A corannulene-based metallobox for the encapsulation of fullerenes

A corannulene-bis-N-imidazolium salt was used for the synthesis of two corannulene-bis-N-heterocyclic carbenes of dirhodium(i) complexes of formula (corannulene-di-NHC)[RhCl(COD)]₂ and (corannulene-di-NHC)[RhCl(CO)₂]₂. Both complexes were characterized by spectroscopic techniques, and the electron-donating properties of the corannulene-di-NHC ligand were studied by means of infrared spectroscopy and cyclic voltammetry. The complex (corannulene-di-NHC)[RhCl(COD)]₂ was used for the encapsulation of fullerenes C₆₀ and C₇₀, generating host-guest complexes with 2 : 1 stoichiometry, as evidenced by ¹H NMR and ITC titrations. Then, a tetra-rhodium(i) metallo-rectangle supported by two corannulene-bis-imidazolylidene ligands and two cofacial 4,4'-bipyridine ligands was prepared and characterized. This metallobox is capable of quantitatively encapsulating fullerenes C₆₀ and C₇₀, forming complexes that are highly stable even at high temperatures. The molecular structure of the metallobox with encapsulated C₆₀ reveals a perfect size and shape complementarity that benefits from the concave-convex π-π interaction between the polyaromatic surfaces of the host and the guest.