Synthesis and catalytic activity of dinuclear imido titanium complexes: The molecular structure of [Ti(NPh)Cl(μ-Cl)(THF)2]2

Article abstract of DOI:10.1016/j.poly.2004.10.006

Reaction of TiCl₄ with the reagents RN(SiMe₃) ₂ in dichloromethane precipitates red to black powders (R = 1-adamantyl, phenyl, pentafluorophenyl, 3,5-bis(trifluoromethyl)phenyl), which on treatment with tetrahydrofuran giv

Full text of DOI:10.1016/j.poly.2004.10.006

Polyhedron 24 (2005) 151–156
www.elsevier.com/locate/poly
Synthesis and catalytic activity of dinuclear imido titanium
complexes: the molecular structure of [Ti(NPh)Cl(l-Cl)(THF)2]2
a
Dale A. Pennington , Peter N. Horton , Michael B. Hursthouse ,
b
b
a,
a,
*
Manfred Bochmann *, Simon J. Lancaster
a
Wolfson Materials and Catalysis Centre, School of Chemical Sciences and Pharmacy, University of East Anglia,
Earlham Road, Norwich NR4 7TJ, UK
b
School of Chemistry, University of Southampton, Highfield, Southampton SO17 1BJ, UK
Received 4 October 2004; accepted 29 October 2004
Available online 21 November 2004
Abstract
Reaction of TiCl4 with the reagents RN(SiMe3)2 in dichloromethane precipitates red to black powders (R = 1-adamantyl, phenyl,
pentafluorophenyl, 3,5-bis(trifluoromethyl)phenyl), which on treatment with tetrahydrofuran gives the new THF adducts
[Ti(NR)Cl(l-Cl)(THF)2]2. The complexes are dimeric in the solid state with bridging chloride and terminal imido ligands. Activation
with MAO (methylaluminoxane) gives ethene polymerisation catalysts with productivities of up to 31 kg PE [(mol complex)
h bar]ꢀ1
.
ꢀ 2004 Elsevier Ltd. All rights reserved.
Keywords: Titanium; Imido; Catalysis; Polymerisation; Methylaluminoxane
1. Introduction
tions for alkene polymerisation catalysis using titanium
imido precatalysts [6,11]. We report here the synthesis,
structure and polymerisation activity of compounds of
the type [Ti(NR)Cl2(THF)2].
Metal imido complexes are known to adopt a number
of structural motifs [1]. For example, titanium forms
complexes in which imido ligands adopt either bridging
(for example I, Chart 1) [2] or terminal (II) [3] bonding
modes [4]. We recently reported the synthesis and struc-
ture of [Ti(l-NArP)Me2(THF)]2 (III) (ArP = m-
C6H4P(3,5-(CF3)2C6H3)2) in which the imido ligand is
bridging [5]. This result contrasts with NielsonÕs 2-tert-
butyl- (IV) and 2-phenyl-phenylimido complexes which
form chloride-bridged dimers [6] and CarmaltÕs exclu-
sively chloride-bridged tetramer (V) [7]. In the absence
of basic co-ligands structures with even higher nuclearity
have been observed [8–10]. We continue to be interested
in the factors dictating whether the imido ligand adopts
a bridging or terminal bonding mode and the implica-
2. Results and discussion
Most commonly imidotitanium complexes are pre-
pared through an imido exchange reaction between
[Ti(NBut)Cl2(L)x] and the corresponding primary amine
[6]. We chose to employ an alternative dehalosilylation
methodology in order to access the base-free compounds
[12]. The ligand precursors RN(SiMe3)2 (1a–g) were
readily prepared by the step-wise deprotonation of the
parent amine and reaction with trimethylsilylchloride
(Scheme 1). Treating TiCl4 with 1a–d in dichlorometh-
ane solution led to the precipitation of sparingly soluble
red to black solids (Scheme 2). Unfortunately the
poor solubility of these crude materials in non-basic
*
Corresponding authors. Tel./fax: +44 1603 592009.
