Modular Synthesis of Asymmetric Triazacyclononane Derivatives and Potential Aerobic Copper Oxidation Catalyst Supported by a Bridging Bulky Triazacyclononane Open Access

Buru, Cassandra Terez (2015)

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Metalloenzymes carry out synthetically challenging oxidations, usually involving an earth abundant bimetallic center and atmospheric oxygen. 1,4,7-triazacyclononane (tacn) derivatives have historically been used to model the active sites in these enzymes. However, above cryogenic temperatures, these model systems oxidize the ligand, preventing catalysis at ambient temperatures. Until recently, there had been no precedent for creating bulky substituents on tacn to prevent ligand degradation. This report will describe the scope of the tBu3tacn synthesis to other tacn derivatives, in particular, to binucleating tacn derivatives with tert-butyl substituents, and the corresponding coordination chemistry. Furthermore, studies on intramolecular oxidation of these bimetallic complexes will be described. Finally, preliminary results will demonstrate progress to prevent ligand degradation.

Table of Contents

1.0 Introduction: An Oxidation Problem. 1

1.1 Oxidations in Biology

1.2 Copper and Dioxygen in Synthetic Systems

1.2.1 Binucleating Systems

1.2.2 Ligand Degradation

1.3 Previous Derivatives of tacn

1.4 Goals of the Project

2.0 Results and Discussion. 11

2.1 Alternative Synthesis to Known tacn Derivatives

2.2 Di- and Mono- tert-butyl tacn

2.3 Bridging tacn Synthesis

2.4 Bridging Copper tacn Complexes

3.0 Future Studies. 22

3.1 Spectroscopic Studies

3.2 New Bridging Ligands

3.2.1 Aryl-Bridging Unit

3.2.2 Methyl-Protected Bridging Unit

4.0 Conclusions. 25

5.0 Experimental. 26

5.1 General Considerations

5.2 Ligand Syntheses

5.2.1 Chloro-acetylation

5.2.2 Cyclizations

5.2.3 Oxidation/Reductions

5.3 Metal Complexes

6.0 Supporting Information. 34

7.0 References. 44

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