Highly active titanium-based olefin polymerization catalysts bearing bulky aminopyridinato ligands

Article abstract of DOI:10.1021/ic200318h

A series of titanium complexes have been prepared using either salt metathesis or amine elimination reactions. Reacting the potassium salt of Ap*H {Ap*H = N-(2,6-diisopropylphenyl)-[6-(2,4,6-triisopropylphenyl) pyridin-2-yl]amine} (1) with [TiCl₄(THF)₂] results in the formation of a nucleophilic ring-opening product of the coordinated tetrahydrofuran (THF) ligand [Ap*TiCl₂(OC₄H ₈Cl)] (7). Alkylation with benzylmagnesium chloride gave rise to the corresponding benzyl complex [Ap*TiBn₂(OC₄H ₈Cl)] (8). However, THF ring opening was overcome by adopting an amine elimination route instead of salt metathesis. Mono(aminopyridinato) titanium trichloro complexes were prepared in high yields using [(CH ₃)₂NTiCl₃], together with the corresponding sterically demanding aminopyridine as the starting material. The synthesized complexes could then be alkylated selectively. These complexes were characterized by spectroscopic methods, and their behavior in olefin polymerization and copolymerization of ethene and propene was explored. These mono(aminopyridinato)titanium trichloro complexes are less active if activated with methylaluminoxane (MAO). However, the activity increases strongly if MAO is replaced by d-MAO ("dry methylaluminoxane"). The catalysts show moderate activity toward propene polymerization, while ethylene-propylene copolymers in high-productivity with separated propene units were observed. The catalysts are also highly active in the co- and terpolymerization of 2-ethylidenenorbornene (ENB) with ethylene or ethylene-propylene, together with a very good incorporation of ENB. In all cases, the activity increases with an increase in the steric bulk of the protecting ligand.

Full text of DOI:10.1021/ic200318h

ARTICLE
pubs.acs.org/IC
Highly Active Titanium-Based Olefin Polymerization Catalysts Bearing
Bulky Aminopyridinato Ligands
Awal Noor,† Winfried P. Kretschmer,†,‡ Germund Glatz,† and Rhett Kempe*,†
†Lehrstuhl f€ur Anorganische Chemie II, Universit€at Bayreuth, 95440 Bayreuth, Germany
‡Center for Catalytic Olefin Polymerization, Stratingh Institute for Chemistry, University of Groningen, Nijenborgh 4, NL-9747 AG
Groningen, The Netherlands
S Supporting Information
b
ABSTRACT: A series of titanium complexes have been prepared using either salt
metathesis or amine elimination reactions. Reacting the potassium salt of Ap*H
{Ap*H = N-(2,6-diisopropylphenyl)-[6-(2,4,6-triisopropylphenyl)pyridin-2-yl]-
amine} (1) with [TiCl4(THF)2] results in the formation of a nucleophilic
ring-opening product of the coordinated tetrahydrofuran (THF) ligand
[Ap*TiCl2(OC4H8Cl)] (7). Alkylation with benzylmagnesium chloride gave
rise to the corresponding benzyl complex [Ap*TiBn2(OC4H8Cl)] (8). However,
THF ring opening was overcome by adopting an amine elimination route instead
of salt metathesis. Mono(aminopyridinato)titanium trichloro complexes were
prepared in high yields using [(CH3)2NTiCl3], together with the corresponding
sterically demanding aminopyridine as the starting material. The synthesized complexes could then be alkylated selectively. These
complexes were characterized by spectroscopic methods, and their behavior in olefin polymerization and copolymerization of
ethene and propene was explored. These mono(aminopyridinato)titanium trichloro complexes are less active if activated with
methylaluminoxane (MAO). However, the activity increases strongly if MAO is replaced by d-MAO (“dry methylaluminoxane”).
The catalysts show moderate activity toward propene polymerization, while ethyleneꢀpropylene copolymers in high-productivity
with separated propene units were observed. The catalysts are also highly active in the co- and terpolymerization of
2-ethylidenenorbornene (ENB) with ethylene or ethyleneꢀpropylene, together with a very good incorporation of ENB. In all
cases, the activity increases with an increase in the steric bulk of the protecting ligand.
Scheme 1. Aminopyridinato (left) and Amidinate (right)
Ligands ([M] = Group 4 Metal Complex Moiety; R, R0 =
Substituents)
’ INTRODUCTION
Aminopyridinato ligands (Scheme 1, left) have been investi-
gated intensively during the past decade.1ꢀ3 They are monoanionic
ligands suited to stabilizing early transition metals in high oxidation
states. The ligand “asymmetry” caused by the two different donor
functionalities, the pyridine and amido functions, might be con-
sidered as an additional interesting feature, especially in comparison
to the closest “relatives”, the amidinates (Scheme 1, right).4
Titanium aminopyridinates have been described especially
with regard to olefin polymerization chemistry.5 Recently, we started a
research program involving very bulky aminopyridinato ligands.6 A
variety of these (non-titanium) complexes have proven to be efficient
olefin polymerization catalysts. Hence, we became interested in
exploring the olefin polymerization chemistry of titanium complexes
stabilized by these bulky versions of aminopyridinato ligands. It has
been observed in the past that the best way to synthesize aminopyr-
idinatotitanium complexes is “direct synthesis” or amine elimination
reactions.5 Salt metathesis involving lithiated aminopyridines often
leads to low yields.5 To increase the yield, we used the potassium salt
of the corresponding ligand. This has been shown to be an efficient
alternative for the preparation of lanthanoid aminopyridinates, where
lithiated aminopyridines were also unable to give the desired
product.6b Unfortunately, we observed that the use of the potassium
salt of aminopyridine led to ring opening of the coordinated
tetrahydrofuran (THF), yielding an alkoxy species. Here, we report
on the synthesis and structure of titanium complexes stabilized by
bulky aminopyridinato ligands and their behavior in olefin homo-, co-,
and terpolymerization. The production of EPDM (= ethylene,
propylene, diene, and monomers) rubber by such catalyst systems
will be discussed as well.