E-mail address: S.Lancaster@uea.ac.uk (S.J. Lancaster).
0277-5387/$ - see front matter ꢀ 2004 Elsevier Ltd. All rights reserved.
doi:10.1016/j.poly.2004.10.006

152
D.A. Pennington et al. / Polyhedron 24 (2005) 151–156
Me
N
Me
Ti
THF
N
PR'2
Me
N
N
N
Me
Me
Cl
N
N
(C6F5)2B
Cl
Ti
Ti
Ti
Ti
Cl
B(C6F5)2
N
Cl
R'2P
ButN
Me
THF
Me
II
III
I
NH2But
Cl
ButH2N
ButN
Cl
Ti
N
N
Cl
Cl
Cl
Ti
Cl
N
Ti
Cl
ButH2N
Cl
Ti
Cl
N
NBut
Cl
Cl
N
N
Ti
Ti
NH2But
t Cl
NBu
V
IV
Chart 1.
solvents, which presumably reflects high nuclearity, pre-
cluded spectroscopic characterisation or attempts to ob-
tain X-ray quality crystals. However, the solids reacted
exothermically on dissolution in tetrahydrofuran and
could be isolated as THF adducts 2a–d on crystallisation
from THF/light petroleum mixtures. 1H NMR spectros-
copy of 2a–d confirmed that quantitative dehalosilyla-
tion had taken place and indicated a ligand RN:THF
ratio of 1:2, which was supported by the elemental anal-
ysis. This composition differs from that observed for
[Ti(l-NArP)Cl2(THF)]2 where the ligand RN:THF ratio
is 1:1 [5], but is consistent with a formulation analogous
to complex IV, which has a chloride-bridged structure
with terminal imido ligands. While the dehalosilylation
route is effective for the introduction of meta-substituted
aryl imido ligands, the ortho disubstituted reagents 1e
and 1f failed to react with TiCl4, even after refluxing
in toluene, presumably as a consequence of steric
encumbrance. However, the mononuclear complex
[Ti(NAr00)Cl2(py)3] (Ar00 = 2,6-diisopropylphenyl, py =
pyridine) is accessible through an imido exchange reac-
tion [3c]. The o-OMe compound 1g reacted with TiCl4
but the resulting product was intractable and could
not be isolated even after treatment with THF.
The structure of 2b (Fig. 1) was determined by X-ray
crystallography and confirmed as a chloride-bridged di-
mer with two edge-sharing octahedral metal coordina-
tion spheres. Each distorted octahedron is completed
by terminal chloride and imido ligands opposite the
bridging chlorides and two mutually trans THF ligands.
The geometry resembles the 2-tert-butylphenyl imido
complex IV, which has trans pyridine ligands.
Selected bond lengths and angles for complex 2b are
shown in Table 1. While the terminal imido bond length
is insensitive to the differences between 2b, IV and the
mononuclear complex [Ti(NC6H5)Cl2(py)3] at 1.710(2),
˚
1.702(2) and 1.714(2) A, respectively, the C1–N1–Ti1
angle decreases from the almost linear, 177.5(2)ꢁ, in
[Ti(NC6H5)Cl2(py)3] to 167.5(2)ꢁ in 2b and 165.9(2)ꢁ in
IV, which reflects the increase in steric crowding.
a, R = 1-adamantyl;
b, R = phenyl;
c, R = pentafluorophenyl;
d, R = 3,5-bis(trifluoromethyl)phenyl;
e, R = 2,4,6-trimethylphenyl
f, R = 2,6-diisopropylphenyl
g, R = 2-methoxyphenyl
SiMe3
SiMe3
SiMe3
H
(i), (ii)
(i), (ii)
R
N
R
N
R
N
H
H
1a-g
Scheme 1. Reagents and conditions: (i) n-BuLi, THF, ꢀ78 ꢁC to room temperature; (ii) SiClMe3, THF, ꢀ78 ꢁC to room temperature.
