Researchers from The University of Osaka achieve redox reaction using main-group element gallium from group 13 in a move away from rare-earth and precious metals

Osaka, Japan – Catalysts are vital substances that speed up many chemical reactions fundamental to modern life, including fertilizer, pharmaceutical, and energy production. However, many catalysts depend on expensive transition-metal elements, and their supply damages the environment and is vulnerable to geopolitical disruption. Recently, a team in Japan has developed a way to achieve a crucial type of chemical transformation without relying on transition-metal element resources.

In an article due to be published in the Journal of the American Chemical Society, researchers from The University of Osaka describe a new reaction using a main-group element, instead of transition-metal elements, for synthesizing important building-block molecules.

Catalysts increase the rate of a chemical reaction without being consumed, enabling reactions that would otherwise be impractical. Transition metals, including well-known catalysts such as palladium, rhodium, and platinum, are highly versatile and essential in numerous chemical reactions. These elements commonly catalyze transformations through changes in their oxidation state as reduction–oxidation (redox) catalysts. In contrast, main-group elements, like gallium, belong to groups 1, 2, and 13 to 18 of the periodic table, and are not often used as redox catalysts.

The team at The University of Osaka created a main-group element redox reagent that behaves like a transition-metal element in terms of redox activity under exposure to visible light. Making a redox reagent with this property is an important advancement for main-group redox catalysts, even though the reagent is consumed during the reaction, unlike a catalyst.

“There have been breakthroughs in using heavier group 14 and 15 elements in redox reagents for organic chemistry, but none using group 13 elements,” says lead author Nijito Mukai. “Our redox reagent is the first organic gallium compound to show this type of redox activity.”

Their gallium reagent mediated an unusual ring-forming redox reaction under visible light irradiation that allowed the efficient synthesis of phenylenediamines, which are chemical compounds fundamental for many pharmaceuticals and functional materials.

“This is an important proof-of-concept that shows that group 13 elements can be used in redox reagents,” adds senior author Takuya Kodama. “Overcoming the challenges of using a group 13 element will expand the use of main-group elements in redox catalysts.”

The findings offer a new strategy for sustainable catalysis that uses earth-abundant main-group elements. In turn, use of these elements could help to ease reliance on unreliable and environmentally costly rare-earth metal resources.
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The article, “Synthesis of Phenylenediamines via (4+1+1) Photocycloaddition of 1,3-Dienes and Isocyanides Enabled by a Gallium(I)/(III) Redox: The Key Role of a Phenalenyl-Based Ligand,” appears in Journal of the American Chemical Society at https://doi.org/10.1021/jacs.5c15802