Alkylalumination of arylacetylene catalyzed by zirconocene catalysts supported on solid materials

Article abstract of DOI:10.1016/j.molcata.2010.02.004

Zirconocene dichloride (Cp₂ZrCl₂) supported on montmorillonite K-10, which has previously been shown to be an efficient catalytic system for olefin polymerization, was found to be comparable to the highly activated homogeneous combin

Full text of DOI:10.1016/j.molcata.2010.02.004

Journal of Molecular Catalysis A: Chemical 321 (2010) 71–76
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Journal of Molecular Catalysis A: Chemical
journal homepage: www.elsevier.com/locate/molcata
Alkylalumination of arylacetylene catalyzed by zirconocene catalysts
supported on solid materials
Ryukichi Takagia,∗, Nao Igataa, Kazuhiro Yamamotoa,b,∗∗, Satoshi Kojimaa
a Department of Chemistry, Graduate School of Science, Hiroshima University, 1-3-1 Kagamiyama, Higashi-Hiroshima 739-8526, Japan
b Polyolefin Science & Technology Center, Japan Polychem Corporation, 1 Toho-cho, Yokkaichi, Mie 510-8530, Japan
a r t i c l e i n f o
a b s t r a c t
Article history:
Zirconocene dichloride (Cp2ZrCl2) supported on montmorillonite K-10, which has previously been shown
to be an efficient catalytic system for olefin polymerization, was found to be comparable to the highly
activated homogeneous combination of Cp2ZrCl2 and methylaluminoxane (MAO), and more reactive
than the originally reported homogeneous catalytic system of Cp2ZrCl2/Me3Al in the methylalumination
reaction of an aryl substituted terminal alkyne. Examination of solvent effects in the ethylalumination
reaction using Cp2ZrCl2 supported on montmorillonite K-10, SiO2/LiOH, and SiO2/MgO, indicated that
the anionic counterpart of the actual catalytically active zirconocenium cation is highly delocalized, thus
suggesting that the actual active zirconocenium cation is only very weakly coordinating with the anionic
moiety. This accounts for the high activity of systems using solids such as co-catalysts and as supporting
materials in olefin polymerization in general.
Received 28 October 2009
Received in revised form 29 January 2010
Accepted 1 February 2010
Available online 6 February 2010
Keywords:
Zr-catalyzed alkylalumination
Supported zirconocene catalyst
Modified SiO2
© 2010 Elsevier B.V. All rights reserved.
1. Introduction
to alkynes using zirconocene dichloride (Cp2ZrCl2) with alkylalu-
miniums [3,8,9]. Notable improvements to this reaction have been
Zirconocene catalysts have been attracting much attention due
to their applications in olefin polymerization [1] and organic
synthesis [2,3]. In these reactions, the zirconocene catalysts
are generally used in a combination with trialkylaluminium.
Disproportionation between the zirconocene catalysts and trialky-
laluminiums afford monoalkyl zirconocenium cation intermediates
(Cp2ZrR+) as the actual catalytic species [4]. In the olefin polymer-
ization reaction, these monoalkyl zirconocenium cations have also
been generated by the addition of co-catalysts such as borates,
boranes, and methylaluminoxane (MAO), which also serve to “sta-
bilize” the cations by forming weakly coordinating Lewis bases
(Fig. 1) [5]. The necessity of heterogeneous systems for industrial
gas phase and slurry processes in olefin polymerization has stim-
ulated studies on supported zirconocene catalysts [6] and acidic
catalysts such as clay have been found to be highly effective [7].
The Negishi carboalumination reaction (Scheme 1) has been
widely used as a versatile method for introducing alkyl groups on
reported by Wipf and Lim who have disclosed that reactivity is
significantly increased by using MAO in the place of Me3Al [10],
and by Lipshutz et al. who have found that the use of Cp mod-
ified catalysts improves the regioselectivity [9]. Otherwise there
have been relatively few studies on modifications. In this study, we
have examined how the reactivity would change upon using var-
ious supported zirconocene catalysts, which are useful for olefin
polymerization.
2. Experimental
2.1. General
All reactions involving air- and moisture-sensitive reagents
were carried out under N2. Tetrahydrofuran (THF) was distilled
after refluxing over Na-benzophenone prior to use. CH2Cl2 and
benzene were distilled over CaH2 prior to use.
1H and 13C NMR spectra were recorded at 500 and 125 MHz,
respectively. The internal reference for 1H NMR spectra was
0.0 ppm (Me4Si) for CDCl3. Chemical shifts for 13C NMR spectra
were referenced to CDCl3 (77.0 ppm). MS were recorded under
electron ionization (EI; 70 eV) conditions.SiO2 (P-10) [11] was pur-
chased from Fuji Silysia Chemicals Co. Montmorillonite K-10 [12]
was purchased from Aldrich and dried at 220 ◦C for 2 h under
reduced pressure.
∗
Corresponding author. Department of Chemistry, Graduate School of Science,
Hiroshima University, 1-3-1 Kagamiyama, Higashi-Hiroshima 739-8526, Japan.
Tel.: +81 82 424 7434; fax: +81 82 424 0727.
∗∗
Corresponding author at: Polyolefin Science & Technology Center, Japan Poly-
chem Corporation, 1, Toho-cho, Yokkaichi, Mie 510-8530, Japan. Tel.: +81 59 345
7085.
E-mail addresses: rtakagi@hiroshima-u.ac.jp (R. Takagi),
Yamamoto.Kazuhiro@mp.japanpe.co.jp (K. Yamamoto).
1381-1169/$ – see front matter © 2010 Elsevier B.V. All rights reserved.
doi:10.1016/j.molcata.2010.02.004

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R. Takagi et al. / Journal of Molecular Catalysis A: Chemical 321 (2010) 71–76
mixture for 1 h, a solution of acetylene 1 was added at room temper-
ature. The reaction mixture was stirred at room temperature and
quenched with 1N HCl at 0 ◦C. The resulting mixture was extracted
with Et2O. The combined organic layer was washed with H2O and
brine, dried over MgSO4, and evaporated. The resulting residue was
purified by silica gel column chromatography.
2.3.2. Heterogeneous alkylalumination
Trialkylaluminium (2.0 equiv.) was added to a solid material
(100.0 mg) in a solvent at room temperature. After stirring the
mixture for 1 h, Cp2ZrCl2 (0.1 equiv., 25.0 mg, 85 ␮mol) was added.
To the mixture was added acetylene 1 (135.0 mg, 0.85 mmol). The
reaction mixture was stirred at room temperature and quenched
with 1N HCl at 0 ◦C. The resulting mixture was filtered through
Celite and the filtrate was extracted with Et2O. The combined
organic layer was washed with H2O and brine, dried over MgSO4,
and evaporated. The resulting residue was purified by silica gel
column chromatography.
Fig. 1. Examples of ion pairs between zirconium monoalkyl cation (Cp2ZrR+) and
co-catalysts.
2.2. Preparation of modified solid materials
2.2.1. SiO2 modification with MAO (SiO2/MAO)
5.8 g of SiO2 (P-10) and 9.0 mL of MAO (19.5 wt% MAO in toluene)
were mixed at 40 ◦C to give a slurry. The slurry was then dried at
40 ◦C in vacuo. The resulting solid, SiO2/MAO, was stored under
nitrogen.
2.3.3. 2-(4-tert-Butylphenyl)-1-propene (2a) [13]
1H NMR (500 MHz, CDCl3) ı 7.44–7.33 (m, 4 H), 5.35 (s, 1 H),
5.04 (dq, J = 3.0, 1.5 Hz, 1 H), 2.14 (s, 3 H), 1.32 (s, 9 H).
2.2.2. SiO2 modification with LiOH (SiO2/LiOH) [11]
1 g of SiO2 (P-10) and 71.4 mg of LiOH were mixed in 20 mL of
H2O and the mixture was refluxed for 4 h. Then the mixture was
heated to 150 ◦C with an oil bath to remove H2O, to furnish a white
solid. The solid was dried for an additional 2 h at 200 ◦C in vacuo
and the resulting solid was stored under nitrogen.
2.3.4. 2-(4-tert-Butylphenyl)-1-butene (2b) [14]
1H NMR (500 MHz, CDCl3) ı 7.38–7.33 (m, 4 H), 5.27 (s, 1 H),
5.02 (q, J = 1.5 Hz, 1 H), 2.51 (q, J = 7.4 Hz, 2 H), 1.32 (s, 9 H), 1.11 (t,
J = 7.4 Hz, 3 H).
