Preparation of ansa-metallocenes for production of poly(α-olefin) lubricants

Article abstract of DOI:10.1039/c4dt00997e

An ansa-zirconocene bearing methyl substituents at all positions adjacent to the bridgehead [(-C(Ph)HC(Ph)H-)(η⁵-2,5-Me₂C ₅H₂)₂ZrCl₂] (4) was prepared in high yields (78%) through the reductive dimerization of 1,4-dimethyl-6-phenylfulvene utilizing ZrCl₂·DME generated in situ. The structure of 4 was subsequently confirmed using X-ray crystallography. 4 exhibited excellent catalytic performance with regard to 1-decene oligomerization, which was carried out with the intention of preparing lubricant base stocks. High activities (21 × 10⁶ g mol^-1 Zr h^-1 activity; TON = 150 000; TOF = 42 s^-1) were observed at temperatures as high as 120 °C and the oligomer distribution was appropriate for lubricant application. The simulated distillation (SIMDIS) data confirmed that a wide range of oligomers were formed, ranging from the dimer (2-mer) to 20-mer. A minimal amount of the dimer and oligomers larger than the 10-mer was formed (13 and 25 wt%, respectively). Alternatively, a typical unbridged complex such as (η⁵-nBuC₅H₄)₂ZrCl₂ primarily produced dimers (54 wt%), whereas the ansa-zirconocene (EBI)ZrCl ₂ primarily produced oligomers larger than 10-mer (62 wt%). The methyl substituents at the positions adjacent to the bridgehead in 4 played a significant role in the catalytic performance.

Full text of DOI:10.1039/c4dt00997e

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Preparation of ansa-metallocenes for production
of poly(α-olefin) lubricants†
Cite this: Dalton Trans., 2014, 43,
10132
Ji Hae Park,a Young Eun Jang,a Jong Yeob Jeon,a Min Jeong Go,b Junseong Lee,b
Sung Kwan Kim,c Sang-Ick Leec and Bun Yeoul Lee*a
An ansa-zirconocene bearing methyl substituents at all positions adjacent to the bridgehead [(–C(Ph)HC-
(Ph)H–)(η5-2,5-Me2C5H2)2ZrCl2] (4) was prepared in high yields (78%) through the reductive dimeriza-
tion of 1,4-dimethyl-6-phenylfulvene utilizing ZrCl2·DME generated in situ. The structure of 4 was
subsequently confirmed using X-ray crystallography. 4 exhibited excellent catalytic performance with
regard to 1-decene oligomerization, which was carried out with the intention of preparing lubricant base
stocks. High activities (21 × 106 g mol−1 Zr h−1 activity; TON = 150 000; TOF = 42 s−1) were observed at
temperatures as high as 120 °C and the oligomer distribution was appropriate for lubricant application.
The simulated distillation (SIMDIS) data confirmed that a wide range of oligomers were formed, ranging
from the dimer (2-mer) to 20-mer. A minimal amount of the dimer and oligomers larger than the 10-mer
Received 4th April 2014,
Accepted 9th May 2014
was formed (13 and 25 wt%, respectively). Alternatively,
a typical unbridged complex such as
(η5-nBuC5H4)2ZrCl2 primarily produced dimers (54 wt%), whereas the ansa-zirconocene (EBI)ZrCl2
primarily produced oligomers larger than 10-mer (62 wt%). The methyl substituents at the positions
adjacent to the bridgehead in 4 played a significant role in the catalytic performance.
