Insertion and sigma-bond metathesis reactions of acetylene with (C5H5)(2)ZrCH3+. All-electron density functional (B3LYP) study

All-electron DFT (B3LYP) calculations with a split-valence basis set of dou ble- and triple-xi quality have been used to study the reaction paths of th e first and second step insertion as well as of the sigma-bond metathesis f or the reaction of Geometry optimizations of the reactants, intermediates, transition states and products were acetylene with (C2H5)(2)ZrCH3+ carried out without symmetry constraints. The nature of the particular points on th e potential energy surfaces was verified by the analytical calculation of t he Hessian matrices. The relative electronic energies are corrected for ZPV E, entropic and thermal contributions, and correspond to the Gibbs free ene rgies (Delta Delta G(298)). It is, shown that the propagation step of acety lene polymerization is a facile process from kinetic and thermodynamic poin t of view, and that the investigated insertion reactions are kinetically an d thermodynamically favoured over the sigma-bond metathesis reaction. The c alculated energetics and structures of either reaction are compared with av ailable theoretical and experimental data of relevant complexes of group II I and IV transition metals. (C) 2000 Elsevier Science B.V. All rights reser ved.