Foliacenes: Ab Initio Modeling of Metallocomplexes Exhibiting a Unique Form of 16-Electron, Metal-Induced Aromaticity

Ab initio calculations predict that the cyclic trefoilenes 2 can be stabilized by formation of a complex 4 with early transition metals. The metal atom within the complex is nested within the carbon ring and is considerably closer to the ring centroid than in traditional metallocene complexes. Stabilization is explained by a unique form of 16-electron delocalization involving the metal atom, for which we suggest the name “foliate aromaticity”. The aromaticity of various polyfoliate systems such as 9 suggests this 16-electron motif is more robust than Clar-like aromatic 6π-sextets. The open hemisphere of the metal in such foliacene complexes is predicted to coordinate a variety of ligands.