HYPERVALENT IODINE METHODS FOR CARBON–NITROGEN AND CARBON–CARBON BOND FORMATION
AuthorSousa e Silva, Felipe Cesar
AdvisorWengryniuk, Sarah E.
Committee memberSieburth, Scott McNeill
Permanent link to this recordhttp://hdl.handle.net/20.500.12613/2074
MetadataShow full item record
AbstractCarbon-carbon and carbon-nitrogen bond forming events are essential in chemistry. Although numerous stoichiometric/catalytic methods provided elegant and powerful solutions enabling those processes, the use of scarce/toxic reagents and harsh conditions is still ubiquitous in this field. As a result, extensive research has been conducted in the development of environmentally benign and inexpensive reagents for such transformations, however, general solutions remain a challenge. In this context, one of the focuses of our lab is to enable those processes in a more practical and sustainable fashion by using hypervalent iodine reagents. In this dissertation we demonstrate the synthetic applications of λ3-iodane reagents towards the formation of challenging carbon-carbon and carbon-nitrogen bonds in a complementary way to the methods already reported. Chapter 1 of this dissertation outlines the general electronic structure, geometry, synthesis and reactivity of λ3-iodanes as serves and background regarding these reagents. Chapter 2 highlights the applications of λ3-iodanes to access high-oxidation state transition metals until the year of 2017. This literature review provides detailed information about how λ3-iodanes can be applied to access 1st, 2nd and 3rd row high-oxidation complexes, as well as mechanistic details and synthetic utility of high-valent transition metals. Chapter 3 demonstrates our efforts to generate selective carbon-nitrogen and carbon-carbon products from a high-valent nickel complex. This led to important information of this mechanism adopted by the reaction and how the choice of oxidant can impact 1e- versus 2e- oxidative pathways on “hard” nickel pincer scaffolds. Chapter 4 describes our efforts towards the selective formation of α-C(sp2)-C(sp2) bonds at the α-position of enones via a reductive Iodonium-Claisen rearrangement. We demonstrate the utility of β-pyridinium silyl enol ethers as a platform for direct α-arylation, and how the 2-iodo-aryl-α-arylated enones can be used to access diverse heterocyclic structures. Chapter 5 demonstrates our initial efforts towards the selective C2 or C3 carbon-nitrogen bond formation on indoles. By exposing different indoles to (bis)cationic nitrogen-ligated HVI (N-HVI) reagents we found that selective C2 or C3 C-H indole-pyridinium salts can be formed in good to excellent yield. Although, this project is not finished yet, we anticipate the indole-pyridinium salts generated could serve as platform for accessing diverse piperidines, pyridones and primary amines through straightforward procedures. The combined chapters of this dissertation highlight the applications of λ3-iodanes towards transition metals and emphasize the applications of these reagents to enable challenging C–C and C–N bond formation events. More importantly, this dissertation serves as a guide for future development of the hypervalent iodine field.
ADA complianceFor Americans with Disabilities Act (ADA) accommodation, including help with reading this content, please contact email@example.com
Showing items related by title, author, creator and subject.
Carbon dioxide sequestration by mineral carbonation of iron-bearing mineralsStrongin, Daniel R.; Stanley, Robert J.; Wunder, Stephanie L.; Schoonen, Martin A. A., 1960- (Temple University. Libraries, 2015)Carbon dioxide (CO2) is formed when fossil fuels such as oil, gas and coal are burned in power producing plants. CO2 is naturally found in the atmosphere as part of the carbon cycle, however it becomes a primary greenhouse gas when human activities disturb this natural balanced cycle by increasing levels in the atmosphere. In light of this fact, greenhouse gas mitigation strategies have garnered a lot of attention. Carbon capture, utilization and sequestration (CCUS) has emerged as a possible strategy to limit CO2 emissions into the atmosphere. The technology involves capturing CO2 at the point sources, using it for other markets or transporting to geological formations for safe storage. This thesis aims to understand and probe the chemistry of the reactions between CO2 and iron-bearing sediments to ensure secure storage for millennia. The dissertation work presented here focused on trapping CO2 as a carbonate mineral as a permanent and secure method of CO2 storage. The research also explored the use of iron-bearing minerals found in the geological subsurface as candidates for trapping CO2 and sulfide gas mixtures as siderite (FeCO3) and iron sulfides. Carbon dioxide sequestration via the use of sulfide reductants of the iron oxyhydroxide polymorphs lepidocrocite, goethite and akaganeite with supercritical CO2 (scCO2) was investigated using in situ attenuated total reflection Fourier transform infrared spectroscopy (ATR-FTIR), X-ray diffraction (XRD) and transmission electron microscopy (TEM). The exposure of the different iron oxyhydroxides to aqueous sulfide in contact with scCO2 at ~70-100 ˚C resulted in the partial transformation of the minerals to siderite (FeCO3). The order of mineral reactivity with regard to siderite formation in the scCO2/sulfide environment was goethite < lepidocrocite ≤ akaganéite. Overall, the results suggested that the carbonation of lepidocrocite and akaganéite with a CO2 waste stream containing ~1-5% H2S would sequester both the carbon and sulfide efficiently. Hence, it might be possible to develop a process that could be associated