Efficient synthesis of aluminium-terminated polyethylene by means of irreversible coordinative chain-transfer polymerisation using a guanidinatotitanium catalyst

Article abstract of DOI:10.1002/ejic.201301610

A series of guanidinato-ligand-stabilised titanium complexes has been synthesised and characterised. These compounds can be prepared by carbodiimide insertion into titanium-amide bonds. Reaction of carbodiimides N,N′-bis(2,6-diisopropylphenyl)carbodiimide, N,N′-bis(2,6-dimethylphenyl)carbodiimide and N-tert-butyl-N′-(2,6-diisopropylphenyl)carbodiimide (2a-2c, respectively) with [(Et₂N)TiCl₃] led to mono(guanidinato)trichloridotitanium(IV) complexes (3a-3c). Subsequent conversion with methylmagnesium chloride gave the corresponding trimethyl complexes (4a and 4b). Single-crystal X-ray diffraction analyses were carried out for all complexes. Compound 4a showed very high activities in the polymerisation of ethylene in the presence of very high amounts of triethylaluminium and undergoes polymeryl chain transfer to aluminium. Irreversible coordinative chain-transfer polymerisation and a unique combination of catalyst economy and high activity were observed. In the presence of 1000 equivalents of aluminium, a chain elongation of 83.3 % could be achieved with an activity of 9900 kg_PE mol_cat^-1 h^-1 bar^-1. The influence of the steric demand of the ligand on the polymerisation capability is significant and was investigated too. A series of novel mono(guanidinato)titanium(IV) complexes has been synthesised and characterised. Single-crystal analyses were performed for all complexes. Compound 4a showed very high activities in the polymerisation of ethylene in the presence of very high amounts of aluminium after activation with fluorinated borates. Irreversible coordinative chain transfer to aluminium was observed.

Full text of DOI:10.1002/ejic.201301610

FULL PAPER
DOI:10.1002/ejic.201301610
Efficient Synthesis of Aluminium-Terminated Polyethylene
by Means of Irreversible Coordinative Chain-Transfer
Polymerisation Using a Guanidinatotitanium Catalyst
Johannes Obenauf,[a] Winfried P. Kretschmer,[a] and Rhett Kempe*[a]
Keywords: Polymerization / Titanium / Guanidinates / Aluminum
A series of guanidinato-ligand-stabilised titanium complexes
has been synthesised and characterised. These compounds
can be prepared by carbodiimide insertion into titanium–
amide bonds. Reaction of carbodiimides N,NЈ-bis(2,6-diiso-
propylphenyl)carbodiimide, N,NЈ-bis(2,6-dimethylphenyl)-
carbodiimide and N-tert-butyl-NЈ-(2,6-diisopropylphenyl)-
carbodiimide (2a–2c, respectively) with [(Et2N)TiCl3] led to
mono(guanidinato)trichloridotitanium(IV) complexes (3a–
3c). Subsequent conversion with methylmagnesium chloride
gave the corresponding trimethyl complexes (4a and 4b).
Single-crystal X-ray diffraction analyses were carried out for
all complexes. Compound 4a showed very high activities in
the polymerisation of ethylene in the presence of very high
amounts of triethylaluminium and undergoes polymeryl
chain transfer to aluminium. Irreversible coordinative
chain-transfer polymerisation and a unique combination of
catalyst economy and high activity were observed. In the
presence of 1000 equivalents of aluminium, a chain elong-
ation of 83.3% could be achieved with an activity of
9900 kgPE molcat–1 h–1 bar–1. The influence of the steric de-
mand of the ligand on the polymerisation capability is signifi-
cant and was investigated too.
oped. Mechanistic studies have been carried out by the
groups of Bochman[40,41] and Norton.[42,43] The kinetics of
chain growth at Al have been studied when catalysed by a
Zr complex. The reaction is first order in [olefin] and [cata-
lyst] and of inverse first order in [AlR3] (R = PE polymeric
chain).[42] This inverse first-order dependence results in a
rather low catalyst economy of the catalyst systems re-
ported so far. It prohibits the use of high CTA/catalyst ra-
tios because high amounts of CTA result in a poor overall
polymerisation activity. The catalyst is essentially transfer-
ring polymeryl chains but is no longer able to grow chains.
Introduction
Polyethylene (PE) is the most important plastic world-
wide. It is essential for our modern lifestyle because of its
low cost and its broad applicability. Unfortunately, its com-
patibility with other important polymers or materials is lim-
ited owing to the rather apolar nature of PE. Compatibility
agents that consist of a PE block and a block of another
polymer or material could solve this problem. Furthermore,
PE-based block copolymers themselves allow for nanos-
tructuring by means of microphase separation and enable
access to nanostructured PE materials and to novel applica-
tions of such materials.[1] Both approaches rely on an ef-
ficient synthesis of PE with an end group that allows the
easy introduction of further polymer blocks. Coordinative
chain transfer polymerisation (CCTP) is a polymerisation
protocol that produces metal-terminated PE that can easily
be converted into PE that carries such reactive end groups
(Scheme 1).[2–4] Pioneering work that involved well-defined
molecular polymerisation catalysts was reported by Eisen-
berg and Samsel[5,6] as well as Mortreux and co-workers.
Meanwhile, ethylene CCTP catalyst systems that use rare-
earth metals (RE) and transition metals (TM) in combina-
tion with different chain-transfer agents (CTA) such as
Mg-,[7–12] Zn-,[13–25] and Al-[5,6,26–39] alkyls, have been devel-
[a] Lehrstuhl für Anorganische Chemie II, Universität Bayreuth,
95440 Bayreuth, Germany
Scheme 1. Net reaction and mechanism of CCTP involving alumin-
ium alkyls. Top: CTS (chain-transfer state); bottom: CGS (chain
growing state). [M] = cationic or neutral transition metal or RE
complex; R1, R2 = alkyl moiety; n, m = natural numbers.
E-mail: kempe@uni-bayreuth.de
http://www.ac2.uni-bayreuth.de
Supporting information for this article is available on the
WWW under http://dx.doi.org/10.1002/ejic.201301610.
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Scheme 2. Synthesis of symmetric and nonsymmetric guanidinatotitanium(IV) complexes 3a–4b.
Recently, we communicated a guanidinatotitanium cata- with three equivalents of an appropriate Grignard reagent
lyst (3a) that showed very high activity in the presence of (methylmagnesium chloride; Scheme 2) led to the trialkyl
very high amounts of CTA (triethylaluminium).[37] The cat- complexes 4a and 4b. After two hours of reaction time, the
alyst system seemed to be able to mediate chain growth and solvent was removed and the residue was extracted with
chain transfer in a parallel fashion. Unfortunately, the chain hexane. Bright yellow crystals could be obtained from a
transfer was not highly reversible. In such a regime, multiple concentrated hexane solution at –30 °C. All complexes were
insertions might also compensate efficiency loss caused by characterised by 1H and 13C NMR spectroscopy along with
high CTA/catalyst ratios.[44,45] Herein, we report in more elemental analysis. The molecular structures of the com-
detail on such guanidinatotitanium catalysts. In particular, plexes were confirmed by single-crystal structure analysis.
we discuss structural features that enable high catalyst econ-
omy and address the issue of transfer efficiency. As a result,
Structural Investigations
a cheap metal catalyst system (Ti–Al) is provided that ef-
ficiently allows the production of end-group-functionalised
PE.
The molecular structures of 3b, 3c, 4a and 4b are pre-
sented in Figures 1, (4a) 2 (3b and 4b) and 3 (3c). Selected
bond lengths and angles are listed in Table 1. Crystallo-
graphic details are available in the Supporting Information
(Table S1). The structure analysis revealed mono(guanidin-
ato)titanium(IV) complexes, as expected. For all com-
pounds a distorted trigonal-bipyramidal coordination of
the titanium atoms was observed. The metal atom is coordi-
nated by two nitrogen atoms and three chlorine or carbon
atoms. The Ti–N bond lengths of the chlorido complexes
are about 2.01 Å and become significantly extended (to
about 2.09 Å) for the methyl compounds. The exchange of
the chlorido by the methyl ligands also results in a re-
duction of the N1–Ti1–N2 bond angle from 65.41° (3b) and
65.68° (3c) to 62.70° (4a) and 62.96° (4b). The sum of bond
Results and Discussion
Ligand and Complex Synthesis
Guanidinato-trichloridotitanium(IV) complexes are gen-
erally accessible through carbodiimide insertion into tita-
nium–amide bonds (Scheme 2).[37] The required carbodi-
imides are accessible by desulfurisation of N,NЈ-substituted
thioureas with a three-component system of PPh3, CCl4
and triethylamine[46] and subsequent fractional crystallisa-
tion from ethanol. Symmetric thioureas 1a and 1b are ac-
cessible from the reaction of two equivalents of aniline and
carbon disulfide in the presence of two equivalents of
triethylamine in water.[47]
After recrystallisation from dichloromethane, the re-
sulting thioureas can be obtained in high yields. Nonsym-
metric thioureas can be synthesised from the reaction of
isothiocyanates with the corresponding aniline in acetone
solution.[48] After removal of Ph3PS (crystallisation from
ethanol), 2c can be obtained by distillation as a colourless
oil. The synthesis of the guanidinatotitanium(IV) com-
plexes 3a–3c (Scheme 2) were performed by the reaction of
equimolar amounts of the corresponding carbodiimides
and diethylamido trichloridotitanium(IV) in toluene. They
were obtained in high yields. Guanidinatotitanium(IV)
alkyl complexes can be synthesised by means of a salt-elimi-
Figure 1. Molecular structure of 4a. Hydrogen atoms are omitted
nation reaction. Treatment of the trichlorido complexes for clarity. Ellipsoids are at 30% probability level.
