AB Initio Investigations of Chemical Reactions Influenced by Transition Metal Catalysts

Abstract

A short survey about quantum chemical descriptions of some polymerization reactions using transition metal complexes is collected in the introduction. In the case of mono-olefins the insertion reaction of the monomer takes place into the metal carbon σ-bond. For butadiene we investigated the insertion into a η3-coordinated π-allyl head group of the growing polymer chain. For the catalytic reactions the unsaturated molecule is bonded to the coordination sphere of the metal; due to the reorganization of the electronic structure the molecules becomes “activated” for the insertion step. The structure of ethylene, allyl and butadiene π-complexes with Ni° and Ni2+ was optimized with Density Function Theory (DFT) and traditional post-Hartree-Fock methods (MP2, MP4 and CCSD). The different kinds of coordinative interaction between the olefins and the metal can been discussed by the role of the frontier orbitals of a particular symmetry. Both components of the donation and back-donation bond were characterized by Charge Density Analysis (CDA) and Natural Bond Orbital (NBO) populations as well. In case of the butadiene ligand the s-cis and s-trans conformer and the transition state of their rearrangement were localized.