Chromium imine and amine complexes as homogeneous catalysts for the trimerisation and polymerisation of ethylene

Article abstract of DOI:10.1016/j.jorganchem.2004.09.080

Cr(III) complexes of tridendate imine and amine ligands with N, P, O, S donor atoms 1 and 2 have been prepared and tested as catalysts in the oligomerisation and polymerisation of ethylene giving excellent selectivity towards 1-hexene and polymerisation to polyethylene when activated with cocatalysts. X-ray structure analyses of the precatalysts 1a-c, 1i, and 2b are investigated. The metal-ligand binding in 1a and 1b is nearly the same, which leads to similar catalytic activities of these precatalysts.

Full text of DOI:10.1016/j.jorganchem.2004.09.080

Journal of Organometallic Chemistry 690 (2005) 713–721
www.elsevier.com/locate/jorganchem
Chromium imine and amine complexes as homogeneous catalysts
for the trimerisation and polymerisation of ethylene
*
Martin E. Bluhm , Olaf Walter, Manfred Do¨ring
Forschungszentrum Karlsruhe, Institute for Technical Chemistry (ITC-CPV), P.O. Box 3640, 76021 Karlsruhe, Germany
Received 1 June 2004; accepted 14 September 2004
Available online 24 November 2004
Abstract
Cr(III) complexes of tridendate imine and amine ligands with N, P, O, S donor atoms 1 and 2 have been prepared and tested as
catalysts in the oligomerisation and polymerisation of ethylene giving excellent selectivity towards 1-hexene and polymerisation to
polyethylene when activated with cocatalysts. X-ray structure analyses of the precatalysts 1a–c, 1i, and 2b are investigated. The
metal–ligand binding in 1a and 1b is nearly the same, which leads to similar catalytic activities of these precatalysts.
ꢀ 2004 Elsevier B.V. All rights reserved.
Keywords: Trimerisation; Polymerisation; Single-site catalysts; Ethylene; Chromium
1. Introduction
suitable compounds for the trimerisation of ethylene
after activation with H(Et2O)2B[C6H3(CF3)2]4 [13].
ONN imine Cr(III) complexes have also been described
as polymerisation catalysts [14].
Here, we report new complexes of Cr(III) with sym-
metrical and asymmetrical N, P, O, S ligands that pro-
duce in combination with methylaluminoxane either
selectively 1-hexene or polyethylene.
Catalytic oligomerisations are used in the SHOP
process to produce a variety of linear a-olefins
(C6-C20-LAO) [1]. The increasing demand especially of
1-hexene as comonomer for the production of linear
low density polyethylene (LLDPE) recommends selec-
tive methods in the production of 1-hexene [2]. The tech-
nically used Phillips catalyst contains
a Cr(III)
compound, pyrrole, and is partially used together with
alkyl aluminum [3]. Neutral phosphorous containing lig-
ands [4–6] are used as well as 1,3,5-triazacyclohexanes
[7,8] as ligands for Cr(III) catalyst precursors. Recently,
Cr(III) coordination compounds with symmetrical
PNP- or SNS-ligands derived from bis(chloro-
ethyl)amine were described as highly active catalysts
for the trimerisation of ethylene with methylaluminox-
ane (MAO) [9–12]. Other substituted PNP chro-
mium(III) precatalysts have recently been described as
2. Experimental
All handlings were carried out under an atmosphere
of argon using standard Schlenk techniques. NMR spec-
tra were recorded on a Bruker spectrometer 250 MHz
(1H) and 62.9 MHz (13C) at 293 K. Mass spectra were
obtained using electron ionisation (EI), electron spray
ionisation (ESI) or field ionisation (FI). Oligomer prod-
ucts were analysed by GC with a flame ionisation detec-
tor, using a 50-m DB1 column, injector temperature 300
ꢁC and the following temperature program: 40 ꢁC/5 min,
40–300 and 5 ꢁC/10 min. The products were quantified,
using n-tridecane as internal standard.
*
Corresponding author. Tel.: +49 7247 82 2383; fax: +49 7247 82
2244.
E-mail address: martin.bluhm@itc-cpv.fzk.de (M.E. Bluhm).
0022-328X/$ - see front matter ꢀ 2004 Elsevier B.V. All rights reserved.
doi:10.1016/j.jorganchem.2004.09.080

714
M.E. Bluhm et al. / Journal of Organometallic Chemistry 690 (2005) 713–721
2.1. Materials
3.59 (m), 1.96–2.02 (m), 1.64–1.74 (m); 13C{31P} NMR
(CDCl3) d 159.6, 139.3, 138.6, 137.2, 136.6, 133.7,
133.2, 132.5, 129.9, 128.6, 128.4, 128.2, 128.1, 127.7,
62.0, 27.0, 25.3; 31P NMR (CDCl3) d ꢀ12.0, ꢀ14.8;
EI+-MS m/z = 516 (M+).
Methylaluminumoxide MAO (10 mol% solution in
toluene) and ethyl aluminum sesquichloride were pur-
chased commercially and used as received.
2.2. Synthesis of ligands
2.2.4. Ligand Id
See Refs. [15,16].
2.2.1. Ligand Ia
To a solution of 2-(diphenylphosphino)benzaldehyde
(560 mg, 1.9 mmol) in 50 mL of CH2Cl2 is added 2-
(diphenylphosphino)ethylamine (442 mg, 1.9 mmol).
