Switchable ethylene tri-/tetramerization with high activity: Subtle effect presented by backbone-substituent of carbon-bridged diphosphine ligands

Article abstract of DOI:10.1021/cs400651h

The effect of backbone-substituent of carbon-bridged diphosphine ligands of the types {Ph₂PCH(R)CH₂PPh₂} and {Ph ₂PC(R)iCHPPh₂} on the catalyst performance in ethylene oligomerization has been explore

Full text of DOI:10.1021/cs400651h

Research Article
pubs.acs.org/acscatalysis
Switchable Ethylene Tri-/Tetramerization with High Activity: Subtle
Effect Presented by Backbone-Substituent of Carbon-Bridged
Diphosphine Ligands
Jun Zhang,*,† Xiao Wang,† Xuejun Zhang,† Weijie Wu,† Gengtao Zhang,† Sheng Xu,† and Min Shi†,‡
†Key Laboratory for Advanced Materials and Institute of Fine Chemicals, School of Chemistry & Molecular Engineering, East China
University of Science and Technology, 130 Mei Long Road, Shanghai 200237, China
‡State Key Laboratory of Organometallic Chemistry, Shanghai Institute of Organic Chemistry, Chinese Academy of Sciences, 354
Fenglin Road, Shanghai 200032, China
S
* Supporting Information
ABSTRACT: The effect of backbone-substituent of carbon-
bridged diphosphine ligands of the types {Ph2PCH(R)-
CH2PPh2} and {Ph2PC(R)CHPPh2} on the catalyst
performance in ethylene oligomerization has been explored.
Cr complex bearing a methyl-substituted diphosphine ligand
with saturated linker exhibited the highest selectivity of 64.7%
toward 1-octene. Cr complex bearing a tert-butyl-substituted
diphosphine ligand with unsaturated linker showed a high
activity of 4238 kg/(g Cr/h) at 40 bar and 40 °C and achieved
a high total selectivity of 79.1% toward valuable 1-hexene and 1-octene. The 1-hexene selectivity could be improved up to 55.2%
(19.4% 1-octene) at 20 bar and 80 °C. Some of the new complexes are even more active than the well-known most efficient
ethylene tri/tetramerization catalyst systems.
KEYWORDS: ethylene trimerization, ethylene tetramerization, backbone-substituent, diphosphine ligand, chromium(III) catalysts
INTRODUCTION
■
The oligomerization of ethylene generally gives a broad
distribution of α-olefins which requires fractional distillation
of the products to give relatively low yields of the desired
fractions. To meet demand growth for 1-hexene and 1-octene,
the selective ethylene tri/tetramerization has received a great
deal of attention from the academic and industrial communities
throughout the world in the last two decades.1 Although this
was first achieved with Cr-based catalysts in 1977,2 there are
Figure 1. Selected diphosphine ligands A−E in Cr-catalyzed ethylene
tri/tetramerization and targeted carbon-bridged diphosphine ligands F
and G.
few highly active and selective catalysts for ethylene
trimerization3 and they include the Phillips pyrrolide,3a,b the
BP diphosphinoamine,3c and the Sasol mixed heteroatomic3d
systems. Recently, one of us and Hor have developed Cr(III)
catalytic systems with a variety of tridentate heteroscorpionate
pyrazolyl ligands, exhibiting excellent selectivity (up to 98 wt
%) for ethylene trimerization.4 Other diphosphine ligands5 and
P,N-ligands6 have also been used in Cr-based ethylene
trimerization catalysts.
In 2004, by modification of the BP diphosphinoamine (PNP)
ligand A (R = Me, Ar = o-OMe-Phenyl) (Figure 1), the
researchers from Sasol found removing ortho-substitution from
the phosphine phenyl groups and increasing the steric bulk of
the N-substituent from methyl group to isopropyl group cause
a switch in selectivity from 1-hexene to 1-octene.7 1-Octene
selectivity up to 70% was achieved using PNP ligand A (R = iPr,
Ar = Ph) at 45 bar. A further increase in steric bulk of the N-
substituent enhances the combined selectivity toward the two
desired products (1-hexene and 1-octene) while lowering the 1-
octene/1-hexene ratio.8 Thus, the C6 selectivity ranged from
13% using N-isopropyl PNP ligand to 41% using the more
bulky N-2,6-dimethylcyclohexyl PNP ligand, while C8 selectiv-
ity decreased from 70% to 48%. Recently, several carbon-
bridged diphosphine ligands including B, C, and D were also
found to be active in Cr-catalyzed tri/tetramerization catalysts
(Figure 1).9 For these carbon-bridged diphosphine ligands,
bridge unsaturation and the rigidity of backbone also
significantly affect catalyst performance. Cr complex based on
the bis(diphenylphosphino)benzene ligand B exhibited very
Received: August 6, 2013
Revised: September 2, 2013
© XXXX American Chemical Society
2311
dx.doi.org/10.1021/cs400651h | ACS Catal. 2013, 3, 2311−2317

ACS Catalysis
Research Article
high activity toward tri/tetramerization and is among the most
active ethylene tri/tetramerization catalyst systems, which is
much more active than those bearing C, D, and even typical
PNP ligand A.9 Most modifications of these carbon-bridged
diphosphines have been made on the length of carbon-bridge
and very few on their backbone substitution. Kang and
researchers from S-K Energy reported a series of bis-
(diphenylphosphino) ethane E with a dimethyl-substituted
chiral backbone for selective ethylene tetramerization.10
Compared to Cr catalyst based on the related ligand D with
no substituent on its backbone, the Cr complex of ligand E
exhibited enhanced selectivity toward ethylene tetramerization
and showed very high activity. However, although various
efficient ethylene tri/tetramerization catalyst systems have been
established,11 achieving very high activity without compromis-
ing total selectivity toward valuable 1-hexene and 1-octene has
remained a challenge. Only a few catalyst systems could achieve
industrially acceptable high activity, such as the Sasol’s PNP
(A), S-K Energy’s diphosphine (E), and bis-
(diphenylphosphino)benzene (B) catalytic systems. Very
surprisingly, there is no asymmetric carbon-bridged diphos-
phine ligand reported for ethylene tri/tetramerization up to
now, though those carbon-bridged diphosphine ligands, such as
B and E, have been proved to be particularly promising. With
our aim of understanding well the influence of ligand structure
on catalyst performance in ethylene oligomerization,4,12 we
decided to explore the influence of backbone-substituent of
diphosphine ligands of type C and D. We herein report our
study on two kinds of asymmetric carbon-bridged diphosphine
ligands with one substituent on their backbones, i.e., bis-
(diphenylphosphino) ethane with a saturated linker (F) and
bis(diphenylphosphino) ethene with an unsaturated linker (G).
