Heterogenization of Molecular Organo-Iodine Oxidation Catalysts through Incorporation in Metal-Organic Frameworks (MOFs): Tackling the Problems of Decomposition and Deactivation Through Site-Isolation
by
Babak Tahmouresilerd, M.S.
A Dissertation
In
Chemistry
Submitted to the Graduate Faculty of Texas Tech University in Partial Fulfillment of the Requirements for the Degree of
DOCTOR OF PHILOSOPHY
Approved
Anthony F. Cozzolino Chair of Committee
Michael Findlater
Dominick Casadonte
Joshua D. Howe
Mark Sheridan Dean of the Graduate School
August 2020
Copyright 2020, Babak Tahmouresilerd Texas Tech University, Babak Tahmouresilerd, August 2020
ACKNOWLEDGMENTS I would like to thank my advisor, Dr. Anthony Cozzolino for all the help and support during my time in graduate school. I have learned many things from him and been shown a great amount of kindness.
I would like to thank Dr. Michael Findlater and Dr. Dominick Casadonte as my committee members for taking the time and effort to review my dissertation. I highly appreciate their support during my Ph.D. degree.
I would like to thank all my past and present group members for their help and advice over the last few years. Obtaining a Ph.D. degree alongside living with them in the group provided me with a lot of experiences.
I would like to thank Dr. Daniel Unruh, Dr. Piotr Dobrowolski, and Dr. Mike Mayer for providing X-ray crystallography and nuclear magnetic resonance facilities. I appreciate Dr. Hopeweeks’s group, Dr. Zhao, and MADOX center for assisting me for doing some of the important structural characterizations.
I highly acknowledge the chemistry graduate student organization (CGSO), Study abroad, and graduate school at Texas Tech University for providing financial aid by giving scholarships.
ii
Texas Tech University, Babak Tahmouresilerd, August 2020
Table of Contents ACKNOWLEDGMENTS ...... ii ABSTRACT ...... v LIST OF ACRONYMS ...... vi LIST OF TABLES ...... vii LIST OF FIGURES ...... xiv 1. Introduction to Oxidation Catalysts via Hypervalent Iodine ...... 1 1.1. Hypervalent Iodine Compounds ...... 1 1.2. Application of Hypervalent Iodine Compounds ...... 3 1.3. Limitations, Drawbacks, and Practical Solution to Overcome ...... 4 1.4. Metal-organic Frameworks (MOFs) as an Alternative Solution ...... 5 1.5. Research Objective and Dissertation Overview ...... 20 2. Proving the Concept: MOFs as Supports for Organo-iodine Catalysts .... 22 2.1. Design a MOF to Support Iodine Catalyst ...... 22 2.2. Preparation of MOF Catalysts ...... 23 2.3. Preliminary Catalyst Evaluation ...... 23 2.4. Preparation and Characterization of MTV-MOF Catalysts ...... 25 2.5. Catalytic Performance MTV-MOF Catalysts ...... 37 2.6. Catalytic Performance MTV-MOF Catalysts in the Oxidation of other Hydroquinones ...... 41 2.7. Effect of Solvent, Terminal Oxidant, and Recycling on Catalytic Oxidation of Hydroquinone ...... 44 2.8. Comparison with Related Systems ...... 48 2.9. Conclusions ...... 49 2.10. Experimental Details ...... 50 3. MOF as Support for Iodine Catalyst: Isoreticular Expansion ...... 93 3.1. Strategy to Open the Pore of MOF for Efficient Reagents Diffusion ...... 93 3.2. Preparation and Characterization of Iodine Containing Frameworks ...... 95 3.3. Catalytic Evaluation ...... 104 3.4. Evaluation of Other Substrates ...... 112 3.5. Conclusions ...... 115 3.6. Experimental Details ...... 116 4. Iodine Supported MOF: Dearomatization Reaction ...... 143 4.1. Introduction ...... 143 4.2. Results and Discussion ...... 145 4.3. Conclusion ...... 158 4.4. Experimental Details ...... 159 5. Current Progress and Future Directions ...... 176 5.1. Toward an Asymmetric Catalyst ...... 176 5.2. The study of Halogen-bonding Interactions of I2BODIPY and Pyridine-type Acceptors ...... 182 6. General Experimental Methods ...... 192 6.1. Powder X-ray Diffraction ...... 192 6.2. General Data Collection Single Crystal Diffraction ...... 192 6.3. Refinement Details ...... 193 6.4. FTIR Spectroscopy ...... 193 6.5. NMR Spectroscopy ...... 194 6.6. Nitrogen Adsorption ...... 194 6.7. Computational Details and Results ...... 194 7. Summaries and Conclusions ...... 195
iii
Texas Tech University, Babak Tahmouresilerd, August 2020
BIBLIOGRAPHY ...... 196
iv
Texas Tech University, Babak Tahmouresilerd, August 2020
ABSTRACT The main goal of this research is to investigate metal-organic frameworks (MOFs) as solid supports for molecular organo-iodine catalysts. To achieve this goal a few different strategies are examined. Firstly, using a multivariate strategy, iodine- functionalized Zr and Al-based metal-organic frameworks (MOFs) are prepared. These MOFs were found to be active heterogeneous catalysts for the oxidation of phenol derivatives. Secondly, a combination of a multivariate and isoreticular approach was employed to ensure an ideal balance between the internal surface area and catalytic site in the pores of the frameworks.
The impact of increased pore size and the catalytic activity of the MOFs on the oxidation of more challenging phenol derivatives is discussed. The catalytic oxidation using hypervalent iodine supported metal-organic frameworks is further extended to flow chemistry in consideration of the concepts of green chemistry.
Lastly, iodine-containing molecules with the ability to switch their electronic properties in response to an external stimulus are explored. These systems potentially can be used for catalysis purposes in the near future.
v
Texas Tech University, Babak Tahmouresilerd, August 2020
LIST OF ACRONYMS CSD: Cambridge Structural Database 7
DMF: N,N-dimethylformamide 8
EHS: Environmental Health & Safety 157
FTIR: Fourier-transform infrared 9
H2BDC: 1,4-benzene dicarboxylic acid 22
Hyperol: Urea/hydrogen peroxide complex 45
IBA: 2-iodosobenzoic acid 2
IBD: Iodobenzene dichloride 2
IBDA: Iodobenzene diacetate 2
IBX: 2-iodoxybenzoic acid 2 mCPBA: Metachloroperbenzoic acid 3
MOF: Metal-organic framework 5
Oxone: Potassium peroxymonosulfate 3
SEM: Scanning electron microscope 45
Thr: Threonine 174
vi
Texas Tech University, Babak Tahmouresilerd, August 2020
LIST OF TABLES
1.1. Names and abbreviations of important hypervalent iodine compound ...... 2
1.2. Representations of nodes, linkers, and corresponding MOF structures...... 10
2.1. Initial catalytic screening for the oxidation of hydroquinone to benzoquinone in MOF-supported I ...... 25
2.2. Incorporation of 2-iodoterephthalic acid in MTV-MOFs from 1H NMR digestions ...... 26
2.3. Comparison of onset temperature for thermal decomposition under aerobic conditions as determined from TGA of the MTV-MOFs (values shown are from activated MOFs)...... 27
2.4. MTV-MIL-53 inter-planar angles (assigned from matched PXRD) for the as-synthesized (AS) and activated (AA) form of each phase as a measure of the openness of the pores. The radius (r) of the cylinder that can fit in the pore is provided in Å in parentheses ...... 33
2.5. Brunauer-Emmett-Teller (BET) surface areas and pore volumes for the activated UiO-66 25, 50, and 100%-I obtained from nitrogen adsorption isotherms at 77 K ...... 36
2.6. Oxidation of hydroquinone to probe the effect of linker ratio in MTV-MOFs ...... 37
2.7. Oxidation of hydroquinone derivatives with iodine-functionalized MTV-MOFs ...... 43
2.8. Catalyst mol% variation for catalytic oxidation of hydroquinone (HQ) to benzoquinone (BQ)...... 48
2.9. Comparison of alkyl and aryl iodide-based catalysts and reagents for the oxidation of hydroquinone...... 49
2.10. Composition of the reaction mixtures in the synthesis of the MTV-UiO-66 (Zr) ...... 52
2.11. Composition of the reaction mixtures in the synthesis of the MTV-MIL-53 (Al) ...... 53
vii
Texas Tech University, Babak Tahmouresilerd, August 2020
2.12. Single crystal information and refinement parameters at 100 K...... 55
2.13. Estimate crystallite sizes for MIL-53 25% (HT, and DMF) by Scherrer equation ...... 56
2.14. Catalyst optimization for catalytic oxidation of hydroquinone (HQ) to benzoquinone (BQ) in the presence of 20 mol% MTV- UiO-66, ~2.9 equivalent of mCPBA, 4 mL acetonitrile (ACN) at 50 °C for 60 minutes ...... 71
2.15. Catalyst optimization for catalytic oxidation of hydroquinone (HQ) to benzoquinone (BQ) in the presence of 20 mol% MTV- MIL-53, 2.9 equivalent of mCPBA, 4 mL acetonitrile (ACN) at 50 °C for 60 minutes ...... 71
2.16. 2-Iodoterephthalate as a homogenous analogue of supporting iodine MOFs catalyst for catalytic oxidation of hydroquinone (HQ) to benzoquinone (BQ) in the presence of 20 mol% catalyst, 2.9 equivalent of mCPBA, 4 mL acetonitrile (ACN) at 50 °C for 60 minutes ...... 72
2.17. Solvent variation of MTV-UiO-66 25%-I for catalytic oxidation of hydroquinone (HQ) to benzoquinone (BQ) in the presence of 20 mol% catalyst, 2.9 equivalent of mCPBA, 4 mL specified solvent at 50 °C for 60 minutes...... 73
2.18. Solvent variation of MTV-MIL-53 25%-I (DMF) for catalytic oxidation of hydroquinone (HQ) to benzoquinone (BQ) in the presence of 20 mol% catalyst, 2.9 equivalent of mCPBA, 4 mL specified solvent at 50 °C for 60 minutes ...... 74
2.19. Solvent variation of MTV-UiO-66 25%-I for catalytic oxidation of hydroquinone (HQ) to benzoquinone (BQ) in the presence of 20 mol% catalyst, 2.9 equivalent of mCPBA, 4 mL specified solvent at 50 °C for 2 minutes...... 75
2.20. Solvent variation of MTV-MIL-53 25%-I (DMF) for catalytic oxidation of hydroquinone (HQ) to benzoquinone (BQ) in the presence of 20 mol% catalyst, 2.9 equivalent of mCPBA, 4 mL specified solvent at 50 °C for 2 minutes ...... 76
2.21. Control reactions for temperature variation of oxidation of hydroquinone (HQ) to benzoquinone (BQ) in the presence of 2.9 equivalent of mCPBA at a specified temperature in 4 mL solvent for 60 minutes ...... 77
viii
Texas Tech University, Babak Tahmouresilerd, August 2020
2.22. Temperature variation of catalytic oxidation of hydroquinone (HQ) to benzoquinone (BQ) in the presence of 20 mol% MTV- MIL-53 25%-I (DMF), 2.9 equivalent of mCPBA at the specified temperature in 4 mL solvent for 60 minutes ...... 78
2.23. Terminal oxidant loading variation for catalytic oxidation of hydroquinone (HQ) to benzoquinone (BQ) in the presence of 20 mol% catalyst, specified equivalent of mCPBA in 4 mL nitromethane (NM) at 50 °C for 60 minutes ...... 79
2.24. Terminal oxidant variation for catalytic oxidation of hydroquinone (HQ) to benzoquinone (BQ) in the presence of 20 mol% MTV-UiO-66 25%-I, 2.9 equivalent of specified terminal oxidant in nitromethane/ water (3:1 v:v) at 50 °C for 60 minutes ...... 80
2.25. Terminal oxidant variation for catalytic oxidation of hydroquinone (HQ) to benzoquinone (BQ) in the presence of 20 mol% MTV-MIL-53 25%-I (DMF), 2.9 equivalent of specified terminal oxidant in nitromethane/ water (3:1 v:v) at 50 °C for 60 minutes ...... 81
2.26. Catalyst mol% variation for catalytic oxidation of hydroquinone (HQ) to benzoquinone (BQ) using 4 equivalent oxone in nitromethane/water (3:1 v:v) at 50 °C for 60 minutes ...... 82
2.27. The recyclability test for catalysts with 2.9 equivalent of mCPBA in 4 mL nitromethane at 50 °C for 60 minutes ...... 83
2.28. Split test of MTV-UiO-66 25%-I with 2.9 equivalent of mCPBA in 4 mL acetonitrile (ACN) at 50 °C...... 85
2.29. Split test of MTV-MIL-53 25%-I (DMF), 2.9 equivalent of mCPBA in 4 mL acetonitrile (ACN) ...... 86
2.30. Catalytic oxidation of hydroquinone derivatives in the presence of 20 mol% MTV-UiO-66 25%-I and MTV-MIL-53 25%-I (DMF) as catalysts, 2.9 equivalent of mCPBA, 4 mL nitromethane for 60 minutes ...... 87
2.31. DFT calculated C−I stretching frequencies ...... 88
2.32. DFT calculated core orbital energies (eV)...... 88
2.33. Cartesian coordinates for IC6H5 (iodobenzene)...... 89
ix
Texas Tech University, Babak Tahmouresilerd, August 2020
2.34. Cartesian coordinates for H2IBDC...... 90
2.35. Cartesian coordinates for ((AcO)2I)C6H5 ((diacetoxyiodo)benzene)...... 91
2.36. Cartesian coordinates for ((HO)2I)C6H5 ((dihydroxyiodo)benzene)...... 92
3.1. Molar Brunauer-Emmett-Teller (BET) surface areas and pore volumes for the UiO-67 (Zr) and DUT-5 (Al) obtained from nitrogen adsorption isotherms at 77 K ...... 101
3.2. The yield of catalytic oxidation of hydroquinone and catechol derivatives with iodo-functionalized MOFs ...... 107
3.3. The results of catalytic oxidation of hydroquinone (HQ) to benzoquinone (BQ) for UiO-67 0%-I, and DUT-5 0%-I, UiO-67 25%-I, DUT-5 25%-I and control in the presence of 20 mol% catalyst, 2.9 equivalent of mCPBA, 4 mL nitromethane at 50 °C for 60 minutes ...... 129
3.4. Catalytic oxidation of hydroquinone (HQ) to benzoquinone (BQ) in the presence of 20 mol% UiO-67 25%-I and DUT-5 25%-I, 2.9 equivalent of mCPBA at 50 °C and room temperature in 4 mL nitromethane for 60 minutes...... 129
3.5. Effect of 2,2,2-Trifluoroethanol (TFE) on catalytic oxidation of hydroquinone (HQ) to benzoquinone (BQ) in the presence of 20 mol% UiO-67 25%-I, 2.9 equivalent of mCPBA, 4 mL specified solvent at 50 °C for 60 minutes...... 130
3.6. Catalyst mol% variation for catalytic oxidation of hydroquinone (HQ) to benzoquinone (BQ) using 2.9 equivalent mCPBA in 4 mL nitromethane at 50 °C for 60 minutes...... 130
3.7. Catalytic oxidation of hydroquinone (HQ) to benzoquinone (BQ) in the presence of 20 mol% UiO-67 25%-I, UiO-67 100%-I, DUT-5 25%-I, DUT-5 100%-I, and 2.9 equivalent of mCPBA at 50 °C in 4 mL acetonitrile for 60 minutes ...... 131
3.8. Catalytic oxidation of hydroquinone (HQ) to benzoquinone (BQ) in the presence of 20 mol% UiO-67 25%-I, UiO-67 100%-I, DUT-5 25%-I, DUT-5 100%-I, and 2.9 equivalent of mCPBA at 50 °C in 4 mL nitromethane for 60 minutes ...... 131
x
Texas Tech University, Babak Tahmouresilerd, August 2020
3.9. Catalytic oxidation of 2,5-di-tert-butylhydroquinone to the corresponding oxidation product in the presence of 20 mol% UiO-67 100%-I, DUT-5 100%-I, and 2.9 equivalent of mCPBA at room temperature in 4 mL nitromethane for 60 minutes ...... 132
3.10. Control reactions for catalytic oxidation of hydroquinone (HQ) to benzoquinone (BQ) in the presence of 2.9 equivalent of mCPBA at 50 °C in 4 mL solvent for 60 minutes ...... 132
3.11. The recyclability test for catalysts with 2.9 equivalent of mCPBA in 4 mL nitromethane at 50 °C for 60 minutes ...... 133
3.12. Catalytic oxidation of hydroquinone and catechol derivatives in the presence of 20 mol% catalysts, 2.9 equivalent of mCPBA, 4 mL nitromethane for 60 minutes...... 135
3.13. Split test of DUT-5 25%-I and UiO-67 25%-I, 2.9 equivalent of mCPBA in 4 mL nitromethane at 50 °C at specified time of reactions ...... 137
3.14. DFT optimized cartesian coordinates for Me2IBDC (EHOMO = – 5.9928 eV) ...... 141
3.15. DFT optimized cartesian coordinates for Me2IBPDC (EHOMO = – 6.0337 eV)...... 142
4.1. Evaluation of oxidative dearomatization of p-cresol to the corresponding p-quinol ...... 148
4.2. Molar Brunauer-Emmett-Teller (BET) surface areas and pore volumes for the Zr and Al-based MOFs obtained from nitrogen adsorption isotherms at 77 K...... 149
4.3. Control reactions for oxidative dearomatization of p-cresol...... 150
4.4. The catalytic yield of oxidative dearomatization of p-cresol to the corresponding p-quinol using I-DUT-5 with a loading of X and Y equiv. of terminal oxidant ...... 152
4.5. Hirschfeld charges in phenoxenium ions containing electron- donating and withdrawing groups at C2 (ortho), C4(para), and C6(ortho) ...... 154
4.6. The result of the substrate scope for nucleophilic oxidative dearomatization of para-methyl phenol derivatives to the corresponding p-quinol products ...... 156 xi
Texas Tech University, Babak Tahmouresilerd, August 2020
4.7. Comparison of iodo-based reagents or catalysts for the oxidative dearomatization of p-cresol into p-quinol ...... 158
4.8. The results of initial control reactions for the oxidative dearomatization of para-cresol (PC) to para-quinol (PQ) in the presence of 20 mol% either I-MOFs or parents MOF, 3.0 equivalent of oxone or mCPBA, 4 mL nitromethane and DI water (3:1 v:v) at 50 °C for 24 h ...... 162
4.9. The results of control reactions for the oxidative dearomatization of para-cresol (PC) to para-quinol (PQ) in the presence of 3.0 equivalents of oxone or mCPBA, 4 mL specified solvent and nucleophile at 50 °C for 24 h ...... 163
4.10. The results of oxidative dearomatization of para-cresol (PC) to para-quinol (PQ) in the presence 20 mol% DUT-5 25%-I, 3.0 equivalents of oxone or mCPBA, 4 mL specified solvent and nucleophile at 50 °C for 24 h ...... 163
4.11. The results of oxidative dearomatization of para-cresol (PC) to para-quinol (PQ) in the presence 20 mol% UiO-67 25%-I, 3.0 equivalents of oxone or mCPBA, 4 mL nitromethane and specified nucleophile at 50 °C for 24 h ...... 164
4.12. The results of oxidative dearomatization of para-cresol (PC) to para-quinol (PQ) in the presence 20 mol% UiO-66 25%-I, 3.0 equivalents of oxone or mCPBA, 4 mL nitromethane and specified nucleophile at 50 °C for 24 h ...... 164
4.13. The results of oxidative dearomatization of para-cresol (PC) to para-quinol (PQ) in the presence 20 mol% MIL-53 25%-I, 3.0 equivalents of oxone or mCPBA, 4 mL nitromethane and specified nucleophile at 50 °C for 24 h...... 165
4.14. The results of oxidative dearomatization of para-cresol (PC) to para-quinol (PQ) in the presence 20 mol% esterified linker Me2I- BPDC, 3.0 equivalents of oxone, 4 mL nitromethane and specified nucleophile at 50 °C for 24 h...... 166
4.15. The results of oxidative dearomatization of para-cresol (PC) to para-quinol (PQ) in the presence of different mol% of DUT-5 25%-I, 3.0 equivalents of oxone, 4 mL nitromethane and DI water (1:3 v:v) at 50 °C for 24 h ...... 167
4.16. The results of oxidative dearomatization of para-cresol (PC) to para-quinol (PQ) in the presence of different equivalents of xii
Texas Tech University, Babak Tahmouresilerd, August 2020
oxone, 20 mol% DUT-5 25%-I, 4 mL nitromethane and DI water (1:3 v:v) at 50 °C for 24 h ...... 167
4.17. The results of oxidative dearomatization of substrates to the corresponding p-quinol products in the presence of 15 mol% DUT-5 25%-I, 3.0 equivalents of oxone, 4 mL nitromethane and DI water (1:3 v:v) at RT and 50 °C for 24 h ...... 168
4.18. The recyclability test for DUT-5 25%-I (15 mol%) with 3.0 equiv. equivalent of oxone in 4 mL nitromethane and DI water (1:3 v:v) at 50 °C for 18 h...... 171
4.19. Split test of DUT-5 25%-I, 3.0 equivalent of oxone in 4 mL nitromethane and deionized water (1:3 v:v) at 50 °C ...... 173
4.20. The continuous flow chemistry for DUT-5 25%-I (1.0 equiv.) with 3.0 equiv. equivalent oxone in 20 mL nitromethane and deionized water (1:1 v:v) at 50 °C for 24 h...... 175
xiii
Texas Tech University, Babak Tahmouresilerd, August 2020
LIST OF FIGURES
1.1. Molecular orbital (MO) illustration of the three-center-four- electron bond in hypervalent iodine(III) molecules RIL2 ...... 2
1.2. Catalytic use of hypervalent iodine(V) compound for the oxidation of the primary and secondary alcohols ...... 4
1.3. The proposed mechanism for alcohol oxidation using hypervalent iodine compounds in the presence of mCPBA as terminal oxidant ...... 4
1.4. Examples of some of the I catalyst supported by different solid systems ...... 5
1.5. A general scheme for the MOF preparation. A metal ion is mixed with organic linkers using a suitable solvent ...... 6
1.6. The schematic of the structure of MOF-5. Metal nodes are demonstrated in light blue clusters (Zn4O) connected by terephthalic acid linkers. Hydrogen atoms are omitted for clarity. The yellow sphere shows the pore of the framework ...... 7
1.7. Some of the important applications for the metal-organic framework (MOFs) ...... 8
1.8. The schematic of the structure of HKUST-1. Copper nodes are demonstrated in blue. The terminal metal nodes are shown as the cluster. Metal nodes are connected by trimesic acid linkers. The light blue sphere shows the pore of the framework. Hydrogen atoms are omitted for clarity ...... 9
1.9. The schematic of the structure of FMOF-2. Ag, N, and F are shown in off white, blue, and green. Hydrogen atoms are omitted for clarity ...... 12
1.10. Publications related to catalysis using metal-organic frameworks (MOFs) over the past decade. Collected from Sci Finder using “catalysis by MOFs” keyword ...... 13
1.11. The main catalytic active sites in the MOF structure including inorganic metal node, organic linkers, and the pore space ...... 14
1.12. The schematic of the single layer of 2D cadmium-based MOF...... 14
xiv
Texas Tech University, Babak Tahmouresilerd, August 2020
1.13. The schematic of the structure of MFU-4l and its node transformation to Cr3+exchanged MFU-4l. Reaction condition: i) CrCl2, CrCl3.3THF, DMF, 7 days, ii) MeOH wash, 150 °C, 18 hours, vacuum. Zn, N, O, and Cl are shown in light blue, blue, red, and green. Hydrogen atoms are omitted for clarity ...... 15
1.14. The catalytic oxidation–acetalization reactions of benzaldehyde using Pd@UiO-66-NH2 ...... 16
1.15. The catalytic transfer hydrogenation reaction of methyl levulinate with 2-butanol catalyze with UiO-66-SO3H to produce γ- valerolactone (GVL) ...... 16
1.16. The Knoevenagel condensation of benzaldehyde with ethyl cyanoacetate and ethyl acetoacetate using IRMOF-3. Catalytic reaction condition: i) 20 mol% catalyst (IRMOF-3), 7 mmol ethyl cyanoacetate or ethyl acetoacetate, and 8 mmol benzaldehyde in 5 mL of DMSO under inert atmosphere ...... 17
1.17. Styrene oxide ring-opening reaction catalyzed by DUT-4 MOF in the presence of methanol at 55 °C ...... 18
1.18. Scheme showing the preparation of MOF-Co.2THF. Reaction condition: i) CoCl2, THF, 24 h, ii) NaBEt3H, THF, 15 min ...... 18
2.1. Depiction of the MIL-53 (Al) (left), and the octahedral pore in UiO-66 (Zr) (right). Metal coordination spheres are represented with polyhedra. Hydrogen/halogen atoms have been removed for clarity. The yellow sphere shows the pore of the framework ...... 23
2.2. The oxidation of hydroquinone to benzoquinone shown with typical catalytic conditions...... 24
2.3. Illustration of the MTV-MOFs consisting of metal ions or clusters (black circle) coordinated to organic linkers (red arrows for IBDC2− and blue lines for BDC2−) ...... 25
2.4. Thermogravimetric (TGA) analysis of MTV-UiO-66 25%-I under air before and after the activation ...... 27
2.5. Thermogravimetric (TGA) analysis of MTV-MIL-53 25%-I under air before and after the activation ...... 28
2.6. Di-ATR FTIR of as-synthesized MTV-MIL-53 (0, 25, 50, 75, and 100%-I) plotted as attenuation ...... 29
xv
Texas Tech University, Babak Tahmouresilerd, August 2020
2.7. Di-ATR FTIR of activated MTV-MIL-53 (0, 25, 50, 75, and 100%-I) plotted as attenuation ...... 29
2.8. Di-ATR FTIR of activated MTV-UiO-66 (0, 25, 50, 75 and 100%-I) plotted as attenuation ...... 30
2.9. PXRD patterns of activated MTV-UiO-66 (0, 25, 50, 75 and 100%-I) and simulated UiO-66 0%-I ...... 31
2.10. MTV-MIL-53 pore with interplanar angle and sphere of radius r depicted (left), activated MIL-53 25%-I with Al−Al−Al angle of 108.9° (middle) and activated MIL-53 100%-I with Al−Al−Al angle of 124.9° (right). I atoms are disordered over all sites. A random distribution of I atoms are depicted to match the experimental ratio of BDC2−:IBDC2−. All structures depicted along (0,1,0). Metal coordination spheres are represented with polyhedra. Hydrogen atoms have been removed for clarity...... 32
2.11. PXRD patterns of activated MTV MIL-53 (0, 25, 50, 75, and 100%-I) MOFs, MTV-MIL-53 25%-I synthesized in DMF, simulated MIL-53(136.4°), activated MIL-53 (100%-I) 124.9° and 108.9° from single-crystal structures ...... 34
2.12. Nitrogen adsorption isotherms for the MTV-UiO-66 25 (–▲–), 50 (–□–), and 100%-I (–●–)...... 35
2.13. Nitrogen adsorption isotherms for the MTV-MIL-53 25%-I synthesized with H2O (–▲–), DMF (–□–) ...... 35
2.14. Pore volume distribution for the MTV-UiO-66 25, 50, and 100%- I ...... 36
2.15. Pore volume distribution for the MTV-MIL-53 25%-I synthesized with H2O and DMF ...... 37
2.16. Split test where catalysts (MTV-UiO-66 25%-I in yellow, MTV- MIL-53 25%-I in red, no catalyst in green and blue) were hot filtered from the reaction mixture after 2 minutes for MTV-UiO- 66 25%-I and 10 minutes for MTV-MIL-53 25%-I. Samples were characterized after 1 hour...... 39
2.17. XPS spectra of I 3d5/2 for MTV-MIL-53 50%-I and UiO-66 25%- I before (top) and after (bottom) the oxidation reaction of hydroquinone to benzoquinone in the presence of 20 mol% catalyst, ~4.3 eq. mCPBA, acetonitrile, at 50oC for 5h ...... 40 xvi
Texas Tech University, Babak Tahmouresilerd, August 2020
2.18. Catalytic oxidation of hydroquinone to benzoquinone as a function of solvent after 2 minutes (solid color) and 1h (solid + hashed color) with 20 mol% catalyst and 2.9 eq. mCPBA. Values were determined by 1H NMR in the presence of MSM as an internal standard...... 41
2.19. Recyclability of catalytic conversion after 1 h for hydroquinone to benzoquinone in the presence of MTV-UiO-66 25%-I (top), and MTV-MIL-53 25%-I (bottom). 20 mol% of catalyst, 2.9 eq. mCPBA, nitromethane, 50 °C. Values were determined by 1H NMR in the presence of MSM as an internal standard ...... 45
2.20. PXRD patterns of MTV-UiO-66 25%-I before the catalytic reaction, after the first run, and the fourth run ...... 45
2.21. PXRD patterns of MTV-MIL-53 25%-I before the catalytic reaction and after four cycles ...... 46
2.22. Scanning electron micrographs of MTV-UiO-66 25%-I before (left) and after (right) the catalytic reactions...... 47
2.23. Preparation of 2-iodoterephthalic acid ...... 51
2.24. Preparation of dimethyl 2-iodobenzene-1,4-dicarboxylate ...... 51
2.25. 1H NMR spectrum for digested MTV-UiO-66 0%-I in 500 μL (CD3)2SO and 100 μL D2SO4...... 57
2.26. 1H NMR spectrum for digested MTV-UiO-66 25%-I in 500 μL (CD3)2SO and 100 μL D2SO4...... 58
2.27. 1H NMR spectrum for digested MTV-UiO-66 50%-I in 500 μL (CD3)2SO and 100 μL D2SO4...... 59
2.28. 1H NMR spectrum for digested MTV-UiO-66 75%-I in 500 μL (CD3)2SO and 100 μL D2SO4...... 60
2.29. 1H NMR spectrum for digested MTV-UiO-66 100%-I in 500 μL (CD3)2SO and 100 μL D2SO4...... 61
1 2.30. H NMR spectrum for digested MIL-53 0%-I in 570 μL D2O and 200 μL of NaOD solution 40 wt. % in D2O...... 62
1 2.31. H NMR spectrum for digested MIL-53 25%-I in 570 μL D2O and 200 μL of NaOD solution 40 wt. % in D2O...... 63
xvii
Texas Tech University, Babak Tahmouresilerd, August 2020
1 2.32. H NMR spectrum for digested MIL-53 50%-I in 570 μL D2O and 200 μL of NaOD solution 40 wt. % in D2O...... 64
1 2.33. H NMR spectrum for digested MIL-53 75%-I in 570 μL D2O and 200 μL of NaOD solution 40 wt. % in D2O...... 65
1 2.34. H NMR spectrum for digested MIL-53 100%-I in 570 μL D2O and 200 μL of NaOD solution 40 wt. % in D2O ...... 66
2.35. XPS spectra of MTV-MIL-53 50%-I: (top) survey scan; (bottom right) C 1s; (bottom left) I 3d5...... 68
2.36. XPS spectra of oxidized MTV-MIL-53 50%-I: (top) survey scan; (bottom right) C 1s; (bottom left) I 3d5...... 68
2.37. XPS spectra of MTV-UiO-66 25%-I: (top) survey scan; (bottom right) C 1s; (bottom left) I 3d5...... 69
2.38. XPS spectra of oxidized MTV-UiO-66 25%-I: (top) survey scan; (bottom right) C 1s; (bottom left) I 3d5 ...... 69
2.39. Observed products in the catalytic oxidation reaction of hydroquinone ...... 70
3.1. The depiction of DUT-5 (Al) (left), and the octahedral pore in UiO-67 (Zr) (right). Metal coordination spheres are represented with polyhedra. Hydrogen atoms have been removed for clarity. The yellow sphere shows the pore of the framework ...... 95
3.2. Preparation of H2IBPDC. Conditions and reagents: i) HNO3, H2SO4, 0-4 °C, 5 h, ii) MeOH, HCl, Sn, 80 °C, iii) NaNO2, HCl, 0-4 °C, NaI, 22 °C, iv) KOH, THF, reflux...... 95
3.3. PXRD patterns of activated DUT-5 25%-I, DUT-5 0%-I, and simulated DUT-5 0%-I (top), and UiO-67 25%-I, UiO-67 0%-I and simulated UiO-67 0%-I (bottom) ...... 97
3.4. TGA of activated UiO-67 25%-I (yellow) and DUT-5 25%-I (red) at a ramp rate of 10 °C min-1 under a flow of air ...... 98
3.5. Di-ATR FTIR of as-synthesized and activated UiO-67 25%-I (top) and DUT-5 25%-I (middle), and linkers (bottom). All spectra plotted as attenuation ...... 100
xviii
Texas Tech University, Babak Tahmouresilerd, August 2020
3.6. Nitrogen sorption isotherm (filled triangles or circles absorption, open triangles or circles desorption) of UiO-67 25 and 100%-I (top) and DUT-5 25 and 100%-I (bottom) (77 K) ...... 102
3.7. Top, a) EDS spectrum of UiO-67 25%-I, b) SEM image, and c, d) EDS–mapping results for Zr and I over UiO-67 25%-I particles coated with Au/Pd after activation, bottom, a) EDS spectrum of DUT-5 25%-I, b) SEM image, and c, d) EDS–mapping results for Zr and I over DUT-5 25%-I particles coated with Au/Pd after activation ...... 103
3.8. The oxidation of aromatic diols shown with typical catalytic conditions ...... 105
3.9. The effect of different catalyst loading (5, 10, and 20 mol%) on the yield of quinone for UiO-67 25%-I and DUT-5 25%-I. Shaded areas show the extent of background reaction, TONs beyond background presented at the top of each column ...... 108
3.10. Cyclic Voltammogram (CV) of dimethyl 2-iodoterephthalate and dimethyl 2-iodo-[1,1'-biphenyl]-4,4'-dicarboxylate in acetonitrile + in 0.1 M Bu4NBF4 at 100 mV/s vs. Fc/Fc ...... 109
3.11. Proposed in situ generated hypervalent iodine(III) supported by nucleophile Nu- in the pores (highlighted in blue for DUT-5 and UiO-67) of a) DUT-5 25%-I or UiO-67 25%-I or b) MIL-53 25%- I or UiO-66 25%-I ...... 110
3.12. Catalyst recyclability for the oxidation of hydroquinone to benzoquinone in the presence of UiO-67 25%-I compared to UiO-66 25%-I (top), and DUT-5 25%-I compared to MIL-53 25%-I (bottom). Conditions: 1 h, 20 mol% catalyst, 2.9 eq. mCPBA, nitromethane, 50 °C. Values were determined by 1H NMR in the presence of MSM as an internal standard ...... 111
3.13. PXRD patterns of UiO-67 25%-I before the catalytic reaction, and the fourth run ...... 112
3.14. CVs of a) hydroquinone and hydroquinone derivatives containing electron donation groups, b) hydroquinone derivatives containing electron-withdrawing groups, c) catechol and catechol derivatives containing electron donation groups. All obtained in + acetonitrile in 0.1 M Bu4NPF6 at 100 mV/s vs. Fc/Fc ...... 113
3.15. 1H NMR spectrum of 2-nitro-[1,1'-biphenyl]-4,4'-dicarboxylate in DMSO-d6 ...... 117 xix
Texas Tech University, Babak Tahmouresilerd, August 2020
3.16. 1H NMR spectrum for synthesized dimethyl 2-amino-[1,1'- biphenyl]-4,4'-dicarboxylate in DMSO-d6...... 118
3.17. 1H NMR spectrum of dimethyl 2-iodo-[1,1'-biphenyl]-4,4'- dicarboxylate in DMSO-d6...... 120
3.18. 1H NMR spectrum of 2-iodo-[1,1'-biphenyl]-4,4'-dicarboxylic acid in DMSO-d6...... 121
3.19. Di-ATR FTIR of activated UiO-67 25%-I before (black) and after (blue) digestion. Spectra are plotted as attenuation...... 124
1 3.20. H NMR spectrum for digested DUT-5 25%-I in 570 μL D2O and 200 μL of NaOD solution 40 wt. % in D2O. (A: D2BPDC, B: D2IBPDC) ...... 125
1 3.21. H NMR spectrum for digested UiO-67 25%-I in 570 μL D2O and -2 200 μL of NaOD solution 40 wt. % in D2O. (A: BPDC , B: IBPDC-2) ...... 126
3.22. Pore size distribution of DUT-5 25%-I (top) and UiO-67 25%-I (bottom) (77 K) ...... 127
3.23. Representative 1H NMR of hydroquinone in the acetonitrile reaction mixture in DMSO-d6 with MSM as an internal standard for analysis of product distribution ...... 128
3.24. SEM analysis for UiO-67 25%-I before (a, b) and after the 4th run (c, d) of the catalytic oxidation of hydroquinone (HQ) to benzoquinone (BQ) ...... 134
3.25. Split test for catalysts UiO-67 25%-I (yellow) and DUT-5 25%-I (Red), filtered UiO-67 25%-I (dotted green), and DUT-5 25%-I (dotted blue) after 30 minutes ...... 138
3.26. Estimated minimum and maximum radii of hydroquinone and catechol derivatives evaluated from MM2 minimized structures...... 139
3.27. Estimated pore apertures for DUT-5 0%-I and UiO-67 0%-I (triangular pore) ...... 140
4.1. Representative catalytic iodine sites in DUT-5 (top) and UiO-67 (bot-tom) ...... 145
4.2. PXRD patterns of I-MIL-53, I-UiO-66, IDUT-5, and I-UiO-67, and simulated patterns of parent MOFs ...... 147 xx
Texas Tech University, Babak Tahmouresilerd, August 2020
4.3. The model reaction for oxidative dearomatization of 4- methylphenol (p-cresol) ...... 147
4.4. Comparison of pore apertures in DUT-5 0%-I (left) and UiO-67 0%-I (right) ...... 149
4.5. The conversion of the dearomatization of p-cresol to the p-quinol beyond the control reaction. Solid colors CH3NO2: H2O (3:1 v:v) are compared to vertical stripes (1:3 v:v) as a modified ratio. Reaction conditions: 20 mol% cat., ∼3.0 equiv. of the terminal oxidant, 24 h, at 50 °C...... 151
4.6. The mechanism for catalytic oxidative dearomatization of p-cresol by I-DUT-5 in presence of oxone ...... 153
4.7. Nucleophilic attack susceptibility based on the Fukui function (first row), and electrostatic potential map (second row) for p- cresol derivatives scaled in Hartree. Isosurface value is 0.01 a.u...... 155
4.8. Cyclic Voltammogram (CV) of para-methyl phenol derivatives containing electron-donating and withdrawing groups obtained in + acetonitrile in 0.1 M Bu4NBF4 at 100 mV/s vs. Fc/Fc ...... 157
4.9. The oxidative dearomatization of p-cresol into p-quinol under continuous flow conditions with a stoichiometric amount of I- DUT-5 (1.0 equiv.) ...... 157
4.10. The oxidative dearomatization of p-cresol (1) into p-quinol (2) or o-quinol as possible side products ...... 161
4.11. The comparison between starting oxidant before the catalytic reaction and solid came out of the aqueous phase after the catalytic reaction ...... 172
4.12. PXRD patterns of DUT-5 25%-I after catalytic oxidative dearomatization run #1, 2, and 3 ...... 172
4.13. The continuous flow catalysis setup for oxidative dearomatization of p-cresol ...... 174
5.1. The axillary amino acid used in homochiral MOF synthesis...... 177
5.2. The synthesized ThrꞏMOF crystal a) with a ratio of 10:1 and b) 1:1 for amino acid to organic linker...... 178
xxi
Texas Tech University, Babak Tahmouresilerd, August 2020
5.3. Preparation of chiral MOFs with different organic linkers and auxiliary amino acid. Conditions and reagents: Zn(NO3)2ꞏ6H2O, DMF, 120 °C, 48 h...... 178
5.4. PXRD patterns of ThrꞏMOFs synthesized with different organic linkers...... 179
5.5. A view of the chiral chains in the structure of ThrꞏMOF along the a axis. Hydrogen atoms are omitted for clarity. Zinc (Zn), nitrogen (N), oxygen (O), carbon (C) are shown in light blue, dark blue, red, and gray...... 180
5.6. The depiction of the 3D structure of ThrꞏMOF. Metal nodes are represented with polyhedra. Hydrogen atoms have been removed for clarity...... 180
5.7. Synthesis of I2BODIPY (1). Reaction condition: i) CH2Cl2, Et3N, BF3ꞏEt2O, RT, 2h, ii) N-iodosuccinimide (NIS), CH2Cl2, RT, 1h...... 183
5.8. Chemical structures of co-crystals in this work...... 183
5.9. Structure of I2BODIPY (1). Carbon (C), hydrogen (H), boron (B), nitrogen (N), fluorine (F), and iodine (I) atoms are represented by gray, white, pink, blue, green, and purple, respectively...... 184
5.10. The asymmetric unit of I2BODIPYꞏBIPY (2). Carbon (C), hydrogen (H), boron (B), nitrogen (N), fluorine (F), and iodine (I) atoms are represented by gray, white, pink, blue, green, and purple, respectively. Halogen bonding interactions are depicted as hashed bonds...... 185
5.11. The structure of I2BODIPYꞏBPE (3). Carbon (C), hydrogen (H), boron (B), nitrogen (N), fluorine (F), and iodine (I) atoms are represented by gray, white, pink, blue, green, and purple, respectively. Halogen bonding interactions are depicted as hashed bonds ...... 186
5.12. Di-ATR FTIR of I2BODIPYꞏBPE (3) plotted as attenuation ...... 186
5.13. Structure of I2BODIPY co-crystallized with 4,4′-Azopyridine (α- phase) (4). Carbon (C), hydrogen (H), boron (B), nitrogen (N), fluorine (F), and iodine (I) atoms are represented by gray, white, pink, blue, green, and purple, respectively. Halogen bonding interactions are depicted as hashed bonds...... 187
5.14. Di-ATR FTIR of I2BODIPYꞏAzo (4) plotted as attenuation...... 187 xxii
Texas Tech University, Babak Tahmouresilerd, August 2020
5.15. Structure of I2BODIPY co-crystallized with mixed 4,4′- Azopyridine and 1,2-Di(4-pyridyl)ethylene (5). Carbon (C), hydrogen (H), boron (B), nitrogen (N), fluorine (F), and iodine (I) atoms are represented by gray, white, pink, blue, green, and purple, respectively. Halogen bonding interactions are depicted as hashed bonds...... 188
5.16. Di-ATR FTIR of I2BODIPYꞏAzoꞏBPE (5) plotted as attenuation...... 189
5.17. Structure of I2BODIPY co-crystallized with 4,4′-Azopyridine (β- phase) (6). Carbon (C), hydrogen (H), boron (B), nitrogen (N), fluorine (F), and iodine (I) atoms are represented by gray, white, pink, blue, green, and purple, respectively. Halogen bonding interactions are depicted as hashed bonds...... 189
5.18. Structure of I2BODIPY co-crystallized with 3-Chloro-4,4′- diazopyridine (7). Carbon (C), hydrogen (H), boron (B), nitrogen (N), fluorine (F), chlorine (Cl), and iodine (I) atoms are represented by gray, white, pink, blue, green, dark green and purple, respectively. Halogen bonding interactions are depicted as hashed bonds...... 190
5.19. Synthesis steps for preparation of the BODIPY-derived ligand ...... 191
xxiii
Texas Tech University, Babak Tahmouresilerd, August 2020
Chapter I
1. Introduction to Oxidation Catalysts via Hypervalent Iodine The current chapter will briefly discuss the chemistry of hypervalent iodine, potential applications, and the known drawbacks in oxidation reactions. Some of the recent efforts to overcome the obstacles associated with stoichiometric and catalytic oxidation reactions, along with the advantages and disadvantages of the approaches are discussed. In the end, an alternative solution to overcome these drawbacks is proposed.
