10.1002/cplu.202000553
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reactions were conducted at 60 ˚C and 45 bar ethylene pressure with a
total catalyst and solvent volume of 100 ml.
Cr(III) complexes considered, effectively favouring a quartet (S3) ground
state.
The HP model 6890 gas chromatograph equipped with a flame ionization
detector and split injection mode was used for GC analysis. The
instrument was fitted with a PONA capillary column (50m x 0.25mm id x
0.25 μm), using hydrogen as carrier gas. The temperature program used
for the analysis of all ethylene oligomerisation reaction product mixtures
was as follows: Initial temp: 50 °C; Initial time: 5 min.; Rate 6 °C/min;
Final temp: 300 °C; Final time: 10 min.
Acknowledgements
The authors thank Sasol South Africa (Pty) Ltd for funding and
permission to publish this work.
Keywords: ethylene oligomerisation • ligands • reaction
mechanisms • selectivity • structure-activity relationships
Catalytic reaction procedure
The reactor was allowed to cool to room temperature under nitrogen
following heating at 120 ˚C under vacuum for one hour. The pre-weighed
reaction solvent was added to the reactor and then heated to the
operating temperature. The desired ligand was dissolved in 25 ml of
solvent and an aliquot combined with the chromium catalyst solution in a
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Schlenk vessel and stirred for ca.
5 minutes. The resulting
solution/suspension was then transferred to the Parr reactor following
addition of the activator. The reactor was then immediately charged with
ethylene to the desired pressure and the reaction temperature was
controlled by circulating water through the cooling coils during the course
of the catalytic run. Ethylene was fed on demand and thorough mixing
was ensured by stirring at rates of 1200 rpm or more. The reaction was
terminated after 160 g of ethylene was fed to the reactor followed by
cooling the reactor contents using ice to around 10 °C. Following careful
releasing of the excess ethylene from the autoclave, the reaction mixture
was then quenched with ethanol. Nonane was then added to the reaction
mixture as a standard and the liquid phase was analysed by GC-FID.
The remainder of the organic layer was filtered to isolate the polymeric
material, which was dried in an oven overnight and weighed.
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Computational details
All geometry optimizations were performed with the DMol3 density
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a comparable set of linearly
independent Gaussian functions and have been demonstrated to have
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coordinates significantly reduces the number of geometry optimisation
iterations needed to optimise larger molecules compared to the use of
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trimerisation/tetramerisation is commonly performed in nonpolar solvents
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Quartet (S3) spin states were calculated to be consistently lower in
energy compared to the corresponding doublet (S1) spin states for all the
8
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