DOI: 10.1039/c4dt00997e
www.rsc.org/dalton
production of lubricant base stocks.17 PAO is typically pro-
duced on industrial scale through the cationic oligomerization
Introduction
Since the discovery of the homogeneous Ziegler (metallocene) of α-olefins such as 1-decene.18 The cationic initiator produces
catalyst by Kaminsky in the late 1970s, extensive research has a mixture of branched oligomers with a distribution that
been conducted on this topic in both academic and industrial peaks around a trimer. After hydrogenation, these products
laboratories.1 Group 4 metallocene catalysts were eventually become outstanding lubricants with excellent viscosity
expanded to include half-metallocenes constructed using a indices, low pour points, and high oxidative stabilities. During
cyclopentadienyl and an amido ligand,2–5 and recently to post- the cationic oligomerization, significant skeletal isomerization
metallocenes comprising non-cyclopentadienyl ligands.6–10 also occurs and this subsequently produces a variety of compli-
Homogeneous Ziegler catalysts are now commercially used in cated structures. In particular, many methyl groups are gene-
the production of polyethylene and polypropylene on
million-ton scale as well as specialty polymers including metallocene catalysts are used, skeletal isomerization can be
cycloolefin copolymers on a thousand-ton scale.11,12
avoided because the structure results from the chain growth
a
rated at random positions along the carbon chain. When
Recently, the application of metallocene catalysts has been through 1,2-insertions followed by chain transfer through
expanded to the production of poly(α-olefin) (PAO) lubricants β-eliminations. In the preparation of PAO lubricants using
or fuels.13 α-Olefins are produced through the selective oligo- metallocene catalysts, controlling the degree of polymerization
merization of ethylene.14–16 ExxonMobil has announced the is a key factor, which is dependent on the catalyst structure.
construction of a metallocene catalyst-based PAO plant for the α-Olefin polymerizations have been previously investigated
using various metallocene,19–23 half-metallocene,24,25 and
post-metallocene catalysts, which typically aim to produce
high-molecular-weight polymers.26–28 Most of the experiments
aDepartment of Molecular Science and Technology, Ajou University, Suwon 443-749,
in these studies generated PAO with Mw > 10 000, which are
not useful as lubricant base stocks. α-Olefin polymerizations
to produce lubricant base stocks have been disclosed in
patents. It was reported that the unbridged zirconocene
(η5-RC5H4)2ZrCl2 (R = H, Me, iPr, nBu) primarily produced
dimers (∼50%) in the polymerization of 1-decene at 110 °C.29,30
South Korea. E-mail: bunyeoul@ajou.ac.kr; Tel: +82-31-219-1844
bDepartment of Chemistry, Chonnam National University, 77 Yongbong-ro, Buk-gu,
Gwangju 500-757, Korea
cInstitute of Technology, SK Innovation, Daejeon 305-712, South Korea
†Electronic supplementary information (ESI) available: The CIF files, crystal
data, structure refinement for 4. CCDC 995260 and 998923. For ESI and crystallo-
graphic data in CIF or other electronic format see DOI: 10.1039/c4dt00997e
10132 | Dalton Trans., 2014, 43, 10132–10138
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The isolated dimer was further oligomerized with 1-decene chromatography (Scheme 1). Purification by column chromato-
using a cationic initiator for use as a lubricant base stock. graphy is inconvenient in large-scale synthesis and should
A doubly bridged ansa-metallocene [(1,1′-Me2Si)(2,2′-Me2Si)- always be avoided whenever possible. Thus, intermediate 2
(η5-C5H3)ZrCl2] was also disclosed for the preparation of PAO was prepared with an excellent yield (15 g-scale, 97%) and was
lubricants.31 However, its synthesis was quite complicated used in the next step without further purification. Fulvene 3
with a very low yield (overall yield was ∼1%). The development was prepared in high yield (11 g-scale, 87%) by utilizing NaH
of other types of catalytic systems that produce α-olefin oligo- in THF. The product was then purified by vacuum distillation
mers has been an active field.32–35 In this report, we disclose a (62 °C/7.5 × 10−2 mmHg).
new ansa-zirconocene that was specifically designed for the
production of PAO lubricant base stocks.
Eisch reported a convenient procedure to prepare C2-
bridged ansa-metallocenes [(–C(Ar)HC(Ar)H–)(η5-C5H4)2ZrCl2]
by reacting 6-arylfulvene with ZrCl2, which was generated
in situ upon exposing ZrCl4 to two equiv. of nBuLi.41,42 The reduc-
tive dimerization of fulvene occurred in the presence of Zr(II)
Cl2, while the Zr atom concomitantly coordinated to the two
cyclopentadienyl ligands generated by the reductive dimeriza-
tion. When the same procedure was applied to 1,4-dimethyl-6-
phenylfulvene (3), the desired ansa-metallocene (4) was
obtained in a very low yield (<10%) along with a variety of side
products. We attributed the failure to the low solubility of
ZrCl2 in toluene used as the solvent in this reaction. When an
equimolar amount of ZrCl4·DME (where DME refers to di-
methoxyethane) was used instead of ZrCl4, the formation of
the desired complex 4 was more favorable but the conversion
of fulvene stopped at ∼50% completion. By using two equiv. of
ZrCl4·DME, the complete conversion of fulvene was achieved.