1.1. Hypervalent Iodine Compounds Hypervalent iodine compounds are known with oxidation states ranging from 3 to 7.1,2 Iodobenzene dichloride, the first hypervalent organic iodine compound was initially prepared by C. Willgerodt in 1886.3 This generated a flurry of research activity in this field; more than 500 new hypervalent organic iodine compounds were prepared by 1914.4 Since the early 21st century there has been a renaissance in hypervalent iodine chemistry due to the commercial availability and the very useful oxidizing properties.1 The development of new hypervalent iodine compounds and the exploration of the enantioselective catalytic systems have been driving forces in the expansion of this field.1 The oxidation state and pendant groups on the iodine are used to tune the properties of the hypervalent iodine compounds. Some examples of these hypervalent iodine compounds, ranging from oxidation state +3 to +7 are provided in Table 1.1. In 1969, the term of “hypervalent” was defined as ions of the elements of group 15-18 which exceeds octet rule, by J. I. Musher.5 It has been well-established that, contrary to many general chemistry explanations, a model for understanding hypervalent compounds does not require hybridization with the d-orbitals, but rather can be described as a combination of a three-center four-electron bonds (3e-4c, Figure 1.1) and an ionic bond.6,7
1 Texas Tech University, Babak Tahmouresilerd, August 2020
Figure 1.1. Molecular orbital (MO) illustration of the three-center-four-electron bond in 8 hypervalent iodine(III) molecules RIL2. Table 1.1. Names and abbreviations of important hypervalent iodine compound.8
Compound Common Name Common Abbreviation
ICl3 iodine trichloride None
Iodobenzene dichloride IBD
Iodobenzene diacetate IBDA
2-iodosobenzoic acid IBA
IF5 iodine pentafluoride None
HIO3 iodic acid None
2-iodoxybenzoic acid IBX
IF7 Iodine heptafluoride None
HIO4 periodic acid None
2 Texas Tech University, Babak Tahmouresilerd, August 2020
The highly polarized nature of hypervalent bonds comes from the highest occupied molecular orbital which has a node in the center. This feature of the hypervalent bonds plays a key role in the formation of secondary bonds as noncovalent interactions. Secondary bonding results from the high London dispersion forces associated with the heavy elements augmented by highly directional electrostatic and orbital contributions.9 In the case of hypervalent iodine compounds, secondary bonding plays an important role in crystal packing and the self-assembly of molecules in the solid-state.10,11
1.2. Application of Hypervalent Iodine Compounds Hypervalent iodine compounds have a variety of applications as stoichiometric or catalytic oxidants in organic synthesis. The total synthesis of natural products,12 oxidative functionalizations of unsaturated compounds,13 oxidative halogenation,14,15, and oxidation of the alcohol1 are just some of the important uses of these compounds. Catalytic reactions using hypervalent iodine compounds have attracted attention in the past decade. In 2005, the catalytic oxidations of a primary alcohol or a ketone using iodine(III) hypervalent compounds in the presence of metachloroperbenzoic acid (mCPBA) were independently reported by Kita16 and Ochiai, respectively.17 In 2005 and 2006, the catalytic oxidation of primary and secondary alcohol using iodine(V) hypervalent compounds and potassium peroxymonosulfate (oxone) were independently reported by Vinod18 and Giannis,19 respectively which was followed by the exploration of many other catalytic reactions. In work by Vinod,18 the catalytic application of hypervalent iodine(V) compounds in the presence of oxone as a terminal oxidant was illustrated for the oxidation of both the primary and secondary alcohols as it is shown in Figure 1.2. Kita,16 showed the efficient catalytic application of hypervalent iodine(III) compounds in the presence of mCPBA as terminal oxidant at room temperature.
3 Texas Tech University, Babak Tahmouresilerd, August 2020
O O
R1 OH R1 OH R1 H OH Hypervalent iodine (V) reagents O Co-oxidant R2 R3 R2 R3
Figure 1.2. Catalytic use of hypervalent iodine(V) compound for the oxidation of the primary and secondary alcohols.18
Figure 1.3. The proposed mechanism for alcohol oxidation using hypervalent iodine compounds in the presence of mCPBA as terminal oxidant.18 This reaction provided a high yield of the reaction. The proposed mechanism, in general, features the oxidation of a low-valent iodine species to the higher oxidation state. This hypervalent iodine species in-turn oxidizes the substrate and is reduced back to the lower oxidation state (Figure 1.3).
1.3. Limitations, Drawbacks, and Practical Solution to Overcome The advantages of using hypervalent iodine compounds consist of their stability toward air and moisture, availability, and mild reaction conditions.20 They are considered to be eco-friendly as they circumvent the use of heavy metals. There are, however, some disadvantages. In many cases, the hypervalent iodine compound is poorly soluble or completely insolubility in common solvents. The isolated oxidized compounds have also been reported to be shock and/or heat sensitivity. The compounds that have been functionalized to improve solubility are not easily recovered and therefore not easily recycled.21,22,23 Furthermore, in the effort to enhance the functionality of these catalysts to compete with metal-based catalysts, synthetic procedures that involve many steps are often employed.24,25 Most recently, simple and fast reaction optimization and recyclability of the supporting hypervalent iodine
4 Texas Tech University, Babak Tahmouresilerd, August 2020 polymers overcame some of these drawbacks.26–28 Also, a few groups reported supporting hypervalent iodine on polystyrene,29 silica,30 macroporous beads, and graphene oxide (Figure 1.4).32 Measuring the molecular weight and appropriate amounts of the hypervalent iodine compounds is a challenge associated with these recoverable systems and the ability to systematically tune these materials can be limited. Furthermore, the geometry around the catalytic site is not always clear or static. An alternative strategy that seeks to overcome these drawbacks is to support an iodine catalyst in a metal-organic framework (MOF).
Figure 1.4. Examples of some of the I catalyst supported by different solid systems.
1.4. Metal-organic Frameworks (MOFs) as an Alternative Solution MOFs are a promising class of porous materials consisting of metal ions or clusters coordinated to organic linkers to form three-dimensional crystalline structures (Figure 1.5). The combination of metal ions and organic linkers into a highly ordered array offers many opportunities to tune their function and stability.33,34 MOFs can be modified with organic and inorganic moieties to create heterogeneous catalysts that mimic the function of a homogeneous catalyst or the nodes can be used as entirely novel
5 Texas Tech University, Babak Tahmouresilerd, August 2020 catalysts. This leads to a variety of chemical reactions that can be facilitated by MOFs.35,36
Figure 1.5. A general scheme for the MOF preparation. A metal ion is mixed with organic linkers using a suitable solvent. Back in 1995, Yaghi and Li reported the hydrothermal synthesis of a copper- based 3D crystalline material under the name of metal-organic framework.37 Four years later in 1999, they reported the design and synthesis of the next metal-organic framework called MOF-5 with higher porosity and stability (Figure 1.6).38 They introduced this MOF with a permanent porosity in which the framework avoids collapse after eliminating the guest molecules including the solvent and unreacted reagents in the pore.
6 Texas Tech University, Babak Tahmouresilerd, August 2020
Figure 1.6. The schematic of the structure of MOF-5. Metal nodes are demonstrated in light blue clusters (Zn4O) connected by terephthalic acid linkers. Hydrogen atoms are omitted for clarity. The yellow sphere shows the pore of the framework.38 The permanent porosity of this MOF was a milestone in the field that gated a wide variety of applications due to a high potential for tunability, for rational design and functionalization of the structure. Today there are a broad number of MOF structures deposited in the Cambridge Structural Database (CSD) which are constructed with different inorganic nodes (i.e., metal clusters or ions) and organic linkers. The porosity alongside with the tunable nature of this material has made it a good candidate to study in different applications including, but are not limited to, bio-related area (e.g., drug delivery),39 energy conversion,40,41 gas storage,42,43 chemical separation,44,45 catalysis.46
7 Texas Tech University, Babak Tahmouresilerd, August 2020
Figure 1.7. Some of the important applications for the metal-organic framework (MOFs). 1.4.1. Synthesis, Activation, and Characterization MOFs can be synthesized via different methods including, but not limited to, solvothermal, microwave-assisted, and electrochemical process.47 In all methods, the condition should be favorable to continuously form metal-linker (M-L) bonds to give a 3D crystalline material. A variety of factors must be considered in MOF synthesis including the type of precursors, solvent, temperature, time, and concentration.48
Solvothermal synthesis is the most frequently employed method to prepare different MOFs. In a typical solvothermal process metal and linker precursors are mixed in a suitable solvent at an elevated temperature over a specified time to self-assemble crystalline material. For example, the mixture of zinc (II) nitrate as the metal source and terephthalic acid as the organic linker in N,N-dimethylformamide (DMF) yields MOF- 5 in which Zn2+ ions and deprotonated linkers self-assemble.38 The next example of MOF solvothermal synthesis is HKUST-1 (i.e., synthesized MOF in Hong Kong University of Science and Technology). In this case, cupric nitrate trihydrate is mixed with trimesic acid in ethanol and water at high temperature to give a 3D Cu-based porous structure where copper ions are coordinated to the carboxylate groups in the
8 Texas Tech University, Babak Tahmouresilerd, August 2020 organic linkers (Figure 1.8).49 This synthesis process can be employed to obtain a wide variety of MOFs including, but not limited to MIL-53 (i.e., synthesized MOF in Material of Institute Lavoisier),50 MIL-100 and 101,51 MOF-74,52 UiO-66 (i.e., synthesized MOF in University of Oslo).53
Table 1.2 shows the corresponding node and linker elements and the representations of some of the MOF structures which typically are synthesized under solvothermal synthesis.
Figure 1.8. The schematic of the structure of HKUST-1. Copper nodes are demonstrated in blue. The terminal metal nodes are shown as the cluster. Metal nodes are connected by trimesic acid linkers. The light blue sphere shows the pore of the framework. Hydrogen atoms are omitted for clarity.49 In 2015, Mounfield and Walton reported MIL-53 synthesis via a solvothermal process in the presence of DMF at two different temperatures.50 The structure of MIL- 53 consists of aluminum-based chains coordinated to deprotonated terephthalic acid linkers to generate a solid 3D framework. Schubert’s research group for the first time reported a zirconium-based framework which later was named UiO-66 by scientists at 54,55 the University of Oslo. This framework comprises Zr6O4(OH)4 clusters connected to carboxylate groups of terephthalic acid.
The downside of the solvothermal process is that solvent molecules together with unreacted reactants are stuck inside the frameworks. An activation process could
9 Texas Tech University, Babak Tahmouresilerd, August 2020 provide the framework with a higher internal surface area and porosity by the removal of these molecules from pores. This process can be done in two main ways based upon the stability of MOFs: I) heating at high temperature (up to 330 °C), and II) drying under high vacuum after a solvent exchange of a high boiling point with a low boiling point solvent.56 This process is very critical prior to use of MOFs for different applications and can be readily examined via Fourier-transform infrared spectroscopy (FTIR) by tracking IR active functional groups of guest molecules in the pores of the framework. One famous example is the stretching vibration of C=O in DMF which can be observed at ⁓1600-1700 cm-1.
Table 1.2. Representations of nodes, linkers, and corresponding MOF structures.a Metal Node Organic Linker MOF Reference
[53]
Zr6O4(OH)4 BDC UiO-66
[50]
Al(OH) BDC MIL-53
[52]
Mg(OH) BDC-(OH)2 MOF-74 a Zr, Al, and Mg are shown in blue, pale green, and purple. Hydrogen atoms are omitted for clarity.
10 Texas Tech University, Babak Tahmouresilerd, August 2020
The other standard characterization methods for MOFs include X-ray
crystallography, N2 adsorption analysis, thermogravimetric analysis (TGA), and nuclear magnetic resonance (NMR) spectroscopy. Both the single and powder X-ray diffraction (SXRD and PXRD) provide useful information about a MOF.57 Powder X-ray diffraction is typically used to make sure the synthesized bulk material is crystalline and pure. Despite the challenging process of growing a single crystal of a MOF for the SXRD experiment, it provides very useful information about the connectivity of atom and the shape of the structure. Comparison of simulated PXRD pattern obtained from the SXRD experiment with the experimental PXRD pattern is typically used to confirm a MOF phase purity. Nitrogen adsorption analysis gives valuable information about the surface area, pore-volume, and pore size distribution of a MOF. Thermogravimetric analysis typically is used to measure the thermal stability of the framework. In this method, the weight of a MOF is measured as a function of time as the temperature is increasing. This analysis provides useful information on the thermal decomposition of chemicals in a MOF based upon mass loss. The NMR spectroscopy for digested MOF also gives valuable information about different contents of the frameworks (e.g., solvent, linker(s)). This method primarily is used to determine the linker ratio in the framework if a MOF is synthesized with multiple linkers.
1.4.2. Rational Design for MOF Synthesis The ultimate goal of MOF synthesis is to take advantage of its stability, porosity, and tenability in different applications.38 A variety of factors should be considered in the design process to ensure the MOF can maintain its characteristics when exposed to moisture or even harsh conditions (e.g., acidic, or basic conditions). Hence, considering a rational design strategy for MOF synthesis respective to the target application is very crucial.58,59 The most fundamental aspect of MOF stability can be described by the Pearson acid-base (HSAB) concept.59 An early example of employing the HSAB concept to synthesize a stable MOF was introduced by Serre et al. in 2002. They developed synthesis and characterization of a chromium-based MOF with high thermal stability and sorption capacities consist of a high-valent metal as a hard acid coordinated
11 Texas Tech University, Babak Tahmouresilerd, August 2020 to carboxylate groups on the linkers as hard base.60 This MOF can be synthesized with other high-valent metals (e.g., Al3+ and Fe3+) with roughly the same topology and competitive stability.59 The other class of ultra-stable MOF, according to HSAB concept, is zirconium-based MOF, which Zr4+ strongly coordinates to a carboxylate type linker.53
Other factors including metal-linker coordination environment and hydrophobicity of the framework play a vital role alongside abovementioned (HASB) concept in establishing the stability of MOFs.61 In 2011, Yang et al. revealed the effect of hydrophobicity on the stability of a series of fluorous-based MOFs constructed Ag(I) coordinated to 3,5-bis(trifluoromethyl)-1,2,4-triazolate linkers (Figure 1.9).62 They demonstrated that incorporating fluorine groups in the pores of the frameworks can generate an ultra-air and moisture stable MOF as a result of very poor host-guest interactions of water molecules and the walls in the framework.
Figure 1.9. The schematic of the structure of FMOF-2. Ag, N, and F are shown in off white, blue, and green. Hydrogen atoms are omitted for clarity.62
The stability of MOF can be readily tracked using PXRD and N2 adsorption analyses to see if the PXRD pattern or the amount of porosity undergoes any change
12 Texas Tech University, Babak Tahmouresilerd, August 2020
after being exposed to air, moisture, or harsh acidic or basic conditions. Over the last few years, the application of MOF has grown as the stability has been enhanced. Catalysis is one of the most important areas that has benefited from MOFs as versatile heterogeneous platforms over the last few years.46
1.4.3. Metal-organic Frameworks (MOFs) for Catalytic Applications MOFs have emerged as promising heterogeneous catalysts for a wide variety of reactions.46 These tunable materials offer a superior surface area, enhanced densities of catalytic sites, and improved thermal stability compared with the other solid supports.63 The active catalytic sites in the MOFs’ structures can be designed by varying the metal nodes, linkers, and post-synthetic modification.64 Thus, over the past decade, a large number of MOFs have been designed and synthesized with various metal ions and linkers to screen their ability in organic transformations as catalyst. The development of thermally and chemically stable MOFs and the design of a homochiral framework for enantioselective catalysis can be driving forces in the growth of this increasingly continuous field (Figure 1.10).
Figure 1.10. Publications related to catalysis using metal-organic frameworks (MOFs) over the past decade. Collected from Sci Finder using “catalysis by MOFs” keyword. (Last update: April 18th, 2020) In general, three structural facets in a MOF that can be utilized as active catalytic sites including, but not limited to, I) inorganic metal node, II) pore space, and III) organic linker into the framework.65
13 Texas Tech University, Babak Tahmouresilerd, August 2020
Figure 1.11. The main catalytic active sites in the MOF structure including inorganic metal node, organic linkers, and the pore space.66 1.4.4. Inorganic metal node as the active site in MOF catalysis The catalytic reaction using the inorganic node can be done in two general ways: I) intrinsic site or II) introduced by post-synthetic modification. For the first time in 1994, Fujita et al. reported the catalytic activity of a cadmium nodes in a 2D framework synthesized with 4,4’-bipyridine and cadmium nitrate in ethanol and water at ambient temperature over 24 hours (Figure 1.12).67 The cadmium node in the 2D framework acted as the active Lewis-acid site and catalyzed the cyanosilylation of aldehydes under mild conditions. This catalytic reaction can also be done more efficiently with copper and chromium nodes in the frameworks of HKUST-1 and MIL-101.68,69
Cd N N Cd N N
N N Cd N N Cd
Figure 1.12. The schematic of the single layer of 2D cadmium-based MOF.67
14 Texas Tech University, Babak Tahmouresilerd, August 2020
The metal nodes also can be modified by the metal exchange process for catalysis. As a recent example, Park et al. revealed the gas-phase polymerization of 3+ 70 ethylene via Cr exchanged MFU-4l. Cr exchanged nodes after treating with Al(CH3)3 generates active catalytic sites. MFU-4l originally was synthesized by treating dialkylzinc with a triazole-type linker under an inert condition.71
Figure 1.13. The schematic of the structure of MFU-4l and its node transformation to 3+ Cr exchanged MFU-4l. Reaction condition: i) CrCl2, CrCl3.3THF, DMF, 7 days, ii) MeOH wash, 150 °C, 18 hours, vacuum. Zn, N, O, and Cl are shown in light blue, blue, red, and green. Hydrogen atoms are omitted for clarity.70 1.4.5. Pores of the Framework for Catalysis Active catalytic sites (e.g., nanoparticles (NPs), complexes, and clusters) can be encapsulated into the pores as solid support due to the stability alongside a large pore, and high surface area of the framework.72 For instance, in the case of NPs encapsulation, pores of the framework prevent particle aggregation.73 Li et al. studied the impact of chemical environment on catalytic properties of palladium NPs in UiO-66 bearing 74 different functional groups on the linker. The synthesized Pd@UiO-66-NH2 catalysts gave benzaldehyde ethylene acetal with high selectivity as the major product, while the same catalyst containing -H or -OMe on the linker yielded 2-hydroxyethyl benzoate as
a result of NH2-Pd interaction.
15 Texas Tech University, Babak Tahmouresilerd, August 2020
Figure 1.14. The catalytic oxidation–acetalization reactions of benzaldehyde using 74 Pd@UiO-66-NH2. 1.4.6. Organic Linker as Catalytic Site in Metal-organic Framework The other strategy is functionalizing the linker with an appropriate group to generate a catalytically active site. This can result in a tunable heterogeneous catalyst. This approach can be extended to a multivariate strategy (i.e., incorporation of multiple linkers into MOF).75 Hu et al. reported the efficient and selective fructose dehydration to 5-hydroxymethylfurfural (HMF) using a Hf-based MOF functionalized with a sulfonic acid-functionalized linker.76 They revealed that NUS-6 (i.e., MOF that is synthesized in the National University of Singapore) shows a very high conversion and selectivity as a result of Brønsted acidity of the sulfonic acid group on the linker and well-defined pore size which can avoid a side reaction. Kuwahara et al. reported a high catalytic activity for a UiO-66 (Zr) analogue which contains a sulfonic acid- functionalized linker for the catalytic transfer hydrogenation of methyl levulinate to γ- valerolactone at 140 °C up to a yield of 85% (Figure 1.15).77 The Brönsted-acidity of
sulfonic acid on the linker in cooperation with Zr6O4(OH)4 clusters as Lewis bases in the presence of 2-butanol can catalyze the catalytic transfer hydrogenation process to yield γ-valerolactone (GVL).80
Figure 1.15. The catalytic transfer hydrogenation reaction of methyl levulinate with 2- 80 butanol catalyze with UiO-66-SO3H to produce γ-valerolactone (GVL).
16 Texas Tech University, Babak Tahmouresilerd, August 2020
Gascon et al. reported the Knoevenagel condensation of ethyl cyanoacetate and ethyl acetoacetate with benzaldehyde using IRMOF-3 as a catalyst (Figure 1.16).78
Figure 1.16. The Knoevenagel condensation of benzaldehyde with ethyl cyanoacetate and ethyl acetoacetate using IRMOF-3. Catalytic reaction condition: i) 20 mol% catalyst (IRMOF-3), 7 mmol ethyl cyanoacetate or ethyl acetoacetate, and 8 mmol benzaldehyde in 5 mL of DMSO under inert atmosphere.78 IRMOF-3 is a MOF-5 analogue in which the linkers are functionalized with a - 79 NH2 group. IRMOF-3 led to enhanced basicity as a result of intramolecular interaction with the carboxylate group in the framework. IRMOF-3 catalyzed these condensation reactions with excellent yield and high selectivity. Two years later, Cortese and Duca suggested that the increased activity of IRMOF-3 comes mostly from the water adsorption capability of the framework.80
Wang et al. synthesized a series of Al-based MOF using different amounts of 2,6-naphthalene dicarboxylic acid-functionalized with sulfonic acid (DUT-4: 81 [Al(OH)(NDC)1-x(NDC-SO3H)x]). They employed this MOF as a catalyst (acidic character of the sulfonic acid groups on the linker) for the ring-opening reaction for styrene oxide under mild conditions. DUT-4 with a 30% sulfonic acid functionalized
17 Texas Tech University, Babak Tahmouresilerd, August 2020 linker gave a 99% conversion in 5 hours with the ability to recycle up to three times without significant loss in reactivity.
Figure 1.17. Styrene oxide ring-opening reaction catalyzed by DUT-4 MOF in the presence of methanol at 55 °C.81 The active metal complexes can also be grafted onto the linker. This method involves two steps: I) covalently functionalizing the linker with chelating sites II) metalation with suitable metal via coordination. Zhang et al. reported the design and synthesis of a highly robust zirconium-based MOF consisting of a bipyridine or phenanthroline type linker as the chelating sites and a cobalt complex as the active catalytic site (Figure 1.18).82 These MOFs can be synthesized under a solvothermal reaction as a result of treating the ZrCl4 with the proper amount of linker(s) in DMF at 100 °C for 5 days.
Figure 1.18. Scheme showing the preparation of MOF-Co.2THF. Reaction condition: i) 82 CoCl2, THF, 24 h, ii) NaBEt3H, THF, 15 min. They examined these catalysts for 1) alkene hydroboration and hydrogenation, aldehyde, and ketone hydroboration, and lastly arene C-H borylation. The highest activity and stability was observed when the phenanthroline based MOF catalyzed the alkene hydrogenation with turnover numbers and turnover frequencies of ∼2.5 × 106
18 Texas Tech University, Babak Tahmouresilerd, August 2020
and ∼1.1 × 105 h–1, respectively. They attributed this to lack of an intermolecular deactivation in the catalytic reaction.
1.4.7. Advantages and Limitations of MOFs as Practical Catalysts Among the porous material for the catalytic application, the highest porosity belongs to the metal-organic framework (MOFs). Furthermore, the shape and size of the pores of the frameworks are readily tunable. This is in contrast with other porous materials where the diversity of components for a rational design is highly limited. The most important advantages of MOFs can be considered as:83,84
High diversity of components (e.g., metal ions and organic linkers) allowing for the rational design of heterogeneous catalysts. Implementation of organic and inorganic moieties as pre-catalysts in the metal node, organic linker, or the pore space via simple methods. Tunable pore size: allowing generation of a size-selective passive reaction media. The high density of the catalytic active site Catalyst recyclability as a result of being a heterogeneous catalyst
These advantages can be considered as the most key features of MOFs in the growing field of catalysis. However, there are some important limitations for MOFs in catalytic reactions. Regardless of the many reported highly robust MOFs,53,85 some of the frameworks suffer from a very low thermal, chemical, or mechanical stability.61,86 For example, in MOF-5 the Zn-O coordinative bonds can readily undergo hydrolysis in the presence of moisture which hinders the utility of this MOF in catalysis.87 The copper-based MOF (HKUST-1) significantly loses its crystallinity beyond a certain pressure as a result of a low mechanical stability.88 Most of the designed and synthesized MOFs are thermally stable up to 300 °C which is high enough to cover most of the catalytic reactions in the liquid phase. However, caution should be taken about the exposure time of these frameworks to higher temperature and the presence of an acidic or basic condition in the catalytic reactions. The continual reuse of MOFs in catalytic
19 Texas Tech University, Babak Tahmouresilerd, August 2020
reactions is another critical issue that restricts MOFs stability. The metal nodes and organic linkers can interact with guest molecules. These can deactivate the MOFs activities for catalytic reactions by blocking the pores of the frameworks and avoiding a sufficient diffusion of reagents into the frameworks.46
1.4.8. Summary Utilizing MOFs as a heterogeneous catalyst has remarkably developed over the past decade. A wide range of characterizations including, but not limited to, PXRD, FTIR,
TGA, NMR, and N2 analysis can provide detailed information. These frameworks offer a superior internal surface area, high density of the catalytic active site, tunability, and recyclability. The metal node, pore space, and organic linker can be designated as the catalytic site for a wide range of catalytic reactions. The pore size of the framework can be tuned for size selectivity of the substrate in different organic reaction transformations. A well-defined pore can also prevent particle aggregation in catalytic reactions. However, in contrast to all the MOFs advantages in catalysis, an amorphization for some frameworks can happen upon exposure to moisture, acidic or basic reaction conditions, high temperatures, or mechanical pressure. Designing new MOFs for catalysis is a fast-expanding area, although generating a structurally stable MOF for heterogeneous catalysis represents a significant challenge.
1.5. Research Objective and Dissertation Overview In short, the general idea of this research is aimed at adapting known homogeneous organo-iodine systems into MOFs that can facilitate their use in oxidative catalysis by overcoming inherent solubility issues and by allowing for ready reuse and recovery. Chapter 2 details a multivariate strategy for introducing an organo-iodine species into a MOF linker and validates its utility in oxidative catalysis with hydroquinones. Chapter 3 expands on this work by introducing an isoreticular expansion strategy that allows for enhanced diffusion. This comes with the drawback that certain reactions do not take place as readily as they do in the smaller frameworks due to changes to the electronic structure of the catalyst. Chapter 4 highlights the applications of these novel catalytic systems to a more challenging substrate class for
20 Texas Tech University, Babak Tahmouresilerd, August 2020 oxidative dearomatization reaction. Chapter 5 details some recent progress with our efforts to expand on iodine-containing molecules for catalysis. Chapter 6 describes the general experimental and computational methods employed for this work.
21 Texas Tech University, Babak Tahmouresilerd, August 2020
Chapter II
2. Proving the Concept: MOFs as Supports for Organo- iodine Catalysts This chapter is an adapted version of “Make room for iodine: systematic pore tuning of multivariate metal-organic frameworks for the catalytic oxidation of hydroquinones using hypervalent iodine, B. Tahmouresilerd, P. J. Larson, D. K. Unruh and A. F. Cozzolino, Catal. Sci. Technol., 2018, 8, 4349–4357, https://doi-org.lib- e2.lib.ttu.edu/10.1039/C8CY00794B” with permission from The Royal Society of Chemistry. In this chapter, a few synthesized MOFs structures and their chemical stability is discussed. A useful strategy to increase access to the catalytic active site is demonstrated.
1.6. Design a MOF to Support Iodine Catalyst Metal-organic frameworks are a class of catalysts that merge the benefits of homogeneous and heterogeneous catalysts.89 Although inherently insoluble, MOFs have enormous internal surface areas that can facilitate access to a catalytic site. Because of the site-isolation of the iodine, it is not prone to aggregation in a similar manner to molecular hypervalent iodine species such as iodosylbenzene. A variety of factors must be considered in the design including pore shape, pore size, the density of catalytic sites, the stability of framework, nature of oxidant, and shape of the reagent. Our initial targets include the very stable (chemical, thermal, and mechanical) MOFs MIL-53 (Al) and UiO-66. Importantly, these frameworks do not contain redox-active metals that can interfere with the I-mediated catalysis. As shown in Figure 2.1, MIL-53 has columnar pores that can change volume due to the breathing nature of this MOF while UiO-66 has rigid tetrahedral and octahedral pores.
22 Texas Tech University, Babak Tahmouresilerd, August 2020
Figure 2.1. Depiction of the MIL-53 (Al)50 (left), and the octahedral pore in UiO-66 (Zr)53 (right). Metal coordination spheres are represented with polyhedra. Hydrogen/halogen atoms have been removed for clarity. The yellow sphere shows the pore of the framework. Using a model reaction, we show that MOF-supported iodine sites are catalytically active and can be easily recovered and reused in certain instances. Here, the approach of making multivariate MOFs has proved essential to unlocking the reactivity of these systems.
1.7. Preparation of MOF Catalysts Ultra-stable MOFs UiO-66 and MIL-53 were prepared through modified literature procedures by treating the appropriate metal salt with 1,4-benzene dicarboxylic acid (H2BDC) derivatives under solvothermal and/or hydrothermal conditions.90,91 Iodine can be introduced directly into the MOF by substituting 1,4- benzene dicarboxylic acid with a 2-iodo-1,4-benzene dicarboxylic acid (H2IBDC) in the MOF synthesis to give MIL-53 XX%-I or UiO-66 XX%-I, where XX designates the percentage of the linker that is IBDC2− and not BDC2−. One critical adaptation was to avoid the use of oxidizing anions, such as nitrates, in the preparation of the MIL-53
MOFs as NMR digestions revealed that the linker no longer matched H2IBDC which was confirmed by spiking with an authentic H2IBDC sample. Aluminum chloride hexahydrate or zirconium (IV) chloride served as appropriate metal sources.
1.8. Preliminary Catalyst Evaluation The oxidation reaction of hydroquinone to benzoquinone (Figure 2.2) was chosen as a model reaction to evaluate the catalytic behavior of the MOFs prepared with
23 Texas Tech University, Babak Tahmouresilerd, August 2020
H2IBDC. Under a typical set of conditions (acetonitrile and ~2.9 eq. mCPBA as solvent and terminal oxidant, respectively, 20% catalyst loading, 60 min and 50 °C), the esterified linker was able to catalyze the oxidation of hydroquinone to benzoquinone with 93% (above the level of the control reaction) conversion and yield. An equivalent experiment with either UiO-66 or MIL-53 100%-I resulted in negligible conversions beyond the level of the control reaction performed in the absence of MOF or with the MOF containing 0%-I (Table 2.1).
Figure 2.2. The oxidation of hydroquinone to benzoquinone shown with typical catalytic conditions. Given the good performance of the esterified linker, we proposed that this was likely the result of an inability of the reagents to flow into or out of the framework as a result of the large size of I. The typical approach when such a problem is encountered is to make a longer linker to increase the pore size.92 An alternative approach is to reduce the density of iodine sites by preparing multivariate MOFs (MTV-MOFs) where some of the IBDC2– are replaced with the smaller BDC2–.
24 Texas Tech University, Babak Tahmouresilerd, August 2020
Table 2.1. Initial catalytic screening for the oxidation of hydroquinone to benzoquinone in MOF-supported I.a MOF Conversion (%)b MIL-53 100%-I 1 UiO-66 100%-I 0 MIL-53 0%-I -2 UiO-66 0%-I 2 Me2IBDC 93 a Reaction conditions: 20 mol% cat., ~2.9 eq. mCPBA, acetonitrile, 60 min, 50 °C. Values were determined by 1H NMR in the presence of methylsulfonylmethane (MSM) as an internal standard.
b Reported in excess of the control reaction with no catalyst.
1.9. Preparation and Characterization of MTV-MOF Catalysts An illustration of the MTV-MOFs with a combination of linkers BDC2− and IBDC2− is shown in Figure 2.3. Although the distribution of linkers is random, appropriate ratios of linkers can be selected to maximize the average open space in the pore to facilitate mass transport, while maximizing the density of catalytic sites. Multivariate MIL-53 and UiO-66 (MTV-MIL-53 and MTV-UiO-66) were successfully prepared by adapting literature procedures for the pure linker MOFs.90,91 Linker ratios 93 of 0, 25, 50, 75 and 100% H2IBDC:H2BDC were used. It has been reported that MTV- MOFs do not necessarily incorporate the different linkers in the same ratio that they are added to the reaction mixture.94 To confirm the ratio of linkers in the MTV-MOFs that were prepared, NMR digestions were performed on all samples. For all MTV-MOFs, the anticipated ratio of linkers, based on reaction stoichiometry, was approximately observed as summarized in Table 2.2.
Figure 2.3. Illustration of the MTV-MOFs consisting of metal ions or clusters (black circle) coordinated to organic linkers (red arrows for IBDC2− and blue lines for BDC2−).
25 Texas Tech University, Babak Tahmouresilerd, August 2020
Table 2.2. Incorporation of 2-iodoterephthalic acid in MTV-MOFs from 1H NMR digestions. MTV-MOF 25%-I 50%-I 75%-I 100%-I UiO-66a 24% 49% 66% 100% MIL-53b 19% 45% 73% 100% a Digested in 5:1 (CD3)2SO:D2SO4.
b Digested in 3:1 D2O:40% NaOD in D2O. Thermogravimetric analysis (TGA) for both MOFs was used to establish the thermal stability and the temperature limits for activation and reactions. All frameworks were shown to be stable up to 400 °C (Table 2.3). Apart from MTV-MIL-53 (50%-I), a trend of decreasing stability with increasing iodine was observed. The MTV-MIL-53 samples were treated with hot methanol for 16 hours followed by heating at 320 °C for 3 days in order to remove residual materials from the pores. The MTV-UiO-66 samples were activated by washing with hot DMF (x3) and soaking overnight once with hot methanol before filtering and heating at 150 °C for 16 hours under vacuum. TGA analysis under the airflow for MTV-UiO-66 25%-I (Figure 2.4) and MTV-MIL-53 25%-I (Figure 2.5) before and after the activation. For activated MTV-MOFs, no significant weight loss is seen until 420±20 °C. A big mass loss after 420±20 °C suggests that decomposition occurs. After decomposition, ⁓25 and ⁓35% of the starting weight remains for MTV-MIL-53 25%-I and MTV-UiO-66 25%-I respectively which corresponds to the formation of relevant metal oxide. Thermal decomposition under aerobic conditions for all multivariate activated MOFs as determined from TGA is summarized in Table 2.3.
26 Texas Tech University, Babak Tahmouresilerd, August 2020
Table 2.3. Comparison of onset temperature for thermal decomposition under aerobic conditions as determined from TGA of the MTV-MOFs (values shown are from activated MOFs).a IBDC2− (%)b Temperature (°C) MIL-53 UiO-66 0% 535 500 25% 445 440 50% 420 455 75% 500 425 100% 490 400 a 20 mg of activated MOFs under fellow of air (20 mL min−1) with a heating rate of 10 °C min−1.
Figure 2.4. Thermogravimetric (TGA) analysis of MTV-UiO-66 25%-I under air before and after the activation.
27 Texas Tech University, Babak Tahmouresilerd, August 2020
Figure 2.5. Thermogravimetric (TGA) analysis of MTV-MIL-53 25%-I under air before and after the activation.
IR spectroscopy was used to probe for the presence of H2BDC, H2IBDC, or other impurities in the MOF cavities following activation. MIL-53 has been reported to 95 crystallize with free H2BDC in the pore, , and in the case where the free linker is
H2IBDC, this could lead to ready homogeneous catalysis if the linker is not removed prior to catalysis. The FTIR data are in good agreement with reported literature for both MOFs.90 In the case of as-synthesized MTV-MIL-53 MOFs, the peak at 1690 cm–1 indicates the presence of free linker within the pores of the framework (Figure 2.6). Following activation, this signal was not observed for any multivariate MOFs (Figure 2.7). For UiO-66, the peak at 1667 cm-1 indicates the presence of residual DMF molecules. These are strongly adsorbed in the framework and are only partially removed upon activation (Figure 2.8). No signal could be conclusively identified for the C–I stretching mode, but this vibration is reported to be between 200 and 600 cm–1 and DFT calculations predict lower than 300 cm-1, which is outside the mid-IR range.
28 Texas Tech University, Babak Tahmouresilerd, August 2020
Figure 2.6. Di-ATR FTIR of as-synthesized MTV-MIL-53 (0, 25, 50, 75, and 100%-I) plotted as attenuation.
Figure 2.7. Di-ATR FTIR of activated MTV-MIL-53 (0, 25, 50, 75, and 100%-I) plotted as attenuation.
29 Texas Tech University, Babak Tahmouresilerd, August 2020
Figure 2.8. Di-ATR FTIR of activated MTV-UiO-66 (0, 25, 50, 75 and 100%-I) plotted as attenuation. Powder X-ray diffraction patterns were obtained for the MTV-MOFs and were compared with the predicted powder patterns of known MOF structures to verify that the anticipated framework was formed. All of the powder X-ray diffraction (PXRD) patterns for the MTV-UiO-66 MOFs are in good agreement with the simulated pattern of UiO-66 (Figure 2.9).53
The PXRD patterns of the activated framework revealed that the crystallinity was retained in all cases. For MIL-53, a breathable MOF, the Al−Al−Al angle (see Figure 2.10) is used to describe the structures and is denoted as MIL-53(angle). The patterns of the as-synthesized MOFs with 0 and 25% IBDC2− could be matched to the known phase MIL-53(109.8°).95 After activation, only the MIL-53 0%-I had a powder pattern that corresponded to a narrow pore phase, MIL-53(136.4°).96 Samples with 25% or more IBDC2− had patterns that were unique from any structure in the CSD. To ensure that the desired MOF had been prepared, single crystals of MIL-53 100%-I were obtained, and the structure was evaluated. Due to the high level of disorder, the iodine occupancies are less than expected in the single-crystal structures, but NMR digestion
30 Texas Tech University, Babak Tahmouresilerd, August 2020
data of single crystals and bulk powder reveals that only H2IBCD is present in MIL-53 100%-I.
Figure 2.9. PXRD patterns of activated MTV-UiO-66 (0, 25, 50, 75 and 100%-I) and simulated UiO-66 0%-I.
31 Texas Tech University, Babak Tahmouresilerd, August 2020
Figure 2.10. MTV-MIL-53 pore with interplanar angle and sphere of radius r depicted (left), activated MIL-53 25%-I with Al−Al−Al angle of 108.9° (middle) and activated MIL-53 100%-I with Al−Al−Al angle of 124.9° (right). I atoms are disordered over all sites. A random distribution of I atoms are depicted to match the experimental ratio of BDC2−:IBDC2−. All structures depicted along (0,1,0). Metal coordination spheres are represented with polyhedra. Hydrogen atoms have been removed for clarity. The powder pattern predicted from this phase was found to be in good agreement with the experimental patterns for the as-synthesized MIL-53 with 50-100% I. Two unique phases were found for the activated material; a narrow pore and a large pore phase, MIL-53(124.9°) and MIL-53(108.9°), respectively. Simulation of the powder patterns reveals that the MIL-53 75%- and 100%-I bulk samples consist primarily of the MIL-53(124.9°) phase. The MIL-53 50%-I bulk powder is also a mix of the two phases but primarily consists of the larger pore phase MIL-53(108.9°) (
Figure 2.11). The PXRD patterns of the activated MIL-53 25%-I reveal that it only consists of MIL-53(108.9°). MIL-53 can also be prepared solvothermally in DMF instead of deionized water. A sample of MIL-53 25%-I obtained in this way has the same large pore framework (MIL-53(108.9°),
Figure 2.11). describes the Al–Al–Al angles and pore diameters in each of the MIL-53 phases and clearly shows that the MIL-53 25- and 50%-I samples maintain relatively large pores before and after activation, suggesting that the pore will remain open at all points during a reaction.
