Chromium-Catalyzed Highly Selective Oligomerization of Ethene to 1-Hexene with N,N-Bis[chloro(aryl)phosphino]amine Ligands

Article abstract of DOI:10.1002/cctc.201700448

Different N,N-bis[chloro(aryl)phosphino]amines were synthesized and characterized. The synthesized compounds were tested as ligands in the Cr-catalyzed oligomerization of ethene. The effect of the successive increase of the steric bulk either at one of th

Full text of DOI:10.1002/cctc.201700448

Accepted Article
Title: Chromium Catalyzed Highly Selective Oligomerization of Ethene
to 1-Hexene with N,N-bis{chloro(aryl)-phosphino}-amine Ligands
Authors: Uwe Rosenthal, Martha Höhne, Normen Peulecke, Katharina
Konieczny, and Bernd Harald Müller
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10.1002/cctc.201700448
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Chromium Catalyzed Highly Selective Oligomerization of Ethene
to 1-Hexene with N,N-bis{chloro(aryl)-phosphino}-amine
Ligands
Martha Höhne,[a] Normen Peulecke,[a] Katharina Konieczny,[a] Bernd H. Müller[a] and Uwe Rosenthal*[a]
In memory of Günther Wilke (passed away december 9, 2016).
Abstract: Different N,N-bis{chloro(aryl)-phosphino}-amines were
synthesized and characterized. All synthesized compounds were
tested as ligands in the chromium catalyzed oligomerization of
Results and Discussion
ethene. The dependence of successively increasing the steric bulk
either at one of the phosphorus´ substituents or at the nitrogen
center on the product distribution of the oligomerization reaction was
examined. We found a highly active and selective trimerization
system with purities of the hexene fraction up to 99.9 % of 1-hexene.
Furthermore we suppose an in situ methylation of the chlorinated
ligands into the corresponding N,N-bis{methyl(aryl)-phosphino}-
amines.
The most important systems for the homogeneously catalyzed
selective oligomerization of ethene are illustrated in Table 1 and
compared to the new system we present herein. For better
comparability all systems discussed are based on a chromium
source and activated with methylaluminoxane, commonly called
MAO except the one of Chevron Phillips. The Phillips ethylene
oligomerization catalyst is the pioneer in the field of selective
trimerization and was developed during the 1980´s. It consists of
a chromium source, a 2,5-dimethylpyrrole ligand, AlEt3 as
cocatalyst and a modifier. In comparison to a non-selective
Schulz-Flory distribution the product mixture contains up to 90%
Introduction
C6, unfortunately nothing is said concerning the purity of the
Linear alpha olefins (LAOs) are useful and versatile
intermediates for many industrially important substances like co-
monomers for high-density polyethylene (HDPE) and linear low-
density polyethylene (LLDPE), surfactants for detergents, base
stock and additives for synthetic lubricants or alcohols for
plasticizers. Since the conventional technologies for producing
LAOs result in a Schulz-Flory or Poisson product distribution
whose purification is very cost-intensively the demand for the
development of alternative selective catalyst systems is
3]
hexene fraction.[1a,
In 2002 Wass et al. at BP chemicals
discovered P-ortho-methoxyaryl diphosphinoamines to be
excellent ligands for trimerization catalysts in combination with
CrCl3(THF)3 and a large excess of MAO as cocatalyst in toluene.
The Wass system achieved high activities and an 1-hexene
purity within the C6 fraction above 99.9 Wass assumed the oMe
group at the aryl substituent to act as a pendant donor to the
chromium center.[4] Later on Bollmann et al. at Sasol found the
possibility to switch the Wass system towards octene (C8) when
omitting the ortho methoxy group. The combination of the
NiPr(PPh2)2 ligand, CrCl3(THF)3 and MAO as cocatalyst leads to
32.7 % C6 (86.5 % 1-C6) and 60.6 % octene (99.2 % 1-C8).[5]
As reported by Blann and Overett et al. at Sasol ortho alkyl
substituted derivatives (without donor functionality) proved to be
highly active and selective towards ethene trimerization (93 %
C6; 99.8 % 1-C6) when combined with CrCl3(THF)3 and MAO.
