Reversible chain transfer between organoyttrium cations and aluminum: Synthesis of aluminum-terminated polyethylene with extremely narrow molecular-weight distribution

Article abstract of DOI:10.1002/chem.200600660

Aminopyridinato-ligand-stabilized organoyttrium cations are accessible in very good yield through alkane elimination from trialkyl yttrium complexes with sterically demanding aminopyridines, followed by abstraction of one of the two alkyl functions using

Full text of DOI:10.1002/chem.200600660

FULL PAPER
DOI: 10.1002/chem.200600660
Reversible Chain Transfer between Organoyttrium Cations and Aluminum:
Synthesis of Aluminum-Terminated Polyethylene with Extremely Narrow
Molecular-Weight Distribution
Winfried P. Kretschmer,*[a] Auke Meetsma,[a] Bart Hessen,[a] Thomas Schmalz,[b]
Sadaf Qayyum,[b] and Rhett Kempe*[b, c]
Abstract: Aminopyridinato-ligand-sta-
bilized organoyttrium cations are ac-
cessible in very good yield through
alkane elimination from trialkyl yttri-
um complexes with sterically demand-
ing aminopyridines, followed by ab-
straction of one of the two alkyl func-
tions using ammonium borates. At
808C and in the presence of small
amounts of aluminum alkyl com-
pounds, very high ethylene polymeriza-
tion activities are observed if very
bulky aminopyridinato ligands are
used. During these polymerizations a
reversible polyethylene chain transfer
is observed between the organoyttrium
cations and aluminum alkyls. The
chain-transfer catalyst system described
here is able to produce relatively long-
chain (up to 4000 gmolÀ1) Al-terminat-
ed polyethylene with molecular-
a
weight distribution <1.1. In the synthe-
sis of higher molecular PE a slight in-
crease in polydispersity with increasing
chain length (15600 gmolÀ1, ~1.4) is
observed owing to reduced reversibility
caused by higher viscosity and precipi-
tation of polymer chains (temperature
of 80–1008C).
Keywords: aluminum · chain trans-
fer · lanthanides · polymerization ·
yttrium
Introduction
chain transfer.[3] Lanthanide alkyls like “
[Cp2SmPE]” are
A
usually less efficient in ethylene insertion than organolan-
thanide cations.[4] Early and late transition-metal PE chain-
transfer catalysts on the other hand are limited to rather
low-molecular-weight polymers. Such systems transfer effi-
ciently at room temperature and are able to polymerize with
a polydispersity less than 1.1, up to a molecular weight of
1200 gmolÀ1.[5] We report here on aminopyridinato-ligand-
stabilized[6] organoyttrium cations and the reversible PE
chain transfer between these cations and aluminum to syn-
thesize aluminium-terminated PE chains with a very narrow
molecular-weight distribution. The rather high thermal sta-
bility of these cations in combination with suppressed b-H
transfer allows for the synthesis of relatively high-molecular-
weight Al-terminated PE, functionalized polyethylene
blocks to build novel polymer architectures.[7] More than 50
years ago, Karl Ziegler and co-workers discovered the Auf-
baureaktion[8]—the insertion of ethylene into an aluminum–
alkyl bond at very high ethylene pressures. The “Nickelef-
fekt”[9] and subsequent explorations of the influence of
other metals with regard to ethylene insertion led to transi-
tion-metal-catalyzed ethylene polymerization.[10] We report
here on a lanthanide-catalyzed version of the Aufbaureak-
tion.
The unusually large coordination sphere and high Lewis
acidity of the lanthanides give rise to unique coordination
chemistry, for instance between Ln and main-group
alkyls.[1,2] The optimization of such coordinative interactions
between “
ethylenyl) and “
ACHTREUNG
ACHTREUNG
fined PE materials and diblock copolymers by reversible
[a]Dr. W. P. Kretschmer, Dr. A. Meetsma, Prof. Dr. B. Hessen
Stratingh Institut for Chemistry and Chemical Engineering
Center for Catalytic Olefin Polymerization
University of Groningen
Nijenborgh 4 9747 AG Groningen (The Netherlands)
Fax : (+31)503-634-315
E-mail: W.P.Kretschmer@rug.nl
[b]Dr. T. Schmalz, S. Qayyum, Prof. Dr. R. Kempe
Lehrstuhl Anorganische Chemie II, Universität Bayreuth
95440 Bayreuth (Germany)
Fax : (+49)921-552-157
E-mail: Kempe@Uni-Bayreuth.de
[c]Prof. Dr. R. Kempe
Leibniz-Institut für Katalyse
Albert-Einstein-Strasse 29, 18059 Rostock (Germany)
Chem. Eur. J. 2006, 12, 8969 – 8978
ꢀ 2006 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
8969

Results and Discussion
Synthesis and structure of the
organoyttrium cations: The re-
action of the sterically de-
manding aminopyridine[11] 1a
(Scheme 1) with one equiva-
lent
[Y
G
N
leads to the dialkyl 2a in good
yield (Scheme 2). The proton
and 13C NMR signals of the
CH2 groups of the two alkyl li-
gands show coupling constants
of 2J
39.74 Hz, as well as 2J-
(29Si,1H) = 8.3 or 1J(29Si,13C)
46.5 Hz. The 29Si NMR
A
G
=
A
ACHTREUNG
=
spectrum of 2a shows a dou-
blet at À4.3 ppm with a cou-
pling constant 2J(89Y,29Si)
=
A
1.9 Hz. The reaction of 2a with
ammonium borates leads selec-
tively and quantitatively to an
elimination of one of the two
alkyl ligands. The organoyttri-
Scheme 1. Synthesis of sterically demanding aminopyridines 1a–1c.
um cation 3a obtained in the presence of THF by using the
anilinium borate [C6H5NH
A
ACHTREUNG
terized by X-ray crystal structure analysis. The molecular
structure is shown in Scheme 2. Crystallographic details are
summarized in Table 1.
À
The mean Y C bond length (2.382(4) Š) of 3a is slightly
À
À
shorter than the expected value of a Y C bond of a CH2Si-
Abstract in German: Aminopyridinato-Ligand-stabilisierte
Organoyttrium-Kationen sind in sehr guten Ausbeuten via
Alkaneliminierung ausgehend von sterisch anspruchsvollen
Aminopyridinen und Trialkylyttrium-Komplexen und ans-
chließender Abstraktion einer der beiden Alkylfunktionen
durch Ammoniumborate zugänglich. Bei erhçhter Tempera-
tur (808C) und in Gegenwart geringer Mengen von Alkylalu-
minium-Verbindungen werden für solche Kationen sehr hohe
Aktivitäten in der Olefinpolymerisation beobachtet, wenn
sterisch äußerst anspruchsvolle Aminopyridinato-Liganden
zum Einsatz kommen. Während der Polymerisation erfolgt
ein reversibler Polyethylen-Kettentransfer zwischen den Or-
ganoyttrium-Kationen und den eingesetzten Alkylaluminium-
Verbindungen. Das hier beschriebene Kettentransfer-Kataly-
satorsystem eignet sich, um relativ langkettiges (bis zu
4000 gmolÀ1) Al terminiertes Polyethylen mit Molekularge-
wichtsverteilungen < 1.1 herzustellen. Bei der Darstellung
von hçhermolekularem PE nehmen die Verteilungen mit der
Kettenlänge zu (15600 gmolÀ1, ~1.4), da durch eine erhçhte
Viskosität und das “Ausfallen” von Polymerketten (Tempera-
turen von 80–1008C) eine reduzierte Reversibilität beobachtet
wird.
