Synthesis, reactivity and structural characterization of lanthanide hydroxides stabilized by a carbon-bridged bis(phenolate) ligand

Article abstract of DOI:10.1016/j.poly.2008.11.031

The synthesis of lanthanide hydroxo complexes stabilized by a carbon-bridged bis(phenolate) ligand 2,2'-methylene-bis(6-tert-butyl-4-methylphenoxo) (MBMP^2-) was described, and their reactivity toward phenyl isocyanate was explored. Reactions of

Full text of DOI:10.1016/j.poly.2008.11.031

Polyhedron 28 (2009) 574–578
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Polyhedron
journal homepage: www.elsevier.com/locate/poly
Synthesis, reactivity and structural characterization of lanthanide hydroxides
stabilized by a carbon-bridged bis(phenolate) ligand
*
Xiao-Ping Xu, Rui-Peng Qi, Bin Xu, Ying-Ming Yao , Kun Nie, Yong Zhang, Qi Shen
Key Laboratory of Organic Synthesis of Jiangsu Province, College of Chemistry, Chemical Engineering and Materials Science, Dushu Lake Campus, Soochow University,
Suzhou 215123, PR China
a r t i c l e i n f o
a b s t r a c t
Article history:
The synthesis of lanthanide hydroxo complexes stabilized by a carbon-bridged bis(phenolate) ligand 2,2’-
methylene-bis(6-tert-butyl-4-methylphenoxo) (MBMP2À) was described, and their reactivity toward
phenyl isocyanate was explored. Reactions of (MBMP)Ln(C5H5)(THF)2 with a molar equiv. of water in
Received 9 October 2008
Accepted 21 November 2008
Available online 26 December 2008
THF at À78 °C afforded the bis(phenolate) lanthanide hydroxides as dimers [{(MBMP)Ln(
[Ln = Nd (1), Yb (2)] in high yields. Complexes 1 and 2 reacted with phenyl isocyanate in THF, after
2-O2CNHPh)(THF)2]2 [Ln = Nd
l-OH)(THF)2}2]
workup, to give the desired OÀH addition products, [(MBMP)Ln(
l- :g
g1
Keywords:
Lanthanide
Bis(phenolate)
Hydroxide
Isocyanate
Reactivity
(3), Yb (4)] in excellent isolated yields. These complexes were well characterized, and the molecular
structures of complexes 2 to 4 were determined by X-ray crystallography. The ytterbium atom in com-
plex 2 is coordinated to six oxygen atoms to form a distorted octahedral geometry, whereas each metal
center in complexes 3 and 4 is seven-coordinated, and the coordination geometry can be best described
as a distorted pentagonal bipyramid.
Crystal structure
Ó 2008 Elsevier Ltd. All rights reserved.
1. Introduction
only initiate efficiently e-caprolactone polymerization, but also
activate carbodiimide to give lanthanide guanidinate complexes
[18]. During our further study of the reactivity of [(MBMP)Nd{N(Si-
Me3)2}(THF)2] with phenyl isocyanate, an unexpected by-product
Carbon-bridged bis(phenol)s, such as 2,2’-methylene-bis(6-tert-
butyl-4-methylphenol) (MBMPH2) and 2,2’-ethylidene-bis(4,6-di-
tert-butylphenol) (EDBPH2), have been used in transition and main
group metal coordination chemistry for a long time. These ligands
have been found to be able to act as dianionic ligands, which have
the advantage of providing a stereochemically rigid framework for
the metal center that could affect stereospecific transformations.
Meanwhile, some of these transition and main group metal com-
plexes have shown great potential application in homogeneous
catalysis [1–13]. In contrast, the synthesis and reactivity of lantha-
nide complexes stabilized by carbon-bridged bis(phenolate)
groups has seldom been studied.
[{(MBMP)Nd(l- :g
g1 2-O2CNHPh)(THF)2}2] was isolated. The pro-
posed formation mechanism of this complex is that the partial
hydrolysis of bis(phenolate) neodymium amide forms the corre-
sponding neodymium hydroxide first, and then phenyl isocyanate
inserts to the OÀH bond to form the final product as shown in
Scheme 1. Although the lanthanide hydroxides have been known
for a long time, to our best knowledge, there is only one paper
which reported the regioselective transformation of the hydroxo
group of the organolanthanide hydroxides. Zhou et al. recently
reported the reactivity of the lanthanocene hydroxides toward
some small molecules [20]. This promoted us to study the synthe-
sis and reactivity of bis(phenolate) lanthanide hydroxides. Here we
report the results.
