ω-Phenoxyalkyl substituted bis(indenyl)zirconium dichloride complexes as catalysts for homogeneous ethylene polymerization

Inorganica Chimica Acta 433 (2015) 63–71

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x-Phenoxyalkyl substituted bis(indenyl)zirconium dichloride complexes as catalysts for homogeneous ethylene polymerization Khalil Ahmad, Helmut G. Alt ⇑ Laboratorium für Anorganische Chemie, Universität Bayreuth, Postfach 101251, D-95440 Bayreuth, Germany

a r t i c l e

i n f o

Article history: Received 18 March 2015 Received in revised form 20 April 2015 Accepted 30 April 2015 Available online 9 May 2015 Keywords: x-Phenoxyalkyl substituted bis(indenyl)zirconium dichloride complexes Homogeneous ethylene polymerization Polyethylene

a b s t r a c t Nine bis(indenyl)zirconium dichloride complexes of the type [C9H6-(CH2)n-O-Ar]2ZrCl2 (n = 3–5; Ar = Ph, t-Bu-Ph) were synthesized, characterized, activated with methylalumoxane (MAO) and tested for ethylene polymerization. Structure–property-relationship studies showed that the activities of the catalysts depend on the length of the bridging chain between the indenyl and the phenoxy group as well as on the bulk at the phenoxy substituent. A t-Bu substituent at the ortho position of the phenoxy group (5a/MAO) gives a much higher catalyst activity (27,500 kg PE/mol cat h) than the isomer 8a/MAO with a t-Bu substituent at the para position of the phenoxy group (16,700 kg PE/mol cat h). Obviously substituents in the ortho position of the phenyl ring generate a bulkier catalyst cation and this can keep the MAO anion at a further distance to allow easier ethylene coordination and chain growth in the polymerization steps. The mono substituted bis(indenyl) complex (C9H7)[C9H6-(CH2)4-O-4-t-Bu]ZrCl2 shows lower activity (11,700 kg PE/mol cat h) than 8a indicating that the electronic effect is dominating in this type of catalysts. Ó 2015 Published by Elsevier B.V.

1. Introduction During the past 30 years an enormous amount of group (IV) metallocene complexes has been synthesized and tested for catalytic ethylene polymerization reactions. The scope of this research is mainly justified by the fact that slight modifications in the ligand structure of such complexes can result in drastic consequences in the catalyst performance and the properties of the produced polymers [1–10]. In many cases, structure–property-relationship studies allowed the production of tailored polymers. The size and nature of the substituents linked to cyclopentadienyl or indenyl ligands play an important role on the catalytic activity as well as on the molecular weight and molecular weight distributions of the produced polyolefins. Several metallocene complexes containing functional groups linked to cyclopentadienyl or indenyl ligands have been reported [11–34]. Donor atoms can alter the activity of a catalyst by coordinating reversibly or irreversibly to the metal center and block the vacant coordination site. Electron donating alkyl groups on bis(indenyl)zirconium dichloride complexes have a favourable effect on the ethylene polymerization activity of the catalyst while electron withdrawing groups decrease the catalyst activity and the molecular weight of the polyethylene produced

⇑ Corresponding author. Tel.: +49 921 43864. E-mail address: [email protected] (H.G. Alt). http://dx.doi.org/10.1016/j.ica.2015.04.035 0020-1693/Ó 2015 Published by Elsevier B.V.

[17]. Alkoxy- and siloxy substituents are applied to immobilize metallocene catalysts on dehydroxylated silica [35] and oxygen containing bridges are used for the synthesis of symmetric and dissymmetric dinuclear metallocene complexes [36–39]. We are reporting herein the synthesis and catalytic ethylene polymerization properties of nine zirconocene dichloride complexes bearing x-phenoxyaryl substituents on the indenyl ligands.

2. Results and discussion 2.1. Synthesis and characterization of the x-phenoxyalkyl substituted indenes 1–9 The substituted indene compounds 1–9 were synthesized according to Scheme 1 via a two step reaction. In the first step the reaction of a phenol with an excess of an a,x-dibromoalkane in the presence of potassium carbonate and catalytic amounts of a crown ether (18-crown-6) under reflux conditions gave x-bromo-1-phenoxyalkanes in good yields. The reaction of x-bromo-1-phenoxyalkanes with indenyl lithium provided xphenoxyalkyl substituted indene compounds in almost quantitative yields. The synthesized compounds were characterized by GC/MS and NMR spectroscopy (Table 2). In the 1H NMR spectrum of compound 4 (Fig. 1), the signals at d = 7.56–7.53 (m, 1H), 7.50–7.47 (m, 1H),

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K. Ahmad, H.G. Alt / Inorganica Chimica Acta 433 (2015) 63–71

R Br

Br

+

+

HO

+

Br

18-crown-6

K2CO3

acetone reflux

n

Li

1 (n = 3; R = H) 2 (n = 4; R = H) 3 (n = 5; R = H)

O n

-LiBr

4 (n = 3; R = 2-t-Bu) 5 (n = 4; R = 2-t-Bu) 6 (n = 5; R = 2-t-Bu)

Br

O n

O n

R

R

7 (n = 3; R = 4-t-Bu) 8 (n = 4; R = 4-t-Bu) 9 (n = 5; R = 4-t-Bu)

Scheme 1. Synthesis of the indene compounds 1–9.

