Rare-earth-metal mixed hydride/aryloxide complexes bearing mono(cyclopentadienyl) ligands. synthesis, CO2 fixation, and catalysis on copolymerization of CO2 with cyclohexene oxide

Article abstract of DOI:10.1021/om800170x

Hydrogenolysis of mono(cyclopentadienyl)-ligated rare-earth-metal bis(alkyl) complexes Cp′Ln(CH₂SiMe₃) ₂(THF) (Ln = Y (1a), Dy (1b), Lu (1c); Cp′ = C ₅Me₄SiMe₃) with PhSiH₃ afforded the mixed hydride/alkyl complexes [Cp′Ln(μ-H)(CH₂SiMe ₃)(THF)]₂ (Ln = Y (2a), Dy (2b), Lu (2c)). The overall structure of complexes 2a-c is a C₂-symmetric dimer containing a planar symmetric Ln₂H₂ core at the center of the molecule. Deprotonation of ArOH (Ar = C₆H₂-^tBu ₂-2,6-Me-4) by the metal alkyl group of 2a-c led to formation of the mixed hydride/aryloxide derivatives [Cp′Ln(μ-H)(OAr)]₂ (Ln = Y (3a), Dy (3b), Lu (3c)), which adopt the dimeric structure through hydride bridges with transaccommodated terminal aryloxide groups. Complexes 3a-c swiftly reacted with CO₂ to generate the mixed formate/carbonate complexes [Cp′Ln(μ-η¹:η¹-O₂CH)(μ- η¹:η¹-O₂COAr)]₂ (Ln = Y (4a), Dy (4b), Lu (4c)). The two Cp'Ln fragments in these complexes are bridged by the formate and carbonate species, respectively, to form two square-pyramidal geometries around the metal centers. Furthermore, complexes 3a-c initiated the copolymerization of CO₂ and cyclohexene oxide (CHO) under mild conditions to afford polymers with modest molecular weights and high carbonate linkages (92-99%).

Full text of DOI:10.1021/om800170x

2428
Organometallics 2008, 27, 2428–2435
Rare-Earth-Metal Mixed Hydride/Aryloxide Complexes Bearing
Mono(cyclopentadienyl) Ligands. Synthesis, CO2 Fixation, and
Catalysis on Copolymerization of CO2 with Cyclohexene Oxide
Dongmei Cui,†,‡ Masayoshi Nishiura,† Olivier Tardif,† and Zhaomin Hou*,†
Organometallic Chemistry Laboratory, RIKEN (The Institute of Physical and Chemical Research),
Hirosawa 2-1, Wako, Saitama 351-0198, Japan, and State Key Laboratory of Polymer Physics and
Chemistry, Changchun Institute of Applied Chemistry, Chinese Academy of Sciences, Changchun 130022,
People’s Republic of China
ReceiVed February 23, 2008
Hydrogenolysis of mono(cyclopentadienyl)-ligated rare-earth-metal bis(alkyl) complexes Cp′Ln-
(CH2SiMe3)2(THF) (Ln ) Y (1a), Dy (1b), Lu (1c); Cp′ ) C5Me4SiMe3) with PhSiH3 afforded the
mixed hydride/alkyl complexes [Cp′Ln(µ-H)(CH2SiMe3)(THF)]2 (Ln ) Y (2a), Dy (2b), Lu (2c)). The
overall structure of complexes 2a-c is a C2-symmetric dimer containing a planar symmetric Ln2H2 core
at the center of the molecule. Deprotonation of ArOH (Ar ) C6H2-tBu2-2,6-Me-4) by the metal alkyl
group of 2a-c led to formation of the mixed hydride/aryloxide derivatives [Cp′Ln(µ-H)(OAr)]2 (Ln )
Y (3a), Dy (3b), Lu (3c)), which adopt the dimeric structure through hydride bridges with trans-
accommodated terminal aryloxide groups. Complexes 3a-c swiftly reacted with CO2 to generate the
mixed formate/carbonate complexes [Cp′Ln(µ-η1:η1-O2CH)(µ-η1:η1-O2COAr)]2 (Ln ) Y (4a), Dy (4b),
Lu (4c)). The two Cp′Ln fragments in these complexes are bridged by the formate and carbonate species,
respectively, to form two square-pyramidal geometries around the metal centers. Furthermore, complexes
3a-c initiated the copolymerization of CO2 and cyclohexene oxide (CHO) under mild conditions to
afford polymers with modest molecular weights and high carbonate linkages (92-99%).
metal complex. We have now found that such mixed hydride/
alkyl complexes can also be prepared for other rare-earth metals
such as Y and Dy in a similar way. Moreover, these complexes,
which are different from the rare-earth metallocene monohydride
or monoalkyl complexes6a,b or the linked-cyclopentadienyl-
amido rare-earth-metal monohydride or monoalkyl complexes,6c–g
can serve as convenient precursors to the corresponding half-
sandwich mixed hydride/aryloxide complexes via selective
elimination of the alkyl group by the aromatic alcohol. This
synthetic route is strikingly different from that reported by
Schaverien,3c which allows us to isolate and characterize the
Introduction
Transition metal alkoxides have recently attracted great
interest because of their ability to catalyze many reactions such
as the enantioselective alkylation of aldehydes,1a asymmetric
epoxidation of R,ꢀ-unsaturated ketones,1b decarboxylation of
carboxylic acids,1c polymerization of lactones and lactides, and
copolymerization of carbon dioxide with epoxides.1d–g Rare-
earth-metal alkoxide complexes bearing two cyclopentadienyl
ligands or non-cyclopentadienyl ligands have also been exten-
sively studied.2 In contrast, the mono(cyclopentadienyl)-ligated
rare-earth-metal alkoxide complexes, which are expected to
show unique reactivities, have been less explored, and well-
defined examples have so far been limited almost to yttrium
owing to difficulty in isolation and structural characterization,3
although their transition metal counterparts are well known and
can exhibit tremendous catalytic activity toward the polymer-
ization of ethylene.4 During our recent studies on preparation
and reactivity of mono(cyclopentadinenyl)-ligated rare-earth-
metal bis(alkyl)s and dihydrides,5 we isolated the lutetium mixed
hydride/alkyl complex [Cp′Lu(µ-H)(CH2SiMe3)(THF)]2,5a which
represented a rare example of a mixed hydride/alkyl rare-earth-
(2) For examples of lactone and lactide polymerization by metallocene
or non-metallocene rare-earth-metal alkoxide complexes see: (a) Yamashita,
M.; Takemoto, Y.; Ihara, E.; Yasuda, H. Macromolecules 1996, 29, 1798–
1806. (b) Nishiura, M.; Hou, Z.; Koizumi, T.; Imamoto, T.; Wakatsuki, Y.
