Chemists at Saarland University have created pentasilacyclopentadienide, a silicon analogue of a stable aromatic compound, ending decades of failed attempts. The breakthrough, published in Science, replaces carbon atoms with silicon in a five-atom ring structure. This achievement opens potential for new materials and catalysts in industry.
For nearly 50 years, researchers worldwide pursued a silicon-based aromatic molecule, facing repeated setbacks. Now, a team at Saarland University in Germany has succeeded in synthesizing pentasilacyclopentadienide, a compound featuring a five-atom silicon ring that exhibits aromatic stability.
David Scheschkewitz, Professor of General and Inorganic Chemistry, led the effort alongside doctoral student Ankur and Bernd Morgenstern from the university's X-Ray Diffraction Service Centre. Their work replaces the carbon atoms in cyclopentadienide—a planar, five-carbon ring known for its exceptional stability—with silicon atoms. Aromatic compounds derive their durability from evenly distributed electrons around the ring, as described by Hückel's rule, named after physicist Erich Hückel.
"To be classified as aromatic, a compound needs to have a particular number of shared electrons that are evenly distributed around the planar ring structure, and this number is expressed by Hückel's rule," Scheschkewitz explained.
Silicon's more metallic nature means it holds electrons less tightly than carbon, potentially yielding compounds with unique properties. Such molecules could enhance catalysts in plastics production. "In polyethylene and polypropylene production, for example, aromatic compounds help make the catalysts that control these industrial chemical processes more durable and more effective," Scheschkewitz noted.
Prior to this, the only known silicon aromatic was a three-membered ring analogue of cyclopropenium, created in 1981. Independently, Takeaki Iwamoto's group at Tohoku University in Sendai, Japan, produced the same five-silicon ring compound. Both teams published their findings together in the journal Science (2026; 391(6785):579, DOI: 10.1126/science.aed1802).
This development marks a key step in silicon chemistry, potentially enabling novel materials for industrial applications.
