Lanthanide borohydride complexes with an aryloxide ligand: Synthesis, structural characterization and polymerization activity

Article abstract of DOI:10.1016/j.jorganchem.2006.01.045

Reactions of LnCl₃, NaBH₄ and ArONa (Ar = C₆H₂-t-Bu₃-2,4,6) in a molar ratio of 1:3:1 in THF afforded the aryloxide lanthanide borohydrides of (ArO)Ln(BH₄)₂(THF)₂ (Ln = Yb (1), Er (2)). They were characterized by elemental analysis, infrared spectrum and X-ray crystallography. The two complexes are neutral and isostructural. The lanthanide atom is nine-coordinated by an aryloxide ligand, two borohydride ligands and two THF ligands in a trigonal bipyramidal geometry. Both of the BH₄ ligands in each monomeric complex are η³-coordinated. These complexes displayed moderate high catalytic activities for the polymerization of methyl methacrylate. The polymerization temperature had great influence on the catalysis. At about 0 °C, the catalysts showed the polymerization activity best.

Full text of DOI:10.1016/j.jorganchem.2006.01.045

Journal of Organometallic Chemistry 691 (2006) 2534–2539
www.elsevier.com/locate/jorganchem
Lanthanide borohydride complexes with an aryloxide ligand:
Synthesis, structural characterization and polymerization activity
*
Fugen Yuan , Jing Yang, Lifeng Xiong
Department of Chemistry, University of Science and Technology of Suzhou, Suzhou 215009, China
Received 4 August 2005; received in revised form 22 January 2006; accepted 26 January 2006
Available online 3 March 2006
Abstract
Reactions of LnCl3, NaBH4 and ArONa (Ar = C6H2-t-Bu3-2,4,6) in a molar ratio of 1:3:1 in THF afforded the aryloxide lanthanide
borohydrides of (ArO)Ln(BH4)2(THF)2 (Ln = Yb (1), Er (2)). They were characterized by elemental analysis, infrared spectrum and X-
ray crystallography. The two complexes are neutral and isostructural. The lanthanide atom is nine-coordinated by an aryloxide ligand,
two borohydride ligands and two THF ligands in a trigonal bipyramidal geometry. Both of the BH4 ligands in each monomeric complex
are g3-coordinated. These complexes displayed moderate high catalytic activities for the polymerization of methyl methacrylate. The
polymerization temperature had great influence on the catalysis. At about 0 ꢀC, the catalysts showed the polymerization activity best.
ꢁ 2006 Elsevier B.V. All rights reserved.
Keywords: Aryloxide; Lanthanide; Borohydride; Polymerization
1. Introduction
realm of metallocene complexes promoted us to try the
synthesis of lanthanide borohydrides with aryloxide ligand,
for aryloxide ligands are strongly bonded with lanthanide
elements and can be steric fine tuned by the judicious
choice of the substituents. Aryloxide lanthanide borohy-
drides have not been reported yet [12].
The chemistry of lanthanide borohydrides is an impor-
tant part of organolanthanide chemistry. Although the syn-
thesis of homoleptic Ln(BH4)3 has been known for a long
time [1], the chemistry of lanthanide borohydrides has
remained relatively undeveloped, especially when
compared with that of alkyl [2] and amido [3] lanthanide
complexes. Some lanthanide borohydride complexes have
been synthesized and structurally characterized including
Y(BH4)3(THF)3 [4], [(t-Bu2C5H3)2Ln(BH4)]2 (Ln = Ce [5],
Sm [6]), (CH3OCH2CH2C5H4)2Ln(BH4) (Ln = Y [7], Yb
[7], Pr [8], Nd [8]), (CH3OCH2CH2C9H6)2Ln(BH4) (Ln =
Y, La) [9], [{(C13H8)CPh2(C5H4)}Ln(BH4)2][Li(THF)4]
(Ln = La, Nd) [10], [(COT)Nd(BH4)(THF)]2 (COT =
C8H8) [11] and so on. Most of them were supported by tra-
ditional cyclopentadienyl ligands. Attempt to extend the
lanthanide borohydride chemistry beyond the traditional
Meanwhile, lanthanide borohydrides have seldom been
introduced as polymerization catalysts, and their catalytic
activity for the polymerization has not received much
attention until recently. Guillaume and coworkers reported
the ring-opening polymerization of e-caprolactone by
Ln(BH4)3(THF)3 (Ln = La, Nd, Sm) [13], and studied the
polymerization mechanism with CpꢀSmðBH4ÞðTHFÞ [14].