’ RESULTS AND DISCUSSION
Synthesis and Structures of Complexes. The aminopyri-
dines 1ꢀ4 (Scheme 2) can be synthesized according to pub-
lished procedures.6a,d,7
Received: February 16, 2011
Published: April 12, 2011
r
2011 American Chemical Society
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ARTICLE
Scheme 2. Applied Aminopyridines
Scheme 4. Synthesis of 7
Scheme 3. Synthesis of 6 (R = Isopropyl)
Figure 2. Molecular structure of 7. Hydrogen atoms are omitted for
clarity. Selected bond lengths [Å] and angles [deg]: Ti1ꢀO1 1.745(3),
Ti1ꢀN2 1.989(4), Ti1ꢀC37 2.113(4), Ti1ꢀC44 2.122(5), Ti1ꢀN1
2.338(3); O1ꢀTi1ꢀC37 99.96(16), N2ꢀTi1ꢀC37 116.89(17),
O1ꢀTi1ꢀC44 98.35(17), C37ꢀTi1ꢀC44 115.6(2), O1ꢀTi1ꢀN1
163.02(14), N2ꢀTi1ꢀN1 61.48(13), C37ꢀTi1ꢀN1 88.83(15),
C44ꢀTi1ꢀN1 90.76(15).
Scheme 5. Synthesis of 8 (R1 = R2 = R3 = i-Pr, R4 = H), 9 (R1 =
R4 = H, R2 = Me, R3 = i-Pr), 10 (R1 = R2 = i-Pr, R3 = R4 = Me),
and 11 (R1 = R2 = R3 = R4 = Me)
Figure 1. Molecular structure of 6. Hydrogen atoms are omitted for
clarity. Selected bond lengths [Å] and angles [deg]: N1ꢀTi1 2.269(3),
N2ꢀTi1 1.972(3), Cl1ꢀTi1 2.3472(12), Cl2ꢀTi1 2.3349(12),
Ti1ꢀO2 1.741(3), Ti1ꢀO1 2.173(3); O2ꢀTi1ꢀO1 95.60(11),
N2ꢀTi1ꢀO1 164.88(11), O2ꢀTi1ꢀN1 162.11(12), N2ꢀTi1ꢀN1
62.71(10), Cl2ꢀTi1ꢀCl1 160.32(5).
The reaction of 1 equiv of the potassium salt of 16a in THF
with [TiCl4(THF)2] and crystallization from hexane at low
temperature lead to the formation of THF ring-opening product
6, in very good yield (Scheme 3).
Such kind of behavior appears reasonable and has been
explained as being the result of a nucleophilic THF ring-opening
reaction through nucleophilic attack by the free Clꢀ on the
activated CꢀO bond of the coordinated THF.8 This process
would give rise to complex 6. Previous examples of this type of
reactivity between the [Cp2Zr(R)(THF)]þ species and certain
nucleophilic reagents, namely, NR3 and PMe2Ph, have been
described by Jordan et al.9 Furthermore, nucleophilic attack of a
chloride anion on a coordinated THF molecule has been
previously observed in other instances where THF is bound to
an electrophilic center, namely, boron and uranium.10 Recently,
such a nucleophilic THF ring opening has been reported for
yttrium β-diketiminate complexes.11
Complex 6 can be crystallized from a concentrated hexane
solution as dark-red crystals. The coordination sphere around the
titanium atom is pseudooctahedral (Figure 1), with two chlorides
[Cl2ꢀTi1ꢀCl1 160.32(5)°] in the trans position to each other. The
coordination sphere consists of two nitrogen atoms, two oxygen
atoms, and two chloride atoms, and the reason for the distortion is
the small angle of the aminopyridinato four-membered ring
[N2ꢀTi1ꢀN1 62.71(10)°]. In an attempt to get rid of the alkoxy
ligand and to synthesize the trialkyl complex, 3 equiv of benzylmag-
nesium chloride was reacted with 6 in ether at room temperature.
Compound 7 was formed in very good yield (Scheme 4).
Crystals of 7 partially suitable (the quality of the diffraction
data is rather low) for X-ray analysis were obtained from pentane.
