Synthesis of a new class of compounds containing a Ln-O-Al arrangement and their reactions and catalytic properties

Article abstract of DOI:10.1021/ja050521s

Synthesis of a new class of compounds containing a Ln-O-Al moiety has been accomplished by the reaction of LAIOH(Me) (L = HC(CMeNAr)₂, Ar = 2,6-iPr₂C₆H₃) with a series of Cp₃Ln compounds. The terminal AI-OH group shows selective reactivity, and the complexes Cp₂Ln(THF)-O-AIL(Me) (Ln = Yb, 1; Er, 2; Dy, 3), Cp ₂Yb-O-AIL(Me) (4), and Cp₃Ln(μ-OH)AIL(Me) (Ln = Er, 5; Dy, 6; Sm, 7) were obtained. This allows further insight into the proton exchange process, and two different mechanisms, intermolecular and intramolecular elimination of CpH, are proposed under different conditions. Complexes 1-4, 6, and 7 have been characterized by X-ray structural analyses which reveals a Ln-O-Al or Ln(μ-OH)Al core in these complexes. The obtuse Ln-O-Al angles fall in the range 151.9-169.8°. The reaction of 1 or 4 with Me₃SnF in toluene under refluxing conditions unexpectedly yielded the compounds [Cp₂Yb-(μ-OSnMe₃)]₂ (8) and LAI(Me)F (9). Reactions of LAIOH(Me) with the mono- and dicyclopentadienyl complexes LYbCp(Cl) (10) and LYbCp₂ (11) supported by the bulky β-diketiminate ligand were unsuccessful. However, the reaction of LAI(OH)Me with LYbN(SiMe₃)₂Cl (12) containing a labile Yb-N bond leads to the formation of LYbCl-O-AIL(Me) (13) under elimination of HN(SiMe ₃)₂. Furthermore, complexes 1, 3, 4, and 6 exhibit good catalytic activity for the polymerization of ε-caprolactone.

Full text of DOI:10.1021/ja050521s

Published on Web 04/30/2005
Synthesis of a New Class of Compounds Containing a
Ln-O-Al Arrangement and Their Reactions and Catalytic
Properties
Jianfang Chai,† Vojtech Jancik,† Sanjay Singh,† Hongping Zhu,† Cheng He,†
Herbert W. Roesky,*,† Hans-Georg Schmidt,† Mathias Noltemeyer,† and
Narayan S. Hosmane‡
Contribution from the Institut fu¨r Anorganische Chemie der UniVersita¨t Go¨ttingen,
Tammannstrasse 4, D-37077 Go¨ttingen, Germany, and Department of Chemistry and
Biochemistry, Northern Illinois UniVersity, Dekalb, Illinois 60115-2862
Received January 26, 2005; E-mail: hroesky@gwdg.de
Abstract: Synthesis of a new class of compounds containing a Ln-O-Al moiety has been accomplished
by the reaction of LAlOH(Me) (L ) HC(CMeNAr)2, Ar ) 2,6-iPr2C6H3) with a series of Cp3Ln compounds.
The terminal Al-OH group shows selective reactivity, and the complexes Cp2Ln(THF)-O-AlL(Me) (Ln )
Yb, 1; Er, 2; Dy, 3), Cp2Yb-O-AlL(Me) (4), and Cp3Ln(µ-OH)AlL(Me) (Ln ) Er, 5; Dy, 6; Sm, 7) were
obtained. This allows further insight into the proton exchange process, and two different mechanisms,
intermolecular and intramolecular elimination of CpH, are proposed under different conditions. Complexes
1-4, 6, and 7 have been characterized by X-ray structural analyses which reveals a Ln-O-Al or Ln(µ-
OH)Al core in these complexes. The obtuse Ln-O-Al angles fall in the range 151.9-169.8°. The reaction
of 1 or 4 with Me3SnF in toluene under refluxing conditions unexpectedly yielded the compounds [Cp2Yb-
(µ-OSnMe3)]2 (8) and LAl(Me)F (9). Reactions of LAlOH(Me) with the mono- and dicyclopentadienyl
complexes LYbCp(Cl) (10) and LYbCp2 (11) supported by the bulky â-diketiminate ligand were unsuccessful.
However, the reaction of LAl(OH)Me with LYbN(SiMe3)2Cl (12) containing a labile Yb-N bond leads to the
formation of LYbCl-O-AlL(Me) (13) under elimination of HN(SiMe3)2. Furthermore, complexes 1, 3, 4,
and 6 exhibit good catalytic activity for the polymerization of ꢀ-caprolactone.
Evans1a,5 and Yasuda3b,c,6 on the synthesis and catalytic proper-
ties of the lanthanide aluminum heterometallic complexes is
Introduction
There is widespread interest in the chemistry of lanthanides
containing heterometal atoms, especially those where aluminum
is present as the other component.1 One aspect is the synthesis
of mixed-metal solid-state materials with unusual physical
properties.2 The other is the fact that lanthanide aluminum
heterobimetallic complexes are good catalysts for the polym-
erization of olefinic monomers, methyl methacrylate (MMA),
lactones, and cyclic carbonates;3 this is analogous in manner to
the development of group 4 metal and aluminum bimetallic
olefin polymerization catalysts.4 In this regard, the work of
notable. Although a variety of structural types and compositions
have been identified thus far, the majority of them are aluminum
alkyl adducts formed through OR or OAr bridges.1,5 Thus, it
was of interest to develop a synthetic strategy to incorporate
rare-earth metals on Al-O systems to generate compounds
containing the Ln-O-Al unit, where the oxygen atom is not
bonded to alkyl or aryl groups. It was envisaged that the Ln-
O-Al unit would provide a stable framework to assemble new
complexes of practical application such as catalysts.
We were encouraged with the results we obtained on
syntheses, structures, and applications of alumoxanes,7 aided
by the complexes containing terminal Al-OH groups.7a-d The
utility of such molecules as suitable synthons for the preparation
of various building blocks has already been shown by as-
sembling tri- and tetranuclear alumoxanes.7b,8 Furthermore, we
have also shown that the compound Cp2Zr(Me)-O-AlL(Me)
when activated with methylalumoxane (MAO) serves as a good
† Institut fu¨r Anorganische Chemie der Universita¨t Go¨ttingen.
‡ Northern Illinois University.
(1) (a) Evans, W. J.; Ansari, M. A.; Ziller, J. W. Polyhedron 1997, 16, 3429-
3434 and references therein. (b) Fischbach, A.; Herdtweck, E.; Anwander,
R.; Eickerling, G.; Scherer, W. Organometallics 2003, 22, 499-509 and
references therein. (c) Giesbrecht, G. R.; Gordon, J. C.; Brady, J. T.; Clark,
D. L.; Keogh, D. W.; Michalczyk, R.; Scott, B. L.; Watkin, J. G. Eur. J.
Inorg. Chem. 2002, 723-731.
(2) Selected samples: (a) Bradley, D. C. Chem. ReV. 1989, 89, 1317-1322.
(b) Bradley, D. C. Polyhedron 1994, 13, 1111-1121. (c) Mehrotra, R. C.;
Singh, A. Chem. Soc. ReV. 1996, 1-14.
(3) (a) Bambirra, S.; Bouwkamp, M. W.; Meetsma, A.; Hessen, B. J. Am. Chem.
Soc. 2004, 126, 9182-9183. (b) Yasuda, H.; Ihara, E. Bull. Chem. Soc.
Jpn. 1997, 70, 1745-1767. (c) Yasuda, H. J. Polym. Sci., Part A: Polym.