In this study, we establish an ethylene tri/tetramerization
catalyst system with a high activity of up to 4238 kg/(g Cr/h)
and a high total selectivity of up to 80% toward 1-hexene and 1-
octene, and a new insight into the subtle effect of varying the
backbone-substituent on the overall oligomerization perform-
ance and in particular on the selectivity was also presented.
Scheme 1. Synthesis of Cr Complexes 1−5 Based on
Carbon-Bridged Diphosphine Ligands L1−L5
Figure 2. Known Cr precatalysts 6−10 bearing diphosphine ligands
L6−L10 chosen for comparison.
bearing carbon-bridged diphosphine ligands were highly active
in the selective tri/tetramerization reaction. Precatalyst 1
bearing diphosphine ligand with saturated linker exhibited the
highest selectivity of 64.7% toward 1-octene with considerable
activity of 577 kg/(g Cr/h) (Table 1, entry 1). Increasing the
steric bulk of backbone-subsituent by replacement of the
methyl group (in 1) with a phenyl group (in 2) enhanced the
activity and led to more production of 1-hexene at the expense
of 1-octene, and more polymer was observed when using 2
(Table 1, entries 1 and 2). Very high activities (1900 kg/(g Cr/
h) for 4, and 1926 kg/(g Cr/h) for 5) were obtained using
precatalysts 4 and 5 bearing diphosphine ligands with
unsaturated linkers, which are more active than the precatalyst
3 bearing less bulky backbone-substituent (phenyl group)
(Table 1, entries 3−5). It is worth noting that the amount of
polymer obtained by 4 and 5 was much less than that when
using 1 and 2. These results indicate that backbone-substituent
and/or ligand rigidity play an important role in catalyst
performance. Under the same reaction condition, the activities
achieved by 4 and 5 even surpass those obtained by the most
efficient catalyst systems (Table 1, entries 9−11), such as 6
bearing a PNP ligand, 7 bearing a bis(diphenylphosphino)-
benzene ligand, and 8 bearing a carbon-bridged diphosphine
ligand with two chiral backbone-substituents, while the
selectivities to 1-octene were lower than that using precatalyst
7. Since the reactor was almost full after runing the
oligomerization reaction for 30 min when using 4 and 5
(Table 1, entries 4 and 6), the reaction was then terminated
RESULTS AND DISCUSSION
■
Asymmetric carbon-bridged diphosphine ligands of the type
{Ar2PCH(R)CH2PAr2} (L1−L2) and {Ar2PC(R)CHPAr2}
(L3−L5) were simply prepared by two-step synthesis from
commerially available alkynes or diols according to literature
methods.13,14 Treatment of the diphosphine ligands L1−L5 with
[CrCl3(THF)3] in CH2Cl2 or toluene afforded the correspond-
ing Cr(III) complexes 1−5 (Scheme 1). The Cr complexes, 1−
5, were not structurally characterized due to failure to obtain
the single crystals suitable for X-ray analysis but are proposed to
adopt the chloride bridged dinuclear structures as those found
in other known related Cr complexes bearing carbon-bridged
diphosphines such as B, C, D, and E (Figure 1).9,10
To investigate the effect of backbone-substituent of ligands
L1−L5 on catalyst performance, Cr complexes 1−5 were taken
for catalytic testing. The results, with a comparison against the
known efficient Cr precatalysts (6−8) based on diphosphine
ligands, i.e., Ph2PN(iPr)PPh2 (L6), Ph2P(C6H4)PPh2 (L7), and
Ph2P{CH(Me)CH(Me)}PPh2 (L8), and those Cr precatalysts
(9, 10) bearing related ligands Ph2P(CHCH)PPh2 (L9) and
Ph2P(CH2CH2)PPh2 (L10) (Figure 2), are summarized in
Table 1.
