Isospecific polymerization of 1-hexene by C1-symmetric half-metallocene dimethyl complexes of group 4 metals with bidentate N-substituted iminomethylpyrrolyl ligands

Article abstract of DOI:10.1039/c2dt32481d

Non-bridged half-metallocene dimethyl complexes of group 4 metals 2a-4a with an N-4-methoxyphenyl(iminomethyl)pyrrolyl ligand 1a were synthesized and characterized by NMR spectroscopy and X-ray analysis. Upon activation with [Ph₃C][B(C₆F₅)₄], these complexes became active catalysts for the polymerization of 1-hexene. A series of hafnium complexes with various N-substituents on the imine group of ligands 1b-1g were also prepared and applied as catalysts for 1-hexene polymerization. The activation parameters for the exchange process between the two methyl groups bound to the metal for Cp*MMe₂(R-pyr) complexes were estimated by NMR shape analysis at various temperatures. The findings indicated that the transition state of the ligand flipping process might be associated with the isoselectivity of the polymerization reaction.

Full text of DOI:10.1039/c2dt32481d

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Isospecific polymerization of 1-hexene by C1-symmetric
half-metallocene dimethyl complexes of group
4 metals with bidentate N-substituted
Cite this: Dalton Trans., 2013, 42, 9120
iminomethylpyrrolyl ligands†
Takahiro Yasumoto, Keishi Yamamoto, Hayato Tsurugi and Kazushi Mashima*
Non-bridged half-metallocene dimethyl complexes of group 4 metals 2a–4a with an N-4-methoxyphenyl-
(iminomethyl)pyrrolyl ligand 1a were synthesized and characterized by NMR spectroscopy and X-ray
analysis. Upon activation with [Ph3C][B(C6F5)4], these complexes became active catalysts for the polymer-
ization of 1-hexene. A series of hafnium complexes with various N-substituents on the imine group of
ligands 1b–1g were also prepared and applied as catalysts for 1-hexene polymerization. The activation
parameters for the exchange process between the two methyl groups bound to the metal for
Cp*MMe2(R-pyr) complexes were estimated by NMR shape analysis at various temperatures. The findings
indicated that the transition state of the ligand flipping process might be associated with the isoselecti-
vity of the polymerization reaction.
Received 17th October 2012,
Accepted 21st November 2012
DOI: 10.1039/c2dt32481d
www.rsc.org/dalton
a tetradentate diamine bis(phenolate) ligand that catalyze the
highly isoselective polymerization of 1-hexene.3 Coates4 and
Introduction
Well-defined organometallic complexes of group 4 metals as Fujita5 independently reported that titanium complexes
single-site olefin polymerization catalysts have undergone con- bearing two phenoxy-imine ligands produce isotactic poly-
tinuous development over the last three decades with regard to propylene via enantiomorphic site-control, while titanium
precise manipulations of the microstructures of polyolefins, complexes having phenoxy-imine ligands with ortho-fluorinated
including branching, polydispersity, and stereochemistry, fea- N-aryl groups or bulky ortho-phenol substituents yield highly
tures that directly define the physical properties of the poly- syndiotactic polypropylene via chain-end control, and nickel
mers.1 Among these tunable factors, stereoregularities of complexes supported by an α-diimine ligand with a bulky
polyolefins are most straightforwardly associated with the substituent at the o-position of the phenyl group produce
design of the ligand architecture. In general, for ansa-type isotactic poly(olefin)s.6
metallocene complexes, C2- and Cs-symmetric complexes
Of particular interest are the C1-symmetric metallocene
afford isotactic and syndiotactic polypropylenes, respectively, catalysts, which mediate different types of stereoselectivities
whereas C1-symmetric complexes give variable stereoregular due to the differentiation of two coordination sites.7–9 Concep-
polyolefins, such as atactic, hemiisotactic, and isotactic poly- tually, migratory insertion at each site during the polymeriza-
mers.2 The development of non-metallocene precatalysts tion propagation step provides different stereoselectivity of
allows for more versatile and flexible design access to the backbone of the polymer with or without site epimeriza-
the stereoregularity of poly(olefin)s. Notable efforts in the tion.10 In fact, the same enantioface preference of the olefin
last decade were targeted toward C2-symmetric complexes. monomer or rapid-site epimerization that is faster than the
Kol reported titanium and zirconium complexes with propagation results in the isoselective polymerization of
α-olefins. An intriguing example is the C1-symmetric half-
metallocene complexes of zirconium and hafnium with an
asymmetrical amidinate ligand reported by Sita et al. as cata-
lysts for the living, isoselective polymerization of 1-hexene, in
which the migratory insertion of the monomer followed by
the rapid-site shift of the polymer chain end to the less bulky
site results in successive insertion of the monomer through
the same coordination site and the same enantioface
Department of Chemistry, Graduate School of Engineering Science, Osaka University,
Toyonaka, Osaka 560-8531, Japan. E-mail: mashima@chem.es.osaka-u.ac.jp;
Tel: +81-6-6850-6245
†Electronic supplementary information (ESI) available: NMR spectra for complex
4e and cationic species 5a were included. CCDC 903413 (2a), 903414 (3a),
903415 (4c), and 903416 (4g). For ESI and crystallographic data in CIF or other
electronic format see DOI: 10.1039/c2dt32481d
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Fig. 1 C1-Symmetric half-metallocene complexes of group 4 metals for stereo-
specific α-olefin polymerization.
preference (Fig. 1a).11 Accordingly, the high isotactic polymeri-
zation achieved using such C1-symmetric half-metallocene
complexes requires that the monomer insertion rate is much
faster than the epimerization rate around the metal center
through a bidentate ligand flipping process.
Fig. 2 Transition states of the ligand flipping process.
As part of our ongoing interest in the catalytic performance
of group 4 metal complexes bearing various 2-iminomethyl-
pyrrolyl ligands as olefin polymerization precatalysts,12–15 we
reported that some half-metallocene dimethyl complexes of
hafnium, upon activation with [Ph3C][B(C6F5)4], became
unique initiators of living and isoselective 1-hexene polymeri-
zation.13e These hafnium complexes are the second example of
isoselective polymerization precatalysts with a C1-symmetric
half-metallocene fragment (Fig. 1b). Herein, we report the full
details of the synthesis and structural characterization of half-
metallocene complexes of titanium, zirconium and hafnium
with various iminopyrrolyl ligands and their catalytic perform-
ance for 1-hexene polymerization, as well as studies of the
correlation between isospecific polymerization and site flux-
ionality of the dimethyl precursors.
Table 1 Activation parameters for the exchange process of dimethyl com-
plexes 2a, 3a, and 4a
ΔG‡
ΔH‡
ΔS‡
c
Complex Tc (K) (kcal mol−1
)
(kcal mol−1
)
(cal mol−1
)
Mode
2a
3a
4a
353
233
268
17.4
11.2
13.0
24.9 0.4
9.0 0.3
12.4 0.7
21.2 1.2
−9.2 1.2
−3.4 2.6
B
A
A
for 3a; δ 0.38 for 4a) compared with the corresponding
trimethyl complexes Cp*ZrMe3 (δ 0.23)17 and Cp*HfMe3
(δ 0.07).18 The broadening of the signals at 35 °C indicated
racemization via a rapid ligand flipping process over the NMR
time scale (Fig. 2). Consistent with these 1H NMR spectral
data, the 13C NMR spectral data of 2a, 3a, and 4a at 35 °C dis-
played two resonances at δ 73.2 and 74.3 for 2a due to two dia-
stereotopic methyl carbons, and one resonance each was
observed for 3a (δ 50.5) and 4a (δ 56.3).
Results and discussion
Syntheses of half-metallocene dimethyl complexes of group
4 metals bearing a 2-{N-(4-methoxyphenyl)iminomethyl}-
pyrrolyl ligand
We previously reported the synthesis of Cp*HfMe2(R-pyr)
(4a: R-pyr = 4-MeOC6H4–NvCH-pyr) by treating Cp*HfMe3
(Cp* = η5-C5Me5) with 2-{N-(4-methoxyphenyl)iminomethyl}-
pyrrole (1a).13e We conducted the same protocol to prepare the
corresponding titanium complex 2a and zirconium complex 3a
by reactions of Cp*TiMe3 and Cp*ZrMe3 with 1a (eqn (1)).
These newly prepared complexes 2a and 3a were characterized
by NMR spectral data, combustion analysis, and X-ray ana-
1
lyses. The H NMR spectra of 2a and 3a displayed essentially
the same pattern as that of 4a. The singlet resonance due to
the imine proton shifted upfield from that of free ligand 1a,
suggesting that the imine nitrogen atom is coordinated to the
ð1Þ
The activation parameters for the exchange process
metal in solution. Two singlet resonances (δ 1.07 and 1.27) between the two methyl groups bound to the metal in com-
16
were shifted downfield from that (δ 0.73) of Cp*TiMe3 due plexes 2a–4a were estimated by NMR shape analysis at various
to the diastereotopic methyl groups bound to the titanium temperatures and are summarized in Table 1, because such
atom of 2a at 35 °C, consistent with the C1-symmetric four- parameters could be directly associated with stereoregularity
legged piano stool structure. In contrast, broad singlet reson- during 1-hexene polymerization. The ΔG‡c values for 3a and 4a
ances of two methyl groups bound to the zirconium atom of complexes were lower than that (17.4 kcal mol−1) of 2a, pre-
3a and the hafnium atom of 4a were shifted downfield (δ 0.61 sumably due to differences in the fluxional process (vide infra)
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caused by the disparity of the ionic radii between the titanium the bis(iminopyrrolyl)titanium dichloride complex, TiCl2(Ph–
atom and others, indicating that the steric hindrance around NvCH-pyr)2 [Ti–Npyr: 2.043(2) and 2.033(2) Å; Ti–Nimine: 2.215(2)
the metal increased the barrier of the exchange process. The and 2.185(2) Å].14a The Ti–C11 [2.136(5) Å] and Ti–C12 [2.110(5)
ΔG‡ value of 2a was 2–3 kcal mol−1 higher than that Å] distances of 2a are normal and comparable to those
c
(14–15 kcal mol−1) of the reported titanium complexes bearing [2.154(3) and 2.116(3) Å] of a half-titanocene dimethyl amidi-
a dissymmetric amidinate ligand, Cp*TiMe2[R1NC(CH3)NR2],19 nate complex, Cp*TiMe2[RNC(Me)NR] [R = CH(Me)(Ph)].19a
suggesting that the steric repulsion between the Cp* ligand The N1–Ti–N2 bite angle [74.77(16)°] of 2a is comparable to
and the bidentate ligand increased as the chelate ring size the mean bite angle [72.50(6)° and 76.22(6)°] in TiCl2(Ph–
increased. Two possible fluxionalities can explain the ligand NvCH-pyr)2,14a but larger than that [61.27(8)°] of Cp*Ti-
flipping process: one is a distorted trigonal bipyramidal tran- Me2[RNC(Me)NR] [R = CH(Me)(Ph)].19a For complex 3a, the Zr–
sition state (mode A), in which the ΔS‡ value is negative or N1 [2.2529(15) Å] and Zr–N2 [2.3897(14) Å] bond distances are
small, while the other is a tetrahedral transition state (mode ca. 0.15 Å longer than those of 2a, a difference that can be
B), in which the ΔS‡ value is positive and the ΔH‡ value should rationalized by taking into account the difference in the ionic
be large because it requires the release of the imino moiety radii, and longer than that of a bis(iminopyrrolyl) complex,
from the metal.20 The observed positive value of ΔS‡ as well as ZrCl2(Ar–NvCH-pyr)2 [Ar = 4-MeOC6H4: Zr–Npyr: 2.191(5) Å;
the large value of ΔH‡ for 2a confirmed that titanium complex Zr–Nimine: 2.280(4) Å].13a The Zr–C11 [2.2543(17) Å] and Zr–C12
2a preferred the tetrahedral transition state B. In contrast, the [2.2656(18) Å] bond lengths are also ca. 0.15 Å longer than
negative values of ΔS‡ for 3a and 4a were due to the ring-flip- those of 2a. The N1–Zr–N2 bite angle [70.97(5)°] of 3a is
ping process through the distorted trigonal bipyramidal tran- smaller than that of 2a, confirming that the steric hindrance
sition state A, in which the rather larger atomic radius resulted around zirconium complex 3a is less than that of titanium
in adapting the trigonal bipyramidal transition state A.
