The aromaticity of ferrocene and some derivatives, ruthenocene and dibenzenechromium as determined via ring current assessment and 13C anisotropic contributions to the 1H NMR shielding

Abstract

The concept of aromaticity is examined in terms of a delocalised ring current contribution to the proton NMR shielding of ferrocene and related compounds. The source of the ring current is derived as a delocalised contribution to the experimentally determined chemical shift, where the local contribution is calculated from predictions based on the experimental ¹³C shielding tensors. Examined are dibenzenechromium, ruthenocene, benzene, hexamethylbenzene and several derivatives of ferrocene with attention to: (i) the effects of complexation of the benzene ring, (ii) the protons in an aliphatic bridge on a ferrocene cyclopentadienyl ring, and (iii) the electric field effects of the permanent electric dipole moment in pentamethylferrocene.