Catalytic Systems Based on Chromium(III) Silylated

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Catalytic Systems Based on Chromium(III) SilylatedDiphosphinoamines 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 Downloaded from http://pubs.acs.org on October 10, 2018

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ACS Catalysis

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,*,‡ 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

056005, China

ACS Paragon Plus Environment

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ABSTRACT: 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 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 switch the ethylene tetramerization systems to ethylene trimerization systems.

KEYWORDS: ethylene, trimerization, tetramerization, α-olefins, silylated-diphosphinoamine ligands, chromium, catalysis, DFT calculations


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ACS Catalysis

Introduction From an industrial perspective, linear α-olefins (predominantly 1-hexene and 1-octene) have attracted significant and prolonged attention over the last two decades.1 In contrast to conventional ethylene oligomerization technologies, which produce a broad range of products, many ethylene trimerization2 and tetramerization2a facilities are now actively involved in the selective production of highly demanded and valuable 1-hexene and 1-octene.1b, 2a, 3 Although a general mechanism involving a metallacycle has been established,1b,

4

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 theoretical studies.1b, 5 The Cr-based PNP diphosphines deliver the most efficient catalytic systems for ethylene tetramerization with the capability of producing 1-octene with 70% selectivity.6 Attempts in further enhancement, many alternative ligands with diphosphines scaffolds6a, 7 were made and scrutinized for selective ethylene tetramerization; however, these modifications proved unproductive. Consequently, investigations were extended to ligands beyond the diphosphine framework,8 and other alternatives were identified for selective ethylene tetramerization.2b, 8-9 To elucidate the origin of the high selectivity and the role of the Cr redox dynamism,5d, 10 Albahily et al.11 altered the ligand framework by substituting the methylene carbons flanking the nitrogen with dimethyl silyl groups (large electropositive substituents may control the stereochemistry of the reaction and influence the structure of the complex12) of the most efficient Cr-SNS trimerization system,13 and found that a simple modification in the ligand framework had a profound effect on the catalytic activity of the Cr-SNS system. Subsequently, Zhang et al.14


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incorporated silyl groups into the diphosphine framework and established a new class of efficient tetramerization catalysts with the potential to deliver as much as 16.8×106 g(product)·g(Cr)-1·h-1 high catalytic activity with 99% total α-selectivity. Considering the unique properties of silicon-based ligands11, 14 and their ability to increase the activity and selectivity toward α-olefins, we aimed to design and use a new class of silylatedPNP (Si-PNP) ligands for selective ethylene oligomerization. The Cr catalysts with the target SiPNP ligands were successfully activated for tri-/tetramerization, providing 83% C8 selectivity and more than 76,700 g(product)·g(Cr)-1·h-1 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 N-substituents on the overall catalytic performance and the relationship between the P-Cr-P bite angle and the product selectivity have also been established. Results and discussion Silylated-diphosphinoamine Ph2PN(R)Si(CH3)2CH2PPh2-type ligands (L1-L3) were prepared by a convenient salt metathesis method. Treatment of silylated-PNP ligands L1-L3 with [CrCl3(THF)3] in dichloromethane afforded corresponding Cr(III) complexes 1-3 (Scheme 1). The Cr(III) complexes 1-3 were not structurally characterized because single crystals suitable for X-ray analysis could not be obtained; nonetheless, the single-crystal analysis of [Cr(CO)4(L2)] (Figure 1) suggested that these complexes adopt a mononuclear k2-P, P bidentate binding mode. To investigate the effect of backbone N-substituents in ligands L1-L3 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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ACS Catalysis

Scheme 1. Synthesis of silylated-PNP ligands (L1-L3) and Cr complexes (1-3) At 1.0 MPa ethylene and 45 °C, in the presence of DMAO/Et3Al cocatalyst, the precatalysts (1-3) were found to be active in the selective tri-/tetramerization reaction (Table 1). Precatalyst 3, bearing an iPr moiety, exhibited high selectivity (69%) toward 1-octene with considerable catalytic activity (Table 1, entry 3). Increasing the steric bulk of the backbone N-substituents by replacement of the iPr group (in 3) with 2,6-diisopropylphenyl (in 2) and cyclopentyl (in 1) diminished the catalytic activity and resulted in the production of more 1-hexene at the expense of 1-octene with increased polymer formation (Table 1, entries 1-2). Similar trends in selectivity were reported for PNP6a and carbon-bridged diphosphine7b ligands in which an increase in the steric bulk of the backbone N-substituent decreases the 1-octene/1-hexene ratio and increases the production of 1-hexene. 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 catalyst is also present in the system.8c The very low catalytic activities of precatalysts 1 and 2 were attributed to their low stabilities.6a, 15 The inadequate separation between the Cr cations and the counterions in the reaction medium may also contribute to the low catalytic activities.16 These results indicate that the backbone N-substituent in these ligands strongly affects the catalytic performance. Table 1. Ethylene Oligomerization with Novel Silylated-PNP Based Complexes 1-3a Entry

Precatalyst

Product selectivity (wt %)

Activityb C4

a

c

C6

c

1-C6

cy-C6

c

C8

c, f

C10-C14

c

PE (g)d

1

1

925

3.83

54.63

96.38

1.45

41.54

Trace

1.23

2

2

842

2.93

50.97

92.91

2.57

46.10

trace

1.97

3

e

7461

˂1

33.96

85.44

4.89

69.16

trace

0.67

3

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(AlEt3), 4:1; b

g(product)·g(Cr)-1·h-1; cwt % of liquid products (oligomers); dwt of PE; en(precatalyst), 2.4

µmol; fC8 contains 100% 1-C8. To investigate the coordination chemistry and thus to elucidate the effect of the backbone Nsubstituent on the catalytic performance of the Si-PNP ligands, the L2-based Cr(CO)4 complex was selected for single-crystal X-ray diffraction analysis. The reaction of L2 with [Cr(CO)6] in refluxing toluene led to the formation of the desired [Cr(CO)4(k2-P, P-L2)] complex (6, Scheme 2). Single crystals suitable for X-ray diffraction analysis were obtained by slow diffusion of nhexane into a CH2Cl2 solution of 6 at -35 °C. The structure of complex 6 is illustrated in Figure 1.


