept in the ultrasonic bath for 20 min. Then, 4.20e (27 mg, 0.050 mmol) was added. CH2Cl2 was evaporated and replaced by toluene (1.9 mL) and the mixture was heated at 100 °C for 2 h. The reaction mixture was washed with sat. aq. NH4Cl (2 x 2 mL), NaCl (2 mL), dried (MgSO4), and filtered. After solvent removal and purification by column chromatography (silica gel, hexanes/ CH2Cl2 1:1), 4.21e (12 mg, 45%) was obtained as a yellow solid.

Pd homocoupling reaction. To a mixture of [PdCl2(PPh3)2] (4.1 mg, 0.0058 mmol), CuI (1.2 mg,

0.064 mmol), and dry i-Pr2NH (0.053 mL) was added 4.20e (85 mg, 0.16 mmol) in dry THF (2.1 mL). Ethyl bromoacetate (17 μL, 0.16 mmol) was added, and the mixture was stirred at rt under N2 atmosphere for 24 h. H2O (3 mL) was added, and the resulting mixture extracted with CH2Cl2 (3 mL). The organic layer was washed with sat. aq. NaCl (2 x 2 mL), dried (MgSO4), and filtered. The resulting solution was concentrated under vacuum. After purification by column chromatography

(silica gel, hexanes/CH2Cl2 1:1), 4.21e (70 mg, 82%) was obtained as a yellow solid. Rf = 0.75

(hexane/CH2Cl2 1:1). Mp = 329 °C (decomp). IR (ATR) 3055 (vw), 3025 (vw), 2956 (vw), 2924 (vw), 2849 (vw), 2833 (vw), 2209 (w), 1604 (m), 1509 (m), 1441 (w), 1398 (w), 1292 (m), 1249

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Chapter 5: Experimental section

–1 (m), 1167 (w), 1071 (w), 1027 (m) cm . UV-vis (CH2Cl2) λmax (ε) 394 (3400), 358 (15700), 316 1 (37900), 294 (41800), 227 (37100). H NMR (300 MHz, CDCl3) δ 7.15–6.98 (m, 24H), 6.95–6.57 13 (m, 24H), 3.66 (s, 6H). C NMR (75.5 MHz, CDCl3) δ 159.5, 144.7, 144.2, 142.9, 141.7, 140.6, 139.8, 139.3, 139.1, 138.0, 133.2, 131.1, 131.0 130.7, 130.4, 129.9, 128.0, 127.2, 127.1, 126.5, 125.73, 125.69, 124.3 123.6, 115.3, 113.7, 98.2, 87.1, 81.7, 81.4, 55.1. APPI HRMS m/z calcd for + C82H54O2 (M ): 1070.4118; found: 1070.4121.

5.4 References

1. O. Robles, F. E. McDonald, Org. Lett. 2008, 10, 1811−1814. 2. H. Lütjens, S. Nowotny, P. Knochel, Tetrahedron: Asymmetry, 1995, 6, 2675−2678. 3. S. Eisler, N. Chahal, R. McDonald, R. R. Tykwinski, Chem. Eur. J. 2003, 9, 2542−2550. 4. A. M. Boldi, J. Anthony, C. B. Knobler, F. Diederich, Angew. Chem. Int. Ed. 1992, 31, 1240−1242. 5. J. Anthony, A. M. Boldi, I. Rubin, M. Hobi, G. Volker, C. B. Knobler, P. Seiler, F. Diederich, Helv. Chim. Acta, 1995, 78, 13−45. 6. Y. Rubin, S. S. Lin, C. B. Knobler, J. Anthony, A. M. Boldi, F. Diederich, J. Am. Chem. Soc. 1991, 113, 6943−6949. 7. R. Suzuki, H. Tsukuda, N. Watanabe, Y. Kuwatani, I. Ueda, Tetrahedron 1998, 54, 2477−2496. 8. T. Luu, E. Elliott, A. D. Slepkov, S. Eisler, R. McDonald, F. A. Hegmann, R. R Tykwinski, Org. Lett. 2005, 7, 51−54. 9. H. L. Anderson, A. P. Wylie, K. Prout, J. Chem. Soc. Perkin Trans. 1998, 1, 1607−1611. 10. A. Walser, T. Flynn, C. Mason, H. Crowley, C. Maresca, M. O’Donnell, J. Med. Chem. 1991, 34, 1440−1446. 11. I. C. Khoo, S. Webster, S. Kubo, W. J. Youngblood, J. D. Liou, T. E. Mallouk, P. Lin, D. J.

Hagan, E. W. Stryland, J. Mat. Chem. 2009, 19, 7525−7531.

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12. I. Van Overmeire, S. A. Boldin, K. Venkataraman, R. Zisling, S. D. Jonghe, S. Van Calenbergh, D. De Keukeleire, A. H. Futerman, P. Herdewijn, J. Med. Chem. 2000, 43, 4189−4199. 13. A. Auffrant, F. Diederich, Helv. Chim. Acta. 2004, 87, 3085−3105.

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6: Appendix

Figure 6.1. 1H NMR spectrum of 4.10a.

Figure 6.2. 13C NMR spectrum of 4.10a. 108

6: Appendix

Figure 6.3. 1H NMR spectrum of 4.11a.

Figure 6.4. 13C NMR spectrum of 4.11a. 109

6: Appendix

Figure 6.5. 1H NMR spectrum of 4.12a.

Figure 6.6. 13C NMR spectrum of 4.12a. 110

6: Appendix

Figure 6.7. 1H NMR spectrum of 4.13a.

Figure 6.8. 13C NMR spectrum of 4.13a. 111

6: Appendix

Figure 6.9. 1H NMR spectrum of 4.15a.

Figure 6.10. 13C NMR spectrum of 4.15a.

112

6: Appendix

Figure 6.11. 1H NMR spectrum of 4.15b.

Figure 6.12. 13C NMR spectrum of 4.15b. 113

6: Appendix

Figure 6.13. 1H NMR spectrum of 4.15c.

Figure 6.14. 13C NMR spectrum of 4.15c. 114

6: Appendix

Figure 6.15. 1H NMR spectrum of 4.15d

Figure 6.16. 13C NMR spectrum of 4.15d.

115

6: Appendix

Figure 6.17. 1H NMR spectrum of 4.15e.

Figure 6.18. 13C NMR spectrum of 4.15e.

116

6: Appendix

Figure 6.19. 1H NMR spectrum of 4.15f.

Figure 6.20. 13C NMR spectrum of 4.15f. 117

6: Appendix

Figure 6.21. 1H NMR spectrum of 4.20a.

Figure 6.22. 13C NMR spectrum of 4.20a. 118

6: Appendix

Figure 6.23. 1H NMR spectrum of 4.20b.

Figure 6.24. 13C NMR spectrum of 4.20b. 119

6: Appendix

Figure 6.25. 1H NMR spectrum of 4.20c.

Figure 6.26. 13C NMR spectrum of 4.20c.

120

6: Appendix

Figure 6.27. 1H NMR spectrum of 4.20e.

Figure 6.28. 13C NMR spectrum of 4.20e.

121

6: Appendix

Figure 6.29. 1H NMR spectrum of 4.21a.

Figure 6.30. 13C NMR spectrum of 4.21a.

122

6: Appendix

Figure 6.31. 1H NMR spectrum of 4.21b.

Figure 6.32. 13C NMR spectrum of 4.21b. 123

6: Appendix

Figure 6.33. 1H NMR spectrum of 4.21e.

Figure 6.34. 13C NMR spectrum of 4.21e.

124

6: Appendix

125