Highly active chromium-based selective ethylene tri-/tetramerization catalysts supported by N,N-diphospholylamines

Article abstract of DOI:10.1016/j.ica.2017.05.042

We have developed novel Cr(III) catalysts supported by asymmetic N,N-diphospholylamine ligands bearing a phenoxaphosphine group. Upon activation with MMAO-3A, the Cr(III) catalysts supported by the PNP ligands are highly active for ethylene tri-/tetramerization with considerable selectivity. The ligand substitution and oligomerization conditions are found to be essential to achieve high activity and controllable selectivity. The catalytic system with asymmetric diphospholylamine ligands exhibited higher activity than that supported by symmetric ligands. Asymmetric diphospholylamine ligand with a N-cyclohexyl group achieved the highest activity of 282.2?kg/(g?Cr/h) with a high total selectivity of 83.2% toward valuable 1-hexene (28.7%) and 1-octent (54.5%) at 35?bar under 80?°C.

Full text of DOI:10.1016/j.ica.2017.05.042

Accepted Manuscript
Highly Active Chromium-Based Selective Ethylene Tri-/Tetramerization Cat-
alysts Supported by N,N-Diphospholylamines
Xiaoyu Ji, Liubing Song, Chengye Zhang, Jiajun Jiao, Jun Zhang
PII:
S0020-1693(17)30379-1
http://dx.doi.org/10.1016/j.ica.2017.05.042
ICA 17612
DOI:
Reference:
Inorganica Chimica Acta
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17 May 2017
22 May 2017
Please cite this article as: X. Ji, L. Song, C. Zhang, J. Jiao, J. Zhang, Highly Active Chromium-Based Selective
Ethylene Tri-/Tetramerization Catalysts Supported by N,N-Diphospholylamines, Inorganica Chimica Acta (2017),
doi: http://dx.doi.org/10.1016/j.ica.2017.05.042
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Inorganica Chimica Acta
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Highly Active Chromium-Based Selective Ethylene Tri-/Tetramerization Catalysts
Supported by N,N-Diphospholylamines
Xiaoyu Jia, Liubing Songa, Chengye Zhanga, Jiajun Jiaoa, Jun Zhanga,∗
aKey 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
ARTICLE INFO
ABSTRACT
Article history:
Received
Received in revised form
Accepted
We have developed novel Cr(III) catalysts supported by asymmetic N,N-diphospholylamine
ligands bearing a phenoxaphosphine group. Upon activation with MMAO-3A, the Cr(III)
catalysts supported by the PNP ligands are highly active for ethylene tri-/tetramerization with
considerable selectivity. The ligand substitution and oligomerization conditions are found to be
essential to achieve high activity and controllable selectivity. The catalytic system with
asymmetric diphospholylamine ligands exhibited higher activity than that supported by
symmetric ligands. Asymmetric diphospholylamine ligand with a N-cyclohexyl group achieved
the highest activity of 282.2 kg/(g Cr/h) with a high total selectivity of 83.2 % toward valuable
1-hexene (28.7 %) and 1-octent (54.5 %) at 35 bar under 80 oC.
Available online
Keywords:
