2-(1-(Arylimino)propyl)quinolin-8-olate half-titanocene dichlorides: Synthesis, characterization and ethylene (co-)polymerization behaviour

Article abstract of DOI:10.1039/c1dt10068h

A series of 2-(1-(arylimino)propyl)quinolin-8-olate half-titanocene dichlorides, Cp′TiCl₂L (Cp′ = η⁵-C ₅H₅ or η⁵-C₅Me₅, L = 2-(1-(2,6-R¹-4-R²-phenylimino)propyl)quinolin-8-olate), was synthesized via the stoichiometric reaction of Cp′TiCl₃ with the corresponding potassium 2-(1-(2,6-R¹-4-R²- phenylimino)propyl)quinolin-8-olate salt. All titanium compounds were characterized by elemental analysis, ¹H NMR and ¹³C NMR spectroscopy; the molecular structures of two representative compounds were determined by single crystal X-ray diffraction. On activation with methylaluminoxane (MAO), all half-titanocene compounds showed high activity in ethylene polymerization, and furthermore, performed with good to high activities in the co-polymerization of ethylene with either 1-hexene or 1-octene affording polyethylenes with high co-monomer incorporation. Less bulky ortho-substituents (R¹) on the phenylimino groups were found to enhance the catalytic activities of their titanium compounds. In general, the titanium pro-catalysts containing η⁵-C₅Me₅ (C7-C12) exhibited higher activities than did their analogues bearing η⁵-C ₅H₅ (C1-C6). Some of the resultant polyolefins were ultrahigh molecular weight polyethylene.

Full text of DOI:10.1039/c1dt10068h

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PAPER
2-(1-(Arylimino)propyl)quinolin-8-olate half-titanocene dichlorides:
Synthesis, characterization and ethylene (co-)polymerization behaviour†
Wei Huang,a Wen–Hua Sun*a and Carl Redshaw*b
Received 13th January 2011, Accepted 12th April 2011
DOI: 10.1039/c1dt10068h
A series of 2-(1-(arylimino)propyl)quinolin-8-olate half-titanocene dichlorides, Cp¢TiCl2L (Cp¢ =
5
5
h -C5H5 or h -C5Me5, L = 2-(1-(2,6-R1-4-R2-phenylimino)propyl)quinolin-8-olate), was synthesized via
the stoichiometric reaction of Cp¢TiCl3 with the corresponding potassium 2-(1-(2,6-R1-4-R2-
phenylimino)propyl)quinolin-8-olate salt. All titanium compounds were characterized by elemental
analysis, 1H NMR and 13C NMR spectroscopy; the molecular structures of two representative
compounds were determined by single crystal X-ray diffraction. On activation with methylaluminoxane
(MAO), all half-titanocene compounds showed high activity in ethylene polymerization, and
furthermore, performed with good to high activities in the co-polymerization of ethylene with either
1-hexene or 1-octene affording polyethylenes with high co-monomer incorporation. Less bulky
ortho-substituents (R1) on the phenylimino groups were found to enhance the catalytic activities of their
5
titanium compounds. In general, the titanium pro-catalysts containing h -C5Me5 (C7–C12) exhibited
5
higher activities than did their analogues bearing h -C5H5 (C1–C6). Some of the resultant polyolefins
were ultrahigh molecular weight polyethylene.
with poor co-polymerization behaviour.1a–1c As part of our efforts,
1. Introduction
multi-dentate anionic ligands were designed for use within half-
titanocene complexes,12 which were shown to be good pro-
catalysts with high activities in ethylene (co-)polymerization.
Inspired by the FI catalysts,1a–1c our half-titanocene pro-catalysts
bearing multidentate alkyloxy-sp2-N ligands were found to lead to
enhanced activities and in certain cases produced polyolefins with
high molecular weights. Given the need for toughening up and
reinforcing polyolefins for a number of applications, (ultra)high
molecular weight polyolefins are in demand.1 Recently, newly
designed 2-(1-(arylimino)propyl)quinolin-8-ols13 were successfully
used to prepare aluminium pro-catalysts for the highly active
ring-opening polymerization of e-caprolactone13a and trichloroti-
tanium complexes for ethylene polymerization.13b Herein the
synthesis, characterization and catalytic behaviour of the title
complexes towards ethylene (co-)polymerization are reported in
detail. Specifically, 2-(1-(arylimino)propyl)quinolin-8-olate half-
titanocene dichlorides, when activated with methyl-aluminoxane
(MAO), performed with high activity in ethylene polymerization
and with good to high activity in the co-polymerization of ethylene
with either 1-hexene or 1-octene; some of the resultant polymers
possessed molecular weights in excess of one million.
Over the last couple of decades, the fine-tuning of pro-catalysts
has been exploited for tailoring and controlling the microstruc-
ture of resultant polyolefins, and particular attention have
been given to pro-catalysts deploying early-transition metals1
(including metallocene2 and half-metallocene3) as well as late-
transition metals.4 Bridged half-metallocene type catalysts, known
as constrained geometry compounds (CGC), represent a highly
useful and efficient family of pro-catalysts,3a,3b however, diffi-
culties have been encountered with their synthesis and there
is a need to develop new systems to avoid expensive patent
issues by developing new intellectual property. More recently,
non-bridged half-metallocene complexes of the type Cp¢MLXn
(M = Ti, Zr, Hf; L = anionic ligand; X = halogen or alkyl),
have been extensively explored by employing various anionic lig-
ands such as aryloxy,5 ketimide,6 acetamidinato,7 iminophenoxy,8
pyridinylalkyl-oxy9 and N-substituted (iminomethyl)pyrrolides10
amongst others.11 In separate studies, bis(iminophenoxy)titanium
dihalides (known as FI catalysts) have been found to ultimately
afford very high catalytic activity within a short lifetime, but
aKey Laboratory of Engineering Plastics and Beijing National Laboratory for
Molecular Sciences, Institute of Chemistry, Chinese Academy of Sciences,
Beijing, 100190, China. E-mail: whsun@iccas.ac.cn; Fax: +86 10 62618239;
Tel: +86 10 62557955
2. Results and discussion
bSchool of Chemistry, University of East Anglia, Norwich, NR4 7TJ, UK.