Our recent studies have demonstrated that the carbon-bridged
bis(phenolate) lanthanide complexes also have interesting reactiv-
ity [14–19]. For example, the neutral trivalent lanthanide alkoxo
complexes based on these ligand systems can initiate efficiently
the ring-opening polymerization of e-caprolactone in a controlled
2. Results and discussion
manner [15,17]; the neutral and anionic lanthanide amides stabi-
lized by the MBMP2À group can be synthesized in a controlled
2.1. Synthesis and characterization of bis(phenolate) lanthanide
hydroxides
manner using [(MBMP)Ln(l-Cl)(THF)2]2 as the precursors by tun-
ing of the molar ratio of the reagents, and the neutral bis(pheno-
late) lanthanide amides [(MBMP)Ln{N(SiMe3)2}(THF)2] cannot
In order to confirm the above postulation, we intend to synthe-
size the bis(phenolate) lanthanide hydroxides and explore their
reactivity toward phenyl isocyanate. Our previous work has
demonstrated that carbon-bridged bis(phenolate) lanthanide
* Corresponding author. Tel.: +86 512 65882806; fax: +86 512 65880305.
E-mail address: yaoym@suda.edu.cn (Y.-M. Yao).
0277-5387/$ - see front matter Ó 2008 Elsevier Ltd. All rights reserved.
doi:10.1016/j.poly.2008.11.031

X.-P. Xu et al. / Polyhedron 28 (2009) 574–578
575
tBu
NH
tBu
tBu
But
O
THF
Nd
THF
(THF)2
O
PhNCO
O
O
H2O
O
O
O
2
O
O
N(TMS)2
Nd
2
OH
Nd
Nd
O
O
THF
THF
(THF)2
HN
O
tBu
tBu
But
tBu
Scheme 1.
cyclopentadienyl complexes, [(MBMP)Ln(C5H5)(THF)n], are good
precursors for the synthesis of the corresponding lanthanide deriv-
atives via protic exchange reactions and a partial hydrolysis
product was isolated [15,19]. Thus, [(MBMP)Ln(C5H5)(THF)n] were
used as starting materials to synthesize the bis(phenolate)
lanthanide hydroxides by controlled hydrolysis reaction.
[(MBMP)Ln(C5H5)(THF)2] (Ln = Nd, Yb) reacted with distilled water
in THF in a 1:1 molar ratio at À78 °C, the color of the solution chan-
ged gradually from blue to pale blue (for neodymium) or yellow to
pale yellow (for ytterbium). After workup, pale blue (complex 1) or
pale yellow (complex 2) microcrystals were obtained in good iso-
lated yields. Elemental analysis results revealed that these com-
plexes consist of one dianionic bis(phenolate) group (MBMP2À),
one hydroxide, and two coordinated THF molecules at the metal
center. Their IR spectra show the characteristic absorption bands
of hydroxo group at about 3605 cmÀ1, and aromatic rings in the re-
gion 1400–1600 cmÀ1 (skeletal vibrations). Further molecular
structure determination of complex 2 confirmed that they have
remarkable feature of the structure of complex 2 is that there is re-
mote OÀHÁÁÁYb interaction involving the hydroxide hydrogen
atom. The Yb(2)ÀH(5A) bond length of 2.75(4) Å is significantly
longer than the LnÀH bond lengths in most of the organolantha-
nide hydrides [24,25], but it accords with the Lu(1)ÀH(2) of
2.70(5) Å in [{(C5Me4SiMe3)LuH2}4] [25], and Y(1)ÀH(16e) of
t
2.935(6) Å in [(C5Me5)Y(OC6H3 Bu2)CH(SiMe3)2] [26].