The reaction mixture is stirred for 12 h. The solvent is
removed in vacuo and the residue is recrystallized from
2.2.5. Ligand Ie
See Ref. [17]. To a solution of 2-(diphenylphosph-
ino)benzaldehyde (500 mg, 1.7 mmol) in 40 mL of ben-
zene is added 2-(dimethylamino)ethylamine (150 mg, 1.7
mmol). The reaction mixture is heated under reflux for 2
h. The solvent is removed in vacuo and the residue is
recrystallized from hot n-hexane. Yield: 448 mg, 1.2
1
hot n-hexane. Yield: 505 mg, 1 mmol (53%). H NMR
(C6D6) d 8.94 (d, 1H), 8.11–8.16 (m, 1H), 7.31–7.41
(m, 8H), 6.93–7.15 (m, 16H), 3.51–3.61 (m, 2H), 2.16–
1
1
2.22 (m, 2H); H{31P} NMR (C6D6) d 8.94 (s), 8.11–
mmol (73%). H NMR (CDCl3) d 8.82 (d, 1H), 7.87–
7.92 (m, 1H), 7.15–7.32 (m, 12H), 6.75–6.81 (m, 1H),
3.49–3.55 (m, 2H), 2.27–2.32 (m, 2H), 2.11 (s, 6H);
1H{31P} NMR (CDCl3) d 8.82 (s), 7.87–7.92 (m),
7.15–7.32 (m), 6.75–6.81 (m), 3.52 (t), 2.30 (t), 2.11 (s);
13C{31P} NMR (CDCl3) d 160.4, 139.4, 137.3, 136.5,
134.0, 133.8, 133.2, 132.0, 130.1, 129.0, 128.8, 128.7,
128.6, 127.6, 59.8, 59.4, 45.6; 31P NMR (CDCl3) d
ꢀ12.2; EI+-MS m/z = 516 (M+).
8.16 (m), 7.31–7.41 (m), 6.93–7.15 (m), 3.51 (t), 2.22
(t); 13C{31P} NMR (C6D6) d 159.2, 139.5, 138.0, 137.8,
134.4, 133.8, 133.2, 130.3, 128.9, 128.6, 127.6, 58.3,
30.4; 31P NMR (C6D6) d 1.8, ꢀ4.8; EI+-MS m/z = 501
(M+).
2.2.2. Ligand Ib
To a solution of 2-(diphenylphosphino)benzaldehyde
(500 mg, 1.7 mmol) in 30 mL of CH2Cl2 is added 2-(eth-
ylthio)ethylamine hydrochloride (244 mg, 1.7 mmol)
and 0.25 mL of triethylamine. The reaction mixture is
stirred for 4 h. The CH2Cl2 is removed in vacuo and
the residue is suspended in n-hexane. Insoluable solids
are filtered and the hexane is removed in vacuo. The res-
idue is recrystallized from hot n-hexane. Yield: 213 mg,
0.6 mmol (33%). 1H NMR (CDCl3) d 8.81 (d, 1H), 7.87–
7.92 (m, 1H), 7.18–7.28 (m, 12H), 6.78–6.82 (m, 1H),
3.59–3.62 (m, 2H), 2.48–2.54 (m, 2H), 2.36–2.45 (m,
2.2.6. Ligand If
To a solution of 2-(methylthio)benzaldehyde (250
mg, 1.6 mmol) in 40 mL of CH2Cl2 is added 2-(diph-
enylphosphino)ethylamine (377 mg, 1.6 mmol). The
reaction mixture is stirred for 22 h. The solvent is re-
moved in vacuo and the residue is recrystallized first
from hot n-hexane and then from methanol. Yield: 246
1
mg, 0.7 mmol (42 %). H NMR (CDCl3) d 8.60 (m,
1H), 7.69 (m, 1H), 7.35–7.66 (m, 4H), 7.15–7.24 (m,
8H), 7.04–7.10 (m, 1H), 3.64–3.73 (m, 2H), 2.40–2.43
(m, 2H), 2.33 (s, 3H); 31P NMR (CDCl3) d ꢀ17.7;
FI+-MS m/z = 363 (M+).
1
2H), 1.10–1.16 (m, 3H); H{31P} NMR (CDCl3) d 8.81
(s), 7.87–7.92 (m), 7.18–7.28 (m), 6.78–6.82 (m), 3.59
(t), 2.51 (t), 2.41 (q), 1.12 (t); 13C{31P} NMR (CDCl3)
d 160.3, 138.9, 137.1, 136.2, 133.6, 133.5, 133.0, 131.6,
130.0, 128.8, 128.6, 128.5, 128.3, 127.4, 60.5, 31.8,
25.7, 14.5; 31P NMR (CDCl3) d ꢀ12.3; EI+-MS
m/z = 361 (M+).
2.2.7. Ligand Ig
a
To
solution of 2-(methylthio)benzaldehyde
(500 mg, 3.3 mmol) in 40 mL of CH2Cl2 is added
2-methoxy-ethylamine (246 mg, 3.3 mmol). The reaction
mixture is stirred for 12 h. The solvent is removed in va-
cuo. For purification, the major part of the product is
dissolved in hot n-hexane and filtered from insoluable
byproducts. After cooling, the n-hexane is removed in
vacuo to give a yellow oil. Yield: 552 mg, 2.6 mmol
2.2.3. Ligand Ic
To a solution of 2-(diphenylphosphino)benzaldehyde
(500 mg, 1.7 mmol) in 40 mL of CH2Cl2 is added 3-
(diphenylphosphino)-1-propylamine (419 mg, 1.7
mmol). The reaction mixture is stirred for 4 h. The sol-
vent is removed in vacuo and the residue is recrystallized
1
1
from hot n-hexane. Yield: 545 mg, 1 mmol (62%). H
(80%). H NMR (CDCl3) d 8.68 (s, 1H), 7.78 (m, 1H),
NMR (CDCl3) d 8.88 (d, 1H), 7.96–8.00 (m, 1H),
7.21–7.45 (m, 6H), 6.90–6.94 (m, 17H), 6.82–6.91 (m,
1H), 3.53–3.59 (m, 2H), 1.96–2.02 (m, 2H), 1.64–1.74
7.12–7.23 (m, 3H), 3.73 (m, 2H), 3.62 (m, 2H), 3.29 (s,
3H), 2.36 (s, 3H); 13C NMR (CDCl3) d 160.6, 139.1,
134.1, 133.0, 130.6, 128.4, 128.2, 127.9, 127.5, 127.3,
125.1, 124.9, 122.2, 72.0, 60.9, 58.7, 16.8; EI+-MS
m/z = 210 (M + H+).
