Zirconium and hafnium complexes based on 2-aryl-8-arylaminoquinoline ligands: Synthesis, molecular structure, and catalytic performance in ethylene copolymerization

Article abstract of DOI:10.1039/c2dt31856c

A general and efficient approach toward new zirconium and hafnium complexes based on 2-aryl-8-arylaminoquinoline ligands was developed. These precursors, when activated with MAO/borate cocatalyst and supported on silica, result in active olefin polymeriza

Full text of DOI:10.1039/c2dt31856c

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Zirconium and hafnium complexes based on 2-aryl-8-
arylaminoquinoline ligands: synthesis, molecular
structure, and catalytic performance in ethylene
copolymerization†
Cite this: DOI: 10.1039/c2dt31856c
Ilya E. Nifant’ev,*a,b Pavel V. Ivchenko,a Vladimir V. Bagrov,a Sandor M. Nagy,*c
Linda N. Winslow,c Jean A. Merrick-Mack,c Shahram Mihand and Andrei V. Churakove
A general and efficient approach toward new zirconium and hafnium complexes based on 2-aryl-8-aryl-
aminoquinoline ligands was developed. These precursors, when activated with MAO/borate cocatalyst
and supported on silica, result in active olefin polymerization catalysts. The ethylene copolymers pro-
duced under industrially relevant conditions show very high molecular weights and unique microstruc-
tures defined by the multisite nature of the catalyst. A site-diversification mechanism is proposed to
explain the presence of at least five individual sites, as deduced from 3D-TREF analysis of ethylene–
butene copolymers.
Received 14th August 2012,
Accepted 26th September 2012
DOI: 10.1039/c2dt31856c
www.rsc.org/dalton
Introduction
We continue to witness remarkable progress toward new poly-
olefins enabled by an increasing number of post-metallocene
catalyst precursors based on various chelating-ligand topolo-
gies.1 Selected recent examples of catalyst precursors with
various multi-dentate ligands and metal centers are presented
in Scheme 1. Phenoxyimine–titanium complexes A were shown
to be active catalyst precursors capable of sustaining the living
polymerization of olefins under certain conditions,2 whereas
bis-imino pyridine complexes of iron B, depending on the
nature of the aryl substituent, led to a wide range of oligomeric
to high-molecular-weight products.3 Complexes C,4 D5 and E6
further illustrate the fascinating diversity of chelating-ligand
environments that support catalytically active sites of respect-
able activity.
The purpose of the current study is to present a general syn-
thetic approach that leads to a large variety of [CNN] chelate
Scheme 1 Post-metallocene catalyst precursors.
aDepartment of Chemistry, M. V. Lomonosov Moscow State University, Leninskie
Gory, 1-3, Moscow 119991, Russia. E-mail: inif@org.chem.msu.ru
bA. V. Topchiev Institute of Petrochemical Synthesis RAS, 29 Leninsky Prosp., Moscow
119991, Russia
complexes based on the quinoline scaffold F, which is struc-
turally related to the popular pyridine-based [CNN] chelate
topology E6 (Scheme 1).
cEquistar Chemicals LP, Cincinnati, OH 45249, USA.
The quinoline building block explored in recent studies7
proved to be a very prolific ligand framework because of the
relative ease of independent variation of the substituents in
positions 2 and 8 of the quinoline ring systems. These vari-
ations generate a wide range of ligand precursors, which, in
turn, allows broad control of the electronic and steric
E-mail: Sandor.Nagy@lyondellbasell.com
dBasell Polyolefine GmbH, Frankfurt am Main, D-65926, Germany
eN. S. Kurnakov Institute of General and Inorganic Chemistry RAS, 31 Leninsky
Prosp., Moscow, 119991, Russia
†Electronic supplementary information (ESI) available. CCDC 859965–859967.
For ESI and crystallographic data in CIF or other electronic format see DOI:
10.1039/c2dt31856c
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Fig. 1 General synthetic strategy toward complexes F.
Scheme 2 Preparation of 2-aryl-8-arylaminoquinolines 7–12.
properties of the inner coordination sphere of the metal reaction rate and increased selectivity via suppression of the
center. Recent publications from several groups clearly indi- hydrolytic deborylation side reaction.10e
cate the rapidly increasing popularity of the quinoline tem-
An alternative method to prepare the bi-aryls is the Negishi
plate in the design of next-generation polymerization systems.7 cross-coupling of zinc-organic compounds with aryl-halides.11
This method has been successfully used12 to prepare 2-aryl-
pyridines through the use of in situ aryl-zinc compounds gen-
erated via the reaction of aryl-lithium compounds with ZnCl2.
Results and discussion
In this study, we successfully demonstrated that dibromo-qui-
2,8-Dibromoquinoline 1, which was selected as a convenient
noline 1 can be efficiently arylated in the 2-position using in
starting material for the complexes F in this study, can be
situ ArZnCl and the Pd(dba)2/PPh3 catalyst, which results in
easily prepared in three steps from 2-bromoaniline using
high yields of 5 and 6. To the best of our knowledge, this is the
first example of the utilization of Negishi coupling to prepare
2-aryl-quinolines.
Because the sterically hindered amides and imides of tran-
sition metals with ortho-substituted aryl fragments usually
known procedures.8 The general approach toward the various
ligand precursors is based on the significantly different reac-
tivity of bromine atoms attached to the azine versus the
benzene parts of the ring system – position 2 vs. 8 (Fig. 1).
demonstrate improved performance compared to un-hindered
Preparation of quinoline-based CNN-type ligands
analogues,6 we selected 2,6-dimethyl- and 2,6-di-isopropyl-ani-
The transformation of 2,8-dibromoquinoline 1 into the [CNN]-
lines for further functionalization of intermediates 2–6
type ligand precursors were accomplished in two consecutive
(Scheme 2). The amination of 2-aryl-8-bromoquinolines is fast
steps. In the first stage, selective substitution of the bromine
atom at position 2 resulted in 2-aryl-8-bromoquinolines 2–6;
and selective in the presence of the (N-[2′-(dicyclohexylphos-
phino)[1,1′-biphenyl]-2-yl]-N,N-dimethylamine)
ligand,13
subsequent Buchwald–Hartwig amination of these intermedi-
ates resulted in the target compounds 7–12 (Scheme 2); this
procedure is similar to that previously reported for the syn-
thesis of 2-phenyl-8-phenylaminoquinoline.8b
whereas several attempts to use more accessible phosphines
(PPh3, P(o-tolyl)3, PCy3) resulted in low yields of the desired
compounds.
