Design and synthesis of pentacene derivatives
Design und Synthese von Pentacenderivaten
Der Naturwissenschaftlichen Fakultät
der Friedrich-Alexander-Universität Erlangen-Nürnberg
zur
Erlangung des Doktorgrades Dr. rer. nat.
vorgelegt von
Andreas R. Waterloo
aus Eschenbach i. d. Opf. Als Dissertation genehmigt von der Naturwissenschaftlichen Fakultät der Friedrich- Alexander Universität Erlangen-Nürnberg
Tag der mündlichen Prüfung: 26.11.2014
Vorsitzender des Promotionsorgans: Prof. Dr. Jörn Wilms
Gutachter/in: Prof. Rik R. Tykwinski PhD
Prof. Dr. Nicolai Burzlaff Die vorliegende Arbeit wurde am Institut für Organische Chemie der Friedrich- Alexander-Universität Erlangen-Nürnberg in der Zeit von Juni 2010 bis September 2014 unter Anleitung von Prof. Rik R. Tykwinski PhD angefertigt. For my family, my friends, and for Simone “Learn the rules like a pro, so you can break them like an artist.“ – Pablo Picasso Acknowledgments
First of all I want to thank my supervisor Prof. Rik R. Tykwinski for giving me the chance to carry out research in his laboratories. He has put enormous efforts in my education and helped me to understand at least some parts of the world of organic chemistry. He has made a synthetic organic chemist out of me. Working in his group has also the great side effect of reinventing own English skills. Thanks also to Dr. Milan Kivala who helped with chemical problems at any time.
The Graduate School of Molecular Science (GSMS) and the Georg-Kurlbaum- Stiftung are gratefully acknowledged for financial support.
Thanks to Prof. Oana Jurchescu at Wake Forest University (Winston-Salem, United States), to Sebastian Etschel, and the Halik group at FAU for performing the transistor devices. Thanks to Frank Strinitz (Burzlaff group) at FAU for the collaboration and the interest in our precursor materials. Thanks to Dr. Rubén D. Costa and Ruben Casillas (Guldi group) at FAU for performing the singlet fission topic.
I want to thank the whole Tykwinski group as well as the Kivala group for the very nice group atmosphere, especially, Dominik Prenzel, Maximilian Krempe, Vincent Oerthel, Johanna Januszewski, Stephanie Frankenberger, Michael Franz, Dominik Wendinger, Vroni Walter, Katrin Schmidt, Sebastian Etschel, Matthias Schulze, Julia Tyrach, Fabian Fritze, Bettina Gliemann, Theresa Mekelburg, Michael Grunst, Tobias Schaub, and Ute Meinhardt for some unforgettable times during my PhD studies, most of them in our “Souschl Room”. Special thanks go to Dr. Adrian Murray. During his stay in Erlangen we have become good friends. Thank you to Dr. Eike Jahnke for the help at the very beginning of my career. Thank you to Matthias Adam (Maze) for the discussions about computer problems.
Special thanks go to the X-ray crystallographic staff members, Dr. Frank Hampel and Wolfgang Donaubauer, for the large number of solved structures. Thank you to the service staff members: Christian Placht (NMR), Dr. Harald Maid (NMR), Prof. Dr. Walter Bauer (NMR), Margarte Dzialach (MS analysis), Wolfgang Donaubauer (MS analysis), Eva Zeisel (microanalysis), Holger Wolfarth (electricity facility), Horst Meier (mechanics facility), Stefan Fronius (glas blower facility), Bahram Saberi (glas blower facility), and Pamela Hampel (group secretary). Thank you very much Simone Berngruber. You are simply great!
Special thanks to Dr. Wolfgang Brenner. We have tried to revolutionize the GSMS Winterschool in Kirchberg. Thanks to Thomas Nasser, Thomas Dotzauer, Sebastian Lohner, Dominik Brütting, and Johannes Bayerl for being the closest friends I have. Thanks to Arno Lücken, with whom I have betted that he will make it into this thesis.
Last but not least, I say thank you very much to my parents and my whole family. Without your endless support and understatement this thesis would not have been possible. Curriculum vitae
Personal data
Name: Andreas Reinhard Waterloo
Date of birth: 20.02.1983
Born in: Eschenbach i.d. Opf.
Academic career
June 2010 - present PhD program in the group of Prof. Rik R. Tykwinski at the Institut für Organische Chemie at FAU Erlangen
Thesis title: “Design and synthesis of pentacene derivatives”
August 2009 - May 2010 Diploma thesis in the group of Prof. Rik R. Tykwinski at the Insitut für Organische Chemie at FAU Erlangen
Thesis title: “Unsymmetrically substituted pentacenes”
October 2003 - July 2009 Academic studies of chemistry at FAU Erlangen
Military service
July 2002 - May 2003 Obligatory military service at the german army (Bundeswehr) in Oberviechtach, Bavaria
School education
September 1993 - June 2002 Gymnasium Eschenbach i. d. Opf. (Abitur)
September 1989 - 1993 Primary school, Eschenbach i . d. Opf List of publications
[1] “Acenes with a Click” Waterloo, A. R.; Kunakom, S.; Hampel, F.; Tykwinski, R. R. Macromol. Chem. Phys. 2012, 213, 1020–1032. [2] “Isomerically Pure syn-Anthradithiophenes: Synthesis, Properties, and FET Performance” Lenherr, D.; Waterloo, A. R.; Goetz, K. P.; Payne, M. M.; Hampel, F.; Jurchescu, O. D.; Anthony, J. E.; Tykwinski, R. R. Org. Lett. 2012, 14, 3660–3663. [3] “An unsymmetrical pentacene derivative with ambipolar behavior in organic thin-film transistors” Etschel, S.; Waterloo, A. R.; Markgraf, J. T.; Amin, A. Y.; Hampel, F.; Jäger, C. M.; Clark, T.; Halik, M.; Tykwinski, R. R. Chem. Commun. 2013, 49, 67256727. [4] “Allenylidene Complexes Based on Pentacenequinone” Strinitz, F.; Waterloo, A. R.; Tucher, J.; Hübner, E.; Tykwinski, R. R.; Burzlaff, N. Eur. J. Inorg. Chem. 2013, 51815186. [5] “Aryl Substitution of Pentacenes” Waterloo, A. R.; Sale, A.-C.; Lehnherr, D.; Hampel, F.; Tykwinski, R. R. Beilstein J. Org. Chem. 2014, 10, 16921705. [6] “Carbon-Rich Ruthenium Allenyliden Complexes Bearing Heteroscorpionate Ligands” Strinitz, F.; Tucher, J.; Januszewski, J. A.; Waterloo, A. R.; Stegner, P.; Förtsch, S.; Hübner, E.; Tykwinski, R. R.; Burzlaff, N. Organometallics, 2014, DOI: 10.1021/om5002777. Poster presentations
[1] Waterloo, A. R.; Hampel, F.; Tykwinski, R. R. “Pentacenechinocumulenes: New Semiconductors?” Gordon Research Conference on Physical Organic Chemistry, June 2013, Holderness School, USA. [2] Waterloo, A. R.; Lehnherr, D.; Hampel, F.; Goetz, K. P.; Payne, M. M.; Jurchescu, O. D.; Anthony, J. E. Tykwinski, R. R. “Isomerically Pure syn- Anthradithiophenes” ORGCHEM 2012, September 2012, Weimar, Germany. [3] Waterloo, A. R.; Kunakom, S.; Hampel F.; Tykwinski R. R. “Pentacene Chromophores via Click Chemistry.” International Symposium of Novel Aromatic Compounds (ISNA 14), July 2011, Eugene (Oregon), USA. [4] Tykwinski, R. R.; Waterloo, A. R.; Konishi, A.; Lehnherr, D.; Hampel, F. “Tautomerization in 6,13-Derivatives of Pentacene.” International Symposium of Novel Aromatic Compounds (ISNA 14), July 2011, Eugene (Oregon), USA. [5] Waterloo, A. R.; Hampel, F.; Tykwinski, R. R. “Functionalization of Pentacene.” European Association of Chemical and Molecular Science (EuChems 3), August 2010, Nürnberg, Germany. [6] Waterloo, A. R.; Hampel, F.; Tykwinski, R. R. “Pentacenes and Click- Chemistry.” Funmols workshop, April 2010, Muggendorf, Germany. Summary
The scope of this research work was the synthesis and characterization of pentacene derivatives and pentacene-related materials. The most important characterization method for the products formed in the present work has been X-ray crystallographic analysis. On the basis of this work, pentacene derivatives can be classified by generally observed solid-state arrangements, of which some are beneficial for the use in optoelectronic devices. The solid-state motifs are closely related to the substitution pattern of pentacene derivatives. The present work discusses the influence of different substituents on the solid-state arrangement of pentacenes. The X-ray crystallographic theme is applied to the characterization of isomerically pure syn-anthradithiophenes, as analogs to pentacenes, and the characterization of 6,13- pentacenequinone-based materials. An attempt is made to draw correlations between solid-state structures of the detailed compounds and their properties, although this evaluation is extremely complex.
Chapter 1 of this thesis gives a short introduction into the chemistry of pentacene and the distinct features of pentacene derivatives evaluated by X-ray crystallography. The introduction summarizes the current state of the field, also bridging to material science, and gives examples of previously synthesized pentacenes.
Chapter 2 discusses the synthesis of unsymmetrically substituted pentacene derivatives in 6- and 13-positions. The functional groups appended to the pentacene framework include 1,2,3-triazolyl-, aryl-, and alkyl moieties. The synthesized 1,2,3- triazolyl-pyridyl-substituted pentacene derivatives can be used to investigate pentacene-porphyrin assemblies. The applied groups at the 6-and 13-postions have little effect on electronic properties of the pentacene derivatives, which is verified by UV-vis spectroscopy, emission spectroscopy, and electrochemical measurements. Nevertheless, functionalization by anthracenyl groups affords pentacene derivatives that show interesting solid-state packing and several packing motifs are compared. The reactivity of a methyl-substituted pentacene derivative is briefly discussed. The chapter closes with the synthesis and characterization of a monosubstituted pentacene derivative.
Chapter 3 discusses the successful synthesis of isomerically pure syn- anthradithiophenes. A detailed study comparing syn-isomers and isomerically mixed anthradithiophenes has been conducted by UV-vis spectroscopy, emission spectroscopy, thermal analysis, and X-ray crystallographic analysis. The present work determines only small differences between the syn-isomers and the isomerically mixed analogs. The chapter closes with attempted derivatizations of isomerically pure syn-anthradithiophenes.
Chapter 4 discusses the Knoevenagel reaction of pentacenone building blocks with malononitrile. The discussion explores different reaction pathways to investigate the conversion of ketones to 1,1-dicyanovinyl species. The targeted products could potentially be used to provide an electron-acceptor group on the pentacenone scaffold. A general protocol for the functionalization of the 6,13-pentacenequinone framework by the [3]cumulene skeleton is also described, and this general protocol offers the possibility to functionalize the pentacenone framework by Ru-containing allenylidene complexes.
Chapter 5 gives the experimental details of the compounds discussed in this research work and Chapter 6 provides the NMR spectral data of selected compounds. Zusammenfassung
Die vorliegende Arbeit hatte das voranginge Ziel neuartige Synthesen von Pentacenderivaten zu entwickeln. Die wichtigste Methode zur Charakterisierung der in dieser Arbeit vorgestellten Moleküle ist die Röntgenstrukturanalyse. Auf der Basis der zugrundeliegenden Arbeit lassen sich Pentacenderivate in verschiedene Festkörperanordnungen, das sogenannte Packungsmuster, klassifizieren. Einige dieser Packungsmuster sind vorteilhaft für die potentielle Anwendung, beispielsweise in Feldeffekttransistoren. Diese Festkörperanordnung ist jedoch stark von der Art des Substituenten am Pentacengrundgerüst abhängig, und in dieser Forschungsarbeit wird der Einfluss von Substituenten am Pentacengrundgerüst auf die Anordnung im Festkörper diskutiert. Das Thema Röntgenstrukturanalyse leitet als roter Faden durch die gesamte Arbeit und wird sowohl auf die Charakterisierung von syn- Anthradithiophenen als auch auf die Charakterisierung von 6,13- Pentacenquinonähnlichen Verbindungen angewendet. Es wurde, trotz der Kompexität des Themengebiets, versucht einen Zusammenhang zwischen Festkörperstruktur der untersuchten Verbindungen und deren physikalischen Eigenschaften herauszuarbeiten.
Kapitel 1 der vorliegenden Arbeit gibt eine kurze Einführung in die „Chemie der Pentacene“. Die physikalischen Eigenschaften und unterschiedliche Festkörperanordnungen einiger Pentacenderivate werden vorgestellt.
Kapitel 2 zeigt die erfolgreiche Synthese von in 6- und 13-Position unsymmetrisch substituierten Pentacenderivaten. Das Substitutionsmuster deckt 1,2,3-Triazoyl-, Aryl-, und Alkyl-Reste ab. Speziell die durch Cycloaddition erhaltenen 1,2,3-Triazolyl- Pyridyl-Pentacene können an Porphyrinsysteme koordinativ gebunden werden. Es konnte mittels UV-vis Spektroskopie, Fluoreszenzspektroskopie und elektrochemischen Messungen gezeigt werden, dass sich die elektronischen Eigenschaften nahezu aller unsymmetrisch funktionalisierten Pentacenderivate weitestgehend ähneln. Nichtsdestotrotz führt die Funktionalisierung mit Anthracenyl- Resten zu interessanten Festkörperanordnungen. Einige Anthracenyl-substituierte Pentacene werden gegenüberstellend in ihrem Packungsmuster verglichen. Kurz wird noch die Reaktivität eines Methyl-substituierten Pentacenderivats beleuchtet und abschließend wird die Synthese und die Charakterisierung eines monosubstituierten Pentacenderivats vorgestellt. Kapitel 3 zeigt die erfolgreiche Darstellung von isomerenreinen syn- Anthradithiophenen. In einer detaillierten Studie werden die dargestellten syn- Isomere mit Isomerengemischen von Anthradithiophenen verglichen. Ein signifikanter Unterschied in den elektronischen, optischen und thermischen Eigenschaften zwischen isomerenreinen syn-Anthradithiophenen und den analogen Isomerengemischen konnte nicht gefunden werden. Speziell die Anordnung im Festkörper ist fast komplett identisch. Abschließend werden Versuche gezeigt um das isomerenreine syn-Anthradithiophengerüst weiter zu funktionalisieren.
Kapitel 4 behandelt die Knoevenagel Reaktion des Pentacenongrundgerüstes und Malonsäuredinitril. Verschiedenste Reaktionswege um ein Keton in einen 1,1- Dicyanovinyl-Rest umzuwandeln, werden diskutiert. Die so erhaltenen Verbindungen könnten synthetisch genutzt werden um Pentacenoneinheiten mit Elektronakzeptor Strukturen zu funktionalisieren. Im Allgemeinen ist eine Synthesestrategie erläutert die es zulässt den 6,13-Pentacenquinongrundkörper mit einem [3]Kumulen zu funktionalisieren. Die beschriebene allgemeine Syntheseroute ebnet schließlich den Weg um Ru-basierte Allenylidenkomplexe zu erhalten.
Kapitel 5 enthält alle experimentellen Details zu den in dieser Arbeit synthetisierten Verbindungen und in Kapitel 6 sind NMR spektroskopische Daten ausgewählter Zielverbindungen abgebildet. List of Symbols
Å Angstrom chemical shift (NMR) molar extinction coefficient
max wavelength of maximum absorbance micro, absorption coefficient (X-ray) J coupling constant (NMR)
List of Abbreviations
ADT anthradithiophene AFM atomic force microscopy APPI atmospheric pressure photoionization aq aqueous ATR attenuated total reflection BnBr benzylbromide bdmpza bis(3,5-dimethylpyrazol-1-yl)acetate calcd calculated CCDC Cambridge Crystallographic Data Centre cm centimeter(s) conc concentrated Compd compound CSP crystal structure prediction CuAAC Cu(I)-catalyzed alkyne-azide Huisgen cycloaddition CV cyclic voltammetry d doublet (NMR), day(s) DCTB trans-2-[3-{4-tert-butylphenyl}-2-methyl-2-propenylidene]malononitrile DMF N,N-dimethylformamide DSC differential scanning calorimetry
Eg band gap energy Elemt Anal elemental analysis equiv equivalent(s) ESI electrospray ionization EtOAc ethylacetate EtOH ethanol (m)eV (milli)electron volts g gram(s) h hour(s) HOMO highest occupied molecular orbital HRMS high resolution mass spectrometry Hz Hertz i iso i-PrOH iso-propanol IUPAC International Union of Pure and Applied Chemistry IR infrared LDI laser desorption ionization LDA lithium diisopropylamide LiHMDS lithium hexamethyldisilazide LUMO lowest unoccupied molecular orbital m multiplet (NMR), medium (IR) M molar MALDI matrix assisted laser desorption ionization MeI Iodomethane MeOH methanol mg milligram(s) MHz megaHertz min minute(s) mL milliliter(s) mmol millimole(s) mol mole(s) Mp melting point MPA melting point analysis MS mass spectrometry m/z mass-to-charge ratio NBS N-bromosuccinimide n-BuLi n-butyllithium NFSI N-fluorbenzenesulfonimide nm nanometer(s) NMR nuclear magnetic resonance OFET organic field-effect transistor ORTEP oak ridge thermal ellipsoid plot OPV organic photovoltaic PAH polycyclic aromatic hydrocarbon PCBM [6,6]-phenyl-C61-butyric acid methyl ester Ph phenyl ppm parts per million (NMR) q quartet (NMR) ref reference
Rf retention factor rt room temperature SAM self-assembled monolayers s singlet (NMR), strong (IR) satd saturated t triplet (NMR) TBAF tetra-n-butylammonium fluoride t-Bu tert-butyl TCNE tetracyanoethylene Td decomposition temperature TES triethylsilyl TGA thermogravimetric analysis TMEDA tetramethylenediamine TMS trimethylsilyl THF tetrahydrofuran TIPS triisopropylsilyl
TIPS-Pc 6,13bis(triisopropylsilylethynyl)pentacene TLC thin layer chromatography Tr* supertrityl = [tris(3,5-di-t-butylphenyl)methyl] UV-vis ultraviolet-visible w weak (IR) XRD X-ray diffraction Table of Contents
Chapter 1 Introduction 1 1.1. A brief history of polycyclic aromatic hydrocarbons 1 1.2. From PAHs to pentacene 1 1.3. Functionalization, solid-state structure, and semiconductive materials 3 1.3.1. Functionalization of pentacene 3 1.3.2. Solid-state structures 4 1.3.3. From crystal structures to device performance 5 1.4. Synthesis of pentacene derivatives 8 1.4.1. Halogenated pentacene 8 1.4.2. Alkyne functionalization of pentacenes 10 1.4.3. Oligomers and polymers based on pentacene 12 1.4.4. Unsymmetrically substituted pentacene derivatives 13 1.5. Summary 15 1.6. References 16
Chapter 2 Unsymmetrically functionalized pentacenes 22 2.1. Introduction 22 2.2. Functionalization by click chemistry 22 2.2.1. Acenes with a click 22 2.2.2. Electronic properties of 1,2,3-triazole containing pentacenes 29 2.2.3. Solid-state analysis of 2.7a and 2.7e 31 2.2.4. Synthetic limits of the CuAAC reaction 33 2.2.5. Pentacene-porphyrin assemblies 34 2.3. Aryl substitution of pentacenes 40 2.3.1. Functionalization by nucleophilic addition 40 2.3.2. Functionalization by Suzuki reaction 43 2.3.3. Electronic properties of aryl-substituted pentacenes 43 2.3.4. Thermal analysis of aryl-substituted pentacenes 51 2.3.5. Solid-state analysis of aryl-substituted pentacenes 52 2.3.6. Comparison of anthracene-substituted pentacenes 62 2.3.7. Synthetic limits of aryl substitution of pentacenes 64 2.3.8. From anthracenyl-substituted pentacenes to higher PAHs 65 2.4. Alkyl substitution of pentacenes 67 2.4.1. Functionalization by nucleophilic addition 67 2.4.2. Electronic properties of alkyl-substituted pentacene derivatives 69 2.4.3. Solid-state analysis of alkyl-substituted pentacene derivatives 70 2.4.4. Synthetic limits of alkyl substitution of pentacene derivatives 73 2.4.5. Reactivity of 2.32a 74 2.5. Monosubstituted pentacene 77 2.5.1. Reduction toward monosubstituted pentacene 77 2.5.2. Electronic properties of pentacenes 2.35a and 2.35b 80 2.5.3. Solid-state analysis of pentacene 2.35a 82 2.6. Conclusion 83 2.7. Outlook 85 2.7.1. CuAAC reaction 85 2.7.2. Larger PAHs from anthracenyl-substituted pentacenes 85 2.7.3. Pentacene dimers for studies of singlet fission 86 2.7.4. Monosubstituted pentacene as building block 87 2.8. References 87
Chapter 3 Isomerically pure syn-anthradithiophenes 96 3.1. Introduction 96 3.2. Synthesis of fluorinated isomerically pure syn-ADTs 99 3.2.1. Synthesis of building blocks 99 3.2.2. Attempted synthesis of fluorinated syn-ADTs via deprotonation 101 3.2.3. Changing the synthetic strategy via halogen-lithium exchange 104 3.3. Synthesis of brominated mix-ADTs 106 3.4. Comparison between syn-ADTs and mix-ADTs 108 3.4.1. Electronic properties of syn-ADTs and mix-ADTs 108 3.4.2. Electronic properties of by-products 115 3.4.3. Summary of electronic properties 117 3.4.4. Thermal properties of syn-ADTs and mix-ADTs 119 3.4.5. Solid-state analysis of syn-ADTS and mix-ADTs 121 3.4.6. Solid-state analysis of by-products 130 3.4.7. Summary of solid-state analysis 132 3.5. Attempted derivatizations of syn-isomers 136 3.5.1. A pentacene-ADT chromophore 136 3.5.2. Reduction of syn-3.4 140 3.6. Conclusion 141 3.7. Outlook 141 3.8. References 142
Chapter 4 Pentacenequinone-based building blocks 146 4.1. Introduction 146 4.2. Attempts to realize a [5]cumulene-based acceptor 148 4.2.1. A [5]cumulene via the Knoevenagel reaction 148 4.2.2. Finding the right leaving group 151 4.2.3. Exploring different reaction conditions 153 4.2.4. Solid-state analysis 155 4.3. Attempts to realize a [3]cumulene-based acceptor 158 4.3.1. Synthesis of a pentacenequinone-based [3]cumulene 158 4.3.2. Electronic properties of 4.20a 161 4.3.3. Solid-state analysis of 4.20a 162 4.4. Organometallic approaches 164 4.4.1. Synthesis of building blocks for allenyliden complexes 164 4.5. Conclusion 166 4.6. References 167
Chapter 5 Experimental data 170 5.1. General Information 170 5.2. Synthesis of known compounds 171 5.3. Synthesis of new compounds 174 5.4. Appendix compounds 250 5.5. References 255
Chapter 6 Spectral data 257 Chapter 1 – Pentacene, a short journey from synthesis to material science Chapter 1 – Pentacene, a short journey from synthesis to material science
1.1 A brief history of polycyclic aromatic hydrocarbons
Polyarenes – or more commonly referred to as polycyclic aromatic hydrocarbons (PAHs) – are a class of organic molecules which have been investigated in both academic and industrial research. PAHs are also found in oil and coal sources and hence, are also of considerable importance as sources of energy. From a historic perspective, Erich Clar is considered as one of the most important scientist in the field of PAH chemistry, and provided Clar´s rule, which gives a theoretical and straightforward model for the stability of PAHs and which is commonly accepted in the scientific community.[1,2] Since the postulation of the first field-effect transistor in the 1930s[3] and the discovery of the first organic field-effect transistor based on polythiophene thin films,[4] PAHs have gained significant scientific interest outside of pure synthetic organic chemistry. The discovery of graphene in 2004 by Geim and Novoselov,[5] which was awarded with the Nobel Prize in Physics in 2010,[6] can be regarded as the latest benchmark in PAHs history, as (nano-)graphene can be seen as an infinite network of polyarenes.[7]
1.2 From PAHs to pentacene
In the large field of PAHs, linearly fused benzene rings are classified as acenes. Pentacene (1.1) is a PAH consisting of five linearly fused benzene rings (Figure 1.1). From a historic perspective, research on pentacene suffered a small setback, because of the scandalous reports of Jan Hendrik Schön, who falsely reported superconductive properties of pentacene in 2000 amongst other properties.[8] Nevertheless, pentacene has proved useful as a semiconductor in several interdisciplinary fields bridging chemistry, physics, and engineering.
Figure 1.1. Chemical structure of pentacene (left) and its schematic numbering (right) as proposed by IUPAC.
1 Chapter 1 – Pentacene, a short journey from synthesis to material science
Pentacene was first synthesized by Erich Clar in 1929.[2] Later in 1953, Ried and Anthöfer published a formal synthetic route (Scheme 1.1) involving a base-catalyzed four-fold aldol condensation of o-phthalaldehyde and 1,4-cyclohexandione, giving 6,13-pentacenequinone (1.2).[9] Pentacene can then be obtained by reduction of 1.2 with aluminium in cyclohexanol.[10] Alternative reduction reagents have also been used more conveniently and more efficiently to afford pentacene, such as hydriodic [11] [12] acid or LiAlH4. A second synthesis was also reported in 1953, although it uses a less convenient methodology (Scheme 1.2), based on the addition of 1,2- dimethylenecyclohexane with 1,4-benzoquinone to yield dione 1.3. The latter is deoxygenated by formation of the bisdithioacetale followed by treatment with Raney- Nickel (1.4) and subsequent catalytic dehydrogenation affords pentacene.[13]
Scheme 1.1. Synthetic pathway to afford pentacene.[9,10]
Scheme 1.2. Alternative synthesis to afford pentacene.[13]
Pentacene is a deep blue crystalline solid with a molecular weight of 278.33 g/mol. Unfortunately, it has limited solubility in most common organic solvents, but it does [14] show a characteristic UV-vis absorption maxima at max = 576 nm in benzene. X- ray analysis of pentacene shows C-C bond alternations which are in good agreement with structures derived from theoretical calculations.[15,16] Pentacene is a reactive molecule that undergoes photooxidation of the chromophore when solutions
2 Chapter 1 – Pentacene, a short journey from synthesis to material science are exposed to air (Scheme 1.3). Several decomposition pathways of pentacene have been explored including, a) the reaction with molecular oxygen to give the endo-peroxide 1.5[17] or b) dimerization to form butterfly-shaped compounds 1.6.[18]
Scheme 1.3. Major decomposition pathways of pentacene.[17,18]
1.3 Functionalization, solid-state structure, and semiconductive materials
1.3.1 Functionalization of pentacene
Pentacene shows an excellent charge carrier mobility and has been identified as a good candidate for p-type semiconducting devices,[19a] due to, in part, the high electron density of the conjugated framework.[19b] To address the solubility and stability problems of pentacene, chemical modification has been used. The field of semiconductive and optoelectronic materials based on PAHs has profited enormously from synthetic organic chemistry; namely the research areas including field-effect transistors,[20] OLEDs,[21] photovoltaics,[22] and, more recently, battery technologies.[23] A landmark discovery in the field of pentacene chemistry was the synthesis of 6,13bis(triisopropylsilylethynyl)pentacene (TIPS-Pc, 1.7a, Figure 1.2) by Anthony in 2001.[24,25] Pentacene 1.7a is stable in solution and in the solid state with high solubility in many common organic solvents and can therefore be easily processed from solution. This is beneficial for purification and thin film deposition for semiconductive devices. Interestingly, pentacene 1.7b has been prepared in comparison to 1.7a, but, is unstable when exposed to air.
3 Chapter 1 – Pentacene, a short journey from synthesis to material science
Figure 1.2. Pentacene derivatives 1.7a and 1.7b, respectively.[24]
In addition to the improved stability of pentacene 1.7a, it also demonstrates changes in its electronic properties, compared to bare pentacene 1.1. The lowest energy absorption maximum is red shifted to max = 643 nm (measured in CH2Cl2) which is due to extended conjugation via the two alkyne substituents.[26] A more significant red shift in the UV-vis absorption is observed for films of 1.7a drop casted from CH2Cl2 [26] with absorption maximum at max = 705 nm. This has been attributed due to better --interactions of neighboring molecules in the solid state.
1.3.2 Solid-state structures
One of the most powerful methods to characterize pentacene derivatives is X-ray crystallography, which allows for elucidating -stacking interactions in the solid state. This rather simple analysis can potentially give predictions of effectiveness of these pentacene derivatives for further use in electronic devices based on the observed packing motif (vide infra). Pentacene was first crystallographically analyzed by Campbell in 1961 and the structure was revised in 1962.[15] It has also been described that pentacene can crystallize in several different polymorphs.[27,28] Similar to anthracene and tetracene, pentacene crystallizes in a 1-D face-to-edge motif which is referred to as herringbone motif (Figure 1.3).[29]
The crystal packing of acenes generally depends on CH and CC interactions as investigated by Gavezzotti.[30] If the acene contains a relatively large number of H- atoms, a herringbone structure is observed, although the exact ratio is, unfortunately, not given by the authors.[30] In contrast, a more graphite-like structure is present if the number of CC interactions is increased.[30]
4 Chapter 1 – Pentacene, a short journey from synthesis to material science
Figure 1.3. Herringbone packing of pentacene.[15,31]
The packing motif also changes dramatically upon functionalization with alkyne groups in the 6- and 13-positions of the aromatic pentacene skeleton such as of TIPS-Pc (1.7a). TIPS-Pc adopts face-to-face -stacking, which is often referred to as 2-D bricklayer arrangement, with interplanar distances of 3.47 Å (Figure 1.4). This two-dimensional solid-state arrangement is sought to positively influence the electronic communication between the aromatic pentacene molecules.[32]
Figure 1.4. Face-to-face bricklayer packing of pentacene derivative 1.7a.[33]
1.3.3 From crystal structures to device performances
Efforts have been made to employ pentacene in organic semiconductors, optoelectronic devices, and organic field-effect transistors (OFET).[34] The charge carrier mobility is an effective unit to characterize an organic semiconductor and is defined as how quickly a charged particle (holes in cases of p-type and electrons in
5 Chapter 1 – Pentacene, a short journey from synthesis to material science the case of n-type materials) can move through a metal or semiconductor when an electric field is applied.[35] Pentacene 1.1 shows excellent charge carrier mobilities of 2 1.4 cm /Vs for a single crystal device using SiO2 as the gate dielectric which was treated with self-assembled monolayers.[36] Charge carrier mobilities of up to 35 cm2/Vs at room temperature (or even up to 58 cm2/Vs at 225 K) have been reported for ultrapure pentacene single crystals.[37] In contrast to single crystal devices, thin films of pentacene 1.7a can be easily processed from solution to afford high charge carrier mobilities of about 1.5 cm2/Vs.[38]
The charge carrier mobilities in OFET devices are typically dependent on the solid- state packing motif of pentacene derivatives. X-ray crystallographic analysis helps to elucidate the solid state arrangement of the pentacene materials. As outlined in Figure 1.5, pentacene derivatives typically pack in four major solid-state arrangements. Most commonly found are (a) herringbone packing, (b) sandwich- herringbone packing, (c) a 1-D slipped packing along one of the crystallographic axes, and (d) the 2-D bricklayer packing.
(a) (b)
(c) (d)
Figure 1.5. Schematic classification of four common solid-state arrangements of pentacene derivatives (a) herringbone packing, (b) sandwich-herringbone packing (c) 1-D slipped packing, and (d) 2-D bricklayer packing.
6 Chapter 1 – Pentacene, a short journey from synthesis to material science
Interestingly, it has been observed by Anthony and coworkers that pentacene derivatives, which adopt a 2-D bricklayer motif, show excellent charge carrier mobilities in planar devices, such as OFETs where 2-D bricklayer packing motifs form large crystalline domains. The large crystalline domains are seemingly beneficial for superior performance in OFET devices.[38] The same derivatives which show a 2-D bricklayer packing motif, however, perform poorly in solar cell devices. In sharp contrast, pentacene derivatives which adopt a sandwich-herringbone packing motif are seemingly beneficial for organic solar cell applications, such as bulk heterojunction solar cells.[39] This is due to domains that are formed, which have a characteristic size on the order of exciton diffusion lengths.[40] Unfortunately, it is in general hard to predict the crystal structure for pentacene materials based on chemical structure, since small chemical modifications can lead to completely different solid-state arrangements.
Polymorphism plays a role in the performance of OFET devices. As a result of weak interaction energies, organic molecules can adopt different crystal structures, depending on the crystallization conditions.[41] For thin films of pentacene, at least four different polymorphs have been identified with different d001 spacing of 14.1, 14.5, 15.1, and 15.4 Å.[27b] Two of these polymorphs are usually found in films formed by vacuum deposition, depending on the growth conditions, such as substrate, temperature, and film thickness.
It has been found that not only the molecular arrangement, but also the morphology of the organic (pentacene) semiconducting layer plays a significant role in the performance of OFETs. If the molecules pack along the current direction in the conducting channel, device performance would be achieved in a more efficient way.[34] In 2011, Bao and coworkers published a way of improving the charge carrier mobility of a solution-processed TIPS-Pc device by increasing the strain of the thin film.[42] The increase in lattice strain alters significantly the -stacking distances to 3.08 Å and modified the molecular packing leading to an improved charge carrier mobility from 0.8 cm2V 1s 1 to 4.6 cm2V 1s 1. Recently, Brédas and coworkers published theoretical work on pentacene monolayers on an amorphous silica dielectric,[43] and explained that effective charge carrier transport in thin film OFETs takes place in the first molecular layers of pentacene in contact with the gate dielectric. Calculations by molecular dynamics simulations show that the 7 Chapter 1 – Pentacene, a short journey from synthesis to material science electrostatics of the SiO2 surface of the dielectric has influence on the molecular packing of the pentacene thin films and, thus, the electrostatics of the dielectric have influence on the charge carrier mobilities.
Pentacene gives high performances in OFET devices, but nevertheless, such high performances have only been achieved in top-contact devices by evaporating the source and drain electrodes onto the pentacene film. The interactions between the pentacene semiconductor and the metal electrodes have also influence on the morphology of the organic (pentacene) layer within the OFET device.[41]
It is clear that device performance of pentacene derivatives strongly relies on many different physical factors. The solid-state arrangement may not be the most important, but it is the first and easiest way to predict and interpret performance of a pentacene derivative in a device. It is not only synthetic methods of the organic compounds that have to be considered for the design of organic electronic devices, but also morphological aspects and the control of polymorphism of the organic active layer plays an important role in device performance.
1.4 Synthesis of pentacene derivatives
1.4.1 Halogenated pentacene
Synthetic strategies to improve the electronic properties of pentacene involve incorporating electron withdrawing groups such as fluorine into the pentacene skeleton (Scheme 1.4). This has been successfully accomplished by Tokito and coworkers,[44] beginning with a Friedel-Crafts reaction from tetrafluorophthalic anhydride 1.8 with hydroquinone under harsh conditions to yield anthraquinone derivative 1.9 in 71%. Subsequently, 1.9 was reduced using tin under acidic conditions to give 2,3-dihydro-1,4-anthracenedione 1.10 in 95% yield. A Friedel- Crafts reaction of 1.10 with 1.8 gives pentacenequinone 1.11 in 85%. Complete fluorination of 1.11 was achieved with sulfur tetrachloride in hydrogenfluoride at 150 °C, followed by treatment with zinc to give perfluorinated pentacene derivative 1.13.
8 Chapter 1 – Pentacene, a short journey from synthesis to material science
Scheme 1.4. Synthetic procedure to afford perfluorinated pentacene derivative 1.13.[44]
Interestingly, fluorinated pentacene derivative 1.13 also crystallizes in the herringbone packing motif as observed for pentacene 1.1 (Figure 1.6). The edge-to- face angle found in derivative 1.13 is nearly 90°, however, which is in sharp contrast to an edge-to-face angle of 52° in pentacene 1.1. OFET devices built from 1.13 show n-type character with electron mobilities of up to 0.022 cm2/Vs. These results show that fluorination of pentacene can change the physical properties towards n-type semiconductors.
Figure 1.6. Solid sate arrangement of perfluorinated pentacene derivative 1.13.[44] 9 Chapter 1 – Pentacene, a short journey from synthesis to material science
1.4.2 Alkyne functionalization of pentacenes
The discovery that alkyne substituents in the 6- and 13-positions of pentacene dramatically improve the stability and processability, has led to the synthesis of hundreds of symmetrically substituted pentacene derivates. The topic is simply too large to be comprehensively shown in this thesis and, hence, only a few representative derivatives are discussed herein.[19,26,29,34]
Anthony and coworkers have reported on the influence of trialkylsilylethynyl groups on the pentacene -stacking interactions.[25] Commonly, these pentacene derivatives are synthetically accessible via a two-step protocol, starting from 6,13- pentacenequinone (1.2). Without the isolation of the intermediate diol, pentacene derivatives 1.7a and 1.141.17 are typically obtained via reductive aromatization, using SnCl2 under acidic conditions, in good to excellent yields (Scheme 1.5). The authors systematically analyzed the -stacking motif via X-ray crystallographic analysis and suggested that a silyl substituent connected to the pentacene framework with a relatively rigid acetylenic spacer requires approximately half the spherical diameter of the acene framework in order to adopt a 2-D bricklayer packing motif.
Scheme 1.5. Synthetic procedure to afford trialkylsilylethynyl substituted pentacene derivative 1.7a1.17.[19,25]
Another synthetic strategy toward functionalized pentacene derivatives is substitution in the 2,3- and 9,10-positions (or pro cata-positions), in order to provide a method to further tune the electronic properties. Prominent examples include introduction of cyclic ether functionalities (Figure 1.7) which improve the donor qualities of the
10 Chapter 1 – Pentacene, a short journey from synthesis to material science molecule.[45] Pentacene derivative 1.18 shows a significant red shift in absorption maxima to max = 674 nm compared to 1.7a (max = 643 nm), suggesting that the lone pairs of the ether functionality contribute to the conjugated pentacene backbone. Notably, it has been reported that pentacenes bearing a non-cyclic ether substituent such as methoxy-groups in the pro cata-positions are unstable under ambient conditions.[45a]
Figure 1.7. Selected examples of pentacene ethers.[45]
Introduction of alkyl- and alkyne substituents to the pro cata-positions has been realized by Anthony[19a] and Neckers.[46] Alkyl-substituted pentacene derivative 1.21 shows a decreased oxidation potential compared to pentacene 1.7a (about 0.7 V for 1.21 and 0.85 V for 1.7a), and -stacking was significantly disrupted towards a 1-D packing motif.[19a] Alkyne substituted pentacene derivatives 1.22 show a significant red shift in max of up to 70 nm in thin film UV-vis analysis, suggesting strong intermolecular -interactions in the solid state.[46]
Figure 1.8. Pentacene derivatives 1.21 and 1.22, substituted by alkyl- or alkyne groups in their pro cata-positions, respectively.[19a,46] 11 Chapter 1 – Pentacene, a short journey from synthesis to material science
The decrease of interplanar distances in the solid-state arrangement of pentacene derivatives should also improve the electronic properties. To achieve a decrease of interplanar distances, partial fluorination as well as cyanation of the pentacene backbone has been realized. Pentacene derivatives 1.23 and 1.24 (Figure 1.9) have been synthesized via a three-step protocol starting from tetrafluoranhydride 1.8.[47] Substitution of CN-groups has been accomplished via Pd-catalyzed cross coupling of a brominated pentacene derivative using CuCN as the transmetalation agent, affording 1.25 in 40% yield. Partial fluorination of pentacene derivate 1.24 shows an interplanar distance of 3.28 Å and improved charge carrier mobilities of up to 0.045 cm2/Vs (under the same applied deposition conditions reported in this study, TIPS-Pc 1.7a shows charge carrier mobilities of 0.001 cm²/Vs).[47]
Figure 1.9. Pentacene derivatives 1.231.25 bearing electron withdrawing groups in the pro cata-positions.[47]
1.4.3 Oligomers and polymers based on pentacene
Both oligomeric and polymeric materials based on pentacene building blocks have been synthesized in order to improve the electronic properties or in order to improve the solid-state packing. Wu and coworkers have reported pentacene dimer 1.26 (Figure 1.10) where the pentacene aromatic skeleton is directly linked in the 13- position.[48] The authors propose a new method for minimizing the macroscopic disorder which is present in the organic layer of a semiconductive device. The new method includes an improved solid-state packing of the parent pentacene. Indeed, pentacene dimer 1.26 shows a zig-zag--stacking along two crystallographic axes, which could potentially facilitate charge transport in an electronic device. Another approach involves connecting pentacene units by acetylenic spacers,[49] to effectively
12 Chapter 1 – Pentacene, a short journey from synthesis to material science alter the HOMO-LUMO gap by elongation of the conjugated electronic system (Figure 1.10). Tykwinski and coworkers have used Hay coupling and Cadiot- Chodkiewicz coupling to build up pentacene oligomers, such as dimer 1.27. Unfortunately, solubility issues are a major drawback of the higher order oligomers. Single crystal analysis of pentacene dimer 1.27 shows a 2-D slipped stack arrangement, which is proposed to provide even 3-D electronic communication in the solid state.
Figure 1.10. Pentacene dimers 1.26 and 1.27.[48,49]
Only a few pentacene-based polymers have been realized since the first report of a polymer based on pentacene units by Tokito[26] in 2001. Since this time, various approaches toward pentacene polymers have been reported, using different synthetic pathways, such as Suzuki cross-coupling or Sonogashira cross-coupling reactions.[26,50,51] Also dendrimers, where the pentacene units are linked via non- conjugated ester moieties, have been synthesized.[52] This thesis does, however, not focus on either pentacene polymers or co-polymers, so the described examples are representative models.
1.4.4 Unsymmetrically substituted pentacene derivatives
In contrast to approaches that have been developed to form symmetrically functionalized pentacenes, unsymmetrical functionalization has also been used to modify the electronic properties of the conjugated pentacene skeleton. Different alkyne substituents have been appended to the reactive 6- and 13-positions (short molecular axis) by Tykwinski and coworkers, creating electronically polarized (donor- acceptor-like) pentacene derivatives 1.281.35 (Figure 1.11).[53] The electronically 13 Chapter 1 – Pentacene, a short journey from synthesis to material science polarized chromophores are air and moisture stable and show good solubility in organic solvents. Alkoxy-groups introduced at the alkyne substituents in 1.28 and 1.29 alter the HOMO-LUMO gaps of the pentacene derivatives, compared to symmetrically substituted analogue 1.7a, which was determined by UV-vis and emission spectroscopy. X-ray crystallographic analysis for compound 1.30 shows, however, that the overall -stacking arrangement does not adopt the optimal 2-D packing motif. Another prominent example of unsymmetrically substituted pentacene derivatives has been achieved by Lehnherr et al. by linking large PAHs and pentacene skeletons via acetylenic spacers (1.361.41, Figure 1.11).[54] This substitution pattern leads to cofacial -stacking interactions between the different aromatic moieties, as well as improved absorption in thin films in the low-energy IR region.
Figure 1.11. Unsymmetrical pentacenes 1.281.35 and pentacene-based PAHs 1.361.41.[53,54]
Another example of an unsymmetrically substituted pentacene is, from Dehaen and coworkers,[55] derivative 1.42, in which different aryl-groups are placed in the 6- and 13-positions of the pentacene core (Figure 1.12). Monosubstituted pentacene compounds such as 1.43 and 1.44 were synthesized by Nuckolls.[56] and Wong,[57] respectively. In 2013, Teki and coworkers reported the first pentacene derivatives appended with stable free radicals which demonstrated increased stability against
14 Chapter 1 – Pentacene, a short journey from synthesis to material science photodegradation.[58] Compounds 1.45 and 1.46 have been obtained from aldehyde precursors in a two-step synthetic approach. These radical species offer an opportunity for magnetic control of hole or electron transport in electronic devices based on pentacene derivatives. Finally, the substitution pattern of compound 1.47 has been shown to afford pentacene derivatives that are stable against photodecomposition through a combination of steric and electronic effects.[59]
Figure 1.12. Examples of unsymmetrically substituted pentacenes.[55,56,57,58,59]
1.5 Summary
Over the last decade, a wide variety of functionalized pentacene derivatives has been synthesized and implemented in semiconductive devices as the active layer specifically in OFETs. Synthetically, the reactive 6- and 13-positions along the short molecular axis of the pentacene backbone are the most promising sites for functionalization to alter the electronic properties. These positions allow for the introduction of a plethora of functionalities by a simple synthetic manner.
One of the most important methods to characterize new pentacene derivatives is by X-ray crystallographic analysis, which allows for a quick and relatively straightforward evaluation of the intermolecular -interactions. This specific information is important for the elaboration of pentacene derivatives in materials for use in
15 Chapter 1 – Pentacene, a short journey from synthesis to material science optoelectronic devices as well as developing a fundamental understanding of structure-property relationships for packing of pentacene derivatives.
1.6 References
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21 Chapter 2 – Unsymmetrically functionalized pentacenes Chapter 2 – Unsymmetrically functionalized pentacenes
2.1 Introduction
Substitution by trialkylsilylethynyl groups in the reactive 6- and 13-positions of the pentacene skeleton established bench-top stable materials.[1] By far the most promising group to date is triisopropylsilylethynyl (TIPS-group) as it provides both stability and solubility to the parent pentacene backbone.[2] Due to the relative bulk of the TIPS-group, the aromatic, linear pentacene molecules crystallizes with significant face-to-face arrangements in the solid state.[3] This face-to-face arrangement is seemingly beneficial for the improvement of optoelectronic devices with pentacene derivatives. Although functionalization of pentacene has been successfully realized,[4] unsymmetrically substitution is in the focus of synthetic chemists only since a few years.[5] The implementation of a TIPS-group in the 6-position of the pentacene skeleton should allow for the control of solubility, stability, and solid-state arrangement, while the 13-position of the pentacene skeleton can then be functionalized with other groups, such as aryl or alkyl groups. This substitution method addresses some questions:
How does this substitution pattern influence the electronic properties?
What is the influence of such groups on stability?
What is the solid-state order of such unsymmetrically functionalized pentacene derivatives?
2.2 Functionalization by click chemistry †
2.2.1 Acenes with a click
Ideally, functionalization of pentacenes should implement cheap starting materials, non-toxic reagents, and mild reaction conditions. The Cu(I)-catalyzed alkyne-azide Huisgen cycloaddition (CuAAC) fulfills these requirements in large part.[6] Unfortunately, a terminal acetylene moiety directly attached to an aromatized
†Portions of this section have been published. Reproduced with permission from: Waterloo, A. R.; Kunakom, S.; Hampel, F.; Tykwinski, R. R Macromol. Chem. Phys. 2012, 213, 1020–1032. Copyright @2012 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim. 22 Chapter 2 – Unsymmetrically functionalized pentacenes pentacene backbone such as in compound 2.1 is not easily applicable for synthetic or post-synthetic elaborations (Figure 2.1).[7] The combined presence of the reactive aromatic core and a terminal acetylene unit leads to decomposition of the pentacene chromophore, most likely to Diels-Alder reactions, forming undefined polymeric products.[8] Although the conversion of 2.2 to 2.1 has been successfully performed in some cases,[9] an alternative synthetic route has to be sought in order to prevent unwanted side reactions. Protected pentacene precursor 2.3 presents an opportunity to use terminal acetylenes in the CuAAC reaction. Compound 2.3 offers an attractive synthetic starting point, as the formation of 2.3 has been developed earlier by Tykwinski and coworkers for the use as a building block for oligomeric pentacene derivatives,[10] and the two ether groups are easily removed in the last synthetic step to yield the pentacene framework.
Figure 2.1. Pentacenes 2.1, 2.2, and precursor 2.3.
The synthesis for precursor 2.3 starts with selective functionalization of 6,13- pentacenequinone 1.2 (Scheme 2.1).[11] A suspension of 1.2 in dry, deoxygenated THF was treated with lithiated TIPS-acetylene at 78 °C to afford mono-addition product 2.4 in good isolated yield after aqueous workup and purification. Notably, when the reaction is performed in THF very little bis-addition product is observed.[11] Thus, ketone 2.4 is further treated with lithiated TMS-acetylene in dry THF and was stirred for 24 h at rt. The reaction is quenched by an excess of MeI to trap the resulting alkoxide. After further 18 h at rt, aqueous workup, and following purification, compound 2.5 is isolated in 90% yield. Selective removal of the TMS-group with KOH in THF (or alternatively with K2CO3) affords terminal acetylene 2.3 in 71% yield.
23 Chapter 2 – Unsymmetrically functionalized pentacenes
Scheme 2.1. Selective functionalization of 1.2 to afford 2.3.
The general synthetic protocol, as envisioned for combining the CuAAC reaction with the pentacene chromophore, has been outlined in Scheme 2.2. It derives from the reaction of 2.3 with an azide partner to provide intermediates 2.6. The formation of triazoles was first explored using Cu(OAc)2 as catalyst. Thus, compound 2.3 and a slight excess of the corresponding azide were dissolved in dry, deoxygenated THF.
After adding a solution of Cu(OAc)2 and sodium ascorbate in H2O as reducing agent, the mixture was stirred for 1214 h at rt. After aqueous workup, the mixture was further purified using a simple method, namely the crude mixture was adsorbed on silica gel and eluted first with CH2Cl2 to remove all by-products and unreactive starting material. Then, the triazole products 2.6 could be eluted from the silica gel plug using EtOAc.
24 Chapter 2 – Unsymmetrically functionalized pentacenes
Scheme 2.2. Derivatization of pentacene precursor 2.3 via CuAAC reaction.
The combined results for the CuAAC reaction of 2.3 with a variety of azide partners have been summarized in Table 2.1. Notably, the CuAAC reaction with Cu(OAc)2 as catalyst gave mixed results in terms of product purity and isolated yields. Therefore,
CuSO4 was also explored as catalyst but gave similar mixed results. Although it seemed that yields deriving from alkyl azides were little higher than the aryl azide analogues, no specific trend in terms of the choice of the catalyst could be determined.
Table 2.1. Synthesis of 1,2,3-triazole containing pentacenes 2.7ah.
Compound R Catalyst 2.6 (%)[a] 2.7 (%)[c]
[b] Cu(OAc)2 46 (>95%) 42 a [b] CuSO4 26 (>95) 21
[b] Cu(OAc)2 76 (>95) 73 b CuSO 90 (90)[b] 78 4
[b] Cu(OAc)2 90 (>95) 73 c [b] CuSO4 72 (85) 48
[b] Cu(OAc)2 58 (90) 40 d [d] CuSO4 43
25 Chapter 2 – Unsymmetrically functionalized pentacenes
Compound R Catalyst 2.6 (%)[a] 2.7 (%)[c]
[d] Cu(OAc)2 15 e [d] CuSO4 15
[d] Cu(OAc)2 34 f [e] CuSO4 34
g CuSO [e] 55 4
[e] h CuSO4 35
[a] isolated yield. [b] Purity estimated by 1H NMR spectroscopy. [c] Yield over two steps from 2.3. [d] Product isolated with purity <85%, no yields detected. [e] Product carried on directly to aromatization.
Following the general procedure as described in Scheme 2.2, the pentacene precursors 2.6af were subjected to reductive aromatization in THF using a slight
excess of SnCl2 2H2O under acidic conditions. The resulting deep blue mixtures were stirred for 46 h at rt under the absence of light. In many cases, the resulting pentacene derivatives 2.7 could be isolated by simply filtering the mixture through a short pad of silica gel (e.g., 2.7af). When necessary, further purification was achieved by column chromatography or recrystallization (e.g., 2.7g and2.7h). Notably, the yields over two steps vary from good to moderate, only with the exception of 2.7e and 2.7f. Compound 2.7e was isolated in 15% yield over two steps, and 2.7f was isolated in 34% yield over two steps, regardless which catalyst was used.
As this synthetic study proceeded, however, it became clear that purification of pentacene derivatives 2.7 could be achieved after the aromatization step, thus, 2.7g and2.7h were synthetically realized without the isolation of the intermediates 2.6gand2.6h. This procedure greatly simplified the synthetic elaboration of pentacenes via the CuAAC reaction. It is worth to notice, that all isolated pentacenes 2.7ah were bench-top stable materials in the solid state and could be stored over
26 Chapter 2 – Unsymmetrically functionalized pentacenes months under ambient laboratory conditions without showing any decomposition.
Compounds 2.7ah were soluble in common organic solvents such as CH2Cl2,
CHCl3, toluene, and THF.
Besides the optimization of the purification process, it was possible to isolate some of the intermediates of the CuAAC reaction with precursor 2.3 in analytically purity by recrystallization from n-pentane (2.6ac), and a curious outcome was observed during the analysis of the 1,2,3-triazole containing intermediates 2.6a and 2.6b, using 1 either Cu(OAc)2 or CuSO4 as a catalyst. Analysis by H NMR spectroscopy suggested partial or complete transformation of one of the OMe-groups in an OH- group during the CuAAC reaction. While it was difficult to assign which of the methyl groups was affected, based on NMR spectra, X-ray crystallographic analysis for 2.6a and 2.6b provided a conclusive answer, that is, loss of one of the methyl groups appears to occur at the propargylic alcohol moiety (Figure 2.2). Notably, in any case where the intermediate could be isolated (2.6ad) such a transformation was observed by NMR spectroscopy. However, a detailed understanding of the mechanistic details of this transformation has not been investigated during the scope of this thesis.
(a) (b)
Figure 2.2. X-ray crystallographic analysis showing molecular structures of (a) 2.6a, (b) 2.6b. Solvent molecules and hydrogen atoms are omitted for clarity (ORTEPs drawn at 50% probability level).
The synthetic route developed for triazole-containing pentacene derivatives allows for the formation of larger, oligomeric pentacene systems,[12] using azides 2.82.10 (Scheme 2.3). Hence, a slight excess of precursor 2.3 along with the corresponding azide partner 2.8, 2.9, or 2.10[13] was dissolved in dry THF. To this solution was
added CuSO4 5H2O and sodium ascorbate, both dissolved in H2O. The resulting homogenous mixture was stirred for 24 h at rt. After aqueous workup and removal of 27 Chapter 2 – Unsymmetrically functionalized pentacenes unreactive 2.3 and by-products by passing the crude residue through a pad of silica
gel, the mixture was subjected to reductive aromatization using SnCl2 2H2O and diluted H2SO4. Purification was accomplished by recrystallization (2.11), by passing the crude mixture through a small pad of silica gel (2.12), or by column chromatography (2.13) at the stage of the final pentacene oligomers. Compounds 2.112.13 were isolated in reasonable yields (1537%) considering the complexity of the synthesized pentacene oligomers.
Scheme 2.3. Syntheses of pentacene oligomers 2.112.13; Reagents and
conditions: a) CuSO4 5H2O, Na-ascorbate, THF/H2O (1:1), 24 h, rt; b) SnCl2 2H2O, aq. H2SO4, THF, 6 h, rt. 28 Chapter 2 – Unsymmetrically functionalized pentacenes
Although the oligomeric intermediates of the CuAAC reaction of 2.3 with azides 2.8, 2.9, or 2.10 were not isolated, in one case single crystals suitable for X-ray crystallographic analysis of an intermediate could be obtained. The crude product of the CuAAC reaction of 2.3 with azide 2.8 was crystallized, and interestingly, X-ray analysis shows clearly that all OMe-groups remained intact for this sample (Figure 2.3). Unfortunately, NMR spectra of the crude mixture were not measured. Therefore, a more detailed discussion about the intact OMe-groups has not been possible.
Figure 2.3. Molecular structure of precursor of 2.11. Solvent molecules and hydrogen atoms are omitted for clarity (ORTEPs drawn at 50% probability level).
2.2.2 Electronic properties of 1,2,3-triazole containing pentacenes
The electronic absorption characteristics of 1,2,3-triazole containing pentacene derivatives 2.7ah have been examined by UV-vis spectroscopy in CH2Cl2 solutions. Two representative examples are shown in Figure 2.4, containing either an alkyl (2.7a) or an aryl (2.7e) substituent.
29 Chapter 2 – Unsymmetrically functionalized pentacenes
Figure 2.4. UVvis spectra of pentacene derivatives 2.7a and 2.7e, as measured in
CH2Cl2.
The synthesized pentacene derivatives 2.7ah show characteristic absorption bands at ca. 310 nm and a weak band at ca. 350 nm. In the lower energy region, three absorption maxima with a characteristic band structure are observed at 535, 574, and 621 nm. Conclusively, the triazole substituent is seemingly inefficient in mediating electronic coupling between pentacene fragments.[4,14]
There is little variance observed in the absorption maxima for pentacene dimers 2.112.13 compared to pentacene monomers 2.7ah (2 nm) (Figure 2.5). This effect is attributed to a lack of electronic conjugation between the pentacene 3 fragment, the triazole substituent, and the sp -hybridized benzyl group. The max values of compounds 2.7ah and oligomers 2.112.13 are blue shifted compared to [11] symmetrical analogue TIPS-Pc (1.7a; max = 643 nm measured in CH2Cl2), but strongly red shifted compared to unsubstituted pentacene (max = 576 nm measured in benzene).[4a,15] Finally, as it can be seen in Figure 2.5, the molar extinction coefficient steadily increases from 2.7a to 2.13 due to the increasing number of pentacene chromophores.
30 Chapter 2 – Unsymmetrically functionalized pentacenes
Figure 2.5. UVvis spectra of pentacene derivatives 2.7a, 2.11, and 2.13, as measured in CH2Cl2.
