Conjugated Schiff Base-Type Metal-Containing Polymers

CONJUGATED SCHIFF BASE-TYPE METAL-CONTAINING POLYMERS

ALFRED CHI WOOK LEUNG

B.Sc. (Hon,), The University of British Columbia, 2001

A THESIS SUBMITTED IN PARTIAL FULFILLMENT OF THE REQUIREMENTS FOR THE DEGREE OF

DOCTOR OF PHILOSOPHY

THE FACULTY OF GRADUATE STUDIES

(Chemistry)

THE UNIVERSITY OF BRITISH COLUMBIA

(Vancouver)

July 2008

The work in this thesis describes the synthesis and characterization of a series of conjugated polymers containing Schiff base transition metal complexes. High molecular weight poly(salphenyleneethynylene)s (PSPEs) were synthesized using the Sonogashira-Hagihara protocol and they were characterized using nuclear magnetic resonance spectroscopy and gel permeation chromatography. Their optical properties were investigated by UV-vis and fluorescence spectroscopies. PSPEs containing Zn saiphen moieties were found to exhibit strong aggregation that is facilitated by the presence of Zn to 0 interactions, and it was discovered that the polymers interact with various Lewis bases to undergo aggregation and deaggregation. New ladder-type conjugated polymers, as well as a series of model compounds that are representative of the repeating units of the polymers, were synthesized using Schiff base condensation methods.

The electronic and magnetic properties of these ladder-polymers were studied using cyclic voltammetry, electron paramagnetic resonance spectroscopy, and magnetic susceptibility measurements.

11 Table of Contents

Abstract ii

Table of Contents iii

List of Tables v

List of Figures vi

List of Schemes x

List of Symbols and Abbreviations xiii

Acknowledgements xviii

Dedication xix

Co-Authorship Statement xx

CHAPTER 1 Introduction

.1 Metal-Containing Polymers 1 1.2 Schiff Base Complexes 4 1.3 Scope of Introduction 5 1.4 Early Research 6 1.5 Chemically Polymerized Schiff Base Polymers 8 1.5.1. Salen-Containing Homopolymers 8 1.5.2 Salen-Containing Copolymers 10 1.6 Helical Schiff Base polymers 26 1.7 Electrochemically Polymerized Schiff Base Polymers 37 1.8 Goals and Scope 49 1.9 References 53

CHAPTER 2 Poly(salphenyleneethynylene)s : Soluble, Conjugated, Metal- 58 Containing Polymers

2.1 Introduction 58 2.2 Monomer Synthesis and Characterization 63 2.3 Polymer Synthesis and Characterization 69 2.4 Conclusions 73 2.5 Experimental 74 2.5.1 General 74 2.5.2 Procedures 75 2.5.3 X-Ray Diffraction Studies 80 2.6 References 83

111 CHAPTER 3 Poly(salphenyleneethyynylene)s and Their Unique 88 Supramolecular Crosslinking Behavior

3.1 Introduction 88 3.2 Synthesis of Monomers and Polymers 92 3.3 Polymer Characterization 96 3.4 Aggregation and Sensing 100 3.5 Conclusions 108 3.6 Experimental 109 3.6.1 General 110 3.6.2 Procedures 110 3.7 References 120

CHAPTER 4 The Ladder-Chelate Approach to Soluble Conjugated Metal- 123 Containing Polymers

4.1 Introduction 123 4.2 Synthesis of Starting Materials 129 4.3 Synthesis and Characterizations of Model Compounds 133 4.3.1 Model Compounds Synthesis and NMR Studies 133 4.3.2 Electrochemical, EPR, and Magnetic Susceptibility 148 Studies of the Model Compounds 4.4 Synthesis and Characterization of Ladder Polymers 154 4.5 Conclusions 165 4.6 Experimental 166 4.6.1 General 166 4.6.2 Procedures 167 4.6.3 X-Ray Diffraction Studies 185 4.7 References 191

CHAPTER 5 Conclusions and Future Directions 194

5.1 Overview 194 5.2 Poly(salphenyleneethynylene)s (PSPEs) 195 5.3 Schiff Base Ladder Metallopolymers 197 5.4 Future Directions 200 5.5 References 205

iv Lists of Tables

Table 2.1 X-ray diffraction data for compound 196b 81

Table 2.2 Selected bond lengths (A)and angles (°) for 196b 82

Table 3.1 Molecular weights (Mm,M) and polydispersities of polymers 98 216a-c and 217a-c. Measurements were made with a GPC system equipped with triple detection (refractive index, light-scattering, and viscosity).

Table 4.1 X-ray diffraction data for compound 231a 185

Table 4.2 Selected bond lengths (A)and angles (°) for 231a 188

V List of Figures

Figure 1.1. 1-D phthalocyanine coordination polymer 1 (“shish-kebab” 3 polymers), monomer for the synthesis of 2-D phthalocyanine sheets 2 (“parquet” polymers), and porphyrin-containing PPE 3.

Figure 1.3. SEM images of(a) Cu polymer 110 and analogous (b) Ni (c) Zn and 34 (d) Co polymer. Scale bar represents 1 JIm,and the inset shows a plot of the frequency vs. microsphere diameter. Reprinted with permission from reference 52a. Copyright 2003 Wiley-VCH.

Figure 1.4. Structure of model compound 113 as determined by X-ray 36 crystallography. Hydrogen atoms and tert-butyl groups are omitted for clarity.

Figure 1.5. SEM images of 117 electrochemically synthesized in (a) MeCN and 40 (b) C1CH Reprinted with permission from reference 56. Copyright 1989 American.2 Chemical Society. Figure 1.6. General structures of the target polymers prepared in this thesis 51

Figure 2.1. Fast synthesis and screening of conjugated polymers. Dibromoaryl 62 monomers I-XII and diethynylaryl monomers A-H were polymerized through Pd-catalyzed Sonogashira coupling.

Figure 2.2. Solution fluorescence of the 96 polymers measured at 530 nm 63 Polymers GXI and GXII correspond to PPEs containing Zn and Ni Schiff base complexes 191a and 192a. Figure 2.3. ‘H NMR spectrum (300 MHz) of Ni monomer 196b in 3CDC1 65 Figure 2.4. Single crystal X-ray diffraction structure of monomer 196b (a) 66 perpendicular and (b) parallel to the plane of the salphen ligand. Thermal ellipsoids are shown at the 50% probability level. Solvent molecules are removed for clarity. Red = oxygen, blue = nitrogen, purple = iodine, green = nickel. The packing pattern of 196b in the solid state is illustrated in (c), and the packing pattern along the b axis is shown in (d).

Figure 2.5. Photograph of thin films of polymers 202a-c. In THF, the polymers 70 form intensely colored solutions (ca. 10 mg mL’).

Figure 2.6. Gel permeation chromatogram for polymer 202c. Weight averaged 71 molecular weight M for 202c is 84,000 Da.

vi Figure 2.7. (a) UV-visible spectra for polymers 202a-c in THF, (b) Emission 72 spectrum of polymer 202a in THF (2exc = 406 nm).

Figure 3.1. PPE sensor 203 has superior sensitivity over molecular sensor 205 89 to electron deficient molecules such as paraquat (204).

Figure 3.2. Porphyrin containing polymer 190 self-assembled into a 90 supramolecular polymer ladder 206 in the presence of 4,4’-bipyridine.

Figure 3.3. Intensely colored films of polymers 216a-c were obtained through 95 simple suction filtration. The polymers dissolve in THF to give red solutions. Figure 3.4. 1H NMR spectrum of polymer 217a. 3(CDCI + 1% pyridine-d 96 Inset: Expanded view of region from 3 to 9 ppm. )5 Figure 3.5. UV-vis absorption (normalized) spectra of polymers 216a-c and 99 217a-c in 2CICH (the polymers were dissolved in THF and diluted with 2C1CH to appropriate concentration, see procedures on P.24 for details). Figure 3.6. UV-Vis absorption (normalized) spectra of 218 and 219 in 2C1CH 99 Figure 3.7. Illustration of dimerization in Zn salphen complexes. Strong 101 interactions between the 2Zn center and the phenolic oxygens of the metal complexes hold the dimer together.

Figure 3.8. UV-vis and fluorescence spectra of 216a C1(CH 5.00 x l0 M) 103 titrated with a) pyridine (1.03 x 106_ 1.13 x M; step2 size: 1.03 x 10.6M) and l0 b) 4,4’ bipyridine (4.30 x i0 —6.45 x l0 M; step size:, 4.30 x M). Figure 3.9. UV-vis and fluorescence spectra of 219 C1(CH 5.00 x 10 M) 104 108 titrated with a) pyridine (1.03 x — 1.65 x i0 M;2step size: 1.03 x 10 M) and b) UV-vis and fluorescence spectra of 219 titrated with, 4,4’ bipyridine (1.08 x o 6_2.40 x step size: 1.08 x 610M). Figure 3.10. UV-vis and fluorescence spectra of 217a C1(CH 5.00 x 10 M) 107 10.6 titrated with a) pyridine (1.03 x 106 — 1.03 x M; step2 size: 1.03 x M) and b) 4,4’ bipyridine (4.30 x 10-5 — 3.01 x M; step, size: 4.30 x i0 M). Figure 3.11. Cartoon illustrating the disruption of the polymer crosslinks upon 108 the addition of pyridine.

Figure 4.1. Oligoacenes 220, hexa-peri-benzocoronenes (HBCs) 221, and 125 polyrylene 222 are examples of highly conjugated organic compounds investigated for applications as organic electronics.

Figure 4.2. Target Schiff base ladder polymers 230 and 232, and bimetallic 129 model compounds 229 and 231. (R = alkoxy)

vii Figure 4.3. Phenylenediamine derivatives with pendant solubilizing groups that 133 were used in the preparation of Schiff base ladder polymers.

Figure 4.4. ‘H NMR spectrum C1(CD 300 MHz) of proligand 248b showing 138 the expected resonance signals. Inset:2 Expanded view of region from 6.7 to 8.7 ppm. , Figure 4.5. 1H NMR (DMSO-d 300 MHz) spectrum of bimetallic Zn model 139 compound 229a. Inset:6 Expanded view of region from ö 6.3 to 9 ppm. Figure 4.6. 1H NMR titration, experiments illustrating the aggregation of 229a in 141 non-coordinating solvents. 2C1CD was added to a solution of DMSO-d containing 229a, up to a concentration of 1:4 /CDDMSO-d 6 Significant signal broadening and upfield shift of the aromaticC1 signals suggests aggregation of 229a in the presence of non-coordinating solvents.62 Figure 4.7. ‘H NMR spectrum C1(CD 400 MHz) of the product obtained 144 from attempted synthesis of bimetallic2 Ni model. compound 249. Inset: MALDI TOF mass spectrometry confirms, the product contains a mixture of compounds containing one and two Ni atoms.

Figure 4.8. Single crystal X-ray diffraction structure of model compound 231a 146 (a) perpendicular (thermal ellipsoids are shown at the 50% probability level) and (b) a side on view of the bimetallic Zn metal complex. Solvent molecules are removed for clarity. Red = oxygen, blue = nitrogen, purple = zinc, gray carbon. The packing pattern of 231a in the solid state is illustrated in (c), showing the presence of dimeric aggreagates. In (d), adjacent bimetallic salphen moieties are shown to aggregate in opposite directions along the plane of the molecules.

Figure 4.9. An illustration of the different spin alignment patterns between 148 model compounds 229 and 231 as predicted by a simple spin alignment model.

Figure 4.10. Cyclic voltammograms of Cu model compounds recorded in 0.1 M 150 x x NJPF[(n-Bu) /THF solutions containing: (a) 1 M 246b; (b) 1.6 M 229b.46 Scan rate 0.5 V/s. Figure 4.11. EPR powder spectra of(a) 246b, (b) 229b and (c) 231b obtained at 151 77.3 K.

Figure 4.12. Temperature dependence of magnetic susceptibility (diamonds) for 154 (a) 246b, (b) 229b and (c) 231b. The solid lines correspond to the best fit curves obtained from the Curie-Weiss Law in (a) and (b), and the Bleaney-Bowers Equation in (c). Figure 4.13. GPC chromatogram of organic polymer 253a (R = H25OC, 157 showing the presence of short oligomers. )2 Figure 4.14. Polymer 230a was obtained as a shiny black solid. The intensely 160 colored material can be cast into solid shapes or films.

viii Figure 4.15. UV-vis spectra of model compounds 246a and 229a, and ladder 161 polymer 230a. The observed bathochromic shifts correspond to the extension in conjugation.

Figure 4.16. UV-vis spectra of ladder polymer 230b and 230c 163

Figure 4.17. Single crystal X-ray diffraction structure of model compound 231a 185 (thermal ellipsoids are shown at the 50% probability level). Solvent molecules are removed for clarity. Red = oxygen, blue = nitrogen, purple = zinc, gray = carbon.

Figure 5.1. Poly(salphenyleneethynylene)s (PSPE)s synthesized in this thesis 196 (BuOct = 2-ButylOctyl).

Figure 5.2. Ladder-type Schiff base conjugated polymers and model compounds 198 synthesized in this thesis.

Figure 5.3. Schiff base macrocycles and dendrimers synthesized in the 201 MacLachlan Research group.

Figure 5.4. Monomers such as diiodofluorene 269, diiodoanthracene 270 204 diiodophenanthrene 271, and pentiptycene 272 should be explored as possible components for new PSPEs.

ix List of Schemes

Scheme 1.1. Synthesis of Schiff base transition metal complexes 5

Scheme 1.2. Synthesis of M(salphen)-containing polymers 11 and 12 6

Scheme 1.3. Synthesis of Schiff base polymers 18 (M = Cu, Ni, Co, Zn, and Mn) 7

Scheme 1.4. Hydrolytic kinetic resolution of terminal epoxides catalyzed by 27 9 and 28

Scheme 1.5. Synthesis of copolymer 32 by thermal curing 11

Scheme 1.6. Synthesis of salen-polyurethane copolymer 41 13

Scheme 1.7. Synthesis of siloxane-Schiff base copolymer 46 14

Scheme 1.8. Synthesis of siloxane-Schiff base copolymer 49 15

Scheme 1.9. Synthesis of polysilane-salen copolymer 52 15

Scheme 1.10. Synthesis of crosslinked polysilane-copper salen copolymer 58 17

Scheme 1.11. Synthesis of crown ether-cobalt salphen copolymer 61 18

Scheme 1.12. Aerobic oxidation of cyclohexene catalyzed by 61 18

Scheme 1.13. Synthesis of linear polychelate 64 and crosslinked polychelate 66 19 and 68

Scheme 1.14. Synthesis of manganese Schiff base crosslinked polymers 71 21

Scheme 1.15. Synthesis of platinum salen-fluorene copolymer 74 22

Scheme 1.16. Synthesis of zirconium salphen- poly(tetrahydrofuran) block 24 copolymer 79.

Scheme 1.17. Synthesis of zirconium and cerium Schiff base polymers 83 - 85 25

Scheme 1.18. Synthesis of helical ladder polymer 89 27

Scheme 1.19. Synthesis of helical ladder polymer 93 28

Scheme 1.20. Synthesis of helical zinc and manganese polymers 97 and 98 29

Scheme 1.21. Synthesis of macrocycle 102 and oligomer 103 31

Scheme 1.22. Synthesis of Ni polymer 106 31

x Scheme 1.23. Synthesis of copolymer 107.33 Scheme 1.24. Synthesis of double-helical copper polymer 110 35

Scheme 1.25. Synthesis of model compound 113 36

Scheme 1.26. Preparation of electropolymerized polymer 115 37

Scheme 1.27. Preparation of bis(salphen)s 132—135 and 144 — 149 42

Scheme 1.28. Electrochemical synthesis of polymer 152 43

Scheme 1.29. Electrochemical synthesis of polymer 161 46

Scheme 1.30. Electrochemical synthesis of polymer 166 47

Scheme 1.31. Electrochemical synthesis of polymer 170 47

Scheme 2.1. The synthesis of porphyrin containing polymer 190 reported by 61 Anderson et al. Branched alkyl substituents (R = 2-ethyihexyl) were incorporated onto the porphyrin moiety to improve solubility.

Scheme 2.2. Synthesis of monomers 196a-c 64

Scheme 2.3. Synthesis of diethynylaryl monomer 201 68

Scheme 2.4. Synthesis of the PSPEs 202a-c 69

Scheme 3.1. Synthesis of phenylenediamine 210 93

Scheme 3.2. Synthesis of monomers 212a-c 94

Scheme 3.3. Synthesis of monomers 215a-c 94

Scheme 3.4. Synthesis of conjugated metallopolymers 216a-c 94

Scheme 3.5 Synthesis of conjugated metallopolymers 217a-c 94

Scheme 4.1. Phthalocyanine 223 is an attractive component for conjugated 126 metal-containing polymers. Phthalocyanine-containing coordination polymer such as 224 can be assembled via addition of bidentate coordinating ligands.

Scheme 4.2. The synthesis of fully conjugated “porphyrin tape” reported by 127 Osuka et at. The extensive conjugation of the polymer is evident by an extremely red-shifted electronic spectrum.

Scheme 4.3. The synthesis of insoluble Schiff base-type ladder polymer by 128 Menecke et at.

xi Scheme 4.4. Proposed synthetic route to obtain Schiff base conjugated ladder 130 polymer 230.

Scheme 4.5. Proposed synthetic route to obtain Schiff base conjugated ladder 130 polymer 232 with a bent structure.

Scheme 4.6. Synthesis of 1,4-dihydroxy-2,5-diformylbenzene 227 according to a 131 procedure reported by Wasielewski et a!.

Scheme 4.7. A shorter synthetic route to 1,4-dihydroxy-2,5-diformylbenzene 132 227.

Scheme 4.8. The synthesis of 4,6-diformylresorcinol 233 according to a 132 procedure reported by Worden et a!.

Scheme 4.9. Synthesis of model compounds 246a-b via standard Schiff base 134 condensation.

Scheme 4.10. Synthesis of bimetallic model compounds 229a-b (EtHex = 2- 136 ethyihexyl).

Scheme 4.11. Attempts to synthesize bimetallic Ni complex 249a resulted in a 143 mixture of products containing two or one Ni atoms. The side product containing one Ni is postulated to have structures 249b and 249c.

Scheme 4.12. Synthesis of Zn and Cu bimetallic model compounds 231a and 145 231b.

Scheme 4.13. Two synthetic routes to prepare Schiff-base ladder polymer 230 156

Scheme 4.14. The synthesis of macrocycle 257 in C1CH By altering the 165 2 232a can be synthesized. experimental conditions, it was anticipated that polymer.

xii List of Symbols and Abbreviations

Abbreviation Description

g-value

o degrees

°C degrees Celsius

A Angstrom

o chemical shift

6 molar extinction coefficient (M’ cm’)

lambda wavelength

excitation wavelength

9 theta

I(MoKcL) absorption coefficient

v wavenumber

AFM atomic force microscopy

Ar aryl

BINOL 1,1‘-Bi-2-naphthol

bipy bipyridine

Ca. approximately

CCD charge coupled detector

CD circular dichroism

cm centimeter

molar magnetic susceptibility 1cm wavenumber

xlii COD cyclooctadiene

CV cyclic voltammetry d doublet

Da Dalton

DCC N,N’-dicyclohexylcarbodiimide

DDQ 2,3-dichloro-5,6-dicyanobenzoquinone

DMF dimethylformamide

DNA deoxyribonucleic acid

DSC differential scanning calorimetry

EDOT 3,4-ethylenedioxythiophene ee enantiomeric excess

EL electroluminescence

peak potential

EPR electron paramagnetic resonance equiv. equivalent

ESI electrospray ionization 20Et diethyl ether F000 number of electrons in the unit cell F calculated structure factor

FET field effect transistor

0F observed structure factor g grams

GPC gel permeation chromatography

HBC hexa-peri-benzocoronene

xiv Hz Hertz

JR infrared

L litre

LED light emitting diode

M molar m multiplet m meta m/z mass/charge

MALDI matrix assisted laser desorption ionization

MHz megaHertz

M number averaged molecular weight

MoKc molybdenum Ka radiation mol moles

Mp. melting point

M weight averaged molecular weight

NLO nonlinear optical nm nanometer

NMR nuclear magnetic resonance o ortho

OAc acetate

OLED organic light emitting diode

ORTEP oak ridge thermal ellipsoid plot

OTf triflate p para

xv PCC pyridinium chlorochromate

Pd/C palladium on carbon (catalyst)

PDI polydispersity index

Ph phenyl

PPE poly(phenyleneethynylene) ppm parts per million

PPP poly(p-phenylene)

PPV poly(p-phenylenevinylene)

PSPE poly(salphenyleneethynylene)

S Siemen s singlet salen 2,2’-N,N’-bis(salicylidene)ethylenediamine salphen -N,N’-bis(salicylidene)phenylenediamine SEM 2,2scanning electron microscopy SQUID superconducting quantum interference device

STM scanning tunneling microscopy t triplet tert tertiaryt TGA thermal gravimetric analysis

THF tetrahydrofuran

TMEDA tetramethylethylenediamine

TNT trinitrotoluene

TOF time of flight

UV-vis ultraviolet-visible

xvi V Volt

WAXS wide-angle X-ray scattering

XPS X-ray photoelectron spectroscopy

xvii Acknowledgements

I would like to thank my very enthusiastic and charming supervisor Prof. Mark

MacLachian for his “excellent” guidance throughout this work. Mark is an exceptional teacher and a great friend, and his wisdom and optimism made this challenging project possible. I am grateful to have the opportunity to meet the many brilliant minds in the MacLachlan research group. Their friendship and encouragement have made my doctoral work a fantastic experience.

Prof. Michael Wolf and Jonathan Chong faithfully read through the rough drafts of this thesis, and their advices are greatly appreciated. This work would not have been possible without the contributions of the many outstanding colleagues and friends in the Chemistry Department of

UBC, especially from members in the Wolf, Orvig, Gates, and Kennepohi group, who generously donated their time and efforts when I needed help.

I would like to thank my lovely mother, sister and brothers for their love and support throughout these long years of studies. My beautiful family means the world to me and we will remain strong together. Last but not least, I want to thank my gorgeous girlfriend Sharon, who shared my grieves and burdens in difficult times, for her unconditional love and patience.

xviii Dedication

This thesis is dedicated to my beloved father Kwok Chiu Leung (1945 —2008)who was a brave firefighter, loving husband, and magnificent father. He provided endless love, courage, and inspiration for my family and I, and he is dearly missed.

xix Co-Authorship Statement

A version of chapter 1 has been published as a review article: Leung, A. C. W.;

MacLachian, M. J. “Schiff Base Complexes in Macromolecules” I Inorg. Organomet. Polym.

2007, 17, 57. I am the primary author of this review article under the supervision of Prof. Mark

MacLaclan.

A version of chapter 2 has been published as a communication to the editor: Leung, A.

C. W.; Chong, J. H.; Patrick, B. 0.; MacLachian, M. J. “Poly(salphenylene-ethynylene)s: A New

Class of Soluble, Conjugated, Metal-Containing Polymers” Macromolecules 2003, 36, 5051. I am the primary author and principal investigator of this work under the supervision of Prof.

Mark MacLachlan. Jonathan Chong was an undergraduate student who contributed to the synthesis of some starting materials. Brian Patrick performed the X-ray Crystallography experiment of compound 196b.

A version of chapter 3 has been published as a paper: Leung, A. C. W.; MacLachlan, M.

J. “Poly(salphenylene-ethynylene)s: soluble, conjugated metallopolymers that exhibit supramolecular crosslinking behavior” J. Mater. Chem. 2007, 17, 1923. I am the primary author and principal investigator of this work under the supervision of Prof. Mark MacLachian.

A version of chapter 4 will be submitted for publication: Leung, A. C. W.; Hui, K. —H.;

Chong, J. H.; MacLachlan, M. J. “The Ladder-Chelate Approach to Soluble Conjugated Metal-

Containing Polymers”. I am the primary author and principal investigator of this work under the supervision of Prof. Mark MacLachlan. Joseph Hui synthesized compound 231a-b and 233.

Jonathan Chong synthesized compound 245 and performed the X-ray Crystallography experiment for 231a.

xx CHAPTER 1

INTRODUCTIONt

§ 1.1 Metal-Containing Polymers

There is tremendous interest in the development of polymers with novel electronic, magnetic, and catalytic properties.’ Recent advances in conjugated organic polymer chemistry have led to their application in diverse emerging technologies such as organic light emitting 2diodes, photoconductors, and static 4dissipaters. Metal-containing polymer chemistry is a growing3 field in which the synthetic materials are anticipated to offer properties unique from their individual organic and inorganic components. These polymers may have useful semiconducting, magnetic, and luminescence 5properties, and may serve as processable precursors to novel 6ceramics. Moreover, the coordinating ability of the metal within the polymer backbone permits these materials to act as 7sensors, and as building blocks for supramolecular 8structures.

t A version of this chapter has been published as a review article: Leung, A. C. W.; MacLachlan, M. J. “Schiff Base Complexes in Macromolecules” I Inorg. Organomet. Polym. 2007, 17, 57.

1 The preparation of metal-containing polymers has been delayed by the limited synthetic routes to these 9materials. One strategy that has emerged is the polymerization of functionalized metal-containing complexes, such as phthalocyanines and porphyrins.’°

Phthalocyanine metal complexes have been studied extensively because of their potential applications as organic semiconductors. By organizing the complexes to maximize intermolecular 71 orbital overlap that allows delocalization of electrons, researchers strive to generate materials with high conductivities. This goal has been realized with the synthesis of

1-D phthalocyanine stacks 1 (e.g., “shish-kebab” polymers), phthalocyanine-containing ladder polymers, and 2-D phthalocyanine sheets 2 (“parquet” polymers), new materials with high conductivities, Figure 1.1.11 Porphyrin complexes, another important class of compounds with useful biological and catalytic applications,’ have been incorporated into conjugated as 2 organic polymers such poly(p-phenylenevinylene) (PPV), and poly(p phenyleneethynylene) (PPE) 3 to generate new materials with promising conductive, electroluminescent, and non!inear optical (NLO) 13properties.

2 1 2

Figure 1.1. l-D phthalocyanine coordination polymer 1 (“shish-kebab” polymers), monomer for the synthesis of 2-D phthalocyanine sheets 2 (“parquet” polymers), and porphyrin containing PPE 3.

3 § 1.2 Schiff Base Complexes

C)) _N\ ,N_ —N N_

_N\ ,N— —N ,N—

3OCH 3HCO 6 7

Schiff base metal complexes are a broad class of compounds that have received much less attention than porphyrins or phthalocyanines for the incorporation into macromolecules.

N,N’-Bis(salicylidene)ethylenediamine, 4 (“M(salen)”), is the archetype of this family of complexes. Preparation of Schiff base complexes typically involves simple condensation between salicylaldehyde derivatives with a variety of diamines, as illustrated by Scheme 1.1. The central 20N pocket is capable of chelating different transition metals, and these materials are known to possess interesting 4magnetic,’ electroluminescent,’ 6NLO,’ oxygen 7transport,’ and catalytic 8properties.’ Related compounds,5 such as M(salphen) 5, M(salpn) 6, and M(3-MeOsaltMe) 7 demonstrate the breadth of chemical structures available within this class of compounds, maintaining the central 20N binding pocket that is formed by two imines and two phenoxides. For nearly 50 years, researchers have worked to integrate

M(salen)-type complexes into polymers and oligomers in the hope of generating materials with favorable characteristics.

4 /O _N\ /N_ Mx 2 J_OH + 2HN 2NH 2 :O/MNO:

Scheme 1.1. Synthesis of Schiff base transition metal complexes.

§ 1.3 Scope of Introduction

This introduction covers the highlights in the development of metal-containing polymers

incorporating Schiff base complexes having the general structure related to 4 — 7. In particular, polymers where the complex is either in the backbone of the polymer or attached directly to the main chain are emphasized. Early attempts to synthesize metal salen containing polymers will be discussed first, although these materials are generally insoluble and poorly characterized. The discussion will then cover more recent research in chemically prepared Schiff base polymers. For example, metal salen complexes have been copolymerized with various monomers to generate new materials with improved mechanical and thermal properties. Finally, selected salen-containing polymers that are prepared electrochemically, often as polymer-modified electrodes, and their applications as sensors, semiconductors, and electrochromic materials will be discussed.

A note about nomenclature: To simplify the text, macromolecules that include metal complexes of the sort exemplified by 4 — 7 are called “salen-type” or “salen-containing” polymers, recognizing that this does not specifically mean N,N’- bis(salicylidene) ethylenediamine, but more generally this family of complexes. It would be useful if there were a simple name for the central 20N ligand, as in “porphyrin”, but unfortunately no such simple nomenclature exists.

5 § 1.4 Early Research

Marvel and TarkOy reported the first example of polymeric Schiff base chelates containing ,2Zn ,2Ni ,2Cu ,2Fe and 29.’Co These polymers were prepared by condensation of bis(salicylaldehyde) 8 with o-phenylenediamine 10 to yield a polymeric

organic Schiff base ligand that was subsequently metallated with metal acetate salts to yield

insoluble polymers 11, Scheme 1.2. These materials have high thermal stability (less than

2% weight loss at 300 °C), but, unfortunately, the insolubility of these new materials made purification difficult and prevented proper characterization. Related polymers 12 were

prepared from bis(salicylaldehyde) 9 and their thermal stabilities were compared. No

significant differences in thermal stabilities were found between polymers 11 and 12.

2M(OAC) H:R:H + HNH 8R=CH 2 10 IIR=CH “ 29R=S0 212R=S0 2 002+) (M = ,2Zn ,2Ni 2 ,2Cu ,2Fe

Scheme 1.2. Synthesis of M(salphen)-containing polymers 11 and 12.

Goodwin and Bailer, building on the work of Marvel, synthesized pentadentate and hexadentate Schiff base polymers from bis(salicylaldehyde) 8 and amines 13 - 15 employing similar polymerization 2procedures. Divalent ,2(Cu ,2Ni )2Co and trivalent ,3(Co ,3Al )3Cr ions were used to°metallate the polymeric chelates. It was observed that the thermal

6 stability of the insoluble polymers improves when the ionic charge of the metal is balanced

by the charge on the chelating ligand.

(NHHN 2NH 2NH NH 2NH 2NH 2 2HN 13 14 15

Sawodny and co-workers prepared polymeric Schiff base complexes analogous to

polymer 11 utilizing l,4-diaminobutane. These organic Schiff base polymers were converted into their corresponding2 alkali metal salts by reaction with Li, Na, or K metal. Subsequent transmetallation with monovalent heavy metal ions (Tl, Cu, Hg), divalent alkaline earth metals ,2(Mg ,2Ca ,2Sr 2),Ba and a variety of transition metals yielded metal-containing polymers. Again, the poor solubility of these polymers limited

characterization and hindered further research efforts. (CH /26 \ (1) -NHN-(CH ) 26H 17 HO (2) ) 2M(OAc) n 16 18

Scheme 1.3. Synthesis of Schiff base polymers 18 (M = Cu, Ni, Co, Zn, and Mn).

Schiff base polymers 18 were prepared by Patel and co-workers by condensation of

bis(bromosalicylaldehyde) 16 with 1,6-diaminohexane 17, and insoluble chelates of Cu, Ni, 3)22 Co, Zn, and Mn were synthesized (Scheme 1 The authors determined the coordination

7 geometry of the chelated metal ions via electronic reflectance spectroscopy and magnetic susceptibility measurements. It was reported that the 2Cu metal center in the polychelates adopts a square-planar geometry, 2Co ions are tetrahedral, while 2Mn and 2Ni have octahedral and distorted octahedral geometry, respectively. Thermal gravimetric analysis

(TGA) indicated that decomposition occurs above ca. 250 °C. Not surprisingly, Schiff base polymers containing aliphatic amines are less thermally stable than their counterparts constructed from aromatic amines.

§ 1.5 Chemically Polymerized Schiff Base Polymers

1.5.1 Salen-Containing Homopolymers Q

20 21

2HN 2NH 23

Manganese salen complex 19 (Jacobsen’s catalyst) is an effective catalyst for asymmetric epoxidation of 23alkenes. Although the Mn complex has good catalytic activity and enantioselectivity, there are often difficulties in the separation of catalyst and product, along with poor reusability of the catalyst. Kureshy and co-workers prepared new heterogeneous polymeric catalysts in an attempt to overcome these 24disadvantages. Chiral

8 3Mn Schiff base polymers 20 and 21 were prepared through condensation of bis(tert

butylsalicylaldehyde) 22 with 1S,2S-1,2-diaminocyclohexane or 1R,2R- 1,2-diphenyl-1,2- diaminoethane 23. The molecular weights of the polymers were determined by vapor pressure osmometry to be ca. 5,000 Da (Ma). The polymers were tested as catalysts for

enantioselective epoxidation of chromenes, indenes, and styrenes, and the polymers

effectively catalyzed epoxidations of most of the compounds tested with near quantitative conversions and good enantiomeric selectivities (75 — 99% ee). After reaction, the polymers can be retrieved by precipitation, and they can be recycled up to five times without significant deterioration in catalytic activity. Other chiral 3Mn Schiff base polymers 24 - 26 were prepared by Zheng and co-workers using other derivatives of bis(salicylaldehyde) 22.25

Catalytic activities and enantiomeric selectivities comparable to Jacobsen’s catalyst were achieved.

24R=CH 27R=CH 225 R = CHOCH 282 R = C(CH 26 R = )32C(CH )32

OH 2H0, 3Co polymer catalyst +

Scheme 1.4. Hydrolytic kinetic resolution of terminal epoxides catalyzed by 27 and 28.

9 Zheng and co-workers also investigated the use of cobalt(III) Schiff base polymers 27

and 28 as catalysts for hydrolytic kinetic resolution of terminal epoxides to yield the 426 corresponding chiral epoxides and diols, Scheme 1 Excellent conversions (Ca.50%) and

enantiomeric selectivities (> 90% ee in most cases) were observed for the substrates tested.

The authors observed dissolution of the polymeric catalyst into the aqueous phase during the course of reaction, and 20Et could be used to precipitate the polymer when the reaction was complete. The recovered catalyst can be reused without significant loss of reactivity. No

significant differences in catalytic performance were found between polymers bridged by

methylene (polymer 27) or dimethylmethylene (polymer 28) groups.

1.5.2 Salen-Containing Copolymers

The copolymerization of salen complexes with other monomers may provide access to new materials with improved thermal, mechanical, and luminescent properties. In addition, it may enhance solubility of the otherwise intractable materials. Chantarasiri and co-workers reported the synthesis of new salen-containing polymers 32 from the diglycidyl ether of bisphenol A 29 and hydroxyl-functionalized Schiff base complexes 30.27 The Schiff base monomers were synthesized by first condensing 2,4-dihydroxybenzaldehyde with 1,3- diaminopropane, followed by addition of the appropriate metal acetates and KOH in water.

Attempts to isolate the organic Schiff base ligand were unsuccessful due to decomposition of the product. Polymers 31 were prepared by curing 29 and 30 in the presence of 4BuNOH, Scheme 1.5, to form crosslinked epoxy resins. Curing of the polymers was monitored by IR spectroscopy with the disappearance of the band at 917 1cm corresponding to the opening of the epoxide groups of 29. DSC studies indicated the use of 4BuNOH lowers the curing

10 temperature and shortens the reaction time. It was found that the copper-containing

copolymer having a 12:1 molar ratio of 29: 30 has the best thermal stability and highest tensile strength.

O\ +

29 30 M = ,2Cu ,2Co 2Ni

n 32

Scheme 1.5. Synthesis of copolymer 32 by thermal curing.

11 H ,_ 0 0 II II CNND OCN NH-C-0-R-O-C-NH I NCO 3CH 3OH 35 0N R = -(CHCH)- 33 M = Zn Ni ) 2 2 CH , 2 3 M = ,2Ni 2Zn R = -(OH )--(CHCH)-24 2 3OH

Chantarasiri extended this work by copolymerizing Schiff base monomers 30 and 33 with maleic anhydride 34 and bisphenol A 29,28 and with urethane-ureas 35•29 The former polymers have similar mechanical and thermal properties with polymer 32. In contrast, the polyurethane-urea copolymers 36 are soluble, and the viscosity of the polymers could be measured. The authors investigated the possibility of using these polymers as flame- retardant materials, and it was found that increasing the metal content of the copolymers generally improves flame retardation.

12 -c—NCOOCN——CH + HOOH 2 38

3CH 3CH M = ,2Co ,2Ni 2Cu HO OH 40 )24-OHHO-(CH

Scheme 1.6. Synthesis of salen-polyurethane copolymer 41.

Raghavan and co-workers also reported the synthesis of new soluble salen-containing polyurethanes. The authors prepared the new polymerizable monomer 40, and subsequent °3copolymerization with diisocyanate 37, poly(oxytetramethylene) glycol-2000 38, and 1,4- dihydroxybutane, afforded new metal-containing polyurethanes 41, Scheme 1.6. Soluble in

DMF and DMSO, the polymers have molecular weights between ca. 12,000 - 44,000 Da (Ma,

GPC). TGA measurements of the metal-containing polyurethanes indicate that the introduction of Schiff base complexes increases the overall thermal stability of the polymers.

Mechanical properties such as tensile strength and elongation of the polymers were also

13 _

reported, but no general trends were observed between the polymers of different metal

content.

OH 0

2 + N—R—NH H CH CH HO 2 3 3 42 43 R = —(CH--fSi—O-1---Si—(CH )23— 3CH 3CH mlor9 OHHO HO OH M(OAc) + 2 COOHSiOSi(CHHOOC(CH Me Me Me Me 46 23 45 M ,2Cu ,2Ni ,2Co ,2Cd 2Zn Scheme) 1.7. Synthesis of siloxane-Schiff base copolymer 46.

Cazacu and co-workers prepared siloxane-Schiff base copolymers 46.31

Polymerizable salen-siloxane ligand 44 was first prepared by condensation of 2,4-

dihydroxybenzaldehyde 42 with siloxane-diamine 43, Scheme 1.7. Polymerization of 44 and

45 was achieved by a dehydration reaction catalyzed by acetic anhydride or N,N’ dicyclohexylcarbodiimide (DCC) to afford soluble polymers that can be cast into yellow or brown films. The polymers were characterized by IR, UV-vis, and 1H NMR spectroscopies, but no molecular weights were reported. Incorporation of short segments of polysiloxanes

into the polymer induces good processability by improving solubility and lowering melting points.