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The coordination around the metal center can best be de-
scribed as distorted trigonal bipyramidal (Figure 2). Again, the
reason for the distortion is the small NꢀTiꢀN bond angle
[61.48(13)°] due to strained binding of the aminopyridinato
ligand. The different TiꢀN distances of 6 [TiꢀN1 2.269(3) Å;
TiꢀN2 1.972(3) Å] and 7 [TiꢀN1 2.338(3) Å; TiꢀN2
1.989(4) Å] indicate localization of the anionic function at
the amido nitrogen atom. The 1H NMR spectrum of 7 shows a
pentate and two triplets at 1.01 (4H, H2CH ), 2.88 (2H,
2
CH Cl), and 3.59 (2H, HOCH ) ppm, respectively, for the
2
2
H
opened THF ring. The two nonequivalent CH2 protons of the
benzyl ligands gave rise to two doublets (AB system) at 2.71
and 2.82 ppm.
In order to avoid such a ring opening of the coordinated THF,
THF-free chloro complexes 8ꢀ11 were prepared in quite good
yields, adopting an amine elimination route by reacting 1 equiv of the
corresponding aminopyridine precursor with [(CH3)2NTiCl3]
(Scheme 5) in ether or hexane. Despite steric variation, the ligands
1ꢀ4 are bulky enough to avoid the formation of any bis-
(aminopyridinato) complexes, as is also reflected by their very high
yield synthesis.
Compounds 8 and 11 were crystallized as purple crystals from
a concentrated ether solution at low temperature. X-ray crystal
structures were determined for both compounds. The molecular
structure of compound 8 is shown in Figure 3. Both compounds
adopt a distorted octahedral coordination due to the additional
dimethylamine ligand, which was released during the amine elim-
ination reaction.
Figure 3. Molecular structure of 8. Hydrogen atoms and one molecule
are omitted for clarity. Selected bond lengths [Å] and angles [deg]:
N1ꢀTi1 2.261(5), N2ꢀTi1 1.981(4), N3ꢀTi1 2.233(5), Cl1ꢀTi1
2.3269(18), Cl2ꢀTi1 2.2857(18), Cl3ꢀTi1 2.2430(16); N2ꢀTi1ꢀN3
63.05(16), N2ꢀTi1ꢀCl3 88.95(13), N3ꢀTi1ꢀCl3 151.99(13),
N3ꢀTi1ꢀN1 118.72(15), Cl3ꢀTi1ꢀCl2 102.55(7), Cl3ꢀTi1ꢀCl1
99.94(6), Cl2ꢀTi1ꢀCl1 152.65(7).
To explore the nature of coordinated amine and its possible
role in the aminopyridinatotitanium-catalyzed olefin polymeri-
zation reactions, alkylation of complex 8 was modeled. The
reaction of 8 with benzylmagnesium chloride in diethyl ether
yielded the amine-free trialkyl 12 (Scheme 6).
Scheme 6. Synthesis of 12
After removal of all volatiles and extraction of the residue with
1
hexane, the H NMR spectrum of the red crystalline material
obtained at low temperature shows that all of the benzyl protons
in 12 are equal. The CH2-group resonance of these ligands was
observed as a single sharp signal at 3.10 ppm. No resonances related
to dimethylamine could be detected. The tribenzyltitanium complex
was not stable in solution at room temperature, leading to toluene
Table 1. Details of the X-ray Crystal Structure Analyses
6
7
8
11
formula
cryst syst
space group
a [Å]
C
40H59Cl3N2O2Ti
C50H65ClN2OTi
monoclinic
P21/c
C25H32Cl3N3Ti
monoclinic
Cc
C34H50Cl3N3Ti
monoclinic
P21/c
orthorhombic
Pccn
19.6630(10)
27.6460(11)
15.2850(6)
11.0340(10)
20.3610(10)
20.4070(10)
96.583(8)
4554.5(5)
0.8 ꢁ 0.4 ꢁ 0.3
1.157
29.6950(6)
12.9390(4)
18.5580(5)
91.387(2)
7128.3(3)
0.24 ꢁ 0.21 ꢁ 0.13
1.221
13.1900(12)
12.1140(10)
16.4750(14)
92.589(7)
2629.7(4)
0.29 ꢁ 0.13 ꢁ 0.12
1.336
b [Å]
c [Å]
β [deg]
V [Å3]
cryst size [mm3]
8309.0(6)
0.69 ꢁ 0.54 ꢁ 0.35
1.206
F
calcd [g cmꢀ3
]
μ(Mo KR) [mmꢀ1
]
0.433
0.283
0.491
0.648
T [K]
133(2)
1.27ꢀ25.79
7891
133(2)
133(2)
191(2)
θ range [deg]
1.42ꢀ25.76
8590
1.37ꢀ25.65
6779
1.55ꢀ25.71
4971
no. of unique reflns
no. of obsd reflns [I > 2σ(I)]
no. of param
5211
5653
4502
2816
433
496
771
298
wR2 (all data)
0.177
0.200
0.070
0.117
R value [I > 2σ(I)]
0.064
0.081
0.033
0.062
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Table 2. Ethylene Polymerization Catalyzed by 6 and 8ꢀ11
entry
precatalysta
MAO [mmol]
d-MAO [mmol]
T [°C]
mPol. [g]
activity [kgPE molcatꢀ1 hꢀ1 barꢀ1
]
Mw [g molꢀ1
]
Mw/Mn
1
8
1
1
50
80
30
50
80
50
50
50
50
80
1.20
0.30
7.10
4.90
4.80
3.30
2.40
2.20
2.00
4.70
480
120
66 162
55 267
93 686
85 109
95 602
67 190
89 093
63 716
45 507
172 177
2.3
2.3
2.5
2.6
3.1
2.3
2.7
2.9
5.5
3.3
2
8
3
8
1
1
1
1
1
1
1
1
2840
1960
1920
1320
960
4
8
5
8
8
9
6
10
11
6
7
880
9
800
10
6
1880
a Precatalyst: 2 μmol. Toluene: 260 mL. p = 5 bar. t = 15 min.