Scheme 2. Synthesis of 2a and 3a and molecular structure of the cation
of 3a (TiPP = 2,4,6-tri(isopropyl)phenyl, DiPP = 2,6-di(isopropyl)phen-
yl, R = CH3, R’ = C6H5, Ar = C6H5). Two independent cations were
À
found per asymmetric unit; selected bond lengths [Š]and angles [ 8] : Y
À
À
N1 2.302(3), Y N2 2.421(3), Y C 2.382(4); N1-Y-N2 57.41(11) Y-C-Si
143.8(2). The compounds 2b and 2c as well as 3b and 3c are synthesized
analogously to 2a and 3a using 1b and 1c, respectively, (Scheme 1) in-
stead of 1a.
(CH3)3 ligand (2.401 Š)[12] and goes along with the shorten-
ing expected because of the cationic nature of the yttrium
center. The mean Y-C-Si angle (143.8(2)8) of 3a is around
108 larger than the mean observed value of these ligands
(134.38).[13] NMR spectroscopic investigations of the organo-
yttrium cation 3a revealed similar coupling patterns as for
8970
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Chem. Eur. J. 2006, 12, 8969 – 8978

Al-Terminated Polyethylene
FULL PAPER
Table 1. Details of the X-ray crystal structure analyses of 3a, 3c, and 4.
Compound
3a
3c
4
crystal system
space group
triclinic
P1
triclinic
P1
triclinic
P1
¯
¯
¯
a [Š]13.258(2)
b [Š]20.221(3)
c [Š]27.745(4)
a [8]71.180(2)
b [8]80.953(2)
g [8]86.622(2)
V [Š3]6952.6(18)
11.8440(6)
14.7060(7)
18.8650(10)
76.945(4)
84.642(4)
84.478(4)
3177.4(3)
0.6”0.5”0.3
1.176
9.02
193(1)
1.43–25.75
27688
9.201(1)
10.786(1)
20.025(2)
99.345(2)
101.742(2)
93.622(2)
1910.4(3)
Figure 2. Molecular structure of 4. Selected bond lengths [Š]and angles
À
À
À
À
[8] : Al N1 1.935(2), Al N2 1.991(2), Al C33 1.965(3), Al C37 1.963(3);
N1-Al-N2 68.77(8), C33-Al-C37 120.34(12).
crystal size [mm3]0.5”0.4”0.2
0.4”0.3”0.1
0.80
1calcd [gcmÀ3]1.156
1.038
m [cmÀ1](Mo
T [K]100(1)
)
9.82
100(1)
2.29–28.08
11992
Ka
Organoyttrium-catalyzed ethylene polymerization, depend-
ence of the activity on the steric bulk of the aminopyridina-
to ligand: The Ap-ligand-stabilized (Ap = aminopyridinato)
organoyttrium cations can polymerize ethylene with very
high activity[14] in the presence of small amounts of alumi-
num alkyls (Table 2, entry 1). The presence of aluminum
q range [8]2.39–29.15
reflections unique
refl. obs. [I>2s(I)]17070
6856
9619
4253
no. of parameters
1523
0.1887
694
0.1609
402
0.1297
wR2 (all data)
R value [I>2s(I)]0.0636
0.0681
0.0597
Table 2. Ethylene polymerization activity—dependence of the steric bulk
of the Ap ligand.[a]
2a. Furthermore, the good thermal stability of 3a was ob-
served by NMR spectroscopy; over a period of several days
at room temperature no decomposition was detected.
As in the synthesis of 2a, reaction of 1b or 1c (Scheme 1)
Entry Ligand mPol. Activity
Mw
[gmolÀ1
]
Mw/Mn
À1
[g][kg
PEmolcat
A
hÀ1 barÀ1
]
with [Y
A
G
1
2
3
1a
1b
1c
13.4
5.0
5.4
1072
400
432
66500[b]
3.2
4.3 (1.5)
28.8 (2.4)
46100[b] (10800[c]
)
2b and 2c, respectively. Nearly quantitative yields were ob-
served by NMR spectroscopy. These dialkyls formed orga-
noyttrium cations in the presence of ammonium borates.
263900[b] (16300[c]
)
[a]Conditions: Dialkyl ( 2a–c): 10 mmol, ammonium borate: [R2N-
(CH3)H]+[B(C6F5)4]À (R
C16H31–C18H35), Y/B 1/1.1, aluminum
A
G
=
=
The reactions of 2b and 2c with [PhNMe2H][B(C6H5)4]gave
N
alkyl: TIBAO (tetraisobutylalumoxane), Y/Al = 1/20, 260 mL toluene,
temperature: 808C, pressure: 5 bar, time: 15 min. [b]Bimodal. [c] Mw of
the main fraction (>90%).
rise to 3b and 3c, respectively (Schemes 1 and 2). The struc-
ture of 3c was determined by X-ray crystallography
(Figure 1); crystallographic details are listed in Table 1.
In analogy to the trialkyl yttrium [Y
N
N
the aluminum trialkyl [Al{CH2CH(CH3)2}3]reacts almost
A
ACHTREUNG
quantitatively with one equivalent of 1a to give rise to the
aminopyridinato-ligand-stabilized aluminum dialkyl 4. The
structure of 4 was determined by X-ray crystallography
(Figure 2); crystallographic details are listed in Table 1.
alkyl is essential to observe polymerization activity (Table 4,
entry 1). The efficient steric shielding of the metal center
À
and/or the Y N bonds seems to be important to observe the
very high activities.
The reduction of the steric demand of the Ap ligand (1b
compared with 1a for instance (Scheme 1); 2,6-dimethyl-
phenyl instead of 2,4,6-triisopropylphenyl substituents at the
pyridine ring of the Ap ligand) goes along with a decrease
of the ethylene polymerization activity by about 60%. The
same behavior was found for the inversion of the substitu-
tion patterns of the sterically less demanding version (1c
versus 1b; 2,4,6-trimethylphenyl at the amido N atom in-
stead at the pyridine ring (Scheme 1)). Coordination chemi-
cal studies show that less bulky aminopyridinato ligands like
1b and 1c have the tendency to form bisaminopyridinato
complexes.[11b] We did not observe such species during the
formation of the corresponding cations 3b and 3c but can
not completely rule out that under catalytic conditions bisa-
minopyridinato complexes are formed by ligand redistribu-
tion and PE elimination. Such species can no longer catalyze
chain growth since they do not have a metal–carbon bond
into which to insert ethylene, and thus may contribute to the
slightly decreased activity.
Figure 1. Molecular structure of 3c. Selected bond lengths [Š]and angles
À
À
À
À
[8]: C30 Y1 2.376(4), N1 Y1 2.427(3), N2 Y1 2.273(3), Y1 O3 2.322(3),
À
À
Y1 O2 2.374(3), Y1 O1 2.361(3); O2-Y1-C30 159.34(13), O3-Y1-O1
109.88(10), N2-Y1-N1 57.81(10).