t
after 15 min. In shorter reaction time, 5 bearing bulkier Bu
backbone-substituent exhibited very high activities of 3277 kg/
(g Cr·h), which is more active than cyclohexyl-substituted
complex 4 (Table 1, entries 5 and 7). Precatalyst 5 retained
high activity even at low catalyst concentration (0.6 μmol in 30
At 40 bar ethylene and 40 °C and in the presence of 500
molar excess of MMAO-3A, all of the precatalysts (1−5)
2312
dx.doi.org/10.1021/cs400651h | ACS Catal. 2013, 3, 2311−2317

ACS Catalysis
Research Article
a
Table 1. Ethylene Oligomerization with New Complexes 1−5 and Complexes 6−10
oligomer distribution (wt %)
b
b
b
b
c
entry (cat.) yield (g) activity (kg/g Cr/h) 1-C6 (wt %)
1-C6 in C6 (%) cy-C6 (wt %)
1-C8 (wt %)
1-C8 in C8 (%) C10+ (wt %)
PE (wt %)
1 (1)
2 (2)
3 (3)
4 (4)
5 (4)
6 (5)
7 (5)
8 (5)
9 (6)
15.0
24.4
25.6
49.4
27.4
50.1
42.6
14.9
7.9
577
937
13.6
28.9
17.6
23.1
24.2
39.8
40.7
24.7
9.2
55.5
74.2
49.7
61.4
63.4
83.1
82.6
66.6
63.8
66.5
89.3
10.4
9.9
64.7
53.6
52.5
50.3
51.4
40.4
39.5
55.3
72.7
53.0
52.9
59.3
46.7
99.2
98.9
98.2
98.1
99.4
98.6
99.0
99.6
99.2
98.6
99.5
9.1
8.3
3.3
5.8
0.8
0.8
0.2
0.1
0.3
0.9
1.7
1.1
0.7
4.9
984
17.5
14.3
13.8
8.1
9.2
1900
2105
1926
3277
1908
305
11.5
9.7
d
11.3
10.6
6.8
d
e
8.2
12.2
5.2
10.2
11.5
9.4
10 (7)
11 (8)
12 (9)
43.2
40.4
1660
1552
144
23.0
33.4
15.7
7.3
11.3
4.0
f
8.7
f
13 (10)
303
17.3
5.2
a
b
Conditions: 120 mL reactor, 1.0 μmol of precatalyst, 500 equiv. of MMAO-3A, 40 bar of ethylene, 30 mL of methylcyclohexane, 40 °C, 30 min. wt
c
d
e
f
% of liquid products (oligomers). wt % of total product (oligomers + polymer). 15 min. 0.6 μmol of precatalyst. 50 bar of ethylene, 60 °C, taken
from ref 9.
mL of methylcyclohexane) (Table 1, entry 8). Poor activities
were obtained using the related precatalysts 9 and 10 bearing
carbon-bridged diphosphine ligands without backbone-sub-
situent (Table 1, entries 12 and 13).11 It suggests the significant
influence of backbone-subsituent in these carbon-bridged
diphosphine ligands on the outcome of the catalysis.
For the precatalysts 1−5, increasing the steric bulk of
backbone-subsituent leads to lowering the 1-octene/1-hexene
ratio and producing more 1-hexene. The selectivity trend is
similar to those reported for the PNP ligand catalyst system,
where increasing the steric bulk of N-subsituent also leads to a
decrease in the 1-octene/1-hexene ratio. In order to establish
the coordination mode of the carbon-bridged diphosphine
ligands and thus to understand well the subtle effect presented
by backbone-substituent on the catalyst preformance, Cr
complex based on ligand L5 was selected for structural analysis
by single-crystal X-ray diffraction. Reaction of L5 with
[Cr(CO)6] under reflux in toluene led to the formation of
the desired [Cr(CO)4(L5)] (11) (Scheme 2). Single crystals,
Scheme 2. Synthesis of Cr Complexes 11 Based on Ligand L5
Figure 3. Molecular structure of Cr complex 11.
Complex 11 has a larger bite angle than the PNP ligand in
12, but a smaller CPh−P−Cr angle is found in 11 (Figure 4).15
This is expected to be highly relevant to the lower 1-octene/1-
hexene ratio and the very high activitiy achieved by 5. The
effect presented by backbone-substituent could be well
understood by taking the steric environment around the
catalyst center into account. Figure 5 depicts possible reaction
intermediates and shows the proposed steric interactions
between diphosphine ligands and the growing metallacycle.
For the PNP−Cr catalyst system, the lowest 1-hexene/1-octene
ratio of 1:1 was achieved when using N-2,6-dimethylcyclohexyl
PNP ligand (LPNP, Figure 5).8d The authors assumed that
introducing a second methyl group in the N-cyclohexyl group
of PNP ligand leads to more pronounced interactions between
the methyl group with the catalyst center. As chromacyclono-
nane is sterically more demanding than chromacycloheptane,
the increased steric interaction in the intermediate causes the
coordination of ethylene to a seven-membered chromacyclic
intermediate unfavorable, which thus leads to lower 1-octene/
suitable for X-ray diffraction study, were obtained by slow
diffusion of n-hexane into CH2Cl2 solution of 11, and the
structure is illustrated in Figure 3. Complex 11 crystallizes with
two molecules in the asymmetric unit where the two
crystallographically independent molecules adopt similar
conformations. Complex 11 displays a distorted-octahedral
geometry with an expected planar Cr−P−C−C−P ring. In 11,
the repulsion between the backbone-substituent tert-butyl
group and adjacent phosphine phenyl groups results in a
smaller P1−C1−C2 angle (113.3°), compared to another P2−
C2−C1 angle (122.4°), and thus a smaller CPh−P1−Cr angle
(average, 113.9°), compared to another CPh−P2−Cr angle
(average, 119.0°).