14 Me Me CI—CH+Si—O-—SHCH -CI Me mMe n 47 48 49 2 m = 1,7.5,14 M 2Cu 2NE Scheme 1.8. Synthesis of siloxane-Schiff base copolymer 49.

Polysiloxane-Schiff base copolymers 49 were synthesized by a different strategy,

Scheme 1.8.32 Copper and nickel salen-diol monomers were first converted to the corresponding alkali metal salt 47 through the addition of NaOH. Subsequent polycondensation with chloromethyl-terminated poly(dimethylsiloxane) 48 afforded the polymers as brown (Cu) and orange (Ni) solids. The polymers were characterized by IR,

UV-vis, and ‘H NMR spectroscopies. TGA indicated copolymers with longer polysiloxane segments have improved thermal stability.

NEt3 + CfrCHI -CH2CI \=< CH3 \CH3J H3 CH3 (Ph \ C HO OH m 0 O—CH-Si-—-1—SI--j---SI—CH 50 51 3CH 31\CH 3CH 2 52 ’ Scheme 1.9. Synthesis of polysilane-salen copolymer 52.

Polysilanes are known to exhibit a-delocalization and these materials may be 33semiconducting. Their incorporation into metallopolymers, such as poly(ferrocenylsilanes), have led to new materials that show both metal-metal interactions and 34c-delocalization. Sacarescu and co-workers prepared polysilane-salen copolymers 52 by polycondensation of

Ni(salen) diol 50 with chloromethyl-terminated polysilane 51 in the presence of

•9•35 triethylamine, Scheme I The polymers were characterized by ‘H NMR spectroscopy,

15 and GPC analysis indicated the presence of low molecular weight materials (M = 5,600 Da).

TGA showed thermal decomposition of the polymer beginning at 100 °C, possibly due to the

loss of solvent trapped within the polymer matrix.

Crosslinked polysilane-salen copolymer 58 was synthesized according to Scheme

1.10.36 Polysilane 55 with pendant iodopropyl groups, prepared by Pt-catalyzed hydrosilylation of 53 with allyl iodide 54, was condensed with Schiff base ligand 56 in the presence of 23KC0 to form crosslinked polymer 57, which was then metallated to form copper-containing polymer 58. The polymer was characterized with IR and ‘H NMR spectroscopies, although the peaks in the ‘H NMR spectra were severely broadened. GPC measurements indicated a bimodal molecular weight distribution (M ca. 9,600 and 14,000

Da) characteristic of crosslinked polymers. It is very likely that the presence of highly crosslinked polymers formed by intermolecular condensation of the two hydroxyl functionalities on the salicylideneimine moiety contributed to the observed high molecular weight and bimodal distribution. As expected, the UV-vis spectrum of polymer 58 is nearly identical to the combination of the starting polysilane and Cu salen complex, indicative of minimal electronic communication between the polysilane backbone and the tethered Cu salen complex.

16 Ph 3CH PtCI Ph 3CH f4i+F4i + 26H Ph 54 55 *1

3KCO

Ph 3CH 3CH 4-hi I I Ph/ nm p

Cu(OAc) 4 2 HO HOOH N1 N OH

58 57

Scheme 1.10. Synthesis of crosslinked polysilane-copper salen copolymer 58.

Wang and co-workers synthesized new Schiff base polymer 61 incorporating both a crown ether and a Co(salphen) complex by interfacial polymerization of 59 and 60, Scheme

17 37i.ii. The insoluble polymer was characterized by IR, XPS, TGA, and SEM, but no

molecular weight information was reported. The solid polymer was tested for catalytic

aerobic oxidation of cyclohexene, Scheme 1.12. It was found that the new polymer oxidizes

cyclohexene in the allyl position to give a mixture of its corresponding ketone and alcohol. +2N HO-(OOD-OH 59

NaOH 0H Q

Scheme 1.11. Synthesis of crown ether-cobalt saiphen copolymer 61.

Cocatalyst61 Q a + Scheme 1.12. Aerobic oxidation of cyclohexene catalyzed by 61.

18 HO_€J-OH

n 62 64

Scheme 1.13. Synthesis of linear polychelate 64 and crosslinked polychelate 66 and 68.

Kim and co-workers synthesized cobalt(IIJ) Schiff base polymers by polymerizing ligands 62 with hydroquinone 63, phioroglucinol 65, and 1,1,1-tris(4-hydroxyphenyl)ethane

67 to yield linear polymer 64, and crosslinked polymers 66 and 68, respectively (Scheme

3)•38 1.1 The polymeric ligands were then metallated with 2Co(OAc) and the 2Co metal was oxidized to 3Co using a ferrocenium salt. The polymers were characterized by JR spectroscopy and were tested for catalytic activities for enantioselective hydrolysis of terminal epoxides to diols. Upon testing the catalytic activity in polymers with

epichiorohydrine, styrene oxide, 1,2-epoxybutane, and 1,2-epoxyhexane, it was found that they were effective in producing a mixture of approximately equal amounts of the corresponding epoxides and diols with excellent ee in the range of 97 to 99%. The polymeric

19 catalysts can be reused up to seven times without significant loss in catalytic activity after

simple filtration from the reaction mixture. No significant difference in catalytic performance

was observed between linear or crosslinked polymers.

Gotheif and co-workers synthesized conjugated hyperbranched Schiff base polymers

71 through a one-pot condensation of an aromatic trialdehyde 69 and diamines 23 or 70,

Scheme The organic polymers formed were insoluble, but solid-state NMR and powder X-ray synchrotron diffraction data obtained were consistent with the presence of a rigid polymeric network with a small degree of local order. When the reaction was performed in the presence of 2Mn(OAc) insoluble metal-containing polymers precipitated and were tested as chiral catalysts, for asymmetric epoxidation of alkenes. The epoxidation of cis-2-methylstyrene in the presence of this catalyst afforded 73% conversion, and the enantioselectivity for the cis isomer is 57%.

20 69

Ph Ph 2HN 2NH 2HN Q2NH 23 70 2Mn(OAc)

R’

Scheme 1.14. Synthesis of manganese Schiff base crosslinked polymers 71.

21 Platinum-containing Schiff base complexes are known to exhibit intense yellow-green

phosphorescence in solution, and their incorporation into electroluminescent devices was successful in generating white light with high 40efficiency. Statistical copolymers 74 containing Pt(salen) monomer 72 were synthesized by Scherf and co-workers, Scheme

1.15.’ Yamamoto-type Ni(0)-mediated aryl-aryl coupling of 72 and 73 in THF was

accomplished using a microwave heat source to synthesize the high molecular weight

copolymers (M of ca. 24,000 — 170,000 Da) with short reaction times (ca. 12 mins). The

molar ratio of incorporated Pt(salen) units was determined from ‘H NMR spectra to be only

2.1 - 8%. Although the solution emission spectra of the copolymers were dominated by

poly(fluorene) emission, phosphorescence originating from the Pt(salen) complex was

observed in the solid state (575 nm). When copolymers 74 were employed in OLED devices, the observed electroluminescence (EL) efficiencies were low, probably due to the presence of

aggregate quenching.

+ Br\Br ci/oci COD,b:y,THF

Scheme 1.15. Synthesis of platinum salen-fluorene copolymer 74.

Thus far, all of the polymers discussed possess organic backbones. Although a number of studies of inorganic polymers have involved the synthesis of materials with metal organic bonds in the 42backbone, there have been very few studies of this type with Schiff base complexes. Typically these interactions are weaker and are expected to reduce the stability of the polymers. Tong and Archer reported block copolymers containing zirconium Schiff base complexes and 43poly(tetrahydrofuran). Novel eight-coordinated Zr-containing 22 Schiff base monomer 77 was obtained through addition reaction of complex 75 with tolylene

2,4-diisocyanate 76, Scheme 1.16. The resulting Zr complex contained two reactive

isocyanate groups, which were subsequently condensed with poly(THF) 78 to afford the new

block copolymer 79 as an orange-red transparent film. It is noteworthy that the Zr monomers

were copolymerized with an excess of low molecular weight poly(THF) (—1000Da) to obtain

soluble low molecular weight materials for characterization. The copolymer was

characterized by IR, ‘H NMR and UV-vis spectroscopies. GPC analysis showed a molecular weight (Mw)of 10,300 Da, indicative of polymers with an average of five repeat units. The novel Zr Schiff base monomers with pendant isocyanate functional groups should readily react with a variety of primary alcohols and amines, allowing facile assembly of linear Zr

containing copolymers.

23 + NC0

II H H ‘ul H H Me 0 cN_OZNONL 0 Me

77 O)mHH0(CH 2CH 78 c’---’H 0N.H H NON /0 -N-. NcH H CH0)mN..0_(CHH 0 0 Me0 2

79 n

Scheme 1.16. Synthesis of zirconium saiphen- poly(tetrahydrofuran) block copolymer 79.

Archer also prepared new Zr Schiff base polymers from bis(tetradentate) Schiff base ligands 80 - The ligands were first deprotonated with NaOH, followed by addition of a zirconium precursor to afford the new homopolymers 83 - 85, Scheme 1.17. GPC analysis revealed molecular weights (Ma) of ca. 9,000 — 20,000 Da, and the molecular weights were also confirmed by 1H NMR end-group analysis after capping the polymers with excess

24 salicylaldehyde. Analogous cerium polymers were prepared by a similar 45strategy, although it was found that the polymers can be prepared from simple metallation of the ligand with 4Ce(acac) or from a two-step method by first adding salicylaldehyde to 4Ce metal salts followed, by condensation with the appropriate tetraamine. Cerium-containing polymers with molecular weights as high as 30,000 Da (Ma, GPC and ‘H NMR end group analysis) were

reported. Films of both the Ce and Zr polymers were examined with scanning electron

microscopy, revealing a featureless and continuous morphology. TGA revealed that these polymers have excellent thermal stabilities, with the Zr polymers retaining > 95% of their mass at 400 °C, while the Ce counterparts are stable to 350 C, retaining more than 98% of their original mass. Conductivities measured using a two-probe instrument indicated that these polymers have high intrinsic (ca. iO S cm’), and doped (12, i0 S )1cm conductivities.

- I I - Zr(sal) or 0 0 -N R 0 4 N N)RN Ce(acac) rcc 4Na 4 I

80R=- 83R=- M=Zr,Ce 81R=CH 84R=CH 282R=S0 285R=S0 Scheme 1.17. Synthesis of zirconium and cerium Schiff base polymers 83 - 85.

Highly luminescent analogues of polymers 83 and 84 can be prepared according to Scheme 1.17 with 3Eu and y3 46metals. These polymers have molecular weights (Ma) of ca. 7,000-20,000 Da, as measured by GPC and end group analysis (‘H NMR spectroscopy).

Polymers 86 and 87 were prepared by addition of both metal salts (Eu, Y) in various ratios

25 during polymerization; copolymer 87 (m = 1, n = 4) has the highest quantum yield (74%) of

the series. The authors proposed the improvement in luminescence is likely due to additional

intramolecular energy transfer from yttrium centers to the europium centers, analogous to the

antenna effect. Excellent thermal stability and luminescence characteristics make this class

of Schiff base polymers good candidates for applications requiring luminescent polymers

(e.g., lasers, LEDs).

I I I —en

86 R = - 87 R = 2CH

§ 1.6 Helical Schiff Base Polymers

Katz and co-workers synthesized the first fully conjugated ladder polymers that have a helical 47structure. Helicene bis(salicylaldehyde) 88, prepared in 7 steps, was condensed with o-phenylenediamine and metal acetates to afford polymers 89 with helical structures,

Scheme 1.18. It was necessary to first synthesize the organic polymer backbone and subsequently react the polymeric ligand with metal salts. The polymeric structure of Ni polymer 89 was confirmed using ‘H NMR, ‘3C NMR, and JR spectroscopies as well as MALDI-TOF mass spectrometry. The MALDI-TOF mass spectra of the polymers showed peaks corresponding to oligomers, terminated with either the expected salicylaldehyde end group or end groups that are likely benzimidazoles 90 and 91. The molecular weight

26 estimated by ‘H NMR end group analysis was Ca. 5000 or 10,000 Da (Me) depending on

whether the polymer is capped by one or two salicylaldehyde groups, respectively.

(1) 2HN 2NH (2) 2M(OAc)

88 89 M = Ni, Cu, Co R = n-BuOCH 2CH R = 2CHn-BuOCH Scheme 1.18. Synthesis of helical ladder polymer 89.

H R = 2CHn-BuOCH R = 2CHn-BuOCH

90 91

Helicene bis(salicylaldehyde) 92, having the orientation of its aldehyde and hydroxyl functional groups switched relative to 88, was employed to prepare a different helical polymer 93 using a similar procedure, Scheme 1.19. Figure 1.2 illustrates the different structures of polymers 89 and 93. Based on GPC measurements and ‘H NMR end group analysis, the molecular weight of polymer 91 is ca. 700O Da (Me). The circular dichroism spectra of the two polymers 89 and 93 are very similar, and the absorptions associated with

27 metal-to-ligand charge transfer are very large in comparison to monomeric Ni(salphen) complexes.

(1) 2HN Q2NH (2) 2Ni(OAc) 92 R = 2CHn-BuOCH 93 R = 2CHn-BuOCH

Scheme 1.19. Synthesis of helical ladder polymer 93.

(a) (b)

Takata and co-workers synthesized chiral salen polymers 97 and 98 by the condensation of chiral binaphthyl bis(salicylaldehyde) derivative 94 with diamine 95,

2048,49,50 Scheme 1 The chirality of the binaphthyl unit leads to the formation of helical polymers which are synthesized in two steps by first preparing the organic backbone 96 followed by the insertion of the appropriate transition metal. Notably, the metal-free

28 polymeric Schiff bases have high molecular weights (M up to 13,000 Da), while a considerable drop in molecular weight (M = 1800 Da for 97, 1700 Da for 98) was observed after the incorporation of 2M(OAc) The authors attributed this observation to the inability of GPC to correct for the .polyionic structure of the polymer, in addition to changes in conformations to form compact helices. Model compounds 99 and 100 were synthesized and their UV-vis and CD spectra were compared with the polymers. It was found that the absorption band of the naphthalene unit exhibited a significant red shift in the polymers compared to the model compounds, in agreement with the proposed helical structure for which the naphthalene units are in close proximity. The change in Cotton effect in the CD spectra of the polymers in comparison to the model compounds also supports the helical structure. )23HNHN(CH R_4\_R 10 94 R = 8CH17 2EtZn

+ Ac0

98 iR

Scheme 1.20. Synthesis of helical zinc and manganese polymers 97 and 98.

29 ______+

Ac0

99 R = 49CH 100 R = 49CH

Takata explored the use of these new helical metallopolymers for asymmetric catalysis. The addition of 5 mol% of Zn polymer 97 catalyzed the addition of diethylzinc to benzaldehyde with enantioselectivity up to 95% ee, compared to only 5% ee with Zn model compound 99. Manganese polymer 98 catalyzed the epoxidation of alkenes using Jacobsen’s protocol, but low catalytic activities and low enantioselectivities were observed.

30 (1) 2HN Q2NH (2) 2Ni(OAc) 101

Ni(OAc) 2 102 ,N 2NH p

103

Scheme 1.21. Synthesis of macrocycle 102 and oligomer 103.

2HNR 2Ni(OAc) + 2HNLR 104 H1837105R=0C

106

Scheme 1.22. Synthesis of Ni polymer 106.

31 Pu and co-workers attempted to synthesize soluble conjugated Ni(salphen) polymers from BINOL dialdehyde 101 and bis(salicylaldehyde) 104.’ When BINOL monomer 101 is reacted with o-phenylenediamine, a macrocyclic product is formed instead of the anticipated polymeric product, and the addition of 2Ni(OAc) yields a paramagnetic product with proposed structure 102, Scheme 1.21. The authors suggested the formation of macrocycle 102 containing a planar 2Ni salphen and a tetrahedral 2Ni center resulted from steric congestion of the macrocyclic product. Condensation of 101 with o-phenylenediamine in the presence of 2Ni(OAc) afforded low molecular weight polymers 103 (M Ca. 3,600 Da, GPC). The oligomers are also paramagnetic, suggesting the presence of non-planar coordination of 2Ni units. Condensation of 104 with bis(octadecyloxy)phenylenediamine 105 yielded soluble polymers 106 with low molecular weights (M ca. 4900 Da, GPC), Scheme 1.22.

The polymer is also paramagnetic or strongly aggregated since no NMR signals could be detected in the expected region. A broad absorption band was observed at 700 - 1200 nm in the UV-vis spectrum of 106, which is not present in the UV-vis spectra of square planar

Ni(salphen). Copolymerization of the phenylenediamine 105 with both 101 and 104 was conducted to determine whether the chirality of the binaphthyl units can induce a helical chiral structure in copolymer 107, Scheme 1.23. CD spectra of the copolymers, which had low molecular weights (M ca. 3,400 — 5,400 Da, GPC), showed a linear increase in the CD peak maxima with an increase of chiral binaphthyl monomer content. This result indicates that the introduction of chiral binaphthyl units cannot induce the formation of a main chain helix, probably due to the presence of non-planar Ni centers.

32 NR + m n + 2H I 2HN R

104 101 105 2Ni(OAc)

107 R = CH1837

Scheme 1.23. Synthesis of copolymer 107.

Insoluble double-helical metallopolymer 110 was synthesized by Houjou and co workers by a one-pot precipitation polymerization of bis(salicylaldehyde) 108, dianiline 109, and copper(II) acetate, Scheme 1.24.52 Surprisingly, SEM images revealed that the brown powdery solid was composed of nearly monodisperse microspheres with average diameters of 1.35 urn. These metal-bound polyimine microspheres can be fabricated with different dimensions using different metal salts: Co, 0.80 Jim; Ni, 1.34 u.tm;and Zn, 0.51 urn, Figure

1.3. The microspheres have high thermal stability, with TGA showing no significant degradation below 300 °C. SEM images of the materials after pyrolysis at 500 °C showed no

33 change in the shape of the particles. Bimetallic microspheres were also investigated using mixtures of 2Zn and .2Cu Based on microanalysis of individual particles, the researchers deduced that the particles have a gradient Zn/Cu composition originating from differential rates of coordination to the polyimine. This is potentially an elegant route to developing microspheres with tunable magnetic properties.

el:

Figure 1.3. SEM images of (a) Cu polymer 110 and analogous (b) Ni (c) Zn and (d) Co polymer. Scale bar represents 1 tm, and the inset shows a plot of the frequency vs. microsphere diameter. Reprinted with permission from reference 52a. Copyright 2003

Wiley-VCH.

34 distorted imine bis(salicylaldehyde) Scheme 1.25. JCHO /\ A ligands 108 A single 1.24. square OH model CHO assembled Synthesis + crystal planar compound 111 NH 2 X-ray geometry. of into with 109 double-helical 113 a structure p-methoxyaniline double for Based NH 2 the helix (Figure on double copper Cu(OAc) 2 bridged the crystal 1.4) 112 helical polymer by of in structure Cu this the polymer 110. atoms, Cu presence complex of which was the 110 of model prepared are Cu(OAc) 2 , confirmed coordinated compound, by reacting the Scheme two in the 35 n a authors proposed that the formation of colloidal microspheres may be a result of helical entanglement of the polyimine chains to form highly crosslinked structures.

BUt5CHO 2NH tBu

+ Cu(OAc) OH /\ OMe CHO Bu But 111 112

113

Scheme 1.25. Synthesis of model compound 113.

Figure 1.4. Structure of model compound 113 as determined by X-ray crystallography.

Hydrogen atoms and tert-butyl groups are omitted for clarity.

36 § 1.7 Electrochemically Polymerized Schiff Base Polymers

The development of polymer-modified electrodes is of great interest to researchers because of their potential applications in electrocatalysts, chemical sensors, and electrochromic displays. One common strategy for electrochemical synthesis of metal containing polymers is to attach polymerizable groups such as thiophene or pyrrole functionalities onto metal 53complexes. In the case, of salen-type polymers, these extra synthetic steps can be avoided because Schiff base complexes can be conveniently prepared by direct electropolymerization.

eIeropoIymerization

— 3‘OH 114 — 3‘OH 115 M = ,2Ni ,2Co 2Mn

Scheme 1.26. Preparation of electropolymerized polymer 115.

Murray and co-workers reported the first electrochemically synthesized polymers containing Schiff base metal 54complexes. Aniline-substituted salen complexes (meansalen) 114 were electropolymerized to form non-conjugated polymers 115, Scheme 1.26. Nickel and cobalt monomers of 114 were polymerized by potential scanning between 0 and +0.8 V in 0.1 M EtNBF/MeCN, whereas formation of the manganese polymer of 115 required scanning to4 a slightly higher potential (+0.9 V). The voltammograms obtained during polymerizations of all of the monomers exhibited peaks at +0.5 V, which is very close to the formal potential (+0.45 V) of N,N-dimethylaniline dimerization to form N,N,N’,N’ tetramethylbenzidine, confirming that the polymerization proceeds through coupling of the aniline moieties. Thin films of Ni and Co polymers of 115 exhibited CV traces that

37 resembled their corresponding monomers, while Mn polymers produced poorly defined electrochemical responses. The authors attributed the poor electro-responsiveness of the Mn polymer to the slow electron transport rate for the 23Mn couple. Ni Nicb4

116 117 118

_N\ 7N— _N\ ,N_ C—O”OCH 3OH 3CH 119 H 120 Goldsby and co-workers demonstrated3 for the first time that Ni(salen) complexes 116 can be directly electropolymerized in weak donor solvents such as acetonitrile, acetone, and dichloromethane to form insoluble yellow thin films of polymer 117. Energy dispersive X ray spectroscopy was used to confirm the presence of Ni in the polymer film, and UV-vis spectra of polymer 117 coated on ITO surfaces showed characteristics of Ni(salen) complex

116. Goldsby proposed the polymerization mechanism occurs via oxidative carbon-carbon coupling para to the phenolic oxygen. Salen complexes 118 - 120 were prepared to elucidate the site where polymerization occurs. It was observed that only Ni(salen) 119 with unsubstituted para positions on the phenolic ring underwent polymerization, thus providing indirect evidence to the molecular structure of polymer 117.

_N\ /N_

121M N, R = CH 122MNi,ROCH 3 125M=Ni 123MCu,RCH 126M=Cu 1243 M= Cu, R = 3OCH 38 Goldsby electropolymerized Ni and Cu salen-containing complexes 121 — 124 by cycling a platinum electrode in the potential region 0.4 — 1.4 V, and 0.5 — 1.4 V, 56respectively. it was observed that the film growth of Ni complexes 121 and 122 increased linearly for several scans, followed by a gradual decrease in the rate of film growth. After Ca.

50 scans, film growth stopped and the electrode became passivated. Polymer film growth from Cu monomers 123 and 124 behaved similarly to that of 121 and 122, although passivation of the electrodes occurred much earlier. A number of weak donor solvents,

including acetone, dichloromethane, and propylene carbonate, were tested as solvents for the electropolymerizations. The resulting Ni and Cu polymer films exhibited similar electrochemical behaviors regardless of the solvents used for polymerizations. Nickel polymers of 125 prepared with phenylenediamines were electrochemically more stable than the corresponding polymers prepared from 116, 121, and 122 bridged by ethylenediamines, whereas the Cu polymers were considerably less stable. Scanning electron microscopy

(SEM) revealed all of the polymer films have surface structures comprised of small amorphous spheres. Polymers 117 prepared in acetonitrile were observed to be extensively aggregated, polymers prepared in acetone were moderately aggregated, and a more uniform film structure was observed for polymers prepared in dichioromethane, Figure 1.5. Attempts to polymerize the organic ligands resulted in poly(phenyl ether) films, and subsequent metallations were unsuccessful.

39 (a)

Goldsby’s reports on direct polymerization of Schiff base metal complexes spurred research interests in developing variants of these polymers and study of their electronic and chemical properties. Shortly following the aforementioned reports, new polymer modified electrodes containing Co, Fe, Mn, Pd, Pt, and Zn were 575859reported. While these polymers were prepared using similar electrochemical methods,’ it is noteworthy that some of them were investigated as potential electrochromic materials and catalysts. Cu, Co, Ni, and Zn salen containing polymers with methoxy substituent analogous to 122 were found to be electrochromic and are 60semi-conductive. Ni polymer 117 was found to be capable of catalyzing reduction of a6 variety of 62haloalkanes. Analogous Co and Fe salen containing polymers catalyzed 02 reduction’ to form 6364 ’2H0. Audebert reported the synthesis of ladder polymers containing Schiff base 65complexes. Templated synthesis allowed the preparation of numerous derivatives such as symmetric bimetallic bis(salphen) complexes 132 - 135, the bis(salphen)s with methoxy substituents on only one of the salphen moiety 144, 145, 148 and 149, and bis(salphen)s containing two different metals 146 - 149, Scheme 1.27. However, the poor solubility of the 2Cu complexes and mixed-metal 2Cu/Ni bis(salphen) complexes impeded electrochemical 40 polymerization. As a result, only polymers of Ni complexes were reported.

Electropolymerizations of the ladder polymers were performed at a controlled potential or upon repeated cycling in 0.1 M EtNC1O/MeCN electrolyte as in typical electropolymerization of poly(salen)s. 4The bis(salphen) complexes behave as two independent saiphens, possibly due to the weak conjugation through the tetraamine bridge.

The authors reported that the degree of polymer crosslinking depends on the synthesis potential. When a given polymer was synthesized at relatively low potential, CV in fresh electrolyte revealed that the first few scans were very different from the stabilized voltammogram. The authors attributed this behavior to overoxidation of the polymer films to form highly crosslinked polymers. This interesting characteristic of the ladder polymers should allow easy control of polymer properties via controlling the electropolymerization potential. More interestingly, if the solubility of the mixed-metal monomers can be improved, new bimetallic materials can be synthesized.

41 2NH H0 0 0.5 eq (J0H 2HN 129

R 127 R = H 128 R = 3OCH ç0H H0 0\ /0

130 R=H 131 3R=OCH 136 M = Ni; R = H

1 eq 137 M = Ni; R = OCH 3 of 129 M(C10 138M=Cu;R=H 42 139M=Cu;R=OCH ) R R 2HN 2NH 3 N’ N 140 M = Ni; R = H 141 M = Ni; R = 3OCH 142 M = Cu; R = H _N\ /N_ 143 M = Cu; R = 3OCH

NciN

1136139

132 M = Ni; R = H R R 133 M = Ni; R = 3OCH 134 M = Cu; R = H 0\ /0 135 M = Cu; R = 3OCH

132 1M = 2M = Ni; R = H 133 1M = 2M = Ni R = 3OCH 134 1M = 2M = Cu; R = H 135 1M = 2M = Cu; R = OCH =M144M =NIR=H;R0CH3 /N 12145 1M = 2M = Cu; R = H; R = 3OCH 146 1M = Ni; 2M = Cu; R = R = H 147 1M = Ni;2M3 = Cu; R = R = 3OCH 148 1M = Ni;2M = Cu; R = H; R = 3OCH 149 1M = Ni;2M = Cu; R = OCH R = H R R ;3

Scheme 1.27. Preparation of bis(salphen)s 132 — 135 and 144 — 149.

42 Reddinger and Reynolds prepared new Schiff base complexes incorporating a thiophene moiety by condensation of 3,4-diaminothiophene 150 with salicylaldehyde followed by addition of metal acetates, Scheme 1.28.66 Nickel and copper monomers 151 were subjected to repeated potential cycling between -0.5 V and +0.9 V in 0.1 M CIBu!CHNCIO to form thin films. Increases in potential peaks corresponding to polymer 42oxidation (+0.55 V) and reduction (+0.50 V) after repeated potential scanning indicated the formation of polymeric product. Films of polymers 152 grown on platinum electrodes were found to be very redox stable, exhibiting less than 7% loss of electroactivity after 50 repeated scans in the potential range of -0.5 to +1.0 V. The same polymers were prepared on ITO electrodes for the study of their electrochromic behavior. The Cu polymer is transparent light green in its reduced state and transparent dark green in its oxidized state, and the Ni polymer toggles between transparent orange (reduced) and transparent green (oxidized).

2HN 2NH — (1) )Meiectropoiymerization HO 150 (2) 2M(QAc) S 127 151 152 M = Ni, Cu

Scheme 1.28. Electrochemical synthesis of polymer 152.

Reynolds determined the structure of polymers 152 employing a similar strategy used by Goldsby of placing methyl substituents on positions where the polymeric linkage can possibly occur. As expected, it was found that blocking the position para to the phenolic oxygen in monomer 151 inhibited polymerization, thereby indirectly confirming the structure of polymer 152. The electropolymerization of other monomers 153 - 155 containing terthiophenes was investigated. Copper complex 153 exhibited similar electrochemical behavior at slightly higher potentials than 152, and the CV traces suggested the polymer

43 contains both phenyl and thiophene linkages. When the para position of the phenolic ring in

Cu complex 154 was blocked, electropolymerization proceeded and redox activities different than 151 and 153 were observed at lower potentials. When both the ortho and para position to the phenolic position were blocked, as in complex 155, polymerization occurred with electrochemical behavior closely resembling that of complex 154. The authors attributed these observations to the formation of Schiff base polymers 156 with a polythiophene backbone. It is interesting that these monomers can be functionalized to build either polymers with poly(phenylene) linkages or poly(thiophene) linkages. 3HC—cON,O—CH 153MCu,RzH,R’tH 156 154M=Cu,R=Me,R=H 155M=CuR=MeR=Me

Reynolds synthesized new salen-type polymers 161 containing crown ether moieties to afford new conjugated polymers that are capable of complexing multiple metal 67ions.

Schiff base complexes 160 were synthesized using a templation method, Scheme 1.29. Due to the instability of the Schiff base ligand, bis(salicylaldehyde) 158 bridged by a glyme chain was complexed with 2Ba prior to condensation with diamine 157 and metallation with transition metals. The complexed template 2Ba ions can then be removed by treatment with guanidine sulfate to afford monomer 160. Polymers 161 were prepared as thin films by repeated potential cycling between -0.3 and +0.8 V in 0.1 M BuC1/CHNC1O The ability of the polymers to sense alkali metals was tested on polymers42 grown on platinum electrodes . 44 in electrolytes containing alkali and alkaline earth perchlorate salts. Small shifts in the anodic and cathodic peak potentials were observed for polymers exposed to alkali cations (10

— 80 mV), and the complexed ions can be exchanged by simply stirring the polymer films in electrolytes containing the exchanged alkali ions. Incorporation of alkaline earth cations resulted in larger shifts in the anodic and cathodic peak potentials (70 — 140 my); however, the coordination appeared to be irreversible since no change occurred in the cyclic voltammograms when the electrode was exposed to electrolyte containing alkali cations. In addition to cation sensing, the polymers are also capable of detecting Lewis bases.

Voltammograms of the Ni polymer modified electrodes in the presence of dilute pyridine solution showed Ca. 75% loss in electroactivity. The authors attributed this behavior to the formation of adducts between the transition metal ion and the Lewis base, which inhibits electronic interaction between the polymer chains.

45 2 4C10

2HN 2NH 158 2M(OAc) 157

Polymerization

161 M = Ni, Cu 160

Scheme 1.29. Electrochemical synthesis of polymer 161.

Swager and co-workers prepared new monomer 165 having pendant thiophene groups via palladium-catalyzed Stille coupling of 162 and 163 followed by condensation with ethylenediamine and then metallation with 2Cu(OAc) Scheme 1.30.68 Cobalt complex 165 was then electrochemically polymerized in ,MeCN by scanning the potential between -0.75 and +0.85 V to afford yellow films. Conductivity measurements indicated that polymer 166 has a conductivity of 40 S cm’; however, in-situ conductivity measurements indicated that the ’23Co redox couple did not contribute to the overall conductivity. Analogous polymer 170 with 3,4-ethylenedioxythiophene (EDOT) was synthesized using a similar strategy to the preparation of 166, Scheme 1.31. The redox potential of the organic polymer backbone was

46 shifted toward lower potential to coincide with the ’23Co redox wave. Conductivity measurements revealed polymer 170 to have high conductivity of 250 S .1cm Interestingly, exposure of the polymers to Lewis base such as pyridine and 2,6-lutidine resulted in a significant loss in conductivity (ca. 66% decrease), as observed for polymer 166.

OH BuSn> OHIII 0 3 () HN 2NH Stille coupling (2) 2Co(OAc) Br 162 electropolymerization 164

166

Scheme 1.30. Electrochemical synthesis of polymer 166. 35SnBu OH 0 \ OHO O 1670 I (1) HNNH 0 N N Stille coupling (2) Co(OAc)2 2 169 — 0 Br 162 electropolym erization 168

Scheme 1.31. Electrochemical synthesis of polymer 170.

47 _

Swager and co-workers systematically investigated the relationship between interchain interactions (i.e., it aggregation) and the bulk conductivity of salen-type

69polymers. A series of Cu, Ni, and 2U0 polymers 171 — 185 with diamine bridges of varying steric bulk were prepared. Cyclic voltammetry indicated varying interchain spacing with substituents of different sizes on the polymer to have a large effect. Copper polymer

172 with the least sterically encumbered ethylenediamine bridge displayed four one-electron redox processes, whereas polymers with sterically hindering diamine substituents such as 178 displayed only two redox waves, These results from CV, together with spectroelectrochemistry and in-situ EPR measurements indicated that the increase in steric bulkiness of the substituents on the polymers has a large effect on the ability of the polymers to form it aggregates, which in turn affects electronic communication between polymer chains. Conductivity measurements indicate a decrease in conductivity in the order of 171

174 > 180 > 183 > 177, correlating well with the bulkiness of the substituents. On the contrary, the Ni polymers all displayed high conductivities, and they appeared to be less sensitive to the steric hindrance of the substituents. The authors attributed these observations to the rigid square planar geometry of the Ni complexes and the available d2 orbital facilitating electron hopping between polymer chains.

IThQQ 2HN 2NH = 2HN 2NH 2HN 2NH 2HN 2NH 2HN 2NH 2HN 2NH 171M=Ni 174M=Ni 177M=Ni 180M=Ni 183M=Ni 172M=Cu 175M=Cu 178M=Cu 181 MCu 184M=Cu 2173M=U0 2176M=U0 2179M=U0 2182M=U0 2185M=U0 48 Cobalt polymer 170 was investigated for potential applications as an oxygen-reducing electrocatalyst and as a nitric oxide ’7sensor. The development of materials capable of electrocatalytic7 reduction of 02 to is relevant to fuel cell technologies. Films of polymer ° 20H 170 coated on glassy carbon surfaces were studied with CV in 0.1 M /KPOKHHPO buffer solutions. It was observed that in the presence of 02, a new reduction24 peak (+0.05V) emerges in the cyclic voltammogram. Rotating ring-disc voltammetry measurements suggested the polymer catalyzes a four electron process to reduce 02 to 2H0, without significant production of 20H as a side product. However, polymer degradation is observed in acidic media typical to conditions found in fuel cells, which is likely due to imine hydrolysis. Polymer 170 was also investigated as a sensing material for nitric oxide (NO). When the polymer is exposed to NO in a 0.1 M BuNPF/MeCN electrolyte, CV revealed that the 23Co couple shifted slightly toward positive46 potential such that there is a better overlap between the 23Co couple and the redox potential of the organic polymer framework. This electrochemical response to NO is reversible, as the CV of the polymer film quickly returned to its original state when the film is placed into fresh NO-free electrolyte. In addition, the polymer exhibited reversible changes in conductivity by Ca.30% upon exposure to NO, which is probably due to better redox matching of the conducting polymer backbone and the transition metal center.

§ 1.8 Goals and Scope

Since the first report of insoluble polymers containing Schiff base complexes by

Marvel and Tarkoy nearly 50 years ago, the emergence of new synthetic methods and

49 characterization techniques has allowed major developments in the field of metal-containing polymers. Although Schiff base complexes were demonstrated to have unique catalytic, nonlinear optical, luminescent, conductive, and sensory properties, their integration into macromolecules remains difficult due to their inherent insolubility. Through copolymerization with soluble monomers, and addition of solubilizing groups onto the metal complexes, soluble high molecular weight polymers can be prepared and their chemical and physical properties have been carefully studied. By choosing appropriate co-monomers, mechanical, thermal, chemical, and electronic behavior of the polymers can be tailored to meet specific applications. The discovery of electrochemically polymerized metal Schiff base polymers by Goldsby presented a new strategy to form stable polymeric films on a large variety of electrode surfaces. A great deal of effort has been devoted to elucidating the mechanism of electropolymerization, and studying redox and charge transport properties of the polymer films. Several potential applications for these polymer-modified electrodes have been proposed in the area of catalysis, conductivity, electrochromism, and sensors for small molecules.

In the past two decades, the discovery of conductive t-conjugated polymers has spurred extensive research effort to incorporate a variety of functional molecules into polymeric 7t-conjugated frameworks. Among the large amount of literature on conjugated polymers, the combination of metal complexes such as metalloporphyrins and phthalocyanines have drawn much attention as these materials have properties that are not found in other organic-based polymers. Surprisingly, there are only a few reports of it conjugated polymers containing metal Schiff base complexes despite the attractive properties exhibited in their molecular or non-conjugated polymeric counterparts. Therefore, the research projects described in this thesis aim to develop new functional materials through the

50 incorporation of Schiff base transition metal complexes into conjugated organic polymer frameworks. Much of my efforts were spent on developing synthetic strategies to obtain polymerizable monomers and soluble polymers, as well as investigations of their physical and chemical properties. In particular, it is anticipated that these new materials will possess unique electronic properties due to the extended conjugation within the macromolecules and exhibit interesting supramolecular behaviors due to the coordinating abilities of the transition metals within the polymeric backbone. My target polymers include Schiff base complexes- containing poly(phenyleneethynylene)s 186 and 187, and fully conjugated ladder polymers

188, Figure 1.6.

n n 186 187

188

Figure 1.6. General structures of the target polymers prepared in this thesis.

51 Chapter 2 of this thesis describes initial efforts to synthesize polymers 186 and their

subsequent characterization. In chapter 3, I discuss my work to improve solubility of these polymers and investigation of their sensory interactions with coordinating ligands.

