California State University, Northridge the Synthesis and Electrochemical

California State University, Northridge

The Synthesis and Electrochemical Characterization of Phosphole Containing Oligomers and Polymers

A thesis submitted in partial fulfillment of the requirements For the degree of Master of Science in Chemistry By Robert Pankow

May 2015

The thesis of Robert Pankow is approved:

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Dr. Eric Kelson Date

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Dr. Yann Schrodi Date

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Dr. Katsu Ogawa, Chair Date

California State University, Northridge ii

Acknowledgments

I would like to thank my mother, father, sister, Judith, and John for their love and support in all of my endeavors. To my lifelong friends Henry, Addison, and Ryan, thank you.

I would like to thank Dr. Katsu Ogawa for allowing me to work in his lab and giving me the chance to learn and grow as a student of chemistry. You are an excellent mentor, and I will forever cherish you as a teacher. You have provided me with knowledge and insight to tackle problems, both professional and personal. Also, thank you Kenny Cooper, for joining me in the battle against low yields or no yields. Without your help, this thesis would not be as complete. I would like to thank Steven Ruark, who synthesized enough starting material to get me through a Masters program.

I would like to thank Drs. Yann Schrodi and Eric Kelson for being members of my thesis committee and for being excellent instructors. It was in your classrooms I was able to expand my knowledge of chemistry and gain direction as to what interested me chemically. I would like to thank Drs. Thomas Minehan, Jeff Charonnat, and Simon

Garrett for their excellent instruction and for further expanding my knowledge of chemistry. Despite the knowledge I have gained, I will forever remain a student only seeking to learn more.

Finally, I would like to thank Michelle Chan, who provided love and support during difficult times, and Jhauvy, Alex, Kaveh, Capek,Yehan, Zach Perez, and Jaime for their friendship.

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Table of Contents

Signature Page ii

Acknowledgments iii

List of Figures vi

List of Tables x

Abstract xii

Chapter 1. Introduction 1

1.1 π-Conjugated Polymers and Oligomers for Organic Photovoltaics 1

1.2 Pt-containing Poly(aryleneethynylenes) 6

1.3 Phosphole Oligomers 11

Chapter 2. Synthesis of Phosphole Oligomers and Derivatives 23

2.1 Synthesis of Butadienes 23

2.2 Synthesis of Phospholes 29

2.3 Synthesis of Phosphole Derivatives 39

Chapter 3. Electrochemical Characterization of Phospholes 43

Chapter 4. Phosphole-Pt Containing Poly(aryleneethynylenes) 52

4.1 Synthesis of Phosphole-Pt Containing Poly(aryleneethynylenes) 52

4.2 Electrochemistry of Phosphole-Pt poly(aryleneethynylenes) 56

Chapter 5. Conclusion 64

Chapter 6. Experimental 66 iv

References 75

Appendix A: NMR and cyclic-voltammetry data for select compounds 79

List of Figures

Figure 1-1 Common π-conjugated polymers 2

Figure 1-2 Electron transfer from the donor to acceptor material in a 3 solar cell

Figure 1-3 Modifying the substituents of the polymer backbone 5

Figure 1-4 Hagihara coupling to prepare Pt-containing poly-arylenes 7

Figure 1-5 Pt containing poly(phenyleneethylene) 8

Figure 1-6 Variation of the aryl linker for conjugated organometallic 9 polymers

Figure 1-7 Common Heteroacenes 11

Figure 1-8 Fused ring system phosphole oligomers 13

Figure 1-9 Synthetic methods for the preparation of phospholes 14

Figure 1-10 Fused bithiophene and naptholene [c]-fused phospholes 15

Figure 1-11 Diacenanaptho[1,2-b:1’2’-d]phospholes 17

Figure 1-12 2,5-bis(aryl)phospholes studied by Réau 18

Figure 1-13 Fused bi-aryl phospholes and derivatives 20

Figure 2-1 Synthesis of butadienes via silane-homocoupling 23

Figure 2-2 Synthesis of butadienes via Wittig olefination 23

Figure 2-3 Palladacycles potentially derived from 2-pyridylhalides and 26 2-thiazolehalides.

Figure2-4 Copper mediated homocoupling of substituted 27 pyridyldimethyl(vinyl)silanes

Figure 2-5 Dimerization of 2H-phospholes 29

Figure 2-6 Rearrangement of 1,2,5-triarylphoshpoles 33

Figure 2-7 31P NMR spectra showing rearranged phosphole byproducts 34 for entries 5 (top) and 3 (bottom) of Table 2-4

Figure 2-8 31P NMR spectra showing dimer by products for entries 1 36 (top) and 4 (bottom) of Table 2-4

Figure 2-9 31P NMR spectra for Pt complexes 61a and 61b 42

Figure 3-1 Cyclic-voltammograms of compounds 17b, 49b, and 60b. 44 Measured in MeCN using Pt disk working electrode, Bu4NPF6 as the supporting electrolyte, and ferrocene as an internal standard

Figure 3-2 Cyclic-voltammograms of phospholes 49a-c. Measured in 46 MeCN using Pt disk working electrode, Bu4NPF6 as the supporting electrolyte, and ferrocene as an internal standard

Figure 3-3 Cyclic-voltammograms of complexes 61a,b. Measured in 50 DCM using Pt disk working electrode, Bu4NPF6 as the supporting electrolyte, and ferrocene as an internal standard

Figure 3-4 Oxidative electropolymerisation of phosphole oxide 60b 51 (middle) and Pt complex 61b (right). The left panel shows decomposition of phosphole 49b. Measured in DCM using Pt disk working electrode, Bu4NPF6 as the supporting electrolyte, and ferrocene as an internal standard

Figure 4-1 1H NMR spectra for polymer 63b 54

Figure 4-2 31P NMR spectra for polymer 63b 54

Figure 4-3 1H NMR spectra for polymer 63a 55

Figure 4-4 31P NMR spectra for polymer 63a 55

Figure 4-5 From top to bottom, cyclic-voltammograms of phosphole 58 ligands 49a,b, Pt complexes 61a,b, and polymers 63a,b. Measured in DCM using Pt disk working electrode, Bu4NPF6 as the supporting electrolyte, and ferrocene as an internal standard

Figure 4-6 Cyclic-voltammograms of polymers 63a,b. Measured in DCM 59 using Pt disk working electrode, Bu4NPF6 as the supporting electrolyte, and ferrocene as an internal standard

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Figure 4-7 Cyclic-voltammograms of polymers 63a,b were measured in 62 DCM using Pt disk working electrode, Bu4NPF6 as the supporting electrolyte, and ferrocene as an internal standard, and cyclic-voltammograms of polymer films prepared from 63a,b. aFilms were prepared by drop casting a solution of the polymer in CHCl3 onto ITO glass plates and measured in MeCN using Bu4NPF6 as the supporting electrolyte and ferrocene as an internal standard

Figure A-1 1,2,5-triphenylphosphole 1H NMR Spectrum 79

Figure A-2 1,2,5-triphenylphosphole 13C NMR spectrum 80

Figure A-3 1,2,5-triphenylphosphole 31P NMR spectrum 81

Figure A-4 1,2,5-triphenylphosphole HSQC NMR spectrum 82

Figure A-5 2,5-bis(4-pyridyl)4-anisole phosphole 1H NMR spectrum 83

Figure A-6 2,5-bis(4-pyridyl)4-anisole phosphole 31P NMR spectrum 84

Figure A-7 2,5-bis(4-pyridyl)4-anisole phosphole COSY NMR Spectrum 85

Figure A-8 2,5-bis(4-pyridyl)4-anisole phosphole HMBC NMR 86 spectrum.

Figure A-9 2,5-bis(4-pyridyl)4-anisole phosphole HMBC NMR 87 spectrum.

Figure A-10 2,5-bis(4-pyridil)phenyl phosphole 1H NMR spectrum 88

Figure A-11 2,5-bis(4-pyridil)phenyl phosphole 13C NMR spectrum 89

Figure A-12 2,5-bis(4-pyridil)phenyl phosphole 31P NMR spectrum 90

Figure A-13 2,5-bis(4-pyridil)phenyl phosphole COSY NMR spectrum 91

Figure A-14 2,5-bis(4-pyridil)phenyl phosphole COSY NMR spectrum 92

Figure A-15 2,5-bis(2-thienyl)phenyl phosphole 1H NMR spectrum 93

Figure A-16 2,5-bis(2-thienyl)phenyl phosphole 13C NMR spectrum 94

Figure A-17 2,5-bis(2-thienyl)phenyl phosphole 31P NMR spectrum 95

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Figure A-18 2,5-bis(2-thienyl)phenyl phosphole COSY NMR spectrum 96

Figure A-19 2,5-bis(2-thienyl)phenyl phosphole HSQC NMR spectrum 97

Figure A-20 1,2,5-tris(4-fluorophenyl)phosphole 1H NMR spectrum 98

Figure A-21 1,2,5-tris(4-fluorophenyl)phosphole 13C NMR spectrum 99

Figure A-22 1,2,5-tris(4-fluorophenyl)phosphole 31P NMR spectrum 100

Figure A-23 1,2,5-tris(4-fluorophenyl)phosphole 19F NMR spectrum 101

Figure A-24 1,2,5-tris(4-fluorophenyl)phosphole COSY NMR spectrum 102

Figure A-25 1,2,5-tris(4-fluorophenyl)phosphole HMBC NMR spectrum 103

Figure A-26 1,2,5-tris(4-fluorophenyl)phosphole HSQC NMR spectrum 104

Figure A-27 Figure A-27.Cyclic-voltammograms for compounds 17a,c- 105 60a,c

List of Tables

Table 1-1 Photophysical and Electrochemical data for [c]-fused phospholes 16

Table 1-2 Photophysical and Electrochemical data for Diacenanaptho[1,2- 17 b:1’2’-d]phospholes

Table 1-3 Photophysical and electrochemical data for selected 2,5- 19 bis(aryl)phospholes

Table 1-4 Photophysical and electrochemical data for compounds 32-37 21

Table 2-1 Synthesis of aryl substituted pyridyldimethyl(vinyl)silanes. 25

Table 2-2 Experimental data for the homocoupling of pyridyl(vinyl)silanes 27

Table 2-3 Dependence of phosphole yield and purity on the heat source 30

Table 2-4 Microwave assisted phosphole synthesis via McCormack reaction 31

Table 2-5 Phosphole 13C chemical shifts and coupling constants. 38

Table 2-6 Phosphole 1H chemical shifts and coupling constants. 38

Table 2-7 Experimental and NMR data for phosphole oxides. 40

Table 2-8 Synthesis of complexes 61a,b 41

Table 3-1 Electrochemical data for butadienes17a-c, phospholes 49a-c, and 45 phosphole oxides 60a-c. Measured in MeCN using Pt disk working electrode, Bu4NPF6 as the supporting electrolyte, and ferrocene as an internal standard

Table 3-2 Electrochemical data for phospholes 49a-c and 27 and 28. 47 Measurements for phospholes 49a-c were performed in MeCN using Pt disk working electrode and Bu4NPF6 as the supporting electrolyte. Measurements for 27 and 28 performed in DCM using Pt disk working electrode and Bu4NPF6 as the supporting electrolyte. All potentials were referenced to ferrocene as an internal standard

Table 3-3 Table 3-3. Electrochemical data of complexes 61a,b. Measured in 49 DCM using Pt disk working electrode, Bu4NPF6 as the supporting electrolyte, and ferrocene as an internal standard.

Table 4-1 Synthesis of phosphole-Pt containing 53 poly(phenyleneethylynenes) using Hagihara coupling

Table 4-2 Electrochemical data for compounds 49a,b-63a,b. Measured in 59 DCM using Pt disk working electrode, Bu4NPF6 as the supporting electrolyte, and ferrocene as an internal standard

Table 4-3 Electrochemical data of polymers 63a,b. Measured in DCM using 60 Pt disk working electrode, Bu4NPF6 as the supporting electrolyte, and ferrocene as an internal standard

Table 4-4 Electrochemical data for polymers in bulk solution and as a film 63 on ITO. Polymers 63a,b were measured in DCM using Pt disk working electrode, Bu4NPF6 as the supporting electrolyte, and ferrocene as an internal standard. aFilms were prepared by drop casting a solution of the polymer in CHCl3 onto ITO glass plates and measured in MeCN using Bu4NPF6 as the supporting electrolyte and ferrocene as an internal standard

Abstract

The Synthesis and Electrochemical Characterization of Phosphole Containing Oligomers and Polymers

By Robert Pankow

Master of Science in Chemistry

Phospholes are π-conjugated systems that have remained relatively unexplored despite their potential utility in various optoelectronics, such as organic photovoltaics.

These heteroacenes are intriguing because the orbital energies of phosphole containing conjugated systems can be easily tuned through synthetic modification at the phosphorous center, such as oxidation or metal coordination. 1,2,5-triarylphospholes were synthesized using the McCormack reaction and subsequently modified at the phosphorous center to provide the corresponding oxidized derivatives. It was found that microwave heating in the McCormack reaction allowed rapid access to phospholes and avoided byproduct formation. Pt(II) complexes were also prepared using the phospholes as ligands. Hagihara coupling of the platinum complexes with an aryl acetylide linker formed a phosphole containing platinum acetylide polymer. All of the aforementioned materials were characterized electrochemically to determine the changes in the frontier molecular orbital energies as a consequence of synthetic modification. Oxidation or metal coordination of the phospholes lead to a reduction in band gap through stabilization of the xii

LUMO, and polymerization of the complexes further reduced the band gap through further stabilization of the LUMO. New phosphole containing oligomers and polymers can be tailored based on the observed electrochemical properties and synthesized using the outlined synthetic methods.

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Chapter 1. Introduction

1.1 π-Conjugated Polymers and Oligomers for Organic Photovoltaics

The quality of life for most societies is dictated by the ability of people to access affordable energy sources, and much of society is reliant on large amounts of electricity usage to maintain their quality of life. To avoid exhausting major fuel sources, such as fossil fuels, technologies must be improved in terms of efficiency and alternative energy sources need to be developed, that outperform or are equivalent to their predecessors. The sun provides an inexhaustible amount of energy, but harvesting this energy through photovoltaics has proven difficult. Most solar cells employed today, whether on a rooftop or in a field for a solar farm, are made with crystalline silicon or other inorganic components. While inorganic based solar cells are currently the most efficient in terms of their power conversion efficiency (PCE), they are bulky and have limited processability making the range of their applications more finite, and the cost of their manufacturing is too high to make them competitive with current energy sources1,2.

An alternative to inorganic based solar cells are organic π-conjugated polymer solar cells or organic photovoltaics (OPV).While most polymers are typically insulating materials made of saturated hydrocarbon chains, π-conjugated polymers are a molecular wire consisting of a vast π-system formed by the overlap of many p-orbitals within a material. As the name implies, this overlapped network allows for conjugation and the transport of electrons through the material. Common π-conjugated materials encountered, as shown in Figure 1.-1, include polyacetylene, poly(p-phenylenevinylene) or PPV, and poly(3-hexylthiophene) or P3HT.

Figure 1-1. Common π-conjugated polymers.

