Dioxygen Activation and Magnetostructural Correlation of Metal Complexes of Redox Non-innocent Ligands and Metal Acetates: Oxidation of Substituted Dioxolene and Phenols

Dey, Suman Kr (2015) Dioxygen Activation and Magnetostructural Correlation of Metal Complexes of Redox Non-innocent Ligands and Metal Acetates: Oxidation of Substituted Dioxolene and Phenols. PhD thesis, Indian Institute of Science Education and Research Kolkata.

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Abstract

The present work started with a focus on collating the known data in literature on small molecule mimics of CO and PHS and discuss the mechanistic aspects and correlate the activity. Following catalytic oxidation of substituted dioxolene and 2-amino phenol, since the metal ions of similar properties may also be capable of C-H activation in certain phenols hence oxidative coupling reactions of the relevant sterically hindered phenols have been included. The work on this oxophilic redox non-innocent ligand based MnIII complex 9 provided us with the indication that there is great deal to consider while designing a biomimetic catalysts inspired by nature and it should not necessarily involve using the same metal ion as nature. It showed that there are multiple ways to generate efficient biomimetic catalysts rather than the widely used methodology which starts by first designing a ligand to form a complex that would be a structural mimic of the active site in terms of coordination and geometry. We found that presence of labile sites and having redox potential in the proper range may lead to efficient catalysts for a specific reaction viz. catechol oxidation, aminophenol oxidation and oxidative C-C bond coupling of 2,6- DTBP and 2,4-di-tert-butylphenol (2,4-DTBP). Hence in chapter V we probed the efficiency of MnIII acetate dihydrate as oxygen activation catalyst in the above type of reactions and the evidences of intermediates obtained through various analytical techniques facilitated the proposition of reaction mechanism for the oxidation of catechol or 2-aminophenol. We needed to know if among the 3d-metals the efficiency of Mn is the best for the above two bio-inspired catalytic purposes. Hence, we investigated for the most active 3d-transition metal among the metals used for designing biomimetic complexes of catechol oxidase (CO) and phenoxazinone synthase (PHS) over past few decades and their efficiency were compared irrespective of their coordination environment. The results show that indeed Mn although not chosen by nature yet seems to be the best choice in laboratory conditions as CO and PHS mimics.

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