MOLECULAR-DYNAMICS OF TRICARBONYL(PENTAMETHYLBENZENE)-CHROMIUM - A C-13 SOLID-STATE NUCLEAR-MAGNETIC-RESONANCE STUDY

Carbon-13 cross polarization magic angle spinning NMR spectra of [Cr(e ta(6)-C(6)HMe(5))(CO)(3)] have shown unambiguously that there is rapid exchange between the CO groups at room temperature in the solid state . Chemical shift anisotropy measurements at 296 and 155 K have indicat ed that the angle between the C-O bond and the axis of rotation is 127 .4 +/- 0.2 degrees. The activation energy barrier for the process was estimated to be 31 +/- 4 kJ mol(-1), which is significantly lower than that observed in related complexes. The aromatic group appears not to be undergoing rapid rotation at room temperature.