Table 3. Ethylene Copolymerization Catalyzed by 6 and 8ꢀ11
pressure [bar]
entry
precatalysta
ethene
propene
T [°C]
mPol. [g]
activity [kgPE molcatꢀ1 hꢀ1
]
Mw [g molꢀ1
]
Mw/Mn
1
8
5
2
2
2
2
2
50
50
50
50
50
50
50
50
50
3.1
16.00
14.80
15.30
7.30
6.70
16.50
5.7
200
32 000
29 600
30 600
14 600
2 680
nd
nd
2
8
5
5
5
5
5
5
5
5
104 374
103 502
120 954
87 162
186 796
133 287
2.1
2.0
2.1
1,9
2.1
2.4
3
9
4
10
11
6
5
6
7b
8c
9d
8
33 000
11 400
8 000
8
8
2
4.00
56 261
1.9
a Precat: 2 μmol. Toluene: 260 mL. d-MAO = 1 mmol. t = 15 min. b 10 mL of 1-hexene. c 10 mL of ENB. d 1 mL of ENB.
elimination and the formation of unidentified species, while at low
temperature, it could be stored for weeks.
’ POLYMERIZATION STUDIES
Because the aim of this work was to evaluate the potential of
titanium complexes stabilized by bulky Ap ligands in olefin
polymerization, the use of these complexes in ethylene homo-
and copolymerization was examined. Activation of 8 with MAO
leads to an active single-site catalyst at 50 °C but shifted to
moderate with an increase in the temperature to 80 °C (Table 2,
entries 1 and 2). Because of possible decomposition and ligand
transfer from titanium to aluminum,6i,p we switched to d-MAO
(“dry methylaluminoxane”) and found that 8 activated with
d-MAO gives rise to a highly active single-site catalyst. A slight
decrease in the activity has been observed with an increase in the
temperature but still high enough to be called “very high
activity”.12 For the less sterically protected systems 9ꢀ11,
Figure 4. 1H NMR spectrum of poly(ethylene-co-propene) obtained
with the 8/d-MAO system catalyst.
comparatively lower activities have been observed. The intro-
duction of an additional directing alkoxy ligand in 6 leads to a
decrease in activity compared to 8 (Table 2, entries 4 and 9) and
produces polymer with a bimodal distribution. At 80 °C, the
polymerization behavior of 6 was very similar to that of 8,
probably because of a fast alkoxy-ligand transfer to aluminum,
leaving the active system 8/d-MAO behind. The selective ligand
transfer has also been verified and supported by an independent
synthesis of the corresponding tribenzyl complex 12. The activity
shown by complexes 6 and 8ꢀ11 is very high compared to that
already known for aminopyridinatotitanium systems5 and could
be attributed to the steric bulk of the ligands of these complexes.
The catalyst system 8/d-MAO shows moderate activity
toward propylene polymerization (Table 3, entry 1). How-
ever, the presence of ethylene reactivates the catalyst and
provides a copolymer with narrow molecular weight distribu-
1
tion. The H and 13C NMR spectroscopic analyses reveal
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Figure 7. 13C NMR spectrum of ethyleneꢀpropeneꢀENB terpolymer
obtained with the 8/d-MAO system catalyst.
Figure 5. 13C NMR spectrum of poly(ethylene-co-propene) (with
nearly 7 mol % incorporation of propene) obtained with the 8/d-MAO
system catalyst.
with 8/d-MAO (Table 3, entry 9) gives a highly active ethylene
consumption, leading to a glassy transparent polymer. Unfortu-
nately, further analysis of the polymer could not be achieved because
of very fast cross-linking under air. To overcome this problem, we
reduced the amount of ENB to 1 mL and switched to terpolymer-
ization by adding additional propylene to the autoclave, yielding a
rubberlike polymer that was soluble in tetrachloroethane and has been
characterized by NMR spectroscopy (Figures 6 and 7).14d,15c,15d
Besides the characteristic peaks of the ethylene/propylene (EP)
copolymer, additional peaks for the incorporated ENB could
be observed in the 13C NMR spectra. We also observe peaks
for the unreacted double bond in the olefinic region. A decrease
in the activity compared to the EP copolymerization under the
same conditions has been observed, but this decrease is
comparatively low.
The mono(aminopyridinato)titanium catalyst systems are
stable for the entire period of co- and homopolymerization (15 min)
with a slight drop over time.