Many consumer devices currently employ inorganic based materials, and the alternative would also be π-conjugated polymers and oligomers. Given their optical and electronic properties, these materials are classified as organic optoelectronics. Current research efforts are heavily focused on developing solar cells that provide a sufficient power conversion efficiency (PCE) for them to be implemented into easily accessible solar cells. The desired OPV devices would be used for applications where the bulky, rigid inorganic counterparts could not. While the future looks bright for these materials in solar cells, there are still many improvements to be made, most of which relate to the engineering of the solar cell. Many π-conjugated materials have been discovered and tested in devices, but there are is still a significant research effort to designing and implementing new π-conjugated polymers.

π-Conjugated polymers can be implemented into electronic devices because of their vast, overlapping p-orbitals comprising a π-system down the backbone of the polymer chain. The simplest example is polyacetylene, shown in Figure 1-1. Each carbon in polyacetylene is involved in a π-bond with the adjacent carbon, allowing for an extensive π-conjugated system. It was because of the initial discovery of the increase in conductivity of polyacetylene by doping with iodine vapor by MacDiarmid, Heeger, and

Shirakawa3,4, that opened the door to the flood of research and discovery in the conjugated polymer field. It was through this discovery that organic based polymers had

the potential as semi-conductors, which rivaled their inorganic counterparts. Through these initial results, the utility of an organic material in an electronic device seemed plausible. Shortly thereafter, π-conjugated polymers were implemented into the first OPV device5, and by understanding the processes associated with the photovoltaic effect has helped in the design and discovery of new materials and their implementation into solar cells.

While there are a number of different types of solar cells available, most π- conjugated polymers are implemented into the highly efficient bulk heterojunction (BHJ) solar cells6,7,8. These cells contain a blend composed of a donor and an acceptor material between two electrodes (indium tin oxide (ITO) and aluminum). In a BHJ cell, the donor material is referred to as such because it donates an electron to the acceptor material.

Most often, the π-conjugated polymer functions as the donor material, a popular example being P3HT, and the acceptor material is typically phenyl-C61-butyric acid methyl ester

(PCBM).

Donor exciton

Electron transfer Hole to anode Electron to cathode

LUMO of acceptor

Figure 1-2. Electron transfer from the donor to acceptor material in a solar cell.

After the absorption of light and generation of an excited state, an electron-hole pair is formed within the donor material, and it is referred to as the exciton. The exciton propagates through the donor material until it encounters the interface of an acceptor 3

material where the electron is transferred. The electron can then be shuttled to an electrode leading to the generation of current, as depicted in Figure 1-2. An external circuit resupplies an electron to the donating material, filling the hole, and the process continues. Thus, designing a π-conjugated polymer suitable for a solar cell is a multi- faceted process, some considerations include: the material must have a low band-gap (Eg) to allow for excitation at wavelengths of light ranging from the ultra-violet to the infrared region of the electromagnetic spectrum, it must allow for a prolonged excited state that avoids radiationless decay and minimizes vibrational relaxation, the material must be stable, and it must be processable.6,8,9

The band gap energy (Eg) describes the energy input required to promote an electron from the valence to the conduction band of a material, and it is best represented in a conjugated system as the energy required to promote an electron from the highest occupied molecular orbital (HOMO) to the lowest unoccupied molecular orbital (LUMO) of the material. Since the energy input into π-conjugated polymer used in photovoltaics is desired to be minimal, synthetic chemists have been left with the task of engineering the

10,11,12,13 band gap . This entails minimizing Eg so that the promotion of an electron through the absorption of sunlight is a facile process. For high conductivity, a material that has an overlapping HOMO and LUMO is desired, since this would provide an Eg = 0, but as previously discussed Eg is not the only factor to consider when designing a material for a solar cell. Another important requirement includes having a spectral match for the material similar to the solar flux, or the most of intense wavelength of light provided by the sun and available for absorbtion. Other important parameters for the cell to consider, which dictate device performance, are the Isc, short-circuit current, and Voc, open-circuit

14,15 voltage . The Isc, which occurs when the potential is zero, describes the maximum amount of current capable of flowing through the device under no load. If a materials Eg is small, then it is possible to obtain a high level of conductivity for the material. The Voc occurs when the current is zero, and is the maximum potential for the cell. It describes the amount of charge recombination within a cell: if there is a large level of recombination

16,17 then the Voc will be small .It increases as Eg increases, and so to maximize the power output for a solar cell it is important to balance Eg so that Voc and Isc are maximized. If Eg is too small, then electron transfer may not occur from the polymeric material to the acceptor, and this would result in a low Voc. In order to find a material with optimal absorption properties and that balances Eg, Voc, and Isc, numerous aryl groups and substituents that provide extended conjugation have been explored.

Figure 1-3.Modifying the substituents of the polymer backbone.

Since synthetically modifying the π-conjugated backbone of the polymer is a direct route to altering the band gap, numerous variations have been made to the polymer backbone and this introduction cannot describe all of them for the sake of brevity, but some examples are provided. As seen with Figure 1-3, modifying the π-system of the polymeric material can be achieved by the incorporation of heteroatoms, such as nitrogen or sulfur, electron donating substituents, such as ethoxides, electron accepting substituents, such as benzothiadiazole, 1, and metal atoms forming an organometallic 5

polymer (OP). Adding alternating donor and acceptor units, D-A in Figure 1-3, in the π- system achieves a smaller Eg, through the combination of the respective donor and acceptor units’ frontier molecular orbitals (FMO)10. This can also be accomplished by forming a copolymer between PEDOT and 1, for example. The incorporation of metal atoms into a polymer system offers material properties not available to purely organic systems18,19.

When Hagihara introduced the coupling of arylacetylides onto a platinum(II) metal center in the late 1970’s, a new realm of conjugated materials chemistry opened up20-21. The inclusion of a metal complex into a conjugated polymeric material or conjugated system allows for unique advantages not available to regular conjugated polymers. The first is the facile manipulation of the electronics of a material through the variation of the metal center or the attached ligands. Variation of the ligands can alter the electronics directly, by serving as the chromophore or electrophore for the material, and they can alter the geometry of the complex, such as preference of a cis/trans isomer. The optical properties of these rigid molecular wires are the most attractive features of these materials and a reason for their current extensive investigation.

1.2 Pt-containing Poly(aryleneethynylenes)

It has been shown that the introduction of a heavier atom, i.e. relatively large atomic number, within the π-system can help to induce intersystem crossing, ISC, from singlet to triplet excited state via spin-orbital coupling22,23. This occurs because of the large magnetic moment resulting from the spinning nucleus of the heavy atom. The atom must be heavy so as to provide a magnetic moment large enough in magnitude to induce

a spin-flip of an electron allowing for an increase in the triplet excited state population.

Photophysically, the high population of triplet versus singlet within an organometallic polymer, due largely to spin-orbital coupling, is another attractive feature for modifying the excited state lifetimes, emission properties, and quantum efficiencies. Though the binding energy of the triplet state is larger than that of the singlet, the longer lifetime of the triplet state relative to the singlet makes materials with high triplet state populations attractive for photovoltaics8. From a synthetic standpoint, these polymers are readily accessible through established methods, such as Hagihara coupling outlined in

Figure 1-4.

PBu 3 CuI PBu3 Cl Pt Cl + Ar Pt Ar n PBu Amine 3 PBu3 3 2 4 N S S Ar = N

Figure 1-4.Hagihara coupling to prepare Pt-containing poly(aryleneethynylenes).

A popular choice for metal centers in organometallic polymers includes Ru(III),

Ir(III), and Pt(II). The metal center is chosen by the desired coordination complex and chemistry. While the incorporation of most group 10 metals can be found in various organometallic polymers, Pt(II) is frequently used due to its large atomic size, increasing the opportunity for dπ to pπ overlap with the attached ligands and the consequent spin- orbital coupling18,19,24,25. Typical ligands for Pt(II) organometallic polymers are arylacetylides. These can be added to the metal center through Hagihara coupling, and phosphine ligands, such as tri-n-butyl phosphine, are typically employed to stabilize the metal center.

The longest conjugation path within the Pt(II) arylacetylide polymers is the along the arylacetylide chain, largely due to the orbital overlap from the metal center and the acetylide linker. This has prompted extensive studying regarding the effect of modifying the aryl group of the acetylide linker18-19. By varying this, polymers with different electronic and physical properties can be obtained. Modification of the phosphine ligands has not been thoroughly explored, however, and most polymers simply incorporate the strong σ-donor, tri-n-butyl phosphine, to provide a metal center with a high electron density.

P(Bu)3 Pt n P(Bu)3

Figure 1-5. Pt containing poly(phenyleneethylynene).

For most of the Pt-containing poly(heteroaryleneethynylenes), the aryl linker serves as the chromophore of the polymer, and so its variation allows for the tuning of the

HOMO and LUMO levels. Early devices incorporating a phenylene spacer, see Fig. 1.4, achieved photon-to-current efficiencies of up to 2% after the addition of C60 to the polymer blend, as studied by Kohler and colleagues26,27. Quenching studies showed that the C60 quenched the triplet excited state, leading to charge separation despite the high binding energy of the triplet excited state. The long lifetime of the triplet excited state allows for excitons migration to the interface where charge separation is possible. This prompted the study for other architectures, shown in Figure 1-6, since such a large PCE was obtained for a very simple system, and the most evident way was to modify the aryl linker.

Figure 1-6.Variation of the aryl linker for organometallic polymers and oligomers.

It is important to know that the extent of conjugation is inherently limited with Pt- containing poly(heteroaryleneethynylenes), since the metal center can act as a road block for delocalization. This is due to the large difference in energy levels between the metals

6p and 5d orbitals and the organic fragments 2p, while overlap does occur it is inefficient28. This can make the HOMO more localized and not spread through the entire polymer backbone, and the photophysical and electrochemical properties of the polymer can greatly resembles those of the monomer24. Extended π-conjugation is best obtained with an aryl linker that has an extensive π-system, and the previously discussed synthetic

modifications to alter the band gap and material properties apply, such as the inclusion of donor-acceptor copolymers. Figure 1-6 highlights the variety of aryl linkers already studied.

Assuming the PCEs reported are for optimized devices, comparisons of these values along with the band gaps for the materials 5, 6, and 7 allow for the insight into the structure-property relationships of the material. As stated previously, a PCE of 2% was obtained for 526,27. This material was the benchmark for Pt containing poly(aryleneethylenes). Incorporating a donor-acceptor aryl linker, as seen in 6 and 7, provided band gaps of 1.85 eV and 1.84 eV, respectively24. These polymers were then incorporated into a blend with PCBM (1:4), which provided devices that yielded PCEs of

4.10% and 2.45%, respectively. It is interesting to note that the band gaps are very similar despite the incorporation of bithiophene in 7, which would presumably provide a narrower band gap due to the extension of conjugation. Also, despite having similar band gaps, the device performance for 6 is much greater than that of 7.

Given that PCBM, a C60 derivative, is the most widely used electron accepting material for BHJ type solar cells, an interesting idea is to directly link the donor material to the acceptor, and this was done in the Schanze group providing 829. This architecture provided a PCE of 0.056%, but it outperformed similar architectures that did not incorporate the C60 moiety. While the PCE is not as high as that for 6 and 7, this architecture shows the breadth of substituents explored in order to find a suitable material for these devices.

Of all the Pt containing poly(aryleneethylene) systems described, none have modified the phosphine ligand attached to the platinum metal center. Aside from the

incorporation of N-heterocycliccarbene ligands, modification of the phosphine ligands has been unexplored30. A simple modification that can provide changes in the electronic properties of the metal center is by substituting the traditional phosphine ligand, such as changing the tri-alkylphosphine for a tri-arylphosphole ligand. Phospholes have been used in numerous applications as ligands for metal complexes and can function as the chromophores for a variety of conjugated systems, but they have not been applied to any organometallic polymers.

1.3 Phosphole Oligomers

Relative to the aforementioned conjugated systems, the study of π-conjugated organophosphorus compounds has only begun recently31,32, and it is in its infancy in comparison to other heterocycles, such as thiophene, pyrrole, and furan, shown in Fig

1.7.

H H P N S O

phosphole pyrrole thiophene furan

Figure1-7.Common heteroacenes.

When compared to the other heterocycles, phospholes are a class of heteroacenes structurally similar to pyrroles, which have gained recent popularity as a material for organic optoelectronics. Unlike pyrroles, which are flat and aromatic, phospholes possess a pyramidal structure and possess a lower aromaticity, due to the insufficient n-π orbital interaction between the phosphorous and the dienemoeity33. Delocalization of electrons 11

within the phosphole ring arises from a σ*-π hyperconjugative interaction between the exocyclic bond between the phosphorous and its substituent and the diene moiety33.

The poor interaction between the phosphorous lone pair and the diene of the phosphole is a blessing and not a curse. It allows for synthetic modification at the phosphorous lone pair, such as metal coordination or chemical oxidation. The ability to modify the oxidation sate of the heteroatom is not found with other common heterocycles such as pyrrole or furan. An important application of modifying the phosphorous center is the tuning of orbital energies of the π-conjugated system. This allows for the facile preparation of a series of compounds that vary in the energies of their FMO.

The ability to modify the oxidation state of the phosphorous center is of great appeal, because it provides rapid access to a range in compounds, and depending on the electronic or physical properties of these oxidized derivatives there can be an increase in applications. Current applications of phospholes include catalysis, organic photovoltaics, and organic light emitting diodes31,32. The variety of applications is a driving force for the study of phospholes. This makes it imperative that the synthesis of phospholes is well understood, so as to allow for a wide variety of phospholes and their derivatives.

Most phospholes being currently studied typically contain fused ring systems and are functionalized in every position of the phosphole ring. The fused rings may allow for extended conjugation with the phosphole ring, incorporating an unsaturated system, or a saturated system, such as a carbocycle. Some phosphole oligomers that have undergone more extensive study are shown in Figure 1-8.This figure only highlights the substitution pattern for certain phospholes, it by no means show the breadth and variety of aryl groups or conjugated substituents incorporated into these scaffolds.

S S

Ph P Ph P Ph P Ph Ph Ph Ph 9 10 11

Figure 1-8.Fused ring system phosphole oligomers.

Each of the phospholes shown in Figure 1-8 has the 3 and 4 positions of the phosphole ring substituted. The reason for this is due to the synthetic method employed, which will be discussed. Those studied predominately by Réau, incorporate the aliphatic carbocycle moiety in the 3 and 4 positions of the phosphole ring, as seen with 934.

Baumgartner35 has popularized the fused aryl system, 10, and Matano36 and his colleagues have seemingly combined the systems popularized by Réau and Baumgartner by synthesizing phospholes with fused aryl rings in the 3 and 4 positions, but allowing for non-fused substituents in the 2 and 5, as shown with 11. Each phosphole system has its own intrinsic properties, but they are not very distinct. One system does not outweigh the other, and all have been extensively derivatized to yield the corresponding oxides, transition metal complexes, and incorporated into other conjugated systems or polymers.

The synthesis of phospholes has been well studied, and numerous methods are available37,33,31. The most widely used being: the McCormack reaction, aryl halide metalation cyclization, and Fagan-Nugent cyclization, which are outlined in Figure 1-9.