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Figure 3. Molecular structure of 3c. Hydrogen atoms are omitted
for clarity. Ellipsoids are at 30% probability level.
crease the electron density at the titanium metal to result in
stronger bonding of the ligand.
Ethylene Polymerisation
We recently developed a titanium-based catalyst system
stabilised by bulky guanidinato ligands, which is highly ef-
ficient in CCTP.[37] We pointed out that the variation of the
substituents at the non-coordinating nitrogen atom has only
a marginal influence on the catalytic performance. As a re-
sult, we became interested in the variation of the steric bulk
of the ligand at the coordinating N atoms and the exchange
of the chlorido ligands with alkyls to drastically reduce the
Figure 2. Molecular structures of 3b (top) and 4b (bottom). Hydro-
gen atoms are omitted for clarity. Ellipsoids are at 30% probability
level. The carbon atoms C22 and C24 are disordered (C22A/C22B
and C24A/C24B; 88/12%).
angles around N3 and C1 is approximately 360° and con- catalyst induction period. Initial polymerisation studies
firms sp2-hybridised nitrogen and carbon atoms. It indicates (Table 2) showed that significantly higher activities could be
the participation of the lone pair of the non-coordinating achieved by replacing chlorido ligands with methyl ligands.
nitrogen atom in the π system of the ligand, which can in- Activities of up to 12000 kgPE molcat–1 h–1 bar–1 in the pres-
Table 1. Selected bond lengths [Å] and bond angles [°] for complexes 3a,[37] 3b, 3c, 4a and 4b.
3a
3b
3c
4a
4b
Ti1–N1
Ti1–N2
Ti1–Cl (avg.)
Ti1–Cmethyl (avg.)
C1–N1
C1–N2
C1–N3
N1–Ti1–N2
N1–C1–N2
Σ Ͻ (C1)
Σ Ͻ (N3)
2.015(3)
2.027(4)
2.2385
–
1.368(6)
1.356(5)
1.352(5)
65.11(14)
106.0(3)
359.9
2.0174(14)
2.0115(14)
2.2410
1.9979(12)
2.0214(13)
2.2524
2.1082(19)
2.0895(19)
–
2.087(4)
2.112(4)
–
–
–
2.080
2.041
1.366(2)
1.358(2)
1.326(2)
65.41(6)
106.10(14)
359.99
1.3450(19)
1.3674(19)
1.3473(18)
65.68(5)
106.95(12)
359.98
1.329(3)
1.367(3)
1.367(3)
62.70(7)
108.22(18)
359.97
1.341(6)
1.350(6)
1.355(6)
62.96(15)
109.2(4)
360.00
360.00
359.5
360.00
359.88
359.71
Table 2. Initial polymerisation studies investigating the chain-extension efficiency of complex 4a. Conditions: p = 2 bar, T = 50 °C, t =
15 min, toluene 150 mL, activator ammonium borate {[R2N(CH3)H][B(C6F5)4] (R = C16H33–C18H37), Ti/B = 1:1.1} and triethylalumin-
ium.
[b]
Entry
4a
[μmol]
Al/Ti
Activity[a]
Mn
Mw/Mn
Nexp./Ntheo.
[gmol–1]
[%]
1
2
3
4
2
250
5000
10000
25000
1900
7000
13000
12000
3000
2400
2450
2550
2.2
1.8
2.1
1.9
42.0
9.8
8.9
1.6
0.2
0.2
0.1
[a] [kgPE molcat–1 h–1 bar–1]. [b] Nexp.: experimental chain number [yield PE (in g)/Mn]; Ntheo.: theoretical chain number, assuming three
growing chains per Al atom.
