Copolymerization of ethylene with norbornene catalyzed by cationic rare earth metal fluorenyl functionalized N-heterocyclic carbene complexes

Article abstract of DOI:10.1039/b910306f

Rare earth metal bis(alkyl) complexes attached by fluorenyl modified N-heterocyclic carbene (NHC) (Flu-NHC)Ln(CH₂SiMe₃) ₂ (Flu-NHC = (C₁₃H₈CH₂CH ₂(NCHCCHN)C₆H₂

Full text of DOI:10.1039/b910306f

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www.rsc.org/dalton | Dalton Transactions
Copolymerization of ethylene with norbornene catalyzed by cationic rare
earth metal fluorenyl functionalized N-heterocyclic carbene complexes†
Baoli Wang,a,b Tao Tang,a Yuesheng Lia and Dongmei Cui*a
Received 26th May 2009, Accepted 30th July 2009
First published as an Advance Article on the web 24th August 2009
DOI: 10.1039/b910306f
Rare earth metal bis(alkyl) complexes attached by fluorenyl modified N-heterocyclic carbene
(NHC) (Flu-NHC)Ln(CH2SiMe3)2 (Flu-NHC = (C13H8CH2CH2(NCHCCHN)C6H2Me3-2,4,6);
Ln = Sc (2a); Y (2b); Ho (2c); Lu (2d)), (tBuFlu-NHC)Ln(CH2SiMe3)2 (tBuFlu-NHC =
2,7-tBu2C13H6CH2CH2(NCHCCHN)C6H2Me3-2,4,6; Ln = Sc (1a); Lu (1d)) and attached
by indenyl modified N-heterocyclic carbene (Ind-NHC)Ln(CH2SiMe3)2 (Ind-NHC =
C9H6CH2CH2(NCHCCHN)C6H2Me3-2,4,6; Ln = Sc (3a); Lu (3d)), under the activation of AliBu3 and
[Ph3C][B(C6F5)4], showed varied catalytic activities toward homo- and copolymerization of ethylene
and norbornene. Among which the scandium complexes, in spite of ligand type, exhibited medium to
high catalytic activity for ethylene polymerization (105 g molSc h-1 atm-1), but all were almost inert to
-1
norbornene polymerization. Remarkably, higher activity was found for the copolymerization of
ethylene and norbornene when using Sc based catalytic systems, which reached up to 5 ¥ 106 g
-1
molSc h-1 atm-1 with 2a. The composition of the isolated copolymer was varying from random to
alternating according to the feed ratio of the two monomers (rE = 4.1, rNB = 0.013). The molecular
structure of complex 1d was characterized by X-ray analysis. The influences of structural factors of
complexes and polymerization conditions on both the catalytic activity and the norbornene content in
the copolymer were discussed.
these catalysts for copolymerization, especially for that of E and
Introduction
NB, has remained as a fascinating and challenging subject.
The copolymer (P(E-co-NB)) of ethylene (E) and norbornene
In this subject, one essential step is to improve the catalytic
(NB) has been extensively studied owing to its good process
activity and selectivity of rare earth metal complexes, which
ability and other remarkable properties, such as a relatively
could be finely tuned by the type of the central metal ion
high glass transition temperature (Tg), excellent optical trans-
as well as the steric bulkiness and electric effect of the ancil-
parency and high refractive indices.1 The properties of P(E-
lary moiety. Compared with some widely studied ligands, such
co-NB) are determined by its microstructure and NB content,
as cyclopentadienyls (mono-Cp, bis-Cp, donor-functionalized
Cp, etc.),6 b-diketiminates, anilido imines, benzamidinates and
which are primarily controlled by the catalyst structure and
polymerization conditions. At present most catalysts for copoly-
merization of E with NB are confined to transition metals
such as group 4 metallocene2 and group 10 post-metallocene3
pyrrolyliminates etc.,7 deprotonated aza crowns and crown ethers,8
and phosphides,9 thermally stable N-heterocyclic carbene (NHC)
compounds have emerged as versatile auxiliaries to stabilize
and activate transition metal10 centers and intermediates in
quite different key catalytic steps, whereas they have been less
utilized in rare earth metals.11,12 A review about f-block N-hetero-
cyclic carbene complexes has been released very recently,12
however, the reactivity of these complexes, especially catalysis
on polymerization have been rarely investigated.13,14 We have
previously reported the synthesis of indenyl and fluorenyl modified
N-heterocyclic carbene supported rare earth metal bis(alkyl)
complexes 2 and 3. Among which 2b, 2c or 2d activated by
aluminum alkyls and [Ph3C][B(C6F5)4] initiated the living poly-
merization of isoprene with high activity, high 3,4-selectivity and