The product was isolated in high yields (78%) by carrying out a
Soxhlet extraction with cyclohexane. Using this procedure, 4
was isolated on the 6 g scale. The metalation yield of this
product was excellent considering that the direct metalation
yield from the related bridged ligand (Me2C5H3-CH2CH2-
C5H3Me2) following the conventional procedure was only
31%.37 The isolated complex was a mixture of two diastereo-
mers because of the presence of two chiral centers at the
bridge-unit. In the 1H NMR spectrum, two sets of signals
having a 1.0 : 0.50 ratio were observed. The cyclopentadienyl
protons were observed as a pair of doublets (J = 3.2 Hz) at
6.3–6.6 ppm, while the protons from the ethylene-bridge unit
were observed as a singlet at 5.64 ppm (major isomer) and
5.39 ppm (minor isomer). 6-tButyl-1,4-dimethylfulvene also
produced the desired ansa-zirconocene 5 but the yield was low
(25%).
Results and discussion
Preparation of ansa-zirconocenes
Approximately 10 years ago, we reported the preparation of
methylene (–CH2–) and ethylene (–CH2CH2–) bridged ansa-
zirconocenes [(–CH2– or –CH2CH2–)(η5-2,5-Me2C5H2)2ZrCl2]
bearing methyl substituents at the 2,5-positions adjacent to
the bridgehead.36,37 Because of the favorable electronic effects
of the methyl group (without congesting the reaction site),
these complexes exhibited desirable catalytic performances in
the copolymerization of ethylene and bulky monomers such as
norbornene. However, the large scale synthesis of these com-
plexes is not feasible mainly because of the unavailability of
the starting materials, 1,4-pentadiyne or 1,5-hexadiyne, in
large amounts. The feasibility of large-scale synthesis at a
reasonable cost is a critical factor in determining the commer-
cial applications of metallocene catalysts.5,12,38 We also develo-
ped
a large-scale synthetic procedure (80 g-scale) for
synthesizing 2-bromo-3-methoxy-1,3-dimethylcyclopentene (1),
from which 6-R-1,4-dimethylfulvenes (R = H, Me, nPr, iPr, tBu)
were easily prepared (Scheme 1).39 The synthesis of these
fulvenes also facilitated the preparation of various C1-bridged
(–RCH–) ansa-metallocenes.23,40 Upon utilizing this same pro-
cedure, 1,4-dimethyl-6-phenylfulvene (3) was prepared in high
yields (with a two-step overall yield of 84%) and large amounts
(>10 g in a laboratory setting) without the use of column
The success of this procedure was limited to the fulvene
possessing an aryl or tertiary alkyl substituent at the 6-posi-
tion. When a fulvene possessing a primary alkyl or secondary
alkyl substituent at the 6-position was used as the starting
material, an unbridged side product was also generated along
with the desired ansa-zirconocene (eqn (1)). Therefore, when
1,4-dimethyl-6-pentylfulvene was reacted with ZrCl2·DME gene-
rated in situ, the unbridged side product was generated as a
major product with the production of a small amount of
the desired ansa-zirconocene (side-unbridged complex–ansa-
complex = 1.0 : 0.20) (see ESI†). Upon recrystallization in
hexane, the unbridged complex was selectively deposited as
1
crystals. In the H NMR spectrum of the separated unbridged
complex, two Cp–H signals were observed at 5.38 and
5.45 ppm as singlets and the trans-vinyl (Cp–CHvCH–CH2)
Scheme 1 Preparation of ansa-zirconocenes.
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signals were observed at 6.40–6.38 and 5.98–5.88 ppm exhibit- The metrical parameters around the Zr center were nearly
ing the characteristic coupling pattern (dt, J = 15, 1.6 Hz and identical to those observed for the ethylene (–CH2CH2–)
J = 15, 7.2 Hz); this confirms the formation of the structure bridged analog.37 The bridge (–C(Ph)HC(Ph)H–) connected the
illustrated in eqn (1). 6-Isopropyl-1,4-dimethylfulvene pro- two cyclopentadienyl units without causing severe distortions;
duced the desired ansa-type complex as a major product; the Cp(centroid)–C(bridgehead)–C(bridge) angles were 175°,
however, the side-unbridged complex was also formed (side- and the C(1)–C(8)–C(15)–C(22) and C(9)–C(8)–C(15)–C(16) tor-
unbridged complex/ansa-complex = 1.0 : 1.4). We hypothesize sional angles were tilted toward the eclipsed conformation
that two radicals were generated by Zr(II)Cl2, which either (30° and 35°, respectively). The phenyl groups attached to the
coupled to form the desired ansa-complex or disproportio- bridge-unit repelled the methyl group attached to the cyclo-
nated to form the side-unbridged complex.
