Tropylium tetrafluoroborate

Tropylium tetrafluoroborate is an organic compound with the formula [C7H7]+[BF4]−. Containing the tropylium cation and the non-coordinating tetrafluoroborate counteranion, tropylium tetrafluoroborate is a rare example of a readily isolable carbocation. It is a white solid.

This compound may be prepared by the reaction of cycloheptatriene with phosphorus pentachloride, followed by tetrafluoroboric acid.