Flattening of a Curved-Surface Buckybowl (Corannulene) by η⁶ Coordination to {Cp*Ru}⁺

The corannulene complex [Cp*Ru(η6-C20H10)]+ (3+; where Cp* = η5-C5Me5), prepared by the reaction of [Cp*Ru(μ3-Cl)]4 with Ag+ and the curved-surface buckybowl C20H10 (1), has a structure in which the bowl is slightly flattened as compared with the case for free corannulene. The corannulene unit in [(Cp*Ru)2(μ2-η6:η6-C20H10)][PF6]2 (4[PF6]2), containing two η6-{Cp*Ru}+ units coordinated on opposite sides of the corannulene, is flattened substantially more. The X-ray-determined structure of the corresponding SbF6- salt, [(Cp*Ru)2(μ2-η6:η6-C20H10)][SbF6]2 (4[SbF6]2), shows that the corannulene bowl is almost completely flat. Low-temperature NMR studies of the analogous 1,2,5,6-tetramethylcorannulene complex [(Cp*Ru)2(μ2-η6:η6-C20H6Me4)]2+ (62+) show that there is a very low barrier to inversion of the bowl, even at −90 °C. Computational investigations reproduce the major structural features of 3+ and 42+ and account for the low corannulene inversion barrier in 42+.