Bowl-shaped carbocations: easy to produce, hard to reduce

Stable nonplanar polyaromatic carbocation, [C20H10CH2Cl]+ (1) having the chloromethyl group covalently bound to the hub site of corannulene was prepared by reaction of C20H10 with CH2Cl2 and GaCl3 in the presence of SnCl2. The X-ray diffraction study of the resulting salt, [1]center dot[(SnCl)(GaCl4)2], revealed the presence of two rotational isomers for 1 in the crystal lattice. In the solid state, a complex polymeric inorganic anion of the overall composition [(Sn2Cl2)center dot(GaCl4)4]8 is formed with the cationic p-bowls being attached to its backbone. Both X-ray and nuclear magnetic resonance spectroscopic data of 1 indicate the sp3 hybridization of the C-atom of corannulene at the attachment point. An electrochemical investigation of 1 and the series of related corannulene cations, [C20H10R]+ (R?=?CHxCl3x (x?=?03) and CH2CH2Cl), was carried out to elucidate the electronic consequences triggered by the above changes. This study revealed that the surface decoration of corannulene core makes the reduction of the resulting [C20H10R]+ species significantly more difficult (by about 0.3?V) with respect to the parent bowl. To evaluate the consequences of the observed one-electron reduction and conceivable but not seen second-electron reduction on the corannulene core, theoretical calculations at the density functional theory level have been carried out. Copyright (C) 2012 John Wiley & Sons, Ltd.