Synthesis of linked half sandwich rare-earth metal chlorido and borohydrido complexes and their catalytic behavior towards MMA polymerization

Article abstract of DOI:10.1039/c001824d

A series of rare-earth metal complexes attached by an amino-functionalized cyclopentadienyl ligand (C₅Me₄H-C₆H ₄-o-NMe₂) (1) was prepared. The metathesis reaction of the ligand lithium salt [C₅Me₄-C₆H ₄-o-NMe₂]Li with LnCl₃(THF)_n afforded the dichlorido complexes [(C₅Me₄-C ₆H₄-o-NMe₂)₂Ln₂Cl ₄][LiCl(THF)₂] (Ln = Y (2a), Lu (2b)), which are trinuclear connected by μ₃-Cl and μ₂-Cl multiple bridges. The straightforward metathesis reaction of Ln(BH₄) ₃(THF)_n with equimolar [C₅Me₄-C ₆H₄-o-NMe₂]Li in THF medium yielded the first linked half sandwich ligand stabilized THF-free rare-earth metal bis(borohydrido) complexes (C₅Me₄-C₆H ₄-o-NMe₂)Ln(BH₄)₂ (Ln = Sc (3a), Sm (3b)), respectively. The single component borohydrido complex 3a showed high activity towards the bulk polymerization of methyl methacrylate without specific control, which showed high iso-selectivity (mm = 80%) when the polymerization was performed in benzene medium, and switched to syndio-selectivity (rr = 74% at -20 °C) in polar THF medium, whilst the metal chlorido species was inert. The binary catalyst system of 3a/MgⁿBu₂ had similar catalytic performances when compared with 3a in THF medium, but provided enriched syndio-control in benzene solution that was in contrast to the iso-control of 3a. Surprisingly, 3a upon activation with ⁿBuLi displayed an extremely high activity (1.1 × 10⁶ g mol _Sc^-1 h^-1) and afforded syndiotactic PMMA (rr = 75%) at low polymerization temperature (-20 °C) in THF. The Royal Society of Chemistry 2010.

Full text of DOI:10.1039/c001824d

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www.rsc.org/dalton | Dalton Transactions
Synthesis of linked half sandwich rare-earth metal chlorido and borohydrido
complexes and their catalytic behavior towards MMA polymerization†
Zhongbao Jian,a,b Wei Zhao,a,b Xinli Liu,a Xuesi Chen,a Tao Tanga and Dongmei Cui*a
Received 27th January 2010, Accepted 17th May 2010
First published as an Advance Article on the web 22nd June 2010
DOI: 10.1039/c001824d
A series of rare-earth metal complexes attached by an amino-functionalized cyclopentadienyl ligand
(C5Me4H-C6H4-o-NMe2) (1) was prepared. The metathesis reaction of the ligand lithium salt
[C5Me4-C6H4-o-NMe2]Li with LnCl3(THF)n afforded the dichlorido complexes
[(C5Me4-C6H4-o-NMe2)2Ln2Cl4][LiCl(THF)2] (Ln = Y (2a), Lu (2b)), which are trinuclear connected by
m3-Cl and m2-Cl multiple bridges. The straightforward metathesis reaction of Ln(BH4)3(THF)n with
equimolar [C5Me4-C6H4-o-NMe2]Li in THF medium yielded the first linked half sandwich ligand
stabilized THF-free rare-earth metal bis(borohydrido) complexes (C5Me4-C6H4-o-NMe2)Ln(BH4)2
(Ln = Sc (3a), Sm (3b)), respectively. The single component borohydrido complex 3a showed high
activity towards the bulk polymerization of methyl methacrylate without specific control, which showed
high iso-selectivity (mm = 80%) when the polymerization was performed in benzene medium, and
switched to syndio-selectivity (rr = 74% at -20 ◦C) in polar THF medium, whilst the metal chlorido
species was inert. The binary catalyst system of 3a/MgnBu2 had similar catalytic performances when
compared with 3a in THF medium, but provided enriched syndio-control in benzene solution that was
in contrast to the iso-control of 3a. Surprisingly, 3a upon activation with nBuLi displayed an extremely
high activity (1.1 ¥ 106 g molSc h-1) and afforded syndiotactic PMMA (rr = 75%) at low
-1
polymerization temperature (-20 ◦C) in THF.
