Highly cis-1,4-selective living polymerization of 1,3-conjugated dienes and copolymerization with ε-caprolactone by bis(phosphino)carbazolide rare-earth-metal complexes

Article abstract of DOI:10.1021/om1009395

Bis(phosphino)carbazole, HL (HL = 3,6-(tBu)₂-1,8-(PPh ₂)₂-carbazole), reacted with rare-earth-metal tris(aminobenzyl) complexes (Ln(CH₂C₆H₄N(Me) ₂-o)₃) to afford the f

Full text of DOI:10.1021/om1009395

760 Organometallics 2011, 30, 760–767
DOI: 10.1021/om1009395
Highly Cis-1,4-Selective Living Polymerization of 1,3-Conjugated Dienes
and Copolymerization with ε-Caprolactone by Bis(phosphino)carbazolide
Rare-Earth-Metal Complexes
Lingfang Wang,† Dongmei Cui,*,† Zhaomin Hou,*,‡ Wei Li,§ and Yang Li§
†State Key Laboratory of Polymer Physics and Chemistry, Changchun Institute of Applied Chemistry,
Chinese Academy of Sciences, Changchun 130022, People’s Republic of China,
‡Organometallic Chemistry Laboratory, RIKEN Advanced Science Institute, 2-1 Hirosawa, Wako,
Saitama 351-0198, Japan, and §College of Chemical Engineering, Dalian University of Technology,
People’s Republic of China
Received September 30, 2010
Bis(phosphino)carbazole, HL (HL = 3,6-(tBu)2-1,8-(PPh2)2-carbazole), reacted with rare-earth-
metal tris(aminobenzyl) complexes (Ln(CH2C6H4N(Me)2-o)3) to afford the first PNP-carbazolide
rare-earth-metal bis(alkyl) complexes, LLn(C6H4CH2N(Me)2)2 (Ln=Y (1), Sc (2), Er (3)). The
yttrium complex 1 was characterized by X-ray diffraction analysis as a solvent-free monomer, in
which the carbazolide ligand coordinates to the Y3þ ion in a κP:κN:κP0-tridentate mode and the two
aminobenzyl groups coordinate to the Y3þ ion in η1C:κN-bidentate modes. Complexes 1-3
combined with [Ph3C][B(C6F5)4] gave cationic catalyst systems that initiated cis-1,4-polymeriza-
tions of 1,3-conjugated dienes with high activities. Especially, the system 1/[Ph3C][B(C6F5)4]
displayed excellent cis-1,4-selectivity (>99%) and living mode at a broad range of polymerization
temperatures (0-80 °C). Remarkably, the living yttrium-polydiene active species could further
initiate the ring-opening polymerization of ε-caprolactone to give selectively poly(cis-1,4-diene)-
b-polycaprolactone block copolymer with controllable molecular weight (Mn = (10-70) ꢀ 104)
and narrow polydispersity (PDI = 1.15-1.47).
Introduction
molecular weight distribution.3 Lanthanidocene-mediated
catalysts4 and some modified titanium catalysts5 exhibit
excellent living mode together with high cis-1,4-selectivity,
albeit at low polymerization temperatures. The cationic rare-
earth-metal catalysts have been reported recently to show
considerably high cis-1,4-selectivity, even at elevated temper-
atures.6 However, to date catalyst systems that show both high
cis-1,4-selectivity and living character are still scarce.
Cis-1,4-regulated polydienes are one of the most impor-
tant rubbers, whose rheological and mechanical properties
are significantly influenced by their microstructures such as
molecular weight, molecular weight distribution, and espe-
cially cis-1,4-regularity. A direct consequence of a minor
increase in cis-1,4-regularity is strain-induced crystallization
of raw rubbers and vulcanizates, which significantly influ-
ences mechanical properties: e.g. tensile strength, resistance
to abrasion and fatigue, etc.1 Therefore, for half a century the
investigation of homogeneous catalyst systems that provide
over 98% cis-1,4-selectivity and living mode has been one of
the most fascinating and challenging subjects in both aca-
demic and industrial fields. The conventional Ziegler-Natta
type catalysts created in the 1960s are easy to prepare, are
cheap, and have been applied in industry but produce
polydienes with relatively low cis-1,4-regularity (<97%)
and poorly controlled molecular weight due to multisited
initiation centers.2 Modified Ziegler-Natta catalysts based
on heterometallic lanthanide methylaluminates display an
obvious improvement in selectivity and control of the
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*To whom correspondence should be addressed. D.C.: e-mail,
dmcui@ciac.jl.cn; fax, þ86 431 85262773. Z.H.: e-mail, houz@riken.
jp; fax, þ81 48 4624665.
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r
pubs.acs.org/Organometallics
Published on Web 02/03/2011
2011 American Chemical Society

Article
On the other hand, incorporation of polar functional
Organometallics, Vol. 30, No. 4, 2011 761
anionic) mechanism,18 the resultant copolymer usually has
poor regularity and less controlled molecular weight or is a
mixture of homopolymers. Therefore, copolymerization of
conjugated dienes and functional monomers in a regio- and
stereospecific manner has been a challenge. Obviously, the
development of new catalysts that show not only specific
selectivity and living character for the polymerization of
dienes but also activity for the polymerization of polar
monomers is required.
On the basis of our recent studies on the (co)polymer-
ization of 1,3-conjugated dienes by using well-defined orga-
no rare-earth-metal catalysts,6a,b,19,20 we designed a new
PNP-tridentate carbazolide ligand to stabilize rare-earth-
metal dialkyl species. Although carbazole derivatives are
used to support low-coordinate metals21a,b and transition
metals,21c-e the multidentate carbazolide transition-metal
complexes were structurally defined only recently,21f-i and
no analogous rare-earth-metal alkyl complexes have yet been
reported.22 To date, the use of carbazolide metal complexes
as polymerization catalysts has been unexplored, although
the catalytic activity for Nozaki-Hiyama and other reac-
tions has been reported.23
groups into nonpolar polymers endows the hydropho-
bic materials with remarkable adhesive, dyeing, moisture
absorption, etc. surface properties, miscibility with other
polymers, and rheological properties.7 To reach this target,
strategies such as modifying the nonpolar polymers with
functional groups8-10 or using nonpolar polymers as macro-
initiators to incorporate polar blocks11 have been adopted.