Chem. 2001, 39, 1955-1959.
(5) (a) Evans, W. J.; Boyle, T. J.; Ziller, J. W. J. Am. Chem. Soc. 1993, 115,
5084-5092. (b) Evans, W. J.; Ansari, M. A.; Ziller, J. W. Inorg. Chem.
1995, 34, 3079-3082. (c) Evans, W. J.; Anwander, R.; Ziller, J. W.
Organometallics 1995, 14, 1107-1109. (d) Evans, W. J.; Boyle, T. J.; Ziller,
J. W. J. Organomet. Chem. 1993, 462, 141-148.
(6) Yamamoto, H.; Yasuda, H.; Yokota, K.; Nakamura, A. Chem. Lett. 1988,
1963-1966.
(4) (a) ComprehensiVe Organometallic Chemistry; Wilkinson, G., Stone, F.
G. A., Abel, E. W., Eds.; Pergamon Press: Oxford, U.K., 1982. (b) Sinn,
H.; Kaminsky, W. AdV. Organomet. Chem. 1980, 18, 99-149.
9
10.1021/ja050521s CCC: $30.25 © 2005 American Chemical Society
J. AM. CHEM. SOC. 2005, 127, 7521-7528
7521

A R T I C L E S
Scheme 1
Chai et al.
Scheme 2
The reaction of Cp3Sm and LAlOH(Me) in THF did not occur
even under refluxing conditions; instead, Cp3Sm(THF) was
formed. However, when the reaction was carried out in toluene
the adduct Cp3Sm(µ-OH)AlL(Me) (7) was isolated. Further-
more, the dissociation of 7 to Cp3Sm(THF) and LAlOH(Me)
was observed when 7 was treated with THF (Scheme 2). This
indicates that LAlOH(Me) is a weaker base than THF.
catalyst for ethylene polymerization.7f Therefore, in the follow-
ing we report on the reaction of Cp3Ln (Ln ) Yb, Er, Dy, and
Sm) with aluminum monohydroxide LAlOH(Me) (L ) HC-
(CMeNAr)2, Ar ) 2,6-iPr2C6H3). Complexes of general com-
position Cp2Ln(THF)-O-AlL(Me) (Ln ) Yb, Er, and Dy),
Cp2Yb-O-AlL(Me), and Cp3Ln(µ-OH)AlL(Me) (Ln ) Er, Dy,
and Sm) were obtained. Consequently, it turned out that the
complex LAlOH(Me) with terminal Al-OH group is a suitable
precursor to prepare a new class of lanthanide aluminum
heterobimetallic compounds, which has a selective reactivity
for the reported lanthanide series and can act as a Brønsted acid
or a Lewis base. In addition, reactions of LAlOH(Me) with
ytterbium complexes supported by a bulky â-diketiminate ligand
were also examined. The reactivity and catalytic properties of
these new complexes have been primarily investigated.
Although Cp3Ln is widely employed to prepare dicyclopen-
tadienyl derivatives through protolytic exchange and elimination
of CpH,9 limited information is available concerning the reaction
pathway due to the higher reactivity of the precursor used, such
as carboxylic acids9a and alcohols.9b,c The mild reactivity of
the Al-OH unit allows the isolation of some of the intermedi-
ates and sheds light on the reaction pathway. On the basis of
the facts discussed above, it is obvious that the formation of
the Ln-O-Al unit is a multiple-step process. The first step is
the coordination of a Lewis base to the unsaturated lanthanide
center. The adduct Cp3Ln(THF) is preferentially formed, in the
presence of THF, while with toluene as a solvent, LAlOH(Me)
acts as a Lewis base and coordinates to the Ln center to yield
Cp3Ln(µ-OH)AlL(Me) (Scheme 3). The latter dissociates to Cp3-
Ln(THF) and LAlOH(Me) when THF was added. The second
step involves formation of the Ln-O-Al moiety through a
protolytic exchange, which proceeds with either an intermo-
lecular elimination of CpH between Cp3Ln(THF) and LAlOH-
(Me) in THF or an intramolecular elimination of CpH from
Cp3Yb(µ-OH)AlL(Me) in toluene. However, Cp3Sm(THF) and
Cp3Ln(µ-OH)AlL(Me) (Ln ) Er, Dy, and Sm) are stable enough
to be isolated and do not react further under the given conditions.
Compounds 1-7 were isolated as crystalline and thermally
stable solids, which are moderately air- and moisture-sensitive.
Complexes 1-3 and 5-7 have a poor solubility in THF or
toluene at ambient temperature, but can be dissolved under slight
heating. Compound 4 is soluble in toluene at room temperature.
The melting point of the complexes 5-7 lies in the range 5
(205-207 °C) < 6 (258-260 °C) < 7 (323-325 °C). The
molecular ions of 1-3 were detected in the EI-MS without the
coordinated THF molecule albeit in low intensity, followed by
the most intense peak corresponding to [M-THF-Me]+, which
indicates stability of the Ln-O-Al core. The peaks at m/z 758,
754, and 742 can be attributed to [M-CpH-Me]+ for 5-7,
respectively. In the IR spectra of 5-7, a broad absorption band
near 3500 cm-1 is assigned to the stretching frequency of the
bridging hydroxide group.
Results and Discussion
Reaction of LAlOH(Me) with Cp3Ln and Formation of
Complexes 1-7. Reaction of LAlOH(Me) with 1 equiv of Cp3-
Ln was carried out in THF at room temperature to afford Cp2-
Ln(THF)-O-AlL(Me) (Ln ) Yb, 1; Er, 2; Dy, 3) (Scheme 1)
in good yields accompanied by color change and precipitate
formation. The elimination of CpH and the formation of the
Ln-O-Al moiety was confirmed by EI-MS, elemental analyses,
and X-ray structural analyses. A coordinated THF molecule
allows the lanthanide ion to be of preferred tetrahedral geometry.
In the meantime, we were also interested in exploring the
reactions in noncoordinating solvent such as toluene. Thus, the
reaction of Cp3Yb and LAlOH(Me) in toluene yielded the
compound Cp2Yb-O-AlL(Me) (4) followed by the color
change from dark green to yellow-green. However, the reaction
of Cp3Ln (Ln ) Er and Dy) and LAlOH(Me) in toluene leads
to the formation of compounds Cp3Ln(µ-OH)AlL(Me) (Ln )
Er, 5; Dy, 6), with the Al-OH unit coordinated as a Lewis
base to the Ln center. Elimination of CpH was not observed
even in refluxing toluene. Compounds 4-6 can be converted
to 1-3, respectively, when treated with THF.
(7) (a) Bai, G.; Peng, Y.; Roesky, H. W.; Li, J.; Schmidt, H.-G.; Noltemeyer,
M. Angew. Chem., Int. Ed. 2003, 42, 1126-1132. (b) Bai, G.; Roesky, H.
W.; Li, J.; Noltemeyer, M.; Schmidt, H.-G. Angew Chem., Int. Ed. 2003,
42, 5502-5506. (c) Peng, Y.; Bai, G.; Fan, H.; Vidovic, D.; Roesky, H.
W.; Magull, J. Inorg. Chem. 2004, 43, 1217-1219. (d) Jancik, V.; Pineda,
L. W.; Pinkas, J.; Roesky, H. W.; Neculai, D.; Neculai, A. M.; Herbst-
Irmer, R. Angew. Chem., Int. Ed. 2004, 43, 2142-2145. (e) Roesky, H.
