Synthetic optimization and scale-up of imino-amido hafnium and zirconium olefin polymerization catalysts

Article abstract of DOI:10.1021/acs.oprd.5b00047

Improved synthetic protocols were developed for the safe, efficient, and scalable preparation of imino-amido Hf and Zr complexes that are precatalysts for olefin polymerizations. Facile syntheses of four imino-amido complexes were achieved in high yields by direct reactions of 4 equiv of MeMgBr with mixtures of the corresponding bisimines or imine-amines and MCl₄ (M = Hf, Zr). These synthetic routes eliminate the use of the pyrophoric reagents AlMe₃ and n-BuLi used previously, avoid cryogenic conditions, and lead to significant yield improvements. Notably, competing reaction pathways between the bis-imine and MeLi were observed. This led to the discovery of the selective addition of MeMgBr to the bis-imine, which was successfully applied in the synthesis of the imine-amine ligand.

Full text of DOI:10.1021/acs.oprd.5b00047

Article
pubs.acs.org/OPRD
Synthetic Optimization and Scale-Up of Imino−Amido Hafnium and
Zirconium Olefin Polymerization Catalysts
Chunming Zhang,* Heqi Pan, Jerzy Klosin,* Siyu Tu, and Arvind Jaganathan
Corporate R&D, The Dow Chemical Company, Midland, Michigan 48674, United States
Philip P. Fontaine
Performance Plastics R&D, The Dow Chemical Company, Freeport, Texas 77541, United States
S
* Supporting Information
ABSTRACT: Improved synthetic protocols were developed for the safe, efficient, and scalable preparation of imino−amido Hf
and Zr complexes that are precatalysts for olefin polymerizations. Facile syntheses of four imino−amido complexes were achieved
in high yields by direct reactions of 4 equiv of MeMgBr with mixtures of the corresponding bisimines or imine−amines and MCl4
(M = Hf, Zr). These synthetic routes eliminate the use of the pyrophoric reagents AlMe3 and n-BuLi used previously, avoid
cryogenic conditions, and lead to significant yield improvements. Notably, competing reaction pathways between the bis-imine
and MeLi were observed. This led to the discovery of the selective addition of MeMgBr to the bis-imine, which was successfully
applied in the synthesis of the imine−amine ligand.
catalytic activities at high temperatures, the ability to form very
high molecular weight polymers, and the capability to undergo
reversible chain transfer with diethylzinc to produce olefin
block copolymers.2b
The reported syntheses of complexes 1−3 are reproduci-
ble2b,7 but have some disadvantages for larger-scale preparation.
We sought to improve the efficiency (higher yields) and
scalability of all synthetic steps. Herein we report much
improved synthetic protocols that eliminate the use of AlMe3
and n-BuLi and afford complexes 1−3 in high overall yields.
The effectiveness of the newly developed transformations was
subsequently demonstrated by large-scale preparations of these
complexes.
INTRODUCTION
■
Molecular olefin polymerization catalysts continue to attract
attention among academic and industrial chemists as a result of
their ability to produce improved polyolefins relative to those
prepared by heterogeneous catalysts.1 Recently we have been
interested in olefin polymerization catalysts derived from
complexes ligated by bidentate monoanionic ligands containing
two nitrogen donors.2−6 Within this class of complexes, we and
others have examined the polymerization characteristics of
imino−amido2−4 (e.g., 1−3), imino−enamido5 (e.g., 4) and
amidoquinoline6 (e.g., 5) Zr and Hf complexes (Figure 1).
Such catalysts exhibit several desirable features, including high
RESULTS AND DISCUSSION
■
Imino−amido complexes 1, 2, and 3 were prepared previously
from bis-imine 6 as outlined in Scheme 1.2b,7 A key
transformation in this reaction sequence is the preparation of
ligand 7, which involves the reaction between bis-imine 6 and
AlMe3 followed by hydrolysis of the resulting Al complex.
While this reaction is highly selective, the transformation is not
atom-economical, as only one of the three methyl groups of
AlMe3 is incorporated into the product. Another challenging
step in this synthesis is the hydrolysis of 7 to 8, which occurs in
very low yield (29.1%). The other reactions depicted in Scheme
1 proceed in moderate yields, giving moderate overall yields
(52−54%) of complexes 1 and 2 and a low overall yield (12%)
of complex 3. We sought to develop an improved synthesis of
Special Issue: Non-precious Metal Catalysis
Received: February 16, 2015
Figure 1. Imino−amido-type olefin polymerization catalysts.
© XXXX American Chemical Society
A
DOI: 10.1021/acs.oprd.5b00047
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Scheme 1. Previously reported synthesis of precatalysts 1−32b,7
these imino−amido complexes to facilitate their large-scale
preparation.
of 6 gave the desired imino−amido Zr complex 1, which was
isolated as a bright-yellow solid in 94% yield. It is worth noting
that when ZrCl4 and MeMgBr were mixed at ambient
temperature, rapid gas evolution was observed, indicative of
the decomposition of ZrMe4; subsequent addition of bis-imine
6 to this mixture did not produce complex 1. The
corresponding Hf complex 2 was prepared in 97% yield in a
fashion analogous to that for the Zr complex. The Hf reaction
proceeded more slowly, taking over 24 h at ambient
temperature to reach completion, compared with the formation
of 1, which was complete by the time the reaction mixture
reached ambient temperature. The reaction progress was
monitored by 1H NMR spectroscopy. In cases where the
reaction was not fully complete, extra MeMgBr could be added
to the reaction mixture to drive the reaction to completion.
Typically, a slight excess of MeMgBr (4.1−4.5 equiv total) was
used in order to achieve complete conversion and a high yield.
The facile reaction of bis-imine 6 with in situ-generated
MMe4 to form 1 and 2 in high yields significantly shortens the
previously described synthesis from four steps to a one-pot
process. However, because of the instability of the tetrame-
thylmetal complexes (MMe4), the reactions required cryogenic
conditions (e.g., −35 °C), which is not desirable for large-scale
preparations.
