Insight into Group 4 Metallocenium-Mediated Olefin
Polymerization Reaction Coordinates Using a Metadynamics Approach
Alessandro Motta
Ignazio
L. Fragalà
Tobin J. Marks
10.1021/ct400259a.s001
https://acs.figshare.com/articles/journal_contribution/Insight_into_Group_4_Metallocenium_Mediated_Olefin_Polymerization_Reaction_Coordinates_Using_a_Metadynamics_Approach/2387965
We
report here the first application of the computationally efficient
metadynamics approach for analyzing single-site olefin polymerization
mechanisms. The mechanism of group 4 metallocenium catalysis for ethylene
homopolymerization is investigated by modeling the ethylene insertion
step at the cationic (η<sup>5</sup>-C<sub>5</sub>H<sub>5</sub>)Zr(CH<sub>3</sub>)<sub>2</sub><sup>+</sup> center using molecular
dynamics simulations within the Density Functional Theory (DFT) framework.
In particular, the metadynamics formalism is adopted to enable theoretical
characterization of covalent bond forming/breaking processes using
molecular dynamics ab initio tools. Analysis of the ethylene insertion
step free energy surface indicates a slightly exoergic process (−3.2
kcal/mol) with a barrier of 8.6 kcal/mol, in good agreement with conventional
ab initio static calculations. Analysis of the structural and dynamic
aspects of the simulated reaction coordinate reveals a preferred olefin
configuration which aligns parallel to the Zr–CH<sub>3</sub> vector in concert with insertion and a slightly bent conformation
of the product <i>n-</i>propyl chain to avoid nonbonded
repulsion between methylene groups. It is found that the unsaturated/electrophilic
CpZr(CH<sub>3</sub>)<sub>2</sub><sup>+</sup> center drives the insertion
step, thus promoting the formation of the Zr–alkyl bond. The
metadynamics analysis uniquely encompasses all energetically possible
reaction coordinates, thus providing a more detailed mechanistic picture.
These results demonstrate the potential of metadynamics in the conformational
and geometrical analysis of transition metal-centered homogeneous
catalytic processes.
2013-08-13 00:00:00
5H
covalent bond
Density Functional Theory
nonbonded repulsion
energy surface
metadynamics formalism
methylene groups
kcal
Zr
olefin configuration
ethylene insertion step
insertion step
ethylene homopolymerization
metadynamics analysis
metadynamics approach
DFT
group 4 metallocenium catalysis
dynamics ab initio tools
mechanism
reaction coordinates
ab initio
center
Metadynamics ApproachWe report
dynamics simulations