Influence of elevated temperature and pressure on the chromium-catalysed tetramerisation of ethylene

Article abstract of DOI:10.1002/adsc.200606062

A catalyst system comprising a diphenylphosphineamine (PNP) ligand, chromium(III) acetylacetonate and a methylaluminoxane-based activator was studied for the selective tetramerisation of ethylene. The reaction was investigated over a broad temperature and pressure range and the resulting product mixture was interpreted in the light of the recently published, enlarged metallacycle mechanism. Vapour-liquid equilibrium (VLE) data were calculated for the binary ethylene-cyclohexane mixture over the relevant temperature and pressure ranges to deconvolute the influence of ethylene concentration and temperature. Good agreement of the experimental data with the proposed mechanism was found. Enlargement of the metallacycloheptane ring by insertion of ethylene was found to be dependent on the ethylene concentration, albeit to a lesser extent than assumed. The 1-octene selectivity, which reaches a maximum of 72-74 mass %, thus seems to be primarily dependent on the temperature. The formation of the cyclic side products methyl- and methylenecyclopentane was in effect independent of the ethylene concentration. This is in good accordance with the proposed mechanism, since it indicates that the formation of the products occurs via rearrangement of a metallacycle intermediate.

Full text of DOI:10.1002/adsc.200606062

FULL PAPERS
DOI: 10.1002/adsc.200606062
Influence of Elevated Temperature and Pressure on the
Chromium-Catalysed Tetramerisation of Ethylene
Sven Kuhlmann,a John T. Dixon,b Marco Haumann,a David H. Morgan,b
Jimmy Ofili,a Oliver Spuhl,c Nicola Taccardi,a and Peter Wasserscheida,*
a
Lehrstuhl für Chemische Reaktionstechnik der Universität Erlangen-Nürnberg, Egerlandstraße 3, 91058 Erlangen,
Germany
Fax : (+49)-9131-852-7521; e-mail: Wasserscheid@crt.cbi.uni-erlangen.de
Sasol Technology (Pty) Ltd, R&D Division, 1 Klasie Havenga Road, Sasolburg, 1947, South Africa
b
Fax : (+27)-11-522-1529
c
Lehrstuhl für Thermische Verfahrenstechnik der Universität Erlangen-Nürnberg, Egerlandstraße 3, 91058 Erlangen,
Germany
Fax : (+49)-9131-852-7441
Received: February 20, 2006; Accepted: April 24, 2006
Supporting information for this article is available on the WWW under http://asc.wiley-vch.de/home/.
Abstract: A catalyst system comprising a diphenyl- sertion of ethylene was found to be dependent on
phosphineamine (PNP) ligand, chromium(III) acetyl- the ethylene concentration, albeit to a lesser extent
G
acetonate and a methylaluminoxane-based activator than assumed. The 1-octene selectivity, which reach-
was studied for the selective tetramerisation of ethyl- es a maximum of 72–74 mass%, thus seems to be
ene. The reaction was investigated over a broad tem- primarily dependent on the temperature. The forma-
perature and pressure range and the resulting prod- tion of the cyclic side products methyl- and methyl-
uct mixture was interpreted in the light of the recent- enecyclopentane was in effect independent of the
ly published, enlarged metallacycle mechanism. ethylene concentration. This is in good accordance
Vapour-liquid equilibrium (VLE) data were calculat- with the proposed mechanism, since it indicates that
ed for the binary ethylene-cyclohexane mixture over the formation of the products occurs via rearrange-
the relevant temperature and pressure ranges to de- ment of a metallacycle intermediate.
convolute the influence of ethylene concentration
and temperature. Good agreement of the experimen- Keywords: chromium; ethylene tetramerisation; eth-
tal data with the proposed mechanism was found. ylene-cyclohexane VLE; homogeneous catalysis;
Enlargement of the metallacycloheptane ring by in- metallacycle mechanism
Introduction
mediate.[2] The first process for the selective produc-
tion of 1-hexene has been recently commercialised by
The oligomerisation of ethylene yielding linear alpha Chevron Phillips in its 47,000 metric-ton-per-year 1-
[3]
olefins (LAOs) is a process of vital importance for hexene plantin Mesaieed, Qaatr.