Geometrically different derivatives, polymers 187, were prepared and their characterization and supramolecular behavior are also discussed. Chapter 4 discusses my efforts to prepare fully conjugated polymer 188, model compounds, and their properties. Chapter 5 ends the thesis with a summary and discussion of the future outlook of this work.

52 § 1.9 References

(1) Skotheim, T. A.; Elsenbaumer, R. L.; Reynolds, J.R. (Eds.), Handbook of Conducting

Polymers, Second Edition; Dekker: New York, 1998.

(2) Friend, R. H.; Gymer, R. W.; Holmes, A. B.; Burroughes, J. H.; Marks, R. N.; Taliani, C.;

Bradley, D. D. C.; Dos Santos, D. A.; Brédas, J. L.; Logdlund, M.; Salaneck, W. R. Nature

1999, 397, 121.

(3) Chen, C.-T. Chem. Mater. 2004, 16, 4389.

(4) Groenendaal, L. B.; Jonas, F.; Freitag, D.; Pielartzik, H; Reynolds, J. R. Adv. Mater.

2000, 12, 481.

(5) (a) Kingsborough, R. P.; Swager, T. M. Frog. Inorg. Chem. 1999, 48, 123. (b) Manners, I.

Science 2001, 294, 1664.

(6) Manners, I. Chem. Comm. 1999, 857.

(7) McQuade, T. D.; Pullen, A. E.; Swager, T. M. Chem. Rev. 2000, 100, 2537.

(8) Screen, T. E. 0; Thorne, J. R. G.; Denning, R. G.; Bucknall, D. G.; Anderson, H. L. I

Am. Chem. Soc. 2003, 124, 9712.

(9) Manners, I. Angew. Chem.1996, 35, 1603.

(10) Wohrle, D. I Porphyrins Phthalocyanines 2000, 4, 418.

(11) McKeown, N. B. I Mater. Chem. 2000, 10, 1979.

(12) Jasat, A.; Dolphin, D. Chem. Rev. 1997, 97, 2267.

(13) (a) Anderson, H. L. Chem. Comm. 1999, 23, 2323. (b) Bao, Z.; Yu, L. Trends Polym.

Sci. 1995,3, 159.

(14) Miyasaka, H.; leda, H.; Matsumoto, N.; Sugiura, K.; Yamashita, M. Inorg. Chem. 2003,

42, 3509.

53 (15) Sano, T.; Nishio, Y.; Ramada, Y.; Takahashi, H.; Usuki, T.; Shibata, K. I Mater. Chem.

2000, 10, 157.

(16) Lacroix, P. G. Eur. I Jnorg. Chem. 2001, 2, 339.

(17) Bailes, R. H.; Calvin, M. I Am. Chem. Soc. 1947, 69, 1886.

(18) Zhang, W.; Lee, N. H.; Jacobsen, E. N.J Am. Chem. Soc. 1994, 116, 425.

(19) (a) Marvel, C. S.; Tarkoy, N. I Am. Chem. Soc. 1957, 79, 6000. (b) Marvel, C. S.;

Tarkoy, N. I Am. Chem. Soc. 1958, 80, 832.

(20) Goodwin, H. A.; Bailar, J. C. I Am. Chem. Soc. 1961, 83, 2467.

(21) (a) Sawodny, W.; Riederer, M. Angew. Chem. mt.Ed. 1977, 89, 897. (b) Sawodny, W.;

Riederer, M.; Urban, E. Inorg. Chim. Acta 1978, 29, 63.

(22) Patel, V. J.; Patel, M. N. Indian I Chem., SectA 1989, 28,428.

(23) Zhang, W.; Loebach, J. L.; Wilson, S. R.; Jacobsen, E. N. I Am. Chem. Soc. 1990, 112,

2801.

(24) Kureshy, R. I.; Khan, N. H.; Abdi, S. H. R.; Singh, S.; Ahmed, I.; Jasra, R. V. I Mol.

Catal. A: Chem. 2004, 218, 141.

(25) (a) Yao, X.; Chen, H.; Lu, W.; Pan, G.; Hu, X.; Zheng, Z. Tetrahedron Lett. 2000, 41,

10267. (b) Song, Y.; Yao, X.; Chen, H.; Pan, G.; Hu, X.; Zheng, Z. I Chem. Soc., Perkin

Trans. 1, 2002, 7, 870.

(26) Song,Y.; Yao, X.; Chen, H.; Bai, C.; Hu, X.; Zheng, Z. Tetrahedron Lett. 2002, 43, 6625.

(27) Chantarasiri, N.; Tuntulani, T.; Tongraung, P.; Seangprasertkit-Magee, R.; Wannarong,

W. Eur. Polym. 1 2000, 36, 695.

(28) Chantarasiri, N.; Sutivisedsakm, N.; Pouyuan, C. Eur. Polym. 1 2001, 37, 2031.

(29) Chantarasiri, N.; Damrongkosit, T,; Jangwong, W.; Sridaeng, D.; Suebphan, S. Eur.

Polym. 1 2004, 40, 1867.

54 (30) Senthilkumar, N.; Raghavan, A.; Nasar, A. S. Macromol. Chem. Phys. 2005, 206, 2490.

(31) Marcu, M.; Cazacu, M.; Viad, A.; Racles, C. Appi. Organomet. Chem. 2003, 17, 693.

(32) Cazacu, M.; Marcu, M.; Viad, A.; Vasiliu, M. I Macromol. Sci., Pure Appi. Chem.

2004, A41, 565.

(33) Miller, R. D.; Michl, J. Chem. Rev. 1989, 89, 1359.

(34) Rulkens, R.; Resenses, R.; Verma, A.; Manners, I.; Murti, K.; Fossum, E.; Miller, P.;

Matyjaszewski, K. Macromolecules 1997, 30, 8165.

(35) Sacarescu, G.; Ardeleanu, R.; Sacarescu, L.; Simionescu, M. I Organomet. Chem. 2003,

685, 202.

(36) Sacarescu, L.; Ardeleanu, R.; Sacarescu, G.; Simionescu, M. Polym. Bull. 2005, 54, 29.

(37) Wang, R.-M.; Duan, Z.-F,; He, Y.-F.; Yang, B.-Y.; Wang, Y.-P.; Komatsu, T.;

Tsuchida, E. I Macromol. Sci., Pure Appi. Chem. 2005, 42, 231.

(38) Kwon, M.; Kim, G.-J. Catal. Today 2003, 87, 145.

(39) Nielsen, M.; Thomsen, A. H.; Jensen, T. R.; Jakobsen, H. J.; Skibsted, J.; Gothelf, K. V.

Eur. I Org. Chem. 2005, 2, 342.

(40) Che, C.—M.;Chan, 5.—C.;Xiang, H.—F.;Chan, M. C. W.; Liu, Y.; Wang, Y. Chem.

Commun. 2004, 1484.

(41) Galbrecht, F.; Yang, X. H.; Nehls, B. S.; Neher, D.; Farrell, T.; Scherf, U. Chem.

Commun. 2005, 2378.

(42) (a) Sonogashira, K.; Takahashi, S.; Hagihara, N. Macromolecules 1977, 10, 879. (b)

Lavastre, 0.; Plass, J.; Bachmann, P.; Guesmi, S.; Moinet, C.; Dixneuf, P. H.

Organometallics 1997, 16, 184. (c) Kean, C. L.; Pickup, P. G. Chem. Commun. 1999, 2471.

(43) Tong, W.; Archer, R. D. Inorg. Chem. 1992, 31, 3332.

55 (44) (a) Chen, H.; Cronin, J. A.; Archer, R. D. Macromolecules 1994, 27, 2174. (b) Chen, H.;

Cronin, J. A.; Archer, R. D. Inorg. Chem. 1995, 34, 2306.

(45) Cronin, J. A.; Palmer, S. M.; Archer, R. D. Inorg. Chim.Acta 1996, 251, 81.

(46) Chen, H.; Archer, R. D. Macromolecules 1996, 29, 1957.

(47) (a) Dai, Y.; Katz, T. J.; Nichols, D. A.Angew. Chem. mt.Ed. Engl. 1996, 35, 2109. (b)

Dai, Y.; Katz, T. J. I Org. Chem. 1997, 62, 1274.

(48) Furusho, Y.; Maeda, T.; Takeuchi, T.; Makino, N.; Takata, T. Chem. Lett. 2001, 10,

1020.

(49) Maeda, T.; Furusho, Y.; Takata, T. Chirality 2002, 14, 587.

(50) Maeda, T.; Takeuchi, T.; Furusho, Y.; Takata, T. I Polym. Sci., Part A: Polym. Chem.

2004, 42, 4693.

(51) Zhang, H.-C.; Huang, W.-S.; Pu, L. I Org. Chem. 2001, 66, 481.

(52) (a) Houjou, H.; Shimizu, Y.; Koshizaki, N.; Kanesato, M. Adv. Mater. 2003, 15, 1458.

(b) Houjou, H.; Sasaki, T.; Shimizu,Y.; Koshizaki,N.; Kanesato,M. Adv.Mater. 2005, 17,606.

(53) (a) Denisevich, P.; Abruna, H. D.; Leidner, C. R.; Meyer, T. J.; Murray, R. W. Inorg.

Chem. 1982, 21, 2153. (b) Bruti, E. M.; Giannetto, M.; Mori, G.; Seeber, R. Electroanalysis

1999, 11,565. (c) Wolf, M. 0.; Zhu, Y.Adv. Mater. 2000, 12, 599.

(54) Horwitz, C. P.; Murray, R. W. Mol. Cryst. Liq. Cryst. 1988, 160, 389.

(55) K. A. Goldsby, J. K. Blaho, and L. A. Hoferkamp, Polyhedron 8, 112 (1989).

(56) Hoferkamp, L. A.; Goldsby, K. A. Chem. Mater. 1989, 1, 348.

(57) (a) Vilas-Boas, M.; Freire, C.; de Castro, B.; Hillman, A. R. I Phys. Chem. 1998, 102,

8533. (b) Vilas-Boas, M.; Freire, C.; de Castro, B.; Christensen, P. A.; Hillman, A. R. Chem.

Eur. I 2001, 7, 139. (c) Vilas-Boas, M.; Santos, I. C.; Henderson, M. J.; Freire, C.; Hiliman,

A. R.; Vieil, E. Langmuir 2003, 18, 7460.

56 (58) (a) Shagisultanova, G. A.; Kuznetsova, N. N. Russ. J. App!. Chem. 2003, 29, 703. (b)

Shagisultanova, G. A.; Ardasheva, L. P. Russ. J. Appi. Chem. 2003, 76, 1626. (c)

Shagisultanova, G. A.; Ardasheva, L. P.; Orlova, I. A. Russ. J. App!. Chem. 2003, 76, 1631.

(59) Shagisultanova, G. A.; Orlova, 1.A.; Borisov, A. N. I Photochem. Photobiol., A 1997,

103, 249.

(60) (a) Audebert, P.; Capdevielle, P.; Maumy, M. Synth.Met. 1991, 43, 3049. (b) Audebert,

P.; Capdevielle, P.; Maumy, M. New I Chem. 1991, 15, 235. (c) Audebert, P.; Capdevielle,

P.; Maumy, M. New I Chem. 1992, 16, 697.

(61) Bedioui, F.; Labbe, E.; Gutierrez-Granados, S.; Devynck, J. I E!ectoanal. Chem. 1991,

301, 267.

(62) (a) Dahm, C. E.; Peters, D. G. Anal. Chem. 1994, 66, 3117. (b) Dahm, C. E.; Peters, D.

G. I Electroanal. Chem. 1996, 406, 119. (c) Dahm, C. E.; Peters, D. 0.; Simonet, J. I

Electroanal. Chem. 1996, 410, 163.

(63) Okada, T.; Katou, K.; Hirose, T.; Yuasa, M.; Sekine, I. Chem. Lett. 1998, 27, 841.

(64) Miomandre, F.; Audebert, P.; Maumy, M.; Uhi, L. I Electroanal. Chem. 2001, 516, 66.

(65) Aubert, P.-H.; Audebert, P.; Roche, M.; Capdevielle, P.; Maumy, M.; Ricart, 0. Chem.

Mater. 2001, 13, 2223.

(66) (a) Reddinger, J. L.; Reynolds, J. R. Synth.Met. 1997, 84, 225. (b) Reddinger, J. L.;

Reynolds, J. R. Macromolecules 1997, 30, 673.

(67) Reddinger, J. L.; Reynolds, J. R. Chem. Mater. 1998, 10, 1236.

(68) Kingsborough, R. P.; Swager, T. M. Adv. Mater. 1998, 14, 1100.

(69) Kingsborough, R. P.; Swager, T. M. I Am. Chem. Soc. 1999, 121, 8825.

(70) Kingsborough, R. P.; Swager, T. M. Chem. Mater. 2000, 12, 872.

(71) Shioya T.; Swager, T. M. Chem. Commun.2002, 1364.

57 CHAPTER 2

Poly(salphenyleneethynylene)s : Soluble, Conjugated, Metal- Containing PoIymers

§2.1 Introduction

Recent developments in conjugated organic polymers, such as poly(p-phenylene)s (PPPs) and poly(p-phenylenevinylene)s (PPVs), have met with tremendous success and have led to useful applications such as organic light-emitting diodes,’ semiconductors, and photovoltaic 3devices. Among the large variety of these conjugated polymers,2 poly(phenyleneethynylene)s (PPEs) are a relatively new and distinctive class of conjugated polymers that have drawn a great deal of attention. Extensive research efforts have focused on the synthesis of new polymeric PPE 4materials, along with other oligomeric structures such as 5macrocycles, 6foldamers, and 7dendrimers. Potential applications for these materials are especially promising in the area of chemosensing and biosensing, where various PPE derivatives were demonstrated to function as sensors for chemical analytes such as trinitrotoluene (TNT) and biological agents such as DNA and carbohydrates. Other potential applications as electroluminescent 9materials, nonlinear optical8 (NLO) 0materials,’ and liquid crystals’ were also explored.

t A version of this chapter has been published as a communication to the editor: Leung, A. C. W.; Chong, J. H.; Patrick, B. 0.; MacLachlan, M. J. “Poly(salphenylene ethynylene)s: A New Class of Soluble, Conjugated, Metal-Containing Polymers” Macromolecules 2003, 36, 5051.

58 We identified Schiff base complexes (saiphen 5) as building blocks for new conjugated polymers and supramolecular structures. As discussed in the previous chapter, these molecules have attracted enormous attention as they are known to catalyze oxidation and epoxidation reactions, and have recently been used as highly luminescent molecules for LED applications.’ A few conjugated polymers / oligomers incorporating 5 have been prepared, but”23 most are of low molecular weight or 514insoluble. Others have prepared conjugated Schiff base polymers by electropolymerization ”(e.g., 166) and these polymers have interesting redox and catalytic 6properties.’ Among the diverse collection of conjugated organic polymers prepared by polymer chemists, poly(phenyleneethynylene)s (PPE)s stand out as an ideal organic framework for the insertion of transition metal Schiff base complexes due to the versatility of the Sonogashira-Hagihara coupling reaction that is employed to prepare these 7polymers,’ as well as their attractive properties in the area of chemical sensing and other 8applications.’ PPEs containing metal complexes such as porphyrins and ferrocenes have demonstrated unique electronic 9properties’ and supramolecular 20behavior. Although these organometallic PPEs exhibit attractive properties, relatively few examples of these metallopolymers have appeared in the literature, largely due to the synthetic difficulties in obtaining polymerizable metal- containing monomers and the polymers’ insolubilitjes. It was my intention to synthesize new PPEs containing Schiff base complexes and’2 investigate their properties as new materials.

_N\p/N_

166 n

59 The impetus of this work originated from the work of Anderson et al. on conjugated porphyrin- containing 22polymers, and the work of Lavastre et. al. on combinatorial synthesis and screening of conjugated 23polymers. Anderson reported a synthesis of high molecular weight polymer 190, polymerized via oxidative Glaser coupling (Scheme 2.1). The polymer was found to exhibit unique supramolecular and NLO properties. In this elegant work, viable synthetic strategies were developed to obtain soluble high molecular weight polymers and the extraordinary properties of metal-containing conjugated polymers were demonstrated. Attempts to prepare PPEs containing Schiff base complexes were reported by Lavastre et al. in 2002 when they developed a new method, analogous to combinatorial synthesis, to synthesize and screen a large library of fluorescent conjugated polymers. A series of dibromoaryl monomers (I-XII) were condensed with a library of diethnylaryl monomers (A-H) to yield 96 different conjugated polymers, Figure 2.1. These polymer samples were then subjected to solid state and solution fluorescence measurements, Figure 2.2. Among the polymers, the postulated structures 191a and 192a incorporating Schiff base 2Zn and 2Ni complexes were found to be highly luminescent and may be excellent candidates for applications in LEDs. In this Chapter, I report on my efforts to synthesize and characterize this class of polymers, and preliminary investigations of their properties.

60 i2R 2NR 2RN 2NR

CuCI,TMEDA,°2

2RN. - 2NR 2RN. - 2NR 0 0 189 190

Scheme 2.1. The synthesis of porphyrin containing polymer 190 reported by Anderson et at.

Branched alkyl substituents (R = 2-ethyihexyl) were incorporated onto the porphyrin moiety to improve solubility.

n 191a (M = Zn, R = 8CH17 191b (M=Zn, R = CH1633 192a (M= Ni, R )8CH17) 192b (MN1, R = )CH1633)

61 BrBr BrBr 0

II A 2NH BrBr BrBr III IV B

OOct

Br Br Br Br* C OctO V VI 2NO BrBr &N D “S’Br vii viii

02N 2NO E 8Br”-’Br Q OOct F _N\ N_ 2NH OctO BrO/NOBr G

XIMZn H XII M = Ni

Figure 2.1. Fast synthesis and screening of conjugated polymers. Dibromoaryl monomers I-XII and diethynylaryl monomers A-H were polymerized through Pd-catalyzed Sonogashira coupling.

62 0 C D

>. 0 C 41) C a) C) C C) 0C-) a) 0

Figure 2.2. Solution fluorescence of the 96 polymers measured at 530 nm. Polymers GXI and

GXIIcorrespond to PPEs containing Zn and Ni Schiff base complexes 191a and 192a.

§2.2 Monomer Synthesis and Characterization

It was very surprising that polymers 191a and 192a were soluble in THF as our group’s work in this area has shown that rigid, metal-containing polymers are difficult to dissolve. The synthesis of polymers 191 and 192 was repeated according to the method in the literature, via

Pd(0)-catalyzed Sonogashira cross-coupling of bromo- or iodosalphen complexes with 1,4- dialkoxy-2,5-diethynylbenzene.’ It was found that the polymers were insoluble in THF. In fact, when the substituents were changed from octyl in 191a and 192a to hexadecyl in 191b and 6192b, the polymers obtained were still nearly insoluble in THF. Based on these observations, it is quite likely that the luminescence reported in the literature was due to oligomers or remaining dibromosaiphen complexes, which are both luminescent and soluble in THF. The measured quantum efficiencies of the dibromosaiphen complexes are 0.5 % (MZn), and 0.3 % (MNi).

63 CH0\1225 H1225,0C CH0\1225 H1225,0C 1225 0C —o 0CH H1225 M(OAc) or2 THF M(acac) 2 I0H NN + HNH IOH HOI 193 2 194 195 196a(M=Zn) 196b (M = Ni) 2 196c (M VO) Scheme 2.2. Synthesis of monomers 196a-c.

To synthesize soluble poly(salphenyleneethynylene)s (PSPEs), we prepared a new saiphen ligand 195 was prepared possessing two dodecyloxy substituents and two iodo groups,

Scheme 2.2. Compound 195 was prepared in 81% yield and isolated as a bright orange solid. Subsequent reaction of pro-ligand 195 with 2Zn(OAc) 2Ni(OAc) and 2VO(acac) yielded metal- containing monomers 196a-c, respectively,, in 87-96%, yield. These were recrystallized 2-3 times to afford pure compounds; ‘H and ‘3C NMR data, IR spectra, UV-vis spectra, mass spectra, and elemental analyses confirmed the composition and purity of these compounds.

Figure 2.3 displays a ‘H NMR spectrum of 196b showing the expected resonances for the Schiff base complex. JR spectra of the monomers show an intense C=N stretching mode at 1603-1612 cm’. The V=O stretching mode of monomer 196c (978 cm’) indicates that it is monomeric in the solid 24state. UV-visible spectra of 196a-c all show multiple bands between 200 and —55O nm, the compounds appearing yellow, red, and orange, respectively, in the solid state. Unlike the fluorescent bromo analogues employed in the synthesis of 191 and 192, monomers 196a-c are non-emissive in solution or as solids.

64 C12HO H12OC cm

N0N

1b CH

-o

I, E z0

OCth

10 8 7 6 5 4 3 1 0 Chemical Shift (ppm) Figure 2.3. 1H NMR spectrum (300 MHz) of Ni monomer 196b in .3CDCI

The structure of 196b was verified by single crystal X-ray diffraction, Figure 2.4. Crystals of 196b suitable for X-ray diffraction studies were obtained by slow diffusion of 20Et into a solution containing 196b in .3CHC1 The structure shows the 2Ni ion is in a square planar geometry (mean deviation of 0.007(1) A from the plane). The alkoxy substituents are extended and project from the plane of the didodecyloxybenzene ring at an angle of Ca. 25 degrees. The packing pattern of 196b is illustrated in Figure 2.4c; the nickel salphen molecules are arranged in a fashion such that they are stacked along the plane in opposite directions, with adjacent units arranged in a similar fashion normal to the plane. Figure 2.4d portrays the packing diagram of

196b along the b axis, showing that the long alkoxy chains are interdigitated. X-ray diffraction data and selected bond lengths and angles are given in Table 2.1 and Table 2.2 in the experimental section of this chapter.

65 99

(3)

(q) ()

probability

purple

(c),

Figure

(b)

and parallel

2.4.

the

iodine,

packing

level.

Single

the

green

Solvent

plane

pattern crystal

nickel.

molecules

along

X-ray

the

The

saiphen

diffraction

are

packing

axis

removed

ligand.

structure

shown

pattern

for

Thennal

clarity.

(d).

196b

monomer

ellipsoids

Red

the 196b

solid

oxygen,

are

(a)

state

shown

perpendicular

blue

illustrated at

nitrogen,

the

50%

and

67 in H16330C H16330C 23KC0 CHBr1633 ,3Kb 12 )=J , Acetone HOAc, S0 24H >=J HO 0CH1633 0CH1633 197 198 199 TMS-CCH )32(PPhPdCI CuP, 2NH’Pr H16330C , H16330C KOH = = TMS = TMS 1633 1633= 0CH 201 0CH 200

Scheme 2.3. Synthesis of diethynylaryl monomer 201.

2,5-Dihexadecyloxy-l,4-diiodobenzene monomer 201 was synthesized according to known procedures reported by Wrighton et al. starting with hydroquinone 197, Scheme 2.3.25

The hexadecyl substituents were attached through Williamson ether synthesis in acetone, converting 197 to 198 in 75% yield. Subsequent iodination of 198 with 3Kb and ‘2 in acetic acid and sulfuric acid afforded 199 in 82% yield. However, it was observed that the work-up procedure involving the use of aqueous 24SONa producing a small amount of sulfur that cannot be easily separated from the pure product. This complication can be avoided by employing a slightly different procedure developed by West et al.26 By using 4K10 instead of ,3Kb the crude product can be readily precipitated in water and recrystallized in ethanol to afford the pure product. Finally, Sonogashira-Hagihara coupling of 199 with trimethylsilylacetylene and subsequent deprotection of 200 yielded monomer 201 in 84% yield.

68 §2.3 Polymer Synthesis and Characterizations. 0CH1225 H12250C 0CH1225 H12250C

—N0N— 0CH1633 —N0N— 0CH1633 IOXObH + H16330C TF’ H16330C 196a(M=Zn) 201 202a(M=Zn) 196b (M = Ni) 202b (M = Ni) 196c(M=VO) 202c(M=VO)

Scheme 2.4. Synthesis of the PSPEs 202a-c.

Sonogashira Pd-catalyzed cross-coupling of 196a-c with 201 in THF I 2FIN’Pr afforded the new polymers 202a-c (Scheme 2.4) in high yields (77 - 86%) after precipitation. These polymers, though very soluble in THF, were still insoluble in other solvents such as chloroform and toluene despite the additional alkoxy substituents. The polymers were purified by multiple precipitations from THF into methanol and acetone. The resulting red, film-forming polymers

(Figure 2.4) were characterized by GPC and UV-vis, IR, and NMR spectroscopies.

69 this weights samples optimization the components 202b, are colored Figure polymers high polymer and The 2.5. solutions obtained. enough prepared. 84,000 new is (Figure Photograph of are amorphous, temperature to PSPEs essentially (ca. Wide-angle for ensure In 2.6). 10 202c, particular, readily

of 4:. (M=Zn) mg substantial 202a The exhibiting thin monomodal and mU’). PDIs X-ray form synthetic films solvent the of free-standing interchain scattering of only 2-4) THF:HN’Pr 2 (molecular polymers procedure as an with

(M=Ni) * bimodal 202b

amorphous ‘I (WAXS) entanglement. shoulders 202a-c. films, weights ratio for distributions preparation halo indicating had analysis In visible (Mw) THF, centered a (M=VO) GPC strong

202c I of of corresponding were the that 37,000 of of polymer at these the polymers effect their characteristic 20° PSPEs for 20. polymers molecular 202b on 202a, form the to indicated showed oligomeric 17,000 molecular intensely of required weights many that that for 70 50.00 5 45.00 x 40.00 a) 35.00 .? 30.00 ‘4—’ J C.) - a) 20.00 15.O°-i 15.00 20.00 25.00 30.00 35.00 Retention time (mins)

Figure 2.6. Gel permeation chromatogram for polymer 202c. Weight averaged molecular weight M for 202c is 84,000 Da.

‘H NMR spectroscopy of polymers 202a-b showed broad peaks corresponding to the alkoxy substituents on the polymers. The aromatic peaks could not be resolved as they are severely broadened. This broadening is probably due to slow tumbling of the rigid polymers in the very viscous 27solution. However, the absence of sharp peaks indicates that there are no monomers or small molecules present in the samples. JR spectroscopy of the polymers indicated the starting material was absent and the salphen moieties were still intact (VC=N 1609-1612cm

‘). Moreover, the spectra of the polymers were more complicated than the starting monomers and consistent with an alternating copolymer made up of 196a-c and 201. A new peak at 2200

1em was observed in each polymer; this is assigned to the CC stretching mode. In the case of polymer 202c, the VV=O mode was observed at 998

UV-visible spectra of the polymers (Figure 2.7a) show peaks that are broader than for the monomers. Notably, the spectra of 202a-c show an enhancement of the peak near 400 nm relative to the monomers; this is probably due to the transitions associated with the

71 conjugated backbone. In addition, they show a tail at Ca. 450-600 nm that appears to be associated with the metal complexes since the tails are also observed in the monomers.

0.5

0.4

0.3 A

0.2

0.1

0.0 300 400 500 600 700 2(nm)

0.5

0.4

0.3 A

0.2

0.1

0.0 300 400 500 600 700 800 ?(nm)

Figure 2.7. (a) UV-visible spectra for polymers 202a-c in THF. (b) Emission spectrum of polymer 202a in THF (Xexc = 406 fin).

72 We anticipated that PSPE polymers 202a and 202b would be highly luminescent in solution. Unfortunately, when illuminated with a UV source, polymer 202a was only weakly luminescent (Figure 2.7b) and 202b showed virtually no emission at all (202c was also non emissive as expected for a paramagnetic 28polymer). The luminescence spectrum of 202a in THF shows a maximum at 546 nm; an excitation spectrum of 202a is similar to the UV-vis spectrum, indicating that the luminescence arises from the polymer rather than an impurity. We postulate that energy transfer from the polymer absorption into localized states of the metal complexes is responsible for the poor emission properties of these materials.

§2.4 Conclusions

In summary, we have prepared the first examples of soluble poly(salphenyleneethynylene)s containing Zn, Ni, and VO Schiff base transition metal complexes. The polymers were prepared using the Sonogashira-Hagihara coupling reaction and the reaction parameters were optimized to yield high molecular weight polymers. Preliminary studies of these polymers indicate that they are not good candidates for LED applications due to their low fluorescence efficiency. However, they may be suitable for new chemical sensors or for assembly into nanogrids and other supramolecular structures. The next Chapter will describe my efforts to investigate supramolecular behaviors of these polymers in the presence of coordinating ligands.

73 §2.5 Experimental

2.5.1 General

Materials. Copper(I) iodide, zinc(JI) acetate, nickel(II) acetate, vanadyl acetylacetonate, and 5- bromosalicylaldehyde were obtained from Aldrich. Tetrakis(triphenylphosphine)palladium was obtained from Strem Chemicals, Inc. Deuterated solvents were obtained from Cambridge Isotope Laboratories, Inc. Tetrahydrofuran was distilled from sodium/benzophenone under .2N 2NH’Pr was distilled from NaOH under .2N 5-iodosalicylaldehyde (193) and 1,2-didodecyloxy- 4,5-diaminobenzene (194) were prepared by literature 329methods. Equipment. All reactions were carried out under a 2N’° atmosphere unless otherwise noted. 300 MHz 1H NMR spectra and 75.5 MHz ‘3C NMR spectra were recorded on a Bruker AV-300 spectrometer. UV-Vis spectra were obtained in THF (ca. 5 x 106 M) on a Varian Cary 5000

UV-vis/near-JR spectrometer using a 1 cm cuvette. Fluorescence spectra were obtained in

distilled THF (ca. 5 x 106 M) on a Varian Cary Eclipse fluorimeter using a 1 cm cuvette.

Quantum yields were referenced to a solution of anthracene in EtOH (1 = 0.30). The sample solutions were degassed by bubbling 2N into the cell for 5 minutes. JR spectra were obtained as

KBr discs with a Bomem MB-series spectrometer. Molecular weights were estimated by gel permeation chromatography (GPC) using a Waters liquid chromatograph equipped with a

Waters 515 HPLC pump, Waters 717 plus autosampler, Waters Styragel® columns (4.6 %

300mm) HR2, HR4 and HR5E and a Waters 2410 differential refractometer (refractive index

detector). A flow rate of 0.3 mL/min was used and samples were dissolved in THF (ca. 1 mg/mL) and filtered before injection. Narrow molecular weight polystyrene standards were used for calibration purposes. Electrospray ionization (ESI) mass spectra were obtained at the UBC

Microanalytical Services Laboratory on a Micromass LCT time-of-flight (TOF) mass spectrometer equipped with an electrospray ion source. The sample was analyzed in

74 3MeOH:CHC1 at 1 tM. Electron Impact (El) mass spectra and elemental analyses were performed at the UBC Microanalytical Services Laboratory. Melting points were obtained on a

Fisher-John’s melting point apparatus and are corrected. Wide-angle X-ray scattering analyses were obtained on a Rigaku Rotaflex diffractometer equipped with a copper (Cu Kct, 2 = 1.54184

A)rotating anode source.

2.5.2 Procedures

Synthesis of Polymers 191 and 192. Polymers 191a,b and 192a,b were prepared according to

the literature procedure.’° The black solids

_N\/N_ RO obtained from the preparation of 191 were only

slightly soluble in refluxing THF while the black

°OR 19 Zn,R=0C solids obtained from reactions to form 192 were =8H17 (16 insoluble. ) The orange THF solutions containing 191 were filtered to remove the insoluble matter and precipitated into MeOH under vigorous stirring to yield an orange solid (7 — 15% yield) presumably containing oligomeric product. Due to the insolubility of these materials, we were unable to characterize 191 and 192 with ‘HNMR spectroscopy or GPC.

Synthesis of Ligand 195. A solution of 193 (0.500 g, 2.02 mmol) and 194 (0.464 g, 0.97 mmol)

0C in 10 mL THF was heated to reflux at 70 C for 24 h. After cooling 2CHO12 /\ H1225 of — to room temperature, 10 mL of MeOH were added to the reaction IDH HoI mixture under air. Orange needles were obtained overnight, and were isolated by vacuum filtration. The product was recrystallized from THF/MeOH (1:1) to yield

0.740 g (0.79 mmol) of product 195 (81%).

75 Data for 195. ‘3C NMR (75.5 MHz, )3CDC1 160.8, 160.2, 149.5, 141.3, 140.1, 135.0, 121.6, 119.9, 104.5, 79.5, 69.8, 31.9, 29.7, 29.6, 29.4, 29.4, 29.2, 26.0, 22.7, 14.1 ppm; 1H NMR (300 MHz, )3CDC1 ö 13.14 (s, 2H, 01]), 8.49 (s, 2H, CH=N), 7.65 (d, J=2.3 Hz, 2H, aromatic CR), 7.57 (dd, J=2.3, 8.8 Hz, 2H, aromatic Cl]), 6.82 (d, J=8.8 Hz, 2H, aromatic Cl]), 6.76 (s, 2H, aromatic Cl]), 4.04 (t, J=6.6 Hz, 4H, 2),OCH 1.84 (m, 4H, 2),CH 1.49 (m, 4H, 2),CH 1.25 (m, 32H, 2),CH 0.86 (t, J=6.8 Hz, 6H, )3CH ppm; UV-vis (THF): 2m (E)= 405 (7520), 348nm (22600), 261 (27600), 255 nm (33200), 250 (30000), 244 (25000) nm (L mold cm’). ESI-MS: m/z = 960 (M+Na, 80%), 938 (M+1, 100%). JR (KBr): v = 2921, 2851, 1612, 1503, 1473, 1385,

1360, 1349, 1320, 1273, 1172, 1131, 1019, 960, 923, 873, 822, 721 cm’. Mp. = 130-131 °C Anal. Calc’d for :1204CHN4462 C, 56.41; H, 6.09; N, 2.99. Found: C, 54.70; H, 6.83; N, 2.84. Synthesis of Monomer 196a. Compound 195 (1.000 g, 1.07 mmol) and zinc acetate dihydrate

OC 1 0CH1225 /\ 2H25 (0.35 g, 1.60 mmol) were combined in 20 mL of THF under air. — The suspension was heated to reflux at 80 C for 24 h to give a yellow i__4j—o’ “o—Y)——i solution. Following cooling to room temperature and the addition of

20 mL of MeOH, yellow needles were obtained and collected via vacuum filtration.

Recrystallization from THFIMeOH gave 1.026 g (1.03 mmol, 96%) of monomer 196a as yellow needles.

Data for 196a. 1H NMR (300 MHz, 6DMSO-d 8 8.93 (s, 2H, CHN), 7.75 (d, J=2.4 Hz, 2H, aromatic CR), 7.45 (s, 2H, aromatic CR),) 7.37 (dd, J=2.4, 9.0 Hz, 2H, aromatic Cl]), 6.53 (d, J9.0 Hz, 2H, aromatic CR), 4.08 (t, J=6.0 Hz, 4H, 2),OCH 1.75 (m, 4H, 2),CH 1.46 (m, 4H, 2),CH 1.23 (broad, 32H, 2),CH 0.84 (t, J=6.5 Hz, 6H, )3CH ppm; UV-vis (THF): (s) 453 (30100), 414 (55000), 360 (30100), 302 (32500), 254 (77000) nm (L 1mo[ cm’). ESI-MS: m/z

76 = 999 (M+1, 70%), 937 ([M+1]-Zn, 100%). JR (KBr): v = 2923, 2853, 1612, 1507, 1465, 1370, 1309, 1266, 1216, 1167, 1139, 824 .1cm Mp. = 308-310 °C Anal. Calc’d for CHNO4460Zn: C, 52.84; H, 6.05; N, 2.80. Found: C, 51.77; H, 6.24; N, 2.76. I24

Synthesis of Monomer 196b. Monomer 196b was prepared by a procedure identical to that for

1225 12250C 196a except nickel acetate was used in the place of zinc acetate. Red 0CH /\ H — monomer 196b was purified by recrystallization from THF/MeOH

(1:1) (95% yield). Single crystals suitable for X-ray diffraction were obtained from the slow diffusion of ether into a solution of 196b in chloroform.

Data for 196b. ‘3C NMR (75.5 MHz, )3CDC1 164.3, 150.8, 149.8, 142.4, 140.5, 135.6, 123.8, 122.6, 98.3, 75.7, 69.7, 31.9, 29.8, 29.7, 29.5, 29.4, 29.2, 26.0, 22.7, 14.1 ppm; ‘H NMR (300 MHz, )3CDC1 ö 7.82 (s, 2H, CHN), 7.55 (d, J2.1 Hz, 2H, aromatic CR), 7.38 (dd, J=2.1 Hz, 9.0 Hz, 2H, aromatic CR), 6.98 (s, 2H, aromatic CR), 6.84 (d, J=9.0 Hz, 2H, aromatic CR), 3.97 (t, J6.5 Hz, 4H, 2),OCH 1.81 (m, 4H, 2),CH 1.46 (m, 4H, 2),CH 1.26 (broad, 32H, 2),CH 0.87 (t, J6.7 Hz, 6H, )3CH ppm; UV-vis (THF) Xmax (6) 493 (15400), 409 (25500), 386 (42800), 297 (23400), 256 (81000) nm (L 1moF 1).cm EI-MS: m/z = 992 (M, 75%), 866 (M—I, 100%), 740 (M-2I, 25%). JR (KBr): v = 2923, 2852, 1606, 1590, 1513, 1454, 1369, 1319, 1280, 1194, 1180, 1116, 819 cm’. Mp. 315-317°C Anal. Calc’d for CHN4460NiO C, 53.19; H, 6.09; N, 2.82. Found: C, 53.05; H, 6.27; N, 2.87. :I24

77 Synthesis of Monomer 196c. Monomer 196c was prepared by a procedure identical to that for

0C 196a except was acetate. 0CH1225 /\ H1225 2VO(acac) used in the place of zinc The — orange product was purified by recrystallization from THFIMeOH

(1:1). Yield: 87%.