medium syndioselectivity.14a However, the scandium analogue 2a
is inert. Interestingly, opposite phenomenon has been discovered
in this work that 2a had the highest catalytic activity for the
copolymerization of E with NB in the present of aluminum alkyls
and [Ph3C][B(C6F5)4]. Herein, we report the catalytic performances
for the copolymerization of E and NB with these complexes
and the newly synthesized 2,7-di-tert-butyl fluorenyl modified
whereas little attention has been paid to rare earth metal
counterparts.4 Only one kind of cationic rare earth metal half-
sandwich species Cp¢Sc(CH2SiMe3)2(THF) (Cp¢ = C5Me4SiMe3,4a
1,3-(SiMe3)2C5H3,4a C5Me5,4a or C5Me4SiMe2(C6F5)4b) has been
reported to copolymerize E and NB with high activity, although a
number of cationic rare earth metal catalysts has been successfully
employed in various homogeneous polymerizations of ethylene,
styrene and 1,3-dienes etc.5 Obviously, extending the utilization of
aState Key Laboratory of Polymer Physics and Chemistry, Changchun
Institute of Applied Chemistry, Chinese Academy of Sciences, 5625 Renmin
Street, Changchun, 130022, China. E-mail: dmcui@ciac.jl.cn; Fax: +86
431-8526-2773
bGraduate School of the Chinese Academy of Sciences, Beijing, 100039,
China
† Electronic supplementary information (ESI) available: DSC curves and
13C NMR spectra of P(E-co-NB)s. CCDC reference number 732597. For
ESI and crystallographic data in CIF or other electronic format see DOI:
10.1039/b910306f
This journal is
The Royal Society of Chemistry 2009
Dalton Trans., 2009, 8963–8969 | 8963
©

N-heterocyclic carbene ligated rare earth metal bis(alkyl) com-
plexes (1a and 1d) in the presence of AliBu3 and [Ph3C][B(C6F5)4].
The influences of the molecular structures of the catalysts and
polymerization conditions on the catalytic activity and composi-
tion of the polymer will be presented.
Results and discussion
Preparation of complexes
Preparation of complexes 2 and 3 was in accordance with the
literature.14 Complex 1 was synthesized as described as fol-
lows: ethylene bridged 2,7-di-tert-butyl-fluorenyl N-heterocyclic
carbene (tBuFluH-NHC) was obtained by treatment of 2,7-
di-tert-butyl fluorenyl modified imidazolium bromide (2,7-
tBu2C13H7CH2CH2(NCHCHCHN)C6H2Me3-2,4,6)Br ((tBuFluH-
NHC-H)Br) with 1 equiv. LiCH2SiMe3. tBuFluH-NHC reacted
with rare earth metal tris(alkyl)s (Ln(CH2SiMe3)3(THF)2) to
afford the constrained geometry configuration (CGC) type rare
earth metal bis(alkyl) complexes (tBuFlu-NHC)Ln(CH2SiMe3)2
(Ln = Sc (1a); Lu (1d)) via alkane elimination (Scheme 1).
Complexes 1a and 1d are analogous THF-free monomers. The 1H
NMR spectra of complexes 1a and 1d display AB spin systems at
the upfield (i.e. high frequency) region (d -1.4 ppm to d -2.2 ppm)
that are assigned to the diastereotopic methylene protons of the
metal alkyl species (LnCH2SiMe3). The resonances at the very low
field region in 13C NMR spectra around d 187.68 and 199.08 ppm
arise from the Ln–Cylidene, suggesting that the coordination of the
carbene moiety to the central metal ion is robust and is maintained
in solution. This further confirmed a rigid and chiral metal center.
The molecular structure of 1d in the solid state was confirmed by
X-ray diffraction analysis (Fig. 1). The CGC tBuFlu-NHC ligand
Fig. 1 X-Ray structure of 1d with 30% probability of thermal ellipsoids.
Hydrogen atoms and the other equivalent molecule containing Lu(2)
◦
˚
are omitted for clarity. Selected bond distances (A) and angles ( ) in
Lu(1) molecule: Lu(1)–Cring 2.677 (av.), Lu(1)–Ccent 2.382, Lu(1)–planeCp
2.379, Lu(1)–C(1) 2.653(4), Lu(1)–C(6) 2.696(4), Lu(1)–C(7) 2.719(4),
Lu(1)–C(12) 2.697(4), Lu(1)–C(13) 2.618(4), Lu(1)–C(24) 2.482(4),
Lu(1)–C(36) 2.317(4), Lu(1)–C(37) 2.293(4); C(36)–Lu(1)–C(37)
106.43(16),
C(36)–Lu(1)–C(24)
109.65(14),
C(37)–Lu(1)–C(24)
103.38(15), Lu(1)–C(24)–N(2) 132.4(3). Corresponding bond distances
◦
˚
(A) and angles ( ) in Lu(2) independent molecule: Lu(2)–Cring 2.668
(av.), Lu(2)–Ccent 2.373, Lu(2)–planeCp 2.372, Lu(2)–C(44) 2.690(4),
Lu(2)–C(49) 2.660(4), Lu(2)–C(50) 2.666(4), Lu(2)–C(55) 2.674(4),
Lu(2)–C(56) 2.652(4), Lu(2)–C(67) 2.493(4), Lu(2)–C(79) 2.315(4),
Lu(2)–C(80) 2.308(4); C(79)–Lu(2)–C(80) 104.56(17), C(79)–Lu(2)–C(67)
112.49(15), C(80)–Lu(2)–C(67) 104.21(14), Lu(2)–C(67)–N(4) 131.0(3).
