Hafnium amidoquinoline complexes: Highly active olefin polymerization catalysts with ultrahigh molecular weight capacity

Article abstract of DOI:10.1021/om3005417

The preparation and characterization of a new class of polyolefin procatalysts is described. Hafnium tribenzyl procatalysts, supported by amidoquinoline ligands, were prepared in two steps from commercially available materials. Solid-state structures, determined by single-crystal X-ray analyses, revealed that all the hafnium complexes display approximate trigonal-bipyramidal geometry around the metal center. The complexes were evaluated in an ethylene/1-octene copolymerization study and were found to be highly active at elevated temperatures (120 °C). The best catalyst, derived from ((2,6-dimethylphenyl)(2,4-dimethylquinolin-8-yl)amino)tribenzylhafnium (6d), compares favorably to previously reported systems supported by bidentate nitrogen-based ligands. In particular, this catalyst exhibits very high molecular weight capacity and high catalytic activity, with a moderate 1-octene response. Alkyl substitution at the carbon ortho to the quinolino nitrogen was found to be an important factor for improving polymer compositional homogeneity, as evidenced by a narrowing of the polydispersity index and a single melting temperature in the resulting copolymer.

Full text of DOI:10.1021/om3005417

Article
pubs.acs.org/Organometallics
Hafnium Amidoquinoline Complexes: Highly Active Olefin
Polymerization Catalysts with Ultrahigh Molecular Weight Capacity
Philip P. Fontaine*
Performance Plastics R&D, The Dow Chemical Company, Freeport, Texas 77541, United States
Jerzy Klosin
Corporate R&D, The Dow Chemical Company, 1776 Building, Midland, Michigan 48674, United States
Nolan T. McDougal
Corporate R&D, The Dow Chemical Company, Freeport, Texas 77541, United States
S
* Supporting Information
ABSTRACT: The preparation and characterization of a new
class of polyolefin procatalysts is described. Hafnium tribenzyl
procatalysts, supported by amidoquinoline ligands, were
prepared in two steps from commercially available materials.
Solid-state structures, determined by single-crystal X-ray
analyses, revealed that all the hafnium complexes display
approximate trigonal-bipyramidal geometry around the metal
center. The complexes were evaluated in an ethylene/1-octene
copolymerization study and were found to be highly active at
elevated temperatures (120 °C). The best catalyst, derived from ((2,6-dimethylphenyl)(2,4-dimethylquinolin-8-yl)amino)-
tribenzylhafnium (6d), compares favorably to previously reported systems supported by bidentate nitrogen-based ligands. In
particular, this catalyst exhibits very high molecular weight capacity and high catalytic activity, with a moderate 1-octene response.
Alkyl substitution at the carbon ortho to the quinolino nitrogen was found to be an important factor for improving polymer
compositional homogeneity, as evidenced by a narrowing of the polydispersity index and a single melting temperature in the
resulting copolymer.
are capable of producing olefin copolymers with high molecular
weight and readily engage in reversible chain transfer with
diethylzinc, allowing for OBC production.2e,f
INTRODUCTION
■
The polyolefins industry continues to seek new catalysts1 that
are capable of producing materials with fundamentally new
microstructures and properties2 or that can improve the current
polymerization processes.3 Ideally, these catalysts should
comprise supporting ligand frameworks that are inexpensive,
easily prepared, and modular in nature. Moreover, high
activities and the ability to operate at elevated temperatures
are often critical features when assessing commercial viability.
As of yet, there are still relatively few supporting ligand
frameworks that can satisfy all the above-mentioned require-
ments.
One drawback of several of the previously reported systems
is the relatively low stability of the procatalysts or ligand
precursors. For example, previously reported imino-amido
complexes undergo structural rearrangements at elevated
temperature to produce species that are less catalytically
competent (e.g., 1a → 1b and 2a → 2b, Scheme 1).5a,e The
thermal instability was eliminated for analogous cyclic imino-
enamido complexes (e.g., 3a), although the ligand itself is prone
to acid-induced isomerization, resulting in a new ligand, which
upon metalation gives rise to a less competent catalyst (3b)
(Scheme 2).5f Such rearrangements are undesirable, as they can
make it more difficult to prepare or store a given catalyst, and
hence limit commercial viability. Our goal, then, was to develop
a ligand scaffold that retains (or improves upon) the positive
attributes of the above-mentioned catalytic systems, while
suppressing some of these unwanted isomerization pathways.
In this regard, there has been an increasing focus on non-
metallocene systems,4 which can be attractive targets owing to
their ease of preparation and high temperature stability.
Additionally, such catalysts have been used to access novel
and industrially relevant polyolefin structures such as olefin
block copolymers (OBCs).2e Of particular interest are several
recent reports describing group IV complexes comprising
simple bidentate nitrogen-based ligands, which are useful
procatalysts for polyolefin polymerizations.5 In addition to
being highly active over wide temperature ranges, these systems
Received: June 15, 2012
Published: August 16, 2012
© 2012 American Chemical Society
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Scheme 1. Thermal Rearrangements of Imino-Amido
a5a,e
,
Complexes
Figure 1. Molecular structure of 5d. Hydrogen atoms, except H1, are
omitted for clarity. Thermal ellipsoids are shown at the 40%
probability level. Selected bond lengths (Å) and angles (deg): C1−
N1 = 1.3843(15), C6−N2 = 1.3701(14), C1−C6 = 1.4338(15), C1−
N1−C10 119.62(9).
a
DIP = 2,6-diisopropyl; Bn = benzyl.
