Jordan Journal of Chemistry Vol. 2 No.3, 2007, pp. 219-233

JJC Diimine Chromium Complexes as Catalyst Precursors for

Homogeneous Ethylene Polymerization 1

Alexandra Kestel-Jakob, Helmut G. Alt*

Laboratorium für Anorganische Chemie, Universität Bayreuth, D-95440 Bayreuth, Germany

Received on July 8, 2007 Accepted on Nov. 15, 2007

Abstract The synthesis and characterization of 19 new α- and β-diimine chromium complexes are

reported. After activation with methyl aluminoxane (MAO), these complexes are catalysts for

homogeneous ethylene polymerization. The influences of various substituents and the ligand

backbone on the catalyst activities and the polymer properties are discussed. Oligomers with

odd and even numbers of carbon atoms can be obtained. This is an indication that these

catalysts cannot only oligomerize and polymerize but also isomerize and metathesize olefins

simultaneously.

Keywords: Diimine chromium complexes; Catalysis; Ethylene oligomers with odd

and even numbers of carbon atoms.

Introduction Various types of chromium catalysts for the homogeneous polymerization of

olefins are still of big interest [1-5]. One of the latest research activities describes

salicylaldimines bearing bulky ortho-phenoxy substituents and small imine substituents

to give very active chromium catalysts for ethylene polymerization [6]. Chromium

complexes with tridentate pyridine-based ligands as highly active precatalysts for the

oligomerization of ethylene are already known [7,8]. Also complexes with tridentate

ligands such as triazacyclohexane are highly active polymerization catalysts [9,10].

Chromium complexes with bidentate „nacnac“ ligands seem to be very

interesting.

The ligand structure was developed in the sixties of the last century [11-13].

The first chromium complex of this kind was described in 1989 [14]. These

complexes were used in the catalytic polymerization of ethylene several years

later [15-20].

In this report, chromium complexes with α- and β-dimimine ligands were

synthesized and used as catalysts for the polymerization and oligomerization of

ethylene. One highlight is the catalytic production of oligomers with odd numbers of

carbon atoms.

1 Dedicated to Professor Dr.Drs.h.c.mult.Wolfgang A. Herrmann on the occasion of his 60th birthday (April

18, 2008) * Corresponding author. Tel.:+49-921-55-2555; fax: +49-921-55-2044.

E-mail: helmut.alt@uni-bayreuth.de (H.G.Alt)

220

Experimental NMR spectroscopic investigations were performed with a Bruker ARX 250

instrument. All samples were measured at 25 °C. CDCl3 served as solvent. The

chemical shifts (δ) in the 1H NMR spectra are referenced to the residual proton signal

of the solvent (δ = 7.24 ppm for chloroform) and in 13C NMR spectra to the solvent

signal (δ = 77.0 ppm for chloroform-d1).

MS spectra were recorded with a VARIAN MAT CH7 mass spectrometer (direct

inlet system, electron impact ionization, 70 eV). In addition, a Hewlett Packard 5917A

mass spectrometer was routinely used to record MS spectra and in combination with a

Hewlett Packard Series II 5890 gas chromatograph to record GC/MS spectra.

Molecular weight determinations of the polyethylene samples were performed

using a HT-GPC equipment.

Gas chromatograms were recorded using a Perkin Elmer Auto System gas

chromatograph with flame ionization detector (FID) and helium as carrier gas (5.7

mL/min).

The temperature program was as follows.

Starting phase: 3 min at 50 °C

Heating phase: 4 °C/min (15 min)

Plateau phase: 250 °C (37 min)

Methylaluminoxane was supplied by Witco GmbH, Bergkamen, as 30% solution

in toluene (average molecular weight 1100 g/mol, aluminum content: 13.1%, 3.5% as

trimethylaluminum).

General synthesis procedure for the diimine compounds 1 - 8

To a solution of 40 mmol of the respective aniline derivative in dichloromethane,

15 mmol of the corresponding diketo compound and a catalytic amount of p-toluene

sulfonic acid were added. The mixture was heated under reflux for 3-36 h. The

progress of the reaction was observed by GC. The reaction mixture was cooled to

room temperature and filtered over silica. After removing the solvent in vacuo, the

product was washed with cold methanol. For purification, the products were

recrystallized from a methanol/ethanol mixture. The products were obtained as yellow

crystals. Yields: 25-80%.

