An Unusual Relationship between ⁴⁹Ti Chemical Shift and Ti(2p_3/2) Binding Energy. The Use of ⁴⁹Ti NMR in Evaluating the Electronic Effect of Methyl Substitution on the Cyclopentadienyl Ligand

The ⁴⁹Ti NMR chemical shifts of a series of titanocene derivatives have been shown to have an inverse relationship to the Ti(2P_3/2) binding energies of these same compounds as measured by X-ray photoelectron spectroscopy (ESCA). Replacement of one cyclopentadienyl (Cp) group of the titanocene difluorides, dichlorides, and dibromides by a pentamethylcyclopentadienyl (Cp^⋆;) moiety resulted in an average downfield shift in the ⁴⁹Ti NMR absorption of 148 ppm. Substitution of both Cp groups by Cp^⋆ groups resulted in an average downfield shift of 312 ppm.