Scheme 3. Synthesis and Metalation of Aminoquinoline
Ligands
Scheme 2. Isomerization of Imino-Enamido Ligands5f
We postulated that aminoquinolines6,7 could provide such a
scaffold, since the aforementioned rearrangements would be
precluded by the aromatic framework. Additionally, the core
structure of the previously reported complexes, a five-
membered metallacycle formed by coordination of the two
nitrogen donors to the hafnium center, would be retained. This
report details the synthesis of such aminoquinoline ligands,
their respective hafnium tribenzyl complexes, and their utility in
copolymerization reactions of ethylene and 1-octene.
dimethylaniline group (Figure 1). Bond angles and distances
are similar to previously characterized aminoquinolines.6,8
The 1H NMR spectrum of 5a at ambient temperature shows
a single broad resonance corresponding to the CH3 groups of
the isopropyl moieties, indicative of a relatively slow chemical
exchange process. This is likely due to hindered rotation of the
aniline group as a result of steric interactions between the ortho
isopropyl groups and the quinolino core. Fast (on the NMR
time scale) rotations of the isopropyl groups and the anilino
group itself along the C−N bond axis would result in the
chemical equivalence of all four of the CH3 groups, which
RESULTS AND DISCUSSION
■
Preparation of Aminoquinoline Ligands. An attractive
feature of the targeted aminoquinoline ligands is their ease of
preparation. Starting from commercially available 8-bromoqui-
nolines (4a and 4b), the ligands can be synthesized in a single
synthetic step (Scheme 3). Specifically, a Pd-catalyzed coupling
reaction of 4a or 4b with the desired substituted aniline
furnished the desired compounds (5a−d) in modest to good
(38−73%) isolated yields. Purification was accomplished via
flash chromatography; 5a, 5b, and 5d were isolated as yellow
solids, while 5c was isolated as a viscous yellow oil. All solid
ligands showed appreciable solubility in aliphatic hydrocarbons
and could be recrystallized if desired. The solid-state structure
of 5d shows a planar quinolino core with an orthogonal 2,6-
1
would appear as one doublet in the H NMR spectrum. In the
case of 5c, containing only one ortho isopropyl group, a single
sharp doublet was observed for the two CH3 groups, indicating
fast rotation of the 2-isopropylphenyl fragment along the N−
C(ipso) bond. Isopropyl groups are convenient indicators of a
ligand’s rotational flexibility; the analogous information on
rotational barriers cannot be gleaned from the ligands
containing ortho methyl groups, 5b and 5d.
Synthesis and Characterization of Hafnium Amido-
quinoline Complexes. The metalations proceeded readily by
stirring the aminoquinolines in a toluene solution with
tetrabenzylhafnium (Scheme 3). These reactions are charac-
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Table 1. Crystallographic Data for Complexes 6a−d, 1a, and 3a
6a
6b
6c
6d
1a
3a
Bond Lengths
2.340(2)
Hf−N1
Hf−N2
Hf−Bn1
Hf−Bn2
Hf−Bn3
2.3453(18)
2.1155(16)
2.2698(22)
2.2344(22)
2.2723(22)
2.3418(1)
2.1170(1)
2.2535(1)
2.2743(0)
2.2858(1)
2.351(3)
2.102(3)
2.166(6)
2.209(6)
2.286(4)
2.313(2)
2.100(2)
2.243(2)
2.288(2)
2.266(2)
2.301(3)
2.074(3)
2.288(3)
2.259(3)
2.253(3)
2.1176(20)
2.2688(25)
2.2559(18)
2.2903(21)
Bond Angles
71.57(6)
N1−Hf−N2
N1−Hf−Bn1
N1−Hf−Bn2
N1−Hf−Bn3
72.02(6)
125.06(7)
111.55(8)
92.46(7)
71.61(5)
123.63(5)
112.58(6)
91.18(6)
72.47(10)
123.8(3)
120.1(3)
87.39(12)
72.57(10)
116.63(11)
123.33(12)
92.93(12)
72.03(6)
117.91(7)
118.56(7)
88.93(7)
125.88(8)
107.56(7)
89.83(7)
terized by an immediate color change to orange-red, indicative
of the formation of the desired complexes. Generally, the
reactions were quite clean, although recrystallization was
performed for all products in order to obtain the complexes
in high purity. The isolated hafnium tribenzyl complexes were
orange to red in color, and all showed limited solubility in
aliphatic hydrocarbons and excellent solubility in toluene and
benzene. The structures of all the hafnium complexes (6a−d)
were confirmed by single-crystal X-ray diffraction, and all show
similar bond distances and angles. These metrical parameters
also match closely with the previously reported imino-amido
complexes5e,f (Table 1). Figure 2 shows the structures of 6a
and 6d as representative examples for the substituted and
unsubstituted quinolino cores, respectively (molecular struc-
tures of 6b and 6c are presented in the Supporting
Information). For the nitrogen donors of the hafnium-bound
amidoquinolines, the anionic Hf−N bond is notably shorter, by
about 0.22 Å, than the neutral quinolino donor, while the Hf−
C bonds to the benzyl groups are all comparable in length. For
6a−c, there is an apparent interaction between the hafnium
center and an ipso carbon from one of the benzyl groups. Pi
donation from the aromatic system to the metal center would
be expected in this case, as the electron-deficient (formally a 10-
electron count) complexes would likely be stabilized in this
manner. All the complexes adopt an approximate trigonal-
bipyramidal structure in the solid state, with the anilino donor
and two of the benzyl ligands occupying the equatorial plane.
The axial quinolino donor is canted slightly to accommodate
the five-membered metallacycle. That is, the rigidity of the
ligand backbone dictates a N−Hf−N angle of ∼72° within the
five-membered ring, rather than the 90° expected for trigonal-
bipyramidal geometry. Likewise, the interactions of the hafnium
center with the ipso carbons of the benzyl groups in 6a−c result
in some deviations from the expected bond angles (Table 1).
The dynamic nature of 6a−d was evidenced by NMR
spectroscopy, which shows the chemical equivalence of the
three benzyl groups, in contrast with their solid-state structures.
1
More specifically, the H NMR spectra for both 6b and 6c at
ambient temperature show sharp resonances at 2.20 and 2.27
ppm, respectively, corresponding to the three equivalent benzyl
groups. For 6a and 6d, however, the analogous resonances are
broad at ambient temperature, indicative of a higher barrier for
the benzyl group exchange process. Fluxional behavior was
further confirmed by heating the NMR solutions of 6a and 6d,
resulting in the expected sharpening of the broad resonances.
The aromatic region of variable-temperature H NMR spectra
of 6d in toluene-d8 is presented in Figure 3, showing resonance
coalescence at 30 °C and fast exchange at 100 °C. This
Figure 2. Molecular structures of 6a (top) and 6d (bottom).
Hydrogen atoms are omitted for clarity. Thermal ellipsoids are
shown at the 40% probability level.