Table 1 Ethylene polymerization activities and thermal analysis data for complexes 1a–9a. Complex No. n R

Activitya DHm [J/g] Tm [°C] Crystallinity (a) (kg PE/mol cat h)

1a 2a 3a 4a 5a 6a 7a 8a 9a

3860 9450 3380 16,300 27,500 7670 6670 16,700 9430

3 4 5 3 4 5 3 4 5

H H H 2-t-Bu 2-t-Bu 2-t-Bu 4-t-Bu 4-t-Bu 4-tBU

– – – 121.9 134.3 131.2 135.1 130.7 112.9

– – – 126.3 127.7 127.2 133.2 126.3 126.0

– – – 0.42 0.46 0.45 0.46 0.45 0.39

DHm = heat of fusion, Tm = melting temperature, a = degree of crystallinity (1,0 = 100%). a Polymerization conditions: M: Al = 1: 2000; 250 mL n-pentane; 65 °C; 10 bar ethylene pressure; 1 h.

7.41–7.37 (m, 2H), 7.32–7.22 (m, 2H) and 7.00–6.92 (m, 2H) ppm derive from the aryl protons H7, H6, H5, H4, H16, H15, H14 and H13. The signal at d = 6.34 (br, 1H) ppm is assigned to H2, while the signal at d = 4.14 (t, 3JH,H = 6.2 Hz, 2H) ppm is due to the methylene group attached to the oxygen atom (H10). The protons of the indenyl CH2 group appear at d = 3.42 (br, 2H) ppm. The signals at d = 2.93–2.87 (m, 2H) and 2.36–2.28 (m, 2H) ppm can be assigned to the methylene protons H8 and H9. The methyl protons of the tertiary butyl group can be observed at d = 1.57 (s, 9H) ppm. The J-modulated 13C NMR spectrum of compound 4 (Fig. 2) shows positive signals for CH and CH3 groups and negative signals for CH2 groups and Cquart. Comparisons with similar bis(indenyl) complexes proved the following signal assignments: The signal for the quaternary carbon atom C11 arises at d = 157.8 ppm, while the signals at d = 145.2, 144.5 and 143.6 ppm can be assigned to the indenyl quaternary carbon atoms C7a, C3a and C3. The signal at d = 137.9 ppm belongs to the quaternary carbon atom C12. The signals at d = 128.2, 127.0, 126.6, 126.0, 124.6, 123.8, 120.1 and 118.9 ppm can be assigned to the CH groups C15, C14, C13, C7, C6, C5, C4 and C2. At d = 111.7 ppm, the signal for the aryl CH carbon atom C16 can be observed. The signal for the CH2 carbon atom C10 arises at d = 67.1 ppm, while the signals at d = 37.7, 34.8 and 29.9 ppm derive from C1, C17 and C18. The signals at d = 28.0 and 24.8 ppm can be assigned to the alkyl chain carbon atoms C8 and C9.

2.2. Synthesis and characterization of the zirconocene dichloride complexes The zirconocene dichloride complexes 1a–9a were synthesized according to Scheme 2 by deprotonating the indene compounds 1– 9 with n-butyllithium followed by the reaction with zirconium tetrachloride in an appropriate solvent. Complexes 1a–9a were characterized by 1H and 13C NMR spectroscopy (Table 3) and elemental analysis (Table 4). They exist as a mixture of rac and meso isomers, each rotamer with its own spectrum. The 1H NMR spectrum of complex 4a (Fig. 3) shows signals at d = 7.55–7.51 (m, 4H), 7.35–7.30 (m, 6H), 7.20–7.07 (m, 6H), 7.02–6.88 (m, 12H) and 6.62–6.55 (m, 4H) ppm for 32 protons (rac and meso H7, H6, H5, H4, H16, H15, H14 and H13). Four signals appear at d = 6.14 (d, 3JH,H = 3.2 Hz, 2H), 5.92 (d, 3 JH,H = 3.2 Hz), 5.50 (d, 3JH,H = 3.2 Hz) and 5.47 (d, 3JH,H = 3.2 Hz) ppm for the indenyl protons H2 and H3 (rac and meso). The methylene protons attached to the oxygen atom (H10) can be observed as two sets of triplets at d = 3.60–3.50 (8H) ppm. Two multiplet signals at d = 3.25–3.13 (4H) and 3.05–2.93 (4H) ppm can be assigned to rac and meso H8. The signal at d = 2.00–1.76 (m, 8H) ppm belongs to H9. The signals for the tertiary butyl groups (H18) appear at d = 1.56 (s, 18H) and 1.52 (s, 18H) ppm. The J-modulated 13C NMR spectrum of complex 4a (Fig. 4) shows two sets of signals for both rac and meso isomers. Only one set of signals will be described here. The signal for the quaternary carbon atom C11 appears at d = 158.0 ppm. At d = 138.0 ppm the signal for the quaternary carbon atom C12 shows up. The signals for the indenyl quaternary carbon atoms C7a, C3a and C1 appear at d = 127.4, 126.4 and 122.4 ppm. The signals at d = 127.3, 127.0 and 120.8 ppm can be assigned to the CH carbon atoms C13, C14 and C15. At d = 112.2 ppm, the signal for the CH group ortho to the phenolic oxygen atom can be observed. The signals at d = 126.5, 125.8, 125.7, 124.2 and 122.4 ppm can be assigned to the indenyl carbon atoms C7, C6, C5, C4 and C3, while the signal for C2 appears at d = 99.2 ppm. The signals at d = 66.8, 35.1 and 30.3 ppm can be assigned to the methylene group attached to the oxygen atom (C10) and the tertiary-butyl group (C17 and C18), while the signals at d = 30.1 and 25.5 ppm can be assigned to the alkyl chain carbon atoms C8 and C9.

