In Okinawa, Japan, on July 7, 2025, a team of researchers at the Okinawa Institute of Science and Technology (OIST) made a groundbreaking discovery. They synthesized a stable 20-electron derivative of ferrocene, an iron-based organometallic compound. This challenges the established 18-electron rule, a cornerstone of organometallic chemistry.
The 18-electron rule has long dictated the stability of transition metal complexes, suggesting that 18 valence electrons around the metal atom lead to optimal stability. Ferrocene, discovered in 1951, perfectly fits this rule. The OIST team, led by Dr. Satoshi Takebayashi, developed a novel ligand system to stabilize the 20-electron ferrocene derivative, previously deemed unlikely.
This breakthrough significantly enhances our understanding of metallocenes, which have a "sandwich" structure. The additional two valence electrons in the new derivative introduce unconventional redox properties. This could broaden ferrocene's applications in catalysis and materials science. Traditionally, ferrocene's oxidation states have been limited, but this discovery may unlock new states through the formation of an Fe–N bond.
The study, published in Nature Communications, involved collaborations with scientists from Germany, Russia, and Japan. This advancement could pave the way for sustainable chemistry, including green catalysts and advanced materials. Ferrocene derivatives are already used in solar cells, pharmaceuticals, and medical devices. This discovery could lead to new applications and inspire entirely new ones.