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R. Kempe, W. P. Kretschmer et al.
Temperature dependence of the organoyttrium-catalyzed
ethylene polymerization: Since the organoyttrium cations
based on 1a showed the highest ethylene polymerization ac-
tivity, we proceeded to explore these catalyst systems in
more detail. An extremely unusual temperature dependence
was observed (Table 3, Figure 3).
Table 3. Temperature dependence of the ethylene polymerization using
organoyttrium cations based on 1a.[a]
Entry
T
mpol.
Activity
Mw
[gmolÀ1
]
Mw/Mn
À1
[8C][g] [kg
PEmolcat
G
hÀ1 barÀ1
]
1
2
3
4
30
50
80
0.5
2.5
13.4
10.1
40
67900[b] (1950)[c]
76400[d]
43.0 (1.3)
19.1
3.2
Figure 3. Molecular-weight distribution (SEC) of the polymerization ex-
periments listed in Table 3.
200
1072
808
66500[d]
100
15600
1.4
[a]Conditions: 2a: 10 mmol, ammonium borate: [R2N
A
ACHTREUNG
308C run. After precipitation, two fractions are observed
(bimodal distribution: the fraction still soluble under the ap-
plied conditions and the precipitated fraction, the fraction
that most likely continues to grow). The improved solubility
Y/Al = 1/20, 260 mL toluene, pressure: 5 bar, time: 15 min. [b]Contains
a small amount of high molecular PE. [c] Mw of the main fraction
(>95%). [d]Bimodal distribution.
At 308C a mainly monomo-
dal distribution with a relative-
ly low molecular weight was
observed. At 508C a polymer
with a bimodal distribution is
observed. One of the distribu-
tions shows a molecular weight
similar to the main fraction of
the 308C run, the second has a
significantly higher Mw. At
808C an overlapping bimodal
distribution can be seen, also
with an increase of the mean
molecular weight with increas-
ing temperature. At 1008C the
polymerization
under
the
given conditions (Table 3)
again produces a monomodal
distribution.
The overall trend from 30 to
808C is an unusual increase in
activity together with an in-
Scheme 3. Proposed mechanism for the organoyttrium cation catalyzed ethylene polymerization.
crease in the molecular weight. These observations could be
explained by a reversible chain transfer[3] between the orga-
noyttrium cation—responsible for chain growth—and the
aluminum center—responsible for chain storage in combina-
tion with (partial) precipitation of PE (Scheme 3). At 308C,
relatively slow chain growth proceeds (blocking of the
active side by strongly bonded aluminum alkyls at low tem-
perature), giving rise to a short, narrowly distributed and
soluble Al-terminated main fraction. At 50 and 808C, chain
growth proceeds much faster, and since the same number of
chains is grown, longer chains that precipitate are produced.
Substantial amounts of precipitated polymer were observed
at 50 and 808C, whereas only traces were obtained for the
at 808C relative to 508C leads to overlapping bimodal distri-
bution at this temperature and to a monomodal distribution
at 1008C (Figure 3). NMR spectroscopy of the polymers ob-
tained (after hydrolytic workup) revealed saturated poly-
mers with isopropyl end groups (Figure 4). Even at 1008C
nearly no b-H elimination takes place, indicating that chain
transfer is much faster than b-H elimination. Increasing the
aluminum-to-yttrium ratio (Table 4) is accompanied by an
increase in the intensity of the end-group proton NMR
signal relative to the PE signal (Figure 5). The PE signal
also becomes very narrow, indicating a very narrow molecu-
lar weight distribution if the appropriate aluminum-to-yttri-
um ratio is used.
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Al-Terminated Polyethylene
FULL PAPER
Figure 6. Time-dependent increase in the molecular weight of the poly-
Figure 4. 1H NMR spectrum (C2D2Cl4, 1208C) of isopropyl-terminated
PE (Table 3, entry 4).
mers (SEC). Conditions: 2a: 10 mmol, ammonium borate: [R2N
[B
(C6F5)4]À (R = C16H31–C18H35), Y/B = 1/1.1, aluminum alkyl: TIBAO,
Y/Al = 1/150, 260 mL toluene, pressure: 5 bar.
A
AHCTREUNG
Figure 5. 1H NMR spectra (C2D2Cl4, 1208C) of PE produced by polymer-
ization runs (Table 4).
Figure 7. Influence of polymer precipitation on the molecular-weight dis-
tribution (SEC); before (15 min), at the beginning of (22 min,) and after
(30 min) precipitation (Table 4, entries 4, 6, and 7).
Time dependence of the chain growth: In the organoyttri-
um-cation-catalyzed ethylene polymerization, two major pe-
riods can be distinguished. In the first “homogeneous”
period, slow continuous ethylene consumption together with
an increase of the molecular weight but without significant
broadening[15] of the distribution (Figure 6) is observed.
With ongoing chain growth, partial polymer precipitation
occurs together with a strong increase in ethylene uptake;
this is the second “heterogeneous” period. In Figure 7 the
molecular-weight distributions before, at, and after the pre-
cipitation point are shown. It can be seen that polymeriza-
tion continues up to the precipitation point without signifi-
cant broadening of the molecular weight. Beyond the pre-
cipitation point a bimodal distribution is observed. It seems
(as mentioned above) that only the precipitated chain
grows, while the molecular weight of the lower Mn fraction
is barely raised with increasing time. This indicates that with
reduced reversibility due to higher viscosity, fast multiple
ethylene insertion into the active organoyttrium species
(Scheme 3) occurs, which then precipitates with an attached
polymer chain and continues to grow heterogeneously.
Dependence of the ethylene polymerization on the alumi-
num alkyl used and the aluminum-to-yttrium ratio: Reaction
temperature, polymerization time, and the aluminum-to-yt-
trium ratio can be tuned to ensure that the Al-terminated
PE stays soluble during the polymerization process and
allows for the synthesis of very narrowly distributed poly-
mers (Table 4, entries 4 and 5, Figure 8). The stability of the
organoyttrium cations in combination with a nearly sup-
pressed b-H elimination at even 1008C allows for the syn-
thesis of relatively long-chain polymers with a polydispersity
<1.1. Increasing viscosity and precipitation of the Al-termi-
nated polymer chains results in a reduction of the reversibil-
ity of the chain transfer and thus broader polydispersities
are observed.
The Mortreux system, which allows operation at elevated
temperatures, shows mainly a-olefin side products at
1008C.[3a] Transition-metal-based chain-transfer catalyst sys-
tems[5] are intended to work at room temperature, which re-
stricts the production of long-chain polymers, most likely be-
cause of solubility problems. Molecular weights with a dis-
persity of around 1.1 up to a Mw of about 1200 gmolÀ1 are
Chem. Eur. J. 2006, 12, 8969 – 8978
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8973

R. Kempe, W. P. Kretschmer et al.
Table 4. Ethylene polymerization catalyzed by 2a as a function of the
ethylene polymerization activity. This behavior can best be
explained by the stronger coordination of the aluminum tri-
alkyls to the organoyttrium cation,[1,2] relative to the less
electron-rich aluminoxanes. This results in a shift of the
equilibrium between “free” organoyttrium, able to insert
ethylene, and the yttrium–aluminum complex responsible
for chain transfer (Scheme 3). Aluminum cations stabilized
by aminopyridinato ligands are nearly inactive in ethylene
polymerization. The activation of 4 with ammonium borates
aluminium-to-yttrium ratio.[a]
Entry
Al:Y
mpol.