However, the most efficient and direct method, copolymer-
ization of nonpolar and polar monomers by using coordina-
tion catalysts, has been retarded, as the active metal centers
facilitating the polymerization of nonpolar monomers are
extremely oxophilic and are easily poisoned by polar mono-
mers. The stalemate was broken by the invention of lantha-
nidocenes that initiate the block copolymerization of simple
olefins such as ethylene with MMA (or cyclic esters).12
A
fascinating improvement13-16 is attributed to the recent
discovery of transition-metal-based systems that exhibit
distinguished activity or high incorporation rate of polar
monomers. In contrast, the copolymerization of conjugated
dienes with polar monomers by using coordination catalysts
remains less explored.17 Although such copolymerization
can be accessed by using macroinitiators via an ATRP (or
Herein we report the synthesis and characterization of
unique PNP-pincer carbazolide rare-earth-metal bis(alkyl)
complexes. On activation with organoborate these com-
plexes transferred into corresponding cationic species that
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762 Organometallics, Vol. 30, No. 4, 2011
Scheme 1. Synthesis of Bis(phosphino)carbazolide Rare-Earth-Metal Bis(aminobenzyl) Complexes
Wang et al.
showed high activity, distinguished regioselectivity, and ex-
cellent living modes for the polymerizations of dienes. More
strikingly, the cationic living metal-polydiene species could
further initiate the ring-opening polymerization (ROP) of
the polar monomer ε-caprolactone (ε-CL) to give block
copolymers of poly(cis-1,4-diene)-b-polylactone selectively.
Results and Discussion
Synthesis of PNP-Carbazolide Rare-Earth-Metal Bis-
(alkyl) Complexes. Rare-earth-metal alkyl complexes have
attracted increasing attention in the past decade, as highly
active single-component catalysts or crucial precursors of the
cationic counterparts after being activated by MAO or bo-
rates, and have shown tremendous catalytic activities toward
olefin polymerizations4f,24 and specific selective polymeriza-
tions of conjugated monomers4c,d and polar monomers.25
However, the preparation of such complexes usually encoun-
ters problems of salt addition, dimerization, ligand scram-
bling, and unpredictable C-H activation, due to the highly
active character of the metal-carbon bonds and relatively
less crowded steric environment of the molecules.26 In
order to overcome these drawbacks, we designed a sub-
stituted bis(phosphino)carbazole (HL, 3,6-(tBu)2-1,8-(PPh2)2-
carbazole) possessing PNP-tridentate coordination sites and
“soft” and “large” phosphine atoms that were anticipated to
stabilize rare-earth-metal bis(alkyl) species electronically
and sterically. This PNP-tridentate carbazole was synthe-
sized according to the modified literature procedure.21d,27
3,6-(tBu)2-1,8-Br2-carbazole was lithiated stepwise with
Figure 1. X-ray molecular structure of 1 with 35% probability
thermal ellipsoids. Hydrogen atoms and the solvent molecule
˚
are omitted for clarity. Selected bond distances (A) and angles
(deg): Y(1)-C(45)=2.449(4), Y(1)-C(54)=2.444(4), N(1)-Y-
(1)=2.408(3), N(2)-Y(1)=2.588(3), N(3)-Y(1) = 2.578(3), P-
(1)-Y(1)=3.1770(9), P(2)-Y(1)=3.116(1); N(1)-Y(1)-N(3)=
84.44(10), C(54)-Y(1)-N(3)=68.06(11), N(1)-Y(1)-N(2)=
124.83(10), C(45)-Y(1)-N(2)=67.55(11), N(3)-Y(1)-N-
(2)=149.96(10), N(1)-Y(1)-P(2)=63.36(7), C(45)-Y(1)-
P(2)=82.54(9), N(3)-Y(1)-P(2)=88.99(7), N(2)-Y(1)-P(2)=
98.16(7), N(1)-Y(1)-P(1)=64.84(7), C(54)-Y(1)-P(1)=
73.83(9), N(3)-Y(1)-P(1)=117.16(7), P(2)-Y(1)-P(1)=
118.06(3).
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n-butyllithium and then tert-butyllithium. A metathesis re-
action of the lithiation product with PPh2Cl afforded HL.
Deprotonation of HL by rare-earth-metal tris(aminobenzyl)
species, Ln(CH2C6H4NMe2-o)3,28 generated the targeted
bis(aminobenzyl) derivatives, LLn(CH2C6H4NMe2-o)2
(Ln = Y (1), Sc (2), Er (3)) (Scheme 1). The NMR spectro-
scopic analyses of complexes 1 and 2 (3 is paramagnetic)
displayed the absence of the carbazole amino proton and
resonances of the carbazolide moiety slightly different from
those of the free ligand, suggesting that the ligand success-
fully chelated to the metal centers. Meanwhile, the methylene
protons of the metal alkyl moieties Ln-σ-CH2 gave reso-
nances shifted downfield compared with those in the
homoleptic precursors Ln(CH2C6H4NMe2-o)3 (Y-σ-CH2:
δ 1.95 vs δ 1.79; Sc-σ-CH2: δ 2.39 vs δ 1.64), respectively.
