Molecular Zinc(II) Complexes for the CO₂/epoxide Copolymerisation

by Moritz Johannes Joswig
Doctoral thesis
Date of Examination:2025-06-12
Date of issue:2025-09-03
Advisor:Prof. Dr. Franc Meyer
Referee:Prof. Dr. Franc Meyer
Referee:Prof. Dr. Philipp Vana
Persistent Address: http://dx.doi.org/10.53846/goediss-11487

 

 

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Abstract

English

In this thesis, series of novel {ONO}-pincer zinc(II) complexes were synthesized and evaluated as catalysts for the copolymerization of CO₂ and cyclohexene oxide (CHO) under both high (50 bar) and ambient (1 bar) CO₂ pressures. Ligand backbone modifications with electron-donating and -withdrawing substituents were found to influence the catalytic performance significantly. The parent complex, 1H, exhibited the highest activity and chemoselectivity across all conditions. Methoxysubstituted complexes displayed enhanced selectivity and tunable activity, while bulky substituents resulted in diminished performance. Mechanistic investigations using NMR and mass spectrometry revealed cyclohex-2-en-1-olate and cyclohexanolate as consistent end groups, prompting a new initiation pathway involving a C–H activation step. The addition of benzyl alcohol as an external initiator improved both molecular weight control and polymer dispersity without compromising selectivity. These findings underscore the critical role of ligand design and initiation chemistry in optimizing zinc-based catalysts for sustainable CO₂ utilization.
Keywords: CO₂; epoxide; copolymerisation; polycarbonate; zinc