Data for lOc. 1H NMR (300 MHz, )3CDC1 ö 1.91 (broad), 1.28 (broad), 0.88 (s, 6H, )3CH ppm; UV-vis (THF) 2max (E) = 460 (21900), 424 (33800), 371 4),(1.87x10 315 (20400), 261 (74000), 255 (83200), 250 (74400) nm (L moF’ cm’). EI-MS: m/z = 1001 (M, 100%), 875 (M-I). IR

(KBr): v 2923, 2852, 1603, 1589, 1516, 1453, 1364, 1299, 1278, 1222, 1187, 1138, 1115,978, 967, 820 .1cm Mp. 325-326 °C Anal. Calc’d for NOV:60CH C, 52.76; H, 6.04; N, 2.80. Found: C, 52.67; H, 5.97; N, 3.20. I25

Synthesis of Polymer 202a. Monomer 196a (0.1000 g, 0.100 mmol) and 201 (0.6158 g, 0.101

iC12 mmol were combined in a 100 mL vessel. To these

solids were added 10 mL of distilled THF and 4 mL of distilled 2NH’Pr via syringe. The reaction mixture was then degassed by three freeze/pump/thaw cycles. In a glovebox, 5 mol% of 34Pd(PPh and 5 mol% of CuT were added. The reaction mixture was subsequently freeze/pump/thawed) one more time. A red-black solution was obtained after heating the reaction mixture at 70 °C for 24 h. After cooling to room temperature, the solvent was removed by rotary evaporation, and the remaining black solid was dissolved in

10 mL of THF under reflux. The solution was then filtered through glass wool into 400 mL of

MeOH to yield an orange precipitate. Further purification was performed by precipitating the polymer twice from THF into acetone. During the second dissolution of the polymer into TI-IF,a

78 very fine beige precipitate appeared that was removed by centrifugation. The above procedure yielded polymer 202a as a dark orange film (0.116 g, 86%).

Data for 202a. ‘H NMR (300 MHz, )8THF-d ö 2.5 (broad). 1.3 (broad), 0.8 (broad) ppm; UV vis (THF) 2max 475 (30700), 407 (80600) nm (L mol’ cm’). JR (KBr): v = 2923, 2852, 2202, 1611, 1587, 1502, 1467, 1414, 1376, 1271, 1215, 1172, 1124, 1022, 832, 805, 722 .1cm GPC (THF): M = 36727 (M/M 3.0).

Synthesis of Polymer 202b. Polymer 202b was prepared by a procedure identical to that for 0CH1225 /\ H12250C 202a, beginning with monomer 196b. Polymer — 202b was obtained as a dark red film (0.169 g, 83%). H16330C Data for 202b. ‘H NMR (300 MHz, )8THF-d 7-8 (broad, m), 2.5 (broad), 1.3 (broad), 0.9 (broad) ppm; UV-vis (THF) Xm = 509 (18500), 407 (83400) nm (L mol’ cm’). JR (KBr): v

2923, 2852, 2201, 1609, 1514, 1583, 1501, 1466, 1417, 1374, 1353, 1327, 1278, 1215, 1182, 1116, 1026, 829, 722 .1cm GPC(THF): M= 17205 (M/M2.1).

Synthesis of Polymer 202c. Polymer 202c was prepared by a procedure identical to that for 2CHO12 /\ H12250C 202a, beginning with monomer 196c. Polymer — 202c was obtained as a dark orange film (0.084 g, _N\ ,N— 0CH1633 77%). H16330C

79 Data for 202c. UV-vis (THF) = 481 (16100), 396 (50200) nm (L 1mo1 1).cm JR (KBr): v = 2923, 2852, 2199, 1612, 1589, 1502, 1467, 1434, 1413, 1377, 1271, 1214, 1168, 1097, 1028,

998, 833, 747, 722, 694 cm’. GPC (THF): M = 84057 (M/Iv1 = 3.9).

2.5.3 X-Ray Diffraction Studies

3 30 41 28 39

26 37

24 35 22 4 17

19 16 ‘15

2 . 5 13 2 3 9

Figure 2.8. Single crystal X-ray diffraction structure of monomer 196b. Thermal ellipsoids are shown at the 50% probability level. Solvent molecules are removed for clarity. Red = oxygen, blue = nitrogen, purple iodine, green = nickel.

X-Ray Diffraction Study of 196b. Crystals of 196b suitable for X-ray diffraction were grown by slow diffusion of 20Et into a solution containing 196b in 3CHC1 A red needle crystal of x . x 25CHNO4564NiI having approximate dimensions of 0.50 0.15 0.03 mm was mounted on a

80 glass fiber. All measurements were made on a Rigaku/ADSC diffractometer with graphite monochromated Mo-KcLradiation.

Table 2.1 X-ray diffraction data for compound 196b.

A. Crystal data Empirical Formula 4564NiI Formula Weight 25CHNO1025.52 Crystal Color, Habit red, needle Crystal Dimensions 0.50 x 0.15 x 0.03 mm Crystal System monoclinic Lattice Type Primitive Lattice Parameters a = 21.247(2) A b=8.9428(4) A c25.280 A 1= 111.589(3)° V = 4501.8(5) 3A Space Group P 2i/a (#14) Z value 4 Dcalc 1.513 3g/cm F000 2088.00 i(MoKcc) 18.48 1cm B. Intensity Measurements Diffractometer Rigaku/ADSC CCD Radiation MoKa (? = 0.71069 A) graphite monochromated Detector Aperture 94 mm x 94 mm

Data Images 460 exposures @51.0 seconds Detector Position 38.78 mm

2Om 55.8° No. of Reflections Measured Total: 40195

81 Unique: 10117 1=(R 0.071) Corrections Lorentz-polarization Absorption! scaling/decay

(corr. Factors : 0.7155 — 1.0000) C. Structure Solution and Refinement Structure Solution Direct Methods (S1R92) Refinement Full-matrix least-squares

2 22 Function Minimized w(Fo -Fc) Least Squares Weights w 1/(a(Fo)+(0.02 129P) where2 P = 2,0)(Max(Fo + 2)/32Fc Anomalous Dispersion All non-hydrogen atoms No. Observations (T>0.OOa(I)) 9575 No. Variables 611 Reflection/Parameter Ratio 15.67 Residuals (refined on ,2F all data): Ri; wR2 0.075; 0.081 Goodness of Fit Indicator 0.88 No. Observations (I>2.OOa(I)) 6015 Residuals (refined on F): Ri; wR2 0.038; 0.072 Max Shift/Error in Final Cycle 0.01

Maximum peak in Final Diff. Map 0.73 Minimum peak in Final Diff. Map -0.79 3e/A

Table 2.2 Selected bond lengths (A)and angles (°) for 196b.

I(1)—C(4) 2.101(4) N(1)—C(7) 1.298(4) C(8)—C(9) 1.418(5) I(2)—C(11) 2.112(5) N(1)—C(15) 1.422(4) C(9)—C(10) 1.366(5) Ni(1)—O(1) 1.841(2) N(2)—C(14) 1.304(4) C(l0)—C(11) 1.395(6) Ni(1) — 0(2) 1.845(3) N(2) — C(20) 1.423(5) C(11)—C(12) 1.363(5) Ni(1)—N(2) 1.861(3) C(1)—C(6) 1.403(5) C(12)—C(13) 1.421(5) Ni(1) — N(1) 1.864(3) C(1) — C(2) 1.425(5) C(13) — C(14) 1.425(5) O(1)—C(1) 1.309(4) C(2)—C(3) 1.372(5) C(15)—C(20) 1.383(5) 0(2) — C(8) 1.312(4) C(3) — C(4) 1.397(5) C(15) — C(16) 1.391(5) 0(3) — C(17) 1.356(5) C(4) — C(S) 1.367(5) C(16) — C(17) 1.378(5) 0(3) — C(21) 1.433(5) C(S) — C(6) 1.425(5) C(17) — C(18) 1.409(5) 0(4) — C(18) 1.367(4) C(6) — C(7) 1.420(5) C(i 8) — C(19) 1.377(5)

82 0(4) — C(33) 1.438(4) C(8) — C(1 3) 1.393(5) C(19) — C(20) 1.396(5)

0(1)—Ni(1)-0(2) 83.72(11) C(3)-C(2)-C(1) 120.1(4) C(8)-C(13)-C(12) 119.6(4)

0(1 )-Ni( 1)-N(2) 178.83(12) C(2)-C(3)-C(4) 121.2(4) C(8)-C( 13)-C(14) 122.6(3)

0(2)-Ni(1)-N(2) 95.27(12) C(5)-C(4)-C(3) 119.7(3) C(12)-C(13)-C(14) 117.7(3)

0(1)-Ni(1)-N(1) 95.08(12) C(5)-C(4)-I(1) 121.1(3) N(2)-C(14)-C(13) 125.2(3)

0(2)-Ni(1)-N(1) 178.08(11) C(3)-C(4)-I(1) 119.2(3) C(20)-C(15)-C(16) 120.1(3)

N(2)-Ni(1 )-N(1) 85.93(12) C(4)-C(5)-C(6) 120.8(4) C(20)-C(15)-N(1) 114.1(3)

C(1)-O(1)-Ni(1) 127.6(2) C(1)-C(6)-C(7) 122.6(3) C(16)-C(15)-N(1) 125.8(3)

C(8)-0(2)-Ni( 1) 127.4(2) C( 1)-C(6)-C(5) 119.3(3) C(17)-C( 16)-C( 15) 120.0(3)

C( 17)-O(3)-C(2 1) 119.3(3) C(7)-C(6)-C(5) 118.1(4) 0(3)-C( 17)-C( 16) 125.4(3)

C( 18)-0(4)-C(33) 117.2(3) N(1)-C(7)-C(6) 125.0(4) 0(3)-C( 17)-C(1 8) 114.8(3)

C(7)-N(1)-C(1 5) 121.2(3) 0(2)-C(8)-C(13) 123.9(4) C(16)-C(17)-C(1 8) 119.8(4)

C(7)-N( 1)-Ni( 1) 125.9(3) 0(2)-C(8)-C(9) 118.5(4) 0(4)-C( 18)-C(19) 125.2(3)

C(15)-N(1)-Ni(1) 112.9(2) C(13)-C(8)-C(9) 117.6(3) 0(4)-C(1 8)-C(17) 114.7(3)

C( I4)-N(2)-C(20) 121.3(3) C( 10)-C(9)-C(8) 121.8(4) C( 19)-C(1 8)-C( 17) 120.1(3)

C( 14)-N(2)-Ni( 1) 125.5(3) C(9)-C( 10)-C( 11) 120.0(4) C( 18)-C( 19)-C(20) 119.6(3)

C(20)-N(2)-Ni( 1) 113.1(2) C( 12)-C(1 1)-C( 10) 119.7(4) C( 15)-C(20)-C( 19) 120.3(3)

0(1)-C(1)-C(6) 123.6(3) C(12)-C(1 1)-I(2) 121.3(3) C(15)-C(20)-N(2) 113.8(3)

0(1)-C(1)-C(2) 117.5(3) C(10)-C(1 1)-I(2) 118.8(3) C(19)-C(20)-N(2) 125.8(3)

C(6)-C( 1)-C(2) 118.8(3) C(1 1)-C( 12)-C( 13) 121.0(4) 0(3)-C(2 1)-C(22) 106.9(5)

83 §2.6 References.

(1) Friend, R. H.; Gymer, R. W.; Holmes, A. B.; Burroughes, J. H.; Marks, R. N.; Taliani, C.;

Bradley, D. D. C.; Dos Santos, D. A.; Brédas, J. L.; Logdlund, M.; Salaneck, W. R. Nature 1.99,

397, 121.

(2) (a) Eley, D. D.; Pacini, B. M. Polymer 1968, 9, 159. (b) Miyashita, K.; Kaneko, M. Synth.

Met. 1995, 68, 161.

(3) Durstock, M. F.; Spry, R. J.; Baur, J. W.; Taylor, B. E.; Chiang, L. Y. I Appi. Phys. 2003,

93, 3253.

(4) (a) Yamamoto, T.; Yamaguchi, I.; Yasuda, T. Adv. Polym. Sci. 2005, 177, 181. (b) Bunz, U.

H. F. Adv. Polym. Sci. 2005, 177, 1. (c) Bunz, U. H. F. Chem. Rev. 2000, 100, 1605. (d) Weder,

C. Chem. Commun. 2005, 5378.

(5) (a) Hoger, S. Angew. Chem mt.Ed. 2005, 44, 3806. (b) Zhang, W.; Moore, J. S. Angew.

Chem. mt.Ed. 2006, 45, 4416.

(6) Stone, M. T.; Moore, J. S. Org. Lett. 2004, 6, 469.

(7) Grayson, S. M.; Fréchet, J. M. J. Chem. Rev. 2001, 101, 3819.

(8) Zheng, J.; Swager, T. M. Adv. Polym. Sci. 2005, 177, 151.

(9) (a) Hager, H.; Heitz, W. Macromol. Chem. Phys. 1998, 199, 1821. (b) Pang, Y.; Li, J.; Hu,

B.; Karasz, F. E. Macromolecules 1998, 31, 6730. (c) Hirohata, M.; Tada, K.; Kawei, T.; Onoda

M.; Yoshino, K. Synth. Met. 1997, 85, 1273. (d) Schmitz, C.; Posch, P.; Thelakkat, M.; Schmidt,

H.-W.; Montali, A.; Felman, K.; Smith, P.; Weder, C. Adv. Funct. Mater. 2001, 11, 41.

(10) Screen, T. E. 0. ; Lawton, K. B.; Wilson, G. S.; Dolney, N.; Ispasoiu, R.; Goodson, T.;

Martin, S. J.; Bradley, D. D. C.; Anderson, H. L. I Mat. Chem. 2001, 11, 312.

84 (11) Steiger, D.; Smith, P.; Weder, C. Macromol. Rapid Commun. 1997, 18, 643; Altmann, M.;

Bunz, U. H. F. Angew. Chem. 1995, 34, 569; Altmann, M.; Enkelmann, V.; Lieser, G.; Bunz, U.

H. F. Adv. Mat. 1995, 7, 726.

(12) (a) Palucki, M.; Pospisil, P. J.; Zhang, W.; Jacobsen, E. N. I Am .Chem. Soc. 1994, 116,

9333. (b) Zhang, W.; Lee, N. H.; Jacobsen, E. N. I Am. Chem. Soc. 1994, 116, 425. (c)

Corden, B. B.; Drago, R. S.; Perito, R. P. 1 Am. Chem. Soc. 1985, 107, 2903.

(13) (a) Kim, S. M.; Kim, J. S.; Sohn, B. C.; Kim, Y. K.; Ha, Y. Y. Mol. Cryst. Liq. Cryst. 2001,

371, 321. (b) Sano, T.; Nishio, Y.; Hamada, Y.; Takahashi, H.; Usuki, T.; Shibata, K. I Mater.

Chem. 2000, 10, 157. (c) Tao, X. T.; Suzuki, H.; Watanabe, T.; Lee, S. H.; Miyata, S.; Sasabe,

H. Appi. Phys. Lett. 1997, 70, 1503.

(14) (a) Kim, D. H.; Cho, H. 1.;Zyung, T.; Do, L.-M.; Bark, K.-M.; Shin, G. C.; Shin, S. C. Eur.

Polym. 12001,38, 133. (b)Zhang, H. C.; Huang, W. S.; Pu, L.I Org. Chem. 2001, 66, 481.

Angew. Chem. mt.Ed. Engi. 1996, 35, 2109. (e) Marvel, C. S.; Tarkoy, N. I Am. Chem.Soc.

1957, 79, 6000. (f) Marvel, C. S.; Tarkoy, N.J Am. Chem. Soc. 1957, 80, 832.

(15) For examples of non-conjugated polymers containing Schiff-base complexes, see: (a)

Sailaja, S.; Reddy, K.R.; Rajasekharan, M.V.; Hureau, C.; Riviere, E.; Cano, J.; Girerd, J.J.

Inorg. Chem. 2003, 42, 180. (b) Tsuchimoto, M. Bull. Chem. Soc. Jpn. 2001, 74, 2101. (c)

Cronin, J. A.; Palmer, S. M.; Archer, R. D. Inorg. Chim.Acta 1996, 251, 81. (d) Patel, M. N.;

Sutaria, D. H.; Pate!, S. D. Angew. Makromol. Chem. 1996, 234, 13. (e) Archer, R. D.;

I!lingsworth, M. L.; Rau, D. N.; Hardiman, C. J. Macromolecules 1985, 18, 1371.

(16) (a) Kingsborough, R. P.; Swager, T. M. I Am. Chem. Soc. 1999, 121, 8825. (b)

Kingsborough, R. P.; Swager, T. M Adv. Materials 1998, 14, 110. (c) Reddinger, J. L.;

85 Reynolds, J. L. Macromolecules 1997, 30, 673. (d) Vilas-Boas, M; Freire, C.; de Castro, B.;

Christensen, P. A.; Hiliman, A. R. Inorg. Chem 1997, 36, 4919.

(17) (a) Sonogashira, K.; Tohda, Y.; Hagihara, N. Tetrahedron Lett. 1975, 50, 4467. (b)

Sonogashira, K. J Organomet. Chem. 2002, 653, 46.

(18) (a) Wilson, J. N.; Windscheif, P. M.; Evans, U.; Myrick, M. L.; Bunz, U. H. F.

Macromolecules 2002, 35, 8681. (b) Erdogan, B.; Wilson, J. N.; Bunz, U. H. F.

Macromolecules 2002, 35, 7863. (c) Moon, J. H.; Swager, T. M. Macromolecules 2002, 35,

6086. (d) Bunz, U. H. F. Chem. Rev. 2000, 100, 1605.

(19) Yamamoto, T.; Morikita, T.; Maruyama, T.; Kubota, K.; Katada, M. Macromolecules 1997,

30, 5390.

(20) (a) Anderson, H. L. Inorg. Chem, 1994, 33, 972. (b) Taylor, P. N.; Andersen, H. L. I Am.

Chem. Soc. 1999, 12], 11538.

(21) (a) Pautzsch, T.; Klemm, E. Macromolecules 2002, 35, 1569. (b) Naka, K.; Uemura, T.;

Chujo, Y. I Polym. Sci., Part A: Polym. Chem. 2001, 39, 4083. (c) Ley, K. D.; Li, Y.; Johnson,

J. V.; Powell, D. H.; Schanze, K. S. Chem. Commun. 1999, 1749. (d) Altmann, M.; Bunz, U. H.

F. Angew. Chem. mt.Ed. Engl. 1995, 34, 569. (e) Altmann, M.; Enkelmann, V.; Lieser, G.;

Bunz, U. H. F. Adv. Mater. 1995, 7, 726.

(22) (a) Screen, T. E. 0.; Thorne, J. R. G.; Denning, R. G.; Bucknall, D. G.; Anderson, H. L. I

Am. Chem. Soc. 2002, 235, 9712. (b) Screen, T. E. 0.; Thorne, J. R. G.; Denning, R. G.;

Bucknall, D. G.; Anderson, H. L. I Mater. Chem. 2003, 13, 2796.

(23) Lavastre, 0.; Illitchev, I.; Jegou, G.; Dixneuf, P. H. I Am. Chem. Soc. 2002, 124, 5278.

(24) Riley, P. E.; Pecoraro, V. L.; Carrano, C. J.; Bonadies, J. A.; Raymond, K. N. Inorg. Chem.

1986, 25, 154.

(25) Swager, T. M.; Gil, C. J.; Wrighton, M. S. I Phys. Chem. 1995, 99, 4886.

86 (26) Li, H.; Powell, D. R.; Hayashi, R. K.; West, R. Macromolecules 1998, 31, 52.

(27) Solutions containing as little as I wt% of polymer form highly viscous solutions. It was necessary to analyze very dilute solutions by NMR spectroscopy.

(28) The quantum efficiency of polymer 202a was < 0.1% in THF, using a solution of anthracene in EtOH (1 = 0.30) as reference standard.

(29) Pavia, M. R.; Cohen, M. P.; Dilley, G. J.; Dubuc, G. R.; Durgin, T. L.; Forman, F. W.;

Hediger, M. E.; Milot, G.; Powers, T. S.; Sucholeiki, I.; Zhou, S.; Hangauer, D. G. Bioorg. Med.

Chem. 1996, 4, 659.

(30) Antonisse M. M. G.; Snellink-Ruël B. H. M.; Yigit I.; Engbersen J. F. J.; Reinhoudt D. N.

I Org. Chem. 1997, 62, 9034.

87 CHAPTER 3

PoIy(salphenyleneethyynylene)s and their unique Supramolecular Crosslinking Behaviort

§3.1 Introduction

Poly(phenyleneethynylene)s are an important class of conjugated polymers that have found application in many areas such as semiconductors, light emitting diodes (LEDs), and as non-linear optical (NLO) materials.’ In particular, a great deal of research has been devoted to the investigation of using PPEs as sensors for small molecules; their excellent sensitivity to chemical stimuli is a direct result of the extended conjugation of the polymer backbone and their desirable energy transport 2properties. Swager pioneered the development of PPE conjugated polymer sensors, often referred to as “molecular wires”, and has demonstrated their superior photophysical characteristics. An exquisite example of a

PPE for sensing is illustrated in Figure 3.1. 3PPE 203 containing oligo(ethylene glycol) cyclophane moieties in every repeating unit of the polymer was found to be an excellent sensor for electron deficient molecules such as paraquat 2O4. Upon exposure of the polymer to the analyte, outstanding sensitivity was achieved as only binding of a small percentage of the many receptor sites in the polymer chain is necessary to diminish the fluorescence of the

t A version of this chapter has been published as a paper: Leung, A. C. W.; MacLachlan, M. J. “Poly(salphenylene-ethynylene)s: soluble, conjugated metallopolymers that exhibit supramolecular crosslinking behavior” I Mater. Chem. 2007, 17, 1923.

88 polymer. It is believed that the receptors with bound analytes function as low energy defect sites in which radiationless recombination occurs, quenching the luminescence of the polymer strand over an extended conjugation length. In comparison, the analogous molecular sensor 205 requires exposure to a much higher concentration of paraquat to completely diminishes its fluorescence. Hence, a significant signal amplification can be achieved by the polymeric sensor over the molecular counterpart.

204

H1225 n Oct 2N 203 205

Figure 3.1. PPE sensor 203 has superior sensitivity over molecular sensor 205 to electron deficient molecules such as paraquat (204).

Realizing the great potential of PPEs as sensory materials, researchers have strived to synthesize new polymers that can function as chemosensors and biosensors by combining a diverse library of monomers, attaching functional units such as crown 5ethers, and carbohydrates 6 to the PPEs. New polymers that are capable of detecting chemical analytes such as trinitrotoluene (TNT) and biological agents such as DNA were 7discovered. Besides the use of organic molecules as monomeric units, incorporating metals into conjugated polymers has also attracted enormous attention as the hybrid materials may exhibit novel properties distinct from their individual organic and inorganic components. Integrating metals into conjugated frameworks offers the opportunity for new materials that can perform coordination chemistry,

89 supramolecular chemistry, and catalysis; new polymers with unique electronic, magnetic, and optical properties may be 8constructed. An example that illustrates these concepts is porphyrin- containing polymer 190, in which the rigid metal-containing polymer serves as a scaffold for supramolecular chemistry, allowing facile assembly of the metallopolymers into supramolecular 9structures. The formation of polymer ladder 206 was accomplished through the addition of coordinating ligands such as 4,4’-bipyridine to the polymer in solution, Figure 3.2.’° It was observed that the formation of polymer ladders increased the overall conjugation of the polymer and enhanced the third order NLO response of the polymer by an order of magnitude.

2RN N2R

2RN. N2R

0 0 n 190 206

Figure 3.2. Porphyrin containing polymer 190 self-assembled into a supramolecular polymer ladder 206 in the presence of 4,4’-bipyridine.

In the previous chapter of this thesis, I have discussed efforts to synthesize a new series of soluble PPEs containing Schiff base transition metal complexes with the goal of producing new luminescent materials. However, studies of their luminescent properties indicated that these polymers were poorly emissive, and would not be suitable for

90 electroluminescent devices. Although polymers 202 do not possess intense luminescence, we anticipated these materials to have interesting properties in other areas due to the fact that

Schiff base metal complexes, such as complexes of N,N’-bis(salicylidene)ethylenediamine, 4 (“M(salen)”), are known to exhibit interesting magnetic,” 2NLO,’ oxygen 3transport,’ 4catalytic,’ and 5sensory’ properties. In addition, our research group has investigated many macrocycles that contain salen complexes, and these may be thought of as cyclic oligomers of the polymers described in this chapter. These macrocycles exhibit interesting supramolecular behavior, forming molecular cluster complexes and self-assembling into tubular 6assemblies.’ Coordination and binding of small molecules to the macrocycles were found to strongly affect the optical properties of these materials, making them good candidates for sensors. Other researchers have reported the incorporation of salen-type complexes into conjugated backbones with variable success, and these have been utilized as catalysts, electroluminescent materials, and microspheres for photonic applications.’ In this chapter I discuss the synthesis a new series conjugated metallopolymers7 186 and 187 of of designed to form linear and helical or zig-zag conformations, respectively. I will discuss on their optical properties as well as the aggregation behavior of the zinc-containing polymers.

186 187

91 §3.2 Synthesis of Monomers and Polymers

Chapter 2 described the preparation of soluble poly(salphenylene-ethynylene)s

(PSPEs) by incorporating two dodecyloxy substituents onto the salphen monomer. Although the resulting polymers were soluble in THF, long periods of stirring and heating were necessary to fully dissolve the polymers, and they become less soluble upon aging.

Therefore, we sought to prepare PSPE derivatives with improved solubility through the addition of racemic 2-butyloctyloxy substituents, branched chains with chiral centers.

Scheme 3.1 shows the synthetic route to the required precursor, substituted phenylenediamine 210. Efforts to prepare compound 208 using standard Williamson ether synthesis conditions with 23KC0 or NaOH as the base led only to a low yield (24%) of 208, with large amounts of mono-substituted side-product and unreacted catechol remaining even after 2 weeks of heating at reflux. The efficiency of this procedure can be significantly improved using NaH as the base, first forming salts of 207 followed by slow addition of 1- bromo-2-butyloctane; compound 208 was obtained as a colorless oil in excellent yield (96%). Compound 208 was subsequently nitrated with 3I-1N0 and reduced with Raney Ni and hydrazine to afford the target diamine 210. Soluble salphen ligand 211 was prepared by reaction of 5-iodosalicylaldehyde 193 and diamine 210 under nitrogen in THF, and was isolated as a bright orange solid in 79% yield, Scheme 3.2. Reaction of 211 with 2Zn(OAc) 2Ni(OAc) and 2Cu(OAc) afforded salphen monomers 212a-c as yellow, red, and, brown ,solids, respectively, in 85 - 92% yield. These monomers with iodo functionality opposite the hydroxyl groups are expected to give linear polymers.

92 HO OH OctBuO OBuOct OctBuO OBuOct OctBuO OBuOct / NaH, BuOctBr — 3HNO — Raney Ni, 24NH — — THF THF 02N 2NO 2HN 2NH 207 208 209 210

Scheme 3.1. Synthesis of phenylenediamine 210.

In an effort to develop metallopolymers with the potential to form 8helices,’ we constructed Schiff base monomers with a bent structure. Schiff base ligand 214 with iodo functionality meta to the hydroxyl moiety was prepared from 4-iodosalicylaldehyde 213 in 73% yield, Scheme 3.3. Subsequent reaction with 2Zn(OAc) 2Ni(OAc) and 2Cu(OAc) yielded metal-containing monomers 215a-c, respectively,, in 90 - 93%, yield. Compounds 212a-c and 215a-c were reprecipitated 2-3 times to afford pure compounds, and their composition and purities were confirmed with ‘H and ‘3C NMR spectroscopy, JR spectroscopy, UV-vis spectroscopy, MALDI-TOF mass spectrometry, and elemental analysis. The monomers all display an intense C=N stretching mode at 1600-1615 1cm in their JR spectra. Mass spectra of monomers 212a-c and 215a-c showed the expected molecular mass, and dimeric species were observed for both Zn monomers 212a and 215a.

UV-vis spectra of the monomers all show multiple bands in the region between 200 to 550 nm, showing strong absorption peaks centered at ca. 400 nm, and broad tails that extend to

550 nm. Fluorimetry measurements indicated that none of the monomers fluoresce, not surprising since they all have iodide substituents and the luminescence of these compounds are quenched via the heavy atom effect.

93 OctBuO OBuOct OctBuO OBuOct

O OH OctBuO OBuOct

+ M(OAc) THF THF —N0,N— 2HN 2NH I-_JOH HOJ__I

193 210 211 212a ( M = Zn) 212b ( M = Ni) 212c ( M = Cu)

Scheme 3.2. Synthesis of monomers 212a-c.

OctBuO OBuOct OctBuO OBuOct OctBuO OBuOct O OH M(OAc) 2j THF THE _N ,N— 2HN 02NH OHHO

213 210 215a(MZn) 215b ( M = Ni) 215c ( M = Cu)

Scheme 3.3. Synthesis of monomers 215a-c.

OctBuO OBuOct

OctBuO OBuOct 33OC 6H N ,N 0CH1633 Pd(P Ph Cu —N ,N— )34 THF,, 2HN’Pr /M\_ / = H1633OC 201 212a (M = Zn) 216a (M = Zn) 212b (M = Ni) 216b (M = Ni) 212c (M Cu) 216c (M = Cu) BuOct = 2-butyloctyl

Scheme 3.4. Synthesis of conjugated metallopolymers 216a-c.

OctBuO OBuOct 16330C1-1 —N0,N— Pd(PPh Cul ,)34THF, 2HN’Pr H16330C 215a(M’Zn) 201 215b( M = Ni) 215c ( M = Cu)

217a (M = Zn) 217b (M Ni) 217c (M = Cu) BuOct = 2-butyloctyl

Scheme 3.5 Synthesis of conjugated metallopolymers 217a-c.

94 improved 217a-c weights toluene. THF, precipitations polymers yield 217a-c mixture Figure filtration. after but Polymerization 3.3. are were are of These The solubility were remain 3-4 much high THF/HN’PR 2 , Intensely prepared polymers from precipitations polymers more enough more insoluble THF of colored of soluble dissolve employing 217 soluble, to 212a-c into form affording ensure is in from films methanol likely flexible in in other dissolving proceeds substantial THF THF organic an of high a polymers common identical to into free result and give

molecular I via in solvents acetone standing hexane. interchain Pd-catalyzed red solvents of 216a-.c organic procedure, solutions. the weight and and films, polymers’ Polymers were such entanglement, solvents methanol, were Sonogashira polymers suggesting Scheme obtained as chloroform therefore 216a-c helical such Scheme 3.5, through Figure 216a-c that as cross readily or but purified chloroform and 3.4. coil their 3.3. simple in coupling the THF. dissolve structures, 72 molecular Polymers Polymers resulting by — suction 90% The in and 3-4 95 in a inhibiting strong interchain interactions that can lead to aggregation. Consistent with this, polymers 217 do not readily form films, and were isolated as waxy solids.

§3.3 Polymer Characterization

14 13 12 11 10 9 8 7 6 5 4 3 2 1 0 ppm Figure 3.4. ‘H NMR spectrum of polymer 217a. 3(CDC1 + 1% 5).pyridine-d Inset: Expanded view of region from 8 3 to 9 ppm.

‘H NMR spectra of polymers 216a-b and 217a-b in 3CDC1 showed very broad peaks in the expected aromatic and alkyl regions, including a broad peak characteristic of the imine

3•4•19 residue at ca. 8.5 ppm, Figure The severe broadening is likely due to slow tumbling of the rigid polymers in the viscous solution, combined with strong aggregation between the

96 polymer strands. The absence of terminal alkyne signals, residual monomer, or oligomer corroborated the formation of polymers with high molecular weight. IR spectroscopy confirms the absence of any starting monomers, and the presence of a VC=N (1600 — 1615 cm

1) stretching mode verified that the saiphen moiety remained intact. A new signal at Ca.2200

1cm was observed in all of the polymers, corresponding to the CEC stretching mode as expected with the formation of alkyne linkages in the polymeric backbone. UV-vis spectroscopy of the polymers showed peaks that are broader than for the monomers, but the general absorption pattern resembled the starting salphen complexes. Absolute molecular weights of the polymers were established to be between Ca. 19,000 to 74,000 Da. (Mw)using

GPC. The high molecular weights measured correspond to degrees of polymerization ranging from 14 to 55, and the molecular weight and other related information of the individual polymer samples are summarized in Table 3.1.

Schiff base complexes have been incorporated into polymers to generate high temperature 20materials. Thermal gravimetric analysis (TGA) indicated that PSPEs 216a-c and 217a-c are stable to ca. 200 °C, with less than 2% mass loss below this temperature.

Differential scanning calorimetry (DSC) studies were performed on all of the polymers, but no noticeable transitions occurred between temperatures of-60 — 300 °C.

97 Table 3.1. Molecular weights (Mw,M) and polydispersities of polymers 216a-c and 217a-c.

Measurements were made with a GPC system equipped with triple detection (refractive index, light-scattering, and viscosity).

216a 216b 216c 217a 217b 217c

M 18700 73600 33700 32800 60400 63200

M 17200 52000 32400 24300 42400 50700

PDI 1.09 1.42 1.04 1.35 1.43 1.25

UV-vis spectra of polymers 216a-c and 217a-c show strong absorption peaks between ca.

400 — 500 nm, Figure 3.5. Linear polymers 216a-c all have similar absorption peaks centered at shorter wavelength (ca. 410 nm) and broad shoulders that extend toward 575 nm.

On the other hand, absorption spectra of non-linear polymers 217a-c possess broad peaks with less obvious shoulders. The linear polymers 216 all show significant blue-shifts in absorption relative to the non-linear analogues 217. We postulate that there is extended conjugation through the aromatic system on the salphen unit in the case of non-linear polymers 217, whereas in linear polymers 216 the conjugation pathway is interrupted by the metal centers, leading to shorter conjugation length and thus a blue-shifted absorption. To corroborate our observations, the absorption spectra of model compunds 218 and 219 with phenylacetylene substituents para and meta to the phenol moiety, respectively, were compared. As shown in Figure 3.6, the absorption spectrum of 219 is slightly red shifted in comparison to 218, but the absorption shoulder extends to significantly longer wavelength

(ca. 20 nm shift). This observed change in absorption behavior between the model compounds agrees with the observed trend for the polymers, correlating the absorption changes with increase of conjugation.

98 0.5

216a 0.4 --—-- 216b 7 216c / —217a \ \ \ 03 / —217c A // \\\ 1/ \\ 0.2 / \

:: 300 400 500 600 700 2Jnm Figure 3.5. UV-vis absorption (normalized) spectra of polymers 216a-c and 217a-c in 2C1CH (the polymers were dissolved in THF and diluted with 2C1CH to appropriate concentration, see procedures on P.24 for details).

2.0 /r\ —218 / \ 219 1.5 A10

0.5

0.0• 300 400 500 600 700

XInm Figure 3.6. UV-Vis absorption (normalized) spectra of 218 and 219 in .2C1CH

99 o o o 218o g219

§3.4 Aggregation and Sensing

Self-association of Zn salen complexes is well-documented in the literature, forming dimeric complexes in solution and the solid-state. In rigid salphen ligands, the 2Zn ion is unable to acquire a tetrahedral geometry, and therefore dimerizes to expand its coordination

3•7•21 number as shown in Figure We have reported the reversible aggregation of zinc containing Schiff base macrocycles mediated by a Zn•••O interaction between the phenolic oxygen and 2Zn metal center of Zn salphen 22moieties. In these phenyleneethynylene-type macrocycles, strong aggregation was observed in non-polar solvents, but deaggregation occurred upon the addition of coordinating ligands such as pyridine that competitively coordinate to the zinc ions.

100 R—OjO—R RO;OZDRRR : RR

Figure 3.7. Illustration of dimerization in Zn saiphen complexes. Strong interactions between the 2Zn center and the phenolic oxygens of the metal complexes hold the dimer together.

Zinc-containing Schiff base polymer 216a is insoluble in most organic solvents, such as 2C1CH Upon addition of Ca. 1% pyridine to a sample of 216a in 2C1CH the polymer dissolved.. On the other hand, when 2,6-lutidine was added instead of pyridine,, the polymer did not dissolve, even in pure lutidine. Lutidine is a stronger base than pyridine, but bulky methyl substituents inhibit coordination to metal centers. This observation suggested that the coordination of pyridine to the polymer was necessary to disrupt strong intermolecular interactions between the polymer strands.

To further probe this interaction, we studied the addition of Lewis bases to the polymer in solution. The UV-vis spectrum of polymer 216a in 2C1CH shows an absorption peak at 400 nm with a broad shoulder that extends to approximately 550 nm. Fluorescence measurements in 2C1CH indicated that the polymer is weakly luminescent, having a quantum yield of only 0.073%. Upon the addition of pyridine to a solution of 216a in 2C1CH a gradual but minor decrease in the absorption maximum at ca. 400 nm was ,observed, together with small increases to the absorption shoulder at ca. 500 nm, Figure

3.8a. A pseudo-isosbestic point was observed at Ca. 530 nm, but was not well-defined, consistent with the complexity of the polymer deaggregation process as pyridine binds to the

101 metal saiphen complexes. In the emission spectra, a much more pronounced effect was observed upon the addition of pyridine, where the fluorescence maximum at Ca. 580 nm increased about four-fold after 2 equivalents of pyridine were added (c1 = 0.27% after saturation). A blue shift from 590 to 546 nm was also observed in the fluorescence spectrum. When 2,6-lutidine was added to solutions of polymer 216a in solution, no changes in the absorption or emission spectra were observed.

102

pyridine

— Figure

6.45 3.8.

(1.03

UV-vis M;

0.1

0.0’

0.3

0.5

0.4

0.0

0.1

0.2

0.3

0.5

0.4

106

step

300 300

—

and

size:

1.13

(a)

(b)

fluorescence 4.30

400 400 x

step

spectra

M);

size:

excitation

500 500

)Jnm k/nm

1.03

11/

216a

1 N

I wavelength

1”\

106

(CH 2 C1 2 ,

600 600

and 5.00

2exc

4,4’

700

404

10.6

bipyridine

nm.

titrated

(4.30 with

103

o a) 0.20 (a)

0.15

A 0.10

0.05

0.00

300 400 500 600 700

X/nm

0.14 (b) I 0.12

0.10

A 0.08 0.06

0.04

0.02

0.00

300 400 500 600 700 ?Jnm Figure 3.9. UV-vis and fluorescence spectra of 219 2C1(CH 5.00 x 10 M) titrated with a) x 108 x 108 pyridine (1.03 — 1.65 M; step size: 1.03 x, M) and b) UV-vis and fluorescence 106 spectra of 219 titrated with 4,4’ bipyridine (1.08 x — 2.40 x i0 M; step size: 1.08 x 10

M); excitation wavelength exc 406 flm..