2.2.3 Solid-state analysis of 2.7a and 2.7e
X-ray crystallographic analysis has been accomplished for two derivatives, namely benzyl substituted chromophore 2.7a and phenyl substituted chromophore 2.7e.
Compound 2.7a crystallizes in the space group P21/c with four molecules in the unit cell. The triazole substituent is twisted by an angle of 61° relative to the pentacene backbone (Figure 2.6). Pentacene 2.7a crystallizes as centrosymmetric pair of molecules centered about the triazole moieties. This motif places the triazole moieties in a face-to-face arrangement with an interplanar distance of about 3.13 Å.[16] The packing motif can be regarded as 1-D slipped packing of neighboring pentacene units with an interplanar distance of 3.45 Å[17] and approximately two of the aromatic pentacene rings overlapping.
31 Chapter 2 – Unsymmetrically functionalized pentacenes
(a) (b)
(c)
Figure 2.6. X-ray crystallographic analysis showing (a) molecular structure of 2.7a, and (b) illustration of the overlapping aromatic rings, and (c) packing motif (triisopropylsilyl group, benzyl group, and hydrogen atoms omitted for clarity); ORTEPs drawn at 50% probability level.
Pentacene 2.7e crystallizes in the space group P1 with two molecules in the unit cell. The triazole substituent and the phenyl moiety are nearly coplanar, showing only a slight twist of ca. 9°, while the triazole unit and the pentacene backbone are arranged with a twisting angle of ca. 68°, such as similarly observed for the case of 2.7a (Figure 2.7). In contrast to the packing of 2.7a, phenyl substituted derivative 2.7e packs in a 1-D slipped stacking arrangement in which the pentacene chromophores show two different interplanar distances of 3.38 Å and 3.44 Å.[17] Neighboring pentacene chromophores show an overlap of approximately four
32 Chapter 2 – Unsymmetrically functionalized pentacenes aromatic rings. Additionally, the co-crystallized CDCl3 molecules do not allow for - interactions between the triazole moieties.
(a) (b)
(c)
Figure 2.7. X-ray crystallographic analysis showing (a) molecular structure of 2.7e, and (b) packing motif (solvent molecules, triisopropylsilyl group, phenyl group, and hydrogen atoms omitted for clarity, ORTEPs drawn at 50% probability level).
2.2.4 Synthetic limits of the CuAAC reaction
Water-soluble organic molecules consisting of large -systems are of interest, because of their aggregation behavior in polar media.[18] Hence, it was anticipated that azide containing amino acid 2.14, after removal of the protecting Boc-group, could facilitate the solubility of the pentacene backbone in more polar solvents such as MeOH or even H2O via attachment by the CuAAC reaction (Scheme 2.4). Thus, azide 2.14 was treated together with precursor 2.3 under the developed CuAAC
33 Chapter 2 – Unsymmetrically functionalized pentacenes reaction conditions using CuSO4 as the catalyst. Without the isolation of the intermediate, reductive aromatization with SnCl2/H2SO4 in THF formed a deep blue solution as it is typically observed for aromatized pentacene derivatives. The desired compound 2.15 could not be isolated, however, due to decomposition during aqueous workup. Unfortunately, it was not possible to isolate and characterize any decomposition product.
Scheme 2.4. Attempted synthesis of amino acid containing pentacene derivative
2.15 via CuAAC reaction. Reagents and conditions: a) CuSO4 5H2O, Na-ascorbate,
THF/H2O (1:1), 14 h, rt; b) SnCl2 2H2O, aq. H2SO4, THF, 6 h, rt.
2.2.5 Pentacene-porphyrin assemblies
Metal-pyridine complexation has been extensively used in coordination chemistry[19] especially in the formation of porphyrin-containing architectures.[20] Axial complexation of pyridyl moieties to metalloporphyrin centers can lead to supramolecular assemblies such as cages,[21] polymers,[22] or tweezers.[23] It was anticipated that a combination of pyridyl containing pentacene derivatives 2.7gand2.7h and a metalloporphyrin could lead to pentacene-porphyrin dyads with potentially interesting electronic and/or optical properties.[24] Thus, compound 2.7g or2.7h was dissolved in benzene along with a stoichiometric amount of Ru(II)- porphyrin 2.16 (Scheme 2.5).[25] The solution was slightly heated to 50 °C for 3 h. After removal of the solvent and purification by precipitation from n-hexanes, pentacene-porphyrin dyads 2.17 and 2.18 were obtained in good yields (67% and 74%, respectively).
34 Chapter 2 – Unsymmetrically functionalized pentacenes
Scheme 2.5. Synthesis of pentacene-porphyrin dyads 2.17 and 2.18.
IR spectroscopic analysis of 2.17 suggests that the desired supramolecular assembly has formed, which can be attributed to the shift of the CO vibrational band from 1943 cm 1 (for 2.16) to 1966 cm 1 (for 2.17), as can be seen in Figure 2.8.
35 Chapter 2 – Unsymmetrically functionalized pentacenes
Figure 2.8. Shift of CO vibration of 2.16 compared to 2.17.
1H NMR spectroscopy was finally used to provide the evidence of formation for the pentacene-porphyrin dyad 2.17. In the 1H NMR spectrum of compound 2.7h, the pyridyl protons give rise to signals at 8.84 and 7.91 ppm.[26] The triazole proton resonates at 8.48 ppm (Figure 2.9, top). Upon coordination to Ru(II)-porphyrin 2.16 the pyridyl signals of 2.17 shift drastically toward 1.86 and 4.72 ppm, while that of the triazole shifts to 6.30 ppm. This is due to the diamagnetic anisotropy of the porphyrin ring, and is especially drastic for the ortho-protons of the pyridin ring.[20] Similar shifts in resonances have been observed for the pyridyl protons of pentacene-porphyrin complex 2.18 (Figure 2.10). The ortho-pyridyl protons of 2.7g give rise to signals at 9.29 ppm and 8.81 ppm and are shifted in the case of 2.18 to 2.42 ppm and 1.95 ppm, respectively. Furthermore, the meta-proton in 2.7g resonates at 7.63 ppm and the para-proton at 8.43 ppm. These signals are also shifted in the case of compound 2.18 to 4.30 ppm (for the meta-proton) and 5.62 ppm (for the ortho-proton). The triazole proton is shifted upfield from 8.46 ppm in the case of 2.7h to 6.80 ppm in the case of complex 2.18. Unfortunately, the synthesized pentacene-porphyrin dyads are relatively unstable in solution and therefore 13C NMR spectroscopic analysis has not been possible to perform.
36 Chapter 2 – Unsymmetrically functionalized pentacenes
1 1 Figure 2.9. H NMR spectrum (300 MHz, CDCl3) of pentacene 2.7h (top). H NMR spectrum (300 MHz, C6D6) of 2.17 (bottom). In both cases, the resonances assigned to the pyridyl and triazolyl protons are highlighted. + = silicon grease; * = hexanes.
37 Chapter 2 – Unsymmetrically functionalized pentacenes
1 1 Figure 2.10. H NMR spectrum (400 MHz, CDCl3) of pentacene 2.7g (top). H NMR spectrum (300 MHz, C6D6) of 2.18 (bottom). In both cases, the resonances assigned to the pyridyl and triazolyl protons are highlighted.
38 Chapter 2 – Unsymmetrically functionalized pentacenes
Solution-state UV-vis analysis gives, to some extent, rise to the electronic properties of the synthesized pentacene-porphyrin assembly and was investigated for 2.18 (Figure 2.11). Pentacene 2.7h, in comparison, shows a strong absorption at 308 nm along with a weak absorption band at 348 nm. In the low energy region, absorption bands at 574 nm and 621 nm are present. Pentacene-porphyrin dyad 2.18 shows a strong and a weak absorption centered at 309 nm and 346 nm. The porphyrinic Soret-band at 415 nm is characteristically observed. The low energy region shows three absorption maxima centered at 533, 571, and 622 nm. Ultimately, the UV-vis spectrum of 2.18 demonstrates that there is no significant change in electronic properties of pentacene-porphyrin dyad 2.18 compared to pentacene 2.7h. The electronic communication between the porphyrin and the pentacene chromophore is limited and thus the UV-vis absorption spectrum of 2.18 can be regarded as a summation of pentacene and porphyrin absorptions.
39 Chapter 2 – Unsymmetrically functionalized pentacenes
Figure 2.11. UV-vis spectra of 2.7g (top) and of 2.18 (bottom), as measured in
CH2Cl2.
2.3 Aryl substitution of pentacenes ‡
2.3.1 Functionalization by nucleophilic addition
Previous work on unsymmetrically substituted pentacene derivatives has shown promising solid-state arrangements and interesting electronic properties.[7] If the pentacene skeleton is linked by an acetylenic spacer to other PAH moieties, the - ‡ Portions of this section have been published, see: Waterloo, A. R.; Sale, A.-C.; Lehnherr, D.; Hampel, F.; Tykwinski, R. R. Beilstein J. Org. Chem., 2014, 10, 16921705. 40 Chapter 2 – Unsymmetrically functionalized pentacenes systems can arrange in a coplanar fashion, which can help to maximize the intermolecular overlap of the aromatic systems in the solid state. Hence, as can be seen in Figure 2.12, the anthracene substituent of 1.41 packs between two pentacene units and vice versa in a 1-D slipped stacking arrangement.[7] Thus, this solid-state arrangement is anticipated to be beneficial for the use in electronic devices, although this hypothesis has not yet been thoroughly tested.
(a) (b)
Figure 2.12. Example of pentacene-based PAH 1.41 showing (a) molecular structure and (b) packing in the solid state; hydrogen atoms omitted for clarity (ORTEPs drawn at 50% probability level, X-ray data from ref. [7], CCDC 736052).
To provide an opportunity to explore the effect of a substitution pattern based on a direct linkage between the PAH moieties and a pentacene chromophore, a general synthetic route has been targeted to give easy access to unsymmetrically substituted pentacenes 2.21aj, shown in Scheme 2.6. A starting point for the envisioned synthetic pathway is either ketone 2.4 or 2.22.[11,27] Commercially available aryl halides[28] dissolved in dry, deoxygenated 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 lithium-halogen exchange and thus avoid the possibility of competitive addition of the nucleophilic butyl anion to the ketone group. After adding the corresponding ketone 2.4 or 2.22 and reaction with the appropriate aryl lithium species, the reaction was quenched with a proton source, resulting in a crude residue containing diol intermediates 2.23ai. Previous work (Section 2.2) has shown that aromatized products were more easily purified following the last step, and, hence, it was deemed procedurally more efficient to eliminate the intermediate purification step for diols 2.23ai. Thus, once formed the diols 2.23ai were carried on directly to reductive aromatization with 41 Chapter 2 – Unsymmetrically functionalized pentacenes
SnCl2/H2SO4 without further purification, ultimately yielding pentacene products 2.21ai. Pentacenes 2.21ai were obtained in moderate yield over two steps as deep-blue solids.
To expand the system in a linear fashion along the short molecular axis of the pentacene core, the general synthetic procedure described above was changed slightly, and ketone 2.4 was treated with a solution of, commercially available, biphenyl-magnesiumbromide in dry, deoxygenated THF. After workup and isolation of the crude intermediate diol 2.23j, reductive aromatization gave pentacene 2.21j in moderate yield over the two steps.
Scheme 2.6. Synthesis of unsymmetrical pentacenes 2.21aj by nucleophilic addition.
42 Chapter 2 – Unsymmetrically functionalized pentacenes
2.3.2 Functionalization by Suzuki reaction
The general idea of elongation of the pentacene backbone along the short molecular axis could be further elaborated by using a Pd-catalyzed cross-coupling reaction with pentacene 2.21g, as it is shown in Scheme 2.7. Hence, iodo-aryl bearing pentacene 2.21g was treated under Suzuki-Miyaura coupling conditions with two different arylboronic acids,[29] and the desired pentacenes 2.21k–l were obtained in yields of 92 and 68%, respectively. Notably, anthracenyl substituted pentacene 2.21l was the least stable of all derivatives examined in this study. Compound 2.21l slowly decomposed in solution when exposed to ambient laboratory conditions and was unstable toward silica gel chromatography. Compound 2.21l, however, could be purified by recrystallization from a mixture of MeOH and acetone and is nevertheless stable as a solid under ambient conditions for months.
Scheme 2.7. Functionalization of iodoaryl pentacene 2.21g using the Suzuki cross- coupling reaction.
2.3.3 Electronic properties of aryl-substituted pentacenes
The solution state absorption characteristics of aryl-substituted pentacenes 2.21al have been examined by UV-vis spectroscopy in CH2Cl2. Two representative series are shown in Figure 2.13.
43 Chapter 2 – Unsymmetrically functionalized pentacenes
Figure 2.13. UV–vis spectra of pentacenes 2.21ac (top) and 2.21jl (bottom), as –5 measured in CH2Cl2 (~10 M).
Pentacenes 2.21al show characteristic absorptions centered at ca. 310 nm. In the lower energy region, absorption maxima are located at ca. 578 nm and ca. 622 nm. In comparison, unsubstituted pentacene (1.1) shows an absorption maximum 44 Chapter 2 – Unsymmetrically functionalized pentacenes
[15] centered at max = 576 nm (measured in benzene), while symmetrically substituted
TIPS-Pc (1.7a) shows max located at ca. 643 nm in CH2Cl2, due to more efficient electronic conjugation through two alkyne substituents.[4] Pentacene-based PAH 1.41
(Figure 2.12) shows an absorption maximum of max = 671 nm, which can be attributed to the larger, planar conjugated electron system.[7] As shown in Figure 2.13, the nature and the size of the aryl substituent does not substantially alter the electronic properties of the pentacene chromophores. This trend is demonstrated, for example, in the case of 2.21c, where two strictly separated absorption maxima at
max = 256 nm and max = 310 nm represent the electronically decoupled anthracene and pentacene -systems, respectively. A similar trend is observed within the series of pentacenes 2.21i, 2.21j, and 2.21l and the UVvis spectra clearly document lack of communication between the aryl substituent and the pentacene unit, as a result of hindered rotation about the aryl-pentacene C–C bond and a preferred conformation in which the -system of the aryl group is orthogonal to that of the pentacene.
The electronic absorption characteristics found in solution are also reproduced to a large extent in spectra obtained from solid-state films. Samples of 2.21al were drop casted from a concentrated CH2Cl2 solution onto a quartz surface, and after air- drying, the absorption spectra were measured by UV–vis spectroscopy. As can be seen in Figure 2.14 and Table 2.2, absorptions of thin films in the lower energy region show a red shift (7 to 33 nm) in comparison to analogous absorptions in solution.
45 Chapter 2 – Unsymmetrically functionalized pentacenes
Figure 2.14. Thin film UV–vis spectra of pentacenes 2.21ac (top) and 2.21jl
(bottom, measured on quartz, drop cast from CH2Cl2 solution).
46 Chapter 2 – Unsymmetrically functionalized pentacenes
Table 2.2. Optical properties of pentacenes 2.21al, unsubstituted pentacene (1.1), TIPS-Pc (1.7a), and pentacene-based PAH (1.41).
[b] red shift max (in max (film) [c] Compound Egap, opt[eV] [a] CH2Cl2) [nm] [nm] [nm]
2.21a 621 637 16 1.89
2.21b 621 635 14 1.91
2.21c 623 632 9 1.92
2.21d 623 637 14 1.91
2.21e 621 634 13 1.89
2.21f 622 655 33 1.87
2.21g 621 628 7 1.90
2.21h 622 638 14 1.92
2.21i 623 635 12 1.91
2.21j 623 641 18 1.88
2.21k 623 633 10 1.88
2.21l 623 635 12 1.89
1.1 576[d] 673[e] 97 2.15
1.7a 643[f] 705[g] 62 1.84[f]
47 Chapter 2 – Unsymmetrically functionalized pentacenes
[b] red shift max (in max (film) [c] Compound Egap, opt[eV] [a] CH2Cl2) [nm] [nm] [nm]
1.41 671[h] 712[h] 41 1.74[h]
[a] Lowest energy absorption maxima. [b] Cast from CH2Cl2 onto quartz. [c] Determined using the intercept of the x-axis and the tangent applied to the longest wavelength absorption peak. [d] Measured in benzene and taken from Ref [15]. [e] Data taken from Ref [30a]. [f] Data taken from Ref [4a]. [g] Data taken from Ref [11]. [h] Data taken from Ref [7].
The red shifted max in the solid state is often ascribed to local electronic interactions between the respective pentacene molecules in the solid state. Of the aryl pentacenes studied here, veratrole derivative 2.21f shows the largest red shift (33 nm) as a film compared to solution-state UV–vis spectroscopy, although the origin of change in the solid state is not understood. It is worth noting, however, that more significant red-shifted max-values are often observed for samples which give good films from solution with significant -stacking between molecules, such as for example TIPS-Pc (1.7a), in which max shifts from 643 nm in solution to ca. 705 nm in the solid-state film.[4,11] The same effect is observed for pentacene 1.41, where the [7] max value shifts to 712 nm in thin films. This logic also suggests that the minimal difference between the absorption characteristics of 2.21c and 2.21h results from both a lack of influence from the different silyl groups, as well as the absence of strong -stacking for both derivatives in the solid films.
Electrochemical analysis by cyclic voltammetry (CV) was used to investigate the electronic properties of pentacenes 2.21al in CH2Cl2 (ca. 1.5 mM) using tetrabutylammonium hexafluorophosphate as supporting electrolyte and ferrocene as internal standard.[31] Pentacenes 2.21al each show one reversible oxidation event in the range between 0.30–0.37 V, and a second quasi-reversible oxidation process in the range of 0.800.99 V. There is only little dependence observed for the oxidation potentials based on the substitution pattern of the aryl moieties, although both oxidations appear somewhat easier for pentacene 2.21f as a result of the two electron donating methoxy groups attached to the pendent phenyl ring. Pentacenes 2.21al 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 dependence that can be identified in the reduction potentials based on substitution 48 Chapter 2 – Unsymmetrically functionalized pentacenes pattern, aside from the observation that the silyl substituent might have a slight impact on reduction (2.21h is slightly harder to reduce than 2.21c), and the reduction of thienyl derivative 2.21d (–1.59 V) stands out as lower than the others. Pentacenes
2.21al are slightly easier to oxidize compared to TIPS-Pc 1.7a (Eox1 = 0.39 V), and oxidation of 2.21a–l is comparable to the pentacene-based PAH dyad 1.41. The range of oxidation potentials between 1.7a, 1.41, and 2.21al 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. Compound 1.41 is most easily reduced while 2.21al are the most difficult, and the reduction of 1.7a falls at approximately a midpoint between the two other classes. Thus, the biggest influence of the substituents in the 6,13-positions appears to be related to the energy of the LUMO. The HOMO–LUMO gap estimated for pentacenes 2.21al by CV (1.94–2.02 eV) is larger than the HOMO–LUMO gap of 1.7a (1.91 eV), while incorporation of ethynyl spacer in 1.41 provides for the lowest HOMO–LUMO gap (1.71 eV) of the molecules discussed here. The results from CV analysis suggest similar trends to that outlined by UV-vis analysis.
Table 2.3. Electrochemical properties of 2.21al compared to 1.7a and 1.41.[a]
E E E E [b] Compound R ox1[V] ox2[V] red1[V] gap,el [eV]
2.21a i-Pr 0.34 0.87 –1.63 1.97
2.21b i-Pr 0.37 0.99 –1.61 1.98
2.21c i-Pr 0.36 0.93 –1.65 2.01
2.21h Et 0.32 0.91 –1.68 2.00
49 Chapter 2 – Unsymmetrically functionalized pentacenes
E E E E [b] Compound R ox1[V] ox2[V] red1[V] gap,el [eV]
2.21d i-Pr 0.35 0.87 –1.59 1.94
2.21e i-Pr 0.32 0.87 –1.68 2.00
2.21f i-Pr 0.30 0.80 –1.67 1.97
2.21g i-Pr 0.34 0.87 –1.65 1.99
2.21j i-Pr 0.32 0.87 –1.66 1.98
2.21k i-Pr 0.32 0.93 –1.67 1.99
2.21l i-Pr 0.35 0.88 –1.67 2.02
1.7a i-Pr 0.39 0.99 –1.52 1.91
1.41[c] i-Pr 0.33 – 1.38 1.71
[a] Cyclic voltammetry was performed in CH2Cl2 solutions (1.5 mM) containing 0.1 M n-Bu4NPF6 as supporting electrolyte at a scan rate of 150 mV/s. Pt wire was used as counter electrode, Ag/AgNO3 as reference electrode, and Pt working electrode. The potential values (E) were calculated using the following equation E = (Epc + Epa)/2, where Epc and Epa correspond to the cathodic and anodic peak
50 Chapter 2 – Unsymmetrically functionalized pentacenes potentials, respectively. Potentials are referenced to the ferrocenium/ferrocene (Fc/Fc+) couple used as an internal standard. All potentials represent a reversible one-electron reduction or oxidation event.
[b] Electrochemical HOMO-LUMO gaps determined by Egap,el = Eox1 – Ered1. [c] Data taken from ref [7].
2.3.4 Thermal analysis of aryl-substituted pentacenes
The thermal stability of selected aryl pentacenes has been explored by traditional melting point analysis (MPA) in open capillary tubes, thermal gravimetric analysis (TGA), and differential scanning calorimetry (DSC) measurements; the results are summarized in Table 2.4. TGA shows clearly that significant mass loss occurs in the range of 400 °C, which is also common for ethynylated pentacenes such as 1.7a and 1.41.[7,10] There appears to be little evidence of a trend based on the size of the aryl group versus the temperature of observed mass loss in the TGA. By comparing the TGA data with that of MPA made in open capillary tubes, however, it is clear that all pentacene derivatives undergo either a phase change or decomposition prior to the mass loss observed in the TGA. This premise is also confirmed by DSC analyses, which show a melting point in all cases except for thienyl derivative 2.21d (which decomposed directly in the solid state). In the case of 2.21a and 2.21h, melting is followed immediately by decomposition. While no correlation between pendent substitution and stability emerges from this analysis, an important point is nevertheless noted, as exemplified by the examination of 2.21c and 2.21d. Traditional MPA is often insufficient for characterization of pentacene derivatives, in which subtle changes in the samples can be difficult to discern due to the deep, dark color of the sample, and conflicting results are often observed for MPA versus more analytical techniques such as DSC.
Table 2.4. Thermal properties of a representative selection of pentacenes.
DSC mp TGA Td MPA d Compound (DSC p) /°C [a] mp /°C [b] /°C [c]
177 2.21a 370 162–165 (178/179)
51 Chapter 2 – Unsymmetrically functionalized pentacenes
DSC mp
TGA Td MPA d Compound (DSC p) /°C [a] mp /°C [b] /°C [c]
2.21b 370 244–246 248
2.21c 375 306–308[d] 197[e]
-- 2.21d 372 316–318[d]
(206/247)
287 2.21h 410 291–293 (288/290)
2.21j 380 211–214 225
2.21k 380 233–235 220[f]
[a] Measured under a nitrogen atmosphere. Td = decomposition temperature [b] Traditional open capillary melting point analysis (MPA), measured under ambient conditions, uncorrected. [c] Measured under a nitrogen atmosphere, dp = decomposition point, shown as onset/peak temperatures. [d] Decomposition observed in that temperature range, with no indication of melting or decomposition at lower temperature. [e] Endotherm, although apparently not a true mp based on traditional mp analysis. [f] The strongest of several endotherms.
2.3.5 Solid-state analysis of aryl-substituted pentacenes
The solid-state arrangements of pentacene derivatives provide beneficial understanding of intermolecular interactions, thus single crystals of aryl-substituted pentacenes 2.21ad and 2.21gk have been grown and their structural features determined by X-ray crystallographic analysis. Pentacene 2.21a crystallizes in the
52 Chapter 2 – Unsymmetrically functionalized pentacenes space group C2/c with eight molecules in the unit cell. The phenyl ring is twisted towards the pentacene chromophore, showing a torsion angle of ca. 71° (Figure 2.15). Pentacene 2.21a arranges as dimeric pair of molecules, with a packing referred to as sandwich herringbone motif.[32] Each dimeric pair packs within a distance of ca. 3.40 Å[17] and a total overlap of approximately four of the pentacene rings.
(a) (b)
(c)
Figure 2.15. X-ray crystallographic analysis of 2.21a, showing (a) molecular structure, (b) illustration of the overlapping aromatic rings, and (c) packing motif (triisopropylsilyl group omitted for clarity); hydrogen atoms omitted, ORTEPs drawn at 50% probability level.
Pentacene 2.21b crystallizes in the space group P1 with two molecules in the unit cell. The naphthyl unit is twisted relative to the pentacene backbone with an angle of ca. 81° and is disordered over two unique positions (Figure 2.16). Pentacene 2.21b shows 1-D slipped packing with two different -stacking distances of ca. 3.42 Å and 3.51 Å.[17] Within one row of packed pentacene molecules the chromophores overlap with nearly three of the aromatic rings. Additionally, every second naphthyl unit of a 53 Chapter 2 – Unsymmetrically functionalized pentacenes row of pentacene molecules interacts with two neighboring pentacene skeletons via CH...-interactions with distances of ca. 2.84 Å[33] and ca. 2.70 Å.[34]
(a) (b)
(c)
Figure 2.16. X-ray crystallographic analysis of 2.21b showing (a) molecular structure, (b) illustration of the overlapping aromatic rings, and (c) packing motif (triisopropylsilyl group omitted for clarity); hydrogen atoms omitted, disorder in naphthyl group not shown, ORTEPs drawn at 50% probability level.
Compound 2.21c crystallizes in the space group P21/c with four molecules in the unit cell. The pentacene backbone and the anthracenyl substituent are placed nearly perpendicular to each other, showing a twist angle of ca. 90° (Figure 2.17). This motif also places the anthracene moieties in a face-to-face packing 1-D slipped stack arrangement, although the interplanar distance of ca. 3.61 Å is sizable.[35] The aromatic pentacene cores pack in a 2-Dbricklayer arrangement, with approximately two pentacene rings overlapping and with interplanar distances of ca. 3.52 Å and 3.46 Å, respectively.[17]
54 Chapter 2 – Unsymmetrically functionalized pentacenes
(a) (b)
(c)
Figure 2.17. X-ray crystallographic analysis of 2.21c showing (a) molecular structure, (b) illustration of the overlapping aromatic rings, and (c) packing motif (triisopropylsilyl group omitted for clarity); hydrogen atoms omitted, ORTEPs drawn at 50% probability level.
Pentacene 2.21d crystallizes in the space group P21/n with four molecules in the unit cell. The TIPS-group and the thiophene unit are disordered within the molecular structure. With a twist angle of ca. 90°, the thienyl unit is essentially perpendicular to the pentacene skeleton (Figure 2.18). Centrosymmetric dimeric pairs of pentacene 2.21d pack with an interplanar distance of 3.52 Å[17] and these pairs then arrange into a sandwich herringbone stacking pattern, similar to compound 2.21a. Within one pair of pentacenes, the molecules overlap with nearly three of the aromatic rings. Additionally, one TIPS-group of a neighboring pentacene molecule is placed via CH…-interactions above a neighboring pentacene at a distance of ca. 2.89 Å.[36]
55 Chapter 2 – Unsymmetrically functionalized pentacenes
(a) (b)
(c)
Figure 2.18. X-ray crystallographic analysis of 2.21d showing (a) molecular structure, (b) illustration of the overlapping aromatic rings, and (c) packing motif (triisopropylsilyl group omitted for clarity); hydrogen atoms omitted, disorder in the thiophene unit not shown, ORTEPs drawn at 50% probability level.
Pentacene 2.21g crystallizes in the space group P21/n with four molecules in the unit cell. The phenyl moiety is twisted with an angle of ca. 70° relative to the pentacene group (Figure 2.19). Two neighboring molecules of 2.21g arrange into a dimeric pair with an interplanar distance of 3.42 Å,[17] and these pairs then pack in a sandwich herringbone arrangement with overlap of three of the aromatic pentacene rings. Additionally, a neighboring pentacene molecule places a TIPS-group via CH…- interactions above a neighboring pentacene group at a distance of 2.90 Å.[37]
56 Chapter 2 – Unsymmetrically functionalized pentacenes
(a) (b)
(c)
Figure 2.19. X-ray crystallographic analysis of 2.21g showing (a) molecular structure, (b) illustration of the overlapping aromatic rings, and (c) packing motif (some triisopropylsilyl groups omitted for clarity); hydrogen atoms omitted, ORTEPs drawn at 50% probability level.
Pentacene 2.21h crystallizes in the space group P21/c with four molecules in the unit cell. The anthracenyl substituent is twisted relative to the pentacene skeleton with an angle of ca. 74° (Figure 2.20), less than that found for 2.21c (90°). Interestingly, pentacene 2.21h shows an unusual solid-state arrangement not typically observed for pentacene derivatives. Namely, the pentacene molecules form channels along the crystallographic a-axis, which are composed of only two tiers of a brick wall structure. The pentacene molecules within these channels are stacked with an interplanar distance of 3.57 Å,[17] showing an overlap of approximately two of the pentacene rings. The mentioned channels are macroscopically arranged as staircases, dictated 57 Chapter 2 – Unsymmetrically functionalized pentacenes
by the anthracenyl moieties that are oriented such that CH interactions of ca. 2.90 Å[38] between two neighboring anthracene units may play a role in directing the packing.
(a) (b)
(c)
(d) (e)
Figure 2.20. X-ray crystallographic analysis of 2.21h showing (a) molecular structure, (b) illustration of the overlapping aromatic rings, and (c) packing motif (triethylsilyl 58 Chapter 2 – Unsymmetrically functionalized pentacenes groups omitted for clarity), (d) CH...interactions of anthracene units, and (e) observed staircase organization; hydrogen atoms omitted, ORTEPs drawn at 50% probability level.
Pentacene 2.21i crystallizes in the space group P1 with two molecules in the unit cell. The anthracenyl substituent is twisted relative to the pentacene skeleton in a nearly perpendicular fashion (ca. 89°) (Figure 2.21). One pentacene group is placed in an edge-to-face fashion towards a neighboring anthracene unit showing
CH interactions with distances of ca. 2.77 Å.[39] This solid-state arrangement creates a packing motif in which two pentacene units alternately pack between one anthracene unit, resulting in a 1-D staircase arrangement. Furthermore, one anthracene unit interacts with another overlying pentacene framework via
CH interactions with a shortened distance of ca. 2.73 Å.[40] This arrangement is most likely responsible for that fact that no significant -stacking between pentacene units is observed, i.e. only distances of ca. 3.85 Å[17] between neighboring pentacene groups are found.
(a)
(b)
59 Chapter 2 – Unsymmetrically functionalized pentacenes
(c) (d)
Figure 2.21. X-ray crystallographic analysis of 2.21i showing (a) molecular structure, (b) topview of packing motif, and (c) front view of packing motif (triisopropylsilyl groups omitted for clarity), and (d) schematic representation of packing motif; hydrogen atoms omitted, ORTEPs drawn at 50% probability level.
Pentacene 2.21j crystallizes in the space group P1 with two molecules in the unit cell. The benzene ring directly attached to the pentacene framework is nearly perpendicular to the pentacene core with an angle of ca. 81°, while the torsion angle between the two rings of the biphenyl unit is 32° (Figure 2.22). The biphenyl substituent is slightly bent from linearity with an angle of ca. 6°.[41] Pentacene 2.21j arranges as centrosymmetric pairs which adopts a 1-D slipped stacking motif along the crystallographic caxis, with rather short stacking distances of ca. 3.35 and ca. 3.28 Å[17] and approximately three of the aromatic pentacene rings overlapping.
(a) (b)
60 Chapter 2 – Unsymmetrically functionalized pentacenes
(c)
Figure 2.22. X-ray crystallographic analysis of 2.21j showing (a) molecular structure with the bending of the biphenyl unit, (b) illustration of the overlapping aromatic rings, and (c) packing motif (triisopropylsilyl groups omitted for clarity); hydrogen atoms omitted, ORTEPs drawn at 50% probability level.
Pentacene 2.21k crystallizes in the space group P1 with two molecules in the unit cell. Interestingly, the pentacene core and the naphthyl group are nearly coplanar (4°), while the intervening benzene ring is nearly perpendicular to both the pentacene (ca. 90°) and the naphthyl (ca. 86°) groups (Figure 2.23). Compound 2.21k arranges in a 1-D slipped stacking arrangement along the crystallographic baxis with two different interplanar distances of ca. 3.50 Å and 3.32 Å[17] with an overlap of approximately two of the aromatic pentacene rings.
(a) (b)
61 Chapter 2 – Unsymmetrically functionalized pentacenes
(c)
Figure 2.23. X-ray crystallographic analysis of 2.21k showing (a) molecular structure, (b) illustration of the overlapping aromatic rings, and (c) packing motif (triisopropylsilyl groups omitted for clarity); hydrogen atoms omitted, ORTEPs drawn at 50% probability level.
2.3.6 Comparison of anthracenyl-substituted pentacenes §
Anthony and co-workers performed X-ray crystallographic studies on symmetrically substituted pentacenes, functionalized with different silylethynyl groups, and concluded that the solid-state arrangement of such compounds depends highly on the spherical diameter of the substituent.[42] The seemingly beneficial 2-D bricklayer packing is realized if the trialkylsilyl substituent has a diameter of ca. 7 Å, which is approximately half the size of the pentacene skeleton. If the substituent is significantly smaller than 7 Å, drastic deviations toward 1-D packing patterns are observed. In this section, the packing motif of five different anthracenyl-substituted pentacenes is comprehensively studied (Figure 2.24) and an influence of the substituents on the packing is tried to examine.
The crystalline state of anthracene-based pentacene 2.21c is also referred to as a 2- D bricklayer packing motif (Figure 2.17). The anthracene moiety is slightly bigger (ca. 8.9 Å along the long molecular axis) than the triisopropylsilyl group (ca. 7.5 Å in spherical diameter).[42] The combination of the size of the anthracene unit and the observed face-to-face -interactions of two neighboring anthracene moieties appear to direct the solid-state arrangement towards a 2-D packing (Figure 2.24). § Portions of this section have been published, see: Etschel, S. E.; Waterloo, A. R.; Margraf, J. T.; Amin, A. Y.; Hampel, F.; Jäger, C. M.; Clark, T.; Halik, M.; Tykwinski, R. R. Chem. Commun. 2013, 49, 67256727. Reproduced by permission of The Royal Society of Chemistry. 62 Chapter 2 – Unsymmetrically functionalized pentacenes
Substitution by a smaller triethylsilyl group (ca. 6.6 Å in spherical diameter),[42] such as is compound 2.21h, results in a packing motif change to a 1-D pattern. The macroscopic staircase arrangement still appears to be dictated by the -interactions of neighboring anthracene units. Enlarging the spherical diameter of the silyl group, such as in derivative 2.21m[43] with a triisobutylsilyl group (ca. 9.5 Å in spherical diameter)[44] disrupts the packing motif towards a 1-D solid-state arrangement, although considerable CH…-interactions between an anthracene unit and a neighboring pentacene backbone may also play a role. Changing the anthracene unit slightly by substitution with one fluorine atom in the peri-position, such as in compound 2.21n,[43] leads to a significant change in the packing motif from 2-D (in compound 2.21c) towards a 1-D arrangement, where considerable CH…- interactions between one anthracene and neighboring pentacene units are involved. The same result is observed by substitution of the anthracene moiety in the peri- position by a CH3-group, such as in compound 2.21i. The slightly elongated short molecular axis of 2.21i leads to a 1-D packing motif, where only long range - interactions between pentacene units are present, but overall the anthracene unit appears to dictate the packing pattern as a result of CH...-interactions between one anthracene and neighboring pentacene unit. Thus, the solid-state packing motif of unsymmetrically anthracene-based pentacenes may be influenced by a combination of size dependence of the silyl substituents and the anthracene substituent.[45]
Si Si along the a-axis
2.21c 2.21h
Si
2.21m along the a-axis
63 Chapter 2 – Unsymmetrically functionalized pentacenes
Figure 2.24. Schematic illustration of the comparison of solid-state arrangements of different anthracenyl-substituted pentacene derivatives.
2.3.7 Synthetic limits of aryl substitution of pentacenes
Aryl-substituted pentacenes have been successfully implemented in OFET devices although these results have not been presented here.[43] It has been shown that such compounds are stable towards the fabrication procedure and in some cases, show reasonable charge carrier mobilities (even ambipolar behavior for compound 2.21n was observed).[43] Hence, it was anticipated that with the developed synthetic procedure in hand, even larger PAHs might be attached to the pentacene skeleton. To test this hypothesis, several pentacene derivatives were targeted based on the developed synthetic procedure for aryl-substituted pentacenes, as shown in Scheme 2.8. The appropriate aryl-bromide[46] was dissolved in dry, deoxygenated THF at 78 °C and a substoichiometric amount of n-BuLi was added. Ketone 2.4 was then added and the mixture was stirred for 16 h at rt. The reaction was quenched via the addition of aq. NH4Cl, and after aqueous workup, the crude diols were subjected to reductive
aromatization with SnCl2 2H2O under acidic conditions. The characteristic blue color of the crude mixtures vanished over a short period of time for 2.24a and 2.24d suggesting significant decomposition of the desired pentacene derivatives. In the case of 2.24b and 2.24c the typical blue color of the aromatized reaction mixture was not observed, suggesting uncompleted/unsuccessful bromine-lithium exchange and thus incomplete formation of the corresponding diols. Unfortunately, no product(s) from any of these reactions could be isolated and identified.
64 Chapter 2 – Unsymmetrically functionalized pentacenes
Scheme 2.8. Attempted synthesis of unsymmetrical pentacenes functionalized with larger PAHs. The desired products could not be isolated, due to maybe, a) incomplete/unsuccessful bromine-lithium exchange, or b) decomposition of the desired pentacene derivatives.
2.3.8 From anthracenyl-substituted pentacenes to higher PAHs
Cyclodehydrogenation is an oxidation process that involves the elimination of hydrogen.[47] Perhaps one of the most prominent example involves Lewis acids as catalysts, such as FeCl3 and has been investigated by Müllen and coworkers to construct large PAHs such as hexabenzocoronene and giant graphite sheets.[48] It was anticipated that anthracenyl-substituted pentacene derivatives, such as 2.21c, could serve as candidates to build up hithero unknown PAH systems, as hypothetically shown in Scheme 2.9. Hence, pentacene derivatives 2.21cand 2.21h have been tested with several methods of oxidative cyclodehydrogenation, which are in particular a) Lewis acid-catalyzed cyclodehydrogenation (Scholl reaction),[47] b) base-induced cyclodehydrogenation,[49] and c) oxidative photocyclization in the [50] presence of I2 (Mallory reaction). 65 Chapter 2 – Unsymmetrically functionalized pentacenes
Scheme 2.9. Attempted synthesis of large PAHs, starting from anthracene- substituted pentacenes 2.21cand 2.21h, which involve a) Lewis acid-catalyzed cyclodehydrogenation, b) base-induced cyclodehydrogenation, and c) oxidative photocyclization (Mallory reaction).
For Lewis acid-catalyzed cyclodehydrogenation, compound 2.21c was attempted under various Lewis-acid catalyzed cyclodehydrogenation conditions
[51] [52] [52] [53] (FeCl3/CH3NO2, MoCl5, PIFA/BF3 Et2O, and CH3SO3H/DDQ ). In all cases, however, only decomposition of the starting material was observed as indicated by TLC analysis, in which only baseline material was found. Unfortunately, none of the chosen reaction pathways led to successful isolation of the desired PAHs 2.25a or2.25b. The most important observation, however, was made in the case of Lewis acid-catalyzed cyclodehydrogenation, with CH3SO3H/DDQ as oxidants. It was observed by the naked eye, that the solution turns its characteristic color from dark blue toward dark green, indicating a possible ring closure and the increase in effective electronic conjugation expected for hypothetical compound 2.25a. However, upon exposure to air and performing TLC analysis, this dark green color vanished immediately, indicating decomposition of the product under ambient laboratory conditions.
For base-induced cyclodehydrogenation, pentacene 2.21c was dissolved in ethanolamine along with a large excess of K2CO3. The mixture was heated under inert gas atmosphere for 16 h at 160 °C. Only starting material was observed by TLC analysis of the reaction mixture.
For oxidative photocyclization, the Mallory reaction has been performed under inert gas atmosphere and with high diluted reaction mixtures. Thus, 10 mg of pentacene 2.21h were dissolved in 300 mL of dry toluene, and the mixture was deoxygenated by bubbling N2 for further 10 min through the solution, and an excess of I2 and 66 Chapter 2 – Unsymmetrically functionalized pentacenes isopropyleneoxide was added. After irradiation of the mixture via mercury lamp for 48 h, however, only starting material was observed by TLC analysis.
It was thought that perhaps the triple bond in 2.21cand 2.21h underwent unwanted side reactions under the Lewis acid-catalyzed oxidative cyclodehydrogenation reaction conditions. Ideally, a relative bulky substituent on the acetylene possibly might prevent such side reactions. Hence, ketone 2.26[54] bearing a supertritylacetylene (Tr*) group was synthesized and treated by an excess of lithiated anthracene in dry, deoxygenated THF. After aqueous workup, the crude mixture was subjected to reductive aromatization using SnCl2/H2SO4, affording pentacene derivative 2.27 in low yield. Compound 2.27 was further treated under Lewis-acid catalyzed cyclodehydrogenation reaction conditions.[51] Unfortunately, the desired PAH 2.28 could not be isolated, and the reaction mixture only showed decomposed material as indicated by TLC analysis.
Scheme 2.10. Synthesis of supertrityl bearing pentacene derivative 2.27 and attempted conversion to 2.28 via FeCl3/CH3NO2 as oxidant.
2.4 Alkyl substitution of pentacenes
2.4.1 Functionalization by nucleophilic addition
Kanno and coworkers published on the synthesis and characterization of 2.29 in 2007 (Figure 2.25a).[55] Compound 2.29 is only stable under inert gas atmosphere, but nevertheless the solid-state structure could be determined by X-ray crystallographic analysis. Pentacene 2.29 packs in a 1-D slipped packing arrangement consisting of rows of pentacene molecules, thus leading to a herringbone packing motif. Similarly, pentacene derivative 2.30 substituted by
67 Chapter 2 – Unsymmetrically functionalized pentacenes electron withdrawing CF3-groups was synthesized and isolated by Koert and coworkers, recently (Figure 2.25c).[56] Compound 2.30 packs in a sandwich herringbone pattern but, interestingly, the attached CF3-groups do not alter the stability of the parent pentacene, as 2.30 is unstable towards oxygen.
(a) (b)
CF3
CF3
(c) 2.30 (d)
Figure 2.25. Examples of symmetrically substituted pentacene derivatives 2.29 and 2.30, showing (a) molecular structure of 2.29, (b) its packing in the solid state, (c) molecular structure of 2.30, and (d) its packing in the solid state (hydrogen atoms omitted, ORTEPs drawn at 50% probability level, X-ray data for 2.29 from ref. [55], X- ray data for 2.30 from ref. [56], CCDC 916473).
The general synthetic method developed for the functionalization of pentacenes by aryl groups (Section 2.3) can be used to realize unsymmetrical substitution by alkyl groups in a similar fashion. The general substitution pattern uses the common triisopropylsilyl group in one of the reactive positions, which is synthetically
68 Chapter 2 – Unsymmetrically functionalized pentacenes accessible through ketone 2.4. Ketone 2.4 was dissolved in dry, deoxygenated THF and an excess of the corresponding, commercially available, alkyl-lithium or alkyl- Grignard solution was added at rt (Scheme 2.11). The mixture was stirred for 1618 h at rt and after aqueous workup the crude residue was subjected to reductive aromatization using SnCl2/H2SO4, thus avoiding the isolation and purification of the intermediate diols 2.31ac. After stirring the mixture for 6 h at rt under the protection from light, pentacenes 2.32ac could be isolated in moderate yields. Compounds 2.32ac are soluble in common organic solvents and feature good stability as solids under ambient laboratory conditions.
Scheme 2.11. Synthesis of unsymmetrical pentacenes 2.32ac by nucleophilic addition.
2.4.2 Electronic properties of alkyl-substituted pentacenes
The solution state absorption characteristics of alkyl-substituted pentacenes 2.32ac have been explored by UV-vis spectroscopy in CH2Cl2. As can be seen in Figure 2.26, pentacenes 2.32ac show characteristic absorption features centered at ca. 310 nm. In the low energy region, pentacenes 2.32ac show major absorptions at ca. 580 nm and ca. 620 nm. These observations are consistent with the results obtained for aryl-substituted pentacenes 2.21al (Section 2.3.3), as no electronic communication between the pentacene backbone and a sp3-hybridized carbon chain is present such as in compounds 2.32ac.
69 Chapter 2 – Unsymmetrically functionalized pentacenes
–5 Figure 2.26. UV–vis spectra of pentacenes 2.32ac, as measured in CH2Cl2 (~10 M).
2.4.3 Solid-state analysis of alkyl-substituted pentacenes
Crystals suitable for X-ray crystallographic analyses of compounds 2.32ac have been grown and analyzed to study their solid-state packing. Pentacene 2.32a[57] crystallizes in the space group P21/c with four molecules in the unit cell. Interestingly, the acetylene chain is slightly bent from linearity by an angle of ca. 5° (Figure 2.27). Pentacene 2.32a arranges in a 1-D slipped packing motif with an interplanar distance of ca. 3.48 Å[17] and with nearly all of the five aromatic rings overlapping. Notably, every second pentacene molecule within one stack is slightly slipped aside, which is maybe due to steric repulsion of one methyl group and the electron rich triple bond of a neighboring pentacene molecule.
(a) (b) 70 Chapter 2 – Unsymmetrically functionalized pentacenes
(c) (d)
Figure 2.27. X-ray crystallographic analysis of 2.32a showing (a) molecular structure with the bent acetylene unit, (b) illustration of the overlapping aromatic rings, (c) 1-D slipped packing with interplanar distances, and (d) packing motif view along the crystallographic c-axis (triisopropylsilyl groups omitted for clarity); hydrogen atoms omitted, ORTEPs drawn at 50% probability level.
Pentacene 2.32b crystallizes in the space group P1 with two molecules in the unit cell. Pentacene derivative 2.32b packs in dimeric pairs with an overlap of nearly all of the aromatic pentacene rings (Figure 2.28). Interestingly, the butyl group is orientating away from a neighboring triple bond, caused maybe by repulsive forces. The dimeric pairs are arranged in a 1-D slipped stacking fashion along the crystallographic a-axis. This motif causes two different interplanar distances of ca. 3.45 Å and 3.41 Å.[17]
(a) (b)
71 Chapter 2 – Unsymmetrically functionalized pentacenes
(c)
Figure 2.28. X-ray crystallographic analysis of 2.32b showing (a) molecular structure, (b) illustration of the overlapping aromatic rings within one dimeric pair, (c) packing motif (triisopropyl groups omitted for clarity); hydrogen atoms omitted, ORTEPs drawn at 50% probability level.
Pentacene 2.32c crystallizes in the space group P1 with two molecules in the unit cell. Compound 2.32c packs in dimeric pairs with an overlap of nearly all of the aromatic pentacene rings (Figure 2.29). The allyl group is disordered in the structure over two unique positions and is orientating away from a neighboring triple bond. The dimeric pairs are arranged in a 1-D slipped stacking arrangement and this motif causes two different interplanar distances of ca. 3.46 Å and 3.41 Å.[17] In general, the observed packing of 2.32c is very similar to pentacene 2.32b.
(a) (b)
72 Chapter 2 – Unsymmetrically functionalized pentacenes
(c)
Figure 2.29. X-ray crystallographic analysis of 2.32c, showing (a) molecular structure, (b) illustration of the overlapping aromatic rings within one dimeric pair, and (c) packing motif (triisopropyl groups omitted for clarity); hydrogen atoms omitted, disorder in ally group not shown, ORTEPs drawn at 50% probability level.
2.4.4 Synthetic limits of alkyl substitution of pentacenes
The developed synthetic protocol for alkyl-substituted pentacenes should in principle allow for the unsymmetrically functionalization of the pentacene skeleton by any alkyl group. During this study, it was attempted to functionalize compound 2.4 with an ethyl- and a vinyl group (Scheme 2.12). In both cases, the corresponding, commercially available, Grignard reagent was added to a solution of 2.4 in dry, deoxygenated THF at rt. The mixture was stirred for 16 h at rt. After quenching the reaction with a proton source and aqueous workup, the obtained residue was subjected to reductive aromatization using SnCl2/H2SO4. The reaction was performed under the absence of light without isolation and purification of the corresponding diol intermediates. Unfortunately, after aqueous workup, the characteristic deep blue solution bleached rapidly under ambient laboratory conditions, suggesting decomposition of 2.32d and 2.32e. In the case of 2.32e unwanted polymerization by the vinyl substituent may be the reason for the observed decomposition, although decomposition products could not be identified. The reason for the instability of compound 2.32d is unknown.
73 Chapter 2 – Unsymmetrically functionalized pentacenes
Scheme 2.12. Attempted functionalization of 2.4 by either ethyl- or vinyl substituents.
2.4.5 Reactivity of 2.32a
The reactivity of pentacene derivatives toward oxygen plays a crucial role, as acenes quite typically undergo a reaction with oxygen to form endoperoxides.[58] It is a significant synthetic challenge to develop compounds with higher stability against oxidation and to understand the reactivity-versus-structure relationship. Hence, compound 2.32a was tested towards its reactivity against oxygen (Scheme 2.13). A solution of pentacene 2.32a in CH2Cl2 was exposed to sunlight under aerobic conditions. The characteristic deep blue color of the solution vanished within two hours and after aqueous workup and purification, endo-peroxide 2.33 could be isolated in 70% yield. Interestingly, heating a solid sample of 2.33 under ambient conditions up to ca. 160 °C recovered the characteristic deep blue color of 2.32a, suggesting the reversibility of the endo-peroxide formation, although the obtained blue solid was not analyzed toward possible formed side products.[59]
Scheme 2.13. Photooxidation of 2.32a and reversible deoxygenation of 2.33.
The molecular structure of endo-peroxide 2.33 was investigated by X-ray crystallographic analysis (Figure 2.30). Endo-peroxide 2.33 crystallizes in the space group P1 with two independent molecules and four molecules in the unit cell.
74 Chapter 2 – Unsymmetrically functionalized pentacenes
Interestingly, no significant --interactions between the parent aromatic units are found. The angle between the both units is ca. 109°, which is consistent with the angle found for the only other crystallographically analyzed endoperoxide of 6,13- dithienylpentacene.[60]
(a) (b)
Figure 2.30. X-ray crystallographic analysis of 2.33 showing (a) molecular structure and the two independent molecules of the unit cell (b) illustration of the bending angle between the two naphtalene units (triisopropyl groups omitted for clarity); hydrogen atoms omitted, ORTEPs drawn at 50% probability level.
The observed possibility to deoxygenate 2.33 towards 2.32a could make 2.33 interesting for potential applications as a “pentacene-storage” material. Diels-Alder reactions (and retro-Diels-Alder reactions) in general could store and release pentacene materials.[61] Following this idea, pentacene 2.32a was tested toward the reactivity against the strong dienophile TCNE (Scheme 2.14). Hence, pentacene
2.32a was dissolved in dry CH2Cl2 and a slight excess of TCNE dissolved in dry
CH2Cl2 was added at rt. The deep blue pentacene solution discolored immediately, suggesting a very fast Diels-Alder reaction. After evaporating the solvent and washing the residue with MeOH, the Diels-Alder product 2.34 was isolated in 63% yield. Notably, the other possible structural isomer, which is the second-ring monoadduct of TCNE with 2.32a, was not observed.[62] A retro-Diels-Alder reaction such as for the oxygenation-deoxygenation for 2.32a, was not possible in the case of 2.34. Heating a solid sample of 2.34 under ambient conditions to ca. 200 °C does not lead to a color change back to deep blue.
75 Chapter 2 – Unsymmetrically functionalized pentacenes
Scheme 2.14. Diels-Alder reaction of 2.32a and TCNE to form 2.34.
The molecular structure of 2.34 was investigated by X-ray crystallographic analysis (Figure 2.31). Compound 2.34 crystallizes in the space group P1 with two molecules in the unit cell. The naphthalene units show -interactions along the crystallographic c-axis with two different interplanar distances of 3.48 Å and 3.52 Å.[63] The twisting angle between the two naphthalene units is ca. 108°. This X-ray structure is to the best of our knowledge the only crystallographically analyzed Diels- Alder product of a pentacene derivative with TCNE.
(a) (b)
(c)
Figure 2.31. X-ray crystallographic analysis of 2.34 showing (a) molecular structure, (b) illustration of the bending angle between the two naphtalene units, and (c) packing motif along the crystallographic c-axis (triisopropyl groups omitted for clarity); hydrogen atoms omitted, ORTEPs drawn at 50% probability level. 76 Chapter 2 – Unsymmetrically functionalized pentacenes 2.5 Monosubstituted pentacene
2.5.1 Reduction toward monosubstituted pentacene
Three monosubstituted pentacene derivatives were crystallographically analyzed to date and two derivatives are shown in Figure 2.32 as they relate the most to this research work. Nuckolls and coworkers reported on phenyl-substituted compound 1.43.[64] Compound 1.43 packs in a sandwich herringbone motif reflecting two different types of intermolecular interactions, namely edge-to-face contacts and - interactions between two pentacene units. Although the authors did not comment on the stability of 1.43 in this report, thin film transistors of 1.43 were fabricated but showed unfortunately poor device characteristics. Teki and coworkers established a straightforward method to stabilize the pentacene chromophore by the functionalization with radical species.[65] In contrast to 1.43, X-ray crystallographic analysis of 1.45 shows a significantly different solid-state arrangement. Compound 1.45 arranges in an edge-to-face motif via the pro cata-positions of a neighboring pentacene molecule. Additionally, the packing motif is seemingly dictated by the oxo- verdazyl radical, which shows -interactions with a neighboring pentacene unit
(a) (b)
(c) (d)
Figure 2.32. Monosubstituted pentacene derivatives 1.43 and 1.45, showing (a) molecular structure of 1.43, (b) its packing in the solid state, (c) molecular structure of 1.45, and (d) its packing in the solid state (cocrystallized solvent molecules not
77 Chapter 2 – Unsymmetrically functionalized pentacenes shown); hydrogen atoms omitted, ORTEPs drawn at 50% probability level, X-ray data for 1.43 from ref. [64], X-ray data for 1.45 from ref. [65], CCDC 919509.
In principle the keto-functionality of 2.4 should allow the reduction by LiAlH4 to 6- (triisopropylsilyl)pentacene 2.35a (Scheme 2.15).[66] To avoid the use of a large excess of LiAlH4, the acidic proton of the propargyl alcohol in 2.4 was protected as methyl ether. Hence, 6,13-pentacenequinone (1.2) was suspended in dry, deoxygenated THF and a solution of lithiated TIPS-acetylene in dry, deoxygenated THF was added. The mixture was stirred for 24 h at rt and an excess of MeI was added. After aqueous workup and purification by column chromatography,[67] ketone 2.36 could be isolated in 72% yield. Subsequently, compound 2.36 was dissolved in dry, deoxygenated THF and an excess of LiAlH4 was carefully added at 0 °C. The mixture was heated at reflux for 3 h and after cooling to rt and aqueous workup, a crude residue was isolated. Notably, the isolated crude residue aromatized during aqueous workup, as a color change to blue was observed. Nevertheless, to ensure complete reductive aromatization, the crude residue was dissolved in THF and treated with SnCl2/H2SO4 in the absence of light. After aqueous workup and purification by column chromatography, pentacene 2.35a was isolated in 19% yield. After several repetitions of this procedure, the yield for 2.35a could not be improved, but a second strongly fluorescent material was isolated. NMR spectroscopy and mass spectrometry could not be used to successfully define the structure of this product. X-ray crystallographic analysis, however, provided the molecular structure to be 2.35b (Figure 2.33), although the quality of the grown crystals did not allow for publishable structural refinement. The spectroscopic data (NMR and MS) obtained for 2.35a is consistent with the data obtained by X-ray crystallography. Compound 2.35b is the result of a Diels-Alder reaction of the acetylenic triple bond of 2.35a with the inner ring of another pentacene 2.35a and affords 2.35b in 9% yield. Unfortunately, all attempts to grow better single crystals of compound 2.35b have been unsuccessful to date.
78 Chapter 2 – Unsymmetrically functionalized pentacenes
Scheme 2.15. Synthesis of monosubstituted pentacene 2.35a and byproduct 2.35b.
Figure 2.33. Structural solution of Diels-Alder product 2.35b.
Pentacenes 2.35a and 2.35b show good solubility in common organic solvents. Compounds 2.35a and 2.35b are bench-top stable as solids for months, but are unstable in solution under ambient laboratory conditions. This may also be the reason for the observed low isolated yields, as polymerization through Diels-Alder reactions is most likely the preferred side reaction. The Diels-Alder product 2.35b can be envisioned to react with either another molecule 2.35a or with itself, to form undefined polymeric mixtures. The reversible process, namely a retro-Diels-Alder reaction of 2.35b was not investigated within this research work.