2.2. Reactivity with phenyl isocyanate
Reactions of complexes 1 and 2 with phenyl isocyanate in THF,
after workup, gave the desired OÀH addition products, [{(MBMP)
Ln(l- :g
g1 2-O2CNHPh)(THF)2}2] [Ln = Nd (3), Yb (4)] in excellent
isolated yields as shown in Scheme 3. Complexes 3 and 4 were char-
acterized by elemental analysis and IR spectroscopy, and their defin-
itive molecular structures were provided by single-crystal X-ray
diffraction. These reactionsare quite differentfrom those of lanthan-
ocene hydroxides with phenyl isocyanate reported by Zhou et al. and
complexes 3 and 4 can be considered as the proposed intermediate
species (II) in the latter [20]. Attempts to eliminate the NÀH proton
with [(C5H5)3Ln(THF)] as that reported by Zhou were unsuccessful,
and the isolated compound is the starting material. These results re-
vealed that the ancillary ligands have a profound effect on the reac-
tivity of the corresponding lanthanide complexes.
Complexes 3 and 4 are isostructural, and only the molecular
structure of complex 3 is shown in Fig. 2, and their selected bond
lengths and angles are provided in Table 2. Both complexes have sol-
vated C2 symmetric dimeric structures. Two molecules are con-
nected together by two bridged oxygen atoms from carbaminate
groups PhNHCO2, and the eight atoms Nd(1), O(3), C(24), O(4),
Nd(1A), O(3A), C(24A), and O(4A) form an interlinked tricyclic struc-
ture via the two bridged Nd–O bonds [Nd(1)–O(3A) and Nd(1A)–
solvated dimeric structures [{(MBMP)Ln(l-OH)(THF)2}2] [Ln = Nd
(1), Yb (2)] as shown in Scheme 2.
The molecular structure of complex 2 is shown in Fig. 1, and its
selected bond lengths and angles are listed in Table 1. Complex 1
has a dimeric structure, and two molecules are connected together
by two bridged hydroxo groups. The molecule has approximate C2
symmetry. Each ytterbium atom is six-coordinated with two oxy-
gen atoms from one bridged bis(phenolate) group, two oxygen
atoms from two bridged hydroxo groups and two oxygen atoms
from two THF molecules. The coordination geometry at ytterbium
atom can be described as a distorted octahedron, in which O(1),
O(2), O(5) and O(6) can be considered to occupy the equatorial
positions, and O(7) and O(8) to occupy the apical positions, and
the angle of O(7)ÀYbÀO(8) is distorted away from the idealized
180° to 171.9(2)°.
O(3)]. The corn structure is similar to those of [{(CH3C5H4)2Y(
2-S2CNPh2)}2] [27], and [{Cp2Ln(
(Ln = Yb, Er, Y) [20], but different from that of [{(C5Me5)2Sm(
l
-
The average Yb–O(Ar) bond length of 2.085(6) Å falls in the
range of Yb–O(Ar) bond lengths in other carbon-bridged bis(phe-
g1
:g
l
-
g1
:g
2-O2CCHEtPh)}2]
l
-
nolate) ytterbium complexes, such as [{(MBMP)2Yb(
OPri)(THF)2}2] [15], [Li(THF)4][(MBMP)Yb{N(SiMe3)2}2], and
[{(MBMP)Yb(
l-
O2CEPh)}2] [28]. Each central metal atom is seven-coordinated by
two oxygen atoms from one bridged bis(phenolate) ligand, and
one oxygen atom from a PhNHCO2 group, and two oxygen atoms
from another PhNHCO2 group, and two oxygen atoms from two
THF molecules. The coordination geometry around the central metal
atom can be described as a distorted pentagonal bipyramid, in which
O(1), O(5), O(4A), O(3A) and O(3) can be considered to occupy the
equatorial positions with the sum of the bond angles of 360.2° in
complex 3, and 359.7° in complex 4, respectively, and O(2) and
O(6) to occupy the axis positions. The bond angles of O(2)–Ln–
O(6) are slightly distorted away from the ideal value of 180° to
164.6(1)° in complex 3, and 162.8(1)° in complex 4, respectively.
