Synthesis of alumina-terminated linear PE with a hafnium aminopyridinate catalyst

Article abstract of DOI:10.1021/om200355q

Five different Ap (aminopyridinato) ligand stabilized hafnium complexes were synthesized and characterized through NMR spectroscopy, elemental analysis, and (to some extent) by X-ray crystal structure analysis. Moreover, a tunable ethylene polymerization catalyst system based on these complexes was tested in CCTP (coordinative chain transfer polymerization) with TEA (triethylaluminum) as the chain transfer agent. The catalyst precursor giving the highest degree of control, [Cp*Hf(Ap_HDIP)Me₂ (Cp* = 1,2,3,4,5-pentamethylcyclopentadienyl ligand, Ap_HDIP-H = N-(2,6-diisopropylphenyl)pyridine-2-amine, Me = methyl), in the presence of high amounts of TEA was investigated regarding different parameters: e.g., temperature, ethylene pressure, catalyst/chain transfer agent ratio, and reaction time. The results showed that the new catalyst system is able to tolerate up to 5000 equiv of TEA and was able to produce linear alumina-terminated polyethylene with polydispersities down to 1.2.

Full text of DOI:10.1021/om200355q

ARTICLE
pubs.acs.org/Organometallics
Synthesis of Alumina-Terminated Linear PE with a Hafnium
Aminopyridinate Catalyst
Isabelle Haas, Winfried P. Kretschmer, and Rhett Kempe*
Lehrstuhl Anorganische Chemie II, Universit€at Bayreuth, 95440 Bayreuth, Germany
S Supporting Information
b
ABSTRACT: Five different Ap (aminopyridinato) ligand stabilized
hafnium complexes were synthesized and characterized through NMR
spectroscopy, elemental analysis, and (to some extent) by X-ray crystal
structure analysis. Moreover, a tunable ethylene polymerization catalyst
system based on these complexes was tested in CCTP (coordinative
chain transfer polymerization) with TEA (triethylaluminum) as the
chain transfer agent. The catalyst precursor giving the highest degree of
control, [Cp*Hf(ApHDIP)Me2] (Cp* = 1,2,3,4,5-pentamethylcyclopen-
tadienyl ligand, ApHDIP-H = N-(2,6-diisopropylphenyl)pyridine-
2-amine, Me = methyl), in the presence of high amounts of TEA was
investigated regarding different parameters: e.g., temperature, ethylene pressure, catalyst/chain transfer agent ratio, and reaction
time. The results showed that the new catalyst system is able to tolerate up to 5000 equiv of TEA and was able to produce linear
alumina-terminated polyethylene with polydispersities down to 1.2.
Bochmann and Lancaster first reported that the exchange of
alkyl chains between Hf (or Zr) cations and Al occurs via the
formation of a Hf/Al (or Zr/Al) bimetallic complex (CTS).13
Rate constants kct (Scheme 1) for a variety of metallocene
cations (Ti, Zr, and Hf) and trimethylaluminum were reported
by Norton and Petros in 2004.14 Recently Norton and co-
workers reported a detailed mechanistic picture of the zirco-
nium complex catalyzed chain growth of Al alkyls.15 The
kinetics of chain growth has been studied when catalyzed by
[(EBI)Zr(μ-Me)2AlMe2][B(C6F5)4] (EBI = ethylene-bridged
bis(indenyl), Me = methyl). The reaction is first order in
[olefin] and [catalyst] and inverse first order in [AlR3].15
Thus, high amounts of Al alkyl result in poor overall CCTP
activity. On the other hand, high Al to catalyst ratios are
desired to minimize (process) costs. A possibility to solve this
problem is the design of a new catalyst system undergoing a
relatively slow chain exchange or a fast but not too fast chain
growth in comparison to chain exchange that still suppresses
β-H elimination and transfer processes. Under these condi-
tions the influence of the added amount of Al alkyl still reduces
activity but due to multiple insertions a certain overall chain
growth activity is observed.
1. INTRODUCTION
Zieglers “Aufbaureaktion”,1 the rather slow insertion of ethy-
lene into AlÀC bonds or the syn addition of Al alkyls to ethylene
(carboalumination), is an industrial process of great importance.
This process gains access to long-chain Al alkyls, which can easily
be transformed to the corresponding alcohols via oxidation with
O2. These aliphatic alcohols have a chain length of (for instance)
6À22 carbon atoms and are called Ziegler or fatty alcohols. Fatty
alcohols have wide applications in areas such as personal care and
polymer/leather/metal processing as well as agriculture and are
used in cosmetics, flavors, fragrances, plastics (as softener),
paints, coatings, industrial cleaning materials, and biocides.2
A further expansion of the described wide range of applications
would be possible if fatty alcohols with a chain lengths signifi-
cantly higher than 22 carbon atoms were efficiently accessible.
A polymerization method which is able to produce longer chain
Al alkyls (in a highly controlled fashion) is CCTP (coordinative
chain transfer polymerization).3,4
Since Eisenberg and Samsel5 as well as Mortreux and co-
workers6 cleared the way for CCTP in the early 1990s, a few very
interesting ethylene/propylene CCTP systems across the ranks
of RE (rare earth metals) and transition metals with different
CTAs (chain transfer agent)s, such as Mg,6 Zn,7À9 and Al
alkyls,10,11 have been discovered. Furthermore, enhancements
of the CCTP concept such as “chain shuttling”9 and “ternary
CCTP”12 have been developed. A simplified mechanism of
CCTP is shown in Scheme 1.
The CGS elongates the polymer chain. The CTS is used to
transfer the polymer chain between the catalyst and the CTA.
At the CTA chain growth is very slow and polymerization is of
low relevance as long as the CTA bears the polymer chain.
Herein, we present a ethylene polymerization catalyst system
based on Ap (aminopyridinato) ligand16À19 stabilized hafnium
Cp* complexes and its behavior in CCTP with TEA (triethyl-
aluminum). The effect of changing different parameters, e.g.
temperature, ethylene pressure, catalyst/CTA ratio, and reaction
time, is discussed.