1
dynamic exchange could be the result of a Berry pseudorotation
or a turnstile motion, well-known dynamic processes for
trigonal-bipyramidal organometallic complexes.9 The barrier of
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incorporation, and higher polymer molecular weight. Note that
6a can be viewed as analogous to 1a and 3a since all these
derivatives contain a 2,6-diisopropylanilino moiety, although for
the amidoquinoline ligand decreasing the bulk of the ortho
groups results in several desirable catalytic properties. Similarly,
a comparison of 6a and 6c shows that the latter, with one
unsubstituted ortho position, resulted in poorer efficiency,
comonomer incorporation, and decreased polymer molecular
weight.
The copolymers produced by 6a and 6b comprised multiple
crystallization temperatures, as determined by DSC. This
bimodality is evidence for multiple active catalytic species, a
relatively common phenomenon for high-temperature solution-
phase copolymerization reactions. However, it is often desirable
that the catalyst produce polymers with compositional
homogeneity (i.e., single-site behavior). In general, single-site
catalysts are more easily modeled and controlled in continuous
production processes, and the resulting compositional homo-
geneity can lead to certain microstructural changes, such as
narrowed polydispersity index (PDI). One hypothesis for the
cause of the multisite behavior in the present case is that the
carbon ortho to the quinolino nitrogen could be prone to attack
during the course of the polymerization reaction. Additions of
organometallic reagents to this position are well known,
resulting in dearomatized 2-alkylated quinolines, and can be
mediated by lithium, magnesium, or aluminum species.10 One
possible culprit in the present example, then, is a reaction
between the active catalyst and an aluminum component of
MMAO-3A, which was used as an impurity scavenger in the
copolymerization reactions. For example, the addition of
trimethylaluminum, a component of MMAO-3A, to quinolines
has been reported.10d,e Although additions of trialkylaluminums
across carbon−nitrogen double bonds of nitrogen-containing
heterocycles are notoriously sluggish, in our case the reactivity
could be enhanced by the binding to a strongly Lewis acidic
cationic hafnium center, and the elevated temperatures should
enhance the kinetic feasibility of such a reaction. We reasoned
that an alkyl substitution at this ortho position might protect
against such an attack and decided to prepare a procatalyst
containing the 2,4-dimethylquinoline framework (6d). Indeed,
the copolymer produced by 6d showed a single crystallization
temperature by DSC (Figure 4) and a narrow PDI, evidence
that a single active catalytic species was dominant in this case.
Gratifyingly, 6d also provided a substantial increase in polymer
molecular weight, while retaining good catalytic efficiency and
comonomer incorporation.
Figure 3. Fragment of the variable-temperature 1H NMR spectra of 6d
in toluene-d8 at 30, 65, and 100 °C.
this process seems to trend with the steric bulk of the aniline
group, as a higher barrier is observed for 6a than for 6b or 6c.
The notion that the substitution pattern on the aniline can
impact the energetics of the metal-bound alkyls suggests that
this might be an important element in determining the nature
of the resulting active polymerization catalyst. It is also worth
noting that again the presence of isopropyl moieties on the
aniline ring can provide additional information about the
dynamics of metal complexes. In the case of both 6a and 6c,
two chemically inequivalent CH3 groups are observed as
doublets, indicating hindered rotation about the C−N bond.
The same phenomenon may be occurring for complexes 6b
and 6d, which contain a 2,6-dimethylaniline fragment, although
this cannot be probed directly using NMR spectroscopy.
Copolymerization Study. All new complexes 6a−d were
evaluated as procatalysts for ethylene/1-octene copolymeriza-
tions within a one gallon batch reactor at 120 °C, with 425 psi
of ethylene pressure and 250 g of 1-octene. For comparison,
procatalysts 1a and 3a were also tested under the same reactor
conditions. The copolymers obtained were characterized by
density measurements, gel permeation chromatography (GPC),
differential scanning calorimetry (DSC), and comonomer
content via NMR spectroscopy. The complete results are
presented in Table 2.
Procatalysts 6a−c entail variations in the aniline moiety, with
the quinolino core left unsubstituted. Indeed, the aniline
substitution pattern was observed to have a substantial impact
on the resulting polymerization behavior. The smaller methyl
ortho groups of 6b, in comparison with the isopropyl groups of
6a, resulted in higher catalytic efficiency, improved comonomer
From this set of data, it is apparent that the catalyst derived
from 6d possessed the most desirable combination of catalytic
a
Table 2. Batch Reactor Ethylene/1-Octene Copolymerization Data at 120 °C
procatalyst
octene incorp (wt %)
polymer (g)
activity (g poly/mmol cat)
MW (g/mol)
Mn (g/mol)
PDI
TC (°C)
1a
3a
6a
6b
6c
6d
9.8
18.3
13.4
16.5
6.9
18.3
23.5
19.2
30.9
10.6
28.3
24 339
31 352
25 599
41 165
14 094
37 715
390 690
604 130
280 300
403 610
159 800
632 200
124 180
145 290
100 500
116 760
54 580
3.27
4.16
2.79
3.46
2.93
2.97
108
87
95, 107
89, 115
122
14.9
212 500
93
a
Reactor size = 1 gal. Ethylene pressure = 425 psi (145 g of ethylene). The reactor was also charged with 250 g of 1-octene, 1350 g of Isopar E, and
20 mmol of H2 and heated to 120 °C. Then 0.75 μmol of each catalyst was injected along with 0.85 μmol of cocatalyst
([HNMe(C18H37)2][B(C6F5)4]) and 22.5 μmol of MMAO-3A. Run time was 10 min; all catalysts were inactive after 10 min run time under
these conditions, as evidenced by ethylene uptake monitoring.8
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result of which was the rapid and exothermic production of
poly-1-octene.8
SUMMARY
■
An ongoing goal in our research is to develop new and
improved polyolefin catalysts based on ligands that are easily
accessible, thermally and chemically stable, modular in nature,
and that lead to highly active catalysts at elevated temperatures.
The amidoquinoline complexes described here, inspired by
previously reported polyolefin catalysts comprising bidentate
nitrogen ligands,5e,f meet the above requirements. The ligands
were prepared in a single step, utilizing standard coupling
methods, and the subsequent metalations proceeded cleanly to
provide the desired procatalysts in high yields as hafnium
tribenzyl complexes. Importantly, the aromaticity of these
ligands provides a supporting framework that is resistant to the
isomerization reactions inherent to the previously reported
imino-amido systems.
