NUCLEAR-MAGNETIC-RESONANCE STUDIES OF SULFUR INVERSION IN BIS(CYCLOPENTADIENYL)-MOLYBDENUM AND BIS(CYCLOPENTADIENYL)-TUNGSTEN COMPLEXES WITH DITHIOETHERS

The metallocene thioether derivatives [Cp2M(MeSCH2CH2SMe)][PF6]2 (1, M = Mo; 2, M = W), [Cp2Mo(SCH2CH2SMe)][PF6](3) and [Cp2M(SCH2CH2S)] (4, M = Mo; 5, M = W) exhibit temperature-dependent fluxional behavior in solution, owing to the pyramidal sulfur inversion process. The activation energies for this process were determined from proton band-shape analysis in the cases of 1 (54.9 +/- 2 kJ mol-1), 2 (51.2 +/- 4.6 kJ mol-1) and 3 (30.0 +/- 3.1 kJ mol-1). Extended Huckel calculations on related model complexes suggest that local inversion at the sulfur atoms, rather that an inversion of the complete S-C-C-S chain, is responsible for the observed fluxional behaviour.