Method B: Preparation of Imino−Amido Zr and Hf
Complexes 1 and 2 from in Situ-Generated (Bisimine)MCl4
Complexes. It is well-known that bisimines can react with MCl4
(M = Zr, Hf) to form (bis-imine)MCl4 complexes.11−13 We
postulated that the reaction of in situ-formed (bis-imine)MCl4
complexes with 4 equiv of MeMgBr might also lead to imino−
amido complexes 1 and 2.14 Mixing of bis-imine 6 with ZrCl4 in
anhydrous toluene at ambient temperature for 1 h,15 addition
of MeMgBr in ether (4.0 to 4.5 equiv) at −40 °C, and warming
of the reaction mixture to ambient temperature produced the
desired imino−amido complex 1 in 89% isolated yield. Since
this new approach most likely does not generate unstable metal
alkyls, we reasoned that cryogenic conditions might not be
necessary. The reaction between 4 equiv of MeMgBr and a
mixture of bis-imine 6 and MCl4 at ambient temperature
indeed led to the clean and high yielding formation of 1 (86%)
and 2 (98%) (Scheme 4).
Development of New Syntheses for Imino−Amido
Precatalysts 1 and 2. Method A. Preparation of Imino−
Amido Zr and Hf Complexes 1 and 2 from in Situ-Generated
MMe4 (M = Zr, Hf). We previously reported that the reaction of
bis-imine 6 with MBn4 (M = Zr, Hf) led to the formation of
imino−amido tribenzyl complexes via migratory insertion of a
benzyl group into a CN bond (Scheme 2).2a We
Scheme 2. Synthesis of imino−amido complexes via the
reaction of a bis-imine with MBn4 (M = Zr, Hf; Bn =
benzyl)2a
hypothesized that an analogous reaction between bis-imine 6
and MMe4 (M = Zr, Hf) might lead to the desired imino−
amido complexes 1 and 2 (Scheme 3), which would greatly
Scheme 3. Preparation of 1 and 2 from bis-imine 6 and in
situ-generated MMe4 (M = Zr, Hf) (method A)
simplify the preparation of these complexes. Unlike the
homoleptic benzyl complexes ZrBn4 and HfBn4, the analogous
tetramethyl complexes MMe4 are unstable at ambient temper-
8−10
ature. ZrMe4
decomposes to release methane even below
−15 °C.8 Thus, we decided not to pursue isolation of ZrMe4
and HfMe4 but instead to generate these species in situ and
react them with 6 (Scheme 3). Addition of 4 equiv of MeMgBr
(3.0 M solution in diethyl ether) to a stirred suspension of
ZrCl4 in anhydrous toluene at −35 °C followed by the addition
Method B is a more practical approach for the large-scale
preparation of 1 and 2, as it eliminates cryogenic reaction
B
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Scheme 4. Preparation of 1 and 2 from the reaction of 6, MCl4, and MeMgBr (method B)
Scheme 5. Proposed preparation of imine−amine 7 from the reaction of bis-imine 6 and MeLi
a
Table 1. Reactions between bis-imine 6 and MeLi or MeMgX
b
entry
methylation reagent
solvent
temperature (°C)
time (h)
yield of 6 (%)
yield of 7 (%)
1
2
3
4
5
6
7
MeLi
ether
−20 to −40
72
5.0
22
70
21
70
3.5
7.0
13
12
82
MeLi
ether
RT
RT
RT
60
81
MeMgCl
MeMgCl
MeMgCl
MeMgCl
MeMgBr
MeMgBr
THF
92
5.5
37
toluene
toluene
hexane
toluene
toluene
51
12
86
60
6.0
<0.1
85
c
c
60
99.5 (93.3)
99.5 (99.5)
d
8
60
<0.1
a
b
Reaction conditions: 6 (0.5 mmol), MeLi (0.55 mmol, 1.1 equiv) or MeMgX (1.0 mmol, 2 equiv), solvent (10 mL). GC samples were prepared by
c
taking one drop (10−15 mg) of the reaction mixture, adding it to 2 mL of aq. NH4Cl, and subsequently extracting with 2 mL of EtOAc. Isolated
yields. On a 5 mmol scale of 6 with 1.2 equiv of MeMgBr.
d
conditions and avoids in situ preparation of thermally unstable
metal alkyls. This method was subsequently demonstrated on a
0.10 mol scale to prepare complex 2 in 97% yield. Imino−
amido Zr and Hf complexes such as 1 and 2 can be now
conveniently prepared in high yields from bis-imines and metal
halides using this one-pot synthesis.
Preparation of Complexes 3 (M = Hf) and 15 (M = Zr).
It was recently reported16 that treatment of bis-imine 6 with
MeLi in diethyl ether at ice-bath temperature generated the Li
salt 10, which was isolated in 75% yield as the ether solvate 10·
Et2O. We were interested in generating 10 in this manner and
determining whether its subsequent treatment with a proton
source would produce the desired imine−amine 7 (Scheme 5,
path A). If successful, such a transformation would be an
attractive alternative to the previous method that used AlMe3 as
an alkylating agent to prepare 7.7
the formation of imine−amine 7 in 82% yield and 13% recovery
of the starting bis-imine 6, as measured by GC analysis (area %)
(Table 1). To account for the observed product distribution,
we hypothesized that MeLi might also act as a base and
deprotonate a methyl group from 6 to form lithium salt 11
(path B), which upon a water quench could regenerate bis-
imine 6. Such reactivity between MeLi and the sterically less
encumbered mesityl derivative of 6 was observed previously.16
In fact, in that case this reaction was reported to lead to the
exclusive formation of the mesityl analogue of 11. To gain a
better understanding of the outcome of this reaction, the
reaction mixture of 6 and MeLi (1.2−1.5 equiv) was quenched
with water at 0 °C, and the residue obtained from the organic
phase was analyzed by H NMR spectroscopy. The H NMR
spectrum (Figure 2A) showed the presence of two products in
a molar ratio of about 4:1, with the major one being the desired
imine−amine 7. In addition to other resonances, the minor
product of the mixture showed two characteristic vinyl
resonances at 4.41 and 4.13 ppm and was assigned as imine−
N-vinylamine 12,17 which is undoubtedly the protonation
1
1
In our hands, however, treatment of 6 with MeLi in diethyl
ether (1.2 to 1.5 equiv), either under cryogenic conditions
(−40 to −20 °C) or at near-ambient temperatures (0 °C to
ambient temperature), followed by a water quench resulted in
C
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1
Figure 2. Fragments of H NMR spectra (in C6D6) for (A) the products obtained from the reaction of 6 and MeLi quenched with H2O, (B)
compound 12 prepared from the reaction of bis-imine 6 and LDA, and (C) compound 12 isomerized to 6 after 10 days in solution at ambient
temperature.