To prepare the intermediates 2–4, we selected the general
Suzuki–Miyaura method9 and started from commercially avail-
Preparation of group 4 metal complexes
able arylboronic acids (Scheme 2) using the Pd(OAc)2/ We found that group 4 complexes based on the new ligand pre-
P(o-tolyl)3 catalyst in a two-phase DME/water system.10 The cursors 7–12 can be conveniently generated by their reaction
undesirable need for an excess of arylboronic acids can be with ZrBn4 or HfBn4 reagents14 (Scheme 3). This successful
avoided through the use of sterically demanding phosphines synthesis results from the coordination of the metal to the
instead of the traditional PPh3, which ensures a higher nitrogen atom of the quinoline system with subsequent
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Scheme 3 Preparation of group 4 metal complexes 13–21.
Fig. 3 Molecular structures of 15 and 16. Displacement ellipsoids are drawn at
Fig. 2 1H NMR (400 MHz) monitoring on the reaction of 7 with an excess of
the 50% probability level. Hydrogen atoms are omitted for clarity.
ZrBn4 in C6D6: after 5 min at 20 °C (top), and after 1 h at 60 °C (bottom).
the reaction of the 2,6-diisopropyl-N-[[6-(1-naphthyl)-2-pyridi-
nyl](phenyl)-methyl]aniline ligand during the preparation of
complex E with ZrBn4 also failed to detect the presumable tri-
benzyl intermediates.15 The interaction of ligands 7–9 with
HfBn4 (Scheme 3) is somewhat slower than with the Zr reagent
and requires 4–6 h at 60–70 °C.
The fast and highly selective interaction of quinoline-based
[CNN] ligand precursors with the metal source allowed us, in
several cases, to circumvent the need to isolate the metal
complex pre-catalysts for our polymerization studies and to
use the solutions of neutral ligands with the tetra-benzyl metal
reagents as in situ precursors to prepare the catalysts.
formation of the intermolecular amide bond and cyclo-metal-
lation through the reaction of the metal center with the 2-aryl
group.
Remarkably, the reaction of compounds 7–12 with ZrBn4 is
very fast: the combination of the reagents at ambient tempera-
ture immediately resulted in the formation of a red solution
with a gradual increase in the intensity of the color with time.
The reaction is complete in 10–15 h at room temperature,
whereas it is complete in approximately 1 h at 60 °C, as con-
firmed by NMR monitoring of the reaction mixture of com-
pound 7 with an excess of ZrBn4 (Fig. 2).
The reaction is very selective and results in the formation of
the sole target complex 13 without the detection of the
hypothetical tribenzyl-amide intermediates. The observed high
reactivity of the quinoline-based ligand precursors contrasts
sharply with the similar reaction of the previously reported
pyridine analogues,15 which usually requires extended heating
to complete the process (12–18 h, 70 °C). NMR monitoring of
X-ray structure determination of 15, 16, and 18
The structures of closely related dibenzyl Hf and Zr complexes
15, 16, and 18 with 2-(8-(phenylamino)quinolin-2-yl)naphthyl-
C,N,N′ ligands are shown in Fig. 3 and 4.
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Table 1 Selected bond lengths (Å) and angles (°) in 15, 16, and 18
15, M = Zr
16, M = Hf
18, M = Hf
M–C(1)
2.295(4)
2.305(3)
2.163(3)
2.285(4)
2.309(4)
3.029(4)
2.646(4)
104.9(2)
86.0(2)
2.266(3)
2.269(2)
2.128(2)
2.241(3)
2.257(3)
2.894(3)
2.740(3)
100.1(2)
92.26(19)
2.281(6)
2.274(6)
2.148(6)
2.232(7)
2.234(8)
2.910(8)
2.777(7)
101.5(5)
95.3(5)
M–N(1)
M–N(2)
M–C(21)
M–C(31)
M–C(22)
M–C(32)
C(22)–C(21)–M
C(32)–C(31)–M
1
observed for all complexes as doublet of doublets in H NMR
spectra with characteristic 2J ∼ 10–12 Hz (diastereotopic –CH2–
hydrogen atoms), and as a singlet in 13C NMR spectra. No
short intermolecular contacts were observed in the structures
of 15, 16, and 18. To the best of our knowledge, only two struc-
tures of metal complexes (Pt and Pd) bearing 2-aryl-8-quinoli-
namine ligands have been reported to date.8b
Ethylene/1-butene co-polymerization
Fig. 4 Molecular structure of 18. Displacement ellipsoids are drawn at the
A series of ethylene co-polymerization reactions were per-
formed with complexes 13–21, as well as with the earlier
reported C1-symmetric Hf–pyridylamido complex E6 under
industrially relevant slurry polymerization conditions using
silica-supported recipes pre-activated with MAO and an
optional borate cocatalyst (Table 2).
50% probability level. Hydrogen atoms are omitted for clarity.
The geometry of the metal core is similar in all three struc-
tures. The central metal atoms have irregular coordination
polyhedral with CN = 6. Expectedly, the M–N(2) single bonds
are approximately 0.15 Å shorter than the M←N(1) coordi-
nation bonds.
Under our testing conditions, the Zr complexes were more
active than their Hf analogues (complexes 13, 15, 17 vs. 14, 16,
18, correspondingly). The utilization of a mixed MAO/borate
activator results in a further increase in the catalyst pro-
ductivity compared to the individual components, as illus-
trated by the comparison of run 12 to runs 10 and 11 and
further by the comparison of runs 7 vs. 6 and 24 vs. 23. The
catalyst in this study showed a steep deactivation, as illustrated
by the ethylene consumption curves vs. time (Fig. 5), which
show only a small effect of the polymerization temperature on
the profile. The initial, extremely high activity during the first
10 min of the test (50 000 kg mol M−1 h−1 and higher in some
cases) usually decreases to moderate values between 10 000
and 5 000 kg mol M−1 h−1. The catalyst samples exhibited a
good shelf-life, and, in the case of complex 17, the catalyst was
demonstrated to retain its initial performance in a supported
MAO/borate pre-activated recipe for more than 1 month.