Macromolecules 1999, 32, 8245–8251. (c) Stevels, W.; Ankone´, M. J. K.;
Dijkstra, P. J.; Feijen, J. Polym. Prepr. 1996, 37, 190–198. (d) Stevels,
W. M.; Ankone´, M. J. K.; Dijkstra, P. J.; Feijen, J. Macromolecules 1996,
29, 3332–3333. (e) Stevels, W. M.; Ankone´, M. J. K.; Dijkstra, P. J.; Feijen,
J. Macromolecules 1996, 29, 6132–6138. (f) Simic, V.; Spassky, N.; Hubert-
Pfalzgraf, L. G. Macromolecules 1997, 30, 7338–7340. (g) Chamberlain,
B. M.; Sun, Y.; Hillmyer, M. A.; Tolman, W. B. Macromolecules 1999,
32, 2400–2402. (h) Chamberlain, B. M.; Jazdzewsky, B. A.; Pink, M.;
Hillmyer, M. A.; Tolman, W. B. Macromolecules 2000, 33, 3970–3977.
(i) Cai, C.; Amgoune, A.; Lehmann, C. W.; Carpentier, J. F. J. Chem. Soc.,
Chem. Commun. 2004, 330, 331. (j) Martin, E.; Dubois, Ph.; Je´ro¨me, R.
Macromolecules 2003, 36, 5934–5941. (k) Tortosa, K.; Hamaide, T.;
Boisson, C.; Spitz, R. Macromol. Chem. Phys. 2001, 202, 1156–1160.
(3) The only example of half-sandwich yttrium aryl oxide complex,
[(C5Me5)Y(µ-H)(OC6H3-tBu2-2,6)]2, was synthesized but not X-ray char-
acterized; see:(a) Schaverien, C. J.; Frijns, J. H. G; Heeres, H. J.; van den
Hende, J. R.; Teuben, J. H.; Spek, A. L. J. Chem. Soc., Chem. Commun.
1991, 642, 643. (b) Schaverien, C. J. J. Chem. Soc., Chem. Commun. 1992,
11, 13. (c) Schaverien, C. J. Organometallics 1994, 13, 69–82.
* Corresponding author. E-mail: houz@riken.jp.
†
RIKEN.
‡ Chinese Academy of Sciences, Changchun.
(1) (a) Kitamura, N.; Suga, S.; Oka, H.; Noyori, R. J. Am. Chem. Soc.
1998, 120, 9800–9809. (b) Yu, H.; Zheng, X.; Lin, Z.; Hu, Q.; Huang, W.;
Pu, L. J. Org. Chem. 1999, 64, 8149–8155. (c) Darensbourg, D. J.;
Holtcamp, M. W.; Longridge, E. M.; Khandelwal, B.; Klausmeyer, K. K.;
Reibenspies, J. H. J. Am. Chem. Soc. 1995, 117, 318–328. (d) Cheng, Ming.;
Attygalle, A. B.; Lobkovsky, E. B.; Coates, G. W. J. Am. Chem. Soc. 1999,
121, 11583–11584. (e) Dinger, M. B.; Scott, M. J. Inorg. Chem. 2001, 40,
1029–1036. See review: (f) Coates, G. W. J. Chem. Soc., Dalton Trans.
2002, 467, 475. (g) Moor, D. R.; Cheng, M.; Lobkovsky, E. B.; Coates,
G. W. J. Am. Chem. Soc. 2003, 125, 11911–11924, and references therein.
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10.1021/om800170x CCC: $40.75
2008 American Chemical Society
Publication on Web 05/08/2008

Rare-Earth-Metal Mixed Hydride/Aryloxide Complexes
Organometallics, Vol. 27, No. 11, 2008 2429
Table 1. Summary of Crystallographic Data for Complexes 2a-ca
Scheme 1. Synthesis of Mono(cyclopentadienyl)-Ligated
Rare-Earth-Metal Mixed Hydride/Alkyl and Mixed Hydride/
Aryloxide Complexes
2a
2b
2c
formula
fw
cryst syst
space group
a, Å
b, Å
c, Å
R, deg
ꢀ, deg
γ, deg
V, Å3
C40H82Y2O2Si4 C40H82Dy2O2Si4 C40H82Lu2O2Si4
885.24
1032.42
triclinic
P1
1057.36
triclinic
P1
triclinic
j
j
j
P1
9.888(2)
11.153(3)
12.721(3)
73.878(3)
85.735(3)
64.925(3)
1219.2(5)
1
9.9249(1)
11.2281(1)
12.7924(3)
73.973(1)
85.791(2)
64.861(1)
1238.8(1)
1
9.867(1)
11.159(1)
12.709(1)
73.567(1)
85.782(1)
65.046(1)
1215.2(2)
1
Z
Dc, g/cm3
1.206
1.384
1.445
µ, cm-1
24.95
31.17
41.65
no. of reflns collcd 6551
7304
9482
no. of reflns with
>Io > 2σ(Io)
no. of variables
Rint
4435
5204
6442
231
0.0308
1.030
231
0.0184
0.986
231
0.0263
1.069
GOF
R
Rw
0.0394
0.0686
0.0619
0.0709
0.0293
0.0748
0.0327
0.0760
0.0315
0.0692
0.0369
0.0704
mixed hydride/aryloxide complexes of various rare-earth ele-
ments. In addition, these mixed hydride/aryloxide complexes
exhibit high activity for CO2 fixation and the copolymerization
of CO2 with cyclohexene oxide (CHO). The copolymerization
of CO2 with epoxides has received much current interest,
because it provides an environmentally friendly route to convert
CO2 into biodegradable polymers and a pathway to a value-
added product incorporating the ubiquitous CO2 molecule as a
C1 feedstock. A variety of complexes based on transition metals
such as zinc,7 aluminum,8 chromium,9 cadmium and magne-
sium,10 and cobalt11 have been reported as efficient catalysts
for the copolymerization of CO2 with epoxides, whereas
catalytic systems based on lanthanide elements, which usually
need a cocatalyst, are few.12 Herein we report the preparations
and structures of half-sandwich rare-earth-metal mixed hydride/
alkyl complexes, mixed hydride/aryloxide complexes, and their
CO2 fixation derivatives, as well as the preliminary results of
the copolymerization of CO2 with CHO.
R (all data)
Rw (all data)
a Data for complex 2c are cited from ref 5a.
Figure 1. X-ray structure of 2a with 30% probability thermal
ellipsoids. Hydrogen atoms are omitted for clarity.
