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Synthesis and study of chelating diamide complexes of titanium: new alkyne cyclotrimerization catalysts… Kah, Daniel Alverson Tan Kiang 1999

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Synthesis and Study of Chelating Diamide Complexes of Titanium: New Alkyne Cyclotrimerization Catalysts and New Electroluminescent Oligomers and Polymers by Daniel Alverson Tan Kiang Kah B.Sc, University of British Columbia, 1996 A THESIS SUBMITTED IN PARTIAL FULFILLMENT OF THE REQUIREMENTS FOR THE DEGREE OF MASTER OF SCIENCE in THE FACULTY OF GRADUATE STUDIES (Department of Chemistry) We accept this thesis as conforming to the required standard. THE UNIVERSITY OF BRITISH COLUMBIA April 1999 © Daniel Alverson Tan Kiang Kah ,1999 In presenting this thesis in partial fulfilment of the requirements for an advanced degree at the University of British Columbia, I agree that the Library shall make it freely available for reference and study. I further agree that permission for extensive copying of this thesis for scholarly purposes may be granted by the head of my department or by his or her representatives. It is understood that copying or publication of this thesis for financial gain shall not be allowed without my written permission. Department of The University of British Columbia Vancouver, Canada Date DE-6 (2/88) ABSTRACT Titanium complexes containing a propylene bridged diamide ligand [RN(CH2)3NR]2" (1.6a,b) (a, R - 2,6-(CH3)2C6H3 (BAMP); b, R = 2,6- iPr2C6H3 (BAIP)) were synthesized. The dichloride derivatives, [RN(CH2)3NR]TiCl2 (1.10a,b), were prepared by reacting the silylated diamines R(Me3Si)N(CH2)3N(SiMe3)R (1.9a,b) with TiCLj. In the presence of two equivalents of diphenylacetylene, the reduction of complex 1.10a with an excess of 1% Na/Hg amalgam yielded the metallacyclopentadiene complex (BAMP)Ti(C4Ph4) (1.11). At ambient temperature, complex 1.11 catalyzes the cyclotrimerization of 1-hexyne to 1,3,5- and 1,2,4-tributylbenzenes. A proton nuclear magnetic resonance ('H NMR) spectroscopy study shows that the rate of cyclotrimerization increases with temperature. Analysis of the resulting tributylbenzene by gas chromatography coupled to mass spectroscopy reveals the formation of both isomers in equal amounts. Using this method, phenylacetylene was also converted to the corresponding triphenylbenzene. Reaction with trimethylsilylacetylene and 1-phenyl-1-propyne was also attempted, but only slight amounts of the substituted arenes were formed. No substituted benzene is detected when either 3-hexyne or 4-octyne was used as a substrate. The metallacyclopentadiene complex (BAIP)Ti(C4Et4) (1.12) was synthesized by the reduction of complex 1.10b in the presence of 3-hexyne. Cyclotrimerization of 1-hexyne was also achieved by complex 1.12, but at a higher temperature than for complex 1.11. At 141 °C, complete conversion of 1-hexyne to 1,3,5- and 1,2,4-ii tributylbenzene by complex 1.12 is observed by 'H NMR spectroscopy. In this case, the ratio of isomers obtained was 5:4, but the identity of the two isomers could not be determined unambiguously. In addition, complex 1.12 was found to catalyze the cyclotrimerization of diphenylacetylene to hexaphenylbenzene. Similar results as those found for complex 1.11 were obtained when trimethylsilylacetylene, 1-phenyl-l-propyne, 3-hexyne, and 4-octyne were used as substrates for cyclotrimerization by complex 1.12. The preparation of poly(l,4-phenylenevinylene) (PPV) containing either sulfonate or carboxylate polar groups was attempted. The synthesis of the sodium salt of poly[2,5-bis(3-sulfonatopropoxy)-l,4-phenylenevinylene] (BSP-PPV) (2.14) by the sulfonium precursor and the modified Gilch routes was attempted. Using the modified Gilch route, a fluorescent solution was obtained, but the isolation of BSP-PPV was unsuccessful. A 'H NMR study of the fluorescent solution shows primarily the presence of monomer. Similar results were obtained for the synthesis of the sodium salt of poly(2,5-dicarboxy-l,4-phenylenevinylene) (DC-PPV) (2.24). Both the sulfonium precursor and the modified Gilch routes were attempted but we were unable to isolate pure DC-PPV, although the solution was fluorescent consistent with the presence of conjugated materials. Two compounds (2.27 and 2.28) of carboxy-substituted /7-phenylenevinylene were synthesized via the Wittig reaction. Both compounds are highly luminescent with fluorescence quantum yields of 0.57 in cyclohexane and 0.91 in dichloromethane, respectively. Both compounds exhibit a lower quantum yield in THF. Two oligomers ' iii (2.32 and 2.34) containing two and six methyl ester groups on p-phenylenevinylene, respectively, were synthesized via the Wittig reaction. These oligomers were found to be insoluble in any organic solvent. However, solid state UV-vis spectra of oligomers 2.32 and 2.34 were obtained and their absorption maxima are blue-shifted in comparison to unsubstituted PPV, due to the electron-withdrawing nature of methyl ester groups. iv Table of Contents ABSTRACT ii TABLE OF CONTENTS v LIST OF SCHEMES ix LIST OF FIGURES x LIST OF ABBREVIATIONS xii ACKNOWLEDGMENTS xv DEDICATION xvi GRADUATION xvii CHAPTER 1: ALKYNE CYCLOTRIMERIZATION 1 1.1 INTRODUCTION 1 1.1.1 Background 1 1.1.2 Transition Metal Catalyzed Alkyne Cyclotrimerization 2 1.1.3 Mechanism of Alkyne Cyclotrimerization 3 1.1.4 Metal Amides 5 1.2 PROPYLENE-BRTDGED DIAMTDE COMPLEXES OF TITANIUM 7 1.2.1 Propylene-Bridged Diamines 7 1.2.2 Chelating Diamide Complexes of Titanium 9 1.2.3 Titanacyclopentadienes 10 1.2.4 Alkyne Cyclotrimerization 11 1.3 CONCLUSIONS 19 CHAPTER 2: CONJUGATED OLIGOMERS AND POLYMERS FOR ELECTROLUMINESCENT APPLICATIONS 20 2.1 INTRODUCTION 20 2.1.1 Background 20 2.1.2 PPV 21 2.1.3 Electroluminescent Devices 24 2.1.4 PPV Derivatives 27 2.1.5 Other Light-Emitting Polymers 30 2.1.6 Research Objectives 31 2.2 SULFONATE SIDE CHAINS 33 2.2.1 Attempted Preparation of the Sodium Salt of Poly[2,5-bis(3-sulfonatopropoxy)-l,4-phenylenevinylene] (BSP-PPV) 33 2.3 CARBOXYLATE SIDE CHAINS 37 2.3.1 Attempted Preparation of the Sodium Salt of Poly(2,5-dicarboxy-l,4-phenylenevinylene) (DC-PPV) 37 2.4 OLIGOMERS WITH CARBOXYLATE SIDE CHAINS 41 2.4.1 Synthesis of Compond 2.27 41 2.4.2 Characterization of Compound 2.27 42 2.4.3 Chain Length Elongation 44 2.4.4 Synthesis of Oligomers 45 2.4.5 Characterization of Oligomers 48 VI 2.5 CONCLUSIONS AND FUTURE CONSIDERATIONS 52 CHAPTER 3: EXPERIMENTAL DETAILS 54 3.1 GENERAL 54 3.2 PROPYLENE-BRIDGED DIAMINES 56 Preparation of (BAMP)H2 (1.6a) 56 Preparation of (BAEP)H2 (1.6b) 56 Preparation of (BAMP)(TMS)2 (1.9a) 57 Preparation of (BAIP)(TMS)2 (1.9b) 58 3.3 CHELATING DIAMTDE COMPLEXES OF TITANIUM 59 Preparation of (BAMP)TiCl2 (1.10a) 59 Preparation of (BAIP)TiCl2 (1.10b) 59 3.4 TITANACYCLOPENTADIENES 60 Preparation of (BAMP)Ti(C4Ph4) (1.11) 60 Preparation of (BArP)Ti(C4Et4) (1.12) 60 3.5 CYCLOTRIMERIZATION OF ALKYNES 61 3.6 SULFONATE SIDE CHAINS 62 Preparation of 2,5-dibromomethyl-l,4-bis(3-chloropropoxy)benzene (2.11) 62 Preparation of 2,5-bis(3-chloropropoxy)-1,4-phenylenedimethylene bis(tetrahydrothiophenium bromide) (2.12) 62 Preparation of l,4-bis(3-chloropropoxy)benzene (2.15) 63 Preparation of l,4-bis(3-bromopropoxy)benzene (2.16) 64 Preparation of 2,5-dichloromethyl-l,4-bis(3-bromopropoxy)benzene (2.17a) 64 vii Preparation of 2,5-dibromomethyl-l,4-bis(3-bromopropoxy)benzene (2.17b) 65 3.7 CARBOXYLATE SIDE CHAINS 66 Preparation of 2,5-dibromo-p-xylene (2.18) 66 Preparation of 2,5-dicyano-p-xylene (2.19) 66 Preparation of 2,5-dimethylterephthalic acid (2.20) 67 Preparation of dimethyl 2,5-dimethylterephthalate (2.21) 67 Preparation of dimethyl 2,5-dibromomethylterephthalate (2.22) 67 Preparation of 2,5-bis(methylcarboxy)-1,4-phenylenedimethylene bis(tetrahydrothiophenium bromide) (2.23) 68 3.8 FLUORESCENT COMPOUNDS 69 Preparation of 2,5-bis(methylcarboxy)-l,4-phenylenedimethylene bis(triphenylphosphonium bromide) (2.25) 69 Preparation of compound 2.27 69 Preparation of compound 2.28 70 3.9 OLIGOMERS 71 Preparation of dimethyl 2-bromomethyl-5-methylterephthalate (2.29) 71 Preparation of 2,5-bis(methylcarboxy)-l-methyl-4-phenylenemethylene triphenylphosphonium bromide (2.30) 71 Preparation of oligomer 2.32 72 Preparation of oligomer 2.34 73 REFERENCES „ i 74 viii List of Schemes Scheme 1.1: Mechanism of cyclotrimerization 4 Scheme 1.2: Synthesis of propylene-bridged diamines 1.6a,b 7 Scheme 1.3: Side reaction of propylene-bridged diamines 8 Scheme 1.4: Silylation of propylene-bridged diamines 8 Scheme 1.5: Synthesis of [RN(CH2)3NR]TiCl2 9 Scheme 1.6: Synthesis of titanacyclopentadiene complexes 1.11 and 1.12 11 Scheme 2.1: Synthesis of PPV 4 8 22 Scheme 2.2: Synthesis of PPV derivatives by the Gilch route 28 Scheme 2.3: Synthesis of the cyano-containing PPV. 4 9 29 Scheme 2.4: Synthesis of BSP-PPV 33 Scheme 2.5: Synthesis of 2,5-dihalomethyl-l,4-bis(3-halopropoxy) benzenes 34 Scheme 2.6: Synthesis of dimethyl 2,5-dibromomethylterephthalate (2.22) 38 Scheme 2.7: Synthesis of DC-PPV 39 Scheme 2.8: Synthesis of compound 2.27 41 Scheme 2.9: Synthesis of compound 2.28 44 Scheme 2.10: Synthesis of monosubstituted phosphonium salt 2.30 46 Scheme 2.11: Synthesis of oligomer 2.32 47 Scheme 2.12: Synthesis of oligomer 2.34 47 ix List of Figures Figure 1.1: Valence tautomerization of n,6-C6Me6 ligand.9 4 Figure 1.2: Chelating diamide complexes of titanium 5 Figure 1.3: ! H NMR (300MHz) spectrum of complex 1.11 containing excess 1-hexyne in toluene-ds at 20 °C 13 Figure 1.4: lH NMR (300MHz) spectrum of the reaction of complex 1.11 with 1-hexyne to form 1,2,4- and 1,3,5-tributylbenzenes in toluene-afg at 20 °C for 90 min 14 Figure 1.5: ! H NMR (300MHz) spectrum of the reaction of complex 1.11 with 1-hexyne to form 1,2,4- and 1,3,5-tributylbenzenes in toluene-Jg at 140 °C for 90 min 15 Figure 1.6: 'H NMR (300MHz) spectrum of the reaction of complex 1.12 with 1-hexyne to form 1,2,4- and 1,3,5-tributylbenzenes in toluene-fifo at 140 °C for 90 min 16 Figure 1.7: Statistical distribution of 1,2,4- and 1,3,5-trisubstituted benzenes 17 Figure 2.1: The progress of inorganic LEDs 21 Figure 2.2: Monomers used for the synthesis of PPV precursor polymers 24 Figure 2.3: Schematic cross-section of a typical polymer LED 24 Figure 2.4: Charge confinement with a hole-blocking layer and PPV in a LED. 5 1 . . . . 27 Figure 2.5: Molecular self-assembly of oppositely charged species 32 x Figure 2.6: UV-vis absorption of oligomer 2.32 as a Nujol mull 50 Figure 2.7: UV-vis absorption of oligomer 2.34 as a Nujol mull 50 Figure 2.8: FT-IR absorption of oligomer 2.32 as a Nujol mull 51 Figure 2.9: FT-IR absorption of oligomer 2.34 as a Nujol mull 51 1 xi List of Abbreviations 5 Chemical shift O Fluorescence quantum yield A Heat to reflux Amax Wavelength of maximum absorbance Ar Aryl group a.u. Arbitrary units BAIP {CH2[CH2N(2,6-,Pr2C6H3)]2}2" BAMP {CH2[CH2N(2,6-Me2C6H3)]2}2-B U 4 N O H Tetrabutylammonium hydroxide 'BuOK Potassium tert-butoxide 'BuOH terf-Butanol 1 3 C {1H} Carbon-proton decoupled 1 3 C NMR Carbon Nuclear Magnetic Resonance Cp Cyclopentadienyl d doublet DCI Desorption Chemical Ionization DMF Dimethylformamide DMSO Dimethylsulfoxide EI Electron Ionization Et Ethyl FT-IR Fourier Transform - Infrared xii GC/MS Gas chromatography/mass spectroscopy 1 H NMR Proton Nuclear Magnetic Resonance h Hours LED Light-emitting diode m Multiplet M* Positive ion parent peak m.p. Melting point Me Methyl MeOH Methanol min Minutes mmol Millimoles m/z Mass to charge ratio pent pentet Ph Phenyl PPP Poly(j?