2
Mountford and coworkers found that methyl methacrylate
(MMA) can be polymerized by lanthanide borohydride
complexes with polydentate diamide–diamide ligand [15].
Very recently, the trans-specific diene polymerization by
Nd(BH4)3(THF)3 in the presence of MgBu2 was also
achieved [16]. These results revealed the promising future
for lanthanide borohydride complexes in catalytic polymer-
ization. It has been well recognized that the coordination
ligand has great influence on the catalytic property of a
complex. Hence the study on the catalytic property of
*
Corresponding author.
E-mail address: yuanbox@szcatv.com.cn (F. Yuan).
0022-328X/$ - see front matter ꢁ 2006 Elsevier B.V. All rights reserved.
doi:10.1016/j.jorganchem.2006.01.045

F. Yuan et al. / Journal of Organometallic Chemistry 691 (2006) 2534–2539
2535
lanthanide borohydride complexes with aryloxide ligand is
interesting and important to understand the relationship
between the property and the ligand.
Because the synthesis of Ln(BH4)3(THF)x has well been
understood [1,4], Ln(BH4)3(THF)x was better prepared
in situ. ‘One pot’ reaction of the slurry of YbCl3 and excess
NaBH4 with an equivalent of ArONa resulted in a red
mixture at once, indicating the reaction proceeding. After
the workup of procedure, red crystals of (ArO)-
Yb(BH4)2(THF)2 (1) were successfully obtained from the
diethyl ether solution. This reaction was also applicable
for Er element. Similar reaction of ErCl3, NaBH4 and
ArONa in a molar ratio of 1:3:1 in THF afforded the anal-
ogous (ArO)Er(BH4)2(THF)2 (2).
Under these consideration, we started to synthesize
aryloxide lanthanide borohydrides and tested their cata-
lytic activities for the polymerization of MMA. We found
that ‘one pot’ reactions of LnCl3, NaBH4 and ArONa
(Ar = C6H2-t-Bu3-2,4,6) in THF in a molar ratio of 1:3:1
in THF could afford the expected complexes (ArO)-
Ln(BH4)2(THF)2 (Ln = Yb (1), Er (2)). Both of the prod-
ucts displayed moderate high catalytic activities for the
polymerization of MMA.
LnCl3 þ 2NaBH4 þ NaOAr
! ðArOÞLnðBH4Þ2ðTHFÞ2 þ 3NaCl ðLn ¼ Ybð1Þ; Erð2ÞÞ
2. Results and discussion
Complexes 1 and 2 are rather sensitive to air and mois-
ture. Diborane gas was found to release when they were
exposed to moisture. However, they are thermally stable
and can be stored under argon at room temperature for
several months without decomposition.
2.1. Synthesis
The reaction of Ln(BH4)3(THF)x with alkali anionic
reagents is a convenient synthetic route to some lanthanide
borohydride complexes. Successful examples include
[(COT)Nd(BH4)(THF)]2 [11], (THF)(BH4)2Nd(l-g7:g7-
C7H7)Nd(BH4)(THF)2 [17], [K(18-crown-6){(C13H8)-
CPh2(C5H4)Nd(BH4)2}]2 Æ C4H8O2 [18] and so on. We wish
to synthesize (ArO)Ln(BH4)2(THF)x similarly by the
reaction of Ln(BH4)3(THF)x with ArONa. Because the
aryloxide ligand has less steric bulk and lower coordination
number than the traditional cyclopentadienyl ligand, the
possible equilibrium between the homoleptic and hetero-
leptic complexes will favor the former. Hence, whether
the desired complexes are stable is still a problem.
Moreover, ate complex was usually obtained [10,18] by this
synthetic route.
2.2. Molecular structures
The solid state structures of complexes 1 and 2 were
determined by the single crystal diffraction analysis. To
understand more about the aryloxide ligand, the molecular
structure of NaOAr was also determined. The single crys-
tals of [(ArO)Na(OEt2)]2 were obtained from the diethyl
ether solution.