Each of the hafnium complexes adopted an approximate
trigonal-bipyramidal geometry in the solid state, although in
solution an exchange process was observed that rendered the
three benzyl groups equivalent. The rate of this process, likely a
Berry pseudorotation or a turnstile rotation, is influenced by the
steric bulk of the ligand. For the complexes of the larger ligands,
6a and 6d, the barrier for this dynamic process is high enough
at ambient temperatures that broad resonances corresponding
to the benzyl groups are observed. The procatalyst 6d was
reacted with B(C6F5)3, resulting in the clean formation of the
ion-separated dibenzyl complex 7d, which we propose is the
active species for the polymerization catalysis.
Figure 4. DSC overlay of copolymers produced by 6b and 6d.
attributes. To further investigate the nature of the active
species, an NMR experiment was conducted in which B(C6F5)3,
a commonly used activator, was added to a solution of 6d in
C6D5Cl (Scheme 4). The 1H NMR spectrum showed relatively
Scheme 4. Reaction of 6d with B(C6F5)3 to Form an Ion Pair
The modularity of the aminoquinoline framework was
demonstrated by the preparation of procatalysts with
substitution variations in both the anilino and the quinolino
portions of the ligand, which in turn resulted in the formation
of catalysts with substantially different properties. Specifically,
the alkyl groups in both ortho positions of the aniline group
were found to be beneficial, with 2,6-dimethylaniline being the
optimal choice in the set presented here. Subsequent
modification of the quinolino core, the substitution of methyl
groups in the C2 and C4 positions, served to further improve
the catalytic properties. The resultant procatalyst, 6d, compares
favorably to the previously reported catalysts, providing
incremental improvements in activity and molecular weight
capacity.
clean conversion to the cationic dialkyl species 7d, which is the
result of benzyl group abstraction by the borane activator. The
1H NMR spectrum indicates the formation of a Cs symmetric
species with benzyl groups symmetrically positioned above and
below the plane of symmetry. This is evidenced by the
appearance of two doublets at 2.03 and 1.83 ppm (2JH−H = 10.3
Hz), which correspond to two diastereotopic methylene
protons of the benzyl groups. Additionally, the abstracted
benzyl group is chemically distinct; for example the B-CH2-Ph
protons appear as a slightly broad singlet at 3.35 ppm. Similarly,
the 19F NMR spectrum of 7d is also indicative of ion pair
formation. The chemical shift difference between the meta and
para fluorine resonances (Δδ(m,p-F)) of the major species is
only 2.75 ppm, which indicates that the anion is not
coordinated to the metal center.11 The noncoordinating nature
of the borate anion was also observed for 2a, in which case the
formation of a separated ion pair was ascribed to steric
congestion at the metal center.5a For 7d though, a second
minor species (∼3%) is observable with a larger Δδ(m,p-F) of
4.49 ppm, consistent with a borate anion coordinated to the
hafnium center, although the exact nature of this complex could
not be established with certainty. It should be noted that, upon
standing at ambient temperature overnight, most of 7d
decomposed into three different major species. The thermal
stability is of course an important parameter of the active
species; however, ultimately it is the corresponding thermal
stability in the presence of ethylene, along with the polymer-
ization kinetics, that dictates the catalyst activity. In order to
confirm that 7d was in fact an active species, it was added (3
μmol) to neat 1-octene (11 mL) at room temperature, the
EXPERIMENTAL SECTION
■
General Considerations. Materials were obtained from Aldrich
and used directly, except where noted below. The bromoquinolines 4a
and 4b were purchased from ArkPharm Inc. and Princeton
BioMolecular Research, respectively; both were used directly. rac-
[1,1′-Binaphthalene]-2,2′-diol (rac-BINAP) was obtained from Fluka
and used directly. Isopar E was obtained from Exxon Mobil.
[HNMe(C18H37)2][B(C6F5)4] was obtained from Boulder Scientific.
MMAO-3A was obtained from AkzoNobel. Air-sensitive manipu-
lations were performed in a Vacuum Atmospheres inert atmosphere
glovebox under a dry nitrogen atmosphere or by using standard
Schlenk and vacuum line techniques. Toluene, hexane, and Isopar E
were degassed and dried over alumina and molecular sieves prior to
use as solvents for the air-sensitive procedures.
NMR spectra were recorded on Bruker Avance-400 and Varian
1
VNMRS-400 spectrometers. H NMR data are reported as follows:
chemical shift (multiplicity (br = broad, s = singlet, d = doublet, t =
triplet, q = quartet, sp = septet, and m = multiplet), integration, and
1
assignment). Chemical shifts for H NMR data are reported in ppm
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downfield from internal tetramethylsilane (TMS, δ scale) using
residual protons in the deuterated solvent (C6D6, 7.15 ppm; toluene-
1
d8, 2.09 ppm) as references. 13C NMR data were determined with H
decoupling, and the chemical shifts are reported in ppm vs
tetramethylsilane (C6D6, 128 ppm; toluene-d8, 20.4 ppm). Elemental
analyses were performed at Midwest Microlab, LLC. High-resolution
mass spectroscopy (HRMS) analyses were carried out using flow
injection (0.5 mL of 50/50 v/v % of 0.1% formic acid in water/THF)
on an Agilent 6520 quadrupole-time-of-flight MS system via a dual-
spray electrospray interface operating in the positive ion mode.
Synthesis of Aminoquinolines. A general procedure is as
follows. A round-bottomed flask equipped with a reflux condenser
was charged with Pd2(dba)3 (0.090 mmol), rac-BINAP (0.207 mmol),
and NaOt-Bu (4.05 mmol) in toluene (15 mL). To the resulting
suspension were added the substituted aniline (2.88 mmol) and the
desired bromoquinoline (2.88 mmol). The mixture was heated under
reflux overnight and then pumped down to dryness under vacuum.