All compounds were characterized by NMR spectroscopy (Table 1).

General synthesis procedure for the diimine compounds 9 - 21 To a solution of 40 mmol of the respective aniline derivative in toluene, 15 mmol

of the corresponding diketo compound and a catalytic amount of p-toluene sulfonic

acid were added. The mixture was heated under reflux in a Dean Stark apparature for

3-48 h. The produced water was permanently removed. The progress of the reaction

221

was observed by GC. The reaction mixture was cooled to room temperature and

filtered over silica. After removing the solvent in vacuo, the product was washed with

cold methanol. For purification, the products were recrystallized from a

methanol/ethanol mixture. The ligands were obtained as yellow crystals. Yields: 25-

80%.

All compounds were characterized by NMR spectroscopy (Table 1).

General synthesis procedure for the diimine chromium complexes 22 – 29 and 38 - 42

To 0.7 mmol of the respective diimine compound dissolved in 50 mL THF, 0.7

mmol of trichlorotris(tetrahydrofuran)chromium(III) were added under argon

atmosphere. The mixture was stirred 8-15 h at room temperature. For purification, the

volume of the solvent was reduced in vacuo and the complexes were precipitated by

adding pentane. After washing several times with pentane until the solvent stayed

colorless, the products were dried in vacuo. The complexes were obtained as green

powders. Yield: 30-60 %.

The complexes were identified by mass spectrometry (Table 2).

General synthesis procedure for the diimine chromium complexes 30 - 37

To 0.7 mmol of the respective diimine compound dissolved in 50 mL THF at -30

°C, 0.7 mmol methyllithium (1.6 M in ether) were added. After stirring over night, 0.7

mmol of trichlorotris(tetrahydrofuran)chromium(III) were added under argon

atmosphere. The mixture was stirred for 8-15 h at room temperature. For purification,

the volume of the solvent was reduced in vacuo and the complexes were precipitated

by adding pentane. After washing several times with pentane until the solvent stayed

colorless, the products were dried in vacuo. The complexes were obtained as green

powders. Yield: 60-80 %.

The complexes were identified by mass spectrometry (Table 2).

General procedure for the activation of the complexes

An amount of 5–10 mg of the corresponding complex was suspended in toluene

and activated with an excess of MAO (Al/Cr = 2500). The solvent was removed in

vacuo and the activated catalyst was suspended in 50 mL n-pentane. The catalyst

suspension was used for ethylene polymerization.

Homogenous polymerization of ethylene

n-Pentane, 250 mL, was placed in a 1 L Büchi laboratory autoclave, mixed with

the catalyst solution and the autoclave thermostated at 60 °C. An ethylene pressure

(99.98 % ethylene) of 10 bars was applied after an inside temperature of 50 °C was

reached. The mixture was stirred for 1 h at 60(± 2) °C, and subsequently the reaction

was terminated by releasing the pressure in the reactor. For the separation of the

oligomers and the polymers, the polymerization mixture was filtered and the remaining

222

polymer was washed with half concentrated hydrochloric acid in order to remove MAO.

After that it was dried in vacuo and weighed. The pentane of the oligomer solution was

removed by destillation over a Vigreux column and the oligomers were analyzed by

GC. The obtained polymer was dried in vacuo.

Results and discussion Synthesis of the diimine chromium complexes Synthesis of the diimine compounds 1 - 21

The diimine compounds can be synthesized by a condensation reaction of two

equivalents of an aniline derivative and one equivalent of a diketone according to

Scheme 1. They can be divided in different classes according to the ligand backbone.

R'

R'

R'

R

R N

NR

R O

O

+ 2

NH2

[H+]

- 2H2O

R = substituents at the backbone

R' = substituents at the phenyl rings Scheme 1. Synthesis of the diimine compounds.

All compounds are listed in Figure 1 and were characterized by NMR

spectroscopy (Table 1). Compounds 1 [21], 2 [22], 3 [23], 4 [24], 5 [25], 8 [26], 9 [17-19], 10 [27], 13 [17-19] and 20 [28] are already known in the literature.