complex 2a. The bond lengths and angles around the zirco-
Fig. 3 shows the ORTEP drawings of complexes 2a and 3a, nium atom in 3a are quite similar to those of the hafnium
and their selected bond distances and angles are summarized complex 4a, whose structural features were discussed in our
in Table 2. Both complexes adopt the C1-symmetric four- previous communication.13e
legged piano stool geometry. The imine nitrogen atom and the
pyrrolyl nitrogen atom coordinate in a chelating manner to
Observation of cationic species by NMR spectroscopy
the metal and consequently two methyl groups occupy the cis-
positions of the four legs. The Ti–N1 [2.096(5) Å] and Ti–N2
[2.295(4) Å] distances of 2a are slightly longer than those of
The addition of 1 equivalent of [Ph3C][B(C6F5)4] to complexes
2a, 3a, and 4a in C6D5Br was monitored by H NMR spectro-
1
scopy, which revealed the immediate formation of Ph3CCH3
in all reactions. The cationic monomethyl complex 5a was
cleanly formed and stable at room temperature for a few
hours, although the cationic complexes of titanium and zirco-
nium decomposed immediately at room temperature. The res-
onance due to a methyl group bound to the cationic metal
center was observed as a sharp singlet (5a: δ 0.72), and shifted
downfield from that of the corresponding neutral dimethyl
complexes (4a: δ 0.38) (Scheme 1).
1-Hexene polymerization by complexes 2a, 3a, and 4a
With a series of complexes of group 4 metals in hand, the role
of the central metals was exemplified by polymerization of
1-hexene using a mixture of dimethyl complexes and 1 equi-
valent of [Ph3C][B(C6F5)4] in chlorobenzene, and the results are
summarized in Table 3. Titanium complex 2a showed very low
activity, yielding atactic poly(1-hexene). Because 2a produced a
Fig. 3 ORTEP drawings of the molecular structures of Cp*MMe2(R-pyr) (M = Ti,
Zr) complexes 2a and 3a.
Table 2 Bond distances (Å) and angles (°) of complexes 2a and 3a
2a
3a
M–C11
M–C12
M–N1
M–N2
C11–M–C12
N1–M–N2
C11–M–N2
C12–M–N1
2.136(5)
2.110(5)
2.096(5)
2.295(4)
83.8(2)
74.77(16)
83.04(18)
82.59(19)
2.2543(17)
2.2656(18)
2.2529(15)
2.3897(14)
87.89(7)
70.97(5)
85.02(6)
82.87(6)
Scheme 1 Generation of cationic monomethyl species.
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Table 3 1-Hexene polymerization by complexes 2a, 3a, and 4a at 25 °Ca
Run
Cat.
Time (h)
Activity (g mol−1 h)
Mn b (×103)
Mw b (×103)
Mw b/Mn
[mmmm]c (%)
Mode
1
2
3
2a
3a
4a
1.5
3
3
350
6000
5700
113.2
1.0
13.0
174.3
3.6
19.0
1.5
Atactic
Atactic
65
B
A
A
3.4d
1.5
a Conditions: [cat.]:[Ph3C][B(C6F5)4]:[1-hexene] = 0.020 : 0.020 : 10 (mmol) in C6H5Cl (2.75 mL) at 25 °C. b Determined by GPC analysis at 40 °C in
THF. c Determined by 13C NMR measurement. d Bimodal molecular weight distribution.
very high molecular weight polymer, the initiation efficiency of
2a was estimated to be quite low. The zirconium 3a and
hafnium 4a complexes had higher activities than the titanium
complex 2a. The molecular weight distribution of poly-
(1-hexene) obtained by using 3a was bimodal, indicating that
there were two active species under the polymerization con-
ditions, presumably due to the thermal instability of the cataly-
tically active species. It is notable that atactic poly(1-hexene)
was yielded by the zirconium complex, while the hafnium ana-
logous complex 4a afforded isotactic rich poly(1-hexene)
([mmmm] = 65%). Consequently, we selected hafnium as the
best metal for polymerizing 1-hexene in terms of the catalytic
activity and stereospecificity.