79 Chapter 2 – Unsymmetrically functionalized pentacenes
2.5.2 Electronic properties of pentacenes 2.35a and2.35b
The solution state absorption characteristics of pentacenes 2.35a and 2.35bhave been explored by UV-vis spectroscopy in CH2Cl2 (Figure 2.34 and Table 2.5). Compound 2.35a shows a strong absorption centered at 307 nm and a weak absorption at 349 nm. In the low energy region two weak absorptions are present, which are centered at ca. 576 nm and ca. 610 nm. Compound 2.35b features strong absorptions located at ca. 257 nm and ca. 305 nm. In the low energy region, three characteristic absorptions are observed, located at ca. 513 nm, ca. 552 nm, and ca. 597 nm. Overall, the UV-vis absorption of 2.35b features sharper and well-resolved absorption characteristics than for 2.35a and the longest wavelength absorption for 2.35b is slightly blue shifted (ca. 14 nm) compared to compound 2.35a. A sample of
2.35b was drop casted from a concentrated CH2Cl2 solution onto a quartz surface and after air-drying UV-vis absorptions were recorded (Figure 2.35). Interestingly, only a small red shift in max values for 2.35b was observed (ca. 7 nm), thus concluding that no strong -interactions are present in the solid state. Nevertheless, the solid-state UV-vis spectrum of 2.35b shows well-resolved absorption bands, which indicates that the film consists of very homogenous large- sized crystallites.[30b] Homogenous large-sized crystallites could be interesting for OFET devices, as the homogenous morphology of the active layer component plays a crucial role for charge carrier mobilities.[68] Notably, solid-state UV-vis spectroscopy for 2.35a was not possible to perform under standard laboratory conditions, as a significant degradation, suggesting to give 2.35b, was observed during the slow air- drying process.
80 Chapter 2 – Unsymmetrically functionalized pentacenes
Figure 2.34. UV–vis spectra of pentacene derivatives 2.35aand2.35b, as measured –5 in CH2Cl2 (~10 M).
Figure 2.35. Thin film UV–vis spectra of pentacene 2.35b (on quartz, drop cast from
CH2Cl2 solution).
81 Chapter 2 – Unsymmetrically functionalized pentacenes
Table 2.5. Optical properties of pentacenes 2.35aand 2.35b.
max (in (film)[b] red shift [a] max [c] Compound CH2Cl2) Egap, opt[eV] [nm] [nm] [nm]
2.35a 611 --[d] -- 1.92
2.35b 597 604 7 2.03
[a] Lowest energy absorption maxima. [b] Cast from CH2Cl2 onto quartz. [c] Determined using the intercept of the x-axis and the tangent applied to the longest wavelength absorption peak. [d] Degradation of the sample during air-drying observed.
2.5.3 Solid-state analysis of pentacene 2.35a
X-ray crystallographic analysis of 2.35a has been performed, to explore possible - interactions (Figure 2.36). Pentacene 2.35a crystallizes in the space group P1 with eight molecules in the unit cell. The acetylene unit is slightly bent from linearity by an angle of ca. 6°. Pentacene 2.35a arranges as centrosymmetric dimeric pairs with a total overlap of nearly all of the five aromatic rings and an interplanar distance of 3.45 Å.[17] The dimeric pairs are ordered in a sandwich herringbone fashion. This solid- state arrangement is supported by CH…-interactions between neighboring pentacene molecules with distances of 2.77 Å.[69] The solid-state arrangement is seemingly dictated by two types of intermolecular interactions, which is very similar observed for derivative 1.43.
82 Chapter 2 – Unsymmetrically functionalized pentacenes
(a) (b)
(c)
Figure 2.36. X-ray crystallographic analysis of 2.35a showing (a) molecular structure with the bend acetylene unit, (b) illustration of the overlapping aromatic rings, (c) sandwich herringbone packing motif with interplanar distances and illustration of the CH…-interactions (triisopropylsilyl groups omitted for clarity); hydrogen atoms omitted, ORTEPs drawn at 50% probability level.
2.6 Conclusion
In summary, new synthetic strategies for the unsymmetrically functionalization of pentacene have been developed. This allows for the synthesis of 1,2,3-triazole- substituted pentacenes, as demonstrated in Section 2.2. The established method outlines the formal compatibility of the CuAAC reaction with the pentacene framework. A variety of azide partners can be used as precursors, including alkyl azides, aryl azides, and heteroaryl azides. The established synthetic method also
83 Chapter 2 – Unsymmetrically functionalized pentacenes allows for the synthesis of oligomeric pentacene chromophores. Pyridyl-containing pentacene derivatives from the CuAAC reaction can be used to build pentacene- porphyrin assemblies.
In Section 2.3 and Section 2.4, a library of unsymmetrically aryl- and alkyl- substituted pentacenes has been synthesized by a straightforward procedure that requires only one purification step. The starting point for this synthetic route is the versatile ketone 2.4 or 2.22. Slightly changing the synthetic starting point by switching to ketone 2.36 instead, allows for the reduction to monosubstituted pentacene 2.35a, such as demonstrated in Section 2.5.
All pentacene derivatives synthesized in this chapter are soluble in common organic solvents and are stable as solids under ambient laboratory conditions for months. When investigated in solution, methyl-substituted pentacene 2.32a shows significant reactivity with molecular oxygen or the strong dienophile TCNE. The inner aromatic pentacene ring is the most reactive site in the observed oxidations or Diels-Alder reactions. The reversible oxygenation-deoxygenation process, which was observed for compound 2.33, offers a possibility to use unsymmetrically substituted pentacenes as “pentacene-storage” materials.[61] Monosubstituted pentacene 2.35a was the least stable pentacene examined in this research work. Compound 2.35a tends to react with itself via Diels-Alder reaction to form 2.35b.
The synthesized 1,2,3-triazolyl, aryl-, and alkyl-substituted pentacenes in the present study show similar electronic properties, which was verified by UV-vis spectroscopy and – in some cases CV experiments. The detailed unsymmetrically substituted pentacenes all show HOMO-LUMO bandgaps of approximately 1.92.1 eV.
The substitution pattern of pentacenes explored in this research work has a considerable effect on the solid-state arrangement of the molecules, and X-ray crystallographic analysis afforded insight on the packing arrangements of some synthesized pentacenes. In spite of the large number of crystal structures that have been examined herein, however, general trends are difficult to establish based on, for example, either the number of and CH… interactions or the size of the group appended to the pentacene skeleton. It does seem, however, that anthracenyl substitution affords beneficial -stacking amongst other derivatives examined. The
84 Chapter 2 – Unsymmetrically functionalized pentacenes obtained data could help for crystal structure prediction (CSP) in pentacene materials.[70]
2.7 Outlook
2.7.1 CuAAC reaction
The method developed for unsymmetrical substitution of pentacenes by the CuAAC reaction could serve for the synthetic elaboration of pentacenes such as derivative 2.37 (Scheme 2.16). The CuAAC reaction of 2.3 with a phosphonate anchor group 2.38 and further reduction could serve for pentacene 2.37. Compound 2.37 could be useful for realizing self-assembled (SAM) monolayers and 2.37 could be used in OFETs to control the morphology of the first monolayer within the device.[71]
.
Scheme 2.16. Possible synthetic pathway to pentacene 2.37 bearing a phosphonate anchor group for the use in self-assembled monolayers.
2.7.2 Larger PAHs from anthracenyl-substituted pentacenes
Pentacenes are potential candidates to serve as synthetic building blocks for larger PAHs. The attempts detailed in the present work to realize such PAHs by starting from anthracenyl-substituted pentacenes were unsuccessful to date, maybe due to the instability of the resulting PAH. To circumvent the stability issue of the PAH, the “open edge” of the PAH could be partially “protected” by functional groups. An impressive synthesis by Konishi et al uses substituted anthracenes to realize quarteranthene.[72] This synthetic strategy could be adapted and start from ketone 2.4 (Scheme 2.17). Treatment of the latter by lithiated anthracene derivative 2.39 and reductive aromatization should lead to pentacene derivative 2.40. Subsequent 85 Chapter 2 – Unsymmetrically functionalized pentacenes treatment under the right cyclodehydrogenation reaction conditions could then form large PAH 2.41.
Scheme 2.17. Potential synthetic route towards larger PAHs starting from ketone 2.4 via using the developed synthetic method for aryl-substituted pentacene derivatives.
2.7.3 Pentacene dimers for studies of singlet fission
X-ray crystallographic analysis of alkyl-substituted pentacene derivatives shows that the alkyl chains are orientated away from the neighboring pentacene molecule. The synthesis of pentacene dimers, spaced by alkyl chains (2.42 in Figure 2.37a), could maybe offer a possibility to create novel packing geometries in the solid-state such as hypothetically illustrated in Figure 2.37b. This packing motif could be interesting for the studies of singlet fission.[73]
(a) (b)
Figure 2.37. (a) Hypothetical pentacene dimers 2.42 and (b) the potentially adopted solid-state arrangement.
86 Chapter 2 – Unsymmetrically functionalized pentacenes
2.7.4 Monosubstituted pentacene as building block
Pentacene 2.35a offer the possibility to use its unsubstituted site for further functionalization, e.g. bromination (Scheme 2.18). Although direct bromination of unsubstituted pentacene has never been reported, bromination has been well established in anthracene-based chemistry.[74] The fact that one of the most reactive positions in 2.35a is blocked by an acetylene moiety could allow for a selective bromination and the obtained hypothetical pentacene derivative 2.43 might potentially be further used as building block for C-C-coupling reactions to realize cyano-substituted pentacene derivative 2.44.
Scheme 2.18. Hypothetical pentacene derivative 2.44, obtained via selective bromination of 2.35a and further Pd-mediated cross coupling reaction of 2.43.
2.8 References
[1] (a) Anthony, J. E. Chem. Rev. 2006, 106, 5028–5048. (b) Anthony, J. E. Angew. Chem. Int. Ed. 2008, 47, 452–483.
[2] Anthony, J. E.; Brooks, J. S.; Eaton, D. L.; Parkin, S. R. J. Am. Chem. Soc. 2001, 123, 9482–9483.
[3] Anthony, J. E.; Eaton, D. L.; Parkin, S. R. Org. Lett. 2002, 4, 15–18.
[4] (a) Lehnherr, D.; Tykwinski, R. R. Materials 2010, 3, 2772–2800. (b) Lehnherr, D.; Tykwinski, R. R. Aust. J. Chem. 2011, 64, 919929.
[5] Besides the studies on unsymmetrically substituted pentacene derivatives in the Tykwinski laboratories, see: (a) Vets, N.; Smet, M.; Dehaen, W. Synlett 2005, 2, 217222. (b) Miao, Q.; Chi, X.; Xiao, S.; 87 Chapter 2 – Unsymmetrically functionalized pentacenes Zeis, R.; Lefenfeld, M.; Siegrist, T.; Steigerwald, M. L.; Nockulls, C. J. Am. Chem. Soc. 2006, 128, 13401345. (c) Wang, Y.-M.; Fu, N.-Y.; Chan, S.-H.; Lee, H.-K.; Wong, H. N. C. Tetrahedron 2007, 63, 8586- 8597. (d) Kawanaka, Y.; Shimizo, A.; Shinada, T.; Tanaka, R.; Teki, Y. Angew. Chem. Int. Ed. 2013, 52, 66436647. (e) Zhang, J.; Pawle, R. H.; Haas, T. E.; Thomas, S. W. Chem. Eur. J. 2014, 20, 58805884.
[6] (a) Tornøe, C. W.; Christensen, C.; Meldal, M. J. Org. Chem. 2002 , 67, 30573064. (b) Rostovtsev, V. V.; Green, L. G.; Fokin, V. V.; Sharpless, K. B. Angew. Chem. Int. Ed. 2002, 41, 25962599. (c) Hein, J. E.; Fokin, V. V. Chem. Soc. Rev. 2010, 39, 13021315. (d) Amblard, F.; Cho, J. H.; Schinazi, R. F. Chem. Rev. 2009, 109, 42074220. (e) Meldal, M.; Tornøe, C. W. Chem. Rev. 2008, 108, 29523015. (f) Meldal, M. Macromol. Rapid Commun. 2008, 29, 10161051. (g) Johnson, J. A.; Finn, M. G.; Koberstein, J. T.; Turro, N. J. Macromol. Rapid Commun. 2008, 29, 10521072. (h) Tron, G. C.; Pirali, T.; Billington, R. A.; Canonico, P. L.; Sorba, G.; Genazzani, A. A. Med. Res. Rev. 2008, 28, 278308. (i) Lutz, J.-F. Angew. Chem. Int. Ed. 2007, 46, 10181025. (j) Moses, J. E.; Moorhouse, A. D. Chem. Soc. Rev. 2007, 36, 12491262. (k) Bock, V. D.; Hiemstra, H. J.; Maarseveen, H. van Eur. J. Org. Chem. 2006, 5168.
[7]Lehnherr, D.; Murray, A. H.; McDonald, R.; Ferguson, M. J.; Tykwinski, R. R. Chem. Eur. J. 2009, 15, 1258012584 .
[8] Payne, M. M.; Odom, S. A.; Parkin, S. R.; Anthony, J. E. Org. Lett. 2004, 6, 33253328.
[9] (a) Susumu, K.; Duncan, T. V.; Therien, M. J. J. Am. Chem. Soc. 2005, 127, 51865195. (b) Lin, C.-Y.; Wang, Y.-C.; Hsu, S.-J.; Lo, C.-F.; Diau, E. W.-G. J. Phys. Chem. C 2010, 114, 687693.
88 Chapter 2 – Unsymmetrically functionalized pentacenes [10] Lehnherr, D.; Murray, A. H.; McDonald, R.; Tykwinski, R. R. Angew. Chem. Int. Ed. 2010, 49, 61906194.
[11] Lehnherr, D.; McDonald, R.; Tykwinski, R. R. Org. Lett. 2008, 10, 41634166.
[12] (a) Lehnherr, D.; McDonald, R.; Ferguson, M. J.; Tykwinski, R. R. Tetrahedron 2008, 64, 11449-11461. (b) Lehnherr, D.; Tykwinski, R. R. Org. Lett. 2007, 9, 45834586.
[13] Azides 2.9 is commercially available. For the synthesis of azide 2.8, see: (a) Ramírez-Lopéz, P.; de la Torre, M. C.; Montenegro, H. E.; Asenjo, M.; Sierra, M. A. Org. Lett. 2008, 10, 35553558. For the synthesis of azide 2.10, see: (b) Song, Y.; Kohlmeir, E. K.; Meade, T. J. J. Am. Chem. Soc. 2008, 130, 66626663.
[14] Gholami, M.; Tykwinski, R. R. Chem. Rev. 2006, 106, 49975027.
[15] Maulding, D. R.; Roberts, B. G. J. Org. Chem. 1969, 34, 17341736.
[16] Interplanar distances have been calculated by generating planes through the atoms of each 1,2,3-triazolyl group. [17] Interplanar distances have been calculated by generating planes through the atoms of each pentacene group.
[18] Görl, D.; Zhang, X.; Würthner, F. Angew. Chem. Int. Ed. 2012, 51, 63286348.
[19] (a) Thornton, D. A. Coordin. Chem. Rev.1990, 104, 251295. (b) Singh, P. K.; Singh, V. K. Pure Appl. Chem. 2010, 82, 18451853, and references herein.
[20] Campbell, K.; McDonald, R.; Tykwinski, R. R. J. Porphyr. Phthalocya. 2005, 9, 794802.
89 Chapter 2 – Unsymmetrically functionalized pentacenes [21] Hwang, I.-W.; Kamada, T.; Ahn, T. K.; Ko, D. M.; Nakamura, T.; Tsuda, A.; Osuka, A.; Kim, D. J. Am. Chem. Soc. 2004, 126, 1618716198.
[22] Ikbal, S. A.; Brahma, S.; Rath, S. P. Inorg. Chem. 2012, 51, 96669676.
[23] Brahma, S.; Ikbal, S. A.; Rath, S. P. Inorg. Chim. Acta 2011, 372, 6270.
[24] Conjugated acene-modified porphyrins have been synthesized, see Ref [9b].
[25] The synthesis of the Ru(II)-porphyrin 2.16 has been accomplished by Dr. Rainer Lippert from the research group of Dr. Jux, at FAU.
[26] The protons of the pyridyl ring in ortho- and para-positions have been assigned by comparison, see ref [20].
[27] The synthesis of ketone 2.22 is similar to compound 2.4, details see: Lehnherr, D. Ph. D. Thesis, University of Alberta, Edmonton, Canada, 2010.
[28] For the synthesis of 9-bromo-10-methyl-anthracene, see: Zhu, L.; Al- Kaysi, R. O.; Dillon, R. J.; Tham, F. S.; Bardeen, C. J. Cryst. Growth Des. 2011, 11, 49754983.
[29] The corresponding aryl-boronic acids are commercially available.
[30] (a) Ostroverkhova, O.; Shcherbyna, S.; Cooke, D. G.; Egerton, R. F.; Hegmann, F. A.; Tykwinski, R. R.; Parkin, S.R.; Anthony, J. E. J. Appl. Phys. 2005, 98, 003701. (b) Lee, K. O.; Gan, T. T. Chem. Phys. Lett. 1977, 51, 120124.
[31] CV measurements were done by Anna-Chiara Sale, at FAU Erlangen.
[32] Lim, Y.-F.; Shu, Y.; Parkin, S. R.; Anthony, J. E.; Malliaras, G. G. J. Mater. Chem. 2009, 19, 3049–3056. 90 Chapter 2 – Unsymmetrically functionalized pentacenes [33] The distance is calculated as the average distance of H(53), H(63A), and H(64A) to the generated plane through the neighboring pentacene backbone.
[34] The distance is calculated from H(27) to the generated plane through the neighboring naphthyl unit.
[35] Interplanar distances have been calculated by generating planes through the atoms of each anthracenyl group.
[36] The distance was calculated from H(9) to the generated plane through the neighboring pentacene backbone.
[37] The distance was calculated from H(6) to the generated plane through the neighboring pentacene backbone.
[38] The distance was calculated from H(54) to the generated plane through the neighboring anthracenyl unit.
[39] The distance was calculated from H(26) to the generated plane through the neighboring anthracenyl unit.
[40] The distance was calculated from H(54) to the generated plane through the neighboring pentacene backbone.
[41] Measured as angle between the centroid of the pentacene backbone and the two centroids of each of the phenyl rings.
[42] For the study of the size dependence of silyl substituents on the packing motif of pentacenes, see Ref [3].
[43] The synthesis and device performance for derivatives 2.21m and 2.21n was done by S. Etschel as part of his master thesis at FAU, under my supervision. This work has been published, see: Etschel, S. E.; Waterloo, A. R.; Margraf, J. T.; Amin, A. Y.; Hampel, F.; Jäger, C. M.;
91 Chapter 2 – Unsymmetrically functionalized pentacenes Clark, T.; Halik, M.; Tykwinski, R. R. Chem. Commun. 2013, 49, 67256727.
[44] The measured distance is the largest observed distance between two hydrogen atoms in the triisobutylsilyl group. CIF.file taken from ref [43]; CCDC 927706.
[45] The polarizability changes the -interactions between aromatic compounds, for details, see: Martinez, C. R.; Iverson, B. L. Chem. Sci. 2012, 3, 21912201, and references herein.
[46] (a) For the synthesis of 9-bromo-10-(triisopropylsilylethynyl)anthracene, see: de Montigny, F.; Argouarch, G.; Lapinte, C. Synthesis 2006, 02930298. (b) For the synthesis of 5-bromo-tetracene, see: Müller, A. M.; Avlasevich, Y. S.; Schoeller, W. W.; Müllen, K.; Bardeen, C. J. J. Am. Chem. Soc. 2007, 129, 1424014250. (c) For the synthesis of 1- bromo-pyrene, see: He, C.; He, Q.; Chen, Q.; Cao, H.; Cheng, J.; Deng, C.; Lin, T. Tetrahedron Lett. 2010, 51, 13171321.
[47] (a) Scholl, R.; Seer, C. Justus Liebigs Ann. Chem. 1912, 394, 111177. (b) Scholl, R.; Seer, C. Chem. Ber. 1922, 55, 109117.
[48] (a) Iyer, V. S.; Wehmeier, M.; Brand, J. D.; Keegstra, M. A.; Müllen, K. Angew. Chem. Int. Ed. 1997, 36, 16041607. (b) Simpson, C. D.; Brand, J. D.; Berresheim, A. J.; Przybilla, L.; Räder, H. J.; Müllen, K. Chem. Eur. J. 2002, 8, 14241429.
[49] Yao, J. H.; Chi, C.; Wu, J.; Loh, K.-P. Chem. Eur. J. 2009, 15, 92999302.
[50] Wood, C. S.; Mallory, F. B. J. Org. Chem. 1964, 29, 33733377.
[51] Wu, J.; Pisula, W.; Müllen, K. Chem. Rev. 2007, 107, 718747.
92 Chapter 2 – Unsymmetrically functionalized pentacenes [52] King, T. B.; Kroulík, J.; Robertson, C. R.; Rempala, P.; Hilton, C. L.; Korinek, J. D.; Gortari, L. M. J. Org. Chem. 2007, 72, 22792288.
[53] Thamatam, R.; Skraba, S. L.; Johnson, R. P. Chem. Commun. 2013, 49, 91229124.
[54] For the synthesis of ketone 2.26, see: Adam, M. Diploma Thesis, FAU Erlangen-Nürnberg, Germany, 2010.
[55] Takahashi, T.; Kashima, K.; Li, S.; Nakajima, K.; Kanno, K.-I. J. Am. Chem. Soc. 2007, 129, 1575215753.
[56] Schwaben, J.; Münster, N.; Breuer, T.; Klues, M.; Harms, K.; Witte, G.; Koert, U. Eur. J. Org. Chem. 2013, 16391643.
[57] Single crystals suitable for X-ray crystallographic analysis of compound 2.32a have been grown earlier by Dr. Dan Lehnherr.
[58] Fudickar, W.; Linker, T. J. Am. Chem. Soc. 2012, 134, 1507115082.
[59] A similar trend was observed for symmetrically substituted 2-thienyl- pentacene, see: Ono, K.; Totani, H.; Hiei, T.; Yoshino, A.; Saito, K.; Eguchi, K.; Tomura, M.; Nishida, J.-I.; Yamashita, Y. Tetrahedron 2007, 63, 96999704.
[60] The angle between the two naphthyl units of 6,13-dithienylpentacene- endoperoxide is ca. 112°, see ref [59].
[61] For recent reviews on this topic, see: (a) Watanabe, M.; Chen, K.-Y.; Chang, Y. J.; Chov, T. J. Acc. Chem. Res. 2013, 46, 16061615. For another example for the release of pentacene, see: (b) Uoyama, H.; Yamada, H.; Okujima, T., Uno, H. Tetrahedron 2010, 66, 68896894.
[62] Pentacene (1.1) reacts with TCNE at rt to yield the center-ring adduct, as well as the second-ring adduct. Furthermore, the center-ring adduct
93 Chapter 2 – Unsymmetrically functionalized pentacenes is in equilibrium with the second-ring adduct when irradiating a sample with different wavelengths, according to: Johns, V. T.; Shi, Z.; Hu, W.; Johns, J. B.; Zou, S.; Liao, Y. Eur. J. Org. Chem. 2012, 27072710.
[63] Distances have been calculated by generating planes through the atoms of each naphthyl unit.
[64] Miau, Q.; Chi, X.; Xiao, S.; Zeis, R.; Lefenfeld, M.; Siegrist, T.; Steigerwald, M. L.; Nuckolls, C. J. Am. Chem. Soc. 2006, 128, 13401345.
[65] Kawanaka, Y.; Shimizu, A.; Shinada, T.; Tanaka, R.; Teki, Y. Angew. Chem. Int. Ed. 2013, 52, 66436647.
[66] Pentacene derivative 2.35a was envisioned to be investigated and compared with derivative 2.32a and symmetrical analogue 1.7a toward its capability in the process of singlet fission. The physical measurements and calculations have been performed in collaboration with the research group of Prof. D. Guldi at FAU and will not be discussed within this thesis.
[67] Compound 2.36 can also be purified by recrystallization from MeOH; for details, see Chapter 5.
[68] Viani, L.; Risko, C.; Toney, M. F.; Breiby, D. W.; Brédas, J.-L. ACS Nano 2014, 8, 690700.
[69] The distance was calculated from H(25) through the plane of a neighboring pentacene backbone.
[70] CSP is one of the most important challenges in chemistry since decades, see: (a) Desiraju, G. R. Nature Materials 2002, 1, 7779. (b) Woodley, S. M.; Catlow, R. Nature Materials 2008, 7, 937946. (c) Gavezzotti, A. Synlett 2002, 2, 02010214. (d) Price, S. L. Chem. Soc. Rev. 2014, 43, 20982111. 94 Chapter 2 – Unsymmetrically functionalized pentacenes [71] Phosphonates as anchor groups have been successfully used in SAM devices, see: (a) Halik, M.; Hirsch, A. Adv. Mater. 2011, 23, 26892695. Supported also by theoretical calculations, see (b) Bauer, T.; Schmaltz, T.; Lenz, T.; Halik, M.; Meyer, B.; Clark, T. ACS Appl. Mater. Interfaces 2013, 5, 60736080.
[72] Konishi, A.; Hirao, Y.; Matsumoto, K.; Kurata, H.; Kishi, R.; Shigeta, Y.; Nakano, M.; Tokunaga, K.; Kamada, K.; Kubo, T. J. Am. Chem. Soc. 2013, 135, 14301437.
[73] Geometric distortions play a crucial role in the process of singlet fission in the solid-state, according to: Siebbeles, L. D. A. Nature Chemistry 2010, 2, 608609.
[74] Selective bromination in the 9-position of anthracene has been successfully performed, see: (a) Hock, H.; Ernst, F. Chem. Ber. 1959, 92, 27322740. (b) House, H. O.; Ghali, N. I.; Haak, J. L.; VanDerveer, D. J. Org. Chem. 1980, 45, 18071817.
95 Chapter 3 – Isomerically pure syn-anthradithiophenes Chapter 3 – Isomerically pure syn-anthradithiophenes
3.1 Introduction
Formally, the replacement of the peripheral benzene rings in pentacene by thiophenes leads to the isoelectronic structure of anthradithiophene (ADT, 3.1). Originally synthesized by Katz and coworkers in 1998,[1] ADTs can be regarded as an early effort to discover novel compounds for the use in optoelectronic devices. The fusion of thiophenes onto a linear carbon skeleton results in a framework in which two structural isomers are possible, namely the syn-isomer (syn-3.1) and the anti- isomer (anti-3.1). The synthesis of ADTs starts with a four-fold aldol condensation of thiophene-2,3-dicarboxaldehyde and 1,4-cyclohexandione to give the corresponding quinones (mix-3.2, similar to the synthesis of 6,13-pentacenequinone, see Chapter 1).[2,3] Further reduction of mix-3.2 yields the corresponding ADTs. As can be seen in Scheme 3.1, the major drawback of this synthetic strategy is the formation of ADTs as an inseparable mixture of both the syn- and the anti-isomers (mix-ADTs).[1]
Scheme 3.1. Synthesis of syn-3.1 and anti-3.1 as inseparable isomeric mixtures.[3]
The semiconductive properties of organic materials are affected by inhomogeneity in their crystalline morphology,[4] which may also include mixtures of isomers. Therefore, several research groups have conducted the synthesis of isomerically pure ADTs. In 2011, Geerts and coworkers have described the regiospecific synthesis of anti-ADTs alkylated in 2- and 8-postions, accomplished in six steps,[5] however, without describing the device performance of the synthesized anti-ADTs in this report. Takimiya and coworkers[6] have established a straightforward synthetic route to anti-ADTs methylated in 2- and 8- positions, starting from 2,6- dimethoxyanthracene. This study has investigated OFET devices and reports charge
96
Chapter 3 – Isomerically pure syn-anthradithiophenes carrier mobilities of 0.3 cm2/Vs. Tokito and coworkers have developed the stereoselective synthesis of both syn-3.1 and anti-3.1.[7] The different isomers syn- 3.1 and anti-3.1 can be prepared independently, beginning from different isomerically pure starting materials. Interestingly, the authors claim a significant improvement in charge transport for the syn-isomer, which is supported by X-ray crystallographic analysis, XRD, and AFM measurements. However, the anti-isomer shows, one order of magnitude, higher charge carrier mobilities than the syn-isomer. This counterintuitive fact is attributed to the centrosymmetric geometry of the anti-isomer, which causes lower disorder in the crystal lattice. The same research group[8] has described the stereoselective synthesis of syn- and anti-ADTs methylated in 2- and 8-position. By investigating OFET device performance, however, the anti-isomer shows a remarkably better performance than the syn-isomer in this study. This is also attributed to differences in the symmetry and intermolecular interactions found in the solid state, although the packing motif is referred to as a herringbone packing arrangement for both the syn- and anti-isomer. The C2-symmetric syn-isomer shows higher disorder in the crystal lattice than the centrosymmetric anti-isomer.
Analogous to the pentacene functionalization approach, a strategy where the ADT skeleton is substituted by trialkylsilylethynyl groups has also been applied. Starting with quinones mix-3.2, mix-3.3, or mix-3.4, varieties of trialkylsilylacetylides can be attached to the ADT core to yield mix-3.53.7 (Scheme 3.2).[9] Perhaps the most prominent examples have been investigated by Anthony and coworkers,[10] in 2008. Fluorine substituted ADTs mix-3.6a and mix-3.6b show a remarkable increase in stability and crystallinity, thus, showing high charge carrier mobilities of 6 cm2/Vs in single crystal OFETs.[11] In addition, brominated mix-3.7a and mix-3.7b derivatives have been used to synthesized polymeric structures by Pd(II)-mediated cross coupling reactions.[12]
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Chapter 3 – Isomerically pure syn-anthradithiophenes
Scheme 3.2. Synthesis of functionalized mix-ADTs.[3,9,10,12]
Interestingly, and similar to the pentacene approach, different sized trialkylsilyl groups lead to different solid-state arrangements of mix-ADTs.[3] TES-substitution in mix-3.5b and in mix-3.6b appears to direct the ADT packing toward a 2-D bricklayer arrangement, such as it is realized in the case of symmetrically substituted pentacene derivative 1.7a. The dense packing found for mix-3.6b is seemingly beneficial for the excellent charge carrier mobilities and OFET performance, as described above.
ADTs mix-3.7b have been used as starting material to form amide-functionalized mix-ADTs.[13] The amide substituents allow for the separation of the syn- and anti- isomers by selective crystallization. Using pure isomers, studies have shown that the syn-isomer enhances better performance in solar cells than the anti-isomer, and this difference was attributed to the different solid-state arrangements for the syn- and anti-isomers.
Lehnherr, however, synthesized brominated, isomerically pure syn-3.7a and syn-3.7b during his PhD work, but a comparison (i. e. electronic properties, solid-state arrangements, etc) with mix-ADT counterparts, namely mix-3.7a and mix-3.7b has not been investigated.
Despite the facts described in this introduction, several questions needed to be answered (Figure 3.1):
Are isomerically pure syn-3.6a and syn-3.6b synthetically achievable?
Are syn-3.6a and syn-3.6b more or less stable than mix-3.6a and mix-3.6b?
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Chapter 3 – Isomerically pure syn-anthradithiophenes
Do the electronic properties of syn-3.5a3.7b differ from the electronic properties of mix-3.5a3.7b?
Do the solid-state arrangements of syn-3.5a3.7b differ from the solid-state arrangements of mix-3.5a3.7b?
Comparison SiR3 SiR3 between syn-ADTs and mix-ADTs
vs. S X X X X S S S
X SiR3 SiR3 S
syn-3.5a R=i-Pr, X = H mix-3.5a R=i-Pr, X = H syn-3.6a R=i-Pr, X = F mix-3.6a R=i-Pr, X = F syn-3.6b R=Et,X=F mix-3.6b R=Et,X=F syn-3.7a R=i-Pr, X = Br mix-3.7a R=i-Pr, X = Br syn-3.7b R=Et,X=Br mix-3.7b R=Et,X=Br
Figure 3.1. Comparison between syn-ADTs and mix-ADTs achieved in this research work.
3.2 Synthesis of fluorinated isomerically pure syn-ADTs §
3.2.1 Syntheses of building blocks
As mentioned throughout the present research work, the assembly of acene-like structures relies heavily on the availability of quinone precursors. The precursor quinone compounds are usually formed in a four-fold aldol condensation of 1,2- dialdehydes and 1,4-cyclohexandione (see for example the synthesis of mix-3.2 in Scheme 3.1). In order to utilize a regiospecific aldol condensation for the construction of syn-ADTs, two modifications of the starting materials have to be considered: a) Selective protection of one of the aldehyde functionalities in the thiophene building block,
§ Portions of this section have been published. Reprinted with permission from: Lehnherr, D.; Waterloo, A. R.; Goetz, K. P.; Payne, M.; Hampel, F.; Anthony, J. E.; Jurchescu, O. D.; Tykwinski, R. R. Org. Lett. 2012, 14, 36603663. Copyright @ (2012) American Chemical Society.
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Chapter 3 – Isomerically pure syn-anthradithiophenes b) Selective protection of one of the keto functionalities in the 1,4-cyclohexandione synthon.[14]
For point a), the attempted synthetic pathway toward, fluorinated, isomerically pure syn-ADTs starts with commercially available 3-thiophene carbaldehyde 3.8 (Scheme 3.3). The latter can be protected as an acetal using a Dean-Stark trap to remove [2] H2O, yielding 3.9 quantitatively. Compound 3.9 was envisioned to be treated with n- BuLi at 78 °C and the reaction quenched by the addition of N-bromosuccinimide (NBS) to afford derivative 3.10. The reaction was performed several times, but after aqueous workup only complex mixtures were detected by TLC analysis, which did not allow for the isolation of compound 3.10. Therefore, the envisioned synthetic pathway via derivative 3.11 toward thiophene building block 3.12 could not be accomplished.
Scheme 3.3. Attempted synthesis toward thiophene building block 3.12.
The synthetic pathway toward fluorinated isomerically pure syn-ADTs was changed by starting with an easily available thiophene building block 3.13. It was envisioned that fluorination would be realized in a later synthetic step.[15] Thus, acetal 3.9 was treated with n-BuLi at 78 °C (Scheme 3.4). The mixture was stirred for 30 min at – 78 °C and the reaction quenched by the addition of dry, deoxygenated DMF.[2] After aqueous workup, purification could be achieved by passing the crude residue through a small pad of silica gel, eluting with CH2Cl2, to afford thiophene building block 3.13 in 61% yield as an oil that solidifies upon cooling in the refrigerator.
O 1) THF, nBuLi O O 78 °C, 30 min O
2) DMF, THF H S S rt, 4 h O 3.9 3.13 61%
Scheme 3.4. Synthesis of thiophene building block 3.13.[2]
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Chapter 3 – Isomerically pure syn-anthradithiophenes
For point b) protection of the 1,4-cyclohexandione, previous studies by Dan Lehnherr showed that the use of non-cyclic acetals is crucial for the later formation of the syn- ADT framework. Thus, commercially available 1,4-dioxaspiro[4.5]decan-8-one 3.14 was treated first with NaBH4 in dry MeOH at 20 °C, followed by addition of concentrated H2SO4 at –78 °C (Scheme 3.5). After stirring for 2 h at –78 °C, activated molecular sieves were added, and the mixture further stirred for 1 h. Finally, [16] after adding pre-dried NEt3, stirring to warm the mixture to rt, and aqueous workup, the mixture was purified by passing it through a short pad of silica gel using Et2O as an eluent. The desired acetal 3.15 could be isolated in good yields (52%), considering four steps of the one-pot reaction.[17] Compound 3.15 was then treated under Swern-oxidation conditions using dry DMSO and oxalylchloride in dry CH2Cl2. After aqueous workup and purification by column chromatography using a solvent [17] mixture of Et2O/hexanes/MeOH, compound 3.16 was obtained in 81% yield. Selective oxidation of 3.15 to 3.16 can also be achieved by using pyridiniumchlorochromate (PCC) in dry CH2Cl2, however, in lower isolated yields.
Scheme 3.5. Synthesis of 1,4-cyclohexandione synthon 3.16 from commercially available 3.14.[17]
3.2.2 Attempted synthesis of fluorinated syn-ADTs via deprotonation
An excess of aldehyde 3.13 was dissolved, along with 3.16, in EtOH/THF (3:1) and a small amount of 15% aqueous KOH was added (Scheme 3.6). The mixture was stirred for 5 h at rt. After aqueous workup and purification by column chromatography, compound 3.17 was isolated in 44% yield. Compound 3.17 was then dissolved in acetone and 24 mol% In(OTf)3 was added. The mixture was heated for 6 h at reflux and during that time, a red solid began to form, which later could be easily separated by filtration to give the product syn-3.2 in 75% yield. The red solid was characterized only by 1H NMR spectroscopy and HRMS analysis, because a meaningful characterization by 13C NMR spectroscopy suffers from the poor solubility
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Chapter 3 – Isomerically pure syn-anthradithiophenes of syn-3.2 in common organic solvents.[18] Quinone syn-3.2 was treated with an excess of lithiated TIPS-acetylene in dry THF at –78 °C. After aqueous workup a crude, red residue was obtained, which was further subjected to reductive aromatization in THF, using SnCl2 and small amounts of H2SO4 (without attempting to purify the intermediate diol; similar to unsymmetrically substituted pentacene derivatives, see Chapter 2). After aqueous workup, product purification was achieved by passing the mixture through a small pad of silica gel eluting with CH2Cl2/hexanes (1:1). The strong orange band was collected, and after recrystallization, isomerically pure syn-3.5a was isolated in 43% yield over two steps.[19]
Scheme 3.6. Synthesis of isomerically pure syn-3.5a.
Compound syn-3.5a was then attempted to fluorination using the electrophilic fluorine source NFSI (Scheme 3.7 and Table 3.1).[20] Thus, syn-3.5a was dissolved in dry THF and n-BuLi was added at –78 °C. After stirring for 30 min at –78 °C, an excess of NFSI, dissolved in dry THF, was added. The mixture was stirred for 18 h at rt. TLC analysis showed the total consumption of syn-3.5a, however, after aqueous workup the desired derivative syn-3.6a could not be isolated (entry 1). It was observed that the crude residue from the reaction with NFSI shows only poor solubility in CH2Cl2, which is not expected for ADT derivatives functionalized in 5- and 11- positions.[21] The reaction conditions were tried to adjust by using weaker bases along with the
transmetallation agent ZnCl2 Et2O (entries 24). In each case, derivative syn-3.5a was dissolved in dry THF, the solution was cooled to 78 °C, and the corresponding 102
Chapter 3 – Isomerically pure syn-anthradithiophenes base[22] was added in one portion. The mixture was stirred for 3060 min at 78 °C
and ZnCl2 Et2O was then added. The mixture was allowed to warm to rt, stirred for 2 h, and NFSI, dissolved in dry THF, was added. The mixture was then stirred for 18 h at rt and after aqueous workup, the product mixture was analyzed by TLC. The use of LiHMDS/ZnCl2 is seemingly not strong enough to deprotonate syn-3.5a (entry 2).
In the case of LDA/ZnCl2, trace amounts of an undefined product could be determined by TLC analysis (entry 3), but unfortunately isolation of this product was conducted to be impossible. The transmetallation agent ZnCl2 does not affect the outcome of the reaction of syn-3.5a with n-BuLi, because decomposition of the reaction mixture was observed in the case of using n-BuLi/ZnCl2 (entry 4).
Scheme 3.7. Attempted synthesis of syn-3.6a.
Table 3.1. Attempted reaction conditions for the synthesis of syn-3.6a.
Entry Solvent Temperature Base Additive Yield
1 THF 78 °C to rt n-BuLi -- --[a]
[b] 2 THF 78 °C to rt LiHMDS ZnCl2 Et2O --
[c] 3 THF 78 °C to rt LDA ZnCl2 Et2O --
[a] 4 THF 78 °C to rt n-BuLi ZnCl2 Et2O --
[a] Decomposition of the reaction mixture observed by TLC analysis. [b] Only starting material was observed by TLC analysis. [c] A fluorescent product was determined by TLC analysis, but was not isolated. 103
Chapter 3 – Isomerically pure syn-anthradithiophenes
3.2.3 Changing the synthetic strategy via halogen-lithium exchange
The synthetic pathway toward fluorinated isomerically pure syn-ADTs was changed with the expectation that brominated ADT derivatives syn-3.7a and syn-3.7b could be used for electrophilic fluorination via lithium-halogen exchange. It was envisioned that a bromine atom can potentially stabilize the lithium-ADT complex.[23] As mentioned in the introduction of this chapter, syn-3.7a and syn-3.7a have been realized by D. Lehnherr,[24] however, the synthesis is repeated in Scheme 3.8. Bromination was achieved at the beginning of synthetic pathway by treatment of 3- thiophenecarbaldheyde 3.8 with Br2 in refluxing CH2Cl2 in the presence of AlCl3 to afford 3.18 in 61% yield. Protection of the aldehyde function as an acetal to afford compound 3.19 was achieved in 81% yield, using a Dean-Stark trap to remove H2O. Introduction of the second aldehyde group was realized by treatment of 3.19 with n- BuLi at 78 °C and further reaction with ethylformate to afford 3.20 in 69% yield. Compound 3.20 underwent a two-fold aldol condensation with 3.16 to yield 3.21 in
89%. Refluxing 3.21 in the presence of 24 mol% In(OTf)3 in acetone gave isomerically pure syn-3.4 in 90% yield. Finally, treatment of syn-3.4 with lithiated trialkylsilylacetylenes in THF yielded the intermediate diols syn-3.22a and syn-3.22b in 47% and 59%, respectively. Reductive aromatization using SnCl2 and H2SO4 affords the desired brominated isomerically pure syn-3.7a and 3.7b in excellent yields (93% and 96%, respectively). Notably, the combined yields over two steps from syn-3.4 to syn-3.7a (44%) did not differ from the yield from syn-3.2 to syn-3.5a (43%). This observation generally predicts that the isolation of the intermediate diol may be avoided during the synthesis of syn-ADTs (similar to the synthesis of unsymmetrically substituted pentacenes in Chapter 2).
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Scheme 3.8. Synthesis of syn-3.7a and syn-3.7b.[14]
To complete the fluorination of the syn-ADT backbone, isomerically pure syn-3.7a or syn-3.7b were dissolved in dry THF and cooled to –78°C (Scheme 3.9). The mixture was treated with a small excess of n-BuLi and stirred for 30 min at –78 °C. The reaction was quenched by the addition of a tenfold excess NFSI in dry THF and the mixture was further stirred for 18 h at rt. Reaction workup was achieved by suspending the reaction mixture in hexanes and filtering this mixture through a short pad of silica gel eluting with hexanes and the strong orange band was collected. The solvent was evaporated and the obtained crude residue further purified by column chromatography. Using this procedure fluorinated syn-3.6a and syn-3.6b could be isolated in moderate yields (38% and 29%, respectively). Interestingly, in the case of the reaction of syn-3.7a with NFSI, monofluorinated syn-3.6c could be separately afforded from the silica gel column in 12% yield, while an analogous compound syn- 3.6d was not isolated.
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Chapter 3 – Isomerically pure syn-anthradithiophenes
Scheme 3.9. Synthesis of fluorinated syn-3.6a and syn-3.6b, along with the isolated by-products syn-3.6c, syn-3.23a and syn-3.23b.
It was also of interest to consider by-products that were formed during the electrophilic fluorination reaction (Scheme 3.9). Hence, the filter cake of the hexanes suspension from the reaction of syn-3.7a and syn-3.7b with NFSI was examined. The filter cake was dissolved and eluted from the pad of silica gel with CH2Cl2. The solvent was evaporated and the obtained residue further separated by automatic flash column chromatography. Based on this procedure, derivatives syn-3.23a and syn-3.23b could be isolated in low yields (5% and 2%, respectively). The structure of syn-3.23a could be determined by X-ray crystallographic analysis, which was crucial, because standard characterization methods such as NMR spectroscopy, HRMS, and MS/MS experiments were not conclusive.
All isolated syn-ADTs examined in the present research work show excellent solubility in common organic solvents, such as CH2Cl2, THF, or CHCl3. Additionally, ADTs syn-3.6a, syn-3.6b, and syn-3.6c show moderate solubility in non-polar solvents such as hexanes or n-pentane.
3.3 Synthesis of brominated mix-ADTs
Although brominated ADTs mix-3.7a and mix-3.7b have been reported,[25] own synthetic efforts will be discussed briefly, as they relate to the work in this thesis (Scheme 3.10).
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Chapter 3 – Isomerically pure syn-anthradithiophenes
Scheme 3.10. Synthesis of mix-3.7a and mix-3.7b.[25]
Commercially available 2,3-thiophenedicarbaldehyde was dissolved in CHCl3 along with an excess of Br2 . The mixture was stirred for 72 h at rt. After aqueous workup and purification by flash column chromatography, compound 3.24 was isolated in 75% yield. It is worth to mention, that it was conducted difficult to reproduce 3.24 following the reported procedure, and thus, some modifications of the reported procedure had to be considered. First, the thiophene-2,3-dicarboxaldehyde had to be purified before using it in the bromination step. Hence, the dialdehyde was dissolved in CHCl3 and this solution was passed through a short pad of Al2O3 to remove insoluble parts. The second modification of the original procedure was to significantly elongate the reaction time to 72 h (stirring for 18 h is reported in the original procedure).[25] To achieve the mix-ADT backbone, compound 3.24 was dissolved in EtOH along with a substoichiometric amount of 1,4-cyclohexandione. The mixture was treated with 15% aqueous KOH and stirred for 18 h at rt. The obtained red precipitate was filtered, washed, and air dried to afford quinone mix-3.4 in 66%. Compound mix-3.4 was suspended in dry THF and an excess of lithiated TIPS- acetylene in dry THF was added. The mixture was stirred for 18 h at rt. After aqueous workup and purification by chromatography and recrystallization, diol mix-3.25a was isolated in 29% yield. Compound mix-3.25a was then subjected to reductive aromatization using SnCl2/H2SO4. After aqueous workup, purification by column chromatography, and recrystallization, mix-3.7a was obtained in 28% yield. The same synthetic protocol was investigated to synthesize mix-3.7b. The isolation of the
107
Chapter 3 – Isomerically pure syn-anthradithiophenes intermediate diol was, however, avoided. Hence, a suspension of mix-3.4 was treated with an excess of lithiated TES-acetylene in dry THF. The mixture was stirred for 18 h at rt. After aqueous workup, the crude residue was subjected to reductive aromatization using SnCl2/H2SO4 for 6 h at rt. After aqueous workup and purification by column chromatography, mix-3.7b was isolated in low yield (26% over two steps).
Notably, the isolated yields of derivatives mix-3.7a and mix-3.7b differ significantly from the isolated yields of isomerically pure syn-3.7a and syn-3.7b. The reason for the difference in isolated yields is unknown.
3.4 Comparison between syn-ADTs and mix-ADTs
In the present research work it was tried to evaluate potential differences in the physical properties between isomerically pure syn-materials and mix-materials. Therefore, comparisons between own obtained data to reported literature have been made. In some cases, specific data for known mix-ADTs was not available. If this were the case, the dataset has been completed by experiments done as part of this thesis work under similar conditions.
3.4.1 Electronic properties of syn-ADTs and mix-ADTs
The electronic absorption characteristics of syn- and mix-ADT samples have been examined by UV-vis spectroscopy, measured in CH2Cl2 solutions (Table 3.2). Compound syn-3.5a shows a strong absorption at ca. 306 nm and a shoulder at ca. 331 nm. In the lower energy region, three major absorption bands are observed, centered at 480, 513, and 553 nm (Figure 3.2).
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Chapter 3 – Isomerically pure syn-anthradithiophenes
-5 Figure 3.2. UV-vis spectrum of syn-3.5a measured in CH2Cl2 (~10 M).
The absorption characteristics of syn-3.5a are largely reproduced in samples of mix- 3.5a.[26] Compound mix-3.5a shows a strong absorption band at ca. 309 nm. Three bands are present in the lower energy region, centered at 480, 514, and 555 nm. The UV-vis data for mix-3.5a is extracted from ref [26].
Fluorinated syn-3.6a and syn-3.6b show both similar UV-vis absorption characteristics (Figure 3.3, top). Compound syn-3.6a shows a strong absorption band located at ca. 305 nm along with a weak shoulder at ca. 322 nm and four weak absorptions are observed, located at ca. 344, 365, 396, and 420 nm. In the lower energy region three major absorption bands are located at ca. 458, 489, 526 nm. Compound syn-3.6b shows a strong absorption at ca. 305 nm along with a shoulder at ca. 321 nm. Four weak absorption bands are located at ca. 342, 366, 396, and 420 nm and in the lower energy region three bands are observed, which are centered at ca. 458, 484, and 525 nm.
Similar UV-vis characteristics are found for mix-3.6a and mix-3.6b (Figure 3.3 bottom).[27] ADT mix-3.6a shows a strong absorption band centered at 305 nm. Interestingly, the shoulder at ca. 320 nm, such as observed for derivative syn-3.6a, is not found. Four weak absorptions are located at ca. 342, 365, 396, and 419 nm and in the lower energy region three absorption bands are centered at ca. 458, 489, and 526 nm. ADT mix-3.6b also shows a strong absorption at 306 nm and a shoulder associated with this absorption is also not found in the case of syn-3.6b. Four weak
109
Chapter 3 – Isomerically pure syn-anthradithiophenes absorption bands are centered at ca. 341, 366, 396, and 419 nm, and three bands are located at lower energy at ca. 458, 489, and 525 nm.
Figure 3.3. UV-vis spectra of syn-3.6a and syn-3.6b (top), compared to mix-3.6a and 5 mix-3.6b (bottom) measured in CH2Cl2 (~10 M). 110
Chapter 3 – Isomerically pure syn-anthradithiophenes
Brominated compound syn-3.7a shows a strong absorption in the high energy region, located at ca. 311 nm, along with a weaker absorption at ca. 336 nm. ADT syn-3.7a gives rise to two weak absorption bands at ca. 406, 431 nm and in the lower energy region three absorption bands are centered at ca. 471, 504, and 543 nm.[14] ADT syn- 3.7b shows the exact same absorption characteristics as observed for syn-3.7a, along with similar extinction coefficients.[14] UV-vis data for compounds syn-3.7a and syn-3.7b are extracted from ref [14].
In comparison to syn-3.7a and syn-3.7b, compounds mix-3.7a and mix-3.7b show little variations in their absorption behavior (Figure 3.4). In detail, mix-3.7a shows a broad absorption band in the high energy region, which is fragmented into two maxima centered at ca. 310 and 319 nm, along with a shoulder at 333 nm. Three weak absorptions are observed centered at ca. 379, 404, and 427 nm. In the lower energy region, three characteristic bands are located at ca. 473, 506, and 545 nm. ADT mix-3.7b shows a broad absorption band in the high energy region, fragmented into two absorption maxima, centered at ca. 310 and 321 nm. Three weak absorptions are located at ca. 380, 404, and 427 nm, along with three characteristic absorptions in the lower energy region centered at ca. 473, 506, and 544 nm.
6 Figure 3.4. UV-vis spectra of mix-3.7a and mix-3.7b measured in CH2Cl2 (~10 M in the case of mix-3.7a and ~10 5 in the case of mix-3.7b).
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Chapter 3 – Isomerically pure syn-anthradithiophenes
Solid-state films have been prepared by dropcasting a concentrated solution of the ADTs on a quartz surface, and after air-drying, the absorption spectra have been recorded by UV-vis spectroscopy (Figure 3.5). In general, syn-ADTs show similar thin-film performance as their mix-ADT counterparts. In detail, syn-3.6a and mix-3.6a show similar longest wavelength absorptions at ca. 530 and 533 nm. Compounds [14] [14] syn-3.7a (max = 555 nm), mix-3.7a (max = 550 nm), syn-3.7b (max = 561 nm), and mix-3.7b (max = 556 nm) all share similar max-values. The exception to this trend is the case of syn-3.6b (max = 543 nm) compared to mix-3.6b (max = 523 nm).
The origin of this rather large difference in max-values is, however, not well understood.
(a)
(b)
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Chapter 3 – Isomerically pure syn-anthradithiophenes
(c)
(d)
113
Chapter 3 – Isomerically pure syn-anthradithiophenes
(e)
(f)
Figure 3.5. Thin film UV–vis spectra of (a) syn-3.6a, (b) syn-3.6b, (c) mix-3.6a, (d) mix-3.6b, (e) mix-3.7a, and (f) mix-3.7b (measured on quartz, drop cast from CH2Cl2 solution).
Solution-state emission spectra of syn- and mix-ADT derivatives were measured in
CH2Cl2 (Table 3.2). All compared pairs of syn- and mix-ADTs show similar emission properties and a small Stokes shift of 69 nm. This suggests minimal molecular reorganization upon photoexcitation of the ADT chromophore.
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Chapter 3 – Isomerically pure syn-anthradithiophenes
3.4.2 Electronic properties of by-products
The UV-vis spectra of the by-products syn-3.6c and syn-3.23a have been recorded in
CH2Cl2 (Figure 3.6). ADT syn-3.6c shows a strong absorption at ca. 306 nm along with a weak shoulder at ca. 326 nm and a weak band at ca. 348 nm. Compound syn- 3.6c shows weak absorption bands at ca. 398 and 421 nm and in the low energy region three absorption bands are present at ca. 467, 501, and 539 nm. In contrast, syn-3.23a shows a strong absorption at ca. 312 nm along with two weaker absorptions at ca. 345 and 365 nm. Two weak absorptions are present, at ca. 404 and 430 nm and in the low energy region syn-3.23a shows three absorptions at ca. 480, 516, and 555 nm. The UV-vis absorption of syn-3.23a features a big red shift of
max of ca. 16 nm compared to derivative syn-3.6c, but only a small red shift (2 nm) compared to fully protonated syn-3.5a (Table 3.2).
-5 Figure 3.6. UV-vis spectra of syn-3.6c and syn-3.23a measured in CH2Cl2 (~10 M).
Samples of syn-3.6c and syn-3.23a were drop casted from a concentrated CH2Cl2 solution onto a quartz surface, and after air-drying, the absorption spectra were measured by UV-vis spectroscopy (Figure 3.7). Thin-film UV-vis traces of syn-3.6c are not significantly red shifted compared to the obtained solution-state traces and a
max of 541 nm is observed. In contrast, syn-3.23a shows a max of 604 nm, which is
115
Chapter 3 – Isomerically pure syn-anthradithiophenes strongly red shifted (ca. 49 nm) compared to the UV-vis absorption obtained from solution. The solid-state UV-vis spectrum of syn-3.23a shows well-resolved absorption bands, which indicates that the film consists of very homogenous large- sized crystallites.[28]
(a)
(b)
Figure 3.7. Thin film UV-vis spectra of (a) syn-3.6c and (b) syn-3.23a (measured on quartz, drop cast from CH2Cl2 solution).
Solution-state emission spectra of syn-3.6c and syn-3.23a were measured in CH2Cl2 (Table 3.2). ADT syn-3.6c shows a small Stokes shift of 9 nm, while compound syn- 3.23a shows the largest Stokes shift (12 nm) in the series of all ADT derivatives
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Chapter 3 – Isomerically pure syn-anthradithiophenes
investigated in this research work. In general, the emission properties of syn-3.6c are similar to the emission properties observed for syn-3.23a.
3.4.3 Summary of electronic properties
Generally, isomeric purity has no or only little effect on the UV-vis absorption characteristics of ADT molecules studied so far (Table 3.2). The solution-state absorption characteristics of syn-ADTs are remarkably similar to their mix-ADT counterparts, although mix-3.7a and mix-3.7b show broader and more diverse absorption behavior in the high energy region than their isomeric counterparts, syn- 3.7a and syn-3.7b. The absorption characteristics of monofluorinated ADT syn-3.6c might be regarded as a compromise between the absorption characteristics found for
derivative syn-3.5a and derivative syn-3.6a, although the max value of syn-3.6c closely resembles the former. Solid-state UV-vis spectroscopy could not determine significant differences in the electronic properties between syn- and mix-ADTs. This observation is consistent with the data reported for syn-3.1 and anti-3.1,[7] where no differences between both isomers are observed. Solution-state emission spectra also could not determine significant differences between syn- and mix-ADTs.
Table 3.2. Optical properties of a selection of ADTs.
max max em Stokes red shift Egap, [a] [b] [d] Shift Compound (CH2Cl2) (film) [c] (CH2Cl2) [nm] opt[eV] [nm] [nm] [nm] [nm](meV)
syn-3.5a 553 --[e] --[e] 2.18 559, 604 6 (24)
mix-3.5a 555[f] --[e] --[e] --[e] 561[f] 6 (24)
syn-3.6a 526 530 4 2.29 532, 573 6 (27)
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Chapter 3 – Isomerically pure syn-anthradithiophenes
max max em Stokes red shift Egap, Compound [a] [b] [d] Shift (CH2Cl2) (film) [c] (CH2Cl2) [nm] opt[eV] [nm] [nm] [nm] [nm](meV)
mix-3.6a 526 533 7 2.29 532, 572 6 (27)
syn-3.6b 525 543 18 2.29 534, 573 9 (40)
mix-3.6b 525 523 2 2.30 532, 573 6 (31)
syn-3.6c 539 541 2 2.23 548, 589 9 (38)
syn-3.7a 543[g] 555[g] 12[g] 2.19[g] 549, 594[g] 6 (25)[g]
mix-3.7a 545 550 5 2.20 551, 593 6 (25)
syn-3.7b 543[g] 561[g] 18[g] 2.20[g] 549, 594[g] 6 (25)[g]
mix-3.7b 544 556 12 2.20 551,592 7 (29)
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Chapter 3 – Isomerically pure syn-anthradithiophenes
max max em Stokes red shift Egap, Compound [a] [b] [d] Shift (CH2Cl2) (film) [c] (CH2Cl2) [nm] opt[eV] [nm] [nm] [nm] [nm](meV)
syn-3.23a 555 604 49 2.15 567, 607 12 (47)
syn-3.1 488[h] 544[h] 56 --[e] --[e] --[e]
anti-3.1 489[h] 545[h] 56 --[e] --[e] --[e]
[a] Lowest energy absorption maxima. [b] Cast from CH2Cl2 onto quartz. [c] Determined using the intercept of the x-axis and the tangent applied to the longest wavelength absorption peak. [d]
Measured using exc = second longest absorption wavelength. [e] Data not measured. [f] Data taken from ref [26]. [g] Data taken from ref [14]. [h] Data taken from ref [7].
