Carbon dioxide fixation and utilization

Carbon Dioxide Fixation and Utilization Siti Nurhanna Riduan B. Appl. Sci. (Hons), Applied Chemistry National University of Singapore, Singapore, 2005 A Thesis Submitted For the Degree of Doctor of Philosophy Department of Chemistry National University of Singapore 2012 Abstract In recent years, the fixation and utilization of carbon dioxide has been the focus of intense research, so as to the mitigate the levels of the greenhouse gas released to the atmosphere. While carbon capture and storage (CCS) has been rigorously studied for the past decade, there has been a paradigm shift towards the fixation and utilization of CO as a feedstock, to yield fuels and synthetically useful intermediates. In the first part of this thesis, the fixation and utilization of carbon dioxide as a feedstock to form methanol was realized by the reduction of CO with hydrosilanes over Nheterocyclic carbene (NHC) organocatalysts. The reaction was found to proceed at ambient temperatures and pressures, and was tolerant to oxygen, a feature not found in transition metal catalysts. The reaction yielded 90% methanol (based on Si-H) after base hydrolysis. The rate of reaction was found to be accelerated with the use of polar aprotic solvents, where beneficial Lewis acid-base interactions between the solvent and the hydrosilane reducing agent was believed to be the contributing factor. The rate of reaction was also affected by the steric hindrance about both the catalytic carbene center, and the electropositive silane center, where bulky R’-groups on the carbene catalyst or bulky trisubstituted silanes caused the reaction to be sluggish. The reaction mechanism was also investigated, and from our GC-MS and NMR monitoring studies, it was found that the reaction took place with the formation of formoxysilane and bi-silylacetal intermediates before total reduction to a methoxysilane end product. R3SiH CO2 NHC R' N Catalyst: NHC Catalyst N R' R3SiOCH3 R3SiOSiR3 OHCH3OH Chapter examined the reaction in detail by combining experimental observations with density functional theory calculations. Our calculations revealed that the exothermic reaction took place with a three-step cascade reaction, in which the energy level of each step of the reaction was found to be lower than that of the preceding step, with an overall ∆E value of 79 kcal/mol. The first hydrosilylation step to form a formoxysilane intermediate was the rate determining step with the largest activation energy barrier. This was mirrored in our experimental findings, in which the reaction had a tendency to form the silyl methoxide end product, and the formoxysilane intermediate was only observed at the initial stages of the reaction, even with excess amounts of CO in the system. The high selectivity of the reaction towards the formation of the silyl methoxide end product, and ultimately, methanol, with over 95% hydrogen transferring yield (with the use of equiv of CO ) was thus explained. The extension of the homogeneous reaction system to a heterogeneous one was also realized with the use of polymeric NHC catalyst particles, which acted as the first recyclable heterogeneous catalyst for CO hydrosilylation. These particles were found to be comparable in activity with a homogeneous system, and remained active over several runs. Regeneration of spent catalyst was also possible with the simple addition of base. This study, described in Chapters and 3, demonstrated the potential of CO reduction under mild conditions using NHC organocatalysts. The second part of the thesis considered the use of CO as a tool for organic transformations. A simple procedure for the stereoselective coupling of terminal alkynes and thiols under CO atmosphere was presented in Chapter 4. To the best