Table 4 Activation parameters of the methyl group exchange process
ΔG‡
ΔH‡
ΔS‡
c
Complex Tc (K) (kcal mol−1
)
(kcal mol−1
)
(cal mol−1
)
Mode
4a
4b
4c
4d
4e
4f
268
266
218
228
298
313
328
13.0
12.9
ND
10.5
14.2
15.1
16.0
12.4 0.7
12.8 0.7
ND
11.0 0.4
14.1 0.3
15.2 0.4
21.0 0.4
−3.4 2.6
−0.3 2.7
ND
2.4 1.4
−0.3 1.1
0.7 1.4
15.9 1.2
A
A
—
B
A
A
B
4g
Syntheses of half-metallocene dimethyl complexes of hafnium
bearing various iminopyrrolyl ligands
Because hafnium complex 4a exhibited isospecific polymeriz-
ation for 1-hexene,13e its derivatives were prepared to finetune
the catalytic activity as well as the isoselectivity of hafnium pre-
catalysts. Complexes 4b and 4f, together with 4a, were reported
previously, and other hafnium complexes 4c–e, and 4g were
synthesized and characterized following the same procedure
as for 4a (eqn (2)). All complexes were characterized by NMR
spectroscopy and combustion analyses together with X-ray
analyses for 4c and 4g.
Fig. 4 ORTEP drawings of the molecular structures of Cp*HfMe2(R-pyr) com-
plexes 4c and 4g.
Table 5 Bond distances (Å) and angles (°) of complexes 4c and 4g
4c
4g
Hf–C11
Hf–C12
Hf–N1
Hf–N2
C11–Hf–C12
N1–Hf–N2
C11–Hf–N2
C12–Hf–N1
2.255(3)
2.224(3)
2.238(3)
2.374(3)
87.87(14)
70.20(10)
80.56(11)
85.16(12)
2.296(4)
2.248(4)
2.216(3)
2.430(3)
83.92(14)
71.76(10)
90.39(12)
81.99(13)
ð2Þ
The activation parameters of the methyl group exchange for
hafnium complexes 4 were determined by NMR shape analysis
at various temperatures and are summarized in Table 4. The
barriers for the methyl group exchange of 4c were too low to
determine the activation parameters. Interestingly, in contrast
to our presumption that the bulky substituent on the ortho
position of the aromatic ring made the ligand-flipping barrier
high, hafnium complex 4d had a low ΔG‡ value and a positive
ΔS‡ value, consistent with the transition state B. On the other
hand, complexes 4e–4g with an alkyl substituent at the imine
nitrogen had a higher barrier in the order of CH2Ph < Cy <
tBu. Complex 4g exhibited large positive ΔS‡ value,
a
suggesting that complex 4g adopted a tetrahedral transition
state B after releasing the imine moiety, presumably due to the
t
steric repulsion between the Bu group and the two Me groups
bound to the hafnium atom.
The crystal structures of complexes 4c and 4g are shown in
Fig. 4 and selected bond distances and angles are summarized
in Table 5. These complexes also adopt a C1-symmetric four-
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legged piano stool geometry and the structural features are
almost the same as those of 2a–4a.
Conclusion
The synthesis and characterization of half-metallocene
complexes of group 4 metals bearing various N-substituted
iminopyrrole ligands, and their catalytic performance for
polymerization of 1-hexene are reported. The ligand flipping
process of the bidentate iminopyrrolyl ligand was clarified by
VT-NMR studies, which revealed that the ligand flipping pro-
ceeded through a distorted trigonal bipyramidal (mode A) or a
tetrahedral transition state (mode B). The dimethyl complexes
of group 4 metals became catalysts for 1-hexene polymeriz-
ation by the addition of 1 equivalent of [Ph3C][B(C6F5)4]. The
high isoselectivity in 1-hexene polymerization was associated
with the flipping process of the bidentate iminopyrrolyl ligand
attached to the half-metallocene fragments.
1-Hexene polymerization by hafnium complexes bearing
various iminopyrrolyl ligands
In the presence of 1 equivalent of [Ph3C][B(C6F5)4], hafnium
complexes 4b–g became catalysts for 1-hexene polymerization
and the results are summarized in Table 6 together with the
results of 4a. The steric hindrance around the metal sup-
pressed the catalytic activity: hafnium complexes bearing imino-
pyrrole ligands having ortho-substituted aromatic rings or
bulky alkyl groups on the imine nitrogen had lower activities
and yielded atactic polymers (runs 5 and 6). Furthermore, the
polymers yielded by 4c and 4d had a trimodal molecular
weight distribution, implying that the decomposition of cat-
ionic species led to unexpected catalytic species.
Because the catalytically active species were thermally
unstable and decomposed at room temperature, polymeriz-
ation of 1-hexene was conducted at −20 °C. As shown in
Table 6, the isoselectivities of complexes 4a, 4b, and 4f
Experimental section
General procedures
increased, whereas their activities decreased at −20 °C. In All manipulations involving air- and moisture-sensitive organo-
complex 4e, isoselectivity was slightly decreased ([mmmm] = metallic compounds were carried out under an atmosphere of
25%), although the catalytic activity, which reflected its argon using the standard Schlenk techniques. Complexes
propagation rate, and the barrier for ligand flipping were Cp*TiCl3,21 Cp*ZrCl3,17 Cp*TiMe3,16 Cp*HfCl3,22 Cp*HfMe3,18
higher than those of 4a and 4b (runs 7 and 8). The isoselectiv- and Cp*HfMe2(R-pyr) complexes, 4a, 4b, and 4f13e were pre-
ity of complex 4f was higher than that of 4e although the pared according to the literature. Bidentate iminopyrrole
activity of 4f was much lower than that of 4e, indicating that ligands were prepared by condensation of the 2-formylpyrrole
the higher barrier for the ligand flipping of 4f led to increased with the corresponding aniline derivatives. [Ph3C][B(C6F5)4]
isoselectivity. It is noteworthy that the isospecific polymeriz- was prepared according to the literature.23 Hexane, THF,
ation of 1-hexene was associated with the fluxional nature of toluene, and diethyl ether were dried and deoxygenated by dis-
catalyst precursors. Dimethyl complexes adopting mode tillation over sodium benzophenone ketyl under argon.