Results and Discussion
Table 2. Selected Bond Lengths (Å) and Angles (deg) for Complexes
2a-ca
Syntheses and Structures of Mono(cyclopentadienyl)
Rare-Earth-Metal Mixed Hydride/Alkyl Complexes. Fol-
lowing the literature procedure for the synthesis of [Cp′Lu(µ-
H)(CH2SiMe3)(THF)]2 (2c),5a treatment of rare-earth-metal
bis(alkyl) complexes bearing a mono(cyclopentadienyl)
ligand, Cp′Ln(CH2SiMe3)2(THF) (Ln ) Y (1a), Dy (1b); Cp′
) C5Me4SiMe3), with 1 equiv of PhSiH3 was performed in
hexane at -30 °C for 12 h to afford the corresponding mixed
hydride/alkyl complexes [Cp′Ln(µ-H)(CH2SiMe3)(THF)]2 (Ln
) Y (2a), Dy (2b)) through hydrogenolysis of one metal
alkyl moiety (Scheme 1). Addition of an excess amount of
PhSiH3 would result in the replacement of another alkyl
ligand to give dihydride complexes [Cp′Ln(µ-H)2]4(THF).
Pure 2a and 2b were white powders, while 2c was a yellow
solid. They had good solubility in aromatic solvents but were
almost insoluble in hexane. Complexes 2a-c changed slowly
to 1a-c and other unknown hydride species in benzene or
THF within several days at room temperature. X-ray analysis
displayed that complexes 2a and 2b were dimers of C2
symmetry, analogous to 2c (Table 1). Each metal cordinates
to a Cp′ unit, an alkyl ligand (CH2SiMe3), and a solvated
THF molecule to form an Ln fragment (Figure 1 for 2a).
Two Ln fragments are connected by equivalent hydride
bridges to form a rhombic Ln2H2 core with equal Ln-H bond
2a
(Ln ) Y)
2b
2c
(Ln ) Dy)
(Ln ) Lu)
Ln-C(Cp′)(av)
Ln(1)-O
2.651 (3)
2.396 (2)
2.21 (3)
3.635 (1)
31.0 (7)
2.659 (4)
2.426 (3)
2.09 (4)
3.6457 (4)
31.3 (11)
2.610 (4)
2.360 (3)
2.12 (5)
3.5491 (4)
31.5 (12)
Ln(1)-H(1)
Ln(1)-Ln(1)*
H(1)*-Ln(1)-H(1)
a Data for complex 2c are cited from ref 5a.
lengths (Table 2). The 1H NMR spectrum of complex 2a
showed a sharp triplet for the hydride ligands at δ 5.80 with
a JY-H ) 27.2 Hz in the temperature range -70 to 25 °C,
reflecting that 2a formed a stable dimeric structure in solution,
consistent with its crystal structure in the solid state.
Interestingly, the methylene protons of 2a displayed variable
resonances. At room temperature, only a broad resonance at
δ -0.74 was observed, which, however, split into two
doublets at δ -0.64 and -0.79, respectively, with a geminal
proton coupling (J ) 10.3 Hz) (Figure 2) when the temper-
ature was lowered to -25 °C. This result suggests that the
rotation of the methylene group around the Y-C(1) bond is
restricted at low temperature.

2430 Organometallics, Vol. 27, No. 11, 2008
Cui et al.
H)(THF)]2 (2.13(9)-2.57(5) Å).6e The average bond length of
Ln-Oterminal in 3a-c (Y-O, 2.076(2) Å; Dy-O, 2.083(1) Å;
Lu-O, 2.048(2) Å) is comparable to that of Y-Oterminal
(2.096(4), 2.059(3) Å) in [(C5Me5)Y(OC6H3But2)2],3a but shorter
than the bond distances between rare-earth metals and the
oxygen of the neutral THF donor in 2a-c (Y-O 2.396(2) Å,
Dy-O 2.426(3) Å, Lu-O 2.360(3) Å). The Y · · · Y distance of
3.5721(7) Å in 3a is comparable to 3.53 and 3.58 Å in methyl-
bridgedyttriumdimers[(C5H5)2Y(µ-Me)]2and[(1,3-Me2C5H3)2Y(µ-
Me)]2, respectively.15 The Ln-C(ring) bond distances varying
from 2.575(3) to 2.626(3) Å fall in the normal range for the
Ln-C(ring) bonds.5
1
Figure 2. Methylene region in the H NMR spectra of complex
2a.
Syntheses and Structures of Mono(cyclopentadienyl)
Rare-Earth-Metal Mixed Hydride/Aryloxide Complexes.
Complex 2a reacted with 2 equiv of ArOH (Ar ) C6H2-tBu2-2,6-
Me-4) at room temperature for 2 days to give the corresponding
mixed hydride/aryloxide yttrium complex 3a ([Cp′Y(µ-H)(OAr)]2)
in a high yield via elimination of the metal alkyl moiety (Scheme
1). The hydride ligand remained untouched in the presence of
excess ArOH, indicating the stable Ln-H fragment. A similar
phenomenon had been observed in the reaction of lutetium
dihydrides with excess butyrolactone.5b Monitoring the reaction
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by H NMR spectroscopic technique showed that the upfield
resonance at δ -0.74 for the methylene protons of the yttrium
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reminiscent of their congeners 2a-c except for the absence of a
THF molecule, which could be attributed to the coordination of
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Å)14andY-Hin[(C5Me4SiMe2NCMe3)Y(µ-H)(THF)]2(1.98(6)-
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Z. Angew. Chem., Int. Ed. 2006, 45, 8184–8188. (i) Hou, Z.; Nishiura, M.;
Shima, T. Eur. J. Inorg. Chem. 2007, 2535, 2545.
(6) (a) Ephritikhine, M. Chem. ReV. 1997, 97, 2193–2242. (b) Evans,
W. J.; Dominguez, R.; Hanusa, T. P. Organometallics 1986, 5, 263–270.
(c) Shapiro, P. J.; Cotter, W. D.; Schaefer, W. P.; Labinger, J. A.; Bercaw,
J. E. J. Am. Chem. Soc. 1994, 116, 4623–4640. (d) Hultzsch, K. C.; Voth,
P.; Beckerle, K.; Spaniol, T.; Okuda, J. Organometallics 2000, 19, 228–
243. (e) Arndt, S.; Voth, P.; Spaniol, T.; Okuda, J. Organometallics 2000,
19, 4690–4700. (f) Trifonov, A.; Spaniol, T.; Okuda, J. Organometallics
2001, 20, 4869–4874. (g) Hultzsch, K. C.; Voth, P.; Beckerle, K.; Spaniol,
T.; Okuda, J. Angew. Chem., Int. Ed. 1999, 38, 227–230.
(15) (a) Holton, J.; Lappert, M. F.; Ballard, D. G.; Pearce, R.; Atwood,
J. L.; Hunter, W. E. J. Chem. Soc., Dalton, Trans. 1979, 54, 61. (b) Evans,
W. J.; Drummond, D. K.; Hanusa, T. P.; Doedens, R. J. Organometallics
1987, 6, 2279–2285.