They claimed that the sterical demand of the aryl substituents in
Ar2PN(R)PAr2 has an effect on the product distribution.[6]
McGuinness and coworkers took up the ideas of pendant donor
functionalities as well as encumbered ligands and performed
theoretical and experimental investigations. They could find a
relation between additional donors at the ligands or different
coordinating anions as well as steric bulk and the selectivities in
the oligomerization reaction.[7] Even NOVA Chemicals
developed a oligomerization system based on a PNP type ligand
similar to the (Ph)2PN(iPr)P(Ph)2 of Sasol differing in that at least
one halide substituent is directly bound to at least one
phosphorus atom of the ligand. Their catalyst system results in a
mixture of C6 (20-40 %) and C8 (35-75 %) and reaches purities
above 95 % within in the 1-olefin fractions.[8] The group of
Rosenthal et al. in an association with SABIC and Linde
succeeded in developing another highly selective trimerization
system using a PNPNH ligand, which is used in combination
immense.[1]
A selective trimerization of ethene was first
described by Manyik et al. at Union Carbide Corporation in the
late 1960s.[2] Thereupon a multitude of selective oligomerization
systems were invented and investigated in order to produce
LAOs which match the market demand. A lot of these systems
lack of sufficient activity combined with highest selectivity to 1-
hexene (1-C6). High purities of the hexene (C6) fraction is
essential for the use of 1-hexene as comonomer. Herein we
present a P-N-P based ligand class that leads to high C6
percentages with very high purities within the hexene fraction.
Moreover a correlation between the ligands structure and the
product distribution in the catalyzed oligomerization reaction
could be observed.
[a]
M. Höhne, Dr. N. Peulecke, K. Konieczny, Dr. B. H. Müller, Prof. U.
Rosenthal*
Leibniz Institute for Catalysis at the University of Rostock
Albert-Einstein-Str. 29A, 18059 Rostock (Germany)
E-mail: uwe.rosenthal@catalysis.de
Supporting information for this article is given via a link at the end of
the document.((Please delete this text if not appropriate))
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10.1002/cctc.201700448
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with Cr(acac)3. In dependence on the cocatalyst it is possible to
change the product distribution and the purity of its fractions. It is
possible to reach 92.2 % C6 containing 99.0 % 1-C6 when
using AlEt3.[9]
Now we could shows that a diphosphinoamine ligand neither
requires two sterical demanding substituents nor a chlorine atom
at the phosphorus centers of for a highly active
Table 1. Different catalyst systems for the selective oligomerization of ethylene.
company
year
catalyst, cocatalyst
Cr-source; AlEt3
ligand
product distribution
> 90 % C6
purity of fraction
n.d.
Chevron
1990´s
Phillips[1a, 10]
BP[4]
2002
CrCl3(THF)3; MAO
91.5 % C6
99.7 % 1-C6
Sasol[5-6]
2004
2004
CrCl3(THF)3; MAO
CrCl3(THF)3; MAO
C6/C8 (32.7
/60.6 %)
%
86.5
99.2 % 1-C8
%
1-C6/
93.0 % C6
99.8 % 1-C6
NOVA
2012
2015
Cr-source, MAO
C6/C8 (20-40
C6/ 35-75 % C8)
%
> 95 %
Chemicals[8]
SABIC, Linde[9, 11]
Cr(acac)3; MAO
Cr(acac)3; AlEt3*
Cr(acac)3; MMAO
C6/C8 (28.7
/61.8 %)
%
%
78.3
97.4 % 1-C8
%
1-C6/
C6/C8 (92.2
/0.4 %)
99.0
65.8 % 1-C8
%
1-C6/
herein
2016
94.7 % C6
99.9 % 1-C6
* With additition of 8 eq. DoTriMAC (dodecyltrimethylammonium chloride).
and selevtive trimerization catalyst system. To date there is no
system with such an extraordinary C6 selectivity and high 1-
hexene purity within it.