223

R =

N

N

R

R

R =

Bu NMe2

Ph

5 6 7 8

1 2 3 4

Cl Br

NR

NR

H

NMe2

R =

R =

13 14 15 16

9 10 11 12

butanediimines pentanediimines

N

NR

R

NMe2Cl

R =

R =

20 21

18 1917

hexanediimines

Figure 1. Synthesized diimine compounds.

Table 1. NMR data of compounds 1-21.

1H-NMRa) 13C-NMRb)

1 7.37 (vt, 2H, 3JHH = 7.5 Hz); 7.12 (vt, 4H, 3JHH = 7.5 Hz); 6.79 (d, 4H, 3JHH = 7.5 Hz);

2.15 (s, 6H)

Cq: 168.3, 150.9

CH: 129.0, 123.8, 118.7

CH3: 15.4

2 7.12 (m, 8H), 6.93 (dt, 2H, 3JHH = 7.5 Hz, 4JHH = 1.2 Hz), 6.55 (dd, 2H, 3JHH = 7.8 Hz, 4JHH = 0.9 Hz),2.03 (s, 6H)

Cq: 167.7, 149.5, 126.7

CH: 130.4, 126.4, 123.9, 117.6

CH3: 17.8, 15.6

3 7.04 (s, 2H), 7.01 (d, 2H, 3JHH = 7.5), 6.55

(d, 2H, 3JHH = 7.5), 2.32 (s, 6H), 2.12 (s,

6H), 2.09 (s, 6H)

Cq: 167.8, 146.9, 133.2, 133.1

CH: 131.1, 126.8, 117.6

CH3: 20.8, 17.7, 15.5

4 6.92 (s, 4H), 2.32 (s, 6H), 2.07 (s, 6H), 2.03

(s, 12H)

Cq: 168.3, 145.9, 132.4, 124.5

CH: 128.6

CH3: 20.7, 17.7, 15.8

224

1H-NMRa) 13C-NMRb)

5 7.14 (d, 4H, 3JHH = 7.5), 6.68 (d, 4H, 3JHH =

7.5), 2.62 (t, 4H, 3JHH = 7.5), 2.13 (s, 6H),

1.59 (tt, 4H, 2J = 11, 3J = 7.5? ), 1.33 (qt,

4H, 2J = 11, 3J = 7.5), 0.92 (t, 6H, 3JHH =

7.5)

Cq: 168.2, 148.5, 138.3

CH: 128.8, 118.8

CH2: 35.0, 33.7, 22.3

CH3: 15.4, 14.0

6 7.23 (m, 16H), 6.63 (m, 2H), 3.89 (s, 4H),

1.84 (s, 6H)

Cq: 167.9, 149.3, 140.6, 130.2

CH: 130.6, 130.4, 128.8, 128.7, 128.3, 127.0,

125.9, 124.0, 118.0

CH2: 38.1

CH3: 15.4

7 7.88 (dd, 2H, 3JHH = 6.4 Hz, 4JHH = 2.1 Hz),

7.82 (dd, 2H, 3JHH = 7.3 Hz, 4JHH = 2.1 Hz),

7.66 (d, br, 2H, 3JHH = 8.3 Hz), 7.51 (m,

6H), 6.84 (dd, 2H, 3JHH = 7.3 Hz, 4JHH = 0.9

Hz), 2.03 (s, 6H)

Cq: 169.1, 147.0, 134.1

CH: 128.1, 126.3, 125.8, 125.7, 124.1, 123.4,

113.0

CH3: 15.9

8 7.26 (d, 4H, 3JHH = 7.5), 6.81 (d, 4H, 3JHH =

7.5), 3.43 (s, 12H), 2.71 (s, 6H).

Cq: 167.6, 147.8, 140.7

CH: 121.2, 113.06

CH3: 41.0, 15.6

9 7.23 (t, 4H, 3JHH = 7.5 Hz), 6.99 (t, 2H, 3JHH

= 7.5 Hz), 6.91 (d, 2H, 3JHH = 7.5 Hz), 4.87

(s, 1H), 3.40 (br, 1H), 1.95 (s, 6H)

Cq: 159.7, 145.9

CH: 129.0, 123.4, 122.8, 97.5

CH3: 21.1

10 7.14 (m, 4H), 6.98 (vt, 2H, 3JHH = 7.5), 6.91

(d, 2H, 3JHH = 7.5), 4.90 (s, 1H), 2.19 (s,

6H), 1.90 (s, 6H)

