Aminotroponiminato hafnium and zirconium complexes: Synthesis and ethylene/1-octene copolymerization study

Article abstract of DOI:10.1021/om200362v

Four new aminotroponiminato hafnium and zirconium tribenzyl complexes were prepared by reacting neutral ligands with the corresponding tetrabenzyl complexes. Aminotroponimine ligands were prepared in four steps starting from tropolone. An air-stable ethox

Full text of DOI:10.1021/om200362v

ARTICLE
pubs.acs.org/Organometallics
Aminotroponiminato Hafnium and Zirconium Complexes: Synthesis
and Ethylene/1-Octene Copolymerization Study
Endre Szuromi and Jerzy Klosin*
Corporate R&D, The Dow Chemical Company, 1776 Building, Midland, Michigan 48674, United States
Khalil A. Abboud
Department of Chemistry, University of Florida, Gainesville, Florida 32611, United States
S Supporting Information
b
ABSTRACT:
Four new aminotroponiminato hafnium and zirconium tribenzyl complexes were prepared by reacting neutral ligands with the
corresponding tetrabenzyl complexes. Aminotroponimine ligands were prepared in four steps starting from tropolone. An air-stable
ethoxy-amino-tropylium cation intermediate isolated during ligand synthesis was found to react directly with amines significantly
faster than the neutral intermediate proposed previously. This tropylium cation represents a convenient way to prepare a large array
of aminotroponimines. An ethylene/1-octene copolymerization study conducted at 120 °C demonstrated that the aminotropo-
niminato hafnium and zirconium complexes are catalytically active, but their activity is lower than that observed for the
corresponding iminoꢀenamido complexes. Polymer analysis data (GPC and DSC) indicated that aminotroponiminato complexes
generate at least two catalytically active species under polymerization conditions.
’ INTRODUCTION
importantly, exhibit higher polymerization activity, produce
higher molecular weight polymers, and incorporate more 1-octene
into the polymer backbone than the corresponding iminoꢀamido
complexes.9 Very promising results obtained with iminoꢀenamido
complexes made us consider the preparation and evaluation of
complexes similar to 3, but with ligands containing different ring
sizes. The ring size of iminoꢀenamine ligands should influence
the NꢀCꢀCꢀN geometry, thus affecting the bite angle
(NꢀMꢀN), a feature that might lead to a different polymeriza-
tion behavior. The direct seven-membered-ring analogue of 3
most likely cannot be prepared by the same methodology used to
synthesize 3, because such a seven-membered-ring ligand exists
in the bis-imine rather than iminoꢀenamine form, on the basis of
experimental10 and computational data.9a Therefore, we consid-
ered the preparation of analogues of 3, but with aminotroponi-
mine ligands which have a fully aromatic seven-membered-ring
fragment (e.g., structures 4 and 5 in Scheme 2; only one
resonance form is shown).
Discovery of new molecular olefin polymerization catalysts
continues to attract the attention of academic and industrial
chemists.1 This research has been driven by the desire to create
new polyolefin-based materials2 and improve the current polym-
erization processes.3 Recently, we4ꢀ6 and others7,8 reported hafnium
and zirconium iminoꢀamido complexes as useful procatalysts
for olefin polymerization. These complexes exhibit good catalytic
activities at temperatures above 100 °C, are capable of producing
very high molecular weight ethylene-based copolymers, and have
the ability to undergo reversible chain transfer with diethylzinc
to produce olefin block copolymers.5 One undesired feature of
these complexes is their thermal instability at elevated temperature.
For example, iminoꢀamido complexes containing the trimethy-
lethylidene ligand bridge (e.g., 1) undergo 1,2-methyl shift to
form isomeric complexes (e.g., 2) which exhibit significantly lower
polymerization activity than the original complexes (e.g., 1)
(Scheme 1).6
Various aminotroponiminato complexes have been described
in the literature;11 however, to our knowledge, their use as olefin
polymerization catalysts has been only demonstrated by Jordan
To address the thermal instability of iminoꢀamido complexes,
new iminoꢀenamido complexes (e.g., 3; Scheme 2) were prepared
which have bonding features similar to those of iminoꢀamido
complexes, but their ligand framework eliminates all decomposi-
tion pathwaysencounteredwithiminoꢀamido complexes.9 Iminoꢀ
enamido complexes are not only thermally very stable, but more
Received: May 1, 2011
Published: August 08, 2011
r
2011 American Chemical Society
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Scheme 1. Thermal Rearrangement of IminoꢀAmido
Scheme 3. Synthesis of Aminotropone 8
Complex 1
Scheme 4. Postulated (Path A)21a,23 and Observed (Path B)
Routes to Aminotroponimines
Scheme 2. IminoꢀEnamido Complex 3 and Analogous
Aminotroponiminato Complexes 4 and 5
and co-workers, who showed that the cationic aluminum complexes
[{(i-Pr)2ATI}AlR][B(C6F5)4] (R = Et, i-Bu; (i-Pr)2ATI = N,N0-
diisopropylaminotroponiminate) are capable of polymerizing
ethylene to linear polymer, albeit with low activity.12 Addition-
ally, the {(i-Pr)2ATI}AlR+ (R = Et, n-Pr, i-Bu) cations catalyze
the head-to-tail dimerization of tert-butylacetylene by an insertion/
σ-bond metathesis mechanism.13,14 Moreover, {(i-Pr)2ATI}AlR+
cations initiate the polymerization of propylene oxide and iso-
butylene.13 Aminotroponiminato zinc complexes have been studied
extensively for the catalytic hydroamination of alkenes (inter- and
intramolecular) and alkynes (intermolecular).15 In addition, Roesky
and co-workers described aminotroponiminato complexes of alka-
line-earth and lanthanide metals as catalysts for hydroamination/
cyclization reactions.16 Dinuclear zinc aminotroponiminato com-
plexes have been reported to catalyze the copolymerization of
epoxides (propylene oxide, cyclohexene oxide, or mixtures thereof)
and CO2 to give low yields of polycarbonate products.17
A little over a decade ago, Lippard and co-workers developed a
multicomponent system for the preparation of unsymmetrical
diols from carbonyl compounds, CO, and aminotroponiminato
titanium dialkyl complexes.18 Synthesis of Hf(IV) and Zr(IV)
aminotroponiminato19 and related tropocorand20 complexes have
been described in the literature, but none of these complexes were
evaluated as procatalysts for olefin polymerization. Moreover, all
reported hafnium and zirconium aminotroponiminato complexes,
with the exception of one dinuclear complex,20a contain at least two
ligands per metal center, whereas our objective was to prepare and
evaluate mononuclear complexes containing a single aminotropo-
niminato ligand. In this contribution, we describe the synthesis and
full characterization of four aminotroponiminato tribenzyl hafnium
and zirconium complexes and their evaluation as procatalysts for
ethylene/1-octene copolymerization reactions.