The crystal data and details of data collection and struc-
ture refinement of these complexes are listed in Table 1.
Table 2 lists the selected bond distances and angles for 1
Table 1
X-ray crystallographic data
Complex
1
2
[(ArO)Na(OEt2)]2
Formula
Fw
C26H53B2O3Yb
608.34
C26H53B2O3Er
602.56
C44H78Na2O4
717.04
Crystal system
Space group
Monoclinic
c2/c
15.613(3)
13.533(2)
16.076(3)
90
116.640(5)
90
3036.3(10)
193(2)
Monoclinic
c2/c
15.609(2)
13.5691(19)
16.076(3)
90
116.493(3)
90
3047.3(8)
193(2)
Triclinic
ꢀ
P1
˚
a (A)
9.6500(19)
9.768(2)
12.695(3)
102.421(6)
92.529(4)
99.087(6)
1150.1(4)
193(2)
˚
b (A)
˚
c (A)
a (ꢀ)
b (ꢀ)
c (ꢀ)
3
˚
V (A )
T (K)
˚
Wavelength (A)
Z
0.71070
4
1.331
3.101
1252
0.71070
4
1.313
2.775
1244
0.71070
1
1.035
0.080
Dcalc (g/cm3)
l (Mo Ka) (mmꢁ1
F(000)
Dimensions (mm3)
Total reflections
)
396
0.50 · 0.42 · 0.11
14638
0.37 · 0.32 · 0.23
14499
0.61 · 0.39 · 0.20
11457
Unique reflections
Observed reflections
Goodness-of-fit
2778 (Rint 0.0247)
2694
1.077
2785 (Rint 0.0229)
2674
1.114
4196 (Rint 0.0212)
3503
1.074
R, wR (observed data)
R, wR (all data)
0.0367, 0.0915
0.0378, 0.0923
0.0352, 0.0925
0.0365, 0.0937
0.0557, 0.1396
0.0679, 0.1490

2536
F. Yuan et al. / Journal of Organometallic Chemistry 691 (2006) 2534–2539
Table 2
˚
Selected bond lengths (A) and angles (ꢀ) for 1 and 2
1
2
Bond lengths
Ln(1)–O(1)
Ln(1)–O(2)
Ln(1)–B(1)
O(1)–C(1)
2.042(5)
2.338(5)
2.460(10)
1.351(9)
2.056(4)
2.360(4)
2.483(8)
1.371(7)
Bond angles
O(1)–Ln(1)–O(2)
O(1)–Ln(1)–O(2A)
O(1)–Ln(1)–B(1)
O(1)–Ln(1)–B(1A)
O(2)–Ln(1)–O(2A)
O(2)–Ln(1)–B(1)
O(2)–Ln(1)–B(1A)
B(1)–Ln(1)–B(1A)
C(1)–O(1)–Ln(1)
88.53(11)
88.53(10)
123.8(3)
123.8(3)
177.1(2)
92.7(3)
89.0(3)
112.5(7)
180.000(1)
88.30(8)
88.30(8)
123.7(3)
123.7(2)
176.60(16)
92.8(3)
89.0(3)
112.6(5)
180.000(1)
Fig. 1. Molecular structures of (ArO)Ln(BH4)2(THF)2 (Ln = Yb (1), Er
(2)).
and 2. The molecular structures of 1, 2 and [(ArO)-
Na(OEt2)]2 are presented in Figs. 1 and 2, respectively.
Complexes 1 and 2 are isostructural. The lanthanide
atom is coordinated by an aryloxide ligand, two borohy-
dride ligands and two THF molecules in symmetric geom-
etry. Each complex possesses a trigonal bipyramidal
structure, in which two THF ligands (O(2) and O(2A)
atoms) are placed at the apical positions, and two BH4
groups (B(1) and B(1A) atoms) and an aryloxide ligand
(O(1) atom) are laid on the equatorial plane. The three
atoms of O(2)–Ln(1)–O(2A) nearly lie in a line (bond
angles of 177.1(2)ꢀ and 176.60(16)ꢀ, respectively), and the
Ln atom is coplanar with the B(1), B(1A) and O(1) atoms.
Complexes 1 and 2 are monomeric and unfavorable to
form clusters in our experiment. However, it has been
found that lanthanide borohydrides with mono-cyclopen-
tadienyl ligand were inclined to form clusters [19]. This
reflects the great effect of ligand on the structure.
