Polycyclic Aromatic Hydrocarbons with Corannulene Subunits

Automated Template C: Created by James Nail 2011V2.01

Polycyclic aromatic hydrocarbons with corannulene subunits

Michael Yanney

A Dissertation Submitted to the Faculty of Mississippi State University in Partial Fulfillment of the Requirements for the Degree of Doctor of Philosophy in Chemistry in the Department of Chemistry

Mississippi State, Mississippi

May 2013

Michael Yanney

2013

Polycyclic aromatic hydrocarbons with corannulene subunits

Michael Yanney

Approved:

______Andrzej Sygula Dongmao Zhang Professor of Chemistry Assistant Professor of Chemistry (Director of Dissertation) (Committee Member)

______William P. Henry Keith T. Mead Associate Professor of Chemistry Professor of Chemistry (Committee Member) (Committee Member)

______Stephen C. Foster R. Gregory Dunaway Associate Professor and Graduate Professor and Interim Dean Coordinator of Chemistry College of Arts & Sciences (Committee Member)

Name: Michael Yanney

Date of Degree: May 11, 2013

Institution: Mississippi State University

Major Field: Chemistry

Major Professor: Andrzej Sygula

Title of Study: Polycyclic aromatic hydrocarbons with corannulene subunits

Pages in Study: 106

Candidate for Degree of Doctor of Philosophy

The study of polycyclic aromatic hydrocarbons (PAHs) with curved surfaces, also known as buckybowls or fullerene fragments, represent an area which is under intense investigation by organic chemists and material scientists. This dissertation describes research that contributes to this field. The availability of multi-gram quantities of the smallest buckybowl, corannulene, has led to the synthesis of several larger systems with buckybowl subunits.

Cyclotrimerization of corannulyne using palladium(0) as the catalyst is described.

The resulting product, C60H24, is a highly nonplanar hydrocarbon with very interesting conformational dynamics. The X-ray crystallography of the cyclotrimer confirms the

“twist” conformation with C1 symmetry. The cyclotrimer also shows three distinct corannulene bowls with very different inversion barriers as confirmed by both experiment and calculations. The bowl to bowl inversion of the corannulene bowl with the lowest inversion barrier results in pseudorotation of the cyclotrimer, which gives rise to a symmetrized 1H NMR spectrum exhibiting 12 distinct proton signals. 1H NMR line shape analysis gives an estimation of the inversion barrier at 8.5 – 8.6 kcal/mol.

The tetrameric hydrocarbon C80H32 was synthesized through the Diels-Alder reaction of the cyclotrimer and 1,2-didehydrocorannulene. The six membered rings adjacent to the central ring in the cyclotrimer are activated enough to react with another corannulyne. The tetramer exhibits different conformational and optical absorption properties when compared to the cyclotrimer. The tetramer (C80H32), which is highly nonplanar and sterically congested, represents the largest fully characterized oligomer of corannulyne reported to date. This is also the first reported example of a cycloaddition reaction in which a corannulene subunit acts as a diene.

A tripodal molecular receptor (C87H54O6) with three corannulene pincers and a cyclotriveratrylene tether was synthesized. The molecular receptor was evaluated by 1H

NMR titration in toluene-d8 for its ability to bind fullerenes. The experiment demonstrates the formation of 1:1 inclusion complexes of the molecular receptor with fullerenes and provides the association constants of 1500 plus or minus 50 and 1180 plus

-1 or minus 30 M for C60 and C70, respectively.

DEDICATION

This dissertation is dedicated to my wife (Susan Yanney), parents (Mr. Stephen

Yanney and Mrs. Diana Yanney), and siblings (Juliana, Catherine, Jeremiah, and David).

ACKNOWLEDGEMENTS

First and foremost, I must acknowledge and thank the Almighty God for His protection, and blessings in my life and also for listening to my prayers. I wish to express my profound appreciation to my advisor Dr. Andrzej Sygula for all his support and guidance through my years at Mississippi State University. I have learned a lot working in your laboratory and will always be grateful. Special thanks to Mrs Renata Sygula for all her help in my experimental procedures, for faithfully ordering needed chemicals, and for maintaining the laboratory. I know you have the welfare of all Dr. Sygula’s students at heart. I also appreciate all the advice I got from you and Dr. Sygula.

To my committee members (Dr. Dongmao Zhang, Dr. William P. Henry, Dr.

Stephen C. Foster and Dr. Keith T. Mead) I say thank you for being there to guide me through my entire program. To my wife, the love of my life, the one who puts a smile on my face every day, the one whose shoulder I rest upon when life gets tough, words cannot explain how grateful I am to you. You have been there through thick and thin and always by and on my side. Thank you Susan Yanney, and know that I will also be there for you, always. Finally, to all my friends and my laboratory mates, thank you for your friendship and know that you can always count on me.

iii

TABLE OF CONTENTS

DEDICATION ...... ii

ACKNOWLEDGEMENTS ...... iii

LIST OF TABLES ...... vi

LIST OF FIGURES ...... vii

LIST OF ABBREVIATIONS AND CHEMICALS ...... xi

CHAPTER

I. INTRODUCTION ...... 1

1.1 Polycyclic Aromatic Hydrocarbons with Curved Surfaces ...... 1 1.2 Half – Century Quest for Improvement of Corannulene Synthesis ...... 3 1.3 Recent Synthetic Methods Towards Corannulene ...... 4 1.4 Corannulene-based Synthons for Large Buckybowls ...... 8

II. CYCLOTRIMERIZATION OF CORANNULYNE ...... 12

2.2 Synthesis and Characterization of Corannulyne Trimer ...... 13 2.3 Conformational Analysis of 29 ...... 15 2.4 Variable Temperature Studies...... 18 2.5 Attempted Cyclodehydrogenation of 29 ...... 22 2.6 Attempted Dimerization of Corannulyne to Biphenylene ...... 24 2.7 Conclusions ...... 24

III. SYNTHESIS OF CORANNULYNE TETRAMER: A DIELS-ALDER REACTION UTILIZING THE CORANNULENE SUBUNIT AS A DIENE...... 26

3.1 Identification of the Tetrameric Hydrocarbon C80H32 ...... 26 3.2 Synthesis of C80H32 ...... 27 3.3 Conformational Analysis of 37 ...... 30 3.4 Conclusions ...... 34

IV. SYNTHESIS AND CHARACTERIZATION OF A MOLECULAR CLIP WITH THREE CORANNULENE PINCERS ...... 35

4.2 Corannulene CTV-Clip ...... 40 4.3 Conformational Analysis of 49 ...... 44 4.4 Estimation of the Binding Constants of 49 in Toluene-d8 ...... 49 4.4.1 Estimation of the Binding Constants of 41 and 49 in Chlorobenzene-d5 ...... 50 4.4.2 Towards Possible Applications of Molecular Receptors ...... 51 4.5 Conclusions ...... 54

V. EXPERIMENTAL SECTION ...... 55

5.1 Synthesis of 29 ...... 56 5.2 Synthesis of 33 ...... 62 5.3 Synthesis of 36 ...... 64 5.4 Synthesis of 37 ...... 66 5.5 Synthesis of Bromomethylcorannulene 50 ...... 69 5.6 Synthesis of Molecular Receptor 49 ...... 69 5.7 Titration of 49 with C60 in Toluene-d8 ...... 72 5.8 Titration of 49 with C70 in Toluene-d8 ...... 74 5.9 NMR Titration of 49 in Chlorobenzene-d5 ...... 80 5.10 NMR Titration of 41 with C60 in Chlorobenzene-d5 ...... 81 5.11 NMR Titration of 41 with C70 in Chlorobenzene-d5 ...... 85 5.12 NMR Titration of 41 with PC60BM in Toluene-d8 ...... 88 5.13 Titration of 41 with C60 in Toluene-d8 ...... 95

REFERENCES ...... 100

LIST OF TABLES

2.1 Calculated G≠s at various temperatures ...... 21

4.1 NMR chemical shifts [ppm] calculated for 52, 53, 54 and experimental values of 49 in chloroform-d...... 46

4.2 Δδ for C60@49 and C70@49 ...... 48

-1 4.3 Kassoc (M ) for the molecular clips in toluene-d8 and chlorobenzene-d5 determined by 1H NMR titrations ...... 51

1 5.1 H NMR titration data for C60@49 in toluene-d8 ...... 72

1 5.2 H NMR titration data for C70@49 in toluene-d8 ...... 75

1 5.3 H NMR titration data for C60@49 in chlorobenzene-d5 ...... 80

1 5.4 H NMR titration data for C60@41 in chlorobenzene-d5 ...... 82

1 5.5 H NMR titration data for C70@41 in chlorobenzene-d5 ...... 85

1 5.6 H NMR titration data for PC60BM@41 in toluene-d8 ...... 88

1 5.7 ( H NMR titration data for C60@41 in toluene-d8) ...... 96

LIST OF FIGURES

1.1 Structure of C60 fullerene (left) and corannulene C20H10 (right)...... 1

1.2 Bowl depth of corannulene ...... 2

1.3 First synthetic route to corannulene by Lawton and Barth ...... 3

1.4 Craig and Robin’s route to fluoranthene derivatives ...... 4

1.5 First flash vacuum pyrolysis (FVP) based synthesis of corannulene ...... 4

1.6 Siegel’s dimethylcorannulene synthesis ...... 6

1.7 Improvement in the preparation of 2 by Sygula and Siegel ...... 6

1.8 Sygula’s methods leading to the formation of the corannulene core ...... 7

1.9 Formation of corannulyne ...... 9

1.10 Synthesis of corannulenoisofuran ...... 9

1.11 Cycloaddition synthesis of compound 25 ...... 10

2.1 Cyclotrimerization of phenanthryne ...... 12

2.2 Cyclotrimerization of corannulyne ...... 13

2.3 Crystal structure showing one of the symmetry independent molecules in the unit cell...... 14

2.4 Failed synthesis of cyclotrimer 29 by Peichao Cheng ...... 15

2.5 The propeller and twist conformations of hexabenzotriphenylene ...... 16

2.6 Illustration of the exo and endo bonds in 29 ...... 17

o 2.7 Variable temperature NMR of 29 in THF-d8 (20 to -105 C) ...... 18

2.8 B97-D/TZVP optimized structures of 29T conformers with the relative energies and the transition state energies (kcal/mol) ...... 20

vii

2.9 1H NMR spectrum of 29 at 140 oC ...... 22

2.10 Calculated energies (kcal/mol) of cyclodehydrogenation of 29 to 32 with the new C-C bonds shown in red ...... 23

2.11 Attempted dimerization of corannulyne ...... 24

3.1 X-ray crystal structure of 37. Hydrogen atoms and solvating toluene molecules are omitted for clarity ...... 27

3.2 Synthesis of 37 ...... 28

3.3 Average C=C bond lengths in the rings adjacent to the central benzene ring in 29, as determined by X-ray crystallography ...... 29

1 3.4 H NMR spectrum of 37 (600 MHz, CDCl3, rt). The proton signals Ha 3 and Hb (shown in the inset) are coupled by J coupling ...... 30

3.5 MM2 optimized structures of 29 (i) and 37 (ii) showing different corannulene subunits ...... 31

3.6 Upfield shifted protons Ha and Hb of 37 ...... 31

1 1 3.7 H- H COSY of 37. (600 MHz, CDCl3 rt) ...... 32

3.8 UV/VIS absorption spectra of 29 and 37 (1.0 ×10-5 M in DCM) ...... 33

4.1 Concave and convex surfaces of corannulene...... 36

4.2 Planar and curved surface π-π interactions ...... 36

4.3 Model corannulene dimers ...... 37

4.4 Examples of buckybowls that show π-π stacking in solid state ...... 38

4.5 Synthesis of buckycatcher ...... 38

4.6 X-ray crystal structure of C60@41 as reported in ref. 100 ...... 39

4.7 Corannulene based receptors for fullerenes ...... 40

4.8 Synthesis of exTTF-CTV ...... 41

4.9 Synthesis of 49 through Williamson’s route ...... 42

4.10 Synthesis of bromomethylcorannulene using Siegel’s method ...... 42

4.11 Alternative synthetic route to bromomethylcorannulene ...... 43 viii

1 4.12 H NMR spectrum of 49, toluene-d8 (top) and chloroform-d (bottom) ...... 44

4.13 MM2 optimized structures for the three borderline conformations of 49 ...... 45

4.14 Space filling model side view of C60@52 and C60@53 ...... 47

1 4.15 H NMR titration of C70@49 in toluene-d8 ...... 48

4.16 Synthesis of PC60BM ...... 53

1 o 5.1 H NMR for 29 in CDCl3 (T = -5 C) ...... 56

13 o 5.2 C DEPTQ 135 for 29 in THF-d8 (T = -5 C) ...... 57

5.3 MALDI-TOF for 29 (TCNQ used as matrix) ...... 57

1 1 o 5.4 H- H COSY for cyclotrimer 29 at -105 C in THF-d8 ...... 58

1 o 5.5 H NMR spectrum for 29 at -105 C in THF-d8 ...... 58

5.6 1H NMR chemical shifts in ppm (up: PBE1PBE/6-61G*, down: B97- D/TZVP) for 29. The numbers in red (experimental COSY at -105 oC) ...... 59

5.7 gNMR simulation for the four protons Ha-Hd ...... 60

1 5.8 H NMR spectrum for 33 in CDCl3 ...... 63

5.9 MALDI-TOF spectrum for 33 (TCNQ used as matrix)...... 63

1 5.10 H NMR spectrum for 36 in CDCl3 ...... 64

13 5.11 C DEPTQ135 spectrum for 36 in CDCl3 ...... 65

5.12 GC-MS for 36 ...... 65

1 5.13 H NMR spectrum for corannulyne tetramer (37) in CDCl3 ...... 67

5.14 MALDI-TOF spectrum for corannulyne tetramer 37 (TCNQ used as matrix) ...... 67

5.15 13C DEPTQ 135 spectrum for corannulyne tetramer 37 ...... 68

5.16 Theoretically calculated 1H NMR chemical shifts in 37 using PBE1/PBE and 6-31G* basis set on B97-D/TZVP optimized geometry ...... 68

13 5.17 C DEPTQ 135 spectrum for 49 in CDCl3 ...... 70

1 5.18 H NMR spectrum for 49 in CDCl3 at different concentrations at room temperature ...... 71

1 5.19 Aromatic region spectra for C60@49 from H NMR titration in toluene-d8 ...... 71

5.20 Changes of the chemical shifts for protons d and OMe as a function of [C70] in toluene-d8 ...... 78

5.21 Changes of the chemical shifts for protons d and OMe as a function of [C60] in touluene-d8 ...... 78

5.22 Job’s plots for protons d (left) and OMe (right) of the titration of 49 with C60 ...... 79

5.23 Job’s plots for protons d (left) and OMe (right) of the titration of 49 with C70 ...... 79

5.24 Changes of the chemical shifts for protons A and B as a function of [C60] in chlorobenzene-d5 ...... 84

5.25 Changes of the chemical shifts for protons A and B as a function of [C70] in chlorobenzene-d5 ...... 87

5.26 Job’s plots for protons A (left) and B (right) of the titration of 41 with PC60BM in toluene-d8 ...... 93

5.27 Job’s plots for protons C (left) and D (right) of the titration of 41 with PC60BM in toluene-d8 ...... 93

5.28 Changes of the chemical shifts for protons A and B as a function of [PC60BM] ...... 94

5.29 Changes of the chemical shifts for protons C and D as a function of [PC60BM] ...... 94

5.30 Job’s plots for protons A (left) and B (right) of the titration of 41 with C60 in toluene-d8 ...... 99

5.31 Job’s plots for protons C (left) and D (right) of the titration of 41 with C60 in toluene-d8 ...... 99

LIST OF ABBREVIATIONS AND CHEMICALS

AcOH Acetic acid

AIBN Azobisisobutyronitrile

AlBr3 Aluminum bromide

AlMe3 Trimethylaluminum anh Anhydrous

B3LYP Becke, three-parameter, Lee-Yang-Parr

B97-D DFT method (Grimme's functional including dispersion) BPO Benzoylperoxide

Br2 Bromine bs Broad singlet oC Degree celsius cc-PVQZ Correlation-Consistent Polarized Valence Quadruple-Zeta CDCl3 Deuterated chloroform

C6D5Cl Deuterated chlorobenzene

C7D8 Deuterated toluene

(COCl)2 Oxalyl chloride

COSY Correlation Spectroscopy

CTV Cyclotriveratrylene

CuCl2 Copper chloride d doublet dd Doublet of doublet

DCM Dichloromethane

DFT Density Functional Theory

DDQ 2,3-Dichcloro-5,6-dicyano benzoquinone

∆E Energy change ex-TTF Extended tetrathiafulvalene

FVP Flash Vacuum Pyrolysis

G Gibbs free energy h Hours

H2SO4 Sulfuric acid

HCOOH Formic acid

HMDS Hexamethyldisilazane

HOMO Highest Occupied Molecular Orbital hv Light mediated

(i-Pr)2NH Diisopropylamine

IUPAC International Union of Pure and Applied Chemistry J Coupling constant

K kelvin k Rate constant

Ka = Kassoc Association constant

xii

KOH Potassium hydroxide

LiAlH4 Lithium aluminum hydride

LUMO Lowest Unoccupied Molecular Orbital

LTMP Lithium 2,2,6,6-tetramethylpiperidide m Multiplet

MALDI Matrix Assisted Laser Desorption Ionization

MeCN Acetonitrile

Mg Magnesium

MM2 Molecular Mechanics

NaOH Sodium hydroxide

NaOMe Sodium methoxide

NBS N-Bromosuccinimide n-BuLi n-Butyllithium

Ni(dppp)Cl2 Bis(diphenylphosphino)propane nickel(II) chloride NMR Nuclear Magnesium Resonance

PAH Polyaromatic Hydrocarbon

Pd2(dba)3 Tris(dibenzylideneacetone)dipalladium(0)

Pd/C Palladium on carbon rt Room temperature

S Entropy s Singlet

TCNQ Tetracyanoquinodimethane

xiii

TD Time dependent

Tf Trifluoromethanesulfonate

THF Tetrahydrofuran

THP Tetrahydropyranyl

TiCl3 Titanium trichloride

TMS Trimethylsilyl

TOF Time of flight

TZVP Triple-Zeta Valence Polarization

TS Transition state v/v Volume by volume

xiv

CHAPTER I

INTRODUCTION

1.1 Polycyclic Aromatic Hydrocarbons with Curved Surfaces

The study of polycyclic aromatic hydrocarbons (PAHs) with curved surfaces, also known as buckybowls or fullerene fragments represent an area which is under vigorous investigation by organic chemists and material scientists. The curvature of buckybowls can be explained by Euler’s theorem which states that a network of fused hexagons will assume a curved surface with the introduction of at least one pentagonal unit. When the number of pentagons reaches twelve, a spherical surface is formed.1 Similarly, buckybowls have curved surfaces due to the strain induced by the presence of a five membered ring embedded in a network of six membered rings.

The smallest buckybowl which can be recognized on the convex surface of buckminsterfullerene (buckyball) 1 is corannulene 2, a member of the family of circulenes, with the IUPAC name of dibenzo[ghi,mno]fluoranthene.

1 2

Figure 1.1 Structure of C60 fullerene (left) and corannulene C20H10 (right) 1

Corannulene 2 is bowl shaped, as confirmed by its X-ray crystal structure. It has a bowl depth of 0.87 Å, defined as the distance between the plane of the ten rim carbon atoms from the plane of the central five membered ring.2, 3

(0.87 Å)

Figure 1.2 Bowl depth of corannulene

Interest in buckybowls escalated after the discovery of fullerenes4 which sparked unprecedented research activity in a number of areas which include nanoscience,5-9 polymer science10-12 and medicinal fields.13-16Although fullerenes are readily formed by arc discharge using graphite electrodes17 and the combustion of hydrocarbons,18 their

“wet” syntheses have been elusive. The only chemical synthesis of C60 (1) is a very

19 strenuous and low yield route reported by Scott and de Meijere in 2002. In this context buckybowls are of importance since they can be regarded as the model systems for fullerenes and may eventually lead to their rational synthesis. Also, with the anticipated broader industrial applications of fullerenes, researchers may soon have to deal with their fragments; it is therefore imperative to conduct more research on buckybowls. In contrast to buckyballs, buckybowls have both the concave and the convex surfaces available for reactions and complexation. The complexation abilities of buckybowls could therefore be employed in separation science and material science.

1.2 Half – Century Quest for Improvement of Corannulene Synthesis

The first synthesis of corannulene (C20H10, 2) was reported in 1966 by Lawton and Barth.20, 21 The synthesis took seventeen steps starting with acenaphthene (3) (Figure

1.3). Compound 4 (3-carbomethoxy-4H-cyclopenta[def]phenanthrene) which has four rings of 2 in the “right” positions, had earlier been synthesized by Sieglitz and Schildo.22

Barth and Lawton took advantage of the fact that compound 4 was two rings away from the target compound and prepared 2 from 4 in twelve synthetic steps.

CO2CH3 5 steps 12 steps

2 3 4

Figure 1.3 First synthetic route to corannulene by Lawton and Barth20

The resulting overall yield of the above synthesis was very low (less than 1 %).

Since this synthetic route is very labor intensive with low yield, new routes were sought.

Some failed attempts to improve the synthesis of 2 were reported.23-25 It is however worth mentioning that even though Craig and Robin’s route23 to 2 failed, their synthesis which made use of the reactive diene 5 through the Diels-Alder reaction with norbornadiene (6), introduced an efficient means of preparing fluoranthene derivatives which have four rings of 2 in the “right” positions. This method is still used by many researchers (Figure 1.4).

O O O O O EtO OEt EtO OEt 6

5 7 Figure 1.4 Craig and Robin’s route to fluoranthene derivatives23

1.3 Recent Synthetic Methods Towards Corannulene

A few years after the discovery of fullerenes, Scott’s group made a breakthrough by providing a convenient route using flash vacuum pyrolysis (FVP) for the synthesis of corannulene (Figure 1.5).26 The ring closure failures23, 25 in the earlier attempts to synthesize 2 are presumably due to the high transition state (TS) energies involved in forcing the planar (strainless) starting materials into the bowl shaped (strained) products.

By contrast, the high temperature conditions (about 1100 oC) used in FVP provides enough thermal energy to overcome the high activation barrier. Also, the competing intermolecular side reactions leading to polymerization of starting materials are minimized since FVP reactions occur in the gas phase.26

H H FVP

1000oC

2 8 10 % Figure 1.5 First flash vacuum pyrolysis (FVP) based synthesis of corannulene26

Siegel’s27 and Zimmermann’s28 groups followed with alternate pathways to 2, also using FVP in the final step of their syntheses. Milligram quantities of 2 became available, leading to more detailed studies on corannulene including the first experimentally determined bowl to bowl inversion barrier (ΔG≠ = 10.2 ± 0.2 kcal/mol) in corannulenyl-dimethylcarbinol.29

Even though the FVP based preparation of 2 was an improvement over the earlier synthetic routes it also had several shortcomings. As stated by Scott’s group, the FVP

“yields of 20-30% range are not uncommon, and higher yields are rare”.30 In addition, the yields decrease dramatically for the formation of larger systems due to the low volatility of precursors.31 Also, the high temperature used in the process leads to the decomposition of most of the functional groups which limits the scope of the FVP-based synthetic routes.

Solution phase synthesis seemed more practical. In 1996, Siegel’s group32 prepared 2,5-dimethylcorannulene (9) through “wet” synthesis by closing the flanks of

(1,6 –bis(bromomethyl)-7,10-bis(1-bromoethyl)-fluoranthene (10). This was the first successful solution phase synthesis of the corannulene system after Barth and Lawton’s route. Low valent titanium was used to prepare tetrahydrodimethylcorannulene (11) from compound 10, followed by aromatization using DDQ to give 9 in a modest combined yield of 18 %.

H3CBrHC CHBrCH3 TiCl3 , LiAlH4 DDQ BrH C 2 CH2Br

10 11 9 18 % Figure 1.6 Siegel’s dimethylcorannulene synthesis32

Later, Sygula33 and Siegel34, 35 independently used the octabromide 12 in the presence of vanadium (0) or titanium (0), respectively, to improve the yield of 2 by avoiding the aromatization step used in the previous synthesis (Figure 1.7).

Br HC CHBr 2 2 Ti(0) or V(0) Br HC 2 CHBr2

12 2

70-80 % Figure 1.7 Improvement in the preparation of 2 by Sygula and Siegel

In 2001, a more convenient and cost effective preparation of 2 was introduced by

Sygula et al.36 Refluxing octabromide 12 for fifteen minutes in the presence of aqueous sodium hydroxide in dioxane gave 1,2,5,6-tetrabromocorannulene 13, with yields greater than 80 % (Figure 1.8a). This allowed multi-gram scale synthesis of corannulene as well as other buckybowls and is presently being used as the means of forming the corannulene core by most laboratories. Nickel powder was also found to be effective in forming the

core structure of corannulene through intramolecular coupling of the bromomethyl and dibromethyl groups in 14 , followed by debromination to give 15 (Figure 1.8b).37

Br Br Br2HC CHBr2 NaOH a) Dioxane/water Br HC Br Br 2 CHBr2

12 13 83 %

MeO2C CO2Me MeO2C CO2Me

BrH C CH Br b) 2 2 Ni Powder o Br HC DMF, 60 C 2 CHBr2

14 15 60 % Figure 1.8 Sygula’s methods leading to the formation of the corannulene core36, 37

Despite the improvements in corannulene synthesis, the long and tedious synthetic route involving toxic solvents and low yields of some of the steps still make it an arduous task to accomplish. Currently, the price of corannulene from TCI America is

$ 190 for 20 mg (11/22/2012).38 Sigma Aldrich and Alfa-Aesar, two of the leading companies that sell research chemicals in the United States, do not sell corannulene as of now.

In 2012, Siegel’s research group optimized the existing synthesis of corannulene.

The improved synthesis which made use of less toxic solvents, and avoided

chromatographic purifications was cost effective and also greener.39 For over half a century the synthesis of corannulene has been improved from milligram to gram scale, and subsequently, from gram to kilogram scale. However, more research is required to improve the overall yield, reduce reaction time for some of the steps, and also to reduce the number of the synthetic steps involved.40

1.4 Corannulene-based Synthons for Large Buckybowls

Several derivatives of corannulene have been synthesized using both FVP and solution phase synthesis.30, 41, 42 The versatility of two of such derivatives introduced by our research group needs to be mentioned here. The first is 2-trimethylsilylcorannulenyl trifluoromethanesulfonate (16), an efficient benzyne precursor generating 1,2- didehydrocorannulene (17) in the presence of fluoride ions under mild conditions.43

Synthesis of 16 is shown in Figure 1.9. Compound 17 acts as a reactive dienophile and readily combines with dienes in cycloaddition reactions to generate larger systems.43

Before the synthesis of 16, 1,2- didehydrocorannulene was generated from bromocorannulene (18) with sodium amide and potassium tert-butoxide.44 However, the harsh conditions employed in this procedure limited the scope of the reaction.

Br OMe OMe NaOMe, CuCl2 NBS,(i-Pr)2NH 60 % 96 % Br

18 19 20

OH OTMS OTf HBr/aq HMDS 1.n-BuLi 2. Tf O Br Br 2 TMS

21 22 16 39 % from 20

NaNH Br 2 t-BuOK

18 17 Figure 1.9 Formation of corannulyne43, 44

Another versatile derivative of corannulene is corannulenoisofuran (23 ), which serves as a reactive diene to react with dienophiles in the Diels- Alder reactions to form larger PAHs with corannulene subunits.45 Compound 23 was synthesized from 24 (a furan adduct of corannulyne) as shown in Figure 1.10.

N NN N O O 94 %

24 23 Figure 1.10 Synthesis of corannulenoisofuran45

Compounds 16 and 23, being reactive dienophile and diene, readily undergo a cycloaddition reaction to give compound 25 with a high yield of 96 % (Figure 1.11).43

Earlier attempts to synthesize 25 from benzyne generated from 18 failed. This demonstrates the versatility of 16 over 18 in acting as a benzyne precursor.

OTf CsF O O TMS 96 %

16 23 25 Figure 1.11 Cycloaddition synthesis of compound 2543

The improved synthetic methods described above have made available multi- gram quantities of 2 in our laboratory, (It is important to note that 2 can be used as a starting material for more complicated systems) which has led to the synthesis of several larger systems with buckybowl subunits.42

This dissertation makes use of some of the synthons described in the Introduction to prepare larger curved surface PAHs with more than two corannulene subunits.

Chapter 2 reports the palladium catalyzed cyclotrimerization of corannulyne using synthon 16. The resulting product (C60H24) exhibits interesting conformational dynamics.

Chapter 3 describes the synthesis of a tetrameric hydrocarbon C80H32, which represents the largest fully characterized oligomer of corannulyne to date. It also represents the first example of the corannulene subunit acting as a diene in the Diels-

Alder reaction.

The final Chapter 4 focuses on the synthesis of a molecular receptor for fullerenes with three corannulene units as pincers and a cyclotriveratrylene (CTV)-derivative as the tether. The affinity of the resulting tridental molecular clip towards both C60 and C70 was evaluated by 1H NMR titration method.

CHAPTER II

CYCLOTRIMERIZATION OF CORANNULYNE

[2+2+2] cyclotrimerization reaction of acetylenes is an efficient tool for the synthesis of substituted benzenes.46 Smaller unsubstituted as well as substituted PAHs have been prepared through [2+2+2] transition metal mediated synthesis.47-50 The first transition metal catalyzed cyclotrimerization of alkynes was reported by Reppe et al. as early as in 1948.51 Triphenylenes have also been prepared by this approach through palladium catalyzed cyclotrimerization of benzynes (1,2-didehydrobenzenes).47 Even sterically hindered PAHs can be prepared, as demonstrated by the synthesis of hexabenzotriphenylene (26), synthesized more recently from 10- trimethylsilylphenanthryl 9-trifluoromethanesulfonate (27) with a good yield of 39 %

(Figure 2.1).48

OTf Pd2(dba)3

CsF TMS

27 28 26 Figure 2.1 Cyclotrimerization of phenanthryne48

The successful synthesis of various cyclotrimerized products from their aryne precursors using palladium(0) prompted us to attempt the cyclotrimerization of corannulyne.

2.2 Synthesis and Characterization of Corannulyne Trimer

Following the synthetic route in Figure 2.2, cyclotrimer 29 (C60H24 hydrocarbon) was prepared in good yields of 40-45 % using palladium(0) as the catalyst and cesium fluoride as the source of fluoride ions.52

OTf Pd2(dba)3 CsF TMS

16 17 29 Figure 2.2 Cyclotrimerization of corannulyne52

The MALDI-TOF of the product showed the expected mass of the corannulyne

+ 13 1 trimer (m/z 744.1) corresponding to the molecular ion C60H24 . Both the C and H

NMR spectra of compound 29 at room temperature exhibited broad signals, complicating the structure determination of the product. The final evidence for the structure of 29 was provided by the X-ray structure determination showing a racemic mixture of two symmetry independent molecules of C1 symmetry in the unit cell. Three different corannulene bowls were observed in the crystal structure of 29, the “up-down” bowl

labeled A, the “up-up” bowl labeled B and the “down-down” bowl labeled C (Figure

2.3).

Figure 2.3 Crystal structure showing one of the symmetry independent molecules in the unit cell52

The unsuccessful synthesis of compound 29 had been reported by Peichao Cheng following the route shown in Figure 2.4.53 The synthesis failed presumably due to the failure to generate corannulyne 17 from bromocorannulene 18.

Br LTMP THP 1. Diels-Alder 2. [O]

18 17 29 30 Figure 2.4 Failed synthesis of cyclotrimer 29 by Peichao Cheng53

2.3 Conformational Analysis of 29

Compound 29 falls into a group of overcrowded PAHs formally with the idealized

D3h symmetry. However, the steric congestion in these compounds usually lowers the symmetry. Two borderline conformations are observed for such systems, i.e. the propeller and the twist conformers (Figure 2.5). The propeller-type conformations adopt the “up-down”, “up-down”, “up-down” orientations of the three rim subunits while the twist type conformers adopt the form with “up-down”, “up-up”, “down-down” orientations of the three formally identical subunits.54

down down

up up up down

down up down down

up up

Propeller "D3" Twist "C2" Figure 2.5 The propeller and twist conformations of hexabenzotriphenylene54

The bowl-shape of corannulene subunits combined with their low inversion barriers complicate the conformational analysis of the cyclotrimer 29 even further, leading to a large number of possible conformations. However, MM2 calculations predict the twist conformer of 29 observed in the X-ray crystal structure to be strongly preferred over other possible conformers. Higher level calculations done at B97-D/cc-

PVDZ//B97-D/TZVP level predict C3 propeller conformer of 29 to be less stable than the twist conformer by 12.3 kcal/mol.52 In contrast, the simpler analog, hexabenzotriphenylene (26), prefers the D3 propeller conformer as predicted by theory and found by experiment.54, 55

A study of the crystal structures and computational analysis of substituted triphenylenes led Pascal to propose a simple “rule of thumb” for the overcrowded “D3h”

PAHs. His prediction of the preferred conformer centered on the aromaticity of the central benzene ring. According to the rule, the propeller conformation is usually adopted by the overcrowded PAHs with more aromatic central ring (with less bond

length alternation) while the twist conformation are usually adopted by PAHs with less- aromatic central rings.54 Analysis of the X-ray crystal structures of the cyclotrimer 29 shows no significant bond length alternation of the endo and exo bonds in the central ring. Averaged bond lengths of the six symmetry independent bonds of the enantiomeric pair in the X-ray unit cell of the endo and exo bonds are 1.437 and 1.435 Å, respective ly.

According to Pascal’s rule, the lack of bond alternation in 29 should prefer the propeller conformation but instead the twist conformer is found to be significantly more stable by both experiment and calculations. This finding indicates the limited scope of Pascal’s rule.

up-up

endo F exo

E H G up-down down-down

Figure 2.6 Illustration of the exo and endo bonds in 29

2.4 Variable Temperature Studies

The conformational kinetics of 29 was studied using variable temperature NMR spectroscopy (Figure 2.7).

o 52 Figure 2.7 Variable temperature NMR of 29 in THF-d8 (20 to -105 C)

Significant reversible changes were observed in the 1H NMR of 29. The broad signals observed at room temperature begin to sharpen upon cooling and, at about 0 oC, the spectrum shows 12 proton signals. The C1 symmetry 29 should give 24 distinct proton signals. The symmetrized spectrum at 0 oC indicates a fast dynamic process which averages the protons in 29. A look at Figure 2.7 indicates that even at -50 oC this dynamic process is still fast on the NMR time scale. Could the inversion barrier of any of

the corannulene bowls (A, B or C) of 29 be responsible for the fast chemical exchange leading to the symmetrized spectrum of 29? The inversion barriers of the three corannulene bowls A, B and C (Figure 2.3) were calculated at the B97-D/cc-PVQZ//B97-

D/TZVP level.52 Interestingly, very different inversion barriers were found for each corannulene bowl. While the inversion of bowl B or bowl C leads to the conversion of

29T to their diestereomeric counterparts 29TB and 29TC with inversion barriers of 13.8 and 17.3 kcal/mol respectively, the flipping of bowl A (with the inversion barrier of only

8.4 kcal/mol) results in the pseudorotation of the cyclotrimer 29 (Figure8 2. ). This inversion barrier is significantly lower than the inversion barrier in corannulene which is about 11 kcal/mol.29, 56-58 The 12 distinct proton signals observed between 0 and -50 oC rather than 24 can therefore be attributed to the pseudorotation process in 29 caused by the “up-down” bowl inversion. The low barrier inversion of bowl A causes the site exchange between the related protons in the upper half and lower half of bowl A, as well as the exchange between the protons of bowl B and bowl C, simplifying the1H NMR spectrum of 29 to 12 protons.

Figure 2.8 B97-D/TZVP optimized structures of 29T conformers with the relative energies and the transition state energies (kcal/mol)52

Upon further cooling the spectrum’s signals broaden over a wide temperature range (between -65 to about -95 oC). At -100 oC, the signals begin to re-emerge and at

-105 oC when most of the chemical exchange processes are slow, all 24 proton signals of

29 could be accounted for, as expected for the C1 symmetry of the molecule. Even at

-105 oC the signals were still broad, and we could not go to lower temperatures because of the technical limitations of the NMR spectrometer.

Because the signals of 29 were broad over a wide temperature range (-65 to about

-95 oC), it was impossible to determine the inversion barrier of bowl A from the coalescence temperature, therefore a line shape analysis was conducted using the gNMR59 program to extract kinetic data from the NMR spectra. The estimated ΔG≠ from the line shape analysis were essentially constant over the studied temperature range of 0 to -105 oC (Table 2.1). This implies that ΔS≠ for the inversion Gibbs energy of bowl A is near zero, in accord with the previously reported results of the inversion studies of related

60, 61 ≠ systems. As a result, the experimentally determined ΔG T values are quite close to the calculated inversion barrier of bowl A.

Table 2.1 Calculated G≠s at various temperatures52

T [K] 68 173 178 243 253 263 273

k [s-1] 6 60 115 125,000 230,000 450,000 800,000

≠ G T [kcal/mol] 8.5 8.5 8.6 8.5 8.5 8.5 8.6

When the cyclotrimer 29 was heated to 140 oC (Figure 2.9), where the dynamic processes are expected to be very fast, the broad room temperature 1H NMR signals were simplified into three set of signals, i.e. two sets of doublets (six protons each) at 8.85 (3J

= 8.8 Hz) and 7.86 (3J = 8.8 Hz) ppm, and a singlet at 7.94 ppm (twelve protons). The spectrum of 29 at 140 oC is consistent with a fast chemical exchange of protons related by

the ideal “D3h” symmetry through the higher barrier conformational changes (e.g. twist to twist or twist to propeller conversions).

Figure 2.9 1H NMR spectrum of 29 at 140 oC52

2.5 Attempted Cyclodehydrogenation of 29

The oxidative cyclodehydrogenation of 29 through Scholl chemistry62-66 or

Mallory’s oxidative photochemical cyclization67-69 could lead to the giant bowl 32 shown in Figure 2.10. Compound 33 was easily synthesized by treating 29 with iodine in refluxing chloroform with the irradiation of a sun lamp (120 W) for two hours. Leaving the reaction for longer time (over ten hours) did not lead to 34 or 32. Other oxidative reagents such as FeCl3 and DDQ were used, but still failed to force further cyclodehydrogenation. Different equivalents (1, 3, 6 and 18) of FeCl3 dissolved in a 1:1 mixture of dry dichloromethane and nitromethane were used for the reaction. Both cyclotrimer 29 and compound 33 were employed as starting materials for the reaction but neither resulted in the formation of the desired product 34 or 32. Similarly, the use of three equivalents of DDQ in a mixture of dichloromethane and methane sulfonic acid

(9:1) resulted in the generation of unidentifiable products. 22

Figure 2.10 Calculated energies (kcal/mol) of cyclodehydrogenation of 29 to 32 with the new C-C bonds shown in red

Accordingly, theoretical calculations done at the B97- D/QZVP//B97-D/TZVP level predict the first step of the oxidative cyclodehydrogenation (29 to 33) to be exothermic with ∆E = -7.8 kcal/mol, while the following two steps appear to be endothermic (33 to 34 and 34 to 32 with ∆E = 6 and 2.3 kcal/mol respectively). This shows that while the first ring closure may be relatively easy to accomplish, the second and third ring closures would require processes with significantly higher TSs.

2.6 Attempted Dimerization of Corannulyne to Biphenylene

Biphenylenes (benzyne dimers) are often formed in benzyne reactions as side products.70 However, we failed in our attempt to dimerize corannulyne 17 generated from

2-trimethylsilylcorannulenyl trifluoromethanesulfonate (16). The reaction was attempted by dissolving the benzyne precursor 16 and CsF in a mixture of 1:2 dichloromethane and acetonitrile. It led to the formation of fluorocorannulene 36 instead of the desired compound 35. Compound 36 possibly resulted from a nucleophilic attack of fluoride ion on 17 (Figure 2.11).

2+2 OTf 35 CsF

TMS F F 16 17

36 Figure 2.11 Attempted dimerization of corannulyne

2.7 Conclusions

Cyclotrimerization of corannulyne 17 using palladium(0) as a catalyst resulted in the formation of the cyclotrimer 29, which is highly nonplanar and exhibits very interesting stereochemistry and conformational dynamics. The three corannulene subunits which are formally identical in the idealized C3 or D 3h symmetry show very 24

different bowl to bowl inversion barriers. Attempted cyclodehydrogenation of 29 to 32 was not successful; we were able to prepare compound 33 using Mallory’s oxidative photochemical cyclization. The attempted dimerization of 1,2-didehydrocorannulene

(17) failed but led to the formation of fluorocorannulene (36). Compound 29 can also serve as starting material for the synthesis of even larger buckybowls, as demonstrated in the next chapter where 29 is used as a diene in the Diels-Alder cycloaddition reaction.

CHAPTER III

SYNTHESIS OF CORANNULYNE TETRAMER: A DIELS-ALDER REACTION

UTILIZING THE CORANNULENE SUBUNIT AS A DIENE

3.1 Identification of the Tetrameric Hydrocarbon C80H32

The Diels-Alder reaction is one of the most useful synthetic ways of building larger molecules through the formation of new six-membered rings.71-78 In this chapter the Diels-Alder reaction is used to synthesize the tetrameric hydrocarbon C80H32 (37) from the cyclotrimer 29. In Chapter 2 the synthesis of the hydrocarbon (29) through palladium catalyzed cyclotrimerization of corannulyne was descibed.52 In the process of purifying 29 a minor red-orange side product 37 (ca. 5 % of the total yield) was isolated from the reaction mixture. Compounds 29 and 37 had very similar retention times on

TLC with most organic solvents, so earlier attempts to separate them by column chromatography failed. Column chromatography separation of small portions of the

29/37 mixture was finally achieved with cyclohexane and DCM (9:1). On a larger scale

37 was separated from 29 by recrystallization from toluene. MALDI-TOF of the side product showed a mass of 992.1 m/z, corresponding to four corannulyne units fused together with the molecular formula of C80H32. The structure of the tetramer was difficult to determine by 1H / 13C NMR due to the complicated spectra. The final structure of 37 was confirmed by X-ray determination of a single crystal of 37 grown by slow evaporation of toluene/ethanol solution (Figure 3.1). 26

From the crystal structure, 37 is a product of the cycloaddition of 29 with 1,2- didehydrocorannulene resulting from the attack of 17 on one of the six membered rings adjacent to the central ring of the cyclotrimer 29. To test this hypothesis the synthesis of compound 37 was attempted.

Figure 3.1 X-ray crystal structure of 37. Hydrogen atoms and solvating toluene molecules are omitted for clarity79

3.2 Synthesis of C80H32

Treatment of the cyclotrimer 29 with one equivalent of 1,2-didehydrocorannulene

(17) generated from 2-trimethylsilcorannulenyl triflate (16) results in the formation of 37 with good yield of 65-70 %. This cycloaddition was achieved under mild conditions (two hours stirring of reactants in the presence of CsF, Figure 3.2).

OTf

TMS 16

CsF

4+2 65-70% DCM rt, 2 h

29 17 37

no reaction

2 Figure 3.2 Synthesis of 3779

Even though cycloaddition of 17 to 29 readily occurs, under similar conditions the cycloaddition product of 17 with corannulene 2 was not detected. Similarly, the simpler analog o-benzyne does not react with corannulene even though o-benzynes are known to add to naphthalene and anthracene to give 9,10-dihydro, 9,10–ethanoanthracene and

9,10-dihydro, 9,10[1’,2’]benzenoanthracene, respectively.80, 81 Most of the reported reactions of corannulene have been rim functionalization reactions.30, 41, 42 Very few reactions of corannulene involves the loss of its C=C bonds.82-85 To the best of our knowledge, corannulene has not been employed as a diene in a Diels-Alder reaction. A computational study done at the B3LYP/6-31G* level on the potential of corannulene acting as a diene or dienophile in the Diels-Alder reaction with ethylene and 1,3- butadiene identified corannulene as being a better dienophile than a diene. However, the

Gibbs free activation energy calculated at 298 K for the cycloaddition of corannulene to 28

ethylene as compared to the unactivated 1,3-butadiene/ethylene pair shows the former to be higher by about 15 kcal/mol.86 This indicates the very limited reactivity of corannulene as a diene in Diels-Alder reactions. By contrast, compound 29 readily undergoes cycloaddition to give 37. This is the first reported experimental evidence of a corannulene subunit acting as a diene in the Diels-Alder reaction. The regioselectivity of the cycloaddition shows that some benzene rings in 29 are activated enough to undergo the reaction. The X-ray crystal structure shows that the benzene rings adjacent to the central ring in 29 are significantly distorted in comparison with corannulene. Significant changes in bond lengths and distortions of the torsional angles of the six membered rings adjacent to the central ring in 29 make them activated enough to react as a diene with corannulyne (Figure 3.3).

Figure 3.3 Average C=C bond lengths in the rings adjacent to the central benzene ring in 29, as determined by X-ray crystallography 29

3.3 Conformational Analysis of 37

The tetramer 37, which is highly nonplanar and sterically congested, exhibits a sharp 1H NMR spectrum in which all the 32 protons can be identified (Figure 3.4). This is in contrast to 29 which shows broad 1H NMR signals at room temperature.

1 Figure 3.4 H NMR spectrum of 37 (600 MHz, CDCl3, rt). The proton signals Ha and 3 79 Hb (shown in the inset) are coupled by J coupling

Apparently, the presence of the fourth corannulene subunit D on bowl A prevents some of the higher barrier bowl- to-bowl inversion as well as the bowl “flipping” conformational changes at room temperature, leading to the sharp 1H NMR signals

(Figure 3.4). This suggests much larger inversion barriers for the tetramer.

Figure 3.5 MM2 optimized structures of 29 (i) and 37 (ii) showing different corannulene subunits

Compound 37 is soluble in most organic solvents (e.g. DCM, THF, toluene, etc.) which is quite unusual for such a large PAH. The tetrameric hydrocarbon 37 also represents the largest fully characterized oligomer of corannulyne to date. Interestingly,

3 two of the 32 protons (labeled Ha and Hb, with a coupling constant of 9.1 Hz, J, Figure

3.6) absorb unusually upfield at 1.78 and 4.36 ppm, respectively, while the rest of the signals appear in the typical aromatic range between 6 and 9 ppm.

Figure 3.6 Upfield shifted protons Ha and Hb of 37 31

This is in agreement with theoretical calculations performed at the PBE1/6-

31G//B97-D/TZVP level which predict the chemical shifts of Ha and Hb to be 1.46 and

79 4.34 ppm respectively. A closer look at the protons Ha and Hb show that they are located over the concave side of bowl B and are likely to be affected by its diamagnetic ring currents. 2D COSY NMR shown in Figure 3.8 shows that Ha and Hb are coupled to each other.

1 1 Figure 3.7 H- H COSY of 37. (600 MHz, CDCl3 rt )

Significant differences exist between the UV/Vis of 29 and 37 (Figure 3.8). The tetramer, which is red-orange in DCM, shows a broad absorption band with a relatively weak intensity in the range 460-580 nm. This feature is not observed in the UV/Vis spectrum of the cyclotrimer 29, which has a greenish-yellow color in the same solvent.

This difference is also predicted by calculations (TD DFF) which finds a lower HOMO-

LUMO gap for 37.79

Figure 3.8 UV/VIS absorption spectra of 29 and 37 (1.0 ×10-5 M in DCM)79

3.4 Conclusions

In conclusion, the Diels-Alder reaction of cyclotrimer 29 and 1,2- didehydrocorannulene 17 under mild conditions produced a large, highly nonplanar polyaromatic hydrocarbon 37, which is highly congested and exhibits a sharp 1H NMR spectrum at room temperature. This is the first reported example of a cycloaddition reaction in which a corannulene subunit acts as a diene. The resulting compound 37 also represents the largest fully characterized oligomer of corannulyne reported to date. The tetramer exhibits different conformational and optical absorption properties from the cyclotrimer 29.

CHAPTER IV

SYNTHESIS AND CHARACTERIZATION OF A MOLECULAR

CLIP WITH THREE CORANNULENE PINCERS

In host-guest chemistry, the hosts or molecular receptors are usually referred to as molecular tweezers or clips. As indicated by Harmata,87 there are no dramatic differences between the two terms in regard to their structural motifs. The term molecular tweezers was first introduced by Chen and Whitlock in 1978 when they designed molecular tweezers with caffeine pincers that bind planar π conjugated molecules.88 The authors defined the three features necessary for an efficient molecular receptor to be able to form inclusion complexes: (a) spacers should be present to prevent self-association of the pincers, (b) a proper distance should exist between the spacer and the pincers to accommodate the host, and (c) spacers should provide a preferred syn orientation of the pincers. Generally, these features have been the guiding principles in the design of molecular receptors.

Before the discovery of fullerenes almost all the reported molecular clips employed planar pincers. Interest in molecular receptors with corannulene pincers arose because the concave surface of 2 could align perfectly to the convex surface of fullerenes.

Such complementarity should provide favorable π-π interactions which can be utilized in the design of molecular receptors for fullerenes.89

Figure 4.1 Concave and convex surfaces of corannulene.

Also, with the large convex surface of fullerenes, molecular receptors with two or more corannulene pincers can be designed to encapsulate fullerenes much better than their planar analogues. Since fullerenes are good electron acceptors, complexes formed with buckybowls could be of importance in materials and separation sciences.

Figure 4.2 Planar and curved surface π-π interactions

It is interesting to speculate about the extent to which the - interactions in concave-convex systems mimic their planar analogues. Benchmark calculations done by

Sygula and Saebo on the model corannulene dimer with a concave-convex orientation revealed that the - stacking interactions of such systems are of similar magnitude to the

- interactions in the dimer with the corannulene subunits forced to be planar (Figure

4.3).90, 91 Thus, the curvature of a buckybowl does not diminish the - attractions significantly. However, part of the binding energy in the concave-convex dimer results from electrostatic dipole-dipole interactions since the bowl shaped corannulene has a significant dipole moment which is in contrast to the planar conformers.

Figure 4.3 Model corannulene dimers90, 91

It is important to mention that even though calculations predict the favorable - stacking interaction in corannulene, X-ray analysis does not reveal any stacking of the bowls in the crystal. On the other hand, cyclopentacorannulene (38),92 circumtriindene

(39)93-95 and semifullerene (40),60, 96-98 are examples of buckybowls that show π-π stacking in their X-ray crystal structures. The - stacking is therefore not a universal packing pattern in the crystal structures of buckybowls.

40 38 39 Figure 4.4 Examples of buckybowls that show π-π stacking in solid state

In addition, there is a lack of evidence for strong - interaction between corannulenes and fullerenes in solution. Therefore the conclusion was drawn that “the attractive force of the concave-convex interactions is not so significant, if at all”.99 It has become obvious that in order to increase the attractive forces in these systems, two or more corannulene pincers would have to be incorporated into the efficient molecular receptors for fullerenes. Indeed, the buckycatcher 41 which has two corannulene units as pincers arranged on a tetrabenzocyclooctatetraene tether, showed the formation of a

100 stable 1:1 inclusion complex with C60 and C70 in the solid state (Figure 4.5).

1. DCM, 60 OC O + 2. Ti (0)

23 42 41

Figure 4.5 Synthesis of buckycatcher

The buckycatcher also forms 1:1 inclusion complexes in toluene solutions as demonstrated by 1H NMR titration experiments.

The association constant (Kassoc) of C60@41 and C70@41 were reported to be 8600±500

-1 and 6800 ± 400 M , respectively, in toluene-d8, the highest so far in terms of the fullerene receptors having corannulene pincers.100

Figure 4.6 X-ray crystal structure of C60@41 as reported in ref. 100

Other corannulene based receptors for fullerenes have also been reported. For example corannulene derivatives 43, 44 and 45 were synthesized and tested for their ability to form supramolecular complexes with fullerenes.101, 102 NMR titration

-1 experiments provided the association constant for C60@45 to be 1420 ± 54 M , while the other corannulene derivatives had relatively low Kassoc values. The relatively high association constant for C60@45 was attributed to the electron donating groups in 45, which presumably interacted favorably with the electron deficient convex surface of C60.

Ar S Ar S MeO OMe S Ar S S Ar S S S S S S Ar S S

S S S S Ar = OMe 43a S S

Ar = 43b MeO OMe 44 45 Figure 4.7 Corannulene based receptors for fullerenes101, 102

4.2 Corannulene CTV-Clip

In the search for efficient molecular receptors for fullerenes, the work reported by de Mendoza and his colleagues in 2010, was reviewed. The authors used three “extended tetrathiafulv alenes” (exTTF) 46 as pincers and cyclotriveratrylene (CTV) derivative 47

103, 104 as the tether to construct the molecular receptor 48 (Figure 4.7).105

SS 46

SS 48

HO OMe DIAD, PPh O OMe MeO OH 3 MeO O OMe OH OMe O S S 47 S S S S S S S S S S

ex-TTF-CTV Figure 4.8 Synthesis of exTTF-CTV105

Inclusion complexes of exTTF-CTV with C60 and C70 resulted in very high Kassoc of 2×105 and 2×106 M-1, respectively, as demonstrated by UV-Vis titration.

Determination of the binding constants by NMR titration was not attempted due to negligible chemical shift changes upon binding with C60 or C70. The strong binding constants reported for C60@exTTF-CTV and C70@exTTF-CTV are presumably due to all the three pincers being in contact with the guest fullerene molecules.

Because of the possibility of attaching three pincers to 47 it was used as the tether, consequently, molecular receptor 49 was synthesized by reacting 47 with bromomethylcorannulene (50) through Williamson’s synthesis (Figure 4.8).106

HO OMe MeO OH OMe OH O OMe MeO O 47 OMe O Williamson Synthesis

CH2Br

50 Figure 4.9 Synthesis of 49 through Williamson’s route106

Bromomethylcorannulene had earlier been synthesized by Siegel’s group in three reaction steps (Figure 4.9).57 The combined yield for all three steps was reported to be about 20 %.107

Br Me CH2Br

Br2 AlMe3 NBS

Ni(dppp)Cl2 BPO, hv

2 18 51 50 Figure 4.10 Synthesis of bromomethylcorannulene using Siegel’s method57

Due to the low yield of the above synthesis, alternative routes to 50 were sought.

Bromomethylation of smaller aromatic compounds using paraformaldehyde in acidic media is a well known synthetic route.108-110 Although the standard bromomethylation in aqueous HBr failed with corannulene, compound 50 was obtained with 50 % yield when 42

the bromomethylation was done using anhydrous HBr in acetic acid (Figure 4.10). This is a significant synthetic improvement over the older method since it reduces the number of steps from three to one and increases the total yield.

CH2Br Paraformaldehyde anh. HBr

2 41 50 % Figure 4.11 Alternative synthetic route to bromomethylcorannulene106

The target compound 49 was then obtained in a moderate yield of 35-40 %. The

MALDI-TOF showed m/z of 1193.2 corresponding to the mass of the compound

1 (C87H54O6). Also, H NMR spectrum which represents an average spectrum of several possible conformations showed the expected number of protons upon integration (Figure

4.11). Compound 49 is quite flexible due to the free rotation of the single bonds and the low inversion barrier of the corannulene bowls. The 1H NMR spectrum of 49 was solvent dependent; when the solvent was switched from chloroform-d to toluene-d8, a significant change in chemical shift was observed for proton d of the CTV tether (Figure

4.11).

1 106 Figure 4.12 H NMR spectrum of 49, toluene-d8 (top) and chloroform-d (bottom)

4.3 Conformational Analysis of 49

A full conformational analysis of 49 is difficult due to the free rotation of single bonds and the bowl to bowl inversion of the corannulene pincers resulting in a plethora of distinct conformations. Although a full analysis has not been attempted, three interesting borderline conformations of 49 are discussed (Figure 4.12). In the first conformer, the corannulene pincers wrap around the CTV tether leading to an “onion” type conformation

52. In the second conformer, the corannulene pincers are far apart from each other and there is more free rotation leading to an “open” type conformer 53 and, finally, a “stacked conformer” 54, exhibits concave-convex π-π stacking of the corannulene pincers only.

Figure 4.13 MM2 optimized structures for the three borderline conformations of 49

MM2 energy minimization of these conformers show the stacked conformer being preferred over the other two. In solution however, the open conformers are likely to prevail due to solvent stabilization and more favorable entropic contributions to Gibbs free energy.

NMR calculations done at the B97-D/6-31G*//PBE1PBE/6-31G* level predict dramatic upfield shifts for protons a, b, c and d in the “onion” conformer 52 (Table

4.1).106 This is not consistent with the experimental NMR spectrum (Figure 4.11). This implies that the “onion” conformer 52 is not a major contributor in solution. A look at

Table 4.1 shows that the experimental chemical shifts more closely resemble those calculated for the “open” and “stacked” conformers.

Table 4.1 NMR chemical shifts [ppm] calculated for 52, 53, 54 and experimental values of 49 in chloroform-d.

Proton a b c d

49 experimental 4.7 3.5 6.7 7.1

52 0.0 -3.5 3.3 2.0

53 4.7 3.8 7.0 7.4

54 4.2 3.3 6.3 6.9

“Open” conformers like 53 will possibly have a large area of accessible concave surface of the corannulene pincers interacting with the convex surface of fullerenes leading to a strong association complex. However, several inclusion complexes of 49 with fullerenes are possible. Since attempts to obtain X-ray quality crystals of C60@49 or C70@49 have been unsuccessful, the preferred structures of the inclusion complexes are uncertain. MM2 calculations on two possible arrangements C60@52 and C 60@53 serve as examples. The optimized structures for C60@52 and C60@53 show that the gas phase binding energy of the latter is much higher (42.1 kcal/mol) than the former (14.2 kcal/mol).

Figure 4.14 Space filling model side view of C60@52 and C60@53

It can be seen from Figure 4.13 that binding with fullerenes will occur at different regions in 52 and 53. While binding is likely to take place in the cavity of the CTV tether of 52, binding in 53 will involve all the corannulene pincers. Another possible situation among many is that only two out of the three corannulene pincers are involved in the binding. For inclusion complexes to form, the binding energy involved in the complexation process must be strong enough to overcome the solvation and entropic penalties associated with the binding.

1 H NMR titration carried out by addition of C60 to 49 in toluene-d8 solution suggested that C60 and 49 were interacting with each other through binding. Changes in

NMR chemical shifts of 49 were observed upon addition of C60. Most of the chemical shift changes were downfield movement of protons on the CTV tether except for proton c and f which moved slightly upfield. Even more pronounced chemical shift changes were observed upon addition of C70 to 49 (Figure 4.14). The pattern was however similar to the effects from the titration of C60 to 49 with the exception of proton c which moves

downfield. The chemical shift changes, defined as Δ = observed- free are shown in Table

4.2.

Table 4.2 Δδ for C9 60@4 and C70@49

Proton/s OMe b a c d f

Δ (C60@49) ppm 0.131 0.021 0.021 -0.011 0.15 -0.036

Δ (C70@49) ppm 0.266 0.076 0.079 0.017 0.309 -0.088

1 Figure 4.15 H NMR titration of C70@49 in toluene-d8

4.4 Estimation of the Binding Constants of 49 in Toluene-d8

Kassoc was evaluated from the changes in chemical shifts by applying a nonlinear curve-fitting tool using the equation shown below:111

(4.1)

where

X = [Guest]total, Y= [Host]total,

L = Δ max = bound- free; that is Δ at 100 % complexation (4.2)

Ka = Kassoc= [Guest@Host] / [Guest]×[Host] (4.3)

H = × bound + (1- ) × free (4.4)

is defined as the mole fraction of the inclusion complex, which implies that

= [Guest@Host] / [Host]total (4.5)

Kassoc and L were optimized as parameters in the non-linear curve fitting tool using

Origin© (v. 8.0).112

-1 The calculated Kassoc values were 1451 ± 53 and 1551 ± 42 M for protons d and

- OMe respectively in the C60 NMR titration experiment, and 1154 ± 35 and 1214 ± 28 M

1 for the same protons in the C70 titration experiment. The average Kassoc values were

-1 -1 113 therefore 1502 ± 50M for C60@49 and 1184 ± 30 M for C70@49. Job’s plots suggest a 1:1 complex formation for both fullerene complexes.

From the relatively low Kassoc values of 49 with fullerenes as compared to that of the buckycatcher 41, it suggests that the flexibility in 49 does not allow all three

corannulene pincers to be involved in the binding process. Complexes involving all three pincers would have severe solvation and entropic penalties. On the other hand the pre- organized pincers of the buckycatcher allows for stable complex formation with less entropic penalties.

4.4.1 Estimation of the Binding Constants of 41 and 49 in Chlorobenzene-d5

The low Kassoc values obtained for C60@49 and C70@49 (1502 ± 50 and 1184 ±

-1 30 M , respectively) in toluene-d8 as compared to the very high Kassoc of 48 with

5 6 -1 fullerenes (2×10 and 2×10 M for C 60@exTTF-CTV and C 70@exTTF-CTV,

105 respectively) in chlorobenzene-d5, suggested a study of the binding abilities of molecular receptor 49 in chlorobenzene-d5 would be interesting. Molecular receptor 49

1 showed very small changes in the H NMR chemical shifts upon the addition of C60. The maximum chemical shift change was only 0.02 ppm for proton d, which prevented the determination of Kassoc by this method. As stated previously, similar effects were also

105 observed by de Mendoza et al. for their molecular clip 48 in chlorobenzene-d5.

To gain deeper insight into the solvent effects on the complexation of 49 with fullerenes, the association of buckycatcher 41 with both C60 and C70 in chlorobenzene-d5 was reexamined. Buckycatcher 41 showed moderate 1H NMR chemical shift changes upon titrating with C60 or C70, but the changes were lower than those reported in toluene- d8. The association constants obtained for C60@41 and C70@41 in chlorobenzene-d5 were 590 ± 55 and 715 ± 135 M-1 respectively, and were significantly lower than those

-1 100,114 measured in toluene-d8 (8600 ± 500 and 6800 ± 400 M ). All titration results are shown in Table 4.3. At the moment, the reason for the significant differences in 50

association constants measured in toluene-d8 and chlorobenzene-d5 are unclear. Fu rther solvent studies are being carried out using calorimetry to study the association thermodynamics of both the buckycatcher 41 and the tridental molecular receptor 49 towards fullerenes in toluene, chlorobenzene and dichlorobenzene.

-1 Table 4.3 Kassoc (M ) for the molecular clips in toluene-d8 and chlorobenzene-d5 determined by 1H NMR titrations

Toluene-d8 Chlorobenzene-d5

100 C60@41 (8600 ± 500) 590 ± 55

114 C70@41 (6800 ± 400) 715 ± 135

PC60BM@41 1940 ± 60

C60@49 1500 ± 50 Negligible chemical shift changes

C70@49 1180 ± 30

4.4.2 Towards Possible Applications of Molecular Receptors

The affinities of the buckycatcher 41 and the tridental molecular clip 49 toward fullerenes could make them attractive candidates for novel materials, including photovoltaic devices. Fullerenes and their derivatives are commonly used as electron acceptors in polymer based solar cell devices.115, 116 An important factor in the supramolecular assemblies of 41 and 49 with fullerenes is the shape complementarity. It has been recently shown that molecular shape complementarity between donors and acceptors in organic polymer solar cell devices give rise to the higher efficiency of power conversion.117 51

Other means of exploring the possible use of our molecular clips in photovoltaic devices is to immobilize them on solid supports such as gold nanoparticles and study their charge transfer response. In order to move forward with the applications of the molecular clips on solid supports, polar groups need to be introduced on either the host or the guest. Also, in performing solution studies, the solubility of the clips and fullerenes need to be taken into account. Since fullerenes are known to be insoluble in most

118 common organic solvents, the known derivative of C60 fullerene [6,6] PC60BM 55 with the IUPAC name (1-3(-(methoxycarbonyl)propyl)-1-phenyl[6,6]C61 was thought of as the likely substitute to C60 (Figure 4.15). This is because the presence of alkyl chain and the polar ester group increases the solubility of 55 in most organic solvents. In addition, the ester functional group can be easily converted into other functional groups which can act as “anchors” allowing for the attachment of the fullerene derivative to a solid support.

PC60BM was therefore used in the preliminary solution studies.

O S O O S O NH NH N O O O O O CH OH 3 NH2 O OH O H2SO4 57 59 58

O O

O O 7

55 56 118 Figure 4.16 Synthesis of PC60BM

1 H NMR titration studies show binding between the buckycatcher 41 and PC60BM

-1 55 with an association constant in toluene-d8 of 1940 ± 60 M . This is lower than Kassoc

-1 100 (8600 ± 500 M ) obtained for the buckycatcher with C60 and is probably due to the interferences in the binding process caused by the alkyl group in 55. However, the Gibbs free energy (∆G = -RTInKassoc) of binding for both complexes are similar (-5.3 and -4.5 kcal/mol for C60@41 and PC60BM@41, respectively) implying that the affinity of 41 towards both C60 and PC60BM are similar. Future studies will look at the possibility of attaching 55 to gold nanoparticles and also investigate the possible formation of molecular bilayers with the buckycatcher.

4.5 Conclusions

The tripodal molecular receptor 49 (C87H54O6) with three corannulene pincers and a cyclotriveratrylene tether was synthesized and found to be efficient for complex

1 formation with fullerenes. H NMR titration experiment carried out in toluene-d8 suggests a 1:1 complex formation for C60@49 and C70@49 with Kassoc of 1502 ± 50 and

-1 1 1180 ± 30 M , respectively. An H NMR titration studies done in chlorobenzene-d5 for

49 showed small changes in chemical shifts which prevented the determination of Kassoc for the process. A significant decrease in the Kassoc of buckycatcher 41 with both C60 and

1 C70was observed by the H NMR titration in chlorobenzene-d5 as compared to the Kassoc in toluene-d8.

A derivative of C60, PC 60BM (55) was evaluated for its binding abilities in toluene-d8 using molecular receptor 41. Future studies will investigate the possibility of attaching 55 to a solid support and the formation of bilayers with the buckycatcher.

CHAPTER V

EXPERIMENTAL SECTION

All chemicals used in the reactions were purchased from Sigma Aldrich or Alfa-

Aesar. Reaction solvents were further purified using a solvent purification system (Pure

Solv MD-3 from Innovative Technology). All the reactions were performed under inert atmosphere using either nitrogen or argon. All flash chromatographs were performed using silica gel stationary phase. 13C and 1H NMR data were recorded using 600 MHz and 300 MHz spectrometers from Bruker (AVANCE III). All chemical shifts were reported in ppm (parts per million) using the following NMR standard solvents: chloroform-d, toluene-d8, tetrahydrofuran-d8 and chlorobenzene-d5. Splitting patterns were classified as follows: singlet(s), doublet (d), triplet (t), quartet (q), multiplet (m), and doublet of doublets (dd). The coupling constants (J) are reported in Hertz (Hz). MALDI-

TOF ABI 4700 (Applied Biosystems) and GC-MS QP2010S (SHIMADZU) were used for mass determination of new compounds. The line shape analysis was done using the gNMR program (gNMR Version 5.0, IvorySoft). All Ab initio calculations were done by Dr. Sygula.

5.1 Synthesis of 29

46 mg (0.3 mmol) of finely powdered CsF was added to a solution of 48 mg (0.1 mmol) of 2-trimethylsilylcorannulenyl triflate (16) and 6 mg (6.0 µmol) of )Pd2(dba 3 in 4 mL of MeCN and 1 mL of DCM and the mixture was stirred overnight at room temperature under argon. The reaction mixture was then diluted with DCM, washed with water, dried over anhydrous MgSO4 and the solvents were removed under reduced pressure. The resulting dark residue was chromatographed over silica gel with cyclohexane/dichloromethane (95:5 v/v). The red-orange fraction was collected, the solvents were removed and the resulting red-orange solid was recrystallized from

1 o ethanol/toluene giving 10 mg (40 %) of a yellow solid. H NMR (600 MHz, CDCl3, -5

C) δ 7.48 (d, J = 8.9 Hz, 1H), 7.75-7.96 (m, 8H), 8.19 (d, J = 8.9 Hz, 1H), 8.94 (d, J = 8.8

13 o Hz, 1H), 9.04 (d, J = 8.8 Hz, 1H). C DEPT-Q135 (600 MHz, THF-d8, -5 C) δ 125.6,

126.4, 126.8, 126.9, 127.0, 127.4, 127.5, 129.5, 129.9, 130.3, 130.5, 130.9, 131.1, 131.6,

131.7, 132.1, 132.5, 133.3, 134.3, 135.2, 135.7, 136.6, 137.0, 138.9.

1 o Figure 5.1 H NMR for 29 in CDCl3 (T = -5 C)

13 o Figure 5.2 C DEPTQ 135 for 29 in THF-d8 (T = -5 C)

(M+)

Figure 5.3 MALDI-TOF for 29 (TCNQ used as matrix)

1 1 o Figure 5.4 H- H COSY for cyclotrimer 29 at -105 C in THF-d8

1 o Figure 5.5 H NMR spectrum for 29 at -105 C in THF-d8

Figure 5.6 1H NMR chemical shifts in ppm (up: PBE1PBE/6-61G*, down: B97- D/TZVP) for 29. The numbers in red (experimental COSY at -105 oC)52

The four protons Ha to Hd used for the line-shape analysis. gNMR simulations through the line shape analysis for the four protons Ha to Hd are shown below:

52 Figure 5.7 gNMR simulation for the four protons Ha-Hd

Figure 5.7 (Continued)

5.2 Synthesis of 33

In a 5 mL round bottom flask were added 5 mg of 29 (6.7 µmol) and 10.2 mg (40

µmol) of Iodine in 2 mL of CHCl3. The mixture was irradiated by sun lamp and refluxed for 2 hrs under nitrogen. The resulting mixture was cooled and washed with sodium thiosulfate. The organic layer was washed twice with water and the solvent was removed under vacuum giving 4 mg of 33 (80 % yield). 1H NMR at room temperature (600 MHz,

CDCl3, ppm) δ 7.61 (br s, 2H), 7.69 (2H), 7.84 (d, J = 8.70 Hz, 1H), 7.93 (m, 3H), 8.73

(s, 1H), 8.92 (d, J = 8.61 Hz, 1H), 9.43 (d, J = 8.50 Hz, 1H).

1 Figure 5.8 H NMR spectrum for 33 in CDCl3

45000 CT 40000 742.1 (M+)

35000

30000 743.1 25000 741.2

20000 Intensity

15000

10000

5000

0 720 740 760 780 M/Z

Figure 5.9 MALDI-TOF spectrum for 33 (TCNQ used as matrix)

5.3 Synthesis of 36

In a 5 mL round bottom flask were added 24 mg of 2-Trimethylsilylcorannulenyl

Triflate (16) (0.05 mmol), and 23 mg of cesium fluoride (0.15 mmol) in 3 mL of

MeCN/DCM (2:1 v/v). The mixture was sonicated for 3 hrs at room temperature and the solvent removed under vacuum. The resulting yellow material was chromatographed over silica gel using cyclohexane/dichloromethane (95:5 v/v). The first fraction was collected and dried under reduced pressure to give 12 mg of fluorocorannulene, 88 %

1 yield. H NMR at room temperature (600 MHz, CDCl3, ppm) δ 7.38 (d, J = 12.99 Hz,

13 1H), 7.78-7.87 (m, 5H), 7.96 (d, J = 8.81 Hz, 1H). C DEPT-Q135 (150 MHz, CDCl3, ppm) 109.99 (d, J = 24.22 Hz), 121 (d, J = 22.97 Hz), 122.51, 126.80, 126.86 (d, J =

4Hz), 127.16, 127.42, 127.67, 127.93, 128.00, 130.40, 131.22 (d, J = 3.33 Hz), 132.29 (d,

J = 9.94 Hz), 132.83, 134.93 (d, J = 3.32 Hz), 136.00, 136.34, 136.65 (d, J = 8.00 Hz),

160.08 (d, JCF = 258.58 Hz).

1 Figure 5.10 H NMR spectrum for 36 in CDCl3

13 Figure 5.11 C DEPTQ135 spectrum for 36 in CDCl3

Figure 5.12 GC-MS for 36

5.4 Synthesis of 37

6 mg (39 µmol) of finely powdered CsF was added to a solution of 5 mg (6.7

µmol) of cyclotrimer (29) and 6.2 mg (13 µmol) of 2-trimethylsilylcorannulenyl triflate

(16) in 2 ml of DCM and stirred for 2 h at room temperature under nitrogen. The reaction mixture was washed with water, more DCM was added and the organic layer was separated, dried over anhydrous MgSO4. Removal of the solvent under reduced pressure produced red-orange residue which was chromatographed over silica gel

(cyclohexane/dichloromethane, 9:1 v/v) to give 4.5 mg (67 %) of a red-orange solid.

1 H NMR (600 MHz, CDCl3, rt) δ 1.78 (d, J = 9.1 Hz, 1H), 4.36 (d, J = 9.1 Hz, 1H), 6.51 (d, J = 8.9 Hz, 1H), 6.97 (d, J = 8.9 Hz, 1H), 7.01 (d, J = 9.1 Hz, 1H), 7.03 (d, J = 9.2 Hz, 1H), 7.15 (d, J = 8.9 Hz, 1H), 7.39 (d, J = 8.9 Hz, 1H), 7.41 (d, J = 9.2 Hz, 1H), 7.54 (d, J = 8.7 Hz, 1H), 7.55 (d, J = 8.4 Hz, 1H), 7.61 (d, J = 8.5 Hz, 1H), 7.65 (d, J = 9.0 Hz, 1H), 7.68 (d, J = 8.6 Hz, 1H), 7.69 (d, J = 8.6 Hz, 1H), 7.72 (d, J = 7.9 Hz, 1H), 7.74 (d, J = 9.2 Hz, 1H), 7.76 (bs, 2H), 7.79 (d, J = 8.7 Hz, 1H), 7.83 (d, J = 9.0 Hz, 1H), 7.91 (d, J = 8.70 Hz, 1H), 7.92 (d, J = 7.9 Hz, 1H), 7.98 (d, J = 9.0 Hz, 1H), 8.04 (d, J = 8.6 Hz, 1H), 8.05 (d, J = 8.8 Hz, 1H), 8.10 (d, J = 8.6 Hz, 1H), 8.12 (d, J = 9.0 Hz, 1H), 8.15 (d, J = 8.9 Hz, 1H), 8.40 (d, J = 9.0 Hz, 1H), 8.63 (d, J = 8.7 Hz, 1H), 8.74 (d, J = 9.0 Hz, 1H). 13 C DEPT-Q135 (150 MHz, CDCl3, ppm) δ 61.21, 66.51, 121.24, 123.02, 123.99, 124.41, 125.46, 125.59, 125.81, 126.30, 126.63, 126.81, 126.84, 127.04, 127.18, 127.24, 127.55, 127.68, 127.72, 127.78, 127.80, 127.97, 128.38, 128.42, 128.55, 128.77, 128.88, 129.09, 129.23, 129.27, 129.45, 130.35, 130.57, 130.82, 130.84, 130.95, 131.19, 131.38, 131.50, 131.52, 131.53, 131.70, 131.73, 131.99, 132.36, 133.04, 133.13, 133.36, 133.80, 134.23, 134.47, 134.56, 135.16, 135.32, 135.41, 135.66, 135.75, 136.31, 136.79, 137.13, 137.19, 137.53, 137.57, 137.78, 137.98, 138.92, 140.18, 144.31, 145.34, 146.87, 155.43, 155.93.

1 79 Figure 5.13 H NMR spectrum for corannulyne tetramer (37) in CDCl3

(M+)

Figure 5.14 MALDI-TOF spectrum for corannulyne tetramer 37 (TCNQ used as matrix)79

Figure 5.15 13C DEPTQ 135 spectrum for corannulyne tetramer 3779

Figure 5.16 Theoretically calculated 1H NMR chemical shifts in 37 using PBE1/PBE and 6-31G* basis set on B97-D/TZVP optimized geometry79 68

5.5 Synthesis of Bromomethylcorannulene 50

A solution of 0.1 g (0.4 mmol) of corannulene 2 and 0.2 g (6.2 mmol) of paraformaldehyde in 4 mL of AcOH and 0.5 mL of 33 wt. % anhydrous HBr in AcOH was refluxed for 1 h on an oil bath. The reaction mixture was then cooled, 5 mL of

DCM was added and the mixture was washed three times with water. The organic layer was separated, dried with MgSO4 and the solvent was removed under reduced pressure.

The crude material was purified by triturating with methanol or by chromatography on

1 silica gel with cyclohexane to give 68 mg (50 %) of 50. H NMR (300 MHz, CDCl3):

13 5.04 (s, 2H), 7.71-7.87 (m, 8H), 8.04 (d, J = 9.0 Hz, 1H). C NMR (75 MHz, CDCl3):

31.4, 124.5, 126.9, 127.10, 127.14, 127.2, 127.48, 127.50, 127.9, 130.4, 130.5, 130.9,

131.00, 131.01, 131.2, 135.70, 135.73, 135.8, 136.0, 136.16, 136.18.

5.6 Synthesis of Molecular Receptor 49

16 mg (0.04 mmol) of 47 was added to a suspension of anhydrous 64 mg K2CO3

(12 eq) in 8 mL of acetone. 40 mg (0.12 mmol) of 50 dissolved in 2 mL of DCM was added and the mixture was refluxed overnight. The reaction was cooled to rt and diluted with water. The products were extracted with DCM and the organic layer was washed with brine, dried with MgSO4 and the solvent was removed under reduced pressure. The resulting crude material was purified by chromatography on silica gel with DCM/ cyclohexane (4:1) to give 18 mg (38 %) of colorless product. 1H NMR (600

MHz,CDCl3): 3.43 (s, 9H, OCH3), 3.52 (d, 3H, ArCH2eqAr, J = 13.9 Hz), 4.74 (d, 3H,

ArCH2axAr, J = 13.8 Hz), 5.58 (bs, 6H, CH2-Cor ), 6.72 (s, 3H, Ar-H), 7.08 (s, 3H, Ar-

13 H), 7.72-7.84 (m, 8H), 7.97 (d, 1H, J = 8.9 Hz) ; C NMR (150 MHz, CDCl3,

RT): 36.5, 55.9, 70.5, 113.7, 116.8, 124.9, 125.8, 126.9, 127.0, 127.2, 127.3, 127.4,

129.5, 130.6, 130.7, 130.8, 130.9, 131.7, 133.1, 135.5, 135.6, 135.7, 135.8, 136.0, 136.1,

147.0, 148.8

+ 1800 1193.22 (M )

1600 1194.2

1400

1200

1000

intensity 800

600

400

200

0 1186 1188 1190 1192 1194 1196 1198 1200 1202 1204 m/z MALDI-TOF spectrum for 49 (TCNQ was used as matrix)106

13 106 Figure 5.17 C DEPTQ 135 spectrum for 49 in CDCl3

1 Figure 5.18 H NMR spectrum for 49 in CDCl3 at different concentrations at room temperature

1 Figure 5.19 Aromatic region spectra for C60@49 from H NMR titration in toluene-d8

5.7 Titration of 49 with C60 in Toluene-d8

-4 2.2 mg of 49 was dissolved in 5 mL of toluene-d8 to give 3.68×10 M stock solution. 600 µL of the above solution was titrated against 20, 40, 60, 80, 100, 130, 170,

-4 230, 300, 400, 500 and 1500 µL of 9.6×10 M solution of C60 in toluene-d8 and the changes in 1H NMR spectrum was recorded after each addition. Association constant

Kassoc was estimated from the changes in chemical shifts using the non-linear curve fitting tool in Origin 8.0.

1 Table 5.1 H NMR titration data for C60@49 in toluene-d8

C60 added (µL) [49] [C60]

0 0.000368 0

20 0.000356 0.000031

40 0.000345 0.000060

60 0.000335 0.000087

80 0.000325 0.000113

100 0.000315 0.000137

130 0.000302 0.000171

170 0.000287 0.000212

230 0.000266 0.000266

300 0.000245 0.000320

400 0.000221 0.000384

500 0.000201 0.000436

1500 0.000105 0.000686

Table 5.1 (Continued)

Proton d (7.6 ppm) ∆δ of d P rotons OMe (3.2 ppm) ∆δ of OMe

7.6357 0 3.2513 0

7.6447 0.009 3.2597 0.0084

7.6536 00179 3.2674 0.0161

7.6613 0.0256 3.2741 0.0228

7.6697 0.0340 3.2814 0.0301

7.6767 0.0410 3.2876 0.0363

7.6855 0.0498 3.2954 0.0441

7.6972 0.0615 3.3054 0.0541

7.7114 0.0757 3.3181 0.0668

7.7245 0.0888 3.3294 0.0781

7.7401 0.1044 3.343 0.0917

7.7507 0.1150 3.3523 0.101

7.7936 0.1579 3.3894 0.1381

Table 5.1 (Continued)

Mole fraction (MR) MR×∆δ of d MR×∆δ Of OMe

1 0 0

0.92 0.0083 0.0077

0.85 0.0153 0.0137

0.79 0.0203 0.0181

0.74 0.0252 0.0223

0.69 0.0286 0.0253

0.64 0.0318 0.0282

0.57 0.0354 0.0311

0.50 0.0378 0.0334

0.43 0.0385 0.0339

0.37 0.0381 0.0334

0.32 0.0362 0.0318

0.13 0.0209 0.0184

5.8 Titration of 49 with C70 in Toluene-d8

-4 2.2 mg of 49 was dissolved in 5 mL of toluene-d8 to give 3.68×10 M stock solution. 500 µL of the solution was titrated against 20, 40, 60, 80, 100, 130, 170, 230,

-3 300, 400, 500, 600, 800 and 1500 µL of 1.26×10 M solution of C70 in toluene-d8 and the changes in 1H NMR spectrum was recorded after each addition. Association constant

Kassoc was estimated from the changes in chemical shifts using the non-linear curve fitting tool in Origin 8.0. 74

1 Table 5.2 H NMR titration data for C70@49 in toluene-d8

C70 added (µL) [49] [C70]

0 0.000368 0

20 0.000354 0.000048

60 0.000329 0.000135

80 0.000317 0.000174

100 0.000307 0.000210

130 0.000292 0.000260

170 0.000275 0.000320

230 0.000252 0.000397

300 0.000230 0.000473

400 0.000204 0.000560

500 0.000184 0.000630

600 0.000167 0.000687

800 0.000142 0.000775

1500 0.000092 0.000945

Table 5.2 (Continued)

Proton d (7.6 ppm) ∆δ of d Protons OMe (3.2 ppm) ∆δ of OMe

7.6357 0 3.2513 0

7.6594 0.0237 3.2719 0.0206

7.6987 0.0630 3.3063 0.0550

7.7164 0.0807 3.3215 0.0702

7.7310 0.0953 3.3341 0.0828

7.7517 0.1160 3.3521 0.1008

7.7753 0.1396 3.373 0.1217

7.8021 0.1664 3.3951 0.1438

7.8239 0.1882 3.417 0.1657

7.8521 0.2164 3.4387 0.1874

7.8718 0.2361 3.4557 0.2044

7.8854 0.2497 3.4679 0.2166

7.9068 0.2711 3.486 0.2347

7.9446 0.3089 3.5179 0.2666

Table 5.2 (Continued)

Mole fraction (MR) MR× ∆δ of d MR×∆δ of OMe

1 0 0

0.88 0.0208 0.0181

0.71 0.0447 0.0389

0.65 0.0521 0.0454

0.59 0.0566 0.0491

0.53 0.0614 0.0533

0.46 0.0645 0.0562

0.39 0.0646 0.0558

0.33 0.0616 0.0542

0.27 0.0579 0.0501

0.23 0.0534 0.0462

0.19 0.0489 0.0424

0.15 0.0418 0.0362

0.09 0.0274 0.0237

Figure 5.20 Changes of the chemical shifts for protons d and OMe as a function of [C70] in toluene-d8

Figure 5.21 Changes of the chemical shifts for protons d and OMe as a function of [C60] in touluene-d8

Figure 5.22 Job’s plots for protons d (left) and OMe (right) of the titration of 49 with C60

Figure 5.23 Job’s plots for protons d (left) and OMe (right) of the titration of 49 with C70

Mole fraction (χ) = [49] / ([49]+[ C60]) (5.1)

5.9 NMR Titration of 49 in Chlorobenzene-d5

-4 0.54 mg of 49 was dissolved in 1 mL of chlorobenzene-d5 to give 4.52×10 M stock solution. 600 µL of the solution was titrated against 20, 40, 60, 80, 100, 130, 170,

-3 230, 300, 400, 500 and 1500 µL of 2.14×10 M solution of C60 in chlorobenzene-d5 and the changes in 1H NMR spectrum was recorded after each addition. Association constant

Kassoc was estimated from the changes in chemical shifts using non-linear curve fitting tool in Origin 8.0

1 Table 5.3 H NMR titration data for C60@49 in chlorobenzene-d5

C60 added (µL) [49] [C60]

0 0.000452 0

20 0.000440 0.000069

40 0.000420 0.000134

60 0.000410 0.000195

80 0.000400 0.000252

100 0.000390 0.000305

130 0.000370 0.000381

170 0.000350 0.000472

230 0.000330 0.000593

300 0.000300 0.000713

400 0.000270 0.000856

500 0.000250 0.000973

1500 0.000130 0.001529

Table 5.3 (Continued)