pentadienyl ligand and the C(7)–C(5)–C(4) angle was sub-
sequently smaller (121.5°) than the corresponding angle at the
opposite side of the molecule (C(6)–C(2)–C(3), 124.9°). The
crystal structure of 5 was also determined by X-ray crystallogra-
phy; it exhibited disorder at the bridge unit (see ESI†). The two
isomers of 5 did not exhibit the vastly different solubility in
toluene as observed with 4.
ð1Þ
α-Olefin oligomerization studies
The newly prepared 4 exhibited excellent catalytic perform-
ances in the oligomerization of 1-decene (Table 1). When the
oligomerization was performed in 1-decene (500 mL) without
additional solvents at 120 °C for 60 min using 10 µmol of 4
(after activation with 20 µmol of [Ph3C]+[B(C6F5)4]− in the pres-
ence of 2.0 mmol of iBu3Al), 57% of the 1-decene was con-
verted to oligomers, which corresponds to an activity of 21 ×
106 g mol−1 Zr h−1, a TON of 150 000, and a TOF of 42 s−1. The
activity value is nearly the same as those obtained during the
ethylene/α-olefin copolymerization process using a highly
active catalyst such as CGC ([Me2Si(η5-Me4C5)(NtBu)]TiCl2)
(36 × 106 g mol−1 Ti h−1).10 The distribution of oligomers was ana-
lyzed by the simulated distillation (SIMDIS) system (Fig. 2 and
Table 1) in which the products were fractionated with respect
to their boiling points in the range of 310–740 °C with each
fraction being analyzed by gas chromatography. The oligomer
distribution as well as boiling point distribution (see ESI†) was
obtained after the analysis. A wide range of oligomers ranging
from the dimer (2-mer) to 20-mer were formed (Fig. 2(a) and
entry 1 in Table 1). The dimer was the largest fraction of the
reaction mixture and the fraction gradually decreased as the
size of the oligomers increased; however, the dimer fraction
was as low as 13 wt%. The fraction corresponding to oligomers
larger than or equal to the 10-mer was 25 wt% and the fraction
corresponding to the 3–5-mers was 35 wt%. This distribution
is appropriate for use as lubricant base stocks. 4 also exhibited
nearly the same catalytic performance in 1-octene oligomeriza-
tion with respect to activity (21 × 106 g mol−1 Zr h−1) and oligo-
mer distribution (entry 2). 5 was inferior to 4 in terms of both
activity and oligomer distribution; the activity was nearly half
(13 × 106 g mol−1 Zr h−1) that of 4 and oligomer distribution
contained a higher percentage of dimers (17 wt%) (entry 3).
The 1H NMR spectrum of the oligomers formed by 4 exhibi-
ted three vinyl end group signals observed at 4.8–5.0 ppm,
5.2–5.35 ppm, and 5.4–5.5 ppm, which were assigned to vinyli-
dene (CvCH2), trisubstituted vinylene (–(C)CvCH–), and dis-
ubstituted vinylene (–CHvCH–), respectively (Fig. 3(a)).43,44
The integration ratios of the three signals were 16 : 10 : 1.0,
The major isomer in the isolated diastereomeric mixture of
4 was significantly less soluble in toluene than the minor
isomer; thus single crystals of the major isomer were selec-
tively deposited in toluene at −30 °C. Fig. 1 displays the struc-
ture of the major isomer, determined by X-ray crystallography.
The two phenyl groups of the bridge-unit were situated in the
same direction; i.e., the major isomer was the meso-compound.
