Doctor of Philosophy, University of Toledo, 2020, Chemistry

Transition-metal-catalyzed hydroelementation is one of the most important methods for the synthesis of functionalized molecules. Hydroboration and hydrosilylation are two important classes of hydroelementation reactions. In chapter 1, the applications of these transformations, recent catalyst development, and the operating mechanisms are briefly discussed. The challenges and scope in base-metal catalysis for hydroboration and hydrosilylation are also described. In chapter 2, the selective hydroboration of aldehydes and N-allylimines utilizing a well-defined cationic nickel complex is described. The catalyst displayed excellent selectivity toward aldehydes in the presence of ketones. A wide variety of functional groups were tolerated, including halogens, nitro, cyano, and alkenes for both aldehydes and imines. Electron-rich substrates were found to be significantly more reactive than their electron poor counterparts, a unique feature, reported for the first time in metal-catalyzed hydroboration. Stoichiometric reactions with the catalyst disclosed that the substates were activated through a Lewis acidic interaction and undergo hydroboration with pinacolborane (HBpin) under mild reaction conditions. In chapter 3, seven structurally similar cationic nickel(II)−alkyl complexes were synthesized by using a series of P, N ligands, following the previously developed protocol from our lab and their reactivity was explored in the hydrosilylation of alkenes. Newly synthesized catalysts were characterized by NMR spectroscopy, elemental analysis, and X-ray crystallography. The study showed that more electron-rich phosphines enhanced the overall reactivity of the hydrosilylation; in contrast, groups on the imine donor had little impact. Overall, these catalysts displayed reactivity and selectivity that was previously unknown or very rare in nickel-catalyzed hydrosilylation. In reactions with Ph2SiH2, 1,2-disubstituted vinylarenes showed complete benzylic selectivity for sil (open full item for complete abstract)

Committee: Joseph A. R. Schmidt (Committee Chair); Mark R. Mason (Committee Member); Wei Li (Committee Member); L.M. Viranga Tillekeratne (Committee Member) Subjects: Chemistry; Inorganic Chemistry; Organic Chemistry

PhD, University of Cincinnati, 2017, Arts and Sciences: Chemistry

The development of new catalysts for the reduction of carbon dioxide is of utmost importance to both limit the harmful greenhouse gas as well as to provide usable C1 feedstock chemicals. One method to reduce this CO2 is through the use of a metal hydride complex. Of these metal complexes, nickel POCOP pincer hydride complexes have been highly successful at catalyzing the reduction of carbonyl functionalities. Although these catalysts are effective at catalyzing this reduction, there are few processes to make these hydrides. Additionally, not much is known about which factors will improve catalytic reduction or what other reactions they can catalyze. Nickel chloride complexes bearing POCOP pincer ligands were easily synthesized using a microwave reactor. Through this methodology nickel POCOP pincer chloride complexes can be made in as little as 5 minutes in very high purities and yields. Nickel complexes with iPr, cPe, Cy, Ph, and tBu substituents on the phosphorous atoms can all be synthesized using this method. Additionally, palladium chloride complexes bearing isopropyl substituted POCOP ligands can be made. This method was also found to greatly limit the solvent needed to make these complexes. Alternative routes to synthesize nickel hydride complexes is an important problem due to the harsh methods used to synthesize them. To explore an additional method for hydride synthesis, nickel fluoride complexes bearing POCOP pincer ligands were synthesized. These complexes can be easily converted to hydride complexes using silanes or boranes. The factors that influence a metal hydrides ability to reduce CO2 were investigated. To determine which factors had an impact on the reduction of CO2 to formate complex, a series of nickel hydride and formate complexes were synthesized. The complexes were tested to determine the relative thermodynamic favorability for the reduction of CO2 to formate. Complexes bearing more electron donating ligands were found to be (open full item for complete abstract)

Committee: Hairong Guan Ph.D. (Committee Chair); William Connick Ph.D. (Committee Member); Allan Pinhas Ph.D. (Committee Member) Subjects: Chemistry

Doctor of Philosophy, Case Western Reserve University, 2006, Chemical Engineering

Neuroprosthetic devices that electrically stimulate paralyzed muscles require implantable power sources with exceptional cycle life, safety, and sufficient energy and power density. Of the rechargeable battery technologies, lithium ion batteries have the highest energy density; however, they have limited cycle life of about 1000 cycles. Nickel-hydrogen batteries, currently used in space applications are remarkable for long cycle life (40,000) and low maintenance; however they utilize high hydrogen pressures (60 atm) making them unsuitable for implantable applications. The present work involves design and development of low pressure nickel-hydrogen batteries (1 atm) by utilizing a metal hydride (MH) to store hydrogen, rather than as a negative electrode in the nickel-metal hydride battery. A method to increase the exchange current density of the negative platinum electrode using cyclic voltammetry was developed. A nickel mesh was chosen as the current collector because of its low resistance and stability in alkaline solutions. The tested separators, zirconium oxide and polypropylene, were not significantly different from each other. A pasted type nickel hydroxide electrode was fabricated by two means: screen printing and spatula pressing. The mechanism of electrode formation, the effect of different formation rates with and without overcharge and the effect of binder and nickel content on utilization were studied. Addition of filamentary nickel to the electrode increases the utilization by 10% by decreasing the oxygen evolution. A low pressure nickel-hydrogen battery with and without MH was assembled. Charge and pressure data were analyzed to study the oxygen evolution, the recombination reaction and the self discharge of the cell. Oxygen evolution increases with the depth of charge; however the evolved oxygen recombines completely – 70% during charging and the remainder during the first hour of the rest period. About 40-45% hydrogen from the metal hydride was used a (open full item for complete abstract)

