Bonding in and gas-phase pyrolysis of the arsoranes and stibanes EMe3X2(E = As or Sb, X = F or Cl) and SbMe4F: ultraviolet photoelectron and field-ionization mass spectrometric studies

Abstract

The He I (and partially He II) photoelectron spectra of the gaseous Group 5 molecules AsMe₃F₂, AsMe₃Cl₂, SbMe₃F₂, SbMe₃Cl₂, and SbMe₄F are presented and assigned using the known ionization potentials of SbMe₅ and EMe₃(E = As or Sb) and simple molecular-orbital models. Calculations have been performed for the series AsH₃, AsH₅, AsH₃F₂ using the SCC–Xα method. Upon pyrolysis both AsMe₃Cl₂ and SbMe₃Cl₂ undergo unimolecular elimination of HCl in the gaseous phase, indicating the intermediacy of new transient species ‘EMe₃Cl₂–nHCl.’ However, reductive elimination of MeF is favoured by the gaseous fluorides. These results are strongly supported by high-temperature field-ionization mass spectrometry under similar conditions. Loss of HCl was also observed during solid-state pyrolysis of ionic PMe₃Cl₂in vacuo.