No resonances from THF molecules were detected, confirm-
ing the absence of solvent coordination. Meanwhile, Y-P
coupling was observed in the 31P NMR spectrum (JYP
=
27.1 Hz),6b suggesting that the carbazolide ligand coordi-
nates to the Y3þ ion via phosphine atoms. X-ray diffraction
analysis confirmed further the molecular structure of the

Article
Organometallics, Vol. 30, No. 4, 2011 763
Table 1. Polymerization of Isoprene and Butadiene with Complexes (1-3)/[Ph3C][B(C6F5)4] a
b
entry
Ln
[M]/[Ln]
temp (°C)
time (min)
conversn (%)
Mn ꢀ10-4
Mw/Mn
cis-1,4c (%)
effd (%)
1
2
3
4
5
6
7
8
Y
Sc
Er
Y
Y
Y
Y
Y
Y
Y
Y
Y
Y
Y
Y
Y
1000
1000
1000
1000
1000
1000
2000
3000
5000
10000
1000
1000
1000
1000
500
25
25
25
0
10
5
30
120
10
5
30
45
90
150
45
45
45
45
150
150
100
100
100
71
96
84
11.7
11.6
10.3
12.0
14.6
17.8
19.4
27.3
58.0
160.0
7.6
1.07
1.49
1.08
1.06
1.06
1.07
1.09
1.06
1.14
1.24
1.11
1.12
1.11
2.96
1.07
1.06
>99
98.3
97.6
>99
>99
98.8
>99
>99
>99
>99
98.8
99.0
98.6
98.9
>99
>99
58.1
58.6
66.0
40.0
44.7
32.0
70.0
71.0
58.6
42.5
89.5
81.5
90.5
50
80
25
25
25
25
25
25
25
25
25
25
100
95
9
100
100
100
100
100
95
10
11e
12e
13e
14e
15f
16f
8.3
7.5
1.7
2.9
80
71
74.5
46.1
1000
8.2
a Conditions: Ln, 10 μmol; B, 10 μmol (B = [Ph3C][B(C6F5)4]); 10/1 toluene/isoprene (v/v). b Determined by means of gel permeation
chromatography (GPC) against polystyrene standards. c Measured by means of 1H NMR and 13C NMR spectroscopy in CDCl3. d Catalyst efficiency,
calculated by Mn(calcd)/Mn(measd). e Addition of AlMe3 (entry 11), AlEt3 (entry 12), AliBu3 (entry 13), and HAlEt2 (entry 14) at an Al to Y ratio of 10.
f Polymerization of butadiene ([BD] = 1.67 mol/L).
yttrium complex 1 as a THF-free seven-coordinate monomer
(Figure 1). The carbazolide ligand binds to the Y3þ ion via
the two phosphine atoms and an nitrogen atom in a κP:κN:κP0-
tridentate mode to form a planar pincer geometry; the Y3þ ion
deviates slightly out of the plane owing to the steric conges-
tion arising from the phenylphosphine groups. Meanwhile,
both aminobenzyl ligands chelate to the Y3þ ion via nitrogen
and carbon atoms in η1C:κN-bidentate modes, with one
occupying the exo position and the other occupying the endo
position with respect to the carbazolide backbone plane.
This is in contrast to the case for the flexible bis(phosphi-
nophenyl)amido yttrium bis(alkyl) complex, in which the
Y3þ ion combined with the phosphine atoms and the
amino nitrogen atom to generate a tetrahedral geometry.6b
obtained PIP samples with H2 afforded perfect poly-
(ethylene-alt-propylene) rubbers.31
More remarkably, the catalyst system composed of yt-
trium complex 1 (or erbium complex 3) and [Ph3C][B(C6F5)4]
also exhibited a living mode. With the monomer to initiator
ratios varying from 1000:1 to 10 000:1, the molecular weight
of the resultant PIP increased linearly from 11.7 ꢀ 104 to
160.0 ꢀ 104, values slightly higher than the corresponding
theoretical values, showing moderate to high catalytic effi-
ciencies (42-71%). Meanwhile, the molecular weight dis-
tribution stayed in a very narrow range (PDI = 1.06-1.09),
although it became broader when the monomer to initiator
ratio was over 10 000 (PDI = 1.24) owing to the difficulty of
monomer diffusion (Table 1, entries 7-10). It was note-
worthy that addition of an excess amount of AlR3 (Al:Y =
10:1, R = Me, Et, iBu) to the binary system 1/[Ph3C][B-
(C6F5)4] did not have an obvious influence on the catalytic
performances (Table 1, entries 11-14).32 This was in con-
trast to some other catalyst systems such as [(C5Me5)2Gd]
[B(C6F5)4],4c [2,6-(2,6-C6H3R2NdCH)2-C6H3]LnCl2(THF)2,6a
[YMe2(thf)5]þ[BPh4]-,6e and (Flu-NHC)Ln(CH2SiMe3)2
(Flu-NHC = C13H8CH2CH2(NCHCCHN)C6H2Me3-2,4,6;
Ln = Sc, Y, Ho, Lu),33 which were inert in the absence of
AlR3, or the catalyst system [(NCNdipp)Y(CH2C6H4NMe2-
o)2]/[Ph3C][B(C6F5)4],19a which upon addition of AlMe3
switched from iso-3,4-selectivity to cis-1,4-selectivity. This
suggested that AlR3 did not coordinate to the active metal
center bearing a sterically bulky ligand. However, in con-
trast, addition of the aluminum alkyl hydride HAlEt2 to
the binary system 1/[Ph3C][B(C6F5)4] led to a dramatic drop
in the molecular weight of PIP due to its strong chain
transfer effect.
˚
˚
The average Y-C (2.446 A) and Y-P (3.146 A) bond lengths
fall in the normal ranges found in yttrium alkyl com-
plexes19a,20b,29 and phosphine chelated yttrium complexes,
respectively.26e,30
(Co-)Polymerization of Isoprene and Butadiene. Complexes
1-3 alone were inert to the polymerization of 1,3-conjugated
dienes but on activation with [Ph3C][B(C6F5)4] showed high
activity toward isoprene (IP) polymerization. Complete
conversion was achieved within 5 min for the scandium
complex 2 and 10 min for the yttrium counterpart 1. The
erbium analogue 3 was slightly less active, which needed 1/2 h
to complete the polymerization under the same conditions.
Meanwhile, all these catalyst systems exhibited high cis-1,4-
selectivity (97.6-99%), among which the combination
1/[Ph3C][B(C6F5)4] was the best to afford polyisoprene
(PIP) with higher than 99% cis-1,4-regularity (Table 1,
entries 1-3). Strikingly, this distinguished performance
seemed not to be affected by the polymerization tempera-
ture. Therefore, polyisoprene with as high as 98.8% cis-1,4-
regularity could be obtained when the polymerization was
performed at or below 80 °C (Table 1, entries 4-6). To date,
few systems can maintain their specific selectivity at high
polymerization temperatures,6a,b indicating the thermal sta-
bility of the present active species. Hydrogenation of the
The catalytic performance of 1/[Ph3C][B(C6F5)4] for bu-
tadiene (BD) polymerization was similar to that of IP
polymerization, albeit with a lower activity (Table 1, entries
15 and 16). Therefore, the random copolymer P(IP-co-BD)
(31) The hydrogenation of polyisoprene was carried out in cyclohex-
ane solution at 60 °C under 4 MPa H2 atmosphere for 3 h with nickel
naphthenate/aluminum triisobutyl catalyst, to give a perfect alternating
copolymer of polyethylene and polypropylene (see Figures 7 and 8 in the
Supporting Information).