Committee: Jesse Wainright (Advisor) Subjects: Energy; Engineering, Chemical

PhD, University of Cincinnati, 2017, Arts and Sciences: Chemistry

This dissertation research focuses on the development of tridentate ligand supported nickel complexes for both catalytic and stoichiometric bond activation reactions. One of the main objectives of this research is to understand how the flexibility of ligands impacts the reactivity of transition-metal complexes. To this end, three different ligands with varying degree of flexibility have been studied. Chelating ligands have been used to enhance the stability of transition-metal complexes because compared to monodentate ligands these ligands are less likely to dissociate from the metal. Guided by this hypothesis, a chelating secondary phosphine oxide (SPO) ligand has been synthesized and shown to act as either a bidentate or a pseudo tridentate ligand depending on the electronic demand and geometry at the nickel center. Nickel(0) species supported by this SPO is a more effective catalyst than Ni(0)–Ph2P(O)H for cross-coupling of aryl iodides with aryl thiols. Both electron-donating and electron-withdrawing groups including OMe, CF3, CN, pyridyl or ester groups are tolerated in this catalytic system. However, low isolated yields are observed with sterically crowded aryl iodides and aryl thiols. Nickel complexes bearing a tridentate pyridine bis-amide ligand have also been studied for carbon-sulfur cross-coupling reaction of aryl iodide with aryl thiol. One of the nickel chloride complexes in which (o-Me)2C6H3 group is the substituent on the amide nitrogens has been used as the catalyst. Harsh reaction conditions including high catalyst loadings, high temperatures and long reaction times are required to obtain nearly quantitative yields. Two cationic nickel hydride complexes containing a PNHPiPr ligand have been synthesized. For the cationic hydride with Br- as the counter anion, NaBH4 is the main hydride source whereas alcohol and residual water are the proton sources for NH hydrogen. These cationic hydrides have been studied for the reduction of CO2. The rate of CO2 i (open full item for complete abstract)

Committee: Hairong Guan Ph.D. (Committee Chair); William Connick Ph.D. (Committee Member); Allan Pinhas Ph.D. (Committee Member) Subjects: Chemistry; Inorganic Chemistry; Organic Chemistry

PhD, University of Cincinnati, 2012, Arts and Sciences: Chemistry

This dissertation is focused on the synthesis of well-defined nickel hydride complexes bearing a bis(phosphinite) pincer ligand (commonly known as a POCOP ligand) and utilities of these metal complexes in varieties of useful organic transformations. Aldehydes insert cleanly and selectively into the Ni-H bonds of (POCOP)NiH complexes to form nickel alkoxide complexes. These nickel alkoxide compounds further react with phenylsilane to regenerate (POCOP)NiH and produce silyl ethers. Based on these observations, an efficient and chemoselective hydrosilylation process has been developed utilizing nickel hydrides as catalysts. The process is highly compatible with varieties of functional groups in aldehydes. A nickel hydride complex with smaller substituents on the POCOP ligand proves to be more effective hydrosilylation catalyst. In case of ketones, partial hydrosilylation occurs. (POCOP)NiH complexes also react with CO2 to produce nickel formate complexes. When stoichiometric amounts of boranes are used, nickel hydrides are cleanly reformed. The use of catalytic amounts of nickel hydrides and excess of boranes reduces CO2 to the corresponding methanol derivatives. The initial reduction products can be further hydrolyzed to yield methanol. The overall transformation is comprised of three catalytic cycles. A catalyst with more bulky substituents on the phosphorus atoms of pincer ligand is a more effective catalyst than those containing smaller substituents. This phenomenon has been rationalized by invoking more favorable dihydridoborate adduct formation between less bulky nickel hydrides and boranes. One of such dihydridoborate adduct has been successfully isolated and its influence on the catalytic CO2 reduction has been demonstrated. (POCOP)NiH complexes have been found be active catalysts for the decomposition of formic acid to release dihydrogen. When the kinetics the reaction is monitored by in-situ IR spectroscopy, a unique sigmoidal pattern is observed. Seve (open full item for complete abstract)

Committee: Hairong Guan PhD (Committee Chair); William Connick PhD (Committee Member); Allan Pinhas PhD (Committee Member) Subjects: Chemistry

Doctor of Philosophy, University of Toledo, 2005, Electrical Engineering

The nickel metal hydride (NiMH) batteries used in most hybrid electric vehicles (HEVs) provide satisfactory performance but are quite expensive. In spite of their lower energy density, lead acid batteries are much more economical, but they are prone to sulfation in HEV applications. However, sulfation can be greatly reduced by a circuit that uses an ultracapacitor in conjunction with the battery. This research presents a new cost-effective method for using these two energy storage components together in order to extend the life of the battery. This system is presently quite expensive, but it will provide much cheaper energy storage if ultracapacitor prices can be reduced to the levels predicted by some manufacturers. This dissertation studies two different methods for implementation on a hybrid electric vehicle and presents performance data for a variety of simulations.

Committee: Thomas Stuart (Advisor) Subjects: