Prismatic cyclopentadienyl

The prismatic cyclopentadienyl and benzene complexes of transition metals are reminiscent of the polycyclic hydrocarbon pris-manes. Figure 3-28 shows ferrocene, (C5H5)2Fe, for which both the barrier to rotation and the free energy difference between the prismatic (eclipsed) and antiprismatic (staggered) conformations are very small [75], Figure 3-28 also presents a prismatic model with Ay, symmetry for dibenzene chromium, (C6F[6)2Cr. 

Theoretically, metallocenes and arene 7t-complexes can exhibit conformational isomerism. The cyclopentadienyl rings in ferrocene should exist in two extreme conformations, either eclipsed [5-20] (prismatic ferrocene) or staggered [5-21] (antiprismatic ferrocene). According to x-ray diffraction... 

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