Asymmetric Polymerization initiated by Cationic Zirconocene Complexes possessing Chiral Counter Anions

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Title: Asymmetric Polymerization initiated by Cationic Zirconocene Complexes possessing Chiral Counter Anions
Author: Lee, Hyun-Su
Advisors: Tonelli Alan E, Committee Member
Bruce M. Novak, Committee Chair
T. Brent Gunnoe, Committee Member
David A. Shultz, Committee Member
Abstract: Chiral induction in cationic polymerization was studied. New cocatalysts, Sodium rac-tris(tetra-chlorobenzenediolato)phosphate(V) and triphenylcarbenium rac-tris(tetra-chlorobenzenediolato)phosphate(V) for cationic zirconocene complexes were synthesized, respectively. The X-ray single crystal structure of triphenylcarbenium tris(tetra-chlorobenzenediolato)phosphate(V) showed that the crystal structure is a racemic mixture and there are four ion pairs in the asymmetric unit and eight ion pairs in the unit cell. The most interesting part is that the distribution of delta-isomers and lambda-isomers is equal in the unit cell, but the anionic isomers in the asymmetric unit are predominantly (75%) one isomer. Poly (tert-butyl vinyl ether) samples were synthesized by the initiating system of bis(cyclopentadienyl)dimethylzirconium and triphenylcarbenium tris(tetra-chlorobenzenediolato)phosphate(V) and by the initiating system of Sodium tris(tetra-chlorobenzenediolato)phosphate(V) and bis(cyclopentadienyl)zirconiumdichloride. The polymers exhibited reasonable yields, reasonable molecular weights, and reasonable molecular weight distributions, respectively and both are atactic polymers. These two systems did not control the stereoregularity of the polymers. Chiral induction in coordination-insertion polymerization of carbodiimides was studied. New chiral cocatalysts, sodium delta-tris(tetra-chlorobenzenediolato)phosphate(V) and triphenylcarbenium delta-tris(tetra-chlorobenzenediolato)phosphate(V) for cationic zirconocene complexes possessing chiral counter anions were synthesized, respectively. The catalytic system with bis(cyclopentadienyl)dimethylzirconium and trityl rac-TRISPHAT polymerized carbodiimide monomers and the resulting polymers have reasonable yields. The asymmetric carbodiimide polymerization by using cationic zirconocene complexes with delta-TRISPHAT anion yielded polymers. Unfortunately, we did not observe chiral counter anion with cationic catalytic site can generate single handed helical polymer in this polymerization system. Using ¹H-NMR spectroscopy, a mononuclear cationic complex [Cp₂ZrCH₃][rac-TRISPHAT] formed in catalytic system with Cp₂Zr(CH₃)₂ and [CPh₃][rac-TRISPHAT] was studied. Addition of N,N'-di-n-hexylcarbodiimides to the catalytic system and further ¹H-NMR spectroscopic monitoring showed that the catalytic system [Cp₂ZrCH₃][rac-TRISPHAT] initiates and polymerizes N,N'-di-n-hexylcarbodiimides. A new chiral half-sandwich zirconium amidinate complex, CpZrCl₂[N(R)C(Me)N(R)] (R = (R)-1-cyclohexylethyl) was synthesized. A new synthetic method of new dianionic C₂H₂–bridged Cp⁄guanidinate ligands for new chiral catalysts was discovered.
Date: 2006-08-07
Degree: PhD
Discipline: Chemistry

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