α-Diimine complexes of transition metals for the polymerisation of lower α-olefins

[摘要] In this study several potential polymerisation catalysts were synthesised. This wasaccomplished by coordinating α-diimine ligands such as N,N'-diferrocenyldiazabutadiene(DFDAB), N,N'-dimesityldiazabutadiene (DMDAB) as well as thebidentate amine N,N,N',N'-tetramethylethylenediamine (TMEDA), to several transitionmetals.The multi-step synthesis of N,N'-diferrocenyldiazabutadiene (DFDAB) from ferroceneinvolved the use of lithiated ferrocene, iodoferrocene, N-ferrocenylphthalimide andaminoferrocene; the latter three were characterised. This ligand was coordinated to thetransition metal ions iron(II) and zinc(II) to form Fe(DFDAB)Cl2 and Zn(DFDAB)Cl2respectively. 1H and 13C NMR, FT-IR and mass spectrometry revealed that the expectedproduct 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) andsilver(I) to form Zn(DMDAB)Cl2 and Ag(DMDAB)2 respectively. Characterisation nowalso include molecular and crystallographic structural determinations by means of X-raydiffractometry.Another N-donor complex, Cr(CO)4(TMEDA), was also prepared by coordinatingN,N,N',N'-tetramethyl ethylenediamine (TMEDA) to Cr(CO)5(THF). This was done togive an indication of the activity of low oxidation state complexes in the catalysis ofolefin polymerisation.The metal-α-diimine complexes mentioned above were employed in the polymerisationof the monomers ethylene and 1-pentene probably according to a cationic mechanism.High density, high molar mass polyethylene products with narrow polydispersities wereobtained. The chromium(TMEDA) complex produced polyethylene exhibiting ultra-highmolar mass (> 10 000 kg/mol). The polymerisation of 1-pentene, using theFe(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) modifiedFischer-type carbene complex, the (CO)5Cr=C(OMe)(ferrocene) complex was eventuallyinsolated. Elucidation of its molecular structure was accomplished by X-raydiffractometry.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 statemetals in polymerisation reactions [compare to Cr(CO)4(TMEDA) unit above]. Thesensitivity of this complex towards moisture and air prevented such action.

[发布机构] Stellenbosch University