Ka-Ho Tam
Published: 2017-01-27
Total Pages:
Get eBook
This dissertation, "Group 4 Complexes Bearing Tridentate Aryloxide-based Ancillary Ligands: Synthesis, Characterization and Application as Olefin Polymerization Catalysts" by Ka-ho, Tam, 譚家豪, was obtained from The University of Hong Kong (Pokfulam, Hong Kong) and is being sold pursuant to Creative Commons: Attribution 3.0 Hong Kong License. The content of this dissertation has not been altered in any way. We have altered the formatting in order to facilitate the ease of printing and reading of the dissertation. All rights not granted by the above license are retained by the author. Abstract: Abstract of thesis entitled GROUP 4 COMPLEXES BEARING TRIDENTATE ARYLOXIDE- BASED ANCILLARY LIGANDS: SYNTHESIS, CHARACTERIZATION AND APPLICATION AS OLEFIN POLYMERIZATION CATALYSTS Submitted by Tam Ka Ho for the degree of Doctor of Philosophy at The University of Hong Kong in 2006 The preparation, characterization, crystal structures and olefin polymerization behavior of a class of Group 4 complexes, and in particular the Zr(IV) derivatives 1 1 [Zr(L )Cl (D)] [H L = 2,6-di(3-tert-butyl-5-methylphen-2-ol)pyridine; D = ethers, 2 2 ketones and Cl(HPR )], have been undertaken. These [O, N, O] catalysts exhibit excellent activities with MAO for ethylene polymerization. Studies to assess the impact of the donor group during catalysis suggest that the same active species is generated and the donor does not play an active role. Superior activities were observed with the Bu Al/Ph CB(C F ) cocatalyst in ethylene polymerization and - 3 3 6 5 4 -1 -1 propylene copolymerization (36,590 and 15,700 g mmol h respectively). Insight into the behavior of the catalytic system with MAO has been derived from gel permeation chromatography and NMR analyses of the polymers prepared under 1 13 different reaction conditions. H and C NMR end-group analyses reveal resonances for saturated methyl chain-end groups only, and undetectable levels of unsaturated vinyl chain ends. This indicates that for the polymerization chain-transfer mechanism, the conventional β-H transfer reactions are insignificant and the unusual chain transfer to Al pathway is vastly dominant. Group 4 complexes supported by unsymmetric tridentate [O, N, O] ligands bearing different substituents on the two aryloxide rings have been prepared, in order to develop new catalytic systems capable of stereospecific α-olefin polymerization. Their activities for ethylene polymerization with MAO are significantly lower than the symmetric [O, N, O] analogues. A number of group 4 bis(benzyl) complexes supported by tridentate pyridine-2- phenolate-6-aryl [O, N, C] ligands, with alkyl and halogen substituents at the R position ortho to the metal, have been prepared. This enabled direct comparison with the CF -substituted [O, N, C] analogues, which were recently reported to exhibit novel C-H---F-C contacts in solution with potential applications for attractive ligand---polymer interactions. The molecular structure of the Zr derivative bearing an ortho-Cl group was determined, revealing the benzyl moieties in an unusual 'anti, anti' configuration. Saliently, this polyethylene catalyst in conjunction with Bu Al/Ph CB(C F ) displayed the best activity thus far observed for [O, N, C] 3 3 6 5 4 -1 -1 catalysts (8630 g mmol h ). A series of group 4 bis(benzyl) complexes supported by newly designed [O, C, N] ligands bearing R substituents ortho to the metal has been prepared, such that the σ- aryl moiety resides trans to the alkyl/polymer chain, and catalyst decomposition pathways such as olefin insertion into the M-C(sp ) bond are impeded. The crystal structure of the CF -substituted hafnium(IV) complex features weak intramolecular 31 C-H---F-C (CF ---methylene) interactions. The H NMR spectra of [M(O, C, N- CF )(CH Ph) ] analogues revealed coupling (assigned to J [via M---F] for Hf and