2.4. (1E)-1-(4-tert-Butylphenyl)-1-butene (2c) [15]
2.2.3. SiO2 modification with MgO (SiO2/MgO) [11]
1 g of SiO2 (P-10) and 0.12 g of MgO were mixed in 20 mL of H2O
and the mixture was refluxed for 1 hour. Then the mixture was
heated to 150 ◦C with an oil bath to remove H2O, to furnish a white
solid. The solid was dried for an additional 2 h at 200 ◦C in vacuo
and the resulting solid was stored under nitrogen.
1H NMR (500 MHz, CDCl3) ı 7.33–7.26 (m, 4 H), 6.35 (d,
J = 16.0 Hz, 1 H), 6.22 (dt, J = 16.0, 6.5 Hz, 1 H), 2.25–2.18 (m, 2 H),
1.31 (s, 9 H), 1.08 (t, J = 7.5 Hz, 3 H).
2.5. (1Z)-1-(4-tert-Butylphenyl)-1-butene (2d) [15]
2.3. General procedure for the alkylalumination of acetylene 1
1H NMR (500 MHz, CDCl3) ı 7.33–7.26 (m, 4 H), 6.34 (d,
J = 11.4 Hz, 1 H), 5.61 (dt, J = 11.4, 7.3 Hz, 1 H), 2.39–2.32 (m, 2 H),
1.31 (s, 9 H), 0.88 (t, J = 7.5 Hz, 3 H).
2.3.1. Homogeneous alkylalumination
To a solution of Cp2ZrCl2 (0.1 equiv.) was added trialkylalu-
minium (2.0 equiv., Me3Al: 2.0 M in hexane, Et3Al: 1.0 M in hexane,
MAO: 6.5 wt% in toluene) at room temperature. After stirring the
2.6. 1-tert-Butyl-4-vinylbenzene (2e) [16]
1H NMR (500 MHz, CDCl3) ı 7.35 (s, 4 H), 6.70 (dd, J = 17.7,
11.0 Hz, 1 H), 5.70 (dd, J = 17.7, 1.0 Hz, 1 H), 5.19 (dd, J = 11.0, 1.1 Hz,
1.0 H), 1.32 (s, 9 H).
2.7. 2,4-Bis-(4-tert-butylphenyl)-1,3-hexadiene (2f)
1H NMR (500 MHz, CDCl3) ı 7.44–7.28 (m, 8 H), 6.40 (s, 1 H),
5.61 (s, 1 H), 5.19 (s, 1 H), 2.66 (q, J = 7.5 Hz, 2 H), 1.34 (s, 9 H),
1.32 (s, 9 H), 0.97 (t, J = 7.5 Hz, 3 H); 13C NMR (125 MHz, CDCl3)
ı 150.7, 150.1, 145.0, 144.9, 139.1, 137.9, 126.9, 126.2 (×2), 126.1
(×2), 125.2 (×2), 125.1 (×2), 113.1, 34.5, 34.5, 31.4 (×3), 31.3 (×3),
23.2, 13.9; HR-EIMS m/z: calcd. for C26H34 [M+] 346.2661. Found
346.2657.
2.8. 1-(4-tert-Butylphenyl)-1-butanone (3) [17]
1H NMR (500 MHz, CDCl3) ı 7.92–7.89 (m, 2 H), 7.49–7.45 (m, 2
H), 2.93 (t, J = 7.2 Hz, 2 H), 1.81–1.83 (m, 2 H), 1.34 (s, 9 H), 1.00 (t,
J = 7.4 Hz, 3 H).
2.9. 3-(4-tert-Butylphenyl)-3-buten-1-ol (4) [18]
1H NMR (500 MHz, CDCl3) ı 7.36 (s, 4 H), 5.41 (d, J = 1.3 Hz, 1 H),
5.12 (q, J = 1.3 Hz, 1 H), 3.74 (t, J = 6.4 Hz, 2 H), 2.79 (td, J = 6.4, 1.3 Hz,
Scheme 1. Alkylalumination of acetylene 1.

R. Takagi et al. / Journal of Molecular Catalysis A: Chemical 321 (2010) 71–76
73
Scheme 2. Methylalumination of 1.