Activity
Mw
[gmolÀ1
]
Mw/Mn
À1
[mol/mol][g] [kg
PE molcat
G
hÀ1 barÀ1
]
1
2
3
4
5
6
7
8
0
5
20
50
100
50[c]
50[d]
100[d]
0
0
n.d.
n.d.
2.3
3.2
1.09
1.05
1.4
13.5
13.4
4.7
2.1
7.5
14.5
6.0
1080
1072
376
168
409
580
240
88100
66500[b]
3940
1460
5920
(10 mmol, ammonium borate: [R2N
N
N
73900
5830
7.7
1.3
(R C16H31–C18H35), Al/B 1/1.1, aluminum alkyl:
=
=
TIBAO, Al/Al = 1/20, 260 mL toluene, pressure: 5 bar,
15 min) under the same conditions applied for 2a (Table 3,
entry 3) results in an activity of 8 kgPE molcatÀ1 hÀ1 barÀ1. In
other words, the yttrium-free catalyst system is not able to
accomplish the chain growth that leads to the polymeric ma-
terials described above. By varying the substituents at the
aluminum alkyl and the workup, alcohol derivatives are ac-
cessible. For examples, see Figures 9–11.
[a]Conditions: 2a: 10 mmol, ammonium borate: [R2N
A
ACHTREUNG
260 mL toluene, pressure: 5 bar. [b]Bimodal. [c]22 min run time.
[d]30 min run time.
Figure 8. Molecular-weight distribution (SEC) of the polymerization ex-
periments listed in Table 4, entries 2–5.
described for these catalyst systems, which corresponds to
about 43 ethylene insertions per growing chain.
Figure 9. 1H NMR spectrum (C2D2Cl4, 1208C) of PE after oxidative
workup (Table 4, entry 6).
As shown in Table 5, the organoyttrium-cation-catalyzed
chain growth on aluminum is not limited to TIBAO them-
selves, but can be carried out with a wide variety of alumi-
num alkyls. However, the use of partially hydrolyzed alumi-
num alkyls seems to have a strong beneficial effect on the
Table 5. Ethylene polymerization catalyzed by 2a: influence of the alu-
minum alkyl.[a]
Entry Al-alkyl
Al/Y mpol.
Activity Mw
[gmolÀ1
Mw/Mn
À1
A
PE molcat
G
]
hÀ1 barÀ1
]
1
2
3
4
5
6
7
TOA
TIBA
100
100
100
100
100
5
0.5
0.9
4.3
1.9
2.1
4.6
1.9
40
80
n.d.
n.d.
n.d.
n.d.
1.2
1.1
1.05
TIBA[a]
TOAO
TIBAO
TPPAO
TPPAO
129
152
168
368
152
2660
2580
1460
111000 2.1
2770 1.2
50
[a]Conditions: 2a: 10 mmol, ammonium borate: [R2N
ACHTREUNG
A
Figure 10. 1H NMR spectrum (C2D2Cl4, 1208C) of PE after oxidative
workup (Table 5, entry 4).
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Chem. Eur. J. 2006, 12, 8969 – 8978

Al-Terminated Polyethylene
FULL PAPER
25 wt% in toluene, Aldrich), tri-n-octylaluminum (TOA, 25 wt% in tol-
uene, Aldrich) and TIBA (Witco) were used as received.
[Y
A
G
N,N-dimethylanilinium(tetraphenyl)borate
(C6H5)4]),[17] tetra-isobutylaluminoxane ([i-Bu2Al]2O,
([C6H5NH
G
TIBAO),[18] tetra-n-octylaluminoxane ([Oct2Al]2O, TOAO),[18] tetra-(2-
phenyl-)propylaluminoxane ([CH3CH(Ph)CH2]2Al}2O, TPPAO),[18] 1a,
and 1b[11a] were prepared according to published procedures.
Preparation of 1-MgBr-[2,4,6-iPr3C6H2]: Magnesium turnings (0.94 g,
38.7 mmol) were added to 1-Br-[2,4,6-iPr3C6H2](35.2 mmol, 9.97 g) in
THF (30 mL) and activated using 1,2-dibromoethane. When the resulting
suspension was stirred, an exothermic reaction took place and an ice
bath was used to cool the mixture if it became too vigorous. After about
2 h the reaction mixture was cooled, stirred overnight, and filtered. The
filtrate was used directly in the preparation of B.
Preparation of B: 2,6-Dibromopyridine (7.91 g, 33.4 mmol), THF
(35 mL), tricyclohexylphosphine (0.075 mmol), and [(dme)NiBr2]
(0.012 g, 0.0375 mmol) were added together in a Schlenk flask under
argon. The Grignard reagent described above was then added to the stir-
red suspension resulting in a beige precipitate. The reaction mixture was
kept at 508C for 72 h. Water and CHCl3 were added and the resulting
suspension transferred to a separating funnel. The organic phase was col-
lected and the residue extracted with CHCl3 (2”). The combined organic
phases were washed with a saturated NaCl
Figure 11. 1H NMR spectrum (C2D2Cl4, 1208C) of PE after oxidative
workup (Table 5, entry 6).
Conclusion
Aminopyridinato-ligand-stabilized organoyttrium cations
can show very high ethylene polymerization activity in the
presence of small amounts of aluminum alkyl compounds
(trialkyls and aluminoxanes) at elevated temperature. Re-
versible polyethylene chain transfer between the organoyt-
trium cations and the aluminum compounds can be ob-
served. Since b-H elimination is nearly suppressed even at
1008C, relatively high-molecular-weight Al-terminated poly-
mer chains with a very narrow polydispersity can be pro-
duced.
solution and dried over Na2SO4. The solvent
was removed to afford a white precipitate,
which was recrystallized from hexane
(20 mL) (7.05 g, yield 58%). M.p. 232–2338C;
1H NMR (250.13 MHz, CDCl3, 298 K): d =
1.00–1.30 (m, 18H; CH3), 2.44 (sept, 2H;
H13,15), 2.88 (sept, 1H; H14), 7.02 (s, 2H;
H9,11), 7.21 (d, 3J = 7.4 Hz, 1H; H5), 7.43 (d,
3
3J = 8.0 Hz, 1H; H3), 7.59 ppm (dd, J = 8.0,
3J = 7.4 Hz, 1H; H4); 13C NMR (62.9 MHz,
CDCl3, 298 K): d = 23.8 (s; CH3), 24.1 (s; CH3), 24.2 (s; CH3), 30.4 (s;
C13,15), 34.4 (s; C14), 120.8 (s; C9,11), 123.9 (s; C3,5), 125.9 (s; C3,5), 134.9 (s;
C7), 137.9 (s; C4), 141.5 (s; C2), 146.1 (s; C8,12), 149.3 (s; C10), 161.3 ppm
(s; C6); elemental analysis calcd (%) for C20H26BrN (360.3): C 66.67, H
7.27, N 3.89; found: C 67.56, H 7.48, N 3.78.
