Reactions involving fluoride ion .41. Synthesis of hexakis(trifluoromethyl)cyclopentadiene and derived cyclopentadienide salts

An efficient synthesis of hexakis(trifluoromethyl)cyclopentadiene 4, which shows a remarkably low reduction potential, is described. Various donors promote one-electron transfer to 4, leading to corresponding salts of pentakis(trifluoromethyl)cyclopentadienide 5. A novel approach to the synthesis of metal derivatives involves heating, or photolysis, of 4 directly with metals (including Cu, Ni, Fe and Co), leading to the corresponding ionic salts. X-Ray structural analysis was difficult because of rotation of trifluoromethyl groups in these salts, but structural data on 20, 24 and 30 has been obtained that reveals interesting conformations and stacking of the ions.