complexes contain two different substituents on the nitrogen
atoms, and therefore it is necessary to introduce the amine and
imine groups sequentially, a strategy that has been described
previously in the literature. The first nitrogen-containing sub-
stituent was introduced in two steps starting from tropolone
(6),15g,21 as shown in Scheme 3. Synthesis of 2-triflatotropone
(7)21a and 2-(2,6-diisopropylphenyl)aminotropone (8)21b was
accomplished by following published procedures.
The second nitrogen-containing group was introduced by the
reaction of aminotropones with Et3OBF4 and an amine. This
transformation was postulated to proceed via a neutral 2-imino-
O-ethyltropone15g,22,23 (10) (Scheme 4, path A), which subse-
quently reacts with excess amine to form aminotroponimines
(11).15g,23 2-Arylimino-O-ethyltropone intermediates (Ar =
p-bromophenyl, pyrrol-1-yl) have been isolated.23 However, they
are slow to form (days), and their reaction with arylamines to form
aminotroponimines takes several days at 40 °C.23 Interestingly,
reaction of 8 with Et3OBF4 did not produce the corresponding
2-arylimino-O-ethyltropone but instead generated tropylium inter-
mediate 12 cleanly in 3 h (Scheme 4, path B) under conditions
identical to those previously reported for the synthesis of amino-
troponimines. This tropylium derivative (12) can be isolated easily
by precipitation with excess diethyl ether and it is air stable. NMR
tube experiments showed that 12 reacts rapidly (ca 10 min) with
excess n-butylamine and N,N-dimethylhydrazine to give the desired
aminotroponimines 13 and 14, respectively, in high yields.
Isolation of tropylium derivative 12 and its very fast reaction
with amines to form aminotroponimines, coupled with the very
slow reaction of 2-imino-O-ethyltropones with amines to form
aminotroponimines, suggest that 2-imino-O-ethyltropones might
not be direct intermediates in these reactions. Tropylium derivatives
’ RESULTS AND DISCUSSION
Ligand Synthesis. Ligands needed for the preparation of the
desired aminotroponiminato hafnium and zirconium tribenzyl
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Scheme 5. Possible Mechanism for the Formation of 11 from 9
Figure 2. Molecular structure of ligand 13. Hydrogen atoms (except
H2A) are omitted for clarity. Thermal ellipsoids are shown at the 40%
probability level. Selected bond distances (Å) and angles (deg):
N1AꢀC1A = 1.299(3), N2AꢀC7A = 1.337(3), C1AꢀC7A =
1.489(3), N2AꢀH2A = 0.88(2); N1AꢀC1AꢀC7A = 113.5(2),
C7AꢀN2AꢀH2A = 111(1).
Figure 1. Molecular structure of compound 12. Hydrogen atoms (except
H1) are omitted for clarity. Thermal ellipsoids are shown at the 40%
probability level. Selected bond distances (Å) and angles (deg): O1ꢀC7 =
1.342(2), N1ꢀC1 = 1.335(2), C1ꢀC7 = 1.450(2), N1ꢀH1 = 0.86(2);
O1ꢀC7ꢀC1 = 109.39(14), C1ꢀN1ꢀH1 = 116.6(13).
isolation of 10 is known to be significantly faster than from
isolated 10.15g,23,27 On the basis of these considerations, we
propose that aminotroponimines are always generated from
tropylium intermediate 15, as outlined in Scheme 5.
are likely to be products of the reactions between 9 and
Et3OBF4.24 It is well-known that aminotropones can react with
various electrophiles to form the corresponding tropylium deriv-
atives.24,25 However, under suitable conditions, neutral O-alkyl
iminotropones (10) can be also generated.22,23,25 In some cases
the synthesis of 10 involved the reaction of aminotropone with
dimethyl sulfate followed by treatment with sodium bicarbonate
(e.g., R = C6H4-p-Me, CH2Ph, C6H11),22,25 while in other cases
(R = C6H4-p-Br, pyrrol-1-yl) the neutral 2-arylimino-O-ethyl-
tropones (10) were isolated in low to moderate yield from
dichloromethane solutions of the corresponding aminotropones
and Et3OBF4.23 It is possible that, depending on the nature of
the N-substituent, compound 15 (Scheme 5) may undergo slow
deprotonation to form 10 during the course of the reaction.
Subsequent formation of aminotroponimines from 10 is very
slow,23,26 suggesting that slow reverse protonation of 10 is
necessary to regenerate tropylium 15, which then undergoes
rapid nucleophilic aromatic substitution with amines to form the
cycloheptatriene derivative 16, an intermediate leading to the
final aminotroponimine 11. Reaction of tropylium derivatives
with various nucleophiles is well-documented in the literature.24
Furthermore, the one-pot synthesis of 11 from 9 without the
The ability to isolate tropylium derivatives such as 12 provides
an opportunity for a more efficient and convenient way to prepare a
library of aminotroponimines. Compound 12 was characterized
by NMR spectroscopy, X-ray crystallography, and elemental
analysis. The molecular structure of 12 is shown in Figure 1.
The 1H NMR spectrum of 12 shows the tropylium ring protons
shifted significantly downfield from their positions found in
neutral compounds.6,9,28 Ring protons were assigned on the basis
of 1D TOCSY and 1D NOESY NMR spectroscopy. The isopropyl
methine protons appear as a single septet at 2.79 ppm, indicating
identical chemical environments for the two isopropyl groups.
