Catalytic Systems Based on Chromium(III) Silylated-Diphosphinoamines for Selective Ethylene Tri-/Tetramerization

Article abstract of DOI:10.1021/acscatal.8b02698

The N-substituents on the backbone of Ph₂PN(R)Si(CH₃)₂CH₂PPh₂- and [Ph₂PCH₂Si(CH₃)₂]₂N(R)-type silylated-diphosphinoamine (Si-PNP) systems have been observed to have a significant impact on their catalytic performance in ethylene oligomerization reactions. Cr precatalyst 3, bearing an isopropyl (ⁱPr) substituent, affords the most efficient catalytic system and exhibited the highest selectivity (83%) toward 1-octene (1-C₈) and showed a catalytic activity of more than 76,700 g(product)·g(Cr)^-1·h^-1 under experimental conditions. Single-crystal analysis results revealed the influence of steric constraints around the catalytically active center and established a relationship between the product selectivity and the P-Cr-P bite angle. Furthermore, DFT calculations indicate that the catalytic system based on precatalyst 3 faces a low energy barrier in the formation of 1-C₈ and therefore shows high selectivity toward the 1-C₈ fraction. Modification in the backbone length may alter the binding mode of the ligands from mononuclear-bidentate (k²-P, P) to mononuclear-tridentate (k³-P, N, P), which consequently switches the ethylene tetramerization systems to ethylene trimerization systems.

Full text of DOI:10.1021/acscatal.8b02698

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Article
Catalytic Systems Based on Chromium(III) Silylated-
Diphosphinoamines for Selective Ethylene Tri-/Tetramerization
Fakhre Alam, Le Zhang, Wei Wei, Jiadong Wang, Yanhui Chen, Chunhua Dong, and Tao Jiang
ACS Catal., Just Accepted Manuscript • DOI: 10.1021/acscatal.8b02698 • Publication Date (Web): 10 Oct 2018
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Catalytic Systems Based on Chromium(III)
SilylatedꢀDiphosphinoamines for Selective Ethylene
Triꢀ/Tetramerization
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†
†,‡
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*,‡
Fakhre Alam, Le Zhang, Wei Wei, Jiadong Wang, Yanhui Chen, Chunhua Dong, Tao
*
,†
Jiang
†
College of Chemical Engineering and Material Science, Tianjin University of Science and
Technology, Tianjin 300457, China
‡
Handan Key Laboratory of Organic Small Molecule Materials, Handan University, Handan
0
56005, China
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ABSTRACT: The Nꢀsubstituents on the backbone of Ph PN(R)Si(CH ) CH PPh ꢀ and
2
3 2
2
2
[
Ph PCH Si(CH ) ] N(R)ꢀtype silylatedꢀdiphosphinoamine (SiꢀPNP) systems have been
2 2 3 2 2
observed to have a significant impact on their catalytic performance in ethylene oligomerization
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reactions. Cr precatalyst 3, bearing an isopropyl ( Pr) substituent, affords the most efficient
catalytic system and exhibited the highest selectivity (83%) toward 1ꢀoctene (1ꢀC ) and showed a
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ꢀ1
ꢀ1
catalytic activity of more than 76,700 g(product)·g(Cr) ·h under experimental conditions.
Singleꢀcrystal analysis results revealed the influence of steric constraints around the catalytically
active center and established a relationship between the product selectivity and the PꢀCrꢀP bite
angle. Furthermore, DFT calculations indicate that the catalytic system based on precatalyst 3
faces a low energy barrier in the formation of 1ꢀC and therefore shows high selectivity toward
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1
ꢀC fraction. Modification in the backbone length may alter the binding mode of the ligands
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2
3
from mononuclearꢀbidentate (k -P, P) to mononuclearꢀtridentate (k -P, N, P), which
consequently switch the ethylene tetramerization systems to ethylene trimerization systems.
KEYWORDS: ethylene, trimerization, tetramerization, αꢀolefins, silylatedꢀdiphosphinoamine
ligands, chromium, catalysis, DFT calculations
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Introduction
From an industrial perspective, linear αꢀolefins (predominantly 1ꢀhexene and 1ꢀoctene) have
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attracted significant and prolonged attention over the last two decades. In contrast to
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conventional ethylene oligomerization technologies, which produce a broad range of products,
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many ethylene trimerization and tetramerization facilities are now actively involved in the
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b, 2a, 3
selective production of highly demanded and valuable 1ꢀhexene and 1ꢀoctene.
Although a
1
b, 4
general mechanism involving a metallacycle has been established,
many questions, in
particular the oxidation state of the active metal, the origin of the unusual selectivity and the role
of the ligand in these catalytic transformations, remain elusive and therefore have inspired
1
b, 5
theoretical studies.
The Crꢀbased PNP diphosphines deliver the most efficient catalytic systems for ethylene
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tetramerization with the capability of producing 1ꢀoctene with 70% selectivity. Attempts in
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a, 7
further enhancement, many alternative ligands with diphosphines scaffolds
were made and
scrutinized for selective ethylene tetramerization; however, these modifications proved
unproductive. Consequently, investigations were extended to ligands beyond the diphosphine
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2b, 8ꢀ9
framework, and other alternatives were identified for selective ethylene tetramerization.
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d, 10
To elucidate the origin of the high selectivity and the role of the Cr redox dynamism,
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Albahily et al. altered the ligand framework by substituting the methylene carbons flanking the
nitrogen with dimethyl silyl groups (large electropositive substituents may control the
12
stereochemistry of the reaction and influence the structure of the complex ) of the most efficient
13
CrꢀSNS trimerization system, and found that a simple modification in the ligand framework
1
4
had a profound effect on the catalytic activity of the CrꢀSNS system. Subsequently, Zhang et al.
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incorporated silyl groups into the diphosphine framework and established a new class of efficient
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tetramerization catalysts with the potential to deliver as much as 16.8×10 g(product)·g(Cr) ·h
high catalytic activity with 99% total αꢀselectivity.
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1, 14
Considering the unique properties of siliconꢀbased ligands
and their ability to increase the
activity and selectivity toward αꢀolefins, we aimed to design and use a new class of silylatedꢀ
PNP (SiꢀPNP) ligands for selective ethylene oligomerization. The Cr catalysts with the target Siꢀ
PNP ligands were successfully activated for triꢀ/tetramerization, providing 83% C selectivity
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ꢀ1 ꢀ1
and more than 76,700 g(product)·g(Cr) ·h catalytic activity under appropriate conditions. The
high selectivity of the best catalytic system 3 was also rationalized by using DFT calculations.
Furthermore, the influence of backbone Nꢀsubstituents on the overall catalytic performance and
the relationship between the PꢀCrꢀP bite angle and the product selectivity have also been
established.
Results and discussion
1
3
Silylatedꢀdiphosphinoamine Ph PN(R)Si(CH ) CH PPh ꢀtype ligands (L -L ) were prepared
2
3 2
2
2
1
3
by a convenient salt metathesis method. Treatment of silylatedꢀPNP ligands L -L with
CrCl (THF) ] in dichloromethane afforded corresponding Cr(III) complexes 1-3 (Scheme 1).
[
3
3
The Cr(III) complexes 1-3 were not structurally characterized because single crystals suitable for
2
Xꢀray analysis could not be obtained; nonetheless, the singleꢀcrystal analysis of [Cr(CO) (L )]
4
2
(
Figure 1) suggested that these complexes adopt a mononuclear k -P, P bidentate binding mode.
1
3
To investigate the effect of backbone Nꢀsubstituents in ligands L -L on the catalytic
performance, Cr complexes 1-3 were subjected to catalytic testing. The results of ethylene
oligomerization screening of precatalysts 1-3 are summarized in Table 1.
