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Doyle Group Publishes on Excited States of Nickel Complexes

Research Highlights- - By Wendy Plump

The Doyle Group and the Scholes Group published research this week that contributes to an understanding of the excited states of nickel (Ni) complexes, and provides a basis for developing light-driven coupling reactions that do not require an exogenous photocatalyst. 

The paper appears in the Journal of the American Chemical Society (JACS).

“Our group is generally interested in the invention of strategies and synthetic methods that use Ni as a catalyst,” said Professor of Chemistry Abigail Doyle. “This study provides insight into how Ni complexes relevant to some of these catalytic methods interact with light.”

The paper’s lead author, Stephen Ting, a third-year graduate student with the Doyle Group, explained that Ni is commonly used as a catalyst in cross-coupling reactions, which join two smaller building blocks into a more complex one.

A prominent area of research involves using light energy to augment the Ni catalysis, since light can allow access to high-energy reactive species. Such light-driven chemistry often relies on a second catalyst – a “photocatalyst” – but the Group’s research suggests that interesting things can occur even when there is no photocatalyst: when light is shone on a common intermediate in nickel-catalyzed reactions, it generates an excited state with weaker bonds to nickel.

Shining light on common intermediates in Ni-catalysis leads to a 3d-d excited state that can undergo homolytic rupture of the Ni-aryl bond. This process may serve as a mechanism for catalyst activation.
Image courtesy of the authors

“We think that the bond weakening can allow one of the bonds to split and generate a form of the catalyst that could potentially be more active for product formation,” said Ting. “So basically, you have a mediocre or poor catalyst, and light can turn it into a good catalyst.”

Doyle said her Group expects the research will serve as a foundation to design improved and new synthetic methods of high-potential impact for the biomedical and commodity chemical fields.

The Department of Chemistry at North Carolina State University also collaborated on the research.

The paper, “3d-d Excited States of Ni(II) Complexes Relevant to Photoredox Catalysis: Spectroscopic Identification and Mechanistic Implications,” can be read in full here: https://pubs.acs.org/doi/10.1021/jacs.0c00781.