Rare-Earth-Metal Mixed Hydride/Aryloxide Complexes
Organometallics, Vol. 27, No. 11, 2008 2431
Table 3. Summary of Crystallographic Data for Complexes 3a-c and 4a-c
3a 3b 3c 4a
1005.26 1152.44 1177.38 1181.30
4b
1328.48
4c
1353.42
fw
formula
fw
cryst syst
space group
a, Å
b, Å
c, Å
C54H90Y2O2Si2
1005.26
monoclinic
P2 (1)/n
13.239 (1)
10.2802 (9)
20.597 (2)
90
91.044 (2)
90
2802.7 (4)
2
C54H90Dy2O2Si2
1152.44
monoclinic
P2 (1)/n
13.210 (1)
10.234 (1)
20.566 (3)
90
91.110 (2)
90
2780.1 (6)
2
1.377
27.45
14 808
5422
289
C54H90Lu2O2Si2
1177.38
monoclini
P2 (1)/n
13.059 (1)
10.168 (1)
20.550 (2)
90
91.842 (1)
90
2727.1 (5)
2
1.434
36.79
14 793
5365
289
C58H90Y2O10Si2
1181.30
monoclini
P2 (1)/c
13.3954 (9)
13.4091 (9)
17.599 (1)
90
106.135 (1)
90
3036.7 (3)
2
1.292
19.94
17 684
6625
339
C58H90Dy2O10Si2
1328.48
monoclini
P2 (1)/c
13.403 (10)
13.414 (10)
17.451 (13)
90
105.954 (11)
90
3017 (4)
2
1.463
25.50
15 363
5345
339
C58H90Lu2O10Si2
1353.42
monoclini
P2 (1)/n
12.239 (1)
16.509 (1)
15.141 (1)
90
91.539 (2)
90
3058.2 (5)
2
1.470
33.01
18 242
6945
343
R, deg
ꢀ, deg
γ, deg
V, Å3
Z
Dc, g/cm3
1.191
21.38
9147
4713
µ, cm-1
no. of reflns collcd
no. of reflns with Io > 2σ(Io)
no. of variables
289
Rin
GOF
0.0336
1.020
0.0207
1.055
0.0326
0.997
0.0279
0.975
0.0782
1.030
0.018
1.007
R
Rw
0.0405
0.0845
0.0681
0.0900
0.0233
0.0589
0.0303
0.0614
0.0234
0.0422
0.0348
0.0434
0.0299
0.0699
0.0464
0.0801
0.0290
0.0954
0.0352
0.1050
0.0209
0.0513
0.0269
0.0524
R (all data)
Rw (all data)
Scheme 2. Reaction of Mono(cyclopentadienyl)-Ligated Rare-
Earth-Metal Mixed Hydride/Aryloxido Complexes with CO2
Carbon Dioxide Fixation of Mono(cyclopentadienyl)
Rare-Earth-Metal Mixed Hydride/Aryloxide Complexes.
When 3a was exposed to a CO2atmosphere (1 atm), the reaction
took place rapidly even at 0 °C to generate a clean insertion product,
[Cp′Y(µ-η1:η1-O2CH)(µ-η1:η1-O2COAr)]2 (4a), in a short period
of time (5-30 min, 100% yield) (Scheme 2). Apparently, two
carbon dioxide molecules inserted into Y-H bonds to form formate
units, while another two carbon dioxide molecules inserted into
Y-O bonds to generate carbonate species. The absorption at 1639
cm-1 in the IR spectrum of complex 4a could be assigned to the
CdO bond stretch of the formate groups, while the absorption at
1556 cm-1 was assigned to the carbonate functional group. This
result was in agreement with the 1H-13C HMQC spectrum
analysis. The resonances at δ 161.02 and 173.92 could be assigned
to the carbonate carbon and the formate carbon, respectively. An
X-ray diffraction study revealed that 4a was a centrosymmetric
dimer (Figure 4 and Table 3). The formate and carbonate species
bridge two Cp′Y units to form two eight-membered rings
perpendicular to each other at the core of the molecule. The
oxygen atoms and the centroids of the Cp′ ligands generate
pyramidal geometries around yttrium centers. The formate
ligands coordinate to yttrium atoms asymmetrically, resulting
in a large Y(1)-O(1)-C(1) bond angle of 175.4(1)° and a much
smaller Y(1)*-O(2)-C(1) bond angle of 100.4(1)°. In contrast,
the carbonate units bond to yttrium atoms symmetrically, leading
to similar Y-O-C bond angles (Y(1)-O(3)-C(2), 134.5(1)°
vs Y(1)*-O(4)-C(2), 136.5(1)°) (Table 5). The Y-O bond
lengths ranging from 2.261(1) to 2.345(1) Å in 4a are com-
parable to that in the complexes {(C5Me4)SiMe2(CH2-
C H d C H 2 ) Y ( µ - η 1 : η 1 - O 2 C C H 2 S i M e 3 ) ( µ - η 1 : η 2 -
Figure 3. X-ray structure of 3a with 30% probability thermal
ellipsoids. Hydrogen atoms are omitted for clarity.
Table 4. Selected Bond Lengths (Å) and Angles (deg) for Complexes
3a-c
3a
(Ln ) Y)
3b
3c
(Ln ) Dy)
(Ln ) Lu)
Ln-C(Cp′)(av)
Ln(1)-O(1)
Ln(1)-H(1)
2.618 (3)
2.076 (2)
2.15 (2)
2.626 (3)
2.083 (1)
2.14 (3)
2.575 (3)
2.048 (2)
2.09 (3)
Ln(1) · · · Ln(1)*
Ln(1)*-Ln(1)-H(1)
3.5721 (7)
33.8 (6)
3.5712 (4)
32.2 (8)
3.4516 (4)
33.0 (7)

2432 Organometallics, Vol. 27, No. 11, 2008
Cui et al.
Figure 4. X-ray structure of 4a with 30% probability thermal
ellipsoids. Hydrogen atoms are omitted for clarity.
Figure 5. X-ray structure of 4c with 30% probability thermal
ellipsoids. Hydrogen atoms are omitted for clarity.
Table 5. Selected Bond Lengths (Å) and Angles (deg) for Complexes
4a-c
4a
(Ln ) Y)
4b
4c
(Ln ) Dy)
(Ln ) Lu)
Ln-C(Cp′)(av)
Ln(1)-O(1)
2.623 (2)
2.276 (1)
2.345 (1)
2.292 (1)
2.261 (1)
3.7505 (4)
1.259 (3)
1.235 (3)
1.253 (2)
1.253 (2)
1.356 (2)
132.79 (6)
141.43 (1)
175.4 (1)
100.4 (1)
134.5 (1)
136.5 (1)
122.9 (2)
127.6 (1)
2.627 (4)
2.296 (3)
2.357 (3)
2.277 (3)
2.310 (3)
3.759 (2)
1.263 (5)
1.226 (5)
1.245 (4)
1.261 (4)
1.352 (4)
132.47 (9)
141.55 (9)
174.1 (3)
99.3 (3)
2.579 (1)
2.229 (1)
2.244 (1)
2.274 (1)
2.221 (1)
3.6548 (3)
1.253 (3)
1.250 (3)
1.250 (3)
1.260 (3)
1.342 (3)
142.56 (6)
135.61 (6)
134.2 (1)
134.5 (1)
101.1 (1)
179.2 (1)
127.4 (2)
122.9 (2)
Ln(1)-O(2)*
Ln(1)-O(3)
Ln(1)-O(4)*
Ln(1) · · · Ln(1)*
C(1)-O(1)
C(1)-O(2)
C(2)-O(3)
C(2)-O(4)
C(2)-O(5)
O(1)-Ln(1)-O(2)*
O(3)-Ln(1)-O(4)*
Ln(1)-O(1)-C(1)
Ln(1)*-O(2)-C(1)
Ln(1)-O(3)-C(2)
Ln(1)*-O(4)-C(2)
O(1)-C(1)-O(2)
O(3)-C(2)-O(4)
136.4 (2)
134.4 (2)
123.2 (4)
127.6 (3)
1
Figure 6. H NMR spectrum of complex 4a in THF-d8.