The Nd–O(Ar) bond distances are 2.267(3) and 2.154(4) Å, giving
the average of 2.210(4) Å, which is very close to those observed in re-
l
-Cl)(THF)2}2] [18] [2.059(2)À2.120(3) Å]. The Yb–
O(H) bond lengths range from 2.211(4) to 2.241(4) Å, giving the
average of 2.227(5) Å, which is comparable well with the corre-
sponding bond lengths in [{(MBMP)2Yb(THF)2}2(
OH)] [2.211(4) Å] [15], [{Yb(OC6H3-2,4,6-But3)2(
[2.208(6) Å] [21], [{Yb(OC6H3-2,6-But2)2(
-OH)(THF)}2] [2.217(7)
l
-OCH2Ph)(
l-
l-OH)(THF)}2]
l
Å] [22] and [(Me3SiC5H4)2Yb(l-OH)2] [2.29(2) Å] [23]. The most
tBu
But
H
tBu
THF
THF
THF
O
2 H2O
THF, -78oC
O
O
O
O
Ln
Ln
Ln
2
O
lated neodymium complexes [{(MBMP)2Nd(
l
-OPri)(THF)2}2]
-OiPr)(THF)}2] [2.225(5) Å] [17],
[2.200(2) Å], and [Li(THF)4]
O
O
H
THF
THF
THF
tBu
tBu
[2.215(6) Å] [15], [{(EDBP)Nd(
[(MBMP)Nd{N(TMS)2}(THF)2]
l
But
Ln = Nd (1), Yb (2)
[(MBMP)Nd{N(TMS)2}2] [2.195(3) Å] [18]. The carbaminate group
is asymmetricallycoordinated to the neodymiumatom with the var-
Scheme 2.

576
X.-P. Xu et al. / Polyhedron 28 (2009) 574–578
Fig. 1. ORTEP diagram of complex 2 showing atom-numbering scheme. Thermal ellipsoids are drawn at the 30% probability level. Hydrogen atoms are omitted for clarity.
Table 1
Selected bond distances (Å) and angles (°) for complex 2.
Bond distance
Yb(1)ÀO(1)
Yb(1)ÀO(2)
Yb(1)ÀO(5)
Yb(1)ÀO(6)
O(1)ÀC(1)
O(2)ÀC(7)
2.085(4)
2.088(4)
2.221(4)
2.237(4)
1.344(6)
1.351(6)
Yb(2)ÀO(3)
Yb(2)ÀO(4)
Yb(2)ÀO(5)
Yb(2)ÀO(6)
O(3)ÀC(24)
O(4)ÀC(30)
2.078(4)
2.090(4)
2.241(4)
2.211(4)
1.338(6)
1.340(6)
Bond angle
O(1)ÀYb(1)ÀO(2)
O(2)ÀYb(1)ÀO(6)
O(5)ÀYb(1)ÀO(6)
O(1)ÀYb(1)ÀO(5)
O(8)ÀYb(1)ÀO(7)
97.4(2)
88.8(2)
71.7(1)
102.9(1)
171.9 (2)
O(3)ÀYb(2)ÀO(4)
O(4)ÀYb(2)ÀO(5)
O(5)ÀYb(2)ÀO(6)
O(6)ÀYb(2)ÀO(3)
O(9)ÀYb(2)ÀO(10)
97.8(2)
90.6(2)
71.9(1)
100.8(2)
172.7(1)
iation in Nd–O bond lengths of about 0.07 Å [2.493(3) and
2.563(3) Å, respectively], which is similar to those found in
[{Cp2Ln(l- :g
g1 2-O2CCHEtPh)}2] (Ln = Yb, Er, Y) [20]. The Nd–O(3)
bond length of 2.395(3) Å is comparable with the averaged bridged
Nd–O(Ar) bond length in neodymium bis(phenolate) guanidinate
Fig. 2. ORTEP diagram of complex 3 showing atom-numbering scheme. Thermal
ellipsoids are drawn at the 30% probability level. Hydrogen atoms and carbon atoms
of THF molecules are omitted for clarity. Complex 4 is isostructural with complex 3.
complex [{(l
-O-MBMP)Nd[(iPrN)2CN(TMS)2]}2] (2.401 Å) [18], but
is apparently smaller than the bond lengths of Nd–O(3A) [2.493(3)
Å] and Nd–O(4A) [2.563(3) Å]. The latter compare well with the
bond lengths of Nd–O(THF) [2.458(3) and 2.567(4) Å], which re-
vealed that these bonds are donating bond of neutral oxygen-donor
ligands. It is worthy to note that the bridged Nd–O(3A) bond is short-
er than the terminal Nd–O(4A) bond, which is quite different from
erally, the bridged bond is longer than the terminal one. The shorter
bridged Nd–O bond length in our case might be attributed to the rel-
atively weak electron delocalization within the carbaminate group.