Fig. 1 Thermal ellipsoid plots (30% probability level) of 4. Hydrogen
atoms are omitted for clarity. Selected bond distances (Å) and angles (°):
Zr–Cl(1), 2.440(2); Zr–Cl(2), 2.458(2); Zr–Cp(centroid), 2.200(1) and
2.194(1); Cl(1)–Zr–Cl(2), 99.23(9); Cp(centroid)–Zr–Cp(centroid), 126.16(4);
Cp(centroid)–C(22)–C(15), 175.2(8); Cp(centroid)–C(1)–C(8), 175.0(8);
C(1)–C(2)–C(6), 128.0(8); C(6)–C(2)–C(3), 124.9(8); C(1)–C(5)–C(7),
127.3(8); C(7)–C(5)–C(4), 121.5(8); C(1)–C(8)–C(15)–C(22), 30 (1); C(9)–
C(8)–C(15)–C(16), 35 (1).
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Table 1 Results of 1-decene oligomerizationa
Oligomer distributionc (wt%)
Entry
Catalyst
Conversion (%)
Activityb
2-mer
3-mer
4-mer
5-mer
6-mer
7-mer
8-mer
9-mer
>10-mer
1
4
4
5
6
7
8
9
57.3
60.4
34.2
48.0
35.2
80.9
18.6
21.2
21.4
12.7
17.8
13.0
29.9
6.6
13.3
13.1
17.0
54.8
33.3
2.0
14.3
14.1
18.4
26.2
26.8
5.3
11.3
11.8
13.9
10.5
16.1
4.0
9.5
10.0
11.1
4.6
8.9
5.4
7.8
8.7
9.0
2.1
5.0
5.6
2.3
7.2
7.5
7.1
0.8
3.7
5.6
3.3
6.2
5.9
5.4
1.0
2.2
5.1
3.0
5.2
5.5
4.6
0
1.3
4.7
3.7
25.2
23.4
13.5
0
2.7
62.3
64.5
2d
3
4
5
6
7
9.6
7.0
4.0
2.6
a Oligomerization conditions: 1-decene (500 mL), zirconocene (10 µmol), [Ph3C]+[B(C6F5)4]− (20 µmol) and iBu3Al (2.0 mmol), 120 °C, 60 min.
b Activity in units of 106 g mol−1 Zr h−1
1-decene.
.
c Determined on the SIMDIS (simulated distillation) system. d 1-Octene (500 mL) was used instead of
Fig. 3 13C NMR (a) and 1H NMR (b) spectra of oligomers produced by 4.
which corresponded to the molar ratios of vinylidene
(CvCH2), trisubstituted vinylene (–(C)CvCH–), and disubsti-
tuted vinylene (–CHvCH–) being 16 : 20 : 1.0. This assignment
agreed with the integration values observed for allylic CvC–
CH2– and CvC–CH3 signals at 2.0–2.2 ppm and 1.6–1.8 ppm,
respectively. Scheme 2 displays the formation of these end
groups. Thus, when using 4 as a catalyst, most of the chain
transfer reactions occurred via 1,2-insertion and the chain
transfer reactions via 2,1-misinsertion only accounted for ∼3%
of the total chain transfer reactions. The chain transfer reac-
tions via 1,2-insertion were facilitated after rearrangement and
subsequently generated a large amount of the trisubstituted
vinylene (–(C)CvCH–) end group. Because of the atactic struc-
ture, the 13C NMR signals in the aliphatic region (15–45 ppm)
were quite complicated, which differ from the spectra of iso-
tactic or syndiotactic structures (Fig. 3(b)).43,44 It has been pre-
viously reported that atactic PAO is better for lubricant
applications because it exhibits a low pour point relative to the
isotactic- or syndiotactic-rich analogs.31
Fig. 2 Oligomer distributions for PAOs prepared using catalysts 4 (a),
6 (b), and 8 (c).
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Conclusions
An ansa-zirconocene catalyst bearing methyl substituents at all
the positions adjacent to the bridgehead (4) was prepared in
high yields (78%) through the reductive dimerization of 1,4-
dimethyl-6-phenylfulvene by utilizing ZrCl2·DME, which was
generated in situ. 1,4-Dimethyl-6-phenylfulvene was prepared
on the 10 g scale without the use of column chromatography.