2 H), 1.32 (s, 9 H); 13C NMR (125 MHz, CDCl3) ı 150.7, 144.4, 137.3,
125.7 (×2), 125.3 (×2), 113.8, 61.0, 38.5, 34.5, 31.3.
2.10. (3E)-(4-tert-Butylphenyl)-3-buten-1ol (5) [19]
1H NMR (500 MHz, CDCl3) ı 7.35–7.28 (m, 4 H), 6.48 (d,
J = 15.5 Hz, 1 H), 6.16 (dt, J = 15.5, 7.2 Hz, 1 H), 3.74 (t, J = 6.2 Hz, 2
H), 2.52–2.45 (m, 2 H), 1.31 (s, 9 H); 13C NMR (125 MHz, CDCl3) ı
150.4, 134.4, 132.6, 125.7 (×2), 125.5 (×2), 125.4, 62.1, 36.4, 34.7,
34.5, 31.3.
Fig. 3. Time-course of the methylalumination in CH2Cl2. Me3Al, MAO, Me3Al–H2O:
0.53 M solution of 1. Me3Al–montnorillonite K-10, Me3Al–SiO2/MAO: 0.32 M solu-
tion of 1.
in our studies and most of acetylene 1 was consumed after
2 h. Heterogeneous systems using solid materials (SiO2/MAO and
montmorillonite K-10), previously reported to be highly effective
in olefin polymerization [6,24], were found to be equally effective
as the homogeneous reaction using MAO. Especially noteworthy is
the reaction of montmorillonite K-10 which clearly showed that
MAO is not necessarily required for rate accelerating.
The similarity in high reactivity between the homogeneous
(MAO; Me3Al-H2O) and heterogeneous MAO (Me3Al, SiO2/MAO)
systems indicates the counteranion moiety of the actual catalyti-
cally active zirconocenium cation to be similar between the two
systems, with coordination between the cation and the counteran-
ion moiety being weak. Because of its similar high reactivity, a
similar situation is anticipated for the montmorillonite K-10 sup-
ported zirconocene system using Me3Al, although the identity of
the added aluminium agent is quite different.
Next, we decided to examine the ethylalumination of acety-
lene 1 catalyzed by zirconocene supported on solid materials in
CH2Cl2 and hexane (Scheme 3). Precedence shows that when Et3Al
is used, in addition to products corresponding to those in the
carboalumination reaction using Me3Al, which is speculated to
involve zirconocenium cation intermediates, products that can be
attributed to arise via zirconacycles are produced [20b,25]. An
examination of the reaction of 1-decene using (NMI)2ZrCl as cata-
lyst revealed that the products were dependent on the polarity of
solvent, with products involving zirconocenium cation intermedi-
ates favored in polar solvents such as (CH2Cl)2, whereas products
via the zirconacycle intermediate were preferred in nonpolar sol-
vents such as hexane (Scheme 4) [25]. These results indicate that
the ion pair of the zirconocenium cation and its counteranion,
generated from the disproportionation between Cp2ZrCl2 and tri-
ethylaluminium, was destabilized in nonpolar hexane due to the
highly polar nature of the ion pair, thereby favoring product forma-
tion via the relatively nonpolar zirconacycle intermediate [26–28].
For our supported system, since the cation moiety is common
with the homogeneous system (Cp2ZrCl2/R3Al), and the negative
charge of the anionic moiety is delocalized on the support surface,
the polarity of the active cationic catalyst–counterion ion pair as
3. Results and discussion
The alkylalumination reaction of tert-butylphenylacetylene 1
was chosen as the type reaction [20] to evaluate zirconocene cat-
alysts supported on solid materials (SiO2/MAO, montmorillonite
K-10) (Scheme 2). In order to choose an appropriate solvent for
the reaction, several solvents were examined under the conven-
tional homogeneous reaction conditions using only Cp2ZrCl2 and
Me3Al as the catalyst and methylating reagent (Fig. 2). The time-
course of the methylalumination was monitored by the measuring
the 1H NMR of the crude product. When CH2Cl2 was used as the
solvent, most of acetylene 1 was converted to styrene 2 after 24 h.
THF, benzene, and hexane were also examined. The reaction rates
increased in the order of CH2Cl2 > hexane > benzene > THF. These
results suggest that moderate polarity and low nucleophilicity are
favorable for high reactivity. This is the same tendency observed for
zirconocene catalyzed olefin polymerization and is in accord with
cationic nature of the actual active catalytic species [4a,21].
On the basis of the examination of solvents, the time-courses
of the methylalumination catalyzed by zirconocene supported on
solid material were measured in CH2Cl2 and compared with reac-
tions carried out under conventional homogeneous conditions
(Fig. 3). Negishi carboalumination of alkynes [10] and alkenes [22],
and zirconocene catalyzed olefin polymerization [4a,23] are con-
siderably accelerated when MAO or Me3Al treated with a small
amount of water are used in the place of Me3Al. The accelerat-
ing ability of MAO and water treated Me3Al was also confirmed
Fig. 2. Screening of solvents in homogeneous methylalumination using Cp2ZrCl2
and Me3Al (0.53 M solution of 1).
Scheme 3. Ethylalumination of 1.

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R. Takagi et al. / Journal of Molecular Catalysis A: Chemical 321 (2010) 71–76
Scheme 4. Solvent effect in the ethylalumination of 1-decene.
a whole is expected to be low compared with that of the homo-
geneous system. This would mean that the active zirconocenium
ion pair from the supported catalyst should be relatively more sta-
ble than that from the homogeneous catalyst in nonpolar solvents.
Thus, it was anticipated that an increase in the proportion of prod-
uct 2b would be observed in reactions using solid supports carried
out in nonpolar solvents, in comparison with homogeneous reac-
tions carried out in the absence of solid supports (Scheme 5). To
verify this hypothesis, we carried out the ethylalumination reaction
in nonpolar hexane.
supported on base modified SiO2 (namely SiO2/MgO, SiO2/LiOH,
and SiO2/NaOH) as catalysts for non-MAO ethylene polymeriza-
tion [11]. It was found that in the ethylene polymerization reaction,
the performance of the catalysts were on the same high level
with activity being 67 kg PE/g Zr/h for SiO2/MgO (3.0 mmol base/g
SiO2), 57.5 kg PE/g Zr/h for SiO2/LiOH (0.8 mmol base/g SiO2), and
11.5 kg PE/g Zr/h for SiO2/NaOH (0.5 mmol base/g SiO2), respec-
tively. On the premise of these results, we examined these
solid materials in the ethylalumination reaction. Results using
SiO2/LiOH, and SiO2/MgO turned out to be practically the same as
those of the homogeneous system and the reaction using SiO2/MAO
(Table 1, entries 2–4).
Results of reactions carried out in hexane are summarized in
Table 2. When acetylene 1 was treated with Cp2ZrCl2 (0.1 equiv.)
and Et3Al (2.0 equiv.) in hexane for 8 h, a mixture of styrene deriva-
tives 2b, c and 2e, f was obtained along with the oxygenated
products 3–5, which probably formed by the adventitious traces
of oxygen in the solvents (Table 2, entry 1). In contrast with the
reaction in CH2Cl2, 2c was slightly favored over 2b. The increase of
styrene 2c in this nonpolar solvent implies the preference for the
zirconacycle pathway (Scheme 6). The use of SiO2/MAO resulted
in an even distribution of 2b and 2c (Table 2, entry 2). On the
The ethylalumination of
1 was first examined in CH2Cl2
(Table 1). When the ethylalumination reaction was performed for
8 h in the absence of solid materials, styrene 2b was preferen-
tially obtained as the major product along with a small amount
(16%) of recovered acetylene 1 (2b:2c = ca. 5:1, Table 1, entry 1)
and minute amounts of by-products 2d–f. Extending the reaction
time to 24 h did not conduce to improvement of the conversion
of 1 [29]. For reactions using solid supports, SiO2/MAO gave results
similar to those of the homogenous reaction (Table 1, entry 2). How-
ever, when montmorillonite K-10 was used as the solid support,
the proportion of 2c increased somewhat (2b:2c = ca. 5:2) (Table 1,
entry 5). We had recently disclosed the efficiency of zirconocene
Scheme 5. Proposed mechanism of the ethylalumination of acetylene 1.

R. Takagi et al. / Journal of Molecular Catalysis A: Chemical 321 (2010) 71–76
75
Table 1
Ethylalumination of 1 catalyzed by zirconocene supported on solid materials in CH2Cl2.a.