3.4.4 Thermal properties of syn-ADTs and mix-ADTs
The thermal stability of selected ADT derivatives has been explored by thermal gravimetric analysis (TGA), and differential scanning calorimetry (DSC) measurements and the results are summarized in Table 3.3. TGA shows clearly the improved stability from protonated syn-3.5a to brominated (syn-3.7a and syn-3.7b) and to fluorinated (syn-3.6a and syn-3.6b) ADTs. The decomposition temperature measured by TGA steadily increased from ca. 211 °C for syn-3.5a, to ca. 315 °C for syn-3.7a, and to ca. 325 °C for syn-3.6a. This trend is consistent with the improved stability issues for fluorinated mix-3.6a and mix-3.6b compared to mix-3.5a, reported by Anthony and coworkers.[10] Interestingly, substitution by only one fluorine atom such as in syn-3.6c is seemingly enough to enhance the stability of the ADT molecule. The decomposition temperature for syn-3.6c (ca. 315 °C) is analogous to that of symmetrically fluorinated syn-3.6a (ca. 325 °C). TGA suggest no significant change in stability depending on isomeric purity. The compared pairs of syn-ADTs (syn-3.6a and syn-3.6b) and mix-ADTs (mix-3.6a and mix-3.6b) show similar decomposition temperatures, and these trends are, in large part, reproduced by DSC 119
Chapter 3 – Isomerically pure syn-anthradithiophenes analyses. All of the investigated ADT derivatives show sharp melting points regardless of isomeric purity. The isomerically pure syn-ADT material (syn-3.6a and syn-3.6b) show a slightly lower melting point (ca. 10 °C) than the mix-ADT material (mix-3.6a and mix-3.6b), while decomposition is observed at about the same temperature range. ADT derivatives substituted by the bulkier TIPS-group (syn-3.6a, mix-3.6a, and syn-3.7a) show a significant higher melting point (and decomposition temperature) than their TES-substituted counterparts (syn-3.6b, mix-3.6b, and syn- 3.7b).
Table 3.3. Thermal properties of a selection of syn-ADTs compared to a selection of mix-ADTs.
TGA DSC DSC dp T Compound d mp
/ºC [a] /ºC [b] Onset /ºC Peak /ºC
syn-3.5a 211 199 n.a n.a
syn-3.6a 325 239 341 370
mix-3.6a 320 247 368 371
syn-3.6b 285 190 291 320
mix-3.6b 287 200 267 321
syn-3.6c 315 253 349 379
syn-3.7a 315[c] 315[c] 350[c] n.a.[c]
syn-3.7b 295[c] 273[c] 298[c] 313[c]
[a] Measured under a nitrogen atmosphere, Td = decomposition temperature. [b] Measured under a nitrogen atmosphere, mp = melting point, shown as peak temperatures; dp = decomposition point, shown as onset/peak temperatures. [c] data taken from ref [14].
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Chapter 3 – Isomerically pure syn-anthradithiophenes
3.4.5 Solid-state analysis of syn-ADTs and mix-ADTs
To evaluate the solid-state arrangement of syn-ADTs, crystals suitable for X-ray crystallographic analysis have been grown[29] by slow evaporation of a concentrated
CH2Cl2 solution layered with acetone at 4 °C. This method was unsuccessful for compound syn-3.6b, but nevertheless, crystals could be obtained for this compound by slow evaporation of a concentrated n-pentane solution at –20 °C.
ADT syn-3.5a crystallizes in the space group P21/c with two molecules in the unit cell (Figure 3.8). Compound syn-3.5a shows a 1-D slipped packing along the crystallographic a-axis with an interplanar distance[30] of ca. 3.49 Å and approximately two of the aromatic rings overlapping. The rows of stacking molecules are macroscopically ordered within a herringbone motif. The sulfur atoms S1/S1´ of the thiophene unit are disordered over four unique positions and show 50:50 occupancies. Further disorder is found in the isopropyl groups.
(a) (b)
(c)
Figure 3.8. X-ray crystallographic analysis showing (a) molecular structure of syn- 3.5a, (b) illustration of the unit cell (triisopropylsilyl group and hydrogen atoms omitted for clarity), and (c) packing motif (triisopropylsilyl group and hydrogen atoms
121
Chapter 3 – Isomerically pure syn-anthradithiophenes omitted for clarity); disorder in isopropyl groups not shown, ORTEPs drawn at 50% probability level.
The structural information of syn-3.5a is largely reproduced in the X-ray crystallographic analysis of mix-3.5a as reported by Anthony and coworkers.[31] ADT mix-3.5a crystallizes in the space group P21/c with two molecules in the unit cell (Figure 3.9). Compound mix-3.5a packs in a 1-D slipped stacking motif along the crystallographic a-axis with an interplanar distance[30] of ca. 3.45 Å and approximately two of the aromatic rings overlapping. Interestingly, the thiophene units in mix-3.5a are disordered throughout the solid, showing occupancies of 60:40 for the S1:S1´atoms. Further disorder is found in two of the isopropyl groups. In summary, the crystal structures of ADTs syn-3.5a and mix-3.5a share the exact same symmetry operations (identity, C2-axis, inversion center, and glide plane).
(a) (b)
(c)
Figure 3.9. X-ray crystallographic analysis showing (a) molecular structure of mix- 3.5a, (b) illustration of the unit cell (triisopropylsilyl group and hydrogen atoms omitted for clarity), and (c) packing motif (triisopropylsilyl group and hydrogen atoms omitted for clarity); disorder in isopropyl groups not shown, ORTEPs drawn at 50% probability level.[31]
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Chapter 3 – Isomerically pure syn-anthradithiophenes
ADT syn-3.6a crystallizes in the space group P1 with one molecule in the unit cell (Figure 3.10). Compound syn-3.6a packs in a 2-D bricklayer arrangement with interplanar distances of 3.30 and 3.34 Å and approximately two of the aromatic rings overlapping. The 2,8-difluoroanthra[2,3-b:7,6-b’]dithiophene group is disordered about the crystallographic inversion center showing occupancies of 50:50 for the S1/F1:S1´/F1´unit. Each of the isopropyl groups show disorder throughout the solid.
(a) (b)
(c)
Figure 3.10. X-ray crystallographic analysis showing (a) molecular structure of syn- 3.6a, (b) illustration of the unit cell, and (c) packing motif (triisopropylsilyl group and hydrogen atoms omitted for clarity), disorder in isopropyl groups not shown, ORTEPs drawn at 50% probability level).
The structure of ADT mix-3.6a has been reported,[32] and it shows that this derivative also crystallizes in the space group P1 with one molecule in the unit cell (Figure 3.11). Compound syn-3.6a packs in a 2-D bricklayer arrangement with two interplanar distances[30] of 3.29 and 3.31 Å and approximately two of the aromatic rings overlapping. The 2,8-difluoroanthra[2,3-b:7,6-b’]dithiophene group is disordered 123
Chapter 3 – Isomerically pure syn-anthradithiophenes about the crystallographic inversion center showing occupancies of 53:47 for the S5/F1:S7´/F1´unit. One of the isopropyl-groups in mix-3.6a is disordered. In summary, the crystal structures of ADTs syn-3.6a and mix-3.6a share the exact same symmetry operations (identity and inversion center).
(a) (b)
(c)
Figure 3.11. X-ray crystallographic analysis showing (a) molecular structure of mix- 3.6a, (b) illustration of the unit cell, and (c) packing motif (triisopropylsilyl group and hydrogen atoms omitted for clarity), disorder of the isopropyl groups not shown, ORTEPs drawn at 50% probability level).[32]
ADT syn-3.6b crystallizes in the space group P1 with one molecule in the unit cell (Figure 3.12). Compound syn-3.6b packs in a 2-D bricklayer arrangement with interplanar distances[30] of 3.31 and 3.40 Å and approximately two of the aromatic rings overlapping. Neighboring stacks of molecules are in close contact with each other, showing S…F-distances of ca. 3.50 Å. The 2,8-difluoroanthra[2,3-b:7,6- b’]dithiophene group is disordered about the crystallographic inversion center
124
Chapter 3 – Isomerically pure syn-anthradithiophenes showing occupancies for the S25/F1:S25A/F1A unit of approximately 50:50. Disorder of the trialkylsilyl group is not observed.
(a) (b)
(c) (d)
Figure 3.12. X-ray crystallographic analysis showing (a) molecular structure of syn- 3.6b, (b) illustration of the unit cell (triethylsilyl group and hydrogen atoms omitted for clarity), and (c) packing motif (triethylsilyl group and hydrogen atoms omitted for clarity), and (d) illustration of S…F-distances ORTEPs drawn at 50% probability level).
In large part, the crystallographic characteristics of syn-3.6b are reproduced in the crystal structure of mix-3.6b as reported by Anthony and coworkers.[33] Compound mix-3.6b crystallizes in the space group P1 with one molecule in the unit cell (Figure 3.13). Compound mix-3.6b packs in a 2-D bricklayer arrangement with an interplanar distance[30] of ca. 3.36 Å and approximately two of the aromatic rings overlapping. Neighboring stacks of molecules are in close contact with each other, showing S…F-distances of ca. 3.22 Å which are shorter than the S…F-distances found for syn-3.6b. The 2,8-difluoroanthra[2,3-b:7,6-b’]dithiophene group is disordered 125
Chapter 3 – Isomerically pure syn-anthradithiophenes about the crystallographic inversion center showing occupancies for the S5/F1:S5´/F1´ unit of approximately 69:31. Further disorder in the triethyl groups is not observed. In summary, the crystal structures of ADTs syn-3.6b and mix-3.6b share the exact same symmetry operations (identity and inversion center).
(a) (b)
(c) (d)
Figure 3.13. X-ray crystallographic analysis showing (a) molecular structure of mix- 3.6b, (b) illustration of the unit cell, (c) packing motif (triethylsilyl group and hydrogen atoms omitted for clarity), and (d) illustration of S…F-distances ORTEPs drawn at 50% probability level).[33]
ADT syn-3.7a crystallizes in the space group P1 with one molecule in the unit cell
(Figure 3.14) and one molecule of co-crystallized CH2Cl2. ADT syn-3.7a shows a 1-D slipped stacking motif along the crystallographic a-axis with interplanar distances[30] of ca. 3.52 Å and approximately two of the aromatic rings overlapping. The 2,8- dibromoanthra[2,3-b:7,6-b’]dithiophene group is disordered showing occupancies for the S1/Br1:S2/Br2 unit of 50:50. In general, the mode of disorder spans the whole conjugated framework, while the TIPS-groups in syn-3.7a are not disordered.
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Chapter 3 – Isomerically pure syn-anthradithiophenes
(a) (b)
(c) Figure 3.14. X-ray crystallographic analysis showing (a) molecular structure of syn- 3.7a, (b) illustration of the unit cell, and (c) packing motif (triisopropylsilyl group and hydrogen atoms omitted for clarity), solvent molecules omitted, ORTEPs drawn at 50% probability level).[29]
ADT mix-3.7a crystallizes in the space group P1 with one molecule in the unit cell and without co-crystallized solvent molecules (Figure 3.15). Notably, the quality of the crystals did not allow for a perfect refinement (R-value ~11.6%). ADT mix-3.7a shows a 1-D slipped stacking motif along the crystallographic a-axis with interplanar distances[30] of ca. 3.60 Å and approximately two of the aromatic rings overlapping. The 2,8-dibromoanthra[2,3-b:7,6-b’]dithiophene group is disordered showing occupancies for the S25/Br1:S25A/Br4 unit of approximately 76:24. Interestingly, and in contrast to compound syn-3.7a, one TIPS-group of mix-3.7a shows disorder. In summary, the crystal structures of ADTs syn-3.7a and mix-3.7a share the exact same symmetry operations (identity and inversion center).
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Chapter 3 – Isomerically pure syn-anthradithiophenes
(a) (b)
(c)
Figure 3.15. X-ray crystallographic analysis showing (a) molecular structure of mix- 3.7a, (b) illustration of the unit cell, and (c) packing motif (triisopropylsilyl group and hydrogen atoms omitted for clarity), disorder in the isopropyl groups not shown, ORTEPs drawn at 30% probability level[34]).
ADT syn-3.7b crystallizes in the space group P1 with one molecule in the unit cell (Figure 3.16). Compound syn-3.7b shows a 1-D slipped stacking motif along the crystallographic a-axis with interplanar distances[30] of ca. 3.51 Å and approximately three of the aromatic rings overlapping. The 2,8-dibromoanthra[2,3-b:7,6- b’]dithiophene group is disordered, showing occupancies for the S1/Br1:S2/Br2 unit of 50:50. The mode of disorder spans throughout the whole conjugated backbone of syn-3.7b, but disorder in the triethylsilyl groups is not observed.
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Chapter 3 – Isomerically pure syn-anthradithiophenes
(a) (b)
(c)
Figure 3.16. X-ray crystallographic analysis showing (a) molecular structure of syn- 3.7b, (b) illustration of the unit cell, and (c) packing motif (triethylsilyl group and hydrogen atoms omitted for clarity), ORTEPs drawn at 50% probability level).[14]
The structural characteristics of syn-3.7b are largely reproduced in the crystal structure of mix-3.7b (Figure 3.17). ADT mix-3.7b crystallizes in the space group P1 with one molecule in the unit cell and shows a 1-D slipped stacking motif along the crystallographic a-axis with interplanar distances[30] of ca. 3.51 Å and approximately three of the aromatic rings overlapping. The 2,8-dibromoanthra[2,3- b:7,6-b’]dithiophene group is disordered and shows occupancies for the S25/Br1:S25A/Br1A unit of approximately 62:38. Further disorder in the triethylsilyl groups is not observed. In summary, the crystal structures of ADTs syn-3.7b and mix-3.7b share the exact same symmetry operations (identity and inversion center).
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Chapter 3 – Isomerically pure syn-anthradithiophenes
(a) (b)
(c)
Figure 3.17. X-ray crystallographic analysis showing (a) molecular structure of mix- 3.7b, (b) illustration of the unit cell, and (c) packing motif (triethylsilyl group and hydrogen atoms omitted for clarity), ORTEPs drawn at 50% probability level).
3.4.6 Solid-state properties of by-products
Crystals suitable for X-ray crystallographic analysis of syn-3.6c and syn-3.23a have been grown by slowly evaporation of a concentrated CH2Cl2 or THF solution layered with acetone at 4 °C, respectively. ADT syn-3.6c crystallizes in the space group P1 with one molecule in the unit cell (Figure 3.18). Compound syn-3.6c shows a 2-D packing arrangement with similar interplanar distances[30] of 3.37 Å and 3.34 Å and approximately one of the aromatic rings overlapping. The 2-fluorothiophene groups, as well as the 8-hydrothiophene groups are disordered about the crystallographic inversion center. The S25:S25A unit was refined using 50:50 occupancies, while 25:25 occupancies were used for the F25/H25:F25A/H25A unit. Four out of six isopropyl groups show disorder throughout the solid.
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Chapter 3 – Isomerically pure syn-anthradithiophenes
(a) (b)
(c)
Figure 3.18. X-ray crystallographic analysis showing (a) molecular structure of syn- 3.6c, (b) illustration of the unit cell (triisopropylsilyl group and hydrogen atoms omitted for clarity), and (c) packing motif (triisopropylsilyl group and hydrogen atoms omitted for clarity); disorder in isopropyl groups not shown, ORTEPs drawn at 50% probability level.
ADT syn-3.23a crystallizes in the space group P1 with two molecules in the unit cell along with one THF molecule co-crystallized per asymmetric unit (Figure 3.19). ADT syn-3.23a shows a 2-D packing motif with two similar interplanar distances[30] of 3.34 Å and 3.37 Å. Stacks of derivative syn-3.23a along the crystallographic a-axis are in close contact with neighboring stacks of molecules showing S…O-mediated distances of 2.85 Å. This close contact of neighboring stacks of syn-3.23a leads to a dense packing motif and could perhaps explain the large red shift in the solid-state UV-vis characteristics. The 2-fluorothiophene shows disorder with occupancies for 80:20 for the S1/F1:S1A/F1A as well as for the S2:S2A unit. No disorder is found for the isopropyl groups. 131
Chapter 3 – Isomerically pure syn-anthradithiophenes
(a) (b)
(c) (d)
Figure 3.19. X-ray crystallographic analysis showing (a) molecular structure of syn- 3.23a, (b) illustration of the unit cell (triisopropylsilyl group and hydrogen atoms omitted for clarity), (c) packing motif (triisopropylsilyl group and hydrogen atoms omitted for clarity), and (d) illustration of S…O-mediated distances between the stacks of syn-3.23a; solvent molecules omitted, ORTEPs drawn at 50% probability level.
3.4.7 Summary of solid-state analysis
Only minor differences in solid-state structural data between syn-ADTs and mix- ADTs could be determined (Table 3.4). In general, all compared pairs of syn- and mix-ADT materials share the same symmetry operations and have similar unit cell parameters. In each of the analyzed crystal structures of syn-isomers, the 2,8- dihaloanthra[2,3-b:7,6-b’]dithiophene group is disordered about the inversion center of the molecule and faces occupancies of approximately 50:50. These observed occupancies are in contrast to the occupancies in crystal structures of mix-ADTs. All analyzed mix-ADTs show deviations in their occupancies for the 2,8- dihaloanthra[2,3-b:7,6-b’]dithiophene group, spanning a wide range from 53:47 (for 132
Chapter 3 – Isomerically pure syn-anthradithiophenes mix-3.6a) to 76:24 (for mix-3.7a). This suggests a significant portion of anti-isomers incorporated within the crystal lattice of mix-ADTs, although a distribution between syn-and anti-isomers on the basis of the crystal lattice is impossible. Particularly, the mode of disorder in brominated derivatives (syn-3.7a and syn-3.7b) is spanned through the whole conjugated backbone, while the disorder in analogues mix-ADTs (mix-3.7a and mix-3.7b) is located only at the thiophene units (different asymmetric units). The crystal structures of syn- and mix-ADTs show similar disorder in the trialkylsilyl groups. The exception of this observation is syn-3.7a, where the TIPS- groups are not disordered, while in mix-3.7a one of the TIPS-groups shows disorder.
In general, isomeric purity has only little or no effect on the solid-state packing arrangements (packing motifs, interplanar distances, and total -overlapping), which is principally consistent with the reported data for syn-3.1 and anti-3.1.[7] In the case of syn-3.6b, however, the distances between neighboring 2-D stacks of molecules seem to be larger than the distances between neighboring 2-D stacks of molecules of mix-3.6b (Figure 3.12 and Figure 3.13). Unfortunately, the reason for this observation is unknown.
ADT syn-3.6c seemingly does not show significant differences in the packing motif and in interplanar distances compared to fully fluorinated ADT syn-3.6a. ADT syn- 3.23a is functionalized by a relative bulk substituent in its 8-positions, but this seemingly does not affect the 2-D packing motif.
The crystallographic characteristics analyzed in this research work are in agreement with the crystal data for syn-3.1 and anti-3.1 (Figure 3.20). In the case of syn-3.1, two independent molecules are found in the unit cell showing both occupancies of 50:50 for the S1A:S2A unit. In the case of anti-3.1, two independent molecules are found spanning occupancies of 68:32 and 90:10 for the thiophene units (S1A:S1B), respectively. The mode of disorder for syn-3.1 is spanning the whole aromatic backbone, while for anti-3.1 disorder is located only at the thiophene units.[7] Both isomers are arranged within a herringbone packing motif, showing only little differences in their tilt angles (53.0° for syn-3.1 and 51.8° for anti-3.1, respectively).[7]
133
Chapter 3 – Isomerically pure syn-anthradithiophenes
(a) (b)
(c) (d)
Figure 3.20. X-ray crystallographic analysis showing (a) molecular structure of syn- 3.1 along with the observed disorder, (b) molecular structure of anti-3.1, (c) herringbone packing motif of syn-3.1 (hydrogen atoms omitted for clarity), and (d) herringbone packing motif of anti-3.1 (hydrogen atoms omitted for clarity); ORTEPs drawn at 50% probability level, data taken from ref [7].
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Chapter 3 – Isomerically pure syn-anthradithiophenes
Table 3.4. Crystallographic data of compared ADT isomers.
Compd Space Crystal Z packing a [ Å] b [Å] c [Å] group System motif syn-3.5a P21/c monoclinic 2 1-D slip 8.7901(2) 17.7238(8) 12.2596(5) 90 90.390(3) 90
[a] mix-3.5a P21/c monoclinic 2 1-D slip 8.7865(3) 17.6967(7) 12.1065(5) 90 90.4638(18) 90 syn-3.6a P1 triclinic 1 2-D 7.5855(7) 8.1701(8) 16.2295(12) 100.990(7) 92.320(7) 98.594(8) mix-3.6a[b] P1 triclinic 1 2-D 7.5766(4) 8.1796(5) 16.1503(10) 100.846(3) 92.621(3) 98.790(2) syn-3.6b P1 triclinic 1 2-D 7.0493(17) 7.9236(15) 16.025(2) 87.014(13) 84.846(15) 63.64(2) mix-3.6b[b] P1 triclinic 1 2-D 7.1044(5) 7.1739(5) 16.6481(12) 98.214(4) 92.598(5) 107.335(4) syn-3.7a[c] P1 triclinic 1 1-D slip 8.5173(2) 10.3469(3) 12.7616(4) 97.6951(3) 101.2361(3) 102.4484(3) mix-3.7a P1 triclinic 1 1-D slip 8.9196(12) 10.6329(13) 11.0012(13) 108.470(11) 95.340(10) 91.467(11) syn-3.7b[c] P1 triclinic 1 1-D slip 7.2206(4) 10.3360(5) 11.2116(6) 84.7708(6) 90.0225(6) 81.1673(6) mix-3.7b P1 triclinic 1 1-D slip 7.1824(5) 10.3950(7) 11.1870(7) 95.222(5) 90.339(5) 98.604(6) syn-3.1[d] P1 triclinic 2 herringbone 5.8865(8) 7.5079(10) 14.347(2) 96.106(4) 94.285(4) 90.414(4) anti-3.1[d] P1 triclinic 2 herringbone 5.9155(16) 7.772(2) 13.991(4) 86.589(10) 78.271(8) 86.424(9)
[a] Data taken from ref [26]. [b] Data taken from ref [10]. [c] Data taken from ref [14] [d] Data taken from ref [7].
135
Chapter 3 – Isomerically pure syn-anthradithiophenes 3.5 Attempted derivatizations of syn-isomers
3.5.1 A pentacene-ADT chromophore
Bao and coworkers have used mix-ADTs as a building block to form ADT-containing polymers.[35] The obtained polymer forms lamellar structures in thin films and shows good charge carrier mobilities. Such a strategy was attempted using a combination of the syn-ADT and the pentacene skeleton (Scheme 3.11). Thus, pentacene precursor 2.3 (see Chapter 2) was treated under Sonogoshira cross coupling conditions with syn-3.7a using Pd(PPh3)2Cl2, CuI, and diisopropylamine in dry, deoxygenated THF. The mixture was heated for 18 h at reflux. After aqueous workup and purification by column chromatography, syn-3.26 was isolated in 56% yield. Compound syn-3.26 was then subjected to reductive aromatization using SnCl2/H2SO4 to form the pentacene backbones. After total consumption of syn-3.7a and aqueous workup, however, a complex mixture was obtained, which was impossible to separate. The color of the mixture suggested formation of the desired syn-3.27, but the product could not be identified.
ADT syn-3.26 has been characterized by UV-vis spectroscopy in CH2Cl2 (Figure 3.21, top). The spectrum shows three strong absorptions located at ca. 247, 320, and 369 nm along with a shoulder centered at ca. 392 nm. ADT syn-3.26 shows two weak absorption bands located at ca. 433, and 460 nm and three strong absorptions in the lower energy region are centered at ca. 491, 528 and 571 nm. The red shift in
max (18 nm) of syn-3.26 compared to unsubstituted ADT syn-3.5a is attributed to the triple bonds attached in the 2- and 8-positions.
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Chapter 3 – Isomerically pure syn-anthradithiophenes
Scheme 3.11. Attempted two-step synthesis of pentacene-based ADT syn-3.27.
137
Chapter 3 – Isomerically pure syn-anthradithiophenes
5 Figure 3.21. UV-vis spectrum of syn-3.26 measured in CH2Cl2 (~10 M, top) and thin film UV-vis spectrum of syn-3.26 (drop cast from CH2Cl2 on quartz, bottom).
A sample of syn-3.26 was drop casted from a concentrated CH2Cl2 solution onto a quartz surface, and after air-drying, the absorption spectrum was measured by UV- vis spectroscopy (Figure 3.21, bottom). ADT syn-3.26 shows very broad and poorly resolved UV-vis absorptions in the high energy region. In the lower energy region, however, three strong absorption bands are located at ca. 493, 530 and 574 nm but
138
Chapter 3 – Isomerically pure syn-anthradithiophenes only a small red shift of ca. 3 nm in max is observed compared to solution-state UV- vis absorption. This suggests the absence of strong --interactions in the solid state.
Crystals suitable for X-ray crystallography have been grown by slow evaporation of a concentrated solution of syn-3.26 in CH2Cl2 layered with acetone at 4 °C (Figure 3.22). ADT syn-3.26 crystallizes in the space group P1 with one molecule in the unit cell along with one disordered CH2Cl2 molecule per asymmetric unit. Although syn- 3.26 does not show any strong intermolecular -stacking interactions, the solid- state arrangement appears to be dictated by the naphthyl moieties, with distances of approximately 2.95 Å. The interactions of the naphthyl units afford a staircase-like packing motif of molecules of syn-3.26 along the crystallographic a-axis. The thiophenes of syn-3.26 show disorder and were refined using 50:50 occupancies for the S28:S28A unit. Additionally, one of the isopropyl groups of the syn-ADT backbone is disordered.
(a)
(b)
Figure 3.22. X-ray crystallographic analysis showing (a) molecular structure of syn- 3.26 and (b) illustration of the packing mediated neighboring naphthyl units 139
Chapter 3 – Isomerically pure syn-anthradithiophenes
(triisopropyl groups omitted for clarity); solvent molecules not shown, ORTEPs drawn at 50% probability level.
3.5.2 Reduction of syn-3.4
Quinone syn-3.4 offers, in principle, the possibility to reduce the keto functionalities to afford syn-3.30 (Scheme 3.12).[36] Hence, compound syn-3.4 was suspended in dry
THF and an excess of LiAlH4 was carefully added at 0 °C. The mixture was heated for 3 h at reflux. After cooling to rt, concentrated HCl was added and the mixture was heated further for 3 h at reflux. After cooling to rt, the obtained solid residue was filtered, washed, and air dried. The solid residue afforded very poor solubility in common organic solvents, and separation by e.g. column chromatography was impossible. Hence, the desired product syn-3.30 could not be isolated. Mass spectral analysis, however, revealed that syn-3.30 had likely been formed, but unfortunately along with various undefined by-products (Figure 3.23).
Scheme 3.12. Attempted synthesis toward syn-3.30.
Figure 3.23. MS MALDI spectrum showing the presence of syn-3.30 along with various undefined by-products (measured with 2,5-dihydroxybenzoic acid as matrix).
140
Chapter 3 – Isomerically pure syn-anthradithiophenes 3.6 Conclusion
The synthesis of fluorinated isomerically pure syn-3.6a and syn-3.6b has been developed by the use of brominated ADTs syn-3.7a and syn-3.7b via halogen-lithium exchange. A detailed comprehensive study between syn-isomers and isomerically mixed anthradithiophenes by UV-vis spectroscopy, emission spectroscopy, thermal analysis, and X-ray crystallographic analysis provides that isomeric purity has seemingly little effect on the electronic, thermal, and solid-state properties of ADT materials. Although not presented in this research work, the elaborated trend is also consistent with single-crystal OFET device performances,[37] where no significant differences in charge carrier mobilities between the syn- and mix-ADTs could be determined. ADTs syn-3.7a and syn-3.7b can be in principle used as building blocks toward higher conjugated syn-ADT materials via Pd(II)-mediated cross coupling reactions, although this has not been successfully realized within this research work.
3.7 Outlook
Despite the successful synthesis of in 5,11-positions ethynylated isomerically pure syn-ADTs, a synthetic procedure for an unsymmetrically substitution of the ADT backbone in 2- and 8-positions still awaits. The reliable construction of push-pull ADTs, as can be seen in hypothetical derivatives syn-3.31 (Figure 3.24) might be synthetically challenging. Nevertheless, unsymmetrically substituted ADTs syn-3.31 could serve for improved electronic properties compared to symmetrically substituted syn-ADTs. The packing motif of ADTs syn-3.31 could also be tuned by the right choice of the functionalities appended to the ADT skeleton in the 2- and 8-positions, and thus, materials such as syn-3.31 could provide improved charge carrier mobilities in optoelectronic devices.
Figure 3.24. Hypothetical ADT-based materials syn-3.31.
141
Chapter 3 – Isomerically pure syn-anthradithiophenes
3.8 References
[1] Laquindanum, J. G.; Katz, H. E.; Lovinger, A. J. J. Am. Chem. Soc. 1998, 120, 664672.
[2] De la Cruz, P.; Martin, N.; Miguel, F.; Seoane, C.; Albert, A.; Cano, F. H.; Gonzalez, A.; Pingarron, J. M. J. Org. Chem. 1992, 57, 61926198.
[3] Anthony, J. E. Chem. Rev. 2006, 106, 50285048.
[4] (a) Neumann, T.; Danilov, D.; Lennartz, C.; Wenzel, W. J. Comput. Chem., 2013, 34, 27162725. (b) Yokoyama, D. J. Mater. Chem. 2011, 21, 1918719202. (c) Mas-Torrent, M.; Rovira, C. Chem. Rev. 2011, 111, 48334856.
[5] Tyllemann, B.; Vande Velde, C. M. L.; Balandier, J.-Y.; Stas, S.; Sergeyev, S.; Geerts, Y. H. Org. Lett. 2011, 13, 52085211.
[6] Nakano, M.; Niimi, K.; Miyazaki, E.; Osaka, I.; Takimiya, K. J. Org. Chem. 2012, 77, 80998111.
[7] Mamada, M.; Katagiri, H.; Mizukami, M.; Honda, K.; Minamiki, T.; Teraoka, R.; Uemura, T.; Tokito, S. ACS Appl. Mater. Interfaces 2013, 5, 96709677.
[8] Mamada, M.; Minamiki, T.; Katagiri, H.; Tokito, S. Org. Lett. 2012, 14, 40624065.
[9] Anthony, J. E.; Subramanian, S.; Parkin, S. R.; Park, S. K.; Jackson, T. N. J. Mater. Chem. 2009, 19, 79847989.
[10] Subramanian, S.; Park, S. K.; Parkin, S. R.; Podzorov, V.; Jackson, T. N.; Anthony, J. E. J. Am. Chem. Soc. 2008, 130, 27062707.
[11] Jurchescu, O. D.; Subramanian, S.; Kline, J.; Hudson, S. D.; Anthony, J. E.; Jackson, T. N.; Gundlach, D. J. Chem. Mater. 2008, 20, 67336737.
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Chapter 3 – Isomerically pure syn-anthradithiophenes
[12] Lehnherr, D.; Tykwinski, R. R. Aust. J. Chem. 2011, 64, 919929.
[13] Li, Z.; Lim, Y.-F.; Kim, J. B.; Parkin, S. R.; Loo, Y.-L.; Malliaras, G. G.; Anthony, J. E. Chem. Comm. 2011, 47, 76177619.
[14] Lehnherr, D. Ph. D. Thesis, University of Alberta, Edmonton, Canada, 2010.
[15] The functionalization of the mix-ADT skeleton in the 2- and 8- positions has been achieved by treating a solution of mix-ADTs in THF with n- BuLi and further quenching the reaction with an electrophile, see: Balandier, J.-Y.; Sebaihi, N.; Boudard, P.; Lemaur, V.; Quist, F.; Niebel, C.; Stas, S.; Tylleman, B.; Lazzaroni, R.; Cornil, J.; Geerts, Y. H. Eur. J. Org. Chem. 2011, 31313136.
[16] NEt3 was dried over KOH under ambient laboratory conditions for several days before being used in this reaction.
[17] The synthesis of compound 3.16 from 3.14 has been first developed by D. Lehnherr, see ref [14].
[18] During the progress of this research work, building blocks 3.17 and syn- 3.2 have been published for the use in the synthesis of hexathienocoronenes, see: Chen, L.; Puniredd, S. R.; Tan, Y.-Z.; Baumgarten, M.; Zschieschang, U.; Enkelmann, V.; Pisula, W.; Feng, X.; Klauk, H.; Müllen, K. J. Am. Chem. Soc. 2012, 134, 1786917872.
[19] The isomeric purity of syn-3.5a can be demonstrated by 13C NMR spectroscopy, where the acetylenic carbon atoms give rise to four different signals, according to ref [13].
[20] Davis, F. A.; Han, W.; Murphy, C. K. J. Org. Chem. 1995, 60, 47304737.
[21] Isomeric mixtures of ADTs functionalized by trialkylsilylethynyl groups
show good solubility in CH2Cl2, see ref [10].
143
Chapter 3 – Isomerically pure syn-anthradithiophenes
[22] LDA and ZnCl2 Et2O are commercially available, while LiHMDS was prepared freshly.
[23] Halogen-lithium exchange is determined to be a equilibrium process favoring (in most cases) the formation of the more stable, less basic, organolithium, see: Gilman, H.; Jones, R. G. J. Am. Chem. Soc. 1941, 63, 14411443.
[24] For the synthesis of chlorinated and brominated isomerically pure syn- ADTs, see ref [14].
[25] Okamoto, T.; Jiang, Y.; Qu, F.; Mayer, A. C.; Parmer, J. E.; McGehee, M. D.; Bao, Z. Macromolecules 2008, 41, 69776980.
[26] Payne, M. M.; Odom, S. A..; Parkin, S. R.; Anthony, J. E. Org. Lett. 2004, 6, 33253328.
[27] UV-vis characteristics of mix-3.6a and mix-3.6b, see also ref [10].
[28] Lee, K. O.; Gan, T. T. Chem. Phys. Lett. 1977, 51, 120124.
[29] Crystals of syn-3.7a and syn-3.7b suitable for X-ray crystallographic analysis have been grown earlier by D. Lehnherr, see ref [14].
[30] Interplanar distances were calculated as the distance between planes generated through the atoms of each anthradithiophene group.
[31] For the CIF file of mix-3.5a, see ref [26].
[32] For the CIF file of mix-3.6a, see ref [10].
[33] For the CIF file of mix-3.6b, see ref [10].
[34] ORTEPS of mix-3.7a are drawn at 30% probability level for better resolution of the shown graphics.
[35] Jiang, Y.; Mei, J.; Ayzner, A. L.; Toney, M. F.; Bao, Z. Chem. Commun. 2012, 48, 72687288.
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Chapter 3 – Isomerically pure syn-anthradithiophenes
[36] The synthesis of anti-ADTs has been realized by reduction of anti-
quinones, using LiAlH4, see ref [5].
[37] Single-crystal device performance has been conducted in collaboration with Prof. Jurchescu from Wakeforest University, Winston-Salem, USA, see: Lehnherr, D.; Waterloo, A. R.; Goetz, K. P.; Payne, M.; Hampel, F.; Anthony, J. E.; Jurchescu, O. D.; Tykwinski, R. R. Org. Lett. 2012, 14, 36603663.
145
Chapter 4 – Pentacenequinone-based building blocks Chapter 4 – Pentacenequinone-based building blocks
4.1 Introduction
Prototype electron acceptors currently used in organic photovoltaics (OPVs) are typically C60 and related derivatives, namely [6,6]-phenyl-C61-butyric acid methyl ester (PCBM).[1] The search for novel non-fullerene based acceptor molecules for the use in OPV devices is an intense field, and numerous non-fullerene based materials have been synthesized and tested for their electron-acceptor abilities.[2] While pentacene and pentacene derivatives are usually used as p-type semiconductors in optoelectronic devices,[3] the precursors for pentacene materials, namely 6,13- pentacenequinone (1.2) and related quinones, have been explored as potential n- type semiconductors, although solubility issues might hamper thin film formation and have to be considered.[4] A possibility to enhance solubility has been demonstrated in Chapter 2 and Chapter 3, that is the functionalization of an aromatic skeleton by trialkylsilylethynyl groups. Another possibility to overcome the poor solubility of polycyclic aromatic systems is to change its planar molecular shape toward a curved geometry, which disrupts the strong stacking behavior and should therefore provide improved solubility. For example, Fréchet and coworkers demonstrated the fabrication of efficient organic photovoltaic cells based on a subphthalocyanine/C60 donor-acceptor system.[5] The cone-shaped structural features of the subphthalocyanine unit along with its photophysical properties allow for the solution processing of thin films with good charge transport properties. This important finding demonstrates that charge transport in semiconductive devices is not limited to planar molecules.
In particular, 15,15,16,16-tetracyano-6,13-pentacenediquinodimethane (4.1, Figure 4.1) is an electron acceptor that fulfills the argument of good solubility by changing the molecular shape. The synthesis for 4.1 has been developed by Hanack in 1988 [6] via TiCl4-mediated Knoevenagel condensation. X-ray crystallographic data has been obtained from crystals formed via physical vapor transport by Frisbie and coworkers in 2009,[7] and the experimental data is in good agreement with theoretical calculations.[8] The 1,1-dicyanovinyl groups are seemingly forcing the molecule into a cone-shaped geometry and therefore enhancing the solubility of 4.1 compared to e. g., 6,13-pentacenequinone.
146 Chapter 4 – Pentacenequinone-based building blocks
(a) (b)
Figure 4.1. (a) Schematic molecular structure of 6,13-TCPQ (4.1) and (b) molecular structure obtained by X-ray crystallographic analysis showing the cone-shaped geometry (Data taken from ref [7]; hydrogen atoms omitted, ORTEPs drawn at 50% probability level).
In principle, the precursors for unsymmetrically substituted pentacenes used in Chapter 2 offer the possibilty to serve as a starting point for the synthesis of non- fullerene based acceptor materials. The desired building block 4.2 (Scheme 4.1) with its terminal acetylene makes an elongation of the conjugated electronic system possible through the formation of 4.3. [9]
To the best of our knowledge, only one example is reported in literature for the synthesis of a cumulene from 6,13-pentacenequinone (Scheme 4.2).[10] Ried and Dankert reported on pentacenequinone-based [3]cumulene 4.4a. Hence, adapting the reported synthetic strategy gives an opportunity for the construction of [3]cumulene-based acceptor systems, such as 4.4b.
The following synthetic questions have been targeted:
Is it possible to synthetically realize building block 4.2?
Is it possible to realize non-fullerene acceptor molecule 4.3?
Is it possible to realize acceptor molecules such as 4.4b based on further derivatization of 4.4a?
147 Chapter 4 – Pentacenequinone-based building blocks
Scheme 4.1. Synthetic motivation for non-fullerene acceptor molecule 4.3 via building block 4.2.
Scheme 4.2. Synthetic motivation for non-fullerene acceptor molecule 4.4b.
4.2 Attempts to realize a [5]cumulene-based acceptor
4.2.1 A [5]cumulene via the Knoevenagel reaction
The quest for a synthetic route toward 4.2 leads back to the method developed for methyl ether protected ketones such as 2.36 (Chapter 2). The developed synthetic procedure can be used to functionalize the 6,13-pentacenequinone framework with different trialkylsilylethynyl groups and can also be adapted to attach various acetylenic scaffolds to the pentacenequinone framework.[11]
As described in Chapter 2 for the synthesis of 2.36, a lithiated trialkylsilylacetylene was added to a suspension of 6,13-pentacenequinone and stirred for 24 h at rt (Scheme 4.3). The reaction was quenched via addition of an excess of MeI and further stirred for 1418 h at rt. After aqueous workup and purification by recrystallization or column chromatography, derivatives 2.36 and 4.5 were isolated in moderate to good yields.
148 Chapter 4 – Pentacenequinone-based building blocks
Scheme 4.3. Selective functionalization of 6,13-pentacenequinone by trialkylsilylacetylenes to obtain 2.36 and 4.5.
In order to test the compatibility of such pentacenequinone derivatives against TiCl4- mediated Knoevenagel conditions,[12] either compound 2.36 or 4.5 and a tenfold excess of malononitrile were added in dry CH2Cl2 at rt (Scheme 4.4). The homogenous mixture was vigorously stirred while an excess of both TiCl4 and dry pyridine were carefully added. The mixture was subsequently heated at reflux for 1824 h. After cooling to rt, aqueous workup, and purification by recrystallization, a yellow solid was isolated. The isolated precipitate was characterized by 1H NMR, 13C
NMR, and IR spectroscopy, which established that the products of the TiCl4-mediated Knoevenagel reaction were 4.6a and 4.6b in 52% and 61% yield, respectively, instead of derivatives 4.6c and 4.6d. X-ray crystallographic analysis of 4.6a confirmed the structure and the replacement of the methyl ether group by a malononitrile group.
Scheme 4.4. Exploring the TiCl4-mediated Knoevenagel reaction starting from 2.36 or 4.5.
In order to explore the use of 4.6a toward forming a [5]cumulene scaffold, the TIPS- group in compound 4.6a had to be removed (Scheme 4.4). Unfortunately, desilylation using either TBAF or CsF led to decomposition of 4.6a. On the other 149 Chapter 4 – Pentacenequinone-based building blocks hand, treatment of 4.6b with K2CO3 in wet THF/MeOH afforded derivative 4.6e in 85% yield after precipitation from hexanes. As well, desilylation of 4.5 under similar conditions gave terminal acetylene 4.7. Notably, compound 4.7 was also tested under TiCl4-mediated Knoevenagel reaction conditions toward formation of 4.6e, but this reaction gave only complex mixtures as evaluated by TLC analysis. The structures of 4.5 and 4.6e have both been evaluated by X-ray crystallographic analysis.
The terminal acetylene 4.6e offers an opportunity to elongate the acetylenic scaffold via a Hay coupling reaction (Scheme 4.5). Hence, derivative 4.6e was dissolved in
CH2Cl2 and a freshly prepared solution of CuCl and TMEDA in CH2Cl2 was added. The mixture was stirred for 24 h under ambient conditions. After aqueous workup, a complex mixture (detected by TLC analysis), unable for further purification attempts was obtained, and thus, diyne 4.8a could not be isolated.
Scheme 4.5. Attempted Hay coupling of 4.6e.
Similar results were obtained when trying to effect the Knoevenagel reaction at a later point in the synthesis (Scheme 4.6). In detail, compound 4.7 was dissolved in
CH2Cl2 and a freshly prepared solution of CuCl and TMEDA in CH2Cl2 was added. The mixture was stirred for 24 h under ambient conditions, affording a yellow suspension. After aqueous workup, precipitation, and recrystallization diyne 4.8b was obtained in 40% yield. Diyne 4.8b was then treated under TiCl4-mediated Knoevenagel reaction conditions, but this reaction afforded a complex mixture of products based on TLC analysis. Unfortunately, no product could be characterized.
150 Chapter 4 – Pentacenequinone-based building blocks
Scheme 4.6. Synthesis of diyne 4.8b under Hay conditions and attempted Knoevenagel condensation of 4.8b.
4.2.2 Finding the right leaving group
MS MALDI experiments performed on compound 4.6a revealed that it fragments to
+ give [M – CH(CN)2] , as illustrated in Figure 4.2, suggesting that the CH(CN)2-moiety might act as a leaving group, perhaps to give acceptor 4.3 (see Scheme 4.1).
Figure 4.2. MS MALDI spectrum of 4.6a (sinapinic acid as matrix) suggesting that the CH(CN)2-group could potentially act as a leaving group.
On the one hand, the aforementioned dimerization of 4.6e via Hay coupling was unsuccessful. It was anticipated that the acidic proton at the CH(CN)2-moiety of 4.6e could potentially be problematic under Hay coupling conditions. On the other hand, it 151 Chapter 4 – Pentacenequinone-based building blocks was demonstrated that the OMe-group in either 2.36 or 4.5 is not a suitable protecting group under the TiCl4-mediated Knoevenagel reaction conditions. Thus, two different synthetic strategies have been explored, that are: a) Substitution of the acidic proton of the CH(CN)2-moiety in 4.6e. b) Explore a different protecting group at the propargylic alcohol of either 2.36 or 4.5, which may perhaps afford higher stability against the TiCl4-mediated Knoevenagel reaction conditions.
For point a), compound 4.6b was dissolved in dry THF and cooled to –78 °C (Scheme 4.7). LDA was added and the solution was stirred for 15 min at 78 °C. The reaction was quenched by the addition of MeI and stirred at rt for 2 d.[13] After aqueous workup and purification, derivative 4.9 was isolated in 58% yield.
Unfortunately, desilylation using K2CO3 in wet THF/MeOH results in a residue which could not be separated by either column chromatography (poor solubility of the obtained residue) or by recrystallization. In summary, the desired product 4.10 could not be isolated.
Scheme 4.7. Attempted synthetic route toward derivative 4.10.
For point b), the synthetic procedures developed for compounds 2.36 or 4.5 offer the possibility to functionalize the propargylic alcohol group by trapping the intermediate lithium alkoxide (Scheme 4.4) with a variety of electrophiles. Unfortunately, quenching of this intermediate alkoxide directly by weaker electrophiles than MeI, such as allylbromide or benzylbromide, resulted in complex mixtures that could not be separated by column chromatography. On the other hand, it was envisioned that the propargylic alcohol can be protected in a second synthetic step. Protection of the propargylic alcohol can be realized by treating, for example, ketone 2.4 with a base and trapping the resulting alkoxide with an electrophile (Scheme 4.8). Thus, ketone
152 Chapter 4 – Pentacenequinone-based building blocks
2.4 or 4.11[14] was dissolved in dry THF along with a slight excess of NaH and tetrabutylammonium iodide. An excess of benzylbromide (BnBr) was added in one portion and the mixture was stirred at rt for 18 h. After aqueous workup and purification by either precipitation or column chromatography, derivatives 4.12a and, surprisingly by simultaneously removal of the TMS group, 4.12b[15] were isolated in
84% and 63% yield, respectively. Treatment of 4.12a under TiCl4-mediated Knoevenagel condensation conditions, however, gave compound 4.6a in 45% yield. In summary, this obtained experimental result suggests that the protecting group at the propargylic alcohol of the pentacenone derivative has little influence on the outcome of the TiCl4-mediated Knoevenagel reaction.
Scheme 4.8. Synthesis of derivatives 4.12a and 4.12b and treatment of 4.12a under
TiCl4-mediated Knoevenagel conditions to afford 4.6a.
4.2.3 Exploring different reaction conditions
Different reaction conditions to realize 4.6d have been explored and the starting point for all attempts was compound 4.5 (Table 4.1). In each case, compound 4.5 and malononitrile were dissolved in the appropriate solvent under inert gas atmosphere. The catalyst/reagent was then added in one portion (via cannula or syringe). The mixture was stirred at the given temperature for the given time. After aqueous workup, the crude product mixture was analyzed by TLC.
Table 4.1. Applied reaction conditions to realize compound 4.6d.
153 Chapter 4 – Pentacenequinone-based building blocks
Isolated [a] Entry Catalyst/Reagent Solvent T t compound (yield)
1 1 equiv TiCl4 (1 equiv)/pyridine CH2Cl2 reflux 18 h 4.13 (13%)
2 10 equiv Piperine/pyridine CH2Cl2 reflux 18 h 4.5
3 10 equiv 1H-imidazole CH2Cl2 reflux 18 h 4.5
4 10 equiv Et3N toluene 90 °C 24 h 4.5
5 10 equiv acetic anhydride THF reflux 24 h --
6 2 equiv -- DMF reflux 18 h --
7 -- THF rt 18 h 4.5 [b] PPh3/ /LDA
8 -- THF rt 18 h 4.7 (65%) [c]
9 10 equiv Ti(Oi-Pr)4/pyridine CH2Cl2 reflux 24 h 4.5
10 10 equiv Ti(Oi-Pr)4 i-PrOH 80 °C 48 h 4.5
CH2Cl2/i- 11 10 equiv Ti(Oi-Pr)4 reflux 48 h 4.5 PrOH
[d] [e] 12 7 equiv Ti(Oi-Pr)4 CH2Cl2 reflux 72 h 4.6d (traces)
[a] Dry solvent used. [b] 3.0 equiv PPh3, 3.3 equiv 2-bromomalononitrile, and 3.5 equiv LDA in dry THF were stirred for 15 min at 78 °C before being transferred into a solution of 4.5 in dry THF at rt. [c]
formed in situ by adding 5 equiv NaN(TMS)2 to a solution of malononitrile in dry THF at 78 °C. [d] Added portionwise over a period of 72 h. [e] 7 equiv added portionwise over a period of 72 h.
Performing the Knoevenagel condensation with 4.5 and with stoichiometric amounts
of malononitrile and TiCl4 (entry 1) yielded 4.13 in 13% rather than 4.6d, suggesting that the reactivity at propargylic carbon position in 4.5 is enhanced compared to the
154 Chapter 4 – Pentacenequinone-based building blocks ketone. The use of different bases as catalysts/reagents has no influence on the outcome of the reaction (entries 2-4),[16] and only starting material was observed at the conclusion of the reaction. Switching to acetic anhydride as catalyst/reagent and THF as solvent resulted in decomposition of the starting material 4.5 (entry 5). Similar results were obtained when heating the mixture of 4.5 and malononitrile in dry DMF for 24 h under reflux without any catalyst/additive (entry 6).[17] When applying a
Wittig-type reaction with PPh3/2-bromomalononitrile/LDA, only starting material was observed (entry 7).[18] Interestingly, when using an in situ formed sodium salt of malononitrile in the reaction with 4.5, complete removal of the TMS-group occurred and compound 4.7 was isolated in 65% yield (entry 8). When switching to Ti(Oi-Pr)4 as catalyst in combination with dry pyridine, only starting material was observed (entry 9).[19] Similar results were obtained when performing the reaction with Ti(Oi-
Pr)4 as catalyst in either dry i-PrOH at 80 °C or in dry CH2Cl2/i-PrOH under reflux (entries 10-11).[19] The most promising result was achieved when an excess of Ti(Oi- [19] Pr)4 was used in only dry CH2Cl2 under reflux. The reaction time was extended to 72 h and after every 24 h period another three equivalents of both malononitrile and
Ti(Oi-Pr)4 was added. After cooling the reaction mixture to rt and aqueous workup, a strongly yellow fluorescent spot was observed by TLC analysis. Separation by column chromatography yielded compound 4.6d in trace amounts (entry 12), and 4.6d could be characterized by 1H NMR spectroscopy and HRMS analysis. Notably, the structure of 4.6d has also been evaluated by X-ray crystallography. The reaction conditions to form reasonable amounts of 4.6d, however, could not be further improved during the timescale of this project.
In summary, Ti(Oi-Pr)4 could be used as a mild catalyst/reagent in the Ti(IV)- mediated Knoevenagel reaction with malononitrile and compound 4.5. Unfortunately, the amount of 4.6d isolated was not enough to carry on toward forming compound 4.3.
4.2.4 Solid state analysis
Crystals of compounds 4.5, 4.6a, 4.6d, and 4.6e suitable for X-ray crystallographic analysis have been obtained. Compound 4.5 crystallizes in the space group P1 with two molecules in the unit cell arranged as a centrosymmetric pair (Figure 4.3). The solid-state arrangement is seemingly dictated by interactions between the oxygen
155 Chapter 4 – Pentacenequinone-based Building Blocks atom of the ketone and the CH3-ether moiety of a neighboring molecule with distances of approximately 2.81 Å.
(a) (b)
Figure 4.3. X-ray crystallographic analysis showing (a) molecular structure of 4.5 and … (b) illustration of packing arrangement via O H3C-interactions; other hydrogen atoms omitted for clarity; ORTEPs drawn at 50% probability level.
Compound 4.6a crystallizes in the space group C2/c with eight molecules in the unit cell, and one molecule CDCl3 per asymmetric unit. Substitution by a 1,1-dicyanovinyl functionality leads to a cone-shaped skeleton showing an angle of ca. 114° between the two naphthyl units (Figure 4.4).[20] The naphthyl units of two neighboring molecules are arranged in a face-to-face fashion as part of a centrosymmetric dimeric pair with interplanar distances[21] of ca. 3.50 Å. The 1,1-dicyanovinyl subunits of neighboring molecules are pointed toward each other with distances of ca. 3.41 Å[22].
(a) (b)
156 Chapter 4 – Pentacenequinone-based Building Blocks
Figure 4.4. X-ray crystallographic analysis showing (a) molecular structure of 4.6a and (b) illustration of packing arrangement (triisopropylsilyl groups not shown); solvent molecules and hydrogen atoms omitted for clarity, ORTEPs drawn at 50% probability level.
Compound 4.6d crystallizes in the space group P21/n with four molecules in the unit cell. Two of the methyl groups in the trimethylsilyl group of 4.6d are disordered about two unique positions. The angle between the two naphthyl moieties within the cone- shaped molecule is calculated to ca. 116° (Figure 4.5). Compound 4.6d arranges as centrosymmetric dimeric pairs where the naphthyl units of neighboring molecules overlap in a face-to-face arrangement with an interplanar distance[21] of approximately 3.61 Å. The 1,1-dicyanovinyl groups of neighboring molecules are pointed toward each other with a distance[22] of ca. 3.61 Å.
(a) (b)
Figure 4.5. X-ray crystallographic analysis showing (a) molecular structure of 4.6d (disorder in trimethylsilyl group not shown) and (b) illustration of packing arrangement; trimethylsilyl groups and hydrogen atoms omitted for clarity, ORTEPs drawn at 50% probability level.
Compound 4.6e crystallizes in the space group P21/c with four molecules in the unit cell. The angle between the two naphthyl units is calculated to ca. 116° (Figure 4.6). The packing characteristics observed for 4.6a and 4.6d are reproduced in large parts in the crystal packing of 4.6e. The naphthyl units of two centrosymmetric neighboring molecules show face-to-face -interactions with interplanar distances[21] of ca. 3.30 Å. The 1,1-dicyanovinyl subunits of pairs of compound 4.6e are pointed toward each other with a distance[22] of 2.94 Å.
157 Chapter 4 – Pentacenequinone-based Building Blocks
(a) (b)
Figure 4.6. X-ray crystallographic analysis showing (a) molecular structure of 4.6e and (b) illustration of packing arrangement; hydrogen atoms omitted for clarity, ORTEPs drawn at 50% probability level.
4.3 Attempts to realize a [3]cumulene-based acceptor
4.3.1 Synthesis of a pentacenequinone-based [3]cumulene
The original work on quinocumulenes by Ried and Dankert deals with phenyl substitution of the cumulene (derivative 4.4a in Scheme 4.2) resulting in poor [10] solubility of 4.4a. To improve solubility, tert-butyl groups and CF3-groups were appended to the aryl substituents (Scheme 4.9).
158 Chapter 4 – Pentacenequinone-based Building Blocks
Scheme 4.9. Synthesis of [3]cumulene building blocks 4.18a and 4.18b.
The synthesis starts with commercially available aryl-bromides 4.14a and 4.14b, which were dissolved in dry THF, cooled to –78 °C. A slight excess of n-BuLi was added in order to achieve a complete halogen-lithium exchange. The mixture was stirred for one hour at –78 °C. The corresponding commercially available aldehyde was added in one portion and the mixture was stirred for 2.518 h at rt. After aqueous workup and purification by recrystallization, alcohol 4.15a was isolated in 84% yield, while 4.15b did not allow for recrystallization and was therefore used in the following step without further purification. Alcohols 4.15a and 4.15b were oxidized using pyridinium chlorochromate (PCC) in a suspension of Celite and molecular sieves (4 Å) in dry CH2Cl2. After aqueous workup and purification by recrystallization, compounds 4.16a and 4.16b were isolated in 43% and 56% yield, respectively (over two steps in the case of 4.16b). Compounds 4.16a and 4.16b were subsequently dissolved in dry THF and a solution of lithiated TMS-acetylene was added via cannula. The mixture was stirred for 4 h at rt. The reaction was quenched by the addition of MeI and the resulting solution was stirred for 18 h at rt. After aqueous workup and purification by recrystallization, compound 4.17a was isolated in 85% yield. In contrast, 4.17b could not be purified by recrystallization and was used in the next step without further purification. Compound 4.17a (or the crude mixture containing derivative 4.17b) was desilylated using K2CO3 in wet THF/MeOH and the
159 Chapter 4 – Pentacenequinone-based Building Blocks corresponding terminal acetylenes 4.18a and 4.18b were isolated in 60% and 88% yield (in the case of 4.18b calculated over two steps), respectively.
The terminal acetylenes 4.18a and 4.18b were dissolved in dry THF cooled to –78 °C and n-BuLi was added (Scheme 4.10). The mixture was transferred to a suspension of 6,13-pentacenequinone (1.2) in dry THF. The mixture was stirred for 18 h at rt and, after aqueous workup and recrystallization, compounds 4.19a and 4.19b were isolated in 62% and 44% yield, respectively.
Scheme 4.10. Synthesis of 4.20a and attempted synthesis of 4.4c.
160 Chapter 4 – Pentacenequinone-based Building Blocks
The [3]cumulenic scaffold 4.20a was realized via reductive elimination using
SnCl2 2H2O/HCl in THF and the solution protected from light. While 4.20a could be isolated in 28% yield as a red solid after recrystallization, the reduction of 4.19b toward 4.20b gave only complex mixtures that could not be separated by either column chromatography or recrystallization. Therefore, the isolation and characterization of [3]cumulene 4.20b was not accomplished within this research work. Notably, changing the reductive elimination conditions for 4.19b using different solvents (dioxane, diethylether), or different acids (diluted HCl, H2SO4) did not alter the outcome of the reaction.