’ CONCLUSIONS
Figure 6. 1H NMR spectrum of ethyleneꢀpropeneꢀENB terpolymer
obtained with the 8/d-MAO system catalyst.
A series of conclusions can be drawn from the present
studies. The best way to prepare mono(aminopyridinato)-
titanium complexes in high yields is via amine elimination
because salt elimination may lead to ring opening of coordi-
nated THF ligands. Mono(aminopyridinato)titanium complexes
show less stability in the ethylene homo- and copolymerization if
activated with MAO but are highly active if MAO is replaced by
d-MAO. If one applies these catalyst systems to EP copolymer-
ization, a high regioselectivity is observed. Propylene is inserted
only after ethylene, and no propylene/propylene sequences
were detected. Cyclic comonomers like ENB could be incorpo-
rated to yield highly valuable EPD terpolymers.
long-chain copolymer with isolated propylene units (Figures 4
and 5).6m
Catalyst systems based on 9 and 10 are slightly less active
compared to 8 with nearly identical molecular weights for the
formed copolymers, while for the least bulky system 11/d-MAO,
a significant decrease in the activity to almost half was observed
(Table 3, entry 6). It is notable that replacement of propylene by
10 mL of 1-hexene leads not to the formation of an ethyleneꢀ
hexene copolymer but surprisingly to a strong enhancement of
the ethylene polymerization activity (Table 3, entry 7).
After these motivating copolymerization results, we also
became interested in the incorporation of cyclic olefin mono-
mers like dicyclopentene,13 norbornene,14 and 5-ethylidene-2-
norbornene.15 The latter one is often used in the synthesis of highly
valuable EPDM rubber polymers.16 The addition of 10 mL of
2-ethylidenenorbornene (ENB) to the ethylene polymerization
’ EXPERIMENTAL SECTION
Synthesis and Structure Analysis. All manipulations were
performed with rigorous exclusion of oxygen and moisture in Schlenk-
type glassware on a dual-manifold Schlenk line or in an argon-filled
glovebox (mBraun 120-G) with a high-capacity recirculator (<0.1 ppm O2).
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Nonhalogenated solvents were dried by distillation from sodium wire/
benzophenone. [(CH3)2NTiCl3] was prepared according to literature
procedures.17 Commercial [C6H5CH2MgCl] (1.0 M in diethyl ether;
Aldrich) and [TiCl4(THF)2] and [TiCl4] (Acros) were used as re-
ceived. Deuterated solvents were obtained from Cambridge Isotope
Laboratories and were degassed, dried, and distilled prior to use.
Toluene for polymerization (Aldrich, anhydrous, 99.8%) was passed
over columns of Al2O3 (Fluka), a BASF R3-11-supported copperꢀoxy-
gen scavenger, and molecular sieves (Aldrich, 4 Å). Ethylene (AGA
polymer grade) was passed over a BASF R3-11-supported copperꢀ
oxygen scavenger and molecular sieves (Aldrich, 4 Å). Poly-
(methylaluminoxane) (PMAO, [MeAlO]n, 4.9 wt % in aluminum;
Akzo) were used as received. d-MAO was prepared by the removal of
all volatiles from PMAO (4.9 wt % in aluminum; Akzo). NMR spectra
were recorded on a Bruker ARX 250 MHz, and chemical shifts are
reported in ppm relative to the deuterated solvent. Elemental analyses
(CHN) were determined using a Vario EL III instrument. X-ray crystal
structure analyses were performed by using a STOE-IPDS II equipped
with an Oxford Cryostream low-temperature unit. Structure solution
and refinement were accomplished using SIR97,18 SHELXL97,19 and
WinGX.20 Crystallographic details are summarized in Table 1
The reported values are the average of at least two independent
determinations.
Synthesis of 6. To 1 (0.497 g, 1 mmol) and [TiCl4 (THF)2] (0.334
g, 1 mmol) was added THF (20 mL) at room temperature. The resulting
maroon solution was stirred overnight. THF was evaporated to dryness,
and the product was extracted with 10 mL of hexane, which upon
standing at room temperature afforded dark-red crystals of the product.
Yield: 0.508 g, 68%. Elem anal. Calcd for C40H58Cl3N2O2Ti (751.30):
C, 63.79; H, 7.76; N, 3.72. Found: C, 63.11; H, 7.89; N, 3.78. 1H NMR
(C6D6, 298 K): δ 1.05 (d, 6H, H28,29,32,33), 1.11 (d, 6H, H30,31), 1.52 (d,
6H, H24,25,26,27), 1.33 (m, 8H, H2CH , β-CH2, THF), 1.41 (d, 6H,
2
H
24,25,26,27), 1.56 (d, 6H, H28,29,32,33), 2.96 (t, 2H, HCH Cl), 2.96 (sept,
2
1H, H15), 3.21 (sept, 2H, H13,14), 3.60 (br m, 6H, H22,23, R-CH2, THF),
3
5
4.05 (t, 2H, H OCH ), 5.50 (d, 1H, H ), 6.63 (d, 1H, H ), 6.93 (t, 1H,
H4), 7.17 (s, 3H, H18,19,20), 7.22 (s, 2H, H9,11). 13C NMR (C6D6, 298
K): δ 23.2 (C28,29,32,33), 24.3 (C24,25,26,27), 24.7 (C24,25,26,27), 25.6
(C28,29,32,33), 26.6 (β-CH2, THF), 28.4 (C30,31), 28.9 (C22,23), 29.3
2
(C2CH ), 31.1 (C13,14), 34.8 (C15), 44.3 (CCH Cl), 70.0 (R-CH2, THF),
2
2
3
5
19
82.8 (COCH ), 100.3 (C ), 119.8 (C ), 120.8 (C ), 124.4 (C9,11), 128.2
(C18,20) 134.0 (C7), 140.0 (C4), 143.6 (C10), 143.7 (C17,21), 147.6
(C8,12), 150.0 (C16), 156.0 (C6), 164.0 (C2).
