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Synthesis and study of phosphinothiophene compounds Stott, Tracey Lynn 2005

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SYNTHESIS A N D STUDY OF PHOSPHINOTHIOPHENE COMPOUNDS by T R A C E Y L Y N N STOTT B.Sc , Hon, Dalhousie University, 2000 A THESIS SUBMITTED IN PARTIAL F U L F I L L M E N T OF THE REQUIREMENTS FOR THE DEGREE OF DOCTOR OF PHILOSOPHY in THE F A C U L T Y OF G R A D U A T E STUDIES (Chemistry) THE UNIVERSITY OF BRITISH C O L U M B I A August 2005 © Tracey Lynn Stott, 2005 Abstract The synthesis and characterization of a series of phosphinothiophenes and transition metal complexes thereof are reported. The influence of the metals on the electronic properties and the structures of the oligomers are investigated with N M R spectroscopy, X-ray crystallography, absorption and emission spectroscopy, and cyclic voltammetry. The phosphinothiophenes were characterized by absorption and emission spectroscopy, and the spectra were found to be dependent on the length of the oligothiophene. The emission from 65, 66, 68, and 69 is assigned to a n*—>n transition, whereas emission from 67 and 70 is assigned to thienyl-based, n*—>n transitions. Phosphine oxides, phosphine sulfides, and phosphonium salts of selected phosphinothiophenes were synthesized and characterized with absorption and emission spectroscopy. Au(I) complexes of the phosphinothiophenes were synthesized and characterized (79-85). The solid state crystal structures of 82 and 85 were found to be dimers exhibiting gold-gold interactions. Variable temperature N M R spectroscopy and emission spectroscopy indicate a monomer-dimer equilibrium in solution for these complexes. The X-ray crystal structure of 81 does not exhibit gold-gold interactions, and emission of the bi- and terthienyl gold complexes is assigned to re*—>7T. transitions of the oligothiophene. The synthesis of coordination polymers of Au(I) and Ag(I) was attempted by the reaction of 68, 69, or 70 and metal starting material. The resulting complexes exhibit lability in solution. Emission from the Au(I) complex of 68 was assigned to a metal based transition. The absorption and emission of the bi- and terthienyl Au(I) and Ag(I) complexes are similar to those of the corresponding Au(I) complexes described above. The structure of the Ag(I) complexes are dependent on the length of the oligothiophene. ii Pd(II) and Pt(II) complexes 99-108 exist as cis and trans isomers, depending on the metal centre and the ligand. In the solid state, 101 is the trans isomer, and exhibits intermolecular n-stacking of the terthienyl groups, whereas 105 is the cis isomer, and exhibits intramolecular 7i-stacking. The absorption spectra of the Pd and Pt complexes are very similar to the corresponding ligands, indicating weak interaction between the metal and oligothiophene. The synthesis of Ru(II) bis(bipyridine) complexes 117-119 is described. Complexes 117-119 are characterized with absorption spectroscopy and cyclic voltammetry. The absorption spectra exhibit thienyl-based TI—»7r* transitions and Ru—»bpy M L C T transitions. The cyclic voltammograms do not show metal-metal coupling. PTP (68) P T 2 P (69) P T 3 P (70) 79 n=1 82 n=1 85 80 n=2 83 n=2 81 n=3 84 n=3 iii 99 M=Pd, n=1 103 M=Pt, n=1 100 M=Pd, n=2 104M=Pt, n=2 101 M=Pd, n=3 105 M=Pt, n=3 CUM MCI Ph 2 Ph 2 102 M=Pd, n=3 106 M=Pt, n=1 107 M=Pt, n=2 108 M=Pt, n=3 P h 2 P ^ / S s \ pphj CI(bpy)2Ru \ V — y / n Ru(bpy)2CI 117 n=1 118 n=2 119 n=3 iv Table of Contents Abstract ii Table of Contents v List of Tables viii List of Figures ix List of Schemes xii List of Charts xiii List of Symbols and Abbreviations xv Acknowledgements xix Chapter 1 Introduction 1 1.1 Overview 1 1.2 Conjugated materials 2 1.3 Metal-organic materials 5 1.4 Literature Review 10 1.4.1 Carbon-bound complexes 10 1.4.2 rc-complexes 11 1.4.3 Acetylene complexes 15 1.4.4 Pyridines, bipyridines, and terpyridines 17 1.4.5 Oxygen-bound complexes 23 1.4.6 Other linker groups 25 1.5 Goals and Scope 27 1.6 References 29 Chapter 2 Phosphinothiophene Ligands and Derivatives: Synthesis and Electronic Spectra 35 2.1 Introduction 35 2.2 Experimental 39 2.2.1 General 39 2.2.2 Procedures 40 2.3 Results and Discussion 45 2.3.1 Synthesis 45 2.3.2 Absorption Spectra 47 2.3.3 Emission Spectra 55 2.4 Conclusions 61 2.5 References 63 Chapter 3 Structural and Luminescence Studies of Au(I) Complexes 67 3.1 Introduction 67 3.2 Experimental , 70 3.2.1 General..... '. '. 70 3.2.2 Procedures : 70 v 3.2.3 X-ray Crystallographic Analyses 72 3.3 Results and Discussion 73 3.3.1 Synthesis 73 3.3.2 Solid State Crystal Structures 75 3.3.3 V T N M R Spectroscopy 78 3.3.4 Absorption Spectra 84 3.3.5 Emission Spectra 89 3.4 Conclusions 96 3.5 References 98 Chapter 4 Synthesis and characterization of Au(I) and Ag(I) complexes 103 4.1 Introduction 103 4.2 Experimental 104 4.2.1 General 104 4.2.2 Procedures 104 4.2.3 X-ray Crystallographic Analysis 106 4.3 Results and Discussion 107 4.3.1 Synthesis 107 4.3.2 Solid State Crystal Structures 108 4.3.3 N M R Spectroscopy 113 4.3.4 Electronic Spectroscopy 120 4.4 Conclusions 125 4.5 References 128 Chapter 5 Synthesis and Characterization of Pd(II) and Pt(II) Complexes 131 5.1 Introduction 131 5.2 Experimental 134 5.2.1 General 134 5.2.2 Procedures 134 5.2.3 X-ray Crystallographic Analyses 138 5.3 Results and Discussion 141 5.3.1 Synthesis 141 5.3.2 Solid State Crystal Structures 143 5.3.3 N M R Spectroscopy 151 5.3.4 Absorption Spectra 157 5.3.5 Cyclic Voltammetry 164 5.4 Conclusions • 165 5.5 References...... 168 Chapter 6 Synthesis and Characterization of Ru(II) complexes 173 6.1 Introduction 173 6.2 Experimental 174 6.2.1 General 174 6.2.2 Procedures 175 6.3 Results and Discussion 177 vi 6.3.1 Synthesis 177 6.3.2 Absorption Spectra 178 6.3.3 Cyclic Voltammetry 180 6.4 Conclusions 182 6.5 References 184 Chapter 7 Conclusions and Future Work 186 7.1 General Conclusions 186 7.2 Suggestions for Future Work 188 7.3 References 191 Appendix 1 Crystal structure data 192 vii List of Tables Table 2.1. Comparison of electronic data of a,a"-substituted terthiophenes 38 Table 2.2 Electronic spectroscopy data for 65-70 50 Table 2.3 Electronic spectroscopy data for 74a-c, 75a-c, and 76a-c 55 Table 3.1 Selected interatomic distances and angles for 81 77 Table 3.2 Selected interatomic distances and angles for 82 78 Table 3.3 Solution absorption data for gold complexes 79-85 86 Table 3.4 Solid state electronic absorption data for gold complexes 79-85 89 Table 3.5 Emission data for gold complexes 79-85 96 Table 4.1 Selected interatomic distances and angles for 90 112 Table 4.2 Solution and solid state absorption data for 86-91 125 Table 4.3 Solution and solid state emission data for complexes 86-91 125 Table 5.1 Selected interatomic distances and angles for 100 145 Table 5.2 Selected interatomic distances and angles for 101 146 Table 5.3 Selected interatomic distances and angles for 102 148 Table 5.4 Selected interatomic distances and angles for 105 150 Table 5.5 Solution and solid state absorption data for 99-108 163 Table 6.1 Solution absorption and electrochemical data for 117-119 180 Table A l . l Selected crystal structure data for 81, 82, and 85 192 Table A 1.2 Selected crystal structure data for 90 194 Table A 1.3 Selected crystal structure data for 100,101,102, and 105 195 v in List of Figures Figure 1.1 Representative conjugated polymers 2 Figure 1.2 Evolution of the molecular orbitals of oligothiophenes 4 Figure 1.3 Schematic of three types of transition metal-conjugated organic hybrid materials.7 Figure 1.4 Schematic of a bimetallic Type III complex 9 Figure 2.1 Solution UV-visible spectra of 65-70 49 Figure 2.2 Calculated frontier orbitals of 65-67 and orbital energies of 65-70 and 74a 51 Figure 2.3 Solid state UV-visible spectra of 65-70 52 Figure 2.4 Solution absorption and emission spectra of 74a-c 53 Figure 2.5 Solution'absorption and emission spectra of 75a-c 54 Figure 2.6 Solution absorption and emission spectra of 76a-c 54 Figure 2.7 Solution excitation and emission spectra of phosphines 65-70 in hexanes 56 Figure 2.8 Solution excitation and emission spectra of 68-70 in CH2CI2 57 Figure 2.9 Solid state excitation and emission spectra of 65-70 60 Figure 3.1 ORTEP view of 81 76 Figure 3.2 ORTEP view of 82 77 Figure 3.3 Variable temperature N M R spectra of 79 in CD2CI2 81 Figure 3.4 Variable temperature N M R spectra of 82 in CD2CI2 82 Figure 3.5 Variable temperature N M R spectra of 85 in CD2CI2 83 Figure 3.6 UV-visible spectra of gold complexes 79-84 85 Figure 3.7 Comparison of UV-visible spectra of 68, 82, and 85 87 Figure 3.8 Solid state UV-visible spectra of gold complexes 79-85 88 Figure 3.9 Solution excitation and emission spectra of 82 and 85 91 ix Figure 3.10 Solution excitation and emission spectra of 80, 81, 83, and 84 92 Figure 3.11 Solid state excitation and emission spectra of 79, 82, and 85 94 Figure 3.12 Solid state excitation and emission spectra of 80, 81, 83, and 84 95 Figure 4.1 ORTEP view of 90 110 Figure 4.2 Packing diagram of 90, showing a layer of Ag(I), bridged by 69 and NC>3~ 111 Figure 4.3 Packing diagram of 90, showing layered structure of the crystal I l l Figure 4.4 View of Ag(I) coordination sphere in 90 112 Figure 4.5 Variable temperature N M R spectra of 86 114 Figure 4.6 Variable temperature N M R spectra of 89 117 Figure 4.7 3 1 P{H} N M R spectrum of 89 at 218 K in CD 2 C1 2 118 Figure 4.8 Variable temperature N M R spectra of 91 119 Figure 4.9 Solution absorption and emission spectra of 86-88 121 Figure 4.10 Solid state absorption and emission spectra of 86-88 122 Figure 4.11 Comparison of the solution absorption spectra of 68, 82, and 86 122 Figure 4.12 Solution absorption and emission spectra of 89 and 91 124 Figure 4.13 Solid state absorption and emission spectra of 89-91 124 Figure 5.1 ORTEP view of 100 144 Figure 5.2 ORTEP view of 101 146 Figure 5.3 ORTEP view of 102 148 Figure 5.4 ORTEP view of 105 150 Figure 5.5 Variable temperature N M R spectra of 102 in CD 2 C1 2 153 Figure 5.6 3 1 P{H} N M R spectra of 102 with 0, 0.5, 1, 2, 4, and 10 equivalents of 70 added, in CD 2 C1 2 155 Figure 5.7 'Hand 3 1 P{H} N M R spectra of 102 in CD 2 C1 2 , at 2.1, 4.0, 5.9, and 10.5 m M . . 156 x Figure 5.8 Comparison of 3 1P{H} N M R spectrum of 101,102, 102 with 2 equivalents of 70, and a concentrated solution (10 mM) of 102 157 Figure 5.9 Solution absorption spectra of 99-102 160 Figure 5.10 Solid state absorption spectra of 99-102 160 Figure 5.11 Solution absorption spectra of 99,100, and 101 in C H 3 C N , CH2CI2, and toluene 161 Figure 5.12 Solution absorption spectra of 103-108 162 Figure 5.13 Solid state absorption spectra of 103-108 163 Figure 5.14 Cyclic voltammogram of 108 in C H 3 C N : 165 Figure 6.1 3 1P{H} N M R spectra of 117,118, and 119 in C D 3 C N 178 Figure 6.2 Solution UV-visible spectra of 117-119 179 Figure 6.3 Cyclic voltammograms of 117, 118, and 119 in C H 3 C N 182 Figure A 1.1 ORTEP view of 85 193 Figure A1.2 ORTEP diagram of 81, showing Tt-stacking of phenyl rings in the lattice 193 Figure A1.3 ORTEP view of crystal packing of 101, showing intermolecular 71-stacking of terthiophene groups 196 Figure A l .4 ORTEP view of crystal packing of 105, showing intramolecular 71-stacking of phenyl and thiophene moieties 196 xi List of Schemes Scheme 2.1 46 Scheme 2.2 47 Scheme 3.1 74 Scheme 3.2 74 Scheme 4.1 107 Scheme 4.2 108 Scheme 5.1 143 Scheme 5.2 143 Scheme 5.3 151 Scheme 5.4 154 Scheme 6.1 178 Scheme 7.1 190 xi i List of Charts Chart 1.1 3 Chart 1.2 7 Chart 1.3 8 Chart 1.4 9 Chart 1.5 11 Chart 1.6 12 Chart 1.7 13 Chart 1.8 14 Chart 1.9 15 Chart 1.10 16 Chart 1.11 16 Chart 1.12 17 Chart 1.13 19 Chart 1.14 20 Chart 1.15 21 Chart 1.16 23 Chart 1.17 24 Chart 1.18 25 Chart 1.19 26 Chart 2.1 36 Chart 2.2 '.. 36 Chart 2.3 37 xiii Chart 3.1 67 Chart 3.2 68 Chart 3.3 84 Chart 4.1 109 Chart 4.2 116 Chart 4.3 116 Chart 5.1 133 Chart 6.1 174 Chart 7.1 190 xiv List of Symbols and Abbreviations Abbreviation Description A Angstrom z angle a. u. arbitrary units Ac acetate Anal. analysis bpy bipyridine Bu butyl cm centimeter C V cyclic voltammogram °C degrees Celsius Cp cyclopentadienyl Cp* pentamethylcyclopendienyl CT charge transfer A difference 5 chemical shift (ppm) d doublet dd doublet of doublets (NMR), metal state ddd doublet of doublets of doublets A E peak separation in a cyclic voltammogram A G * free enthalpy of activation D density DFT density functional theory o degrees deg degrees 8 molar absorptivity (M"'cm"') El/2 half wave redox potential (V) EQX peak potential, oxidation process (V) X V EI electron ionization ESI electrospray ionization E S R electron spin resonance Et ethyl eV electron volts g gram G P C gel permeation chromatography hapticity h Planck's constant H E high energy H P L C high-pressure liquid chromatography H O M O highest occupied molecular orbital H z Hertz i.e. id est IR infrared I V C T intervalence charge transfer J magnetic coupling constant, N M R coupling constant K Ke lv in k rate constant kQ Boltzmann constant kJ kilojoule L ligand X wavelength (nm) ^Em emission wavelength (nm) excitation wavelength (nm) -^max wavelength at band maximum (nm) L E low energy L E D light emitting diode L L C T ligand-to-ligand charge transfer L M C T ligand-to-metal charge transfer L U M O lowest unoccupied molecular orbital M molarity (molL" 1) xvi m multiplet u bridging u energy of X-rays used for crystallographic determination m M mmolL"1 m/z mass-to-charge ratio M A L D I - T O F matrix-assisted laser desorption ionization time of flight Me methyl M L C T metal-to-ligand charge transfer mg milligram M H z Megahertz mmol millimole M S mass spectra m V millivolts M W molecular weight mL milliliter mol mole v frequency n- normal near-IR near-infrared nm nanometer N M R nuclear magnetic resonance O R T E P Oak Ridge Thermal Ellipsoid Plot p pentet Ph phenyl ppm parts per million PT 2-diphenylphosphinothiophene P T 2 2-diphenylphosphino-5,2'-bithiophene P T 3 2- diphenylphosphino-5,2':5',2"-terthiophene PTP 2,5-bis(diphenylphosphino)thiophene P T 2 P 2,5'-bis(diphenylphosphino)-5,2'-bithiophene PT 3 P 2,5"-bis(diphenylphosphino)-5,2':5',2"-terthiophene q quartet xvii s singlet S Siemens sh shoulder SCE saturated calomel electrode s.v. sub verbo t triplet T temperature T thiophene T 2 bithiophene T 3 terthiophene T4 quaterthiophene t- tertiary terpy terpyridine TLC thin layer chromatography THF tetrahydrofuran tht tetrahydrothiophene T M E D A tetramethylethylene diamine Tp* tris(3,5-dimethylpyrazol-l-yl)hydroborate Ts tosyl U B C University of British Columbia U V ultraviolet V Volts V volume v. very vis visible VPO vapor pressure osmometry V T variable temperature vol:vol volume to volume ratio X halogen 1 transmission coefficient Z number of molecules in a crystallographic unit cell xviii Acknowledgements The first person I must acknowledge is, of course, my supervisor for the past five years, Dr. Mike Wolf. Mike, you have taught me many lessons about research and chemistry, and life. I feel that I have grown as a chemist and a person since joining your group. Thank you for the opportunity to work on this project. I am grateful to Dr. Derek Gates for reading this thesis in its entirety. Also, a huge thank you to my fellow group member Kristin Matkovich, who, unfortunately for her but very fortunately for me, was around all summer to also read my entire thesis. Kristin, your quick reading (when necessary) and careful editing have certainly improved the quality of this thesis. To the other members of the Wolf group, past and present, with whom I have had the great pleasure of working: Thank you! What a great group of smart, hard-working, supportive people. I wish all grads students the same positive experience with their co-workers. Thanks for the ever-exciting lunchroom chats and the varied and sundry group meeting snacks. I have made many friends here that I hope to keep for many years. Also, an acknowledgement of the MacLachlan group, our next-door neighbours, seems appropriate. They have generously allowed me to use their equipment, chemicals, and glassware when needed, and they are also just fun to see every day. Much of this work could not have been accomplished without the very capable support staff in our department. Brian Patrick and Anita Lam solved all the crystal structures presented in this thesis, even with all the disorder and twinning I threw at them. Brian was also always very helpful with questions and concerns. The N M R staff often gave me useful tips and the mass spectrometry lab did a great job with both mass spectral and elemental analysis data. There are many other staff members, too numerous to name individually, who xix also helped me along, including members of the mechanical shop, the glass blower, and secretarial staff. Outside of the chemistry department, my family has been a great support to me over the course of my university studies. My aunt and uncle, Tim Stott and Jessie MacDonald, have aided and encouraged me from my first year of university onwards, and I must thank them for all their help. To my parents, my personal cheerleaders, who have always supported and assisted me, I could not have done this without you. Finally, to my wonderfully understanding, kind, thoughtful, helpful, and, best of all, very funny husband Mike: for everything, thank you. xx Chapter 1 Introduction 1.1 Overview Functional materials surround us in our daily life, from natural materials like diatomaceous earth to modern materials, like plastics. Many synthetic materials have been serendipitously discovered;1 however, scientists do attempt the design of materials with specific goals in mind. One of the major goals in materials science is the miniaturization of electronic devices to molecular dimensions. The design of molecule-based electronics has captured the imagination of chemists and opened a new field of study. Prototype devices made of a single molecule have been reported.2 Conjugated organic materials show promise in this area, as they can act as molecular wires to transport charge. These materials also exhibit other interesting properties, for example, electroluminescence, which may lead to applications in other areas, such as in LEDs. 3 By combining transition metal chemistry with organic materials, new materials may be developed that marry the chemical, electronic, and optical properties of transition metal complexes with conjugated materials. This chapter contains important concepts for understanding the work that follows. It introduces conjugated organic materials, and discusses the interactions between metals and conjugated, organic ligands. A summary of the possible types of hybrid materials and a literature review of relevant complexes follows. Finally, the goals and scope of the thesis are stated. 1 1.2 Conjugated materials Conjugated polymers and oligomers are an exciting new class of materials, which are interesting from both an academic and an application-based point of view because of their electronic and optical properties.4'5 Several common conjugated polymers are shown in Figure 1.1. A thoroughly studied class of conjugated materials is the oligo- and polythiophenes.6 They are synthetically versatile and robust, and exhibit interesting electronic (the conductivity of doped polythiophene can be as high as 103 Scm"1)4 and optical properties. Thiophene has two positions at which it can undergo carbon-carbon bond formation, the a, or 2, position and the P, or 3, position (Chart 1.1). Polythiophenes with ct,a-linkages are desirable, as they have a more planar conformation, and thus exhibit improved electronic properties over those with ct,P- or P,P-linkages. 7 ' 8 polythiophene polypyrrole poly(p-phenylenevinylene) polyaniline Figure 1.1 Representative conjugated polymers H 2 Chart 1.1 Thiophene is an aromatic molecule with delocalized rc-electrons. A simplified molecular orbital diagram showing the HOMO and L U M O of thiophene is displayed in Figure 1.2. When two thiophene molecules are linked, two new energy levels are added to the molecular orbital diagram, the HOMO increases in energy, and the L U M O decreases in energy. As more thiophene molecules are added to the oligomer, the number of energy levels increases, and the HOMO and L U M O become closer in energy. In polythiophene, an infinite chain of thiophene units, the molecular orbital diagram resembles that of a semiconductor; it consists of a continuum of energy levels with a conduction band and a valence band. The decrease in the H O M O - L U M O gap as the chain length of an oligothiophene is increased can be observed by absorption spectroscopy. For example, thiophene absorbs with a A, m a x at 231 nm, 2,2'-bithiophene at 303 nm, 2,2':5',2"-terthiophene at 354 nm, 9 and polythiophene at 480 nm. 6 An increase in the energy of the HOMO of a series of oligothiophenes as the chain length increases can be verified by comparing the oxidation potentials of the compounds, as measured by cyclic voltammetry.8 3 LUMO Energy Conduction Band Band Gap HOMO 4 Valence Band In n = 1 n = 2 n = 3 n=oo Figure 1.2 Evolution of the molecular orbitals of oligothiophenes as a function of chain length. The synthesis and characterization of oligomers is an important area of research in the field of conjugated materials. 8 Polymers exists with a distribution of molecular weights and may also have structural defects, whereas oligomers are discrete molecules, and so can be purified and well characterized. Oligomers can, therefore, be used to determine structure-property relationships that, in turn, can be related to the corresponding polymers. Some oligomers also exhibit enhanced properties, such as charge transport, as compared to the polymeric f o r m . 1 0 ' 1 1 4 1.3 Metal-organic materials Modification and enhancement of the properties of conjugated materials are goals of materials research. This has been achieved through both synthetic modifications of the organic backbone, 7 ' 1 2 ' 1 3 and by physical methods, for example, the method of deposition of solid films.14 One promising method of control is the coordination of transition metal centres to the polymer backbone, as may allow for the interaction of the chemical, electronic, and optical properties of the metal centre with the organic moiety . 1 5 - 1 9 A transition metal may affect, and be affected by, a conjugated ligand both structurally and electronically. For example, a metal group may control the solid state packing of oligomers 2 0 or it may hold the oligomer in a particular conformation, increasing21 n-orbital overlap in the system. Electronic interactions can occur through several mechanisms. 1 6 ' 1 7 ' 2 2 Inductive interactions usually result in weak effects, but stronger interactions are observed with charge transfer. Ligand- to- metal or metal- to- ligand charge transfers may occur, depending on the energies of the orbitals involved. In a multimetallic system, good orbital overlap may also result in electron or hole transfer from one metal centre to another, through the conjugated linker. If the complex is homobimetallic, this can create a mixed valence species, where the two metals are in different oxidation states. Energy and electron transfer can also quench the emission of a bridging ligand. Several methods can be used to measure the electronic coupling between a conjugated group and a metal centre.23 UV-visible and near-IR absorption spectroscopies are widely used techniques. A bathochromic shift in the spectrum of a complex as compared to uncoordinated ligand indicates derealization of electrons to the metal centre. Charge transfer bands can also be monitored by absorption spectroscopy. Electrochemistry, generally cyclic 5 voltammetry, is used to probe changes in the energy levels of the metal and the organic moiety. It can also be used to determine the extent of electronic interaction of two metal groups across a conjugated bridge. If there is no coupling, the oxidation of the metal groups should occur simultaneously and the C V will exhibit one oxidation wave. Any electronic coupling of the metal centres will cause the oxidation of the second metal group to occur at a higher energy. Combining absorption spectroscopy and cyclic voltammetry creates a very useful technique known as spectroelectrochemistry. It allows for observation of the absorption spectra of species generated with oxidation or reduction of the metal or ligand, which can show charge transfer bands or increased electron derealization over the ground state complex. The observation of mixed valence species, through the appearance of intervalence charge transfer (IVCT) bands in the visible or near-IR spectrum, is possible with spectroelectrochemistry. Other techniques such as ESR, magnetic measurements, and emission spectroscopy can also be used, depending on the nature of the metal centre and the conjugated moiety. Three types of transition metal-conjugated organic hybrid materials can be envisioned, and are shown in Figure 1.3. Type I materials have the metal centre tethered at a distance from the conjugated backbone. The tether is typically a saturated organic group. Swager and Holliday have identified this class of compounds as "outer sphere", in reference to classical inorganic electron transfer theory.1 7 An example of a Type I complex is shown in Chart 1.2.24 The absorption spectrum and the cyclic voltammogram of 1 do not indicate any interaction between the terthienyl group and the metal centre. 6 Figure 1.3 Schematic of three types of transition metal-conjugated organic hybrid materials. Chart 1.2 1 A second class of hybrid materials shown in Figure 1.3 has a transition metal closely coordinated to the conjugated backbone, but the metal is not inserted directly into the conjugation pathway (Type II). A Type II material may or may not exhibit interaction between the metal and the organic moiety, depending on the nature of the linker between the two, and the energy levels of the system. Complexes 2 2 5 and 3 2 1 (Chart 1.3) are examples of 7 Type II complexes. The N i and the terthienyl group in 2 do not appear to interact significantly by cyclic voltammetry. Complex 2 has been electropolymerized, and the films exhibit one metal-based peak, indicating little interaction between metal centres. In contrast, coordination of R u 2 + in 3 has a significant effect on the terthienyl group, as indicated by absorption spectroscopy and cyclic voltammetry. Chart 1.3 2 3 Finally, in a Type III material the metal is inserted directly into the conjugation pathway. The metal and the organic moiety should couple strongly in this motif, i.e. this is an "inner sphere"17 complex. Complex 4 is an example of a Type III material.2 6 The metal centre was shown to interact with the terthienyl group by absorption spectroscopy and by cyclic voltammetry. 