E-mail: carl.redshaw@uea.ac.uk; Fax: +44 (0)1603 592003; Tel: +44
(0)1603 593137
2.1 Synthesis and characterization of half-titanocene complexes
(C1–C12)
Complexes C1–C12 were prepared by reaction of the potassium
salts of (1-(phenylimino)propyl)quinolin-8-ol with one equivalent
† CCDC reference numbers 807618–807619. For crystallographic data in
CIF or other electronic format see DOI: 10.1039/c1dt10068h
6802 | Dalton Trans., 2011, 40, 6802–6809
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of Cp¢TiCl3 in toluene. Analytically pure titanium complexes,
LCp¢TiCl2 (C1–C12, Scheme 1), were isolated as red crystalline
solids in moderate to high yields. Compositions were confirmed
by elemental analyses and NMR spectroscopy.
Fig. 2 ORTEP drawing of C5 with thermal ellipsoids drawn at the 30%
probability level. Hydrogen atoms are omitted for clarity. Selected bond
◦
˚
lengths (A) and angles ( ): Ti(1)–O(1) 1.946(2), Ti(1)–N(1) 2.128(2),
Ti(1)–N(2) 2.389(2), Ti(1)–Cl(1) 2.4509(10), Ti(1)–Cl(2) 2.4422(10),
Ti1–Cpcent 2.076, O(1)–Ti(1)–N(1) 77.18(9), O(1)–Ti(1)–N(2) 146.36(9),
N(1)–Ti(1)–N(2) 69.19(9), O(1)–Ti(1)–Cl(2) 89.10(7), N(1)–Ti(1)–Cl(2)
76.01(7), N(2)–Ti(1)–Cl(2) 81.99(6), O(1)–Ti(1)–Cl(1) 88.50(7),
N(1)–Ti(1)–Cl(1) 76.21(7), N(2)–Ti(1)–Cl(1) 84.65(6), Cl(2)–Ti(1)–Cl(1)
151.95(3).
Scheme 1 Synthesis of complexes C1–C12.
Single crystals of complexes C1 and C5 suitable for X-ray
crystallographic studies were obtained from dichloromethane
solutions when layered with n-heptane. The molecular structures
are illustrated in Fig. 1 and Fig. 2; selected bonds and angles are
given in each caption.
(s, 5H) for the Cp in the 1H NMR spectrum (and 125.1 ppm in 13
C
5
NMR spectrum), demonstrating the delocated feature of h -Cp
ring. The dihedral angle defined by the two chelating planes of
Ti1–O1–C1–C6–N1 and Ti1–N1–C9–C10–N2 is 0.48◦, indicative
of the coplanar nature of the titanium, oxygen and nitrogen atoms.
In complex C5 (Fig. 2), the titanium centre exhibits a similarly
distorted octahedral geometry to that observed for C1. The
dihedral angle defined by the two chelating rings (Ti1–O1–C1–
C6–N1, Ti1–N1–C9–C10–N2) is 2.04◦, which is somewhat larger
than observed in complex C1. The nature of the Ti–N bond (Ti(1)–
˚
N(1) = 2.128(4) A) is the same as that in complex C1, whereas the
˚
Ti–N bond (Ti(1)–N(2) = 2.389(2) A) is longer than that found in
complex C1, presumably due to the differences of substituent at
the ortho-position of the aryl group. The Ti–Cl bond lengths and
˚
˚
angles (Ti(1)–Cl(1) = 2.4509(10) A, Ti(1)–Cl(2) = 2.4422(10) A,
Cl(1)–Ti(1)–N(1) = 76.21(7) ◦, Cl(2)–Ti(1)–N(1) = 76.21(7) ◦) are
essentially the same, leading to the adoption of symmetrically
bonded chloride atoms. The dihedral angle of the aryl-imine and
the quinoline ring is 89.04◦.
Fig. 1 ORTEP drawing of C1 with thermal ellipsoids drawn at the
30% probability level. Hydro◦gen atoms are omitted for clarity. Selected
˚
bond lengths (A) and angles ( ): Ti(1)–O(1) 1.953(4), Ti(1)–N(1) 2.128(4),
Ti(1)–N(2) 2.379(4), Ti(1)–Cl(1) 2.4502(16), Ti(1)–Cl(2) 2.4177(17),
Ti1–Cpcent 2.072, O(1)–Ti(1)–N(1) 77.22(16), O(1)–Ti(1)–N(2) 146.15(15),
N(1)–Ti(1)–N(2) 68.95(15), O(1)–Ti(1)–Cl(2) 88.89(12), N(1)–Ti(1)–Cl(2)
76.29(12), N(2)–Ti(1)–Cl(2) 84.28(11), O(1)–Ti(1)–Cl(1) 87.87(12),
N(1)–Ti(1)–Cl(1) 75.69(12), N(2)–Ti(1)–Cl(1) 82.96(11), Cl(2)–Ti(1)–Cl(1)
151.82(6).
2.2 Catalytic behavior for ethylene polymerization
Based on our prior work,12,13b where we screened a variety of
co-catalysts for ethylene polymerization, we have chosen MAO
here as the co-catalyst for the polymerization of ethylene to
examine the catalytic performance of the pro-catalysts. Ethylene
polymerization using the C7/MAO system was conducted to
investigate the influence of the polymerization conditions such
as the Al/Ti molar ratio, the reaction temperature and time
constraints on the catalytic behavior. The results are illustrated
in Table 1. Changing the molar ratio of Al/Ti at 20 ◦C achieved a
high activity of 6.44 ¥ 106 g mol-1(Ti)·h-1 when the ratio of Al/Ti
was 1000; the lower molar ratio of Al/Ti is effective to reduce the
cost. Increasing temperatures led to◦a decrease in catalytic activity
from 6.44 ¥ 106 g mol-1(Ti)·h-1 at 20 C to 1.48 ¥ 106 g mol-1(Ti)·h-1
at 80 ◦C (Runs 3, 6–8, Table 1), caused by the greater potential for
chain transfers and terminations at elevated temperatures. When
considering the reaction period of the ethylene polymerization, the
data for the activities were observed over the time periods of 5 min,
15 min and 30 min (Runs 3, 9, and 10), and the highest activity was
As shown in Fig. 1, the complex C1 contains only one imine-
containing ligand set, together with two chlorine atoms and one Cp
ring around the pseudo octahedral titanium center. The chlorine
atom (Cl1) bends away from both the Cp ring and the ancillary
˚
ligand L1. The Ti1–Cl1 bond length at 2.4502(16) A, is longer than
the values found in related complexes.13b,14 The two Ti–N bonds
˚
˚
(Ti(1)–N(1) = 2.128(4) A, Ti(1)–N(2) = 2.379(4) A) are in the range
commonly observed for titanium complexes, but the Ti(1)–N(1)
bond length is shorter than the corresponding Ti(1)–N(2) bond
length. The distance between the centroid of the Cp ring and the
˚
titanium is 2.072 A, whilst the Ti–C bond lengths are slightly
˚
different within the range of Ti–C 2.334(5) to 2.441(6) A (DTi–C =
˚
0.107 A) and these carbon atoms, C(21), C(22), C(23), C(24) and
C(25) are coplanar, which is the same structural feature previously
observed.12e Moreover, there is only one single peak at 6.73 ppm
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Table 1 Ethylene polymerization results by C7/MAO systemsa
◦
T/◦C
t (min)
Polym (g)
Actb
Mw
Mw/Mn
Tm ( C)
c,d
d
e
Run
Al/Ti
1
2
3
4
5
6
7
8
500
750
20
20
20
20
20
40
60
80
20
20
15
15
15
15
15
15
15
15
5
1.04
1.59
1.61
1.43
1.12
1.24
0.58
0.37
0.14
2.60
4.16
6.36
6.44
5.72
4.48
4.96
2.32
1.48
1.68
5.20
12.2
13.3
12.2
9.56
4.62
8.69
2.72
0.84
11.1
5.52
2.56
2.96
3.15
3.29
8.17
2.93
6.97
7.04
2.68
7.75
140.7
141.7
139.2
138.4
134.7
137.3
130.7
128.0
140.0
135.9
1000
1250
1500
1000
1000
1000
1000
1000
9
10
30
a Condition: 1 mmol complex C7, toluene (total volume 100 mL), 10 atm. b Activity: 106 g mol-1(Ti)·h-1; c 105 g mol-1. d Determined by GPC. e Determined
by DSC.
Table 2 Ethylene polymerization results by C1–C12/MAO systemsa
observed at 15 min, meaning that there was a initial period for the
polymerization reaction and the slow deacativation of the active
◦
c,d
d
e
Run
Cat.
Polym (g)
Actb
Mw
Mw/Mn
Tm ( C)
species, and which was commonly observed by half-metallocenes.5
The GPC analysis results indicated that some polyethylenes
obtained at 20 ◦C had a molecular weight of higher than a million;
the polyethylenes produced at increased reaction temperature had
lower molecular weights (Fig. 3). Moreover, increasing the molar
ratio of Al/Ti resulted in the formation of polyethylene with
lower molecular weight, caused by the enhanced chain transfer
from the titanium species to aluminium; further elimination
happened at both elevated reaction temperature and on increasing
the aluminium concentration.15 Meanwhile the molecular weight
distribution of the polyethylenes obtained also increased at
elevated reaction temperature and with improving molar ratio
of aluminium to titanium. These observations were consistent
with chain transfer from the active species to aluminium as well
as enhanced chain termination at aluminium.15 Compared with
their trichlorotitanium analogues,13b the current half-titanocene
procatalysts produced the polyethylenes with higher molecular
weights.
1
2
3
4
5
6
7
8
C7
1.61
1.22
0.65
1.47
0.53
0.34
0.55
0.34
0.17
0.62
0.22
0.47
6.44
4.88
2.60
5.88
2.12
1.36
2.20
1.36
0.68
2.48
0.88
1.88
12.2
9.59
2.35
2.46
1.13
0.84
2.05
3.47
4.02
3.15
4.36
1.93
3.15
5.90
10.4
12.9
12.6
10.4
13.3
15.1
17.1
16.8
16.1
16.4
139.2
136.7
129.4
128.0
130.0
129.2
130.9
137.2
136.7
134.7
136.2
129.7
C8
C9
C10
C11
C12
C1
C2
9
C3
10
11
12
C4
C5
C6
a Condition: 1 mmol complex, Al/Ti = 1000, toluene (total volume 100 mL),
15 min, 20 ◦C, 10 atm. b Activity: 106 g mol-1(Ti)·h-1; c 105 g mol-1;
d Determined by GPC. e Determined by DSC.
donating Cp* stabilizes the active species, leading to the higher
observed activity. Catalytic activities followed the order C1 (Me) >
C2 (Et) > C3 (iPr), C7 (Me) > C8 (Et) > C9 (iPr), and although the
iPr group could provide more donation into Ti, the steric effect
was more evident (reducing the monomer access to the active
sites). Additionally, the activities of the pro-catalysts were also
affected by the ligands with an additional para-methyl substituent,
for example in the pro-catalysts C10 and C11: C7 (R1 = Me, R2 =
H) > C10 (R1 = Me, R2 = Me), C8 (R1 = Et, R2 = H) > C11 (R1 = Et,
R2 = Me), reflecting the electronic influence played by the ligands
in this process. In general, the pro-catalysts containing a Cp*
possessed higher activities than did their analogues bearing Cp. A
combination of factors such as the better solubility of complexes
bearing Cp*, together with electronic/steric influences, no doubt
all play a role. In addition, polyethylenes obtained by the Cp*-pro-
catalysts showed narrower molecular weight distributions than did
those produced by the Cp pro-catalyst systems. The influence of the
substituents of ligands was similarly observed within the imino-
indolate half-titanocenes12b and amidate half-titanocenes.12e
Fig. 3 GPC profiles of PEs obtained from Runs 3 and 6–8 in Table 1. (a:
T = 20 ◦C, Run 3; b: T = 40 ◦C, Run 6; c: T = 60 ◦C, Run 7; d: T = 80 ◦C,
Run 8).
In further investigations, the other pro-catalysts herein were
studied using the reaction conditions Al/Ti 1000 at 20 ◦C over
15 min (Table 2). As seen from Table 2, the substituents on the
Cp¢ groups had a significant influence on the observed catalytic
properties, with the catalysts containing Cp* exhibiting higher
activity than catalysts containing a Cp group, although all the
catalyst activities were higher than those of the corresponding
trichlorotitanium complexes.12b,12c,13b It is thought that Cp¢ offers
more p donation into Ti, which along with the more electron
2.3 Co-polymerization of ethylene with 1-hexene or 1-octene
As well as the homo-polymerization of ethylene, it is interesting
to study the co-polymerization of ethylene with other a-olefins,
which potentially can produce branched polyolefins.16 As a repre-
sentative example, the co-polymerization of ethylene/1-hexene by
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Table 3 Co-polymerization of ethylene with 1-hexene by C7–C12/MAOa
◦
c,d
d
e
Run Cat. 1-C6
Polym (g) Actb Mw
Mw/Mn
Tm ( C)
1
2
3
4
5
6
7
8
C7
C7
C7
C8
C9
1 M
0.13 0.52 2.61
28.9
n.d.