104 For comparison, I examined model compound 219, a Zn salphen complex that is monomeric in solution. As shown in Figure 3.9, the absorption spectrum of 219 changes gradually with the addition of pyridine or 4,4’-bipyridine, but no significant change to the fluorescence spectrum is observed.

These results suggest that in solution, polymer 216a exists in an aggregated

(crosslinked) state held together by Zn•••O interactions. In this form, the luminescence is mostly quenched due to excimer-like inter-strand interactions, along with energy transfer of the polymer absorption into localized states of the metal complexes. Upon addition of a Lewis base that can coordinate to the 2Zn ions, the crosslinks are broken and the polymer becomes more soluble. The polymer emission also increases intensity and undergoes a blue shift, supporting the disruption of an excimer-like species.

I investigated the addition of 4,4’-bipyridine to polymer 216a to see whether a ladder polymer would form, where the metal ions are bridged by the bipyridine ligand. A similar approach to porphyrin-based ladder polymers has been reported by Anderson et al as shown in Fig 3.2.10 Addition of bipyridine to 216a in 2C1CH yielded similar changes to the absorption spectrum as for the addition of pyridine, but an abrupt decrease to the emission peak was observed, Figure 3.8b. The decrease in emission ceased after ca. 0.2 equivalents of

4,4’-bipyridine were added to the sample, and the Stern-Volmer plot for the fluorescence quenching shows a non-linear curve, indicative of static quenching. The observed behavior is consistent with the formation of polymers with the bidentate 4,4’-bipyridine ligand bridging the polymer strands.

Polymer 217a is expected to adopt a helical or coil structure in which inter-strand interactions are reduced in comparison to 216a, inhibiting aggregation. Polymer 217a is considerably more soluble than 216a, suggesting that there are fewer crosslinks within the polymer. Moreover, the optical properties of polymer 217a are affected by Lewis bases in a

105 different way than polymer 216a. As shown in Figure 3.10, gradual changes were observed in the absorption spectra upon addition of pyridine or 4,4’-bipyridine, suggesting that coordination of the ligands occurs as in the case of polymer 216a. However, only a very minor increase to the polymer’s emission at 590 nm was observed upon addition of pyridine, and a similarly small decrease to the fluorescence peak occurred in response to the addition of 4,4’-bipyridine. These results from UV-vis and fluorescence spectroscopy, along with sharper signals in the 1H NMR spectrum and the good solubility of this material confirms that the polymer 217a has a weaker tendency to from strong aggregates in the dilute 2C1CH solution. However, it is likely that intrachain association of the salphen moieties leads to the weak luminescence (1 = 0.15%).

106

pyridine Figure — 3.01 3.10. x (1.03 A02i//j\ A 02 . UV-vis M; x 0.4

0.0 0.1 :: 106_ step 300 300 and size: 1.03 (a) fluorescence 4.30 x 400 400 x M; step M); spectra size: excitation 500 500 2k/nm of

1.03 /

217a

1/ / x wavelength 106 (CH 2 C1 2 , 600 600 M) and 5.00 Xexc b) 4,4’ 700 700 = x 341 10 bipyridine nm. M) titrated (4.30 with x 107 a) Polymers 216b-c and 217b-c containing square planar 2Ni and 2Cu ions showed no significant changes to their absorption spectra upon the addition of coordinating bases. The lack of response from these polymers is expected as the metal centers are square planar in geometry and do not readily expand their coordination numbers.

Overall, we believe that the Zn••O interaction is involved in crosslinking conjugated polymer 216a. This supramolecular interaction can be disrupted by addition of bases or by designing a polymer structure that reduces interchain interactions, as in polymer 217a. This new reversible crosslinking mechanism involving Zn•••O interactions, illustrated in Figure

3.11, is potentially useful for developing thermoplastic and elastomeric materials.

Figure 3.11. Cartoon illustrating the disruption of the polymer crosslinks upon the addition of pyridine.

§3.5 Conclusions

In summary, I have prepared a new series of high molecular weight conjugated PPE polymers containing Zn, Ni, and Cu salphen metal complexes in the backbone. The insolubility of the rigid metallopolymers was overcome through the addition of racemic

108 branched alkoxy substituents, and the introduction of a bent geometry to the conjugated backbone. Strong aggregation of the linear Zn metallopolymers that is facilitated by the presence of Zn•••O interactions was observed. Deaggregation occurs when the polymer is treated with a coordinating base such as pyridine, and strong response in polymer emission makes these polymers possible sensors for Lewis bases. Analogous zig-zag Zn metallopolymers, on the other hand, were less responsive to the addition of coordinating ligands and only small optical changes were observed. We hypothesize that these polymers exhibit a coil-like structure in solution and their luminescence is quenched via an intramolecular mechanism.

§3.6 Experimental

3.6.1 General

Materials. Copper(I) iodide, zinc(II) acetate, nickel(II) acetate, and copper(II) acetate were obtained from Aldrich. Tetrakis(triphenylphosphine)palladium was obtained from Strem

Chemicals, Inc. Deuterated solvents were obtained from Cambridge Isotope Laboratories, Inc. Tetrahydrofuran was distilled from sodium/benzophenone under .2N 2NH’Pr was distilled from NaOH under .2N 5-lodosalicylaldehyde 193, 4-iodosalicylaldehyde 213, and 1,4- dihexadecyloxy-2,5-diethynylbenzene 201 were prepared by literature 23methods. The synthesis of model compound 219 was previously reported by our 22group, and compound 218 was prepared by an analogous procedure.

UV-vis and Fluorescence measurements. Polymers 216a-c and 217a-c were initially dissolved in a small smount of THF (ca. 2 mL) and diluted to appropriate concentrations (1.0

109 x 106 M for quantum efficiency measurements, 5.0 x 106 M for titration studies) with 2C1CH so that the final concentration of THF was < 0.1%. Titrations experiments were performed in a 1 cm cuvette. The addition of appropriate Lewis bases in 2C1CH to the polymer samples with a microsyringe was followed by a short period of mixing and subsequent UV-vis and fluorescence measurements. No significant differences in the absorption and emission spectra were found between samples of polymers 5a prepared via the above method and samples prepared by dilution in pure 2C1CH The UV-vis spectra in Figure 3.5 and 3.6 are normalized to the absorbance of. the sample with the highest absorbance such that the spectra can be superimposed in the same scale. Florescence spectra are recorded using an excitation wavelength at the absorption maximum of the specific sample.

3.6.2 Procedures

Synthesis of 1,2-Bis(2-butyloctyloxy)benzene 208. Catechol (2.21 g, 20.1 mmol), NaH (1.0 g, OctBuOOBuOct 0.42 mmol), and 4BuNBr (ca. 0.1 g, 0.31 mmol) were combined in 500 mL of

THF. The reaction was refluxed for 1 h until a thick white precipitate formed.

2-Butyloctylbromide (20.0 g, 80.2 mmol) was then added dropwise over a period of 2 h, followed by reflux for an additional 72 h. After cooling the reaction to room temperature, the precipitate was removed by filtration and the THF was removed from the filtrate via rotary evaporation. Excess 2-butyloctylbromide was removed by distillation under high vacuum. Flash chromatography in 2CICH furnished 208 (8.60 g, 19.3 mmol, 96% yield) as a colorless oil.

Data for 208. C13 NMR (75.5 MHz, )3CDC1 ö 149.9, 121.0, 114.1, 72.1, 38.4, 32.1, 31.6, 31.3, 30.0, 29.3, 27.1, 23.3, 22.9, 14.3 ppm; 1H NMR (400 MHz, )3CDC1 6 6.87 (s, 4H, aromatic CR),

110 3.84 (d, J=5.6 Hz, 4H, 2),OCH 1.80 (m, J=5.6, 23.2 Hz, 2H, 2),CH 1.25-1.55 (m, 32H, 2),CH 0.89 (m, 12H, )3CH ppm; EI-MS: m/z 446.4, 278.2 (15%), 166.1 (11%), 108.6 (100%). Anal. Calc’d for :02CH3054 C, 80.65; H, 12.18. Found: C, 80.40; H, 11.81.

Synthesis of 1,2-Bis(2-butyloctyloxy)-4,5-dinitrobenzene 209. Compound 208 (6.00 g, 13.4

OctBuOOBuOct mmol) was added to 100 mL of 3HNO in a 1 L round bottom flask under air. The reaction was heated to 110 °C for Ca. 5 mins until a brown gas evolved, 02N 2NO then the temperature of the reaction was lowered to 80 °C and left stirring for 16 h. After cooling to room temperature, 100 mL of water was added. The product was then extracted into ,3CHCI washed with 2H0, followed by 5% 3NaHCO solution. The resulting yellow 3CHC1 solution was dried over 4MgSO and rotary evaporated to dryness. Flash chromatography in 2C1CH afforded 209 (6.05 g, 11.3 mmol, 84%) as a yellow oil.

Data for 209. C13 NMR (100.6 MHz, )3CDC1 152.3, 136.6, 107.7, 72.8, 38.0, 32.0, 31.4, 31.1, 29.9, 29.2, 27.0, 23.2, 22.9, 14.3, 14.2ppm; ‘H NMR (300 MHz, )3CDC1 ö 7.24 (s, 2H, aromatic CR), 3.93 (d, J=3.0 Hz, 4H, 2),OCH 1.83 (m, 2H, 2),CH 1.20-1.50 (m, 32H, 2),CH 0.87 (m, 12H, 3);CH ppm; EI-MS: 536.2 , 506.3 (22%), 184.0 (25%), 168.1 (20%), 109.8 (45%); Anal. Calc’d for :206CHN3052 C, 67.13; H, 9.76; N, 5.22. Found: C, 67.29; H, 9.80, N, 5.18. Synthesis of 1,2-bis(2-butyloctyloxy)-4,5-diaminobenzene 210. Compound 209 (5.00 g, 9.31

OctBuO>

111 nickel catalyst. Removal of solvent in vacuo afforded 210 (3.61 g, 7.56 mmol, 81%) as a light brown oil.

Data for 210. ‘3C NMR (100.6 MHz, )3CDC1 6 143.9, 123.4, 106.8, 13.7, 38.5, 32.1, 31.5, 31.2, 30.0, 29.3, 27.1, 23.3, 22.4, 14.31, 14.29ppm; ‘H NMR (300 MHz, )3CDC1 6400 MHz, )3CDC1 6.35 (s, 2H, aromatic Cl]), 3.74 (d, J=6.0 Hz, 4H, 2),OCH 3.16 (s, 4H, 2),NH 1.73 (m, 2H, 2),CH 1.25-1.70 (m, 32H, 2),CH 0.87 (m, 12H, )3CH ppm; EI-MS: m/z = 476, 140 (50%); Anal. Calc’d for :20CHN3056 C, 75.57; H, 11.84; N, 5.88. Found: C, 75.79; H, 11.98; N, 6.10. Synthesis of Schiff base ligand 211. A solution of 210 (0.500 g, 1.05 mmol) and 193

OctBuO,OBuOct (0.572 g, 2.31 mmol) in 20 mL of THF was heated to reflux for 24

h. After cooling to room temperature, 50 mE of MeOH was added IOH HOI to the reaction mixture under air to precipitate the orange product.

Precipitation in THF/MeOH was repeated once to afford 211 (0.735 g, 0.785 mmol, 79%) as an orange solid.

Data for 211. C13 NMR (100.6 MHz, )3CDC1 6 161.0, 160.2, 150.0, 141.4, 140.3, 135.0, 121.8, 120.1, 104,2, 79.8, 72.5, 38.4, 32.1, 31.6, 31.4, 30.0, 29.3, 27.1, 23.3, 22.9, 14.3 ppm; ‘H NMR (400 MHz, )3CDC1 6 13.19 (s, 2H, OR), 8.53, (d, J6.8 Hz, 2H, CHN), 7.65 (d, J=2 Hz, 2H, aromatic Cl]), 7.55 (q, J=2, 10.8 Hz, 2H, aromatic CM), 6.81 (d, J8.8 Hz, 2H, aromatic Cl]), 6.74 (s, 2H, aromatic Cl]), 3.91 (d, J=5.6 Hz, 4H, 2),OCH 1.83 (m, 2H, CM)), 1.25-1.60 (m, 32H, CM)), 0.87 (m, 12H, )2CH ppm; UV-vis 2):CI(CH 2max (E)361 (log 6 1.67), 390 (1.60) nm (L 1mo! 1).cm MALDI-TOF: m/z = 937.3. IR (KBr): v 2956, 2926, 2856, 1889, 1612, 1557, 1510, 1471, 1351, 1272, 1220, 1410, 1351, 1272, 1220, 1180, 1130,

112 1018, 933, 870, 845, 819, 766, 727 .1cm Mp. 166-168 C Anal. Calc’d for CHN4462 C, H, C, H, 3.24. 1204 56.41; 6.67; N, 2.99. Found: 56.41; 6.64; N, :

Synthesis of zinc monomer 212a. Compound 211 (0.300 g, 0.320 mmol) and zinc acetate

OctBuO\,,OBuOct dihydrate (0.084 g, 0.038 mmol) were combined in 10 mL of THF

under air. The reaction was heated to reflux for 24 h to give a

yellow solution. Cooling to room temperature followed by addition of 40 mL of MeOH furnished 212a (0.289 g, 0.289 mmol, 90%) as a yellow solid.

Data for 212a. ‘3C NMR (100.6 MHz, 6DMSO-d ö 170.8, 159.5, 149.3, 143.1, 141.1, 132.5, 125.8, 122.6, 100.3, 71.9, 71.0, 37.6, 31.3,) 31.0, 30.6, 29.2, 28.6, 26.3, 22.5, 22.1, 13.9; 1HNMR (400 MHz, 6DMSO-d ö 8.94, (d, J=6.8 Hz, 2H, CHN), 7.77 (d, J=2 Hz, 2H, aromatic Cl]), 7.45 (s, 2H,)aromatic Cl]), 7.38 (q, J=2.4, 11.2 Hz, 2H, aromatic Cl]), 6.54 (d, J8.8 Hz, 2H, aromatic Cl]), 3.98 (d, J=4.8 Hz, 4H, 2),OCH 1.76 (b, 2H, 2),CH 1.2-1.5 (m, 32H, 2),CH 0.87 (m, 12H, )3CH ppm; UV-vis 2):C1(CH 2max 304 (log E 1.96), 402 (2.34) nm (L 1mor cm’). MALDI TOF: m/z = 998.3. JR (KBr): v = 2918, 2859, 1888, 1614, 1504, 1466, 1374, 1309, 1263, 1218,

1170, 1139, 1119, 1018, 961, 937, 873, 826, 773, 726 cm’. Mp. decomp. > 290 °C. Anal. Calc’d for I24CHNO4460Zn: C, 52.84; H, 6.05, N, 2.80. Found: C, 55.24; H, 6.53; N, 3.19. Synthesis of nickel monomer 212b. Monomer 212b was prepared by a procedure identical

OctBuO,OBuOct to that for 212a except nickel acetate was used in the place of zinc

acetate. The monomer was isolated as a red solid (85%). _N\ ,N—

113 Data for 212b. ‘3C NMR (100.6 MHz, )3CDC1 ö 164.7, 151.2, 150.5, 142.5, 140.8, 135.8, 124.2, 123.0, 98.0, 75.6, 72.4, 38.3, 32.2, 31.5, 31.2, 30.0, 29.4, 27.2, 23.3, 23.0, 14.4 ppm; 1H NMR (400 MHz, )3CDC1 7.77, (s, 2H, CH=N), 7.52 (s, 2H, aromatic CM), 7.32 (d, J=9.2 Hz, 211, aromatic CR), 6.90 (s, 2H, aromatic Cl]), 6.73 (d, J=8.8 Hz, 2H, aromatic CM), 3.94 (d, J5.2 Hz, 4H, 2),OCH 1.83 (m, 2H, 2),CH 1.33 (m, 32H, 2),CH 0.89 (m, 12H, )3CH ppm; UV-vis )2C1(CH (s)=267 (log 7.11), 387 (3.80), 493 (1.42) nm (L mol’ cm’). MALDI-TOF: m/z = 992.3. IR (KBr): v = 2928, 2854, 1607, 1590, 1556, 1515, 1452, 1411, 1368, 1318, 1279, 1245, 1224, 1184, 1140, 1115, 1017, 933, 821, 787 .1cm Mp. decomp. > 260 °C. Anal. Calc’d for J24CHN4460NiO C, 53.19; H, 6.09; N, 2.82. Found: C, 53.11; H, 6.44; N, 2.96. Synthesis: of copper monomer 212c. Monomer 212c was prepared by a procedure identical OctBuO\,,OBuOct to that for 212a except copper acetate was used in the place of zinc

acetate. The monomer was isolated as a brown solid (92%). —N /N_

Data for 212c. UV-vis )2C1(CH 2fflax (6) = 255 (log 8 6.08), 373 (2.50), 420 (3.40) nm (L moF’ cm’). MALDI-TOF: m/z = 997.8. JR (KBr): v = 2924, 2855, 1894, 1732, 1607, 1589, 1507, 1457, 1371, 1316, 1246, 1220, 1175, 1138, 1118, 1017, 956, 824, 776, 726 .1cm Mp. = 230-232 °C. Anal. Calc’d for CHNO4460Cu C, 52.94; H, 6.06; N, 2.81. Found: C, 53.33,11,6.12, N, 3.18. I24

114 Synthesis of Schiff base ligand 214. A solution of 210 (0.617 g, 1.29 mmol) and 213

OctBuO\,,OBuOct (0.706 g, 2.85 mmol) in 20 mL of THF was heated to reflux for 24 h.

After cooling to room temperature, 50 mL of MeOH was added to the OH HO reaction mixture under air to precipitate the orange product.

I Precipitation in THF/MeOH was repeated once to afford 214 (0.883 g,

0.942 mmol, 73%) as an orange solid.

Data for 211. ‘3C NMR (100.6 MHz, )3CDC1 ö 161.5, 161.3, 149.9, 135.0, 133.0, 128.5, 127.1, 119.0, 104.7, 99.9, 72,6, 38.4, 32.1, 31.6, 31.3, 30.0, 29.4, 27.1, 23.3, 22.9, 14.1 ppm; ‘H NMR (400 MHz, )3CDC1 ö 13.38 (s, 2H, 01]), 8.51, (s, 2H, CH=N), 7.42 (s, 2H, aromatic Cl]), 7.24 (q, J=0.8, 8.8 Hz, 2H, aromatic Cl]), 7.03 (d, J=8.0 Hz, 2H, aromatic Cl]), 6.75 (s, 2H, aromatic Cl]), 3.91 (d, J=5.2 Hz, 4H, 2),OCH 1.83 (m, 2H, 2),CH 1.2-1.6 (m, 32H, 2),CH 0.87 (m, 12H, )3CH ppm; UV-vis 2):CI(CH 2max(E)289 (log 3.12), 344 (2.19), 387 (1.93) nm (L mol’ cm’). MALDI-TOF: m/z 937.3. JR (KBr): v = 2927, 2857, 1601, 1553, 1515, 1484, 1464, 1358, 1268, 1252, 1018, 1060, 1018, 939, 905, 860, 850, 793 .1cm Mp. 99- 101 °C. Anal. Calc’d for CHN4462 C, 56.41; H, 6.67; N, 2.99. Found: C, 56.58; H, 6.67; N, 3.16. :1204

Synthesis of zinc monomer 215a. Compound 214 (0.300 g, 0.320 mmol) and zinc acetate

OctBuO,,OBuOct dehydrate (0.084 g, 0.038 mmol) were combined in 10 mL of THF

under air. The reaction was heated to reflux for 24 h to give a yellow

solution. Cooling to room temperature followed by addition of 40 mL

I of MeOH furnished 215a (0.294 g, 0.294 mmol, 92%) as a yellow solid.

115 Data for 215a. ‘3C NMR (100.6 MHz, 6DMSO-d 171.2, 160.3, 149.2, 137.0, 132.5, 131.6, 121.8, 119.3, 111.1, 102.5, 100.5, 71.1,)31.3, 31.0, 30.6, 29.2, 28.6, 26.3, 22.5, 22.1, 13.9; ‘H NMR (400 MHz, 6DMSO-d 8.92, (s, 2H, CH=N), 7.43 (s, 2H, aromatic Cl]), 7.17 (d, J9 Hz, 2H, aromatic )Cl]), 7.11 (s, 2H, aromatic Cl]), 6.85 (q, J=3.0, 9.0 Hz, 2H, aromatic CR’), 3.98 (d, J3.0 Hz, 4H, 2),OCH 1.75 (b, 2H, Cl])), 1.2-1.5 (m, 32H, 2),CH 0.86 (m, 12H, Cl])) ppm; UV-vis 2):C1(CH 2rnax 312 (log 3.04), 390 (3.28) nm (L mol’ cm’). MALDI-TOF: m/z = 998.3, 1997.4 (dimer 2(M+H)). JR (KBr): v = 2925, 2856, 1610, 1579, 1502, 1463, 1405, 1376, 1268, 1217, 1174, 1117, 911, 865, 833, 774, 732 .1cm Mp. decomp.>320°C. Anal. Calc’d for CHNO4460Zn: C, 52.84; H, 6.05, N, 2.80. Found: C, 52.48; H, 6.20; N, 3.20. I24

Synthesis of nickel monomer 215b. Monomer 215b was prepared by a procedure identical

OctBuO\,,OBuOct to that for 215a except nickel acetate was used in the place of zinc

acetate. The monomer was isolated as a red solid (93%). _NN /N_

Data for 215b. C13 NMR (75.5 MHz, )3CDC1 164.4, 151.5, 150.4, 136.0, 134.0, 130.5, 124.7, 120.0, 102.5, 97.8, 72.2, 38.4, 32.2, 31.6, 31.2, 30.0, 29.4, 27.3, 23.3, 23.0, 14.4 ppm; ‘H NMR (400 MHz, )3CDC1 ö 7.57, (s, 2H, CH=N), 7.33 (d, J=1.2 Hz, 2H, aromatic Cl]’), 6.87 (s, 2H, aromatic Cl]), 6.83 (q, J=1.5, 9.9 Hz, 2H, aromatic Cl]’),6.73 (d, J=8.4 Hz, 2H, aromatic Cl]’), 3.90 (d, J=5.4 Hz, 4H, 2),OCH 1.82 (m, 2H, Cl])), 1.42 (m, 32H, Cl])), 0.90 (m, 12H, )2CH ppm; UV-vis )2C1(CH 2max ()=262 (log e 6.19), 320 (4.21), 390 (6.59), 473 (2.52) nm (L mor’cm’), MALDI-TOF: m/z = 992.7. JR (KBr): v 2926, 2856, 1608, 1585, 1496, 1463, 1420, 1368,

116 1279, 1245, 1224, 1186, 1115, 1015, 917, 856, 776 .1cm Mp. 190-192 °C. Anal. Calc’d for I24CHN4460NiO C, 53.19; H, 6.09; N, 2.82. Found: C, 53.35; H, 6.17; N, 2.91 :Synthesis of copper monomer 215c. Monomer 215c was prepared by a procedure identical

OctBuO\,,OBuOct to that for 215a except copper acetate was used in the place of zinc

acetate. The monomer was isolated as a brown solid (90%).

Data for 215c. UV-vis )2C1(CH 2max(8) = 274 (log c 3.40), 327 (3.84), 366 (2.96), 416 (5.02) nm (L moF’ cm’). MALDI-TOF: m/z = 997.8. JR (KBr): v 2928, 2858, 1606, 1581,

1499, 1461, 1416, 1375, 1275, 1244, 1222, 1182, 1138, 1116, 1057, 1018, 943, 914, 859, 839, 777, 731 .1cm Mp. 128-130 °C. Anal. Calc’d for CHNO4460Cu C, 52.94; H, 6.06; N, 2.81. Found: C, 53.18; H, 6.22; N, 2.94. J24

Synthesis of zinc polymer 216a. Monomers 212a (0.2007 g, 0.2007 mmol) and 201

Oct (0.1218 g, 0.2007 mmol) were combined in a 100

mL vessel. To these solids were added 10 mL of distilled THF and 4 mL of distilled 2NH’Pr via syringe. The reaction mixture was then degassed by three freeze/pump/thaw cycles. In a glovebox, 5 mol% of 34Pd(PPh and 5 mol% Cul were added. The brown reaction mixture was subsequently freeze/pump/thaw) one more time and heated to 75 °C for 24 h. The reaction mixture was then filtered through glass wool and precipitated with 400 mL of MeOH to yield an orange solid. Further purification was performed by precipitating the polymer once from THF into MeOH, and twice into acetone.

During the dissolution of the polymer into THF, a very fine beige precipitate would

117 sometimes appear, and was removed by filtration. This procedure yielded polymer 216a

(0.229 g, 85%) as a dark red film.

Data for 216a. ‘H NMR (400MHz, ,3CDCI 1%5pyridine-d 9 - 6 (broad, m), 3.3 - 4,5 (broad), 3.2—0.1 (broad, m) ppm; UV-vis )2C1(CH )= 331 (log 8 3.64), 404 (7.60) nm (L mol’ cm ‘).IR(KBr):v2854,2203, 1732, 1620, 1506, 1469, 1413, 1379, 1319, 1274, 1216, 1168, 1125, 1025, 881, 853, 833, 750, 721 .1cm GPC (THF): M = 18,700 (M/M = 1.09). Anal. Calc’d for 26CHNO86Zn129 C, 74.22; H, 9.47; N, 2.28. Found: C, 76.38; H, 9.61; N, 2.01.

Synthesis of nickel polymer 216b. Polymer 216b was prepared by a procedure identical to

OctBuO,,OBuOct that for 216a, starting with monomer 212b.

Precipitations furnished polymer 4b (84%) as a _NN ,N— 0CH1633 dark red film.

16 33 fl Data for 216b. UV-vis )2C1(CH max = 277 (log 5.81), 412 (9.33) nm (L mol’ cm’). JR (KBr): v 2922, 2204, 1732, 1610, 1494, 1453, 1378, 1274, 1181, 1029, 829, 756 .1cm GPC (THF): M 52,000 (M/M = 1.42). Anal. Calc’d for CHNONi86129 C, 76.76; H, 9.66; N, 2.08. Found: C, 72.44; H, 9.36; N, 2.35. 26

Synthesis of copper polymer 216c. Polymer 216c was prepared by a procedure identical to

OctBuO\,,OBuOct that for 216a, starting with monomer 212c. N/N Precipitations furnished polymer 216c (80%) as a O33 dark red film. 16 33 fl

118 Data for 216c. UV-vis )2C1(CH ?m = 279 (log 4.55), 412 (9.25) nm (L mol’ 1).cm JR (KBr): v= 2923, 2852, 2204, 1735, 1609, 1586, 1516, 1454, 1414, 1376, 1325, 1274, 1216, 1174, 1124, 1019, 832, 753 .1cm GPC (THF): M = 33,700 (M/M = 1.04). Anal. Calc’d for 26CHNO86Cu129 C, 76.48, H, 9.63; N, 2.07. Found: C, 76.09; H, 9.64; N, 2.40.

Synthesis of zinc polymer 217a. Polymer 217a was prepared using a procedure identical to

OctBuO\,,OBuOct that for 216a, starting with monomer 215a.

Purification of the polymer was performed /Zfl\ / \ 0 / \ by precipitation from THF into hexane

// twice, and into MeOH twice. Polymer 217a

1633 0C 0 H1633 (77%) as a red solid. 0CH / H1633 0CH1533 was isolated dark

n Data for 217a. ‘H NMR (400MHz, ,3CDCI 1% 5pyridine-d ö 8.8 - 8.5 (broad, s), 6.5 — 7.8 (broad, m) 3.7 - 4.3 (broad, d), 2.4 — 0.7 (broad, )m) ppm; UV-vis )2C1(CH Xm 341 (log E 3.10), 430 (6.06) nm (L 1mo1 1).cm JR (KBr): v = 2926, 2850, 2206, 1606, 1503, 1467.21, 1413, 1379, 1270, 1215, 1175, 1116, 1018, 986, 867, 723 .1cm GPC (THF): M 32,800 (M/M 1.35). Anal. Calc’d for CHNO86Zn129 C, 74.22; H, 9.47; N, 2.28. Found: C, 72.57; H, 9.37; N, 2.10. 26

119 Synthesis of nickel polymer 217b. Polymer 217b was prepared by a procedure identical to

OctBuO\_,,OBuOct that for 217a, starting with monomer 215b.

Precipitations furnished polymer 217b =N. ,N=\ 7 /N\ /\ /\ (72%) as a dark red solid. // 0CH1633 \/ H16330C 0CH1633 H16330C

n Data for 217b. 1H NMR (400MHz, ,3CDC1 1% 5pyridine-d ö 8.2 — 6.6 (broad, m), 3.5 - 4.5 (broad), 3.2 — 0.4 (broad, m); UV-vis )2C1(CH 2max) = 277 (log 4.74), 402 (3.43) nm (L moF’ cm’). JR (KBr): v 2927, 2852, 2201, 1732, 1604, 1494, 1468, 1275, 1217, 1029, 866, 722 cm. GPC (THF): M = 60,400 (M/M = 1.43). Anal. Calc’d for CHNONi86129 C, 76.76; H, 9.66; N, 2.08. Found: C, 70.34; H, 8.93; N, 2.10. 26

Synthesis of copper polymer 217c. Polymer 217c was prepared by a procedure identical to

OctBuO,,OBuOct that for 217a, starting with monomer 215c.

Precipitation furnished polymer 217c (90%) /N ,N=\ as a dark red solid. H1633O—— SNI H1633916O-—- C C n Data for 216c. UV-vis )2C1(CH 2max = 276 (log 6 3.85), 344 (3.27), 448 (7.00) nm (L moF’cm ‘).IR(KBr):v=2913,2866,2204, 1734, 1610, 1523, 1490, 1464, 1379, 1273, 1186, 1142, 1113,

1013, 984, 872, 825, 791, 721cm’. GPC (THF): M = 50,700 (M/M = 1.25). Anal. Calc’d for 26CNOH,8629Cu C, 76.48, H, 9.63; N, 2.07. Found: C, 70.80; H, 8.89; N, 2.01.

120 §3.7 References

(1) Bunz, U. H. F. Chem. Rev. 2000, 100, 1605.

(2) McQuade, D. T.; Pullen, A. E.; Swager, T. M. Chem. Rev. 2000, 100, 2537.

(3) Swager, T. M. Acc. Chem. Res. 1998, 31, 201.

(4) Zhou, Q.;Swager, T. M. I Am. Chem. Soc. 1995, 117, 12593.

(5) Kim, J.; McQuade, D. T.; McHugh, S. K.; Swager, T. M. Angew. Chem. mt.Ed. 2000, 39,

3868.

(6) (a) Babudri, F.; Colangiuli, D.; DiLorenzo, P. A.; Farinola, G. M.; Omar, 0. H.; Naso, F.

Chem. Comm. 2003, 130. (b) Erdogan, B.; Wilson, J. M.; Bunz, U. H. F. Macromolecules 2002,

35, 7863.

(7) Zheng, J.; Swager, T. M. Adv. Polym. Sci. 2005, 177, 151.

(8) (a) Holliday, B. J.; Swager, T. M. Chem. Commun.2005, 25. (b) Pickup, P. G. I Mater.

Chem. 1999, 9, 1641.

(9) Ruben, M.; Rojo, J.; Romero-Salguero, F. J.; Uppadine, L. H.; Lehn, J.-M. Angew. Chem. mt.Ed. 2004, 43, 3644.

(10) (a) Anderson, H. L. Inorg. Chem., 1994, 33, 972. (b) Taylor, P. N.; Anderson, H. L. I Am.

Chem. Soc., 1999, 12], 11538.

(11) Miyasaka, H.; leda, H.; Matsumoto, N.; Sugiura, K.; Yamashita, M. Inorg. Chem. 2003, 11,

3509.

(12) Lacroix, P. G. Eur. I Inorg. Chem. 2001, 2, 339.

(13) Bailes, R. H.; Calvin, M. I Am. Chem. Soc. 1947, 69, 1886.

(14) Zhang, W.; Lee, N. H.; Jacobsen, E. N. I Am. Chem. Soc. 1994, 116, 425.

(15) Cametti, M.; Nissinen, M.; Dalla Cort, A.; Mandolini, L. I Am. Chem. Soc. 2005, 127,

3831.

121 (16) (a) Ma, C. T. Z.; MacLachian, M. J. Angew. Chem. mt.Ed. 2005, 44, 4178. (b) Gallant, A.

J.; Chong, J. H.; MacLachlan, M. J. Inorg. Chem. 2006, 45, 5248.

(17) (a) Furusho, Y.; Maeda, T.; Takeuchi, T.; Makino, N.; Takata, T. Chem. Lett. 2001, 10,

1020. (b) Maeda, T.; Furusho, Y.; Takata, T. Chirality 2002, 14, 587. (c) Maeda, T.; Takeuchi,

T.; Furusho, Y.; Takata, T. I Polym. Sci., Part A: Polym. Chem. 2004, 42, 4693. (d) Galbrecht,

F.; Yang, X. H.; Nehls, B. S.; Neher, D.; Farrell, T.; Scherf, U. Chem. Commun. 2005, 2378. (e)

Houjou, H.; Shimizu, Y.; Koshizaki, N.; Kanesato, M. Adv. Mater. 2003, 15, 1458,

(18) (a) Dai, Y.; Katz, T. J.; Nichols, D. A. Angew. Chem. mt.Ed. Engi. 1996, 35, 2109. (b)

Dai, Y.; Katz, T. J. J. Org. Chem. 1997, 62, 1274. (c) Zhang, H.-C.; Huang, W.-S.; Pu, L. I

Org. Chem. 2001, 66, 481.

(19) Approximately 1% of deuterated pyridine was added to the NMR samples to promote dissolution of the polymers.

(20) (a) Marvel, C. S.; Tarkoy, N. I Am. Chem. Soc. 1957, 79, 6000. (b) Chantarasiri, N.;

Tuntulani, T.; Tongraung, P.; Seangprasertkit-Magee, R.; Wannarong, W. Eur. Polym. I 2000,

36, 695. (c) Senthilkumar, N.; Raghavan, A.; Nasar, A. S. Macromol. Chem. Phys. 2005, 206,

2490.

(21) Kleij, A. W.; Kuil, M.; Luts, M.; Tooke, D. M.; Spek, A. L.; Kamer, P. C. J.; Van

Leeuwen, P. W. N. M.; Reek, J. N. H. Inorg. Chim.Acta, 2006, 359, 1807.

(22) Ma, C. T. Z.; Lo, A.; Abdolmaleki, A.; MacLachian, M. J. Org. Lett. 2004, 6, 3841.

(23) (a) Pavia, M. R.; Cohen, M. P.; Dilley, G. J.; Dubuc, G. R.; Durgin, T. L.; Forman, F. W.;

Hediger, M. E.; Milot, G.; Powers, T. S.; Sucholeiki, I.; Zhou, S.; Hangauer, D. G. Bioorg. Med.

Chem. 1996, 4, 659. (b) Swager, T. M.; Gil, C. J.; Wrighton, M. S. I Phys. Chem. 1995, 99,

4886.

122 CHAPTER 4

The Ladder-Chelate Approach to Soluble Conjugated Metal- Containing Polymers

§4.1 Introduction

“Organic electronics” commonly refers to an area of chemistry that studies the use of conjugated organic compounds, to serve as active components in electronic and optoelectronic devices, replacing traditional inorganic materials such as copper and silicon.’ These materials have promising applications in light emitting diodes (LEDs), field effect transistors (FETs) and photovoltaics, and have already been used in commercial products such as electronic paper and smart 2windows. In particular, significant research efforts have been devoted to the study of rigid organic molecules that have highly conjugated structures due to their attractive properties as organic semiconductors. Organic molecules such as oligoacenes 220 and hexa-peri benzocoronenes (HBC5) 221, having rigid planar structures and extensively delocalized t systems, are outstanding candidates that are being comprehensively studied and have been successfully applied as organic semiconductors and photoconductors. To improve the electronic properties of these materials, scientists have attempted3 to alter the chemical structure of these molecules. For example, various modifications to HBCs, such as the functionalization

t A version of this chapter will be submitted for publication. Leung, A. C. W.; Hui, J. K. - H; Chong, J. H.; MacLachian, M. J. “The Ladder-Chelate Approach to Soluble Conjugated Metal-Containing Polymers”.

123 of the aromatic core with aliphatic chains and with various functional groups, were investigated as methods to induce and control the formation of highly ordered structures such as linear aggregates, liquid crystals and 5nanotubes. The construction of ordered structures maximizes 71-it interactions between adjacent molecules, therefore improving the charge-carrier mobility and the overall conductivity of the material.

Conjugated polymers such as polyphenylenevinylenes (PPVs), polythiophenes, and polyacetylenes are another class of materials that have received tremendous attention in the development of organic electronic 6materials. While researchers have synthesized a large variety of conjugated polymers with different chemical structures, achieving good electronic properties is often difficult due to twisting of the polymeric backbones and the presence of chemical defects, which interrupts the conjugated pathways of the polymers. An effective strategy to extend the delocalization within these conjugated polymers is to construct a ladder-like polymeric 7framework. Conjugated ladder polymers contain multiple conduction pathways, usually in the form of aromatic rings joined by the sides (e.g. polyrylene 222), and they were found to have extraordinary electronic properties due to their strongly delocalized it-electronic system. In addition, the presence of multiple bonds throughout the entire length of the ladder polymer restricts rotations of the conjugated chain, thus reducing interruptions in the conjugation pathways.

124 coo

220 221 222

Figure 4.1. Oligoacenes 220, hexa-peri-benzocoronenes (HBCs) 221, and polyrylene 222 are examples of highly conjugated organic compounds investigated for applications as organic electronics.