2
General Description of Ethylene Polymerization Experiments
with MAO. The catalytic ethylene polymerization reactions were
performed in a stainless steel 1 L autoclave (Medimex) in semibatch
mode (ethylene was added by a replenishing flow to keep the pressure
constant). The reactor was temperature- and pressure-controlled and
equipped with separate toluene, catalyst, and cocatalyst injection
systems and a sample outlet for continuous reaction monitoring. For
up to 15 bar of ethylene pressure, multiple injections of the catalyst
with a pneumatically operated catalyst injection system were used.
During polymerization runs, the pressure, ethylene flow, inner and
outer reactor temperatures, and stirrer speed were monitored con-
tinuously. In a typical semibatch experiment, the autoclave was
evacuated and heated for 1 h at 125 °C prior to use. The reactor was
then brought to the desired temperature, stirred at 600 rpm, and
charged with 230 mL of toluene, together with PMAO (550 mg of a
toluene solution, 4.9 wt % aluminum, 1 mmol), as was not mentioned
different in the text. After pressurization with ethylene to reach 5 bar of
total pressure, the autoclave was equilibrated for 5 min. Subsequently,
1 mL of a 0.002 M catalyst stock solution in toluene was injected,
together with 30 mL of toluene, to start the reaction. During the run,
the ethylene pressure was kept constant to within 0.2 bar of the initial
pressure by a replenishing flow. After 15 min of reaction time, the
reactor was vented and the residual aluminum alkyls were destroyed by
the addition of 100 mL of ethanol. A polymeric product was collected,
stirred for 30 min in acidified ethanol, and rinsed with ethanol and
acetone on a glass frit. The polymer was initially dried in air and
subsequently in vacuo at 80 °C.
Synthesis of 7. [C6H5CH2MgCl] (2.1 mL, 2.1 mmol) was added to
6 (0.475 g, 0.7 mmol) in ether (20 mL), at ꢀ30 °C as the color started
changing to red. The solution mixture was allowed to reach room
temperature and was further stirred for 2 h. The solution was evaporated
to dryness, and the product was extracted with pentane (10 mL). Filtrate
was cooled at ꢀ25 °C to afford red crystals of the product. Yield: 0.259 g,
47%. Elem anal. Calcd for C50H65ClN2OTi (793.38): C, 75.69; H, 8.26;
N, 3.53. Found: C, 74.89; H, 8.60; N, 3.59. 1H NMR (C6D6, 298 K): δ
1.01 (p, 4H, H2CH ), 1.10ꢀ1.36 (m, 30H, H24,25,26,27,28,29,30,31,32,33), 2.71
2
and 2.82 (two doublets AB system, 4H, HCH (benzyl)), 2.88 (t, 2H,
2
H
CH Cl), 3.15 (sept, 5H, H13,14,15,22,23), 3.59 (t, 2H, HOCH ), 5.53 (d,
2
2
1H, H3), 6.50 (d, 1H, H5), 6.60 (d, 4H, HCH(benzyl)), 6.86 (t, 1H, H4),
6.94 (t, 1H, H19), 7.06ꢀ7.12 (m, 8H, H18,20,CH(benzyl)), 7.30 (s, 2H,
H
9,11). 13C NMR (C6D6, 298 K): δ 22.4 (C28,29,32,33), 24.4 (C24,25,26,27),
2 2
27.2 (CCH ), 28.7(C30,31), 28.8 (C2CH ), 29.9(C22,23), 31.6 (C13,14), 34.9
(C15), 44.9 (CCH Cl), 76.4 (COCH ), 87.7 (CCH (benzyl)), 102.1 (C3),
116.3 (C5), 121.3 (C9,11), 122.4 (C(benzyl)), 124.0 (s, C18,20), 126.7 (C19),
127.0 (C(benzyl)), 134.6 (C7), 140.9 (C4), 143.1 (C10), 143.7 (C(benzyl)),
147.2 (C17,21), 148.0 (C8,12), 151.1 (C10), 150.5 (C16), 156.5 (C6),
167.9 (C2).
2
2
2
Description of EP Copolymerization Experiments. The
general procedure and conditions as described above were followed,
using successively 2 bar of propylene and 5 bar of ethylene to pressurize
the reactor.