Cq: 159.3, 144.3, 130.4

CH: 130.0, 125.8, 123.3, 122.7, 96.2

CH3: 20.5, 18.0

11 6.92 (d, 2H, 3JHH = 7.5), 6.91 (s, 2H), 6.80

(d, 2H, 3JHH = 7.5), 4.86 (s, 1H), 2.29 (s,

6H), 2.15 (s, 6H), 1.88 (s, 6H)

Cq: 159.5, 141.7, 132.7, 130.3

CH: 130.7, 126.3, 122.7, 95.8

CH3: 20.5, 20.4, 17.9

12 7.02 (vt, 2H, 3JHH = 7.5), 6.89 (d, 2H, 3JHH =

7.5), 6.77 (d, 2H, 3JHH = 7.5), 4.88 (s, 1H),

2.27 (s, 6H), 2.11 (s, 6H), 1.86 (s, 6H)

Cq: 159.6, 144.2, 137.0, 129.3

CH: 125.1, 125.0, 120.9, 95.5

CH3: 20.4, 20.2, 13.8

13 7.25 (d, 4H, 3JHH = 7.5), 7.23 (vt, 2H, 3JHH =

7.5), 4.96 (s, 1H), 3.39 (qq, 1H, 3JHH = 7.5),

1.73 (s, 6H), 1.25 (d, 24H, 3JHH = 7.5)

Cq: 160.9, 142.2, 141.8

CH: 125.3, 123.0, 93.7, 28.0

CH3: 23.9, 22.8

14 7.09 (d, 2H, 4JHH = 2.4 Hz), 7.80 (dd, 2H, 3JHH = 8.8 Hz, 4JHH = 2.4 Hz), 6.76 (d, 2H, 3JHH = 7.5 Hz), 4.84 (s, 1H), 3.00 (br, 1H),

2.08 (s, 6H), 1.82 (s, 6H)

Cq: 160.2, 143.3, 132.7, 128.8

CH: 130.3, 126.4, 124.2, 97.3

CH3: 21.0, 18.4

15 7.37 (d, 4H, 3JHH = 8.6), 6.80 (d, 4H, 3JHH =

8.6), 4.88 (s, 1H), 1.97 (s, 6H)

Cq: 159.3, 144.2, 115.9

CH: 131.5, 123.8, 97.7

CH3: 20.5

16 6.89 (d, 4H; 3JHH = 8.8), 6.79 (d, 4H, 3JHH =

8.8), 4.71 (s, 1H), 2.82 (s, 12H), 1.98 (s,

6H)

Cq: 159.7, 147.1, 135.5

CH: 123.9, 112.9, 95.5

CH3: 40.8, 20.3

225

1H-NMRa) 13C-NMRb)

17 6.28 (vt, 2H, 3JHH = 7.5), 7.04 (vt, 4H, 3JHH =

7.5), 6.70 (d, 4H, 3JHH = 7.5), 2.56 (q, 4H, 3JHH = 7.5), 1.00 (t, 6H, 3JHH = 7.5)

Cq: 171.5, 150.7

CH: 128.9, 123.4, 118.3

CH2: 21.9

CH3: 12.6

18 7.31 (d, 2H, 3JHH = 7.5 Hz); 7.19-7.1 (m,

4H); 6.62 (d, 2H, 3JHH = 7.5 Hz); 2.95 (m,

2H); 2.64 (q, 4H, 3JHH = 7.5 Hz); 1.22 (d,

12H, 3JHH = 7.5 Hz); 1.11 (t, 6H, 3JHH = 7.5

Hz)