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Scheme 1. Synthesis of silylatedꢀPNP ligands (L -L ) and Cr complexes (1-3)
At 1.0 MPa ethylene and 45 °C, in the presence of DMAO/Et Al cocatalyst, the precatalysts
3
(1-3) were found to be active in the selective triꢀ/tetramerization reaction (Table 1). Precatalyst 3,
i
bearing an Pr moiety, exhibited high selectivity (69%) toward 1ꢀoctene with considerable
catalytic activity (Table 1, entry 3). Increasing the steric bulk of the backbone Nꢀsubstituents by
i
replacement of the Pr group (in 3) with 2,6ꢀdiisopropylphenyl (in 2) and cyclopentyl (in 1)
diminished the catalytic activity and resulted in the production of more 1ꢀhexene at the expense
of 1ꢀoctene with increased polymer formation (Table 1, entries 1ꢀ2). Similar trends in selectivity
6a
7b
were reported for PNP and carbonꢀbridged diphosphine ligands in which an increase in the
steric bulk of the backbone Nꢀsubstituent decreases the 1ꢀoctene/1ꢀhexene ratio and increases the
production of 1ꢀhexene. The formation of a large amount of PE in almost all catalytic runs
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suggests that in addition to the selective oligomerization catalyst, an independent polymerization
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catalyst is also present in the system. The very low catalytic activities of precatalysts 1 and 2
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were attributed to their low stabilities.
The inadequate separation between the Cr cations and
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the counterions in the reaction medium may also contribute to the low catalytic activities.
These results indicate that the backbone Nꢀsubstituent in these ligands strongly affects the
catalytic performance.
a
Table 1. Ethylene Oligomerization with Novel SilylatedꢀPNP Based Complexes 1-3
Product selectivity (wt %)
b
d
Entry Precatalyst
Activity
PE (g)
c
c
c
c, f
c
C4
C6
1ꢀC6
96.38
92.91
85.44
cyꢀC6
1.45
2.57
4.89
C8
C ꢀC
10 14
1
2
3
1
2
925
842
3.83
2.93
˂1
54.63
50.97
33.96
41.54
46.10
69.16
Trace
trace
trace
1.23
1.97
0.67
e
3
7461
a
General conditions: n(precatalyst), 1.2 µmol; pressure, 1.0 MPa; solvent, methylcyclohexane
(20 mL); reaction time, 30 min; T, 45 °C; n(Al)/n(Cr), 500 equiv; n(DMAO)/n(AlEt ), 4:1;
3
b
ꢀ1 ꢀ1
c
d
e
g(product)·g(Cr) ·h ; wt % of liquid products (oligomers); wt of PE; n(precatalyst), 2.4
f
µmol; C contains 100% 1ꢀC .
8
8
To investigate the coordination chemistry and thus to elucidate the effect of the backbone Nꢀ
2
substituent on the catalytic performance of the SiꢀPNP ligands, the L ꢀbased Cr(CO) complex
4
2
was selected for singleꢀcrystal Xꢀray diffraction analysis. The reaction of L with [Cr(CO) ] in
6
2
2
refluxing toluene led to the formation of the desired [Cr(CO) (k -P, P-L )] complex (6, Scheme
4
2
). Single crystals suitable for Xꢀray diffraction analysis were obtained by slow diffusion of nꢀ
hexane into a CH Cl solution of 6 at ꢀ35 °C. The structure of complex 6 is illustrated in Figure
2
2
1
.
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Scheme 2. Synthesis of Cr complex 6 based on ligand L
Figure 1. Molecular structure of Cr complex 6 with partial thermal ellipsoids drawn at 50%
probability; H atoms and solvent molecules are omitted for clarity. Selected bond lengths (Å):
Cr1ꢀP1, 2.3883(10); Cr1ꢀP2, 2.4190(9); Cr1ꢀC1, 1.886(2); Cr1ꢀC2, 1.855(2); Cr1ꢀC3, 1.887(2);
Cr1ꢀC4, 1.863(2); selected bond angles (deg): P1ꢀCr1ꢀP2, 101.70(3); C1ꢀCr1ꢀP1, 92.61(7); C2ꢀ
Cr1ꢀP1, 89.25(7); C3ꢀCr1ꢀP1, 83.69(7); C4ꢀCr1ꢀP1, 172.96(6); C1ꢀCr1ꢀP2, 89.03(7); C2ꢀCr1ꢀP2,
1
68.96(7); C3ꢀCr1ꢀP2, 93.40(7); C4ꢀCr1ꢀP2, 85.32(7).
Complex 6, with a planar CrꢀPꢀCꢀSiꢀNꢀP ring, displays a distorted octahedral geometry. In 6,
the repulsion between the backbone Nꢀsubstituent (2,6ꢀdiisopropylphenyl) and the adjacent
Ph
2
phosphine phenyl groups (Figure 2) results in a smaller C ꢀP ꢀCr angle (average, 112.56°)
Ph
1
1
2
compared to the other C ꢀP ꢀCr angle (average, 116.63°). The large P ꢀCrꢀP bite angle
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Ph
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(
101.70(3)°) with the smaller C ꢀP ꢀCr angle in complex 6 favors the interaction between the
backbone substituent and the catalytic center and consequently hinders the coordination of
ethylene to the chromacycloheptane intermediate to form the chromacyclononane, which favors
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the formation of 1ꢀhexene (translated steric effect).
Furthermore, the extraꢀlarge P ꢀCrꢀP
bite angle may also be responsible for the weak coordination between the ligands and Cr
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precursors, which in turn delivers low catalytic activity.
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b, 17
PNP
Figure 2. Proposed steric interactions between the ligand and the metallacycle.
(L
=
Ph PN(2,6ꢀdimethylcyclohexyl)PPh ).
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2
The catalytic activity and product selectivity for ethylene oligomerization were strongly
influenced by the reaction conditions (catalyst mass, reaction temperature, Al/Cr molar ratio and
ethylene pressure). Therefore, to improve the catalyst performance, precatalysts 1-3 were further
investigated under different reaction conditions. Precatalysts 1-3 were first tested under various
reaction temperature, and the results are shown in Table 2. Increasing the reaction temperature
enhanced the catalytic activities of precatalysts 1-2 (Table 2, entries 4 and 8), and higher
temperature may help to activate the catalysts in these systems. Precatalyst 3 exhibits a relatively
high activity at 45 °C (Table 2, entry 10); however, a further increase in the temperature reduces
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the activity (Table 2, entries 11ꢀ12), showing that an increase in temperature from the optimum
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may lead to deactivation of precatalyst 3ꢀbased catalytic system.
Increasing temperature diminished the C selectivities and enhanced the C selectivities of
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precatalysts 1-3, which can be attributed to the more favored pathway of reductive elimination
for metallacycloheptane and the high rate of chain transfer rather than propagation, resulting
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9
more C fraction at a higher temperature. The lower ethylene concentration at higher
6
20
temperature may also decrease the selectivity toward C8.
4d, 15, 21
Like many other catalytic systems,
the cyclicꢀC6 (methylcyclopentane and
methylenecyclopentane) fraction was found in an almost 1:1 ratio in all the oligomerization
products. The branched coꢀoligomer C ꢀC products generated by precatalyst 1 is due to the
1
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secondary coꢀtrimerization and coꢀtetramerization reactions of 1ꢀhexene and 1ꢀoctene with
4
d, 15, 22
4d
ethylene.
The selectivity for this fraction was attributed to a ligand selectivity effect. The
amount of coꢀoligomerization products formed in a selective ethylene oligomerization is
4d
proportional to the productivity of the reaction. Thus, for precatalyst 1, more coꢀ
oligomerization products (C ꢀC ) were observed when the catalytic activity was high (Table 2,
1
0
14
entries 1ꢀ4; Table 3, entry 3; Table 4, entries 2ꢀ4 and Table 5, entries 1ꢀ4), while no coꢀoligomers
were seen when the activity was very low (Table 3, entries 1, 2 and 4; Table 4, entry 1). As
increasing temperature increases the catalytic activity which in turn promote the formation of coꢀ
oligomers at the expense of C and C and consequently decreases the αꢀselectivity of C and C
8
6
8
6
fraction (Table 2, entries 1ꢀ4). This indicates that for precatalyst 1, a higher temperature favors
coꢀoligomerization reaction.