Inorganic chemists have taken a similar approach to prepare new conductive materials, employing highly conjugated molecules that contain 8metals. The incorporation of metals into the conjugated framework offers new electronic and magnetic properties, as well as versatility in controlling the macroscopic order of the molecules. New coordination sites are available for ligand coordination allowing facile assembly of metal complexes into supramolecular 9structures. For example, macroscopic order of the inorganic material can be introduced by simply adding bidentate ligands that connect adjacent molecules into a coordination network, as illustrated by the synthesis of phthalocyanine coordination polymer 224 via the addition of pyrazine to phthalocyanine 223 in Scheme 4.1. The formation of the linear coordination network maximizes it-orbitals overlap between the phthalocyanine units, thereby improving the conductive properties of the bulk 0material.’ Porphyrins are another class of molecules to be assembled into conjugated frameworks due to their attractive conductive, electroluminescent, and NLO properties.” Recent research has mainly focused on coupling porphyrins to the backbone of organic polymers such as PPE and 2PPV.’ Attempts to improve the electronic properties of porphyrin-containing conjugated polymers were met with tremendous success 125 when Osuka and coworkers successfully developed new synthetic strategies to prepare ladder polymers. Fully conjugated, rigid porphyrin-containing ladder polymer 226 was prepared by scandium (III) catalyzed oxidative coupling of meso-meso-linked zinc porphyrin polymer 225 that has adjacent porphyrin units perpendicular to each other (Scheme 4.2).13 The presence of multiple bonds throughout the ladder polymer enforces planarity of the conjugated framework, and delocalization within the polymeric backbone improves dramatically - evident by an extremely red-shifted adsorption spectrum that reaches into the infrared region! These extraordinary polymers are expected to have important applications as molecular wires.

R R

223 R 2CHCHEtBu

224

Scheme 4.1. Phthalocyanine 223 is an attractive component for conjugated metal-containing polymers. Phthalocyanine-containing coordination polymer such as 224 can be assembled via addition of bidentate coordinating ligands.

126 Ar

225

DDQ, 3Sc(OTf)

226

Ar =

Scheme 4.2. The synthesis of fully conjugated “porphyrin tape” reported by Osuka et al. The extensive conjugation of the polymer is evident by an extremely red-shifted electronic spectrum.

Schiff base chemistry has also been explored as a method to build rigid conjugated metal- containing ladder polymers. Manecke et al. first attempted to build Schiff base ladder polymer

228 via condensation of 1,4-dihydroxy-2,5-diformylbenzene 227 and o-phenylenediamine 10,

Scheme 4•3•14 Due to the rigid structure of these polymers, the materials obtained were completely insoluble in organic solvents. Although the insolubility of these materials prevented proper characterization, they were found to be semiconducting and have excellent thermal stability. I identified Schiff base condensation as an attractive strategy to generate soluble, conjugated ladder polymers with transition metals in every repeat unit. Figure 4.2 illustrates the target ladder polymers and model compounds that are being pursued in this work. Ladder

127 polymer 230 is similar to the insoluble polymers (228) reported by Menecke et al., having the same rigid conjugated structure, but with flexible groups installed on the periphery of the polymers to improve the solubility of the materials. Target polymer 232 is a bent version of polymer 230 that may adopt a helical or coil-like structure. The chemical structure and conjugation pathway of 232 is expected to alter the electronic and chemical properties significantly in comparison to 230. In addition, a series of bimetallic model compounds 229 and

231, representative of the repeating units of polymers 230 and 232, respectively, were prepared to facilitate understanding of the chemical and electronic properties associated with these novel materials.

OH 0 2MX + QNH I 2HN 2 O OH n 227 10 228

Scheme 4.3. The synthesis of insoluble Schiff base-type ladder polymer by Menecke et. al.

128 n

229 230

n 231 232

Figure 4.2. Target Schiff base ladder polymers 230 and 232, and bimetallic model compounds

229 and 231. (R alkoxy)

§4.2 Synthesis of Starting Materials

Our approach in the synthesis of salphen-containing polymers utilizes a condensation reaction between 1,4-dihydroxy-2,5-diformylbenzene 227 and phenylenediamine derivatives containing pendant solubilizing groups. This reaction may be templated through the addition of metal salts to give a fully conjugated, ladder-type polymer 230 as illustrated in Scheme 4.4,

Similarly, Schiff base ladder polymers 232 with a bent structure may be synthesized using a similar strategy employing 4,6-diformylresorcinol 233 as a starting material (Scheme 4.5). 129 OHO R R 2MX

0 OH 2HN 2NH n 227 230

Scheme 4.4. Proposed synthetic route to obtain Schiff base conjugated ladder polymer 230.

R R RR MX + 2 HOOH 2HN 2NH 233 232

Scheme 4.5. Proposed synthetic route to obtain Schiff base conjugated ladder polymer 232 with a bent structure.

Synthesis of our target model compounds 229 and polymers 230 requires I,4-dihydroxy-

2,5-diformylbenzene 227 as a starting material, which can be synthesized according to a

procedure reported by Wasielewski et at. starting with 1,4-dimethoxybenzene 234 (Scheme

4.6). 15 Bromomethylation of 234 with paraformaldehyde and HBr afforded compound 235 in 89% yield. Subsequently, 235 was acetylated (75%), reduced with 4LiA1H (97%) and oxidized to dialdehyde 238 with pyridinium chlorochromate (PCC) (77%). Finally, demethylation with 3BBr afforded the target dialdehyde 227 in 84% yield. Although the above procedure gave our desired product in good yields, the rather lengthy synthesis encouraged the search for another route to dialdehyde 227.

130 3OCH 3OCH 3OCH O),(CH HBr KOAc, BuNBr OAc 2 ‘- Br 4 I HOAc Br MeCN AcO 3OCH 3OCH 3OCH 234 235 236 4LIAIH THF

OH 0 3OCH 3OCH 3BBr LCHO PCC TOH 2CICH OHC’f 2CICH 0 OH 3OCH 3OCH 227 238 237

Scheme 4.6. Synthesis of 1,4-dihydroxy-2,5-diformylbenzene 227 according to a procedure reported by Wasielewski et aT

Alternatively, compound 227 can be synthesized in multigram quantities using a shorter route, Scheme 4.7. Attempts to directly incorporate formyl groups onto 234 by ortho-lithiation of 234 yielded mono-formylated side product along with 238.16 The mono-substituted product can be avoided by first brominating 234 to obtain dibromo species 239 (76%),’ followed by lithiation and quenching with DMF to yield compound 238 (72%). Subsequent demethylation with 3BBr afforded dialdehyde 227 in 84% yield. This synthetic route is more efficient then the aforementioned synthetic route described in Scheme 4.6 insofar that it is less time-consuming and very little purification is required.

131 3OCH 3OCH OH 0 1(L ,2Br HOAc 1) rBuLi 3BBr Brf 2) DMF 2CICH 3OCH 3OCH 0 OH 234 239 238 227

Scheme 4.7. A shorter synthetic route to 1,4-dihydroxy-2,5-diformylbenzene 227.

4,6-Diformylresorcinol 233, an isomer of 227 with formyl groups meta to each other, is required to synthesize polymers 232 and model compound 231. The dialdehyde was synthesized according to a procedure reported by Worden et al. (Scheme 4.8), starting with bromination of 1,3-dimethoxybenzene 240 to yield intermediate 241 (83%).18 Treatment of 241 with BuLi followed by quenching with DMF afforded dialdehyde 242 in 64% yield. Subsequent demethylation with 3BBr yielded the desired product 4,6-diformylresorcinol 233 in 84% yield.

Bra,HOAc Br-Br 1) BuLi 3BBr o(jo 1 2) DMF CICH CO’OCH COOCH COOCH 2 HOOH 3H 240 3H 241 3H 242 233 Scheme 4.8. The synthesis of 4,6-diformylresorcinol 233 according to a procedure reported by

Worden et al.

To obtain soluble polymers, phenylenediamine derivatives containing various solubilizing groups were synthesized, Figure 4.3. Diamine 194 containing two linear dodecyloxy chains, as well as diamines 210 containing two chiral 2-butyloctyloxy substituents, were used in the synthesis of the target ladder polymers. These diamines have also been used in the synthesis of PSPEs, and their synthetic procedures are detailed in the Experimental sections

132 of Chapter 2 and Chapter 3•19 Phenylenediamine derivatives 243 and 244 containing 2- ethyihexyloxy and 2-decyltetradecyloxy substituents, respectively, were prepared using procedures analogous to the synthesis of 210.20 Triptycene-type diamine 245 was prepared by Jonathan Chong of the MacLachian research ’2group.

0CH1225 H12250C

2HN 02NH 2HN 2NH 2HN 2NH 194 210 243 CH1021 CH1225 CH1021CH1225 2H

2HN 2NH 244 245

Figure 4.3. Phenylenediamine derivatives with pendant solubilizing groups that were used in the preparation of Schiff base ladder polymers.

133 § 4.3 Synthesis and Characterizations of Model Compounds

4.3.1 Model Compounds Synthesis and NMR studies

To gain a better understanding of the chemical and electronic properties of our target conjugated ladder polymers, a series of model compounds containing one and two saiphen moieties were synthesized. Simple Schiff base salphen derivatives 246a-b were synthesized using standard Schiff base condensations (Scheme 4.9), and these compounds represent the single Schiff base components of our target 22polymers. A new synthetic strategy was also developed to synthesize new bimetallic model compounds 229a-b, comprising two salphen units that are connected by a rigid conjugated linker. The close proximity of the two metal centers and the strong delocalization within the molecule should promote strong metal-metal interactions.

Through comparison of the different model compounds 246 and 229, better understanding of the electronic and magnetic properties of our target polymers may be obtained, in particular to elucidate whether cooperative electronic and magnetic interactions exist.

HexEtO OEtHex

,‘=O HexEtO OEtHex / \ M(oAc) — 2 + - H2H2 127 243 246a M=Zn 24Gb M=Cu EtHex = 2-ethyihexyl

Scheme 4.9. Synthesis of model compounds 246a-b via standard Schiff base condensation.

The synthetic route to the desired bimetallic model compounds 229 is outlined in Scheme

4.10. The initial strategy to prepare soluble model compounds was to incorporate diamines 194 134 with linear dodecyloxy chains into the target model compounds. Condensation product 247a

was prepared in 76% yield by heating 2 equivalents of diamine 194 and 1 equivalent of dialdehyde 227 in THF. A bright red powder of pure 247a was isolated by precipitation of the product in THF with methanol, and ‘H NMR spectroscopy, JR spectroscopy, mass spectrometry and elemental analyses confirmed the composition and purity of this compound. The desired organic pro-ligand 248a was synthesized by reacting 247a with salicylaldehyde, although early attempts to synthesize this compound in organic solvents (such as ethanol and THF) using excess

(up to 10 equiv.) salicylaldehyde resulted in a mixture containing 248a and other incomplete condensation products. However, it was later found that pure samples of 248a can be prepared by simply heating a solution of 247a in neat salicylaldehyde, followed by precipitation with methanol to yield a red powder (97%). Unfortunately, attempts to metallate proligand 248a with metal salts such as 2Zn(OAc) and 2Cu(OAc) resulted in insoluble materials.

135 OHO R R

+ -OH iiILrJ

227 194 1225(R=0C 243 )H(R=OEtHex) 247a 1225(R=0C 247b H(R=OEtHex) OH) 0

OH HO*OH HO

248b (R=OEtHex) 248a H1225(R=0C M(OAc) ) 2M(OAc)

R R Insoluble Products (M Zn, Cu)

_N\0/N=\

229a (M=Zn;R=OEtHex) 229b (M=Cu; R=OEtHex)

Scheme 4.10. Synthesis of bimetallic model compounds 229a-b (EtHex = 2-ethylhexyl).

136 To improve solubility, diamine 243 with chiral 2-ethyihexyloxy chains (racemic origin) was incorporated into the model compounds. Employing the same synthetic strategy that was used to prepare 248a, reaction of dialdehyde 227 with 2 equivalents of 243 afforded a red product that crystallized from hexane to afford pure intermediate 247b as red crystals in 70% yield. Condensation product 247b is stable in air and organic solvents, but is susceptible to acid hydrolysis. ‘H NMR experiments in 3CDC1 resulted in significant decomposition of 247b, most likely due to trace acid in this solvent. This problem was overcome by using 2CICD as solvent. Subsequent reaction of 247b with salicylaldehyde afforded proligand 248b as a red powder that can be conveniently isolated by precipitation with methanol (96%). The ‘H NMR spectrum of 248b is shown in Figure 4.4. Disappearance of the amine )2(NH signal together with the appearance of the two distinct imine (CH=N) and the two hydroxyl (OR) signals clearly suggests the formation of the target pro-ligand. Reaction of 248b with 2Zn(OAc) and 2Cu(OAc) afforded soluble bimetallic model compounds 229a-b in 69% and 76% yield, respectively. Compounds

229a-b are soluble in THF, DMSO, and pyridine, and cubic crystals of 229a can be obtained by slow diffusion of acetone into a solution of 229a in pyridine. Unfortunately, X-ray crystallography experiments were unsuccessful due to inadequate diffraction intensity from crystals of 229a. Figure 4.5 illustrates a ‘H NMR spectrum of 229a in 6DMSO-d the presence of the expected resonance signals along with the disappearance of the; hydroxyl (OR) signal confirms the successful synthesis of the intended model compound. It was observed that 229a undergoes demetallation and hydrolysis if the material remains in wet organic solvents over prolonged periods of time (i.e. > Ca. 3 hours). No signs of decomposition were observed, however, when samples of 229a were stored in dry solvents under inert 2N atmosphere, or in the solid-state under air.

137 CH2

8.5 8.0 7.5 7.0 ppm CHDCI2 to to 90t (‘1 (N tC’( rt CH3 (‘4 (‘4 .‘4c’4 c4

OH\ CHN ArH OCH2 -

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

Figure 4.4. ‘H NMR spectrum 2C1(CD 300 MHz) of proligand 248b showing the expected resonance signals. Inset: Expanded, view of region from ö 6.7 to 8.7 ppm.

138 ArH DMSO CH=N

CH2 CH3 I.. 85 8.0 7.5 7.0 6.5 ppm

.. . pp

Figure 4.5 ‘H NMR 6(DMSO-d 300 MHz) spectrum of bimetallic Zn model compound 229a. Inset: Expanded view ,of region from 6 6.3 to 9 ppm.

During the NMR experiments to characterize bimetallic Zn model compound 229a, it was observed that the resonance signals broadened significantly in non-coordinating solvents such as 3CDCI and 2C1CD The broadening in NMR resonance signals was attributed to the strong aggregation commonly. observed between Zn salphen complexes. As discussed in the previous chapter, Zn saiphen complexes have strong tendencies to aggregate into dimeric species through a Zn•••O interaction between the phenolic oxygen and the 2Zn metal center between adjacent units, and it is believed that the same aggregation behavior is occurring for bimetallic

Zn model compound 229a. The self association of this Zn dimer can be interrupted through the

139 addition of coordinating solvents such as DMSO and pyridine, and Figure 4.6 portrays a NMR titration experiment to illustrate this aggregation-deaggregation behavior. In this experiment, 2CICD was added to a solution of 6DMSO-d containing 229a, up to a concentration of 1:4 (v:v) CI/CDDMSO-d It was observed that the NMR signals gradually broaden and shift upfield as the62 concentration of 2CICD is increased in the NMR sample. The broadening of the NMR .signals and upfield shifts are consistent with aggregation and self-assembly of the Zn saiphen units, as similar changes in NMR signals have been observed and correlated with aggregation of other planar metal 23complexes. The formation of dimeric aggregates can also be observed in the MALDI-TOF mass spectra as a signal at 2388.6 m/z, a value that is double the molecular weight of the monomeric model compound 229a (mlz = 1194.5). Further evidence to the aggregation of

229a was observed as the solubility of the bimetallic model compound changes in the presence of coordinating ligands. Model compound 229a is insoluble in chlorinated solvents such as 2CICH but upon the addition of a small amount (ca. 1%) of coordinating ligands such as pyridine, and acetoacetone, the compound dissolved. This observation provides corroboration that the coordination of ligands to the 2Zn centers can be used to disrupt the strong intermolecular Zn•••O interactions.

140 1:4 DMSO.4OCD2CI2 A

2:3 DMSO-d6:CD2CI2

90 85 80 7-5 70 65 ppm

Figure 4.6. 1H NMR titration experiments illustrating the aggregation of 229a in non- coordinating solvents. 2C1CD was added to a solution of 6DMSO-d containing 229a, up to a concentration of 1:4 C1/CDDMSO-d Significant signal broadening and upfield shift of the aromatic signals suggests.62 aggregation of 229a in the presence of non-coordinating solvents. It was anticipated that bimetallic model compounds containing a variety of transition metals could be easily prepared by simple reactions combining the corresponding metal salts and pro-ligand 248b. In this way, bimetallic model compounds containing ,2Cu ,2Co and 2VO were prepared, and their presence was confirmed by observation of a peak at a m/z value in ESI

MS corresponding to the mass of the compound. Attempts to confirm the purity of these compounds with elemental analysis, however, were unsuccessful as the measurements of carbon

141 contents in the samples is always low, a problem that is often observed in the characterization of

Schiff base metal complexes and is likely due to the incomplete combustion and coordination of solvent 24molecules. Similarly, it was expected that the addition of 2Ni(OAc) to proligand 248b would produce bimetallic nickel complex 249a that can be easily characterized by NMR spectroscopy. Surprisingly, the ‘H NMR spectrum of the resulting product has a very complicated pattern together with severe signal broadening (Figure 4.7), suggesting the presence of an unsymmetrical product. MALDI-TOF mass spectrometry indicated that the major product in the sample contains only one nickel atom (observed m/z = 1121.4; calculated m/z for postulated structure 249b = 1122.6), Figure 4.7 inset. A second weaker signal is observed at m/z

= 1196.2, and this was identified as being due to a monohydrate of the desired product 249a

(calculated m/z = 1196.5). It is postulated that the binding of 2Ni ions to ligand 248b triggers an enol-keto tautomerisation to form a quinone-like structure 249c, hampering the insertion of a second Ni atom, Scheme 4.11. The tautomerisation of Schiff base ligands containing multiple binding sites was previously observed in a dendritic ligand prepared in the MacLachlan research group, where keto-enol tautomerisation of the hydroxyl group in the Schiff base moiety prevented chelation of transition metal 25ions.

142 HexEtO0OEtHex 2 2Ni(OAc) OH HO*OH H09

HexEtO0OEtHex 248b 249a

HexEtO OEtHex HexEtO OEtHex 0 _N\ 0 ,Ni N_ H09 /\ HO / N

HexEtO0OEtHex HexEtO0QEtHex 249b 249c

Scheme 4.11. Attempts to synthesize bimetallic Ni complex 249a resulted in a mixture of products containing two or one Ni atoms. The side product containing one Ni is postulated to have structures 249b and 249c.

143

confirms Figure

synthesis

4.7.

the

product

bimetallic

‘H

NMR

m/z

contains

spectrum

model

mixture

(CD 2 CI 2 ,

compound

compounds

400

249.

M1-Iz)

Inset:

containing

the

MALDI-TOF

product

one

and

obtained

two

mass

from

atoms.

spectrometry

attempted 144 60CH13 13 HO>OH + 2

I2H

233 250 251

OH 0 2M(OAc) 2df 60CH13

231a M=Zn 231b M =Cu

Scheme 4.12. Synthesis of Zn and Cu bimetallic model compounds 231a and 231b.

Bimetallic model compounds 231a-b were prepared using a similar strategy to that used to prepare 229a-b, Scheme 4.12. Reaction of 4,6-diformylresorcinol with phenylenediamine 250 afforded condensation product 251 as a red solid (85%). Subsequently, a one pot reaction with 251 and salicylaldehyde in the presence of 2Zn(OAc) and 2Cu(OAc) afforded the target bimetallic model compounds 231a and 231b in 72% and 70% yield, respectively. The desired products 231a-b have good solubility in organic solvents such as THF, DMSO, and 2C1CH and it was not necessary to incorporate bulkier diamines with chiral ethylhexyloxy groups, as in the case of 229a-b. The structure of 231a was verified by single crystal X-ray diffraction, Figure

4.8. Crystals of 231a suitable for X-ray diffraction studies were obtained by slow diffusion of

MeOH into a solution containing 231a in DMSO. As illustrated by the ORTEP structure in

145 Figure 4.8a, the alkoxy substituents are extended from the Schiff base moiety in an irregular fashion and the large size of the ellipsoids suggests that there is significant disorder in the alkoxy chains. The 2Zn metal centers are situated in a distorted square pyrimidal geometry with one

MeOH molecule coordinated to the axial position. Figure 4.8b illustrates a stick diagram of the

XRD structure of 231a from a side view, depicting that the central phenoxy ring is puckered from the plane of the molecule. The packing diagram (Figure 4.8c-d) of the structure illustrates that the bimetallic Zn molecules form dimeric aggregates, with the adjacent molecules aligning in the opposite direction along the plane of the salphen moiety. X-ray diffraction data and selected bond lengths and angles are given in Table 4.1 and Table 4.2 in the experimental section of this chapter.

(a) (b)

Figure 4.8. Single crystal X-ray diffraction structure of model compound 231a (a) perpendicular (thermal ellipsoids are shown at the 50% probability level) and (b) a side on view of the bimetallic Zn metal complex. Solvent molecules are removed for clarity. Red = oxygen, blue nitrogen, purple zinc, gray = carbon.

146

the

Figure

aggregate

presence

4.8

(d) (C)

(colit.).

opposite

dimeric

The

directiofl5

aggregates.

packing

along

paerfl

the

(d),

plane

231a

adjacent

the

molecules.

bimetallic

solid

state

salphen

iluSat

moieties

(c),

shoWfl

showing

147 to 4.3.2 Electrochemical, EPR, and Magnetic Susceptibility Studies of the Model

Compounds

To elucidate whether cooperative electronic and magnetic communication exist within the conjugated model compounds, a series of electrochemical, electron paramagnetic resonance

(EPR), and magnetic susceptibility experiments were conducted. Bimetallic model compounds

229 and 231 contain two transition metal atoms that are embedded in a filly conjugated organic framework connected by a phenolic (O-Ar-O) linkage. Although the two bimetallic model compounds 229 and 231 are structurally very similar, the different geometry between the metal atoms may have significant influence on the electronic and magnetic properties of the two structural isomers. For example, using the simple spin alignment rule, one can expect an opposite spin alignment pattern between the metal atoms in 229 and 231 (Figure 4•9)26

229 231 R

Figure 4.9. An illustration of the different spin alignment patterns between model compounds

229 and 231 as predicted by a simple spin alignment model.

148 Cyclic voltammetry (CV) is a convenient method to determine the existence of electronic communication in multinuclear metal 27complexes. The presence of multiple redox waves in the voltammogram pertaining to metal atoms that are in identical chemical environments is indicative of electronic interactions between the metal atoms. For example, the two metal atoms in 229b are in identical chemical environments and, without any electronic interaction, the Cu atoms should appear as electrochemically equivalent. If electronic interactions exist between the metal atoms, however, oxidation or reduction of one of the metal atoms will modify the electrochemical environment of the second metal atom, such that they become electrochemically inequivalent and can be seen as two separate redox waves in the voltammogram. Cyclic voltammetry was performed on mononuclear Cu Schiff base complex 246b and bimetallic Cu model compounds 229b and 231b in 0.1 M N]PF!THF.[(n-Bu) Mononuclear copper Schiff base complex 246b did not undergo oxidation46in the applied potential range of-1.6 to 1.3 V and only an irreversible reduction occurred at E = -0.70 V, together with a return peak at E = -0.25

V (Figure 4.10). An increase of the scan rate (up to 1 VIs) resulted only in the amplification of the observed signal, but no sign of chemical reversibility was observed. Similarly, the voltammogram of bimetallic copper model compound 229b did not show any signals corresponding to the oxidation of the 2Cu atoms, and only a single irreversible reduction wave was observed at E = — 0.70 V. The irreversible reduction waves in the CV traces of 229b and

246b that the model compounds are not stable to oxidation or reduction, possibly due to decomposition of the copper complexes. Cyclic voltammetry was also performed on organic ligand 248b and bimetallic copper model compound 231b, but no significant redox activities were observed in the applied potential range of-1.5 — 1.5 V.

149 -1.5

-1.0 () -1,0 (b)

-0.5 -0.5 0.0 0,0 0.5 1,0 0.5 1.0 1,5

2.0

2.5 2.0 -1.5 .1.0 .0.5 0.0 0.5 1.0 1.6 -1.5 -10 -0.5 0.0 0.5 1.0 1.5 Potentiat (V) PoterUai (‘I)

Figure 4.10. Cyclic voltammograms of Cu model compounds recorded in 0.1 M N]PF[(n-Bu)

1 x 1 x 1 46 /THF solutions containing: (a) 0 M 246b; (b) 1.6 0 M 229b. Scan rate 0.5 V/s.

Electron paramagnetic resonance (EPR) analysis was performed on model compounds

246b, 229b, and 231b at 77.2K, and the corresponding spectra are illustrated in Figure 4.11. The

EPR spectra of model compounds 246b, 229b, and 231b closely resemble each other, with the signals centered at Ca. 3260 G. Broad features that are associated with hyperfine coupling extend to Ca. 2900 G, and the g-values () for model compounds 246b, 229b and 231b are calculated to be 2.057, 2.064, and 2.075, respectively. The striking similarity between the spectra of the mononuclear Schiff base complex 246b with the bimetallic model compounds

229b and 231b indicates that no significant electronic coupling exists between the paramagnetic copper metal centers at liquid nitrogen temperature (77.3 K). The spectrum for compound 231b, however, shows a decrease fine-structure at Ca. 31OOG,which may be indicating a very weak interaction.

150 3000 3200 3400 3600 3000 3200 3400 3800 Fiek (0) FeId (0)

3000 200 3400 3600 Fie’d(0)

Figure 4.11. EPR powder spectra of(a) 246b, (b) 229b and (c) 231b obtained at 77.3 K.

The magnetic properties (XM vs. T) of model compounds 246b, 229b, and 231b are illustrated in Figure 4.12. The general feature of the XM vs. T plot for Schiff base saiphen complex 231b and bimetallic Cu model compound 229b indicates that these compounds behave

x as simple paramagnets. The observed XMfor Schiff base complex 246b is 1.2 iO 3cm moF’ at

200 K, and increases slowly until Ca. 50K. At temperatures below Ca. 50K, the XM increases abruptly, which is indicative of weak antiferromagnetism within the sample. The magnetic data were fit to the Curie-Weiss Law:

151 Eqn.4.1 _L_(T—8) ZM C where XM is the molar magnetic susceptibility, C is the Curie constant, and 8 is the Curie temperature. The data fit well with the equation with C = 0.29(±0.01) and 0 -0.26(±0.01) K.

Bimetallic model compound 229b exhibited magnetic behavior similar to 246b with an approximately constant XM (3.7 x i0 3cm mol’ at 200 K) in the temperature range of 300 — 50

K. Below 50 K, XM increases sharply and the XMvs T curve was fitted to the Curie Weiss Law to obtain C = 0.72(±0.01) and 0 = -l.55(±O.05) K. The similarity in the magnetic susceptibility profile between Cu saiphen complex 246b and Cu model compound 229b indicates that despite the conjugated structure, no significant magnetic interactions are observed between the two Cu centers in 229b.

Figure 4.12c shows plots of xM versus T for model compound 231b. The XMvalue is 6.0 x cm at 200 K. Between the temperature ranges 300 — 150 K, the value is 3 1mol XM approximately constant, and then it increases to a local maximum at Ca. 13 K (XM = 4.1 x 102

3cm mol’). The XM of 231b decreases upon further cooling from 13 K, but increases again below Ca.4 K. The two-component magnetic profile of 231b is indicative of two different types of antiferromagnetic interactions between the Cu metal centers. It is hypothesized that an intramolecular interaction between the 2 Cu centers through the conjugated ligand gives rise to the first maximum that occurred at 13 K, while intermolecular interactions between Cu centers in adjacent molecules are responsible for the second increase in XM below 4 K. The magnetic data were analysed on the basis of the Bleaney-Bowers expression:

2Ng Eqn.4.2 XM— 2fi kT[3 + exp(—

152 Where g is the effective g-factor, 1B is the Bohr magneton, k is the Boltzmann constant, and 2J is the exchange coupling parameter. The best fit of the magnetic susceptibility data between 300 —

4 K yielded J = -13.1(±0.3) cm’ and g = 2.52(±0.01). The J value indicates that weak antiferromagnetic interactions are dominant in the model compound 231b, and this may explain the subtle difference in the EPR spectra of 229b and 231b. The second increase in XMbetween 4

— 2 K was not included in the analysis due to insufficient data points.

The antiferromagnetic coupling observed in 231b is very weak. In comparison, Robson type macrocycles such as 252 exhibit very strong anti-ferromagnetic interactions between the Cu

28 centers with reported values of J = - 408 1cm and g = 2.11 In the case of compound 8b, the metal-metal separation (calculated to be Ca. 8.174 A) appears to be too large to mediate substantial magnetic coupling.

252

153 0.14 0.25 (a) 0.12 0.20 0.10

0 0.08 0,15 E E

0.10

0.05

0 o 0.00 0 50 100 150 200 250 300 0 50 100 150 200 250 300 Temperature (K) Temperature (K)

0.05

0.04

0.03

0.02

0.01

0.00 0 50 100 150 200 250 300 Temperature (K)

Figure 4.12. Temperature dependence of magnetic susceptibility (diamonds) for (a) 246b, (b)

229b and (c) 231b. The solid lines correspond to the best fit curves obtained from the Curie-

Weiss Law in (a) and (b), and the Bleaney-Bowers Equation in (c).

§4.4 Synthesis and Characterization of Ladder Polymers

There are two different synthetic strategies to obtain the target ladder polymers 230,

Scheme 4.13. The first route involves reacting dialdehyde 227 with the appropriate diamine to first generate the organic polymer framework, followed by metallation to yield the metal containing polymers. Synthesis via this route is advantageous in that characterization of the polymeric organic framework may be carried out conveniently with techniques such as ‘H NMR

154 spectroscopy prior to metallation. In addition, if the organic polymer 253 can be synthesized on a large scale, a variety of metal-containing polymers containing different transition metals can then be conveniently synthesized by simple metallations. Attempts to synthesize organic polymer 253a with dialdehyde 227 and diamine 194 (dodecyloxy substituents) via this approach were frustrated with low degree of polymerization. Efforts to synthesize the organic polymer resulted in mixtures of short oligomers as illustrated by the gel permeation chromatogram (GPC) in Figure 4.13. The GPC chromatogram (THF, polystyrene standard) reveals the presence of tetramers (M = 4800), trimers (M = 3600), and dimers (M = 2400). Moreover, metallation of these oligomeric materials with 2Zn(OAc) and 2Ni(OAc) yielded insoluble products. The insolubility of these substances is not surprising, given the rigidity and conjugation of the polymers. The second synthetic strategy is to synthesize the polymer via a one pot reaction mixing dialdehyde 227, diamine 194, and 2Zn(OAc) Synthesis of ladder polymer 230 via this route is anticipated to yield higher molecular. weight materials since the chelation of the transition metal would prevent the reverse hydrolysis of the Schiff base moieties. However, the one pot synthesis of ladder polymer 230 using diamine 194 also yielded an insoluble black solid.

155 OH 0 RR

2HN 2NH 227 MX/

n n

230 253

230a R = 2-butyloctyloxy,M = Zn 230b R = 2-butyloctyloxy,M = Cu 2MX

n 230

230a R = 2-butyloctyloxy,M = Zn 230b R = 2-butyloctyloxy,M = Cu

Scheme 4.13. Two synthetic routes to prepare Schiff-base ladder polymer 230.

156 1S0.00

160.00

> 140.00 E x 120.00- 0 100.00 0 > 80.00 .1 C., 6000- ‘4-I a) 40.00

20,001

0,00m o.bo 5.00 10.00 15.00 20.00 25.00 30.00 36.00 40.00 45.00 Retention time (mins) Figure 4.13. GPC chromatogram of organic polymer 253a (R = )H12250C showing the presence of short oligomers.

1C 253a poorly soluble, oligomeric 254 Insoluble

255 Oily product 256 Insoluble

157 To improve the solubility of the resulting polymers, a variety of substituted diamines containing different solublizing groups were tested as components for our target ladder polymers. Soluble bimetallic model compounds were synthesized by incorporating diamine 243 substituted with racemic 2-ethyihexyloxy substituents, but polymerizations utilizing diamine 243 and dialdehyde 227 resulted in insoluble materials (254). The “dove-tail” substituents, racemic

2-decyltetradecyloxy chains, have been successfully incorporated into rigid conjugated molecules such as HBCs to improve the solubility of the otherwise insoluble 29materials. Incorporation of diamines 244, containing two dove-tail substituents, into the target ladder polymers (255) resulted in an oily product that cannot be purified adequately using precipitation.

There have been reports that incorporation of triptycenyl units into polymeric frameworks improves solubility by preventing aggregation due to the molecule’s 3-D 30structure. However, reaction of triptycenyl diamine 244 with dialdehyde 227 yielded only sparingly-soluble materials

(256), and GPC of the soluble fractions of the product indicated the presence of oligomeric materials with molecular weight (Mw)less than 1000 Da.

Following the unsuccessful attempts to produce soluble ladder polymers, diamine 210 containing two 2-butyloctyloxy chains was used to prepare target ladder polymer 230. The resulting polymers were soluble in THF, and the products can be easily purified through precipitation into hexanes, methanol, and acetone. The polymerizations of 230a have been carried out as a one pot reaction mixing dialdehyde 227, diamine 210, and 2Zn(OAc) under inert atmosphere )2(N in a sealed vessel using a variety of dry solvents such as THF, ,3CHC1 and toluene, but high molecular weights cannot be achieved (typically M = Ca. 3000 — 6000 Da. was observed). The procedure that yielded the highest molecular weight materials was to simply combine the reactants in a Schlenk tube and heat the reaction mixture overnight under a dynamic vacuum. It is postulated that the continuous removal of water under reduced pressure throughout

158 the polymerization process drives the equilibrium forward and towards high molecular weight.

The resulting black solid was then dissolved in THF and purified by multiple precipitations into hexane and acetone to yield a shiny black solid, Figure 4.14. However, the reproducibility of this procedure is poor as the molecular weights of the samples vary significantly even though great care was taken to perform the polymerizations using identical conditions. This fluctuation in the molecular weight of different samples is typical of polymers that are prepared via condensation polymerization, due to the high sensitivity of the reaction to accurate monomer ratio and the requirement of high monomer purity. The sample of Zn ladder polymer 230a with the highest molecular weight was determined by GPC to have molecular weight M = 15,000Da

(M 8,900 Da) (THF), corresponding to an average degree of polymerization of ca. 10.

However, due to the rigid nature of ladder polymer 230a, it is uncertain whether the molecular weights that are measured with the GPC are accurate, considering that the GPC is calibrated using polystyrene standards which have a flexible backbone. Unfortunately, due to the strong optical absorption of the polymers, common molecular weight measurement techniques that can be used to establish absolute molecular weights, such as light scattering measurements and

MALDI-TOF mass spectrometry, cannot provide any useful data.

159 Figure 4.14. Polymer 230a was obtained as a shiny black solid. The intensely colored material can be cast into solid shapes or films.

Polymer 230a was characterized by UV-visible spectroscopy, JR spectroscopy, ‘H NMR spectroscopy, thermogravimetric analysis, and elemental analysis. The ‘H NMR spectrum of polymer 230a (M=Zn) showed broad peaks corresponding to the alkoxy substituents and aromatic protons. This broadening is probably due to strong aggregation of the rigid polymers in solution. Although the signal broadening of the ‘H NMR spectrum hampered structure determination and molecular weight determination, the absence of signals from the starting dialdehyde 227 and diamine 210 is consistent with the polymeric structure of the materials. JR spectroscopy shows the presence of the expected VC=N stretching mode at 1604 cm’, confirming the formation of the imines within the polymer. The presence of a weak VC=O (1666 - 1673 cni’) stretch and a broad signal associated with VOH and v2 centered at ca. 3400 cm’ was also observed, which may be assigned to the expected end-groups for the target polymer. TGA indicates that the polymers is stable to 329 °C, retaining more than 95% of its original mass at this temperature. Differential Scanning Calorimetry (DSC) measurements in the temperature

160 range of -60 — 300 °C did not reveal any transitions that could be assigned to a glass transition, as expected due to the rigid nature of the ladder polymer. Preliminary conductivity measurements were also undertaken on a pressed pellet of polymer 230a using a 3 probe method, but the material was determined to be an insulator.

HexEtO OEtHex 0.4 0znc 246a 0.3 j HexEtO OEtHex A02

229a

0.1 HexEtO OEtHex

OctRuO OBuOct 0.0 1 1 300 400 500 600 700 800 t(ro

OctBO OBuOct

Figure 4.15. UV-vis spectra of model compounds 246a and 229a, and ladder polymer 230a.

The observed bathochromic shifts correspond to the extension in conjugation.

To ascertain the extent of conjugation in these materials, the UV-vis absorption spectra of the model compounds and the ladder polymer are compared. Figure 4.15 compares the absorption spectrum of Zn model compounds 246a and 229a, and Zn polymer 230a. The UV vis spectrum of model compound 246a exhibits a strong absorption at Ca. 400 nm with an absorption tail that extends to Ca. 520 nm, which resembles the absorption pattern of the many Zn saiphen complexes prepared in the MacLachlan 3laboratory. Bimetallic model compound ’ 161 229a has an absorption pattern that is similar to 246a in the 400 nm region, but the absorption extends to a slightly longer wavelength (ca. 540 nm), and a second broad absorption is observed at Ca.700 nm. Although it is unclear from where this second absorption originates, it is likely to be a result of a metal-to-ligand transition. The absorption spectrum of polymer 230a is significantly red-shifted in comparison to 246a and 229a, with an absorption maximum at Ca.

460 nm and a tail that extends beyond 800 nm. Clearly, the observed bathochromic shift in the absorption spectrum indicates an increase in the degree of conjugation from the monomer to the polymer.

The ability of the Zn ladder polymer to interact with coordinating ligands was evaluated in 2C1CH Similar to the interactions that are observed in bimetallic model compound 229a, solubility. changes were observed for polymer 230a in response to coordinating ligands.

Although polymer 230a has good solubility in THF, it is insoluble in other common organic solvents such as 2C1CH The addition of small amount (ca. 1%) of Lewis bases such as pyridine and acetoacetone. to the solution containing 230a renders the polymer soluble. Again, 2CICH this observation is attributed to the capability of organic pro-ligands to interact with the metal centers, breaking up aggregations of the polymers. UV-vis titration experiments were performed, but the absorption of polymer 230a did not show any significant changes in response to the addition of pyridine and acetoacetone in THF.

