The structure and dynamics of cationic zirconocene complexes with phenyl coordination

Density functional computations (BP86/ECP1 and B3LYP/II level) have revealed that the phenyl group in [Zr(eta -C5H5)(eta -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. eta (1)-bonded aryl group) is also found for the [Zr(eta -C5H4CH2C6H5)(2)](2+) dication.