The isopropyl methyl groups give rise to two nonequivalent
doublets resonating at 1.22 and 1.12 ppm. The appearance of two
separate resonances for the isopropyl methyl groups is due to
restricted rotation around the NꢀC(ipso) bond, which makes
the chemical environment for the methyl groups pointing toward
and away from the tropylium ring different. This is observed
commonly for compounds with the bulky 2,6-diisopropylanilino
substituent.6,9,29 NOESY experiments indicated that the methyl
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Scheme 6. Synthesis of Aminotroponiminato Hafnium and Zirconium Complexes
groups corresponding to a doublet at 1.12 ppm point toward the
tropylium ring. The 19F NMR spectrum of 12 shows two peaks at
152.72 and 152.77 ppm in a 1:4 ratio, which is due to the different
chemical shifts of the 10BF4 and 11BF4 isotopomers.30 This phe-
nomenon has been documented previously in the literature.31
Preparative-scale synthesis of 13 was accomplished in 80%
yield by the reaction of 8 with Et3OBF4 to generate compound
12 in situ, which was reacted subsequently in the same reaction
vessel with n-butylamine. Since the product formation from 12
requires a deprotonation step, it is necessary to use excess amine
for this reaction to reach high conversion.32 Using an excess of
volatile amine is a convenient way to drive the reaction to
completion. The molecular structure of ligand 13 and its
representative bond distances are shown in Figure 2. The
CꢀN bond distances are consistent with the assignment of the
amine and imine nitrogen atoms. The structural information
obtained from NMR spectroscopy are consistent with the X-ray
crystal structure data. The position of the amine hydrogen in the
solution phase could not be assigned unequivocally on the basis
of NOESY NMR measurements. Protons attached to the seven-
membered ring of the ligand were assigned with the aid of 1D
TOCSY and 1D NOESY NMR spectroscopy. Similar to the case
for 12, the isopropyl groups in 13 have the same chemical
environment, as shown by the appearance of only one methine
resonance at 2.98 ppm. The isopropyl methyl groups appear as
two doublets at 1.20 and 1.14 ppm. The isopropyl methyl groups
pointing toward the seven-membered ring resonate at 1.14
ppm on the basis of the NOESY NMR spectra.
atom resided on the same nitrogen atom in both 13 and 14,
one would expect very similar chemical shifts, at least for H2
protons. The inversion of chemical shifts for protons H2 and H6 in
13 and 14 is consistent with inversion of the double bonds in these
ligands.
Following the successful synthesis of ligands 13 and 14, the
preparation of other new ligands was explored. For example,
a dimeric aminotroponimine ligand (19) was prepared via the
reaction of 12 with 1,4-butanediamine.33 However, the attempt
to prepare an aminotroponimine with 2,6-diisopropylaniline sub-
stituents on both amine and imine nitrogen atoms failed,
presumably due to steric hindrance.
Synthesis of Metal Complexes. Ligands 13 and 14 were
converted to their corresponding Hf and Zr complexes via reaction
with tetrabenzyl hafnium (HfBn4) and tetrabenzyl zirconium
(ZrBn4) over ca 2 h in benzene at 25 °C (Scheme 6). All com-
plexes were isolated in a crystalline form by slow diffusion of
hexane into benzene solutions at ꢀ45 °C. NMR yields were close
to quantitative; however, the isolated yields of the first crop of
crystals varied between 30 and 80%.
All metal complexes were fully characterized by NMR spec-
troscopy and elemental analysis, and the molecular structures of
4 and 17 were determined by X-ray crystallography. Similar to
iminoꢀenamido complexes, aminotroponiminato complexes 4,
1
5, 17, and 18 were stable at 75 °C for 18 h. The H NMR
spectrum of 4 shows a broad singlet at 2.21 ppm corresponding
to the benzyl CH2 groups and a broad signal at 6.91 ppm for the
ortho CH2Ph protons, suggesting a relatively fast exchange of the
benzyl groups at ambient temperature. The 1H NMR spectra of 5
and 17 reveal similar behavior. The molecular structures of
complex 4 and 17 are shown in Figures 3 and 4, respectively,
whereas comparisons among representative bond distances of 3,
4, and 17 are presented in Figure 5. Comparison of the C1ꢀN1,
C7ꢀN2, N1ꢀHf, and N2ꢀHf bond distances in complexes
3 and 4 clearly shows that the imine bond is completely
delocalized over the N1ꢀC1ꢀC7ꢀN2 bonds in 4. Similar to
the case for 4, the nearly identical C1ꢀN1 and C7ꢀN2 bond
distances of 17 indicate a delocalized electron structure over the
N1ꢀC1ꢀC7ꢀN2 bonds. The sum of angles around N1, N2,
and N3 equals 359.7, 359.6, and 341.4°, respectively. This
indicates that N1 and N2 are virtually planar, whereas N3 is
pyramidized. The dimethylamine fragment is perpendicular to
the plane of the metallacycle. The HfꢀCꢀCipso bond angles in
complexes 4 and 17 are in the range of 108.4 and 117.2°, indi-
cating a η1-bonding mode for all benzyl groups.
The preparative-scale synthesis of 14 was carried out in 95%
yield by the reaction of isolated tropylium derivative 12 and N,N-
dimethylhydrazine at 25 °C. Ligand 14 was characterized by
NMR spectroscopy and elemental analysis. Unlike in 13, the
nitrogen atom with the 2,6-diisopropylphenyl substituent in 14 is
the amine nitrogen. This conclusion is based on the observation
of only one doublet for the isopropyl methyl groups resonating at
1
1.09 ppm in the H NMR spectrum of 14, indicating that all
isopropyl methyl groups are in the same chemical environment.
A single bond between the amine nitrogen and the C1 carbon of
the seven-membered ring allows for free rotation around this
bond, which in turn facilitates free rotation of the NꢀC(ipso)
bond. A similar phenomenon was observed in the case of the
iminoꢀenamine ligand of complex 3.9 Another indication that
the hydrogen atom resides on different nitrogen atoms in 13 and
14 comes from a comparison of chemical shifts of protons H2
and H6 attached to the seven-membered ring of these ligands.