The catalysts generated using the new complexes based on
the quinoline template show a high molecular weight potential
in co-polymerization experiments without H2; this potential
significantly exceeds that of complex E based on the pyridine
scaffold. The strongly pronounced deactivation kinetic profile
of these complexes is a general observation and needs further
understanding. Traditional supported metallocenes or mag-
nesium chloride supported Ziegler–Natta catalysts tested in
these conditions usually show much less dramatic decay of
activity with time.
Both the quinoline and naphthyl moieties are planar within
0.140(6) Å. In all of the structures, these fragments lie in
approximately the same plane because the angles between
them are 26.7(1), 10.1(1) and 18.2(2)° for 15, 16, and 18,
respectively. As a consequence, in all cases, the central metal
atoms and the coordinated atoms C(1), N(1), and N(2) also lie
in the same planes (within 0.147(3) Å). The C(21) benzyl atoms
are arranged approximately perpendicular to these planes,
whereas the C(31) benzyl atoms lie in the trans-position rela-
tive to the N(1) atoms. The M–C(21) and M–C(31) bond lengths
are consistent with those expected for Hf and Zr complexes.16
However, the coordination modes of apical (containing C(21)
atoms) and equatorial (containing C(31) atoms) benzyl ligands
are noticeably different. All of the M–C(32) distances are sig-
nificantly shorter than the M–C(22) distances (see Table 1).
On the other side, the C(22)–C(21)–M angles are close to
the tetrahedral value, whereas the C(32)–C(31)–M angles
(86.0(2)–95.3(5)°) are significantly less than 109.2°.
Thus, the apical benzyl ligand may be treated as η1-coordi-
nated, whereas the equatorial one represents the η2-coordi-
nation mode. Probably, the latter case is the result of
electronic effects induced by the 2-(8-(phenylamino)quinolin-
2-yl)naphthyl-ligands. In solution under ambient conditions
benzyl groups are equivalent: the signal of –CH2-groups is
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Table 2 Ethylene co-polymerization with 1-butene with MAO (and optional [Ph3C][B(C6F5)4])-activated and silica-supported complexesa
[Ph3C] [B(C6F5)4]/
M molar ratio
Activity,
Mw, ×103
Ethyl branches/
1000C
Run
Complex
Polym. T, °C
H2, mmol
kg mol−1 M × h
g mol−1
MwMn
1
2
E
E
70
70
1.1
1.1
0
84.9
5491
2592
23.4
Wax
15.3
37.8
3
4
5
13
13
14
70
70
70
1.1
1.1
0
0
84.9
0
9411
7479
0
1063
182
11.7
8.3
15.6
14.6
6
7
8
9
15
15
15
16
70
70
70
70
0
0
1033
5703
6794
0
1594
Insoluble
279
22.6
13.4
15.8
20.0
19.0
1.1
1.1
0
0
84.9
0
10
11b
12
13
14
15
16
17
18c
19d
20
21
22
23
24
17
17
17
17
17
17
17
17
17
17
17
17
17
18
18
70
70
70
70
70
70
70
70
70
70
55
60
80
70
70
0
0
1747
789
1533
1348
Insoluble
804
16.8
97.5
10.2
10.3
17.4
16.8
16.5
14.0
17.1
20.8
44.6
na
1.1
1.1
1.1
1.1
1.1
1.1
1.1
1.1
1.1
1.1
1.1
1.1
0
0
0
5069
9637
10 959
11 062
10 410
5735
10 624
2426
5576
7611
5660
0
4.0
11.5
14.2
15.5
19.7
21.2
18.0
42.6
24.4
15.7
17.5
7.9
507
34.0
84.9
169.8
169.8
169.8
169.8
169.8
169.8
0
476
287
211
143
256
280
16.6
18.8
25.3
266
130
1.1
0
1068
Insoluble
24.9
25
26
19e
19e
70
70
1.1
1.1
0
84.9
3811
3450
Insolublef
Insolubleg
6.7
7.2
27
29
20
20
70
70
1.1
1.1
0
84.9
5273
4724
Insoluble
255
15.0
13.0
9.7
29
30
21
21
70
70
1.1
1.1
0
84.9
6783
8908
Insoluble
224
18.6
20.7
10.5
a Polymerizations were performed in a 2 L autoclave reactor with 3–8 μmol of metal complex in 1 L of isobutene diluent at 15 bar partial
pressure of ethylene in the presence of 100 mL of 1-butene co-monomer and 1 mL of 1 M triisobutylaluminum scavenger. The
supported catalyst was injected into an equilibrated reactor at the polymerization temperature and pressure, and the ethylene pressure
was maintained throughout the 30–60 min test. The silica-supported catalysts were prepared by dissolving the optional [Ph3C][B(C6F5)4]
cocatalyst in 4.21 M MAO solution in toluene, followed by the complex (Al : B : metal: 200 : 1.1 : 1) and adding the resulting solution to a
silica support calcined at 600 °C; this reaction resulted in a free-flowing powder, which was aged overnight before testing. b The [Ph3C]-
[B(C6F5)4] was used only as an activator. c A short, 11 min run. d Homopolymerization of ethylene. e Complex prepared in situ by reacting
an equimolar amount of complex 19 with tetrabenzylzirconium. f The intrinsic viscosity determined in decalin at 145 °C was 18.2 dl g−1
.
g The intrinsic viscosity determined in decalin at 145 °C was 17.7 dl g−1
.
When the samples were sufficiently soluble to allow gel
permeation chromatography (GPC), the Mw was greater than
106 g mol−1. Hydrogen is an effective chain-transfer agent in
the polymerization that allows the molecular weight to be con-
trolled over a broad range of values (Fig. 6, Table 2). All poly-
mers produced with the new catalyst exhibit
a broad
molecular-weight distribution (Table 2), which indicates the
presence of several active sites.