The crude residue was purified by flash column chromatography
eluting with 9:1 pentane/diethyl ether.
dd, 3JH−H = 8.2 Hz, 4JH−H = 1.5 Hz, H7), 7.30 (3H, m, H12, H13, and
H14), 7.06 (6H, br t, 3JH−H = 7.5 Hz, H19, H21), 6.94 (1H, t, 3JH−H
=
3
8.2 Hz, H3), 6.81 (3H, br t, JH−H = 7.5 Hz, H20), 6.70 (6H, br d,
3JH−H = 7.5 Hz, H18, H21), 6.59 (1H, dd, 3JH−H = 8.2 Hz, 4JH−H = 1.0
Hz, H4), 6.46 (1H, dd, 3JH−H = 5.0, 8.2 Hz, H8), 6.07 (1H, dd, 3JH−H
=
4
3
8.2 Hz, JH−H = 1.0 Hz, H2), 3.32 (2H, sp, JH−H = 6.8 Hz, C11−
CH(Me)2 and C15−CH(Me)2), 2.33 (6H, br s, H16), 1.30 (6H, d,
3JH−H = 6.8 Hz, CH(CH3)2), 0.98 (6H, d, 3JH−H = 6.8 Hz, CH(CH3)2).
13C{1H} NMR (C6D6): 154.6, 148.8 (C9), 145.5, 145.0, 144.0, 140.6
N-(2,6-Diisopropylphenyl)quinolin-8-amine (5a): yellow solid in
38% yield. 1H NMR (C6D6): 8.56 (1H, d, 3JH−H = 3.5 Hz), 7.92 (1H,
s, NH), 7.53 (1H, d, 3JH−H = 8.1 Hz), 7.23−7.04 (4H, m), 6.79 (1H, d,
3JH−H = 8.1 Hz), 6.77 (1H, dd, 3JH−H = 8.1, 4.0 Hz), 6.35 (1H, d, 3JH−H
(C7), 139.5, 129.6, 129.2 (C3), 128.9, 128.0 (C18, C22), 127.2 (C13),
125.1 (C12, C14), 122.4 (C20), 120.5 (C8), 114.8 (C4), 112.7 (C2),
86.7 (C16), 28.9 (C11-CH(Me)2 and C15-CH(Me)2), 26.1 (CH-
(CH3)2), 24.4 (CH(CH3)2). Anal. Calcd for C42H44N2Hf: C 66.79, H
5.87, N 3.71. Found: C 66.53, H 5.92, N 3.73.
3
= 7.5 Hz), 3.32 (2H, sp, JH−H = 6.8 Hz), 1.10 (12H, br). 13C{1H}
NMR (C6D6): 148.3, 147.3, 145.5, 138.4, 136.1, 135.8, 129.3, 128.1,
124.3, 121.7, 114.9, 106.5, 28.8, 24.9, 23.3. ES-HRMS (m/e): calcd for
C21H24N2 (M + H)+ 305.201, found 305.201.
((2,6-Dimethylphenyl)(quinolin-8-yl)amino)tribenzylhafnium
(6b). A solution of 5b (0.206 g, 0.830 mmol) in toluene (5 mL) was
N-(2,6-Dimethylphenyl)quinolin-8-amine (5b): pale yellow solid in
73% yield. 1H NMR (C6D6): 8.60 (1H, dd, 3JH−H = 4.0 Hz, 4JH−H = 1.5
Hz), 7.83 (1H, s, NH), 7.59 (1H, dd, 3JH−H = 8.1 Hz, 4JH−H = 1.5 Hz),
3
3
7.11 (1H, t, JH−H = 7.9 Hz), 7.03 (3H, br), 6.92 (1H, d, JH−H = 8.1
Hz), 6.83 (1H, dd, 3JH−H = 8.3, 4.0 Hz), 6.35 (1H, dd, 3JH−H = 7.7 Hz,
4JH−H = 0.7 Hz), 2.15 (6H, s). 13C{1H} NMR (C6D6): 147.2, 143.5,
138.7, 138.6, 137.0, 136.0, 129.3, 128.9, 128.1, 126.6, 121.5, 115.1,
106.2, 18.4. ES-HRMS (m/e): calcd for C17H16N2 (M + H)+ 249.131,
found 249.139.
N-(2-Isopropylphenyl)quinolin-8-amine (5c): viscous yellow oil in
57% yield. 1H NMR (C6D6): 8.57 (1H, dd, 3JH−H = 4.2 Hz, 4JH−H = 1.7
Hz), 8.37 (1H, s, NH), 7.59 (1H, dd, 3JH−H = 8.1 Hz, 4JH−H =1.3 Hz),
7.52 (1H, 3JH−H = 7.5 Hz), 7.25 (1H, dd, 3JH−H = 7.3 Hz, 4JH−H = 1.3
cooled to −40 °C, then added to a vial containing HfBn4 (0.425 g,
0.783 mmol). The resulting solution turned red immediately and was
allowed to warm to room temperature and stirred for 1 h. The volume
of toluene was reduced to ca. 2 mL, and hexane (ca. 8 mL) was added,
at which point the solution was cooled to −40 °C. After 1 day, the
resulting red crystals were collected and dried under vacuum, affording
3
4
Hz), 7.17−7.05 (m, 4H), 6.94 (1H, dd, JH−H = 7.7 Hz, JH−H = 1.3
Hz), 6.83 (1H, dd, 3JH3−H = 8.3, 4JH−H = 4.2 Hz), 3.35 (1H, sp, 3JH−H
=
6.8 Hz), 1.14 (6H, d, JH−H = 6.8 Hz). 13C{1H} NMR (C6D6): 147.4,
142.99, 142.97, 139.2, 139.1, 136.1, 129.3, 127.9, 126.8, 126.7, 124.9,
124.2, 121.7, 115.8, 107.3, 28.4, 23.3. ES-HRMS (m/e): calcd for
C18H19N2 (M + H)+ 263.154, found 263.154.