The McCormack reaction is a Diels-Alder type reaction occurring between a phosphine and a diene, in which a chlorophosphonium intermediate is formed during heating and

eliminated during the workup through the treatment with a base.

Aryl Halide Metallation Cyclization

1) RLi

2) PhPCl2 P Br Br 12 Ph 13 Fagan-Nugent Cyclization

R Cp2ZrCl2 PhPCl2 R R R R R n-BuLi Zr P 14 Cp Cp 15 Ph 16 McCormack Reaction

R PhPCl2 R R P R  18 17 Ph

Figure 1-9. Synthetic methods for the preparation of phospholes.

The high temperatures and long reaction times necessary for the reaction to yield a desirable amount of phosphole product can lead to excessive byproduct formation, which diminishes the appeal of this method significantly38. Aryl bromide metalation cyclization proceeds with first a lithium halogen exchange on the aryl bromide substituents, 12, followed by the addition of a halophosphine to annulate the aryl groups and form the phosphole product, 13. The Fagan-Nugent cyclization incorporates acetylenes, 14, and a low-valent metal species, generated in situ, to form the cyclometalated intermediate, 15.

A halo phosphine is then added to this to form the phosphole product, 16, after undergoing transmetalation with the metallacycle. Réau and colleagues have shown the utility of the zirconacene for the Fagan-Nugent method, while Matano has generated a large catalog of phospholes using the Fagan-Nugent method, but employing a titanium(II) isopropoxy species generated in situ from titanium(IV) isoproxide rather than a

zirconacene species. As mentioned above, the arylhalide metalation cyclization and the

Fagan-Nugent method require the use of highly reactive reagents for their synthetic schemes, and these can be costly and difficult to handle. Of these methods listed, the only one known to provide 3,4-unfunctionalized 1,2,5-triarylphospholes without the employment of an organometallic reagent is the McCormack reaction, which only requires heating of the butadiene in the presence of a dichlorophosphine to yield the phosphole product, 18.

Matano and Imahori have extensively studied phospholes incorporating extended

π-systems from the 3 and 4 positions of the phosphole ring, as seen in Figure 1-10. They reported the tunability of the fused π-backbone by studying bithiophene and napthalene fused phospholes, prepared using the Fagan-Nugent method36,39-40.

S S S S S S

Ph Ph Ph Ph P Ph P Ph P Ph Ph Ph 19 20 21

Ph Ph P Ph Ph P Ph P Ph Ph Ph Ph 22 23 24

Figure 1-10.Fused bithiophene and napthalene [c]-fused phospholes.

The interest in these conjugated systems stems from the tunability of the phosphorous center, mentioned above, and the recent developments of phosphorous materials,

specifically as potential candidates for n-type semiconducting materials. These [c]-fused phospholes have not yet become the subject of study for other researchers due to their intrinsic instability.

Compound λabs/nm (log ε) λem (nm) Eox(V) Ered(V) Eg (eV) 19 462 (3.89) 600 0.45 -2.14 2.59 20 395 (3.36) 548 0.66 -2.35 3.01 21 472 (3.66) 609 0.47 -2.09 2.56 22 399 (4.12) 480 0.64 -2.38 3.02 23 404 (4.23) 482 0.52 -2.42 2.94 24 464 (3.89) - 0.74 -1.76 2.50 Table 1-1.Photophysical and Electrochemical data for [c]-fused phospholes. Measured in 36,39-40 DCM using Bu4NPF6 and ferrocene as an internal standard . Altering the connectivity of the fused aryl group and the extent of the conjugation can lead to changes in the electronics of the phosphole as a result, as shown in Table 1-1.

It is evident that 19 and 21 have similar electronic properties, only differing very slightly.

This is likely due to the α-position of the bithiophene being directly connected to the phosphole π-system, which highlights the dependence of the connectivity of the aryl substituents to the phosphole ring on the observed electronic properties. To further this point, 20 has great variations in both its photophysical and electrochemical properties relative to 19 and 21. Stabilization of the HOMO and destabilization of the LUMO is shown both by a blue shift in absorption and emission properties and the increase in both oxidation and reduction potentials, which implies an increase in band gap for 20. This can be attributed to the better delocalization of electrons within the π-system for 19 and 21.

To highlight the effects of modifying the aryl groups identity, when the fused aryl group is altered from bithiophene to napthalene, an overall blue shift in absorption and emission is observed, the Stoke’s shift becomes narrower, and the electrochemical band gap increases. The only exception is compound 20, which shares similar absorbance and 16

electrochemical properties as compounds 22 and 23.

Matano and Imahori also studied phosphole systems incorporating multiple fused naphthalene rings to the phosphole40, shown in Figure 1-11. This provides a phosphole with a highly extended π-system accessed readily using aryl bromide metalation cyclization, and it provided a class of compounds they wanted to explore after fusing one naphthalene ring to a phosphole, as shown above.

Figure 1-11.Diacenanaptho[1,2-b:1’2’-d]phospholes.

The sulfide is shown to highlight the effect of oxidation of the phosphorous center on the electronic properties of the phosphole.

Compound λabs/nm (log ε) λem/nm Eox (V) Ered(V) Eg (eV) 25 539 (3.72) 622 0.28 -1.76 2.04 26 587 (3.54) 678 0.66 -1.36 2.02 Table 1-2. Photophysical and Electrochemical data for Diacenanaptho[1,2-b:1’2’- 40 d]phospholes. Measured in DCM using Bu4PF6 and ferrocene as an internal standard .

As seen in Table 1-2, fusing two naphthalene rings to the α and β carbons of the phosphole remarkably alters the electronics when comparing 25 and 26 to phospholes 19-

24 shown in Table 1-1. This is due to the due to the extension of conjugation through the phosphole ring. There is an overall red shift observed for the absorption and emission, and the electrochemical band gap greatly decreases. Oxidation of the phosphorous center

shows a further red shift in the optical properties, and the HOMO and LUMO are stabilized almost equally, relative to 25. It should be noted that all of the reductive features for the phospholes discussed (19-26) were reversible, which highlights the potential utility of these materials as n-type semiconductors31.

Réau and coworkers directed their attention to the study of 2,5-substituted phospholes, but their phospholes incorporate a carbocycle fused in the 3 and 4 positions of the phosphole ring, shown in Figure 1-12. These phospholes are readily prepared using the Fagan-Nugent method, which was an appeal for their study34,41-42.

S P P P S Ph Ph N Ph N 27 28 29

S P S N N P Ph S O S Ph 30 31

Figure 1-12. 2,5-bis(aryl)phospholes studied by Réau.

These phosphole systems are again of particular interest since, as shown above, altering the connectivity of the phosphole’s substituents can induce dramatic changes in the electronic properties. From a qualitative perspective, the orbital overlap and inclusion within the π-system is minimized when compared to the fused ring systems described above.

Compound λabs/nm (log ε) λem/nm Eox (V) Ered (V) Eg (eV) 27 354 (4.20) 466 0.40 -2.88 3.28 28 412 (3.93) 501 0.69 -2.10 2.79 29 390 (4.02) 463 0.83 -2.45 3.28 30 427 (4.43) 579 1.10 - - 31 434 (3.97) 556 1.26 - - Table 1-3.Photophysical and electrochemical data for selected 2,5-bis(aryl)phospholes. 34,41-42 Measured in DCM using Bu4NPF6 and ferrocene as an internal standard .

From the selected photophysical and electrochemical data in Table 1-3, definite trends are established based on the aryl group. Compound 28 shows a red shift relative to the pyridyl and phenyl containing phospholes, 27 and 29, respectively, which display similar photophysical properties. Also, the electrochemical band gap of 28 is lower than

27 and 29. This data signifies the more efficient orbital overlap of the thienyl substituent with that of the phosphole ring, allowing for more efficient electron delocalization within the π-system. Compound 30 has interesting structural features since it contains a mixed donor and acceptor system where the donating thienyl groups are connected into the accepting pyridyls, and it shows a red shift and a more stabilized HOMO, based on the higher anodic peak potential, relative to phospholes 27-29. Oxidizing the phosphorous center of 28 affords 31, which displays a red shift and more stabilized HOMO relative to its parent phosphole. Polymer films were prepared from compound 31 by electrochemical oxidative polymerization onto a platinum disk electrode. These films showed a more stabilized HOMO at 1.38 V, which is not typical for conjugated polymers where the

HOMO is typically destabilized due to the extension of conjugation of the π-system. It

should be noted that the cathodic peak potentials were not reported for compounds 30 and

31.

Baumgartner and coworkers explored the fused biaryl phospholes shown in

Figure 1-13. These phospholes are of interest because they explore another method

S S S S

N N N P P P Ph Ph Ph 32 33 34

S S S S

N N N P P P Ph O Ph O Ph O 35 36 37

Figure 1-13. Fused bi-aryl phospholes and derivatives. of substituting a phosphole ring, and they can be prepared in high yields using the aryl halide metalation cyclization35, 43-44. These phospholes are not classical in the sense that the lone pair on phosphorous exhibits minimal delocalization within the π-system. This is because the bi-aryl units will maintain aromaticity without the inclusion of the phosphorus lone pair. Baumgartner and his colleagues almost exclusively work with the bi-thienyl phosphole, 32 and 35, and have not sought to study the bi-phenyl analogue.

They have recently reported phospholes containing the bi-thiazole, 33 and 36, and pyridil-phenyl, 34 and 3745. An exhaustive catalogue of phospholes have been created incorporating these substituents with variations on the aryl groups and phosphorous center, aside from those shown above.

Compound λabs/nm (log ε) λem/nm Eox (V) Ered (V) Eg (eV) 32 344 (4.26) 422 1.35 - - 33 322 (3.86) 396 - - - 34 - - 1.13 -2.67 3.80 35 374 (4.09) 460 1.59 - - 36 350 (3.58) 396 - -1.90 - 37 280 (4.17) - - -2.27 - Table 1-4.Photophysical and electrochemical data for compounds 32-37. Measured in DCM versus SCE35, 43-44. The data shown in Table 1-4 highlights the dramatic difference in photophysical and electrochemical properties the fused bi-aryl phospholes possess relative to the others reported above. This can be attributed to the lack of classical phosphole character these materials possess, since the π-system is limited to the extent of the aryl substituents. The thienyl containing phosphole, 32, shows a notable red shift in its photophysical properties relative to 33, and its HOMO is destabilized relative to that of 35. Compound 34 showed no photophysical activity, and it was reported that it oxidized too rapidly to allow for proper measurement. Electrochemical data for compound 34 shows that the HOMO and

LUMO are both lower in energy than the other fused bi-aryls, 32 and 33. The oxidized derivatives, 35-37, show similar trends observed where a red shift is observed in absorbance and emission; however, compound 37 did not emit. Electrochemically, the

HOMO or the LUMO for the oxidized derivatives are stabilized relative to the parent phospholes.

Given the extensive study of the fused ring phospholes described above, little attention has been paid to 1,2,5-triarylphopholes that do not incorporate fused ring systems. To provide a more complete understanding of the effects of substitution on the electronics of the phosphole ring, it is necessary for these materials to be synthesized, 21

derivatized, and characterized. The phosphole ligands can be appended to a platinum metal center to yield a platinum complex, which can be polymerized using Hagihara coupling to form the Pt-containing polyphenylene acetylene polymers. The effects on the electronic properties due to polymerization and complexation relative to the free ligand can then be used to establish structure-property relationships the trends associated with synthetic modification.

Chapter 2. Synthesis of PhospholeOligomers and Derivatives.

2.1 Synthesis of Butadienes.

The McCormack reaction was chosen to access 1,2,5-triarylphospholes because it is a relatively inexpensive reaction, since it does not require any organometallic reagents only the diaryl butadiene and the haloarylphosphine. The diarylbutadienes, 17, can be accessed synthetically with a variety of methods and routes as outlined in Figures 2-1 and

2-2.

Figure 2-1.Synthesis of butadienes via silane-homocoupling.

Figure 2-2. Synthesis of butadienes via Wittig olefination.

The high reactivity of an unsubstituted phospholes requires the substituents to be added to the phosphole starting materials prior to the phosphole synthesis, as seen in the synthetic methods outlined in Figure 1-9. Preparing these materials using a route that employs a Wittig olefination as a final step to yield the desired butadiene, as shown in

Figure 2-2, is the most conventional. However, this route is relatively inefficient in that there is no common starting material if the production of a catalogue of butadienes is desired, requiring the synthesis of each acrolein for a respective aryl substituent.

To alleviate the necessary synthetic steps and to rapidly access the butadiene starting materials, the synthetic route outlined in Figure 2-1 was chosen46. This route requires the same number of steps overall as the scheme outlined in Figure 2-2, but employs 2-pyridyldimethyl(vinyl)silane, 40, as a common starting material. Once the synthesis of 40 is accomplished, the synthesis of a specific butadiene is reduced to two steps. This helps to expedite the synthesis of the butadiene starting material and reduce the amount of chemical waste and time spent due to additional synthetic steps. Following

Figure 2-1, the lithiation of 2-bromopyridine followed by the addition of

2-chlorodimethyl(vinyl)silane afforded 40 in 60% yield. With that in hand a catalogue of olefins, 41, were prepared using Heck coupling. This was followed by a copper mediated homocoupling to prepare 17, in accordance with the procedure outlined by Yoshida46.

Our results for the Heck coupling are outlined in Table 2-1.

Heck coupling is a useful procedure for preparing a variety of substituted olefins when starting with an aryl or vinyl halide and alkene using a palladium catalyst, and the catalytic cycle as well as the scope of the reaction has been extensively explored47.Though the reported procedure was followed, the scope of this reaction

scheme needed to be explored in order to access an expansive catalogue of butadienes46.

Olefins substituted with aromatic heterocycles, such as pyridine or thiazole were not pursued in the report. Tetrasubstituted butadienes incorporating the 4-anisole and 4- fluorophenyl substituents were previously prepared using this procedure, but tetrasubstituted butadienes are not useful for phosphole synthesis; however, it was presumed that this route can be used to prepare the disubstituted butadienes for the aforementioned aryl groups.

Entry R Ligand Time (hr) % yield 1 Iodo-4-anisole Tri-2-furyl phosphine 24 60 (41a) 5 3-iodothiophene Tri-2-furyl phosphine 24 70 (41b) 3 2-iodopyridine Tri-2-furyl phosphine 24 N.R. 4 2-iodopyridine Tri-t-butyl phosphine 24 N.R. 2 Iodo-4-fluorophenyl Tri-2-furyl phosphine 24 40 (41c) 6 Bromothiazole Tri-t-butyl phosphine 24 N.R. 7 2-bromopyridine Tri-t-butyl phosphine 24 N.R. 8 Bromo-4-fluorophenyl Tri-2-furyl phosphine 24 N.R. 8 Bromo-4-anisole Tri-2-furyl phosphine 24 N.R. 9 3-Bromothiophene Tri-2-furyl phosphine 24 N.R. Table 2-1. Synthesis of aryl substituted pyridyldimethyl(vinyl)silanes. N.R. = no reaction.