Lu(1*)-O(4)-C(2)(179.2(1)°)andamuchsmallerLn(1)-O(3)-C(2)
angle (101.1(1)°) (Table 5). Nevertheless, in all complexes
4a-c, the C-O bond lengths in both formate and carbonate
moieties are similar, ranging from 1.226(3) to 1.261(3) Å, which
are shorter than a C-O single bond, such as C(2)-O(5)
(1.342(3)-1.356(2) Å) but longer than a C-O double bond,
indicating that there are no localized CdO bonds. Interestingly,
complexes 4a-c retained their dimeric structures in THF
solution, which was evident in the 1H NMR spectrum of 4a in
THF-d8 (Figure 6). The triplet resonance at δ 8.22 can be
assigned to the methine proton of the formate species coupling
16
O2CCH2SiMe3)}2 (Y-O: 2.270(1) and 2.328(1) Å) and
[Cp′Y(µ-η1:η1-O2CCH2SiMe3)2]2
(Y-O: av 2.284(1) Å).
12f
These bond lengths are longer than Y-Oterminal in 3a (2.076(2)
Å) and in [(C5Me5)Y(OC6H3But2)2] (2.096(4) and 2.059(3) Å)3a
but shorter than the bridging Y-η2-O (2.40(2)-2.42(2) Å) in
the yttrocene complex (C5H5)2Y[η2-O2C(CH2)3NMe2].17 The
Y · · · Y distance of 3.7505(4) Å is comparable to 3.7085(8) Å
in [Y(C5Me4CH2SiMe2NCMe3)(THF)(µ-H)]2,6f but much longer
than that in its precursor 3a due to the more specific crowding
of the molecule. Product 4b was prepared by reaction of CO2
with 3b, which is an analogue of 4a (Table 3). The similar
reaction between CO2 and the lutetium 3c afforded 4c albeit
with slightly different coordination geometry (Figure 5). The
formate bridges coordinate to Lu metals symmetrically with
similar Lu-O-C bond angles (Lu(1)-O(1)-C(1) ) 134.2(1)°,
Lu(1*)-O(2)-C(1) ) 134.5(1)°), while the carbonate species
connect to Lu metals asymmetrically with an almost linear angle
3
with two yttrium atoms with a JYOCH ) 2 Hz, much smaller
3,6
than 34.6 Hz of JYH
.
This is in contrast to the metallocene
samarium allyl complex (C5Me5)2Sm(η3-CH2CHCH2), which
inserts CO2 to form a bimetallic product existing in equilibrium
withtheTHF-coordinatedmonomericanalogue.16 Themonomer-
dimer equilibrium is also observable in ꢀ-diiminate zinc acetate
and alkoxide systems depending on the concentration of the
complex and temperature.1g
(16) Evans, W. J.; Seibel, C. A.; Ziller, J. W.; Doedens, R. J.
Organometallics 1998, 17, 2103–2112.
CO2 has been used successfully as an insertion substrate in
transition metal chemistry. For example, CO2 has been reported
(17) Schumann, H.; Meese-Marktscheffel, J. A; Dietrich, A.; Go¨rlitz,
F. J. Organomet. Chem. 1992, 430, 299–315.

Rare-Earth-Metal Mixed Hydride/Aryloxide Complexes
Organometallics, Vol. 27, No. 11, 2008 2433
Table 6. Copolymerization of CO2 with Cyclohexene Oxide (CHO) by Complexes 3a-ca
d
d
entry
cat
temp (°C)
time (h)
TONb
TOFc(h-1
)
Mn × 10-3
Mw/Mn
carbonate linkages (%)e
1
2
3
4
5
6
7
3a
3b
3c
3c
3c
3c
3c
70
70
70
50
70
90
110
48
48
48
24
24
24
24
220
176
219
trace
139
187
226
4.9
3.7
4.8
ndf
5.8
7.8
9.4
16.1
13.7
24.4
nd
14.5
25.6
24.7
1.65
3.30
2.09
nd
3.10
5.69
6.15
92
92
95
nd
97
98
99
a Condition: 12 atm of CO2, toluene: 2 mL, [Ln] ) 16.3 mmol/L, [CHO] ) 5.0 mol/L. b TON ) mole cyclohexene oxide consumed by per mole
catalyst (mol/mol · Ln). c TOF ) mol/(mol · Ln h). d Determined by GPC against polystyrene standard. e Calculated by integration of methine resonances
in 1H NMR of copolymer (CDCl3, 300 MHz). f nd: not determined.
to insert into M-C bonds of (C5H5)2Ti-(CH3)218 and M-H bonds
of[(C5H5)Ti(µ-H)]2(C10H8),19 Ru(dmpe)2H2,20 and(C5H5)2Zr(H)(µ-
H)(µ-NtBu)Ir(C5Me5),21 generating carboxylate or mixed hy-
dride/terminal formate derivatives, respectively, although in
some cases, decaboxylation or CO2 extrusion might occur.22 In
contrast, only a few examples of CO2 reaction with rare-earth-
metal complexes have been reported,5c,12f,16,17,23 and CO2
insertion into M-H and M-O bonds simultaneously in one
molecule like 3a-c is really rare.5c
decomposition reactions became obvious, in agreement with
previous reports.7e,9b,12f,24
Conclusion
We have demonstrated that mono(cyclopentadienyl)-ligated
mixed hydride/aryloxide complexes of varying lanthanide
elements can be synthesized easily by the acid-base reaction
between the mixed hydride/alkyl complexes and an aryl alcohol.
These complexes can swiftly fix CO2 molecule to generate
mixed formate/carboxylate derivatives of novel structures.
Moreover, they can also act as moderately active initiators for
the copolymerization of CO2 and cyclohexene oxide under mild
conditions to produce alternating copolymers without require-
ment of a cocatalyst.