2313
dx.doi.org/10.1021/cs400651h | ACS Catal. 2013, 3, 2311−2317

ACS Catalysis
Research Article
poor selectivity and poor activity when using the PCP ligand in
Cr-catalyzed ethylene oligomerization.9,16
Several studies have reported that the catalytic activity and
selectivity for ethylene oligomerization were strongly influenced
by the reaction conditions, such as temperature, ethylene
pressure, Al/Cr ratio, etc. In an attempt to improve the catalyst
performance, precatalysts 1, 4, and 5 were selected for further
investigation under different reaction conditions. The precata-
lysts were first tested under various reaction temperature and
ethylene pressure, and the results are shown in Table 2. For 1,
4, and 5, increasing temperature from 40 to 60 °C leads to an
increase in activity and 1-hexene selectivity. A decrease in the
formation of undesirable cyclic C6 products was observed and
thus led to an increase in selectivity to 1-hexene within the C6
fraction (Table 2, entries 1, 2, and 4). At 40 bar ethylene and at
60 °C, 5 achieved very high activity of up to 3869 kg/(g Cr/h)
with 53.2% 1-hexene selectivity and an increased selectivity
(93.4%) to 1-hexene within the C6 fraction, while selectivity
toward 1-octene drops to 25.8% (Table 2, entry 4). For 5,
further increasing reaction temperature to 80 °C slightly
decreased activity and the total selectivity toward 1-hexene and
1-octene and increased the formation of PE (Table 2, entry 5).
5 achieved high activity of 1324 kg/(g Cr/h) with the highest
1-hexene selectivity of 55.2% at low ethylene pressure of 20 bar
under 80 °C (Table 2, entry 7). For 4, decreasing ethylene
pressure from 40 to 30 bar causes a dramatic decrease in
activity, while 5 remained highly active at 30 bar similar to that
at 40 bar (Table 2, entries 3 and 6).
Figure 4. Comparison of molecular structure of complex 11 with
related complexes [Cr(CO)4(L6)] (12)15 and [Cr(CO)4(LPCP)] (LPCP
= Ph2PC(Me)PPh2, 13).16
The effect of Al/Cr molar ratio on catalytic properties and
selectivity were investigated next, and the results are shown in
Table 3. For 1, 4, and 5, increasing the Al/Cr molar ratio from
500 to 700 enhanced the activities and produced more 1-
hexene at the expense of 1-octene (Table 3, entries 1, 2, and 3).
An extremely high activity of 4238 kg/(g Cr/h) was obtained
using 5 with a high total selectivity of 79.1% toward valuable 1-
hexene (46.0%) and 1-octene (33.1%) (Table 3, entry 3).
Lowering the amount of MMAO-3A to 300 equiv led to a
decrease in the activity for 5 and produced more PE (Table 3,
entry 4).
Figure 5. Proposed steric interactions between ligand and metallacycle
(LPNP = Ph2PN(2,6-dimethylcyclohexyl)PPh2).
1-hexene ratio and form more 1-hexene. In the case of
t
complexes 3−5, the introduction of bulky Bu backbone-
substituent in 5 leads to more repulsion between backbone-
substituent and the adjacent phosphine phenyl groups, which
leads to more steric crowding around the catalytic center, and
then results in a shift toward 1-hexene formation. The repulsion
effect could be confirmed by the observation of a smaller CPh−
P1−Cr angle in 11. It is worth noting that the smaller CPh−P1−
Cr angle could also offer more protection for the active metal
center during the catalytic process, which probably attributes to
the very high catalytic activity achieved by 5. Compared to 12,
complex 13 bearing a PCP ligand (dppm) has larger bite angle
and larger CPh−P−Cr angle, which offers an explanation for the
CONCLUSIONS
■
Novel Cr(III) complexes with carbon-bridged diphosphine
ligands of the types {Ph2PCH(R)CH2PPh2} and {Ph2PC(R)
CHPPh2} have been prepared, which upon activation with
MMAO-3A, are highly active for ethylene tri/tetramerization
with considerable selectivity. We have presented that the ligand
backbone substitution and bridge unsaturation play an
a
Table 2. Evaluation of 1, 4, and 5/MMAO-3A for Selective Oligomerization under Different Reaction Conditions
oligomer distribution (wt %)
entry
(cat.)
C2H4 pressure
(bar)
activity
(kg/g Cr/h)
1-C
1-C6 in C6
(%)
cy-C
1-C
1-C8 in C8
(%)
C10+
(wt %)
PE
c
6 b
6 b
8 b
b
T (°C)
(wt %)
(wt %)
(wt %)
(wt %)
1 (1)
40
40
30
40
40
30
20
60
60
40
60
80
40
80
1100
2694
920
25.2
35.0
19.2
53.2
49.7
41.6
55.2
75.8
77.1
53.8
91.3
93.4
84.5
92.5
7.9
10.4
16.2
4.8
54.4
42.8
52.9
25.8
17.5
35
99.4
99.2
98.3
99.0
98.0
99.3
98.3
11.3
13.5
9.5
6.4
1.0
0.8
3.4
9.8
1.0
0.8
d
2 (4)
3 (4)
4 (5)
5 (5)
6 (5)
7 (5)
d
d
3869
3227
2188
1324
15.4
28.3
15.7
20.3
2.9
7.4
3.9
19.4
a
b
Conditions: 120 mL reactor, 1.0 μmol of precatalyst, 500 equiv. of MMAO-3A, 30 mL of methylcyclohexane, 30 min. wt % of liquid products
c
d
(oligomers). wt % of total product (oligomers + polymer). 15 min.
