Pentiptycene-based concave NHC-metal complexes.

The reaction of 1-amino,4-hydroxy-pentiptycene with diacetyl or acenaphthene-1,2-dione gave the respective diimines, followed by alkylation of the hydroxyl groups, and cyclization of the alkylated diimines to the respective bispentiptycene-imidazolium salts NHC·HCl. The azolium salts, being precursors to N-heterocyclic carbenes, were converted into metal complexes [(NHC)MX] (MX = CuI, AgCl, AuCl) and [(NHC)IrCl(cod)] and [(NHC)IrCl(CO)2] in good yields. In the solid state [(NHC)AgCl] displays a bowl-shaped structure of the ligand with the metal center buried within the concave unit.