THF
Cl
THF
R
a, R = 1-adamantyl;
b, R = phenyl;
c, R = pentafluorophenyl;
d, R = 3,5-bis(trifluoromethyl)phenyl;
SiMe3
SiMe3
Cl
N
N
(iii), (iv)
Ti
Ti
R
N
Cl
Cl
R
THF
THF
2a-d
1a-d
Scheme 2. Reagents and conditions: (iii) TiCl4, CH2Cl2, room temperature; (iv) tetrahydrofuran, room temperature.

D.A. Pennington et al. / Polyhedron 24 (2005) 151–156
153
less, it remains possible that dinuclear imido-bridged
complexes are formed during the reaction of 2a–d with
the catalyst activator methylaluminoxane (MAO).
3. Polymerisation studies
Complexes 2a–d were screened as ethene polymerisa-
tion pre-catalysts in combination with MAO (methyla-
luminoxane) and the results are presented in Table 2.
The productivities are in the region of 10 kg [(mol com-
plex) h bar]ꢀ1, and there is no suggestion of mass
transport limitation. The gel permeation chromatogra-
phy (GPC) traces indicated bi- or polymodal distribu-
tions preventing the assignment of meaningful
polydispersities and implying the formation of more
than one active species. In each of the systems studied
increasing the polymerisation temperature from 20 to
60 ꢁC resulted in significantly lower molecular weight
polymer. The effect of raising the polymerisation tem-
perature on the productivity appears to be highly
dependent on the nature of the imido substituent, such
that 2a and 2d showed a modest increase in productiv-
ity, while in contrast 2b and 2c showed a decrease, pos-
sibly as a result of catalyst decomposition. Mountford
has recently reported a dramatic productivity depend-
ence on polymerisation temperature for imido titanium
catalysts of the type illustrated by II [11b]. Our results
are broadly comparable with those observed for
[Ti(NC6H4–Ph-2)Cl(l-Cl)(tmeda)]2 (12.7 kg PE [(mol
complex) h bar]ꢀ1 at 20 ꢁC) [6] but they do not
approach the 1.1 · 106 g PE [(mol complex) h bar]ꢀ1
we obtained with III/MAO [5].
Fig. 1. The molecular structure of 2b with thermal ellipsoids at 50%
probability and the hydrogen atoms, the solvent THF and one half of
the co-ordinated disordered THF removed for clarity.
Table 1
˚
Selected bond lengths (A) and angles (ꢁ) for 2b
Bond lengths
Cl1–Ti1
Cl1–Ti1
Ti1–O11
Ti1–Cl1i
2.4845(9)
2.6408(8)
2.085(2)
Cl2–Ti1
Ti1–N1
Ti1–O21
C1–N1
2.3734(9)
1.710(2)
2.114(2)
1.387(3)
2.6408(8)
Bond angles
Ti1–Cl1–Ti1i
N1–Ti1–Cl2
O21–Ti1–Cl2
O11–Ti1–Cl1
Cl2–Ti1–Cl1
O11–Ti1–Cl1i
Cl2–Ti1–Cl1i
C1–N1–Ti1
103.21(3)
N1–Ti1–O11
O11–Ti1–O21
O11–Ti1–Cl2
N1–Ti1–Cl1
O21–Ti1–Cl1
N1–Ti1–Cl1i
O21–Ti1–Cl1i
Cl1–Ti1–Cl1i
97.18(10)
168.94(8)
87.96(7)
90.84(9)
91.90(6)
167.42(9)
84.48(6)
76.79(3)
103.90(9)
87.87(6)
89.54(7)
165.24(3)
85.18(6)
88.51(3)
167.5(2)
Symmetry transformations used to generate equivalent atoms: (i)
ꢀx + 3/2, ꢀy + 1/2, ꢀz + 1.