The polymer samples for NMR spectroscopic measurements were
prepared by dissolving 15 mg of the polymer in 0.5 mL of C2D2Cl4 at
100 °C for 3 h before measurement. Gel permeation chromatography
analysis was carried out on an Agilent PL-GPC220 chromatograph,
equipped with a capillary differential-pressure detector, a refractive-
index detector, and a two-angle (15° and 90°) light-scattering photo-
meter at 150 °C using 1,2,4-trichlorobenzene as the mobile phase. The
samples were prepared by dissolving the polymer (0.1% w/v) in the
mobile-phase solvent in an external oven and were run without filtration.
The molecular weight was referenced to polyethylene (Mw = 50 000 g
molꢀ1) and polystyrene (Mw = 520ꢀ3 000 000 g molꢀ1) standards.
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δ 20.0 (C28,29), 20.9 (C30), 22.7 (C14,15,17,18), 24.3 (C14,15,17,18), 26.9
Synthesis of 8. Ether (30 mL) was added to 1 (0.913 g, 2 mmol)
and [(CH3)2NTiCl3] (0.397 g, 2 mmol) at room temperature. The
resulting purple reaction mixture was stirred overnight. The solvent was
evaporated completely to give the desired purple product. Yield: 1.278 g,
98%. Elem anal. Calcd for C34H50Cl3N3Ti (655.01): C, 62.34; H, 7.69;
N, 6.42. Found: C, 61.78; H, 8.04; N, 6.05. 1H NMR (C6D6, 298 K): δ
1.01 (d, 6H, H30,31), 1.16 (m, 12H, H28,29,32,33), 1.48 (d, 6H,
HN(CH3)2
(C20,21), 31.2 (C13,16), 34.8 (C19), 38.8 (C
), 101.4 (C3),
120.6 (C9,11), 120.7 (C5), 129.4 (C24,26), 132.9 (C23,27), 133.2 (C25),
136.8 (C7), 140.0 (C4), 146.7 (C22), 147.9 (C8,12), 148.9 (C10), 150.5
(C6), 153.3 (C2).
24,25,26,27), 1.65 (d, 6H, H24,25,26,27), 1.80 (6H, H(CH ) NH), 2.75
3
2
H
(sept, 1H, H15), 3.02 (sept, 2H, H13,14), 3.99 (sept, 2H, H22,23), 5.64
(d, 1H, H3), 6.64 (d, 1H, H5), 6.91 (t, 1H, H4), 7.11 (s, 2H, H9,11),
7.23 (s, 3H, H18,19,20). 13C NMR (C6D6, 298 K): δ 22.6 (C28,29,32,33),
24.2 (C24,25,26,27), 24.9 (C24,25,26,27), 26.9 (C28,29,32,33), 28.2
(C30,31), 28.7 (C22,23), 31.2 (C13,14), 34.8 (C15), 38.83
(C(CH ) NH), 101.8 (C3), 101.9 (C5), 120.6 (C9,11), 121.0 (C19),
124.4 (C18,20), 133.1 (C7), 139.7 (C4), 143.8 (C10), 147.9 (C17,21),
148.2 (C16), 150.6 (C8,12), 153.1 (C6), 162.4 (C2).
3
2
Synthesis of 11. 4 (0.661 g, 2 mmol) in ether (20 mL) was added
to brown [(CH3)2NTiCl3] (0.397 g, 2 mmol) in ether (5 mL) at
room temperature. A color change from brown to maroon red and
then to purple was observed. The reaction mixture was stirred
overnight. The solution was evaporated, leaving behind a purple
product. Yield: ≈100%. Elem anal. Calcd for C25H32Cl3N3Ti
(528.77): C, 56.79; H, 6.10; N, 7.95. Found: C, 56.67; H, 5.97; N,
1
7.94. H NMR (C6D6, 298 K): δ 1.85 (s, 6H, HHN(CH ) ), 2.12 (s,
3H, H15), 2.17 (s, 6H, H23), 2.30 (s, 6H, H22,24), 2.64 (s, 6H, H13,14),
5.59 (dd, 1H, H3), 6.24 (dd, 1H, H5), 6.72 (s, 2H, H18,20), 6.80ꢀ6.87
3
2
(m, 4H, H4,9,11,NH). 13C NMR (C6D6, 298 K): δ 19.9 (C22,24), 20.8
Synthesis of 9. Ether (20 mL) was added to 2 (0.358 g, 1 mmol)
and [(CH3)2NTiCl3] (0.198 g, 1 mmol). The resulting purple solution
was stirred overnight. Ether was evaporated, leaving behind a purple
product, which was dried under vacuum. Yield: 0.546 g, 98%. Elem anal.
Calcd for C27H36Cl3N3Ti (556.82): C, 58.24; H, 6.52; N, 7.55. Found:
(C13,14), 20.9 (C23), 21.0 (C15), 38.8 (CN(CH ) ), 101.1 (C ), 119.1
(C5), 128.1 (C9,11), 129.4 (C18,20), 132.9 (C7), 135.2 (C4),
136.8 (C16), 138.4 (C17,21), 141.1 (C8,12), 148.9 (C10), 153.7 (C6),
161.0 (C2).