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ACS Catalysis

Scheme 2. Synthesis of Cr complex 6 based on ligand L2

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): Cr1-P1, 2.3883(10); Cr1-P2, 2.4190(9); Cr1-C1, 1.886(2); Cr1-C2, 1.855(2); Cr1-C3, 1.887(2); Cr1-C4, 1.863(2); selected bond angles (deg): P1-Cr1-P2, 101.70(3); C1-Cr1-P1, 92.61(7); C2Cr1-P1, 89.25(7); C3-Cr1-P1, 83.69(7); C4-Cr1-P1, 172.96(6); C1-Cr1-P2, 89.03(7); C2-Cr1-P2, 168.96(7); C3-Cr1-P2, 93.40(7); C4-Cr1-P2, 85.32(7). Complex 6, with a planar Cr-P-C-Si-N-P ring, displays a distorted octahedral geometry. In 6, the repulsion between the backbone N-substituent (2,6-diisopropylphenyl) and the adjacent phosphine phenyl groups (Figure 2) results in a smaller CPh-P2-Cr angle (average, 112.56°) compared to the other CPh-P1-Cr angle (average, 116.63°). The large P1-Cr-P2 bite angle


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(101.70(3)°) with the smaller CPh-P2-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 the formation of 1-hexene (translated steric effect).6b, 7b Furthermore, the extra-large P1-Cr-P2 bite angle may also be responsible for the weak coordination between the ligands and Cr precursors, which in turn delivers low catalytic activity.7a, 7c

Figure 2. Proposed steric interactions between the ligand and the metallacycle.7b, 17 (LPNP = Ph2PN(2,6-dimethylcyclohexyl)PPh2). 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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ACS Catalysis

the activity (Table 2, entries 11-12), showing that an increase in temperature from the optimum may lead to deactivation of precatalyst 3-based catalytic system.18 Increasing temperature diminished the C8 selectivities and enhanced the C6 selectivities of 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 more C6 fraction at a higher temperature.19 The lower ethylene concentration at higher temperature may also decrease the selectivity toward C8.20 Like many other catalytic systems,4d,

15,

21

the cyclic-C6 (methylcyclopentane and

methylenecyclopentane) fraction was found in an almost 1:1 ratio in all the oligomerization products. The branched co-oligomer C10-C14 products generated by precatalyst 1 is due to the secondary co-trimerization and co-tetramerization reactions of 1-hexene and 1-octene with ethylene.4d, 15, 22 The selectivity for this fraction was attributed to a ligand selectivity effect.4d The amount of co-oligomerization products formed in a selective ethylene oligomerization is proportional to the productivity of the reaction.4d Thus, for precatalyst 1, more cooligomerization products (C10-C14) were observed when the catalytic activity was high (Table 2, entries 1-4; Table 3, entry 3; Table 4, entries 2-4 and Table 5, entries 1-4), while no co-oligomers 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 cooligomers at the expense of C6 and C8 and consequently decreases the α-selectivity of C6 and C8 fraction (Table 2, entries 1-4). This indicates that for precatalyst 1, a higher temperature favors co-oligomerization reaction.


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Table 2. Evaluation of the Effect of Reaction Temperature on Selective Oligomerizationa Entry

Precatalyst

T (°C)


Activityb C4

1

c

C6

c

1-C6

cy-C6

c

C8

c, f

C10-C14

c

PE (g)d

30

2096

7.31

60.67

97.05

1.70

26.63

5.39

0.39

45

3308

7.02

63.19

99.23

0.44

11.51

18.28

0.45

3

60

3500

3.40

63.67

99.60

0.23

6.55

26.38

0.26

4

75

4423

0.43

45.73

99.39

0.24

7.77

46.07

0.30

5

30

215

1.80

67.88

97.45

1.93

30.32

---

1.59

45

250

3.31

51.73

87.58

4.06

44.96

---

0.73

7

60

492

0.75

85.34

98.51

1.11

13.91

---

0.74

8

75

860

0.76

84.87

98.64

0.95

14.37

---

1.04

9

30

1381

2.91

23.09

76.90

5.07

74.00

---

0.35

45

7461

0.44

30.40

83.60

4.97

69.16

---

0.67

11

60

3538

0.38

37.94

89.87

4.07

61.68

---

0.27

12

75

2981

0.48

49.00

93.04

3.35

50.52

---

0.20

2 1

6 2

10

a

3e


(20 mL); reaction time, 30 min; n(Al)/n(Cr), 500 equiv; n(DMAO)/n(AlEt3), 4:1; b


µmol; fC8 contains 100% 1-C8. 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 13). This decrease in activity may be explained by the fact that catalyst loadings above the optimum concentration may interfere with the formation of the catalytically active species.23 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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ACS Catalysis

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 5-8). The results obtained for precatalyst 2 show that only a small amount of precatalyst 2 is converted into the active species during the oligomerization.23 For precatalysts 1 and 2, the octene to hexene ratio (OTH) decreases with increasing catalyst mass (Table 3, entries 1-8), showing that more C6 was formed at the expense of C8, while precatalyst 3 shows the opposite trend in C8 selectivity (Table 3, entries 9-13). The selectivity switching between C8 and C6 for precatalysts 1-3 might be attributed to a shift in the equilibria between different active species,8c, 24 which are responsible for the formation of C6 and C8 at different catalyst loadings. Table 3. Evaluation of the Effect of Mass Loading of 1-3 Precatalysts on the Catalytic Performancea Product selectivity (wt %)

Catalyst mass (µmol)

Activityb

1.2

925

3.83

2.4

1233

3

4.8

4 5

Entry

Precatalyst

c

C8

c, e

C10-C14

c

PE (g)d

cy-C6

54.63

96.38

1.45

41.54

---

1.23

8.69

70.33

97.59

0.94

20.98

---

1.59

3308

7.02

63.19

99.23

0.44

11.51

18.28

0.45

9.6

496

6.14

83.93

98.88

0.51

9.93

---

0.58

1.2

842

2.93

50.97

92.91

2.57

46.10

---

1.97

2.4

450

2.75

62.12

94.25

2.44

35.13

---

2.03

7

4.8

250

3.31

51.73

87.58

4.06

44.96

---

0.73

8

9.6

113

3.04

73.80

96.20

2.58

23.16

---

0.99

9

0.6

2173

2.41

42.34

91.51

3.55

55.25

---

0.97

10

1.2

5231

0.61

33.96

85.44

4.89

65.43

---

0.79

2.4

7461

0.44

30.40

83.60

4.97

69.16

---

0.67

12

4.8

7211

0.53

32.27

84.13

5.1

67.20

---

0.53

13

9.6

2019

1.00

30.31

83.08

4.94

68.69

---

0.49

2

C6

c

1-C6

1

C4

c

1

6 2

11

3


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General conditions: pressure, 1.0 MPa; solvent, methylcyclohexane (20 mL); reaction time, 30