32 Texas Tech University, Babak Tahmouresilerd, August 2020
Table 2.4. MTV-MIL-53 inter-planar angles (assigned from matched PXRD) for the as- synthesized (AS) and activated (AA) form of each phase as a measure of the openness of the pores. The radius (r) of the cylinder that can fit in the pore is provided in Å in parentheses.a % IBDC2− AS θ (°) AA θ (°) 0 109.8 (3.2) 136.4 (1.9) 25 109.8 (3.2) 108.9 (3.3) 50 101.3 (3.5) 108.9b (3.3) 75 101.3 (3.5) 124.9b (2.6) 100 101.3 (3.5) 124.9b (2.6) a Van der Waals's radius of carbon has been subtracted; value assumes benzene rings are tangential to pore.
b The angle in the predominant phase.
33 Texas Tech University, Babak Tahmouresilerd, August 2020
Figure 2.11. PXRD patterns of activated MTV MIL-53 (0, 25, 50, 75, and 100%-I) MOFs, MTV-MIL-53 25%-I synthesized in DMF, simulated MIL-53(136.4°),96 activated MIL-53 (100%-I) 124.9° and 108.9° from single-crystal structures. The effect of iodine on pore size and accessibility can be readily seen from the change in the structure of the MTV-MIL-53 MOFs. With the MTV-UiO-66 frameworks, the effect of the amount of iodine on the internal surface area and pore size can be determined by nitrogen adsorption measurements. MTV-UiO-66 (25, 50, and 100%-I) and MTV-MIL-53 25%-I MOFs show type-I adsorption isotherms (Figure 2.12 Figure 2.13). As the ratio of IBDC2− increases in the
34 Texas Tech University, Babak Tahmouresilerd, August 2020 frameworks, the molar surface area decreases from the reported value for UiO- 66 0%-I (∼313000 m2/mol) as depicted in Table 2.5.91
Figure 2.12. Nitrogen adsorption isotherms for the MTV-UiO-66 25 (–▲–), 50 (–□–), and 100%-I (–●–).
Figure 2.13. Nitrogen adsorption isotherms for the MTV-MIL-53 25%-I synthesized with H2O (–▲–), DMF (–□–). More important to this study, the pore volume decreases linearly with the increased loading of I to the point where the pores may become inaccessible for
35 Texas Tech University, Babak Tahmouresilerd, August 2020 substrates/oxidants. The pore volume distributions for UiO-66 25, 50, and 100%- I showed two major pores in the frameworks with pore widths of 6 and 10 Å. As the ratio of the linkers containing I increase in the frameworks, the differential pore volume decreases (Figure 2.14).
Table 2.5. Brunauer-Emmett-Teller (BET) surface areas and pore volumes for the activated UiO-66 25, 50, and 100%-I obtained from nitrogen adsorption isotherms at 77 K. MOF BET surface area Pore volume (mL/mol)a (×103 m2ꞏmol-1)a UiO-66 0%-I97 313 120 UiO-66 25%-I 250 117 UiO-66 50%-I 213 103 UiO-66 100%-I 165 93 MIL-53 25%-I (H2O) 457 173 MIL-53 25%-I (DMF) 447 178 a Based on idealized formula and normalized to Zr for UiO-66 and Al for MIL-53.
Figure 2.14. Pore volume distribution for the MTV-UiO-66 25, 50, and 100%-I. In the case of multivariate MIL-53, the pore volume distribution revealed that MIL-53 25%-I prepared in DMF has a uniform pore with a width of 6 Å and a higher differential pore volume in the framework when compared to MIL-53 25%-I synthesized hydrothermally (Figure 2.15).
36 Texas Tech University, Babak Tahmouresilerd, August 2020
Figure 2.15. Pore volume distribution for the MTV-MIL-53 25%-I synthesized with H2O and DMF. 1.10. Catalytic Performance MTV-MOF Catalysts Catalytic reactions involving these multivariate MOFs revealed that the conversion was strongly dependent on the percentage of IBDC2– in the framework. The oxidation reaction of hydroquinone to benzoquinone under a typical set of conditions (Figure 2.2), demonstrated clear catalysis (Table 2.6).
Table 2.6. Oxidation of hydroquinone to probe the effect of linker ratio in MTV-MOFs.a IBDC2− (%) Avg. Conversion (%)b MIL-53 UiO-66 0% -2 2 25% 11 (12c) 44 50% 4 9 75% 1 11 100% 1 0 a Reaction conditions: 20 mol% cat., ~2.9 eq. mCPBA, acetonitrile, 60 min, and 50 °C. Values were determined by 1H NMR in the presence of MSM as an internal standard.
b Conversions reported in excess of the control reaction (5%).
c MIL-53 25%-I prepared in DMF. For both MOFs, the yields appear to be inversely proportional to the amount of incorporated I down to 25%. This was consistent with the increase in
37 Texas Tech University, Babak Tahmouresilerd, August 2020 the internal surface area and pore volume for UiO-66. Assuming that the catalysis is occurring in the larger octahedral pore, this amounts to 1.5 I sites per pore and represents a near-ideal balance between a high density of catalytic sites and sufficient space for mass transport to efficiently occur. With MIL-53 25%-I the higher yield is attributed to an increase in internal surface area that results from a balance between lower I loading and a more open structure in the breathable MOF.
Analysis of the PXRD patterns of the activated and as-synthesized MOFs reveals that MIL-53 25%-I remains in an open and accessible form (angles closest to 90°) under different conditions and therefore has sufficient internal space to facilitate mass transport. Under identical catalytic conditions, no improvement in conversion was observed for MIL-53 25%-I prepared in DFM as opposed to water, but the yield of the desired product increased from 8 to 12%, above the control reaction, suggesting that the MIL-53 25%-I prepared in DMF is more selective.
The sizes of the crystalline domains were estimated from the line broadening at the FWHM of the PXRD peaks. Values of 70 nm and 14 nm were obtained for MIL-53 25%-I prepared in water and DMF, respectively. The lack of apparent effect of crystallite size on conversion suggests that the conversion is independent of the particle surface area and that the reaction is occurring inside the pores of the framework rather than on the surface. This is consistent with the differences in reactivity going from 25%-I to 100%-I. The multivariate UiO-66 25%-I and MIL-53 25%-I prepared in DMF were selected for further investigation.
To ensure that the catalysis was occurring heterogeneously and not through the leaching of the linker molecule, a split test was performed with both catalysts (Figure 2.16). Upon removal of the catalysts by a hot filtration no more conversion was observed. This was in contrast to continuing conversion in the samples that remained in the presence of the catalysts. This confirms that the
38 Texas Tech University, Babak Tahmouresilerd, August 2020
MOF is supporting the catalyst and that the conversion that occurs in excess of the background reaction is occurring heterogeneously.
Figure 2.16. Split test where catalysts (MTV-UiO-66 25%-I in yellow, MTV-MIL-53 25%-I in red, no catalyst in green and blue) were hot filtered from the reaction mixture after 2 minutes for MTV-UiO-66 25%-I and 10 minutes for MTV-MIL-53 25%-I. Samples were characterized after 1 hour. In order to identify the oxidation state change of the iodine, X-ray photoelectron spectroscopy (XPS) analysis was performed on MIL-53 50%-I and UiO-66 25%-I before and after oxidation with mCPBA. Figure 2.17 shows the high resolution I 3d5/2 XPS signals. The spectra confirm the presence of iodine in two distinct oxidation states ((I) at 618.5 eV and (III) at 620.9 eV. DFT calculations of I(I) and I(III) species revealed a change in chemical shift of ~2 eV between I(I) and I(III), consistent with the experiment. I(V) has been reported to have a much higher chemical shift (623.8 eV) then those observed here (Table 2.33).98 For MIL-53 50%-I, chemical shifts of 618.5 eV and 620.8 eV were observed both before and after oxidation. An increase in relative intensity was observed for the higher energy shift after oxidation. This suggests that the synthesis or aerobic activation leads to oxidation of the iodine prior to catalysis.
39 Texas Tech University, Babak Tahmouresilerd, August 2020
UiO-66 25%-I shows very little oxidized iodine prior to the reaction, but significant amounts following the reaction.
Figure 2.17. XPS spectra of I 3d5/2 for MTV-MIL-53 50%-I and UiO-66 25%-I before (top) and after (bottom) the oxidation reaction of hydroquinone to benzoquinone in the presence of 20 mol% catalyst, ~4.3 eq. mCPBA, acetonitrile, at 50oC for 5h. The choice of solvent can have a significant influence on the reaction. Different solvents were screened under the aforementioned conditions (Figure 2.18). The reaction was catalyzed in the presence of acetonitrile, nitromethane, ethyl acetate, acetone, ethanol, and methanol; superior conversions to acetonitrile and high selectivities were observed in all solvents for UiO-66 25%-I.
40 Texas Tech University, Babak Tahmouresilerd, August 2020
Figure 2.18. Catalytic oxidation of hydroquinone to benzoquinone as a function of solvent after 2 minutes (solid color) and 1h (solid + hashed color) with 20 mol% catalyst and 2.9 eq. mCPBA. Values were determined by 1H NMR in the presence of MSM as an internal standard. In methanol, the catalyst could not be readily evaluated after 60 min due to the high conversion associated with the control reaction. For MIL-53 25%-I, superior conversions were only observed with nitromethane. Lower selectivities were observed with MIL-53 25%-I as compared to UiO-66 25%-I, as other oxidation byproducts (2,5-dihydroxy-1,4-benzoquinone and maleic acid) 99 were observed by 1H NMR. The reduction of the reaction time to 2 minutes revealed high conversions in nitromethane, ethanol, and methanol for UiO-66 25%-I. This demonstrates that the MTV-MOFs act as efficient catalysts, even in methanol. Reduction of the equivalents of terminal oxidant in nitromethane revealed no significant change for UiO-66 25%-I but a proportional loss in activity with MIL- 53 25%-I. Conversely, an increase in equivalents of oxidant used did not increase the conversion in either case but did increase the conversion in the control reaction.
1.11. Catalytic Performance MTV-MOF Catalysts in the Oxidation of other Hydroquinones The effect of size and electronic structure of substrates were evaluated using according to the conditions listed in Table 2.7.
41 Texas Tech University, Babak Tahmouresilerd, August 2020
The effect of substrate size was evaluated using reactions of hydroquinone and 2,5-di- tert-butylhydroquinone to the corresponding ketones. In the case of UiO-66 25%-I, a yield of 32% and 54% for hydroquinone and 2,5-di-tert-butylhydroquinone, respectively, were obtained (Entry 2 and 15) which is consistent with 2,5-di-tert- butylhydroquinone being easier to reduce.100 This contrasts with MIL-53 25%-I which has more restricted pores and has a lower conversion for the larger, easier to oxidize substrate. UiO-66 100%-I gives no conversion beyond the control reaction with both substrates which is consistent with the catalysis occurring within the pores of the MOF, rather than on the external surface (Entry 3, 17). The electronic properties of the substrates in the catalytic reaction were studied by adding the Me and tBu as electron- donating and Br and Cl as electron-withdrawing groups to the substrate with a comparison to the hydroquinone at room temperature and 50 oC, respectively.
42 Texas Tech University, Babak Tahmouresilerd, August 2020
Table 2.7. Oxidation of hydroquinone derivatives with iodine-functionalized MTV- MOFs.
Entry Substrate MTV-MOF Temp. Yield a,b R1 R2 (°C) (%) 1 H H No catalyst RT 3 2 UiO-66 25%-I 35 (32) 3 UiO-66 100%-I 5 (2) 4 MIL-53 25%-I 13 (10) 5 H H No catalyst 50 8 6 UiO-66 25%-I 93 (85) 7 MIL-53 25%-I 45 (37) 8 H Me No catalyst RT 29 9 UiO-66 25%-I 57 (28) 10 MIL-53 25%-I 36 (7) 11 H tBu No catalyst RT 31 12 UiO-66 25%-I 62 (31) 13 MIL-53 25%-I 34 (3) 14 tBu tBu No catalyst RT 41 15 UiO-66 25%-I 95 (54) 16 MIL-53 25%-I 43 (2) 17 UiO-66 100%-I 42 (1) 18 H Cl No catalyst 50 24 19 UiO-66 25%-I 64 (40) 20 MIL-53 25%-I 44 (20) 21 Br Br No catalyst 50 5 22 UiO-66 25%-I 72 (67) 23 MIL-53 25%-I 15 (10) a Values were determined by 1H NMR using MSM as an internal standard.
b The yield of reaction beyond the background reaction is provided in parentheses. The catalytic oxidation of substrates containing electron-donating groups at room temperature showed a better yield of reaction for UiO-66 25%-I when compared to hydroquinone (Entries 9, 12, and 15), consistent with the oxidation potentials.100 Catalytic oxidations of substrates containing electron-withdrawing group at 50 °C showed a drastic drop from 85% for hydroquinone (Entry 6) to 40% and 67% for 2- chlorohydroquinone and 2,5-dibromohydroquinone, respectively in the presence of UiO-66 25%-I (Entry 19, 22), again consistent with the oxidation potential of these
43 Texas Tech University, Babak Tahmouresilerd, August 2020 species.100 Regardless of the oxidation potential of the substrate, the yields were lower with MIL-53 25%-I as compared to hydroquinone, which suggests that size is the predominant determinant.
1.12. Effect of Solvent, Terminal Oxidant, and Recycling on Catalytic Oxidation of Hydroquinone The ability to recycle the catalyst was probed using hydroquinone (Figure 2.19). In the case of UiO-66 25%-I, the catalytic conversion dropped from 94% to 47% after the first run and finally leveled off at ~30% for the 3rd and 4th cycle, approximately double control reaction. (Figure 2.19, top). These results contrast with the more sluggish MIL-53 25%-I. In nitromethane, the conversion and yield held nearly constant over 4 recycles (Figure 2.19, bottom). While the small losses in conversion with MIL-53 25%- I could be rationalized as catalyst attrition from manipulations between recycles, the abrupt loss in activity of the UiO-66 catalyst was unexpected and encouraged further study.
44 Texas Tech University, Babak Tahmouresilerd, August 2020
Figure 2.19. Recyclability of catalytic conversion after 1 h for hydroquinone to benzoquinone in the presence of MTV-UiO-66 25%-I (top), and MTV-MIL-53 25%-I (bottom). 20 mol% of catalyst, 2.9 eq. mCPBA, nitromethane, 50 °C. Values were determined by 1H NMR in the presence of MSM as an internal standard. The PXRD patterns for the catalysts after the first and fourth runs were obtained. Figure 2.20 and Figure 2.21 show that both frameworks retain their crystallinity.
Figure 2.20. PXRD patterns of MTV-UiO-66 25%-I before the catalytic reaction, after the first run, and the fourth run
45 Texas Tech University, Babak Tahmouresilerd, August 2020
Figure 2.21. PXRD patterns of MTV-MIL-53 25%-I before the catalytic reaction and after four cycles. Two possible explanations for the loss in reactivity arise: I) access to either the pores or active sites is being prevented by the accumulation of large organic groups bound to the hypervalent iodine species, or II) a macroscopic effect such as particle aggregation is occurring and slowing reactivity. Scanning electron microscope (SEM) images of the catalysts before and after the reaction (both were sonicated prior to deposition) revealed that the UiO-66 25%-I particles were aggregating during the reaction. In the case of a sample of MIL-53 25%-I treated the same way, no aggregation was observed. The aggregation of MOF particles has been previously observed and was found to be a function of pH in that case.101 Here, the acidic oxidant could be having a similar effect.
46 Texas Tech University, Babak Tahmouresilerd, August 2020
Figure 2.22. Scanning electron micrographs of MTV-UiO-66 25%-I before (left) and after (right) the catalytic reactions. While mCPBA is a typical oxidant used with I for catalytic oxidations, a variety of other terminal oxidants have been used in the literature.1 The performance of the catalysts with mCPBA, oxone, hydrogen peroxide, tert-butyl hydroperoxide, and the urea/hydrogen peroxide complex (Hyperol) were tested in a 3:1 nitromethane:water mixture. With UiO-66 25%-I, good conversions with high selectivities were observed with mCPBA (76% conv. and 75% yield) and oxone (80% conv. and 78% yield) over 60 min at 50 °C. With MIL-53 25%-I good conversions with modest selectivities were observed with mCPBA (49% conv. and 37% yield) and oxone (86% conv. and 70% yield).
With oxone, the catalyst loading with UiO-66 25%-I could be reduced to 10% with no change in the outcome of the reaction over 60 minutes. Further reduction in catalyst loading to 5 and 1% reduced the yields/conversions to 51/67% and 31/49%, respectively. With MIL-53 25%-I the yield/conversions decreased linearly with the catalyst loading (Table 2.8).
47 Texas Tech University, Babak Tahmouresilerd, August 2020
Table 2.8. Catalyst mol% variation for catalytic oxidation of hydroquinone (HQ) to benzoquinone (BQ). Entry Catalyst MTV-MOF Yield Loading (mol %) (%) 1 20 UiO-66 25%-I 78 2 10 77 3 5 51 4 1 31 5 20 MIL-53 25%-I 70 6 10 45 7 5 34 8 1 23 9 - No Catalyst 0 Reaction conditions: ~4 eq. oxone, nitromethane/water (3:1 v:v), 60 min and 50 °C. Values were determined by 1H NMR in the presence of MSM as an internal standard.
1.13. Comparison with Related Systems Table 2.9 compares the oxidation of hydroquinone with a variety of aryl or alkyl hypervalent iodine reagents or catalysts. Iodosyl benzene has the lowest conversion at the highest temperature.102 This is largely due to its low solubility. Functionalizing the hypervalent iodine with acetate or trifluoroacetate leads to a significant improvement in yield under much milder conditions.103 These reagents are commercially available, but are used stoichiometrically and are not readily recovered, reoxidized and reused. Polymer-supported hypervalent iodine reagents have overcome this issue, allowing for ready recovery and reuse.104,105 Fluorinated alkyl chains appended either directly to the hypervalent I of the pendant to an aryl iodide have allowed for the ready recovery and reuse of these efficient reagents as a result of their ready partitioning into fluorinated solvents following the reaction.106,107 A recyclable form of an iodine catalyst was prepared by appending iodobenzene to magnetic nanoparticle support. Here yields of over 80% were reported for the oxidation of hydroquinone with efficient recovery of the catalyst through magnetic separation. 108 It should be noted that this system requires 2,2,2- trifluoroethanol as a solvent, and increasing reaction times with each recycle to maintain efficiency. The MOF-based systems reported here have the advantages
48 Texas Tech University, Babak Tahmouresilerd, August 2020 of being catalytic, being readily recovered by filtration or centrifugation, proceeding under mild conditions, and working in a variety of solvents.
Table 2.9. Comparison of alkyl and aryl iodide-based catalysts and reagents for the oxidation of hydroquinone. Catalyst/Reagent Loading Solvent Time Temp. Yield (min) (°C) (%) PhI=O102 2 eq. Acetone/DCE 10 90 61
103 PhI(OAc)2 1 eq. MeOH N/A RT 94
b, c, 106 ArI(OAc)2 1.2 eq. MeOH 120- RT 95 180 b, c, 107 RI(O2CCF3)2 1 eq. MeOH 10 RT >99 Polymer supported 1.3 eq. MeOH 240 RT 96 b PhI(OAc)2 Polymer supported 2 eq. MeOH 480 60 >99 b, 104 PhI(OAc)2
b Fe3O4 NPs 10 mol% CF3CH2OH/H2O 30 RT 81 supported iodoarene108 UiO-66 25%-Ia 20 mol% MeOH 2 50 92
a MIL-53 25%-I 20 mol% CH3NO2/H2O 60 50 70 a The synthesized catalysts in this work.
b Reagents can be recovered and reused
c Ar represents arene with fluorinated alkyl chains, R represents fluorinated alkyl chain
1.14. Conclusions Iodine is readily incorporated into ultra-stable MOFs by covalent modification of the linkers. The simple inclusion of the iodine element is not sufficient to guarantee a catalytically active site. Analysis of the structures reveals that there is insufficient room in the framework to accommodate reagents and oxidants. A multivariate approach was used to overcome this and allow for catalytic oxidation to occur within the MOF. The Al and Zr MOFs maintained their crystallinity over four recycles and only in the case where particle agglomeration was observed was there a notable loss in performance. XPS revealed that the oxidation states of the iodine sites were limited to +1 and +3. Future studies should augment the multivariate approach with a linker extension
49 Texas Tech University, Babak Tahmouresilerd, August 2020
approach to increase the space in the pores to allow for more challenging substrates to be targeted. Furthermore, a longer linker should allow for the inclusion of I species that are known to achieve the +5 oxidation state or diiodine species that can bridge.
1.15. Experimental Details 1.15.1. General Methods Aluminum chloride hexahydrate (99.0%, Acros Organics), zirconium
tetrachloride (98.0%, Merck KGaA), terephthalic acid (H2BDC, >99.0%, TCI), 2-
aminoterephthalic acid (H2BDC-NH2, 99.0%, Acros Organics), hydroquinone (>99.5%, Merck KGaA), 2,5-dibromohydroquinone (97%, Alfa Aesar), methylhydroquinone (>98.0%, TCI), 2,5-di-tert-butylhydroquinone (97%, Ark Pharm, Inc.), tert- butylhydroquinone (97%, Acros Organics), chlorohydroquinone (90%, Acros Organics), N,N-dimethylformamide (DMF, >99.9%, EMD Millipore), hydrochloric acid (36.5-38.0% BDH), dichloromethane (99.9%, Fisher Scientific), meta- chloroperoxybenzoic acid (70.0-75.0%, Acros Organics), hydrogen peroxide (30.0%, Fisher Scientific), potassium permanganate (>99.0%, J.T.Baker), sulfuric acid 96.0%,
J.T.Baker), dimethyl sulfoxide-d6 (DMSO-d6, >99.0%, Cambridge Isotope Laboratories), dimethyl sulfone (>99.0%, TCI), ethyl acetate (99.9%, Fisher Scientific), tert-butyl hydroperoxide (70.0% aq. sol., Alfa Aesar), ethanol (99.5%, Pharmco- AAPER), methanol (>99.9%, Fisher Scientific), acetonitrile (>99.9%, Fisher Scientific), urea hydrogen peroxide adduct (97.0%, Alfa Aesar), nitromethane (>98.0%, Alfa Aesar), deuterium oxide (>99.0%, Cambridge Isotope Laboratories), sodium
deuteroxide solution 40 wt. % in D2O (>99.0%, Acros Organics), potassium iodide (>99.0%, Fisher Scientific), acetone (>99.7%, Macron Fine Chemicals), sodium bisulfite (98.5%, Fisher Scientific) and sodium nitrite (>99.0%, J.T.Baker) were used as purchased without further purification.
50 Texas Tech University, Babak Tahmouresilerd, August 2020
1.15.2. Synthesis
1.15.2.1. Preparation of 2-iodoterephthalic Acid (H2BDC-I).
2-Iodoterephthalic acid was synthesized as previously reported using the Sandmeyer reaction (Figure 2.23).109
Figure 2.23. Preparation of 2-iodoterephthalic acid
1.15.2.2. Preparation of Dimethyl 2-iodobenzene-1,4-dicarboxylate
Dimethyl 2-iodobenzene-1,4-dicarboxylate was prepared through a Fischer esterification (Figure 2.23).110 2-Iodoterephthalic acid (1.50 g, 5.6 mmol) was combined
in methanol (10 mL) with good stirring. Concentrated H2SO4 (0.5 mL) was added dropwise, and the reaction mixture was refluxed with stirring overnight. Methanol was removed and the resulting material was dissolved in dichloromethane and washed with water. The aqueous phase was further extracted with water (2x). The organic phases
were combined and dried over MgSO4 before being taken to dryness to yield a light 1 brown crystalline solid (1.2 g, 67%). H NMR (CDCl3) δ3.95 (s, 3H), 3.96 (s, 3H), 7.81 (d, 1H), 8.05 (dd, 1H), 8.63 (d, 1H).
Figure 2.24. Preparation of dimethyl 2-iodobenzene-1,4-dicarboxylate
1.15.2.3. Synthesis of MTV-UiO-66 (Zr)
The MTV-UiO-66 (Zr) frameworks were synthesized via solvothermal methods 91 adapted from the literature preparation of UiO-66. ZrCl4 was added to DMF. The mixture of ligands was dissolved in DMF with a small amount of deionized water was
51 Texas Tech University, Babak Tahmouresilerd, August 2020 added to the first solution. Amounts are provided in Table 2.10. The reaction mixtures were heated at 100 °C for 3 days to yield the MTV-UiO-66 (0, 25, 50, 75, or 100%-I) MOFs. The solids were washed with hot DMF (x3) and soaked for 16 h in hot methanol (x1) before being heated at 150 °C for 16 hours under vacuum.
Table 2.10. Composition of the reaction mixtures in the synthesis of the MTV-UiO-66 (Zr) MTV-MOFs Reagents Amount (mmol) Yield (mg) a ZrCl4 H2BDC H2BDC-I H2O DMF UiO-66 0%-I 8.60 8.60 0.00 11.11 1420.71 310 UiO-66 25%-I 8.60 6.45 2.15 11.11 1420.71 380 UiO-66 50%-I 8.60 4.30 4.30 11.11 1420.71 400 UiO-66 75%-I 8.60 2.15 6.45 11.11 1420.71 390 UiO-66 100%-I 8.60 0.00 8.60 11.11 1420.71 430
a H2BDC: 1,4-benzene dicarboxylic acid
1.15.2.4. Synthesis of MTV-MIL-53 (Al) in Water.
Preparations of MTV-MIL-53 (0, 25, 50, 75, or 100%-I) MOFs were carried out under hydrothermal conditions in a 23 mL Teflon-lined stainless-steel autoclave using aluminum chloride hexahydrate, terephthalic acid, 2-iodoterephthalic acid, and deionized water (6.0 mL). The procedure was adapted from the reported procedure for preparing MIL-53 0%-I.90 The chloride salt was chosen as the nitrate salt used in the original procedure led to oxidation of the linker. The amounts that were used are reported in Table 2.11. The reaction was performed for three days at 220 °C. The as- synthesized MOF, MIL-53(as), was obtained after filtering and washing with deionized water. To empty the pores of residual materials, the as-synthesized MOF was washed with DMF (x3) and treated with hot methanol for 16 hours followed by heating at 320 °C for 3 days in the air.
52 Texas Tech University, Babak Tahmouresilerd, August 2020
Table 2.11. Composition of the reaction mixtures in the synthesis of the MTV-MIL-53 (Al) MTV-MOFs Reagents Amount (mmol) Yield AlCl3.6H2O H2-BDC H2BDC-I H2O (mg) MIL-53 0%-I 4.00 2.00 0.00 333 230 MIL-53 25%-I 4.00 3.00 1.00 333 230 MIL-53 50%-I 4.00 1.00 1.00 330 210 MIL-53 75%-I 4.00 1.00 3.00 330 350 MIL-53 100%-I 4.00 0.00 2.00 330 260
1.15.2.5. Synthesis of Multivariate MIL-53 25%-I (Al) with DMF.
Multivariate MIL-53 25%-I (DMF) was prepared under solvothermal conditions by adapting a previously reported synthesis of MIL-53.50 Aluminum chloride
hexahydrate (2.1 mmol, 0.51 g), I-H2BDC (0.51 g, 3.1 mmol), H2BDC (0.30 g, 1.0 mmol) was added to 30 mL DMF. The mixture was placed in a 100 mL Teflon-lined stainless-steel autoclave and heated for 72 h at 120 °C in an oven under static conditions. (Yield: 550 mg).
1.15.3. Single Crystal Growth Experiment Single crystals of MIL-53 100%-I was obtained by mixing 0.1207 g (0.5 mol)
AlCl3ꞏ6H2O and 0.1465 g (0.5 mol) 2-iodoterephthalic acid in a small vial placed in the
autoclave reactor containing 5 ml of ultrapure H2O. The reactor was sealed in a stainless-steel chamber and heated to 220 °C for 12 days. From the mixture a single phase of crystals (MIL-53 100%-I AS) could be observed, consistent with the PXRD. Single crystals were activated following the same procedure as used with the bulk powders. The crystals underwent a single crystal-to-single crystal transformation. Under inspection, two unique phases could be distinguished, one more prevalent than the other, MIL-53 100%-I Act Phase I and II, respectively.
1.15.4. Crystallography A unit cell collection was then carried out. After it was determined that the unit cell was not present in the CCDC database a sphere of data was collected. Omega scans were carried out with a 20 sec/frame exposure time for MIL-53 100%-I AS and α-MIL- 53 100%-I Act and 70 sec/frame for β-MIL-53 100%-I Act. All structures were collected
53 Texas Tech University, Babak Tahmouresilerd, August 2020 with a rotation of 0.50° per frame. After data collection, the crystal was measured for size, morphology, and color. These values are reported in Table 2.12.
54 Texas Tech University, Babak Tahmouresilerd, August 2020
Table 2.12. Single crystal information and refinement parameters at 100 K. Identification code MIL-53 100%-I AS α-MIL-53 100%-I Act β-MIL-53 100%-I Act Crystal Habit Block Block block Empirical formula C8H4.19AlI0.82O5 C8H4.36AlI0.64O5 C8H4.30AlI0.70O5.25 Formula weight 310.83 288.67 300.1 Crystal system Orthorhombic Orthorhombic Orthorhombic Space group Imma Imma Imma Unit cell dimensions a = 16.501(4) Å α = 90° a = 18.466(17) Å α = 90° a = 17.107(11) Å α = 90 °. b = 6.6194(18) Å β = 90° b = 6.635(5) Å β = 90° b = 6.622(4) Å β = 90 °. c = 13.210(4) Å γ = 90° c = 9.627(7) Å γ = 90° c = 12.229(8) Å γ = 90 °. Volume (Å3), Z 1442.9(7), 4 1179.5(16), 4 1385.2(16), 4 Calculated density (g/cm3) 1.431 1.626 1.439 Absorption coefficient (mm-1) 1.883 1.843 1.703 F(000) 594 557 557 Theta range for data collection 1.975 to 25.367° 2.206 to 25.500° 2.047 to 25.485° Limiting indices -19<=h<=19, -7<=k<=7, 15<=l<=15 -22<=h<=22,-8<=k<=7, 11<=l<=11 -20<=h<=20, -8<=k<=7, - 14<=l<=14 Reflections collected / unique 6080 / 754 [R(int) = 0.0558] 5570 / 619 [R(int) = 0.0974] 6789 / 730 [R(int) = 0.0878] Completeness to θ 25.242° (100%) 25.242° (100%) 25.242° (99.70%) Refinement method Full-matrix least-squares on F2 Full-matrix least-squares on F2 Full-matrix least-squares on F2 Data / restraints / parameters 754 / 61 / 80 619 / 60 / 66 730 / 51 / 75 Goodness-of-fit on F2 1.123 1.183 1.149 Final R indices [I>2sigma(I)] R1 = 0.1270, wR2 = 0.3491 R1 = 0.1352, wR2 = 0.3299 R1 = 0.1067, wR2 = 0.2786 R indices (all data) R1 = 0.1326, wR2 = 0.3533 R1 = 0.1448, wR2 = 0.3346 R1 = 0.1215, wR2 = 0.2903 Largest diff. peak and hole (e/Å3) 1.740 and -0.689 0.964 and -1.438 0.637 and -0.529
55 Texas Tech University, Babak Tahmouresilerd, August 2020
1.15.5. Characterization
1.15.5.1. Crystal Size Estimation
Crystallite size estimation was done using Match! software (Phase Identification from Powder Diffraction) version 3.4.2 based on Scherrer equation and Corundum
sample (Al2O3) as standard.
Equation 1. Scherrer equation to estimate crystallite sizes.
kλ 𝐷 β cosθ
Where Scherrer constant k=0.94, wavelength λ=1.5418740 A (Cu-Ka), β as the full width of the peak at half maximum (FWHM), and θ is the Bragg angle.
Table 2.13. Estimate crystallite sizes for MIL-53 25% (HT, and DMF) by Scherrer equation. MOFs Estimated Crystallite Size (nm)a MIL-53 25%-I (HT) ⁓70 MIL-53 25%-I (DMF) ⁓14 a The calculation was performed with Match! software (Phase Identification from Powder Diffraction) version 3.4.2 based on Scherrer equation and corundum sample (Al2O3) as standard.
1.15.5.2. NMR Digestions
NMR digestions were performed on the MTV-MOFs to establish the ratio that the different ligands were incorporated and to ensure that no ligand decomposition had taken place. When aluminum nitrate was used as the salt for MIL-53 synthesis the NMR spectrum of the digested MOF was inconsistent with the spectrum of 2-iodoterephthalic
acid. Digested MTV-UiO-66 was prepared by sonication 50 mg of in 500 μL (CD3)2SO
and 100 μL D2SO4. In the case of MTV-MIL-53, 50 mg of the material was digested
with 570 μL D2O and 200 μL of NaOD solution 40 wt. % in D2O by sonication. All the clear solutions were analyzed by 1H NMR. For all other MTV-MOFs, the anticipated ratio of ligands was observed (Figure 2.25 to Figure 2.34).
56 Texas Tech University, Babak Tahmouresilerd, August 2020
1 Figure 2.25. H NMR spectrum for digested MTV-UiO-66 0%-I in 500 μL (CD3)2SO and 100 μL D2SO4.
57 Texas Tech University, Babak Tahmouresilerd, August 2020
1 Figure 2.26. H NMR spectrum for digested MTV-UiO-66 25%-I in 500 μL (CD3)2SO and 100 μL D2SO4.
58 Texas Tech University, Babak Tahmouresilerd, August 2020
1 Figure 2.27. H NMR spectrum for digested MTV-UiO-66 50%-I in 500 μL (CD3)2SO and 100 μL D2SO4.
59 Texas Tech University, Babak Tahmouresilerd, August 2020
1 Figure 2.28. H NMR spectrum for digested MTV-UiO-66 75%-I in 500 μL (CD3)2SO and 100 μL D2SO4.
60 Texas Tech University, Babak Tahmouresilerd, August 2020
1 Figure 2.29. H NMR spectrum for digested MTV-UiO-66 100%-I in 500 μL (CD3)2SO and 100 μL D2SO4.
61 Texas Tech University, Babak Tahmouresilerd, August 2020
1 Figure 2.30. H NMR spectrum for digested MIL-53 0%-I in 570 μL D2O and 200 μL of NaOD solution 40 wt. % in D2O.
62 Texas Tech University, Babak Tahmouresilerd, August 2020
1 Figure 2.31. H NMR spectrum for digested MIL-53 25%-I in 570 μL D2O and 200 μL of NaOD solution 40 wt. % in D2O.
63 Texas Tech University, Babak Tahmouresilerd, August 2020
1 Figure 2.32. H NMR spectrum for digested MIL-53 50%-I in 570 μL D2O and 200 μL of NaOD solution 40 wt. % in D2O.
64 Texas Tech University, Babak Tahmouresilerd, August 2020
1 Figure 2.33. H NMR spectrum for digested MIL-53 75%-I in 570 μL D2O and 200 μL of NaOD solution 40 wt. % in D2O.
65 Texas Tech University, Babak Tahmouresilerd, August 2020
1 Figure 2.34. H NMR spectrum for digested MIL-53 100%-I in 570 μL D2O and 200 μL of NaOD solution 40 wt. % in D2O.
66 Texas Tech University, Babak Tahmouresilerd, August 2020
1.15.5.3. Nitrogen Adsorption
Nitrogen sorption measurements were performed at 77 K on a Quantichrome Autosorb iQ gas sorption analyzer. Approximately 50 mg of the MOFs were added to a preweighed 6 mm sample cell. All samples were activated under vacuum at 200 °C for 13 hours under vacuum. The sample weight was then collected to accurately depict the activated weight. The activated MOFs had weights of approximately 40 mg, which were used as the final weight of the material. Analysis time of 20 hours and 15 minutes. Brunauer-Emmett-Teller surface areas and pore volumes were calculated using the DFT method in the Quantachrome ASiQwin software. The NLDFT equilibrium (cylinder/slit) model was chosen for the pore volume measurements.
1.15.5.4. X-ray Photoelectron Spectroscopy (XPS)
The X-ray photoelectron spectroscopy (XPS) measurements were performed on a Physical Electronics PHI 5000 VersaProbe spectrometer (base pressure in the analysis chamber less than 1 × 10-7 Pa) using monochromatic Al Kα (hν = 1486.6 eV) X-ray source (25 W, 15 kV, 100 µm analysis spot size). The survey scans in the 0-1400 eV binding energy (BE) range were collected with a pass energy of 187.85 eV and a step of 0.8 eV. For the narrow energy scans, the pass energy was 23.5 eV with a step of 0.1 eV. To correct for sample charging, the BE of the spectra was referenced to the adventitious carbon C 1s BE at 284.8 eV.
67 Texas Tech University, Babak Tahmouresilerd, August 2020
Figure 2.35. XPS spectra of MTV-MIL-53 50%-I: (top) survey scan; (bottom right) C 1s; (bottom left) I 3d5.
Figure 2.36. XPS spectra of oxidized MTV-MIL-53 50%-I: (top) survey scan; (bottom right) C 1s; (bottom left) I 3d5.
68 Texas Tech University, Babak Tahmouresilerd, August 2020
Figure 2.37. XPS spectra of MTV-UiO-66 25%-I: (top) survey scan; (bottom right) C 1s; (bottom left) I 3d5.
Figure 2.38. XPS spectra of oxidized MTV-UiO-66 25%-I: (top) survey scan; (bottom right) C 1s; (bottom left) I 3d5.
69 Texas Tech University, Babak Tahmouresilerd, August 2020
1.15.6. Catalytic Experiments
1.15.6.1. Typical Catalytic Reaction Procedure
In a typical catalytic reaction, the catalyst (20 mol%), terminal oxidant (0.579 mmol, 0.0999), and substrate (0.145 mmol, 0.0160 g) were mixed in the specified solvent or solvent mixture (4.0 mL) in a 2-dram clear glass vial. The vial was charged with a Teflon coated stir bar placed on the hot plate when it was 50 °C. After the specified time had been reached, the catalyst was separated using centrifugation and the liquid was decanted and 3 drops taken. The collected sample was dissolved in the
DMSO-d6 to determine the catalytic conversion and yield via integration of the relevant peaks in the 1H NMR spectrum corresponding to the possible products as shown in Figure 2.39. All control reactions were done in the absence of MOF.
Figure 2.39. Observed products in the catalytic oxidation reaction of hydroquinone.
1.15.6.2. Experimental Procedure For Catalyst Optimization
0.3400 g (3.612 mmol) methylsulfonylmethane (MSM) as an internal standard and 0.3975 g (3.610 mmol) hydroquinone (HQ) as the substrate were dissolved in acetonitrile to a final volume of 25.0 mL. 1.0 mL was taken and added to a 2-dram clear glass vial using a 1.0 mL volumetric pipet. 0.0999 g (70-75%, ~0.419 mmol, ~2.9 equivalent) mCPBA as co–oxidant was dissolved in 3.0 mL ACN and added to the reaction mixture. The reaction mixture was stirred in a closed cap vial at 50 °C. After 60 minutes, the catalyst was separated by centrifugation and 3 drops of the reaction
mixture were dissolved in 0.5 mL of DMSO-d6 to determine the catalytic conversion and yield as summarized in Table 2.14, Table 2.15, and Table 2.16.
70 Texas Tech University, Babak Tahmouresilerd, August 2020
Table 2.14. Catalyst optimization for catalytic oxidation of hydroquinone (HQ) to benzoquinone (BQ) in the presence of 20 mol% MTV-UiO-66, ~2.9 equivalent of mCPBA, 4 mL acetonitrile (ACN) at 50 °C for 60 minutes. Total Normalized Normalized Normalized Normalized normalized Sample Time Solvent integrated Integrated integrated integrated integrated Yield Conversion (min) intensity intensity intensity intensity of intensity of (%) (%) of MSM of HQ of BQ products 3 and reactants 4 and products Control 60 ACN 1.00 0.95 0.04 0.00 0.99 4 5 UiO-66 0%-I 60 ACN 1.00 0.93 0.07 0.00 1.00 7 7 UiO-66 25%-I 60 ACN 1.00 0.51 0.48 0.00 0.99 48 49 UiO-66 50%-I 60 ACN 1.00 0.86 0.13 0.00 0.99 13 14 UiO-66 75%-I 60 ACN 1.00 0.84 0.15 0.00 0.99 15 16 UiO-66 60 ACN 1.00 0.95 0.04 0.00 0.99 4 5 100%-I Table 2.15. Catalyst optimization for catalytic oxidation of hydroquinone (HQ) to benzoquinone (BQ) in the presence of 20 mol% MTV-MIL-53, 2.9 equivalent of mCPBA, 4 mL acetonitrile (ACN) at 50 °C for 60 minutes. Total Normalized Normalized Normalized Normalized normalized Sample Time Solvent integrated integrated integrated integrated integrated Yield Conversion (min) intensity of intensity of intensity of intensity of intensity of (%) (%) MSM HQ BQ products 3 reactants and and 4 products Control 60 ACN 1.00 0.95 0.04 0.00 0.99 4 5 Mil-53 0%-I 60 ACN 1.00 0.97 0.03 0.00 0.99 3 3 Mil-53 25%-I 60 ACN 1.00 0.84 0.11 0.00 0.95 12 16 Mil-53 25%-I 60 ACN 1.00 0.83 0.17 0.00 1.00 17 17 (DMF) Mil-53 50%-I 60 ACN 1.00 0.91 0.08 0.00 0.99 8 9 Mil-53 75%-I 60 ACN 1.00 0.95 0.05 0.00 1.00 5 6 Mil-53 100%-I 60 ACN 1.00 0.94 0.05 0.00 0.99 5 6
71 Texas Tech University, Babak Tahmouresilerd, August 2020
Table 2.16. 2-Iodoterephthalate as a homogenous analogue of supporting iodine MOFs catalyst for catalytic oxidation of hydroquinone (HQ) to benzoquinone (BQ) in the presence of 20 mol% catalyst, 2.9 equivalent of mCPBA, 4 mL acetonitrile (ACN) at 50 °C for 60 minutes. Total Normalized Normalized Normalized Normalized normalized Sample Time Solvent integrated integrated integrated integrated integrated Yield Conversion (min) intensity of intensity of intensity of intensity of intensity of (%) (%) MSM HQ BQ products 3 reactants and 4 and products Control 60 ACN 1.00 0.95 0.04 0.00 0.99 4 5 2-Iodoterephthalate 60 ACN 1.00 0.02 0.88 0.06 0.96 97 98
72 Texas Tech University, Babak Tahmouresilerd, August 2020
1.15.6.3. Experimental Procedure for Solvent Variation for the Oxidation of Hydroquinone to Benzoquinone.
Experimental procedure for solvent variation was the same as the catalyst optimization. The solvent and time are summarized in Table 2.17, Table 2.18, Table 2.19, and Table 2.20.