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ence of 25000 equivalents of aluminium were obtained at especially relevant, because the cation, which binds the N
50 °C and 2 bar ethylene pressure. The resulting PE showed ligand more strongly, is not yet formed.[32,33] Hence, the
a molecular weight of 2550 gmol–1 and a molecular-weight methyl complexes show more activity since more of the cat-
1
distribution of 1.9 (Table 2, entry 4). High-temperature H alytically active species are generated. The nonsymmetric
NMR spectroscopic experiments are indicative of poly- guanidinatotitanium(IV) complex 3c showed almost no ac-
meryl chain transfer to aluminium owing to the absence of tivity in the polymerisation of ethylene under the same con-
olefinic resonances after hydrolytic workup of the resulting ditions. Ligand transfer to aluminium proceeds so fast that
polymers (Figure S1 in the Supporting Information). no further active catalyst can be formed. Reduction to TiIII
Furthermore, the activity increases significantly as the Al/ species indicated by colour changes was not observed dur-
Ti ratio increases. It appears that the fraction of elongated ing the activation of any of the catalysts.
chains significantly decreased as the aluminium amount in-
Owing to the relevance of steric protection and the
creased from 42% at 250 equiv. to 1.6% at 25000 equiv. (un- higher activity of the methyl complexes, we focused on 4a
der the given conditions). The percentage of elongated in further studies. By increasing the ethylene pressure from
chains expresses how many of the ethyl groups of the CTA 2 to 5 bar, the molecular weight of the polymer was more
triethylaluminium were extended/elongated in the polymeri- than doubled from 2450 to 5800 gmol–1 in the presence of
sation process. It is a crucial number and should be as high 10000 equivalents of triethylaluminium (Table 4, entry 12).
as possible to avoid unused triethylaluminium in the CCTP The polydispersity slightly increased from 2.1 (Table 2, en-
system.
try 3) to 2.6 (Table 4, entry 12). In all polymerisation experi-
The reduction of the steric bulk of the guanidinato li- ments at 50 °C a precipitation of the polymer could be ob-
gand from 2,6-diisopropylphenyl to 2,6-dimethylphenyl served whereby the reaction solution became turbid after a
substituents led to a significant decrease in the activity, es- short period of time. To achieve an increased solubility of
pecially when high amounts of triethylaluminium were used the resulting aluminium-terminated polyethylene, the tem-
(Table 3, entries 5–8). A lower steric protection of the guan- perature of the experiments was increased from 50 to 80 °C.
idinato ligand allows an easier transfer of the ligand This resulted in a clear reaction solution over the entire
towards aluminium.[36] It becomes especially relevant at reaction time. The number of elongated chains could be
high Al concentrations. Compound 3b is almost inactive increased from 31.6 up to 51.7% in the presence of
with 10000 equivalents of aluminium. The use of the corre- 1000 equivalents of aluminium (Table 4, entry 13) owing to
sponding trimethyl compound 4b could increase the activity an increase in activity. In the presence of 10000 equiv., the
(Table 3, entries 9 and 10) but on a significantly lower level reaction solution still became slightly turbid after longer
relative to 4a. In both cases, the methyl compounds are reaction times (90 min).
more active than the chlorido complexes. The use of the
To gain more insight into the nature of the chain-transfer
chlorido complexes goes along with a long induction period process, time-dependent experiments were performed in the
as can be seen from the ethylene consumption profiles. presence of 10000 and 5000 equivalents of triethylalumin-
Within the induction periods, ligand transfer to Al can be ium [80 °C and 5 bar ethylene pressure (Table 5)]. Revers-
Table 3. Polymerisation studies comparing complexes 3b and 4b. Conditions: Precatalyst 2 μmol, p = 2 bar, T = 50 °C, t = 15 min, toluene
150 mL, activator ammonium borate {[R2N(CH3)H][B(C6F5)4] (R = C16H33–C18H37), Ti/B = 1:1.1} and triethylaluminium.
Activity[a]
Mn
Mw/Mn
Nexp./Ntheo.
[b]
Entry
Precat.
[μmol]
Al/Ti
[gmol–1]
[%]
5
6
7
8
9
10
3b
3b
100
500
1000
10000
500
500
450
360
traces
920
900
6000
2200
1700
n.d.
2200
1800
2.0
2.0
1.5
n.d.
1.6
1.6
3b
3b[c]
4b
4b
n.d.
