Modulating the Catalytic Activity of First-Row Transition Metal Complexes Supported by Redox-Active Ligand Scaffolds Public

Abstract

To pursue alternatives to the environmentally detrimental and toxic second- and third-row transition metal catalysts currently utilized in industry, the development of highly-efficient first-row transition metal catalysts for aerobic catechol oxidation and oxidative coupling were pursued in this work. Two redox-active ligands, N-(2-(phenylamino)phenyl)isobutyramide (H2L^iPr) and 1-(tert-butyl)-3-(2-(phenylamino)phenyl)urea (H3L^Urea) were synthesized and characterized. Cobalt(II), copper(II), and zinc(II) complexes ([M(L^iPr)2]^2- and [M(HL^Urea)2]^2-) supported by each of the two ligand scaffolds were synthesized and characterized. X-ray diffraction data demonstrated that each ligand system stabilizes the mononuclear cobalt(II), copper(II), and zinc(II) complexes in a distorted tetrahedral geometry. Electrochemical properties of the complexes were examined through cyclic voltammetry which showed three reversible electrochemical events for each copper(II) complex and two reversible electrochemical events for each cobalt(II) and zinc(II) complex. When exposed to dioxygen, the six complexes presented herein catalytically oxidize 3,5-Di-tert-butylcatechol to 3,5-Di-tert-butyl-o-quinone. Cobalt(II) and copper(II) complexes supported by H2L^iPr and H3L^Urea ligand scaffolds were shown to aerobically catalyze oxidative phenolate coupling reactions, resulting in a biphenyl product.

Table of Contents

1.     Introduction……………………………………………………………………….…...........……1

2.     Results and Discussion………………………………………………………………….......…6

2.1  Synthesis and Characterization of Redox-Active Ligands…………….……….…6

2.2  Synthesis and Characterization of Metal Complexes…………………………..…...8

2.3  Crystallographic Characterization of Metal Complexes……………………....…11

2.4  Electrochemical Characterization of Metal Complexes…………………………....16

2.5  Monitoring Catechol Oxidation with UV-Visible Spectroscopy………………....23

2.6  Reactivity Studies of Catechol Oxidation……………………………………...........…25

2.7  Reactivity Studies of Oxidative Phenolate Coupling……………………………......29

3.     Conclusion and Future Directions….………………………………………………....…....31

4.     Experimental….…………………………………………………...................................33

4.1  General Methods….……………………………..………........................................33

4.2  Ligand Synthesis….……………………………..………........................................34

4.3  Metal Complex Synthesis….……………………………..……….............................35

4.4  Monitoring Aerobic Catechol Oxidation with UV-Visible Spectroscopy………39

4.5  Catalytic Aerobic Substrate Oxidation………………………………………….............40

5.     References…….…………………………………………………....................................41

About this Honors Thesis

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School	Emory College
Department	Chemistry
Degree	B.A.
Submission	Honors Thesis
Language	English
Research Field	Chemistry, General Chemistry, Inorganic
Mot-clé	aerobic oxidation inorganic chemistry redox-active ligand hydrogen-bonding catalysis green chemistry
Committee Chair / Thesis Advisor	MacBeth, Cora, Emory University
Committee Members	Ristaino, Christine, Emory University Brathwaite, Antonio, Emory University Blakey, Simon, Emory University

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