Mononuclear complexes with heterocyclic ligands as ethylene polymerization catalysts for single-reactor bimodal polyethylene technology

Accepted Manuscript Mononuclear complexes with heterocyclic ligands as ethylene polymerization catalysts for single-reactor bimodal polyethylene technology Hamdi Ali Elagab, Helmut G. Alt PII: DOI: Reference:

S0014-3057(15)00380-8 http://dx.doi.org/10.1016/j.eurpolymj.2015.07.032 EPJ 6998

To appear in:

European Polymer Journal

Received Date: Revised Date: Accepted Date:

30 May 2015 9 July 2015 17 July 2015

Please cite this article as: Elagab, H.A., Alt, H.G., Mononuclear complexes with heterocyclic ligands as ethylene polymerization catalysts for single-reactor bimodal polyethylene technology, European Polymer Journal (2015), doi: http://dx.doi.org/10.1016/j.eurpolymj.2015.07.032

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1

Mononuclear complexes with heterocyclic ligands as ethylene polymerization catalysts for single-reactor bimodal polyethylene technology

Hamdi Ali Elagab, Helmut G. Alt1 Laboratorium für Anorganische Chemie, Universität Bayreuth, Postfach 10 12 51, D-95440 Bayreuth, Germany

Keywords: Complexes with heterocyclic ligands Ethylene polymerization Mononuclear complexes Bimodal resins Single-reactor technology Abstract 27 complexes of titanium, zirconium and vanadium with 1,2-bis(benzimidazolyl)benzene , 1,2-bis(benzimidazolyl)ethane and 1,1-bis(benzimidazolyl)methane ligands have been synthesized and characterized. After activation with methylalumoxane (MAO) these complexes proved as good catalysts for ethylene polymerization inspite of the hetero atoms in the ligands and the oxophilicity of the metals. Nearly all produced polyethylenes showed bimodal or multimodal molecular weight distributions indicating more than one active site of the catalysts in the various polymerization steps. Obviously, after activation with MAO, a mononuclear catalyst molecule can interact differently with the cocatalyst. This is an easy and elegant approach to single-reactor bimodal/multimodal polyethylene technology. The polymerization activity of the catalyst system 1,2-bis(benzimidazolyl) benzene zirconium tetrachloride (29/MAO) was investigated at different polymerization temperatures and

1

Corresponding author: Tel.: +49-921-43864 E-mail-address: [email protected] (H.G. Alt)

2 structure-property-relationships were studied. The effect of the polymerization temperature on both molecular weights and polydispersities of the polymers produced with catalyst 29/MAO was investigated at 20, 40, and 60 °C. The molecular weights Mw were 1.3·106, 1.2·106 and 9.7·105 g/mol and the polydispersity indices PDI 693, 248 and 223 respectively.

1. Introduction Mononuclear complexes as catalysts for olefin polymerization in homogeneous solution have many advantages because every molecule can act as a catalyst and hence provide high activity [1-3]. In most cases, the molecular weights of the produced resins have narrow molecular weight distributions due to the fact that only one active site is generated in the activation process of the catalyst precursor. This can be disadvantageous when processing polyolefins, and solutions are needed to overcome this problem. So far, special support materials and methods, the mixture of different catalysts, the application of dinuclear or multinuclear catalysts and the use of two or more reactors were applied [4-13]. However, the best solution is the design of catalysts that can solve all these problems in one step and in one reactor. In this contribution we report the synthesis and characterization of complexes with heterocyclic ligands that are perfect candidates for this challenge. 1,2-Bis-benzimidazoles and 2,6-bis(benzimidazolyl) pyridine are well known ligand precursors for

transition metal

complexes [14-24]. So far, for ethylene polymerization, 1,2-bis(benzimidazolyl) benzene copper [25], titanium, zirconium and vanadium complexes were reported [26-28] that can be activated with methyalumoxane (MAO) and then be applied successfully for catalytic ethylene polymerization. The vanadium complexes of bis(benzimidazole) amine tridentate ligands [N,N,N], are active ethylene polymerization catalysts after activation with alkylaluminum compounds [29] and 2,6-bis(2-benzimidazolyl) pyridine zirconium dichloride / MAO polymerizes methylacrylate [30]. Herein we report the first zirconium, titanium and vanadium complexes of 1,2-bis(benzimidazolyl, benzothiazolyl, and benzoxazolyl benzene, and 2,6-bis(benzothiazolyl, benzoxazolyl)pyridine and their applications in catalytic ethylene polymerization after activation with MAO.

2. Results and Discussion 2.1. General synthesis of the ligand precursors

3 The condensation reaction of a dicarboxylic acid or an acid anhydride in preheated polyphosphoric acid is a well established procedure for the preparation of the imidazole based ligands precursors [31,32] in high yields (Scheme 1).

B R1

HN

B

NH N

O

2

O

N

PPA / 175°C, 3-5h -3H2O

O NH2

NH2

R1

R1

Compound No.

Bridging unit (B)

R1

1

CH2

H

2

CH2

CH3

3

CH2

Cl

4

CH2CH2

H

5

CH2CH2

CH3

6

CH2CH2

Cl

7

1,2-C6H4

H

8

1,2-C6H4

CH3

9

1,2-C6H4

Cl

Scheme 1. Synthesis of the ligand precursors 1-9.

2.2. Synthesis of coordination compounds 2.2.1 Synthesis of titanium and zirconium complexes The complexes 10-36 were synthesized according to Scheme 2. The titanium and zirconium complexes were prepared by ligand displacement reactions. The reaction of the tetrahydrofuran adducts of zirconium and titanium tetrachloride with the corresponding ligand precursor in methylene chloride results in an immediate colour change and the complexes could be isolated in very high yields (80-95%). The complexes were characterized by NMR, mass spectrometry and elemental analysis.