Table 2.17. Solvent variation of MTV-UiO-66 25%-I for catalytic oxidation of hydroquinone (HQ) to benzoquinone (BQ) in the presence of 20 mol% catalyst, 2.9 equivalent of mCPBA, 4 mL specified solvent at 50 °C for 60 minutes. Sample Time Solvent Normalized Normalized Normalized Normalized Total Yield Conversion (min) integrated integrated integrated integrated normalized (%) (%) intensity of intensity of intensity of intensity of integrated MSM HQ BQ products 3 intensity of and 4 reactants and products Control 1.00 0.95 0.04 0.00 0.99 4 5 UiO-66 25%-I 60 ACN 1.00 0.50 0.48 0.00 0.98 48 49 Control 1.00 0.85 0.08 0.06 0.99 8 15 UiO-66 25%-I 60 NM 1.00 0.06 0.93 0.00 0.99 93 94 Control 1.00 0.97 0.03 0.00 1.00 3 3 UiO-66 25%-I 60 EA 1.00 0.37 0.63 0.00 1.00 63 63 Control 1.00 0.95 0.03 0.00 0.98 4 5 UiO-66 25%-I 60 Acetone 1.00 0.27 0.68 0.00 0.95 68 73 Control 1.00 0.86 0.10 0.00 0.96 11 15 UiO-66 25%-I 60 EtOH 1.00 0.01 0.97 0.00 0.98 98 98 Control 1.00 0.0 0.94 0.00 0.98 95 96 UiO-66 25%-I 60 MeOH 1.00 0.04 0.95 0.00 0.99 95 95
73 Texas Tech University, Babak Tahmouresilerd, August 2020
Table 2.18. Solvent variation of MTV-MIL-53 25%-I (DMF) for catalytic oxidation of hydroquinone (HQ) to benzoquinone (BQ) in the presence of 20 mol% catalyst, 2.9 equivalent of mCPBA, 4 mL specified solvent at 50 °C for 60 minutes. Sample Time Solvent Normalized Normalized Normalized Normalized Total Yield Conversion (min) integrated integrated integrated integrated normalized (%) (%) intensity of intensity of intensity of intensity of integrated MSM HQ BQ products 3 intensity of and 4 reactants and products Control 1.00 0.95 0.04 ⁓ 0.00 0.99 4 5 Mil-53 25%-I 60 ACN 1.00 0.83 0.17 ⁓ 0.00 1.00 17 17 Control 1.00 0.86 0.08 0.06 1.00 8 15 Mil-53 25%-I 60 NM 1.00 0.42 0.45 0.1 0.97 45 57 Control 1.00 0.97 0.03 ⁓ 0.00 1.00 3 3 Mil-53 25%-I 60 EA 1.00 0.75 0.25 ⁓ 0.00 1.00 25 25 Control 1.00 0.95 0.04 ⁓ 0.00 0.99 4 5 Mil-53 25%-I 60 Acetone 1.00 0.83 0.06 ⁓ 0.00 0.89 6 17 Control 1.00 0.86 0.11 ⁓ 0.00 0.97 11 15 Mil-53 25%-I 60 EtOH 1.00 0.77 0.12 ⁓ 0.00 0.89 12 23 Control 1.00 0.04 0.94 ⁓ 0.00 0.98 95 96 Mil-53 25%-I 60 MeOH 1.00 0.02 0.97 ⁓ 0.00 0.99 97 98
74 Texas Tech University, Babak Tahmouresilerd, August 2020
Table 2.19. Solvent variation of MTV-UiO-66 25%-I for catalytic oxidation of hydroquinone (HQ) to benzoquinone (BQ) in the presence of 20 mol% catalyst, 2.9 equivalent of mCPBA, 4 mL specified solvent at 50 °C for 2 minutes. Sample Time Solvent Normalized Normalized Normalized Normalized Total Yield Conversion (min) integrated integrated integrated integrated normalized (%) (%) intensity of intensity of intensity of intensity of integrated MSM HQ BQ products 3 intensity of and 4 reactants and products Control 1.00 0.95 0.04 0.00 0.99 4 5 UiO-66 25%-I 2 ACN 1.00 0.69 0.30 0.00 1.00 30 30 Control 1.00 0.93 0.06 0.00 0.99 6 7 UiO-66 25%-I 2 NM 1.00 0.06 0.77 0.15 0.98 77 94 Control 1.00 1.00 0.00 0.00 1.00 0 0 UiO-66 25%-I 2 EA 1.00 0.47 0.51 0.00 0.98 51 5 Control 1.00 0.99 0.00 0.00 0.99 0 1 UiO-66 25%-I 2 Acetone 1.00 0.34 0.66 0.00 1.00 66 66 Control 1.00 0.96 0.04 0.00 1.00 4 4 UiO-66 25%-I 2 EtOH 1.00 0.02 0.80 0.00 0.82 80 98 Control 1.00 0.89 0.11 0.00 1.00 11 11 UiO-66 25%-I 2 MeOH 1.00 0.07 0.92 0.00 0.99 92 93
75 Texas Tech University, Babak Tahmouresilerd, August 2020
Table 2.20. Solvent variation of MTV-MIL-53 25%-I (DMF) for catalytic oxidation of hydroquinone (HQ) to benzoquinone (BQ) in the presence of 20 mol% catalyst, 2.9 equivalent of mCPBA, 4 mL specified solvent at 50 °C for 2 minutes. Total Normalized Normalized Normalized Normalized normalized Sample Time Solvent integrated integrated integrated integrated integrated Yield Conversion (min) intensity of intensity of intensity of intensity of intensity of (%) (%) MSM HQ BQ products 3 reactants and 4 and products Control 1.00 0.95 0.04 0.00 0.99 4 5 Mil-53 25%-I 2 ACN 1.00 0.93 0.06 0.00 0.99 6 7 Control 1.00 0.93 0.06 0.00 0.99 6 7 Mil-53 25%-I 2 NM 1.00 0.71 0.23 0.04 0.98 24 28 Control 1.00 1.00 0.00 0.00 1.00 0 0 Mil-53 25%-I 2 EA 1.00 0.89 0.08 0.00 0.97 8 11 Control 1.00 0.99 0.00 0.00 0.99 0 1 Mil-53 25%-I 2 Acetone 1.00 0.97 0.03 0.00 1.00 3 3 Control 1.00 0.96 0.04 0.00 1.00 4 4 Mil-53 25%-I 2 EtOH 1.00 0.93 0.05 0.00 0.98 5 7 Control 1.00 0.89 0.11 0.00 1.00 11 11 Mil-53 25%-I 2 MeOH 1.00 0.56 0.42 0.00 0.98 42 44
1.15.6.4. Experimental Procedure for Temperature Variation for the Oxidation of Hydroquinone to Benzoquinone.
The experiment procedure for temperature variation was the same as described for the catalyst optimization at specified temperature and solvent in 60 minutes as shown in Table 2.21 and Table 2.21. Control reactions for temperature variation of oxidation of hydroquinone (HQ) to benzoquinone (BQ) in the presence of 2.9 equivalent of mCPBA at a specified temperature in 4 mL solvent for 60 minutes.
76 Texas Tech University, Babak Tahmouresilerd, August 2020
Table 2.22. Control reactions for temperature variation of oxidation of hydroquinone (HQ) to benzoquinone (BQ) in the presence of 2.9 equivalent of mCPBA at a specified temperature in 4 mL solvent for 60 minutes. Sample Temp. Time Normalized Total (°C) (min) Normalized Normalized Normalized integrated normalized Solvent integrated integrated integrated intensity of integrated Yield Conversion intensity of intensity of intensity of products 3 intensity of (%) (%) MSM HQ BQ and 4 reactants and products Control 0 60 ACN 1.00 0.99 0.00 0.00 0.99 0 1 24 60 ACN 1.00 0.97 0.02 0.00 0.99 2 3 50 60 ACN 1.00 0.95 0.04 0.00 0.99 4 5 75 60 ACN 1.00 0.72 0.13 0.12 0.97 13 28 75 60 Acetone 1.00 0.88 0.1 0.00 0.98 10 12 75 60 EA 1.00 0.70 0.27 0.00 0.97 27 29 75 60 NM 1.00 0.43 0.29 0.27 0.99 29 57 75 60 EtOH 1.00 0.15 0.82 0.00 0.97 82 85 75 60 MeOH 1.00 0.00 0.97 0.00 0.97 97 100
77 Texas Tech University, Babak Tahmouresilerd, August 2020
Table 2.23. Temperature variation of catalytic oxidation of hydroquinone (HQ) to benzoquinone (BQ) in the presence of 20 mol% MTV-MIL-53 25%-I (DMF), 2.9 equivalent of mCPBA at the specified temperature in 4 mL solvent for 60 minutes. Sample Temp. Solvent Normalized Normalized Normalized Normalized Total Yield Conversion (°C) integrated integrated integrated integrated normalized (%) (%) intensity of intensity of intensity of intensity of integrated MSM HQ BQ products 3 intensity of and 4 reactants and products Control 50 ACN 1.00 0.95 0.04 0.00 0.99 4 5 75 1.00 0.85 0.14 0.00 0.99 14 15 Mil-53 25%-I 50 1.00 0.83 0.17 0.00 1.00 17 17 75 1.00 0.53 0.44 0.00 0.97 44 47 Control 50 Acetone 1.00 0.95 0.04 0.00 0.99 4 5 75 1.00 0.88 0.1 0.00 0.98 10 12 Mil-53 25%-I 50 1.00 0.83 0.06 0.00 0.89 6 17 75 1.00 0.82 0.12 0.05 0.99 12 18 Control 50 EA 1.00 0.97 0.03 0.00 1.00 3 3 75 1.00 0.70 0.27 0.00 0.97 27 29 Mil-53 25%-I 50 1.00 0.75 0.25 0.00 1.00 25 25 75 1.00 0.69 0.14 0.16 0.99 14 31
78 Texas Tech University, Babak Tahmouresilerd, August 2020
1.15.6.5. Experimental Procedure for Terminal Oxidant Loading Variation for the Oxidation of Hydroquinone to Benzoquinone.
The experimental procedure for terminal oxidant loading variation was the same as described for the catalyst optimization but with 1.45, 2.9, and 4.4 equivalents of mCPBA at 50 °C for 60 minutes as shown in Error! Reference source not found..
Table 2.24. Terminal oxidant loading variation for catalytic oxidation of hydroquinone (HQ) to benzoquinone (BQ) in the presence of 20 mol% catalyst, specified equivalent of mCPBA in 4 mL nitromethane (NM) at 50 °C for 60 minutes. Sample mCPBA Normalized Normalized Normalized Normalized Total integrated integrated integrated integrated normalized intensity of intensity of intensity of intensity of integrated Yield Conversion MSM HQ BQ products 3 intensity of (%) (%) and 4 reactants and products Control 1.45 1.00 0.82 0.09 0.08 0.99 9 18 Mil-53 25%-I equiv. 1.00 0.7 0.27 0.03 1.00 27 30 (DMF) UiO-66 25%-I 1.00 0.03 0.82 0.10 0.95 83 97 Control 2.9 1.00 0.86 0.08 0.06 1.00 8 15 Mil-53 25%-I equiv. 1.00 0.42 0.45 0.1 0.97 45 57 (DMF) UiO-66 25%-I 1.00 0.06 0.93 0.00 0.99 93 94 Control 4.4 1.00 0.67 0.17 0.12 0.96 17 32 Mil-53 25%-I equiv. 1.00 0.47 0.40 0.09 0.96 40 52 (DMF) UiO-66 25%-I 1.00 0.03 0.89 0.06 0.98 89 97
79 Texas Tech University, Babak Tahmouresilerd, August 2020
1.15.6.6. Experimental Procedure for Variation of Terminal Oxidant for the Oxidation of Hydroquinone to Benzoquinone.
The experiment procedure for variation of terminal oxidant was the same as described for the catalyst optimization with
2.9 equivalent of mCPBA, 4 equivalent each of oxone, hydrogen peroxide (30 % (w/w) in H2O) (H2O2), tert-butyl hydroperoxide t (70 wt. % in H2O) ( BuOOH), and hydrogen peroxide-urea (Hyperol) in 4 mL nitromethane/ water (3:1 v:v) as the solvent at 50 °C for 60 minutes as shown in Table 2.25 and Table 2.26.
Table 2.25. Terminal oxidant variation for catalytic oxidation of hydroquinone (HQ) to benzoquinone (BQ) in the presence of 20 mol% MTV-UiO-66 25%-I, 2.9 equivalent of specified terminal oxidant in nitromethane/ water (3:1 v:v) at 50 °C for 60 minutes Sample Terminal Normalized Normalized Normalized Normalized Total normalized Yield Conversion oxidant integrated integrated integrated integrated integrated (%) (%) intensity of intensity of intensity of intensity of intensity of MSM HQ BQ products 3 and reactants and 4 products Control mCPBA 1.00 0.72 0.00 0.05 0.77 0 28 UiO-66 25%-I 1.00 0.23 0.74 0.00 0.97 75 76 Control oxone 1.00 0.84 0.00 0.06 0.90 0 15 UiO-66 25%-I 1.00 0.20 0.77 0.00 0.97 78 80
Control H2O2 1.00 0.94 0.00 0.05 0.99 0 6 UiO-66 25%-I 1.00 0.72 0.24 0.00 0.96 24 28 Control tBuOOH 1.00 0.92 0.00 0.05 0.97 0 8 UiO-66 25%-I 1.00 0.32 0.06 0.61 0.99 6 68 Control Hyperol 1.00 0.90 0.00 0.08 0.98 0 10 UiO-66 25%-I 1.00 0.75 0.09 0.15 0.99 9 25
80 Texas Tech University, Babak Tahmouresilerd, August 2020
Table 2.26. Terminal oxidant variation for catalytic oxidation of hydroquinone (HQ) to benzoquinone (BQ) in the presence of 20 mol% MTV-MIL-53 25%-I (DMF), 2.9 equivalent of specified terminal oxidant in nitromethane/ water (3:1 v:v) at 50 °C for 60 minutes Sample Terminal Normalized Normalized Normalized Normalized Total normalized Yield Conversion oxidant integrated integrated integrated integrated integrated (%) (%) intensity of intensity of intensity of intensity of intensity of MSM HQ BQ products 3 and reactants and 4 products Control mCPBA 1.00 0.72 0.00 0.05 0.77 0 28 Mil-53 25%-I 1.00 0.51 0.37 0.10 0.98 37 49 Control oxone 1.00 0.84 0.00 0.06 0.90 0 15 Mil-53 25%-I 1.00 0.14 0.70 0.16 1.00 70 86
Control H2O2 1.00 0.94 0.00 0.05 0.99 0 6 Mil-53 25%-I 1.00 0.82 0.00 0.03 0.85 0 18 Control tBuOOH 1.00 0.92 0.00 0.05 0.97 0 8 Mil-53 25%-I 1.00 0.90 0.00 0.07 0.97 0 10 Control Hyperol 1.00 0.90 0.00 0.08 0.98 0 10 Mil-53 25%-I 1.00 0.93 0.04 0.00 0.97 4 7
1.15.6.7. Experimental Procedure for Variation of the mol% of Catalyst for Oxidation of Hydroquinone to bBenzoquinone.
The experimental procedure for temperature variation was same as described for the catalyst optimization with different mol% of catalyst (20, 10, 5, and 1) and 4 equivalent oxone in nitromethane/water (3:1 v:v) at 50 °C for 60 minutes as shown in Table 2.27.
81 Texas Tech University, Babak Tahmouresilerd, August 2020
Table 2.27. Catalyst mol% variation for catalytic oxidation of hydroquinone (HQ) to benzoquinone (BQ) using 4 equivalent oxone in nitromethane/water (3:1 v:v) at 50 °C for 60 minutes. Sample Catalyst Normalized Normalized Normalized Normalized Total Yield Conversion (mol %) integrated integrated integrated integrated normalized (%) (%) based on I intensity of intensity of intensity of intensity of integrated MSM HQ BQ products 3 intensity of and 4 reactants and products Control 0 1.00 0.84 0.00 0.06 0.90 0 15 UiO-66 25%-I 20 1.00 0.20 0.78 0.00 0.98 78 80 10 1.00 0.16 0.77 0.06 0.99 77 83 5 1.00 0.33 0.51 0.15 0.99 51 67 1 1.00 0.51 0.31 0.16 0.98 31 49 Mil-53 25%-I 20 1.00 0.14 0.70 0.16 1.00 70 86 (DMF) 10 1.00 0.34 0.46 0.19 0.99 45 66 5 1.00 0.55 0.34 0.11 1.00 34 45 1 1.00 0.64 0.23 0.12 0.99 23 36
1.15.6.8. Experimental Procedure for Recyclability Test of Multivariate MOFs.
The recyclability tests for MTV-UiO-66 25%-I and MTV-MIL-53 25%-I were the same as described for the catalyst optimization with ~2.9 equivalent of mCPBA in 4 mL nitromethane (NM) at 50 °C for 60 minutes as shown in Table 2.28. After each run, the catalyst was separated using centrifugation and the liquid was decanted and 3 drops of liquid were dissolved in 0.5
mL DMSO-d6 to determine the catalytic conversion and yield of catalytic conversion of hydroquinone (HQ) to benzoquinone (BQ). The leftover catalyst was washed three times with nitromethane and acetone. To the dried catalyst were added prepared
82 Texas Tech University, Babak Tahmouresilerd, August 2020
1.00 mL of prepared solution of (MSM:HQ) as described before, 2.9 equivalent of mCPBA, and 4 mL nitromethane (NM). The closed cap 2-dram clear glass vial was placed on the hot plate when the temperature was 50 °C for 60 minutes.
Table 2.28. The recyclability test for catalysts with 2.9 equivalent of mCPBA in 4 mL nitromethane at 50 °C for 60 minutes. Sample Run Normalized Normalized Normalized Normalized Total Yield Conversion integrated integrated integrated integrated normalized (%) (%) intensity of intensity of intensity of intensity of integrated MSM HQ BQ products 3 intensity of and 4 reactants and products Control - 1.00 0.86 0.08 0.06 1.00 8 15 1st 1.00 0.06 0.93 0.00 0.99 93 94 2nd 1.00 0.52 0.43 0.03 0.98 43 48 UiO-66 25%-I 3rd 1.00 0.71 0.26 0.03 1.00 26 29 4th 1.00 0.7 0.26 0.04 1.00 26 30 1st 1.00 0.42 0.45 0.1 0.97 45 57 Mil-53 25%-I 2nd 1.00 0.54 0.43 0.03 1.00 43 46 (DMF) 3rd 1.00 0.52 0.43 0.03 0.98 43 47 4th 1.00 0.52 0.41 0.03 0.96 41 47
83 Texas Tech University, Babak Tahmouresilerd, August 2020
1.15.7. Split Test for Multivariate MOFs. In order to study of any possible leaching of incorporated linkers in the multivariate MOFs during catalytic oxidation reaction of hydroquinone to benzoquinone split test was done with 1 equivalent methylsulfonylmethane (MSM) as internal standard, 1 equivalent hydroquinone (HQ) as substrate, ~2.9 equivalent mCPBA as terminal oxidant in 4 mL acetonitrile. The split test for MTV-UiO-66 25%-I and MTV-MIL-53 25%-I was done at 50 °C and 75 °C, respectively. For each catalyst, two reactions were running under the same condition simultaneously. For MTV-UiO-66 25%-I, after 2 minutes one of the reactions was interrupted and the catalyst was separated using centrifugation. The hot filtrate was immediately transferred to another vial and the reaction was then allowed to continue under the same conditions. In the case of MTV-MIL-53 25%-I, after 30 minutes one of the reactions was interrupted and the catalyst was separated using centrifugation. Hot filtrate immediately was transferred to another vial and reaction was then allowed to continue under the same conditions. After 60 minutes no significant yield and conversion change was observed after filtration. The observed catalytic yields and conversions were summarized in Table 2.28 and 2.29.
84 Texas Tech University, Babak Tahmouresilerd, August 2020
Table 2.29. Split test of MTV-UiO-66 25%-I with 2.9 equivalent of mCPBA in 4 mL acetonitrile (ACN) at 50 °C.
Sample Time Temp. Normalized Normalized Normalized Total Yield Conversion (min) (°C) integrated integrated integrated Normalized normalized (%) (%) intensity of intensity of intensity of integrated integrated MSM HQ BQ intensity of intensity of products 3 reactants and 4 and products Control 2 50 1.00 0.95 0.04 0.00 0.99 4 5 60 1.00 0.95 0.04 0.00 0.99 4 5 UiO-66 25%-I 2 1.00 0.67 0.30 0.00 0.97 30 30 Filtration was 60 1.00 0.66 0.33 0.00 0.99 33 34 done after 2 min UiO-66 25%-I 60 1.00 0.51 0.48 0.00 0.99 48 49
85 Texas Tech University, Babak Tahmouresilerd, August 2020
Table 2.30. Split test of MTV-MIL-53 25%-I (DMF), 2.9 equivalent of mCPBA in 4 mL acetonitrile (ACN). Total Normalized Normalized Normalized Normalized normalized Sample Time Temp. integrated integrated integrated integrated integrated Yield Conversion (min) (°C) intensity of intensity of intensity of intensity of intensity of (%) (%) MSM HQ BQ products 3 reactants and and 4 products 10 1.00 0.93 0.07 0.00 1.00 7 7 Control 30 1.00 0.80 0.09 0.10 0.99 9 20
60 1.00 0.72 0.13 0.12 0.97 13 28 75 MIL-53 25%-I 10 1.00 0.84 0.16 0.00 1.00 16 16 30 1.00 0.74 0.22 0.01 0.97 22 26 Filtration was done 60 1.00 0.75 0.24 0.00 0.99 24 25 after 30 minutes MIL-53 25%-I 60 1.00 0.53 0.44 0.00 0.97 44 47
86 Texas Tech University, Babak Tahmouresilerd, August 2020
Table 2.31. Catalytic oxidation of hydroquinone derivatives in the presence of 20 mol% MTV-UiO-66 25%-I and MTV-MIL- 53 25%-I (DMF) as catalysts, 2.9 equivalent of mCPBA, 4 mL nitromethane for 60 minutes. Substrate Sample Temp. Normalized Normalized Normalized Normalized Total Yield Conversion (°C) integrated integrated integrated integrated normalized (%) (%) intensity of intensity of intensity of intensity of integrated MSM substrate desired byproducts intensity of product reactants and products 2,5- Control 50 1.00 0.94 0.05 0.00 0.99 5 6 dibromohydroquinone UiO-66 25%-I 1.00 0.2 0.72 0.00 0.92 72 80 MIL-53 25%-I 1.00 0.83 0.15 0.00 0.98 15 16 2-chlorohydroquinone Control 50 1.00 0.75 0.24 0.00 0.99 24 25 UiO-66 25%-I 1.00 0.35 0.64 0.00 0.99 64 65 MIL-53 25%-I 1.00 0.54 0.44 0.00 0.98 44 46 2,5-di-tert- Control 24 1.00 0.58 0.41 0.00 0.99 41 42 butylhydroquinone UiO-66 25%-I 1.00 0.04 0.95 0.00 0.99 95 95 MIL-53 25%-I 1.00 0.56 0.43 0.00 0.99 43 44 UiO-66 25%-I 1.00 0.58 0.41 0.00 0.99 42 42 tert-butylhydroquinone Control 24 1.00 0.68 0.3 0.00 0.98 31 32 UiO-66 25%-I 1.00 0.35 0.62 0.00 0.97 62 65 MIL-53 25%-I 1.00 0.65 0.34 0.00 0.99 34 35 methylhydroquinone Control 24 1.00 0.69 0.3 0.00 0.99 29 31 UiO-66 25%-I 1.00 0.4 0.57 0.00 0.97 57 59 MIL-53 25%-I 1.00 0.7 0.29 0.00 0.99 36 37
87 Texas Tech University, Babak Tahmouresilerd, August 2020
1.15.8. Computational Details and Results Analytical frequencies calculations were performed on optimized structures to provide an estimate of the C−I stretching frequency. (Table 2.32)
Table 2.32. DFT calculated C−I stretching frequencies
-1 Molecule vC–I (cm ) iodobenzene 260 Me2IBDC 205
Estimates of XPS chemical shift differences were determined by comparing orbital energies of the occupied core orbitals in the optimized geometries. (Table 2.33)
Table 2.33. DFT calculated core orbital energies (eV).
III I Molecule I 3d5/2 ∆E(I −I ) iodobenzene −606.26 - Me2IBDC −606.40 - ((AcO)2I)C6H5 −608.45 −2.19 ((OH)2I)C6H5 −608.12 −1.86
88 Texas Tech University, Babak Tahmouresilerd, August 2020
1.15.9. DFT Minimized Cartesian Coordinates
Table 2.34. Cartesian coordinates for IC6H5 (iodobenzene). Atom x y z C 1.356910 0.094285 0.022542 C 0.638252 1.280953 -0.135223 C -0.755935 1.264496 -0.167923 C -1.435853 0.053202 -0.042126 C -0.730950 -1.141580 0.116265 C 0.662593 -1.108466 0.147292 I 1.741234 -2.912021 0.387440 H 2.444080 0.109757 0.048180 H 1.178717 2.221439 -0.233207 H -1.311100 2.192728 -0.291006 H -2.524510 0.030013 -0.066316 H -1.263435 -2.084803 0.214081
89 Texas Tech University, Babak Tahmouresilerd, August 2020
Table 2.35 Cartesian coordinates for H2IBDC. Atom x y z C 1.380518 0.072682 -0.005548 C 0.537541 1.190904 -0.155305 C -0.842778 1.085755 -0.141814 C -1.429722 -0.173711 0.027881 C -0.615953 -1.299067 0.175213 C 0.775605 -1.191205 0.158879 I 1.771151 -3.051995 0.363481 H 1.024122 2.155553 -0.282981 H -1.465805 1.968153 -0.259759 H -1.096696 -2.265708 0.304305 C 2.842988 0.414323 -0.044376 O 3.256417 1.532379 -0.295094 C -2.907333 -0.382920 0.066016 O -3.449053 -1.437375 0.336312 O 3.653179 -0.626319 0.225621 C 5.063517 -0.326938 0.191240 H 5.563655 -1.268665 0.427375 H 5.352965 0.031036 -0.802661 H 5.307777 0.441895 0.932202 O -3.585238 0.748451 -0.252817 C -5.020515 0.612711 -0.241719 H -5.408994 1.595905 -0.515769 H -5.337793 -0.146138 -0.965473 H -5.369554 0.320297 0.754788
90 Texas Tech University, Babak Tahmouresilerd, August 2020
Table 2.36. Cartesian coordinates for ((AcO)2I)C6H5 ((diacetoxyiodo)benzene). Atom x y z C -1.672781 1.323538 -1.956854 C -2.276920 2.405516 -2.599603 C -2.211356 3.681545 -2.040067 C -1.543675 3.881741 -0.831841 C -0.941498 2.807711 -0.174129 C -1.015271 1.543684 -0.750692 I -0.095348 -0.106538 0.244988 H -1.728338 0.327108 -2.388637 H -2.796904 2.245260 -3.542749 H -2.682096 4.522408 -2.546745 H -1.490801 4.876408 -0.391983 H -0.415713 2.963043 0.764890 O 1.702543 1.205621 0.025149 O -2.188692 -0.888987 0.146652 C 2.664168 0.495719 0.568248 C -2.102651 -2.058618 0.736209 C 4.020412 1.164324 0.551960 H 4.755062 0.523079 1.043479 H 3.965221 2.133637 1.060555 H 4.324348 1.355937 -0.483790 C -3.397812 -2.838501 0.777892 H -3.336299 -3.614070 1.544999 H -3.551861 -3.317225 -0.197656 H -4.248022 -2.174800 0.962345 O -1.043980 -2.497472 1.200549 O 2.475858 -0.627470 1.049846
91 Texas Tech University, Babak Tahmouresilerd, August 2020
Table 2.37. Cartesian coordinates for ((HO)2I)C6H5 ((dihydroxyiodo)benzene). Atom x y z I 2.402409 6.767402 1.008879 O 0.843189 8.172527 0.812741 O 3.908231 5.305128 1.205556 H 4.034000 5.156449 2.157667 C 1.361906 3.874773 0.939743 C 0.923766 5.187810 1.015880 C 0.398336 2.862124 0.941243 H 0.718374 1.823181 0.874970 C -1.361854 4.510190 1.102298 H -2.419418 4.761165 1.171539 C -0.415079 5.538531 1.095838 C -0.958190 3.177119 1.023704 H -1.702277 2.382097 1.026757 H 0.680311 8.282037 -0.139051 H -0.701187 6.588004 1.152612 H 2.427734 3.658272 0.879705
92 Texas Tech University, Babak Tahmouresilerd, August 2020
Chapter III
3. MOF as Support for Iodine Catalyst: Isoreticular Expansion This chapter is an adapted version of “The impact of an isoreticular expansion strategy on the performance of iodine catalysts supported in multivariate zirconium and aluminum metal-organic frameworks B. Tahmouresilerd, M. Moody, L. Agogo and A. F. Cozzolino, Dalton Trans., 2019, 48, 6445–6454, https://doi-org.lib- e2.lib.ttu.edu/10.1039/C9DT00368A” with permission from The Royal Society of Chemistry. In this chapter, the impact of an isoreticular strategy in combination with a multivariate strategy on the catalytic performance of MOF is discussed.
1.16. Strategy to Open the Pore of MOF for Efficient Reagents Diffusion One useful strategy for translating successful homogeneous catalysts into MOFs is to incorporate them into the organic linkers.111–114 Reticular design strategies allow these linkers to be installed in known crystal topologies, either uniformly, or mixed with a linker of the same length to give a multivariate MOF. One of the important considerations in the choice of linker and topology is framework stability. To this end, MOFs with enhanced chemical and thermal stability are being developed.115–117 Another critical consideration is pore and pore-aperture size. This affects the ability of substrates to diffuse through the pores and reach the catalytic site. It can also constrain the catalyst which can presumably influence the stability of transition states. To address the pore and aperture size concerns, a key strategy that has emerged is to increase the pore size by increasing the length of the organic linkers, the so-called isoreticular expansion strategy.33,92,118–120 Limitations of this strategy include increased fragility of the framework and also the possibility of an interpenetrated structure. Considering that modification of a linker to include a catalytically active site usually increases the radius of the linker, and therefore decreases accessible pore volumes, an alternative strategy is to prepare multivariate MOFs where only one
93 Texas Tech University, Babak Tahmouresilerd, August 2020 linker per pore (or less) contains the catalyst, thereby reducing the occupied space.121,122
Hypervalent iodine has found use as an oxidant in many chemical transformations, including as facile and green reagents in organic synthesis.123–125 Some iodine-mediated transformation can be performed catalytically with appropriate terminal oxidants.126–129 We have recently reported a recyclable iodine catalyst supported in a metal-organic framework catalyst that was competent for the oxidation of hydroquinones.66 A multivariate approach was used to maximize pore and aperture size in order to accommodate reagents and oxidants in the pores of the framework and allow for catalytic oxidation to occur within the MOF. Frameworks, where 25% of the linkers contained the catalysts, showed an ideal balance between catalyst loading catalyst accessibility. There were, however, some limitations in the catalytic performance of MOFs with respect to the yields of the reaction, the scope of substrates, the size of the substrate, and the recyclability of the catalysts. Herein we study the impact of a combination of multivariate and isoreticular expansion strategies on the catalytic performance iodine supported in larger zirconium and aluminum-based MOFs (Figure 3.1). We highlight an often-overlooked consideration with the isoreticular expansion strategy – namely that the lengthening of the linker can have unintended consequences with regards to the electronic structure of the catalyst itself.
94 Texas Tech University, Babak Tahmouresilerd, August 2020
Figure 3.1. The depiction of DUT-5 (Al) (left)130, and the octahedral pore in UiO-67 (Zr) (right).131 Metal coordination spheres are represented with polyhedra. Hydrogen atoms have been removed for clarity. The yellow sphere shows the pore of the framework.
1.17. Preparation and Characterization of Iodine Containing Frameworks Iodine-containing MOFs with larger accessible inner volumes were prepared using a combination of multivariate and isoreticular expansion strategies. The iodine-containing linker (H2IBPDC) was prepared by adapting reported literature procedures as shown in Figure 3.2.132–134
COOMe COOMe COOMe COOMe COOH
i) ii) iii) iv) NO2 NH2 I I
COOMe COOMe COOMe COOMe COOH
Figure 3.2. Preparation of H2IBPDC. Conditions and reagents: i) HNO3, H2SO4, 0-4 °C, 132 134 132 5 h, ii) MeOH, HCl, Sn, 80 °C, iii) NaNO2, HCl, 0-4 °C, NaI, 22 °C, iv) KOH, THF, reflux.134
A 3:1 ratio of H2BPDC:H2IBPDC was used in the synthesis of the MOFs to allow for a balance between high internal volume and a high number of catalytic sites, consistent with the values identified as ideal for the smaller MOFs.66 The MOFs were prepared by treating the appropriate mixture of linkers with zirconium (IV) chloride or aluminum chloride hexahydrate; an adaption of
95 Texas Tech University, Babak Tahmouresilerd, August 2020 literature conditions for the parent frameworks. This yielded the multivariate UiO-67 X%-I or DUT-5 X%-I where X represents the percentage of linkers that are functionalized with I.130,135–137
Powder X-ray diffraction (PXRD) analyses were performed upon isolation of the frameworks and also following activation of the frameworks. The patterns were compared with simulated patterns from the crystal structures of the parent MOFs to verify that the anticipated framework was formed and retained. All the PXRD patterns for UiO-67 25%-I and DUT-5 25%-I are in the good agreement those of UiO-67 and DUT-5 (Figure 3.3).130,131
96 Texas Tech University, Babak Tahmouresilerd, August 2020
Figure 3.3. PXRD patterns of activated DUT-5 25%-I, DUT-5 0%-I, and simulated DUT-5 0%-I130 (top), and UiO-67 25%-I, UiO-67 0%-I and simulated UiO-67 0%-I (bottom).131 Thermogravimetric analysis (TGA) was used to establish the thermal stability and the temperature limits for activation and reactions. Both frameworks demonstrate good stability up to 400 °C (Figure 3.4). These values are slightly lower than the values reported for UiO-67 0%-I136 (500 °C) and DUT-5 0%-I130 (430 °C). It has been previously demonstrated that multivariate DUT-5 frameworks show a decrease in stability with increasing functionalization.135
97 Texas Tech University, Babak Tahmouresilerd, August 2020
These iodo-functionalized frameworks show roughly the same stability as the smaller analogs.66 TGA analysis for both UiO-67 25%-I and DUT-5 25%-I after activation revealed three distinguishable profiles of weight loss. The first profile of 1% weight loss (A→B, 50-100 °C) and the second profile of additional 6% and 3% weight loss (100–400 °C) for UiO-67 25%-I and DUT-5 25%-I can be assigned to the loss of some partial water which is trapped in the framework. The third profile with a weight loss of 60% and 78% for UiO-67 25%-I and DUT-5 25%-I can be assigned to the thermal decomposition of the frameworks and the formation of the appropriate metal oxide, ZrO2, and Al2O3, respectively.
Figure 3.4. TGA of activated UiO-67 25%-I (yellow) and DUT-5 25%-I (red) at a ramp rate of 10 °C min-1 under a flow of air. ATR-FTIR spectroscopy was performed on both UiO-67 25%-I and DUT- 5 25%-I to verify the absence of impurities in the pores of the activated frameworks. In particular, DMF from the synthesis or excess neutral linker could be present. Excess unreacted ligands could leach during catalytic experiments and perform catalysis homogeneously. The spectra of the activated MOFs revealed that the bands attributed to impurities in the as-synthesized frameworks are absent, consistent with full activation of the materials (Figure 3.5). The spectrum for DUT-5 25%-I shows vibrational bands in the typical region for symmetric and
98 Texas Tech University, Babak Tahmouresilerd, August 2020 asymmetric stretching modes (1421 cm-1 and 1595 cm-1, respectively) of the bridging carboxylate groups which is in good agreement with the synthesized DUT-5 0%-I reported in the literature.130 Similarly, the bands at 1404 and 1593 cm‐1 in UiO-67 25%-I can be assigned to the symmetric and asymmetric stretching modes of the carboxylate; an excellent match with the reported bands values for UiO-67 0%-I.53
The nitrogen adsorption-desorption measurements for activated UiO-67 25%-I and DUT-5 25%-I were conducted to establish the specific surface areas, pore size distributions, and pore volumes. Analysis of the isotherms reveals a type I isotherm for both UiO-67 25%-I and DUT-5 25%-I confirming the expected microporosity with narrow pore size distributions (Figure 3.6). The calculated 2 surface area and pore volume for UiO-67 25%-I (SBET = 1795 m /g, Vmicro = 0.877 2 mL/g) and DUT-5 25%-I (SBET = 1120 m /g, Vmicro = 0.550 mL/g) are in a good agreement with the values reported in the literature (Table 3.1).130,135–137 Nitrogen sorption for DUT-5 25%-I shows a lower surface area and pore volume than the literature value for the framework without the iodo-functionalized linker, consistent with the large iodine occupying space in the pores. The multivariate strategy prevents the large iodine from occupying a significant fraction of the pore, in line with other functionalized DUT-5 analogues. Importantly, the surface area and micropore volume for both MOFs are significantly higher than the previously reported catalysts UiO-66 25%-I and MIL-53 25%-I which should allow for more efficient diffusion of molecules within the framework. The pore size distribution analysis for UiO-67 25%-I showed two different pore sizes with diameters 1.02 nm and 1.96 nm, assigned to the tetrahedral and octahedral pores, respectively. The pore size distribution for DUT-5 25%-I indicated a major pore with a width of 1.02 nm.
99 Texas Tech University, Babak Tahmouresilerd, August 2020
Figure 3.5. Di-ATR FTIR of as-synthesized and activated UiO-67 25%-I (top) and DUT-5 25%-I (middle), and linkers (bottom). All spectra plotted as attenuation.
100 Texas Tech University, Babak Tahmouresilerd, August 2020
Table 3.1. Molar Brunauer-Emmett-Teller (BET) surface areas and pore volumes for the UiO-67 (Zr) and DUT-5 (Al) obtained from nitrogen adsorption isotherms at 77 K. BET surface Pore volume MOF area (×103 (mL/mol) Source m2ꞏmol-1)a UiO-67 0%-I 771 469 138 UiO-67 25%-I 690 334 This work UiO-67 100%-I 171 113 This work DUT-5 0%-I 567 193 130 DUT-5 25%-I 354 174 This work DUT-5 100%-I 317 153 This work
Based on the idealized formula [Zr6O4(OH)4(L)6] for UiO-67 and [Al4(OH)4(L)4] for DUT-5, normalized to one Zr or Al, respectively.
101 Texas Tech University, Babak Tahmouresilerd, August 2020
Figure 3.6. Nitrogen sorption isotherm (filled triangles or circles absorption, open triangles or circles desorption) of UiO-67 25 and 100%-I (top) and DUT-5 25 and 100%- I (bottom) (77 K). It is conceivable that the material is a mixture of two pure-phase MOFs containing either 0% IBPDC2- or 100% IBPDC2-. To ensure the even distribution of iodo-functionalized linker in the frameworks, energy-dispersive X-ray spectroscopy (EDS) analyses were performed.
102 Texas Tech University, Babak Tahmouresilerd, August 2020
Figure 3.7. Top, a) EDS spectrum of UiO-67 25%-I, b) SEM image, and c, d) EDS– mapping results for Zr and I over UiO-67 25%-I particles coated with Au/Pd after activation, bottom, a) EDS spectrum of DUT-5 25%-I, b) SEM image, and c, d) EDS– mapping results for Zr and I over DUT-5 25%-I particles coated with Au/Pd after activation.
103 Texas Tech University, Babak Tahmouresilerd, August 2020
EDS–mapping results for activated UiO-67 25%-I and DUT-5 25%-I particles coated with Au/Pd confirm that the iodo-functionalized linker is consistently distributed throughout both frameworks (Figure 3.7).
The ratio of the iodo-functionalized linker to unsubstituted linker was verified through NMR analysis of the digested frameworks. For both frameworks, the anticipated ratio of linkers, based on reaction stoichiometry, was approximately observed (28%-I in UiO-67 25%-I and 30% for DUT-5 25%-I).