Although various sites generated from the same precursor
are likely to already be present in the pre-activated supported
catalyst before the test, the transformation of the existing sites
is clearly indicated to continue during the polymerization, as
illustrated by the effect of residence time in runs 17 and 18 on
the Mw, Mw/Mn and GPC profiles (Table 2, Fig. 7). The co-
monomer incorporation level in the ethylene–butene
Fig. 5 Ethylene consumption curves in runs 20 (55 °C), 21 (60 °C) and 17
(70 °C) in co-polymerization tests conducted in the presence of 169.8 mmol of
H2 with a catalyst based on complex 17.
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Fig. 6 Effect of H2 on the Mw of ethylene/1-butene copolymer from polymer-
ization tests at 70 °C and 15 bar ethylene partial pressure using a catalyst based
on complex 17.
Scheme 4 Site diversification for quinoline-based complexes: the more
obvious processes.
copolymer samples also changes with residence time, with the
sample prepared in 11 min showing twice the average number
of ethyl branches compared to the 1 h sample. This result
implies that the balance of sites shifts with time toward those
with higher Mw potentials and reduced co-monomer incorpor-
ation ability.
This conclusion is confirmed by the 3D-TREF analysis of
the samples from runs 17 and 18 (Fig. 8), which shows at least
five polymer modes with various degrees of branching from
the highest (1) to the lowest (5). The relative contribution of
the less-branched modes (3)–(5) clearly increases with resi-
dence time relative to the contribution of the highly branched
fractions (1) and (2).
Fig. 7 GPC profiles of polymers prepared with a catalyst based on complex 17
with different residence time in the reactor: 11 min in run 18 (red line) and 1 h
in run 17 (blue line).
A comparison of the intensities of the peaks detected by
the infra-red detector (a measure of polymer concentration) vs.
the light scattering and viscosity detectors (a combined
measure of both concentration and Mw) indicates that the less-
branched modes have a higher molecular weight, whereas the
highly branched modes have low molecular weights. This
difference in molecular weights results in a branching distri-
bution in the samples that is similar to that observed with
Ti-based Ziegler–Natta catalysts.18
Site diversification processes
Metallocene-based polymerization catalysts are usually single-
site systems, the ancillary cyclopentadienyl-type ligands are
not involved in specific interactions with the cocatalyst and
polymerization medium, resulting in a Flory-like molecular
weight distribution. This situation is frequently not the case
with “post-metallocene” catalyst precursors based on chelating
Fig. 8 3D-TREF profiles of ethylene–butene copolymer samples prepared with
complex 17 using short (thin line) and long (bold line) residence times.
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Fig. 9 Localization of the lowest unoccupied orbital in the cationic site Type A
(Scheme 4) calculated using the hybrid DFT method B3LYP/6-31G** (Spartan
’06, Wavefunction, Inc.).
Fig. 10 Relative stabilization (ΔEstab) of hypothetic cationic active site models
vs. their ethylene coordination energy (ΔEπ) calculated using the hybrid DFT
method B3LYP/6-31G** (Spartan ’06, Wavefunction, Inc.).
Scheme 5 Model reactions used to define the reactivity indexes.
reaction monitoring of the nature and transformation of active
components using analytical techniques is unrealistic. While
we are considering a future continuation of this study of using
model homogeneous systems and polymerization conditions,
we turned to computational estimates to rationalize our
observations.
ligands. The literature contains numerous indications of site
diversification during complex activation17 and in the process
of polymerization.15 This site diversification is the case for the
new quinoline-based complexes, as indicated by the analysis
of the microstructure of polymerization products discussed in
the previous section. Scheme 4 summarizes the more obvious
processes that lead to a large variety of hypothetical active
sites.
The obvious primary Sites A, which are generated via the
usual path of leaving-group abstraction and alkylation by a
cocatalyst (Path A, Scheme 4), are expected to undergo second-
ary transformation during activation or ageing (Paths B and C)
and during the polymerization process. Path B involves metal-
lation of the substituent in the amido-phenyl ring, as was
demonstrated in a recent paper,15 whereas Path C is initiated
by a nucleophilic attack (e.g., Me– from the MAO activator) at
the quinoline ring at positions with high LUMO orbital coeffi-
cients (Fig. 9).
To estimate the effect of site diversification on the proper-
ties of the resulting hypothetical active species, the geometry
of various methylated precursors and the corresponding
cations and π-complexes with ethylene were optimized using
the hybrid DFT method B3LYP/6-31G19 implemented in the
Spartan ’06 package. The resulting energies were used to deter-
mine the reactivity indexes ΔEstab (relative stability) and ΔEπ
(reactivity toward ethylene) based on the calculated enthalpies
of the model reactions in Scheme 5. While the exact nature of
rate limiting steps in the polymerization process based on
these catalysts is not clear (site activation, monomer coordi-
nation or insertion, etc.), we thought that these very simple
indexes provide a fair ranking of stability/reactivity of the
hypothetical sites. The calculated energies of the fully opti-
mized structures and atomic coordinates of the cationic
models are provided in the ESI.†
The resulting Sites C (Scheme 4) can initiate the polymeri-
zation process via insertion into the Zr–CAr bond and can con-
tinue the polymerization at the centers stabilized by the
resulting bidentate [N–N] ligand. The site diversification along
Path D during the polymerization process is similar to the
process proposed earlier for the related pyridylamido
systems.17
The resulting values, as plotted in the chart in Fig. 10, indi-
cate a broad range of variation of the expected properties of
the active species proposed in Scheme 4. This range exceeds
that observed for the series of metallocenes-type analogues.