4. Conclusion
Since complexes 2b, IV and [Ti(NCMe3)Cl(l-
Cl)(NH2CMe3)2]2 [6] all adopt similar dimeric structures
with bridging chlorides, its seems likely that the remain-
ing examples 2a,c,d, which all have two THF ligands per
metal centre, have a similar structure. Our complexes
are consistent with the pattern illustrated by II and IV,
whereas bridging imido ligands are preferred to bridging
chloride ligands only in relatively electron rich com-
plexes, with low steric hindrance.
We reasoned that exchanging the chloride for methyl
ligands in complexes 2a–2d might result in structural
analogues to III. Unfortunately, attempts to isolate the
products of treating 2a–d with the alkylating agents
LiMe, MgClMe and ZnMe2 were unsuccessful, yielding
only black tars. 1 This is in sharp contrast to the reaction
of [Ti(l-NArP)Cl2(THF)]2 with LiMe which proceeds
smoothly in diethyl ether at 0 ꢁC to give III. Neverthe-
Titanium tetrachloride undergoes a facile dehalosily-
lation reaction with the relatively unhindered bis(silyl)a-
mines 1a–1d but fails to react with 2,6-substituted silyl
anilines (1f, 1g). The resulting products react with tetra-
hydrofuran to give the adducts [Ti(NR)Cl(l-
Cl)(THF)2]2 (2a–2d). 2a–d are chloride-bridged dimers
with terminal imido ligands. Activation of 2a–2d with
MAO (methylaluminoxane) gives ethene polymerisation
catalysts with moderate productivity.
5. Experimental
5.1. General
Syntheses were performed under nitrogen using
standard Schlenk techniques. Solvents were distilled
over sodium–benzophenone (diethyl ether, tetra-
hydrofuran), sodium (toluene), sodium–potassium alloy
1
Similar difficulties were reported in [6].

154
D.A. Pennington et al. / Polyhedron 24 (2005) 151–156
Table 2
Ethene polymerisation results for 2a–d/MAOa
Run
Complex (lmol)
MAO (mmol)
T (ꢁC)
t (min)
Polymer yield (g)
Productivityb
Mw
1
2
3
4
5
6
7
8
a
2a(10)
2a(10)
2b(10)
2b(10)
2c(10)
2c(10)
2d(10)
2d(10)
10
10
10
10
10
10
10
10
20
60
20
60
20
60
20
60
30
30
30
30
10
10
10
10
0.078
0.150
0.040
0.004
0.052
0.013
0.009
0.028
16
30
8
370 000
23 000
270 000
150 000
220 000
83 000
0.7
31
8
5.5
17
270 000
23 000
In 50 cm3, 1 bar ethene pressure.
In kg PE [(mol complex) h bar]ꢀ1
b
.
(light petroleum, b.p. 40–60 ꢁC), or CaH2 (dichloro-
methane). NMR solvent (CDCl3) was dried over acti-
˚
vated 4 A molecular sieves and degassed by several
5.2.2. C6H5N(SiMe3)2 (1b)
1b was prepared from aniline following the procedure
outlined for 1a. The product was purified by vacuum
distillation, 81 ꢁC at 15 mbar giving the product as a col-
freeze thaw cycles. NMR spectra were recorded using
a Bruker DPX300 spectrometer. Data are reported in
ppm and referenced to residual solvent resonances (1H,
13C); 19F is relative to CFCl3. IR spectra were measured
as nujol mulls on a Perkin–Elmer Spectrum 1000 FT IR
spectrometer in the range of 600–4000 cmꢀ1. Nitrogen
and ethene (BOC, 99.5%) were purified by passing
through columns of supported P2O5 with moisture indi-
1
ourless oil in 80% yield. H NMR (300 MHz, 293 K,
CDCl3): d 7.26 (t, 2H, J = 7.0 Hz, Ar), 7.11 (t, 1H,
J = 7.3 Hz, Ar), 6.96 (d, 2H, J = 6.9 Hz, Ar), 0.14 (s,
18H, Si(CH3)3). 13C NMR (75.5 MHz, 293 K, CDCl3):
d 148.4, 130.6, 128.7, 123.9 (Ar), 2.5 (Si(CH3)3).