1
(m, 2H); H{31P} NMR (CDCl3) d 8.88 (s), 7.96–8.00
(m), 7.21–7.45 (m), 6.90–6.94 (m), 6.82–6.91 (m), 3.53–

M.E. Bluhm et al. / Journal of Organometallic Chemistry 690 (2005) 713–721
715
2.2.8. Ligand Ih
128.6, 128.0, 71.8, 61.3, 58.6; 31P NMR (CDCl3) d
ꢀ12.6; EI+-MS m/z = 348 (M + H+).
See Ref. [18]. To a solution of 2-methoxybenzalde-
hyde (1.5 g, 0.01 mol) in 40 mL of CH2Cl2 is added 2-
(methylthio)anilin (1.5 g, 0.01 mol). The reaction mix-
ture is stirred for 12 h. The solvent is removed in vacuo
giving a yellow residue. Yield: 2.2 g, 8.7 mmol (79%). 1H
NMR (CDCl3) 8.92 (s, 1H), 8.24 (d, 1H), 7.35–7.41 (m,
1H), 6.85–7.15 (m, 6H), 3.82 (s, 3H), 2.38 (s, 3H); 13C
NMR (CDCl3) 159.7, 133.6, 130.4, 128.5, 126.5, 125.9,
125.1, 121.0, 118.3, 111.6, 111.0, 108.3, 103.5, 102.4,
100.8, 55.6, 15.2.
2.2.12. Ligand IIa
To a suspension of Ia (505 mg, 1 mmol) in 30 mL of
methanol is added under argon NaBH4 (113 mg, 3
mmol). The reaction mixture is stirred for 12 h. The
methanol is removed in vacuo and the residue is taken
up in water. Extraction with CH2Cl2 (three times) gives
a colourless organic phase. After seperation, the organic
phase is dried over Na2SO4. Solids are filtered from the
solution and the CH2Cl2 is removed in vacuo giving a
colourless solid, which is recrystallized from hot n-hex-
ane. Yield: 160 mg, 0.3 mmol (30%). 1H NMR (CDCl3)
d 7.05–7.51 (m, 23H), 6.77–6.81 (m, 1H), 3.98 (s, 2H),
2.2.9. Ligand Ii
To a solution of 2-(methylthio)benzaldehyde (358
mg, 2.4 mmol) in 30 mL of CH2Cl2 is added 2-(ethyl-
thio)ethylamine hydrochloride (500 mg, 3.5 mmol, 1.5
eq.) and 0.5 mL of triethylamine. The reaction mixture
is stirred for 5 h. The CH2Cl2 is removed in vacuo and
the residue is suspended in n-hexane. Insoluable solids
are filtered and the hexane is removed in vacuo giving
a colourless oil. Yield: 212 mg, 0.9 mmol (37%). 1H
NMR (CDCl3) d 8.69 (s, 1H), 7.78 (d, 1H), 7.13–7.25
(m, 3H), 3.78 (t, 2H), 2.80 (t, 2H), 2.53 (q, 2H), 2.39
(s, 3H), 1.19 (t, 3H); 13C NMR (CDCl3) d 160.6,
139.7, 134.5, 131.2, 128.7, 128.5, 128.2, 127.8, 125.9,
61.4, 32.9, 26.7, 17.3, 15.3.
1
2.65 (m, 2H), 2.18 (m, 2H); H{31P} NMR (CDCl3) d
7.05–7.51 (m), 6.77–6.81 (d), 3.98 (s), 2.65 (t), 2.18 (t);
13C{31P} NMR (CDCl3) d 135.8, 134.0, 133.8, 132.7,
132.0, 131.9, 131.8, 130.1, 129.4, 129.0, 128.7, 128.5,
128.4, 128.3, 49.9, 44.9, 26.7; 31P NMR (CDCl3) d
ꢀ15.1, ꢀ19.5; EI+-MS m/z = 504 (M + H+).
2.2.13. Ligand IIb
To a suspension of Ib (270 mg, 0.7 mmol) in 40 mL of
methanol is added under argon NaBH4 (81 mg, 2
mmol). The reaction mixture is stirred for 12 h. The
methanol is removed in vacuo and the residue is taken
up in water. Extraction with CH2Cl2 (three times) gives
a colourless organic phase. After seperation, the organic
phase is dried over Na2SO4. Solids are filtered from the
solution and the CH2Cl2 is removed in vacuo giving a
colourless solid, which is recrystallized from n-hexane.
2.2.10. Ligand Ij
To a solution of 2-(methylthio)benzaldehyde (500
mg, 3.3 mmol) in 50 mL of CH2Cl2 is added to 2-
(dimethylamino)ethylamine hydrochloride (290 mg, 3.3
mmol). The reaction mixture is stirred for 16 h. The
CH2Cl2 is removed in vacuo. For purification, the major
part of the product is dissolved in hot n-hexane and fil-
tered from insoluable byproducts. After cooling, the n-
hexane is removed in vacuo giving a colourless oil.
1
Yield: 194 mg, 0.5 mmol (70%). H NMR (CDCl3) d
7.04–7.46 (m, 13H), 6.77–6.81 (m, 1H), 3.97 (s, 2H),
2.66 (m, 2H), 2.44–2.49 (m, 2H), 2.33–2.41 (q, 2H),
1.12 (t, 3H); 13C{31P} NMR (CDCl3) d 142.9, 136.4,
135.9, 133.8, 133.7, 131.9, 131.8, 129.4, 129.1, 129.0,
128.7, 128.6, 128.5 127.6, 51.4, 47.6, 31.1, 25.7, 14.8;
1
Yield: 364 mg, 1.6 mmol (49%). H NMR (CDCl3) d
8.68 (s, 1H), 7.77 (d, 1H), 7.10–7.26 (m, 3H), 3.70 (t,
2H), 2.58 (t, 2H), 2.36 (s, 3H), 2.24 (s, 3H); 13C NMR
(CDCl3) d 159.7, 138.9, 134.1, 130.4, 128.1, 127.0,
125.3, 59.9, 59.7, 45.6, 16.6; EI+-MS m/z = 223
(M + H+)
31P NMR (CDCl3)
(M + H+).