Received: April 27, 2011
Published: August 26, 2011
r
2011 American Chemical Society
4854
dx.doi.org/10.1021/om200355q Organometallics 2011, 30, 4854–4861
|

Organometallics
ARTICLE
Scheme 1. Net Reaction and Mechanism of CCTP: (top)
CTS (Chain Transfer State); (bottom) CGS (Chain Growing
State)a
[Cp*HfMe3] was synthesized according to published proce-
dures.22,25,26 Reaction of 1 equiv of 1with [Cp*HfMe3] intolueneat
room temperature results in the formation of 6 by methane
elimination (Scheme 2).
The compounds 7À10 were synthesized analogously to 6
using 2À5, respectively, instead of 1. Recrystallization of the raw
product in hexane gave access to good yields of complexes 6À10
as yellow crystalline materials. Figure 1 shows the synthesized
hafnium catalyst precursors.
All compounds were characterized by NMR spectroscopy and
elemental analysis. Crystals of complexes 6, 7, and 9 suitable for
X-ray analysis were grown from hexane solutions. The molecular
structure of 6 is shown in Figure 2. For the molecular structures
of 7 and 9 as well as details of the X-ray crystal structure analyses
of all three complexes, see the Supporting Information.
All obtained crystal structures of the aminopyridinato ligand
stabilized Hf complexes feature a nearly 58° N1ÀHfÀN2 Ap
angle (58.39(14)° for 6, 58.63(14)°, for 7 and 58.1(3)° for 9).
In contrast, the C1ÀHfÀC2 angle varies from 90° to 96°, depend-
ing on the steric demand of the substituent at the 6-position of
the pyridine ring (90.9(2)° for 7, 93.2(3)° for 9, and 96.0(2)°
for 6). The mean HfÀC bond length (2.222 Å) of all the three
compounds is comparable to the expected value of a HfÀC bond
of a methyl ligand (2.261 Å).27 The dialkyl 6 forms organohaf-
nium cations in the presence of activators such as ammonium
borates ([R2N(CH3)H]+[B(C6F5)4]À (R = C16H33ÀC18H37) or
[PhNMe2H]+[B(C6F5)4]À) and trityl borate [(C6H5)3C]+-
[B(C6F5)4]À (BF20). The reaction of 6 with BF20 gave rise to 11.
Figure 3 shows the 1H NMR spectra of catalyst precursor 6 and
its activation with BF20.
The NMR spectroscopic investigations of the organohafnium
cation 11 revealed a single signal set as observed for 6. The
abstraction of one methyl group by the activator BF20 leads to a
further splitting of the three isopropyl signals (5/11, 6/7/12/13)
due to a decrease in symmetry of the complex.
2.2. Ethylene Polymerization Studies. For the polymeriza-
tion of ethylene with the Ap ligand stabilized organohafnium
cations the presence of aluminum alkyl is essential (Table 1, entry 1).
Only the catalyst precursor 6 is able to reach a polydispersity
lower than 2 (Table 1, entry 2). The precatalysts 8 and 9 do not
show any activity under the tested ethylene polymerization
conditions of 50 °C and 15 min reaction time (Table 1, entries
4 and 6). Polymer formation can be observed at higher reaction
temperatures or longer reaction times (Table 1, entries 5 and 7).
The organohafnium cations based on 6 gave the best polymer-
ization results, and we proceeded to explore this catalyst system
in more detail.
a Legend: [M] = cationic or neutral transition metal or RE complex;
R1, R2 = alkyl moiety. kct1, kct2, kco1, kco2 and kcg are rate constants. n,
m = natural numbers. β-H elimination termination steps must be
suppressed. intermolecular chain exchange is preferred over intramole-
cular (CTS).14
Scheme 2. Synthesis of the Hafnium Catalyst Precursor 6
2.2.1. Termination Reaction Study. NMR spectroscopy of the
polymers obtained (after hydrolytic workup) revealed saturated
1
polymers (Figure 4). The H NMR spectra of the polymeric
product of entry 2 (Table 1) shows no signals for olefinic protons.
No β-H elimination seems to occur during the polymerization
process.
2.2.2. Temperature and Pressure Dependence of the Orga-
nohafnium-Catalyzed Ethylene Polymerization. Temperature
plays a very sensitive role in CCTP. Temperature influences the
insertion rate and the transfer rate (Scheme 1), but not necessa-
rily to the same extent. Furthermore, with growing chain length
the PE chains become more and more insoluble, which causes
precipitation at some stage. This precipitation blocks the transfer
of the growing chain which is essential for the CCTP mechanism,
and a bimodal distribution is observed (temporarily).6c,10 Entries
2. RESULTS AND DISCUSSION
2.1. Synthesis and Structure of the Hafnium Complexes.
The applied Ap ligands 1 (ApHDIP-H = N-(2,6-diisopropylphenyl)-
pyridine-2-amine), 2 (ApMeDIP-H = N-(2,6-diisopropylphenyl)-6-
methylpyridine-2-amine), 3 (ApBrDIP-H = 6-bromo-N-(2,
6-diisopropylphenyl)pyridine-2-amine), 4 (ApClDIP-H = 6-chloro-
N-(2,6-diisopropylphenyl)pyridine-2-amine), and 5(ApHTMA-H =
N-mesityl-4-methylpyridine-2-amine) were prepared as reported.20À24
4855
dx.doi.org/10.1021/om200355q |Organometallics 2011, 30, 4854–4861

Organometallics
ARTICLE
Figure 1. Synthesized catalyst precursors.
Figure 2. Molecular structure (40% thermal ellipsoids) of compound 6.