Because the C(24)–O(4) bond length of 1.249(6) Å falls in the range
those in [{Cp2Ln(
l-
g1
:g
2-O2CCHEtPh)}2] (Ln = Yb, Er, Y) [20]. Gen-
N
C
tBu
O
But
NH
But
But
THF
tBu
tBu
H
O
H
O
(THF)2
THF
THF
O
THF
O
O
O
O
O
2PhNCO
THF
O
O
O
O
O
O
Ln
Ln
Ln
Ln
Ln
Ln
O
O
THF
O
THF
tBu
O
THF
tBu
(THF)2
O
H
O
THF
But
O
But
HN
tBu
But
H
C
N
Ln = Nd (3), Yb (4)
Scheme 3.

X.-P. Xu et al. / Polyhedron 28 (2009) 574–578
577
Table 2
Selected bond distances (Å) and angles (°) for complexes 3 and 4.
3
4
3
4
Bond length
Ln(1)ÀO(1)
Ln(1)ÀO(3)
Ln(1)ÀO(4A)
Ln(1)ÀO(6)
O(3)ÀC(24)
2.267(3)
2.395(3)
2.565(3)
2.567(4)
1.307(5)
2.157(3)
2.285(3)
2.421(3)
2.407(4)
1.308(6)
Ln(1)ÀO(2)
Ln(1)ÀO(3A)
Ln(1)ÀO(5)
Ln(1)ÀC(24A)
O(4)ÀC(24)
2.154(4)
2.493(3)
2.458(3)
2.924(5)
1.249(6)
2.068(3)
2.368(3)
2.326(3)
2.780(5)
1.240(6)
Bond angle
O(2)ÀLn(1)ÀO(6)
O(5)ÀLn(1)ÀO(4A)
O(3A)ÀLn(1)ÀO(3)
Ln(1)ÀO(3)ÀLn(1A)
164.6(1)
76.1(1)
64.9(1)
115.2(1)
162.8(1)
76.3(1)
64.5(1)
115.6(1)
O(1)ÀLn(1)ÀO(5)
O(4A)ÀLn(1)ÀO(3A)
O(3)ÀLn(1)ÀO(1)
87.7(1)
51.7(1)
79.8(1)
84.9(1)
54.4(1)
79.6(1)
of C@O double bond and the C(24)–O(3) bond length of 1.307(5) Å
falls in the range of C–O single bond, and the deviation of their bond
distances is apparently larger than the corresponding values found
found in the neutral arene ytterbium complex [Yb(
C6Me6)(AlCl4)3] [2.87(4) Å] [32], which indicating the presence of
g
6-1,3,5-
strong interaction. Similar to that in complex 3, the terminal
p
in [{Cp2Ln(
l-
g1
:g
2-O2CCHEtPh)}2] (Ln = Yb, Er, Y) [20]. There is a
Yb–O(4A) bond is longer than the bridged Yb–O(3A) bond.
strong interaction of the carbon atom of the carbaminate group
p
with the neodymium atom. The NdÀC(24A) bond length of
3. Conclusion
2.924(5) Å is apparently lower than the NdÀC contact observed in
[{(MBMP)Nd(l
-OiPr)(THF)2}2] [3.101(7) Å] [15] and compares well
In summary, the lanthanide hydroxides stabilized by a carbon-
bridged bis(phenolate) ligand were prepared, and their reactivity
toward phenyl isocyanate was explored. The structural properties
of some of these complexes were provided by X-ray diffraction.
