The Methyl Group Geometry in Trichloromethyltitanium: A Reinvestigation by Gas Electron Diffraction

Arecent preliminary communication on the molecular structure of CIJTiCHJ as determined by gas electron diffractionl suggested an unusual methyl group geometry: C-H bond distance 115.8 (1.6) pm and valence angle LTiCH = 101.0 (2.2)°, presumably due to partial donation of C-H bonding electrons into vacant d orbitals on Ti. Such an interaction is also consistent with the observation of an unusually large positive H,H coupling constant of + 11.3 Hz and an unusually low CHJ rocking mode of 580 cm-l as compared to 825 cm-l in CIJGeCHJ.l Very recently Williamson and Hall have reported the results of extensive SCFMO and GVB calculations on CIJTiCHJ.2 On the basis of structure optimizations at different levels they predict a normal C-H bond distance of 110 :i: I pm and a slightly less-than-tetrahedral angle of 107 :i: 1°.2 The calculations reproduce the lowering of the rocking mode relative to CIJGeCHJ but provide no indication for Ti..(C-H) interactions. We prepared CIJTiMe (Me = CHJ or CDJ) with the intention of determining the molecular structure by MW spectroscopy. We have, however, been unable to record a MW spectrum, probably because CIJTiMe decomposes rapidly on the metal walls of the waveguide. It was then decided to record the GED data for both compounds with use of an all-glass inlet system. These experiments proceeded without difficulty. We hope to record MW spectra