A exhibited two adjacent sites in the C1-symmetric struc- 1-Hexene was distilled from sodium benzophenone ketyl and
ture differentiated by the iminopyrrolyl ligand that play a then distilled from CaH2 by trap-to-trap distillation before use
pivotal role in controlling the stereochemistry of the polymer for polymerization. Chlorobenzene and bromobenzene were
microstructure.
distilled from CaH2 and then distilled from CaH2 by trap-to-
Table 6 1-Hexene polymerization by hafnium complexesa
Run
Cat.
Time (h)
Temp (°C)
Activity (g mol−1 h)
Mn b (×103)
Mw b (×103)
Mw b/Mn
[mmmm]c (%)
Mode
1
2
3
4a
4a
4b
3
6
3
25
−20
25
570
1600
7000
13.0
23.5
9.1
19.0
25.1
12.7
0.7
24.1
260.4
27.6
1.0
128.1
19.0
1.1
16.7
1.1
1.5
1.1
1.4
1.1
1.1
1.5
1.5
1.1
1.6
1.1
1.1
2.1
1.1
1.8
1.4
1.1
1.8
65
90
45
A
A
A
0.6
4
5
4b
4c
6
6
−20
25
1200
310
22.5
178.4
18.7
0.9
82.4
17.1
0.9
7.9
1.0
41.4
5.9
9.0
90
Atactic
A
—
6
7
4d
4e
3
3
25
25
830
Atactic
30
B
A
1410
8
9
10
11
4e
4f
4f
4g
6
3
6
3
−20
25
−20
25
1900
3000
480
73.4
8.4
9.7
25
40
75
Atactic
A
A
A
B
1400
16.0
28.2
a Conditions: [cat.]:[Ph3C][B(C6F5)4]:[1-hexene] = 0.020 : 0.020 : 10 (mmol) in C6H5Cl (2.75 mL) at 25 °C. b Determined by GPC analysis at 40 °C in
THF. c Determined by 13C NMR measurement.
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1
trap distillation before use for polymerization. Benzene-d6 and (75 MHz, C6D6, 35 °C): δ 11.6 (q, JC–H = 127 Hz, C5(CH3)5),
1
1
toluene-d8 were distilled from P2O5 and thoroughly degassed 50.5 (q, JC–H = 115 Hz, Zr–CH3), 55.0 (q, JC–H = 143 Hz,
1
1
by trap-to-trap distillation before use. Bromobenzene-d5 was OCH3), 114.0 (d, JC–H = 160 Hz, m-C6H4), 114.7 (d, JC–H
=
1
distilled from CaH2 and degassed.
169 Hz, 4-pyr), 121.2 (s, C5(CH3)5), 121.4 (d, JC–H = 168 Hz, 3-
The H NMR (300 MHz), 13C NMR (75 MHz), and 19F NMR pyr), 124.7 (d, JC–H = 160 Hz, o-C6H4), 138.6 (s, 2-pyr), 141.0
1
1
1
(282 MHz) spectra were measured on a VARIAN-UNITY-I- (d, JC–H = 180 Hz, 5-pyr), 144.9 (s, ipso-C6H4), 158.1 (s,
NOVA-300 Spectrometer. Assignments for 1H and 13C NMR p-C6H4), 160.6 (d, JC–H = 164 Hz, NvCH). Anal. calcd for
1
peaks for some of the complexes were aided by 2D 1H–1H C24H32N2OZr: C, 63.25; H, 7.08; N, 6.15. Found: C, 62.84; H,
COSY, 2D 1H–1H NOESY, 2D 1H–13C HETCOR spectra. The 6.68; N, 5.85.
elemental analyses were recorded by using a Perkin Elmer
2400 at the Faculty of Engineering Science, Osaka University. Synthesis of Cp*HfMe2[XYL-pyr] (4c)
All melting points were measured in sealed tubes under an
argon atmosphere, and were not corrected.
The gel permeation chromatographic analysis of poly-
(1-hexene) was carried out at 40 °C by using a Shimadzu
This compound was prepared from Cp*HfMe3 (177 mg,
0.493 mmol) and 2-{N-(2,6-dimethylphenyl)iminomethyl}-
pyrrole 1c (97.5 mg, 0.492 mmol) in toluene by the same pro-
cedure described above. 4c (91.7 mg, 0.169 mmol, 34%).
LC-10A liquid chromatograph system and a RID 10A refractive
1H NMR (300 MHz, C6D6, 35 °C): δ 0.08 (s, 6H, Hf–CH3), 1.92
index detector, equipped with a Shodex KF-806L column,
which was calibrated versus commercially available polystyrene
standards.
3
(s, 15H, Cp*), 2.17 (s, 6H, Ar–CH3), 6.42 (dd, 1H, JH–H
=
3
3
3.6 Hz, JH–H = 1.9 Hz, 4-pyr), 6.69 (dd, 1H, JH–H = 3.6 Hz,
3
4JH–H = 1.1 Hz, 3-pyr), 6.96 (m, 3H, Ar), 7.08 (dd, 1H, JH–H
=
1.9 Hz, JH–H = 1.1 Hz, 5-pyr), 7.18 (s, 1H, NvCH). 13C NMR
3
Synthesis of Cp*TiMe2[p-ANI-pyr] (2a)
1
(75 MHz, C6D6, 35 °C): δ 12.3 (q, JC–H = 126 Hz, C5(CH3)5),
20.1 (q, JC–H = 127 Hz, Ar–CH3), 55.7 (q, JC–H = 112 Hz,
In a Schlenk tube, Cp*TiMe3 (240 mg, 1.05 mmol) was dis-
solved in toluene (5 mL). Ligand 1a (211 mg, 1.05 mmol) was
added to the solution at room temperature, and then the solu-
tion was stirred overnight. After removal of solvent in vacuo,
the resulting red oil was added to a small amount of hexane
and dried under vacuum to give 2a as a brown powder
(451 mg, 1.09 mmol, quantitative yield). Mp 121 °C (dec.).
