Sterically hindered organometallics:: multi-n-rotor (n=5, 6 and 7) molecular propellers and the search for correlated rotations

For the past several years, we have focused our attention on the design, syntheses and analyses of the dynamic behaviour of sterically encumbered complexes of the type (CnRn)MLx, where R = alkyl or aryl, n = 5, 6 or 7, and ML, is an organometallic fragment. As archetypes of propellers or gear-wheels, the challenge is to construct molecules in which the internal rotations are restricted, and possibly even correlated. The incorporation of appropriate probes allows the independent measurement, by variabletemperature NMR spectroscopy, of the associated rotational barriers in these chiral arrays. In recent studies, we have successfully devised five-, six- and seven-membered ring systems that include naphthyl and other bulky organic substituents, and have further shown that an organometallic addendum can be used to monitor the stereodynamics of such conformationally flexible architectures. (C) 2002 Elsevier Science B.V. All rights reserved.