8 Chart 1.4 s P h 2 P x PPh 2 s w /r\ /ri feRur=i ^r\\ /rxj . Ph 2 P x P P h 2 The coordination of transition metals to conducting oligomers and polymers is a large area of study, and many reviews in this area have been publ ished. 1 5 - 1 9 ' 2 7 This thesis is concerned with Type III oligomers, in which an oligothiophene bridges two transition metals (Figure 1.4). These complexes can serve as model complexes for polymers and may also exhibit interesting properties on their own. There are many examples of Type III materials known, incorporating different transition metals, notably Fe, Ru, and Pt, and several different coordinating groups have been used to link the metal centre to the oligothiophene. Pyridine derivatives and 7i-complexes are common linkers, and other coordinating atoms such as oxygen and carbon have been used. A literature review of relevant Type III oligomers, classified by linker groups, follows. A more detailed review of the literature up to 2003 has been published.2 8 M W // M ( M ) = metal group L/ = linker group Figure 1.4 Schematic of a bimetallic Type III complex. 9 1.4 L i terature Review 1.4.1 Carbon-bound complexes The direct coordination of a transition metal to an oligothiophene through the a-carbon seems a promising route to strong electronic coupling between the two, and several complexes of this type have been reported. For example, Sonogashira has reported Pt complexes of thiophene and bithiophene (5 in Chart 1.5).29 The TI—»TC* transition of the bithienyl complex is shifted from that of 2,2'-bithiophene by 49 nm, indicating an extension of the rc-system over the metal centres. Lin and co-workers obtained additional evidence for derealization of electron density to Pt by synthesizing a series of ferrocenyl-capped thienyl complexes (6). 3 0 These complexes exhibited red shifts in the UV-visible spectra and the oxidation potential of the ferrocenyl group was found to decrease as compared to the corresponding complexes that did not contain Pt. Complex 7 was reported to show a large electrochemical interaction of 550 m V . 3 1 Crystal structures were reported for 8 3 2 and 9; 3 3 however, the electronic properties were not investigated. 10 Chart 1.5 B u 3 P C l - P t -B u 3 P S. n P B u 3 Pt-CI P B u 3 5 n=1,2 6 M = Pt, Pd n = 1, 2 7 M e 3 P B r - P d M e 3 P S P M e 3 Pd-Br P M e 3 P-P = 1,1 '-bis(diphenylphosphino)ferrocene 8 n=1,2 9 1.4.2 7t-complexes Cyclopentadienyl. Ferrocenyl end groups are widely used in the study of metal-metal interactions over conjugated bridges.3 4 They are easy to synthesize and often stable in both the oxidized and reduced forms. Several examples are shown in Chart 1.6. Complex 10 showed coupling by cyclic voltammetry, with A E = 150 m V . 3 5 Longer oligothiophenes (11 and 12) have also been synthesized, and, although they show no electrochemical coupling, when oxidized with one equivalent of FeCb a ligand-to-metal charge transfer (LMCT) band appears in the near IR region. 3 6" 3 8 Compounds incorporating vinyl and alkynyl groups (13-2 0 ) 3 9 ' 4 0 have also been investigated. The n—>n* absorptions of 13-15 are red-shifted with respect to the unsubstituted thiophene, indicating extended conjugation, but no electrochemical coupling was observed. In 16-20, when both Fe groups were electrochemically oxidized, a broad, low- energy band was observed in the near IR region 11 (875 - 1290 nm), which was assigned as an oligothiophene-»Fe(III) L M C T band. The intensity and position of the L M C T are related to the extent of derealization in the complex, and the intensity increases and energy decreases with an increase in the conjugation length of the oligothiophene. Chart 1.6 16 n=1 19 n=1 17 n=2 20 n=2 18 n=3 ri 6-Phenyl. Another n-type ligand that can be attached to an oligothiophene is a phenyl group. Mann and co-workers 4 1 ' 4 2 have synthesized 21-24. The free ligand does not polymerize electrochemically and the oxidation potential changes very little from 12 terthiophene, indicating poor conjugation of the terthiophene core with the phenyl groups. However, the UV-visible spectrum of the ligand shows a red shift with respect to terthiophene. Upon complexation of the metal, the emission is red shifted and the quantum yield of emission is reduced with respect to the free ligand. Absorption is also slightly red shifted in the complex. The oxidation potentials increase by about 150 mV per ruthenium group, due to an increase in positive charge, and a new, metal-based reduction process appears, but no electrochemical coupling was observed. Spectroelectrochemical studies were performed, but no IVCT band was observed. In fact, upon one- and two-electron oxidation, the spectra of the complexes were very similar to those of other ct-capped terthiophenes, suggesting that the positive charge is localized on the terthienyl moiety. Chart 1.7 A phenyl group has been fused directly to an oligothiophene to create an inflexible ligating group 4 3 and this ligand was complexed to [CpRu(CH 3CN) 3] to yield 25. Similar to 21-24, a red-shift of the n—»TC* band in the UV-visible absorption was observed, the emission 13 of the free ligand was quenched, the oxidation potentials were raised, and a metal-based reduction process appears in the C V upon coordination of the R u 2 + centre. No electrochemical coupling was observed, and the spectroelectrochemistry was not investigated. An X-ray crystal structure of 25 was obtained, and the terthienyl core was found to be planar. Chart 1.8 r|5-Thiophene. Thiophene can coordinate in an n 5 manner to transition metal centres, similar to cyclopentadiene. For example, 26-29 were synthesized by reacting the appropriate oligothiophene with two equivalents of [CpRu(CH 3CN)] + or [Cp*Ru(CH 3CN)] + (Cp* = pentamethylcylopentadiene).41'42 Upon electrochemical oxidation, all four complexes formed a conducting film on the electrode, but none showed evidence for metal-metal interaction by CV. In fact, binding a metal to one ring of the oligothiophene in an r|5-fashion effectively removed that ring from conjugation. 14 Chart 1.9 26 n=1 28 n=1 27 n=2 29 n=2 1.4.3 Acetylene complexes Acetylene groups are attractive for coordinating transition metals to oligothiophenes, as they are easy to synthesize by organometallic cross-coupling reactions and form stable coordination complexes with many metals.4 4 Acetylene groups should also extend the conjugation of the oligothiophene, as they contain delocalized rc-electron. Lapinte and coworkers have isolated Fe complex 30 (Chart 1.10), and its mixed-valence analogue.45 The C V of 30 exhibited a large separation of 340 mV between the F e 2 + / 3 + oxidation waves, indicating strong electronic coupling across the conjugated bridge. New absorption bands, which are probably due to L M C T transitions, appear in the spectrum of the mixed valence compound. Mossbauer and near-IR spectroscopy indicated derealization of the unpaired electron. A series of thiophene-bridged acetylene complexes with Mo, W, Fe, and Ru have been synthesized (31); however, no electronic data was reported for these complexes.46 Several ruthenium acetylides incorporating thienyl groups have been synthesized and their non-linear optical properties have been probed. 4 7 ' 4 8 The thienyl chains were found to facilitate Ti-electron derealization. 15 Chart 1.10 P h 2 P ' F ? ~ ~ = 6 ( C O ) n M ^ 0 ^ ^ F e - p p h 2 'n M = Mo, W, Fe, Ru; n = 2,3 30 31 Pt forms stable acetylide complexes, and several have been reported. For example, a series of bimetallic complexes (32) were isolated.4 9 Bathochromic shifts were observed in the spectra of the complexes as compared to the ligands. X-ray crystal structures were obtained for the complexes with n = 1 and 2 and the conjugated linkers were found to be planar in both cases. A series of mixed Pt/ferrocene complexes have been synthesized (33). 5 0 The incorporation of the Pt centre causes red shifts in the absorption spectra and lowers the oxidation potential of the ferrocenyl group. X-ray crystal structures are reported for the bithienyl complexes, and all exhibit planar conformations, indicating rc-overlap across the system. Chart 1.11 32 n = 1-3 33 n = 1-3 16 Acetylide complexes of Hg(II) (34)51 and Au(I) (35)5 2 were also isolated and characterized by X-ray crystallography and absorption and emission spectroscopy. The absorption and emission spectra of the Hg complexes are red shifted relative to the corresponding ligands, indicating n-electron derealization over the metal centre. Calculations indicating a small metal contribution to both the H O M O and L U M O supported the assignment of absorption and emission to metal-perturbed, n—>K* transitions. Crystal structures were obtained for n = 1 and 2; the bithienyl complex has a dihedral angle of 27°. In the Au complexes, the n-systems for all three were found to be planar in the solid state. The absorption and emission spectra of the complexes are red shifted relative to the corresponding ligands. In comparing the Pt, Hg, and Au complexes, the bathochromic shifts in the electronic spectra as compared to the ligands decrease in the order Pt > Au > Hg. Chart 1.12 MeHg = / V S > y \ — = — H g M e P h 3 P A u = / V S ^ V - = — A u P P h 3 n n 34n = 1-3 35 n = 1-3 1.4.4 Pyridines, bipyridines, and terpyridines Pyridines, bipyridines, and terpyridines are useful as ligating groups. They form complexes with many metals, notably ruthenium, and the complexes are often stable in a variety of oxidation states, allowing access to mixed valence complexes. Metal complexes of these ligands, particularly R u 2 + bipyridine derivatives, often exhibit interesting optical 17 properties. Also, the synthesis of the metal pyridine complexes and the corresponding ligands is well established and straightforward. Pyridine. Several pyridyl-capped oligothiophenes that have been coordinated to transition metals are shown in Chart 1.13. Complexes 36-39 5 3 were complexed to Mo(Tp*) (Tp* = tris(3,5-dimethylpyrazol-l-yl)hydroborate). The Mo complexes of 36-38 and 40 showed evidence of metal-metal interaction via C V (AE = 450, 220, 60 mV, and 50 mV, respectively) upon reduction. In 36-40, both unpaired electrons are coupled to both Mo nuclei, as observed by ESR spectroscopy. The emission intensity of these complexes is lower then that of the corresponding free ligands due to quenching by the metal, and the n—>n* transition of the ligand is red-shifted on complexation. A ruthenium complex of 36 ([Ru(NFf3)5]2-36) was also prepared.54 Although only a single oxidation peak was seen in the CV, an IVCT band appears when the mixed valence species is formed. The C V of complex 4 1 5 5 showed no evidence of metal-metal interaction. However, the absorption spectrum was red shifted relative to the ligand, and the luminescence of the complex is quenched relative to the free ligand. 18 Chart 1.13 Bipyridine. Ruthenium coordination compounds incorporating bipyridine (bpy) ligands have been extensively studied, and the electrochemical and optical properties of these complexes are well understood.5 6"5 8 Therefore, bipyridine has been incorporated into oligomeric complexes and polymers; selected examples are shown in Chart 1.14. The TT—>7X* absorptions for the bridging ligands in 42-44 are red shifted with respect to the unsubstituted thiophene core, which indicates electron derealization onto the pyridine rings. 5 9 In the complexes, the n—>n* bands appear to red shift relative to the ligands, but they overlap with the Ru->bpy M L C T and full assignment of the spectra is difficult. No electrochemical coupling of the metal centres was observed, but the oxidation potential of the bridging ligand was raised due to coordination of the positively charged Ru centre. Derealization in the conjugated bridges of 45 and 46 was observed in the electronic spectra, but the metal groups did not show any interaction by C V . 6 0 > 6 1 19 Chart 1.14 Ru(bpy)2 46 An interesting application of metal-metal coupling over a conjugated bridge is the photochromic switch 47. 6 2 Dithienylethene is photochromic, switching from open to closed 20 forms upon irradiation with light (Chart 1.15). Although the open form is not conjugated, the closed form is, and incorporation of this group into a bimetallic system leads to switchable coupling of the metal centres. The CVs of both the open and closed forms exhibit a single, reversible R u 2 + / 3 + oxidation wave; however, upon oxidation to the mixed valence state of the closed form, an IVCT band was observed in the near-IR. Terpyridine. The RuL2(bpy)2 end group is chiral, resulting in dimetallic products that are mixtures of diastereomers. Several groups have explored the use of synthetic and separation techniques to produce enantiomerically pure complexes; 6 3" 6 6 a second option is to 21 start with an achiral metal complex. Terpyridine (terpy) is an attractive alternative to bpy because it has similar chemical properties, but the M L C T is short-lived in terpy complexes and the complexes are generally not emissive at room temperature.67 However, even with these disadvantages, many terpyridine-oligthiophene R u 2 + and Os 2 + complexes have been reported. For example, a series of ruthenium and osmium complexes 48-50 were synthesized with a terpyridyl-thiophene l igand. 6 8 ' 6 9 Interestingly, the addition of the thiophene ring to the terpyridine ligating group raises the luminescence lifetime and efficiency over that of [Ru(terpy)2]2+ because of the increased conjugation of the ligand. Also, the M L C T band red shifts, s increases, and luminescence lifetime and efficiency increase as the number of metal centres increases. This indicates a stabilization of the M L C T levels through metal-metal communication. In the mixed ruthenium-osmium complex, energy transfer between the metal centres is observed via time-resolved luminescence experiments. However, the homometallic species exhibited no metal coupling in the respective CVs. An X-ray crystal structure of 48 was obtained, and it showed that the central terpy ring was co-planar with the thienyl moiety. Complex 51 is analogous to 45 and has similar properties. The absorption spectrum of the ligand is at much lower energy than thiophene; however, the coordination of the metal centre does not shift the ligand-based transitions substantially. The metals do not exhibit coupling in the CV, but the oxidation potential of the metal is higher in energy than [Ru(terpy)2J2+ due to the electron-withdrawing ethynyl-thiophene group. 22 Chart 1.16 48 M 1 =M 2 =Ru 49 M 1 =M 2 =Os 50 M 1 =Ru, M 2= Os 51 1.4.5 Oxygen-bound complexes Oxygen-containing groups have been used to coordinate oligothiophenes to two early transition metals, molybdenum and tungsten. Complexes 52 and 53 7 0> 7 1 are interesting as they incorporate metal-metal bonds into the conjugation pathway. The n = 1 complexes exhibit two metal-based waves in the respective CVs, indicating coupling across the bridge; however, only one metal-based peak is seen in the C V of the bithienyl complex. In the absorption spectra of the n = 1 complexes, intense absorptions in the visible region are observed, which arise from metal-»thiophene (8-MI*) transitions. These M L C T transitions occur at lower energy and are more intense in the tungsten complexes, because the orbital energies of tungsten are closer to those of the bridging group than molybdenum. This is also 23 supported by ESR experiments in which the mixed valence species of the n = 1 complexes were prepared by oxidation with ferrocenium. The ESR spectra showed that the unpaired electron in the Mo complex is delocalized over two metal centres, whereas in the W complex it is delocalized over four metals. Chart 1.17 //"? s ? - \ 52 M=Mo(0 2C fBu) 3 n=1-3 53 M=W(0 2C'Bu) 3 n=1-3 Complexes 54-56 showed strong metal-metal coupling by cyclic voltammetry (AE values of 370 mV, 250 mV, and 170 mV, respectively).72 Upon electrochemical generation of the mixed valence species, intense and broad bands characteristic in position and intensity of phenolate—»Mo(VI) L M C T appeared in the near-IR region, which obscure the expected IVCT bands. Complex 54 also exhibited weak antiferromagnetic coupling (J = -3.6 cm"1). Two similar ligands incorporating naphthyl in place of phenyl, 57 and 58, 7 3 were also synthesized and complexed to Mo. Interestingly, the addition of the large naphthyl groups reduces AE to 250 mV and 140 mV, respectively. This was attributed to a larger dihedral angle between the naphthyl and thienyl groups in 57 and 58 than between the phenyl and 24 thienyl groups in 54. Intense L M C T bands in the near-IR region obscure the expected IVCT bands in these compounds as well. Chart 1.18 1.4.6 Other linker groups Examples also exist of complexes incorporating less common linker groups (Chart 1.19). Mirkin and co-workers have reported the synthesis of 59, where the Ru centre is coordinated to the oligothiophene through both an alkyl tether and the sulfur atom of the terminal thiophene rings. 2 4 The metal oxidation is not accessible in this complex. However, the oxidation of the oligothienyl moiety occurs at a higher potential in this complex than a similar complex in which the metal centre is coordinated to the oligothiophene only through the saturated, alkyl group. A red shift in the absorption spectrum is also observed upon 25 coordination of the metal to the sulfur. An interesting coordination mode is seen in 60, where two Co atoms are coordinated via a Tt-bond.74 These complexes did not show coupling between the metal centres across the oligothienyl bridge by cyclic voltammetry, but the absorption spectra exhibit M L C T bands and red shifts relative to the ligand spectra. Cyclic voltammograms obtained at low temperature for a similar, thienyl-bridged complex did exhibit two metal-based waves. 7 5 Rhodium is inserted into the terminal thiophene rings in 61; no electronic properties were reported for this complex. 7 6 Chart 1.19 60 61 n = 1-3 R = n-butyl, phenyl 26 1.5 Goals and Scope The goal of this thesis is to investigate the electronic and structural interaction between transition metal centres and a series of a- and ct,a"-substituted phosphinothiophene ligands of varying length. The resulting complexes are Type III, similar to those reviewed above, which have a diphenylphosphino group as the linker. Phosphine was chosen as the linker group as it has been shown to facilitate energy transfer from a conjugated ligand to a meta l . 7 7 - 8 0 Phosphines also coordinate to many transition metals, which is useful in a linker group as comparisons can then be made between several transition metals. By varying both the metal centre and the length of the oligothiophene, it may be possible to elucidate factors that influence the strength of the interaction between the metal and the oligothiophene. Chapter 2 describes the synthesis and spectroscopic characterization of the phosphinothiophene ligands. The effect of the diphenylphosphino group on the thienyl moiety is discussed and compared to known systems. Chapters 3, 4, 5, and 6 describe transition metal complexes of the ligands. In several cases, dynamic processes are observed in solution and variable temperature N M R spectroscopy is used to determine the species in solution. X-ray crystallography, where applicable, is used to investigate the structural and packing influence of the metal on the oligothiophene. Absorption and emission spectroscopy are used to probe the electronic overlap between the metal, linker, and organic moiety. In Chapter 3, Au(I) complexes are presented. Phosphine complexes of gold are known to have interesting structural and electronic properties; these are briefly reviewed in the introduction to the chapter. Some of the complexes exhibit gold-gold interactions in the solid state. Chapter 4 deals with attempts to synthesize Au(I) and Ag(I) coordination polymers of the phosphinothiophenes. The complexes exhibited lability in solution, and the structure of the 27 complexes depends on the length of the oligothiophene. In Chapter 5, a series of Pd(II) and Pt(II) complexes are presented. The metal centre is found to influence the solid state packing of the thienyl moieties. Chapter 6 describes Ru(II) complexes, and Chapter 7 contains general conclusions and suggestions for future work. 28 References Thomas, J. M . J. Chem. Soc, Dalton Trans. 1991, 555. Flood, A . H. ; Stoddart, J. F.; Steuerman, D. W.; Heath, J. R. Science 2004, 306, 2055. Moliton, A. ; Hiorns, R. C. Polym. Int. 2004, 53, 1397. 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Organometallics 1997, 16, 1517. Hong, B.; Woodcock, S. R.; Saito, S. K.; Ortega, J. V. J. Chem. Soc, Dalton Trans. 1998, 16, 2615. Ortega, J. V . K. , Kay; van der Veer, Wytze E.; Ziller, Joseph; Hong, Bo. Inorg. Chem. 2000, 39, 6038. Xu, D.; Hong, B. Angew. Chem. Int. Ed. 2000, 39, 1826. 33 (80) Xu, D.; Zhang, J. Z.; Hong, B. J. Phys. Chem. A 2001, 105, 7979. 34 Chapter 2 Phosphinothiophene Ligands and Derivatives: Synthesis and Electronic Spectra 2.1 Introduction A search of the scientific literature results in over 11 000 entries containing the word or concept "phosphine ligands", confirming the utility and widespread use of phosphines as ligands in inorganic chemistry.1 This is due to the ease with which many different phosphines may be synthesized and varied, both electronically and sterically, and the versatility of these ligands in coordinating to many different transition metals. Triaryl phosphines are a well-known group of phosphine ligands, which are relatively air stable. Our group has focused on the use of diphenylthienyl phosphines as ligands to coordinate transition metal centres to oligothiophenes. Previous workers have synthesized a variety of (3-substituted phosphino(oligothiophenes)2"7 (Chart 2.1); a-substituted phosphinothiophenes 65-70 (Chart 2.2) were synthesized in this thesis for comparison. To determine the effect of transition metal coordination on the electronic properties of the conjugated system, an investigation of the absorption and emission properties of 65-70 was undertaken. 35 Chart 2.1 Chart 2.2 PTP (68) PT 2P (69) PT 3 P (70) Phosphine oxides and phosphine sulfides are easily synthesized derivatives of phosphines, and are useful for comparison to the phosphines and metal complexes. These derivatives could also be used as ligands. 8" 1 3 Benzyl phosphonium salts, while unable to act as ligands, are useful for comparison to the free phosphines. Polymers of these phosphonium salts could also be made by reaction of a bisphosphine and a dihaloalkane. 36 A variety of a-substituted oligothiophenes have been synthesized and characterized. These derivatives generally exhibit some interaction between the thiophene moiety and the substituent, indicated by bathochromic shifts in the absorption and emission spectra and lower redox potentials as compared to the parent oligomers. Electronic data for a,a"-substituted terthiophenes is summarized in Table 2.1. The extent and nature of the interaction is determined by the substituent. For example, the bathochromic shift for the amino-substituted compound is large, and is attributed to derealization of the nitrogen lone pair over the aromatic system.1 4 The silanylene-substituted terthiophene, on the other hand, shows a much smaller red shift, which is thought to be due to n-asi conjugation.15 The extremely large bathochromic shift upon dicyanomethylene substitution is due to the formation of a quinoid-type structure (Chart 2.3), which is supported by an X-ray crystal structure of a butyl-substituted analogue.16 Chart 2.3 N N 71 37 Table 2.1. Comparison of electronic data of a,a"-substituted terthiophenes, A X m a x as compared to T 3 (absorption, Xmax = 354 nm; emission, A, m a x = 426 nm). 1 7 Substituent Absorption (solvent) Emission E o x / V vs. SCE AA,m a x/nm E o x T 3 = 0.98 vs. S C E 1 8 (solvent) (solvent/electrolyte) Reference -C(CN) 2 - N 0 2 -C(0)H -NPh 2 -C4H3S -Ph -PPh 2 -SH -CN -Br 289 (CH 2C1 2) 84 (THF) 79 (THF) 69 (toluene) 62 (CHCI3) 54 (CH 2C1 2) 41 (CH 2C1 2) 35 (THF) 23 (toluene) 19 (THF) 12 (benzene) -Si(Me)3 8 (n-hexane) 98 75 (CHCI3) 61 (hexanes) 10 (toluene) 11 («-hexane) 0.42/1.89 (benzonitrile/[(rc-Bu)4N]PF6) 0.925 0.902, 1.28 (CH 2Cl 2/[(«-Bu) 4N]PF 6) 0.90 (CH 2Cl 2/[(tt-Bu) 4N]PF 6) 1.506 (CH 3CN/[(«-Bu) 4N]PF 6) - C H 3 (CH 3 CN) 0.99 (CH 3 CN/[Et 4 N]BF 4 ) 16 19 20 21 18 22 23 24 25 19 26 15 27 38 In this chapter, the synthesis and electronic spectroscopy of phosphinothiophenes 65-70 are reported. The absorption and emission spectra show dependence on the length of the thiophene oligomer, and molecular modeling is used to support the assignment of the emission bands. This work has been published.2 3 The synthesis and electronic spectroscopy of the oxides 74a-c, sulfides 75a-c, and the benzyl bromide salts 76a-c are also reported. The absorption and emission spectra of these compounds are compared to those of the corresponding unsubstituted phosphine. 2.2 Experimental 2.2.1 General A l l reactions were performed under a nitrogen atmosphere, using standard Schlenk techniques and dry solvents, except where indicated. Diethyl ether, toluene, and hexanes were dried by passing over an activated alumina column. C H 3 C N was dried over 3A molecular sieves and degassed by sparging with N 2 for 20 min. PPh 2 Cl was purchased from Aldrich and was distilled prior to use. The following compounds were made by literature methods: 2,2'-bithiophene,28 2,2':5',2"-terthiophene,28 3,3"'-dihexyl-2,2':5',2":5",2"'-quaterthiophene,29 P T 2 (66), 3 0 P T 2 P (69), 3 1 P T 3 (67),4 and P T 3 P (70). 3 0 ' H and 3 I P{'H} N M R experiments were performed on either a Bruker AC-200E, Bruker AV-300, or Bruker AV-400 spectrometer. Spectra were referenced to residual solvent ('H) or external 85% H3PO4 ( 3 1P). Absorption spectra were obtained on a Cary 5000 in HPLC grade CH 2 C1 2 . Emission spectra were obtained on a Cary Eclipse or a Photon Technology International QuantaMaster fluorimeter, in HPLC grade solvent. Solid state absorption and emission 39 spectra were obtained by casting a thin film of the compound from a CH2CI2 solution onto quartz slides. Some emission and excitation spectra contain peaks from excitation or emission overtones; these are indicated with an asterisk. Microanalyses were performed at UBC. DFT calculations were performed using a B3LYP/6-31G* basis set implemented in the Spartan 02 software package.3 2 Mass spectrometry was performed on a Kratos MS50 spectrometer. 2.2.2 Procedures 2-diphenylphosphinothiophene (PT) (65). A solution of thiophene (1 mL, 12.5 mmol) in 100 mL dry E t 2 0 was cooled to 0 °C, and 9.4 mL (15 mmol) 1.6 M rc-butyl lithium was added dropwise via syringe. The resulting white suspension was warmed to room temperature, stirred for 2 hours, and then cooled again to 0 °C. After 2.3 mL (15 mmol) of PPh 2 Cl was added via syringe, the ice bath was removed and the reaction mixture was stirred overnight at room temperature. 