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Issue 13, 2020
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Probing the electronic and mechanistic roles of the μ4-sulfur atom in a synthetic CuZ model system

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Abstract

Nitrous oxide (N2O) contributes significantly to ozone layer depletion and is a potent greenhouse agent, motivating interest in the chemical details of biological N2O fixation by nitrous oxide reductase (N2OR) during bacterial denitrification. In this study, we report a combined experimental/computational study of a synthetic [4Cu:1S] cluster supported by N-donor ligands that can be considered the closest structural and functional mimic of the CuZ catalytic site in N2OR reported to date. Quantitative N2 measurements during synthetic N2O reduction were used to determine reaction stoichiometry, which in turn was used as the basis for density functional theory (DFT) modeling of hypothetical reaction intermediates. The mechanism for N2O reduction emerging from this computational modeling involves cooperative activation of N2O across a Cu/S cluster edge. Direct interaction of the μ4-S ligand with the N2O substrate during coordination and N–O bond cleavage represents an unconventional mechanistic paradigm to be considered for the chemistry of CuZ and related metal–sulfur clusters. Consistent with hypothetical participation of the μ4-S unit in two-electron reduction of N2O, Cu K-edge and S K-edge X-ray absorption spectroscopy (XAS) reveal a high degree of participation by the μ4-S in redox changes, with approximately 21% S 3p contribution to the redox-active molecular orbital in the highly covalent [4Cu:1S] core, compared to approximately 14% Cu 3d contribution per copper. The XAS data included in this study represent the first spectroscopic interrogation of multiple redox levels of a [4Cu:1S] cluster and show high fidelity to the biological CuZ site.

Graphical abstract: Probing the electronic and mechanistic roles of the μ4-sulfur atom in a synthetic CuZ model system

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Supplementary files

Article information


Submitted
10 Dec 2019
Accepted
14 Feb 2020
First published
17 Feb 2020

This article is Open Access
All publication charges for this article have been paid for by the Royal Society of Chemistry

Chem. Sci., 2020,11, 3441-3447
Article type
Edge Article

Probing the electronic and mechanistic roles of the μ4-sulfur atom in a synthetic CuZ model system

S. C. Rathnayaka, S. M. Islam, I. M. DiMucci, S. N. MacMillan, K. M. Lancaster and N. P. Mankad, Chem. Sci., 2020, 11, 3441
DOI: 10.1039/C9SC06251C

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