Controlled hydrolysis of bis(phenolate) lanthanide cyclopentadi-
enyl complexes in THF at low temperature gave the corresponding
lanthanide hydroxides as dimers. These lanthanide hydroxo com-
plexes reacted with phenyl isocyanate in THF to give the desired
OÀH addition products, which provided an alternative route to
synthesize lanthanide carbaminate complexes. In comparison with
the final products of the reactions of lanthanocene hydroxides with
phenyl isocyanate, theses results revealed that the ancillary ligands
have a profound effect on the reactivity of the corresponding lan-
thanide complexes.
with those observed in the neutral arene neodymium complexes
[Nd(
6-C6H6)(AlCl4)3] [2.933(18) Å] [29], [Nd( 6-C6H5Me)(AlCl4)3]
6-1,3,5-C6H3Me3)(AlCl4)3] [2.916(9) Å]
interaction was considered to exist
g
g
[2.926(5) Å] [30], and [Nd(
[31], in which the NdÀC
unambiguously.
g
p
In complex 4, the average Yb–O(Ar) bond length is 2.112(3) Å,
which accords with those found in the carbon-bridged bis(pheno-
late) lanthanide complexes mentioned above when the difference
in ionic radii is considered. The Yb–O(3) bond distance of
2.285(3) Å is also apparently smaller than the Yb–O(3A) and Yb–
O(4A) bond distances, which revealed the Yb–O(3A) and Yb–
O(4A) bond are donating bond. The Yb–C(24A) bond length of
2.780(5) Å compares well with that in complex 3, when the differ-
ence in ionic radii is considered, but apparently lower than that
4. Experimental
Table 3
4.1. Materials and methods
Details of the crystallographic data and refinements for complexes 2À4.
All of the manipulations described below were performed under
an argon atmosphere, using the standard Schlenk techniques. Sol-
vents were dried and freed of oxygen by refluxing over sodium or
sodium benzophenone ketyl and distilled under argon prior to use.
[(MBMP)Ln(C5H5)(THF)2] were prepared according to the literature
methods [15,19]. The other reagents were purchased from Acros
and used as received without further purification. Metal analyses
were carried out using complexometric titration. Carbon, hydro-
gen, and nitrogen analyses were performed by direct combustion
on a Carlo Erba-1110 instrument; Quoted data are the average of
at least two independent determinations. IR spectra were recorded
on a Nicolet-550 FTIR spectrometer as KBr pellets. The uncorrected
melting points of crystalline samples in sealed capillaries (under
argon) are reported as ranges.
Compound
2 Á 3.5THF
C76H122O13.50Yb2
1597.81
3 Á 2C7H8
C90H120N2Nd2O12
1710.36
193(2)
Monoclinic
P21/n
14.398(2)
17.475(2)
17.148(2)
4 Á 2C7H8
C90H120N2O12Yb2
1767.96
193(2)
Monoclinic
P21/n
14.064(2)
17.228(3)
17.453(3)
Formula
Formula weight
T (K)
Crystal system
Space group
a (Å)
293(2)
Triclinic
ꢀ
P1
13.081(1)
15.570(1)
19.844(2)
85.319(5)
87.009(5)
80.354(4)
3968.0(6)
2
b (Å)
c (Å)
a
(°)
b (°)
102.362(3)
99.842(3)
c
(°)
V (Å3)
4214.4(8)
2
1.348
1.278
1780
4166.7(11)
2
1.409
2.291
1820
Z
Dcalc (g/cmÀ3
)
1.336
2.399
1650
l
(mmÀ1
)
F(000)
Crystal size (mm)
2h range (°)
Reflections
0.80 Â 0.48 Â 0.39 0.50 Â 0.40 Â 0.20 0.60 Â 0.48 Â 0.20
4.2. Synthesis of [{(MBMP)Nd(l-OH)(THF)2}2] (1)
50.7
50.7
50.7
37676
40212
39220
collected
Independent
reflections
Reflections with
I P 2.0r(I)
Parameters refined
GOF
R
A solution of [(MBMP)Nd(C5H5)(THF)2] (1.47 g, 2.13 mmol) in
THF (30 mL) was cooled to À78 °C. The solution was stirred half
an hour, and then a THF solution (30 mL) containing distilled water
(38 mg, 2.13 mmol) was added dropwise. The color of the solution
was changed gradually from blue to pale blue. The mixture was
stirred for 2 h, and then warmed to room temperature and stirred
overnight. Little precipitate was separated by centrifugation, and
the resulting pale blue solution was concentrated to about
14415
11882
7698
6591
7611
6685
829
512
488
1.109
0.0471
0.1033
1.185
0.0546
0.1103
1.145
0.0456
0.0968
wR

578
X.-P. Xu et al. / Polyhedron 28 (2009) 574–578
18 mL. Pale blue microcrystals were obtained at room temperature
in a few days (0.97 g, 71%), m.p.: 176–178 °C (dec). Anal. Calc. for
C62H94Nd2O10: C, 57.82; H, 7.36; Nd, 22.40. Found: C, 57.58; H,
7.81; Nd, 22.66%. IR (KBr pellet, cmÀ1): 3607(m), 3385(m),
2955(s), 2913(m), 1605(m), 1461(s), 1433(s), 1350(m), 1212(s),
1158(s), 867(w), 729(w).