50 mL of 0.1 M HC1 and crushed ice were added to the mixture, which was then washed three times with CH3CI. The organic phases were combined, washed with saturated NaHCC>3 solution and saturated NaCl solution, and dried over Na2SC>4. The solvent was removed, which yielded a viscous, clear oil. This crude product was purified by column chromatography on silica gel with 1:4 CLbC^hexanes eluent. Two bands were isolated as viscous oils, the first was the desired product, and the second was 68. Yield: 60%. Anal. C i 6 H, 3 PS requires: C, 71.62; H , 4.88. Found: C, 71.41; H, 4.99. MS (EI) m/z: 268. *H N M R (CDC13): 5 7.58 (dd, J = 4.8, 1.2 Hz, 1H), 7.41-7.29 (m, 11H), 7.12 (ddd, J = 4.8, 3.7, 1.2 Hz, 1H). 3 1 P{ ! H} N M R (CDC13) 5 -18 (s). 2,5-bis(diphenylphosphino)thiophene (PTP) (68). A solution of thiophene (1 mL, 12.5 mmol) and T M E D A (3.8 mL, 25 mL) in 50 mL of hexanes was cooled to 0 °C, and 15.7 40 mL (25 mmol) 1.6 M «-butyl lithium was added dropwise via syringe. The ice bath was removed, the solution was heated to reflux for 30 minutes, and the resultant white suspension was cooled again in an ice bath. 4.7 mL (25 mmol) of PPI12CI was added via syringe, the ice bath was removed, and the reaction mixture was stirred overnight at room temperature. 50 mL of 0.1 M HC1 and crushed ice were added to the mixture, which was then washed three times with hexanes. The organic phases were combined, washed with saturated NaHCC>3 solution and saturated NaCl solution, and dried over Na2SC»4. The solvent was then removed, which yielded viscous, light yellow oil. The crude product was purified by column chromatography on silica gel with 1:3 CH2Cl2:hexanes as the eluent. Two bands were isolated as viscous oils, the first was 65, and the second was the desired product. The oil was recrystallized in ethanol with 2% CH2CI2 added to give large clear, colorless crystals. Yield: 25%. Anal. C28H22P2S requires: C, 74.32; H, 4.90. Found: C, 74.58; H, 4.88. MS (EI) m/z: 452. ' H N M R (CDCI3): 5 7.37-7.27 (m, 10H), 7.17 (dd, J = 4.2, 2.3 Hz, 1H). 3 1 P{'H} N M R (CDCl 3 )8-19(s). 3,3"'-dihexyl-2,5"'-diiodo-5,2':5',2":5",2"'-quaterthiophene (IT 4I) (72). Without regard for the exclusion of oxygen, 0.763 g (3.38 mmol) of N-iodosuccinimide was stirred with 0.844 g (1.69 mmol) 3,3"'-dihexyl-2,2':5',2":5",2"'-quaterthiophene in a 1:1 mixture of CH 3C1 and acetic acid, in the absence of light for 12 hours. The reaction mixture was washed with three 25 mL portions of H 2 0 , then dried over MgSC>4 and gravity filtered. The solvent was removed by rotary evaporation, and the resulting dark orange solid was purified by silica column, using hexanes as the eluent. IT4I was isolated as a dark yellow powder. Yield: 75%. Anal. C28H32I2S4 requires: C, 44.80; H, 4.30. Found: C, 45.20; H, 4.60. MS (EI) m/z 750. l H N M R (CDCI3): 5 7.09 (d, J = 3.8 Hz, 1H), 7.06 (s, 1H), 6.94 (d, J = 3.8 Hz, 1H), 2.70 (t, J = 41 7.7 Hz, 2H), 1.59 (p, J = 7.7 Hz, 2H), 1.37-1.24 (m, 5H), 0.87 (t, J = 6.6 Hz, 3H). UV-vis: 252 nm (e = 1.3 x 104 M ' W 1 ) , 390 nm (s = 2.6 x 104 M ' W 1 ) . Emission: ^ m a x = 470 nm. 2,5"'-bis(diphenyIphosphino)- 5,2':5',2":5",2"'-quaterthiophene (PT 4P) (73). IT 4I (0.4 mmol), 1.6 mol NEt3, and 0.15 mol% Pd(OAc)2 were stirred together in dry, degassed C H 3 C N . Upon addition of PPI12H (0.8 mmol), the yellow solution turned a deep red, and the mixture was then heated to 85 °C for 12 h. The reaction was cooled to room temperature, and 30 mL of H2O and 30 mL of CH2CI2 were added. The organic phase was separated, washed three times with saturated NaCl solution, dried over NaS0 4 , and gravity filtered. The solvent was removed by rotary evaporation. The resulting sticky, orange solid was purified via column chromatography (8:1 hexanes:CH2Cl2), and the product was obtained as yellow oil. Yield: 56%. ' H N M R (CDC13): 5 7.42-7.32 (m, 10H), 7.14 (d, J = 6.4 Hz, 1H), 7.05 (d, J = 3.7 Hz, 1H), 6.96 (d, J = 3.7 Hz, 1H), 2.73 (t, J = 7.6 Hz, 2H), 1.62 (p, J = 7.6 Hz, 2H), 1.38-1.24 (m, 5H), 0.86 (t, J = 6.5 Hz, 3H). 3 1 P{'H} N M R (CDC13) 5-18 (s). Synthesis of phosphine oxides. These compounds were synthesized by modification of a literature procedure.5 Without regard for the exclusion of oxygen, an excess of 30% H2C»2 in H2O (0.05 mL) was added, with stirring, to the appropriate ligand in 50 mL of a 1:1 solution of CHCI3:acetone. The mixture was stirred for 1 h and the solvent was then removed by rotary evaporation. The crude product was dissolved in acetone, gravity filtered, and precipitated in hexanes. The resulting powder was further purified by recrystallization in H2O or a 1:20 mixture of H20:acetone. 2,5-bis(diphenylphosphine oxide)thiophene (74a). Yield: 75%. Anal. C28H22O2P2S requires: C, 68.57; H , 4.52. Found: C, 68.70; H , 4.65. MS (EI) m/z 484. ' H N M R (CDCI3): 8 7.78-7.65 (m, 4H), 7.6-7.52 (m, 2H), 7.51-7.42 (m, 5H). 3 1 P{'H} N M R (CDCI3) 8 21 (s). 42 2,5'-bis(diphenylphosphine oxide)-5,2'-bithiophene (74b). Yield: 56%. Anal. C32H24P2O2S2 requires: C, 67.83; H, 4.27. Found: C, 67.62; H , 4.30. MS (EI) m/z: 566. ' H N M R (CDCI3): 5 7.76-7.69 (m, 4H), 7.58-7.52 (m, 2H), 7.49-7.43 (m, 4H), 7.35-7.32 (dd, J = 7.3, 3.9 Hz, 1H), 7.24-7.22 (dd, J = 3.9, 1.9 Hz, 1H). 3 1 P{'H} N M R (CDCI3) 5 22 (s). 2,5"-bis(diphenylphosphine oxide)-5,2':5',2"-terthiophene (74c). Yield: 86%. Anal. C 3 6 H 2 6 P 2 0 2 S 3 - H 2 0 requires: C, 64.85; H, 4.53. Found: C, 64.63; H, 4.43. HRMS (EI): Calc. for C36H2602P2S3: 648.05702; found: 648.05779. ' H N M R (CDC13): 5 7.78-7.71 (m, 4H), 7.59-7.53 (m, 2H), 7.50-7.44 (m, 4H), 7.56-7.20 (dd, J = 7.3, 3.7 Hz, 1H), 7.21-7.19 (dd, J = 3.7, 1.8 Hz , 1H), 7.10 (s, 1H). 3 1 P{'H} N M R (CDC13) 5 22 (s). Synthesis of phosphine sulfides. These compounds were synthesized by modification of a literature procedure.33 Without regard for the exclusion of oxygen, the appropriate ligand was stirred with an excess of S8 in 50 mL of CH2CI2. The reaction was monitored by TLC, and when the phosphine was completely consumed, the solvent was removed by rotary evaporation. The crude product was purified by column chromatography on silica, using a 1:4 CH2Cl2:hexanes mixture to remove less polar impurities. The product was then washed off the column with CH2G2, and the resulting powder was recrystallized in hexanes/CFbCh. 2,5-bis(diphenylphosphine suIfide)thiophene (75a). Yield: 70%. Anal. C28H 2 2P 2S3 requires: C, 65.10; H, 4.92. Found: C, 64.88; H, 4.60. MS (EI) m/z 516. ' H N M R (CDC13): § 7.76-7.70 (m, 4H), 7.54-7.43 (m, 7H). 3 1 P{'H} N M R (CDCI3) 5 34 (s). 2,5'-bis(diphenylphosphine sulfide)-5,2'-bithiophene (75b). Yield: 82%. Anal. C3 2H24P2S3 requires: C, 64.20; H, 4.04. Found: C, 64.06; H , 4.18. MS (EI) m/z: 598. ' H 43 N M R (CDCI3): 5 7.78-7.73 (m, 4H), 7.53-7.50 (m, 2H), 7.47-7.42 (m, 4H), 7.31-7.28 (dd, J = 8.2, 3.6 Hz, 1H), 7.24-7.22 (dd, J = 3.7, 1.5 Hz, 1H). 3 1 P{'H} N M R (CDCI3) 5 34 (s). 2,5'-bis(diphenylphosphine sulfide)-5,2':5',2"-terthiophene (75c). Yield: 80%. Anal. C36H26P2S5 requires: C, 63.51; H, 3.85. Found: C, 63.18; H , 3.94. MS (EI) m/z: 680. N M R (CDCI3): 5 7.82-7.74 (m, 4H), 7.59-7.42 (m, 6H), 7.50-7.44 (m, 4H), 7.33-7.30 (dd, J = 8.1, 3.9 Hz, 1H), 7.18-7.16 (dd, J = 3.9, 1.9 Hz, 1H), 7.10 (s, 1H). 3 1 P{'H} N M R (CDC13) 5 34 (s). Synthesis of phosphonium bromides. The appropriate ligand and an excess of benzylbromide were heated to reflux in 50 mL of toluene for 24 h. The reaction mixture was then cooled to room temperature, and the resulting solid was filtered and washed with toluene and hexanes. The crude product was recrystallized from hexanes/C^Cb. Benzyldiphenylthienylphosphonium bromide (76a). Yield: 75%. Anal. C 2 3H 2oBrPS requires: C, 62.88; H, 4.59. Found: C, 63.15 H, 4.51. MS (EI) m/z 358 (MW -Br). ' H N M R (CDC13): 5 8.08-8.01 (m, 2H), 7.81-7.74 (m, 6H), 7.64-7.59 (m, 4H), 7.42-7.39 (m, 1H), 7.23-7.20 (m, 1H), 7.14-7.12 (m, 2H), 5.39 (d, J = 14.6 Hz, 2H). 3 1 P{ 1 H} N M R (CDC1 3)5 18 (s). Benzyldiphenyl(2,2'-bithienyl)phosphonium bromide (76b). Yield: 82%. Anal. C27H 2 2BrPS2 requires: C, 62.19; H, 4.25. Found: C, 61.95; H, 4.25. MS (EI) m/z: 350 (MW -Br). ' H N M R (CDCI3): 5 8.09-8.60 (dd, J = 7.9, 4.0 Hz, 1H), 7.83-7.74 (m, 6H), 7.64-7.59 (m, 6H), 7.38-7.37 (dd, J = 4.0, 2.4 Hz, 1H), 7.36-7.34 (dd, J = 4.9, 0.9 Hz, 1H), 7.24-7.20 (m, 2H), 7.18-7.12 (m, 4H), 5.43 (d, J = 14.3 Hz, 2H). 3 1 P{'H} N M R (CDCI3) 5 18 (s). Benzyldiphenyl(2,2':5',2"-terthienyl)phosphonium bromide (76c). Yield: 70%. Anal. C 3 i H 2 4 B r P S 3 requires: C, 61.68; H, 4.01. Found: C, 61.28; H, 4.15. MS (EI) m/z: 522 44 (MW - Br). ' H N M R (CDC13): 5 8.10-8.08 (dd, J = 7.6, 3.9 Hz, 1H), 7.84-7.75 (m, 6H), 7.66-7.61 (m, 4H), 7.37-7.38 (dd, J = 3.9, 2.4 Hz, 1H), 7.27-7.22 (m, 5H, includes C H C I 3 ) , 7.27-7.25 (dd, J = 5.2, 1.2 Hz, 1H), 7.20-7.19 (dd, J = 3.7, 0.9 Hz, 1H), 7.14-7.17 (m, 3H), 7.08 (d, J = 3.7 Hz, 1H), 7.03-7.01 (dd, J = 4.9, 3.7 Hz, 1H), 5.43 (d, J - 14.3 Hz, 1H). 3 1 P{'H} N M R (CDC1 3)5 18 (s). 2.3 Results and Discussion 2.3.1 Synthesis Lithiation of the oligothiophene followed by quenching with chlorodiphenylphosphine was a successful, yet low-yielding, route to the desired phosphine in most cases. The low yields are probably due to side reactions of the lithiated oligothiophenes. However, synthesis of 73 by this method resulted only in recovery of starting material or oxidized 73. The resulting phosphine oxide could be reduced,34 but this added another step to the synthesis and did not improve the overall yield. Our group has recently used a second synthetic route to phosphinothiophenes employing a Pd-catalyzed cross-coupling reaction.6 The compounds synthesized by lithiation and subsequent reaction with chlorodiphenylphosphine were isolated in low yields, while the second method resulted in higher yields; however, the catalytic reaction requires an iodo-substituted starting material, adding an extra synthetic step. To synthesize the shorter oligomers 65-70, the lithiation procedure was chosen, while the preparation of 73 required the catalytic procedure. A l l the phosphines oxidize in the solid state and in solution, as evidenced by the eventual appearance of phosphine oxides by TLC and in the N M R spectra; however, the 45 oxidation of 73 occurs rapidly. As reasonably air-stable phosphines were desired to facilitate the straightforward synthesis of metal complexes, 73 was rejected as a potential ligand. The mechanism of oxidation was not determined, but it is known that increased conjugation length can lead to increased reactivity at the a-position. For example, Bauerle and co-workers found it impossible to monobrominate quaterthiophene, as the dibrominated product was formed immediately.3 5 Controlled oxidation of 68-70 was readily achieved by reaction with an excess of hydrogen peroxide or Ss, as shown in Scheme 2.1. The compounds were purified by column chromatography and/or recrystallization. Satisfactory elementary analysis could not be obtained for 74c due to the presence of H2O; however, high-resolution mass spectrometry confirmed the identity of the compound. The phosphonium salts were prepared by heating a mixture of 65, 66, or 67 and benzylbromide to reflux (Scheme 2.2). An excess (1.5-2 equivalents) of benzyl bromide was used to ensure complete reaction. The products precipitated out of the reaction mixture as powders, which were then recrystallized to yield analytically pure compounds. Scheme 2.1 X X n = 1, PTP (68) n = 2, PT 2 P (69) n = 3, PT 3 P (70) n = 1, X = O, 74a n = 2, X = O, 74b n = 3, X = O, 74c n = 1 ,X = S, 75a n = 2, X = S, 75b n = 3, X = S, 75c 46 Scheme 2.2 H n P P h 2 toluene, reflux 24h — > ~ H n n n 1, PT (65) 2, PT 2 (66) 3, PT 3 (67) n = 1,76a n = 2, 76b n = 3, 76c 2.3.2 Absorption Spectra Phosphines. The absorption spectra of the mono- and bisphosphines are shown in Figure 2.1, and the data are collected in Table 2.2. The spectra show a band between 275 and 400 nm, which is assigned to a TI—>TX* transition. This band undergoes a bathochromic shift with increasing oligothiophene length. In addition, a shoulder is observed at approximately 250 nm, which is assigned as an n—>n* transition. An n—»rc* transition is seen in the spectrum of triphenylphosphine at 263 n m 3 6 " 3 8 and a localized n—» TC* absorption of thiophene is usually seen in the 250-270 nm region in the spectra of oligothiophenes.3 9 - 4 1 This peak is likely due to a combination of both transitions. The presence of the phosphine group results in a red shift of the absorbance bands relative to the unsubstituted thiophene oligomers by 20-69 nm, depending on the length of the oligothiophene and the number of phosphine substituents (T (231 nm), T 2 (303 nm), and T 3 (354 nm)). 1 7 A red shift is also observed in the spectra of other phosphines containing aromatic substituents,3 6'4 2 and in many other substituted oligothiophenes (see Table 2.1). In phosphines 65-70 the interaction between the aryl moiety and the phosphorus is of intermediate strength, as compared to various compounds in the literature. It may be due to 47 both inductive and resonance interactions between the aromatic n* orbitals and the phosphorus lone pair and empty a* orbital. 4 3 To aid in understanding the nature of this interaction in the thienyl phosphine compounds, DFT calculations were carried out at the B3LYP/6-31G* level, and the results are shown in Figure 2.2. The calculated values of the H O M O - L U M O gaps for the compounds are similar to and follow the same trends as the experimental values obtained from absorption spectroscopy. The calculations indicate that the L U M O is stabilized by interaction between the n system and the phosphorus, while the HOMO is slightly destabilized. The calculations also reveal that the degree of phosphorus lone pair character in the HOMO diminishes significantly as the oligomer length increases (from 65 to 67, and from 68 to 70). This correlates well with the experimental data: As the length of the oligothienyl group increases, the relative change in absorption maximum with each additional ring is reduced. Typically, in an oligomeric series, red shifts decrease with increasing length until a saturation point is reached, 1 7 ' 2 8 and this effect is also seen in other substituted oligothiophenes. 1 5- 2 1 ' 2 5 ' 2 6 With two phosphine substituents (68-70) the bathochromic shift relative to the unsubstituted analog is larger than that observed for the corresponding monophosphine. For example, Xmax for 65 is red-shifted by 34 nm relative to T, while for 68 it is shifted 69 nm. This is also seen in the calculations, which show smaller H O M O - L U M O energy differences for the disubstituted compounds than for the monosubstituted analogs. The major absorption bands of the terthienyl compounds (67 and 70) have low energy shoulders and the peak for 70 is broad. This may be due to the presence of multiple conformations in solution, a common effect in oligothiophenes.3 9-4 4 Generally, as the length of the oligomer increases, the molar absorptivity of the transition also increases. The solid 48 state absorption spectra (Figure 2.3) are very similar to the solution data. They are dominated by the n—>n* transition, which increases with oligothiophene length. There is a very small (1-6 nm) bathochromic shift in the spectra when compared to the solution data. 250 300 350 400 450 AVnm Figure 2.1 Solution UV-visible spectra of 65-70. 49 Table 2.2 Electronic spectroscopy data for 65-70. Compound Solution absorption A,m a x/nm (Emax/M^cm" 1) Solid state absorption X m a x /nm Solution emission A-max/nm (excitation wavelength) Solid-state emission X,m a x/nm PT (65) 265 (1.0 x 104) no distinct peak 496 (260) 475 P T 2 (66) 3 3 0(1.6 x 104) 248,333 485 (327) 478 P T 3 (67) 2 5 0(1.1 x 104), 3 74 (2.0 x 104) 260, 375, 420 (sh) 424, 446 (368) 480 PTP(68) 258 (sh) (1.7 x 104), 300 (1.3 x 104) no distinct peak 496 (300) (hexanes) 518(301)(CH 2C1 2) 481 PT 2 P (69) 245 (sh) (2.0 x 104), 350 (2.5 x 104) 250, 353 430, 460 (343) (hexanes) 528 (350) (CH 2C1 2) 470 PT 3 P (70) 245 (2.5 x 104), 389 (3.6 x 104) 255,395,430 (sh) 441,465 (383) (hexanes) 450, 470 (384) (CH 2C1 2) 488 50 HOMO LUMO LUMO + 1 LUMO HOMO HOMO -1 Figure 2.2 a) Calculated frontier orbitals of 65-67, and b) calculated HOMO-1, HOMO, L U M O , LUMO+1 energies for phosphines, unsubstituted thiophenes, and 74a. 51 . — i — i — i — ^ V ^ - — i — i — i — i — i — Y~~~*~-vw PTP (68) K ^ / ^ pj2(66) ^Xw/^^y""^ ( 69 ) i 1 1 1 1 1 | 1~. | P 1 " 3 ( 6 7 ) 1 i 1 i 1 1 1 1 —^ 1 ; 250 300 350 400 450 250 300 350 400 450 X/nm Figure 2.3 Solid state UV-visible spectra of 65-70. Oxides, sulfides, and phosphonium bromides. The solution absorption and emission data for the phosphine derivatives are collected in Table 2.3. The absorption and emission spectra of the oxides (74a-c) are shown in Figure 2.4, the sulfides (75a-c) in Figure 2.5, and the phosphonium salts (76a-c) in Figure 2.6. The absorbance spectra of the derivatives are dominated by TT—»TT* transitions, similar to the spectra of 65-70. A l l the spectra show the characteristic vibrational structure of benzene between 250-280 nm, which is obscured by the n—>n* transition in the spectra of the phosphines.45 For the oxides (74a-c) and the sulfides (75a-c), the 7i—>7t* band is blue shifted when compared to the parent phosphine, as a result of the change in oxidation state from P(II1) to P(V). 3 6 > 4 5 The oxides 52 show a larger shift than the sulfides because of the greater electronegativity of oxygen. The blue shift decreases as the length of the thiophene group increases, echoing the results obtained for the phosphines: Substituents have less effect on the frontier orbitals of the compounds as oligothiophene length increases. The absorption maxima for the oxides and sulfides occur at lower energies than those of the unsubstituted thiophenes, which may be due to the inductive effect of the substituents.42'46 Interestingly, the series of phosphonium salts (76a-c) exhibits a bathochromic shift when compared to the corresponding phosphine, and 76c (19 nm) shows double the shift of 76b (8 nm). A small decrease in energy of absorption (7 nm) was also seen by Smith and Protasiewicz 4 6 upon quaternization of a tris(styrylphenyl)phosphine. In this case, the positively charged phosphonium acts as a strongly electron-withdrawing group. | 20000 3 TO 03 C (U _c c o U3 E LU 600 Figure 2.4 Solution absorption (—) and emission (—) spectra of phosphine oxides 74a-c. 53 E 20000 3 CD CO C CD c g 'cn CO 'E LU 600 Figure 2.5 Solution absorption (—) and emission (—) spectra of phosphine sulfides 75a-c. Figure 2.6 Solution absorption (—) and emission (—) spectra of phosphonium bromides 76a-c. 54 Table 2.3 Electronic spectroscopy data for 74a-c, 75a-c, and 76a-c. Complex Solution absorption A,max/nm (Bmax/M^cm"1) 74a 258 (2.1 x 104), 266 (1.9 x 104), 273 (1.3 x 104) 315 (258) (v.weak) 74b 260 (7.4 x 332 (2.5 x 103), 267 (8.0 x 105) 103), 273 (7.6 x 104), 324 (2.5 x 104), 387 (327) 74c 260 (9.9 x 103), 266 (1.0 x 104), 273 (8.3 x 103), 378 (3.3 x 104) 430, 455 (373) 75a 252 (6.9 x 103), 269 (1.1 x 105), 275 (1.4 x 104) -75b 262 (1.3 x 341 (2.6 x 104), 26 8 (1.2 x 104) 104), 276 (1.0 x 104), 334 (2.6 x 104), 392 (336) 75c 261 (1.5 x 104), 269 (1.3 x 104), 276 (9.9 x 103), 383 (3.6 x 104) 435, 460 (380) 76a 262 (1.0 x 104), 268 (9.7 x 103), 276 (5.5 x 104) -76b 263 (8.5 x 103), 269 (8.5 x 103), 277 (6.7 x 103), 338 (2.0 x 104) 406 (338) 76c 262 (1.2 x 104), 268 (1.2 x 104), 276 (1.0 x 104), 393 (2.4 x 104) 481 (392) Solution emission A,m a x/nm (excitation wavelength) 2.3.3 Emission Spectra Phosphines. The emission data for the mono- and bisphosphines are collected in Table 2.2, and the spectra are shown in Figure 2.7. Initially, emission spectra were collected in CH 2 C1 2 solution; however, over time, the spectra of 66 and 69 exhibited two emission bands in this solvent. The corresponding excitation spectra for these two bands are different, which indicates the presence of two compounds in solution. It was postulated that oxidation of the phosphines was occurring, as has been observed for similar compounds.47 To verify, a sample of 69 was treated with hydrogen peroxide in solution. The resulting spectrum showed 55 only a single emission band, which was very similar to the higher energy band observed in the spectrum of 69. Surprisingly, neither the thienyl nor the terthienyl compounds showed any evidence for oxidation in CH2CI2 under identical conditions. When the spectra of 66 and 69 were obtained in hexanes, a single emission band was observed, which is similar to the lower energy band of the spectrum in CH2C12. Therefore, to eliminate the possibility of oxide formation, the emission spectra for 65-70 were obtained in hexanes. For comparison, the emission spectra of 68-70 were obtained in degassed CH 2Cl2 (Figure 2.8). Figure 2.7 Solution excitation (—) and emission (—) spectra of phosphines 65-70 in hexanes. 56 - PTP (68) •£ i 1 i 1 i ni- - 11. i i i i 1 i 1 i > » ' VI -i * PT 2P (69) - '55 £ ' £ c O " i I i l i c C/) s - ' -. ' 1 1 i 1 <f> o X LU -/ \ PT 3P (70) 'E UJ — i 1 : — i — • — i 1 1 — r 1 ' I 300 400 500 600 700 A/nm Figure 2.8 Solution excitation (—) and emission (—) spectra of 68-70 in CH2CI2. The emission of both 68 (496 nm) and 65 (485 nm) in solution is weak and exhibits a large Stokes shift (Figure 2.7). Unsubstituted thiophene is known to phosphoresce at approximately 430 nm; 1 7 therefore, this emission is not assigned as thiophene-based. Triphenylphosphine exhibits a large Stokes shift, with emission at 450 nm in diethyl ether36 and 475 nm in acetonitrile.48 The emission is assigned as a re*—>n transition, as triphenylphosphine oxide emits at 290 nm. 3 6 A large Stokes shift can indicate a large difference in geometry between the ground and excited states. For triphenylphosphine the change is believed to be a fast geometrical conversion from a pyramidal ground state to a more planar excited state.36 The emission bands of 65 and 68 are consequently assigned to re*—»n transitions from excited states that are more planar than the ground state, analogous to 57 the behavior of triphenylphosphine. The DFT calculations for 65 support this assignment, as the HOMO has significant phosphorus lone pair character whereas the L U M O is more localized on the aryl groups. The assignment of this transition as re*—>n is also supported by the large (22 nm), positive solvatochromism of 68 in hexanes and CH2CI2. This indicates some charge transfer character in the transition, or, a polar excited state is formed, which is stabilized by a polar solvent. A 7t*->n transition is expected to exhibit more charge transfer character than a n*—>n transition. The emission spectra for 66 and 69 in hexanes (Figure 2.7) are significantly red-shifted relative to unsubstituted 2,2'-bithiophene, which has a maximum emission at 362 nm, 1 7 and are similar in appearance to the emission spectra of 65 and 68. This suggests that these emission bands are also due to n*—>n transitions. The spectrum of 69 shows a broad emission in hexanes, which may contain multiple bands. The intensities of these bands vary slightly among samples, possibly due to conformational effects. Similar to 68, 69 exhibits strong, positive solvatochromism, with a shift of 68 nm when the polarity of the solvent is increased from hexanes to CH2CI2. This, as for 68, supports the assignment of the emission to a n*—»n transition. Unlike the shorter oligomers, the emission spectra of 67 and 70 show small Stokes shifts, and 70 does not exhibit positive solvatochromism. The DFT calculations show that the frontier orbitals for these compounds are mainly of terthienyl 71-character. Both excitation and emission processes do not appear to involve the phosphine group significantly, and emission appears to be a typical oligothiophene n*—>n transition. The emission maxima for both compounds are red shifted as compared to 2,2':5',2"-terthiophene (426 nm). 1 7 The emission maximum for the bisphosphine 70 also occurs at a longer wavelength than for 67, 58 consistent with the data from the absorption spectra. In the excitation spectra of both 67 and 70 a second, smaller band is also seen at 250 nm. A similar band is observed in the excitation spectrum of terthiophene, suggesting that this may be due to a local thiophene n—mt* excitation. 3 9" 4 1 Solid-state emission spectra for the phosphines are shown in Figure 2.9 and the data are collected in Table 2.2. A l l the spectra have an excitation band between 220-250 nm which may be due to a local thienyl-based n—>TT* excitation. 3 9 - 4 1 65, 68, 66, and 69 exhibit spectra in the solid-state that are very similar to those observed in solution. The emission bands show Stokes shifts, larger in the monothienyl compounds than in the bithienyl compounds. The bands are assigned to 7t*—»n transitions, similar to solution. The terthienyl compounds 67 and 70 have structured emission spectra and the transitions are assigned as TC*—>7i, which are substantially red-shifted compared to solution (42 and 34 nm, respectively). A bathochromic shift of 33 n m 4 9 relative to solution is seen in the solid state emission of T 3 , and other substituted oligothiophenes also exhibit red shifts in the solid state.2 1-3 9 The shift is thought to be due to increased planarity in the solid state, as compared to essentially free rotation in solution. 4 0 59 Figure 2.9 Solid state excitation (—) and emission (—) spectra of 65-70. Oxides, sulfides, and phosphonium bromides. The bi- and terthiophene phosphine oxides (74a-c), sulfides (75a-c), and phosphonium bromides (76a-c) are all emissive. The spectra are shown in Figure 2.4, Figure 2.5, and Figure 2.6, and the data are collected in Table 2.3. The emission of 74a is very weak, and low concentrations of emissive impurities can affect the appearance of the spectrum. Multiple peaks are sometimes observed in the 60 emission spectra of 74a, and these are attributed to impurities in the sample. A peak at 315 nm was seen, similar to triphenylphosphine oxide . 3 6 ' 4 8 Emission is assigned to rc*—>TI transitions in all cases, as the phosphorus lone pair is no longer present. The large Stokes shift seen in 66 and 69 is not seen in these spectra, confirming the assignment of the emission in 66 and 69 as 7i*—»n. As in the absorption spectra, the oxides and sulfides show a hypsochromic shift relative to the free phosphines. The shift is larger for the oxides than the sulfides, due to the larger electronegativity of oxygen as compared to sulfur. The bands for 74c and 75c are structured, with spacings between bands of 1180 cm"1 and 1249 cm"1, respectively, corresponding to the energy of C=C stretching modes. 