5.2.3. C6F5N(SiMe3)2 (1c)
˚
cator, and activated 4 A molecular sieves. MAO was
1c was prepared from pentafluoroaniline following
the procedure outlined for 1a. The product was purified
by vacuum distillation, 75 ꢁC at 15 mbar to give a col-
purchased from Witco as a 10% solution in toluene
and used as received. GPC analyses were performed
on a Polymer Labs PL-GPC-220 chromatograph. Ele-
mental analyses were performed by the School Micro-
analysis Service.
1
ourless oil in 90% yield. H NMR (300 MHz, 293 K,
CDCl3): d 0.13 (s, 18H, Si(CH3)3). 13C NMR (75.5
MHz, 293 K, CDCl3): d 146.4 (d, JC–F = 242 Hz, o-C),
138.0 (d, JC–F = 249 Hz, m-C), 127.9 (i-C),
1.6 (Si(CH3)3). 19F NMR (283.4 MHz, 293 K, CDCl3):
d ꢀ147.5 (d, 2F, JF–F = 20 Hz, o-F), ꢀ162.5 (tr, 1F,
JF–F = 20 Hz, p-F), ꢀ165.0 (tr, 2F, JF–F = 20 Hz, m-F).
5.2. Ligand synthesis
5.2.1. (1-Adamantyl)N(SiMe3)2 (1a)
To a stirred solution of 1-adamantylamine (4.6 cm3,
50 mmol) in tetrahydrofuran (100 cm3), held at
ꢀ78 ꢁC, was slowly added n-butyllithium (31.3 cm3 of
a 1.6 M hexane solution, 50 mmol). The reaction was
stirred for 2 h at room temperature before slow addition
of trimethylsilylchloride (6.4 cm3, 50 mmol). The result-
ing mixture was stirred for 2 h at room temperature
before cooling to ꢀ78 ꢁC and treatment with a second
portion of n-butyllithium (31.3 cm3 of a 1.6 M hexane
solution, 50 mmol). This suspension was stirred for
2 h at room temperature before adding further trimeth-
ylsilylchloride (6.4 cm3, 50 mmol) and stirring for 2 h to
ensure complete reaction. The volatiles were removed
under reduced pressure and the product extracted with
light petroleum (2 · 50 cm3). The product was purified
by vacuum distillation, 65 ꢁC at 0.1 mbar to give a col-
5.2.4. C6H3(CF3)2N(SiMe3)2 (1d)
1d was prepared from 3,5-bis(trifluoromethyl)aniline
following the procedure outlined for 1a. The product
was purified by vacuum distillation, 70 ꢁC at 20 mbar
to give a colourless oil in 80% yield. 1H NMR (300
MHz, 293 K, CDCl3): d 7.60 (s, 1H, p-H), 7.34 (s, 2H,
o-H), 0.12 (s, 18H, Si(CH3)3). 13C NMR (75.5 MHz,
293 K, CDCl3): d 150.9 (p-C), 132.2 (q, JC–F = 33 Hz,
m-C(CF3)), 130.2 (o-C), 123.7 (q, JC–F = 273 Hz, CF3),
117.5 (i-C), 2.2 (Si(CH3)3). 19F NMR (283.4 MHz, 300
K, CDCl3): d ꢀ63.5 (s, 6F, CF3).
5.2.5. C6H2Me3N(SiMe3)2 (1e)
1e was prepared from 2,4,6-trimethylaniline follow-
ing the procedure outlined for 1a. The product was puri-
fied by vacuum distillation, 95 ꢁC at 15 mbar to give a
1
ourless oil in 80% yield. H NMR (300 MHz, 293 K,
1
CDCl3): d 0.51 (br m, 3H, (CH)3), 0.18 (br m, 6H
(CH2)3), 0.1 (br m, 6H (CH2)3), 0.08 (s, 18H, Si(CH3)3).