The first attempts to prepare the olefins used arylbromides, as seen in Table 2-1 entries 6 to 9. The unreactive nature of the bromine containing substrates was attributed to the inability of the arylbromide to oxidatively add to the active palladium catalyst and enter the catalytic cycle. This appeared to be true when aryliodides afforded the desired product. Tris(2-furyl)phosphine was chosen as the ligand because it led to better yield than other phosphine ligands, such as triphenyl phosphine, most likely due to its

relatively stronger lone pair donating property, as reported in the literature48.

The reaction time of 24 hours provided the best results for most of the aryl iodides, even if conversion was not 100%. This is because as the amount of product increased in the reaction mixture, the likelihood for it to reenter the catalytic cycle increased and produce the diaryl olefin. This byproduct was encountered frequently with the 4-fluorophenyl and 4-anisoleiodides. Further extending the reaction time also lead to isomerization of the olefin product from trans to cis. However, this was not as detrimental to the reaction yield because the cis/trans mixtures of products could isomerize to the desired stereochemistry in subsequent steps.

Figure 2-3.Palladacycles potentially derived from 2-pyridylhalidesand 2-thiazolehalides.

This methodology could only be applied to a limited number of aromatic heterocycles (entry 2).For any heterocycle where a nitrogen atom was present alpha to the halogen substituted carbon there would be no reaction. To account for the lack of reactivity with these nitrogen containing heterocycles, it was theorized that after oxidative addition the following complex would dimerize to form a palladacycle, shown in Figure 2-3 with 47 and 48, which has been shown to occur with similar palladium complexes49. This is likely, since the nitrogen atom possesses a lone pair available for coordination to a metal center, and the dimerization to form the palladacycles shown above leads to an increase in entropy and is therefore energetically favorable. In an

attempt to avoid this, the strong lone pair donor tri-t-butylphosphine was chosen as a ligand in an effort to provide greater stability to the oxidized palladium(II) intermediate.

This ligand also has bulky t-butyl groups pendant to the phosphorous, which may sterically crowd the metal center and prevent dimerization through steric repulsion.

Unfortunately, modifying the ligand still resulted in no reaction, and the pursuit of the aza compounds would be done using the alternative Wittig route (Figure 2-2).

With the aryl substituted pyridyldimethyl(vinyl)silanes, 41a-c, in hand, the next step was to perform the copper mediated homocoupling to yield the respective butadienes, 17a-c. It required an excess of copper iodide and the fluoride salt. While there has not been a mechanistic study for this reaction, the theory is the homocoupling occurs through first a coordination of the alkene and the nitrogen lone pair to the copper metal.

In the procedure followed, isolation of this intermediate as a dimer was successful, shown in Figure 2-446. Treatment with a fluoride salt promotes transmetalation of the olefin from the silane to copper to form an alkenyl copper species. This then undergoes homocoupling to yield the butadiene product, and Table 2-2 outlines these results.

Figure 2-4.Copper mediated homocoupling of substituted pyridyldimethyl(vinyl)silanes.

Entry R Time %yield 1 4-anisole (hr)24 20 (17a) 2 3-thienyl 24 35 (17b) 3 4-fluorophenyl 24 25 (17c) Table 2-2. Experimental data for the homocoupling of pyridyl(vinyl)silanes.

As the above figure shows, the optimized yields were low to moderate for the homocoupling steps, but the yield obtained for 3-thienyl, entry 2, is close to that reported

(40%). Since the exact mechanism is not known, it is difficult to postulate what hinders the yield for the 4-anisole and 4-fluorophenyl substituted butadienes. A theory based off of experimentation, is that the butadiene product coordinates to the copper metal. This is because a large volume of insoluble material formed as the reaction proceeded, and isolation of this material followed by treatment of this material with KF did not yield any product, which would be expected if this material is not the copper dimer intermediate.

The 24 hour reaction time is required since the conversion of starting material is slower in using KF as a fluoride source. Potassium fluoride was chosen because cesium fluoride is extremely hygroscopic in comparison, and dry reaction conditions are required. Using cesium fluoride outside of a dry box, the isolated yields were <10%. Limiting the possible inclusion of adsorbed water during transfer from the balance to the reaction flask significantly improved the yield.

Since the pyridyl functionalized butadienes were not accessible using the methods described above, a different synthetic route other than the one provided, such as the established Wittig route shown above in Figure 2-2. The Wittig reaction is a classic, well studied method used to prepare substituted olefins50. At first, the synthesis of 43 was attempted through aldol condensation of 42 with acetylaldehyde, but the sensitivity of the acrolein product or the pyridylcarboxaldehyde starting material to basic conditions

restricted this, since no product or starting material could be recovered from the reaction.

Obtaining the 4-pyridyl acrolein using a literature procedure that employs Wittig reaction with (triphenylphosphoranyldiene)actylaldehyde, as shown in Figure 2-2, was successful51. The Arbuzov reaction yields 45 from 44, and the subsequent Wittig reaction between the acrolein and the phosphonate yields the 1,4-bis(4-pyridyl)butadiene, 17d. It was found that the order of the addition of substrates was crucial for the Wittig reaction between 45 and 43. If 43 was added before 45, no butadiene product was observed. This is likely again due to the decomposition of the pyridylacrolein under basic conditions.

2.2 Synthesis of Phospholes.

To prepare a catalogue of 1,2,5-triarylphospholes the already established

McCormack reaction was chosen as the synthetic route38.This method is advantageous because it allows for the synthesis of the phospholes under solvent free conditions, requiring only the butadiene and the dihaloarylphosphine, and in the absence of any organometallic reagent providing a lower cost; however, the current procedure requires the reflux of the dihaloarylphosphine (>200°C) and extended reaction times

(>10 hours)38. 1,2,5-triphenylphosphole was synthesized in this manner, and so expanding the scope of this reaction in order to build a library of phosphole ligands.

While this synthetic scheme appears quite simple in theory, the [1,5]-sigmatropic shifts that occur leading to dimerization, depicted in Figure 2-5, with substituted phospholes make this reaction complex. This mechanism proposed by Mathey52, highlights the transient nature of the phosphole sigma bonds.

Figure 2-5. Dimerization of 2H-phospholes.

These rearrangements are based on the pyramidal geometry the phosphorous center has within the phosphole ring. This allows for considerable overlap between σ-bond of the exocyclic P-R’ bond and the π* of the diene moiety of the phosphole. What was found, which makes these rearrangements undesirable, is that the rearranged products are inseparable from the parent phosphole. This is undesired because a high purity is required for accurate analysis of a materials photophysical and electrochemical properties. It was found that through the careful control of temperature and reaction time, these byproducts can be avoided.

Entry R R’ Method Time(hrs) Temp(°C) Yield % Purity 1 Phenyl Phenyl Conventional 15 210 50 >99 2 Phenyl Phenyl Conventional 60 150 22 100 3 Phenyl Phenyl Microwave 3 150 57 100 4 Phenyl Phenyl Microwave 1.5 190 65 100 5 2-Thienyl Phenyl Conventional 20 170 20 30 6 2-Thienyl Phenyl Conventional 90 150 13 >99 7 2-Thienyl Phenyl Conventional 120 130 2 100 8 2-Thienyl Phenyl Microwave 2 150 35 85 9 2-Thienyl Phenyl Microwave 5 135 40 85 10 2-Thienyl Phenyl Microwave 2 135 20 100 Table2-3. Dependence of phosphole yield and purity on the heat source.

As shown in Table2-3, the purity and yield of a desired phosphole product depends on the reaction time and the method of heating. The synthesis of 49a is established and is easily reproduced38.The synthesis of 49b using a conventional heat source was attempted, but the phosphole readily undergoes dimerization (Entry 5). If the temperature is lowered to avoid dimer formation, then the reaction time must be prolonged significantly resulting in unwanted oligomeric byproducts (Entry 7). This relates directly to the method of heating, since conventional heating results in a temperature gradient such that the walls of the reaction vessel are hot, but the center of the reaction mixture is significantly lower in temperature53.In order to invert this temperature gradient microwave heating is essential. In comparing entries 2 and 3, it is evident that microwave heating promotes higher yields in less time, since conventional heating yielded 22% phosphole product after 60 hours, while microwave heating provided a 57% yield at the same temperature in 3 hours. Given that microwave heating could allow for the access of phospholes unobtainable via the McCormack reaction using conventional heating, expansion of the scope of this reaction was desired. This was accomplished using the other butadienes for which the synthesis was previously discussed.

Desired Temp Time Yield Entry R R’ 49 : 50 : 55 Product (°C) (min) (%) 1 p-fluorophenyl p- fluorophenyl 49c 125 3 25 100 : 0 : 0 2 p-fluorophenyl phenyl 49d 120 2 27 41 : 0 : 59 3 p-fluorophenyl phenyl 49d 170 2 54 27 : 0 : 73 4 p-anisole p-anisole 49e 120 1 12 92 : 8 : 0 5 p-anisole phenyl 49f 135 1.5 36 62 : 0 : 38 6 4-pyridyl phenyl 49g 115 6 20 100 : 0 : 0 7 4-pyridyl p-anisole 49h 115 3 7 100 : 0 : 0 8 4-pyridyl p-anisole 49h 135 3 5 93 : 7 : 0 9 3-thienyl phenyl 49i 135 2 14 39 : 61 : 0 Table 2-4. Microwave assisted phosphole synthesis via McCormack reaction.

What was encountered in expanding the scope of this reaction were the rearranged products of the phosphole due to 1,5-sigmatropic shifts. The transient nature of the phosphole substituents prominent feature of this heterocycle, and are encountered when the phosphole is subjected to high temperature. These rearrangements have been studied in great detail, often using them to access other phosphole containing materials52. This was discovered based on additional resonances observed in 31P NMR, where the phosphole range is 0 to 10 ppm and the phosphole dimers appear around -10 to -20 ppm.

It was found, as seen in entries 2 and 3, that phenyl substituents migrated to form the rearranged phospholes, but resisted dimer formation. This rearrangement of phospholes was unavoidable, since a high temperature is required for product formation. The incorporation of heterocycles onto the phosphole gave only dimer byproducts, but no other rearranged byproducts. It was hypothesized that this byproduct formation follows a 32

similar pathway, shown in Figure 2-6, and that the mixtures contain the most stable rearranged products for the respective substituents.

Figure 2-6. Rearrangement of 1,2,5-triarylphoshpoles via 1,5-sigmatropic shifts.

Figure 2.6 details the proposed pathway for rearrangement leading to the product mixtures. Since the intermediates 52-54 and 56-58 in this pathway are non-aromatic, it is likely only the aromatic phosphole compounds shown in the figure were observed. Since the isolation of the individual rearranged products is not possible, the rearranged products are described cumulatively as compound 55 for the entries of Table 2-4. The aryl migration of the phosphole substituents in the 2 and 5 positions of the phosphole was observed through F-P coupling (J = 3 Hz) through the incorporation of the 4-fluorophenyl

moiety in the phosphole, entries 1 to 3 of Table 2-4. As shown in 19F and 31P NMR spectra (Figure 2-7 and Appendix A), coupling was only observed when a 4-fluorophenyl moiety was present on the phosphorus. This provides greater evidence that the compounds observed in the mixtures correspond to the structures proposed in the above figure.

Figure 2-7.31P NMR spectra showing rearranged phosphole byproducts for entries 5 (top) and 3 (bottom) of Table 2-4.

At lower temperatures (entry 2) a singlet at 3.46 ppm and a doublet at 0.40 ppm were observed in 31P NMR, but at higher temperatures (entry 3) a new singlet and doublet appeared at 3.09 and 0.04 ppm, respectively. The 31P NMR spectrum for entry 3 is shown above in Figure 2-7. Described in Figure 2-6, the additional resonances must correspond to an aryl migration from 49 to 55.At higher temperatures, enough energy is provided to promote further aryl migrations to form 59. Using the data provided from the 4- fluorophenyl substituents, it can be assumed that the p-anisole containing phospholes, entry 1 of Table 2-4, are in equilibrium between 49 and 55. This is assumed because of the relatively low reaction temperature and the large difference in chemical shift seen between the 31P resonances shown in Figure 18. The absence of dimer formation is very intriguing since that was the only byproduct observed for the 2-thienyl substituent (Table

2-3 entry 5). From this data, it is apparent that the hydrides are resistant to migration even at elevated temperatures, since the energy barrier to form 62 from 60 must be high due to exclusion of dimeric byproducts. This is indicative of the effect of orbital overlap between the σ-bond of the exocyclic P-R’ bond and the π* of the diene moiety of the phosphole.

Figure 2-8.31P NMR spectra showing dimer by products for entries 1(top) and 4 (bottom) of Table 2-4.

When the same phenyl based group was incorporated (entries 1 and 4), only dimer formation was observed and rearranged phosphole products, see Figure 2-8. This dimer formation could be suppressed in the case of the 4-fluorophenyl but not the 4-anisole 36

containing phospholes, even at the lowest temperature possible for product formation.

To counter the resistance for hydride migration encountered with the phenyl containing phospholes to form the 1H phosphole, 58,hydride migration was preferred for the heterocyclic containing phospholes (entries 6-9) as evidenced by exclusive dimer formation, despite the mixed aryl systems. This highlights the reactivity of the intermediates in Figure 2-6, namely 58, and the preference for hydride migration relative to the aryl groups. The energy barrier to form 58 must be low for the heterocyclic containing phospholes relative to their phenyl counterparts. Suppressing the dimer formation was possible for the 4-pyridyl containing phospholes (entries 6 and 7), and while dimer formation could be avoided for the 2-thienyl containing phosphole it was unavoidable with the 3-thienyl moiety at the lowest product forming temperature (entry

9). To rationalize the observed experimental data, computational modeling of the energy of the transition states and intermediates is necessary for all of the aforementioned phospholes. This would provide the relative energies of the transition states, which would provide greater insight as to why certain aryl groups lead to different phosphole mixtures.

13C NMR Phosphole P-Aryl 1 2 1 2 3 4 Phosphole C2 JP-C C3 JP-C ipso JP-C o JP-C m JP-C p JP-C 49a 151.5 0 132.0 9.5 130.8 8.0 133.9 19.7 128.8 8.0 129.6 1.5 49b 143.6 3.6 131.7 7.3 131.2 13.1 134.1 20.4 129.0 8.7 130.1 1.5 49c 150.6 0 131.8 9.5 125.7 8.0 135.8 21.1 116.3 9.6 163.9 0 4 3 2 1 0 0 JF-C 3.6 JF-C 8.8 JF-C 20.6 JF-C 248.6 49g 151.5 0 135.0 9.5 128.0 7.3 134.0 20.4 129.3 9.5 130.7 2.2 49h 151.7 0 134.3 9.5 118.0 3.8 135.8 20.3 115.0 10.6 161.6 1.5 Table 2-5. Phosphole13C NMR chemical shifts and coupling constants for compounds 49a-h.

1H NMR Phosphole P-Aryl 3 3 3 4 4 3 3 5 Phosphole H3 JP-H o JP-H JH-H JF-H m JP-H JH-H JF-H p JP-H 49a 7.29 10.4 7.40 (m) 7.18 (m) 7.18 (m) 49b 7.08 10.0 7.50 (m) 7.29 (m) 7.29 (m) 49c 7.18 10.6 7.34 0.8 8.8 5.5 6.90 0.8 8.8 8.8 - 49g 7.53 9.5 7.33 (m) 7.24 (m) 7.33 (m) 49h 7.48 9.5 7.26 8.8 8.8 6.76 1.0 8.8 - Table 2-6. Phosphole1H NMR chemical shifts and coupling constants for compounds 49a-h.