1.18. Catalytic Evaluation The catalytic oxidation of hydroquinone to benzoquinone (Figure 3.8) was chosen as a model reaction to evaluate the performance of these larger frameworks. Catalysis was performed in nitromethane with 2.9 eq. mCPBA as terminal oxidant, 20 mol% I catalyst, 60 min, and 50 °C. mCPBA was chosen as it is well-established as a suitable terminal oxidant for catalytic oxidations with iodine.139,140
104 Texas Tech University, Babak Tahmouresilerd, August 2020
Figure 3.8. The oxidation of aromatic diols shown with typical catalytic conditions. MOFs with 0% (the same number of moles of MOF were used as with 25%-I), 25%, and 100% iodine functionalized ligands were tested against these conditions. Almost no difference was observed (Table 3.2, entry 1) in the yield of the reaction from the two control conditions (no MOF and MOF with no I), indicating that the framework itself is inactive and that iodine is necessary for catalysis to occur. UiO-67 25%-I and DUT-5 25%-I were the most competent catalysts for the oxidation of hydroquinone to benzoquinone with 75% and 73% yield (entry 1), respectively, beyond the background reaction without MOF (8%). Consistent with expectation, MOFs with 100% I functionalized linker performed worse than those with 25% iodine functionalized linker. This behaviour aligns with the smaller pore volumes in the MOFs with higher iodine loading (Table 3.1). Notably, this effect is not as dramatic as it was with the smaller MOFs, UiO-66 and MiL-53.66 Similarly higher yields were observed in acetonitrile for the MOFs with 25% iodine-containing linker. With the much larger substrate, 2,5-di-tert- butylhydroquinone, higher yields were again observed in the frameworks with
105 Texas Tech University, Babak Tahmouresilerd, August 2020 less iodine per pore. Due to the superior performance, UiO-67 25%-I and DUT- 5 25%-I were used for subsequent reactions. A split test was performed with both iodo-functionalized MOFs to verify that catalysis occurs heterogeneously, rather than as a result of catalyst leaching. After the separation of catalyst from the reaction mixture, no additional conversion was observed, confirming heterogeneous catalysis.
106 Texas Tech University, Babak Tahmouresilerd, August 2020
Table 3.2. The yield of catalytic oxidation of hydroquinone and catechol derivatives with iodo-functionalized MOFs.a # Product Temp. Yield (%)a, b (°C) DUT-5 25%-I UiO-67 25%-I Backgroundd 1 24 19 (22) 33 (36) 3 50 0 (8)c 0 (8)c 8 50 73 (81) 75 (83) 8 2 24 21 (50) 25 (54) 29
3 24 8 (39) 11 (42) 31
4 24 29 (70) 24 (65) 41
5 50 72 (96) 52 (76) 24
6 50 85 (92) 73 (80) 7
7 50 90 (97) 79 (86) 7
8 50 89 (94) 77 (82) 5
9 24 13 (13) 48 (48) 0 50 42 (42) 56 (56) 0 10 24 26 (47) 41 (62) 21
11 24 58 (63) 85 (90) 5
12 24 29 (79) 27 (77) 50
a Values were determined by 1H NMR using methylsulfonylmethane (MSM) as an internal standard.
b The yield of reaction beyond the background reaction is provided, the total yield is in parentheses.
c Performed with UiO-67 0%-I or DUT-5 0%-I.
d Direct oxidation of substrate with mCPBA The effect of catalyst loading (5, 10, and 20 mol%) on the oxidation of hydroquinone under the conditions listed in Error! Reference source not found. was studied. The yield of reaction for UiO-67 25%-I (75%) showed no
107 Texas Tech University, Babak Tahmouresilerd, August 2020 change when catalyst loading was reduced from 20% to 10 mol%. Further reduction in catalyst loading to 5 mol% reduced the yield to 50%. With DUT-5 25%-I the yield of reaction decreased (73, 50, and 25) with the catalyst loading (20, 10, and 5 mol%, respectively) as depicted in Figure 3.9. A catalyst loading of 20 mol% was used for all subsequent reactions.
Figure 3.9. The effect of different catalyst loading (5, 10, and 20 mol%) on the yield of quinone for UiO-67 25%-I and DUT-5 25%-I. Shaded areas show the extent of background reaction, TONs beyond background presented at the top of each column. In the case of UiO-67 25%-I, a yield of 33% and 75% for the oxidation of hydroquinone at 24 °C and 50 °C, respectively, was observed. These values are roughly the same as the yields obtained with UiO-66 25%-I under similar conditions. Due to the larger pore size in UiO-67 25%-I, an increase in the yield of the reaction was expected; however, a slight decrease in yield for the catalytic oxidation of hydroquinone was observed. To rationalize this behaviour, the effect of the linker elongation strategy on the catalytic site itself was evaluated. The oxidation potential of both linkers (BDC2- and BPDC2-) was evaluated homogeneously using the methyl esters of the two linkers, Me2IBPDC and
Me2IBDC, as model systems. Cyclic voltammetry revealed that the shorter linker is more readily oxidized by 0.2 V (Figure 3.10).
108 Texas Tech University, Babak Tahmouresilerd, August 2020
Figure 3.10. Cyclic Voltammogram (CV) of dimethyl 2-iodoterephthalate and dimethyl 2-iodo-[1,1'-biphenyl]-4,4'-dicarboxylate in acetonitrile in 0.1 M Bu4NBF4 at 100 mV/s vs. Fc/Fc+. This contrasts with the DFT calculated energies of the HOMOs, iodine lone pairs, which are the same in both molecules within 0.04 eV. One reason for the difference in the experimentally determined oxidation potential is the ability of the ester oxygen to engage in an intramolecular halogen bond with the oxidized iodine,141 thus stabilizing the higher oxidation state. This is only possible in the shorter linker where the iodine is ortho to the ester. In the MOFs, the same interaction would occur with the carboxylate groups that are bound to the metals (Figure 3.11). As a result, the catalyst in the larger pore framework is less readily oxidized and therefore, less efficient even though there is more space. This effect is not observed with MIL-53/DUT-5 as the increase in accessible space appears to offset the change to the catalytic site. Using DUT-5 25%-I for the oxidation of hydroquinone at 24 and 50 °C, a yield of 19 and 73% were observed when compared to the MIL-53 25%-I (10 and 37%).
109 Texas Tech University, Babak Tahmouresilerd, August 2020
Figure 3.11. Proposed in situ generated hypervalent iodine(III) supported by nucleophile Nu- in the pores (highlighted in blue for DUT-5 and UiO-67) of a) DUT-5 25%-I or UiO-67 25%-I or b) MIL-53 25%-I or UiO-66 25%-I. Despite having good catalytic performance, UiO-66 25%-I was not able to be recycled with retained activity towards the oxidation of hydroquinone.66 With the larger UiO-67 25%-I, however, the catalytic conversion remained constant over four runs (Figure 3.12, top). In the case of DUT-5 25%-I, for the first and second runs, a conversion of 85% was observed. For the third and fourth runs, the catalytic conversion dropped to 84% and 82%, respectively. This small loss in conversion for the third and the fourth run are attributed to catalyst attrition from manipulations between recycles. These series of conversion for DUT-5 25%-I show improvement when compared to the same family of MOF with the smaller linker (Figure 3.12, bottom).66 PXRD patterns for the catalysts after the first and
110 Texas Tech University, Babak Tahmouresilerd, August 2020 fourth runs were obtained and both frameworks retain their crystallinity (Figure 3.13). In the smaller MOFs, restricted access to the catalyst as a result of an accumulation of organic groups bound to the hypervalent iodine species may be a limiting factor in the ability to recycle the frameworks. With the larger frameworks, this appears to be overcome.
Figure 3.12. Catalyst recyclability for the oxidation of hydroquinone to benzoquinone in the presence of UiO-67 25%-I compared to UiO-66 25%-I (top),66 and DUT-5 25%- I compared to MIL-53 25%-I (bottom).66 Conditions: 1 h, 20 mol% catalyst, 2.9 eq. mCPBA, nitromethane, 50 °C. Values were determined by 1H NMR in the presence of MSM as an internal standard. The choice of solvent can play a significant role in mediating these oxidation reactions. Nitromethane was previously found to promote both high reactivity and selectivity with the smaller frameworks.66 Halogenated solvents were not previously tested with the smaller MOFs, but it has been shown that they can accelerate the yield of catalytic reactions with hypervalent iodine.142 The catalytic oxidation of hydroquinone to quinone was examined over 1 h in the presence of (4 mL) ethyl alcohol or 2,2,2-trifluoroethanol (TFE), 20 mol% UiO-
111 Texas Tech University, Babak Tahmouresilerd, August 2020
67 25%-I, 2.9 equivalent mCPBA at 50 °C. With ethyl alcohol as a solvent, a yield of 12% was observed over 1 h. The yield of a catalytic reaction in the presence of 2,2,2-Trifluoroethanol (TEF) reached 51% after just 10 minutes. Nevertheless, the reaction required longer to go to completion when compared to the same reaction in nitromethane.
Figure 3.13. PXRD patterns of UiO-67 25%-I before the catalytic reaction, and the fourth run.
1.19. Evaluation of Other Substrates The scope of the substrates was expanded to other aromatic diols. The first set of para-hydroquinone substrates increase in size through the incorporation of electron-rich alkyl groups (entries 1-4). These more electron-rich substrates react readily with mCPBA at 50 °C, so a lower temperature was used to evaluate the catalytic activity. At 24 °C, the observed trend was an increase in the background reaction, from 3% for p-hydroquinone to 41% for 2,5-di-tert-butylhydroquinone.
112 Texas Tech University, Babak Tahmouresilerd, August 2020
This increase in background reactivity mirrors the decrease in oxidation potential characterized by cyclic voltammetry (Figure 3.14 a, 0.97 eV to 0.84 eV). In the presence of the catalyst, a similar trend in the reaction yield was not observed. For DUT-5, no significant change was observed for the symmetrical hydroquinones and a decrease in the activity that could be attributed to the catalyst was observed for UiO-67.
Figure 3.14. CVs of a) hydroquinone and hydroquinone derivatives containing electron donation groups, b) hydroquinone derivatives containing electron-withdrawing groups, c) catechol and catechol derivatives containing electron donation groups. All obtained + in acetonitrile in 0.1 M Bu4NPF6 at 100 mV/s vs. Fc/Fc . Considering the increase in pore size, this is a surprising result. A possible explanation is that the direct reaction of mCPBA with the substrate is sufficiently
113 Texas Tech University, Babak Tahmouresilerd, August 2020 favorable given that higher oxidation potential of the catalyst and the lower oxidation potentials of these substrates that the catalytic reaction is circumvented under these conditions. This is consistent with the catalytic activity observed with the more readily oxidized UiO-66 25%-I.66
Hydroquinone derivatives containing electron-withdrawing groups (Table 3.2, entries 5-8) were probed. The chlorinated and brominated derivatives have a similar size profile to the methyl-substituted hydroquinone but are not as readily oxidized (Figure 3.14 b). With these substrates, a high yield of reaction beyond the background reaction was observed at 50 °C. The yields of the catalytic reactions for oxidation of chlorohydroquinone and 2,5-dibromohydroquinone (entries 5, 8) were reported to be 40 and 67% for UiO-66 25%-I and 20 and 10% for MIL-53 25%-I.66 For both substrates, the larger-pore catalysts proved to be more efficient catalysts. This enhanced performance is attributed to the increase in pore size associated with the larger MOFs. Additional substrates 2- bromohydroquinone and 2,5-dichlorohydroquinone (entries 6 and 7) were tested with all four catalysts. In the presence of the smaller MOFs, the yields were significantly lower than with the larger frameworks. This is, again, consistent with the combination of larger pores and a catalyst that is a more potent oxidant.
Given the success of these extended frameworks with substrates that have higher oxidation potentials the substrate scope was expanded to include catechol. Catechol itself has an oxidation potential of 0.14 V higher than hydroquinone. This increase in oxidation potential leads to a low yield of the desired product with the smaller MOFs, MIL-53 25%-I or UiO-66 25%I (6-7%), at 50 °C. The oxidation of catechol, 4-methylcatechol, 4-tert-butylcatechol, and 2,5-di-tert- butylhydroquinone at 24 °C using DUT-5 25%-I (entries 9-12) gave the yields of 13%, 26%, 58%, and 29%. The same reactions with UiO-67 25%-I as the catalyst gave yields of 48%, 41%, 85%, and 27%, demonstrating that these larger MOFs can accommodate larger and more difficult to oxidize substrates. Notably, the yields appear to drop off with the most readily oxidized substrate, 2,5-di-tert-
114 Texas Tech University, Babak Tahmouresilerd, August 2020 butylhydroquinone. This can be attributed to the larger size of the substrate having a limiting effect on diffusion in the pores. Consistent with expectations, raising the reaction temperature for the oxidation of catechol from 24 to 50 °C improved the yields with both frameworks.
Selectivity was measured by contrasting the total yield of the desired product with the overall conversion. In addition to higher yields, these isoreticularly expanded MOF catalysts lead to higher selectivities for the desired products. The exception to this is with the larger electron-rich substrates such as 3,5-di-tert-butylcatechol and 2,5-di-tert-butylhydroquinone. Here, likely due to an inability to readily diffuse within the pores, the catalytic yields are low and the selectivity for the desired product low. This contrasts with the high yields and selectivities for the electron-poor hydroquinones and the catechols that were studied.
1.20. Conclusions Two new expanded-pore iodine-functionalized robust frameworks, based on DUT-5 (Al) and UiO-67 (Zr), were prepared as oxidization catalysts. Their performance was inferior to the analogous smaller-pore MOFs with electron-rich substrates. This resulted from an unintended change to the electronic structure as a result of the pore-expansion strategy and should serve as a cautionary note for linker elongation as a blanket strategy for creating more void volume in a MOF. This slightly poorer performance was offset by greater stability towards the recycling of the catalyst. With substrates that were more difficult to oxidize, the expanded-pore frameworks were superior catalysts as compared to their smaller analogues. This is likely a result of the combination of more space for diffusion within the framework and the higher oxidation potential of the iodine catalysts.
115 Texas Tech University, Babak Tahmouresilerd, August 2020
1.21. Experimental Details 1.21.1. General Methods Aluminum chloride hexahydrate (99.0%, Acros Organics), zirconium tetrachloride (98.0%, Merck KGaA), 4-tert-butylcatechol (99.0%, Acros Organics), 3,5-
di-tert-butylcatechol (99.0%, Acros Organics), hydroquinone (>99.5%, Merck KGaA), catechol (99%, Alfa Aesar), 4-methylcatechol (98%, Acros Organics), 2,5- dibromohydroquinone (97%, Alfa Aesar), 2,5-dichlorohydroquinone (97%, Alfa Aesar), methylhydroquinone (>98.0%, TCI), bromohydroquinone (94%, Acros Organics), 2,5-di-tert-butylhydroquinone (97%, Ark Pharm, Inc.), tert- butylhydroquinone (97%, Acros Organics), chlorohydroquinone (90%, Acros Organics), N,N-dimethylformamide (DMF, >99.9%, EMD Millipore), hydrochloric acid (36.5-38.0%, BDH), isopropanol alcohol (99.5%, BDH), dichloromethane (99.9%, Fisher Scientific), dimethyl-[1,1'-biphenyl]-4,4'-dicarboxylate (>97%, Brown molecular), [1,1'-biphenyl]-4,4'-dicarboxylic acid (97%, Ark Pharm), tetrahydrofuran (99.0%, Fisher Scientific), nitric acid (68.0-70.0%, AR® ACS, Macron Fine Chemicals™), meta-chloroperoxybenzoic acid (70.0-75.0%, Acros Organics), 2,2,2- trifluoroethanol (>99%, Sigma-Aldrich), potassium hydroxide (≥85.0%, Fisher Scientific), sulfuric acid (96.0%, J.T.Baker), magnesium sulfate anhydrous (≥99.0%,
J.T.Baker), dimethyl sulfoxide-d6 (DMSO-d6, >99.0%, Cambridge Isotope Laboratories), methylsulfonylmethane (>99.0%, TCI), tin mossy (95.5%, Alfa Aesar), tert-butyl hydroperoxide (70.0% aq. sol., Alfa Aesar), ethanol (99.5%, Pharmco- AAPER), methanol (>99.9%, Fisher Scientific), nitromethane (>98.0%, Alfa Aesar), deuterium oxide (>99.0%, Cambridge Isotope Laboratories), sodium deuteroxide
solution 40 wt. % in D2O (>99.0%, Acros Organics), potassium iodide (>99.0%, Fisher Scientific), sodium bisulfite (98.5%, Fisher Scientific) and sodium nitrite (>99.0%, J.T.Baker) were used as purchased without further purification. All measurements, unless noted otherwise, were carried out at 298 K and NMR chemical shifts were given in ppm.
116 Texas Tech University, Babak Tahmouresilerd, August 2020
1.21.2. Synthesis
1.21.2.1. Preparation of dimethyl 2-nitro-[1,1'-biphenyl]-4,4'-dicarboxylate132
A cold solution of nitric acid (56%, 2.6 mL) and concentrated sulfuric acid (3.2 mL) was added dropwise to a solution of dimethyl [1,1'-biphenyl]-4,4'-dicarboxylate (5.00 g, 18.5 mmol) in 50 mL of concentrated sulfuric acid once solution is clear at 0 °C under intense stirring. The reaction mixture turned yellow while the temperature was maintained at 0 °C for 5 h. The solution was then poured onto crushed ice at which point a milky white solid precipitated. The solids were separated by filtration and washed with water. The solid was dissolved in hot isopropanol and the desired product was collected 1 after recrystallization occurred at 40 °C (Yield: 4.9 g, 86%). H NMR (DMSO-d6 , 400 MHz), δ: 3.89 (s, 3H), 3.94 (s, 3H), 7.56 (d, 2H, J = 8 Hz), 7.76 (d, 1H, J= 8 Hz), 8.05 (d, 2H, J= 8 Hz), 8.29 (dd, 1H, J= 4.0 Hz) , 8.31 (d, J = 4.0 Hz, 1H), 8.50 (s, 1H). (Figure 3.15)
Figure 3.15. 1H NMR spectrum of 2-nitro-[1,1'-biphenyl]-4,4'-dicarboxylate in DMSO- d6.
117 Texas Tech University, Babak Tahmouresilerd, August 2020
1.21.2.2. Preparation of dimethyl 2-amino-[1,1'-biphenyl]-4,4'-dicarboxylate133
To a solution of dimethyl 2-nitro-[1,1'-biphenyl]-4,4'-dicarboxylate (2.45g, 7.77 mmol) in methanol (100 mL), tin powder (5.53g, 46.6 mmol) was added in small portions. hydrochloric acid (1 M, 150 mL) was slowly added and the reaction mixture was heated under reflux condition for 2 h. The solution was then poured onto crushed ice at which point a yellowish solid precipitated upon addition of 1 M aq. NaOH. The product was extracted with warm ethyl acetate and was recrystallized from hot ethanol 1 and dried under reduced pressure (Yield: 1.64 g, 74%). H NMR (DMSO-d6, 400 MHz), δ: 3.85 (s, 3H), 3.89 (s, 3H), 7.27 (d, 1H, J=8 Hz), 7.43 (d, 1H, J=4 Hz), 7.45 (d, 1H, J=4 Hz), 7.63 (d, 2H, J=8 Hz), 8.05 (d, 2H,J=12 Hz). (Figure 3.16)
Figure 3.16. 1H NMR spectrum for synthesized dimethyl 2-amino-[1,1'-biphenyl]-4,4'- dicarboxylate in DMSO-d6.
118 Texas Tech University, Babak Tahmouresilerd, August 2020
1.21.2.3. Preparation of dimethyl 2-iodo-[1,1'-biphenyl]-4,4'-dicarboxylate132
A solution of dimethyl 2-amino-[1,1'-biphenyl]-4,4'-dicarboxylate (1.50 g, 5.3 mmol) in ultrapure water/HCl (100 mL, 1:1 v:v), was cooled to 0-5 °C. A cold solution of sodium nitrite (1.1 g, 15.9 mmol) in ultrapure water (5mL) was added dropwise to the suspension over 2 h. The reaction mixture was stirred at 0-5 °C for an additional 60 min and then poured into a solution of potassium iodide (8.34 g, 50.3 mmol) in ultra- pure water (10 mL). The color of the solution changed to dark brown and the reaction mixture was started to bubble. The reaction mixture was stirred at 60 °C for 24 h. Sodium hydrogen sulfite was added in portions to stirring reaction mixture until the dark color turned to light brown. The resulting solid was filtered and then dissolved in dichloromethane and washed with water. The aqueous phase was further extracted with water (2x). The organic phases were combined and dried over MgSO4 before being taken to dryness to yield a brown crystalline solid. (Yield: 1.51 g, 72%). 1H NMR
(DMSO-d6, 400 MHz), δ: 3.89 (s, 6H), 7.50 (d, 1H, J=8 Hz), 7.52 (d, 2H, J=8 Hz), 8.03 (d, 1H, J=8 Hz), 8.06 (d, 2H, J=8 Hz), 8.49 (s, 1H). (Figure 3.17)
119 Texas Tech University, Babak Tahmouresilerd, August 2020
Figure 3.17. 1H NMR spectrum of dimethyl 2-iodo-[1,1'-biphenyl]-4,4'-dicarboxylate in DMSO-d6.
1.21.2.4. Preparation of dimethyl 2-iodo-[1,1'-biphenyl]-4,4'-dicarboxylic acid134
Dimethyl 2-iodo-[1,1'-biphenyl]-4,4'-dicarboxylate (1.50 g, 3.79 mmol) was dissolve in 20 mL of tetrahydrofuran (THF). A solution of potassium hydroxide (0.22 g, 3.79 mmol) in 20 mL water was added and the reaction mixture was refluxed for 20 h. The THF was removed under reduced pressure and 6M HCl was added until the solution had a pH of 1. The solid was filtrated and washed with water and dried under 1 vacuum (Yield: 1.3 g, 93%). H NMR (NaOD/ D2O, 400 MHz), δ: 6.82 (d, 1H, J=8 Hz), 6.87 (d, 2H, J= 8 Hz), 7.35 (dd, 1H, J=8 Hz), 7.39 (d, 2H, J= 8 Hz), 7.89 (d, J= 2 Hz, 1 1H). H NMR (DMSO-d6, 400 MHz), δ: 7.48 (d, 1H, J=8 Hz), 7.49 (d, 2H, J= 8 Hz), 8.01 (d, 1H, J=8 Hz), 8.03 (d, 2H, J= 8 Hz), 8.47 (s, 1H). (Figure 3.18)
120 Texas Tech University, Babak Tahmouresilerd, August 2020
8.47 8.04 8.02 8.02 8.00 7.50 7.49 7.48 7.47 2.50 DMSO-d6 1.00 3.04 3.05
Figure 3.18. 1H NMR spectrum of 2-iodo-[1,1'-biphenyl]-4,4'-dicarboxylic acid in DMSO-d6.
1.21.2.5. Synthesis of UiO-67 25%-I
UiO-67 25%-I was prepared via solvothermal methods adapted from the previously reported method for UiO-67.136,137 Zirconium tetrachloride (0.46 g, 2.0 mmol) was added to (60 mL) DMF. The mixture of [1,1'-biphenyl]-4,4'-dicarboxylic acid (0.364 g, 1.50 mmol) and 2-iodo-[1,1'-biphenyl]-4,4'-dicarboxylic acid (0.184 g, 0.500 mmol) were dissolved in DMF (10 mL) with a small amount of ultrapure water (0.050 mL, 2.8 mmol) and this was added to the first solution. The reaction mixture was heated in a round bottom flask fitted with a condenser at 95 °C for 100 h to yield a light brown solid as UiO-67 25%-I MOFs. The solid was washed with hot DMF (x3) and soaked in hot methanol (x1) overnight prior to being heated at 160 °C for 24 hours under vacuum. (Yield: 0.63 g)
121 Texas Tech University, Babak Tahmouresilerd, August 2020
1.21.2.6. Synthesis of UiO-67 100%-I
UiO-67 100%-I was prepared via solvothermal methods adapted from the previously reported method for UiO-67.136,137. Zirconium tetrachloride (0.067 g, 0.28 mmol) was added in an 8-dram vial. A solution of hydrochloric acid (12 M, 0.5 mL) in (5 mL) DMF was added to the vial containing Zirconium tetrachloride. 2-iodo-[1,1'- biphenyl]-4,4'-dicarboxylic acid (0.136 g, 0.37 mmol) were dissolved in (10 mL) DMF and this was added to the first solution. The reaction mixture was placed pre-heated oven at 80 °C for 18 h to yield a brown solid as UiO-67 100%-I MOFs. The solid was washed with hot DMF (x3) and soaked in hot methanol (x1) overnight prior to being heated at 160 °C for 24 hours under vacuum. (Yield: 0.22 g)
1.21.2.7. Synthesis of DUT-5 25%-I
The DUT-5 25%-I framework was prepared by adapting the reported procedure for DUT-5.130,135 Preparation of DUT-5 25%-I was carried out under solvothermal conditions in a 100 mL round bottom flask using aluminum chloride hexahydrate (0.51 g, 2.1 mmol), [1,1'-biphenyl]-4,4'-dicarboxylic acid (0.294 g, 1.2 mmol), 2-iodo-[1,1'- biphenyl]-4,4'-dicarboxylic acid (0.149 g, 0.4 mmol), and (75 mL) DMF. The chloride salt was chosen as the nitrate salt used in the original procedure led to oxidation of the iodine-functionalized linker. The flask was fitted with a condenser and heated at 120 °C for 24 h. The as-synthesized MOF, DUT-5 25%-I (as), was obtained after filtering and washing with hot DMF. To empty the pores of residual materials, the as-synthesized MOF was washed with DMF (x3) and soaked for overnight in hot methanol (x1) prior to being heated at 160 °C for 24 hours under vacuum. (Yield: 0.51 g)
1.21.2.8. Synthesis of DUT-5 100%-I
The DUT-5 100%-I framework was prepared by adapting the reported procedure for DUT-5.130,135 Preparation of DUT-5 25%-I was carried out under solvothermal conditions in a 100 mL round bottom flask using aluminum chloride hexahydrate (0.51 g, 2.1 mmol), 2-iodo-[1,1'-biphenyl]-4,4'-dicarboxylic acid (0.779 g, 1.6 mmol), and (75
122 Texas Tech University, Babak Tahmouresilerd, August 2020
mL) DMF. The flask was fitted with a condenser and heated at 120 °C for 24 h. The as- synthesized MOF, DUT-5 100%-I (as), was obtained after filtering and washing with hot DMF. To empty the pores of residual materials, the as-synthesized MOF was washed with DMF (x3) and soaked for overnight in hot methanol (x1) prior to being heated at 160 °C for 24 hours under vacuum. (Yield: 0.63 g)
1.21.3. Crystallography
1.21.3.1. Powder X-ray Diffraction
The diffraction patterns were collected on a Rigaku Ultima III powder diffractometer. X-ray diffraction patterns were obtained by using 2θ-θ scans with a range of 5-30°, step size = 0.05°, and scan time of 1 second/step. The X-ray source was Cu Kα radiation (λ=1.5418 Å) with an anode voltage of 40 kV and a current of 44 mA. The beam was then discriminated by Rigaku's Cross Beam optics to create a monochromatic parallel beam. Diffraction intensities were recorded on a scintillation detector after being filtered through a Ge monochromator. Powder mounts were prepared by packing the powder into a well on a glass slide.
1.21.4. Characterization
1.21.4.1. NMR Digestion
NMR digestions were performed on the MOFs to establish the ratio that the different ligands were incorporated and to ensure that no ligand decomposition had taken place. Digested solutions of UiO-67 25%-I and DUT-5 25%-I were prepared by
soaking 5-10 mg of MOF in 570 μL D2O and 200 μL of NaOD solution (40 wt. % in
D2O) for 18 h followed by sonication for 2 h. The solutions were then filtered to remove the inorganic salts (Figure 3.19) and the resulting clear solutions were analyzed by 1H NMR (Figure 3.20 and Figure 3.21).
123 Texas Tech University, Babak Tahmouresilerd, August 2020
Figure 3.19. Di-ATR FTIR of activated UiO-67 25%-I before (black) and after (blue) digestion. Spectra are plotted as attenuation.
124 Texas Tech University, Babak Tahmouresilerd, August 2020
8.24 7.78 7.76 7.73 7.70 7.70 7.68 7.68 7.57 7.55 7.23 7.21 7.17 7.15 .02 .01 .00 8.67 .13 5.92 2 1 1 1 1 1
1 Figure 3.20. H NMR spectrum for digested DUT-5 25%-I in 570 μL D2O and 200 μL of NaOD solution 40 wt. % in D2O. (A: D2BPDC, B: D2IBPDC) 125 Texas Tech University, Babak Tahmouresilerd, August 2020
8.21 7.76 7.74 7.71 7.67 7.66 7.65 7.64 7.52 7.50 7.16 7.14 6.10 .12 .00 7.96 .02 1 2 1 1 1
1 Figure 3.21. H NMR spectrum for digested UiO-67 25%-I in 570 μL D2O and 200 μL of NaOD solution 40 wt. % in D2O. (A: BPDC-2, B: IBPDC-2) 126 Texas Tech University, Babak Tahmouresilerd, August 2020
1.21.4.2. Nitrogen Adsorption
Nitrogen sorption measurements were performed at 77 K on a Quantichrome Autosorb iQ (ASiQ) gas sorption analyzer. Approximately 20 mg of the MOFs were added to a preweighed 6 mm sample cell. All samples were activated under vacuum at 200 °C for ~10 hours. The sample weight was then collected. The surface areas, pore volumes, and pore size were calculated using the DFT method in the Quantachrome ASiQwin software. The NLDFT equilibrium (cylinder/slit) model was chosen for the pore volume measurements.
Figure 3.22. Pore size distribution of DUT-5 25%-I (top) and UiO-67 25%-I (bottom) (77 K).
127 Texas Tech University, Babak Tahmouresilerd, August 2020
1.21.5. Catalytic Experiment
1.21.5.1. Typical Catalytic Reaction Procedure
In a typical catalytic reaction, the catalyst (20 mol%), terminal oxidant (0.579 mmol, 0.0999), and substrate (0.145 mmol, 0.0160 g) were mixed in the specified solvent or solvent mixture (4.0 mL) along with the internal standard (methylsulfonylmethane) in a 2-dram clear glass vial. The vial was charged with a Teflon coated stir bar and placed on a hot plate preheated to 50 °C. After the specified time had been reached, the catalyst was separated by centrifugation, the liquid was decanted, and 3 drops were taken for analysis. The collected sample was dissolved in
the DMSO-d6 to determine the catalytic conversion and yield via integration of the relevant peaks in the 1H NMR spectrum. All control reactions were done in the absence of MOF.
Figure 3.23. Representative 1H NMR of hydroquinone in the acetonitrile reaction mixture in DMSO-d6 with MSM as an internal standard for analysis of product distribution.
128 Texas Tech University, Babak Tahmouresilerd, August 2020
1.21.6. Results of All Catalytic Experiments
Table 3.3. The results of catalytic oxidation of hydroquinone (HQ) to benzoquinone (BQ) for UiO-67 0%-I, and DUT-5 0%-I, UiO-67 25%-I, DUT-5 25%-I and control in the presence of 20 mol% catalyst, 2.9 equivalent of mCPBA, 4 mL nitromethane at 50 °C for 60 minutes. Total Normalized Normalized Normalized Normalized normalized Sample Time Solvent integrated integrated integrated integrated integrated Yield Conversion (min) intensity of intensity of intensity of intensity of intensity of (%) (%) MSM HQ BQ products 3 reactants and 4 and products Control 1.00 0.85 0.08 0.06 0.99 8 15 UiO-67 0%-I 1.00 0.84 0.08 0.07 0.99 8 16 DUT-5 0%-I 60 NM 1.00 0.81 0.08 0.09 0.99 8 18 UiO-67 25%-I 1.00 0.12 0.84 0.03 0.99 83 86 DUT-5 25%-I 1.00 0.13 0.82 0.04 0.99 81 85
Table 3.4. Catalytic oxidation of hydroquinone (HQ) to benzoquinone (BQ) in the presence of 20 mol% UiO-67 25%-I and DUT-5 25%-I, 2.9 equivalent of mCPBA at 50 °C and room temperature in 4 mL nitromethane for 60 minutes. Total Normalized Normalized Normalized Normalized normalized Sample Temp. Solvent integrated integrated integrated integrated integrated Yield Conversion (°C) intensity of intensity of intensity of intensity of intensity of (%) (%) MSM HQ BQ products 3 reactants and and 4 products Control 1.00 0.93 0.03 0.03 0.99 3 7 DUT-5 25%-I 24 1.00 0.72 0.22 0.06 1.00 22 28
UiO-67 25%-I 1.00 0.49 0.36 0.15 1.00 36 51 NM Control 1.00 0.85 0.08 0.06 0.99 8 15 DUT-5 25%-I 50 1.00 0.13 0.82 0.04 0.99 81 85 UiO-67 25%-I 1.00 0.12 0.84 0.03 0.99 83 86
129 Texas Tech University, Babak Tahmouresilerd, August 2020
Table 3.5. Effect of 2,2,2-Trifluoroethanol (TFE) on catalytic oxidation of hydroquinone (HQ) to benzoquinone (BQ) in the presence of 20 mol% UiO-67 25%-I, 2.9 equivalent of mCPBA, 4 mL specified solvent at 50 °C for 60 minutes. Total Normalized Normalized Normalized Normalized normalized Sample Time Solvent integrated integrated integrated integrated integrated Yield Conversion (min) intensity of intensity of intensity of intensity of intensity of (%) (%) MSM HQ BQ products 3 reactants and 4 and products Control 1.00 1.00 0.00 0.00 1.00 0 0 UiO-67 25%-I 10 1.00 0.86 0.14 0.00 1.00 14 14 Control 1.00 1.00 0.00 0.00 1.00 0 0 UiO-67 25%-I 20 EtOH 1.00 0.83 0.16 0.00 0.99 16 17 Control 1.00 1.00 0.94 0.06 1.00 6 6 UiO-67 25%-I 60 1.00 0.81 0.18 0.00 0.99 18 19 Control 1.00 0.90 0.10 0.00 1.00 10 10 UiO-67 25%-I 10 1.00 0.38 0.61 0.00 0.99 61 62 Control 1.00 0.85 0.14 0.00 0.99 14 15 UiO-67 25%-I 20 TFE 1.00 0.37 0.61 0.00 0.98 62 63 Control 1.00 0.72 0.28 0.00 1.00 28 28 UiO-67 25%-I 60 1.00 0.32 0.68 0.00 1.00 68 68 Table 3.6. Catalyst mol% variation for catalytic oxidation of hydroquinone (HQ) to benzoquinone (BQ) using 2.9 equivalent mCPBA in 4 mL nitromethane at 50 °C for 60 minutes. Total Catalyst Normalized Normalized Normalized Normalized normalized Sample (mol %) integrated integrated integrated integrated integrated Yield Conversion based on I intensity of intensity of intensity of intensity of intensity of (%) (%) MSM HQ BQ products 3 reactants and and 4 products Control 0 1.00 0.85 0.08 0.06 0.99 8 15 UiO-67 25%-I 20 1.00 0.12 0.84 0.03 0.99 83 86 10 1.00 0.12 0.84 0.03 0.99 83 86 5 1.00 0.40 0.58 0.00 0.98 58 60 DUT-5 25%-I 20 1.00 0.13 0.82 0.04 0.99 81 85 10 1.00 0.31 0.58 0.11 1.00 58 69 5 1.00 0.56 0.33 0.10 0.99 33 44
130 Texas Tech University, Babak Tahmouresilerd, August 2020
Table 3.7. Catalytic oxidation of hydroquinone (HQ) to benzoquinone (BQ) in the presence of 20 mol% UiO-67 25%-I, UiO-67 100%- I, DUT-5 25%-I, DUT-5 100%-I, and 2.9 equivalent of mCPBA at 50 °C in 4 mL acetonitrile for 60 minutes. Total Catalyst Normalized Normalized Normalized Normalized normalized Sample (mol %) integrated integrated integrated integrated integrated Yield Conversion based on I intensity of intensity of intensity of intensity of intensity of (%) (%) MSM HQ BQ products 3 reactants and and 4 products Control 0 1.00 0.99 0.00 0.00 0.99 0 0 UiO-67 25%-I 1.00 0.71 0.29 0.00 1.00 29 29 UiO-67 100%-I 20 1.00 0.83 0.17 0.00 1.00 17 17 DUT-5 25%-I 1.00 0.05 0.94 0.00 0.99 94 95 DUT-5 100%-I 1.00 0.11 0.87 0.00 0.98 87 89
Table 3.8. Catalytic oxidation of hydroquinone (HQ) to benzoquinone (BQ) in the presence of 20 mol% UiO-67 25%-I, UiO-67 100%- I, DUT-5 25%-I, DUT-5 100%-I, and 2.9 equivalent of mCPBA at 50 °C in 4 mL nitromethane for 60 minutes. Total Catalyst Normalized Normalized Normalized Normalized normalized Sample (mol %) integrated integrated integrated integrated integrated Yield Conversion based on I intensity of intensity of intensity of intensity of intensity of (%) (%) MSM HQ BQ products 3 reactants and and 4 products Control 0 1.00 0.85 0.08 0.06 0.99 8 15 UiO-67 100%-I 1.00 0.60 0.23 0.15 0.98 23 40 DUT-5 100%-I 20 1.00 0.12 0.70 0.17 0.99 71 86
131 Texas Tech University, Babak Tahmouresilerd, August 2020
Table 3.9. Catalytic oxidation of 2,5-di-tert-butylhydroquinone to the corresponding oxidation product in the presence of 20 mol% UiO- 67 100%-I, DUT-5 100%-I, and 2.9 equivalent of mCPBA at room temperature in 4 mL nitromethane for 60 minutes. Total Catalyst Normalized Normalized Normalized Normalized normalized Sample (mol %) integrated integrated integrated integrated integrated Yield Conversion based on I intensity of intensity of intensity of intensity of intensity of (%) (%) MSM HQ BQ products 3 reactants and and 4 products Control 0 1.00 0.58 0.41 0.00 0.99 41 42 UiO-67 100%-I 1.00 0.40 0.48 0.12 1.00 48 68 DUT-5 100%-I 20 1.00 0.35 0.49 0.14 0.98 49 65
Table 3.10. Control reactions for catalytic oxidation of hydroquinone (HQ) to benzoquinone (BQ) in the presence of 2.9 equivalent of mCPBA at 50 °C in 4 mL solvent for 60 minutes. Total Normalized Normalized Normalized Normalized normalized Sample Solvent integrated integrated integrated integrated integrated Yield Conversion intensity of intensity of intensity of intensity of intensity of (%) (%) MSM HQ BQ products 3 reactants and and 4 products NO MOF 1.00 0.85 0.08 0.06 0.99 8 15 UiO-67 0%-I NM 1.00 0.84 0.08 0.07 0.99 8 16 DUT-5 0%-I 1.00 0.81 0.08 0.09 0.99 8 18
NO MOF 1.00 0.99 0.00 0.00 0.99 0 0 UiO-67 0%-I ACN 1.00 0.99 0.00 0.00 0.99 0 0 DUT-5 0%-I 1.00 0.94 0.04 0.01 0.99 4 6
132 Texas Tech University, Babak Tahmouresilerd, August 2020
1.21.7. Experimental Procedure for Recyclability test of Multivariate MOF The recyclability tests for UiO-67 25%-I and DUT-5 25%-I was performed in the presence of ~2.9 equivalent of mCPBA in 4 mL nitromethane (NM) at 50 °C for 60 minutes as shown in Table 3.11. After each run, the catalyst was separated using centrifugation
and the liquid was decanted and 5 drops of liquid were dissolved in 0.5 mL DMSO-d6 to determine the catalytic conversion and yield of catalytic conversion of hydroquinone (HQ) to benzoquinone (BQ). The leftover catalyst was washed three times with nitromethane. A 1.00 mL solution containing MSM and HQ was added to the catalyst followed by 2.9 equivalent of mCPBA, and 4 mL nitromethane (NM). The closed cap 2-dram clear glass vial was placed on the hot plate when the temperature was 50 °C for 60 minutes.
Table 3.11. The recyclability test for catalysts with 2.9 equivalent of mCPBA in 4 mL nitromethane at 50 °C for 60 minutes. Total Normalized Normalized Normalized Normalized normalized Sample Run integrated integrated integrated integrated integrated Yield Conversion intensity of intensity of intensity of intensity of intensity of (%) (%) MSM HQ BQ products 3 reactants and 4 and products Control - 1.00 0.86 0.08 0.06 1.00 8 15 1st 1.00 0.12 0.84 0.03 0.99 83 86 UiO-67 25%-I 2nd 1.00 0.14 0.75 0.11 1.00 75 86 3rd 1.00 0.14 0.76 0.10 1.00 76 86 4th 1.00 0.14 0.74 0.12 1.00 76 86 1st 1.00 0.13 0.82 0.04 0.99 81 85 DUT-5 25%-I 2nd 1.00 0.15 0.81 0.00 0.96 80 85 3rd 1.00 0.16 0.81 0.00 0.97 80 84 4th 1.00 0.18 0.80 0.00 0.98 79 82
133 Texas Tech University, Babak Tahmouresilerd, August 2020
Figure 3.24. SEM analysis for UiO-67 25%-I before (a, b) and after the 4th run (c, d) of the catalytic oxidation of hydroquinone (HQ) to benzoquinone (BQ).