min; T, 45 °C; n(Al)/n(Cr), 500 equiv; n(DMAO)/n(AlEt3), 4:1; bg(product)·g(Cr)-1·h-1; cwt % of liquid products (oligomers); dwt of PE; eC8 contains 100% 1-C8. Generally, a higher Al/Cr ratio was found to be favorable for the activity of precatalysts 1-3 (Table 4), showing that excess cocatalyst was needed for complete activation.25 The coordination strength of catalyst ion-pair and the extent of its separation may influence the C6 and C8 selectivity, which in turn related with the cocatalyst concentration.26 Increasing cocatalyst concentration may increase the coordination strength of the ion-pairs of precatalyst 1 and 2, resulting inadequate separation and block further ethylene uptake to chromacycloheptane to form chromacyclononane.16 The chromacycloheptane may undergo β-hydride elimination and form more C6 than C8. Furthermore, increasing the cocatalyst ratio may increase the rate of chain 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 β-hydride elimination in chromacycloheptane, resulting more C6 (Table 4, entries 1-8).27 On the other hand, precatalyst 3 needs more cocatalyst for its complete activation, as its activity and C8 selectivity more enhanced 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 C8 selectivity at the expense of C6 when the Al/Cr ratio is increased (Table 4, entries 9-12).


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ACS Catalysis

Table 4. Evaluation of the Effect of Al/Cr Molar Ratios on Selective Oligomerizationa Entry

Precatalyst

n(Al)/n(Cr)


Activityb C4

1

c

C6

c

1-C6

cy-C6

c

C8

c, f

PE (g)d C10-C14

c

100

296

4.90

57.95

97.14

1.2

37.15

---

1.51

300

2538

3.32

60.30

99.24

0.34

8.29

28.09

1.20

3

500

3308

7.02

63.19

99.23

0.44

11.51

18.28

0.45

4

700

2577

3.91

66.01

99.24

0.38

9.30

20.78

0.50

5

100

281

2.00

45.28

93.65

2.29

52.72

---

2.35

300

185

1.09

68.15

95.23

2.53

30.76

---

1.23

7

500

250

3.31

51.73

87.58

4.06

44.96

---

0.73

8

700

473

1.22

50.62

91.70

3.81

48.16

---

0.48

9

100

58

3.85

40.82

86.83

4.92

55.33

---

0.05

300

740

2.66

43.39

90.00

3.99

53.95

---

0.65

11

500

7461

0.44

30.40

83.60

4.97

69.16

---

0.67

12

700

13385

0.32

28.58

81.54

4.80

71.10

---

0.23

2 1

6 2

10

a

3e


(20 mL); reaction time, 30 min; T, 45 °C; n(DMAO)/n(AlEt3), 4:1; bg(product)·g(Cr)-1·h-1; cwt % of liquid products (oligomers); dwt of PE; en(precatalyst), 2.4 µmol; fC8 contains 100% 1-C8. The cocatalyst composition had a considerable impact on the catalyst behavior.16, 28 Therefore, the effect of the DMAO/Et3Al ratio on the catalytic behavior was investigated for precatalysts 13 (Table 5). An optimum ratio of DMAO/Et3Al is needed to completely activate the catalytic system and thus produce a high activity. The use of a large amount of Et3Al may deactivate the system while using less may not fully activate the catalytic system.16, 29 Precatalyst 1 shows the lowest combine selectivity (C6 + C8) at the lowest DMAO/Et3Al ratio (Table 5, entry 4). This low combine selectivity of C6 and C8 might be attributed to the involving of these fractions in cooligomerization reactions at these catalytic conditions, resulting more C10-C14 co-oligomers which consequently decrease the selectivity of C6 and C8 fractions (Table 5, entries 1-4). On the


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other hand, decreasing the DMAO/Et3Al ratio switched the precatalyst 2-based catalytic system to trimerization and resulted in the formation of more C6. It might be due to the chain transfer to aluminum because of the increased ratio of Et3Al (Table 5, entries 5-8).27 Precatalyst 3 produces 76% C8 fraction at a 2:3 DMAO/Et3Al ratio and shows considerable activity (Table 5, entry 11). Table 5. Evaluation of the Effect of DMAO/Et3Al on Selective Oligomerizationa Entry

Precatalyst

1

DMAO/Et3Al

Activityb


PE

C4c

C6c

1-C6

cy-C6c

C8c, f

C10-C14c

(g)d

4:1

3308

7.02

63.19

99.23

0.44

11.51

18.28

0.45

3:2

4923

4.33

62.09

99.33

0.30

9.56

24.02

0.37

3

2:3

5250

2.11

54.17

98.92

0.36

8.33

35.39

0.18

4

1:4

3923

1.25

44.62

98.91

0.34

5.54

48.59

0.19

5

4:1

250

3.31

51.73

87.58

4.06

44.96

---

0.73

3:2

363

1.07

81.81

97.39

1.67

17.12

---

1.16

7

2:3

233

1.74

86.81

96.45

2.01

11.45

---

0.60

8

1:4

852

2.11

75.88

95.02

2.46

22.01

---

0.60

9

4:1

7461

0.44

30.40

83.60

4.97

69.16

---

0.67

3:2

7519

0.69

27.87

80.04

5.51

71.44

---

0.07

11

2:3

4231

0.98

22.99

76.98

4.85

76.03

---

0.21

12

1:4

1221

6.86

24.83

72.17

4.02

68.32

---

0.09

2 1

6 2

10

a

3e


(20 mL); reaction time, 30 min; T, 45 °C; n(Al)/n(Cr), 500 equiv; bg(product)·g(Cr)-1·h-1; cwt % of liquid products (oligomers); dwt of PE; en(precatalyst), 2.4 µmol; fC8 contains 100% 1-C8. 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 g(product)·g(Cr)-1·h-1) 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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ACS Catalysis

higher ethylene solubility under these conditions.6a,

20

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 ethylene concentration in the solvent,30 which in turn enhances the chain propagation rate and thus improves the catalytic activity and C8 selectivity. The formation of C10-C14 fraction by 3 (Table 6, entries 4-6) was attributed to the product concentration22e when the catalytic activity was higher. Table 6. Evaluation of 3 for Selective Oligomerization under Different Reaction Conditionsa Catalyst (µmol)

Pressure (MPa)

T (°C)

n(Al)/n(Cr)

1

2.4

1

45

1000

13, 077

2

1.2

1

45

2000

3

0.6

1

45

4

2.4

4

5

2.4

6

Entry

Product Selectivity (wt %)

