Room-Temperature C-C Bond Cleavage of an Arene by a Metallacarborane

摘要

The activation and cleavage of C-C bonds by transition-metal species is an area of intense current interest, and, although they are still relatively rare, a number of systems that afford the breaking of C-C single bonds are known. In contrast, the cleavage of aromatic C-C bonds is considered to be extraordinarily difficult. Six-carbon aromatic rings can be cleaved in the gas phase at high temperatures, whereas under less extreme conditions such rings are cleaved by enzymes, an important part of the global carbon cycle. However, there are very few reports of low-temperature cleavage reactions of aromatic rings in nonbiological systems. Of the examples that are known, (biomimetic) oxidative cleavage is the more common process but is generally regarded as difficult to control,whereas reductive cleavage is much more rare. However, both oxidative and reductive cleavage reactions typically involve significant initial chemical modification of the aromatic ring. Sattler and Parkin recently described the cleavage of a C-C bond in an aromatic heterocycle (a quinoxaline) at 90 °C. We report herein the unprecedented cleavage of an aromatic C-C bond in a simple arene at room temperature by a metallacarborane without other chemical modification to the arene.