Mono(cyclopentadienyl) Rare-Earth-Metal Mixed Hy-
dride/Aryloxide Complexes Catalyze the Copolymeriza-
tion of CO2 with Cyclohexene Oxide. The copolymerization
of CO2 and CHO was successfully performed with complexes
3a-c in the absence of a cocatalyst under 12 atm of CO2 at 70
°C for 48 h in toluene (TON: 139-220 mol/(mol · Ln)) (Table
6). The resulting copolymers showed high contents of carbonate
linkages (>92%) and moderate molecular weights and molecular
weight distributions. The Lu and Y complexes showed similar
activities, which were higher than that of the Dy counterpart
(Table 6, entries 1-3). The copolymerization also showed a
strong temperature dependence. When the reaction was per-
formed at 50 °C, only a trace amount of product could be
isolated. At 70 °C, a TON of 139 mol/mol · Ln was obtained,
which reached 226 mol/(mol · Ln) when the temperature was
increased to 110 °C. Meanwhile the content of carbonate
linkages of the resulting copolymer increased gradually to 99%
at 110 °C, indicating that the CO2 insertion reaction was favored
at elevated temperature. The molecular weight of the product
increased when the temperature was raised to some extent, but
dropped slightly when the temperature was over 90 °C, which
was accompanied by the broadened molecular weight distribu-
tion (Table 6, entries 4-7). This could be imputed to the effect
of the ceiling temperature where the depolymerization and
Experimental Section
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. Samples for
NMR spectroscopic measurements were prepared in the glovebox
1
by use of J. Young valve NMR tubes. H and 13C NMR spectra
1
were recorded on JNM-EX 300 (FT, 300 MHz for H; 75 MHz
for 13C) and JNM-EX 400 spectrometers. The NMR assignments
were confirmed by the 1H-13C HMQC and 1H-13C HMBC
experiments. Elemental analyses were performed by Chemical
Analysis Team, Advanced Development and Supporting Center,
RIKEN. IR spectra were recorded on a Shimadzu FTIR-8100 M
spectrometer using Nujol mulls between KBr disks. The molecular
weight and molecular weight distribution of the polymers were
measured by GPC (Tosoh HLC-8220 GPC; column, super HZM-H
× 3; temperature, 40 °C; eluent, THF; polystyrene standard).
Solvents were distilled from sodium/benzophenone ketyl, degassed
by the freeze-pump-thaw method (three times), and dried over
fresh Na chips in the glovebox. Cyclohexene oxide was dried over
molecular sieves (4 Å) for 2 days and distilled from CaH2 under
reduced pressure. CO2 (Purity grade, 99.995%), PhSiH3, and 2,6-
di-tert-butyl-4-methylphenol were used as purchased. Complexes
1a-c and 2c were prepared according to the literature procedure.5a,12f
X-ray Crystallographic Studies. Crystals for X-ray analysis
were obtained as described in the preparations. The crystals were
manipulated in a glovebox under a microscope and were sealed in
thin-walled glass capillaries. Data collections were performed at
-80 °C on a Bruker SMART APEX diffractometer with a CCD
(18) Johnson, R. F.; Cooper, J. C. Organometallics 1987, 6, 2448–2449.
(19) Ni, J.; Qiu, Y.; Cox, T. M.; Jones, C. A.; Berry, C.; Melon, L.;
Bott, S. Organometallics 1996, 15, 4669–4671.
(20) Whittlessey, M. K.; Perutz, R. N.; Moore, M. H. Organometallics
1996, 15, 5166–5169.
(21) Hanna, T. A.; Baranger, A. M.; Bergman, R. G. J. Am. Chem. Soc.
1995, 117, 11363–11364.
(22) (a) Schlo¨rer, N. E.; Berger, S. Organometallics 2001, 20, 1703–
1704. (b) Schlo¨rer, N. E.; Cabrita, E. J.; Berger, S. Angew. Chem., Int. Ed.
2002, 41, 107–109. (c) Darensbourg, D. J.; Wiegreff, H. P.; Wiegreff, P. W.
J. Am. Chem. Soc. 1990, 112, 9252–9257.
(23) (a) Evans, W. J.; Brady, J. C.; Ziller, J. W. J. Am. Chem. Soc.
2001, 123, 7711–7712. (b) Bochkarev, M. N.; Khramenkov, V. V.; Rad’kov,
Y. F.; Zakharov, L. N. J. Organomet. Chem. 1992, 429, 27–39. (c)
Bochkarev, G. S.; Kalinina, G. A.; Razuvaev, G. A. J. Organomet. Chem.
1989, 372, 217–224.
(24) (a) Super, M.; Beckman, E. J. Macromol. Symp. 1998, 127, 89–
108. (b) Zhang, M.; Chen, L.; Qin, G.; Liu, B.; Yan, Z.; Li, Z. J. Appl.
Polym. Sci. 2003, 87, 1123–1128. (c) Mang, S.; Cooper, A. I.; Colclough,
M. E.; Chauhan, N.; Holmes, A. B. Macromolecules 2000, 33, 303–308.

2434 Organometallics, Vol. 27, No. 11, 2008
Cui et al.
area detector, using graphite-monochromated Mo KR radiation (λ
) 0.71073 Å). The determination 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 anisotro-
pically for all non-hydrogen atoms by the full-matrix least-squares
method. The hydride atoms in complexes 2a,b and 3a-c and the
methine protons of formate units in 4a-c were located by difference
Fourier synthesis, and their coordinates and isotropic parameters
were refined. Other hydrogen atoms were placed at the calculated
positions and were included in the structure calculation without
further refinement of the parameters.
[Cp′Y(µ-H)(CH2SiMe3)(THF)]2 (2a). Under -30 °C, to a
hexane solution (10 mL) of Cp′Y(CH2SiMe3)2(THF) (1a) (4.366
g, 8.256 mmol) was added dropwise 1 equiv of cold PhSiH3 (0.892
g, 8.256 mmol) under stirring. The reaction mixture was kept at
this temperature overnight to afford white crystalline 2a deposited
on the bottom of the flask. After decantation of the upper clear
solution, the solid was washed with hexane (3 × 2 mL) and dried
in vacuo to afford a white powder of 2a in 74% yield (2.704 g,
3.055 mmol). Colorless blocks for X-ray analysis were isolated from
the hexane/toluene (2:1 (v/v)) solution at -30 °C in 3-4 days. 1H
NMR (300 MHz, C6D6, 22 °C): -0.74 (s, 4H, CH2SiMe3), 0.38 (s,
18H, CH2SiMe3), 0.46 (s, 18H, C5Me4SiMe3), 1.36 (s, 8H, THF),
2.15 (s, 12H, C5Me4SiMe3), 2.37 (s, 12H, C5Me4SiMe3), 3.85 (s,
8H, THF), 5.80 (t, JY-H ) 27.2 Hz, 2H, µ-H). 13C NMR (75 MHz,
C6D6, 22 °C): 3.08 (C5Me4SiMe3), 5.24 (CH2SiMe3), 12.37 (C5-
Me4SiMe3), 15.30 (C5Me4SiMe3), 25.24 (THF), 39.31 (CH2-
SiMe3), 71.77 (THF), 113.40 (ipso-C5Me4SiMe3), 123.22 (C5Me4-
SiMe3), 126.40 (C5Me4SiMe3). IR (Nujol): ν 1323, 1242, 1171,
1130, 1018, 849, 754, 721 cm-1. Anal. Calcd for C40H82O2Si4Y2:
C, 54.27; H, 9.34. Found: C, 53.81; H, 9.26.