Activityb

C6

c

c

C8

c, e

C10-14

c

PE (g)d

1-C6

cy-C6

0.32

23.13 79.53

4.58

76.55

-

0.20

8, 269

0.41

19.97 79.54

4.05

79.62

-

0.29

4000

10, 173

0.29

18.65 75.28

4.25

81.06

-

0.11

15

500

76, 731

0.42

18.21 76.63

4.12

71.22

10.15

3.09

3

15

500

70, 577

0.39

17.89 75.15

4.32

71.96

9.76

1.05

0.6

4

15

1000

59, 615

0.72

18.51 74.05

4.61

70.54

10.23

3.31

7

0.3

4

15

2000

43, 461

0.86

15.87 62.34

5.70

83.27

-

0.51

8

0.3

3

15

2000

8, 846

1.52

17.38 58.32

6.38

81.03

-

0.20

9

0.1

4

15

6000

7, 711

2.20

17.88 66.61

5.35

79.92

-

0.10

a

C4

c

General conditions: solvent, methylcyclohexane (20 mL); reaction time, 30 min;

n(DMAO)/n(AlEt3), 4: 1; bg(product)·g(Cr)-1·h-1; cwt % of liquid products (oligomers); dwt of PE; eC8 contains 100% 1-C8. 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 1-hexene or 1-octene. Moreover, changing the ligands scaffold and steric constraints may promote the formation of either monochromium or


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dichromium species and hence influence the 1-C8 selectivity.7d,

Page 16 of 35

24

In an effort to change the

equilibrium between monochromium and dichromium catalytic species and to explore its effect on 1-C8 selectivity, other silylated-PNP [{Ph2PCH2Si(CH3)2}2N(R)]-type ligands (L4 and L5) were prepared by a one-pot reaction method. Treatment of L4 and L5 with [CrCl3(THF)3] in dichloromethane afforded corresponding Cr(III) complexes 4 and 5 (Scheme 3).

Scheme. 3 Synthesis of silylated-PNP ligands (L4-L5) 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 7-8). This selectivity switching to 1hexene could not be attributed to the equilibrium shifting between monochromium and dichromium species,7e, 24 instead, we assumed that the presence of a third donor N in the L4 and L5 framework switch the catalytic systems 4 and 5 from mononuclear-bidentate (k2-P, P) (Scheme 1, 1-3) to mononuclear-tridentate (k3-P, N, P) (Scheme 3, 4-5) binding mode,6b,


31

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which consequently switch the tetramerization systems to trimerization and produce more C6.13, 29a, 32

Moreover, modification of the ligands backbone may also change the steric constraints

around the catalytic active center and alters the P1-Cr-P2 bite angle, these factors might also contribute to selectivity switching and low catalytic activity of precatalysts 4 and 5.6c, 7a, 7c, 33 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 ethylene-rich environment for the catalysts. No selectivity for C8 was observed when using toluene as 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 form the chromacyclononane intermediate.21a Table 7. Evaluation of 4 for Selective Oligomerization under Different Reaction Conditionsa Entry


Activityb C4

a

c

C6

c

1-C6

cy-C6

c

C8

c, k

PE (g)d

1e

619

6.76

84.84

93.82

1.40

8.39

0.18

2

644

6.15

77.57

91.67

1.97

16.28

0.20

3f

475

6.54

56.90

85.59

3.29

36.56

0.26

4g

577

1.06

77.85

97.34

1.83

21.09

0.35

5h

913

0.75

88.19

98.22

1.47

11.06

0.55

6i

315

2.62

74.50

95.25

1.97

22.88

0.34

7j

308

4.63

74.81

92.30

2.02

20.56

0.14





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Page 18 of 35

µmol; fn(precatalyst), 1.2 µmol; gT, 60 °C; hn(Al)/n(Cr), 700 equiv; in(DMAO)/n(AlEt3), 3:2; j

n(DMAO)/n(AlEt3), 2:3; kC8 contains 100% 1-C8.

Table 8. Evaluation of 5 for Selective Oligomerization under Different Reaction Conditionsa Entry


Activityb C4

a

c

C6

c

1-C6

cy-C6

c

C8

c, l

PE (g)d

1e

111

1.60

85.30

96.38

2.32

13.10

0.35

2

261

0.99

87.44

95.31

2.22

11.57

0.43

3f

354

1.03

77.99

93.09

2.62

20.99

0.48

4g

125

1.84

79.82

90.30

3.04

18.34

0.09

5h

456

0.71

91.44

93.29

1.77

7.85

0.21

6i

142

1.29

80.99

83.74

3.19

17.72

0.13

7j

140

2.10

82.77

85.33

3.43

15.13

0.12

8k

158

33.35

66.65

84.49

1.01

-

0.35




µmol; fn(precatalyst), 1.2 µmol; gT, 60 °C; hn(Al)/n(Cr), 700 equiv; iCH2Cl2 used as solvent for the coordination; jtoluene used as solvent for the coordination; ktoluene used as solvent for the coordination and screening; lC8 contains 100% 1-C8. To further rationalize the high selectivity of precatalyst 3 toward 1-C8, DFT calculations were conducted. Previous theoretical studies31,

33b

suggested that the M06L34 density functional is

more accurate for analyzing the multiple spin states, oxidative coupling and reductive elimination steps involved in the Cr metallacycle-based mechanism.4b-d,

35

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 1-C6/1-


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C8 selectivity.36 Moreover, DFT was also used to rationalize the effect of steric bulk on selectivity of tri- verses tetramerization for PCNCP-based Cr complexes.37 Figure 3 shows the relative Gibbs free energy profiles of 1-hexene and 1-octene formation catalyzed by Cr precatalyst 3. Initially, bisethylene complex 62 faces a high energy barrier (38.9 kcal/mol) to form the metallacycle on the sextet surface; therefore, intermediate 62 is converted to intermediate

4

2 through spin crossing (see the Supporting Information for MECP

calculation)38 and forms chromacyclopentane 3b (an important intermediate in the metallacycle mechanism4a, 4c, 22a, 39) 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 (rate-determining intermediate for path 1 and path 3). Upon coordination of the second ethylene, intermediate 5 may pass through TS6e, 7 (rate-determining transition state in path 1) with a 13.7 kcal/mol energy barrier and form 1-C8. Depending on the type of ligand and experimental conditions, β-H elimination may compete with the coordination of a second ethylene in intermediate 5 and cause the reaction to pass through path 3 and release 1-C6 via TS5, 9 (rate-determining transition state in path 3) with a total energy barrier of 17.1 kcal/mol. Considering path 2 (double coordination pathway), upon coordination of two ethylene units, 3b (rate-determining intermediate in path 2) may pass through TS5, 6a (rate-determining transition state in path 2) with a 14.4 kcal/mol energy barrier and liberate 1C8. Small energy barriers (13.7 kcal/mol for path 1 and 14.4 kcal/mol for path 2) indicate that both pathways (single and double coordination) are energetically favored and can produce 1-C8 under mild conditions, and this is in full agreement with our experimental results (production of 1-C8 under mild conditions). In general, the low energy barriers for path 1 and path 2 suggest that single and double coordination may occur simultaneously, nevertheless a slightly lower free