Scheme 6. Preparation of keto amine 8
product of salt 11. There was virtually no detectable amount of
bis-imine 6, indicating complete conversion of the starting
material. Thus, the presence of bis-imine 6 in the GC analysis
was likely due to tautomerization of imine−N-vinylamine 12 to
bis-imine 6 at elevated temperature on the GC column. To
further confirm that the vinyl protons observed in the NMR
spectrum belong to imine−N-vinylamine 12, compound 12 was
prepared independently by the reaction of bis-imine 6 with
LDA16 followed by a water quench. This reaction resulted in a
mixture of 12 and 6 in a molar ratio of about 3:1. Trituration of
the crude product with ethanol afforded pure 12 (Figure 2B),
which was found to undergo complete tautomerization to bis-
imine 6 after 10 days at ambient temperature (Figure 2C),
indicating a very low barrier for this tautomerization. These
experiments indicated that the reaction between 6 and MeLi
leads to two competing pathways (Scheme 5, paths A and B)
generating the two lithium salts 10 and 11, which, when treated
with water, generate compounds 7 and 12, respectively.
To suppress the generation of salt 11 during the preparation
of 7, we considered other organometallic reagents for this
transformation that are nucleophilic but less basic than MeLi
(Table 1). Treatment of bis-imine 6 with 2 equiv of MeMgCl in
THF at ambient temperature generated imine−amine 7 in only
5.5% yield as determined by GC analysis. The resulting mixture
consisted mostly of the starting material 6 (entry 3). The yield
of 7 improved to 37% in toluene at ambient temperature (entry
4) and further increased to 86% when the reaction was
performed at 60 °C (entry 5). The reaction conducted in
hexanes at 60 °C also gave high yields of 7, but it was slower
than the reaction carried out in toluene and some byproducts
were also observed (entry 6). A significantly improved reaction
was observed when MeMgBr was used in place of MeMgCl,
resulting in clean conversion to 7 (99.5% yield as determined
by GC analysis) with less than 0.1% 6 in toluene at 60 °C
(entry 7). A high reaction yield was also obtained when a lower
amount of MeMgBr (1.2 equiv) was used (entry 8). With
MeMgBr as the methylation reagent, imine−amine 7 was
obtained in yields of 93−99.5% with 99.5% purity on reaction
scales of 0.5 to 5.0 mmol. The reaction was subsequently
demonstrated on a scale of over 0.5 mol (200 g), giving 7 in
99% isolated yield. This new synthetic method not only
significantly improves the yield of 7 but also leads to a much
safer and scalable process.
In addition to the synthetic improvements identified for
complexes 1 and 2, we were also interested in developing an
improved synthetic method for the preparation of imino−
amido complexes containing different substituents on the imino
and amido nitrogen atoms (e.g., 3). Keto amine 8 is a key
building block for the preparation of imine−amine ligands (via
the reaction with a variety of primary amines), but it was
previously prepared in low yields (29−41%)2b,7 by hydrolysis of
imine−amine 7 (Scheme 6). We found that this hydrolysis
reaction cleanly gave keto amine 8 and 2,6-diisopropylaniline.
The low isolated yields reported previously might have been
due to the loss of product during the isolation and separation of
keto amine 8 from 2,6-diisopropylaniline. We modified both
the reaction conditions and the isolation procedures to increase
the final yield of 8 to 91%. We performed the hydrolysis of 7 in
a mixture of ethanol and water (1:1 volume ratio) in the
presence of sulfuric acid at 65 °C. The amount of sulfuric acid
was reduced from 4 equiv, as reported in the original
synthesis,2b,7 to 2 equiv without loss of reaction efficiency.
D
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After the reaction mixture was quenched with NaOH, keto
amine 8 and 2,6-diisopropylaniline were extracted with ethyl
acetate (EtOAc) and thoroughly washed with water (in order
to completely remove the inorganic base) before the volatiles
were evaporated. Keto amine 8 and 2,6-diisopropylaniline were
then separated by distillation under reduced pressure with a
short-path distillation apparatus: 2,6-diisopropylaniline was
effectively removed at 58−60 °C/0.8 mmHg to leave keto
amine 8 in near-quantitative yield with 97% purity. The crude
keto amine 8 could be further purified by crystallization from a
small amount of hexane, resulting in a yield of 91% with >99%
purity. The preparation of 8 using this modified procedure was
demonstrated on a scale of over 0.4 mol (100 g), and the net
yield improvement was from 29% to 96−99%.
Scheme 8. Preparation of imino−amido complexes 3 and 15
The preparation of imine−amine ligand 9 was achieved by
straightforward condensation of keto amine 8 with n-octyl-
amine in the presence of a small amount of formic acid catalyst
(p-toluenesulfonic acid monohydrate could also be used) in
refluxing toluene (Scheme 7). Water generated in the reaction
Scheme 7. Preparation of imine−amine ligand 9
Figure 3. Molecular structure of 15. Hydrogen atoms have been
omitted for clarity. Thermal ellipsoids are shown at 50% probability.
Selected bond lengths (Å) and angle (deg): Zr1−N1 = 2.385(4), Zr1−
N2 = 2.062(4), N1−C5 = 1.290(6), N2−C6 = 1.485(6), Zr1−C1 =
2.366(4), Zr1−C2 = 2.259(5), Zr1−C3 = 2.245(6), N1−Zr1−N2 =
70.03(15).
complex 3 (method A, 75% yield). However, this method is less
practical and robust, as it involves cryogenic reaction conditions
and requires in situ preparation of thermally unstable metal
alkyls.