4 was highly active in 1-decene oligomerization at 120 °C (21 ×
106 g mol−1 Zr h−1 activity; TON = 150 000; TOF = 42 s−1). The
oligomer distribution observed in the SIMDIS system was
appropriate for use as lubricant base stocks. A wide range of
oligomers was created, from the dimer to 20-mer, without the
formation of a significant amount of the dimer or oligomers
above 10-mer (13 and 25 wt%, respectively). Alternatively, the
typical unbridged complex (η5-nBuC5H4)2ZrCl2 primarily pro-
duced dimers (54 wt%), while the typical ansa-zirconocene
(EBI)ZrCl2 primarily produced heavy oligomers consisting of
the 10-mer or higher (62 wt%) under identical oligomerization
conditions. The methyl substituents at the positions adjacent
to the bridgehead in 4 played a crucial role in the catalytic per-
formance, and the related complex that did not contain any
methyl substituents [(–CH2CH2–)(η5-C5H4)2ZrCl2] primarily
produced heavy oligomers consisting of the 10-mer or higher
(65 wt%) with 1/3rd the catalytic activity of 4. Therefore, 4 is
potentially applicable to the commercial production of PAO-
based lubricants.
Scheme 2 Chain transfer reaction and end groups.
Chart 1 Zirconocene catalysts for 1-decene oligomerization.
Experimental
General remarks
Complexes 6–9 (Chart 1) were evaluated as a catalyst in
1-decene oligomerization under identical conditions. The
unbridged complex (η5-nBuC5H4)2ZrCl2 (6) exhibited activity All manipulations were performed under an inert atmosphere
that was comparable to 4 (48 × 106 g mol−1 Zr h−1, entry 4). using a standard glove box and Schlenk techniques. Diethyl
However, the main product in these reactions was the dimer ether, THF, pentane, hexane, toluene and C6D6 were distilled
(54 wt%), which is not useful for lubricant base stocks (Fig. 2(b)). from benzophenone ketyl. DME and DMF were purified over
In the 1H NMR spectrum of the sample prepared by 6, the CaH2. 1-Decene and 1-octene used for the oligomerization
vinylidene (CvCH2), trisubstituted vinylene (–(C)CvCH–), and reaction were purchased from Aldrich and purified by passing
disubstituted vinylene (–CHvCH–) signals corresponded to a through water and oxygen scavenger columns. 1H NMR
molar ratio of 6.5 : 4.8 : 1.0, indicating that more chain transfer (400 MHz) and 13C NMR (100 MHz) spectra were recorded on a
reactions via 2,1-misinsertion occurred than in the sample Varian Mercury plus 400. Elemental analyses were carried out
prepared using 4. The unbridged bulky complex (η5- at the Analytical Center, Kyunghee University. Mass spectra
Me4C5H)2ZrCl2 (7) shifted the product distribution to favor the were obtained on a JEOL JMS-700. 1,4,6-Trisubstituted fulvenes
heavier oligomers but the main fraction was still dimer (33 wt%, and 1 were synthesized according to previously reported
entry 5). However, activity was significantly reduced (13 × procedures.39
106 g mol−1 Zr h−1) probably because of steric congestion.
Compound 2. To a solution of 1 (15.0 g, 73.1 mmol) in
A typical ansa-zirconocene (EBI)ZrCl2 (8) primarily pro- diethyl ether (90 mL) was added nBuLi (45.7 mL, 73.1 mmol,
duced heavy oligomers consisting of the 10-mer or higher 1.6 M in hexane) at −30 °C. The solution was allowed to warm
(62 wt%) and the heavy fractions were not well fractionated in to room temperature and stirred for 30 min, resulting in the
the SIMDIS system, which produced a broad baseline (Fig. 2(c)). formation of a white precipitate. Benzaldehyde (8.54 g,
The methyl groups in 4 played a critical role in the high activity 80.5 mmol) was added to the solution after chilling the reac-
and oligomer distribution and the ansa-zirconocene catalyst 9, tion mixture to −30 °C. After the resulting solution was stirred
which did not contain any methyl substituents, produced heavy for 20 min at −30 °C, all volatiles were removed under vacuum.
oligomers consisting of the 10-mer or higher (65 wt%) and the Anhydrous DMF (75 mL) and NaH (1.76 g, 73.1 mmol) were
activity was significantly reduced (6.6 × 106 g mol−1 Zr h−1
entry 7).