In order to realize acceptor 4.4c (Scheme 4.10), the TiCl4-mediated Knoevenagel conditions were applied. In detail, derivative 4.20a was dissolved in dry CH2Cl2, and
TiCl4 and dry pyridine were carefully added. The mixture was heated at reflux for 18 h. During that period, degradation of 4.20a was observed, as noted by the color of the solution changing from dark red toward colorless. After aqueous workup, TLC analysis showed a very complex mixture of products that could not be separated by column chromatography. Therefore, the synthesis and isolation of 4.4c could not be accomplished. In general, these experimental results suggest that a cumulene scaffold does not tolerate the rather harsh TiCl4-mediated Knoevenagel reaction conditions. Unfortunately, testing 4.20a in reactions with malononitrile under milder Knoevenagel reaction conditions could not be accomplished during the timescale of this research project.
4.3.2 Electronic properties of 4.20a
To investigate the electronic properties of 4.20a, UV-vis spectra were recorded in
CH2Cl2 (Figure 4.7, top). Compound 4.20a shows a weak absorption at 244 nm, followed by a strong absorption located at 285 nm, along with another weak absorption centered at ca. 326 nm. In the lower energy region cumulene 4.20a shows two broad absorption bands centered at ca. 503 and 544 nm. The longest wavelength absorption of 4.20a is red shifted by ca. 124 nm compared to symmetrically substituted tetraphenyl[3]cumulene (measured in benzene).[9] The UV- vis characteristics of 4.20a are reproduced in large parts for solid-state UV-vis spectra acquired by dropcasting a sample of 4.20a from CH2Cl2 onto a quartz surface (Figure 4.7, bottom) In the solid-state spectrum, compound 4.20a shows a weak absorption at ca. 245 nm, a strong absorption band at ca. 286 nm, and another weak 161 Chapter 4 – Pentacenequinone-based Building Blocks shoulder at ca. 329 nm. In the lower energy region two broad absorptions are found at ca. 507 and 557 nm. In general, the longest wavelength absorption observed in solid-state UV-vis spectra is slightly redshifted (ca. 13 nm) in comparison to the analogous solution-state measurement.
5 Figure 4.7. Solution-state UV-vis spectrum of 4.20a (top) in CH2Cl2 (~10 M) and solid-state UV-vis spectrum of 4.20a (bottom) on quartz (drop cast from CH2Cl2).
4.3.3 Solid-state analysis of 4.20a
A crystal suitable for X-ray crystallographic analysis of compound 4.20a has been grown by slow evaporation of a concentrated CH2Cl2 solution of 4.20a layered with
162 Chapter 4 – Pentacenequinone-based Building Blocks
MeOH/i-PrOH (1:1) at 4 °C over a period of several months. Compound 4.20a crystallizes in the space group P1 with two molecules in the unit cell. The bond lengths for the cumulenic double bonds are 1.354(3), 1.273(3), and 1.355(3) Å, which is in good agreement with reported values for [3]tetraarylcumulenes (Figure 4.8).[23] In comparison to the cumulenic double bonds, the carbonyl group shows a CO bond length of 1.223(3) Å. The aryl substituents are arranged with an angle of 121°, and are twisted out of the plane of the cumulene chain by 32° and 19°. Compound 4.20a does not show -stacking between neighboring pentacenone units, but molecules of 4.20a are placed such as that the [3]cumulene scaffold is above a neighboring molecule within a distance of approximately 3.34 Å.[24] One of the aryl substituents also shows -interaction with a neighboring pentacenone unit with a distance of approximately 3.5 Å.[25] In general, the absence of strong -stacking interactions is in good agreement with the obtained solid-state UV-vis spectrum.
(a) (b)
Figure 4.8. X-ray crystallographic analysis showing (a) molecular structure of 4.20a with bond lengths and (b) illustration of packing arrangement (tert-butyl groups omitted for clarity); hydrogen atoms omitted for clarity, ORTEPs drawn at 50% probability level.
163 Chapter 4 – Pentacenequinone-based Building Blocks
4.4 Organometallic approaches
4.4.1 Synthesis of building blocks for allenylidene complexes ††
While binuclear pentacenyl-6,13-diacetylide complexes have been studied to probe the effect of metal coordination on the pentacene framework,[26] an organometallic approach using 6,13-pentacenequinone-based materials is unknown. Therefore, it was of interest to synthesize building blocks based on the 6,13-pentacenquinone scaffold and the afforded building blocks were used for the synthesis of Ru- containing pentacenone-allenylidene complexes, which should then eventually be explored as potential electron-acceptor materials. The building blocks based on the 6,13-pentacenequinone framework have been realized as part of the present research work, while the organometallic complexes have been synthesized and characterized by Frank Strinitz in the research group of Prof. Burzlaff at FAU as part of his PhD research.
Two strategies have been investigated in the present research work, which apply pentacenequinone-based compounds for the synthesis of Ru-containing pentacenone-allenylidene complexes. The first strategy targeted the synthesis of an unsymmetrically substituted precursor 4.21 based on 6,13-pentacenequinone (Scheme 4.11). Therefore, compound 2.4 was desilylated using TBAF in wet THF. After precipitation and air drying, terminal acetylene 4.21 was obtained in 95% [27] yield. The latter was treated with [Ru(bdmpza)(PPh3)2Cl] in dry THF for 96 h under reflux to yield two isomers of neutral heteroscorpionate Ru-allenylidene complexes (4.22a and 4.22b). Isomer 4.22b, for example, could be structurally analyzed by X- ray crystallography (Figure 4.9).[28] Although isomer 4.22b co-crystallizes with solvent molecules (CH2Cl2), it shows -stacking between neighboring pentacenone units overlapping with interplanar distances of ca. 3.64 Å.[29]
†† Portions of this section have been published. Reproduced with permission from: Strinitz, F; Waterloo, A.; Tucher, J.; Hübner, E.; Tykwinski, R. R.; Burzlaff, N. Eur. J. Inorg. Chem. 2013, 51815186. Copyright @2013 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim. Reproduced with permission from: Strinitz, F.; Tucher, J.; Januszewski, J. A.; Waterloo, A. R.; Stegner, P.; Förtsch, S.; Hübner, E.; Tykwinski, R. R.; Burzlaff, N. Organometallics, 2014, DOI: 10.1021/om5002777. Copyright @2014 American Chemical Society. 164 Chapter 4 – Pentacenequinone-based Building Blocks
Scheme 4.11. Synthesis of Ru-allenylidene complexes 4.22a and 4.22b via building block 4.21. The synthesis and characterization of 4.22a and 4.22b was carried out by Frank Strinitz.
(a) (b)
Figure 4.9. X-ray crystallographic analysis showing (a) molecular structure of 4.22b and (b) illustration of packing arrangement; hydrogen atoms and solvent molecules omitted for clarity, ORTEPs drawn at 50% probability level. CCDC 925993.
The second synthetic strategy involves binuclear Ru-allenylidene complexes, bridged by one pentacenone unit. The synthesis started with ketones 2.4 or 4.9 (Scheme 4.12). In detail, compound 2.4 or 4.11 was dissolved in dry THF and a solution of freshly prepared lithium trialkylsilylacetylene was added via cannula. The mixture was stirred for 18 h at rt. After aqueous workup and purification by column
165 Chapter 4 – Pentacenequinone-based building blocks chromatography, compound 4.23a and 4.23b could be isolated in 46% yield, for both reactions. Desilylation of 4.23a using TBAF in THF led to decomposition of the starting material. Compound 4.23b was treated under mild desilylation conditions using K2CO3 in wet THF/MeOH, and after aqueous workup and recrystallization 4.24 was isolated in 85% yield. Compound 4.24 was envisioned to be used for the synthesis of binuclear Ru-allenyliden complexes, but however, experimental results of this organometallic approach were not yet available during the write-up of the present research thesis.
Scheme 4.12. Synthesis of building block 4.24.
4.5 Conclusion
[6] The reported conditions of the TiCl4-mediated Knoevenagel reaction with malononitrile were applied for the conversion of a ketone to a 1,1-dicyanovinyl moiety using pentacenone derivatives. The investigated reaction conditions lead to an unwanted substitution of the propargylic alcohol or ether by malononitrile. The acidic proton of this malononitrile group hinders further synthetic elaborations of the product. By using Ti(Oi-Pr)4 instead of TiCl4 in the Knoevenagel reaction with malononitrile, it was observed that Ti(Oi-Pr)4 did not affect the substitution of the propargylic alcohol. Hence, Ti(Oi-Pr)4 might be an alternative reagent for the conversion of a ketone to a 1,1-dicyanovinyl moiety, although the reaction conditions have still to be further improved.
6,13-Pentacenequinone can be functionalized to give a cumulene. One [3]cumulene could be synthetically achieved within the present research work by adapting the reported synthetic procedure. The [3]cumulene product 4.20a shows improved UV- vis absorptions compared to symmetrically substituted tetraaryl[3]cumulenes. X-ray
166 Chapter 4 – Pentacenequinone-based building blocks crystallographic analysis of 4.20a reveals little -stacking interactions between neighboring molecules in the solid state. The ketone functionality of the [3]cumulene could not be converted to a 1,1-dicyanovinyl moiety by adapting the TiCl4-mediated Knoevenagel reaction with malononitrile. 6,13-Pentacenone-acetylenes are suitable building blocks for allenylidene complexes and Ru-containing allenylidene complexes could help to derive novel semiconductors besides only pure organic materials.
4.6 References
[1] Hummelen, J. C.; Knight, B. W.; LePeq, F.; Wudl, F.; Yao, J.; Wilkins, C. L. J. Org. Chem. 1995, 60, 532538.
[2] (a) Anthony, J. E. Chem. Mater. 2011, 23, 583590. (b) Kivala, M.; Diederich, F. Acc. Chem. Res. 2009, 42, 235248.
[3] (a) Anthony, J. E. Chem. Rev. 2006, 106, 50285048. (b) Anthony, J. E. Angew. Chem. Int. Ed. 2008, 47, 452–483. (c) Lehnherr, D.; Tykwinski, R. R. Materials 2010, 3, 2772–2800. (d) Lehnherr, D.; Tykwinski, R. R. Aust. J. Chem. 2011, 64, 919929.
[4] Liang, Z.; Tang, Q.; Liu, J.; Li, J.; Yan, F.; Miao, Q. Chem. Mater. 2010, 22, 64386443.
[5] Ma, B.; Woo, C. H.; Miyamoto, Y.; Fréchet, J. M. J. Chem. Mater. 2009, 21, 14131417.
[6] Martín, N.; Hanack, M. J. Chem. Soc., Chem. Commun., 1988, 15221524.
[7] Bader, M. M.; Pham, P.-T. T.; Nassar, B. R.; Lin, H.; Xia, Y.; Frisbie, D. C. Cryst. Growth Des. 2009, 9, 45994601.
[8] Viruela, R.; Viruela, P. M.; Ortí, E.; Martín, N. Synthetic Met. 1995, 70, 10311032.
167 Chapter 4 – Pentacenequinone-based building blocks [9] Januszewski, J. A.; Tykwinski, R. R. Chem. Soc. Rev. 2014, 43, 31843203.
[10] Ried, W.; Dankert, G. Chem. Ber. 1959, 92, 12231236.
[11] A similar approach has been realized to synthesize pentacene di-, tri-, and tetramers, see: Lehnherr, D.; Murray, A. H.; McDonald, R.; Tykwinski, R. R. Angew. Chem. Int. Ed. 2010, 49, 61906194.
[12] The original procedure by Hanack affords 4.1 using TiCl4 in dry pyridine in 54% yield, see ref [6].
[13] The reaction was performed over the weekend.
[14] Compound 2.4 has been used in Chapter 2 to achieve unsymmetrically substituted pentacene derivatives. Compound 4.11 has been prepared earlier by D. Lehnherr, see Ref [11].
[15] Complete desilylation was observed under the chosen reaction conditions.
[16] a) Knoevenagel, E.; Ber. Dtsch. Chem. Ges. 1898, 31, 25962619. b) Heravi, M. M.; Tehrani, M. H.; Bakhtiari, K.; Oskooie, H. A. J. Chem. Res. 2006, 9, 561562.
[17] Vallejos, S.; Kaoutit, H. E.; Estévez, P; García, F. C.; de la Pena, J. L.; Serna, F.; García, J. M. Polym. Chem. 2011, 2, 11291138.
[18] It was assumed that the phosphonium-ylidene forms in situ, although no spectroscopic evidence of its existence had been sought.
[19] For the original procedure of the Knoevenagel condensation of
benzophenone with malononitrile using Ti(Oi-Pr)4, see: Yamashita, K.; Tanaka, T.; Hayashi, M. Tetrahedron 2005, 61, 79817985.
[20] The calculated angle is consistent with the angle between the two naphthyl units found for symmetrical derivative 4.1. 168 Chapter 4 – Pentacenequinone-based building blocks [21] Interplanar distances calculated by generating planes through each the naphthyl units.
[22] Distance calculated by generating planes through each of the 1,1- dicyanovinyl subunit.
[23] Januszewski, J. A.; Wendinger, D.; Methfessel, C. D.; Hampel, F.; Tykwinski, R. R. Angew. Chem. Int. Ed. 2013, 52, 18171821.
[24] The distance was calculated by generating a plane through the pentacenone unit and the centroid of the four cumulene carbon atoms.
[25] The distance was calculated by generating a plane through the pentacenone unit and the centroid derived from the six carbon atoms of the aryl ring.
[26] M.-H. Nguyen, J. H. K. Yip, Organometallics 2011, 30, 6383–6392.
[27] Compound 4.21 was previously synthesized using an alternative procedure, see: Lehnherr, D. Ph. D. Thesis, University of Alberta, Edmonton, Canada, 2010.
[28] Crystals suitable for X-ray crystallographic analysis were grown by Frank Strinitz. Refinement of the structure was performed in the Burzlaff research group.
[29] Interplanar distances were calculated by generating planes through the pentacenone units.
169 Chapter 5 Experimental data
Chapter 5 – Experimental data
5.1 General information
All reagents were purchased in reagent grade from commercial suppliers and used without further purification. Unless otherwise stated, all reactions were performed in standard, dry glassware under an inert atmosphere of nitrogen. All solvents were dried and/or distilled.
Dry, deoxygenated THF was distilled from sodium/benzophenone, dry CH2Cl2 was distilled from CaH2, and dry MeOH was distilled from magnesium. NMR spectra were recorded on a Bruker Avance 300 operating at 300 MHz (1H NMR) and 75 MHz (13C NMR), or on a Bruker Avance 400 operating at 400 MHz (1H NMR) and 100 MHz (13C NMR) at rt. The signals were referenced to the residual solvent peaks ( in parts per million (ppm). Coupling constants are reported as observed (±0.5 Hz). Mass spectra were obtained from a Kratos MS50G (EI), Micromass Zabspec (EI), Bruker 9.4T Apex-Qe FTICR (MALDI), Agilent Technologies 6220 oaTOF (ESI), Bruker micro TOF II, and Bruker maxis 4G (APPI, ESI) instruments. For mass spectral analyses, low-resolution data are provided in cases when M+ is not the base peak; otherwise, only high-resolution data are provided. IR spectra were recorded on a Varian-660 IR spectrometer in ATR mode. UV-vis absorption spectra were acquired at rt using a Varian Cary 5000 spectrophotometer
–1 –1 (for all the solution-state and solid-state data); max in nm ( in L•mol •cm ). Emission spectra were recorded using a Horiba Jobin Yvon fluoromax-4 spectrofluorometer. Differential scanning calorimetry (DSC) measurements were made on a Mettler Toledo TGA/ STDA 851e/1100/SF. Thermogravimetric analyses (TGA) were achieved on a Mettler Toledo DSC 821e/ Sensor FRS5-Ceramic. All thermal analyses were carried out under a flow of nitrogen with a heating rate of 10 °C/min. Thermal decomposition temperature as measured by TGA (as sample weight loss) is reported as Td in which the temperature listed corresponds to the intersection of the tangent lines of the baseline and the edge of the peak corresponding to the first significant weight loss, typically >5%. Melting points from DSC analysis are reported as the peak maxima, except in cases when the sample decomposed, in which case the onset temperature of the decomposition exothermic peak is reported, as 170
Chapter 5 Experimental data well as the exothermic maxima corresponding to the decomposition. Crystallographic data for unpublished compounds is available from the X-ray Crystallographic Laboratory, Institute for Organic Chemistry, University of Erlangen-Nürnberg.
5.2 Synthesis of known compounds
2.3: Compound 2.3 has been synthesized according to Tykwinski and coworkers.[1]
2.4: Compound 2.4 has been prepared according to Tykwinski and coworkers[2].
2.22: Compound 2.22 has been synthesized according to Lehnherr.[3]
171
Chapter 5 Experimental data
2.26: Compound 2.26 has been synthesized according to Adam.[4]
O S Br Br S O Br S mix-3.4: Compound syn-3.4 has been synthesized according to Bao.[9]
syn-3.7a: Compound syn-3.7a has been synthesized according to Lehnherr.[3]
Si
Br Br S S
Si syn-3.7b: Compound syn-3.7b has been synthesized according to Lehnherr.[3]
172
Chapter 5 Experimental data
3.9: Compound 3.9 has been synthesized according to Dunne and coworkers.[5]
3.13: Compound 3.13 has been synthesized according to Hibino and coworkers.[6]
3.15: Compound 3.15 has been synthesized according to Lehnherr.[3]
3.16: Compound 3.16 has been synthesized according to Lehnherr.[3]
O
OH
Si
4.11: Compound 4.11 has been synthesized according to Lehnherr.[3]
173
Chapter 5 Experimental data
5.3 Synthesis of new compounds
Experimental data for new compounds is given in order of appearance.
General Procedure A for the CuAAC reaction: Unless indicated otherwise, to a solution of 2.3 (1 equiv) and the azide (1.2 equiv) in THF
(10 mL) was added an aqueous solution of the Cu(II) salt (2.5 equiv in 5 mL of H2O) and sodium ascorbate (2.5 equiv in 5 mL of H2O) in this order under ambient conditions at rt. The reaction was allowed to stir vigorously for 12–14 h at rt. The reaction was then quenched via the addition of saturated aq NH4Cl (10 mL) and extracted with CH2Cl2 (3 × 50 mL). The combined organic layers were washed with brine (50 mL), dried over Na2SO4, filtered, and the solvent removed in vacuo. The residue was dissolved in a minimal amount of CH2Cl2 and loaded onto a plug of silica gel (~ 50 g on a 5 cm diameter fritted funnel). The starting material and byproducts were eluted with CH2Cl2 and the product was then removed from the silica plug by eluting with EtOAc, affording 2.6a–f. Unless otherwise stated, this product was then carried on to the subsequent aromatization step without further purification.
General Procedure B for the CuAAC reaction: Unless indicated otherwise, to a solution of 2.3 (1.2 equiv per azide group) and the azide (1
equiv) in THF (10 mL) was added an aqueous solution of CuSO4 5H2O (3 equiv in 5 mL
H2O) and sodium ascorbate (3 equiv in 5 mL H2O) in this order under ambient conditions at rt. The reaction was allowed to stir vigorously for 24 h at rt. The reaction was then quenched via the addition of saturated aq NH4Cl (10 mL) and extracted with CH2Cl2 (3 × 50 mL). The combined organic phases were washed with brine (50 mL), dried (Na2SO4), filtered, and the solvent removed in vacuo. The residue was dissolved in a minimal amount of CH2Cl2 and loaded onto a plug of silica gel (~ 50 g on a 5 cm diameter fritted funnel). The starting material and byproducts were eluted with CH2Cl2 and the product was then removed from the silica plug by eluting with EtOAc, which were carried on to the subsequent aromatization step without further purification.
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Chapter 5 Experimental data
General Procedure C for aromatization of pentacenes: The crude product obtained from the CuAAC reaction (1 equiv) was dissolved in THF (15
mL) and the flask wrapped in aluminum foil. SnCl2 2H2O (3 equiv per pentacene unit) and
10% aq H2SO4 (0.2 mL) were added, affording a dark solution. The reaction mixture was stirred vigorously for 4–6 h at rt. The mixture was extracted with CH2Cl2 (4 × 20 mL). The combined organic phases were washed with brine (2 × 50 mL), dried (Na2SO4), filtered, and the solvent removed in vacuo to afford a dark blue product. The crude product was dissolved in a minimal CH2Cl2, passed through a plug of silica gel (~ 12 g on a 10 cm diameter fritted funnel), and eluted with CH2Cl2. The solvent was evaporated and the blue solid was dried in vacuo, yielding 2.7a–h and 2.1113. In some cases, further purification was accomplished by recrystallization or column chromatography, as noted in the individual procedures.
175
Chapter 5 Experimental data
2.6a:
Procedure with CuSO4. The CuAAC reaction of 2.3 (0.300 g, 0.551 mmol), benzylazide
(0.088 g, 0.66 mmol), CuSO4 5H2O (0.344 g, 1.37 mmol), and sodium ascorbate (0.273 g,
1.37 mmol) in dry, deoxygenated THF (20 mL) and H2O (20 mL) according to General Procedure A afforded 2.6a as a light tan solid (0.096 g, 26%, >95% pure by 1H NMR spectroscopy) after recrystallization in CH2Cl2/n-pentane.
Procedure with Cu(OAc)2. The CuAAC reaction of 2.3 (0.700 g, 1.28 mmol), benzylazide
(0.180 g, 1.41 mmol), Cu(OAc)2 (0.581 g, 3.20 mmol), and sodium ascorbate (0.634 g, 3.20 mmol) in dry, deoxygenated THF (20 mL) and H2O (20 mL) according to General Procedure A afforded 2.6a as a colorless solid (0.390 g, 46%, >95% pure by 1H NMR spectroscopy) after recrystallization from CH2Cl2/n-pentane. Mp = 232–234 °C; IR (ATR): 3170 (br), 3052 (w), 2938 (s), 2861 (s), 2165 (w), 1458 (m),
1 1 881 (s) cm ; H NMR (300 MHz, CDCl3): 9.00 (s, 2H), 8.03 (s, 2H), 7.90–7.79 (m, 4H), 7.67 (s, 1H), 7.48–7.47 (m, 4H), 7.46 (s, 3H), 7.34–7.21 (m, 2H), 5.35 (s, 2H), 3.21 (s, 3H),
13 1.27 (bs, 21H). C NMR (100 MHz, CDCl3): 137.1, 133.9, 133.2, 133.1, 129.0, 128.9, 128.7, 128.3, 127.6, 126.5, 126.4, 125.5, 117.9, 109.2, 88.4, 70.1, 54.3, 18.8, 11.4; MALDI
+ HRMS (dctb) calcd for C43H44N3OSi ([M – OH] ) m/z 646.3248, found 646.3249. Single crystals of 2.6a suitable for X-ray crystallographic analysis were grown by slow
evaporation of a CH2Cl2/n-pentane solution at rt. X-ray data for 2.6a n-pentane:
C48H57N3O2Si, Fw = 736.06; monoclinic crystal system, space group P21/c; crystal size = 0.3 x 0.2 x 0.1 mm3; = 0.7107 Å; a = 18.9114(6) Å, b = 8.5543(3) Å, c = 26.6849(9) Å; =
3 3 1 95.819(2)°; V = 4294.7(2) Å ; Z = 4; (calcd) = 1.138 g/cm ; 2max = 50.08° ; = 0.095 mm ;
2 T = 173(2) K; total data collected = 11331; R1 = 0.0790 [7394 observed reflections with F0
176
Chapter 5 Experimental data
2 2 2 2(F0 )]; R2 = 0.2226 for 482 variables with [F0 3(F0 )]; largest difference, peak and hole = 1.104 and –0.484 eÅ 3.
2.6b:
Procedure with CuSO4. The CuAAC reaction of 2.3 (0.300 g, 0.551 mmol),
[7a] (2-azido)methylnapththalene (0.121 g, 0.661 mmol), CuSO4 5H2O (0.344 g, 1.37 mmol), sodium ascorbate (0.273 g, 1.37 mmol) in dry, deoxygenated THF (20 mL) and H2O (20 mL) according to General Procedure A afforded 2.6b as a colorless solid (0.344 g, 90%, ~90% pure by 1H NMR spectroscopy). This product was used in the aromatization step without further purification.
Procedure with Cu(OAc)2. The CuAAC reaction of 2.3 (0.546 g, 1.00 mmol),
[7a] (2-azido)methylnapththalene (0.379 g, 2.07 mmol), Cu(OAc)2 (0.454 g, 2.50 mmol), and sodium ascorbate (0.495 g, 2.50 mmol) in dry, deoxygenated THF (20 mL) and H2O (20 mL) according to General Procedure A afforded 2.6b as a colorless solid (0.527 g, 76%,
1 >95% pure by H NMR spectroscopy) after recrystallization from CH2Cl2/n-pentane. Mp = 173–175 °C; IR (ATR): 3174 (br), 3050 (w), 2939 (s), 2861 (s), 2164 (m), 1462 (m),
1 1 884 (s), 737 (s) cm ; H NMR (300 MHz, CDCl3): 8.99 (s, 2H), 7.93 (s, 2H), 7.89–7.86 (m, 4H), 7.78–7.73 (m, 3H), 7.54 (s, 1H), 7.51–7.36 (m, 8H), 5.79 (s, 2H), 3.12 (s, 3H), 1.25 (bs,
13 21H). C NMR (75 MHz, CDCl3): 155.7, 149.7, 137.1, 133.82, 133.80, 133.2, 133.0, 131.2, 131.1, 130.0, 129.2, 128.9, 128.7, 128.3, 128.2, 127.6, 127.3, 126.4, 126.3, 125.5,
125.3, 122.8, 117.9, 109.1, 88.3, 70.1, 52.3, 18.8, 11.4; ESI HRMS calcd for C47H46N3OSi (M ) m/z 696.3405, found 696.3397. Single crystals of 2.6b suitable for X-ray crystallographic analysis were grown by slow
evaporation of a CH2Cl2/acetone solution at rt. X-ray data for 2.6b acetone: C50H53N3O3Si,
177
Chapter 5 Experimental data
Fw = 772.04; monoclinic crystal system, space group C2/c; crystal size = 0.35 x 0.20 x 0.10 mm3; = 0.7107 Å; a = 44.102(6) Å, b = 8.568(1) Å, c = 27.360(3) Å; = 121.154(6)°; V =
3 3 1 8847.4(19) Å ; Z = 8; (calcd) = 1.159 g/cm ; 2max = 49.90° ; = 0.097 mm ; T = 173(2) K;
2 2 total data collected = 3983; R1 = 0.0837 [1981 observed reflections with F0 2(F0 )]; R2
2 2 = 0.2110 for 515 variables with [F0 3(F0 )]; largest difference, peak and hole = 0.206 and –0.189 eÅ 3.
2.6c:
Procedure with CuSO4. The CuAAC reaction of 2.3 (0.265 g, 0.485 mmol),
[7b] 1-azidohexane (0.074 g, 0.58 mmol), CuSO4 5H2O (0.303 g, 1.21 mmol), sodium ascorbate (0.240 g, 1.21 mmol) in dry, deoxygenated THF (20 mL) and H2O (20 mL) according to General Procedure A afforded 2.6c as a colorless solid (0.230 g, 72%, ~85% pure by 1H NMR spectroscopy). This product was used in the aromatization step without further purification.
Procedure with Cu(OAc)2. The CuAAC reaction of 2.3 (0.318 g, 0.585 mmol),
[7b] 1-azidohexane (0.089 g, 0.70 mmol), Cu(OAc)2 (0.266 g, 1.46 mmol), sodium ascorbate
(0.290 g, 1.46 mmol) in dry, deoxygenated THF (20 mL) and H2O (20 mL) according to General Procedure A afforded 2.6c as a colorless solid (0.346 g, 90%, >95% pure by 1H NMR spectroscopy). This product was used in the aromatization step without further purification. IR (ATR): 3212 (b), 3052 (w), 2937 (s), 2862 (s), 2158 (w), 1460 (s), 1048 (s), 880 (s) cm 1;
1 H NMR (300 MHz, CDCl3): 8.99 (s, 1H), 8.07 (s, 1H), 7.90–7.81 (m, 4H), 7.75 (s, 1H), 7.49–7.44 (m, 4H), 7.33 (s, 1H), 4.18 (t, J = 7.4 Hz, 2H), 3.25 (s, 3H), 1.80 (t, J = 6.9 Hz,
13 2H), 1.301.22 (m, 29H), 0.80 (t, J = 6.7 Hz, 3H). C NMR (75 MHz, CDCl3): 155.5,
178
Chapter 5 Experimental data
137.1, 134.0, 133.2, 133.1, 128.9, 128.3, 127.6, 126.5, 126.3, 125.5, 117.9, 109.2, 88.4, 70.1, 51.6, 50.5, 30.9, 30.0, 26.0, 22.2, 18.8, 13.8, 11.5 (one signal coincident or not
+ observed); ESI HRMS calcd for C42H50N3OSi ([M OCH3] ) m/z 640.3718, found 640.3711.
2.6d:
Procedure with CuSO4. The CuAAC reaction of 2.3 (0.100 g, 0.184 mmol),
1-azidoadamantane (0.039 g, 0.22 mmol), CuSO4 5H2O (0.115 g, 0.460 mmol), sodium ascorbate (0.091 g, 0.46 mmol) in dry, deoxygenated THF (20 mL) and H2O (20 mL) according to General Procedure A afforded 2.6d as a colorless solid that was used in the aromatization step without further purification.
Procedure with Cu(OAc)2. The CuAAC reaction of 2.3 (0.300 g, 0.551 mmol),
1-azidoadamantane (0.117 g, 0.662 mmol), Cu(OAc)2 (0.115 g, 1.38 mmol), sodium ascorbate (0.273 g, 1.38 mmol) in dry, deoxygenated THF (20 mL) and H2O (20 mL) according to General Procedure A afforded 2.6d as a yellow solid (0.231 g, 58%, ~90% pure by 1H NMR spectroscopy). This product was used in the aromatization step without further purification.
1 H NMR (400 MHz, CDCl3): 9.02 (s, 2H), 8.09 (s, 2H), 7.93–7.86 (m, 5H), 7.53–7.47 (m, 4H), 3.30 (s, 3H), 2.21 (s, 3H), 2.16 (s, 3H), 1.75 (bs, 6H), 1.32–1.29 (m, 24H); EI MS m/z
+ 659 ([M H2O OCH3] ).
179
Chapter 5 Experimental data
2.6e:
Procedure with CuSO4. The CuAAC reaction of 2.3 (0.400 g, 0.732 mmol),
[7c] 1-azidobenzene (0.105 g, 0.878 mmol), CuSO4 5H2O (0.457 g, 1.83 mmol), sodium ascorbate (0.363 g, 1.83 mmol) in dry, deoxygenated THF (20 mL) and H2O (20 mL) according to General Procedure A afforded 2.6e as a light-yellow solid that was used in the aromatization step without further purification.
Procedure with Cu(OAc)2. The CuAAC reaction of 2.3 (0.300 g, 0.551 mmol),
[7c] 1-azidobenzene (0.078 g, 0.66 mmol), Cu(OAc)2 (0.250 g, 1.38 mmol), sodium ascorbate
(0.273 g, 1.38 mmol) in dry, deoxygenated THF (20 mL) and H2O (20 mL) according to General Procedure A afforded 2.6e as a crude green oil that was used in the aromatization step without further purification.
1 H NMR (300 MHz, CDCl3): 9.02 (s, 2H), 8.22 (s, 1H), 8.14 (s, 2H), 7.93–7.83 (m, 4H), 7.64–7.37 (m, 9H), 7.36–7.33 (m, 9H), 3.29 (s, 3H), 1.291.27 (m, 21H); MALDI MS (dctb)
+ m/z 632 ([M H2O] ).
2.6f: The CuAAC reaction of 2.3 (0.300 g, 0.551 mmol), 2-azidonaphthalene[7d] (0.116 g, 0.662 mmol), Cu(OAc)2 (0.250 g, 1.38 mmol), sodium ascorbate (0.273 g, 1.38 mmol) in dry, deoxygenated THF (20 mL) and H2O (20 mL) according to General Procedure A afforded 2.6f as a yellow oil that was used in the aromatization step without further purification. 180
Chapter 5 Experimental data
IR (ATR): 3136 (br), 2936 (s), 2860 (s), 2180 (w), 1459 (s), 1100 (s), 887 (s) cm 1; 1H NMR
(300 MHz, CDCl3): 9.03 (s, 2H), 8.36 (s, 1H), 8.17 (s, 2H), 8.08 (s, 1H), 7.92–7.76 (m, 8H), 7.54–7.47 (m, 6H), 7.09 (s, 1H), 3.30 (s, 3H), 1.271.28 (m, 21H). 13C NMR (75 MHz,
CDCl3): 156.4, 137.1, 134.2, 133.7, 133.4, 133.2, 133.1, 132.8, 129.9, 129.1, 128.4, 128.2, 127.9, 127.7, 127.4, 127.0, 126.7, 126.5, 125.8, 118.9, 118.6, 116.8, 109.2, 88.6, 70.2, 53.4, 51.7, 18.9, 11.5; MALDI MS (sin) m/z 682 ([M OH]+).
Single crystals suitable for X-ray crystallographic analysis were grown by slow evaporation of a solution (CH2Cl2/MeOH) containing the crude product at rt. X-ray data:
C90H120N6O12Si2, Fw = 1534.10; triclinic crystal system, space group P1; crystal size = 0.9 x 0.5 x 0.5 mm3; = 0.7107 Å; a = 10.1781(8) Å, b = 14.1587(12) Å, c = 16.6175(8) Å; =
3 3 86.101(5)°, = 95.819(2)°, = 70.024(3)°; V = 2145.7(3) Å ; Z = 1; (calcd) = 1.187 g/cm ;
1 2max = 50.28°; = 0.104 mm ; T = 173(2) K; total data collected = 14611; R1 = 0.0726
2 2 2 [7601 observed reflections with F0 2(F0 )]; R2 = 0.1882 for 496 variables with [F0
2 3 3(F0 )]; largest difference, peak and hole = 0.729 and –0.504 eÅ .
181
Chapter 5 Experimental data
2.7a:
Aromatization of 2.6a from CuSO4 5H2O CuAAC reaction. The reaction of 2.6a (0.090 g,
0.14 mmol), SnCl2 2H2O (0.095 g, 0.42 mmol), and 10% aq H2SO4 (0.2 mL) in THF (15 mL) was conducted according to General Procedure C, providing pentacene 2.7a as a dark blue solid (70 mg, 81%).
Aromatization of 2.6a from Cu(OAc)2 CuAAC reaction. The reaction of 2.6a (0.150 g,
0.230 mmol), SnCl2 2H2O (0.156 g, 0.690 mmol), and 10% aq H2SO4 (0.2 mL) in THF (15 mL) was conducted according to General Procedure C, providing pentacene 2.7a as a dark blue solid (131 mg, 92%).
Mp = 190192 °C; UV-vis (CH2Cl2) max (): 309 (270 000), 350 (6 900), 410 (1 600), 435 (2 700), 535 (3 800), 574 (8 600), 621 (13 000) nm; IR (ATR): 3042 (w), 2935 (s), 2861 (s),
1 1 2132 (w), 1375 (m), 1052 (s), 873 (s) cm ; H NMR (300 MHz, CDCl3): 9.32 (s, 2H), 8.40 (s, 2H), 7.93 (d, J = 8.4 Hz, 2H), 7.83 (s, 1H), 7.71 (d, J = 8.4 Hz, 2H), 7.477.28 (m, 9H),
13 5.83 (s, 2H), 1.371.36 (m, 21H). C NMR (75 MHz, CDCl3): 144.6, 134.8, 131.8, 131.7, 130.6, 129.2, 129.1, 128.9, 128.5, 128.4, 128.0, 125.9, 125.6, 125.5, 125.4, 125.2, 118.9, 106.2, 104.5, 54.4, 18.9, 11.6 (one signal coincident or not observed); MALDI HRMS (dctb)
+ calcd for C42H41N3Si (M ) m/z 615.3064, found 615.3068. Single crystals of 2.7a suitable for X-ray crystallographic analysis were grown by slow evaporation of a CH2Cl2 solution at rt. X-ray data for 2.7a: C42H41N3Si, Fw = 615.87; monoclinic crystal system, space group P21/c, a = 21.1783(5) Å, b = 8.6447(2) Å, c =
3 3 18.9499(5) Å; = 96.941(1)°; V = 3443.92(15) Å ; Z = 4; (calcd) = 1.188 g/cm ; 2 max =
1 55.22°; = 0.102 mm ; T = 173(2) K; total data collected = 7949; R1 = 0.0470 [5289
2 2 2 observed reflections with F0 2(F0 )]; R2 = 0.1208 for 421 variables with [F0
2 3 3(F0 )]; largest difference, peak and hole = 0.324 and 0.299 eÅ .
182
Chapter 5 Experimental data
2.7b:
Aromatization of 2.6b from CuSO4 5H2O CuAAC reaction. The reaction of 2.6b (0.340 g,
0.476 mmol), SnCl2 2H2O (0.323 g, 1.43 mmol), and 10% aq H2SO4 (0.2 mL) in THF (15 mL) was conducted according to General Procedure C, providing pentacene 2.7b as a dark blue solid (286 mg, 90%).
Aromatization of 2.6b from Cu(OAc)2 CuAAC reaction. The reaction of 2.6b (0.150 g,
0.214 mmol), SnCl2 2H2O (0.145 g, 0.642 mmol), and 10% aq H2SO4 (0.2 mL) in THF (15 mL) was conducted according to General Procedure C, providing pentacene 2.7b as a dark blue solid (139 mg, 98%).
Mp = 233235 °C; UV-vis (CH2Cl2) max (): 309 (314 000), 350 (7 100), 410 (1 100), 435 (2 100), 534 (4 000), 574 (10 000), 621 (15 600) nm; IR (ATR): 3043 (m), 2925 (s), 2859 (s),
1 1 2131 (m), 1459 (s), 1050 (s), 874 (s) cm ; H NMR (300 MHz, CDCl3): 9.28 (s, 2H), 8.26 (s, 2H), 8.11 (d, J = 8.1 Hz, 1H), 7.96–7.88 (m, 4H), 7.687.49 (m, 7H), 7.357.23 (m, 4H),
13 6.29 (s, 2H), 1.361.24 (m, 21H). C NMR (75 MHz, CDCl3): 144.5, 134.1, 131.8, 131.7, 131.2, 130.6, 130.3, 129.8, 129.2, 129.1, 128.5, 128.4, 128.2, 127.4, 126.5, 125.8, 125.5, 125.4, 125.2, 124.8, 122.9, 118.9, 106.2, 104.6, 53.2, 19.0, 11.6 (two signals coincident or not observed); MALDI HRMS (dctb) calcd for C46H43N3Si (M ) m/z 665.3221, found 665.3219.
183
Chapter 5 Experimental data
2.7c:
Aromatization of 2.6c from CuSO4 5H2O CuAAC reaction. The crude product 2.6c (0.100 g, 0.152 mmol) was dissolved in THF (15 mL) and subjected to aromatization with
SnCl2 2H2O (0.103 g, 0.456 mmol) and 10% aq H2SO4 (0.2 mL) according to General Procedure C, providing pentacene 2.7c as a deep blue solid (62 mg, 67%).
Aromatization of 2.6c from Cu(OAc)2 CuAAC reaction. The crude product 2.6c (0.308 g,
0.469 mmol) was dissolved in THF (15 mL) and subjected to aromatization with SnCl2 2H2O
(0.371 g, 1.64 mmol) and 10% aq H2SO4 (0.2 mL) according to General Procedure C, providing pentacene 2.7c as a dark blue solid (230 mg, 81%).
Mp = 8285 °C; UV-vis (CH2Cl2) max (): 308 (250 000), 350 (7 000), 410 (2 400), 435 (2 400), 535 (3 500), 574 (7 300), 621 (11 000) nm; IR (ATR): 3046 (w), 2929 (s), 2860 (s)
1 1 2129 (m), 1459 (s), 874 (s) cm ; H NMR (300 MHz, CDCl3): 9.35 (s, 2H), 8.43 (s, 2H) 7.94 (d, J = 8.4 Hz, 2H), 7.84 (s, 1H), 7.75 (d, J = 8.4 Hz, 2H), 7.38–7.26 (m, 4H), 4.60 (t, J = 7.0 Hz, 2H), 2.10 (pent, J = 7.5 Hz, 2H), 1.451.25 (m, 27H), 0.960.94 (m, 3H). 13C NMR
(75 MHz, CDCl3): 144.0, 131.7, 131.6, 130.6, 129.1, 128.40, 128.36, 127.9, 125.8, 125.6, 125.5, 125.2, 125.1, 118.8, 106.0, 104.5, 50.6, 31.1, 30.2, 29.6, 22.4, 18.9, 13.9, 11.5; ESI
+ HRMS calcd for C41H48N3Si ([M + H] ) m/z 610.3612, found 610.3607.
184
Chapter 5 Experimental data
2.7d:
Aromatization of 2.6d from CuSO4 5H2O CuAAC reaction. The crude product 2.6d (0.171 g, 0.236 mmol) was dissolved in THF (15 mL) and subjected to aromatization with
SnCl2 2H2O (0.160 g, 0.708 mmol) and 10% aq H2SO4 (0.2 mL) according to General Procedure C, providing pentacene 2.7d as a deep blue solid (155 mg, 43% from 2.3).
Aromatization of 2.6d from Cu(OAc)2 CuAAC reaction. The crude product 2.6d (0.231 g, 0.318 mmol) was dissolved in THF (15 mL) and subjected to aromatization with
SnCl2 2H2O (0.215 g, 0.954 mmol) and 10% aq H2SO4 (0.2 mL) according to General Procedure C, providing pentacene 2.7d as a deep blue solid (145 mg, 69%).
Mp = 258–260 °C; UV-vis (CH2Cl2): max (): 309 (220 000), 350 (5 600), 410 (1 100), 435 (1 700), 535 (3 000), 574 (6 800), 621 (10 000) nm. IR (ATR): 3112 (w), 3044 (w), 2910 (s),
1 1 2856 (s), 2133 (m), 1455 (m), 872 (s) cm ; H NMR (300 MHz, CDCl3): 9.35 (s, 2H), 8.46 (s, 2H), 7.98 (s, 1H), 7.94 (d, J = 8.4 Hz, 2H), 7.80 (d, J = 8.6 Hz, 2H), 7.38–7.28 (m, 4H), 2.53–2.52 (m, 6H), 2.39–2.34 (m, 3H), 1.90 (bs, 6H), 1.461.32 (m, 21H). 13C NMR (75
MHz, CDCl3): 143.3, 131.8, 131.7, 130.8, 129.2, 128.6, 128.4, 126.2, 125.83, 125.80,
121.9, 118.7, 106.0, 104.6, 60.1, 43.2, 35.9, 29.5, 18.9, 11.6; ESI HRMS calcd for C45
+ H50N3Si ([M H] ) m/z 660.3769, found 660.3762.
185
Chapter 5 Experimental data
NN N
Si
2.7e:
Aromatization of 2.6e from CuSO4 5H2O CuAAC reaction. The crude product 2.6e (0.270 g, 0.415 mmol), was dissolved in THF (15 mL) and subjected to aromatization with
SnCl2 2H2O (0.282 g, 1.25 mmol) and 10% aq H2SO4 (0.2 mL) according to General Procedure C, providing pentacene 2.7e as a deep blue solid (65 mg, 15% from 2.3).
Aromatization of 2.6e from Cu(OAc)2 CuAAC reaction. The crude product 2.6e (0.070 g,
0.11 mmol) was dissolved in THF (15 mL) and subjected to aromatization with SnCl2 2H2O
(0.075 g, 0.33 mmol) and 10% aq H2SO4 (0.2 mL) according to General Procedure C, providing pentacene 2.7e as a deep blue solid (48 mg, 15% from 2.3).
Mp = 188190 °C; UV-vis (CH2Cl2) max (): 309 (220 000), 350 (8 600), 409 (4 300), 435 (3 500), 534 (3 900), 574 (8 000), 621 (12 000) nm; IR (ATR): 3048 (w), 2923 (s), 2860 (s),
1 1 2131 (w), 1500 (m), 731 (s), 666 (s) cm ; H NMR (400 MHz, CDCl3): 9.37 (s, 2H), 8.53 (s, 2H), 8.40 (s, 1H), 8.02 (d, J = 8.1 Hz, 2H), 7.95 (d, J = 8.4 Hz, 2H), 7.80 (d, J = 8.4 Hz, 2H) 7.64 (t, J = 7.2 Hz, 2H), 7.52 (t, J = 7.5 Hz, 1H), 7.38–7.28 (m, 4H), 1.411.37 (m, 21H).
13 C NMR (100 MHz, CDCl3): 145.1, 137.1, 131.97, 131.95, 130.8, 130.0, 129.3, 129.0, 128.6, 128.5, 126.1, 126.0, 125.8, 125.2, 124.9, 123.3, 120.5, 119.3, 106.5, 104.6, 19.0,
+ 11.7; ESI HRMS calcd for C41H39N3Si (M ) m/z 601.2908; found 601.2907, calcd for
+ C41H40N3Si ([M + H] ) m/z 602.2986, found 602.2974. Single crystals of 2.7e suitable for X-ray crystallographic analysis were grown by slow
evaporation of a CDCl3 solution at rt. X-ray data for 2.7e CDCl3: C42H40Cl3N3Si, Fw = 721.21; triclinic crystal system, space group P1; crystal size = 0.2 x 0.1 x 0.1 mm3; = 0.7107 Å; a = 10.8952(5) Å, b = 11.4875(9) Å, c = 16.2121(12) Å; = 81.871(4) °; V =
3 3 1 1838.86(17) Å ; Z = 2; (calcd) = 1.303 g/cm ; 2max = 50.36 °; = 0.317 mm ; T = 173(2) K;
186
Chapter 5 Experimental data
2 2 total data collected = 6522; R1 = 0.1415 [1981 observed reflections with F0 2(F0 )]; R2
2 2 = 0.1506 for 442 variables with [F0 3(F0 )]; largest difference, peak and hole = 0.286 and –0.342 eÅ 3.
2.7f:
Aromatization of 2.6f from Cu(OAc)2 CuAAC reaction. The crude product 2.6f (0.222 g,
0.317 mmol), was dissolved in THF (15 mL) and subjected to aromatization with SnCl2
2H2O (0.215 g, 0.951 mmol) and 10% H2SO4 (0.2 mL) according to General Procedure C, providing pentacene 2.7f as a deep blue solid (124 mg, 34% from 2.3). Synthesis of 2.7f without purification of the intermediate 2.6f. The CuAAC reaction of 2.3 (129 mg, 0.237 mmol), 2-naphthylazide[7d] (50 mg, 0.28 mmol),
CuSO4 5H2O (148 mg, 0.593 mmol), and sodium ascorbate (118 mg, 0.593 mmol) in dry, deoxygenated THF (20 mL) and H2O (20 mL) was subjected to General Procedure A. The crude product was dissolved in THF (15 mL) and subjected to aromatization with
SnCl2 2H2O (160 mg, 0.711 mmol) and 10% aq H2SO4 (0.2 mL) according to General Procedure C, providing pentacene 2.7f as a dark blue solid (53 mg, 34% from 2.3).
Mp = 269271 °C; UV-vis (CH2Cl2) max (): 308 (200 000), 350 (6 200), 410 (1 100), 435 (1 700), 535 (3 100), 575 (7 000), 622 (11 000) nm; IR (ATR): 3046 (w), 2936 (s), 2861 (s),
1 1 2128 (m), 1461 (m), 872 (s), 736 (s) cm ; H NMR (400 MHz, CDCl3): 9.38 (s, 2H), 8.57 (s, 2H), 8.53 (s, 1H), 8.42 (s, 1H), 8.16 (d, J = 1.9 Hz, 1H), 8.13 (d, J = 1.8 Hz, 1H), 7.95 (d, J = 8.6 Hz, 4H), 7.80 (d, J = 8.7 Hz, 2H), 7.60–7.57 (m, 2H), 7.38–7.27 (m, 4H), 1.421.38
13 (m, 21H). C NMR (75 MHz, CDCl3): 145.1, 134.3, 133.2, 132.9, 131.83, 131.80, 130.6, 130.1, 129.2, 128.44, 128.41, 128.2, 127.9, 127.5, 127.0, 126.0, 125.9, 125.6, 125.1,
187
Chapter 5 Experimental data
124.7, 123.3, 119.2, 118.7, 118.3, 106.4, 104.5, 18.9, 11.5; ESI HRMS calcd for C45H41N3Si (M+) m/z 651.3064, found 651.3062.
2.7g: The CuAAC reaction of 2.3 (272 mg, 0.499 mmol), 3-azidopyridine[7e] (84 mg, 0.70 mmol),
CuSO4 5H2O (312 mg, 1.25 mmol), and sodium ascorbate (248 mg, 1.25 mmol) in dry, deoxygenated THF (20 mL) and H2O (20 mL) was subjected to General Procedure A. The crude product was dissolved in THF (15 mL) and subjected to aromatization with
SnCl2 2H2O (339 mg, 1.50 mmol) and 10% aq H2SO4 (0.2 mL) according to General
Procedure C. Recrystallization from CH2Cl2 layered with MeOH at 15 °C provided pentacene 2.7g as a dark blue solid (166 mg, 55% from 2.3).
Mp = 258260 °C; Rf = 0.1 (CHCl3); UV-vis (CH2Cl2) max (): 308 (240 000), 347 (7 400), 410 (2 000), 435 (2 700), 534 (4 100), 574 (8 700), 622 (13 500) nm; IR (ATR): 3047 (w),
1 1 2939 (m), 2861 (s), 2130 (s), 1460 (m), 871 (s) cm ; H NMR (400 MHz, CDCl3): 9.39 (s, 2H), 9.29 (d, J = 2.3 Hz, 1H), 8.81 (d, J = 3.7 Hz, 1H), 8.49 (s, 2H), 8.46 (s, 1H), 8.44 (dt, J = 8.2 Hz, 1.5 Hz, 2H), 7.96 (d, J = 8.6 Hz, 2H), 7.80 (d, J = 8.5 Hz, 2H), 7.63 (dd, J = 4.8 Hz,
13 3.4 Hz, 1H), 7.40–7.30 (m, 4H), 1.421.36 (m, 21H). C NMR (75 MHz, CDCl3): 150.0, 145.6, 141.5, 133.7, 131.9, 131.8, 130.6, 129.2, 128.5, 128.4, 128.0, 126.1, 126.0, 125.8,
124.8, 124.4, 124.1, 123.1, 119.6, 106.7, 104.4, 19.0, 11.6; ESI HRMS calcd for C40H39N4Si ([M + H]+) m/z 603.2939, found 603.2930.
188
Chapter 5 Experimental data
2.7h: The CuAAC reaction of 2.3 (283 mg, 0.519 mmol), 4-azidopyridine[7e] (75 mg, 0.62 mmol),
CuSO4 5H2O (325 mg, 1.30 mmol), and sodium ascorbate (258 mg, 1.30 mmol) in dry, deoxygenated THF (20 mL) and H2O (20 mL) was subjected to General Procedure A. The crude product was dissolved in THF (15 mL) and subjected to aromatization with
SnCl2 2H2O (352 mg, 1.56 mmol) and 10% aq H2SO4 (0.2 mL) according to General
Procedure C. Recrystallization from CH2Cl2 layered with MeOH at 15 °C provided pentacene 2.7h as a dark blue solid (108 mg, 35% from 2.3).
Mp = 255258 °C; UV-vis (CH2Cl2) max (): 308 (260 000), 348 (7 200), 410 (1 400), 436 (2 100), 534 (3 400), 574 (9 200), 621 (15 000) nm; IR (ATR): 3038 (w), 2939 (s), 2862 (s),
1 1 2130 (m), 1586 (s), 870 (s) cm ; H NMR (300 MHz, CDCl3): 9.35 (s, 2H), 8.84 (d, J = 5.3 Hz, 2H), 8.48 (s, 1H), 8.41 (s, 2H), 7.95–7.90 (m, 4H), 7.75 (d, J = 8.5 Hz, 2H), 7.38–7.25
13 (m, 4H), 1.451.34 (m, 21H). C NMR (75 MHz, CDCl3): 151.7, 145.7, 142.9, 131.8, 131.7, 130.4, 129.0, 128.4, 128.2, 126.0, 125.9, 125.7, 124.6, 123.6, 122.4, 119.6, 113.5,
+ + 106.7, 104.3, 18.8, 11.5; MALDI MS (dctb) m/z 602 (M , 85), 574 ([M N2] ), 100). ESI + HRMS calcd for C40H39N4Si ([M + H] ) m/z 603.2939, found 603.2934.
189
Chapter 5 Experimental data
N N Si N
N Si N N
2.11: The CuAAC reaction of 2.3 (354 mg, 0.640 mmol), 1,4-bis(azidomethyl)benzene[7f] (50 mg,
0.27 mmol), CuSO4 5H2O (202 mg, 0.81 mmol), and sodium ascorbate (161 mg, 0.810 mmol) in dry, deoxygenated THF (20 mL) and H2O (20 mL) was subjected to General Procedure B. The crude product (0.12 mg, 0.094 mmol) was dissolved in THF (15 mL) and
subjected to aromatization with SnCl2 2H2O (127 mg, 0.564 mmol) and 10% aq H2SO4 (0.2 mL) according to General Procedure C. Purification was performed by pouring the reaction mixture into MeOH (80 mL). The resulting precipitate was filtered, washed with MeOH, and finally purified by recrystallization from CH2Cl2 /MeOH at 15 °C to provide 2.11 as a dark blue solid (66 mg, 37%).
Mp = 332335 °C; UV-vis (CH2Cl2) max (): 309 (350 000), 349 (10 300), 410 (2 200), 435 (3 100), 534 (5 300), 574 (12 500), 622 (19 300) nm; IR (ATR): 3043 (w), 2938 (s), 2861 (s),
1 1 2127 (m), 1459 (s), 872 (s), 732 (s) cm ; H NMR (300 MHz, CDCl3): 9.30 (s, 4H), 8.37 (s, 4H), 7.91–7.87 (m, 6H), 7.66–7.63 (m, 8H), 7.29–7.15 (m, 8H), 5.92 (s, 4H), 1.37–1.35
13 (m, 42H). C NMR (75 MHz, CDCl3): 144.8, 135.6, 131.6, 131.5, 130.4, 128.9, 128.8, 128.2, 128.1, 125.8, 125.7, 125.5, 125.3, 124.8, 118.9, 106.1, 104.3, 53.8, 18.8, 11.4 (one
+ signal coincident or not observed); ESI HRMS calcd for C78H76N6Si2 (M ) m/z 1152.5665, found 1152.5656.
190
Chapter 5 Experimental data
2.12: The CuAAC reaction of 2.3 (253 mg, 0.456 mmol), 6-bis(4-
azidobenzylidene)-4-methylcyclohexane (70 mg, 0.19 mmol), CuSO4 5H2O (142 mg, 0.570 mmol), and sodium ascorbate (113 mg, 0.570 mmol) in dry, deoxygenated THF (20 mL) and H2O (20 mL) was subjected to General Procedure B. The crude product (150 mg,
0.103 mmol) was dissolved in THF (15 mL) and subjected to aromatization with SnCl2 2H2O
(140 mg, 0.618 mol) and 10% aq H2SO4 (0.2 mL) according to General Procedure C. Purification was performed by pouring the reaction mixture into MeOH (80 mL). The resulting precipitate was filtered, washed with MeOH, dried, dissolved in an minimal amount of CH2Cl2 and this solution passed through a short plug of silica gel ( ~ 12 g on a 10 cm diameter fritted funnel). Solvent removal provided 2.12 as a green-blue solid (54 mg, 21%).
Mp > 400 °C; UV-vis (CH2Cl2) max (): 309 (280 000), 349 (40 000), 410 (9 000), 435 (6 000), 535 (4 400), 575 (10 000), 623 (15 700) nm; IR (ATR): 3046 (w), 2939 (s), 2861 (s),
1 1 2130 (m), 1602 (s), 1515 (s), 876 (s), 740 (s) cm ; H NMR (300 MHz, CDCl3): 9.37 (s, 4H), 8.52 (s, 4H), 8.44 (s, 2H), 8.07 (d, J = 8.6 Hz, 4H), 7.95 (d, J = 8.4 Hz, 4H), 7.87 (bs, 2H), 7.79 (d, J = 8.5 Hz, 4H), 7.69 (d, J = 8.7 Hz, 4H), 7.38–7.27 (m, 8H), 3.12–3.08 (m,
13 4H), 2.60–2.51 (m, 3H), 1.95 (bs, 1H), 1.43-1.31 (m, 42H). C NMR (125 MHz, CDCl3): 189.4, 145.2, 136.5, 136.3, 136.2, 135.7, 131.89, 131.84, 131.5, 130.6, 129.2, 128.5, 127.9, 126.0, 125.9, 125.7, 125.0, 124.5, 123.0, 120.1, 119.4, 106.6, 104.5, 36.4, 29.2,
+ 21.6, 18.9, 11.6; ESI HRMS calcd for C91H86N6OSi2 (M ) m/z 1334.6396, found 1334.6370;
+ calcd for C91H86N6NaOSi2 ([M + Na] ) m/z 1357.6294, found 1357.6269.