Ethylene oligomerization
Chromium complex
Ethylene trimerization
Ethylene tetramerization
2009 Elsevier Ltd. All rights reserved.
1. Introduction
In view of the importance of 1-hexene and 1-octene in the production of polyethylene, the selective ethylene tri-/tetramerization have
been paid considerable attention from the academic and industrial communities throughout the world in the last two decades.[1-4] Since
the first Cr-based catalysts for ethylene trimerization emerged in 1977,[5] only few highly active and selective catalytic systems have
been reported for ethylene trimerization[6-22], such as the Phillips pyrrolide,[7] the BP diphosphinoamine,[8] and the Sasol mixed
heteroatomic[10] systems. One of us and Hor have also developed Cr(III) catalytic systems with tridentate heteroscorpionate pyrazolyl
ligands, exhibiting excellent selectivity (up to 98 wt%) for the production of 1-hexene.[23-25] PCNCP diphosphine ligands[26] and
amidine-containing P,N-ligands[27,28] were also been employed in Cr-based ethylene trimerization catalysts. In 2004, through
modification of the BP diphosphinoamine ligand (PNP; Fig. 1, A), Sasol research group has developed efficient Cr-based ethylene tri-
/tetramerization catalysts, where 1-octene selectivity up to 70% was achieved.[29] From then on, it is
gaining rapidly increasing attention to develop new Cr cataysts supported by different ligand donor set for the tri-/tetramerization
processes, most of which are based on the modification of the PNP ligand (A) system.[30-34] Numerous studies focused on varying the
R substituent on the central nitrogen atom in A, but a little attention has been paid to the modification of the P-substituent. Wass and co-
workers reported that by in situ combination with CrCl3(thf)3 and methylaluminoxane (MAO), PNP ligands B and C containing the
dibenzophosphole moiety are active in ethylene polymerization, producing only a very small amount of oligomeric products.[35]
However, the structurally related PNP ligands bearing 2,3,4,5-tetraethylphosphole moiety exhibit activity in Cr-catalyzed ethylene
oligomerization with excellent selectivity to 1-hexene and 1-octene. The authors proposed that the different catalytic performance of the
two kinds of ligands is possibly attributed to the rigidity of the dibenzophosphole moiety.[35]
∗ Corresponding author. Tel.: +086-021-64252995; e-mail: zhangj@ecust.edu.cn

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Inorganica Chimica Acta
Figure 1. Selected diphophine ligands for selective ethylene tri-/tetramerization.
As part of our studies on the design and synthesis of novel supporting ligands and their application in organometallic catalysis,[36-40]
particularly Cr-catalyzed ethylene tri-/tetramerization,[41] we recently reported Cr(III) catalysts supported by PNPO diphosphazane
ligand of the type Ph2PN(R)P(Ph)OAr, upon activation with MMAO-3A, are highly active for ethylene tri-/tetramerization with
considerable selectivity.[42] Herein, we report for the first time the synthesis of a family of new PNP ligands D and E generated by
replacing one or both PPh2 groups in ligand A with phenoxaphosphine moieties (Fig. 1). The catalytic performance of the new ligands
in Cr-catalyzed ethylene tri-/tetramerization was also evaluated.
2. Experimental
2.1. 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 methylaluminoxane) (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: 77.0 ppm). Mass spectra were recorded on the HP-5989 instrument by ESI
methods. 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. X-ray diffraction analysis was performed by using a Bruker Smart-1000X-ray diffractometer. 10-
chlorophenoxahosphine, Ph2PN(iPr)H and Ph2PN(Cy)H are known compounds, and were prepared according to modified literature
methods, respectively.[43,44] Their spectra were consistent with that of the published data.
2.2. Synthesis of of ligand L1:
o
In a representative procedure, 2.6 mL of n-butyllithium (1.6 M in hexanes. 4.11 mmol) was added dropwise at 0 C to a stirred
solution of 1.0 g of Ph2PN(iPr)H (4.11 mmol) in 15 mL of toluene. The reaction mixture was stirred for 30 min. Next, at 0 oC a solution
of 10-chlorophenoxahosphine (730 mg, 4.11 mmol) in 15 mL of toluene was added, and the reaction mixture was stirred for 4 h. The
solvent was removed under vacuum. The crude product was purified by column chromatography (silica gel; v/v, PE/ EtOAc = 20:1) to
afford L1 (285 mg ,15.7%). 1H NMR (400 MHz, CDCl3) :δ = 7.42-7.38 (m, 3H), 7.29-7.28 (m, 6H), 7.22-7.20 (m, 6H), 7.11-7.07 (m,
3H), 3.37-3.28 (m, 1H), 1.02 (d, J = 6.4 Hz, 6H). 13C NMR (100 MHz, CDCl3) :δ = 155.3, 135.5, 135.1, 132.8, 132.6, 131.1, 131.1,
130.8, 130.6, 129.0, 128.8, 128.4, 127.9, 127.9, 123.0, 122.9, 117.7, 51.6, 24.6. 31P NMR (162 MHz, CDCl3): δ = -16.1, -1.1 (br).