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2
3
4
5
6
7
8
9
1
1
1
1
1
1
1
1
1
1
2
2
2
2
2
2
2
2
2
2
3
3
3
3
3
3
3
3
3
3
4
4
4
4
4
4
4
4
4
4
5
5
5
5
5
5
5
5
5
5
6
a
Table 2. Evaluation of the Effect of Reaction Temperature on Selective Oligomerization
Product selectivity (wt %)
b
d
Entry
Precatalyst T (°C) Activity
PE (g)
c
c
c
c, f
c
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
C4
C6
1ꢀC6
97.05
99.23
99.60
99.39
97.45
87.58
98.51
98.64
76.90
83.60
89.87
93.04
cyꢀC6
1.70
0.44
0.23
0.24
1.93
4.06
1.11
0.95
5.07
4.97
4.07
3.35
C8
C ꢀC
10 14
1
2
3
4
5
6
7
8
9
30
45
60
75
30
45
60
75
30
45
60
75
2096
3308
3500
4423
215
7.31
7.02
3.40
0.43
1.80
3.31
0.75
0.76
2.91
0.44
0.38
0.48
60.67
63.19
63.67
45.73
67.88
51.73
85.34
84.87
23.09
30.40
37.94
49.00
26.63
11.51
6.55
5.39
18.28
26.38
46.07
ꢀꢀꢀ
0.39
0.45
0.26
0.30
1.59
0.73
0.74
1.04
0.35
0.67
0.27
0.20
1
2
7.77
30.32
44.96
13.91
14.37
74.00
69.16
61.68
50.52
250
ꢀꢀꢀ
492
ꢀꢀꢀ
860
ꢀꢀꢀ
1381
7461
3538
2981
ꢀꢀꢀ
1
0
ꢀꢀꢀ
e
3
11
ꢀꢀꢀ
1
2
ꢀꢀꢀ
a
General conditions: n(precatalyst), 4.8 µmol; pressure, 1.0 MPa; solvent, methylcyclohexane
(20 mL); reaction time, 30 min; n(Al)/n(Cr), 500 equiv; n(DMAO)/n(AlEt ), 4:1;
3
b
ꢀ1 ꢀ1
c
d
e
g(product)·g(Cr) ·h ; wt % of liquid products (oligomers); wt of PE; n(precatalyst), 2.4
f
µmol; C contains 100% 1ꢀC .
8
8
The catalytic activities of precatalysts 1 and 3 increase with increasing catalyst loading up to a
certain limit (Table 3, entries 3 and 11) and then dramatically decrease (Table 3, entries 4 and
1
3). This decrease in activity may be explained by the fact that catalyst loadings above the
2
3
optimum concentration may interfere with the formation of the catalytically active species.
Alternatively, the high catalyst loading may limit the ethylene concentration, which leads to low
activity. Very high and very low catalyst loading was found to be inappropriate for the
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2
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4
5
6
7
8
9
performance of precatalysts 1 and 3. On the other hand, precatalyst 2 shows the opposite trend
for mass loading compared to what was seen for 1 and 3 (Table 3, entries 5ꢀ8). The results
obtained for precatalyst 2 show that only a small amount of precatalyst 2 is converted into the
2
3
1
1
1
1
1
1
1
1
1
1
2
2
2
2
2
2
2
2
2
2
3
3
3
3
3
3
3
3
3
3
4
4
4
4
4
4
4
4
4
4
5
5
5
5
5
5
5
5
5
5
6
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
active species during the oligomerization. For precatalysts 1 and 2, the octene to hexene ratio
OTH) decreases with increasing catalyst mass (Table 3, entries 1ꢀ8), showing that more C was
(
6
formed at the expense of C , while precatalyst 3 shows the opposite trend in C selectivity (Table
8
8
3
, entries 9ꢀ13). The selectivity switching between C and C for precatalysts 1-3 might be
8 6
8c, 24
attributed to a shift in the equilibria between different active species,
for the formation of C and C at different catalyst loadings.
which are responsible
6
8
Table 3. Evaluation of the Effect of Mass Loading of 1-3 Precatalysts on the Catalytic
a
Performance
Product selectivity (wt %)
Catalyst
mass (µmol)
b
d
Entry
Precatalyst
Activity
PE (g)
c
c
c
c, e
c
C4
C6
1ꢀC6 cyꢀC6
C8
C ꢀC
10
14
1
2
1.2
2.4
4.8
9.6
1.2
2.4
4.8
9.6
0.6
1.2
2.4
4.8
9.6
925
1233
3308
496
3.83 54.63 96.38
8.69 70.33 97.59
7.02 63.19 99.23
6.14 83.93 98.88
2.93 50.97 92.91
2.75 62.12 94.25
3.31 51.73 87.58
3.04 73.80 96.20
2.41 42.34 91.51
0.61 33.96 85.44
0.44 30.40 83.60
0.53 32.27 84.13
1.00 30.31 83.08
1.45
0.94
0.44
0.51
2.57
2.44
4.06
2.58
3.55
4.89
4.97
5.1
41.54
20.98
11.51
9.93
ꢀꢀꢀ
ꢀꢀꢀ
1.23
1.59
0.45
0.58
1.97
2.03
0.73
0.99
0.97
0.79
0.67
0.53
0.49
1
3
18.28
ꢀꢀꢀ
4
5
842
46.10
35.13
44.96
23.16
55.25
65.43
69.16
67.20
68.69
ꢀꢀꢀ
6
450
ꢀꢀꢀ
2
3
7
250
ꢀꢀꢀ
8
113
ꢀꢀꢀ
9
2173
5231
7461
7211
2019
ꢀꢀꢀ
10
ꢀꢀꢀ
11
ꢀꢀꢀ
1
1
2
3
ꢀꢀꢀ
4.94
ꢀꢀꢀ
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2
3
4
5
6
7
8
9
1
1
1
1
1
1
1
1
1
1
2
2
2
2
2
2
2
2
2
2
3
3
3
3
3
3
3
3
3
3
4
4
4
4
4
4
4
4
4
4
5
5
5
5
5
5
5
5
5
5
6
a
General conditions: pressure, 1.0 MPa; solvent, methylcyclohexane (20 mL); reaction time, 30
b
ꢀ1 ꢀ1 c
min; T, 45 °C; n(Al)/n(Cr), 500 equiv; n(DMAO)/n(AlEt ), 4:1; g(product)·g(Cr) ·h ; wt % of
3
d
e
liquid products (oligomers); wt of PE; C contains 100% 1ꢀC
8
8.
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
Generally, a higher Al/Cr ratio was found to be favorable for the activity of precatalysts 1-3
25
(Table 4), showing that excess cocatalyst was needed for complete activation. The coordination
6
strength of catalyst ionꢀpair and the extent of its separation may influence the C and C8
2
6
selectivity, which in turn related with the cocatalyst concentration. Increasing cocatalyst
concentration may increase the coordination strength of the ionꢀpairs of precatalyst 1 and 2,
resulting inadequate separation and block further ethylene uptake to chromacycloheptane to form
1
6
chromacyclononane. The chromacycloheptane may undergo βꢀhydride elimination and form
more C than C . Furthermore, increasing the cocatalyst ratio may increase the rate of chain
6
8
transfer to aluminum in precatalyst 1 and 2, which in turn may reduce the rate of chain growth of
chromacycloheptane to chromacyclononane and promote the βꢀhydride elimination in
2
7
chromacycloheptane, resulting more C (Table 4, entries 1ꢀ8). On the other hand, precatalyst 3
6
needs more cocatalyst for its complete activation, as its activity and C selectivity more enhanced
8
with the increase of cocatalyst concentration. Therefore, the available cocatalyst in the catalytic
system might be insufficient to promote chain transfer to aluminum in precatalyst 3 based
catalyst. Consequently, precatalyst 3 displays high catalytic activity and C selectivity at the
8
expense of C when the Al/Cr ratio is increased (Table 4, entries 9ꢀ12).
6
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2
3
4
5
6
7
8
9
a
Table 4. Evaluation of the Effect of Al/Cr Molar Ratios on Selective Oligomerization
Product selectivity (wt %)
b
d
Entry
Precatalyst
n(Al)/n(Cr)
Activity
PE (g)
c
c
c
c, f
c
C4
C6
1ꢀC6
cyꢀC6
1.2
C8
C ꢀC
10
14
1
2
3
4
5
6
7
8
9
100
300
500
700
100
300
500
700
100
300
500
700
296
2538
3308
2577
281
4.90 57.95 97.14
3.32 60.30 99.24
7.02 63.19 99.23
3.91 66.01 99.24
2.00 45.28 93.65
1.09 68.15 95.23
3.31 51.73 87.58
1.22 50.62 91.70
3.85 40.82 86.83
2.66 43.39 90.00
0.44 30.40 83.60
0.32 28.58 81.54
37.15
8.29
ꢀꢀꢀ
1.51
1.20
0.45
0.50
2.35
1.23
0.73
0.48
0.05
0.65
0.67
0.23
1
1
1
1
1
1
1
1
1
1
2
2
2
2
2
2
2
2
2
2
3
3
3
3
3
3
3
3
3
3
4
4
4
4
4
4
4
4
4
4
5
5
5
5
5
5
5
5
5
5
6
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
0.34
0.44
0.38
2.29
2.53
4.06
3.81
4.92
3.99
4.97
4.80
28.09
18.28
20.78
ꢀꢀꢀ
1
11.51
9.30
52.72
30.76
44.96
48.16
55.33
53.95
69.16
71.10
185
ꢀꢀꢀ
2
250
ꢀꢀꢀ
473
ꢀꢀꢀ
58
ꢀꢀꢀ
1
0
740
ꢀꢀꢀ
e
3
11
7461
13385
ꢀꢀꢀ
1
2
ꢀꢀꢀ
a
General conditions: n(precatalyst), 4.8 ꢁmol; pressure, 1.0 MPa; solvent, methylcyclohexane
b
ꢀ1 ꢀ1 c
(20 mL); reaction time, 30 min; T, 45 °C; n(DMAO)/n(AlEt ), 4:1; g(product)·g(Cr) ·h ; wt %
3
d
e
f
of liquid products (oligomers); wt of PE; n(precatalyst), 2.4 ꢁmol; C contains 100% 1ꢀC .
8
8
1
6, 28
The cocatalyst composition had a considerable impact on the catalyst behavior.
Therefore,
the effect of the DMAO/Et Al ratio on the catalytic behavior was investigated for precatalysts 1-
3
3
(Table 5). An optimum ratio of DMAO/Et Al is needed to completely activate the catalytic
3
system and thus produce a high activity. The use of a large amount of Et Al may deactivate the
3
1
6, 29
system while using less may not fully activate the catalytic system.
Precatalyst 1 shows the
lowest combine selectivity (C + C ) at the lowest DMAO/Et Al ratio (Table 5, entry 4). This
6
8
3
low combine selectivity of C and C might be attributed to the involving of these fractions in coꢀ
6
8
oligomerization reactions at these catalytic conditions, resulting more C ꢀC coꢀoligomers
10
14
which consequently decrease the selectivity of C and C fractions (Table 5, entries 1ꢀ4). On the
6
8
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2
3
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5
6
7
8
9
1
1
1
1
1
1
1
1
1
1
2
2
2
2
2
2
2
2
2
2
3
3
3
3
3
3
3
3
3
3
4
4
4
4
4
4
4
4
4
4
5
5
5
5
5
5
5
5
5
5
6
other hand, decreasing the DMAO/Et Al ratio switched the precatalyst 2ꢀbased catalytic system
3
to trimerization and resulted in the formation of more C It might be due to the chain transfer to
6
.
2
7
aluminum because of the increased ratio of Et Al (Table 5, entries 5ꢀ8). Precatalyst 3 produces
3
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
7
6% C fraction at a 2:3 DMAO/Et Al ratio and shows considerable activity (Table 5, entry 11).
8 3
a
Table 5. Evaluation of the Effect of DMAO/Et Al on Selective Oligomerization
3
Product selectivity (wt %)
PE
(g)
b
Entry Precatalyst DMAO/Et Al Activity
3
d
c
c
c
c, f
c
C4
C6
1ꢀC6
cyꢀC6
0.44
0.30
0.36
0.34
4.06
1.67
2.01
2.46
4.97
5.51
4.85
4.02
C8
C ꢀC
10 14
1
2
4:1
3:2
2:3
1:4
4:1
3:2
2:3
1:4
4:1
3:2
2:3
1:4
3308
4923
5250
3923
250
7.02 63.19 99.23
4.33 62.09 99.33
2.11 54.17 98.92
1.25 44.62 98.91
3.31 51.73 87.58
1.07 81.81 97.39
1.74 86.81 96.45
2.11 75.88 95.02
0.44 30.40 83.60
0.69 27.87 80.04
0.98 22.99 76.98
6.86 24.83 72.17
11.51
9.56
18.28
24.02
35.39
48.59
ꢀꢀꢀ
0.45
0.37
0.18
0.19
0.73
1.16
0.60
0.60
0.67
0.07
0.21
0.09
1
2
3
8.33
4
5.54
5
44.96
17.12
11.45
22.01
69.16
71.44
76.03
68.32
6
363
ꢀꢀꢀ
7
233
ꢀꢀꢀ
8
852
ꢀꢀꢀ
9
7461
7519
4231
1221
ꢀꢀꢀ
10
11
ꢀꢀꢀ
e
3
ꢀꢀꢀ
1
2
ꢀꢀꢀ
a
General conditions: n(precatalyst), 4.8 ꢁmol; pressure, 1.0 MPa; solvent, methylcyclohexane
b
ꢀ1 ꢀ1 c
(20 mL); reaction time, 30 min; T, 45 °C; n(Al)/n(Cr), 500 equiv; g(product)·g(Cr) ·h ; wt %
d
e
f
of liquid products (oligomers); wt of PE; n(precatalyst), 2.4 ꢁmol; C contains 100% 1ꢀC .
8
8
To optimize the catalyst in term of activity and selectivity, precatalyst 3 was chosen for further
screening under various reaction conditions (Table 6). The highest catalytic activity (76731
ꢀ1
ꢀ1
g(product)·g(Cr) ·h ) was obtained using 2.4 µmol catalyst loading at 15 °C and 4 MPa of
ethylene pressure (Table 6, entry 4). This may be attributed to the increased catalyst stability and
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8
9
6a, 20
higher ethylene solubility under these conditions.
The relatively high cocatalyst/catalyst
molar ratio, high ethylene pressure, low temperature and low catalyst loading increases C8
selectivity of precatalyst 3 up to 83% (Table 6, entry 7). High ethylene pressure may increases
30
1
1
1
1
1
1
1
1
1
1
2
2
2
2
2
2
2
2
2
2
3
3
3
3
3
3
3
3
3
3
4
4
4
4
4
4
4
4
4
4
5
5
5
5
5
5
5
5
5
5
6
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
ethylene concentration in the solvent, which in turn enhances the chain propagation rate and
thus improves the catalytic activity and C selectivity. The formation of C ꢀC fraction by 3
8
10
14
2
2e
(
Table 6, entries 4ꢀ6) was attributed to the product concentration when the catalytic activity
was higher.
a
Table 6. Evaluation of 3 for Selective Oligomerization under Different Reaction Conditions
Product Selectivity (wt %)
Catalyst Pressure
T
(°C)
b
d
Entry
n(Al)/n(Cr) Activity
PE (g)
(
µmol)
(MPa)
c
c
c
c, e
c
C4
13, 077 0.32 23.13 79.53 4.58
8, 269 0.41 19.97 79.54 4.05
C6 1ꢀC6 cyꢀC6
C8
C ꢀ
10 14
1
2
3
4
5
6
7
8
2.4
1.2
0.6
2.4
2.4
0.6
0.3
0.3
0.1
1
1
1
4
3
4
4
3
4
45
45
45
15
15
15
15
15
15
1000
2000
4000
500
76.55
79.62
81.06
ꢀ
ꢀ
ꢀ
0.20
0.29
0.11
3.09
1.05
3.31
0.51
0.20
0.10
10, 173 0.29 18.65 75.28 4.25
76, 731 0.42 18.21 76.63 4.12
70, 577 0.39 17.89 75.15 4.32
59, 615 0.72 18.51 74.05 4.61
43, 461 0.86 15.87 62.34 5.70
71.22 10.15
71.96 9.76
70.54 10.23
500
1000
2000
2000
6000
83.27
81.03
79.92
ꢀ
ꢀ
ꢀ
8, 846
7, 711
1.52 17.38 58.32 6.38
2.20 17.88 66.61 5.35
9
a
General conditions: solvent, methylcyclohexane (20 mL); reaction time, 30 min;
b
ꢀ1 ꢀ1
c
d
n(DMAO)/n(AlEt ), 4: 1; g(product)·g(Cr) ·h ; wt % of liquid products (oligomers); wt of
3
e
PE; C contains 100% 1ꢀC .
8
8
Some authors assumed that the monochromium and dichromium catalytic species may coexist
in the selective ethylene oligomerization system and that each of the two arrangement may
responsible for the formation of either 1ꢀhexene or 1ꢀoctene. Moreover, changing the ligands
scaffold and steric constraints may promote the formation of either monochromium or
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Page 16 of 35
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2
3
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5
6
7
8
9
1
1
1
1
1
1
1
1
1
1
2
2
2
2
2
2
2
2
2
2
3
3
3
3
3
3
3
3
3
3
4
4
4
4
4
4
4
4
4
4
5
5
5
5
5
5
5
5
5
5
6
7d, 24
dichromium species and hence influence the 1ꢀC selectivity.
In an effort to change the
8
equilibrium between monochromium and dichromium catalytic species and to explore its effect
4
5
on 1ꢀC selectivity, other silylatedꢀPNP [{Ph PCH Si(CH ) } N(R)]ꢀtype ligands (L and L )
8
2
2
3 2 2
4
5
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
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7
8
9
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
were prepared by a oneꢀpot reaction method. Treatment of L and L with [CrCl (THF) ] in
3
3
dichloromethane afforded corresponding Cr(III) complexes 4 and 5 (Scheme 3).
4
5
Scheme. 3 Synthesis of silylatedꢀPNP ligands (L -L ) and Cr complexes (4-5)
Precatalysts 4 and 5 were investigated for selective ethylene oligomerization under various
reaction conditions and observed that their selectivity dramatically switches from tetramerization
to trimerization with very low catalytic activity (Table 7ꢀ8). This selectivity switching to 1ꢀ
hexene could not be attributed to the equilibrium shifting between monochromium and
7
e, 24
4
dichromium species,
instead, we assumed that the presence of a third donor N in the L and
5
2
L framework switch the catalytic systems 4 and 5 from mononuclearꢀbidentate (k -P, P)
3
6b, 31
(
Scheme 1, 1-3) to mononuclearꢀtridentate (k -P, N, P) (Scheme 3, 4-5) binding mode,
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6
7
8
9
13,
which consequently switch the tetramerization systems to trimerization and produce more C6.
2
9a, 32
Moreover, modification of the ligands backbone may also change the steric constraints
1
2
around the catalytic active center and alters the P ꢀCrꢀP bite angle, these factors might also
6
c, 7a, 7c, 33
1
1
1
1
1
1
1
1
1
1
2
2
2
2
2
2
2
2
2
2
3
3
3
3
3
3
3
3
3
3
4
4
4
4
4
4
4
4
4
4
5
5
5
5
5
5
5
5
5
5
6
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
contribute to selectivity switching and low catalytic activity of precatalysts 4 and 5.
At
this point, we also turned our attention to the reaction medium and attempted the ethylene
oligomerization reactions in aliphatic and aromatic solvents. Methylcyclohexane was found to be
an excellent solvent for ethylene oligomerization. The results showed that more ethylene could
be dissolved in methylcyclohexane than in toluene, which provides a more ethyleneꢀrich
environment for the catalysts. No selectivity for C was observed when using toluene as
8
oligomerization solvent (Table 8, entry 8), showing that aromatic solvents may coordinate to the
active Cr center and inhibits the catalytic cycle by preventing the ethylene uptake required to
2
1a
form the chromacyclononane intermediate.
a
Table 7. Evaluation of 4 for Selective Oligomerization under Different Reaction Conditions
Product selectivity (wt %)
b
d
Entry
Activity
PE (g)
c
c
c
c, k
C4
C6
1ꢀC6
93.82
91.67
85.59
97.34
98.22
95.25
92.30
cyꢀC6
1.40
1.97
3.29
1.83
1.47
1.97
2.02
C8
e
1
619
644
475
577
913
315
308
6.76
6.15
6.54
1.06
0.75
2.62
4.63
84.84
77.57
56.90
77.85
88.19
74.50
74.81
8.39
0.18
0.20
0.26
0.35
0.55
0.34
0.14
2
16.28
36.56
21.09
11.06
22.88
20.56
f
3
g
4
h
5
i
6
j
7
a
General conditions: n(precatalyst), 2.4 µmol; pressure, 1.0 MPa; solvent, methylcyclohexane
(20 mL); reaction time, 30 min; T, 45 °C; n(Al)/n(Cr), 500 equiv; n(DMAO)/n(AlEt ), 4:1;
3
b
ꢀ1 ꢀ1
c
d
e
g(product)·g(Cr) ·h ; wt % of liquid products (oligomers); wt of PE; n(precatalyst), 4.8
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9
1
1
1
1
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1
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1
1
1
2
2
2
2
2
2
2
2
2
2
3
3
3
3
3
3
3
3
3
3
4
4
4
4
4
4
4
4
4
4
5
5
5
5
5
5
5
5
5
5
6
f
g
h
i
µmol; n(precatalyst), 1.2 µmol; T, 60 °C; n(Al)/n(Cr), 700 equiv; n(DMAO)/n(AlEt ), 3:2;
3
j
k
n(DMAO)/n(AlEt ), 2:3; C contains 100% 1ꢀC .
3
8
8
a
Table 8. Evaluation of 5 for Selective Oligomerization under Different Reaction Conditions
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
Product selectivity (wt %)
b
d
Entry
Activity
PE (g)
c
c
c
c, l
C4
C6
1ꢀC6
96.38
95.31
93.09
90.30
93.29
83.74
85.33
84.49
cyꢀC6
2.32
2.22
2.62
3.04
1.77
3.19
3.43
1.01
C8
e
1
111
261
354
125
456
142
140
158
1.60
0.99
1.03
1.84
0.71
1.29
2.10
33.35
85.30
87.44
77.99
79.82
91.44
80.99
82.77
66.65
13.10
11.57
20.99
18.34
7.85
0.35
0.43
0.48
0.09
0.21
0.13
0.12
0.35
2
f
3
g
4
h
5
i
6
17.72
15.13
ꢀ
j
7
k
8
a
General conditions: n(precatalyst), 2.4 µmol; pressure, 1.0 MPa; solvent, methylcyclohexane
(
20 mL); reaction time, 30 min; T, 45 °C; n(Al)/n(Cr), 500 equiv; n(DMAO)/n(AlEt ), 4:1;
3
b
ꢀ1 ꢀ1
c
d
e
g(product)·g(Cr) ·h ; wt % of liquid products (oligomers); wt of PE; n(precatalyst), 4.8
f
g
h
i
µmol; n(precatalyst), 1.2 µmol; T, 60 °C; n(Al)/n(Cr), 700 equiv; CH Cl used as solvent for
2
2
j
k
the coordination; toluene used as solvent for the coordination; toluene used as solvent for the
l
coordination and screening; C contains 100% 1ꢀC .
8
8
To further rationalize the high selectivity of precatalyst 3 toward 1ꢀC , DFT calculations were
8
3
1, 33b
34
conducted. Previous theoretical studies
suggested that the M06L density functional is
more accurate for analyzing the multiple spin states, oxidative coupling and reductive
4bꢀd, 35
elimination steps involved in the Cr metallacycleꢀbased mechanism.
Recently, a
computational study of Cr catalysts based on phosphine monocyclic imine (P, N) ligands
suggested that DFT can also be used as a powerful tool for the quantitative prediction of 1ꢀC /1ꢀ
6
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C selectivity. Moreover, DFT was also used to rationalize the effect of steric bulk on
8
3
7
selectivity of triꢀ verses tetramerization for PCNCPꢀbased Cr complexes.
Figure 3 shows the relative Gibbs free energy profiles of 1ꢀhexene and 1ꢀoctene formation
1
1
1
1
1
1
1
1
1
1
2
2
2
2
2
2
2
2
2
2
3
3
3
3
3
3
3
3
3
3
4
4
4
4
4
4
4
4
4
4
5
5
5
5
5
5
5
5
5
5
6
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
6
catalyzed by Cr precatalyst 3. Initially, bisethylene complex 2 faces a high energy barrier (38.9
6
kcal/mol) to form the metallacycle on the sextet surface; therefore, intermediate 2 is converted
4
to intermediate 2 through spin crossing (see the Supporting Information for MECP
3
8
calculation) and forms chromacyclopentane 3b (an important intermediate in the metallacycle
4a, 4c, 22a, 39
mechanism
) via TS2, 3a, which makes three pathways available for this reaction. Upon
coordination with ethylene, 3b may follow path 1 (single coordination pathway), pass through
TS4, 5 and form chromacycloheptane intermediate 5 (rateꢀdetermining intermediate for path 1
and path 3). Upon coordination of the second ethylene, intermediate 5 may pass through TS6e, 7
(
rateꢀdetermining transition state in path 1) with a 13.7 kcal/mol energy barrier and form 1ꢀC8.
Depending on the type of ligand and experimental conditions, βꢀH elimination may compete with
the coordination of a second ethylene in intermediate 5 and cause the reaction to pass through
path 3 and release 1ꢀC via TS (rateꢀdetermining transition state in path 3) with a total energy
6
5, 9
barrier of 17.1 kcal/mol. Considering path 2 (double coordination pathway), upon coordination
of two ethylene units, 3b (rateꢀdetermining intermediate in path 2) may pass through TS5, 6a
(
rateꢀdetermining transition state in path 2) with a 14.4 kcal/mol energy barrier and liberate 1ꢀ
C . Small energy barriers (13.7 kcal/mol for path 1 and 14.4 kcal/mol for path 2) indicate that
8
both pathways (single and double coordination) are energetically favored and can produce 1ꢀC8
under mild conditions, and this is in full agreement with our experimental results (production of
1
ꢀC under mild conditions). In general, the low energy barriers for path 1 and path 2 suggest
8
that single and double coordination may occur simultaneously, nevertheless a slightly lower free
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1
1
2
2
2
2
2
2
2
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3
3
3
3
4
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4
4
4
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4
4
4
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5
5
5
5
5
5
5
5
5
6
energy barrier for path 1 shows that single coordination is thermodynamically more favorable
3
for the L ꢀbased catalyst under normal conditions. Herein, the effect of high ethylene pressure
may not be ignored on double coordination pathway as it is second order in ethylene and high
2
2d,
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
pressure may lead the path 2 more favorable for 1ꢀC formation (see Supporting Information).
8
40
27
Besides the energy perspective, the chain transfer to aluminum, the involvement of C and C
6
8
4
d, 15, 22
26
fractions in coꢀoligomerization reactions
and the insufficient separation of the ionꢀpair
are the other important factors which significantly influence the C selectivity and therefore
8
should be taken into account.
To provide a theoretical base for the switching of the binding mode from tetramerization to
4
trimerization, we speculated that when a third donor is present in the ligand framework (as in L
5
and L ), intermediate 5 has no vacant coordination sites available for another ethylene to
coordinate and form chromacyclononane 7. Consequently, βꢀH elimination overcomes an energy
barrier of 17.1 kcal/mol and liberates more 1ꢀhexene from intermediate 9.
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3
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0
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3
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9
0
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2
3
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9
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
6
Figure 3. Relative Gibbs free energy profiles for the ethylene triꢀ/tetramerization catalyzed by chromium precatalyst 3 ( 1); all
stationary points are cationic.
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1
1
1
2
2
2
2
2
2
2
2
2
2
3
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3
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3
3
3
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4
4
4
4
4
4
4
4
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5
5
5
5
5
6
In summary, we have reported Cr(III) precatalysts with {Ph PN(R)Si(CH ) CH PPh )}ꢀ and
2
3 2
2
2
[
{Ph PCH Si(CH ) } N(R)]ꢀtype silylatedꢀdiphosphinoamine ligands, which upon activation
2 2 3 2 2
with DMAO/Et Al, can produce active and selective triꢀ/tetramerization systems. We observed
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
3
that the backbone Nꢀsubstituents and experimental conditions strongly influence the catalytic
i
performance of these precatalysts. Precatalyst 3, bearing an Pr substituent on the backbone N,
efficiently formed C , while precatalyst 2, having a bulkier Nꢀsubstituent (2,6ꢀ
8
diisopropylphenyl), favors C formation. A relatively low catalyst mass, low temperature and
6
high ethylene pressure promote C selectivity; and the selectivity of precatalyst 3 can be tuned
8
from 69% to 83%. The highest catalytic activity was obtained with precatalyst 3 using 2.4 µmol
catalyst loading at 15 °C and 4.0 MPa of ethylene, and the activity was attributed to the greater
catalyst stability and higher ethylene solubility under these conditions. The high 1ꢀC selectivity
8
of precatalyst 3 was rationalized by DFT calculations and found to be consistent with the
experimental results. The small energy barrier in the path of 1ꢀC formation made precatalyst 3
8
an efficient catalyst for the tetramerization. Crystallographic investigations showed that the
1
2
Ph
larger P ꢀCrꢀP bite angle with smaller C ꢀPꢀCr angle can shift the C selectivity toward C in
8
6
these precatalysts. Modification of the length of the ligands backbone may change the
coordination mode, which consequently switch the tetramerization systems to trimerization
systems. Further studies to fully elucidate the potential of Siꢀbased ligands for selective ethylene
oligomerization are underway.
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ASSOCIATED CONTENT
1
1
1
1
1
1
1
1
1
1
2
2
2
2
2
2
2
2
2
2
3
3
3
3
3
3
3
3
3
3
4
4
4
4
4
4
4
4
4
4
5
5
5
5
5
5
5
5
5
5
6
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
Supporting Information.
Synthesis procedures, NMR characterizations, catalysis procedures, computational details (PDF),
solvent corrected absolute free energies (Ha), electronic energies (Ha), and Cartesian coordinates
(Å) of all the optimized structures and MECP (XYZ), crystallographic data (CIF) for 6.
AUTHOR INFORMATION
Corresponding Authors
*
*
Eꢀmail: jiangtao@tust.edu.cn
Eꢀmail: dongchunhua@iccas.ac.cn
Author Contributions
The manuscript was written through contributions of all authors. All authors have given approval
to the final version of the manuscript.
ACKNOWLEDGMENT
This research was sponsored by The National Key Research and Development Program of China
(2017YFB0306700) and the Tianjin Application Foundation and Cuttingꢀedge Technology
Research Program (Grant: 16JCZDJC31600).
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2
2
2
2
2
2
2
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REFERENCES
0
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3
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0
(1) (a) Dixon, J. T.; Green, M. J.; Hess, F. M.; Morgan, D. H. Advances in Selective Ethylene
TrimerisationꢀA Critical Overview. J. Organomet. Chem. 2004, 689, 3641ꢀ3668. (b)
McGuinness, D. S. Olefin Oligomerization via Metallacycles: Dimerization, Trimerization,
Tetramerization, and Beyond. Chem. Rev. 2011, 111, 2321ꢀ2341. (c) Agapie, T. Selective
Ethylene Oligomerization: Recent Advances in Chromium Catalysis and Mechanistic
Investigations. Coord. Chem. Rev. 2011, 255, 861ꢀ880. (d) Van Leeuwen, P. W.; Clément, N. D.;
Tschan, M. J.ꢀL. New Processes for the Selective Production of 1ꢀOctene. Coord. Chem. Rev.
2
011, 255, 1499ꢀ1517.
(2) (a) Breuil, P.A. R.; Magna, L.; OlivierꢀBourbigou, H. Role of Homogeneous Catalysis in
Oligomerization of Olefins: Focus on Selected Examples Based on Group 4 to Group 10
Transition Metal Complexes. Catal. Lett. 2015, 145, 173ꢀ192. (b) Peitz, S.; Peulecke, N.; Aluri,
B. R.; Hansen, S.; Müller, B. H.; Spannenberg, A.; Rosenthal, U.; AlꢀHazmi, M. H.; Mosa, F.
M.; Wöhl, A. A Selective Chromium Catalyst System for the Trimerization of Ethene and its
Coordination Chemistry. Eur. J. Inorg. Chem. 2010, 2010, 1167ꢀ1171. (c) Peitz, S.; Peulecke,
N.; Aluri, B. R.; Müller, B. H.; Spannenberg, A.; Rosenthal, U.; AlꢀHazmi, M. H.; Mosa, F. M.;
Wöhl, A.; Müller, W. Activation and Deactivation by Temperature: Behavior of
Ph PN(iPr)P(Ph)N(iPr)H in the Presence of Alkylaluminum Compounds Relevant to Catalytic
2
Selective Ethene Trimerization. Chem. Eur. J. 2010, 16, 12127ꢀ12132.
(3) Sydora, O. L.; Jones, T. C.; Small, B. L.; Nett, A. J.; Fischer, A. A.; Carney, M. J. Selective
Ethylene Triꢀ/Tetramerization Catalysts. ACS Catal. 2012, 2, 2452ꢀ2455.
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2
3
4
5
6
7
8
9
(
4) (a) Emrich, R.; Heinemann, O.; Jolly, P. W.; Krüger, C.; Verhovnik, G. P. The Role of
Metallacycles in the ChromiumꢀCatalyzed Trimerization of Ethylene. Organometallics 1997, 16,
1511ꢀ1513. (b) Meijboom, N.; Schaverien, C. J.; Orpen, A. G. Organometallic Chemistry of
Chromium(VI): Synthesis of Chromium(VI) Alkyls and their Precursors. Xꢀray Crystal Structure
1
1
1
1
1
1
1
1
1
1
2
2
2
2
2
2
2
2
2
2
3
3
3
3
3
3
3
3
3
3
4
4
4
4
4
4
4
4
4
4
5
5
5
5
5
5
5
5
5
5
6
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
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0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
t
of the Metallacycle Cr(N Bu) {oꢀ(CHSiMe ) C H }. Organometallics 1990, 9, 774ꢀ782. (c)
2
3 2
6
4
Agapie, T.; Schofer, S. J.; Labinger, J. A.; Bercaw, J. E. Mechanistic Studies of the Ethylene
Trimerization Reaction with ChromiumꢀDiphosphine Catalysts: Experimental Evidence for a
Mechanism Involving Metallacyclic Intermediates. J. Am. Chem. Soc. 2004, 126, 1304ꢀ1305. (d)
Overett, M. J.; Blann, K.; Bollmann, A.; Dixon, J. T.; Haasbroek, D.; Killian, E.; Maumela, H.;
McGuinness, D. S.; Morgan, D. H. Mechanistic Investigations of the Ethylene Tetramerisation
Reaction. J. Am. Chem. Soc. 2005, 127, 10723ꢀ10730.
(5) (a) Thapa, I.; Gambarotta, S.; Korobkov, I.; Duchateau, R.; Kulangara, S. V.; Chevalier, R.
Switchable Chromium(II) Complexes of a Chelating Amidophosphine (NꢀP) for Selective and
Nonselective Ethylene Oligomerization. Organometallics 2010, 29, 4080ꢀ4089. (b) Albahily, K.;
Koç, E.; AlꢀBaldawi, D.; Savard, D.; Gambarotta, S.; Burchell, T. J.; Duchateau, R. Chromium
Catalysts Supported by a Nonspectator NPN Ligand: Isolation of SingleꢀComponent Chromium
Polymerization Catalysts. Angew. Chem. Int. Ed. 2008, 47, 5816ꢀ5819. (c) Jabri, A.; Crewdson,
P.; Gambarotta, S.; Korobkov, I.; Duchateau, R. Isolation of a Cationic Chromium(II) Species in
a Catalytic System for Ethylene Triꢀ and Tetramerization. Organometallics 2006, 25, 715ꢀ718.
(d) Jabri, A.; Temple, C.; Crewdson, P.; Gambarotta, S.; Korobkov, I.; Duchateau, R. Role of the
Metal Oxidation State in the SNSꢀCr Catalyst for Ethylene Trimerization: Isolation of Diꢀ and
Trivalent Cationic Intermediates. J. Am. Chem. Soc. 2006, 128, 9238ꢀ9247. (e) McDyre, L. E.;
Hamilton, T.; Murphy, D. M.; Cavell, K. J.; Gabrielli, W. F.; Hanton, M. J.; Smith, D. M. A cw
ACS Paragon Plus Environment
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ACS Catalysis
Page 26 of 35
1
2
3
4
5
6
7
8
9
1
1
1
1
1
1
1
1
1
1
2
2
2
2
2
2
2
2
2
2
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3
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3
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3
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3
3
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4
4
4
4
4
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4
4
5
5
5
5
5
5
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5
5
5
6
EPR and ENDOR Investigation on a Series of Cr(I) Carbonyl Complexes with Relevance to
+
Alkene Oligomerization Catalysis:[Cr(CO) L] (L = Ph PN(R)PPh , Ph P(R)PPh ). Dalton
4
2
2
2
2
Trans. 2010, 39, 7792ꢀ7799. (f) Brückner, A.; Jabor, J. K.; McConnell, A. E.; Webb, P. B.
Monitoring Structure and Valence State of Chromium Sites During Catalyst Formation and
Ethylene Oligomerization by In Situ EPR Spectroscopy. Organometallics 2008, 27, 3849ꢀ3856.
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
(g) Carter, E.; Cavell, K. J.; Gabrielli, W. F.; Hanton, M. J.; Hallett, A. J.; McDyre, L.; Platts, J.
+
A.; Smith, D. M.; Murphy, D. M. Formation of [Cr(CO) (Ph PN(iPr)PPh )] Structural Isomers
x
2
2
by Reaction of Triethylaluminum with a Chromium N,NꢀBis(diarylphosphino)amine Complex
+
[
Cr(CO) (Ph PN(iPr)PPh )] : An EPR and DFT Investigation. Organometallics 2013, 32, 1924ꢀ
4
2
2
1931.
(6) (a) Bollmann, A.; Blann, K.; Dixon, J. T.; Hess, F. M.; Killian, E.; Maumela, H.;
McGuinness, D. S.; Morgan, D. H.; Neveling, A.; Otto, S. Ethylene Tetramerization: A New
Route to Produce 1ꢀOctene in Exceptionally High Selectivities. J. Am. Chem. Soc. 2004, 126,
1
4712ꢀ14713. (b) Overett, M. J.; Blann, K.; Bollmann, A.; Dixon, J. T.; Hess, F.; Killian, E.;
Maumela, H.; Morgan, D. H.; Neveling, A.; Otto, S. Ethylene Trimerisation and Tetramerisation
Catalysts with PolarꢀSubstituted Diphosphinoamine Ligands. Chem. Commun. 2005, 622ꢀ624.
(c) Blann, K.; Bollmann, A.; Dixon, J. T.; Hess, F. M.; Killian, E.; Maumela, H.; Morgan, D. H.;
Neveling, A.; Otto, S.; Overett, M. J. Highly Selective ChromiumꢀBased Ethylene Trimerisation
Catalysts with Bulky Diphosphinoamine Ligands. Chem. Commun. 2005, 620ꢀ621.
(7) (a) Overett, M. J.; Blann, K.; Bollmann, A.; de Villiers, R.; Dixon, J. T.; Killian, E.;
Maumela, M. C.; Maumela, H.; McGuinness, D. S.; Morgan, D. H. CarbonꢀBridged Diphosphine
Ligands for ChromiumꢀCatalysed Ethylene Tetramerisation and Trimerisation Reactions. J. Mol.
Catal. A: Chem. 2008, 283, 114ꢀ119. (b) Zhang, J.; Wang, X.; Zhang, X.; Wu, W.; Zhang, G.;
ACS Paragon Plus Environment
26

Page 27 of 35
ACS Catalysis
1
2
3
4
5
6
7
8
9
Xu, S.; Shi, M. Switchable Ethylene Triꢀ/Tetramerization with High Activity: Subtle Effect
Presented by BackboneꢀSubstituent of CarbonꢀBridged Diphosphine Ligands. ACS Catal. 2013,
3, 2311ꢀ2317. (c) Dulai, A.; de Bod, H. t.; Hanton, M. J.; Smith, D. M.; Downing, S.; Mansell, S.
M.; Wass, D. F. CꢀSubstituted Bis(diphenylphosphino)methaneꢀType Ligands for Chromiumꢀ
Catalyzed Selective Ethylene Oligomerization Reactions. Organometallics 2009, 28, 4613ꢀ4616.