W.; Singh, S.; Jancik, V.; Chandrasekhar, V. Acc. Chem. Res. 2004, 37,
969-981. (f) Bai, G.; Singh, S.; Roesky, H. W.; Noltemeyer, M.; Schmidt,
H.-G. J. Am. Chem. Soc. 2005, 127, 3449-3455. (g) Neculai, D.; Roesky,
H. W.; Neculai, A. M.; Magull, J.; Walfort, B.; Stalke, D. Angew. Chem.,
Int. Ed. 2002, 41, 4294-4296.
X-ray Structural Analyses. Crystals of complexes 1-4,
6-8, 11, and 12 have been investigated by single-crystal X-ray
technique (Table 1). Unfortunately, due to the poor crystal
quality of 5 satisfactory data could not be obtained. Selected
structures (2, 4, 7, and 11) are shown in Figures 1-4, whereas
(9) (a) Maginn, R. E.; Mannastyrskyj, S.; Dubeck, M. J. Am. Chem. Soc. 1963,
85, 672-676. (b) Wu, Z.; Xu, Z.; You, X.; Zhou, X.; Jin, Z. Polyhedron
1992, 11, 2673-2678. (c) Stehr, J.; Fischer, R. D. J. Organomet. Chem.
1993, 459, 79-86.
(8) Singh, S.; Kumar, S. S.; Chandrasekhar, V.; Ahn, H.-J.; Biadene, M.;
Roesky, H. W.; Hosmane, N. S.; Noltemeyer, M.; Schmidt, H.-G. Angew.
Chem., Int. Ed. 2004, 43, 4940-4943.
9
7522 J. AM. CHEM. SOC. VOL. 127, NO. 20, 2005

New Class of Compounds with a Ln
−O
−Al Arrangement
A R T I C L E S
Scheme 3
Table 1. Crystallographic Data for Complexes 1-4, 6-8, 11, and 12
1
2
3
4
‚
2 toluene
6
formula
fw
C44H62AlN2O2Yb
850.98
C44H62AlErN2O2
845.20
C44H62AlDyN2O2
840.44
C54H70AlN2OYb
963.14
C45H60AlDyN2O
834.43
cryst syst
space group
monoclinic
P21/n
monoclinic
P21/n
monoclinic
P21/n
monoclinic
P21/n
monoclinic
P21/m
temp, K
100(2)
133(2)
133(2)
133(2)
133(2)
λ, Å
1.54178
8.812(1)
37.845(2)
12.032(1)
97.06(1)
0.71073
8.850(1)
37.991(5)
12.072(3)
97.07(3)
0.71073
8.854(1)
37.975(2)
12.106(1)
97.17(1)
0.71073
9.130(2)
12.498(3)
42.211(8)
93.36(3)
0.71073
a, Å
10.188(2)
19.669(4)
10.536(2)
109.43(3)
1991(1)
b, Å
c, Å
â, deg
V, Å3
3982(1)
4028(1)
4039(1)
4808(2)
Z
4
4
4
4
2
crystal color
yellow
5655/190/512
1.041
0.0199, 0.0503
0.0210, 0.0511
0.415/-0.537
pink
6766/126/502
0.980
0.0221, 0.0506
0.0294, 0.0523
0.496/-0.902
colorless
6937/191/511
0.917
0.0545, 0.0748
0.1169, 0.0874
0.714/-1.120
yellow
7906/350/594
1.276
0.0340, 0.0808
0.0378, 0.0819
0.780/-1.319
colorless
3476/222/295
1.109
0.0508, 0.1022
0.0575, 0.1046
2.238/-2.436
no. of data/restraints/params
GoF on F2
R1,a wR2b (I > 2σ(I))
R1,a wR2b (all data)
largest diff. peak/hole, e Å-3
7
8
11
‚
0.5 hexane
12
formula
fw
C45H60AlN2OSm
822.28
C26H38O2Sn2Yb2
966.02
C42H58N2Yb
763.94
C35H59ClN3Si2Yb
786.524
cryst syst
space group
monoclinic
P21/m
monoclinic
P21/n
monoclinic
P21/n
monoclinic
P21/c
temp, K
100(2)
133(2)
133(2)
133(2)
λ, Å
1.54178
0.71073
0.71073
0.71073
a, Å
10.214(1)
19.606(1)
10.556(1)
109.37(1)
1994(1)
8.288(2)
16.180(6)
10.394(2)
98.53(2)
1378(1)
16.326(2)
9.565(1)
23.801(4)
94.17(1)
3707(1)
17.120(3)
18.184(4)
12.887(3)
104.48(3)
3884(1)
b, Å
c, Å
â, deg
V, Å3
Z
2
2
4
4
crystal color
yellow
yellow
red
red
no. of data/restraints/params
2950/206/294
1.206
0.0302, 0.0683
0.0314, 0.0686
0.600/-0.526
2366/0/148
1.033
0.0153, 0.0305
0.0186, 0.0313
0.354/-0.492
6344/259/500
1.031
0.0174, 0.0379
0.0209, 0.0388
0.343/-0.470
6663/0/399
1.045
0.0191, 0.0470
0.0228, 0.0481
0.712/-0.839
GoF on F2
R1,a wR2b (I > 2σ(I))
R1,a wR2b (all data)
largest diff. peak/hole, e Å-3
all the structures and structural fit of compounds 1-3, 6, and 7
for the sake of comparison are depicted in Figures S1-S12 in
the Supporting Information. Compounds 1-3 are isomorphous
(Figures S1-S4), and the lanthanide ion possesses a pseudo-
tetrahedral geometry surrounded by two cyclopentadienyl rings
and two oxygen atoms (Figure 1). The central Ln-O-Al core
is obtuse (1, 169.5°; 2, 168.6°; 3, 167.4°). The Ln-O (Yb-
O(1) 2.020 Å, Er-O(1) 2.043 Å, Dy-O(1) 2.056 Å) and
average Ln-XCp (XCp is the centroid of the Cp group, Yb-
similar to the corresponding ones in [(C5H4Me)2YbTHF]2-
(µ-O)11 (2.02 and 2.35 Å) and (Ar′O)2(THF)2Yb(µ-OAr′)2AlMe25b
(Ar′ ) 2,6-Me2C6H3) (2.06 and 2.37 Å). Compounds 2 and 3
are rare examples of structurally characterized Er and Dy
compounds containing Ln-O bonds.
The Yb center in compound 4 is not coordinated to a solvent
molecule (Figure 2) and the O(1)YbXCp1XCp2 core is almost
planar with the sum of angles 357°. However, the coordination
sphere of the Yb atom is partly saturated by two agostic
interactions to two hydrogen atoms H(28A) and H(28C) (2.66
and 2.53 Å) from the iPr moiety of the ligand (Figure 2). The
Yb-O-Al angle (168.8°) is similar to that in 1. The shorter
Yb-O (2.000 Å) and longer Al-O (1.713 Å) distances (Table
XCp 2.37 Å, Er-XCp 2.40 Å, Dy-XCp 2.43 Å), Al-O (av 1.69
Å) and Al-N (av 1.94 Å) distances are almost unaffected by
the different covalent radii of the corresponding lanthanide ion
(Yb 1.94, Er 1.73, Dy 1.75 Å).10 The Yb-O distances in 1 are
(10) For covalent atomic radii see web page of Cambridge Structural Database:
http://www.ccdc.cam.ac.uk/products/csd/radii/.
(11) Adam, M.; Massarweh, G.; Fischer, R. D. J. Organomet. Chem. 1991, 405,
C33-C37.
9
J. AM. CHEM. SOC. VOL. 127, NO. 20, 2005 7523

A R T I C L E S
Chai et al.
