Dynamical Density Functional Study of the Multistep CO Insertion into Zirconium-Carbon Bonds Anchored to a Calix[4]arene Moiety

The multistep migratory insertion reaction of CO into the zirconium-carbon bonds in [calix[4](OMe)2(O)2ZrMe2] has been investigated by means of both static and dynamic density functional calculations. A relatively stable facial CO complex has been observed with a negligible barrier for CO insertion into one of the Zr-Me bonds, leading to the formation of an ?2-acyl complex. The insertion of the residual alkyl group into the acyl moiety, leading to an ?2-bound acetone, has also been investigated, and a small energy barrier, 2.3 kcal/mol, has been found. Dynamics simulations have been performed on the [calix[4](OMe)2(O)2Zr(Me)2]-CO adduct in order to study the detailed features of the whole multistep insertion and show that the migratory insertion leads to the formation of an out-of-plane ?1-acyl complex, which is readily converted into the more stable ?2-acyl isomer within 1.5 ps. The subsequent methyl to acyl migration has been observed within 5 ps, leading to the formation of the ?2-bound acetone by a facial attack of the migrating methyl to the acyl carbon. A comparison with the migratory insertion of CO into the metal-alkyl bond in (Me)2Zr(Cp)2 has been performed, showing substantial differences in the reactivity of the calix[4]arene and bis(cyclopentadienyl) substrates.