New molecule sets stage for nickel as a 'greener' photocatalyst, reveals key steps in reaction process

The word in precious metals is palladium.

The demand for this rare silvery white transition metal continues to outstrip supply, driving its price per ounce far above gold and silver.

Platinum, iridium, and ruthenium are precious metals that are crucial in chemical transformations and are used in the development of pharmaceutical drugs and other useful chemicals.

The scarcity and expense of precious metals has created a need to develop catalysts from transition metals that are more abundant and cheaper, like nickel.

The last decade has seen a dramatic expansion of new bond-forming transformations involving nickel.

Liviu Mirica, William H. and Janet G. Lycan Professor of Chemistry at the University of Illinois, said that nickel complexes are better than other transition metals.

Mirica said that nickel catalysts that can be directly photo initiated by light have proven to be a very successful area of research, producing reactions that have not been previously possible.

They still need an additional photocatalyst based on precious metals such as iridium or ruthenium, which are more expensive than palladium.

In a paper recently published in Nature Communications, Mirica and Hanah Na report their work on the development of a catalyst that can be directly activated by light to form a carbon-oxygen bond without the use of an additional catalyst. C-O bonds are found in many products.

Mirica and Na believe that their new class of pyridinophane ligands (R N3) can be used for detailed mechanical studies of nickel-catalyzed chemical reactions and can lead to the development of new nickel catalysts.

Mirica said that it is a competent catalyst and can do photocatalysis by itself.

Mirica had already developed a novel four-pronged molecule known as a tetradentate ligand, which has a pocket-like structure. The structure promoted rapid C-C bond forming reactivity while also stabilizing the higher oxidation states of nickel.

It is very stable. Over the past decade, all of those intermediates have been too stable. Mirica said they are not competent in catalytic applications.

The bidentate framework bipyridyl is used in nickel photocatalytic processes and provides enhanced reactivity and the ability to adjust the optimal reaction.

Mirica said that it's great for catalytic chemistry, but you can't see the special nickel species.

Mirica explained that classic organic chemists have a particular chemical transformation in mind and try whatever catalysts they think will be good, and whatever conditions or Additives would be useful andOptimizing it, focusing on a very specific transformation.

He said that nickel is the metal of interest and that they have a slightly different approach.

The latest structure is between the two others.

We open up a coordination site and remove one of the nitrogens to allow other things to bind to it and eventually allow you to do catalytic activity.

For the first time, they were able to reveal the key reaction steps and intermediate species in this cycle. The researchers explain in the report that an in-depth mechanistic understanding of Ni-mediated photocatalysis is essential for rational reaction design and maximization of the nickel-mediated chemical process.

Nuclear magnetic resonance, electron paramagnetic resonance, in situ IR, and computational studies were used in the mechanistic study.

The Ni-mediated redox cycle has remained a mystery despite the fact that the photocatalytic cycle is well-understood. The nickel centers are assumed to be part of the process, but have not been thoroughly investigated, and the key steps of oxidation, trans-metalation, and reductive elimination have never been directly observed.

In the past several decades, visible light-mediated photoredox catalysis has made important contributions to the field of synthetic organic chemistry. New methodologies are often achieved by trial and error rather than being based on a thorough understanding of the underlying reaction mechanism.

Understanding the underlying chemistry requires a major contribution from the organometallic chemistry fields, including the synthesis and characterization of related metal complexes and study of their photochemistry and photophysics.

Na said that they want to contribute to this emerging research field mostly focusing on unraveling clues to understand underlying reaction mechanisms, which is not done by organic chemists.

Mirica explained that the goal is to unleash new reactivity that could be helpful to organic chemists, who could then use it for very particular synthetic targets.

Mirica said that they hope that their new Ni catalysts will be used a lot in the future because they are not as good as the systems that people use in an organic lab.

More information: Hanah Na et al, Deciphering the mechanism of the Ni-photocatalyzed C‒O cross-coupling reaction using a tridentate pyridinophane ligand, Nature Communications (2022). DOI: 10.1038/s41467-022-28948-8 Journal information: Nature Communications Citation: New molecule sets stage for nickel as a 'greener' photocatalyst, reveals key steps in reaction process (2022, April 26) retrieved 26 April 2022 from https://phys.org/news/2022-04-molecule-stage-nickel-greener-photocatalyst.html This document is subject to copyright. Apart from any fair dealing for the purpose of private study or research, no part may be reproduced without the written permission. The content is provided for information purposes only.