1000
[a] [kgPE molcat–1 h–1 bar–1]. [b] Nexp.: experimental chain number [yield PE (in g)/Mn]; Ntheo.: theoretical chain number, assuming three
growing chains per Al atom. [c] 0.2 μmol.
Table 4. Variation of the polymerisation conditions by increasing the ethylene pressure using complex 4a. Conditions: p = 5 bar, T =
50 °C, t = 15 min, toluene 150 mL, activator ammonium borate {[R2N(CH3)H][B(C6F5)4] (R = C16H33–C18H37), Ti/B = 1:1.1} and
triethylaluminium.
Activity[b]
Mn [gmol–1]
Mw/Mn
Nexp./Ntheo. [%]
[c]
Entry
4a [μmol]
Al/Ti
11
12
13
14
2
1000
10000
1000
3800
7600
4520
13200
2000
5800
3700
4100
1.9
2.6
2.0
2.2
31.6
5.5
51.7
13.4
0.2
2[a]
0.2[a]
10000
[a] T = 80 °C. [b] [kgPE molcat–1 h–1 bar–1]. [c] Nexp.: experimental chain number [yield PE (in g)/Mn]; Ntheo.: theoretical chain number,
assuming three growing chains per Al atom.
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ible chain transfer is indicated by an increase in the molecu- Table 6. Polymerisation experiments using several concentrations of
complex 4a with a constant amount of triethylaluminium. Condi-
lar weight of the polymer over time. Irreversible chain
transfer would lead to more polymer of the same molecular
tions: p = 5 bar, T = 80 °C, t = 15 min, toluene 150 mL, activator
ammonium borate {[R2N(CH3)H][B(C6F5)4] (R = C16H33–C18H37),
weight. In the case of both 10000 and 5000 equivalents of
Ti/B = 1:1.1} and triethylaluminium (0.54 mL, 25 wt.-% in tolu-
triethylaluminium, a significant decrease in the activity was
observed with increased reaction time and the system al-
most became inactive after 90 min. The molecular weight
remained more or less constant and the number of elon-
gated chains increased over time. A slight increase of the
molecular weight distribution was obtained, likely on ac-
count of the increased viscosity of the reaction solution and
the corresponding deterioration of ethylene diffusion. An
experiment with a constant amount of triethylaluminium
and varied catalyst concentrations showed that for an Al/Ti
ratio of 500 a chain-elongation percentage of 73.5% was
achieved (Table 6, entry 25). It seems that the maximum
percentage of elongated chains lies between 70 and 80%.
Finally, we became interested in the question of what hap-
pens after the maximum chain elongation is reached
(Table 7). A CTA/catalyst ratio of 1000 was used for this
investigation. A maximum of 83.3% for the elongated
chains was achieved after 30 min. After 30 min and at lower
percentage of elongated chains, the catalyst was still active
and chains were still elongated/extended. After the maxi-
mum chain elongation was reached, a significant decrease
in the activity was observed. In addition, the formation of a
high-molecular-weight polymer fraction could be observed
(Figure 4).
ene).
Entry
4a
[μmol]
Al/Ti Activity[a]
Mn
Mw/Mn
Nexp./
Ntheo. [%]
[gmol–1]
[b]
23
24
25
0.2
0.8
2.0
5000
1250
500
27200
17700
8600
7200
8900
9700
2.1
2.1
2.2
31.7
66.7
73.5
[a] [kgPE molcat–1 h–1 bar–1]. [b] Nexp.: experimental chain number
[yield PE (in g)/Mn]; Ntheo.: theoretical chain number, assuming
three growing chains per Al atom.
Table 7. Time-dependent polymerisation experiments using com-
plex 4a. Conditions: precatalyst 1.0 μmol, p = 5 bar, T = 80 °C,
toluene 150 mL, activator ammonium borate: [R2N(CH3)H]-
[B(C6F5)4] (R = C16H33–C18H37), Ti/B = 1:1.1, triethylaluminium:
1 mmol (Al/Ti = 1000:1).
Entry
t
Activity[a]
Mn
Mw/Mn
Nex[bp].
/
[min]
[gmol–1]
Ntheo. [%]
26
27
28
29
30
60
90
9900
4000
3200
2300
9800
11200
10600
11700
2.4
5.5
3.9
5.8
83.3
58.5
75.0
65.5
120
[a] [kgPE molcat–1 h–1 bar–1]. [b] Nexp.: experimental chain number
[yield PE (in g)/Mn]; Ntheo.: theoretical chain number, assuming
three growing chains per Al atom.