In 13, H2 resonates at higher frequency than H6 (6.50 ppm vs
5.96 ppm), a trend which is reversed in 14, with H2 and H6
resonating at 5.87 and 7.39 ppm, respectively. If the hydrogen
Table 1 shows the NꢀHfꢀN bite angles, NꢀC1ꢀC7ꢀN
torsion angles, and dihedral angles of the least-squares planes
defined by NꢀC1ꢀC7ꢀN and NꢀHfꢀN atoms for complexes
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Figure 3. Molecular structure of complex 4. Hydrogen atoms are
omitted for clarity. Thermal ellipsoids are shown at the 40% probability
level. Selected bond distances (Å) and angles (deg): N1ꢀC1 =
1.359(4), N2ꢀC7 = 1.338(4), C1ꢀC7 = 1.462(4), Hf1ꢀN1 =
2.208(3), Hf1ꢀN2 = 2.160(3); N2ꢀHf1ꢀN1 = 69.62(10).
Figure 5. Comparison of important bond lengths (Å) in compounds 3,
4, 12, 13, and 17.
Table 1. Select Structural Parameters (deg) for Complexes 1,
3, 4 and 17
1
3
4
17
NꢀHfꢀN angle
72.6
4.6
72.0
6.0
69.6
4.6
67.0
0.7
NꢀC1ꢀC7ꢀN torsion anglea
dihedral angleb
10.7
12.7
9.7
3.7
a Absolute values are shown. b The angle between the N1ꢀC1ꢀC7ꢀN2
and N1ꢀHf1ꢀN2 least-squares planes.
aminotroponiminato catalysts exhibited a pale yellow color upon
isolation, which faded upon exposure to sunlight over the course
of a few hours. This is mostly likely due to highly colored, highly
conjugated residual organic fragments originating from ligand
decomposition. A comparison of the results given in Table 2
reveals that aminotroponiminato catalysts are active for olefin
polymerization, with hafnium derivatives (4, 17) exhibiting
higher activity than their zirconium analogues (5, 18). However,
even the best aminotroponiminato procatalyst identified in this
work (4) is about 5 times less active than the analogous
iminoꢀenamido hafnium complex 3. The DSC scans revealed
bimodal melting transitions for all polymer samples prepared by
aminotroponiminato procatalysts. Additionally, GPC chromato-
grams for polymers produced by two of the four new complexes
show a bimodal molecular weight distribution. These results
indicate that the aminotroponiminato catalysts are unstable
under the polymerization conditions, producing more than one
active catalytic species. Aminotroponiminato complexes led to
lower 1-octene incorporation than iminoꢀenamido procatalyst 3
under identical conditions. The molecular weights of polymers
Figure 4. Molecular structure of complex 17. Hydrogen atoms are
omitted for clarity. Thermal ellipsoids are shown at the 40% probability
level. Selected bond distances (Å) and angles (deg): N1ꢀC1 =
1.345(3), N2ꢀC7 = 1.343(3), C1ꢀC7 = 1.467(3), Hf1ꢀN1 =
2.293(2), Hf1ꢀN2 = 2.094(2); N2ꢀHf1ꢀN1 = 67.02(8).
1, 3, 4, and 17. These parameters are not significantly different
between acyclic (1), six-membered-ring cyclic (3), and seven-
membered-ring cyclic aromatic (4, 17) backbone structures,
indicating similar geometries for the core five-membered-ring
metallacycle in all of these complexes.
Polymerization Results. Ethylene/1-octene copolymeriza-
tion reactions were conducted in a 2 L batch reactor at 120 °C.
Procatalysts were activated with 1.2 equiv (relative to procatalyst) of
{[HNMe(C18H37)2][B(C6F5)4]} activator. All polymerization
reactions were carried out for 10 min and stopped by venting the
ethylene pressure. The polymeric products were characterized by
differential scanning calorimetry (DSC) and gel permeation
chromatography (GPC). Interestingly, polymers prepared by
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Table 2. Polymerization Results for 3ꢀ5, 17, and 18a
run no.
cat. (amt (μmol))
yield (g)
efficiencyb
Tm (°C)
74.0
Mw (g/mol)
Mw/Mn
octene content (mol %)c
1
2
3
4
5
3 (0.4)
4 (1)
45.3
24.0
10.3
13.8
12.2
113 250
24 000
5 150
1 280 000
497 746
434 983
445 415
354 212
1.8
2.8
8.6
7.7
6.3
4.2
4.1
80.2/106.0
91.4/111.3
104.0/116.4
106.2/118.2
5 (2)
1.8
17 (1)
18 (2)
13 800
6 100
9.6d
12.8d
a Polymerization conditions: temperature = 120 °C; 533 g of Isopar E, 250 g of 1-octene, 10 mmol of H2, 460 psi of ethylene; 10 min run time; activator
[HNMe(C18H37)2][B(C6F5)4], (1.2 equiv); MMAO-3A (10 equiv); b Efficiency = polymer (g)/metal (mmol). c Determined by IR. d GPC traces are
bimodal.
made from aminotroponiminato procatalysts are very high (Mw
values of up to 500 KDa) but are lower compared to ultra-high
molecular weight polymers produced by 3. Polymerization data
indicate that aminotroponiminato complexes exhibit poorer
overall performance as procatalysts for olefin polymerization in
comparison to the analogous imino-enamido complexes.
and 2-(2,6-diisopropylanilino)tropone21b were prepared according to
reported procedures. NMR spectra were recorded on a VNMRS-500
spectrometer. H NMR data are reported as follows: chemical shift
1
(multiplicity (br = broad, s = singlet, d = doublet, t = triplet, q = quartet,
p = pentet, and m = multiplet), integration, and assignment). Chemical
1
shifts for H NMR data are reported in ppm downfield from internal
tetramethylsilane (TMS, δ scale) using residual protons in the deuter-
ated solvent (C6D6, 7.15 ppm; CD2Cl2, 5.32 ppm) as references. 13
C
’ CONCLUSIONS
NMR data were determined with 1H decoupling, and the chemical shifts
are reported in ppm vs tetramethylsilane (C6D6, 128 ppm; CD2Cl2,
53.80 ppm). The 19F NMR data are reported in ppm relative to neat
CFCl3. All compounds were synthesized and stored in a Vacuum Atmo-
spheres glovebox under a dry nitrogen atmosphere unless otherwise
noted. Elemental analyses were performed at Midwest Microlab, LLC.