Hydrogen atoms have been removed for clarity. Selected bond lengths
(Å) and angles (deg): Hf1ÀN2 = 2.195(4), Hf1ÀN1 = 2.359(4),
N1ÀC15 = 1.357(6), N2ÀC15 = 1.357(6), Hf1ÀC1 = 2.221(5),
Hf1ÀC2 = 2.238(5); Hf1ÀN1ÀC15 = 92.0(3), Hf1ÀN2ÀC15 =
99.4(3), N1ÀC15ÀN2 = 110.2(4), N1ÀHf1ÀN2 = 58.39(14),
C1ÀHf1ÀC2 = 96.0(2), C15ÀN2ÀC20 = 118.7(4).
Figure 3. 1H NMR (C6D6) spectra: (bottom) spectrum of catalyst
precursor 6; (top) spectrum after the activation of 6 with BF20.
higher pressures the insertion rate is increased independently
from the chain transfer rate, leading to an increase in poly-
dispersity, molecular weight, and activity. At higher pressure,
an increase in activity, an increase of the molecular weight,
and an increase in polydispersity is observed (entries 2 and 4,
Table 2).
In order to optimize the polymerization process with respect
to the highest control, it was decided to use 50 °C and 2 bar as
reaction conditions for the following studies.
2.2.3. Effect of the Al Concentration. Mainly CCTP catalyst
systems which handle CTA/catalyst ratios between 50 and 100
are described in the literature. Only one example by Mortreux
and co-workers6c gives an experiment with an Mg/Sm ratio of 1000,
and one work by Gibson and co-workers7c gives an experiment
1À3 in Table 2 show the effect of temperature, and entries 2 and
4 in Table 2 shows the effect of pressure on the organohafnium
catalyst system based on 6.
The rise in temperature (entries 1À3, Table 2) goes along with
an increase in activity and productivity. At 80 °C a bimodal
distribution and substantial amounts of precipitated polymer
were observed. Chain growth can proceed more quickly at
80 °C, which is in accordance with the increase in activity. This
increase in activity might have a much stronger effect than the
increased polymer solubility at 80 °C so that precipitation
takes place and a bimodal distribution is observed.6c,10 Pre-
ssure is also an important parameter to influence the polym-
erization result. Due to an increase in ethylene solubility28 at
4856
dx.doi.org/10.1021/om200355q |Organometallics 2011, 30, 4854–4861

Organometallics
ARTICLE
Table 1. Comparison of the Ethylene Polymerization of All Synthesized Organohafnium Catalyst Precursors 6À10a
entry precursor Al/Hf (amt of TEA (mmol)) time (min) temp (°C) yield (g) activity (kg/(mol h bar))
Mw
PDI Nexptl/Ntheor (%)c
1
2
3
4
5
6
7
8
6À10
0 (0)
10 000 (20)
10 000 (20)
10 000 (20)
10 000 (20)
10 000 (20)
10 000 (20)
10 000 (20)
90
15
15
15
90
15
15
15
50
50
50
50
50
50
80
50
0
0
630
740
0
n.d.
n.d.
6
0.62
0.74
0
380
1.3
2.5
n.d.
4
7
2 500
n.d.
13
8
8
2.69
0
450
0
58 000 3.8
<1
9
n.d.
n.d.
3.5
9
2.64
0.14
2 600
140
5 000
3
2
10
36 000 27.6
a Conditions: dialkyl (6À10); 2 μmol; ammonium borate, [R2N(CH3)H]+[B(C6F5)4]À (R = C16H33ÀC18H37); Hf/B = 1/1.1; aluminum alkyl, TEA;
c
290 mL of toluene; pressure, 2 bar. Nexptl, experimental chain number (yield PE (in g)/Mn); Ntheor, theoretical chain number, considering three
growing chains per Al atom.
molecular weights with nearly the same narrow polydispersities.8a,10
With the Hf catalyst system described here, this is not the case.
Table 4 shows the time dependence of the catalyst system based on
6, and Figure 6 gives the molecular weight distribution of the experi-
ments in Table 4. An increase in yield and activity with increasing
time takes place as well as the formation of a bimodal distribution.
The second peak could be explained by a transformation of the
catalytically active species into a second, yet unknown, catalyst
species (6a) during polymerization. This new species does not
carry out chain transfer but produces high-molecular-weight
polymers (Table 4, entries 2À4 peak 2). The first peak nearly
remains at its molecular weight and shows just a slight increase in
PDI (Table 4, entries 1À4 peak 1). Furthermore, the amount of
extended chains increases. A very long polymerization time is
necessary to elongate all theoretically possible chains if such a high
amount of Al alkyl is present during polymerization. Because of the
Figure 4. 1H NMR spectrum of the obtained polymer of entry 2 in
Table 1. The inset shows the signal of the methyl end groups.
transformation of the CCTP catalyst species derived from 6 to 6a, it
is impossible to observe a quantitative Al alkyl chain elongation here.
If we add high Al amounts to traditional ethylene CCTP cata-
lysts such as the aminopyridinate and amidinate yttrium catalyst
with a Zn/Zr ratio of 2800. The great advantage of the Hf system,
described here, is the tolerance to very high amounts of alumi-
system,11f the catalysts are dead already at Al/Y ratios of about 400.
num alkyls. Table 3 summarizes the results concerning the
variation of the Al/Hf ratio in the CCTP of ethylene with
3. CONCLUSION
organohafnium cations based on 6.
A few conclusions can be drawn from the studies discussed
here. First, aminopyridines react cleanly with [Cp*HfMe3] to
form mixed Cp*/Ap dimethyl complexes. Second, these Hf
complexes can be activated with borates to undergo chain
transfer polymerization with ethylene in the presence of large
amounts of aluminum alkyls. Linear PE with saturated end
groups is observed after hydrolysis. Most likely, relatively slow
chain transfer (in relation to chain growth) leads to multiple
insertions and a lesser degree of control in comparison to
traditional CCTP catalyst systems. Third, the transformation
of the active chain transfer catalyst into a second (polymerization
active) species which produces a higher molecular weight PE
fraction is assumed. The formation of this species prevents
quantitative chain elongation.
For this catalyst system monomodal molecular weight dis-
tributions with a polydispersity between 1.2 and 3.2 and Mw
between 400 and 22 000 (Figure 5) were observed. Whereas
narrow dispersities and low molecular weights were observed
with high amounts of TEA, broad polydispersities and high
molecular weights were observed with low amounts of TEA. In
entry 3 of Table 3, two elongated alkyl chains per Al atom are
observed with a rather broad PDI. The higher PDI may result
from the relatively high molecular weight (far behind the
precipitation point).6c,10 A higher amount of CTA (Table 3,
entries 4À6) results in lower molecular weights and lower PDI.
Low to very low amounts of extended chains are observed at high
Al to Hf ratios. Aluminum cations stabilized by aminopyridinato
ligands are nearly inactive in ethylene polymerization.10,29 If no 6
is added, no polymerization takes place (entry 7, Table 3).
2.2.4. Time Dependence of the Organohafnium-Catalyzed
Ethylene Polymerization. The observation of the polymerization
results with increasing time gives important information on the
nature of the chain transfer. If very fast chain transfer takes place
during polymerization, the level of control is very high and it is
possible to produce polymeric materials over a large range of
Further efforts should be directed toward the development of
more stable catalysts able to tolerate high Al alkyl amounts and to
achieve quantitative chain elongation.
4. EXPERIMENTAL SECTION
General Comments. All manipulations of air- or moisture-sensi-
tive compounds were carried out under N2 and Ar using glovebox,
4857
dx.doi.org/10.1021/om200355q |Organometallics 2011, 30, 4854–4861

Organometallics
Table 2. Temperature and Pressure Dependence of Ethylene Polymerization Using Organohafnium Cations Based on 6a
ARTICLE
entry
pressure (bar)
temp (°C)
activity (kg/mol h bar)
productivity ((g of PE)/(g of cat.))
yield (g)]
Mw
PDI
Nexptl/Ntheor (%)c
1
2
3
4
2
2
2
5
30
50
80
50
240
430
200
360
0.24
0.43
1.96
1.74
1010
880
1.9
1.2
12.1b
2
2
1960
700
1640
1460
8000
1020
10
2.1
12
a Conditions: dialkyl (6), 2 μmol; ammonium borate, [R2N(CH3)H]+[B(C6F5)4]À (R = C16H33ÀC18H37); Hf/B = 1/1.1; aluminum alkyl, TEA; Hf/Al =
1/5000; 290 mL of toluene; time, 15 min. b Bimodal distribution: (1) peak Mw 45 000, PDI 1.8; (2) peak Mw 1100, PDI 2.2. c Nexptl = experimental chain
number (yield PE (in g)/Mn); Ntheor = theoretical chain number, considering three growing chains per Al atom.
À
6.2 wt % B(C6F5)4 in Isopar, DOW Chemicals) and triethylaluminum
(TEA, 25 wt % in toluene, Aldrich) were used as received.
Table 3. Dependence of the Ethylene Polymerization on the
Aluminum to Hafnium Ratioa
The precursor materials [Cp*HfCl3]22,25 and [Cp*HfMe3]26 as well as
the ligands ApHDIP-H (N-(2,6-diisopropylphenyl)pyridine-2-amine),20
ApMeDIP-H (N-(2,6-diisopropylphenyl)-6-methylpyridine-2-amine),21
ApBrDIP-H (6-bromo-N-(2,6-diisopropylphenyl)pyridine-2-amine),22
ApClDIP-H (6-chloro-N-(2,6-diisopropylphenyl)pyridine-2-amine),23
and ApHTMA-H (N-mesityl-4-methylpyridine-2-amine)24 were pre-
pared according to published procedures.
Al/Hf (amt
activity (kg/ yield
N
exptl/Ntheor
(%)c
entry of TEA (mmol)) (mol h bar)) (g)
Mw PDI
n.d. n.d.
1
2
3
4
5
6
7b
0 (0.0)
0
110
2800
5500
400
430
0
0
50 (0.1)
0.84 618 000 12.4
2.80 22 000 3.2
6
66
12
6
100 (0.2)
500 (1.0)
1 000 (2.0)
5 000 (10.0)
(20.0)
0.55 2 500
0.40 1 570
0.43 880
1.5
1.4
1.2
n.d.
Preparation of Cp*HfApHDIPMe2. ApHDIP-H (0.200 g, 0.786
mmol) and [Cp*HfMe3] (0.282 g, 0.786 mmol) were dissolved in
toluene (15 mL), and the mixture was stirred overnight. All volatiles
were removed under reduced pressure, and the residue was suspended in
hexane (10 mL). The overlaying orange solution was filtered, and the
residue was extracted with hexane (2 × 5 mL). Removal of the solvent
afforded 6 as a yellow spectroscopically pure compound (0.324 g, 69%).
Crystals suitable for an X-ray analysis were available through crystal-
lization out of a saturated hexane solution at À22 °C. Anal. Calcd for
C29H42HfN2 (598.28): C, 58.33; H; 37.09; N 4.69. Found: C, 58.57; H,
7.51; N, 4.61. 1H NMR (400 MHz, C6D6, 298 K): δ 7.40 (dd, 3J = 4.6
Hz, 1H, H1), 7.26À7.18 (m, 3H, H9, H10), 6.71 (dd, 3J = 7.7 Hz, 3J = 7.7
Hz, 1H, H3), 5.90 (dd, 3J = 6.6 Hz, 3J = 6.6 Hz, 1H, H2), 5.49 (d, 3J = 8.5
Hz, 1H, H4), 3.53 (sept, 3J = 6.8 Hz, 2H, H8), 1.96 (s, 15H, H14), 1.38
2
0
n.d.
a Conditions: dialkyl (6), 2 μmol; ammonium borate, [R2N(CH3)H]+-
[B(C6F5)4]À (R = C16H33ÀC18H37); Hf/B = 1/1.1; aluminum alkyl,
TEA; 290 mL of toluene; pressure, 2 bar; temperature, 50 °C; time,
c
15 min. b No catalyst precursor. Nexptl = experimental chain number
(yield PE (in g)/Mn); Ntheor = theoretical chain number, considering
three growing chains per Al atom.
standard Schlenk, or vacuum-line techniques. Solvents and reagents
were purified by distillation from LiAlH4, potassium, Na/K alloy, or
sodium ketyl 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 Å). Ethylene (AGA polymer grade) was passed over
BASF R3-11 supported Cu oxygen scavenger and molecular sieves
(Aldrich, 4 Å). Elemental analyses were carried out with a Vario
elementar EL III apparatus.