13C NMR (75.5 MHz, 293 K, CDCl3): d 36.7 (CH), 30.4
(CH2), 30.1 (CH2), 3.3 (Si(CH3)3).
colourless oil in 80% yield. H NMR (300 MHz, 293
K, CDCl3): d 6.89 (s, 2H, m-H), 2.31 (s, 6H, o-CH3),
2.31 (s, 3H, p-CH3), 0.18 (s, 18H, Si(CH3)3). 13C
NMR (75.5 MHz, 293 K, CDCl3): d 143.5 (p-C), 136.8

D.A. Pennington et al. / Polyhedron 24 (2005) 151–156
155
(m-C), 132.7 (i-C), 129.5 (o-C), 21.2 (p-CH3), 20.8 (o-
CH3), 2.9 (Si(CH3)3).
(300 MHz, 293 K, CDCl3): d 7.05 (t, 2H, J = 7.7 Hz,
Ar), 6.80–6.88 (m, 3H, Ar), 4.47 (m, 8H, THF), 2.11
(m, 8H, THF). 13C NMR (75.5 MHz, 293 K, CDCl3):
d 128.0 (Ar), 123.5 (Ar), 123.1 (Ar), 75.3 (THF), 25.5
(THF). IR (cmꢀ1): 1576m, 1342m, 1315s, 1246m,
1172w, 1066m, 1042m, 1017s, 970m, 825m, 860s, 772s,
684m, 649w, 619w. Anal. Calc. for C28H42N2Cl4O4Ti2:
C, 47.48; H, 5.98; N, 3.96; Cl, 20.02. Found: C, 46.20;
H, 6.02; N, 3.40; Cl, 19.31%.
i
5.2.6. C6H3 Pr2N(SiMe3)2 (1f)
1f was prepared from 2,6-di(isopropyl)aniline follow-
ing the procedure outlined for 1a. The product was puri-
fied by crystallisation from light petroleum at ꢀ30 ꢁC to
1
give white crystals in 90% yield. H NMR (300 MHz,
293 K, CDCl3): d 7.07 (m, 3H, Ar), 3.49 (sep, 2H,
J = 6.9, CH(CH3)2), 1.21 (d, 12H, J = 6.9 Hz,
CH(CH3)2), 0.11 (s, 18H, Si(CH3)3). 13C NMR (75.5
MHz, 293 K, CDCl3): d 147.4 (m-C), 143.6 (p-C),
124.5 (i-C), 123.9 (o-C), 27.9 (CH(CH3)2), 25.5
(CH(C3)2), 2.9 (Si(CH3)3).
5.3.3. [Ti(NC6F5)Cl(l-Cl)(THF)2]2 (2c)
2c was prepared following a similar procedure to 2a
from TiCl4 (0.54 cm3, 5 mmol) and 1c (1.6 g, 5 mmol)
giving a red solid. The product was crystallised from a
tetrahydrofuran (20 cm3)/petroleum (5 cm3) mix at
ꢀ30 ꢁC to give dark red block crystals in 70% yield.
1H NMR (300 MHz, 293 K, CDCl3): d 4.50 (m, 4H,
THF), 2.15 (m, 4H, THF). 13C NMR (75.5 MHz, 293
K, CDCl3): d 76.4 (THF), 26.0 (THF). 19F NMR
(283.4 MHz, 293 K, CDCl3): d ꢀ152.8 (d, 2F, o-F),
ꢀ164.7 (t, 1F, p-F), ꢀ165.5 (d, 2F, m-F). IR (cmꢀ1):
