CONJUGATED LOW COORDINATE ORGANOPHOSPHORUS MATERIALS: SYNTHESIS, CHARACTERIZATION AND PHOTOCHEMICAL STUDIES By VITTAL BABU GUDIMETLA Submitted in partial fulfillment of the requirements for the degree of Doctor of Philosophy Thesis Advisor: Dr. John D. Protasiewicz Department of Chemistry CASE WESTERN RESERVE UNIVERSITY January, 2010 CASE WESTERN RESERVE UNIVERSITY SCHOOL OF GRADUATE STUDIES We hereby approve the thesis/dissertation of _____________________________________________________ candidate for the ______________________degree *. (signed)_______________________________________________ (chair of the committee) ________________________________________________ ________________________________________________ ________________________________________________ ________________________________________________ ________________________________________________ (date) _______________________ *We also certify that written approval has been obtained for any proprietary material contained therein. Dedicated to my parents Table of Contents List of Tables………………………………………………………………………………i List of Figures…………………………………………………………………………….iii List of Charts…………………………………………………………………………….vii List of Schemes……………………………………………………………………………x List of Abbreviations…………………………………………………………………….xii Acknowledgement………………………………………………………………………xiv Abstract…………………………………………………………………………………xvi Chapter 1. Introduction 1.1 Conjugated Organic Materials: General Introduction …………….………1 1.2 Mutiple (pπ-pπ ) Bonding in Main Group Elements: Brief Historical Background………………………………………………………………..3 1.3 Double Bond Rule and σ vs π Bonding in Main Group Elements…….…..5 1.4 Acyclic π-Conjugated Organophosphorus Materials…………..……..…...7 1.5 Cyclic π-Conjugated Organophosphorus Materials…………..…..……...11 1.5.1 Six Membered Cyclic Compounds………………………………12 1.5.2 Five Membered Cyclic Compounds……………………………..12 1.6 Conjugated Organophosphorus Materials: Phosphorus the Carbon Copy……………………………………………………………………..13 1.7 Recent Developments in Conjugated Organophosphorus Materials…….15 1.7.1 π-Conjugated Organophosphorus Polymers and Materials….......16 1.8. Proposed Research Studies………………………………………………18 1.8.1 meta-Terphenyl Phosphaalkenes: Synthesis, Characterization and Photochemical Studies……………………………………………….......18 1.8.2 meta-Terphenyl Phosphaalkenes Bearing Electron Donating and Accepting Groups……..…………………………………………………20 1.8.3 meta-Terphenyl Phosphaalkenes to 2,6-Diarylsubstituted-Benzo- bis(oxaphospholes)………………………………………….………..….21 1.9 References………………………………………………………..............22 Chapter 2. Photochemical Isomerization of meta-Terphenyl Protected Phosphaalkenes…………………………………………………………………..27 2.1. Introduction………………………………………………………………27 2.2 Results and Discussion…………………………………………………..32 2.3 UV-vis Spectral Studies of E and Z Isomers………………………….…40 2.4 Single Crystal Structure Analysis of E and Z Isomers…………………...41 2.5 Variable Temperature 1H NMR Studies…………………………………45 2.6 Conclusions………………………………………………………………49 2.7 Experimental Section…………………………………………………….50 2.8 References………………………………………………………………..54 Chapter 3. meta-Terphenyl Phosphaalkenes Bearing Electron Donating and Accepting Groups………………………………..………………………………………57 3.1. Introduction………………………………………………………………57 3.2. Results and Discussion…………………………………………………..61 3.2.1. Synthesis of phosphaalkenes and functionalized meta-terphenyls..61 3.2.2. UV-vis Absorption Data…………………………………………..65 3.2.3. X-ray Crystallographic Studies……………………………………67 3.2.4. Electrochemical Studies…………………………………………...72 3.2.5. Nonlinear Optical Studies…………………………………………77 3.3. Conclusions………………………………………………………………77 3.4. Experimental Section…………………………………………………….78 3.5. References………………………………………………………………..91 Chapter 4. Synthesis and Studies of 2,6-Diaryl-Benzo-bis(1,3-oxaphospholes)………...96 4.1 Introduction…………………………………………………………………..96 4.2. meta-Terphenyl Phosphaalkenes to Benzoxaphospholes…………..……….97 4.3. Benzoxaphospholes……………………………………………………...…100 4.4. Results and Discussions……………………………………………………101 4.4.1. Benzoxaphospholes: Synthesis of Key Intermediates…………...104 4.4.2.Synthesis of 2,6-Diaryl-Benzo-bis(1,3-oxaphospholes)…….……107 4.4.3. Spectroscopic Studies……………………………………………111 4.4.4. Electrochemical Studies…………………………………...……..114 4.5. Conclusions………………………………………………………………...117 4.6. Experimental Section………………………………………………………117 4.7. References………………………………………………………………….123 Chapter 5. Summary……………...………………………………………….…………127 5.1. Photochemical Isomerization ………………………………...…..…….127 5.2. Effect of Substituents on meta-Terphenyl Phosphaalkenes…………….129 5.3. Synthesis and Studies of 2,6-Diaryl-Benzo-bis(1,3-oxaphospholes)…. 133 Appendix………………………………………………….....………………………….135 Bibilogrphy……………………………………………………………………..………223 List of Tables Chapter 1. Table 1.1. The σ and π bond strengths for selected diatomic molecule……………..