The improved total synthesis of imino−amido complexes 3
and 15 containing different substituents on the imido and
amido nitrogen atoms is summarized in Scheme 9. In
comparison with the previous total synthesis of 3, the new
process described here eliminates the use of pyrophoric AlMe3
and n-BuLi, simplifies individual procedures and product
isolation, and substantially improves the overall yield from
12% to 77%.
was azeotropically removed using a Dean−Stark trap. Typically,
a small excess of n-octylamine (1.2−1.3 equiv total) was used in
this reaction to facilitate the complete conversion, as a small
amount of n-octylamine was usually lost in the Dean−Stark
trap. The use of excess n-octylamine resulted in fast conversion
to the desired product and also hindered the competitive
reaction of keto amine 8 with 2,6-diisopropylaniline when 8
contaminated with a small amount of 2,6-diisopropylaniline was
used in the reaction. Imine−amine ligand 9 was isolated in over
99% yield with 99% purity.
As shown in Scheme 1, imino−amido complex 3 was
prepared previously by converting imine−amine ligand 9 into
the corresponding lithium salt with n-BuLi. This salt was
subsequently reacted with HfCl4 to form the ligated hafnium
trichloride derivative, which in turn was alkylated with 3 equiv
of MeMgBr.7 We envisioned that complex 3 and its Zr
analogue (15) could be prepared directly by addition of ligand
9 to in situ-generated MMe4 (M = Zr, Hf) (method A) or via
the reaction of MeMgBr with a mixture of ligand 9 and MCl4
(method B), the methods developed for the preparation of 1
and 2.
Since method B was found previously to be more practical
than method A, it was examined first for the preparation of
imino−amido complexes 3 and 15. Addition of MeMgBr (4.0−
4.5 equiv) to a mixture of ligand 9 and HfCl4 in toluene at 0 °C,
followed by warming of the reaction mixture to ambient
temperature, produced the desired complex 3, which was
isolated in 87% yield (Scheme 8). The Zr complex 15 was
prepared in 86% yield following an analogous procedure. The
molecular structure of 15 was determined by single-crystal X-
ray analysis (Figure 3), and its metrical parameters are very
similar to those of the hafnium analogue.2b The preparation of
3 by method B was demonstrated on a 0.10 mol scale (52 g,
87% yield).
CONCLUSIONS
■
Two processes were developed for the preparation of imino−
amido Zr and Hf complexes 1 and 2 directly from bis-imine 6,
ZrCl4 or HfCl4, and MeMgBr in a one-pot synthesis. Method A
involves the reaction of in situ-generated ZrMe4 and HfMe4
(from ZrCl4 and HfCl4 and MeMgBr) with bis-imine 6 to
produce imino−amido complexes 1 and 2, respectively, in near-
quantitative yields. Alternatively, 1 and 2 can be conveniently
prepared from the reaction of MeMgBr with a mixture of bis-
imine 6 and MCl4 (M = Zr, Hf) (method B). Method B has an
advantage over method A, as it eliminates cryogenic reaction
conditions and the need for in situ preparation of unstable
metal alkyls.
A significantly improved method for the preparation of
imino−amido complexes containing two different substituents
on the imine and amine nitrogen atoms was also developed. It
was discovered that very selective nucleophilic addition of
MeMgBr and bis-imine 6 can be achieved, affording imine−
amine 7 in 99% yield. Optimization of the hydrolysis reaction
of imine−amine 7 led to a reduction in the amounts of both
sulfuric acid and sodium hydroxide and a subsequent increase
in the yield of keto amine 8 from 29% to 96−99%. Imino−
amido complexes 3 and 15 were prepared in high yields (3,
The reaction of ligand 9 with HfMe4 generated in situ from
the reaction of HfCl4 and MeMgBr at −35 °C also produced
E
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Scheme 9. Improved synthesis of imino−amido complexes 3 and 15
87%; 15, 86%) by the reaction of MeMgBr with a mixture of
imine−amine ligand 9 and MCl4 (M = Zr, Hf). The overall
yield of the improved total synthesis of 3 is 77%, which is six
times higher than that of the previously reported synthesis.
corresponding to a yield of 88.56% with over 98% purity as
determined by GC analysis (with less than 2% isomers). Note:
technical grade, 90% 2,6-diisopropylaniline was used. H NMR
(CDCl3, 400 MHz) δ 7.19−7.10 (m, 6H, Ph), 2.71 (septet, 4H,
CH), 2.07 (s, 6H, CH3), 1.19 (dd, 24H, CH3).
1
Preparation of Imino−Amido Zr and Hf Complexes from
in Situ-Generated MMe4 (Method A). Preparation of (N-
(2,6-Diisopropylphenyl)-N-(3-(2,6-diisopropylphenyl)-
imino-2-methylbutan-2-yl)amino)trimethylzirconium
(1). To a suspension of ZrCl4 (2.33 g, 10.0 mmol) in anhydrous
toluene (50 mL) in a 125 mL three-neck flask equipped with
stir bar, a thermometer, and a nitrogen pad at −40 °C was
added dropwise a solution of 3.0 M MeMgBr solution in
diethyl ether (15 mL, 45 mmol) over 10 min while the
temperature was maintained. The resulting mixture was stirred
at −40 to −35 °C for an additional 30 min, and then a solution
of N,N′-bis(2,6-diisopropylphenyl)-1,4-diaza-2,3-dimethyl-1,3-
butadiene (6) (4.046 g, 10 mmol) in toluene (15 mL) was
added over 10 min at −40 to −35 °C. The resulting suspension
was allowed to stir at −40 to −35 °C for 1 h, and then the
reaction mixture was allowed to warm to ambient temperature
(25 °C) over 40 min by removal of the cooling bath, to give a
dark-brown to black mixture. An aliquot (0.3 mL) was taken
from the reaction mixture and filtered through a syringe filter
EXPERIMENTAL SECTION
■
General Considerations. Solvents and reagents were
obtained from commercial sources and used as received, unless
otherwise noted. All syntheses and manipulations of air-
sensitive materials were carried out under an inert atmosphere
(nitrogen). Solvents (toluene, hexane, diethyl ether) were first
saturated with nitrogen and then dried by passage through
activated alumina and Q-5 catalyst (available from Engelhard
Chemicals, Inc.) prior to use. Benzene-d6 (C6D6) was dried
over molecular sieves and filtered prior to use. NMR spectra
1
were recorded on a Bruker 400 (FT 400 MHz, H; 101 MHz,
1
13C) spectrometer. H NMR data are reported as follows:
chemical shift (multiplicity, coupling constant, integration,
assignment). Multiplicities are denoted as follows: br = broad, s
= singlet, d = doublet, t = triplet, q = quartet, p = pentet, m =
1
multiplet, hept = heptet. Chemical shifts for H NMR data are
reported in parts per million downfield from internal
tetramethylsilane (TMS, δ scale) using residual protons in
the deuterated solvent (C6D6, 7.15 ppm) as a reference. 13C
NMR data were determined with 1H decoupling, and the
chemical shifts are reported in parts per million versus
tetramethylsilane (C6D6, 128 ppm). Elemental analyses were
performed at Midwest Microlab, LLC.