HRMS (ESI): m/z [M + H]+ calcd. for C27H26NOP2+: 442.1490; found: 442.1487; Anal. Calcd. for C27H25NOP2 (%): C, 73.46; H, 5.71;
N, 3.17; found: C, 73.51; H, 5.78; N, 3.39.
2.3. Synthesis of ligand L2:
L2 has been prepared similarly to L1 with yield of 11.8%, starting fromn-butyl lithium (1.6 M in hexanes. 4.11 mmol), Ph2PN(Cy)H
1
(100 mg, 0.20 mmol) and 10-chlorophenoxahos -phine (730 mg, 4.11 mmol). H NMR (400 MHz, CDCl3) :δ = 7.42-7.38 (m, 2H),
7.28-7.21 (m, 14H), 7.11-7.08 (m, 2H), 2.87-2.81 (m, 1H), 1.82-1.79 (m, 2H), 1.60-1.57 (m, 3H), 0.98-0.85 (m, 5H). 13C NMR (100
MHz, CDCl3) :δ = 155.2, 135.6, 135.2, 132.7, 132.5, 131.1, 128.4, 127.9, 127.8, 123.0, 122.9, 117.6, 59.9, 35.5, 26.3, 25.4. 31P NMR
(162 MHz, CDCl3): δ = 1.1, 56.3 (br). HRMS (ESI): m/z [M + H]+ calcd. for C30H30NOP2+: 482.1803, found: 482.1808; Anal. Calcd.
for C30H29NOP2 (%): C, 74.83; H, 6.07; N, 2.91; found: C, 74.67; H, 6.33; N, 3.19.
2.4. Synthesis of ligand L3:
At 0 oC Et3N (2.3 mL，11.08 mmol) was added dropwise to a solution of 10-chlorophenoxahosphine (731 mg, 4.11 mmol) in 15 mL
of dichloromethane and the reaction mixture was stirred for 10 min. Then isopropylamine (0.17 mL，1.94 mmol) was added, and the
reaction mixture was stirred for 4-5 h. All volatiles were removed under vacuum, and the rude product was purified by column
1
chromatography using silica gel (v/v, PE/ EtOAc = 20:1) to afford the L3 as a white solid (224 mg, 12.7%). H NMR (400 MHz,
CDCl3): δ = 7.41-7.38 (m, 4H), 7.20-7.18 (m, 4H), 7.06-6.94 (m, 4H), 6.92-6.85 (m, 4H), 3.02-2.88 (m, 1H), 0.91 (d, J = 6.8 Hz, 6H).
13C NMR (100 MHz, CDCl3): δ = 154.7, 135.3, 135.0, 131.1, 123.0, 122.9, 117.6, 51.1, 24.5. 31P NMR (162 MHz, CDCl3): δ = 3.1 (br).

HRMS (ESI): m/z [M + H]+ calcd. for C27H24NO2P2+: 456.1282, found: 456.1277; Anal. Calcd. for C27H23NO2P2 (%): C, 71.21; H, 5.09;
N, 3.08; found: C, 70.97; H, 5.19; N, 3.10.
2.5. Synthesis of ligand L4:
L4 has been prepared similarly to L3 with yield of 11.8%, starting from Et3N (2.3 mL, 16.10 mmol), cyclohexylamine (100 mg, 0.20
1
mmol) and 10-chlorophenoxahosphine (1.0 g, 4.26 mmol). H NMR (400 MHz, CDCl3): δ = 7.39-6.55 (m, 16H), 2.49-2.43 (m, 1H),
1.77-1.68 (m, 2H), 1.55-1.43 (m, 2H), 1.05-1.01 (m, 1H), 0.98-0.77 (m, 5H). 13C NMR (100 MHz, CDCl3): δ = 154.7, 135.5, 135.1,
131.1, 122.9, 122.8, 117.5, 59.5, 35.4, 26.4, 25.3. 31P NMR (162 MHz, CDCl3): δ = 3.7 (br). HRMS (ESI): m/z [M + H]+ calcd. for
C30H28NO2P2+: 496.1595, found: 496.1587; Anal. Calcd. for C30H27NO2P2 (%): C, 72.72; H, 5.49; N, 2.83; found: C, 72.61; H, 5.55; N,
2.84.