It was anticipated that a variety of ladder polymers 230 containing different transition metals could be synthesized employing the same method that was used in the synthesis of Zn polymer 230a, Unfortunately, efforts to synthesize Cu (230b) and VO (230c) containing polymers, using 2Cu(OAc) and 2VO(OAc) were unsuccessful and only resulted in short oligomers. The molecular weights (Mw) of these materials were determined to be 3,200 Da,

(230b) and 2,800 Da. (230c) using GPC. JR spectroscopy indicated the presence of the expected

162 VC=N stretching mode at 1601 cm’, confirming the formation of the imine within the polymer. The presence of VC=O (1667 cm’) and v2 (3400 )1cm stretching modes was also observed, corresponding to the presence of CO and 2NH end-groups. Figure 4.16 illustrates the absorption spectra of Cu and VO oligomers 230b and 230c. Similar to the observed absorption of Zn polymer 230a, the UV-vis spectra of polymers 230b and 230c consist of broad absorptions that extend to long wavelengths.

0.10

0.08

0.06 A

0.04

0.02

0.00 300 400 500 600 700 800 2(nm)

Figure 4.16. UV-vis spectra of ladder polymer 230b and 230c.

Target polymer 232 is a bent version of polymer 230 that may be synthesized using 4,6- diformyiresorcinol 233. Other members in the MacLachian research group have been successful in synthesizing macrocycle 257 employing dialdehyde 233 and dianiine 250 (R 6),H130C which can be viewed as cyclic analogues of our target 32polymer. It is anticipated that by altering the experimental conditions to favour polymerization, ladder polymers with a coil-like structure may be synthesized, Scheme 4.14. Using the procedure that was used to synthesize Zn

163 ladder polymer 230a, 2Zn(OAc) dialdehyde 233, and diamine 210 were combined in a Schienk tube and heated under, a dynamic vacuum. Unlike the polymerization of linear ladder polymer 230a that formed an intensely colored material with limited solubility in organic solvents, precipitation of 232a yielded an orange material that is soluble in a variety of organic solvents such as 2C1CH and THF. Estimation of the molecular weight of 232a with GPC, however, indicated that the materials are oligomeric (M = 2,300). Polymerization using the same procedure with 2Cu(OAc) to synthesize Cu polymer 232b yielded similarly low molecular weight materials (M 1,900). It is postulated that the cyclic structure of the target polymer, together with the rigidity of the polymer backbone and steric bulkiness of the solublizing groups, imposed severe restrictions for the polymerizations to achieve high molecular weights.

164 RR HO-OH + + 2Zn(OAc) 2HN 2NH 233

C%/’ neat reaction

232a R = 2-butyloctyl

257 R = 6CH13 Scheme 4.14. The synthesis of macrocycle 257 in 2C1CH By altering the experimental conditions, it was anticipated that polymer 232a can be synthesized..

§4.5 Conclusions

In summary, bimetallic model compounds representative of the target ladder polymers containing Zn and Cu have been prepared. Although the metal centers are connected through ligand systems that have extensively delocalized it-systems, no significant electronic interactions between the 2Cu centers were observed in 229b and 231b by CV or EPR experiments. SQUID

165 magnetometry experiments revealed that magnetic interactions between the Cu metal centers occur in 231b but not in 229b.

Zn model compound 229a is capable of interacting with coordinating ligands such as pyridine and acetoacetone, inducing solubility in 2C1CH for which the compounds are otherwise insoluble. Great efforts were devoted to developing viable synthetic strategies to obtain the target ladder polymers 230 and 232, but progress was hampered by the insolubility of the materials and difficulties in achieving high molecular weight materials. Zn ladder polymer230a was successfully prepared using a one pot synthesis and the highest molecular weight achieved was determined to be ca. 15,000 Da. (Mw) using GPC. UV-vis spectroscopy indicated a significant trend of increased delocalization from the model compounds to the ladder polymers, with the absorption of Zn ladder polymer 230a reaching beyond 800 nm.

§4.6 Experimental

4.6.1 General

Materials. Zinc(II) acetate, copper(II) acetate, 1,4-dimethoxybenzene 234, and salicylaldehyde were obtained from Aldrich. Deuterated solvents were obtained from

Cambridge Isotope Laboratories, Inc. Tetrahydrofuran was distilled from sodium/benzophenone under .2N Phenylenediamine derivatives 194 (R = ),H12250C 210 (R 2-butyloctyloxy), and 243 (R = 2-ethylhexyloxy) were prepared by literature methods.

Diamine 244 (R = 2-decyldodecyloxy) was prepared using a procedure analogous to the preparation of 243. Triptycene-type diamine 245 was synthesized by Jonathan Chong in the

MacLachlan research group.

166 Cyclic Voltammetry. Cyclic voltammetry measurements were performed with an Autolab

PGstatl2 potentiostat in dry THF using a sealed glass three-electrode electrochemical cell. A silver wire (reference electrode), platinum wire (counter electrode), and platinum (working electrode) were used. The platinum working electrode surface was cleaned with acetone and dried with 2N before use. Potentials are referenced to the decamethylferrocene/decamethylferrocenium couple used as an internal standard. The measured half-wave potential )(E112 for the decamethylferrocene/decamethylferrocenium internal standard is +0.66 V versus the reference electrode at a scan rate of 0.50 Vs’.

Electron Paramagnetic Resonance (EPR) analysis. EPR analysis was performed on a

Bruker Elexsys E 500 series continuous wave spectrometer. Samples were mixed with boron nitride and ground to a fine powder using a mortar and pestle. Low temperature analyses were carried out using a liquid 2N dewar.

Superconducting Quantum Interference Device (SQUID) Analysis. Magnetic measurements of model compounds 246b, 229b, and 231b were performed in the SQUID facility (Quantum Design MPMS XL) at Simon Fraser University. Samples were measured accurately into gelatin caps (purchased from Finlandia, Vancouver, size 4), and were fitted into a disposable clear straw. Samples were measured over the temperature range of 2 — 300

K using a magnetic field of 10 T.

167 4.6.2 Procedures

Synthesis of 2,5-bis(bromomethyl)-1,4-bis(methoxy)benzene 235. In a 100 mL round bottom

3OCH flask, 1,4-dimethoxybenzene 234 (10.0 g, 72.4 mmol) was combined with - Br Br acetic acid (100 mL), paraformaldehyde (4.50 g, 145 mmol), and HBr (28.8 3OCH mL, 36 wt % in solution). The mixture was heated to 70 °C with stirring for 2 h. Upon cooling, a thick white precipitate appeared, and the suspension was poured into water

(500 mL). The white precipitate was filtered and washed with water and air dried. Precipitation of the crude product in DCM with methanol afforded the desired product 235 (16.9 g, 52.4 mmol, 72%).’

Data for 235. 1H NMR (300 MHz, )3CDCI 6 6.86 (s, 2H, aromatic CR), 4.55 (s, 4H, 2CHBr), 3.84 (s, 6H, )3OCH ppm. EI-MS: m/z = 324.

Synthesis of 2,5-bis(acetylmethyl)-1,4-dimethoxybenzene 236. In a 1 L round bottom flask,

3OCH 235 (16.9 g, 52.4 mmol), sodium acetate (12.9 g, 157 mmol), and tetra-n QAc AcO — butylammonium bromide (2.6 g, 8.1 mmol) were combined with acetonitrile 3OCH (200 mL) and chloroform (100 mL). The reaction mixture was heated to reflux overnight and poured into water, followed by extractions with chloroform (3 x 100 mL) and washes with water (3 x 100 mL). Treatment of the organic extracts with drying agents )4(MgSO followed by rotary evaporation afforded a white product that was recrystallized from ethanol to afford 236 (11.1 g, 39.3 5mmol,75%).’

168 Data for 236. ‘H NMR (300 MHz, )3CDC1 ö 6.87 (s, 2H, aromatic Cl]), 5.15 (s, 4H, 2CHOAc), 3.86 (s, 6H, 3),OCH 2.12 (s, 6H, )3COOCH ppm. EI-MS: m/z = 282.

Synthesis of 2,5-Bis(hydroxymethyl)-1,4-dimethoxybenzene 237. Under an inert atmosphere 3OCH of ,2N a solution of 236 (6.8 g, 24.0 mmol) in dry THF (100 mL) was added OH HO ..— dropwise to a 500 mL Schlenk flask containing 4LiA1H (3.4 g, 89.6 mmol) 3OCH and dry THF (200 mL). The reaction mixture was stirred at room temperature for 2 h. Ethyl acetate (10 mL) was added to the reaction mixture dropwise to quench the excess 4LiA1H The reaction mixture was then poured into water (100 mL), extracted with chloroform .(3 x 100 mL), and washed with water (3 x 100 mL). Treatment of the organic extracts with drying agents 4(MgSO followed by rotary evaporation afforded 237 as a white solid (4.6 g, 23.3 ‘ ) mmol, 97%)

Data for 237. ‘H NMR (300 MHz, )3CDCI 6.85 (s, 2H, aromatic Cl]), 4.66 (s, 4H, 2CHOH), 3.84 (s, 6H, 3),OCH 2.21 (broad, 2H, 01]) ppm. EI-MS: m/z = 198.

Synthesis of 2,5-Dimethoxyterephthalaldehyde 238. To a 500 mL round bottom flask

3OCH containing methylene chloride (200 mL) was added 237 (1.4 g, 7.1 mmol) and CHO

OHC pyridinium chlorochromate (PCC) (6.0 g, 28.0 mmol). The reaction mixture 3OCH was stirred at room temperature for 2 h. The reaction mixture was then purified by flash chromatography with 2C1CH to afford a fluorescent yellow solution. Removal of solvent with rotary evaporation affords 238 as a fluorescent yellow solid (1.2 g, 5.5 mmol,

77%) 15

169 Data for 238. ‘H NMR (300 MHz, )3CDC1 ö 10.51 (s, 2H, CHO), 7.44 (s, 2H, aromatic CR), 4.02 (s, 6H, )3OCH ppm. EI-MS: m/z = 194.

Synthesis of 1,4-dihydroxy-2,5-diformylbenzene 227. Under an inert atmosphere of ,2N a 500 OH mL Schienk flask containing dry methylene chloride (100 mL) and 238 (3.0 g, 15.5 mmol), was added 3BBr (3.9 mL, 41.2 mmol). The reaction mixture was stirred at room temperature for 12 h, and then poured into ice water (100 mL). The reaction mixture was extracted with chloroform (3 x 100 mL), washed with water (3 x 100 mL), and the organic extract was treated with drying agents )4(MgSO followed by rotary evaporation. The orange solid was recrystallized from toluene to afford 227 as orange crystals (2.15 g, 12.9 mmol,

84%).’

Data for 227. ‘H NMR (300 MHz, )3CDC1 10.21 (s, 2H, OH), 9.94 (s, 2H, CHO), 7.22 (s, 2H, aromatic CR) ppm. EI-MS: m/z = 166.

Synthesis of 2,5-dibromo-1,4-dimethoxybenzene 239. In a 250 mL round bottom flask

3OCH containing 1,4-dimethoxybenzene 234 (20 g, 145 mmol) and 250 mL acetic acid, Br was added 2Br (50 g, 313 mmol) in 15 mL acetic acid dropwise using an addition 3OCH funnel. The reaction mixture was stirred at room temperature for 2 h. The white precipitate was collected, washed with water and methanol, and recrystallized in a 1:1 mixture of methylene chloride and ethanol to afford 239 as white crystals (32.8 g, 111 mmol, 76%).’

Data for 239. ‘H NMR (300 MHz, )3CDCI 7.09 (s, 2H, aromatic CM), 3.83 (s, 6H, )3OCH ppm. EI-MS: m/z = 294.

170 Synthesis of 2,5-Dimethoxyterephthalaldehyde 238 (Lithiation route, Scheme 4.7). Under

3OCH an inert atmosphere of 2N a 250 mL Schienk flask containing 239 (5.0 g, 16.9 CHO ,

OHC mmol) and dry ether (200 mL) was cooled in an icebath. n-BuLi (40 mL, 1.6 M 3OCH in hexane, 40.0 mmol) was added to the reaction mixture and stirred for 2 mm.

Dimethylformamide (3.3 mL, 42.3 mmol) was added, and the reaction mixture was stirred for an

additional 5 mm. The reaction mixture was poured into HC1(300 mL, 4 M) and stirred for 1 h.

The yellow precipitate was filtered and washed with water. Drying in vacuo afforded 238 as a yellow solid (2.36 g, 12.2 mmol, 72%).

Data for 238. ‘H NMR (300 MHz, )3CDCI 10.51 (s, 2H, CHO), 7.44 (s, 2H, aromatic CR), 4.02 (s, 6H, )3OCH ppm. EI-MS: m/z = 294.

Synthesis of 1,3-dibromo-4,6-dimethoxybenzene 241. In a 250 mL round bottom flask

Br Br containing 1,3-dimethoxybenzene 240 (4.7 g, 33.8 mmol) and acetic acid (100 HCO QH 3 3 mL), was added 2Br (10.8 g, 67.6 mmol) in acetic acid (10 mL) dropwise using an addition funnel. The reaction mixture was stirred at room temperature for 2 h, then poured in ice water, and the white precipitate collected and washed with water. Recrystallization from ethanol afforded 241 as white crystals (8.3 g, 27.9 mmol, 83%).18

Data for 241. ‘H NMR (300 MHz, )3CDC1 ö 7.63 (s, 1H, aromatic CR), 6.47 (s, 1H, aromatic CR), 3.88 (s, 6H, )3OCH ppm. EI-MS: m/z = 194.

171 Synthesis of 1,3—dimethoxy-4,6-diformylbenzene 242. Under an inert atmosphere of ,2N a 250 o mL Schlenk flask containing 241 (1.0 g, 3.6 mmol) and dry ether (50 mL) was 3HCO 3OCH cooled in an icebath. n-BuLi (4.4 mL, 1.6 M in hexane, 7.1 mmol) was added to the reaction mixture and stirred for 2 mm. Dimethylformamide (0.6 mL, 7.1 mmol) was added to the reaction mixture and stirred for an additional 5 mm. The reaction mixture was

poured into HC1(200 mL, 4 M) and stirred for 1 hour. The yellow precipitate was filtered and washed with water. Drying in vacuo afforded 242 as a white solid (0.45 g, 2.3 mmol, 64.1%).

Data for 242. ‘H NMR (400 MHz, 6Acetone-d ö 10.28 (s, 2H, CHO), 8.19 (s, 1H, aromatic CR), 6.93 (s, 1H, aromatic CR), 4.12 (s,) 6H, )3OCH ppm. EI-MS: m/z = 294

Synthesis of 1,3—dihydroxy-4,6-diformylbenzene 233. Under an inert atmosphere of ,2N 3BBr rj (3.9 mL, 41.2 mmol) was added to a 500 mL Schienk flask under 2N atmosphere

I-JO OH containing dry methylene chloride (100 mL) and 242 (3.0 g, 15.5 mmol). The reaction mixture was stirred at room temperature for 12 h, and then poured into ice water (100 mL). The reaction mixture was extracted with chloroform (3 x 100 mL), washed with water (3 x 100 mL), and the organic extract treated with a drying agent )4(MgSO followed by rotary evaporation. The white solid was crystallized from toluene to afford 233 aswhite crystals (2.15 g, 12.9 mmol, 84%).

Data for 233. ‘H NMR (300 MHz, )3CDCI ö 11.76 (s, 2H, OR), 9.78 (s, 2H, CHO), 7.81 (s, 1H, aromatic CR), 6.45 (s, 1H, aromatic CR) ppm. EI-MS: m/z = 166.

172 Synthesis of Schiff base complex 246a (R = 2-ethyihexyloxy). Under an inert atmosphere of R/\ R ,2N diamine 243 (0.5 g, 1.37 mmol), salicylaldehyde (0.29 mL, 2.74 — mmol), and 2Zn(OAc) (0.30 g, 1.37 mmol) were added to a 100 mL Schienk flask containing dry THF (10 mL). The yellow reaction mixture was heated to reflux for 12 h. Precipitation with methanol afforded Schiff base complex 246a as a yellow solid (0.80 g, 1.29 mmol, 94%).

Data for 246a. C13 NMR (100.6 MHz, 6DMSO-d 8 171.7, 160.6, 150.0, 135.8, 133.6, 132.7, 122.9, 119.7, 112.7, 100.6, 70.8, 30.2,) 28.6, 23.5, 22.6, 13.9, 11.2; 1H NMR (400 MHz, 6DMSO-d 8 8.34, (s, 2H, CHN), 7.00 (m, 6H, aromatic CR), 6.57 (d, J9.2 Hz, 2H, )aromatic Cl]), 6.45 (t, J= 8.5 Hz, 2H, aromatic Cl]), 4.01 (d, J5.5 Hz, 4H, 2),OCH 1.75 (b, 4H, 2),CH 1.2-1.5 (m, 14H, 2),CH 0.86 (m, 12H, )3CH ppm; UV-vis (THF): 2max (log ) 300 (4.40), 356 (4.29), 411(4.60) nm (L 1mol 1).cm MALDI-TOF MS: m/z = 635.1. JR (KBr): v = 2958, 2925, 2865, 1614, 1505, 1465, 1384, 1330, 1279, 1259, 1204, 1160, 1115, 1032, 930, 898, 843, 672, 639, 617 .1cm Mp. = 287-291 °C. Anal. Calc’d for 2O246aH 24HNO(C3646Zn): C, 66.10; H, 7.40, N, 4.28. Found: C, 66.05; H, 7.36; N, 4.49, Synthesis of Schiff base complex 246b (R = 2-ethylhexyloxy). Under an inert atmosphere of R/\ R ,2N diamine 243 (0.5 g, 1.37 mmol), salicylaldehyde (0.29 mL, 2.74 — mmol), and Cu(OAc) (0.25 g, 1.37 mmol) were added to a 100 mL —N N— 2 Q,CU\Q Schlenk flask containing dry THF (10 mL). The brown reaction mixture was heated to reflux for 12 h. Precipitation with methanol afforded Schiff base complex 246b as brown crystals (0.80 g, 1.26 mmol, 92%).

173 Data for 246b. UV-vis (THF) ?max (log ) = 303 (4.42), 364 (4.37), 416 (4.57) nm (L mol’ cm’), MALDI-TOF MS: m/z = 633.4. JR (KBr): v 2958, 2924, 2872, 1608, 1524, 1463 1374, 1332, 1274, 1244, 1185, 1149, 1112, 1028, 954, 916, 846, 825, 814, 754, 736 .1cm Mp. = 204-207 °C. Anal. Calc’d for CHNO3646Cu C, 68.17; H, 7.31; N, 4.42. Found: C, 67.61; H, 7.29; N, 4.67. 24

Synthesis of Condensation Product 247b (R = 2-ethyihexyloxy). Under an inert atmosphere R R of ,2N diamine 243 (1.0 g, 2.74 mmol) and dialdehyde 227 (0.21 g, \ / 2HN 1.25 mmol) were added to a 100 mL Schlenk flask containing dry HooH THF (20 mL). The red reaction mixture was heated to reflux for 12

h, and the solvent was removed using rotary evaporation.

Recrystallization of the red solid from hexane yielded 247b as red R — R crystals (0.75 g, 0.88 mmol, 70%).

Data for 247b. C13 NMR (75.5 MHz, )2C1CD 6 157.7, 154.0, 153.0, 14.2, 138.5, 127.2, 123.9, 119.5, 106.4, 103.1, 74.7, 72.8, 41.3, 41.0, 32.0, 31.9, 30.6, 30.5, 25.3, 24.5, 15.29, 15.28, 12.4, 12.3 ppm; ‘H NMR (300 MHz, )2C1CD 6 12.53 (s, 2H, OR), 8.56, (s, 2H, CH=N), 7.03 (s, 2H, aromatic Cl]), 6.83 (s, 2H, aromatic CR), 6.37 (s, 2H, aromatic CR), 6.75 (s, 2H, aromatic CR), 3.92 (broad, 4H, 2),NH 3.91 (d, J=5.6 Hz, 811, 2),OCH 1.72 (m, 4H, 2),CH 1.3-1.5 (m, 32H, 2),CH 0.94 (m, 24H, )3CH ppm. MALDI-TOF MS: m/z = 857.7. JR (KBr): v = 3482, 3350, 2954, 2926, 2870, 2858, 1619, 1602, 1504, 1461, 1434, 1401, 1378, 1332, 1277, 1231, 1254, 1231, 1199, 1137, 1013, 971, 950, 903, 856, 833, 816, 773, 727, 620 ,1cm Mp. = 145-148 °C. Anal. Calc’d for :406CHN5282 C, 72.69; H, 9.62; N, 6.52. Found: C, 72.69; H, 9.64; N, 6.48. 174 Synthesis of Pro-ligand 248b (R = 2-ethyihexyloxy). To a 100 mL round bottom flask

R R containing salicylaldehyde (10 mL, 93.8 mmol) was added 0 247b (0.20 g, 0.23 mmol). The red reaction mixture was DH HooH Ho9 heated at 12 h at 70 °C. Precipitation with methanol yielded N/\ N a red solid that was collected via filtration and washed with methanol to remove excess salicylaldehyde. Reprecipitation R — R of the red solid in THF and methanol afforded 248b as a red solid (0.24 g, 0.22 mmol, 96%).

Data for 248b. ‘3C NMR (75.5 MHz, )2C1CD , 162.8, 161.6, 161.0, 153.4, 150.6, 150.1, 136.5, 135.3, 132.8, 123.2, 120.1, 119.5, 119.4, 117.7, 105.0, 104.4, 72.5, 40.2, 31.2, 29.7, 24.5, 23.7, 14.5, 11.6 ppm; ‘H NMR (300 MHz, )2CICD 13.19 (s, 2H, OR), 12.54 (s, 2H, OR), 8.66 (s, 2H, CH—N), 8.62 (s, 2H, CH=N), 7.47 (d, J=1.35 Hz, 2H, aromatic CR), 7.42 (t, J=7.2 Hz,

2H, aromatic CR), 7.02 (s, 2H, aromatic CR), 6.99 (d, J=6 Hz, 2H, aromatic CR), 6.94 (t, J9.0

Hz, 2H, aromatic CR), 6.88 (s, 2H, aromatic CR), 6.83 (s, 2H, aromatic CR), 3.97 (d, J=4.7 Hz, 8H, 2),OCH 1.79 (m, 4H, CR), 1.3-1.5 (m, 32H, 2),CH 0.94 (m, 24H, )3CH ppm. UV-vis (THF) 2max (log 6) = 376 (4.63), 461 (4.51) nm (L mo[’ cm’). MALDI-TOF MS: m/z = 1091.0

[M+Naj. IR (KBr): v = 2958, 2925, 2865, 1614, 1505, 1465, 1384, 1330, 1279, 1259, 1204, 1160, 1115, 1032, 930, 843, 756 .1cm Mp. = 234-238 °C. Anal. Calc’d for 408CHN6690 C, 74.26; H, 8.50; N, 5.25. Found: C, 74.11; H, 8.69;N, 5.22. :

175 Synthesis of Model Compound 229a (R = 2-ethyihexyloxy). Under an inert atmosphere of ,2N pro-ligand 253 (0.10 g, 0.09 mmol) and 2Zn(OAc) (0.07 g, 0.26 mmol) were added to a 100 mL Schienk flask

containing dry TI-IF (10 mL). The green reaction mixture

was heated to reflux for 2 h. Precipitation with methanol

afforded 229a as a dark green solid (0.07 g, 0.06 mmol,

69%).

Data for 229a. 1H NMR (300 MHz, 6DMSO-d 6 8.92, (s, 2H, CH=N), 8.88, (s, 2H, CHN), 7.45 (s, 2H, aromatic Cl]), 7.42 (s, 2H,) aromatic CM),7.39 (d, J=9.9 Hz, 2H, aromatic CM),7.17

(t, J8.5 Hz, 2H, aromatic CR), 6.85 (s, 2H, aromatic CM), 6.64 (d, J = 8.7 Hz, 2H, aromatic CR), 6.47 (t, J = 7.3 Hz, 2H, aromatic Cl]), 4.00 (d, J=5.5 Hz, 8H, 2),OCH 1.72 (m, 4H, CR), 1.2-1.6 (m, 32H, 2),CH 0.89 (m, 24H, )3CH ppm; UV-vis 2):CI(CH ?max (log ) = 319 (4.58), 407 (4.80), 667 (4.02) nm (L 1mo1 cmj. MALDI-TOF MS: m/z = 1194.4, 2388.6 (dimer 2(M+H)). JR (KBr): v = 2930, 2844, 1697, 1607, 1514, 1466, 1354, 1264, 1214, 1177, 1035, 937, 908, 839, 754, 740 cm’. Mp. > 320 °C. Anal. Calc’d for 2O229a4H HNO(C6686Zn C, 62.60; H, N, C, 62.75; H, ): 7.48; 4.42. Found: 7.42; N, 4.43. 482

Synthesis of Model Compound 229b (R = 2-ethyihexyloxy). Under an inert atmosphere of ,2N pro-ligand 253 (0.10 g, 0.09 mmol) and 2Cu(OAc) (0.04 g, 0.23 mmol) were added to a 100 mL Schlenk flask

containing dry THF (10 mL). The brown reaction mixture

was heated to reflux for 2 h. Precipitation with acetonitrile

afforded 229b as a black solid (0.08 g, 0.07 mmol, 76%).

176 Data for 229b. UV-vis 2):C1(CH Xmax (log e) = 329 (4.80), 418 (5.08), 736 (4.27) nm (L moF’ cm’). MALDI-TOF MS: m/z = 1191.8. JR (KBr): v 2958, 2924, 2859, 1655, 1609, 1583,

1509, 1459, 1358, 1325, 1271, 1246, 1215, 1186, 1152, 1115, 1030, 958, 945, 911, 893, 854, 832, 788, 754, 739, 701 .1cm Mp. = 312-314 °C. Anal. Calc’d for 2O229bH HNO(C6688Cu C, 65.59; H, 7.34; N, 4.64. Found: C, 65.60; H, 7.52; N, 4.94. 492):

Synthesis of Condensation Product 251 (R = 6).H130C Under an inert atmosphere of ,2N 4,5- R R diamino-1,2-dihexyloxybenzene 250 (0.37 g, 1.2 mmol) and R. R N dialdehyde 233 (0.10 g, 0.60 mmol) were added to a 100 mL 2NH 2NH HO OH Schienk flask containing dry ethanol (40 mL). The red reaction mixture was stirred at room temperature for 48 h. The red precipitate was collected and washed with methanol (0.43 g, 0.57 mmol, 94%).

Data for 251 ‘3C NMR (75.5 MHz, )3CDCI 166.7, 158.9, 151.8, 143.7, 137.8, 137.4, 127.8, 115.0, 107.8, 105.5, 103.8, 72.6, 70.6, 33.1, 33.0, 31.0, 30.6, 27.1, 24.0, 15.4 ppm; ‘H NMR (300 MHz, )3CDC1 ö 14.01 (s, 2H, Of]), 8.43 (s, 2H, CH=N), 7.36 (s, 1H, aromatic Cl]), 6.71 (s, 2H, aromatic Cl]), 6.51 (s, 1H, aromatic Cl]), 6.32 (s, 211,aromatic Cl]), 3.94 (t, J5.9 Hz, 8H, 2),OCH 3.86 (broad, 4H, 2),NH 1.76 (m, 8H, 2),CH 1.42 (m, 8H, 2),CH 1.33 (m, 16H, 2),CH 0.89 (t, 12H, )3CH ppm. ESI-MS: m/z = 769.6 [M+Naj. JR (KBr): v 3394, 3292, 3168, 2955, 2928, 2856, 1634, 1576, 1522, 1466, 1429, 1388, 1363, 1332, 1289, 1261, 1241, 1229, 1207, 1178, 1165, 1137, 1069, 1045, 1014, 997, 951, 930, 906, 872, 838, 787, 758, 721 .1cm Mp. = 120-121 °C. Anal. Calc’d for 406CHN4466 C, 70.74; H, 8.91; N, 7.50. Found: C, 70.61; H, 8.72; N, 7.31. :

177 Synthesis of Model Compound 231a (R = 6).H130C Under an inert atmosphere of ,2N 254 (0.20 g, 0.27 mmol), salicylaldehyde (0.06 mL, 0.59 mmol), and R R Zn(OAc) (0.15 g, 0.67 mmol) were added to a 100 mL Schienk I - _zn—N. 2 0 flask containing dry THF (50 mL). The orange reaction mixture c:5 was heated to reflux for 12 h. Precipitation with methanol afforded 231a as an orange solid (0.23 g, 0.20 mmol, 72%).

Data for 231a. ‘3C NMR (100.6 MHz, 6DMSO-d ö 176.6, 172.3, 160.8, 159.1, 149,8, 149.5, 148.4, 136.3, 134.1, 134.0, 132.8, 123.5,) 120.5, 115.0, 113.3, 110.3, 101.9, 100.8, 69.5, 69.1, 31.6, 29.4, 25.9, 22.7, 14.5 ppm; ‘H NMR (400 MHz, 6DMSO-d 8,93, (s, 2H, CHN), 8.77, (s, 2H, CHN), 7.66 (s, 2H, aromatic CR’),7.45 (s, 2H,) aromatic Cl]), 7.40 (d, J7.2 Hz, 2H, aromatic CR’),7.37 (s, 2H, aromatic CR), 6.85 (s, 2H, aromatic Cl]’), 7.20 (t, J 7.2 Hz, 2H, aromatic CM), 6.71 (d, J = 8.4 Hz, 2H, aromatic Cl]’),6.50 (t, J=7.2 Hz, 2H, aromatic CR’),4.10 (broad, 4H, 2),OCH 1.76 (m, 8H, 2),CH 1.5-1.3 (m, 28H, 2),Cl]’ 0.90 (m, 12H, )3CH ppm; UV-vis 2):C1(CH 2max(log 6) = 303 (4.64), 361 (4.73), 441 (4.82), 477 (4.78), 501 (4.75) nm (L mol’ cmj. MALDI-TOF MS: m/z = 1082.1, 2164.1 (dimer 2(M+H)). JR (KBr): v = 2927, 2856, 1608, 1568, 1506, 1462, 1442, 1359, 1268, 1221, 1173, 1149, 1115, 1018, 953, 909, 849, 826, 754, 739 cm* Mp. > 320 °C. Anal. Calc’d for 2O231aH HNO(C5872Zn C, 63.33; H, 6.60; N, 5.09. Found: C, 63.75; H, 6.44; N, 5.37. 492):

178 Synthesis of Model Compound 231b (R = 6).H130C Under an inert atmosphere of ,2N 254 (0.20 g, 0.27 mmol), salicylaldehyde (0.06 mL, 0.59 mmol), and R 2Cu(OAc) (0.13 g, 0.67 mmol) were added to a 100 mE Schienk flask containing dry THF (50 mL) The brown reaction mixture

was heated to reflux for 2 h. Precipitation with acetonitrile afforded 231b as a brown solid (0.21 g, 0.19 mmol, 70%).

Data for 231b. UV-vis 2):C1(CH 2max(log ) =363 (4.78), 450 (4.74), 481 (4.73) nm (L mo[’ cm’). MALDI-TOF: m/z = 1191.8. JR (KBr): v = 2931, 2858, 1615, 1504, 1462, 1443, 1385, 1265, 1171, 1114, 1016, 949, 907, 840, 804, 752 .1cm Mp. = 252-256 °C. Anal. Calc’d for 2O231b2H 42):HNO(C587410Cu C, 62.52; H, 6.69; N, 5.03. Found: C, 62.90; H, 6.49; N, 5.33. Synthesis of Polymer 230a (R = 2-butyloctyl). In a glovebox under an inert atmosphere of ,2N dialdehyde 227 (0.040 g, 0.24 mmol), diamine 210 (0.115 g, 0.24 mmol), and 2Zn(OAc) (0.053 g, 0.24 mmol) were measured accurately into a 10 mL Schlenk tube. The reaction

, mixture was heated at 75 °C under reduced pressure (ca. 200

mtorr) for 48 h with stirring. The resulting black solid was dissolved in THF, filtered, and precipitated into acetone (400 mL). Repeated precipitations (2 x acetone, 2 x hexane) yielded polymer 230a as a black solid (0.116 g, 0.17 mmol, 72%).

Data for 230a. 1H NMR (400MHz, ,3CDC1 1% 5pyridine-d 8.8 — 5.9 (broad, m), 4.5 — 3.0 (broad), 2.0 — 0.0 (broad, m) ppm; UV-vis )2C1(CH ) 2m (log E) = 348 (4.98), 404 (5.09) nm (L 1mol cm’). JR (KBr): v = 2920, 2851, 1673, 1666, 1604, 1581, 1553, 1511, 1504, 1462, 1454,

179 1348, 1315, 1265, 1214, 1163, 1011, 842, 800, 721 .1cm GPC (THF): M = 15,000 (M/M = 1.69). Anal. Calc’d for CHNO3857Zn: C, 67.99; H, 8.56; N, 4.17. Found: C, 64.45; H, 8.67; N, 4.35. 24

Synthesis of Polymer 230b (R = 2-butyloctyl). In a glovebox under an inert atmosphere of ,2N R dialdehyde 227 (0.062 g, 0.37 mmol), diamine 210 (0.178 g, 0.37 mmol), and 2Cu(OAc) (0.068 g, 0.37 mmol) were measured accurately into a 10 mL Schlenk tube. The reaction

n mixture was heated at 75 °C under reduced pressure (ca. 200

Data for 230b. UV-vis )2C1(CH 2max (log E) = 284 (4.78), 434 (4.36) nm (L 1mof 1).cm JR (KBr): v= 2954, 2925, 2855, 1667, 1601, 1573, 1493, 1456, 1354, 1320, 1269, 1241, 1216, 1179, 1148, 1009, 852, 839, 799, 724, 601 .1cm GPC (THF): M = 3,200 (M/M = 1.21). Anal. Calc’d for 24CHNO3857Cu: C, 68.18; H, 8.58; N, 4.18. Found: C, 64.23; H, 9.01; N, 4.22. Synthesis of Polymer 232a (R = 2-butyloctyl). In a glovebox under an inert atmosphere of ,2N dialdehyde 227 (0.065 g, 0.39 mmol), diamine 210 (0.187 g, 0.39 mmol), and 2Zn(OAc) (0.086 g, 0.39 mmol) were measured accurately into a 10 mL Schienk tube. The reaction

mixture was heated at 75 °C under reduced pressure (ca. 200 mtorr) for 48 h with stirring. The resulting black solid was dissolved in THF, filtered, and

180 precipitated into methanol (400 mL). Repeated precipitations (2 x methanol, 2 x hexane) yielded polymer 232a as a black solid (0.193 g, 0.29 mmol, 73%).

111 Data for 232a. NMR (400 MHz, )3CDC1 ö 9.1 — 6.3 (broad, m), 4.3 — 3.8 (broad), 2.0 — 0.5 (broad, m) ppm; UV-vis )2C1(CH ?max(log ) = 325 (4.86), 459 (4.67) nm (L mol cm’). JR (KBr): v 2953, 2922, 2854, 1602, 1556, 1504, 1463, 1463, 1434, 1390, 1356, 1258, 1226, 1167, 1013, 961, 934, 86, 740, 724, 685 .1cm GPC (THF): M = 2,300 (M/M = 1.22). Anal. Calc’d for 24CHNO3857Zn: C, 67.99; H, 8.56; N, 4.17. Found: C, 65.32; H, 8.74; N, 4.43. Synthesis of Polymer 232b (R = 2-butyloctyl). In a glovebox under an inert atmosphere of ,2N R R dialdehyde 227 (0.060 g, 0.36 mmol), diamine 210 (0.172 g, R R 0.36 mmol), and 2Cu(OAc) (0.066 g, 0.36 mmol) were \ measured accurately into a 10 mL Schienk tube. The reaction

I mixture was heated at 75 °C under reduced pressure (ca. 200 n mtorr) for 48 hours with stirring. The resulting black solid was dissolved in THF, filtered, and precipitated into methanol (400 mL). Repeated precipitations (2 x methanol, 2 x hexane) yielded polymer 232b as a black solid (0.176 g, 0.26 mmol, 73%).

Data for 232b. UV-vis )2C1(CH 2m (log ) = 348 (4.83), 436 (4.96) nm (L 1mol 1).cm IR (KBr): v 1952, 2921, 2853, 1641, 1598, 1538, 1504, 1463, 1455, 1393, 1349, 1262, 1193,

1166, 1009, 948, 846, 825, 788, 724, 690 cm* GPC (THF): M = 1,900 (M/M 1.15). Anal. Calc’d for 24CHNO3557Cu C, 68.18; H, 8.58; N, 4.18. Found: C, 64.93; H, 8.34; N, 3.99.

181 Synthesis of Polymer 253 (R = ).H12250C In a glovebox under an inert atmosphere of ,2N dialdehyde 227 (0.125 g, 0.75 mmol) and diamine 194

(0.359 g, 0.75 mmol) were measured accurately into a 10

mL Schlenk tube. Dry THF (10 mL) was added to the

n reaction vessel and the reaction mixture was heated at 75 °C

for 16 h. The resulting red solution was filtered and precipitated into hexanes (400 mL) twice to afford 253 as a red solid (0.452 g, 0.72 mmol, 96%).

Data for 253. ‘H NMR (400MHz, )3CDCI 13.2 (b, OR), 12.5 (b, OH), 8.7-8.5 (b, CHN), 7.5 -6.5 (b, aromatic CR), 4.0-3.7 (b, 2),OCH 2.0-0.5 (b, 2CH and )3CH ppm; UV-vis )2C1(CH Xmax (log ) = 288 (4.54), 466 (4.32) nm (L mor’cm’). IR (KBr): v = 2954, 2917, 2848, 1662, 1607,

1505, 1466, 1433, 1391, 1334, 1313, 1259, 1238, 1206, 1148, 1070, 1012, 997, 838, 826, 794,

721, 665, 640 cm’. GPC (THF): M = 5100 (M/M 1.01), M = 3800 (M/M = 1.00),M 2600 (M/M 1.02). Anal. Calc’d for 204CHN3859 C, 75.08; H, 9.78; N, 4.61. Found: C, 71.01; H, 9.88; N, 4.38. :

Synthesis of Polymer 254. In a glovebox under an inert atmosphere of ,2N dialdehyde 227 (0.048 g, 0.29 mmol), diamine 243 (0.105 g, 0.29 mmol), and 2Zn(OAc) (0.063 g, 0.29 mmol) were measured accurately into a 10 mL Schlenk tube. The reaction mixture was heated

n at 75 °C under reduced pressure (Ca. 200 mtorr) for 48 hours

with stirring. The resulting black solid was washed with THF and hexane to yield polymer 254 as an insoluble black solid (0.128 g, 0.23 mmol, 80%).