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Page 20 of 35

energy barrier for path 1 shows that single coordination is thermodynamically more favorable for the L3-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 pressure may lead the path 2 more favorable for 1-C8 formation (see Supporting Information).22d, 40

Besides the energy perspective, the chain transfer to aluminum,27 the involvement of C6 and C8

fractions in co-oligomerization reactions4d, 15, 22 and the insufficient separation of the ion-pair26 are the other important factors which significantly influence the C8 selectivity and therefore should be taken into account. To provide a theoretical base for the switching of the binding mode from tetramerization to trimerization, we speculated that when a third donor is present in the ligand framework (as in L4 and L5), intermediate 5 has no vacant coordination sites available for another ethylene to coordinate and form chromacyclononane 7. Consequently, β-H elimination overcomes an energy barrier of 17.1 kcal/mol and liberates more 1-hexene from intermediate 9.


20

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Figure 3. Relative Gibbs free energy profiles for the ethylene tri-/tetramerization catalyzed by chromium precatalyst 3 (61); all stationary points are cationic.


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Page 22 of 35

In summary, we have reported Cr(III) precatalysts with {Ph2PN(R)Si(CH3)2CH2PPh2)}- and [{Ph2PCH2Si(CH3)2}2N(R)]-type silylated-diphosphinoamine ligands, which upon activation with DMAO/Et3Al, can produce active and selective tri-/tetramerization systems. We observed that the backbone N-substituents and experimental conditions strongly influence the catalytic performance of these precatalysts. Precatalyst 3, bearing an iPr substituent on the backbone N, efficiently formed

C8 ,

while

precatalyst

2,

having

a

bulkier

N-substituent

(2,6-

diisopropylphenyl), favors C6 formation. A relatively low catalyst mass, low temperature and high ethylene pressure promote C8 selectivity; and the selectivity of precatalyst 3 can be tuned 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 1-C8 selectivity 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 1-C8 formation made precatalyst 3 an efficient catalyst for the tetramerization. Crystallographic investigations showed that the larger P1-Cr-P2 bite angle with smaller CPh-P-Cr angle can shift the C8 selectivity toward C6 in 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 Si-based ligands for selective ethylene oligomerization are underway.


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ASSOCIATED CONTENT 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 *E-mail: [email protected] *E-mail: [email protected] 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 Cutting-edge Technology Research Program (Grant: 16JCZDJC31600).


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Page 24 of 35

REFERENCES (1) (a) Dixon, J. T.; Green, M. J.; Hess, F. M.; Morgan, D. H. Advances in Selective Ethylene Trimerisation-A Critical Overview. J. Organomet. Chem. 2004, 689, 3641-3668. (b) McGuinness, D. S. Olefin Oligomerization via Metallacycles: Dimerization, Trimerization, Tetramerization, and Beyond. Chem. Rev. 2011, 111, 2321-2341. (c) Agapie, T. Selective Ethylene Oligomerization: Recent Advances in Chromium Catalysis and Mechanistic Investigations. Coord. Chem. Rev. 2011, 255, 861-880. (d) Van Leeuwen, P. W.; Clément, N. D.; Tschan, M. J.-L. New Processes for the Selective Production of 1-Octene. Coord. Chem. Rev. 2011, 255, 1499-1517. (2) (a) Breuil, P.A. R.; Magna, L.; Olivier-Bourbigou, 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, 173-192. (b) Peitz, S.; Peulecke, N.; Aluri, B. R.; Hansen, S.; Müller, B. H.; Spannenberg, A.; Rosenthal, U.; Al-Hazmi, 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, 1167-1171. (c) Peitz, S.; Peulecke, N.; Aluri, B. R.; Müller, B. H.; Spannenberg, A.; Rosenthal, U.; Al-Hazmi, M. H.; Mosa, F. M.; Wöhl, A.; Müller, W. Activation and Deactivation by Temperature: Behavior of Ph2PN(iPr)P(Ph)N(iPr)H in the Presence of Alkylaluminum Compounds Relevant to Catalytic Selective Ethene Trimerization. Chem. Eur. J. 2010, 16, 12127-12132. (3) Sydora, O. L.; Jones, T. C.; Small, B. L.; Nett, A. J.; Fischer, A. A.; Carney, M. J. Selective Ethylene Tri-/Tetramerization Catalysts. ACS Catal. 2012, 2, 2452-2455.


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(4) (a) Emrich, R.; Heinemann, O.; Jolly, P. W.; Krüger, C.; Verhovnik, G. P. The Role of Metallacycles in the Chromium-Catalyzed Trimerization of Ethylene. Organometallics 1997, 16, 1511-1513. (b) Meijboom, N.; Schaverien, C. J.; Orpen, A. G. Organometallic Chemistry of Chromium(VI): Synthesis of Chromium(VI) Alkyls and their Precursors. X-ray Crystal Structure of the Metallacycle Cr(NtBu)2{o-(CHSiMe3)2C6H4}. Organometallics 1990, 9, 774-782. (c) Agapie, T.; Schofer, S. J.; Labinger, J. A.; Bercaw, J. E. Mechanistic Studies of the Ethylene Trimerization Reaction with Chromium-Diphosphine Catalysts: Experimental Evidence for a Mechanism Involving Metallacyclic Intermediates. J. Am. Chem. Soc. 2004, 126, 1304-1305. (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, 10723-10730. (5) (a) Thapa, I.; Gambarotta, S.; Korobkov, I.; Duchateau, R.; Kulangara, S. V.; Chevalier, R. Switchable Chromium(II) Complexes of a Chelating Amidophosphine (N-P) for Selective and Nonselective Ethylene Oligomerization. Organometallics 2010, 29, 4080-4089. (b) Albahily, K.; Koç, E.; Al-Baldawi, D.; Savard, D.; Gambarotta, S.; Burchell, T. J.; Duchateau, R. Chromium Catalysts Supported by a Nonspectator NPN Ligand: Isolation of Single-Component Chromium Polymerization Catalysts. Angew. Chem. Int. Ed. 2008, 47, 5816-5819. (c) Jabri, A.; Crewdson, P.; Gambarotta, S.; Korobkov, I.; Duchateau, R. Isolation of a Cationic Chromium(II) Species in a Catalytic System for Ethylene Tri- and Tetramerization. Organometallics 2006, 25, 715-718. (d) Jabri, A.; Temple, C.; Crewdson, P.; Gambarotta, S.; Korobkov, I.; Duchateau, R. Role of the Metal Oxidation State in the SNS-Cr Catalyst for Ethylene Trimerization: Isolation of Di- and Trivalent Cationic Intermediates. J. Am. Chem. Soc. 2006, 128, 9238-9247. (e) McDyre, L. E.; Hamilton, T.; Murphy, D. M.; Cavell, K. J.; Gabrielli, W. F.; Hanton, M. J.; Smith, D. M. A cw