1
into an NMR tube for H NMR analysis in C6D6, which
showed that the reaction was complete. The volatiles were
removed under reduced pressure, and the residue was extracted
twice with anhydrous hexane (100 mL, 50 mL). The combined
hexane solution was concentrated under reduced pressure to
Preparation of N,N′-Bis(2,6-diisopropylphenyl)-1,4-
diaza-2,3-dimethyl-1,3-butadiene (6). Bisimine 6 was
prepared by modification of a reported procedure.18 Into a 2
L three-neck round-bottom flask equipped with an overhead
agitator, a cold water condenser, a nitrogen pad, a heating
mantle, and a thermocouple were loaded 2,3-butanedione
(86.09 g, 1.0 mol), 2,6-diisopropylaniline (DIPA) (354.58 g, 2.0
mol), ethanol (800 mL), and 98% formic acid (2 mL). The
mixture was heated at 60−65 °C for 50 h. The resulting
mixture was then allowed to cool to ambient temperature
overnight. The precipitated product was filtered, rinsed with
cold ethanol (4 °C, 200 mL), suction-dried, and dried under
reduced pressure to give a first crop of product (310.1 g). The
mother liquor/filtrate was concentrated to a black residue (102
g). Ethanol (100 mL) was added to the residue, and the
resulting mixture was placed in a refrigerator overnight. The
precipitate was filtered, rinsed with cold ethanol (50 mL), and
dried under reduced pressure to give a second crop of product
(54.5 g). The total mass of product obtained was 364.6 g,
give product 1 as a yellow solid (5.25 g, 94%). The 1H and 13
C
NMR spectra are consistent with those reported in the
literature.2b 1H NMR (400 MHz, C6D6) δ 7.22−7.16 (m,
3H), 7.12−7.03 (m, 3H), 3.75 (hept, J = 6.9 Hz, 2H), 2.86
(hept, J = 6.8 Hz, 2H), 1.48 (s, 3H), 1.39 (d, J = 6.8 Hz, 6H),
1.32 (d, J = 6.8 Hz, 6H), 1.30 (d, J = 6.8 Hz, 6H), 1.21 (s, 6H),
1.03 (d, J = 6.8 Hz, 6H), 0.58 (s, 9H). 13C NMR (101 MHz,
C6D6) δ 195.48, 148.99, 145.33, 142.06, 139.19, 126.83, 126.46,
124.73, 124.37, 72.91, 48.65, 29.55, 28.70, 28.62, 26.23, 25.30,
24.56, 24.20, 19.28.
Preparation of (N-(2,6-Diisopropylphenyl)-N-(3-(2,6-
diisopropylphenyl)imino-2-methylbutan-2-yl)amino)-
trimethylhafnium (2). HfCl4 (3.203 g, 10 mmol) and
anhydrous toluene (60 mL) were loaded into a 125 mL
three-neck flask equipped with a stir bar and a thermometer
under a nitrogen atmosphere. The suspension was cooled to
−40 °C. A 3.0 M solution of MeMgBr in diethyl ether (13.7
mL, 41 mmol) was added through a syringe at such a rate to
F
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Article
maintain the reaction temperature below −35 °C. The addition
took about 5 min. The resulting yellow suspension was stirred
at −40 to −35 °C for 1.0 h. A solution of 6 (4.046 g, 10 mmol)
in anhydrous toluene (15 mL) was added at −40 to −35 °C
over 5 min. The resulting mixture was stirred at −40 to −35 °C
for 2 h and then warmed to ambient temperature by removal of
the cooling bath. The mixture was allowed to stir at ambient
temperature (25 °C) until the conversion was complete as
temperature for an additional 1 h. A 0.3−0.5 mL sample of the
reaction mixture was taken and filtered through a syringe filter
into an NMR tube for H NMR analysis with C6D6 as an
1
external reference, which showed that the reaction was
complete. The volatiles were removed under reduced pressure,
and the residue was extracted twice with anhydrous hexane
(100 mL, 50 mL). The combined hexane solution was
concentrated under reduced pressure to give the desired
1
1
monitored by H NMR spectroscopy (0.3−0.5 mL of the
product 1 (4.78 g, 86%). The H and 13C NMR spectra are
reaction mixture was taken and filtered through a syringe filter
consistent with those of the compound synthesized according
to method A as well as those reported in the literature.2b
Preparation of 2. To a suspension of HfCl4 (3.203 g, 10.0
mmol) in anhydrous toluene (60 mL) in a 125 mL three-neck
flask equipped with a stir bar and a thermometer under a
nitrogen atmosphere at ambient temperature (23 °C) was
added 6 (4.046 g, 10.0 mmol). The resulting mixture was
stirred at ambient temperature for 1 h. A 3.0 M solution of
MeMgBr in diethyl ether (15 mL, 45 mmol) was slowly added
at such a rate to maintain the reaction temperature between 23
and 40 °C. The addition took about 15 min, and the
temperature rose to 36 °C. The reaction mixture was allowed
to stir at ambient temperature for another 2 h. A 0.3−0.5 mL
sample of the reaction mixture was taken and filtered through a
1
into an NMR tube under nitrogen for H NMR analysis with
C6D6 as an internal reference). Whenever the 1H NMR
spectrum showed that MeMgBr was completely consumed and
the reaction was not complete, additional MeMgBr was added.
The reaction took over 24 h, and the reaction mixture turned
dark-brown to black. Upon completion of the reaction, the
volatiles were removed under reduced pressure, and the residue
was extracted twice with anhydrous hexane (100 mL, 50 mL).