4

2.2.2 Synthesis of vanadium complexes The vanadium complexes were synthesized by dissolving vanadium trichloride in diethyl ether followed by the addition of the ligand precursor with constant stirring overnight. The product yields ranged from 60-78 %. B

B HN

1- MCl4(THF)2, CH2 Cl2

NH N

HN

2- MCl3, Et2 O

N

NH N

N

r. t., 24h

R

1

Complex No. 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

R

1

MCln

1- M =Ti, Zr 2- M = V

Bridging unit (B) CH2 CH2 CH2 CH2 CH2 CH2 CH2 CH2 CH2 CH2CH2 CH2CH2 CH2CH2 CH2CH2 CH2CH2 CH2CH2 CH2CH2 CH2CH2 CH2CH2 1,2-C6H4 1,2-C6H4 1,2-C6H4 1,2-C6H4 1,2-C6H4 1,2-C6H4 1,2-C6H4 1,2-C6H4 1,2-C6H4

R

1

R1

R1

M

H H H CH3 CH3 CH3 Cl Cl Cl H H H CH3 CH3 CH3 Cl Cl Cl H H H CH3 CH3 CH3 Cl Cl Cl

Ti Zr V Ti Zr V Ti Zr V Ti Zr V Ti Zr V Ti Zr V Ti Zr V Ti Zr V Ti Zr V

Scheme 2. Synthesis of the coordination compounds 10-36.

5 2.3. Characterization 2.3.1. 1H and 13C NMR spectroscopy The ligand precursors 1-9 and their titanium and zirconium complexes were characterized by 1

H and 13C NMR spectroscopy. The vanadium complexes, due to their paramagnetism, were

characterized by mass spectrometry. The 1H NMR spectrum of compound 1 (Scheme 3) shows four sets of resonance signals. A broad signal at δ =12.41 ppm is assigned to the NH protons, while the multiplet signals at δ = 7.49-7.46 and 7.12- 7.10 ppm belong to an AA´BB´ pattern of H1,4 and H2,3. The methylene protons H5 appear as a singlet at δ = 4.46 ppm.

Scheme 3. 1H NMR spectrum of compound 1 in DMSO-d6.

The

13

C NMR spectrum of compound 1 (see Scheme 4) reveals five signals at δ = 150.8,

138.4, 122.9, 115.2 and 29.8 ppm that can be assigned to C1/6, C8, C3/4, C2/5 and C7.

6

Scheme 4. 13C NMR spectrum of compound 1 in DMSO-d6. The 1H NMR spectrum of complex 10 (Scheme 5) shows an AA´BB´ pattern for H1,4 and H2,3 as multiplets at δ = 7.52-7.49 and 7.17-7.11 ppm. The protons of the bridging group (H6) appear as a singlet at δ = 4.55 ppm. The broad signal at δ =11.45 ppm is assigned to the NH protons,

Scheme 5. 1H NMR spectrum of complex 10 in DMSO-d6.

The

13

C NMR spectrum of complex 10 (see Scheme 6) shows five signals at δ = 150.7,

138.9, 122.8, 115.5 and 29.7 ppm that belong to C7, C1/6, C3,4, C2,5 and C8.

7

Scheme 6.13C NMR spectrum of complex 10 in DMSO-d6.

2.3.2. Mass spectrometry The mass spectrum of compound 1 shows the molecular ion peak at m/z = 248. The peak at m/z = 156 is obtained by loss of one phenylene group (see Scheme 7).

Scheme 7. Mass spectrum of compound 1.

The mass spectrum of complex 10 (Scheme 8) does not show the molecular ion peak but only the ion with mass m/z = 248 representing the free ligand. Such a fragmentation pattern is typical for thermally labile complexes with n-donor ligands.

8

Scheme 8. Mass spectrum of complex 10.

Polymerization results The complexes of titanium, zirconium, and vanadium with ligands derived from 1,2bis(benzimidazolyl) benzene, 1,2-bis(benzimidazolyl) ethane and 1,1-bis(benzimidazolyl) methane compounds were activated with methylalumoxane (MAO) in toluene solution assuming a mechanism as proposed for the activation of metallocene [33,34] and 2,6bis(imino) pyridine iron [35] complexes. The homogeneous catalyst solution was used for ethylene polymerization. The catalyst systems showed variable activities for ethylene polymerization. Their activities were found to depend on the ligand environment, the nature of the hetero atom in the ligand and on the metal atom.

Table 1. Ethylene polymerization activities of complexes 10-36/MAO

Complex No.

Activitya)

Polymerization

[kg PE/ mol

Mw [ g/ mol]

PDI

temperature Al: M

cat.h]

[°C]

10

315.70

2500:1

50

1149594

8.4

11

172.41

2500:1

50

1906473

5.4

12

173.33

2500:1

50

424279

3.2

13

244.70

2500:1

50

466376

5.6

14

43.20

2500:1

50

268276

4.9

9 15

178.60

2500:1

50

246996

3.1

16

148.15

2500:1

50

437259

3.6

17

21.74

2500:1

50

n.d.

n.d.

18

337.50

2500:1

50

920237

1.8

19

207.80

2500:1

50

n.d.

n.d.

20

129.50

2500:1

50

n.d.

n.d.

21

285.10

2500:1

50

434343

6.9

22

340.70

2500:1

50

444669

9.1

23

37.23

2500:1

50

n.d.

n.d.