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EPR and ENDOR Investigation on a Series of Cr(I) Carbonyl Complexes with Relevance to Alkene Oligomerization Catalysis:[Cr(CO)4L]+ (L = Ph2PN(R)PPh2, Ph2P(R)PPh2). Dalton Trans. 2010, 39, 7792-7799. (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, 3849-3856. (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)x(Ph2PN(iPr)PPh2)]+ Structural Isomers by Reaction of Triethylaluminum with a Chromium N,N-Bis(diarylphosphino)amine Complex [Cr(CO)4(Ph2PN(iPr)PPh2)]+: An EPR and DFT Investigation. Organometallics 2013, 32, 19241931. (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 1-Octene in Exceptionally High Selectivities. J. Am. Chem. Soc. 2004, 126, 14712-14713. (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 Polar-Substituted Diphosphinoamine Ligands. Chem. Commun. 2005, 622-624. (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 Chromium-Based Ethylene Trimerisation Catalysts with Bulky Diphosphinoamine Ligands. Chem. Commun. 2005, 620-621. (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. Carbon-Bridged Diphosphine Ligands for Chromium-Catalysed Ethylene Tetramerisation and Trimerisation Reactions. J. Mol. Catal. A: Chem. 2008, 283, 114-119. (b) Zhang, J.; Wang, X.; Zhang, X.; Wu, W.; Zhang, G.;


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Xu, S.; Shi, M. Switchable Ethylene Tri-/Tetramerization with High Activity: Subtle Effect Presented by Backbone-Substituent of Carbon-Bridged Diphosphine Ligands. ACS Catal. 2013, 3, 2311-2317. (c) Dulai, A.; de Bod, H. t.; Hanton, M. J.; Smith, D. M.; Downing, S.; Mansell, S. M.; Wass, D. F. C-Substituted Bis(diphenylphosphino)methane-Type Ligands for ChromiumCatalyzed Selective Ethylene Oligomerization Reactions. Organometallics 2009, 28, 4613-4616. (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. 2012, 51, 1366-1369. (8) (a) Yang, Y.; Gurnham, J.; Liu, B.; Duchateau, R.; Gambarotta, S.; Korobkov, I. Selective Ethylene Oligomerization with Chromium Complexes Bearing Pyridine-Phosphine Ligands: Influence of Ligand Structure on Catalytic Behavior. Organometallics 2014, 33, 5749-5757. (b) Shaikh, Y.; Gurnham, J.; Albahily, K.; Gambarotta, S.; Korobkov, I. Aminophosphine-Based Chromium Catalysts for Selective Ethylene Tetramerization. Organometallics 2012, 31, 74277433. (c) Yang, Y.; Liu, Z.; Liu, B.; Duchateau, R. Selective Ethylene Tri-/Tetramerization by In Situ-Formed Chromium Catalysts Stabilized by N, P-Based Ancillary Ligand Systems. ACS Catal. 2013, 3, 2353-2361. (9) (a) Müller, W.; Wöhl, A.; Peitz, S.; Peulecke, N.; Aluri, B. R.; Müller, B. H.; Heller, D.; Rosenthal, U.; Al-Hazmi, M. H.; Mosa, F. M. A Kinetic Model for Selective Ethene Trimerization to 1-Hexene by a Novel Chromium Catalyst System. Chemcatchem 2010, 2, 11301142. (b) Peulecke, N.; Müller, B. H.; Peitz, S.; Aluri, B. R.; Rosenthal, U.; Wöhl, A.; Müller, W.; Al-Hazmi, M. H.; Mosa, F. M. Immobilized Chromium Catalyst System for Selective Ethene Trimerization to 1-Hexene with a PNPNH Ligand. Chemcatchem 2010, 2, 1079-1081. (c) Müller, B. H.; Peulecke, N.; Peitz, S.; Aluri, B. R.; Rosenthal, U.; Al-Hazmi, M. H.; Mosa, F.


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Page 28 of 35

M.; Wöhl, A.; Müller, W. Activity Enhancement of a Catalyst System for the Selective Trimerization of Ethene to 1-Hexene by Modification of the Chromium to Chloride to Aluminium Ratio. Chem. Eur. J. 2011, 17, 6935-6938. (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 Re-Oxidation Pathway. Angew. Chem. Int. Ed. 2006, 118, 7208-7211. (11) Albahily, K.; Gambarotta, S.; Duchateau, R. Ethylene Oligomerization Promoted by a Silylated-SNS Chromium System. Organometallics 2011, 30, 4655-4664. (12) Fleming, I.; Barbero, A.; Walter, D. Stereochemical Control in Organic Synthesis Using Silicon-Containing Compounds. Chem. Rev. 1997, 97, 2063-2192. (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 1-Hexene. J. Am. Chem. Soc. 2003, 125, 5272-5273. (14) (a) Zhang, L.; Meng, X.; Chen, Y.; Cao, C.; Jiang, T. Chromium-Based Ethylene Tetramerization Catalysts Supported by Silicon-Bridged Diphosphine Ligands: Further Combination of High Activity and Selectivity. Chemcatchem 2017, 9, 76-79. (b) Zhang, L.; Wei, W.; Alam, F.; Chen, Y.; Jiang, T. Efficient Chromium-Based Catalysts for Ethylene Tri/Tetramerization Switched by Silicon-Bridged/N, P-Based Ancillary Ligands: A Structural, Catalytic and DFT Study. Catal. Sci. Technol. 2017, 7, 5011-5018. (15) Härzschel, S.; Kühn, F. E.; Wöhl, A.; Müller, W.; Al-Hazmi, M. H.; Alqahtani, A. M.; Müller, B. H.; Peulecke, N.; Rosenthal, U. Comparative Study of New Chromium-Based