d
ꢀ14.9; EI+-MS m/z = 380
2.2.14. Ligand IIc
To a suspension of Ih (1 g, 3.9 mmol) in 90 mL of
methanol is added under argon NaBH4 (0.44 g, 11
mmol). The reaction mixture is stirred for 3 h. The
methanol is removed in vacuo and the residue is taken
up in water. Extraction with CH2Cl2 (three times) gives
a yellow organic phase. After seperation, the organic
phase is dried over Na2SO4. Solids are filtered from
the solution and the CH2Cl2 is removed in vacuo giving
2.2.11. Ligand Ik
To a solution of 2-(diphenylphosphino)benzaldehyde
(300 mg, 1 mmol) in 30 mL of CH2Cl2 is added 2-meth-
oxy-ethylamine (78 mg, 1 mmol). The reaction mixture
is stirred for 16 h. The solvent is removed in vacuo
and the residue is recrystallized from n-hexane. Yield:
1
134 mg, 0.38 mmol (39%). H NMR (CDCl3) d 8.86
(d, 1H), 7.98 (m, 1H), 7.15–7.34 (m, 12H), 6.78–6.81
(m, 1H), 3.60 (m, 2H), 3.39 (m, 2H), 3.14 (s, 3H);
1H{31P} NMR (CDCl3) d 8.86 (s), 7.98 (d), 7.15–7.34
(m), 6.78–6.81 (m), 3.60 (t), 3.39 (t), 3.14 (s); 13C{31P}
NMR (CDCl3) d 161.5, 136.4, 134.0, 133.9, 133.7,
133.4, 133.1, 132.2, 131.9, 130.5, 129.0, 128.9, 128.7,
1
a yellow oil. Yield: 668 mg, 2.6 mmol (66%). H NMR
(CDCl3) d 7.32 (d, 1H), 7.07–7.20 (m, 3H), 6.79–6.85
(m, 2H), 6.60–6.63 (m, 2H), 4.34 (s, 2H), 3.81 (s, 3H),
2.27 (s, 3H); 13C NMR (CDCl3) d 157.8, 134.5, 129.9,
129.1, 128.9, 120.9, 111.9, 110.6, 55.7, 44.2, 18.7.

716
M.E. Bluhm et al. / Journal of Organometallic Chemistry 690 (2005) 713–721
2.2.15. Preparation of 1 and 2
2c: ESI+-MS: m/z 436 [M + NH4]+; C15H17NOSCl3-
Cr Æ THF Æ CH2Cl2: Calcd. (Found) C 41.79 (42.13), H
4.73 (4.79), N 2.44 (2.23), S 5.58 (5.38).
The synthesis of the complexes 1 and 2 is illustrated
by the procedure applied for 1a. A solution of ligand
Ia (218 mg, 0.43 mmol) in 20 mL of dry THF was added
under argon to a solution/suspension of CrCl3(thf)3 (151
mg, 0.43 mmol) [19] in 20 mL of dry THF. The reaction
mixture is stirred for 15 h at r.t. The THF is removed in
vacuo and the solid is washed with diethylether/CH2Cl2.
The solid is then dried in vacuo. Yield: 269 mg, 0.41
mmol (95%). All complexes 1 and 2 were prepared in
an identical fashion with yields of over 80% in each case.
1a: FI+-MS: m/z 658.0246 (calcd.), found 658.0151
(a) Low-pressure tests. The precatalyst was dissolved
in 30 mL of toluene in a Schlenk flask under argon. A
complete solution was obtained by leaving the flask in
an ultrasonic bath for several minutes. A 150 mL glass
reactor was evacuated and then filled with argon. The
precatalyst solution was added under argon into the
reactor vessel. Under stirring the cocatalyst MAO (0.6
mL, approx. 100 eq. of a 10 mol% MAO solution in tol-
uene) and n-tridecane standard solution were added un-
der argon. For several minutes ethylene was bubbled
through the reactor to displace the argon. Then the reac-
tor was closed and pressurized to 3 bar with ethylene.
The reactor pressure was maintained constant through-
out the oligomerisation run by manually controlled
addition of ethylene. Runs were terminated by venting
off volatiles and extracting the solution with dilute
hydrochloric acid and water. Quantitative GC analysis
of the organic layer was performed immediately after
the extraction.
for
12C331H2914N31P235Cl352Cr,
d = 9.5
mDa;
C33H29NP2Cl3Cr Æ 2THF Æ CH2Cl2: Calcd. (Found) C
56.74 (57.36), H 5.33 (4.98), N 1.58 (1.58).
1b: FI+-MS: m/z 533.9838 (calcd.), found 533.9846
12
for
C
23
1H2414N31P32S35Cl352Cr,
d = 0.8
mDa;
C23H24NPSCl3Cr Æ 2THF Æ CH2Cl2: Calcd. (Found) C
50.24 (49.97), H 5.53 (5.54), N 1.83 (1.60), S 4.19 (4.54).
1c: FI+-MS: m/z 674.0470 (calcd.), found 674.0451
12
1
for
C
13C2 H3114N31P235Cl352Cr, d = 9.5 mDa;
32
C34H31NP2Cl3Cr Æ 2THF Æ CH2Cl2: Calcd. (Found) C
57.19 (57.43), H 5.47 (5.67), N 1.55 (1.45).
1d: FI+-MS: m/z 551.0070 (calcd.), found 551.0108
(b) High-pressure tests. The same procedure as de-
scribed for low-pressure tests was applied. Instead of a
glass reactor was used a 150 mL stainless steel reactor
with cooling mantle. After the reactor was closed it
was pressurized to 30 bar with ethylene.
12
for
C
1H2314N231P35Cl352Cr,
d = 3.8
mDa;
26
C26H23N2PCl3Cr Æ 2THF Æ CH2Cl2: Calcd. (Found) C
53.76 (54.16), H 5.28 (5.14), N 3.58 (4.08).
1e: FI+-MS: m/z 517.0226 (calcd.), found 517.0156
12
for
C
1H2514N231P35Cl352Cr,
d = 7.0
mDa;
23
C23H25N2PCl3Cr Æ 2THF Æ CH2Cl2: Calcd. (Found) C
51.39 (51.68), H 5.79 (6.12), N 3.75 (4.11).