-phenylene) PPV Poly(p-phenylenevinylene) 'Pr Isopropyl s Singlet sept Septet SPR Sulfonium precursor route t Triplet THF Tetrahydrofuran xiii THT Tetrahydrothiophene tmeda N,N,N' ,N' -Tetramethylethylenediamine TMSC1 Chlorotrimethylsilane TMS Trimethylsilyl triphos MeC(CH2PPh2)3 xiv Acknowledgments I would like express my deepest gratitude to my supervisor, Dr. Michael Wolf, first, for accepting me into his research group to continue my studies; second, for his guidance and patience; and last but not the least, for his constant encouragement and support. I would also like to thank the Wolf Pack for many valuable discussions and suggestions. Thanks also go to my former supervisor, Dr. David McConville, and his research group for their help and great ideas on the first half of my studies. I would also like to thank my acting supervisor, Dr. Peter Legzdins, for reading and editing my work from the McConville group. Many thanks also go to the following individuals and groups for their help, the use of their instruments or "endless" supply of chemicals: Dr. Leslie Burtnick, Dr. Dana Zendrowski, Liane Darge, Marietta Austria, Victor Sanchez, Jim Sawada, Matt Netherton, Fryzuk's group, Fyfe's group, James' group, Piers' group, Scheffer's group, Sherman's group, Tanner's group, Weiler's group, Withers' group and l'equipe d' Orvig. xv For the K A H Family, especially mum, dad, Kim, and Jenn xvi GRADUATION Struggle! Struggle! Caterpillar - struggle and mingle Over days Over nights Butterfly becoming! Touching with light. Fly! Fly! Stretch the wings and fly Ignore wind Ignore rain on high Raise the body and reach on high. Struggle! Struggle! We struggle for the future Over months Over years Al l becomes harder yet stronger. Go! Go! Bring your heart and soul Pass mountains Pass oceans Achieve your goal and your mark in the world. Daniel Kah xvii CHAPTER 1 ALKYNE CYCLOTRIMERIZATION 1.1 INTRODUCTION 1.1.1 Background The process of alkyne cyclotrimerization has been known since 1866 when Bertholet first described the thermal cyclization of acetylene to benzene at a temperature greater than 400 °C. 1 This type of reaction can be utilized to synthesize starting materials used for the preparation of natural and unnatural products as well as other complex organic molecules. However, it was not until 1949 that Reppe et al. first reported the use of transition-metal complexes to catalyze a similar reaction at much lower temperatures. Since then, a wide variety of transition-metal compounds has been found to catalyze the cyclotrimerization of substituted or functionalized alkynes to their benzene derivatives. Among these catalysts are early transition-metal compounds based on Ti, 3 Zr,4'5 Nb,6"8 Ta,9 and late transition-metal complexes of Co,1 0"1 2 Rh, 1 3 Ir,13'14 and Pd. 1 5 Nonmetallic compounds have also been observed to catalyzed alkyne cyclotrimerizations.16'17 The following sections present a brief overview of the previous studies of alkyne cyclotrimerization with emphasis on the types of ligands used in the transition metal catalysts for such reactions. 1 1.1.2 Transition Metal Catalyzed Alkyne Cyclotrimerization The chemistry of the transition metals is often governed by the steric and electronic properties of ancillary ligands. In other words, much of the chemistry at the metal can be fine-tuned by varying the stereo-electronic properties of the ligands. Most cyclotrimerization catalysts contain either one or two cyclopentadienyl (Cp) ligands attached to the metal center. Substituted Cp ligands have also been used in such catalysts. The Cp ligand is considered unreactive with respect to insertion or elimination and is thus an excellent choice of ligand for this reaction. Combination of Cp and phosphine or carbonyl ligands with cobalt has been thoroughly reviewed by Bercaw, Bergman and Vollhardt.10'11 A kinetic study by Bercaw and Bergman10 showed that in the catalytic cyclotrimerization of 2-butyne using CpCo(PPh3)2, the rate-determining step is loss of triphenylphosphine. Replacement of triphenylphosphine by the more strongly coordinating triethyl- or trimethylphosphine prevents ready dissociation of these ligands from the metal and thus inhibits the cyclotrimerization reaction. In this case, the electronic properties of the phosphine ligands are believed to be crucial in controlling formation of a coordinatively unsaturated intermediate by phosphine dissociation. In terms of steric hindrance, Wigley et al.9 have demonstrated that substitution of the Cp ligand by the more sterically congested 2,6-diisopropylphenoxide group in Ta(0-2,6-'Pr2C6H3)3Ci2 prevents the addition of a third alkyne to the tantallacyclopentadiene intermediate and therefore prevents this tantalum complex from being able to catalyze cyclotrimerizations. On the other hand, aryloxide 2 complexes of titanium such as (H3C6Ph2-2,6-0)2Ti(C4Pv4) were shown by Rothwell et al.3 to be versatile catalysts for alkyne cyclotrimerization. They claim that for group 4 metals, the flexible electron-donating potential of the aryloxide ligands allows ready expansion of the coordination sphere, thereby increasing the number of reaction pathways to include those not available to their metallocene counterparts. 1.1.3 Mechanism of Alkyne Cyclotrimerization The mechanism of alkyne cyclotrimerization by transition-metal complexes has been widely discussed in the literature.3'4'9"14'18 The generally accepted mechanism is depicted in Scheme 1.1.18 Initially, two equivalents of alkyne coordinate to the metal center, and subsequently undergo oxidative coupling to form the coordinatively unsaturated metallacyclopentadiene 1.2. The formation of this metallacyclopentadiene is the key intermediate in the cyclotrimerization reaction. The addition of a third alkyne is proposed to occur either through (i) insertion of a coordinated alkyne into the M - C a bond leading to metallacycloheptatriene 1.4, or (ii) Diels-Alder addition of a coordinated alkyne to 1.2 generating the "7-metallanorbornadiene" adduct 1.5. In either case, the final step is reductive elimination of the desired arene with regeneration of the transition-metal fragment. In the presence of another two equivalents of alkyne the cycle begins again. Although routes (i) and (ii) are both possible pathways, the Diels-Alder process appears to be the most favorable mechanism. Recently, a tantalum compound, (Tl6-C6Me6)Ta(0-2,6-'Pr2C6H3)2Cl, was obtained by Wigley and co-workers9 which 3 favors the Diels-Alder process. They suggested that the r|6-C6Me6 fragment undergoes valence tautomerization (Figure 1.1) in order to explain the singlet resonance of the arene methyl groups in the 'H NMR spectrum. L n M + 2: 2 L 1.1 Scheme 1.1: Mechanism of cyclotrimerization. 4 1.1.4 Metal Amides The history of metal amides dates back to as early as 1856 when Frankland described the synthesis of bis(dimethylamido)zinc,19 However, the first transition-metal amide was not discovered until 1935 when Derner and Fernelius reported the preparation of tetrakis(diphenylamido)titanium.20 Since then, countless syntheses of transition-metal amides have been reported, with complexes of the early transition metals being more common than those of the late transition metals. The use of chelating diamines as ligands for transition-metal complexes has been studied by several researchers.21"24 Most of these complexes have been considered as potential Ziegler-Natta type catalysts. Chelating diamide complexes of 25 27 titanium such as those shown in Figure 1.2, " are not uncommon. However, most of these reports focus on the synthesis and characterization of such complexes and rarely discuss their applications. Although polyfunctional amido ligands have recently been shown to offer efficient kinetic stabilization of early transition-metal compounds through steric shielding, little mention has been made of alkyne cyclotrimerization by these complexes.28"30 'Bu I A Me 2Si\ /TiCL, N ]Bu Me M e 2 S i ^ N \ M e 2 S i ^ N ' Me TiBr, Me Me2Si—N Ti(CH2Ph)2 Me2Si—N Me Figure 1.2: Chelating diamide complexes of titanium. 5 Amide ligands can donate up to 4 electrons to early transition metals. When compared with Cp ligands, amide ligands donate two less electrons and hence increase the electrophilicity of the metal towards substrates like alkynes. The stereo-electronic properties of amide ligands can be manipulated by varying the substituents on the nitrogen atom. The size of the chelating ring and the type of substituents on the nitrogen atom has been extensively explored by the McConville research group at the University of British Columbia. In this thesis, propylene-bridged diamines containing 2,6-dimethylanilide or 2,6-diiopropylanilide groups are investigated as chelating ligands for titanium complexes to be used as alkyne cyclotrimerization catalysts. 6 1.2 PROPYLENE-BRIDGED DIAMTDE COMPLEXES OF TITANIUM 1.2.1 Propylene-Bridged Diamines The one-pot synthesis of propylene-bridged diamines was developed by Scollard in the McConville group at UBC (Scheme 1.2), with an overall yield of 40%.31 + BuLi N'HLi THF/-78°C R ^ X / R a) R = Me b) R - 'Pr - Butane 1. tmeda/0°C 2. 1/2 Br(CH2)3Br / 20 °C R R Nf H 2LiBr R N H 1.6a,b R Scheme 1.2: Synthesis of propylene-bridged diamines 1.6a,b. Due to the crystallinity of compound 1.6a, it can be easily separated from impurities by filtration. The impurities are generated from the incomplete reaction between lithiated anilines and 1,3-dibromopropane (Scheme 1.3). The presence of species 1.7 and 1.8 can be demonstrated by 'H NMR spectroscopy. Unfortunately, the isopropyl groups in compound 1.6b prevent it from precipitating out of solution. On the other hand, the diammonium form of compound 1.6b is highly insoluble in both organic and aqueous solutions, and hence acidifying the final solution with concentrated HC1 allows ready separation of the product. Pure compound 1.6b is then recovered simply by neutralizing the isolated salt with K2CO3. 1.8 Scheme 1.3: Side reaction of propylene-bridged diamines. 1.6a,b a) R = Me b) R = 'Pr + 2MeLi THF / -78 °C 2CH, Scheme 1.4: Silylation of propylene-bridged diamines. 8 In order to facilitate a subsequent reaction with a metal, the nucleophilicity of the diamines toward the metal may be increased by the addition of trimethylsilyl (TMS) groups. These silylated diamines are readily prepared by deprotonation of compounds 1.6a and 1.6b with methyllithium followed by addition of chlorotrimethylsilane (TMSC1) (Scheme 1.4). 1.2.2 Chelating Diamide Complexes of Titanium The highly crystalline, red-orange dichloride derivatives [RN(CH2)3NR]TiCl2 (1.10a,b) were prepared by reacting the silylated diamines R(Me3Si)N(CH2)3N(SiMe3)R (1.9a,b) with TiCL under pyrolytic conditions, with a yield of 74% (Scheme 1.5)31. The elimination of TMSC1 in the reaction provides the driving force for this high-yield synthesis. According to Scollard et al, another route 31 to complexes 1.10a,b is also possible, but with a much lower yield. Scheme 1.5: Synthesis of [RN(CH2)3NR]TiCl2. 9 1.2.3 Titanacyclopentadienes In the presence of two equivalents of diphenylacetylene, the reduction of complex 1.10a with an excess of 1% Na/Hg amalgam in benzene yields the tetraphenyltitanacyclopentadiene complex 1.11 (Scheme 1.6). The synthesis of similar titanacyclopentadiene complexes with other internal alkynes such as 3-hexyne and 1-phenyl-1-propyne was attempted. l H NMR spectroscopy shows the presence of their corresponding metallacycles, but their isolation from unidentified byproducts was unsuccessful. It is believed that the high solubility of these complexes render their separation difficult. However, this is not the case for complex 1.11 since the four phenyl groups offer some rigidity to the complex and thus increase its crystallinity relative to the other metallacycles containing only alkyl groups. In addition to internal alkynes, phenylacetylene was also tried in the same reaction, but the isolation of the corresponding metallacycle was unsuccessful. It appears that cyclotrimerization of this less bulky substrate occurs, since the ! H NMR spectrum shows intense resonances in the phenyl region compared to those due to complex 1.10a. A similar result was obtained by Rothwell et al. when they tried to prepare the metallacyclopentadiene with phenylacetylene. Although the reduction of complex 1.10a in 3-hexyne failed to produce an isolable metallacyle, the reduction of complex 1.10b in 3-hexyne was very successful. Conversely, the reduction of complex 1.10b in the presence of diphenylacetylene, 1-phenyl-1-propyne or some less bulky alkynes such as phenylacetylene and trimethylsilylacetylene failed to generate the corresponding titanacyclopentadiene. 