24

158.70

2500:1

50

378276

4.6

25

250.00

2500:1

50

311274

3.6

26

39.90

2500:1

50

n.d.

n.d.

27

133.33

2500:1

50

n.d.

n.d.

28

252.42

2500:1

50

1273127

19.2

29

116.2

2500:1

20

1271018

693

29

225.5

40

1177503

248

29

285.50

2500:1

50

1638338

16.4

29

227.9

2500:1

60

972211

223

29 30

191

2500:1

80

n.d.

n.d.

404.80

2500:1

50

408352

6.7

31

202.40

2500:1

50

439497

5.9

32

66.50

2500:1

50

196803

4.8

33

307.70

2500:1

50

674295

3.6

34

35.70

2500:1

50

n.d.

n.d.

35

122.50

2500:1

50

1510535

6.5

36

165.00

2500:1

50

1311190

9.3

2500:1

a) All polymerization reactions were carried out in 250 ml pentane with MAO as cocatalyst (Al: M = 2500:1) at 50 °C, 10 bar ethylene pressure and 1 h reaction time. n.d. = not determined.

The activities of the titanium complexes derived from the unsubstituted ligand precursors follow the order 10 > 28 > 19 while the activities of the zirconium complexes show a

10 somewhat different trend with the order 29 > 11 > 20 (Scheme 9). The vanadium complexes behave as follows: 30 > 21 > 12. The differences in the catalytic activities of these complexes can be attributed to the nature of the bridge and the different metals. All the other parameters remained constant. The lower activities of the zirconium derivatives could be the consequence of thermodynamically stronger metal carbon bonds slowing down the kinetics of the various polymerization steps [36]. A rigid bridge like a methylene or 1,2-phenylene

Activity[kg PE/mol cat.h]

unit gave higher activities than a 1,2-ethylidene moiety. 450 404.8 400 350 315.7 285.5 285.1 300 252.4 250 207.8 172.4 173.3 200 129.5 150 100 50 0

10

19

28

11

20

29

12

21

30

Scheme 9. Polymerization activities of the titanium complexes 10, 19, 28, the zirconium complexes 11, 20, 29 and the vanadium complexes 12, 21, 30.

Among the catalyst systems derived from 1,2-bis(benzimidazolyl) benzene, 1,2bis(benzimidazolyl) ethane and 1,1-bis(benzimidazolyl) methane the introduction of a substituent R1 in meta position to the imino nitrogen atom influences their catalytic activities compared to the unsubstituted derivatives. Methyl substituted titanium complexes show the following order of activities: 22 > 13 > 31. The catalyst system 22/MAO shows an activity of 340.7 [kg PE/mol cat.h] which is higher than the value obtained by the unsubstituted complex 19/MAO with 207.8 [kg PE/mol cat.h] due to the steric effect imposed by the methyl group on the active center. The lower activities of 13 and 31 compared to the unsubstituted complexes may account for both electronic and steric effects. In the same way of reasoning, zirconium and vanadium complexes show the same activity orders: For zirconium complexes 32 > 14 > 23 and for vanadium complexes: 33 > 15 > 24 (Scheme 10).

Activity[kg PE/mol cat.h]

11

400 350 300 250

340.7 307.7 244.7 202.4

178.6

200 150 100 50

43.2 37.2

158.7

66.5

0

13

22

31

14

23

32

15

24

33

Scheme 10. Effect of a methyl substituent R1 on the activities of the titanium complexes 13, 22, 31, the zirconium complexes 14, 23, 32 and the vanadium complexes 15, 24 and 33.

The introduction of an electron withdrawing chloro substituent in the meta position to the imino nitrogen atoms (Scheme 11) reduces the activities of the catalyst systems compared to the unsubstituted complexes. An exception is the vanadium containing catalyst 18/MAO derived from 1,1-bis(benzimidazolyl) methane. It shows higher activity than the unsubstituted complex by a factor of 2. This could be caused by the –I effect of the substituent reducing the electron density at the active centre. However, this positive effect can also be counter productive as soon as metals with a high oxophilicity are involved as in the case of the zirconium analogues 34, 17 and 26 when active sites at neighboured catalyst molecules can be blocked by these Lewis bases.

Activity[kg PE/mol cat.h]

12

400

337.5

350 300

250

250 165

200 148.2 150

133.3

122.5

100 50

35.7 21.7 39.9

0

16

25

34

17

26

35

18

27

36

Scheme 11. The effect of chloro substituents on the activities of titanium complexes 16, 25 and 34, zirconium complexes 17, 26 and 35 and vanadium complexes 18, 27 and 36.

The activities of the zirconium containing catalyst system 29/MAO were tested at different temperatures. At 20°C the catalyst shows an activity of 116 [kg PE/mol cat.h] and at 50 °C an activity increase to 285 [kg PE/mol cat.h]. At a temperature of 80 °C an activity decrease to 191 [kg PE/mol cat.h] is observed. The decrease of activity with rising temperature may be explained by the deactivation of active centres [37] as a consequence of thermal

Activity[Kg PE/mole cat.h]

decomposition of the original catalyst [38, 39] (Scheme 12).

286

350 300

226

200

228 191

250 116

150 100 50 0

Scheme 12. The effect of the temperature on the polymerization activity of 29/MAO.