Experimental Section
Preparation of 1c: Compound B (2.75 g, 7.63 mmol), 1,3-bis(diphenyl-
phosphino)propane (0.12 g, 0.28 mmol), tris(dibenzylideneacetone) dipal-
ladium(0) (0.13 g, 0.14 mmol), and sodium tert-butoxide (0.83 g,
8.6 mmol) were loaded into a Schlenk tube. After adding 2,4,6-trimethyl-
phenylamine (1.03 g, 7.63 mmol) in toluene (30 mL) the resulting mixture
was heated at about 958C for 24 h. The reaction mixture was cooled to
room temperature, and subsequently water (50 mL) and diethyl ether
(50 mL) were added. The organic phase was separated and the remaining
residue extracted with diethyl ether (3”20 mL). The combined organic
phases were washed with a saturated NaCl solution and dried over
Na2SO4. The solvent was removed under reduced pressure and the result-
ing red solid was purified by using column chromatography (SiO2/
CH2Cl2). Recrystallization at À308C from pentane or hexane afforded
white crystalline materials (2.05 g, 65%). 1H NMR (250.13 MHz, CDCl3,
298 K): d = 1.12 (d, 3J = 6.9 Hz, 6H; H14,15,17,18), 1.18 (d, 3J = 6.9 Hz,
6H; H14,15,17,18), 1.26 (d, 3J = 7.0 Hz, 6H; H20,21),
General: All manipulations of air- or moisture-sensitive compounds were
carried out under N2 using glove-box, standard Schlenk, or vacuum-line
techniques. Solvents and reagents were purified by distillation from
LiAlH4, potassium, Na/K alloy, or sodium ketyl of benzophenone under
nitrogen immediately before use. Toluene (Aldrich, anhydrous, 99.8%)
was passed over columns of Al2O3 (Fluka), BASF R3–11 supported Cu
oxygen scavenger, and molecular sieves (Aldrich, 4 Š). Ethylene (AGA
polymer grade) was passed over BASF R3–11 supported Cu oxygen scav-
enger and molecular sieves (Aldrich, 4 Š).
NMR spectra were recorded on a Varian Gemini 400 (1H: 400 MHz, 13C:
100.5 MHz) or Varian VXR-300 (1H: 300 MHz, 13C: 75.4 MHz) spectrom-
eter. The 1H and 13C NMR spectra, measured at 258C and 1208C, were
referenced internally using the residual solvent resonances, and the
chemical shifts (d) reported in ppm. The polymer samples were prepared
by dissolving 15 mg of the polymer in 0.5 mL CD2Cl2 at 1008C for 3 h
before measuring.
2.20 (s, 6H; H28,29), 2.30 (s, 3H; H30), 2.69 (sept,
3J = 6.9 Hz, 2H; H13,16), 2.91 (sept, 3J = 7.0 Hz,
Gel permeation chromatography (GPC) analysis was carried out on a
Polymer Laboratories Ltd. (PL-GPC210) chromatograph at 1508C using
1,2,4-trichlorobenzene as the mobile phase. The samples were prepared
by dissolving the polymer (0.1% weight/volume) in the mobile phase sol-
vent in an external oven and were run without filtration. The molecular
weight was referenced to polyethylene (Mw = 50000 gmolÀ1) and poly-
styrene (Mw = 100000–500000 gmolÀ1) standards. The reported values
are the average of at least two independent determinations.
1H; H19), 5.92 (dd, 3J = 8.3 Hz, 4J = 0.8 Hz,
1H; H3), 5.97 (br, 1H; HNH), 6.61 (dd, 3J = 7.2,
4J = 0.8 Hz, 1H; H5), 6.95 (s, 2H; H9,11/24,26), 7.05
(s, 2H; H9,11/24,26), 7.37 ppm (dd, 3J = 8.3, 3J =
7.2 Hz, 1H; H4); 13C NMR (62.9 MHz, CDCl3,
298 K): d = 18.2 (s; C28,29), 20.9 (s; C30), 24.0 (s;
C14,15/17,18/20,21), 24.1 (s; C14,15/17,18/20,21), 24.5 (s;
C14,15/17,18/20,21), 30.3 (s; C13,16), 34.5 (s; C19), 103.1
Ligand and complex synthesis: N,N-dimethylanilinium(tetrapentafluoro-
(s; C3), 114.8 (s; C5), 120.7 (s; C9,11/24,26), 129.2 (s;
phenyl)borate ([PhNMe2H][B(C6F5)4], Strem), N,N,N-trialkylammo-
E
C9,11/24,26), 134.3 (s; C7), 136.3 (s; C10), 136.7 (s;
nium(tetrapentafluorophenyl)borate ([R2NMeH][B
A
À
C18H35, 6.2 wt% B(C6F5)4 in Isopar, DOW Chemicals), trimethylalumi-
A
C8,12/27,29), 137.4 (s; C25), 146.0 (s; C8,12/27,29), 148.3
num (TMA, 2.0m in toluene, Aldrich), tri-isobutylaluminum (TIBA,
(s; C4), 157.7 (s; C6), 158.6 ppm (s; C2) (two sig-
Chem. Eur. J. 2006, 12, 8969 – 8978
ꢀ 2006 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
www.chemeurj.org
8975

R. Kempe, W. P. Kretschmer et al.
nals seem to be isochronic); elemental analysis calcd (%) for C29H38N2
(414.63): C 84.01, H 9.24, N 6.76; found: C 84.10, H 9.35, N 6.20.
C3), 111.0 (s; C5), 121.2 (s; C9,11), 129.6 (s; C24,26), 132.6 (s; C25), 133.0 (s;
C23,27), 136.0 (s; C7), 139.8 (s; C4), 144.0 (s; C22), 146.7 (s; C8,12), 149.6 (s;
C10), 156.1 (d; C6), 169.7 ppm (s; C2).
Synthesis of bis(trimethylsilylmethyl)-aminopyridinato-yttrium(tetrahy-
drofurane) complexes 2a–2c: The desired amino pyridine ligand Ap’H
(0.1 mmol: 1a, 45.6 mg; 1b, 41.5 mg; 1c, 33.0 mg; Scheme 1) was dis-
solved in toluene (2 mL) and slowly added to an ice-cooled solution of
Synthesis of 3a: [Y
N
N
in toluene (1 mL), before a solution of 1a (1 mL, 0.3m in toluene,
0.30 mmol) was added. After stirring the mixture for 5 min it was com-
[Y
mixture had been stirred for 30 min, all volatiles were removed to yield
the corresponding, spectroscopically pure [Ap’Y(CH2SiMe3)2(thf)](based
on H NMR, 2a–2c, Scheme 2) as a pale yellow residue in almost quanti-
tative yield.
A
G
bined with
a
suspension of [C6H5NH
U
G
0.30 mmol) in toluene/THF (1.5 mL, 60/40 mol%), and repeatedly
shaken until a clear solution was observed. The slightly yellow oil was
layered with hexane (3.5 mL) and kept at room temperature overnight.