Copolymerization of ethylene with norbornene
5
1
coordinates to Lu ion in a h /k mode via the five-membered
ring and the ylidene carbon, adopting a tetrahedron geometry
around the central Lu ion with the centroid of the five-membered
cyclopentadienyl (Cp) ring as the apex. The two alkyl ligands
locate in cis-positions with one endo and the other exo against the
imidazolyl ring, paralleling to the N-aryl ring. The bond distances
Complexes 1, 2 or 3 (Scheme 1 and Chart 1) activated with
[Ph3C][B(C6F5)4] to generate cationic units showed very low
activity for the homo- and copolymerization of ethylene (E)
or norbornene (NB). This might be ascribed to the impurities
in the polymerization solution or the unstable nature of these
cationic units that decomposed into none active species. Further
in situ generated ternary catalyst systems composed of the
complexes and AliBu3 and [Ph3C][B(C6F5)4] showed moderate
˚
of Lu(1)–Cring, Lu(1)–Ccent and Lu(1)–planeCp in 1d (2.677 A (av.),
˚
˚
˚
˚
˚
2.382 A, 2.379 A), in 2d (2.654 A (av.), 2.357 A, 2.357 A) and
˚
˚
˚
in 3d (2.636 A (av.), 2.344 A, 2.342 A) have a descending trend,
consistent with the steric bulkiness of the ligands. Complex 1d
bearing the most sterically bulky ligand had the longest bond
lengths.
activity for the homopolymerization of E (105 g molSc h-1 atm-1)
-1
and very low activity for that of NB under the same experimental
conditions. Surprisingly, this ternary system could exhibit high
Scheme 1 Synthesis of 2,7-di-tert-fluorenyl N-heterocyclic carbene (tBuFlu-NHC) ligated rare earth metal bis(alkyl) complexes 1a and 1d.
8964 | Dalton Trans., 2009, 8963–8969 This journal is The Royal Society of Chemistry 2009
©

Chart 1 Molecular structures of fluorenyl and indenyl N-heterocyclic
carbene (Flu-NHC and Ind-NHC) ligated rare earth metal bis(alkyl)
complexes 2a–2d, 3a and 3d.
Fig. 2 Fineman–Ross plot for copolymerization of ethylene and nor-
bornene with 2a/AliBu3/[Ph3C][B(C6F5)4] at 40 ◦C (F = [E]/[NB] in feed,
f = [E]/[NB] in copolymer, E = ethylene, NB = norbornene).
catalytic activity for the copolymerization of E and NB, depending
significantly on the structural factors of the catalyst precursors and
polymerization conditions. The Y, Ho and Lu based complexes
showed low activity in spite of ligand types and organoborate
applied, whilst all scandium complexes were highly active. This
was ascribed mainly to the Lewis acidic nature of Sc3+. The
indenyl-modified NHC attached complex 3a (ScInd) exhibited a
was reduced, the incorporation rate into copolymer increased due
to the higher rE value, whereas in contrast, the incorporation of
norbornene could not be improved so obviously due to the much
lower reactivity ratio rNB, as a result an away from alternating
microstructure of the copolymer was obtained.
lower activity (0.28 ¥ 106 g molSc h-1 atm-1), as the strong
-1
The content of NB in the copolymer could be adjusted by
fixing NB feed amount but changing the volume of toluene (that
means changing the feed amount of E) (Table 1, entries 6–8).
