Browsing by Subject "titanium"

Now showing 1 - 4 of 4
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    Development and Mechanistic Studies of Ti-Mediated C-N and N-N Coupling Reactions
    (2022-11) Cheng, Yukun
    This thesis describes our recent efforts on C-N and N-N coupled nitrene transfer reactions via Ti imido complexes. These studies aim to explore the compatibility of Ti(IV/II) redox catalysis with various chemical transformations through mechanistic interrogation and reactivity of model compounds, for the development of new Ti-catalyzed nitrene transfer reactions. Chapter 1 explains the background and challenges in Ti-mediated C-N and N-N coupling reactions. Chapter 2 describes the application of boryl and stannyl alkynes in Ti-catalyzed [2+2+1] pyrrole synthesis and the subsequent Pd-catalyzed cross-coupling reactions for highly functionalized pyrroles. Chapter 3 covers the exploration of alternative nitrene sources in Ti-catalyzed hydroamination via a Ti(IV/II) redox process. Chapter 4 details the mechanistic investigation of the sequential one-electron oxidation processes in the oxidative pyrazole synthesis from diazatitanacyclohexadiene. In chapter 5, a preliminary study on N–N coupled indazole synthesis from diazatitanacyclohexadiene with an extended aromatic system is reported.
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    Development of Ti-mediated multicomponent syntheses via cycloaddition and insertion reactions
    (2023-05) Frye, Connor
    Nitrogen-containing compounds are extremely prevalent in bioactive molecules, dyes, electronics, and other materials. Thus, the development of practical synthetic routes to a diverse library of N-containing compounds is vital. Condensation reactions have been traditionally employed to access highly functionalized N-containing compounds. However, these reactions typically exhibit poor chemoselectivity, and frequently require extensive pre-construction of carbon skeletons. These limitations make the development of metal-mediated or -catalyzed multicomponent reactions from simple starting materials an attractive alternative. Given its high abundance and low-cost, Ti is an excellent candidate for facilitating these reactions. Herein, efforts to develop new Ti-mediated or -catalyzed multicomponent transformations for the synthesis of N-containing organic compounds and N-heterocycles are presented. The modular construction of unsymmetrical α-diimines has been achieved through the diimination of alkynes using Ti imidos, nitrosos, and nitriles. This reaction features a key diazatitanacyclohexadiene intermediate, generated ¬in-situ, that undergoes a series of cycloaddition and retrocyclization reactions. The reactivity of this titanacycle towards other unsaturated substrates and electrophiles has been explored, culminating in the development of a multicomponent method for the synthesis of 1,2-dihydropyrimidines. Finally, a newly developed Ti-catalyzed multicomponent synthesis of 2,3-annulated pyrroles from alkynes, 1,2-cyclononadiene, and azobenzene is presented, and the selectivity of other allenes has been assessed. Importantly, all of these Ti-mediated reactions feature key electrocyclic mechanistic steps, and it is becoming increasingly clear that these are a general feature of titanium’s reactivity that can be exploited for the design of new synthetic methods.
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    Redox non-innocence and formation of nitrogen-nitrogen bonds in organometallic reactions
    (2020-01) Pearce, Adam
    The utilization of redox non-innocent ligands and substrates can grant access to new modes of reactivity in organometallic chemistry, allowing for the development of new sustainable methods with earth-abundant catalysts. Through the use of valence tautomerism in nitrogenous ligands and substrates (azides, azobenzene, isodiazenes, etc.), new organometallic reactions have been developed—the atom economical synthesis of important organic molecules such as pyrroles, pyrazoles and imines through titanium redox catalysis and an exploration of the valence tautomerism of an iridium(III)-hydrazido(2-) capable of oxidative addition.
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    Unsaturated Hydrocarbons as Building Blocks for Polymers and Pyrroles via Homogeneous Organometallic Catalysis
    (2019-04) Chiu, Hsin-Chun
    This thesis covers two common applications of organometallic catalysis: polymerization and small molecule synthesis. The first part of my thesis, Chapters 2 and 3, discusses secondary coordination effects on Ni-catalyzed ethylene polymerizations via the development of two new families of heterobimetallic Ni complexes. The second major section, Chapter 4 and 5, is focused on selective pyrrole synthesis through the modification of our recently discovered Ti-catalyzed pyrrole synthesis from alkynes and azobenzenes. Two different strategies, stereoelectronic control and dative directing group effects, have been found to play a significant role in the chemo- and regiocontrol of this catalysis. Lastly, a new project on the combination of Pd-catalyzed polyketone formation and hydroesterification has been carried out as a novel route of making polyketoesters. Some early screenings will be presented in Chapter 6 with various diphosphine ligands.