The ligands reported in this study are shown in Scheme 1 and
were prepared as reported previously by Rosenthal et al. and
references therein.[12] Dichloroarylphosphanes 2a – 4a were
made by reacting the aryl halide with magnesium in THF. The
resulting Grignard reagents were treated with a large excess of
phosphorus trichloride to avoid multiple substitution of the PCl3.
As starting with the aryl bromide compound 3a requires an
additional halogen exchange with ZnCl2 to convert the ArPX2 (X
= Cl, Br) species into the bis-chloroarylphosphine. Due to the
extended substituents at the aryl part, the reaction with
heptamethyldisilazane proceeded very slowly. To avoid high
reaction temperatures, which cause several byproducts, DMF
was used as solvent.
Scheme 1. Preparation of compounds 1-5 and structural data of 1, 4, 5 based on Rosenthal et al.[11] *When starting with the bromide (in
case of 3a) an additional halogen exchange with ZnCl2 is necessary to avoid mixtures of the Cl/Br and Br/Br species.
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Table 2. Ethene oligomerization using ligands 1-5 under different parameters.
Exp.no.
(Ligand)
activity
solvent
t [min]
Products [g] [kg/(gCr*h)]
C4
C6 (1-C6)
C8
C10+
solid [g]
1 (1)
toluene
60
60
60
40
60
30
60
60
32
30
60
60
90
60
90
30
60
60
25
0
0.0
n.d.
4.4
1.6
0.8
1.4
0.9
1.0
0.3
0.9
0.8
0.7
0.6
1.0
2.1
1.1
0.8
n.d.
2.8
0.6
n.d
n.d.
n.d.
18.6
9.0
6.4
8.9
6.4
5.4
5.5
4.1
5.5
4.9
6.9
3.9
4.8
5.2
3.5
n.d.
8.7
4.9
-
2 (1)
chlorobenzene
toluene
20
25
80
35
80
70
50
80
80
77
88
60
15
40
80
0
19.2
24.0
115.4
33.7
153.9
67.3
48.1
144.3
153.9
74.1
84.6
38.5
14.4
25.7
153.9
0.0
26.4 (48.0)
86.9 (99.4)
89.4 (99.4)
86.9 (99.4)
89.6 (99.4)
86.5 (99.2)
92.0 (99.1)
94.7 (99.9)
93.5 (99.9)
94.1 (99.9)
92.2 (99.9)
94.6 (99.8)
92.2 (99.8)
93.4 (99.7)
95.4 (99.8)
n.d
50.6 (98.4)
2.5 (98)
3.1 (99+)
2.8 (99+)
3.1 (99+)
7.1 (99)
2.2 (99)
0.3 (99+)
0.2 (99+)
0.3 (99+)
0.3 (99+)
0.5 (99+)
0.9 (99+)
0.3 (99+)
0.3 (99+)
n.d.
1.20
0.45
2.60
0.40
1.80
2.0
3 (2)
4 (2)
chlorobenzene
toluene
5 (3)
6 (3)
chlorobenzene
chlorobenzene
toluene
7 (3)A
8 (3)B
9 (4)
7.5
toluene
0.45
2.45
0.38
2.20
0.9
10 (4)
11 (4)*
12 (4)*
13 (4)*A
14 (4)*B
15 (4)*C
16 (4)*D
17 (5)
18 (5)
19 (6)
chlorobenzene
toluene
dichlorobenzene
toluene
toluene
10.0
0.25
0.57
-
toluene
toluene
toluene
chlorobenzene
toluene
45
80
43.3
184.3
30.6 (59)
57.9 (98)
0.4 (99+)
0.7
94.1 (99.9)
1.20
C4, C6, C8, C10+ wt% in the liquid fraction; standard reaction conditions are: pethene = 30 bar, T = 50 °C, co-catalyst = 4.0 mL MMAO-3A (7 wt% Al in n-
heptane), 96.0 mL solvent, [Cr] = 0.002 mmol/L, [Ligand]/[Cr] = 1.5, [Al]/[Cr] = 375 *ligand with Cl/Br-isomers. A) 30°C, B) 75 °C, C) 15 bar, D) 40 bar.