3. Results and discussion
1f: FI+-MS: m/z 521.9748 (calcd.), found 521.9847 for
12
1
C
13C2 H2214N31P32S35Cl352Cr,
d = 9.9
mDa;
The tridentate imine ligands I and the amine ligands
II were prepared via literature procedures or via adapta-
tion of these [20–22]. When reacted with CrCl3(thf)3 [19]
the complexes 1 and 2 are formed and isolated after
workup as green or blue-green powders in 80–100%
yield (Fig. 1 and Table 1) [23].
20
C22H22NPSCl3Cr: Calcd. (Found) C 50.64 (50.16), H
4.25 (4.51), N 2.68 (2.41), S 6.14 (5.96).
1g: FI+-MS: m/z 365.9345 (calcd.), found 365.9342
12
for
C
1H1514N16O32S35Cl352Cr,
d = 0.3
mDa;
11
C11H15NOSCl3Cr Æ THF Æ CH2Cl2: Calcd. (Found) C
36.63 (36.30), H 4.80 (5.10), N 2.67 (2.43), S 6.11 (6.24).
The imine complexes 1a and 1b were tested as most
active for ethylene trimerisation with excellent selectivity
1h:
C15H15NOSCl3Cr Æ THF Æ CH2Cl2:
Calcd.
(Found) C 41.94 (41.55), H 4.40 (4.75), N 2.45 (2.19),
S 5.60 (5.58).
1i: ESI+-MS: m/z 361 [M ꢀ Cl]+; C12H17NS2Cl3Cr:
Calcd. (Found) C 36.24 (36.18), H 4.31 (4.52), N 3.52
(3.43), S 16.12 (16.02).
+ CrCl3(thf)3
- 3 THF
N
N
Z
Z
Cr
X3
Y
Y
1j: ESI+-MS: m/z 343 [M ꢀ Cl]+; C12H18N2SCl3Cr:
Calcd. (Found) C 37.86 (38.01), H 4.77 (5.00), N 7.36
(7.51), S 8.42 (8.44).
I
1a-k
+ NaBH4
1k:
(Found) C 50.67 (50.44), H 5.49 (5.22), N 1.91 (1.68).
C22H22NOPCl3Cr Æ 2THF Æ CH2Cl2:
Calcd.
H
ESI+-MS:
m/z
625
[M ꢀ Cl]+;
+ CrCl3(thf)3
- 3 THF
N
N
H
2a:
C33H31NP2Cl3Cr Æ 2THF Æ CH2Cl2: Calcd. (Found) C
56.61 (56.88), H 5.54 (5.28), N 1.57 (1.41).
Z
Z
Cr
X3
Y
Y
2b:
ESI+-MS:
m/z
556
[M + NH4]+;
II
2a-c
C23H26NPSCl3Cr: Calcd. (Found) C 51.36 (51.19), H
4.87 (5.00), N 2.60 (2.56), S 5.96 (5.91).
Fig. 1. Synthesis of the Cr(III) precatalysts 1 and 2.

M.E. Bluhm et al. / Journal of Organometallic Chemistry 690 (2005) 713–721
717
Table 1
Precatalysts 1 and 2 (X = Cl)
Y
Z
Bridge
1a
1b
1c
1d
1e
1f
PPh2
PPh2
PPh2
PPh2
PPh2
SMe
SMe
OMe
SMe
SMe
PPh2
PPh2
PPh2
OMe
PPh2
SEt
(CH2)2
(CH2)2
(CH2)3
(CH2)2
(CH2)2
(CH2)2
(CH2)2
C6H4
PPh2
C5H4N
NMe2
PPh2
OMe
SMe
SEt
1g
1h
1i
(CH2)2
(CH2)2
(CH2)2
(CH2)2
(CH2)2
C6H4
1j
NMe2
OMe
PPh2
SEt
1k
2a
2b
2c
SMe
towards 1-hexene when activated with 100 eq. MAO
(Table 2, entries 1–4) [23].
SNS and other substituents like nitrogen or oxygen con-
taining groups led to a dramatic decrease in the rate for
trimerisation but increased rate in the formation of
polyethylene (Table 2, entries 7–18). Reaction tempera-
ture and ethylene pressure have both a big influence on
the product distribution. At reaction temperatures be-
tween 70 and 85 ꢁC, and 30 bar of ethylene pressure
the formation of polymer increases (Table 2, entry 3).
At room temperature and 3 bar of ethylene pressure
the rate of trimerisation was increased (Table 2, entry
2). The activity of all complexes 1 and 2 decreases with
low ethylene pressure. When a higher amount of MAO
In 1b, one phosphorous donor is replaced by a sulfur
containing donor group. Both complexes 1a and 1b re-
act similarly under catalytic conditions. This is in line
with earlier observations in PNP and SNS chro-
mium(III) complexes [9–12]. Almost the same effect is
also observed for the amine complexes 2a and 2b which
both have the same backbone, but 2b contains a meth-
ylmercapto instead of a diphenylphosphane substituent.
Both complexes react under the same reaction condi-
tions mainly to polyethylene besides hexene. Here,
Table 2
Ethylene trimerisation/polymerisation with complexes 1 and 2a
Number
Catalyst (lmol)
T (ꢁC)
Run time (h)
PE (wt%)
Hexenes (wt%)
a-Selectivity of oligomers
Productivity (hꢀ1 b
)
1
2
1a (10)
1a (10)
1a (10)
1a (10)c
1a (10)d
1b (10)
1c (10)
1d (10)
1e (10)
1f (10)
1g (10)
1h (10)
1i (10)
1j (10)
1k (10)
2a (10)
2b (10)
2c (10)
24–30
24
85
1
2
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
17
2
83
98
2
98
99
98
99
–
5742
470
3
98
14
2294
4308
2966
2268
3054
943
4
24–30
24–30
24–30
24–30
24–27
24–31
24–30
24–30
24–30
24–30
24–30
24–30
24–30
25–31
25–31
86
–
5
100
18
6
82
27
20
–
10e
12
–
99
99
99
–
7
73
80
8
9
100
81
660
10
11
12
13
14
15
16
17
18
a
97
99
–
8381
525
88
100
100
98
867
–
–
8280
3283
549
2
98
98
99
99
–
97
67
3
33
44
–
2483
1204
3858
56
100
The precatalysts in entries 1–3, 6–18 were first dissolved in 30 mL of toluene in an ultrasonic bath and then activated with approx. 100 eq. MAO
(0.6 mL of a 10 mol% MAO solution in toluene), 30 bar ethylene (entries 1, 3–18) or 3 bar ethylene (entry 2). The yield and the a-olefin content were
determined by GC with a flame ionisation detector using calibration curves with standard solutions.
b
Average turnover frequency of ethylene conversion.
