Combining Fourier transform nuclear quadrupole resonance (FT-NQR) spectroscopy and mass spectrometry (MS) to study the electronic structure of titanocene dichlorides

Abstract

A combination of nuclear quadrupole resonance spectroscopy (NQR) and mass spectrometry (MS) has been used to observe trends in electronic structure in three titanocenes: bis(cyclopentadienyl) titanium dichloride (η⁵-C₅H₅)₂TiCl₂, bis(pentamethylcyclopentadienyl) titanium dichloride (η⁵-C₅(CH₃)₅)₂TiCl₂ and dimethylsilylene-bridged ansabis(cyclopentadienyl) titanium dichloride Si(CH₃)₂(η⁵-C₅H₅)₂TiCl₂. Using MS, electron ionisation mass spectra of these compounds are presented within the context of the entire homologous series with one to five methyl groups on each cyclopentadienyl ligand. A dedicated NQR spectrometer was constructed for this study with a sensitivity sufficient to precisely determine the NQR resonant frequency of ³⁵Cl atoms using 3 g samples of these titanocenes. The observed frequencies are thus 11.784, 11.930 and 10.863 MHz at 298 K. The results demonstrate that NQR using a relatively simple apparatus can be used as a sensitive and cost effective probe into the molecular structure of organometallic chlorides, which complements the information inferred from the mass spectra.