1525m, 1505s, 1334m, 1216w, 1171w, 1377w, 1350s,
1014m, 988m, 949w, 920w, 852m. Anal. Calc. for
C28H32F10N2Cl4O4Ti2: C, 37.87; H, 3.63; N, 3.15; Cl,
15.97. Found: C, 37.26; H, 3.66; N, 3.10; Cl, 15.53%.
5.2.7. C6H4OMeN(SiMe3)2 (1g)
1g was prepared from 2-methoxyaniline following the
procedure outlined for 1a. The product was purified by
vacuum distillation, 85 ꢁC at 15 mbar to give a colour-
less oil in 80% yield. 1H NMR (300 MHz, 293 K,
CDCl3): d 7.09 (t, 1H, J = 6.0 Hz, Ar), 6.98 (d, 1H,
J = 6.3 Hz, Ar), 6.88 (m, 2H, J = 6.2 Hz, Ar), 3.80 (s,
1H, OCH3), 0.12 (s, 18H, Si(CH3)3). 13C NMR (75.5
MHz, 293 K, CDCl3): d 157.5, 137.4, 131.5, 124.8,
120.6, 110.9 (Ar), 55.2 (OCH3), 2.3 (Si(CH3)3).
5.3. Complex synthesis
5.3.4. [Ti(NC6H3(CF3)2-3,5)Cl(l-Cl)(THF)2]2 (2d)
2d was prepared following a similar procedure to 2a
from TiCl4 (1.1 cm3, 10 mmol) and 1d (3.7 g, 10 mmol)
giving a red solid. The product was crystallised from a
tetrahydrofuran (20 cm3)/petroleum (5 cm3) mix at
ꢀ30 ꢁC to give bright red/orange needle-shaped crystals
5.3.1. [Ti(N-1-adamantyl)Cl(l-Cl)(THF)2]2 (2a)
To a stirred solution of TiCl4 (0.54 cm3, 5 mmol) in
dichloromethane (40 cm3), 1a (1.4 g, 5 mmol) was added
drop wise and stirred for 2 h. The volatiles were re-
moved under reduced pressure and the resulting red so-
lid was washed with light petroleum (2 · 20 cm3). The
1
in 75% yield. H NMR (300 MHz, 293 K, CDCl3): d
7.29 (s, 1H, o-H), 7.25 (s, 2H, p-H), 4.44 (m, 4H,
THF), 2.09 (m, 4H, THF). 13C NMR (75.5 MHz,
293 K, CDCl3): d 158.7 (Ar), 132.0 (q, JC–F = 33 Hz,
m-C(CF3)), 129.0 (Ar), 123.8 (Ar), 123.5 (q, JC–F = 271
Hz, CF3), 116.2 (Ar), 76.0 (THF), 26.0 (THF). 19F
NMR (283.4 MHz, 300 K, CDCl3): d ꢀ63.5 (s, 6F,
CF3). IR (cmꢀ1): 1229m, 1089m, 1021s, 920w, 864m,
672w. Anal. Calc. for C32H38F12N2Cl4O4Ti2: C, 39.21;
H, 3.91; N, 2.86; Cl, 14.47. Found: C, 39.31; H, 3.97;
N, 3.60; Cl, 14.72%.
product was crystallised from
(20 cm3)/light petroleum (5 cm3) solvent mixture at
a tetrahydrofuran
ꢀ30 ꢁC to give yellow needle-shaped crystals in 65%
1
yield. H NMR (300 MHz, 293 K, CDCl3): d 4.57 (m,
4H, THF), 2.10 (m, 4H, THF), 1.88 (br m, 3H,
(CH)3), 1.66 (br m, 6H, (CH2)3), 1.44 (br m, 6H,
(CH2)3). 13C NMR (75.5 MHz, 293 K, CDCl3): d 75.6
(THF), 45.2 ((CH)3), 41.4 ((CH2)3), 29.9 ((CH2)3), 26.0
(THF). IR (cmꢀ1): 1278s, 1170m, 1039m, 1024s, 926w,
864m, 698w, 682w. Anal. Calc. for C34H62N2Cl4O4Ti2:
C, 51.02; H, 7.81; N, 3.50; Cl, 17.72. Found: C, 50.81;
H, 7.30; N, 3.42; Cl, 17.56%.