of our knowledge, this was the first instance of determining stereoselectivity with CO as mediator. The reaction system was robust and utilized inexpensive, readily available catalysts and substrates. Under the optimum reaction conditions, a broad range of aryl alkynes and thiols achieved good to high yields, with excellent stereoselectivities. The mechanism of the reaction was studied, whereby the stereoselectivity was realized by the formation of an intermediary species of propiolic acid from the reaction of terminal alkynes and CO . Reactions involving aryl alkynes with strong electron-withdrawing groups suffered from lower selectivities, but this could be circumvented by the use of strong σ-donor ligands and by allowing the reaction to stir for h to assist the carboxylation reaction before the addition of thiol. Water was also found to play a part as a proton ferry for the reaction, as elucidated with our deuterium labeling studies. In this instance, CO was used as a tool for organic synthesis, whereby the reaction of a substrate with CO formed an intermediate for a stereoselective decarboxylation reaction. Further extension of this methodology towards decarboxylation-coupling reactions may soon be realized. Ar Cu(I) SR2 E-isomer Ar Ar H R2SH Cu(I) CO2 Ar SR2 Z-isomer 40 94% isolated yields R = Aryl, Alkyl, heterocyclic Acknowledgements In the name of Allah, Most Beneficient, Most Merciful. This thesis would not be possible without the constant guidance and motivation from my thesis advisors, Dr Yugen Zhang and Prof Jackie Y. Ying. Their faith and trust in my capability far exceeds my self assessment, and I am thankful to have had them as my mentors. I am grateful for the generous financial support received from Institute of Bioengineering and Nanotechnology, with the Scientific Staff Development Award for my graduate studies and research. I would also like to thank my friends, Ben, YY, Liza, Fidah, GR, Dianah, Dianna, Nur and YJ. They have made the past years memorable, and have been an endless source of encouragement when I am sometimes faced with the seemingly impossible. I have learnt so much from all of you, and I truly appreciate the selfless sharing of knowledge and the gift of our friendship. Lastly, this is for my parents, without whom I will not be who and where I am today. Thank you Mak and Abah, for always being there, for your love and untiring support. Table of Contents Abstract Acknowledgements Table of Contents List of Schemes List of Tables 10 List of Figures 11 Chapter – Carbon Dioxide Utilization and Fixation 1.1 Background 13 1.2 Carbon Dioxide as Energy Storage Vehicles 14 1.3 Carbon Dioxide as Building Blocks for Synthetically Useful Intermediates 18 1.4 Carbon Dioxide as a Tool for Organic Transformations 22 1.5 Research Objectives 23 1.6 References 24 Chapter – Conversion of Carbon Dioxide to Methanol with Silanes Over NHeterocyclic Carbene Catalysts 2.1 Introduction 2.2 Materials and Methods 2.3 28 2.2.1 General Information 31 2.2.2 Hydrosilylation of CO 32 2.2.3 Using Dry Air as Feedstock 32 2.2.4 Hydrolysis of Reaction Mixture to Release Methanol 32 Results and Discussion 2.3.1 Initial Reactions 33 2.3.2 13 35 2.3.3 Screening of Reaction Variables 2.3.4 C NMR Monitoring Studies 2.3.3.1 Effects of Solvents and Bases 37 2.3.3.2 Effects of NHCs and Silanes 39 Proposed Mechanism 40 2.3.5 Isolation of Key Intermediate, Formoxysilanes 42 2.3.6 Tolerance of the Reaction Mixture to Oxygen and Air 42 2.3.7 Hydrolysis of Reaction Mixture 43 2.4 Summary 44 2.5 Notes 44 2.5 References 44 Chapter – Mechanistic Insights into the Reduction of Carbon Dioxide to Methanol with Silanes over N-Heterocyclic Carbene Catalysts 3.1 Introduction 3.2 Experimental Methods 3.3 3.4 47 3.2.1 General Information 48 3.2.2 DFT Calculations 49 3.2.3 Hydrosilylation of CO 49 3.2.4 Hydrolysis Reaction to Release Methanol 50 3.2.5 NMR Tube Reaction and Analysis 50 3.2.6 Reaction with a Controlled Amount of CO 50 3.2.7 Preparation of Heterogeneous Catalysts 51 3.2.8 Recycling Reactions 51 3.2.9 Catalyst Regeneration 51 3.2.10 Reactions with In Situ Generated Catalyst 51 Results and Discussion 3.3.1 Elucidation of Reaction Mechanism 52 3.3.2 Density Functional Theory Calculations of Each Step 53 3.3.3 Rate-Determining Step 58 3.3.4 Methanol Yield 59 3.3.5 Effect of Hydrosilanes 60 3.3.6 Formation of a NHC-Si Adduct 65 3.3.7 Formaldehyde as an Intermediate 66 3.3.8 Recyclable Heterogeneous NHC catalysts 67 Summary 72 3.5 Notes 72 3.6 References 73 Chapter – Carbon Dioxide Mediated Stereoselective Coupling of Alkynes and Thiols 4.1 Introduction 4.2 Materials and Methods 4.3 76 4.2.1 General Methods 78 4.2.2 General Procedure for the CO Mediated Stereoselective Coupling of Alkynes and Thiols 78 4.2.3 General Procedure for the Stereoselective Coupling of Propiolic Acids and Thiols 78 4.2.4 General Procedure for the Preparation of (4-Methoxyphenylthio) propenoic acid 79 4.2.5 Deuterium Labeling Studies 80 Results and Discussion 4.3.1 Optimization of Conditions 81 4.3.2 Expansion of Substrate Scope: Thiols 83 4.3.3 Expansion of Substrate Scope: Alkynes 85 4.3.4 Determination of Factors Affecting Stereoselectivity 87 4.3.5 Proposed Mechanism 91 4.4 Summary 93 4.5 Notes 93 4.6 Supporting Data for Isolated Products 94 4.7 References 125 Chapter – Conclusions and Future Directions 5.1 Reduction of Carbon Dioxide to Methanol by Hydrosilanes over NHeterocyclic Carbene Catalysts. 128 5.2 Carbon Dioxide Mediated Stereoselective Coupling of Alkynes and Thiols 131 5.3 References 132 List of Schemes Scheme 1.1. Scheme 1.2. Scheme 1.3. Scheme 1.4. Industrial Synthesis of Methanol from Syngas Synthesis of Methanol from Carbon Dioxide Coupling of Epoxides with Carbon Dioxide Several Carboxylation Transformations 15 15 19 20 Scheme 2.1. Scheme 2.2. Scheme 2.3. Applications of Imidazolium Carboxylates Hydrosilylation of Carbon Dioxide Overall Stoichiometric Reaction for the Reduction of CO to Methanol Proposed Reaction Mechanism and Pathway for the Reduction of CO to Methanol 29 29 31 Overall Reaction Scheme for the Hydrosilylation of CO Yield of Methanol Under Different Conditions Products from a Mixed Silane Feedstock of Ph SiH and PhMe SIH 52 60 63 77 77 Scheme 4.6. Transition Metal Catalysed Hydrothiolation of Alkynes Stereoselectivity Switching Capability of CO towards Z-Vinyl Sulfides in Hydrothiolation of Alkynes Coupling of Phenylacetylene with Various Thiols Coupling of Terminal Alkynes with Thiols Conditions for the Decarboxylation of (Phenylthio)phenylpropenoic acid Reaction with D O additive Scheme 4.7. Proposed Mechanism 92 Scheme 5.1. Scheme 5.2. Alternatives Routes for Hydride Donors for Reduction of CO Examples of Carboxylation / Decarboxylation Coupling of Terminal Alkynes Scheme 2.4. Scheme 3.1. Scheme 3.2. Scheme 3.3. Scheme 4.1. Scheme 4.2. Scheme 4.3. Scheme 4.4. Scheme 4.5. 41 84 86 88 89 129 131 List of Tables Table 2.1. Table 2.2. Hydrosilylation of CO with Diphenylsilane Catalyzed by Imes-CO . Catalytic Efficiency of Various NHC Catalysts 38 40 Table 3.1. Hydrosilylation of CO with Various Silanes over Imes-CO 1, and Their Total Energy Differences 63 Table 4.1. Table 4.2. Screening of Reaction Conditions Variables of Reaction Conditions to Establish Stereoselectivity Determining Factor 82 88 10 3aj (4-ethanolstryryl)(phenyl)sulfane S HO Isolated as yellow solid in 79% yield, E:Z ratio: 18:82. 1H NMR (CDCl , 400 MHz) δ 7.55 – 7.08 (m, 9H), 6.91 (d, 0.18 × 1H, 3J H-H = 15.6 Hz), 6.74 (d, 0.18 × 1H, 3J H-H = 15.6 Hz), 6.61 (d, 0.82 × 1H, 3J H-H = 10.8 Hz), 6.53 (d, 0.82 × 1H, 3J H-H = 10.8 Hz), 4.70 (s, 2H), 1.98 (broad s, 1H). 13C NMR (CDCl , 400 MHz) δ 139.8, 136.0, 132.1, 130.2, 129.4, 129.1, 119 127.5, 127.4, 127.2, 127.0, 126.9, 62.3. HRMS (EI) calculated for C 15 H 14 OS, 242.0765, Found (EI): 242.0757. 3ak (4-Bromostyryl)(phenyl)sulfane19 S Br Isolated as pale yellow solid in 58% yield, E:Z ratio: 76:24. 1H NMR (CDCl , 400 MHz) δ 7.44 – 7.20 (m, 9H), 6.91 (d, 0.76 × 1H, 3J H-H = 15.6 Hz), 6.64 (d, 0.76 × 1H, 3J H-H = 15.6 Hz), 6.57 (d, 0.24 × 1H, 3J H-H = 10.8 Hz), 6.53 (d, 0.24 × 1H, 3J H-H = 10.8 Hz). 13C NMR 120 (CDCl , 400 MHz) δ 137.2, 135.9, 135.5, 131.9, 131.6, 130.5, 130.4, 129.8, 129.4, 129.3, 127.6, 127.5, 127.4, 127.3, 126.0, 125.0, 121.1. C 14 H 11 BrS, GC-MS: 291. 3al (4-Bromostyryl)(phenyl)sulfane19 S Br Isolated as pale yellow solid in 66% yield, E:Z ratio: 12:88. 1H NMR (CDCl , 400 MHz) δ 7.44 – 7.20 (m, 9H), 6.91 (d, 0.12 × 1H, 3J H-H = 15.6 Hz), 6.64 (d, 0.12 × 1H, 3J H-H = 15.6 121 Hz), 6.57 (d, 0.88 × 1H, 3J H-H = 10.8 Hz), 6.53 (d, 0.81 × 1H, 3J H-H = 10.8 Hz). 13C NMR (CDCl , 400 MHz) δ 137.2, 135.9, 135.5, 131.9, 131.6, 130.5, 130.4, 129.8, 129.4, 129.3, 127.6, 127.5, 127.4, 127.3, 126.0, 125.0, 121.1. C 14 H 11 BrS, GC-MS: 291. 3am (4-Chlorostyryl)(phenyl)sulfane19 S Cl 122 Isolated as pale yellow solid in 83% yield, E:Z ratio: 17:83. 1H NMR (CDCl , 400 MHz) δ 7.51 – 7.23 (m, 9H), 6.89 (d, 0.17 × 1H, 3J H-H = 15.6 Hz), 6.66 (d, 0.17 × 1H, 3J H-H = 15.6 Hz), 6.55 (s, 0.83 × 2H). 13C NMR (CDCl , 400 MHz) δ 135.6, 135.2, 135.1, 132.9, 130.4, 130.2, 129.9, 129.6, 129.4, 129.3, 129.0, 128.7, 127.6, 127.4, 127.3, 127.2, 126.0, 124.8. C 14 H 11 ClS GC-MS: 246. 3an (4-Fluorostyryl)(phenyl)sulfane7c S F 123 Isolated as white solid in 44% yield, E:Z ratio: 19:81. 1H NMR (CDCl , 400 MHz) δ 7.55 – 7.08 (m, 9H), 6.82 (d, 0.19 × 1H, 3J H-H = 15.6 Hz), 6.71 (d, 0.19 × 1H, 3J H-H = 15.6 Hz), 6.58 (d, 0.81 × 1H, 3J H-H = 10.8 Hz), 6.50 (d, 0.81 × 1H, 3J H-H = 10.8 Hz). 13C NMR (CDCl , 400 MHz) δ 163.7, 161.2, 136.1, 135.3, 132.9, 130.8, 130.0, 129.4, 127.7, 127.2, 126.4, 125.5, 123.3, 115.9. C 14 H 11 FS, GC-MS: 230. 3ao (4-Cyanostyryl)(phenyl)sulfane11 124 S N Isolated as pale yellow solid in 78% yield, E:Z ratio 23:77. 1H NMR (CDCl , 400 MHz) δ 7.69 – 7.27 (m, 9H), 7.09 (d, 0.23 × 1H, 3J H-H = 15.6 Hz), 6.73 (d, 0.77 × 1H, 3J H-H = 10.8 Hz), 6.56 (d, 0.23 × 1H, 3J H-H = 15.6 Hz), 6.55 (d, 0.77 × 1H, 3J H-H = 10.8 Hz). 13C NMR (CDCl , 400 MHz) δ 141.1, 132.7, 132.3, 131.5, 131.4, 130.7, 129.65, 129.60, 129.2, 129.1, 126.3, 124.9, 119.3, 110.2. C 15 H 11 NS, GC-MS: 237. 4.7. References 125 1. R. J. 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Tu, P. Wu, C.-C. Wang, J.-T. Liu, C.-W. Kuo, Y.-H. Shin, C.-F. Yao, Tetrahedron, 2009, 65, 3878–3885. 128 Chapter 5: Conclusions and Future Directions 5.1. Reduction of Carbon Dioxide to Methanol by Hydrosilanes over N-Heterocyclic Carbene Catalysts We have reported the reduction of CO to methanol with hydrosilanes as hydride donors, over N-heterocyclic carbene (NHC) organocatalysts.1 The reaction proceeds at ambient temperature and pressure, and present superior efficiency as compared to transition metal catalysts. Our catalytic system was also tolerant towards the presence of oxygen, a common drawback for transition metal catalysts. The catalytic reduction of CO by NHCs also provides for a highly selective silyl methoxide end-product in excess of 90% hydrogen transferring yield with gaseous CO or dry air as feedstock. The reaction was examined in detail, with our focus on the mechanism of the reaction. By combining DFT calculations with experimental investigations, it was observed that the reaction pathway consisted of a three-step cascade reaction, whereby all three steps were found to be exothermic and catalyzed by the NHC catalyst. The rate-limiting step was determined to be the first step that involved the hydrosilylation of carbon dioxide, producing a formoxysilane intermediate with the highest activation energy barrier (∆E = 19.6 kcal/mol). This explains the selectivity of the system towards a methoxide end-product, with an excess of 95% hydrogen-transferring yield or carbon yield. We also presented the successful development of poly-NHC as the first recyclable heterogeneous catalyst for CO hydrosilylation. 