……6 Table 1.2. Electronegativities for selected group 14 to group 16 elements…………..…14 Chapter 2. Table 2.1. meta-Terphenyl phosphaalkenes and synthetic yields……………………….33 Table 2.2. UV-Vis absorption spectral data for 2.5a – 2.8a (CHCl3)……………...……34 1 31 Table 2.3. H and P{H} NMR data for E and Z phosphaalkenes (CDCl3)……………35 Table 2.4. E-Z conversion data in a photochemical reactor upon exposure to 350 nm light source for the compounds 2.5a – 2.8a (CDCl3)……………………………………38 Table 2.5. UV-vis absorption data of 2.8a and 2.8b…………………………………….41 Table 2.6. X-ray crystallography data for the compounds 2.8a and 2.8b……………….43 Table 2.7. Selected bond lengths (Å) and bond angles (°) of 2.8a and 2.8b…...……….44 Table 2.8. Variable temperature NMR data and the rate constant obtained from a two site exchange model in WINDNMR…………………………………………………………48 Chapter 3. Table 3.1. Synthesized phosphaalkenes and 31P{1H} NMR data………………………..64 Table 3.2. UV-vis absorption data for the synthesized meta-terphenyl phosphaalkenes in CHCl3………………………………………………………………………………….....66 Table 3.3. Crystallographic data for the compounds 3.8, 3.9, 3.10 and 3.12……………70 Table 3.4. Selected structural data for structures 3.8, 3.9, 3.10 and 3.12…………….…71 Table 3.5. Half wave potentials for the selected phosphaalkenes……………………….76 i Chapter 4. Table 4.1. Cyclic voltammogram data of 4.40 and 4.41……………………………….116 ii List of Figures Chapter 1. Figure 1.1. The highest occupied molecular orbitals (HOMO) in a phosphaaethylene…14 Figure 1.2. Effect of phosphorus incorporation into the conjugated –C=C- system……16 Chapter 2. 31 Figure 2.1. P{H} NMR of 2.8a (CDCl3), before exposure to sunlight………………..36 1 Figure 2.2. H NMR of 2.8a (CDCl3) after exposure to sunlight, a mixture of 2.8a and 2.8b can be seen in the NMR……………………………………………….……………36 1 Figure 2.3. {H} NMR of 2.8a (CDCl3), before exposure to sunlight…………..………37 1 Figure 2.4. H NMR of 2.8a (CDCl3) after exposure to sunlight, mixture of 2.8a and 2.8b can be seen in the NMR…………………………………………………………….……37 Figure 2.5. Model pictorial representation of Rayonet UV photochemical reactor…….38 Figure 2.6. Photochemical equilibration of the phosphaalkene 2.8a -2.8b in the photochemical reactor………………………………………..…………………………..39 Figure 2.7. UV-Vis absorption spectra of 2.8a and 2.8b………………………………..40 Figure 2.8. ORTEP diagram of 2.8a (30% probability ellipsoids)……...………………42 Figure 2.9. ORTEP diagram of 2.8b (30% probability ellipsoids)……………………...42 1 Figure 2.10. H NMR (400MHz) of isolated 2.8b in CDCl3……………………………46 Figure 2.11. Variable temperature (experimental) 1H NMR spectra of 2.8b (Z-isomer) in CDCl3…………………………………………………………………………………….46 Figure 2.12. Variable temperature (simulated by WINDNMR) NMR spectra of 2.8b (Z- isomer) in CDCl3………………………………………..………………………………..47 Figure 2.13. Eyring and Arrhenius plots for calculating the thermodynamic parameters iii for the hindered rotation………………………………………………………………….48 Chapter 3. Figure 3.1. UV-vis absorption spectra of synthesized meta-terphenyl phosphaalkenes in CHCl3.................................................................................................................................65 Figure 3.2. Single crystal X-ray crystallographic structure of E-2,6-Mes2C6H3P=C(H)C6H4-4-NO2 (3.8) shown at the 50% thermal ellipsoid level….67 Figure 3.3. Single crystal X-ray crystallographic structure of E-2,6-Mes2C6H3P=C(H)C6H4-4-CN (3.9) shown at the 50% thermal ellipsoid level…...68 Figure 3.4. Single crystal X-ray crystallographic structure of E-4-MeO-2,6-Mes2C6H2P=C(H)C6H4-4-CN (3.10) shown at the 50% thermal ellipsoid level………………………………………………………………………………………68 Figure 3.5. Single crystal X-ray crystallographic structure of E-4-MeO-2,6-Mes2C6H2P=C(H)C6H5 (3.12) shown at the 50% thermal ellipsoid level..69 Figure 3.6. Substituent effects and the crystal structure of conjugated phosphaalkenes..72 Figure 3.7. Cyclic voltammogram of 3.7, 0.001M E-[2,6-Mes2C6H3P=C(H)C6H5]/0.001M ferrocene in 0.1M [n-Bu4N][BF4] in THF with 0.1 V/s scan rate………………………………………………………………73 Figure 3.8. Cyclic voltammogram of 3.9, 0.001M E-[2,6-Mes2C6H3P=C(H)C6H4-CN]/0.001M ferrocene in 0.1M [n-Bu4N][BF4] in THF with 0.1 V/s scan rate, an overlay of the second redox potential shown in dotted lines………………………………………………………………………………………74 Figure 3.9. Cyclic voltammogram of 3.10, iv 0.001M E-[4-CH3O-2,6-Mes2C6H2P=C(H)C6H4-CN]/0.001M ferrocene in 0.1M [n- Bu4N][BF4] in THF with 0.1 V/s scan rate, an overlay of the second redox potential shown in dotted lines……………………………………………………………..……...74 Figure 3.10. Cyclic voltammogram of 3.12, 0.001M/0.001M ferrocene in 0.1M [n-Bu4N][BF4] in THF with 0.1 V/s scan rate……..75 Chapter 4. Figure 4.1. Molecular structure of (4.3) meta-terphenyl phosphaalkene