10 This is probably due to the steric crowding of the 2,6-diisopropyl groups on the diamide ligand, which restrict bulky substrates from approaching the metal center. Scheme 1.6: Synthesis of titanacyclopentadiene complexes 1.11 and 1.12. 1.2.4 Alkyne Cyclotrimerization Cyclotrimerization of 1-hexyne was demonstrated with both complexes 1.11 and 1.12. In the case of complex 1.11, 1-hexyne was slowly converted to tributylbenzene at ambient temperature in toluene-d8 solvent. Initially, major resonances in the 'H NMR spectrum are attributed to 1-hexyne (Figure 1.3). Over 11 time, the signals due to tributylbenzene become more intense (Figure 1.4). Not surprisingly, the rate of cyclotrimerization increases at elevated temperatures as the conversion is close to 100% after 90 minutes at 140 °C (Figure 1.5). Similar results were obtained during the cyclotrimerization of 1-hexyne with complex 1.12, with the exception that at room temperature the conversion was negligible. However, complete cyclotrimerization is achieved after 90 minutes at 140 °C (Figure 1.6). Interestingly, gas chromatography/mass spectroscopy (GC/MS) analysis of the products formed by reaction with complex 1.11, reveals the formation of both symmetrical and unsymmetrical isomers in equal amounts. In the case of complex 1.12, the ratio of isomers is 5:4, but it is not clear which isomer is formed in higher yield. It was anticipated that the cyclotrimerization of terminal alkynes would predominantly yield the 1,2,4- trisubstituted benzene (Figure 1.7). This is because there are three possible arrangements of terminal alkynes on metallacyclopentadiene formation. Since both catalysts generate approximately the same amount of both isomers, it is believed that they undergo Route C for the addition of the third alkyne. In addition to 1-hexyne, the cyclotrimerization of other terminal and internal alkynes were also investigated. These include phenylacetylene, trimethylsilylacetylene, diphenylacetylene, 1-phenyl-1-propyne, 3-hexyne, and 4-octyne. Both complexes 1.11 and 1.12 cyclotrimerize phenylacetylene to triphenylbenzene. However, it should be noted that the formation of triphenylbenzene was monitored only by 'H NMR spectroscopy. For trimethylsilylacetylene and 1-12 £1 9\ 91 phenyl- 1-propyne, only negligible amounts of cyclized products are observed in the 'H NMR spectra. 1,3,5-trisubstituted benzene Figure 1.7: Statistical distribution of 1,2,4- and 1,3,5-trisubstituted benzenes. Only complex 1.12 catalyzes the cyclotrimerization of diphenylacetylene to hexaphenylbenzene. The formation of hexaphenylbenzene was determined by GC/MS. It is not clear why the sterically more hindered catalyst is capable of cyclotrimerizing a bulky alkyne such as diphenylacetylene, yet the sterically less 17 congested complex 1.11 fails to produce hexaphenylbenzene. It is also difficult to explain why the reduction of complex 1.10b in the presence of diphenylacetylene does not yield the corresponding metallacyclic complex [(BAIP)Ti(C4Ph4)], but the same complex is assumed to form when complex 1.12 successfully catalyzes the cyclotrimerization of diphenylacetylene. Further experiments are required to investigate these questions further. No substituted benzene was detected when either 3-hexyne or 4-octyne was used as a substrate in the cyclotrimerization reaction with either complex 1.11 or 1.12 as the catalyst. 18 1.3 CONCLUSIONS The syntheses of propylene-bridged diamines as chelating ligands and their corresponding titanacyclopentadiene complexes are reported. Some cyclotrimerization reactions with both terminal and internal alkynes were investigated. It is shown that both complexes 1.11 and 1.12 catalyze the conversion of 1-hexyne to 1,2,4- and 1,3,5-tributylbenzenes in approximately the same ratio. Some other terminal alkynes were also used in the cyclotrimerization reaction, but the resulting trisubstituted benzenes were not characterized. However, the presence of these trisubstituted benzenes was established by lH NMR spectroscopy. Attempts to cyclotrimerize internal alkynes with either complexes 1.11 or 1.12 proved fruitless, with the exception of complex 1.12 which is capable of cyclotrimerizing diphenylacetylene to hexaphenylbenzene. Moreover, it is not clear why complex 1.11 is unable to cyclotrimerize diphenylacetylene to hexaphenylbenzene since it is less sterically crowded than complex 1.12. The results show that terminal alkynes are easier to cyclize than internal alkynes. This is not surprising since terminal alkynes present less steric hindrance compared to internal alkynes. 19 CHAPTER 2 CONJUGATED OLIGOMERS AND POLYMERS FOR ELECTROLUMINESCENT APPLICATIONS 2.1 INTRODUCTION 2.1.1 Background Light-emitting diodes (LEDs) are semiconductor diodes that emit light upon application of an electric current. The active elements in conventional LEDs are predominantly GaAs-based semiconducting materials (Figure 2.1). The first commercial GaAsP LEDs were introduced by Monsanto and Hewlett Packard in the late 1960's. Although inorganic LEDs have been shown to exhibit excellent operational characteristics, a major drawback is the cost of fabricating large-area displays from them. Recently, the use of organic materials in LEDs has been recognized for their potential low-cost production and ease of fabrication. There are two major classes of organic compounds that have been employed as the active component in LEDs: (i) low molecular weight compounds such as fluorescent dyes and (ii) conjugated polymeric materials. Among the two classes, we are interested in the conjugated polymers because of their enhanced processibility and attractive semiconductor properties.34 Derealization in the 7t orbitals of conjugated polymers allows charge 20 conduction along the polymer chain. Polymer-based LEDs have been prepared in a wide range of colors by systematic manipulation of the polymer structure, and the addition of substituents to the polymer chain.34 Performance (Lumens/Watt) 10 Red, Yellow, Green AlInGaP y DH AlGaAs / AlGaAs S H AlGaAs / GaAs DH AlGaAs / GaAs Red, Yellow GaAsP:N / Green GaP:N GaP:Zn,0 GaAso.6Po.4 _L_L. i ' i I i i i i—I—i—i—i—i 1965 1970 1975 1980 1985 1990 1995 2000 Figure 2.1: The progress of inorganic LEDs 32 Most of the studies on polymer-based LEDs have involved PPV or its derivatives.35"47 Although the development of polymer-based LEDs is still in its infancy, rapid progress in this field has led to some initial applications of these materials in low information content displays such as cellular phones, microwave ovens, watches, and other alphanumeric displays.34 2.1.2 PPV The first polymer-based LED used PPV as the emitter.48'49 The discovery of electroluminescence in PPV was made by Richard Friend and his research group at 21 Cambridge University in 1990. Initially, the application of PPV in LEDs was restricted by its poor solubility in virtually all solvents which makes processing difficult. This is because a direct synthesis of PPV yields an insoluble and infusible polymer that cannot be readily fabricated into electroluminescent devices. One approach to this problem is to synthesize a solution-processible precursor polymer (2.3), as shown in Scheme 2.1.48 This strategy was first introduced by Wessling and Zimmerman from Dow Chemical Corporation.50'51 The process relies on the preparation of a tetrahydrothiophenium salt intermediate which can be easily converted to the precursor polymer in the presence of an aqueous base. Other sulphonium salts may be used, but they have shown to be less desirable due to the occurrence of unwanted side reactions.34 The amount of base added must be carefully controlled because excess base induces partial elimination of the sulfonium groups which leads to lower solubility of the resulting polymers.34 C1H2C CH2C1 MeOH, 50 °C 2.1 l.NaOH 2. Dialysis 2.3 Scheme 2.1: Synthesis of PPV. 48 22 The final step in this synthesis of PPV involves thermal conversion of the precursor polymer under vacuum once it has been deposited as a thin-film in the electroluminescent device. The construction of a polymer-based electroluminescent device is discussed in Section 2.1.3. The mechanism of this polymerization has not yet been completely elucidated. Some studies suggest that the mechanism involves a radical polymerization since the introduction of radical trapping agents such as oxygen drastically reduces the molecular weight of the resulting polymer.34'35,52 However, the possibility of an anionic polymerization cannot be completely ruled out, because the base can act as an anionic initiator in this polymerization process.52"54 Moreover, the anionic process is believed to account for the formation of low molecular weight oligomers when oxygen is introduced as the radical trap. The synthesis of PPV described in the previous paragraphs is commonly referred to as the sulfonium precursor route (SPR).35 Several other synthetic methods have also been explored to prepare PPV, including ring-opening metathesis polymerization (ROMP) of norbornadiene-type monomers (2.5) (Figure 2.2), using a molybdenum catalyst developed by Grubbs et al.55 The same technique has also been applied by Miao and Bazan to a monomer based on a siloxy-substituted cyclophane (2.6).56 Chemical vapor deposition (CVD) has been used to prepare PPV from a halogenated monomer such as chlorinated cyclophane (2.7) or a,a'-dichloro-/?-xylene (2.8).57'58 However, it should be noted that all these methods rely on the preparation of processible precursor polymers which can be thermally converted to PPV once they have been cast as thin films. 23 2.5 2.6 Figure 2.2: Monomers used for the synthesis of PPV precursor polymers. 2.1.3 Electroluminescent Devices A typical polymer LED consists of a layer of conjugated polymer sandwiched between two electrodes as shown in Figure 2.3. Cathode CCa; Al) Light-emitting layer (conjugated polymer) Anode (indium-tin oxide) Substrate (glass) hv Figure 2.3: Schematic cross-section of a typical polymer LED. A high work function semiconductor such as indium-tin oxide (ITO) is the preferred material for the anode due to its transparent nature which allows light 24 generated from the polymer layer to be emitted from the device. A solution-processible precursor polymer is deposited on top of the anode via spin coating. This technique permits the deposition of a thin-film of the emissive polymer over a large area. LEDs fabricated from inorganic semiconductors are normally deposited as thin-films by sublimation or vapor deposition, which are relatively expensive methods of fabricating large-area devices.34 In polymer-based devices, the cathode is commonly a low work function metal such as calcium or aluminum, which is deposited on the polymer surface via vacuum deposition. However, calcium is moisture sensitive and is easily oxidized under atmospheric conditions. Oxidation at the cathode can interfere with the current flow through the metal and cause the breakdown of the LED by short-circuiting the device. A solution to this problem is encapsulation of the device with a protective coating; however, the encapsulation process also increases the cost of device production. The alternative is to use a more stable metal such as Mg or Al as the cathode. Low work function metal alloys such as Mg/Ag and Li/Al have also been employed as the cathode material.59 LED operation is achieved when a sufficiently large potential is applied to the diode to allow the injection of positive and negative charge carriers (holes and electrons) from opposite electrodes. These oppositely charged carriers diffuse toward each other under the influence of the applied electric field until they recombine to form excitons (either singlet or triplet) within the polymer layer. Subsequently, the relaxation of singlet excitons to the ground state produces light. The emission from a PPV-based LED is in the yellow-green region of the visible spectrum. 