191
Chapter 5 Experimental data
Si Si
N N N N N N
NN N
Si
2.13: The CuAAC reaction of 2.3 (412 mg, 0.756 mmol), 1,3,5-tris(azidomethyl)benzene[7g] (50
mg, 0.21 mmol), CuSO4 5H2O (0.16 g, 0.63 mmol), and sodium ascorbate (0.13 g, 0.63 mmol) in dry, deoxygenated THF (20 mL) and H2O (20 mL) was subjected to General Procedure B. The crude product was dissolved in THF (15 mL) and subjected to
aromatization with SnCl2 2H2O (426 mg, 1.89 mmol) and 10% aq H2SO4 (0.2 mL) according to General Procedure C. Purification was performed by pouring the reaction mixture into MeOH (80 mL). The resulting precipitate was filtered, washed with MeOH, dried, and purified by column chromatography (silica gel, EtOAc) to provide 2.13 as a dark blue solid (52 mg, 15%).
Mp > 400 °C; Rf = 0.65 (EtOAc); UV-vis (CH2Cl2) max (): 309 (495 000), 350 (19 500), 410 (4 200), 435 (6 200), 537 (10 300), 577 (20 000), 624 (29 100) nm; IR (ATR): 3042 (w), 2935 (s), 2860 (s), 2125 (m), 1459 (m), 872 (s), 736 (s), 663 (s) cm 1; 1H NMR (300 MHz,
CDCl3): 9.12 (s, 6H), 8.20 (s, 6H), 7.99 (s, 3H), 7.80–7.75 (m, 9H), 7.41 (d, J = 8.7 Hz, 6H), 7.15–7.10 (m, 6H), 6.81–6.76 (m, 6H), 5.95 (s, 6H), 1.441.31 (m, 63 H). 13C NMR
(125 MHz, CDCl3): 145.1, 137.5, 131.5, 131.4, 130.4, 128.8, 128.2, 127.9, 125.8, 125.7, 125.4, 124.8, 124.7, 119.2, 106.1, 104.7, 53.9, 18.9, 11.7 (two signals coincident or not
+ observed); ESI HRMS calcd for C114H111N9Si3 (M ) m/z 1689.8265, found 1689.8256.
192
Chapter 5 Experimental data
General Procedure D for the complexation of pentacenes 2.7g and 2.7h: A Schlenk flask was charged with the corresponding pyridyl-substituted pentacene derivative (1 equiv) and 5,10,15,20-tetrakis-(4´-(tert-butyl)-phenyl)-porphyrinato-ruthenium
(II) (RutBuPP H2O, 1 equiv). The solids were dissolved in dry, deoxygenated benzene (5 mL) and stirred for 1 h at rt, The mixture was further heated to 50 °C and stirred for 2 h at that temperature. The mixture was cooled to rt and the solvent was removed under reduced pressure. The solid purple residue was redissolved in minimal amount of dry, deoxygenated CH2Cl2 and precipitated by the addition of a large amount of dry, deoxygenated hexanes. The solids were filtered under N2-atmosphere and dried in vacuo to provide the products as deep purple solids.
2.17:
2.7g (10 mg, 0.017 mmol) and RutBuPP H2O (17 mg, 0.017 mmol) were used according to General Procedure D. 2.17 was obtained as a purple, amorphous solid (20 mg, 74%). IR (ATR): 2955 (s), 2863 (s), 1966 (s), 1609 (s), 1350 (s), 1006 (s), 715 (s) cm 1; 1H NMR
(300 MHz, C6D6): 9.62 (s, 2H), 9.10 (s, 8H), 8.42 (dd, J = 7.0 Hz, 2.0 Hz, 4H), 8.27 (s, 2H), 8.21 (dd, J = 7.1 Hz, 2.0 Hz, 4H), 7.90 (d, J = 8.4 Hz, 2H), 7.67 (dd, J = 7.0 Hz, 2.0 Hz, 4H), 7.57 (dd, J = 7.1 Hz, 2.0 Hz, 4H), 7.51 (d, J = 8.4 Hz, 2H), 7.036.88 (m, 5H), 6.30 (s, 1H), 4.744.71 (m, 2H), 1.871.85 (m, 2H), 1.42 (bs, 36H), 1.371.36 (m, 21H); ESI HRMS
102 + calcd for C100H98N8O2 RuSi ([M – CO + H2O] ) m/z 1572.6620, found 1572.6654.
193
Chapter 5 Experimental data
Ar
N Ar N N Ru CO N Ar N N N N Ar
Si
Ar =
2.18:
Pentacene 2.7g (12 mg, 0.020 mmol) and RutBuPP H2O (20 mg, 0.020 mmol) were used according to General Procedure D. Complex 2.18 was obtained as a purple solid (21 mg, 67%).
Mp > 400 °C; UV-vis (CH2Cl2) max (): 247 (50 000), 309 (200 000), 346 (12 500), 415 (150 000), 496 (5 000), 533 (16 000), 571 (11 000), 622 (12 000) nm; IR (ATR): 3029 (w), 2953
1 1 (s), 2862 (s), 2123 (m), 1949 (s), 1262 (s), 1006 (s) cm ; H NMR (300 MHz, C6D6): 9.70 (s, 2H), 9.05 (s. 8H), 8.43 (s, 2H), 8.37 (dd, J = 7.1 Hz, 2.0 Hz, 4H), 8.10 (dd, J = 7.0 Hz, 2.0 Hz, 4H), 7.99 (d, J = 8.7 Hz, 2H), 7.537.40 (m, 11H), 7.30 (dd, J = 7.0 Hz, 2.1 Hz, 4H), 6.80 (s, 1H), 5.62 (d, J = 8.2 Hz, 1H), 4.30 (pseudo q, J = 5.6 Hz, 1H), 2.42 (d, J = 2.4 Hz, 1H), 1.95 (dd, J = 5.0 Hz, 1.2 Hz, 1H), 1.461.45 (m, 21H), 1.34 (s, 36H). ESI HRMS
+ (CH2Cl2/MeOH) calcd for C61H60N4RuO ([RutBuPPCO – 2.18] ) m/z 966.3822, found
102 + 966.3830, calcd for C101H98N8O RuSi ([M MeOH] ) m/z 1568.6676, found 1568.715.
Experimental data – Aryl-substituted pentacenes
General Procedure E for the synthesis of aryl-substituted pentacenes: Unless otherwise noted, to a solution of the corresponding aryl halide (3.0 equiv, 3.0 mmol) in dry, deoxygenated THF (20 mL) at 78 °C was added n-BuLi (2.5 M in hexanes, 2.9 equiv, 2.9 mmol). After stirring for 30 min at 78 °C, 2.4 (1.0 equiv, 1.0 mmol) was added as a solid. The resulting mixture was stirred for 1214 h at rt. The reaction was quenched by the addition of saturated aq NH4Cl (100 mL) and extracted with CH2Cl2 (3 x 50 mL). The
194
Chapter 5 Experimental data
combined organic phases were washed with brine (100 mL), dried over Na2SO4, filtered, and the solvent removed in vacuo. This residue was dissolved in THF (20 mL) and
subjected to reductive aromatization by the addition of SnCl2 2H2O (3.0 equiv, 3.0 mmol) and 10% aq H2SO4 (1 mL). The mixture was stirred for 46 h at rt and saturated aq NH4Cl
(100 mL) was then added. The mixture was extracted with CH2Cl2 (3 x 50 mL, if the phases do not separate and/or the mixture forms an emulsion, then 1020 mL of HCl (conc.) were added to the mixture in the separatory funnel). The combined organic phases were washed with brine (100 mL), dried over Na2SO4, filtered, and the solvent removed in vacuo. The crude product was separated by column chromatography (silica gel, hexanes/CH2Cl2, v/v, see individual procedure) and finally purified by recrystallization from CH2Cl2 layered with MeOH at 15 °C to provide pentacenes 2.21a–j as deep blue solids.
2.21a: According to General Procedure E, phenyllithium (1.8 M in dibutylether, 1.67 mL, 3.00 mmol) and 2.4 (491 mg, 1.00 mmol) in dry, deoxygenated THF (20 mL) were used, followed
by reductive aromatization using SnCl2 2H2O (677 mg, 3.00 mmol) and 10% aq H2SO4 (1 mL) in THF (20 mL). Purification was achieved by column chromatography (silica gel, hexanes/CH2Cl2 3:1) and final recrystallization from CH2Cl2 layered with MeOH. Pentacene 2.21a was obtained as a dark blue solid (274 mg, 51%).
Mp = 162165 °C; Rf = 0.30 (hexanes); UV-vis (CH2Cl2) max (): 253 (18 000), 270 (21 000), 298 (105 000), 310 (240 000), 351 (7 300), 406 (1 300), 435 (1 420), 580 (9 000), 621 (12
300) nm. UV-vis (CH2Cl2 cast film) max: 323, 350, 411, 436, 594, 637 nm; Fluorescence
(CH2Cl2, exc = 615 nm): max, em = 665 nm; IR (ATR): 3046 (w), 2937 (s), 2860 (s), 2130 (m),
–1 1 1374 (s), 874 (s) cm ; H NMR (300 MHz, CDCl3): 9.36 (s, 2H), 8.26 (s, 2H), 7.95 (d, J = 8.5 Hz, 2H), 7.757.67 (m, 5H), 7.567.54 (m, 2H), 7.377.27 (m, 4H), 1.381.37 (m, 21H).
195
Chapter 5 Experimental data
13 C NMR (100 MHz, CDCl3): 139.0, 138.4, 131.9, 131.6, 131.4, 131.0, 128.7, 128.6, 128.5, 127.9, 126.3, 125.8, 125.7, 125.3, 117.3, 105.3, 104.9, 19.0, 11.7 (one signal
+ coincident or not observed); ESI HRMS calcd for C39H38Si (M ) m/z 534.27373, found
534.27406; TGA: Td ~370 °C; DSC: Mp = 177 °C, decomposition: 178 °C (onset), 179 °C (peak). A crystal suitable for X-ray crystallographic analysis has been grown by slowly evaporation of a CH2Cl2 solution at rt. X-ray data for 2.21a: C39H38Si, Fw = 534.78; monoclinic crystal
3 system, space group C2/c; crystal size = 0.3 x 0.2 x 0.2 mm ; = 0.7107 Å; a = 22.6564(6)
3 Å, b = 23.1461(9) Å, c = 11.8317(3) Å; 104.470(2)°; V = 6007.8(3) Å ; Z = 8; (calcd) =
3 1 1.183 g/cm ; 2max = 54.96°; = 0.104 mm ; T = 173(2) K; total data collected = 13174; R1
2 2 = 0.0488 [6875 observed reflections with F0 2(F0 )]; R2 = 0.1345 for 361 variables with
2 2 3 F0 3(F0 ); largest difference, peak and hole = 0.208 and 0.247 e Å .
2.21b: According to General Procedure E, 1-bromonaphthalene (627 mg, 3.00 mmol), n-BuLi (2.5 M in hexanes, 1.16 mL, 2.90 mmol), and 2.4 (491 mg, 1.00 mmol) in dry, deoxygenated
THF (20 mL) were used, followed by reductive aromatization using SnCl2 2H2O (677 mg,
3.00 mmol) and 10% aq H2SO4 (1 mL) in THF (20 mL). Purification was achieved by column chromatography (silica gel, hexanes/CH2Cl2 5:1) and final recrystallization from
CH2Cl2 layered with MeOH. Pentacene 2.21b was obtained as a dark blue-purple solid (142 mg, 25%).
Mp = 244–246 °C; Rf = 0.55 (hexanes/CH2Cl2 5:1); UV-vis (CH2Cl2) max (): 270 (19 500), 298 (sh, 85 800), 309 (250 000), 348 (6 000), 435 (1 350), 576 (7 700), 621 (11 500) nm.
UV-vis (CH2Cl2 cast film) max: 323, 340, 412, 438, 544, 593, 635 nm; Fluorescence (CH2Cl2,
exc = 615 nm): max, em = 656 nm; IR (ATR): 3044 (w), 2938 (s), 2859 (s), 2133 (s), 1459 (s),
–1 1 1357 (s), 727 (s) cm ; H NMR (300 MHz, CDCl3): 9.39 (s, 2H), 8.16 (d, J = 4.2 Hz, 1H), 196
Chapter 5 Experimental data
8.06 (d, J = 4.1 Hz, 1H), 8.00 (s, 2H), 7.94 (d, J = 8.2 Hz, 2H), 7.78 (t, J = 7.1 Hz, 1H), 7.59 (d, J = 8.6 Hz, 1H), 7.55 (d, J = 8.6 Hz, 2H), 7.46 (t, J = 7.6 Hz, 1H), 7.31 (t, J = 8.3 Hz, 2H), 7.21–7.16 (m, 2H), 7.10 (t, J = 8.3 Hz, 1H), 7.00 (d, J = 8.6 Hz, 1H), 1.471.38 (m, 21H).
13 C NMR (100 MHz, CDCl3): 136.7, 136.5, 133.8, 133.7, 132.0, 131.5, 131.0, 129.5, 129.1, 128.6, 128.5, 128.3, 126.7, 126.4, 126.3, 126.1, 125.90, 125.85, 125.80, 125.7,
+ 125.3, 117.6, 105.5, 104.8, 19.0, 11.7; ESI HRMS calcd C43H40Si (M ) m/z 584.28938, found 584.28893; Element. Anal calcd for C43H40Si: C, 88.30; H, 6.89. Found: C, 87.94; H,
6.91. TGA: Td ~ 370 °C; DSC: Mp = 248 °C. A crystal suitable for X-ray crystallographic analysis has been grown by slowly evaporation of a CH2Cl2 solution layered with acetone at 4 °C. X-ray data for 2.21b: C43H40Si, Fw = 584.84; triclinic crystal system, space group P1; crystal size = 0.30 x 0.28 x 0.18 mm3; =
1.5418 Å; a = 11.1091(5) Å, b = 11.6246(6) Å, c = 13.6377(6) Å; = 93.926(4)°,
3 3 100.072(4)°, 103.336(4)°; V = 1676.34(14) Å ; Z = 2; (calcd) = 1.159 g/cm ; 2max =
1 146.56°; = 0.819 mm ; T = 172.9 K; total data collected = 25726; R1 = 0.0719 [6655
2 2 2 2 observed reflections with F0 2(F0 )]; R2 = 0.2454 for 449 variables with [F0 3(F0 )] and 0 restraints; largest difference, peak and hole = 0.622 and 0.496 e Å 3. The naphthyl group showed disorder, which has been resolved and refined to the following occupation factors: 55:45.
2.21c: According to General Procedure E, 9-Bromonanthracene (771 mg, 3.00 mmol), n-BuLi (2.5 M in hexanes, 1.16 mL, 2.90 mmol), and 2.4 (491 mg, 1.00 mmol) in dry, deoxygenated
THF (20 mL) were used, followed by reductive aromatization using SnCl2 2H2O (677 mg,
3.00 mmol) and 10% aq H2SO4 (1 mL) in THF (20 mL). Purification was achieved by column chromatography (silica gel, hexanes/CH2Cl2 5:1) and recrystallization from CH2Cl2
197
Chapter 5 Experimental data layered with MeOH. Pentacene 2.21c was obtained as a dark blue-purple solid (326 mg, 51%).
Mp= 306–308 °C (decomp); Rf = 0.45 (hexanes/CH2Cl2 5:1); UV-vis (CH2Cl2) max ( ): 227 (31 000), 256 (113 600), 300 (81 300), 310 (250 000), 331 (9 000), 349 (11 300), 367 (10
200), 387 (8 600), 435 (1 900), 535 (3 800), 576 (8 500), 623 (13 800); UV-vis (CH2Cl2 cast film) max: 260, 320, 368, 388, 437, 501, 543, 584, 632 nm; Fluorescence (CH2Cl2,exc =
615 nm): max, em = 650 nm; IR (ATR): 3042 (w), 2936 (m), 2857 (s), 2130 (m), 1457 (s),
1 1 1324 (m), 872 (s), 724 (s) cm ; H NMR (300 MHz, CDCl3): = 9.48 (s, 2H), 8.79 (s, 1H), 8.21 (d, J = 8.4 Hz, 2H), 7.96 (d, J = 8.7 Hz, 2H), 7.72 (s, 2H), 7.47 7.42 (m, 2H), 7.39 (d, J = 8.7 Hz, 2H), 7.30 (t, J = 8.4 Hz, 2H), 7.13 (t, J = 7.6 Hz, 2H), 7.07 7.06 (m, 4H),
13 1.441.43 (m, 21H); C NMR (100 MHz, CDCl3): = 135.0, 133.2, 132.1, 131.9, 131.72, 131.66, 131.1, 129.7, 128.64, 128.57, 128.5, 127.6, 127.0, 126.2, 126.1, 126.0, 125.9,
+ 125.4, 125.3, 118.0, 105.8, 104.9, 19.1, 11.8; APPI HRMS calcd C47H42Si (M ) m/z
634.3050, found 634.3048; TGA: Td ~ 375 °C; DSC: Mp = 194 °C (onset), 197 °C (peak). A crystal suitable for X-ray crystallographic analysis has been grown by slowly evaporation of a CH2Cl2 solution layered with MeOH at 4 °C. X-ray data for 2.21c: C47H42Si, Fw = 634.90;
3 monoclinic crystal system, space group P21/c; crystal size = 0.44 x 0.17 x 0.15 mm ; =
1.5418 Å; a = 7.6889(3) Å, b = 31.5880(11) Å, c = 14.4774(4) Å; 91.378(4)°; V =
3 3 1 3515.2(2) Å ; Z = 4; (calcd) = 1.200 g/cm ; 2max = 147.10°; = 0.822 mm ; T = 173.0 K;
2 2 total data collected = 12209; R1 = 0.0510 [6732 observed reflections with F0 2(F0 )];
2 2 R2 = 0.1362 for 439 variables with [F0 3(F0 )]; largest difference, peak and hole = 0.459 and 0.376 e Å 3.
2.21d: According to General Procedure E, 2-bromothiophene (489 mg, 3.00 mmol), n-BuLi (2.5 M
198
Chapter 5 Experimental data in hexanes, 1.16 mL, 2.90 mmol), and 2.4 (491 mg, 1.00 mmol) in dry, deoxygenated THF
(20 mL) were used, followed by reductive aromatization using SnCl2 2H2O (677 mg, 3.00 mmol) and 10% aq H2SO4 (1 mL) in THF (20 mL). Purification was achieved by column chromatography (silica gel, hexanes/CH2Cl2 3:1) and final recrystallization from CH2Cl2 layered with MeOH. Pentacene 2.21d was obtained as a dark blue solid (116 mg, 21%).
Mp = 316–318 °C (color change); Rf = 0.70 (hexanes/CH2Cl2, 3:1); UV-vis (CH2Cl2) max (): 269 (13 200), 297 (sh, 83 600), 309 (220 000), 351 (7 400), 436 (2 000), 535 (3 500), 576 (8
400), 623 (13 200) nm. UV-vis (CH2Cl2 cast film) max: 327, 350, 413, 437, 545, 589, 637 nm; Fluorescence (CH2Cl2, exc = 615 nm): max, em = 655 nm; IR (ATR): 3043 (w), 2936 (s), –1 1 2859 (s), 2125 (m), 1459 (m), 1363 (m), 870 (s), 727 (s) cm ; H NMR (300 MHz, CDCl3): 9.35 (s, 2H), 8.48 (s, 2H), 7.96 (d, J = 8.4 Hz, 2H), 7.82 (d, J = 8.4 Hz, 2H), 7.74 (dd, J = 4.0 Hz, 1.1 Hz, 1H), 7.44–7.42 (m, 1H), 7.387.27 (m, 5H), 1.411.38 (m, 21H). 13C NMR
(75 MHz, CDCl3): 139.0, 131.8, 131.6, 130.6, 130.0, 129.78, 129.76, 128.6, 128.4, 127.3, 127.1, 125.9, 125.7, 125.5, 118.6, 106.0, 104.6, 18.9, 11.6 (one signal coincident or not
+ observed); ESI HRMS calcd C37H36SSi (M ) m/z 540.23015, found 540.23092; Element
Anal calcd for C37H36SSi: C, 82.17; H, 6.71; S, 5.93. Found: C, 81.65; H, 6.98; S, 5.79; TGA:
Td ~ 372 °C; DSC: decomposition, 206 °C (onset), 247 °C (peak). A crystal suitable for X-ray crystallographic analysis has been grown by slowly evaporation of a CH2Cl2 solution layered with acetone at °C. X-ray data for 2.21d: C37H36SiS, Fw =
540.81; monoclinic crystal system, space group P21/n; crystal size = 0.21 x 0.094 x 0.086 mm3; = 1.5418 Å; a = 13.4483(3) Å, b = 13.6265(4) Å, c = 16.7260(4) Å; 91.359(2)°; V
3 3 1 = 3064.22(13) Å ; Z = 4; (calcd) = 1.172 g/cm ; 2max = 146.8°; = 1.474 mm ; T = 2 173.00(10) K; total data collected = 10141; R1 = 0.0641 [5909 observed reflections with F0
2 2 2 2(F0 )]; R2 = 0.1896 for 368 variables with [F0 3(F0 )] and 10 restraints; largest difference, peak and hole = 0.54 and 0.48 e Å 3. The disorder in the thiophene unit was refined using the following occupancies: S52/C55: S52a/C55a = 66:34, C4/C5: C4a/C5a = 60:40.
199
Chapter 5 Experimental data
2.21e: According to General Procedure E, 3-bromoanisole (561 mg, 3.00 mmol), n-BuLi (2.5 M in hexanes, 1.16 mL, 2.90 mmol), and 2.4 (491 mg, 1.00 mmol) in dry, deoxygenated THF (20
mL) were used, followed by reductive aromatization using SnCl2 2H2O (677 mg, 3.00 mmol) and 10% aq H2SO4 (1 mL) in THF (20 mL). Purification was achieved by column chromatography (silica gel, hexanes/CH2Cl2 3:1) and final recrystallization from CH2Cl2 layered with MeOH. Pentacene 2.21e was obtained as a dark blue solid (340 mg, 60%).
Mp = 210–213 °C; Rf = 0.55 (hexanes/CH2Cl2 3:1); UV-vis (CH2Cl2) max (): 270 (19 700), 297 (92 300), 309 (281 000), 351 (6 550), 435 (1 270), 580 (8 260), 621 (11 370) nm.
UV-vis (CH2Cl2 cast film) max: 274, 321, 411, 436, 540, 588, 634 nm; Fluorescence (CH2Cl2,
exc = 615 nm): max, em = 663 nm; IR (ATR): 3043 (w), 2938 (s), 2861 (s), 2128 (m), 1588 (s),
–1 1 1252 (s), 877 (s), 724 (s) cm ; H NMR (400 MHz, CDCl3): 9.37 (s, 2H), 8.32 (s, 2H), 7.97 (d, J = 8.8 Hz, 2H), 7.77 (d, J = 8.8 Hz, 2H), 7.61 (t, J = 7.6 Hz, 1H), 7.36 (t, J = 8.5 Hz, 1H)7.307.27 (m, 1H), 7.307.27 (m, 2H), 7.21 (ddd, J = 8.4 Hz, 2.4 Hz, 0.8 Hz, 1H), 7.16 (dt, J = J = 7.6 Hz, 1.2 Hz, 1H), 7.127.11 (m, 1H), 3.90 (s, 3H), 1.421.37 (m, 21H). 13C
NMR (100 MHz, CDCl3): 159.7, 140.4, 138.1, 131.9, 131.4, 130.9, 129.6, 128.7, 128.5, 128.3, 126.3, 125.9, 125.7, 125.4, 124.1, 117.3, 116.9, 113.6, 105.3, 104.9, 55.4, 19.0, 11.7;
+ ESI HRMS calcd C40H40OSi (M ) m/z 564.28429, found 564.28416.
200
Chapter 5 Experimental data
O O
Si
2.21f: According to General Procedure E, 4-bromoveratrole (651 mg, 3.00 mmol), n-BuLi (2.5 M in hexanes, 1.16 mL, 2.90 mmol), and 2.4 (491 mg, 1.00 mmol) in dry, deoxygenated THF (20
mL) were used, followed by reductive aromatization using SnCl2 2H2O (677 mg, 3.00 mmol) and 10% aq H2SO4 (1 mL) in THF (20 mL). Purification was achieved by column chromatography (silica gel, CH2Cl2/hexanes 2:1) and final recrystallization from CH2Cl2 layered with MeOH. Pentacene 2.21f was obtained as a dark blue solid (345 mg, 58%).
Mp = 255–257 °C; Rf = 0.64 (CH2Cl2/hexanes 1:1); UV-vis (CH2Cl2) max (): 270 (20 000), 298 (86 300), 310 (233 000), 352 (6 050), 435 (1 260), 583 (7 280), 622 (9 370) nm. UV-vis
(CH2Cl2 cast film) max: 321, 412, 437, 525, 565, 618, 655 nm; Fluorescence (CH2Cl2, exc =
615 nm): max, em = 671 nm; IR (ATR): 3040 (w), 2937 (s), 2861 (s), 2125 (s), 1511 (s), 1457
–1 1 (s), 1237 (s), 876 (s), 737 (s) cm ; H NMR (400 MHz, CDCl3): 9.36 (s, 2H), 8.35 (s, 2H), 7.96 (d, J = 8.8 Hz, 2H), 7.78 (d, J = 8.4 Hz, 2H), 7.36 (t, J = 7.2 Hz, 2H), 7.317.27 (m, 2H), 7.187.16 (m, 1H), 7.12–7.09 (m, 1H), 7.077.06 (m, 1H), 4.10 (s, 3H), 3.88 (s, 3H),
13 1.411.36 (m, 21H). C NMR (100 MHz, CDCl3): 148.9, 148.7, 138.2, 131.9, 131.42, 131.37, 131.0, 128.71, 128.66, 128.5, 126.3, 125.9, 125.7, 125.3, 123.9, 117.1, 114.6,
+ 111.3, 105.2, 104.9, 56.02, 55.99, 19.0, 11.7; ESI HRMS calcd C41H42O2Si (M ) m/z
+ 594.29486, found 594.29304, C41H42NaO2Si ([M + Na] ) m/z 617.28463, found 617.28264.
201
Chapter 5 Experimental data
2.21g: According to General Procedure E, 1,4-diiodobenzene (990 mg, 3.00 mmol), n-BuLi (2.5 M in hexanes, 1.16 mL, 2.90 mmol), and 2.4 (491 mg, 1.00 mmol) in dry, deoxygenated THF
(20 mL) were used, followed by reductive aromatization using SnCl2 2H2O (677 mg, 3.00 mmol) and 10% aq H2SO4 (1 mL) in THF (20 mL). Purification was achieved by column chromatography (silica gel, hexanes/CH2Cl2 4:1) and final recrystallization from CH2Cl2 layered with MeOH. Pentacene 2.21g was obtained as a dark blue solid (294 mg, 45%).
Mp = 266–268 °C; Rf = 0.76 (hexanes/CH2Cl2 3:1); UV-vis (CH2Cl2) max (): 269 (20 000),
309 (270 000), 351 (7 500), 435 (1 600), 576 (9 600), 621 (14 000) nm. UV-vis (CH2Cl2 cast film) max: 274, 318, 409, 437, 489, 534, 628 nm; Fluorescence (CH2Cl2, exc = 615 nm):
max, em = 658 nm; IR (ATR): 3041 (w), 2939 (s), 2858 (s), 2136 (m), 1460 (s), 1375 (s), 873
–1 1 (s), 727 (s) cm ; H NMR (300 MHz, CDCl3): 9.35 (s, 2H), 8.22 (s, 2H), 8.02 (d, J = 8.1 Hz, 2H), 7.94 (d, J = 8.5 Hz, 2H), 7.75 (d, J = 8.5 Hz, 2H), 7.38–7.27 (m, 6H), 1.481.30 (m,
13 21H). C NMR (75 MHz, CDCl3): 138.4, 137.7, 133.4, 131.8, 131.4, 130.7, 128.43, 128.38, 128.1, 125.82, 125.75, 125.6, 125.4, 117.6, 105.5, 104.6, 93.7, 18.9, 11.5 (one
+ signal coincident or not observed); ESI HRMS calcd C39H37ISi (M ) m/z 660.17037, found 660.16903. A crystal suitable for X-ray crystallographic analysis has been grown by slowly evaporation of a CH2Cl2 solution layered with acetone at 4 °C. X-ray data for 2.21g: C39H37SiI, Fw =
660.68; monoclinic crystal system, space group P21/n; crystal size = 0.26 x 0.24 x 0.14 mm3; = 0.7107 Å; a = 17.0739(3) Å, b = 9.5155(2) Å, c = 19.8065(4) Å; 90.845(2)°; V
3 3 1 = 3217.54(11) Å ; Z = 4; (calcd) = 1.364 g/cm ; 2max = 58.56°; = 1.058 mm ; T = 146.9 K;
2 2 total data collected = 13795; R1 = 0.0355 [7300 observed reflections with F0 2(F0 )];
202
Chapter 5 Experimental data
2 2 R2 = 0.0834 for 376 variables with [F0 3(F0 )]; largest difference, peak and hole =
0.885 and 1.237 e Å 3.
:
2.21h: According to General Procedure E, 9-bromoanthracene (517 mg, 2.01 mmol), n-BuLi (2.5 M in hexanes, 0.78 mL, 1.9 mmol), and 2.22 (0.30 g, 0.67 mmol) in dry, deoxygenated THF
(20 mL) were used, followed by reductive aromatization using SnCl2 2H2O (454 mg, 2.01 mmol) and 10% aq H2SO4 (1 mL) in THF (20 mL). Purification was achieved by column chromatography (silica gel, hexanes/CH2Cl2 4:1) and final recrystallization from CH2Cl2 layered with MeOH. Pentacene 2.21h was obtained as a dark blue solid (30 mg, 8%).
Mp = 291–293 °C; Rf = 0.47 (hexanes/CH2Cl2 4:1); UV-vis (CH2Cl2) max (): 256 (146 000), 298 (100 000), 310 (315 000), 349 (13 000), 366 (13 000), 387 (11 000), 436 (3 300), 536 (5
500), 576 (12 500), 622 (17 000) nm. UV-vis (CH2Cl2 cast film) max: 260, 324, 349, 369,
390, 437, 503, 545, 592, 638 nm; Fluorescence (CH2Cl2, exc = 615 nm): max, em = 652 nm; – IR (ATR): 3045 (w), 2949 (m), 2878 (s), 2124 (m), 1449 (m), 1323 (m), 875 (s), 724 (s) cm 1;
1 H NMR (300 MHz, CDCl3): 9.43 (s, 2H), 8.79 (s, 1H), 8.21 (d, J = 8.6 Hz, 2H), 7.99 (d, J = 8.6 Hz, 2H), 7.72 (s, 2H), 7.477.42 (m, 2H), 7.38 (d, J = 8.7 Hz, 2H), 7.30 (t, J = 8.5 Hz, 2H), 7.157.02 (m, 6H), 1.36 (t, J = 7.9 Hz, 9H),1.050.97 (q, J = 7.9 Hz, 6H). 13C NMR (75
MHz, CDCl3): 135.1, 133.2, 132.1, 131.8, 131.7, 131.6, 131.0, 129.6, 128.63, 128.56, 128.46, 127.6, 127.0, 126.2, 126.02, 125.95, 125.90, 125.4, 125.3, 117.7, 106.8, 104.2, 8.0,
+ 4.9; ESI HRMS calcd C44H36Si (M ) m/z 592.25808, found 592.25838; TGA: Td ~410 °C; DSC: Mp = 287 °C, decomposition: 288 °C (onset), 290 °C (peak). A crystal suitable for X-ray crystallographic analysis has been grown by slowly evaporation of a CH2Cl2 solution layered with acetone at 4 °C. X-ray data for 2.21h: C34H36Si, Fw =
592.82; monoclinic crystal system, space group P21/c; crystal size = 0.14 x 0.053 x 0.036
203
Chapter 5 Experimental data mm3; = 1.5418 Å; a = 16.1928(4) Å, b = 8.8734(2) Å, c = 23.4480(8) Å; 107.485(3)°; V
3 3 1 = 3213.45(16) Å ; Z = 4; (calcd) = 1.225 g/cm ; 2max = 121.08°; = 0.865 mm ; T = 2 153.00(10) K; total data collected = 7274; R1 = 0.0407 [4679 observed reflections with F0
2 2 2 2(F0 )]; R2 = 0.1133 for 409 variables with [F0 3(F0 )]; largest difference, peak and hole = 0.43 and 0.29 e Å 3.
2.21i: According to General Procedure E, 9-bromo-10-methylantracene[8] (340 mg, 1.25 mmol) and 2.4 (206 mg, 0.420 mmol) in dry, deoxygenated THF (20 mL) were used, followed by
reductive aromatization using SnCl2 2H2O (282 mg, 1.25 mmol) and 10% aq H2SO4 (1 mL) in THF (15 mL). Purification was achieved by column chromatography (silica gel, hexanes/CH2Cl2 5:1) and final recrystallization from CH2Cl2 layered with MeOH to provide 2.21i (35 mg, 13%) as a dark blue solid.
Mp = 321323 °C; Rf = 0.15 (hexanes/CH2Cl2 9:1); UV-vis (CH2Cl2) max (): 260 (87 500), 298 (sh, 61 600), 310 (196 000), 355 (7 500), 377 (8 000), 398 (7 300), 435 (1 200), 576 (6
500), 623 (10 400) nm; UV-vis (CH2Cl2 cast film) max: 259, 323, 378, 400, 437, 503, 590,
635 nm; Fluorescence (CH2Cl2, exc = 615 nm): max, em = 653 nm. IR (ATR): 3041 (m), 2934
1 1 (s), 2859 (s), 2125 (m), 1459 (s), 1338 (s), 874 (s), 732 (s) cm ; H NMR (300 MHz, CDCl3): 9.44 (s, 2H), 8.52 (d, J = 9.0 Hz, 2H), 7.94 (d, J = 8.5 Hz, 2H), 7.72 (s, 2H), 7.497.48 (m, 3H), 7.37 (d, J = 8.6 Hz, 2H), 7.307.24 (m, 2H), 7.137.05 (m, 6H), 3.37 (s, 3H), 1.421.41
13 (m, 21H). C NMR (100 MHz, CDCl3): 135.7, 132.1, 131.7, 131.6, 131.4, 131.1, 130.1, 129.8, 128.7, 128.5, 127.8, 126.3, 126.0, 125.8, 125.4, 125.3, 125.2, 125.0, 117.8, 105.6, 104.9, 19.1, 15.0, 11.7 (one signal coincident or not observed); APPI HRMS calcd for
+ C48H44Si (M ) m/z 648.32068, found 648.32075.
204
Chapter 5 Experimental data
A crystal suitable for X-ray crystallographic analysis has been grown by slowly evaporation of a CH2Cl2 solution layered with acetone at 4 °C. X-ray data for 2.21i: C48H44Si, Fw = 648.92; Triclinic crystal system, space group P1 (No. 2); crystal size = 0.252 x 0.204 x
0.0328 mm3; = 1.5418 Å; a = 12.4596(7) Å, b = 12.8959(7) Å, c = 13.3080(11) Å; =
3 3 86.109(5)°, 64.115(7)°; = 71.752(5)°; V = 1821.1(2) Å ; Z = 2; (calcd) = 1.183 g/cm ;
1 2max = 140.8°; = 0.803 mm ; T = 172.8(9) K; total data collected = 10129; R1 = 0.0837
2 2 2 [6703 observed reflections with F0 2(F0 )]; R2 = 0.2762 for 449 variables with [F0
2 3 3(F0 )]; largest difference, peak and hole = 0.66 and 0.40 e Å .
2.21j: According to General Procedure E, 4-biphenylmagnesiumbromide (0.5 M in THF, 12 mL, 6.0 mmol) and 2.4 (981 mg, 2.00 mmol) in dry, deoxygenated THF (20 mL) were used,
followed by reductive aromatization using SnCl2 2H2O (1.35 g, 6.00 mmol) and 10% aq
H2SO4 (1 mL) in THF (20 mL). Purification was achieved by column chromatography (silica gel, hexanes/CH2Cl2 9:1) and final recrystallization from CH2Cl2 layered with MeOH. Pentacene 2.21j was obtained as a dark blue solid (300 mg, 25%).
Mp = 211–214 °C; Rf = 0.20 (hexanes); UV-vis (CH2Cl2) max (): 267 (27 600), 299 (68 900),
310 (208 000), 351 (6 400), 435 (1 000), 580 (5 900), 623 (8 000) nm. UV-vis (CH2Cl2 cast film) max: 271, 324, 410, 437, 598, 641 nm; Fluorescence (CH2Cl2, exc = 615 nm): max, em = 665 nm; IR (ATR): 2935 (m), 2133 (w), 1593 (s), 1166 (s), 689 (s) cm–1; 1H NMR (300
MHz, CDCl3): 9.38 (s, 2H), 8.36 (s, 2H), 7.98–7.90 (m, 4H), 7.84 (d, J = 7.5 Hz, 2H), 7.76
13 (d, J = 8.5 Hz, 2H), 7.63–7.25 (m, 9H), 1.401.39 (m, 21H). C NMR (75 MHz, CDCl3): 140.7, 140.5, 137.96, 137.91, 132.0, 131.9, 131.4, 130.9, 128.9, 128.6, 128.5, 128.4, 205
Chapter 5 Experimental data
127.5, 127.2, 127.1, 126.2, 125.8, 125.7, 125.3, 117.3, 105.3, 104.8, 19.0, 11.6; MS LDI
+ + m/z 610 (M ). APPI HRMS calcd C45H43Si ([M + H] ) m/z 611.31285, found 611.31422; TGA:
Td ~ 380 °C; DSC: Mp = 225 °C. A crystal suitable for X-ray crystallographic analysis has been grown by slowly evaporation of a THF solution layered with MeOH at 4 °C. X-ray data for 2.21j: C45H42Si, Fw = 610.88; triclinic crystal system, space group P1; crystal size = 0.27 x 0.22 x 0.11 mm3; = 1.5418
Å; a = 8.8430(7) Å, b = 13.1980(9) Å, c = 15.6961(10) Å; = 75.899(6)°, 80.962(6)°, =
3 3 1 78.579(6)°; V = 1730.1(2) Å ; Z = 2; (calcd) = 1.173 g/cm ; 2max = 141.52°; = 0.814 mm ; 2 T = 173 K; total data collected = 10087; R1 = 0.0440 [6284 observed reflections with F0
2 2 2 2(F0 )]; R2 = 0.1253 for 421 variables with [F0 3(F0 )]; largest difference, peak and hole = 0.342 and 0.285 e Å 3.
2.27: According to General Procedure E, 9-Bromoanthracene (700 mg, 2.73 mmol), n-BuLi (2.5 M in hexanes, 1.06 mL, 2.64 mmol), and 2.26 (829 mg, 0.908 mmol) were used, followed
by reductive aromatization using SnCl2 2H2O (616 mg, 2.73 mmol) and 10% aq H2SO4 (1 mL) in THF (20 mL). Purification was achieved by column chromatography (silica gel, hexanes/CH2Cl2 5:1 b pure hexanes b hexanes/CH2Cl2 5:1) and then recrystallization from CH2Cl2 layered with MeOH. Pentacene 2.27 was obtained as a deep blue solid (39 mg, 4%).
Mp = 164167 °C; Rf = 0.30 (hexanes/CH2Cl2 5:1); Fluorescence (CH2Cl2, exc = 310 nm):
max, em = 532, 628, 680 nm; IR (ATR): 3049 (w), 2954 (s), 2358 (w), 1589 (s), 1440 (s), 876
1 1 (s), 730 (s) cm ; H NMR (400 MHz, CDCl3): 9.24 (s, 2H), 8.77 (s, 1H), 8.20 (d, J = 8.5 Hz, 2H), 7.717.67 (m, 4H), 7.547.53 (m, 6H), 7.457.41 (m, 2H), 7.3827.378 (m, 4H), 7.34 (d, J = 8.7 Hz, 2H), 7.19 (t, J = 8.4 Hz, 2H), 7.097.06 (m, 6H), 1.28 (s, 54H). 13C NMR (75
MHz, CDCl3): 149.8, 145.3, 133.6, 133.3, 131.8, 131.6, 131.5, 131.4, 130.9, 129.6, 128.5, 206
Chapter 5 Experimental data
128.3, 127.3, 126.9, 125.9, 125.8, 125.7, 125.2, 125.1, 124.9, 123.8, 120.0, 118.8, 110.7,
+ 84.2, 77.0, 58.2, 34.8, 31.4; MALDI MS (sin) m/z 1057 (M ). ESI HRMS calcd for C81H84Na ([M Na]+) m/z 1079.64652, found 1079.64363.
General Procedure F – Suzuki reaction
General Procedure F for aryl-substituted pentacenes: To a solution of Pentacene 2.21g (1 equiv), the corresponding boronic acid (1.5 equiv) and
Pd(PPh3)2Cl2 (5 mol%) in dry, deoxygenated THF (20 mL) was added aqueous Na2CO3 (2 equiv dissolved in 5 mL H2O). The resulting dark solution was heated at 80 °C for 24 h. After cooling to rt the mixture was purified as noted in the individual procedures to provide pure pentacenes 2.21k and 2.21l as deep blue solids.
2.21k: According to General Procedure F, 2.21g (70 mg, 0.11 mmol), 1-naphthylboronic acid (29 mg, 0.16 mmol), Pd(PPh3)2Cl2 (4 mg, 5 mol), Na2CO3 (23 mg, 0.21 mmol) were used. The reaction mixture was plugged through a pad of silica gel, eluting with CH2Cl2/hexanes (1:1) and the blue band was collected. The solvent was removed and the mixture was further recrystallized from CH2Cl2 layered with MeOH at 15 °C to afford pentacene 2.21k as a deep blue solid (67 mg, 92%).
Mp = 233235 °C; Rf = 0.30 (hexanes/CH2Cl2 1:3); UV-vis (CH2Cl2) max (): 258 (41 000), 300 (sh, 105 000), 309 (300 000), 352 (10 500), 386 (2 360), 435 (1 250), 580 (10 500), 623
(13 700) nm. UV-vis (CH2Cl2 cast film) max: 259, 320, 355, 410, 437, 589, 633 nm;
Fluorescence (CH2Cl2, exc = 615 nm): max, em = 665 nm; IR (ATR): 3041 (w), 2938 (s),
207
Chapter 5 Experimental data
–1 1 2860 (s), 2130 (m), 1460 (s), 1374 (s), 874 (s), 732 (s) cm ; H NMR (300 MHz, CDCl3): 9.38 (s, 2H), 8.42 (s, 2H), 8.278.24 (m, 1H), 7.997.93 (m, 4H), 7.82 (d, J = 7.9 Hz, 4H), 7.727.63 (m, 4H), 7.617.57 (m, 2H), 7.387.27 (m, 4H), 1.40137 (m, 21H). 13C NMR (75
MHz, CDCl3): 140.0, 139.7, 137.8, 137.6, 133.7, 131.7, 131.4, 131.3, 131.2, 130.7, 130.0, 128.5, 128.31, 128.25, 127.7, 127.1, 126.0, 125.8, 125.7, 125.6, 125.3, 125.2, 117.1, 105.1,
104.6, 18.8, 11.5 (three signals coincident or not observed); ESI HRMS calcd for C49H44Si
+ (M ) m/z 660.32123, found 660.32065; TGA: Td ~ 380 °C; DSC: Mp = 225 °C. A crystal suitable for X-ray crystallographic analysis has been grown by slowly evaporation of a CH2Cl2 solution layered with MeOH at 4 °C. X-ray data for 2.21k: C49H44Si, Fw = 660.93; triclinic crystal system, space group P1; crystal size = 0.23 x 0.17 x 0.078 mm3; = 1.5418
Å; a = 8.7000(6) Å, b = 13.7195(9) Å, c = 16.1219(11) Å; = 102.755(6)°; = 100.911(6)°;
3 3 = 94.442(5)°; V = 1828.6(2) Å ; Z = 2; (calcd) = 1.200 g/cm ; 2max = 147.24°; = 0.810 1 mm ; T = 173 K; total data collected = 13530; R1 = 0.0527 [7123 observed reflections with
2 2 2 2 F0 2(F0 )]; R2 = 0.1556 for 457 variables with [F0 3(F0 )]; largest difference, peak and hole = 0.771 and 0.312 e Å 3.
2.21l: According to General Procedure F, 2.21g (80 mg, 0.12 mmol), 9-anthracenylboronic acid
(40 mg, 0.18 mmol), Pd(PPh3)2Cl2 (4 mg, 6 mmol), Na2CO3 (26 mg, 0.24 mmol) were used.
The reaction mixture was plugged through a pad of neutral Al2O3, eluted with hexanes/CH2Cl2 (3:1), and the blue band was collected. The solvent was removed and the product was finally purified by recrystallization from MeOH/acetone (40 mL; 1:1) at 15 °C. Pentacene 2.21l was obtained as a deep blue solid (58 mg, 68%).
Mp = 284286 °C; Rf = 0.50 (Al2O3, hexanes/CH2Cl2 1:3); UV-vis (CH2Cl2) max (): 258 (132
208
Chapter 5 Experimental data
000), 310 (230 000), 350 (12 000), 367 (11 500), 387 (9 700), 435 (1 380), 580 (8 500), 623
(11 700) nm. UV-vis (CH2Cl2 cast film) max: 260, 321, 370, 389, 436, 593, 635 nm;
Fluorescence (CH2Cl2, exc = 615 nm): max, em = 665 nm; IR (ATR): 3047 (w), 2937 (s),
–1 1 2859 (s), 2129 (m),1457 (s), 1375 (s), 877 (s), 726 (s) cm ; H NMR (300 MHz, CDCl3): 9.41 (s, 2H), 8.59 (s, 1H), 8.52 (s, 2H), 8.158.11 (m, 2H), 8.047.98 (m, 4H), 7.88 (d, J = 8.4 Hz, 2H), 7.77 (s, 4H), 7.577.52 (m, 4H), 7.42–7.32 (m, 4H), 1.401.39 (m, 21H). 13C
NMR (100 MHz, CDCl3): 138.4, 138.14, 138.08, 136.7, 132.0, 131.7, 131.6, 131.53, 131.52, 131.1, 130.3, 128.8, 128.62, 128.61, 128.56, 126.9, 126.8, 126.3, 126.0, 125.68, 125.67, 125.5, 125.2, 117.5, 105.5, 104.9, 19.0, 11.7; MS ESI (THF) m/z 710 (M+). APPI
+ HRMS calcd for C53H47Si ([M + H] ) m/z 711.34415, found 711.34439.
Experimental data – alkyl-substituted pentacenes
General Procedure G for the syntheses of alkyl-substituted pentacenes: Unless otherwise noted, to a solution of 2.4 (1.0 equiv, 1.0 mmol) in dry, deoxygenated THF (20 mL) was added the corresponding alkyl-lithium or alkyl-Grignard solution (3.05.0 equiv, 3.0 mmol5.0 mmol) at rt. The resulting mixture was stirred for 16 h at rt. The reaction was quenched by the addition of saturated aq NH4Cl (100 mL) and extracted with CH2Cl2 (3 x 50 mL). The combined organic phases were washed with brine (100 mL), dried (Na2SO4), filtered, and the solvent removed in vacuo. The crude residue was dissolved in THF (20 mL)
and subjected to reductive aromatization by the addition of SnCl2 2H2O (1.55–3.00 equiv,
1.553.00 mmol) and 10% aq H2SO4 (1 mL). The mixture was stirred for 46 h at rt and saturated aq NH4Cl (100 mL) was added. The mixture was extracted with CH2Cl2 (3 x 50 mL, if the phases do not separate and/or the mixture forms an emulsion, 10 mL of HCl (conc.) was added to the mixture in the separatory funnel). The combined organic phases were washed with brine (100 mL), dried over Na2SO4, filtered, and the solvent removed in vacuo. The crude product was purified as noted in the individual procedures.
209
Chapter 5 Experimental data
2.32a:
Compound 2.4 (491 mg, 1.00 mmol), MeLi (1.5 M in THF, 2.0 mL, 3.0 mmol), SnCl2 2H2O
(677 mg, 3.00 mmol), and 10% aq H2SO4 (1 mL) were used according to General Procedure G. After aqueous workup, purification was achieved by column chromatography
(silica gel, hexanes/CH2Cl2 3:1) and further recrystallization from a concentrated CH2Cl2 solution layered with MeOH to provide pentacene 2.32a as a deep blue solid (200 mg, 42%).
Mp = 240242 °C; Rf = 0.5 (hexanes/CH2Cl2 4:1); UV-vis (CH2Cl2) max (): 267 (17 900), 298 (103 000), 308 (232 000), 354 (6 600), 586 (7 080), 621 (8 900) nm. Fluorescence
(CH2Cl2, exc = 615 nm): max, em = 665 nm; IR (ATR): 3039 (w), 2940 (s), 2862 (s), 2122 (m),
1 1 1461 (m), 859 (s) cm ; H NMR (400 MHz, CDCl3): 9.22 (s, 2H), 8.72 (s, 2H), 7.887.85
13 (m, 4H), 7.347.28 (m, 4H), 3.30 (s, 3H), 1.441.40 (m, 21H). C NMR (100 MHz, CDCl3): 132.0, 131.6, 131.2, 130.8, 128.7, 128.4, 128.0, 126.2, 125.7, 125.3, 123.7, 115.6, 105.2,
+ 104.3, 19.0, 15.2, 11.8; EI HRMS calcd for C34H36Si (M ) m/z 472.25864, found 472.25846.
Element Anal calcd for C34H36Si: C, 86.38; H, 7.68. Found: C, 86.65; H, 7.66. TGA: Td ~ 330 °C; DSC: Mp = 194 °C, decomposition, 244 °C (onset), 246 °C (peak).
2.32b: Compound 2.4 (491 mg, 1.00 mmol), n-BuLi (2.5 M in hexanes, 2.0 mL, 5.0 mmol),
SnCl2 2H2O (404 mg, 2.15 mmol), and 10% aq H2SO4 (1 mL) were used according to General Procedure G. After aqueous workup, purification was achieved by passing the
210
Chapter 5 Experimental data
crude mixture through a short pad of silica gel eluted with CH2Cl2 and further recrystallization from CH2Cl2 layered with MeOH at 15 °C to provide pentacene 2.32b as a deep blue solid (160 mg, 31%).
Mp = 116119 °C; Rf = 0.85 (CH2Cl2/hexanes 1:1); UV-vis (CH2Cl2) max (): 299 (115 000),
310 (350 000), 357 (6 300), 434 (1 00), 587 (8 100), 622 (9 900). UV-vis (CH2Cl2 cast film)
max: 304, 314, 356, 411, 435, 593, 636 nm; Fluorescence (CH2Cl2, exc = 615 nm): max, em = 666 nm; IR (ATR): 3041 (w), 2923 (s), 2860 (s), 2128 (m), 1457 (m), 1367 (m), 992 (m),
1 1 860 (s), 730 (s), 660 (s), 615 (s) cm ; H NMR (300 MHz, CDCl3): 9.31 (s, 2H), 8.85 (s, 2H), 7.977.90 (m, 4H), 7.367.33 (m, 4H), 3.92 (bt, J = 7.9 Hz, 2H), 1.92 (pent, J = 7.1 Hz, 2H), 1.67 (hex, J = 7.5 Hz, 2H), 1.411.31 (m, 21H), 1.06 (t, J = 7.3 Hz, 3H). 13C NMR (75
MHz, CDCl3): 137.4, 131.7, 131.4, 131.1, 128.7, 128.4, 127.5, 126.4, 125.7, 125.3, 123.6,
115.9, 105.0, 104.5, 33.8, 28.8, 23.5, 19.0, 14.1, 11.6; APPI HRMS calcd for C37H43Si ([M + H]+) m/z 515.31285, found 515.31281. A crystal suitable for X-ray crystallographic analysis has been grown by slowly evaporation of a CH2Cl2 solution at rt. X-ray data for 2.32b: C37H42Si, Fw = 514.80; Triclinic crystal system, space group P1; crystal size = 0.20 x 0.20 x 0.20 mm3; 0.7107 Å; a = 9.9679(3)
Å, b = 12.5324(2) Å, c = 12.8009(4) Å; = 85.442(2)°;70.791(1)°; = 77.302(2)° ;V =
3 3 1 1473.10(7) Å ; Z = 2; (calcd) = 1.161 g/cm ; 2max = 55.2°; = 0.10 mm ; T = 173 K; total
2 2 data collected = 12859; R1 = 0.0449 [6746 observed reflections with F0 2(F0 )]; R2 =
2 2 0.1186 for 343 variables with [F0 3(F0 )]; largest difference, peak and hole = 0.259 and 0.287 eÅ 3.
2.32c: Compound 2.4 (490 mg, 0.999 mmol), allylmagnesiumbromide (1.0 M in diethylether, 5.0
mL, 5.0 mmol), SnCl2 2H2O (350 mg, 1.55 mmol), and 10% aq H2SO4 (1 mL) were used according to General Procedure G. After aqueous workup, purification was achieved by 211
Chapter 5 Experimental data
passing the crude mixture through a short pad of silica gel eluted with CH2Cl2 and further recrystallization from CH2Cl2 layered with MeOH at 15 °C to provide pentacene 2.32c as a deep blue solid (151 mg, 30%).
Mp = 145147 °C; UV-vis (CH2Cl2) max (): 298 (55 500), 309 (190 000), 352 (3 700), 435
(1 000), 576 (4 300), 620 (6 400). UV-vis (CH2Cl2 cast film) max: 317, 340, 350, 412, 436,
595, 636 nm; Fluorescence (CH2Cl2, exc = 615 nm): max, em = 656 nm; IR (ATR): 3047 (m), 2939 (s), 2860 (s), 2124 (m), 1460 (m), 1360 (m), 991 (s), 862 (s), 730 (s), 662 (s) cm 1; 1H
NMR (300 MHz, CDCl3): 9.28 (s, 2H), 8.73 (s, 2H), 7.917.87 (m, 4H), 7.377.29 (m, 4H), 6.30 (ddt, J = 17.2 Hz, 8.7 Hz, 6.9 Hz, 1H), 5.07 (dd, J = 10.2 Hz, 1.4 Hz, 1H), 4.93 (dd, J = 17.2 Hz, 1.5 Hz, 1H), 4.63 (d, J = 5.4 Hz, 2H),1.401.36 (m, 21H). 13C NMR (75 MHz,
CDCl3): 136.3, 133.1, 131.6, 131.4, 130.8, 128.6, 128.3, 127.7, 126.2, 125.6, 125.3, + 123.5, 116.5, 116.4, 104.5, 104.7, 32.8, 18.9, 11.6; APPI HRMS calcd for C36H38Si (M ) m/z 498.27373, found 498.27241. A crystal suitable for X-ray crystallographic analysis has been grown by slowly evaporation of a THF solution layered with MeOH at rt. X-ray data for 2.32c: C36H38Si, Fw = 498.75; triclinic crystal system, space group P1; crystal size = 0.45 x 0.30 x 0.30 mm3; 0.7107
Å; a = 8.4720(2) Å, b = 11.0265(4) Å, c = 15.9075(5) Å; = 96.302(2)°; 103.901(2)°; =
3 3 1 93.618(2)° ;V = 1427.60(8) Å ; Z = 2; (calcd) = 1.160 g/cm ; 2max = 55.2°; = 0.105 mm ; T 2 = 173(2) K; total data collected = 10778; R1 = 0.0672 [5618 observed reflections with F0
2 2 2 2(F0 )]; R2 = 0.1836 for 353 variables and 0 restraints with [F0 3(F0 )]; largest difference, peak and hole = 0.491 and 0.474 eÅ 3. The disorder in the allyl group was refined using the following occupancies: C2/C3 : C2’/C3’ = 60:40.
212
Chapter 5 Experimental data
Experimental data – reactivity of alkyl-substituted pentacenes
2.33:
A solution of pentacene 2.32a (40 mg, 0.085 mmol) was dissolved in CH2Cl2 (10 mL) and exposed to sunlight and air until the deep blue solution bleaches completely (ca. 2 h). The solvent was removed under reduced pressure and MeOH (10 mL) was added. The remaining solid was filtered and washed with MeOH (10 mL) and hexanes (10 mL). After drying, peroxo-pentacene 2.33 was obtained as a colorless solid (30 mg, 70%).
Mp = 160 °C (color change), 190192 °C; Rf = 0.10 (hexanes/CH2Cl2 2:1); UV-vis (CH2Cl2)
max (): 230 (32 500), 252 (71 500) nm; IR (ATR): 2943 (s), 2865 (s), 1626 (s), 883 (s), 681
1 1 (s) cm ; H NMR (400 MHz, CDCl3): 8.25 (s, 2H), 7.88–7.85 (m, 6H), 7.54–7.50 (m, 4H),
13 2.39 (s, 3H), 1.33 (bs, 21H). C NMR (100 MHz, CDCl3): 136.4, 135.3, 132.8, 132.5, 128.4, 128.1, 126.8, 126.7, 122.0, 119.9, 97.7, 96.4, 80.1, 79.2, 18.8, 14.2, 11.3; MALDI MS
+ + + (sin) m/z 472 ([M O2] , 100), 505 ([M] , 70). ESI HRMS calcd for C34H37O2Si ([M + H] ) m/z 505.25573, found 505.25602. A crystal suitable for X-ray crystallographic analysis has been grown by slowly evaporation of a CH2Cl2 solution layered with MeOH at rt. X-ray data for 2.33: C34H36O2Si, Fw = 504.72; triclinic crystal system, space group P1; crystal size = 0.35 x 0.15 x 0.15 mm3; 0.7107
Å; a = 13.0058(4) Å, b = 13.1768(4) Å, c = 17.1362(3) Å; = 82.437(2)°; 76.206(2)°; =
3 3 1 82.737(1)° ;V = 2813.40(13) Å ; Z = 4; (calcd) = 1.192 g/cm ; 2max = 55.2°; = 0.112 mm ; 2 T = 173(2) K; total data collected = 21755; R1 = 0.0485 [11506 observed reflections with F0
2 2 2 2(F0 )]; R2 = 0.1179 for 667 variables with [F0 3(F0 )]; largest difference, peak and hole = 0.321 and 0.326 eÅ 3.