5.4. Polymerisation procedure
A solution of MAO in toluene (50 cm3) was satu-
rated with ethene (1 bar) at the given temperature.
Polymerisation was initiated by addition of a toluene
solution of pre-catalyst into the reactor under vigorous
stirring (1000 rpm). Methanol (1 cm3) was added to
terminate the polymerisation. The polymeric product
was precipitated and separated from aluminium resi-
dues by addition of methanol (ꢁ300 cm3) and 2 M
HCl (ꢁ5 cm3). The polymer was collected by filtration,
washed with methanol, 2 M HCl, distilled water and
5.3.2. [Ti(NPh)Cl(l-Cl)(THF)2]2 (2b)
2b was prepared following a similar procedure to 2a
from TiCl4 (1.1 cm3, 10 mmol) and 1b (2.4 g, 10 mmol)
giving a black powder. Tetrahydrofuran (20 cm3) was
added and stirred for 5 min. An exothermic reaction
took place to give a red solution. The product was crys-
tallised from a tetrahydrofuran (20 cm3)/light petroleum
(5 cm3) mixture at ꢀ30 ꢁC to give red block crystals suit-
1
able for X-ray crystallography in 95% yield. H NMR

156
D.A. Pennington et al. / Polyhedron 24 (2005) 151–156
again with methanol before drying until constant mass
at 80 ꢁC. Each run is the average of at least two
polymerisations.
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Crystal data for 2b: C32H50Cl4N2O5Ti2, Mr = 780.34,
T = 120(2) K, monoclinic, space group C2/c, a =
˚
˚
3
˚
[5] M. Said, D.L. Hughes, M. Bochmann, Dalton Trans. (2004) 359.
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19.5782(8) A, b = 9.0622(4) A, c = 31.5335(9) A, b =
107.507(2)ꢁ, V = 3643.5(3) A , q(calc) = 1.423 Mg/m3,
˚
l = 0.772 mmꢀ1, Z = 4, reflections collected: 19 476,
independent reflections: 4079 (Rint = 0.0554), complete-
ness (to h = 27.48ꢁ) = 97.8%, final R indices [I > 2r(I)]:
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R1 = 0.0461, wR2 = 0.1148,
R1 = 0.0638, wR2 = 0.1248.
R
indices (all data):
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1526.
7. Supplementary material
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1337.
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Wilson, P. Mountford, M. Schro¨der, Inorg. Chem. 39 (2000)
5483;
Crystallographic data (excluding structure factors)
for structure 2b have been deposited with the Cambridge
Crystallographic Data Centre as Supplementary Publi-
cation No. CCDC-251697. Copies of the data can be ob-
tained free of charge on application to CCDC, 12 Union
Road, Cambridge CB2 1EZ, UK [fax: (internat.) +44
1223 336 033, e-mail: deposit@ccdc.cam.ac.uk, or
www at http://www.ccdc.cam.ac.uk].
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Chem. Commun. (2004) 434.
[12] For an example of the dehalosilylation route to imido complexes
´ ´
see: I. Dorado, A. Garces, C. Lopez-Mardomingo, M. Fajardo,
´
A. Rodrıguez, A. Antinolo, A. Otero, J. Chem. Soc., Dalton
Trans. (2000) 2375.
Acknowledgements
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[14] R. Hooft, Nonius B.V., Data collection software, 1998.
[15] Z. Otwinowski, W. Minor, Meth. Enzymol. 276 (1997)
307.
The support of the Engineering and Physical Sciences
Research Council and the University of East Anglia are
gratefully acknowledged. The authors thank Dr. Fu-
quan Song for his assistance with polymer molecular
weight determinations.
[16] (a) R.H. Blessing, Acta Crystallogr. A 51 (1995) 33;
(b) R.H. Blessing, J. Appl. Crystallogr. 30 (1997) 421.
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¨