Preparation of N-[2,6-Bis(1-methylethyl)phenyl]-2-ethox-
ycycloheptatrienylium Tetrafluoroborate (12). Triethyloxo-
nium tetrafluoroborate (1.28 g, 6.74 mmol) was dissolved in CH2Cl2
(5 mL), and a solution of 2-[[2,6-bis(1-methylethyl)phenyl]amino]-
2,4,6-cycloheptatrien-1-one (1.50 g, 5.33 mmol) in CH2Cl2 (10 mL)
was added to it dropwise at 25 °C. The solution was stirred overnight,
followed by precipitation of the product with excess diethyl ether. The
resulting off-white solid was purified by dissolution in a minimum
quantity of CH2Cl2, followed by precipitation with excess Et2O. Finally,
the solid was recrystallized from a concentrated acetone solution layered
with Et2O. Large colorless block crystals formed, which were filtered,
crushed, washed with Et2O, and dried under vacuum to give an air-stable,
white crystalline solid. Yield: 1.38 g, 65%. 1H NMR (CD2Cl2, 500 MHz,
30 °C): 9.25 (br s, 1H, NH), 8.07 (td, JHꢀH = 1.4, 10.4 Hz, 1H, H5), 7.96
(d, JHꢀH = 10.6 Hz, 1H, H6), 7.88 (tm, JHꢀH = 10.3 Hz, 1H, H3), 7.66
(tm, JHꢀH = 9.5 Hz, 1H, H4), 7.55 (tm, JHꢀH = 7.8 Hz, 1H, H11), 7.40
(d, JHꢀH = 7.8 Hz, 2H, H10, H12), 7.19 (d, JHꢀH = 11.6 Hz, 1H, H2),
4.74 (q, JHꢀH = 7.0 Hz, 2H, H14), 2.79 (septet, JHꢀH = 6.8 Hz, 2H,
CH(CH3)2), 1.69 (t, JHꢀH = 7.0 Hz, 3H, H15), 1.22 (d, JHꢀH = 6.8 Hz,
6H, CH(CH3)2), 1.12 (d, JHꢀH = 6.8 Hz, 6H, CH(CH3)2). 13C{1H}
NMR (CD2Cl2, 125 MHz, 30 °C): 159.4 (C7), 158.9 (C1), 145.9 (C9,
C13), 145.4 (C3), 141.7 (C5), 135.0 (C4), 131.1 (C11), 129.7 (C8),
125.6 (C10, C12), 124.5 (C2), 123.9 (C6), 69.4 (C14), 29.3 (CH(CH3)2),
24.1 (CH(CH3)2), 23.4(CH(CH3)2),14.2(C15). 19F{1H} NMR (CD2Cl2,
470 MHz, 30 °C): ꢀ152.7, ꢀ152.8. Anal. Calcd for C21H28BF4NO: C, 63.49;
H, 7.10; N, 3.53. Found: C, 63.44; H, 6.99; N, 3.55.
Iminoꢀamido complexes exhibit interesting olefin polymer-
ization characteristics, but their thermal sensitivity can limit their
application as useful procatalysts. Our recent goal has been to
identify ligands/metal complexes with a bonding environment
similar to that found in iminoꢀamido complexes, but with struc-
tural features which remove thermal degradation pathways. The
search for such molecules led us to the synthesis and evaluation
of iminoꢀenamido and aminotroponiminato classes of com-
plexes. Both of these classes of procatalysts are significantly more
stable than similar iminoꢀamido complexes, a feature which is
undoubtedly due to the lack of alkyl substituents in the bridges of
these ligands. In this work, we showed that aminotroponiminato
hafnium and zirconium complexes can be prepared easily in five
steps starting from readily available tropolone. During the course
of ligand synthesis, an unexpected, air-stable tropylium cation
intermediate was isolated and found to react directly with amines
significantly faster than the neutral intermediate proposed in the
literature. Isolation of this tropylium cation opens up a more
convenient way to synthesize various aminotroponimines. Newly
prepared aminotroponiminato complexes contain a bulky 2,6-
diisopropylphenyl substituent on one of the nitrogen atoms and a
n-butyl or dimethylamino substituent on the other nitrogen
atom. Aminotroponiminato hafnium and zirconium catalysts
are active for olefin polymerization, but their activity is noticeably
lower than that observed for the analogous iminoꢀenamido
complex 3, containing a cyclohex-2-enylidene backbone. The
high thermal stability of aminotroponiminato complexes does
not translate into corresponding high stability under polymeri-
zation conditions. Multiple melting peaks of the polymers and
broad polydispersities identified by DSC and GPC analysis
respectively indicate that aminotroponiminato procatalysts un-
dergo a structural change upon activation and/or under high-
temperature polymerization conditions, leading to multiple
active species.