1H NMR (300 MHz, C6D6, 35 °C): δ 1.07 (s, 3H, Ti–CH3), 1.27
(s, 3H, Ti–CH3), 1.76 (s, 15H, Cp*), 3.35 (s, 3H, –OCH3), 6.44
1
1
1
Hf–CH3), 115.3 (d, JC–H = 164 Hz, 4-pyr), 119.9 (s, C5(CH3)5),
121.4 (d, 1JC–H = 167 Hz, 3-pyr), 123.1 (d, 1JC–H = 150 Hz, m-Ar),
1
128.0 (d, JC–H = 157 Hz, p-Ar), 131.4 (s, o-Ar), 138.2 (s, 2-pyr),
142.1 (d, JC–H = 179 Hz, 5-pyr), 151.3 (s, ipso-Ar), 164.7
(d, JC–H = 165 Hz, NvCH). Anal. calcd for C25H34N2Hf: C,
1
1
55.50; H, 6.33; N, 5.18. Found: C, 54.81; H, 6.02; N, 5.28.
Synthesis of Cp*HfMe2[DIP-pyr] (4d)
3
3
3
(dd, JH–H = 1.9 Hz, JH–H = 3.6 Hz, 1H, 4-pyr), 6.70 (d, JH–H
=
3
This compound was prepared from Cp*HfMe3 (383 mg,
1.07 mmol) and 1d (272 mg, 1.07 mmol) in toluene by the
same procedure described above. 4d (374 mg, 0.626 mmol,
59%). 1H NMR (300 MHz, C6D6, 35 °C): δ 0.08 (s, 6H, Hf–CH3),
9.1 Hz, 2H, C6H4), 6.74 (d, JH–H = 3.4 Hz, 1H, 3-pyr), 6.92 (d,
3JH–H = 9.1 Hz, 2H, C6H4), 7.00 (m, 1H, 5-pyr), 7.53 (s, 1H,
NvCH). 13C NMR (75 MHz, C6D6, 35 °C): δ 13.0 (q, JC–H
=
1
1
126.7 Hz, C5(CH3)5), 55.5 (q, JC–H = 143.4 Hz, OCH3), 73.2
(q, JC–H = 123.8 Hz, Ti–CH3), 74.3 (q, JC–H = 121.5 Hz, Ti–
CH3), 114.3 (d, JC–H = 160.9 Hz, m-C6H4), 114.3 (d, JC–H
168.1 Hz, 4-pyr), 119.7 (d, JC–H = 168.1 Hz, 3-pyr), 125.7
(d, JC–H = 160.6 Hz, o-C6H4), 125.8 (s, C5(CH3)5), 138.4 (s,
2-pyr), 140.4 (d, JC–H = 179.6 Hz, 5-pyr), 147.1 (s, ipso-C6H4),
158.4 (s, p-C6H4), 160.1 (d, JC–H = 163.5 Hz, NvCH). Anal.
3
3
1
1
1.02 (d, 6H, JH–H = 6.9 Hz, CH(CH3)2), 1.35 (d, 6H, JH–H
=
=
3
1
1
6.9 Hz, CH(CH3)2), 1.95 (s, 15H, Cp*), 3.20 (sep, 2H, JH–H
=
1
6.9 Hz, CH(CH3)2), 6.43 (dd, 1H, 3JH–H = 1.9 Hz, 3JH–H = 3.6 Hz,
3
4
1
4-pyr), 6.71 (dd, 1H, JH–H = 3.6 Hz, JH–H = 1.1 Hz, 3-pyr), 7.09
(m, 1H, 5-pyr), 7.10–7.14 (m, 3H, Ar), 7.73 (s, 1H, NvCH). 13C
NMR (75 MHz, C6D6, 35 °C): δ 12.1 (q, JC–H = 126.1Hz,
C5(CH3)5), 23.1 (q, JC–H = 126 Hz, CH(CH3)2), 26.0 (q, JC–H
126 Hz, CH(CH3)2), 29.3 (d, JC–H = 124 Hz, CH(CH3)2), 56.0
1
1
1
1
1
=
calcd for C24H32N2OTi: C, 69.90; H, 7.82; N, 6.79. Found: C,
69.88; H, 8.04; N, 6.80.
1
1
1
(q, JC–H = 113 Hz, Hf–CH3), 115.7 (d, JC–H = 168 Hz, pyr),
Synthesis of Cp*ZrMe2[p-ANI-pyr] (3a)
120.0 (s, C5(CH3)5), 121.4 (d, 1JC–H = 168 Hz, pyr), 123.6 (d, 1JC–H
=
1
157 Hz, m-C6H3), 126.7 (d, JC–H = 159 Hz, p-C6H3), 137.4 (s,
This compound was prepared from Cp*ZrCl3 (944 mg,
2.84 mmol), MeLi (7.2 mL, 8.6 mmol, 3.0 equiv., 1.20 M in
diethyl ether) and 1a (514 mg, 2.57 mmol, 0.91 equiv.) in
diethyl ether by the same procedure described for 2a. Recrys-
tallization from toluene–hexane yielded yellow crystals of 3a
(483 mg, 1.06 mmol, 41% yield). Mp 114 °C (dec.). 1H NMR
(300 MHz, C6D6, 35 °C): δ 0.61 (s, 6H, Zr–CH3), 1.80 (s, 15H,
1
2-pyr), 142.1 (s, o-C6H3), 142.3 (d, JC–H = 179 Hz, 5-pyr), 149.2
(s, ipso-C6H3), 164.7 (d, 1JC–H = 165 Hz, NvCH). Anal. calcd for
C29H42N2Hf: C, 58.33; H, 7.09; N, 4.69. Found: C, 58.00; H,
7.23; N, 4.76.