,
added to the reaction mixture and the solution was stirred for
30 min at room temperature. After MeI (11.4 g, 80.4 mmol)
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was added, the solution was stirred overnight. Water (150 mL) Hz, 1.3H, meso-Cp–H), 6.46 (d, J = 3.2 Hz, 1.3H, meso-Cp–H),
and hexane (150 mL) were added and the organic phase was 6.44 (d, J = 3.2 Hz, 0.7H, racemic-Cp–H), 6.33 (d, J = 3.2 Hz,
then collected, which was subsequently washed with brine 0.7H, racemic-Cp–H), 5.64 (s, 1.3H, meso-CpCH), 5.39 (s, 0.7H,
(225 mL). The solvent was then removed by a rotary evaporator racemic-CpCH), 2.17 (s, 2.4H, meso-CH3), 1.98 (s, 3.6H, racemic-
and the residue was dissolved in ethyl acetate (15 mL). CH3), 1.80 (s, 3.6H, racemic-CH3), 1.73 (s, 2.4H, meso-CH3)
Aqueous HCl (2 N, 45 mL) was added and the two-phase ppm. 13C{1H} NMR (C6D6): δ 140.28, 129.37, 128.25, 128.07,
mixture was stirred vigorously for 2 min. The aqueous phase 127.76, 126.39, 124.72, 123.40, 121.45, 47.44, 17.10, 14.51 ppm
was removed and the organic phase was then washed with for the meso isomer: 141.61, 128.91, 126.79, 123.06, 122.67,
saturated aqueous NaHCO3 (60 mL). The organic phase was 119.93, 45.03, 15.82, 14.76 ppm for the racemic isomer. Anal.
dried over anhydrous MgSO4 and the solvent was removed by a Calc. (C28H28Cl2Zr): C, 63.86; H, 5.36; Found: C, 63.92; H, 5.51.
rotary evaporator. The crude residue was subsequently used
Complex 5. It was synthesized using the same conditions
for the next reaction without any further purification. Yield = and procedure as those for 4 with 6-tert-butyl-1,4-dimethyl-
1
97% (15.2 g). H NMR (C6D6): δ 7.53 (d, J = 7.2 Hz, 2H, o-Ph), fulvene (0.58 g, 3.57 mmol). The reaction rate was much slower
7.21 (t, J = 7.2 Hz, 2H, m-Ph), 7.09 (t, J = 7.2 Hz, 1H, p-Ph), and the reaction mixture was subsequently stirred for 5 d at
5.84–5.76 (br, 1H, CH), 5.27 (s, 1H, CHOCH3), 3.22 (s, 3H, 110 °C. The product was extracted using a Soxhlet apparatus
OCH3), 2.74–2.68 (m, 2H, CH2), 1.88 (s, 6H, CH3) ppm. 13C{1H} with hexane for 1 h (220 mg, 25%). The 1H NMR spectrum
NMR (C6D6): δ 143.43, 142.41, 141.98, 139.22, 128.34, 127.02, indicated a mixture of two stereoisomers in a ratio of 2.5 : 1.0.
126.60, 125.21, 78.34, 56.27, 44.62, 15.75, 14.13 ppm. HRMS 1H NMR (C6D6): δ 6.53 (d, J = 3.6 Hz, 1.4H, Cp–H), 6.49 (d, J =
(EI): m/z calcd ([M+] (C15H20O) 216.1514. Found: 216.1513.
3.6 Hz, 0.6H, Cp–H), 6.43 (d, J = 3.6 Hz, 0.6H, Cp–H), 6.35 (d,
Compound 3. 2 (15.2 g, 70.9 mmol) was dissolved in THF J = 3.6 Hz, 1.4H, Cp–H), 3.94 (s, 0.6H, CpCH), 3.54 (s, 1.4H,
(74 mL) and NaH (2.04 g, 85.1 mmol) was added under a nitro- CpCH), 2.18 (s, 1.8H, CH3), 1.97 (s, 4.2H, CH3), 1.92 (s, 1.8H,
gen atmosphere. The mixture was then stirred for 3 h at room CH3), 1.89 (s, 4.2H, CH3), 1.06 (s, 5.4H, C(CH3)3), 0.91 (s,
temperature, and the generated hydrogen gas was removed by 12.6H, C(CH3)3) ppm. 13C{1H} NMR (C6D6): δ 132.56, 130.88,
venting. The mixture was filtered and washed with pentane 129.61, 129.13, 124.89, 123.33, 123.18, 128.12, 118.81, 117.22,
until the filtrate became colorless. After the solvent was 108.64, 56.41, 51.11, 40.25, 37.53, 37.02, 35.50, 33.39, 31.69,
removed, the residue was dissolved in hexane again to remove 30.93, 19.69, 19.41, 17.15, 15.94 ppm. Anal. Calc.