213
Chapter 5 Experimental data
2.34:
To a solution of 2.32a (40 mg, 0.085 mmol) in dry, deoxygenated CH2Cl2 (10 mL) was added tetracyanoethylene (TCNE, 12 mg, 0.094 mmol). The solution was slightly heated until the blue color of the solution has been vanished. Subsequently, the solvent was evaporated under reduced pressure and the solid residue was washed with MeOH (50 mL) to afford 2.34 as a colorless solid (32 mg, 63%).
Mp = 270 °C (decomp); Rf = 0.40 (CH2Cl2/hexanes 2:1); IR (ATR): 3059 (w), 2946 (s), 2864
1 1 (s), 2185 (w), 1461 (s), 1260 (s), 1075 (s), 1016 (s) cm ; H NMR (400 MHz, CDCl3): 8.45 (s, 2H), 7.99 (s, 2H), 7.93–7.88 (m, 4H), 7.62–7.57 (m, 4H), 2.64 (s, 3H), 1.371.31 (m,
13 21H). C NMR (100 MHz, CDCl3): 133.1, 132.8, 131.5, 130.5, 128.6, 128.4, 128.1, 128.0, 126.3, 124.3, 110.6, 110.5, 100.3, 96.6, 54.7, 53.4, 52.4, 50.4, 18.8, 16.1, 11.4; MALDI MS
+ + (dhb) m/z 472 ([M + H – TCNE] , 100). APPI HRMS calcd C40H37N4Si ([M + H] ) m/z 601.27820, found 601.27756. A crystal suitable for X-ray crystallographic analysis has been grown by slowly evaporation of a CH2Cl2 solution layered with MeOH at rt. X-ray data for 2.34: C40H36N4Si, Fw = 600.82; triclinic crystal system, space group P1; crystal size = 0.4 x 0.3 x 0.3 mm3; 0.71073 Å; a = 8.9890(2) Å, b = 12.1746(4) Å, c = 16.2907(6) Å; = 88.444(2)°; 74.791(2)°; =
3 3 1 76.563(2)° ;V = 1672.19(9) Å ; Z = 2; (calcd) = 1.193 g/cm ; 2max = 55.06°; = 0.104 mm ; 2 T = 173(2) K; total data collected = 14301; R1 = 0.0482 [7650 observed reflections with F0
2 2 2 2(F0 )]; R2 = 0.1222 for 406 variables with [F0 3(F0 )]; largest difference, peak and hole = 0.572 and 0.336 eÅ 3.
214
Chapter 5 Experimental data
Experimental data – monosubstituted pentacene
2.35a: To a solution of 2.36 (0.505 g, 1.00 mmol) in dry, deoxygenated THF (30 mL) at 0 °C was added LiAlH4 (114 mg, 3.00 mmol) in one portion. The mixture was heated to reflux for 3 h, cooled to rt, and saturated aq NH4Cl (100 mL) was added. The mixture was extracted with
CH2Cl2 (3 x 100 mL). The combined organic phases were washed with brine (100 mL), dried (Na2SO4), filtered, and the solvent removed in vacuo. The solid residue was dissolved
in THF (20 mL) and SnCl2 2H2O (677 mg, 3.00 mmol) and 10% aq H2SO4 (1 mL) were sequentially added. The resulting mixture was stirred for 6 h at rt, protected from light, and then quenched by the addition of saturated aq NH4Cl (100 mL). The mixture was extracted with CH2Cl2 (3 x 50 mL). The combined organic phases were washed with brine (50 mL), dried (Na2SO4), filtered, and the solvent removed in vacuo. The crude mixture was purified by column chromatography in the dark (silica gel, hexanes/CH2Cl2 5:1) and finally recrystallized from CH2Cl2 layered with MeOH at 15 °C. Pentacene 2.35a was obtained as a blue solid (87 mg, 19%).
Mp = 179182 °C; Rf = 0.76 (hexanes/CH2Cl2 2:1); UV-vis (CH2Cl2) max (): 266 (13 000), 296 (sh, 78 700), 307 (269 000), 349 (5 000), 408 (1 000), 432 (1 500), 576 (4 900), 610 (5
900) nm; Fluorescence (CH2Cl2, exc = 610 nm): max, em = 658 nm; IR (ATR): 3040 (w),
1 1 2938 (s), 2859 (s), 2124 (m), 1459 (s), 884 (s), 719 (s) cm ; H NMR (300 MHz, CDCl3): 9.23 (s, 2H), 8.87 (s, 1H), 8.60 (s, 2H), 7.947.89 (m, 4H), 7.387.33 (m, 4H), 1.37 (bs,
13 21H). C NMR (100 MHz, CDCl3): 132.2, 131.5, 131.2, 129.4, 128.8, 128.2, 128.0, 127.0,
+ 125.6, 125.5, 125.4, 116.9, 104.9, 104.7, 19.0, 11.7; ESI HRMS calcd for C33H34Si (M ) m/z 458.24243, found 458.24208. Single crystals suitable for X-ray crystallographic analysis have been grown by slow
215
Chapter 5 Experimental data
evaporation of a CH2Cl2 solution layered with acetone. X-ray data for 2.35a: C33H34Si, Fw = 458.69; triclinic crystal system, space group P1; crystal size = 0.2 x 0.1 x 0.05 mm3; =
1.5418 Å; a = 16.8728(6) Å, b = 17.1542(7) Å, c = 21.0013(8) Å; = 67.284(4)°,
3 3 67.939(4)°, 88.612(3)°; V = 5144.4(4) Å ; Z = 8; (calcd) = 1.184 g/cm ; 2max = 142.1°;
1 = 0.927 mm ; T = 153.00(10) K; total data collected = 31054; R1 = 0.0410 [19102
2 2 2 observed reflections with F0 2(F0 )]; R2 = 0.1225 for 1249 variables with [F0
2 3 3(F0 )]; largest difference, peak and hole = 0.32 and 0.31 eÅ .
2.35b: To a solution of 2.36 (1.00 g, 1.98 mmol) in dry, deoxygenated THF (30 mL) at 0 °C was added LiAlH4 (225 mg, 5.94 mmol) in one portion. The mixture was heated to reflux for 3 h.
The mixture was cooled to rt and SnCl2 2H2O (1.34 g, 5.94 mmol) and 10% aq H2SO4 (5 mL) was added. The mixture was protected from light exposure and stirred for 16 h at rt and
H2O (50 mL) was added. The mixture was extracted with CH2Cl2 (3 x 100 mL) and the combined organic phases were washed with brine (100 mL), dried (Na2SO4), filtered, and the solvent removed in vacuo. The solid residue was plugged through a pad of silica gel
(hexanes/CH2Cl2 2:1) and the blue band was collected. After solvent removal, the mixture was separated by column chromatography (silica gel, hexanes/CH2Cl2 5:1). The first fraction contained 2.35a and the second fraction contained 2.35b which was obtained as purple solid (156 mg, 9%).
Mp = 263265 °C; Rf = 0.81 (hexanes/CH2Cl2 2:1); UV-vis (CH2Cl2) max (): 233 (96 000), 257 (76 000), 293 (sh, 77 000), 305 (303 000), 334 (9 100), 351 (8 100), 514 (3 500), 551 (8
100), 597 (12 500) nm. UV-vis (CH2Cl2 cast film) max: 235, 259, 311, 353, 432, 519, 559,
570, 604 nm; Fluorescence (CH2Cl2, exc = 305 nm): max, em = 601, 652 nm; IR (ATR): 3043
1 1 (w), 2941 (s), 2862 (s), 2182 (w), 1458 (s), 892 (s), 729 (s) cm ; H NMR (400 MHz, CDCl3):
216
Chapter 5 Experimental data
8.88 (s, 1H), 8.55 (s, 2H), 8.21 (s, 2H), 8.04 (s, 2H), 7.94 (d, J = 8.1 Hz, 2H), 7.847.78 (m, 6H), 7.567.46 (m, 4H), 7.19 (t, J = 8.4 Hz, 2H), 6.97 (t, J = 8.5 Hz, 2H), 6.83 (d, J = 8.7 Hz, 2H), 5.97 (s, 1H), 0.65 (sept, J = 7.6 Hz, 3H), 0.580.49 (m, 18H), 0.420.37 (m, 21H). 13C
NMR (100 MHz, CDCl3): 159.1, 147.3, 141.5, 141.1, 135.2, 132.2, 131.8, 131.2, 130.8, 130.0, 129.2, 128.7, 128.3, 127.8, 127.5, 126.5, 126.4, 126.0, 125.9, 125.6, 124.8, 124.4, 121.8, 121.7, 102.4, 92.1, 59.7, 54.3, 19.0, 17.9, 11.8, 10.7; MALDI MS (sin) m/z 458 ([M
+ + M/2] ). APPI HRMS calcd for C66H69Si2 ([M + H] ) m/z 917.49323, found 917.49367.
2.36: Triisopropylsilylacetylene (1.86 mL, 0.757 g, 8.27 mmol) was dissolved in THF (5 mL). The solution was cooled to 0 °C and n-BuLi (2.5 M in hexanes, 2.6 mL, 6.4 mmol) was added. After 15 min, the reaction mixture was added to a suspension of 6,13pentacenequinone (2.00 g, 6.44 mmol) in THF (15 mL) at rt. The suspension was stirred for 16 h. MeI (1.0 mL, 2.3 g, 16 mmol) was added. The flask was wrapped in aluminum foil to prevent light exposure. After another 5 h of stirring, the suspension was cooled to 0 °C and H2O was added. Subsequent filtering yielded about 200 mg of the starting quinone as a yellow solid.
Saturated aq NH4Cl (50 mL) was added to the filtrate. The aqueous layer was extracted with CH2Cl2 (3 x 50 mL). The combined organic layers were washed with brine (150 mL), dried (MgSO4) and filtered. Solvent removal and purification by column chromatography
(silica gel, CH2Cl2/hexanes 1:1) afforded 2.36 (2.36 g, 72%) as an orange solid.
(Purification can be also be achieved by recrystallization from a CH2Cl2 solution layered with MeOH.)
Mp = 124126 °C; Rf = 0.35 (CH2Cl2); IR (ATR): 3055 (w), 2938 (m), 2860 (m), 2165 (w),
1 1 1668 (m), 1624 (m), 1591 (w), 1451 (s) cm ; H NMR (300 MHz, CDCl3): 8.79 (s, 2H), 8.67 (s, 2H), 8.05 (d, J = 7.9 Hz, 2H), 7.93 (d, J = 8.0 Hz, 2H), 7.64–7.57 (m, 4H), 3.13 (s,
13 3H), 1.28–1.24 (m, 21H). C NMR (100 MHz, CDCl3): 185.3, 135.8, 134.9, 132.9, 129.9,
217
Chapter 5 Experimental data
129.7, 129.6, 128.8, 128.4, 128.1, 127.4, 103.5, 93.4, 52.3, 18.8, 11.4; MALDI MS m/z 473
+ + ([M – OCH3] ). MALDI HRMS calcd for C34H36SiO2 (M ) m/z 504.2485, found 504.2488.
Experimental data - isomerically pure syn-ADTs
syn3.2:
To a solution of 3.17 (491 mg, 1.00 mmol) in acetone (30 mL) was added In(OTf)3 (101 mg, 0.18 mmol). The mixture was refluxed for 6 hours. The mixture was cooled to rt and the resulted red precipitate was filtered and washed with MeOH to yield syn-3.2 as a dark red solid (240 mg, 75%). IR (ATR): 3077 (m), 1661 (s), 1571 (s), 1321 (s), 1279 (s) cm -1; 1H NMR (300 MHz,
CDCl3/C6D5Cl 1:1): 9.00 (s, 2H), 8.93 (s, 2H), 7.76 (d, J = 5.5 Hz, 2H), 7.60 (d, J = 5.6 Hz, 2H). 13C NMR: The compound is too insoluble to get meaningful 13C analysis; EI MS m/z
+ 320 (M ); TGA: Td ~ 193 °C.
syn3.5a: To a solution of triisopropylsilylacetylene (1.42 g, 1.75 ml, 7.80 mmol) in dry, deoxygenated THF (20 mL) cooled to 78 °C was added n-BuLi (2.5 M in hexanes, 3.05 mL, 7.64 mmol). The solution was stirred for 10 min at 78 °C and was transferred via cannula into a suspension of syn-3.2 (250 mg, 0.780 mmol) in dry, deoxygenated THF (20 mL). The reaction mixture was stirred for 18 h at rt and saturated aq NH4Cl (100 mL) was added. The mixture was extracted with CH2Cl2 (3 x 50 mL), washed with brine (100 mL), dried (Na2SO4),
218
Chapter 5 Experimental data filtered, and the solvent removed in vacuo to obtain a red oil. This oil was dissolved in THF
(20 mL) and SnCl2 2H2O (528 mg, 2.34 mmol) and 10% aq H2SO4 (1 mL) were added. The solution was wrapped in aluminum foil to limit light exposure and stirred for 6 h at rt. The mixture was plugged through a pad of silica gel (CH2Cl2/hexanes 1:1) and the solvent removed in vacuo. Finally, the residue was purified by recrystallization (CH2Cl2 layered with MeOH at 15 °C) to yield syn-3.5a as a dark red solid (220 mg, 43%).
Mp = 185188 °C; Rf = 0.8 (CH2Cl2/hexanes 1:1); UV-vis (CH2Cl2) max (): 306 (86 000), 331 (25 000), 352 (3 700), 400 (1 000), 423 (1 000), 480 (2 600), 513 (7 900), 553 (15 000);
Fluorescence (CH2Cl2, exc = 511 nm): max, em = 559, 604 nm; IR (ATR): 2939 (s), 2862 (s),
1 1 2126 (m), 1696 (s), 1578 (s), 1404 (s), 1241 (s) cm . H NMR (300 MHz, CDCl3): 9.18 (s, 2H), 9.14 (s, 2H), 7.53 (d, J = 5.7 Hz, 2H), 7.41 (d, J = 5.7 Hz, 2H), 1.321.29 (m, 42H). 13C
NMR (75 MHz, CDCl3): 139.9, 139.5, 129.9, 129.8, 129.7, 123.7, 121.2, 120.0, 118.8, + 116.2, 106.1, 105.5, 104.2, 104.0, 18.9, 11.6; APPI HRMS calcd for C40H51S2Si2 ([M + H] ) m/z 651.29652, found 651.29618. Element Anal calcd for C40H50S2Si2: C, 73.78; H, 7.74; S,
9.85. Found: C, 73.84; H, 8.00; S, 10.00; TGA: Td ~ 211 °C; DSC: Mp = 186 °C (onset), 199 °C (peak). A crystal suitable for X-ray crystallographic analysis was grown by slowly evaporation of a
CH2Cl2 solution layered with acetone at 4 °C. X-ray data for syn-3.5a: C40H50S2Si2, Fw =
3 651.10; monoclinic crystal system, space group P21/c; crystal size = 0.3 x 0.3 x 0.2 mm ;
= 0.7107 Å; a = 8.7901(2) Å, b = 17.7238(8) Å, c = 12.2596(5) Å;= 90.390(3)°; V =
3 3 1 1909.93(12) Å ; Z = 2; (calcd) = 1.132 g/cm ; 2max = 55.04°; = 0.228 mm ; T = 173.15 K;
2 2 total data collected = 7884; R1 = 0.0463 [4374 observed reflections with F0 2(F0 )]; R2
2 2 = 0.1214 for 228 variables and 4 restraints with [F0 3(F0 )]; largest difference, peak and hole = 0.183 and 0.276 e Å 3. The disorder in the thiophene units was refined using the following occupancies: S1:S1’ = 50:50; the disorder in the triisopropyl group was refined using the following occupancies: C11:C11’ = 72:28.
219
Chapter 5 Experimental data
3.17: To a solution of 3.13 (488 mg, 2.65 mmol) and 3.16 (200 mg, 1.26 mmol) in THF (3 mL) and EtOH (9 mL) was added 15% aqueous KOH (1 mL). The solution was stirred for 6 h at rt.
The mixture was plugged through a pad of silica gel eluted with CH2Cl2 and the solvent removed in vacuo. The residue was purified by column chromatography (silica gel, EtOAc/hexanes 1:1) to obtain 3.17 as a yellow solid (270 mg, 44%).
Rf = 0.5 (EtOAc/hexanes 1:1); IR (ATR): 3089 (m), 2883 (m), 1592 (s), 1222 (s), 1089 (s)
–1 1 cm ; H NMR (300 MHz, CDCl3): 8.25 (s, 2H), 7.46 (d, J = 5.2 Hz, 2H), 7.27 (d, J = 5.2 Hz, 2H), 6.10 (s, 2H), 4.18–4.01 (m, 8H), 3.21 (s, 6H), 3.1603.155 (m, 4H).13C NMR (75 MHz,
CDCl3): 187.3, 141.7, 136.1, 129.6, 128.3, 128.1, 127.2, 98.9, 98.1, 65.2, 48.3, 35.4; MS
+ + LDI (sin) m/z 489 ([M H] , 80), 417 ([M – C3H5O2] , 100). APPI HRMS calcd for + + C24H27O7S2 ([M + H] ) m/z 491.11927, found 491.11970, calcd for C23H24O6S2 ([M – OCH3] ) m/z 459.09360, found 459.09368.
General Procedure H for the synthesis of isomerically pure syn-ADTs: To a solution of the corresponding syn-ADT derivative (100 mg, 1.00 equiv) in dry, deoxygenated THF (20 mL) cooled to –78 °C was added dropwise n-BuLi (2.5 M in hexanes, 3.0 equiv). The mixture was stirred for 30 min at –78 °C and a solution of N-fluorobenzenesulfonimide (NFSI, 10 equiv) in dry, deoxygenated THF (10 mL) was added via cannula. The mixture was allowed to warm to rt and stirred for 1618 h. The solvent was removed under reduced pressure. The residue was suspended via ultrasonication (solvent mixture see individual procedures) and this heterogeneous mixture was filtered through a pad of silica gel. The solution corresponding to the orange-red band was collected and the solvent removed in vacuo. The residue was purified as noted in individual procedures.
The insoluble filter cake of the suspension was dissolved in CH2Cl2, eluted with CH2Cl2, 220
Chapter 5 Experimental data
and the solution corresponding to the red band was collected, and the solvent removed in vacuo. The residue was purified as noted in the individual procedures.
syn3.6a: A solution of syn-3.7a (0.100 g, 0.124 mmol) in dry, deoxygenated THF (20 mL) cooled to –78 °C, n-BuLi (2.5 M in hexanes, 0.15 mL, 0.37 mmol), and N-fluorobenzenesulfonimide (NFSI, 0.391 g, 1.24 mmol) in dry, deoxygenated THF (10 mL) were used according to General Procedure H. After solvent removal, workup was performed by suspending the residue in hexanes (20 mL) and this heterogeneous mixture was filtered through a short pad of silica gel eluting with hexanes. The solution corresponding to the orange-red band was collected and the solvent removed in vacuo. By collecting the first fluorescent fraction, column chromatography (silica gel, hexanes) afforded syn-3.6a (0.032 g, 38%) as a red solid.
Mp = 233–235 °C; Rf = 0.80 (hexanes); UV-vis (CH2Cl2) max (): 305 (100 000), 322 (sh, 33 000), 344 (5 000), 365 (2 200), 396 (1 500), 420 (2 600), 458 (4 000), 489 (13 000), 526 (22
000) nm. UV-vis (CH2Cl2 cast film) max: 224, 311, 395, 420, 462, 494, 530 nm;
Fluorescence (CH2Cl2, exc = 489 nm): max,em = 532, 574 nm; IR (ATR): 3096 (w), 3063 (w),
–1 1 2938 (s), 2860 (s), 2131 (s), 1587 (s), 867 (s) cm ; H NMR (300 MHz, CDCl3): 8.94 (s,
3 13 2H), 8.87 (s, 2H), 6.77 (d, JHF = 2.2 Hz, 2H), 1.281.27 (m, 42H). C NMR (75 MHz,
1 3 CDCl3): 165.8 (d, JCF = 298 Hz), 136.6, 136.5, 133.8, 130.2, 129.5, 120.7 (d, JCF = 9.2
2 Hz), 120.4, 117.8, 116.4, 106.1, 105.7, 103.7, 103.5, 102.6 (d, JCF = 11.2 Hz), 18.9, 11.5
19 3 (two signals coincident or not observed). F NMR (282 MHz, CDCl3): 116.35 (d, JFH =
+ 1.6 Hz); APPI HRMS calcd for C40H49F2S2Si2 ([M + H] ) m/z 687.27768, found 687.27493;
TGA: Td ~ 325 °C; DSC: Mp = 239 °C, decomposition, 341 °C (onset), 370 °C (peak). A crystal suitable for X-ray crystallographic analysis has been grown from a solution of
221
Chapter 5 Experimental data
syn-3.6a in CH2Cl2 which had been layered with acetone and allowed to slowly evaporate at 4 °C. X-ray data for syn-3.6a: C40H48F2S2Si2, Fw = 687.08; triclinic space group P1; crystal size = 0.28 x 0.18 x 0.15 mm3; = 1.5418 Å; a = 7.5855(7) Å, b = 8.1701(8) Å, c = 16.2295(12) Å; = 100.990(7)°, = 92.320(7)°, = 98.594(8)°; V = 973.81(15) Å3; Z = 1;
–3 –1 (calcd) = 1.172 g cm ; μ = 2.105 mm ; T = 173 K; 2max = 73.37°; total data collected =
2 2 6376; R1 = 0.0521 [3127 observed reflections with F0 2(F0 )]; wR2 = 0.1520 for 280 variables, 11 restraints, and 3776 unique reflections; largest difference, peak and hole = 0.328 and –0.377 e Å–3. The three disordered isopropyl groups were refined with the following occupancies: C3–C3’ 77:23; C4–C4’, 45:55; C5–C5’, 60:40. Disorder in the fluorinated thiophene moieties was refined with the following occupancies: S1–S1’ 50:50; C26–C26’ 50:50, C27–C27’ 50:50, F1–F1’ 50:50.
syn3.6b: A solution of syn-3.7b (0.100 g, 0.138 mmol) in dry, deoxygenated THF (20 mL), n-BuLi (2.5 M in hexanes, 0.17 mL, 0.43 mmol), and N-fluorobenzenesulfonimide (NFSI, 0.435 g, 1.38 mmol) in dry, deoxygenated THF (10 mL) were used according to General Procedure H. After solvent removal, workup was performed by suspending the residue in 2:1 hexanes/CH2Cl2 (20 mL) and this heterogeneous mixture was filtered through a pad of silica gel eluting with hexanes/CH2Cl2 (2:1). The solution corresponding to the orange-red band was collected and the solvent removed in vacuo. Column chromatography (silica gel, hexanes) and then recrystallization from THF (2 mL) layered with MeOH (30 mL) afforded syn-3.6b (0.024 g, 29%) as a red solid.
Mp = 176–178 °C; Rf = 0.55 (hexanes); UV-vis (CH2Cl2) max (): 305 (135 000), 321 (sh, 25 000), 342 (6 500), 366 (3 200), 396 (1 400), 420 (3 400), 458 (4 900), 489 (15 000), 525 (27
222
Chapter 5 Experimental data
000) nm. UV-vis (CH2Cl2 cast film) max: 221, 317, 399, 422, 514, 543 nm; Fluorescence
(CH2Cl2, exc = 489 nm): max,em = 534, 574 nm; IR (ATR): 3054 (w), 2950 (s), 2872 (s),
–1 1 2132 (s), 1585 (s), 1407 (s), 723 (s) cm ; H NMR (300 MHz, CDCl3): 8.90 (s, 2H), 8.83 3 (s, 2H), 6.80 (d, JHF = 2.7 Hz, 2H), 1.21 (t, J = 7.8 Hz, 9H), 1.81 (t, J = 7.5 Hz, 9H),
13 1 0.92–0.87 (m, 12H). C NMR (75 MHz, CDCl3): 165.8 (d, JCF = 298 Hz), 136.5, 136.4, 5 4 3 133.7 (d, JCF = 1 Hz), 130.0, 129.2 (d, JCF = 4 Hz), 120.5 (d, JCF = 9 Hz), 120.3, 117.8,
2 19 116.4, 107.0, 106.6, 102.9, 102.6, 102.5 (d, JCF = 11.2 Hz), 7.7, 4.6, 4.5. F NMR (282
3 + MHz, CDCl3): 116.3 (d, JFH = 2.0 Hz); ESI HRMS calcd for C34H36F2S2Si2 (M ) m/z
602.17595, found 602.17411; TGA: Td ~ 285 °C; DSC: Mp = 190 °C, decomposition, 291°C (onset), 320 °C (peak). A crystal suitable for X-ray crystallographic analysis has been grown from a solution of syn-3.6b in n-pentane which had been layered with acetone and allowed to slowly evaporate at 20 °C. X-ray data for syn-3.6b: C34H36F2S2Si2, Fw = 602.93; triclinic space group P1; crystal size = 0.19 x 0.090 x 0.034; = 1.5418 Å; a = 7.0493(17) Å, b = 7.9236(15) Å, c = 16.025(2) Å; = 87.014(13)°, = 84.846(15)°, = 63.64(2)°; V = 798.7(3)
3 –3 –1 Å ; Z = 1; calc = 1.253 g cm ; μ = 2.498 mm ; T = –120 °C; 2max = 108.46°; total data
2 2 collected = 1809; R1 = 0.0217 [1173 observed reflections with F0 2(F0 )]; wR2 = 0.1042 for 197 variables, 5 restraints, and 1371 unique reflections; largest difference, peak and hole = 0.17 and –0.21 e Å–3. Disorder in the fluorinated thiophene moieties was refined with the following occupancies: S25/C26/F1/C27:S25a/C26a/F1a/C27a = 50:50.
syn3.6c: A solution of syn-3.6a (0.100 g, 0.124 mmol) in dry, deoxygenated THF (20 mL) cooled to –78 °C, n-BuLi (2.5 M in hexanes, 0.15 mL, 0.37 mmol), and N-fluorobenzenesulfonimide
223
Chapter 5 Experimental data
(NFSI, 0.391 g, 1.24 mmol) in dry, deoxygenated THF (10 mL) were used according to General Procedure H. After solvent removal, workup was performed by suspending the residue in hexanes (20 mL) and this heterogeneous mixture was filtered through a short pad of silica gel eluting with hexanes. The solution corresponding to the orange-red band was collected and the solvent removed in vacuo. By collecting the second fluorescent fraction, column chromatography (silica gel, hexanes) afforded syn-3.6c (10 mg, 12%) as a red solid.
Mp = 239–242 °C; Rf = 0.55 (hexanes); UV-vis (CH2Cl2) max (): 306 (110 000), 326 (sh, 31 300), 348 (6 000), 398 (1 400), 421 (2 200), 467 (3 800), 501 (12 300), 539 (23 400). UV-vis
(CH2Cl2 cast film) max: 227, 241, 274, 308, 400, 424, 519, 541 nm; Fluorescence (CH2Cl2,
exc = 501 nm): max, em = 548, 589 nm; IR (ATR): 3168 (w), 2936 (s), 2860 (s), 2127 (m),
1 1 1586 (m), 1458 (s), 878 (s) cm ; H NMR (300 MHz, CDCl3): 9.15 (s, 1H), 9.11 (s, 1H), 3 3 8.95 (s, 1H), 8.88 (s, 1H), 7.54 (d, JHH = 5.7 Hz, 1H), 7.41 (d, JHH = 5.3 Hz, 1H), 6.76 (d,
3 13 1 JHF = 2.5 Hz, 1H), 1.381.16 (m, 42H). C NMR (75 MHz, CDCl3): 165.6 (d, JCF = 298 3 Hz), 140.0, 139.5, 136.3, 136.2, 133.7, 130.1, 129.8, 129.4, 123.6, 121.1, 120.6 (d, JCF =
2 9.0 Hz), 120.3, 120.0, 118.2, 116.3, 106.0, 105.5, 103.9, 103.7, 102.6, (d, JCF = 11.3), 18.8,
19 11.5 (three signals coincident or not observed). F NMR (282 MHz, CDCl3): 116.5 (d, 3 + JFH = 1.9 Hz); ESI HRMS calcd C40H50FS2Si2 ([M + H] ) m/z 669.28710, found 669.28694;
TGA: Td ~ 310 °C; DSC: Mp = 253 °C, decomposition, 349 °C (onset), 379 °C (peak). A crystal suitable for X-ray crystallographic analysis has been grown from a solution of syn-3.6c in CH2Cl2 which had been layered with acetone and allowed to slowly evaporate at 4 °C. X-ray data for syn-3.6c: C40H49FS2Si2, Fw = 669.09; triclinic crystal system, space group P1; crystal size = 0.27 x 0.15 x 0.090; = 1.5418 Å; a = 7.6017 (9) Å, b = 7.9787 (9) Å, c = 16.4513(17) Å; = 101.333(9)°,= 91.023(9)°, = 99.639(10)°; V = 963.20(19) Å3;
3 1 Z = 1; calc = 1.154 g/cm ; 2max = 146.5°; = 2.077 mm ; T = 173 K; total data collected =
2 2 5596; R1 = 0.0544 [3042 observed reflections with F0 2(F0 )]; R2 = 0.1633 for 251 variables, 4 restraints, and 3638 unique reflections; largest difference, peak and hole = 0.348 and 0.408 e Å 3. The S/C/F versus S/C/H units are disordered over all syn/anti positions and were refined using the following occupancies: 50:50 for S/C and 25 for each
224
Chapter 5 Experimental data
F/H. The disorder in the iso-propyl groups was refined using the following occupancies: C3/4/5:C3a/4a/5a = 51:49, C6/7/8:C6a/7a/8a = 75:25.
syn-3.23b: According to General Procedure H, the insoluble filter cake of syn-3.6b was dissolved and eluted with CH2Cl2, the solvent removed in vacuo, and the residue purified by automatic flash column chromatography (silica gel, hexanes/CH2Cl2 4:1, flow rate 15 mL/min). Compound syn-3.23b was obtained as a dark red solid (3 mg, 2%).
1 Rf = 0.65 (hexanes/CH2Cl2 4:1); H NMR (300 MHz, CDCl3): 9.17 (s, 1H), 9.01 (s, 1H), 8.86 (s, 1H), 8.80 (s, 1H), 8.088.05 (m, 3H), 7.597.53 (m, 4H), 6.76 (bs, 1H), 1.201.13
19 (m, 18H), 0.870.82 (m, 12H). F NMR (282 MHz, CDCl3): 116.2; APPI HRMS calcd + C40H41FO2S3Si2 (M ) m/z 724.17858, found 724.17812.
syn3.23a: According to General Procedure H, the insoluble filter cake of syn-3.6a was dissolved and eluted with CH2Cl2, the solvent removed in vacuo, and the residue purified automatic flash column chromatography (silica gel, hexanes/CH2Cl2 4:1, flow rate 11 mL/min). Compound syn-3.23a was obtained as a dark red solid (5 mg, 5%).
Mp = 137–140 °C; Rf = 0.45 (hexanes/CH2Cl2 1:1); UV-vis (CH2Cl2) max (): 285 (sh, 20
225
Chapter 5 Experimental data
000), 312 (79 000), 345 (20 500), 365 (12 500), 404 (1 800), 430 (1 900), 480 (2 600), 516
(7 500), 555 (12 300). UV-vis (CH2Cl2 cast film) max: 235, 259, 311, 353, 407, 432, 482,
519, 559, 604 nm; Fluorescence (CH2Cl2, exc = 516 nm): max, em = 567, 607 nm; IR (ATR): 3060 (w), 2939 (s), 2862 (s), 2127 (s), 1587 (s), 1154 (s), 879 (s) cm 1; 1H NMR (300 MHz,
CDCl3): 9.23 (s, 1H), 9.08 (s, 1H), 8.93 (s, 1H), 8.88 (s, 1H), 8.118.08 (m, 3H), 7.627.54
3 19 (m, 4H), 6.76 (d, JHF = 2.4 Hz, 1H), 1.331.23 (m, 42H). F NMR (282 MHz, CDCl3):
3 + 116.2 (d, JFH = 2.3 Hz); APPI HRMS calcd C46H54FO2S3Si2 ([M + H] ) m/z 809.28030, found 809.27924. A crystal suitable for X-ray crystallographic analysis has been grown from a solution of syn-3.23a in CH2Cl2/THF which had been layered with acetone and allowed to slowly
evaporate at 4 °C. X-ray data syn-3.23a THF (C50H61O3FSi2S3), Mw = 881.35; triclinic crystal system, space group P1; crystal size = 0.2 x 0.1 x 0.04 mm3; = 1.5418 Å; a = 7.8077(8) Å, b = 17.3879(13) Å, c = 18.6638(11) Å; = 72.565(6)°,= 82.159(7)°, =
3 3 1 81.918(7)°; V = 2381.4(3) Å ; Z = 2; calc = 1.229 g/cm ; 2max = 146.8°; = 2.250 mm ; T =
2 173 K; total data collected = 14157; R1 = 0.0737 [7360 observed reflections with F0
2 2(F0 )]; R2 = 0.2038 for 554 variables, 12 restraints, and 9112 unique reflections; largest difference, peak and hole = 1.714 and 1.266 e Å 3. The disorder in the thiophene units was refined with the following occupancies: 20:80.
226
Chapter 5 Experimental data
Si
OMe
MeO
S Si
Si
S
OMe
MeO
Si syn3.27:
To a solution of syn-3.7a (50 mg, 0.062 mmol), 2.3 (104 mg, 0.190 mmol), Pd(PPh3)2Cl2 (4 mg, 6 mmol), and CuI (10 mg, 3.1 mol) in dry, deoxygenated THF (10 mL) was added dry, deoxygenated HNi-Pr2 (5 mL). The mixture was heated for 18 h at reflux. The mixture was cooled to rt and saturated aq NH4Cl (100 mL) was added. The mixture was extracted with
CH2Cl2 (3 x 50 mL) and the combined organic phases were washed with brine (100 mL), dried (Na2SO4), filtered, and the solvent removed in vacuo. Purification was achieved by column chromatography (silica gel, hexanes/CH2Cl2 2:1) to afford syn-3.27 as a pink solid (60 mg, 56%).
Mp = 130 °C (color change), 290 °C (decomp); Rf = 0.15 (hexanes/CH2Cl2 3:1); UV-vis
(CH2Cl2) max (): 247 (287 000), 320 (169 000), 369 (169 000), 392 (sh, 56 000), 433 (7
000), 460 (9 700), 491 (7 500), 528 (21 600), 571 (39 000). UV-vis (CH2Cl2 cast film) max:
254, 322, 372, 432, 461, 493, 530, 574 nm; Fluorescence (CH2Cl2, exc = 528 nm): max, em = 577, 627 nm; IR (ATR): 3052 (w), 2938 (s), 2861 (s), 2135 (s), 1460 (s), 1063 (s), 876 (s)
–1 1 cm ; H NMR (400 MHz, CDCl3): 8.91 (s, 2H), 8.90 (s, 2H), 8.79 (s, 4H), 8.49 (s, 4H), 8.048.02 (m, 4H), 7.977.94 (m, 4H), 7.617.58 (m, 8H), 7.40 (s, 2H), 3.18 (s, 6H), 3.14 (s,
13 6H), 1.351.22 (m, 84H). C NMR (100 MHz, CDCl3): 139.8, 139.5, 133.6, 133.5, 133.1,
227
Chapter 5 Experimental data
132.8, 130.3, 129.8, 128.8, 128.4, 128.3, 128.2, 127.0, 126.9, 126.8, 125.5, 121.6, 119.1, 116.0, 106.6, 105.6, 104.6, 103.8, 103.7, 99.2, 92.7, 79.3, 76.4, 73.6, 52.3, 52.0, 18.86, 18.83, 11.5, 11.4 (three signals coincident or not observed); ESI HRMS calcd
+ C114H126NaO4S2Si4 ([M + Na] ) m/z 1757.80668, found 1757.80759. A crystal suitable for X-ray crystallographic analysis has been grown from slowly evaporation of a CH2Cl2 solution layered with acetone at 4 °C. X-ray data for
syn-3.27 2CH2Cl2: C116H130O4Si4S2Cl4, Fw = 1906.48; triclinic crystal system, space group P1; crystal size = 0.37 x 0.19 x 0.14 mm3; = 1.5418 Å; a = 11.1270(6) Å, b = 13.2934(9) Å, c = 19.2396(12) Å; = 100.313(5)°, = 90.768(4)°, = 104.046(5)°; V = 2711.3(3) Å3; Z
3 1 = 1; calc = 1.168 g/cm ; 2max = 140.92°; = 2.158 mm ; T = 173.00(10) K; total data
2 2 collected = 16209; R1 = 0.0684 [8012 observed reflections with F0 2(F0 )]; R2 = 0.1867 for 608 variables, 18 restraints, and 9974 unique reflections; largest difference, peak and hole = 0.85 and 0.77 e Å 3. The disorder in the thiophene units and in one triisopropylsilyl unit was refined with the following occupancies: S28/C2a:C28a/C26a = 50:50; C6/7/8:
C6a/7a/8a = 50:50; One CH2Cl2 molecule per asymmetric unit was refinded with Cl11/Cl12: Cl13/Cl14 = 60:40.
Experimental Data – brominated mix-ADTs
mix3.25a: To a solution of triisopropylsilylacetylene (1.01 g, 5.54 mmol) in dry, deoxygenated THF (15 mL) at 78 °C was added nBuLi (2.5 M in hexanes, 1.82 mL, 4.54 mmol). The solution was stirred for 10 min at 78 °C and was transferred via cannula into a suspension of mix3.4 (265 mg, 0.554 mmol). The mixture was stirred for 18 h at rt and saturated aq
NH4Cl (100 mL) was added. The mixture was extracted with CH2Cl2 (3 x 100 mL) and the 228
Chapter 5 Experimental data
combined organic phases were washed with brine (100 mL), dried (Na2SO4), filtered, and the solvent removed in vacuo. Purification was achieved by column chromatography (silica gel, CH2Cl2/hexanes 1:1) and then recrystallization from n-pentane to afford mix3.25a as pink white solid (135 mg, 29%).
Mp = 208210 °C; Rf = 0.57 (CH2Cl2/hexanes 1:1); IR (ATR): 3471 (br), 2940 (s), 2857 (s),
–1 1 2173 (w), 1463 (s), 1058 (s), 881 (s) cm ; H NMR (300 MHz, CDCl3): 8.51 (s, 1H), 8.477 (s, 1H), 8.475 (s, 1H), 8.45 (s, 1H), 7.36 (s, 2H), 3.203.17 (m, 2H), 1.051.00 (m, 42H).
13 C NMR (75 MHz, CDCl3): 141.3, 139.7, 135.60, 135.55, 135.20, 135.15, 126.6, 120.8, 120.7, 119.7, 119.6, 117.2, 109.2, 109.1, 109.0, 89.8, 89.73, 89.70, 69.5, 69.3, 69.1, 18.6,
79 + 11.2, 11.1; APPI HRMS calcd C40H49 Br2OS2Si2 ([M OH] ) m/z 823.11246, found 823.11121.
mix3.7a:
To a solution of mix3.25a (95 mg, 0.11 mmol) in THF (10 mL) was added SnCl2 2H2O (65 mg, 0.29 mmol) and 10% aq H2SO4 (1 mL). The flask was wrapped in aluminium foil to limit light exposure and the mixture stirred for 5 h at rt. The mixture was loaded onto a plug of silica gel, eluted with CH2Cl2/hexanes (1:1) and the orange-yellow band was collected. The solvent was removed and the residue was precipitated from MeOH to provide mix3.7a as a red solid (25 mg, 28%). NMR spectroscopic data consistent with those reported.[9]
Mp = 292295 °C; Rf = 0.81 (hexanes); UV-vis (CH2Cl2) max (): 310 (110 000), 319 (87 000), 333 (sh, 56 000), 379 (3 000), 404 (2 400), 427 (3 800), 473 (5 000), 505 (13 500),
545 (23 000). UV-vis (CH2Cl2 cast film) max: 230, 315, 325, 339, 406, 428, 477, 510, 550 nm; Fluorescence (CH2Cl2, exc = 504 nm): max, em = 551, 593 nm; IR (ATR): 2941 (s), 2856
229
Chapter 5 Experimental data
–1 79 (s), 2123 (m), 1458 (m), 1355 (s), 872 (s), 662 (s) cm ; APPI HRMS calcd C40H48 Br2S2Si2
+ 79 81 + (M ) m/z 806.10972, found 806.11037, calcd for C40H48 Br BrS2Si2 (M ) m/z 808.10803, found 808.10954. A crystal suitable for X-ray crystallography was grown by slow evaporation of solutions of mix3.7a in CH2Cl2 layered with acetone left standing in the refrigerator at 4 °C for several days. X-ray crystallographic data for mix3.7a: C40H48Br2S2Si2, Fw = 808.90; triclinic space group P1; crystal size 0.28 × 0.17 × 0.039 mm 3; = 1.5418 Å; a = 8.9196(12) Å, b = 10.6329(13) Å, c = 11.0012(13) Å; = 108.470(11)°, = 95.340(10)°, = 91.467(11)°; V =
3 –3 –1 983.6(2) Å ; Z = 1; (calcd) = 1.366 g cm ; = 4.382 mm ; T = 152.9(2) K; 2 max = 141.8°;
2 2 total data collected = 5496; R1 = 0.1165 [1907 observed reflections with Fo 2 (Fo )]; wR2 = 0.3729 for 226 variables, 26 restraints and 3618 unique reflections; largest difference, peak and hole = 0.83 and –0.76 e Å–3. The disorder in the thiophene units was refined with the following occupancies: S25/C26/Br1/C27: S25/C26/Br1/C27 = 69:31. The disorder in the iso-propyl group was refined using the following occupancies: 57:43.
mix3.7b: Synthesis according to Bao and coworkers[9] or Anthony and coworkers[10].
Mp = 233235 °C; Rf = 0.54 (hexanes); UV-vis (CH2Cl2) max (): 310 (189 000), 321 (155 000), 380 (4 000), 404 (3 600), 427 (6 000), 473 (8 000), 506 (23 000), 544 (41 000). UV-vis
(CH2Cl2 cast film) max: 229, 316, 338, 350, 429, 482, 517, 556 nm; Fluorescence (CH2Cl2,
exc = 504 nm): max, em = 551, 593 nm; IR (ATR): 2952 (s), 2873 (s), 2127 (s), 1360 (s), 870 –1 79 81 + (m), 722 (s) cm ; APPI HRMS calcd C34H36 Br BrS2Si2 (M ) m/z 724.01456, found 724.01422. A crystal suitable for X-ray crystallography was grown by slow evaporation of solutions of mix3.7b in CH2Cl2 layered with acetone left standing in the refrigerator at 4 °C for several
230
Chapter 5 Experimental data
days. X-ray crystallographic data for mix3.7b: C34H36Br2S2Si2, Fw = 724.75; triclinic space group P1; crystal size = 0.14 × 0.023 × 0.022 mm3; = 1.5418 Å; a = 7.1824(5) Å, b = 10.3950(7) Å, c = 11.1870(7) Å; = 95.222(5)°, = 90.339(5)°, = 98.604(6)°; V =
3 –3 –1 822.25(9) Å ; Z = 1; (calcd) = 1.464 g cm ; = 5.176 mm ; T = 173.00 K; 2 max = 150.9°;
2 2 total data collected = 5652; R1 = 0.0608 [2687 observed reflections with Fo 2 (Fo )]; wR2 = 0.1732 for 307 variables, 5 restraints and 3308 unique reflections; largest difference, peak and hole = 0.88 and –0.48 e Å–3. The disorder in the thiophene units was refined with the following occupancies: S25/C26/Br1/C27: S25a/C26a/Br1a/C27a = 62:38.
Experimental data pentacenequinone-based building blocks
4.5: To a solution of trimethylsilylacetylene (0.35 g, 3.5 mmol) in dry, deoxygenated THF (10 mL) cooled to 78oC was added nBuLi (2.5 M in hexanes, 1.0 mL, 2.5 mmol). The solution was stirred for 15 min and was transferred via cannula into a suspension of 6, 13pentacenequinone (0.87 g, 2.8 mmol) in dry, deoxygenated THF (15 mL) at rt. The reaction mixture was stirred for 4 h at rt. MeI (4.0 mL, 28 mmol) was added and the mixture was further stirred for 14 h at rt. The reaction mixture was cooled to 78 oC and quenched via the addition of saturated aq NH4Cl (20 mL). The suspension was filtered and the solid was washed with THF (3 x 10 mL). The filtrate was collected into a flask containing saturated aq NH4Cl (30 mL). The filtrate was extracted with CH2Cl2 (3 x 50 mL). The combined organic phases were washed with brine (100 mL), dried (Na2SO4), filtered, and the solvent was removed to provide a solid residue. This residue was purified by column chromatography (silica gel, CH2Cl2/hexanes 2:1 b 4:1) and then recrystallization from hexanes.Compound 4.5 was obtained as a light orange solid (450 mg, 48%).
Mp = 191194 °C; Rf = 0.68 (CH2Cl2); IR (ATR): 3048 (w), 2943 (w), 2896 (w), 2163 (w),
231
Chapter 5 Experimental data
1 1 1666 (s), 1247 (s), 845 (s) cm ; H NMR (300 MHz, CDCl3): 8.81 (s, 2H), 8.56 (s, 2H), 8.04 (d, J = 8.0 Hz, 2H), 7.98 (d, J = 8.1 Hz, 2H), 7.667.55 (m, 4H), 3.04 (s, 3H), 0.37 (s,
13 9H). C NMR (75 MHz, CDCl3): 184.8, 135.7, 135.1, 132.9, 129.7, 129.5, 128.8, 128.4,
+ 128.1, 127.4, 102.6, 96.0, 74.7, 52.0, 0.06; LDI MS m/z 389 ([M OCH3] ). ESI HRMS + calcd for C28H24NaO2Si ([M + Na] ) m/z 443.14378, found 443.14341. A crystal suitable for X-ray crystallography was grown by dissolving 4.5 in hot n-octanol and left these solutions stand for several days under ambient conditions. X-ray crystallographic data for 4.5: C29H26OSi, Fw = 418.59; triclinic space group P1; crystal size 0.24 × 0.18 × 0.14 mm3; = 1.5418 Å; a = 9.9472(7) Å, b = 10.8216(8) Å, c = 10.9865(7) Å; =
3 –3 75.783(6)°, = 74.464(6)°, = 83.123(6)°; V = 1102.70(14) Å ; Z = 2; (calcd) = 1.261 g cm ; –1 = 1.070 mm ; T = 172.9(3) K; 2 max = 123.4°; total data collected = 5124; R1 = 0.0515
2 2 [3309 observed reflections with Fo 2 (Fo )]; wR2 = 0.1535 for 284 variables; largest difference, peak and hole = 0.28 and –0.33 e Å–3.
4.6a: To a solution of 2.36 (300 mg, 0.594 mmol) and malononitrile (392 mg, 5.94 mmol) in dry, deoxygenated CH2Cl2 (20 mL) was added pyridine (0.3 mL) and TiCl4 (0.3 mL). The black mixture was refluxed for 24 h. The mixture was cooled to rt and saturated aq NH4Cl (100 mL) was added. The mixture was extracted with CH2Cl2 (3 x 100 mL) and the combined organic phases were washed with brine (100 mL), dried (Na2SO4), filtered, and the solvent removed in vacuo. The residue was dissolved in minimal amount of CH2Cl2 and a large amount of MeOH was added. Purification was achieved by concentration of this solution at 40 °C. The formed precipitate was filtered and washed with small portions of MeOH to afford 4.6a as a yellow solid (303 mg, 61%).
Mp = 243245°C; Rf = 0.31 (CH2Cl2/hexanes 1:1); IR (ATR): 3057 (w), 2961 (s), 2859 (s),
1 1 2221 (s), 1541 (m), 1258 (s), 1013 (s), 799 (s) cm ; H NMR (400 MHz, CDCl3): 8.81 (s, 232
Chapter 5 Experimental data
2H), 8.69 (s, 2H), 8.02 (d, J = 8.1 Hz, 2H), 7.94 (d, J = 7.9 Hz, 2H), 7.737.63 (m, 4H), 3.95
13 (s, 1H), 1.351.29 (m, 21H). C NMR (100 MHz, CDCl3): 161.8, 134.1, 132.4, 130.1, 130.0, 129.3, 129.1, 128.83, 128.79, 128.6, 126.7, 113.9, 110.3, 100.6, 97.2, 80.6, 50.5,
+ 40.1, 18.8, 11.3; APPI HRMS calcd for C36H33N2Si ([M CH(CN)2] ) m/z 521.24075, found 521.24110. A crystal suitable for X-ray crystallography was grown by slow evaporation of a solution of
4.6a in CDCl3 for several days. X-ray crystallographic data for 4.6a CHCl3: C40H35N4SiCl3,
3 Fw = 706.16; monoclinic space group C2/c; crystal size = 0.12 × 0.0080 × 0.034 mm ; = 1.5418 Å; a = 22.3841(5) Å, b = 10.2430(2) Å, c = 33.4521(7) Å; = 106.066(2)°; V =
3 –3 –1 7370.3(3) Å ; Z = 8; (calcd) = 1.273 g cm ; = 2.822 mm ; T = 173.05(10) K; 2 max =
2 123.28°; total data collected = 10129; R1 = 0.0530 [5532 observed reflections with Fo
2 2 (Fo )]; wR2 = 0.1518 for 439 variables and 4655 unique reflections; largest difference, peak and hole = 0.41 and –0.53 e Å–3.
4.6b: To a solution of 4.5 (600 mg, 1.43 mmol) and malononitrile (945 mg, 14.3 mmol) in dry, deoxygenated CH2Cl2 (40 mL) was added pyridine (0.5 mL) and TiCl4 (0.5 mL). The black mixture was refluxed for 24 h. The mixture was cooled to rt and saturated aq NH4Cl (100 mL) was added. The mixture was extracted with CH2Cl2 (3 x 100 mL) and the combined organic phases were washed with brine (100 mL), dried (Na2SO4), filtered, and the solvent removed in vacuo. The residue was dissolved in minimal amount of CH2Cl2 and a large amount of MeOH was added. Purification was achieved by concentration of this solution at 40 °C. The formed precipitate was filtered and washed with small portions of MeOH to afford 4.6b as a yellow solid (370 mg, 52%).
Mp = 235237°C; Rf = 0.65 (CH2Cl2); IR (ATR): 3056 (w), 2959 (w), 2217 (m), 1536 (s),
1 1 1246 (s), 843 (s), 756 (s) cm ; H NMR (300 MHz, CDCl3): 8.693 (s, 2H), 8.685 (s, 2H),
233
Chapter 5 Experimental data
13 8.037.99 (m, 4H), 7.407.63 (m, 4H), 3.92 (s, 1H), 0.47 (s, 9H). C NMR (75 MHz, CDCl3): 161.8, 134.0, 132.3, 130.0, 129.7, 129.2, 129.1, 128.70, 128.66, 128.58, 126.7, 113.9,
+ 110.3, 100.6, 99.0, 80.6, 50.1, 40.0, 0.3; MALDI MS (sin) m/z 438 ([M CH(CN)2] , 100),
+ + 525 ([M Na] , 40). ESI HRMS calcd for C33H22N4NaSi ([M Na] ) m/z 525.15059, found 525.15008.
4.6d:
To a solution of 4.5 (421 mg, 1.0 mmol) in dry, deoxygenated CH2Cl2 (20 mL) was added malononitrile (66 mg, 1.0 mmol) and Ti(i-OPr)4 (0.1 mL). The mixture was refluxed for 72 h and every 24 h one portion of malonitrile (198 mg, 3.0 mmol) and Ti(i-OPr)4 (0.1 mL) was further added. The mixture was cooled to rt, loaded onto a plug of silica silica gel, eluted with CH2Cl2, and the first yellow fluorescent fraction was collected. The solvent was removed and the solid residue was washed with small amounts of n-pentane to yield 4.6d as a yellow solid in trace amounts (ca. 95% purity as estimated by 1H NMR). IR (ATR): 3064 (w), 2951 (m), 2895 (m), 2220 (s), 1249 (s), 1056 (s), 841 (s) cm 1; 1H NMR
(300 MHz, CDCl3): 8.51 (s, 2H), 8.48 (s, 2H), 7.987.90 (m, 4H), 7.667.56 (m, 4H), 3.18
+ + (s, 3H), 0.46 (s, 9H); MALDI MS (sin) m/z 437 ([M OCH3] , 100), 469 ([M + H] , 10), 491 + + ([M + Na] , 20). APPI HRMS calcd for C31H24N2OSi (M ) m/z 468.16579, found 468.16510.
A crystal suitable for X-ray crystallography was grown by slow evaporation of a CH2Cl2 solution of 4.6d layered with MeOH at 4 °C for several days. X-ray crystallographic data for
4.6d: C31H24N2OSi, Fw = 468.61; monoclinic space group P21/n; crystal size = 0.15 × 0.10 × 0.090 mm3; = 1.5418 Å; a = 10.2078(3) Å, b = 11.1343(4) Å, c = 24.0197(6) Å; =
3 –3 –1 100.527(3)°; V = 2684.06(14) Å ; Z = 4; (calcd) = 1.160 g cm ; = 0.957 mm ; T = 172.9(4)
K; 2 max = 123.52°; total data collected = 6947; R1 = 0.0641 [3014 observed reflections with
2 2 Fo 2 (Fo )]; wR2 = 0.1926 for 317 variables and 10 restraints and 4053 unique reflections; largest difference, peak and hole = 0.44 and –0.40 eÅ–3. The disorder in the 234
Chapter 5 Experimental data
SiMe3-group was refined using the following occupancies: C3/ C3a, C4/C4a = 57:43.
4.6e:
To a solution of 4.6b (300 mg, 0.597 mmol) in THF (20 mL) was added a solution of K2CO3
(124 mg, 0.896 mmol) in MeOH (20 mL; for better solubility a few drops of H2O were added).
The mixture was stirred for 3 h at rt and saturated aq NH4Cl (100 mL) was added. The mixture was extracted with CH2Cl2 (3 x 100 mL) and the combined organic phases were washed with brine (100 mL), dried (Na2SO4), filtered, and the solvent removed in vacuo.
The residue was dissolved in minimal amount CH2Cl2 and plugged through a short pad of silica gel, eluted with CH2Cl2, and the solvent removed in vacuo. Purification was achieved by recrystallization from hexanes at 15 °C to afford 4.6e as yellow solid (215 mg, 85%).
Mp = 245°C (decomp); Rf = 0.45 (CH2Cl2); IR (ATR): 3260 (s), 3057 (w), 2901 (s), 2231 (s),
1 1 1535 (s), 1253 (s), 855 (s), 749 (s) cm ; H NMR (300 MHz, CDCl3): 8.73 (s, 2H), 8.71 (s, 2H), 8.03 (d, J = 8.9 Hz, 4H) 7.757.64 (m, 4H), 3.92 (s, 1H), 3.46 (s, 1H). 13C NMR (75
MHz, CDCl3/DMSOd6): 159.7, 132.9, 131.3, 128.9, 128.3, 128.2, 128.0, 127.9, 127.7, 126.2, 113.7, 110.6, 82.0, 81.8, 48.0 (three signals coincident or not observed); MALDI MS
+ + (sin) m/z 365 ([M CH(CN)2] , 100), 453 ([M Na] , 40). APPI HRMS calcd for C30H14N4 (M+) m/z 430.12130, found 430.12121. A crystal suitable for X-ray crystallography was grown by slow evaporation of solutions of
4.6e in CH2Cl2 layered with MeOH left standing in the refrigerator at 4 °C for several days.
X-ray crystallographic data for 4.6e: C30H14N4, Fw = 430.45; monoclinic space group P21/c; crystal size = 0.25 × 0.25 × 0.15 mm3; = 1.5418 Å; a = 8.8691(2) Å, b = 10.7929(2) Å, c =
3 –3 22.5939(6) Å; = 101.056(3)°; V = 2122.62(9) Å ; Z = 4; (calcd) = 1.347 g cm ; = 0.640
–1 mm ; T = 173.00(10) K; 2 max = 117.9°; total data collected = 3628; R1 = 0.0386 [2460
2 2 observed reflections with Fo 2 (Fo )]; wR2 = 0.1046 for 307 variables and 2235 unique reflections; largest difference, peak and hole = 0.17 and –0.24 e Å–3.
235
Chapter 5 Experimental data
4.7: To a solution of 2.36 (1.00 g, 1.98 mmol) in THF (20 mL) was added TBAF (1.0 M in THF, 2.38 mL, 2.38 mmol). The mixture was stirred for 2 h at rt. The mixture was quenched by the addition of saturated aq NH4Cl (10 mL). The mixture was extracted with CH2Cl2 (3 x 100 mL). The combined organic phases were washed with brine (100 mL), dried (Na2SO4), filtered, and the solvent removed in vacuo. Purification was achieved by recrystallization from a CH2Cl2 solution by the addition of MeOH. The resulting solid was filtered and washed with MeOH and hexanes to afford 4.7 as a yellow solid (515 mg, 75%). Alternative procedure for the synthesis of 4.7:
To a solution of 4.5 (421 mg, 1.00 mmol) in THF (10 mL) was added a solution of K2CO3
(207 mg, 1.50 mmol) in MeOH (10 mL; for better solubility a few drops of H2O were added). The mixture was stirred for 6 h at ambient conditions. MeOH was added (50 ml) and the mixture was concentrated under reduced pressure. The formed precipitate was filtered, washed with MeOH/H2O (1:1), and air dried to yield 4.7 as a light yellow solid (300 mg, 86%).