˚
C(1) (1.351(9) and 1.371(7) A, respectively) in 1 and 2
are obviously longer than those in [(ArO)Na(OEt2)]2
˚
(1.324(2) A), and consistent with the corresponding values
˚
in (ArO)2Yb(NPh2)2K(THF)4 (1.350(6) A) [20] and
˚
(ArO)2Sm(N2Ph2)(THF)2 (1.359(7) A) [21].
The most remarkable structural feature of 1 and 2 is the
mode of attachment of the tetrahedral BH4 ligands. The
two boron atoms have the same ligation geometry. Each
of them is attached to the metal center via three bridging
hydrogen atoms. The two g3-BH4 ligands are located at
the neighbor positions, rather than the opposite positions
˚
in Y(BH4)3(THF)3. The Yb–B distances (2.460(10) A, 9
coordinated Yb3+ 1.042 A) in 1 are comparable with the
˚
corresponding Ln-g3-BH4 distances in Y(BH4)3(THF)3
(2.58(1) A, 11 coordinated Y3+ 1.19 A) [4] and
˚
˚
[K(18-crown-6){(C13H8)CPh2(C5H4)Nd(BH4)2}]2 Æ C4H8O2
3+
˚
˚
The aryloxide ligand is monodentate to the lanthanide
metal, different from the bridging coordination fashion in
dimeric [(ArO)Na(OEt2)]2. The bond distances of O(1)–
(2.632(7) A, 12 coordinated Nd 1.27 A) [18], if Shannon’s
˚
ionic radii are taken into account [22]. Allowing 0.02 A for
the difference of ionic radii of Er3+ and Yb3+, the Er–B
˚
Fig. 2. Molecular structure of [(ArO)Na(OEt2)]2. Selected bond distances (A) and angles (ꢀ): Na(1)–O(1) 2.2713(14), Na(1)–O(1A) 2.1815(14), Na(1)–O(2)
2.2816(16), Na(1)–C(1) 3.0038(18), O(1)–C(1) 1.324(2), O(1A)–Na(1)–O(1) 90.35(5), O(1A)–Na(1)–O(2) 149.53(6), O(1A)–Na(1)–C(1) 114.44(5), O(1)–
Na(1)–O(2) 119.93(6), O(1)–Na(1)–C(1) 24.37(4), C(1)–O(1)–Na(1A) 158.16(11), C(1)–O(1)–Na(1) 110.56(10), Na(1)–O(1)–Na(1A) 89.65(5).

F. Yuan et al. / Journal of Organometallic Chemistry 691 (2006) 2534–2539
2537
˚
distances (2.483(8) A) in 2 are comparable with those in 1.
At ꢁ30 ꢀC, the catalysts had no reactivity to the monomers
and could be recovered from the system. We supposed, on
the one hand, the initiation reaction required certain acti-
vation energy. On the other hand, side reactions would
be inevitable at elevated temperature. The two contrary
effects resulted in the occurrence of the optimum tempera-
ture. This phenomenon was quite different from the unique
These Ln–B distances in 1 and 2 are greatly shorter than
the corresponding Ln-g2-BH4 distances in Y(BH4)3(THF)3
(2.68(2) A) and (CH3OCH2CH2C9H6)2Y(BH4) (2.693(8)
˚
˚
A) [9]. The short distances are characteristics of tridentate
BH4 ligands.
In the solid state of [(ArO)Na(OEt2)]2, four atoms of
Na(1)–O(1)–Na(1A)–O(1A) lie in a plane. The Na(1)–
O(1) and Na(1)–O(1A) bonds are inequivalent. The shape
of Na(1)–O(1)–Na(1A)–O(1A) plane is nearly a rectangle.
Two phenyl ring planes are vertical to the Na(1)–O(1)–
Na(1A)–O(1A) plane, but each inclines to a sodium atom.
