Molecular dynamics of tricarbonyl(pentamethylbenzene)-chromium: a 13C solid-state nuclear magnetic resonance study

Abstract

Carbon-13 cross polarization magic angle spinning NMR spectra of [Cr(η⁶-C₆HMe₅)(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 indicated that the angle between the C–O bond and the axis of rotation is 127.4 ± 0.2°. 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.