The trends indicated in Fig. 10 show a stronger π-coordination
Due to very high activity of these new catalysts used in very
small quantities in our testing conditions, in situ or post-
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ability of the chelate-complexes compared to that of the metal- 3.42 mmol) in toluene–hexane (3 : 2, 25 mL) was added at 0 °C
locenes at the same level of active-site stabilization.
to a solution of 7 (1.09 g, 2.85 mmol) in toluene–hexane (3 : 2,
25 mL). The mixture was allowed to warm to room temperature
(the color of the mixture changed from pale-yellow to red
within several minutes), stirred for 6 h at 50–60 °C, and evap-
orated. The residue was recrystallized from hexane. The yield
was 0.95 g (51%). C41H40N2Zr (652.00): calcd C 75.53, H 6.18,
N, 4.30; found C 75.50, H 6.22, N 4.33. 1H NMR (400 MHz,
C6D6, 20 °C) δ: 7.97 (d, 1H, 3J = 7.0 Hz), 7.62 (d, 1H, 3J =
Conclusions
The diversity of possible ligand environments and the vastness
of experimentally “uncharted territories” ensure a promising
and vibrant future for the development of new catalysts for
enhanced products at reduced manufacturing costs. An inte-
grated catalyst–process–product design strategy should be
based on convenient synthesis strategies of ligand candidates
starting from easily accessible precursors and inexpensive pro-
cedures. This study capitalizes on such an approach by taking
advantage of the uniquely diverse topologies offered by the
quinoline scaffold combined with convenient synthetic coup-
ling procedures.
Although the replacement of the stabilizing ancillary cyclo-
pentadienyl ligands of the traditional metallocenes with the
chelating ligands in the post-metallocene systems of recent
years led to a broad diversity of new catalysts and generated
new polyolefins with unique microstructures, it also resulted,
in many cases, in the loss of the comforting “simplicity” of the
single-site paradigm. The higher inherent reactivity of the new
ligands compared to that of the cyclopentadienyl analogues
toward the components of catalyst recipes usually leads to the
generation of multiple active sites and a stronger sensitivity of
the polymer microstructure to the composition of the catalyst
and process conditions, as is clearly demonstrated in this con-
tribution. The more complicated microstructure of these new
polymers compared to the materials with narrow polydisper-
sity prepared with true single-site catalysts could result in
unique and beneficial balance of performance attributes, such
as an improved processability of the produced polymers com-
bined with a higher molecular-weight potential.
3
8.6 Hz), 7.35 (d, 1H, J = 7.7 Hz), 7.27–6.86 (groups of m, 8H,
3
3
aromatic H), 6.68 (t, 4H, J = 7.5 Hz), 6.58 (t, 2H, J = 7.5 Hz),
3
3
6.45 (d, 4H, J = 7.5 Hz, –CH2C6H5), 6.16 (d, 1H, J = 7.7 Hz,
Zr–CvC–H), 3.42 (sept, 2H, 3J = 6.8 Hz, –CH(CH3)2), 2.50 (d,
2H, 2J = 10.4 Hz, –CH2C6H5), 1.94 (d, 2H, 2J = 10.4 Hz,
3
–CH2C6H5), 1.22 (d, 6H, J = 6.8 Hz, –CH(CH3)2), 1.00 (d, 6H,
3J = 6.8 Hz, –CH(CH3)2).
DIBENZYLHAFNIUM N-(2,6-DIISOPROPYLPHENYL)-2-PHENYL-8-QUINOLINA-
MIDE (14). A solution of tetrabenzylhafnium (0.71 g, 1.3 mmol)
in toluene (10 mL) was added at 0 °C to a solution of 7 (0.38 g,
1 mmol) in toluene (10 mL). The color of the mixture changed
from pale-yellow to dark red. The resulting mixture was
allowed to warm to room temperature and was then stirred for
8 h at 60–70 °C. The mixture was evaporated, and hexane
(20 mL) was added. The crystalline precipitate was separated
by decantation, washed by pentane and dried in vacuo. The
product was a red crystalline powder with a yield of 0.36 g
(48%). C41H40HfN2 (739.27): calcd C 66.61, H 5.45, N 3.79;
found C 66.55, H 5.55, N 3.82. 1H NMR (400 MHz, C6D6, 20 °C)
3
3
δ: 8.26 (d, 1H, J = 7.2 Hz), 7.53 (d, 1H, J = 8.8 Hz), 7.43 (d,
3
3
1H, J = 7.7 Hz), 7.38 (t, 1H, J = 7.3 Hz), 7.35–7.01 (groups of
m, 6H), 6.81 (d, 1H, J = 7.3 Hz, aromatic H), 6.75 (t, 4H, J =
7.4 Hz), 6.62 (m, 6H, –CH2C6H5), 6.21 (d, 1H, J = 7.7 Hz, Hf–
3
3
3
3
CvC–H), 3.55 (sept, 2H, J = 6.9 Hz, –CH(CH3)2), 2.46 (d, 2H,
2J = 11.9 Hz, –CH2C6H5), 2.16 (d, 2H, J = 11.9 Hz, –CH2C6H5),
2
3
3
1.26 (d, 6H, J = 6.9 Hz, –CH(CH3)2), 1.03 (d, 6H, J = 6.9 Hz,
–CH(CH3)2).
DIBENZYLZIRCONIUM
N-(2,6-DIMETHYLPHENYL)-2-(1-NAPHTHYL)-8-QUI-
NOLINAMIDE (15). A solution of tetrabenzylzirconium (1.10 g,
2.4 mmol) in toluene (10 mL) was added at 0 °C to a solution
of 8 (0.75 g, 2 mmol) in toluene (20 mL). The color of the
mixture changed from pale-yellow to dark red. The resulting
mixture was allowed to warm to room temperature and was
then stirred for 4 h at 50 °C. The mixture was concentrated to
approximately 10 mL, and hexane (20 mL) was added. The
crystalline precipitate was separated by decantation, washed
with pentane and dried in vacuo. The product was a red-violet
crystalline powder, and the yield was 0.74 g (57%). C41H34N2Zr
(645.95): calcd C 76.24, H 5.31, N 4.34; found C 76.12, H 5.39,
Experimental
Materials and methods
All operations with group IV metal benzyl derivatives were per-
formed under argon using standard Schlenk technique or
under vacuum using a sealed glass “equipped-with-everything”
system. Phenylboronic acid,20 1-naphthylboronic acid,21 4-tert-
butylphenylboronic acid,22 2,8-dibromoquinoline,8 tri(o-tolyl)-
phosphine,23 Pd(dba)2,24 and N-[2′-(dicyclohexylphosphino)-
[1,1′-biphenyl]-2-yl]-N,N-dimethylamine25 were prepared in
accordance with published procedures. Samples of group IV
metal benzyl derivatives were prepared by condensation of
dried (over Na/benzophenone/dibenzo-18-crown-6) and
degassed deuterated solvents (C6D6 or toluene-d8) into NMR
tubes containing 5–10 mg of the complexes.