After 12 h colorless crystals were obtained, which were decanted from
the mother liquor and dried, yielding 247 mg
2a: 1H NMR (400 MHz, C6D6, 298 K): d = À0.42 (d, 4H, 2J
U
(68%) of 3a·(C6H14)0,5.
1H NMR (400 MHz,
G
[D8]THF, 298 K): d = À0.61 (d, 2H, 2J
A
3
3
6H, J
(H,H) = 6.8 Hz; H28,29,32,33), 1.18 (d, 6H, J(H,H) = 6.8 Hz; H30,31),
G
ACHTREUNG
= 3.0 Hz; HYCH2), À0.18 (s, 9H; HSiMe3), 1.03
1.24 (d, 6H, 3J
1.32 (d, 6H, 3J
1.56 (d, 6H, 3J
A
=
=
=
6.8 Hz; H24,25,26,27),
6.8 Hz; H24,25,26,27),
6.8 Hz; H28,29,32,33),
(d, 12H, 3J 7.0 Hz; H28,29,30,31,32,33),
(H,H) =
G
AHCTREUNG
1.20 (d, 6H, 3J
1.27 (d, 6H, 3J
1.30 (d, 6H, 3J
U
=
=
=
7.0 Hz; H24,25,26,27),
7.0 Hz; H24,25,26,27),
7.0 Hz; H28,29,32,33),
AHCTREUNG
2.88 (sept, 1H, 3J(H,H) = 6.8 Hz; H15), 3.11
R
AHCTREUNG
(sept, 2H, 3J
(sept, 2H, 3J(H,H) = 6.8 Hz; H22,23), 3.60 (br,
4H; a-CH2, THF), 5.65 (d, 1H, 3J
(H,H)
8.4 Hz; H3), 6.09 (d, 1H, 3J
(H,H) = 7.2 Hz;
H5), 6.75 (dd, 1H, 3J(H,H) = 8.4, 3J
(H,H) =
(H,H) =
6.8 Hz; H13,14), 3.42
AHCTREUNG
1.73 (m, 12H; b-CH2, THF), 2.82 (sept, 2H,
3J(H,H) = 7.0 Hz; H13,14), 2.93 (sept, 2H, 3J-
(H,H) = 7.0 Hz; H15), 3.22 (sept, 2H, 3J
(H,H)
= 7.0 Hz; H22,23), 3.57 (m, 12H; a-CH2, THF),
5.74 (dd, 1H, 3J 8.8, 4J
(H,H) (H,H)
0.7 Hz; H3), 6.22 (dd, 1H, 3J(H,H) = 7.0, 4J-
(H,H) = 0.7 Hz; H5), 6.66 (tt, 4H, 3J
(H,H) =
7.0, 4J(H,H) = 1.4 Hz; HBC6H5), 6.80 (m, 8H,
3J 7.0 Hz; HBC6H5), 7.12–7.22 (m,
(H,H)
13H; H9,11,18,19,20/BC6H5), 7.25 ppm (dd, 1H, 3J
AHCTREUNG
AHCTREUNG
E
H
ACHTREUNG
AHCTREUNG
A
ACHTREUNG
7.2 Hz; H4), 7.10 (m, 2H; H18,20), 7.16 (m, 1H;
H19), 7.25 ppm (m, 2H; H9,11); 13C NMR
(100 MHz, C6D6, 298 K): d = 4.1 (s; CSiMe3),
23.6 (s; C28,29,32,33), 24.3 (s; C24,25,26,27), 24.4 (s;
C28,29,32,33), 24.9 (s; C24,25,26,27), 25.2 (s; b-CH2,
THF), 26.7 (s; C30,31), 28.8 (s; C22,23), 30.9 (s;
A
=
A
=
AHCTREUNG
G
ACHTREUNG
AHCTREUNG
A
=
U
A
7.0 Hz; H4); 13C NMR (100 MHz, [D8]THF, 298 K): d = 5.1 (s; CSiMe3),
24.7 (s; C28,29,32,33), 25.5 (s; C24,25,26,27), 25.6 (s; C30,31), 26.6 (s; C24,25,26,27),
27.3 (br; b-CH2, THF), 27.6 (s; C28,29,32,33), 29.8 (s; C22,23), 32.3 (s; C13,14),
C13,14), 35.0 (s; C15), 39.8 (d, 1J
C
G
A
121.2 (s; C9,11), 124.2 (s; C18,20), 124.9 (s; C19), 136.0 (s; C7), 139.4 (s; C4),
36.4 (s; C15), 41.0 (d, 2J(Y,C) = 42.9 Hz; CYCH2), 69.2 (s; a-CH2, THF),
E
2
144.0 (s; C17,21), 144.5 (d, J
C
110.1 (s; C3), 114.6 (s; C5), 122.9 (s; C9,11), 123.1 (s; CBC6H5), 126.3 (s;
C18,20), 126.7 (m; CBC6H5), 127.2 (s; C19), 137.2 (s; C7), 138.1 (m; CBC6H5),
C10), 156.0 (d, 2J
G
G
C2).
141.4 (s; C4), 144.8 (s; C16), 145.5 (s; C17,21), 148.7 (s; C8,12), 152.3 (s; C10),
2b: 1H NMR (400 MHz, C6D6, 298 K): d = À0.46 (d, 4H, 2J
C
156.4 (s; C6), 166.2 (q, J
A
1
6H, 3J
H22,23,25,26), 2.36 (s, 6H; H13,14), 3.39 (sept, 2H, 3J
3.70 (br, 4H; a-CH2, THF), 5.59 (d, 1H, 3J-
(H,H) = 8.4 Hz; H3), 5.81 (d, 1H, 3J
(H,H) =
6.6 Hz; H5), 6.79 (dd, 1H, 3J(H,H) = 8.4, 3J-
(H,H) = 6.6 Hz; H4), 7.08 (m, 2H; H17,19), 7.15
(m, 2H; H10,18), 7.18 ppm (m, 2H; H9,11); 13C
A
=
7.0 Hz; H22,23,25,26), 1.22 (d, 6H, 3J
C
mental analysis calcd (%) for [C48H78N2O3SiY]
(1210.47): C 74.42, H 8.74, N 2.31, Y 7.34; found: C 75.11, H 8.53, N 2.09,
Y 7.10.
N
G
AHCTREUNG
Synthesis of 3b and 3c: [Y
A
N
A
ACHTREUNG
dissolved in benzene/THF (0.5 mL, 80:20 vol%), before a solution of 1b
or 1c (0.5 mL, 0.22m in benzene, 0.11 mmol) was added. After stirring
the mixture for 5 min, it was combined with a suspension of [C6H5NH-
AHCTREUNG
AHCTREUNG
A
N
NMR (100 MHz, C6D6, 298 K): d
= 4.2 (s;
CSiMe3), 20.7 (s; C13,14), 24.3 (s; C22,23,25,26), 24.8
80:20 vol%), and repeatedly shaken until a clear solution was observed.
The slightly yellow oil was layered with hexane (3.5 mL) and kept at
room temperature. After three days pale yellow crystals were observed,
which were decanted from the mother liquor and dried, yielding 75 mg
(61%) of 3b or 95 mg (73%) of 3c.
