Chiang Mai Journal of Science

Effects of Silicon-Bridge and π-Ligands on the Electronic Structures and Related Properties of Dimethyl Zirconocene Polymerization Catalysts: A Comparative Theoretical Study

Paper Type	Contributed Paper
Title	Effects of Silicon-Bridge and π-Ligands on the Electronic Structures and Related Properties of Dimethyl Zirconocene Polymerization Catalysts: A Comparative Theoretical Study
Author	Jitrayut Jitonnom* [a] and Wijitra Meelua [a,b]
Email	jitrayut.018@gmail.com
Abstract:  Group 4 metallocene has gained more attention recently as a potential catalyst for ring-opening polymerization of lactones. Introduction of a silicon-bridge and/or modifications of biscyclopentadiene (Cp2) ligand with different π-ligands such as bisindene (Ind2), mixed indene/cyclopentadiene (CpInd) or mixed fluorene/cyclopentadiene (CpFlu) have been found to significantly help improve catalyst activities, polymer yields and molecular weight. In order to relate the silicon bridge (B) and π-ligand (L) effects with the catalyst activities, molecular structures and properties of those bridged dimethylzirconocene complexes as well as their insertion behaviors with ε-caprolactone were investigated by using the density functional theory method. Calculations showed that different π-ligands had a profound effect on the electronic geometries and related properties of the title complexes. All bridged catalysts were geometric constraints compared to the unbridged catalysts. The HOMO-LUMO gap and dipole moments were decreased as the large π-ligands were introduced (Cp2 > CpInd > Ind2 > CpFlu). Only Si and Zr atoms were observed to carry a positive charge with Si having the most. For the monomer-inserted complexes, most catalyst structures shared the same orientation of ε-caprolactone with its ester group pointing away from a methyl group of Zr atom, except the catalyst with Ind2 ligand due to steric hindrance. A planar conformation of the monomer was observed in all catalysts and, hence, is required for each insertion. The data provide a structural basis for both inactivated and activated bridged-dimethylzirconocene complex catalysts with different π-ligands, which will be helpful for further studies on the lactone polymerization initiated by group 4 metallocene.
Start & End Page	1220 - 1229
Received Date	2013-06-02
Revised Date
Accepted Date	2013-07-27
Full Text	Download
Keyword	silicon-bridge, zirconium, metallocene, density functional theory
Volume	Vol.41 No.5/2 (OCTOBER 2014)
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