Chemists create carboranes with 15 and 16 vertices

Chemists have synthesized closed carboranes with 15 and 16 vertices—the largest carbon-boron molecular clusters of this kind ever made. Chemists first made a 14-vertex closed carborane in 2005, but until now, no one had been able to squeeze more boron or carbon atoms into these clusters. Zuowei Xie and colleagues at the Chinese University of Hong Kong managed the feat by introducing silyl groups on the two carbon atoms in the cluster’s starting material. The silyl groups stabilize the carbon anions generated as more boron atoms are added to the cluster (Nat. Commun. 2020, DOI: 10.1038/s41467-020-19661-5). The chemists suggest that this silylation strategy could be used to create clusters with 17 or more vertices. The 15- and 16-vertex clusters are stable in air at room temperature. Closed carboranes like these feature 3-D aromaticity and inherent robustness, which make them attractive for applications in both materials and medicine. Recent reports suggest that they could be used to recover radioactive metals from nuclear waste and as anticancer therapies.