指導教授：邱靜雯臺灣大學：化學研究所馮博彥Feng, Po-YengPo-YengFeng2014-11-252018-07-102014-11-252018-07-102014http://ntur.lib.ntu.edu.tw//handle/246246/261310由非金屬元素所組成之自由基分子，通常是較不穩定的，所以需要特定的電子與立體穩定效應來降低其反應性。至今，將含硼官能基引入有機自由基的例子相當少。由於硼的正電性致使其具有較一般有機取代基要強的sigma-donating能力，此外，硼原子上空的p軌域，亦可離域自由基中的未成對電子，所以引入含硼的官能基預期可以幫助穩定有機自由基。為驗證此想法，我們合成了帶有雙三均甲苯硼基之酚自由基，並且去探討在氧化還原反應中結構上的改變。依據酚自由基之電子自旋共振光譜及其模擬數據得知，硼原子以及均三甲苯基上對位甲基上的氫皆有貢獻，證實了硼取代基的確可以穩定酚自由基上未配對的π電子。除此之外，我們還發現並證實雙三均甲苯硼基酚會藉由一連串的單電子還原-氫原子轉移-單電子還原來形成帶兩個負電荷的酚氫硼酸鹽。另外，電中性的雙三均甲苯硼基酚自由基還可以藉由單電子還原來形成相對應的苯昆硼烯陰離子，並發現苯昆硼烯陰離子中π電子的離域程度會受到陽離子配位能力的影響。Free radicals that are exclusively composed of non-metal elements are relatively unstable, and generally require specific electronic and steric stabilization effects to realize the structural characterization of these open-shelled species. To date, substitution of organic free radicals with diarylboryl group has only been reported for few times. Taking into account the sigma-donating ability governed by the electropositive nature of boron, the boryl substituent should help in stabilizing the electron deficient phenoxyl radical. Furthermore, the empty p-orbital at boron could delocalize the un-paired electron and lead to stable free radicals. To evaluate the idea, we have prepared the dimesityl boryl substituted phenoxyl radical, and to investigate its structural changes under redox events. Interestingly, we have also discovered an electron reduction triggered sequential electron and hydrogen atom transfer process, which leads to transformation from a hydroxyphenyl-substituted borane to a hydridoborate phenoxide dianion. The neutral borylated phenoxyl radical could be further reduced with cobaltocene to the corresponding benzoquinone borataalkene derivative. ESR spectroscopic measurement of the free radical reveals a hyperfine-coupling constant of 3.424 G and 1.142 G to the 11B (I = 3/2) and 10B (I = 3) nuclei, respectively. This result indicated that the boryl substituent indeed stabilizes the open-shelled species through delocalization of the spin density on the phenol ring.口試委員會審定書 # 中文摘要 i ABSTRACT i CONTENTS ii LIST OF FIGURES v LIST OF TABLES vii LIST OF SCHEMES viii Chapter 1 Introduction 1 1.1 Phenoxyl Radical 1 1.2 Generation of Phenoxyl Radical 5 1.2.1 Alkaline Potassium Ferricyanide 5 1.2.2 Lead Oxide 6 1.2.3 Reaction of 4-Halo-2,6-cyclohexadienone with Metals 7 1.2.4 Electrochemical Method 8 1.2.4 Diphenylpicrylhydrazyl (DPPH) 10 1.3 Properties of Phenoxyl Radical 12 1.3.1 Infrared Spectroscopy 12 1.3.2 UV-Vis Spectroscopy 13 1.3.3 ESR Spectroscopy 15 1.4 Reaction of Phenoxyl Radical 16 1.4.1 Reducing Agents 16 1.4.2 Self Dimerization 16 Chapter 2 Results and Duscussion 18 2.1 Triarylborane 18 2.2 Concept 18 2.3 Synthesis and Characterization 19 2.3.1 Synthesis of Borylated Phenol 19 2.3.2 Synthesis of Borylated Phenoxyl Radical 22 2.3.3 Electrochemistry of Borylated Phenol 25 2.3.4 Electrochemistry of Borylated Phenoxyl Radical 31 2.4 Mechanism of the Reducation of 1 34 2.5 Magnetic Property of Borylated Phenoxyl Radical 40 Chapter 3 Conclusion 42 Chapter 4 Experimental