Chromium complexes of amine-bis(phenolate) ligands as copolymerization catalysts

Chen, Hua (2014) Chromium complexes of amine-bis(phenolate) ligands as copolymerization catalysts. Masters thesis, Memorial University of Newfoundland.

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Abstract

Alternating copolymerization of CO₂ with epoxides to provide polycarbonates is a promising reaction for the industrial production of biodegradable thermoplastics, which have been widely used in electronics, optical media, the automotive industry, the medical and healthcare industry, and many consumer goods. Homogeneous catalysts containing transition metals including Co, Cr and Zn have been active for this reaction. Previous work in the group involved using amine-bis(phenolates) with different metals to generate catalysts and reactive species for use in several reactions. It was found that Cr complexes of tetradentate amine-bis(phenolate) ligands were promising catalysts for the copolymerization of CO₂ with cyclohexene oxide (CHO) and propylene oxide (PO). This thesis seeks to further that research by investigating different amine-bis(phenolates) to study their structure-polymerization activity relationship. The ligands used in this thesis were tridentate or tetradentate amine-bis(phenolates) where the substituents on the phenolate groups and pendant arm were varied. Three ligands used were 2-tetrahydrofurfuryl-N,N-bis(2-methylene-4,6-tert-butylphenol), H₂[L1], benzylamino-N,N-bis(2-methylene-4,6-di-tert-butylphenol), H₂[L2], and benzylamino-N,N-bis(2-methylene-4,6-di-tert-amylphenol), H₂[L3]. The synthesis and characterization of related lithium complexes 1, 2 and 3 and also chromiumᴵᴵᴵ complexes 4, 5 and 6 were performed. Three chromium complexes were isolated and characterized by UV-Vis spectroscopy, mass spectrometry, elemental analysis and, for complex 5, single-crystal X-ray diffraction. The copolymerization of cyclohexene oxide with CO₂ to yield polycarbonates was investigated with these chromiumᴵᴵᴵ amine-bis(phenolate) complexes. The resulting polymers were analyzed by ¹H and ¹³C NMR spectroscopy, MALDI-TOF mass spectrometry and gel permeation chromatography.

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