Synthesis of Cp*HfMe2[Bn-pyr] (4e)
3
3
Cp*), 3.35 (s, 3H, –OCH3), 6.44 (dd, JH–H = 1.9 Hz, JH–H = 3.6 This compound was prepared from Cp*HfMe3 (367 mg,
3
Hz, 1H, 4-pyr), 6.73 (d, JH–H = 9.1 Hz, 2H, m-C6H4), 6.74 1.02 mmol) and 2-{N-benzyliminomethyl}pyrrole 1e (188 mg,
3
3
(d, JH–H = 3.6 Hz, 1H, 3-pyr), 6.91 (d, JH–H = 9.1 Hz, 2H, 1.02 mmol) in toluene by the same procedure described above
o-C6H4), 7.19 (m, 1H, 5-pyr), 7.49 (s, 1H, NvCH). 13C NMR to give 4e (382 mg, 0.724 mmol, 71%). 1H NMR (300 MHz,
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Dalton Transactions
Table 7 Crystal data and data collection parameters for 2a, 3a, 4c, and 4g
2a
3a
4c
4g
Empirical formula
Formula weight
Crystal system
Space group
a (Å)
b (Å)
c (Å)
C
24H32N2O1Ti1
C24H32N2O1Zr1
455.74
Triclinic
ˉ
P1
9.1395(4)
9.5693(4)
14.4498(6)
103.4010(10)
97.5500(10)
110.7440(10)
1117.55(8)
2, 1.354
C25H34N2Hf1
541.03
Monoclinic
P21/c
15.6422(9)
8.9096(5)
16.7840(7)
—
90.262(3)
—
2339.1(2)
4, 1.536
1080
4.471
120
C21H34N2Hf1
492.99
Monoclinic
P21/c
14.6866(9)
8.3103(4)
17.7682(10)
—
109.942(3)
—
2038.6(2)
4, 1.606
984
5.122
120
412.42
Triclinic
ˉ
P1
8.9587(7)
14.3777(13)
17.7595(14)
73.418(3)
81.473(3)
81.371(3)
2154.1(3)
4, 1.272
α (°)
β (°)
γ (°)
V (Å3)
Z, Dcalcd (g/cm−3
F(000)
)
880
0.414
120
476
0.508
120
μ[Mo-Kα] (mm−1
T (K)
)
Crystal size (mm)
2θmax (°)
No. of reflections measured
0.41 × 0.26 × 0.12
55
40 235
0.50 × 0.30 × 0.20
54.9
31 628
0.50 × 0.40 × 0.25
61.0
77 116
0.40 × 0.30 × 0.20
65.2
93 855
Unique data (Rint
)
9829 (0.0622)
9829
505
0.1394, 0.1785
0.0530, 0.1492
1.038
5096 (0.0216)
5096
253
0.0245, 0.0789
0.0231, 0.0754
1.177
7135 (0.0642)
7135
253
0.0380, 0.0869
0.0309, 0.0843
1.181
7412 (0.0749)
7412
227
0.0426, 0.0982
0.0369, 0.0949
1.141
No. of observations
No. of variables
R1,a wR2b (all data)
R1,a wR2b (I > 2.0σ(I))
GOF on F2
Δρ (e Å−3
)
0.392, −0.648
0.445, −0.328
1.912, −1.988
2.884, −2.495
a R1 = (Σ||Fo| − |Fc||)/(Σ|Fo|). b wR2 = [{Σw(Fo2 − Fc2)2}/{Σw(Fo4)}]1/2
.
C6D6, 35 °C): δ 0.28 (br, 6H, Hf–CH3), 1.93 (s, 15H, Cp*), 4.34 Observation of cationic species (5a)
3
3
(br, 2H, CH2), 6.36 (dd, 1H, JHH = 3.6 Hz, JH–H = 1.9 Hz,
4-pyr), 6.47 (m, 1H, pyr), 7.04–7.16 (m, 6H, C6H5 and pyr), 7.48
(s, 1H, NvCH). 13C NMR (75 MHz, C6D6, 35 °C): δ 11.5
In a glove box, hafnium complex 4a (10 μmol) and [Ph3C]-
[B(C6F5)4] (10 μmol) were added into an NMR tube and then
C6D5Br (0.6 mL) was added at −30 °C. The reaction mixture
1
1
(q, JC–H = 127 Hz, C5(CH3)5), 54.0 (q, JC–H = 113 Hz, Hf–CH3),
1
was observed by H NMR and 19F NMR spectroscopy at 35 °C.
1
1
59.0 (t, JC–H = 142 Hz, CH2), 114.7 (d, JC–H = 169 Hz, 4-pyr),
1H NMR (300 MHz, C6D5Br, 35 °C): δ 0.72 (s, 3H, Hf–CH3),
1.74 (s, 15H, C5(CH3)5), 2.04 (3H, s, Ph3CCH3), 3.56 (s, 3H,
OCH3), 6.39 (dd, 1H, 3JH–H = 3.7 Hz, 3JH–H = 1.9 Hz, 4-pyr), 6.63
1
119.5 (d, JC–H = 168 Hz, 3-pyr), 119.9 (s, C5(CH3)5), 127.7
(d, 1JC–H = 160 Hz, Ph), 128.9 (Ph), 129.0 (Ph), 138.1 (ipso-Ph or
1
2-pyr), 138.6 (ipso-Ph or 2-pyr), 140.5 (d, JC–H = 180 Hz, 5-pyr),
3
(d, 2H, JH–H = 8.8 Hz, C6H4), 6.81 (d, 2H, 8.8 Hz, C6H4), 6.92
1
161.7 (d, JC–H = 163 Hz, NvCH). Elemental analysis did not
(m, 1H, 3-pyr), 6.96 (m, 1H, 5-pyr), 7.01–7.16 (m, 15H,
(C6H5)3CCH3), 7.91 (s, 1H, NvCH). 19F NMR (282 MHz,
give a satisfactory result, and the 1H and 13C NMR spectra were
shown in ESI.†
3
C6D5Br, 35 °C): δ −167.7 (br t, JF–F = 18 Hz, m-C6F5), −163.9
(t, 3JF–F = 21 Hz, p-C6F5), −133.4 (br, 8F, o-C6F5).