Cq: 171.0; 148.1; 137.3

CH: 126.0; 125.5; 124.0; 117.8; 28.4

CH2: 22.2

CH3: 22.7; 12.2

19 7.8 (t, 2H, 3JHH = 7.5 Hz); 7.06 (t, 2H, 3JHH =

7.5 Hz); 6.66 (d; 4H, 3JHH = 7.5 Hz); 2.61 (q,

4H, 3JHH = 7.5 Hz); 2.45 (t, 4H, 3JHH = 7.5

Hz); 1.63-1.54 (m, 4H); 1.1 (t, 6H, 3JHH =

7.5 Hz); 0.94 (t, 6H, 3JHH = 7.5 Hz)

Cq: 171.1; 149.0; 131.3

CH: 129.6; 126.3; 123.7; 117.8

CH2: 34.0; 22.8; 22.1

CH3: 14.0; 12.2

20 7.11 (t, 2H, 3JHH = 2.9 Hz), 6.77 (d, 2H, 3JHH

= 2.8 Hz), 6.56 (d, 2H, 3JHH = 2.8 Hz), 2.58

(q, 4H, 3JHH = 7.5 Hz), 2.15 (s, 6H), 1.04 (t,

6H, 3JHH = 7.5 Hz)

Cq: 171.7, 150.6, 135.3, 124.6

CH: 126.8, 124.4, 116.0

CH2: 22.1

CH3: 14.9, 12.0

21 7.26 (m, 8H), 3.44 (s, 12H), 3.20 (q, 4H, 3JHH = 7.5), 1.59 (t, 6H, 3JHH = 7.5)

Cq: 153.3, 147.6, 141.0

CH: 120.2, 113.4

CH2: 21.7

CH3: 41.1, 12.7 a) 25°C, in Chloroform-d1, δ [ppm] rel. Chloroform (7.24). b) 25°C, in Chloroform-d1, δ [ppm] rel. Chloroform (77.0).

Synthesis of the (α-diimine) chromium(III) complexes 22 – 29 and 38 - 42

The (α-diimine) chromium(III) complexes were prepared by the reaction of the

corresponding diimine with an equimolar amount of trichlorotris(tetrahydrofuran)

chromium(III) in THF.

+

- 2THFCrCl3 3THF. CrCl3thf

N

NR'

R'

R

RR'

R' N

N

R

R Scheme 2. Synthesis of (α-diimine) chromium(III) complexes.

Synthesis of the (β-diimine) chromium(III) complexes 30 - 37

For the synthesis of the (β-diimine) chromium(III) complexes the ligand precursor

was first deprotonated with BuLi. The lithiumsalt was formed. The reaction with

trichlorotris(tetrahydrofuran)chromium(III) in THF gave the product. This procedure has

been described in the literature [15-20].

226

NR

NR

H+BuLi

-BuH NR

NR

Li+-+ CrCl3 3THF.

- THF- LiCl N

R

NR

CrCl2(thf)2

Scheme 3. Synthesis of (β-diimine) chromium(III) complexes.

The synthesized complexes are summarized in Figure 2.

NMe2

R =

R =

Bu

Ph

N

N

R

R

CrCl3thf

22 23 24 25

26 27 28 29

NR

NR

CrCl2(thf)2

Cl Br NMe2

R =

R =

33

34[17-19] 3635

30[17-19] 31 32

37

38 39 40

41

NMe2Cl

R =

R =

N

N

R

R

CrCl3thf

42

Figure 2. Synthesized chromium complexes.

Due to the paramagnetic nature of these complexes, it is not very informative to

characterize them by NMR spectroscopy. The mass spectrometric analyses did not

reveal the molecular ion in every case. The fragments deriving from the loss of THF

molecules or the chlorine are observed (see Table 2).

227

Table 2. Mass spectrometric data of complexes 22 - 42.

complex fragment [m/z] (intensity [%]) 22 M+(-THF) = 393 (10), 236 (10), 118 (20), 93 (100) 23 M+(-THF) = 421 (5), 316 (10), 264 (10), 249 (50), 132 (40), 106 (100), 77(20) 24 M+(-THF, 3Cl) = 344 (15), 318 (20), 277 (20), 146 (50), 121 (100), 120 (85), 106

(65), 77 (20) 25 M+(-THF) = 477 (10), 371 (10), 305 (55), 160 (100), 119 (25), 91 (20) 26 M+(-THF, 3Cl) = 400 (15), 374 (15), 174 (100), 106 (55), 91 (30) 27 M+(-THF, 3Cl) = 440 (5), 388 (15), 194 (100), 169 (40), 72 (45) 28 M+(-THF, 3Cl) = 388 (10), 336 (70), 168 (100), 127 (65) 29 M+(-THF, 3Cl) = 374 (10), 322 (20), 161 (100), 136 (20), 121 (20) 30 M+ = n. d., 133 (10), 118 (20), 77 (100), 31 M+(-2THF)=399 (80), 364 (20), 329 (10), 277 (20), 173( 50), 132 (100), 106 (20), 91