The polar aprotic solvent increases the SN2 reaction rate as it
stabilizes the nucleophilic character of the intermediate. Thus
the reaction temperature could be dramatically decreased from
140 °C for 1[13] without solvent down to 60 °C for 2 and 3 in DMF
and it was possible to isolate them in moderate yields. To
investigate the effect of varying the surrounding at the nitrogen,
compound 5 was prepared as published by Rosenthal et al.[12a]
The molecular structure of 1, 4 and 5 could be obtained and
were discussed in a former publication.[12a] Neither the increase
of the sterical demand at the phosphorus atoms nor the insertion
of space filling substituents at the nitrogen center led to a
smaller P-N-P angle when compared to 1. Both angles (Scheme
1 ligand 4 and 5) are obviously widened.
All compounds 1-5 were tested in oligomerization reaction of
ethene according to a standard procedure (see experimental
part). Table 2 presents the results of the catalyzed selective
oligomerization under different parameters (p, T, solvents).
In toluene ligand 1 does not show any activity at all. Switching
the solvent to chlorobenzene could effect an increase in activity
and leads to a mixture of C6 (26.4 %, 48.0 % 1-C6) and C8
(50.6 %, 98.4 % 1-C8).
With respect to prior investigations the sterical demand of one
substituent at the phosphorus was raised and its effect on the
catalysis reaction was examined. Thereby it was possible to
observe a correlation between the catalyst´s structure and the
product distribution of the oligomerization reaction.
Whereas the (PPhCl)2NMe (1) shows nearly no activity and
accordingly leads to
a
product mixture of C6/C8 in
chlorobenzene (exp. no. 2), the insertion of even ortho-methyl
groups at the P-aryl substituent (2) causes a tripling of the 1-C6
percentage (in chlorobenzene from 26.4 up to 89.4 %) as well as
a sixfold activity (from 19.2 kg/gCr*h up to 115.4 kg/gCr*h) and a
remarkable increase in the purity of the 1-olefin fraction (48.0 %
up to 89.4 % 1-C6).
The successive increase of sterical bulk at the aryl substituents
provokes a continuous shift towards 1-C6 which climaxes in a
maximum for ligand 4 in exp. no. 9, 10 and 16. Ligand 4 seems
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to act as part of a very active catalyst which procures C6
percentages up to 95.4 % and purities up to 99.9 % 1-C6.
According to NOVA Chemicals there must be at least one
chlorine bound to at least one phosphorus center to be essential
for the trimerization reaction.[8] Due to the very similar product
contributions (in range of 92.2 to 95.4 % C6) and purities within
the C6 fractions (1-C6 > 99.7 %) when using mixed halides (4*)
we claim an in situ conversion of the N,N-bis{chloro(aryl)-
phosphino}-amines into the methylated species due to the large
excess of cocatalyst (MMAO). These N,N-bis{methyl(aryl)-
phosphino}-amines would belong to the actually active catalyst
species in the oligomerization reaction of ethene.
These data as well as the very similar results in the
oligomerization reaction support our assumption of the in situ
methylation.
The activities exhibits a larger range (from 14.4 to 153.9
kg/(gCr*h)) when using 4 or 4* in the oligomerization reaction.
This probably depends on several parameters e.g. on the
solvent, temperature or the halides within the catalytic system.
Chlorinated solvents generally lead to somewhat higher
activities, what has already been investigated as a halide effect.
Suitable halide compounds could significantly enhance both, the
selectivity towards 1-C6 and the catalytic activity.[14] Furthermore
chlorides do obviously show a more positive effect on the
catalytic activity than their corresponding bromides or iodides.
This could explain the lower activities when using the mixed
halogenated ligand 4. Furthermore the in situ methylation of the
different halides (4 and 4*) might take place with different
reaction rates and yields what can impact the concentration of
the active catalyst species ant therefor on the activity.
Scheme 2. Preparation of 6 by reacting 4 with a methyl Grignard reagent.[11]
To prove this hypothesis ligand 6 was prepared directly by the
reaction of 4 with the methyl Grignard (see Scheme 2). It was
tested using the standard procedure and showed a very similar
product contribution (94.1 % C6) and purities (99.9 % 1-C6)
within the C6 fractions when compared to ligand 4.