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K. Ahmad, H.G. Alt / Inorganica Chimica Acta 433 (2015) 63–71 Table 2 NMRa and MS data for compounds 1–9. No. Compound

1

1

7.53–7.50 m (1H), 7.46–7.43 m (1H), 7.38–7.31 m (3H), 7.29–7.24 m (1H), 7.01–6.95 m (3H), 6.29 m (br, 1H, IndH2), 4.09 t (2H, OCH2), 3.87 br (2H, Ind-H1), 2.84–2.78 m (2H, CH2), 2.27–2.20 m (2H, CH2) 7.47–7.43 m (1H), 7.38–7.35 m (1H), 7.32–7.25 m (3H), 7.22–7.17 m (1H), 6.95–6.88 m (3H), 6.23 m (br, 1H, IndH2), 4.00 t (2H, OCH2), 3.32 br (2H, Ind-H1), 2.66–2.59 m (2H, CH2), 1.93–1.85 m (4H, CH2) 7.48–7.44 m (1H), 7.39–7.35 m (1H), 7.32–7.25 m (3H), 7.23–7.17 m (1H), 6.96–6.88 m (3H), 6.20 m (br, 1H, IndH2), 3.96 t (2H, OCH2), 3.32 br (2H, Ind-H1), 2.63–2.55 m (2H, CH2), 1.88–1.72 m (4H, CH2), 1.63–1.54 m (2H, CH2) 7.56–7.53 m (1H), 7.50–7.47 m (1H), 7.41–7.37 m (2H), 7.32–7.22 m (2H), 7.00–6.92 m (2H), 6.34 br (1H, Ind-H2), 4.14 t (2H, OCH2), 3.42 br (2H, Ind-H1), 2.93–2.87 m (2H, CH2), 2.36–2.28 m (2H, CH2), 1.57 s (9H, CH3)

O 3

2

O 4

3

O 5

4

O 3

5

O 4

6

O 5

7

O 3

8

O 4

9

O 5

a

13

H NMR

C NMR

159.0, 145.2, 144.4, 143.6 (Cq), 29.4, 128.2, 126.0, 124.6, 123.7, 120.5, 118.9, 114.5 (CH), 67.2 (OCH2), 37.7 (CH2Ind), 27.6, 24.1 (CH2) 159.0, 145.4, 144.5, 144.1 (Cq), 29.4, 128.0, 126.0, 124.5, 123.7, 120.5, 118.9, 114.5 (CH), 67.6 (OCH2), 37.7 (CH2Ind), 29.2, 27.4, 24.5 (CH2)

MS m/z (%) 250 [M+] (4) 155 (12) 141 (22) 130 (100) 115 (49) 264 [M+] (3) 171 (90) 129 (100)

159.0, 145.4, 144.5, 144.3 (Cq), 129.4, 127.8, 126.0, 124.4, 278 [M+] (1) 123.7, 120.5, 118.9, 114.5 (CH), 67.7 (OCH2), 37.7 (CH2- 185 (49) 129 (100) Ind), 29.2, 27.8, 27.6, 26.1 (CH2) 115 (27) 157.8, 145.2, 144.5, 143.6, 137.9 (Cq), 128.2, 127.0, 126.6, 306 [M+] (3) 126.0, 124.6, 123.8, 120.0, 118.9, 111.7 (CH), 67.1 (OCH2), 157 (44) 129 (100) 37.7 (CH2-Ind), 34.8 (Cq), 29.9 (CH3), 28.0, 24.8 (CH2) 115 (64)

7.46–7.43 m (1H), 7.38–7.35 m (1H), 7.30–7.25 m (2H), 157.8, 145.4, 144.6, 144.1, 138.0 (Cq), 127.9, 127.0, 126.6, 7.21–7.12 m (2H), 6.88–6.83 m (2H), 6.22 br (1H, Ind-H2), 126.0, 124.5, 124.8, 120.0, 119.0, 111.7 (CH), 67.5 (OCH2), 4.01 t (2H-OCH2), 3.32 br (2H, Ind-H1), 2.66–2.61 m (2H, 37.7 (CH2-Ind), 34.9 (Cq), 29.8 (CH3), 29.5, 27.5, 24.9 (CH2) CH2), 1.97–1.91 m (4H, CH2), 1.38 s (9H, CH3)

320 171 129 115

[M+] (2) (100) (68) (18)

157.7, 145.2, 144.4, 144.2, 137.8 (Cq), 127.6, 126.8, 126.4, 125.8, 124.4, 123.6, 119.9, 118.8, 111.6 (CH), 67.4 (OCH2), 37.6 (CH2-Ind), 34.7 (Cq), 29.7 (CH3), 29.4, 27.6, 27.5, 26.3 (CH2)

334 185 129 115

[M+] (1) (100) (60) (22)

7.46–7.43 m (1H), 7.39–7.35 m (1H), 7.31–7.26 m (2H), 7.21–7.12 m (2H), 6.90–6.82 m (2H), 6.20 br (1H, Ind-H2), 3.97 t (2H, OCH2), 3.31 br (2H, Ind-H1), 2.63–2.57 m (2H, CH2), 1.94–1.86 m (2H, CH2), 1.83–1.75 m (2H, CH2), 1.68–1.61m (2H, CH2), 1.41 s (9H, CH3) 7.47–7.43 m (1H), 7.39–7.35 m (1H), 7.32–7.25 m (3H), 7.22–7.16 m (1H), 6.87–6.82 m (2H), 6.23 br (1H, Ind-H2), 4.02 t (2H, OCH2), 3.31 br (2H, Ind-H1), 2.77–2.69 m (2H, CH2), 2.21–2.11 m (2H, CH2), 1.29 s (9H, CH3) 7.45–7.42 m (1H), 7.36–7.33 m (1H), 7.29–7.24 m (3H), 7.20–7.15 m (1H), 6.83–6.79 m (2H), 6.20 br (1H, Ind-H2), 3.96 t (2H, OCH2), 3.30 br (2H, Ind-H1), 2.63–2.57 m (2H, CH2), 1.88–1.83 m (4H, CH2), 1.27 s (9H, CH3) 7.46–7.43 m (1H), 7.37–7.34 m (1H), 7.30–7.26 m (3H), 7.21–7.16 m (1H), 6.84–6.81 m (2H), 6.19 br (1H, Ind-H2), 3.94 t (2H, OCH2), 3.31 br (2H, Ind-H1), 2.60–2.54 m (2H, CH2), 1.86–1.71 m (4H, CH2), 1.61–1.52 m (2H, CH2), 1.29 s (9H, CH3)