134 Texas Tech University, Babak Tahmouresilerd, August 2020
Table 3.12. Catalytic oxidation of hydroquinone and catechol derivatives in the presence of 20 mol% catalysts, 2.9 equivalent of mCPBA, 4 mL nitromethane for 60 minutes. Total Normalized Normalized Normalized Normalized normalized Substrate Sample Temp. integrated integrated integrated integrated integrated Yield Conversion (°C) intensity of intensity of intensity of intensity of intensity (%) (%) MSM substrate desired byproducts of product reactants and products 2,5- Control 1.00 0.94 0.05 0.00 0.99 5 6 dibromohydroquinone DUT-5 25%-I 50 1.00 0.03 0.94 0.00 0.97 94 97 UiO-67 25%-I 1.00 0.16 0.82 0.02 1.00 82 84 2, 5- Control 1.00 0.75 0.07 0.18 1.00 7 25 dichlorohydroquinone DUT-5 25%-I 1.00 0.01 0.97 0.00 0.98 97 99 UiO-67 25%-I 50 1.00 0.13 0.86 0.00 0.99 86 87 MIL-53 25%-I 1.00 0.62 0.2 0.18 1.00 20 38 UiO-66 25%-I 1.00 0.14 0.68 0.18 1.00 68 86 2-bromohydroquinone Control 1.00 0.71 0.07 0.21 0.99 7 29 DUT-5 25%-I 1.00 0.04 0.92 0.01 0.97 92 96 UiO-67 25%-I 50 1.00 0.15 0.80 0.04 0.99 80 85 MIL-53 25%-I 1.00 0.38 0.26 0.36 1.00 26 62 UiO-66 25%-I 1.00 0.1 0.63 0.26 0.99 63 90 2-chlorohydroquinone Control 1.00 0.75 0.24 0.00 0.99 24 25 DUT-5 25%-I 50 1.00 0.00 0.96 0.003 0.98 96 100 UiO-67 25%-I 1.00 0.22 0.76 0.02 1.00 76 78 3, 5-di-tert- Control 1.00 0.50 0.50 0.00 1.00 50 50 butylcatechol DUT-5 25%-I 24 1.00 0.08 0.79 0.12 0.99 79 92 UiO-67 25%-I 1.00 0.00 0.77 0.2 0.97 77 100 4-tert-butylcatechol Control 1.00 0.80 0.04 0.14 0.98 5 20 DUT-5 25%-I 24 1.00 0.08 0.62 0.27 0.97 63 92 UiO-67 25%-I 1.00 0.09 0.9 0.00 0.99 90 91 2,5-di-tert- Control 1.00 0.58 0.41 0.00 0.99 41 42 butylhydroquinone DUT-5 25%-I 24 1.00 0.26 0.69 0.10 0.96 70 74 UiO-67 25%-I 1.00 0.27 0.64 0.08 0.99 65 73 Tert- Control 1.00 0.68 0.3 0.00 0.98 31 32 butylhydroquinone DUT-5 25%-I 24 1.00 0.53 0.39 0.06 0.98 39 47 UiO-67 25%-I 1.00 0.51 0.42 0.06 0.99 42 49 4-methylcatechol Control 1.00 0.72 0.21 0.06 0.99 21 28
135 Texas Tech University, Babak Tahmouresilerd, August 2020
DUT-5 25%-I 24 1.00 0.34 0.46 0.19 0.99 47 66 UiO-67 25%-I 1.00 0.13 0.62 0.25 1.00 62 87 Methylhydroquinone Control 1.00 0.69 0.3 0.00 0.99 29 31 DUT-5 25%-I 24 1.00 0.42 0.49 0.10 0.92 50 58 UiO-67 25%-I 1.00 0.40 0.54 0.06 1.00 54 60 Catechol Control 1.00 0.85 0.00 0.15 0.98 0 16 DUT-5 25%-I 24 1.00 0.71 0.12 0.14 0.97 13 29 UiO-67 25%-I 1.00 0.32 0.48 0.19 0.99 48 68 Control 1.00 0.88 0.00 0.12 1.00 0 12 DUT-5 25%-I 1.00 0.32 0.41 0.26 0.99 42 68 UiO-67 25%-I 50 1.00 0.12 0.56 0.31 0.99 56 88 MIL-53 25%-I 1.00 0.86 0.6 0.06 0.98 6 13 UiO-66 25%-I 1.00 0.87 0.07 0.06 1.00 7 13
1.21.8. Split Test for Multivariate MOFs In order to study of any possible leaching of incorporated linkers in the MOFs during catalytic oxidation reaction of hydroquinone to benzoquinone split test was done with 1 equivalent methylsulfonylmethane (MSM) as internal standard, 1 equivalent hydroquinone (HQ) as substrate, ~ 2.9 equivalent of mCPBA as terminal oxidant in 4 mL nitromethane (NM). The split test for UiO-67 25%-I and DUT-5 25%-I was done at 50 °C. For each catalyst, two reactions were running under the same condition simultaneously. After 30 minutes one of the reactions was interrupted and the catalyst was separated using centrifugation. The hot filtrate was immediately transferred to another vial and the reaction was then allowed to continue under the same conditions. After 60 minutes no significant yield and conversion change was observed following filtration. The observed catalytic yields and conversions are summarized in Table 3.13.
136 Texas Tech University, Babak Tahmouresilerd, August 2020
Table 3.13. Split test of DUT-5 25%-I and UiO-67 25%-I, 2.9 equivalent of mCPBA in 4 mL nitromethane at 50 °C at specified time of reactions. Total Normalized Normalized Normalized Normalized normalized Sample Time integrated integrated integrated integrated integrated Yield Conversion (min) intensity of intensity of intensity of intensity of intensity of (%) (%) MSM HQ BQ products 3 reactants and 4 and products Control 10 1.00 0.91 0.06 0.03 1.00 6 9 30 1.00 0.90 0.06 0.03 0.99 7 10 60 1.00 0.86 0.08 0.06 1.00 8 15 DUT-5 25%-I 10 1.00 0.63 0.30 0.06 0.99 30 37 30 1.00 0.53 0.47 0.00 1.00 47 47 Filtration was done 60 1.00 0.44 0.47 0.08 0.99 47 56 after 30 minutes DUT-5 25%-I 60 1.00 0.13 0.82 0.04 0.99 81 85 UiO-67 25%-I 10 1.00 0.59 0.37 0.00 0.97 38 41 30 1.00 0.53 0.45 0.00 0.98 45 47 Filtration was done 60 42.5 0.55 0.45 0.00 45 47 after 30 minutes 1.00 UiO-67 25%-I 60 1.00 0.12 0.84 0.03 0.99 83 86
137 Texas Tech University, Babak Tahmouresilerd, August 2020
Figure 3.25. Split test for catalysts UiO-67 25%-I (yellow) and DUT-5 25%-I (Red), filtered UiO-67 25%-I (dotted green), and DUT-5 25%-I (dotted blue) after 30 minutes. 1.21.9. Cyclic Voltammetry All CV measurements were performed at 298 K with a Pine Research WaveDriver 10 Potentiostat/Galvanostat. The cell contained a glassy carbon working electrode, a Pt wire auxiliary electrode, and a 0.5 mm diameter Ag wire as a pseudo- reference electrode. All the potentials were measured in acetonitrile with 0.1 M + Bu4NBF4. The potentials are reported relative to the Fc/Fc redox couple.
1.21.10. Computational Details and Results Molecular Mechanics (MM) optimizations were performed on all substrates at the MM2 level of theory. These models were used to evaluate the minimum and maximum radii of the substrates.
138 Texas Tech University, Babak Tahmouresilerd, August 2020
Figure 3.26. Estimated minimum and maximum radii of hydroquinone and catechol derivatives evaluated from MM2 minimized structures.
139 Texas Tech University, Babak Tahmouresilerd, August 2020
This analysis was performed by placing a dummy atom at the geometric center of the molecule and increasing its radius until it encompassed the van der Waals representation of the molecule in the Diamond 4 software package. These measurements are shown in Figure 3.26. MOF apertures were estimated by placing a dummy atom in the center of the aperture (structures obtained from experimental structure determinations) and increasing the radius of the atom until it could just fit in the aperture. (Figure 3.27)
Figure 3.27. Estimated pore apertures for DUT-5 0%-I and UiO-67 0%-I (triangular pore). Density functional theory (DFT) calculations were performed using the ORCA 4.0 quantum chemistry program package from the development team at the Max Planck Institute for Bioinorganic Chemistry.143 The LDA and GGA functionals employed were those of Perdew and Wang (PW-LDA, PW91).144 In addition, all calculations were carried out using the Zero-Order Regular Approximation (ZORA).145,146 For geometry optimizations, frequencies, and thermochemistry the def2-TZVPP147,148 and SARC/J basis sets149 were used for hydrogen atoms and all other atoms respectively. Spin- restricted Kohn–Sham determinants150 were chosen to describe the closed-shell wavefunctions, employing the RI approximation151 and the tight SCF convergence criteria provided by ORCA.
140 Texas Tech University, Babak Tahmouresilerd, August 2020
1.21.11. Optimized Cartesian Coordinates and Energies of HOMOs
Table 3.14. DFT optimized cartesian coordinates for Me2IBDC (EHOMO = –5.9928 eV). Atom x y z C -0.67131 1.226773 0.110787 C 0.721598 1.211468 0.043066 C 1.409741 -0.00342 -0.12921 C 0.656886 -1.18802 -0.22921 C -0.72811 -1.174 -0.18039 C -1.40189 0.040172 -0.01054 H -1.19693 2.16584 0.257167 I 1.674224 3.080753 0.302326 C 2.89595 -0.08862 -0.26848 H 1.18887 -2.12742 -0.35705 H -1.30669 -2.09089 -0.26905 C -2.89379 0.014233 0.042614 O 3.611464 0.771182 -0.7389 O -3.56338 -0.99761 -0.04167 O -3.42355 1.252982 0.196244 O 3.36096 -1.28498 0.179942 C 4.783545 -1.46743 0.029794 C -4.86366 1.290543 0.25541 H 4.995681 -2.45608 0.442882 H 5.32777 -0.69142 0.579301 H 5.066417 -1.41795 -1.02774 H -5.22609 0.702481 1.105896 H -5.29449 0.886594 -0.66747 H -5.12321 2.344835 0.374268
141 Texas Tech University, Babak Tahmouresilerd, August 2020
Table 3.15. DFT optimized cartesian coordinates for Me2IBPDC (EHOMO = –6.0337 eV). Atom x y z C -2.82304 1.225915 0.378949 C -1.4368 1.262487 0.245599 C -0.67954 0.081448 0.137158 C -1.38469 -1.13792 0.149533 C -2.76425 -1.18832 0.283318 C -3.49492 -0.00167 0.405601 H -3.39059 2.148886 0.453695 I -0.54875 3.183295 0.102359 H -0.81314 -2.06207 0.074325 H -3.29577 -2.13746 0.301427 C -4.97509 -0.09741 0.550112 O -5.59752 -1.14269 0.562015 O -5.56001 1.122135 0.669394 C -6.99378 1.091452 0.810667 H -7.27888 0.525281 1.704437 H -7.45534 0.62515 -0.06699 H -7.30055 2.13604 0.899489 C 0.796806 0.035506 0.009668 C 1.383472 -0.63546 -1.07436 C 2.766653 -0.72763 -1.19282 C 3.594438 -0.16091 -0.2153 C 3.014378 0.497361 0.877204 C 1.633503 0.598855 0.986142 H 0.74429 -1.07312 -1.84031 H 3.210515 -1.23826 -2.0438 C 5.081019 -0.22929 -0.27826 H 3.668789 0.921761 1.636163 H 1.194331 1.10369 1.844454 O 5.824326 0.24412 0.560235 O 5.507498 -0.88802 -1.39196 C 6.931585 -1.01788 -1.5651 H 7.205228 -0.51098 -2.49694 H 7.161322 -2.08582 -1.645 H 7.459724 -0.57318 -0.71655
142 Texas Tech University, Babak Tahmouresilerd, August 2020
Chapter IV
4. Iodine Supported MOF: Dearomatization Reaction
1.22. Introduction Over the last few years, hypervalent iodine compounds or their monovalent precursors have been established as versatile oxidants in organic transformations, whether as stochiometric reagents or catalysts.152–155 Beyond the cost efficiency and relatively low toxicity of these compounds, their oxidative performance is considered on par with transition metals.1 Among the numerous reported oxidation reactions in literature, the selective oxidation of para–alkyl phenol derivatives has become an important reaction facilitated by hypervalent iodine compounds.156–159 In particular, iodine(III) has been the preferred oxidation state for the oxidation of para-alkyl phenol derivatives.160,161 The corresponding para-quinol products obtained from oxidative dearomatization reaction have turned out to be precious fragments in organic synthesis. Furthermore, these products play a key role in the skeleton of natural products such as Tetrapetalones, Jacaranone, Frondosin C, Cornoside, etc.162–164
A number of hypervalent iodine compounds are commercially available, stable toward air and moisture, and required a mild reaction condition.1 However, despite these benefits and their importance in selective oxidation in organic synthesis, some of the reported reagents have shown low reactivities resulting from poor solubility in common organic solvents. A strategy for improving their activities is the use of acids such as fluoroboric acid, trifluoromethanesulfonic acid, propionic acid, hydrofluoric acid, boron trifluoride etherate, but not all reactions are amenable to these.165–168 Additionally, the design of improved reagents can be hampered by the low thermal stability, sensitivity to moisture and difficulty of isolation.169–175 Recently, some solid or liquid-based supported-iodine systems, using silica, polymer, hydrophobic ionic liquid, graphene oxide (GO), magnetic nanoparticles (Fe3O4), and DMAP-peptide conjugate, have addressed some of the issues through cleaver design and careful optimization and also include the ability to easily recycle and reuse.176–178 Despite the tremendous benefits of these approaches, limitations such as ambiguity in measuring the molecular weight
143 Texas Tech University, Babak Tahmouresilerd, August 2020 arise. In most of them, a stoichiometric amount of the pre-prepared hypervalent compound is required, and they are limited in their tunability. Likewise, the configuration around the active sites which are responsible for the oxidation reaction is not always well-defined.
Recently, oxidative dearomatization of para-alkyl phenol compounds has been accomplished via singlet oxygen generated from the decomposition of the terminal oxidant.179 This method is considered to be effective just for the simple para-quinol rather than a more functionalized structures.180 Para-quinol can also be obtained through a one-pot metal‐catalyzed procedure in a good yield over tungstate‐exchanged layered double hydroxides in the presence of hydrogen peroxide.181
The use of MOFs as heterogeneous catalysts has seen significant developed over the past decade. MOFs offer a superior internal surface area, high density of the catalytic active site, tunability, and recyclability.46,65,83 The metal node, pore space, and the organic linker can be designed as the catalytic site for a wide range of catalytic reactions. The pore size of the framework can be tuned for size selectivity of the substrate in different organic reaction transformations. The well-defined pore can also prevent particle aggregation in catalytic reactions. Recently, MOF material involving iodine reagents has been an interest of scientists as a practical platform in catalysis, coordination chemistry, and desorption properties.182–184
In our recent study, we employed MOFs as an alternative support for homogeneous iodine catalysts that had been modified to act simultaneously as linkers.185 These heterogeneous systems proved to be competent catalyzes towards the oxidation of a broad range of para-hydroquinone and catechol derivatives to the corresponding quinols. Following the success of these studies, we sought to expand the repertoire of these catalyst to include some more challenging reactions. Herein, we report the application of MOFs containing aryl-iodide linkers (Figure 4.1) towards the oxidative dearomatization of para-alkyl phenol derivatives to the corresponding para- quinol. These MOFs act as efficient, stable, and recyclable catalysts giving yields up to 93% in batch reactions and up to 76% in a fixed-bed flow reactor.
144 Texas Tech University, Babak Tahmouresilerd, August 2020
Figure 4.1. Representative catalytic iodine sites in DUT-5 (top) and UiO-67 (bot-tom).
1.23. Results and Discussion Multivariate (MTV) Zr (I-UiO-66, I-UiO-67) and Al MOFs (I-MIL-53, I-DUT- 5) containing 25% iodo-functionalized linker (collectively denoted I-MOFs) were prepared and characterized as previously described.185 Iodine sites have been incorporated in both MIL-53 (Al) and UiO-66 (Zr) MOFs. A multivariate approach was used to increase the accessible area within the pores to allow for the catalytic oxidation of a model substrate, hydroquinone, to the corresponding quinone. In the process, three new phases of MIL-53 were discovered, one of which proved instrumental in allowing catalysis to occur. Both UiO-66 and MIL-53 with 25% incorporated iodine-containing linkers allowed for a near-ideal balance between high density of catalytic sites and sufficient space for mass transport to enable catalysis to occur. Good conversions and selectivities were observed in nitromethane, ethyl acetate, acetone, and ethanol with UiO-66 which proved to be the more active of the two catalysts. Oxone and 3- chloroperbenzoic acid acted as competent terminal oxidants. X-ray photoelectron spectroscopy revealed that the reaction proceeded through an I(III) oxidation state. The MIL-53 framework was readily recycled while the UiO-66 MOF suffered from catalyst
145 Texas Tech University, Babak Tahmouresilerd, August 2020 deactivation due to particle agglomeration. UiO-66 with 25% iodine containing linker proved to be a competent catalyst for a variety of substituted hydroquinones. Iodine functionalized variants of DUT-5 (Al) and UiO-67 (Zr) were prepared as expanded-pore analogues of MIL-53 (Al) and UiO-67 (Zr). They were prepared using a combination of multivariate and isoreticular expansion strategies. Multivariate MOFs with a 25% iodine-containing linker was chosen to achieve an ideal balance between a high density of catalytic sites and sufficient space for efficient diffusion. Changes to the oxidation potential of the catalyst as a result of the pore-expansion strategy led to a decrease in activity with electron rich substrates. On the other hand, these larger frameworks proved to be more efficient catalysts for substrates with higher oxidation potentials. Recyclability tests for these larger MOFs showed sustained catalytic activity over multiple recycles.70,1 These MOFs are constructed from redox inactive metal clusters containing robust bonds to the carboxylate groups of the linkers. It has been previously demonstrated that the incorporation of only 25% iodo-containing linkers gives an adequate balance between density of the catalytic sites and size of the pore/pore aperture to allow for the efficient oxidative dearomatization of aromatic diols.185
Powder X-ray diffraction (PXRD) patterns were compared with simulated patterns from the crystal structures of the parent MOFs to validate that the expected framework was synthesized and retained. All the PXRD patterns for I-MIL-53, I-UiO- 66, IDUT-5, and I-UiO-67 are in good agreement with simulated patterns of the parent
MOFs (Figure 4.2).53,130,131
146 Texas Tech University, Babak Tahmouresilerd, August 2020
Figure 4.2. PXRD patterns of I-MIL-53, I-UiO-66, IDUT-5, and I-UiO-67, and simulated patterns of parent MOFs.53,130,131 We sought to challenge these MOF catalysts with a more complex reaction. The oxidative dearomatization of 4-methylphenol (p-cresol) was chosen as it is I) not as readily oxidized and II) it is bi-molecular — requiring a nucleophile to be present in the MOF pore for the reaction to occur (Figure 5.3). The reaction can also have varying regioselectivity depending on the oxidation state of iodine and also whether the nucleophile attacks the substrate while it is bound to the iodine or following dissociation.186
OH MOF catalyst O terminal oxidant
NO2Me: H2O OH
Figure 4.3. The model reaction for oxidative dearomatization of 4-methylphenol (p- cresol). In a typical reaction, the terminal oxidant selectively oxidizes the iodine in the framework to generate a hypervalent iodine species. This in situ generated hypervalent iodine site mediates the oxidative dearomatization reaction in the presence of a nucleophile. The oxidative dearomatization of p-cresol was performed in the presence
147 Texas Tech University, Babak Tahmouresilerd, August 2020 of 20 mol% of I-MOF catalysts and 3.0 equivalent of terminal oxidant, with the specified solvent, and nucleophile for 24 h at 50 °C. All of the I-MOFs (Table 4.1, entries 3-10) catalyzed the oxidation of p-cresol to the corresponding p-quinol product ranging from 16 to 74% yield. Here it should be noted that the solvent mixture is biphasic. Water performs a dual role as a solvent for the oxone and nucleophile.
Table 4.1. Evaluation of oxidative dearomatization of p-cresol to the corresponding p- quinol.a
# I-MOF Terminal Yield (%)b Conversion (%)b catalyst oxidant 1 - mCPBA 22 23 2 - oxone 6 6 3 I-MIL-53 mCPBA 26 79 4 I-MIL-53 oxone 16 64 5 I-DUT-5 mCPBA 74 81 6 I-DUT-5 oxone 63 68 a Reaction condition: substrate (0.145 mmol), 3.0 equivalents of terminal oxidant, 4 mL nitromethane and DI water (3:1 v:v), at 50 °C for 24 h.
b Values are determined by 1H NMR in the presence of methylsulfonylmethane (MSM) as an internal standard. The catalytic reaction in the presence of the smaller MOFs I-UiO-66 and I-MIL- 53 gave the lower values (Table 4.1, entries 3-6). The lower activities of these MOFs compared to the larger MOFs (I-UiO-67 and I-DUT-5) can be attributed to the smaller pore size and poor diffusion of organic reagents into the frameworks.66,185 Table 4.2 shows a comparison between the values of the surface area and the pore volume of all four frameworks as obtained in our earlier studies.
148 Texas Tech University, Babak Tahmouresilerd, August 2020
Table 4.2. Molar Brunauer-Emmett-Teller (BET) surface areas and pore volumes for the Zr and Al-based MOFs obtained from nitrogen adsorption isotherms at 77 K. MOF BET surface Pore volume area (×103 (mL/mol) m2ꞏmol-1)a I-UiO-6666 246 115 I-MIL-5366 191 81 I-UiO-67185 690 334 I-DUT-5185 354 174 a Based on the idealized formula [Zr6O4(OH)4(L)6] for UiO-66 and UiO-67 and [Al4(OH)4(L)4] for MIL-53 and DUT-5, normalized to one Zr or Al, respectively. Under similar reaction conditions, I-MIL-53 and I-DUT-5 are more efficient catalysts than I-UiO-66 and I-UiO-67, respectively. This is seemingly at odds with the larger pore volumes and surface areas associated with the UiO series and indicates that another parameter may be more important. It has been demonstrated that a small pore aperture can severely hamper the ability of substrates to diffuse into and through the framework.187 The higher catalytic activity is, therefore, proposed to result from the larger pore apertures associated with the I-MIL-53 and I-DUT-5 frameworks (Error! Reference source not found.).
Figure 4.4. Comparison of pore apertures in DUT-5 0%-I (left) and UiO-67 0%-I (right). In order to accurately evaluate the activities of I-MOF catalysts, several control reactions were performed to determine the extent of any competing reaction pathways (Table 4.3). The first control reaction (A) was conducted with no MOFs/I-MOFs or terminal oxidant and a negligible conversion (≤1) was observed, as expected. The second and third control reactions were performed in the presence of the oxidant (B) or in the presence of the oxidant and the parent MOFs (C). In both cases, mCPBA showed
149 Texas Tech University, Babak Tahmouresilerd, August 2020 higher activity over oxone. The fact the no difference is observed between trials B and C indicates that the observed reactivity results from a direct reaction with the oxidant. The last control reaction (D) was run with the I-MOFs in the absence of any oxidant. The observed conversion (10±2%) is, at first unexpected. It has been previously shown by XPS that some oxidation of the iodine in I-MIL-53 and I-UiO-66 occurs prior to the reaction, likely during activation which is performed in air.66 This small amount of pre- oxidized iodine could account for the observed conversion in control reaction D.
Table 4.3. Control reactions for oxidative dearomatization of p-cresol. # Terminal I-MOFs Parent Conversion (%) oxidant MOFs A - - - ≤1 B ✓ - - 6±3a, 23±3b C ✓ - ✓ 6±3a, 19±3b D - ✓ - 10±2 a Reaction condition: 20 mol% either I-MOF/ or parents MOFs, 3.0 equiv. terminal oxidant a) oxone or b) mCPBA, CH3NO2: H2O (3:1), at 50 °C for 24 h.
b Values were determined by 1H NMR in the presence of methylsulfonylmethane (MSM) as an internal standard. Across the board, higher conversions in control reactions were obtained with mCPBA as compared with oxone as the oxidant. Oxone, however, was deemed the superior oxidant for these reactions as a result of its more sluggish performance in the direct oxidation of the substrate (see control reactions B, C in Table 4.3). Additional benefits of oxone include higher stability and the more environmentally friendly by products.
The moderate yield of reaction for entries 3-10 in Table 4.1 can be attributed to insufficient nucleophile present in the catalyst pore. An equivalent experiment with a significantly higher concentration of nucleophile caused an enhancement in the yield and conversion of catalytic reaction for all the catalysts as depicted in Figure 4.5. This result is independent of the oxidant used, pore aperture, or linker, a strong the increased concentration of nucleophile in the pore that accounts for the enhanced reactivity.
150 Texas Tech University, Babak Tahmouresilerd, August 2020
Figure 4.5. The conversion of the dearomatization of p-cresol to the p-quinol beyond the control reaction. Solid colors CH3NO2: H2O (3:1 v:v) are compared to vertical stripes (1:3 v:v) as a modified ratio. Reaction conditions: 20 mol% cat., ∼3.0 equiv. of the terminal oxidant, 24 h, at 50 °C. Under the modified ratio, the yield of 39% and 89% (beyond the control reaction) was observed catalyzed by I-DUT-5 in the presence of oxone and mCPBA as terminal oxidant, respectively. (Table 4.4, entries 11-12). Entries 12-13 in Table 4.4 report the yield as a function of catalyst loading. A lower amount of catalyst loading of reaction up to 15 mol% in the presence of oxone gave 68% yield (Table 4.4, entries 13). Furthermore, lowering the amount of oxone to 2.0 equivalent, decreased the yield of reaction to 61% (Table 4.4,, entries 14). Maximizing the amount of nucleophile by performing the reaction in water, however, resulted in a lower yield (Table 4.4, entry 15). Alternatively, a THF/water mixture did not result in a significant yield (Table 4.4, entry 16). These results underscore the importance of nitromethane, a polar nonnucleophilic solvent, in the reaction. It is proposed that the high dielectric of nitromethane, as compared to THF, allows it to better stabilize the phenoxenium ion that forms following the redox decomposition of the aryl-λ3-iodane.
151 Texas Tech University, Babak Tahmouresilerd, August 2020
Table 4.4. The catalytic yield of oxidative dearomatization of p-cresol to the corresponding p-quinol using I-DUT-5 with a loading of X and Y equiv. of terminal oxidant.a # Terminal X Y Solvent/ Yield oxidant Nucleophile (%)b 11 mCPBA 20 3 CH3NO2: H2O (1:3) 39 12 oxone 20 3 CH3NO2: H2O (1:3) 89 13 oxone 15 3 CH3NO2: H2O (1:3) 68 14 oxone 20 2 CH3NO2: H2O (1:3) 61 15 oxone 20 3 H2O 50 16 oxone 20 3 THF: H2O (1:3) 17 a Reaction condition: substrate (0.145 mmol), X mol% I-DUT-5, Y equivalents of terminal oxidant, 4 mL nitromethane and DI water (3:1 v:v), at 50 °C for 24 h.
b Values are reported beyond the control reaction and determined by 1H NMR in the presence of methylsulfonylmethane (MSM) as an internal standard. To make sure that the catalyst is not leaching, a split test was conducted. The result of the split test confirms that the reaction is not occurring homogeneously due to leaching linker. Moreover, the ability to recycle the I-DUT-5 catalyst was probed using the oxidative dearomatization of p-cresol. The catalytic yield of reaction showed a moderate decrease of ⁓9%. This can be attributed to catalyst attrition from manipulations between the runs and the impact of the time of reaction on the stability of the MOF. On the third cycle, the yield dropped to 32%. Following this run, a decrease in crystallinity can be observed by PXRD indicating that the long-term stability of this MOF under these conditions in somewhat limited.
A loading of 15 mol% was chosen for the evaluation of other substrates to ensure that differences in reactivity could be appreciated. A typical mechanism for oxidative dearomatization reactions is shown in Figure 4.6. This pathway is considered for hypervalent iodine(III)-mediated catalytic dearomatization oxidative reaction, where a 2,5-cyclohexadienone type compound is hypothetically formed.
152 Texas Tech University, Babak Tahmouresilerd, August 2020
Figure 4.6. The mechanism for catalytic oxidative dearomatization of p-cresol by I- DUT-5 in presence of oxone. The first step of the mechanism for I-MOF requires activation of the pores (i.e., washing impurities from the pores via solvent exchange and heating up it under vacuum to remove residual solvent) to ensure the catalytic reaction is heterogeneous rather than the result of unreacted linker leaching from the pores (Figure 4.6, step I). This step can simply be monitored by FTIR analysis to track the loss of the peak corresponding to the C=O vibrational modes in DMF and unreacted linker. This reaction can be described in three general processes, including oxidation of the iodine, ligand exchange, and reductive elimination, similar to some reaction mechanisms with transition metals.1 The activated I-MOF is oxidized by a terminal oxidant in order to generate a hypervalent iodine species (Figure 4.6, step II, oxidation). Previous X-ray photoelectron spectroscopic (XPS) analysis of I-UiO-66 and I-MIL-53 demonstrated that the iodine was oxidized to the +3 oxidation state to form a λ3-iodane in the framework after
153 Texas Tech University, Babak Tahmouresilerd, August 2020 treatment with mCBPA.66 The next step involves the ligand exchange at the iodine(III) center with the substrate (Figure 4.6, step III). Step III from Figure 4.6 can proceed in one of two ways: I) dissociation of a phenoxenium ions and then undergoes an attack by a nucleophile, or II) direct attack of the nucleophile (reductive elimination) to give the p-quinol product(s).188 Regardless of the pathway, nucleophilic attack can occur at the para position to give compound 2 or the ortho position to give 3 (see scheme associated with
Table 4.6). Steric and electronic factors can contribute to selectivity on both pathways. Table 4.5 and Figure 4.7 demonstrated the calculated Hirschfeld charge distributions, nucleophilic attack susceptibility, and electrostatic potential map of phenoxenium ions of p-cresol and some of its derivatives containing electron-donating and withdrawing groups. According to the Hirschfeld charge distributions, the 4- methylphenoxonium (1a′) para attack is favored. This is consistent with the experimental result following the reactions conditions specified in
Table 4.6. Under these conditions, a catalytic yield of 77% and 57% for the formation of 2a was observed at 50 °C and RT, respectively.
Table 4.5. Hirschfeld charges in phenoxenium ions containing electron-donating and withdrawing groups at C2 (ortho), C4(para), and C6(ortho).
Substrate C2 (ortho) C4 (para) C6 (ortho) 1a′, -H 0.14 0.21 0.12 1b′, -Cl 0.15 0.18 0.09 1c′, -Br 0.14 0.17 0.09 1d′, -Me 0.14 0.19 0.11 1e′, -OMe 0.15 0.14 0.07 1f′, -tBu 0.11 0.18 0.12
154 Texas Tech University, Babak Tahmouresilerd, August 2020
Figure 4.7. Nucleophilic attack susceptibility based on the Fukui function (first row), and electrostatic potential map (second row) for p-cresol derivatives scaled in Hartree. Isosurface value is 0.01 a.u. This is also in good agreement with the Fukui function which predicts sites of susceptibility for nucleophilic attack. Here a para-substituted product is also anticipated (Figure 4.7). The scope of the substrates was extended to other derivatives of the p- cresol containing electron-donating (EDG) and withdrawing groups (EWG) including - t Br, -Cl, -CH3, -OCH3, and Bu. A modest yield of the reaction was observed for p-cresol derivatives containing the EWG groups. For 1b and 1c, the para-substituted product (2b or 2c) was exclusively formed as predicted in a calculation study based on the Fukui function. These results are, therefore, consistent with the dissociative pathway. The reaction with substrates containing EDG groups including 2,4-dimethylphenol (1d) and 2-methoxy-4-methylphenol (1e) are less selective and also undergo nucleophile attack at ortho position; in line with
Table 4.6 and Figure 4.7. The catalytic reaction of 1d at 50 °C favors the formation of an ortho-substituted product (3d), up to 29% yield. At a lower temperature, a lower ortho-selectivity was observed (higher para-selectivity up to 56%) highlighting the role of reaction temperature on selectivity here. 2-methoxy-4-methylphenol (1e) seems to be an anomaly among the derivatives of p-cresol. The catalytic reaction at 50 °C shows 0% yield for (2e) and (3e). A low yield of (2e) and (3e) was observed when the reaction was run at RT. The low yields of desired products, in light of the reasonable conversions suggest that an alternate reaction pathway is being followed or a subsequent reaction that consumes 2e and 3e is occurring.189
155 Texas Tech University, Babak Tahmouresilerd, August 2020
In contrast to (1d) and (1e), 2,6-di-tBu-p-cresol (1f) undergoes an attack at the para position as the ortho position is highly hindered by bulky -tBu groups. For 2,6-di- tBu-p-cresol (1f), a very low yield of reactions was observed at RT and 50 °C. This is likely the result of it being too big to readily diffuse into the pores of the MOF, or to access the catalytic center.
Table 4.6. The result of the substrate scope for nucleophilic oxidative dearomatization of para-methyl phenol derivatives to the corresponding p-quinol products.a
Substrate 2a yield 3a yield Total Yield Conversion p-Selectivity (%)b (%)b (%)b (%)b (%) (1a) 77 (57) 2 (2) 79 (59) 80 (62) 97 (97) (1b) 58 (43) 4 (2) 62 (45) 91 (72) 94 (96) (1c) 51 (39) 5 (2) 56 (41) 95 (73) 91 (95) (1d) 13 (29) 29 (23) 42 (52) 96 (88) 31 (56) (1e) 0 (4) 0 (14) 0 (18) 77 (69) 0 (22) (1f) 9 (5) 1(0) 10 (5) 12 (5) 90 (100) a Reaction conditions: 15 mol% catalyst, ∼3.0 equiv. oxone, CH3NO2: H2O (1:3 v:v), at RT⁓24 °C or 50 °C for 18 h.
b The values in parenthesis show the RT results. In order to study the electronic effect of the different substrates on the results of the catalysis, a cyclic voltammetry (CV) experiment was conducted (Figure 4.8). The values of the oxidation potentials for all the substrates ranging from 0.95 V to 1.39 V.
The lower oxidation potential for -OCH3 (1e) is consistent with our assumption in which it is undergoing another pathway.
156 Texas Tech University, Babak Tahmouresilerd, August 2020
Figure 4.8. Cyclic Voltammogram (CV) of para-methyl phenol derivatives containing electron-donating and withdrawing groups obtained in acetonitrile in 0.1 M Bu4NBF4 at 100 mV/s vs. Fc/Fc+. We decided to assess the oxidation of p-cresol with I-DUT-5 as a catalyst in a fixed-bed continuous-flow reactor. The column filled with finely grounded I-DUT-5 packed between sand and held in place with a cotton plug (Figure 4.9). Solutions of p- cresol and oxone were supplied from separate syringes. The reaction was run for a total of 24 h. This rate corresponds to a residence time of less than 60 min on the catalyst bed and leads to complete conversion of p-cresol yielding 76% of p-quinol beyond the control reaction (3% of 2a). This corresponds to a similar conversion to the batch reaction, but at a much shorter time in contact with the catalyst. The flow system can be reused a second time, loss in activity is observed on the third run consistent with the recycling experiments.
Figure 4.9. The oxidative dearomatization of p-cresol into p-quinol under continuous flow conditions with a stoichiometric amount of I-DUT-5 (1.0 equiv.)
157 Texas Tech University, Babak Tahmouresilerd, August 2020
Table 4.7 compares the oxidative dearomatization of p-cresol with a variety of iodo-based reagents. Pseudocyclic aryl‐λ3‐iodanes and aqua complexes containing aryl iodonium ions stabilized by the coordination of crown ether with 71 to 87% yield at RT have the highest activity. This is likely due to enhanced solubility, stability, and reactivity. (Diacetoxyiodo)benzene, [bis(trifluoroacetoxy)iodo]benzene, and 4- iodophenylacetic acid have a moderate activity by giving a yield ranging from 39-48%.
Table 4.7. Comparison of iodo-based reagents or catalysts for the oxidative dearomatization of p-cresol into p-quinol.
Catalyst /Reagent Loading Solvent/Nu Time Temp. Yield (equiv.) (h) (°C) (%) 190 PhI(OAc)2 2.6 CH3CN/H2O 0.5 0 44 191 PhI(OAc)2 1.05 CH3CN/H2O 1 25 39 192 PhI(O2CCF3)2 1.1 CH3CN/H2O 0.25 0 48 Pseudocyclic benziodoxole 1.2 CH3CN/H2O 24 RT 50 triflate193 194 Heterocycle Stabilized Iodanes 0.91 CH3CN/H2O 0.2 0 71 Crown ether complexes of 1.2 H2O 3 RT 87 aqua(hydroxy)(aryl)iodonium Ions59 I-DUT-5 in flow 1.0 CH3NO2/H2O 24 50 76 196 4-iodophenoxyacetic acid 0.1 THF/H2O 4 RT 40 I-DUT-5 in batch 0.15 CH3NO2/H2O 18 RT-50 57-77
The lower yield with these reagents can be attributed to lower stability under the given reaction conditions.191,192 The MOF-based system reported in this study has the advantages of being a tunable catalyst and reusable by simple filtration.
1.24. Conclusion Four robust, iodo-functionalized MOFs were applied as catalysts in the oxidative dearomatization reaction of p-quinols. All the frameworks were able to catalyze the oxidation of p-cresol into the p-quinol product. The performance of I-DUT-5, synthesized based on a combination of multivariate and isoreticular expansion strategies, was superior to the other I-MOFs. The study of catalytic performance of p- cresol was extended to its derivatives, alongside with theoretical analysis to identify the favorable product. We have thus demonstrated I-DUT-5 under both batch and flow
158 Texas Tech University, Babak Tahmouresilerd, August 2020
reaction systems has high reactivity, stability, and recyclability as a catalyst in the oxidative dearomatization of p-cresol to p-quinol.
1.25. Experimental Details 1.25.1. General Methods Aluminum chloride hexahydrate (99.0%, Acros Organics), zirconium
tetrachloride (98.0%, Merck KGaA), terephthalic acid (H2BDC, >99.0%, TCI), 2-
aminoterephthalic acid (H2BDC-NH2, 99.0%, Acros Organics), N,N- dimethylformamide (DMF, >99.9%, EMD Millipore), hydrochloric acid (36.5-38.0%, BDH), isopropanol alcohol (99.5%, BDH), dichloromethane (99.9%, Fisher Scientific), dimethyl-[1,1'-biphenyl]-4,4'-dicarboxylate (>97%, Browm molecular), [1,1'- biphenyl]-4,4'-dicarboxylic acid (97%, Ark Pharm), tetrahydrofuran (99.0%, Fisher Scientific), nitric acid (68.0-70.0%, AR® ACS, Macron Fine Chemicals™), meta- chloroperoxybenzoic acid (70.0-75.0%, Acros Organics), potassium hydroxide (≥85.0%, Fisher Scientific), sulfuric acid (96.0%, J.T.Baker), magnesium sulfate
anhydrous (≥99.0%, J.T.Baker), dimethyl sulfoxide-d6 (DMSO-d6, >99.0%, Cambridge Isotope Laboratories), dimethyl sulfone (>99.0%, TCI), tin mossy (95.5%, Alfa Aesar), ethanol (99.5%, Pharmterminal AAPER), methanol (>99.9%, Fisher Scientific), nitromethane (>98.0%, Alfa Aesar), deuterium oxide (>99.0%, Cambridge Isotope
Laboratories), sodium deuteroxide solution 40 wt. % in D2O (>99.0%, Acros Organics), potassium iodide (>99.0%, Fisher Scientific), sodium bisulfite (98.5%, Fisher Scientific) and sodium nitrite (>99.0%, J.T.Baker), oxone, monopersulfate compound (Oakwood Chemical), 2-methoxy-4-methylphenol (>98.0%, Alfa Aesar), 2,4- dimethylphenol (99.0%, Acros Organics), butylated hydroxytoluene (Ward's Science), 2-chloro-4-methylphenol (>95.0%, Matrix Scientific), p-cresol (>99.0%, Acros Organics), 3-Bromo-4-methylphenol (98.0%, Alfa Aesar) were used as purchased without further purification.
All measurements, unless noted otherwise, were carried out at 298 K and NMR chemical shifts were given in ppm. The 1H NMR spectra were referenced to the residual
159 Texas Tech University, Babak Tahmouresilerd, August 2020
1H residue in the deuterated solvent. All IR spectra were obtained using a Nicolet iS 5 FT-IR spectrometer equipped with a diamond ATR accessory.
1.25.2. Safety Statement for Handling and Disposing of Peroxides. Beyond all the basic safety instructions in the laboratory, special precautions must be taken when handling and disposal of the peroxides as they have different levels of instability, so they can be very unpredictable. Peroxides can react violently if they interact with incompatible compounds. Likewise, some of the hypervalent iodine are heat or/ and shock sensitive. So, it is safer using the least possible amount of peroxides for experiments and knowing the compatibilities of them with other employed material. All leftover reaction mixture containing peroxides were dilute with water and neutralized with sodium sulfite. The wastes were disposed according to the Environmental Health & Safety (EHS) waste collection directions at Texas Tech University. In this study, we did not observe any incompatibility between I-MOFs or esterified iodo-linker when interacted with peroxides under the given conditions.
1.25.3. Catalytic Experiments
1.25.3.1. Typical Catalytic Reaction Procedure
In a typical catalytic reaction, the catalyst (20 mol%), terminal oxidant (0.435 mmol, 3.0 equivalent ), and substrate (0.145 mmol) were mixed in the specified solvent or solvent mixture (4.0 mL) along with the internal standard (equimolar with substrate) in a 2-dram clear glass vial. The vial was charged with a Teflon coated stir bar and placed on a hot plate at the specified temperature. After the specified time had been reached, the catalyst was separated by centrifugation, the liquid was decanted, and the organic phase was separated using ethyl acetate, washed three times with DI water, and dried at ambient temperature after treating with magnesium sulfate. The solid was
dissolved in the deuterated CDCl3 or DMSO to determine the catalytic conversion and yield via integration of the relevant peaks in the 1H NMR spectrum.