The Na(1)–C(1) distance is 3.0038(18) A. This distance is
greatly shorter than the sum of van der Waals radii of car-
bon atom (1.85 A) and sodium atom (2.31 A). It means
that Na–C(arene) close interaction exists in the dimeric
complex.
pioneering report of [Sm(N2NNTMS)BH4]2 [N2NNTMS
=
(2-C5H4N)CH2N(CH2CH2NSiMe3)2] [15]. Complex [Sm-
(N2NNTMS)BH4]2 still showed catalytic activity at
ꢁ78 ꢀC. As [Sm(N2NNTMS)BH4]2 contains two Ln–N
active bonds simultaneously [3], we are not clear whether
this reactivity at low temperature comes from the BH4
group. The stereoregularity analysis showed that the
PMMA was mainly syndiotactic (ca. 60%). The content
of isotactic part was about 6%. The tacticity of polymers
varied little as the polymerization temperature and time
changed.
˚
˚
˚
2.3. Polymerization activity
The polymerization character of the Er complex was
similar to that of the Yb complex. Complexes 1 and 2
displayed comparable catalytic activities for the polymeri-
zation of MMA.
Lanthanide borohydride complexes have seldom been
introduced as polymerization catalysts. Although several
recent reports have touched this area, their catalytic activ-
ity for the polymerization has not well been evaluated. We
found that both of 1 and 2 can catalyze the polymerization
of methyl methacrylate in moderate high catalytic activi-
ties. Detailed polymerization results were listed in Table 3.
Although the catalytic activities of 1 and 2 are not good
enough when compared with those of alkyl [2] and amido
[3] lanthanocenes, the catalytic behavior has its own fea-
ture, especially on the effect of polymerization temperature.
For complex 1, as temperature rose from 0 to 25 ꢀC, the
yield of polymer decreased from 60.1% (run 5) to 13.1%
(run 7). It nearly could not catalyze the polymerization at
above 40 ꢀC. However, as temperature decreased below
0 ꢀC, the polymerization activity did not increase any more.
3. Conclusions
We have successfully synthesized the first aryloxide lan-
thanide borohydrides. The structures of (ArO)Ln(BH4)2-
(THF)2 (Ln = Yb (1), Er (2)) were elucidated. We have also
described their catalytic behavior for the polymerization of
MMA. These results reveal that aryloxide ligand has great
influence on the catalytic property of a lanthanide borohy-
dride complex and lanthanide borohydride systems have
considerable scope for development. Further studies on
lanthanide borohydride complexes with other ligands are
in progress and will be reported in due course.
Table 3
Polymerization of MMA by 1 and 2
Run
Catalyst
Temperature (ꢀC)
Time (h)
Yield (%)
Molecular weight (·104)
Tacticity (%)
rr
mr
mm
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
1
1
1
1
1
1
1
1
2
2
2
2
2
2
2
2
ꢁ30
ꢁ10
0
1.0
1.5
0.5
1.0
1.5
2.0
3.0
5.0
1.0
1.5
0.5
1.0
1.5
2.0
3.0
5.0
0
–
–
–
–
47.1
36.7
49.1
60.1
51.3
13.1
5.4
9.80
6.84
6.96
8.34
7.64
–
59.5
60.6
59.4
59.2
60.1
–
33.6
34.0
34.6
34.0
34.1
–
6.9
5.4
6.0
6.8
5.8
–
0
0
10
25
40
ꢁ30
ꢁ10
0
0
0
10
25
40
–
–
–
–
–
–
–
–
0
41.3
32.5
49.2
57.5
50.5
14.3
5.7
9.65
5.08
5.07
6.97
5.06
–
63.4
60.1
60.7
60.0
60.6
–
31.5
34.3
34.3
34.5
33.8
–
5.1
5.6
5.0
5.5
5.6
–
–
–
–
–
Polymerization conditions: n (MMA/Ln) = 200 (mol. ratio), [MMA] = 4.644 mol/L, solvent = toluene.

2538
F. Yuan et al. / Journal of Organometallic Chemistry 691 (2006) 2534–2539
4. Experimental
4.1. General procedure
the x-2h scan technique with Mo Ka radiation
(k = 0.71070 A). All data were corrected for Lorentz and
˚
polarization effect, and the structure was solved by direct
method. The hydrogen atoms were located and refined
from geometric consideration. The non-hydrogen atoms
were refined anisotropically. All calculations were per-
formed using SHELXS-97 and SHELXL-97 program packages
[23].
All manipulations were carried out under an atmosphere
of argon using Schlenk techniques. Tetrahydrofuran
(THF), toluene and diethyl ether (OEt2) were distilled from
sodium/benzophenone ketyl. Sodium 2,4,6-tri-tert-butyl-
phenolate (NaOAr) was prepared from metallic sodium
and 2,4,6-tri-tert-butylphenol (Acros reagent) in THF.
Carbon and hydrogen elemental analyses were carried
out by using an EA1110-CHNSO elemental analyzer. Lan-
thanide metal analysis was carried out by complexometric
titration. Melting point was measured in a sealed Ar-filled
capillary and uncorrected. MMA was dried over CaH2 and
distilled. The molecular weight of polymers was calculated
according to the intrinsic viscosity, determined by a viscos-
ity detector. The microstructure of PMMA was determined
The solution of structure for 2 is similar to that of 1.
Crystallographic details of 1 and 2 are listed in Table 1.
4.5. Polymerization reaction
A flask equipped with a magnetic stirring bar, to which
were added the catalyst and toluene solvent, was then
placed in a thermostatic bath. After some time, the mono-
mer was added into the flask using a syringe. The contents
of the flask were stirred for a determined time. The reaction
was quenched by addition of ethanol containing hydro-
chloric acid. The polymer was washed with ethanol con-
taining acid, dried under vacuum at 45 ꢀC and weighed.
1
by its H NMR spectrum, which was obtained by using a
Unity Inova-400 spectrometer.
4.2. Synthesis of (ArO)Yb(BH4)2(THF)2 (1)
5. Supplementary material
A flask was charged with YbCl3 (0.57 g, 2.04 mmol) and
excess NaBH4 (0.31 g, 8.20 mmol), and THF (about
20 mL) was condensed in. The reaction mixture was stirred
at room temperature for 24 h. To the white slurry of above
mixture was added the THF solution of ArONa (about
3.3 mL, 2.04 mmol) with a syringe. The reaction mixture
became red at once. After being stirred at room tempera-
ture for another 48 h, the mixture was evaporated under
vacuum. The residue was extracted with diethyl ether and
centrifugalized to separate the NaCl and excess NaBH4.
The red clear solution was concentrated and kept at
ꢁ20 ꢀC. Red crystals of 1 (0.41 g, 0.67 mmol, 32.8%) were
produced. M.p.(dec.): 116 ꢀC. Anal. Found: C, 51.12; H,
8.72; Yb, 28.31. Calc. for C26H53B2O3Yb: C, 51.33; H,
8.78; Yb, 28.44%. IR (cmꢁ1): 2958(s), 2382(w), 2294(m),
2228(w), 1635(m), 1436(s), 1364(s), 1236(s), 1161(s),
1124(s), 998(br,m), 810(w).
Crystallographic data for the structural analyses have
been deposited with the Cambridge Crystallographic Data
Center, CCDC No. 260692 for complex 1, CCDC No.
279958 for complex 2 and CCDC No. 260693 for [(ArO)-
Na(OEt2)]2. Copies of these information may be obtained
from The Director, CCDC, 12 Union Road, Cambridge
CB2 1EZ, UK (fax: +44 1223 336033; e-mail: deposit
@ccdc.cam.ac.uk).
Acknowledgements
Financial support from the Qinglan Foundation of
Jiangsu Province (HB 2001-27) and the Foundation of
Educational Commission of Jiangsu Province (04KJD-
560171) is gratefully acknowledged.
References
4.3. Synthesis of (ArO)Er(BH4)2(THF)2(2)
[1] (a) U. Mirsaidov, T.G. Rotenberg, T.N. Dymove, Dokl. Akad.
Nauk. Tadzh. SSR 19 (1976) 30 (Russ); CA 85: 136374n (1976);
(b) E. Zange, Chem. Ber. 93 (1960) 652.
[2] (a) H. Yasuda, E. Ihara, Bull. Chem. Soc. Jpn. 70 (1997) 1745;
(b) H. Yasuda, H. Yamamoto, M. Yamashita, K. Yokota, A.
Nakamura, S. Miyake, Y. Kai, N. Kanehisa, Macromolecules 26
(1993) 7134;
(c) Y. Nakayama, H. Yasuda, J. Organomet. Chem. 689 (2004) 4489.
[3] Q. Shen, Y. Yao, J. Organomet. Chem. 647 (2002) 180.