(100) 32 M+(-2THF) = 427 (5), 305 (5), 291 (10), 187 (100), 146 (70), 106 (20), 105 (80), 91

(35), 77 (100) 33 M+(-2THF, 2Cl) =357 (5), 306 (30), 291 (25), 187 (85), 146 (100), 106 (40), 105

(40), 91 (15), 77 (35) 34 M+ = n. d., 417 (10), 403 (100), 375 (28), 202 (100), 187 (60), 160 (30), 91(20) 35 M+ = n. d., 346 (20), 207 (100), 166 (70), 125 (30), 77 (10) 36 M+ = n. d., 407 (5), 237 (40), 197 (40), 171 (70), 157 (50), 91 (50), 65 (70), 36 (100) 37 M+(-2THF, Cl) = 422 (10), 387 (5), 335 (20), 321 (20), 258 (20), 202 (70), 161 (50),

136 (20) 38 M+(-THF, 3Cl) = 316 (10), 264 (20), 132 (100) 39 M+(-THF, 2Cl) = 436 (10), 348 (10), 174 (80), 135 (50), 120 (100), 40 M+ = n. d., 348 (10), 305 (30), 174 (100), 91 (10) 41 M+ = n. d., 360 (10), 180 (100), 125 (20), 106 (60) 42 M+(-THF, 3Cl) = 402 (10), 350 (20), 175 (100), 136 (65)

Polymerization of ethylene

All catalyst precursors are chromium chloride complexes. They were activated

with MAO (Al:Cr = 2500) and they were used for the homogeneous polymerization of

ethylene.

In the activation step an electronically and sterically unsaturated cationic

chromium methyl cation is formed that represents the actual catalyst.

isomerisation

β-H-eliminination

metathesis

N

N

Cr R

N

N

CrH

R

- R N

N

CrH

N

N

Cr

H

R

N

N

Cr

H

R

N

N

Cr

H

R

R-

-

The obtained products were in some cases mixtures of oligomers and polymers.

The polymerization results are summarized in Table 3.

228

Table 3. Results of the homogeneous ethylene polymerization reactions with 22 – 42 activated with MAO.

complex activity [kg(Prod)/mol(Cr)⋅h]

polymer share [wt. %]

HT-GPC (polymer share)

Mn [g/mol] Mw [g/mol] Mz [g/mol]

Mz+1 [g/mol] MP [g/mol]

D

α

22 868 78.5 n. b. n. d. 23 487 85.1 10 800

217 900 1 041 400 1 660 900

65 500 20.2

0.97

24 636 84.6 10 300 1 037 700 6 172 800 9 576 700

73 200 100.6

0.93

25 594 100 18 700 904 600

5 591 100 9 127 700

68 800 48.3

-

26 923 87.5 9 700 274 500

1 131 200 1 683 200

75 700 28.3

n. d.

27 223 100 12 900 278 100

1 106 600 1 688 300

49 500 21.6

-

28 638 48.2 n. b. 0.93 29 142 100 109 600

303 300 668 000

1 133 700 200 000

2.8

-

30 140 100 5 600 536 600

3 662 500 6 763 500

54 900 95.2

-

31 152 100 6 500 622 600

7 675 000 13 660 400

46 200 96.4

-

229

complex activity [kg(Prod)/mol(Cr)⋅h]

polymer share [wt. %]

HT-GPC (polymer share)

Mn [g/mol] Mw [g/mol] Mz [g/mol]

Mz+1 [g/mol] MP [g/mol]

D

α

32 85 100 12 800 857 300

4 241 600 6 613 700

95 500 66.8

-

33 1 820 54.8 5 900 176 600

1 066 900 1 726 700

33 900 30.0

0.95

34 102 100 2 000 12 400

106 200 245 000

1 400 6.6

-

35 211 100 7 300 805 900

7 970 200 14 239 200

54 500 109.7

-

36 514 100 12 100 362 100

1 304 300 1 855 400

71 500 29.9

-

37 54 100 62 000 378 200

1 199 100 1 806 200 102 700

6.1

-

38 57 100 19 900 171 900 603 400 918 200 51 700

8.7

-

39 440a 78.9 n. b. n. d. 40 388 38.8 n. b. 0.98 41 541 78.6 n. b. n. d. 42 137 100 5 800