28

Page 29 of 35 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

ACS Catalysis

Catalysts for the Selective Tri- and Tetramerization of Ethylene. Catal. Sci. Technol. 2015, 5, 1678-1682. (16) McGuinness, D. S.; Rucklidge, A. J.; Tooze, R. P.; Slawin, A. M. Cocatalyst Influence in Selective Oligomerization: Effect on Activity, Catalyst Stability, and 1-Hexene/1-Octene Selectivity in the Ethylene Trimerization and Tetramerization Reaction. Organometallics 2007, 26, 2561-2569. (17) Kuhlmann, S.; Blann, K.; Bollmann, A.; Dixon, J. T.; Killian, E.; Maumela, M. C.; Maumela, H.; Morgan, D. H.; Prétorius, M.; Taccardi, N. N-Substituted Diphosphinoamines: Toward Rational Ligand Design for the Efficient Tetramerization of Ethylene. J. Catal. 2007, 245, 279-284. (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 Chromium-Catalysed Tetramerisation of Ethylene. Adv. Synth. Catal. 2006, 348, 1200-1206. (19) Mao, G.; Ning, Y.; Hu, W.; Li, S.; Song, X.; Niu, B.; Jiang, T. Synthesis of a Novel TripleSite Diphosphinoamine (PNP) Ligand and its Applications in Ethylene Tetramerization. Chin. Sci. Bull. 2008, 53, 3511-3515. (20) Zhuze, T.; Zhurba, A. Solubilities of Ethylene in Hexane, Cyclohexane, and Benzene under Pressure. Russ. Chem. Bull. 1960, 9, 335-337. (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 N-Substituted Diphosphinoamine Ligands. J. Catal. 2007, 249, 244249. (b) Elowe, P. R.; McCann, C.; Pringle, P. G.; Spitzmesser, S. K.; Bercaw, J. E. Nitrogen-


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Page 30 of 35

Linked Diphosphine Ligands with Ethers Attached to Nitrogen for Chromium-Catalyzed Ethylene Tri- and Tetramerizations. Organometallics 2006, 25, 5255-5260. (22) (a) Agapie, T.; Labinger, J. A.; Bercaw, J. E. Mechanistic Studies of Olefin and Alkyne Trimerization with Chromium Catalysts: Deuterium Labeling and Studies of Regiochemistry Using a Model Chromacyclopentane Complex. J. Am. Chem. Soc. 2007, 129, 14281-14295. (b) Bowen, L. E.; Wass, D. F. Selective Cotrimerization of Ethene and Styrenic Comonomers. Organometallics 2006, 25, 555-557. (c) Bowen, L. E.; Charernsuk, M.; Hey, T. W.; McMullin, C. L.; Orpen, A. G.; Wass, D. F. Ligand Effects in Chromium Diphosphine Catalysed Olefin CoTrimerisation and Diene Trimerisation. Dalton Trans. 2010, 39, 560-567. (d) Britovsek, G. J.; McGuinness, D. S.; Wierenga, T. S.; Young, C. T. Single- and Double-Coordination Mechanism in Ethylene Tri- and Tetramerization with Cr/PNP Catalysts. ACS Catal. 2015, 5, 4152-4166. (e) Walsh, R.; Morgan, D. H.; Bollmann, A.; Dixon, J. T. Reaction Kinetics of an Ethylene Tetramerisation Catalyst. Appl. Catal., A 2006, 306, 184-191. (23) Do, L. H.; Labinger, J. A.; Bercaw, J. E. Spectral Studies of a Cr(PNP)-MAO System for Selective Ethylene Trimerization Catalysis: Searching for the Active Species. ACS Catal. 2013, 3, 2582-2585. (24) Peitz, S.; Aluri, B. R.; Peulecke, N.; Müller, B. H.; Wöhl, A.; Müller, W.; Al-Hazmi, M. H.; Mosa, F. M.; Rosenthal, U. An Alternative Mechanistic Concept for Homogeneous Selective Ethylene Oligomerization of Chromium-Based Catalysts: Binuclear Metallacycles as a Reason for 1-Octene Selectivity? Chem. Eur. J. 2010, 16, 7670-7676. (25) (a) Rucklidge, A. J.; McGuinness, D. S.; Tooze, R. P.; Slawin, A. M.; Pelletier, J. D.; Hanton, M. J.; Webb, P. B. Ethylene Tetramerization with Cationic Chromium(I) Complexes. Organometallics 2007, 26, 2782-2787. (b) Oh, J. S.; Lee, B. Y.; Park, T. H. Recycling of


30

Page 31 of 35 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

ACS Catalysis

Methylaluminoxane (MAO) Cocatalyst in Ethylene Polymerization with Supported Metallocene Catalyst. Korean J. Chem. Eng. 2004, 21, 110-115. (26) (a) Beck, S.; Lieber, S.; Schaper, F.; Geyer, A.; Brintzinger, H.-H. Anion Exchange in Alkyl-Zirconocene Borate Ion Pairs. Are Solvated Alkyl-Zirconocene Cations Relevant Intermediates? J. Am. Chem. Soc. 2001, 123, 1483-1489. (b) Landis, C. R.; Rosaaen, K. A.; Uddin, J. Heavy-Atom Kinetic Isotope Effects, Cocatalysts, and the Propagation Transition State for Polymerization of 1-Hexene Using the rac-(C2H4(1-indenyl)2)ZrMe2 Catalyst Precursor. J. Am. Chem. Soc. 2002, 124, 12062-12063. (27) (a) Britovsek, G. J.; Bruce, M.; Gibson, V. C.; Kimberley, B. S.; Maddox, P. J.; Mastroianni, S.; McTavish, S. J.; Redshaw, C.; Solan, G. A.; Strömberg, S. Iron and Cobalt Ethylene Polymerization Catalysts Bearing 2,6-bis(Imino)pyridyl Ligands: Synthesis, Structures, and Polymerization Studies. J. Am. Chem. Soc. 1999, 121, 8728-8740. (b) Gollwitzer, A.; Dietel, T.; Kretschmer, W. P.; Kempe, R. A Broadly Tunable Synthesis of Linear α-Olefins. Nat. Commun. 2017, 8, 1226. (c) Hey, T. W.; Wass, D. F. On the Formation of Odd-Number Olefins in Chromium-Catalyzed Selective Ethylene Oligomerization Reactions: Evidence for Chain Transfer to Aluminum. Organometallics 2010, 29, 3676-3678. (d) Bazan, G. C.; Rogers, J. S.; Fang, C. C. Catalytic Insertion of Ethylene into Al-C Bonds with PentamethylcyclopentadienylChromium(III) Complexes. Organometallics 2001, 20, 2059-2064. (e) Rogers, J. S.; Bazan, G. C.