1
the desired product in high purity (0.390 g, 71%). H NMR (C6D6):
7.73 (1H, dd, 3JH−H = 5.0, 4JH−H = 1.5 Hz, H9), 7.45 (1H, dd, 3JH−H
=
N-(2,6-Dimethylphenyl)-2,4-dimethylquinolin-8-amine (5d): pale
8.2, 4JH−H = 1.4 Hz, H7), 7.16 (2H, d, 3JH−H = 7.3 Hz, H12 and H14),
1
yellow solid in 46% yield. H NMR (C6D6): 7.95 (1H, s, NH), 7.16−
3
3
3
4
7.07 (1H, dd, JH−H = 7.3, 7.3 Hz, H13), 7.04 (6H, br t, JH−H = 7.4
7.05 (5H, m), 6.97 (1H, s), 6.41 (1H, d, JH−H = 7.3 Hz, JH−H = 0.9
Hz), 2.55 (3H, s), 2.25 (3H, s), 2.21 (6H, s). 13C{1H} NMR (C6D6):
155.2, 144.2, 143.5, 139.1, 137.8, 137.1, 128.9, 127.4, 126.8, 126.5,
123.0, 111.1, 106.3, 25.1, 18.7, 18.5. ES-HRMS (m/e): calcd for
C19H20N2 (M + H)+ 277.170, found 277.170.
3
Hz, H19 and H21), 6.96 (1H, t, JH−H = 7.9 Hz, H3), 6.81 (3H, t,
3JH−H = 7.4 Hz, H20), 6.66 (6H, d, JH−H = 7.4 Hz, H18, H22), 6.62
3
3
4
3
(1H, dd, JH−H = 7.9 Hz, JH−H = 1.0 Hz, H4), 6.49 (1H, dd, JH−H
=
3
4
5.0, 8.2 Hz, H8), 6.06 (1H, dd, JH−H = 7.9 Hz, JH−H = 1.0 Hz, H2),
2.20 (6H, s, H16), 2.09 (6H, s, C11−CH3 and C15−CH3). 13C{1H}
NMR (C6D6): 152.7, 148.7 (C9), 147.1, 144.5 (C7), 140.5, 139.8,
135.3, 130.3 (C3), 129.5 (C12 and C14), 129.3, 129.0 (C19 and C21),
128.2 (C18 and C22), 126.2 (C13), 122.6 (C20), 120.5 (C8), 114.6
(C4), 110.1 (C2), 85.3 (C16), 18.4 (C11-CH3 and C15-CH3). Anal.
Calcd for C38H36N2Hf: C 65.28, H 5.19, N 4.01. Found: C 65.09, H
5.31, N 4.07.
Synthesis of Hafnium Tribenzyl Complexes. Full multinuclear
and multidimensional spectroscopic characterization by NMR was
conducted, and the complete results, including actual NMR spectra,
1
are presented in the Supporting Information. From these data, H
NMR and 13C{1H} NMR assignments were made, where possible, as
indicated below. The numbering convention used for these assign-
ments is consistent with that used for the solid-state structures.
((2,6-Diisopropylphenyl)(quinolin-8-yl)amino)tribenzylhafnium
(6a). A solution of 5a (0.285 g, 0.936 mmol) in toluene (5 mL) was
cooled to −40 °C, then added to a vial containing HfBn4 (0.480 g,
0.883 mmol). The resulting solution turned deep red immediately and
was allowed to warm to room temperature and stirred for 1 h. The
volume of toluene was reduced to ca. 2 mL, and hexane (ca. 8 mL) was
added, at which point the solution was cooled to −40 °C. After 1 day,
the resulting deep red crystals were collected and dried under vacuum,
((2-Isopropylphenyl)(quinolin-8-yl)amino)tribenzylhafnium (6c).
A solution of 5c (0.203 g, 0.774 mmol) in toluene (5 mL) was
cooled to −40 °C, then added to a vial containing HfBn4 (0.396 g,
0.730 mmol). The resulting solution turned orange immediately and
was allowed to warm to room temperature and stirred for 1 h. The
volume of toluene was reduced to ca. 2 mL, and hexane (ca. 8 mL) was
added, at which point the solution was cooled to −40 °C. After 1 day,
the resulting orange crystals were collected and dried under vacuum,
1
1
affording the desired product in high purity (0.515 g, 80%). H NMR
affording the desired product in high purity (0.383 g, 74%). H NMR
(C6D6): 7.72 (1H, dd, 3JH−H = 5.0 Hz, 4JH−H = 1.5 Hz, H9), 7.42 (1H,
(C6D6): 7.72 (1H, dd, 3JH−H = 5.0 Hz, 4JH−H = 1.5 Hz, H9), 7.43 (1H,
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dd, 3JH−H = 8.2 Hz, 4JH−H = 1.5 Hz, H7), 7.40 (1H, m, H12), 7.22 (2H,
m, H13, H14), 7.03 (6H, dd, 3JH−H = 7.4, 7.8 Hz, H19 and H21), 6.95
3JH−H = 7.4 Hz, H18, H22), 6.09 (1H, dd, 3JH−H = 7.3 Hz, 3JH−H = 1.3
Hz, H2), 3.35 (2H, br, B(CH2Ph)), 2.36 (3H, s, C7-CH3), 2.03 (2H,
d, 3JH−H = 10.3 Hz. H16a), 1.93 (C11-CH3 and C15-CH3), 1.83 (2H,
(1H, t, J = 8.0 Hz, H3), 6.87 (1H, m, H15), 6.78 (3H, t, J = 7.4 Hz,
3
H20), 6.68 (6H, d, J = 7.8 Hz, H18 and H22), 6.60 (1H, dd, JH−H
=
8.0, 4JH−H = 1.0 Hz, H4), 6.50 (1H, dd, 3JH−H = 5.0, 8.2 Hz, H8), 6.07
3
3
3
3
d, JH−H = 10.3 Hz, H16b), 1.54 (3H, s, C9-CH3). 19F NMR
(1H, dd, JH−H = 8.0 Hz, JH−H = 1.0 Hz, H2), 3.31 (1H, sp, JH−H
=
2
3
6.8 Hz, C11−CH(Me)2), 2.29 (3H, d, JH−H = 12.1 Hz, H16), 2.25
(C6D5Cl): (major species, free anion) −130.5 (2F, d, JF−F = 23 Hz,
2
3
ortho-C6F5), −164.1 (1F, t, 3JF−F = 21 Hz, para-C6F5), −166.9 (2F, dd,
(3H, d, JH−H = 12.1 Hz, H16), 1.28 (3H, d, JH−H = 6.8 Hz,
CH(CH3)2), 1.04 (3H, d, 3JH−H = 6.8 Hz, CH(CH3)2). 13C{1H} NMR
(C6D6): 154.8, 148.5 (C9), 146.11, 146.08, 144.3, 140.2 (C7), 139.9,
129.8 (C3), 129.3 (C15), 129.0 (C19 and C21), 128.1 (C18 and
C22), 127.7 (C12), 127.5 (C14), 127.0 (C13), 125.6, 122.5 (C20),
120.6 (C8), 114.4 (C4), 111.7 (C2), 84.7 (C16), 28.0 (C11-
CH(Me)2), 25.3 (CH(CH3)2), 24.1 (CH(CH3)2). Anal. Calcd for
C39H38N2Hf: C 65.68, H 5.37, N 3.93. Found: C 65.76, H 5.59, N
3.72.