160 Texas Tech University, Babak Tahmouresilerd, August 2020
Figure 4.10. The oxidative dearomatization of p-cresol (1) into p-quinol (2) or o-quinol as possible side products.
161 Texas Tech University, Babak Tahmouresilerd, August 2020
1.25.3.2. Results of All Catalytic Experiments
Table 4.8. The results of initial control reactions for the oxidative dearomatization of para-cresol (PC) to para-quinol (PQ) in the presence of 20 mol% either I-MOFs or parents MOF, 3.0 equivalent of oxone or mCPBA, 4 mL nitromethane and DI water (3:1 v:v) at 50 °C for 24 h.a Sample Normalized Normalized Normalized Total Yield Conversion integrated integrated integrated normalized (%)b (%)b Entry intensity of intensity of intensity of integrated (MSM) (PC) (PQ) intensity of reactants and products Control A NO MOFs, NO oxidants 1.00 0.99 0.01 1.00 1 1 Control B NO MOFs, oxone 1.00 0.93 0.06 0.99 6 6 Control B* NO MOFs, mCPBA 1.00 0.76 0.23 0.99 22 23 Control C Parent MOF, oxone 1.00 0.93 0.06 0.99 6 6 Control C* Parent MOF, mCPBA 1.00 0.81 0.16 0.97 16 19 Control D I-MOF, No oxidant 1.00 0.90 0.09 0.99 9 10 a Reaction condition:
(A) Substrate (0.145 mmol), 4 mL nitromethane and DI water (3:1 v:v) at 50 °C for 24 h.
(B) Substrate (0.145 mmol), 3.0 equivalent oxone, 4 mL nitromethane and DI water (3:1 v:v) at 50 °C for 24 h, (B)* was performed in the presence of 3.0 equivalent of mCPBA.
(C) Substrate (0.145 mmol), 20 mol% DUT-5 0%-I, 3.0 equivalent oxone or mCPBA, 4 mL nitromethane and DI water (3:1 v:v) at 50 °C for 24 h, (C)* was performed in the presence of 3.0 equivalent of mCPBA.
(D) Substrate (0.145 mmol), 20 mol% DUT-5 25%-I, 4 mL nitromethane and DI water (3:1 v:v) at 50 °C for 24 h.
b Values were determined by 1H NMR in the presence of methylsulfonylmethane (MSM) as an internal standard.
162 Texas Tech University, Babak Tahmouresilerd, August 2020
Table 4.9. The results of control reactions for the oxidative dearomatization of para-cresol (PC) to para-quinol (PQ) in the presence of 3.0 equivalents of oxone or mCPBA, 4 mL specified solvent and nucleophile at 50 °C for 24 h.a Solvent Normalized Normalized Normalized Total Yield Conversion integrated integrated integrated normalized (%)b (%)b intensity of (MSM) intensity of intensity of integrated Terminal (PC) (PQ) intensity of oxidant reactants and products Nitromethane: H2O (1:3 v:v) 1.00 0.86 0.09 0.95 9 14
Nitromethane : H2O (3:1 v:v) oxone 1.00 0.93 0.06 1.00 6 6 H2O 1.00 0.96 0.03 0.99 3 4 Nitromethane: H2O (1:3 v:v) mCPBA 1.00 0.76 0.22 0.98 22 25 Nitromethane : H2O (3:1 v:v) 1.00 0.76 0.23 0.99 22 23 a Reaction condition: substrate (0.145 mmol), 3.0 equivalent oxone or mCPBA, 4 mL specified solvent and the nucleophile at 50 °C for 24 h. b Values were determined by 1H NMR in the presence of methylsulfonylmethane (MSM) as an internal standard. Table 4.10. The results of oxidative dearomatization of para-cresol (PC) to para-quinol (PQ) in the presence 20 mol% DUT-5 25%-I, 3.0 equivalents of oxone or mCPBA, 4 mL specified solvent and nucleophile at 50 °C for 24 h.a Solvent Normalized Normalized Normalized Total Yield Conversion integrated integrated integrated normalized (%)b (%)b intensity of (MSM) intensity of intensity of integrated Terminal (PC) (PQ) intensity of oxidant reactants and products Nitromethane: H2O (3:1 v:v) 1.00 0.32 0.63 0.95 63 68 Nitromethane : H2O (1:3 v:v) 1.00 0.02 0.98 0.98 98 100 H2O oxone 1.00 0.31 0.53 0.84 53 69 THF: H2O (1:3 v:v) 1.00 0.59 0.17 0.76 17 41 Nitromethane: H2O (3:1 v:v) mCPBA 1.00 0.20 0.74 0.94 74 81 Nitromethane : H2O (1:3 v:v) 1.00 0.00 0.61 0.61 61 100 a Reaction condition: substrate (0.145 mmol), 3.0 equivalent oxone or mCPBA, 4 mL specified solvent and the nucleophile at 50 °C for 24 h. b Values were determined by 1H NMR in the presence of methylsulfonylmethane (MSM) as an internal standard.
163 Texas Tech University, Babak Tahmouresilerd, August 2020
Table 4.11. The results of oxidative dearomatization of para-cresol (PC) to para-quinol (PQ) in the presence 20 mol% UiO-67 25%-I, 3.0 equivalents of oxone or mCPBA, 4 mL nitromethane and specified nucleophile at 50 °C for 24 h.a Solvent Normalized Normalized Normalized Total Yield Conversion integrated integrated integrated normalized (%)b (%)b intensity of (MSM) intensity of intensity of integrated Terminal (PC) (PQ) intensity of oxidant reactants and products Nitromethane: H2O (3:1 v:v) 1.00 0.54 0.45 0.99 45 45 Nitromethane : H2O (1:3 v:v) oxone 1.00 0.38 0.47 0.85 47 62 Nitromethane: H2O (3:1 v:v) 1.00 0.57 0.41 0.98 41 43 Nitromethane : H2O (1:3 v:v) mCPBA 1.00 0.31 0.61 0.92 61 69 a Reaction condition: substrate (0.145 mmol), 3.0 equivalent oxone or mCPBA, 4 mL specified solvent and the nucleophile at 50 °C for 24 h. b Values were determined by 1H NMR in the presence of methylsulfonylmethane (MSM) as an internal standard. Table 4.12. The results of oxidative dearomatization of para-cresol (PC) to para-quinol (PQ) in the presence 20 mol% UiO-66 25%-I, 3.0 equivalents of oxone or mCPBA, 4 mL nitromethane and specified nucleophile at 50 °C for 24 h.a Solvent Normalized Normalized Normalized Total Yield Conversion integrated integrated integrated normalized (%)b (%)b intensity of (MSM) intensity of intensity of integrated Terminal (PC) (PQ) intensity of oxidant reactants and products Nitromethane: H2O (3:1 v:v) 1.00 0.69 0.26 0.95 26 30 Nitromethane : H2O (1:3 v:v) oxone 1.00 0.17 0.46 0.63 46 83 Nitromethane: H2O (3:1 v:v) 1.00 0.59 0.23 0.82 23 41 Nitromethane : H2O (1:3 v:v) mCPBA 1.00 0.28 0.23 0.51 23 73 a Reaction condition: substrate (0.145 mmol), 3.0 equivalent oxone or mCPBA, 4 mL specified solvent and the nucleophile at 50 °C for 24 h. b Values were determined by 1H NMR in the presence of methylsulfonylmethane (MSM) as an internal standard.
164 Texas Tech University, Babak Tahmouresilerd, August 2020
Table 4.13. The results of oxidative dearomatization of para-cresol (PC) to para-quinol (PQ) in the presence 20 mol% MIL-53 25%-I, 3.0 equivalents of oxone or mCPBA, 4 mL nitromethane and specified nucleophile at 50 °C for 24 h.a Solvent Normalized Normalized Normalized Total Yield Conversion integrated integrated integrated normalized (%)b (%)b intensity of (MSM) intensity of intensity of integrated Terminal (PC) (PQ) intensity of oxidant reactants and products Nitromethane: H2O (3:1 v:v) 1.00 0.36 0.16 0.52 16 64 Nitromethane : H2O (1:3 v:v) oxone 1.00 0.08 0.1 0.21 10 92 Nitromethane: H2O (3:1 v:v) 1.00 0.21 0.26 0.47 26 79 Nitromethane : H2O (1:3 v:v) mCPBA 1.00 0.17 0.33 0.51 33 83 a Reaction condition: substrate (0.145 mmol), 3.0 equivalent oxone or mCPBA, 4 mL specified solvent and the nucleophile at 50 °C for 24 h. b Values were determined by 1H NMR in the presence of methylsulfonylmethane (MSM) as an internal standard.
165 Texas Tech University, Babak Tahmouresilerd, August 2020
Table 4.14. The results of oxidative dearomatization of para-cresol (PC) to para-quinol (PQ) in the presence 20 mol% esterified linker a Me2I-BPDC, 3.0 equivalents of oxone, 4 mL nitromethane and specified nucleophile at 50 °C for 24 h. Solvent Normalized Normalized Normalized Total Yield Conversion integrated integrated integrated normalized (%)b (%)b intensity of (MSM) intensity of intensity of integrated Terminal (PC) (PQ) intensity of oxidant reactants and products Nitromethane: H2O (1:3 v:v) oxone 1.00 0.57 0.34 0.91 34 43 a Reaction condition: substrate (0.145 mmol), 3.0 equivalent oxone or mCPBA, 4 mL specified solvent and the nucleophile at 50 °C for 24 h. b Values were determined by 1H NMR in the presence of methylsulfonylmethane (MSM) as an internal standard.
166 Texas Tech University, Babak Tahmouresilerd, August 2020
Table 4.15. The results of oxidative dearomatization of para-cresol (PC) to para-quinol (PQ) in the presence of different mol% of DUT- 5 25%-I, 3.0 equivalents of oxone, 4 mL nitromethane and DI water (1:3 v:v) at 50 °C for 24 h.a Catalyst loading (mol%) Normalized Normalized Normalized Total Yield Conversion integrated integrated integrated normalized (%)b (%)b intensity of (MSM) intensity of intensity of integrated (PC) (PQ) intensity of reactants and products Control B 1.00 0.93 0.06 0.99 6 6 DUT-5 25%-I (20 mol%) 1.00 0.02 0.98 0.98 98 100 DUT-5 25%-I (15 mol%) 1.00 0.20 0.77 0.97 77 80
a Reaction condition: substrate (0.145 mmol), 3.0 equivalent oxone or mCPBA, 4 mL specified solvent and the nucleophile at 50 °C for 24 h. b Values were determined by 1H NMR in the presence of methylsulfonylmethane (MSM) as an internal standard. Table 4.16. The results of oxidative dearomatization of para-cresol (PC) to para-quinol (PQ) in the presence of different equivalents of oxone, 20 mol% DUT-5 25%-I, 4 mL nitromethane and DI water (1:3 v:v) at 50 °C for 24 h.a Equivalents of oxone Normalized Normalized Normalized Total Yield Conversion integrated integrated integrated normalized (%)b (%)b intensity of (MSM) intensity of intensity of integrated (PC) (PQ) intensity of reactants and products 2.0 equiv. Control 1.00 0.94 0.04 0.98 4 6 DUT-5 25%-I 20 mol% 1.00 0.30 0.65 0.95 65 70 a Reaction condition: substrate (0.145 mmol), 3.0 equivalent oxone or mCPBA, 4 mL specified solvent and the nucleophile at 50 °C for 24 h. b Values were determined by 1H NMR in the presence of methylsulfonylmethane (MSM) as an internal standard.
167 Texas Tech University, Babak Tahmouresilerd, August 2020
Table 4.17. The results of oxidative dearomatization of substrates to the corresponding p-quinol products in the presence of 15 mol% DUT-5 25%-I, 3.0 equivalents of oxone, 4 mL nitromethane and DI water (1:3 v:v) at RT and 50 °C for 24 h.a Substrate Sample Temp. Normalized Normalized Normalized Normalized Total Yield Conversion (°C) integrated integrated integrated integrated normalized (%) (%) intensity of intensity of intensity of intensity of integrated Entry MSM substrate the desired side intensity product product of reactants and products 4-methylphenol Control 1.00 0.95 0.05 0.00 1.00 5 5 (para-cresol) DUT- 5 24 1.00 0.38 0.57 0.00 0.96 57 62 1a 25%-I Control 1.00 0.93 0.06 0.00 0.99 6 6 DUT- 5 50 1.00 0.20 0.77 0.00 0.97 77 80 25%-I 2-bromo-4- Control 1.00 0.98 0.00 0.00 0.98 0 2 methylphenol DUT- 5 24 1.00 0.28 0.43 0.00 0.71 43 72 1b 25%-I Control 1.00 0.93 0.02 0.00 0.95 2 7 DUT- 5 50 1.00 0.09 0.58 0.04 0.71 58 91 25%-I 2-chloro-4- Control 1.00 0.96 0.00 0.00 0.96 0 4 methylphenol DUT- 5 24 1.00 0.27 0.39 0.02 0.69 39 73 1c 25%-I Control 1.00 0.96 0.02 0.00 0.98 2 4 DUT- 5 50 1.00 0.05 0.51 0.05 0.61 51 95 25%-I
168 Texas Tech University, Babak Tahmouresilerd, August 2020
Substrate Sample Temp. Normalized Normalized Normalized Normalized Total Yield Conversion (°C) integrated integrated integrated integrated normalized (%) (%) intensity of intensity of intensity of intensity of integrated Entry MSM substrate desired byproducts intensity of product reactants and products 2,4- Control 1.00 0.83 0.08 0.04 0.95 8 18 dimethylphenol DUT- 5 24 1.00 0.13 0.29 0.23 0.65 29 88 1d 25%-I Control 1.00 0.37 0.07 0.08 0.52 7 63 DUT- 5 50 1.00 0.05 0.13 0.29 0.47 13 96 25%-I 2-methoxy-4- Control 1.00 0.57 0.04 0.00 0.61 4 43 methylphenol DUT- 5 24 1.00 0.31 0.04 0.14 0.49 4 69 1e 25%-I Control 1.00 0.33 0.04 0.00 0.37 4 68 DUT- 5 50 1.00 0.23 0.00 0.00 0.23 0 77 25%-I 2,6-di-tert-butyl- Control 1.00 0.98 0.01 0.00 0.99 1 2 4-methylphenol DUT- 5 24 1.00 0.94 0.05 0.00 0.99 5 5 1f 25%-I Control 1.00 0.95 0.00 0.00 0.96 0 5 DUT- 5 50 1.00 0.88 0.09 0.01 0.98 9 12 25%-I a Reaction condition: substrate (0.145 mmol), 3.0 equivalent oxone or mCPBA, 4 mL nitromethane and DI water (1:3 v:v) at 50 °C for 18 h. b Values were determined by 1H NMR in the presence of methylsulfonylmethane (MSM) as an internal standard.
169 Texas Tech University, Babak Tahmouresilerd, August 2020
1.25.3.3. 1H NMR Shifts of p-quinol Products
All the 1H NMR shifts of the products are in agreement with the already known and reported compounds in the literature.
# Product Shifts in CDCl3
1 4-hydroxy-4-methylcyclohexa-2,5-dien-1-one (1a): H NMR (400 MHz, CDCl3) δ 1.49 (3H, s), 2.09 (1H, s), 6.14 (2H, d, 2a J = 10.0 Hz), 6.89 (2H, d, J = 10.0 Hz).197
1 2-bromo-4-hydroxy-4-methylcyclohexa-2,5-dien-1-one (2a): H NMR (400 MHz, CDCl3) δ 1.53 (3H, s), 2.04 (1H, s), 2b 6.27 (1H, d, J = 10.0 Hz), 6.92 (1H, dd, J = 10.0, 2.8 Hz), 7.34 (1H, d, 2.8 Hz).198
1 2-chloro-4-hydroxy-4-methylcyclohexa-2,5-dien-1-one (3a): H NMR (400 MHz, CDCl3) δ 1.54 (3H, s), 2.30 (1H, s), 2c 6.24 (1H, d, J = 10.0 Hz), 6.90 (1H, dd, J = 10.0, 2.8 Hz), 7.06 (1H, d, 2.8 Hz).199
1 4-hydroxy-2-methoxy-4-methylcyclohexa-2,5-dien-1-one (4a): H NMR (400 MHz, CDCl3) δ 1.47 (3H, s), 2.37 (1H, br) 2d 3.65 (3H, s), 5.75 (1H, m), 6.20 (1H, m), 6.88 (1H, dd, J = 10.0, 2.8 Hz).200,201
1 4-hydroxy-2,4-dimethylcyclohexa-2,5-dien-1-one (5a): H NMR (400 MHz, CDCl3) δ 1.45 (3H, s), 1.86 (3H, d, 2e J=1.2 Hz), 2.14 (1H, br), 6.11 (1H, d, J=10.0 Hz), 6.65 (1H, m), 6.84 (1H, dd, J=10.0, 3.2 Hz).
1 2,6-di-tert-butyl-4-hydroxy-4-methylcyclohexa-2,5-dien-1-one (6a): H NMR (400 MHz, CDCl3) δ 1.22 (s, 18H), 1.43 (s, 2f 3H), 1.76 (s, 1H), 6.56 (s, 2H).202
1.25.4. Experimental Procedure for Recyclability Test of Multivariate MOFs. The recyclability tests for DUT-5 25%-I was performed in the presence of ~3.0 equivalent oxone in 4 mL nitromethane and deionized water (1:3 v:v) at 50 °C for 18 h. After each run, the catalyst was separated using centrifugation and the liquid was decanted
and 5 drops of liquid were dissolved in 0.5 mL CDCl3 or DMSO-d6 to determine the catalytic conversion. The leftover catalyst was
170 Texas Tech University, Babak Tahmouresilerd, August 2020 washed three times with nitromethane. A 4.0 mL solution containing MSM and p-cresol was added to the catalyst followed by 3.0 equivalent of oxone. The closed cap 2-dram clear glass vial was placed on the hot plate when the temperature was 50 °C for the next cycle for 18 h.
Table 4.18. The recyclability test for DUT-5 25%-I (15 mol%) with 3.0 equiv. equivalent of oxone in 4 mL nitromethane and DI water (1:3 v:v) at 50 °C for 18 h. Sample Run Normalized Normalized Normalized Total Yield Conversion integrated integrated integrated normalized (%) (%) intensity of intensity of intensity of integrated MSM substrate the product intensity of reactants and products Control B - 1.00 0.93 0.06 0.99 6 6 1st 1.00 0.20 0.77 0.97 77 80 DUT-5 25%-I 2nd 1.00 0.30 0.68 0.98 68 70 3rd 1.00 0.65 0.32 0.97 32 34 a Reaction condition: substrate (0.145 mmol), 3.0 equivalent oxone or mCPBA, in 4 mL nitromethane and DI water (1:3 v:v) at 50 °C for 24 h. b Values were determined by 1H NMR in the presence of methylsulfonylmethane (MSM) as an internal standard.
171 Texas Tech University, Babak Tahmouresilerd, August 2020
Figure 4.11. The comparison between starting oxidant before the catalytic reaction and solid came out of the aqueous phase after the catalytic reaction.
Figure 4.12. PXRD patterns of DUT-5 25%-I after catalytic oxidative dearomatization run #1, 2, and 3.
172 Texas Tech University, Babak Tahmouresilerd, August 2020
1.25.5. Split Test for Multivariate MOFs. In order to study of any possible leaching of incorporated linkers in the MOFs during catalytic oxidation reaction of p-cresol to p-quinol split test was done with 1.0 equivalent methylsulfonylmethane (MSM) as internal standard, 1.0 equivalent p-cresol as substrate, 3.0 equivalent oxone as the terminal oxidant in 4 mL nitromethane and deionized water (1:3 v:v) at 50 °C. Two reactions were running under the same condition simultaneously. After 8 hours one of the reactions was interrupted and the catalyst was separated using centrifugation. The hot filtrate was immediately transferred to another vial and the reaction was then allowed to continue under the same conditions. After 18 h no significant yield and conversion change was observed following filtration as summarized in Table 4.19.
Table 4.19. Split test of DUT-5 25%-I, 3.0 equivalent of oxone in 4 mL nitromethane and deionized water (1:3 v:v) at 50 °C. Sample Time Normalized Normalized Normalized Total Yield Conversion (h) integrated integrated integrated normalized (%) (%) intensity of intensity of intensity of integrated MSM HQ BQ intensity of reactants and products Control 8 1.00 0.98 0.02 1.00 2 2 Control 18 1.00 0.93 0.06 0.99 6 6 DUT-5 25%-I 8 1.00 0.46 0.53 0.99 53 54 Filtration after 8 h 18 1.00 0.46 0.53 0.99 53 54 DUT-5 25%-I 18 1.00 0.20 0.77 0.97 77 80 a Reaction condition: substrate (0.145 mmol), 3.0 equivalent oxone or mCPBA, 4 mL nitromethane and DI water (1:3 v:v) at 50 °C for 8-18 h. b Values were determined by 1H NMR in the presence of methylsulfonylmethane (MSM) as an internal standard.
173 Texas Tech University, Babak Tahmouresilerd, August 2020
1.25.6. Continuous Flow Chemistry In a typical procedure 1 equivalent of DUT-5 25%-I was packed between cotton and sand in both sides in a stainless-steel column with a length of 10 cm and inside diameter of 0.5 cm. IDUT-5 was transferred into the one-end sealed reactor and compacted until the reactor was filled. The other side also was sealed with cotton and sand for flow catalysis. For each run precursor solutions containing a) oxone dissolved in 10 mL deionized water, and b) p-cresol in 10 mL nitromethane were pumped continuously. Two solutions were mixed via a T shape piece before moving into the reactor at 50 oC
Figure 4.13. The continuous flow catalysis setup for oxidative dearomatization of p- cresol.
174 Texas Tech University, Babak Tahmouresilerd, August 2020
Table 4.20. The continuous flow chemistry for DUT-5 25%-I (1.0 equiv.) with 3.0 equiv. equivalent oxone in 20 mL nitromethane and deionized water (1:1 v:v) at 50 °C for 24 h. Sample Run Normalized Normalized Normalized Total Yield Conversion integrated integrated integrated normalized (%) (%) intensity of intensity of intensity of integrated MSM substrate the product intensity of reactants and products Control - 1.00 0.96 0.03 0.99 3 4 1st 1.00 0.00 0.79 0.79 79 100 DUT-5 25%-I 2nd 1.00 0.15 0.72 0.87 72 85 3rd 1.00 0.67 0.26 0.93 26 36 1.25.7. Cyclic Voltammetry All CV measurements were performed at 298 K with a Pine Research WaveDriver 10 Potentiostat/Galvanostat. The cell contained a glassy carbon working electrode, a Pt wire auxiliary electrode, and a 0.5 mm diameter Ag wire as a pseudo-reference + electrode. All the potentials were measured in acetonitrile with 0.1 M Bu4NBF4. The potentials are reported relative to the Fc/Fc redox couple.
175 Texas Tech University, Babak Tahmouresilerd, August 2020
Chapter V
5. Current Progress and Future Directions Chapter 5 details some recent progress with our efforts to expand on iodine containing molecules for catalysis. The first part of this chapter discusses MOF design strategies toward preparation of a homochiral framework for enantioselective catalysis. The second part explores the supramolecular chemistry of BODIPY (i.e., 4,4-difluoro-4-bora-3a,4a-diaza-s-indacene) derivative substituted with iodine, as a prelude to assessing the potential as a hypervalent iodine catalyst.
1.26. Toward an Asymmetric Catalyst Asymmetric catalysis refers to catalysis where a chiral catalyst preferentially lowers the activation barrier for the formation of one enantiomer over the other. This is achieved by incorporating chirality into the catalyst near the active site. Often, this chirality is introduced to the catalyst through tedious chemical synthesis and costly purifications. The catalytic asymmetric dearomatization reactions of hypervalent iodine is one of the most important reactions in the total synthesis of many natural products.162– 164 Chiral hypervalent iodine can be generated after being oxidized via a suitable terminal oxidant (e.g., oxone and mCPBA). The generated hypervalent iodine can mediate the asymmetric dearomatization reaction when the substrate stays bound while nucleophilic attack occurs, rather than through a dissociation-first pathway. We propose that the pores of the framework can facilitate selectivity by providing an asymmetric cavity around the catalytic site. This moves the chiral information closer to the reaction site. The constrained space of the pore can aid in organizing the substrates. These reactions can also suffer from regioselectivity and a carefully designed MOF pore can facilitate both regio- and stereoselectivity. For this reason, the design and synthesis of an enantioselective catalyst can be challenging. We are pursuing a multivariate approach where we combine the known catalytically active linker with an amino acid linker to create a homochiral MOF containing catalytically relevant iodine sites.
176 Texas Tech University, Babak Tahmouresilerd, August 2020
1.26.1. Design Strategy to Prepare a Robust Homochiral MOFs Here, we investigate the incorporation of chiral linker into the framework to create a robust homochiral MOF with potential for enantioselective catalysis. However, the design process provides fundamental challenges in how the enantioselective MOF catalyst can create the driving force to catalyze a specific enantiomer. The design process can be broken into a few steps: I) The preparation of new homo-chiral MOFs from inexpensive and tunable linkers, II) The incorporation of catalytic sites into the framework and III) Tuning of the chiral linkers to achieve enhanced selectivities. We are initially targeting the incorporation of commercially available amino acids including threonine, serine, and cysteine as cheap and tunable sources of chirality alongside a ditopic organic linker and a metal ion to form the homochiral platform (Figure 5.1).
Figure 5.1. The axillary amino acid used in homochiral MOF synthesis. 1.26.2. Synthesis of Unique Homochiral MOF using Threonine The homochiral MOFs prepared with amino acids were synthesized solvothermally at elevated temperatures (Figure 5.3). In general, a mixture of zinc nitrate (1 mmol), threonine (0.5 mmol), and terephthalic acid (5 mmol) were dissolved in 5 mL of DMF in a scintillation vial. The clear solution was capped and heated up at 120 °C for 2 days. Crystalline solids were recovered and washed 3 times with DMF before heating up at 275 °C under vacuum for 3 days in order to activate the framework.
The synthesis of the threonine based MOF (ThrꞏMOF) was extended to employ organic linkers with the same topology including 2-amino terephthalic
177 Texas Tech University, Babak Tahmouresilerd, August 2020
acid, 2-hydroxy terephthalic acid, and 2-iodo terephthalic acid with the same molar ratio as reported for terephthalic acid.
Our efforts to synthesize a pure ThrꞏMOF were initially unsuccessful due to the higher affinity of terephthalic acid to the metal ion and forming a MOF-5 without any amino acid in the structure. No success was attained while using different solvents (or solvent combination), temperatures, and modulators or additives until a dominant ratio of amino acid to organic linker (10:1) was used. Figure 5.2 indicates the differences in the purity of the synthesized ThrꞏMOF.
Figure 5.2. The synthesized ThrꞏMOF crystal a) with a ratio of 10:1 and b) 1:1 for amino acid to organic linker.
COOH HO Chiral Zn MOF COOH (Threonine) NH2 X
+ COOH HO Chiral Zn MOF (Serine) NH COOH 2
COOH HS Chiral Zn MOF (Cysteine)
NH2 X: H, I, OH, NH2
Figure 5.3. Preparation of chiral MOFs with different organic linkers and auxiliary amino acid. Conditions and reagents: Zn(NO3)2ꞏ6H2O, DMF, 120 °C, 48 h. 1.26.3. X-ray Crystallography All the synthesized ThrꞏMOFs with different organic linkers show a similar pattern as shown in Figure 5.4. The crystal structure for ThrꞏMOF synthesized with terephthalic acid shows that the amino acid is coordinated to the
178 Texas Tech University, Babak Tahmouresilerd, August 2020 zinc ions by a deprotonated carboxylic acid and hydroxy groups. However, the bond distance of Zn2+ ions and the hydroxy oxygen atom of the threonine in ThrꞏMOF is 2.131 Å. This is longer than the distance of zinc ions with deprotonated hydroxy group in the organic linker. Additionally, the amino acid has to be doubly deprotonate based on our proposed idealized formula for a fully activated framework [Zn4(Thr)2(BDC)2], but that it is not immediately clear whether it is an amide or an alkoxide, although bond distances are consistent with an amide and alcohol. The amide unit is rare in MOF chemistry due to the low acidity of the amine, which is not readily deprotonated under the synthetic conditions. The zinc ions and threonine generate a chiral chains growing along the a axis which are connected to organic linkers to form a porous framework as depicted in Figure 5.5 and Figure 5.6.
Figure 5.4. PXRD patterns of ThrꞏMOFs synthesized with different organic linkers.
179 Texas Tech University, Babak Tahmouresilerd, August 2020
Figure 5.5. A view of the chiral chains in the structure of ThrꞏMOF along the a axis. Hydrogen atoms are omitted for clarity. Zinc (Zn), nitrogen (N), oxygen (O), carbon (C) are shown in light blue, dark blue, red, and gray.
Figure 5.6. The depiction of the 3D structure of ThrꞏMOF. Metal nodes are represented with polyhedra. Hydrogen atoms have been removed for clarity. The X-ray crystallography analysis shows that a similar synthesis procedure with serine and cysteine in the presence of terephthalic acid as the linker provides a unique MOF with different chiral moieties. Although the
180 Texas Tech University, Babak Tahmouresilerd, August 2020 threonine and cysteine MOFs show a low stability in the presence of the moisture, the serine MOF demonstrates a high stability when soaked in water for several weeks. As a result of a high stability, the serine MOF could be considered for a wide variety of applications including asymmetric catalysis as well as chiral separations.
181 Texas Tech University, Babak Tahmouresilerd, August 2020
1.27. The Study of Halogen-bonding Interactions of I2BODIPY and Pyridine-type Acceptors This section is part of a collaborate effort with Jinchun Qiu (Cozzolino group) who is responsible for DFT calculations of energetics and properties, and solution binding studies, as well as Gary George (Hutchins group) who is responsible for analysis of the thermal expansion/contraction properties of these systems. This work is currently in preparation for submission.
BODIPY (i.e., 4,4-difluoro-4-bora-3a,4a-diaza-s-indacene) is a fluorescent chemical compound that has been used in the design of sensors, bioimaging agents, and catalysts.203–206 Most of the BODIPY derivatives display unique photophysical properties alongside high stability.203,207,208 The sterically accessible nature of the BODIPY core and its derivatives containing heavy halogen atoms predicate its contribution in non-covalent interactions such as π-π stacking, hydrogen bonding, and halogen bonding.209,210 However, in contrast to other organic dyes such as porphyrin,211 squaraine,212 and rylene,213 the supramolecular assembly and solid-state chemistry of BODIPY has been considerably less studied.
The BODIPY core very electron-withdrawing – suggesting that iodine- substituted BODIPY molecules would make strong halogen bond donors – indeed, a recent study demonstrated that the photophysical properties of 2,6-diiodo BODIPY are sensitive to halogen bond acceptors.209 The near collinearity of the two CI bonds make it an ideal candidate for crystal engineering, particularly when coupled with ditopic halogen bond acceptors. A concern is the possibility of negative cooperativity, as the two I’s are electronically coupled through a highly conjugated core – halogen bonding on one side may turn it off on the other. Here we probe the possibility of negative cooperativity with the solid-state study.
1.27.1. Synthesis 214,215 The synthetic procedure of the I2BODIPY (1) is shown in Figure 5.7.
182 Texas Tech University, Babak Tahmouresilerd, August 2020
Figure 5.7. Synthesis of I2BODIPY (1). Reaction condition: i) CH2Cl2, Et3N, BF3ꞏEt2O, RT, 2h, ii) N-iodosuccinimide (NIS), CH2Cl2, RT, 1h. In general, co-crystals of 1 with ditopic halogen bond acceptors were prepared by dissolving an equimolar amount (0.025 mmol) of 1 and halogen-bond acceptors in 4 mL toluene and ethanol as shown in Figure 5.8.210 Vials were monitored under slow- evaporation conditions and single crystals suitable for X-ray diffraction were observed after ~2 days. Analysis of unit cells was performed to identify new phases.
Figure 5.8. Chemical structures of co-crystals in this work.
183 Texas Tech University, Babak Tahmouresilerd, August 2020
1.27.2. Results and Discussion A suitable single crystal to be used for thermal expansion studies of 1 was grown by slow evaporation from a mixture of dichloromethane and hexanes (1:2 v:v). The
space group is P21/c and the asymmetric unit is depicted in Figure 5.9. This structure matches one of the four known polymorphs of 1.216 The four polymorphs can largely be divided into two categories, structures where IꞏꞏꞏI halogen bonds (HaB) direct the packing, and structures where the I interacts with a F in a IꞏꞏꞏF HaB.217–220 In the present structure, IꞏꞏꞏF HaBs (3.245(2) Å, 94% ΣrvdW)221 are observed to direct the formation of a 1D chain parallel to the b axis. Only one iodine in each molecule of 1 is observed to form HaBs suggesting that there may be some negative co-operativity occurring upon the formation of the first interaction. Long CHPhꞏꞏꞏAryl and CHPhꞏꞏꞏF contacts appear to facilitate the stacking of these chains along the c axis to create a layer. These layers stack with no obvious directional intermolecular interactions.
Figure 5.9. Structure of I2BODIPY (1). Carbon (C), hydrogen (H), boron (B), nitrogen (N), fluorine (F), and iodine (I) atoms are represented by gray, white, pink, blue, green, and purple, respectively. The ditopic HaB acceptor 4,4′-bipyridine (BIPY) was co-crystalized with 1. It was anticipated that infinite chains would form through IꞏꞏꞏN HaBs. The structure is depicted in Figure 5.10. Rather than infinite chains, it is comprised of discrete
supramolecular trimers of 1 and BIPY with a formula 12ꞏBIPY (2) in which both nitrogen atoms on BIPY are engaged in IꞏꞏꞏN HaBs with a distance of 2.997(3) at 190K.
The structure of 2 is extended through weak CHPhꞏꞏꞏF and πBODIPYꞏꞏꞏF interactions that
184 Texas Tech University, Babak Tahmouresilerd, August 2020
are perpendicular to the BODIPY plane. Additional CHPhꞏꞏꞏπ interactions complete the supramolecular network. The most striking aspect of the structure of 2 is the presence of only one halogen bonding per 1.
Figure 5.10. The asymmetric unit of I2BODIPYꞏBIPY (2). Carbon (C), hydrogen (H), boron (B), nitrogen (N), fluorine (F), and iodine (I) atoms are represented by gray, white, pink, blue, green, and purple, respectively. Halogen bonding interactions are depicted as hashed bonds. The study was extended to include the ditopic HaB acceptors 1,2-di(4- pyridyl)ethylene (BPE), 4,4′-azopyridine (Azo), and 3-chloro-4,4′-diazopyridine (Cl- Azo). The co-crystals of these with 1 clearly demonstrate the utility of 1 as a ditopic
HaB donor. The structure of I2BODIPYꞏBPE (3) is shown in Figure 5.11. The asymmetric unit contains two molecules of I2BODIPY (1) and two molecules of BPE. Halogen bonds between the I and the pyridyl nitrogen atoms lead to infinite 1D chains that propagate approximately along with the [1,0,2] axis. There are four unique halogen bonds that range from 2.923–3.025 Å. These distances are approximately the same as those observed in the literature.222 Molecules of 1 and BPE form π-stacked dimers along [0,1,0]. This dimer interacts with additional molecules along [0,1,0] through CH-Aryl contacts. The IR spectrum confirmed the presence of the C=C with a stretch at 1594 cm- 1 (see Figure 5.12).
185 Texas Tech University, Babak Tahmouresilerd, August 2020
Figure 5.11. The structure of I2BODIPYꞏBPE (3). Carbon (C), hydrogen (H), boron (B), nitrogen (N), fluorine (F), and iodine (I) atoms are represented by gray, white, pink, blue, green, and purple, respectively. Halogen bonding interactions are depicted as hashed bonds.
Figure 5.12. Di-ATR FTIR of I2BODIPYꞏBPE (3) plotted as attenuation. Co-crystal 4, shown in Figure 5.13, is isostructural with 3. Here there are two molecules of 1 and two Azo molecules generate four distinct IꞏꞏꞏN HaBs distances ranging from 2.962–3.090 Å. These are shorter than the HaBs observed in 3. Halogen bonds along [1,0,2] axis results in infinite 1D chains. The other packing features are
186 Texas Tech University, Babak Tahmouresilerd, August 2020 similar to 3. The FTIR analysis indicates a peak at 1586 cm–1 verifying the presence of N=N stretching vibration as shown in Figure 5.14.
Figure 5.13. Structure of I2BODIPY co-crystallized with 4,4′-Azopyridine (α-phase) (4). Carbon (C), hydrogen (H), boron (B), nitrogen (N), fluorine (F), and iodine (I) atoms are represented by gray, white, pink, blue, green, and purple, respectively. Halogen bonding interactions are depicted as hashed bonds.
Figure 5.14. Di-ATR FTIR of I2BODIPYꞏAzo (4) plotted as attenuation. Co-crystal (5) was prepared under the same condition except, a (1:0.5:0.5) stoichiometric mixture of (1), BPE, and Azo was used (Figure 5.15). The crystallographic analysis revealed that this co-crystal was isostructural with 3 and 4. Interestingly, the asymmetric unit of 5 consists of two molecules of 1, halogen bonded
187 Texas Tech University, Babak Tahmouresilerd, August 2020 to either a unique molecule of BPE or a unique molecule of Azo, rather than a having a disordered mixture of the two bipyridine molecules. The distances of halogen bonding between (1) and BPE linked by IꞏꞏꞏN were 2.944 and 3.018 Å. These are relatively shorter when compared to the distance of IꞏꞏꞏN in I2BODIPY (1) and Azo (3.014 and 3.16 Å). FTIR analysis revealed two distinct peaks at 1594 and 1585 cm–1 corresponding to C=C and N=N stretching vibrations, respectively, and confirming the presence of both Azo and BPE in the bulk phase (see Figure 5.16).
Figure 5.15. Structure of I2BODIPY co-crystallized with mixed 4,4′-Azopyridine and 1,2-Di(4-pyridyl)ethylene (5). Carbon (C), hydrogen (H), boron (B), nitrogen (N), fluorine (F), and iodine (I) atoms are represented by gray, white, pink, blue, green, and purple, respectively. Halogen bonding interactions are depicted as hashed bonds.
188 Texas Tech University, Babak Tahmouresilerd, August 2020
Figure 5.16. Di-ATR FTIR of I2BODIPYꞏAzoꞏBPE (5) plotted as attenuation.
I2BODIPYꞏAzo (β phase) (6) was prepared under a 1:2 ratio of 1 and Azo
(Figure 5.17). The asymmetric unit of (6) consists of a molecule of I2BODIPY and an Azo molecule. The distances of halogen bonding of IꞏꞏꞏN were 2.977 and 3.118 Å which are relatively longer than the (4) in α phase.
Figure 5.17. Structure of I2BODIPY co-crystallized with 4,4′-Azopyridine (β-phase) (6). Carbon (C), hydrogen (H), boron (B), nitrogen (N), fluorine (F), and iodine (I) atoms are represented by gray, white, pink, blue, green, and purple, respectively. Halogen bonding interactions are depicted as hashed bonds.
189 Texas Tech University, Babak Tahmouresilerd, August 2020
Cl-Azo was isolated as an impurity from commercial samples It was previously reported that halogenated derivatives of Azo are contained as impurities in the purchased material.223 The asymmetric unit of 7 consists of a molecule of 1 and a molecule of Cl-Azo. There are two unique halogen bonds with an IꞏꞏꞏN distance of 3.058 and 3.083 Å. (Figure 5.18)
Figure 5.18. Structure of I2BODIPY co-crystallized with 3-Chloro-4,4′-diazopyridine (7). Carbon (C), hydrogen (H), boron (B), nitrogen (N), fluorine (F), chlorine (Cl), and iodine (I) atoms are represented by gray, white, pink, blue, green, dark green and purple, respectively. Halogen bonding interactions are depicted as hashed bonds. 1.27.3. Toward Photocatalysis via BODIPY Derivatives Containing iodine
The next step of this study can be employing the I2BODIPY as a sensitizer for oxidation catalysis. The structure of BODIPY can be substituted with different functional groups.208 Here we are aiming to functionalize the meso position with a spacer along carboxylate group, and then incorporate into the framework to the fill the defect sites of the MOFs as shown in Figure 5.19. The site-isolation would prevent the oxidative coupling at the methyl groups that we have observed in our lab.224
190 Texas Tech University, Babak Tahmouresilerd, August 2020
HO O HO O
O H N iii + I I N N N N B B O OH F F F F
Figure 5.19. Synthesis steps for preparation of the BODIPY-derived ligand
191 Texas Tech University, Babak Tahmouresilerd, August 2020
Chapter VI
6. General Experimental Methods
1.28. Powder X-ray Diffraction The diffraction patterns were collected on a Rigaku Ultima III powder diffractometer. X-ray diffraction patterns were obtained by using 2θ-θ scans with a range of 5-30°, step size = 0.05°, and scan time of 1 second/step. The X-ray source was Cu Kα radiation (λ=1.5418 Å) with an anode voltage of 40 kV and a current of 44 mA. The beam was then discriminated by Rigaku's Cross Beam optics to create a monochromatic parallel beam. Diffraction intensities were recorded on a scintillation detector after being filtered through a Ge monochromator. Powder mounts were prepared by packing the powder into a well on a glass slide.
