Issue 9, 2024

Single electron reduction of NHC–CO2–borane compounds

Abstract

The carbon dioxide radical anion [CO2˙] is a highly reactive species of fundamental and synthetic interest. However, the direct one-electron reduction of CO2 to generate [CO2˙] occurs at very negative reduction potentials, which is often a limiting factor for applications. Here, we show that NHC–CO2–BR3 species – generated from the Frustrated Lewis Pair (FLP)-type activation of CO2 by N-heterocyclic carbenes (NHCs) and boranes (BR3) – undergo single electron reduction at a less negative potential than free CO2. A net gain of more than one volt was notably measured with a CAAC–CO2–B(C6F5)3 adduct, which was chemically reduced to afford [CAAC–CO2–B(C6F5)3˙]. This room temperature stable radical anion was characterized by EPR spectroscopy and by single-crystal X-ray diffraction analysis. Of particular interest, DFT calculations showed that, thanks to the electron withdrawing properties of the Lewis acid, significant unpaired spin density is localised on the carbon atom of the CO2 moiety. Finally, these species were shown to exhibit analogous reactivity to the carbon dioxide radical anion [CO2˙] toward DMPO. This work demonstrates the advantage provided by FLP systems in the generation and stabilization of [CO2˙]-like species.

Graphical abstract: Single electron reduction of NHC–CO2–borane compounds

Supplementary files

Transparent peer review

To support increased transparency, we offer authors the option to publish the peer review history alongside their article.

View this article’s peer review history

Article information

Article type
Edge Article
Submitted
27 11 2023
Accepted
18 1 2024
First published
20 1 2024
This article is Open Access

All publication charges for this article have been paid for by the Royal Society of Chemistry
Creative Commons BY-NC license

Chem. Sci., 2024,15, 3165-3173

Single electron reduction of NHC–CO2–borane compounds

A. Morales, C. Gonçalves, A. Sournia-Saquet, L. Vendier, A. Lledós, O. Baslé and S. Bontemps, Chem. Sci., 2024, 15, 3165 DOI: 10.1039/D3SC06325A

This article is licensed under a Creative Commons Attribution-NonCommercial 3.0 Unported Licence. You can use material from this article in other publications, without requesting further permission from the RSC, provided that the correct acknowledgement is given and it is not used for commercial purposes.

To request permission to reproduce material from this article in a commercial publication, please go to the Copyright Clearance Center request page.

If you are an author contributing to an RSC publication, you do not need to request permission provided correct acknowledgement is given.

If you are the author of this article, you do not need to request permission to reproduce figures and diagrams provided correct acknowledgement is given. If you want to reproduce the whole article in a third-party commercial publication (excluding your thesis/dissertation for which permission is not required) please go to the Copyright Clearance Center request page.

Read more about how to correctly acknowledge RSC content.

Social activity

Spotlight

Advertisements