Table 5. Time-dependent polymerisation experiments using com-
plex 4a. Conditions: Precatalyst 0.1 μmol (entries 15–18), 0.2 μmol
(entries 19 and 22), p = 5 bar, T = 80 °C, toluene 150 mL, activator
ammonium borate: [R2N(CH3)H][B(C6F5)4] (R = C16H33–C18H37),
Ti/B = 1:1.1, triethylaluminium = 1 mmol.
[b]
Entry
t
Al/Ti Activity[a]
Mn
Mw/Mn
Nexp./Ntheo.
[min]
[gmol–1]
[%]
15
16
17
18
19
20
21
22
15 10000
30 10000
60 10000
90 10000
15400
12100
8200
6400
6400
7000
5500
6900
6800
7500
7000
1.9
1.9
1.9
2.2
1.9
1.9
2.1
2.5
10.1
15.7
19.4
25.4
18.5
26.0
25.0
30.1
5600
15
30
60
90
5000
5000
5000
5000
15200
10600
5600
4200
[a] [kgPE molcat–1 h–1 bar–1]. [b] Nexp.: experimental chain number
[yield PE (in g)/Mn]; Ntheo.: theoretical chain number, assuming
three growing chains per Al atom.
Figure 4. Molecular-weight distribution plot of polymerisation ex-
periments described in Table 7.
A comparison of 4a with other CCTP catalysts in terms
of catalyst economy, activity and percentage of extended
chains is difficult but possible. There are not many exam- here, we observed (with a CTA-to-catalyst ratio of 10000
ples with CTA catalyst ratios of 1000 (and higher). Recently and with a chain elongation of 10%) an activity of
we reported a very good catalyst system in terms of high 77000 kgPE molcat–1 h–1.
Under
maximum
chain-
CTA/catalyst ratio and high activity, as well as irreversible elongation conditions, we observed an activity of
CCTP.[30] There, we observed 5200 kgPE molcat–1 h–1 for a 50000 kgPE molcat–1h–1 at a CTA/catalyst ratio of 1000.
CTA/catalyst ratio of 10000. Unfortunately, the chain Mortreux and co-workers have published the best reversible
elongation for such runs is only very low: 3%. One can system (and the only one that was explored at high
push the chain elongation to 66% but only with a CTA/ CTA/catalyst ratios).[7,12] It shows an activity of
catalyst ratio of 100 (activity at 5600 kgPE molcat–1 h–1). 40 kgPE molcat–1 h–1 with a CTA/catalyst ratio of 1000 and
With the irreversible CCTP catalyst system described a chain elongation of 100%.
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ally by using the residual solvent resonances. Deuterated solvents
were obtained from Cambridge Isotope Laboratories and were de-
gassed, dried and distilled prior to use. Chemical shifts (δ) are re-
ported in ppm.
Conclusion
Trichlorido-guanidinatotitanium(IV) complexes are ac-
cessible through carbodiimide insertion into titanium–
amide bonds. Alkylation of these trichlorido complexes
with methylmagnesium chloride selectively leads to the cor-
responding trimethyl complexes in high yields.
These complexes are suitable precatalysts for the poly-
merisation of ethylene in the presence of high aluminium
alkyl amounts if sterically demanding guanidinato ligands
are used. Reduction of the steric demand of the ligands
results in a significant decrease in the activity.
The absence of olefinic resonances in the high-tempera-
ture NMR spectra of the resulting polymers after hydrolytic
workup indicates chain transfer to aluminium. We observed
no increase in the molecular weight over time but did note
an increase in the number of elongated chains over time.
These observations indicate irreversible coordinative chain-
transfer polymerisation.
A quantity of elongated chains of up to 83.3% in the
presence of 1000 equivalents of aluminium could be
achieved with an activity of 9900 kgPE molcat–1 h–1 bar–1.
With increasing reaction time (Ͼ30 min) at such high Al/
catalyst ratios, no continuous increase in elongated chains
was observed but rather a decomposition of the catalyst
towards a species that produces high-molecular-weight PE.
The catalyst system discussed here is ideally suited to
produce Al-terminated high-density PE with a unique com-
bination of high activity and high catalyst economy.