2314
dx.doi.org/10.1021/cs400651h | ACS Catal. 2013, 3, 2311−2317

ACS Catalysis
Research Article
a
Table 3. Evaluation of the Effect of Co-Catalyst on Selective Oligomerization
oligomer distribution (wt %)
entry
(cat.)
MMAO-3A
(equiv)
activity
(kg/g Cr/h)
1-C
1-C6 in C6
(%)
cy-C
1-C
1-C8 in C8
(%)
C10+
(wt %)
PE
c
6 b
6 b
8 b
b
(wt %)
(wt %)
(wt %)
(wt %)
1 (1)
2 (4)
3 (5)
700
700
700
300
1542
3223
4238
1711
27.9
31.2
46.0
43.3
77.3
73.5
87.6
85.7
8.0
11.3
6.4
54.1
43.3
33.1
34.5
99.3
99.2
99.3
99.2
9.1
13.4
13.5
14.4
1.5
0.6
0.3
6.8
d
4 (5)
7.1
a
b
Conditions: 120 mL of reactor, 1.0 μmol of precatalyst, MMAO-3A, 40 bar of ethylene, 30 mL of methylcyclohexane, 40 °C, 15 min. wt % of
c
d
liquid products (oligomers). wt % of total product (oligomers + polymer). 30 min.
important role in determining the activity and selectivity of
these ethylene oligomerization catalytic systems. Introduction
of a bulky group on the backbone in diphosphine ligand with
unsaturated linker dramatically increases the activity and favors
the formation of 1-hexene. The Cr complexes bearing
diphosphine ligand with an unsaturated linker achieved
extremely high activities, which are higher than those bearing
diphosphine ligand with a saturated linker. The highest
selectivity of 64.7% toward 1-octene was achieved using
diphosphine ligand with a methyl-substituted saturated linker,
and the highest activity of 4238 kg/(g Cr/h) was obtained
using diphosphine ligand L5 with a tert-butyl-substituted
unsaturated linker. The selectivity to 1-hexene can be improved
up to 55.2% using L5 at 20 bar and 80 °C. X-ray single-crystal
crystallographic analysis shows, although Cr complex 11
bearing L5 has a larger bite angle than that bearing a typical
PNP ligand, a smaller CPh−P−Cr angle is observed in it. The
feature could offer an explanation to the very high activity and
good total selectivity toward valuable 1-hexene and 1-octene
achieved by complex 5.
With the fine-tuned ligand backbone, such backbone-
substituent of carbon-bridged diphosphine ligand system
would allow for extensive ligand variation by further modifying
the backbone-substituents on the two backbone-carbon atoms
and the phosphine substituents and thus probably offer a mode
for precise understanding of the impact of ligand variations on
catalytic performance. Ongoing experiments are directed at the
development of other phosphine ligand systems especially on
the use of carbon-bridged diphosphine ligands to support olefin
oligomerization.
literature method,13 and their spectra were consistent with that
of the published data.17,18 L3 and L5 were prepared according to
the literature method,14 and their spectra were consistent with
that of the published data.14
Preparation and Characterization. Synthesis of Diphos-
phine Ligand L1, {Ph2PCH(Me)CH2PPh2}. 1,2-Propanediol (1.0
g, 13.2 mmol) and NEt3 (4.0 mL, 28.9 mmol) was dissolved in
CH2Cl2 (50 mL), and then methanesulfonyl chloride (2.15 mL,
27.6 mmol) was added dropwise. After 20 min, the mixture was
warmed to room temperature and stirred overnight. After full
consumption of the reagents, water was added, and the mixture
was extracted with CH2Cl2; the combined organic layers were
washed with brine and dried with anhydrous Na2SO4.
Evaporating the solvent afforded the crude MeCH(OMs)-
CH2(OMs), which was used without characterization. MeCH-
(OMs)CH2(OMs) was dissolved in THF (30 mL); the
solution was cooled to −78 °C, and a THF solution of
LiPPh2, prepared from nBuLi (1.6 M, 16.4 mL, 26.3 mmol) and
HPPh2 (4.8 g, 26.3 mmol), was added dropwise. After 20 min,
the mixture was warmed to room temperature and stirred
overnight. The solvent was removed under vacuum, and water
was added to give a white solid. The solid was filtered and then
purified by chromatography on short silica gel to yield L1 (3.1
1
g, 57.2%). H NMR (400 MHz, CDCl3): δ = 7.41−7.21 (m,
20H), 2.31−2.26(m, 2H), 1.90−1.81 (m, 1H), 1.28 (dd, 3H).
Synthesis of Diphosphine Ligand L2, {Ph2PCH(Ph)-
CH2PPh2}. The ligand L2 was prepared via a similar procedure,
in yield of 61.7%, illustrated below for L1. 1H NMR (400 MHz,
CDCl3): δ = 7.38−6.81 (m, 25H), 3.34−3.27 (m, 1H), 2.58−
2.43 (m, 2H).