Figure 1. Molecular structure of 2 (50% probability thermal ellipsoids).
Hydrogen atoms and the disorder of the THF molecule are omitted for
clarity.
Figure 3. Molecular structure of 7 (50% probability thermal ellipsoids).
Hydrogen atoms of the C-H bonds, second positions of the disordered
isopropyl, and Cp groups are omitted for clarity.
Figure 4. Molecular structure of 11 (50% probability thermal ellipsoids).
Solvating hexane molecule and the hydrogen atoms are omitted for clarity.
Figure 2. Molecular structure of 4 (50% probability thermal ellipsoids).
Solvating toluene molecules and hydrogen atoms, except those on C(28),
are omitted for clarity.
compared with those of Dy-O(THF) in Cp3Dy(THF) (2.46 Å)13
and 3 (2.36 Å) and is longer than that of Dy-O(1) in 3 (2.056
Å). The Sm-OH distance (2.500 Å) in 7 is similar to that in
Cp3Sm(THF) (2.51 Å).13b The Al-O distances (1.766 Å) in 6
and (1.758 Å) 7 are much longer than those in complexes 1-4
due to their coordinative character and steric bulk of the LnCp3
moiety. However, the Dy-O-Al and Sm-O-Al angles (153.6°
and 151.9°) (Table 2) are less obtuse than those in 1-4. Selected
bond lengths and angles for complexes 1-7 are given in Table
2.
Reaction of 1 and 4 with Me3SnF. The Me group in LAlOH-
(Me) has been used thus far as the fourth substituent on Al and
has played only the role of a spectator ligand. It was of interest
to prepare other derivatives by using the Me group. It is well-
known that the reaction of aluminum alkyls with Me3SnF results
in the formation of aluminum florides;14 therefore, formation
2) compared to the corresponding ones in 1 indicate the stronger
bonding interaction of the Yb and O atoms in 4. The Yb-O
bond lengths in 1 (2.020 Å) and in 4 (2.000 Å) are the shortest
Yb-O separations observed thus far.11,12 The Yb-XCp distance
(2.34 Å) is a little shorter than that in 1 (2.37 Å) due to the
lower coordination number of the Yb center.
Compounds 6 and 7 crystallize in the monoclinic space group
P21/m with half of a molecule in the asymmetric unit and are
isomorphous (Table 1). The mirror plane passes through the
Ln(µ-OH)Al unit (Figure 3). The coordination sphere of Dy
and Sm in 6 and 7 is similar to that in Cp3Dy(THF) and Cp3-
Sm(THF).13 The Dy-OH distance (2.431 Å) in 6 can be
(12) (a) Rabe, G. W.; Berube, C. D.; Yap, G. P. A.; Lam, K.-C.; Concolino, T.
E.; Rheingold, A. L. Inorg. Chem. 2002, 41, 1446-1453. (b) Deacon, G.
B.; Feng, T.; Nickel, S.; Ogden, M. I.; White, A. H. Aust. J. Chem. 1992,
45, 671-683. (c) Bradley, D. C.; Chudzynska, H.; Frigo, D. M.; Hammond,
M. E.; Hursthouse, M. B.; Mazid, M. A. Polyhedron 1990, 9, 719-726.
(d) Deacon, G. B.; Forsyth, C. M.; Wilkinson, D. L. Chem.-Eur. J. 2001,
7, 1784-1795. (e) Beer, P. D.; Drew, M. G. B.; Kan, M.; Leeson, P. B.;
Ogden, M. I.; Williams, G. Inorg. Chem. 1996, 35, 2202-2211.
(13) (a) Ye, Z.; Wang, S.; Yu, Y.; Shi, L. Inorg. Chim. Acta 1990, 177, 97-
100. (b) Wu, Z.; Xu, Z.; You, X.; Zhou, X.; Huang, X.; Chen, J. Polyhedron
1994, 13, 379-384.
(14) Roesky, H. W. Inorg. Chem. 1999, 38, 5934-5943.
9
7524 J. AM. CHEM. SOC. VOL. 127, NO. 20, 2005

New Class of Compounds with a Ln
−O
−Al Arrangement
A R T I C L E S
Table 2. Selected Bond Distances (Å) and Angles (deg) for 1-4, 6, and 7
1a
2a
3a
4‚
2 tolueneb
6c
7c
Al-N(1)
1.931(2)
1.939(2)
1.692(2)
1.980(2)
2.020(1)
2.32(1)
2.37(1)
2.37(1)
94.8(1)
117.8(1)
169.8(1)
94.8(3)
112.1(3)
109.4(3)
129.1(3)
1.933(2)
1.939(2)
1.690(2)
1.976(2)
2.043(2)
2.34(2)
2.39(1)
2.40(1)
94.9(1)
117.8(1)
168.6(1)
96.1(1)
111.8(2)
109.4(2)
128.9(2)
1.920(7)
1.934(6)
1.690(6)
1.963(8)
2.056(5)
2.36(1)
2.42(2)
2.43(2)
95.7(3)
118.2(3)
167.4(3)
95.2(7)
112.2(5)
109.4(4)
128.9(5)
1.919(4)
1.921(3)
1.713(3)
1.951(5)
2.000(3)
2.66(4), 2.53(4)
2.34(3)
1.905(5)
equiv to Al-N(1)
1.766(6)
1.956(9)
2.431(6)
2.45(2)
2.46(2)
equiv to Ln-XCp1
96.7(3)
114.2(4)
153.6(4)
105.4(5)
97.0(5)
equiv to O-Ln-XCp1
118.0(5)
1.906(3)
equiv to Al-N(1)
1.758(4)
1.962(5)
2.500(4)
2.50(2)
2.51(2)
equiv to Ln-XCp1
97.0(2)
113.6(2)
151.9(2)
106.6(4)
96.4(4)
equiv to O-Ln-XCp1
118.0(4)
Al-N(2)
Al-O(1)
Al-C
Ln-O(1)
Ln-X
Ln-XCp1
Ln-XCp2
2.34(3)
94.6(2)
N(1)-Al-N(2)
C-Al-O(1)
Al-O(1)-Ln
O(1)-Ln-X
O(1)-Ln-XCp1
O(1)-Ln-XCp2
XCp1-Ln-XCp2
114.3(2)
168.8(2)
68(1), 95(1)
112.5(3)
114.7(3)
129.6(3)
a
b
c
X ) O(2) from THF. X ) H(28A), H(28C). X ) XCp3
.