Fig. 3 showed the typical 13C NMR spectra of the resultant
P(E-co-NB)s, the assignment of which was according to the
literatures.18 The common feature seen from these spectra is that
the NB repeat unit is discrete, indicating that there is no NB
homopolymerization sequence. This was in agreement with the
lower rNB according to Fineman–Ross plot. With the reducing of
toluene volume meaning that NB-to-E ratio increased, the chance
of incorporating NB into copolymer became higher, when the
volume was low enough, the almost alternating arrangement of
E and NB was achieved (Table 1, entries 6 and 7; Fig. 3). The
13C NMR spectrum of the P(E-alt-NB) (entry 7) showed the typical
eight singles around d 45.80, 45.20, 40.01, 39.52, 31.00, 28.72,
28.33 and 28.06 ppm, respectively. It was not surprised that with
the increase of the feed value of NB-to-E, the polymerization
became sluggish, which could be explained that the coordi-
nated NB resided longer at the catalyst center before insertion
compared with E.19 Solvent-fractionation experiments revealed
negligible quantities of homopolymer impurities (The alternating
P(E-co-NB)s were soluble in toluene, whereas homopolyethylene
and homopolynorbornene were insoluble).
electron donating nature of indenyl fragment reduced the Lewis
acidity of the central Sc3+. Whilst complex 2a (ScFlu), bearing the
fluorenyl-modified NHC, displayed the highest activity 2.37 ¥
106 g molSc h-1 atm-1 under the same conditions owing to the
-1
relatively weak electron donating ability of the fluorenyl group.15
This could be further confirmed by the catalytic performance
of 1a (SctBuFlu) stabilized by tert-butyl fluorenyl modified NHC,
which showed moderate activity 1.25 ¥ 106 g molSc h-1 atm-1
-1
compared with 2a, because tert-butyl groups were electron-
donating and their spacial sterics blocked E or NB insertion
into the copolymer chain. It was noteworthy that when using the
Brønsted base [PhMe2NH][B(C6F5)4] or borane B(C6F5)3 instead
of [Ph3C][B(C6F5)4], the resultant ternary system still showed
similar high activity (4 ¥ 105 g molSc-1 h-1 atm-1), different from the
previous systems composed of B(C6F5)3 that are inactive.4a,4b
On the basis of its excellent performance, the catalytic system
2a/AliBu3/[Ph3C][B(C6F5)4] was chosen to examine the influence
of the polymerization conditions. Keeping the other factors
constant, the copolymerization was carried out under various
temperatures. The results showed that both higher and lower
temperatures were not preferred and 40 ◦C was optimised.
Meanwhile the NB content of copolymer also decreased with
temperature from 37.3% (40 ◦C) to 33.7% (50 ◦C) in spite of
the increasing NB-to-E ratio.16 The reason was complicated, as
temperature affected not only the concentration of ethylene in the
reaction medium (toluene) but also the reactivity ratios of the two
monomers. The Fineman–Ross17 plot for the copolymerization of
E with NB performed at 40 ◦C is depicted in Fig. 2. A plot of
F(f - 1)/f as ordinate and (F2/f ) as abscissa is a straight line
whose slope is rE and whose intercept is minus rNB (F = [E]/[NB]
in feed, f = [E]/[NB] in copolymer). The monomer reactivity
ratios were calculated to be rE = 4.1 and rNB = 0.013, respectively,
indicating a much higher activity for homopolymerization of
ethylene as compared to that of norbornene. Thus, at a higher
temperature, although the content of ethylene in reaction medium
The NB content of resultant P(E-co-NB) indeed showed
significant influence on Tg value of the copolymer, which increased
from 26.8 to 46.3% resulting in an obvious change of Tg from 56.8
to 117.3 ◦C. The NB content and Tg value had perfect linear
correlation as shown in Fig. 4 (Tg = 2.66 (NB%) - 11.3).19c
Conclusion
We have demonstrated that a ternary catalyst system composed
of rare earth metal bis(alkyl) complexes bearing CGC-type func-
tional NHC ancillaries and aluminum alkyls and organoborates,
presented various activity for the copolymerization of ethylene
This journal is
The Royal Society of Chemistry 2009
Dalton Trans., 2009, 8963–8969 | 8965
©

Table 1 Copolymerization of ethylene with norbornene by 1a, 2a or 3a/AliBu3/[Ph3C][B(C6F5)4]a
tol/mL [E]/mol L-1 [NB]/[E]
T/◦C t/min Activityb NB cont.c (mol%) Mn ¥10-4 Mw/Mn
Tge/◦C
d
d
Entry Sc NB-feed mmol
V
1
2
3
4
5
6
7
8
9
1a
2a
3a
2a
2a
2a
2a
2a
50
50
50
50
50
50
50
50
100
100
100
100
100
20
0.108
0.108
0.108
0.133
0.095
0.108
0.108
0.108
0.108
0.108
4.63
4.63
4.63
3.76
5.26
23.15
9.26
2.31
9.26
4.63
40
40
40
25
50
40
40
40
40
40
5
5
5
5
5
5
5
5
5
2
1.25
2.37
0.28
0.058
0.27
0.43
1.61
2.02
1.86
5.08
30.1
37.1
37.1
n.d.f
33.7
46.3
44.5
26.8
43.5
37.4
3.98
7.12
0.89
n.d.