The combined hexane solution was concentrated under
reduced pressure to give product 2 as a yellow solid (6.24 g,
1
97%). The H and 13C NMR spectra are consistent with those
reported in the literature.2b 1H NMR (400 MHz, C6D6) δ
7.221−7.16 (m, 3H), 7.12−7.03 (m, 3H), 3.76 (hept, J = 6.9
Hz, 2H), 2.89 (hept, J = 6.8 Hz, 2H), 1.42 (s, 3H), 1.40 (d, J =
6.8 Hz, 6H), 1.31 (d, J = 6.8 Hz, 6H), 1.28 (d, J = 6.8 Hz, 6H),
1.17 (s, 6H), 1.00 (d, J = 6.8 Hz, 6H), 0.36 (s, 9H). 13C NMR
(101 MHz, C6D6) δ 197.25, 148.59, 144.90, 143.99, 139.54,
127.07, 125.98, 124.62, 124.40, 73.38, 61.25, 29.85, 28.63,
28.59, 26.22, 25.24, 24.61, 24.32, 19.44.
1
syringe filter into an NMR tube for H NMR analysis with
C6D6 as an internal reference, which showed that the reaction
was complete. The volatiles were removed under reduced
pressure, and the residue was extracted twice with anhydrous
hexane (100 mL, 50 mL). The combined hexane solution was
concentrated under reduced pressure to give the desired
1
Preparation of Imino−Amido Zr and Hf Complexes from
in Situ-Generated Bisimine·MCl4 (Method B). Preparation of
1. Method B-1: Addition of MeMgBr at −40 to −35 °C. To a
suspension of ZrCl4 (2.33 g, 10.0 mmol) in anhydrous toluene
(60 mL) in a 125 mL three-neck flask equipped with a stir bar,
a thermometer, and a nitrogen pad at ambient temperature (23
°C) was added 6 (4.046 g, 10.0 mmol). After 1 h of stirring at
ambient temperature, the resulting mixture was cooled to −40
°C, and a 3.0 M solution of MeMgBr in diethyl ether (15 mL,
45 mmol) was slowly added at such a rate to maintain the
reaction temperature below −35 °C. The addition took about 5
min. The resulting mixture was allowed to stir at −40 to −35
°C for 1 h, subsequently allowed to warm to ambient
temperature (23 °C) over 2 h, and further stirred at ambient
temperature (23 °C) for 1 h. A 0.3 mL aliquot of the reaction
mixture was taken and filtered through a syringe filter into an
product 2 (6.33 g, 98%). The H and 13C NMR spectra are
consistent with those of the compound synthesized according
to method A as well as those reported in the literature.2b The
reaction was also carried out on a 0.1 mol scale, and 2 was
isolated in 97% yield (62.5 g).
Preparation of N-(3-(2,6-Diisopropylphenylamino)-3-
methylbutan-2-ylidene)-2,6-diisopropylbenzenamine
(7). Into a 3 L three-neck round-bottom flask equipped with an
overhead agitator, a cold water condenser, a nitrogen pad, a
heating mantle, and a thermocouple were loaded 6 (202.0 g,
0.499 mol) and anhydrous toluene (800 mL). The mixture was
stirred at ambient temperature to form a yellow solution. A 3.0
M solution of methylmagnesium bromide in diethyl ether (220
mL, 0.66 mol) was added slowly at ambient temperature over
30 min. A slightly exothermic reaction occurred, and the
temperature rose from 18 to 22 °C. The reaction mixture was
then heated and stirred at 60 °C until the reaction was
complete (3 h) as monitored by GC. The resulting mixture was
cooled to 0 to 5 °C with an ice−water bath. Aqueous NH4Cl
solution (20 wt %, 500 mL) was slowly added19 over 30 min,
and the reaction mixture was stirred for another 30 min. The
product was extracted with ethyl acetate (250 mL × 2), and the
organic phase was washed with water (500 mL). The volatiles
were removed under reduced pressure by rotary evaporation,
and the residue was dried in a vacuum oven at 45 °C/<1
mmHg overnight, which gave the desired product 7 (208.0 g)
in 99.0% yield with over 98% purity as measured by GC area %
1
NMR tube for H NMR analysis with C6D6 as an internal
reference, which showed that the reaction was complete. The
volatiles were removed under reduced pressure, and the residue
was extracted twice with anhydrous hexane (100 mL, 50 mL).
The combined hexane solution was concentrated under
1
reduced pressure to give product 1 (4.97 g, 89%). The H
and 13C NMR spectra are consistent with those of the
compound synthesized according to method A as well as those
reported in the literature.2b
Method B-2: Addition of MeMgBr at Ambient Temper-
ature. To a suspension of ZrCl4 (2.33 g, 10.0 mmol) in
anhydrous toluene (60 mL) in a 125 mL three-neck flask
equipped with a stir bar, thermometer, and a nitrogen pad at
ambient temperature (23 °C) was added 6 (4.046 g, 10.0
mmol). The resulting mixture was stirred at ambient temper-
ature for 1 h. A 3.0 M solution of MeMgBr in diethyl ether (15
mL, 45 mmol) was added via a syringe pump at 23 to 25 °C
over 1 h. The reaction mixture was allowed to stir at ambient
1
(with less than 2% isomers as determined by GC analysis). H
NMR (400 MHz, CDCl3) δ 7.20−7.02 (m, 6H), 4.34 (s, 1H),
3.53 (dt, J = 13.7, 6.8 Hz, 2H), 2.81 (dt, J = 13.7, 6.9 Hz, 2H),
1.87 (s, 3H), 1.35 (s, 6H), 1.24−1.15 (m, 24H). 13C NMR
(101 MHz, CDCl3) δ 176.46, 146.59, 145.99, 140.17, 136.27,
124.51, 123.26, 123.10, 123.01, 61.74, 28.39, 27.88, 27.10,
24.20, 23.52, 23.21, 16.41.
G
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Article
Preparation of 3-(2,6-Diisopropylphenylamino)-3-
methylbutan-2-one (8). Into a 3 L three-neck round-bottom
flask equipped with an overhead agitator, a cold water
condenser, a nitrogen pad, a heating mantle, and a
thermocouple was loaded N-(3-(2,6-diisopropylphenylamino)-
3-methylbutan-2-ylidene)-2,6-diisopropylbenzenamine (7)
(206.0 g, 489.7 mmol) and anhydrous ethanol (800 mL).
