Wideline NMR studies of solid dicyclopentadienyl, dibenzene, and dicyclooctatetraenyl metal complexes

Abstract

The wideline NMR spectra of a number of solid metallocene, dibenzene, and dicyclooctatetraenyl metal complexes were examined in the temperature range 178–381 K and the second moments of the linewidths were calculated. Experimental second moments were then compared with theoretical values based on the Van Vleck model. The calculations are consistent with essentially free rotation about the principle molecular symmetry axes, which is indicative of very low ring rotational barriers in all species studied. No substantial difference in metal-ring bonding is found between metallocene and dibenzene complexes. In the case of U(C 8H 8) 2, the second moment investigations support the results of recent crystallographic work showing the existence of distinct rotomers.