A MAGIC-ANGLE-SPINNING C-13 NMR-STUDY OF (CO)-C-13-LABELED RICARBONYL(HEXAHAPTO-HEXAMETHYLBENZENE)CHROMIUM(0) AND TRICARBONYL (HEXAHAPTO-DURENE)CHROMIUM(0)

At 293 K, the slow magic angle spinning carbonyl subspectrum of crysta lline (CO)-C-13-labelled tricarbonyl(hexahapto-hexamethylbenzene) chro mium(0) (1) displays an extensive manifold of spinning side bands. The se have been analysed to yield the principal elements of the shielding tenser which are appropriate to an axially symmetric anisotropy patte rn. In contrast, only a single signal at a position corresponding to t he isotropic chemical shift is observed at 293 K for the carbonyl carb on atoms of (CO)-C-13-labelled tricarbonyl(hexahaptodurene)chromium (0 ) (2). The intensity of this signal is highly temperature-dependent an d the changes are considered in the context of the known crystal and m olecular structures of 1 and 2.