d (ppm) rel. CHCl3 (7.24 ppm, 1H NMR) and rel. CDCl3 (77.0 ppm,

13

156.8, 145.3, 144.5, 143.7, 143.2 (Cq), 128.2, 128.1, 126.2, 306 [M+] (8) 126.0, 124.6, 123.8, 119.0, 114.0 (CH), 67.3 (OCH2), 37.8 176 (78) 161 (81) (CH2-Ind), 34.0 (Cq), 31.5 (CH3), 27.7, 24.2 (CH2) 129 (100) 115 (56) 156.8, 145.5, 144.6, 144.2, 143.1 (Cq), 128.0, 126.2, 126.0, 320 [M+] (6) 124.5, 123.8, 119.0, 114.0 (CH), 67.7 (OCH2), 37.7 (CH2171 (100) 129 (78) Ind), 34.0 (Cq), 31.5 (CH3), 29.2, 27.4, 24.5 (CH2) 115 (22) 156.8, 145.5, 144.5, 144.4, 143.1 (Cq), 127.8, 126.1, 125.9, 334 [M+] (3) 124.4, 123.7, 118.9, 113.9 (CH), 67.8 (OCH2), 37.7 (CH2- 204 (6) 185 (100) Ind), 34.0 (Cq), 31.5 (CH3), 29.2, 27.8, 27.7, 26.1 (CH2) 135 (74) 117 (65) 115 (23)

C NMR) at 298 K.

Fig. 1. 1H NMR spectrum of compound 4 in CDCl3.

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K. Ahmad, H.G. Alt / Inorganica Chimica Acta 433 (2015) 63–71

Fig. 2. J-modulated

13

C NMR spectrum of compound 4 in CDCl3.

R

n ZrCl4

2 n-BuLi O n

-2 n-BuH

-2 LiCl

O n

Li

O

Cl Zr Cl O n R

1a (n = 3; R = H)

4a (n = 3; R = 2-t-Bu)

7a (n = 3; R = 4-tBu)

2a (n = 4; R = H)

5a (n = 4; R = 2-t-Bu)

8a (n = 4; R = 4-t-Bu)

3a (n = 5; R = H)

6a (n = 5; R = 2-t-Bu)

9a (n = 5; R = 4-tBu)

Scheme 2. Synthesis of complexes 1a–9a.

2.3. Ethylene polymerization The metallocene complexes 1a–9a were activated with an excess of MAO (Al: Zr = 2000: 1). The activated complexes were applied for homogeneous ethylene polymerization in 250 ml of n-pentane, at 10 bar ethylene pressure and the desired temperature. The polymerization activities of the activated complexes, the thermal analysis data of the representative polymer samples and their crystallinities [41] are listed in Table 1.

active than catalyst 1a without a substituent. This can be attributed to the fact that the bulky t-butyl group protects the cationic metal centre of the activated catalyst from the approaching oxygen atom of the phenoxy group. Catalyst 4a shows higher activity than catalyst 7a because the tertiary butyl group at the ortho position to the donor oxygen atom of the phenoxy group provides more protection than a tertiary butyl group at the para position. The same trend is obvious for catalysts 2a, 5a and 8a as well as for 3a, 6a and 9a.

2.4. Influence of the bulk on the polymerization activities of the zirconocene dichloride complexes 1a–9a

2.5. Influence of the spacer length on the polymerization performance

In the series of complexes 1a–9a bearing x-phenoxyalkyl substituents on the indenyl groups, catalyst 5a with a 2-Bu substituent showed the highest activity for ethylene polymerization while catalyst 3a without a substituent at the phenyl ring showed the lowest activity (Fig. 5). A comparison of the activities of catalysts 1a, 4a and 7a with equal distances (three CH2 groups) between the indenyl and the phenoxy group showed that catalysts 4a and 7a bearing a tertiary butyl group on the phenoxy substituent were more

A comparison of the activities of catalysts 4a, 5a and 6a differing in the chain length between the indenyl and the phenoxy groups showed that catalyst 5a with four methylene bridging units was more active (27,500 kg PE/mol cat h) than catalyst 4a with three methylene bridging units (16,300 kg PE/mol cat h) and catalyst 6a with five methylene bridging units (7670 kg PE/mol cat h). The same trend could be observed for catalysts 1a–3a and 7a–9a. This can be explained by the fact that the 1-substituted

67

K. Ahmad, H.G. Alt / Inorganica Chimica Acta 433 (2015) 63–71 Table 3 H and 13C NMR data of complexes 1a–9a.

1

1

No. Complex

H NMR [d (ppm)]

a

1a

O

3

Cl Zr Cl

13

C NMR [d (ppm)]

7.63–7.60 m (2H), 7.58–7.53 m (4H), 7.43–7.40 m (2H), 7.30–7.16 m 158.8, 127.3, 126.2, 122.2 (Cq), 129.4, 126.4, 125.6, 124.6, 123.8, (16H), 6.94–6.81 m (12H), 6.29 d (J = 3.2 Hz, 2H, Ind-H), 6.04 d 122.2, 120.6, 114.5, 99.3 (CH), 66.7 (OCH2), 29.4, 24.2 (CH2) (J = 3.2 Hz, 2H, Ind-H), 5.81 d (J = 3.2 Hz, 2H, Ind-H), 5.66 d (J = 3.2 Hz, 2H, Ind-H), 3.97–3.83 m (8H), 3.20–3.07 m (4H), 2.98– 2.81 m (4H), 2.19–1.92 m (8H)

O

3

2aa

O

4

Cl Zr Cl

7.57–7.54 m (2H), 7.52–7.47 m (4H), 7.38–7.35 m (2H), 7.24–7.09 m 158.9, 127.3, 125.9, 123.0 (Cq), 129.4, 126.3, 125.6, 125.5, 123.8, (16H), 6.86–6.75 m (12H), 6.25 d (J = 3.2 Hz, 2H, Ind-H), 5.97 d 122.0, 120.5, 114.4, 99.1 (CH), 67.4 (OCH2), 29.1, 27.9, 26.6 (CH2) (J = 3.2 Hz, 2H, Ind-H), 5.77 d (J = 3.2 Hz, 2H, Ind-H), 5.57 d (J = 3.2 Hz, 2H, Ind-H), 3.90–3.80 m (8H), 3.00–2.60 m (8H), 1.82– 1.56 m (16H)

O

4

3aa

O

5

Cl Zr Cl

7.58–7.55 m (2H), 7.52–7.47 m (4H), 7.39–7.35 m (2H), 7.26–7.12 m 159.0, 127.3, 125.9, 123.2 (Cq), 129.4, 126.2, 125.7, 125.4, 123.8, (16H), 6.87–6.77 m (12H), 6.23 d (J = 3.2 Hz, 2H, Ind-H), 5.97 d 122.1, 120.5, 114.5, 99.2 (CH), 67.6 (OCH2), 29.8, 29.0, 28.1, 26.0 (J = 3.2 Hz, 2H, Ind-H), 5.74 d (J = 3.2 Hz, 2H, Ind-H), 5.57 d (CH2) (J = 3.2 Hz, 2H, Ind-H), 3.87–3.81 m (8H), 2.95–2.82 m (4H), 2.74– 2.56 m (4H), 1.79–1.37 m (24H)

O

5

4aa

O

3

Cl Zr Cl

7.55–7.51 m (4H), 7.35–7.30 m (6H), 7.20–7.07 m (6H), 7.02–6.88 m 158.0, 138.0, 127.4, 126.4, 122.4 (Cq), 127.3, 127.0, 126.5, 125.8, (12H), 6.62–6.55 (m, 4H), 6.14 d (J = 3.2 Hz, 2H, Ind-H), 5.92 d 125.7, 124.2, 122.1, 120.8, 112.2, 99.2 (CH), 66.8 (OCH2) (J = 3.2 Hz, 2H, Ind-H), 5.50 d (J = 3.2 Hz, 2H, Ind-H), 5.47 d 35.1 (Cq), 30.3 (CH3), 30.1, 25.5 (CH2) (J = 3.2 Hz, 2H, Ind-H), 3.60–3.50 m (8H, CH2), 3.25–3.13 m (4H, CH2), 3.05–2.93 m (4H, CH2), 2.00–1.76 m (8H, CH2), 1.56 s (18H), 1.52 s (18H)

O

3

5aa

O

4

Cl Zr Cl

7.60–7-56 m (2H), 7.53–7.47 m (4H), 7.39–7.35 m (2H), 7.24–7.02 m 157.7, 137.8, 127.3, 125.8, 123.0 (Cq), 126.9, 126.5, 126.3, 125.6, (16H), 6.81–6.69 m (8H), 6.26 d (J = 3.2 Hz, 2H, Ind-H), 5.98 d 125.5, 123.8, 122.2, 120.0, 111.7, 99.1 (CH), 67.2 (OCH2), 34.8 (Cq), (J = 3.2 Hz, 2H, Ind-H), 5.76 d (J = 3.2 Hz, 2H, Ind-H), 5.56 d 29.8 (CH3), 29.4, 28.0, 26.9 (CH2) (J = 3.2 Hz, 2H, Ind-H), 3.93–3.82 m (8H, CH2), 3.02–2.89 m (4H, CH2), 2.81–2.61 m (4H, CH2), 1.86–1.68 m (16H, CH2), 1.28 s (18H), 1.26 s (18H)

O

4

6aa

O

5

Cl Zr Cl

157.7, 137.9, 127.3, 125.9, 123.2 (Cq), 126.9, 126.5, 126.2, 125.7, 7.66–7.53 m (4H), 7.45–7.10 m (20H), 6.90–6.77 m (8H), 6.31 d (J = 3.2 Hz, 2H, Ind-H), 6.04 d (J = 3.2 Hz, 2H, Ind-H), 5.82 d 125.4, 123.8, 122.1, 120.0, 111.7, 99.1 (CH), 67.4 (OCH2), 34.8 (Cq), (J = 3.2 Hz, 2H, Ind-H), 5.04 d (J = 3.2 Hz, 2H, Ind-H), 4.04–3.83 m 29.8 (CH3), 29.2, 28.1, 27.7, 26.3 (CH2) (8H, CH2), 3.04–2.87 m (4H, CH2), 2.81–2.56 m (4H, CH2), 1.88–1.44 m (24H, CH2), 1.34 s (18H)

O

5

(continued on next page)

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K. Ahmad, H.G. Alt / Inorganica Chimica Acta 433 (2015) 63–71

Table 3 (continued) 1

No. Complex

13

H NMR [d (ppm)]

a

7a

O

3

C NMR [d (ppm)]

7.63–7.53 m (6H), 7.44–7.40 m (2H), 7.30–7.18 m (16H), 6.83–6.75 156.6, 143.4, 127.3, 126.0, 122.2 (Cq), 126.4, 126.2, 125.7, 125.6, m (8H), 6.29 d (J = 3.2 Hz, 2H, Ind-H), 6.07 d (J = 3.2 Hz, 2H, Ind-H), 123.8, 122.1, 114.0, 99.4 (CH), 66.8 (OCH2), 34.1 (Cq), 31.5 (CH3), 5.82 d (J = 3.2 Hz, 2H, Ind-H), 5.67 d (J = 3.2 Hz, 2H, Ind-H), 3.98–3.82 29.4, 24.6 (CH2) m (8H, CH2), 3.19–3.06 m (4H, CH2), 2.98–2.80 m (4H, CH2), 2.18– 1.90 m (8H, CH2), 1.30 s (18H), 1.28 s (18H)

Cl Zr Cl O

3

8aa

O

7.58–7.36 m (8H), 7.25–7.13 m (16H), 6.76–6.70 m (8H), 6.25 (d, J = 3.2 Hz, 2H, Ind-H), 5.98 (d, J = 3.2 Hz, 2H, Ind-H), 5.76 (d, J = 3.2 Hz, 2H, Ind-H), 5.57 (d, J = 3.2 Hz, 2H, Ind-H), 3.88–3.81 (m, 8H), 3.00–2.60 (m, 8H), 1.80–1.55 (m, 16H), 1.21 (s, 36H)

156.7, 143.2, 127.3, 125.9, 123.0 (Cq), 126.2, 126.1, 125.7, 125.5, 123.8, 122.1, 113.9, 99.2 (CH), 67.5 (OCH2), 34.0 (Cq), 31.5 (CH3), 129.2, 127.9, 126.6 (CH2)

4

Cl Zr Cl O

4

9aa

O

5

7.67–7.57 m (6H), 7.49–7.45 m (2H), 7.34–7.22 m (16H), 6.86–6.79 156.7, 143.1, 127.3, 126.0, 123.2 (Cq), 126.2, 126.1, 125.7, 125.4, m (8H), 6.33 d (J = 3.2 Hz, 2H, Ind-H), 6.07 d (J = 3.2 Hz, 2H, Ind-H), 123.8, 122.0, 113.9, 99.2 (CH), 67.6 (OCH2), 34.0 (Cq), 31.5 (CH3), 5.85 d (J = 3.2 Hz, 2H, Ind-H), 5.67 d (J = 3.2 Hz, 2H, Ind-H), 3.96–3.88 29.8, 29.1, 28.1, 26.0 (CH2) m (8H, CH2), 3.06–2.92 m (4H, CH2), 2.84–2.66 m (4H, CH2), 1.83– 1.46 m (24H, CH2), 1.33 s (18H), 1.32 s (18H)

Cl Zr Cl O

5

a

d (ppm) rel. CHCl3 (7.24 ppm, 1H NMR) and rel. CDCl3 (77.0 ppm,

13

C NMR) at 298 K.

2.6. Influence of the temperature on the polymerization behaviour

Table 4 Elemental analysis data for complexes 1a–9a. No.

Cexp (%)

Ctheor (%)

Hexp (%)

Htheor (%)

1a 2a 3a 4a 5a 6a 7a 8a 9a

65.75 65.37 67.03 68.34 68.79 69.94 68.46 68.71 69.75

65.44 66.26 67.02 68.37 68.97 69.53 68.37 68.97 69.53

5.95 5.50 6.20 6.82 6.94 6.80 6.79 7.04 7.18

5.19 5.56 5.91 6.52 6.79 7.05 6.52 6.79 7.05

metallocene complexes are able to exist in different conformations [40]. The reason for the higher activities of catalysts 2a, 5a and 8a could be that the conformation obtained with four methylene bridging units minimizes the intramolecular deactivation of the active species via interaction of the oxygen atom and the oxophilic metal more efficiently than a conformation with three or five methylene groups. The deactivation can also happen via intermolecular interactions. A comparison with dissymmetric mono substituted bis(indenyl) complexes with this type of ligands showed that the disubstituted species have a somewhat better performance [42].

To study the effect of the temperature, the ethylene polymerization activity of catalyst 5a was investigated at different temperatures (Fig. 6). By increasing the polymerization temperature from 55 to 65 °C the activity increased. A further increase of the temperature resulted in a sharp decrease of activity. The reason could be decomposition reactions of the active species at higher temperatures. DSC measurements (see Table 1) showed that the catalyst systems 1a–9a/MAO produced polyethylenes with comparatively low melting points, low degrees of crystallinity and low heats of fusion.

3. Experimental 3.1. General Schlenk technique was used to carry out the experimental work. Argon was purified before its use as an inert gas. Methylene chloride was distilled over phosphorus pentoxide. Toluene, tetrahydrofuran, diethyl ether and n-pentane were purified by distillation over Na/K alloy. Diethyl ether was additionally distilled over lithium aluminum hydride, while toluene was

K. Ahmad, H.G. Alt / Inorganica Chimica Acta 433 (2015) 63–71

Fig. 3. 1H NMR spectrum of complex 4a (rac and meso isomers) in CDCl3.

Fig. 4. J-modulated

13

C NMR spectrum of complex 4a in CDCl3.

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K. Ahmad, H.G. Alt / Inorganica Chimica Acta 433 (2015) 63–71

Fig. 5. Ethylene polymerization activities of complexes 1a–9a/MAO.

Fig. 6. Effect of the temperature on the ethylene polymerization activity of 5a/MAO.

additionally distilled over phosphorus pentoxide. Deuterated solvents (CDCl3 and C6D6) were purchased from Eurisotop and stored over molecular sieves (3 Å). Argon (5.0) and ethylene (3.5) were purchased from Riebner Company. Methylalumoxane (10% in toluene) was purchased from Chemtura Europe Limited. All other starting materials were commercially available and used as received. 3.2. NMR spectroscopy NMR spectra were recorded with a Varian Inova (400 MHz) spectrometer. All spectra were recorded at 298 K. In the 1H NMR spectra the chemical shift of the residual proton signal of the solvent was used as a reference (d = 7.24 ppm for chloroform and d = 7.16 ppm for benzene), while in the 13C NMR spectra the chemical shift of the solvent was used as a reference (d = 77.0 ppm for chloroform-d1 and d = 128.0 ppm for benzene-d6). 3.3. GC/MS GC/MS spectra were recorded with a FOCUS Thermo gas chromatograph combined with a DSQ mass detector. A 30 m HP-5 fused silica column (internal diameter 0.32 mm, film 0.25 lm and flow 1 mL/min) was used and helium (4.6) was applied as carrier gas. The measurements were recorded using the following temperature program: Starting temperature: 50 °C, duration: 2 min; Heating rate: 20 °C/min, duration: 12 min; Final temperature: 290 °C, duration: 27 min.

3.4. Elemental analysis Elemental analyses were performed with a Vario EL III CHN instrument. The values of C, H and N were calibrated using acetamide as a standard. 3.5. DSC analysis DSC analyses were performed on a Mettler Toledo DSC/SDTA 821e instrument. The polymer samples were prepared by enclosing 4–6 mg of the polymer in standard aluminum pans. The samples were introduced into the auto sampler of the instrument and the measurements were recorded using the following temperature program: First heating phase: from 50 °C to 160 °C (10 °C/min); Cooling phase: 160 °C to 50 °C (10 °C/min); Second heating phase: from 50 °C to 160 °C (10 °C/min). Nitrogen was used as a cooling medium. Melting enthalpies and melting points were taken from the second heating phase. The values were calibrated using indium as a standard (m.p. 429.78 K, Hm = 28.45 J/g). 3.6. General synthesis procedure for the x-phenoxyalkyl-substituted indene compounds 1–9 An amount of 10 mmol of an appropriate phenol, 10 mmol of potassium carbonate, 30 mmol of the desired a,x-dibromoalkane and catalytic amounts of 18-crown-6 were refluxed in acetone for 24–72 h. The reaction mixture was cooled, the solvent was

K. Ahmad, H.G. Alt / Inorganica Chimica Acta 433 (2015) 63–71

removed followed by the addition of distilled water and extraction with diethyl ether (2  100 mL). After passing over sodium sulfate and removing the solvent, the residue was distilled to obtain the x-bromo-1-phenoxyalkane compound. An amount of 5 mmol of n-butyllithium (1.6 M in n-hexane) was added to 5 mmol of indene dissolved in 100 ml of diethyl ether at 78 °C. After warming up to room temperature and stirring for further 3 h, the solution was cooled to 78 °C and an amount of 5 mmol of the x-bromo-1-phenoxyalkane was added. The solution was allowed to warm up to room temperature and stirred for further 12 h. The solution was washed with distilled water and dried over sodium sulfate. Removal of the solvent provided the desired x-phenoxyalkyl-substituted indene in 80% yield. 3.7. General synthesis procedure for the zirconocene dichloride complexes 1a–9a An amount of 2 mmol of the appropriate substituted indenyl compound was dissolved in 50 mL of diethyl ether. To this solution, an amount of 2 mmol of n-butyllithium (1.6 M in hexanes) was added at 78 °C. This solution was allowed to come to room temperature and stirred for further 3 h. Then it was added to 1 mmol of zirconium tetrachloride suspended in 50 ml of diethyl ether at 78 °C. The mixture was slowly allowed to come to room temperature and stirred for further 24 h. Diethyl ether was removed and an amount of 100 ml of toluene was added. The toluene suspension was filtered, the volume of the filtrate was reduced and the complexes were precipitated by addition of n-pentane. After filtration, the precipitate was washed several times with n-pentane and dried in vacuo to obtain the desired complex as yellow powder in 50% yield. 3.8. Polymerization of ethylene For the homogeneous polymerization of ethylene, 3–5 mg of the corresponding complexes were dissolved in toluene (5–10 mL) and activated with methylalumoxane (MAO). The activated complexes were suspended in pentane (250 mL) and transferred to a 1 L Büchi autoclave under inert atmosphere. The temperature of the thermostat was adjusted to the desired value and an ethylene pressure of 10 bar was applied for one hour. After releasing the pressure, the obtained polymer was filtered over a frit, washed with dilute hydrochloric acid, water, and finally with acetone and dried under vacuum. 4. Conclusions Bis(indenyl)zirconium dichloride complexes of the type [C9H6(CH2)n-O-Ar]2ZrCl2 (n = 3–5; Ar = Ph, t-Bu-Ph) can be activated with MAO and then be applied as efficient ethylene polymerization catalysts in solution They have higher activities as the unsubstituted or mono phenoxyalkyl substituted indenyl derivatives. Because of the high oxophilicity of zirconium, the crucial presence of oxygen in the phenoxy substituent must be compensated with steric shielding of bulky substituents like t-Bu in order to achieve high activities. In this context also the length of the alkylphenoxy substituent plays an important role. Four CH2-groups gave the best

