Thesis (Ph. D.)--Virginia Polytechnic Institute and State University, 1994. / Vita. Abstract. Includes bibliographical references (leaves 125-130). Also available via the Internet.

New chiral half-sandwich Ru hydride enantiomers with asymmetric disubstitution on the Cp ligand have been successfully synthesized and resolved. An enantiopure thiolate ligand was installed on the Ru center to form a pair of diastereomers, which were separated by crystallization via vapor diffusion of pentane into their saturated Et2O solution. Racemization occurred at elevated temperatures, but a room temperature conversion pathway was developed to remove the chiral thiolate ligand and generate the enantiopure hydride complex. Two new Rh(III) hydride complexes and their Ir analogues have been synthesized and characterized. The hydride complexes readily transfer H– to the N-carbophenoxypyridinium cation at room temperature, giving mixtures of 1,2- and 1,4-dihydropyridine products. In CD3CN, all four hydrides give nearly the same product ratio, demonstrating that the hydride transfer mechanism is outer sphere. In weak or non-coordinating solvents, the resulting 16-electron cations catalyze the isomerization of 1,2- to 1,4-dihydropyridine at rates that depend upon the cation and the solvent. The fastest isomerization was observed with the Rh(III) cation [Cp*Rh(2-(2-pyridyl)phenyl)]+, Acetonitrile can trap the 16-electron cations resulting from hydride transfer, dramatically slowing the isomerization process. The thermodynamics and kinetics of hydride, hydrogen atom and proton transfer reactions of the Rh(III) hydride, Cp*Rh(2-(2-pyridyl)phenyl)H, were studied both thermodynamically and kinetically. This hydride is both a good hydride and hydrogen atom donor, but a poor proton donor. This previously unobserved combination of properties is due to the high energy of the hydride’s conjugate base, [Cp*Rh(2-(2-pyridyl)phenyl)]−. Its exceptional hydride donor ability makes Cp*Rh(2-(2-pyridyl)phenyl)H a very efficient catalyst for the ionic hydrogenation of iminium cations.

Thesis (Ph. D.)--University of Washington, 2001. / Vita. Includes bibliographical references (leaves 144-149).

Thesis (M.S.)--University of Hawaii at Manoa, 2007. / Includes bibliographical references (leaves 87-92). / viii, 92 leaves, bound ill. 29 cm

Radical cyclizations have become a mainstay of synthetic organic chemistry – useful for the construction of C–C bonds in laboratory-scale applications. However, they are seldom used the industrial scale. In large part, this is because of a reliance on Bu3SnH, widely regarded as the best synthetic equivalent to a hydrogen atom. Transition metal hydrides have emerged as promising alternative hydrogen atom sources. Over the last decade, the Norton group has studied three transition metal systems, with an emphasis on quantifying the M–H bond dissociation energies. Over time, the group has shown that, thermodynamically, first-row transition metal hydrides are good hydrogen atom donors; they often have weak M–H bonds. Modest adjustments to the M–H bond strength result in substantial changes to how a hydride processes a given organic substrate. The Norton group has also studied the kinetics of hydrogen atom transfer, and shown that transition metal hydrides are kinetically competent at transferring hydrogen atoms, both to olefinic substrates and to organic radicals. Some of the transition metal complexes are made catalytic under modest pressures of H2, so they can be used for effecting atom-economical radical reactions. I have leveraged the fundamental kinetic and thermodynamic information that has been gathered by the group to develop new radical reactions – ones that cannot be done by Bu3SnH. Herein are described two cases studies: the first is the generation of α-alkoxy radicals by hydrogen atom transfer to enol ethers (Chapter 2). The second is the development of a radical isomerization and cycloisomerization reactions (Chapter 3). Both of these developments have relied upon an understanding of M–H thermochemistry. Discovering new hydrogen atom donors will lead to discovering new radical reactions. In Chapter 4, I revisit two previously reported transition metal hydrides that are likely to transfer hydrogen atoms: (TMS3tren)CrIV–H and [CpV(CO)3H]–. Although the anionic vanadium hydride was reported as a potent hydrogen atom donor nearly forty years ago, my studies suggest that its M–H bond is actually relatively strong. I have therefore reevaluated the reactivity of [CpV(CO)3H]–, and found that although the 18 electron anionic hydride is not a good hydrogen atom donor, the oxidized 17-electron neutral CpV(CO)3H is an extremely potent one. I have made the reactions with [CpV(CO)3H]– catalytic under H2 (now the reactions are done with an added base). The catalytic reactions that use [CpV(CO)3H]– can enact the exact same transformations that tin does, so I have developed a true catalytic replacement for Bu3SnH.

Thesis (Ph. D.)--University of Washington, 2007. / Vita. Includes bibliographical references (leaves 119-130).

No description available.