1.57
1.20
2.47
6.13
5.06
3.12
1.83
1.75
1.53
n.d.
2.09
1.96
1.60
1.70
1.79
1.39
60.4
83.4
86.3
n.d.
79.0
117.3
104.9
56.8
100.9
87.0
50
200
100
100
2a 100
2a 50
10
-1
a Conditions: Sc (10 mmol), [Ph3C][B(C6F5)4] (10 mmol), AliBu3 (200 mmol), pethylene = 1 atm. b 106 g of copolymer g molSc h-1 atm-1. c NB content
determined by 13C NMR spectroscopy in C2D4Cl2. d Determined by means of gel permeation chromatography (GPC) against polystyrene standards.
e Determined by differential scanning calorimetry (DSC). f n.d. = not determined.
Fig. 3 13C NMR spectra of P(E-co-NB)s with 2a/AliBu3/[Ph3C][B(C6F5)4] (Table 1, entries 2 and 6–8).
with norbornene. The catalytic activity is significantly dependent
on the type of the central metal ion and the electronics and
Experimental
General considerations
sterics of the ancillary moiety. The more Lewis acidic scandium
complex 2a bearing the less electron-donating and sterically
bulky Flu-NHC ligand, shows the highest activity as compared
to its analogues containing Ind-NHC or tBuFlu-NHC ligand.
The microstructures of the copolymers vary from random to
alternating adjusted by the NB-to-E feed ratio during the course of
polymerization, in which the NB units exist only as isolated frag-
ments owing to its very low reactivity ratio calculated according
to Fineman–Ross method. This is a rare example to utilize a rare
earth metal catalytic system for the copolymerization of ethylene
with norbornene.
All manipulations were performed under a dried and oxygen-
free argon atmosphere using standard high vacuum Schlenk
techniques or in a glove box.
Materials
All solvents were purified from MBRAUN SPS system. In-
dene (98%), fluorene (98%), AliBu3 (1.0 M in hexane) and
LiCH2SiMe3 solution (1.0 M in pentane) were purchased from
Aldrich. Polymerization grade ethylene was donated by the China
8966 | Dalton Trans., 2009, 8963–8969
This journal is
The Royal Society of Chemistry 2009
©

Polymer characterization
13C NMR spectra for the copolymers were obtained using C2D2Cl4
as a solvent on a Bruker AV400 (FT, 400 MHz for 1H; 100 MHz for
13C) working at 100 ◦C. Hexamethyldisiloxane was used as internal
reference. The NB contents in the P(E-co-NB) were calculated
from the 13C NMR spectra by using eqn (1).18c
I
+ IC
+ 2IC
/C
3 7
1
3
C
/C
1
4
2
mol NB% =
×100
(1)
ICH
2
Where IC2 is the integral of signals between 39.5 and 40.1 ppm,
/C
4
IC2
is the integral of signals between 45.0 and 46.0 ppm, IC7
/C
3
Fig. 4 Dependence of glass transition temperature (Tg) upon NB content
in copolymers (Table 1, entries 2 and 5–10).
is the integral of signals between 30.5 and 31.0 ppm and ICH
is the integral of signals between 27.0 and 29.0 ppm. (dC2
72.11 ppm, chemical shifts referred to hexamethyldisiloxane)
2
=
D
Cl
4
2
Petroleum & Chemical Corporation. Norbornene (99%, Alfa)
was purified by stirring it over potassium at 80 ◦C for 48 h
and distilled before use. Bromoethylidene, mesitylamine, glyoxal,
para-formaldehyde, etc., were bought from the National Medicine
Company (China), and were used without further purification.
The rare earth metal bis(alkyl) complexes (2a, 2b, 2c, 2d, 3a and
3d),14 [Ph3C][B(C6F5)4],20a [PhMe2NH] [B(C6F5)4],20b 2,7-di-tert-
fluorene21 and 1-(mesityl)imidazole22 were prepared according to
the literature.
The number average molecular weights (Mn) and molecular
weight distributions (Mw/Mn) of the copolymer samples were
measured by means of gel permeation chromatography (GPC) on
a PL-GPC 220 type high-temperature chromatograph equipped
with three PL-gel 10 mm Mixed-B LS type columns at 150 ◦C.
1,2,4-Trichlorobenzene (TCB), containing 0.05 w/v% 2,6-di-tert-
butyl-p-cresol (BHT) was employed as the solvent at a flow rate of
1.0 mL min-1. The calibration was made by polystyrene standard
Easi Cal PS-1 (PL Ltd).