13 The GPC analyses of the polyethylenes produced with benzimidazole based complexes revealed that the catalysts were capable to produce polymers with very high molecular weights associated with broad or bimodal molecular weight distributions. The bimodality may arise from different interactions of the bulky MAO counter anion with the Lewis basic hetero atoms of the catalyst ligands thus generating different active sites in the activation process [40]. Since MAO consists of a dynamic equilibrium of MeAlO building blocks, containing a Lewis acidic center Al and a Lewis basic center O, various shapes and sizes of the MAO counter anions can cause different interactions with the hetero atoms of the ligand. The effect of the polymerization temperature on both molecular weights (Scheme13) and polydispersities (Scheme 14) of the polymers produced with catalyst 29/MAO was investigated. At 20 °C (Scheme 15), the molecular weight Mw was found to be 1.3·106 g/mol and the polydispersity index PDI = 693.

Molecular weight

1400000

1300000

1200000

1200000 970000

1000000 800000 600000 400000 200000 0

29(20°C)

29(40°C)

29(60°C)

Scheme 13. The effect of polymerization temperature on molecular weights

800 700

693

600 PDI

500 400 300

248

223

29(40°C)

29(60°C)

200 100 0 29(20°C)

Scheme 14. The effect of polymerization temperature on polydispersity index (PDI)

14

HN

NH N

N

Zr Cl

Cl

Cl

Cl

Scheme 15. HT- GPC profile of polyethylene produced with 29/MAO at 20°C. At 40 °C (Scheme 16) a polyolefin with Mw = 1.2·106 g/mol and PDI = 248 was obtained. Increasing the polymerization temperature to 60 °C (Scheme 17) both molecular weight (Mw = 9.7·105 g/mol) and PDI = 223 decreased. The high molecular weight resins and the decrease of molecular weight with increasing polymerization temperature suggest that the rate of propagation reactions (the activation barrier for propagation is usually low if existent at all) [41,42] are much faster than the rate of termination (the termination reactions are subjected to activation barriers).

HN

NH N

N

Zr Cl Cl

Cl Cl

Scheme 16. HT- GPC profile of polyethylene produced with 29/MAO at 40 °C.

15

Scheme 17. HT- GPC profile of polyethylene produced with 29/MAO at 60 °C.

DSC measurements (Table 2) showed that the catalyst systems produced HDPE with a moderate degree of crystallinity.

Table 2. Thermal analysis data for representative polymer samples produced with complexes 12, 16, 29, 30, 33, 36/MAO Complex No. 12 16 29 30 33 36

Polymerization Temperature [°C] 50 50 50 50 50 50

Al: M

Tm °C

Tx °C

α %

2500:1 2500:1 2500:1 2500:1 2500:1 2500:1

137.8 138.1 138.0 136.7 136.2 139.3

118.6 118.1 117.7 119.5 120.5 120.5

28.3 25.5 38 33 25.2 36

Tm = melting temperature, Tx = crystallization temperature, α = degree of crystallinity For example, the melting and crystallization temperatures of polyethylene produced with 12/MAO was 137.8 and 118.6 °C respectively and the degree of crystallinity α = 28.3% (Scheme 18).

16

Scheme 18. DSC profile of polyethylene produced with 12/MAO.

The melting and crystallization temperatures of the polyethylene produced with 16/MAO (Scheme 19) was 138.1 and 118.1°C respectively and the degree of crystallinity α = 25.5%. The melting and crystallization temperatures of the polyethylene produced with 36/MAO was 139.3 and 121.2 °C respectively and the degree of crystallinity α = 36% (Scheme 20).

Scheme 19. DSC profile of polyethylene produced with 16/MAO.

17 Scheme 20. DSC profile of polyethylene produced with 36/MAO.

3. Experimental All experimental work was routinely carried out using Schlenk technique unless otherwise stated. Anhydrous and purified argon was used as inert gas. n-Pentane, diethyl ether, toluene and tetrahydrofuran were purified by distillation over Na/K alloy. Diethyl ether was additionally distilled over lithium aluminium hydride. Methylene chloride was dried with phosphorus pentoxide and additionally with calcium hydride. Methanol and ethanol were dried over magnesium. Deuterated solvents (CDCl3, DMSO-d6) for NMR spectroscopy were stored over molecular sieves (3Ǻ). Methylalumoxane (30 % in toluene) was purchased from Crompton (Bergkamen) and Albemarle (Baton Rouge, USA / Louvain – La Neuve, Belgium). Ethylene (3.0) and argon (4.8/5.0) were supplied by Rießner Company (Lichtenfels). All other starting materials were commercially available and were used without further purification. The titanium and zirconium adducts were synthesized via published procedures [43].

3.1 NMR spectroscopy The spectrometer Bruker ARX 250 was available for

recording

the NMR spectra.

The samples were prepared under inert atmosphere (argon) and routinely recorded at 25 °C. The chemical shifts in the 1H NMR spectra are referred to the residual proton signal of the solvent (δ = 7.24 ppm for CDCl3, δ = 2.50 ppm for DMSO-d6) and in 13

C NMR spectra to the solvent signal (δ = 77.0 ppm for CDCl3, δ = 39.5 ppm for

DMSO-d6).

3.2 Mass spectrometry Mass spectra were routinely recorded at the Zentrale Analytik of the University of Bayreuth with a VARIAN MAT CH-7 instrument (direct inlet, EI, E = 70 eV) and a VARIAN MAT 8500 spectrometer.

3.3 Gel permeation chromatography (GPC) GPC measurements were routinely performed by SABIC Company (Riyadh, Saudi Arabia).

18 3.4 Elemental analysis Elemental analyses were performed with a VarioEl III CHN instrument. The raw values of the carbon, hydrogen, and nitrogen contents were multiplied with calibration factors (calibration compound: acetamide).

