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