University of Nevada, Reno Matrix Isolation of Aryl(trifluoromethyl)carbenes, Heteroaryl(trifluoromethyl)carbenes and Phenylbis(trifluoromethyl)carbenes A dissertation submitted in partial fulfillment of the requirements for the degree of Doctor of Philosophy in Chemistry by Pei Wang Dr. Robert S. Sheridan/Dissertation Advisor August, 2015 THE GRADUATE SCHOOL We recommend that the dissertation prepared under our supervision by PEI WANG Entitled Matrix Isolation Of Aryl(Trifluoromethyl)Carbenes, Heteroaryl(Trifluoromethyl)Carbenes And Phenylbis(Trifluoromethyl)Carbenes be accepted in partial fulfillment of the requirements for the degree of DOCTOR OF PHILOSOPHY Dr. Robert S. Sheridan, Advisor Dr. Kent M Ervin, Committee Member Dr. Chris Jeffrey, Committee Member Dr. Paula J Noble, Committee Member Dr. W. Patrick Arnott, Graduate School Representative David W. Zeh, Ph. D., Dean, Graduate School August, 2015 i Abstract We have isolated and studied 2-naphthyl(trifluoromethyl)carbene, 1- naphthyl(trifluoromethyl)carbene, 4-pyridyl (trifluoromethyl)carbene, 2-pyridyl (trifluoromethyl)carbene, 3-pyridyl (trifluoromethyl)carbene, 3-bromo-5-pyridyl (trifluoromethyl)carbene, meta-phenylbis(trifluoromethyl)carbene and para- phenylbis(trifluoromethyl)carbene in low temperature matrices for the first time. The naphthyl(trifluoromethyl)carbenes are photostable and have triplet ground states in matrices as most of the other studied ary(trifluoromethyl)carbenes. The 1- and 2- naphthyl(trifluoromethyl)diazirines, the precursors of 1- and 2- naphthyl(trifluoromethyl)carbenes, have dissimilar geometric structures leading to different UV/Vis absorptions. In the studied pyridyl(trifluoromethyl)carbenes, 4- pyridyl(trifluoromethyl)carbene was the most stable one in matrice: no photoproduct from 4- pyridyl(trifluoromethyl)carbene was observed. However, we obtained a small amount of photoproducts of 2 - pyridyl(trifluoromethyl)carbene, even though the result was not repeatable. The most reactive isomer was 3 - pyridyl(trifluoromethyl)carbene, which could decompose under prolonged irradiation. The derivative of 3 - pyridyl(trifluoromethyl)carbene, 3 - bromo - 5 - pyridyl(trifluoromethyl)carbene, was more photolabile and could be converted to other intermediates with comparatively short term irradiation. All the studied pyridylcarbenes have triplet ground states. Although they were photostable, phenyl(trifluoromethyl)biscarbenes attracted our attention due to their interesting electronic structures. meta- Phenyl(trifluoromethyl)carbene has a quintet ground state, while the overall multiplicity of para - phenyl(trifluoromethyl)carbene is a singlet with a diradical structure. ii Acknowledgements I would never have been able to finish my dissertation without the guidance of my committee members, help from friends, and support from my family. First and foremost, I would like to express my deepest gratitude to my advisor, Dr. Robert S. Sheridan, for his excellent guidance, patience, and introducing me into this fascinating field - carbenes. As an outstanding scientist and a dedicated educator, Dr. Robert S. Sheridan inspired me with his passion for research, illuminating views on Chemistry. I have been amazingly fortunate to receive my Ph.D training in his lab. I would like to thank previous and current Sheridan group members, Dr. Peter