25 It is known that electron injection is more difficult to achieve than hole injection in PPV. 3 4' 4 9 In order to obtain high electroluminescent efficiencies from a device, it is crucial to have balanced charge injection from the cathode and the anode. One strategy is to introduce an organic charge-transporting or charge-blocking layer between the emissive polymer and one or both of the electrodes.49 This creates an energy barrier for electrons or holes at the interface and acts to confine charge carriers within the emissive layer. The advantage of confining charges at the interface is that it promotes the balance of electron and hole injection as well as restricts the passage of charges to the opposing electrodes which can act as quenching sites for singlet excitons.34'49 In the case of PPV, oxadiazole-containing compounds have been shown to be effective in blocking holes from reaching the cathode and allow balanced charge recombination to occur at the heterojunction (Figure 2.4).34'60 Other factors such as the thickness and the uniformity of the polymer film are equally important for obtaining efficient devices.61 The drive voltage applied to the device is proportional to the film thickness, so a thick polymer film requires a higher voltage for device operation, which can cause damage to both the polymer and electrode materials as a result of heating. This may lead to shortened lifetimes for such devices. Film inhomogeneity also leads to "weak interactions" between polymer chains and decreases the stability of electroluminescent devices. Considerable efforts have been made in both academic and industrial labs to improve device performance.34 26 © © A A I © x A 0 V hv Cathode Hole-blocking Layer PPV Anode Substrate (glass) Figure 2.4: Charge confinement with a hole-blocking layer and PPV in a LED. 51 2.1.4 PPV Derivatives Since the initial demonstration of electroluminescence in PPV, the poly(arylenevinylene) family has been extensively explored for its potential application in LEDs. Most approaches involve the derivatization of monomers with a solubilizing side chain which can be polymerized to a soluble polymer that may be cast into thin-films without the final thermal conversion step. The introduction of mono-and dialkoxy groups has been the most common method to confer solubility to the conjugated polymer.36'38'41 The electron-donating nature of the alkoxy groups also alters the bandgap, and hence the emission maximum is red-shifted compared with that of PPV. Changing the bandgap not only causes a shift in the emission color, but it may also improve device efficiency by placing the polymers' conduction and valence bands closer in energy to the work functions of the electrodes, thereby facilitating electron and hole injection 63 27 The preparation of alkoxy substituted PPV derivatives is usually carried out via the Gilch route.35,64 In this method, the polymerization of bis(halomethyl)benzene derivatives is promoted by the use of a base, such as potassium -^butoxide (Scheme 2.2). Unfortunately, polymer gelation results if excess base is used, even with solubilizing substituents on the PPV backbone.35,42,44 Swatos and Gordon have reported that if one equivalent of potassium /-butoxide is used, polymer gelation may be avoided.35'65 The modified Gilch route generates a soluble halo precursor polymer that can be converted to the conjugated form in much the same way as the sulfonium precursor is converted in the SPR. Although the sulfonium precursor route can be applied to the polymerization of mono- or dialkoxy substituted monomers, it is not the preferred method since precipitation is frequently encountered during the polymerization of these electron-rich monomers.35 In addition, not all alkoxy bis(halomethyl)benzene derivatives can be readily converted to their corresponding sulfonium salts.35 RO RO X = Cl, Br R = alkyl Scheme 2.2: Synthesis of PPV derivatives by the Gilch route. 28 Other PPV derivatives such as those with alkyl or aryl groups on the phenyl ring have also been reported to have improved solubility when compared to ppy 37,42,44,66 g y ^ e ^ 0 f these polymers has been achieved with many of the same methods described for the preparation of alkoxy substituted PPVs. While the majority of known PPV derivatives contain electron-donating substituents, the use of electron-withdrawing groups has not been investigated to the same extent. Only a few examples are reported in the literature using cyano or halo groups.49'67"69 PPV with cyano substituents was synthesized from the Knoevenagel condensation of terephthaldehyde 2.9 and dinitrile 2.10 (Scheme 2.3).49'70 The cyano groups are present in the vinylene linkage and the alkoxy substituents are added to the phenyl rings to increase the solubility of the polymer. The synthesis of PPV derivatives with halo groups in the benzylic position is very similar to the sulfonium precursor route where the pyrolytic vacuum elimination of tetrahydrothiophene provides the driving force for the formation of the conjugated polymer.69 OHC O C 6 H 1 3 X / C H O O C 6 H 1 3 + NO O C 6 H 1 3 2.10 €N BuOH, THF, A Bu4NOH 2.9 O C 6 H 1 3 Scheme 2.3: Synthesis of a cyano-containing PPV. 49 29 The introduction of electron-withdrawing groups has the advantage of increasing the electron affinity of PPV, thus facilitating the injection of electrons from the cathode. This is particularly useful for LEDs with high work function cathodes such as Al where electron injection is difficult. The device efficiency may also be improved because a better balance of electron and hole recombination may be achieved and the quenching of holes at the cathode may be reduced. In addition, an increase in electron affinity could eliminate the need for a hole-blocking or an electron-transporting layer in the device. 2.1.5 Other Light-Emitting Polymers In addition to PPV and its derivatives, another conjugated polymer that exhibits electroluminescence is PPP. In its neutral form, PPP is highly luminescent and has been successfully used as the active emitting material in LEDs, emitting blue light.71'72 Unsubstituted PPPs are often highly insoluble and infusible materials containing irregular structures which are difficult to study.73 Not surprisingly, derivatization of PPP has been carried out by several groups to achieve well-defined and more processible conjugated polymers.74"77 In addition, efforts have been made 79 T\ 7R 81 into developing methods for synthesizing PPPs that are soluble in water. ' J '°" S 1 The discovery of a water-soluble Pd(0) catalyst system has greatly enhanced progress in this area. Novak et al. have utilized this catalyst system to make carboxy-substituted PPPs with an average of one carboxylic acid group for every two phenylene rings.79'80 Kaeriyama et al. have also prepared a series of carboxy-substituted PPPs that are 30 81 soluble in aqueous base using a Ni(0) catalyst. Other water-soluble PPPs include those containing y-sulfonatoalkoxy groups, which have also been prepared using the Pd(0) catalyst.72'73 2.1.6 Research Objectives The objectives of the work described in this chapter are to synthesize new conjugated polymers and oligomers containing charged pendant groups, which may have potential application as the emitting layer in LEDs. We have chosen to prepare a PPV polymer backbone with charged side chains as substituents. Many of the derivatives of PPV described earlier in this chapter are soluble in organic solvents such as THF and chloroform. Very little attention has been paid to the synthesis of PPVs that are soluble in water. Based on the success of water-soluble PPPs, we propose that the introduction of charged pendant groups should give access to water-soluble PPV derivatives. The ability to process electroluminescent polymers in water could offer advantages over polymers soluble in organic solvents. The use of water-soluble polymers may avoid the harmful and toxic effects of organic solvents and thus make the processing more environmentally friendly. Water-soluble polymers also enable low-cost processing for the fabrication of electroluminescent devices since water is readily available and inexpensive. In addition, water soluble light-emitting polymers may have potential application in ink-jet printers where emissive logos can be printed on regular paper, as the ink in current ink-jet printers is water-based.82 Light-emitting polymers that are only soluble in organic solvents are not suitable for 31 this application because these solvents tend to dissolve key components of standard 82 printers. Another advantage of charged side chains is that they can be utilized to control the thickness of the polymer film in a LED via a technique first applied by Rubner et a/.83"86 In this technique, layer-by-layer molecular-level manipulation of conjugated polyelectrolytes can be achieved by spontaneous adsorption of oppositely charged polymers from dilute aqueous solutions. An illustration of this process is depicted in Figure 2.5. In this way, it should be possible to control, at the molecular level, both the thickness and the uniformity of the polymer films in electroluminescent devices. Figure 2.5: Molecular self-assembly of oppositely charged species. 32 2.2 SULFONATE SIDE CHAINS 2.2.1 Attempted Preparation of the Sodium Salt of Poly[2,5-bis(3-sulfonatopropoxy)-l,4-phenylenevinylene] (BSP-PPV) Our initial attempt to synthesize a PPV derivative with a charged pendant group focused on adding sulfonate-containing side chains to the backbone. We chose to make polymer 2.14 (BSP-PPV) which should be accessible in three steps from 2,5-dibromomethyl-l,4-bis(3-chloropropoxy) benzene (2.11) (Scheme 2.4). 0(CH2)3C1 CH 2Br BrFLC 2.0 THT / MeOH 0(CH2)3C1 2.11 R(H 2C) 30 P(CH 2) 3R ^ ^ - C H - C H -2.14 0(CH2)3C1 ( f ) 1 C H 2 - S + - ^ Br-0(CH2)3C1 2.12 2.5 Na 2S0 3 /H 2 0 1. 0.4MNaOH/ MeOH 2. A, H + 2NaCl A 0(CH2)3R CH2—S Br 0(CH2)3R 2.13 R=SO _ 3Na + Scheme 2.4: Synthesis of BSP-PPV. 33 We prepared compound 2.11 using the sequence of reactions shown in Scheme 2.5. Compound 2.15 was successfully synthesized in 41% yield using slight on modifications of a literature procedure. The reaction can be easily monitored by color changes since deprotonation of the hydroxyl groups of hydroquinone gives an intense yellow color. This color slowly disappears when compound 2.15 is formed. However, it is important that the deprotonated hydroquinone be added to the solution of 1,3-dichloropropane in ethanol in this order in order to prevent polymerization. 0(CH2)3C1 0(CH2)3C1 CH2Br l.HBr ( a q )/Dioxane B r H 2 C y 2. excess CH 2 0 ( a q ) , 37% 0(CH2)3C1 0(CH2)3C1 2.11 2.15 4.0 C1(CH2)3C1 OH 2.5KOH/EtOH A -2H 2 0 4.0Br(CH2)3Br 0(CH2)3Br 0(CH2)3Br CH 2 X l.HX ( a q )/Dioxane X H 2 C y 2.excess CH 2 0 ( a q ) , 37% 0(CH2)3Br 3.HX ( g ) 0(CH2)3Br 2.17a,b 2.16 a) X = Cl b) X = Br Scheme 2.5: Synthesis of 2,5-dihalomethyl-l,4-bis(3-halopropoxy) benzenes. 