1
3
N 4.35. H NMR (400 MHz, toluene-d8, 20 °C) δ: 8.38 (d, 1H, J
3
3
= 8.4 Hz), 8.06 (d, 1H, J = 7.9 Hz), 7.97 (d, 1H, J = 8.8 Hz),
3
3
7.69 (t, 2H, J = 8.8 Hz), 7.54 (d, 1H, J = 7.9 Hz), 7.40–7.27 (m,
4H), 7.17–6.96 (m, 3H, aromatic H), 6.60 (t, 4H, 3J = 7.5 Hz),
6.53 (t, 2H, J = 7.5 Hz), 6.39 (d, 4H, J = 7.5 Hz, –CH2C6H5),
3
3
Preparation of Zr and Hf complexes
3
2
6.18 (d, 1H, J = 7.5 Hz, Zr–CvC–H), 2.30 (d, 2H, J = 10.1 Hz,
DIBENZYLZIRCONIUM N-(2,6-DIISOPROPYLPHENYL)-2-PHENYL-8-QUINOLI- –CH2C6H5), 2.16 (s, 3H, –CH3), 2.11 (s, 3H, –CH3), 1.81 (d, 2H,
NAMIDE (13). A solution of tetrabenzylzirconium (1.56 g, 2J = 10.1 Hz, –CH2C6H5).
Dalton Trans.
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DIBENZYLHAFNIUM N-(2,6-DIMETHYLPHENYL)-2-(1-NAPHTHYL)-8-QUINOLI- evaporated. The residue was recrystallized from hexane
NAMIDE (16). The synthesis of 16 was carried out in the same (30 mL). The precipitate (side product) was filtered off, and the
way as that described for 15, but tetrabenzylhafnium was used, mother liquor was evaporated and dried to yield a red–violet
and the reaction time was 8 h at 60–70 °C. The yield was 63%. glass solid. The yield was 1.52 g (63%). C45H48N2Zr (708.10):
C41H34HfN2 (733.22): calcd C 67.16, H 4.67, N 3.82; found C calcd C 76.33, H 6.83, N 3.96; found C 76.30, H 6.95, N 4.04.
1
67.12, H 4.70, N 3.85. H NMR (400 MHz, toluene-d8, 20 °C) δ: 1H NMR (400 MHz, C6D6, 20 °C) δ: 8.10 (bs, 1H), 7.64 (d, 2H, 3J
3
3
3
8.34 (d, 1H, J = 8.5 Hz), 8.18 (d, 1H, J = 8.0 Hz), 7.97 (d, 1H, = 8.6 Hz), 7.41–6.93 (group of m, 6H), 6.79 (t, 4H, J = 7.7 Hz),
3J = 8.7 Hz), 7.58 (t, 2H, 3J = 8.7 Hz), 7.45–7.15 (m, 5H), 6.65 (t, 2H, 3J = 7.7 Hz), 6.60 (d, 4H, 3J = 7.7 Hz), 6.39 (d, 2H, 3J
7.05–6.70 (m, 3H), 6.50–6.30 (m, 10H, aromatic H), 6.09 (d, = 7.3 Hz, aromatic H), 6.25 (d, 1H, 3J = 7.7 Hz, Zr–CvC–H),
1H, 3J = 7.7 Hz, Hf–CvC–H), 2.28 (d, 2H, 2J = 10.5 Hz, 3.51 (sept, 2H, 3J = 6.8 Hz, –CH(CH3)2), 2.66 (d, 2H, 2J =
2
–CH2C6H5), 2.22 (s, 3H, –CH3), 2.15 (s, 3H, –CH3), 1.98 (d, 2H, 10.3 Hz, –CH2C6H5), 1.98 (d, 2H, J = 10.3 Hz, –CH2C6H5), 1.40
2J = 10.5 Hz, –CH2C6H5).
(s, 9H, –C(CH3)3), 1.27 (d, 6H, 3J = 6.8 Hz, –CH(CH3)2), 1.04
DIBENZYLZIRCONIUM N-(2,6-DIISOPROPYLPHENYL)-2-(1-NAPHTHYL)-8-QUI- (d, 6H, 3J = 6.8 Hz, –CH(CH3)2).
NOLINAMIDE (17). A solution of tetrabenzylzirconium (1.23 g,
DIBENZYLZIRCONIUM N-(2,6-DIISOPROPYLPHENYL)-2-(4-METHYLPHENYL)-
2.7 mmol) in toluene (10 mL) was added at 0 °C to a solution 8-QUINOLINAMIDE (20). A solution of tetrabenzylzirconium
of 9 (0.95 g, 2.2 mmol) in toluene (20 mL). The color of the (1.25 g, 2.74 mmol) in hexane–toluene (1 : 1, 20 mL) was added
mixture changed from pale-yellow to dark-red. The resulting at 0 °C to a solution of 11 (0.90 g, 2.28 mmol) in hexane–
mixture was allowed to warm to room temperature and then toluene 1 : 1 (20 mL). The mixture was allowed to warm to
stirred for 8 h at 60 °C. The toluene was evaporated, and the room temperature and was then stirred for 6 h at 50–60 °C.
residue was extracted with pentane. The product crystallizes The color of the mixture changed from pale-yellow to dark-red.