(Mw/Mn = 1.02–1.05) albeit at a very low temperature (-95 ◦C).6,7
Introduction
Henceforth, lanthanide complexes containing Ln–C (alkyl, allyl
During the past decades, organolanthanide complexes have ex-
or benzyl), Ln–N (amido), or Ln–H bonds have been synthesized
and applied for the specific selective polymerization of MMA.8,9
However lanthanide borohydrides had not been found as efficient
initiators for MMA polymerization until 2005 when samarium
borohydride complexes bearing diamide–diamine ligands showed
activity albeit with low selectivity.10 Hence investigations have
been directed to the lanthanide homoleptic borohydrides and
their analogues bearing one or two bulky ligands.11–14 It is
noteworthy that the involved complexes are based on larger
rare-earth metals providing unsatisfactory catalytic activity for
MMA polymerization, and those attached to smaller rare-earth
metals such as scandium have been less explored. The main
reason might be the synthetic difficulty of scandium borohydrido
complexes that usually suffer ligand scrambling, coordination of
THF and especially ring-opening of THF when performing the
reaction in the presence of THF, which are attributed to the less
steric environment of the borohydrides and the high oxophilicity
of scandium ion. Therefore only two borohydrido scandocenes,
perienced rapid development and have exerted marvelous perfor-
mances in various chemical transformations and polymerizations
of polar and non-polar monomers.1 The extensively investigated
complexes usually contain Ln–s-C, Ln–s-H bonds, which usually
encounter problems of thermo-stability, ligand redistribution,
solvent-addition as well as sensitivity to moisture and oxygen.2
Meanwhile the more stable lanthanide chlorides are noted for
their sparing solubility in common solvents. Thus lanthanide
borohydrides have attracted increasing attention as an alternative
owing to their stability, good solubility and structural diversity as
compared with their chloride counterparts. In the past few years,
the use of borohydride as a reactive ligand has been common in
organolanthanide chemistry, but rather limited. Further explo-
ration on their catalytic activity towards the polymerization of
polar and non-polar monomers remained rather limited.3–5
On the other hand, polymerization of methyl methacrylate
(MMA) via coordination mechanism has been a research hot topic
since the landmark (C5Me5)2LnR (R = alkyl, H) realized syn-
dioselective (>95% rr) polymerization of MMA in a living mode
Cp2Sc(BH4) and [Cp(TMS) ]2Sc(BH4), have been reported in the
2
literature (Cp = cyclopentadienyl).15 Very recently, mono-Cp
scandium bis(borohydride)s was successfully obtained that was
accompanied by byproducts of a borohydrido scandocene and
a THF ring-opening complex;3k,16 meanwhile, the first bis-THF
solvated borohydrido La and Lu complexes bearing a non-Cp
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
85262774; Tel: +86 431 85262773
bGraduate School of the Chinese Academy of Sciences, Beijing, 100039,
China
pyrrolyl bis(imido) ligand were isolated although BH4 addition to
17
=
the C N group of the ligand took place.
† CCDC reference numbers 743596 (2a), 743597 (2b) and 743598 (3a).
For crystallographic data in CIF or other electronic format see DOI:
10.1039/c001824d
Herein, we report the synthesis and structures of rare-earth
metal chlorido and borohydrido complexes that are stabilized
This journal is
The Royal Society of Chemistry 2010
Dalton Trans., 2010, 39, 6871–6876 | 6871
©

by a rigid aminophenyl-functionlized-cyclopentadienyl, a linked-
half-sandwich ligand. Although the linked-half-sandwich ligands
have been widely employed to stabilize metal complexes,18 the
rigid phenyl linked half-sandwich ligands and the corresponding
lanthanide complexes are scarce.19 All the complexes reported
here are novel, which alone or under the activation of cocatalysts,
display varied catalytic performances towards the polymerization
of MMA. The factors that influence the catalytic activity and
the specific regularity of the isolated polymer will also be
presented.