3.5 General procedures for the syntheses of the complexes 3.5.1. Syntheses of organic compounds 1-12 A diamine compound (0.05mol) was mixed with a dicarboxylic acid or an acid anhydride (0.025mol) and the mixture was poured in 50 ml of preheated (100°C) polyphosphoric acid. The mixture was stirred and heated at 175°C for 3-5 hours. The reaction mixture was then poured into ice cold water and allowed to stand overnight. The precipitate was removed by filtration and washed several times with diluted sodium hydrogen carbonate solution and finally with water. The reaction product was then air dried and weighed. The products were characterized by NMR and mass spectrometry (Table 4). Representative samples were characterized by elemental analyses (Table 3).

3.5.2 Titanium complexes To an amount of 0.87g, (2.6 mmol) TiCl4(thf)2 in dichloromethane was added an amount of 2.6 mmol of the solid free ligand. The reaction mixture was stirred overnight at room temperature, filtered and washed several times with dichloromethane then with pentane, dried in vacuo and weighed. The products were characterized by NMR and mass spectroscopy (Table 4). Representative samples were characterized by elemental analyses (Table 3).

3.5.3 Zirconium complexes To an amount of 0.45g (1.2mmol) ZrCl4(thf)2 in dichloromethane was added an amount of 1.2 mmol of the free ligand. The reaction mixture was stirred overnight at room temperature, filtered and washed several times with dichloromethane, then with pentane, dried in vacuo and weighed. The products were characterized by NMR and mass spectroscopy (Table 4). Representative samples were characterized by elemental analyses (Table 3).

3.5.4 Vanadium complexes To an amount of 0.41g (2.6 mmol) VCl3 in ether was added an amount of 2.6 mmol of the free ligand. The reaction mixture was stirred overnight at room temperature, filtered and

19 washed several times with ether and pentane, dried in vacuo and weighed. The products were characterized by mass spectrometry. Representative samples were characterized by elemental analyses (Table 3).

Table 3. Elemental analysis data for representative free ligands 1, 4, 7, 8 and complexes 13, 15, 19, 21, 32, 33. Calculated

Compound

Found

No.

C

H

N

C

H

N

1

72.6

4.8

22.6

71.8

4.6

22.4

4

73.3

5.3

21.4

72.9

5.4

21.4

7

77.42

4.52

18.06

77.38

4.49

18.13

8

78.11

5.33

16.57

78.62

5.17

17.12

13

44.3

3.00

13.8

44.6

3.2

13.5

15

47.1

3.7

12.9

46.7

3.9

13.1

19

42.5

3.1

12.4

42.8

2.9

12.1

21

45.8

3.3

13.4

45.5

3.6

13.2

32

46.23

3.15

9.81

47.06

3.23

8.97

33

53.33

3.64

11.31

54.12

3.71

10.96

3.6 Polymerization of ethylene An amount of 2 – 5 mg of the desired complex was suspended in 5 ml of toluene. Methylalumoxane (30% in toluene) was added resulting in an immediate colour change. The mixture was added to a 1 litre Schlenk flask filled with 250 ml npentane. This mixture was transferred to a 1 litre Büchi laboratory autoclave under inert atmosphere and thermostated. An ethylene pressure of 10 bar was applied for one hour. The polymer was filtered over a frit, washed with diluted hydrochloric acid, water, and acetone, and finally dried in vacuo.

20 Table 4. NMR and mass spectroscopic data of ligand precursors 1-9 and complexes 10-36. 1

Compound No.

1

2

3 4

5

6

7

8

9

10

11

12

H NMR δ [ppm] 12.41(s,2H, NH), 7.46(m,4H), 7.11(m,4H), 4.43(s,2H,CH2) 7.32(d,2H), 7.23(s,2H), 6.91(d,2H), 4.35(s,2H,CH2), 2.33(s,6H,CH3) 7.54(s,2H), 7.48(d,2H), 7.14(d,2H), 4.46(s,2H,CH2) 7.57 (m,4H), 7.26 (m,4H), 3.56(s,4H,2CH2) 7.31 (d,2H), 7.22(s,2H),) 6.90 (d,2H), 3.51 (s,4H,CH2), 2.33(s,6H,CH3) 7.50 (s,2H), 7.44(d,2H), 7.09(d,2H), 3.36 (s,4H,2CH2) 7.88 (d,1H), 7.80(d,1H), 7.69(t,2H), 7.64(s,2H, NH), 7.61(m,4H), 7.26(m,4H),

13

C NMR δ [ppm] 150.8, 138.4 122.9, 115.4, 29.8

Mass m/z[%] 248 M°+ (100)

150.6, 139.2 137.9, 131.2, 123.5, 115.3, 114.7, 30.0, 21.9

276 M°+ (100)

317 M°+ (100) n.d. 153.8, 135.4, 124.3, 114.6, 25.4 154.2, 138.7, 137.4, 131.2, 123.5, 115.0, 114.5, 27.0, 21.9

262 M°+ (100)

156.2, 140.6, 138.0, 126.3, 122.1, 116.2, 115.1 27.0 151.6, 137.9, 133.5, 131.9, 129.4, 123.5, 115.5

331 M°+ (100)

8.05(s,2H), 7.78(s,2H,N- 151.6, 139.0, 137.8, H), 7.63(s,2H), 132.2, 132.0, 130.4, 7.56(d,2H), 7.35(s,2H), 129.9, 115.9, 115.1, 7.00(d,2H), 22.0 2.37(s,6H,CH3) 8.14 (s,2H), 7.61 (br,4H), 154.3, 141.4, 138.9, 7.55 (d,2H), 7.12(d,2H) 132.1, 130.4, 130.3, 126.6, 122.4, 117.1, 115.8 7.52-7.49(m,4H), 7.52- 149.0, 135.4, 124.4, 7.14(m,4H), 115.1, 27.5 4.55(s,2H,CH2)

338 M°+ (100)

7.63-7.62(m,4H), 7.337.30 (m,4H), 4.91(s,2H,CH2)

n.d.

150.6, 138.7, 122.6, 115.3, 29.6

n.d.

290 M°+ (100)

310 M°+ (100)

378 M°+ (100)

438 M°+(1), 402 M°+Cl (2), 367 M°+-2Cl (2), 248 M°+-TiCl4 (100) 481 M°+(1), 444 M°+Cl (2), 407 M°+-2Cl (1), 370 M°+-3Cl (2), 336 M°+-4Cl (1), 248 M°+-ZrCl4 (100) 406 M°+(3), 368 M°+Cl (7), 334 M°+-2Cl (10), 299 M°+-3Cl

21 1

Compound No.

13

14

15

16

17

18

H NMR δ [ppm]

13

C NMR δ [ppm]

7.63(d,2H), 7.54(s,2H), 7.31(d,2H), 5.25(s,2H,CH2), 2.42(s,6H,2CH3)

146.3, 136.3, 132.3, 130.1, 127.8, 114.3, 114.1, 25.8, 21.8

7.55(d,2H), 7.47(s,2H), 7.21(d,2H), 5.05 (s,2H,CH2), 2.40(s,6H,2CH3)

147.5, 135.0, 134.0, 132.2, 126.7, 114.6, 114.3, 26.6, 21.8

n.d.

n.d.

7.88(s,2H), 7.80(d,2H), 7.51(d,2H), 5.18(s,2H,CH2)

149.3, 134.7, 132.6, 129.8, 125.9, 116.5, 114.9, 26.9

7.89(s,2H), 7.80(d,2H), 7.52(d,2H), 5.23(s,2H, CH2)

149.1, 134.3, 132.2, 130.1, 126.1, 116.5, 114.8, 26.7

n.d.

n.d.

152.5, 132.6, 125.6, 114.6, 24.5

19

7.76-7.70(m,4H), 7.507.43(m,4H), 3.95(s,4H,2CH2)

152.7, 133.3, 125.3, 114.7, 24.7

20

7.73-7.71(m,4H), 7.457.42(m,4H), 3.84(s,4H,2CH2)

21

22

23

n.d.

n.d.

7.62(d,2H), 7.53(s,2H), 7.30(d,2H), 3.87(s,4H,2CH2), 2.46(s,6H,2CH3)

151.1, 136.3, 133.0, 130.0, 126.7, 114.7, 114.4, 24.7, 21.9

7.66(d,2H), 7.57(s,2H),

151.6, 136.0, 132.3,

Mass m/z[%] (20), 248 M°+-VCl3 (100) 466 M°+(1), 428 M°+Cl(5), 393 M°+-2Cl (5), 357 M°+-3Cl (3), 319 M°+-4Cl (2), 276 M°+TiCl4 (100) 510 M°+(2), 477 M°+Cl (5), 440 M°+-2Cl (5), 405 M°+-3Cl (2), 276 M°+-ZrCl4 (100) 433 M°+(2), 397 M°+Cl (5), 360 M°+-2Cl (10), 324 M°+-3Cl (5), 276 M°+-VCl3 (100) 506 M°+(3), 470 M°+Cl (2), 434 M°+-2Cl (5), 397 M°+-3Cl (10), 316 M°+-TiCl4 (100) 549 M°+(2), 513 M°+Cl (5), 476 M°+-2Cl (10), 440 M°+-3Cl (5), 316 M°+-ZrCl4 (100) 473 M°+(5), 437 M°+Cl (2), 401 M°+-2Cl (70), 368 M°+-3Cl (10), 316 M°+-VCl3 (20) 435 M°+-NH (5), 416M°+-Cl (5), 380 M°+-2Cl (2), 345 M°+3Cl (10), 308 M°+-4Cl (5), 262 M°+-TiCl4 (70) 495M°+(2), 458M°+-Cl (2), 422 M°+-2Cl (5), 387 M°+-3Cl (3), 351 M°+-4Cl (2), 262 M°+ZrCl4 (50) 420 M°+(15), 385 M°+Cl (15), 343 M°+-2Cl (10), 310 M°+-4Cl (2), 262 M°+-VCl3 (80) 480 M°+(2), 443 M°+Cl (2), 408 M°+-2Cl (5), 372 M°+-3Cl (5), 336 M°+-4Cl (2), 290 M°+-TiCl4 (100) 523 M°+(2), 487 M°+-

22 1

Compound No.

24

H NMR δ [ppm] 7.35(d,2H), 3.85(s,4H,2CH2), 2.48 (s,6H,2CH3)

n.d.

13

C NMR δ [ppm] 130.0, 127.5, 114.1, 114.0, 24.4, 21.8

n.d.

25

7.84(s,2H), 7.78(d,2H), 7.50(d,2H), 3.78(s,4H,2CH2)

154.3, 135.5, 133.6, 130.3, 125.0, 116.2, 115.0, 25.7

26

7.83(s,2H), 7.75(d,2H), 7.48(d,2H), 3.76(s,4H,2CH2)

154.4, 134.6, 132.5, 129.7, 125.5, 116.2, 114.7, 24.9

27

28

29

30

31

32

33

n.d.

n.d.

8.37(d,2H), 8.08(t,2H), 7.924-7.835(m,4H), 7.637-7.625(m,4H)

148.2, 134.0, 133.8, 133.6, 126.5, 125.1, 115.4

8.28-8.25(dd,2H), 7.94(t,2H), 7.717.67(m,4H), 7.457.42(m,4H)

149.1, 135.0, 132.5, 126.2, 125.4, 115.3, 114.8

n.d. 8.18-8.16(dd,2H), 7.927.90(dd,2H), 7.54(d,2H), 7.44(s,2H), 7.24(d,2H), 2.40(s,6H,2CH3) 8.27(t,2H), 8.03(d,2H), 7.64(d,2H), 7.54(s,2H), 7.36(d,2H), 2.49(s,6H,2CH3) n.d.

n.d. 147.7, 137.6, 133.2, 131.9, 129.6, 128.9, 127.6, 126.1, 114.8, 114.5, 21.8 147.2, 136.2, 133.8, 133.5, 133.3, 131.8, 127.8, 124.7, 114.7, 114.43, 21.9 n.d.

Mass m/z[%] Cl (2), 451 M°+-2Cl (5), 414 M°+-3Cl (3), 377 M°+-4Cl (2), 290 M°+-ZrCl4 (100) 447 M°+(5), 411 M°+Cl (5), 376 M°+-2Cl (2), 340 M°+-3Cl (2), 290 M°+-VCl3 (100) 518 M°+(1), 485 M°+Cl (5), 450 M°+-2Cl (1), 413 M°+-3Cl (1),377 M°+-4Cl (3) 330 M°+-TiCl4 (100) 564 M°+(1), 528 M°+Cl (5), 493 M°+-2Cl (2), 456 M°+-3Cl (3),419 M°+-4Cl (2) 331 M°+-ZrCl4 (100) 488 M°+(2), 452 M°+Cl (5), 415 M°+-2Cl (2), 379 M°+-3Cl (2), 331 M°+-VCl3 (100) 500 M°+(1), 463 M°+Cl (2), 428 M°+-2Cl (3), 394 M°+-3Cl (5), 357 M°+-4Cl (2), 310 M°+-TiCl4 (100) 543 M°+(1), 506 M°+Cl (1), 437 M°+-3Cl (3), 400 M°+-4Cl (5), 310 M°+-ZrCl4 (100) 467 M°+(1), 430 M°+Cl (5), 393 M°+-3Cl (2), 310 M°+-VCl3 (100) 530 M°+(2), 492 M°+Cl (10), 454 M°+-2Cl (5), 418 M°+-3Cl (2), 338 M°+-TiCl4 (50) 571 M°+(1), 498 M°+2Cl (1), 464 M°+-3Cl (1), 429 M°+-4Cl (1), 338 M°+-ZrCl4 (100) 495 M°+(2), 425 M°+2Cl (1), 388 M°+-3Cl (1), 338 M°+-VCl3 (100)

23 1

Compound No.

34

35

13

H NMR δ [ppm] 8.22(d,2H), 7.92(t,2H), 7.74(s,2H), 7.69(d,2H), 7.43(d,2H)

C NMR δ [ppm] 151.0, 136.6, 134.5, 132.4, 132.1, 129.3, 126.6, 125.3, 116.8, 115.1

8.08(d,2H), 7.76(t,2H), 7.67(s,2H), 7.61(d,2H), 7.25(d,2H)

151.7, 137.7, 135.4, 131.9, 128.7, 127.7, 124.6, 123.4, 116.8, 115.3

36

n.d.

n.d.

Mass m/z[%] 568 M°+(1), 481 M°+2Cl-NH (2), 462 M°+3Cl (10), 426 M°+-4Cl (2), 378 M°+-TiCl4 (100) 611 M°+(2), 541 M°+2Cl (3), 503 M°+-3Cl (2), 467M°+-4Cl (5), 378 M°+-ZrCl4 (100) 535 M°+(1), 464 M°+2Cl (2), 428 M°+-3Cl (5), 378 M°+-VCl3 (100)

Solvent = DMSO-d6; n.d. = not determined

Conclusions Mononuclear transition metal complexes with hetero atoms in the ligand system can offer a big advantage: After activation with MAO, more than one active center can be generated and as a consequence bimodal or multimodal resins are produced in catalytic ethylene polymerization reactions. Obviously the hetero atoms of the activated catalysts undergo different interactions with the Lewis acidic moieties of MAO. Structure-property-relationship studies indicate that the nature of the hetero atom, the metal, and steric and electronic conditions in the coordination sphere are strongly involved in the performance of such catalysts.

Acknowledgements We thank SABIC company (Riyadh, Saudi Arabia) for GPC measurements and University of Juba (Khartoum, Sudan) for the financial support of H.A.E. for the first year.

References [1] W. Kaminsky, M Fernandes, Polyolefins 2 (2015) 1. [2] C. Redshaw, Y. Tang, Chem. Soc. Rev. 41 (2012) 4484. [3] M.C. Baier, M.A. Zuideveld, S. Mecking, Angew. Chem. Int. Ed. 53 (2014) 9722. [4] G.G. Hlatky, Chem. Rev. 100 (2000) 1347.