Synthesis of Diphosphine Ligand L4, {Ph2PC(Cy)
CHPPh2}. Carbon-bridged diphosphine ligand L4 was prepared
in yield of 51.8%, according to literature method14 starting from
EXPERIMENTAL SECTION
■
General Information. Unless otherwise stated, all reactions
and manipulations were performed using standard Schlenk
techniques. All solvents were purified by distillation using
standard methods. Commercially available reagents were used
without further purification. MMAO-3A (modified methylalu-
minoxane) (7 wt % in heptane solution) was purchased from
Akzo-Nobel. NMR spectra were recorded by using a Bruker
400 MHz spectrometer. Chemical shifts are reported in ppm
from tetramethylsilane with the solvent resonance as the
internal standard (1H NMR CDCl3: 7.26 ppm; 13C NMR
CDCl3: 100.0 ppm). X-ray diffraction analysis was performed
by using a Bruker Smart-1000 X-ray diffractometer. Elemental
analyses were performed by the microanalytical laboratory in
house. Quantitative gas chromatographic analysis of the
products of oligomerization was performed on an Agilent
6890 Series GC instrument with a J&W DB-1 column working
at 36 °C for 10 min and then heating at 10 °C min−1 until 250
°C. n-Nonane was used as an internal standard. Diphosphine
ligands L1 and L2 were prepared according to modified
1
commerially available cyclohexylethyne. H NMR (400 MHz,
CDCl3): δ = 7.23−7.37 (m, 20H), 7.03 (d, J = 36 Hz, 1H),
2.08−2.02 (m, 1H), 1.49−1.52 (m, 2H), 1.35−1.38 (m, 2H),
1.23−1.31 (m, 2H), 1.13−1.19 (m, 2H). 13C NMR (100 MHz,
CDCl3): δ = 161.21, 161.05, 161.02, 160.09, 141.01, 140.94,
140.71, 140.65, 139.98, 139.96, 139.90, 139.87, 136.63, 136.59,
136.53, 136.48, 133.52, 133.36, 133.12, 132.91, 132.76, 132.58,
132.13, 128.31, 128.27, 128.22, 128.13, 128.10, 44.05, 26.59,
26.41, 25.97. 31P NMR (CDCl3): δ = −4.08 (dd, J1 = 34.9 Hz,
J2 = 166.4 Hz); −25.83 (d, J = 166.4 Hz).
Synthesis of Complexes 1−5. [L1CrCl2(μ-Cl)]2 (1). To a
solution of Ph2PCH(Me)CH2PPh2 L1 (0.123 g, 0.30 mmol) in
dry CH2Cl2 (3 mL) was added [CrCl3(THF)3] (0.105 g, 0.28
mmol), and the resulting mixture was stirred at room
temperature for 8 h. The solvent was evaporated, and 10 mL
of n-hexane was added to complete precipitation. The product
was collected by filtration, washed with 10 mL of n-hexane, and
dried in vacuo, yielding 1 (0.146 g, 92.1%) as blue powders.
2315
dx.doi.org/10.1021/cs400651h | ACS Catal. 2013, 3, 2311−2317

ACS Catalysis
Research Article
Anal. Calcd for C54H52Cl6Cr2P4 (%): C, 56.81; H, 4.59. Found:
C, 57.02; H, 4.25.
AUTHOR INFORMATION
■
Corresponding Author
*E-mail: zhangj@ecust.edu.cn.
[L2CrCl2(μ-Cl)]2 (2). The complex 2 was prepared as blue
powder via a similar procedure, in yield of 93.0%, illustrated
below for 1. Anal. Calcd for C64H56Cl6Cr2P4 (%): C, 60.73; H,
4.46. Found: C, 60.61; H, 4.53.
Notes
The authors declare no competing financial interest.
[L3CrCl2(μ-Cl)]2 (3). To a solution of Ph2PC(Ph)CHPPh2
L3 (0.141 g, 0.30 mmol) in dry toluene (10 mL) was added
[CrCl3(THF)3] (0.105 g, 0.28 mmol). The resulting mixture
was stirred at 80 °C for 8 h, and a blue precipitate formed. The
product was collected by filtration, washed with 10 mL of n-
hexene, and dried in vacuo, yielding 3 (0.168 g, 95.3%) as blue
powder. Anal. Calcd for C64H52Cl6Cr2P4 (%): C, 60.92; H,
4.15. Found: C, 60.39; H, 4.67.
ACKNOWLEDGMENTS
■
Financial support from Shanghai Pujiang Talent Program
(11PJ1402500), the Fundamental Research Funds for the
Central Universities (WK1114014), and the National Natural
Science Foundation of China (21171056) is greatly acknowl-
edged.
[L4CrCl2(μ-Cl)]2 (4). The complex 4 was prepared as blue
powder via a similar procedure, in yield of 96.1%, illustrated
below for 3. Anal. Calcd for C64H64Cl6Cr2P4 (%): C, 60.35; H,
5.06. Found: C, 60.76; H, 5.39.
REFERENCES
■
(1) (a) McGuinness, D. S. Chem. Rev. 2011, 111, 2321. (b) Dixon, J.
T.; Green, M. J.; Hess, F. M.; Morgan, D. H. J. Organomet. Chem.
