Tropylium tetrafluoroborate

Tropylium tetrafluoroborate is an organic compound with the formula C7H7BF4. 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 trichloride, followed by tetrafluoroboric acid.