Ethylene-bridged C1-symmetric ansa-(3-R-indenyl)(fluorenyl) zirconocene complexes for propylene dimerization or polymerization: The effect of R group

Article abstract of DOI:10.1016/j.poly.2014.03.019

A series of ethylene-bridged C₁-symmetric ansa-(3-R-indenyl) (fluorenyl) zirconocene complexes 3a-i (R = 2-[2-(4-methylphenyl)propyl], 3a; R = 2-[2-(3,5-dimethylphenyl)propyl], 3b; R = 2-(2-benzylpropyl), 3c; R = 2-methylbenzyl, 3d; R = 2-(2-cyclohexylpropyl), 3e; R = 2-[2-(1-cyclohexenyl) propyl], 3f; R = 2-(2-n-butylpropyl), 3g; R = cyclohexyl, 3h; R = ⁱPr, 3i) were synthesized by a salt metathesis method and characterized by NMR spectroscopy, elemental analysis (or HRMS) and X-ray diffraction (3e and 3h). Upon activation with methylaluminoxane, most of these zirconocene complexes exhibited sufficient catalytic activities up to 2.5 × 10⁵ g C₆/(mol-Zr·h) and high selectivities up to 99% toward propylene dimerization, affording 2-methyl-1-pentene as the major isomer which was confirmed by gas chromatography. Remarkably, the selectivity and activity of complexes 3a-i were significantly influenced by the structural features of the substituent on the 3-position of indenyl ring: a pendant aryl or alkyl group linked by a quaternary carbon bridge provided the complex with high selectivities in the range of 89.9-99.0% for 2-methyl-1-pentene and low to moderate catalytic activities; the lack of a quaternary carbon bridge within the substituent would lead to mainly polypropylenes of low molecular weight. The steric hindrance around the active metal center induced by the pendant group might be responsible for the catalytic dimerization behavior, and the presumed mechanism was discussed. In addition, for complexes 3h and 3i, the selectivity for propylene dimerization could also be enhanced with the increase of reaction temperature. Noticeably, most of these ansa-zirconocene complexes exhibit excellent thermal stability at 100 °C, which is important with regard to industrial application. 2014 Elsevier Ltd. All rights reserved.

Full text of DOI:10.1016/j.poly.2014.03.019

Polyhedron 76 (2014) 81–93
Contents lists available at ScienceDirect
Polyhedron
journal homepage: www.elsevier.com/locate/poly
Ethylene-bridged C1-symmetric ansa-(3-R-indenyl)(fluorenyl)
zirconocene complexes for propylene dimerization or polymerization:
The effect of R group
⇑
⇑
Yan Wang, Wenzhong Huang, Haiyan Ma , Jiling Huang
Laboratory of Organometallic Chemistry, East China University of Science and Technology, Shanghai 200237, PR China
a r t i c l e i n f o
a b s t r a c t
Article history:
A series of ethylene-bridged C1-symmetric ansa-(3-R-indenyl)(fluorenyl) zirconocene complexes 3a–i
(R = 2-[2-(4-methylphenyl)propyl], 3a; R = 2-[2-(3,5-dimethylphenyl)propyl], 3b; R = 2-(2-benzylpro-
pyl), 3c; R = 2-methylbenzyl, 3d; R = 2-(2-cyclohexylpropyl), 3e; R = 2-[2-(1-cyclohexenyl)propyl], 3f;
R = 2-(2-n-butylpropyl), 3g; R = cyclohexyl, 3h; R = iPr, 3i) were synthesized by a salt metathesis method
and characterized by NMR spectroscopy, elemental analysis (or HRMS) and X-ray diffraction (3e and 3h).
Upon activation with methylaluminoxane, most of these zirconocene complexes exhibited sufficient cat-
alytic activities up to 2.5 ꢀ 105 g C6/(mol-Zrꢁh) and high selectivities up to 99% toward propylene dimer-
ization, affording 2-methyl-1-pentene as the major isomer which was confirmed by gas chromatography.
Remarkably, the selectivity and activity of complexes 3a–i were significantly influenced by the structural
features of the substituent on the 3-position of indenyl ring: a pendant aryl or alkyl group linked by a
quaternary carbon bridge provided the complex with high selectivities in the range of 89.9–99.0% for
2-methyl-1-pentene and low to moderate catalytic activities; the lack of a quaternary carbon bridge
within the substituent would lead to mainly polypropylenes of low molecular weight. The steric hin-
drance around the active metal center induced by the pendant group might be responsible for the cata-
lytic dimerization behavior, and the presumed mechanism was discussed. In addition, for complexes 3h
and 3i, the selectivity for propylene dimerization could also be enhanced with the increase of reaction
temperature. Noticeably, most of these ansa-zirconocene complexes exhibit excellent thermal stability
at 100 °C, which is important with regard to industrial application.
Received 15 January 2014
Accepted 12 March 2014
Available online 22 March 2014
Keywords:
Propylene
Dimerization
Catalysis
Zirconocene complex
C1-symmetric
Ó 2014 Elsevier Ltd. All rights reserved.
1. Introduction
propylene dimerization under mild conditions. Unfortunately, as
described in the literature, these complexes exhibit low selectivity
As important raw materials, the oligomers of ethylene and
a
-
toward a specific dimer, in most of the cases giving a mixture of
hexenes, methyl pentenes and dimethyl butene.
olefins especially propylene have been widely applied in petro-
chemical industry [1,2]. 2-Methyl-1-pentene, a dimer of propylene,
is useful for the production of branched copolymers [3] and the
synthesis of organic chemicals [4]. Nowadays, aluminum alkyl
complexes [5], such as AlEt3, have been industrially introduced to
produce 2-methyl-1-pentene by catalyzing propylene dimeriza-
tion. However, extremely tough conditions (300 °C, 250 bar) have
to be adopted to realize such transformation. Considering the risk
of the processes, many efforts have been devoted to the single-site
transition metal catalysts, such as nickel [6], cobalt [7], iron [8] and
vanadium [9] complexes with bis(imino)pyridine, diimine or phos-
phorus-based chelating ligands, which are capable of catalyzing
Rare examples of Group-IV metallocene complexes were
reported for propylene oligomerization or dimerization [10].
Kaminsky [11] reported that ethylene-bis(tetrahydroindenyl) zir-
conium dichloride could dimerize propylene to 2-methyl-1-pen-
tene with a selectivity of 99.8% in all products by adopting an
extremely low monomer concentration. However, due to the neg-
lectable catalytic efficiency, no activity data were reported [11].
Okuda and co-workers [12] described a series of unbridged hafno-
cene complexes, for example (tBuC5Me4)2HfCl2, which showed
moderate activity for propylene oligomerization with the percent-
age of 4-methyl-1-pentene up to 61.6% in all products. Recently,
we reported a series of ethylene bridged C1-symmetric ansa-(3-R-
indenyl)(fluorenyl) zirconocene complexes bearing a pendant aryl
group on the 3-position of indenyl ring. Unlike those reported in
⇑
Corresponding authors. Tel./fax: +86 21 64253519.
E-mail address: haiyanma@ecust.edu.cn (H. Ma).
http://dx.doi.org/10.1016/j.poly.2014.03.019
0277-5387/Ó 2014 Elsevier Ltd. All rights reserved.

82
Y. Wang et al. / Polyhedron 76 (2014) 81–93
solution was titrated with standard hydrochloric acid (yield 71%).
R
The obtained solution was cooled to 0 °C, then a solution of 6,6-
dimethylbenzofulvene (5.2 g, 33 mmol) in diethyl ether (20 mL)
was added dropwise. The resultant orange solution was stirred
overnight and then hydrolyzed with 50 mL of aqueous ammonium
chloride. The organic phase was separated and the aqueous layer
was extracted with Et2O. The combined organic phases were dried
over anhydrous MgSO4 and evaporated. The residue was distilled
under reduced pressure to give 3-{2-[2-(4-methylphenyl)pro-
pyl]}indene (1a) as a pale yellow oil (120–122 °C/0.1 mmHg,
6.2 g, 75%). 1H NMR (400 MHz, 298 K, CDCl3): d 7.49 (d, J = 7.3 Hz,
1H, Ar–H), 7.27 (d, J = 7.6 Hz, 2H, Ar–H), 7.17–7.10 (m, 3H, Ar–H),
7.07 (pesudo-t, J = 7.6 Hz, 1H, Ar–H), 6.81 (d, J = 7.5 Hz, 1H, Ar–H),
6.52 (d, J = 1.8 Hz, 1H, 2-Ind–CH), 3.46 (d, J = 1.8 Hz, 2H, 1-Ind–
CH), 2.36 (s, 3H, Ph–CH3), 1.73 (s, 6H, C(CH3)2).
1 R = H
Zr
Cl
Cl
2
R = Me
Chart 1. Ethylene-bridged C1-symmetric ansa-zirconocene complexes.
the literature [13], these complexes with such a specific substitu-
ent on the 3-position of indenyl ring, represented by 1 and 2 in
Chart 1, exhibited moderate activities for propylene dimerization
to give 2-methyl-1-pentene with high selectivities up to 98.4%
[14].
To a solution of 1a (2.1 g, 8.5 mmol) in 30 mL of Et2O at 0 °C was
added dropwise a solution of n-butyllithium in n-hexane (2.4 M,
3.5 mL, 8.5 mmol). The solution was stirred at room temperature
overnight and then added via cannula to a solution of 9-(2-bromo-
ethyl)-fluorene (2.3 g, 8.5 mmol) in 20 mL of Et2O. The reaction
mixture was stirred overnight at room temperature and then
hydrolyzed with 50 mL of aqueous ammonium chloride. The
organic phase was separated, and the aqueous layer was extracted
with diethyl ether. The combined organic phases were dried
over anhydrous MgSO4 and evaporated. The residue was purified
by a silica gel column chromatography (eluent: petroleum ether)
to afford 1-(9-fluorenyl)-2-{1-[3-(2-(2-(4-methylphenyl)pro-
pyl))indenyl]}ethane (2a) as a pale yellow oil (2.0 g, 54%), which
was used directly in the next step without further purification.
1H NMR (400 MHz, 298 K, CDCl3): d 7.77 (d, J = 7.5 Hz, 2H, Ar–H),
7.53 (d, J = 7.1 Hz, 1H, Ar–H), 7.45 (d, J = 7.1 Hz, 1H, Ar–H), 7.38
(pesudo-td, J = 7.6 Hz, 2.0 Hz, 2H, Ar–H), 7.35–7.29 (m, 2H, Ar–H),
7.22 (d, J = 7.3 Hz, 1H, Ar–H), 7.18 (d, J = 8.2 Hz, 2H, Ar–H), 7.05
(m, 3H, Ar–H), 6.97 (pesudo-t, J = 7.4 Hz, 1H, Ar–H), 6.66 (d,
J = 7.6 Hz, 1H, Ar–H), 6.34 (d, J = 2.0 Hz, 1H, 2-Ind–H), 4.00 (t,
J = 5.3 Hz, 1H, 9-Flu–H), 3.38 (pesudo-td, J = 6.2 Hz, 2.0 Hz, 1-Ind–
H), 2.30 (s, 3H, CH3–Ph), 2.23–2.12 (m, 1H, Ind–CH2CH2–Flu),
2.04–1.91 (m, 1H, Ind–CH2CH2–Flu), 1.85–1.70 (m, 1H, Ind–CH2-
CH2–Flu), 1.64 (s, 3H, C(CH3)2), 1.63 (s, 3H, C(CH3)2), 1.50–1.35
(Ind–CH2CH2–Flu). 13C NMR (100 MHz, 298 K, CDCl3) d 151.8,
149.0, 147.3, 147.2, 145.2, 143.7, 141.5, 141.4, 135.3, 132.2,
129.2, 127.2, 127.1, 126.2, 125.9, 124.5, 124.3, 122.9, 122.6,
120.1, 120.0, 48.3 (1-Ind–CH2), 47.6 (9-Flu–CH), 40.2 (C(CH3)2),
30.3 (CH2CH2), 29.6 (C(CH3)2), 29.5 (C(CH3)2), 27.2 (CH2CH2), 21.2
(CH3–Ph).
To a solution of 2a (2.0 g, 4.5 mmol) in 30 mL of Et2O at 0 °C was
added dropwise 2 equiv. of n-butyllithium in n-hexane (2.4 M,
3.8 mL, 9.0 mmol). The resulting suspension was stirred for 48 h
at room temperature. ZrCl4 (1.0 g, 4.5 mmol) was added to the sus-
pension as solid. The resultant orange mixture was stirred for 48 h
at room temperature, and the solvents were removed under vac-
uum. The residue was dissolved with 30 mL of CH2Cl2. After filtra-
tion, the solution was concentrated and stored at ꢂ20 °C to give 3a
as red solids (0.26 g, 9.6%). 1H NMR (400 MHz, 298 K, CDCl3): d 8.07
(d, J = 8.3 Hz, 1H, Ar–H), 7.92 (d, J = 8.3 Hz, Ar–H), 7.89 (d,
J = 8.5 Hz, 1H, Ar–H), 7.78 (d, J = 8.4 Hz, 1H, Ar–H), 7.66 (pesudo-t,
J = 7.6 Hz, 1H, Ar–H), 7.52 (d, J = 8.8 Hz, 1H, Ar–H), 7.44 (pesudo-t,
J = 7.6 Hz, 1H, Ar–H), 7.29 (pesudo-t, J = 7.6 Hz, 1H, Ar–H), 7.11–
7.04 (m, 2H, Ar–H), 6.99 (pesudo-t, J = 7.6 Hz, 1H, Ar–H), 6.94–
6.89 (m, 1H, Ar–H), 6.86 (d, J = 8.2 Hz, 2H, Ar–H), 6.75 (d,
J = 8.2 Hz, 2H, Ar–H), 6.21 (s, 1H, 2-Ind–CH), 4.75–4.65 (m, 1H,
Ind–CH2CH2–Flu), 4.27–4.17 (m, 1H, Ind–CH2CH2–Flu), 4.05–3.94
(m, 2H, Ind–CH2CH2–Flu), 2.17 (s, 3H, CH3–Ph), 1.94 (s, 3H,
C(CH3)2), 1.54 (s, 3H, C(CH3)2). 13C NMR (100 MHz, 298 K, CDCl3):
d 150.7, 135.0, 132.5, 131.6, 129.1, 128.7, 127.7, 127.6, 126.9,
126.2, 126.0, 125.93, 125.6, 125.3, 125.0, 124.3, 124.2, 123.4,
In order to understand the factors governing the high selectivity
for propylene dimerization to 2-methyl-1-pentene, herein we fur-
ther modified the ligand skeleton of this series of ethylene-bridged
C1-symmetric zirconocene complexes by introducing different
pendant aryl groups, bridging units (between indenyl and pendant
group), and alkyl groups that have no conjugated system, trying to
establish an acceptable mechanism likely involved in this highly
selective propylene dimerization process.
2. Experimental
2.1. Material and instrumentation
All manipulations were carried out under a pure argon atmo-
sphere using standard Schlenk techniques unless otherwise indi-
cated. Tetrahydrofuran, diethyl ether, n-hexane, petroleum ether
and toluene were distilled under argon from sodium-benzophe-
none prior to use. Dichloromethane was distilled from calcium
hydride. Chloroform-d was dried over calcium hydride under argon
and stored in the presence of activated 4 Å molecular sieves. nBuLi
(2.4 M in n-hexane) were purchased from Acros. 9-(2-Bromoeth-
yl)-fluorene [13a], 6,6-dimethyllbenzofulvene [15], 2-methyl ben-
zyl chloride [16], and 3-isopropylindene [17] were prepared
according to literature procedures. Zirconium tetrachloride was
purchased from Aldrich and freshly sublimed under vacuum prior
to use. The co-catalyst methylaluminoxane (MAO, 1.53 M in tolu-
ene) was purchased from Witco GmbH. Polymer grade ethylene
was used directly for polymerization.
1H (400 MHz) and 13C (100 MHz) NMR spectroscopic measure-
ments were obtained on a Bruker-ADVANCE 400 spectrometer in
CDCl3 at ambient temperature. Chemical shifts were referenced
internally using the residual solvent resonances and reported rela-
tive to tetramethylsilane (TMS). Elemental analyses were carried
out on an Elementar III Vario EI analyzer. Agilent 6890N-5975
GC–MS equipped with HP-5MS chromatographic column
(30 m ꢀ 0.25 mm ꢀ 0.25 m) was used to detect and identified the
dimers. GC 9700 made by Lanzhou Analyze Equipment Factory
with a FID detector was also used.
2.2. Synthesis
2.2.1. Synthesis of ethylene-1-(9-fluorenyl)-2-{1-[3-(2-(2-(4-
methylphenyl)propyl))indenyl]} zirconium dichloride (3a)
A mixture of 4-methylbromobenzene (8.0 g, 47 mmol) and
petroleum ether (40 mL) was cooled to 0 °C, and then a solution
of n-butyllithium in n-hexane (2.4 mol/L, 20 mL, 47 mmol) was
added dropwise. The reaction mixture was warmed to room tem-
perature and stirred for 4 days. White precipitates separated out
gradually. After filtration, the solid residue was washed with
10 mL of petroleum ether and dried under vacuum. The obtained
white solids were dissolved in 50 mL of diethyl ether and the

Y. Wang et al. / Polyhedron 76 (2014) 81–93
83
121.9, 121.5, 117.7, 103.9, 40.9 (C(CH3)2), 32.5 (CH2CH2), 31.5 (CH2-
CH2), 30.3 (C(CH3)2), 25.9 (C(CH3)2), 21.0 (CH3–Ph). Anal. Calc. for
6-dimethylbenzofulvene (8.0 g, 52 mmol) was added and the
resultant mixture was refluxed overnight. The reaction mixture
was hydrolyzed with 50 mL of aqueous ammonium chloride at
0 °C. The organic phase was separated, and the aqueous layer
was extracted with Et2O. The combined organic phases were dried
over anhydrous MgSO4 and evaporated. The residue was distilled
under reduced pressure, and 3-[2-(2-benzylpropyl)]indene (1c)
was collected as a pale yellow oil (106–110 °C/0.1 mmHg, 2.1 g,
17%). 1H NMR (400 MHz, 298 K, CDCl3): d 7.78 (d, J = 7.7 Hz, 1H,
Ar–H), 7.49 (d, J = 7.3 Hz, 1H, Ar–H), 7.33 (pesudo-t, J = 7.7 Hz, 1H,
Ar–H), 7.22 (pesudo-t, J = 7.3 Hz, 1H, Ar–H), 7.14–7.09 (m, 3H, Ar–
H), 6.92–6.85 (m, 2H, Ar–H), 6.01 (s, 1H, 2-Ind–CH), 3.25 (s, 2H,
1-Ind–CH), 3.07 (s, 2H, Ph–CH2), 1.53 (s, 6H, C(CH3)2).
Following the procedure described for 2a, 1c (2.1 g, 8.5 mmol), a
solution of n-butyllithium in n-hexane (2.4 M, 3.5 mL, 8.5 mmol),
and 9-(2-bromoethyl)-fluorene (2.0 g, 7.7 mmol), were reacted to
give the product as an orange oil (1.2 g, 32%), containing 1-(9-flu-
orenyl)-2-{1-[3-(2-(2-benzylpropyl))indenyl]}ethane (2c, ꢃ80%)
and 1-(9-fluorenyl)-2-{3-[1-(2-(2-benzylpropyl))indenyl]}ethane
(ꢃ20%), which was used directly in the next step without further
purification. 1H NMR (400 MHz, 298 K, CDCl3): d 7.78–7.70 (m,
3H, Ar–H), 7.40–7.35 (m, 3H, Ar–H), 7.34–7.27 (m, 5H, Ar–H),
7.20 (t, J = 7.3 Hz, 1H, Ar–H), 7.10–7.03 (m, 3H, Ar–H), 6.88 (dd,
J = 7.3 Hz, 1.8 Hz, 2H, Ar–H), 5.82 (d, J = 2.0 Hz, 1H, 2-Ind–H), 3.89
(t, J = 5.5 Hz, 1H, 9-Flu–H), 3.25–3.15 (m, 2H, 1-Ind–H + Ph–CH2–),
2.94 (d, J = 13.2 Hz, 1H, CH2–Ph), 1.95–1.75 (m, 2H, Ind–CH2CH2–
Flu), 1.55–1.45 (m, 1H, Ind–CH2CH2–Flu), 1.42–1.25 (m, 1H, Ind–
CH2CH2–Flu), 1.35 (s, 3H, C(CH3)2), 1.29 (s, 3H, C(CH3)2). 13C NMR
(100 MHz, 298 K, CDCl3): d 150.0, 149.2, 147.0, 147.0, 143.9,
141.3, 139.0, 133.6, 130.3, 127.4, 126.9, 126.8, 126.0, 125.8,
124.3, 124.3, 124.2, 123.2, 122.3, 119.8, 47.9 (1-Ind–CH2), 47.3
(9-Flu–CH), 46.5 (CH2–Ph), 37.6 (C(CH3)2), 28.9 (CH2CH2), 27.9
(CH2CH2), 27.6 (C(CH3)2), 26.3 (C(CH3)2).
Following the procedure described for 3a, the orange oil
obtained above (1.2 g, 2.7 mmol), a solution of n-butyllithium in
n-hexane (2.4 M, 2.2 mL, 5.4 mmol), and ZrCl4 (0.62 g, 2.7 mmol),
were reacted to give 3c as red solids (0.53 g, 33%). 1H NMR
(400 MHz, 298 K, CDCl3): d 8.05 (d, J = 8.7 Hz, 1H, Ar–H), 7.90 (d,
J = 8.4 Hz, 1H, Ar–H), 7.77 (pesudo-t, J = 8.4 Hz, 2H, Ar–H), 7.75 (d,
J = 8.7 Hz, 1H, Ar–H), 7.61 (pesudo-t, J = 7.6 Hz, 1H, Ar–H), 7.55 (d,
J = 8.6 Hz, 1H, Ar–H), 7.35 (pesudo-t, J = 7.6 Hz, 1H, Ar–H), 7.30
(pesudo-t, J = 7.6 Hz, 1H, Ar–H), 7.24–6.96 (m, 6H, Ar–H), 6.50 (d,
J = 6.8 Hz, 2H, Ar–H), 5.72 (s, 1H, 2-Ind–CH), 4.65–4.50 (m, 1H,
Ind–CH2CH2–Flu), 4.05–3.85 (m, 3H, Ind–CH2CH2–Flu), 3.03 (d,
J = 12.9 Hz, 1H, CH2–Ph), 2.69 (d, J = 12.9 Hz, 1H, CH2–Ph), 1.52 (s,
3H, C(CH3)2), 1.16 (s, 3H, C(CH3)2). 13C NMR (100 MHz, 298 K,
CDCl3): d 138.7, 130.7, 129.6, 128.9, 128.5, 128.1, 127.9, 127.5,
126.6, 126.5, 126.0, 125.6, 125.4, 125.2, 124.4, 123.8, 123.6,
123.2, 121.6, 121.5, 116.4, 103.8, 49.6 (C(CH3)2), 38.7 (CH2–Ph),
31.5 (CH2CH2), 30.1 (CH2CH2), 27.4 (C(CH3)2), 25.6 (C(CH3)2). Anal.
Calc. for C34H30Cl2Zrꢁ0.17CH2Cl2: C, 66.71; H, 4.97. Found: C,
66.39; H, 4.97%.
C
34H30Cl2Zrꢁ0.5CH2Cl2: C, 64.42; H, 4.86. Found: C, 63.98; H,
5.38%. HRMS (EI, m/z) for C34H30Cl2Zr: Calcd., 598.0772; Found,
598.0773.
2.2.2. Synthesis of ethylene-1-(9-fluorenyl)-2-{1-[3-(2-(2-(3,5-
dimethylphenyl)propyl))indenyl]} zirconium dichloride (3b)
Following the procedure described for 1a, 3,5-dimethylbromo-
benzene (6.8 g, 37 mmol), a solution of n-butyllithium in n-hexane
(2.4 mol/L, 15 mL, 37 mmol) and 6,6-dimethylbenzofulvene (4.0 g,
25 mmol) were reacted to give 3-{2-[2-(3,5-dimethylphenyl)pro-
pyl]}indene (1b) as a pale yellow oil (130–134 °C/0.1 mmHg,
4.3 g, 65%). 1H NMR (400 MHz, 298 K, CDCl3): d 7.47 (d, J = 6.7 Hz,
1H, Ar–H), 7.12 (pesudo-t, J = 7.2 Hz, 1H, Ar–H), 7.06 (pesudo-t,
J = 6.9 Hz, 1H, Ar–H), 6.98 (s, 2H, Ar–H), 6.89–6.78 (m, 2H, Ar–H),
6.49 (s, 1H, 2-Ind–CH), 3.44 (s, 2H, 1-Ind–CH), 2.29 (s, 6H, CH3–
Ph), 1.70 (s, 6H, C(CH3)2).
Following the procedure described for 2a, 1b (1.8 g, 6.8 mmol),
a solution of n-butyllithium in n-hexane (2.4 M, 2.8 mL, 6.8 mmol),
and 9-(2-bromoethyl)-fluorene (1.4 g, 6.8 mmol), were reacted to
give 1-(9-fluorenyl)-2-{1-[3-(2-(2-(3,5-dimethylphenyl)pro-
pyl))indenyl]}ethane (2b) as a light yellow oil (1.0 g, 32%), which
was used directly in the next step without further purification.
1H NMR (400 MHz, 298 K, CDCl3): d 7.76 (d, J = 7.5 Hz, 2H, Ar–H),
7.53 (d, J = 7.3 Hz, 1H, Ar–H), 7.44 (d, J = 7.5 Hz, 1H, Ar–H), 7.37
(pesudo-td, J = 7.3 Hz, 3.3 Hz, 2H, Ar–H), 7.34–7.28 (m, 2H, Ar–H),
7.22 (d, J = 7.3 Hz, 1H, Ar–H), 7.04 (pesudo-t, J = 7.1 Hz, 1H, Ar–H),
6.97 (pesudo-t, J = 7.1 Hz, 1H, Ar–H), 6.89 (s, 2H, Ar–H), 6.80 (s,
1H, Ar–H), 6.70 (d, J = 7.5 Hz, 1H, Ar–H), 6.33 (d, J = 1.9 Hz, 1H, 2-
Ind–H), 3.99 (t, J = 5.4 Hz, 1H, 9-Flu–H), 3.39 (pesudo-td,
J = 5.4 Hz, 1.9 Hz, 1H, 1-Ind–H), 2.22 (s, 6H, CH3–Ph), 2.18–2.12
(m, 1H, Ind–CH2CH2–Flu), 2.00–1.90 (m, 1H, Ind–CH2CH2–Flu),
1.84–1.74 (m, 1H, Ind–CH2CH2–Flu), 1.62 (s, 3H, C(CH3)2), 1.62 (s,
3H, C(CH3)2), 1.51–1.39 (m, 1H, Ind–CH2CH2–Flu). 13C NMR
(100 MHz, 298 K, CDCl3): d 151.7, 148.7, 147.9, 147.1, 147.0,
143.6, 141.2, 137.4, 131.9, 127.5, 127.0, 126.9, 125.7, 124.3,
124.0, 123.9, 122.6, 122.4, 119.9, 119.8, 48.0 (1-Ind–CH2), 47.5
(9-Flu–CH), 40.1 (C(CH3)2), 30.0 (CH2CH2), 29.4 (C(CH3)2), 29.2
(C(CH3)2), 27.1 (CH2CH2), 21.6 (CH3–Ph).
Following the procedure described for 3a, 2b (0.8 g, 1.8 mmol),
a solution of n-butyllithium in n-hexane (2.4 M, 1.4 mL, 3.6 mmol),
and ZrCl4 (0.40 g, 1.8 mmol) were reacted to give 3b as red solids
(0.22 g, 15%). 1H NMR (400 MHz, 298 K, CDCl3):
d 8.07 (d,
J = 8.5 Hz, 1H, Ar–H), 7.91 (d, J = 8.4 Hz, 1H, Ar–H), 7.88 (d,
J = 8.5 Hz, 1H, Ar–H), 7.78 (d, J = 8.4 Hz, 1H, Ar–H), 7.66 (pesudo-t,
J = 7.6 Hz, 1H, Ar–H), 7.52 (d, J = 8.6 Hz, 1H, Ar–H), 7.42 (pesudo-
td, J = 7.6 Hz, 0.8 Hz, 1H, Ar–H), 7.30 (pesudo-t, J = 7.6 Hz, 1H, Ar–
H), 7.12–7.04 (m, 2H, Ar–H), 6.98 (pesudo-td, J = 7.6 Hz, 0.8 Hz,
1H, Ar–H), 6.92 (pesudo-td, J = 7.6 Hz, 0.8 Hz, 1H, Ar–H), 6.63 (s,
1H, Ar–H), 6.49 (s, 2H, Ar–H), 6.21 (s, 1H, 2-Ind–CH), 4.78–4.62
(m, 1H, Ind–CH2CH2–Flu), 4.31–4.15 (m, 1H, Ind–CH2CH2–Flu),
4.11–3.93 (m, 2H, Ind–CH2CH2–Flu), 2.11 (s, 6H, CH3–Ph), 1.92 (s,
3H, C(CH3)2), 1.53 (s, 3H, C(CH3)2). 13C NMR (100 MHz, 298 K,
CDCl3): d 137.2, 128.0, 127.7, 127.6, 127.3, 126.9, 126.2, 126.0,
125.9, 125.3, 125.1, 124.9, 124.2, 124.0, 123.6, 123.3, 121.8,
121.2, 117.6, 116.8, 49.7 (C(CH3)2), 32.8 (CH2CH2), 32.6 (CH2CH2),
30.3 (C(CH3)2), 26.0 (C(CH3)2), 21.0 (CH3–Ph). Anal. Calc. for C35H32-
Cl2Zrꢁ0.10CH2Cl2: C, 67.64; H, 5.21. Found: C, 67.63; H, 5.43%.
2.2.4. Synthesis of ethylene-1-(9-fluorenyl)-2-{1-[3-(2-
methylbenzyl)indenyl]} zirconium dichloride (3d)
To a solution of indene (5.4 g, 47 mmol) in 30 mL of dry THF at
0 °C was added dropwise a solution of n-butyllithium in n-hexane
(2.4 M, 19 mL, 47 mmol). The reaction mixture was stirred over-
night at room temperature and then a solution of 2-methylbenzyl
chloride (7.3 g, 52 mmol) in 30 mL of THF was added dropwise to it
at 0 °C. After being stirred for additional 2 h, the reaction mixture
was hydrolyzed with 50 mL of aqueous ammonium chloride at
0 °C. The organic phase was separated, and the aqueous layer
was extracted with Et2O. The combined organic phases were dried
over anhydrous MgSO4 and evaporated. The residue was distilled
under reduced pressure, and the target product was collected as
2.2.3. Synthesis of ethylene-1-(9-fluorenyl)-2-{1-[3-(2-(2-
benzylpropyl))indenyl]} zirconium dichloride (3c)
A mixture of magnesium (1.5 g, 56 mmol), THF (80 mL), and a
catalytic amount of iodine was cooled to 0 °C. After benzyl chloride
(6.5 g, 39 mmol) was added dropwise, the reaction mixture was
warmed to room temperature and stirred for 2 h. Then 6,

84
Y. Wang et al. / Polyhedron 76 (2014) 81–93
a pale yellow oil (116–118 °C/0.1 mmHg, 7.2 g, 54%), containing 3-
(2-methylbenzyl)indene (1d, ꢃ80%) and 1-(2-methylben-
zyl)indene (1d0, 20%). Major isomer 1d: 1H NMR (400 MHz,
298 K, CDCl3): d 7.40–7.35 (m, 1H, Ar–H), 7.32–7.10 (m, 7H, Ar–
H), 6.81 (d, 1H, J = 5.4 Hz, 1H, 3-Ind–CH), 6.42 (d, 1H, J = 5.4 Hz,
2-Ind–CH), 3.70 (t, J = 8.2 Hz, 1H, 1-Ind–CH2), 3.15 (dd, J = 13.6,
8.2 Hz, CH2–Ph), 2.59 (dd, J = 13.6 Hz, 8.2 Hz, 1H, CH2–Ph), 2.35
(s, 3H, CH3–Ph). Minor isomer 1d0: 1H NMR (400 MHz, 298 K,
CDCl3): d 7.47, (d, J = 7.2 Hz, 1H, Ar–H), 7.32–7.10 (m, 7H, Ar–H),
5.90 (s, 1H, 2-Ind–CH), 3.85 (s, 2H, CH2–Ph), 3.32 (s, 2H, 1-Ind–
CH2), 2.30 (s, 3H, CH3–Ph).
chlorocyclohexane (15 g, 58 mmol) was added dropwise, the mix-
ture was warmed to room temperature slowly and stirred for 8 h,
and then stood for 24 h. After filtration, the solution was titrated
with standard HCl solution, and the yield of resultant cyclohexylli-
thium was 73%. The obtained solution was cooled to 0 °C, and a
solution of 6,6-dimethylbenzofulvene (5.5 g, 35 mmol) in 10 mL
of toluene was added dropwise. The mixture was warm to room
temperature slowly and stirred for 2 h. After being hydrolyzed
with 50 mL of aqueous ammonium chloride, the organic phase
was separated and the aqueous layer was extracted with Et2O.
The combined organic phases were dried over anhydrous MgSO4
and evaporated. The residue was distilled under reduced pressure,
and the product was obtained as a light green oil (98–100 °C/
0.1 mmHg, 5.3 g, 53%), containing 3-[2-(2-cyclohexylpro-
pyl)]indene (1e, ꢃ95%) and 1-[2-(2-cyclohexylpropyl)]indene
(1e0, ꢃ5%). Major isomer 1e: 1H NMR (400 MHz, 298 K, CDCl3): d
7.65 (d, J = 7.5 Hz, 1H, Ar–H), 7.46 (d, J = 7.5 Hz, 1H, Ar–H), 7.26
(pesudo-t, J = 7.5 Hz, 1H, Ar–H), 7.17 (pesudo-t, J = 7.5 Hz, 1H, Ar–
H), 6.17 (t, J = 2.1 Hz, 1H, 2-Ind–H), 3.28 (d, J = 2.1 Hz, 2H, 1-Ind–
H), 1.98 (m, 1H, Cy–CH), 1.78–1.57 (m, 5H, Cy–H), 1.28 (s, 6H,
C(CH3)2), 1.23–0.93 (m, 5H, Cy–H).
Following the procedure described for 2a, the light green oil
obtained above (0.9 g, 3.9 mmol), a solution of n-butyllithium in
n-hexane (2.4 M, 1.6 mL, 3.9 mmol), and 9-(2-bromoethyl)-fluo-
rene (1.0 g, 3.9 mmol) were reacted to give 1-(9-fluorenyl)-2-{1-
[3-(2-(2-cyclohexylpropyl))indenyl]}ethane (2e) as a colorless oil
(1.0 g, 65%), which was used directly in the next step without fur-
ther purification. 1H NMR (400 MHz, 298 K, CDCl3): d 7.75 (d,
J = 7.2 Hz, 1H, Ar–H), 7.74 (d, J = 7.2 Hz, 1H, Ar–H), 7.56 (d,
J = 7.6 Hz, 1H, Ar–H), 7.49 (d, J = 7.2 Hz, 1H, Ar–H), 7.44–7.26 (m,
5H, Ar–H), 7.24–7.18 (m, 2H, Ar–H), 7.12 (pesudo-t, J = 7.2 Hz, 1H,
Ar–H), 6.06 (d, J = 1.6 Hz, 1H, 2-Ind–H), 3.95 (t, J = 5.4 Hz, 1H, 9-
Flu–H), 3.28–3.21 (m, 1H, 1-Ind–H), 2.13–2.00 (m, 1H, Ind–CH2-
CH2–Flu), 2.00–1.80 (m, 2H, Ind–CH2CH2–Flu), 1.78–1.58 (m, 5H,
Cy–H), 1.40–1.30 (m, 1H, Ind–CH2CH2–Flu), 1.24 (s, 6H, C(CH3)2),
1.20–0.82 (m, 6H, Cy–H). 13C NMR (100 MHz, 298 K, CDCl3): d
152.3, 149.5, 147.3, 147.2, 144.0, 141.5, 141.4, 132.8, 127.14,
127.12, 127.05, 127.04, 126.0, 124.52, 124.48, 124.2, 123.2, 122.5,
120.03, 119.98, 47.9, 47.6, 44.3, 39.5, 29.4, 28.2, 28.0, 27.5, 27.2,
27.0, 24.5, 24.3.
Following the procedure described for 2a, the yellow oil
obtained above (2.2 g, 10 mmol), a solution of n-butyllithium in
n-hexane (2.4 M, 4.2 mL, 10 mmol), and 9-(2-bromoethyl)-fluorene
(2.7 g, 10 mmol), were reacted to give the product as a light yellow
oil (1.0 g, 34%), containing 1-(9-fluorenyl)-2-{1-[3-(2-methylben-
zyl)indenyl]}ethane (2d, ꢃ80%) and the isomer 2d0 (ꢃ20%) resulted
from wrong connection of ethylene bridge, which was used
directly in the next step without further purification. Major isomer
2d: 1H NMR (400 MHz, 298 K, CDCl3): d 7.73 (d, J = 7.5 Hz, 2H, Ar–
H), 7.44 (d, J = 7.2 Hz, 1H, Ar–H), 7.40–7.32 (m, 3H, Ar–H), 7.31–
7.27 (m, 5H, Ar–H), 7.25–7.14 (m, 5H, Ar–H), 5.80 (d, J = 1.8 Hz,
1H, 2-Ind–H), 3.94 (t, J = 5.6 Hz, 1H, 9-Flu–H), 3.80 (d, J = 2.0 Hz,
2H, CH2–Ph), 3.36–3.25 (m, 1H, 1-Ind–H), 2.30 (s, 3H, Ph–CH3),
2.15–2.05 (m, 1H, Ind–CH2CH2–Flu), 1.95–1.88 (m, 1H, Ind–CH2-
CH2–Flu), 1.67–1.57 (m, 1H, Ind–CH2CH2–Flu), 1.35–1.28 (m, 1H,
Ind–CH2CH2–Flu). 13C NMR (100 MHz, 298 K, CDCl3): d 148.3,
147.2, 147.1, 145.1, 142.2, 141.5, 141.4, 137.8, 136.8, 134.8,
130.4, 129.9, 127.1, 127.1, 126.6, 126.5, 126.2, 125.0, 124.5,
124.4, 123.1, 120.1, 120.0, 119.3, 48.9 (1-Ind–CH2), 47.5 (9-Flu–
CH), 32.2 (CH2–Ph), 29.5 (CH2CH2), 26.7 (CH2CH2), 19.7 (CH3–Ph).
Minor isomer 2d0: 1H NMR (400 MHz, 298 K, CDCl3): d7.74 (d,
J = 7.5 Hz, 2H, Ar–H), 7.44 (d, J = 7.2 Hz, 1H, Ar–H), 7.37–7.33 (m,
4H, Ar–H), 7.25–7.14 (m, 4H, Ar–H), 7.04 (d, J = 7.2 Hz, 1H, Ar–H),
7.00–6.90 (m, 2H, Ar–H), 6.89–6.81 (m, 1H, Ar–H), 6.70 (d,
J = 7.6 Hz, 1H, Ar–H), 6.60 (d, J = 5.4 Hz, 1H, 3-Ind–H), 6.18 (d,
J = 5.4 Hz, 1H, 2-Ind–H), 3.94–3.90 (m, 1H, 9-Flu–H), 2.92 (d,
J = 13.6 Hz, 1H, CH2–Ph), 2.75 (d, J = 13.6 Hz, 1H, CH2–Ph), 2.15–
2.05 (m, 1H, Ind–CH2CH2–Flu), 2.03 (s, 3H, Ph–CH3), 1.95–1.88
(m, 1H, Ind–CH2CH2–Flu), 1.67–1.57 (m, 1H, Ind–CH2CH2–Flu),
1.35–1.28 (m, 1H, Ind–CH2CH2–Flu).
Following the procedure described for 3a, 2e (0.9 g, 2.1 mmol), a
solution of n-butyllithium in n-hexane (2.4 M, 1.8 mL, 4.2 mmol),
and ZrCl4 (0.50 g, 2.1 mmol) were reacted to give 3e as red primatic
crystals (0.20 g, 16%). 1H NMR (400 MHz, 298 K, CDCl3): d 8.01 (d,
J = 8.5 Hz, 1H, Ar–H), 7.90 (d, J = 8.4 Hz, 1H, Ar–H), 7.83 (d,
J = 8.5 Hz, 1H, Ar–H), 7.77 (d, J = 8.4 Hz, 1H, Ar–H), 7.66–7.58 (m,
2H, Ar–H), 7.54 (d, J = 8.6 Hz, 1H, Ar–H), 7.40 (pesudo-t, J = 7.6 Hz,
1H, Ar–H), 7.29 (pesudo-t, J = 6.8 Hz, 1H, Ar–H), 7.17–7.01 (m, 3H,
Ar–H), 5.92 (s, 1H, 2-Ind–H), 4.60 (m, 1H, IndCH2CH2Flu), 4.08
(m, 1H, IndCH2CH2Flu), 4.03–3.92 (m, 2H, IndCH2CH2Flu), 1.71 (t,
J = 12.0 Hz, 2H, Cy–H), 1.54 (s, 3H, C(CH3)2), 1.51–1.29 (m, 3H,
Cy–H), 1.11 (s, 3H, C(CH3)2), 1.09–1.02 (m, 1H, Cy–H), 1.00–0.80
(m, 2H, Cy–H), 0.72 (ddt, J = 25.6 Hz, 12.8 Hz, 3.6 Hz, 1H, Cy–H),
0.59 (ddd, J = 24.7 Hz, 12.3 Hz, 3.2 Hz, 1H, Cy–H), 0.30–0.19 (m,
1H, Cy–H). 13C NMR (100 MHz, 298 K, CDCl3): d 130.5, 129.4,
128.8, 128.0, 127.9, 127.0, 126.5, 126.2, 125.6, 125.5, 125.3,
125.3, 125.1, 125.0, 124.3, 123.9, 123.5, 123.2, 121.5, 121.0,
116.9, 103.8, 49.0, 40.4, 31.8, 30.2, 28.2, 27.6, 27.3, 27.2, 26.8,
25.5, 20.2. Anal. Calc. for C33H34Cl2ZrꢁCH2Cl2: C, 60.26; H, 5.35.
Found: C, 59.52; H, 5.54%. HR-MS (EI, m/z) for C33H34Cl2Zr: Calcd.,
590.1085; Found, 590.1079.
Following the procedure described for 3a, the yellow oil
obtained above (1.0 g, 1.9 mmol of 2d), a solution of n-butyllithium
in n-hexane (2.4 M, 2.0 mL, 4.8 mmol), and ZrCl4 (0.56 g, 2.4 mmol)
were reacted to give 3d as red solids (0.21 g, 16%). 1H NMR
(400 MHz, 298 K, CDCl3): d 7.99 (d, J = 8.4 Hz, 1H, Ar–H), 7.89 (d,
J = 8.4 Hz, 1H, Ar–H), 7.70 (d, J = 8.4 Hz, 2H, Ar–H), 7.66 (d,
J = 8.4 Hz, 1H, Ar–H), 7.59 (pesudo-t, J = 7.6 Hz, 1H, Ar–H), 7.39 (d,
J = 8.4 Hz, 1H, Ar–H), 7.35 (d, J = 8.3 Hz, 1H, Ar–H), 7.25–7.22 (m,
2H, Ar–H), 7.12–6.96 (m, 5H, Ar–H), 6.66 (d, J = 7.5 Hz, 1H, Ar–H),
5.89 (s, 1H, 2-Ind–CH), 4.36–4.26 (m, 1H, Ind–CH2CH2–Flu), 4.24–
4.07 (m, 1H, Ind–CH2CH2–Flu), 4.05–3.97 (m, 1H, Ind–CH2CH2–
Flu), 3.95 (d, J = 5.7 Hz, 2H, Ph–CH2–), 3.90–3.82 (m, 1H, Ind–CH2-
CH2–Flu), 2.18 (s, 3H, Ph–CH3). 13C NMR (100 MHz, 298 K, CDCl3):
d 138.9, 136.6, 130. 2, 128.9, 128. 9, 128.8, 128.1, 127.5, 126.5,
126.4, 126.3, 126.0, 125.8, 125.7, 125.6, 125.5, 125.3, 124.9,
124.1, 123.7, 122.9, 122.7, 122.1, 121.1, 120.9, 114.6, 104.0, 31.5
(CH2–Ph), 30.1 (CH2CH2), 29.5 (CH2CH2), 20.0 (CH3–Ph). Anal. Calc.
for C32H26Cl2Zrꢁ0.8CH2Cl2: C, 61.49; H, 4.34. Found: C, 61.76; H,
4.87%. HR-MS (EI, m/z) for C32H26Cl2Zr: Calcd., 570.0459; Found,
570.0450.
2.2.5. Synthesis of ethylene-1-(9-fluorenyl)-2-{1-[3-(2-(2-
cyclohexylpropyl))indenyl]} zirconium dichloride (3e)
2.2.6. Synthesis of ethylene-1-(9-fluorenyl)-2-{1-[3-(2-(2-(1-
cyclohexenyl)propyl))indenyl]} zirconium dichloride (3f)
A mixture of lithium (2.0 g, 0.13 mol), toluene (200 mL), and a
small amount of glass cullet was cooled to 0 °C. After
A mixture of lithium (1.2 g, 0.17 mol), Et2O (30 mL), and a small
amount of glass cullet was cooled to 0 °C. After 1-chlorocyclohex-

Y. Wang et al. / Polyhedron 76 (2014) 81–93
85
ene (8.0 g, 69 mmol) was added dropwise, the mixture was
warmed to room temperature slowly and stirred for 8 h, and then
stood for 24 h. After filtration, the solution was titrated with stan-
dard HCl solution, and the yield of resultant 1-cyclohexenyllithium
was 51%. The obtained solution was cooled to 0 °C, and a solution
of 6,6-dimethylbenzofulvene (5.5 g, 35 mmol) in 10 mL of Et2O was
added dropwise. The mixture was warmed to room temperature
slowly and stirred for 2 days. After being hydrolyzed with 50 mL
of aqueous ammonium chloride, the organic phase was separated,
and the aqueous layer was extracted with Et2O. The combined
organic phases were dried over anhydrous MgSO4 and evaporated.
The residue was purified via a silica gel column chromatography
with petroleum ether as the eluent to afford an orange oil (1.2 g,
14%), containing 3-{2-[2-(1-cyclohexenyl)propyl]}indene (1f,
ꢃ85%) and 1-{2-[2-(1-cyclohexenyl)propyl]}indene (1f0, ꢃ15%).
Major isomer 1f: 1H NMR (400 MHz, 298 K, CDCl3): d 7.52 (d,
J = 7.6 Hz, 1H, Ar–H), 7.42 (d, J = 7.6 Hz, 1H,Ar–H), 7.21 (pesudo-t,
J = 7.6 Hz, 1H, Ar–H), 7.14 (pesudo-t, J = 7.6 Hz, 1H, Ar–H), 6.27 (s,
1H, 2-Ind–CH), 5.78–5.72 (m, 1H, cyclohexenyl–C@CH), 3.30 (s,
2H, 1-Ind–CH2), 2.16–2.07 (m, 2H, cyclohexenyl–H), 1.84–1.74
(m, 2H, cyclohexenyl–H), 1.53–1.45 (m, 4H, cyclohexenyl–H),
1.41 (s, 6H, C(CH3)2).
NMR (100 MHz, 298 K, CDCl3): d 143.1, 130.5, 127.7, 126.4, 125.6,
125.2, 125.1, 124.3, 124.0, 123.8, 123.6, 123.0, 122.1, 120.6,
120.3, 117.9, 117.3, 102.5, 40.7, 31.2, 29.0, 25.2, 24.3, 23.7, 23.6,
22.2, 21.3. Anal. Calc. for C33H32Cl2ZrꢁCH2Cl2: C, 60.44; H, 5.07.
Found: C, 60.91; H, 5.39%. HR-MS (EI, m/z) for C33H32Cl2Zr: Calcd.,
588.0928; Found, 588.0930.
2.2.7. Synthesis of ethylene-1-(9-fluorenyl)-2-{1-[3-(2-
(2-nbutylpropyl))indenyl]} zirconium dichloride (3g)
To a solution of n-butyllithium in n-hexane (2.4 M, 26.7 mL,
64.0 mmol) and Et2O (30 mL), a solution of 6,6-dimethylbenzoful-
vene (10 g, 64 mmol) in 30 mL of Et2O was added dropwise at 0 °C.
The mixture was warmed to room temperature slowly and stirred
overnight. After being hydrolyzed with 50 mL of aqueous ammo-
nium chloride, the organic phase was separated, and the aqueous
layer was extracted with Et2O. The combined organic phases were
dried over anhydrous MgSO4 and evaporated. The residue was
purified via a silica gel column chromatography with petroleum
ether as eluent to afford 3-[2-(2-nbutylpropyl)]indene (1g) as an
orange oil (6.6 g, 46%). 1H NMR (400 MHz, 298 K, CDCl3): d 7.64
(d, J = 7.5 Hz, 1H, Ar–H), 7.47 (d, J = 7.4 Hz, 1H, Ar–H), 7.27
(pesudo-t, J = 7.5 Hz, 1H, Ar–H), 7.18 (pesudo-t, J = 7.4 Hz, 1H, Ar–
H), 6.19 (t, J = 2.1 Hz, 1H, 2-Ind–CH), 3.31 (d, J = 2.1 Hz, 2H, 1-
Ind–CH2), 1.81–1.74 (m, 2H, –CH2CH2CH2CH3), 1.34 (s, 6H,
C(CH3)2), 1.27–1.18 (m, 2H, –CH2CH2CH2CH3), 1.17–1.06 (m, 2H,
–CH2CH2CH2CH3), 0.83 (t, J = 7.3 Hz, 3H, –CH2CH2CH2CH3).
Following the procedure described for 2a, the obtained orange oil
(1.0 g, 4.2 mmol), a solution of n-butyllithium in n-hexane (2.4 M,
1.8 mL, 4.2 mmol), and 9-(2-bromoethyl)-fluorene (1.1 g,
4.2 mmol), were reacted to afford a colorless oil (1.0 g, 55%), contain-
ing
1-(9-fluorenyl)-2-{1-[3-(2-(2-(1-cyclohexenyl)propyl))inde-
Following the procedure described for 2a, 1g (1.5 g, 7.0 mmol),
a solution of n-butyllithium in n-hexane (2.4 M, 2.9 mL, 7.0 mmol),
and 9-(2-bromoethyl)-fluorene (1.5 g, 7.0 mmol) were reacted to
give 1-(9-fluorenyl)-2-{1-[3-(2-(2-nbutylpropyl))indenyl]}ethane
(2g) as a yellow oil (1.9 g, 40%), which was used directly in the next
step without further purification. 1H NMR (400 MHz, 298 K,
CDCl3): d 7.75 (d, J = 7.3 Hz, 1H, Ar–H), 7.74 (d, J = 7.3 Hz, 1H, Ar–
H), 7.55 (d, J = 7.3 Hz, 1H, Ar–H), 7.50 (d, J = 7.3 Hz, 1H, Ar–H),
7.43–7.27 (m, 5H, Ar–H), 7.25–7.19 (m, 2H, Ar–H), 7.13 (t,
J = 7.3 Hz, 1H, Ar–H), 6.06 (d, J = 2.0 Hz, 1H, 2-Ind–H), 3.95 (t,
J = 5.6 Hz, 1H, 9-Flu–H), 3.26 (pesudo-td, J = 6.4 Hz, 2.0 Hz, 1H, 1-
Ind–H), 2.15–2.05 (m, 1H, Ind–CH2CH2–Flu), 1.95–1.83 (m, 1H,
Ind–CH2CH2–Flu), 1.82–1.63 (m, 3H, –CH2CH2CH2CH3 + Ind–CH2-
CH2–Flu), 1.42–1.02 (m, 5H, –CH2CH2CH2CH3 + Ind–CH2CH2–Flu),
1.31 (s, 3H, C(CH3)2), 1.30 (s, 3H, C(CH3)2), 0.80 (t, J = 7.2 Hz, 3H,
–CH2CH2CH2CH3). 13C NMR (100 MHz, 298 K, CDCl3): d 144.4,
131.7, 129.0, 127.6, 126.9, 126.40, 126.37, 126.29, 126.1, 125.6,
125.3, 125.0, 124.9, 124.2, 123.3, 121.9, 121.5, 119.2, 118.6,
103.8, 42.0, 32.5, 30.4, 26.5, 25.5, 25.0, 24.9, 23.5, 22.5.
nyl]}ethane (2f, ꢃ92%) and the isomer 2f0 (ꢃ8%) resulted from a
wrong connection of ethylene bridge, which was used directly in
the next step without further purification. Major isomer 2f: 1H
NMR (400 MHz, 298 K, CDCl3): d 7.75 (d, J = 7.3, Hz, 1H, Ar–H),
7.74 (d, J = 7.3 Hz, 1H, Ar–H), 7.49 (d, J = 7.3 Hz, 1H, Ar–H), 7.44–
7.09 (m, 9H, Ar–H), 6.15 (d, J = 2.0 Hz, 1H, 2-Ind–CH), 5.75–5.71
(m, 1H, cyclohexenyl–C@CH), 3.95 (t, J = 5.6 Hz, 1H, 9-Flu–CH),
3.35–3.25 (m, 1H, 1-Ind–CH), 2.14–2.06 (m, 2H, cyclohexenyl–H),
2.06–2.00(m, 1H, Ind–CH2CH2–Flu), 1.94–1.82(m, 1H, Ind–CH2CH2–
Flu), 1.80–1.74 (m, 2H, cyclohexenyl–H), 1.76–1.64 (m, 1H, Ind–CH2-
CH2–Flu), 1.56–1.45 (m, 4H, cyclohexenyl–H), 1.44–1.32 (m, 1H,
Ind–CH2CH2–Flu), 1.39 (s, 3H, CH3), 1.37 (s, 3H, CH3). 13C NMR
(100 MHz, 298 K, CDCl3): d 151.1, 148.9, 147.3, 147.3, 144.4, 143.1,
141.5, 141.4, 132.3, 127.1, 127.1, 126.0, 124.53, 124.51, 124.3,
122.9, 122.03, 119.99, 119.88, 48.0, 47.6, 41.4, 29.3, 27.7, 27.21,
27.15, 25.9, 25.5, 23.6, 22.7. Minor isomer 2f0: 1H NMR (400 MHz,
298 K, CDCl3): d 7.80–7.02 (m, 12H, Ar–H), 6.76 (d, J = 5.4 Hz, 1H,
3-Ind–CH), 6.22 (d, J = 5.4 Hz, 1H, 2-Ind–CH), 4.83 (s, 1H, cyclohexe-
nyl–HC = CH), 4.78 (t, J = 1.2 Hz, 1H, cyclohexenyl–HC = CH), 3.86 (t,
J = 5.3 Hz, 1H, 9-Flu–CH), 3.77–3.69 (m, 1H, cyclohexenyl–H), 2.14–
0.83 (m, 11H, Ind–CH2CH2–Flu + cyclohexenyl–H), 1.39 (s, 3H, CH3),
1.37 (s, 3H, CH3).
Following the procedure described for 3a, 2g (1.5 g, 4.0 mmol),
a solution of n-butyllithium in n-hexane (2.4 M, 3.3 mL, 8.0 mmol),
and ZrCl4 (0.9 g, 4.0 mmol) were reacted to give 3g as red solids
(0.60 g, 26%). 1H NMR (400 MHz, 298 K, CDCl3):
d 8.04 (d,
Following the procedure described for 3a, the colorless oil
obtained above (1.2 g, 2.6 mmol of 2f), a solution of n-butyllithium
in n-hexane (2.4 M, 2.3 mL, 5.6 mmol), and ZrCl4 (0.7 g, 2.8 mmol)
were reacted to give 3f as red solids (0.16 g, 10%). 1H NMR
(400 MHz, 298 K, CDCl3): d 8.15–8.09 (m, 1H, Ar–H), 7.91 (d,
J = 8.5 Hz, 1H, Ar–H), 7.87 (d, J = 8.5 Hz, 1H, Ar–H), 7.78 (d,
J = 8.4 Hz, 1H, Ar–H), 7.66 (pesudo-t, J = 7.6 Hz, 1H, Ar–H), 7.53 (d,
J = 8.5 Hz, 1H, Ar–H), 7.50–7.40 (m, 2H, Ar–H), 7.30 (pesudo-t,
J = 7.6 Hz, 1H, Ar–H), 7.14–7.05 (m, 3H, Ar–H), 6.02 (s, 1H, 2-Ind–
H), 5.51 (t, J = 3.6 Hz, 1H, cyclohexene–C@CH), 4.78–4.65 (m, 1H,
Ind–CH2CH2–Flu), 4.26–4.10 (m, 1H, Ind–CH2CH2–Flu), 4.03–3.90
(m, 2H, Ind–CH2CH2–Flu), 2.04–1.90 (m, 2H, cyclohexenyl–H),
1.66 (s, 3H, C(CH3)2), 1.63–1.58 (m, 1H, cyclohexenyl–H), 1.43–
1.21 (m, 3H, cyclohexenyl–H), 1.34 (s, 3H, C(CH3)2), 1.17–1.05 (m,
1H, cyclohexenyl–H), 0.76–0.64 (m, 1H, cyclohexenyl–H). 13C
J = 8.8 Hz, 1H, Ar–H), 7.90 (d, J = 8.4 Hz, Ar–H), 7.83 (d, J = 8.8 Hz,
1H, Ar–H), 7.77 (d, J = 8.4 Hz, 1H, Ar–H), 7.66–6.57 (m, 2H, Ar–H),
7.53 (d, J = 8.8 Hz, 1H, Ar–H), 7.40 (pesudo-t, J = 7.6 Hz, 1H, Ar–H),
7.29 (pesudo-t, J = 7.6 Hz, 1H, Ar–H), 7.15–7.04 (m, 3H, Ar–H),
6.21 (s, 1H, 2-Ind–CH), 4.70–4.55 (m, 1H, Ind–CH2CH2–Flu), 4.18–
4.05 (m, 1H, Ind–CH2CH2–Flu), 4.03–3.93 (m, 2H, Ind–CH2CH2–
Flu), 1.63 (td, J = 12.7 Hz, 4.5 Hz, 1H, –CH2CH2CH2CH3), 1.45 (s,
3H, C(CH3)2), 1.38 (td, J = 13.1, 3.5 Hz, 1H, –CH2CH2CH2CH3), 1.23
(s, 3H, C(CH3)2), 1.13–0.92 (m, 3H, –CH2CH2CH2CH3), 0.68 (t,
J = 7.0 Hz, 3H, –CH2CH2CH2CH3), 0.50–0.36 (m, 1H, –CH2CH2CH2-
CH3). 13C NMR (100 MHz, 298 K, CDCl3): d 129.7, 129.5, 128.9,
127.9, 127.8, 126.6, 126.5, 126.1, 125.8, 125.6, 125.3, 125.1,
125.0, 124.3, 123.9, 123.5, 123.3, 121.6, 121.4, 116.5, 103.7, 44.1,
37.3, 31.9, 30.2, 27.5, 26.7, 25.5, 23.2, 14.1. Anal. Calc. for C31H32Cl2-
Zrꢁ0.07CH2Cl2: C, 65.16; H, 5.66. Found: C, 64.95; H, 5.80%.

86
Y. Wang et al. / Polyhedron 76 (2014) 81–93
2.2.8. Synthesis of ethylene-1-(9-fluorenyl)-2-[1-(3-
2-Ind–H), 3.97 (t, J = 5.5 Hz, 1H, 9-Flu–H), 3.29 (pesudo-t,
cyclohexylindenyl)] zirconium dichloride (3h)
J = 6.3 Hz, 1H, 1-Ind–H), 2.89 (Sept, J = 6.8 Hz, 1H, CH(CH3)2),
2.18–2.06 (m, 1H, Ind–CH2CH2–Flu), 2.00–1.88 (m, 1H, Ind–CH2-
CH2–Flu), 1.76–1.64 (m, 1H, Ind–CH2CH2–Flu), 1.45–1.30 (m, 1H,
Ind–CH2CH2–Flu), 1.28 (d, J = 6.8 Hz, 3H, CH(CH3)2), 1.25 (d,
J = 6.8 Hz, 3H, CH(CH3)2). 13C NMR (100 MHz, 298 K, CDCl3): d
150.4, 148.6, 147.3, 147.2, 144.8, 141.4, 141.3, 130.3, 127.1,
127.0, 126.9, 126.3, 124.7, 124.53, 124.50, 123.1, 120.0, 119.9,
119.6, 48.7, 47.6, 29.7, 27.1, 27.1, 22.2, 22.1.
To a solution of indene (5.0 g, 43 mmol) in 30 mL of dry THF at
0 °C was added dropwise a solution of n-butyllithium in n-hexane
(2.4 M, 18.0 mL, 43.0 mmol). The reaction mixture was stirred
overnight at room temperature and then added dropwise to a solu-
tion of chlorocyclohexane (5.8 g, 49.0 mmol) in 30 mL of THF at
0 °C. After 2 h, the reaction mixture was hydrolyzed with 50 mL
of aqueous NH4Cl. The organic phase was separated, and the aque-
ous layer was extracted with Et2O. The combined organic phases
were dried over anhydrous MgSO4 and evaporated. The residue
was distilled under reduced pressure to give a colorless oil (92–
96 °C/5 mmHg, 3.8 g, 44%), containing 3-cyclohexylindene (1h,
ꢃ90%) and 1-cyclohexylindene (1h0, 10%). Major isomer 1h: 1H
NMR (400 MHz, 298 K, CDCl3): d 7.46 (d, J = 7.5 Hz, 1H, Ar–H),
7.41 (d, J = 7.5 Hz, 1H, Ar–H), 7.29 (pesudo-t, J = 7.5 Hz, 1H, Ar–H),
7.19 (pesudo-t, J = 7.5 Hz, 1H, Ar–H), 6.20–6.15 (m, 1H, 2-Ind–H),
3.32–3.28 (m, 2H, 1-Ind–H), 2.58 (m, 1H, Cy–CH), 2.10–2.00 (m,
2H, Cy–H), 1.91–1.73 (m, 3H, Cy–H), 1.50–1.20 (m, 5H, Cy–H).
Following the procedure described for 2a, the obtained colorless
oil (1.9 g, 9.8 mmol), a solution of n-butyllithium in n-hexane
(2.4 M, 4.1 mL, 9.8 mmol), and 9-(2-bromoethyl)-fluorene (2.7 g,
9.8 mmol) were reacted to give 1-(9-fluorenyl)-2-[1-(3-cyclo-
hexylindenyl)]ethane (2h) as a white solid (1.1 g, 31%), which
was used directly in the next step without further purification.
1H NMR (400 MHz, 298 K, CDCl3): d 7.74 (d, J = 7.2 Hz, 2H, Ar–H),
7.56 (d, J = 7.2 Hz, 1H, Ar–H), 7.49 (d, J = 7.2 Hz, 1H, Ar–H), 7.44–
7.26 (m, 6H, Ar–H), 7.24–7.18 (m, 1H, Ar–H), 7.12 (pesudo-t,
J = 7.4 Hz, 1H, Ar–H), 6.06 (s, 1H, 2-Ind–H), 3.95 (t, J = 5.4 Hz, 1H,
9-Flu–H), 3.25 (t, J = 5.4 Hz, 1H, 1-Ind–H), 2.50 (t, J = 10.6 Hz, 1H,
Cy–CH), 2.17–1.60 (m, 8H, Ind–CH2CH2–Flu + Cy–H), 1.50–1.20
(m, 6H, Cy–H). 13C NMR (100 MHz, 298 K, CDCl3): d 149.5, 148.5,
147.3, 147.3, 144.9, 141.5, 141.4, 130.6, 127.1, 127.07, 127.05,
126.3, 124.7, 124.6, 124.54, 124.52, 123.1, 120.02, 119.99, 119.4,
48.8, 47.6, 37.1, 32.8, 29.7, 27.1, 26.9, 26.8.
Following the procedure described for 3a, 2i (1.2 g, 3.4 mmol), a
solution of n-butyllithium in n-hexane (2.4 M, 2.9 mL, 6.8 mmol),
and ZrCl4 (0.8 g, 3.4 mmol) were reacted to give 3i as red solids
(0.22 g, 13%). 1H NMR (400 MHz, 298 K, CDCl3):
d 7.96 (d,
J = 8.4 Hz, 1H, Ar–H), 7.90 (d, J = 8.4 Hz, 1H, Ar–H), 7.76 (d,
J = 8.4 Hz, 1H, Ar–H), 7.70 (d, J = 8.4 Hz, 1H, Ar–H), 7.50 (pesudo-t,
J = 7.2 Hz, 1H, Ar–H), 7.46–7.27 (m, 5H, Ar–H), 7.08–6.99 (m, 2H,
Ar–H), 6.32 (s, 1H, 2-Ind–H), 4.32–4.22 (m, 1H, IndCH2CH2Flu),
4.19–4.08 (m, 1H, IndCH2CH2Flu), 4.07–3.99 (m, 1H, IndCH2CH2-
Flu), 3.75–3.66 (m, 1H, IndCH2CH2Flu), 3.22 (Sept, J = 6.8 Hz, 1H,
HC(CH3)2), 1.09 (d, J = 6.8 Hz, 3H, HC(CH3)2), 0.96 (d, J = 6.8 Hz,
3H, HC(CH3)2). 13C NMR (100 MHz, 298 K, CDCl3): d 132.5, 129.2,
128.4, 128.3, 127.0, 126.8, 125.8, 125.5, 125.39, 125.36, 125.1,
125.0, 124.5, 123.9, 123.2, 122.9, 122.7, 122.2, 120.6, 119.5,
108.9, 104.3, 29.2, 28.2, 27.7, 24.0, 20.3. Anal. Calc. for C27H24Cl2-
Zrꢁ0.5CH2Cl2: C, 59.72; H, 4.56. Found: C, 60.19; H, 4.84%. HR-MS
(EI, m/z) for C27H24Cl2Zr: Calcd., 508.0302; Found, 508.0304.
2.3. X-ray crystallography
Suitable crystals of complexes 3e and 3h for X-ray diffraction
analysis were obtained from a saturated dichloromethane solution
at ꢂ20 °C, respectively. Diffraction data were collected on a Bruker
AXSD 8 diffractometer with graphite-monochromated Mo K
a
(k = 0.71073 Å) radiation. All data were collected at 20 °C using
the -scan techniques. All structures were solved by direct meth-
x
Following the procedure described for 3a, 2h (1.3 g, 3.3 mmol),
a solution of n-butyllithium in n-hexane (2.4 M, 2.8 mL, 6.6 mmol),
and ZrCl4 (0.3 g, 3.3 mmol) were reacted to give 3h as red crystals
(0.60 g, 26%). 1H NMR (400 MHz, 298 K, CDCl3): d 7.97 (d, J = 8.4 Hz,
1H, Ar–H), 7.90 (d, J = 8.4 Hz, 1H, Ar–H), 7.75 (d, J = 8.4 Hz, 1H, Ar–
H), 7.67 (d, J = 8.4 Hz, 1H, Ar–H), 7.51 (pesudo-t, J = 7.6 Hz, 1H, Ar–
H), 7.46–7.41 (m, 1H, Ar–H), 7.37 (dd, J = 15.8 Hz, 8.3 Hz, 2H, Ar–H),
7.31 (pesudo-t, J = 7.6 Hz, 2H, Ar–H), 7.07–6.97 (m, 2H, Ar–H), 6.29
(s, 1H, 2-Ind–H), 4.32–4.21 (m, 1H, IndCH2CH2Flu), 4.18–4.00 (m,
2H, IndCH2CH2Flu), 3.73–3.64 (m, 1H, IndCH2CH2Flu), 2.88 (t,
J = 7.6 Hz, 1H, Cy–H), 2.00 (d, J = 12.8 Hz, 1H, Cy–H), 1.78–1.64
(m, 3H, Cy–H), 1.50 (d, J = 12.0 Hz, 1H, Cy–H), 1.43–1.26 (m, 2H,
Cy–H), 1.26–1.08 (m, 2H, Cy–H), 0.94 (ddd, J = 25.2 Hz, 12.4 Hz,
2.8 Hz, 1H, Cy–H). 13C NMR (100 MHz, 298 K, CDCl3): d 131.6,
129.2, 128.4, 128.2, 126.9, 126.8, 125.8, 125.34, 125.30, 125.1,
125.0, 124.7, 123.8, 123.3, 122.9, 122.7, 122.2, 120.6, 119.7,
109.3, 104.3, 37.6, 34.9, 30.6, 29.2, 28.3, 27.0, 26.8, 26.5. Anal. Calc.
for C30H28Cl2Zrꢁ0.01CH2Cl2: C, 65.35; H, 5.12. Found: C, 64.79; H,
5.20%.
ods and refined using Fourier techniques. An absorption correction
based on SADABS was applied [18]. All non-hydrogen atoms were
refined by full-matrix least-squares on F2 using the SHELXTL program
package [19]. Hydrogen atoms were located and refined by the
geometry method. The cell refinement, data collection, and reduc-
tion were done by Bruker SAINT. The structure solution and refine-
ment were performed by SHELXS-97 [20] and SHELXL-97 [21],
respectively. Molecular structures were generated using ORTEP-3
for windows (v. 2.00) [22].
2.4. General procedure for propylene dimerization or polymerization
A 100 mL stainless steel reactor equipped with a magnetic
stirrer was heated under vacuum for 1 h over 100 °C, then
allowed to be cooled to the required temperature under propyl-
ene atmosphere, and then charged with 20 mL of toluene. The
reactor was sealed and pressurized to 6 bar of propylene pres-
sure. After being stirred for about 30 min to ensure that the solu-
tion was equilibrated and the required reaction temperature was
established, the pressure was then released. Proper amount of
2.2.9. Synthesis of ethylene-1-(9-fluorenyl)-2-{1-[3-(2-
MAO in toluene and zirconocene complex (1.25 lmol) in 1 mL
propyl)indenyl]} zirconium dichloride (3i)
of toluene were added sequentially. The reactor was sealed and
pressurized to required propylene pressure. After the reaction
was carried out for 30 min, the reactor was cooled rapidly by
an ice-salt bath to quench the further reaction and avoid any lose
of possible low boiling point fraction. When the reactor was com-
pletely cooled down, the pressure was released and 1 mL of
methanol was injected immediately. 0.20 mL of heptane was
added as an internal standard. An aliquot of the reaction solution
was withdrawn, filtered and then analyzed by GC. The residual
solution was quenched by the addition of 3% HCl–ethanol and
Following the procedure described for 2a, 3-isopropylindene
(1i) (3.0 g, 19 mmol), a solution of n-butyllithium in n-hexane
(2.4 M, 7.9 mL, 19 mmol), and 9-(2-bromoethyl)-fluorene (4.0 g,
19 mmol), were reacted to give 1-(9-fluorenyl)-2-{1-[3-(2-pro-
pyl)indenyl]}ethane (2i) as a white solid (4.4 g, 82%), which was
used directly in the next step without further purification. 1H
NMR (400 MHz, 298 K, CDCl3): d 7.82–7.68 (m, 2H, Ar–H), 7.51
(d, J = 7.3 Hz, 1H, Ar–H), 7.43 (d, J = 7.3 Hz, 1H, Ar–H), 7.40–7.27
(m, 7H, Ar–H), 7.16 (pesudo-t, J = 7.2 Hz, 1H, Ar–H), 6.09 (s, 1H,

Y. Wang et al. / Polyhedron 76 (2014) 81–93
87
R
washed three times with water. After evaporation of all the sol-
vents of the solution, the resultant residue was vacuum dried
at 60 °C for 16 h. The gas chromatography equipped with a flame
ionization detector was used for the measurement of selectivity.
The yield of oligomers was calculated by referring to the mass
of the heptane which was added quantitatively as an internal
standard, on the basis of the prerequisite that the mass of each
fraction was approximately proportional to its integrated areas
in the GC trace.
Hydrolysis
R
RM
M = Li or MgCl
1a-1c, 1e-1g
(1) nBuLi
(2)
2a
2b
R = 4-methylphenyl
R = 3,5-dimethylphenyl
2c R = benzyl
Br
2e
R = Cy
2f R = 1-cyclohexenyl
2g
R = nBu
3. Results and discussion
Scheme 1. Synthesis of proligands 2a–c and 2e–g.
3.1. Synthesis and structural characterization of zirconocene
complexes
R
nBuLi
R
X
As illustrated in Schemes 1 and 2, substituted indenes 1a–i
were synthesized via two methods: (1) the reaction of 6,6-diph-
enylbenzofulven with proper lithium or magnesium agent; (2)
the reaction of indenyllithium with corresponding alkylchloride.
Then, the lithium salts of these indenes were reacted with 9-(2-
bromoethyl)-fluorene to give the proligands 2a–i in moderate to
high yields of 31–82% as pale yellow/green or colorless oil. It
should be noted that during the synthesis of 2d, one isomer
denoted as 2d0, likely resulted from a wrong connection of ethylene
bridge, could also be detected via 1H NMR spectroscopy in a certain
amount of 20% (Fig. 1). Due to the lack of an active proton in the
indenyl ring, this isomer could not generate the target zirconcene
complex. Unfortunately, further purification by column chroma-
tography was unsuccessful due to the quite similar polarity of 2d
and 2d0. Same type of isomers was also observed in the synthesis
of 2f and 2i.
Zirconocene complexes 3a–i were prepared according to the
standard salt metathesis reactions between ZrCl4 and dilithium
salts of the proligands [13] as shown in Scheme 3, and were
obtained as red powders or crystals after recrystallization from
dichloromethane solutions. All these complexes were character-
ized by NMR spectroscopy and elemental analysis or high resolu-
tion mass spectroscopy.1 The 1H NMR spectra of 3a–i exhibit a
single set of resonances, consistent with the C1-symmetric structure
of these bridged indenyl–fluorenyl zirconium complexes. Single
crystals of complexes 3e and 3h suitable for X-ray diffraction analy-
sis were obtained at ꢂ20 °C from saturated CH2Cl2 solutions. The
unit cells of both C1-symmetric complexes are composed of pairs
of enantiomers. Their molecular structures are shown in Figs. 2
and 3. The solid-state molecular structures of 3e and 3h exhibit
essentially similar geometrical parameters with the previously
reported complex 1 which bears a pendant phenyl group (Table 1).
X=Cl or Br
1d 1h 1i
,
,
R
(1)nBuLi
(2)
2d
R = o-methylbenzyl
R = Cy
R = 2-Pr
2h
2i
Br
Scheme 2. Synthesis of proligands 2d, 2h and 2i.
3.2. Propylene dimerization by zirconocene complexes with pendant
aryl group
As reported in our previous work [14], complexes 1 and 2 bear-
ing a sterically bulky substituent on the 3-position of indenyl ring
exhibited moderate activities for propylene dimerization to give 2-
methyl-1-pentene with high selectivities at 100 °C. However, it
was also reported that some ansa-zirconocene complexes bearing
bulky substituents, such as {C2H4-1-(9-C13H8)-2-[1-(3-tBu)C9H5]}-
ZrCl2 [13c], {Me2C[3-(2-CH3-2-adamantyl)C5H3](9-C13H8)}ZrCl2
[13d], could polymerize propylene to high molecular weight poly-
mers. These entirely different results declared that the steric bulk-
iness of the substituent on the 3-position of indenyl ring might not
be the key factor accounting for the dimerization activity and
selectivity of 1 and 2. Hessen and coworkers [23,24] ever reported
highly selective ethylene trimerization catalyzed by half-sandwich
titanium complexes with similar substituent, for instance, [(C6H5)-
C(CH3)2(C5H4)]TiCl3. Based on extensive NMR spectroscopic studies
and DFT calculation they suggested that a hemilable coordination
effect of the pendant aryl group to the titanium center should be
responsible for the trimerization selectivity. Furthermore, Green
and co-workers [25] proved that an agostic effect between the
ortho-proton of the pendant phenyl ring and the metal center does
exist in the corresponding cationic species generated from the 16-
electron zirconocene complex {Cp[(C6H5)C(CH3)2(C5H4)]}ZrCl2. Is it
possible that the propylene dimerization selectivity of complexes 1
and 2 might be due to a plausible agostic effect between metal cen-
ter and the pendant phenyl group? However, one conflicting aspect
is that complexes 1 and 2 only exhibit dimerization activity at
100 °C or above, and no product could be obtained at or below
90 °C. This temperature is much higher than ꢂ60 °C at which the
mentioned coordination effect could be detected [26]. This embar-
rassing result promoted us to pursue a more reasonable explana-
tion for the highly selective propylene dimerization obtained by
these complexes.
Correspondingly, the Zr–CentInd and Zr–CentFlu distances,
a and b
angles are almost identical in these molecules. However, by compar-
ing the data listed in Table 1, we do find that the substituent on the
indenyl ring has somewhat of influence on the solid-state structure
of the complex. Complex 3h with a cyclohexyl group on the 3-posi-
tion of indenyl ring possesses slightly shorter Zr–CentInd and Zr–
CentFlu distances and smaller b angle, indicative of a more compact
structure than those of the other two complexes. For complex 3e,
the bond lengths between zirconium center and carbon atoms of
the p-bonding five-membered ring in fluorenyl unit vary to a certain
degree (0.28 Å between the shortest to the longest bond lengths),
suggesting a slip of the coordination mode of the central five-mem-
bered ring from g5 to g3
.
1
For some of the zirconocene complexes synthesized in this work, satisfied
elemental analysis could not be obtained even after several recrystallization
procedures (C% errors around ꢃ1%). These complexes were therefore characterized
by HRMS method.
With this aim in mind, we synthesized complexes 3a and 3b
having methyl group substituted at the para- or meta-position(s)

88
Y. Wang et al. / Polyhedron 76 (2014) 81–93
1
Fig. 1. The H NMR spectrum of proligand 2d and isomer 2d0 (400 MHz, CDCl3; #, CHCl3; ##, H2O).
2 nBuLi
Et2O
ZrCl4
3a-i
2a i
-
Zr
Zr
Zr
Zr
Cl
Cl
Cl
Cl
Cl
Cl
Cl
Cl
3c
3d
3a
3b
Zr
Zr
Zr
Zr
Zr
Cl
Cl
Cl
Cl
Cl
Cl
Cl
Cl
Cl
Cl
3e
3f
3g
3h
3i
Scheme 3. Synthesis of zirconocene complexes.
of the pendant aryl group; complex 3c was designed to introduce
more flexibility between the pendant aryl group and the quater-
nary carbon bridge; a methylene linkage instead of a quaternary
carbon bridge was included in 3d in order to understand the effect
of substituents at the carbon linkage. Thus complexes 3a–d were
investigated for the catalytic transformation of propylene under
different conditions upon activation with MAO. The results are
compared with those of the previously reported complexes 1 and
2 and summarized in Table 2. 2-Methyl-1-pentene, 4-methyl-1-
pentene and 4-methyl-2-pentene components in the reaction end
products were detected by GC–MS, and these results were further
confirmed by GC of standard substances using heptane as an inter-
nal standard (Fig. S20 in SI).
As shown in Table 2, complexes 3a–b could catalyze the forma-
tion of 2-methyl-1-pentene but with very low activities (1–
10 ꢀ 103 g/(mol-Zrꢁh), Run 3–8, Table 2). Complex 3c bearing a
pendant benzyl group exhibits the highest dimerization activity
among them at 110 °C, which is much higher than those of 3a
and 3b, and a high selectivity of 97% toward 2-methyl-1-pentene
can also be achieved (Run 11, Table 2). The major product of 3d
(with ortho-methylbenzyl at the 3-position of indenyl ring) is how-
ever a wax fraction identified as polypropylenes of low molecular
weight (ꢃ1250 g/mol, Run 15–17, Table 2). These results suggest
that the activity and selectivity of these complexes toward propyl-
ene dimerization are significantly affected by the substituent on
the indenyl ring.

Y. Wang et al. / Polyhedron 76 (2014) 81–93
89
The total productivity of 3d including dimers and wax fraction
is the highest among these complexes. Obviously, the methylene
unit connecting indenyl and the pendant aryl group plays an
important role in this process. Hessen and co-workers [23,24] also
reported that, when a methylene linkage instead of a quaternary
carbon bridge was adopted, the resultant titanium complex, [(C6-
H5)CH2(C5H4)]TiCl3, lost the selectivity for ethylene trimerization
and became active for polymerization. It was therefore suggested
by the authors that the alkyl substituents on the quaternary carbon
bridge would force the pendant aryl group to approach the metal
center which facilitated the occurrence of a hemilabile interaction
in the active species [23,24,26]. Furthermore, in the synthesis of
group IV metallocene complexes bearing similar substituents, the
easy formation of metaloxacyclic complexes when two ethyl
groups were substituted on the carbon bridge also evidenced such
tendency [14,27]. Based on these facts, the quaternary carbon
bridge should also force the pendant aryl group to be close to the
metal center when 3a–c were activated with MAO. The steric hin-
drance around the metal center resulted from the approach of pen-
dant aryl group might prevent the further growth of any active
propagation chain longer than 6 carbons, leading to exclusively
dimerization products and at the same time low catalytic activities.
In 3c, the introduction of additional methylene unit between the
quaternary carbon bridge and the pendant phenyl might compen-
sate the disadvantage of the rigid linkage, providing complex 3c
with highest selectivity and activity for propylene dimerization.
In comparison with 3a-c, the easier oscillation of the pendant aryl
group around the methylene unit in 3d might reduce the probabil-
ity of pendant aryl group blocking the active site, and make the
polymer chain propagate readily without significant disturbance
(Chart 2).
Fig. 2. ORTEP view of the molecular structure of complex 3e. H atoms are omitted
for clarity; ellipsoids are drawn at 50% probability level. Selected bond distances (Å)
and angles (°) are as follows: Zr(1)–C(1) 2.586(5), Zr(1)–C(6) 2.719(5), Zr(1)–C(7)
2.702(5), Zr(1)–C(12) 2.583(5), Zr(1)–C(13) 2.437(5), Zr(1)–C(16) 2.470(5), Zr(1)–
C(17) 2.494(5), Zr(1)–C(18) 2.612(5), Zr(1)–C(19) 2.672(5), Zr(1)–C(20) 2.598(5),
Zr(1)–Cl(1) 2.4403(17), Cl(1)–Zr(1)–Cl(2) 97.61(6).
According to the literature [13], for most metallocene com-
plexes the optimized propylene polymerization temperature is
below 70 °C, while this series of complexes only exhibit dimeriza-
tion activity at 100 °C or above. This phenomenon should be an evi-
dence to support the assumption proposed above. At low
temperature, the pendant phenyl may lie close to the active center,
and exclude the coordination/insertion of monomer; with the
increase of temperature to 100 °C, the molecular thermal motion
of the pendant aryl group becomes fierce and allows the monomer
to coordinate and insert. Such reduction in steric hindrance is how-
ever limited due to the presence of a quaternary carbon bridge, and
only a dimerization process could occur selectively. The neglect-
able activity of 3a and 3b in comparison with that of complex 1
is also in consistent with this assumption; the introduction of
methyl group at the para- or meta-position(s) of the pendant aryl
group increases the steric bulkiness of this group significantly,
blocking the coordination/insertion of propylene monomer even
at high reaction temperature.
Fig. 3. ORTEP View of the molecular structure of complex 3h. H atoms are omitted for
clarity; ellipsoids are drawn at 50% probability level. Selected bond distances (Å)
and angles (°) are as follows. Zr(1)–C(5) 2.665(2), Zr(1)–C(6) 2.542(2), Zr(1)–C(7)
2.436(2), Zr(1)–C(8) 2.564(2), Zr(1)–C(9) 2.674(2), Zr(1)–C(16) 2.455(2), Zr(1)–
C(17) 2.481(2), Zr(1)–C(18) 2.595(2), Zr(1)–C(19) 2.623(2), Zr(1)–C(20) 2.568(2),
Zr(1)–Cl(1) 2.4141(7), Cl(1)–Zr(1)–Cl(2) 95.35(3).
Table 1
Related angles and distances of zirconocene complexes 1, 3e and 3h.
3.3. Propylene dimerization by zirconocene complexes with alkyl or
alkenyl substituent
From the above discussion, we could conclude that the quater-
nary carbon bridge in the substituent plays a crucial role in forcing
the pendant aryl group to be close to the metal center of the active
species, which consequently leads to the selectivity for propylene
dimerization. However, it is still not clear whether there exists
any interaction (coordination, or more possibly, an agostic interac-
tion) between the pendant aryl group and the metal center which
acts as the key factor accounting for the dimerization selectivity, or
alternatively whether the presence of the pendant aryl group is
essential for the dimerization process. Therefore, the pendant aryl
group was replaced by alkyl or alkenyl groups in complexes 3e–g;
complex 3h without a quaternary carbon bridge and complex 3i
Complex
a
(°)
b (°)
Zr–CentInd (Å)
Zr–CentFlu (Å)
1 [14]
3e
3h
64.3
63.6
64.0
128.26
127.97
127.14
2.250
2.263
2.240
2.290
2.304
2.271

90
Y. Wang et al. / Polyhedron 76 (2014) 81–93
Table 2
Propylene dimerization or polymerization catalyzed by complexes 1, 2, 3a–d/MAO.a
Run
Cat.
Tp (°C)
Al/Zr
C6-yieldb (mg)
C6-activityd (104 g/(mol-Zrꢁh))
Selectivity of 2-M-1-Pe (%)
Selectivity of waxf (%)
2-M-1-Pc
4-M-1-Pc
4-M-2-Pc
1 [14]
2 [14]
3
4
5
6
7
8
9
10
11
12
13
1
2
3a
100
100
100
100
110
100
100
110
100
100
110
120
100
4000
4000
4000
2000
2000
4000
2000
2000
4000
2000
2000
2000
4000
23.3
42.9
0.7
1.1
0.7
5.3
1.3
6.6
95.7
130.1
151.3
27.8
20.3
–
–
–
–
–
–
–
–
–
–
–
–
0.8
1.2
–
–
–
–
–
–
2.6
14.6
4.9
–
3.9
7.1
0.1
0.2
0.1
0.9
0.2
1.1
15.7
23.1
25.0
5.9
96.7
97.3
<1.0
<1.0
<1.0
<1.0
<1.0
<1.0
<1.0
<1.0
<1.0
<1.0
<1.0
<1.0
>99.0
>99.0
>99.0
>99.0
>99.0
>99.0
97.3
89.9
96.9
>99.0
3.0
3b
3c
3d
8.6
2.3
5.0
95.4
(0.65 g)g
94.8
14
15
100
110
2000
2000
28.7
52.0
9.7
3.4
7.7
6.7
3.6
8.5
(0.76 g)
77.9
14.0
11.8
(0.48 g)
a
b
c
d
e
f
Conditions: [Cat.] = 0.05
Measured by GC, the mass of different propylene dimers.
2-M-1-P represents 2-methyl-1-pentene; 4-M-1-P represents 4-methyl-1-pentene; 4-M-2-P represents 4-methyl-2-pentene.
The catalytic activity of all C6 components.
The percentage of 2-methyl-1-pentene in all products.
lmol/mL, Ppropylene = 6 bar, V = 25 mL, Time = 30 min.
The percentage of wax fraction which is soluble in toluene.
g
The molecular weight based on an end-group analysis via 1H NMR spectroscopy is around 1250 g/mol.
with a small isopropyl substituent were also obtained for a com-
parison purpose.
As summarized in Table 3, except for 3h, all of these complexes
are effective and selective for propylene dimerization under the
investigated conditions upon activation with MAO to afford 2-
methyl-1-pentene as the major product. Complex 3e with a pen-
dant cyclohexyl group shows higher dimerization activity than
complex 1 but with similar selectivity towards 2-methyl-1-pen-
tene (Run 2 and 5, Table 3). Unexpectedly, its cyclohexenyl ana-
logue 3f exhibits a very low activity, and only trace amount of
Zr
Zr
R
CH3
CH3
R
Chart 2. Position of the pendant phenyl guided by different bridging unit.
Table 3
Propylene dimerization or polymerization catalyzed by complexes 1, 3e–3i/MAO.a
Run
Cat.
Tp (°C)
Al/Zr
C6-yieldb (mg)
C6-activityd (104 g/(mol-Zrꢁh))
Selectivity of 2-M-1-Pe (%)
Selectivity of waxf (%)
2-M-1-Pc
4-M-1-Pc
4-M-2-Pc
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
1 [14]
100
100
50
8000
4000
4000
4000
4000
2000
2000
4000
2000
2000
4000
4000
2000
2000
4000
30.4
23.3
–
–
–
–
–
–
–
–
–
–
–
–
–
–
–
14.3
0.7
0.8
–
5.0
3.9
–
97.7
96.7
–
<1.0
<1.0
–
3e
90
–
–
–
–
–
100
100
110
100
100
110
50
100
100
110
100
73.9
43.8
25.3
8.9
7.7
9.5
1.6
1.1
0.8
–
–
–
12.1
7.2
4.2
1.4
1.2
1.5
1.5
11.3
15.7
13.2
23.7
97.8
97.6
97.0
>99.0
>99.0
>99.0
>99.0
97.0
97.6
96.9
14.7
<1.0
<1.0
<1.0
<1.0
<1.0
<1.0
<1.0
<1.0
<1.0
<1.0
82.2
(0.68 g)
<1.0
<1.0
<1.0
3f
3g
9.1
–
68.7
95.8
79.8
122.4
2.1
2.4
2.5
11.3
3h
3i
16
17
18
100
100
110
4000
2000
2000
128.0
17.6
63.1
–
–
–
12.8
2.3
7.1
22.5
3.2
11.2
90.9
88.7
89.8
a
b
c
d
e
f
Conditions: V = 25 mL, Ppropylene = 6 bar, [Cat.] = 0.05
Measured by GC, the mass of different propylene dimers.
2-M-1-P represents 2-methyl-1-pentene; 4-M-1-P represents 4-methyl-1-pentene; 4-M-2-P represents 4-methyl-2-pentene.
The catalytic activity of all C6 components.
The percentage of 2-methyl-1-pentene in all products.
l
mol/mL, Time = 30 min.
The percentage of wax fraction which is soluble in toluene.

Y. Wang et al. / Polyhedron 76 (2014) 81–93
91
dimeric product could be detected (Run 8–10, Table 3). Complex 3g
with an nbutyl group exhibits moderate activity and is more active
than 3e and 1, affording 2-methyl-1-pentene with high selectivi-
ties of 96.9–97.6% (Run 12–14, Table 3). Complex 3i, with a small
isopropyl group, under the conditions of 100 °C and Al/Zr = 4000,
achieves a moderate dimerization activity of 2.25 ꢀ 105 g/(mol-
Zrꢁh) and a relatively high selectivity of 90.9% for 2-methyl-1-pen-
tene (Run 16, Table 3). Although the dimerization activity of 3h is
high (2.37 ꢀ 105 g/(mol-Zrꢁh)), the major product of 3h for propyl-
ene transformation is the wax fraction identified as low molecular
weight polypropylenes (Run 15). These results imply that the
introduction of an alkyl group could also lead to a selective propyl-
ene dimerization process as the pendant aryl group revealed. The
previously assumed weak interaction between the pendant aryl
group and the metal center might not exist or at least might not
be the dominant factor regarding the dimerization selectivity.
It is reported that {C2H4-1-(9-C13H8)-2-[1-(3-tBu)C9H5]}ZrCl2
with a tert-butyl group on the indenyl ring could catalyze the poly-
merization of propylene [13c,13e], therefore it is rather unex-
pected that complex 3i with a smaller isopropyl group exhibits
moderate activity and good selectivity for propylene dimerization,
and that complex 3h with a relatively larger cyclohexyl displays
low selectivity for dimerization. All these conflicting results pro-
mote us to further study the catalytic behavior of this series of
complexes at different temperatures. Complexes 3e and 3f prove
to be not active below 100 °C; complex 3g shows very low activity
at 50 °C, but the high selectivity for dimerization is maintained
(Run 11, Table 3). At 60 °C, the major product (98.8%) obtained
by 3h is polypropylenes of low molecular weight (Run 19, Table 4).
Elevating the temperature from 60 to 120 °C results in an increase
of the selectivity for 2-methyl-1-pentene to 57.9% (Run 19, 21, 24–
25, Table 4). Complex 3i behaves as an active propylene polymer-
ization catalyst and gives no detectable dimers at or below 50 °C
(Run 26–28, Table 4); with the increase of reaction temperature,
the percentage of dimeric product increases and only dimers are
obtained at 100 °C (Run 31, Table 4). Based on the results listed
in Tables 3 and 4, it is therefore suggested that the presence of a
pendant alkyl group no matter cyclic or linear and therefore
induced steric hindrance around the metal center might be the
key factor accounting for the highly selective dimerization process
observed for 3e–g. For complexes 3h and 3i without a pendant
Zr
Zr
R
R
Scheme 4. Presumed reaction between the pendant cyclohexenyl group and the
cationic metal center.
β-H elimination
1,2-insertion
[Zr]
[Zr]
2,1-insertion
1,2-insertion
[Zr]
[Zr]
H
2,1-insertion
1,2-insertion
2,1-insertion
[Zr]
[Zr]
[Zr]
Scheme 5. The formation pathways of propylene dimers via b-H elimination
process.
[Zr] CH3
1,2-insertion
β-CH3 elimination
[Zr]
1,2-insertion
[Zr]
Scheme 6. The formation pathways of 4-methyl-1-pentene by b-CH3 elimination.
group, increasing the reaction temperature could also switch the
polymerization process to dimerization partially or completely
depending on the structure of substituent, likely due to a relatively
faster chain termination step than chain propagation process.
Table 4
Propylene dimerization or polymerization catalyzed by 3h, 3i/MAO.a
Run Cat. Tp (°C) Al/Zr C6-yieldb (mg)
2-M-1-Pc 4-M-1-Pc 4-M-2-Pc
Yield of wax (g) Activityd (106 g/(mol-Zrꢁh)) Selectivity of 2-M-1-Pe (%) Selectivity of waxf (%)
19
20
21
22
23
24
25
26
27
28
29
30
31
3h
60
100
100
100
100
110
120
0
0
50
70
90
2000 11.5
1000 74.1
2000 83.8
4000 122.4
6000 15.0
2000 143.3
2000 222.4
1.3
4.5
8.7
14.3
5.0
14.3
8.5
–
–
–
–
–
0.9
4.2
7.1
11.3
1.1
11.4
25.1
–
–
–
–
–
1.20
0.42
0.84g
0.68
0.58
0.56
0.13
1.30
0.086
1.20g
2.20
1.80
trace
1.8
0.80
1.5
1.3
0.97
1.2
0.61
2.1
0.14
1.8
3.8
3.4
1.0
14.9
8.9
14.7
2.5
19.8
57.9
–
–
–
6.7
14.8
90.9
98.8
83.3
89.4
82.2
96.5
76.7
33.3
>99.0
>99.0
>99.0
93.3
95.2
<1.0
3i
4000
8000
4000
–
–
–
4000 157.1
4000 314.1
4000 128.0
100
–
12.8
0.22
a
b
c
d
e
f
Conditions: V = 25 mL, Ppropylene = 6 bar, [Cat.] = 0.05
Measured by GC, the mass of different propylene dimers.
2-M-1-P represents 2-methyl-1-pentene; 4-M-1-P represents 4-methyl-1-pentene; 4-M-2-P represents 4-methyl-2-pentene.
The catalytic activity of all components.
The percentage of 2-methyl-1-pentene in all products.
lmol/mL, Time = 30 min.
The percentage of wax fraction which is soluble in toluene.
g
The molecular weights based on an end-group analysis via 1H NMR spectroscopy are around 1583 g/mol (Run 21) and 6743 g/mol (Run 28).

92
Y. Wang et al. / Polyhedron 76 (2014) 81–93
2
Zr
Zr
H
1,2-insertion
A
B
Zr
Fast Epimerization
Propagation
Inhibited
β-H Elimination
2
Zr
Zr
Zr
H
1,2-insertion
A'
B'
C
Scheme 7. Proposed mechanism of selective propylene dimerization to 2-methyl-1-pentene.
It is found that the nature of pendant alkyl group has consider-
the dominant active species in the catalytic system should be the
cationic [Et(Ind’)(Flu)Zr–H]+ species which is generated after a nor-
mal activation step with MAO followed by insertions of propylene
monomer and then a sequential b-H elimination. The C1-symmet-
ric structural feature of the precursor zirconocene complexes
brings on two different coordination sites: one is the site near
the pendant group and is sterically more hindered (outward site);
the other site is sterically more open (inward site). The propagation
reaction starts from the intermediate A with an initiating group
[Zr]–H at the outward site. After two sequential 1,2-migratory
insertion of propylene, the intermediate B is formed. The signifi-
cantly enhanced repulsion interaction between the C6-propagation
chain and the pendant group leads to a fast epimerization of B to
produce the intermediate B0 with the growing chain at the less ste-
rically hindered inward site. Due to the steric hindrance at the out-
ward site induced by the bulky pendant group, the further
propagation of growing chain in intermediate C via migratory
insertion is thermally inhibited. As a result, b-H elimination takes
place to form 2-methyl-1-pentene and regenerates the intermedi-
ate A. On the other hand, if the reaction starts from the intermedi-
ate A0 with the initiating group [Zr]–H at the inward site, two
sequential 1,2-migratory insertion of propylene will afford the
intermediate B0. Afterwards, the same catalytic cycle takes place.
able influence on the dimerization activity. Instead of a rigid, pen-
dant phenyl ring adopted in complex 1, complex 3e bears a
pendant cyclohexyl group, which is much softer and easily folded.
This structural variation reduces the steric hindrance to a certain
degree, and makes the coordination of monomer to metal center
easier and more stable, resulting in an obvious increase of the
dimerizaiton activity observed for 3e. The moderate activity of
complex 3g with a pendant long alkyl chain is consistent with
the further decrease of the steric bulkiness of the pendant group.
Complex 3f bearing a pendant cyclohexenyl group, which is
analogous to the one in 3e and was designed to possess weaker
coordination ability than phenyl, exhibits unexpectedly an extre-
mely low activity for dimerization. According to the literature
[28], the low activity might arise from an insertion reaction
between C–C double bond and the cationic metal center as shown
in Scheme 4; the resultant intermediate might be no more active
for propylene transformation.
3.4. Proposed mechanism of propylene dimerization
Non selective propylene dimerization usually affords a mixture
of hexenes, methyl pentenes and dimethyl butene as shown in
Scheme 5. The major product of propylene dimerization catalyzed
by complexes 3a–c, 3e, 3g is 2-methyl-1-pentene, companied with
trace amount of 4-methyl-2-pentene. Kaminsky and co-workers
[11] reported that the formation of 2-methyl-1-pentene is via an
initiation from [Zr]–H active center, followed by two sequential
1,2-insertion of propylene and then b-H elimination; while 4-
methyl-2-pentene goes along a different path of two sequential
2,1-insertion of propylene into [Zr]–H followed by b-H elimination.
Due to the formation of a dormant state, this pathway usually leads
to a low activity. It is also the case in this work; the amount of 4-
methyl-2-pentene produced by complexes 3a–c, 3e, 3g is much
less than that of 2-methyl-1-pentene. In the reaction end product
catalyzed by 3d and 3h, 4-methyl-1-pentene could be detected,
which might be formed via a pathway similar to 4-methyl-2-pen-
tene (Scheme 5), or alternatively via two sequential 1,2-insertion
of propylene into [Zr]-Me followed by b-CH3 elimination process,
as reported by Okuda and co-workers [12] (Scheme 6).
4. Conclusions
In summary, a series of ethylene-bridged C1-symmetric ansa-(3-
R-indenyl)(fluorenyl) zirconocene complexes have been synthe-
sized and characterized. In the presence of MAO, 3a–c and 3e–g
with a pendant aryl or alkyl group linked by a quaternary carbon
bridge to indenyl ring exhibit low to moderate catalytic activities
and high selectivities toward propylene dimerization to produce
2-methyl-1-pentene as the major product. The activity for propyl-
ene dimerization is significantly influenced by the steric bulkiness
of the pendant group. The main product of propylene transforma-
tion catalyzed by 3d, 3h–i without a quaternary carbon bridge is
polypropylenes of low molecular weight. Moreover, the reaction
temperature is also a concernful factor: the composition of product
obtained by 3h–i could be greatly changed at different tempera-
ture. Remarkably, most of the complexes exhibit excellent thermal
stability at 110 °C, with regard to industrial requirements. A plau-
sible mechanism regarding to the dimerization selectivity has been
discussed with emphasizing the inhibited chain propagation and a
fast epimerization of the active center both induced by the steri-
cally bulky pendant group on indenyl ring.
On the basis of above investigations, a plausible mechanism to
declare the high selectivity of propylene dimerization toward
2-methyl-1-pentene catalyzed by the synthesized C1-symmetric
zirconocene complexes 3a–c, 3e, 3g is outlined in Scheme 7. Since
2-methyl-1-pentene is formed as the major product in these cases,

Y. Wang et al. / Polyhedron 76 (2014) 81–93
93
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