Table 3. Selected Bond Distances (Å) and Angles (deg) for 8, 11, and 12
8
11
‚
0.5 hexane
12
Yb(1)-O(1)
2.187(2)
2.191(2)
2.37(2)
2.36(2)
2.010(2)
77.7(1)
102.3(1)
127.7(1)
129.4(1)
123.4(4)
Yb(1)-N(1)
2.303(2)
2.336(2)
2.39(2)
2.31(2)
85.6(2)
125.9(4)
112.8(4)
106.0(4)
111.1(4)
107.8(4)
Yb(1)-N(1)
2.234(2)
2.258(2)
2.182(2)
2.491(1)
2.67(2)
2.70(2)
2.75(2)
85.4(1)
Yb(1)-O(1A)
Yb(1)-N(2)
Yb(1)-N(2)
Yb(1)-XCp1
Yb(1)-XCp1
Yb(1)-XCp2
Yb(1)-N(3)
Yb(1)-Cl(1)
Yb(1)-XCp2
Sn(1)-O(1)
N(1)-Yb(1)-N(2)
XCp1-Yb(1)-XCp2
N(1)-Yb(1)-XCp1
N(1)-Yb(1)-XCp2
N(2)-Yb(1)-XCp1
N(2)-Yb(1)-XCp2
Yb(1)-H(12A)
Yb(1)-H(26A)
Yb(1)-H(35A)
N(1)-Yb(1)-N(2)
N(3)-Yb(1)-Cl(1)
N(1)-Yb(1)-N(3)
N(2)-Yb(1)-N(3)
O(1)-Yb(1)-O(1A)
Yb(1)-O(1)-Yb(1A)
Yb(1)-O(1)-Sn(1)
Yb(1)-O(1)-Sn(1A)
XCp1-Yb(1)-XCp2
113.8(1)
129.7(1)
114.9(1)
SnCH2(Me2)Si)2CC]O}216 and is longer than those (1.96-1.98
Scheme 4
Å) in Sn3O3 heterocycles.17
Investigation on Reaction of LAlOH(Me) with â-Diketimi-
nate Ytterbium Complexes. Recently, the bulky â-diketiminate
ligand L (L ) CH(CMeNAr)2, Ar ) 2,6-iPrC6H3) was found
to be an ideal ligand to stabilize mixed-ligand ytterbium
complexes due to its steric and electronic properties.18 Therefore,
â-diketiminate complexes containing cyclopentadienyl groups
were primarily investigated. The mono- and dicyclopentadienyl
ytterbium complexes 10 and 11 were readily obtained from the
reaction of LYbCl2(THF)2 with 1 and 2 equiv of CpNa,
respectively, in THF in high yields (Scheme 5). However,
compounds 10 and 11 reveal no reactivity toward LAlOH(Me)
in toluene or THF, even under refluxing conditions.
of the complexes Cp2Ln-O-AlL(F) can be anticipated in the
reaction of Cp2Ln-O-AlL(Me) with Me3SnF. On the contrary,
reaction of 1 and Me3SnF in refluxing toluene yielded compound
[Cp2Yb(µ-OSnMe3)]2 (8) accompanied by the formation of
LAlF(Me) (9) (Scheme 4), which was identified by EI-MS, 1H,
and 19F NMR. The same result was obtained when 4 was used
instead of 1. This shows that the Ln-O-Al unit is reactive
and affords a new route for the preparation of lanthanide
heterobimetallic complexes with a Ln-O-M (M ) metal) core.
Compound 8 was obtained as yellow crystals and has been
characterized by X-ray structural analysis. The structural
investigation reveals a centrosymmetric dimer of composition
[Cp2Yb(µ-OSnMe3)]2. The central Yb2O2 core is planar due to
the symmetry and is linked to two terminal Me3Sn groups. The
low steric demand of the Me3Sn groups possibly leads to the
aggregation of the monomeric unit. The Yb-O distance (av
2.19 Å) (Table 3) is significantly longer than the corresponding
Yb-O(1) distance in 1 and 4 and can be compared to the
Lanthanide amides show a diverse chemistry due to the labile
Ln-N bond.19 Therefore, it was an obvious route to prepare
Ln-O-Al units from compounds containing Ln-N bonds.
Treatment of LYbCl2(THF)2 with 1 equiv of NaN(SiMe3)2 in
THF afforded LYb(N(SiMe3)2)Cl (12) as red crystals in moder-
ate yield. Efforts to prepare LYb(N(SiMe3)2)2 under similar
conditions resulted in decomposition products. Further reaction
of 12 with an equivalent amount of LAlOH(Me) in toluene
smoothly yielded LYbCl-O-AlL(Me) (13) under elimination
of HN(SiMe3)2 (Scheme 6).
9b
bridging ones in [Cp2Yb(µ-OnPr)]2 (2.20 Å) and [(Me3-
(16) Schulte, M.; Schuermann, M.; Dakternieks, D.; Jurkschat, K. Chem.
Commun. 1999, 1291-1292.
SiC5H4)2Yb(µ-OH)]215 (2.29 Å), but is shorter than Yb-O(THF)
in 1. The Sn-O distance (2.01 Å) is similar to that for the
exocyclic Sn-O distance (2.02 Å) in cis-{[(Me3SiCH2(Cl)-
(17) Janssen, J.; Magull, J.; Roesky, H. W. Angew. Chem., Int. Ed. 2002, 41,
1365-1367.
(18) (a) Yao, Y.; Zhang, Y.; Shen, Q.; Yu, K. Organometallics 2002, 21, 819-
824. (b) Bourget-Merle, L.; Lappert, M. F.; Severn, J. R. Chem. ReV. 2002,
102, 3031-3066.
(15) Hitchcock, P. B.; Lappert, M. F.; Prashar, S. J. Organomet. Chem. 1991,
413, 79-90.
(19) Sheng, E.; Wang, S.; Yang, G.; Zhou, S.; Cheng, L.; Zhang, K.; Huang, Z.
Organometallics 2003, 22, 684-692 and references therein.
9
J. AM. CHEM. SOC. VOL. 127, NO. 20, 2005 7525

A R T I C L E S
Scheme 5
Chai et al.
Mw/Mn
Table 4. Polymerization of ꢀ-Caprolactonea
compound
solvent
T (
°C)
time (h)
yield (%)
Mn
1
1
1
3
3
4
4
6
6
THF
toluene
THF
THF
THF
toluene
toluene
toluene
toluene
22
70
70
22
70
22
70
22
70
3
96
95
96
95
96
94
95
95
97
51766
18556
24172
61345
33256
21807
17718
20934
39690
1.6
2.3
2.1
1.7
1.7
1.5
1.8
1.6
1.7
0.5
0.5
3
0.5
5
0.5
5
0.5
a
Cat. ) [0.01 mol/L]; caprolactone/cat. ) 100.
the polymer and high polydispersity compared to that at ambient
temperature for 1, 3, and 4, whereas for 6 polymerization at
high temperature shows the opposite trend for the molecular
weight with almost similar polydispersity. The polymers
obtained have molecular weight (Mn) in the range of 1.8-6.1
× 104, and the polydispersity (Mw/Mn) ranges from 1.5 to 2.3.
The yield is almost quantitative (Table 4). As discussed before,
the Mn and Mw/Mn vary with the temperature of polymerization.
The values can be compared with those of polymers obtained
with Ln(O-iPr)3 and organolanthanide(II) complexes.3b,22 The
polydispersity index (1.7-2.3) is larger than that (1.1) obtained
with Cp′2LnOR (Cp′ ) Cp, Cp*; Ln ) Sm, Y; R ) Me, Et).
The difference in the results is probably due to the conditions
of polymerization (e.g., different temperature and reaction
time).20 The application of such molecules for other polymer-
ization reactions is currently being pursued.
Scheme 6
Compound 13 was isolated as yellow crystals and is soluble
in toluene and THF. The molecular ion of 13 in the EI-MS
spectrum is silent, and the most intense peak at m/z 1086
corresponds to [M - Me]+.
Complexes 11-13 have been characterized by X-ray struc-
tural analyses. The structure of 13 is highly disordered due to
the similar coordination sphere of the Yb and Al atoms and
can be solved in both P1 and P1h space group. The ball and
stick model of 13 refined in P1 is depicted in Figure S12. The
ytterbium ion in 11 is of pseudotetrahedral geometry surrounded
by two cyclopentadienyl substituents and two nitrogen atoms
of the chelating ligand (Figure 4). The coordination sphere of
the ytterbium atom in 12 is more complicated and is formed by
three nitrogen and one chlorine atom and further by agostic
interaction to three hydrogen atoms (Yb-H 2.67, 2.70, and 2.75
Å, Figure S11). The C3N2Yb six-membered ring in both
compounds adopts a boat conformation with the Yb at the prow
and C(3) at the stern. The Yb-N(endocyclic) distances in 11 (2.303
and 2.336 Å) are a little longer than those in 12 (2.234 and
2.258 Å) (Table 3) and LYbCl(µ-Cl)3YbL(THF)18a (2.27 Å) due
to the bulky Cp substituents.
