Browsing by Subject "Inorganic synthesis"

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    Synthesis, characterization, and reactivity of metal-metal bonded complexes with cobalt, iron, and manganese
    (2014-11) Tereniak, Stephen J.
    Metal-metal bonding is important in dirhodium catalysts that mediate carbene insertions into C-H bonds, cyclopropanations, aziridinations, and ylide formations. Additionally, it has been suggested that certain intermediates in NiFe hydrogenases contain a nickel-iron bond. In light of the successful applications of dirhodium complexes in organic chemistry, as well as the role metal-metal bonds play in biology, the design of synthetic bimetallic complexes with mid-to-late first-row transition metals is of great interest. Yet, few examples of mid-to-late first-row transition metal complexes exhibiting metal-metal bonding have been reported, and even more strikingly, very few mid-to-late heterobimetallic complexes have been prepared. In the second chapter of this thesis, the synthesis and characterization of an isostructural series of dicobalt, cobalt-iron, cobalt-manganese, diiron, and iron-manganese complexes supported by a new binucleating ligand is disclosed. The diiron compound has a much shorter crystallographic metal-metal distance than the other four complexes. Experimental and theoretical work suggests that the short iron-iron distance is due to the full delocalization of the d orbitals, which leads to an S = 3 ground state. This is in contrast to the other four bimetallics, in which the magnetic interactions are modeled as high-spin metal centers that antiferromagnetically couple. In the third chapter, the synthesis and characterization of a dicobalt organometallic complex and a series of organometallic aluminum-cobalt complexes is described. Isostructural dicobalt benzyl and aluminum-cobalt benzyl compounds are compared using experiment and theory. A series of C-C bond forming experiments from the reaction of R-X compounds with the metal-cobalt benzyl complexes suggests that both the dicobalt compound and the aluminum-cobalt compound are capable of one-electron chemistry, whereas only the aluminum-cobalt complex undergoes two-electron reactions. These results are explained by the electronic structure of the two compounds: the aluminum-cobalt complex has the aluminum(III)cobalt(I) oxidation state, whereas calculations suggest that the dicobalt complex is cobalt(II)cobalt(II). In the fourth chapter, the synthesis and characterization of a series of hexairon and tetrairon clusters related by one-, two-, or three-electron redox steps is reported. In the fifth chapter, the role of some of these clusters in the dioxygen reactivity of a diiron(II) complex is revealed.
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    Tuning Nickel Electronics and Hydrogenation Reactivity with Rare Earth Metalloligands
    (2020-08) Ramirez, Bianca
    Industrially, many chemical transformations require the use of expensive precious metal catalysts to proceed. A major chemical pursuit aims at replacing these expensive metals with inexpensive, Earth-abundant transition metals. Unfortunately, Earth-abundant transition metals are often poor catalysts for challenging multi-electron processes. One strategy to circumvent this problem makes use of σ-accepting (or Z-type) ligands to control the electronic characteristics and reactivity of a metal center. However, a heavy focus on main group metals within this field has yielded a lack of diversity in the metals employed as Z-type ligands. In this vein, this dissertation investigates the use of rare earth metals as Z-type ligands to promote homogenous transition metal catalysis. A series of nickel–rare earth (Sc, Y, lanthanides) heterobimetallic complexes were synthesized using new phosphinoamide ligands. The complexes were characterized using a suite of spectroscopic, electrochemical, and computational methods. The electronic effects of the rare earth supporting metals poised the Ni metal center for the hydrogenation of olefins to alkanes as well as alkynes to (E)-alkenes. Furthermore, it was found that altering the coordination sphere of the rare earth support significantly impacts the resulting properties and catalytic activity of the active Ni metal center. By quantitatively comparing structure, redox properties, and mechanistic intermediates, the effects of the supporting metal on the Ni electronics, catalytic activity, and kinetics of the Ni−M complexes were elucidated. Collectively, this work demonstrates that modulating a transition metal center via an appended rare earth support metal can favorably alter the properties of inexpensive metals, thus promoting a new reactivity paradigm in homogenous transition metal catalysis.