18.4
n.d.
n.d.
20.7
n.d.
n.d.
125.1
126.2
128.4
125.9
126.1
130.0
125.9
126.4
0.5 M 0.45
0.1 M 1.30
0.1 M 1.09
0.1 M 0.43
1.80 n.d.
5.20 7.22
4.36 n.d.
1.72 n.d.
4.76 3.45
1.56 n.d.
0.88 n.d.
C10 0.1 M 1.19
C11 0.1 M 0.39
C12 0.1 M 0.22
a Condition: 1 mmol complex, Al/Ti = 1000, toluene (total volume 100 mL),
15 min, 20 ◦C, 10 atm; b Activity: 106 g mol-1(Ti)·h-1; c 105 g mol-1;
d Determined by GPC. e Determined by DSC; n.d.: polymer partly
unsolvable.
Fig. 4 13C NMR spectrum of the ethylene/1-hexene co-polymer by the
C7/MAO system (Run 1 in Table 3).
spectrum showed that the obtained poly(ethylene-1-hexene) con-
tained ethylene (EEE), and EHE, EHH, HEH, etc.18
In the same way, the ethylene/1-octene co-polymer obtained by
the C7/MAO system (Run 1 in Table 4) was measured by 13C NMR
spectroscopy at 112 ◦C, and its 13C NMR spectrum indicated the
incorporation of 1-octene was 6.53 mol % (Fig. 5).
Table 4 Co-polymerization of ethylene with 1-octene by C7–C12/MAOa
◦
Run Cat
1-C8
1 M
0.5 M 0.26
0.1 M 1.26
0.1 M 0.92
0.1 M 0.62
Polym (g) Actb Mw
Mw/Mn
Tm ( C)
c,d
d
e
1
2
3
4
5
6
7
8
C7
C7
C7
C8
C9
0.23
0.92
1.04
5.04
3.68
2.48
4.28
2.16
1.21
2.83 29.5
n.d. n.d.
1.76 24.6
n.d.
n.d.
2.74 25.2
n.d.
n.d.
120.1
125.8
126.4
126.1
126.1
127.4
126.7
125.1
n.d.
n.d.
C10 0.1 M 1.07
C11 0.1 M 0.54
C12 0.1 M 0.31
n.d.
n.d.
a Condition: 1 mmol complex, Al/Ti = 1000, toluene (total volume 100 mL),
15 min, 20 ◦C, 10 atm; b Activity: 106 g mol-1(Ti)·h-1; c 105 g mol-1;
d Determined by GPC. e Determined by DSC. n.d.: polymer partly
unsolvable.
C7–C12/MAO was successfully carried out and the results are
presented in Table 3. The results showed that the catalytic activity
decreased with improving co-monomer concentration; similar
observations have appeared in the literature.12b,12c Complex C7
exhibited a higher catalytic activity than did C8–C12, which is in
agreement with the homo-polymerization results. Such differences
of activities are attributed to the electronic rather than the steric
effects associated with the substituents present. Comparing the co-
polymers to the linear polyethylene, the melting points were much
lower, because the incorporation of the 1-hexene co-monomer,
which produces butyl branches and results in crystallization at
lower temperature.
The results for the ethylene/1-octene co-polymerization are
summarized in Table 4, and the variations of their catalytic
activities were almost identical with the ethylene/1-hexene co-
polymerization. The melting points were a little lower than those of
the ethylene/1-hexene copolymers. DSC analysis of the resultant
co-polymers showed melting points from 120.1 to 127.4 ◦C,
which are lower for all co-polymers than those recorded for the
linear polyethylenes. The GPC analysis indicated wider molecular
weight distributions for the co-polymers than those obtained for
the polyethylene runs. In general, the half-titanocen complexes
showed higher activities and better incoporation of co-monomers
than did their trichlorotitanium analogues.13b
Fig. 5 13C NMR spectrum of ethylene/1-octene co-polymer by the
C7/MAO system (Run 1 in Table 4).
3. Conclusion
The molecular structures of complexes C1 and C5 were confirmed
by single crystal X-ray diffraction analysis. The titanium com-
plexes LCp¢TiCl2 (Cp¢ = C5H5, C5Me5, L = imino-quinoline ligand,
C1–C12), were shown to be highly efficient catalysts for ethylene
polymerization when activated with MAO. The pro-catalysts (C7–
C12) bearing a Cp* ligand exhibited higher activities than did their
analogues (C1–C6) containing a Cp ligand, catalytic activities in
the order of C1 (Me) > C2 (Et) > C3 (iPr), C7 (Me) > C8 (Et) > C9
(iPr) was observed. Such complexes showed good catalytic activity
for ethylene polymerization (up to 6.44 ¥ 106 g mol-1(Ti)·h-1) and
co-polymerization (up to 5.20 ¥ 106 g mol-1(Ti)·h-1) using MAO as
a co-catalyst; the incorporation of co-monomer was confirmed in
up to a molar ratio of 11.6% for 1-hexene and 6.53% for 1-octene.
4. Experimental section
4.1 General Procedures
The 13C NMR spectrum (Fig. 4) of the ethylene/1-hexene co-
polymer by the C7/MAO system (Run 1 in Table 3) revealed
typical characteristics of linear low density polyethylene,17 and
indicated the incorporation of 11.6 mol % of 1-hexene. The
monomer sequence distributions determined by the 13C NMR
All manipulations of air and/or moisture-sensitive compounds
were performed under nitrogen atmosphere in a glovebox or using
standard Schlenk techniques. Methylaluminoxane (MAO, 1.46 M
in toluene) was purchased from Albemarle. Toluene, n-hexane
and n-heptane were refluxed over sodium and benzophenone,
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CCH2CH3). 13C NMR (CDCl3, 100 MHz, ppm): d 178.3,
˚
distilled and then stored over activated molecular sieves (4 A) for
N
24 h under nitrogen atmosphere. Dichloromethane (CH2Cl2), 1-
hexene and 1-octene were refluxed over calcium hydride, distilled
167.1, 148.4, 142.3, 137.9, 135.1, 133.1, 129.2, 127.3, 126.7, 125.1,
123.5, 120.9, 117.2, 111.8, 29.8, 24.7, 14.4, 11.4. Anal. Calcd. for
C27H28Cl2N2OTi: C, 62.93; H, 5.48; N, 5.44. Found: C, 62.72; H,
5.57; N, 5.41.