Oligomerization-Transmetalation

Reactions

of

Cp*CrMe2(PMe3)/Methylaluminoxane

Catalysts. Chem. Commun. 2000, 1209-1210. (f) Kempe, R. How to Polymerize Ethylene in a Highly Controlled Fashion? Chem. Eur. J. 2007, 13, 2764-2773. (28) (a) Vadake Kulangara, S.; Haveman, D.; Vidjayacoumar, B.; Korobkov, I.; Gambarotta, S.; Duchateau, R. Effect of Cocatalysts and Solvent on Selective Ethylene Oligomerization.


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Page 32 of 35

Organometallics 2015, 34, 1203-1210. (b) Jiang, T.; Liu, X.; Ning, Y.; Chen, H.; Luo, M.; Wang, L.; Huang, Z. Performance of Various Aluminoxane Activators in Ethylene Tetramerization Based on PNP/Cr(III) Catalyst System. Catal. Commun. 2007, 8, 1145-1148. (c) Choi, E. M.; Park, J. E.; Park, G. S.; Shong, B.; Kang, S. K.; Son, K. s. Selective Ethylene Oligomerization with In-Situ-Generated Chromium Catalysts Supported by TrifluoromethylContaining Ligands. J. Polym. Sci., Part A: Polym. Chem. 2018, 56, 444-450. (29) (a) McGuinness, D. S.; Brown, D. B.; Tooze, R. P.; Hess, F. M.; Dixon, J. T.; Slawin, A. M. Ethylene Trimerization with Cr-PNP and Cr-SNS Complexes: Effect of Ligand Structure, Metal Oxidation State, and Role of Activator on Catalysis. Organometallics 2006, 25, 3605-3610. (b) McGuinness, D. S.; Overett, M.; Tooze, R. P.; Blann, K.; Dixon, J. T.; Slawin, A. M. Ethylene Tri- and Tetramerization with Borate Cocatalysts: Effects on Activity, Selectivity, and Catalyst Degradation Pathways. Organometallics 2007, 26, 1108-1111. (c) Bochmann, M.; Sarsfield, M. J. Reaction of AlR3 with [CPh3][B(C6F5)4]: Facile Degradation of [B(C6F5)4]- by Transient “[AlR2]+”. Organometallics 1998, 17, 5908-5912. (30) Jiang, T.; Ning, Y.; Zhang, B.; Li, J.; Wang, G.; Yi, J.; Huang, Q. Preparation of 1-Octene by the Selective Tetramerization of Ethylene. J. Mol. Catal. A: Chem. 2006, 259, 161-165. (31) Britovsek, G. J.; McGuinness, D. S.; Tomov, A. K. Mechanistic Study of Ethylene Tri- and Tetramerisation with Cr/PNP Catalysts: Effects of Additional Donors. Catal. Sci. Technol. 2016, 6, 8234-8241. (32) (a) McGuinness, D. S.; Wasserscheid, P.; Morgan, D. H.; Dixon, J. T. Ethylene Trimerization with Mixed-Donor Ligand (N, P, S) Chromium Complexes: Effect of Ligand Structure on Activity and Selectivity. Organometallics 2005, 24, 552-556. (b) McGuinness, D. S.; Wasserscheid, P.; Keim, W.; Hu, C.; Englert, U.; Dixon, J. T.; Grove, C. Novel Cr-PNP


32

Page 33 of 35 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

ACS Catalysis

Complexes as Catalysts for the Trimerisation of Ethylene. Chem. Commun. 2003, 334-335. (c) Bluhm, M. E.; Walter, O.; Döring, M. Chromium Imine and Amine Complexes as Homogeneous Catalysts for the Trimerisation and Polymerisation of Ethylene. J. Organomet. Chem. 2005, 690, 713-721. (33) (a) Höhne, M.; Peulecke, N.; Konieczny, K.; Müller, B. H.; Rosenthal, U. ChromiumCatalyzed

Highly

Selective

Oligomerization

of

Ethene

to

1-Hexene

with

N,N-

Bis[chloro(aryl)phosphino]amine Ligands. Chemcatchem 2017, 9, 2467-2472. (b) Britovsek, G. J.; McGuinness, D. S. A DFT Mechanistic Study on Ethylene Tri- and Tetramerization with Cr/PNP Catalysts: Single versus Double Insertion Pathways. Chem. Eur. J. 2016, 22, 1689116896. (c) Blann, K.; Bollmann, A.; Dixon, J.; Neveling, A.; Morgan, D.; Maumela, H.; Killian, E.; Hess, F.; Otto, S.; Pepler, L. Tetramerization of Olefins. Patent WO, 56479, 2004. (34) (a) Zhao, Y.; Truhlar, D. G. The M06 Suite of Density Functionals for Main Group Thermochemistry, Thermochemical Kinetics, Noncovalent Interactions, Excited States, and Transition Elements: Two New Functionals and Systematic Testing of Four M06-Class Functionals and 12 Other Functionals. Theor. Chem. Acc. 2008, 120, 215-241. (b) Zhao, Y.; Truhlar, D. G. Density Functionals with Broad Applicability in Chemistry. Acc. Chem. Res. 2008, 41, 157-167. (35) Briggs, J. R. Process for Trimerization. U.S. Patent 4,668,838, 1987. (36) Kwon, D.-H.; Fuller, J. T.; Kilgore, U.; Sydora, O. L.; Bischof, S. M.; Ess, D. H. Computational Transition-State Design Provides Experimentally Verified Cr (P, N) Catalysts for Control of Ethylene Trimerization and Tetramerization. ACS Catal. 2018, 8, 1138-1142.


33

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Page 34 of 35

(37) Klemps, C.; Payet, E.; Magna, L.; Saussine, L.; Le Goff, X. F.; Le Floch, P. PCNCP Ligands in the Chromium-Catalyzed Oligomerization of Ethylene: Tri- versus Tetramerization. Chem. Eur. J. 2009, 15, 8259-8268. (38) McGuinness, D. S.; Chan, B.; Britovsek, G. J.; Yates, B. F. Ethylene Trimerisation with CrPNP Catalysts: A Theoretical Benchmarking Study and Assessment of Catalyst Oxidation State. Aust. J. Chem. 2014, 67, 1481-1490. (39) Briggs, J. R. The Selective Trimerization of Ethylene to Hex-1-ene. J. Chem. Soc., Chem. Commun. 1989, 674-675. (40) Kuhlmann, S.; Paetz, C.; Hägele, C.; Blann, K.; Walsh, R.; Dixon, J. T.; Scholz, J.; Haumann, M.; Wasserscheid, P. Chromium Catalyzed Tetramerization of Ethylene in a Continuous Tube Reactor-Proof of Concept and Kinetic Aspects. J. Catal. 2009, 262, 83-91.


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ACS Catalysis

Graphical Abstract


35

Catalytic Systems Based on Chromium(III) Silylated

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