While a number
the chemical industry as the formed products are of selective ethylene trimerisation catalysts based on
useful intermediates for the synthesis of polymers chromium[4] and other transition metals[5] have been
(i.e., 1-hexene and 1-octene are the most important developed, the selective formation of higher olefins
co-monomers for LLDPE production), lubricants and such as 1-octene was only discovered very recently.[6]
plasticiser alcohols. While the major percentage of
the world LAO production is still produced via pro- 1-octene was demonstrated successfully using a chro-
cesses that yield a Schulz–Flory distribution (i.e., the mium source [i.e., Cr(acac3)], a diphosphineamine
The selective tetramerisation of ethylene yielding
AHCTREUNG
Shell higher olefin process and Ziegler-type process- ligand of the general structure (Ph2P)2N-R and a
es),[1] an interesting alternative to this inflexible, and methylaluminoxane (MAO)-based activator. From a
thus disadvantageous route, has evolved over the last mechanistic point of view, this reaction is of funda-
two decades. The selective trimerisation of ethylene mental relevance, since it suggests an extension of the
gives access to co-monomer grade 1-hexene and is metallacycloheptane intermediate to yield a metalla-
therefore the route of choice to this valuable inter- cyclononane intermediate which gives rise to 1-
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Chromium-Catalysed Tetramerisation of Ethylene
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octene. Recent DFT studies for chromium and other
metals support this possibility.[7]
It has to be noted that in situ studies on the reac-
tion mixture using conventional analytical techniques
are complicated by the paramagnetic nature of Cr(I–
G
III) compounds and fast reaction rates. A metallacy-
cle mechanism was initially regarded as a highly un-
likely route to the formation of long-chain olefins due
to the relatively high energy barrier for the insertion
Figure 1. 1,2,3,4-Tetrahydronaphthylamine-bis(diphenylphos-
phine).
of further ethylene molecules in the metallacyclohep- concentration dependence of the product distribution
tane intermediate, compared to the facile reductive in general and the formation of 1-octene in particu-
elimination to yield 1-hexene. However, extensive lar.[12] This discovery prompted us to carry out an ex-
deuterium labelling studies in two independent inves- tended study over a very wide pressure range (from
tigations have indicated that long-chain linear alpha 45 to 100 bar) in order to examine whether 1-octene
olefins can indeed be formed by means of a metalla- selectivity could be further boosted. Since tempera-
cycle mechanism. Overett et al. demonstrated in their ture is known to be an important factor for tri- vs. tet-
studies that the formation of 1-octene from a C2H4/ ramerisation as well, we decided to include a temper-
C2D4 mixture involved no H/D-scrambling, which is ature variation from 40 to 808C in our studies. This
in accordance with a metallacycle mechanism and not should allow further insight into the reaction mecha-
with a Cossee–Arlman mechanism.[8] Furthermore, nism and the limits of the process parameters with re-
the authors were able to shed light on the formation spect to 1-octene formation. It should be noted that
of the cyclic C6 side products, methylenecyclopentane our study was not aimed at providing conclusive ki-
and methylcyclopentane, which are formed in a 1:1 netic data for the design of a commercial reactor.
ratio by means of a disproportionation pathway. Their However, throughout the study we ensured that the
findings are in good agreement with observations catalyst efficiencies remained in the same order of
made by Bercaw et al. on the selective chromium-cat- magnitude to allow for a realistic comparison of selec-
alysed trimerisation of ethylene[9] and Gibson etal.
for the oligomerisation of ethylene by chromium cat- dronaphthylamine-bis(diphenylphosphine)
tivity data. Our ligand of choice was 1,2,3,4-tetrahy-
(=THN
alysis according to a Schulz–Flory type of distribu- PNP, see Figure 1), since this ligand gives a very high
tion.[10] In all these research activities, carried out by yield of the most desired products, namely 1-octene
established groups in the field of ethylene oligomeri- and 1-hexene (i.e., 90% combined yield with THN
sation, a metallacycle mechanism was proven for the PNP vs. 80–85% for i-Pr PNP). This should facilitate
selective, Cr-catalysed ethylene oligomerisation.
more meaningful mechanistic insight, as side reactions
In the present paper, additional experimental data become less significant.
is provided to verify the proposed mechanism for the
Table 1 displays the results from the above-men-
tetramerisation of ethylene. For this purpose, a de- tioned pressure (45–100 bar) and temperature (40–
tailed investigation of the temperature and pressure 808C) variation studies. 1-Octene and 1-hexene are
dependency of the tetramerisation reaction has been clearly the main products under these conditions and
carried out. The results of this study allow further in- their combined yield represents around 90% of the
sight into the detailed mechanism of the Cr-catalysed liquid products (column “Sa” in Table 1). This com-
ethylene tetramerisation.
bined yield was constant throughout the pressure and
temperature range with a variance of only 3–4% over
the whole set of experiments. The same applies for
the combined C6 and C8 fractions, which correspond
to approximately 95% of the liquid products. The
Results and Discussion
Since the recent discovery of the selective tetrameri- main side products of the reaction are methylenecy-
sation of ethylene to 1-octene, extensive research has clopentane and methylcyclopentane, which were
been carried out to elucidate the influence of ligand formed in a 1:1 ratio and are given as “SC6 cyclics” in
structure on the reaction. Particular emphasis was Table 1.
placed on determining possible switches from tri- to
Changes in product distribution of the three main
tetramerisation and vice versa through a systematic products (1-octene, 1-hexene and cyclic C6 species)
investigation of different substituents at the P-Ar was in good accordance with the metallacycle mecha-
moiety.[11] Furthermore, kinetic studies on the catalyst nism proposed by Overett et al.[8] (Scheme 1)
system Cr(acac)3, i-Pr PNP, MAO in cumene as reac- throughout the pressure variation experiments (e.g.,
G
tion solvent, have revealed that an increase in pres- entries 4–9, Table 1). According to this mechanism,
sure from 20 to 45 bar led to an increased formation the aluminoxane-activated chromium catalyst 1 readi-
of 1-octene. This is indicative of a strong ethylene ly coordinates two ethylene molecules through oxida-
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Table 1. Pressure and temperature variation for 1,2,3,4-tetrahydronaphthyl PNP.[a]
No T [8C] p [bar] nproduct [g] Efficiency[b] [ggÀ1 CrÀ1] Selectivity[b] [%]
[c]
S1ÀC6 SC6 cyclics S1ÀC8 Sa
SC6+C8 S1ÀC6 in C6 S1ÀC8 in C8
1
2
3
4
5
6
7
8
40
40
40
60
60
60
60
60
60
80
80
80
45
70
100
45
60
70
80
90
100
45
39.9
31.5
36.4
18.3
31.9
29.8
35.6
33.6
35.3
16.4
15.3
25.7
156,556
120,973
140,258
70,556
122,730
114,458
136,812
129,045
135,575
63,196
16.3
14.1
13.6
32.1
28.6
27.4
26.4
26.0
25.7
49.1
41.6
40.2
3.8
3.6
3.6
2.8
2.8
2.7
2.7
2.8
2.8
1.8
1.9
2.1
72.7
74.6
74.5
58.8
62.6
63.3
64.8
65.4
64.8
41.5
46.4
50.8
88.9 94.4
88.7 94.0
88.1 94.2
90.9 96.6
91.2 95.7
90.7 95.2
91.1 95.6
91.4 96.7
90.5 95.8
89.2 94.5
88.0 92.7
91.1 95.9
77.7
74.9
74.4
86.9
87.4
87.2
87.8
87.2
86.8
92.6
91.6
92.3
99.2
99.2
98.2
98.7
99.3
99.4
98.9
97.8
97.9
98.0
98.1
97.3
9
10
11
12
70
100
58,674
98,657
[a]
5 mmol Cr(acac3), L:[Cr]=1:1, activator: MMAO-3 A (7 wt% solution in heptane from Akzo Nobel), MMAO-3 A:[Cr]=
A
1:270, solvent: 200 mL of cyclohexane, reaction time: 20 min.
[b] Calculations based on liquid products alone.
[c]
Sa =total alpha selectivity=S1CÀ6 +S1ÀC8
.
Scheme 1. Metallacycle mechanism for the selective tetramerisation of ethylene as postulated by Overett et al. (the most
prominentproducts are boxed).
tive addition (species 2 in Scheme 1) to form the met- pathway is the suggested rearrangement of 5 t o a cy-
allacyclopentane intermediate 3. A further ethylene clopentylmethyl hydride species 6 (r3 in Scheme 1).
unit is inserted into this species via intermediate 4 The formation of methylenecyclopentane and methyl-
yielding the metallacycloheptane compound 5. This cyclopentane is proposed to occur via a subsequent
species can then undergo several possible reaction disproportionation step.
pathways which will lead to the three main products.
This proposed mechanism is in good accordance
From an analysis of the final product mixture, the with the experimental data found in our set of experi-
most prevalent route is the insertion of a fourth ethyl- ments. Upon increasing the ethylene pressure, and
ene unit into the metallacycle ring (step r5, thus ethylene concentration, r5 is favoured over r4
Scheme 1), thus forming the metallacyclononane in- which leads to an increased formation of 1-octene at
termediate 8 which undergoes rapid elimination to the expense of 1-hexene. Since the insertion of a fifth
the main reaction product, 1-octene.
ethylene unit into intermediate 8 leading to the for-
The second possible pathway is the reductive elimi- mation of 1-decene occurs to a relatively small extent,
nation of 1-hexene from the metallacycloheptane in- the ethylene concentration dependency of this step
termediate 5 (r4 in Scheme 1) and the third potential cannot be resolved and is therefore neglected in
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Chromium-Catalysed Tetramerisation of Ethylene
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Figure 2. Pressure variation at 608C; S
N
N
tivities relative to the overall amount of C6 and C8, respectively.
Scheme 1. The same applies for the likely rearrange- formation of these products is not dependent on the
mentof 8 to give cyclic C8 products, which is also an ethylene concentration, which is in good accordance
alternative pathway to r6. This step plays a minor role with the proposed mechanism that suggests that meth-
and is therefore also ignored. This is consistent with ylene- and methylcyclopentane are formed by rear-
the fact that the effect of ethylene concentration is rangementof species 5 or 7.
only detectable in the ratio of the three main prod-
The results of the temperature study (see Table 1)
ucts. The effect of ethylene concentration on the reveal considerable changes in the product distribu-
minor products was too small to make any sensible tion with temperature variation. In this study the tem-
conclusions. This is exemplified by Figure 2 which perature was varied from 40 to 60 to 808C (athtree
provides an overview of the product distribution with ethylene pressures of 45, 70 and 100 bar). The
varying ethylene pressure at 608C.
common trend here is a significant increase in selec-
It is remarkable that the formation of 1-octene only tivity towards 1-hexene with increasing temperature,
increased by 6% upon increasing the pressure from which occurs at the expense of 1-octene and cyclic C6
45 to 80 bar, while a further increase in pressure to products. On the other hand, the total a-selectivity
100 bar did notincrease S
A
(Sa) remained constant at 89–91% throughout the
show below, the ethylene concentration in the liquid whole temperature range. Concurrently, an increase
phase more than doubles over this pressure range, in temperature leads to a decrease in the formation of
and we would therefore expect a significant shift in cyclic C6 products and thus an increase in selectivity
selectivity. However, a maximum yield to 1-octene to 1-hexene within the C6 fraction (see column “S1ÀC6
seems to be reached that cannot be exceeded. Pres- in C6” in Table 1). In terms of the reaction mechanism
sure variation experiments at 408C (entries 1–3, depicted in Scheme 1 it can be concluded that at
Table 1) and 808C (entries 10–12, Table 1) are consis- higher temperatures, the reductive elimination of 1-
tent with the same general trend of increasing 1- hexene (r4) is favoured over b-hydride transfer to
octene selectivity with increasing ethylene pressure. It chromium (r3), i.e., “Scyclic C6” drops from 4 to 2%
is noteworthy that this effect was more pronounced at upon increasing the temperature from 40 to 808C
higher temperatures (i.e., 9% vs. 2% absolute change while “S1ÀC6 in C6” in turn increases from 76 to 92%.
at80 vs. 408C).
Furthermore, r4 is favoured over r5 (elimination of 1-
The formation of the cyclic C6 side products seems hexene from the metallacycloheptane species is fav-
to be independent of ethylene concentration over this oured over further insertion of ethylene to form the
pressure range. For example, the selectivity towards metallacyclononane species), i.e., “S1ÀC6” increases
methylenecyclopentane
and
methylcyclopentane from 16 to 49% when going from 40 to 808C, while
stayed at a precisely constant level of 2.8Æ0.1% “S1ÀC8” concurrently decreases from 72 to 41%.
upon varying the pressure from 45 to 100 bar at 608C. Whereas the first effect should be independent of eth-
This indicates that the rate-determining step for the ylene pressure as indicated above, the second is clear-
Adv. Synth. Catal. 2006, 348, 1200 – 1206
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Sven Kuhlmann etal.
