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Issue 40, 2020
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A facile biomimetic catalytic activity through hydrogen atom abstraction by the secondary coordination sphere in manganese(iii) complexes

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Abstract

This paper describes the synthesis and structural characterization of four new manganese(III) complexes (1–4) derived from N3O donor Schiff base ligands and their biomimetic catalytic activities related to catechol oxidase and phenoxazinone synthase. X-ray crystallography reveals that the Schiff bases coordinate the metal centre in a tridentate fashion, leaving the pendant tertiary amine nitrogen atom either protonated or free to balance the charge of the system, and these pendant triamines participate in strong hydrogen bonding interactions in the solid state. The hydrogen bonding ability of the pendant triamines at the second coordination sphere plays a crucial role in the substrate recognition and the stability of the complex–substrate intermediates. The effect of substitution at the phenolate ring towards the redox potential of the metal centre and the catalytic activity of these complexes has been observed. Detailed kinetic studies further disclose the deuterium kinetic isotope effect in which the transfer of the proton along the hydrogen bond from the substrates to the pendant triamine group at the secondary coordination sphere occurs at the key step in the catalytic reaction. The present reactivity nicely resembles the biochemical reactivities in the natural system in which a concerted electron and proton transfer to different species is usually observed. Remarkably, although some sort of influence of the secondary coordination sphere on catalytic activity has been reported mimicking the function of these metalloenzymes, such a direct participation of the secondary coordination sphere, particularly in modelling phenoxazinone synthase, has not been observed to date.

Graphical abstract: A facile biomimetic catalytic activity through hydrogen atom abstraction by the secondary coordination sphere in manganese(iii) complexes

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Supplementary files

Article information


Submitted
09 Jul 2020
Accepted
14 Sep 2020
First published
15 Sep 2020

Dalton Trans., 2020,49, 14216-14230
Article type
Paper

A facile biomimetic catalytic activity through hydrogen atom abstraction by the secondary coordination sphere in manganese(III) complexes

N. Ch. Jana, P. Brandão, A. Frontera and A. Panja, Dalton Trans., 2020, 49, 14216
DOI: 10.1039/D0DT02431G

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