CONVERSION OF A DIATROPIC BRIDGED ANNULENE INTO A PARATROPIC SPECIES ON METAL COMPLEXATION

A delocalized 4n pi system is present in the macrocyclic annulene unit of the metal complex 1. The existence of a paratropic ring current is revealed unambiguously by the deshielding of the ''inner'' methyl protons and the shielding of the protons on the benzene part as well as their H-1-H-1 coupling constants. Apparently, therefore, the metal complexation results in transformation of an aromatic to an antiaromatic ring system.