Test for Catalytic Activity and the Polymerization of
E-Caprolactone. Ring-opening polymerization of lactones is an
important process since the polymer is biodegradable and of
practical application.20 Lanthanide alkoxides are known to
catalyze polymerization of lactones.21 Thus, the catalytic
property of complexes 1, 3, 4, and 6 for the polymerization of
ꢀ-caprolactone were preliminarily investigated. These complexes
show living catalyst activity at ambient or higher temperature
in THF or toluene (Table 4). This indicates that the catalytic
activity is maintained even when the R group is replaced by
the Al unit. It is notable that compound 6 also shows high
activity. This is probably due to the coordinating character of
the lactone, which leads to the elimination of CpH and formation
of Cp2Dy(ꢀ-caprolactone)-O-AlL(Me) as the catalytic precur-
sor. The coordination of the lactone has been observed.21
The general trend for the catalyst activity shows that the high-
temperature polymerization leads to low molecular weight of
Conclusions
In summary, we describe the synthesis of a new class of
compounds containing the Ln-O-Al moiety from the reaction
of LAlOH(Me) (L ) HC(CMeNAr)2, Ar ) 2,6-iPr2C6H3) and
selected lanthanide precursor. The terminal Al-OH group shows
selective reactivity for the lanthanide series when Cp3Ln was
used, and different types of lanthanide aluminum complexes
containing either oxo-bridged Ln-O-Al or coordinated OH
as Ln(µ-OH)Al were obtained depending on the varying
lanthanide ion and solvent. This shows that the reaction of Cp3-
Ln and LAlOH(Me) provides a facile route to synthesize
lanthanide aluminum complexes. The formation of Ln-O-Al
arrangement is a multiple-step process, and the elimination of
CpH occurs through different mechanisms accompanied by the
formation of different intermediates under different conditions.
Furthermore, complexes 1, 3, 4, and 6 are useful catalysts for
the polymerization of ꢀ-caprolactone. The reaction of 1 or 4
with Me3SnF affords 8 containing a Yb-O-Sn core, which
indicates that the Ln-O-Al unit is reactive and affords a new
route to lanthanide heterobimetallic complexes containing a Ln-
O-M unit. In addition, reactions of 10 and 11 with LAlOH-
(Me) show that mono- and dicyclopentadienyl derivatives are
not suitable to act as CpH-eliminating reagents. The labile Ln-N
bond can also be exploited as another method to prepare Ln-
O-Al complexes. The reaction of LAlOH(Me) with lanthanide
complexes containing two or three amide groups in different
ratios is presently under investigation.
Experimental Section
General. All reactions were performed using standard Schlenk and
drybox techniques. Solvents were appropriately dried and distilled under
(20) Yamashita, M.; Takemoto, Y.; Ihara, E.; Yasuda, H. Macromolecules 1996,
29, 1798-1806.
(21) Evans, W. J.; Shreeve, J. L.; Doedens, R. J. Inorg. Chem. 1993, 32, 245-
246 and references therein.
(22) (a) Evans, W. J.; Katsumata, H. Macromolecules 1994, 27, 2330-2332.
(b) Evans, W. J.; Katsumata, H. Macromolecules 1994, 27, 4011-4013.
9
7526 J. AM. CHEM. SOC. VOL. 127, NO. 20, 2005

New Class of Compounds with a Ln
−O
−Al Arrangement
A R T I C L E S
dinitrogen prior to use. Elemental analyses were performed by the
Analytisches Labor des Instituts fu¨r Anorganische Chemie der Uni-
versita¨t Go¨ttingen. H NMR spectra were recorded on a Bruker AM-
Mp: 205-207 °C. Anal. Calcd for C45H60AlErN2O (839.20): C, 64.35;
H, 7.15; N, 3.34. Found: C, 64.15; H, 7.33; N, 3.48. EI-MS: m/z (%)
) 772 (1) [M - CpH]+, 758 (60) [M - CpH - Me]+, 461 (100) [M
- Me - Cp3Er]+. IR (KBr, Nujol mull, cm-1): ν˜ ) 3438 (w), 1653
(w), 1625 (w), 1587 (w), 1525 (m), 1311 (m), 1261 (s), 1193 (w), 1175
(w), 1098 (s), 1019 (s), 960 (w), 940 (w), 875 (w), 801 (s), 761 (m),
711 (w), 654 (w), 642 (w), 605 (w), 540 (w), 464 (w), 451 (w).
Cp3Dy(µ-OH)AlL(Me) (6). The procedure is the same as that for 3
with toluene instead of THF. Yield: 0.68 g (81%). Mp: 258-260 °C.
Anal. Calcd for C45H60AlDyN2O (834.43): C, 64.71; H, 7.19; N, 3.35.
Found: C, 64.39; H, 7.21; N, 3.37. EI-MS: m/z (%) ) 768 (1) [M -
CpH]+, 754 (33) [M - CpH - Me]+, 461 (100) [M - Me - Cp3-
Dy]+. IR (KBr, Nujol mull, cm-1): ν˜ ) 3580 (w), 1624 (w), 1587
(w), 1525 (s), 1312 (s), 1257 (s), 1193 (w), 1177 (w), 1107 (m), 1055
(w), 1019 (s), 942 (m), 877 (m), 846 (w), 802 (s), 777 (s), 760 (s), 714
(s), 625 (w), 643 (m), 606 (m), 537 (w), 450 (w).
Cp3Sm(µ-OH)AlL(Me) (7). The procedure is the same as that for
6 with Cp3Sm (0.35 g, 1 mmol) instead of Cp3Dy. Yield 0.67 g (81%).
Mp: 323-325 °C. Anal. Calcd for C45H60AlN2OSm (822.29): C, 65.67;
H, 7.30; N, 3.41. Found: C, 65.26; H, 7.43; N, 3.51. EI-MS: m/z (%)
) 758 (1) [M - CpH]+, 742 (30) [M - CpH - Me]+, 461 (100) [M
- Me - Cp3Sm]+. IR (KBr, Nujol mull, cm-1): ν˜ ) 3588 (w), 1652
(w), 1586 (w), 1523 (s), 1311 (m), 1257 (m), 1193 (w), 1176 (w), 1106
(w), 1055 (w), 1019 (s), 936 (m), 876 (w), 802 (m), 774 (m), 758 (s),
717 (m), 642 (w), 607 (w), 449 (w).
1
200 instrument. The chemical shifts were reported in ppm with reference
to external standards, more explicitly, SiMe4 for 1H nucleus. Mass
spectra were obtained on a Finnigan Mat 8230. IR spectra were recorded
on a Bio-Rad Digilab FTS-7 spectrometer as Nujol mulls between KBr
plates. Cp3Ln,22 LYbCl2(THF)2,18a Me3SnF,23 and LAlOH(Me)8 (L )
HC(CMeNAr)2, Ar ) 2,6-iPr2C6H3) were prepared according to the
literature methods. ꢀ-Caprolactone (Aldrich) was dried over molecular
sieves and degassed prior to use. Molecular weight data were recorded
on a Waters 2410 refractive index detector with a procedure similar to
that reported in the literature.24 The polycaprolactone was characterized
1
by H and 13C NMR.