1
1
1
1
1
1
1
1
1
1
2
2
2
2
2
2
2
2
2
2
3
3
3
3
3
3
3
3
3
3
4
4
4
4
4
4
4
4
4
4
5
5
5
5
5
5
5
5
5
5
6
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
(
d) Shaikh, Y.; Albahily, K.; Sutcliffe, M.; Fomitcheva, V.; Gambarotta, S.; Korobkov, I.;
Duchateau, R. A Highly Selective Ethylene Tetramerization Catalyst. Angew. Chem. Int. Ed.
012, 51, 1366ꢀ1369.
8) (a) Yang, Y.; Gurnham, J.; Liu, B.; Duchateau, R.; Gambarotta, S.; Korobkov, I. Selective
2
(
Ethylene Oligomerization with Chromium Complexes Bearing PyridineꢀPhosphine Ligands:
Influence of Ligand Structure on Catalytic Behavior. Organometallics 2014, 33, 5749ꢀ5757. (b)
Shaikh, Y.; Gurnham, J.; Albahily, K.; Gambarotta, S.; Korobkov, I. AminophosphineꢀBased
Chromium Catalysts for Selective Ethylene Tetramerization. Organometallics 2012, 31, 7427ꢀ
7
433. (c) Yang, Y.; Liu, Z.; Liu, B.; Duchateau, R. Selective Ethylene Triꢀ/Tetramerization by In
SituꢀFormed Chromium Catalysts Stabilized by N, PꢀBased Ancillary Ligand Systems. ACS
Catal. 2013, 3, 2353ꢀ2361.
(9) (a) Müller, W.; Wöhl, A.; Peitz, S.; Peulecke, N.; Aluri, B. R.; Müller, B. H.; Heller, D.;
Rosenthal, U.; AlꢀHazmi, M. H.; Mosa, F. M. A Kinetic Model for Selective Ethene
Trimerization to 1ꢀHexene by a Novel Chromium Catalyst System. Chemcatchem 2010, 2, 1130ꢀ
1142. (b) Peulecke, N.; Müller, B. H.; Peitz, S.; Aluri, B. R.; Rosenthal, U.; Wöhl, A.; Müller,
W.; AlꢀHazmi, M. H.; Mosa, F. M. Immobilized Chromium Catalyst System for Selective
Ethene Trimerization to 1ꢀHexene with a PNPNH Ligand. Chemcatchem 2010, 2, 1079ꢀ1081. (c)
Müller, B. H.; Peulecke, N.; Peitz, S.; Aluri, B. R.; Rosenthal, U.; AlꢀHazmi, M. H.; Mosa, F.
ACS Paragon Plus Environment
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ACS Catalysis
Page 28 of 35
1
2
3
4
5
6
7
8
9
1
1
1
1
1
1
1
1
1
1
2
2
2
2
2
2
2
2
2
2
3
3
3
3
3
3
3
3
3
3
4
4
4
4
4
4
4
4
4
4
5
5
5
5
5
5
5
5
5
5
6
M.; Wöhl, A.; Müller, W. Activity Enhancement of a Catalyst System for the Selective
Trimerization of Ethene to 1ꢀHexene by Modification of the Chromium to Chloride to
Aluminium Ratio. Chem. Eur. J. 2011, 17, 6935ꢀ6938.
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
(10) Temple, C.; Jabri, A.; Crewdson, P.; Gambarotta, S.; Korobkov, I.; Duchateau, R. The
Question of the Cr Oxidation State in the {Cr(SNS)} Catalyst for Selective Ethylene
Trimerization: An Unanticipated ReꢀOxidation Pathway. Angew. Chem. Int. Ed. 2006, 118,
7
208ꢀ7211.
(11) Albahily, K.; Gambarotta, S.; Duchateau, R. Ethylene Oligomerization Promoted by a
SilylatedꢀSNS Chromium System. Organometallics 2011, 30, 4655ꢀ4664.
(12) Fleming, I.; Barbero, A.; Walter, D. Stereochemical Control in Organic Synthesis Using
SiliconꢀContaining Compounds. Chem. Rev. 1997, 97, 2063ꢀ2192.
(13) McGuinness, D. S.; Wasserscheid, P.; Keim, W.; Morgan, D.; Dixon, J. T.; Bollmann, A.;
Maumela, H.; Hess, F.; Englert, U. First Cr(III)ꢀSNS Complexes and Their Use as Highly
Efficient Catalysts for the Trimerization of Ethylene to 1ꢀHexene. J. Am. Chem. Soc. 2003, 125,
5
272ꢀ5273.
(14) (a) Zhang, L.; Meng, X.; Chen, Y.; Cao, C.; Jiang, T. ChromiumꢀBased Ethylene
Tetramerization Catalysts Supported by SiliconꢀBridged Diphosphine Ligands: Further
Combination of High Activity and Selectivity. Chemcatchem 2017, 9, 76ꢀ79. (b) Zhang, L.; Wei,
W.; Alam, F.; Chen, Y.; Jiang, T. Efficient ChromiumꢀBased Catalysts for Ethylene Triꢀ
/Tetramerization Switched by SiliconꢀBridged/N, PꢀBased Ancillary Ligands: A Structural,
Catalytic and DFT Study. Catal. Sci. Technol. 2017, 7, 5011ꢀ5018.
(15) Härzschel, S.; Kühn, F. E.; Wöhl, A.; Müller, W.; AlꢀHazmi, M. H.; Alqahtani, A. M.;
Müller, B. H.; Peulecke, N.; Rosenthal, U. Comparative Study of New ChromiumꢀBased
ACS Paragon Plus Environment
28

Page 29 of 35
ACS Catalysis
1
2
3
4
5
6
7
8
9
Catalysts for the Selective Triꢀ and Tetramerization of Ethylene. Catal. Sci. Technol. 2015, 5,
1
678ꢀ1682.
(16) McGuinness, D. S.; Rucklidge, A. J.; Tooze, R. P.; Slawin, A. M. Cocatalyst Influence in
Selective Oligomerization: Effect on Activity, Catalyst Stability, and 1ꢀHexene/1ꢀOctene
Selectivity in the Ethylene Trimerization and Tetramerization Reaction. Organometallics 2007,
1
1
1
1
1
1
1
1
1
1
2
2
2
2
2
2
2
2
2
2
3
3
3
3
3
3
3
3
3
3
4
4
4
4
4
4
4
4
4
4
5
5
5
5
5
5
5
5
5
5
6
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
2
6, 2561ꢀ2569.
(17) Kuhlmann, S.; Blann, K.; Bollmann, A.; Dixon, J. T.; Killian, E.; Maumela, M. C.;
Maumela, H.; Morgan, D. H.; Prétorius, M.; Taccardi, N. NꢀSubstituted Diphosphinoamines:
Toward Rational Ligand Design for the Efficient Tetramerization of Ethylene. J. Catal. 2007,
245, 279ꢀ284.
(18) Kuhlmann, S.; Dixon, J. T.; Haumann, M.; Morgan, D. H.; Ofili, J.; Spuhl, O.; Taccardi, N.;
Wasserscheid, P. Influence of Elevated Temperature and Pressure on the ChromiumꢀCatalysed
Tetramerisation of Ethylene. Adv. Synth. Catal. 2006, 348, 1200ꢀ1206.
(19) Mao, G.; Ning, Y.; Hu, W.; Li, S.; Song, X.; Niu, B.; Jiang, T. Synthesis of a Novel Tripleꢀ
Site Diphosphinoamine (PNP) Ligand and its Applications in Ethylene Tetramerization. Chin.
Sci. Bull. 2008, 53, 3511ꢀ3515.
(
20) Zhuze, T.; Zhurba, A. Solubilities of Ethylene in Hexane, Cyclohexane, and Benzene under
Pressure. Russ. Chem. Bull. 1960, 9, 335ꢀ337.
21) (a) Blann, K.; Bollmann, A.; de Bod, H.; Dixon, J. T.; Killian, E.; Nongodlwana, P.;
(
Maumela, M. C.; Maumela, H.; McConnell, A. E.; Morgan, D. H. Ethylene Tetramerisation:
Subtle Effects Exhibited by NꢀSubstituted Diphosphinoamine Ligands. J. Catal. 2007, 249, 244ꢀ
2
49. (b) Elowe, P. R.; McCann, C.; Pringle, P. G.; Spitzmesser, S. K.; Bercaw, J. E. Nitrogenꢀ
ACS Paragon Plus Environment
29