Results and discussion
Synthesis and characterization of dichlorido complexes 2
The aminophenyl-functionalized-Cp compound 1, (C5Me4H-
C6H4-o-NMe2), was prepared according to the literature by treat-
ment of ortholithiated N,N-dimethylaniline (LiC6H4-o-NMe2)
with 2,3,4,5-tetramethylcyclopentenone (C5H2Me4O) followed by
acidic workup and further treatment with ammonia as a yellow
viscous liquid (54% yield).20 Lithiation of 1 with an equimolar
amount of BuLi at -78 ◦C gave [C5Me4-C6H4-o-NMe2]Li that
n
reacted with LnCl3(THF)n to generate the corresponding dichlo-
rides [(C5Me4-C6H4-o-NMe2)2Ln2Cl4][LiCl(THF)2] (Ln = Y (2a),
Lu (2b)) in moderate to high yields (Scheme 1). As 1 exists in three
isomers, the Cp-proton gives multi resonances around d 3.5 ppm
and the four Cp-methyl groups show multi signals accordingly.20
Thus the formation of complexes 2 can be easily recognized by
the disappearance of the multiple Cp-proton resonances and the
presence of more clearer two singlet resonances assigned to Cp-
methyl groups (d 1.94, 2.04 ppm in 2a vs d 1.96, 2.18 ppm
in 2b). X-Ray diffraction analyses reveal that complexes 2 are
trinuclear in the solid state. The aminophenyl-functionalized-Cp
ligand coordinates to the Ln ion in a h /k linked-half-sandwich
mode. Two such units and a two-THF solvated lithium chloride are
connected by the chloride multiple bridges in Ln–m3-Cl–Li, Ln–
m2-Cl–Ln and Ln–m2-Cl–Li modes, respectively (Fig. 1). For the
yttrium complex 2a, the bond length of Y–m2-Cl–Li (Y(1)–Cl(2)),
Fig. 1 X-Ray structures of complexes 2a and 2b with 35% probability of
thermal ellipsoids. Hydrogen atoms and solvents are omitted for clarity.
Synthesis and characterization of bis(borohydrido) complexes 3
The straightforward metathesis reaction of Ln(BH4)3(THF)n with
one equivalent of [C5Me4-C6H4-o-NMe2]Li in THF medium at
-40 ◦C to r.t., followed by an extraction with toluene, yielded off-
white solids of complexes (C5Me4-C6H4-o-NMe2)Ln(BH4)2, (Ln =
Sc (3a), Sm (3b)), respectively (yields: 80%, 73%) (Scheme 2). The
1H NMR spectroscopic analysis of the scandium complex 3a (3b
is paramagnetic) clearly indicated that no THF ring-opening and
even no THF coordination can be observed. The very broad
signals appearing in the upfield region between d 0.71 and d
1.53 are assignable to the borohydrido protons of Sc–BH4, which
are comparable to those in (C5Me5)Sc(BH4)2(THF) (d 0.3 and
1.7).3k In the 11B NMR spectra, a single peak was seen at d
-19.72 ppm in C6D6, which shifted to d -22.63 ppm in THF-d8,
5
1
˚
˚
2.624(1) A, is shorter than 2.760(1) A of Y–m2-Cl–Y (Y(1)–Cl(3))
˚
and 2.717(1) A of Y–m3-Cl–Li (Y(1)–Cl(1)), which is comparable
to the terminal Y–Clterminal bond length (av. 2.617 A and 2.60 A)
in the literature (Table 1).21 Meanwhile, the distance between
˚
˚
˚
Y(1) and Y(1A) (3.909(7) A) is out of a reasonable bonding
range.22
◦
˚
Table 1 Selected bond distances (A) and angles ( ) for 2a and 2b
Parameter
2a (Ln = Y)
2b (Ln = Lu)
Ln(1)–C(Cp)(av.)
Ln(1)–Ccent
Ln(1)–Cl(1)
Ln(1)–Cl(2)
Ln(1)–Cl(3)
Li–Cl(1)
Ln(1)–Li
Ln(1)–Ln(1A/2)
N(1)–Ln(1)–Ccent
Ln(1)–Cl(1)–Ln(1A/2)
Ln(1A/2)–Cl(3)–Ln(1)
2.632(8)
2.340(3)
2.717(1)
2.624(1)
2.760(1)
2.833(8)
3.726(8)
3.909(7)
94.6(4)
2.599(8)
2.303(5)
2.673(1)
2.582(1)
2.692(1)
2.794(1)
3.705(1)
3.850(3)
95.8(7)
90.01(3)
90.16(4)
89.25(4)
91.47(4)
Scheme 1 Synthesis of trinuclear rare-earth metal dichlorido complexes
2a and b.
6872 | Dalton Trans., 2010, 39, 6871–6876
This journal is
The Royal Society of Chemistry 2010
©

Table 2 Summary of crystallographic data for 2a, 2b, and 3a
2a·toluene
2b·2THF
3a
Formula
C49H68Cl5Li–
N2O2Y2
0.25 ¥ 0.20 ¥
0.19
1079.00
Monoclinic
C2/c
21.3695(16)
13.2414(10)
18.2197(14)
90
98.6180(10)
90
5097.3(7)
4
1.396
Mo-Ka
(0.71073)
52.12
C50H76Cl5Li–
N2O4Lu2
0.23 ¥ 0.19 ¥
0.16
1303.26
Triclinic
¯
P1
12.5151(8)
14.1980(9)
15.5689(10)
88.6990(10)
80.8860(10)
84.2540(10)
2717.7(3)
2
C17H30B2-
NSc
Crystal size/mm
0.20 ¥
0.18 ¥ 0.09
315.00
Monoclinic
P21/c
9.4847(9)
8.6593(9)
22.574(2)
90
92.259(2)
90
1852.6(3)
4
Fw
Crystal system
Space group
˚
a/A
˚
b/A
˚
c/A
a/◦
b/◦
g /◦
Fig. 2 X-Ray structure of 3a with 35% probability of thermal el-
3
lipsoids. Hydrogen atoms are ◦partially omitted for clarity. Selected
˚
V/A
˚
bond distances (A) and angles ( ): Sc(1)–C(Cp)(av.) 2.453(2), Sc(1)–Ccent
Z
Dc/g cm-3
1.593
1.129
2.138(2), Sc(1)–HB (av.) 2.15(3), Sc(1)–B(1) 2.334(3), Sc(1)–B(2) 2.348(3),
Sc(1)–B (av.) 2.341(3), Sc(1)–N(1) 2.378(2), B–HT 1.10(3), B–HB 1.15(3);
Ccent–Sc(1)–N(1) 102.8(3), Ccent–Sc(1)–B(1) 121.10(2), Ccent–Sc(1)–B(2)
118.50(3), B(2)–Sc(1)–B(1) 107.97(1). HB = bridged hydrogen atom, HT =
terminal hydrogen atom.
˚
Radiation (l)/A
Mo-Ka
(0.71073)
52.08
38.99
1304
Mo-Ka
(0.71073)
52.32
3.90
680
◦
2qmax
/
m/cm-1
F(000)
25.66
2200
5043
No. of obsd reflns
10 475
3696
No. of params refnd
271
1.010
0.0457
0.1210
539
1.062
0.0380
0.1027
228
0.761
0.0409
0.1355
but were completely inactive after 120 min, which could be
attributed to the stronger bridging Ln–Cl bonds. To our delight,
the borohydrido complexes 3a and 3b displayed various catalytic
activity and specific selectivity, suggesting that Ln–BH4 species
could initiate the MMA polymerization.10,13 As shown in Table 3,
3a alone displayed high activity for the bulk polymerization
of MMA but afforded atactic product (mm 42%, mr 39%, rr
19%) (run 1). When the polymerization was performed in non-
polar solvent benzene with 3a, high specific control could be
achieved albeit with a decreased activity. The resultant poly(methyl
methacrylate) (PMMA) had high isotacticity (mm 80%) and
narrow molecular weight distribution (Mw/Mn = 1.58) (run 2),
suggesting the single-site nature of the active species. Thus with
the increase of monomer-to-initiator ratio varying from 500 and
800 to 1000, respectively, the molecular weight of the resultant
PMMA increased correspondingly from 12.5 ¥ 103 and 14.8 ¥ 103
to 16.6 ¥ 103 g mol-1, meanwhile, the molecular weight distribution
and tacticity remained unchanged (runs 2–4), indicating the con-
trollable nature of this polymerization even though not livingness.
When polar solvent THF was employed instead of benzene, 3a
exhibited an obvious improved activity, but, in contrast, switched
to syndio-selectivity (rr 61%, run 5), meaning that solvent played a
decisive role in governing the catalyst performances. Noteworthy
was that lowering the polymerization temperature to -20 ◦C
gave rise in specific selectivity (rr 74%) but sacrificed the activity
(run 7).
The addition of cocatalyst also exhibited dramatic influence on
both catalytic activity and specific selectivity3f,11 but in a different
way from that of solvent. Upon addition of 2 equiv. MgnBu2, the
resultant binary system 3a/MgnBu2 showed a comparable syndio-
selectivity with the single component 3a when the polymerization
was carried out in THF solution albeit with a worse activity
(run 10); whilst in benzene medium the binary catalyst system
provided syndiotactic-enriched PMMA (run 11) in contrast to 3a
that displayed iso-control under the same condition. When 3 equiv.
of nBuLi was used to replace MgnBu2, we found that the conversion
of monomer was 80% even though the polymerization time was
prolonged to 360 min at 20 ◦C (run 12), which was ascribed to
GOF
R1
wR2
Scheme 2 Synthesis of rare-earth metal bis(borohydrido) complexes 3a
and b.
confirming further the existence of BH4 groups. Complexes 3a
and 3b showed good solubility in THF and toluene but were
slightly soluble in hexane. Colorless crystals of 3a were readily
grown from a mixture of toluene and hexane at -30 ◦C within
12 h, which allowed the resolution of its molecular structure in the
solid state by X-ray diffraction analysis (Table 2, Fig. 2). Complex
3a is monomeric bis(borohydride)s, THF-free, consistent with
that deduced in the solid state. The aminophenyl-functionalized-
Cp ligand coordinates to the Sc3+ ion in a h /k CGC-mode.
5
1
Meanwhile both borohydrido groups BH4 bond to the Sc3+ ion
3
in a tridentate h -mode evidenced by the short Sc–B bond lengths
˚
˚
of 2.334(3) A and 2.348(3) A, as the bidentate coordinating
borohydrido moiety gives a longer metal–boron bond (2.551(5)
23
˚
A). The Cp centroid together with the N, B and Sc atoms
generate a pseudo tetrahedral geometry. The strong influence of
the geometry of this linked-half-sandwich ligand is reflected by the
shorter bond length of Sc–Ccent, 2.138(3) A, compared to 2.156 A
of Sc–Ccent in the non-linked mono-Cp (C5Me5)Sc(BH4)2(THF).3k
Complex 3a represents the first linked half sandwich scandium
bis(borohydride)s.
˚
˚
Catalysis on the polymerization of MMA
In preliminary experiments, the chlorido complexes 2a and 2b
were tested for the polymerization of MMA in THF medium
This journal is
The Royal Society of Chemistry 2010
Dalton Trans., 2010, 39, 6871–6876 | 6873
©

Table 3 Results of MMA polymerization using 3a and b as precursorsa
Tacticityd
mm-mr-rr (%)
T/◦C
t/min
Activityb
Mn (¥10-3)
Mw/Mn
c
c
Run
Cat.
Co-cat.
Solvent
1
3a
3a
3a
3a
3a
3a
3a
3b
3b
3a
3a
3a
3a
3a
3a
3b
3b
3b
3b
20
20
20
20
20
0
-20
20
20
20
20
20
-20
-40
20
20
0
12
130
13
10
8
70
50
4
11.4
12.5
14.8
16.6
14.1
25.7
92.2
15.3
21.6
19.1
8.2
11.1
68.4
190
10.8
15.6
46.9
119.7
246.3
1.67
1.58
1.52
1.49
1.68
1.99
2.51
1.39
1.62
1.59
4.17
1.56
2.06
2.01
1.54
1.58
1.81
1.97
2.26
42-39-19
80-14-6
76-20-4
73-25-2
5-34-61
5-30-65
2-24-74
43-37-20
9-33-58
7-26-67
19-24-57
14-35-51
0-25-75
0-20-80
56-32-12
8-38-54
8-29-63
7-27-66
4-24-72
2
Benzene
Benzene
Benzene
THF
THF
THF
Benzene
THF
THF
Benzene
THF
THF
THF
Benzene
THF
THF
THF
120
120
120
120
150
720
150
60
90
90
360
2.5
5
360
60
3e
4f
5
6
7
8
4
9
42
15
15
7
1116
552
2
40
56
396
13
10
11
12
13
14
15
16
17
18
19
MgnBu2
MgnBu2
nBuLi
nBuLi
nBuLi
nBuLi
nBuLi
nBuLi
nBuLi
nBuLi
40
5
60
-20
-40
THF
a Conditions: Ln (10 mmol), solvent (1 ml), [MMA]/[Cat.] = 500, [MgnBu2]/[Cat.] = 2, [nBuLi]/[Cat.] = 3. b Given in kg of PMMA molLn-1 h-1. c Measured
1
by GPC calibrated with standard polystyrene samples. d Determined by H NMR spectroscopy in CDCl3. e [MMA]/[Cat.] = 800. f [MMA]/[Cat.] =
1000.
the decomposition of the catalyst and inevitable side reactions.24
Surprisingly when the polymerization temperature was dropped
to -20 ◦C, the system showed extremely high activity meaning
almost completeness could be reached in 2.5 min, meaning a TOF
of 1.1 ¥ 106 g molSc-1 h-1. As far as we are aware, this is the highest
catalytic activity for the MMA polymerization with lanthanide
borohydrido complexes reported to date that simultaneously
display a syndio-selectivity up to 75%. Although the bridged-
indenyl yttrium benzyl complex was reported to show the highest
trinuclear dichlorido complexes, and especially the first non-
solvated scandium and samarium bis(borohydride)s without
ligand scrambling, coordination of THF and/or ring-opening
of THF, have been successfully synthesized and well defined.
Moreover, the borohydrido complexes alone or in the presence
of cocatalysts showed various catalytic performances depending
on the nature of reaction medium, the type of the cocatalysts as
well as the polymerization temperature. Whatever the nature of the
complexes and co-catalysts, syndiotactic PMMA was obtained in
polar THF medium. The PMMA stereoregularity was changed
by adding MgnBu2 to 3a from iso-control to syndio-control but
activity (6.0 ¥ 106 g molY h-1) in the research field of MMA
-1
polymerization using rare-earth metal complexes, unfortunately,
the isolated PMMA was completely without stereo-control (mm
30.0%, mr 31.5%, rr 38.5%).9k The activity was halved with a
n
retained iso-control by adding BuLi, when polymerization was
carried out in non-polar benzene. The scandium borohydrido
complex was found to be better than its samarium counterpart
regarding stereocontrol and activity, in contrast to the previous
reported large lanthanide effect, moreover, which upon activation
◦
further decrease in temperature to -40 C. Correspondingly, the
syndio-selectivity improved with the lowering of the temperature
to reach rr = 80%. Similarly, carrying out the polymerization in
n
n
non-polar benzene, the addition of BuLi caused a decrease in
of BuLi exhibited extremely high activity at low polymerization
activity at room temperature, however, which seemed not to bring
about the switch of iso-to-syndio selectivity (run 15) as that of
MgnBu2.
temperature.
Experiment
It has been reported that the central metal type influenced the
catalytic performances and the microstructures of the isolated
polymers from the polymerizations of both the polar or non-polar
monomers. For MMA polymerization, research usually focuses
on the samarium or neodymium based complexes since these
larger metals are well known to afford efficient polymerization
catalysts.10,13,24 In this work it was seen that the scandium complex
3a was more active and provided better stereo-control as compared
to the samarium 3b in non-polar benzene or polar THF medium,
or in the presence of cocatalysts or not (runs 16–19).
General methods
All reactions were carried out under a dry and oxygen-free argon
atmosphere by using Schlenk techniques or under a nitrogen
atmosphere in an MBraun glovebox. All solvents were purified
from MBraun SPS system. Organometallic samples for NMR
spectroscopic measurements were prepared in the glovebox by
use of NMR tubes sealed by paraffin film. H and 13C NMR
1
spectra were recorded on a Bruker AV400 (FT, 400 MHz for 1H;
100 MHz for 13C) spectrometer. NMR assignments were confirmed
by 1H–1H COSY and 1H–13C HMQC experiments when necessary.
11B NMR spectrum was referenced to an external standard
of BF3·Et2O (0.0 ppm) in C6D6 or THF-d8. The molecular
weight and molecular weight distribution of the polymers were
Conclusions
We have demonstrated that by introduction of a linked-half-
sandwich ligand, aminophenyl-functionalized-Cp, new lanthanide
6874 | Dalton Trans., 2010, 39, 6871–6876
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©

measured by a TOSOH HLC-8220 GPC. Elemental analyses were
performed at National Analytical Research Centre of Changchun
Institute of Applied Chemistry (CIAC). MgnBu2 (1.0 M in
heptane), nBuLi (2.5 M in hexane), LnCl3, and NaBH4 were
purchased from Aldrich or Fluka. Methyl methacrylate (MMA)
was dried over CaH2 under stirring for 48 h and distilled under
vacuum before use. Ln(BH4)3(THF)n25 was prepared according to
the literature. Ligand 1 (1-(2-N,N-dimethylaminophenyl)-2,3,4,5-
tetramethylcyclopentadiene) was prepared by following the known
procedure.20
two THF molecules in the lattice) for X-ray analysis grew from
the mixture of THF and toluen◦e at -30 ◦C within several days.
1H NMR (400 MHz, CDCl3, 25 C): d 1.77 (br s, 8H, THF), 1.96
(s, 12H, C5Me4), 2.18 (s, 12H, C5Me4), 2.90 (s, 12H, NMe2), 3.67
(br s, 8H, THF), 7.18 (d, JH–H = 3.0 Hz, 3H, C6H4), 7.32–7.35 (m,
3H, C6H4), 7.39–7.42 ppm (m, 2H, C6H4). 13C NMR (100 MHz,
CDCl3, 25 ◦C): d 12.58 (s, 4C, C5Me4), 13.04 (s, 4C, C5Me4), 26.34
(s, 4C, THF), 59.14 (s, 4C, NMe2), 69.35 (s, 4C, THF), 117.08
(s, 4C, C5Me4), 118.92 (s, 4C, C5Me4), 123.15 (s, 2C, o-NC6H4),
124.62 (s, 2C, ipso-C5Me4), 130.16 (s, 2C, p-NC6H4), 132.04 (s,
2C, m-NC6H4), 135.68 (s, 2C, o-C5Me4C6H4), 137.52 (s, 2C, ipso-
C5Me4C6H4), 160.07 ppm (s, 2C, ipso-NC6H4). Anal. calcd for
C50H76N2O4Cl5LiLu2 (%): C, 46.08; H, 5.88; N, 2.15. Found: C,
45.79; H, 5.68; N, 2.07.
X-Ray crystallographic studies
Crystals for X-ray analysis were obtained as described in the
preparations. The crystals were manipulated in a glovebox. Data
collections were performed at -86.5 ◦C on a Bruker SMART
APEX diffractometer with a CCD area detector, using graphite-
Synthesis of complex (C5Me4-C6H4-o-NMe2)Sc(BH4)2 (3a)
˚
monochromated Mo-Ka radiation (l = 0.71073 A). The deter-
Under a nitrogen atmosphere, to a THF suspension (20 mL) of
Sc(BH4)3(THF)1.5 (0.198 g, 1.0 mmol), 1 equiv. of [C5Me4-C6H4-o-
NMe2]Li (0.247 g, 1.0 mmol) prepared by the reaction of ligand 1
with nBuLi, was added slowly at -40 ◦C. The reaction mixture was
allowed to warm to room temperature gradually and was stirred
for 12 h. Removal of volatiles under reduced pressure, extracting
the residue with toluene, and evaporating the toluene to dryness
afforded 3a as white powder (0.254 g, 80%). Single crystals for
X-ray analysis grew from a mixture of toluene and hexane at
-30 ◦C within 12 h. 1H NMR (400 MHz, C6D6, 25 ◦C): d between
0.71 and 1.53 (very br s, 8H, BH4), 2.11 (s, 6H, C5Me4), 2.24 (s,
6H, C5Me4), 2.53 (s, 6H, NMe2), 6.71–6.73 (m, 1H, C6H4),◦7.05–
7.16 ppm (m, 3H, C6H4). 13C NMR (100 MHz, C6D6, 25 C): d
12.87 (s, 2C, C5Me4), 14.27 (s, 2C, C5Me4), 53.81 (s, 2C, NMe2),
121.50 (s, 1C, o-NC6H4), 125.02 (s, 2C, C5Me4), 126.15 (s, 2C,
C5Me4), 126.61 (s, 1C, ipso-C5Me4), 128.11 (s, 1C, p-NC6H4),
129.76 (s, 1C, m-NC6H4), 132.60 (s, 1C, o-C5Me4C6H4), 133.68 (s,
1C, ipso-C5Me4C6H4),◦155.99 ppm (s, 1C, ipso-NC6H4). 11B NMR
(96.3 MHz, C6D6, 25 C): d -19.72 ppm. 11B NMR (96.3 MHz,
THF-d8, 25 ◦C): d -22.63 ppm. Anal. calcd for C17H30NB2Sc (%):
C, 64.82; H, 9.60; N, 4.45. Found: C, 64.41; H, 9.43; N, 4.34.
mination of crystal class and unit cell parameters was carried
out by the SMART program package. The raw frame data were
processed using SAINT and SADABS to yield the reflection
data file. The structures were solved by using the SHELXTL
program. Refinement was performed on F2 anisotropically for all
non-hydrogen atoms by the full-matrix least-squares method. The
hydrogen atoms were placed at the calculated positions and were
included in the structure calculation without further refinement of
the parameters.
Synthesis of complex [(C5Me4-C6H4-o-NMe2)2Y2Cl4][LiCl(THF)2]
(2a)
Under a nitrogen atmosphere, to a THF suspension (20 mL) of
YCl3(THF)3.5 (0.448 g, 1.0 mmol), 1 equiv. of [C5Me4-C6H4-o-
NMe2]Li (0.247 g, 1.0 mmol) prepared ◦by the reaction of ligand
n
1 with BuLi, was added slowly at -78 C. The reaction mixture
was allowed to warm to room temperature gradually and was
stirred for 24 h. Removal of volatiles under reduced pressure,
extracting the residue with toluene and evaporating toluene to
dryness, afforded 2a as white powder (0.322 g, 65%). Single crystals
(with one toluene molecule in the lattice) for X-ray analysis grew
from a mixture of THF and toluene at -30 ◦C within several days.
1H NMR (400 MHz, CDCl3, 25 ◦C): d 1.78 (br s, 8H, THF), 1.94 (s,
12H, C5Me4), 2.04 (s, 12H, C5Me4), 2.80 (s, 12H, NMe2), 3.69 (br s,
8H, THF), 7.11–7.34 ppm (m, 8H, C6H4). 13C NMR (100 MHz,
CDCl3, 25 ◦C): d 12.42 (s, 4C, C5Me4), 12.88 (s, 4C, C5Me4), 26.57
(s, 4C, THF), 54.57 (s, 4C, NMe2), 69.48 (s, 4C, THF), 115.98
(s, 4C, C5Me4), 117.14 (s, 4C, C5Me4), 122.24 (s, 2C, o-NC6H4),
123.42 (s, 2C, ipso-C5Me4), 129.06 (s, 2C, p-NC6H4), 130.74 (s,
2C, m-NC6H4), 133.97 (s, 2C, o-C5Me4C6H4), 136.12 (s, 2C, ipso-
C5Me4C6H4), 158.27 ppm (s, 2C, ipso-NC6H4). Anal. calcd for
C49H68N2O2Cl5LiY2 (%): C, 54.54; H, 6.35; N, 2.60. Found: C,
54.21; H, 6.20; N, 2.49.
Synthesis of complex (C5Me4-C6H4-o-NMe2)Sm(BH4)2 (3b)
Following a similar procedure described previously, treatment of
[C5Me4-C6H4-o-NMe2]Li (0.247 g, 1.0 mmol) with 1 equiv. of
Sm(BH4)3(THF)3 (0.411 g, 1.0 mmol) afforded 3b as white powder
(0.304 g, 73%). Anal. calcd for C17H30NB2Sm (%): C, 48.57; H,
7.19; N, 3.33. Found: C, 48.27; H, 7.08; N, 3.24.
MMA polymerization
A detailed polymerization procedure (run 13, Table 3) is described
as a typical example. In a glove box, 3.2 mg of complex 3a (1.0 ¥
10-5 mol) was dissolved in 1 mL of dry and degassed THF. Three
n
equivalents of BuLi (3.0 ¥ 10-5 mol) were then added with a
Synthesis of complex
[(C5Me4-C6H4-o-NMe2)2Lu2Cl4][LiCl(THF)2] (2b)
microsyringe. Several seconds later the solution turned to pale
yellow. The glass ampule was then taken outside, placed in a -20 ◦C
thermostatic bath and stirred for 20 min. 0.5 g of MMA (0.005
mol) was added and the reaction was carried out for 2.5 min to
generate a viscous solution. Methanol was injected to terminate
the polymerization. The reaction mixture was poured into a large
Following a similar procedure described for the preparation of
2a, complex 2b was isolated from the reaction of LuCl3(THF)3
(0.498 g, 1.0 mmol) with 1 equiv. of [C5Me4-C6H4-o-NMe2]Li
(0.247 g, 1.0 mmol) in a 74% yield (0.430 g). Single crystals (with
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Dalton Trans., 2010, 39, 6871–6876 | 6875
©

quantity of methanol and then dried under vacuum at ambient
temperature to a constant weight (0.465 g, 93%).
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Acknowledgements
We thank financial supports from The National Natural Science
Foundation of China for project No. 20934006. The Min-
istry of Science and Technology of China for projects Nos.
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The Royal Society of Chemistry 2010
©