Aside from establishing trends as to the rearrangement pathways for the desired phosphole product, NMR was a useful tool in establishing trends in chemical shifts for the isolated 1,2,5-triarylphospholes. The carbon and proton assignments were configured based on extensive 1D and 2D NMR experimentation (see Appendix A). Tables 2-5 and

2-6 show the trends observed regarding the chemical shifts and coupling constants associated with the NMR spectroscopic data. This data highlights the major trends associated with each phosphole NMR spectra, helping for compound identification, and allows for easier detection of the exceptions to these trends. For example, as shown in

Table 2-5, the C2 carbon of the phosphole ring is ~151 ppm, but the C2 carbon for phosphole 49b is furtherupfield at 143.6 ppm, and it is a doublet (J = 3.6 Hz). The 38

chemical shifts for the C3 carbon for each phosphole are very similar and a similar coupling constant (J = 9.5 Hz) is observed, excluding 49b for which J = 7.6 Hz. The chemical shifts of the carbons not included in the phosphole ring were dependent on the identity of the aryl group, but similar coupling constants were observed due to P-C coupling. For the aryl group pendant to the phosphorus, a similar coupling constant was observed for the ortho, meta, and para carbons where J = 19.7-21.1, 8.0-10.6, and 1.5-2.2

Hz, respectively. For the aryl group attached to the C2 carbon, similar coupling constants, due to P-C coupling, were observed despite the differences in substituents. For the ipso and ortho carbons, coupling constants where J = ~17-20 and 7.3-9.5 Hz were observed, respectively. A similar trend was observed for the 1H NMR spectra outlined in Table 2-6, specifically regarding H3 or the proton attached to C3 of the phosphole ring. The chemical shift was between 7.08 – 7.48 ppm, depending on the aryl group attached to the phosphole, but due to coupling with the phosphorus atom a doublet was observed with J

= 9.5-10.6 Hz. Establishing the trends associated with the NMR spectra allows for the easier assignment of future 1,2,5-triaryl phospholes.

2.3 Synthesis of Phosphole Derivatives.

The ability to further functionalize the phosphole oligomers by oxidation or metal coordination has garnered most of the appeal of these aromatic heterocycles. The phospholes chosen to form the corresponding oxides were the phenyl, tris(4- fluorophenyl), and 2-thienyl containing phospholes. Platinum(II) dichloride complexes were prepared for the phenyl and thienyl containing phospholes.

3 1 2 Entry R R’ Yield (%) JP-H (Hz) JP-C (C1) JP-C (C2) 1 phenyl phenyl 70% 37.2 94.7 27.2 2 thienyl phenyl 90%(%) 36.0 95.4 25.8 3 fluorophenyl R’=R 82% 37.6 95.6 29.2 Table 2-7. Experimental and NMR data for phosphole oxides 60a-c.

The oxide derivatives were prepared by treating with H2O2, which is outlined in

Table 2-7. The strong desire for the phosphorous center to be oxidized, even under ambient conditions, makes this a facile and relatively high yielding reaction. Comparison of the 31P NMR spectra of the phosphole and its oxidized derivative, shows the large deshielding effect the addition of the electrophilic oxygen moiety has on the phosphorous center since oxidation shifts the 31P resonance to ~ 40 ppm. This provides insight into the highly polarized nature of the phosphorous-oxide bond. For the newly synthesized phosphole oxides 60b and 60c, the 31P chemical shift aligns well with that of the already known 1,2,5-triphenylphosphole oxide (see experimental). An almost fourfold increase in

3 JP-H coupling constant is also observed, when comparing to the values in of Table 2-6 to

2-7, seen as a well-defined doublet. Similar to the phosphole precursors, these values help to provide characterization tools for future phosphole oxides and show the effect of

synthetic modification on the observed spectral features.

31 1 Entry Ar Yield (%) P (ppm) JPt-P(Hz) 1 phenyl 70 22.7 2519.2 2 2-thienyl 90 29.0 2571.0 Table 2-8.Synthesis of Pt complexes 61a,b.

The synthesis of the phosphole containing platinum(II) dichloride complexes, outlined in

Table 2-8, was more challenging than the oxide derivative. Due to the lack of dissolving groups, the phosphole is generally only soluble in chlorinated solvents and sparingly soluble in more polar solvents, such as ethanol. The solvent system found to work best, after attempting literature procedures that failed to yield the complex54, was to spin the

55 phosphole ligand with the platinate salt in a DCM/H2O elmusion . The complex precipitated out and could be filtered off, and it required no further purification. The complexes of the phenyl and thienyl containing phospholes were targeted for synthesis due to the availability of these ligands.

22.3 29.1

J = 2519 Hz J = 2571Hz

61a 61b

Figure 2-9. 31P NMR spectra for Pt complexes 61a and 61b.

Comparing the 31P NMR spectra of the phosphole ligand and the corresponding complex, as seen in Figure 2-9, the deshielding effect of the platinum(II) metal center most apparent since the value for the chemical shift has changed by ~20 ppm when compared to the free ligand. Satellite coupling signals due to the JP-Pt coupling can also be seen flanking the major phosphorous resonance forming a doublet. The coupling between the

P and Pt centers is convenient because the size of the coupling constant can be correlated to the geometry of the complex. Typically, cis-phosphole platinum(II) dichloride complexes exhibit a JP-Pt coupling constant of ~3000 Hz, and the trans complexes are

~2500 Hz56,57. The coupling constants observed, as shown in Figure 2-9, are signifying a trans geometry for the complexes since they are close to 2500 Hz. Knowing that they are trans rather than cis is incredibly important, not only for compound characterization, but because obtaining the trans geometry is essential for the production of a more linear polymer chain in the subsequent Hagihara coupling. From the proton spectra, similar resonances appeared for the complex as that of the free ligand, but they were more

3 downfield and the large doublet due to JP-H coupling was absent.

Chapter 3. Electrochemical Characterization of Phospholes.

In order to obtain the energy values of the FMO and to observe the change in these energy levels through synthetic modification, electrochemical data must be obtained. Using cyclic voltammetry, the redox features of a material can be observed, as long as they are within the potential window governed by the solvent used for the measurement. Through cyclic voltammetry, electrochemistry provides the absolute energy levels for the LUMO and HOMO, and these are important since electron transfer between various materials is an important part of electronic devices. This is most relevant in photo-induced electron transfer found in heterojunction solar cells between the electron donating conjugated polymer and the electron accepting material. It is imperative to have a donor material where the LUMO is higher in energy than the LUMO of the acceptor material (Figure 1-2). This helps to ensure that the electron transfer from the donor to the acceptor material is an energetically favorable process. In this fashion electrons and holes can be shuttled to their respective electrodes.

Obtaining electrochemical data allows for insight into the structure-property relationships of the material, or how the electronics of the material are influenced by substitution and functionalization, and this is crucial in tailoring new materials for electronic applications. It allows for a more systematic approach, rather than random, to the design of new classes of materials. In terms of the materials synthesized above, the main interest is in how the energy levels of the FMOs change from the butadiene, to the phosphole, to the oxidized derivatives.

-5

-10

-15

-20 Current(uA) -25

-30

-35 17b

1 0 -1 -2 Potential (V)

-10 Current(uA)

-20 49b

-30 1 0 -1 -2 Potential (V)

-10 Current(uA) -20

-30 60b

-40 1 0 -1 -2 Potential (V)

Figure 3-1. Cyclic-voltammograms of compounds 17b, 49b, and 60b. Measured in MeCN using Pt disk working electrode, Bu4NPF6 as the supporting electrolyte, and ferrocene as an internal standard.

Compound Ar Eox (mV) Ered1 (mV) Ered2 (mV) Eg (eV) 17a 920 - - - 49a 854 -2265 - 3.12

60a 1120 -1770 -2360 2.89 17b 597 - - - 49b 635 -2070 - 2.70 60b 848 -1775 -2258 2.62 17c 803 - - - 49c 875 -2274 - 3.15 60c 1187 -1761 -2179 2.95 Table 3-1. Electrochemical data for butadienes17a-c, phospholes 49a-c, and phosphole oxides 60a-c. Measured in MeCN using Pt disk working electrode, Bu4NPF6 as the supporting electrolyte, and ferrocene as an internal standard. As seen in Figure 3-1 and Table 3-1, annulation of the butadienes, 17a-c, to form the phospholes, 49a-c, and then oxidation of the phospholes to the corresponding oxides,

60a-c, changes the FMO energy levels. The general trend observed for each aryl group is a stabilization of the LUMO as a consequence of synthetic modification. The thienyl functionalized series is only shown for brevity, but the remaining cyclic-voltammograms can be found in the appendix (A-27). For all of the butadienes, only an oxidative feature is observed within the potential window. Annulation to form the aromatic phosphole ring, provides stabilization of the LUMO and of the HOMO; however, annulation of the phenyl functionalized butadiene, 17a, to form the corresponding phosphole, 49a, resulted in destabilization of the HOMO. Oxidation of the phosphole and the consequent loss of aromaticity stabilizes both the HOMO and LUMO when compared to the butadienes and the parent phospholes, but the LUMO is stabilized more resulting in a decrease of the bandgap.

-10 Current(uA) -20

-30 49a -40 1 0 -1 -2 Potential (V)

-10 Current(uA)

-20 49b -30 1 0 -1 -2 Potential (V)

-10

-20 Current(uA)

-30

-40 49c -50 1 0 -1 -2 Potential (V)

Figure 3-2. Cyclic-voltammograms of compounds 49a-c. Measured in MeCN using Pt disk working electrode, Bu4NPF6 as the supporting electrolyte, and ferrocene as an internal standard.

Modifying the functional group pendant to the 2 and 5 positions of the phosphole ring, i.e. phenyl, thienyl, or 4-fluorophenyl, results in changes in the redox potentials, as seen in Figure 3-2 and Table 3-1. The thienyl functionalized compounds, 17b, 49b, and

60b, show lower values for oxidation and reduction potentials relative to the phenyl based compounds. The result is a decrease in band gap for the thienyl functionalized phospholes and phosphole oxides relative to the phenyl and 4-fluorophenyl functionalized compounds. The phenyl and 4-fluorophenyl functionalized compounds show relatively similar values in potentials for their corresponding phospholes and phosphole oxides, but not the butadienes for which the phenyl shows a more stabilized HOMO.

Compound Eox (mV) Ered1 (mV) Eg (eV) 49a 854 -2265 3.12 49b 635 -2070 2.70 49c 875 -2274 3.15 27 400 -2880 3.28 28 690 -2110 2.79 Table 3-2. Electrochemical data for phospholes 49a-c and 27 and 28. Measurements for phospholes 49a-c were performed in MeCN using Pt disk working electrode and Bu4NPF6 as the supporting electrolyte. Measurements for 27 and 28 performed in DCM using Pt disk working electrode and Bu4NPF6 as the supporting electrolyte. All potentials were referenced using ferrocene as an internal standard.

When comparing the values for the HOMO and LUMO levels, as well as the

34,41-42 electrochemical bandgap (Eg), to other known phosphole systems , there are some

interesting differences. Phospholes 27 and 28 are very structurally similar to the phospholes 49a and 49b, but they contain an aliphatic carbocycle in the 3 and 4 positions of the phosphole ring. And while this substitution may seem insignificant, it does have effects on the observed electrochemical properties. As shown in Table 3-2, the values obtained for oxidation for phospholes 27 and 28are 400 and 690 mV, respectively. These values differ from the phospholes 49a,b synthesized in this report employing the same aryl groups, for which 854 and 635 mV was obtained, respectively. It is unclear how the carbocycle can have such a significant destabilizing effect on the HOMO of only the phenyl containing phosphole, while the thienyl containing phosphole remains similar to

49b. The reduction potentials for the phenyl, 27, and thienyl, 28, phospholes are -2880 and -2110 mV, respectively. The LUMO for phosphole 27 is destabilized relative to 49a by 600 mV. The differences in potential, however slight, widens the bandgap for phospholes 27 and 28, relative to 49a and 49b, to 3.28 and 2.79 eV, respectively.

1.0 1.0

0.8 0.8

0.6 0.6

0.4

0.4 A) 

0.2

0.2 Current(uA)

Potential ( Potential 0.0 0.0

-0.2 -0.2

61a -0.4 61b -0.4 1.0 0.5 0.0 -0.5 -1.0 -1.5 -2.0 -2.5 1.0 0.5 0.0 -0.5 -1.0 -1.5 -2.0 -2.5 Potential (V) Potential (V)

Figure 3-3. Cyclic-voltammograms of complexes 61a,b. Measured in DCM using Pt disk working electrode, Bu4NPF6 as the supporting electrolyte, and ferrocene as an internal standard.

Compound Eox (mV) Ered1 (mV) Eg (eV) 61a - -1889 - 61b 674 -1687 2.36 Table 3-3. Electrochemical data of complexes 61a,b. Measured in DCM using Pt disk working electrode, Bu4NPF6 as the supporting electrolyte, and ferrocene as an internal standard.

Figure 3-3 and Table 3-3 display the voltammograms and electrochemical data of the platinum(II) complexes for the phenyl and thienyl containing phospholes, compounds

61a and 61b. The experiments were conducted in dichloromethane, due to the extremely low solubility of the complexes in non-halogenated solvents. This narrows the potential window greatly and, as a consequence, the oxidative peak potential for the 61a series is not observed. The complex 61b still has an oxidative feature in the solvent window at 674 mV, and is comparable in energy to the free phosphole ligand. This oxidative feature is most likely attributed to the thienyl moiety of the phosphole. The reversible reductive feature is absent for both complexes, and for complex 61a only one reductive feature at -

1889 mV is observed while complex 61b has two at -1687 mV and -1844 mV. This can be attributed to the greater stabilization between the thienyl and phosphole, due to the near match in orbital energies between the thienyl groups and the phosphole ring33.

Platinum (II) complexes for tri-aryl phospholes have not been studied electrochemically so there is no precedent for comparison; however, metal coordination provides a similar shift in potentials relative to the phosphole ligand as oxidation. Thus, the reduction most likely corresponds to a reduction of the phosphole ligand. If it was the metal center being reduced directly, then the electronic effects the ligand have on the metal center would shift the peak potential values. The complex 61a, having a weaker donor aryl substituent than 61b, would show a less negative cathodic peak potential than 49

complex 61b, since the phosphole ligand for 61a would be withdrawing electron density from the metal center allowing for a more facile reduction process. This counters intuition, however, and the 31P NMR data presented above shows a more deshielded phosphorous center for 61b. This infers a stronger binding of the lone pair to the Pt(II) metal center for 61b due to the observed loss of electron density at the phosphorous center. The absence of reversibility is due to decomposition of the reduced species, which will be discussed in further detail in the next chapter.