4 0- 5 0 The emission bands of the phosphonium salts are also assigned to n*—>n transitions. However, as in the absorption spectra, the terthienyl compound (76c) exhibits a bathochromic shift (35 nm) as compared to the free phosphine. This is attributed to the strongly electron-withdrawing properties of the phosphonium group. 2.4 Conclusions In this chapter, a series of mono- and bisphosphinothiophenes are described. The diphenylphosphino group has a moderate strength interaction with the thiophene group, as compared to a variety of other a-substituted oligothiophenes. The strength of the interaction was investigated with absorption and emission spectroscopy, and the nature of the interaction was probed with DFT calculations. The addition of the diphenylphosphino group red shifts the absorption as compared to the unsubstituted thiophene. The energy and intensity of absorption increase with increasing length of the oligothiophene moiety for the series. 61 However, the increase as compared to the parent oligomer (for example, 67 as compared to T 3 ) decreases as the length of the oligothiophene increases. These effects are explained by the DFT calculations, which show that the frontier orbitals become more thienyl-based as the length of the oligothiophene is increased. The calculations are also used to explain the emission spectra. The mono- and bithienyl phosphines exhibit large Stokes shifts in both solution and the solid state. The emission for these complexes is assigned to a TC*—>n transition, similar to triphenylphosphine. However, the emission of the terthienyl phosphines does not show a large Stokes' shift and is therefore assigned to a TC*—>K transition, which is essentially terthiophene-based. Phosphine oxides, phosphine sulfides, and phosphonium bromides were also synthesized and characterized with absorption and emission spectroscopy. The absorption and emission of the oxides and sulfides are hypsochromically shifted relative to the free phosphines, due to coordination of the phosphorus lone pair. 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Phys. 1994, 100, 2571. 66 Chapter 3 Structural and Luminescence Studies of Au(I) Complexes 3.1 Introduction Interest in the coordination chemistry of gold has grown in recent years with the discovery of the unusual electronic and structural properties of gold complexes.1"3 Gold(I) compounds can exhibit weak gold-gold interactions,4"6 a property that has been termed "aurophilicity". The interactions are similar in strength to hydrogen bonds (20-50 kJ/mol), and are between 2.8-3.3 A in length.3"5'7 This results in a variety of structures of gold complexes (Chart 3.1), including dimers 8" 1 0 and polymers. 1 1 - 1 5 Many gold complexes have been shown to exhibit luminescence in solution and in the solid state, 2 ' 9- 1 6 ' 1 7 and this has resulted in some being tested in luminescent devices 2- 1 8 ' 1 9 and sensors.20 Our group has recently prepared some Au(I) phosphine complexes that exhibited intramolecular Au-Au interactions (Chart 3.2). 2 1 The interactions affected the structure and the optical and electrochemical properties of the oligothiophenes. Chart 3.1 Au—L—Au Au—L—Au Au—L—Au monomer dimer polymer 67 Chart 3.2 The nature of the interaction between two closed shell Au(I) atoms is of great interest to both experimental and computational chemists. Through calculations and experiment, it has been shown that aurophilicity is a dispersion interaction, which is strengthened by relativistic effects. 4 ' 5 ' 2 2 The Au(I) centre is polarizable, which leads to dispersion interactions consisting of both the attraction between instantaneously polarized molecules (van der Waals type interaction) and instantaneous charge transfer between molecules.7-2 2 Dispersion interactions also involve the ligand orbitals, so aurophilicity is not exclusively gold-based.22 Relativistic effects are found to be especially large in gold and contribute to aurophilicity. For light atoms, relativistic effects have little consequence; however, as the mass of the nucleus increases, they become increasingly important. The inner, or core, electrons are influenced by a large nuclear charge in heavy atoms. As a result, they move at very high speeds, which are on the order of the speed of light. This causes an increase in the relativistic mass of the electrons, which, in turn, causes a contraction of the s and p orbitals. The d and f orbitals are consequently screened from the nucleus, resulting in an expansion of 68 these orbitals.5-2 3 Relativity, therefore, has many consequences in heavy atoms, most markedly in gold. For example, gold atoms and ions are smaller than silver atoms and ions, and gold-ligand bond lengths are both shorter and stronger than those of silver. 3" 5- 2 3 Relativistic effects enhance aurophilicity by increasing the electrophilicity of gold via contraction of the 6s and 6p orbitals, and by contributing to electrostatic and dispersion interactions via expansion of the 5d orbitals.7 Measurable emission is observed in a wide variety of gold complexes,1 including Au(I) phosphines,2 4"2 8 Au(I) thiolates,2 9"3 1 and complexes exhibiting gold-gold interactions. 1 2 ' 1 6- 1 7 ' 3 2" 3 5 The origin of the emission is not the same in all cases, and hinges on the structure of the compound. For example, mononuclear phosphine emission can be ligand-based (generally r e * — » T r . ) 2 4 > 2 5 - 2 8 or metal-based (6pz—»5dxy, 5d x 2. y 2), 2 8> 3 6 depending on the ligands and the coordination number. In the case of thiolates, emission is assigned to an L M C T (S—»Au) o r i g i n . 1 2 ' 2 0 ' 3 0 ' 3 1 The emission from complexes that have gold-gold interactions can be due to either a metal-centred transition (either 6p z -»5d z 2 or 6pz—»5dx2. y2)35,37,38 o r a n L M C T or M L C T transition. 1 6 ' 3 4- 3 9 In this chapter, the synthesis and characterization of a series of phosphinothiophene gold(I) complexes are reported. X-ray crystal structures are presented for 81 and 82. Complexes 82 and 85 exhibit aurophilic interactions in the solid state. Variable temperature N M R spectroscopy suggesting a monomer-dimer equilibrium in solution for 85 is also presented. The absorption and emission properties in both solution and the solid state are discussed, and the emission data supports the existence of a monomer-dimer equilibrium in solution for 85. This work has been published 4 0 69 3.2 Experimental 3.2.1 General Au(tht)Cl (tht = tetrahydrothiophene) was made by the literature method.41 ' H and 3 1 P{'H} N M R experiments were performed on either a Bruker AV-300 or a Bruker AV-400 spectrometer. Spectra were referenced to residual solvent ('H) or external 85% H3PO4 (31P)-Electronic spectra were obtained on a Cary 5000 in HPLC grade CH2CI2. Emission spectra were obtained on a Cary Eclipse Spectrometer, also in HPLC grade CH2CI2. Solid state absorption and emission spectra were obtained by drop casting the compound from a CH2CI2 solution onto a quartz slide. Some spectra contain peaks from excitation or emission overtones; these are indicated with an asterisk. Microanalyses were performed at UBC. Vapor pressure osmometry measurements were performed by Galbraith Laboratories, Tennessee, U. S. A . 3.2.2 Procedures General synthesis of Au(I) complexes. Au(tht)Cl and the appropriate ligand in either a 1:1 or a 2:1 molar ratio were stirred together for one hour in CH2CI2. The solvent was removed, the resulting powder was dissolved in a minimum amount of CH2CI2, and the complex was precipitated in 100 mL hexanes. The precipitate was collected by filtration, washed with hexanes, and dried under vacuum, which yielded analytically pure samples. (PT)AuCI (79). Yield: 67%. Anal. C 1 6 Hi 3 AuClPS requires: C, 38.38; H, 2.62. Found: C, 38.74; H , 2.60. ' H N M R (CDCI3): 5 7.79 (ddd, J = 4.6, 1.2, 3.1 Hz, 1H), 8 7.62-7.40 (m, 11H), 5 7.22 (ddd, J = 5.0, 3.9, 1.5 Hz, 1H), 3 , P{ 1 H} N M R (CDC13) 5 20 (s). 70 (PT 2 )AuCl (80). Yield: 75%. Anal. C20H15A11CIPS2 requires: C, 41.21; H, 2.59. Found: C, 41.20; H, 2.57. ' H N M R (CDC13): 5 7.61-7.44 (m, 10H), 8 7.41 (dd, J = 9.1, 3.7 Hz, 1H), 5 7.28 (dd, J = 4.9, 0.91 Hz, 1H), 5 7.24 (m, incl. CD 3C1, 2H), 8 7.20 (dd, J = 3.7, 0.91 Hz, 1H), 8 7.01 (dd, J = 4.9, 3.7 Hz, 1H). 3 1 P{'H} N M R (CDC13) 8 20 (s). (PT 3 )AuCl (81). Yield: 93%. Anal. C 2 4 H , 7 A u C l P S 3 requires: C, 43.35; H, 2.58. Found: C, 43.61; H , 2.50. ] H N M R (CDC13): 8 7.64-7.44 (m, 10H), 8 7.41 (dd, J = 8.9, 3.9 Hz, 1H), 8 7.23 (dd, J = 3.9, 1.2 Hz, 1H), 8 7.09 (s, 1H). 3 1 P{'H} N M R (CDCI3) 8 20 (s). AuCl(PTP)AuCl (82). Yield: 78%. Anal. C 2 8 H 2 2 A u 2 C l 2 P 2 S requires: C, 36.66; H, 2.42. Found: C, 36.99; H , 2.41. ] H N M R (CDCI3): 8 7.60-7.45 (m). 3 1 P{'H} N M R (CDC13) 8 20 (s). AuCl(PT 2 P)AuCl (83). Yield: 62%. Anal. C 3 2H24Au2Cl 2P2S2 requires: C, 38.46; H, 2.42. Found: C, 38.85; H , 2.36. ' H N M R (CDCI3): 8 7.62-7.44 (m, 10H), 8 7.39 (dd, J = 8.9, 3.9 Hz, 1H), 8 7.28 (dd, J = 3.8, 1.0 Hz, 1H). 3 1 P{'H} N M R (CDCI3) 8 21 (s). AuCl(PT 3 P)AuCl (84). Yield: 57%. Anal. C 3 6 H 2 6 A u 2 C l 2 P 2 S 3 requires: C, 39.98; H, 2.42. Found: C, 40.28; H, 2.34. ] H N M R (CD 2C1 2): 8 7.61-7.42 (m, 10H), 8 7.36 (dd, J = 8.9, 3.9 Hz, 1H), 8 7.23 (dd, J = 3.9, 1.2 Hz, 1H), 8 7.09 (s, 1H). 3 1 P{ 1 H} N M R (CD2C12) 8 21 (s). AuI(PTP)AuI (85). This complex was synthesized by a modification of a literature procedure. 3 4 A mixture of 82 (0.05 mmol) and KI (1 mmol) was heated to reflux for 1 hour in a 1:1 (vohvol) degassed mixture of acetone and CH 2 C1 2 under N 2 . The solution was then stirred for 24 hours. The solvent was removed by rotary evaporation and the resulting solid was washed with H 2 0 . Yield: 75%. Anal. C 2 8 H 2 2 A u 2 I 2 P 2 S requires: C, 30.57; H, 2.02. 71 Found: C, 30.17; H , 2.14. *H N M R (CDCI3): § 7.62-7.45 (m). 3 1 P{'H} N M R (CDC13) 5 27 (s). 3.2.3 X-ray Crystallographic Analyses Suitable crystals of 81, 82, and 85 were each mounted in oil on a glass fiber, and the data for each compound were collected at 173(1) K. The structures were solved using direct methods and refined using Shelxl-97. 4 2 The structure of 85 was solved using heavy-atom Patterson methods43 and refined using teXsan. 4 4 Data for 81 were collected to a maximum 29 of 55.8° on a Rigaku/ADSC CCD diffractometer in a series of two scan sets. Scans were carried out using 0.50° oscillations with 35.0 second exposures. Data were collected using the d*TREK program4 5 and processed (integrated and corrected for absorption) using the TwinSolve function of CrystalClear. 4 6 The structure of 81 was determined by first indexing the unit cell as a two-component "split crystal" wherein the major and minor components are related by a rotation of 8.5° about an axis normal to an imaginary (-1.74, -9.14, 1.00) plane. Data for both components were then integrated, and the solution and subsequent refinements were carried out using an HKLF4 format data set containing only non-overlapped reflections. A l l non-hydrogen atoms were refined anisotropically, while all hydrogen atoms were included in calculated positions. Data for 82 were collected to a maximum 29 of 56.4° on a Bruker X8 A P E X diffractometer in a series of ten scan sets. Scans were carried out using 0.50° oscillations with 7.0 second exposures. Data were collected and integrated using the SAINT suite of software47 and corrected for absorption using S A D A B S . 4 8 The material crystallizes with one half-molecule residing on an inversion centre. In addition, one half-molecule of methylene 72 chloride, disordered about an inversion centre, and one whole molecule of hexane solvent are found in the asymmetric unit. A l l non-hydrogen atoms were refined anisotropically, while all hydrogen atoms were included in calculated positions. Data for 85 were collected to a maximum 29 value of 50.0°. Data were collected in a series of scans in 0.50° oscillations with 30.0 second exposures. Data were integrated using the SAINT suite of software,47 corrected for absorption using S A D A B S , 4 8 and were corrected for Lorentz and polarization effects. The material crystallizes as a two-component twin, with the second component related to the first by a 180° rotation about the reciprocal 1,0,0 axis. The material crystallizes with one half-molecule of hexane and one half molecule of methylene chloride in the asymmetric unit. While the final residuals are acceptable, the final anisotropic displacement parameters (ADPs) for the phenyl and thiophene carbons are unacceptably distorted in a manner inconsistent with disordered fragments. The acceptable residuals are likely a result of reasonable modeling of the positions and ADPs of the majority of the electron density contained in the Au and I atoms. The distorted carbon atoms may arise from an incomplete description of the twinning, or an inadequate absorption correction. The structures were obtained by Dr. Brian Patrick at UBC. Appendix 1 contains crystallographic data for the structures presented in this chapter. 3.3 Results and Discussion 3.3.1 Synthesis Gold complexes were prepared according to the reactions shown in Scheme 3.1 and were readily isolated as analytically pure compounds by precipitation from hexanes. The 73 complexes are stable in the solid state and in solution. Gold-gold interactions are influenced by the ligands coordinated to the gold centre; 4' 7- 2 2 by using a softer ligand, the distance between the gold centres can be reduced. 1 6 ' 4 9 I is a softer ligand than Cl , and has been shown to increase the strength of the aurophilic interaction. 8 ' 3 4 ' 5 0 The iodo complex 85 was synthesized by halogen exchange (Scheme 3.2), and purified by washing with water. Scheme 3.1 C H 2 C I 2 PT(65) n=1 PT2(66) n=2 PT3(67) n=3 (PT)AuCI (79) n=1 (PT2)AuCI (80) n=2 (PT3)AuCI (81) n=3 C H 2 C I 2 PTP(68) n=1 PT 2P (69) n=2 PT 3P (70) n=3 AuCI(PTP)AuCI (82) n=1 AuCI(PT2P)AuCI (83) n=2 AuCI(PT3P)AuCI (84) n=3 Scheme 3.2 AuCI(PTP)AuCI (82) Aul(PTP)Aul (85) 74 3.3.2 Solid State Crystal Structures Single crystals of 79 were grown by the slow diffusion of hexanes into a dichloromethane solution of the complex. The molecular structure could not be completely refined due to disorder in the structure; however, it was established that no gold-gold contacts exist in the solid state. Single crystals of 81 were also grown by the slow diffusion of hexanes into a dichloromethane solution of the complex. The molecular structure of 81 is shown in Figure 3.1 and selected interatomic distances and angles are collected in Table 3.1. The complex crystallizes as a monomer, with no gold-gold interactions present. The shortest Au-S (Au-S(l)) distance in the structure is 3.707 A, which is beyond the sum of the van der Waals radii of these elements (S, 1.80 A; Au, 1.66 A). 5 1 The Au-Cl and Au-P bond lengths are very similar to those in (PPh 3)AuCl (Au-Cl 2.279 A and Au-P 2.235 A) . 5 2 The P-Au-Cl bond angle is somewhat less linear than in (PPh3)AuCl (179.63°). The P-C bond lengths to the phenyl groups are slightly longer than the corresponding bond to the terthienyl group and are similar to the P-C bond lengths of (PPh.3)AuCl. The first two rings of the terthienyl moiety are essentially coplanar, with an inter-annular torsion angle (Z S-C-C-S) of 178.2°, whereas the ring furthest from the phosphine substituent is twisted slightly more with an inter-annular torsion angle between the second and third rings of -161.3 °. In the lattice two of the phenyl rings are within rc-stacking distance, 5 3 ' 5 4 with a distance of 3.787 A between rings (see Figure A 1.2, Appendix 1). The X-ray crystal structure of 82 is shown in Figure 3.2, and selected interatomic distances and angles are presented in Table 3.2. The complex was crystallized by the slow diffusion of hexanes into a dichloromethane solution of the complex. It crystallizes as a dimer with two gold-gold interactions of 3.0966 A. Related structures have been observed, 1 0 ' 5 5 ' 5 6 with comparable Au-Au distances. The Au-P and Au-Cl bond lengths and 75 the P-Au-Cl bond angles are similar to those in 81. There is no Au-S interaction in this complex, as the shortest Au-S distance in the structure is 3.504 A (Au(2)-S(l)). The formation of gold-gold interactions is influenced by many factors, including the ligands coordinated to gold and packing interactions in the solid state. It is not clear why the bimetallic complexes have gold-gold interactions in the solid state while the mononuclear complexes do not. Crystals of 85 that appeared to be of X-ray quality were grown by the slow diffusion of hexanes into a dichloromethane solution of the complex. Unfortunately, the crystals were twinned and complete refinement was impossible due to difficulty modeling all the solvent in the lattice. However, it was determined that 85 crystallizes as a dimer with a structure similar to 82. The gold-gold contacts were found to be 3.0210(9) A, 0.0756 A shorter than in the chloro-complex. The ORTEP view of 85 can be seen in Appendix 1, Figure A L L Figure 3.1 ORTEP view of 81. The hydrogen atoms are omitted for clarity, and thermal ellipsoids are drawn at 50% probability. 76 Table 3.1 Selected interatomic distances (A) and angles (deg) for 81. Bond length /A Bond angle /deg Au(l)- Cl(l) 2.2899(19) P(l)-Au(l)-Cl(l) 175.28(8) Au(l)-P(l) 2.2345(19) Au(l)-P(l)-C(19) 114.6(2) P(l)-C(19) 1.824(8) Au(l)-P(l)-C(13) 114.6(3) P(l)-C(13) 1.830(8) Au(l)-P(l)-C(l) 109.6(3) P(l)-C(l) 1.776(7) P(l)-C(l)-S(l) 120.7(4) C(l)-S(l) 1.725(7) C(l)-S(l)-C(4) 93.0(4) C(4)-S(l) 1.725(7) Torsion angle/deg S(l)-C(4)-C(5)-S(2) 178.2 S(2)-C(8)-C(9)-S(3) -161.3 Figure 3.2 ORTEP view of 82. The hydrogen atoms are omitted for clarity, and thermal ellipsoids are drawn at 50% probability. 77 Table 3.2 Selected interatomic distances (A) and angles (deg) for 82. Bond length /A Bond angle /deg Au(l)-Au(2) 3.0966(5) P(l)-Au(l)-Cl(l) 173.07(4) Au(l)- Cl( l ) 2.3041(10) P(2)-Au(2)-Cl(2) 175.75(4) Au(2)-Cl(2) 2.2997(12) P(l)-Au(l)-Au(2) 103.45(3) Au(l)-P(l) 2.2346(10) P(2)-Au(2)-Au(l) 96.54(3) Au(2)-P(2) 2.2404(11) Cl(l)-Au(l)-Au(2) 83.00(3) P(l)-C(l) 1.813(4) Cl(2)-Au(2)-Au(l) 87.67(4) P(l)-C(7) 1.813(4) C(7)-P(l)-Au(l) 109.70(13) P(l)-C(13) 1.803(4) C(13)-P(l)-Au(l) 115.68(13) P(2)-C(16) 1.802(4) C(17)-P(2)-Au(2) 116.07(17) P(2)-C(17) 1.812(5) C(23)-P(2)-Au(2) 114.16(14) P(2)-C(23) 1.815(4) 3.3.3 VT NMR Spectroscopy Variable temperature (VT) 'iT and 3 1 P N M R experiments were performed on 79 and 31 82 in CD2CI2 and are presented in Figure 3.3 and Figure 3.4, respectively. The P resonance for 79 shifts slightly with temperature (143 Hz over 110 K) . This is very similar to the temperature dependence of the 3 , P N M R shift of PPh3, which was found to be 1.3 ± 0.3 Hz/deg. 5 7 There is some broadening in the ' H spectrum, but no peaks are significantly shifted. These minor changes suggest that no dynamic process is occurring for 79 over this temperature range. More dramatic changes are seen in the 3 1 P and ' H N M R spectra of 82 as the temperature is decreased from 300 to 191 K. In the ' H N M R spectrum, the peaks broaden and a shoulder begins to separate out. The 3 1 P N M R spectrum consists of a singlet that shifts by 208 Hz over the temperature range, and begins to broaden below 210 K. It is very broad at 78 the lowest accessible temperature of 191 K, but it does not split into two peaks. This indicates that a dynamic process is occurring in solution, but it is still too rapid to allow observation of separate resonances on the N M R timescale. Variable temperature ' H and 3 1 P N M R spectra in CD2CI2 solution were also obtained for 85, and are shown in Figure 3.5. As the temperature is decreased from 300 K to 191 K, broadening is observed in the ] H N M R spectrum, and a doublet at 5 7.34 separates out at 240 K. In the 3 1 P spectrum, there is a singlet (5 27) at room temperature. However, as the temperature is lowered, the peak begins to broaden significantly, coalescence occurs at 200 K, and two peaks are observed at 191 K (8 14.6, 8 24). The free enthalpy of activation (AG*) for a dynamic process can be calculated from V T N M R data 5 8 using the following relationships: The rate constant at the coalescence temperature (kc) can be determined by: 7tAv - . £ c = ^ ^ = 2.22Av 3.1 where Au is the peak separation in Hz in the absence of exchange. AG* can then be found by: k = xhLe-\jT-) 3.2 h where k^ is the Boltzmann constant, % is the transmission coefficient (usually 1), and h is Planck's constant. Equation 3.2 can be rearranged to give: A G C * = 19.14rc f T \ 10.32+ l o g ^ V kc J J mol 1 3.3 where Tc refers to the coalescence temperature. For 85, An is 1150 Hz; therefore, &200 is 2553 and AG2oo:f is 35 kJ mol"1. 79 It is postulated that the dynamic process occurring in solution is a monomer-dimer equilibrium, as shown in Chart 3.3. The 3 1 P N M R signal seen for 81 at room temperature does not shift over the accessible concentration range (4 mM to 0.2 mM), indicating that the two low temperature peaks are not due to monomer and dimer, but rather due to restricted rotation resulting from the formation of dimer. The formation of a gold-gold interaction is the process that drives the dimerization, and so the energy of this interaction is what is measured in the V T N M R experiment. The energy of a gold-gold interaction as measured by VT N M R has been reported to be between 30 and 50 kJ m o l " 1 , 1 4 ' 3 1 ' 5 9 " 6 1 similar to what is obtained here. The assignment is also supported by the other V T N M R experiments conducted. For example, the process is likely not rotation about a P-Au, P-C, or C-H bond in the monomer, as 79 does not exhibit similar behavior. Also, 85 has a shorter and stronger Au-Au interaction in the solid state than 82, consistent with coalescence occurring at a higher temperature for 85 than 82. The existence of a monomer-dimer equilibrium is also supported by vapor pressure osmometry (VPO) data. VPO is used to measure the molecular weight of a compound in solution by comparing the vapor pressure of a solution to that of pure solvent, and has an accuracy in this molecular weight range of 2%-5%. The calculated molecular weight of monomeric 82 is 916, while the dimer molecular weight is 1832. The molecular weight of 85 is 1100 and the weight of the dimer is 2200. VPO measurements for both complexes were found to be higher (1228 for 82 and 1415 for 85, measured in CH 2C1 2) than would be expected for pure monomer, indicating a mixture of monomer and dimer in solution. 80 a) 300 K 7.80 7.60 7.40 7.20 7.00 6.80 6.60 240 K 220 K 210 K A 1 I 1 1 *1 I 1 1 1 1 I * r p - m - p 29 28 27 26 25 24 23 22 21 20 19 18 17 16 15 14 13 12 l ' l 10 Figure 3.5 Variable temperature a) l H and b) 3 1P{H} N M R spectra of AuI(PTP)AuI (85) in CD 2 C1 2 . 83 Chart 3.3 P h 2 P P P h 2 XAuX XAu' P h 2 P P P h 2 XAuX 2 XAu XAu P h 2 P AuX P P h 2 X = Cl, I 3.3.4 Absorption Spectra The solution absorption spectra for gold complexes 79-84 are shown in Figure 3.6 and the data are summarized in Table 3.3. Similar to the ligands (Figure 2.1), the spectra are dominated by thiophene TC->TC* transitions, which show the expected bathochromic shift with increasing conjugation length. However, the n->rc* transitions are blue-shifted relative to the corresponding ligands, and the n—»TC* transitions, seen at 250 nm in the spectra of the ligands, are not present in the spectra of the complexes. Also, several bands appear in the region between 260 to 280 nm that are assigned as the vibrational structure of the phenyl group. 6 2 These effects result from coordination of the phosphine lone pair, and are comparable to the results for the 74a-c, 75a-c, and 76a-c, presented in Chapter 2. The hypsochromic shifts that occur with coordination of the gold centre decrease with increasing oligothiophene chain length; as is generally seen in substituted oligothiophenes, the effect of the substituents decreases as the chain length increases. Even with the coordination of the phosphine lone pair, the n^>n*_ transitions in the complexes are still of lower energy than those of the corresponding unsubstituted oligomers (T (231 nm), T 2 (303 nm), T3 (354 nm)). 6 3 This may be due to the inductive effect of the substituent or stabilization of the bridge-centred re* L U M O by interaction with an unoccupied orbital on the phosphorus, or 84 most likely, a combination of both factors. The spectra of 80, 81, and 84 all exhibit shoulders, and the bands are broad, likely due to the presence of multiple conformations in solution. 6 4 ' 6 5 40000 30000 A 20000J 10000J r 0-^ 50000-40000-30000-20000-10000-(PT)AuCI (79) (PT2)AuCI (80) •AuCI(PTP)AuCI (82) AuCI(PT2P)AuCI (83) AuCI(PT3P)AuCI (84) 250 300 350 400 450 Figure 3.6 UV-visible spectra of gold complexes 79-84. 85 Table 3.3 Solution absorption data for gold complexes 79-85. Complex kmax/nm (6max/M" lcm"1) (PT)AuCl (79) 245 (sh) (1.7 x 104), 263(sh) (9.9 x 10 3), 269 (sh) (7.9 x 103), 275 (sh) (4.4 x io3) (PT 2)AuCl (80) 268 (sh) (5.9 x 103), 276 (4.8 x 103), 329 (1.9 x 104) (PT 3)AuCl (81) 263 (sh) (1.1 x 104), 276 (sh) (7.1 x IO3), 377 (3.2 x 104) AuCl(PTP)AuCl (82) 269 (2.0 x 104), 277 (2.1 x 104) AuCl(PT 2 P)AuCl (83) 263 (sh) (1.2 x io4), 267 (sh) (1.1 x 10 4), 275 (sh) (9.2 x 104), 334 (sh) (3.2 x 104), 342 (sh) (3.18 x 104) AuCl(PT 3 P)AuCl (84) 263 (sh) (1.2 x io4), 267 (sh) (1.2 x 10 4), 276 (sh) (9.2 x IO3), 386 (3.9 x l 0 4 ) AuI(PTP)AuI (85) 251(sh) (2.8 x 104), 269 (sh) (2.0 x 10 4), 276 (sh) (1.8 x 104), 285 (sh)(1.7x 104) A comparison of the absorbance spectra of 68, 82, and 85 is shown in Figure 3.7. The spectra of the two complexes show features similar to those described above; namely, a blue shift relative to the ligand spectra and the appearance of vibrational bands associated with the phenyl groups. However, the spectrum of the iodo complex is less blue shifted than that of the chloro complex. This effect has been previously explained for related complexes as a change in the HOMO from mainly Au 5d character in the chloro complex to a combination of Au 5d and I filled TC orbital character in the iodo complex . 8 ' 2 4 ' 3 4 ' 6 6 86 ' Figure 3.7 Comparison of UV-visible spectra of 68, 82, and 85. Solid state UV-visible spectra of the gold complexes (79-85) are shown in Figure 3.8 and the results are summarized in Table 3.4. The data generally show the same trends observed in the solution spectra. For example, a red shift in the 7i—>TT* transition occurs with increasing oligothiophene chain length, which decreases in magnitude when the chain length is increased. However, the wavelength of maximum absorption is red-shifted by 7-43 nm relative to solution, which may be due to increased planarity in the solid state. 6 4 ' 6 7" 6 9 87 a (PT)AuCI(79) AuCI(PTP)AuCI (82) I . I , 1 ~ i < — 1 1 1 ^ " — j — - . 1 1 1 1 1-(PT2)AuCI (80) 1 1 1 1 1 1 1 1 1 = = f = AuCI(PT2P)AuCI (83) 1 j i 1 i i 1 1 1 1 1 r • | I AufPiyAuCI (81) i I . 