Browsing by Subject "Organometallic"
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Item Novel organometallic precursors for the Chemical Vapor Deposition of metal thin films(2010-08) Rivers, Joseph Henry; Jones, Richard A., 1954-; Cowley, Alan H.; Holliday, Bradley J.; Magnus, Philip D.; Ekerdt, John G.With the growing demand for miniaturization of devices and for new materials with useful properties, the use of Chemical Vapor Deposition (CVD) for the manufacture of thin films is receiving growing attention. The synthesis of potentially volatile metal complexes and investigation of their use as CVD precursors is an important part of this process. The research presented addresses several major areas of this process, (i) the identification and synthesis of ligands which can impart volatility to a metal complex, (ii) the synthesis, characterization, and assessment of volatility of metal complexes containing these ligands, and (iii) the full materials characterization of thin films grown with these complexes. The use of trimethylphosphine, bis(trifluoromethyl)pyrazolate, and bis(trifluoromethyl)pyrrolyl ligands have been successfully used to synthesize volatile new complexes of cobalt, rhodium, and nickel, some of which show promise for use as potential CVD precursors.Item The Bioorganometallic Chemistry of Iron and the Diatomic Ligands CO and NO as Related to Hydrogenase Active Sites and Dinitrosyl Iron Complexes(2014-08-20) Bethel, Ryan DThe discovery of a diiron organometallic active site, found in the [FeFe]-Hydrogenase (H2ase) enzyme, has led to a revisiting of the classic organometallic chemistry involving the Fe-Fe bond and bridging ligands. This diiron site is connected to a mainstay of biochemistry, a redox active 4Fe4S cluster, and the combination of these units is undoubtedly connected to the enzyme?s performance. The regioselectivity of CO substitution on the diiron framework of the so-called parent model complex (?-pdt)[Fe(CO)3]2, (pdt = propane-1,3-dithiolate), and its derivatives, informs on the interplay of electron density in the diiron core of the enzyme active site. The structural isomers (?-pdt)[Fe(NHC)(NO)(PMe3)][Fe(CO)3]+ and (?-pdt)(?-CO)[Fe(NHC)(NO)][Fe(PMe3)(CO)2]+, synthesized through CO substitution by opposing nucleophilic (PMe3) and electrophilic (NO+) ligands provide insight into the reactivity of both irons as a function of their ?-acidity. The intramolecular fluxional processes of a series of (?-SRS)[Fe(CO)3]2 complexes allows for the generation of an open site mimicking the structure of the H2ase where H+ binds in the catalytic cycle of H2 production. Density Functional Theory (DFT) was used to support the dynamic 1H and 13C NMR spectroscopic studies that established the energy barriers to both the chair/boat interconversion of FeS2C2X, where X = NR or CR2, and the rotation of the Fe(CO)3 moiety, a process essential to the formation of an open site. It was determined that the rotation barrier is correlated with the steric bulk of the bridging ligand that can be directed towards the iron. This is seen with the methyl substituent in both N(CH3) and C(CH3)2 producing a lower barrier to Fe(CO)3 rotation than the NH and CH2 analogues, while the steric bulk of NC(CH3)3 cannot be directed to the iron and results in a higher barrier than both NH and N(CH)3. Another class of bioorganometallic molecules, the dinitrosyl iron complexs (DNICs), is formed in vivo as the product of NO degradation of iron-sulfur clusters; DNICs are thought to have possible NO storage and transport roles in the body. Computational investigations utilizing DFT have been used to support synthetic and kinetic studies of the reactivity of one such complex, (NHC)(SPh)Fe(NO)2, (NHC = N-heterocyclic carbene) with CO.Item Transition metal catalyzed C-C bond formation under transfer hydrogenation conditions(2013-05) Leung, Joyce Chi Ching; Krische, Michael J.Carbon-carbon bond forming reactions are fundamental transformations for constructing structurally complex organic building blocks, especially in the realm of natural products synthesis. Classical protocols for forming a C-C bond typically require the use of stoichiometrically preformed organometallic reagents, constituting a major drawback for organic synthesis on process scale. Since the emergence of transition metal catalysis in hydrogenation and hydrogenative C-C coupling reactions, atom and step economy have become important considerations in the development of sustainable methods. In the Krische laboratory, our goal is to utilize abundant, renewable feedstocks, so that the reactions can proceed in an efficient and atom-economical manner. Our research focuses on developing new C-C bond forming protocols that transcend the use of stoichiometric, preformed organometallic reagents, in which [pi]-unsaturates can be employed as surrogates to discrete premetallated reagents. Under transition metal catalyzed transfer hydrogenation conditions, alcohols can engage in C-C coupling, avoiding unnecessary redox manipulations prior to carbonyl addition. Stereoselective variants of these reactions are also under extensive investigation to effect stereo-induction by way of chiral motifs found in ligands and counterions. The research presented in this dissertation represents the development of a new class of C-C bond forming transformations useful for constructing synthetic challenging molecules. Development of transfer hydrogenative C-C bond forming reactions in the form of carbonyl additions such as carbonyl allylation, carbonyl propargylation, carbonyl vinylation etc. are discussed in detail. Additionally, these methods avoid the use of stoichiometric chiral allenylmetal, propargylmetal or vinylmetal reagents, respectively, accessing diastereo- and enantioenriched products of carbonyl additions in the absence of stoichiometric organometallic byproducts. By exploiting the atom-economical transfer hydrogenative carbonyl addition protocols using ruthenium and iridium, preparations of important structural motifs that are abundant in natural products, such as allylic alcohols, homoallylic alcohols and homopropargylic alcohols, become more feasible and accessible.