Mp = 250 °C (color change), 263265 °C; Rf = 0.44 (CH2Cl2); IR (ATR): 3230 (s), 2952 (w),
1 1 2184 (w), 1676 (s), 1265 (s), 750 (s) cm ; H NMR (300 MHz, CDCl3): 8.83 (s, 2H), 8.57 (s, 2H), 8.067.98 (m , 4H), 7.677.56 (m, 4H), 3.12 (s, 1H), 3.05 (s, 3H). 13C NMR (100
MHz, CDCl3): 184.6, 135.4, 135.1, 132.9, 129.8, 129.7, 129.6, 128.9, 128.4, 128.0, 127.5,
+ 81.7, 78.5, 74.2, 52.1; MS LDI m/z 317 ([MOCH3] ). APPI HRMS calcd for C24H13O ([M
+ + OCH3] ) m/z 317.09609, found 317.09668, calcd for C25H17O2 ([M + H] ) m/z 349.12231, found 349.12108.
236
Chapter 5 Experimental data
4.8b:
Compound 4.7 (500 mg, 1.44 mmol) was dissolved in CH2Cl2 (20 mL) and a solution of Hay-catalyst prepared by dissolving CuCl (143 mg, 1.44 mmol) and TMEDA (335 mg,
2.88 mmol) in CH2Cl2 (20 mL) was added. The mixture was stirred for 24 h at ambient conditions and saturated aq NH4Cl (50 mL) was added. The mixture was extracted with
CH2Cl2 (3 x 100 mL, as suspension). The suspension was washed with brine (100 mL), dried (Na2SO4), filtered, and the solvent removed in vacuo. The residue was suspended in
CH2Cl2 (30 mL) and MeOH was added to precipitate the product. The mixture was filtered and washed with MeOH and hexanes. Final purification was achieved by heating the solid in THF, adding iPrOH, filtered and washed with iPrOH to afford 4.8b as a yellow solid (400 mg, 40%).
Mp = 220 °C (decomp); Rf = 0.38 (CH2Cl2); IR (ATR): 3334 (w), 3052 (w), 2935 (w), 2168
1 1 (w), 1672 (s), 1264 (s), 1055 (s) cm ; H NMR (300 MHz, DMSOd6): 8.87 (s, 4H), 8.64 (s, 4H), 8.288.26 (m, 8H), 7.757.69 (m, 8H), 2.95 (s, 6H). 13C NMR: The compound shows sufficient insolubility to record a meaningful 13C NMR; APPI HRMS calcd for
+ C49H27O3 ([M OCH3] ) m/z 663.19547, found 663.19479, calcd for C48H25O2 ([M + H 2 x
+ OCH3] ) m/z 633.18491, found 633.18366.
4.9: To a solution of 4.6b (300 mg, 0.597 mmol) in dry, deoxygenated THF (20 mL) at 78 °C was added LDA (2.0 M in THF, 0.36 mL, 0.72 mmol). The mixture was stirred for 30 min
237
Chapter 5 Experimental data while was warmed to rt. MeI (0.42 g, 0.19 mL, 3.0 mmol) was added via syringe and the mixture was stirred for 18 h at rt. The reaction was quenched by the addition of NH4Cl (100 mL) and extracted with CH2Cl2 (3 x 100 mL). The combined organic phases were washed with brine (100 mL), dried (Na2SO4), filtered, and the solvent removed in vacuo. The crude residue was dissolved in minimal amount of CH2Cl2 and plugged through a pad of silica gel eluted with CH2Cl2. The solvent was removed and the product was finally purified by precipitation from a CH2Cl2 solution by the addition of hexanes to yield 4.9 as a yellow solid (180 mg, 58%).
Mp = 175178 °C; Rf = 0.80 (CH2Cl2); IR (ATR): 3061 (w), 2956 (w), 2218 (m), 2170 (w),
1 1 1543 (m), 1257 (s), 848 (s), 748 (s) cm ; H NMR (300 MHz, CDCl3): 8.75 (s, 4H),
13 8.068.00 (m, 4H), 7.747.64 (m, 4H), 1.89 (s, 3H), 0.42 (s, 9H). C NMR (75 MHz, CDCl3): 163.5, 134.0, 132.3, 131.6, 129.9, 129.0, 128.9, 128.8, 128.5, 128.1, 127.6, 114.5, 114.4,
101.9, 98.6, 81.9, 53.2, 46.1, 22.9, 0.4; APPI HRMS calcd for C30H21N2Si ([M
+ C(CN)2CH3] ) m/z 437.14685, found 437.14692.
4.12a: To a solution of 2.4 (491 mg, 1.00 mmol) and tetrabutylammonium iodide (0.7 g, 2.0 mmol) in dry, deoxygenated THF (20 mL) at rt was added NaH (48 mg, 2.0 mmol). The mixture was stirred for 5 min at rt and benzylbromide (0.34 g, 0.24 mL, 2.0 mmol) was added. The mixture was protected from light exposure and stirred for 24 h at rt and saturated aq NH4Cl
(100 mL) was added. The mixture was extracted with CH2Cl2 (3 x 50 mL) and the combined organic phases were washed with brine (100 mL), dried (Na2SO4), filtered, and the solvent removed in vacuo. Purification was achieved by recrystallization from a CH2Cl2 solution layered with MeOH. The precipitate was filtered, washed with MeOH, and air dried to yield 4.12a as a colorless solid (487 mg, 84%).
Mp = 145148°C; Rf = 0.24 (hexanes); IR (ATR): 3056 (w), 2930 (s), 2855 (s), 2171 (s),
238
Chapter 5 Experimental data
1 1 1672 (s), 1257 (s), 1021 (s), 748 (s) cm ; H NMR (300 MHz, CDCl3): 8.77 (s, 2H), 8.71 (s, 2H), 8.03 (d, J = 7.8 Hz, 2H), 7.92 (d, J = 8.1 Hz, 2H), 7.667.54 (m, 4H), 7.117.07 (m,
13 3H), 7.016.98 (m, 2H), 4.36 (s, 2H), 1.321.26 (m, 21H). C NMR (75 MHz, CDCl3): 185.5, 137.5, 136.1, 134.8, 132.9, 130.1, 129.7, 129.6, 128.8, 128.4, 128.0, 127.8, 127.4, 127.3, 103.6, 93.6, 75.5, 67.3, 18.8, 11.4 (one signal coincident or not observed); APPI
+ HRMS calcd for C33H33OSi ([M CH2Ph] ) m/z 473.22952, found 473.22994; calcd for + C40H41O2Si ([M + H] ) m/z 581.28703, found 581.28673.
4.12b: To a solution of 4.11 (450 mg, 0.903 mmol) and tetrabutylammonium iodide (667 mg, 1.81 mmol) in dry, deoxygenated THF (20 mL) at rt was added NaH (33 mg, 1.4 mmol). The mixture was stirred for 5 min at rt and benzylbromide (0.31 g, 0.22 mL, 1.8 mmol) was added. The mixture was protected from light exposure and stirred for 18 h at rt and H2O
(100 mL) was added. The mixture was extracted with CH2Cl2 (3 x 100 mL) and the combined organic phases were washed with brine (100 mL), dried (Na2SO4), filtered, and the solvent removed in vacuo. The first fluorescent fraction was collected by column chromatography (silica gel, CH2Cl2). Further recrystallization from a CH2Cl2 solution layered with MeOH yielded 4.12b as a colorless solid (240 mg, 63%, which was ca. 95% pure as estimated by 1H NMR).
Mp = 175177°C; Rf = 0.85 (CH2Cl2); IR (ATR): 3233 (s), 3056 (w), 2852 (w), 2107 (m),
1 1 1666 (s), 1256 (s), 1022 (s), 740 (s) cm ; H NMR (300 MHz, CDCl3): 8.83 (s, 2H), 8.64 (s, 2H), 8.067.98 (m, 4H), 7.707.55 (m, 4H), 7.147.10 (m, 3H), 7.057.01 (m, 2H), 4.24
+ (s, 2H), 3.17 (s, 1H) MALDI MS (sin) m/z 317 ([M CH2Ph] ).
239
Chapter 5 Experimental data
4.13: To a solution of 4.5 (300 mg, 0.713 mmol) and malononitrile (47 mg, 0.71 mmol) in dry, deoxygenated CH2Cl2 (20 mL) was added pyridine (0.2 mL) and TiCl4 (0.14 g, 8.0 L, 0.71 mmol). The mixture was refluxed for 18 h and saturated aq NH4Cl (100 mL) was added.
The mixture was extracted with CH2Cl2 (3 x 100 mL) and the combined organic phases were washed with brine (100 mL), dried (Na2SO4), filtered, and the solvent removed in vacuo. The residue was dissolved in minimal amount of CH2Cl2 and plugged through a pad of silica gel eluted with CH2Cl2. After the removal of the solvent, the residue was dissolved in minimal amount of CH2Cl2 and a precipitate was formed by the addition of hexanes. This precipitate was filtered and washed with hexanes and finally purified by column chromatography (silica gel, CH2Cl2) to yield 4.13 as a yellow-orange solid (57 mg, 13%).
Mp = 211213°C; Rf = 0.36 (CH2Cl2); IR (ATR): 3049 (w), 2959 (s), 2874 (s), 2159 (w),
1 1 1657 (s), 1256 (s), 1093 (s), 1014 (s), 793 (s) cm ; H NMR (300 MHz, CDCl3): 8.83 (s, 2H), 8.69 (s, 2H), 8.058.00 (m, 4H), 7.68 (t, J = 7.5 Hz, 2H), 7.60 (t, J = 7.4 Z, 2H), 4.35 (s,
13 1H), 0.45 (s, 9H). C NMR (75 MHz, CDCl3): 182.9, 135.1, 133.0, 132.0, 130.6, 129.8, 129.6, 128.9, 128.5, 128.4, 128.2, 110.4, 100.7, 98.3, 47.9, 43.6, 0.24; APPI HRMS calcd
+ for C27H21OSi ([M CH(CN)2] ) m/z 389.13562, found 389.13758.; calcd for C30H22N2OSi (M+) m/z 454.14959, found 454.15020.
4.15a: To a solution of 1-bromo-4-(tert-butyl)benzene (2.13 g, 10.0 mmol) in dry, deoxygenated THF (30 mL) at 78 °C was added nBuLi (2.5M in hexanes, 4.8 mL, 12 mmol). The mixture was stirred for 1 h at –78°C and 4-(tert-butyl)benzaldehyde (1.62 g, 1.67 mL, 10.0 mmol) was added. The mixture was stirred for 2.5 h at rt and saturated aq NH4Cl (100 mL) 240
Chapter 5 Experimental data
was added. The mixture was extracted with CH2Cl2 (3 x 100 mL) and the combined organic phases were washed with brine (100 mL), dried (Na2SO4), filtered, and the solvent removed in vacuo. Purification was achieved by recrystallization from n-pentane to afford 4.15a as a colorless solid (2.5 g, 84%). Spectral and physical data was consistent with that reported.[11]
4.16a:
To a solution of 4.15a (4.97 g, 16.8 mmol) in dry, deoxygenated CH2Cl2 (50 mL) was added Celite (10 g), molecular sieves (4 Å, 10 g), and PCC (7.33 g, 34.0 mmol) in that order. The mixture was stirred for 5 h at rt and was plugged through a pad of silica gel eluted with
CH2Cl2 and the solvent was removed in vacuo. Purification was achieved by recrystallization from MeOH to yield 4.16a as a colorless solid (2.81 g, 56%). Spectral and physical data consistent with those reported.[12]
4.15b: To a solution of 1-bromo-4-(trifluoromethyl)benzene (4.14b, 4.5 g, 20 mmol) in dry, deoxygenated THF (20 mL) at 78 °C was added nBuLi (2.5 M in hexanes, 9.6 mL, 24 mmol). The solution was stirred for 1 h at 78 °C and 4-(trifluoromethyl)benzaldehyde (3.48 g, 2.73 mL, 20 mmol) was added. The solution was warmed to rt and stirred for 18 h and saturated aq NH4Cl (100 mL) was added. The mixture was extracted with CH2Cl2 (3 x 100 mL) and the combined organic phases were washed with brine (100 mL), dried (Na2SO4), filtered, and the solvent removed in vacuo to yield an oily residue (6.40 g, 20 mmol) The oily residue was used in the next step without further purification.
4.16b:
The oily residue of 4.15b (6.40 g, 20 mmol) was dissolved in dry, deoxygenated CH2Cl2 (30 241
Chapter 5 Experimental data mL). To that mixture was added Celite (10 g), molecular sieves (4 Å, 10 g), and PCC (8.63 g, 40 mmol) in that order. The mixture was stirred for 18 h at rt. The mixture was plugged through a short pad of silica gel eluted with CH2Cl2 and the solvent was removed in vacuo. Purification was achieved by recrystallization from n-pentane to afford 4.16b as a colorless solid (2.71 g, 43% over two steps). Spectral and physical data consistent with those reported.[13]
4.17a: To a solution of trimethylsilylacetylene (1.2 g, 12 mmol) in dry, deoxygenated THF (30 mL) at 78 °C was added nBuLi (2.5 M in hexanes, 4.9 mL, 12 mmol). The mixture was stirred for 30 min at 78 °C and a solution of 4.16a (3.0 g, 10 mmol) in dry, deoxygenated THF (20 mL) was added via cannula. The mixture was stirred for 4 h at rt and MeI (14.5 g, 6.39 mL,
102 mmol) was added. The mixture was stirred for 18 h at rt and saturated aq NH4Cl (100 mL) was added. The mixture was extracted with CH2Cl2 (3 x 100 mL) and the combined organic phases were washed with brine (100 mL), dried (Na2SO4), filtered, and the solvent removed in vacuo. Purification was achieved by recrystallization from MeOH at 15 °C to afford 4.17a as a colorless solid (2.54 g, 85%).
Mp = 108110°C; Rf = 0.55 (CH2Cl2/hexanes 1:1); IR (ATR): 2956 (s), 2161 (w), 1506 (m),
1 1 1249 (s), 1078 (s), 830 (s) cm ; H NMR (300 MHz, CDCl3): 7.48 (d, J = 8.1 Hz, 4H), 7.32
13 (d, J = 8.4 Hz, 4H), 3.35 (s, 3H), 1.29 (s, 18H), 0.25 (s, 9H). C NMR (75 MHz, CDCl3): 150.2, 140.1, 126.3, 125.0, 104.9, 94.0, 81.0, 52.4, 34.4, 31.3, 0.01; APPI HRMS calcd for
+ + C26H35Si ([M OCH3] ) m/z 375.25025, found 375.25103; calcd for C27H38OSi (M ) m/z 406.26864, found 406.26781.
242
Chapter 5 Experimental data
4.18a:
To a solution of 4.17a (2.30 g, 7.81 mmol) in THF (20 mL) was added a solution of K2CO3
(1.62 g, 11.7 mmol) in MeOH (20 mL, for a better solubility a few drops of H2O were added).
The mixture was stirred for 18 h at rt and saturated aq NH4Cl (100 mL) was added. The mixture was extracted with CH2Cl2 (3 x 100 mL) and the combined organic phases were washed with brine (100 mL), dried (Na2SO4), filtered, and the solvent removed in vacuo. Purification was achieved by recrystallization from MeOH from which a colorless solid was obtained. The remaining filtrate was concentrated and H2O was added dropwise. The formed precipitate was filtered and washed with MeOH/H2O (1/1). This procedure was repeated three times to provide 4.18a as a colorless solid (1.56 g, 60%). Mp = 9496°C; IR (ATR): 3269 (s), 2956 (s), 2114 (w), 1504 (m), 1072 (s), 825 (s) cm 1; 1H
NMR (300 MHz, CDCl3): 7.48 (d, J = 8.4 Hz, 4H), 7.34 (d, J = 8.6 Hz, 4H), 3.36 (s, 3H),
13 2.86 (s, 1H), 1.30 (s, 18H). C NMR (75 MHz, CDCl3): 150.4, 139.8, 126.3, 125.0, 83.5, + 80.5, 77.1, 52.5, 34.4, 31.3; APPI HRMS calcd for C24H30O (M ) m/z 334.22912, found 334.22885.
4.18b: To a solution of trimethylsilylacetylene (742 mg, 7.55 mmol) in dry, deoxygenated THF (30 mL) at 78 °C was added nBuLi (2.5 M in hexanes, 3.0 mL, 7.6 mmol). The mixture was stirred for 30 min at 78 °C and a solution of 4.16b (2.0 g, 6.29 mmol) was added via cannula. The mixture was stirred for 4 h at rt and MeI (8.93 g, 3.93 mL, 62.9 mmol) was added. The mixture was stirred for 18 h at rt and saturated aq NH4Cl (3 x 100 mL) was added. The mixture was extracted with CH2Cl2 (3 x 100 mL), washed with brine (100 mL), dried (Na2SO4), filtered, and the solvent removed in vacuo. The oily residue was dissolved 243
Chapter 5 Experimental data
in THF (20 mL) and a solution K2CO3 (4.35 g, 31.5 mmol) in MeOH (20 mL; for better solubility a few drops of H2O were added) was added. The mixture was stirred for 6 h at rt and saturated aq NH4Cl (100 mL) was added. The mixture was extracted with CH2Cl2 (3 x 100 mL) and the combined organic phases were washed with brine (100 mL), dried
(Na2SO4), filtered, and the solvent removed in vacuo. Purification was achieved by column chromatography (silica gel, hexanes) to afford 4.18b as a colorless liquid which solidifies upon refrigeration (1.98 g, 88%).
1 1 Rf = 0.15 (hexanes); IR (ATR): 3299 (s), 2960 (w), 2121 (w), 1319 (s), 1120 (s) cm ; H
NMR (300 MHz, CDCl3): 7.77 (d, J = 8.3 Hz, 4H), 7.66 (d, J = 8.5 Hz, 4H), 3.43 (s, 3H),
13 3.01 (s, 1H). C NMR (100 MHz, CDCl3): 146.4, 130.4 (d J = 32.5 Hz), 127.0, 125.5 (q, J
19 = 3.7 Hz), 124.1 (d, J = 272 Hz), 81.5, 80.1, 79.0, 52.6. F NMR (282 MHz, CDCl3): 63.09.
4.19a: To a solution of 4.18a (669 mg, 2.00 mmol) in dry, deoxygenated THF (20 mL) at 78 °C was added nBuLi (2.5 M in hexanes, 0.64 mL, 1.6 mmol). The mixture was stirred at 78 °C for 30 min and was transferred into a suspension of 6,13-pentacenequinone (617 mg, 2.00 mmol) via cannula. The mixture was stirred for 18 h at rt and the reaction was quenched by the addition of saturated aq NH4Cl (100 mL). The mixture was filtered and the residue was washed with THF (20 mL). The filtrate was extracted with CH2Cl2 (3 x 100 mL) and the combined organic phases were washed with brine (100 mL), dried (Na2SO4), filtered, and the solvent removed in vacuo. The residue was dissolved in minimal amount of
CH2Cl2 and a solid was precipitated by adding hexanes. The solid was filtered and washed with hexanes. The solid was redissolved in acetone and filtered to remove insoluble impurities and the solvent removed in vacuo. Final purification was achieved by recrystallization from a CH2Cl2 solution layered with MeOH. Compound 4.19a was obtained 244
Chapter 5 Experimental data as a light red solid (795 mg, 62%).
Mp = 243245°C; Rf = 0.61 (CH2Cl2); IR (ATR): 3466 (s), 3049 (w), 2956 (s), 2901 (m),
1 1 2162 (w), 1661 (s), 1262 (s), 1185 (s), 833 (s) cm ; H NMR (300 MHz, CDCl3): 8.81 (s, 2H), 8.59 (s, 2H), 8.00 (d, J = 7.7 Hz, 2H), 7.84 (d, J = 7.9 Hz, 2H), 7.637.53 (m, 4H), 7.497.45 (m, 4H), 7.327.28 (m, 4H), 3.41 (s, 3H), 3.20 (s, 1H), 1.28 (s, 18H). 13C NMR
(75 MHz, CDCl3): 184.2, 150.5, 139.9, 138.9, 135.7, 132.7, 129.8, 129.7, 128.9, 128.2, 128.1, 127.4, 127.3, 126.4, 125.1, 90.9, 88.2, 80.9, 68.2, 52.9, 34.5, 31.3; MALDI MS (sin)
+ + m/z 611 ([M OCH3] ). APPI HRMS calcd for C46H42O3 (M ) m/z 642.31285, found 642.31236.
4.19b: To a solution of 4.18b (1.0 g, 2.8 mmol) in dry, deoxygenated THF (20 mL) at 78 °C was added nBuLi (2.5 M in hexanes, 0.88 mL, 2.2 mmol). The mixture was stirred at 78 °C for 30 min and was transferred into a suspension of 6,13-pentacenequione (860 mg, 2.79 mmol) via cannula. The mixture was stirred for 18 h at rt and the reaction was quenched by the addition of saturated aq NH4Cl (100 mL). The mixture was filtered and the solid residue was washed with THF (20 mL). The filtrate was extracted with CH2Cl2 (3 x 100 mL) and the combined organic phases were washed with brine (100 mL), dried (Na2SO4), filtered, and the solvent removed in vacuo. The residue was dissolved in minimal amount CH2Cl2 and a solid was precipitated by the addition of hexanes. The solid was filtered and washed with hexanes. The solid was redissolved in acetone and filtered to remove insoluble impurities.
Final purification was achieved by recrystallization from a CH2Cl2 solution layered with MeOH. Compound 4.19b was obtained as a light yellow solid (825 mg, 44%).
Mp = 243245°C; Rf = 0.51 (CH2Cl2); IR (ATR): 3309 (s), 3052 (w), 2187 (w), 1617 (s),
1 1 1322 (s), 1117 (s), 755 (s) cm ; H NMR (300 MHz, CDCl3): 8.78 (s, 2H), 8.51 (s, 2H), 7.97 (d, J = 8.0 Hz, 2H), 7.83 (d, J = 8.1 Hz, 2H), 7.667.50 (m, 12H), 3.32 (s, 4H). 13C 245
Chapter 5 Experimental data
NMR (75 MHz, DMSO-d6): 183.5, 146.5, 140.0, 135.2, 132.1, 129.8, 129.3, 128.9, 128.7
2 3 1 (d, JCF = 32 Hz), 128.2, 128.1, 127.5, 126.9, 126.4, 125.5 (q, JCF = 3.6 Hz), 123.9 (d, JCF
19 = 272 Hz), 94.7, 84.3, 79.7, 66.5, 52.4. F NMR (282 MHz, CDCl3): 63.08; APPI HRMS
+ calcd for C39H21F6O2 ([M OCH3] ) m/z 635.14403, found 635.14343; calcd for
+ + C40H23F6O2 ([M OH] ) m/z 649.15968, found 649.15830; calcd for C40H24F6O3 (M ) m/z 666.16242, found 666.16244.
O
C C
4.20a: To a solution of 4.19a (200 mg, 0.311 mmol) in dry, deoxygenated THF (10 mL) was added
SnCl2 2H2O (211 mg, 0.933 mmol) and conc. HCl (1 mL). The mixture was stirred in the dark until the starting material was consumed (3 h, as observed by TLC). The reaction was quenched by the addition of H2O (50 mL) and the dark red mixture was extracted with
CH2Cl2 (3 x 100 mL). The combined organic phases were washed with brine (100 mL), dried (Na2SO4), filtered, and the solvent removed in vacuo. Purification was achieved by precipitation from a concentrated CH2Cl2 solution by the addition of hexanes. The precipitate was filtered, washed with hexanes, and air dried to yield 4.20a as a dark red solid (52 mg, 28%).
Mp = 257260 °C (decomp); Rf = 0.65 (CH2Cl2); UV-vis (CH2Cl2) max (): 244 (20 800), 285 (82 600), 326 (20 200), 376 (6 800), 414 (7 200), 503 (18 500), 544 (19 500) nm. UV-vis
(CH2Cl2 cast film) max: 245, 286, 329, 389, 425, 507, 557 nm; Fluorescence (CH2Cl2, exc =
544 nm): max, em = 613 nm; IR (ATR): 3044 (m), 2952 (s), 2018 (m), 1645 (s), 1280 (s), 743
1 1 (s) cm ; H NMR (400 MHz, CDCl3): 8.93 (s, 2H), 8.35 (s, 2H), 8.00 (d, J = 8.0 Hz, 2H),
13 7.797.75 (m, 6H), 7.617.48 (m, 8H), 1.50 (s, 18H). C NMR (100 MHz, CDCl3): 183.7, 152.5, 148.2, 146.5, 136.1, 135.5, 133.1, 132.1, 130.0, 129.9, 129.3, 128.5, 128.1, 127.86,
+ 127.85, 127.7, 126.7, 125.6, 111.5, 35.0, 31.4; APPI HRMS calcd for C45H39O ([M H] )
246
Chapter 5 Experimental data m/z 595.29954, found 595.29976.
A crystal suitable for X-ray crystallography was grown by slow evaporation of a CH2Cl2 solution of 4.20a layered with MeOH/i-PrOH at 4 °C for several moths. X-ray crystallographic data for 4.20a: C45H38O, Fw = 594.75; triclinic space group P1; crystal size = 0.27 × 0.047 × 0.035 mm3; = 1.5418 Å; a = 6.0250(4) Å, b = 14.8303(12) Å, c = 18.0889(10) Å; = 88.608(6)° ; = 85.064(5)°; = 89.881(6)°; V = 1609.8(2) Å3; Z = 2;
–3 –1 (calcd) = 1.277 g cm ; = 0.543 mm ; T = 173.2(6) K; 2 max = 122.8°; total data collected =
2 2 7345; R1 = 0.0578 [4798 observed reflections with Fo 2 (Fo )]; wR2 = 0.1804 for 421 variables and 0 restraints and 3519 unique reflections; largest difference, peak and hole = 0.25 and –0.22 eÅ–3.
4.21: To a solution of 2.4 (1.0 g, 2.0 mmol) in THF (20 mL) was added TBAF (1.0 M in THF, 2.5 mL, 2.5 mmol) at rt. The mixture was stirred for 2 h under ambient conditions. The reaction was quenched by the addition of saturated aq NH4Cl (1 mL) and H2O (1 mL). The formed precipitate was filtered, washed with MeOH (20 mL), acetone (20 mL), CH2Cl2 (20 mL), and was air dried to provide 4.21 (650 mg, 95%) as a yellow solid. Spectral and physical data consistent as reported, see Lehnherr.[3]
Si
OH
OH
Si
4.23a: To a solution of triisopropylsilylacetylene (1.22 mg, 6.68 mmol) in dry, deoxygenated THF (20 mL) at 78 °C was added nBuLi (2.50 M in hexanes, 2. 6 mL, 6.5 mmol). The mixture was stirred for 30 min at 78 °C and was transferred into a solution of 2.4 (820 g, 1.67 247
Chapter 5 Experimental data mmol) in dry, deoxygenated THF (10 mL) via cannula. The mixture was stirred for 18 h at rt and saturated aq NH4Cl (100 mL) was added. The mixture was extracted with CH2Cl2 (3 x 50 mL) and the combined organic phases were washed with brine (100 mL), dried
(Na2SO4), filtered, and the solvent removed in vacuo. Purification was achieved by plugging the mixture through a pad of silica gel (CH2Cl2/hexanes 1:1), evaporating the solvent, and then recrystallization from n-pentane at 15 °C. Compound 4.23a was obtained as a colorless solid (520 mg, 46%).
Mp = 204206 °C; Rf = 0.43 (CH2Cl2/hexanes1:1); IR (ATR): 3505 (m), 3055 (w), 2942 (s),
1 1 2863 (s), 2160 (w), 1461 (s), 890 (s) cm ; H NMR (300 MHz, CDCl3): 8.66 (s, 4H), 7.927.89 (m, 4H), 7.547.50 (m, 4H), 3.36 (s, 2H), 1.091.02 (m, 42H). 13C NMR (100
MHz, CDCl3): 136.3, 133.2, 128.1, 126.8, 126.0, 109.4, 89.6, 69.7, 18.6, 11.2; MALDI MS + + (dctb) m/z 655 ([M – OH] , 100), 672 (M , 15). APPI HRMS calcd for C44H56NaO2Si2 ([M Na]+) m/z 695.37111, found 695.37174.
Si
OH
OH
Si
4.23b: To a solution of trimethylsilylacetylene (870 mg, 8.85 mmol) in dry, deoxygenated THF (20 mL) at 78 °C was added nBuLi (2.5 M in hexanes, 3.42 mL, 8.56 mmol). The solution was stirred for 30 min at 78 °C and was transferred into a solution of 4.11 (1.20 g, 2.95 mmol) in dry, deoxygenated THF (20 mL) via cannula. The mixture was stirred for 18 h at rt and saturated aq NH4Cl (100 mL) was added. The mixture was extracted with CH2Cl2 (3 x 100 mL) and the combined organic phases were washed with brine (100 mL), dried
(Na2SO4), filtered, and the solvent removed in vacuo. Purification was achieved by column chromatography (silica gel, CH2Cl2/hexanes 3:1) and then recrystallization from n-pentane at 15 °C to provide 4.23b as a colorless solid (685 mg, 46%).
Mp = 244246 °C; Rf = 0.13 (CH2Cl2/hexanes 1:1); IR (ATR): 3537 (s), 3054 (w), 2957 (w),
248
Chapter 5 Experimental data
1 1 2169 (w), 1248 (s), 840 (s) cm ; H NMR (300 MHz, CDCl3): 8.58 (s, 4H), 7.947.91 (m,
13 4H), 7.557.52 (m, 4H), 3.65 (s, 2H), 0.20 (s, 18H). C NMR (100 MHz, CDCl3): 136.1,
133.1, 128.2, 126.9, 125.8, 106.9, 93.5, 69.7, 0.32; ESI HRMS calcd for C32H31OSi2 ([M
+ + OH] ) m/z 487.1908, found 487.1910, calcd for C32H32NaO2Si2 ([M + Na] ) 527.1833, found 527.1834.
H
OH
OH
H 4.24:
To a solution of 4.23b (300 mg, 0.594 mmol) in THF (20 mL) was added a solution of K2CO3
(164 mg, 1.19 mmol) in MeOH (20 mL; for better solubility a few drops of H2O were added).
The mixture was stirred for 2.5 h under ambient conditions and saturated aq NH4Cl (100 mL) was added. The mixture was extracted with CH2Cl2 (3 x 50 mL) and the combined organic phases were washed with brine (100 mL), dried (Na2SO4), filtered, and the solvent removed in vacuo. Purification was achieved by recrystallization from an acetone solution layered with hexanes at 15 °C. The product 4.24 was obtained as a colorless solid (162 mg, 76%).
Mp = 254 °C decomp); Rf = 0.27 (CH2Cl2); IR (ATR): 3497 (s), 3247 (s), 3054 (w), 2121 (m),
1 1 1493 (m), 894 (s) cm ; H NMR (300 MHz, CDCl3): 8.61 (s, 4H), 7.957.92 (m, 4H),
13 7.557.52 (m, 4H), 3.24 (s, 2H), 2.96 (s, 2H). C NMR (75 MHz, CDCl3/DMSOd6): 135.9, 132.7, 127.7, 126.3, 125.7, 86.3, 75.1, 68.0; MALDI MS (sin) m/z 343 ([M OH]+, 100), 383
+ + ([M Na] , 20). APPI HRMS calcd for C26H15O ([M OH] ) m/z 343.11174, found 343.11140;
+ calcd for C26H17O2 ([M H] ) m/z 361.12231, found 361.12178. .
249
Chapter 5 Experimental data
5.4 Appendix Compounds
I
OMe
OMe
I A1: To a solution of 1,4-diiodobenzene (2.0 g, 6.1 mmol) in dry, deoxygenated THF (20 mL) at 78 °C was added n-BuLi (2.5 M in hexanes, 2.7 mL, 6.7 mmol). The mixture was stirred for 30 min at 78 °C and 1,4-naphthalenquinone (432 mg, 2.73 mmol; freshly recrystallized and vacuum dried) was added as a solid. The mixture was stirred for 1.5 h at rt and MeI (9.1 g, 4.0 mL, 64 mmol) was added. The mixture was stirred for 18 h at rt and H2O (50 mL) was added. The mixture was extracted with Et2O (3 x 50 mL) and the combined organic phases were washed with brine (100 mL), dried (Na2SO4), filtered, and the solvent removed in vacuo. The residue was plugged through a small pad of silica gel eluted with EtOAc/hexanes (1:4). After solvent removal, the product was finally recrystallized from a
CH2Cl2 solution layered with MeOH at 15 °C to afford A1 as a colorless solid (521 mg, 32%).
Mp = 187190 °C; Rf = 0.80 (CH2Cl2); IR (ATR): 3033 (w), 2935 (s), 2817 (m), 1479 (s),
1 1 1069 (s), 809 (s) cm ; H NMR (400 MHz, CDCl3): 7.56 (d, J = 8.6 Hz, 4H), 7.387.34 (m, 2H), 7.327.28 (m, 2H) 7.02 (d, J = 8.6 Hz, 2H), 6.06 (s, 2H), 3.15 (s, 6H). 13C NMR (100
MHz, CDCl3): 145.6, 137.6, 137.2, 133.6, 128.5, 128.4, 128.0, 93.1, 76.8, 51.6; APPI + HRMS calcd for C24H20I2O2 (M ) m/z 593.95472, found 593.95405. A crystal suitable for X-ray crystallography was grown by slow evaporation of a solution of
A1 in CH2Cl2 layered with MeOH at 4 °C for several days. X-ray crystallographic data for
A1: C24H20O2I2, Fw = 594.20; triclinic space group P1; crystal dimensions 0.3 × 0.3 × 0.1 mm3; = 0.7107 Å; a = 6.7733(2) Å, b = 8.0729(3) Å, c = 20.9417(4) Å; = 81.544(2)°, =
3 –3 –1 82.668(2)° = 71.246(2)°; V = 1068.56(5) Å ; Z = 2; (calcd) = 1.847 g cm ; = 2.960 mm ;
T = 173.15 K; 2 max = 55.1°; total data collected = 8978; R1 = 0.0316 [3704 observed
250
Chapter 5 Experimental data
2 2 reflections with Fo 2(Fo )]; wR2 = 0.0795 for 255 variables and 4825 unique reflections; largest difference, peak and hole = 0.506 and –1.142 e Å–3.
A2:
Compound 2.4 (491 mg, 1.00 mmol), methyld3lithium (stabilized with lithium iodide, 0.5 M
in THF, 6.0 mL, 3.0 mmol), SnCl2 2H2O (677 mg, 3.00 mmol), and 10% aq H2SO4 (1 mL) were used according to General Procedure G. After aqueous workup, purification was achieved by column chromatography (silica gel, hexanes/CH2Cl2 3:1) and then recrystallization from a concentrated CH2Cl2 solution layered with MeOH to provide pentacene A2 as a deep blue solid (233 mg, 49%).
Mp = 242244 °C; Rf = 0.88 (CH2Cl2/hexanes 1:1); UV-vis (CH2Cl2) max (): 268 (18 200), 298 (121 000), 310 (205 000), 353 (7 500), 586 (8 500), 621 (10 500) nm. Fluorescence
(CH2Cl2, exc = 615 nm): max, em = 666 nm; IR (ATR): 3042 (w), 2940 (s), 2862 (s), 2122 (s),
1 1 1461 (s), 873 (s), 719 (s) cm ; H NMR (400 MHz, CDCl3): 9.34 (s, 2H), 8.91 (s, 2H),
13 7.997.93 (m, 4H), 7.407.35 (m, 4H), 1.391.37 (m, 21H). C NMR (75 MHz, CDCl3): 131.7, 131.3, 130.9, 130.4, 128.6, 128.1, 127.5, 125.7, 125.4, 124.9, 123.5, 115.1, 105.2,
103.9, 19.0, 11.7 (one signal coincident or not observed); ESI HRMS calcd for C34H33D3Si (M+) m/z 475.27746, found 475.27850. A crystal suitable for X-ray crystallographic analysis has been grown by slowly evaporation of a CH2Cl2 solution at rt. X-ray data for A2: C34H36Si, Fw = 472.72; monoclinic crystal
3 system, space group P21/c; crystal size = 0.21 x 0.14 x 0.11 mm ; = 1.5418 Å; a =
14.7279(2) Å, b = 24.0124(3) Å, c = 7.50787(13) Å; 92.2845(15)°; V = 2653.06(7) Å3; Z
3 1 = 4; (calcd) = 1.183 g/cm ; 2max = 151.76°; = 0.912 mm ; T = 173 K; total data collected =
2 2 14692; R1 = 0.0631 [5473 observed reflections with F0 2(F0 )]; R2 = 0.1883 for 323
2 2 3 variables with [F0 3(F0 )]; largest difference, peak and hole = 0.799 and 0.326 eÅ .
251
Chapter 5 Experimental data
I
Si
A3: According to General Procedure E, 4,4´-diiodo-1,1´-biphenyl (1.2 g, 3.0 mmol) and 2.4 (491 mg, 1.00 mmol) in dry, deoxygenated THF (20 mL) were used, followed by reductive
aromatization using SnCl2 2H2O (677 mg, 3.00 mmol) and 10% aq H2SO4 (1 mL) in THF
(15 mL). Purification was achieved by column chromatography (silica gel, hexanes/CH2Cl2
5:1) and final recrystallization from CH2Cl2 layered with MeOH. The yield for this reaction was not determined.
Mp = 278 °C (decomp); Rf = 0.50 (hexanes/CH2Cl2 5:1); UV-vis (CH2Cl2 cast film) max: 273,
321, 413, 438, 599, 641 nm; Fluorescence (CH2Cl2, exc = 615 nm): max, em = 665 nm. IR (ATR): 3036 (m), 2940 (s), 2858 (s), 2133 (s), 1461 (s), 1377 (s), 874 (s), 738 (s) cm 1; 1H
NMR (400 MHz, CDCl3): 9.36 (s, 2H), 8.32 (s, 2H), 7.95 (d, J = 8.7 Hz, 2H), 7.917.84 (m, 4H), 7.76 (d, J = 8.6 Hz, 2H), 7.647.56 (m, 4H), 7.387.27 (m, 4H), 1.381.37 (m, 21H).
13 C NMR (75 MHz, CDCl3): 140.5, 140.2, 139.4, 138.4, 138.0, 132.1, 131.9, 131.4, 130.8, 129.0, 128.9, 128.6, 128.5, 127.1, 126.9, 126.0, 125.8, 125.4, 105.4, 93.7, 93.3, 19.0, 11.6
+ (one signal coincident or not observed); ESI HRMS calcd for C45H41ISi (M ) m/z 736.20167, found 736.20193. A crystal suitable for X-ray crystallographic analysis has been grown by slowly evaporation of a CH2Cl2 solution at 4 °C. X-ray data for A3: C45H41ISi, Fw = 736.77; monoclinic crystal
3 system, space group P21/c; crystal size = 0.26 x 0.15 x 0.091 mm ; = 0.7107 Å; a =
252
Chapter 5 Experimental data
14.2306(3) Å, b = 9.4961(2) Å, c = 27.5955(7) Å; 102.833(3)°; V = 3635.98(15) Å3; Z = 4;
3 1 (calcd) = 1.346 g/cm ; 2max = 59.44°; = 0.944 mm ; T = 174.3 K; total data collected =
2 2 29870; R1 = 0.0711 [8980 observed reflections with F0 2(F0 )]; R2 = 0.2145 for 430
2 2 3 variables with [F0 3(F0 )]; largest difference, peak and hole = 1.48 and 1.82 e Å .
O
OMe
Si
A4: To a solution of triethylsilylacetylene (0.98 g, 7.0 mmol) in dry, deoxygenated THF (15 mL) cooled to 78 °C was added n-BuLi (2.5 M in hexanes, 2.0 mL, 5.0 mmol). The solution was stirred at 78 °C for 15 min and was transferred into a suspension of 6,13-pentacenequinone (1.7 g, 5.6 mmol) via cannula. The mixture was stirred for 4 h at rt and MeI (4.0 g, 28 mmol) was added. The mixture was stirred for 18 h at rt and saturated aq
NH4Cl (30 mL) was added. The suspension was filtered and the solid was washed with THF (3 x 10 mL). The filtrate was collected into a filter flask which already contained saturated aq NH4Cl (50 mL). The mixture was extracted with CH2Cl2 (2 x 50 mL). The combined organic phases were washed with brine (70 mL), dried (Na2SO4), filtered, and the solvent was removed to provide a solid residue. This solid was dissolved in minimal amount CH2Cl2 and precipitated by the addition of hexanes. The precipitate was re-dissolved in acetone and filtered to remove insoluble impurities. The solvent was removed to yield A4 as a light orange solid (1.65 g, 71%).
Mp = 118120 °C; Rf = 0.32 (CH2Cl2/hexanes 1:1); IR (ATR): 3051 (w), 2954 (m), 2877 (m),
1 1 2166 (w), 1670 (s), 1263 (s), 726 (s) cm ; H NMR (300 MHz, CDCl3): 8.79 (s, 2H), 8.62 (s, 2H), 8.04 (d, J = 7.9 Hz, 2H), 7.94 (d, J = 8.0 Hz, 2H), 7.667.57 (m, 4H), 3.08 (s, 3H),
13 1.201.14 (m, 9H), 0.850.82 (m, 6H). C NMR (75 MHz, CDCl3): 185.0, 135.6, 134.9, 132.8, 129.7, 129.6, 129.5, 128.8, 128.3, 128.0, 127.4, 103.1, 94.1, 75.1, 52.1, 7.7, 4.4; MS
+ + LDI m/z 431 ([M OCH3] ). APPI HRMS calcd for C31H31O2Si ([M H] ) m/z 463.20878, found 463.20824.
253
Chapter 5 Experimental data
A5: To a solution of 4.6b (170 mg, 0.338 mmol) and tetrabutylammonium iodide (250 mg, 0.676 mmol) in dry, deoxygenated THF (20 mL) was added NaH (12 mg, 0.507 mmol) at rt. The solution was stirred for 5 min at rt and benzylbromide (116 mg, 0.676 mmol) was added.
The mixture was stirred for 18 h at rt and satd. aq NH4Cl (100 mL) was added. The mixture was extracted with CH2Cl2 (3 x 100 mL) and the combined organic phases were washed with brine (100 mL), dried (Na2SO4), filtered, and the solvent removed in vacuo. The residue was dissolved in minimal amount of CH2Cl2 and plugged through a short pad of silica gel, eluted with CH2Cl2, and the solvent removed in vacuo. Recrystallization from
CH2Cl2 layered with MeOH afforded A5 as a light green solid (75 mg, 37%).
Mp = 171173 °C (decomp); Rf = 0.60 (CH2Cl2); IR (ATR): 3048 (m), 2957 (m), 2218 (s),
1 1 1544 (s), 1260 (s), 844 (s), 759 (s) cm ; H NMR (400 MHz, CDCl3): 8.82 (s, 2H), 8.80 (s, 2H), 8.07 (d, J = 8.0 Hz, 2H), 8.03 (d, J = 8.0 Hz, 2H), 7.757.66 (m, 4H), 7.337.27 (m, 5H),
13 3.32 (s, 2H), 0.470.45 (m, 9H). C NMR (100 MHz, CDCl3): 163.5, 134.0, 132.4, 131.9, 131.3, 130.5, 130.0, 129.9, 129.03, 129.0, 128.87, 128.85, 128.6, 128.3, 127.9, 114.5,
+ 113.2, 102.3, 99.0, 82.1, 54.1, 53.9, 41.1, 0.3; APPI HRMS calcd for C40H28N4Si (M ) m/z
+ 592.20832, found 592.207124; calcd for C30H21N2Si ([M – C10H7N2] ) m/z 437.14740, found 437.14627.
A crystal suitable for X-ray crystallography was grown by slow evaporation of a CH2Cl2 solution of A5 layered with MeOH at 4 °C for several days. X-ray crystallographic data for
A5: C40H28N4Si, Fw = 592.75; monoclinic space group P21/c; crystal size = 0.25 × 0.12 × 0.079 mm3; = 1.5418 Å; a = 10.6142(4) Å, b = 20.2593(8) Å, c = 15.2562(6) Å; =
3 –3 –1 93.399(3)°; V = 3274.9(2) Å ; Z = 4; (calcd) = 1.202 g cm ; = 0.889 mm ; T = 173.00(10)
K; 2 max = 123.57°; total data collected = 10012; R1 = 0.0745 [3532 observed reflections
254
Chapter 5 Experimental data
2 2 with Fo 2 (Fo )]; wR2 = 0.2376 for 409 variables and 4989 unique reflections; largest difference, peak and hole = 0.78 and –0.51 e Å–3.
A6: To a solution of 4.17a (330 mg, 0.987 mmol) in acetone (15 mL) was added
N-bromosuccinimide (263 mg, 1.48 mmol) and AgNO3 (84 mg, 0.49 mmol). The solution was stirred under the protection from light for 4 h at rt. The reaction was quenched by the addition of saturated aq NH4Cl (100 mL) and was extracted with CH2Cl2 (3 x 100 mL). The combined organic phases were washed with saturated aq Na2S2O3 (100 mL), dried
(Na2SO4), filtered, and the solvent removed in vacuo. The mixture was dissolved in minimal amount of CH2Cl2 and plugged through a small pad of silica gel eluting with CH2Cl2. After solvent removal A6 was obtained as light yellow oil which solidifies upon refrigeration to a colorless solid (410 mg, quant.)
Mp = 9597°C; Rf = 0.47 (hexanes); IR (ATR): 3043 (w), 2957 (s), 2875 (m), 2203 (m),
1 1 1462 (s), 1071 (s), 825 (s) cm ; H NMR (300 MHz, CDCl3): 7.437.41 (m, 4H),
13 7.347.31 (m, 4H), 3.34 (s, 3H), 1.29 (s, 18H). C NMR (75 MHz, CDCl3): 150.5, 139.7, 126.3, 125.1, 81.6, 80.2, 52.7, 48.8, 34.5, 31.3; MS LDI m/z 355 ([M tert-Bu]+, 100), 413
+ 79 + [(M) , 20]. APPI HRMS calcd for C23H26 Br ([M OCH3] ) m/z 381.12124, found 381.12101.
5.5 References
[1] Lehnherr, D.; Murray, A. H.; McDonald, R.; Tykwinski, R. R. Angew. Chem. Int. Ed. 2010, 49, 61906194.
[2] Lehnherr, D.; McDonald, R.; Tykwinski, R. R. Org. Lett. 2008, 10, 41634166.
[3] Lehnherr, D. Ph. D. Thesis, University of Alberta, Edmonton, Canada, 2010.
255
Chapter 5 Experimental data
[4] Adam, M. Diploma Thesis, University of Erlangen-Nürnberg, Germany, 2010.
[5] Nurkkala, L. J.; Steen, R. O.; Dunne, S. J. Synthesis 2006, 8, 12951300.
[6] Hibino, S.; Kano, S.; Mochizuki, N; Sugino, E. J. Org. Chem. 1984, 49, 50065008.
[7] For the synthetic procedures for a variety of azides see: (a) Lamani, M.; Prabhu, R. K. Angew. Chem. Int. Ed. 2010, 49, 66226625. (b) Nagarjuna, B.; Yurt, S.; Jadhav, K. G.; Venkatamaran, D. Macromolecules 2010, 43, 80458050. (c) Díez-Gonzáles, S.; Nolan, S. P. Angew. Chem. Int. Ed. 2008, 47, 88818884. (d) Li, S.-G.; Hu, X.-Q.; Jia, Z.-X.; Xu, P.-F. Tetrahedron 2010, 66, 85578561. (e) Ito, S.; Satoh, A.; Nagatomi, Y.; Hirata, Y.; Suzuki, G.; Kimura, T.; Satow, A.; Maehara, S.; Hikichi, H.; Hata, M.; Kawamoto, H.; Ohta, H. Biorg. Med. Chem. 2008, 16, 98179829. (f) Ramírez-Lopéz, P.; de la Torre, M. C.; Montenegro, H. E.; Asenjo, M.; Sierra, M. A. Org. Lett. 2008, 10, 35553558. (g) Song, Y.; Kohlmeir, E. K.; Meade, T. J. J. Am. Chem. Soc. 2008, 130, 66626663.
[8] Zhu, L.; Al-Kaysi, R. O.; Dillon, R. J.; Tham, F. S.; Bardeen, C. J. Cryst. Growth Des. 2011, 11, 49754983.
[9] Okamoto, T.; Jiang, Y.; Qu, F.; Mayer, A. C.; Parmer, J. E.; McGehee, M. D.; Bao, Z. Macromolecules 2008, 41, 6977–6980.
[10] Li, Z.; Lim, Y.-F.; Kim, J. B.; Parkin, S. R.; Loo, Y.-L.; Malliaras, G. G.; Anthony, J. E. Chem. Comm., 2011, 47, 76177619.
[11] Weber, S. G.; Loos, C.; Rominger, F.; Straub, B. F. ARKIVOC 2012, (iii), 226242.
[12] Yasuda, M.; Haga, M.; Baba, A. Organomettalics 2009, 28, 19982000.
[13] Dohi, S.; Moriyama, K.; Togo, H. Tetrahedron 2012, 68, 65576564.
256
Spectral data
Chapter 6 – Spectral data – NMR data of selected compounds
1 H NMR of 2.7a (300 MHz, CDCl3, + = hexanes, # = grease).
257
Spectral data
13 C NMR of 2.7a (75 MHz, CDCl3,).
258
Spectral data
1 H NMR of 2.7b (300 MHz, CDCl3, + = hexanes, # = grease).
259
Spectral data
13 C NMR of 2.7b (75 MHz, CDCl3, # = grease).
260
Spectral data
1 H NMR of 2.7c (300 MHz, CDCl3, # = grease).
261
Spectral data
13 C NMR of 2.7c (75 MHz, CDCl3, # = grease). 262
Spectral data
1 H NMR of 2.7d (300 MHz, CDCl3). 263
Spectral data
13 C NMR of 2.7d (75 MHz, CDCl3, # = grease).
264
Spectral data
1 H NMR of 2.7e (400 MHz, CDCl3, 0 = CH2Cl2, # = grease).
265
Spectral data
13 C NMR of 2.7e (100 MHz, CDCl3, 0 = CH2Cl2).
266
Spectral data
1 H NMR of 2.7f(400 MHz, CDCl3, + = hexanes, # = grease). 267
Spectral data
13 C NMR of 2.7f (100 MHz, CDCl3, # = grease).
268
Spectral data
1 H NMR of 2.7g (400 MHz, CDCl3). 269
Spectral data
13 C NMR of 2.7g (75 MHz, CDCl3, # = grease).
270
Spectral data
1 H NMR of 2.7h (300 MHz, CDCl3, # = grease).
271
Spectral data
13 C NMR of 2.7h (75 MHz, CDCl3, # = grease).
272
Spectral data
1 H NMR of 2.11 (300 MHz, CDCl3).
273
Spectral data
13 C NMR of 2.11 (75 MHz, CDCl3). 274
Spectral data
1 H NMR of 2.12 (300 MHz, CDCl3, 0 = CH2Cl2, # = grease).
275
Spectral data
13 C NMR of 2.12 (75 MHz, CDCl3).
276
Spectral data
1 H NMR of 2.13 (300 MHz, CDCl3, # = grease, + = hexanes). 277
Spectral data
13 C NMR of 2.13 (126 MHz, CDCl3).
278
Spectral data
1 H NMR of 2.21a (300 MHz, CDCl3, rt). 279
Spectral data
13 C NMR of 2.21a (100 MHz, CDCl3, rt). 280
Spectral data
1 H NMR of 2.21b (300 MHz, CDCl3, rt).
281
Spectral data
13 C NMR of 2.21b (100 MHz, CDCl3, rt).
282
Spectral data
1 H NMR of 2.21c (300 MHz, CDCl3, rt).
283
Spectral data
13 C NMR of 2.21c (100 MHz, CDCl3, rt).
284
Spectral data
1 H NMR of 2.21d (300 MHz, CDCl3, rt). 285
Spectral data
13 C NMR of 2.21d (75 MHz, CDCl3, rt).
286
Spectral data
1 H NMR of 2.21e (400 MHz, CDCl3, rt).
287
Spectral data
13 C NMR of 2.21e(100 MHz, CDCl3, rt).
288
Spectral data
1 H NMR of 2.21f (400 MHz, CDCl3, rt). 289
Spectral data
13 C NMR of 2.21f (100 MHz, CDCl3, rt).
290
Spectral data
1 H NMR of 2.21g (300 MHz, CDCl3, rt).
291
Spectral data
13 C NMR of 2.21g (100 MHz, CDCl3, rt).
292
Spectral data
1 H NMR of 2.21h (300 MHz, CDCl3, rt).
293
Spectral data
13 C NMR of 2.21h (75 MHz, CDCl3, rt).
294
Spectral data
1 H NMR of 2.21i (300 MHz, CDCl3, rt). 295
Spectral data
13 C NMR of 2.21i (100 MHz, CDCl3, rt). 296
Spectral data
1 H NMR of 2.21j ((300 MHz, CDCl3, rt, + = silicon grease).
297
Spectral data
13 C NMR of 2.21j (75 MHz, CDCl3, rt, + = silicon grease).
298
Spectral data
1 H NMR of 2.21k ((300 MHz, CDCl3, rt, * = CH2Cl2;+ = silicon grease) 299
Spectral data
13 C NMR of 2.21k ((75 MHz, CDCl3, rt, + = silicon grease).
300
Spectral data
1 H NMR of 2.21l (300 MHz, CDCl3, rt).
301
Spectral data
13 C NMR of 2.21l (100 MHz, CDCl3, rt). 302
Spectral data
1 H NMR of 2.32a (300 MHz, CDCl3, rt).
303
Spectral data
13 C NMR of 2.32a (100 MHz, CDCl3, rt).
304
Spectral data
1 H NMR of 2.32b (300 MHz, CDCl3, rt).
305
Spectral data
13 C NMR of 2.32b (75 MHz, CDCl3, rt).
306
Spectral data
1 H NMR of 2.32c (300 MHz, CDCl3, rt). 307
Spectral data
13 C NMR of 2.32c (75 MHz, CDCl3, rt).
308
Spectral data
1 H NMR of 2.33 (400 MHz, CDCl3, rt). 309
Spectral data
13 C NMR of 2.33 (75 MHz, CDCl3, rt).
310
Spectral data
1 H NMR of 2.34 (400 MHz, CDCl3, rt). 311
Spectral data
13 C NMR of 2.34 (100 MHz, CDCl3, rt).
312
Spectral data
1 H NMR of 2.35a (300 MHz, CDCl3, rt).
313
Spectral data
13 C NMR of 2.35a (100 MHz, CDCl3, rt).
314
Spectral data
1 H NMR of 2.35b (300 MHz, CDCl3, rt). 315
Spectral data
13 C NMR of 2.35b (100 MHz, CDCl3, rt). 316
Spectral data
1 H NMR of syn3.5a (300 MHz, CDCl3, rt).
317
Spectral data
13 C NMR of syn3.5a (75 MHz, CDCl3, rt). 318
Spectral data
1 H NMR of syn3.6a (300 MHz, CDCl3, rt).
319
Spectral data
13 C NMR of syn3.6a (75 MHz, CDCl3, rt). 320
Spectral data
19 F NMR of syn3.6a (282 MHz, CDCl3, rt).
321
Spectral data
1 H NMR of syn3.6b (300 MHz, CDCl3, rt).
322
Spectral data
13 C NMR of syn3.6b (75 MHz, CDCl3, rt).
323
Spectral data
19 F NMR of syn3.6b (282 MHz, CDCl3, rt).
324
Spectral data
1 H NMR of syn3.6c (300 MHz, CDCl3, rt).
325
Spectral data
13 C NMR of syn3.6c (75 MHz, CDCl3, rt).
326
Spectral data
19 F NMR of syn3.6c (282 MHz, CDCl3, rt). 327
Spectral data
1 H NMR of syn3.23a (300 MHz, CDCl3, rt).
328
Spectral data
19 F NMR of syn3.23a (282 MHz, CDCl3, rt). 329
Spectral data
1 H NMR of syn3.23b (300 MHz, CDCl3, rt).
330
Spectral data
19 F NMR of syn3.23b (282 MHz, CDCl3, rt). 331
Spectral data
1 H NMR of 4.5 (300 MHz, CDCl3, rt).
332
Spectral data
13 C NMR of 4.5 (75 MHz, CDCl3, rt).
333
Spectral data
1 H NMR of 4.6b (300 MHz, CDCl3, rt).
334
Spectral data
13 C NMR of 4.6b (75 MHz, CDCl3, rt).
335
Spectral data
1 H NMR of 4.6e (300 MHz, CDCl3/DMSO-d6, rt).
336
Spectral data
13 C NMR of 4.6e (75 MHz, CDCl3/DMSO-d6, rt).
337
Spectral data
1 H NMR of 4.9 (300 MHz, CDCl3, rt).
338
Spectral data
1 H NMR of 4.9 (300 MHz, CDCl3, rt).
339
Spectral data
1 H NMR of 4.13 (300 MHz, CDCl3, rt, # = grease).
340
Spectral data
13 C NMR of 4.13 (75 MHz, CDCl3, rt).
341
Spectral data
1 H NMR of 4.19a (300 MHz, CDCl3, rt).
342
Spectral data
13 C NMR of 4.19a (75 MHz, CDCl3, rt).
343
Spectral data
1 H NMR of 4.20a (400 MHz, CDCl3, rt).
344
Spectral data
13 C NMR of 4.20a (100 MHz, CDCl3, rt).
345