Zuev, Dr.Andrea Song, Dr. Rajendra Ghimire, Chengliang Zhu, Emilia Groso, Danielle Poteete, Alexander Froebel Zehl, Steven Lucas, Cameron Berg for their friendship, support and guidance. I appreciate the members of my committee: Dr. Kent M Ervin, Dr. Chris Jeffrey, Dr. Paula J Noble, and Dr. W. Patrick Arnott who have been extremely helpful in their academic advisements. Appreciation is extended to my parents and my husband for their encouragement and support. iii Table of Contents Abstract i Acknowledgements ii Table of Contents iii List of Schemes v List of Figures vii 1. Introduction 1 2. Matrix Isolation 3 3. Electron paramagnetic resonance (EPR) 5 4. Naphthyl(trifluoromethyl)carbenes 8 4.1 Background 8 4.2 2 - Naphthyl(trifluoromethyl)carbene 13 4.2.1 Matrix Isolation and Potential Energy Surface 13 4.2.2 Oxygen Trapping Reactions 22 4.2.3 EPR Spectrum 24 4.3 1 - Naphthyl(trifluoromethyl)carbene 25 4.3.1 Matrix Isolation 25 4.3.2 Potential Energy Surface 32 4.3.3 Oxygen Trapping Reactions 33 4.3.4 EPR Spectrum 35 4.4 Conclusion 36 4.5 Experimental 36 iv 5. Pyridyl(trifluoromethyl)carbenes 43 5.1 Background 43 5.2 4 - Pyridyl (trifluoromethyl)carbene 48 5.2.1 Matrix Isolation 48 5.2.2 Oxygen Trapping Reactions 56 5.2.3 Potential Energy Surface 57 5.2.4 EPR Spectrum 58 5.3 2 - Pyridyl (trifluoromethyl)carbene 59 5.3.1 Matrix Isolation 60 5.3.2 Potential Energy Surface 68 5.3.3 Oxygen Trapping Reactions 69 5.3.4 EPR Spectrum 72 5.4 3 - Pyridyl (trifluoromethyl)carbene 73 5.4.1 Matrix Isolation 75 5.4.2 Potential Energy Surface 81 5.4.3 Oxygen Trapping Reactions 82 5.4.4 EPR Spectrum 85 5.5 3 - Bromo - 5 - Pyridyl (trifluoromethyl)carbene 86 5.5.1 Matrix Isolation 86 5.5.2 Potential Energy Surface 93 5.5.3 EPR Spectrum 95 5.6 Conclusion 96 5.7 Experimental 97 v 6 Phenylbis(trifluoromethyl)carbenes 109 6.1 Background 109 6.2 meta - Phenylbis(trifluoromethyl)carbene 115 6.2.1 Matrix Isolation and Potential Energy Surface 116 6.2.2 Oxygen Trapping Reactions 124 6.2.3 Matrix Isolation of 3-(trifluoromethyl)diazirine-5-phenyl(trifluoromethyl)carbene 128 6.2.4 EPR Spectra 131 6.3 para - Phenylbis (trifluoromethyl)carbene 133 6.3.1 Matrix Isolation 134 6.3.2 Potential Energy Surface 139 6.3.3 Oxygen Trapping Reactions 141 6.3.4 EPR Spectra 143 6.4 Conclusion 144 6.5 Experimental 145 7. References 151 8. NMR Spectra 157 List of Scheme Scheme 1. Reactions of 1- and 2- naphthylmethylene 10 Scheme 2. Photochemical reaction of 2 - naphthylmethylene 2 10 Scheme 3. Photolysis of 1 - naphthylmethylene 1 11 vi Scheme 4. Photolysis of 1 - naphthylchlorocarbene 2 12 Scheme 5. Photolysis of 1 - naphthylchlorocarbene 13 12 Scheme 6. Expected Photolysis of 1 - and 2 - naphthyl(trifluoromethyl)carbenes (15, 16) 13 Scheme 7. Synthesis of 2- naphthyl(trifluoromethyl)diazirine 26 14 Scheme 8. Photolysis of 2- naphthyl(trifluoromethyl)diazirine 26 and oxygen trapping reactions of 2- naphthyl(trifluoromethyl)carbene 17 15 Scheme 9. Synthesis of 1-naphthyl(trifluoromethyl)diazirine 35 26 Scheme 10. Reactions of 1- naphthyl(trifluoromethyl)carbene 1 26 Scheme 11. Photolysis of 2-pyridylcarbene 41 44 Scheme 12. Photolysis of phenyl azide 44 and 2-diazomethylpyridine 45 44 Scheme 13. Photolysis of Pyridylcarbenes 45 Scheme 14. Photolysis of 3 - pyridylcarbene 48 46 Scheme 15. Photolysis of 3 - (48) and 4 - pyridylcarbene 50 47 Scheme 