2.6 Synthesis of Pd complex 1
The mixture of L1 (50 mg, 0.113 mmol) and Pd(CH3CN)2Cl2 (29.23 mg, 0.11 mmol) was stirred in the DCM (3.0 mL) at room
temperature for 4-5 h. All volatiles were removed under vacuum, and the rude product was washed twice with petroleum ether to afford
1
pure 1 as a yellow solid (45 mg, 64%). H NMR (400 MHz, CDCl3) :δ = 8.30-8.28 (m, 2H), 8.26-8.23 (m, 4H), 8.01-7.96 (m, 4H),
7.74-7.68 (m, 4H), 7.63-7.59 (m, 2H), 7.45-7.35 (m, 2H), 3.31-3.19 (m, 1H), 0.40 (d, J = 6.8 Hz, 6H). 13C NMR (100 MHz, CDCl3): δ
= 156.9, 135.8, 134.5, 134.3, 133.5, 133.4, 129.7, 129.6, 125.4, 125.3, 119.0, 54.1, 29.7. 31P NMR (162 MHz, CDCl3) :δ = 34.3 (d, J =
25.9 Hz), -10.0 (d, J = 25.9 Hz). HRMS (ESI): m/z [M] calcd. for C27H25Cl2NO2P2Pd: 616.9823; found: 616.9820.
2.7 Oligomerization of ethylene
A 120 mL stainless steel reactor was dried at 120 ºC for 3 h under vacuum, and then cooled down to the desired reaction
temperature. The precatalysts and co-catalysts (MMAO) were combined in a Schlenk vessel in the ratios indicated in Table 1. 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 shutting off the ethylene feed, cooling the system at 0 ºC, depressurizing, and
quenched 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
analysed 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.
3. Results and discussion
Asymmetric diphosphine ligands L1 and L2 having two phenoxaphosphine groups were synthesized by a reaction of in-situ prepared
Ph2PNRLi with one equivalent of phenoxaphosphinous chloride[45] (Scheme 1). Symmetric diphosphine ligands L3 and L4 were
prepared by the treatment of RNH2 with two equivalents of phenoxaphosphinous chloride in the presence of Et3N (Scheme 2).
O
R
P
N
Ph2P
P
R
N
nBuLi
Cl
O
toluene, -78 oC
0 o
C
toluene,
H
Ph2P
i
R = Pr,
L1
L2
R = Cy,
Scheme 1. Synthesis of asymmetric diphosphine ligands L1 and L2
O
P
R
N
P
P
, Et3N
Cl
O
O
RNH2
CH2Cl2, rt
i
L3
L4
R = Pr,
R = Cy,
Scheme 2. Synthesis of symmetric diphosphine ligands L3 and L4
Table 1. Ethylene oligomerization with PNP ligands L1~L4 in conjunction with chromium
source and MMAO[a]

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Inorganica Chimica Acta
Oligomer distribution (wt%)
Activity
(kg/g
Cr/h)
Entry
(Ligand)
PE
cy-C6
(wt%)[c]
1-C6
1-C6 in C6
(%)
1-C8
1-C8 in C8
(%)
C10+
(wt%)[b
(wt%)[b]
(wt%)[b]
(wt%)[b]
]
1 (L1)
2 (L2)
102.0
232.3
32.9
20.1
21.7
17.7
10.6
13.2
15.7
10.4
62.7
85.9
43.5
23.5
58.7
62.7
20.8
8.5
3.5
60.8
60.8
53.6
44.4
66.9
63.9
36.0
99.6
99.8
98.9
99.6
99.8
99.8
98.4
6.8
10.1
6.6
13.8
5.2
3 (L3)
20.5
34.5
9.3
1.2
4 (L4)
27.6
10.5
10.5
10.9
13.1
11.1
5.2
5 (L1)[d]
6 (L2)[d]
7 (L2)[e]
81.5
102.3
54.1
9.4
2.4
39.8
12.0
[a] Conditions: 2.5 µmol Cr(acac)3, 1.2 equiv ligand, 600 equiv. MMAO-3A, 35 bar of ethylene, 30 mL
methylcyclohexane, 60oC, 30 min. [b] wt % of liquid products (oligomers). [c] wt % of total product
(oligomers+polymer). [d] 2.5 µmol CrCl3(THF)3, 1.2 equiv ligand. [e] 30 mL toluene as solvent.
