Cagey Arene Cleavage

A carbon-boron cage compound has been discovered doing some challenging chemistry at room temperature—breaking the carbon-carbon bond of an aromatic ring. If a catalytic version of this chemistry could be developed, it might be useful for removing impurities in crude petroleum, the reaction’s discoverers say (Angew. Chem. Int. Ed., DOI: 10.1002/anie.201001555). Chemists have previously cleaved a C–C bond on an aromatic heterocycle at elevated temperatures (C&EN, Feb. 1, page 10). For Stuart A. Macgregor and Alan J. Welch of Scotland’s Heriot-Watt University, their room-temperature arene bond-breaking came unexpectedly. With a ruthenium p-cymene species, their team was trying to add a ruthenium vertex to each of the cages on a bis-carborane. But instead, one cage incorporated two ruthenium p-cymene fragments, and an aromatic C–C bond on one p-cymene was cleaved. Density functional theory calculations carried out by the team suggest that this happened because the p-cymene becomes sandwiched between two ruthenium atoms atop one carborane cage. The other carborane reduces the arene, disrupting its aromaticity and triggering bond-breaking. Adaptations of this chemistry to other arenes are in progress, Welch says.