Functionalized Corannulene Carbocations: A Structural Overview

A detailed structural overview of a family of bowl-shaped polycyclic aromatic carbocations of the type [C20H10R](+) with different R functionalities tethered to the interior surface of corannulene (C20H10) is provided. Changing the identity of the surface-bound groups through alkyl chains spanning from one to four carbon atoms and incorporating a different degree of halogenation has led to the fine tuning of the bowl structures and properties. The deformation of the corannulene core upon functionalization has been revealed based on X-ray crystallographic analysis and compared for the series of cations with R = CH3, CH2Cl, CHCl2, CCl3, CH2CH3, CH2CH2Cl, and CH2CH2Br. The resulting carbocations have been isolated with several metal-based counterions, varying in size and coordinating abilities ([AlCl4](-), [AlBr4](-), [(SnCl)(GaCl4)(2)](-), and [Al(OC(CF3)(3))(4)](-)). A variety of aggregation patterns in the solid state has been revealed based on different intermolecular interactions ranging from cation-anion to pi-pi stacking and to halogen center dot center dot center dot pi interactions. For the [C20H10CH2Cl](+) ion crystallized with several different counterions, the conformation of the R group attached to the central five-membered ring of corannulene moiety was found to depend on the solid-state environment defined by the identity of anions. Solution NMR and UV/Vis investigations have been used to complement the X-ray diffraction studies for this series of corannulene-based cations and to demonstrate their different association patterns with the solvent molecules.