The mixture was heated with stirring to form a solution. A 2.5
N aqueous solution of H2SO4 (776 mL, 970 mmol) was added
over 1 h at 40 °C. The mixture was subsequently heated at 65
°C until the hydrolysis was complete as monitored by GC
analysis (3−4.5 h). The resulting mixture was cooled to 0 to 5
°C with an ice−water bath. A solution of 5.0 N NaOH (388
mL, 1.94 mol) was added at such a rate to remain the
temperature at or below ambient temperature to adjust the pH
to approximately 11. The mixture was then extracted with
hexane (2 × 1 L), and the organic phase was washed with water
(2 × 500 mL). Volatiles were removed under reduced pressure,
and the residue (203 g) as a mixture of keto amine 8 and 2,6-
diisopropylaniline was subjected to distillation at 0.8 mmHg
with a short-path distillation apparatus. 2,6-Diisopropylaniline
(79 g, 91%) was removed at 58−62 °C/0.8 mmHg. The crude
product (123 g, 96%) remained, which was 96.5% as
determined by GC analysis and pure enough for use in the
next step. Further purification of the crude product was
achieved by recrystallization from hexane to give 114.7 g (91%)
of 8 with over 99% purity by GC analysis. 1H NMR (400 MHz,
CDCl3) δ 7.07 (s, 3H), 3.69 (s, 1H), 3.12 (hept, J = 6.9 Hz,
2H), 2.37 (s, 3H), 1.22 (s, 6H), −1.17 (d, J = 6.9 Hz, 12H).
13C NMR (101 MHz, CDCl3) δ 212.85, 145.55, 139.60, 124.72,
123.13, 63.70, 28.28, 25.42, 24.02, 23.94.
stirred at −40 to −35 °C for 1.0 h. A solution of 2,6-
diisopropyl-N-(2-methyl-3-(octyliminobutan-2-yl))-
benzenamine (9) (2.474 g) in anhydrous toluene (20 mL) was
added at −40 to −35 °C over 5 min. The resulting mixture was
stirred at −40 to −35 °C for 2 h and then warmed to ambient
temperature by removal of the cooling bath. The mixture was
allowed to continue stirring at ambient temperature (25 °C)
1
until the conversion was complete as monitored by H NMR
spectroscopy (0.3−0.5 mL of the reaction mixture was taken
and filtered through a syringe filter into an NMR tube under
nitrogen for 1H NMR analysis with C6D6 as an external
1
reference). Whenever the H NMR spectrum showed that
MeMgBr was completely consumed and the reaction was not
complete, additional MeMgBr was added. The reaction took
over 24 h, and the reaction mixture turned dark-brown to black.
Upon completion of the reaction, the volatiles were removed
under reduced pressure, and the residue was extracted with
anhydrous hexane (20 mL). The wet cake was extracted with
additional hexane (2 × 5 mL). The combined hexane solution
was concentrated under reduced pressure to give product 3 as a
1
slightly yellow solid (2.96 g, 75%). The H and 13C NMR
spectra were consistent with those reported in the literature.2b
1H NMR (400 MHz, C6D6) δ 7.28−7.15 (m, 3H), 3.68 (hept, J
= 6.8 Hz, 2H), 3.44−3.35 (m, 2H), 1.55−1.44 (m, 2H), 1.41
(d, J = 7.0 Hz, 6H), 1.40 (s, 3H), 1.29 (d, J = 7.0 Hz, 6H),
1.32−1.18 (m, 10H), 0.98 (s, 6H), 0.93 (t, J = 6.9 Hz, 3H),
0.44 (s, 9H). 13C NMR (101 MHz, C6D6) δ 189.33, 149.27,
140.68, 128.17, 127.93, 126.36, 124.78, 76.30, 56.98, 50.95,
32.18, 29.64, 28.73, 28.50, 28.01, 27.60, 26.84, 24.72, 23.09,
15.50, 14.37.
Method B. To a suspension of HfCl4 (2.23 g, 7.0 mmol) in
anhydrous toluene (40 mL) in a 125 mL three-neck flask
equipped with a stir bar and a thermometer under a nitrogen
atmosphere at ambient temperature (23 °C) was added 9
(2.474 g, 6.64 mmol). The resulting mixture was stirred at
ambient temperature for 0.5 h and then cooled to 0 °C. A 3.0
M solution of MeMgBr in diethyl ether (10.5 mL, 31.5 mmol)
was slowly added at such a rate to maintain the reaction
temperature below 5 °C. The addition took about 5 min. The
reaction mixture was allowed to stir at 0 to 5 °C for another 1 h
and then slowly warmed to ambient temperature overnight. A
0.3−0.5 mL sample of the reaction mixture was taken and
filtered through a syringe filter into an NMR tube for 1H NMR
analysis with C6D6 as an external reference, which showed that
the reaction was complete. The volatiles were removed under
reduced pressure, and the residue was extracted with anhydrous
hexane (30 mL). The wet cake was extracted with additional
hexane (2 × 10 mL). The combined hexane solution was
concentrated under reduced pressure to give the desired
Preparation of 2,6-Diisopropyl-N-(2-methyl-3-(octyli-
minobutan-2-yl))benzenamine (9). Into a 250 mL three-
neck round-bottom flask equipped with an electrical stirrer, a
cold water condenser with a Dean−Stark trap attached, a
nitrogen pad, a heating mantle, and a thermocouple were
loaded 3-(2,6-diisopropylphenylamino)-3-methylbutan-2-one
(8) (20.91 g, 80 mmol), n-octylamine (12.41 g, 96.0 mmol),
toluene (100 mL), and 98% formic acid (40 mg). The mixture
was heated at reflux for 2.5 h, and then additional n-octylamine
(3.0 g, 23 mmol) was added. The mixture was heated at reflux
overnight. The resulting mixture was cooled to ambient
temperature and washed with water (2 × 100 mL). The
volatiles were removed under reduced pressure. The residue
was dried in a vacuum oven at 55−60 °C/1 mmHg overnight,
1
which gave 9 (29.80 g, 100%) as a colorless viscous oil. H
NMR (400 MHz,, CDCl3) δ 7.08−6.86 (m, 3H), 3.37 (hept, J
= 6.8 Hz, 2H), 3.25 (t, J = 7.1 Hz, 2H), 1.84 (s, 3H), 1.69−1.54
(m, 2H), 1.41−1.14 (m, 10H), 1.09 (s, 6H), 1.08 (d, J = 6.9
Hz, 12H), 0.87−0.75 (m, 3H). 13C NMR (101 MHz, CDCl3) δ
171.37, 145.38, 140.60, 123.02, 121.93, 59.97, 50.11, 30.89,
29.89, 28.62, 28.35, 26.86, 26.74, 25.57, 23.24, 21.66, 13.08,
12.21.
