Use of piperazine ligands for bleaching and epoxidation catalysis
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Following reports that the dinuclear manganese complex of the ligand 1, 4, 7-trimethyl-1, 4, 7-triazacyclononane (TMTACN) was a potent bleaching catalyst, its catalytic oxidative activity was thoroughly studied. Apart from its catalytic bleaching activity, it has shown to be a versatile catalyst in terms of its substrate scope. In bleaching, it still remains the benchmark with regards to its catalytic bleaching activity against which systems in development are compared. Chapter one discusses the need for a bleaching catalyst in detergent formulations and the advantages it offers over existing technologies. Studies into the bleaching mechanism involving the manganese TMTACN system are then explored, followed by a description of its application in the oxidation of alkenes amongst other substrates. Other manganese based bleaching and epoxidation catalysts are considered briefly. This is followed by a discussion on ligand design for use in manganese and other first row transition metal based oxidation catalysts and the initially proposed ligand synthesis for this research. Chapter two details the synthetic strategies employed in the synthesis of the planned ligands along with an evaluation of the effectiveness of these strategies. The structural features of a number of novel ligands and their precursors are then explored in terms of their single crystal X-ray structures which were obtained during this research. Chapter three presents the most relevant results obtained during the course of this research with regards to the testing of the synthesised ligands and their efficacy in bleaching and epoxidation catalysis. A number of ligands demonstrated some activity in epoxidation catalysis using different manganese salts. These results are discussed in detail with an attempt to rationalise the observed catalytic activity with reference to the ligand structure and identity of the manganese salt utilised being made. The final chapter provides the necessary details of the experimental work carried out along with supporting characterisation data for the materials prepared.
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