Synthesis, structure and catalytic properties of new half-titanocene complexes bearing substituted cyclopentadienyl and aryloxide ligands

Article abstract of DOI:10.1080/00958972.2013.832760

New cyclopentadienyltitanium aryloxide complexes, 1-phenyl-2,3,4,5- Me4CpTi(O-2,6-ⁱPr2-4-ⁿBu-C6H2)Cl2 (1) and [4,4′-biphenyl-(2,3,4,5-Me4Cp)2][Ti(O-2,6-ⁱPr2-4- ⁿBu-C6H2)Cl2]2 (2), have been prepared by treatment

Full text of DOI:10.1080/00958972.2013.832760

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Synthesis, structure and catalytic
properties of new half-titanocene
complexes bearing substituted
cyclopentadienyl and aryloxide ligands
Mina Hea, Pei Lia, Qing Sua, Qiaolin Wua, Ling Yeb & Ying Muab
a School of Chemistry, Jilin University, Chang Chun, P.R. China
b State Key Laboratory of Supramolecular Structure and Materials,
Jilin University, Chang Chun, P.R. China
Accepted author version posted online: 07 Aug 2013.Published
online: 05 Sep 2013.
To cite this article: Mina He, Pei Li, Qing Su, Qiaolin Wu, Ling Ye & Ying Mu (2013) Synthesis,
structure and catalytic properties of new half-titanocene complexes bearing substituted
cyclopentadienyl and aryloxide ligands, Journal of Coordination Chemistry, 66:18, 3272-3279, DOI:
10.1080/00958972.2013.832760
To link to this article: http://dx.doi.org/10.1080/00958972.2013.832760
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Journal of Coordination Chemistry, 2013
Vol. 66, No. 18, 3272–3279, http://dx.doi.org/10.1080/00958972.2013.832760
Synthesis, structure and catalytic properties of new
half-titanocene complexes bearing substituted
cyclopentadienyl and aryloxide ligands
MINA HE†, PEI LI†, QING SU*†, QIAOLIN WU*†, LING YE‡ and YING MU†‡
†School of Chemistry, Jilin University, Chang Chun, P.R. China
‡State Key Laboratory of Supramolecular Structure and Materials, Jilin University, Chang Chun,
P.R. China
(Received 26 April 2013; accepted 26 July 2013)
New cyclopentadienyltitanium aryloxide complexes, 1-phenyl-2,3,4,5-Me4CpTi(O-2,6-iPr2-4-nBu-
C6H2)Cl2 (1) and [4,4′-biphenyl-(2,3,4,5-Me4Cp)2][Ti(O-2,6-iPr2-4-nBu-C6H2)Cl2]2 (2), have been
prepared by treatment of cyclopentadienyltitanium trichloride complexes [PhMe4CpTiCl3 and
4,4′-biphenyl-(Me4CpTiCl3)2] with 1 or 2 equiv of lithium salt of 2,6-di-isopropyl-4-butylphenol.
Complexes 1 and 2 have been characterized by elemental analysis, 1H and 13C NMR spectroscopy.
The molecular structure of 1 has been determined by single-crystal X-ray diffraction. Upon activa-
i
tion with Bu3Al and Ph3CB(C6F5)4, 1 and 2 both exhibit good catalytic activity for ethylene poly-
merization, producing polyethylene with moderate molecular weight and melting point.
Keywords: Ethylene polymerization; Half-titanocene; Metallocene catalysts; Olefin polymerization;
Polyethylene
1. Introduction
Group 4 metallocene complexes have applications as homogeneous catalyst precursors for a
variety of high performance poly-olefins with tailored structures and properties [1–5]. Many
studies have been devoted to the development of more effective catalysts improving cata-
lytic activities and polymer properties with precise control over molecular weight, polydis-
persity, comonomer enchainment level and pattern, as well as the tacticity of poly-olefins
[6–8]. Bridged half-metallocene pre-catalysts such as constrained geometry complexes
(CGCs) are the most important family of active homogeneous polymerization catalysts,
exhibiting high activity and good incorporation of comonomers [9, 10]. As extension of
half-metallocene pre-catalysts, non-bridged half-titanocene complexes have been developed
by Nomura as high performance catalysts for copolymerization of ethylene with α-olefins,
styrene, and norbornene [11]. Non-bridged half-metallocenes, CpM(OAr)Cl2, exhibit unique
characteristics for the produced polymers in comparison with ordinary metallocene and/or
CGCs. This type of catalyst can be easily synthesized and effectively modified by
*Corresponding authors. Emails: suqing@jlu.edu.cn (Q. Su); wuql@jlu.edu.cn (Q. Wu)
© 2013 Taylor & Francis