(s; C22,23,25,26), 25.3 (s; b-CH2, THF), 28.7 (s;
1
C21,24), 39.2 (d, J
A
(s; a-CH2, THF), 106.1 (s; C3), 108.3 (s; C5),
121.1 (s; C17,19), 124.9 (s; C18), 128.1 (s; C9,11),
128.7 (s; C10), 135.8 (s; C7), 140.6 (s; C4), 144.0
3b: 1H NMR (400 MHz, C6D6, 298 K): d = À0.61 (d, 2H, 2J
ACHTREUNG
(s; C16,20), 144.2 (s; C15), 156.0 (s; C6), 169.6 ppm (s; C2).
3.1 Hz; HYCH2), 0.06 (s, 9H; HSiMe3), 1.04 (d, 6H, 3J
(H,H) =
A
H22,23,25,26), 1.19 (d, 6H, 3J
THF), 2.00 (s, 6H; H13,14), 3.14 (sept, 2H, J
(br; a-CH2, THF), 5.54 (d, 1H, 3J(H,H) = 8.4 Hz; H3), 5.67 (d, 1H, 3J-
(H,H) = 7.0 Hz; H5), 6.70 (dd, 1H, 3J(H,H) = 8.4, 3J
(H,H) = 7.0 Hz;
H4), 6.90 (d, 2H, 3J(H,H) = 7.7 Hz; H9,11,17,19),
7.02 (t, 1H, 3J(H,H) = 7.7 Hz; H10,18), 7.12–7.25
(H,H) = 6.6 Hz; H22,23,25,26), 1.41 (br; b-CH2,
2c: 1H NMR (400 MHz, C6D6, 298 K): d = À0.41 (d, 4H, 2J
A
(H,H) = 6.6 Hz; H21,24), 3.49
3
3.1 Hz; HYCH2), 0.22 (s, 18H; HSiMe3), 1.18 (d, 6H, 3J
ACHTREUNG
H14,15,17,18), 1.24 (br, 4H; b-CH2, THF), 1.32 (d, 6H, 3J
H14,15,17,18), 1.55 (d, 6H, 3J
AHCTREUNG
AHCTREUNG
G
U
ACHTREUNG
A
=
AHCTREUNG
AHCTREUNG
AHCTREUNG
(m, 15H; H9,11,17–20, BC6H5), 7.89 ppm (br, 8H;
Ho-BC6H5); 13C NMR (100 MHz, C6D6, 298 K): d =
4.1 (s, CSiMe3), 20.5 (s, C13,14), 24.5 (s; C22,23,25,26),
25.3 (s; C22,23,25,26), 25.6 (s; b-CH2, THF), 28.1 (s;
AHCTREUNG
3
ACHTREUNG
CH2, THF), 5.70 (d, 1H, J
6.12 (d, 1H, 3J
ACHTREUNG
3
3
ACHTREUNG
1H, J
A
(H,H) = 6.9 Hz; H4), 6.88
C21.24), 39.6 (d, 1J(Y,C) = 43.7 Hz; CYCH2), 68.8
U
(s, 2H; H24,26), 7.25 ppm (s, 2H; H9,11); 13C NMR
(100 MHz, C6D6, 298 K): d = 4.2 (s; CSiMe3), 19.1
(s; C28,29), 20.9 (s; C30), 23.6 (s; C14,15,17,18), 24.4 (s;
C14,15,17,18), 25.2 (s; b-CH2, THF), 26.7 (s; C20,21),
(s; a-CH2, THF), 107.9 (s; C3), 110.1 (s; C5),
122.2 (s; CBC6H5), 124.1 (s; C18), 124.8 (s; C17,19),
126.0 (m; CBC6H5), 129.2 (s; C9,11), 136.0 (s; C7),
137.1 (m; CBC6H5), 139.6 (s; C), 140.3 (s; C), 140.6
(s; C4), 142.5 (s; C16,20), 143.8 (s; C15), 154.7 (s;
30.9 (s; C13,16), 35.0 (s; C19), 39.8 (d, 1J
39.1 Hz; CYCH2), 69.2 (s; a-CH2, THF), 105.1 (s;
A
8976
www.chemeurj.org
ꢀ 2006 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
Chem. Eur. J. 2006, 12, 8969 – 8978

Al-Terminated Polyethylene
FULL PAPER
C6), 165.0 (q, 1J
analysis calcd (%) for [C41H64N2O3SiY]
ACHTREUNG
AHCTREUNG
7.92, N 2.61; found: C 72.92, H 7.75, N 2.35.
3c: 1H NMR (400 MHz, C6D6, 298 K): d = À0.61 (d, 2H, 2J
C
3.0 Hz; HYCH2), 0.08 (s, 9H; HSiMe3), 1.04 (d, 6H, 3J
G
H14,15,17,18), 1.21 (d, 6H, 3J
H14,15,17,18), 1.22 (d, 6H, 3J
C
=
=
H28,29), 2.25 (s, 3H; H30), 2.74 (sept, 1H, J
=
6.6 Hz; H19), 2.78 (sept, 2H, 3J
6.6 Hz; H13,16), 3.44 (br; a-CH2, THF), 5.67 (d,
1H, 3J 8.8 Hz; H3), 6.00 (d, 1H, 3J-
(H,H)
(H,H) = 6.9 Hz; H5), 6.71 (dd, 1H, 3J
(H,H) =
A
A
=
N
ACHTREUNG
8.8, 3J 6.9 Hz; H4), 6.90 (s, 2H;
(H,H) =
T
298 K): d = 0.47 (dd, 2H, 2J
N
ACHTREUNG
H9,11,24.26), 7.06 (s, 2H; H9,11,24.26), 7.12–7.28 (m,
12H; HBC6H5), 7.91 ppm (br, 8H; Ho-BC6H5); 13C
2
3
ACHTREUNG
0.54 (dd, 2H, J
A
H
NMR (100 MHz, C6D6, 298 K):
d = 4.2 (s;
CSiMe3), 19.4 (s; C28,29), 20.9 (s; C30), 23.6 (s;
A
ACHTREUNG
C14,15,17,18), 24.3 (s; C14,15,17,18), 25.6 (s; b-CH2,
AHCTREUNG
(H,H) = 7.0 Hz; H24–33,38–41), 1.41 (d, 6H, 3J(H,H) = 7.0 Hz; H24–33,38–41),
E
THF), 26.6 (s; C20,21), 30.7 (s; C13,16), 34.7 (s;
2.04 (m, 2H, 3J
A
=
6.6 Hz; H35,37), 2.80 (sept, 1H, 3J
C
=
1
C19), 39.0 (d, J
A
6.6 Hz; H15), 2.90 (sept, 2H, J
(H,H) = 6.6 Hz; H13,14), 3.55 (sept, 2H, J-
3
3
a-CH2, THF), 106.7 (s; C3), 112.2 (s; C5), 121.3
(s; C9,11), 122.3 (s; CBC6H5), 126.1 (m; CBC6H5),
3
4
ACHTREUNG
N
U
130.2 (s; C24,26), 132.6 (s; C25), 134.0 (s; C23,27), 135.4 (s; C7), 137.1 (m;
CBC6H5), 140.1 (s; C4), 142.1 (s; C22), 147.2 (s; C8,12), 150.7 (s; C10), 154.7
ACHTREUNG
A
(s; C6), 165.0 (q, 1J
(C,B) = 49.1 Hz; CBC6H5), 168.6 ppm (d, 2J
ACHTREUNG
=
CAlCH2), 22.8 (C28,29,32,33), 24.2 (C24,25,26,27), 24.6 (C28,29,32,33), 24.9 (C24,25,26,27),
26.4 (C38,39,40,41), 26.5 (C38,39,40,41), 27.8 (C30,31), 28.4 (C35,37), 28.7 (C22,23),
30.8 (C13,14), 34.9 (C15), 104.9 (C3), 111.5 (C5), 121.0 (C9,11), 124.4 (C18,20),
126.3 (C19), 138.3 (C7), 139.4 (C4), 141.0 (C17,21), 145.7 (C16), 146.8 (C8,12),
150.2 (C10), 154.7 (C6), 167.3 ppm (C2); elemental analysis calcd (%) for
C40H61AlN2 (596.92): C 80.49, H 10.30, N 4.69; found: C 80.53, H 10.41,
N 4.53.