443 300 4 569 700 8 848 200

57 200 76.4

-

Polymerization conditions: Al/Cr = 2500/1; polymerization in 250 ml pentane, 60 °C, 1 L autoclave, 10 bar ethylene pressure, 60 min.

constant-Flory-Schulz )(

=+

=+

=transferchainofratenpropagatioofrate

npropagatioofrate

kkk

CB

Bα

D = polydispersity Mw/Mn of the polymer share n.d. = not determined

230

Discussion of the polymerization results

(α-Diimine)butane chromium(III) complexes

The highest activities were obtained when the active center of the catalyst was

easily accessible. This is the case for 22 and 26. There are no substituents or only a

butyl group in para-position which is too far away from the active center to block it.

Catalyst 27 has a bulky benzyl group. Therefore the activity decreases.

Figure 3. Polymerization activities of complexes 22 – 29/MAO.

(β-Diimine)pentane chromium(III) complexes

All (β-diimine)pentane chromium(III) complexes show a similar polymerization

behavior. A highlight was the pentanediimine chromium complex 33 which had a very

high activity of 1820 [kg(prod)/mol(Cr)⋅h]. A polymer/oligomer mixture was produced

with an oligomer share of 45%. The GC/MS-spectra revealed oligomers with odd

(25%) and even (75%) numbers of carbon atoms (Figure 7). The formation of

oligomers with odd numbered carbon atoms is indicative for the following reaction

cascade at one and the same active center (Scheme 4): The originally formed even

numbered 1-olefin is isomerized to give the 2-olefin. The 2-olefin and ethylene undergo

an olefin metathesis reaction to yield oligomers with odd numbers of carbon atoms.

This behavior can be explained by the substituents at the phenyl rings. The two methyl

groups are in the ortho and meta position. The positions of the two groups influence

the polymerization behavior in a way that the catalytic active center is blocked for

further insertion reactions. At the same time termination and metathesis reactions are

preferred.

231

Figure 4. Polymerization activities of complexes 30 – 37/MAO.

(α-Diimine)hexane chromium(III) complexes

Compound 38 has the least activity (Figure 5). It is not substituted. The presence

of substituents at the phenyl rings influences the activities due to electronic effects.

Complexes 39, 40 and 41 have electron pushing groups and the activities increase in

contrast to 38. The dimethylamino group in 42 has a negative inductive effect and the

activity decreases.

Figure 5. Polymerization activities of complexes 38 – 42/MAO.

232

1.1.1 Discussion of the oligomers

Figure 6. GC/MS-spectra of the oligomers produced with 28/MAO.

Some complexes produced a mixture of polymers and oligomers. The oligomer

mixtures were studied by GC to determine the Schulz-Flory coefficient which gives

informations about the molecular weight distributions of the oligomers (Table 3).

The various fractions were characterized by GC/MS.

Figure 6 shows the different oligomers from C-6 to C-22. Each fraction consists

of several isomers which are different in terms of the position of the double bond and

branching. The isomers were formed by the isomerizations of the primarily formed 1-

olefins. In the spectra there is also a peak for toluene, the solvent for MAO, which

could not be fully removed. An early termination of the chain growth by β-H elimination

produces the oligomers. The oligomers show a broad molecular weight distribution.

Figure 7. GC/MS-spectra of the oligomers produced with 33/MAO.

233

isomerisation

β-H-eliminination

metathesis

N

N

Cr R

N

N

CrH

R

- R N

N

CrH

N

N

Cr

H

R

N

N

Cr

H

R

N

N

Cr

H

R

R-

-

Scheme 4. Metathesis reaction to form oligomers with odd and even numbers of

carbon atoms.

Acknowledgements We thank SABIC, Riyadh, Saudi Arabia, for the financial support of the project.