Tg of copolymers were measured through differential scanning
calorimetry (DSC) analyses, which were carried out on a Q
100 DSC from TA Instruments under nitrogen atmosphere. The
instrument was calibrated for temperature and enthalpy using
Ligands and complexes analyses
1H and 13C NMR spectra were recorded on a Bruker AV400
1
(FT, 400 MHz for H; 100 MHz for 13C) or a Bruker AV300
◦
pure indium (m.p. = 156.6 C) and sapphire before experiment.
(FT, 300 MHz for 1H; 75 MHz for 13C). NMR assignments
were confirmed by the 1H–1H COSY, 1H–13C HMQC and
1H–13C HMBC experiments when necessary. Elemental analy-
ses were performed at National Analytical Research Centre of
Changchun Institute of Applied Chemistry (CIAC). For the
organometallics the carbon analyses are a bit low probably owing
to carbide formation. Crystallographic data were collected at
-86.5 ◦C on a Bruker SMART APEX diffractometer with a
Measurements during the first heating from 25 ◦C to 250 ◦C and
then the first cooling from◦250 ◦C to 25 ◦C as well as the second
heating from 25 ◦C to 250 C at 10 ◦C min-1 were performed.
Synthesis of 9-(2-bromoethyl)-2,7-di-tert-butyl-9H-fluorene
The synthesis was based on the method reported in the literature.23
◦
At -40 C, 22.4 mL (1.60 mol L-1, hexane) n-butyl lithium
˚
CCD area detector (MoKa, l = 0.71073 A). The determination
was added dropwise to the THF solution (50 mL) of 2,7-di-
tert-fluorenyl (10.000 g, 35.926 mmol) and warmed to room
temperature slowly and kept stirring overnight. The THF–hexane
solution of 2,7-di-tert-fluorenyl lithium was cooled to -40 ◦C,
which was added dropwise to the THF solution (100 mL) of
bromoethylidene (33.736 g, 179.578 mmol) over 2 h and warmed
to room temperature slowly and reacted for more than 12 h.
The solution was treated with a saturated aqueous solution of
NH4Cl and washed several times with water. The organic phase
was separated and dried over MgSO4. Removal of the solvent
and recrystallization from n-pentane yielded a beige solid (10.025,
72.4%). The 1H NMR (400 MHz, CDCl3, 25 ◦C): d 1.44 (s, 18 H,
of crystal class and unit cell parameters was carried out by the
SMART program package. The structures were solved by using
SHELXTL program.
Ethylene/norbornene copolymerization procedure
In the glove box, a Schlenk bottle containing a magnetic stirring
bar was charged with a toluene solution of norbornene and alkyl
aluminum. The reactor was equipped with an ampoule bottle filled
with 2 mL toluene solution of the rare earth metal complexes, alkyl
aluminum and borate. The reactor was taken out of the glove box,
connected to the Schlenk line, and set in the thermostated oil bath.
The solution was degassed and then saturated with ethylene for
15 min under vigorous stirring. The solution of catalyst system
was quickly transferred to the polymerization bottle to initiate the
polymerization. The polymerization was terminated by addition
of acidified ethanol. The reaction mixture was slowly poured into
300 mL ethanol. The precipitated polymer was filtered and washed
with mass ethanol, and then dried under vacuum at 60 ◦C for
several hours.
3
C(CH3)3), 2.52–2.57 (m, 2 H, CH2CH2), 3.43 (t, JH–H = 7.2 Hz,
3
2 H, CH2CH2), 4.16 (t, JH–H = 5.8 Hz, 1 H, fluorene), 7.46,
3
7.67 (AB, JH–H = 8.0 Hz, 4 H, fluorene), 7.58 (s, 2 H, fluorene).
◦
13C NMR (100 MHz, CDCl3, 25 C): d 30.87 (s, 1 C, CH2CH2),
31.62 (s, 6 C, C(CH3)3), 34.86 (s, 2 C, C(CH3)3), 36.94 (s, 1 C,
CH2CH2), 46.40 (s, 1 C, fluorene), 119.25, 121.05, 124.43 (s, 6 C,
fluorene), 138.42, 145.82, 149.95 (s, 6 C, ipso-fluorene) Anal. calcd
for C23H29Br (%): C 71.68, H 7.58. Found: C 71.20, H 7.15.