atoms were held stationary and included in the structure factor
calculation in the final stage of full-matrix least-squares refine-
ment. The structures were solved and refined using SHELEXL-97
programs.
Acknowledgement
4.3. Synthesis of [{(MBMP)Yb(
l
-OH)(THF)2}2] (2)
Financial support from the National Natural Science Foundation
of China (Grants 20632040 and 20771078), the Natural Science
Foundation of Jiangsu province (BK2007505), the Major Basic Re-
search Project of the Natural Science Foundation of the Jiangsu
Higher Education Institutions (07KJA15014), and Key Laboratory
of Organic Synthesis of Jiangsu Province is gratefully
acknowledged.
The synthesis of complex 2 was carried out in the same way as
that described for complex 1, but [(MBMP)Yb(C5H5)(THF)2] (1.34 g,
1.86 mmol) was used instead of [(MBMP)Nd(C5H5)(THF)2]. Pale
yellow microcrystals were obtained at room temperature in a
few days (0.75 g, 60%), m.p.: 180–182 °C (dec). Anal. Calc. for
C62H94O10Yb2: C, 55.35; H, 7.04; Yb, 25.72. Found: C, 55.60; H,
7.10; Yb, 25.42%. IR (KBr, cmÀ1): 3605(m), 3389(m), 2956(s),
2916(m), 1605(m), 1464(s), 1434(s), 1353(m), 1213(s), 1156(s),
864(w), 728(w). The crystals suitable for an X-ray crystal structure
determination were obtained in THF solution at room temperature.
Appendix A. Supplementary data
CCDC 700053, 700054 and 700055 contain the supplementary
crystallographic data for complexes 2À4. These data can be ob-
tained free of charge via http://www.ccdc.cam.ac.uk/conts/retriev-
ing.html, or from the Cambridge Crystallographic Data Centre, 12
Union Road, Cambridge CB2 1EZ, UK; fax: (+44) 1223 336 033; or
e-mail: deposit@ccdc.cam.ac.uk. Supplementary data associated
with this article can be found, in the online version, at
doi:10.1016/j.poly.2008.11.031.
4.4. Synthesis of [{(MBMP)Nd(l- :g
g1 2-O2CNHPh)(THF)2}2] (3)
A Schlenk flask was charged with complex 1 (0.77 g, 0.60 mmol)
and THF (30 mL). Phenyl isocyanate (PhNCO) (0.65 mL, 1.20 mmol)
was added by syringe. The reaction mixture was stirred overnight
at room temperature. After removed the volatiles under reduced
pressure, the pale blue residue was washed with cooled THF twice.
The pale blue powder was dried at room temperature (0.77 g, 84%),
m.p.: 218–220 °C (dec). Anal. Calc. for C76H104N2Nd2O12: C, 59.81;
H, 6.87; N, 1.83; Nd, 18.90. Found: C, 59.41; H, 6.42; N, 1.95; Nd,
19.11%. IR (KBr, cmÀ1): 3346(w), 2953(m), 2904(m), 1616(s),
1590(s), 1538(vs), 1445(s), 1337(m), 1298(s), 1239(m), 1024(m),
864(m), 779(m). The crystals suitable for an X-ray crystal structure
determination were obtained by recrystallization from THF-tolu-
ene solution at room temperature.
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The synthesis of complex 4 was carried out in the same way as
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