16. Synthesis of 4-pyridyl(trifluoromethyl)diazirine 66 49 Scheme 17. Reactions 4-phenyl(trifluoromethyl)carbene (69) 50 Scheme 18. Synthesis of 2-pyridyl(trifluoromethyl)diazirine 79 59 Scheme 19. Photolysis of 2-phenyl(trifluoromethyl)carbene (80) 60 Scheme 20. Oxgen trapping of 2-pyridylcarbene 80 69 Scheme 21. Synthesis of 3 - pyridyl(trifluoromethyl)diazirine 93 74 Scheme 22. Photoreaction of 3-pyridyl(trifluoromethyl)carbene (94) 75 Scheme 23. Oxgen trapping of 2-pyridylcarbene 94 in matrix 82 Scheme 24. Synthesis of 3-Bromo-5-pyridyl(trifluoromethyl)diazirine110 87 Scheme 25. Photoreaction of 3-Bromo-5-pyridyl(trifluoromethyl)carbene 111 88 vii Scheme 26. Indirect observation of diradical 119 from irradiation of the corresponding bisdiazo compound 122 111 Scheme 27. Formation and reaction of diradical 119 112 Scheme 28. Formation of meta-biscarbene 120 112 Scheme 29. Formation of carbene 131 and diradical 133 113 Scheme 30. Formation of biscarbene 142 114 Scheme 31. Formation of m-phenylenebis(chloromethylene) (146) 115 Scheme 32. Synthesis of meta-phenylbisdiazirine 153 116 Scheme 33. Reactions of meta-phenyl(trifluoromethyl)bisdiazirine (1) and meta- phenyl(trifluoromethyl)biscarbene (3) 117 Scheme 34. Formation of ary(trifluoromethyl)carbene 159 128 Scheme 35. Sysnthesis of para-phenylbisdiazirine 166 134 Scheme 36. Reactions of para-phenyl(trifluoromethyl)bisdiazirine (166) and para- phenyl(trifluoromethyl)diradical (169) 135 List of Figures Figure 1. Electronic states of carbene 1 Figure 2. Matrix Isolation Equipment 4 Figure 3. Induction of the spin state energies as a function of the magnetic field B0 5 Figure 4. Energy levels of triplet system 7 Figure 5. Simulated spectrum of absorptions and ZFS parameter 7 Figure 6. Sturctures of 1- (1) and 2- naphthylmethylenes (2) with two geometric isomers (a, b) 9 viii Figure 7. Structures of 1 - and 2 - naphthyl(trifluoromethyl)carbenes (15, 16) 13 Figure 8. UV/Vis spectrum of 2 - naphthyldiazirine 26 16 Figure 9. Geometry of 2-naphthyl(trifluoromethyl)diazirine 26 17 Figure 10. HOMO & LUMO (B3LYP/ 6-31+G**) of 2 - naphthyl(trifluoromethyl)diazirine 18 Figure 11. (a) Experimental UV/Vis spectrum of after irradiation of 2-naphthyldiazirine 26 at 366 nm for 30 min. (b) Calculated (TD-B3LYP) UV/Vis spectrum of 2-naphthylcarbene 17. 19 Figure 12. (a) Experimental IR spectrum of 2-naphthyldiazirine 26 at 366 nm for 30 min. (b) Calculated (B3LYP) IR spectrum of 2-naphthyldiazirine 26. 20 Figure 13. (a) Experimental IR spectrum of after irradiation of 2-naphthyldiazirine 26 at 366 nm for 30 min. (b) Calculated (B3LYP) IR spectrum of 2-naphthylcarbene 17. 21 Figure 14. Relative energy diagram for 2-naphthyl(trifluoromethyl)carbene with singlet, triplet and states and two conformers, at the B3LYP/ 6-31+G** level of theory. Energies in kcal/mol normalized to triplet state and conformer 17b. 22 Figure 15. (a) UV/Vis spectrum of 2-naphthyldiazirine 26. (b) UV/Vis spectrum of 2- naphthylcarbene 17. (c) UV/Vis spectrum of carbonyl oxide 27. (d) UV/Vis spectrum of 2- dioxane 28. 23 Figure 16. IR difference spectra of 2 - naphthylcarbene 17 matrix before and after warming to 30 K. 23 Figure 17. IR difference spectra of carbonyl oxide 20 matrix before and after irradiation at 404 nm for 15 min. Positive peaks correspond to dioxirane 21, and negative peaks to carbonyl oxide 20.