2b (0.730 g, 0.707 mmol) with 2,6-di-tert-butyl-4-methylphenol
(0.312 g, 1.414 mmol) generated a crystalline light yellow solid of
complex 3b (0.578 g, 0.502 mmol, 71%). Recrystallization from
benzene solution at room temperature afforded good colorless
crystals for X-ray analysis in 4-5 days. The 1H NMR spectrum of
3b was not informative because of the influence of the paramagnetic
Dy(III) ion. IR (Nujol): ν 3088, 2850, 1462, 1454, 1421, 1377,
1315, 1261, 1193, 1016, 883, 831 cm-1. Anal. Calcd for
C54H90O2Si2Dy2: C, 56.28; H, 7.87. Found: C, 55.42; H, 7.62.
[Cp′Lu(µ-H)(OC6H2-tBu2-2,6-Me-4)]2 (3c). In the same manner,
complex 3c was isolated by reaction of 2c (0.137 g, 0.130 mmol)
with 2 equiv of 2,6-di-tert-butyl-4-methylphenol (0.057 g, 0.260
mmol) as a colorless solid in 80% yield (0.122 g, 0.104 mmol).
Colorless single crystals for X-ray analysis were isolated by
evaporating slowly the saturated benzene solution in a glovebox at
room temperature. 1H NMR (270 MHz, C6D6, 22 °C): 0.35 (s, 18H,
C5Me4SiMe3), 1.62 (s, 36H, C6H2-tBu2-2,6-Me-4), 2.03 (s, 12H,
C5Me4SiMe3), 2.28 (s, 12H, C5Me4SiMe3), 2.30 (s, 6H, C6H2-tBu2-
2,6-Me-4), 7.14 (s, 2H, C6H2), 9.64 (s, 2H, µ-H). 13C NMR (75
MHz, C6D6, 22 °C): 2.93 (C5Me4SiMe3), 12.44 (C5Me4SiMe3),
15.32 (C5Me4SiMe3), 21.66 (C6H2-tBu2-2,6-Me-4), 33.37 (C6H2-
tBu2-2,6-Me-4), 35.71 (C6H2-tBu2-2,6-Me-4), 117.51 (ipso-C5-
Me4SiMe3), 125.80 (C5Me4SiMe3), 125.84 (C5Me4SiMe3), 126.70
(m-C6H2), 129.41 (p-C6H2), 136.18 (o-C6H2), 158.29 (ipso-C6H2).
IR (nujol): ν 3075, 2852, 1460, 1455, 1421, 1377, 1311, 1273, 1200,
1018, 908, 833 cm-1. Anal. Calcd for C54H90O2Si2Lu2: C, 55.08;
H, 7.70. Found: C, 54.50; H, 7.58.
{Cp′Y(µ-η1:η1-O2CH)(µ-η1:η1-O2COC6H2-tBu2-2,6-Me-4)}2
(4a). A 50 mL Schlenk tube containing a benzene (10 mL) solution
of 3a (0.200 g, 0.199 mmol) was cooled to -10 °C. Removal of
N2 and solvent under reduced pressure was followed by backfilling
with carbon dioxide (1 atm). The reaction mixture was stirred for
0.5 h at 0 °C. The volatile was removed off under reduced pressure
to give a white powder of complex 4a (0.235 g, 0.199 mmol, 100%).
Recrystallization from a mixture of hexane/THF (1:1 v/v) yielded
good colorless cubic crystals for X-ray analysis. 1H NMR (400
MHz, THF-d8, 22 °C): 0.20 (s, 18H, C5Me4SiMe3), 1.33 (s, 36H,
C6H2-tBu2-2,6-Me-4), 1.62 (s, 12H, C5Me4SiMe3), 1.97 (s, 12H,
C5Me4SiMe3), 2.32 (s, 6H, C6H2-tBu2-2,6-Me-4), 7.12 (s, 4H, C6H2-
tBu2-2,6-Me-4), 8.22 (t, JY-H ) 2 Hz, 2H, OC(H)O). 13C NMR
(75 MHz, THF-d8, 22 °C): 2.44 (C5Me4SiMe3), 10.91 (C5-
Me4SiMe3), 13.74 (C5Me4SiMe3), 21.55 (C6H2-tBu2-2,6-Me-4),
31.72 (C6H2-tBu2-2,6-Me-4), 36.13 (C6H2-tBu2-2,6-Me-4), 116.95
(ipso-C5Me4SiMe3), 125.26 (C5Me4SiMe3), 127.26 (m-C6H2), 128.39
(C5Me4SiMe3), 135.03 (p-C6H2), 142.53 (o-C6H2), 148.12 (ipso-
C6H2), 161.02 (O2CO) 173.92 (OC(H)O). IR (Nujol): ν 3072, 2852,
[Cp′Dy(µ-H)(CH2SiMe3)(THF)]2 (2b). Following the same
procedure described for the preparation of 2a, the reaction of
Cp′Dy(CH2SiMe3)2(THF) (1b) (2.112 g, 3.506 mmol in 8 mL of
cold hexane) with PhSiH3 (0.379, 3.506 mmol) afforded 2b in 70%
yield (1.266 g, 1.227 mmol). Single crystals suitable for X-ray
analysis were isolated as colorless blocks from the hexane/toluene
(2:1 (v/v)) solution at -30 °C in 3-4 days. The 1H NMR spectrum
of 2b was not informative because of the influence of the
paramagnetic Dy(III) ion. IR (Nujol): ν 1325, 1246, 1180, 1130,
1039, 846, 754, 721 cm-1. Anal. Calcd for C40H82O2Si4Dy2: C,
46.53; H, 8.01. Found: C, 46.01; H, 7.44.
[Cp′Y(µ-H)(OC6H2-tBu2-2,6-Me-4)]2 (3a). To a benzene (10
mL) solution of 2a (1.130 g, 1.277 mmol) was added 2 equiv of
2,6-di-tert-butyl-4-methylphenol (0.563 g, 2.553 mmol in 5 mL
benzene) at room temperature, and the reaction mixture was stirred
for 2 days. Removal of solvent in vacuo was followed by washing
the residue with hexane (2 × 2 mL) to give a white solid of 3a in
76% yield (0.976 g, 0.971 mmol). Recrystallization from benzene
solution at room temperature afforded good colorless crystals for
1639, 1554, 1462, 1377, 1338, 1244, 1203, 1113, 1028, 837 cm-1
.