0.2

0.0

-0.2

-0.4 A)

 -0.6

-0.8

Current ( Current -1.0

-1.2

-1.4

-1.6 1.4 1.2 1.0 0.8 0.6 0.4 0.2 0.0 -0.2 Potential (V)

Figure 3-4.Oxidative electropolymerisation ofphosphole oxide 60b (middle) and Pt complex 61b (right). The left panel shows decomposition of phosphole 49b from cycling the voltage. Measured in DCM using Pt disk working electrode, Bu4NPF6 as the supporting electrolyte, and ferrocene as an internal standard. Thiophene functionalized monomers and oligomers are of significant use in conjugated polymer chemistry, because they can be oxidatively polymerized very easily.

Figure 3-4 shows the utility of the thienyl substituent, since it can easily be polymerized using electrochemical oxidative polymerization. The voltammogram on the left shows the cycling of voltage for the parent phosphole ligand (49b) that leads to a decrease in the current density due to decomposition of the material at the electrode surface. If the phosphorous center is oxidized (60b) or coordinated to a metal (61b) polymerization will occur as a result of thiophene oxidation rather than decomposition. This is apparent in the middle and far right voltammograms for the phosphole oxide and the Pt complex

derivatives, respectively. This is of utility because it allows for the facile polymerization of phosphole containing materials that possess the thienyl substituent, which can lead to an extension of the conjugated π-system.

Chapter 4. Phosphole-Pt Containing Poly(aryleneethynylenes).

4.1 Synthesis of Phosphole-Pt Containing Poly(aryleneethynylenes).

Entry Ar R Solvent Base Temp. Yield 1 Ph C8H15 Toluene Et3N 110 0% 2 Ph C8H15 ODCB i-Pr2NH 110 72% 3 Ph C8H15 ODCB Et3N 110 0% 4 Th C8H15 ODCB i-Pr2NH 110 70% Table4-1. Synthesis of phosphole-Pt containing poly(phenyleneethylynenes) using Hagihara coupling. Hagihara coupling was used to prepare the phosphole-Pt containing poly(phenyleneethylynenes) 63a and 63b, and the results are outlined in Table 4-1.

Optimizing the reaction conditions required exploring different solvents and amine bases.

The complexes low solubility precluded toluene and tetrahydrofuran, which are the typical solvents for this reaction. ο-Dichlorobenzene showed the highest level of solvating the complex, but additional heat was required to completely dissolve it.

Diisopropylamine was shown to be a suitable base, since no reaction was observed with triethylamine. Once the ideal reaction conditions were met, forming the polymer product was a simple process. Characterization using 1H spectroscopy showed a broadening of signals observed for the aromatic and alkyl protons of the monomers, and 31P NMR

showed a broadening of the resonances for the platinum(II) phosphole complex. This broadening of signals is indicative of the corresponding polymeric product.

1.28

0.90 6.98 7.78 1.83

Figure 4-1. 1H NMR spectra for polymer 63b.

27.3 21.5

J = 2532 Hz J = 2455 Hz

Figure 4-2. 31P NMR spectra for polymer 63b.

1.29 0.87

7.15 1.53 8.09

Figure 4-3. 1H NMR spectra for polymer 63a.

18.3

41.6

42.3 J = 2603 Hz

Figure 4-4.31P NMR spectra for polymer 63a.

As shown in Figures 4-1 to 4-4, the chemical shifts for the polymer 1H NMR spectra are very similar to their respective monomeric units, but the 31P shows a small upfield shift for the respective resonances. This upfield shift for the phosphorous resonances has been shown in other polymeric systems relative to the monomer, which were presented in the 54

introduction.

Assignment of the numerous resonance in the 31P can be determined by locating the P-Pt coupling satellites, which were observed with the monomer. For the 63b, distinguishable, sharper resonances are observed and may correspond to the inner-chain and end-units of the polymeric material. The more upfield resonance at δ21.5ppm (J =

2455.9 Hz) likely corresponds to the internal units, while the more downfield resonance at δ 27.3 ppm (J = 2531.9 Hz), which is closer to the value for the monomeric complex is likely that corresponding to the end-units. This assignment is based off of the similarity in electronic structure the end-units would have, assuming they are capped with the chloride ligands.

Polymer 63a, has only one major resonance with adjacent P-Pt coupling satellites, but this major resonance has finer features. Given the difference in appearance of the spectrum to 63b, it is hard to definitively assign the individual resonances making up the major feature at δ 18.3 ppm. The satellite peaks corresponding to the P-Pt are apparent and provide a coupling constant of 2603 Hz. The sharp resonances at δ 42.6 and 41.3 ppm are difficult to assign, since they do not correspond to free ligand or the monomer.

Discovering the source of these resonances is still underway. Since GPC data has not been collected for these polymeric products, definitive chain lengths and molecular weight distributions cannot be provided. Differences in those values for the polymer products may be the source for discrepancies in each of the respective 31P NMR spectrum for the polymers. While the proton spectra show a polymeric product, the 31P spectra show variability in the identity of that polymer product. Ignoring the P-Pt coupling

satellite peaks, the major resonances observed likely correspond to the internal repeat units while the smaller ones can be attributed to units that endcap the polymer chains.

4.2 Electrochemistry of Phosphole-Pt poly(aryleneethynylenes).

As with the previously discussed phosphole and phosphole derivatives, cyclic- voltammetry experiments with the two polymers provides insight into the difference in energy levels for the FMO. The aryl linker for both polymers is the same, and

so any discrepancy in oxidation and reduction potentials for the polymers could be the result of discrepancies in chain length or the phosphole ligand modifying the electronics via orbital interactions with the platinum metal center, such as backbonding. Since the polymers were not characterized using gel permeation chromatography, GPC, it cannot be stated with absolute certainty the size of the chain lengths or the molecular weight distribution, PDI. Thus, it cannot be stated with certainty that differences in potentials are due to chain lengths. What can be inferred from the data is if the polymerization of the complexes stabilizes the LUMO and destabilizes the HOMO, which is a typical occurrence between a monomer versus its polymer.

0.8

0.0 0.6

0.4

-0.5 0.2 Current (uA) Current

Current(uA) 0.0

-0.2 -1.0 49a 49b -0.4 1.0 0.5 0.0 -0.5 -1.0 -1.5 -2.0 -2.5 1.0 0.5 0.0 -0.5 -1.0 -1.5 -2.0 -2.5 Potential (V) Potential (V)

1.0 1.0 0.8

0.8 0.6 0.6

0.4

A)  0.4 0.2 0.2

Potential ( Potential 0.0 Current(uA) 0.0 -0.2

-0.2 -0.4 61b

1.0 0.5 0.0 -0.5 -1.0 -1.5 -2.0 -2.5 -0.4 61a 1.0 0.5 0.0 -0.5 -1.0 -1.5 -2.0 -2.5 Potential (V) Potential (V)

4 4

2 2

Current (uA) Current Current (uA) Current -2 -2

-4 -4 63a 63b 1.0 0.5 0.0 -0.5 -1.0 -1.5 -2.0 -2.5 1.0 0.5 0.0 -0.5 -1.0 -1.5 -2.0 -2.5 Potential (V) Potential (V)

Figure 4-5. From top to bottom, cyclic-voltammograms of phosphole ligands 49a,b, Pt complexes 61a,b, and polymers 63a,b. Measured in DCM using Pt disk working electrode, Bu4NPF6 as the supporting electrolyte, and ferrocene as an internal standard.

Compound Eox(mV) Ered1 (mV) Ered2(mV) Eg(eV) 49a 838 - - - 61a - -1889 - - 63a 310 -1660 -1822 1.97 49b 633 -2451 - 3.08 61b 674 -1687 - 2.36 63b 636 -1657 -2176 2.29 Table 4-2. Electrochemical data for compounds 49a,b-63a,b.Measured in DCM using Pt disk working electrode, Bu4NPF6 as the supporting electrolyte, and ferrocene as an internal standard.

Figures 4-5 and Table 4-2 show the effects of complexation and polymerization relative to the free ligand. This outlines the structure-property relationships and changes in FMO energy levels due to synthetic modification for this series of compounds. The general trend observed is a stabilization of the LUMO due to synthetic modification, in comparing the free ligand to the complex monomer and polymer product. The other interesting feature, is that in comparing the CV above for 49b, which was collected using

DCM, with that shown in Figure 3-2, which was collected using MeCN, it is apparent that using DCM as the solvent leads to decomposition of the reduced species and thus an irreversibility as shown by the absence of anodic current. This implies a solvent dependency for the reductive features of the phospholes and derivatives synthesized, since the reduced species is not stable on the electrochemical timescale.

2 4

2 0

0 Current (uA) Current

-2 Current (uA) Current

-2 -4 63a 63b -4 1.0 0.5 0.0 -0.5 -1.0 -1.5 -2.0 -2.5 1.0 0.5 0.0 -0.5 -1.0 -1.5 -2.0 -2.5 Potential (V) Potential (V)

Figure 4-6. Cyclic-voltammograms of polymers 63a,b. Measured in DCM using Pt disk working electrode, Bu4NPF6 as the supporting electrolyte, and ferrocene as an internal standard.

Compound Eox(mV) Ered1 (mV) Ered2(mV) Eg(eV) 63a 310 -1660 -1822 1.97 63b 636 -1657 -2176 2.29 Table 4-3. Electrochemical data of polymers 63a,b. Measured in DCM using Pt disk working electrode, Bu4NPF6 as the supporting electrolyte, and ferrocene as an internal standard.

From Table 4-3 and Figure 4-6 the differences in potentials between the polymers, compounds 63a and 63b, in both the bulk solution are apparent. Comparing potentials for measurements with the polymer dissolved in solution, it is important to note that for each polymer there is a stabilization of the LUMO, but only a destabilization of the HOMO relative to the monomeric complex for the phenyl functionalized polymer.

The oxidation potential likely corresponds to that of the aryl linker between metal centers 59

in the polymer chain, which is seen with similar compounds58,28. The interesting and slightly counterintuitive result is that the polymer with the phenyl functionalized phosphole ligand provides a lower oxidation potential relative to the thienyl functionalized. From previous data, the thienyl containing phospholes have provided a more destabilized HOMO and thus oxidation has been a more facile process relative to the phenyl containing compounds. Reasoning for this is not clear, since the thienyl functionalized materials have had a more destabilized HOMO throughout this study.

Relative to the phenyl, thiophene is more electron rich and the thiophene containing phospholes should provide more electron density to the Pt metal center to help stabilize any oxidized species to a greater extent than phenyl; however, a similar report provides similar data where a triphenylphosphine ligand on platinum phenylethynyl complex provided a lower oxidation potential than the tributylphosphine ligand, which was unexplained58.

In comparing the anodic peak potentials for compounds 63a and 63b in solution, it is apparent that the HOMO for the 63a is further destabilized than that of 63b by 326 mV.

The potentials overlapped with the edge of the solvent window, thus the potential value given can be considered an approximation. The greater destabilization for polymer 63a may be indicative of greater extension of the π-system or increased orbital overlap in comparison to 63b, and the reduction at 426 mV for polymer 63b may is indicative of a reversible process for the prior oxidation. The LUMO for each polymer is very close in energy at approximately -1660 mV, but due to the greater destabilization for the HOMO

63a the band gaps differ by 0.21 eV with 63a being lower in energy.

4 4

2 2

Current(uA) Current(uA) -2 -2

-4 63b 63a -4

1.5 1.0 0.5 0.0 -0.5 -1.0 -1.5 -2.0 -2.5 1.5 1.0 0.5 0.0 -0.5 -1.0 -1.5 -2.0 -2.5 Potential (V) Potential (V)

20 20

10 0

-20 -10

-20 -40

Current (uA) Current Current (uA) Current

-30 -60 a a -40 63a 63b -80 1.5 1.0 0.5 0.0 -0.5 -1.0 -1.5 -2.0 -2.5 1.5 1.0 0.5 0.0 -0.5 -1.0 -1.5 -2.0 -2.5 Potential (V) Potential (V)

Figure 4-7.Cyclic-voltammograms of polymers 63a,b were measured in DCM using Pt disk working electrode, Bu4NPF6 as the supporting electrolyte, and ferrocene as an internal standard, and cyclic-voltammograms of polymer films prepared from 63a,b. a Films were prepared by drop casting a solution of the polymer in CHCl3 onto ITO glass plates and measured in MeCN using Bu4NPF6 as the supporting electrolyte and ferrocene as an internal standard.

Compound Eox2(mV) Eox1(mV) Ered1 (mV) Ered2(mV) Eg(eV) 63a - 310 -1660 -1822 1.97 63aa 1118 775 - - - 63b - 636 -1657 -2176 2.29 63ba 1004 - - - - Table 4-4. Electrochemical data for polymers in bulk solution and as a film on ITO. Polymers 63a,b were measured in DCM using Pt disk working electrode, Bu4NPF6 as the supporting electrolyte, and ferrocene as an internal standard. aFilms were prepared by drop casting a solution of the polymer in CHCl3 onto ITO glass plates and measured in MeCN using Bu4NPF6 as the supporting electrolyte and ferrocene as an internal standard. The FMO energy levels for the polymer films, as shown in Table 4-4 and

Figure 4-7, differ greatly from that when in bulk solution. This is due to the absence of the solvent and supporting electrolyte, which can help to stabilize electrochemical processes, and changing the working electrode from Pt disk to ITO. As a film, polymer

63a displays two oxidative features, which were not distinguished when the polymer was characterized in solution. At 1118 mV, the energy of the HOMO differs by approximately 700 mV from that measured of 63a in solution.

A similar trend is observed for the polymer 63b. The HOMO shows stabilization relative to the measurements in preformed with the polymer in solution by approximately

600 mV. The cathodic current observed for the phenyl, 63a, and thienyl, 63b, functionalized polymers is at -957 mV and -1028, respectively. This is due to the reduction of the oxidized species, since it was not observed when only scanning negative potentials. This an interesting feature not observed with similar systems that incorporate a trialkylphosphine ligand rather than a phosphole59.

A reported explanation for the observed oxidation potentials of the films is the oxidation of the Pt(II) metal center to a Pt(IV) metal center59,58. The electrons for this process would come from a non-bonding orbital, and the oxidized species subsequently stabilized by solvent or supporting electrolyte molecules. Support for this is due to 62

extensive studies involving variation in the conjugation lengths for the acetylide ligands.

What was observed as the ligand lengths increased, there was not a noticeable change in the potentials for oxidation. This is indicative of a localized oxidation process rather than one that is delocalized, which can be attributed to a less conjugated HOMO.

Given that the oxidation potentials for the each film are quite similar, a more detailed explanation would involve the aryl linker as the oxidized moiety. The difference in potential would then be due to the phosphole ligand attached to the metal center. It is possible, that the phenyl substituents provide a non-covalent interaction, such as a π-π interaction, between the aryl groups of the phosphole ring and the oxidized aryl species of the polymer backbone or between separate polymer chains. The thienyl groups may not align well with the aryl-linkers in the polymer backbone or with other polymer chains thus not providing as much stabilization. To assert this idea, modeling studies would have to be performed to provide support for increased non-covalent interactions for the 1,2,5- triphenylphosphole ligands versus the thienyl functionalized phosphole ligands.