Gel Permeation Chromatography (GPC): Gel permeation
chromatography analysis was carried out with a PL-GPC 220 (Ag-
ilent, Polymer Laboratories) high-temperature chromatographic
unit equipped with differential pressure (DP) and refractive index
(RI) detectors and three linear mixed-bed columns (Olexis, 13-mi-
cron particle size). GPC analyses were performed at 150 °C and
with 1,2,4-trichlorobenzene as the mobile phase. The samples were
prepared by dissolving the polymer (0.05 wt.-%, c = 1 mgmL–1) in
the mobile phase solvent in an external oven, and the solutions
were run without filtration. The molecular weights of the samples
were referenced to linear PE (Mw = 520–3200000 gmol–1) as stan-
dard. The reported values are the average of at least two indepen-
dent determinations.
X-ray Crystallography: X-ray crystal structure analyses were per-
formed with
a STOE-IPDS II diffractometer [λ(Mo-Kα) =
0.71073 Å] equipped with an Oxford Cryostream low-temperature
unit. Structure solution and refinement were accomplished with
SIR97,[50] SHELXL-97[51] and WinGX.[52]
CCDC-973107 (for 3b), -973108 (for 3c), -973106 (for 4a) and
-973109 (for 4b) contain the supplementary crystallographic data
for this paper. These data can be obtained free of charge from The
Cambridge Crystallographic Data Centre via www.ccdc.cam.ac.uk/
data_request/cif.
Ethylene Polymerisation: The polymerisation experiments were car-
ried out in a 300 mL glass autoclave (Büchi) with ethylene flow
display equipped with external heating (water bath) at constant eth-
ylene pressure. The autoclave was evacuated and purged with ethyl-
ene. Toluene (150 mL) was added into the autoclave and saturated
with ethylene. The stock solutions of precatalyst and co-catalyst
were prepared in a glovebox. After addition of the co-catalyst and
complete saturation with ethylene, the precatalyst was added. To
stop the polymerisation, the reactor was vented and acidified eth-
anol was added. The obtained polymers were filtered, washed with
ethanol and dried at 60 °C.
Experimental Section
General: All manipulations and reactions were carried out under
dry argon or nitrogen using standard Schlenk and glovebox tech-
niques. Solvents were purified by distillation from potassium, Na/
K alloy or sodium ketyl of benzophenone under argon immediately
before use. Toluene used for ethylene polymerisation (Aldrich, an-
hydrous, 99.8%) was passed over columns of Al2O3 (Fluka), BASF
R3–11-supported Cu oxygen scavenger and molecular sieves (Ald-
rich, 4 Å). Ethylene (AGA polymer grade) was passed over BASF
R3-11-supported Cu oxygen scavenger and molecular sieves (Ald-
rich, 4 Å). N,NЈ-Bis(2,6-dimethylphenyl)thiourea (1b),[47] N-tert-
butyl-NЈ-(2,6-dimethylphenyl)thiourea (1c),[48] N,NЈ-bis(2,6-di-
methylphenyl)carbodiimide (2b), N-tert-butyl-NЈ-(2,6-diisoprop-
ylphenyl)carbodiimide (2c),[46] NЈ,NЈЈ-bis(2,6-diisopropylphenyl)-
Synthesis of Complex 4a: Methylmagnesium chloride (1.1 mL,
3.27 mmol) was added dropwise at –78 °C to a solution of NЈ,NЈЈ-
bis(2,6-diisopropylphenyl)-N,N-diethylguanidinatotrichloridotitan-
ium(IV) 3a (0.506 g, 0.86 mmol) in toluene (30 mL), thereby re-
sulting in a colour change of the solution from red to yellow. The
solution was warmed to room temperature and stirred for an ad-
ditional 2 h. Toluene was removed under reduced pressure and the
residue was extracted with n-hexane (30 mL) and filtered. Storage
of the concentrated filtrate at –20 °C led to bright yellow crystals.
Yield 0.45 g (89%). 1H NMR (300 MHz, C6D6): δ = 0.33 [t, J =
7.1 Hz, 6 H, N(CH2CH3)2]; 1.25 [d, J = 6.9 Hz, 12 H, CH(CH3)2];
1.35 [d, J = 6.7 Hz, 12 H, CH(CH3)2]; 1.87 [s, 9 H, Ti(CH3)3]; 2.77
[q, J = 7.8 Hz, 4 H, N(CH2CH3)2]; 3.67 [sept, J = 6.8 Hz, 4 H,
CH(CH3)2]; 7.10 (s, 6 H, ArH) ppm. 13C NMR (75.4 MHz, C6D6):
δ = 11.6 [N(CH2CH3)2]; 24.4 [CH(CH3)2]; 25.9 [CH(CH3)2]; 28.4
[CH(CH3)2]; 40.9 [N(CH2CH3)2]; 72.4 [Ti(CH3)3]; 124.4, 125.6,
143.5, 143.9 (ArC); 169.9 (NCN) ppm. C35H53N3Ti (527.65): calcd.