128 Scheme 5.1. Alternatives Routes for Hydride Donors for the Reduction of CO . R3SiOH, R3SiOSiR3 R3SiH CO2 CH3OH NHC Catalyst H2, suitable cocatalyst This study demonstrated the potential of CO reduction under mild conditions. However, the use of expensive hydrosilane impedes industrial application. The process takes place at ambient conditions, which requires no extra energy input for the transformation, in contrast to known processes for the hydrogenation of CO to methanol, offering the prospect of a carbon neutral process. However, the industrial synthesis of hydrosilane itself requires energy input,2 and the cost of the hydrosilane will drive up the cost of the methanol produced from such a process. Current cost of methanol for Asia-Pacific is 470 USD per metric ton, as compared 40, 000 USD per kg if synthesized via hydrosilylation of CO .3 Handling large amounts of hydrosilanes in an industrial process will also be difficult due to the sensitive nature of the silane towards moisture in air.2 Alternatively, polymethylhydrosiloxane (PMHS), a common byproduct from silicone industry, could be used as a hydride source, as it is inexpensive, readily available, and relatively less sensitive to moisture.2 Other options include recycling spent hydrosilanes in the form of siloxanes via a reduction process to regenerate the active hydride donor, hydrosilanes; however, this process has yet to be realized. 129 Another promising alternative would be the use of molecular hydrogen as the hydride donor. In this case, there needs to be heterolytic dissociation of the hydrogen for the hydrogen to react with the activated carbon dioxide species. The heterolytic fission of the dihydrogen molecule with non-metal based, frustrated Lewis pairs have been the subject of intense research in the past few years,4 and it has also been expanded activate carbon dioxide.5 Ashley et al. has shown the combination of the two activation processes (of both H and CO ) can be used to produce methanol, albeit at an elevated temperature of 160°C and days to effect a 25% conversion.6 The combination of a carbene-boron metal-free, frustrated Lewis pair activation of molecular hydrogen7 with activated CO species over NHC catalyst is an area worth pursuing. Alternatively, molecular hydrogen has also been shown to split heterolytically in the presence of zeolites8 and transition metals.9 The expansion of the process to convert CO to methanol from a homogenous process to a heterogeneous one is certainly a step in the right direction towards large-scale industry realization, due to the ease of catalyst recyclability, with simple catalyst regeneration steps. A further step for current poly-NHC solid catalyst system would be the extension from a batch process to a continuous, flow type reactor, with the polymeric catalyst particles in packed bed. A limitation would be the long residence time required to effect the conversion, and hence, the use of a recirculating flow reactor will be necessary.10 Further characterization of the solid particles before its use in a packed bed flow circulator is also necessary, to ensure that the backpressure from the reactor is within acceptable limits, and that polymers not swell after extended periods of use. The reduction of CO to methanol, at ambient conditions over an organocatalyst, is certainly a promising beginning, though the industrial realization of such a process will only be achieved with further developments of the hydride source. 