Preparation of 7-[[2,6-Bis(1-methylethyl)phenyl]imino]-
N-butyl-1,3,5-cycloheptatrien-1-amine (13). The synthesis
was based on the reported general procedure for the preparation of
N,N0-dialkylaminotroponimines, with modifications.34 To a solution
of triethyloxonium tetrafluoroborate (418 mg, 2.20 mmol) dissolved
in CH2Cl2 (5 mL) was added slowly a solution of 2-[[2,6-bis(1-
methylethyl)phenyl]amino]-2,4,6-cycloheptatrien-1-one (8; 587 mg,
2.09 mmol) in CH2Cl2 (15 mL). After it was stirred at 25 °C for 3 h,
the solution was cooled to ∼0 °C and a precooled solution of n-BuNH2
(1.467 g, 20 mmol) in CH2Cl2 (5 mL) was added. The solution was
warmed to 25 °C and was stirred overnight. The solvent was removed
’ EXPERIMENTAL SECTION
General Considerations. All solvents and reagents were ob-
tained from commercial sources and used as received unless other-
wise noted. Toluene, hexanes, CH2Cl2, and C6D6 were dried and
degassed according to published procedures. 2-Triflatotropone21a
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Organometallics
ARTICLE
under vacuum, and the residue was purified by column chromatography
(eluent hexane/Et2O 3/1 containing 3 vol % Et3N), affording 557 mg of
pure product as an orange solid (80%). H NMR (C6D6, 500 MHz,
Preparation of [N-[2,6-Bis(1-methylethyl)phenyl]-7-(butyl-
imino-kN)-1,3,5-cycloheptatrien-1-aminato-kN]tris(phenyl-
methyl)zirconium (5). 7-[[2,6-Bis(1-methylethyl)phenyl]imino]-N-
butyl-1,3,5-cycloheptatrien-1-amine (13; 250 mg, 0.74 mmol) and
ZrBn4 (339 mg, 0.74 mmol) were dissolved in dry C6D6 (3 mL). The
orange solution was stirred for 4 h and then concentrated under vacuum,
layered with hexane, and cooled to ꢀ45 °C overnight. The resulting
yellow crystals were filtered, washed with cold hexane, and dried under
vacuum. Isolated yield: 204 mg, 39%. 1H NMR (C6D6, 500 MHz,
30 °C): 7.19 (m, 3H, H10, H11, H12), 7.10 (tm, JHꢀH = 7.5 Hz, 6H,
meta CH2Ph), 6.88 (br s, 6H, ortho CH2Ph), 6.85 (m, 3H, para CH2Ph),
1
30 °C): 7.89 (br s, 1H, NH), 7.25 (d, JHꢀH = 7.7 Hz, 2H, H10, H12),
7.15 (tm, JHꢀH = 7.7 Hz, 1H, H11), 6.64 (tm, JHꢀH = 10.1 Hz, 1H,
H5), 6.50 (d, JHꢀH = 12.0 Hz, 1H, H2), 6.31 (m, 1H, H3), 6.02 (tm,
JHꢀH = 9.2 Hz, 1H, H4), 5.92 (d, JHꢀH = 10.0 Hz, 1H, H6), 2.98
(septet, JHꢀH = 6.8 Hz, 2H, CH(CH3)2), 2.86 (t, JHꢀH = 7.0 Hz, 2H,
H14), 1.30 (m, 2H, H15), 1.20 (d, JHꢀH = 6.8 Hz, 6H, CH(CH3)2),
1.17 (m, 2H, H16), 1.14 (d, JHꢀH = 6.8 Hz, 6H, CH(CH3)2), 0.71 (t,
JHꢀH = 7.3 Hz, 3H, H17). 13C{1H} NMR (C6D6, 125 MHz, 30 °C):
155.0 (C1), 151.1 (C7), 146.8 (C8), 138.3 (C9, C13), 134.0 (C5),
133.1 (C3), 123.8 (C10, C12), 123.7 (C11), 121.3 (C2), 119.3 (C4),
104.9 (C6), 42.8 (C14), 30.7 (C15), 28.8 (CH(CH3)2), 23.8
(CH(CH3)2), 23.6 (CH(CH3)2), 20.5 (C16), 13.7 (C17). Anal.
Calcd for C23H32N2: C, 82.09; H, 9.58; N, 8.32. Found: C, 82.36;
H, 9.45; N, 8.42.
6.80 (m, 1H, H5), 6.56 (d, JHꢀH = 11.7 Hz, 1H, H2), 6.52 (d, JHꢀH
=
11.2 Hz, 1H, H6), 6.45 (t, JHꢀH = 8.8 Hz, 1H, H3), 6.24 (t, JHꢀH = 9.3 Hz,
1H, H4), 3.04 (m, 2H, H14), 2.79 (septet, JHꢀH = 6.8 Hz, 2H,
CH(CH3)2), 2.35 (br s, 6H, CH2Ph), 1.35 (m, 2H, H15), 1.23 (d,
J
HꢀH = 6.8 Hz, 6H, CH(CH3)2), 1.11 (sextet, JHꢀH = 7.5 Hz, 2H, H16),
0.93 (d, JHꢀH = 6.8 Hz, 6H, CH(CH3)2), 0.75 (t, JHꢀH = 7.3 Hz, 6H,
H17). 13C{1H} NMR (C6D6, 125 MHz, 30 °C): 168.1 (C1), 161.3
(C7), 146.9 (C8), 145.4 (br, CH2Ph, quat), 142.3 (C9, C13), 135.0
(C5), 134.8 (C3), 129.1 (meta CH2Ph), 128.3 (ortho CH2Ph), 127.0
(C11), 125.0 (C10, C12), 124.2 (C4), 122.4 (para CH2Ph), 119.8 (C2),
115.4 (C6), 76.6 (br, CH2Ph), 47.1 (C14), 29.1 (CH(CH3)2), 28.5
(C15), 25.8 (CH(CH3)2), 24.1 (CH(CH3)2), 20.7 (C16), 13.9 (C17).
Anal. Calcd for C44H52ZrN2: C, 75.48; H, 7.49; N, 4.00. Found: C,
75.15; H, 7.23; N, 7.72.
Preparation of 2-[[2,6-Bis(1-methylethyl)phenyl]amino]-
2,4,6-cycloheptatrien-1-one 2,2-Dimethylhydrazone (14).