The ligands L1~L4 were examined for ethylene oligomerization in conjunction with Cr(acac)3 or Cr(THF)3Cl3 upon activation with
MMAO, and the results are summarized in Table 1.
Upon activation of 600 molar excess of MMAO, all of the Cr precatalysts supported by diphosphine ligands (L1~L4) were active in
selective tri-/tetramerization reaction at 35 bar ethylene and 60 oC. Increasing steric bulk of N-alkyl group by replacing of the isopropyl
group in L1 with a cyclohexyl group in L2 dramatically enhanced the activity with similar selectivity toward both 1-hexene and 1-octene,
and less polymer was observed when using ligand L2 (Table 1, entries 1 and 2). Compared with the catalytic systems with asymmetric
L1 and L2, using those supported by symmetric ligands L3 and L4 led a significant decrease in activity, and produced less 1-hexene and
1-octene and more undesirable cyclic C6 products, respectively (Table 1, entries 3 and 4). The low activities of the catalysts supported
by symmetric ligands L3 and L4 are probably due to the rigidity of the two phenoxaphosphine moieties in them.
Asymmetric ligands L1 and ligand L2 achieved higher activities by using Cr(acac)3 as Cr source than by using CrCl3(THF)3 (Table 1,
entries 1, 2, 5 and 6). Reaction solvent had remarkable impact on the catalytic behavior in this catalyst system. L2 in
methylcyclohexane exhibited much higher activity and selectivity toward 1-hexene and 1-octene than those achieved in toluene (Table
1, entries 2 and 7).
Table 2. Catalyst performance of Cr(acac)3/PNP ligands L1 and L2 in methylcyclohexane[a]

Oligomer distribution (wt%)
Entry
(Ligand)
T
Activity
PE
Al/Cr
(oC) (kg/g Cr/h)
(wt%)[c]
1-C6
1-C6 in C6 cy-C6
1-C8
1-C8 in C8
(%)
C10+
(wt%)[b]
(%)
(wt%)[b] (wt%)[b]
(wt%)[b]
1 (L1)
2 (L2)
3 (L2)[d]
4 (L2)
5 (L2)
600
600
600
400
800
80 147.7
80 282.2
60 101.5
60 75.5
60 235.3
29.1
28.7
15.6
15.3
21.1
81.1
6.8
3.5
8.3
8.2
5.1
53.7
54.5
64.0
64.3
59.9
99.8
99.8
99.7
99.6
99.8
10.4
4.6
6.6
89.1
65.2
65.1
80.3
13.2
11.8
12.0
13.8
4.5
10.9
3.8
[a] Conditions: 2.5 µmol Cr(acac)3, 1.2 equiv ligand, 35 bar of ethylene, 30 mL methylcyclohexane, 30 min. [b] wt % of liquid products
(oligomers). [c] wt % of total product (oligomers+polymer). [d] 25 bar of ethylene.
In general, the catalytic activity and selectivity for ethylene oligomerization were significantly influenced by the reaction conditions,
such as Al/Cr ratio, temperature etc. Aimed to improve the catalyst performance, L1 and L2 were chosen for further investigation under
o
different reaction conditions. The results are shown in the Table 2. For L1 and L2, increasing temperature from 60 to 80 C led to an
increase in activity and selectivity toward 1-hexene, and a decrease in the 1-octene selectivity (Table 2, entries 1 and 2). L2 achieved the
highest activity of 282.2 kg/(g Cr/h) with a high total selectivity of 83.2 % toward valuable 1-hexene (28.7 %) and 1-octent (54.5 %) at
o
35 bar under 80 C (Table 2, entry 2). For L2, decreasing ethylene pressure from 35 to 25 bar causes a dramatic decrease in activity
(Table 2, entry 3). The effect of Al/Cr ratio on the catalytic performance of the Cr catalyst supported by L2 was further investigated.
