Abstract
M.Sc.
In search of developing new pyrazolyl complexes that can be used for ethylene
transformation reactions, bis(pyrazolyl)alky carbonyl and amine complexes were
prepared. The reaction between 3,5-dimethylpyrazole with alkyl-carbonyl chloride
linkers in the presence of triethylamine as a base produced the ligands, 1,3-bis(3,5-
dimethylpyrazol-1-yl)-propan-1-one (L1), 1,2-bis(3,5-dimethylpyrazol-1-yl)-ethane-
1,2-dione (L2), 1,4-bis(3,5-dimethylpyrazol-1-yl)-butane-1,4-dione (L3) and 1,6-
bis(3,5-dimethylpyrazol-1-yl)-hexane-1,6-dione (L4) as white to brown crystalline
solids in good yields.
Ligand L5 was prepared by using bis(2-chloroethyl)-amine hydrochloride and 3,5-
dimethylpyrazolevia via a phase-transfer reaction, while L6 was obtained using the
bis(2-chloroethyl)-amine hydrochloride and 3,5-diphenypyrazole in the presence of
triethylamine as a base. They were isolated in moderate yields, while their ditertiarypyrazole
derivative was not obtained at all. All the ligands were characterized
by a combination of 1H and 13C{1H}-NMR spectroscopy, infrared spectroscopy,
elemental analysis and mass spectrometry. Ligands L1 and L4 were further confirmed
by X-ray crystallography.
Ligands L1 and L6 were subsequently used to prepare their corresponding Pd, Ni and
Cr complexes. L1 was reacted with [PdCl2(NCMe)2] to form a bidentate complex 1,3-
bis-(3,5-dimethylpyrazol-1-yl)-propan-1-one palladium dichloride (1a) when the
reaction was heated at 80 oC, while a tridentate complex 1,3-bis(3,5-dimethylpyrazol-
1-yl)-propan-1-one palladium chloride (1b) was obtained when the reaction was
refluxed. 1,3-bis(3,5-dimethylpyrazol-1-yl)-propan-1-one nickel(II) bromide (2) was
obtained when NiBr2 was reacted with L1 at room temperature while the reaction
between L1 and [CrCl3(THF)3] gave 1,3-bis(3,5-dimethylpyrazol-1-yl)-propan-1-one
chromium(III) chloride (3).
Ligand L6 was reacted with the same metal salts to give bis[2-(3,5-dimethylpyrazol-
1-yl)-ethyl] amine palladium(II) chloride (4), bis[2-(3,5-dimethylpyrazol-1-yl)-ethyl]
amine nickel(II) chloride (5) and bis[2-(3,5-dimethylpyrazol-1-yl)-ethyl] amine
chromium(III) chloride (6). All the complexes were characterized by the already
mentioned characterization techniques and X-ray analysis was performed for 1b and
4.
Ethylene transformation reactions were performed with complexes 1a, 2, 3, 5 and 6,
and complexes 1a and 4 were not used because of their geometrical structures, which
prevented them to be active for such reactions. Using MMAO and EtAlCl2 as cocatalysts
complexes 1a and 3 showed no activity, however complexes 2 and 6 were
active. Complex 2 was used with MMAO and showed no activity, while with EtAlCl2
oligomers were produced. Gas-chromatography analysis of the products showed that
C6-C14+ oligomers were obtained.
Temperature variation reactions performed under standard conditions of 20 bar
ethylene pressure and 200 equivalents of EtAlCl2 in one hour showed that certain
oligomers were not favoured under certain temperatures. Ethylene reactions with
complex 6 and EtAlCl2 did not form any product but with MMAO polymer material
was obtained. Analysis of the polymer by differential scanning calometry proved that
the product was high density polyethylene. Studies of temperature, co-catalyst and
pressure variations were performed. As expected for temperature studies the catalyst
decomposed at high temperatures (above 40 oC), while for co-catalyst studies 3000
equivalents of MMAO gave the lowest TON. Pressure variations studies showed that
an increase in ethylene pressure also increased the TON, but above 30 bar the activity
became stable.