130 5.2. Carbon Dioxide Mediated Stereoselective Coupling of Alkynes and Thiols We have also presented the development of a simple procedure for the stereoselective hydrothiolation of alkynes under CO atmosphere. To the best of our knowledge, this is the first instance of determining stereoselectivity with CO as a mediator. The reaction system was robust and utilized inexpensive, readily available catalysts and substrates. The optimum reaction conditions applied to a broad scope of substrates. A reaction mechanism has also been proposed, in which the stereoselectivity of the transformation was realized via the employment of a direct carboxylation reaction of terminal alkynes to form propiolic acids. Such propiolic acids were the intermediary species that would react selectively with thiols to form one stereoisomer over another. Water was also shown to play a role as a proton ferry for the reaction. In this case, CO was used as a tool for organic synthesis, whereby the reaction of a substrate with CO formed an intermediate for a stereoselective decarboxylation reaction. Such a concept can be extended to other decarboxylation-coupling reactions of propiolic acid species, which could not be realized by conventional coupling protocols such as Suzuki and Sonogashira coupling.11 Some of the promising applications for carbon dioxide mediated coupling reactions are outlined in Scheme 5.2.12 As development on the direct carboxylation reactions progresses, the concept of tandem carboxylation and decarboxylation as a method for C-C coupling may take off. Scheme 5.2. Examples of Carboxylation-Decarboxylation Coupling of Terminal Alkynes. R2 R2 - CO2 CO2 R1 H R1 X R1 COOH HNR2R3 - CO2 Ar - CO2 R1 R2 N R3 I R1 Ar 131 5.3. References 1. S. N. Riduan, Y. Zhang, J. Y. Ying, Angew. Chem. Int. Ed., 2009, 48, 3322–3325. 2. a) T. Hiyama and T. Kesumoto, Hydrosilylation of C=C and C≡C, Comprehensive Organic Synthesis: Selectivity, Strategy and Efficiency in Modern Organic Chemistry. Vol 8: Reduction. Eds. B. M. Trost, I. Fleming, pp. 763–792, Elsevier Science Ltd, 1991; b) D. A. Armitage, Organosilanes, in Comprehensive Organometallic Chemistry, Vol 9, Eds.: G. Wilkinson, F. G. A. Stone, E. W. Abel, pp. 1–203, Elsevier Science Ltd, 1982. 3. a) Price listed on Methanex, http://www.methanex.com/products/documents/ MxPriceSheetJuly272011.pdf, accessed 7th August 2011; b) Price calculated based on diphenylsilane feedstock from commercial sources. 4. a) G. C. Welch, R. R. San Juan, J. D. Masuda, D. W. Stephan, Science, 2006, 42, 4793– 4795; b) P. A. Chase, G. C. Welch, T. Jurca, D. W. Stephan, Angew. Chem. Int. 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Chem., 2011, 25, 4751–4755. 133 [...]... at the α- and β-position, with the replacement of H 2 O with D 2 O in the typical experiment set up Fig 4.2 NMR spectrum of (a) 3b Styryl(p-tolyl)sulfane, (b) with deuterium 91 substitution at the α- and β-position, with the replacement of H 2 O with D 2 O Spectra were obtained for the range δ 7.0−6.4 ppm 12 Chapter 1: Carbon Dioxide Fixation and Utilization 1.1 Background The present carbon dioxide. .. concern, and was universally deemed as the main cause of global warming Increasing pressure from the public and politicians alike, through vehicles such as the United Nations Conference on Climate Change, has motivated countries to attempt to curb their CO 2 emissions Such pressure has pushed for research and development in technologies for carbon dioxide sequestration, fixation and utilization Carbon. .. CO 2 1.3 Carbon Dioxide as a Building Block for Synthetically Useful