1 1 1 1 — n AuCI(PT3P)AuCI (84) 250 300 350 400 450 250 300 350 400 450 X/nm Aul(PTP)Aul (85) 250 300 350 400 450 X/nm gure 3.8 Solid state UV-visible spectra of gold complexes 79-85. 88 Table 3.4 Solid state electronic absorption data for gold complexes 79-85. Complex Xmax /nm (PT)AuCl (79) no clear peak (PT 2 )AuCl (80) 270 (sh), 335, 360 (sh) (PT 3)AuCl (81) 270, 382, 420 (sh) AuCl(PTP)AuCl (82) no clear peak AuCl(PT 2 P)AuCl (83) 250, 275 (sh), 345, 375 (sh) AuCl(PT 3 P)AuCl (84) 250, 275 (sh), 395,431 (sh) AuI(PTP)AuI (85) no clear peak 3.3.5 Emission Spectra Complex 79 is not emissive in solution, while both 82 and 85 are weakly emissive. 82 shows two emission bands, a high energy (HE) band at 345 nm and a low energy (LE) band at 485 nm (Figure 3.9). Both bands have similar excitation spectra, which match the absorbance spectrum of the complex. The iodo complex 85 shows only a single emission band at 490 nm, and the excitation spectrum matches the absorbance spectrum. The L E band seen in the spectra of the complexes 82 and 85 may be due to a metal-based do~*—»po~ transition. This is possible only upon the formation of a gold-gold interaction, which raises the HOMO (da* = 5dz2) and lowers the L U M O (pa = 6 s /p ) 3 5 ' 3 7 ' 3 8 ' 7 0 It may also be from a metal-to-ligand (ML) (Au(d)-»phosphine(7c*)) or a ligand-to-ligand (L—»phosphine(7T*)) (LL) charge transfer state, which is modified by gold-gold interactions.3 4-3 9 This may also account for the slight red-shift found on going from Cl to I. Emission at about 450-480 nm has also been assigned to a ligand-based n*—>a transition in some metal complexes 3 3 ' 7 1 ' 7 2 The rt*—>a transition is considered an intraligand charge 89 transfer (ILCT), analogous to the 71*—>n transition seen in the phosphine ligands. It is generally bathochromically-shifted in complexes as compared to the ligands because of a stabilization of the rj-electrons by the metal centre. However, the absence of this band in 79 indicates that it is dependent on the existence of gold-gold interactions. The emission spectra of several solutions of 82, with absorbances ranging from 0.05 to 2, were obtained, and the intensity of the HE band did increase as the concentration of 82 increased. However, the emission from this complex is weak, and the spectra may be distorted at high concentrations. Although the exact nature of the transition is unknown, it is thought to be either metal-based (da*—»po~) or a CT transition, which is modified by gold-gold interactions. The HE band in the spectrum of 82 is assigned to a triplet n*—>n emission centred on the phenyl moieties, based on comparison to Au(PPh3)Cl and Au(Me2PhP)Cl . 2 4 > 2 5 It is postulated that this emission is from monomeric complexes that do not contain gold-gold interactions. Dual emission is rare, but has been reported for some metal complexes, including some metal phosphine and gold complexes , 1 6 ' 2 4 ' 2 5 - 3 4 ' 3 9 ' 7 1 and is usually explained by thermally nonequilibrated excited states. In this case, though, dual emission is thought to arise from two species in solution: monomeric and dimeric 82. The reason for the absence of the HE band in the spectrum of 79 is unclear; however, it may simply be due to the increased number of phenyl rings per molecule in the bimetallic complex. This band is also absent in the spectrum of 85, most likely because of quenching by the iodo ligand, as the VT N M R and the VPO measurements indicate the presence of monomeric 85 in solution. However, as the emission of these complexes is weak, the possibility of a small amount of emissive impurity as the source of the emission in both 82 and 85 cannot be completely rejected. 90 o 3 o X LU AuCI(PTP)AuCI (82) Em, xc =269 nm Ex Ex, Xn =345 nm ' Em Ex, X^ =485 nm ' Em Aul(PTP)Aul (85) Em, X =269 nm ex Ex, X =490 nm H h 300 400 500 X/nm c 0) g 'E UJ 600 700 Figure 3.9 Solution excitation and emission spectra of 82 and 85. The bi- and terthiophene complexes (80, 81, 83, and 84) do not exhibit dual emission (Figure 3.10). The spectra for these complexes consist of a single band at 392 nm, 400 nm, 459 nm, and 465 nm, respectively, which is assigned to the TC*—>TC transition of the thienyl moiety. Similar to the absorption data, the emission bands are blue-shifted relative to the ligand (Figure 2.7) and red-shifted relative to the unsubstituted oligothiophene.63 The spectra for 83 and 84 show some structure, indicating some vibrational coupling. The spacing 91 between the bands of 84 is 1326 cm" , similar to that seen in the emission spectra of 74c and 75c, which indicates vibrational coupling to C=C stretching modes. 6 9 ' 7 3 Figure 3.10 Solution excitation and emission spectra of gold complexes 80, 81, 83, and 84. Unlike in solution, emission occurs at 390 nm in the solid state for 79 (Figure 3.11, Table 3.5). The excitation spectrum, with a peak at 350 nm, differs from the absorption spectrum of this compound. Complex 82 has a similar emission band at 402 nm (HE), with 92 excitation at 360 nm, which also does not match the absorption spectrum. As well, 82 has a band at 470 nm (LE), very similar to the solution spectrum, with an excitation spectrum that does corresponds to the absorption spectrum. Complex 85 has a similar band at 486 nm; however, the iodo analog does not exhibit the high energy band seen in 79 and 82. The L E emission bands at 470 nm and 486 nm are similar to those seen in the solution data, and are probably due to the same source; namely, a metal-based (do~*—»po~) transition or a CT transition, modified by gold-gold interactions. Several explanations for the HE band in the spectra of 82 and 79 are possible. One is phenyl triplet emission, 2 5 a second is a ligand-to-metal charge transfer (LMCT), similar to that reported by Fackler and coworkers,3 9 and a third explanation is that the band is due to an emissive impurity. However, the emission and excitation spectra do not correspond to ligand, and what this impurity might otherwise be is not clear. The absence of this band in the spectrum of 85 is not understood. As in the solution spectra, the emission from the bi- and terthiophene complexes is assigned to a T X * — H I transition (Figure 3.12). The bands are blue-shifted relative to the ligands (Figure 2.8) and red-shifted relative to the parent oligothiophene. The emission bands are also red-shifted relative to the solution data, which may be due to increased planarity in the solid state. 6 4 ' 6 7" 6 9 The emission spectrum of complex 84 is structured, with a separation of 1033 cm"1 between bands, which correlates to the C=C stretching modes. 6 9 ' 7 3 No emission that could be assigned as gold-based was observed in these complexes. 93 (PT)AuCI (79) AuCI(PTP)AuCI (82) Em, Xn =315 nm Ex Ex, V =402 nm 300 400 500 600 A,/nm Figure 3.11 Solid state excitation and emission spectra of 79, 82, and 85. 94 (PT )AuCI (80) Em, E^x=331 nm Ex, Xc =406 nm ' Em >> '55 c Q> JI c o o X LU (PT)AuCI (81) Em, Xc =382 nm ' Ex Ex, \„ =488 nm 300 3 >* -4—' co c 0J jz c g CO CO 'E LU 3 >, '55 c CD C o o X LU AuCI(PT2P)AuCI (83) Em, xc =330 nm ' Ex Ex, xc =408 nm ' Em -+-AuCI(PT3P)AuCI (84) Em, X , =380 nm Ex Ex, >.r =497 nm, 527 nm ' Em CO c c g CO CO 'E LU 300 400 500 600 700 X/nm Figure 3.12 Solid state excitation and emission spectra of gold complexes 80, 81, 83, and 84. 95 Table 3.5 Emission data for gold complexes 79-85. Complex Solution emission XI nm Solid emission X/nm (PT)AuCl (79) no emission 390 (PT 2 )AuCl (80) 392 406 (PT 3 )AuCl (81) 442 (sh), 459 488 AuCl(PTP)AuCl (82) 345,485 402,470 AuCl(PT 2 P)AuCl (83) 388 (sh), 400 408 AuCl(PT 3 P)AuCl (84) 439,465 497 AuI(PTP)AuI (85) 490 486 3.4 Conclusions In this chapter the synthesis and characterization, via X-ray crystallography and absorption and emission spectroscopy, of a series of gold (I) phosphinothiophene complexes is described. Crystal structures are reported for 81 and 82. The bimetallic complexes 82 and 85 were found to have gold-gold interactions in the solid state, while mononuclear 79 and 81 did not. Complex 85 was found to have a shorter gold-gold interaction than 82. Although the variable temperature N M R data for 79 is unremarkable, the ' H and 3 1 P N M R spectra for the bimetallic complexes (82 and 85) point to a dynamic process occurring in solution for these complexes. Coalescence does not take place at an accessible temperature for 82; however, coalescence occurs for 85 at 200 K. The free enthalpy of activation for this process was found to be 35 kJ mol"1, which is similar to literature values obtained for the formation of 96 gold-gold interactions with V T NMR. Therefore, the dynamic process that occurs in a solution of this complex is postulated to be a monomer-dimer equilibrium. The solution and solid state emission data for these complexes support this assignment. 79 is not emissive in solution, whereas 82 and 85 are weakly emissive. Complex 82 exhibits dual emission in solution, which is assigned to a high energy, ligand-based 7 t*—»TI emission from the monomeric species and a lower energy metal-based (da*—»pa) or CT transition from the dimer. 85 exhibits a very similar lower energy band in both solution and in the solid state. In the solid state, 82 exhibits dimer emission. 79 and 82 also have unassigned bands in the solid state spectra, which may be due to phenyl triplet emission, L M C T emission, or an emissive impurity. The solution and solid state emission spectra of the bi- and terthiophene gold (I) complexes (80, 81, 83, and 84) are dominated by the 7t*—»7r transitions of the thienyl moiety. The absorption and emission bands are blue-shifted relative to the ligands, due to the coordination of the phosphorus and the inductive effect of the gold. However, both the emission and absorption spectra are bathochromically shifted relative to the unsubstituted oligothiophene. This may be due to an inductive effect of the substituent and/or the stabilization of the bridge-centred n* L U M O by interaction with an unoccupied orbital on the phosphorus. These complexes do not exhibit emission from a gold-based state and also do not crystallize readily. 97 References Forward, J. M . ; Fackler, J. 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Phys. 1994, 100, 2571. 102 Chapter 4 Synthesis and characterization of Au(I) and Ag(I) complexes 4.1 Introduction Gold(I) and silver(I) were chosen to attempt the synthesis of coordination polymers of PTP (68), P T 2 P (69), and P T 3 P (70) for several reasons. Silver and gold phosphines exhibit interesting structural and optical properties' Both gold and silver phosphines can exhibit multiple coordination numbers,1 which results in a variety of possible structures including both discrete2"7 and extended3"5'8"1 1 structures, depending on the type of phosphine and the ancillary ligands involved. Three coordinate gold(I) phosphine complexes typically exhibit a characteristic emission at approximately 500 nm, which has been assigned to a metal-based (6pz—>5dxy, 5dx 2.y 2) transition. 8 ' 1 2 ' 1 3 Finally, it is of interest to compare the structure and properties of 1:1 gold to ligand complexes to the 2:1 complexes presented in Chapter 3, and to compare the structural and electronic effects of Au(I) to Ag(I) complexes. In this chapter the synthesis and characterization of phosphinothiophene complexes of gold(I) and silver(I) are presented. An X-ray crystal structure has been determined for 90, and the solution species of 86, 89, and 91 are assigned using 3 1 P N M R spectra. Solution and solid state absorption and emission spectra for these complexes are presented. 103 4.2 Experimental 4.2.1 General Au(tht)Cl (tht = tetrahydrothiophene) was prepared by the literature method.1 4 ' H and 3 1 P{ 1 H} N M R experiments were performed on either a Bruker AV-300 or a Bruker AV-400 1 31 spectrometer. Spectra were referenced to residual solvent ( H) or external 85% H3PO4 ( P). Electronic spectra were obtained on a Cary 5000 in HPLC grade CH2CI2. Emission spectra were obtained on a Cary Eclipse or a Photon Technology International QuantaMaster fluorimeter, in HPLC grade CH2CI2. Solid state absorption and emission spectra were obtained by casting a thin film of the compound from a CH2CI2 solution onto quartz slides. Some spectra contain peaks from excitation or emission overtones; these are indicated with an asterisk. Microanalyses were performed at U B C . The percentage yields and molar absorptivity (s) values reported for complexes 86-91 are based on the stoichiometric amounts of reagents used in the synthesis. 4.2.2 Procedures General synthesis of Au(I) complexes. Equimolar amounts of Au(tht)Cl and the appropriate ligand were stirred together for one hour in CH2CI2. The solvent was removed by rotary evaporation, and the resulting powder was dissolved in a minimum amount of CH2CI2 and precipitated in 100 mL hexanes. The precipitate was collected by suction filtration, washed with hexanes, and dried under vacuum, which yielded analytically pure samples. 86. Yield: 87%. Anal. C 2 8 H 2 2 A U C I P 2 S requires: C, 49.17; H , 3.24. Found: C, 49.14; H, 3.08. J H N M R (CDCI3): 5 7.54-7.39 (m). 3 1 P{'H} N M R (CDCI3) §13 (s), 22 (s, broad). 104 87. A s the reagents were stirred together, a white solid precipitated out of solution. The solid was removed by suction filtration and was not characterized. The resulting yellow solution was then treated with the work up described above. Yie ld : 14%. Anal . C32H24AUCIP2S2 requires: C, 50.11; H, 3.15. Found: C, 50.07; H , 3.41. ] H N M R (CDCI3): 5 7.54-7.50 (m, 4H), 7.45-7.42 (m, 2H), 7.39-7.35 (m, 4H), 7.26 (d, J = 3.7 Hz , 1H), 7.13 (d, J = 3.7 Hz , 1H). 3 1 P{ 'H} N M R (CDCI3) 6 9 (s), 22 (s, broad). 88. Y ie ld : 71%. Anal . C36H26AUCIP2S3 requires: C, 50.92; H , 3.09. Found: C, 51.21; H, 3.22. ' H N M R (CDCI3): 5 7.57-7.52 (m, 4H), 7.44-7.40 (m, 2H), 7.36-7.33 (m, 4H), 7.19 (m, 1H), 7.15 (d, J - 3.0 Hz , 1H), 6.92 (s, 1H). 3 1 P{ 'H} N M R (CDCI3) 5 10 (s), 22 (s, broad). General synthesis of Ag(I) complexes. The appropriate ligand and two equivalents of AgN03 were heated to reflux in a 1:1 mixture of CH 2Cl2 and MeOH for 24 hours. The solvent was then removed by rotary evaporation. The resulting powder was dissolved in a minimum amount of CH2CI2, and precipitated in 100 m L hexanes. The precipitate was collected by filtration, washed with hexanes, and dried under vacuum. 89. Y ie ld : 75%. Anal . C 56H44Ag3N 309P4S2 requires: C, 47.55; H, 3.14; N , 2.97. Found: C, 47.27; H, 3.41; N , 2.85. ! H N M R (CDCI3): § 7.48-7.34 (m). 3 1 P{'H} N M R (CDCI3) § 0 (s, broad). 90. A white, insoluble powder precipitated out of solution over the course of the reaction. Yie ld : 83%. Anal . C32H24Ag2N206P2S2-2MeOH requires: C, 43.52; H, 3.44. Found: C, 43.48; H, 3.05. 91. Y ie ld : 48%. Ana l . C 36H26Ag2N20 6P2S 3 requires: C, 45.21; H , 2.74. Found: C, 46.86; H, 3.07. ' H N M R (CDC13): 5 7.55-7.38 (m, 11H), 7.05 (dd, J = 3.7, 0.9 Hz , 1H), 6.92 (s, 1H). 3 I P{ 'H} N M R (CDCI3) 5 2 (s, broad). 105 4.2.3 X-ray Crystallographic Analysis A suitable crystal of 90 was mounted in oil on a glass fiber, and the data was collected at 173(1) K . The structure was solved using direct methods15 and refined using S H E L X T L . 1 6 The data were collected to a maximum 29 value of 52.4° on a Bruker X8 A P E X diffractometer with graphite monochromated M o - K a radiation. Data were collected in a series of § and co scans in 0.50° oscillations with 10.0 second exposures, and collected and integrated using the Bruker S A I N T 1 7 software package. Data were corrected for absorption, Lorentz, and polarization effects. The material crystallizes as a two-component twin, with the first component related to the second by a 176° rotation about the 0,1,0 axis. The position of the Ag atom is disordered over two positions in approximately a 0.6:0.4 ratio. The material crystallizes with two molecules of methanol in the asymmetric unit. The first molecule resides with its oxygen roughly 2.64 A from the major Ag fragment. The second molecule was disordered in such a way that it was impossible to model the molecule satisfactorily. The structure was modeled without assigning the disordered MeOH peaks, after which the S Q U E E Z E 1 8 function of P L A T O N was used to correct the raw data for any'unassigned electron density. In total 73 electrons were removed from the void spaces in the entire unit cell, equivalent to approximately four molecules of MeOH, or one molecule per asymmetric unit in space group P2\/c. A l l non-hydrogen atoms were refined anisotropically and all hydrogen atoms were included in calculated positions but not refined. The structure was obtained by Dr. Brian Patrick at UBC, and crystallographic data are contained in Appendix 1. 106 4.3 Results and Discussion 4.3.1 Synthesis The gold complexes 86-88 were synthesized by the reaction scheme shown in Scheme 4.1. Purification was achieved by precipitation from hexanes. The N M R spectra of the complexes indicated lability of the phosphine ligands, and are discussed further in Section 4.3.3. Complex 87 was obtained in low yield due to the formation of an insoluble white precipitate during the course of the reaction. Silver complexes 89-91 were prepared according to the reactions shown in Scheme 4.2. Complex 90 precipitated out of the reaction mixture as a white, insoluble powder, which was characterized only by elemental analysis. Similar to the gold complexes, 89 and 91 exhibited broadening in the solution 3 1 P N M R spectra. Complex 91 was found to decompose over time, as evidenced by the appearance of oxidized ligand in the N M R spectrum. Decomposition may also account for the unsatisfactory elemental analysis obtained for this complex. Scheme 4.1 86 n=1 87 n=2 88 n=3 PTP (68) n=1 PT 2 P (69) n=2 PT 3 P (70) n=3 C H 2 C I 2 107 Scheme 4.2 Ph2P- PPh 2 2AgN0 3 89 n=1 90 n=2 91 n=3 PTP (68) n=1 PT 2P(69) n=2 PT 3P(70) n=3 CH 2 CI 2 /CH 3 OH reflux, 24 h 4.3.2 Solid State Crystal Structures Gold complex. Single crystals were grown by the slow diffusion of hexanes into a dichloromethane solution of 86; interestingly, the isolated crystal was found to be AuCl(PTP)AuCl (82) (Figure 3.2). It is known that complexes of the type A u L 2 C l , where L is a phosphine, can partially disproportionate according to Equation 4.1:19,20 In this case, disproportionation would result in a small amount of 82 in solution, which may then preferentially crystallize out of solution as a dimer. Although multiple gold (I) phosphine species can exist in solution, all of these complexes may not crystallize, and the complexes that do crystallize are not necessarily the most abundant in solution. 2 1- 2 2 Many species may form in this case, including 82, 86a, and 86b, as shown in Chart 4.1, as well as larger, oligomeric complexes. It is not known why 82 preferentially crystallizes here; it may be that the gold-gold bond stabilizes this complex. 2AuL 2 Cl ^ A u L 3 C l + AuLCl 4;i 108 Chart 4.1 Silver complex. Single crystals of 90 were grown by the slow evaporation at 10 °C of a CH 2 Cl 2 /MeOH solution of A g N 0 3 and P T 2 P (69). An ORTEP view of the structure is presented in Figure 4.1 and selected interatomic distances and angles are collected in Table 4.1. Complex 90 crystallizes as an extended structure, consistent with the insolubility of both the powder and the crystals of this complex. The ligands are arranged in a zig-zag fashion, bridging the silver centres. The nitrate anions also bridge the silver atoms, resulting in an interconnected sheet of molecules as shown in Figure 4.2. The layers are arranged approximately 10 A apart in the crystal, with no intermolecular interactions between layers (Figure 4.3). The nitrate anion can coordinate in a variety of modes;2 3 examples exist of the coordination to silver phosphines via oxygen in four bonding modes: monodentate,24 bridging monodentate,9'25 bidentate,26 and bridging bidentate.27 In this case, the nitrate groups coordinate in two ways: bridging bidentate and bidentate. Each silver atom is coordinated to two nitrate ions through two of the oxygen atoms on one anion and one of the 109 oxygen atoms on the second anion. The chelated anion then bridges, through one coordinated O atom, to a second silver centre. The silver atoms are also coordinated to one CH3OH, resulting in distorted square pyramidal geometry at the metal centre (Figure 4.4). Although Ag(I) typically coordinates in either linear or tetrahedral geometry, it can exhibit higher coordination numbers. 2 8" 3 0 Figure 4.1 Structure of 90. 110 Figure 4.2 Packing diagram of 90, showing a layer of Ag(I), bridged by P T 2 P (69) and N 0 3 " . Figure 4.3 Packing diagram of 90, showing layered structure of the crystal. Ill Figure 4.4 View of Ag(I) coordination sphere in 90. Table 4.1 Selected interatomic distances (A) and angles (deg) for 90. Bond length/A Bond angle/deg Ag(l)-P(l) 2.390(3) P(l)-Ag(l)-0(1) 126.1(4) Ag(l)-0(1) 2.525(8) P(l)-Ag(l)-0(3) 126.1(4) Ag(l)-0(3)(bidentate) 2.681(7) P(l)-Ag(l)-0(3) 113.91(3) Ag(l)-0(3) 2.443(7) P(l)-Ag(l)-0(MeOH) 117.1(3) Ag(l)-0(MeOH) 2.639(1) 0(l)-Ag(l)-0(3) (bidentate) 48.5(2) P(l)-C(l) 1.813(5) 0(l)-Ag(l)-0(3, monodentate) 75.2(2) P(l)-C(7) 1.822(5) 0(3, monodentate)-Ag(l)-0(l) 87.6(4) P(l)-C(13) 1.810(5) 0(3, bidentate)-Ag-O(MeOH) 80.3(3) S(l)-C(13) 1.727(5) 0(l)-N(l)-0(2) 121.3(5) S(l)-C(16) 1.727(5) 0(l)-N(l)-0(3) 118.3(5) 0(2)-N(l)-0(3) 120.3(5) 112 4.3.3 N M R Spectroscopy Gold complexes. The N M R spectra of the gold complexes 86-88 indicate a dynamic system in solution, as the spectra change with solvent, concentration, and temperature. At room temperature, the 3 1 P N M R spectrum of complexes 86-88 in CDCI3 consist of a very broad peak at approximately 8 10 and a small (10% by 3 1 P NMR) , sharp peak at approximately 8 22. The less intense peak is very close to the P N M R shift of both the corresponding ligand oxide and the corresponding gold complexes presented in Chapter 3. As the complexes were analytically pure, this signal is assigned to a small amount of the corresponding gold complexes, which is reasonable i f the disproportionation shown in Equation 4.1 occurs. Variable temperature N M R spectra in CD2CI2 were obtained for 86, and the ' H and 3 1 P spectra are collected in Figure 4.5. In the ' H spectra, the signals broaden as the temperature is decreased from 295 K to 190 K, and the peak at 8 7 at 295 K shifts to 8 6.2 at 190 K. The signal in the 3 1 P N M R spectra of this complex shifts substantially over the temperature range investigated, and sharpens at 210 K. However, the signal remains somewhat broad, indicating that a dynamic process is still occurring in solution at low temperature. Although it is not possible to assign the 3 1 P N M R signal to specific species, it is known that increasing the number of phosphines coordinated to a gold centre decreases the chemical shift of the complex. 2 1 ' 3 1 - 3 2 Therefore, the signal is assigned as mainly due to species that have two phosphine ligands coordinated to the gold centre. 113 a) 295 K I 1 1 1 1 I 1 1 1 1 I 1 8.0 7.8 7.6 i M 1 1 i 1 1 1 1 i 1 1 1 1 i 1 1 1 1 i 1 1 1 1 i 1 1 1 1 r 7.2 7.0 6.8 6.6 6.4 6.2 6.0 7.4 ppm b) 250 K J \ V X 2 3 0 K 220 K |AA 190 K 20 19 IS I 1 1 1 1 I 1 1 1 1 I 1 1 1 1 I 1 1 1 1 I 1 1 1 1 I 1 ' 1 ' I 1 1 1 1 I 1 1 1 1 I 1 1 1 1 I 17 16 15 14 13 12 11 10 9 8 I 1 ' 1 1 I 7 6 5 ppm Figure 4.5 V T a) ' H and b) 3 1 P{'H} N M R spectra of 86. 114 Silver complexes. Silver exists as two naturally occurring isotopes, 1 0 7 A g and l 0 9 A g , in nearly equal abundance (48.12% and 51.82%, respectively) and both isotopes are spin active, with I = V2.33 Silver phosphines also generally exhibit fluxional behavior in solution, 3 4 and so the room temperature 3 1 P N M R spectra of silver phosphines are often broad . 1 0 ' 3 5 ' 3 6 Low temperature 3 1 P N M R spectroscopy can been used to obtain 3 1 P - 1 0 7 ' 1 0 9 A g coupling constants, which are useful in determining the solution structure of the complex. The value of J 3 1 P - 1 0 7 , 1 0 9 A g for silver phosphines typically decreases with increasing numbers of phosphine ligands coordinated to the metal centre. The values decrease from approximately 700 Hz for species with one phosphine ligand coordinated to the metal centre to 400 Hz for species with two phosphine ligands to 200 Hz for species with three or four phosphines. 34,37,38 1 31 Variable temperature H and P N M R spectra in CD2CI2 were obtained for 89 and 91, and are shown in Figure 4.6 and Figure 4.8, respectively. The *H spectra for 89 broaden substantially as the temperature is decreased from 298 K to 191 K, with no discernable peaks from 228 K to 191 K. The room temperature 3 I P N M R spectrum exhibits a broad peak at 5 0 at room temperature, which splits into two broad doublets at 228 K (Figure 4.7). The doublets are in an approximately 2:1 ratio, and J 3 l p - 1 0 7 l 0 9 A g are approximately 770 Hz and 500 Hz, respectively, indicating two Ag-P fragments and one P-Ag-P fragment in the complex. It is proposed that 89 exists as the trimetallic species shown in Chart 4.2. This structure is supported by the elemental analysis data, which gave a molecular formula of Ag3(N03)3(PTP) 2 . This is surprising, as the products obtained from the reaction of AgA, where A is any anion, and phosphines typically reflect the stoichiometry of the starting materials. However, the disproportionation of AgLNCh (L = tris(2-furyl)phosphine) according to Equation 4.2 has been reported.39 A similar reaction could be occurring here, 115 resulting in the observed product. In a similar reaction, the addition of [Ag(MeCN)][BF4] and KBr or KI to 2,5-bis(diphenylphosphinomethyl)thiophene resulted in a complex of the molecular formula A g 3 L 2 X 3 , where L is 2,5-bis(diphenylphosphinomethyl)thiophene and X is Br or I . 4 0 The broadness of both the ] H and 3 1 P N M R signals suggest that ligand exchange is probably occurring in this system. 2[AgL(N0 3)] U ,[AgL 2(N0 3)] + AgNQ 3 4.2 Chart 4.2 AgN0 3 Chart 4.3 116 a) b) 298 K 7.70 7.60 7.50 7.40 ppm 7.30 7.20 7.10 298 K i/C V . 288 K ,W r / L 278 K 268 K 258 K 248 K 228 K , 218K , ,/ V ,/V VA . 208 K 198 K 191 K 30 20 10 0 ppm -30 Figure 4.6 V T a) ' H and b) 3 1 P{'H} N M R spectra of 89. 117 a 16 14 12 10 8 6 4 2 0 -2 -4 -6 -8 -10 -12 -14 -16 Figure 4.7 3 1 P{H} N M R spectrum of 89 at 218 K in CD 2 C1 2 . a) J 3 y i 0 7 ' 0 9 A g = 770 Hz, b) J 3 1 P -1 0 7 l 0 9 A g = 500 Hz. In contrast to 89, the *H N M R spectra of 91 broaden only slightly as the temperature is decreased from 300 K to 220 K. The peaks also do not shift substantially over this temperature range, and the spectra do not aid in structure determination. Similar to 89, the room temperature 3 1 P N M R spectrum of 91 exhibits a broad peak at S 2, which splits into two broad peaks at 260 K. The two broad peaks resolve into two doublets at 220 K, with J31p-1 0 7 , 1 0 9 A g values of approximately 770 Hz. This is the expected pattern for a linear silver complex with one phosphine ligand; therefore, the structure of 91 is proposed to be that shown in Chart 4.3. Unfortunately, satisfactory elemental analysis could not be obtained for this complex, possibly due to decomposition. 