Synthesis of Cp*HfMe2[tBu-pyr] (4g)
1-Hexene polymerization
This compound was prepared from Cp*HfMe3 (413 mg,
1.15 mmol) and 2-{N-(tert-butyl)iminomethyl}pyrrole (1g,
173 mg, 1.15 mmol) in diethyl ether by the same procedure
described for 4g (400 mg, 0.811 mmol, 70% yield). 1H NMR
(300 MHz, C6D6, 35 °C): δ 0.34 (brs, 3H, Hf–CH3), 0.58 (brs,
3H, Hf–CH3), 1.13 (s, 9H, C(CH3)3), 1.93 (s, 15H, Cp*), 6.45
(m, 1H, 4-pyr), 6.67 (m, 1H, 3-pyr), 7.05 (m, 1H, 5-pyr), 7.96
(s, 1H, NvCH). 13C NMR (75 MHz, C6D6, 35 °C): δ 12.0
In a glove box, a solution of [Ph3C][B(C6F5)4] (20 μmol) in
C6H5Cl was added to a solution of precatalyst (20 μmol) in
C6H5Cl (2.75 mL) and 1-hexene (10 mmol). The reaction
mixture was stirred and then quenched with 1 N HCl in
MeOH. The polymer was extracted with hexane and then
washed with MeOH and dried under vacuum. The isotacti-
city of the poly(1-hexene) was determined by the 13C NMR
measurement.24
1
(q, JC–H = 126 Hz, C5(CH3)5), 31.7 (q, 1JC–H = 126 Hz, C(CH3)3),
1
1
55.5 (q, JC–H = 113 Hz, Hf–CH3), 56.6 (q, JC–H = 113 Hz, Hf–
1
Determination of the activation parameters for the exchange
process
CH3), 59.5 (s, C(CH3)3), 114.6 (d, JC–H = 168 Hz, 4-pyr), 119.7
(d, JC–H = 166 Hz, 3-pyr), 120.5 (s, C(CH3)5), 136.5 (s, 2-pyr),
1
1
1
139.4 (d, JC–H = 180 Hz, 5-pyr), 158.3 (d, JC–H = 160 Hz, The 1H NMR spectra of Cp*MMe2(R-pyr) complexes were
NvCH). Anal. calcd for C21H34N2Hf: C, 51.16; H, 6.95; N, 5.68. measured between 218 K and 353 K, and curve fitting of the
Found: C, 51.24; H, 7.29; N, 5.59.
resonances of M–CH3 protons afforded ν1/2 values. Subtraction
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of the natural line width, obtained at the high temperature
limit, from observed ν1/2 values at each temperature gave the
corrected values, Δν1/2. In the fast exchange limit, only one
line appears and the following approximation, derived from
the Bloch equations, holds: Δt = (2Δν1/2)/{π(δν)2}, where δν
is the separation between the lines in the slow exchange case.
The first order rate constant k is obtained as an inverse of the
conformer lifetime, k = 1/Δt. Activation parameters, ΔH‡ and
ΔS‡ were determined by linear regression analysis of plots of
log(k/T) vs. 1/T.
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Crystals of 2a, 3a, 4c, and 4g suitable for X-ray measurement
were mounted on glass fibers or fixed inside of CryoLoop
(Hampton Research Corp.), and placed in a nitrogen stream.
All measurements were made on a Rigaku RAXIS-RAPID
Imaging Plate diffractometer with graphite monochromated
Mo-Kα radiation. Crystal data and structure refinement para-
meters are summarized in Table 7. Indexing was performed
from 3 oscillations which were exposed for an appropriate
time for each crystal. The camera radius was 127.40 mm.
Readout was performed in the 0.100 mm pixel mode. For the
data collection, reflections were measured at a temperature of
120(1) K.
The structures of complexes 3a, 4c, and 4g were solved by
direct methods (SIR92),25 and the structure of complex 2a
solved by direct methods (SIR97).26 All structures were
refined on F2 by full-matrix least-squares methods, using
SHELXL-97.27 The non-hydrogen atoms were refined aniso-
tropically and all hydrogen atoms were included in the refine-
ment on their carrier atoms. The function minimized was [Σw-
M.
Togrou,
Macromolecules,
2003,
36,
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2
2 2
2
2
(Fo − Fc ) ] (w = 1/[σ2(Fo ) + (aP)2 + bP]), where P = (Max(Fo ,0)
2
2
+ 2Fc )/3 with σ2(Fo ) from counting statistics. The function R1
2
2 2
and wR2 were (Σ||Fo| − |Fc||)/Σ|Fo| and [Σw(Fo − Fc ) /
4
Σ(wFo )]1/2, respectively. The ORTEP-III program was used to
draw the molecule.28 CCDC 903413 (2a), 903414 (3a), 903415
(4c), and 903416 (4g) contain the supplementary crystallo-
graphic data for this paper.
Acknowledgements
This research was supported by a Grant-in-Aid for Scientific
Research on Priority Areas (A) from the Ministry of Education,
Culture, Sports, Science and Technology, Japan.
6 A. E. Cherian, J. M. Rose, E. B. Lobkovsky and G. W. Coates,
J. Am. Chem. Soc., 2005, 127, 13770.
Notes and references
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This journal is © The Royal Society of Chemistry 2013
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