FULL PAPERS
ly influenced by ethylene concentration in the liquid ene solubility clearly reveals that the predominant pa-
phase, which in turn is a function of both pressure rameter which determines r4 and r5 is in fact the tem-
and temperature.
perature. For example, for Xethylene =0.52–0.53 the
In order to elucidate the temperature and pressure total selectivity towards 1-hexene increases from
dependence of steps r4 and r5 further, and more spe- 16.3% at40 8C to 41.6% at 808C, while the selectivity
cifically to be in a position to differentiate ethylene towards 1-octene drops concurrently from 72.7% at
solubility effects from the temperature dependence of 408C to 46.4% at 808C (compare entries 1 and 11,
the individual rate constants, we decided to determine Table 1).
the ethylene solubility (as molar concentration) in cy-
The impact of temperature on selectivity is even
clohexane over the temperature and pressure range more pronounced for reactions at constant pressure
relevant to these experiments. The VLE data for this (and thus decreasing ethylene concentration). For ex-
binary system were calculated using the perturbed ample, at 45 bar the selectivity towards 1-octene
chain SAFT (PC-SAFT) equation of state.[13] This drops from 72.7% to 40.0% upon going from 40 to
equation gives reasonable results for the calculation 808C (compare entries 1 and 10, Table 1) . It can thus
of high-pressure phase equilibria in the sub- and su- be concluded that both r4 and r5 are strongly tempera-
percritical state. In addition to this it can be used to ture dependent. The pressure influence on the C6- vs.
calculate the phase equilibrium without further pa- C8-selectivity is much smaller. This observation is of
rameterisation over a wide pressure and temperature fundamental interest, since it indicates that the stabili-
range.[13] The PC-SAFT equation of state requires ty of larger metallacycle intermediates (in terms of
three parameters for each pure component and one elimination to 1-alkenes) is predominantly controlled
binary interaction parameter. The pure component by the reaction temperature. Increasing the concen-
parameter for ethylene and cyclohexane has been tration of larger metallacycles (i.e., metallacyclono-
published previously[14] and the binary interaction pa- nane) by employing higher ethylene concentrations is
rameter was fitted to published experimental data[15] thus limited to a certain extent. Further optimisation
to yield a value of 0.031 for kij. The interaction pa- of 1-octene formation and the suppression of side-
rameter is not dependent on temperature or composi- products by the adjustment of reaction parameters
tion. Subsequently, the VLE curves were calculated therefore seem unlikely.
over the desired temperature and pressure range (see
the Supporting Information). The molar compositions
of the liquid phase relevant to the interpretation of Conclusions
the catalytic data of this study are summarised in
Table 2.
In conclusion, we have successfully investigated the
As expected, an increase in temperature at constant pressure and temperature dependency of the recently
pressure is accompanied by a decrease in ethylene discovered ethylene tetramerisation reaction over an
concentration (i.e., from Xethylene =0.52 to 0.35 for extended pressure and temperature range. This study
408C and 808C at45 bar, see Table 2). Consequenlty,
was exclusively conducted on the Cr(acac3)/1,2,3,4-
A
reaction conditions with comparable ethylene concen- tetrahydronaphthylamine-bis(diphenylphosphine)/
trations have to be considered, e.g., 408C and 45 bar MMAO-3A catalyst system.
(Xethylene =0.52, entry 1 in Table 1) vs. 808C and
The experimental findings are consistent with the
70 bar (Xethylene =0.53, entry 11 in Table 1) to deter- recently proposed metallacycle mechanism. The inser-
mine the temperature dependency of r5. Comparing tion of ethylene into the metallacycloheptane species
the selectivities at these conditions with similar ethyl- was found to be slightly pressure dependent. Howev-
er, the reaction temperature seems to be the primary
factor that determines whether 1-hexene is eliminated
from the metallacycloheptane intermediate or if fur-
ther ethylene is incorporated to form a larger metalla-
cycle (and ultimately 1-octene). These conclusions
were derived by correlating the ethylene concentra-
tion at specific reaction conditions with the respective
catalytic results at these conditions. The determina-
tion of the ethylene concentration in binary ethylene/
cyclohexane mixtures was conducted by extending lit-
erature VLE curves into the relevant temperature
and pressure range with the perturbed chain SAFT
(PC-SAFT) equation of state.
Table 2. Molar fraction Xethylene in cyclohexane atdifferent
temperatures and pressures.[a]
T [8C] Pressure [bar]
40
45
50
60
70
80
-
90
-
100
40
60
80
0.47 0.52 0.58 0.70 0.83
0.37 0.42 0.46 0.55 0.63 0.72 0.81
-
-
0.31 0.35 0.39 0.46 0.53 0.59 0.66 0.73
[a]
Calculations based on the PC-SAFT equation of state (for
more information see Supporting Information); note that
the fields marked “-” represent a monophasic regime.
Here, the phase composition could not be detected, as no
information on the amount of ethylene in the reactor was
available.
The formation of methylenecyclopentane and
methylcyclopentane seems to be independent of eth-
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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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Bis(diphenylphosphino)-1,2,3,4-tetrahydronaphthylamine
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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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