24 [5] A. Köppl, H.G. Alt, R. Schmidt, J. Organomet. Chem. 577 (1999) 351. [6] H.G. Alt, J. Chem. Soc. Dalton Trans. (1999), 1703. [7] M. Schilling, R. Bal, C. Görl, H.G. Alt, polymer (2007), 7461. [8] M. Schilling, C. Görl, H.G. Alt, Appl. Catal. A General 348 (2008) 79. [9] H.G. Alt, Dalton Trans. 2005, 3271. [10] J.R. Severn, J.C.Chadwick (eds.) “Tailor –Made Polymers”, Wiley-VCH (2008). [11] M. Ruhland, J.R.V. Lang, H.G. Alt, A.H.E. Müller, Eur. J. Inorg. Chem. (2013), 2146. [12] H. Alshammari, H.G. Alt, J.J.C. 9 (2014) 34 and 110. [13] H. Alshammari, H.G. Alt, Polyolefins 1 (2014) 107 [14] A.B.P. Lever, B.S. Ramaswamy, S.H. Simonsen, L.K. Thompson, Can. J. Chem. 48 (1970) 3076. [15] S. Wang, Y. Cui, R. Tan, Q. Luo, J. Shi, Q. Wu, Polyhedron 11 ( 1994) 1661. [16] J. Wang, Y. Zhu, S. Wang, Y. Gao, Q. Shi, Polyhedron 13 (1994) 1405. [17] R.C. Holz, L.C. Thomson, Inorg. Chem. 27 (1988) 4640. [18] S.X. Wang, Y. Zhu, F.G. Zhang, Q.Y. Wang, L.F. Wang, Polyhedron 11 (1992) 1909. [19] A.D. Addison, S. Burman, C.B. Wahlgren, O.A. Raijan, T.W.Rowe, E. Sinn J. Chem. Soc. Dalton Trans. (1987), 2621. [20] S. Ruttimann, C.M. Moreau, A.F. Williams, G. Bernardinelli, A.W. Addison, Polyhedron 11 (1992) 635.

[21] S.M. Nelson, F.S. Esho, M.G.B. Drew, J. Chem. Soc. Dalton Trans. (1982), 407. [22] N. Shashikala, V. Gayathri, N.M.N. Gowda, G.K.N. Reddy, Indian Chem. Soc. 66 (1989) 537.

[23] S.B. Sanni, H.J. Behm, P.T. Beurskens, G.A.V. Albada, J. Reedijk, A.T.H. Lenstra, A.W. Addison, M.J. Palaniandavar , J. Chem. Soc. Dalton Trans. (1988), 1429. [24] G.C. Wellon, D.V. Bautista, L.K. Thompson, F.W. Hartstock, Inorg. Chim. Acta 75 (1983) 271.

[25] Y. Suzuki, T.J.P. Hayashi, Patent 10298231, 1997. [26] H. A. Elagab, H.G. Alt, Inorgan. Chim. Acta 428 ( 2015) 100. [27] H. A. Elagab, H.G. Alt, Eur. Pol. J. 68 (2015)385. [28] H. A. Elagab, H.G. Alt, Inorgan. Chim. Acta 431 (2015) 266. [29] A.K. Tomov, V.C. Gibson, D. Zaher, M.R.J. Elsegood, S.H. Dale, Chem. Commun. (2004), 1956.

[30] H.Y. Cho, N.H. Tarte, L. Cui, D.S. Hong, S.I. Woo, Y.-D. Gong, Macromol. Chem. Phys. 207 ( 2006) 1965.

25 [31] L. Wang, M.M. Joullie, J. Am. Chem. Soc. 79 ( 1957) 5706. [32] C. Rai, J.B. Braunwarth, J. Org. Chem. 26 ( 1961) 3434. [33] M. Bochmann, L.M. Wilson, J. Chem. Soc. Chem. Commun. 21 (1986) 1610. [34] R.F. Jordan, C.S. Bajgur, W.E. Dasher, A.L. Rheingold, Organometallics, 6 (1987) 1041. [35] M. Seitz, W. Milius, H.G. Alt, J. Mol. Catal. A 261 (2007) 246. [36] C. Elschenbroich, Organometallchemie, Teubner (4th edition), 2003. [37] S. Svejda, M. Brookhart, Organometallics 18 (1999) 65. [38] C. Huang, J. Ahn, S. Kwon, J. Kim, J. Lee, Y. Han, H. Kim, Appl. Catal. A General 258 ( 2004) 173. [39] Y. Chen, C. Qian, J. Sun, Organometallics 22 ( 2003) 1231. [40] H.G. Alt, R. Ernst, J. Mol. Catal. A 195 (2003) 11. [41] A.C. Möller, R. Blom, R.H. Heyn, O. Swang, J. Kopf, T. Seraidaris, J. Chem Soc. Dalton Trans.(2006), 2098. [42] A.C. Möller, R. Blom, O. Swang, A. Hannisdal, E. Rytter, J.A. Stovneng , T. Piel, J. Phys. Chem. 112 ( 2008) 4074. [43] L.E. Manzer, Inorganic Synthesis 21 (1982) 135.

26

Highlights -

Ti, Zr and V complexes

-

Heterocyclic ligands

-

Ethylene polymerization

-

Bimodal resins

-

Structure-property-relationships

27 Graphical abstract for Hamdi 7

B

B HN

NH N

N

1- MCl4(THF)2, CH2Cl2 2- MCl3, Et2O

HN

NH N

r. t., 24h

N

MAO

MCln R1

R1

1- M =Ti, Zr 2- M = V

R1

R1

27 bis(benzimidazolyl) complexes of Ti, Zr and V have been prepared, characterized and tested for catalytic ethylene polymerization after activation with methylalumoxane (MAO). Structure-property-relationship studies show a strong influence of the bridging unit B on the performance of the catalysts. Most of the produced polyethylenes show bimodal molecular weight distributions.