An enlargement of the steric bulk at the nitrogen´s substituent
has already been discussed to have an effect on the alpha
selectivity or even to increase 1-C6 selectivity.[15] In order to
compare the effect of increasing the bulkiness at the phosphorus
(1-4, 6) to that at the nitrogen, compound 5 was prepared and
tested in the oligomerization reaction. As depicted in Table 2 5
shows no activity all when the catalysis is performed in toluene.
If the same experiment was run in dichlorobenzene it results in a
C6/C8 (30.6 % C-6/ 57.9 % C-8) mixture with low activity. These
values resemble the C6/C8 ratios and activity of exp. 2 when
applying the unsubstituted ligand 1. Accordingly, the more space
filling N-substitution could not be identified to be responsible for
the product distribution in the oligomerization experiment.
Furthermore, the ability of the PNP ligands to bridge two metal
centers was postulated to allow a binuclear mechanism which
would be reasonable for the tetramerization of ethene by
Rosenthal[16] and Gambarotta et al.[17] Due to the large sterical
demand of the herein reported ligands there might be not
enough space to allow a binuclear catalyst species and leads to
C6 instead. McGuinness and coworkers presented a mono- and
bis-ethylene route: the increasing demand of the ligands hinders
the coordination of further ethene monomers what rather leads
to 1-hexene.[7, 18]
Compared to the dichloro compound 4 the corresponding 31P
NMR resonances of the methylated analogue 6 are round about
100 ppm highfield shifted (from 140/138 to 49/41 ppm).
When adding some MMAO - as it is used in the standard
procedure – to 4, we are able to observe an equivalent highfield
shift (see Figure 1) what might be caused by the reaction with
the cocatalyst MAO. Due to the inhomogeneous nature of MAO
especially MMAO-3A (modified MAO containing differently
alkylated species) there exist different alkylated species of 4.
Both, the broadening and shifting of the signals (when compared
to pure 6 in deuterated solvent) ought to be a consequence of
coordination to the aluminium centers as it can be shown by
adding some MMAO to 6.
Conclusion
In contrast to other publications which discuss a necessity of a
hemilabile donor ligand (oMe etc.) in ortho position of the P-aryl
6b]
group,[4,
the presence of two space filling ortho substituted
aryl substituents at the phosphorus centers[6a] or a chlorine
bound at least to one phosphorus[8] we could reveal that one
sterically demanding substituent per phosphorus center is
sufficient for excellent 1-C6 selectivity. Even the chlorine does
not have to be bonded to the phosphorus as it could be shown
by means of the catalyzed trimerization reaction under use of
the methylated ligand 6 as well as the mixed halide species 4*.
Besides the very similar activities of 4, 4* and 6 indicates an in
Figure 1. Comparison of the 31P NMR spectra of 4 and 6, respectively (with
and without addition of MMAO).
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extracted with n-hexane. After removing the solvent in vacuum the
product was purified by distillation (1·10-2 mbar. 250 °C) (Yield: 2.240 g.
0.001 mol. 26 %). 3) The Mes-PCl2 (2.240 g. 0.010 mol) was dissolved in
DMF (50.0 mL). 0.5 eq. of MeN(SiMe3)2 (0.860 g. 0.005 mol) was added.
The solution was stirred for 2 days at 50 °C before the solvent was
removed in vacuum. The residual oil was extracted twice with n-hexane
and the product was precipitated as a white solid at – 78°C. Compound 3
was obtained as a diastereomeric mixture (ratio 41:59). Yield (isolated):
1.038 g (2.60·10-3 mol, 52 %). Yield overall: 1.038 g (2.60·10-3 mol,
7 %).1H NMR (300 MHz, C6D6, 298 K): δ (ppm) 6.65-6.59 (m, 4H, m-ArH),
2.78 (t, 2JHP = 5.9 Hz, 3H, NCH3. major), 2.72 (t, 2JHP = 5.7 Hz, 3H, NCH3.
minor), 2.62 (br s, 12H, CH3, o-ArCH3, minor), 2.59 (br s, 12H, CH3, o-
ArCH3, major), 1.99 (br s, 6H, CH3, p-ArCH3). 13C (75 MHz, C6D6, 298 K):
δ (ppm) 143.2 (i-ArC), 141.3 (ArCH), 141.1 (ArCH), 131.2 (p-ArC), 35.6
(NCH3), 23.4 (CH3), 20.9 (CH3). 31P (121 MHz. C6D6, 298 K): δ (ppm)
140.6 (minor), 139.9 (major). IR (neat, cm-1, 298 K): ν = 2869 (w), 2922
(m), 2961 (m), 2995 (w), 3022 (w). MS (CI): m/z 400 [C19H25Cl2NP2]+,
384 [C18H22Cl2NP2]+, 364 [C19H25ClNP2]+, 216 [C10H14ClNP+2]+, 180
[C10H14NP+1]+. Element. Anal. Calcd. for C19H25Cl2NP2 (399.08 g/mol): C
57.01, H 6.30, N 3.50, P 15.48. Found: C 57.09, H 6.28, N 3.51, P 15.34.
M.p.: 120 °C.
situ methylation and thus, the N,N-bis{methyl(aryl)-phosphino}-
amines to be part of the active species in the catalysis reaction.
Experimental part
All synthetic work was carried out under oxygen- and moisturefree
conditions using standard Schlenk and Glovebox techniques. THF, n-
hexane and toluene were purified with a Grubbs type column system
Pure Solv MD-5. Deuterated solvent C6D6 was dried over
Na/benzophenone and freshly distilled prior to use. Other chemical
reagents and solvents were obtained from commercial sources and used
without further purification. NMR: 31P{1H}, 13C{1H}- and 1H-NMR spectra
were recorded on BRUKER spectrometers AVANCE 300 and AVANCE
400, respectively. The 1H and 13C NMR chemical shifts were referenced
to the solvent signals (C6D6). The 31P NMR chemical shifts are referred to
H3PO4 (85%). Elemental analysis: C, H, N: Leco TruSpec Micro CHNS
Elementaranalysator. P: ICP-OES Varian/Agilent 715-ES. IR: Bruker
Alpha FT-IR. MS: Thermo Electron MAT 95-XP (CI, EI). Melting Points
are uncorrected (Mettler Toledo MP70). Heating-rate 3 °C min-1 (unless
otherwise stated the clearing points are reported.)
Synthesis of C19H25Cl2NP2 (4/4*): For synthesis and characterization
see Rosenthal et al.[12a] 4* is the crude product before the halogen
exchange with ZnCl2.
Synthesis of C12H12Cl2NP2 (1): The synthesis was done according to
Jefferson et al.[13] For description and characterization see Rosenthal et
al.[12a]
Synthesis of C18H28Cl2NP2 (5): For synthesis and characterization see
Rosenthal et al.[12a]
Synthesis of C17H21Cl2NP2 (2): The reaction was held in several steps.
1) 2-chloro-1.3-dimethylbenzene (3.000 g. 0.021 mol) and 1.1 eq. of
magnesium (0.563 g. 0.023 mol) were refluxed in THF (50.0 mL) for 1
day. 2) After cooling to room temperature the resulting solution was
filtered via cannula to a cooled solution (-78°C) of 10 eq. of PCl3 (18.4
mL. 0.210 mol) in THF. The resulting solution was allowed to warm up to
room temperature overnight. After removing the solvent in vacuum the
resulting residue was extracted with n-hexane. Afterwards the Ar-PCl2
could be crystallized from n-hexane. Yield: 3.203 g (0.015 mol, 74 %). 3)
The isolated Ar-PCl2 was added to a solution of 0.5 eq. of MeN(SiMe3)2
(1.7 mL. 7.77·10-3 mol) in DMF and heated at 60°C. After 3 days the
DMF was removed in vacuum. The resulting residue was dissolved in hot
n-hexane, filtrated and cooled to -78°C. A white solid precipitated and
could be isolated. It was recrystallized from n-hexane. Compound 2 was
obtained as a diastereomeric mixture (ratio 39:61). Yield (NMR): 76 %;
yield (isolated): 1.670 g (4.51·10-3 mol, 58 %). Yield overall: 1.670 g
(4.51·10-3 mol, 42 %). 1H NMR (400 MHz, C6D6, 298 K): δ (ppm) 6.99-
6.91 (m, 2H, p-ArH), 6.81-6.74 (m, 4H, m-ArH), 2.69 (t, 2JHP = 6.0 Hz, 3H,
NCH3, major isomer), 2.69 (t, 2JHP = 5.5 Hz, 3H, NCH3, minor), 2.58 (br s,
12H, o-ArCH3, minor), 2.55 (br s, 12H, o-ArCH3, major). 13C (100 MHz,
C6D6, 298 K): δ (ppm) 143.2 (i-ArC), 133.2 (o-ArC), 131.3 (m-ArC, minor),
131.2 (m-ArC. major), 130.4 (p-ArC), 35.8 (NCH3), 23.5 (o-ArCH3, minor),
23.3 (o-ArCH3. major). 31P (162 MHz, C6D6, 298 K) δ (ppm) 139.6 (minor),
139.3 (major). IR (neat, cm-1, 298 K): ν = 2867 (w), 2928 (w), 2969 (w),
2997 (w), 3052 (w). MS (CI): m/z 323 [C16H18ClNP2+2]+, 171 [C8H9ClP]+.
Element. Anal. Calcd. for C17H21Cl2NP2 (372.21 g/mol): C 54.86, H 5.69,
N 3.76, P 16.64. Found: C 54.83, H 5.69, N 3.82, P 16.78. M.p.: 147 °C.
Synthesis of C33H55NP2 (6): 0.56 mL (1.68·10-3 mol) MeMgCl (3M in
THF) was added at 0°C to a stirred solution of 0.475 g (0.84·10-3 mol) of
4 in THF (10.0 mL). The solution was stirred for 48 hrs at room
temperature and afterwards all volatiles were removed in vacuum. N-
Pentane was added to precipitate MgCl2. After filtration, the supernatant
was stored at - 40°C for several days to give 0.222 g (0.42·10-3 mol) of
colourless crystals of 6. Compound 6 was obtained as a diastereomeric
mixture (ratio 48:52). Yield: 0.222 g (0.42·10-3 mol, 50 %). 1H NMR (300
MHz, C6D6, 298 K): δ (ppm) 7.15-7.05 (m, 8H, ArH), 4.32-4.15 (m, 8H,
iPr-CH), 3.31-3.21 (m, 2H, iPr-CH, minor), 2.81-2.65 (m, 2H, iPr-CH,
3
major), 2.64 (t, 3JHP = 3.7 Hz, 3H, N-CH3, minor), 2.62 (t, JHP = 6.8 Hz,
3H, N-CH3, major), 1.71 (t, 2JHP = 5.4 Hz, 3H, P-CH3, major), 1.57 (t, 2JHP
i
= 5.1 Hz, 3H, P-CH3, minor), 1.36-1.23 (m, 48H, Pr-CH3), 1.20-1.15 (m,
24H, iPr-CH3). 13C (100 MHz, C6D6, 298 K) δ (ppm) 154.7 (o-ArC, t, 2JCP
2
= 8.0 Hz, major), 154.6 (o-ArC, t, JCP = 7.9 Hz, minor), 150.4 (p-ArC,
major), 150.3 (p-ArC, minor), 133.5 (i-ArC, s, minor), 133.4 (i-ArC, s,
2
major), 122.2 (m-ArC, s, minor + major), 34.9 (NCH3, t, JCP = 5.0 Hz,
2
minor), 32.3 (NCH3, t, JCP = 6.2 Hz, major), 34.7 (iPrCH, br s, minor +
3
3
major), 30.9 (iPrCH, t, JCP = 11.2 Hz,), 30.5 (iPrCH, t, JCP = 12.6 Hz,
minor), 25.6 (iPrCH3, br s), 25.4 (iPrCH3, br s), 25.2 (iPrCH3, br s), 24.9
(iPrCH3, br s), 24.2-24.0 (iPrCH3, m), 15.4 (t, 1JCP = 5.1 Hz, PCH3, minor),
15.0 (t, 1JCP = 5.4 Hz, PCH3, major). 31P (121 MHz. C6D6, 298 K): δ (ppm)
48.3 (minor), 44.8 (major). IR (neat, cm-1, 297 K): ν = 2798 (w), 2841 (w),
2841 (w), 2869 (m), 2930 (m), 2957 (s), 3040 (w). MS (CI): m/z 528
[C33H55NP2]+, 512 [C32H52NP2]+, 484 [C30H48NP2]+, 324 [C18H32NP2]+, 278
[C17H29NP]+. Element. Anal. Calcd. for C33H55NP2 (527,76 g/mol): C
75.10, H 10.50, N 2.65, P 11.74. Found: C 74.88, H 10.51, N 2.65, P
11.47. M.p.: 96 °C.
Synthesis of C19H25Cl2NP2 (3): The synthesis was done in three steps.
1) Mes-Br (7.59 g. 0.038 mol) was added to a stirred suspension of 1.1
eq. Mg (1.000 g. 0.040 mol) in THF (40.0 mL). The resulting mixture was
stirred until the magnesium chips have almost vanished. 2) The grey
green coloured solution was filtered via cannula to a cooled solution (-
78 °C) of 10 eq. PCl3 (33.30 mL. 0.380 mol) in THF (40.0 mL). The
stirred solution became yellow and was allowed to warm to room
temperature overnight. Afterwards the THF was removed in vacuum and
the resulting residue was extracted with n-hexane to get rid of the
magnesium salt. After evaporation of the n-hexane. the intermediate
product, Mes-PXY (X= Cl, Br. Y= Cl, Br), was redissolved in THF. In
order to isolate the chlorinated product, a halogen exchange was done
by adding an excess of ZnCl2 (12.000 g. 0.088 mol). It was stirred
overnight at 60 °C before the THF was removed and the residue was
Standard Ethene Oligomerization Reaction was carried out as follows:
A 300 ml pressure reactor, equipped with a dip tube, thermowell, gas
entrainment stirrer, cooling coil, and control units for temperature,
pressure and stirrer speed (all hooked up to a data acquisition system)
was inertized with dry argon. The isobaric ethene supply was maintained
by an aluminum pressurized gas cylinder on a balance to monitor the
ethene consumption over time by means of
a computerized data
acquisition system. For the catalyst preparation, the suitable amounts of
the ligands and the chromium precursor according to the molar ratios
given in Table 2 were weighed and charged to a Schlenk tube under an
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10.1002/cctc.201700448
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FULL PAPER
inert atmosphere. A volume of 95.0 ml anhydrous solvent was added and
the solution was stirred by means of a magnetic stirrer. After dissolving
the Cr-compound and ligand, the appropriate amount of a solution of
MMAO-3A (7 wt% Al in heptane) was added. The solution was
immediately transferred to the reactor and the reaction was started. The
reaction was stopped either when the maximum uptake of ethene
(80.000 g) was reached or after a predefined time (60 min) by closing the
ethene inlet valve, cooling to room temperature, depressurizing and
opening the reactor. The liquid product mixture was quenched with
diluted HCl and analyzed using gas chromatography. The sideproduct
solids (waxes, polyethylene) were filtered, dried and weighed. Before
conducting an experiment, the reactor was heated to 100 °C at reduced
pressure for several hours to eliminate traces of water, oxygen and
oxygenated impurities.
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Keywords: oligomerization • ethene • chromium •
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10.1002/cctc.201700448
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Layout 2:
FULL PAPER
Martha Höhne, Normen Peulecke,
Katharina Konieczny, Bernd H. Müller
and Uwe Rosenthal*
Page No. – Page No.
Chromium Catalyzed Highly Selective
Oligomerization of Ethene to 1-
Hexene with N,N-bis{chloro(aryl)-
phosphino}-amine Ligands
Different N,N-bis{chloro(aryl)-phosphino}-amines were found to form highly active
and selective trimerization catalysts which lead to purities of the hexene fraction up
to 99.9 % of 1-hexene. Furthermore, an in situ methylation of the chlorinated
ligands into the N,N-bis{methyl(aryl)-phosphino}-amines is supposed.
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