(29) Nishiura, M.; Mashiko, T.; Hou, Z. Chem. Commun. 2008, 2019–
2021.
(30) (a) Miao, W.; Li, S.; Cui, D.; Huang, B. J. Organomet. Chem.
2007, 692, 3823–3834. (b) Yang, Y.; Li, S.; Cui, D.; Chen, X.; Jing, X.
Organometallics 2007, 26, 671–678.
(32) Hitzbleck, J.; Beckerle, K.; Okuda, J.; Halbach, T.; Mulhaupt,
R. Macromol. Symp. 2006, 236, 23–29.
(33) Wang, B; Cui, D.; Lv, K. Macromolecules 2008, 41, 1983–1988.

764 Organometallics, Vol. 30, No. 4, 2011
Table 2. Random Copolymerization of Isoprene and Butadiene with 1/[Ph3C][B(C6F5)4]a
Wang et al.
b
entry
feed ratio [BD]:[IP]:[Y]
conversn (%)
Mn ꢀ10-4
Mw/Mn
found ratio BD:IPc
effd(%)
1
2
3
4
5
1500:500:1
2000:500:1
1000:1000:1
2000:1000:1
1000:2000:1
91
84
94
80
93
35.4
44.6
31.4
58.4
59.1
1.14
1.16
1.13
1.24
1.25
239:100
304:100
80:100
153:100
45:100
29.7
26.7
36.6
24.0
29.8
a Conditions: 1, 10 μmol; B, 10 μmol (B = [Ph3C][B(C6F5)4]); toluene, 12 mL; room temperature; 270 min. b Determined by means of gel permeation
chromatography (GPC) against polystyrene standards. c Measured by means of 1H NMR and 13C NMR spectra in CDCl3. d Catalyst efficiency,
calculated by Mn(calcd)/Mn(measd).
Table 3. Copolymerization of Isoprene and ε-Caprolactone with 1/[Ph3C][B(C6F5)4] a
c
entry feed ratio [IP]:[CL]:[Y] T1/T2 (min)b conversn (%) Mn ꢀ10-4 Mw/Mn cis-1,4 d found ratio IP:CL d Tge (°C) Tm (°C) ΔHm (J g-1
)
1
2
3
4
5
6
7
8
800:0:1
0:1000:1
45/0
0/90
100
100
100
100
99
92
97
86
10.0
18.1
15.4
20.0
30.7
44.0
61.7
70.3
1.07
1.52
1.15
1.25
1.28
1.27
1.46
1.47
>99
-64.0
68.9
62.9
66.8
68.0
67.0
67.8
67.5
-61.2
-28.9
-46.8
-49.1
-32.4
-61.6
-35.5
800:300:1
800:600:1
1000:1000:1
2000:1000:1
2000:2000:1
3000:2000:1
45/90
45/90
60/90
90/120
90/120
90/120
>99
>99
>99
>99
>99
>99
315:100
150:100
147:100
288:100
102:100
122:100
-62.4
-62.7
-62.3
-62.1
-62.7
-62.3
a Conditions: complex 1, 10 μmol; [B], 10 μmol (B = [Ph3C][B(C6F5)4]); 10/1 toluene/isoprene (v/v). b Polymerization time: T1 for isoprene, T2 for
ε-CL. c Determined by means of gel permeation chromatography (GPC) against polystyrene standards. d Measured by means of 1H NMR and 13C NMR
spectroscopy in CDCl3. e Determined by differential scanning calorimetry (DSC).
could be easily synthesized by copolymerizing a mixture of IP
and BD (Table 2). The composition of the copolymer could be
roughly adjusted by varying the BD to IP feed ratio to be
slightlyhigherthan the BDtoIPfound ratio, inconsistent with
the lower polymerization rate of BD. However, the molecular
weight of the copolymer increased with an increase of the (IP
þ BD) to Y ratio. More interestingly, both the butenyl and
isopentenyl sequences in the copolymer were highly cis-1,4-
regulated (>99%), and the isopentenyl fragments had a head-
Figure 2. GPC traces of block copolymers of PIP-b-PCL
(Table 3, entries 1 and 3-8). The rightmost is homopolyisoprene.
to-tail arrangement. This means the obtained copolymer
P(IP-co-BD) can be a kind of high-performance rubber. It is
the sole characteristic of rare-earth-metal-based catalytic
show poor activity for chain propagation because of
transesterification.36 To our delight, the catalyst system
systems to display high cis-1,4-selectivity toward both BD
and IP polymerizations simultaneously.
1/[Ph3C][B(C6F5)4] exhibited high activity for ε-CL poly-
Block Copolymerization of Isoprene and ε-Caprolactone.
Polylactone is one of the most important biodegradable and
biocompatible materials in the medical industry. Incorpora-
tion of lactone into polyisoprene will increase its compat-
ibility with other polymers when used in tires or improve its
biocompatibility when used in tissue engineering to replace
bacteria-susceptible natural rubber.34 Although neutral lan-
thanide complexes are efficient initiators for the ring-open-
ing polymerization of ε-CL,35 the ionic catalytic systems
merization (Table 3, entry 2) in addition to its excellent living
mode for diene polymerizations, which inspired us to at-
tempt the copolymerization of isoprene and ε-caprolactone
(ε-CL). Fortunately, when ε-CL was added to a 100%
conversion IP polymerization system, PIP-b-PCL diblock
copolymer was isolated.37 The composition of the copolymer
was close to the IP to ε-CL feed ratio. The molecular weight
of the copolymer increased proportionately with the mono-
mer to Y ratio, consistent with the theoretical value, and
the molecular weight distribution remained narrow and
monomodal (Figure 2). These results suggested that the
yttrium-polyisoprene active species initiated the copoly-
merization with ε-CL with high efficiency and high-molecular-
weight block copolymer could be prepared without difficulty
(Table 3, entry 8, Mn = 70.3 ꢀ 104). The DSC traces of the
copolymers revealed that, with an increase in the content of
(34) Linos, A.; Berekaa, M. M.; Reichelt, R.; Keller, U.; Schmitt, J.;
€
Flemming, H. C.; Kroppensted, R. M.; Steinbuchel, A. Appl. Environ.
Microbiol. 2000, 1639–1645.
(35) (a) Yamashita, M.; Takemoto, Y.; Ihara, E.; Yasuda, H. Macro-
molecules 1996, 29, 1798–1806. (b) Nomura, N.; Taira, A.; Tomioka, T.;
Okada, M. Macromolecules 2000, 33, 1497–1499. (c) Sheng, H.; Xu, F.;
Yao, Y.; Zhang, Y.; Shen, Q. Inorg. Chem. 2007, 46, 7722–7724. (d)
Sarazin, Y.; Howard, R. H.; Hughes, D. L.; Humphrey, S. M.; Bochmann,
M. Dalton Trans. 2006, 340–350. (e) Gao, W.; Cui, D.; Liu, X.; Zhang, Y.;
Mu, Y. Organometallics 2008, 27, 5889–5893.
(37) A triblock copolymer of PBD-b-PIP-b-PCL can also be obtained
by sequential addition of BD, IP, and ε-CL; see Figure 21 in the
Supporting Information.
(36) Kricheldorf, H. R.; Dunsing, R. Makromol. Chem. 1986, 187,
1611–1625.

Article
Organometallics, Vol. 30, No. 4, 2011 765
Scheme 2. Probable Mechanistic Pathway for Block Copolymerization of Isoprene and ε-Caprolactone
the PIP block, the crystallinity of the PCL block became
poor and its ΔHm value was correspondingly lower, suggest-
ing further the formation of block copolymers rather than a
mixture of homopolymers.
PIP-b-PCL were prepared.39 According to the 1H NMR
spectra, the initiating aminobenzyl groups Me2NC6H4CH2
were detected in both oligomers, which give resonances at
δ 7.21 (d), 7.17 (t), 7.11 (t), and 7.01(d) ppm for the aromatic
protons, a signal at 2.73-2.70 ppm for the methylene group
CH2, and a signal at 2.68 ppm arising from NMe2. In
addition the 1H NMR spectrum showed that the end group
of the copolymer was CH2OH by giving resonances around
3.68-3.65 ppm, which is consistent with the literature re-
In order to obtain information about the active species
generated during the polymerization of dienes, the activation
of yttrium complex 1 (LY(CH2C6H4N(Me)2-o)2) with [Ph3C]
[B(C6F5)4] was monitored by NMR spectroscopic techni-
1
ques. According to the integral ratio in the H NMR spec-
ꢀ
trum, the alkyl moiety -CH2C6H4N(Me)2-o in 1 was ab-
stracted by [Ph3C][B(C6F5)4] to form the cationic yttrium
monoalkyl species with release of the coupling product
Ph3CCH2C6H4N(Me)2-o. The resonances of the carbazolide
ligand changed slightly compared with those in 1, while the
31P NMR spectrum gave a doublet for Y-P coupling at
δ -3.58 (JY-P=77.7 Hz)6b shifted downfield compared with
δ -9.09 (JY-P = 27.1 Hz) in 1. Moreover, the 19F NMR
spectrum showed the same pattern as for [Ph3C][B(C6F5)4],
suggesting the absence of coordination between the anion
[B(C6F5)4]- and the cationic active species. The probable
reaction pathway for the copolymerization could be simpli-
fied (Scheme 2): the IP monomer was cis-η4 coordinated to
the cationic yttrium alkyl species, inserted into the Y-CH2
bond, and propagated to cationic yttrium polyisoprene,2 and
then ε-CL monomer coordinated to the yttrium ion via the
carboxyl oxygen, which was followed by nucleophilic attack
of yttrium-polyisoprene species on the carboxyl carbon
to generate an yttrium-oxygen bond via cleavage of an
acyl-oxygen bond (vide supra).38 To prove this assumption,
the oligomers of homopolymers of PIP and copolymers
ported recently on the investigation of PE-b-PCL by Baez
et al.,40 in which hydroxyl is the end group of PE-b-PCL
copolymers. Correspondingly, the 13C NMR spectrum gives
two sets of signals for PCL sequences: one set of strong
signals at 173.48, 34.10, 24.56, 25.52, 28.34, and 64.11 ppm is
attributed to the repeating units (-CO-(CH2)5-O-) and
the other set of weak signals at 173.67, 34.20, 24.66, 25.29,
28.51, and 62.58 ppm are derived from the terminal units
(-CO-(CH2)5-OH). The signal of the ketone carbon-
yl, -CH2-CHdCH(CH3)-CH2-C(O)(CH2)6-, is de-
tected at 210.02 ppm. This peak is the evidence for the
covalent bond between PIP and PCL blocks. The above
information revealed that the PIP active species initiated the
polymerization of caprolactone on the carbonyl carbon via
cleavage of an acyl-oxygen bond, forming a copolymer with
the microstructure (CH3)2NC6H4CH2-PIP-CH2-CHd
CH(CH3)-CH2CO(CH2)5O-PCL-CO(CH2)5OH.
As the precursor Y(CH2C6H4N(Me)2-o)3 combined with
[Ph3C][B(C6F5)4] was also active in the polymerizations of
dienes but was nonselective and not living, the dual catalysis
of 1/[Ph3C][B(C6F5)4] on the specific selective addition-
polymerization of dienes and ring-opening polymerization
of polar ε-CL might be attributed to the introduction of the
bulky and electron-donating PNP-carbazolide ligand.
(38) Sanchez-Barba, L. F.; Hughes, D. L.; Humphrey, S. M.;
Bochmann, M. Organometallics 2005, 24, 3792–3799.
(39) 1H NMR (600 MHz, CDCl3, 25 °C) of the oligomer of homo-
polyisoprenes: δ 7.21 (d, J = 7.2 Hz, 1H, C6H4), 7.17 (t, J = 7.8 Hz, 1H,
C6H4), 7.11 (t, J = 7.8 Hz, 1H, C6H4), 7.01 (d, J = 7.2 Hz, 1H, C6H4), 5.14
(b, 90H, CHdC, cis-1,4 PIP), 2.72-2.66 (m, 2H, C6H4CH2CH2), 2.65 (s,
6H, NMe2), 2.34-2.31 (m, 2H, C6H4CH2CH2), 2.04 (b, 372H, CH2, cis-
1,4 PIP), 1.68 (b, 273H, CH3, cis-1,4 PIP). 1H NMR (600 MHz, CDCl3,
25 °C) ofthe oligomeric copolymers PIP-b-PCL: δ 7.21 (d, J = 7.8 Hz, 1H,
C6H4), 7.16 (t, J = 7.8 Hz, 1H, C6H4), 7.10 (t, J = 7.8 Hz, 1H, C6H4), 7.01
(d, J = 7.8 Hz, 1H, C6H4), 5.14 (b, 166H, CHdC, cis-1,4 PIP), 4.07 (t, J =
6.6 Hz, 22H, CO(CH2)4CH2O), 3.68-3.65 (q, J = 6.0 Hz, 2H, CH2OH),
2.73-2.70 (m, 2H, C6H4CH2CH2), 2.68(s, 6H, NMe2), 2.32 (t, J= 7.2Hz,
26H, C6H4CH2CH2, CH2CO, and COCH2(CH2)4O), 2.18-1.87 (overlap,
686H, mainly CH2 of cis-1,4 PIP), 1.68-1.64 (overlap, 573H, mainly CH3
of cis-1,4 PIP, and COCH2CH2CH2CH2CH2O), 1.42-1.36 (overlap, 32H,
mainly COCH2CH2CH2CH2CH2O). For the 13C NMR spectrum of
oligomeric copolymers PIP-b-PCL, see Figure 22 in the Supporting
Information.
Conclusion
In summary, we have successfully prepared the first PNP-
pincer carbazolide rare-earth-metal bis(alkyl) complexes
without solvent coordination. These complexes, especially
yttrium complex 1 on activation with [Ph3C][B(C6F5)4], exhi-
bited high cis-1,4-selectivity and excellent living mode for
the polymerizations of isoprene and butadiene over a broad
range of polymerization temperatures. More remarkably,
the cationic yttrium-polyisoprene active species could
ꢀ
ꢀ
ꢀ
ꢀ
ꢀ
(40) Baez, J. E.; Ramιrez-Hernandez, A.; Marcos-Fernandez, A.
Polym. Adv. Technol. 2010, 21, 55–64.

766 Organometallics, Vol. 30, No. 4, 2011
Wang et al.
initiate further the ROP of ε-CL to afford pure diblock
copolymers of poly(cis-1,4 dienes)-b-PCL with designable
molecular weight. This represents a well-controlled highly
cis-1,4-selective copolymerization of dienes with ε-CL,
which might shed new light on the design of novel catalyst
precursors and further investigations of mechanisms in-
volved in the homo- and copolymerization of dienes.
122.65 (s, 2,7-carbazole), 117.62 (s, 4,5-carbazole), 116.45 (d,
J
CP = 11.1 Hz, ipso-carbazole), 34.74 (s, C(CH3)3), 31.84 ppm
(s, C(CH3)3). 31P{1H} NMR (161.9 MHz, CDCl3, 25 °C):
δ -14.87 ppm (s, 2P). Anal. Calcd for C44H43NP2: C, 81.58;
H, 6.69; N, 2.16. Found: C, 81.09; H, 6.44; N, 1.89.
Synthesis of LY(CH2C6H4NMe2-o)2 (1). Under a nitrogen
atmosphere, HL (0.26 g, 0.40 mmol), Y(CH2C6H4NMe2-o)3
(0.20 g, 0.40 mmol), and 30.0 mL of toluene were mixed in a
Schlenk tube with a Teflon stopcock and heated to 50 °C for 4 h
and 70 °C for 3 h. Filtration and concentration afforded a
viscous solution. The solution was kept at room temperature for
several hours to give yellow prismatic crystals of 1 (0.20 g,
50.1%). 1H NMR (400 MHz, C6D6, 25 °C): δ 8.56 (s, 2H, 4,5-
carbazole) 7.78 (dd, J = 7.6 Hz, 1.6 Hz, 2H, 2,7-carbazole),
7.66-7.63 (m, 8H, P(C6H5)2), 7.14 (br, 12H, P(C6H5)2), 7.00
(t, J = 6.8 Hz, 2H, γ-CH2C6H4), 6.94 (d, J = 7.2 Hz, 2H, R-
CH2C6H4), 6.79 (t, J = 7.6 Hz, 2H, β-CH2C6H4), 6.72 (d, J =
8.0 Hz, 2H, δ-CH2C6H4), 2.18 (s, 12H, NMe2), 1.95 (s, 4H,
CH2), 1.49 ppm (s, 18H, CMe3). 13C NMR (100 MHz, C6D6,
25 °C): δ 155.97 (d, JCP = 25.1 Hz, ipso-carbazole), 145.98 (s,
ipso-carbazole), 143.85 (s, ipso-C6H4), 141.44 (s, ipso-C6H4),
Experimental Section
General Procedure and Materials. 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 with an
MBRAUN SPS system. Butadiene gas was passed through a
toluene solution of AliBu3, followed by freezing out into cold
toluene. The concentration was determined by weighing the
mass difference. Organometallic samples for NMR spectro-
scopic measurements were prepared in the glovebox by use of
NMR tubes sealed by paraffin film. 1H and 13C NMR spectra
were recorded on a Bruker AV400 (FT, 600 or 400 MHz or
300 MHz) spectrometer. NMR assignments were confirmed by
135.44 (d, JCP = 10.1 Hz, ipso-carbazole), 134.42 (d, JCP
=
14.1 Hz, P(C6H5)2), 129.65 (s, R-C-C6H4), 129.06-128.26 (m,
P(C6H5)2), 127.28 (s, γ-CH2C6H4), 126.49 (s, 2,7-carbazole),
119.57 (s, 4,5-carbazole), 119.50 (s, β-CH2C6H4), 118.70 (s,
δ-CH2C6H4), 117.16 (d, JCP = 12.1 Hz, ipso-carbazole), 53.98
(d, JYC = 28.1 Hz, CH2), 45.87 (s, NMe2), 35.53 (s, CMe3), 32.77
ppm (s, CMe3). 31P{1H} NMR (161.9 MHz, C6D6, 25 °C):
δ -9.09 ppm (d, JYP = 27.1 Hz, 2P). Anal. Calcd for
C62H66N3P2Y: C, 74.17; H, 6.63; N, 4.19. Found: C, 73.70; H,
6.25; N, 3.67.
Synthesis of LSc(CH2C6H4NMe2-o)2 (2). By a procedure
similar to that described for the preparation of 1, treatment
of Sc(CH2C6H4NMe2-o)3 (0.19 g, 0.40 mmol) with HL (0.26 g,
0.40 mmol) gave yellow crystals of 2 (0.15 g, 41.0%). 1H NMR
(400 MHz, C6D6, 25 °C): δ 8.57 (s, 2H, 4,5-carbazole), 7.66 (d,
J = 6.8 Hz, 2H, 2,7-carbazole), 7.43-7.44 (m, 8H, P(C6H5)2),
7.11 (br, 12H, P(C6H5)2), 6.96 (d, J = 6.9 Hz, 4H, R,γ-
CH2C6H4), 6.83-6.89 (m, 2H, β-CH2C6H4), 6.77 (d, J = 8.4 Hz,
2H, δ- CH2C6H4), 2.39 (s, 4H, CH2), 2.41 (s, 12H, NMe2),
1.47 ppm (s, 18H, CMe3). 13C NMR (100 MHz, C6D6, 25 °C):
δ 156.07 (d, JCP = 25.6 Hz, ipso-carbazole), 148.15 (s, ipso-
C6H4), 147.53 (s, ipso-carbazole), 142.06 (s, ipso-C6H4), 136.43
(d, JCP = 3.0 Hz, ipso-carbazole), 134.43 (d, JCP = 14.3 Hz,
P(C6H5)2), 131.90 (s, C6H4), 129.57-128.18 (m, P(C6H5)2),
126.96 (s, 2,7-carbazole), 126.14 (s, C6H4), 121.45 (s, C6H4),
1
1H-1H COSY and H-13C HMQC experiments when neces-
sary. IR spectra were recorded on a VERTEX 70 FT-IR
instrument. The molecular weight and molecular weight dis-
tribution of the polymers were measured with a TOSOH HLC-
8220 GPC instrument. Elemental analyses were performed at
the National Analytical Research Centre of the Changchun
Institute of Applied Chemistry (CIAC). DSC was performed
on a METTLER TOPEM TM DSC instrument at a heating rate
of 10 °C/min under an N2 atmosphere.
X-ray Crystallographic Study. A single crystal of complex 1
suitable for X-ray analysis was 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-
˚
monochromated Mo KR radiation (λ=0.710 73 A). The deter-
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 structure was solved by using the SHELXTL
program. Refinement was performed on F2 anisotropically for
all non-hydrogen atoms by full-matrix least-squares methods.
The hydrogen atoms were placed at calculated positions and
were included in the structure calculation without further
refinement of the parameters.
Synthesis of 1,8-Bis(phosphino)-3,6-di-tert-butylcarbazole (HL).
One equivalent of nBuLi (6.63 mL, 1.50 M in hexane, 10.0 mmol)
was added dropwise to 1,8-dibromo-3,6-di-tert-butyl-9H-car-
bazole (4.37 g, 10.0 mmol) in diethyl ether (150 mL) at 0 °C. The
reaction mixture was stirred for 1 h and then cooled to -78 °C,
and 4 equiv of tBuLi (26.67 mL, 1.50 M in pentane, 40.0 mmol)
was added dropwise. The reaction mixture was warmed natu-
rally to room temperature and stirred overnight to give a pale
yellow suspension. The suspension was cooled to -50 °C, and 2
equiv of chlorodiphenylphosphine (3.59 mL, 20.0 mmol) was
added with continuous stirring at room temperature for 18 h.
The suspension was quenched with 2-propanol (2.0 mL) at 0 °C
and filtered through a pad of Celite. Removal of 2-propanol and
other solvents gave a pale yellow oil, which was dissolved in a
mixture of 10.0 mL of CH2Cl2 and 30.0 mL of pentane and
cooled to -35 °C to afford HL as off-white solids (2.00 g,
30.8%). 1H NMR (CDCl3, 300 MHz, 25 °C): δ 8.45 (s, 2H, 4,5-
carbazole), 8.36 (s, 1H, NH), 7.76 (d, J = 8.0 Hz, 2H, 2,7-
carbazole), 7.45-7.43 (m, 8H, P(C6H5)2), 7.10-7.08 (m, 12H,
P(C6H5)2), 1.42 ppm (s, 18H, C(CH3)3). 13C NMR (100 MHz,
CDCl3, 25 °C): 142.56 (d, JCP = 6.0 Hz, ipso-carbazole), 140.55
(d, JCP = 9.1 Hz, ipso-carbazole), 135.74 (d, JCP = 10.1 Hz,
ipso-carbazole), 133.10 (d, JCP = 19.1 Hz, P(C6H5)2), 130.25 (d,
119.10 (s, C6H4), 118.50 (s, 4,5-carbazole), 117.80 (d, JCP =
6.8 Hz, ipso-carbazole), 59.10 (br, CH2), 46.59 (s, NMe2),
35.47 (s, CMe3), 32.67 ppm (s, CMe3). 31P{1H} NMR (161.9
MHz, C6D6, 25 °C): δ -12.61 ppm. Anal. Calcd for
C62H66N3P2Sc: C, 77.56; H, 6.93; N, 4.38. Found: C, 77.01; H,
6.57; N, 4.11.
Synthesis of LEr(CH2C6H4NMe2-o)2 (3). By a procedure
similar to that described for the preparation of 1, treatment of
Er(CH2C6H4NMe2-o)3 (0.24 g, 0.40 mmol) with HL (0.26 g,
0.40 mmol) afforded yellow solids of 3 (0.18 g, 43.6%). Anal.
Calcd for C62H66N3P2Er: C, 68.80; H, 6.15; N, 3.88. Found: C,
68.41; H, 5.86; N, 3.46.
Monitoring the Reaction of Complex 1 or 2 with [Ph3C]
[B(C6F5)4] by NMR Spectroscopic Techniques. In a glovebox,
complex 1 (20.0 mg, 0.02 mmol) and [Ph3C][B(C6F5)4] (18.6 mg,
0.02 mmol) were dissolved in C6D6, respectively. The combined
1
solutions were transferred into an NMR tube. H NMR (400
MHz, C6D6, 25 °C): δ 8.74 (s, 2H, 4,5-carbazole), 7.87-7.86 (m,
2H, 2,7-carbazole), 7.47 (d, J = 7.2 Hz, 6H, Ph3C), 7.45 (b, 8H,
Ph2P), 7.24-7.08 (m, 21H, Ph3C, Ph2P), 7.07 (m, 2H, CH2C6H4-
NMe2), 6.98 (d, J = 8.0 Hz, 2H, CH2C6H4NMe2), 6.88 (d, J =
8.0 Hz, 2H, CH2C6H4NMe2), 6.77 (t, J = 8.0 Hz, 2H, CH2-
C6H4NMe2), 2.56 (s, 6H, NMe2), 2.40 (s, 2H CH2), 2.39 (s, 2H,
CH2), 2.36 (s, 6H, NMe2), 1.48 (s, 18H, Me3C). 13C NMR
JCP = 19.1 Hz, ipso-P(C6H5)2), 128.66-128.54 (m, P(C6H5)2),

Article
Organometallics, Vol. 30, No. 4, 2011 767
(100 MHz, C6D6, 25 °C): δ 154.97 (s, ipso-carbazole), 149.62
(d, J = 248.41 Hz, 8C, B(C6F5)4), 148.46 (s, ipso-(C6H5)3C),
145.05 (s, ipso-C6H4), 143.38 (d, J = 20.1 Hz, ipso-carbazole),
139.36 (d, J = 244.36 Hz, B(C6F5)4), 137.61 (d, J = 239.33 Hz,
B(C6F5)4), 133.81 (d, J = 14.1 Hz, ipso-carbazole), 133.14 (s,
ipso-C6H4), 131.78 (d, J=28.2 Hz, ipso-P(C6H5)2), 131.24 (s, 2,7-
carbazole), 130.82 (s, (C6H5)3C, P(C6H5)2), 130.36 (s, C6H4),
130.11-128.26 (m, P(C6H5)2, (C6H5)3C, ipso-C6H4), 127.61,
127.29 (s, C6H4), 126.52 (s, ipso-B(C6F5)4), 123.90, 123.51 (s,
C6H4), 122.01 (d, J = 15.1 Hz, ipso-carbazole), 121.40 (s, 4,5-
carbazole), 121.39, 120.78 (s, C6H4), 59.33 (s, CH2), 57.74(s,
(C6H5)3C), 51.30 (s, CH2), 45.56 (s, NMe2), 44.59 (s, NMe2),
35.55 (s, CMe3), 32.44 (s, CMe3). 31P{1H} NMR (161.9 MHz,
C6D6, 25 °C): δ -3.58 (d, JYP = 77.7 Hz, 2P). 19F NMR
(376.3 MHz, C6D6, 25 °C): δ -55.29 (br, 8F, o-B(C6F5)4), -85.68
(t, J = 20.7 Hz, 4F, p-B(C6F5)4), -89.64 ppm (br, 8F, m-
isoprene was added and vigorously stirred for 10.0 min. The
viscous solution was poured into a large quantity (60.0 mL)
of ethanol to give polyisoprene solids that were dried under
vacuum to a constant weight (0.68 g, 100%). The polymeriza-
tion of butadiene was carried out by a similar procedure.
Copolymerization of Isoprene and ε-Caprolactone with 1/[Ph3C]
[B(C6F5)4]. Under a nitrogen atmosphere, 1 (10.0 μmol in 8.0 mL
toluene) and [Ph3C][B(C6F5)4] (10.0 μmol in 2.0 mL of toluene)
were placed in a 25.0 mL flask. Isoprene (0.54 g) was added into
the flask, and the polymerization was carried out for 45.0min with
rapid stirring. Then ε-caprolactone (0.36 g) was added to the
above system and polymerization was continued for another 90.0
min. The viscous reaction mixture was poured into a large
quantity (100 mL) of ethanol to give white solids of a copolymer
that were dried to a constant weight (0.90 g, 100%).
1
B(C6F5)4). H NMR for 2/[Ph3C][B(C6F5)4] (400 MHz, C6D6,
Acknowledgment. We thank the National Natural
Science Foundation of China (Project Nos. 20934006
and 20910102005). The Ministry of Science and Technol-
ogy of China for (Project Nos. 2005CB623802 and
2009AA03Z501), and a Grant-in-Aid for Scientific Re-
search (S) (No. 21225004) from the Japan Society for the
Promotion of Science (JSPS) for financial support.
25 °C): δ 8.60, 8.55 (ss, 2H, 4,5-carbazole), 7.68-7.66 (m, 2H, 2,7-
carbazole), 7.47 (d, J = 8.0 Hz, 6H, Ph3C), 7.44 (b, 8H, Ph2P),
7.24-7.03 (m, 23H, Ph3C, Ph2P, CH2C6H4NMe2), 6.99 (t, J =
8.0 Hz, 1H, CH2C6H4NMe2), 6.91 (t, J = 8.0 Hz, 1H, CH2C6H4-
NMe2), 6.82 (b, 1H, CH2C6H4NMe2), 6.78 (d, J = 8.0 Hz, 1H,
CH2C6H4NMe2), 6.74 (b, 1H, CH2C6H4NMe2), 6.70 (t, J =
8.0 Hz, 2H, CH2C6H4NMe2), 2.41 (s, 6H, NMe2), 2.39 (s, 2H,
CH2), 2.36 (s, 6H, NMe2), 2.29 (s, 2H CH2), 1.42, 1.43 (ss, 18H,
Me3C). 31P{1H} NMR (161.9 MHz, C6D6, 25 °C): δ -3.58 (s,
1P), -5.76 ppm (s, 1P). 19F NMR (282.3 MHz, C6D6, 25 °C):
δ -55.41 (br, 8F, o-B(C6F5)4), -85.46 (t, J = 21.2 Hz, 4F, p-
B(C6F5)4), -90.48 ppm (br, 8F, m-B(C6F5)4).
Supporting Information Available: Figures, tables, and a CIF
file giving the 1H NMR spectrum of complex 1, the 1H and 13
C
NMR spectra and DSC and GPC traces of selected PIP, PBD,
PIP-b-PCL, and PBD-b-PIP-b-PCL samples, and X-ray dif-
fraction analysis data and refinement details for complex 1.
This material is available free of charge via the Internet at
http://pubs.acs.org.
Polymerization of Isoprene with 1/[Ph3C][B(C6F5)4]. Under a
nitrogen atmosphere, complex 1 (10.0 μmol in 8.0 mL toluene)
and [Ph3C][B(C6F5)4] (10.0 μmol in 2.0 mL of toluene) were
placed into a 25.0 mL flask. Then 1.00 mL (0.68 g, 10.0 mmol) of