Differences between insertions of ethylene into metallocene and non‐metallocene ethylene polymerization catalysts

Abstract

Density functional theory (DFT) calculations at ωB97XD/SDD level have been conducted to study the differences between the insertions of ethylene into the non‐metallocene octahedral group 4 catalysts and those into metallocene group 4 catalysts. The study shows that both can be described by the Cossess mechanim, but are different energetically. The latter have energy profiles involving stable π complexes between ethylene and catalysts prior to insertion and the insertion transition states (TSs) being lower than reactants, whereas the π complexes involved in the former are significantly less stable than their counterparts in the latter, and the insertion TSs are higher than or close to the reactants. The energy decomposition analyses on the activation energies indicate that the octahedral catalysts exert more significant steric effects than the metallocene catalysts, which are responsible for the differences. The cis arrangements of two chloride atoms in the precursors of metallocene catalysts were considered to be crucial for their catalytic activity, but the precursors of octahedral catalysts with either cis or trans arrangements of two chloride atoms exhibit activity. Nevertheless, the effective catalysts generated from octahedral precursors with cis chloride atoms have lower activation barriers than those from precursors with trans chloride atoms. Copyright © 2012 John Wiley & Sons, Ltd.

The activation strain model and molecular orbital theory

“…Conveniently, there is no special computer code required to perform activation strain analyses: all necessary quantities can be computed using any of the regular quantum‐chemical software packages available. As a result, the activation strain model has been applied by various research groups, on a range of chemical processes, such as nucleophilic substitution, cycloaddition, oxidative addition, isomerization, and many other processes from organic and organometallic chemistry.…”

Density Functional Theory Study of the Regioselectivity in Copolymerization of bis-Styrenic Molecules with Propylene Using Zirconocene Catalyst

“…BSSE-corrected free energies and enthalpies obtained at the M06 (SMD, solvent = toluene)/BSII level and free energies are discussed in the main text; the relative enthalpies are also given for reference. The reliability of the M06//B3LYP combination is demonstrated by its successful application in explaining various transition metal catalytic reactions [27][28][29][30][31][32][33][34][35][36]. The total energy and Cartesian coordinates of all the optimized structures are provided in the Supplementary Materials (Table S2).…”

Copolymerization Mechanisms of Propylene and Norbornadiene Catalyzed by Zirconocene Complexes: A Density Functional Theory Study

“…In the past decades, many calculations have been carried out to understand the mechanisms of olefin polymerization . Nevertheless, no computational work has been reported for the copolymerization mechanisms of NBD with propylene.…”