Chapter 5.Conclusion

This report describes the synthesis of 1,4-diarylbutadienes using two different routes. The major steps of the first, employed a Heck coupling and a copper-mediated homocoupling to prepare the butadienes. This method was unsuccessful in the preparation of pyridyl containing butadienes, hence the inclusion of a second synthetic route. The second route incorporated a series of Wittig reactions to prepare the pyridyl containing butadienes.

These butadienes were then used to prepare 1,2,5-triarylphospholes via the

McCormack reaction. These phospholes had previously been inaccessible due to the 1,5- sigmatropic shifts that occur with these materials resulting in inseparable product mixtures. It was found that microwave heating allows rapid access to the materials in high purity, and is therefore favorable over conventional heating methods. Phenyl containing phospholes exclusively formed rearranged phosphole byproducts, but no dimer. Heterocyclic aromatics showed a preference to form dimer byproducts exclusively. These phospholes were then used to form the corresponding oxide and Pt(II) complex derivatives. The Pt(II) complexes were then used to prepare the corresponding phosphole-Pt containing poly(aryleneethynylene) polymers using Hagihara coupling.

Electrochemical characterization found that the FMO energy levels vary with synthetic modification. The phospholes possessed a more stabilized LUMO relative to the butadiene, and for the oxide derivatives the LUMO was stabilized even more leading to a decrease in band gap. For the phosphole-Pt containing poly(phenyleneethynylenes), a stabilization of the LUMO was observed allowing for a decrease in band gap, relative to the phosphole-Pt complex monomer. Overall there was a stabilization of the LUMO in 64

moving from the phosphole ligand, to the complex, to the polymer. The oxidative features observed within the potential window were at higher potentials than the values obtained for in-solution measurements. Cathodic current was observed after oxidation of the polymer films showing that the oxidized species are reducible on the electrochemical timescale, which is a feature not observed for structurally similar polymers.

Future work will include the preparation of more phosphole oligomers with varied aryl substituents. These can then be used to prepare the complexes and oxide derivatives.

Additional complexes will allow for the preparation of a catalogue of phosphole-Pt containing poly(aryleneethynelenes), for which the aryl linker can be modified. Tailoring the aryl groups of the phosphole as well as the aryl linker will allow for further discovery of structure-property relationships. Also, the metal center of the complex can be modified to include other group 10 metals, such as Pd and Ni.

Chapter 6. Experimental

General Information. All chemicals were purchased from commercial sources and used as received unless otherwise noted. Microwave assisted syntheses were accomplished using CEM Discover LabMate microwave synthesizer. All NMR spectra were recorded using a Bruker Avance III 400 NMR or Varian 400-MR NMR in CDCl3. Proton, carbon, and phosphorous NMR spectra were calibrated to the chloroform peak at 7.26, CDCl3 at

77, and H3PO4 at 0 ppm, respectively. Infrared spectra were collected on a Perkin Elmer

Spectrum 100 FT-IR spectrometer equipped with an ATR unit. Unless noted otherwise, cyclic voltammetry was performed in 0.1 M Bu4NPF6/CH3CN using a BASi Epsilon EC as the potentiostat, a Pt disk working electrode, a platinum wire counter, and ferrocene as an internal standard using a scan rate of 100 mVs-1. Electrolyte solutions were degassed with Ar for 10 minutes before use. ITO plates submerged in acetone and sonicated for 10 minutes prior to use.

Synthesis of 3-Iodo-thiophene. 3-bromo-thiophene (67 mmol) was dissolved in hexanes

(100 mL), and then n-butyllithium was added dropwise at -78C under N2 atmosphere.

THF (10 mL) was then added to the reaction mixture. After stirring for 15 min, additional hexanes (30 mL) was added and the reaction was warmed to room temperature. Iodine

(74 mmol) was then added, and the reaction mixture was allowed to stir for 30 minutes.

100 mL of H2O was then added and it was then extracted with Et2O (3100 mL). The combined organic phase was dried with Na2SO4, and purified using vacuum-distillation to afford 70% of the title compound60.

Synthesis of 2-Pyridyldimethyl(vinyl)silane. To a solution of 2-bromopyridene (250

mmol) in THF (150 mL) , was added n-butyllithium drop wise at -78C under N2. The mixture was allowed to stir at -78C for 1.5 hours. Chlorodimethyl(vinyl)silane (250 mmol) was then added to the mixture and it was warmed to room temperature. After stirring at room temperature for 1 hour, aqueous saturated NaHCO3 (200 mL) was added and the aqueous phase was extracted using Et2O (3100 mL). The combined organic phase was dried using Na2SO4, and it was purified using vacuum-distillation to afford

60% of the title compound.1H NMR: δ 8.78 (dd, 1H, J = 4.0, 2.0 Hz), 7.55 (td, 1H, J =

8.0, 1.2 Hz), 7.50 (dd, 1H, J = 4.0, 1.2 Hz), 7.18 (ddd, 1H, J = 8.0, 4.6, 1.7 Hz), 6.34 (dd,

1H, J = 20.0, 16 Hz), 6.09 (dd, 1H, J = 16.0, 4.0), 5.80 (dd, 1H, J = 20, 4.0 Hz), 0.40 (s,

6H).

General Synthesis of Alkenyl(2-pyridyl)silanes. To a mixture of Pd(AcO)2 (0.4 mmol) and P(2-furyl)3 (1.2 mmol) in THF (100mL) was added the aryl-iodide (20 mmol), 2- pyridyldimethyl(vinyl)silane (22 mmol), and diisopropylamine (60 mmol). The reaction mixture was stirred at 50C for 36 hours. The solids were then filtered off, the solvent stripped en vacuo, and the residue was purified using column chromatography.

(E)-β-(2-Pyridyldimethylsilyl)-4-fluorostyrene. Obtained from para-fluoro- iodobenzene and 2-Pyridildimethyl(vinyl)silane61. 1H NMR: δ 8.80 (d, 1H, J = 4 Hz),

7.59-7.53 (m, 3H), 7.44-7.41 (m, 2H), 7.22-7.20 (m, 2H), 7.02-6.93 (m, 3H), 6.54 (d, 1H,

J = 19.2), 0.49 (s, 6H).

(E)-β-(2-Pyridyldimethylsilyl)-4-anisolestyrene. Obtained from para-anisole- iodobenzene and 2-Pyridildimethyl(vinyl)silane61.1H NMR: δ 8.80-8.79 (m, 1H), 7.61-

7.54 (m, 2H), 7.41 (d, 2H, J = 8.8) 7.21-7.18 (m, 1H), 6.95 (d, 1H, J = 20.0 Hz), 6.86 (d,

2H, J = 8.0 Hz), 6.48 (d, 1H, J = 20.0 Hz), 3.80 (s, 3H), 0.48 (s, 6H). 67

(E)-β-(2-Pyridyldimethylsilyl)-3-thienylstyrene. Obtained from 3-iodothiophene and 2-

Pyridildimethyl(vinyl)silane46. 1H NMR: δ 8.80-8.78 (m, 1H), 7.58-7.52 (m, 2H), 7.30-

7.28 (m, 1H), 7.25-7.18 (m, 3H), 7.0 (d, 1H, J = 19.2), 6.41 (d, 1H, J = 19.2 Hz).

General Synthesis of 1,4-Diarylbutadienes. To a mixture of CuI (7.5 mmol) and KF (15 mmol) in MeCN, was added the E-β-(2-pyridildimethylsilyl)-arylstyrene (5 mmol). The catalyst and salts were removed by filtration using a short gel pad (CHCl3), the solvent stripped en vacuo, and the residue was purified using column chromatography.

1,4-Bis(3-thienyl)-1,3-butadiene. Obtained from (E)-β-(2-Pyridyldimethylsilyl)-3- thienylstyrene46. 1H NMR: δ 7.30-7.23 (m, 4H), 7.18 (dd, 2H, J = 4.0, 2.4 Hz), 6.81-6.62

(m, 4H).

1,4-Bis(4-anisole)-1,3-butadiene. Obtained from (E)-β-(2-Pyridyldimethylsilyl)-4- anisolestyrene61. 1H NMR: δ 7.36 (d, 4H, J = 8.8 Hz), 6.87 (d, 4H, J = 6.8), 6.83 (dd, 2H,

J = 14.76, ), 6.57 (dd, 2H, J = 11.8, 2.8 Hz), 3.81 (s, 6H).

1,4-Bis(4-fluorophenyl)-1,3-butadiene. Obtained from (E)-β-(2-Pyridyldimethylsilyl)-

4-fluorophenylstyrene61. 1H NMR: δ 7.39 (dd, 4H, J = 8.7, 5.2 Hz), 7.02 (t, 4H, J = 8.7

Hz), 6.84 (dd, 2H, J = 12.0, 2.8 Hz), 6.62 (dd, 2H, J = 12.0, 2.8 Hz).

Synthesis of E-3-(4-pyridil)acrylaldehyde. 4-pyridylcarboxaldehyde (13 mmol) and

(triphenylphosphoranyldiene)actylaldehyde (13 mmol) was dissolved in toluene and heated to refluvx for 24 hours. The solvent was removed en vacuo and the crude was chromatographed ( 10% Hexanes/ EtOAc) to afford 40% of the title compound51.1H

NMR: δ 9.78 (d, 1H, J = 7.2 Hz), 8.70 (d, 2H, J = 4.4 Hz), 7.40 (m, 3H), 6.83 (dd, 1H, J

= 16.0, 8.0 Hz).

Synthesis of E-3-(3-pyridyl)acrylaldehyde. Identical to procedure for E-3-(4-

pyridil)acrylaldehyde, but with 3-pyridylcarboxaldehyde51. 1H NMR: δ 9.74 (d, 1H, J =

7.2 Hz), 8.80 (s, 1H), 8.67 (d, 1H, J = 4.4 Hz), 7.91 (d, 1H, J = 8.0 Hz), 7.44-7.40 (m,

2H), 6.78 (dd, J = 16.0, 8.0 Hz).

Synthesis of 4-[(Diethylphosphono)methyl]pyridine.4-picolyl chloride hydrochloride

(22 mmol) and potassium carbonate (22 mmol) were dissolved in water. The mixture was then extracted with Et2O, dried with Na2SO4, and added to a round-bottom flask, equipped with a condenser and stirbar, containing triethylphosphite (583 mmol). The mixture was then heated to reflux for 5 hours. The excess triethylphosphite was removed envacuo and the crude chromatographed ( 20% MeOH/EtOAc) to afford 60% of the title compound.1H NMR: δ 8.53 ( d, 2H, J = 6.0 Hz), 7.24-7.26 ( m, 2H), 4.04 ( q, 4H, J = 6.0

Hz) 3.12 (d, 2H, J = 24.0 Hz), 1.25 (q, 6H, J = 6.0 Hz). 31P NMR: δ 24.98.

Synthesis of 3-[(Diethylphosphono)methyl]pyridine. Identical to synthesis of 4-

[(Diethylphosphono)methyl]pyridine, but with 3-picolyl chloride hydrochloride. 1H

NMR: δ 8.50 (s, 2H), 7.66 (d, 1H, J = 8.0 Hz), 7.24 (dd, 1H, J = 7.2, 4.0 Hz), 4.04 (q, 4H,

J = 6.0 Hz), 3.11 (d, 2H, J = 24.0 Hz), 1.25 (q, 6H, J = 6.0 Hz). 31P NMR: δ 24.98.

General Synthesis of Pyridyl Containing Butadienes. The pyridylphosphonate(

4mmol) was added to a suspension of tBuOK in THF ( 30 mL) at 0°C. The acrolein was then added dropwise at 0°C and the mixture allowed to stir for 2 hours. The mixture was then extracted with chloroform, dried with Na2SO4, and the solvent stripped envacuo.

The solid crude was treated with Et2O, filtered, and washed with Et2O to yield a tan solid50.

1,4-Bis(4-pyridyl)-1,3-butadiene. 30% yield from E-3-(4-pyridil)acrylaldehyde and 4-

[(Diethylphosphono)methyl]pyridine. 1H NMR: δ 8.57 (d, 4H, J = 8 Hz), 7.30 ( d, 4H, J =

4 Hz), 7.12 (dd, 2H, J = 14.8, 9.2 Hz), 6.69 (dd, 2H, J = 12.4, 8.0 Hz).

1,4-Bis(3-pyridyl)-1,3-butadiene. 25% yield from E-3-(4-pyridil)acrylaldehyde and 4-

[(Diethylphosphono)methyl]pyridine. 1H NMR: δ 8.67 (s, 2H), 8.48 (d, 2H, J = 4.4 Hz),

7.78 (d, 2H, J = 8.0 Hz), 7.31-7.26 (m, 2H), 7.00 (dd, 2H, J = 12.4, 10.8 Hz), 6.72 (dd,

2H, J = 12.0, 8.0).

General Synthesis of Phospholes.To a microwave-reaction vessel equipped with a stirbar was added the aryl butadiene (0.25 mmol), and dichloridephenylphosphine (2.00 mL,

15 mmol) was added under N2 atmosphere. The reaction vessel was then exposed to microwave heating. The reaction mixture was then added to a solution of 15% KOH (20 mL), and then extracted with chloroform (330 mL). The organic layer was dried using

Na2SO4 and purified using column chromatography.

1,2,5-Triphenylphosphole. From 1,4-diphenyl-1,3-butadiene and dichlorophenylphosphine. 1H NMR (400 MHz): δ 7.56-7.53 (m, 4H), 7.42-7.37 (m, 2H),

13 7.29 (d, JP-H = 10.4 Hz, 2H), 7.29 - 7.25 (m, 4H), 7.21 - 7.15 (m, 5H). C NMR (100

MHz): δ151.5, 136.4 (d, JP-C = 16.8 Hz), 133.9 (d, JP-C = 19.7 Hz), 132.0 (d, JP-C = 9.5),

130.8 (d, JP-C = 8.0 Hz), 129.6 (d, JP-C = 1.5 Hz), 128.8 (d, JP-C = 8.0 Hz), 128.6, 127.2 (d,

31 JP-C = 1.5 Hz), 126.4 (d, JP-C = 9.5 Hz). P NMR (162 MHz): δ 2.6. MP 183-185°C.

+ HRMS (ESI) calcd for C22H18P 313.1146, found 313.1158 [M+H] . FT-IR (ATR): 3067,

3016, 2919, 2851, 1593, 1467, 833, 740, 681 cm-1.

1-Phenyl-2,5-bis(2’-thienyl)phosphole. From 1,4-bis(2-thienyl)-1,3-butadiene and dichlorophenylphosphine. 1H NMR (400 MHz): δ 7.52 - 7.47 (m, 2 H), 7.34 -7.24 (m,

3H), 7.11 (dt, 2H, JH-H = 5.1 Hz, JH-H = JP-H = 1.2 Hz), 7.08 (d, JP-H = 10.0 Hz, 2H), 6.98

(dt, 2H, JH-H = 3.7 Hz, JH-H = JP-H = 1.2 Hz), 6.88 (ddd, 2H, JH-H = 5.1 Hz, JH-H = 3.7 Hz, 70

13 JP-H = 0.7 Hz). C NMR (100 MHz): δ 143.6 (d, JP-C = 3.6 Hz), 140.2 (d, JP-C = 21.2 Hz),

134.1 (d, JP-C = 20.4 Hz), 131.7 (d, JP-C = 7.3 Hz), 131.2 (d, JP-C = 13.1 Hz), 130.1 (d, JP-C

31 = 1.5 Hz), 129.0 (d, JP-C = 8.7 Hz), 127.8, 124.4, 124.3 (d, JP-C = 7.3 Hz). P NMR (162

MHz): δ 7.4. FT-IR (ATR): 3065, 2919, 2850, 1503, 1465, 1423, 1303, 1206, 807, 743,

679. MP: 139-141°C HRMS (ESI) calcd for C18H14PS2 325.0275, found 325.0279

[M+H]+.