slowly! The product was a red–violet powder, and the yield was The mixture was concentrated to 10 mL, hexane (30 mL)
0.55 g (36%). C45H42N2Zr (702.06): calcd C 76.99, H 6.03, N was added, and the red–violet precipitate of by-product
1
3.99; found C 76.88, H 6.11, N 4.08. H NMR (400 MHz, C6D6, was separated by decantation. The mother liquor was
20 °C) δ: 8.35 (d, 1H, 3J = 8.3 Hz), 8.15 (d, 1H, 3J = 7.8 Hz), 7.94 then evaporated, and the residue was recrystallized
(d, 1H, 3J = 8.9 Hz), 7.72 (m, 2H), 7.66 (d, 1H, 3J = 8.7 Hz), 7.60 from pentane to yield 0.44 g (29%) of the product (dark-red
3
(d, 1H, J = 7.7 Hz), 7.39–7.06 (m, 4H, aromatic H), 6.67 (t, 4H, crystalline powder). C42H42N2Zr (666.02): calcd C 75.74, H
3
3J = 7.4 Hz), 6.58 (m, 6H, –CH2C6H5), 6.30 (d, 1H, J = 8.5 Hz, 6.36, N 4.21; found C 75.70, H 6.46, N 4.10. 1H NMR
Zr–CvC–H), 3.52 (sept, 2H, 3J = 6.8 Hz, –CH(CH3)2), 2.57 (d, (400 MHz, C6D6, 20 °C) δ: 7.60 (d, 1H, 3J = 8.6 Hz), 7.38 (d, 1H,
2H, 2J = 10.3 Hz, –CH2C6H5), 2.10 (d, 2H, 2J = 10.3 Hz, 3J = 7.7 Hz), 7.30–6.95 (groups of m, 6H), 6.91 (d, 1H, 3J =
3
–CH2C6H5), 1.26 (d, 6H, J = 6.8 Hz, –CH(CH3)2), 1.05 (d, 6H, 8.8 Hz, aromatic H), 6.76 (t, 4H, 3J = 7.7 Hz), 6.60 (m, 6H,
3
3
3J = 6.8 Hz, –CH(CH3)2).
–CH2C6H5), 6.39 (d, 1H, J = 7.0 Hz), 6.20 (d, 1H, J = 7.8 Hz,
DIBENZYLHAFNIUM N-(2,6-DIISOPROPYLPHENYL)-2-(1-NAPHTHYL)-8-QUI- Zr–CvC–H), 3.49 (sept, 2H, 3J = 6.8 Hz, –CH(CH3)2), 2.64 (d,
NOLINAMIDE (18). The synthesis of 18 was carried out in the 2H, 2J = 10.4 Hz, –CH2C6H5), 2.31 (s, 3H, –CH3), 2.12 (d, 2H, J
2
same way as that described for 15, but tetrabenzylhafnium and = 10.4 Hz, –CH2C6H5), 1.25 (d, 6H, 3J = 6.8 Hz, –CH(CH3)2),
ligand 9 were used, and the reaction time was 8 h at 60 °C. 1.02 (d, 6H, 3J = 6.8 Hz, –CH(CH3)2).
The product was a red crystalline powder, and the yield was
DIBENZYLZIRCONIUM N-(2,6-DIISOPROPYLPHENYL)-2-(4-FLUOROPHENYL)-
54%. C45H42HfN2 (789.33): calcd C 68.47, H 5.36, N 3.55; 8-QUINOLINAMIDE (21). A solution of tetrabenzylzirconium
found C 68.50, H 5.44, N 3.50. 1H NMR (400 MHz, C6D6, 20 °C) (1.34 g, 2.95 mmol) in hexane–toluene (1 : 1, 20 mL) was added
3
3
δ: 8.41 (d, 1H, J = 7.7 Hz), 8.31 (d, 1H, J = 8.2 Hz), 7.89 (d, at 0 °C to a solution of 12 (0.98 g, 2.46 mmol) in hexane–
3
3
3
1H, J = 8.8 Hz), 7.76 (d, 1H, J = 7.7 Hz), 7.73 (d, 1H, J = 7.7 toluene (1 : 1, 20 mL). The mixture was allowed to warm to
Hz), 7.57 (m, 2H, 3J = 8.8 Hz), 7.40–7.11 (m, 4H), 6.85 (d, 1H, 3J room temperature and was then stirred for 6 h at 50–60 °C.
= 8.1 Hz, aromatic H), 6.69 (t, 4H, 3J = 7.5 Hz), 6.65 (d, 4 H, 3J = The color of the mixture changed from pale-yellow to red–
7.5 Hz), 6.57 (t, 2H, J = 7.5 Hz, –CH2C6H5), 6.27 (d, 2H, J = violet, and a precipitate formed. The volume of the mixture
7.7 Hz, Hf–CvC–H), 3.59 (sept, 2H, 3J = 6.8 Hz, –CH(CH3)2), was reduced to 10 mL, hexane (30 mL) was added, and the
2.45 (d, 2H, J = 11.9 Hz, –CH2C6H5), 2.22 (d, 2H, J = 11.9 Hz, red–violet precipitate of by-product was separated by decanta-
–CH2C6H5), 1.28 (d, 6H, 3J = 6.8 Hz, –CH(CH3)2), 1.06 (d, 6H, 3J tion. The mother liquor was then evaporated, and the residue
= 6.8 Hz, –CH(CH3)2). 13C NMR (100 MHz, C6D6, 20 °C) δ: was recrystallized from pure hexane to yield 0.37 g (22%) of
3
3
2
2
154.3, 146.8, 143.1, 141.4, 141.0, 139.7, 132.5, 129.8, 129.3, the product (dark-red crystalline powder).
C41H39FN2Zr
128.8, 128.5, 127.6, 127.5, 126.9, 125.4, 125.2, 124.5, 123.7, (669.99): calcd C 73.50, H 5.87, N 4.18; found C 73.59, H 5.99,
1
3
121.3, 114.1, 113.3, 83.5, 28.8, 27.1, 23.6.
N 4.10. H NMR (400 MHz, C6D6, 20 °C) δ: 7.73 (dd, 1H, J =
3
DIBENZYLZIRCONIUM N-(2,6-DIISOPROPYLPHENYL)-2-(4-TERT-BUTYLPHE- 7.7 Hz, JH–F = 2.8 Hz), 7.60 (d, 1H, 3J = 8.6 Hz), 7.29–6.37
3
NYL)-8-QUINOLINAMIDE (19). A solution of tetrabenzylzirconium (groups of m, 18H, aromatic H), 6.20 (d, 1H, J = 8.6 Hz, Zr–
3
(1.86 g, 4.08 mmol) in hexane–toluene (3 : 2, 30 mL) was added CvC–H), 3.44 (sept, 2H, J = 6.6 Hz, –CH(CH3)2), 2.56 (d, 2H,
at 0 °C to a solution of 10 (1.48 g, 3.4 mmol) in hexane– 2J = 10.3 Hz, –CH2C6H5), 1.90 (d, 2H, J = 10.3 Hz, –CH2C6H5),
2
3
3
toluene (3 : 2, 30 mL). The mixture was allowed to warm to 1.22 (d, 6H, J = 6.6 Hz, –CH(CH3)2), 1.00 (d, 6H, J = 6.6 Hz,
room temperature and was then stirred for 6 h at 50–60 °C and –CH(CH3)2).
