Density functional computations (BP86/ECP1 and B3LYP/II level) have revealed that the phenyl group in [Zr(η-C5H5)(η-C5H4CR2C6H5)Me]+ (R = H) is coordinated to the Zr atom via one of the phenyl carbon atoms, rather than via an agostic Zr–H contact, as suggested previously. A stationary point with such an agostic interaction is the transition structure for phenyl rotation with a barrier higher than 50 kJ mol−1 (B3LYP/II level), consistent with results from dynamic NMR spectroscopy for a closely related compound (R = Me). The structural assignments are supported by the good accord between the computed (GIAO-B3LYP/II level) and experimental NMR chemical shifts. A second dynamic process with a very similar activation barrier is indicated to involve dissociation of the coordinated phenyl moiety from the Zr atom and inversion at the latter. The same structural motif (i.e.
η1-bonded aryl group) is also found for the [Zr(η-C5H4CH2C6H5)2]2+ dication.
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