Entry
Co-catalyst
Product (%)b
2b
2c
2d
2e
2f
1
1
2
3
4
5
–
53
47
49
48
44
11
8
9
10
17
1
3
2
2
2
2
0.5
1
0.4
0.7
3
16
18
7
6
6
SiO2/MAO
SiO2/LiOH
SiO2/MgO
Montmorillonite K-10
0.5
0.9
0.8
1
a
Acetylene 1 was treated with Cp2ZrCl2 (0.1 equiv.), Et3Al (2.0 equiv.) and/or co-catalyst in CH2Cl2 (0.17 M solution of 1) at room temperature for 8 h.
Isolated yield.
b
Table 2
Ethylalumination of 1 catalyzed by zirconocene supported on solid materials in hexane.a.
Entry
Co-catalyst
Product (%)b
2b
2c
2e
2f
3
4
5
1
1
2
3
4
5
–
19
26
31
29
23
23
27
26
22
17
1
0.6
1
1
1
–
–
1
1
2
2
2
1
1
1
2
3
2
1
2
2
3
3
2
2
20
7
5
5
4
SiO2/MAO
SiO2/LiOH
SiO2/MgO
Montmorillonite K-10
a
Acetylene 1 was treated with Cp2ZrCl2 (0.1 equiv.), Et3Al (2.0 equiv.) and/or co-catalyst in hexane (0.17 M solution of 1) at room temperature for 8 h.
Isolated yield.
b
Scheme 6. Plausible reaction mechanism for generation of 3–5.
other hand, the addition of solid materials, montmorillonite K-10,
neous reaction using MAO. Therefore, negating the use of MAO
for activation of this reaction is possible by using montmoril-
lonite K-10 which functions as both solid support and co-catalyst.
In the ethylalumination reaction, which is known to give rise
to products via uncharged zirconacycle intermediates in addi-
tion to zirconocenium cation catalyzed products, examination of
solvent effects revealed that in contrast to the homogenous cat-
alyst system (Cp2ZrCl2/R3Al), the heterogeneous systems using
montmorillonite K-10, SiO2/LiOH, and SiO2/MgO are affected only
slightly. This solvent effect indicated that the coordinating ability
of the anionic moiety to the actual active zirconocenium cation is
weakened by the delocalization of negative charge and the polar
nature of the active catalyst–counterion ion pair is low in polarity.
This should account for the high activity observed using montmo-
rillonite K-10, SiO2/LiOH, and SiO2/MgO as supporting materials in
the ethylene polymerization reaction.
SiO2/LiOH, and SiO2/MgO, to the zirconocene catalyst system lead
to a reversal of selectivity, slightly favoring styrene 2b (Table 2,
entries 3–5). These results suggest that the zirconocenium cation
pathway is more favorable with supported systems compared with
the conventional homogeneous system (Cp2ZrCl2/R3Al). Thus, the
supported systems can be considered to be less polar than the
homogeneous system (Cp2ZrCl2/R3Al).
4. Conclusion
Zirconocene catalysts supported on solid materials have been
known to be highly efficient catalysts in practical homogenous
olefin polymerization. In order to see whether such catalytic sys-
tems could be applied to other organic reactions and to obtain
insight on the properties of the solid catalysts as feedback for
gaining an understanding of polymerization reactions, we have
examined the zirconocene catalyzed alkylalumination reaction.
In the methylalumination of acetylene 1, it was found that the
use of montmorillonite K-10 in conjunction with Me3Al gives
rise to reactivity comparable to that exerted by the homoge-
Acknowledgements
NMR and MS measurements were made using JEOL JMN-LA500
and JEOL SX-102A, respectively, at the Natural Science Center for

76
R. Takagi et al. / Journal of Molecular Catalysis A: Chemical 321 (2010) 71–76
Basic Research and Development (N-BARD), Hiroshima Univer-
sity. We thank Dr. Yoshikazu Hiraga, Graduate School of Science,
Hiroshima University, for NMR measurements (JEOL JMN-LA500)
at the Hiroshima Prefectural Institute of Science and Technology.
We thank Dr. Manabu Abe for his helpful discussions.
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[8] For some recent reports related to the application of zirconocene-catalyzed
alkylalumination in organic synthesis:
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