Cp2Yb(THF)-O-AlL(Me) (1). THF (40 mL) was added to a
mixture of LAlOH(Me) (0.48 g, 1 mmol) and Cp3Yb (0.37 g, 1 mmol)
at room temperature. The solution slowly turned from dark green to
yellow accompanied by precipitate formation. The slurry was stirred
for 12 h, and all the volatiles were removed in vacuo. THF (30 mL)
was added and warmed until a clear yellow solution was obtained. The
hot solution was filtered and kept at room temperature to give yellow
crystals, which were collected by filtration, and the mother liquor was
kept at 4 °C to give additional crystalline solid. Total yield: 0.66 g
(78%). Mp: 249-251 °C. Anal. Calcd for C44H62AlN2O2Yb (850.98):
C, 62.05; H, 7.29; N, 3.29. Found: C, 62.15; H, 7.75; N, 3.33. EI-MS:
m/z (%) ) 778 (1) [M - THF]+, 764 (100) [M - THF - Me]+. IR
(KBr, Nujol mull, cm-1): ν˜ ) 1624 (w), 1590 (w), 1552 (w), 1522
(m), 1315 (m), 1261 (m), 1176 (w), 1096 (s), 1021 (s), 917 (s), 875
(w), 801 (s), 761 (w), 722 (m), 663 (w), 643 (w), 605 (w), 534 (w),
452 (w).
Cp2Er(THF)-O-AlL(Me) (2). The procedure is the same as that
described for 1 with Cp3Er (0.36 g, 1 mmol) instead of the Cp3Yb.
Yield: 0.62 g (73%). Mp: 270-272 °C. Anal. Calcd for C44H62-
AlErN2O2 (845.20): C, 62.47; H, 7.34; N, 3.31. Found: C, 62.32; H,
7.54; N, 3.43. EI-MS: m/z (%) ) 774 (1) [M - THF]+, 758 (100) [M
- THF - Me]+. IR (KBr, Nujol mull, cm-1): ν˜ ) 1624 (w), 1585
(w), 1521 (s), 1344 (w), 1314 (s), 1260 (s), 1196 (w), 1178 (m), 1099
(s), 1058 (w), 1019 (s), 936 (w), 913 (s), 887 (w), 877 (w), 800 (s),
776 (m), 762 (m), 722 (w), 604 (w), 534 (w), 451 (w).
Cp2Dy(THF)-O-AlL(Me) (3). The procedure is the same as that
described for 1 with Cp3Dy (0.36 g, 1 mmol) instead of the Cp3Yb.
Yield: 0.63 g (75%). Mp: 263-265 °C. Anal. Calcd for C44H62-
AlDyN2O2 (840.44): C, 62.82; H, 7.38; N, 3.33. Found: C, 62.54; H,
7.64; N, 3.23. EI-MS: m/z (%) ) 768 (1) [M - THF]+, 754 (100) [M
- THF - Me]+. IR (KBr, Nujol mull, cm-1): ν˜ ) 1637 (w), 1585
(w), 1521 (s), 1504 (w), 1344 (w), 1321 (w), 1314 (s), 1255 (s), 1196
(w), 1177 (m), 1105 (m), 1958 (w), 1026 (s), 1012 (s), 936 (w), 908
(s), 887 (w), 800 (m), 774 (s), 762 (m), 754 (m), 723 (w), 660 (w),
643 (m), 605 (m), 534 (w), 451 (w).
Cp2Yb-O-AlL(Me) (4). Toluene (40 mL) was added to a mixture
of LAlOH(Me) (0.48 g, 1 mmol) and Cp3Yb (0.37 g, 1 mmol) at room
temperature. The solution slowly turned from dark green to yellow.
The resulting yellow solution was stirred for 12 h, and all the volatiles
were removed in vacuo. Toluene (15 mL) was added, and a clear yellow
solution was obtained. The solution was filtered and kept at -26 °C
for 3 weeks to give yellow crystals. Yield: 0.54 g (69%). Mp: 274-
276 °C. Anal. Calcd for C40H54AlN2OYb (779.14): C, 61.61; H, 6.93;
N, 3.59. Found: C, 61.31; H,7.24; N, 3.53. EI-MS: m/z (%) ) 764
(4) [M - Me]+, 461 (100) [M - Me - Cp2Yb]+. IR (KBr, Nujol mull,
cm-1): ν˜ ) 1658 (w), 1584 (w), 1534 (s), 1348 (m), 1319 (s), 1261
(s), 1182 (m), 1100 (s), 1058 (w), 1021 (s), 939 (w), 889 (s), 798 (s),
773 (s), 722 (w), 664 (w), 645 (w), 626 (m), 534 (w), 451 (w).
Cp3Er(µ-OH)AlL(Me) (5). The procedure is the same as that
described for 2 with toluene instead of THF. Yield: 0.62 g (73%).
[Cp2Yb(µ-OSnMe3)]2 (8). A mixture of 1 (0.85 g, 1 mmol) and
Me3SnF (0.18 g, 1 mmol) was refluxed in toluene until the insoluble
Me3SnF disappeared. All volatiles were removed in vacuo, and toluene
(15 mL) was added and warmed until a clear solution was obtained.
The hot solution was filtered and kept at room temperature to give
yellow crystals of 8. Yield: 0.26 g (53%). Mp: 230 °C (dec). Anal.
Calcd for C26H38O2Sn2Yb2 (966.02): C, 32.30; H, 3.93. Found: C,
32.15; H, 3.64. EI-MS: m/z (%) ) 951 (4) [M - Me]+, 901 (100) [M
- Cp]+. IR (KBr, Nujol mull, cm-1): ν˜ ) 1653 (w), 1624 (w), 1558
(w), 1307 (w), 1264 (m), 1094 (s), 1019 (s), 867 (w), 800 (s), 722 (m),
662 (w), 625 (w), 600 (w), 533 (w), 514 (w), 456 (w). The mother
liquor was dried in vacuo and extracted with hexane (20 mL). The
hexane solution was concentrated and kept at 4 °C to give a colorless
crystalline solid of LAlF(Me) (9). Yield: 0.20 g (41%). Mp: 202-
204 °C. EI-MS: m/z (%) ) 478 (10) [M]+, 463 (100) [M - Me]+. 1H
NMR (200 MHz, C6D6, ppm): δ ) -0.83 (s, 3 H, AlMe), 1.07, 1.18,
3
1.31, 1.45 (d, 4 × 6 H, JHH ) 6.9 Hz, CHMe2), 1.58 (s, 6 H, CH-
3
(CMe)2), 3.18, 3.66 (sept, 2 × 2 H, JHH ) 6.8 Hz, CHMe2), 4.95 (s,
1 H, CH(CMe)2), 7.03-7.16 (m, 6 H, C6H3). 19F NMR (200 MHz,
C6D6, ppm): -149.9. When 4 was used instead of 1, the same products
were obtained with similar yields.
LYbCp(Cl) (10). CpNa (1.0 mL, 2.0 M in THF, 2.0 mmol) was
added to a solution of LYbCl2(THF)2 (1.61 g, 2 mmol) in THF (30
mL) at -78 °C. The mixture was allowed to warm to room temperature
and was stirred for 14 h. All volatiles were removed in vacuo, and the
residue was extracted with toluene (2 × 15 mL). The solution was
concentrated to ca. 15 mL and kept at 4 °C for 48 h to give red crystals.