3JF−F = 21, 23 Hz, meta-C6F5); (minor species, coordinated anion)
3
3
−130.8 (2F, d, JF−F = 21 Hz, ortho-C6F5), −159.4 (1F, t, JF−F = 21
3
Hz, para-C6F5), −163.9 (2F, t, JF−F = 21 Hz, meta-C6F5).
Structure Determinations of 5d, 6a, 6b, 6c, and 6d. X-ray
intensity data were collected on a Bruker SMART diffractometer using
Mo Kα radiation (λ = 0.71073 Å) and an APEXII CCD area detector.
Raw data frames were read by the program SAINT12 and integrated
using 3D profiling algorithms. The resulting data were reduced to
produce hkl reflections and their intensities and estimated standard
deviations. The data were corrected for Lorentz and polarization
effects, and numerical absorption corrections were applied based on
indexed and measured faces. The structure was solved and refined in
SHELXTL6.1, using full-matrix least-squares refinement. The non-H
atoms were refined with anisotropic thermal parameters, and all of the
H atoms were calculated in idealized positions and refined riding on
their parent atoms. The refinement was carried out using F2 rather
than F values. R1 is calculated to provide a reference to the
conventional R value, but its function is not minimized.
((2,6-Dimethylphenyl)(2,4-dimethylquinolin-8-yl)amino)-
tribenzylhafnium (6d). A solution of 5d (0.155 g, 0.561 mmol) in
Batch Reactor Ethylene/Octene Copolymerizations. A one
gallon (3.79 L) stirred autoclave reactor is charged with ca. 1.35 kg of
Isopar E mixed alkanes solvent and 1-octene (250 g). The reactor is
heated to the desired temperature and charged with hydrogen (20
mmol) followed by approximately 125 g of ethylene to bring the total
pressure to ca. 425 psig (2.95 MPa). The ethylene feed was passed
through an additional purification column. The catalyst composition is
prepared in a drybox under inert atmosphere by mixing the catalyst
and cocatalyst (mixture of 1.2 equiv of [HNMe(C18H37)2][B(C6F5)4]
and 50 equiv of triisobutylaluminum-modified alumoxane (MMAO-
3A)) with additional solvent to give a total volume of about 17 mL.
The activated catalyst mixture is injected into the reactor over ca. 4
min by a pump system. The reactor pressure and temperature are kept
constant by feeding ethylene during the polymerization and cooling
the reactor as needed. After 10 min, the ethylene feed is shut off and
the solution transferred into a nitrogen-purged resin kettle. An additive
solution containing a phosphorus stabilizer (Irgafos 168 from Ciba
Geigy Corp.) and phenolic antioxidant (Irganox 1010 from Ciba Geigy
Corp.) is added to give a total additive content of approximately 0.1%
in the polymer. The polymer is thoroughly dried in a vacuum oven.
The reactor is thoroughly rinsed with hot Isopar E between
polymerizations.
Polymer Characterization. Melting and crystallization temper-
atures of polymers were measured by differential scanning calorimetry
(DSC 2910, TA Instruments, Inc.). Samples were first heated from
room temperature to 180 °C at 10 °C/min. After being held at this
temperature for 2−4 min, the samples were cooled to −40 °C at 10
°C/min, held for 2−4 min, and then heated to 160 °C. Weight average
molecular weights (Mw) and polydispersity values (PDI) were
determined by analysis on a Viscotek HT-350 gel permeation
chromatograph (GPC) equipped with a low-angle/right-angle light-
scattering detector, a four-capillary inline viscometer, and a refractive
index detector. The GPC utilized three Polymer Laboratories PLgel 10
toluene (5 mL) was cooled to −40 °C, then added to a vial containing
HfBn4 (0.287 g, 0.529 mmol). The resulting solution turned orange
immediately and was allowed to warm to room temperature and
stirred for 1 h. The volume of toluene was reduced to ca. 2 mL, and
hexane (ca. 8 mL) was added, at which point the solution was cooled
to −40 °C. After 1 day, the resulting orange crystals were collected and
dried under vacuum, affording the desired product in high purity
1
3
(0.325 g, 85%). H NMR (toluene-d8): 7.14 (2H, d, JH−H = 7.6 Hz,
H12 and H14), 7.06 (1H, dd, 3JH−H = 7.6 Hz, 7.6 Hz, H13), 7.00 (1H,
3
t, JH−H = 8.0 Hz, H3), 6.87 (6H, br, H19 and H21), 6.80 (1H, dd,
3JH−H = 8.0 Hz, 4JH−H = 1.0 Hz, H4), 6.66 (3H, br, H20), 6.55 (6H, br,
H18 and H22), 6.27 (1H, s, H8), 6.12 (1H, dd, 3JH−H = 8.0 Hz, 4JH−H
= 1.0 Hz, H2), 2.46 (6H, br, H16), 2.14 (6H, s, C11-CH3 and C15-
CH3), 2.06 (3H, s, C7-CH3), 2.03 (3H, s, C9-CH3). 13C{1H} NMR
(toluene-d8): 163.1, 156.4, 154.8, 151.7, 151.3 (br), 143.6, 142.1,
140.0, 134.3 (C12 and C14), 133.5 (C3), 132.9 (br, C19 and C21),
132.3 (C18 and C22), 130.8 (C13), 128.9 (C8), 126.7 (br, C20), 116.1
(C4), 115.4 (C2), 93.9 (br, C16), 29.9 (C9-CH3), 23.30 (C11-CH3
and C15-CH3), 23.28 (C7-CH3). Anal. Calcd for C40H40N2Hf: C
66.06, H 5.54, N 3.85. Found: C 66.35, H 5.43, N 3.70.