1-Phenyl-2,5-bis(4’-pyridyl)phosphole. From 1,4-bis(4-pyridyl)-1,3-butadiene and

1 dichlorophenylphosphine. H NMR (400 MHz): δ 8.51 (d, 4H, JH-H = 5.9 Hz), 7.53 (d, JP-

13 H = 9.5 Hz, 2H), 7.42 -7.38 (m, 4H), 7.37 -7.28 (m, 3H), 7.26-7.21 (m, 2H). C NMR

(100 MHz): δ 151.5, 149.7 (d, JP-C = 5.8 Hz), 143.2 (d, JP-C = 17.5 Hz), 135.0 (d, JP-C =

9.5 Hz), 134.0 (d, JP-C = 20.4 Hz), 130.7 (d, JP-C = 2.2 Hz), 129.3 (d, JP-C = 9.5 Hz), 128.0

31 (d, JP-C = 7.3 Hz), 120.8 (d, JP-C = 9.5 Hz). P NMR (162 MHz): δ 4.8. FT-IR (ATR):

3054, 2921, 2851, 1585, 1410, 990, 807,740, 692. MP: 170-172°C HRMS (ESI) calcd for

+ C20H16N2P 315.1046, found 315.1047 [M+H] .

1-Anisole-2,5-bis(4’-pyridyl)phosphole. From 1,4-bis(4-pyridyl)-1,3-butadiene and 4-

1 methoxyphenyl phosphonous dichloride. H NMR (400 MHz): δ 8.48 (dd, 4H, JH-H = 4.6

Hz, JP-H = 1.5 Hz, H2 Py), 7.48 (d, JP-H = 9.5 Hz, 2H, PC=CH), 7.36 (dd, 4H, JH-H = 4.6

Hz, JP-H = 1.0 Hz, H3 Py), 7.26 (t, 2H, JH-H = JP-H = 8.8 Hz, o-H Ph), 6.76 (dd, 4H, JH-H =

13 8.8 Hz, JP-H = 1.0 Hz, m-H Ph). C NMR (100 MHz): δ 161.6 (d, JP-C = 1.5 Hz, p-C Ph),

151.7 (s, PC=CH), 150.0 (s, C2 Py), 142.9 (d, JP-C = 18.2 Hz, C4 Py), 135.8 (d, JP-C =

20.3 Hz, o-C Ph), 134.3 (d, JP-C = 9.5 Hz, PC=CH), 120.7 (d, JP-C = 9.1 Hz, C3 Py), 118.0

31 (d, JP-C = 3.8 Hz, ipso-C Ph), 115.0 (d, JP-C = 10.6 Hz, m-C Ph). P NMR (162 MHz): δ

3.56. FT-IR (ATR): 3065, 3018, 2954, 2833, 1587, 1490, 1411, 1300, 1249, 1173, 1092,

1027, 808, 743, 679. MP: 156-158°C HRMS (ESI) calcd for C21H18N2OP 345.1150, found 354.1140 [M+H]+.

1,2,5-Tris(4’-fluorophenyl)phosphole. From 1,4-bis(4-fluorophenyl)-1,3-butadiene and

1 4-fluorophenyl phosphonous dichloride. H NMR (400 MHz): δ 7.45 (ddd, 4H, JH-H = 8.6

Hz, JF-H = 5.4 Hz, JP-H = 1.2 Hz), 7.34 (ddd, 2H, JH-H = 8.8 Hz, JF-H = 5.5 Hz, JP-H = 0.8

Hz), 7.18 (d, JP-H = 10.6 Hz, 2H), 6.96 (td, 4H, JH-H = JF-H = 8.6 Hz, JP-H = 2.4 Hz) 6.90

13 (td, 2H, JH-H = JF-H = 8.8 Hz, JP-H = 0.8 Hz). C NMR (100 MHz): δ 163.9 (d, JF-C =

248.6 Hz), 162.3 (d, JF-C = 246.4 Hz), 150.6, 135.8 (dd, JP-C = 21.1 Hz, JF-C = 8.8 Hz),

132.3 (dd, JP-C = 17.1 Hz, JF-C = 3.3 Hz), 131.8 (d, JP-C = 9.5 Hz), 127.7 (dd, JP-C = 9.6

Hz, JF-C = 8.6 Hz), 125.7 (dd, JP-C = 8.0 Hz, JF-C = 3.6 Hz), 116.3 (dd, JP-C = 9.6 Hz, JF-C =

31 19 20.6 Hz), 115.7 (d, JF-C = 21.2 Hz). P NMR (162 MHz): δ 0.8 (d, JF-P = 3.0 Hz). F

NMR (377 MHz): δ -114.5, -110.2 (d, JP-F = 3.0 Hz). FT-IR (ATR): 3054, 3004, 2919,

2850, 1887, 1586, 1489, 823, 757. MP: 131-132°C. HRMS (ESI) calcd for C22H15F3P

367.0858, found 367.0857 [M+H]+.

General Procedure for Synthesis of Phosphole Oxides. To a solution of phosphole

(0.25 mmol) in THF (5 mL), 30% H2O2 (1.25 mL) was added dropwise. The reaction mixture was then stirred for 90 min. 5% Na2SO4 (10 mL) was then added, and this mixture was diluted with water (50 mL). The precipitate was collected and purified using a silica plug.

1,2,5-Triphenylphospholeoxide.Obtained from 1,2,5-Triphenylphosphole. 1H NMR: δ

8.16 (dd, 2H, J = 12.4, 7.2 Hz), 7.92 (d, 2H, J = 7.6 Hz) 7.77-7.52 (m, 12H). 13C NMR:

δ138.7 (d, J = 94.7 Hz), 136.6 (d, J = 27.2 Hz), 132.4 ( d, J = 11.7 Hz), 132.2 (d, J = 2.6

Hz), 130.3 ( d, J = 10.9 hz), 129.1 (d, J = 91.1 Hz), 129.1 ( d, J = 12.1 Hz), 128.9, 128.8,

126.4 (d, J = 6.5 Hz). 31P NMR: δ 44.4. MP: 226-229°C.

1-Phenyl-2,5-bis(2’-thienyl)phospholeoxide. Obtained from 1-Phenyl-2,5-bis(2’- thienyl)phosphole. 1H NMR:δ 7.88 (dd, 2H, J = 12.6, 6.8 Hz), 7.87 (d, 1H, J = 12.6),

7.53-7.41 (m, 3H), 7.25 (dt, 2H, J = 4.1, 1.2 Hz), 7.22 (ddd, 2H, J = 3.32 Hz), 6.99 (d,

2H, J = 36.0 Hz), 6.92 (dd, 2H, J = 5.1, 3.7 Hz). 13C NMR: δ 136.1 (d, J = 16.1 Hz),

132.3 (d, J = 95.5 hz),131.5 (d, J = 2.8 Hz), 130.9 (d, J = 25.8 Hz), 130.5 (d, J = 10.9 Hz),

129.2 (d, J = 12.4), 128.5 (d, J = 67.8), 128.3, 127.3 (d, J = 3.6 Hz), 126.3. 31P NMR: δ

40.1 (s). MP: 220-222°C.

1,2,5-Tris(4’-fluorophenyl)phospholeoxide. Obtained from 1,2,5-Tris(4’- fluorophenyl)phosphole. 1H NMR: δ 7.82 (ddd, 2H, J = 11.6, 8.9, 5.5 Hz), 7.60 (dd, 4H, J

= 8.0, 4.0 Hz), 7.21 (d,2H, J = 37.6 Hz), 7.10 (td, 2H, 8.8,4.4, 2.12 Hz), 7.00 (t, 4H, J = 8

Hz). 13C NMR: δ 165.4 (d, J = 252.3 Hz), 163.0 (d, J = 249.2 Hz), 136.6 (d, J = 95.6 Hz),

132.8 (dd, J = 11.6, 8.5 Hz), 132.2 (d, J = 29.0 Hz), 128.3 (dd, J = 12.1, 3.5 Hz), 128.2 (d,

J = 8.0 Hz), 128.1 (d, J = 8.5 Hz) 116.8 (dd, J = 21.2, 13.1 Hz), 116.2 (d, J = 21.9 Hz)

.19F NMR: -105.6, -110.9. 31P NMR: δ 40.6. MP: 196-198°C.

General Procedure for the Synthesis of PhospholePt(II) Complexes. N2 purged water

(4 mL) and DCM (24.6 mL) were added to a flask containing phosphole (0.64 mmol) and

K2PtCl4 (0.32 mmol). The mixture was allowed to stir for 72 hours. The complex was then collected via filtration and washed with water and DCM.

Bis(1,2,5-Triphenylphosphole)platinum(II) dichloride. Obtained from 1,2,5-

Triphenylphosphole. 1H NMR: δ 8.02 (d, 8H, J = 5.2 Hz), 7.51 Hz (dd, 4H, J = 12.0, 8.0

Hz), 7.34-7.23 (m, 7H), 7.15 (t, 8H, J = 4.8 Hz). 13C NMR: δ 145.4 (d, J = 18.4 Hz),

138.1 (t, J = 5.4), 136.3 (t, 4.6 Hz), 135.9 (t, J = 4.2), 133.5, 131.4, 130.9, 130.4, 125.5,

110. 31P NMR: δ 22.3 (d, J = 2519.2 Hz).

Bis(1-Phenyl-2,5-bis(2’-thienyl))platinum(II) dichloride. Obtained from 1-Phenyl-2,5- bis(2’-thienyl)phosphole.1H NMR: δ 7.78 (d, J = 1.6 Hz), 7.66 (dd, J = 8.4, 4.6), 7.34-

7.23 (m), 7.04 (dd, J = 8.0 Hz, ), 6.93 (dd, J = 3.6, 2.2 Hz). 13C NMR: δ 140.3 (t, J = 7.0)

Hz), 138.1 (t, J = 18.0 Hz), 136.9 ( t, J = 5.4 Hz), 136.0 (t, J = 3.8 Hz), 133.8, 131.26,

131.0 (t, J = 4.0 Hz), 130.8, 128.6, 125.5. 31P NMR: δ 26.1 ( J = 2571.0 Hz).

General Procedure for the Synthesis of polyplatinynes. A mixture of ODCB and

DIPA was sparged for 45 min. with N2 and added to a flask containing the phosphole platinum dichloride complex, CuI, and the diethynyl aryl group. The mixture was stirred for 24 hrs at 110°C. The crude was passed through a Si-plug and the solvent stripped.

The residue was then dissolved in CHCl3 and precipitated into cold MeOH. poly(BTPP-Pt). Prepared from Bis(1,2,5-Triphenylphosphole)platinum(II) dichloride.

1H NMR: δ 8.09, 7.15, 3.53, 1.53, 1.29, 0.87. 31P NMR: δ 42.6, 41.4, 18.3 ( J = 2603 Hz). poly(BDTP-Pt). Prepared from Bis(1-Phenyl-2,5-bis(2’-thienyl))platinum(II) dichloride.

1H NMR: δ 7.78, 7.22, 6.98, 3.98, 3.70, 3.55, 1.83, 1.28, 0.90. 31P NMR: δ 27.3 ( J =

2531.9 Hz), 21.5 ( J = 2455.9 Hz).

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Appendix A: NMR data for select compounds.

Figure A-1.1,2,5-triphenylphosphole 1H NMR spectrum.

Figure A-2.1,2,5-triphenylphosphole 13C NMR spectrum.

Figure A-3.1,2,5-triphenylphosphole 31P NMR spectrum.

Figure A-4.1,2,5-triphenylphosphole HSQC NMR spectrum.

Figure A-5.2,5-bis(4-pyridyl)4-anisole phosphole1H NMR Spectrum.

Figure A-6. 2,5-bis(4-pyridyl)4-anisole phosphole31P NMR Spectrum.

Figure A-7. 2,5-bis(4-pyridyl)4-anisole phospholeCOSY NMR Spectrum.

Figure A-8. 2,5-bis(4-pyridyl)4-anisole phospholeHMBC NMR spectrum.

Figure A-9. 2,5-bis(4-pyridyl)4-anisole phospholeHSQC NMR spectrum.

Figure A-10.2,5-bis(4-pyridil)phenyl phosphole1H NMR spectrum.

Figure A-11.2,5-bis(4-pyridil)phenyl phosphole13C NMR spectrum.

Figure A-12.2,5-bis(4-pyridil)phenyl phosphole31P NMR spectrum.

Figure A-13.2,5-bis(4-pyridil)phenyl phospholeCOSY NMR spectrum.

Figure A-14.2,5-bis(4-pyridil)phenyl phospholeCOSY NMR spectrum.

Figure A-15.2,5-bis(2-thienyl)phenyl phosphole1H NMR spectrum.

Figure A-16. 2,5-bis(2-thienyl)phenyl phosphole13C NMR spectrum.

Figure A-17. 2,5-bis(2-thienyl)phenyl phosphole31P NMR spectrum.

Figure A-18. 2,5-bis(2-thienyl)phenyl phospholeCOSY NMR spectrum.

Figure A-19. 2,5-bis(2-thienyl)phenyl phospholeHSQC NMR spectrum.

Figure A-20.1,2,5-tris(4-fluorophenyl)phosphole1H NMR spectrum.

Figure A-21.1,2,5-tris(4-fluorophenyl)phosphole13C NMR spectrum.

Figure A-22.1,2,5-tris(4-fluorophenyl)phosphole31P NMR spectrum.

100

Figure A-23.1,2,5-tris(4-fluorophenyl)phosphole19F NMR spectrum.

101

Figure A-24.1,2,5-tris(4-fluorophenyl)phospholeCOSY NMR spectrum.

102

Figure A-25.1,2,5-tris(4-fluorophenyl)phosphole HMBC NMR spectrum.

103

Figure A-26.1,2,5-tris(4-fluorophenyl)phosphole HSQC NMR spectrum.

104

Figure A-27.Cyclic-voltammograms for compounds 17a,c-60a,c. Measured in MeCN using a Pt disk working electrode and ferrocene as an internal standard.

30 10 20

0 10

-10 0

A)  -20 -10

Current(uA) -20

Current ( -30

-30 -40 60a 17a -40

1 0 -1 -2 1.0 0.5 0.0 -0.5 -1.0 Potential (V) Potential (mV)

10 20

0 10

0 -10

-10 -20

-20 Current(uA)

Current(uA) -30 -30

-40 17c -40 60c -50 -50 1.0 0.8 0.6 0.4 0.2 0.0 -0.2 -0.4 -0.6 -0.8 -1.0 1 0 -1 -2 Potential (mV) Potential (mV)

105