˚
and then stored over activated molecular sieves (4 A) for 24 h
in a glovebox prior to use. CDCl3 was dried over activated
˚
4 A molecular sieves. Elemental analysis was performed on a
(g5-Cyclopentadienyl)dichlorotitanium
2-(1-(2,6-diisopropyl-
Flash EA 1112 microanalyzer. H and 13C NMR spectra were
1
phenylimino)propyl)quinolin-8-olate (C3). Using the same proce-
dure as for the synthesis of C1 with 2-(1-(2,6-diisopropylphenyl-
imino)propyl)quinolin-8-ol (L3) (0.361 g, 1.00 mmol) instead of
L1, C3 was obtained as a dark red solid in 89.5% yield (0.52
recorded on a Bruker DMX 400 MHz instrument at ambient
temperature using TMS as an internal standard. Assignments are
based on COSY, HSQC and HMBC experiments. DSC trace and
melting points of polyethylene were obtained from the second
sca◦nning run on a Perkin–Elmer DSC-7 at a heating rate of
10 C min-1. 13C NMR spectra of the polymers were recorded on
a Bruker DMX-300 MHz instrument at 112 ◦C in deuterated 1,2-
dichlorobenzene with TMS as an internal standard. Molecular
weights and polydispersity indices (PDI) of (co-)polyethylenes
were determined using a Waters Alliance GPC 2000 instrument
equipped with a refractive index (RI) detector and a set of u-
Styragel HT columns containing series of 106, 105, 104, and 103
size pore at 135 ◦C in 1,2,4-trichlorobenzene with polystyrene as
the standard.
1
g). H NMR (CDCl3, 400 MHz, ppm): d 8.45 (d, J = 8.6 Hz,
1H, quino-H), 7.92 (d, J = 8.6 Hz, 1H, quino-H), 7.75 (t, J =
8.4 Hz, 1H, quino-H), 7.43 (d, J = 8.5 Hz, 1H, quino-H), 7.24
(t, J = 7.2 Hz, 1H, quino-H), 7.18 (d, J = 7.7 Hz, 2H, Ar-H),
6.93 (t, J = 7.8 Hz, 1H, Ar-H), 6.72(s, 5H, Cp), 3.31–3.28 (m,
2H, Ar-CH(CH3)2), 2.76–2.74 (m, 2H, N CCH2CH3), 1.49
(d, J = 6.5 Hz, 6H, Ar-CH(CH3)2), 1.37 (t, J = 6.8 Hz, 3H,
N
CCH2CH3), 1.05 (d, J = 7.5 Hz, 6H, Ar-CH(CH3)2). 13C
NMR (CDCl3, 100 MHz, ppm): d 176.3, 153.3, 152.5, 146.2,
137.1, 136.7, 130.8, 129.0, 128.9, 126.7, 123.0, 120.6, 118.0, 110.4,
28.5, 23.6, 13.7, 11.4. Anal. Calcd. For C29H32Cl2N2OTi: C, 64.10;
H, 5.94; N, 5.16. Found: C, 63.84; H, 5.93; N, 5.02.
4.2 Synthesis of Titanium(IV) Complexes (C1–C12)
(g5-Cyclopentadienyl)dichlorotitanium 2-(1-(mesitylimino)-pro-
pyl)quinolin-8-olate (C4). Using the same procedure as for the
synthesis of C1 with 2-(1-(mesitylimino)propyl)quinolin-8-ol (L4)
(0.318 g, 1.00 mmol) instead of L1, C4 was obtained as a dark red
(g5-Cyclopentadienyl)dichlorotitanium 2-(1-(2,6-dimethyl-phe-
nylimino)propyl)quinolin-8-olate (C1). To a stirred solution of 2-
(1-(2,6-dimethylphenylimino)propyl)quinolin-8-ol (L1) (0.304 g,
1.00 mmol) in toluene (30 mL) at -78 ◦C, KH (0.040 g, 1.00 mmol)
was added. The mixture was stirred for an additional 4 h. At
-78 ◦C, 1.00 mmol CpTiCl3 (0.223 g, Cp = cyclopentadienyl) was
added to form the complex. The resultant mixture was allowed
to warm to room temperature and stirred for an additional 24 h.
The residue, obtained by removing the solvent under vacuum, was
extracted with CH2Cl2 (3 ¥ 20 mL) and the combined filtrates were
concentrated in vacuo to reduce the volume to 20 mL. Heptane
(45 mL) was layered and several days later, dark red crystals were
1
solid in 40% yield (0.21 g). H NMR (CDCl3, 400 MHz, ppm):
d 8.46 (d, J = 8.5 Hz, 1H, quino-H), 7.87 (d, J = 8.5 Hz, 1H,
quino-H), 7.77 (t, J = 7.9 Hz, 1H, quino-H), 7.45 (d, J = 8.1 Hz,
1H, quino-H), 7.18 (d, J = 7.5 Hz, 1H, quino-H), 6.91 (s, 2H,
Ar-H), 6.75 (s, 5H, Cp), 2.69-2.61 (m, 2H, N CCH2CH3), 2.37
(s, 3H, Ar-CH3), 1.26 (s, 6H, Ar-CH3), 1.20 (t, J = 9.4 Hz, 3H,
N
CCH2CH3). 13C NMR (CDCl3, 100 MHz, ppm): d 178.5,
167.5, 147.1, 138.0, 133.1, 130.1, 129.7, 129.2, 128.4, 125.1, 122.3,
121.5, 120.7, 117.2, 111.8, 29.5, 24.9, 20.6, 11.4. Anal. Calcd. For
C26H26Cl2N2OTi: C, 62.30; H, 5.23; N, 5.59. Found: C, 62.41; H,
5.11; N, 5.38.