N-[2,6-Bis(1-methylethyl)phenyl]-2-ethoxycycloheptatrienylium tetra-
fluoroborate (12; 410 mg, 1.03 mmol) was dissolved in CH2Cl2 (5 mL),
and excess N,N-dimethylhydrazine (0.84 mL, 11 mmol) was added
dropwise. The solution immediately turned from yellow to red. The
reaction mixture was stirred at 25 °C for 3 h, followed by removal of
volatiles under vacuum. Flash chromatography (eluent hexane/Et2O 3/1
containing 3 vol % Et3N) was performed, and solvents were removed
Preparation of [2-[[2,6-Bis(1-methylethyl)phenyl]amino-j
N]-2,4,6-cycloheptatrien-1-one 2,2-dimethylhydrazonato-k
N1]tris(phenylmethyl)hafnium (17). 2-[[2,6-Bis(1-methylethyl)-
phenyl]amino]-2,4,6-cycloheptatrien-1-one 2,2-dimethylhydrazone
(14; 250 mg, 0.77 mmol) and HfBn4 (420 mg, 0.77 mmol) were
dissolved in dry C6D6 (3 mL), and the orange solution was stirred for
2 h. Completion of the reaction was confirmed by 1H NMR. The
reaction mixture was concentrated under vacuum, layered with hexane,
and cooled to ꢀ45 °C overnight. The resulting yellow crystals were
filtered, washed with cold hexane, and dried under vacuum. Isolated yield:
370 mg, 62%. 1H NMR (C6D6, 500 MHz, 30 °C): 7.16 (m, 9H, H10,
H11, H12, meta CH2Ph), 6.94 (d, JHꢀH = 7.6 Hz, 6H, ortho CH2Ph),
6.88 (t, JHꢀH = 7.3 Hz, 3H, para CH2Ph), 6.76 (m, 2H, H5, H6), 6.68 (d,
JHꢀH = 11.5 Hz, 1H, H2), 6.45 (t, JHꢀH = 10.3 Hz, 1H, H3), 6.25 (td,
JHꢀH = 2.5, 8.5 Hz, 1H, H4), 2.66 (septet, JHꢀH = 6.8 Hz, 2H,
CH(CH3)2), 2.61 (s, 6H, H14, H15), 2.09 (br s, 6H, CH2Ph), 1.17
(d, JHꢀH = 6.8 Hz, 6H, CH(CH3)2), 0.93 (d, JHꢀH = 6.8 Hz, 6H,
CH(CH3)2). 13C{1H} NMR (C6D6, 125 MHz, 30 °C): 167.0 (C1),
161.4 (C7), 147.0 (br, CH2Ph, quat), 146.8 (C8), 142.0 (C9, C13),
135.4 (C3), 134.7 (C5), 128.5 (ortho CH2Ph, meta CH2Ph), 127.1
(C11), 125.6 (C4), 124.9 (C10, C12), 123.2 (C2), 122.1 (para CH2Ph),
114.5 (C6), 85.5 (br, CH2Ph), 43.3 (C14, C15), 29.3 (CH(CH3)2), 25.7
(CH(CH3)2), 23.8 (CH(CH3)2). Anal. Calcd for C42H49HfN3: C,
65.15; H, 6.38; N, 5.43. Found: C, 64.68; H, 6.32; N, 5.57.
1
under vacuum to give a dark red oil. Yield: 317 mg, 95%. H NMR
(C6D6, 500 MHz, 30 °C): 8.46 (br s, 1H, NH), 7.39 (d, JHꢀH = 11.6 Hz,
1H, H6), 7.16 (m, 3H, H10, H11, H12), 6.52 (m, 1H, H5), 6.26 (td,
JHꢀH = 10.1, 1.1 Hz, 1H, H3), 5.92 (tm, JHꢀH = 9.2 Hz, 1H, H4), 5.87
(d, JHꢀH = 10.0 Hz, 1H, H2), 3.06 (septet, JHꢀH = 6.8 Hz, 2H,
CH(CH3)2), 2.46 (s, 6H, H14, H15), 1.09 (d, JHꢀH = 6.8 Hz, 12H,
CH(CH3)2). 13C{1H} NMR (C6D6, 125 MHz, 30 °C): 152.5 (C7),
150.7 (C1), 145.5 (C9, C13), 137.0 (C8), 132.9 (C3), 132.4 (C5), 127.5
(C11), 124.1 (C10, C12), 120.0 (C4), 118.6 (C6), 108.5 (C2), 46.9
(C14, C15), 28.9 (CH(CH3)2), 24.6 (CH(CH3)2), 23.3 (CH(CH3)2).
Anal. Calcd for C21H29N3: C, 77.97; H, 9.04; N, 12.99. Found: C, 78.30;
H, 9.03; N, 12.67.
Preparation of [N-[2,6-Bis(1-methylethyl)phenyl]-7-(buty-
limino-kN)-1,3,5-cycloheptatrien-1-aminato-kN]tris(phenyl-
methyl)hafnium (4). 7-[[2,6-Bis(1-methylethyl)phenyl]imino]-N-
butyl-1,3,5-cycloheptatrien-1-amine (13; 250 mg, 0.74 mmol) and
HfBn4 (403 mg, 0.74 mmol) were dissolved in dry C6D6 (3 mL), giving
an orange solution which wasstirred at 25 °C. Completion of thereaction
1
was confirmed by H NMR spectra taken after 90 min. The reaction
mixture was concentrated under vacuum, layered with hexane, and
cooled to ꢀ45 °C overnight. The resulting yellow crystals were filtered,
washed with cold hexane, and dried under vacuum. Isolated yield: 557
mg, 79%. 1H NMR (C6D6, 500 MHz, 30 °C): 7.21 (m, 3H, H10, H11,
H12), 7.15 (tm, JHꢀH = 7.5 Hz, 6H, meta CH2Ph), 6.91 (dm, JHꢀH = 6.1
Hz, 6H, ortho CH2Ph), 6.85 (m, 3H, para CH2Ph), 6.85 (m, 1H, H5),
6.59 (d, JHꢀH = 11.2 Hz, 1H, H6), 6.50 (m, 1H, H2), 6.48 (m, 1H, H3),
Preparation of [2-[[2,6-Bis(1-methylethyl)phenyl]amino-j
N]-2,4,6-cycloheptatrien-1-one 2,2-dimethylhydrazonato-k
N1]tris(phenylmethyl)zirconium (18). 2-[[2,6-Bis(1-methylethyl)-
phenyl]amino]-2,4,6-cycloheptatrien-1-one 2,2-dimethylhydrazone (14;
150 mg, 0.46 mmol) and ZrBn4 (211 mg, 0.46 mmol) were dissolved in
dry C6D6 (3 mL). The orange solution was stirred for 4.5 h and then
concentrated under vacuum, layered with hexane, and cooled to ꢀ45 °C
overnight. The resulting yellow crystals were filtered, washed with cold
hexane, and dried under vacuum. Isolated yield: 100 mg, 31%. 1H NMR
6.25 (t, JHꢀH = 8.8 Hz, 1H, H4), 3.18 (m, 2H, H14), 2.79 (septet, JHꢀH
=
6.8 Hz, 2H, CH(CH3)2), 2.21 (br s, 6H, CH2Ph), 1.38 (m, 2H, H15),
1.26 (d, JHꢀH = 6.8 Hz, 6H, CH(CH3)2), 1.14 (sextet, JHꢀH = 7.5 Hz,
2H, H16), 0.94 (d, JHꢀH = 6.8 Hz, 6H, CH(CH3)2), 0.77 (t, JHꢀH = 7.3
Hz, 6H, H17). 13C{1H} NMR (C6D6, 125 MHz, 30 °C): 168.5 (C1),
162.4 (C7), 146.2 (br, CH2Ph, quat), 146.0 (C8), 142.6 (C9, C13),
135.2 (C5), 134.9 (C3), 128.6 (meta CH2Ph), 127.9 (ortho CH2Ph),
127.2 (C11), 125.0 (C10, C12), 124.8 (C4), 122.3 (para CH2Ph), 120.2
(C2), 116.7 (C6), 87.0 (br, CH2Ph), 46.8 (C14), 29.2 (CH(CH3)2),
28.4 (C15), 25.8 (CH(CH3)2), 24.0 (CH(CH3)2), 20.8 (C16), 13.9
(C17). Anal. Calcd for C44H52HfN2: C, 67.12; H, 6.66; N, 3.56. Found:
C, 66.40; H, 6.60; N, 3.65.