C 72.84, H 10.12, N 7.96; found C 72.41, H 10.86, N 8.08.
N,N-diethylguanidinatotrichloridotitanium(IV)
(3a)[37]
and
[(Et2N)TiCl3][49] were prepared according to the published pro-
cedures. Commercial n-butyllithium (2.5 m in n-hexane), methyl-
magnesium chloride (3.0 m in thf) (Aldrich), N,NЈ-bis(2,6-diisop-
ropylphenyl)carbodiimide (2a), triethylaluminium (TEA, 25 wt.-%
in toluene, Aldrich), [R2N(CH3)H][B(C6F5)4] (R
C18H37), 6.2 wt.-% B(C6F5)4 in Isopar (Dow Chemicals) and all
other chemicals were used as received without further purification.
= C16H33–
–
Elemental Analyses (C,H,N): Elemental analyses were carried out
with a Vario Elementar EL III apparatus.
Synthesis of Complex 3b: Compound 2b (197 mg, 0.787 mmol) and
[(Et2N)TiCl3] (206 mg, 0.787 mmol) were dissolved in toluene
(40 mL) and stirred overnight. Dark red crystals could be obtained
by layering a concentrated toluene solution with n-hexane. Yield
341 mg (85%). 1H NMR (300 MHz, C6D6): δ = 0.18 [t, J = 7.2 Hz,
NMR Spectroscopy: NMR spectra were recorded with a Varian
1
INOVA 300 (1H: 300 MHz, 13C: 75.4 MHz) spectrometer. The H
and 13C NMR spectra, measured at 25 °C, were referenced intern-
Eur. J. Inorg. Chem. 2014, 1446–1453
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© 2014 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim

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FULL PAPER
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6 H, N(CH2CH3)2]; 2.35 [q, J = 7.2 Hz, 4 H, N(CH2CH3)2]; 2.43
(s, 12 H, ArCH3); 6.85–7.00 (m, 6 H, ArH) ppm. 13C NMR
(75.4 MHz, C6D6): δ = 11.7 [N(CH2CH3)2]; 19.6 (ArCH3); 41.6
[N(CH2CH3)2]; 127.3, 129.3, 132.8, 147.1 (ArC) 167.0 (NCN) ppm.
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Synthesis of Complex 4b: Compound 4b was prepared similarly to
4a by using 3b (500 mg, 1.05 mmol) and MeMgCl (1.05 mL,
3.15 mmol). Yield 390 mg (78%). H NMR (300 MHz, C6D6): δ =
0.30 [t, J = 7.2 Hz, 6 H, N(CH2CH3)2]; 1.72 [s, J = 7.2 Hz, 6 H,
Ti(CH3)3], 2.35 (s, 12 H, ArCH3), 6.80–7.10 (m, 6 H, ArH) ppm.
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1
Synthesis of Complex 3c: Compound 2c (456 mg, 2.25 mmol) and
[(Et2N)TiCl3] (510 mg, 2.25 mmol) were dissolved in toluene and
stirred overnight, whereby a crystalline solid precipitated. Dark red
crystals suitable for single-crystal analysis could be obtained from
a concentrated chloroform solution at room temperature. Yield
850 mg (88%). 1H NMR (300 MHz, CD2Cl2): δ = 1.03 [t, J =
7.1 Hz, 6 H, N(CH2CH3)2]; 1.70 [s, 9 H, C(CH3)3]; 2.30 (s, 6 H,
ArCH3); 3.00 [q, J = 7.2 Hz, 4 H, N(CH2CH3)2]; 7.06 (s, 3 H, ArH)
ppm. 13C NMR (100 MHz, CD2Cl2): δ = 12.8 [N(CH2CH3)2]; 19.7
(ArCH3), 31.5 [C(CH3)3]; 43.5 [N(CH2CH3)2]; 59.0 [C(CH3)3]
127.3, 129.0, 132.5, 152.0 (ArC), 170.3 (NCN) ppm.
C17H28Cl3N3Ti (428.65): calcd. C 47.63, H 6.58, N 9.80; found C
47.57, H 6.43, N 9.76.
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Published Online: February 11, 2014
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© 2014 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim