α-Diimine complexes of transition metals for the polymerisation of lower α-olefins
Date
2005-12
Authors
Fullaway, Phillip V.
Journal Title
Journal ISSN
Volume Title
Publisher
Stellenbosch : University of Stellenbosch
Abstract
In this study several potential polymerisation catalysts were synthesised. This was
accomplished by coordinating α-diimine ligands such as N,N'-diferrocenyldiazabutadiene
(DFDAB), N,N'-dimesityldiazabutadiene (DMDAB) as well as the
bidentate amine N,N,N',N'-tetramethylethylenediamine (TMEDA), to several transition
metals.
The multi-step synthesis of N,N'-diferrocenyldiazabutadiene (DFDAB) from ferrocene
involved the use of lithiated ferrocene, iodoferrocene, N-ferrocenylphthalimide and
aminoferrocene; the latter three were characterised. This ligand was coordinated to the
transition metal ions iron(II) and zinc(II) to form Fe(DFDAB)Cl2 and Zn(DFDAB)Cl2
respectively. 1H and 13C NMR, FT-IR and mass spectrometry revealed that the expected
product had been synthesised in a useful form.
2,4,6-Trimethylaniline reacted with glyoxal to form N,N'-dimesityldiazabutadiene
(DMDAB). The DMDAB ligand was coordinated to the transition metal ions zinc(II) and
silver(I) to form Zn(DMDAB)Cl2 and Ag(DMDAB)2 respectively. Characterisation now
also include molecular and crystallographic structural determinations by means of X-ray
diffractometry.
Another N-donor complex, Cr(CO)4(TMEDA), was also prepared by coordinating
N,N,N',N'-tetramethyl ethylenediamine (TMEDA) to Cr(CO)5(THF). This was done to
give an indication of the activity of low oxidation state complexes in the catalysis of
olefin polymerisation.
The metal-α-diimine complexes mentioned above were employed in the polymerisation
of the monomers ethylene and 1-pentene probably according to a cationic mechanism.
High density, high molar mass polyethylene products with narrow polydispersities were
obtained. The chromium(TMEDA) complex produced polyethylene exhibiting ultra-high
molar mass (> 10 000 kg/mol). The polymerisation of 1-pentene, using the
Fe(DFDAB)Cl2 complex, afforded oligo-pentene with a molar mass of ~800 g/mol. After an unsuccessful attempt to prepare the (CO)5Cr=C(OZrCp2Cl)(ferrocenyl) modified
Fischer-type carbene complex, the (CO)5Cr=C(OMe)(ferrocene) complex was eventually
insolated. Elucidation of its molecular structure was accomplished by X-ray
diffractometry.
Finally, the DFDAB-ligand was coordinated to Fe2(CO)9 to generate Fe(CO)3(DFDAB)
in another attempt to investigate the role of carbonyl groups and also low oxidation state
metals in polymerisation reactions [compare to Cr(CO)4(TMEDA) unit above]. The
sensitivity of this complex towards moisture and air prevented such action.
Description
Thesis (MSc (Chemistry and Polymer Science))--University of Stellenbosch, 2005.
Keywords
Dissertations -- Chemistry, Theses -- Chemistry, Complex compounds, Transition metal complexes, Polymerization, Alkenes