References [1] Leeasubcharoen, S.; Lam, K.-C.; Concolino, T.E.; Rheingold, A.L.; Theopold, K.H.,

Organometallics, 2001, 20, 182. [2] Heinzt, R.A.; Leeasubcharoen, S.; Liable-Sands, L.M.; Rheingold, A.L.; Theopold, K.H.,

Organometallics, 1998, 17, 5477. [3] Döhring, A.; Rust, J.; Verhovnik, G.P.J., Organometallics, 2000, 19, 388. [4] Emrich, R.; Heinemann, O.; Jolly, P.W.; Krüger, C.; Verhovnik, G.P.J., Organometallics,

1997, 16, 1511. [5] Jensen, V.R.; Angermund, K.; Jolly,P.W., Organometallics, 2000, 19, 403. [6] Jones, D.J.; Gibson, V.C.; Green, S.M.; Maddox, P.J., Chem.Commun., 2002, 1038. [7] Small, B.L.; Carney, M.J.; Holman,D.M.; O'Rourke, C.E.; Halfen, J.A., Macromolecules,

2004, 37, 4375. [8] Esteruelas, M.A.; López, A.M.; Méndez, L.; Oliván, M.; Onate, E., Organometallics , 2003,

22, 395. [9] Köhn, R.D.; Haufe, M.; Mihan, S.; Lilge, D., Chem.Commun., 2000, 1927. [10] Köhn, R.D.; Haufe, M.; Kociok-Köhn, G.; Grimm, S.; Wasserscheid, P.; Keim, W.,

Angew.Chem., Int.Ed.Engl., 2000, 32, 4337. [11] Honeybourne, C.L.; Webb, G.A., J.Chem.Soc., Chem.Commun., 1968, 740. [12] Parks, J.E.; Holm, R.H., Inorg.Chem., 1968, 7, 1408. [13] McGeaching, S.G.; Can.J.Chem., 1968, 48, 1903. [14] Richeson, D.S.; Mitchell, J.F.; Theopold, K.H., Organometallics, 1989, 8, 2570. [15] Gibson, V.C.; Maddox, R.J.; Newton, C.; Redshaw, C.; Solan, G.; White, A.J.P.; Williams,

D.J., Chem.Commun., 1998, 1651. [16] Gibson, V.C.; Newton, C.; Redshaw, C.; Solan, G.; White, A.J.P.; Williams, D.J.,

Eur.J.Inorg.Chem., 2001, 1895. [17] Kim, W.K.; Fevola, M.J.; Liable-Sands, L.M.; Rheingold, A.L.; Theopold, K.H.,

Organometallics, 1998, 17, 4541. [18] MacAdams, L.A.; Kim, W.K.; Liable-Sands, L.M.; Guzei, I.A.; Rheingold, A.L.; Theopold,

K.H., Organometallics, 2002, 21, 952. [19] Theopold, K.H.; MacAdams, L.A.; Puttnual, C.; Buffone, G.P.; Rheingold, A.L.,

Polym.Mater.Sci.Eng. , 2002, 310. [20] MacAdams, L.A.; Buffone, G.P.; Incarvito, C.D.; Rheingold, A.L.; Theopold,K.H.,

J.Am.Chem.Soc., 2005, 127, 1082. [21] tom Dieck, H.; Orlopp, A., Angew.Chem., 1975, 87, 246. [22] tom Dieck ,H.; Svoboda, M.; Greiser, T., Z. Naturforsch., Teil B: Anorg.Chem.,

Organ.Chem., 1981, 823. [23] Kiesewetter, J.; Kaminsky, W., European Journal, 2003, 1750. [24] Weinberg, W.H.; McFarland, E.; Goldwasser, I.; Boussie, T.; Turner, H.; van Beek,

J.A.M.; Murphy, V.; Powers, T., PCT Int.Appl.WO 9803521 (1998). [25] Zhao, B.; Berluche, E.; Kacker, S.; Canich, J.A., PCT Int.Appl.WO 2003102005 (2003). [26] Johnson, L.K.; Killian, C.M.; Arthur, S.D.; Feldmann, J.; McCord, E.F.; McLain, S.J.;

Kreutzer, K.A.; Bennett, M.A.; Coughlin, E.B., PCT Int.Appl.WO 9623010 (1996). [27] Budzelaar, P.H.M.; van Oort, A. B.; Orpen, A.G., Eur.J.Inorg.Chem., 1998, 10, 1485. [28] Helldörfer, M.; Backhaus, J.; Milius, W.; Alt, H.G., J. Mol. Cat. A: Chem., 2003, 193, 59.