1
obtained (0.280 g, yield 57.5%). H NMR (CDCl3, 400 MHz,
ppm): d 8.48 (d, J = 8.6 Hz, 1H, quino-H), 7.89 (d, J = 8.6 Hz,
1H, quino-H), 7.78 (t, J = 8.4 Hz, 1H, quino-H), 7.46 (d, J =
8.4 Hz, 1H, quino-H), 7.25 (d, J = 8.1 Hz, 1H, quino-H), 7.20
(d, J = 8.0 Hz, 2H, Ar-H), 6.98 (t, J = 7.8 Hz, 1H, Ar-H), 6.73
(s, 5H, Cp), 2.68–2.62 (m, 2H, N CCH2CH3), 2.42 (s, 6H, Ar-
CH3), 1.23 (t, J = 7.3 Hz, 3H, N CCH2CH3). 13C NMR (CDCl3,
100 MHz, ppm): d 178.0, 167.2, 149.3, 142.3, 138.0, 133.1, 130.6,
129.5, 127.1, 125.1, 123.5, 122.3, 120.8, 116.5, 111.8, 24.9, 20.7,
11.4. Anal. Calcd. for C25H24Cl2N2OTi: C, 61.63; H, 4.96; N, 5.75.
Found: C, 61.13; H, 5.06; N, 5.58.
(g5-Cyclopentadienyl)dichlorotitanium 2-(1-(2,6-diethyl-4-me-
thylphenylimino)propyl)quinolin-8-olate (C5). Using the same
procedure as for the synthesis of C1 with 2-(1-(2,6-diethyl-
4-methylphenylimino)propyl)quinolin-8-ol (L5) (0.346 g,
1.00 mmol) instead of L1, C5 was obtained as a dark red solid in
1
70.1% yield (0.37 g). H NMR (CDCl3, 400 MHz, ppm): d 8.45
(d, J = 8.6 Hz, 1H, quino-H), 7.87 (d, J = 8.6 Hz, 1H, quino-H),
7.76 (t, J = 8.0 Hz, 1H, quino-H), 7.44 (d, J = 8.2 Hz, 1H,
quino-H), 7.24 (d, J = 7.5 Hz, 1H, quino-H), 7.14 (s, 2H, Ar-H),
6.70 (s, 5H, Cp), 2.98–2.90 (m, 2H, Ar-CH2CH3), 2.68–2.62 (m,
2H, N CCH2CH3), 2.53–2.45 (m, 2H, Ar-CH2CH3), 2.43 (s,
3H, Ar-CH3), 1.28 (t, J = 7.8 Hz, 6H, Ar-CH2CH3), 1.22 (t, J =
8.1 Hz, 3H, N CCH2CH3). 13C NMR (CDCl3, 100 MHz, ppm):
178.1, 167.1, 146.2, 142.4, 139.1, 137.8, 136.7, 134.8, 133.0, 130.5,
127.3, 125.1, 120.9, 116.3, 111.8, 25.3, 24.6, 21.3, 14.4, 11.3. Anal.
Calcd. For C28H30Cl2N2OTi: C, 63.53; H, 5.71; N, 5.29. Found: C,
63.67; H, 5.98; N, 5.24.
(g5-Cyclopentadienyl)dichlorotitanium 2-(1-(2,6-diethyl-phenyl-
imino)propyl)quinolin-8-olate (C2). Using the same procedure
as for the synthesis of C1 with 2-(1-(2,6-diethylphenylimino)-
propyl)quinolin-8-ol (L2) (0.332 g, 1.00 mmol) instead of L1, C2
was obtained as a dark red solid in 44.3% yield (0.23 g). 1H NMR
(CDCl3, 400 MHz, ppm): d 8.46 (d, J = 8.6 Hz, 1H, quino-H),
7.88 (d, J = 8.6 Hz, 1H, quino-H), 7.77 (t, J = 8.4 Hz, 1H, quino-
H), 7.44 (d, J = 8.4 Hz, 1H, quino-H), 7.35 (d, J = 8.1 Hz, 1H,
quino-H), 7.18 (d, J = 8.0 Hz, 2H, Ar-H), 6.97 (t, J = 7.8 Hz,
1H, Ar-H), 6.70 (s, 5H, Cp), 3.04–2.98 (m, 2H, N CCH2CH3),
2.66–2.64 (m, 2H, Ar-CH2CH3), 2.55–2.50 (m, 2H, Ar-CH2CH3),
1.28 (t, J = 7.3 Hz, 6H, Ar-CH2CH3), 1.14 (t, J = 7.4 Hz, 3H,
(g5-Cyclopentadienyl)dichlorotitanium 2-(1-(2,6-dichloro-phe-
nylimino)propyl)quinolin-8-olate
(C6). Using
the
same
procedure as for the synthesis of C1 with 2-(1-(2,
6806 | Dalton Trans., 2011, 40, 6802–6809
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6-dichlorophenylimino)propyl)quinolin-8-ol (L6) (0.345 g,
1.00 mmol) instead of L1, C6 was obtained as a dark red solid in
19% yield (0.12 g). 1H NMR (CDCl3, 400 MHz, ppm): d 8.48 (d,
J = 8.6 Hz, 1H, quino-H), 7.95 (d, J = 8.8 Hz, 1H, quino-H), 7.78
(t, J = 8.0 Hz, 1H, quino-H), 7.46 (d, J = 8.3 Hz, 1H, quino-H),
7.31 (t, J = 8.1 Hz, 1H, quino-H), 7.24 (d, J = 8.1 Hz, 2H, Ar-H),
6.97 (d, J = 8.1 Hz, 1H, Ar-H), 6.80 (s, 5H, Cp), 2.75–2.69 (m,
2H, N CCH2CH3), 1.35 (t, J = 7.7 Hz, 3H, N CCH2CH3).
13C NMR (CDCl3, 100 MHz, ppm): d 181.9, 167.2, 138.0,
133.6, 130.9, 129.7, 129.3, 128.8, 128.5, 125.1, 121.2, 118.1,
117.1, 116.5, 112.0, 26.1, 11.8. Anal. Calcd. for C23H18Cl4N2OTi:
C, 52.31; H, 3.44; N, 5.30. Found: C, 52.21; H, 3.33; N,
5.22.
174.3, 153.3, 152.5, 146.2, 137.1, 136.7, 130.8, 129.0, 128.9, 126.7,
123.0, 120.6, 118.0, 110.4, 28.5, 23.6, 13.7, 13.4, 11.4. Anal. Calcd.
For C34H42Cl2N2OTi: C, 66.56; H, 6.90; N, 4.57. Found: C, 66.34;
H, 6.98; N, 4.35.
(g5-Pentamethylcyclopentadienyl)dichlorotitanium 2-(1-(mesity-
limino)propyl)quinolin-8-olate (C10). Using the same procedure
as for the synthesis of C7 with L4 instead of L1, C10 was obtained
as a dark red solid in 48% yield (0.16 g). 1H NMR (CDCl3,
400 MHz, ppm): d 8.50 (d, J = 8.5 Hz, 1H, quino-H), 8.26 (d,
J = 8.2 Hz, 1H, quino-H), 7.51 (t, J = 7.4 Hz, 1H, quino-H), 7.40
(d, J = 7.6 Hz, 1H, quino-H), 7.23 (d, J = 7.1 Hz, 1H, quino-H),
6.91 (s, 2H, Ar-H), 2.81–2.77 (m, 2H, N CCH2CH3), 2.31 (s, 3H,
Ar-CH3), 2.21 (s, 15H, Cp*), 2.04 (s, 6H, Ar-CH3), 1.08 (t, J =
7.3 Hz, 3H, N CCH2CH3). 13C NMR (CDCl3, 100 MHz, ppm): d
171.3, 155.2, 153.4, 152.5, 146.0, 136.7, 132.5, 129.1, 128.8, 128.7,
125.1, 120.5, 118.0, 110.4, 23.1, 20.1, 18.2, 13.5, 11.7. Anal. Calcd.
For C31H36Cl2N2OTi: C, 65.16; H, 6.35; N, 4.90. Found: C, 65.04;
H, 6.48; N, 4.71.
(g5-Pentamethylcyclopentadienyl)dichlorotitanium 2-(1-(2,6-di-
methylphenylimino)propyl)quinolin-8-olate (C7). Using the same
procedure as for the synthesis of C1 with 1.00 mmol Cp*TiCl3
(0.289 g, Cp* = pentamethylcyclopentadienyl) instead of CpTiCl3,
1
C7 was obtained as a dark red solid in 56.8% yield (0.3 g). H
NMR (CDCl3, 400 MHz, ppm): d 8.48 (d, J = 8.4 Hz, 1H, quino-
H), 8.26 (d, J = 8.6 Hz, 1H, quino-H), 7.53 (t, J = 7.7 Hz, 1H,
quino-H), 7.41 (d, J = 8.3 Hz, 1H, quino-H), 7.25 (d, J = 8.1 Hz,
1H, quino-H), 7.10 (d, J = 7.4 Hz, 2H, Ar-H), 6.98 (t, J = 7.8 Hz,
1H, Ar-H), 2.85–2.79 (m, 2H, N CCH2CH3), 2.38 (s, 6H, Ar-
CH3), 2.27 (s, 15H, Cp*), 1.08 (t, J = 7.6 Hz, 3H, N CCH2CH3).
13C NMR (CDCl3, 100 MHz, ppm): d 173.9, 153.1, 152.4, 148.4,
137.0, 136.7, 129.0, 128.8, 128.0, 125.2, 123.2, 120.3, 118.0,
110.4, 23.1, 18.2, 13.5, 11.6. Anal. Calcd. for C30H34Cl2N2OTi:
C, 64.65; H, 6.15; N, 5.03. Found: C, 64.59; H, 6.27; N,
4.98.
(g5-Pentamethylcyclopentadienyl)dichlorotitanium 2-(1-(2,6-di-
ethyl-4-methylphenylimino)propyl)quinolin-8-olate (C11). Using
the same procedure as for the synthesis of C7 with L5 instead
of L1, C11 was obtained as a dark red solid in 64% yield (0.36
1
g). H NMR (CDCl3, 400 MHz, ppm): d 8.47 (d, J = 8.6 Hz,
1H, quino-H), 8.22 (d, J = 8.3 Hz, 1H, quino-H), 7.54 (t, J =
7.9 Hz, 1H, quino-H), 7.33 (d, J = 8.2 Hz, 1H, quino-H), 7.20
(d, J = 7.8 Hz, 1H, quino-H), 6.94 (s, 2H, Ar-H), 2.83–2.75
(m, 2H, N CCH2CH3), 2.48–2.39 (m, 2H, Ar-CH2CH3), 2.36 (s,
15H, Cp*), 2.36 (s, 3H, Ar-CH3), 2.32-2.26 (m, 2H, Ar-CH2CH3),
1.12 (t, J = 7.5 Hz, 6H, Ar-CH2CH3), 1.05 (t, J = 7.4 Hz, 3H,
N
CCH2CH3). 13C NMR (CDCl3, 100 MHz, ppm): d 170.7,
(g5-Pentamethylcyclopentadienyl)dichlorotitanium 2-(1-(2,6-di-
ethylphenylimino)propyl)quinolin-8-olate (C8). Using the same
procedure as for the synthesis of C7 with L2 instead of L1, C8
was obtained as a dark red solid in 68% yield (0.35 g). 1H NMR
(CDCl3, 400 MHz, ppm): d 8.49 (d, J = 8.6 Hz, 1H, quino-H),
8.29 (d, J = 8.5 Hz, 1H, quino-H), 7.55 (t, J = 7.7 Hz, 1H, quino-
H), 7.42 (d, J = 8.2 Hz, 1H, quino-H), 7.25 (d, J = 8.1 Hz, 1H,
quino-H), 7.17 (d, J = 8.0 Hz, 2H, Ar-H), 7.10 (t, J = 7.8 Hz, 1H,
Ar-H), 2.85–2.81 (m, 2H, N CCH2CH3), 2.51–2.43 (m, 2H, Ar-
CH2CH3), 2.30 (s, 15H, Cp*), 2.17–2.10 (m, 2H, Ar-CH2CH3),
1.22 (t, J = 7.5 Hz, 6H, Ar-CH2CH3). 1.10 (t, J = 7.5 Hz, 3H,
153.5, 152.5, 145.0, 137.1, 136.7, 132.6, 130.8, 129.0, 128.8, 126.7,
120.5, 118.0, 110.4, 24.7, 23.3, 21.4, 13.7, 13.4, 11.6. Anal. Calcd.
For C33H40Cl2N2OTi: C, 66.12; H, 6.73; N, 4.67. Found: C, 66.07;
H, 6.83; N, 4.51.
(g5-Pentamethylcyclopentadienyl)dichlorotitanium
2-(1-(2,6-
dichlorophenylimino)propyl)quinolin-8-olate (C12). Using the
same procedure as for the synthesis of C7 with L6 instead of L1,
C12 was obtained as a dark red solid in 34.5% yield (0.21 g).