with large CO2 point sources in locations without suitable sedimentary strata for subsurface sequestration. This thesis also investigates the effect of salinity on the reactions between a ferric-bearing oxide phase, aqueous sulfide, and scCO2. ATR-FTIR was again used as an in situ probe to follow product formation in the reaction environment. X-ray diffraction along with Rietveld refinement was used to determine the relative proportion of solid product phases. ATR-FTIR results showed the evolution of siderite (FeCO3) in solutions containing NaCl(aq) concentrations that varied from 0.10 to 4.0 M. The yield of siderite was greatest under solution ionic strength conditions associated with NaCl(aq) concentrations of 0.1-1 M (siderite yield 40% of solid product) and lowest at the highest ionic strength achieved with 4 M NaCl(aq) (20% of solid product). Based partly on thermochemical calculations, it is suggested that a decrease in the concentration of aqueous HCO3- and a corresponding increase in co-ion formation, (i.e., NaHCO3) with increasing NaCl(aq) concentration resulted in the decreasing yield of siderite product. At all the ionic strength conditions used in this study, the most abundant solid phase product present after reaction was hematite (Fe2O3) and pyrite (FeS2). The former product likely formed via dissolution/reprecipitation reactions, whereas the reductive dissolution of ferric iron by the aqueous sulfide likely preceded the formation of pyrite. These in situ experiments allowed the ability to follow the reaction chemistry between the iron oxyhr(oxide), aqueous sulfide and CO2 under conditions relevant to subsurface conditions. Furthermore, very important results from these small-scale experiments show this process can be a potentially superior and operable method for mitigating CO2 emissions.
Direct anabolic metabolism of three-carbon propionate to a six-carbon metabolite occurs in vivo across tissues and speciesCenter for Metabolic Disease Research (Temple University) (2022-06-07)Anabolic metabolism of carbon in mammals is mediated via the one- and two-carbon carriers S-adenosyl methionine and acetyl-coenzyme A. In contrast, anabolic metabolism of three-carbon units via propionate has not been shown to extensively occur. Mammals are primarily thought to oxidize the three-carbon short chain fatty acid propionate by shunting propionyl-CoA to succinyl-CoA for entry into the TCA cycle. Here, we found that this may not be absolute as, in mammals, one nonoxidative fate of propionyl-CoA is to condense to two three-carbon units into a six-carbon trans-2-methyl-2-pentenoyl-CoA (2M2PE-CoA). We confirmed this reaction pathway using purified protein extracts provided limited substrates and verified the product via LC-MS using a synthetic standard. In whole-body in vivo stable isotope tracing following infusion of 13C-labeled valine at steady state, 2M2PE-CoA was found to form via propionyl-CoA in multiple murine tissues, including heart, kidney, and to a lesser degree, in brown adipose tissue, liver, and tibialis anterior muscle. Using ex vivo isotope tracing, we found that 2M2PE-CoA also formed in human myocardial tissue incubated with propionate to a limited extent. While the complete enzymology of this pathway remains to be elucidated, these results confirm the in vivo existence of at least one anabolic three- to six-carbon reaction conserved in humans and mice that utilizes propionate.
Land-use dynamics influence estimates of carbon sequestration potential in tropical second-growth forestSchwartz, Naomi B.; Uriarte, María; DeFries, Ruth; Gutiérrez-Vélez, Víctor Hugo; Pinedo-Vasquez, Miguel A. (2017-06-11)Many countries have made major commitments to carbon sequestration through reforestation under the Paris Climate Agreement, and recent studies have illustrated the potential for large amounts of carbon sequestration in tropical second-growth forests. However, carbon gains in second-growth forests are threatened by non-permanence, i.e. release of carbon into the atmosphere from clearing or disturbance. The benefits of second-growth forests require long-term persistence on the landscape, but estimates of carbon potential rarely consider the spatio-temporal landscape dynamics of second-growth forests. In this study, we used remotely sensed imagery from a landscape in the Peruvian Amazon to examine patterns of second-growth forest regrowth and permanence over 28 years (1985–2013). By 2013, 44% of all forest cover in the study area was second growth and more than 50% of second-growth forest pixels were less than 5 years old. We modeled probabilities of forest regrowth and clearing as a function of landscape factors. The amount of neighboring forest and variables related to pixel position (i.e. distance to edge) were important for predicting both clearing and regrowth. Forest age was the strongest predictor of clearing probability and suggests a threshold response of clearing probability to age. Finally, we simulated future trajectories of carbon sequestration using the parameters from our models. We compared this with the amount of biomass that would accumulate under the assumption of second-growth permanence. Estimates differed by 900 000 tonnes, equivalent to over 80% of Peru's commitment to carbon sequestration through 'community reforestation' under the Paris Agreement. Though the study area has more than 40 000 hectares of second-growth forest, only a small proportion is likely to accumulate significant carbon. Instead, cycles between forest and non-forest are common. Our results illustrate the importance of considering landscape dynamics when assessing the carbon sequestration potential of second-growth forests.