3
3
2
1
C, 58.68; H, 6.70: N, 7.36. H NMR (C6D6, 298 K): δ 1.18 (d, 6H,
22,23,25,26), 1.64 (d, 6H, H22,23,25,26), 1.80 (s, 6H, HHN(CH ) ), 2.28 (s,
3 2
3
2
H
6H, H13,14), 2.85 (br s, 1H, HHN(CH ) ), 4.00 (sep, 2H, H21,24), 5.58 (d,
1H, H3), 6.15 (d, 1H, H5), 6.82 (t, 1H, H4), 6.86ꢀ7.24 (m, 6H,
H
9,10,11,17,18,19). 13C NMR (C6D6, 298 K): δ 21.0 (C13,14), 24.7
3 2
(C22,23,25,26), 25.0 (C22,23,25,26), 28.7 (C21,24), 38.8 (CHN(CH ) ), 101.7
(C3), 119.0 (C5), 124.4 (C9,11), 127.4 (C17,19), 128.6 (C18), 128.9
(C10), 137.1 (C16,20), 137.7 (C4), 141.0 (C7), 143.8 (C8,12), 148.2
(C15), 153.2 (C6), 162.7 (C2).
Synthesis of 12. To 8 (0.6 g, 0.92 mmol) in ether (20 mL) was
added [C6H5CH2MgCl] (2.78 mL, 2.78 mmol) at ꢀ30 °C as the
color started to change to red. The solution mixture was allowed to
reach room temperature and was further stirred for 2 h. The solution
was evaporated to dryness, and the product was extracted with hexane
(10 mL). The filtrate was cooled at ꢀ25 °C to afford a red crystalline
material of the product. Yield: 0.43 g, 55%. Elem anal. Calcd for
C53H64N2Ti (776.96): C, 81.93; H, 8.30; N, 3.61. Found: C, 80.61;
H, 8.37; N, 3.44. 1H NMR (C6D6, 298 K): δ 1.06 (d, 6H, H28,29,32,33),
Synthesis of 10. Ether (20 mL) was added to 3 (0.829 g, 2 mmol)
and [(CH3)2NTiCl3] (0.396 g, 2 mmol) at room temperature. The
resulting purple solution was stirred overnight. The solvent was
evaporated, leaving behind a purple product, which was then dried
under vacuum. Yield: 1.176 g, 96%. Elem anal. Calcd for
C31H44Cl3N3Ti (612.93): C, 60.75; H, 7.24; N, 6.86. Found: C,
1.13 (d, 6H, H30,31), 1.22 (m, 12H, H24,25,26,27), 1.27 (d, 6H,
H
28,29,32,33), 2.80 (sept, 3H, H13,14,15), 3.10 (s, 6H, HCH ), 3.68
2
(sept, 2H, H22,23), 5.74 (dd, 1H, H3), 6.23 (dd, 1H, H5), 6.51 (d, 6H,
H
CH(benzyl)), 6.81 (t, 1H, H4), 6.87ꢀ7.18 (m, 12H, H18,19,20,CH(benzyl)),
1
61.06; H, 7.46; N, 6.65. H NMR (C6D6, 298 K): δ 1.05 (d, 6H,
7.26 (s, 2H, H9,11). 13C NMR (C6D6, 298 K): δ 22.4 (C28,29,32,33),
23.9 (C24,25,26,27), 24.3 (C30,31), 25.5 (C24,25,26,27), 26.6
(C28,29,32,33), 29.1 (C22,23), 31.1 (C13,14), 34.9 (C15), 104.4
H
14,15,17,18), 1.19 (d, 6H, H14,15,17,18), 1.50 (d, 6H, H20,21), 1.84 (s, 6H,
HHN(CH ) ), 2.14 (s, 3H, H ), 2.63 (s, 6H, H28,29), 2.77 (m, 1H, H19),
30
3
2
3.06 (sep, 2H, H13,16), 5.60 (d, 1H, H3), 6.62 (d, 1H, H5), 6.80 (s, 2H,
H
(C3), 107.9 (CCH (benzyl)), 116.0 (C5), 121.4 (C9,11), 123.6
2
24,26), 6.85 (t, 1H, H4), 7.13 (s, 1H, H9,11). 13C NMR (C6D6, 298 K):
(C(benzyl)), 124.8 (C18,20), 127.2 (C19), 128.9 (C(benzyl)), 134.4
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ARTICLE
(s, C7), 140.7 (C4), 144.8 (C17,21), 145.6 (C16), 148.0 (C(benzyl)),
146.8 (C8,12), 150.5 (C10), 156.0 (C6), 170.2 (C2).
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’ ASSOCIATED CONTENT
S
Supporting Information. X-ray crystallographic data for
b
compounds 6 (CCDC 813068), 7 (CCDC 813069), 8 (CCDC
813070), and 11 (CCDC 813067). This material is available free
of charge via the Internet at http://pubs.acs.org.
’ AUTHOR INFORMATION
Corresponding Author
*E-mail: kempe@uni-bayreuth.de. Fax: þ49 921 55-2157.
’ ACKNOWLEDGMENT
We thank Deutsche Forschungsgemeinschaft (SFB 840) for
supporting this work.
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’ NOTE ADDED AFTER ASAP PUBLICATION
Due to a production error, this paper was published on the
Web on April 12, 2011, with Figure 7 duplicated. The corrected
version was reposted on April 14, 2011.
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