34 Compound 2.15 was bromomethylated to yield 2,5-dibromomethyl-l,4-bis(3-chloropropoxy) benzene (2.11). This synthesis is very similar to the well-known method of chloromethylation, with the exception that a constant flow of HBr gas is not required. In general, chloromethylation requires the use of both aqueous and gaseous HC1.87 If a different halide is used (i.e. bromide), the corresponding acid in the aqueous and gaseous forms is usually applied. In this case, we found the yield (52%) of compound 2.11 to be the same with or without bubbling of HBr gas through the reaction. Precipitation of compound 2.11 allows for easy separation and purification from the excess formaldehyde used in the reaction. In addition to compound 2.11, two other compounds with different combinations of chlorides and bromides on the alkoxy side chains and the phenyl positions were prepared using this method (Scheme 2.5). However, only compound 2.11 is ideal for the subsequent reaction with tetrahydrothiophene (THT) to give 2,5-bis(3-chloropropoxy)-l,4-phenylenemethylene tetrahydrothiophenium bromide (2.12) (Scheme 2.4). Compounds 2.17a,b are not suitable because one equivalent of THT reacts with the bromide on the alkoxy side chains, since bromide is a better leaving group than chloride. We attempted to convert compound 2.12 to the disulfonate salt 2.13 using sodium sulfite in water. During the sulfonation of compound 2.12, the reaction mixture becomes fluorescent, suggesting that conjugated oligomers are present in the solution. It is possible that sodium sulfite acts as a base promoting the polymerization of 2.12. A control experiment was conducted in which the same reaction conditions 35 were used but without any sodium sulfite. Under these conditions, the solution remains colorless even after several days of heating to 100°C. The 'H NMR spectrum of the fluorescent solution contains mainly resonances due to monomer, suggesting that the degree of oligomerization is extremely low. Moreover, there is no evidence for replacement of the chlorides by the sulfonate groups, since the ! H resonances due to the methyl groups have the same chemical shift values as before the addition of sodium sulfite. The synthesis of BSP-PPV using the modified Gilch route was also attempted. In this case, we attempted to synthesize a soluble precursor polymer prior to the sulfonation with sodium sulfite. This is to avoid the possibility of polymerization of compound 2.11 to an insoluble polymer. Unexpectedly, the addition of one equivalent of potassium tert-butoxide to compound 2.11 in benzene at ambient temperature gives a reddish orange precipitate that is insoluble in all solvents attempted. The orange precipitate is also fluorescent under UV light. Due to these solubility problems, we decided to try and incorporate other polar side-groups into PPV. 36 2.3 CARBOXYLATE SIDE CHAINS 2.3.1 Attempted Preparation of the Sodium Salt of PoIy(2,5-dicarboxy-l,4-phenylenevinylene) (DC-PPV) The problems encountered with the preparation of BSP-PPV turned our attention to the use of other functional groups that could be used as polar side-chains on PPV. Our second attempt to prepare water-soluble PPV derivatives involved using carboxylate side chains. There are several methods available for introducing carboxylate groups to an aryl ring. We chose to protect the carboxylate groups as methyl esters until after the conjugated polymer is produced, followed by deprotection to yield the carboxylate groups. The synthesis of DC-PPV was attempted by both the sulfonium precursor route and the modified Gilch route. For both methods, the starting material is dimethyl 2,5-dibromomethylterephthalate (2.22) (Scheme 2.6).88"91 Compound 2.18 was synthesized in 85% yield by the bromination of jt7-xylene oo with neat bromine, followed by reaction with cuprous cyanide to give highly crystalline 2,5-dicyano-p-xylene (2.19). According to the literature, compound 2.19 may be purified by filtration through silica gel, however we found a single recrystallization from CH2CI2 to be sufficient to yield pure 2.19 in higher yield (77%) than reported. Compound 2.19 was then oxidized with concentrated phosphoric acid to give the corresponding 2,5-dimethylterephthaIic acid (2.20) in 99% yield. Compound 2.20 can also be prepared by oxidation of 2,5-dichloromethyl-p-xylene 37 with 40-50% of nitric acid. However, several side products are generated in this reaction, thus making it a less desirable procedure 91 CH 3 CH, CH 3 2.05 Br 2 0 - 25 °C Br Br 2.5 CuCN DMF, A NC CH 3 CH 3 2.18 CN CH 3 2.19 85% H 3 P0 4 A CH, HOOC COOH CH 3 2.20 1. excess SOCl 2 2. excess MeOH / Ether CH 2Br H 3COOC Br COOCH 3 2.0 0^7=0 /CCI4 CH 3 hv, A H 3COOC COOCH, CH 2Br 2.22 CH 3 2.21 Scheme 2.6: Synthesis of dimethyl 2,5-dibromomethylterephthalate (2.22). Compound 2.20 was converted to dimethyl-2,5-dimethylterephthalate (2.21) by esterification. The acid was first converted to the acid chloride using thionyl 38 chloride, which was then reacted in situ with anhydrous methanol to give compound 2.21. The overall yield for this two-step reaction is 89%. Finally, compound 2.21 was brominated with a mild brominating agent, 7V-bromosuccinimide, to generate 2,5-dibromomethyl-l,4-benzyldimethylcarboxylate (2.22). The overall yield is 29 %. The reaction of compound 2.22 with 1.05 equivalents of potassium tert-butoxide in THF results in the formation of a material which emits a blue-green color under UV light (Scheme 2.7). The viscous solution was dialysed against water to remove salts and low molecular weight compounds. The resulting solution does not reveal the presence of DC-PPV by 'H NMR spectroscopy, due to the large amount of water present in the sample. It is possible that the resonances of the product are obscured by the water resonance, however, efforts to dry the sample were unsuccessful. This is not surprising since the polar carboxylate groups can retain water through electrostatic attractions. 1. 1.05 'BuOK/THF 2. 0.5MNaOH/H 2O BrH2C COOCH 3 CH2Br Na'OOC 2.24 C O O C H 3 2.22 0.1MNaOH/H 2O 2.0 THT / MeOH COOCH, CH,—S Bf C O O C H 3 2.23 Scheme 2.7: Synthesis of DC-PPV. 39 In addition to the modified Gilch route, we have also attempted to make polymer 2.24 by the sulfonium precursor route. This requires the synthesis of the sulfonium salt of 2.23. Surprisingly, treatment of compound 2.23 with 0.1 M aqueous sodium hydroxide in water heated to reflux did not yield the corresponding conjugated polymer. Recently, it was shown by Gowri et al. that hydroxyl groups on the vinyl carbon may result when the polymerization of sulfonium monomers is carried out in water.92 This leads to the formation of a stable precursor polymer which cannot be thermally converted to the conjugated form, due to the fact that hydroxide is not a good leaving group. In this case, 0.4 M aqueous HC1 was added to protonate the oxygen atom of the hydroxyl group so that elimination could take place more readily. One drop of the acidified solution of 2.23 was placed on a microscope slide and dried with a heat gun. It was anticipated that upon heating, the corresponding conjugated polymer should form followed by the evaporation of water. Instead, a layer of white, nonfluorescent precipitate was obtained. A 'H NMR study of the acidified solution also failed to show the presence of DC-PPV, as resonances due to vinylic protons (6-8 ppm) were not observed. An UV-vis experiment was performed on the solution before the addition of HC1; and the spectrum showed an unidentified weak but broad band with a shoulder at around 300 nm. Based on this evidence we conclude that we have not obtained the desired polymer. 40 2.4 OLIGOMERS WITH CARBOXYLATE SIDE CHAINS 2.4.1 Synthesis of Compound 2.27 Since the preparation of DC-PPV was unsuccessful, we decided to prepare some model oligomers in order to study their fluorescence behavior. According to Bredas et al., an advantage of oligomer analogs over their parent polymers is that their well-defined chemical structure, together with their improved solubility and processibility, give access to detailed interpretations of experimental measurements on these materials.93 It is well known that the Wittig reaction offers a way to form a carbon-carbon double bond from a carbonyl group and a carbanion. We therefore set out to synthesize a compound containing carboxylate side groups via the Wittig reaction (Scheme 2.8). 2 PPh 3 /THF A H 3COOC 2.25 - 2HBr NaH / DMSO CHO C O O C H 3 2.2 H3COOC - 2POPh3 2.27 Scheme 2.8: Synthesis of compound 2.27. 41 The phosphorus ylide (2.26) was first prepared from compound 2.22 and triphenylphosphine in a two-step process. The first step involves a nucleophilic attack by triphenylphosphine on compound 2.22 to form the phosphonium salt (2.25). In a second step, 2.25 was treated with methylsulphinyl carbanion to form the ylide 2.26. One equivalent of base is added in this reaction, since when two equivalents of base are used, the solution becomes cloudy and an insoluble black precipitate forms. Moreover, a strong base such as BuLi was avoided to prevent cleavage of the ester groups from compound 2.26. Benzaldehyde was then added to the ylide to yield compound 2.27, eliminating triphenylphosphine oxide as a side-product. The yield of compound 2.27 in this reaction is low (5%). Using one equivalent of methylsulphinyl carbanion, incomplete deprotonation of compound 2.25 occurs and leads to a low percentage of the diylide for the subsequent reaction with terephthaldicarboxaldehyde. If two equivalents of base are added, the reaction results in an unidentified black precipitate. Extensive purification of compound 2.27 via chromatography was required accounting for the low isolated yield. 2.4.2 Characterization of Compound 2.27 Compound 2.27 is highly soluble in most organic solvents. A 'H NMR study shows that the vinylic protons are trans with a coupling constant of 16.2 Hz. Both mass spectrometry and elemental analysis confirm the formation of compound 2.27. In the solid state, compound 2.27 is yellow in color, while in solution the compound is green and emits blue-green light under the UV lamp. The UV-vis absorption spectrum 42 of compound 2.27 in THF contains a broad 71-71* transition with A,m a x at 344 nm. The emission spectrum, on the other hand, exhibits a narrower band with X,m a x at 438 nm. The fluorescence quantum yield (O) of compound 2.27, in TFfF is 0.23 with excitation at 356 nm. <J> was determined by comparison with a standard of known fluorescence quantum yield (Equation 2.1).94 Anthracene was chosen as the standard since it has an absorption maximum which overlapped with that of compound 2.27. The reported quantum yield for anthracene is 0.36 in cyclohexane.95 It is interesting to note that the fluorescence quantum yield of compound 2.27 is dependent on solvent. The quantum yield in cyclohexane was found to be 0.57, significantly higher than the quantum yield in THF. Similar behavior was observed by Faulkner et al. for anthracene.96 In order to determine the effect of ester cleavage on the fluorescence properties, a CH2CI2 solution of compound 2.27 was stirred vigorously with 1.0 M aqueous sodium hydroxide for 30 minutes. The <D was remeasured and it was observed that the yield did not change significantly. The absorption maximum of the base-treated compound 2.27 also remains the same. This may mean that the nature of the substituent on the carboxylate side chain has a limited effect on the fluorescence quantum yield of compound 2.27 as well as on its absorption maximum. It is possible that more carboxylate side chains on the oligomer backbone are required to produce a significant change in the quantum yield. 43 n 2 F(v)xdv x 0 (2.1) n s ) 2 F(v)sdv 0 where: O x and O s = fluorescence quantum yields of compounds x and standard, respectively. nx and n s = refractive indices of solutions x and standard, respectively. F(v)x and F(v)s = relative quantum intensities of compounds x and standard, respectively. 2.4.3 Chain Length Elongation The Wittig reaction can be used to prepare longer oligomer or polymer chains by sequential monomer addition. This strategy has previously been utilized by other Q7 OS researchers to generate block copolymers. ' The Wittig reaction requires a carbonyl functional group in one of the starting materials. With slight modifications to the synthesis of compound 2.27, a trimer with carbonyl groups at each end of the benzene ring was synthesized (Scheme 2.9). - 2POPh3 2.28 Scheme 2.9: Synthesis of compound 2.28. 44 In this reaction, the ylide was added to terephthaldicarboxaldehyde, to ensure that the carbonyl functional groups remain at both ends of the chain. This reaction also suffered from a low yield for the same reasons as described for compound 2.27. The elemental analysis and the spectroscopic data from ] H and 1 3 C NMR for compound 2.28 are consistent with the structure shown in Scheme 2.9. The coupling constant of the vinylic protons is 16.3 Hz, indicative of a trans configuration. The n-7 i * absorption for compound 2.28 in THF is observed with a X m a x at 380 nm, which is red-shifted relative to the maximum absorption of compound 2.27. Upon excitation with UV light, a THF solution of compound 2.28 is intensely fluorescent with A,m a x for emission at 436 nm, with a O in THF of 0.51. The higher fluorescence quantum yield for compound 2.28 is attributed to the longer conjugation length in this molecule. A CH2CI2 solution of compound 2.28 was washed with 1.0 M sodium hydroxide, but the quantum yield and A,m a x of the organic layer remain unchanged after this treatment. The solvent effect on fluorescence quantum yield was also observed in compound 2.28. The O in CH2C12 is 0.91, almost twice the value in THF. One possible explanation of this effect is that THF may quench the excited state or promotes the vibrational decay of both compounds 2.27 and 2.28 and hence lowers their fluorescence quantum yields. 2.4.4 Synthesis of Oligomers Using compound 2.28, well-defined oligomers should be accessible by sequential monomer addition via Wittig condensation. Two oligomers were 45 synthesized, one with three carboxy-substituted phenyl groups and the other containing only one such ring. Starting from compound 2.28, the synthesis of an oligomer with three carboxy-substituted rings requires the use of a monosubstituted phosphonium salt containing methyl ester group (Scheme 2.10). Br C H C O O C H 3 0 5 0=^TO/ CC14 XcOOCH 3 H 3COOC T hv,A H 3 C O O C CH 3 CH 3 2.21 2.29 excess PPh3 / CC14 Br" CH 2P +Ph 3 ' COOCH 3 H 3 C O O C CH 3 2.30 Scheme 2.10: Synthesis of monosubstituted phosphonium salt 2.30. Such a phosphonium salt may be prepared by bromination of compound 2.21, using only 0.5 equivalent of N-bromosuccinimide. Under these conditions, 3/5 of compound 2.21 is left unbrominated, but can easily be separated from compound 2.29 in the subsequent reaction with triphenylphosphine since compound 2.30 is highly insoluble in CC14. Once deprotonated, compound 2.30 reacts with compound 2.28 to give oligomer 2.32 (Scheme 2.11). Formation of a yellow precipitate is observed in this reaction after it was stirred for four hours at room temperature. 46 3COOC Scheme 2.11: Synthesis of oligomer 2.32. Scheme 2.12: Synthesis of oligomer 2.34. 47 The synthesis of the oligomer containing one carboxy-substituted ring is similar to that of oligomer 2.32 (Scheme 2.12). In this case, the ylide was generated from commercially available benzyltriphenylphosphonium chloride when one equivalent of base is added. Compound 2.33 was then reacted in situ with compound 2.28 to yield oligomer 2.34. In this reaction, a yellow precipitate was also observed after it was stirred for four hours at 20 °C. 2.4.5 Characterization of Oligomers Unexpectedly, oligomers 2.32 and 2.34 were found to be insoluble in most organic solvents. However, solid state UV-vis spectra were obtained for both oligomers (Figures 2.6, 2.7). They both exhibit a broad absorption in the range 330— 580 nm for oligomer 2.32 and 320-550 nm for oligomer 2.34. The approximate absorption maxima are 330 nm and 420 nm, respectively. The FT-IR spectrum of oligomer 2.32 (Figure 2.8) displays a sharp absorption peak at 954 cm"1, indicating 1Q that the vinylic double bonds are in a trans configuration. An identical IR absorption at 964 cm"1 was also found in oligomer 2.34 (Figure 2.9). Other IR absorptions such as C=0 and C-0 stretches are similar for both oligomers and are consistent with the expected structures. Elemental analyses of both oligomers consistently show a deviation from expected values up to 4.0% for carbon but only up to 0.2% for hydrogen. It is possible that the discrepancy is due to the coordination of water to the oligomers. However, analyses of the oligomers by thermogravimetric analyses (TGA) with a heating rate of 10 °C/min showed only one major weight loss occurring 48 between 400 to 500 °C. This indicates that there is no water coordinated to the oligomers. The deviation in the elemental analyses is therefore likely due to the presence of impurities. When compared to compounds 2.27 and 2.28, the higher melting points of oligomers 2.32 (245-250 °C) and 2.34 (299-305 °C) are consistent with the higher molecular weights of these compounds. Analyses of oligomers 2.32 and 2.34 by mass spectrometry also confirm the correct molecular weights of these compounds. Although the structures of oligomers 2.32 and 2.34 cannot be confirmed with certainty due to solubility problems, the data indicates that both oligomers form, but are isolated with slight impurities. 49 0.7 -I 1 1 1 1 1 1 300 350 400 450 500 550 600 Wavelength (nm) Figure 2.6: UV-vis absorption of oligomer 2.32 as a Nujol mull. 0.84 T 330 380 430 480 530 580 Wavelength (nm) Figure 2.7: UV-vis absorption of oligomer 2.34 as a Nujol mull. 50 Figure 2.8: FT-IR absorption of oligomer 2.32 as a Nujol mull. Figure 2.9: FT-IR absorption of oligomer 2.34 as a Nujol mull. 51 2.5 CONCLUSIONS AND FUTURE CONSIDERATIONS During our initial work on the preparation of PPV-based polymers with sulfonate and carboxylate side chains we encountered synthetic difficulties which prevented us from successfully preparing these materials. The problems with the synthesis of BSP-PPV arose from our inability to introduce sulfonate groups to the alkoxy side chains. To circumvent this problem, an alternate route to the synthesis of compound 2.13 is required. Starting from hydroquinone, it may be possible to incorporate a sulfonate group that is already attached to an alkyl chain. In the case of DC-PPV, no conclusive evidence was obtained from the attempted reactions besides the fact that the solution exhibits fluorescence suggestive of the presence of conjugated materials. The results from the synthesis of oligomers 2.32 and 2.34 may provide an explanation of the problems encountered in DC-PPV. The insolubility of oligomers composed of only five phenyl rings suggests that the synthesis of a soluble DC-PPV might not be feasible. In addition to the carboxylate side chains, a solubilizing functional group is needed to improve the solubility of the final polymer. This may be possible via the use of longer ester alkyl groups. Two compounds of carboxy-substituted /?-phenylenevinylene were synthesized via the Wittig reaction. Compounds 2.27 and 2.28 are luminescent with fluorescence quantum yields of 0.25 and 0.51, respectively in THF. The fluorescence quantum yield is dependent on solvent, and for THF, a lower quantum yield is obtained when compared to those measured in cyclohexane or CH2CI2. A base-treated of such a 52 compound in CH2CI2 shows no change in either the fluorescence quantum yield or the absorption maximum. Despite the successful preparation of these fluorescent compounds, the major drawback for these reactions is the low yield of the syntheses. An optimization of the Wittig reaction to increase the overall yield is needed. Two oligomers with different numbers of methyl ester groups were also synthesized via the Wittig reaction. Unexpectedly, these oligomers were found to be insoluble in any organic solvents as well as in aqueous base. Thus, *H and 1 3 C NMR spectra are not available. FT-IR studies of these oligomers confirm the presence of methyl ester group and the trans configuration of the double bonds. Both elemental analyses and mass spectrometric results suggest that the insoluble precipitates are oligomers 2.32 and 2.34. Addition of a solubilizing side chain is probably the best remedy to overcome the solubility problem. 53 CHAPTER 3 EXPERIMENTAL DETAILS 3.1 GENERAL All reactions, unless otherwise indicated, were conducted under a dry dinitrogen atmosphere using standard Schlenk techniques or in an Innovative Technology Inc. drybox. Solvents were distilled either under argon or dinitrogen using the appropriate methods: sodium/benzophenone ketyl (THF, hexanes, benzene, diethyl ether), molten sodium (toluene, xylenes), CaH2 (dichloromethane), CaS04 (DMF), magnesium turnings/iodine (methanol). Distilled solvents were stored over activated 4A molecular sieves. DMSO was sequentially dried with activated 4A molecular sieves. Fine chemicals were obtained either from Aldrich Chemical Co. Ltd. or Fisher Scientific. All fine chemicals, except where noted, were used as received. 2,6-Dimethylaniline, 2,6-diisopropylaniline, chlorotrimethylsilane, tmeda, 1-hexyne, phenylacetylene, trimethylsilyacetylene, diphenylacetylene, 1-phenyl-1-propyne, 3-hexyne, 4-octyne, thionyl chloride, and benzaldehyde were distilled or sublimed prior to use. ] H and 1 3 C NMR spectra were recorded in C 6 D 6 , toluene-d8, CDC13, DMSO-rf6 or D 2 0 at approximately 20 °C on Varian XL-300, Bruker AC-200E or Bruker WH-400 Fourier transform spectrometers. NMR resonances were referenced to internal 54 C6D5H (5 = 7.15 ppm), C 6 D 5 CD 2 / f (5 = 2.09 ppm), Ci/Cl 3 (5 = 7.24 ppm), CH 3SOCD 2# (5 = 2.49 ppm) or DHO (5 = 4.63 ppm) for ! H and C 6 D 6 (5 = 128.0 ppm), CDC13 (5 = 77.0 ppm) or (CH3)2SO (5 = 39.5 ppm) for 1 3 C . Gas chromatography analyses were performed on a Hewlett Packard Model 5890A instrument with a flame ionization detector using a 30-m HP-5 column (5% diphenyl / 95% dimethylpolysiloxane) with 0.25 mm ID. GC/MS analyses were obtained by using a combination of Carlo Erba 4160 / Kratos MS80 instruments. The column conditions for GC/MS were identical to those described for GC. Mass spectra were performed either on a Kratos MS50 or Kratos MS80 instrument. Electronic absorption spectra were obtained on a UNICAM UV2 UV-vis spectrometer. Solid state UV data were collected on a Varian Cary 5 spectrometer. IR spectra were recorded on a BOMEM MB-Series spectrometer. Samples for solid state UV and IR experiments were prepared as a Nujol mull between two KBr plates. Fluorescence measurements were carried out on a Perkin-Elmer LS-5b fluorometer. Thermogravimetric analyses were carried out under Helium (flow rate = 50 mL/min) using a TGA 51 Thermogravimetric Analyzer. 5-10 mg samples were used with a heating rate of 10 °C/min. Melting point determinations were performed on samples placed in capillary tubes using a Gallenkamp apparatus. Flash chromatographic purification was carried out on silica gel 60 (70-230 mesh) which was obtained from BDH. Elemental analyses were performed by Mr. Peter Borda at the University of British Columbia. 55 3.2 PROPYLENE-BRIDGED DIAMINES Preparation of (BAMP)H2 (1.6a) One equivalent of n-butyllithium (1.60 M, 109 mL, 174 mmol) was added dropwise to a stirred THF (150 mL) solution of 2,6-dimethylaniline (21.10 g, 174.1 mmol) at -78 °C. The reaction mixture was stirred for 30 min before warming to room temperature for an additional 30 min. Tmeda (26.3 mL, 174 mmol) was added dropwise at 0 °C, followed by 1,3-dibromopropane (8.8 mL, 87 mmol) added dropwise at room temperature. The reaction mixture was stirred overnight (12 h); then deionized water (2 x 100 mL) was added to dissolve LiBr, and the product was extracted with dichloromethane (2 x 100 mL). The organic layer was dried over anhydrous Na2S04, and the dichloromethane was removed in vacuo yielding a yellow oil. Recrystallization from hexanes afforded 1.6a as a white crystalline solid (10.84 g, 38.38 mmol, 44%). 'H NMR (200 MHz, C 6D 6) 5 7.00 (m, 4H, m-Ai), 6.90 (m, 2H, p-Ar), 2.85 (t, 4H, NC#2), 2.78 (s, 2H, N#), 2.14 (s, 12H, ArMe), 1.50 (pent, 2H, NCH 2Ci/ 2). 13C{'H} NMR (300 MHz, C 6D 6) 5 146.5, 129.5, 129.2, 122.2, 47.0, 32.8, 18.5. Preparation of (BAIP)H2 (1.6b) One equivalent of n-butyllithium (2.50 M, 21.9 mL, 54.8 mmol) was added dropwise to a stirred solution of 2,6-diisopropylaniline (9.72 g, 54.8 mmol) in THF (80 mL) at -78 °C. After 30 min, the reaction mixture was gradually warmed to room temperature 56 and then stirred for an additional 30 min. This was followed by the addition of tmeda (8.3 mL, 55 mmol) at 0 °C. The reaction mixture was allowed to warm to room temperature before the dropwise addition of 1,3-dibromopropane (2.8 mL, 28 mmol). The resulting yellow solution was stirred overnight (12 h). Deionized water (100 mL) was added to dissolve the LiBr generated from the reaction, and the solution was then extracted twice with dichloromethane (2 x 100 mL). The organic layer was dried over anhydrous Na2SC>4, and dichloromethane was removed in vacuo. The resulting yellow oil was dissolved in diethyl ether (30 mL) and precipitated by adding concentrated HC1 (10 mL). The salt ([RH2N(CH2)3NH2R]Cl2) was collected by filtration, washed with cold diethyl ether, and redissolved in dichloromethane (100 mL). Saturated potassium carbonate solution was added dropwise until the solution tested strongly basic with litmus paper. The organic layer was separated and dried over anhydrous Na2S04. Pure 1.6b was obtained as a viscous oil upon removal of dichloromethane (5.19 g, 13.2 mmol; 48%). ! H NMR (300 MHz, C 6D 6) 6 7.10 (m, 6H, Ar), 3.37 (sept, 4H, CHMe2), 3.02 (t, 4H, NC7/2), 3.00 (s, 2H, N#), 1.79 (pent, 2H, NCH 2C// 2), 1.23 (d, 24H, CHM>2). l3C{lR} NMR (300 MHz, C 6D 6) 5 143.96, 142.64, 124.38, 123.91, 50.81,32.73,28.10,24.57. Preparation of (BAMP)(TMS)2 (1.9a) To a THF solution (80 mL) of 1.6a (7.01 g, 24.8 mmol) at -78 °C, 2.05 equivalents of MeLi (36.2 mL, 51.0 mmol, 1.40 M) were added dropwise. The solution was allowed to warm to room temperature and was stirred for 30 min. Then 2.05 equivalents of 57 TMSC1 (6.5 mL, 51 mmol) were added dropwise at 0 °C. The solution was stirred overnight at room temperature, after which time the solvent was removed in vacuo. Hexanes were added to dissolve the desired product, and the white precipitate (LiCl) was removed by filtering the mixture through Celite. Upon removal of hexanes, 1.9a was obtained as colorless oil (8.48 g, 19.9 mmol, 80%). 'H NMR (300 MHz, C 6D 6) 5 7.00 (m, 4H, m-Ar), 6.90 (m, 2H, ^-Ar), 2.82 (t, 4H, NC#2), 2.16 (s, 12H, ArMe), 1.54 (pent, 2H, NCH2C#2), 0.04 (s, 18H, NSiMe3). 13C{'H} NMR (300 MHz, C 6D 6) 8 146.4, 137.8, 128.8, 125.0, 48.5, 33.0, 19.5, 0.4. Preparation of (BAIP)(TMS)2 (1.9b) Using the same experimental procedure as for 1.9a, 1.9b was obtained as a white solid (7.73 g, 14.3 mmol, 90%). Reagents: 1.6b (6.29 g, 15.9 mmol); MeLi (22.0 mL, 32.6 mmol, 1.50 M); TMSC1 (4.1 mL, 32 mmol). Analysis: *H NMR (300 MHz, C 6D 6) 5 7.08 (m, 6H, Ar), 3.50 (sept, 4H, CHMe2), 3.01 (t, 4H, NC// 2), 1.79 (m, 2H, NCH2C#2), 1.20 (d, 12H, CHM>2), 1.18 (d, 12H, CHM>2), 0.1 (s, 18H, NSiMe3). l3C{lU} NMR (300 MHz, C 6D 6) 5 148.4, 143.6, 126.0, 124.2, 51.1, 32.2, 28.0, 25.2, 24.8, 0.4. 58 3.3 CHELATING DIAMIDE COMPLEXES OF TITANIUM Preparation of (BAMP)TiCI2 (1.10a) TiCLj (0.77 mL, 7.0 mmol) was added dropwise to a stirred solution of 1.9a (3.00 g, 7.03 mmol) in xylenes (50 mL) at ambient temperature. The resulting dark red solution was heated to refluxed overnight. The solvent was then removed in vacuo. Toluene (50 mL) was added to dissolve the desired product, and the mixture was filtered through Celite to remove the insoluble black precipitate which had formed. The solvent was reduced in volume until a red precipitate appeared. Hexanes were added to facilitate the precipitation. The red solid was recrystallized from a mixture of toluenes/hexanes (1:1) to obtain pure 1.10a (2.09 g, 5.24 mmol, 74%). 'H NMR (200 MHz, C 6D 6) 5 6.98 (m, 6H, Ar), 3.48 (t, 4H, NC#2), 2.35 (s, 12H, ArMe), 2.34 (m, 2H, NCH 2C// 2). 13C{'H} NMR (300 MHz, C 6D 6) 8 144.0, 133.1, 129.4, 128.4, 62.0, 32.3,19.1. Preparation of (BAIP)TiCl2 (1.10b) Using the same experimental procedure as for 1.10a, 1.10b was obtained as a red solid (1.50 g, 2.93 mmol, 74%). Reagents: TiCl 4 (0.43 mL, 4.0 mmol); 1.9a (2.13 g, 3.91 mmol). Analysis: ! H NMR (200 MHz, C 6D 6) 5 7.10 (m, 6H, Ar), 3.75 (t, 4H, NCtf2), 3.50 (sept, 4H, CHMe2), 2.49 (m, 2H, NCH 2C// 2), 1.46 (d, 12H, CHMe2), 1.18 (d, 12H, CHMe2). 13C{!H} NMR (300 MHz, C 6D 6) 5 144.4, 143.3, 129.1, 125.0, 64.3, 31.0,28.9,26.1,24.3. 59 3.4 TITANACYCLOPENTADIENES Preparation of (BAMP)Ti(C4Ph4) (1.11) A benzene (30 mL) solution of 1.10a (0.50 g, 1.3 mmol) was added to an excess of 1% Na/Hg amalgam. The solution became green as the titanium complex was reduced. Two equivalents of diphenylacetylene (0.45 g, 2.5 mmol) were then added. The mixture was stirred overnight (12 h) at ambient temperature. The resulting yellow mixture was filtered through Celite to remove the insoluble black precipitate which had formed. The solvent was removed in vacuo, and the red solid was recrystallized from hexanes to obtain pure 1.11 (0.33 g, 0.48 mmol, 38%). *H NMR (300 MHz, C 6D 6) 5 7.00 (m, 6H, K4r), 6.58-6.85 (m, 20H, T i C A ) , 3.56 (t, 4H, NC// 2), 2.50 (m, 2H, NCH 2C// 2), 2.37 (s, 12H, ArMe). uC{lU} NMR (300 MHz, C 6D 6) 5 213.6, 147.6, 145.8, 144.2, 139.5, 133.6, 130.3, 129.2, 127.7, 127.2, 126.9, 126.5, 125.8, 124.6, 57.4, 30.9, 19.7. Calcd for T1C47H44N2: C, 82.44; H, 6.48; N, 4.09. Found: C, 82.70; H, 6.45; N, 3.98. Preparation of (BAIP)Ti(C4Et4) (1.12) Using the same experimental procedure as for 1.11, 1.12 was obtained as a red solid (0.26 g, 0.43 mmol, 44%). Reagents: 1.9b (0.50 g, 0.98 mmol), 3-hexyne (0.16 g, 2.0 mmol). Analysis: 'H NMR (300 MHz, C 6D 6) 8 7.16 (m, 6H, Ar), 3.77 (m, 4H, NC/fc), 3.75 (m, 4H, CHMe2), 2.53 (m, 2H, NCH 2C// 2), 2.43 (q, 4H, TiCaC/72), 2.11 (q, 4H, TiC pC// 2), 1-34 (d, 12H, CHAfe2), 1.32 (d, 12H, CHAfe2), 0.85 (t, 6H, 60 C4CH2Me), 0.83 (t, 6H, C4CH2Me). 13C{'H} NMR (300 MHz, C 6D 6) 5 220.2, 146.9, 144.0, 142.2, 126.3, 124.2, 59.9, 30.7, 29.4, 28.2, 26.7, 24.9, 21.1, 15.5, 15.1. Calcd for TiC 3 9H 6oN 2: C, 77.45; H, 10.00; N, 4.63. Found: C, 77.38; H, 10.16; N, 4.51. 3.5 CYCLOTRIMERIZATION OF ALKYNES All cyclotrimerization experiments were performed in sealed NMR tubes. In each experiment, >30 equivalents of alkynes, relative to the catalyst, were used. The progress of the cyclotrimerization reaction was monitored by *H NMR spectroscopy in toluene-fig. The *H NMR spectrum of each sample was taken before it was heated using an oil bath. A ] H NMR spectrum of each sample was taken again after 30- and 90-minute intervals. After 90 minutes, the sample was removed from the oil bath, the resulting dark yellow solution was filtered through Celite, and the filtrate was analyzed by GC/MS for the presence of substituted arenes. 61 3.6 S U L F O N A T E SIDE C H A I N S Preparation of 2,5-dibromomethyl-l,4-bis(3-chloropropoxy)benzene (2.11) Dioxane (50 mL), Fffir (60 mL), formaldehyde (37% in H2O, 10 mL) and compound 2.15 (4.00 g, 15.2 mmol) were added to a 250 mL 3-neck round-bottom flask at 0 °C. The reaction mixture was gradually warmed to 60 °C, and stirred for 12 h. The resulting grey solid was collected by filtration, washed with MeOH, and recrystallized three times from a mixture of CH2Ci2:MeOH (3:1) to yield 2.11 as a white powder (2.84 g, 6.33 mmol, 42%). *H NMR (300 MHz, CDC13) 5 6.86 (s, 2H, Ar), 4.48 (s, 4 H , CH2BT), 4.14 (t, 4 H , OCH2), 3.80 (t, 4 H , OCH 2CH 2Ci/ 2Cl), 2.26 (pent, 4 H , OCH2C//2). 13C{!H} NMR (300 MHz, CDC13) 8 150.9, 127.4, 114.5, 67.4, 41.8, 30.0, 28.7. Preparation of 2,5-bis(3-chloropropoxy)-l,4-phenylenedimethylene bis(tetrahydrothiophenium bromide) (2.12) THT (1.0 mL, 11 mmol) was added dropwise to a stirred suspension of compound 2.11 (2.50 g, 5.57 mmol) in MeOH (70 mL) at room temperature. The reaction mixture was heated to 60 °C, and left stirring overnight (12 h) under N2. The solvent was then removed by rotary evaporation until a white paste was obtained. The product was precipitated into acetone (1.0 L), and collected by filtration as a white powder (2.45 g, 3.92 mmol, 69%). 'H NMR (200 MHz, D20) 8 7.18 (s, 2H, Ar), 4.49 62 (s, 4H, C/fcTHT), 4.22 (t, 4H, OCH2), 3.78 (t, 4H, 0CH2CH2C#2C1), 3.30-3.57 (m, 8H, SC//2), 2.29 (m, 4H, OCH 2C/f 2), 2.26 (m, 8H, SCH2Cf72). Preparation of l,4-bis(3-chloropropoxy)benzene (2.15) A solution of KOH (12.70 g, 226.4 mmol) in THF (50 mL) was added dropwise to a stirred solution of hydroquinone (10.00 g, 90.82 mmol) in THF (50 mL). The solution was heated at reflux for 1 h to ensure complete deprotonation of the hydroxyl groups. The resulting yellow solution was transferred to a pressure-equalizing dropping funnel, and then added dropwise to a solution of 1,3-dichloropropane (25.9 mL, 273 mmol) in THF (80 mL). The reaction mixture was heated at reflux for 4 h until the yellow color disappeared, after which time the precipitate (KC1) was filtered, and the solvent removed from the filtrate in vacuo. Diethyl ether was added to redissolve the residual white solid. The ether solution was washed with deionized water (2 x 100 mL) to remove any residual KC1. The organic layer was dried over anhydrous Na2S04, and the diethyl ether was removed until crystals appeared. The product was left to crystallize at 0 °C and then collected by filtration to give 2.15 as a white crystalline solid (12.43 g, 47.23 mmol, 52%). 'H NMR (300 MHz, CDC13) 8 6.82 (s, 4H, Ar\ 4.05 (t, 4H, OCH2), 3.72 (t, 4H, OCH 2CH 2Ctf 2Cl), 2.19 (pent, 4H, OCH2C#2). 1 3C{ 1H}NMR(300MHz,CDCl 3)8 152.8, 115.9,68.8,42.0,30.1. 63 Preparation of l,4-bis(3-bromopropoxy)benzene (2.16) A solution of KOH (25.50 g, 454.1 mmol) in THF (100 mL) was added dropwise to a stirred solution of hydroquinone (20.00 g, 181.6 mmol) in THF (100 mL). The solution was heated at reflux for 1 h to ensure complete deprotonation of the hydroxyl groups. The resulting yellow solution was transferred to a pressure-equalizing dropping funnel, and then added dropwise to a solution of 1,3-dibromopropane (55.3 mL, 545 mmol) in THF (100 mL). The reaction mixture was heated at reflux for 4 h until the yellow color disappeared, at which time the precipitate (KBr) was filtered, and the solvent removed from the filtrate in vacuo. Diethyl ether was added to redissolve the residual white solid. The ether solution was washed with deionized water (2 x 150 mL) to remove any residual KBr. The organic layer was dried over anhydrous Na2SC>4, and the diethyl ether was removed until crystals appeared. The product was left to crystallize at 0 °C and then collected by filtration to give 2.16 as a white crystalline solid (26.28 g, 74.65 mmol, 41%). 'H NMR (300 MHz, CDC13) 5 6.82 (s, 4H, Ar), 4.04 (t, 4H, OCH2), 3.59 (t, 4H, OCH2CH2C#2Br), 2.28 (pent, 4H, OCH 2C7/ 2). 1 3C{'H}NMR(300MHz,CDCl 3)5 153.0, 115.5,66.0,32.5,30.1. Preparation of 2,5-dichloromethyl-l,4-bis(3-bromopropoxy)benzene (2.17a) Dioxane (70 mL), HC1 (60 mL), formaldehyde (37% in H 2 0, 10 mL) and compound 2.16 (6.30 g, 17.9 mmol) were added to a 250 mL 3-neck round-bottom flask at 0 °C. The solution was gradually warmed to 60 °C, and hydrogen chloride gas was bubbled into the solution for 7 h. The solution was then stirred for additional 12 h in the 64 absence of hydrogen chloride gas. The resulting grey solid was collected by filtration, washed with MeOH, and recrystallized three times from a mixture of CH 2Cl 2:MeOH (3:1) to yield 2.17a as a white powder (6.22 g, 13.9 mmol, 77%). 