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Title: Super bulky α-diimine ligands and their coordination complexes for use as polymerization catalysts
Author: Megrahi, Abdunnaser
ISNI:       0000 0004 2677 1057
Awarding Body: The University of Manchester
Current Institution: University of Manchester
Date of Award: 2009
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The TiCl4 mediated condensation of benzil with anilines followed by Li mediated cyclodehydrogenation of the resulting benzildiimines to access the superbulky a-dimine ligands Ll (N,N'-bis-(2,6-diisopropylphenyl)-phenanthrene-9, 1 O-diylidendiamine) and L2 (N-(2,6- diisopropylphenyl)-N'-(2,4,6-trimethylphenyl)-phenanthrene-9, 1 O-diylidenediamine) is described in this work. This route has been chosen among many other routes which failed to access these ligands. These ligands have been for the first time synthesized and fully characterized, including their single crystal X-ray structures. Attempts to tetrahedrally coordinate NiBr2 to the super bulky ligand Ll failed due to the axial crowding caused by the aryl substituents in the ortho position. Reducing this axial bulk at one side of the ligand from isopropyl groups to methyl groups as in ligand L2 enabled the synthesis of the tetrahedral NiBr2-complex (L2NiBr2). A failure has been also the attempt to coordinate MO(CO)4 to both these ligands. Instead, with the super bulky ligand Ll, a square planar Ni-allyl complex [(113- LINiC3~COOCH3)t. {B[C6H3(CF3)2k} could be easily accessed. These Ni-complexes have shown to be potent catalysts for ethylene polymerisation. The Ni-allyl version of ligand Ll has not been able to polymerize I-hexene. PdCh complexes (LIPdCh) and (L2PdCh) have been synthesized. Stirring of (LIPdCh) complex with Na B[C6H3(CF3)2]4 in acetonitrile afforded a good yield of the cationic chloroacetonitrile complex [LIPdCINCCH3t.{B[C6H3(CF3)2k}. This reaction with (L2PdCh) afforded also good yields not of the desired [L2PdCINCCH3t.{B[C6H3(CF3)2k} but of the dimer [(L2PdCI)2]2+.2{B[C6H3(CF3)2k}. This behaviour has precedent in the literature and might be due to the reduced bulk of this ligand as compared with Ll. [LIPdCINCCH3t.{B[C6H3(CF3)2]4-} has been successfully methylated with Sn(CH3)4 in DCM as solvent affording good yields of the methyl acetonitrile complex [LIPdCH3NCCH3t.{B[C6H3(CF3)2k}. The methylation of the dimer [(L2PdCI)2]2+.2{B[C6H3(CF3)2]4-} failed in DCM but was succesful in acetonitrile affording a good yield of [L2PdCH3NCCH3t.{B[C6H3(CF3)2]4-}. These palladium methyl acetonitrile complexes have been tested for ethylene, I-hexene and cyclopentene polymerization. Branched polyethylene and polyhexene with relatively high molecular weight have been produced by these catalysts. Catalyst [LIPdCH3NCCH3t.{B[C6H3(CF3)2]4-} was more active and produced higher molecular weight and less branched polymer than catalyst [L2PdCH3NCCH3t.{B[C6H3(CF3)2k } in the polymerization of ethylene. The opposite trend has been observed for I-hexene polymerization where catalyst [L2PdCH3NCCH3t.{B[C6H3(CF3)2k} was more active and produced higher molecular weight polymer than catalyst [LIPdCH3NCCH3t.{B[C6H3(CF3)2]4-}. Atactic polycyclopentene with much lower T g and T m than the ones reported in the literature for isotactic polycyclopentene, has been obtained with these catalysts. Tacticity was determined by 13CNMR.
Supervisor: Not available Sponsor: Not available
Qualification Name: Thesis (Ph.D.) Qualification Level: Doctoral
EThOS ID:  DOI: Not available