Chromium-Catalysed Tetramerisation of Ethylene
FULL PAPERS
sequently, the reaction mixture was cooled to À108C in an
ice/salt bath, 1.0 equivalent of triethylamine was added and
the solution was stirred for 30 min. The reaction was com-
pleted by dropwise addition of 1.0 equivalent of diphenyl-
phosphine chloride and overnight stirring at room tempera-
ture. Precipitated amine hydrochloride was removed by fil-
tration through a Schlenk frit and washed with toluene. Pu-
rification of the crude product was achieved by filtration
over dry silica gel (230–400 mesh) and repeated recrystalli-
sation from toluene/pentane. NMR data were obtained on a
Bruker DPX-300 FT spectrometer. 1H NMR (300 MHz,
CDCl3): d=1.32–3.02 (m, 6H), 4.67 (m, 1H, N-CH<), 7.20
(m, 24H, Ar-H); 13C NMR (75 MHz, CDCl3): d=8.6, 21.8,
29.4, 45.8, 125.3, 126.6, 127.9, 128.1, 128.5, 129.0, 132.4,
133.8, 134.1, 138.3, 139.6; 31P NMR (121 MHz, CDCl3): d=
51.2 ppm.
ylene pressure which indicates that these side prod-
ucts stem from a rearrangement step that does not in-
volve ethylene.
Experimental Section
General Remarks
All chemicals were handled either in a glove box or under
an inert argon atmosphere using standard Schlenk techni-
ques. Solvents were dried using a solvent purification system
(degassing with argon and percolation over neutral alumina
by a commercial solvent purification system). Chromium
acetylacetonate and ligand stock solutions in cyclohexane
were prepared and stored in the glove box for precise cata-
lyst quantification. Ethylene 3.5 was obtained from Linde
Germany. Catalytic runs were conducted in a 450 mL Parr
autoclave equipped with gas entrainment stirrer for opti-
mum gas saturation of the liquid (a publication aiming to
show the importance of sufficient gas transfer for gas-liquid
reactions is in preparation).
Acknowledgements
The authors would like to thank Sasol Technology for finan-
cial support and permission to publish these results. In partic-
ular we would like to thank Drs. Kevin Blann and Annette
Bollmann for great scientific collaboration and helpful advice
and Professor Wolfgang Arlt is acknowledged for fruitful dis-
cussions in the context of the ethylene solubility calculations.
Nicola Taccardi would like to acknowledge the DIAC Poly-
technic of Bari (Italy) for giving him the opportunity to work
under the supervision of Prof. Wasserscheid.
Catalytic Runs
All catalytic runs were carried out according to the follow-
ing procedure. 5 mmol of Cr(acac3) and an equimolar
G
amount of the respective ligand was taken from a prepared
stock solution and transferred into a Schlenk tube inside a
glove box. This solution was made up with cyclohexane to a
total volume of 5 mL. The solution was activated under an
inert argon atmosphere with 270 equivalents MMAO-3A (7
wt% solution in heptane) with respect to the chromium.
This activated solution was transferred immediately into the
autoclave containing 195 mL of cyclohexane at the desired
reaction temperature. The reaction was initiated by pressuri-
sation with ethylene which was fed on demand throughout
the duration of the experiment. The temperature was moni-
tored via an internal thermocouple and maintained by cool-
ing the autoclave with ice water. After 20 min, the reaction
was terminated by closing the ethylene supply, switching off
the gas entrainment stirrer and cooling the autoclave to
08C. Next, the autoclave was depressurised slowly. The
liquid product was filtered and submitted for GC-FID analy-
sis (apparatus: Varian 3900, column CP Sil Pona CB 50 m
0.21 mm).
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Synthesis of 1,2,3,4-Tetrahydronaphthyl PNP
Bis(diphenylphosphino)-1,2,3,4-tetrahydronaphthylamine
was synthesized according to procedures reported in the lit-
erature.[16] A solution of 2.54 equivalents of the correspond-
ing amine in 10 mL of toluene was prepared and reacted
with 1.0 equivalent. diphenylphosphine chloride by dropwise
addition at À58C. The solution was stirred for 30 min. The
precipitate (amine hydrochloride) was removed by filtration
through a Schlenk frit and washed with toluene (5 mL). Sub-
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