The traditional reagent for H• transfer in organic chemistry is 𝓃-Bu₃SnH, which has a Sn–H bond dissociation energy (BDE) of 78.5 kcal/mol. There are, however, many disadvantages of employing 𝓃-Bu₃SnH in radical reactions. The transfer of H• from tin is necessarily stoichiometric, with 𝓃-Bu₃Sn–X being the eventual product. Overall, the tin reactions have poor atom economy; n-Bu3SnH cannot be regenerated from 𝓃-Bu₃Sn• or 𝓃-Bu₃Sn–X with hydrogen, and no general methods of regenerating the tin hydride with other hydride sources have been reported. Standard purification methods leave unacceptable levels of residual tin in the products of n-Bu3SnH reactions. Alternatives are clearly needed. Transition metal hydrides represent a class of promising reagents to replace 𝓃-Bu₃H. Due to their typically weaker M-H bonds, transition metal hydrides are often able to transfer H• to C=C and generate radicals — a reaction that 𝓃-Bu₃SnH cannot do. Furthermore, many transition-metal hydrides can be regenerated from hydrogen gas, an event that requires that the M–H BDE be over 56 kcal/mol. By combining this reaction with the H• transfer, metalloradicals can often catalyze the formation of radicals from H₂. Over the years, the Norton group has studied several transition metal hydride systems and demonstrated their applications in different scenarios. The kinetics and thermodynamics of these systems have been studies in detail, and they are shown be competent hydrogen atom donors to unsaturated organic substrates and to organic radicals. Some of these metal hydrides can be made catalytic under hydrogen pressure, thus providing an atom-economical way to effect radical reactions. Specifically, the thermodynamic properties of the chromium hydride HCpCr(CO)₃ have been carefully studied. Based on this information, I developed a Ti/Cr cooperative catalytic system featuring multiple interactions between the two metal systems. Herein are described three applications of this Ti/Cr catalytic system: anti-Markovnikov hydrogenation of epoxides (Chapter 2), reductive cyclization of epoxy enones under H₂ (Chapter 3), and aziridine isomerization to allyl amines (Chapter 4). I have also explored new hydrogen atom acceptors. I was able to catalyze hydrodefluorination of CF₃-substituted olefins with a nickel hydride (Chapter 5). The reaction was demonstrated to be initiated by a hydrogen atom transfer from the Ni(II)-H to the olefin substrates. This also expands our toolbox of metal hydrides for transferring hydrogen atom to olefin substrates. With a different cobaloxime catalyst, I was able to catalyze the cycloisomerization of CF₃-substituted dienes (Chapter 6). In Chapter 7, I developed a method to achieve a broad range of hydrofunctionalizations of olefins with hydrogen atom transfer from metal hydrides in situ. Hydrogen atom transfer to olefins was followed by TEMPO trapping to form TEMPO adducts. A subsequent photocatalytic substitution on those TEMPO adducts with different nucleophiles affords various hydrofunctionalized products.

The complex, IrH₂(PMe₃)₃Cl (1), was previously found to be, not only unexpectedly water-soluble but also an effective homogeneous catatyst for the hydrogenation of unsaturates in water. The results of extensive ³¹P NMR studies on the aqueous system of (1) indicate that (1) is in equilibrium with the iridium(III) dihydrido “aquo” complex, [IrH₂(PMe₃)₃(H₂O)]⁺, and not the μ-chloro bridged complex, { [IrH₂(PMe₃)₃]₂Cl}⁺ (2), as previously reported. The calculated K_eq value for the aqueous equilibrium is (0.0037 ± 0.0003) M. Thermodynamic data (ΔH = 30.8 kJ/mol, ΔS = 56.0 J/(Kmol), and ΔG = 14.1 kJ/mol) obtained from variable temperature ³¹P NMR studies are consistent with the proposed equilibrium system. The complexes IrH₂(PMe₃)₃X (X = O₂CPh (3), I (4), and Br (6) were synthesized and examined. The complexes IrH₂(PMe₃)₃X (X = H₂O and F) could not be isolated. (3) was determined to dissociate completely in water to form the iridium(III) dihydrido “‘aquo” complex, [IrH₂(PMe₃)₃(H₂O)]⁺, seemingly explaining the greater catalytic activity of (3). Solubility of the halo complexes decreased from moderately soluble (1), to slightly soluble (6), to very slightly soluble (4). The solubilities of (4) and (6) were too low to allow quantification of their equilibria. Finally it was observed that linear relationships exist between the electronegativity of the ligand, X, and the ¹H and ³¹P NMR chemical shifts of the hydrides and the phosphines for the complexes, IrH₂(PMe₃)₃X. These relationships are consistent with the findings of Birnbaum. / Ph. D.

Copper hydrides such as [Ph₃PCuH]₆ (Stryker’s Reagent) are textbook reagents in organic chemistry for the selective hydrogenation of α,β-unsaturated carbonyl compounds. Despite their widespread use both stoichiometrically and catalytically, there are many important questions about polynuclear copper hydrides that have not been answered. I have investigated the electron transfer chemistry of [Ph₃PCuH]₆ and related copper hydrides. Copper hydrides (E₁/₂ = –1.0 to –1.2 V vs FcH/FcH⁺) are good one-electron reducing agents. Stopped-flow techniques have allowed the detection of electron transfer intermediates in copper hydride reactions. The fate of the copper containing products after electron transfer or hydride transfer reactions has been investigated. An unusual cationic copper hydride, [(Ph₃P)₇Cu₇H₆]⁺ was found to be the major product of these reactions. Methods of converting this species back to [Ph₃PCuH]₆ have been investigated. The chemistry of this cationic species plays an important role in catalytic use of copper hydrides.