(d, 3J = 6.9 Hz, 6H, HCH i-Pr), 1.10 (d, 3J = 6.7 Hz, 6H, HCH i-Pr), 0.03 (s,
6H, H11, H12) ppm. 13C NMR (400 MHz, C6D6, 298 K): δ 180.0 (s, 1C,
C5), 144.5 (s, 2C, C7), 143.2 (s, 1C, C1), 143.1 (s, 1C, C6), 140.8 (s, 2C,
C8), 125.9 (s, 1C, C3), 124.2 (s, 1C, C11), 119.2 (s, 5C, C13), 109.6 (s, 1C,
C4), 107.0 (s, 1C, C2), 52.3 (s, 1C, C11), 52.2 (m, 1C, C12), 28.5 (s, 1C,
3
3
C10), 25.4 (s, 2C, CCH i-Pr), 24.2 (s, 2C, CCH i-Pr), 11.5 (s, 5C, C14) ppm.
3
3
NMR Spectroscopy. NMR spectra were recorded on a Varian
INOVA 400 (1H, 400 MHz; 13C, 100.5 MHz) spectrometer. The 1H and
13C NMR spectra, measured at 23 °C, were referenced internally using
the residual solvent resonances, and the chemical shifts (δ) are reported
in ppm. The polymer sample was prepared by dissolving 15 mg of the
polymer in 0.5 mL of C2D2Cl4 at 100 °C for 3 h before measuring.
Gel Permeation Chromatography. GPC analysis was carried
out on a Polymer Laboratories Ltd. (PL-GPC220) chromatograph at
150 °C 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 solvent in an external oven and were run without filtration.
The molecular weight was referenced against linear polyethylene (Mw =
120-3 000 000) and polystyrene (Mw = 510À3 200 000) standards. The
reported values are the average of at least two independent determinations.
X-ray Crystallography. X-ray crystal structure analyses were
performed with a STOE-IPDS II diffractometer equipped with an
Oxford Cryostream low-temperature unit (λ(Mo Kα) = 0.710 73 Å).
Structure solution and refinement were accomplished using SIR97,30
SHELXL-97,31 and WinGX.32 Selected details of the X-ray crystal
structure analyses are given in the Supporting Information.
Preparation of Cp*HfApMeDIPMe2. ApMeDIP-H (0.100 g,
0.373 mmol) and [Cp*HfMe3] (0.134 g, 0.373 mmol) were dissolved in
toluene (10 mL) and stirred overnight. All volatiles were removed under
reduced pressure, and the residue was suspended in hexane (8 mL). The
overlaying orange solution was filtered, and the residue was extracted with
hexane (2 × 5 mL). Removal of the solvent afforded 7 as a yellow
spectroscopically pure compound (0.137 g, 61%). Crystals suitable for an
X-ray analysis were available through crystallization out of a saturated
hexane solution at À22 °C. Anal. Calcd for C30H44HfN2 (612.30):
C, 58.96; H, 7.26; N. 4.58. Found: C, 59.17; H, 6.91; N, 4.60. 1H NMR
(400 MHz, C6D6, 298 K): δ 7.23À7.18 (m, 3H, H10, H11), 6.70 (dd, 3J =
7.3 Hz, 3J = 7.3 Hz, 1H, H4), 5.90 (d, 3J = 7.6 Hz, 1H, H3), 5.35 (d, 3J = 8.6
Hz, 1H, H5), 3.49 (sept, 3J = 6.9 Hz, 2H, H9), 2.06 (s, 3H, H2), 1.97 (s, 15H,
3
3
H15), 1.38 (d, J = 6.9 Hz, 6H, HCH i-Pr), 1.10 (d, J = 6.7 Hz, 6H,
3
Ligand and Complex Synthesis. N,N,N-Trialkylammonium tetrakis-
(pentafluorophenyl)borate ([R2NMeH][B(C6F5)4], R = C16H31ÀC18H35,
CH i-Pr), 0.12 (s, 6H, H12, H13) ppm. 13C NMR (400 MHz, C6D6,
3
H
4858
dx.doi.org/10.1021/om200355q |Organometallics 2011, 30, 4854–4861

Organometallics
ARTICLE
Figure 5. Molecular weight distribution (GPC) of the polymerization experiments listed in Table 3.
Table 4. Time Dependence of Ethylene Polymerization Using Organohafnium Cations Based on 6a
entry
time (min)
activity (kg/(mol h bar))
yield (g)
ethylene consumption (g)
Mn
PDI
Nexptl/Ntheor (%)b
Nexptl/Ntheor (%)c
1
2
15
30
430
720
0.43
1.45
1.46
4.01
760
1.2
20.7
1.3
6
2
910
810
15
peak 1
peak 2
6
11
26
900
23.5
44.9
1.3
3
4
45
60
940
2.82
5.77
6.26
8.51
1 070
820
20
21
peak 1
peak 2
22 000
1 340
730
6.8
1440
152.0
1.6
peak 1
peak 2
31 000
14.5
a Conditions: dialkyl (6), 2 μmol; ammonium borate, [R2N(CH3)H]+[B(C6F5)4]À (R = C16H33ÀC18H37); Hf/B = 1/1.1; aluminum alkyl, TEA; Hf/Al =
1/5000; 290 mL of toluene; pressure, 2 bar; time, 15 min. b Nexptl = experimental chain number (ethene consumption (in g, determined by a Bronkhorst
c
HIGH-TECH EL-FLOW mass flow controller)/Mn); Ntheor = theoretical chain number, considering three growing chains per Al atom. Nexptl
experimental chain number (yield (in g)/Mn); Ntheor = theoretical chain number, considering three growing chains per Al atom.
=
298 K): δ 169.7 (s, 1C, C6), 154.1 (s, 1C, C1), 144.7 (s, 2C, C8), 143.9
(s, 1C, C7), 140.8 (s, 2C, C9), 125.8 (s, 1C, C4), 124.2 (s, 2C, C10),
119.4 (s, 5C, C14), 111.3 (s, 1C, C5), 104.4 (s, 1C, C3), 53.1 (s, 1C,
C29H41BrHfN2 (676.19): C, 51.52; H, 6.11; N, 4.14. Found: C, 51.83;
1
H, 6.23; N, 4.04. H NMR (400 MHz, C6D6, 298 K): δ 7.18À7.16
(m, 3H, H9, H10), 6.29 (dd, 3J = 7.8 Hz, 3J = 7.8 Hz, 1H, H3), 6.21 (d, 3J =
7.4 Hz, 1H, H2), 5.29 (d, 3J = 8.1 Hz, 1H, H4), 3.38 (sept, 3J = 6.7 Hz, 2H,
C12), 53.0 (s, 1C, C13), 28.4 (s, 1C, C11), 25.6 (s, 2C, CCH i-Pr), 24.2
3
(s, 2C, CCH i-Pr), 22.9 (s, 1C, C2), 11.6 (s, 5C, C15) ppm.
H8), 2.05 (s, 15H, H14), 1.34 (d, 3J = 7.1 Hz, 6H, HCH i-Pr), 1.02 (d, 3J =
3
3
6.7 Hz, 6H, HCH i-Pr), 0.24 (s, 6H, H11, H12) ppm. 13C NMR (400 MHz,
3
C6D6, 298 K): δ 170.6 (s, 1C, C5), 144.3 (s, 2C, C7), 143.0 (s, 1C, C1),
141.6 (s, 2C, C8), 137.1 (s, 1C, C6), 126.2 (s, 1C, C3), 124.4 (s, 2C, C9),
120.1 (s, 5C, C13), 114.8 (s, 1C, C4), 106.2 (s, 1C, C2), 54.9 (s, 1C, C11),
54.8 (s, 1C, C12), 28.5 (s, 1C, C10), 25.5 (s, 2C, CCH i-Pr), 24.1 (s, 2C,
3
3
C
CH i-Pr), 11.8 (s, 5C, C14) ppm.
Preparation of Cp*HfApBrDIPMe2. ApBrDIP-H (0.200 g, 0.602
mmol) and [Cp*HfMe3] (0.216 g, 0.602 mmol) were dissolved in
toluene (10 mL) and stirred overnight. All volatiles were removed under
reduced pressure, and the residue was suspended in hexane (8 mL). The
overlaying orange solution was filtered, and the residue was extracted
with hexane (2 × 5 mL). Removal of the solvent afforded 8 as a yellow
spectroscopically pure compound (0.273 g, 67%). Anal. Calcd for
Preparation of Cp*HfApClDIPMe2. ApClDIP-H (0.113 g, 0.392
mmol) and [Cp*HfMe3] (0.141 g, 0.392 mmol) were dissolved in
4859
dx.doi.org/10.1021/om200355q |Organometallics 2011, 30, 4854–4861

Organometallics
ARTICLE
Figure 6. Molecular weight distribution (GPC) of the polymerization experiments given in Table 4.
toluene (10 mL) and stirred overnight. All volatiles were removed under
reduced pressure, and the residue was suspended in hexane (8 mL). The
overlaying orange solution was filtered, and the residue was extracted
with hexane (2 × 5 mL). Removal of the solvent afforded 9 as a yellow
spectroscopically pure compound (0.161 g, 65%). Crystals suitable for
an X-ray analysis were available through slow vaporization of the solvent
hexane out of a saturated solution at room temperature. Anal. Calcd for
C29H41ClHfN2 (632.24): C, 55.15; H, 6.54; N, 4.44. Found: C, 55.54; H,
6.56; N, 4.54. 1H NMR (400 MHz, C6D6, 298 K): δ 7.18À7.16 (m, 3H, H9,
H10), 6.40 (dd, 3J=8.5Hz,3J= 8.5 Hz, 1H, H3),6.01(d,3J= 7.7 Hz, 1H, H2),
5.27 (d, 3J = 8.5 Hz, 1H, H4), 3.41 (sept, 3J = 6.8 Hz, 2H, H8),
(s, 1C, C13), 51.8 (s, 1C, C14), 21.5 (s, 1C, C4), 20.9 (s, 1C, C12), 19.1 (s,
2C, C9), 11.6 (s, 5C, C16) ppm.
3
3
2.04 (s, 15H, H14), 1.35 (d, J = 6.8 Hz, 6H, HCH i-Pr), 1.04 (d, J =
3
Synthesis of the Catalyst Stock Solutions. Complexes 6À10
were prepared as described above. For catalytic ethylene conversion the
intense yellow residues were dissolved in toluene (10 mL) and used
without further purification.
6.8 Hz, 6H, HCH i-Pr), 0.20 (s, 6H, H11, H12) ppm. 13C NMR (400 MHz,
3
C6D6, 298 K): δ 170.4 (s, 1C, C5), 144.3 (s, 2C, C7), 142.9 (s, 1C, C1),
142.0 (s, 2C, C8), 140.0 (s, 1C, C6), 126.2 (s, 1C, C3), 124.4 (s, 2C, C9),
120.1 (s, 5C, C13), 110.4 (s, 1C, C4), 105.7 (s, 1C, C2), 54.6 (s, 1C, C11),
Polymerization Studies: General Description of Polymer-
ization Experiments. The catalytic ethylene polymerization reac-
tions were performed in a stainless steel 1 L autoclave (Versoclave,
B€uchiglasuster) equipped with a mechanical stirrer in semibatch mode
(ethylene was added by replenishing the flow to keep the pressure
constant). The reactor was temperature- and pressure-controlled and
equipped with separate toluene and catalyst/cocatalyst injection sys-
tems. 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 120 °C prior to use. The reactor was
then brought to the desired temperature, stirred at 600 rpm, and
charged with 270 mL of toluene together with the activator N,N,
N-trialkylammonium tetrakis(pentafluorophenyl)borate (2.2 μmol,
24.5 mg, 11% stock solution in Isopar) and the required amount of
aluminum trialkyl. After pressurization with ethylene to reach the
desired total pressure, the autoclave was equilibrated for 5 min.
Subsequently [Cp*Hf(ApHDIP)Me2] (2 mL, 0.001 M stock solution
in toluene) together with toluene (18 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 the flow. After the
desired reaction time the reactor was vented and the residual alu-
minum alkyls were destroyed by addition of ethanol (100 L). The
precipitated polymeric product was collected, stirred for 30 min in
acidified ethanol, and rinsed with ethanol on a glass frit. The polymer
was initially dried at 80 °C to a constant weight.
54.5 (s, 1C, C12), 28.5 (s, 1C, C10), 25.5 (s, 2C, CCH i-Pr), 24.2 (s, 2C,
3
3
C
CH i-Pr), 11.7 (s, 5C, C14) ppm.
Preparation of Cp*HfApHTMAMe2. ApHTMA-H (0.200 g,
0.884 mmol) and [Cp*HfMe3] (0.141 g, 0.392 mmol) were dissolved
in toluene (10 mL) and stirred overnight. All volatiles were removed
under reduced pressure, and the residue was suspended in hexane
(8 mL). The overlaying orange solution was filtered, and the residue
was extracted with hexane (4 × 10 mL). Removal of the solvent afforded
10 as a pale yellow spectroscopically pure compound (0.261 g, 52%).
Anal. Calcd for C27H38HfN2 (570.25): C, 56.98; H, 6.73; N 4.92.
Found: C, 55.74; H, 7.05; N, 4.93. 1H NMR (400 MHz, C6D6, 298 K): δ
7.40 (d, 3J = 5.2 Hz, 1H, H1), 6.94 (s, 2H, H10), 5.86 (d, 3J = 5.4 Hz,
1H, H2), 5.54 (s, 1H, H5), 2.40 (s, 6H, H9), 2.22 (s, 3H, H12), 1.98 (s,
15H, H16), 1.54 (s, 3H, H4), 0.08 (s, 6H, H13, H14) ppm. 13C NMR
(400 MHz, C6D6, 298 K): δ 168.5 (s, 1C, C6), 153.2 (s, 1C, C1), 143.1
(s, 1C, C3), 143.0 (s, 1C, C7), 133.9 (s, 2C, C8), 133.7 (s, 1C, C11), 129.7
(s, 2C, C10), 119.0 (s, 5C, C15), 111.7 (s, 1C, C5), 105.2 (s, 1C, C2), 51.8
4860
dx.doi.org/10.1021/om200355q |Organometallics 2011, 30, 4854–4861

Organometallics
ARTICLE
’ ASSOCIATED CONTENT
(15) Camara, J. M.; Petros, R. A.; Norton, J. R. J. Am. Chem. Soc.
2011, 133, 5263.
(16) For review articles on aminopyridinato ligands see: (a) Kempe,
R.; Noss, H.; Irrgang, T. J. Organomet. Chem. 2002, 647, 12. (b) Kempe,
R. Eur. J. Inorg. Chem. 2003, 791.
S
Supporting Information. Figures giving the molecular
b
structures of 7 and 9 and CIF files and a table giving the param-
eters of the X-ray analysis of 6À8 and detailed information on the
X-ray crystal structure analyses. This material is available free of
charge via the Internet at http://pubs.acs.org.
(17) For discussion of the binding modes see: Deeken, S.; Motz, G.;
Kempe, R. Z. Anorg. Allg. Chem. 2007, 633, 320.
(18) For the general applicability of the ligands see: Glatz, G.;
Demeshko, S.; Motz, G.; Kempe, R. Eur. J. Inorg. Chem. 2009, 1385.
(19) For selected key papers on bulky aminopyridinato ligands
please see: (a) Scott, N. M.; Kempe, R. Eur. J. Inorg. Chem. 2005,
1319. (b) Skvortsov, G. G.; Fukin, G. K.; Trifonov, A. A.; Noor, A.;
D€oring, C.; Kempe, R. Organometallics 2007, 26, 5770. (c) Lyubov,
D. M.; D€oring, C.; Fukin, G. K.; Cherkasov, A. V.; Shavyrin, A. V.;
Kempe, R.; Trifonov, A. A. Organometallics 2008, 27, 2905. (d) Noor, A.;
Wagner, F. R.; Kempe, R. Angew. Chem. 2008, 120, 7356–7359. Angew.
Chem., Int. Ed. 2008, 47, 7246. (e) Noor, A.; Glatz, G.; M€uller, R.; Kaup,
M.; Demeshko, S.; Kempe, R. Nature Chem. 2009, 1, 322.
(20) Noor, A.; Kretschmer, W. P.; Kempe, R. Eur. J. Inorg. Chem.
2006, 2683.
(21) Schareina, T.; Hillebrand, G.; Kempe, R. Eur. J. Inorg. Chem.
2001, 2421.
(22) Blenkers, J.; Hessen, B.; van Bolhuis, F.; Wagner, A. J.; Teuben,
J. H. Organometallics 1987, 6, 459.
(23) Desmarets, C.; Schneider, R.; Fort, Y. Tetrahedron Lett. 2001,
42, 247.
(24) Glatz, G.; Irrgang, T.; Kempe, R. Z. Kristallogr.-New Cryst.
Struct. 2007, 222, 265.
’ AUTHOR INFORMATION
Corresponding Author
*E-mail: kempe@uni-bayreuth.de.
’ ACKNOWLEDGMENT
Financial support from the Deutsche Forschungsgemeinschaft
(SFB 840 “Von partikul€aren Nanosystemen zur Mesotechnologie”),
SASOL Germany GmbH, and the German National Academic
Foundation is gratefully acknowledged.
’ REFERENCES
(1) (a) Ziegler, K.; Gellert, H. G.; K€uhlhorn, H.; Martin, H.; Meyer,
K.; Nagel, K.; Sauer, H.; Zosel, K. Angew. Chem. 1952, 64, 323. (b)
Ziegler, K.; Holzkamp, E.; Breil, H.; Martin, H. Angew. Chem. 1955,
67, 541.
(2) Sasol Olefins & Surfactants, Annual review 2010.
(3) Kempe, R. Chem. Eur. J. 2007, 13, 2764.
(25) Roddick, D. M.; Fryzuk, M. D.; Seidler, P. F.; Hillhouse, G. L.;
Bercaw, J. E. Organometallics 1985, 4, 97.
(4) Sita, L. R. Angew. Chem., Int. Ed. 2009, 48, 2464.
(26) Schock, L. E.; Marks, T. J. J. Am. Chem. Soc. 1988, 110, 7701.
(27) The mean HfÀC bond length of 39 structurally characterized
HfÀCH3 moieties (CCDC) is 2.261 Å.
(5) (a) Samsel, E. G. (Ethyl Corporation) Eur. Patent EP 0539876,
1993. (b) Samsel, E. G.; Eisenberg, D. C. (Ethyl Corporation) Eur.
Patent EP 0574854, 1993.
(6) (a) Pelletier, J.-F.; Mortreux, A.; Olonde, X.; Bujadoux, K. Angew.
Chem., Int. Ed. Engl. 1996, 35, 1854.(b) Pelletier, J.-F.; Bujadoux, K.;
Olonde, X.; Adisson, E.; Mortreux, A.; Chenal, T. U.S. Patent 5,779,942,
1998. (c) Chenal, T.; Olonde, X.; Pelletier, J.-F.; Bujadoux, K.; Mortreux,
A. Polymer 2007, 48, 1844.
(7) (a) Britovsek, G. J. P.; Cohen, S. A.; Gibson, V. C.; Maddox, P. J.;
van Meurs, M. Angew. Chem., Int. Ed. 2002, 41, 489. (b) Britovsek,
G. J. P.; Cohen, S. A.; Gibson, V. C.; van Meurs, M. J. Am. Chem. Soc.
2004, 126, 10701. (c) van Meurs, M.; Britovsek, G. J. P.; Gibson, V. C.;
Cohen, S. A. J. Am. Chem. Soc. 2005, 127, 9913. (d) Kaneyoshi, H.;
Inoue, Y.; Matyjaszewski, K. Macromolecules 2005, 38, 5425.
(8) (a) Zhang, W.; Sita, L. R. J. Am. Chem. Soc. 2008, 130, 442.
(b) Zhang, W.; Wei, J.; Sita, L. R. Macromolecules 2008, 41, 7829.
(9) (a) Arriola, D. J.; Carnahan, E. M.; Hustad, P. D.; Kuhlman, R. L.;
Wenzel, T. T. Science 2006, 312, 714. (b) Hustad, P. D.; Kuhlman, R. L.;
Arriola, D. J.; Carnahan, E. M.; Wenzel, T. T. Macromolecules 2007,
40, 7061. (c) Hustad, P. D.; Kuhlman, R. L.; Carnahan, E. M.; Wenzel,
T. T.; Arriola, D. J. Macromolecules 2008, 41, 4081. (d) Kuhlman, R. L.;
Wenzel, T. T. Macromolecules 2008, 41, 4090. (e) Li Pi Shan, C.; Hazlitt,
L. G. Macromol. Symp. 2007, 257, 80.
(28) Atiqullah, M.; Hammawa, H.; Hamid, H. Eur. Polym. J. 1998,
34, 1511.
(29) Kretschmer, W. P.; Hessen, B.; Noor, A.; Scott, N. M.; Kempe,
R. J. Organomet. Chem. 2007, 692, 4569.
(30) Altomare, A.; Burla, M. C.; Camalli, M.; Cascarano, G. L.;
Giacovazzo, C.; Guagliardi, A.; Moliterni, A. G. G.; Polidori, G.; Spagna,
R. J. Appl. Crystallogr. 1999, 32, 115.
(31) Sheldrick, G. M. SHELX-97, Program for Crystal Structure
Analysis (Release 97-2); Institut f€ur Anorganische Chemie der Uni-
versit€at, G€ottingen, Germany, 1998.
(32) Farrugia, L. J. J. Appl. Crystallogr. 1999, 32, 837.
(10) Kretschmer, W. P.; Meetsma, A.; Hessen, B.; Schmalz, T.;
Qayyum, S.; Kempe, R. Chem. Eur. J. 2006, 12, 8969.
(11) (a) Rogers, J. S.; Bazan, G. C. Chem. Commun. 2000, 1209.
(b) Bazan, G. C.; Rogers, J. S.; Fang, C. C. Organometallics 2001, 20,
2059. (c) Mani, G.; Gabba, F. P. Angew. Chem., Int. Ed. 2004, 43, 2263.
(d) Mani, G.; Gabba, F. P. J. Organomet. Chem. 2005, 690, 5145.
(e) D€oring, C.; Kretschmer, W. P.; Kempe, R. Eur. J. Inorg. Chem.
2010, 18, 2853. (f) Kretschmer, W. P.; Bauer, T.; Hessen, B.; Kempe, R.
Dalton Trans. 2010, 39, 6847.
(12) Wei, J.; Zhang, W.; Sita, L. R. Angew. Chem., Int. Ed. 2010, 49,
1768.
(13) (a) Bochmann, M.; Lancaster, S. J. J. Organomet. Chem. 1995,
497, 55. (b) Bochmann, M.; Lancaster, S. J. Angew. Chem. 1994, 106,
1715.
(14) Petros, R. A.; Norton, J. R. Organometallics 2004, 23, 510.
4861
dx.doi.org/10.1021/om200355q |Organometallics 2011, 30, 4854–4861