2.3 Hz; C2); elemental analysis calcd (%) for [C45H72N2O3SiY]
ACHTREUNG
AHCTREUNG
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20 mmol). Afterwards the tube was sealed and shaken for 5 min to form a
clear solution before measurement.
Polymerization studies:
3a’: 1H NMR (400 MHz, C6D6, 298 K): d = À0.51 (d, 2J
ACHTREUNG
2H; HYCH2), 0.0 (br, 18H; HSiMe3,SiMe4), 1.01 (d, 6H, 3J
ACHTREUNG
General description of polymerization experiments: The catalytic ethylene
polymerization reactions were performed in a stainless steel 1 L auto-
clave (Medimex) in semibatch mode (ethylene was added by replenishing
flow to keep the pressure constant). The reactor was temperature- and
pressure-controlled and equipped with separated toluene, catalyst, and
cocatalyst injection systems, and a sample outlet for continuous reaction
monitoring. Multiple injection of the catalyst with a pneumatically oper-
ated catalyst injection system was used at an ethylene pressure of 5 bar.
During a polymerization run, the pressure, ethylene flow, inner and outer
reactor temperature, and stirrer speed were monitored continuously. In a
typical semibatch experiment, the autoclave was evacuated and heated
for 1 h at 1258C prior to use. The reactor was then brought to the desired
temperature, stirred at 600 rpm, and charged with toluene (230 mL) to-
gether with trialkylammonium (tetrapentafluorophenyl)borate (11 mmol,
0.12 g) and the required amount of aluminum scavenger (1 mL of a 0.1m
stock). After pressurizing with ethylene to reach a total pressure of 5 bar,
the autoclave was equilibrated for 5 min. Subsequently aminopyridina-
toyttrium dialkyl complex (1 mL, 0.01m stock solution in toluene) togeth-
er with toluene (30 mL) was injected to start the reaction. During the run
the ethylene pressure was kept constant to within 0.2 bar of the initial
pressure by replenishing flow. After the desired reaction time the reactor
was vented and the residual aluminum alkyls were destroyed by addition
of ethanol (100 mL). In the case of subsequent oxidation, the reactor was
vented and stirred for 1 h at 808C under an atmosphere of dry air before
ethanol (100 mL) was added. 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
vacuum at 808C.
H28,29,30,31,32,33), 1.03 (d, 6H, 3J
H28,29,30,31,32,33), 1.20 (d, 6H, 3J
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AHCTREUNG
H28,29,32,33), 1.22 (d, 12H, 3J
G
=
HNMe2), 2.77 (sept, 3H, 3J
H13,14,15), 3.15 (sept, 2H, 3J
U
=
=
7.0 Hz;
G
7.0 Hz;
3
R
(H,H) =
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H
A
=
AHCTREUNG
7.08 (s, 2H; H9,11), 7.12–7.25 ppm (m, 5H;
H18,19,20,C6H5N); 13C NMR (100 MHz, C6D6,
298 K): d = 0.0 (s; CSiMe4), 3.9 (s; CSiMe3), 23.2
(s; C28,29,32,33), 24.1 (s; C24,25,26,27), 24.3 (s; C30,31),
25.3 (s; C24,25,26,27), 25.6 (br; b-CH2, THF), 26.3
(s; C28,29,32,33), 28.2 (s; C22,23), 30.7 (s; C13,14),
34.7 (s; C15), 40.2 (s; CNMe2), 41.2 (d, 2J(Y,C) = 42.9 Hz; CYCH2), 68.8 (s;
A
a-CH2, THF), 108.5 (s; C3), 112.7 (s; C5), 113.0 (s; CNC6H5), 117.0 (s; C
NC6H5), 121.4 (s; C9,11), 124.9 (s; C18,20), 126.2 (s) 129.3 (s; CNC6H5), 135.1 (s;
C19), 135.8 (br; CBC6F5), 137.7 (s; C7), 138.2 (br; CBC6F5), 139.8 (s; C4),
142.5 (s; C16), 143.7 (s; C17,21), 147.1 (s; C8,12), 147.9 (br; CBC6F5), 150.2 (br;
CBC6F5), 151.1 (s; C10), 154.5 (s; C6), 170.5 ppm (s; C2); 19F NMR
3
(470 MHz, C6D6, 298 K): d = À167.1 (t, J
A
3
(t, J
A
Synthesis of bis(alkyl)aminopyridinatoaluminum complex 4: A Schlenk
vessel was charged with 1a (45.6 mg, 0.1 mmol) and toluene (2 mL)
before triisobutylaluminum (TIBA, 25 wt% in toluene, 1 mL, 0.1 mmol)
was added. After the mixture had been stirred for 30 min, all volatiles
was removed, to yield the corresponding, spectroscopic pure 4 as a color-
less oil in almost quantitative yield. For X-ray analysis of 4 the residue
was dissolved in hexane (3 mL). Slow evaporation of the solvent over a
period of five days left colorless crystals. 1H NMR (400 MHz, C6D6,
Synthesis of the catalyst stock solutions: The complexes 2a–2c were pre-
pared as described above. For catalytic ethylene conversion the pale
yellow residues were dissolved in toluene (10 mL) and used without fur-
ther purification.
X-ray crystal structure analysis: Data collection was accomplished by
using either a Bruker SMART APEX CCD or a Stoe IPDSII diffractom-
Chem. Eur. J. 2006, 12, 8969 – 8978
ꢀ 2006 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
www.chemeurj.org
8977

R. Kempe, W. P. Kretschmer et al.
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À
[12]The mean Y C bond length of 35 structurally characterized Y-CH2-
Si
A
[13]The mean Y-C-Si angle of 35 structurally characterized Y-CH 2-Si-
(CH3)3 moieties (CCDC) is 134.38.
AHCTREUNG
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Received: May 11, 2006
Published online: September 29, 2006
8978
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Chem. Eur. J. 2006, 12, 8969 – 8978