Lowering the amount of MMAO to 400 equiv led to a decrease in activity for L3 and produced more polymer formation (Table 2, entry
4). Increasing the Al/Cr molar ratio from 600 to 800 enhanced slightly the activities and produced less polymer formation (Table 2,
entry 5).
Scheme 3. Synthesis of Pd Complex 1 Based on Ligand L1
Figure 2. Molecular structure of 1 with 20% probability. H atoms have been omitted for clarity. Selected bond lengths (Å) and angles
(deg): Pd(1)-P(2) 2.2089(13); Pd(1)-P(1) 2.2133(11); Pd(1)-Cl(1) 2.3533(12); Pd(1)-Cl(2) 2.3573(13); P(2)-Pd(1)-P(1) 71.73(5); P(2)-
Pd(1)-Cl(1) 95.07(5); P(1)-Pd(1)-Cl(1) 166.28(3); P(2)-Pd(1)-Cl(2) 167.79(3); P(1)-Pd(1)-Cl(2) 97.06(5); Cl(1)-Pd(1)-Cl(2) 96.40(6);
P(2)-N(1)-P(1) 100.06(14)

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Inorganica Chimica Acta
We next investigated the coordination mode of the novel PNP diphosphine ligands. After massive attempts to isolate single crystals
of Cr complexes ligated by L1~L2 failed, we managed to obtain a single crystal of their counterpart palladium complex 1 suitable for X-
ray diffraction analysis (Scheme 3 and Fig. 2) Pd complex 1, prepared by the reaction of L1 with PdCl2(MeCN)2, adopts a regular
square-planar coordination mode, involving two P atoms and two Cl atoms. This kind of coordination mode is typically observed in
other comparable symmetric PNP-Pd complexes.[46-48] In the coordination environment, the Pd–P bond lengths are 2.2089(13) and
2.2133(11) Å, respectively. Pd complex 1 has an acute P(1)–Pd–P(2) coordination angle (71.73(5)). The phenoxaphosphine group of 1
is directed away from the metal.
4. Conclusion
In summery, novel PNP ligand bearing phenoxaphosphine group have been synthesized. Upon activation with MMAO-3A, the
Cr(III) catalysts supported by the PNP ligands are highly active for ethylene tri-/tetramerization with considerable selectivity. The
ligand substitution and oligomerization conditions are found to be essential to achieve high activity and controllable selectivity. The
catalytic system with asymmetric L1 and L2 exhibited higher activity than that supported by symmetric ligands L3 and L4. Asymmetric
L2 with a N-cyclohexyl group achieved the highest activity of 282.2 kg/(g Cr/h) with a high total selectivity of 83.2 % toward valuable
o
1-hexene (28.7 %) and 1-octent (54.5 %) at 35 bar under 80 C. The Pd complex 1 ligated by L1 adopts a regular square-planar
coordination mode, involving two P atoms and two Cl atoms.
Acknowledgment
Financial support from Shanghai Pujiang Talent Program (11PJ1402500) and the National Natural Science Foundation of China for
financial support (21671066) is greatly acknowledged.
Appendix A. Supplementary data
Supplementary data associated with this article can be found, in the online version, at http://dx.doi.org/10.1016/j.ica.2017.
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8
Inorganica Chimica Acta
Highly active Chromium-Based Selective Ethylene Tri-/Tetramerization Catalysts
Supported by N,N-Diphospholylamines
Xiaoyu Ji, Liubing Song, Chengye Zhang, Jiajiao Jiao, and Jun Zhang
Cr(III) catalysts supported by asymmetic N,N-diphospholylamine ligands bearing a phenoxaphosphine
group are highly active for ethylene tri-/tetramerization with considerable selectivity upon activation with
MMAO-3A. Asymmetric PNP ligand with a N- cyclohexyl group achieved the highest activity of 282.2
kg/(g Cr/h) with a high total selectivity of 83.2 % toward valuable 1-hexene (28.7 %) and 1-octene (54.5
%) at 35 bar under 80 oC.