New half-titanocene
3273
replacement of both the cyclopentadienyl fragment and anionic ancillary ligands to change
steric and/or electronic factors [12]. We recently reported that analogous titanium and zirco-
nium complexes bearing aryloxy or anilides show good catalytic performance for ethylene-
hexene copolymerization and propylene-hexene copolymerization [13]. Generally, ligand
modification has the most profound effect on catalyst performance including catalytic activi-
ties and the properties of the obtained polymers. To improve catalytic performance, we have
introduced the n-butyl chain into this type of non-bridged half-titanocene complexes to
increase solubility, stability, and increase steric bulk. Structural modification of cyclopenta-
dienyl and/or aryloxide ligands should allow us to design well-defined binuclear and poly-
nuclear catalysts with flexible or rigid bridging groups. Recently, dinuclear half-titanocene
complexes have been explored for catalytic properties in olefin polymerization with com-
parison to those of defined mononuclear systems [6b, 14]. Multinuclear metallocene cata-
lysts linked by different bridging units have exhibited cooperative catalytic properties in
olefin polymerization [15]. These results encouraged us to develop well-defined binuclear
and polynuclear half-titanocene catalysts with similar active sites to investigate both their
structural features and catalytic properties. Herein, we report the synthesis and structural
characterization of two new half-titanocene complexes, as well as their application for
homogeneous ethylene polymerization.
2. Results and discussion
2.1. Synthesis of 1 and 2
The new half-titanocene complexes 1 and 2 were readily synthesized by treatment of cyclo-
pentadienyltitanium trichloride complexes [PhMe4CpTiCl3 and 4,4′-biphenyl-(Me4Cp-
TiCl3)2], respectively, with the lithium salt of 2,6-iPr2-4-nBuphenol in toluene according to
modified literature procedure [13a, 16]. The ligand precursor 2,6-diisopropyl-4-butylphenol
was unexpectedly prepared by lithiation of 1-bromo-3,5-diisopropyl-4-methoxybenzene
with n-butyllithium, followed by addition of tetrachlorosilane and tribromoborane. The pro-
cedure was expected to synthesize tetrakis(3,5-diisopropyl-4-hydroxyphenyl)-silane, similar
to the procedure used to prepare tetrakisphenylsilane [17].
Analytically pure 1 and 2 could be obtained by recrystallization from methylene chlo-
ride/hexane mixed solvent as red crystalline solids. Both complexes are soluble in methy-
lene chloride, diethyl ether, tetrahydrofuran, and toluene, while slightly soluble in n-hexane
and n-pentane. Both 1 and 2 are air- and moisture-stable in the solid state, similar to the
analogous aryloxide titanium complexes [11c, 13a]. The two new half-titanocene complexes
are somewhat sensitive to moisture in solution by hydrolysis with H2O and should be stored
and handled under an inert atmosphere. These titanium complexes were characterized by
1
1H and 13C NMR spectroscopy along with elemental analysis. The H NMR spectra of 1
and 2 show two characteristic singlets for the CpCH3 protons from 2.25 to 2.40 ppm, simi-
lar to those of tetramethyl(phenyl)cylopentadienyltitanium trichloride. In 13C NMR spectra,
both 1 and 2 show similar resonances in the aliphatic region with the signals from 13.4
to13.5 ppm assigned to CpCH3. The 13C NMR spectra of 1 and 2 display a downfield reso-
nance from 158.4 to 158.6 ppm, assigned to the carbon adjacent to oxygen in the aryloxy
ligand.

3274
M. He et al.
Figure 1. Molecular structure of 1 (thermal ellipsoids are drawn at the 30% probability level). Hydrogens are
omitted for clarity.
2.2. Crystal structure of 1
The molecular structure of 1 was determined by single-crystal X-ray diffraction. The
ORTEP of the molecule is shown in figure 1. Important bond lengths and angles are
summarized in table 1. The coordination geometry around titanium can be described as
pseudo-octahedral, consisting of a substituted cyclopentadienyl ring, two chlorides, and a
phenolate oxygen. The Ti–C distances in 1 from 2.3440(17) to 2.4204(18) Å are similar to
those previously reported for similar complexes [18, 19]. The average Ti–Cl distance of
2.2661(6) Å is also in the range of observed values (2.250–2.305 Å) for titanium complexes
[20, 21]. The Ti–O bond length (1.7729(13) Å) of 1.772–1.820 Å is reported for the same
kind of titanium complexes [20]. The Cp(cent)–Ti–O angle in 1 of 121.9(1)° is larger than
the one in (TCP)Ti(CH2Ph)2 (107.7°) [22] and Cp–Ti–N angle in Me2Si(Me4C5)(tBuN)
TiCl2 (107.6°) [23], which are related to the sterically open degree in front of the central
titanium for these complexes as catalyst precursors. The Ti–O–C angle of 172.96(12)°
together with the corresponding Ti–O distance suggest that the Ti–O bond may be stabilized
by partial π-donation from the oxygen of phenolate. The dihedral angle between the Cp ring
and the adjacent phenyl plane in 1 (49.2(1)°) is comparable to those of half-titanocene
Table 1. Selected bond lengths (Å) and angles (°) for 1.
Ti(1)−C(1)
Ti(1)−C(2)
Ti(1)−C(3)
Ti(1)−C(4)
2.3838(18)
2.4204(18)
2.4073(19)
2.3491(18)
2.3440(17)
101.32(4)
101.92(4)
101.79(2)
121.9(1)
Ti(1)−Cl(1)
Ti(1)−Cl(2)
Ti(1)−O(1)
2.2637(6)
2.2686(6)
1.7729(13)
2.050(2)
Ti(1)−Cp(cent)
Ti(1)−C(5)
O(1)−Ti(1)−Cl(1)
O(1)−Ti(1)−Cl(2)
Cl(1)−Ti(1)−Cl(2)
Cp(cent)−Ti(1)−O(1)
Cp(cent)−Ti(1)−Cl(1)
Cp(cent)−Ti(1)−Cl(2)
Ti(1)−O(1)−C(16)
O(1)−Ti(1)−C(1)
O(1)−Ti(1)−C(2)
O(1)−Ti(1)−C(3)
O(1)−Ti(1)−C(4)
O(1)−Ti(1)−C(5)
172.96(12)
107.45(6)
142.18(6)
144.62(6)
109.84(6)
90.70(6)
114.7(2)
112.6(1)

New half-titanocene
3275
Table 2. Summary of ethylene polymerization catalyzed by 1 and 2 activated with Al(iBu)3 and Ph3CB(C6F5)4.a
c
c
Run
Catalyst
Al:Ti
T (°C)
Yield (g)
Activityb
Mw × 10−4
Mw /Mn
Tm (°C)d
1
2
3
4
5
6
1
1
1
1
2
2
150
200
300
200
150
200
60
60
60
80
60
60
0.439
0.448
0.253
0.333
0.226
0.240
878
896
506
666
452
480
9.12
8.56
7.82
8.83
9.85
8.71
3.10
2.91
3.36
3.41
4.32
2.09
139.4
137.6
135.7
138.3
140.1
138.4
aPolymerization conditions: solvent 60 mL of toluene, catalyst 2 μmol (1 μmol for 2), B/Ti ratio 1.1, time 5 min, ethylene pressure
3 bar.
bPolymerization activity: 103 kg PE (M Ti)−1 bar−1 h−1
.
cDetermined by GPC in trichlorobenzene at 140 °C vs. polystyrene standards.
dDetermined by DSC at a heating rate of 10 °C min−1
.
complexes reported by our groups (43.7–58.7°) [13a], which should be due to steric interac-
tions among the two bulky aryl groups and the Me4Cp ring in these complexes.
2.3. Ethylene polymerization studies
Ethylene polymerizations were carried out using 1 and 2 as pre-catalysts under different
conditions, and the results are summarized in table 2. Upon activation with Al(iBu)3 and
Ph3CB(C6F5)4, 1 and 2 exhibit catalytic activity for ethylene polymerization, producing
polyethylenes with moderate molecular weight and melting point. Under the same condi-
tions, the 1/Ph3CB(C6F5)4 system displays slightly higher catalytic activities than that
Table 3. Crystal data and structural refinement details for 1.
Empirical formula
Formula mass
C31H42Cl2OTi
549.45
Crystal system
Triclinic
Space group
P-1
a/Å
b/Å
c/Å
α/°
10.7309(5)
11.4544(5)
12.8551(6)
110.3210(10)
92.3750(10)
100.0150(10)
1450.28(11)
2
1.258
584
0.501
1.70 ≤ θ ≤ 26.02
–13 ≤ h ≤ 12
–14 ≤ k ≤ 13
–15 ≤ l ≤ 14
7658/5561
0.0122
β/°
γ/°
V/Å3
Z
Dc/g cm−3
F(000)
Abs. coeff./mm−1
Collect range/°
Limiting indices
Reflections collected/unique
Rint
Data/restraints/parameters
5561/0/325
R1 = 0.0380,
wR2 = 0.0943
R1 = 0. 0433
wR2 = 0.0985
1.035
Final R indices [I>2σ(I)]
b
(R1a/wR2
)
R indices (all data)
Goodness of fit
Largest diff. peak and hole/e Å−3
0.284 and −0.250
aR1 = Σ||Fo| – |Fc||/Σ|Fo|.
bwR2 = [Σ[w(Fo2–Fc2)2] / Σ[w(Fo2)2]]1/2
.

3276
M. He et al.
observed for the 2/Ph3CB(C6F5)4 system, while the molecular weight of the polyethylenes
produced by 2/Ph3CB(C6F5)4 system is slightly higher than that obtained with 1/Ph3CB
(C6F5)4 system under identical conditions. The results also indicate that the catalytic perfor-
mance is influenced by the nature of the substituents on the ligands. GPC and DSC analysis
on the obtained polyethylenes suggest that the catalytically active species formed in binu-
clear catalyst systems might be identical and behave as independent single active sites [24].
The resultant polyethylenes possessed essentially unimodal molecular weight distributions,
similar to those found in other titanium catalyst systems [25].
The effects of the Al/Ti molar ratio and polymerization temperature on the catalytic activ-
ity of 1 and 2 were investigated. The highest catalytic activity is reached at Al/Ti molar
ratio of 200 for both catalyst systems. Further increase in the Al/Ti molar ratio would result
in a decrease in the catalytic activity. These results are in agreement with those observed
for other half-titanocene catalyst systems [13a]. The results demonstrate that the catalytic
performance of these catalysts also depends on polymerization temperature; catalytic
activities of 1 and 2 increase with increase in polymerization temperature, and reach the
highest value around 60 °C.
3. Conclusions
New half-titanocene complexes 1 and 2 were synthesized from the reaction of the lithium
salt of 2,6-diisopropyl-4-butylphenol with the corresponding cyclopentadienyl titanium
trichloride. The molecular structure of 1 was determined by X-ray crystallography. When
activated with Al(iBu)3 and Ph3CB(C6F5)4, both 1 and 2 exhibit reasonable catalytic activity
for ethylene polymerization, producing polyethylene with moderate molecular weight, and
melting point.
4. Experimental
4.1. General comments
All manipulations involving air and moisture sensitive compounds were carried out under
argon (ultra-high purity) using either standard Schlenk techniques or glovebox techniques.
Solvents were dried and distilled prior to use [26]. Polymerization grade ethylene was fur-
ther purified by passage through columns of 5 Å molecular sieves and MnO. 4-Bromo-2,6-
diisopropyl-phenol [27], PhMe4CpTiCl3 [18, 28], 4,4′-biphenyl-(Me4CpTiCl3)2, [29] and
Ph3CB(C6F5)4 [30] were prepared according to literature procedures. NMR spectra were
measured using a Varian Mercury-300 NMR spectrometer. Elemental analyzes were per-
formed on a Perkin-Elmer 240c element analyzer. Melting transition temperatures (Tm) of
the polyethylenes were determined by DSC (Du Pont 910 differential scanning calorimeter)
at a heating rate of 10 °C min−1. Molecular weight of the polyethylenes were determined by
PL-GPC 220 at 140 °C with 1,2,4-trichlorobenzene as the eluent.
4.2. Synthesis of 2,6-diisopropyl-4-butylphenol
To a stirred solution of 4-bromo-2,6-diisopropyl-phenol (5.14 g, 20.0 mM) in THF (50 mL)
was added NaH (0.528 g, 22.0 mM) at 0 °C. The resulting mixture was stirred for 1 h. Then,
MeI (3.12 g, 22.0 mM) was added over 10 min and stirring was continued for another 2 h.

New half-titanocene
3277
The reaction was quenched by addition of H2O (50 mL), stirred for 10 min, and extracted
with Et2O (3 × 30 mL). The organic layer was dried over MgSO4, filtered and evaporated
to give a crude product, which was further purified by silica gel column chromatography
(petroleum ether) to afford 1-bromo-3,5-diisopropyl-4-methoxybenzene (4.96 g, 91.6%) as a
yellowish oil. Anal. Calcd for C13H19BrO (271.19): C, 57.57; H, 7.06. Found: C, 57.53; H,
1
7.16%. H NMR (CDCl3, 300 MHz, 298 K): 1.21 (d, 12H, J = 7.5 Hz, CH(CH3)2), 3.21–
3.34 (m, 2H, CH(CH3)2), 3.71 (s, 3H, OCH3), 7.18 (s, 2H, C6H2).
A solution of n-BuLi (18.3 mM) was added dropwise to a solution of the 1-bromo-3,5-
diisopropyl-4-methoxybenzene (4.96 g, 18.3 mM) in THF (50 mL) at –15 °C. The resulting
mixture was kept at –15 °C for 30 min, and then SiCl4 (0.778 g, 4.58 mM) was added drop-
wise. The mixture was stirred at –15 °C for 30 min and then allowed to warm to room tem-
perature and stirred for an additional 2 h. The reaction was quenched by addition of 1 M
aqueous HCl, stirred for 10 min, and then extracted with Et2O (3 × 30 mL). The combined
extracts were washed with H2O and brine, dried over MgSO4, filtered and concentrated.
The residue was dissolved in CH2Cl2 (20 mL) and then BBr3 (26.0 mM) was added drop-
wise to the solution. The mixture was stirred for 12 h at room temperature. The reaction
was quenched by addition of concentrated hydrochloric acid, stirred for 30 min, and then
extracted with CH2Cl2 (3 × 30 mL). The combined extracts were washed with NaHCO3
and brine, dried over MgSO4, filtered and concentrated. The residue was purified by silica
gel column chromatography (petroleum ether/ethyl acetate) to afford 2,6-diisopropyl-4-
butylphenol (1.84 g, 42.9%) as an oil. Anal. Calcd for C16H26O (234.38): C, 81.99; H,
1
11.18. Found: C, 81.92; H, 11.23%. H NMR (CDCl3, 300 MHz, 298 K): 0.93 (t, 3H,
J = 7.5 Hz, CH3), 1.26 (d, 12H, J = 7.5 Hz, CH(CH3)2), 1.32–1.43 (m, 2H, CH2), 1.52–
1.62 (m, 2H, CH2), 2.53 (t, 2H, J = 7.8 Hz, CH2), 3.06–3.20 (m, 2H, CH(CH3)2), 6.86 (s,
2H, C6H2).
4.3. Synthesis of 1
A solution of n-BuLi (2.0 mM) was added dropwise to a solution of 2,6diisopropyl-4-
butylphenol (0.468 g, 2.0 mM) in Et2O (20 mL) at –20 °C. The reaction mixture was
allowed to warm to room temperature and stirred for 2 h. The solvent was removed in
vacuo and the residue was washed with hexane. The obtained white powder was
dissolved in toluene (10 mL), and then a solution of 1,1-phenyl-2,3,4,5-tetrame-
thylcyclopentadienyltitanium trichloride (0.669 g, 1.90 mM) in toluene (10 mL) was
added at room temperature. The reaction mixture was heated to 80 °C and stirred for
12 h. The mixture was filtered and the precipitate was washed with toluene
(2 × 5 mL). The filtrate was concentrated to leave a black-red residue. Recrystalliza-
tion from CH2Cl2–n-hexane (1 : 3) gave pure 1 as red crystals (0.820 g, 78.5%). Melt-
ing point: 96–97 °C. Anal. Calcd for C31H42Cl2OTi (549.44): C, 67.77; H, 7.70.
Found: C, 67.70; H, 7.62%. 1H NMR (CDCl3, 300 MHz, 298 K): 0.93 (t, 3H,
J = 7.2 Hz, CH3), 1.04 (d, 12H, J = 6.9 Hz, CH(CH3)2), 1.31–1.41 (m, 2H, CH2),
1.50–1.60 (m, 2H, CH2), 2.26 (s, 6H, Cp-CH3), 2.29 (s, 6H, Cp-CH3), 2.53 (t, 2H,
J = 7.5 Hz, CH2), 2.95–3.09 (m, 2H, CH(CH3)2), 6.79 (s, 2H, C6H2), 7.31–7.50 (m,
5H, C6H5). 13C NMR (CDCl3, 75 MHz, 298 K): 13.46, 14.21, 22.78, 23.02, 24.07,
26.94, 34.02, 35.93, 123.2, 126.9, 130.9, 131.3, 132.6, 133.5, 136.1, 138.4, 139.5,
140.2, 158.6.

3278
M. He et al.
4.4. Synthesis of 2
Complex 2 was synthesized from 4,4′-biphenyl-(Me4CpTiCl3)2 by the same procedure as
described for 1. Complex 2 was obtained in 75.3% yield as a red crystalline solid. Melting
point: 185–186 °C. Anal. Calcd for C62H82Cl4O2Ti2 (1096.86): C, 67.89; H, 7.54. Found:
1
C, 67.80; H, 7.65%. H NMR (CDCl3, 300 MHz, 298 K): 0.92 (t, 6H, J = 7.2 Hz, CH3),
1.05 (d, 24H, J = 6.6 Hz, CH(CH3)2), 1.31–1.40 (m, 2H, CH2), 1.51–1.60 (m, 2H, CH2),
2.29 (s, 12H, Cp-CH3), 2.34 (s, 12H, Cp-CH3), 2.53 (t, 4H, J = 7.5 Hz, CH2), 2.98–3.09
(m, 4H, CH(CH3)2), 6.80 (s, 4H, C6H2), 7.59–7.67 (m, 8H, C6H4). 13C NMR (CDCl3,
75 MHz, 298 K): 13.39, 14.11, 22.77, 23.03, 24.06, 26.92, 34.01, 35.92, 123.1, 128.1,
128.4, 130.8, 131.0, 133.2, 133.3, 136.8, 138.1, 139.5, 158.5.
4.5. X-ray structure determinations of 1
Crystals of 1 suitable for X-ray structure determination were obtained from a saturated solu-
tion of CH2Cl2/n-hexane (1:5, v/v) at room temperature. The data were collected at 293 K
on a Rigaku RAXIS-RAPID diffractometer using Mo-Kα radiation. The structures were
solved by direct methods [31] and refined by full-matrix least-squares on F2. All non-hydro-
gen atoms were refined anisotropically and hydrogens were included in idealized positions.
All calculations were performed using the SHELXTL crystallographic software package
[32]. Details of the crystal data, data collections, and structure refinements are summarized
in table 3.
4.6. Polymerization reactions
Ethylene polymerizations were carried out according to the following procedure: A dry 250
mL steel autoclave was charged with 50 mL of toluene, thermostated at the desired tempera-
ture and saturated with 1.0 bar of ethylene. The polymerization reaction was started by addi-
tion of a mixture of catalyst and Al(iBu)3 in toluene (5 mL) and a solution of Ph3CB(C6F5)4
in toluene (5 mL) at the same time. The reaction mixture was stirred for 5 min under 3 bar
of ethylene. The polymerization was then quenched by injecting 120 mL of acidified metha-
nol [HCl (3 M)/methanol = 1 : 1], and the polymer was collected by filtration, washed with
water, methanol, and dried at 60 °C in vacuum to a constant weight.
Supplementary material
Crystallographic data for the structural analysis have been deposited with the Cambridge
Crystallographic Data Center, CCDC reference number: 931,680 (1). Copy of this informa-
tion may be obtained free of the charge from The Director, CCDC, 12 Union Road, Cam-
bridge, CB2 1EZ, UK (Fax: +44–1223-336,033; E-mail: deposit@ccdc.cam.ac.uk or http://
www.ccd.cam.ac.uk).
Acknowledgements
This work was supported by the National Natural Science Foundation of China (No. 21004026).

New half-titanocene
3279
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