Section 44 APPENDIX 52 REFERENCE 90 LIST OF FIGURES Figure 2-1 ORTAP drawing of 1. Hydrogen atom are omitted for clarity. Thermal ellipsoids are set at 50% probability 21 Figure 2-2 Molecular structure of 2 with hydrogen atoms and solvent molecules omitted for clarity. Thermal ellipsoids are set at 50 % probability 24 Figure 2-3 Cyclic voltammogram of 1 in THF 26 Figure 2-4 11B NMR spectrum of 1 in the presence of 0.5, 1, and 2 equivalents of KC8 28 Figure 2-5 Region-selected HMBC spectrum of K2[3] in THF-d8 29 Figure2-6 Left: The tetrameric structure of K2[3]. Right: ORTEP representation of one of the independent molecules of [3]2- 30 Figure 2-7 Cyclic voltammogram of 2 in CH2Cl2 31 Figure2-8 Molecular structure of [CoCp2][4] with hydrogen atoms omitted for clarity. Thermal ellipsoids are set at 50 % probability 33 Figure 2-9 11B NMR spectrum of the reaction mixture with different reaction 36 Figure 2-10 ORTEP drawing of Li[4]. Hydrogen atoms and solvent molecules are omitted for clarity. Thermal ellipsoids are set at 50% probability 39 Figure 2-11 Experimental and simulated EPR spectrum of 2, and hyperfine coupling constants used for simulation 41 Figure 4-1: 11B NMR spectrum of 1 in the presence of 0.5, 1, and 2 equivalents of KC8. 50 Figure 4-2: 11B NMR spectrum of the reaction mixture with different reaction time. 51 LIST OF TABLES Table 1-1 Oxidation potential of phenol dervavitive 10 Table 1-2 The absorption maximum of 2,6-di-tert-butyl-4-R-phenoxyl radicals 14 Table 2-1 Electrochemical reduction potential (V vs. SCE) of aromatic boranes 26 Table A-1 Crystal data and structure refinement for 1 52 Table A-2 Crystal data and structure refinement for 2 57 Table A-3 Crystal data and structure refinement for K2[3] 65 Table A-4 Crystal data and structure refinement for [CoCp2][4] 79 Table A-5 Crystal data and structure refinement for [Li][4] 85 LIST OF SCHEMES Scheme 1-1 The chemical structure of naphthol and phenantrol 2 Scheme 1-2 Resonance structure of phenoxyl radical 3 Scheme 1-3 The example of functionalized phenoxyl radical 3 Scheme 1-4 The resonance structure of galvinoxyl radical 4 Scheme 1-5 The resonance structure of Yang’s biradical 5 Scheme 1-6. Reaction of of 4-Halo-2,6-cyclohexadienone with metals 7 Scheme 1-7 The redox behavior of phenol 9 Scheme 1-8 The reaction of DPPH and phenolic compound 11 Scheme 1-9 The reaction pathway of dehydrogenation of phenol 17 Scheme 2-1 Synthesis of 4-bromo-2,6-di-tert-butylphenol trimethylsilyl ester 20 Scheme 2-2 Synthesis of borylated phenol 21 Scheme 2-3 Synthesis of borylated phenoxyl radical 23 Scheme 2-4 Chemical reduction of compound 1 27 Scheme 2-5 Proposed mechanism of reduction reaction of compound 1 35 Scheme 2-6 The chemical reaction of phenol and borane radical anion 36 Scheme 2-7 Synthetic route of hydrioborate-tethered phenoxyl radical 37 Scheme 2-8 the reaction of borylated phenoxyl radical with LiAlH4 3888140186 bytesapplication/pdf論文公開時間：2019/07/29論文使用權限：同意有償授權(權利金給回饋本人)酚自由基硼烷電子轉移氫原子轉移還原thesishttp://ntur.lib.ntu.edu.tw/bitstream/246246/261310/1/ntu-103-R01223125-1.pdf