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results. It is expected that catalysts with such spacious substituents are suitable oscillating catalysts for propylene polymerization and olefin copolymerization [43]. Acknowledgements We thank to Higher Education Commission of Pakistan (HEC Pakistan) and Deutscher Akademischer Austauschdienst (DAAD) for the financial support. References [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]

W. Kaminsky, M. Fernandes, Polyolefins J. 2 (2015) 1. C. Redshaw, Chem. Soc. Rev. 41 (2012) 4484. M.C. Baier, M.A. Zuideveld, S. Mecking, Angew. Chem., Int. Ed. 53 (2014) 9722. W. Kaminsky, Polyolefins: 50 years after Ziegler and Natta, Adv. Polym. Sci., 14, Springer, 2013, p. 257. H.G. Alt, Polyolefins J. 2 (2015) 17. H.G. Alt, Macromol. Symp. 173 (2001) 65. H.G. Alt, A. Köppl, Chem. Rev. 100 (2000) 1205. H.G. Alt, Dalton Trans. (2005) 3271. H.G. Alt, Coord. Chem. Rev. 250 (2006) 1. H.G. Alt, C. Görl, Tailor-Made Polymers Via Immobilization of Alpha-Olefin Polymerization Catalysts, in: John R. Severn, John C. Chadwick (Eds.), WileyVCH, 2008, p. 305. E.H. Licht, H.G. Alt, M.M. Karim, J. Organomet. Chem. 599 (2000) 275. R. Schmidt, H.G. Alt, J. Organomet. Chem. 621 (2001) 304. H.W. Gschwend, H.R. Rodriguez, Org. React. 26 (1979) 1. H. Sinn, W. Kaminsky, Adv. Organomet. Chem. 18 (1980) 99. K.P. Stahl, G. Boche, W. Massa, J. Organomet. Chem. 277 (1984) 113. J. Amarasekera, T.B. Rauchfuss, Inorg. Chem. 28 (1989) 3875. N. Piccolrovazzi, P. Pino, G. Consiglio, A. Sironi, M. Moret, Organometallics 9 (1990) 1998. R.F. Jordan, Adv. Organomet. Chem. 32 (1991) 325. P. Burger, J. Diebold, S. Gutmann, H.-U. Hund, H.-H. Brintzinger, Organometallics 11 (1992) 1319. T.J. Marks, Acc. Chem. Res. 25 (1992) 57. M. Aulbach, F. Küber, Chem. Unserer Zeit 28 (1994) 197. C. Qian, D. Zhu, J. Chem. Soc., Dalton Trans. (1994) 1599. H.-H. Brintzinger, D. Fischer, R. Mülhaupt, B. Rieger, R.M. Waymouth, Angew. Chem. 107 (1995) 1255. H.G. Alt, E.H. Licht, A.I. Licht, K.J. Schneider, Coord. Chem. Rev. 250 (2006) 2. H. Plenio, D. Burth, J. Organomet. Chem. 519 (1996) 269. E. Barsties, S. Schaible, M.-H. Prosenc, U. Rief, W. Röll, O. Weyand, B. Dorer, H.H. Brintzinger, J. Organomet. Chem. 520 (1996) 63. H.J.G. Luttikhedde, R.P. Leino, C.-E. Wilén, J.H. Näsman, M.J. Ahlgrén, T.J. Pakkanen, Organometallics 15 (1996) 3092. P. Jutzi, T. Redeker, B. Neumann, H.-G. Stammler, Organometallics 15 (1996) 4153. J.A. Ewen, R.L. Jones, M.J. Elder, A.L. Rheingold, L.M. Liable-Sands, J. Am. Chem. Soc. 120 (1998) 10786. C.A.G. Carter, R. McDonald, J.M. Stryker, Organometallics 18 (1999) 820. P. Witte, T.K. Lal, R.M. Waymouth, Organometallics 18 (1999) 4147. S. Knüppel, J.-L. Fauré, G. Erker, G. Kehr, M. Nissinen, R. Fröhlich, Organometallics 19 (2000) 1262. T. Dreier, G. Erker, R. Fröhlich, B. Wibbeling, Organometallics 19 (2000) 4095. T. Dreier, G. Unger, G. Erker, B. Wibbeling, R. Fröhlich, J. Organomet. Chem. 622 (2001) 143. C. Alonso-Moreno, A. Antiñolo, F. Carrillo-Hermosilla, P. Carrión, I. LópezSolera, A. Otero, S. Prashar, J. Sancho, Eur. J. Inorg. Chem. (2005) 2924. F. Lin, J. Sun, X. Li, W.K. Lang, H.F. Li, H. Schumann, Eur. Polym. J. 43 (2007) 1436. X. Xiao, J. Sun, X. Lia, H.F. Li, Y. Wang, J. Mol. Catal. A Chem. 267 (2007) 86. X. Xiao, B. Zhu, X. Zhao, Y. Wang, J. Sun, Inorg. Chim. Acta 360 (2007) 2432. Y. Nie, J. Sun, J. Cheng, H. Ren, H. Schumann, J. Appl. Polym. Sci. 108 (2008) 3702. C.D. Tagge, R.L. Kravchenko, T.K. Lal, R.M. Waymouth, Organometallics 18 (1999) 380. Y. Kong, J.N. Hay, Eur. Polym. J. 39 (2003) 1721. K. Ahmad, H.G. Alt, JJC (2015). in press. S.E. Reybuck, A. Meyer, R.M. Waymouth, Macromolecules 35 (2002) 637.