Mild C–H activation of activated aromatics with [8,8′-μ-I-3,3′-Co(1,2-C2B9H10)2]: Just mix them

Reactions of the iodonium derivative of cobalt bis(dicarbollide) anion [μ-8,8′-I-3,3′-Co(1,2-C2B9H10)2] with activated aromatics were studied. The reactions with ortho- and meta-xylenes result in mild arene C–H activation under ambient conditions, whereas the reaction with para-xylene requires the presence of PPh3 as soft Lewis base. The obtained aryl derivatives [8-Ar-8′-I-3,3′-Co(1,2-C2B9H10)2]− were found to have the transoid conformation both in the solid state and in solution due to intramolecular hydrogen CHcarb⋯IB bonds and aromatic CHcarb⋯π interactions between the dicarbollide ligands. The Lewis acidity of the quasi-borinium cation formed on the breakage of the iodonium bridge was estimated using Beckett–Gutmann method. According to the Gutmann acceptor number AN = 112 (in CD2Cl2), this quasi-borinium cation belongs to the most strong boron Lewis acids and can be considered as Lewis superacid.

Graphical abstractReactions of [μ-8,8′-I-3,3′-Co(1,2-C2B9H10)2] with activated aromatics were studied. The reactions with ortho- and meta-xylenes result in the mild arene C–H activation under ambient conditions. The obtained aryl derivatives [8-Ar-8′-I-3,3′-Co(1,2-C2B9H10)2]− adopt the transoid conformation due to intramolecular hydrogen CHcarb⋯IB bonds and aromatic CHcarb⋯π interactions between the dicarbollide ligands.Figure optionsDownload full-size imageDownload as PowerPoint slideHighlights► Reactions of [μ-8,8′-I-3,3′-Co(1,2-C2B9H10)2] with activated aromatics were studied. ► The C–H activation of o- and m-xylenes proceeds smoothly under ambient conditions. ► The aryl derivatives have the transoid conformation in solid state and in solution. ► Lewis acidity of the reaction intermediate was estimated using Beckett method. ► This quasi-borinium cation belongs to the most strong boron Lewis acids.