Nagoya University's Iron Photocatalyst Cuts Rare Metal Dependency by Two-Thirds in Key Chemical Synthesis
The chemicals used to make pharmaceuticals, agrochemicals, and specialty materials often need to be built in precise three-dimensional shapes. A molecule and its mirror image can have completely different biological activities - one form of a drug might treat a condition, while the mirror form causes side effects. Controlling which form is produced during synthesis is the central challenge of asymmetric catalysis.
Photocatalysis - using light to drive chemical reactions - has become an increasingly powerful tool for this purpose. The dominant photocatalysts in use are based on ruthenium and iridium, metals that are rare, expensive, and geographically concentrated in ways that create supply chain vulnerabilities. Iron is approximately 10,000 times more abundant than iridium and costs a fraction as much. The challenge has been making iron work as well.
Researchers at Nagoya University's Graduate School of Engineering have developed an iron-based photocatalyst that advances this goal substantially. Published in the Journal of the American Chemical Society, their design reduces the use of costly chiral ligands - the molecular templates that control three-dimensional product geometry - by two-thirds compared to the team's own 2023 prototype, while enabling photocatalytic reactions under energy-efficient blue LED light.
The Ligand Problem in Iron Catalysis
Iron forms chemical complexes that are significantly different from ruthenium and iridium in their electronic properties. The long-lived excited states that make ruthenium and iridium photocatalysts effective are absent in simple iron complexes, because iron's excited states typically decay within picoseconds - far too fast to drive useful chemistry. Making iron photocatalytically active requires ligands that stabilize the excited state long enough for productive reactions to occur.
In their 2023 study, the Nagoya team achieved iron photocatalysis using three chiral ligands per iron atom. The chiral ligands provided both the geometric control needed for asymmetric synthesis and the electronic stabilization needed for photocatalytic activity. The problem was efficiency: only one-third of the chiral ligands actually contributed to controlling product geometry, meaning the other two-thirds were present at significant cost without contributing their primary function.
The new design separates these functions. Achiral bidentate ligands - less expensive and available without the geometric specificity of chiral ligands - handle the electronic tuning and excited-state stabilization. A single chiral ligand controls the three-dimensional geometry of the product. By dividing the labor between two types of ligands, the team achieves similar or better catalytic performance while reducing chiral ligand consumption by two-thirds.
From Blue LED Light to Complex Natural Products
The practical test of the new catalyst was the asymmetric total synthesis of (+)-heitziamide A, a natural compound found in medicinal plants that suppresses respiratory bursts - the rapid oxygen-consuming immune response that cells use to destroy pathogens. Total synthesis, meaning building the target molecule from simple starting materials through a sequence of controlled chemical reactions, is a demanding standard for catalyst performance.
The synthesis was completed under blue LED illumination, which is energy-efficient and safe to use in standard laboratory settings. The key reaction step was a radical cation (4+2) cyclization - a process that joins two molecules to form a six-membered ring - using the iron catalyst under light activation. This reaction produced the structural framework common to heitziamide A and similar natural products, with precise control over the three-dimensional arrangement of atoms.
Professor Kazuaki Ishihara, Assistant Professor Shuhei Ohmura, and graduate student Hayato Akao at Nagoya University's Graduate School of Engineering developed the technology.
Where Iron Photocatalysis Stands
The development of effective iron photocatalysts is a priority in synthetic chemistry precisely because it addresses real-world resource and cost constraints. Ruthenium and iridium are produced primarily as byproducts of platinum and nickel mining, respectively, in a small number of countries. Their limited availability and high prices create genuine barriers to scaling up photocatalytic synthesis for industrial applications.
Iron-based alternatives that achieve comparable selectivity and efficiency would not only reduce costs but also simplify supply chains and reduce the environmental footprint of specialty chemical manufacturing. The Nagoya team's design represents a step toward that goal - though scaling from laboratory synthesis to industrial-scale production involves additional engineering challenges around catalyst loading, product isolation, and reaction throughput that remain to be addressed.
The specific synthesis demonstrated here - heitziamide A - is a natural product with potential pharmaceutical relevance due to its immune-modulating properties, but the broader significance of the catalyst lies in the generality of the (4+2) cyclization approach it enables, which produces structural motifs found across a wide range of biologically active natural compounds.