Intermediates The incorporation of carbon dioxide into organic compounds to form synthetically useful intermediates and products has been a focus for many research groups in the past decade The commercial utilization of CO 2 in the industry has been limited to the synthesis of carbamates, urea, salicylic acid, and organic carbonates.6b,8c... cyclic carbonates and polycarbonates is a mature area of research One of the main thrusts of this research area includes the generation of industrially important synthetic materials For example, polycarbonates are typically used 18 for electronics, medical and healthcare products, due to their strength, durability and lightweight properties Cyclic carbonates are often used as solvents with high boiling and. .. fuels and useful bulk products are economical For chemists, CO 2 is an attractive C1 synthon as it is highly functional, abundant and renewable resource that is environmentally friendly.6 However, CO 2 is the stable end product of combustion of carbon- based fuels, and is the most oxidized form of carbon In a recent review, Song outlined several research directions concerning CO 2 conversion and utilization. 7... and flash points, which are particularly advantageous for paint stripping and cleaning processes.22 Scheme 1.3 Coupling of Epoxides with Carbon Dioxide O CO2 catalyst O O * O O polycarbonate * O O cyclic carbonate The earliest discovery on the copolymerization of epoxides with CO 2 to form polycarbonates was reported by Inoue and co-workers in 1969.23 Since this seminal work, a number of single-site... co-catalysts, and CO 2 pressures The formation of cyclic carbonates has been widely studied, and catalysts that are often employed for the transformation are similar to the ones described for the copolymerization process,26 and have been extended to ionic liquid, organocatalytic and poly oxo-metalate systems.27 Just as polycarbonates and cyclic carbonates have widespread applications in the industry... The insertion of CO 2 into a metal -carbon bond is particularly advantageous due to the utilization of CO 2 as a sustainable source, and the relatively mild reaction conditions On the other hand, such syntheses usually require stoichiometric amounts of expensive and sensitive organometallic reagents Other than organolithium and organomagnesium reagents, organocopper29 and organoaluminum30 reagents have... Chapter 2: Conversion of Carbon Dioxide to Methanol with Silanes Over NHeterocyclic Carbene Catalysts 2.1 Introduction CO 2 is attractive as a renewable carbon source and an environmentally friendly chemical reagent.1-4 Significant efforts have been devoted towards exploring technologies for CO 2 transformation, whereby metal catalysts played a key role.5-10 The activation of carbon dioxide with organocatalyst... activated carbon dioxide, reducing CO 2 ultimately to methoxide end products (see Scheme 2.3) The application of the nucleophilic CO 2 moiety of the NHC-CO 2 adduct was also employed by Ikariya and co-workers A catalytic cycle was proposed for the carboxylative cyclicization of propargylic alcohols, and the reaction was carried out under mild conditions.20 Scheme 2.2 Hydrosilylation of Carbon Dioxide . towards the fixation and utilization of CO 2 as a feedstock, to yield fuels and synthetically useful intermediates. In the first part of this thesis, the fixation and utilization of carbon dioxide. Figures 11 Chapter 1 – Carbon Dioxide Utilization and Fixation 1.1 Background 13 1.2 Carbon Dioxide as Energy Storage Vehicles 14 1.3 Carbon Dioxide as Building Blocks for Synthetically. emissions. Such pressure has pushed for research and development in technologies for carbon dioxide sequestration, fixation and utilization. Carbon capture and storage (CCS) has been the focus of intense