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A computational mechanistic investigation into reduction of gold(III) complexes by amino acid glycine: a new variant for amine oxidation

journal contribution
posted on 2023-05-19, 21:13 authored by Chipman, A, Gouranourimi, A, Farshadfar, K, Angus OldingAngus Olding, Brian YatesBrian Yates, Alireza AriafardAlireza Ariafard
Density functional theory (DFT) was utilized to explore the reduction of gold(III) complexes by the amino acid glycine (Gly). Interestingly, when the nitrogen atom of Gly coordinates to the gold(III) center, its Cα -hydrogen atom becomes so acidic that it can be easily deprotonated by a mild base like water. The deprotonation converts the amino acid into a potent reductant by which gold(III) is reduced to gold(I) with a moderate activation energy. To our knowledge, this is the first contribution suggesting that primary amines are oxidized to imines via direct a-carbon deprotonation. This finding may provide new insights into the mechanistic interpretation of amine oxidations catalyzed/mediated by a center with high cathodic reduction potential. This work also provides a rationalization behind why gold(III) complexes with amine-based polydentate ligands are reluctant to undergo a redox process. Gold(III) reduction occurs most efficiently if the Cα proton leaves in the plane of the Cα, N and Au atoms. Chelation prevents this alignment, resulting in the gold(III) complex being unreactive toward reduction. It has been experimentally found that gold(III) is capable of oxidizing Gly to glyoxylic acid (GA) as the initial product. The latter, in the presence of another gold(III) complex, has been reported to undergo oxidative decarboxylation to afford CO2 and HCOOH. This process is found to be mediated by formation of a geminal diol intermediate produced by reaction of water with the aldehyde functional group of the coordinated GA.

Funding

Australian Research Council

University of Wollongong

History

Publication title

Chemistry

Volume

24

Issue

33

Pagination

8361-8368

ISSN

1521-3765

Department/School

School of Natural Sciences

Publisher

Wiley

Place of publication

Germany

Rights statement

Copyright 2018 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim

Repository Status

  • Restricted

Socio-economic Objectives

Expanding knowledge in the chemical sciences