'H NMR (300 MHz, CDC13) 6 6.92 (s, 2H, Ar), 4.59 (s, 4H, C#2C1), 4.13 (t, 4H, OCH2), 3.63 (t, 4H, OCH 2CH 2C// 2Br), 2.33 (pent, 4H, OCH2Cf72). "C^H} NMR (300 MHz, CDC13) 5 150.4, 127.2, 114.5, 66.4, 41.3, 32.4, 30.0. Preparation of 2,5-dibromomethyl-l,4-bis(3-bromopropoxy)benzene (2.17b) Dioxane (80 mL), HBr (100 mL), formaldehyde (37% in H 2 0, 15 mL) and compound 2.16 (7.50 g, 21.3 mmol) were added to a 250 mL 3-neck round4x)ttom flask at 0 °C. The reaction mixture was gradually warmed to 60 °C, and stirred for 12 h. The resulting grey solid was collected by filtration, washed with MeOH, and recrystallized three times from a mixture of CH 2Cl 2:MeOH (3:1) to yield 2.17b as a white powder (7.00 g, 13.0 mmol, 61%). *H NMR (300 MHz, CDC13) 6 6.86 (s, 2H, Ar), 4.48 (s, 4H, C//2Br), 4.13 (t, 4H, OCH2), 3.66 (t, 4H, OCH2CH2Cr72Br), 2.35 (pent, 4H, OCH2C7/2). 13C{'H} NMR (300 MHz, CDCI3) 5 150.5, 127.6, 114.6, 66.2, 32.4, 30.0, 28.5. 65 3.7 CARBOXYLATE SIDE CHAINS Preparation of 2,5-dibromo-/;-xylene (2.18) Bromine (50.0 mL, 971 mmol) was added dropwise to a stirred solution of p-xylene (50.00 g, 471.0 mmol) and I2 (1.20 g, 4.73 mmol) at 0 °C in the dark. The solution was stirred at room temperature for 12 h, after which time 20% aqueous KOH (200 mL) was added to quench the unreacted bromine. The aqueous solution was decanted and the yellow solid was recrystallized from EtOH to give pure 2.18 as a white solid (105.65 g, 400.25 mmol, 85%). [ H NMR (300 MHz, CDC13) 5 7.37 (s, 2H, Ar), 2.31 (s, 6H, ArC#3). ^C^H} NMR (300 MHz, CDC13) 5 136.9, 133.9, 123.3, 22.1. Preparation of 2,5-dicyano-p-xylene (2.19) A mixture of compound 2.18 (43.95 g, 166.5 mmol) and CuCN (38.00 g, 424.3 mmol) in DMF (100 mL) was heated to reflux for 4 h. The color gradually changed from green to yellow and a light brown precipitate formed. The reaction mixture was cooled to 0 °C before it was poured into a solution of aqueous Fe(III)Cl3 (180 g) and concentrated HC1 (50 mL). The resulting grey solid was filtered, and washed with deionized water. Recrystallization from CH2CI2 gave pure 2.19 as a crystalline solid (20.03 g, 128.2 mmol, 77%). 'H NMR (300 MHz, CDC13) 8 7.54 (s, 2H, Ar), 2.52 (s, 6H, ArCi/ 3). uC{lH} NMR (300 MHz, CDC13) 8 139.9, 133.8, 116.9, 116.6, 19.8. 66 Preparation of 2,5-dimethylterephthalic acid (2.20) A suspension of compound 2.19 (14.50 g, 92.84 mmol) in concentrated H3PO4 (350 mL) was brought to reflux for 12 h under N 2 . The resulting white precipitate was filtered, washed with deionized water, and recrystallized from EtOH to afford pure 2.20 as a white powder (17.82 g, 91.77 mmol, 99%). J H NMR (300 MHz, DMSCMO 5 13.07 (s, 2H, COOH), 7.68 (s, 2H, Ar), 2.47 (s, 6H, ArC// 3). '^{'H} NMR (300 MHz, DMSO-tf6) 5 168.2, 136.0, 133.1, 132.9, 20.5. Preparation of dimethyl 2,5-dimethylterephthalate (2.21) A mixture of compound 2.20 (10.00 g, 51.50 mmol) and SOCl2 (150 mL) was heated at reflux under N 2 until the solution became clear. The excess SOCl 2 was distilled off and the residual white solid dried under reduced pressure for 1 h. The solid was then suspended in diethyl ether (50 mL), and dry MeOH (100 mL) was added dropwise. The reaction mixture was heated to reflux at 5 h, after which time the solvent was removed by rotary evaporation. The crude product was recrystallized from diethyl ether to give pure 2.21 as white needles (10.18 g, 45.81 mmol, 89%). ] H NMR (300 MHz, CDCI3) 5 7.73 (s, 2H, Ar), 3.88 (s, 6H, COC#3), 2.54 (s, 6H, ArCH3). 13C{'H} NMR (300 MHz, CDC13) 5 167.5, 137.0, 133.5, 132.4, 52.1,21.0. Preparation of dimethyl 2,5-dibromomethylterephthalate (2.22) A solution of compound 2.21 (2.00 g, 9.00 mmol), N-bromosuccinimide (NBS) (3.20 g, 18.0 mmol), and a catalytic amount of benzoyl peroxide in CCI4 (50 mL) was 67 heated at reflux for 12 h. White light was also applied to the reaction to promote radical formation. The insoluble succinimide which formed was filtered off, and the solvent removed in vacuo. The crude product was recrystallized twice from THF to yield pure 2.22 as a white solid (1.74 g, 4.58 mmol, 51%). ! H NMR (300 MHz, CDC13) 5 8.02 (s, 2H, Ar), 4.90 (s, 4H, ArC//2Br), 3.95 (s, 6H, COCH3). 13C{'H} NMR (300 MHz, CDC13) 5 165.6, 139.4, 134.4, 132.2, 52.7, 30.0. Preparation of 2,5-bis(methylcarboxy)-l,4-phenylenedimethylene bis(tetrahydrothiophenium bromide) (2.23) THT (1.1 mL, 13 mmol) was added dropwise to a stirred suspension of compound 2.22 (2.40 g, 6.32 mmol) in MeOH (70 mL) at 20 °C. The reaction mixture was heated to 60 °C, and left stirring overnight (12 h) under N 2 . The solvent was then removed by rotary evaporation until a white solid precipitated. The product was then precipitated into acetone (1.0 L), and collected by filtration as a white powder (2.03 g, 3.65 mmol, 59%). l H NMR (200 MHz, D 20) 5 8.19 (s, 2H, Ar), 4.70 (s, 4H, CH2TWT), 3.84 (s, 6H, COOC//3), 3.42 (m, 8H, SCH2), 2.24 (m, 8H, SCH 2C// 2)-68 3.8 F L U O R E S C E N T C O M P O U N D S Preparation of 2,5-bis(methylcarboxy)-l,4-phenylenedimethylene bis(triphenylphosphonium bromide) (2.25) A solution of compound 2.22 (0.63 g, 1.7 mmol) and triphenylphosphine (0.87 g, 3.3 mmol) in THF (50 mL) was heated at reflux for 12 h. The resulting white precipitate was collected by filtration, washed with THF, and dried under reduced pressure to give pure 2.25 as a white powder (1.54 g, 2.40 mmol, 72%). 'H NMR (200 MHz, DMSO-rf6) 5 7.50-8.00 (m, 32H, Ar & ?Ph3), 5.50 (d, 4H, ArC/fc), 3.37 (s, 6H, COOC//3)-Preparation of compound 2.27 NaH (0.10 g, 4.2 mmol) was added to DMSO (100 mL) at 65 °C. Compound 2.25 (2.50 g, 3.89 mmol) was added to this solution in small portions to generate the corresponding ylide. The resulting red solution was stirred for 1 h, after which time benzaldehyde (0.8 mL, 8 mmol) was added in one portion. The solution was stirred overnight (12 h), during which time the color changed from red to yellow. The solvent was removed under reduced pressure, and the resulting yellow solid was redissolved in a minimum amount of THF and purified by chromatography on silica gel using CH2Ci2:CHCl3 (1:1) as eluant. The first fraction was collected, and the product recrystallized from THF to afford 2.27 as yellow needles (0.08 g, 0.2 mmol, 5%). 'H NMR (400 MHz, CDC13) 5 8.25 (s, 2H, Ar), 7.89 (d, 2H, CH=CH), 7.54 (d, 69 4 H , Ar), 7.36 (m, 4 H , Ar), 7.27 (m, 2H, Ar), 7.08 (d, 2H, CU=CH), 3.97 (s, 6 H , COOC//3). 13C{'H} NMR (300 MHz, CDC13) 5 167.3, 137.3, 137.1, 132.2, 131.4, 129.1, 128.7, 128.1, 127.0, 125.9, 52.5. mp = 167-169 °C. MS (DCI+) m/z 398.15120 (M+). Calcd. for C 2 6 H 2 2 0 4 : 398.15179. Anal. Calcd. for C26H22O4: C, 78.37; H, 5.56. Found: C, 78.21; H, 5.48. Preparation of compound 2.28 NaH (0.10 g, 4.2 mmol) was added to DMSO (100 mL) at 65 °C. Compound 2.25 (2.50 g, 3.89 mmol) was added to this solution in small portions to generate the corresponding ylide. The resulting red solution was stirred for 1 h before transferred to a pressure-equalizing dropping funnel. The ylide was then added dropwise through the funnel to a solution of terephthaldicarboxaldehyde (1.00 g, 7.46 mmol) in DMSO (100 mL) at 20 °C. The reaction mixture was stirred for 12 h, after which time the color changed from red to yellow. The solvent was removed under reduced pressure and the residual yellow solid was chromatographed on silica gel using acetone :CH2Cl2 (1:1) as eluant. The first fraction was collected, and the product recrystallized from CH2CI2 to give pure 2.28 as a yellow solid (0.31 g, 0.68 mmol, 18%). 'H NMR (300 MHz, CDCI3) 8 10.00 (s, 2H, CHO), 8.30 (s, 2H, Ar), 8.09 (d, 2H, C//=CH), 7.87 (d, 4 H , Ar), 7.69 (d, 4 H , Ar), 7.24 (d, 2H, CH=CH), 4.00 (s, 6 H , COOC//3)- 13C{'H} NMR (300 MHz, CDC1 3 ) 8 191.6, 166.8, 143.0, 137.5, 135.7, 131.6, 131.1, 130.3, 129.5, 129.3, 127.4, 52.7. mp = 173-175 °C. MS (DCI+) m/z 454.14182 (M+). 70 Calcd. for CWEfeOe: 454.14163. Anal. Calcd. for C^HbOe: C, 74^ 00; H, 4.88. Found: C, 74.00; H, 4.84. 3.9 OLIGOMERS Preparation of dimethyl 2-bromomethyl-5-methylterephthaIate (2.29) A solution of compound 2.21 (2.00 g, 9.00 mmol), NBS (0.80 g, 4.5 mmol), and a catalytic amount of benzoyl peroxide in CCU (50 mL) was heated at reflux for 12 h. White light was applied to the reaction to promote radical formation. The succinimide which formed was filtered off, and the solution y was examined by ! H NMR spectroscopy to confirm the presence of 2.29. According to the *H NMR spectrum, only the unbrominated compound 2.21 and the desired product were present in 3:2 ratio. Compound 2.29 was not separated from the starting material, since in the " subsequent reaction, the product can easily be isolated by filtration. ! H NMR (200 MHz, CDCI3) 6 7.94 (s, 1H, Ar), 7.79 (s, 1H, Ar), 4.88 (s, 2H, CH2Br), 3.94 (s, 3H, COOCZ/3), 3.92 (s, 3H, COOC// 3), 2.57 (s, 3H, ArC/ft). Preparation of 2,5-bis(methylcarboxy)-l-methyl-4-phenylenemethylene triphenylphosphonium bromide (2.30) A mixture of the crude 2.29 was dissolved in CCI4 and an excess of triphenylphosphine (3.00 g, 11.4 mmol) added and heated at reflux for 12 h. The 71 resulting white precipitate was collected by filtration, washed with THF and dried under a reduced pressure to give pure 2.30 as a white powder (1.10 g, 1.95 mmol). *H NMR (200 MHz, CDC13) 5 8.01 (s, 1H, Ar), 7.99 (s, 1H, Ar), 7.50-7.86 (m, 15H, PPh3), 5.96 (d, 2H, C//2PPh3), 3.78 (s, 3H, COOC#3), 3.49 (s, 3H, COOCr73), 2.54 (d, 3H, ArCfY3). Preparation of oligomer 2.32 NaH (0.01 g, 0.4 mmol) was added to DMSO (80 mL) at 65 °C. Compound 2.30 (0.25 g, 0.44 mmol) was added to this solution in small portions to generate the corresponding ylide. The resulting red solution was stirred for 1 h, after which time compound 2.28 (0.08 g, 0.2 mmol) was added in one portion. The solution was stirred for 12 h, during which time the color changed from red to orange and then to yellow. The yellow precipitate was collected by filtration, washed with deionized water (2 x 50 mL), THF (2 x 50 mL) and then dried under reduced pressure. The dried yellow solid was ground into a fine powder and rewashed with deionized water (2 x 50 mL) and THF (2 x 50 mL). After drying under vacuum at 100 °C, the product was collected as a yellow powder (0.05 g, 0.06 mmol, 33%). mp = 245-250 °C. IR (nujol) cm"1: 1723 (C=0), 1629 (RHC=CHR, trans), 1304 (RHC=CHR, trans), 1237 (C-O), 1103 (C-O), 954 (RHC=CHR, trans). MS (EI) m/z 862.29749 (M+). Calcd. for C52H46O12: 862.29895. Anal. Calcd. for C 52H4 60i 2: C, 72.38; H, 5.37. Found: C, 69.97; H, 5.42. 72 Preparation of oligomer 2.34 NaH (0.01 g, 0.4 mmol) was added to DMSO (80 mL) at 65 °C. Benzyltriphenylphosphonium chloride (0.17 g, 0.44 mmol) was added to this solution in small portions to generate the corresponding ylide. The resulting red solution was stirred for 1 h, after which time compound 2.28 (0.10 g, 0.22 mmol) was added in one portion. The solution was stirred for 12 h, during which time the color changed from red to orange and then to yellow. The yellow precipitate was collected by filtration, washed with deionized water (2 x 50 mL), THF (2 x 50 mL) and then dried under reduced pressure. The dried yellow solid was ground into a fine powder and rewashed with deionized water (2 x 50 mL) and THF (2 x 50 mL). After drying under vacuum at 100 °C, the product was collected as a yellow powder (0.04 g, 0.07 mmol, 29%). mp = 299-302 °C. IR (nujol) cm"1: 1724 (C=0), 1621 (RHOCHR, trans), 1304 (RHC=CHR, trans), 1236 (C-O), 1101 (C-O), 964 (RHOCHR, trans). MS (EI) m/z 602.24524 (M*). Calcd. for C42H34O4: 602.24573. Anal. Calcd. for C42H34O4: C, 83.70; H, 5.68. Found: C, 79.74; H, 5.48. 73 REFERENCES (1) Bertholet, M. Held. Seances Acad. Sci. 1866, 62, 905. 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