The crystals were collected by filtration, and the filtrate was concen-
trated and kept at -26 °C for 7 d to give additional crystals. Total
yield: 1.17 g (85%). Mp: 281-283 °C. Anal. Calcd for C34H46ClN2-
Yb (690.52): C, 59.09; H, 6.66; N, 4.06. Found: C, 58.94; H, 6.68;
N, 4.05. EI-MS: m/z (%) ) 691 (14) [M]+, 626 (100) [M - Cp]+. IR
(KBr, Nujol mull, cm-1): ν˜ ) 1633 (w), 1531 (m), 1509 (w), 1435
(w), 1317 (w), 1264 (s), 1173 (w), 1099 (s), 1022 (m), 933 (w), 847
(w), 794 (m), 760 (w), 738 (w), 693 (w), 663 (w).
LYbCp2 (11). The procedure is the same as that for 10 when 2 equiv
of CpNa were used. Total yield: 1.25 g (87%). Mp: 267-269 °C.
Single crystals suitable for X-ray analysis were obtained by recrystal-
lization from hexane. Anal. Calcd for C39H51N2Yb (720.94): C, 64.92;
H, 7.07; N, 3.88. Found: C, 64.94; H, 6.85; N, 4.21. EI-MS: m/z (%)
) 721 (3) [M]+, 656 (100) [M - Cp]+. IR (KBr, Nujol mull, cm-1):
(23) Wilkinson, G.; Birmingham, J. M. J. Am. Chem. Soc. 1956, 78, 42-44.
(24) Krause, E. Ber. Dtsch. Chem. Ges. 1918, 51, 1447-1456.
9
J. AM. CHEM. SOC. VOL. 127, NO. 20, 2005 7527

A R T I C L E S
Chai et al.
ν˜ ) 1653 (w), 1521 (m), 1499 (w), 1310 (w), 1261 (m), 1180 (w),
1166 (w), 1097 (m), 1018 (m), 927 (w), 873 (w), 842 (w), 792 (s),
780 (s), 757 (w), 722 (w), 601 (w), 559 (w).
X-ray Structure Determination. Crystals were mounted on glass
fibers in a rapidly cooled perfluoropolyether. Diffraction data of
structures 1 and 7 were collected on a Bruker three-circle diffractometer
equipped with a SMART 6000 CCD detector using Cu KR radiation
(λ ) 1.54178 Å). Data of structure 4 were collected on a Stoe-
Siemens-Huber four-circle diffractometer, and data of structures 2, 3,
6, 8, 11, and 12 were collected on a Stoe IPDS II-array detector system
using Mo KR radiation (λ ) 0.71073 Å). The structures were solved
by direct methods using the program SHELXS-9725 and refined using
F2 on all data by full-matrix least-squares with SHELXL-97.26 All non-
hydrogen atoms were refined anisotropically. All hydrogen atoms were
included in the model at geometrically calculated positions and refined
with the riding model except those in disordered iPr moieties, solvated
toluene (4) and hexane (11) molecules, where the riding model was
not applied. The coordinated THF molecule in 1-3, one of the Cp
rings in 4, one of the iPr groups and one Cp ring in 6 and 7, and the
hexane molecule in 11 are disordered in two positions and were refined
with geometry and distance restraints and restraints for the anisotropic
displacement parameters. The crystallographic data of the reported
structures are given in Table 1.
LYbN(SiMe3)2Cl (12). THF (30 mL) was added to a mixture of
LYbCl2(THF)2 (0.81 g, 1 mmol) and NaN(SiMe3)2 (0.18 g, 1 mmol)
at 0 °C. The resulting solution was warmed to room temperature and
was stirred for 14 h. All volatiles were removed in vacuo, and the
residue was extracted with hexane (2 × 15 mL). The solution was
concentrated to ca. 15 mL and kept at 4 °C for 24 h to give red crystals.
Yield: 0.38 g (48%). Mp: 250-252 °C. Anal. Calcd for C35H59ClN3-
Si2Yb (786.52): C, 53.40; H, 7.50; N, 5.34. Found: C, 53.65; H, 7.49;
N, 5.21. EI-MS: m/z (%) ) 786 (2) [M]+, 771 (80) [M - Me]+, 625
(100) [M - N(SiMe3)2]+. IR (KBr, Nujol mull, cm-1): ν˜ ) 1624(w),
1552 (w), 1525 (w), 1504 (w), 1314 (w), 1261 (m), 1176 (w), 1099
(w), 1058 (w), 1020 (w), 940 (s), 875 (m), 850 (w), 819 (w), 795 (w),
757 (w), 722 (m), 673 (w), 625 (w), 603 (w), 521 (w), 445 (w).
LYbCl-O-AlL(Me) (13). Toluene (40 mL) was added to a mixture
of LAlOH(Me) (0.24 g, 0.5 mmol) and 12 (0.39 g, 0.5 mmol) at room
temperature. The color of the solution slowly turned from orange-red
to yellow. The solution was stirred for 12 h, and all the volatiles were
removed in vacuo. Toluene (10 mL) was added, and a clear yellow
solution was obtained by filtration. Crystals were obtained after the
solution was kept at 4 °C for 48 h. The crystals were collected by
filtration, and the filtrate was concentrated and kept at -26 °C for 4 d
to give additional crystals. Total yield: 0.40 g (72%). Mp: 270-272
°C. Anal. Calcd for C59H85AlClN4OYb (1100.52): C, 64.33; H, 7.72;
N, 5.09. Found: C, 64.54; H, 7.68; N, 5.23. EI-MS: m/z (%) ) 1086
(100) [M - Me]+. IR (KBr, Nujol mull, cm-1): ν˜ ) 1623 (w), 1538
(m), 1315 (w), 1261 (w), 1173 (w), 1098 (m), 1022 (m), 935 (w), 798
(m), 722 (w), 606 (w).
Acknowledgment. We thank Prof. Michael Buback and Dr.
Sabine Beuermann (Institut fu¨r Physikalische Chemie, Univer-
sita¨t Go¨ttingen) for polymer analyses. The work was supported
by the Deutsche Forschungsgemeinschaft and the Go¨ttinger
Akademie der Wissenschaften. S.S. thanks the Graduiertenkolleg
782 for a fellowship. This article is dedicated to Professor Martin
Jansen.
Supporting Information Available: Plots of structures of
compounds 1-4, 6-8, and 11-13 and two plots comparing
the structures 1-3, 6, and 7 (Figure S1-S12, PDF). Details of
the single-crystal X-ray structure determinations of 1-4, 6-8,
11, and 12 (CIF). This material is available free of charge via
the Internet at http://pubs.acs.org.
Polymerization of E-Caprolactone. In a typical procedure, 0.1 mmol
of catalyst was dissolved in 10 mL of solvent by warming. After the
solution was cooled to room temperature, ꢀ-caprolactone (1.11 mL, 10
mmol) was added with stirring. HCl (2.0 M) was added to the mixture
under N2 after the designated time. The resulting mixture was washed
twice with diluted HCl and twice with H2O. The organic layer was
separated and added to hexane (100 mL) to precipitate the polymer.
The polymer was filtered and dried in vacuo. When THF was used as
solvent, toluene was added to the reaction mixture before washing with
HCl.
JA050521S
(25) Sheldrick, G. M. Acta Crystallogr., Sect. A 1990, 46, 467-473.
(26) Sheldrick, G. M. SHELXL-97, Program for Crystal Structure Refinement;
Universita¨t Go¨ttingen: Go¨ttingen, Germany, 1997.
9
7528 J. AM. CHEM. SOC. VOL. 127, NO. 20, 2005