[((2,6-Dimethylphenyl)(2,4-dimethylquinolin-8-yl)amino)-
dibenzylhafnium] [tris(pentafluorophenyl)benzylborate] (7d). Com-
plex 6d (25 mg, 0.03 mmol) was dissolved in 0.6 mL of C6D5Cl. This
solution was added to a vial containing 16.9 mg (0.03 mmol) of
1
B(C6F5)3. NMR spectra were taken 10 min after mixing. H NMR
(C6D5Cl): 7.16 (4H, m, H3, H13, ortho-C6H5CH2B), 7.10 (3H, m,
3
H4, H12, H14), 6.95 (2H, t, JH−H = 7.6 Hz, meta-C6H5CH2B), 6.85
3
3
(6H, tm JH−H = 7.8 Hz, H19, H21), 6.80 (1H, tt, JH−H = 7.3 Hz,
4JH−H = 1.3 Hz, para-C6H5CH2B), 6.78 (1H, t, JH−H = 0.9 Hz, H8),
6.63 (2H, tt, JH−H = 7.6 Hz, JH−H = 1.1 Hz, H20), 6.18 (4H, dm,
4
3
4
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μm MIXED-B columns (300 × 7.5 mm) at a flow rate of 1.0 mL/min
in 1,2,4-trichlorobenzene at either 145 or 160 °C.
26, 3896−3899. (b) Mashima, K.; Ohnishi, R.; Yamagata, T.; Tsurugi,
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(6) For selected examples of metal complexes of aminoquinolines,
see: (a) Lee, J. C.; Muller, B.; Pregosin, P.; Yap, G. P. A.; Rheingold,
A. L.; Crabtree, R. H. Inorg. Chem. 1995, 34, 6295−6301. (b) Peters., J.
C.; Harkins, S. B.; Brown, S. D.; Day, M. W. Inorg. Chem. 2001, 40,
5083−5091. (c) Pi, C.; Zhang, Z.; Pang, Z.; Zhang, J.; Luo, J.; Chen,
Z.; Weng, L.; Zhou, X. Organometallics 2007, 26, 1934−1946.
(d) Betley, T. A.; Qian, B. A.; Peters, J. C. Inorg. Chem. 2008, 47,
11570−11782. (e) Deraeve, C.; Maraval, A.; Vendier, L.; Faugeroux,
V.; Pitie, M.; Meunier, B. Eur. J. Inorg. Chem. 2008, 36, 5622−5631.
(f) Betley, T. A.; Qian, B. A.; Peters, J. C. Inorg. Chem. 2008, 47,
11570−11582. (g) Malassa, A.; Koch, C.; Stein-Schaller, B.; Gorls, H.;
Friedrich, M.; Westerhausen, M. Inorg. Chim. Acta 2008, 361, 1405−
1414. (h) O’Neill, M. K.; Trappey, F. A.; Battle, P.; Boswell, C. L.;
Blauch, D. N. Dalton Trans. 2009, 3391−3394. (i) Liu, D.; Cui, D.
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Octene incorporation was determined by 13C NMR.13 The samples
were prepared by adding approximately 2.7 g of a 50/50 mixture of
tetrachloroethane-d2/ortho-dichlorobenzene containing 0.025 M Cr3+
to 0.25 g of the respective copolymer sample in a Norell 1001-7 10
mm NMR tube. The samples were dissolved and homogenized by
heating the tube and its contents to 150 °C using a heating block and
heat gun. Each sample was visually inspected to ensure homogeneity.
The data were collected using a Bruker AVANCE 400 MHz
spectrometer equipped with a Bruker Dual DUL high-temperature
CryoProbe. The data were acquired using 320 transients per data file, a
6 s pulse repetition delay, 90 degree flip angles, and inverse gated
decoupling with a sample temperature of 120 °C. All measurements
were made on nonspinning samples in locked mode. Samples were
allowed to thermally equilibrate for 7 min prior to data acquisition.
The 13C NMR chemical shifts were internally referenced to the EEE
triad at 30.0 ppm.
ASSOCIATED CONTENT
* Supporting Information
This material is available free of charge via the Internet at
http://pubs.acs.org.
■
S
AUTHOR INFORMATION
Notes
The authors declare no competing financial interest.
(7) For examples of polymerization catalysts utilizing quinoline-based
ligands, see: (a) Nagy, S.; Krishnamurti, R.; Tyrell, J. A.; Cribbs, L. V.;
Cocoman, M. (Occidental Chemical Corporation, USA), Appl.-
WO9633202, 1996. (b) Fontaine, P. P.; Kuhlman, R. L. (Dow Global
Technologies), Appl. WO2011102990, 2011. (c) Nagy, S.; Winslow,
L. N.; Mihan, S.; Chevalier, R.; Lukesova L.; Nifant’ev, I. E.; Ivchenko,
P. V.; (Equistar Chemicals), Appl. WO2011011040, 2011. (d) Nagy,
S.; Winslow, L. N.; Mihan, S.; Chevalier, R.; Lukesova L.; Nifant’ev, I.
E.; Ivchenko, P. V.; Lynch, M. W. (EquistarChemicals), Appl.
WO2011011041, 2011. (e) Lamberti, M.; Bortoluzzi, M.; Paolucci,
G.; Pellecchia, C. J. Mol. Catal. A: Chem. 2011, 351, 112−119.
(f) Nagy, S.; Winslow, L. N.; Mihan, S.; Lukesova, L.; Nifant’ev, I. E.;
Ivchenko, P. V.; Bagrov, V. V. (Basell Polyolefine GmbH, Germany),
Appl. US20120016092, 2012. (g) Song, S.; Xiao, T.; Wang, L.;
Redshaw, C.; Wang, F.; Sun, W.-H. J. Organomet. Chem. 2012, 699,
18−25.
■
ACKNOWLEDGMENTS
■
The authors are grateful to Donald Lowry for carrying out the
batch reactor experiments and Manjiri Paradkar for 13C NMR
determination of octene incorporation.
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dx.doi.org/10.1021/om3005417 | Organometallics 2012, 31, 6244−6251