2004, 689, 3641. (c) Wass, D. F. Dalton Trans. 2007, 816. (d) Agapie,
T. Coord. Chem. Rev. 2011, 255, 861.
[L5CrCl2(μ-Cl)]2 (5). The complex 5 was prepared as blue
powders via a similar procedure, in yield of 91.2%, illustrated
below for 3. Anal. Calcd for C60H60Cl6Cr2P4 (%): C, 58.99; H,
4.95. Found: C, 59.27; H, 5.21.
(2) Manyik, R. M.; Walker, W. E.; Wilson, T. P. J. Catal. 1977, 47,
197.
(3) (a) Reagan, W. K. Phillips Petroleum Company, EP, 0 417 477,
1991. (b) Freeman, J. W.; Buster, J. L.; Knudsen, R. D. Phillips
Petroleum Company, US Pat., 5856257, 1999. (c) Carter, A.; Cohen,
S. A.; Cooley, N. A.; Murphy, A.; Scutt, J.; Wass, D. F. Chem. Commun.
2002, 858. (d) McGuinness, D. S.; Wasserscheid, P.; Keim, W.; Hu,
C.; Englert, U.; Dixon, J. T.; Grove, C. Chem. Commun. 2003, 334.
(e) McGuinness, D. S.; Wasserscheid, P.; Keim, W.; Morgan, D.;
Dixon, J. T.; Bollmann, A.; Maumela, H.; Hess, F.; Englert, U. J. Am.
Chem. Soc. 2003, 125, 5272. (f) Yu, Z.; Houk, K. N. Angew. Chem., Int.
Ed. 2003, 42, 808. (g) Agapie, T.; Schofer, S. L.; Labinger, J. A.;
Bercaw, J. E. J. Am. Chem. Soc. 2004, 126, 1304. (h) Rensburg, W. J.;
Grove, C.; Steynberg, J. P.; Stark, K. B.; Huyser, J. J.; Steynberg, P. J.
Organometallics 2004, 23, 1207. (i) McGuinness, D. S.; Wasserscheid,
P.; Morgan, D. H.; Dixon, J. T. Organometallics 2005, 24, 552.
Synthesis of Complex 11. L5Cr(CO)4 (11). To a solution of
L5 (0.100 g, 0.220 mmol) in dry toluene (5 mL) was added
[Cr(CO)6] (0.064 g, 0.29 mmol), and the resulting mixture was
stirred under reflux for 48 h. The solvent was evaporated, and
the residue was extracted into DCM (1 mL). Six mL of
methanol was added to complete precipitation. The product
was collected by filtration, washed with 10 mL of methanol, and
dried in vacuo, yielding 11 (0.071 g, 52.0%) as white powder.
1H NMR (400 MHz, CDCl3): δ = 7.90 (dd, J = 56.4, 4.4, 1H),
7.65 (t, J = 8.2 Hz, 4H), 7.53 (t, J = 8.2 Hz, 4H), 7.42−7.39 (m,
12H), 1.11 (s, 9H). 13C NMR (100 MHz, CDCl3): δ = 147.36,
146.99, 146.91, 146.53, 137.87, 137.85, 137.51, 137.49, 135.53,
135.50, 135.21, 135.17, 131.57, 131.47, 131.26, 131.15, 129.66,
129.56, 128.72, 128.62, 128.31, 128.21, 40.94, 40.81, 32.95. 31P
NMR (CDCl3): δ = 98.90, 73.18. Anal. Calcd for
C34H30CrO4P2 (%): C, 66.23; H, 4.90. Found: C, 66.36; H,
4.71.
(j) Bluhm, M. E.; Walter, O.; Doring, M. J. Organomet. Chem. 2005,
̈
690, 713. (k) Nenu, C. N.; Weckhuysen, B. M. Chem. Commun. 2005,
1865. (l) Elowe, P. R.; McCann, C.; Pringle, P. G.; Spitzmesser, S. K.;
Bercaw, J. E. Organometallics 2006, 25, 5255. (m) Jabri, A.; Temple,
C.; Crewdson, P.; Gambarotta, S.; Korobkov, I.; Duchateau, R. J. Am.
Chem. Soc. 2006, 128, 9238. (n) Agapie, T.; Labinger, J. A.; Bercaw, J.
E. J. Am. Chem. Soc. 2007, 129, 14281. (o) McGuinness, D. S.; Suttil, J.
A.; Gardiner, M. G.; Davies, N. W. Organometallics 2008, 27, 4238.
(p) Jabri, A.; Mason, C. B.; Sim, Y.; Gambarotta, S.; Burchell, T. J.;
Duchateau, R. Angew. Chem., Int. Ed. 2008, 47, 9717. (q) Vidyaratne,
I.; Nikiforov, G. B.; Gorelsky, S. I.; Gambarotta, S.; Duchateau, R.
Angew. Chem., Int. Ed. 2009, 48, 6552.
(4) (a) Zhang, J.; Braunstein, P.; Hor, T. S. A. Organometallics 2008,
27, 4277. (b) Zhang, J.; Li, A.; Hor, T. S. A. Organometallics 2009, 28,
2935. (c) Zhang, J.; Li, A.; Hor, T. S. A. Dalton Trans. 2009, 9327.
(5) Klemps, C.; Payet, E.; Magna, L.; Saussine, L.; Le Goff, X. F.; Le
Floch, P. Chem.−Eur. J. 2009, 15, 8259.
(6) Sydora, O. L.; Jones, T. C.; Small, B. L.; Nett, A. J.; Fischer, A. A.;
Carney, M. J. ACS Catal. 2012, 2, 2452.
(7) Bollmann, A.; Blann, K.; Dixon, J. T.; Hess, F. M.; Killian, E.;
Maumela, H.; McGuinness, D. S.; Morgan, D. H.; Neveling, A.; Otto,
S.; Overett, M. J.; Slawin, A. M. Z.; Wasserscheid, P.; Kuhlmann, S. J.
Am. Chem. Soc. 2004, 126, 14712.
(8) (a) Blann, K.; Bollmann, A.; Dixon, J. T.; Hess, F.; Killian, E.;
Maumela, H.; Morgan, D. H.; Neveling, A.; Otto, S.; Overett, M. J.
Chem. Commun. 2005, 622. (b) Blann, K.; Bollmann, A.; Dixon, J. T.;
Hess, F. M.; Killian, E.; Maumela, H.; Morgan, D. H.; Neveling, A.;
Otto, S.; Overett, M. J. Chem. Commun. 2005, 620. (c) 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.;
Overett, M. J.; Pretorius, M.; Kuhlmann, S.; Wasserscheid, P. J. Catal.
2007, 249, 244. (d) Kuhlmann, S.; Blann, K.; Bollmann, A.; Dixon, J.
Oligomerization of Ethylene. A 120 mL stainless steel
reactor was dried at 120 °C for 3 h under vacuum and then
cooled down to the desired reaction temperature. The
precatalysts and cocatalysts (MMAO-3A) were combined in a
Schlenk vessel in the ratios indicated in Tables 1−3. The
resultant mixture was stirred for 1 min and immediately
transferred to the reactor. Then, the reactor was immediately
pressurized. After the specified reaction time, the reaction was
stopped by closing the ethylene feed, cooling the system to 0
°C, depressurizing, and quenching by addition of 30 mL of 10%
aq. HCl. A small sample of the upper-layer solution was filtered
through a layer of Celite and analyzed by GC using nonane as
the internal standard. The individual oligomerization products
were identified by GC-MS. The remainder of the upper-layer
solution was filtered to isolate the solid polymeric products.
The solid products were suspended in 10% aq. HCl and stirred
for 24 h, dried under reduced pressure, and weighed.
ASSOCIATED CONTENT
■
S
* Supporting Information
Representative NMR spectra and crystallographic data (CIF)
for 11. This material is available free of charge via the Internet
at http://pubs.acs.org.
2316
dx.doi.org/10.1021/cs400651h | ACS Catal. 2013, 3, 2311−2317

ACS Catalysis
Research Article
T.; Killian, E.; Maumela, M. C.; Maumela, H.; Morgan, D. H.;
Pretorius, M.; Taccardi, N.; Wasserscheid, P. J. Catal. 2007, 245, 279.
́
(9) 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.; Rucklidge, A.; Slawin, A. M. Z. J. Mol. Catal. A: Chem.
2008, 283, 114.
(10) Kim, S. K.; Kim, T. J.; Chung, J. H.; Hahn, T. K.; Chae, S. S.;
Lee, H. S.; Cheong, M.; Kang, S. O. Organometallics 2010, 29, 5805.
(11) (a) Dulai, A.; McMullin, C. L.; Tenza, K.; Wass, D. F.
Organometallics 2011, 30, 935. (b) Licciulli, S.; Thapa, I.; Albahily, K.;
Korobkov, I.; Gambarotta, S.; Duchateau, R.; Chevalier, R.; Schuhen,
K. Angew. Chem., Int. Ed. 2010, 49, 9225. (c) Shaikh, Y.; Gurnham, J.;
Albahily, K.; Gambarotta, S.; Korobkov, I. Organometallics 2012, 31,
7427. (d) Shaikh, Y.; Albahily, K.; Sutcliffe, M.; Fomitcheva, V.;
Gambarotta, S.; Korobkov, I.; Duchateau, R. Angew. Chem., Int. Ed.
2012, 51, 1366.
(12) Zhang, J.; Teo, P.; Pattacini, R.; Kermagoret, A.; Welter, R.;
Rogez, G.; Hor, T. S. A.; Braunstein, P. Angew. Chem., Int. Ed. 2010,
49, 4443.
(13) Bianchini, C.; Lee, H. M.; Meli, A.; Oberhauser, W.; Peruzzini,
M.; Vizza, F. Organometallics 2002, 21, 16.
(14) Kondoh, A.; Yorimitsu, H.; Oshima, K. J. Am. Chem. Soc. 2007,
129, 4099.
(15) Rucklidge, A. J.; McGuinness, D. S.; Tooze, R. P.; Slawin, A. M.
Z.; Pelletier, J. D. A.; Hanton, M. J.; Webb, P. B. Organometallics 2007,
26, 2782.
(16) Dulai, A.; de Bod, H.; Hanton, M. J.; Smith, D. M.; Downing, S.;
Mansell, S. M.; Wass, D. F. Organometallics 2009, 28, 4613.
(17) Yeo, W. C.; Tee, S. Y.; Tan, H. B.; Tan, G. K.; Koh, L. L.;
Leung, P. H. Inorg. Chem. 2004, 43, 8102.
(18) Zhang, Y.; Tang, L.; Pullarkat, S. A.; Liu, F.; Li, Y.; Leung, P. H.
J. Organomet. Chem. 2009, 694, 3500.
2317
dx.doi.org/10.1021/cs400651h | ACS Catal. 2013, 3, 2311−2317