Anal. Calcd for C58H90O10Si2Y2: C, 58.97; H, 7.68. Found: C, 58.79;
H, 7.58.
{Cp′Dy(µ-η1:η1-O2CH)(µ-η1:η1-O2COC6H2-tBu2-2,6-Me-
4)}2 (4b). Following the same procedure described for the formation
of 4a, reaction of 3b (0.150 g, 0.130 mmol in 15 mL of benzene)
with CO2 at 0 °C in a period of 0.5 h afforded 4b as a light yellow
powder (0.165 g, 0.124 mmol, 95%). Recrystallization from a
mixture of hexane/THF (1:1 v/v) yielded good colorless cubic
1
X-ray analysis in 4-5 days. H NMR (400 MHz, C6D6, 22 °C):
0.36 (s, 18H, C5Me4SiMe3), 1.62 (s, 36H, C6H2-tBu2-2,6-Me-4),
2.02 (s, 12H, C5Me4SiMe3), 2.24 (s, 12H, C5Me4SiMe3), 2.30 (s,
6H, C6H2-tBu2-2,6-Me-4), 5.71 (t, JY-H ) 34.6 Hz, 2H, µ-H), 7.13
(s, 4H, C6H2-tBu2-2,6-Me-4). 13C NMR (75 MHz, C6D6, 22 °C):
2.62 (C5Me4SiMe3), 12.13 (C5Me4SiMe3), 14.93 (C5Me4SiMe3),
21.48 (C6H2-tBu2-2,6-Me-4), 33.04 (C6H2-tBu2-2,6-Me-4), 35.34
(C6H2-tBu2-2,6-Me-4), 118.12 (ipso-C5Me4SiMe3), 125.66 (C5-
Me4SiMe3), 126.48, (C5Me4SiMe3), 126.51 (m-C6H2), 129.82 (p-
C6H2), 136.18 (o-C6H2), 157.78 (ipso-C6H2). IR (Nujol): ν 3049,
2852, 1462, 1453, 1421, 1377, 1311, 1263, 1187, 1018, 867, 831
cm-1. Anal. Calcd for C54H90O2Si2Y2: C, 64.51; H, 9.02. Found:
C, 63.97; H, 8.79.
1
crystals for X-ray analysis. The H NMR spectrum of 4b was not
informative because of the influence of the paramagnetic Dy(III)
ion. IR (Nujol): ν 3074, 2855, 1647, 1557, 1460, 1375, 1334, 1244,
1203, 1112, 1028, 837 cm-1. Anal. Calcd for C58H90O10Si2Dy2:
C, 52.83; H, 6.83. Found: C, 52.63; H, 6.62.
{Cp′Lu(µ-η1:η1-O2CH)(µ-η1:η1-O2COC6H2-tBu2-2,6-Me-
4)}2 (4c). The reaction of 3c (0.130 g, 0.110 mmol in 8 mL of
benzene) with CO2 by the same manner described above yielded
complex 4c, selectively (0.149 g, 0.110 mmol, 100%). Recrystal-
lization from a mixture of hexane/THF (1:1 v/v) yielded good
[Cp′Dy(µ-H)(OC6H2-tBu2-2,6-Me-4)]2 (3b). Following a similar
procedure to that described for the preparation of 3a, treatment of
colorless cubic crystals for X-ray analysis. H NMR (300 MHz,
1
THF-d8, 22 °C): 0.20 (s, 18H, C5Me4SiMe3), 1.33 (s, 36H, C6H2-

Rare-Earth-Metal Mixed Hydride/Aryloxide Complexes
Organometallics, Vol. 27, No. 11, 2008 2435
tBu2-2,6-Me-4), 1.61 (s, 12H, C5Me4SiMe3), 1.98 (s, 12H,
C5Me4SiMe3), 2.32 (s, 6H, C6H2-tBu2-2,6-Me-4), 7.12 (s, 4H, C6H2-
tBu2-2,6-Me-4), 8.34 (s, 2H, OC(H)O). 13C NMR (75 MHz, THF-
d8, 22 °C): 2.33 (C5Me4SiMe3), 10.84 (C5Me4SiMe3), 13.69
(C5Me4SiMe3), 21.45 (C6H2-tBu2-2,6-Me-4), 31.64 (C6H2-tBu2-2,6-
Me-4), 36.06 (C6H2-tBu2-2,6-Me-4), 115.84 (ipso-C5Me4SiMe3),
124.13 (C5Me4SiMe3), 127.42 (m-C6H2), 129.03 (C5Me4SiMe3),
135.25 (p-C6H2), 142.70 (o-C6H2), 148.17 (ipso-C6H2), 162.03
(O2CO), 174.07 (OC(H)O). IR (Nujol): ν 3074, 2865, 1659, 1556,
1454, 1377, 1344, 1242, 1192, 1111, 1031, 837 cm-1. Anal. Calcd
for C58H90O10Si2Lu2: C, 51.47; H, 6.70. Found: C, 51.33; H, 6.54.
Copolymerization of CO2 and CHO. A typical procedure for
the copolymerization of CHO and CO2 (Table 6, entry 1): A 100
mL stainless steel autoclave with a stir bar inside was put into a
70 °C oil bath, dried under vacuum for 1 h, cooled to room
temperature, and backfilled with N2. A toluene solution (2.0 mL)
of 3a (0.0251 g, 0.05 mmol) was injected into the autoclave with
a syringe under N2. CHO (1.963 g, 20.0 mmol) was then loaded
([Y] ) 16.3 mmol/L, [CHO] ) 5.0 mol/L). The autoclave was
pressurized to 11 atm with CO2 and then heated to 70 °C, and the
pressure rose to about 12 atm. The mixture was stirred at 70 °C
for 48 h and then cooled to room temperature. The viscous reaction
mixture was dissolved with chloroform and poured into methanol,
filtered, washed with methanol, and then dried at 60 °C for 24 h
under vacuum to give a white powder of polycarbonate (1.56 g).
The percentage of the carbonate linkages was calculated from the
relative intensities of the H NMR signals of the methine protons
adjacent to the carbonate linkages (δ 4.62) and ether linkages (δ
1
3.42).
Acknowledgment. This work was partly supported by a
Grant-in-Aid for Scientific Research on Priority Areas (No.
14078224, “Reaction Control of Dynamic Complexes”) from
the Ministry of Education, Culture, Sports, Science and
Technology of Japan. We are also grateful to Japan Society
for the Promotion of Science (JSPS) for a Postdoctoral
Fellowship for D.C.
Supporting Information Available: Experimental details, ORTEP
drawings, and tables of crystallographic data, atomic coordinates,
thermal parameters, and bond distances and angles for 2a,b, 3a-c,
and 4a-c. This material is available free of charge via the Internet
at http://pubs.acs.org.
OM800170X