1.29. General Data Collection Single Crystal Diffraction Data were collected on a Bruker PLATFORM three circle diffractometer equipped with an APEX II CCD detector and operated at 1500 W (50kV, 30 mA) to generate (graphite monochromated) Mo Kα radiation (λ = 0.71073 Å). Crystals were transferred from the vial and placed on a glass slide in polyisobutylene. A Zeiss Stemi 305 microscope was used to identify a suitable specimen for X-ray diffraction from a representative sample of the material. The crystal and a small amount of the oil were collected on a MῑTiGen cryoloop and transferred to the instrument where it was placed under a cold nitrogen stream (Oxford) maintained at 100 K throughout the experiment. The sample was optically centered with the aid of a video camera to ensure that no translations were observed as the crystal was rotated through all positions.
A unit cell collection was then carried out. After it was determined that the unit cell was not present in the CCDC database a sphere of data was collected. Omega scans were carried out with a 20 sec/frame exposure time. All structures were collected with a rotation of 0.50° per frame. After data collection, the crystal was measured for size, morphology, and color.
192 Texas Tech University, Babak Tahmouresilerd, August 2020
1.30. Refinement Details After data collection, the unit cell was re-determined using a subset of the full data collection. Intensity data were corrected for Lorentz, polarization, and background effects using the Bruker program APEX.7 A semi-empirical correction for adsorption was applied using the program SADABS.8 The SHELXL-2014,9 series of programs was used for the solution and refinement of the crystal structure. During the initial refinement stage, the RIGU restraint was used globally to help produce reasonable thermal ellipsoids. After the Al, C, and O atoms of the MOF framework refined to a stable point, the partially occupied I sites were added in and were allowed to freely refine their SOF values. Once the model reached convergence, the I1A and I1B sites were added together and given a set total SOF value of 0.15 and 0.17 for the MIL-53 100%-I AS and α-MIL-53 100%-I Act structures, respectively. The I2 site was allowed to continue to refine further during sequential refinements. For the β-MIL-53 100%-I Act, the partially occupied I sites were added in and were allowed to free refine their SOF values. Hydrogen atoms bound to carbon atoms were geometrically constrained using the appropriate AFIX commands and their SOF values were set to offset the occupancies of the iodine atoms. The hydrogen atom (H1) bound to O1 was constrained using a DFIX command. After all of these atoms had been structurally determined, the disordered region of electron density within the framework was masked using the SQUEEZE/PLATON program.10,11 For MIL-53-ACT, the SQUEEZE/PLATON routine suggested an electron count of 1 electron. For MIL-53 100%-I AS and β-MIL53 100%-I Act, an extinction correction was also suggested during the final refinement cycles, resulting in an extinction value of 0.1035 and 0.0595, respectively.
1.31. FTIR Spectroscopy All the IR spectra were collected using a Nicolet iS5 FTIR spectrometer equipped with a diamond ATR accessory. Spectra were acquired between 4000 and 400 cm−1 with a resolution of 4 cm−1 and scan rate of 16 s/d in the glovebox filled with nitrogen gas.
193 Texas Tech University, Babak Tahmouresilerd, August 2020
1.32. NMR Spectroscopy A typical NMR samples was prepared by dissolving ~ 10 mg of a given compound in 0.5 mL of deuterated solvent, ensuring a homogeneous solution. NMR spectra were acquired on a JEOL ECS 400 MHz spectrometer. Typical acquisition parameters were 8 scans with a delay time of 5 s for 1H NMR. Spectra were referenced using the residual proton signal of the deuterated solvent.
1.33. Nitrogen Adsorption Nitrogen sorption measurements were performed at 77 K on a Quantichrome Autosorb iQ gas sorption analyzer. Approximately 50 mg of the MOFs were added to a preweighed 6 mm sample cell. All samples were activated under vacuum at 200 °C for 13 hours under vacuum. The sample weight was then collected to accurately depict the activated weight. The activated MOFs had weights of approximately 40 mg, which were used as the final weight of the material. Analysis time of 20 hours and 15 minutes. Brunauer-Emmett-Teller surface areas and pore volumes were calculated using the DFT method in the Quantachrome ASiQwin software. The NLDFT equilibrium (cylinder/slit) model was chosen for the pore volume measurements.
1.34. Computational Details and Results Calculations were performed using the ORCA 3.0.3 or 4.0 quantum chemistry program package from the development team at the Max Planck Institute for Bioinorganic Chemistry.225 The LDA and GGA functionals employed were those of Perdew and Wang (PW-LDA, PW91).144 In addition, all calculations were carried out using the Zero-Order Regular Approximation (ZORA). For all calculations, the def2- TZV(pp) basis sets were used for all atoms. Spin-restricted Kohn-Sham determinants were chosen to describe the closed-shell wavefunctions, employing the RI approximation and the tight SCF convergence criteria provided by ORCA.
194 Texas Tech University, Babak Tahmouresilerd, August 2020
Chapter VII
7. Summaries and Conclusions
The aim of this research presentation was to study the translation of an I catalyst into MOFs for oxidation catalysis. This was initially done to prove the concept by preparation of two robust MOFs. Iodine-functionalized Zr and Al based MOFs were demonstrated promise as active heterogeneous catalysts for the oxidation of hydroquinone derivatives. A multivariate approach was employed to ensure having an ideal balance between the internal surface area and catalytic site in the pores of the frameworks. Hypervalent iodine (III) species in the MOFs was made in situ upon addition of a terminal oxidant as probed by XPS. The catalytic frameworks could be recycled, but in the case of UiO-66, the catalyst degraded as a result of particle agglomeration. The substrates were limited in scope in two ways: I) size and II) oxidation potential. In order to overcome the limitations of these systems, in the next step, the larger frameworks DUT-5 and UiO-67 were prepared by functionalizing biphenyldicarboxylic acid with iodine. The impact of increased pore size and the catalytic activity of the larger MOFs towards the oxidation of various hydroquinone and catechol derivatives was examined. A combination of multivariate and isoreticular approach was used to ensure having an efficient diffusion of reagents accessing catalytic site in the pores of the frameworks. The increased pore size of DUT-5 and UiO-67 allows for larger substrates as well as a larger variability of substrates. Recyclability tests for the multivariate MOFs showed stability over multiple catalytic trials. In continue, the catalytic dearomatization oxidation of phenol derivatives using the I-DUT- 5 was chosen as a challenging reaction to further examine the catalytic activity of the MOF. The catalytic dearomatization oxidation reaction using MOF was extended to a flow chemistry considering the concepts of green chemistry which can be proceeded with a complete conversion. Further, the I-DUT-5 could be recycled over two catalytic trials with no significant loss in catalytic activity.
195 Texas Tech University, Babak Tahmouresilerd, August 2020
BIBLIOGRAPHY 1 A. Yoshimura and V. V. Zhdankin, Chem. Rev., 2016, 116, 3328–3435. 2 F. C. Küpper, M. C. Feiters, B. Olofsson, T. Kaiho, S. Yanagida, M. B. Zimmermann, L. J. Carpenter, G. W. Luther, Z. Lu, M. Jonsson and L. Kloo, Angew. Chem. Int. Ed., 2011, 50, 11598–11620. 3 C. Willgerodt, J. Prakt. Chem., 1886, 33, 154–160. 4 W. Peter, Ueber aliphatische Verbindungen des mehrwertigen Jod’s, C. und J. Goeller, 1907. 5 J. I. Musher, Angew. Chem. Int. Ed. Engl., 1969, 8, 54–68. 6 G. C. Pimentel, The Journal of Chemical Physics, 1951, 19, 446–448. 7 R. J. Hach and R. E. Rundle, J. Am. Chem. Soc., 1951, 73, 4321–4324. 8 V. V. Zhdankin, Hypervalent Iodine Chemistry: Preparation, Structure, and Synthetic Applications of Polyvalent Iodine Compounds, John Wiley & Sons, 2013. 9 P. S. Neelakanta, Handbook of Electromagnetic Materials: Monolithic and Composite Versions and Their Applications, CRC Press, 1995. 10 V. V. Zhdankin, A. E. Koposov, J. T. Smart, R. R. Tykwinski, R. McDonald and A. Morales-Izquierdo, J. Am. Chem. Soc., 2001, 123, 4095–4096. 11 V. N. Nemykin, A. Y. Koposov, B. C. Netzel, M. S. Yusubov and V. V. Zhdankin, Inorg. Chem., 2009, 48, 4908–4917. 12 J. Luiz F. Silva and B. Olofsson, Nat. Prod. Rep., 2011, 28, 1722–1754. 13 O. Prakash, D. Kumar, R. K. Saini and S. P. Singh, Synthetic Communications, 1994, 24, 2167–2172. 14 P. A. Evans and T. A. Brandt, J. Org. Chem., 1997, 62, 5321–5326. 15 M. F. Greaney and W. B. Motherwell, Tetrahedron Letters, 2000, 41, 4467–4470. 16 T. Dohi, A. Maruyama, M. Yoshimura, K. Morimoto, H. Tohma and Y. Kita, Angewandte Chemie International Edition, 2005, 44, 6193–6196. 17 M. Ochiai, Y. Takeuchi, T. Katayama, T. Sueda and K. Miyamoto, J. Am. Chem. Soc., 2005, 127, 12244–12245. 18 A. P. Thottumkara, M. S. Bowsher and T. K. Vinod, Org. Lett., 2005, 7, 2933–2936. 19 A. Schulze and A. Giannis, Synthesis, 2006, 2006, 257–260. 20 M. Ochiai and K. Miyamoto, Eur. J. Org. Chem., 2008, 2008, 4229–4239. 21 A. Ozanne, L. Pouységu, D. Depernet, B. François and S. Quideau, Org. Lett., 2003, 5, 2903–2906. 22 M. Frigerio and M. Santagostino, Tetrahedron Letters, 1994, 35, 8019–8022. 23 P. T. Anastas, I. J. Levy and K. E. Parent, Green Chemistry Education: Changing the Course of Chemistry, American Chemical Society, 2009. 24 P. I. Dalko and L. Moisan, Angewandte Chemie International Edition, 2004, 43, 5138–5175. 25 H. Pellissier, Tetrahedron, 2007, 63, 9267–9331. 26 C. A. McNamara, M. J. Dixon and M. Bradley, Chem. Rev., 2002, 102, 3275–3300. 27 P. Hodge, Current Opinion in Chemical Biology, 2003, 7, 362–373. 28 N.-H. Nam, S. Sardari and K. Parang, J. Comb. Chem., 2003, 5, 479–546.
196 Texas Tech University, Babak Tahmouresilerd, August 2020
29 G. Sorg, A. Mengel, G. Jung and J. Rademann, Angewandte Chemie International Edition, 2001, 40, 4395–4397. 30 M. Mülbaier and A. Giannis, Angewandte Chemie International Edition, 2001, 40, 4393–4394. 31 N. N. Reed, M. Delgado, K. Hereford, B. Clapham and K. D. Janda, Bioorganic & Medicinal Chemistry Letters, 2002, 12, 2047–2049. 32 Y.-H. Kim, H.-S. Jang, Y.-O. Kim, S.-D. Ahn, S. Yeo, S.-M. Lee and Y.-S. Lee, Synlett, 2013, 24, 2282–2286. 33 M. Eddaoudi, J. Kim, N. Rosi, D. Vodak, J. Wachter, M. O’Keeffe and O. M. Yaghi, Science, 2002, 295, 469–472. 34 M. Kandiah, M. H. Nilsen, S. Usseglio, S. Jakobsen, U. Olsbye, M. Tilset, C. Larabi, E. A. Quadrelli, F. Bonino and K. P. Lillerud, Chem. Mater., 2010, 22, 6632–6640. 35 J. Lee, O. K. Farha, J. Roberts, K. A. Scheidt, S. T. Nguyen and J. T. Hupp, Chem. Soc. Rev., 2009, 38, 1450–1459. 36 A. Corma, H. García and F. X. Llabrés i Xamena, Chem. Rev., 2010, 110, 4606– 4655. 37 O. M. Yaghi and H. Li, J. Am. Chem. Soc., 1995, 117, 10401–10402. 38 H. Li, M. Eddaoudi, M. O’Keeffe and O. M. Yaghi, Nature, 1999, 402, 276–279. 39 R. C. Huxford, J. Della Rocca and W. Lin, Current Opinion in Chemical Biology, 2010, 14, 262–268. 40 J.-L. Wang, C. Wang and W. Lin, ACS Catal., 2012, 2, 2630–2640. 41 M. C. So, G. P. Wiederrecht, J. E. Mondloch, J. T. Hupp and O. K. Farha, Chem. Commun., 2015, 51, 3501–3510. 42 J. A. Mason, M. Veenstra and J. R. Long, Chem. Sci., 2013, 5, 32–51. 43 T. M. McDonald, J. A. Mason, X. Kong, E. D. Bloch, D. Gygi, A. Dani, V. Crocellà, F. Giordanino, S. O. Odoh, W. S. Drisdell, B. Vlaisavljevich, A. L. Dzubak, R. Poloni, S. K. Schnell, N. Planas, K. Lee, T. Pascal, L. F. Wan, D. Prendergast, J. B. Neaton, B. Smit, J. B. Kortright, L. Gagliardi, S. Bordiga, J. A. Reimer and J. R. Long, Nature, 2015, 519, 303–308. 44 J. E. Bachman, Z. P. Smith, T. Li, T. Xu and J. R. Long, Nature Materials, 2016, 15, 845–849. 45 J.-R. Li, J. Sculley and H.-C. Zhou, Chem. Rev., 2012, 112, 869–932. 46 J. Gascon, A. Corma, F. Kapteijn and F. X. Llabrés i Xamena, ACS Catal., 2014, 4, 361–378. 47 Y. Sun and H.-C. Zhou, Science and Technology of Advanced Materials, 2015, 16, 054202. 48 N. Stock and S. Biswas, Chem. Rev., 2012, 112, 933–969. 49 S. S.-Y. Chui, S. M.-F. Lo, J. P. H. Charmant, A. G. Orpen and I. D. Williams, Science, 1999, 283, 1148–1150. 50 W. P. Mounfield and K. S. Walton, Journal of Colloid and Interface Science, 2015, 447, 33–39. 51 M. Latroche, S. Surblé, C. Serre, C. Mellot‐Draznieks, P. L. Llewellyn, J.-H. Lee, J.-S. Chang, S. H. Jhung and G. Férey, Angewandte Chemie International Edition, 2006, 45, 8227–8231.
197 Texas Tech University, Babak Tahmouresilerd, August 2020
52 D. Britt, H. Furukawa, B. Wang, T. G. Glover and O. M. Yaghi, PNAS, 2009, 106, 20637–20640. 53 J. H. Cavka, S. Jakobsen, U. Olsbye, N. Guillou, C. Lamberti, S. Bordiga and K. P. Lillerud, J. Am. Chem. Soc., 2008, 130, 13850–13851. 54 G. Kickelbick, P. Wiede and U. Schubert, Inorganica Chimica Acta, 1999, 284, 1– 7. 55 L. Valenzano, B. Civalleri, S. Chavan, S. Bordiga, M. H. Nilsen, S. Jakobsen, K. P. Lillerud and C. Lamberti, Chem. Mater., 2011, 23, 1700–1718. 56 J. E. Mondloch, M. J. Katz, N. Planas, D. Semrouni, L. Gagliardi, J. T. Hupp and O. K. Farha, Chem. Commun., 2014, 50, 8944–8946. 57 F. Gándara and T. D. Bennett, IUCrJ, 2014, 1, 563–570. 58 C. Wang, X. Liu, N. K. Demir, J. P. Chen and K. Li, Chem. Soc. Rev., 2016, 45, 5107–5134. 59 T. Devic and C. Serre, Chem. Soc. Rev., 2014, 43, 6097–6115. 60 C. Serre, F. Millange, C. Thouvenot, M. Noguès, G. Marsolier, D. Louër and G. Férey, J. Am. Chem. Soc., 2002, 124, 13519–13526. 61 N. C. Burtch, H. Jasuja and K. S. Walton, Chem. Rev., 2014, 114, 10575–10612. 62 C. Yang, U. Kaipa, Q. Z. Mather, X. Wang, V. Nesterov, A. F. Venero and M. A. Omary, J. Am. Chem. Soc., 2011, 133, 18094–18097. 63 D. Yang and B. C. Gates, ACS Catal., 2019, 9, 1779–1798. 64 D. Zhao, D. J. Timmons, D. Yuan and H.-C. Zhou, Acc. Chem. Res., 2011, 44, 123– 133. 65 D. Li, H.-Q. Xu, L. Jiao and H.-L. Jiang, EnergyChem, 2019, 1, 100005. 66 B. Tahmouresilerd, P. J. Larson, D. K. Unruh and A. F. Cozzolino, Catal. Sci. Technol., 2018, 8, 4349–4357. 67 M. Fujita, Y. J. Kwon, S. Washizu and K. Ogura, J. Am. Chem. Soc., 1994, 116, 1151–1152. 68 K. Schlichte, T. Kratzke and S. Kaskel, Microporous and Mesoporous Materials, 2004, 73, 81–88. 69 Y. K. Hwang, D.-Y. Hong, J.-S. Chang, S. H. Jhung, Y.-K. Seo, J. Kim, A. Vimont, M. Daturi, C. Serre and G. Férey, Angewandte Chemie International Edition, 2008, 47, 4144–4148. 70 H. D. Park, R. J. Comito, Z. Wu, G. Zhang, N. Ricke, C. Sun, T. Van Voorhis, J. T. Miller, Y. Román-Leshkov and M. Dincă, ACS Catal., 2020, 10, 3864–3870. 71 R. Röß-Ohlenroth, B. Bredenkötter and D. Volkmer, Organometallics, 2019, 38, 3444–3452. 72 M. Ranocchiari and J. A. van Bokhoven, Phys. Chem. Chem. Phys., 2011, 13, 6388– 6396. 73 Q. Yang, Q. Xu and H.-L. Jiang, Chem. Soc. Rev., 2017, 46, 4774–4808. 74 X. Li, T. W. Goh, L. Li, C. Xiao, Z. Guo, X. C. Zeng and W. Huang, ACS Catal., 2016, 6, 3461–3468. 75 H. Deng, C. J. Doonan, H. Furukawa, R. B. Ferreira, J. Towne, C. B. Knobler, B. Wang and O. M. Yaghi, Science, 2010, 327, 846–850.
198 Texas Tech University, Babak Tahmouresilerd, August 2020
76 Z. Hu, Y. Peng, Y. Gao, Y. Qian, S. Ying, D. Yuan, S. Horike, N. Ogiwara, R. Babarao, Y. Wang, N. Yan and D. Zhao, Chem. Mater., 2016, 28, 2659–2667. 77 Y. Kuwahara, H. Kango and H. Yamashita, ACS Sustainable Chem. Eng., 2017, 5, 1141–1152. 78 J. Gascon, U. Aktay, M. D. Hernandez-Alonso, G. P. M. van Klink and F. Kapteijn, Journal of Catalysis, 2009, 261, 75–87. 79 J. L. C. Rowsell and O. M. Yaghi, J. Am. Chem. Soc., 2006, 128, 1304–1315. 80 R. Cortese and D. Duca, Phys. Chem. Chem. Phys., 2011, 13, 15995–16004. 81 G.-B. Wang, K. Leus, K. Hendrickx, J. Wieme, H. Depauw, Y.-Y. Liu, V. V. Speybroeck and P. V. D. Voort, Dalton Trans., 2017, 46, 14356–14364. 82 T. Zhang, K. Manna and W. Lin, J. Am. Chem. Soc., 2016, 138, 3241–3249. 83 D. Farrusseng, S. Aguado and C. Pinel, Angewandte Chemie International Edition, 2009, 48, 7502–7513. 84 Y.-B. Huang, J. Liang, X.-S. Wang and R. Cao, Chem. Soc. Rev., 2017, 46, 126– 157. 85 V. Colombo, S. Galli, H. J. Choi, G. D. Han, A. Maspero, G. Palmisano, N. Masciocchi and J. R. Long, Chem. Sci., 2011, 2, 1311–1319. 86 S. Hausdorf, J. Wagler, R. Moβig and F. O. R. L. Mertens, J. Phys. Chem. A, 2008, 112, 7567–7576. 87 S. Proch, J. Herrmannsdörfer, R. Kempe, C. Kern, A. Jess, L. Seyfarth and J. Senker, Chemistry – A European Journal, 2008, 14, 8204–8212. 88 C. Montoro, F. Linares, E. Quartapelle Procopio, I. Senkovska, S. Kaskel, S. Galli, N. Masciocchi, E. Barea and J. A. R. Navarro, J. Am. Chem. Soc., 2011, 133, 11888– 11891. 89 A. H. Chughtai, N. Ahmad, H. A. Younus, A. Laypkov and F. Verpoort, Chem. Soc. Rev., 2015, 44, 6804–6849. 90 T. Loiseau, C. Serre, C. Huguenard, G. Fink, F. Taulelle, M. Henry, T. Bataille and G. Férey, Chem. Eur. J., 2004, 10, 1373–1382. 91 S. M. Chavan, G. C. Shearer, S. Svelle, U. Olsbye, F. Bonino, J. Ethiraj, K. P. Lillerud and S. Bordiga, Inorg. Chem., 2014, 53, 9509–9515. 92 L. Ma, J. M. Falkowski, C. Abney and W. Lin, Nat Chem, 2010, 2, 838–846. 93 O. M. Fugaeva, I. K. Korobeinicheva and V. V. Bardin, Russ Chem Bull, 1991, 40, 2309–2311. 94 A. D. Burrows, L. C. Fisher, C. Richardson and S. P. Rigby, Chem. Commun., 2011, 47, 3380–3382. 95 X. Wang and A. J. Jacobson, Journal of Solid State Chemistry, 2016, 236, 230–235. 96 G. Ortiz, G. Chaplais, J.-L. Paillaud, H. Nouali, J. Patarin, J. Raya and C. Marichal, J. Phys. Chem. C, 2014, 118, 22021–22029. 97 B. V. de Voorde, I. Stassen, B. Bueken, F. Vermoortele, D. D. Vos, R. Ameloot, J.- C. Tan and T. D. Bennett, J. Mater. Chem. A, 2014, 3, 1737–1742. 98 Z. Bastl and H. Gehlmann, Collection of Czechoslovak Chemical Communications, 1988, 53, 425–432. 99 E. Guibal, T. Vincent, E. Touraud, S. Colombo and A. Ferguson, J. Appl. Polym. Sci., 2006, 100, 3034–3043.
199 Texas Tech University, Babak Tahmouresilerd, August 2020
100 X.-Q. Zhu, C.-H. Wang and H. Liang, The Journal of Organic Chemistry, 2010, 75, 7240–7257. 101 Y.-C. Lai, C.-W. Kung, C.-H. Su, K.-C. Ho, Y.-C. Liao and D.-H. Tsai, Langmuir, 2016, 32, 6123–6129. 102 W. Yang, S. Wang, Q. Zhang, Q. Liu and X. Xu, Chem. Commun., 2014, 51, 661– 664. 103 A. Pelter and S. Elgendy, Tetrahedron Letters, 1988, 29, 677–680. 104 S. Ficht, M. Mülbaier and A. Giannis, Tetrahedron, 2001, 57, 4863–4866. 105 Y. Shang, T. Y. S. But, H. Togo and P. H. Toy, Synlett, 2007, 2007, 0067–0070. 106 Rocaboy Christian and Gladysz John A., Chemistry – A European Journal, 2002, 9, 88–95. 107 V. Tesevic and J. A. Gladysz, Green Chem., 2005, 7, 833–836. 108 Nambu Hisanori, Shimokawa Ikumi, Fujiwara Tomoya and Yakura Takayuki, Asian Journal of Organic Chemistry, 2016, 5, 486–489. 109 A. Kommreddy, M. S. Bowsher, M. R. Gunna, K. Botha and T. K. Vinod, Tetrahedron Letters, 2008, 49, 4378–4382. 110 M. Colonna, C. Berti, M. Fiorini, E. Binassi, M. Mazzacurati, M. Vannini and S. Karanam, Green Chem., 2011, 13, 2543–2548. 111 D. Saha, R. Sen, T. Maity and S. Koner, Langmuir, 2013, 29, 3140–3151. 112 S. A. Burgess, A. Kassie, S. A. Baranowski, K. J. Fritzsching, K. Schmidt-Rohr, C. M. Brown and C. R. Wade, J. Am. Chem. Soc., 2016, 138, 1780–1783. 113 C.-D. Wu, A. Hu, L. Zhang and W. Lin, J. Am. Chem. Soc., 2005, 127, 8940–8941. 114 S. M. Cohen, Z. Zhang and J. A. Boissonnault, Inorg. Chem., 2016, 55, 7281–7290. 115 S. Yuan, L. Feng, K. Wang, J. Pang, M. Bosch, C. Lollar, Y. Sun, J. Qin, X. Yang, P. Zhang, Q. Wang, L. Zou, Y. Zhang, L. Zhang, Y. Fang, J. Li and H.-C. Zhou, Advanced Materials, 2018, 30, 1704303. 116 Y. Bai, Y. Dou, L.-H. Xie, W. Rutledge, J.-R. Li and H.-C. Zhou, Chem. Soc. Rev., 2016, 45, 2327–2367. 117 M. Bosch, M. Zhang and H.-C. Zhou, Advances in Chemistry, 2014, 2014, e182327. 118 S. J. Garibay and S. M. Cohen, Chem. Commun., 2010, 46, 7700–7702. 119 V. Guillerm, F. Ragon, M. Dan-Hardi, T. Devic, M. Vishnuvarthan, B. Campo, A. Vimont, G. Clet, Q. Yang, G. Maurin, G. Férey, A. Vittadini, S. Gross and C. Serre, Angew. Chem. Int. Ed., 2012, 51, 9267–9271. 120 H. Furukawa, N. Ko, Y. B. Go, N. Aratani, S. B. Choi, E. Choi, A. Ö. Yazaydin, R. Q. Snurr, M. O’Keeffe, J. Kim and O. M. Yaghi, Science, 2010, 329, 424–428. 121 H. Fei and S. M. Cohen, Chem. Commun., 2014, 50, 4810–4812. 122 R. Sun, B. Liu, B.-G. Li and S. Jie, ChemCatChem, 2016, 8, 3261–3271. 123 T. Kitamura and Y. Fujiwara, Organic Preparations and Procedures International, 1997, 29, 409–458. 124 V. V. Zhdankin, J. Am. Chem. Soc., 1999, 121, 6971–6971. 125 E. A. Merritt and B. Olofsson, Angewandte Chemie International Edition, 2009, 48, 9052–9070. 126 R. Bikshapathi, P. S. Prathima and V. J. Rao, New J. Chem., 2016, 40, 10300– 10304.
200 Texas Tech University, Babak Tahmouresilerd, August 2020
127 R. Mu, Z. Liu, Z. Yang, Z. Liu, L. Wu and Z.-L. Liu, Adv. Synth. Catal., 2005, 347, 1333–1336. 128 M. S. Yusubov and V. V. Zhdankin, Resource-Efficient Technologies, 2015, 1, 49– 67. 129 R. D. Richardson and T. Wirth, Angewandte Chemie International Edition, 2006, 45, 4402–4404. 130 I. Senkovska, F. Hoffmann, M. Fröba, J. Getzschmann, W. Böhlmann and S. Kaskel, Microporous and Mesoporous Materials, 2009, 122, 93–98. 131 Nakeun Ko, Jisu Hong, Siyoung Sung, Kyle E. Cordova, Hye Jeong Park and Jaheon Kim, Dalton Transactions, 2015, 44, 2047–2051. 132 Vyacheslav K., Dmitrii A. Vasilevskii, Andrei A. Pap, Galina V. Kalechyts, Yurii V. Matveienko, Andrei G. Baran, Nikolay A. Halinouski and Vitalii G. Petushok, ARKIVOC, 2008, 2008, 69–93. 133 K. A. McDonald, N. Ko, K. Noh, J. C. Bennion, J. Kim and A. J. Matzger, Chem. Commun., 2017, 53, 7808–7811. 134 R. K. Deshpande, J. L. Minnaar and S. G. Telfer, Angewandte Chemie International Edition, 2010, 49, 4598–4602. 135 M. A. Gotthardt, S. Grosjean, T. S. Brunner, J. Kotzel, A. M. Gänzler, S. Wolf, S. Bräse and W. Kleist, Dalton Trans., 2015, 44, 16802–16809. 136 S. Chavan, J. G. Vitillo, D. Gianolio, O. Zavorotynska, B. Civalleri, S. Jakobsen, M. H. Nilsen, L. Valenzano, C. Lamberti, K. P. Lillerud and S. Bordiga, Phys. Chem. Chem. Phys., 2012, 14, 1614–1626. 137 M. J. Katz, Z. J. Brown, Y. J. Colón, P. W. Siu, K. A. Scheidt, R. Q. Snurr, J. T. Hupp and O. K. Farha, Chem. Commun., 2013, 49, 9449–9451. 138 E. Langseth, O. Swang, B. Arstad, A. Lind, J. H. Cavka, T. L. Jensen, T. E. Kristensen, J. Moxnes, E. Unneberg and R. H. Heyn, Materials Chemistry and Physics, , DOI:10.1016/j.matchemphys.2019.01.009. 139 T. Dohi and Y. Kita, Chem. Commun., 2009, 2073–2085. 140 A. M. Harned, Tetrahedron Letters, 2014, 55, 4681–4689. 141 F. Heinen, E. Engelage, A. Dreger, R. Weiss and S. M. Huber, Angewandte Chemie International Edition, 2018, 57, 3830–3833. 142 T. Yakura, Y. Tian, Y. Yamauchi, M. Omoto and T. Konishi, Chem. Pharm. Bull., 2009, 57, 252–256. 143 F. Neese, WIREs Comput Mol Sci, 2012, 2, 73–78. 144 J. P. Perdew and Y. Wang, Physical Review B, 1992, 45, 13244–13249. 145 E. van Lenthe, J. Baerends Evert and J. G. Snijders, J. Chem. Phys., 1993, 99, 4597– 4610. 146 J. L. Heully, I. Lindgren, E. Lindroth, S. Lundqvist and A. M. Maartensson-Pendrill, J. Phys. B: At. Mol. Phys., 1986, 19, 2799–2815. 147 F. Weigend and R. Ahlrichs, Phys. Chem. Chem. Phys., 2005, 7, 3297–3305. 148 A. Schäfer, H. Horn and R. Ahlrichs, The Journal of Chemical Physics, 1992, 97, 2571–2577. 149 F. Weigend, Phys. Chem. Chem. Phys., 2006, 8, 1057–1065. 150 W. Kohn and L. J. Sham, Phys. Rev., 1965, 140, A1133–A1138.
201 Texas Tech University, Babak Tahmouresilerd, August 2020
151 R. A. Kendall and H. A. Früchtl, Theor Chem Acta, 1997, 97, 158–163. 152 In Hypervalent Iodine Chemistry, John Wiley & Sons, Ltd, 2013, pp. 337–380. 153 P. J. Stang and V. V. Zhdankin, Chem. Rev., 1996, 96, 1123–1178. 154 V. V. Zhdankin and P. J. Stang, Chem. Rev., 2002, 102, 2523–2584. 155 V. V. Zhdankin and P. J. Stang, Chem. Rev., 2008, 108, 5299–5358. 156 Y. Kita and T. Dohi, The Chemical Record, 2015, 15, 886–906. 157 L. Pouységu, T. Sylla, T. Garnier, L. B. Rojas, J. Charris, D. Deffieux and S. Quideau, Tetrahedron, 2010, 66, 5908–5917. 158 S. Quideau, L. Pouységu, P. A. Peixoto and D. Deffieux, in Hypervalent Iodine Chemistry, ed. T. Wirth, Springer International Publishing, Cham, 2016, pp. 25–74. 159 T. Yakura and T. Konishi, Synlett, 2007, 2007, 765–768. 160 D. Magdziak, S. J. Meek and T. R. R. Pettus, Chem. Rev., 2004, 104, 1383–1430. 161 R. M. Moriarty and O. Prakash, in Organic Reactions, American Cancer Society, 2004, pp. 327–415. 162 X. Wang and J. A. Porco, Angewandte Chemie International Edition, 2005, 44, 3067–3071. 163 A. Rana, S. Bhangalia and H. P. Singh, Natural Product Research, 2013, 27, 1167– 1173. 164 R. M. Taskova, C. H. Gotfredsen and S. R. Jensen, Phytochemistry, 2005, 66, 1440– 1447. 165 A. Saito, N. Hyodo and Y. Hanzawa, Molecules, 2012, 17, 11046–11055. 166 V. V. Zhdankin, M. Mullikin, R. Tykwinski, B. Berglund, R. Caple, N. S. Zefirov and A. S. Koz’min, J. Org. Chem., 1989, 54, 2605–2608. 167 L. Mao, Y. Li, T. Xiong, K. Sun and Q. Zhang, J. Org. Chem., 2013, 78, 733–737. 168 T. Kitamura, S. Kuriki, K. Muta, M. H. Morshed, K. Muta, K. Gondo, Y. Hori and M. Miyazaki, Synthesis, 2013, 45, 3125–3130. 169 T. Kitamura, K. Nagata, T. Nakamura, R. Furuki and H. Taniguchi, Tetrahedron, 1995, 51, 6229–6236. 170 T. Kitamura, L. Zheng, T. Fukuoka, Y. Fujiwara, H. Taniguchi, M. Sakurai and R. Tanaka, J. Chem. Soc., Perkin Trans. 2, 1997, 1511–1516. 171 T. Kitamura, R. Furuki, H. Taniguchi and P. J. Stang, Tetrahedron, 1992, 48, 7149– 7156. 172 N. S. Zefirov, V. V. Zhdankin, Yu. V. Dan`kov, V. D. Sorokin, V. N. Semerikov, A. S. Koz`min, R. Caple and B. A. Berglund, Tetrahedron Letters, 1986, 27, 3971– 3974. 173 R. T. Hembre, C. P. Scott and J. R. Norton, J. Org. Chem., 1987, 52, 3650–3654. 174 E. Kunst, F. Gallier, G. Dujardin and A. Kirschning, Org. Biomol. Chem., 2008, 6, 893–898. 175 E. A. Merritt and B. Olofsson, European Journal of Organic Chemistry, 2011, 2011, 3690–3694. 176 S. Koguchi, A. Mihoya and M. Mimura, Tetrahedron, 2016, 72, 7633–7637. 177 H. Nambu, I. Shimokawa, T. Fujiwara and T. Yakura, Asian Journal of Organic Chemistry, 2016, 5, 486–489. 178 F. Ballaschk and S. F. Kirsch, Green Chem., 2019, 21, 5896–5903.
202 Texas Tech University, Babak Tahmouresilerd, August 2020
179 M. C. Carreño, M. González‐López and A. Urbano, Angewandte Chemie International Edition, 2006, 45, 2737–2741. 180 C. García‐García, M. C. Redondo, M. Ribagorda and M. C. Carreño, European Journal of Organic Chemistry, 2014, 2014, 7377–7388. 181 B. F. Sels, D. E. D. Vos and P. A. Jacobs, Angewandte Chemie International Edition, 2005, 44, 310–313. 182 M. R. Bryant and C. Richardson, Dalton Trans., 2020, 49, 5167–5174. 183 A. D. Cardenal, A. Maity, W.-Y. Gao, R. Ashirov, S.-M. Hyun and D. C. Powers, Inorg. Chem., 2019, 58, 10543–10553. 184 D. Li, Y. Han, D. Li, Q. Kang and D. Shen, Scientific Reports, 2020, 10, 3010. 185 B. Tahmouresilerd, M. Moody, L. Agogo and A. F. Cozzolino, Dalton Trans., 2019, 48, 6445–6454. 186 A. M. Harned, Org. Biomol. Chem., 2018, 16, 2324–2329. 187 C. Y. Lee, Y.-S. Bae, N. C. Jeong, O. K. Farha, A. A. Sarjeant, C. L. Stern, P. Nickias, R. Q. Snurr, J. T. Hupp and S. T. Nguyen, Journal of the American Chemical Society, 2011, 133, 5228–5231. 188 L. Kürti, P. Herczegh, J. Visy, M. Simonyi, S. Antus and A. Pelter, J. Chem. Soc., Perkin Trans. 1, 1999, 379–380. 189 N. Taneja and R. K. Peddinti, European Journal of Organic Chemistry, 2017, 2017, 5306–5314. 190 F.-X. Felpin, Tetrahedron Letters, 2007, 48, 409–412. 191 N. G. Moon and A. M. Harned, Org. Biomol. Chem., 2017, 15, 1876–1888. 192 M. H. Kunzmann and S. A. Sieber, Mol. BioSyst., 2012, 8, 3061–3067. 193 A. Yoshimura, K. C. Nguyen, S. C. Klasen, A. Saito, V. N. Nemykin and V. V. Zhdankin, Chem. Commun., 2015, 51, 7835–7838. 194 A. Boelke, E. Lork and B. J. Nachtsheim, Chemistry – A European Journal, 2018, 24, 18653–18657. 195 M. Ochiai, K. Miyamoto, Y. Yokota, T. Suefuji and M. Shiro, Angewandte Chemie International Edition, 2005, 44, 75–78. 196 T. Yakura, M. Omoto, Y. Yamauchi, Y. Tian and A. Ozono, Tetrahedron, 2010, 66, 5833–5840. 197 R. Sunasee and D. L. J. Clive, Chem. Commun., 2010, 46, 701–703. 198 R. Tello-Aburto, K. A. Kalstabakken, K. A. Volp and A. M. Harned, Org. Biomol. Chem., 2011, 9, 7849–7859. 199 K. A. Volp and A. M. Harned, Chem. Commun., 2013, 49, 3001–3003. 200 R. Saladino, V. Neri, E. Mincione and P. Filippone, Tetrahedron, 2002, 58, 8493– 8500. 201 M. C. Carreño, M. González-López and A. Urbano, Angewandte Chemie International Edition, 2006, 45, 2737–2741. 202 K. Miyamoto, Y. Yokota, T. Suefuji, K. Yamaguchi, T. Ozawa and M. Ochiai, Chemistry – A European Journal, 2014, 20, 5447–5453. 203 A. Loudet and K. Burgess, Chem. Rev., 2007, 107, 4891–4932. 204 C. Y. Lee, O. K. Farha, B. J. Hong, A. A. Sarjeant, S. T. Nguyen and J. T. Hupp, J. Am. Chem. Soc., 2011, 133, 15858–15861.
203 Texas Tech University, Babak Tahmouresilerd, August 2020
205 P. Kaur and K. Singh, J. Mater. Chem. C, 2019, 7, 11361–11405. 206 M. Wang, M. G. H. Vicente, D. Mason and P. Bobadova-Parvanova, ACS Omega, 2018, 3, 5502–5510. 207 N. Boens, V. Leen and W. Dehaen, Chem. Soc. Rev., 2012, 41, 1130–1172. 208 G. Ulrich, R. Ziessel and A. Harriman, Angewandte Chemie International Edition, 2008, 47, 1184–1201. 209 Y. Lee, R. M. Malamakal, D. M. Chenoweth and J. M. Anna, J. Phys. Chem. Lett., 2020, 11, 877–884. 210 E. Bosch, S. J. Kruse, H. R. Krueger and R. H. Groeneman, Crystal Growth & Design, 2019, 19, 3092–3096. 211 J. a. a. W. Elemans, R. van Hameren, R. J. M. Nolte and A. E. Rowan, Advanced Materials, 2006, 18, 1251–1266. 212 S. Sreejith, P. Carol, P. Chithra and A. Ajayaghosh, J. Mater. Chem., 2008, 18, 264– 274. 213 F. Würthner, C. R. Saha-Möller, B. Fimmel, S. Ogi, P. Leowanawat and D. Schmidt, Chem. Rev., 2016, 116, 962–1052. 214 W. Wu, H. Guo, W. Wu, S. Ji and J. Zhao, J. Org. Chem., 2011, 76, 7056–7064. 215 L. Huang, J. Zhao, S. Guo, C. Zhang and J. Ma, J. Org. Chem., 2013, 78, 5627– 5637. 216 R. P. Sabatini, B. Lindley, T. M. McCormick, T. Lazarides, W. W. Brennessel, D. W. McCamant and R. Eisenberg, J. Phys. Chem. B, 2016, 120, 527–534. 217 J. H. Gibbs, L. T. Robins, Z. Zhou, P. Bobadova-Parvanova, M. Cottam, G. T. McCandless, F. R. Fronczek and M. G. H. Vicente, Bioorganic & Medicinal Chemistry, 2013, 21, 5770–5781. 218 S. Swaminathan, C. Fowley, E. R. Thapaliya, B. McCaughan, S. Tang, A. Fraix, B. Captain, S. Sortino, J. F. Callan and F. M. Raymo, Nanoscale, 2015, 7, 14071– 14079. 219 J. Zhou, Y. Zhang, G. Yu, M. R. Crawley, C. R. P. Fulong, A. E. Friedman, S. Sengupta, J. Sun, Q. Li, F. Huang and T. R. Cook, J. Am. Chem. Soc., 2018, 140, 7730–7736. 220 M. Gorbe, A. M. Costero, F. Sancenón, R. Martínez-Máñez, R. Ballesteros-Cillero, L. E. Ochando, K. Chulvi, R. Gotor and S. Gil, Dyes and Pigments, 2019, 160, 198– 207. 221 M. Mantina, A. C. Chamberlin, R. Valero, C. J. Cramer and D. G. Truhlar, J. Phys. Chem. A, 2009, 113, 5806–5812. 222 N. Juneja, D. K. Unruh, E. Bosch, R. H. Groeneman and K. M. Hutchins, New J. Chem., 2019, 43, 18433–18436. 223 P. P. Mazzeo, C. Carraro, A. Arns, P. Pelagatti and A. Bacchi, Crystal Growth & Design, 2020, 20, 636–644. 224 M. C. Andrews, Thesis, 2019. 225 F. Neese, ORCA – an ab initio, Density Functional and Semiempirical program package, Version 2.9.0, Max-Planck-Insitut für Bioanorganische Chemie, Mülheim and der Ruhr, 2013.
204