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(1 mL of a 1 M solution in hexanes), 100 mL of 1-butene co-
monomer and, optionally, hydrogen. The contents were heated
to the desired polymerization temperature and pressurized
with 15 bar of ethylene partial pressure. After the mixture was
allowed to equilibrate for 15 min, the polymerization was
initiated by the injection of the catalyst powder with a small
amount of isobutane. The temperature and pressure was main-
tained throughout the run by supplying ethylene on-demand.
The polymerization was usually terminated after 1 h by cooling
and venting the volatile contents of the reactor.
Table 3 Crystal data, data collection and refinement parameters for 15, 16,
and 18
15
16
18
Formula
C
41H34Zr1N2
C41H34Hf1N2 C51H48Hf1N2
Formula weight
Colour, habit
Cryst size, mm
645.92
733.19
867.40
Block, black
0.25 × 0.20 ×
0.15
Prism, pink
Red, plate
0.08 × 0.08 × 0.15 × 0.06 ×
0.03
0.01
Cryst syst
Space group
a, Å
Monoclinic
P21/c
Monoclinic
P21/c
Monoclinic
P21/c
14.660(3)
13.776(2)
16.926(3)
114.325(2)
3114.8(10)
4
8.0530(5)
19.1170(11)
20.0917(12)
101.416(1)
3031.9(3)
4
13.693(4)
16.488(5)
17.561(6)
99.135(6)
3915(2)
4
b, Å
c, Å
Polymer analysis
β, °
V, Å3
Molecular weight and molecular weight distributions were
determined by GPC (gel permeation chromatography).
Measurements were conducted on a Waters GPCV-LS 2000
with three Polymer Lab Olexis columns. The solvent was tri-
chlorobenzene (TCB), and the temperature was 145 °C.
Selected GPC traces of products are provided in the ESI.† The
flow rate was 1.0 mL min−1. TREF (temperature rising elution
fractionation) was used to characterize the co-monomer distri-
bution of the polymers. In a TREF measurement, the sample is
first dissolved in a solvent (ODCB) at an elevated temperature
(150 °C); the solution is then cooled slowly so that the polymer
crystallizes in layers around small beads in a chromatographic
column based on differences in solubility (crystallizability) of
various polymer fractions; in the elution step, the solvent is
heated at a controlled rate, and the concentration of the
polymer dissolved in the solvent is continuously monitored.
Z
dcalc, g cm−3
μ, mm−1
F(000)
1.377
1.606
1.472
0.385
3.474
2.703
1336
1464
1760
θ range, °
Total no. of
reflns
Unique reflns
Rint
1.52 to 26.00
22 834
1.48 to 27.00 1.70 to 25.25
23 800
28 148
6061
0.0476
6616
7050
0.0394
4957
0.1383
4539
No. with I > 2σ(I) 4729
No. of variables
R1 (I > 2σ(I))
399
399
492
0.0495
0.1426
1.079
0.0262
0.0571
1.018
0.0510
0.1033
0.923
wR2 (all data)
GOOF on F2
Largest diff
0.941/−0.686
0.775/−0.516 1.240/−1.108
peak/hole, e Å−3
X-ray structural determinations of 15, 16, and 18
Experimental intensities were measured on a Bruker SMART Triple detectors in 3D-TREF allow for the continuous monitor-
APEX II diffractometer using graphite-monochromated Mo-Kα ing of concentration (IR detector), solution viscosity (vis-
radiation (λ = 0.71073 Å) at 150 K. Absorption corrections cometer), and molecular weight (light-scattering detector) of
based on measurements of equivalent reflections were the eluting fractions. Fractions with a high level of co-
applied.26 The structures were solved by direct methods and monomer branching are more soluble and elute at lower temp-
were refined by a full-matrix least-squares on F2 27 with aniso- eratures than fractions with lower levels of co-monomer
tropic thermal parameters for all non-hydrogen atoms. In all branching. The viscometer and light-scattering signals provide
structures, all hydrogen atoms were placed in calculated pos- an indication of the relative molecular weights of the various
itions and refined using a riding model. Details of the X-ray fractions. Details of the 3D-TREF technique are described
investigations are given in Table 3.
elsewhere.28
General procedure for the preparation of supported catalyst
samples
Acknowledgements
Trityl tetrakis(pentafluorophenyl)borate (0.052 g, 0.56 mmol)
was added to 2.2 mL of a 4.21 M solution of MAO in toluene
(Albemarle) and stirred for 15 min. A specified amount of
complex precursor (to achieve an Al–metal molar ratio of 200)
was added to the resulting solution, which was stirred for an
additional 15 min. The resulting homogeneous solution was
slowly and evenly added to a stirred bed of 2 g of silica support
(Davison C948, calcined for 6 h at 600 °C), which resulted in a
free-flowing catalyst powder, which was used in polymerization
tests after being aged at least overnight.
We thank LyondellBasell Industries for financial support and
for permission to publish this work.
Notes and references
1 V. C. Gibson and S. K. Spitzmesser, Chem. Rev., 2003, 103,
283, and references therein.
2 (a) H. Makio, N. Kashiwa and T. Fujita, Adv. Synth. Catal.,
2002, 344, 477; (b) H. Makio, H. Terao, A. Iwashita and
T. Fujita, Chem. Rev., 2011, 111, 2363, and references
therein.
General procedure for polymerization tests
A jacketed 2 L stainless steel stirred autoclave was charged
with 1 L of isobutane diluent, triisobutylaluminum scavenger
3 V. C. Gibson, C. Redshaw and G. A. Solan, Chem. Rev.,
2007, 107, 1745, and references therein.
Dalton Trans.
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Dalton Transactions
Paper
View Online
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