Preparation of (N-(1,1-Dimethyl-2-(octylimino-κN)-
propyl)-2,6-diisopropylbenzenaminato-κN)-
trimethylhafnium (3). Method A. HfCl4 (2.127 g, 6.64
mmol) and anhydrous toluene (40 mL) were loaded into a 125
mL three-neck flask equipped with a stir bar and a thermometer
under a nitrogen atmosphere. The suspension was cooled to
−40 °C. A 3.0 M solution of MeMgBr in diethyl ether (9.1 mL,
27.3 mmol) was added through a syringe at such a rate to
maintain the reaction temperature below −35 °C. The addition
took about 5 min. The resulting slightly yellow suspension was
1
product 3 (3.45 g, 87%). The H and 13C NMR spectra were
consistent with those of the compound synthesized according
to method A as well as those reported in the literature.7 The
reaction was also conducted on a 0.10 mol scale, which gave
51.7 g of 3 (86.9% yield).
Preparation of (N-(1,1,-Dimethyl-2-(octylimino-κN)-
propyl)-2,6-diisopropylbenzenaminato-κN)-
trimethylzirconium (15). Method B was used. To a
suspension of ZrCl4 (2.447 g, 10.5 mmol) in anhydrous
toluene (40 mL) in a 125 mL three-neck flask equipped with a
stir bar, a thermometer, and a nitrogen pad at ambient
temperature (23 °C) was added a solution of 9 (3.726 g, 10.0
mmol) in toluene (20 mL). The resulting mixture was stirred at
ambient temperature for 0.5 h and then cooled to 0 °C. A 3.0
H
DOI: 10.1021/acs.oprd.5b00047
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Organic Process Research & Development
Article
M solution of MeMgBr in diethyl ether (15 mL, 45 mmol) was
added via a syringe pump at 0 to 5 °C over 15 min. The
reaction mixture was allowed to stir at 0 to 5 °C for an
additional 1 h and then slowly warmed to ambient temperature
(23 to 25 °C) overnight. A 0.3−0.5 mL sample of the reaction
mixture was taken and filtered through a syringe filter into an
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(15) Because of the heterogeneous nature of the reaction mixture
containing 6 and MCl4 in toluene, the extent of the reaction between
these reagents is not clear, however.
1
NMR tube for H NMR analysis with C6D6 as an external
reference, which showed that the reaction was complete. The
volatiles were removed under reduced pressure, and the residue
was extracted with anhydrous hexane (90 mL). The wet cake
was extracted with additional hexane (10 mL × 2). The
combined hexane solution was concentrated under reduced
pressure to give the desired product 15 (4.4 g, 86%). Anal.
Calcd for C28H52N2Zr: C, 66.21; H, 10.32; N, 5.51. Found: C,
1
66.37; H, 9.95; N, 5.30. H NMR (400 MHz, C6D6) δ 7.20−
7.15 (m, 3H), 3.66 (hept, J = 6.8 Hz, 2H), 3.43−3.34 (m, 2H),
1.56−1.44 (m, 2H), 1.43 (s, 3H), 1.38 (d, J = 6.7 Hz, 6H), 1.27
(d, J = 6.7 Hz, 6H), 1.34−1.13 (m, 10H), 1.00 (s, 6H), 0.92 (t,
J = 6.7 Hz, 2H), 0.66 (s, 9H). 13C NMR (101 MHz, C6D6) δ
187.87, 149.91, 138.33, 126.96, 124.92, 75.39, 51.18, 44.29,
32.18, 29.65, 28.90, 28.50, 28.03, 27.22, 26.83, 24.68, 23.09,
15.18, 14.36.
Structure Determination of 15. 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 SAINT20 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 on the basis 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 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 was calculated to provide a
reference to the conventional R value, but its function was not
minimized.
Crystallographic Data for 15. C28H52N2Zr, MW = 507.93,
triclinic, P1, 0.23 mm × 0.16 mm × 0.16 mm), a = 9.7837(5)
̅
Å, b = 17.3161(10) Å, c = 17.4313(10) Å, α = 80.898(3)°, β =
88.203(3)°, γ = 89.242(3)°, T =100(2) K, Z = 2, V = 2914.4(3)
Å3, R1 = 0.0683, 0.0747, wR2 = 0.1822, 0.1860 (I > 2σ(I), all
data), GOF = 1.154.
ASSOCIATED CONTENT
■
S
* Supporting Information
Synthetic procedures and NMR spectra of all prepared
compounds. The Supporting Information is available free of
charge on the ACS Publications website at DOI: 10.1021/
acs.oprd.5b00047.
(16) Bhadbhade, M.; Clentsmith, G. K. B.; Field, L. D. Organo-
metallics 2010, 29, 6509−6517.
(17) Chia, S.-P.; Li, Y.; Ganguly, R.; So, C.-W. Eur. J. Inorg. Chem.
2014, 526−532.
(18) Van Ausdall, B. R.; Glass, J. L.; Wiggins, J. L.; Aarif, J. L.; Louie,
J. J. Org. Chem. 2009, 74, 7935−7942.
AUTHOR INFORMATION
■
(19) The NH4Cl solution should be added slowly at the beginning
because the excess MeMgBr reacts violently with water, liberating
methane gas.
Corresponding Authors
*E-mail: czhang@dow.com.
*E-mail: jklosin@dow.com.
(20) Sheldrick, G. M. SHELXTL Crystallographic Software Package,
version 6.1; Bruker AXS, Inc.: Madison, WI, 2008.
Notes
The authors declare no competing financial interest.
I
DOI: 10.1021/acs.oprd.5b00047
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