any solid residues. The solvent was then removed by a rotary (C24H36Cl2Zr): C, 59.23; H, 7.46. Found: C, 58.90; H, 7.11.
evaporator and the product was purified by vacuum distillation
1
1-Decene oligomerization
at 62 °C and 7.5 × 10−2 mmHg (11.3 g, 87%). H NMR (C6D6):
δ 7.30–6.90 (m, 6H, phenyl, PhCH), 6.14–6.07 (m, 1H, CH), The bomb reactor was charged with 1-decene (370 g, 2.64 mol)
6.07–6.00 (m, 1H, CH), 2.00 (s, 3H, CH3), 1.79 (s, 3H, CH3) and (iBu)3Al (0.30 g, 1.50 mmol). After the solution was heated
ppm. 13C{1H} NMR (C6D6): δ 147.30, 137.21, 134.07, 133.58, to 120 °C, the activated catalyst (which was prepared by mixing
132.75, 130.17, 129.64, 128.14, 128.00, 127.64, 17.19, zirconocene (0.010 mmol Zr), [CPh3]+[B(C6F5)4]− (0.18 g,
13.13 ppm. HRMS(EI): m/z calcd ([M+] C14H14) 182.1096. 0.020 mmol) and (iBu)3Al (0.10 g, 0.50 mmol) in toluene
Found: 182.1097.
(5 mL)) was added using a syringe. After the oligomerization
Complex 4. nBuLi (38.7 mL, 61.9 mmol, 1.6 M in hexane) was carried out for 1 h, water (5 mL) was added to terminate
was added to ZrCl4·DME (10.0 g, 30.9 mmol) in toluene the reaction. The activities and conversions were calculated by
(200 mL) over 10 min at −78 °C and the solution was then measuring the weight of the product after removing the
stirred for 6 h after warming to room temperature. Approxi- unreacted 1-decene under vacuum. The oligomer distribution
mately half of the solvent was removed and the solution was was determined using the SIMDIS system (Table 1).
stirred for 3 h at 100 °C while venting the generated butane
X-Ray crystallography
and 1-butene gas. 3 (5.64 g, 30.9 mmol) was dissolved in
toluene (10 mL), added to the reaction mixture at room temp- Reflection data for 4 and 5 were collected at 100 K on a Bruker
erature, and stirred for 18 h at 110 °C. All volatiles were APEX II CCD area diffractometer with graphite-monochro-
removed under vacuum and hot toluene (300 mL) was added mated Mo Kα radiation (λ = 0.7107 Å). Specimens of suitable
again. After filtration, the solvent was removed to obtain a quality and size were selected, mounted, and centered in the
solid residue, which was extracted using a Soxhlet apparatus X-ray beam using a video camera. The hemisphere of reflection
with cyclohexane (170 mL) for 2 d. The product was isolated as data was collected as φ and ω scan frames with 0.5° per frame
a gray solid after removing the solvent (6.36 g, 78%). The iso- and an exposure time of 10 s per frame. Cell parameters were
lated solid was sufficiently pure to be used in oligomerization determined and refined using the SMART program. Data
reaction without further purification. The 1H NMR spectrum reduction was performed using the SAINT software. The data
indicated a mixture of two stereoisomers in a meso/racemic were corrected for Lorentz and polarization effects. An empiri-
ratio of 1.0 : 0.50. The meso isomer was selectively deposited cal absorption correction was applied using the SADABS
after the toluene solution was stored in a refrigerator. 1H NMR program. The structures of the compounds were solved by
(C6D6): δ 7.06–6.98 (m, 3.5H, racemic-Ph), 6.94–6.86 (m, 4.3H, direct methods and refined by full matrix least-squares
meso-o, p-Ph), 6.86–6.80 (m, 2.2H, meso-m-Ph), 6.53 (d, J = 3.6 methods using the SHELXTL program package with anisotro-
This journal is © The Royal Society of Chemistry 2014
Dalton Trans., 2014, 43, 10132–10138 | 10137

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Paper
Dalton Transactions
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10138 | Dalton Trans., 2014, 43, 10132–10138
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