500 eq. MAO (0.6 mL of a 10 mol% MAO solution in toluene) used.
c
d
100 eq. Et2AlCl Æ Cl2AlEt used as co-catalyst.
Formation of 9 wt% octenes.
e

718
M.E. Bluhm et al. / Journal of Organometallic Chemistry 690 (2005) 713–721
was used, the product distribution was not changed to
the formation of higher olefins and polymer with no in-
crease of the activity of the complexes (Table 2, entry 4).
On the other hand, ethyl aluminum chlorides used as
cocatalyst increase the formation of polymer with the
precatalyst 1a (Table 2, entry 5). The use of ethyl alum-
inum chlorides as cocatalyst together with diimine-nick-
el(II) catalysts was observed earlier to increase the
formation of higher olefins [24].
Single crystals of 1a–c, 1i, and 2b suitable for X-ray
diffraction studies were grown from a dichloromethane
solution, layered with THF and pentane. The molecu-
lar structures of 1a–c, 1i along with selected bond dis-
tances and angles, are shown in Figs. 2–4. All three
complexes display a slightly distorted octahedral geom-
etry. The chelate bite angles of the PNP and the PNS
ligands in the complexes are similar [82.01(7)ꢁ,
85.17(7)ꢁ (1a); 85.02(6)ꢁ, 88.47(6)ꢁ (1b); 87.22(4)ꢁ,
89.04(4)ꢁ (1c), 84.55(7)ꢁ, 89.79(7)ꢁ (2b)], while the dif-
ference of the bite angles is larger in 1i [84.94(4)ꢁ,
91.50(4)ꢁ]. Accordingly, the Cr–P [2.441(1)–2.474(1)
˚
Fig. 3. Molecular structure of 1b. Selected bond distances (A) and
angles (ꢁ): Cr–P1 2.441(1), Cr–S1 2.456(1), Cr–N1 2.092(2), Cr–Cl1
2.298(1), C1–N1 1.280(3), P1–Cr–N1 88.47(6), S1–Cr–N1 85.02(6),
P1–Cr–S1 170.67(3), N1–Cr–Cl2 179.38(6).
˚
˚
A] and the Cr–S distances [2.454(1)–2.456(1) A] are
similar in the structures of 1a–c and 2b. In 1i (Fig.
5), the Cr–S bond lengths are shorter [2.403(1)–
2.418(1)] compared with the other sulfur coordinated
chromium complexes 1b and 2b. The Cr–N distances
˚
˚
in each complex [2.118(3) A (1a), 2.092(2) A (1b),
˚
2.103(1) A (1c), 2.069(1) (1i), 2.123(2) (2b)] are similar
and within the range of Cr(III) amine bond lengths
˚
(2.05–2.19 A) [9–12,25,26]. The metal–ligand binding
in 1a and 1b is nearly the same, which is confirmed
with the similar catalytic activities of the complexes
1a and 1b (Table 2, entries 1 and 4). Obviously, the
addition of one bridging methylene group in 1c leads
to a decrease in trimerisation activity (Table 2, entry
7 and Table 3).
˚
Fig. 4. Molecular structure of 1c. Selected bond distances (A) and
angles (ꢁ): Cr–P1 2.474(1), Cr–P2 2.503(1), Cr–N1 2.103(1), Cr–Cl1
2.311(1), C1–N1 1.279(2), P1–Cr–N1 87.22(4), P2–Cr–N1 89.04(4),
P1–Cr–P2 172.70(1), N1–Cr–Cl2 177.40(4).
Fig. 2. Molecular structure of 1a. Crystallized thf and CH2Cl2
˚
molecules are not reported in this figure. Selected bond distances (A)
˚
Fig. 5. Molecular structure of 1i. Selected bond distances (A) and
and angles (ꢁ): Cr–P1 2.469(3), Cr–P2 2.464(1), Cr–N1 2.118(3), Cr–
Cl1 2.311(1), C1–N1 1.281(4), P1–Cr–N1 85.17(7), P2–Cr–N1 85.01(7),
P1–Cr–P2 166.76(3), N1–Cr–Cl2 177.83(7).
angles (ꢁ): Cr–S1 2.403(1), Cr–S2 2.418(1), Cr–N1 2.069(1), Cr–Cl1
2.311(1), C8–N1 1.284(2), S1–Cr–N1 91.50(4), S2–Cr–N1 84.94(4), S1–
Cr–S2 168.89(2), N1–Cr–Cl2 177.84(4).

Table 3
Crystallographic data
1a
1b
1c
1i
2b
Empirical formula
CCDC-Nr.
C
66H58Cl6Cr2N2P4 Æ 0.9CH2Cl2 Æ 0.5thf C23H24Cl3CrNPS
C34H31Cl3CrNP2
239777
673.89
C12H17Cl3CrNS2
239778
397.74
C23H26Cl3CrNPS
239779
537.83
234622
1431.91
234623
535.81
200(2)
Formula weight (g molꢀ1
Temperature (K)
)
200(2)
0.71073
200(2)
0.71073
200(2)
0.71073
200(2)
0.71073
˚
Wavelength, k (A)
0.71073
Triclinic
Crystal system
Space group
Unit cell dimensions
Orthorhombic
Pbca (No. 61)
Triclinic
ꢀ
Monoclinic
P21/c (No. 14)
Triclinic
ꢀ
ꢀ
P1 ðNo: 2Þ
P1 ðNo: 2Þ
P1 ðNo: 2Þ
˚
˚
9.761(1) A
a (A)
23.556(2)
14.765(1)
39.613(3)
90
10.440(1)
12.480(1)
12.950(1)
72.156(1)
77.064(1)
83.763(1)
1563.7(2) 1611.6(2)
2
8.375(1)
10.913
17.711
90
10.558
10.927
12.085
˚
b (A)
10.981(1)
12.576(9)
109.984(1)
94.841
˚
c (A)
a (ꢁ)
b (ꢁ)
c (ꢁ)
107.118(2)
99.450(2)
108.058(2)
90
90
95.409
90
105.346(1)
1198.7(2)
2
3
˚
V (A )
13777.5(2)
8
1.381
1206.0(2)
4
1.639
Z
2
1.481
qcalcd. (g cmꢀ3
)
1.485
0.977
1.431
0.750
l (mmꢀ1
F(0 0 0)
)
0.753
5884
1.451
812
0.971
554
550
0.3 · 0.2 · 0.1
1.76–28.30
694
1.0 · 0.6 · 0.5
1.69–28.28
Crystal size (mm3)
0.5 · 0.4 · 0.2
0.2 · 0.2 · 0.1
2.19–28.29
0.4 · 0.15 · 0.1
1.84–28.32
ꢀ14 6 h 6 14,
ꢀ14 6 k 6 14, ꢀ16 6 l 6 16
14,664
h Range for data collection (ꢁ) 1.34–28.31
Index ranges
ꢀ31 6 h 6 31,
ꢀ13 6 h 6 12, ꢀ14 6 k 6 14, ꢀ13 6 h 6 13, ꢀ16 6 k 6 16, ꢀ11 6 h 6 11, ꢀ14
ꢀ19 6 k 6 9, ꢀ52 6 l 6 52
137,175
ꢀ16 6 l 6 16
ꢀ16 6 l 6 16
6 k 6 14, ꢀ23 6 l 6 23
18,808
Reflections collected
12,584
16,405
Independent reflections
Data/restraints/parameters
Goodness-of-fit on F2
Final R indices [I > 2r(I)]a
R indices (all data)a
16,998 [Rint = 0.0528]
16,998/6/839
1.057
5717 [Rint = 0.0376]
5717/0/278
0.885
7313 [Rint = 0.0136]
7313/0/375
1.053
3960 [Rint = 0.0389]
3960/0/180
1.022
5809 [Rint = 0.0478]
5809/0/279
0.886
R1 = 0.0518, wR2 = 0.1681
R1 = 0.0752, wR2 = 0.1794
R1 = 0.0398, wR2 = 0.0749
R1 = 0.0756, wR2 = 0.0806
R1 = 0.0269, wR2 = 0.0755
R1 = 0.0317, wR2 = 0.0779
R1 = 0.0256, wR2 = 0.0607 R1 = 0.0428, wR2 = 0.0824
R1 = 0.0369, wR2 = 0.0624 R1 = 0.0855, wR2 = 0.0914
P
P
P
P
2
2
2
R1 ¼ ½ jF oj ꢀ jF cjꢁ= jF oj; wR2 ¼ ½½ wðjF 2o ꢀ F c2jÞ ꢁ=½ wðF 2oÞꢁꢁ1=2; w ¼ 1=½ðrF oÞ þ ðaPÞ ꢁ. The value of aP was obtained from structure refinement.
a

720
M.E. Bluhm et al. / Journal of Organometallic Chemistry 690 (2005) 713–721
product distributions are as well obtained with 1a and
1b as for the corresponding amine chromium(III) com-
plexes 2a and 2b. The amine precatalysts 2a, b react dif-
ferently in the catalysis with ethylene compared to their
imine based analogues 1a, 1b. 2a, b mainly form poly-
ethylene besides hexene.
4.1. Crystal structure determination
The intensity data for the compounds were collected
by a a Siemens Smart 1000 CCD diffractometer using
graphite-monochromated Mo Ka radiation. Data were
corrected for Lorentz and polarisation effects, but not
for absorption [28,29].
The structures were resolved by direct methods
SHELXS [30]) and refined by full-matrix least squares
(
techniques against F o2
(
SHELXL-97 [31]). The hydrogen
˚
Fig. 6. Molecular structure of 2b. Selected bond distances (A) and
angles (ꢁ): Cr–P1 2.473(1), Cr–S1 2.454(1), Cr–N1 2.123(2), Cr–Cl1
2.290(1), C19–N1 1.502(3), P1–Cr–N1 89.79(7), S1–Cr–N1 84.55(7),
P1–Cr–S1 173.23(3), N1–Cr–Cl3 178.68(8).
atoms were localized by difference Fourier synthesis
and refined isotropically. The data are deposited in the
Cambridge Crystallographic Data Centre [32].
All non-hydrogen atoms were refined anisotropi-
cally [31]. XP (SIEMENS Analytical X-ray Instru-
ments, Inc.) and Ortep [33] were used for structure
representations.
1i only produces polyethylene (Table 2, entry 13).
Although the coordination sphere in the PNS amine
complex 2b (Fig. 6) is similar to the respective imine
complex 1b, the behaviour in the catalysis with ethylene
and MAO as cocatalyst is different under the same reac-
tion conditions. The electronic properties of 2b seem to
be one reason for this different catalytic activity. The
precursor complex 2b produces a mixture of polyethyl-
ene and hexenes as well as the PNP amine chro-
mium(III) complex 2a. The other ONS amine
chromium(III) precursor 2c leads to the formation of
polyethylene (Table 2, entries 16–18).
Investigations about the polymer properties are in
progress, but differential scanning calorimetry already
showed melting ranges between 126 and 142 ꢁC with
energies between 180 and 220 J/g. These values are in
line with values given for HDPE [27]. Investigations
about the possible inclusion of hexene as comonomer
into the polymer chain have to be accomplished.
References
[1] W. Keim, F.H. Kowaldt, R. Goddard, C. Kruger, Angew. Chem.
¨
90 (1978) 493;
W. Keim, F.H. Kowaldt, R. Goddard, C. Kruger, Angew. Chem.
¨
Int., Ed. Engl. 17 (1978) 466.
[2] K. Weissermel, H.-J. Arpe, Industrial Organic Chemistry, Wiley-
VCH Publishers, 1998.
[3] M.E. Lashier, EP 0780353 A1 (1997), to Phillips Petroleum.
[4] F.-J. Wu, US 5 811 618, EP 0622347 B1 (1998), to Amoco.
[5] D.F. Wass, WO 02/04119 (2002), to BP Chemicals.
[6] A. Carter, S.A. Cohen, N.A. Cooley, A. Murphy, J. Scutt, D.F.
Wass, Chem. Commun. (2002) 858.
[7] H. Maas, S. Mihan, R. Ko¨hn, DE 19943544 A1 (2001), to BASF.
[8] R.D. Ko¨hn, M. Haufe, G. Kociok-Ko¨hn, S. Grimm, P. Wass-
erscheid, W. Keim, Angew. Chem. 112 (2000) 4512;
R.D. Ko¨hn, M. Haufe, G. Kociok-Ko¨hn, S. Grimm, P. Wass-
erscheid, W. Keim, Angew. Chem. Int., Ed. Engl. 39 (2000) 4337.
[9] D.S. McGuiness, P. Wasserscheid, W. Keim, C. Hu, U. Englert,
J.T. Dixon, C. Grove, Chem. Commun. (2003) 334.
[10] J.T. Dixon, J.J.C. Grove, P. Wasserscheid, S.D. McGuiness, F.M.
Hess, H. Maumela, D.H. Morgan, A. Bollmann, WO 03/053891
A1 (2003), to Sasol Technology Ltd.
4. Conclusions
In summary, the described chromium(III) complexes
1 and 2 reveal differences in their behaviour as precata-
lysts for the trimerisation or polymerisation of ethylene.
Depending on the ethylene pressure and the nature of
the ligand, both catalysts 1a and 1b show good activities
and selectivities with ethylene in presence of MAO as
cocatalyst for producing 1-hexene. Other precatalysts
mainly produce polyethylene (1e, 1h–k, 2c). X-ray struc-
ture analyses of 1a and 1b show similar Cr–heteroatom
bond lengths and coordination spheres around the chro-
mium(III) metal ions. Similar catalytic activity and
[11] D.S. McGuiness, P. Wasserscheid, W. Keim, D. Morgan, J.T.
Dixon, A. Bollmann, H. Maumela, F. Hess, U. Englert, J. Am.
Chem. Soc. 125 (2003) 5272.
[12] J.T. Dixon, P. Wasserscheid, D.S. McGuiness, F.M. Hess, H.
Maumela, D.H. Morgan, A. Bollmann, WO 03/053890 A1 (2003),
to Sasol Technology Ltd.
[13] T. Agapie, S.J. Schofer, J.A. Labinger, J.E. Bercaw, J. Am.
Chem. Soc. 126 (2004) 1304.
[14] D.J. Jones, V.C. Gibson, S.M. Green, P.J. Maddox, Chem.
Commun. (2002) 1038.
[15] A. Lavery, S.M. Nelson, J. Chem. Soc., Dalton Trans. (1984)
615.

M.E. Bluhm et al. / Journal of Organometallic Chemistry 690 (2005) 713–721
721
[16] R.E. Rulke, V.E. Kaasjager, P. Wehman, C.J. Elsevier,
¨
P.W.N.M. van Leeuwen, K. Vrieze, Organometallics 15 (1996)
3022.
[26] R. Emrich, O. Heinemann, P.W. Jolly, C. Kruger, G.P.J.
¨
Verhovnik, Organometallics 16 (1997) 151.
[27] H.G. Elias, An Introduction to Polymer Science, VCH, Wein-
heim, 1997.
[17] Mentioned, but not further characterized in: E. Shirakawa, Y.
Murota, Y. Nakao, T. Hiyama, Synlett (1997) 1143.
[18] S.E. Livingstone, J.D. Nolan, Analogous to the preparation of
SNS ligands, Aust. J. Chem. 22 (1969) 1817.
[28] COLLECT, Data Collection Software; Nonius B.V., Netherlands,
1998.
[29] Z. Otwinowski, W. Minor, Processing of X-ray Diffraction Data
Collected in Oscillation Mode, in: Methods in Enzymology, in:
C.W. Carter, R.M. Sweet (Eds.), Macromolecular Crystallogra-
phy, Part A, 276, Academic Press, 1997, pp. 307–326.
[30] G.M. Sheldrick, Acta Crystallogr., Sect. A 46 (1990) 467.
[31] G.M. Sheldrick, SHELXL-97, University of Go¨ttingen, Germany,
1993.
[19] W. Herwig, H.H. Zeiss, J. Org. Chem. 23 (1958) 1404.
[20] P. Wehman, R.E. Rulke, V.E. Kaasjager, P.C.J. Kamer, H.
¨
Kooijman, A.L. Spek, C.J. Elsevier, K. Vrieze, P.W.N.M. van
Leeuwen, Chem. Commun. (1995) 331.
[21] E. Shirakawa, Y. Murota, Y. Nakao, T. Hiyama, Synlett (1997)
1143.
[22] S. Antonaroli, B. Crociani, J. Organomet. Chem. 560 (1998)
137.
[32] The CCDC data (1a–c, 1i, 2b) contain the supplementary
crystallographic data for this paper. These data can be obtained
free of charge via www.ccdc.cam.ac.uk/conts/retrieving.html (or
from the Cambridge Crystallographic Data Centre, 12, Union
Road, Cambridge CB2 1EZ, UK; fax: (+44) 1223-336-033; or
deposit@ccdc.cam.ac.uk).
[23] M. Bluhm, M. Do¨ring, applied patents (2004), to Forschungszen-
trum Karlsruhe.
[24] S.A. Svejda, M. Brookhart, Organometallics 18 (1999) 65.
[25] A. Derwahl, F. Wasgestian, D.A. House, W.T. Robinson, Coord.
Chem. Rev. 211 (2001) 45.
[33] L.J. Farrugia, J. Appl. Cryst. 30 (1997) 565.