Proton d (7.6 ppm) ∆δ of d Protons OMe (3.2 ppm) ∆δ of OMe

7.7413 0 3.4993 0

7.742 0.0007 3.4999 0.0006

7.7427 0.0014 3.5005 0.0012

7.7437 0.0024 3.5014 0.0021

7.7443 0.0030 3.5021 0.0028

7.7452 0.0039 3.5026 0.0033

7.7463 0.0050 3.5038 0.0045

7.7476 0.0063 3.5049 0.0056

7.7493 0.0080 3.5066 0.0073

7.7512 0.0099 3.5083 0.0090

7.7528 0.0115 3.5100 0.0107

7.7548 0.0135 3.5118 0.0125

7.7613 0.0200 3.5176 0.0183

5.10 NMR Titration of 41 with C60 in Chlorobenzene-d5

-4 0.39 mg of 41 was dissolved in 1 mL of chlorobenzene-d5 to give 5.20×10 M stock solution. 600 µL of the solution was titrated against 20, 40, 60, 80, 100, 130, 170,

-3 230, 300, 400, 500, 600 and 1500 µL of 2.91×10 M solution of C60 in chlorobenzene-d5 and the changes in 1H NMR spectrum was recorded after each addition. Association constant Kassoc was estimated from the changes in chemical shifts using non-linear curve fitting tool in Origin 8.0

1 Table 5.4 H NMR titration data for C60@41 in chlorobenzene-d5

C60 added (µL) [41] [C60]

0 0.000521 0

20 0.000500 0.000094

40 0.000490 0.000182

60 0.000470 0.000265

80 0.000460 0.000342

100 0.000450 0.000416

130 0.000430 0.000518

170 0.000410 0.000642

230 0.000380 0.000806

300 0.000350 0.000970

400 0.000310 0.001164

500 0.000280 0.001323

1500 0.000150 0.002079

Table 5.4 (Continued)

Proton A (7.8 ppm) ∆δ of A Protons B (7.6 ppm) ∆δ of B

7.8160 0 7.6127 0

7.8193 0.0033 7.6184 0.0057

7.8228 0.0068 7.6242 0.0115

7.8257 0.0097 7.6291 0.0164

7.8291 0.0131 7.6338 0.0211

7.8319 0.0159 7.6388 0.0261

7.8362 0.0202 7.6448 0.0321

7.8400 0.0240 7.6519 0.0392

7.8459 0.0299 7.6604 0.0477

7.8510 0.0350 7.6674 0.0547

7.8555 0.0395 7.675 0.0623

7.8580 0.0420 7.6778 0.0651

7.8705 0.0545 7.6967 0.0840

Figure 5.24 Changes of the chemical shifts for protons A and B as a function of [C60] in chlorobenzene-d5

5.11 NMR Titration of 41 with C70 in Chlorobenzene-d5

-3 1.0 mg of 41 was dissolved in 1 mL of chlorobenzene-d5 to give 1.34×10 M stock solution. 600 µL of the solution was titrated against 20, 40, 60, 80, 100, 130, 170,

-3 230, 300, 400, 500, 600 and 1500 µL of 2.50×10 M solution of C70 in chlorobenzene-d5 and the changes in 1H NMR spectrum was recorded after each addition. Association constant Kassoc was estimated from the changes in chemical shifts using non-linear curve fitting tool in Origin 8.0

1 Table 5.5 H NMR titration data for C70@41 in chlorobenzene-d5

C70 added (µL) [41] [C70]

0 0.001340 0

20 0.001297 0.000081

40 0.001256 0.000156

60 0.001218 0.000227

80 0.001182 0.000294

100 0.001149 0.000357

130 0.001101 0.000445

170 0.001044 0.000552

230 0.000969 0.000693

300 0.000893 0.000833

400 0.000804 0.001000

500 0.000731 0.001136

1500 0.000423 0.001711

Table 5.5 (Continued)

Proton A (7.8 ppm) ∆δ of A Protons B (7.6 ppm) ∆δ of B

7.8150 0 7.6114 0

7.8180 0.003 7.6149 0.0035

7.8209 0.0059 7.6173 0.0059

7.8244 0.0094 7.6205 0.0091

7.8272 0.0122 7.6225 0.0111

7.8297 0.0147 7.6247 0.0133

7.8330 0.018 7.6279 0.0165

7.8379 0.0229 7.6321 0.0207

7.8443 0.0293 7.6381 0.0267

7.8500 0.0350 7.6429 0.0315

7.8567 0.0417 7.6492 0.0378

7.8619 0.0469 7.6539 0.0425

7.8773 0.0623 7.6666 0.0552

Figure 5.25 Changes of the chemical shifts for protons A and B as a function of [C70] in chlorobenzene-d5

5.12 NMR Titration of 41 with PC60BM in Toluene-d8

-4 1.68 mg of 41 was dissolved in 5 mL of toluene-d8 to give 4.5×10 M stock solution. 600 µL of the above solution was titrated against 20, 40, 60, 80, 100, 130, 170,

-3 230, 300, 400, 500 and 1500 µL of 1.76×10 M solution of [6,6] PC60BM in toluene-d8 and the changes in 1H NMR spectrum was recorded after each addition. Association constant Kassoc was estimated from the changes in chemical shifts using non-linear curve fitting tool in Origin 8.0.

1 Table 5.6 H NMR titration data for PC60BM@41 in toluene-d8

PC60BM added (µL) [41] [PC60BM]

0 0.000450 0

20 0.000435 0.000057

40 0.000422 0.000110

60 0.000409 0.000160

80 0.000397 0.000207

100 0.000386 0.000251

130 0.000370 0.000313

170 0.000351 0.000388

230 0.000325 0.000488

300 0.000300 0.000587

400 0.000270 0.000704

500 0.000245 0.000800

1500 0.000129 0.001257

Table 5.6 (Continued)

Proton A (7.4 ppm) ∆δ of A Protons B (7.45 ppm) ∆δ of B

7.6404 0 7.4492 0

7.6487 0.0083 7.4530 0.0038

7.6576 0.0172 7.4593 0.0101

7.6667 0.0263 7.4644 0.0152

7.6726 0.0322 7.471 0.0218

7.6812 0.0408 7.4773 0.0281

7.6877 0.0473 7.4853 0.0361

7.6971 0.0567 7.4945 0.0453

7.7077 0.0673 7.5046 0.0554

7.7168 0.0764 7.5131 0.0639

7.7258 0.0854 7.5213 0.0721

7.7309 0.0905 7.5264 0.0772

7.7492 0.1088 7.5448 0.0956

Table 5.6 (Continued)

Proton C (7.4 ppm) ∆δ of C Protons D (7.41 ppm) ∆δ of D

7.4384 0 7.411 0

7.4405 0.0021 7.4132 0.0022

7.4429 0.0045 7.4166 0.0056

7.4476 0.0092 7.4194 0.0084

7.4521 0.0137 7.4226 0.0116

7.4563 0.0179 7.4244 0.0134

7.4599 0.0215 7.4279 0.0169

7.4643 0.0259 7.4304 0.0194

7.4695 0.0311 7.4328 0.0218

7.4749 0.0365 7.4369 0.0259

7.4795 0.0411 7.4398 0.0288

7.4824 0.0440 7.4436 0.0326

7.4923 0.0539 7.4485 0.0375

Table 5.6 (Continued)

Mole fraction (MR) MR×∆δ of A MR×∆δ of B

1 0 0

0.88 0.0073 0.0034

0.79 0.0136 0.0080

0.72 0.0189 0.0109

0.66 0.0212 0.0143

0.61 0.0247 0.0170

0.54 0.0256 0.0195

0.47 0.0269 0.0215

0.40 0.0269 0.0222

0.34 0.0258 0.0216

0.28 0.0237 0.0200

0.24 0.0212 0.0181

0.09 0.0101 0.0089

Table 5.6 (Continued)

Mole fraction (MR) MR×∆δ of C MR×∆δ of D

1 0 0

0.88 0.0019 0.0019

0.79 0.0036 0.0044

0.72 0.0066 0.0060

0.66 0.0090 0.0076

0.61 0.0108 0.0081

0.54 0.0116 0.0092

0.47 0.0123 0.0092

0.40 0.0124 0.0087

0.34 0.0123 0.0088

0.28 0.0114 0.0079

0.24 0.0103 0.0076

0.09 0.0050 0.0035

Figure 5.26 Job’s plots for protons A (left) and B (right) of the titration of 41 with PC60BM in toluene-d8

Figure 5.27 Job’s plots for protons C (left) and D (right) of the titration of 41 with PC60BM in toluene-d8

Figure 5.28 Changes of the chemical shifts for protons A and B as a function of [PC60BM]

Figure 5.29 Changes of the chemical shifts for protons C and D as a function of [PC60BM]

5.13 Titration of 41 with C60 in Toluene-d8

-4 1.32 mg of 41 was dissolved in 5 mL of toluene-d8 to give 3.53×10 M stock solution. 600 µL of the above solution was titrated against 20, 40, 60, 80, 100, 130, 170,

-3 230, 300, 400, 500 and 1500 µL of 2.51×10 M solution of C60 in toluene-d8 and the changes in 1H NMR spectrum was recorded after each addition. Association constant

Kassoc was estimated from the changes in chemical shifts using non-linear curve fitting tool in Origin 8.0. Protons used for Jobs plot (A = 7.6, B = 7.45, C = 7.44, D = 7.42 ppm).100

1 100 Table 5.7 ( H NMR titration data for C60@41 in toluene-d8)

C60 added (µL) [41] [C60]

0 0.000353 0

20 0.000342 0.000081

40 0.000331 0.000156

60 0.000321 0.000227

80 0.000311 0.000294

100 0.000303 0.000357

130 0.000290 0.000445

170 0.000275 0.000552

230 0.000255 0.000693

300 0.000235 0.000833

400 0.000212 0.001000

500 0.000193 0.001136

1500 0.000101 0.001786

Table 5.7 (Continued)

Mole fraction (MR) MR×∆δ of A MR×∆δ of B-

1 0 0

0.81 0.0144 0.0168

0.69 0.0247 0.0291

0.61 0.0299 0.0347

0.54 0.0331 0.0380

0.49 0.0346 0.0394

0.44 0.0347 0.0402

0.39 0.0341 0.0391

0.34 0.0328 0.0366

0.29 0.0294 0.0337

0.26 0.0268 0.0303

0.24 0.0251 0.0286

0.17 0.0180 0.0205

Table 5.7 (Continued)

Mole fraction (MR) MR×∆δ of C MR×∆δ of D

1 0 0.

0.81 0.0132 0.0113

0.69 0.0224 0.0190

0.61 0.0277 0.0230

0.54 0.0295 0.0249

0.49 0.0310 0.0260

0.44 0.0316 0.0265

0.39 0.0307 0.0262

0.34 0.0278 0.0235

0.29 0.0262 0.0222

0.26 0.0234 0.0198

0.24 0.0221 0.0188

0.17 0.0156 0.0132

Figure 5.30 Job’s plots for protons A (left) and B (right) of the titration of 41 with C60 in toluene-d8

Figure 5.31 Job’s plots for protons C (left) and D (right) of the titration of 41 with C60 in toluene-d8

REFERENCES

1. Beck, A.; Bleicher, M. N.; Crowe, D. W. Excursions into Mathematics; Worth: New York, 1969.

2. Hanson, J. C.; Nordman, C. E. Acta Crystallogr. Sect. B. 1976, 32, 1147-1153.

3. Petrukhina, M. A.; Andreini, K. W.; Mack, J.; Scott, L. T. J. Org. Chem. 2005, 70, 5713-5716.

4. Kroto, H. W.; Heath, J. R.; O'Brien, S. C.; Curl, R. F.; Smalley, R. E. Nature 1985, 318, 162-163.

5. Dodziuk, H.; Hara, T.; Konno, T.; Nakamura, Y.; Nishimura, J.; Boltalina, O. V.; Popov, A. A.; Strauss, S. H.; Shiroka, T.; Bilewicz, R.; Chmurski, K.; Vuorinen, T.; Iwamatsu, S.-I.; Meier, M. S.; Pereira de Freitas, R.; Nierengarten, J.-F., Fullerenes. In Strained Hydrocarbons, Wiley-VCH Verlag GmbH & Co. KGaA: 2009; pp 205-333.

6. Zhang, H. L.; Chen, W.; Huang, H.; Chen, L.; Wee, A. T. S. J. Am. Chem. Soc. 2008, 130, 2720-2721.

7. Chen, W.; Zhang, H. L.; Xu, H.; Tok, E. S.; Loh, K. P.; Wee, A. T. S. J. Phys. Chem. B. 2006, 110, 21873-21881.

8. Feng, M.; Lee, J.; Zhao, J.; Yates; Petek, H. J. Am. Chem. Soc. 2007, 129, 12394-12395.

9. , L. M. A.; Sabki, S. N.; Garfitt, J. M.; Capiod, P.; Beton, P. H. J. Phys. Chem. C. 2011, 115, 7472-7476.

10. Peng, K.-J.; Liu, Y.-L. Macromolecules 2011, 44, 5006-5012.

11. Liu, Y.-L.; Chang, Y.-H.; Chen, W.-H. Macromolecules 2008, 41, 7857-7862.

12. Ravi, P.; Wang, C.; Dai, S.; Tam, K. C. Langmuir 2006, 22, 7167-7174.

13. An, Y.-Z.; Chen, C.-H. B.; Anderson, J. L.; Sigman, D. S.; Foote, C. S.; Rubin, Y. Tetrahedron 1996, 52, 5179-5189.

100

14. Marcorin, G. L.; Da Ros, T.; Castellano, S.; Stefancich, G.; Bonin, I.; Miertus, S.; Prato, M. Org. Lett. 2000, 2, 3955-3958.

15. Friedman, S. H.; DeCamp, D. L.; Sijbesma, R. P.; Srdanov, G.; Wudl, F.; Kenyon, G. L. J. Am. Chem. Soc. 1993, 115 , 6506-6509.

