Toward an Organometallic Molecular Brake with a Metal Foot Pedal: Synthesis, Dynamic Behavior, and X-ray Crystal Structure of [(9-Indenyl)triptycene]chromium Tricarbonyl

The potential use of haptotropic shifts to control rotational barriers has been initiated by the synthesis of (9-indenyl)triptycene (12) and its chromium tricarbonyl derivative (13). Both complexes have been characterized by X-ray crystallography and variable-temperature NMR spectroscopy, revealing barriers to rotation of 12 and 13 kcal mol-1, respectively. In the metal complex, the chromium carbonyl moiety coordinates to one of the blades of the triptycene unit rather than to the more crowded indenyl group.