(C6D6, 500 MHz, 30 °C):7.20(m, 3H, H10, H11, H12), 7.14(tm, JHꢀH
=
7.7 Hz, 6H, meta CH2Ph), 6.91 (m, 9H, ortho CH2Ph, para CH2Ph), 6.76
(d, JHꢀH = 11.7 Hz, 1H, H2), 6.71 (t, JHꢀH = 10.0 Hz, 1H, H5), 6.62
(d, JHꢀH = 10.4 Hz, 1H, H6), 6.41 (tm, JHꢀH = 10.5 Hz, 1H, H3), 6.23
(t, JHꢀH = 9.3 Hz, 1H, H4), 2.70 (septet, JHꢀH = 6.8Hz, 2H, CH(CH3)2),
2.53 (s, 6H, H14, H15), 2.25 (br s, 6H, CH2Ph), 1.20 (d, JHꢀH = 6.8 Hz,
4595
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Organometallics
ARTICLE
6H, CH(CH3)2), 0.97 (d, JHꢀH = 6.8 Hz, 6H, CH(CH3)2). 13C{1H}
NMR (C6D6, 125 MHz, 30 °C): 166.9 (C1), 158.6 (C7), 147.1 (C8),
146.5 (br, CH2Ph, quat), 141.7 (C9, C13), 135.5 (C3), 134.6 (C5), 128.8
(meta CH2Ph), 128.2 (ortho CH2Ph), 126.9 (C11), 125.3 (C4), 124.9
(C10, C12), 123.3 (C2), 122.0 (para CH2Ph), 112.7 (C6), 75.0 (br,
CH2Ph), 43.6 (C14, C15), 29.3 (CH(CH3)2), 25.6 (CH(CH3)2), 23.8
(CH(CH3)2). Anal. Calcd for C42H49ZrN3: C, 73.42; H, 7.19; N, 6.12.
Found: C, 73.67; H, 6.97; N, 5.83.
F values. R1 is calculated to provide a reference to the conventional
R value, but its function is not minimized. The amine hydrogens of 12,
13, and 19 were located in the electron difference maps, and their
positions were fully refined.
’ ASSOCIATED CONTENT
S
Supporting Information. Synthesis of 19, NMR spectra
b
Ethylene/1-Octene Polymerization Procedures and Polymer
Characterization. Ethylene/1-Octene Copolymerization. A 2 L Parr
reactor was used in the polymerizations. All feeds were passed through
columns of alumina and Q-5 catalyst (available from Engelhard Chemicals
Inc.) prior to introduction into the reactor. Procatalyst and cocatalyst
(activator) solutions were handled in the glovebox. A stirred 2 L reactor was
charged with about 533 g of Isopar E (from ExxonMobil) and 250 g of
1-octene comonomer. Hydrogen was added as a molecular weight control
agent by differential pressure expansion from a 75 mL addition tank at 300
psi (2070 kPa). The reactor contents were heated to the polymerization
temperature of 120 °C and saturated with ethylene at 460 psig (3.4 MPa).
Catalysts and cocatalysts, as dilute solutions in toluene, were mixed and
transferred to a catalyst addition tank and injected into the reactor. The
polymerization conditions were maintained for 10 min, with ethylene added
on demand. Heat was continuously removed from the reaction vessel
through an internal cooling coil. The resulting solution was removed from
the reactor, quenched with isopropyl alcohol, and stabilized by addition of
10 mL of a toluene solution containing approximately 67 mg of a hindered
phenol antioxidant (Irganox 1010 from Ciba Geigy Corp.) and 133 mg of a
phosphorus stabilizer (Irgafos 168 from Ciba Geigy Corp.). Between
polymerization runs, a wash cycle was conducted in which 850 g of
mixed alkanes was added to the reactor and the reactor was heated to
150 °C. The reactor was then emptied of the heated solvent immediately
before beginning a new polymerization run. Polymers were recovered by
drying for about 12 h in a temperature-ramped vacuum oven with a final set
point of 140 °C.
Polymer Characterization. Melting and crystallization temperatures
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 tempera-
ture for 2ꢀ4 min, the samples were cooled to ꢀ40 °C at 10 °C/min, held
for 2ꢀ4 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 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. To determine octene incorporation, 140 μL of
each polymer solution was deposited onto a silicon wafer, heated at
140 °C until the trichlorobenzene had evaporated, and analyzed using a
Nicolet Nexus 670 FTIR with 7.1 version software equipped with an
AutoPro auto sampler.
for all compounds, and X-ray data for 4, 12, 13, 17, and 19. This
material is available free of charge via the Internet at http://
pubs.acs.org.
’ AUTHOR INFORMATION
Corresponding Author
*E-mail: jklosin@dow.com.
’ REFERENCES
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Structure Determinations of 4, 12, 13, 17, and 19. X-ray
intensity data were collected on a Bruker SMART diffractometer at
ꢀ100 °C using Mo KR radiation (λ = 0.710 73 Å) and an APEXII CCD
area detector. Raw data frames were read by the program SAINT35 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 polariza-
tion effects, and numerical absorption corrections were applied on the
basisi of 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
H atoms were calculated in idealized positions and refined riding on their
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(33) Details of the synthesis and characterization (including the
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Information.
(34) See general procedure C in ref 15g.
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