[4] B.G. Segal, S.J. Lippard, Inorg. Chem. 17 (1978) 844.
[5] E.B. Lobkovsky, Y.K. Gun’ko, B.M. Bulychev, V.K. Belsky, G.L.
Soloveichik, M.Y. Antipin, J. Organomet. Chem. 406 (1991) 343.
[6] Y.K. Gun’ko, B.M. Bulychev, G.L. Soloveichik, V.K. Belsky, J.
Organomet. Chem. 424 (1992) 289.
The procedure followed was similar to that for 1. Com-
plex 2 was obtained as pink crystals in a 28.6% yield.
M.p.(dec.): 181 ꢀC. Anal. Found: C, 51.76; H, 8.82; Er,
27.66. Calc. for C26H53B2O3Er: C, 51.82; H, 8.86; Er,
27.75%. IR (cmꢁ1): 2958(s), 2384(w), 2294(m), 2228(w),
1634(m), 1436(s), 1364(s), 1236(s), 1161(s), 1123(s),
1022(br,m), 810(w), 765(w), 718(w).
4.4. X-ray structure determination for 1 and 2
A red crystal 1 of dimensions 0.50 · 0.42 · 0.11 mm3
was sealed in a thin walled glass capillary under argon
and placed in the cold nitrogen stream of a Rigaku Mer-
cury CCD diffractometer. Data were collected by use of
[7] D. Deng, X. Zheng, C. Qian, S. Jin, Y. Lin, Acta Chim. Sinica 50
(1992) 1024, in Chinese.
[8] D. Deng, X. Zheng, C. Qian, J. Sun, L. Zhang, J. Organomet. Chem.
466 (1994) 95.

F. Yuan et al. / Journal of Organometallic Chemistry 691 (2006) 2534–2539
2539
[9] C. Qian, G. Zou, W. Nie, J. Sun, D.A. Lemenovskii, M.V. Borzov,
Polyhedron 19 (2000) 1955.
[10] C. Qian, W. Nie, J. Sun, J. Chem. Soc., Dalton Trans. (1999) 3283.
[11] S.M. Cendrowski-Guillaume, M. Nierlich, M. Lance, M. Ephritikh-
ine, Organometallics 17 (1998) 786.
[12] In the period of our submission, lanthanide borohydride complexes
supported by diaminobis(phenoxide) ligands for the polymerization
of e-caprolactone and L- and rac-lactide were reported. F. Bonnet,
A.R. Cowley, P. Mountford, Inorg. Chem. 44 (2005) 9046.
[13] (a) S.M. Guillaume, M. Schappacher, A. Soum, Macromolecules 36
(2003) 54;
[16] (a) F. Bonnet, M. Visseaux, A. Pereira, F. Bouyer, D. Barbier-
Baudry, Macromol. Rapid Commun. 25 (2004) 873;
(b) F. Bonnet, M. Visseaux, A. Pereira, D. Barbier-Baudry, Macro-
molecules 38 (2005) 3162.
[17] T. Arliguie, M. Lance, M. Nierlich, M. Ephritikhine, J. Chem. Soc.,
Dalton Trans. (1997) 2501.
[18] C. Qian, W. Nie, J. Sun, J. Organomet. Chem. 626 (2001) 171.
[19] F. Bonnet, M. Visseaux, D. Barbier-Baudry, A. Hafid, E. Vigier,
M.M. Kubicki, Inorg. Chem. 43 (2004) 3682.
[20] F. Yuan, H. Wang, Y. Zhang, Chinese J. Chem. 23 (2005)
409.
(b) I. Palard, A. Soum, S.M. Guillaume, Macromolecules 38 (2005)
6888.
[21] F. Yuan, X. Liu, Appl. Organomet. Chem. 19 (2005)
877.
[14] I. Palard, A. Soum, S.M. Guillaume, Chem. Eur. J. 10 (2004) 4054.
[15] F. Bonnet, A.C. Hillier, A. Collins, S.R. Dubberley, P. Mountford,
Dalton Trans. (2005) 421.
[22] R.D. Shannon, Acta Crystallogr. A 32 (1976) 751.
[23] G.M. Sheldrick, Acta Crystallogr. A 46 (1990) 467;
SHELXTL Version 5.1, Bruker AXS, Inc., Madison, WI, USA.