Flattening of a curved-surface buckybowl (corannulene) by η6 coordination to {Cp*Ru}+

The corannulene complex [C-p*Ru(eta(6)-C20H10)](+) (3(+); where Cp* = eta(5)-C5Me5), prepared by the reaction of [Cp* Ru(mu(3)-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 the [(Cp*Ru)(2)(mu(2)-eta(6):eta(6)-C20H10)][PF6](2)), containing two eta(6)-{Cp*Ru}(+) units coordinated on opposite sides of the corannulae, is flattened substantiall more. The X-ray-determined structure od the corresponding SbF6- salt, [(Cp*Ru)(2)(mu(2)-eta(6):eta(6)-C20H10)][SbF6](2) (4[SbF6](2)), shows that the corranulene bowl is almost completely flat. Low-temperatures NMR studies of the analogous 1,2,5,6-tetrametylcoran-nulene complex [(Cp*Ru)(2)(mu(2)-eta(6):eta(6)-C20H6Me4](2+) (6(2+)) show that there is a very low barrier to inversion of the bowl, even at -90%degrees C. Computational investigations reproduce the major structural features of 3(+) and 4(2+) and account for the low corannulene inversion barrier in 4(2+).