1H NMR (CDCl3, 400 MHz, ppm): d 8.51 (d, J = 8.6 Hz, 1H,
quino-H), 8.27 (d, J = 8.8 Hz, 1H, quino-H), 7.52 (t, J = 8.0 Hz,
1H, quino-H), 7.46 (d, J = 8.3 Hz, 1H, quino-H), 7.31 (t, J =
8.1 Hz, 1H, quino-H), 7.24 (d, J = 8.1 Hz, 2H, Ar-H), 7.01 (d,
J = 8.1 Hz, 1H, Ar-H), 2.91–2.86 (m, 2H, N CCH2CH3), 2.28
(s, 15H, Cp*), 1.13 (t, J = 7.7 Hz, 3H, N CCH2CH3). 13C NMR
(CDCl3, 100 MHz, ppm): d 174.9, 152.6, 152.5, 147.1, 137.2,
136.9, 134.2, 133.5, 129.3, 128.4, 124.5, 124.3, 120.7, 118.1, 110.6,
24.6, 13.5, 11.5. Anal. Calcd. for C28H28Cl4N2OTi: C, 56.22; H,
4.72; N, 4.68. Found: C, 56.13; H, 4.69; N, 4.37.
N
CCH2CH3). 13C NMR (CDCl3, 100 MHz, ppm): d 173.5,
153.3, 152.5, 147.5, 137.1, 136.7, 130.9, 129.0, 128.9, 125.9, 123.5,
120.4, 118.0, 110.4, 24.7, 23.4, 13.6, 13.4, 11.6. Anal. Calcd. for
C32H38Cl2N2OTi: C, 65.65; H, 6.54; N, 4.79. Found: C, 65.51; H,
6.63; N, 4.56.
(g5-Pentamethylcyclopentadienyl)dichlorotitanium 2-(1-(2,6-di-
isopropylphenylimino)propyl)quinolin-8-olate (C9). Using the
same procedure as for the synthesis of C7 with L3 instead of
L1, C9 was obtained as a dark red solid in 75% yield (0.47 g). 1H
NMR (CDCl3, 400 MHz, ppm): d 8.45 (d, 1H, J = 8.7 Hz, quino-
H), 8.28 (d, 1H, J = 8.3 Hz, quino-H), 7.56 (t, 1H, J = 7.8 Hz,
quino-H), 7.49 (d, 1H, J = 8.1 Hz, quino-H), 7.21 (d, 1H, J =
7.4 Hz, quino-H), 7.17 (d, 2H, J = 7.8 Hz, Ar-H), 7.03 (t, 1H, J =
7.5 Hz, Ar-H), 2.85–2.80 (m, 2H, N CCH2CH3), 2.78–2.72 (m,
2H, Ar-CH(CH3)2), 2.28 (s, 15H, Cp*), 1.23 (d, 6H, J = 7.6 Hz, Ar-
CH(CH3)2), 1.15 (d, 6H, J = 7.4 Hz, Ar-CH(CH3)2), 1.11 (t, 3H,
J = 7.1 Hz, N CCH2CH3). 13C NMR (CDCl3, 100 MHz, ppm): d
4.3 Procedures for ethylene polymerization and
co-polymerization
A 500-mL autoclave stainless steel reactor equipped with a
mechanical stirrer and a temperature controller was heated under
vacuum for at least 2 h at 80 ◦C. It was allowed to cool to the
required reaction temperature under an ethylene atmosphere and
then charged with toluene (with co-monomer), the desired amount
of co-catalyst (MAO) and a toluene solution of the catalytic
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Table 5 Crystallographic data and refinement details for complexes C1
and C5
Acknowledgements
This work is supported by MOST 863 program No.
2009AA034601 and NSFC No.20874105. The EPSRC are thanked
for the awarded of a travel grant (to CR).
C1
C5
Empirical formula
Formula weight
Crystal color
T (K)
C25H24Cl2N2OTi
487.26
Black
C28H30ClN2OTi
529.34
black
173(2)
173(2)
References
˚
Wavelength (A)
0.71073
Monoclinic
C2/c
23.856(5)
13.807(3)
16.621(3)
90
117.68(3)
90
4848.41(7)
8
0.71073
Monoclinic
P21/n
16.971(3)
8.2136(16)
18.503(4)
90
101.64(3)
90
2526.2(9)
4
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477.
Crystal system
Space group
˚
a (A)
˚
b (A)
˚
c (A)
a (◦)
b (◦)
g (◦)
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3
˚
V (A )
Z
Dcalc (Mg m-3)
m (mm-1)
1.335
0.592
2016
1.392
0.575
1104
F (000)
Crystal size (mm)
q range (◦)
Limiting indices
0.40 ¥ 0.11 ¥ 0.10 0.20 ¥ 0.10 ¥ 0.09
1.76–27.50
-30< = h< = 24,
-17< = k< = 16,
-21< = l< = 21
19471
2.72–27.47
-15< = h< = 22,
-10< = k< = 10,
-24< = l< = 20
19951
5713
0.0498
No. of rflns collected
No. of unique rflns
Rint
5537
0.0620
99.7(q = 27.50)
1.130
R1 = 0.0864,
R1 = 0.0652
Completeness to q (%)
Goodness-of-fit on F2
Final R indices [I > 2s(I)]
wR2 = 0.2151
98.8(q = 27.47)
1.170
wR2 = 0.1436
R indices (all data)
wR2 = 0.2254
R1 = 0.1041,
R1 = 0.0729,
wR2 = 0.1487
-3
˚
Largest diff peak, hole (e A- ) 0.668, -0.621
0.534, -0.445
precursor. The total volume was 100 mL. After reaching the
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quenched by addition of a solution of ethanol containing HCl.
The precipitated polymer was washed with ethanol several times
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4.4 Crystal structure determinations
Crystals of C1 and C5 suitable for single-crystal X-ray analysis are
obtained by layering n-heptane on their toluene solutions. Single-
crystal X-ray diffraction for C1 and C5 are performed on a Rigaku
RAXIS Rapid IP diffractometer with graphite-monochromated
˚
Mo-Ka radiation (l = 0.71073 A) at 173(2) K. Cell parameters
were obtained by global refinement of the positions of all collected
reflections. Intensities were corrected for Lorentz and polarization
effects and empirical absorption. The structures were solved by
direct methods and refined by full-matrix least-squares on F2.
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This journal is
The Royal Society of Chemistry 2011
Dalton Trans., 2011, 40, 6802–6809 | 6809
©