This journal is
The Royal Society of Chemistry 2009
Dalton Trans., 2009, 8963–8969 | 8967
©

Synthesis of 2,7-di-tert-fluorenyl imidazolium bromide
tBuFluH-NHC-H)Br
Synthesis of complex (tBuFlu-NHC)Lu(CH2SiMe3)2 (1d)
(
Following the procedure described above, treatment of (tBuFluH-
NHC-H)Br (0.209 g, 0.366 mmol) with LiCH2SiMe3 (0.035 g,
0.366 mmol) and Lu(CH2SiMe3)3(THF)2 (0.213 g, 0.366 mmol)
in 20 mL toluene generated yellow single crystals 1d in a 61.5%
yield (0.189 g). 1H NMR (400 MHz, C6D6, 25 ◦C): d -2.17, -2.11
The synthesis was similar with the method reported in the
literature.14,24 Treatment of 9-(2-bromoethyl)-2,7-di-tert-butyl-9H-
fluorene (5.000 g, 12.974 mmol) with 1-(mesityl)imidazole (2.416 g,
12.974 mmol) in 1,4-dioxane (80 mL) under refluxing for 5 d
gave sticky oils after removal of volatiles. The sticky oils were
dissolved in CH2Cl2 and precipitated with ether. The resulting
viscous products were passed through a silica-gel column with
acetyl acetate as eluent to wash off the movable parts. The silica
gel column was washed with methanol to collect the non-movable
part. Driving of methanol gave the white power anticipated
2
(AB, JH–H = 10.8 Hz, 4 H, Lu-CH2SiMe3), 0.23 (s, 18 H, Lu-
CH2SiMe3), 1.59 (s, 18 H, C(CH3)3), 1.88 (s, 6 H, C6H2Me3), 2.19
(s, 3 H, C6H2Me3), 3.14 (t, 3JH–H = 5.2 Hz, 2 H, CH2CH2), 3.91 (t,
3JH–H = 5.2 Hz, 2 H, CH2CH2), 5.92 (d, 3JH–H = 1.6 Hz, 1 H, NCH),
6.14 (d, 3JH–H = 1.6 Hz, 1 H, NCH), 6.75 (s, 2 H, C6H2Me3), 7.38
(d, 3JH–H = 8.8 Hz, 2 H, fluorene), 7.43 (s, 2 H, fluorene), 8.38 (d,
3JH–H = 8.8 Hz, 2 H, fluorene). 13C NMR (100 MHz, C6D6, 25 ◦C):
d 5.32 (s, 6 C, Lu-CH2SiMe3), 19.15 (s, 2 C, C6H2Me3), 21.39 (s,
1 C, C6H2Me3), 27.62 (s, 1 C, CH2CH2), 32.20 (s, 6 C, C(CH3)3),
35.73 (s, 2 C, C(CH3)3), 47.70 (s, 2 C, Lu-CH2SiMe3), 52.77 (s, 1 C,
CH2CH2), 91.17 (s, 1 C, ipso-fluorene), 112.88 (s, 2 C, fluorene),
116.34 (s, 2 C, ipso-fluorene), 118.84 (s, 2 C, fluorene), 120.98
(s, 1 C, NCH), 122.11 (s, 1 C, NCH), 124.44 (s, 2 C, fluorene),
129.94 (s, 2 C, C6H2Me3), 133.70 (s, 2 C, ipso-fluorene), 135.49 (s,
2 C, ipso-C6H2Me3), 136.20 (s, 1 C, ipso-C6H2Me3), 140.24 (s, 1 C,
ipso-C6H2Me3), 148.20 (s, 2 C, ipso-fluorene), 199.08 ppm (s, 1 C,
Lu-Cylidene); Anal. calcd for C43H63LuN2Si2 (%): C 61.55, H 7.57,
N 3.34. Found: C 60.42, H 7.51, N 3.23.
compound (tBuFluH-NHC-H)Br (5.985 g, 80.7%). The H NMR
1
(300 MHz, CDCl3, 25 ◦C): d 1.37 (s, 18 H, C(CH3)3), 2.00 (s, 6 H,
C6H2Me3), 2.31 (s, 3 H, C6H2Me3), 2.89–2.96 (m, 2 H, CH2CH2),
3
3
4.23 (t, JH–H = 5.1 Hz, 1 H, fluorene), 4.43 (t, JH–H = 6.9 Hz,
2 H, CH2CH2), 6.60 (s, 1 H, NCH), 6.84 (s, 1 H, NCH), 6.96 (s,
3
2 H, C6H2Me3), 7.43, 7.65 (AB, JH–H = 6.9 Hz, 4 H, fluorene),
7.59 (s, 2 H, fluorene), 10.44 (s, 1 H, imidazolium-H). 13C NMR
(100 MHz, CDCl3, 25 ◦C): d 17.58 (s, 2 C, C6H2Me3), 20.87 (s, 1 C,
C6H2Me3), 31.51 (s, 6 C, C(CH3)3), 33.81 (s, 1 C, CH2CH2), 34.83
(s, 2 C, C(CH3)3), 45.03 (s, 1 C, fluorene), 47.47 (s, 1 C, CH2CH2),
119.27 (s, 2 C, fluorene), 121.40 (s, 2 C, fluorene), 122.66 (s, 2
C, NCH), 124.79 (s, 2 C, fluorene), 129.65 (s, 2 C, C6H2Me3),
130.40 (s, 1 C, ipso-C6H2Me3), 133.88 (s, 2 C, ipso-C6H2Me3),
137.95 (s, 1 C, Cylidene), 138.31 (s, 2 C, ipso-fluorene), 141.03 (s, 1
C, ipso-C6H2Me3), 145.08 (s, 2 C, ipso-fluorene), 150.41 (s, 2 C,
ipso-fluorene). Anal. calcd for C35H43BrN2 (%): C 73.54, H 7.58,
N 4.90. Found: C 72.97, H 7.27, N 4.34.
Crystal data for 1d
C43H63LuN2Si2, M = 839.10, monoclinic, space group P21/c, a =
◦
˚
11.2455(6), b = 23.7372(12), c = 33.4091(17) A, b = 92.5170(10) ,
V = 8909.5(8) A , Z = 8, rcalcd = 1.251 g cm-3, m(MoKa) =
3
˚
-1
˚
2.298 mm , T = 187(2) K, l = 0.71073 A, 49 863 reflections
Synthesis of complex (tBuFlu-NHC)Sc(CH2SiMe3)2 (1a)
measured, and 17 559 reflections with I > 2s(I). Rint = 0.0445,
final R1 = 0.0374 (observed data), wR2 = 0.0852 (all data).
(
tBuFluH-NHC-H)Br (0.209 g, 0.366 mmol) and LiCH2SiMe3
(0.035 g, 0.366 mmol) and 10 mL toluene were added to a flask.
After reacting for 1 h under vigorous stirring, the reaction mixture
was added to a toluene solution (10 mL) of Sc(CH2SiMe3)3(THF)2
(0.165 g, 0.366 mmol). The mixture remained stirring for another
12 h at 30 ◦C until turned to clear solution. Concentration,
filtration and cooling at -30 ◦C afforded◦yellow solid 1a (0.149 g,
Acknowledgements
We thank financial supports from The Ministry of Science and
Technology of China for project no. 2005CB623802.
1
57.4%). H NMR (300 MHz, C6D6, 25 C): d -1.44, -1.40 (AB,
Notes and references
2JH–H = 10.5 Hz, 4 H, Sc-CH2SiMe3), 0.21 (s, 18 H, Sc-CH2SiMe3),
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1.57 (s, 18 H, C(CH3)3), 1.90 (s, 6 H, C6H2Me3), 2.18 (s, 3 H,
C6H2Me3), 3.09 (t, 3JH–H = 5.1 Hz, 2 H, CH2CH2), 3.87 (t, 3JH–H
=
5.1 Hz, 2 H, CH2CH2), 5.91 (d, 3JH–H = 1.5 Hz, 1 H, NCH), 6.13
(d, 3JH–H = 1.5 Hz, 1 H, NCH), 6.74 (s, 2 H, C6H2Me3), 7.38 (d,
3JH–H = 8.4 Hz, 2 H, fluorene), 7.40 (s, 2 H, fluorene), 8.43 (d,
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d 4.93 (s, 6 C, Sc–CH2SiMe3), 19.39 (s, 2 C, C6H2Me3), 21.40 (s,
1 C, C6H2Me3), 27.44 (s, 1 C, CH2CH2), 32.31 (s, 6 C, C(CH3)3),
35.73 (s, 2 C, C(CH3)3), 49.64 (br, 2 C, Sc–CH2SiMe3), 52.33 (s, 1
C, CH2CH2), 93.89 (s, 1 C, ipso-fluorene), 113.93 (s, 2 C, fluorene),
117.75 (s, 2 C, ipso-fluorene), 119.50 (s, 2 C, fluorene), 121.69 (s, 1
C, NCH), 122.18 (s, 1 C, NCH), 125.13 (s, 2 C, fluorene), 129.75
(s, 2 C, C6H2Me3), 133.16 (s, 2 C, ipso-fluorene), 135.63 (s, 2 C,
ipso-C6H2Me3), 136.76 (s, 1 C, ipso-C6H2Me3), 139.97 (s, 1 C,
ipso-C6H2Me3), 147.84 (s, 2 C, pso-fluorene), 187.68 ppm (br, 1 C,
Sc-Cylidene); Anal. calcd for C43H63ScN2Si2 (%): C 72.83, H 8.96, N
3.95. Found: C 72.17, H 8.33, N 3.21.
8968 | Dalton Trans., 2009, 8963–8969
This journal is
The Royal Society of Chemistry 2009
©

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-1
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This journal is
The Royal Society of Chemistry 2009
Dalton Trans., 2009, 8963–8969 | 8969
©