[η5-cyclopentadien-1-YL-η4-tetraphenylcyclobutadienecobalt]diphenylmethylium hexafluorophosphate: A metal-stabilized carbonium ion salt

Mercuration of η⁵-cyclopentadienyl-η⁴-tetraphenylcyclobutadienecobalt, followed by transmetalation with n-butyllithium and reaction of the lithium derivative with benzophenone gave η⁴-Ph₄C₄Coη⁵-C₅H₄CPh₂OH. Treatment of this alcohol produced the [η⁴-Ph₄C₄CoC₅H₄CP₂]⁺ cation. This species reacted as a carbon electrophile with methanol, monomethylamine and N-methylpyrrole, as a cobalt electrophile with N,N-dimethylaniline and anisole. In the latter process the C₅H₄CPh₂ ligand was displaced and the η⁶-arene-η⁴-tetraphenylcyclobutadienecobalt complexes were formed. Similar reactions with benzene, toluene and mesitylene proceeded only in the presence of aluminum chloride. The bonding in the cation is discussed on the basis of this chemistry and ¹³C NMR studies.