182 Data for 254. The product was insoluble in common organic solvents such as THF, ,3CHCI and DMSO. JR (KBr): v 2955, 2924, 2857, 1661, 1603, 1574, 1505, 1457, 1412, 1351, 1308,

1261, 1211, 1151, 1118, 1082, 1010, 961, 928, 836, 799, 769, 726 cm’. Anal. Calc’d for 24CHNO3041Zn: C, 64.45; H, 7.39; N, 5.01. Found: C, 59.82; H, 7.36; N, 4.52.

Synthesis of Polymer 255 (R 2-decyldodecyloxy). In a glovebox under an inert atmosphere of ,2N dialdehyde 227 (0.011 g, 0.066 mmol), diamine 244 (0,054 g, 0.066 mmol), and 2Zn(OAc) (0.015 g, 0.066 mmol) were measured accurately into a 10 mL Schienk tube. The

reaction mixture was heated at 75 °C under reduced pressure

(ca. 200 mtorr) for 48 h with stirring. The resulting black solid was dissolved in THF, filtered, and precipitated into methanol (400 mL). Repeated precipitations (2 x methanol, 2 x hexane) yielded polymer 255 as a black solid (0.058 g, 0.056 mmol, 85%).

Data for 255. ‘H NMR (400MHz, ,3CDC1 1% 5pyridine-d ö 8.8 — 5.9 (b, aromatic Cu), 4.5 — 3.0 (b, OCH 2.3 — 0.0 (b, CH and CH ppm;)UV-vis (CH 2max (log = 350 (5.23), 411 2), 2 )3 )2C1 ) (5.33) nm (L moF’cm’). IR(KBr): v=2956, 2924, 2858, 1660, 1603, 1571, 1508, 1459, 1411,

1378, 1352, 1261, 1210, 1154, 1083, 1010, 928, 836, 800, 770, 726, 664 cm’. GPC (THF): M = 5900 (M/M = 1.06). Anal. Calc’d for CHNO5897Zn: C, 73.19; H, 10.27; N, 2.94. Found: C, 70.11; H, l0.3l;N, 2.85. 24

183 Synthesis of Polymer 256. In a glovebox under an inert atmosphere of ,2N dialdehyde 227 (0.042 g, 0.25 mmol), diamine 245 (0.072 g, 0.25 mmol), and 2Zn(OAc) (0.056 g, 0.25 mmol) were measured accurately into a 10 mL Schienk tube. The reaction mixture was heated

at 75 °C under reduced pressure (ca. 200 mtorr) for 48 h with

n stirring. The resulting brown solid was washed with THF and

hexane to yield polymer 255 as a brown solid (0.115 g, 0.24

mmol, 95.6 %).

Data for 256. The product is marginally soluble in common organic solvents such as THF,

CHC1andDMSO. IR(KBr): v 1738, 1663, 1604, 1587, 1458, 1333, 1309, 1217, 1201, 1186, 31151, 1060, 1022, 972, 887, 851, 840, 808, 791, 763, 740, 695, 627 .1cm GPC (THF): M = 2100 (M/M = 1.31). Anal. Calc’d for CHNO2817Zn: C, 65.83; H, 3.35; N, 5.48. Found: C, 62.31; H, 3.54; N, 5.67. 24

4.6.3 X-Ray Diffraction Studies

X-Ray Diffraction Study of 231a. Crystals of 231a suitable for X-ray diffraction were grown by slow diffusion of MeOH into a DMSO solution containing 231a. A red needle of CHNO5870Zn having approximate dimensions of 1.00 x 0.05 x 0.05 mm was mounted on a glass482 fiber. All measurements were made on a Bruker Apex X8 diffractometer with graphite monochromated Mo-Ku radiation.

184 17 If .. O61 i4 1-Y‘16 2O .-1O 6 £29 4 31

Figure 4.17. Single crystal X-ray diffraction structure of model compound 231a (thermal ellipsoids are shown at the 50% probability level). Solvent molecules are removed for clarity.

Red = oxygen, blue nitrogen, purple = zinc, gray carbon.

Table 4.1 X-ray diffraction data for compound 231a.

A. Crystal data Empirical Formula 401CHN6179 12Zn Formula Weight 1175.02

Crystal Color, Habit red, needle

Crystal Dimensions 1.00 x 0.05 x 0.05 mm

Crystal System Triclinic

Lattice Type Primitive 185 Lattice Parameters a = 10.3632(17) A

b = 17.347(3) A

c = 17.738(3) A

c= 113.269(5)°

91.305(6)0 13

y= 91.650(6)0

V = 2926.3(8) 3A

Space Group P-i (#2)

Z value 2

Dcalc 1.334 3g/cm F000 1242 i(MoKct) 8.82 1cm

B. Intensity Measurements

Diffractometer Bruker Apex X8

Radiation MoKc4(X = 0.71069 A)

graphite monochromated

Data Images 2262 exposures @30.0 seconds

Detector Position 35.91 mm

20 52.54°

No. of Reflections Measured Total: 29988 Unique: 8919 1(R 0.0960) Corrections Lorentz-polarization

Absorption! scaling/decay

186 (corr. Factors : 0.668 — 0.957)

C. Structure Solution and Refinement

Structure Solution Direct Methods (S1R92)

Refinement Full-matrix least-squares Function Minimized w (Fo - )2Fe Least Squares Weights w= 12I( 2(Fo )+(0.1163P)+0.8003P

where P 2 + 2,0)(Max(Fo 2)/32Fc Anomalous Dispersion All non-hydrogen atoms

No. Observations (I>0.00(I)) 8919

No. Variables 723

Reflection/Parameter Ratio 12.34 Residuals (refined on ,2F all data): RI; wR2 0.1598; 0.2057 Goodness of Fit Indicator 1.052

No. Observations (1>2.OOa(I)) 5245

Residuals (refined on F): Ri; wR2 0.0722; 0.1627

Max Shift/Error in Final Cycle 0.04 Maximum peak in Final Diff. Map 0.815 3e-/A Minimum peak in Final Diff. Map -0.703 3e-/A

187 Table 4.2 Selected bond lengths(A) and angles0 for 231a.

Zn(1)-O(1) 1.980(4) O(lO)-C(060) 1.421(8) C(15)-C(14) 1.424(8)

Zn(I)-O(2) 1.993(4) N(l)-C(7) 1269(7) C(15)-CQ6) 1.440(8)

Zn(1)-N(2) 2.064(4) N(1)-C(8) 1.418(8) C(23)-C(24) 1.364(8)

Zn(1)-O(9) 2.073(4) C(12)eC(11) 1.372(8) C(9)-C(10) 1.352(9)

Zn(1)-N(1) 2.078(5) C(12)-C(13) 1.386(8) C(9)-C(8) 1.394(8)

Zn(2)-O(4) 1.974(4) N(4)-C(28) 1270(7) C(6)-C(4) 1.401(8)

Zn(2)-O(3) 1.986(4) N(4)-C(27) 1.414(7) C(6)-C(5) 1.419(9)

Za(2)-N(3) 2.056(5) C(18)-C(16) 1.391(8) C(6)-C(7) 1.421(9)

Zn(2)-O(10) 2.072(4) C(l8)-C(20) 1.399(8) C(8)-C(13) 1.393(8)

Zn(2)-N(4) 2.093(5) C(17)-C(15) 1.379(8) C(3)-C(1) 1.355(9)

O(8)-C(25) 1.349(7) C(17)-C(19) 1.386(8) C(3)-C(5) 1.410(9)

O(8)-C(53) 1.425(7) N(2)-C(14) 1.270(7) C(31)-C(33) 1.364(9)

O(4)-C(30) 1.308(7) N(2)-C(13) 1.422(7) C(10)-C(11) 1.402(8)

O(2)-C(16) 1.306(7) C(22)-C(27) 1.382(8) C(2)-C(4) 1363(9)

O(9)-C(063) 1.482(10) C(22)-C(23) 1.389(8) C(2)-C(l) 1.387(10)

O(6)-C(11) 1.358(7) C(29)-C(31) 1.394(8) C(34)-C(33) 1.381(9)

O(6)-C(41) 1.438(7) C(29)-C(30) 1.419(8) C(55)-C(56) 1.496(11)

O(5)-qlO) 1.382(7) C(29)-C(28) 1.429(9) C(42)-C(43) 1.474(13)

O(5)-c(35) 1.422(7) C(27)-C(26) 1.399(8) C(37)-C(38) 1.523(14)

OQ)-C(20) 1291(7) C(25)-C(26) 1357(9) C(56)-C(57) 1.543(13)

0(1)-C(S) 1321(7) C(25)-C(24) 1.422(9) C(40)-C(39) 1.56(2)

1358(7) C(19)-C(21) 1.408(8) C(57)-C(58) 1.457(15)

188 O(7)-C(47) 1.433(7) C(I9)-C(20) 1.441(8) C(38)-C(39) 1.476(9)

N(3)-C(21) 1.282(7) C(32)-C(34) 1.367(9) 0(101)-C(101) 1.376(11)

N(3)-C(22) 1.421(7) C(32)-C(30) 1.418(8)

0(1 )-Zn( I)-0(2) 96.18(17) C(28)-N(4)-Zn(2) 124.5(4) C(24)-C(23)-C(22) 120.8(6)

0(1 )-Zn( 1)-N(2) 163.56(18) C(27)-N(4)-Zn(2) 112.9(4) C(I0)-C(9)-C(8) 121.4(6)

0(2)-Zn( I)-N(2) 88.38(17) C(16)-C( I8)-C(20) 124.4(5) C(4)-C(6)-C(5) 118.1(6)

0(1 )-Zn( I)-0(9) 97.69(17) C( I5)-C( 17)-C(19) 125.0(5) C(4)-C(6)-C(7) 117.3(6)

0(2)-Zn( I)-0(9) 97.14(17) C(14)-N(2)-C(1 3) 122.5(5) C(5)-C(6)-C(7) 124.6(6)

N(2)-Zn( 1)-0(9) 97.39(18) C(14)-N(2)-Zn( 1) 121.9(4) 0(4)-C(30)-C(32) 118.7(5)

0(1 )-Zn( 1)-N( 1) 89.90(18) C( I3)-N(2)-Zn(1) 114.2(4) 0(4)-C(30)-C(29) 123.7(5)

0(2)-Zn( I)-N( 1) 153.41(18) C(27)-C(22)-C(23) 120.1(5) C(32)-C(30)-C(29) 117.6(5)

N(2)-Zn( 1)-N( 1) 79.32(18) C(27)-C(22)-N(3) 116.8(5) 0(7)-C(24)-C(23) 125.1(6)

0(9)-Zn( I)-N( 1) 107.69(18) C(23)-C(22)-N(3) 123.1(5) 0(7)-C(24)-C(25) 115.4(5)

0(4)-Zn(2)-0(3) 95.23(16) C(3 1)-C(29)-C(30) 118.6(6) C(23)-C(24)-C(25) 119.5(6)

0(4)-Zn(2)-N(3) 165.13(18) C(3 I)-C(29)-C(28) 117.7(6) C(13)-C(8)-C(9) 118.1(5)

0(3)-Zn(2)-N(3) 90.34(17) C(30)-C(29)-C(28) 123.7(5) C(I3)-C(8)-N( 1) 116.0(5)

0(4)-Zn(2)-0(10) 95.90(17) C(22)-C(27)-C(26) 119.0(6) C(9)-C(8)-N(1) 125.9(5)

0(3)-Zn(2)-0( 10) 97.28(18) C(22)-C(27)-N(4) 116.5(5) C( 1)-C(3)-C(5) 121.8(7)

N(3)-Zn(2)-0(10) 97.06(19) C(26)-C(27)-N(4) 124.5(5) C(33)-C(31)-C(29) 122.2(6)

0(4)-Zn(2)-N(4) 89.26(17) N(4)-C(28)-C(29) 128.1(6) C( I2)-C(13)-C(8) 120.3(5)

0(3)-Zn(2)-N(4) 152.11(18) 0(8)-C(25)-C(26) 126.2(6) C(12)-C( I3)-N(2) 123.5(5)

N(3)-Zn(2)-N(4) 79.54(18) 0(8)-C(25)-C(24) 114.5(5) C(8)-C(13)-N(2) 116.2(5)

189 0(10)-Zn(2)-N(4) 109.64(18) C(26)-C(25)-C(24) 119.2(5) 0(1)-C(5)-C(3) 118.3(6)

C(30)-0(4)-Zn(2) 130.4(4) C(17)-C( I9)-C(2 1) 116.7(5) 0(1 )-C(5)-C(6) 123.8(5)

C(16)-0(2)-Zn(1) 123.0(4) C(17)-C(19)-C(20) 117.9(5) C(3)-C(5)-C(6) 117.9(6)

C(063)-0(9)-Zn( 1) 124.8(4) C(2 I)-C(19)-C(20) 125.0(5) C(9)-C(1 0)-0(5) 125.1(6)

C(20)-0(3)-Zn(2) 125.1(4) C(34)-C(32)-C(30) 121.8(6) C(9)-C( 10)-C( 11) 120.7(5)

C(5)-0(1)-Zn(1) 128.6(4) C(17)-C(15)-C(14) 117.7(5) 0(5)-C(10)-C(1 1) 114.3(5)

C(24)-0(7)-C(47) 117.1(5) C(17)-C(15)-C(16) 117.7(5) C(4)-C(2)-C(1) 118.9(6)

C(2 1)-N(3)-C(22) 123.8(5) C( 14)-C(15)-C(16) 124.5(5) C(32)-C(34)-C(33) 119.9(6)

C(2 1)-N(3)-Zn(2) 122.4(4) C(25)-C(26)-C(27) 121.4(6) C(2)-C(4)-C(6) 122.6(6)

C(22)-N(3)-Zn(2) 113.6(4) 0(3)-C(20)-C(1 8) 119.3(5) 0(6)-C( 11)-C( 12) 126.3(5)

C(060)-O(10)-Zn(2) 129.1(4) O(3)-C(20)-C(19) 123.5(5) 0(6)-C(1 1)-C(10) 115.1(5)

C(7)-N(1)-C(8) 121.1(5) C(18)-C(20)-C(19) 117.2(5) C(12)-C(1 1)-C(10) 118.7(5)

C(7)-N( 1)-Zn( 1) 125.1(4) N(3)-C(2 I)-C( 19) 126.2(5) N( 1)-C(7)-C(6) 127.2(6)

C(8)-N(1)-Zn(1) 113.8(4) 0(2)-C(16)-C(18) 119.9(5) N(2)-C(14)-C(15) 126.0(5)

C(1 I)-C(12)-C(13) 120.8(6) 0(2)-C(16)-C(15) 122.3(5) C(3 1)-C(33)-C(34) 119.9(6)

C(28)-N(4)-C(27) 122.6(5) C(18)-C( 16)-C( 15) 117.7(5) C(3)-C( 1)-C(2) 120.7(6)

190 §4.7 References

(1) Forrest, S. R.; Thompson, M. E., Chem. Rev. 2007, 107, 923.

(2) (a) Sun, Y; Liu, Y.; Zhu, D., I Mater. Chem. 2005, 15, 53. (b) Gelink, G. H.; Huitema, H. E.

A.; Veenendaal, E. V.; Cantatore, E.; Schrijnemakers, L.; van der Putten, J. B. P. H.; Geuns, T.

C. T.; Beenhakkers, M.; Giesbers,j. B.; Huisman, B.-H.; Meijer, E. J.; Mena benito, E.;

Touwsiager, F. J.; Marsman, A. W.; van Rens, B. J. E.; de Leeuw, D. M. Nat. Mater. 2004, 3,

106. (c) Mortimer, R. J., Chem. Soc. Rev. 1997, 26, 147.

(3) Mondal, R. M.; Shah, K. S.; Neckers, D. C. I Am. Chem. Soc. 2006, 128, 9612.

(4) Schmidt-Mende, L.;Fechtenkotter, A.; Mullen, K.; Moons,E.; Friend, R. H.; MacKenzie, J.

D. Science 2001, 293, 1119.

(5) Yamamoto, Y.; Fukushima, T.; Saeki, A.; Seki, S.; Tegawa, S.; Ishii, N.; Aida, T. I Am.

Chem. Soc. 2007, 129, 9276.

(6) Skotheim, T. A.; Elsenbaumer, R. L.; Reynolds, J. R. (Eds.), Handbook of Conducting

Polymers, Second Edition; Dekker: New York, 1998. (b) Friend, R. H.; Gymer, R. W.; Holmes,

A. B.; Burroughes, J. H.; Marks, R. N.; Taliani, C.; Bradley, D. D. C.; Dos Santos, D. A.;

Brédas, J. L.; Logdlund, M.; Salaneck, W. R. Nature 1999, 397, 121. (c) Gunes, S.; Neugebauer;

Sariciftci, N. S. Chem. Rev. 2007, 107, 1324. (d) Thomas, S. W., III; Joly, G. D.; Swager, T. M.

Chem. Rev. 2007, 107, 1339. (e) Bunz, U. H. F. Chem. Rev. 2000, 100, 1605. (f) McQuade, D.

T. Pullen, A. E.; Swager, T. M. Chem. Rev. 2000, 100, 2537.

(7) (a) Xia, C.; Advincula, R. C. Macromolecules 2001, 34, 6992. (b) Chen, Z.; Amara, J. P.;

Thomas, S. W.; Swager, T. M. Macromolecules 2006, 39, 3203.

(8) (a) Wohrle, D. I Porphyrins Phthalocyanines 2000, 4, 418. (b) Achar, B. A.; Fohlen, G. M.;

Parker, J. A. I Polym. Sci.: Polym. Chem. Ed. 1982, 20, 1785. (c) MacLachian, M. J.; Aroca, P.;

191 Coombs, N.; Manners, I.; Ozin, G. A. Adv,Mater. 1998, 10, 144. (d) Holliday, B. J.; Swager, T.

M. Chem. Commun. 2005, 23. (e) Pickup, P. G. I Mater. Chem. 1999, 9, 1641.

(9) McKeown, N. B. I Mater. Chem. 2000, 10, 1979. (b) Grayson, S. M.; Fréchet, J. M. J.

Chem. Rev. 2001, 101, 3819. (c) Kingsborough, R. P.; Swager, T. M. Frog. Inorg. Chem. 1999,

48, 123. (d) Manners, I. Science 2001, 294, 1664.

(10) Hanack, M.; Hirsch, A.; Lehmann, H. Angew. Chem. mt.Ed. Engi. 1990, 29, 1467.

(11) (a) Anderson, H. L. Chem. Comm. 1999, 23, 2323. (b) Bao, Z.; Yu, L. Trends Polym. Sd.

1995,3, 159.

(12) (a) Anderson, H. L. Inorg. Chem. 1994, 33, 972. (b) Taylor, P. N.; Andersen, H. L. I Am.

Chem. Soc. 1999, 121, 11538. (c) Iqbal, R.; Moratti, S. C.; Holmes, A. B.; Yahioglu, G.;

Milgrom, L. R.; Cacialli, F.; Morgado, J.; Friend, R. H. I Mater. Sci. - Mater. Electron. 2000,

11, 97.

(13) (a) Tsuda, A.; Osuka, A. Science 2001, 293, 79. (b) Aratani, N.; Osuka, A. Chem. Rec,

2003, 3, 255.

(14) Manecke, G.; Wille, W. E.; Kossmehl, G. Makromol. Chem. 1972, 160, 111.

(15) Wang, B.; Wasielewski, M. R. I Am. Chem. Soc. 1997, 119, 12.

(16) Snieckus, V. Chem. Rev. 1990, 90, 879.

(17) Lopez-Alvarado, P; Avendano, C.; Menendez, C. J. Syn. Comm. 2002, 32, 3233.

(18) Worden, L. R.; Kaufman, K. D.; Smith, P. J.; Widiger, G. N. I Chem. Soc. C 1970, 227.

(19) (a) Leung, A. C. W.; Chong, J. H.; Patrick, B. 0.; MacLachlan, M. J. Macromolecules 2003,

36, 5051. (b) Leung, A. C. W.; MacLachian, M. J. I Mat. Chem. 2007, 23, 1923.

(20) Ma, C. T. Z.; Lo, A; Abdolmaleki, A.; MacLachlan, M. J. Org. Lett. 2004, 6, 3841.

(21) Chong, J, H.; MacLachlan, M. J. Inorg. Chem. 2006, 45, 1442,

(22) Ma, C. T. Z.; MacLachian, M. J. Angew. Chem. mt.Ed. 2005, 44, 4178. 192 (23) (a) Yam,V. W.-W.; Chan, K. H.-Y.; Wong, K. M.-C.; Chu, B. W.-K. Angew. Chem.2006,

118, 6315. (b) A. Gourdon, J. P. Launay, Inorg. Chem. 1998, 37, 5336. (c) X. F. Wang, Y. Z.

Shen, Y. Pan, Y. Q.Liang, Langmuir 2001, 17, 3162.

(24) (a) MUller,B. R.; Leibeling, G.; Jager, E.-G. I Magn. Magn. Mater. 2002, 246, 283. (b)

Brandon, E. J.; Arif, A. M.; Burkhart, B. M.; Miller, J. S. Inorg. Chem. 1998, 37, 2792.

(25) Sauer, M.; Yeung, C.; Chong, J. H.; Patrick, B. 0.; MacLachian, M. J. I Org. Chem.2006,

71, 775.

(26) Kahn, 0. Molecular Magnetism, VCH: New York, 1993.

(27) Tannai, H.; Tsuge, K.; Sasaki, Y. Inorg. Chem. 2005, 44, 5206.

(28) Mandal, P. K.; Nag, K.; Manoharan, P. T. Inorg. Chem. 1995, 34, 270.

(29) Kastler, M.; Pisula, W.; Wasserfallen, D.; Pakula, T.; MUllen,K. I Am. C’hem.Soc. 2005,

127, 4268.

(30) Kim, Y.; Zhu, Z.; Swager, T. M. I Am. Chem. Soc. 2004, 126, 452.

(31) Ma, C. T. Z.; MacLachian, M. J. Angew. Chem. mt.Ed. 2005, 44, 4178.

(32) Hui, J. K.-H.; MacLachlan, M. J. Chem. Commun.2006, 2480.

193 CHAPTER 5

Conclusions and Future Direction

§5.1 Overview

Recent research efforts in the area of conductive conjugated polymers have focused on the introduction of functional molecules into polymeric it-conjugated frameworks.’ In particular, the combination of metal complexes with organic conjugated polymers generated novel materials with chemical, electronic, and magnetic properties that are not found in other organic- based 2polymers. The work presented in this thesis aims to develop innovative functional materials through the incorporation of Schiff base transition metal complexes into conjugated organic polymers. A variety of synthetic methods were explored to prepare novel Schiff base complexes that can be polymerized, and different synthetic strategies were investigated to produce polymeric materials with high molecular weights and good solubility. Schiff base complexes containing different transition metals were inserted into conjugated polymers and their corresponding luminescence, electronic and magnetic properties were investigated. In addition, the presence of transition metals within the metallopolymers provided new coordination sites that allow the polymers to interact with different ligands, opening new possibilities for applications as sensors and as building blocks for supramolecular scaffolds. A series of titration experiments was performed to explore the supramolecular and sensory characteristics of the metallopolymers synthesized in this thesis.

194 §5.2 Poly(salphenyleneethynylene)s (PSPEs)

Schiff base complexes were found to be useful materials for LEDs with blue and white electroluminescence. The incorporation of Schiff base complexes into a PPE framework is 3anticipated to produce new polymeric materials with outstanding luminescence properties that may be suitable for LED 4fabrication. I prepared the first examples of soluble PSPEs 202, 216, and 217 containing ,2Zn ,2Ni ,2Cu and 2VO Schiff base 5complexes. Due to the rigid structure of the polymers and their tendency to form aggregates, it was necessary to synthesize new monomers containing bulky solubilising groups in order to promote sufficient solubility.

Through the use of the Sonogashira-Hagihara coupling reaction, soluble high molecular weight

PSPEs were synthesized. The resulting polymers 202 and 216 are intensely coloured, absorbing strongly to long wavelengths of Ca. 550 — 600 nm, and readily form thin films. Investigations of the luminescent and absorption properties of the polymers indicate that only Zn polymers 202a and 216a are luminescent, but they are not good candidates for LED applications due to their low fluorescence efficiency. NMR studies of the polymers revealed very broad features that are indicative of strong aggregation of the polymers. It is postulated that Zn PSPEs 202a and 216a exhibited strong aggregation behaviour which is facilitated by the presence of Zn•••O interactions between the Zn metal center and the phenolic oxygen of adjacent Schiff base complexes. Deaggregation of the polymers can be induced by treating the material with a coordinating base such as pyridine, disrupting the Zn•••O interactions that cause aggregation of the polymers. Fluorescence titration experiments of PSPE 216a with pyridine indicated a strong

“turn-on” response in the polymers’ emission, making these polymers possible sensors for coordinating bases. On the contrary, a “turn-off’ response in the polymers’ emission was observed when polymer 216a was titrated with bidentate ligands such as I,4-bipyridine, suggesting that the addition of bidentate ligands enhances self-association of the polymers.

195 Target polymers 217 are structural variants of linear PSPEs 202 and 216 that are expected to adopt a helical or coil structure. UV-vis spectroscopy revealed that the absorption spectra of polymers 217 are significantly red-shifted relative to linear polymers 216, suggesting the presence of extended conjugation in polymers 217. Florescence studies of the polymers indicate that only Zn polymer 217a exhibited weak luminescence in THF. Titration experiments of 217a with pyridine indicated that the polymer was less responsive to the addition of coordinating ligands and only small optical changes were observed. It is hypothesized that these polymers exhibit a coil-like structure in solution that inhibits aggregation by reducing inter-strand interactions, and their luminescence is quenched via an intramolecular mechanism.

n 202a(M=Zn) 216a(M=Zn) 202b (M = Ni) 216b (M = Ni) 202c(M V0) 216c(M =Cu)

217a (M = Zn) n 217b (M = Ni) 217c (M = Cu)

Figure 5.1. Poly(salphenyleneethynylene)s (PSPE)s synthesized in this thesis (BuOct = 2-

ButylOctyl).

196 § 5.2 Schiff Base Ladder Metallopolymers

I have explored the possiblity of using Schiff base chemistry as a method to build ladder-type conjugated metallopolymers. The construction fully conjugated polymers that contain multiple conjugation pathways is an effective strategy to overcome common difficulties such as the twisting of the polymeric backbones as well as the presence of chemical defects which disrupt delocalization within the 6polymers. The presence of transition metals within the conjugated frameworks is expected to generate interesting chemical, electronic, and magnetic properties, as well as the ability to interact with coordinating ligands.

197 60CH13

229a (M=Zn; ROEtHex) 231a M=Zn 229b (M=Cu; ROEtHex) 231b M =Cu

n 230

230a R = 2-butyloctyloxy, M = Zn 232a R = 2-butyloctyloxy, M = Zn 230b R = 2-butyloctyloxy, M = Cu 232b R = 2-butyloctyloxy, M = Cu

Figure 5.2. Ladder-type Schiff base conjugated polymers and model compounds synthesized in this thesis.

New synthetic strategies were developed to construct bimetallic model compounds

229 and 231 that are representative components of the target ladder polymers 230 and 232 containing Zn and Cu. It was necessary to install bulky branched groups onto the model compounds to induce sufficient solubilty of these rigid compounds in organic solvents. The resulting model compounds 229a-b and 231a-b are intensely coloured, and they have optical absorption spectra that are red shifted relative to Zn and Cu saiphens 246a-b, indicative of extensive delocalization within the conjugated structure. NMR studies indicated that Zn model compound 229a aggregates strongly in non-coordinating solvents, similar to what was

198 observed in the case of Zn PSPEs 202a and 216a. Again, it is postulated that the self- association of saiphen moieties due to a Zn•••O interaction is responsible for the observed aggregation. Zn model compound 229a is capable of interacting with coordinating ligands such as pyridine and acetylacetone, which induce deaggregation and promote solubility in non-coordinating solvents such as 3CHC1 and 2C1CH in which the compounds are otherwise insoluble. Model compound 231a with a bent structure was synthesized using similar synthetic strategies that were used to synthesize 229a, and it was found that the model compound possesses adequate solubility in a variety of organic solvents 2CI(CH ,3CHC1 THF). Solid state X-ray crystallography of compound 231a showed that ,the compound is non-planar and the 2Zn metal centers reside within the ligand system in a distorted square planar conformation. Cyclic voltammetry, EPR spectroscopy, and SQUID magnetometry were employed to explore whether electronic and magnetic interactions exist within the extensively conjugated ligand system. Surprisingly, no significant electronic interaction between the 2Cu centers was observed in 229b and 231b by CV or EPR experiments. SQUID magnetometry experiments revealed that antiferromagnetic interactions exist between the 2Cu metal centers in bent model compound 231b but not in linear model compound 229b.

A few synthetic strategies were explored to develop viable synthetic routes to obtain target ladder polymers 230 and 232, but it was difficult to obtain soluble materials with high molecular weights. Zn ladder polymer 230a containing bulky chiral solubilizing groups was successfully prepared using a one pot synthesis and the highest molecular weight achieved was determined to be ca. 15,000 Da. (Mw) using GPC. The extensive conjugation of ladder polymers 230a is evident by extremely red-shifted UV-vis spectra that absorb to beyond 800 nm. Attempts to synthesize target polymer 232, a bent version of polymer 230, using an

199 identical procedure that was used to synthesize Zn ladder polymer 230a were unsuccessful because only oligomeric materials with low molecular weights were synthesized (M = 2,300, GPC). Polymerization using the same procedure with 2Cu(OAc) to synthesize Cu polymer 232b also yielded low molecular weight materials (M = 1,900). It is postulated that the bent structure of the target polymer, along with the rigidity of the polymer backbone and steric bulkiness of the solublizing groups, prevented high degrees of polymerization.

§5.3 Future Directions

The work presented in this thesis is a part of a larger vision that aims to develop functional materials through the incorporation of Schiff base complexes into various molecular architectures including polymers, dendrimers, and macrocycles. Target macrocycles and dendrimers containing Schiff base complexes, resembling star-shape and cyclic analogs of the 5•37 linear polymers that were synthesized in this work, are illustrated in Figure Fully conjugated Schiff base macrocycle 259, macrocycle 260 with Schiff base complexes linked by ethynylene bridges, and Schiff base dendrimer 261 are examples of some of the target compounds synthesized. A common goal between these projects is to use coordination chemistry and self-assembly methods to construct supramolecular architectures such as nanotubes and nanogrids. For example, Schiff base-containing macrocycles 259 and 260 may be assembled into tubular structures through the use of bidentate coordinating ligands, while the polymers described in this work may be assembled into grids. Further studies on the metallopolymers synthesized in this work may include their supramolecular behavior with various coordinating ligands. While it is established from this work that the polymers do interact with coordinating ligands such as pyridine and bipyridine, it is necessary to perform a

200 comprehensive study with a large library of ligands. It is anticipated that the polymers synthesized in this work can be assembled into porous 2-D or 3-D materials, and a variety of characterization methods, such as high resolution surface imaging techniques like STM and

AFM may prove useful in the elucidation of such structures.

259

R 261

Figure 5.3. Schiff base macrocycles and dendrimers synthesized in the MacLachian Research group (R = alkyl or alkoxy).

201 Schiff base complexes are important classes of complexes that are capable of catalyzing a large variety of transformations. Schiff base ligands can be synthesized using simple condensation reactions, and they are capable of stabilizing many different metals in various oxidation states. In the case where the Schiff base ligand is chiral, they are coined to be

“privileged ligands”, due to the fact that they are able to catalyze a wide variety of transformations with exceptional enantioselectivity and high 8productivity. For example, Schiff base complex 262 containing 3Al is known to catalyze polymerization of oxiranes and ethylene, as well as other well-known organic transformations such as Friedel—Craftsreactions, Diels—

Alder reactions, and Claisen rearrangements. Mn and Cr Schiff base complexes are also important classes of catalysts that9 have been extensively studied because of their exceptional performance in the catalysis of epoxidation reactions)° Achiral Co(Salen) 264 has a well- established ability to bind oxygen, and copolymerization of these complexes into porous materials provides a reversible oxygen carrier that may function in gas 1storage. It is clear that the aforementioned Al, Mn, Cr, and Co Schiff base complexes are interesting molecules with important applications in the area of catalysis, and a yet to be explored area of research is to incorporate these Schiff base molecules into conjugated PPE frameworks using the polymerization reaction parameters that were developed in this thesis. It is possible to synthesize new PSPEs that are catalytically active and may serve as useful solid state catalysts.

In addition, Zn and Cu Schiff base complexes 265 and 266 are known to catalyze transformation reactions such as nitrene transfer and alkynylation of ketones, respectively.’ The Cu and Zn

PSPEs 216a,c and 217a,c synthesized in 2 this work may have catalytic activities in these transformations and this merits further investigation.

202 _N\QN_ _N\ /N_ tBu_O’’O__tBu

tBu tBu tBu tBu 19M=Mn 263M=Cr 262M=AI 264M=Co 265 M = Zn 266 M = Cu

It is anticipated that the insertion of Schiff base complexes into conjugated polymers will yield new materials with exceptional optoelectronic properties. While the PSPEs presented in this work contained Schiff base complexes that are embedded in a PPE framework, other researchers in the MacLachlan research group have prepared PPV-type Schiff base polymer 267 and polythiophene-type Schiff base polymer 268.13 It is evident that the Sonogashira-Hagihara protocol provides a versatile and convenient route to yield high molecular weight PPEs containing Schiff base complexes, and the work in this thesis has established important experimental parameters. To continue with the goal of synthesizing metallopolymers with optoelectronic properties suitable for LED applications, a variety of monomers such as fluorene

269, anthracene 270, phenanthrene 271, and pentiptycene 272 should be explored as possible components for new 4PSPEs.’

267 R = H12250C 268 R = H12250C 203 RR

269 270

3HCO 3OCH

271 272

Figure 5.4. Monomers such as diiodofluorene 269, diiodoanthracene 270, diiodophenanthrene 271, and pentiptycene 272 should be explored as possible components for new PSPEs.

204 § 5.4 References

(1) (a) Bunz, U. H. F. Chem. Rev. 2000, 100, 1605. (b) Bunz, U. H. F. Adv. Folym. Sci. 2005,

177, 1.

(2) (a) Kingsborough, R. P.; Swager, T. M. Frog. Jnorg. Chem. 1999, 48, 123. (b) Manners, I.

Science 2001, 294, 1664.

(3) (a) Kim, S. M.; Kim, J. S.; Sohn, B. C.; Kim, Y. K.; Ha, Y. Y. Mol. Cryst. Liq. Cryst. 2001,

371, 321. (b) Sano, T.; Nishio, Y.; Hamada, Y.; Takahashi, H.; Usuki, T.; Shibata, K.J Mater.

Chem. 2000, 10, 157. (c) Che, C.—M.;Chan, 5.—C.;Xiang, H.—F.;Chan, M. C. W.; Liu, Y.;

Wang, Y. Chem. Commun. 2004, 1484.

(4) Lavastre, 0.; Jllitchev, I.; Jegou, G.; Dixneuf, P. H. I Am. Chem. Soc. 2002, 124, 5278.

(5) (a) Leung, A. C. W.; Chong, J. H.; Patrick, B. 0.; MacLachian, M. J. Macromolecules 2003,

36, 5051. (b) Leung, A. C. W.; MacLachian, M. J. I Mater. Chem. 2007, 17, 1923.

(6) (a) Xia, C.; Advincula, R. C. Macromolecules 2001, 34, 6992. (b) Chen, Z.; Amara, J. P.;

Thomas, S. W.; Swager, T, M. Macromolecules 2006, 39, 3203.

(7) Jonathan Chong, Conjugated Metallodendrimers, B.Sc. Thesis, 2001, University of British

Columbia. (b) Ma, C.; Lo, A.; Abdolmaleki, A.; MacLachian, M. J. Org. Lett. 2004, 6, 3841. (c)

Gallant, A. J.; Hui, J. K. H.; Zahariev, F.; Wang, Y. A.; MacLachlan, M. J. I Org. Chem.2005,

70, 7936

(8) Cozzi, P. G. Chem. Soc. Rev. 2004, 33, 410.

(9) Atwood, D. A.; Harvey, M. J. Chem. Rev. 2001, 101, 37.

(10) (a) Zhang, W.; Loebach, J. L.; Wilson, S. R.; Jacobsen, E. N. I Am. Chem. Soc. 1990, 112,

2801. (b) Jones, D. J.; Gibson, V. N.; Green, S. M.; Maddox, P. J. Chem. Commun. 2002, 1038.

(c)Ruck, R. T.; Jacobsen, E. N. Angew. Chem., mt.Ed. 2003, 42, 4471.

(11) Sharma, A. C.; Borovik, A. S. I Am. Chem. Soc. 2000, 122, 8946.

205 (12) (a) Cozzi, P. G. Angew. Chem., mt.Ed. 2003, 42, 2895. (b) Muller, P.; Fruit, C. Chem.Rev.

2003, 103, 2905.

(13) Jian Jiang, University of British Columbia, unpublished results. (b) Pietrangelo, A.; Sih, B.

C.; Boden, B. N.; Wang, Z.; Li, Q.;Chou, K. C.; MacLachlan, M. J.; Wolf, M. 0. Adv. Mater.

2008, In press.

(14) (a) Rak, S. F.; Lapin, S. C.; Falvey, D. E.; Schuster, G. B. I Am. Chem. Soc, 1987, 109,

5003. (b) Zhao, Z.; Yu, S.; Xu, L.; Wang, H.; Lu, P. Tetrahedron 2007, 63, 7809. (c) Boden, B.

N. ; Jardine, K. J.; Leung, A. C. W.; MacLachian, M. J. Org. Lett. 2006, 8, 1855. (d)

Yamaguchi, S.; Swager, T. M. I Am. Chem. Soc. 2001, 123, 12087.

206