16. Gharbi, N.; Pressac, M.; Hadchouel, M.; Szwarc, H.; Wilson, S. R.; Moussa, F. Nano Lett. 2005, 5, 2578-2585.

17. Kratschmer, W.; Lamb, L. D.; Fostiropoulos, K.; Huffman, D. R. Nature 1990, 347, 354-358.

18. Howard, J. B.; McKinnon, J. T.; Makarovsky, Y.; Lafleur, A. L.; Johnson, M. E. Nature 1991, 352, 139-141.

19. Scott, L. T.; Boorum, M. M.; McMahon, B. J.; Hagen, S.; Mack, J.; Blank, J.; Wegner, H.; de Meijere, A. Science 2002, 295, 1500-1503.

20. Barth, W. E.; Lawton, R. G. J. Am. Chem. Soc. 1966, 88, 380-381.

21. Lawton, R. G.; Barth, W. E. J. Am. Chem. Soc. 1971, 93, 1730-1745.

22. Sieglitz, A.; Schidlo, W. Chem. Ber. 1963, 96, 1098-1108.

23. Craig, J.; Robins, M. Aust. J. Chem. 1968, 21, 2237-2245.

24. Davy, J. R. ; Iskander, M. N.; Reiss, J. A. Tetrahedron Lett. 1978, 19, 4085- 4088.

25. Jacobson, R. H. Ph.D. Dissertation, University of California, Los Angeles, United States, California, 1986.

26. Scott, L. T.; Hashemi, M. M.; Meyer, D. T.; Warren, H. B. J. Am. Chem. Soc. 1991, 113, 7082-7084.

27. Borchardt, A.; Fuchicello, A.; Kilway, K. V.; Baldridge, K. K.; Siegel, J. S. J. Am. Chem. Soc. 1992, 114, 1921-1923.

28. Zimmermann, G.; Nuechter, U.; Hagen, S.; Nuechter, M. Tetrahedron Lett. 1994, 35, 4747-4750.

29. Scott, L. T.; Hashemi, M. M.; Bratcher, M. S. J. Am. Chem. Soc. 1992, 114, 1920-1921.

30. Tsefrikas, V. M.; Scott, L. T. Chem. Rev. 2006, 106, 4868-4884.

101

31. Liu, C. Z.; Rabideau, P. W. Tetrahedron Lett. 1996, 37, 3437-3440.

32. Seiders, T. J.; Baldridge, K. K.; Siegel, J. S. J. Am. Chem. Soc. 1996, 118, 2754-2755.

33. Sygula, A.; Rabideau, P. W. J. Am. Chem. Soc. 1999, 121, 7800-7803.

34. Seiders, T. J.; Elliott, E. L.; Grube, G. H.; Siegel, J. S. J. Am. Chem. Soc. 1999, 121, 7804-7813.

35. Seiders, T. J.; Baldridge, K. K.; Elliott, E. L.; Grube, G. H.; Siegel, J. S. J. Am. Chem. Soc. 1999, 121, 7439-7440.

36. Sygula, A.; Xu, G.; Marcinow, Z.; Rabideau, P. W. Tetrahedron 2001, 57, 3637-3644.

37. Sygula, A.; Karlen, S. D.; Sygula, R.; Rabideau, P. W. Org. Lett. 2002, 4, 3135-3137.

38. http://www.tcichemicals.com/eshop/en/us/commodity/C2572/ (11/22/2012).

39. Butterfield, A. M.; Gilomen, B.; Siegel, J. S. Org. Process Res. Dev. 2012, 16, 664-676.

40. Borman, A. Chem. Eng. News 2012, 90, 49.

41. Wu, Y.-T.; Siegel, J. S. Chem. Rev. 2006, 106, 4843-4867.

42. Sygula, A. Eur. J. Org. Chem. 2011, 9, 1611-1625.

43. Sygula, A.; Sygula, R.; Kobryn, L. Org. Lett. 2008, 10, 3927-3929.

44. Sygula, A.; Sygula, R.; Rabideau, P. W. Org. Lett. 2005, 7, 4999-5001.

45. Sygula, A.; Sygula, R.; Rabideau, P. W. Org. Lett. 2006, 8, 5909-5911.

46. Saito, S.; Yamamoto, Y. Chem. Rev. 2000, 100, 2901-2916.

47. Peña, D.; Escudero, S.; Pérez, D.; Guitián, E.; Castedo, L. Angew. Chem. Int. Ed. 1998, 37, 2659-2661.

48. Peña, D.; Pérez, D.; Guitián, E.; Castedo, L. Org. Lett. 1999, 1, 1555-1557.

49. Peña, D.; Pérez, D.; Guitián, E.; Castedo, L. J. Am. Chem. Soc. 1999, 121, 5827-5828.

102

50. Romero, C.; Peña, D.; Pérez, D.; Guitián, E. J. Org. Chem.2008, 73, 7996- 8000.

51. Reppe, V.W.; Schweckendeik, W.J. Justus Liebigs Ann. Chem. 1948, 560, 104-116.

52. Yanney, M.; Fronczek, F. R.; Henry, W. P.; Beard, D. J.; Sygula, A. Eur. J. Org. Chem. 2011, 33, 6636-6639.

53. Cheng, P. Ph.D. Dissertation, Boston College, United States, Massachusetts, 1996.

54. Barnett, L.; Ho, D. M.; Baldridge, K. K.; Pascal, R. A. J. Am. Chem. Soc 1999, 121, 727-733.

55. Peña, D.; Cobas, A. n.; Pérez, D.; Guitián, E.; Castedo, L. Org. Lett. 2000, 2, 1629-1632.

56. Sygula, A.; Abdourazak, A. H.; Rabideau, P. W. J. Am. Chem. Soc. 1996, 118, 339-343.

57. Seiders, T. J.; Baldridge, K. K.; Grube, G. H.; Siegel, J. S. J. Am. Chem. Soc. 2001, 123, 517-525.

58. Grube, G. H.; Elliott, E. L.; Steffens, R. J.; Jones, C. S.; Baldridge, K. K.; Siegel, J. S. Org. Lett. 2003, 5, 713-716.

59. Van Bramer, S. Concepts in Magnetic Resonance 1998, 10, 195-196.

60. Abdourazak, A. H.; Marcinow, Z.; Sygula, A.; Sygula, R.; Rabideau, P. W. J. Am. Chem. Soc. 1995, 117, 6410-6411.

61. Marcinow, Z.; Sygula, A.; Ellern, A.; Rabideau, P. W. Org. Lett. 2001, 3, 3527-3529.

62. Scholl, R.; Mansfeld, J. Ber. Dtsch. Chem. Ges. 1910, 43, 1734-1746.

63. Wu, J.; Tomović, Ž.; Enkelmann, V.; Müllen, K. J. Org. Chem. 2004, 69, 5179-5186.

64. Boden, N.; Bushby, R. J.; Headdock, G.; Lozman, O. R.; Wood, A. Liq. Cryst. 2001, 28, 139-144.

65. Simpson, C. D.; Mattersteig, G.; Martin, K.; Gherghel, L.; Bauer, R. E.; Räder, H. J.; Müllen, K. J. Am. Chem. Soc. 2004, 126, 3139-3147.

103

66. Navale, T. S.; Thakur, K.; Rathore, R. Org. Lett. 2011, 13, 1634-1637.

67. Mallory, F. B.; Wood, C. S.; Gordon, J. T. J. Am. Chem. Soc. 1964, 86, 3094- 3102.

68. Wood, C. S.; Mallory, F. B. J. Org. Chem. 1964, 29, 3373-3377.

69. Jørgensen, K. B. Molecules 2010, 15, 4334-4358.

70. Beltrán-Rodil, S.; Peña, D.; Guitián, E. Synlett 2007, 2007, 1308-1310.

71. Diels, O.; Alder, K. Justus Liebigs Ann. Chem. 1928, 460, 98-122.

72. Nicolaou, K. C.; Snyder, S. A.; Montagnon, T.; Vassilikogiannakis, G., Angew. Chem. Int. Ed. 2002, 41, 1668-1698.

73. Takao, K.-i.; Munakata, R.; Tadano, K.-i. Chem. Rev. 2005, 105, 4779-4807.

74. Reymond, S. b.; Cossy, J. Chem. Rev. 2008, 108, 5359-5406.

75. Winkler, J. D. Chem. Rev. 1996, 96, 167-176.

76. Fort, E. H.; Donovan, P. M.; Scott, L. T. J. Am. Chem. Soc. 2009, 131, 16006- 16007.

77. Fort, E. H.; Scott, L. T. Angew. Chem. Int. Ed. 2010, 49, 6626-6628.

78. Li, J.; Jiao, C.; Huang, K.-W.; Wu, J. Chemistry – Chem. Eur. J. 2011, 17, 14672-14680.

79. Yanney, M.; Fronczek, F. R.; Sygula, A. Org. Lett. 2012, 14, 4942-4945.

80. Rabideau, P. W. Org. Prep. Proced. Int. 1986, 18, 113-16.

81. Kitamura, T.; Yamane, M.; Inoue, K.; Todaka, M.; Fukatsu, N.; Meng, Z.; Fujiwara, Y. J. Am. Chem. Soc. 1999, 121 , 11674-11679.

82. Zabula, A. V.; Dubceac, C.; Filatov, A. S.; Petrukhina, M. A. J. Org. Chem. 2011, 76, 9572-9576.

83. Sygula, A.; Sygula, R.; Fronczek, F. R.; Rabideau, P. W. J. Org. Chem. 2002, 67, 6487-6492.

84. Preda, D. V.; Scott, L. T. Tetrahedron Lett. 2000, 41, 9633-9637.

104

85. Zabula, A. V.; Spisak, S. N.; Filatov, A. S.; Rogachev, A. Y.; Petrukhina, M. A. Angew. Chem. Int. Ed. 2011, 50, 2971-2974.

86. Jayapal, P.; Sundararajan, M.; Rajaraman, G.; Venuvanalingam, P.; Kalagi, R.; Gadre, S. R. J. Phys. Org. Chem. 2008, 21, 146-154.

87. Harmata, M. Acc. Chem. Res. 2004, 37, 862-873.

88. Chen, C. W.; Whitlock, H. W. J. Am. Chem. Soc. 1978, 100, 4921-4922.

89. Perez, E. M.; Martin, N. Chem. Soc. Rev. 2008, 37, 1512-1519.

90. Sygula, A.; Saebø, S. Int. J. Quantum Chem. 2009, 109, 65-72.

91. Janowski, T.; Pulay, P.; Sasith Karunarathna, A. A.; Sygula, A.; Saebø¸ S. Chem. Phys. Lett. 2011, 512, 155-160.

92. Sygula, A.; Folsom, H. E.; Sygula, R.; Abdourazak, A. H.; Marcinow, Z.; Fronczek, F. R.; Rabideau, P. W. J. Chem. Soc., Chem. Commun. 1994, 22, 2571-2572.

93. Scott, L. T.; Bratcher, M. S.; Hagen, S. J. Am. Chem. Soc. 1996, 118, 8743- 8744.

94. Ansems, R. B. M.; Scott, L. T. J. Am. Chem. Soc. 2000, 122, 2719-2724.

95. Forkey, D. M.; Attar, S.; Noll, B. C.; Koerner, R.; Olmstead, M. M.; Balch, A. L. J. Am. Chem. Soc. 1997, 119, 5766-5767.

96. Mehta, G.; Panda, G.; Srirama Sarma, P. V. V. Tetrahedron Lett. 1998, 39, 5835-5836.

97. Hagen, S.; Bratcher, M. S.; Erickson, M. S.; Zimmermann, G.; Scott, L. T. Angew. Chem. Int. Ed. 1997, 36, 406-408.

98. Petrukhina, M. A.; Andreini, K. W.; Peng, L.; Scott, L. T. Angew. Chem. Int. Ed. 2004, 43, 5477-5481.

99. Kawase, T.; Kurata, H. Chem. Rev. 2006, 106, 5250-5273.

100. Sygula, A.; Fronczek, F. R.; Sygula, R.; Rabideau, P. W.; Olmstead, M. M. J. Am. Chem. Soc. 2007, 129, 3842-3843.

101. Mizyed, S.; Georghiou, P. E.; Bancu, M.; Cuadra, B.; Rai, A. K.; Cheng, P.; Scott, L. T. J. Am. Chem. Soc. 2001, 123, 12770-12774.

105

102. Georghiou, P. E.; Tran, A. H.; Mizyed, S.; Bancu, M.; Scott, L. T. J. Org. Chem. 2005, 70, 6158-6163.

103. Canceill, J.; Gabard, J.; Collet, A. J. Chem. Soc., Chem. Commun. 1983, 3, 122-123.

104. Percec, V.; Imam, M. R.; Peterca, M.; Wilson, D. A.; Heiney, P. A. J. Am. Chem. Soc. 2008, 131, 1294-1304.

105. Huerta, E.; Isla, H.; Pérez, E. M.; Bo, C.; Martín, N.; Mendoza, J. d. J. Am. Chem. Soc. 2010, 132, 5351-5353.

106. Yanney, M.; Sygula, A. Tetrahedron Lett. 2013, in press.

107. Stuparu, M. C. Tetrahedron 2012, 68, 3527-3531.

108. Boehmer, V.; Marschollek, F.; Zetta, L. J. Org. Chem. 1987, 52, 3200-3205.

109. Van der Made, A. W.; Van der Made, R. H. J. Org. Chem. 1993, 58, 1262- 1263.

110. Gates, M. J. Org. Chem. 1982, 47, 578-582.

111. Loukas, Y. L. J. Pharm. Pharmacol. 1997, 49, 944-948.

112. n Origi (OriginLab, Northampton, MA).

113. Job, P. Compt. Rend. 1925, 180, 928.

114. Sygula, A.; Collier, W. E., Molecular Clips and Tweezers with Corannulene Pincers. In Fragments of Fullerenes and Carbon Nanotubes, John Wiley & Sons, Inc.: 2011, pp 1-40.

115. Günes, S.; Neugebauer, H.; Sariciftci, N. S. Chem. Rev. 2007, 107, 1324- 1338.

116. He, Y.; Li, Y. Phys. Chem. Chem. Phys. 2011, 13, 1970-1983.

117. Kang, S. J.; Ahn, S.; Kim, J. B.; Schenck, C.; Hiszpanski, A. M.; Oh, S.; Schiros, T.; Loo, Y.-L.; Nuckolls, C. J. Am. Chem. Soc. 2013, 135, 2207- 2212.

118. Hummelen, J. C.; Knight, B. W.; Lepeq, F.; Wudl, F.; Yao, J.; Wilkins, C. L. J. Org. Chem. 1995, 60, 532-538.

106