118 300 K 7.80 7.60 7.40 7.20 ppm 7.00 6.80 6.60 ^ / A ^ A * ^ 3 0 0 K 250 K M \ / A 240 K k l\ /A ^ 2 3 0 K 12 10 2 0 ppm -4 -6 >ure 4.8 V T a) ' H and b) 3 1 P{'H} N M R spectra of 91 119 4.3.4 Electronic Spectroscopy Gold complexes. The solution and solid state absorption and emission spectra of gold complexes 86-88 are presented in Figure 4.9 and Figure 4.10, respectively and values of A,max and 8 for these complexes are collected in Table 4.2 and Table 4.3. Both the solution and solid state absorption and emission spectra of 87 and 88 are dominated by the TX—>rc* transitions of the thienyl groups. The bands are only slightly shifted relative to the ligand spectra and the spectra of the analogous gold complexes presented in Chapter 3. Similar to other complexes presented, the solid state spectra are red-shifted as compared to the solution spectra and the spectra of the terthienyl complexes are more red-shifted than those of the bithienyl complexes. In contrast to 87 and 88, the absorption and emission spectra of 86 differ from the spectra of both the ligand and AuCl(PTP)AuCl (82). The solution absorption spectra for these three compounds are compared in Figure 4.11. The absorption spectra of 86 are not shifted significantly relative to the ligand spectra, but several shoulders are seen in the spectra of 86 that are not seen in the spectra of PTP (68). For example, shoulders are seen at 269 nm and 277 nm in the solution spectrum of 86, which are not apparent in the spectrum of 68. As in 82, these bands are assigned as the vibrational structure of the phenyl groups. There is also a shoulder in the solution (310 nm) and solid state (330 nm) spectra of 86 that does not appear in either the spectra of 68 or the spectra of 82. The excitation spectrum of 86 corresponds to this band, with A,max at 330 nm. The emission of 86 occurs at 556 nm in solution and 525 nm in the solid state, which does not correspond to either ligand (518 nm, 481 nm) or 82 (345 nm, 485 nm; 402 nm, 470 nm) emission. Based on comparison to literature compounds, 8 ' 1 2 - 1 3 ' 4 1 ' 4 2 it is assigned to a gold-based (6p z -»5d x y , 5dx 2.y 2) transition, from a complex that has two phosphines coordinated to the gold centre. Through 120 calculations, this emission has been shown to exhibit a large red-shift due to a large chang in geometry from a trigonal planar ground state to a T-shaped excited state. 4 1 ' 4 2 40000 30000 .20000 -10000-40000 _ 30000 ' § 20000 ^ 10000 " 40000 30000 20000 10000 0 300 400 500 600 X/nm 700 800 Figure 4.9 Solution absorption (—) and emission (—) spectra of gold complexes 86-88. 121 CD O c 03 J2 t_ O </> JO < 200 300 400 500 Xlnm 600 c Qi c g '(/) E 700 Figure 4.10 Solid state absorption (—) and emission (—) spectra of gold complexes 86-88. The excitation (—) spectrum of 86 is included for comparison. 250 300 350 Xlr\m Figure 4.11 Comparison of the solution absorption spectra of PTP (68) (-AuCI(PTP)AuCl (82) (---), and 86 (—). : 122 Silver complexes. The solution and solid state absorption and emission spectra of silver complexes 89-91 are presented in Figure 4.12 and Figure 4.13, respectively, and values of A.max and s for these complexes are collected in Table 4.2 and Table 4.3. The absorption spectra of 89 and 91 are similar to the spectra of gold complexes 86 and 88. The spectrum of 89 exhibits the vibrational structure of the phenyl groups at 269 nm and 276 nm, and is only slightly blue shifted relative to the spectrum of the ligand. The solid state spectrum is very similar to the solution spectrum. Both the solution and solid state absorption spectra of 91 are very similar to those of PT3P (70). The n—>n* transition of the terthienyl group as compared to 70 is only shifted by 7 nm in the solution spectrum and 2 nm in the solid state spectrum, indicating that the metal centre has little effect on the terthienyl group. Complex 89 is not emissive in solution or in the solid state, supporting the assignment of the emission in the gold complexes 82, 85, and 86 as gold-based. The solid state emission spectrum of 90 is substantially different from that of P T 2 P (69) due to coordination of the phosphine lone pair; however, it is similar to the spectrum of 87. The emission is assigned to the 71*—»7r transition of the bithienyl group. As seen in the absorption data, the emission spectra of 91 are very similar to those of PT3P (70), and emission is assigned as terthienyl-based; however, because the purity of this complex is unknown, the emission may not be due to the Ag(I) complex of 70. Typical of terthienyl emission, the spectra are red shifted in solution as compared to the solid, and the spectra are structured, with spacing of 1165 cm"1 and 1172 cm"1 between bands. 123 3 TO 03 C CP c g 03 03 E LU 600 Figure 4.12 Solution absorption (—) and emission (—) spectra of silver complexes 89 and 91. 124 Table 4.2 Solution and solid state absorption data for 86-91. Complex A,m a x/nm ( emax /M'cm 1 ) W n m , solid state 86 269 (1.6 * 104), 277 (1.4 x 104), 3 08 (7.3 x 103) 272 (sh), 336 87 2 69 (1.2 x 104), 276 (1.1 x 104), 3 44 (2.7 x 104) 274 (sh), 354 88 2 69 (1.3 x 104), 27 8 (9.7 x 103), 3 86 (3.4 x 104) 273 (sh), 406 89 2 69 (2.0 x 104), 276 (1.8 x 104), 2 8 8 (1.7 x 104) 266 (sh), 302 90 91 270 (1.5 x 104), 277 (1.9 x 104), 382 (3.5 x 104), 255 (sh), 397, 439 (sh) 422 (sh)(1.9 x 104) Table 4.3 Solution and solid state emission data for complexes 86-91. Complex A,m a x/nm, solution X m a x /nm, solid state 86 556 525 87 401 426 88 466 500 89 - -90 - 414,437 (sh) 91 442,466 491,520 (sh) 4.4 Conclusions In this chapter the synthesis and characterization of Au(I) and Ag(I) phosphinothiophene complexes is described. Single crystals were obtained from a solution of gold complex 86; unexpectedly, the crystals were found to be AuCl(PTP)AuCI (82) by X -125 ray crystallography. The existence of gold-gold interactions may promote preferential •a 1 crystallization of this structure. P N M R spectra indicated fluxional processes in solution for 86-88. Variable temperature 3 1 P N M R spectra of 86 suggest that the major species have two or three phosphines coordinated to the gold centre; however, they did not allow for definitive determination of the species in solution. The emission and absorption spectra of 86 also indicate bis- or tris(phosphines) in both solution and the solid state for this complex. The absorption and emission spectra of 87 and 88 are similar to those of A u C l ( P T 2 P ) A u C l (83) and AuCl (PT 3 P )AuCl (84). Complex 90 was found to be insoluble; the X-ray crystal structure shows an extended structure with P T 2 P (69) and nitrate anions bridging the Ag(I) centres. In contrast, 89 and 91 were highly soluble in chlorinated solvents, but single crystals could not be obtained for these complexes. However, low temperature 3 1 P N M R spectra of these complexes aided in determination of the solution species via the silver-phosphorus coupling constants. 89 and 91 are proposed to be discrete species in solution, indicating that the choice of phosphinothiophene ligand has an influence on the structure of the complex. Others 4 ' 9 - 4 0 ' 4 3 ' 4 4 have observed a dependence of the structure of silver phosphines on the nature of the phosphine ligands. Generally, comparisons are made between ligands with flexible backbones, such as alkyl groups. These compounds can function either as chelating or bridging ligands; however, the phosphinothiophene ligands reported here cannot chelate. It is not clear why 90 exists as an extended structure, whereas 89 and 91 appear to be discrete complexes. The absorption spectra of 89 and 91 and the emission spectra of 90 and 91 are very similar to those of the corresponding gold complexes, indicating that the Ag(I) centre has a 126 similar affect to Au(I) on the thienyl groups. Complex 89 is not emissive, which supports the assignment of the emission in the corresponding gold complexes as gold-based. 127 4.5 References (1) Cotton, F. A. ; Wilkinson, G.; Murillo, C. A. ; Bochmann, M . , Ed. Advanced Inorganic Chemistry; 6 t n ed.; John Wiley and Sons: New York, 1999. (2) Bachman, R. E.; Andretta, D. F. Inorg. Chem. 1998, 37, 5657. (3) Brandys, M . - C ; Puddephatt, R. J. Chem. Commun. 2001, 1280. (4) Brandys, M . - C ; Puddephatt, R. J. Chem. Commun. 2001, 1508. (5) Catalano, V . J.; Malwitz, M . A. ; Horner, S. J.; Vasquez, J. Inorg. Chem. 2003, 42, 2141. (6) Smith, M . L. ; Almond, P. M . ; Albrecht-Schmitt, T. E.; Hi l l , W. E. Acta Crystallogr., Sect. E 2003, E59, ml013. (7) Wu, M . ; Zhang, L. ; Chen, Z. Acta Crystallogr., Sect. E 2003, E59, mil. (8) Brandys, M . - C ; Puddephatt, R. J. J. Am. Chem. Soc. 2001, 123, 4839. (9) Brandys, M . - C ; Puddephatt, R. J. J. Am. Chem. Soc. 2002, 124, 3946. (10) Lozano, E.; Nieuwenhuyzen, M . ; James, S. L. Chem. Eur. J. 2001, 7, 2644. (11) Xu, X . ; Nieuwenhuyzen, M . ; James, S. L. Angew. Chem., Int. Ed. 2002, 41, 764. (12) King, C ; Khan, M . N . I.; Staples, R. J.; Fackler, J. P., Jr. Inorg. Chem. 1992, 31, 3236. (13) McCleskey, T. M . ; Gray, H. B. Inorg. Chem. 1992, 31, 1733. (14) Uson, R.; Laguna, A . Organomet. Synth. 1986, 3, 322. (15) Altomare, A. ; Cascarano, M . ; Giacovazzo, C ; Guagliardi, A . J. Appl. Cryst. 1994, 26, 343. (16) SHELXTL; Version 5.1; Bruker A X S Inc.: Madison, Wisconsin, USA, 1997. (17) SAINT; Version 6.02 ed.; Bruker A X S Inc.: Madison, Wisconsin, USA, 1999. 128 (18) Van der Sluis, P.; Spek, A . L. Acta Crystallogr., Sect A 1990, 46, 194. (19) McAuliffe, C. A. ; Parish, R. V ; Randall, P. D. J. Chem. Soc, Dalton Tram. 1979, 1730. (20) Muetterties, E. L. ; Alegranti, C. W. J. Am. Chem. Soc. 1970, 92, 4114. (21) Parish, R. V. ; Parry, O.; McAuliffe, C. A. J. Chem. Soc, Dalton Trans. 1981, 2098. (22) Attar, S.; Bearden, W. H.; Alcock, N . W.; Alyea, E. C ; Nelson, J. H . Inorg. Chem. 1990, 29, 425. (23) Addison, C. C ; Logan, N . ; Wallwork, S. C. Quartley Reviews, Chem. Soc. 1971, 25, 289. (24) Tiekink, E. R. T. Acta Crystallogr., Sect. C 1990, C46, 1933. (25) Jones, P. G. Acta Crystallogr., Sect. C 1993, C49, 1148. (26) Barrow, M . ; Biirgi, H.-B.; Camalli, M . ; Caruso, F.; Fischer, E.; Venanzi, L. M . ; Zambonelli, L . Inorg. Chem. 1983, 22, 2356. (27) Stein, R. A. ; Knobler, C. Inorg. Chem. 1977, 16, 242. 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Acta 2004, 357, 2677. 130 Chapter 5 Synthesis and Characterization of Pd(II) and Pt(II) Complexes 5.1 Introduction The use of oligo- and polythiophenes as active materials in applications, such as light-emitting diodes and field effect transistors, requires control over the solid state arrangement of the thiophene groups. Packing regularity and intermolecular interactions, for example, can influence the emission1 and charge mobility2 of the material. One important intermolecular interaction that would be desirable to control is it-stacking in the crystal. n-Stacking is a face-to-face interaction seen in many aromatic molecules3'4 that has been shown to influence the charge mobility and the excitation and emission energy of oligothiophenes.1'5 In thiophene, it is thought to occur mainly through dispersion interactions of the 7i-electrons.5 The properties of oligo- and polythiophenes have been modified by different organic substituents on the oligo- or polythiophene.6"10 A new approach to controlling the solid state arrangement of oligothiophenes is through the coordination of metal centres. For example, our group has recently reported the use of pendant Ru(II) complexes to control the coplanarity of terthiophene rings.1 ]> 1 2 Palladium(II) and platinum(II) are good candidates for these studies, as they readily form well-defined complexes and crystallize wel l . 1 3 Dichlorobis(phosphine) complexes of these metals occur as both cis and trans isomers with square planar geometry, depending on the reaction conditions and ligands used. 1 4" 1 6 The trans isomer is generally found to be more thermodynamically stable, whereas the cis isomer 131 is more kinetically stable. 13,17-19 j n e selective synthesis of each isomer allows for a comparison of the packing arrangement in the crystal lattice. Our group has previously reported the synthesis and characterization of several P-substituted phosphinothiophene palladium(II) complexes (Chart 5 .1) . 2 0 - 2 2 The metal was found to affect both the electronic properties and the structure of the oligothiophene, particularly when directly bound to it, via C or S. It is of interest to compare the properties of these complexes to ct-coordinated Pd(II) complexes. In this chapter, the synthesis and characterization of a series of phosphinothiophene palladium(II) and platinum(II) complexes are reported. X-ray crystal structures are presented for 100, 101, 102, and 105, and the solution structures are determined by 3 1 P N M R spectroscopy. The absorption spectra in both solution and the solid state are discussed for all of the complexes. The cyclic voltammetry of 108 indicates electronic interaction between the terthienyl groups. The synthesis and characterization of 101 and 102 have been published.23 132 Chart 5.1 P h 2 P — P d Cl Cl \ / 133 5.2 Experimental 5.2.1 General ' H and 3 , P{ 'H} N M R experiments were performed on either a Bruker AV-300 or a Bruker AV-4.00 spectrometer. Spectra were referenced to residual solvent ( ]H) or external 85% H3PO4 ( 3 1P). Electronic spectra were obtained on a Cary 5000 in HPLC grade CH 2 C1 2 . Solid state absorption spectra were obtained by drop casting the compound from a CH 2 C1 2 solution onto a quartz slide. Cyclic voltammetry experiments were carried out on a Pine AFCBP1 bipotentiostat using a Pt disk working electrode, Pt coil wire counter electrode, and a silver wire reference electrode. Ferrocene was used as an internal reference to correct the measured potentials with respect to saturated calomel electrode (SCE). The supporting electrolyte, [(«-Bu)4N]PF6, was purified by recrystallizing three times from ethanol and drying for 3 days at 90 °C under vacuum. The scan rate for the experiment was 100 mV/s. Microanalyses were performed at UBC. PdCl 2 and K 2 P t C l 4 were purchased from Strem and used as received. THF was dried over Na and benzophenone, and distilled before use. CH 2 C1 2 was dried by passing over an alumina column. Acetonitrile was dried over 3A molecular sieves and was degassed by sparging with N 2 for 20 minutes. No special precautions for the exclusion of oxygen were taken during synthesis. 5.2.2 Procedures Pd(PT) 2 Cl 2 (99). This compound was synthesized by a modification of the literature procedure.21 PdCl 2 (0.033 g, 0.19 mmol) was dissolved in an HC1/H 2 0 solution (0.2 mL/3 mL), which was then added dropwise to a solution of 0.1 g (0.37 mmol) PT (65) dissolved in an ethanol/acetonitrile mixture (5 mL/4 mL). A yellow precipitate formed immediately, and 134 the yellow slurry was stirred for 1 hour. The solvent was then removed via rotary evaporation, and the resulting sticky material was dissolved in CH2CI2 and acetone, filtered, and a yellow powder was precipitated in hexanes. The product was recrystallized in hexanes/CH2Cl2, yielding analytically pure product. Yield: 80%. Anal. C32H26Cl2P2PdS2 requires: C, 53.83; H, 3.67. Found: C, 53.67; H, 3.67. ] H N M R (CDC13): 5 7.80 (m, 1H), § 7.69- 7.62 (m, 5H), 5 7.46-7.34 (m, 6H), 5 7.13 (m, 1H). 3 1 P{'H} N M R (CDC13) 5 14 (s), 24 (s). P d ( P T 2 ) 2 C l 2 (100). This compound was synthesized by a modification of the literature procedure. 2 4 PdCl 2 (0.025 g, 0.14 mmol) and P T 2 (66) (0.1 g, 0.29 mmol) were mixed together in a 1:2 mixture of C F b C N ^ F h C h for 3 hours. The solvent was removed, and the resulting yellow powder was dissolved in CH2CI2, gravity filtered, and precipitated with hexanes. The product was recrystallized in hexanes/CF^Cb- Yield: 40%. Anal. C40H30CI2P2PCIS4 requires: C, 54.71; H, 3.44. Found: C, 54.31; H, 3.58. ! H N M R (CD 2C1 2): 5 7.73-7.66 (m, 5H), 5 7.47-7.38 (m, 6H), 5 7.31 (dd, J = 5.0, 1.2 Hz, 1H), 5 7.18 (m, 2H), 5 6.98 (dd, J = 5.0, 3.6 Hz, 1H). 3 1 P{'H} N M R (CDC13) 5 13 (s), 23 (s). Pd(PT 3) 2Cl 2 (101). PdCl 2 (0.021 g, 0.12 mmol) was dissolved in an HC1/H 20 solution (0.2 mL/3 mL). This was added dropwise to a solution of 0.1 g (0.23 mmol) of PT3 (67) in THF, and a yellow precipitate began to form almost immediately. The yellow slurry was stirred for 1 hour, and the solvent was then removed via rotary evaporation. The resulting sticky material was dissolved in CH2CI2, filtered, and precipitated in hexanes. The product, a bright yellow powder, was recrystallized in hexanes /C^Cb. Yield: 86%. Anal. C48H3 4Cl2P2PdS6 requires: C, 55.30; H, 3.29. Found: C, 55.06; H , 3.29. *H N M R (CDC13): 5 7.70- 7.63 (m, 4H), § 7.46-7.38 (m, 6H), 5 7.28-7.20 (m, 6H, includes CHCI3), 5 7.18 (d, J = 135 3.6 Hz, 1H), 5 7.15 (d, J = 3.6 Hz, 1H), 5 7.08 (d, J = 3.6 Hz, 1H), 5 7.04 (d, J = 3.6 Hz, 1H), 8 6.99 (dd, J = 5.2, 3.6 Hz, 1H). 3 I P{'H} N M R (CD 2C1 2) 5 14 (s), 24 (s). Pd(PT 3P) 2Cl4 (102). This compound was synthesized by a modification of the literature procedure.24 PdCl 2 (0.025g, 0.14 mmol) and 0.086 g (0.14 mmol) of P T 3 P (70) were stirred together in a 1:2 mixture of CH3CN:CH 2 C1 2 for 3 hours. The solvent was removed, and the resulting orange powder was dissolved in CH 2 C1 2 , gravity filtered, and precipitated with hexanes. The resulting orange powder was recrystallized in hexanes/CH 2Cl 2, which yielded analytically pure 102. Yield: 80%. Anal. C 3 6 H 2 6 C l 2 P 2 P d S 3 requires: C, 54.45; H, 3.30. Found: C, 54.11; H, 3.70. 3 1 P{'H} N M R (CD 2C1 2) 5 13.1 (s), 13.2 (s), 24.7 (s), and 26.8 (s). General Procedure for synthesis of P t (PT n ) 2 Cl 2 complexes. The appropriate ligand was dissolved in 50 mL of CH 2 C1 2 and stirred with a solution of 0.5 equivalents of K 2 PtCU in 10 mL H 2 0 . The reaction was monitored both by the disappearance of the red colour in the H 2 0 layer due to K 2 PtCU, and by the disappearance of ligand via TLC. When the reaction was complete the layers were separated, the organic layer was dried over MgSC«4 and gravity filtered, and the solvent was'removed via rotary evaporation. A minimal amount of CH 2 C1 2 was added to dissolve the resulting solid, which was then precipitated in 300 mL hexanes. The resulting powder was collected via suction filtration and either dried under vacuum or recrystallized from CH2Cl2/hexanes to yield analytically pure samples. P t (PT) 2 Cl 2 (103). Yield: 67%. Anal .C 3 2 H 2 6 Cl 2 P 2 PtS 2 requires: C, 47.89; H, 3.27. Found: C, 47.78; H , 3.57. *H N M R (CDC13): 5 7.65-7.59 (m, 2H), 5 7.47-7.41 (m, 4H), 5 7.32-7.28 (m, 2H), S 7.17-7.13 (m, 4H), 5 7.04-7.01 (m, 1H). 5 3 , P{ 'H} N M R (CDCI3) 6 6 (s, Jp.pt = 3681 Hz). MALDI-TOF: m/z = 766 (MW-C1). 136 Pt(PT 2 ) 2 Cl 2 (104). Yield: 73%. Anal. C 4oH 3oCl 2P 2PtS4 requires: C, 49.69; H , 3.13. Found: C, 49.72; H , 3.39. ' H N M R (CDC13): 8 7.58-7.53 (m, 4H), 5 7.43-7.40 (dd, J = 7.7, 3.8 Hz, 1H), 5 7.36-7.32 (m, 2H), § 7.24-7.19 (m, 6H, includes CHC1 3), 5 7.08-7.07 (dd, J = 3.6, 0.9 Hz, 1H) 5 7.02-7.00 (dd, J = 3.6, 1.1 Hz, 1H) 5 6.98-6.96 (dd, J = 5.1, 3.7 Hz, 1H). 3 1 P{'H} N M R (CDC13) 5 5 (s, Jp.p, = 3685 Hz). MALDI-TOF: m/z = 931 (MW-C1). Pt(PT 3 ) 2 Cl 2 (105). Yield: 81%. Anal. C 48H34Cl 2P 2PtS6 requires: C, 50.97; H , 3.03. Found: C, 50.61; H, 3.27. *H N M R (CD 2C1 2): 5 7.68-7.57 (m, 8H), 6 7.51-7.38 (m, 6H), 5 7.32-7.19 (m, 11H), 5 7.15 (dd, J = 3.53, 1.06 Hz, 2H), 5 7.07-6.98 (m, 7H). 3 1 P{'H} N M R (CD 2C1 2) 5 6 (s, Jp.Pt = 3700 Hz). ESI: m/z = 1095 (MW-C1). Pt(PTP) 2 Cl 4 (106). PTP (68) (0.1 g, 0.22 mmol) was dissolved in 50 mL of CH 2 C1 2 , and stirred with 0.092 g (0.22 mmol) K 2 P t C l 4 dissolved in 10 mL H 2 0 . The reaction was monitored both by the disappearance of the red colour in the H 2 0 layer due to K 2 P t C l 4 and by the disappearance of ligand via TLC. When the reaction was complete, approximately 2 hours, the layers were separated and the organic solvent was removed via rotary evaporation. The solid was washed with hot CH 2 C1 2 and gravity filtered. The CH 2 C1 2 solution was then reduced in volume and a white powder was precipitated in 100 mL hexanes, collected via suction filtration, and dried under vacuum. Yield: 3%. Anal. C56H 4 4 Cl 4 P 4 Pt 2 S 2 requires: C, 46.81; H , 3.09. Found: C, 47.00; H , 3.30. ' H N M R (CD 2C1 2): 5 7.76-7.69 (m, 4H), 8 7.54-7.49 (m, 2H), 5 7.39-7.32 (m, 4H), 5 6.74-6.72 (dd, J = 5.4, 2.5 Hz, 1H). 3 , P{ 1 H} N M R (CD 2C1 2) § 4 (s, Jp.P t = 3718Hz). ESI: m/z = 1401 (MW-C1). Pt(PT 2 P) 2 Cl 4 (107). P T 2 P (69) (0.15 g, 0.28 mmol) was dissolved in 50 mL of CH 2 C1 2 , and stirred with 0.12 g (0.28 mmol) K 2 P t C l 4 in 10 mL H 2 0 . The reaction was monitored both by the disappearance of the red colour in the H 2 0 layer due to K 2 P t C l 4 and 137 by the disappearance of ligand via TLC. When the reaction was complete, approximately 4 hours, the layers were separated. The organic solvent was removed by rotary evaporation and the resulting yellow solid was dissolved in hot CH2CI2. The CH2CI2 solution was gravity filtered and a yellow powder was precipitated in hexanes, collected via suction filtration, and dried under vacuum. Yield: 11%. Anal. C64H48Cl4P4Pt2S4 requires: C, 48.01; H , 3.02. Found: C, 48.29; H , 3.33. *H N M R (CD 2C1 2): 5 7.82-7.74 (m, 4H), 5 7.49-7.44 (m, 2H), 8 7.38-7.32 (m, 4H), § 6.88-6.85 (dd, J = 4.1, 1.4, 1H), 5 6.81-6.80 (dd, J = 3.4, 1.4, 1H). 3 1 P{'H} N M R (CD2CI2) 5 9 (s, Jp.pt = 3111 Hz). MALDI-TOF: m/z = 1565 (MW-C1). ESI: m/z = 1567 (MW-C1). Pt(PT3P)2Cl4 (108). This complex was synthesized by a modification of the literature procedure.15 P T 3 P (70) 0.2 g (0.32 mmol) and 0.13 g (0.32 mmol) K 2 P t C l 4 were heated to reflux in 50 mL degassed 2-methoxyethanol for 4 h. A dark gray precipitate formed over this time. The solvent was removed in vacuo, and the resulting green-gray solid was dissolved in a minimum amount of CH2CI2 and gravity filtered to remove insoluble black material. A yellow solid was precipitated in 300 mL of hexanes, and collected with suction filtration. Yield: 91%. Anal. C72H52Cl4P2Pt2S6 requires: C, 48.98; H , 2.97. Found: C, 49.18; H , 3.37. ] H N M R (CDCI3): § 7.83-7.77 (m, 4H), 5 7.48-7.43 (m, 2H), 5 7.36-7.31 (m, 4H), 5 6.88-6.86 (m, 2H), 5 7 (s, 1H). 3 1 P{'H} N M R (CDCI3) 5 8.7 (s, J P . P t = 3763 Hz). MALDI-TOF: m/z = 1729 (MW-C1). ESI: m/z = 1729 (MW-C1). 5.2.3 X-ray Crystallographic Analyses Suitable crystals of 100, 101, 102, and 105 were mounted in oil on a glass fiber, and the data for each compound were collected at 173(1) K. The structures were solved using 138 direct methods 2 5 ' 2 6 and refined using Shelxl-97. 2 7 A l l measurements were made on a Bruker X8 A P E X diffractometer with graphite monochromated M o - K a radiation. The data for 100 were collected to a maximum 29 value of 55.8°. Data were collected in a series of (j) and co scans in 0.50° oscillations with 10.0 second exposures. Data were collected and integrated using the Bruker S A I N T 2 8 software package and were corrected for absorption effects using the multi-scan technique ( S A D A B S ) . 2 9 The data were corrected for Lorentz and polarization effects. The material crystallizes with one half-molecule residing on an inversion centre. One thiophene ring in the asymmetric unit is disordered and was modeled in two orientations. The atoms of the major disordered fragment were refined anisotropically, while the atoms of the minor fragment (with a relative population of approximately 0.23) were refined isotropically. Restraints were used to ensure the disordered thiophene fragments had reasonable geometries. A l l other non-hydrogen atoms were refined anisotropically. A l l hydrogen atoms were included in calculated positions but not refined. The data for 101 were collected to a maximum 29 value of 55.6°. Data were collected in a series of § and co scans in 0.50° oscillations with 10.0 second exposures. Data were collected and integrated using the Bruker S A I N T 2 8 software package and were corrected for absorption effects using the multi-scan technique (SADABS) 2 9 The data were corrected for Lorentz and polarization effects. A l l non-hydrogen atoms were refined anisotropically, while all hydrogen atoms were included in calculated positions but not refined. The terminal thiophene ring containing S(3) was disordered and modeled in two orientations, with relative populations of 0.77 and 0.23 for the major and minor fragments, respectively. The data for 102 were collected to a maximum 29 value of 45.0°. Data were collected in a series of § and co scans in 0.50° oscillations with 15.0 second exposures. Data were 139 collected and integrated using the Bruker S A I N T 2 8 software package. The material crystallizes as a two component "split-crystal" with the first component related to the second by a 6° rotation about a direction parallel to the real 1, 0.1, 0.08 axis. Data for the major "twin" component were integrated, including overlapped reflections. Data were corrected for absorption effects using the multi-scan technique ( S A D A B S ) . 2 9 The data were corrected for Lorentz and polarization effects. The material crystallizes with two half-molecules in the asymmetric unit, both residing on inversion centres. In addition, there appeared to be a significant amount of residual electron density in voids around the Pd complex. Attempts were made to model this as any of the potential solvent molecules, with little success. As a result, the P L A T O N / S Q U E E Z E 3 0 function was used to correct the raw data for this unresolved electron density. Ultimately, this procedure accounted for 258 electrons per unit cell, or roughly one hexane and one methylene chloride molecule. Finally, the central thiophene ring of each terthiophene moiety was disordered. In each case the ring was modeled in two orientations. The data for 105 were collected to a maximum 29 value of 52.8°. Data were collected in a series of (j) and co scans in 0.50° oscillations with 12.0 second exposures. Data were collected and integrated using the Bruker S A I N T 2 8 software package. Data were corrected for absorption effects using the multi-scan technique (SADABS) 2 9 The data were corrected for Lorentz and polarization effects. A l l non-hydrogen atoms were refined anisotropically. A l l hydrogen atoms were included in calculated positions but not refined. The thiophene ring containing S(6) was disordered and modeled in two orientations, with the populations of the major and minor fragments refined to an approximate 2:1 ratio. 140 The structures were obtained at U B C by Dr. Brian Patrick (100, 101, and 105) and Anita Lam (102). Appendix 1 contains crystallographic data for the structures presented in this chapter. 5.3 Results and Discussion 5.3.1 Synthesis The palladium complexes 99-102 were synthesized by either of two methods: The ligand and PdCh were stirred together in a mixture of CH2CI2 and C H 3 C N , or PdCl 2 was dissolved in dilute HC1 and subsequently added dropwise to a solution of the ligand in an appropriate solvent. The crude products were crystallized in CHaCb/hexanes to yield analytically pure materials in reasonable yields. Palladium bis(phosphine) complexes of this type are know to exhibit cis-trans equilibria in solution, 1 7 which can be observed by 3 1 P N M R spectroscopy. The 3 1 P N M R signals for the trans complexes are generally found at a lower chemical shift than those of the cis isomer. 2 4- 3 1" 3 5 The 3 1 P N M R spectra of 99-102 in CD2CI2 and CDCI3 indicate that, although both cis and trans isomers exist in solution, the trans isomer predominates in these solvents. As a single species in solution is desirable for solution characterization, we chose to synthesize the more inert Pt 1 3 > 3 6 analogues 103-108. The Pt complexes were expected to have cis geometry,17 allowing for comparison of the solid state packing of the thiophene moieties to the trans Pd complexes. Complexes 103-105 were synthesized by stirring together a solution of K^PtCU in H2O and the ligand of choice dissolved in CH2CI2. [PtCU]" is a dark red colour, and the progress of the reaction was monitored by the disappearance of 141 this colour in the water layer. The crude product obtained was either crystallized in CFLC^/hexanes or dried under vacuum. 1 9 5 Pt is a spin active nucleus, with I = Vi and a natural abundance of 33.8%, 3 7 and the 3 1 P- 1 9 5 Pt coupling constant, obtained from the 1 9 5Pt satellites of a 3 1 P N M R spectrum, can be used to determine the geometry at the metal centre. 1 5 ' 3 8 A coupling constant of approximately 3500 Hz indicates a cis-substituted complex, while a coupling constant of approximately 2500 Hz indicates trans geometry. Complexes 103 (5 6), 104 (§ 5), and 105 (§6) have coupling constants of 3681 Hz, 3685 Hz, and 3700 Hz, respectively, which indicate cis complexes. A second, less intense peak was observed in the 3 1 P N M R spectra of analytically pure 105 at 5 11.5. This peak is assigned to the trans isomer, as it should appear downfield to the signal from the cis isomer.3 8 However, due to the low intensity, no l 9 5 Pt satellites are observed for this signal. It may be that the increased steric bulk of the terthienyl group results in the formation of some trans isomer. Complex 108 was synthesized by heating PT 3 P (70) and K 2 P t C l 4 in 2-methoxyethanol. The resulting slurry was then filtered, and analytically pure product was precipitated in high yield from the filtrate with hexanes. The same procedure was attempted for 106 and 107; however, the yields were exceptionally low, due to the low solubility of these complexes. Hil l et al. also reported decreased solubility with a shorter bridging ligand; 1 5 this is presumably due to a decreased ability of the solvent to adequately solvate the complex. The conditions used in the synthesis of 103-105 resulted in a small amount of analytically pure 106 and 107. Complexes 106-108 have cis geometry at the metal centre, as the 3 , P- 1 9 5 Pt coupling constants for 106, 107, and 108 are 3781 Hz, 3111 Hz, and 3763 Hz, respectively. 142 Scheme 5.1 PT(65) n=1 P n 2 p PT 2 (66) n=2 PT 3 (67) n=3 99M=Pd, n=1 103M=Pt, n=1 100 M=Pd, n=2 104M=Pt, n=2 101 M=Pd, n=3 105 M=Pt, n=3 Scheme 5.2 102 M=Pd, n=3 106 M=Pt, n=1 107 M=Pt, n=2 108 M=Pt, n=3 5.3.2 Solid State Crystal Structures Single crystals of 100 were grown by the slow diffusion of hexanes into a dichloromethane solution of the complex. The X-ray crystal structure is shown in Figure 5.1 and selected bond lengths and angles are presented in Table 5.1. The complex is square planar at Pd, and both the Cl-Pd-Cl and P-Pd-P bond angles are 180°. As indicated by the 3 1 P N M R data, the ligands are arranged in trans geometry. The P-Pd (2.3315(9) A) and Cl-Pd (2.2896(9) A) bond lengths are very similar to trans-143 dichlorobis(triphenylphosphine)palladium (P-Pd = 2.337(1) A, Cl-Pd = 2.290(1) A) . 3 9 The thiophene rings of the bithienyl groups are essentially co-planar, with an S-C-C-S torsion angle of 10°. No 7t-stacking of thiophene rings was observed. Figure 5.1 Structure view of 100. 144 Table 5.1 Selected interatomic distances (A) and angles (deg) for 100. Bond length/A Bond angle/deg Pd-Cl 2.2896(9) P-Pd-P* 180.0 Pd-P 2.3315(9) Cl-Pd-Cl* 180.0 Cl*-Pd-P 95.06(3) Cl-Pd-P 84.94(3) Cl*-Pd-P* 84.94(3) Cl-Pd-P* 95.06(3) Torsion angle/deg S(l)-C(4)-C(5)-S(2) 10(2) The X-ray crystal structure of 101 was obtained from crystals grown by the slow diffusion of hexanes into a dichloromethane solution of the complex, and is shown in Figure 5.2. Selected bond lengths and angles are presented in Table 5.2. The complex crystallizes with distorted square planar geometry, as the P-Pd-P and Cl-Pd-Cl bond angles were found to be 175° and 177°, respectively. The ligands are in a trans configuration around the Pd centre, and the P-Pd (2.34 A ) and Cl-Pd (2.31 A ) bond lengths are similar to those of trans-Pd2Cl2(PPh3)2.3 9 The thiophene rings are less coplanar than those of terthiophene (172°-176°). 4 0 Interestingly, the terthienyl groups are oriented on the same side of the molecule. In the crystal lattice, the molecules are organized in stacks with the terthienyl groups from adjacent molecules facing each other, and the interplanar distances for the inner thiophene rings are within the range of Ji-stacking (3.648 A ) . 4 1 > 4 2 (Please see Appendix 1 for a packing diagram of this complex). 145 Figure 5.2 Structure of 101. Table 5.2 Selected interatomic distances (A) and angles (deg) for 101. Bond length/A Bond angle/deg Pd-Cl(l) 2.2996(6) P(l)-Pd-P(2) 174.89(2) Pd-Cl(2) 2.3195(6) Cl(l)-Pd-Cl(2) 177.21(2) Pd-P(l) 2.3313(6) Cl(l)-Pd-P(l) 91.25(2) Pd-P(2) 2.3416(6) Cl(2)-Pd-P(l) 88.48(2) Cl(l)-Pd-P(2) 91.19(2) Cl(2)-Pd-P(2) 89.30(2) Torsion angle/deg S(l)-C(4)-C(5)-S(2) -24.4(3) S(2)-C(8)-C(9)-S(3) -162.21(16) S(4)-C(28)-C(29)-S(5) -169.15(14) S(5)-C(32)-C(33)-S(6) 175.40(14) 146 Single crystals of 102 were grown by the slow diffusion of hexanes into a dichloromethane solution of the complex. The X-ray crystal structure is shown in Figure 5.3 and selected bond lengths and angles are presented in Table 5.3. The complex crystallizes as a metallamacrocycle, and both metal centres are trans substituted. In this structure the terthiophene rings are oriented parallel to each other; however, there is no ^-stacking evident between the terthienyl groups as the closest interplanar spacing between rings is 4.8 A. Intermolecular interactions between the terthiophenes are prevented by the phenyl groups at the vertices of the metallamacrocycle. Other palladium bis(phosphine) complexes of this t ype 4 3 - 4 7 have been reported, with similar bond lengths and angles. The Cl-P bond lengths are 2.303(2) A and 2.319(2) A, and the P-Pd bond lengths are 2.384(2) A and 2.346(2) A. These bond lengths are all slightly longer that those of /rara ,-Pd2Cl2(PPh3)2, but are very similar to those found in 101. The complex exhibits distorted square planar geometry; the P-Pd-P and Cl-Pd-Cl angles are 177° and 173°-, respectively. The S-C-C-S torsion angles are approximately 176°, which is very similar to those in terthiophene. 147 Figure 5.3 Structure of 102. Table 5.3 Selected interatomic distances (A) and angles (deg) for 102. Bond length/A Bond angle/deg Pd(l)-Cl(l) 2.303(2) P(l)-Pd(l)-P(2*) 176.73(7) Pd(l)-Cl(2) 2.319(2) Cl(l)-Pd(l)-Cl(2) 172.87(8) Pd(l)-P(l) 2.384(2) Cl(l)-Pd(l)-P(l) 89.17(8) Pd(l)-P(2*) 2.346(2) Cl(2)-Pd(l)-P(l) 91.89(8) Cl(l)-Pd(l)-P(2*) 90.44(8) Cl(2)-Pd(l)-P(2*) 88.10(8) Torsion angle/deg S(l)-C(16)-C(17)-S(2a) 175.5(12) S(2a)-C(20)-C(21)-S(3) 176.5(12) 148 Single crystals of 105 were obtained by the slow diffusion of hexanes into a dichloromethane solution of the complex. The X-ray crystal structure is shown in Figure 5.4 and selected bond lengths and angles are presented in Table 5.4. In contrast to 101, complex 105 crystallizes as the cis isomer. The complex exhibits distorted square planar geometry, with P-Pt-P and Cl-Pt-Cl angles of 97° and 87°, which is similar to cis-dichlorobis(triphenylphosphine) platinum ( Z P-Pt-P 97.8(1)°, Z Cl-Pt-Cl 87.1(1)°). 4 8 This distortion is likely due to the steric bulk of the phosphine ligands. The bond lengths (P-Pt = 2.2518(14) A, 2.2509(15) A; Cl-Pt = 2.3551(14) A, 2.3320(16) A) are also very similar to those found in c«-PtCl 2 (PPh 3 ) 2 (P-Pt = 2.251(2) A and 2.265(2) A, Cl-Pt = 2.333(2) A, 2.356(2) A). The torsion angles for S(l)-C(4)-C(5)-S(2) and S(2)-C(8)-C(9)-S(3) are larger than terthiophene, but those of the other terthienyl group are very similar. Although no intermolecular rc-stacking is observed in the lattice, intramolecular n-stacking is observed between thienyl ring S(l)-C(l)-C(2)-C(3)-C(4) and phenyl ring C(37)-C(38)-C(39)-C(40)-C(41)-C(42), with a plane to plane distance of 3.516 A. (See Appendix 1) 149 Figure 5.4 Structure of 105. Table 5.4 Selected interatomic distances (A) and angles (deg) for 105. Bond length/A Bond angle/deg Pt-P(l) 2.2518(14) P(l)-Pt-P(2) 97.30(5) Pt-P(2) 2.2509(15) Cl(l)-Pt-Cl(2) 87.17(6) Pt-Cl(l) 2.3551(14) P(l)-Pt-Cl(l) 84.89(5) Pt-Cl(2) 2.3320(16) P(l)-Pt-Cl(2) 172.04(6) P(2)-Pt-Cl(l) 177.13(5) P(2)-Pt-Cl(2) 90.66(6) Torsion angle/deg S(l)-C(4)-C(5)-S(2) 22.9(7) S(2)-C(8)-C(9)-S(3) 140.(4) S(4)-C(28)-C(29)-S(5) -7.6(7) S(5)-C(32)-C(33)-S(6) 8.3(8) 150 5.3.3 N M R Spectroscopy It is well known that dichlorobis(phosphine) palladium complexes can exist as both cis and trans isomers. 2 4 ' 3 1 " 3 5 Mononuclear complexes 99-101 show the expected two peaks in their 3 1 P N M R spectra, which are assigned as the cis and trans species, at approximately 5 24 and § 14, respectively. Interestingly, the room temperature ' H and 3 I P N M R spectra of 102 exhibits multiple peaks, and the spectra change depending on the concentration of 102, the solvent used, and the temperature. A variety of structures are possible for compounds of this type, including cis, cis; trans, trans; and cis, trans macrocycles (Scheme 5.3), as well as larger, oligomeric structures. Scheme 5.3 PhoP- PPh 2 C | Pd Pd c/ \ . S . .S . .S. / x c i ph2R-^ iri iri lrPPh2 CIS, CIS Ph 2P PPh 2 trans, cis 151 In an effort to assign the 3 1 P N M R peaks of 102 to possible structures formed in solution, several N M R experiments were done. Variable temperature H and P N M R spectra were obtained for 102 in CD2CI2 (Figure 5.5). The ' H spectra show significant broadening as the temperature is decreased from 288 K to 190 K ; however, it is difficult to determine the process that is occurring or assign any peaks to specific structures. The 3 1 P N M R spectra are more useful, and it can be seen in Figure 5.5 that the higher field peaks (approximately § 10-16), which are assigned to trans species, shift slightly over the temperature range and do not broaden. On the other hand, the peaks assigned to complexes with cis geometry, at about 5 22-34, broaden and split into two peaks between 218 K and 198 K. Some of these peaks resolve into doublets at 190 K , with coupling constants of approximately 14 Hz. This is a reasonable value for a P-P coupling constant in a cis-Vd complex, 4 9 supporting the assignment of these peaks to species with cis geometry. It is also reasonable that cis complexes would have more hindered rotation than the trans complexes; therefore, no dynamic process is evident for the trans species in this temperature range. 152 ppm Figure 5.5 Variable temperature a) *H and b) 3 1 P{H}NMR spectra of 102 in CD 2 C1 2 . 153 Different amounts of P T 3 P (70) were added to a CD2CI2 solution of 102, and the results are shown in Figure 5.6. The signal for the uncoordinated phosphine ligand can be seen growing in at 8 -17.5 with addition of the ligand. A new peak grows in at 8 14.3, which is very close to the 3 I P N M R shift of 101. Therefore, this signal is assigned to a complex in which two PT3P (70) ligands are attached to only one Pd centre (Scheme 5.4), giving local coordination around the metal similar to 101. It has been noted that ring strain can influence the 3 1 P N M R shift in similar systems.34 The most intense signals at 8 26.8 and 8 13.1 are assigned to the cis, cis and trans, trans macrocycles. The two smaller peaks at 5 24.7 and 8 13.2 are thought to be from a cis, trans macrocycle. The formation of this type of complex may be sterically unfavorable, but an X-ray crystal structure of a cis, trans isomer of the dichloro[p-bis(diphenylarsino)methane] platinum dimer has recently been reported.14 Scheme 5.4 PdCI 2 1 *-154 a) 1A, b) c. 40 30 20 0 ppm -10 -20 -30 Figure 5.6 3 I P{H} N M R (162 MHz) spectra of 102 with (a) 0, (b) 0.5, (c) 1, (d) 2, (e) 4, and (f) 10 equivalents of P T 3 P (70) added, in CD 2 C1 2 at 300 K . The concentration of a CD 2 C1 2 solution of 102 was varied over the solubility range of the complex (2.1 mM -10.5 mM) and the *H and 3 1 P N M R spectra are collected in Figure 5.7. There is little change in the ] H spectra; the signal at 5 7.7 changes shape and broad peaks grow in at 5 7.3 and 5 7.15. In the 3 1 P spectra a broad peak is seen at 8 14.3, similar to 101 and to the complex shown in Scheme 5.4; however, no signal is seen for the uncoordinated phosphine in this experiment. Therefore, this peak is assigned to larger, cyclic, oligomeric species in which the ring strain of the dimer complexes is reduced. A very dilute solution of 102 in THF was analysed by GPC, but no evidence for longer chain species was seen under these conditions. A comparison of the 3 1 P N M R spectra used to determine the species in a CD 2 C1 2 solution of 102 is shown in Figure 5.8. 155 1 ' 1 ' I 1 1 1 1 I 1 1 1 1 I 1 1 1 1 i 1 1 1 1 I 1 1 1 1 I 1 1 1 1 I 1 1 1 1 I 1 1 1 ' I 1 1 1 1 30 28 26 24 22 20 18 16 14 12 10 ppm Figure 5.7 a) ! H and b) 3 1 P{H} N M R spectra of 102 in CD 2 C1 2 , at (i) 2.1 mM, (ii) 4.0 mM, (iii) 5.9 mM, and (iv) 10.5 mM. 156 a) C l , F C l ' - p - p s ,CI i Pd V—p' "Cl b) P I C l -Pd- I Cl C l , , P — i Pd Cl -Pd-CI C l ' > - l P Cl -Pd-CI P P C l -Pd-CI CI,Pd I P -PdCI, - P d) CI 2Pd PdCW I M I | I I M | I I M | M M | I M I | I I M | M I I 18 17 16 15 14 13 12 11 11 1 1 11 1 I " ' i I I U I | I 29 28 27 26 25 24 23 22 21 20 19 ppm Figure 5.8 Comparison of 3 ! P{H} N M R spectrum of (a) 101, (b) 102, (c) 102 with 2 equivalents of PT3P (70), and (d) a concentrated sample (10 mM) of 102. 5.3.4 Absorption Spectra The solid state and solution spectra of palladium complexes 99-102 are shown in Figure 5.9 and Figure 5.10, respectively. Although both cis and trans isomers are present in solutions of these complexes, the amount of cis is low in CH2CI2 (ca. 5% by P NMR), and should not significantly affect the spectra. In the solution spectrum of 99, there are shoulders between 250 nm and 300 nm, and a distinct peak at 352 nm. The higher energy bands are assigned to n—»TI* and 7 t - » 7 t * transitions of the ligands, and are not substantially shifted from the spectra of the uncoordinated PT (65) (Figure 2.1). The band at 352 nm is not seen in the spectra of 65, AuPT (79), or 103. A band at comparable energy and molar absorptivity is seen in the spectra of other dichlorobis(phosphine) palladium complexes 3 1 ' 5 0" 5 5 and is 157 usually assigned to a L M C T transition (Cl—»Pd). The energy of charge transfer bands typically change with the polarity of the solvent;5 6 however, for 99 no significant shift was observed for this band when comparing the spectra in toluene, CH2CI2, and C H 3 C N (Figure 5.11). In the solid state the band does shift slightly (3 nm). Two overlapping bands can be seen in both the solution (322 nm and 374 nm) and solid state (328 nm and 384 nm) absorption spectra of 100. Presumably, one of these peaks is due to a TC—>n* transition in the bithienyl group and the other to a Cl—>Pd charge transfer band, similar to that seen in the spectrum of 99. The higher energy band is assigned as the-re—»rc* transition, as it is very similar in energy to P T 2 (66) (kmax = 333 nm). The Pd centre appears to have little effect on the absorbance properties of the thiophene group. The lower energy band is assigned to the L M C T transition, which is shifted by 22 nm when compared to the spectrum of 99. This indicates that the phosphinothiophene ligand has some influence on the L M C T transition. It is surprising that the shift is so large, but it is known that there is a significant contribution from triphenylphosphine to the L M C T band of trans-dichlorobis(triphenylphosphine) palladium (II), as determined by resonance Raman spectroscopy.51 When the solution spectra for 100 taken in toluene, CH2CI2, and C H 3 C N are compared, as shown in Figure 5.11, a shift in energy and a change in the intensity of the lower energy band are observed. The solution spectrum of 101 consists of a broad band at 372 nm with a shoulder at 415 nm. The peak is assigned to a rc->rc* terthiophene transition. As in the spectrum of 100, it is very similar in energy to the ligand (A,m a x = 374 nm), indicating little influence of the Pd centre on the conjugated moiety. Similar to other terthienyl complexes, the solid state spectrum of 101 appears much the same as the solution spectrum, but the peak broadens and shifts to lower energy (380 nm and 428 nm). These effects may be due to the rc-stacking of 158 the terthienyl groups observed in the crystal structure, or increased planarity of the terthienyl groups in the solid state. 4 0 ' 5 7 ' 5 9 As was seen in the P-substituted phosphinothiophene palladium(II) complexes previously reported,21 no distinct L M C T band is observed here. It may be that this band overlaps with the terthienyl TC—»TC* transition, which would also indicate some phosphinothiophene character in the L M C T . There appears to be a small decrease in the energy of the band as the polarity of the solvent is increased, and the shoulder at 415 nm becomes more prominent (Figure 5.11). This may be due to conformational effects or, if the L M C T overlaps with the terthienyl re—>n* transition, it may be solvatochromism of the L M C T transition. The solution and solid state spectra of 102 have bands at 375 nm and 383 nm, respectively, which are assigned to terthienyl TC—»rc* transitions. Again, no second band that can be assigned as a CT band is observed; however, as in 101, it may overlap with the TI—>TX* transition. When compared to the ligand spectra in solution and in the solid state, the TC->TC* bands of 102 are blue shifted by 14 nm and 11 nm, respectively, which is greater than the shifts observed for 101. This is surprising, as the terthienyl groups of the macrocyclic complex 102 are constrained in a more planar geometry by the metal centres than in 101. A second, higher energy band, which is not observed in the solution spectra of 99-101, is seen in the solution spectra of 102 at 275 nm. It is similar in appearance to the re—»rc* band of the phenyl groups seen in the spectra of the phosphine derivatives 74a-c and 75a-c. It is not known why this is apparent only in the spectrum of 102. 159 250 300 350 400 450 500 Xlnm Figure 5.9 Solution absorption spectroscopy of palladium complexes 99-102. Figure 5.10 Solid state absorption spectroscopy of palladium complexes 99-102. 160 < O c 03 o CO 300 350 400 450 500 l/nm Figure 5.11 Solution absorption spectra of palladium complexes 99,100, and 101 in C H 3 C N (—), CH 2 C1 2 (—), and toluene (•••). The solution and solid state absorption spectra for platinum complexes 103-108 are shown in Figure 5.12 and Figure 5.13, respectively. The spectra are dominated by the 7i-»7r* transitions of the oligothiophene moieties. The spectra of 103 and 106 in solution and in the solid state are very similar to those of PT (65) and PTP (68) (Figure 2.1 and Figure 2.3). In solution, the 7x—>7i* bands of 103-106 and 108 are only slightly shifted relative to those of the ligands, indicating little electronic effect of the metal centre on the thienyl moiety. However, the 7t—»7t* band in the spectrum of 107 is blue shifted by 15 nm relative to the ligand; the bithienyl moiety may be twisted in the bridged compound. In comparing the terthienyl complexes 105 and 108, it can be seen that the TT—»TT* band of 108 does not shift significantly in the solid state spectra as compared with the solution spectra, whereas the rc—»n* band of 161 105 does. This may be because the terthienyl groups of 108 are constrained in the same geometry in both solution and in the solid. The bands for 107 and 108 are narrower than those of 104 and 105. This is likely because of restricted rotation in the macrocyclic complexes, as the shoulders in 104 and 105 have been assigned to conformational effects. 4 0 ' 5 9 Figure 5.12 Solution absorption spectroscopy of platinum complexes 103-108. 162 103 \ 106 \ \ \ ^ x - x 108 300 400 500 300 400 500 \lr\m XI nm Figure 5.13 Solid state absorption spectroscopy of platinum complexes 103-108. Table 5.5 Solution and solid state absorption data for 99-108. Complex ^max/nm (e^ /M^cm" 1 ) A,max/nm, solid state 99 267 (sh) (1.4 x 10 4 ) , 296 (sh) (5.7 x IO 3), 352 (1.9 x lO 4 ) 269 (sh), 355 100 264 (sh) (1.8 x 10 4 ) , 322 (3.7 x 10 4 ) , 374 (sh) (2.3 x 10 4 ) 328, 384 (sh) 101 264 (sh) (2.2 x 10 4 ) , 372 (5.5 x 10 4 ) , 415 (sh) (3.9 x 10 4 ) 380, 428 (sh) 102 273 (3.0 x 10 4 ) , 375 (6.8 x 10 4 ) 281 (sh), 383 103 269 (sh) (1.6 x 10 4 ) , 277 (sh) (1.2 x 10 4 ) 250 (sh) 104 270 (sh) (1.7 x 10 4 ) , 277 (sh)(1.5 x 10 4 ) , 331 (3.6 x 10 4 ) 250 (sh), 340, 364 (sh) 105 269 (sh) (2.1 x i o 4 ) , 277 (sh) (1.6 x 10 4 ) , 377 (5.8 x 10 4 ) 270 (sh), 396 106a 270 (sh) (2.7 x 10 4 ) , 277 (sh) (2.3 10 4 ) x 10 4 ) , 3 00 (sh) (1.5 x 276 (sh) 107 269 (sh) (2.4 x 10 4 ) , 277 (sh) (2.3 x 10 4 ) , 335 (5.2 x 10 4 ) 348 108 270 (sh) (2.9 x 10 4 ) , 277 (sh) (2.1 x 10 4 ) , 387 (7.4 x 10 4 ) 274 (sh), 392 s is estimated, based on comparison of s at X = 277 nm to 107 163 5.3.5 Cyclic Voltammetry Cyclic voltammetry was carried out on 108, and the data are shown in Figure 5.14. Two irreversible, overlapping peaks are seen at 1.21 V and 1.41 V vs. SCE. As the oxidation potential of cz's-[PtCl2(PPh3)] is 2 V vs. S C E , 6 0 these are assigned to the sequential first oxidations of the two terthiophene groups. The second oxidation occurs at a higher potential, possibly due to electronic interaction with the already oxidized terthiophene. The terthiophene moieties may be interacting through space, or the interaction may occur via the Pt centre. The irreversibility is probably due to decomposition of the complexes upon oxidation. The oxidation potentials are substantially higher than for terthiophene (0.98 V vs. S C E 6 1 ) . The addition of the diphenylphosphino group has been found to lower the oxidation potential of terthiophene;21 however, the positively charged metal centre likely draws electron density from the terthienyl group. An increase in oxidation potential over that of the parent oligothiophene was also seen in the P-substituted phosphinothiophene palladium(II) complexes previously reported. 2 0" 2 2 164 C -CD u -o 0.00 0.25 0.50 0.75 1.00 1.25 1.50 1.75 V vs. SCE Figure 5.14 Cyclic voltammogram of 108 in C H 3 C N with 0.1 M [(«-Bu) 4N]PF 6. 5.4 Conclusions In this chapter the synthesis and characterization via N M R spectroscopy, X-ray crystallography, and absorption spectroscopy of a series of palladium(II) and platinum(II) phosphinothiophene complexes is described. Crystal structures are presented for 100, 101, 102, and 105. Although both cis and trans species can be observed in the 3 I P N M R spectra of the palladium complexes 99-102, the solid state structures of 100-102 exhibit trans geometry exclusively. In the crystal structure of 100, the bithienyl groups are arranged on opposite sides of the metal centre, whereas in 101 the terthienyl groups are on the same side, resulting in intermolecular Tt-stacking of the terthienyl groups in the lattice. It is known that 7i-stacking interactions become more favorable as the length of the oligothiophene increases.1 165 Complex 102 crystallizes as a metallamacrocycle, and both Pd centres exhibit trans geometry. No intermolecular interactions are observed in the lattice. By selecting the appropriate substitution, the Pd centre has been shown to control the arrangement of the thienyl groups in the solid. In solution, 102 can exist in a variety of structures, as shown by 3 I P N M R spectroscopy. Several of the peaks were assigned using different N M R experiments, and it is proposed that 102 exists as cis, cis; cis, trans; trans, trans; and larger, oligomeric species in solution. The platinum complexes 103, 104, and 106-108 exist in solution only as the cis isomer, as evidenced by their respective 3 1 P- 1 9 5 Pt coupling constants. However, a solution of the terthienyl complex 105 appears to have both isomers present; the bulkiness of the terthiophene group may force some of the complex to the trans isomer. The solid state structure for 105 exhibits only cis geometry. No inter- or intramolecular n-stacking of the terthienyl groups is observed, but intramolecular n-stacking is observed between phenyl and terthienyl groups. Dichlorobis(phosphine) palladium (II) complexes are typically orange, and the colour is attributed to a Cl->Pd CT transition. In 99-102, the band assigned to this L M C T appears to decrease in energy as the conjugation length of the oligothiophene is increased, indicating that this transition cannot be purely Cl-based. It may be that some of the n-character of the thiophene mixes with the HOMO of the complex. The absorption spectra of the platinum complexes 103-108 are dominated by the thienyl-based n—>n* transitions. Based on the small shifts in the absorption spectra as compared to the ligand spectra, the Pd(II) and Pt(II) metal centres appear to have little effect on the thienyl moieties, similar to the observation for the phosphine-coordinated (3-substituted Pd(II) complexes; however, the Pt(II) centre does raise the oxidation potential of the terthienyl group by approximately 0.23 V . Unlike the Au(I) 166 complexes presented in Chapter 3, none of the palladium or platinum complexes are emissive; the d 8 metal centre probably quenches the thiophene emission. 167 References Zhang, G.; Pei, Y . ; Ma, J.; Yin, K.; Chen, C.-L. J. Phys. Chem. B 2004,108, 6988. Fichou, D.; Ziegler, C. in Handbook of Oligo- and Polythiophenes; Fichou, D., Ed.; Wiley-VCH: Weinheim, 1999, 183. Hunter, C. A . ; Lawson, K. R.; Perkins, J.; Urch, C. J. J. Chem. Soc, Perkin Trans. 2 2001,651. Hunter, C. 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Bauerle, P. in The Handbook of Oligothiophenes; Fichou, D., Ed.; Wiley-VHC: The Handbook of Oligothiophenes, 1999, 89. 172 Chapter 6 Synthesis and Characterization of Ru( I I ) complexes 6.1 Introduction Ruthenium tris(bipyridine) and derivatives, such as Ru(bpy)2L2, generally exhibit interesting electronic properties, including absorption and emission from an M L C T (Ru—>bpy) state, and a reversible R u + 2 / + 3 redox couple.1 These properties make them ideal for the study of electron and charge transfer across bridging ligands, and many dimetallic complexes of this type have been reported.2"6 Charge transfer across bridging ligands can be observed in dimetallic complexes with absorption spectroscopy through the appearance of an intervalence charge transfer transition upon generation of the mixed valence species. It can also be observed with cyclic voltammetry by the appearance of two, separate redox waves for identical metal capping groups.7-8 Our group has published the synthesis and characterization of several Ru(bpy)2 P-phosphinothiophene complexes (Chart 6.1).9>10 Coordination of the metal centre affects both the optical and the electrochemical properties of the ligands, and, conversely, changing the thienyl group influences the electronic properties of the metal. It is of interest to compare these complexes to the a-coordinated Ru complexes reported here. In this chapter the synthesis and characterization of a series of phosphinothiophene Ru(II) complexes are reported. Solution absorption spectra and cyclic voltammetry of these complexes are discussed. 173 Chart 6.1 2 + 2PF 6 Ph2P-Ru(bpy)2 109 R1=R2=H 110 R!=H, R2=Me 111 R1=R2=Me 1 n i + P F 6 112 R1=R2=H 113 R!=H, R2=Me 114 R1=R2=Me 6.2 Experimental 6.2.1 General A l l reactions were performed under a nitrogen atmosphere, using standard Schlenk techniques and dry solvents. *H and 3 1 P{'H} N M R experiments were performed on either a Bruker AC-200E, Bruker AV-300, or Bruker AV-400 spectrometer. Spectra were referenced to residual solvent ('H) or external 85% H 3 P 0 4 ( 3 1P). Electronic spectra were obtained on a Cary 5000 in HPLC grade CH 2 C1 2 . Cyclic voltammetry experiments were carried out on a Pine AFCBP1 bipotentiostat using a Pt disk working electrode, Pt coil wire counter 174 electrode, and a silver wire reference electrode. Decamethylferrocene was used as an internal reference to correct the measured potentials with respect to saturated calomel electrode (SCE). The supporting electrolyte, [(«-Bu) 4N]PF 6, was purified by recrystallizing three times from ethanol and drying for 3 days at 90 °C under vacuum. The scan rate for all experiments was 100 mV/s. Microanalyses were performed at U B C . R U C I 3 H 2 O was purchased from Strem and used as received. The starting material c/s-Rufbpy^Cb was prepared by the literature method.1 1 Acetonitrile and ethylene glycol were dried over molecular sieves and degassed by sparging with N 2 for 20 minutes. THF was dried over Na and benzophenone, and distilled before use. 6.2.2 Procedures General procedure for the synthesis of 117-119. The complexes were synthesized by a modification of the literature procedure.3 The appropriate ligand was stirred together with 2 equivalents of c/s-Ru(bpy)2Cl2 in a mixture of 2:1 THF: ethylene glycol to give a purple solution. The reaction mixture was then heated to reflux for 24 h. The solution turned red, and the THF was removed via rotary evaporation. The resulting ethylene glycol solution was added dropwise to 50 mL of an aqueous solution of 0.5 g NH4PF6, which resulted in a red-orange precipitate. The product was collected by suction filtration and purified by column chromatography on basic alumina with 1:1 C H 3 C N : toluene as the eluent. The first band collected was the monometallic complex, followed by the dimetallic product. The products were obtained as dark red solids. Ru(PTP)Ru (117). Yield: 60%. Anal. C 6 8H54N 8 P 4 SRu2Cl2F 1 2 requires: C, 49.79; H, 3.32; N , 6.83. Found: C, 49.72; H , 3.29; N , 6.83. MS (ESI) m/z 1495 (MW-PFe) .^ N M R (CD 3 CN): 5 8.98 (t, J = 5.8 Hz, 2H), 5 8.92 (d, J = 5.5 Hz, 2H), 5 8.43 (d, J = 5.9 Hz, 2H), 5 175 8.41 (d, J = 5.8 Hz, 2H), 8 8.37 (d, J = 4.9 Hz, 2H), 8 8.35 (d, J = 4.9 Hz, 2H), 8 8.20 (d, J = 8.2 Hz, 2H), 8 8.09-8.01 (m, 4H), 8 7.93-7.81 (m, 4H), 8 7.57 (t, J = 7.3 Hz, 1H), 8 7.48 (t, J = 7.3 Hz, 1H), 8 7.36-7.11 (m, 27H), 8 6.96 (dd, J = 3.6, 2.4 Hz, 1H), 8 6.75 (t, J = 7.3 Hz, 2H). 3 I P{'H} N M R (CD 3 CN) 8 -143 (septet, J V , 9 F = 705 Hz), 8 41 (s), 8 42 (s). Ru(PT 2P)Ru (118). Yield: 50%. Anal. C72H56N 8P4S 2Ru2Cl2F,2 requires: C, 50.21; H, 3.28; N , 6.51. Found: C, 49.32; H, 3.32; N , 6.28. MS (ESI) m/z 1577 (MW-PF 6 ). ! H N M R (CD 3 CN): S 9.16 (d, J = 5.4 Hz, 1H), 8 9.11 (d, J = 5.8 Hz, 1H), 8 8.44 (d, J = 8.1 Hz, 1H), 8 8.38 (d, J = 8.1 Hz, 1H), 8 8.25 (d, J = 7.7 Hz, 1H), 8 8.12 (d, J = 8.1 Hz, 1H), 8 8.05 (td, J = 8.1, 1.16 Hz, 12H), 8 7.97-7.89 (m, 2H), 8 7.63 (tq, J = 8.2, 1.16 Hz, 1H), 8 7.47 (d, J = 5.4 Hz, 1H), 8 7.37-7.12 (m, 15H), 8 7.00 (dd, J = 3.9, 1.5 Hz, 1H), 8 6.86 (m, 1H). 3 l P{ l H} N M R (CD 3 CN) 8-143 (septet, J V , 9 F = 705 Hz), 8 40 (s). Ru(PT 3P)Ru (119). Yield: 62%. Anal. C 76H58N 8P4S 3Ru2Cl2Fi2 requires: C, 50.59; H, 3.24; N , 6.21. Found: C, 51.53; H, 3.74; N , 5.65. MS (ESI) m/z 1659 (MW-PF 6). ' H N M R (CD 3 CN): 8 9.16 (d, J = 5.4 Hz, 1H), 8 9.03 (d, J = 5.8 Hz, 1H), 8 8.45 (d, J = 8.1 Hz, 1H), 8 8.39 (d, J = 8.1 Hz, 1H), 8 8.26 (d, J = 8.1 Hz, 1H), 8 8.14 (d, J = 8.1 Hz, 1H), 8 8.05 (td, J = 8.1, 1.5 Hz, 1H), 8 7.93 (t, J = 8.1, Hz, 1H), 8 7.67 (td,J = 7.7, 1.5 Hz, 1H), 8 7.48 (d, J = 5.8 Hz, 1H), 8 7.39-7.14 (m, 17H), 8 7.09 (dd, J = 3.4, 1.5 Hz, 1H), 8 6.69 (td, J = 7.3, 1.16 Hz, 1H). 3 1 P{'H} N M R (CD 3 CN) 8 -143 (septet, J V 1 9 F = 705 Hz), 8 40 (s). 176 6.3 Results and Discussion 6.3.1 Synthesis Ruthenium complexes 117-119 were synthesized by the reaction shown in Scheme 6.1. Purification was achieved by column chromatography. Unfortunately, satisfactory elemental analyses could not be obtained for 118 or 119, possibly due to the presence of residual solvent and water. Octahedral c/s-Ru(bpy)2L-2 complexes are chiral, and exist as two optical isomers: A and A. The dimetallic complexes 117-119 are, therefore, obtained as mixtures of diastereomers: the rac form, which consists of enantiomers AA and AA, and the meso form, AA and AA. Although the separation of such isomers by both crystallization1 2 and chromatography13"15 has been reported for similar compounds, neither technique was successful here. The ' f l and 3 1 P N M R spectra for 117 show evidence of diastereomers. The 3 I P N M R spectrum of analytically pure 117 has two peaks (8 41 and 5 42); these are assigned to the meso and rac isomers (Figure 6.1). The ' H N M R spectrum has many signals, indicating two symmetric species in solution. It is known that the meso and rac forms of dinuclear Ru(bpy)2L,2 type complexes have different ' H N M R spectra. 1 3>1 6>1 7 Interestingly, the 3 1 P N M R spectra of 118 and 119 contain only a single peak and the ' H N M R spectra of these complexes are much simpler than that of 117. This indicates that the differences between the diastereomers decrease as the distance between the metal centres increases. The complexes did not crystallize, possibly due to the existence of a mixture of diastereomers. 177 Scheme 6.1 ~12 + 2PF6" \§_J) Ru(bpy)2CI2 ^ CI(bpy)2Ru \ \ L J / / N Ru(bpy)2CI 1. THF/ethylene glycol PTP (68) n=1 2. NH 4 PF 6 /H 2 0 117 n=1 PT 2P(69) n=2 1| ^ PT 3 P (70) n=3 6.3.2 Absorption Spectra Absorption spectra of 117, 118, and 119 are shown in Figure 6.2, and A, m a x and £ values for these complexes are collected in Table 6.1. A l l three complexes exhibit an intense absorption at 294 nm, which is assigned to TT—>7r* transitions of the bipyridine groups based on comparison to similar compounds.1'1 1 The spectra of 117 and 118 also have a band at 453 nm, and 119 has a shoulder of similar molar absorptivity at the same energy. These bands are 178 assigned to a Ru—»bpy M L C T transition.11 The thienyl moieties appear to have little influence on the M L C T , as it occurs at the same energy in all three complexes. The spectrum of complex 117 has a shoulder at 337 nm. Several alkyl- and arylphosphines have similar bands assigned to a second Ru—>bpy M L C T . 1 1 The spectra of complexes 118 and 119 exhibit a third band at 338 nm and 389 nm, respectively, which is assigned to the thienyl T C — M I * transition in both cases. The TC—»rc* band of 119 occurs at the same energy as in the ligand, but the TC—»TC* band of 118 is blue shifted by 12 nm relative to P T 2 P (69). Similar to PT3P (70), the TC->TC* band of 119 has a shoulder at 431 nm and it is broad, probably because of conformational effects in solution. 1 8 ' 1 9 300 400 500 600 X/nm Figure 6.2 Solution UV-visible spectra of 117-119. 179 Table 6.1 Solution absorption and electrochemical data for 117-119. Compound Solution absorption E1/2 vs. SCE X,max/nm (e/M'cm 1 ) 117 293 (7.8 x 104), 3 3 7 (1.4 x 104), 452 (1.2 x 104) • 0.93, 1.74 118 294 (7.9 x 104), 3 3 8 (3.4 x 104), 453 (1.3 x 104) 0.93, 1.69 119 2 94 (7.8 x 104), 3 89 (4.1 x 104), 431 (2.8 x 104), 460 (1.6 x 104) 0.92, 1.39 6.3.3 Cyclic Voltammetry Cyclic voltammograms (CV) were obtained for 117, 118, and 119 in C H 3 C N with 0.1 M [(«-Bu)4]PF6 as the supporting electrolyte. The CVs are shown in Figure 6.3 and the data are collected in Table 6.1. A l l three complexes exhibit two oxidation waves in the CV. The lower energy peak, at approximately 0.93 V vs. SCE, does not change in potential as the phosphinothiophene ligand is changed. It is assigned to the R u + 2 / + 3 oxidation, as the oxidation potential of [Ru(bpy)2Cl(PPh3)]PF6 was reported to be 0.94 V vs. S C E . 1 1 The R u + 2 / + 3 redox wave for 117 is slightly broadened, and was determined by deconvolution2 0 to consist of two overlapping waves, with a peak separation of 0.045 V . Although it is possible that the two peaks are due to electronic interaction over the bridge, it is more likely that the two peaks are due to the existence of diastereomers. The second wave at higher potential is assigned as a thienyl-based oxidation, as the potential of the peak decreases as the length of the oligothiophene increases.21 The first wave is reversible in both 117 and 118, but it is only reversible in 119 when the potential is not scanned past the second wave. Complex 119 also exhibits a new peak at approximately 0.5 V on reduction when the potential is scanned past the second wave. Electrolysis was performed on a sample of 119 in an attempt to determine the nature of the 180 species generated. A C V was run on the oxidized and subsequently reduced complex, and a reversible peak was seen at 0.54 V, which is very similar to the potential for the new wave in the C V of 119. A 3 1 P N M R spectrum was obtained for the material, and several peaks were observed between § 35 and § -26, including peaks assigned to ligand and ligand oxide. Column chromatography was used to purify the electrolysis mixture; however, only oxidized ligand was recovered. The electrochemistry of the R u + 2 / + 3 redox couple is well established, and parameters exist for the estimation of the potential of the couple based on the ligands coordinated to the Ru centre.22 The decrease in potential for the new species generated indicates that an electron-rich ligand must be coordinating to the Ru centre, but what the ligand may be is not known. As the oxidation of the terthienyl group is irreversible, it is likely that it undergoes a reaction upon oxidation. After this occurs, the complex may decompose to give an unknown ruthenium species and phosphine ligand, or the phosphinothiophene ligand may undergo a reaction while attached to the metal centre that generates a more electron rich ligand. It is not clear what the ligand oxidation product could be, and, as only oxidized ligand could be isolated as a product of the electrolysis, it appears that the former may be occuring. 181 1 I I 1 I I I I I 1 I I 1 I I I 1 I I I I 1 0.25 0.50 0.75 1.00 1.25 1.50 1.75 2.00 Vvs . SCE Figure 6.3 Cyclic voltammograms of 117 (—), 118 (---), and 119 (—) in C H 3 C N with 0.1 M [(«-Bu) 4N]PF 6, referenced to SCE. 6.4 Conclusions In this chapter the synthesis and characterization, via absorption spectroscopy and cyclic voltammetry, of a series of ruthenium(II) phosphinothiophene complexes is described. The absorption spectra of the three complexes have a band at 452 nm, which is assigned to an M L C T transition. Complexes 118 and 119 also have bands assigned as the re—»rc* transition of the thienyl group. The R u + 2 / + 3 wave in the C V occurs at the same potential in all three complexes, indicating that the length of the thienyl group has little influence on the metal centre in these complexes. This is in contrast to the B-substituted phosphinothiophene 182 complexes, which exhibit direct coordination of Ru to an oligothiophene.10 The complexes are not emissive at room temperature. The d 6 metal centre probably quenches the thienyl-based emission in 118 and 119, and it is known that phosphines cause a destabilization of the M L C T state in Ru(bpy)2L2 complexes that results in increased transitions from the M L C T state to non-emissive dd states.2 3-2 4 183 References Balzani, V . ; Bolletta, F.; Gandolfini, M . T.; Maestri, M . in Top. Curr. Chem.; Springer-Verlag: New York, 1978; Vol . 75, 1. Sullivan, B. P.; Meyer, T. J. Inorg. Chem. 1980, 19, 752. Ortega, J. V . ; Hong, B.; Ghosal, S.; Hemminger, J. C.; Breedlove, B.; Kubiak, C. P. Inorg. Chem. 1999, 38, 5102. Mosher, P. J.; Yap, G. P. A. ; Crutchley, R. J. Inorg. Chem. 2001, 40, 1189. Ishow, E.; Gourdon, A. ; Launay, J.-P.; Chiorboli, C.; Scandola, F. Inorg. Chem. 1999, 38, 1504. Crutchley, R. J. Adv. Inorg. Chem. 1994, 41, 273. Creutz, C. Prog. Inorg. Chem. 1983, 30, 1. Launay, J.-P. Chem. Soc. Rev. 2001, 30, 386. Moorlag, C ; Clot, O.; Wolf, M . O.; Patrick, B. O. Chem. Commun. 2002, 24, 3028. Moorlag, C ; Wolf, M . O.; Bohne, C ; Patrick, B. O. J. Am. Chem. Soc. 2005, 127, 6382. Sullivan, B. P.; Salmon, D. J.; Meyer, T. J. Inorg. Chem. 1978, 17, 3334. Rutherford, T. J.; Pellegrini, P. A. ; Aldrich-Wright, J.; Junk, P. C ; Keene, F. R. Eur. J. Inorg. Chem. 1998, 1677. Fletcher, N . C ; Junk, P. C ; Reitsma, D. A. ; Keene, F. R. J. Chem. Soc, Dalton Tram. 1998, 133. Reitsma, D. A. ; Keene, F. R. J. Chem. Soc, Dalton Tram. 1993, 2859. Lagref, J.-J.; Hosseini, M . W.; Planeix, J .-M.; De Cian, A . ; Fischer, J. Chem. Commun. 1999,2155. Kelso, L. S.; Reitsma, D. A. ; Keene, F. R. Inorg. Chem. 1996, 35, 5144. 184 Hua, X . ; von Zelewsky, A. Inorg. Chem. 1995, 34, 5791. DiCesare, N . ; Belletete, M . ; Marrano, C ; Leclerc, M . ; Durocher, G. J. Phys. Chem. A 1998,702,5142. DiCesare, N . ; Belletete, M . ; Marrano, C ; Leclerc, M . ; Duro.cher, G. J. Phys. Chem. A 1999, 103, 795. Toman, J. J.; Brown, S. D. Anal. Chem. 1981, 53, 1497. Bauerle, P. in The Handbook of oligothiophenes; Fichou, D., Ed.; Wiley-VHC: Weinheim, 1999, 88. Lever, A . B. P.; Dodsworth, E. S. in Inorganic Electronic Structure and Spectroscopy, Volume II: Applications and Case Studies; Solomon, E. I. and Lever, A. B. P., Ed.; John Wiley & Sons, 1999, 227. Klassen, D. M . ; DelPup, R. V . Inorg. Chem. 2002, 41, 3155. Caspar, J. V . ; Meyer, T. J. Inorg. Chem. 1983, 22, 2444. 185 Chapter 7 Conclusions and Future Work 7.1 General Conclusions In this thesis, a series of phosphinothiophene ligands and derivatives were synthesized and characterized. Au(I), Ag(I), Pd(II), Pt(II), and Ru(II) complexes of the phosphines were synthesized, and the structural and electronic affect of the metal centre on the thienyl group and of the thienyl group on the metal centre were investigated with X-ray crystallography, N M R spectroscopy, solution and solid state absorption and emission spectroscopy, and cyclic voltammetry. Detailed conclusions for the complexes presented are discussed within each chapter; general conclusions drawn from this study follow. Coordination of a transition metal through an a-substituted phosphine has little electronic effect on an oligothiophene, as measured by a shift in the absorption and emission spectra of the complexes compared to those of the corresponding ligands. The choice of metal had no significant influence on the interaction, as all the shifts were within approximately ± 20 nm. In the case of the emission spectra of the metal complexes incorporating a bithienyl group, the shifts were much larger because the emission process changes from an n—»n* transition in the phosphine to a TC*—>TC transition in the complex. The changes observed in the spectra of the metal complexes are similar to the effect of oxidizing the phosphine to a phosphine oxide or sulfide. The electronic effects of the metal centres are likely mainly due to the coordination of the phosphine lone pair, with some contribution from the inductive effect of the metal. In fact, the substitution of the diphenylphosphino group has a greater influence on the optical properties of the oligothiophene than the subsequent 186 coordination of a transition metal, particularly in the thienyl and bithienyl cases. The electronic effect of a-substitution decreases as the length of the oligothiophene increases, as observed by absorption and emission spectroscopy. The phosphinoterthiophene compounds; the oxides, sulfides, and phosphonium salts; and the transition metal complexes all exhibited this result. Considering the results presented in this thesis and those outlined in the literature review in Chapter 1, the linker group in transition metal-oligothiophene systems is of great importance in determining the extent of electronic interaction between the metal and the oligothiophene. For significant interaction to occur, the linker group must allow for electron derealization from the metal to the thienyl group, and vice versa. Complexes that demonstrate significant interaction have oxygen, acetylene, and a-carbon coordination as linker groups. These groups ensure close coordination of the metal centre to the oligothiopene and have energy levels that match both the metal centre and the bridging ligand. Although the diphenylphosphino group allows for close proximity of the metal centre to the oligothiophene, the energy levels in the systems do not facilitate strong electronic interactions between the two. The metal centre, however, was shown to affect the crystal packing of several oligothiophenes and may, therefore, indirectly influence the properties of oligothiophenes in the solid state. For example, in comparing the terthienyl complexes Au(PT3)Cl (81), Pd(PT3)2Cl2 (101), and P t (PT 3 ) 2 Cl 2 (105), it can be seen that the choice of mono- or bis(phosphine) and the choice of metal centre determines the solid state packing of the terthienyl group. In 101, the metal centre was shown to increase n-n stacking in the solid state, which may affect the charge mobility of the solid. The lack of electronic interaction between the transition metal and the oligothiophene may be advantageous in cases where the 187 desired property is that of the oligomer, not a hybrid material. This is a new and promising use of metals in conjugated systems. In conclusion, although coordination of a transition metal to an oligothiophene by an a-substituted phosphine results in weak electronic'interaction between the two, the metal centre can control the solid state packing of the oligomer. 7.2 Suggestions for Future W o r k There are several new areas of study that stem from these results. Complexes of other metal could be synthesized, such as Cr, Mo, and W. 1 - 2 These complexes may have accessible redox potentials and may show metal-metal coupling across the oligothiophene bridge. The bithienyl complexes of Mo have recently been reported, and they exist in oligomeric, cyclic structures; however, no electronic data was reported.3 It would also be interesting to crystallize larger oligomers and polymers of the Pd and Pt complexes presented here. This could be achieved through removal of the Cl groups, with AgBF4 for example, and addition of more bis(phosphine). The Pd and Pt complexes may also exhibit significant non-linear optical properties.4 Another intriguing area of potential study would be an investigation of the phosphonium salts presented in Chapter 2. Several phosphonium salts have been shown to have reversible reductions;5'6 quaternized bis(phosphinothiophenes) may show electrochemical coupling of the phosphonium groups across the oligothiophene bridge. Polymers containing electron rich thienyl groups next to the electron poor phosphonium 188 functionality could be synthesized by reaction of the bis(phosphines) and a dihaloalkane. Polymers of this type may also be soluble in water. For a comparison to the phosphinothiophenes presented here, it would be of interest to vary the linker to thiol groups.7 Thiols coordinate many of the same transition metals as phosphines,8 and the resulting complexes could provide insight into the factors that enhance interaction between an oligothiophene and a metal centre. Several complexes of Pt and Pd bound to the ct-carbon of an oligothiophene are shown in Chapter 1; it would be interesting to synthesized organometallic complexes of other metal centres, such as Au(I). 9 Another approach to metallation of the oligothiophene is to coordinate the phosphinothiophene as a chelating ligand, bound through a phosphine and a carbon or sulfur of the thienyl group. 1 0" 1 3 As shown in Chart 7.1, this arrangement would result in a strained, four-membered ring in the complexes presented here; however, with a two carbon bridge between the phosphine and the oligothiophene, a more favourable six-membered ring would be created. Preliminary work on the synthesis of a model complex of this type is promising. Compound 122 was synthesized by the route shown in Scheme 7.1, and characterized by ] H and 3 1 P N M R spectroscopy and mass spectrometry. The phosphine was then coordinated to Ru(bpy)2Cl2, and the 3 1 P N M R shift of the resulting complex indicates coordination through sulfur. Following a procedure developed in our group, 1 2 123 was then heated to reflux with NaOH in an attempt to cyclometallate the thiophene ring. The 3 1 P N M R data indicate successful cyclometallation. Further characterization of these complexes is needed, and extension of the synthesis to longer oligomers would be interesting. 189 Chart 7.1 Scheme 7.1 1 2 0 -OH TsCI CHoCIo ET3>I OTs KPPh, THF PPh: 1 2 2 Ph 2 (bpy) 2Ru—Ps 2+ NaOH Ru(bpy)2CI2 AgBF 4 acetone P h 2 |2+ (bpy) 2Ru—P. C H 3 C N 190 References Magee, T. A. ; Matthews, C. N . ; Wang, T. S.; Wotiz, J. H . J. Am. Chem. Soc. 1961, 53, 3200. Hor, T. S. A. Inorg. Chim. Acta. 1989,158, 5. Myrex, R. D.; Colbert, C. S.; Gray, G. M . ; Duffey, C. H. Organometallics 2004, 23, 409. Zhai, T.; Lawson, C. M . ; Gale, D. C ; Gray, G. M . Opt. Mat. 1995, 4, 455. White, C. K. ; Rieke, R. D. J. Org. Chem 1978, 43, 4638. Kaim, W.; Lechner-Knoblauch, U.; Hanel, P.; Bock, H . Org. Chem. 1983, 48, 4206. de Boer, B. ; Meng, H. ; Perepichka, D. F.; Zheng, J.; Frank, M . M . ; Chabal, Y . J.; Bao, Z. Langmuir 2003, 19, 4272. Cotton, F. A. ; Wilkinson, G.; Murillo, C. A. ; Bochmann, M . Advanced Inorganic Chemistry; 6 t h ed.; John Wiley & Sons:, 1999. Porter, K. A. ; Schier, A. ; Schmidbaur, H. Organometallics 2003, 22, 4922. Clot, O.; Wolf, M . O.; Patrick, B. O. J. Am. Chem. Soc. 2000, 122, 10456. Clot, O.; Wolf, M . O.; Patrick, B. O. J. Am. Chem. Soc. 2001,123, 9963. Moorlag, C ; Clot, O.; Wolf, M . O.; Patrick, B. O. Chem. Commun. 2002, 24, 3028. Moorlag, C ; Wolf, M . O.; Bohne, C ; Patrick, B. O. J. Am. Chem. Soc. 2005, 727, 6382. 191 Appendix 1 Crystal structure data Table A l . l Selected crystal structure data for 81, 82, and 85. (PT 3 )AuCl (81) AuCl(PTP)AuCl (82) AuI(PTP)AuI (85) Formula C 2 4 H , 7 P S 3 C l A u Q9H74P4S2CI6AU C 6 3 H 6 oP 4 S 2 Cl 2 Au2l2 Habit prism tablet prism Dimension/mm 0.30 x 0.20 x 0.20 0.50 x 0.40 x 0.15 0.40X0.25 X0.10 mm T/K 173 173 173 Crystal System monoclinic triclinic triclinic Space Group P2,/n Pi P-l (#2) a/A 9.6606(6) 11.339(1) 11.576(3) blA 18.844(1) 13.439(2) 13.737(3) clA 13.0096(8) 13.935(2) 14.336(3) •a/0 90 67.17(1) 66.66(1) pr 103.84(1) 69.44(1) 66.32(1) y/° 90 78.08(1) 78.45(1) VIA' 2299.6(2) 1826.4(4) 1914.6(8) z 4 1 1 DCaic/g cm"3 1.921 1.902 2.057 Unique data 4683 8476 9013 ju (Mo Ka)/cm"' 68.66 84.11 94.92 R(F)a(I>2cr(I)) 0.044 0.034 0.040 Rw(F2)b (all data) 0.103 0.073 0.118 ° R = Y\F0\-\FC\II\F0 B RW = (!(Fo-Fc2)2/I.»>(Fo)2) 1/2 192 Figure A l . l Structure of AuI(PTP)AuI (85). f Figure A1.2 ORTEP diagram of P T 3 A u C l (81), showing rc-stacking of phenyl rings in the lattice. 193 Table A1.2 Selected crystal structure data for 90. 90 Formula C34H32N208P2S2Ag2 Habit colourless, needle Dimension/mm 0.40x0.15 x 0.05 T/K 173 Crystal System monoclinic Space Group P2 i / c (#14) a/A 12.4072(7) b/k 8.2661(4) elk 20.225(1) al° 90.0 61° 99.286(5) yi° 90.0 vik3 2047.1(2) z 4 D c a i c / g cm"3 1.522 Unique data 3860 p. (Mo Ka)/cm"1 11.84 R(F)a(I>2a(I)) 0.100 Rw(F2)b (all data) 0.139 A R = l\r0\-\FC /l\F0\BRW=(Y.(F*-FC2)2/Y.W(F2)2)U2 194 Table A1.3 Selected crystal structure data for 100, 101, 102, and 105. Pd(PT 2 ) 2 Cl 2 Pd(PT 3 ) 2 Cl 2 Pd(PT 3 P) 2 Cl 4 Pt(PT 3 ) 2 Cl 2 (100) (101) (102) (105) Formula C 4 oH3oCl 2 P 2 S 4 Pd C48H 3 4P 2 S 6 Cl 2 Pd C 7 2 H 5 2 P 4 S 6 C l 4 P d 2 C48H 3 4 S 6 P 2 PtC l 2 Habit yellow, plate orange, rod orange, prism yellow-orange, plate Dimension/mm 0.15x0.05x0.02 0.25x0.10x0.10 0.25x0.16x0.08 0.25x0.25x0.10 77K 173 173 173 173 Crystal System monoclinic monoclinic triclinic monoclinic Space Group P2\/c (#14) P2,/n(#14) P-l (#2) jP2,/n(#14) a/A 9.489(1) 11.8648(8) 12.486(2) 11.749(1) b/A 17.637(2) 20.875(1) 15.077(2) 29.282(2) c/A 11.2772(9) 18.270(1) 20.832(3) 12.609(1) al° 90.0 90.0 9 0 . 1 6 2 ( 7 ) ° 90 pr 100.667(4) 98.054(4) 102.085(7) 93.704(3) yl° 90.0 90.0 101.155(7) 90 VIA3 1854.7(3) 4480.4(4) 3758.5(9) 4328.9(6) Z 2 4 2 4 D c a i c /g cm"3 1.572 1.545 1.403 1.735 Unique data 4056 10054 9677 8887 ju (Mo Ka)/cm" 9.86 9.20 9.11 37.65 R(F)a 0.098 0.033 0.052 0.041 (I>2a(I)) Rw(F2)h 0.093 0.074 0.0151 0.094 (all data) W ( F 0 2 ) 2 ) 1 1 2 195 Figure A1.3 ORTEP view of crystal packing of 101, showing intermolecular rc-stacking of terthiophene groups. The hydrogen atoms, phenyl groups, and chlorines are omitted for clarity, and thermal ellipsoids are drawn at 50% probability. Figure A1.4 ORTEP view of crystal packing of 105, showing intramolecular Tc-stacking of phenyl and thiophene moieties. The hydrogen atoms and other phenyl groups are omitted for clarity, and thermal ellipsoids are drawn at 50% probability. 196 

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