Synthesis and characterization of lanthanide complexes bearing a ferrocene-containing N-aryloxo-β-ketoiminate ligand

Article abstract of DOI:10.1016/j.jorganchem.2010.07.037

A series of organolanthanide complexes supported by a new ferrocene-containing N-aryloxo-functionalized β-ketoiminate ligand FcCOCH₂C(Me)N(2-HO-5-Me-C₆H₃) (LH₂, Fc = ferrocenyl) was synthesized by amine eliminat

Full text of DOI:10.1016/j.jorganchem.2010.07.037

Journal of Organometallic Chemistry 695 (2010) 2726e2731
Contents lists available at ScienceDirect
Journal of Organometallic Chemistry
journal homepage: www.elsevier.com/locate/jorganchem
Synthesis and characterization of lanthanide complexes bearing
a ferrocene-containing N-aryloxo-
b-ketoiminate ligand
*
Xiang-Yong Gu, Xiang-Zong Han, Ying-Ming Yao , Yong Zhang, Qi Shen
Key Laboratory of Organic Synthesis of Jiangsu Province, College of Chemistry, Chemical Engineering & 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:
A series of organolanthanide complexes supported by a new ferrocene-containing N-aryloxo-function-
Received 30 April 2010
Received in revised form
20 July 2010
Accepted 30 July 2010
Available online 7 August 2010
alized
by amine elimination reactions. It was found that the ionic radii have a profound effect on the outcome of
the reactions. Reactions of LH2 with Ln[N(SiMe3)2]3( -Cl)Li(THF)3 in a 1:1 molar ratio in THF gave the
desired lanthanide amido complexes [LLn{N(SiMe3)2}(THF)]2 [Ln ¼ Nd (1), Sm (2), Er (3), Yb (4), Y (5)] in
good isolated yields, whereas the similar reaction of LH2 with La[N(SiMe3)2]3( -Cl)Li(THF)3 gave the
b
-ketoiminate ligand FcCOCH2C(Me)N(2-HO-5-Me-C6H3) (LH2, Fc ¼ ferrocenyl) was synthesized
m
m
unexpected lanthanumelithium heterobimetallic cluster [L2La{m-Li(THF)}2(m-Cl)]2 (6). These complexes
Keywords:
Organolanthanides
were characterized by IR spectroscopy, elemental analysis, and 1H NMR spectroscopy in the case of
complexes 5 and 6. The definitive molecular structures of complexes 1, 2, 4 and 6 were determined by
X-ray diffraction studies. Complexes 1e5 can initiate the ring-opening polymerization of L-lactide with
b-Ketoiminate ligand
Synthesis
moderate activity.
Crystal structure
Polymerization
L-Lactide
Ó 2010 Elsevier B.V. All rights reserved.
1. Introduction
in organolanthanide chemistry, and only a few lanthanide
complexes stabilized by
b-ketoiminate ligands have been
Over the past decades, significant efforts to explore ligands
other than the traditional ancillary ligand bis(cyclopentadienyl)
set in organometallic lanthanide chemistry have led to the
fruitful design of new non-cyclopentadienyl ligand systems to
stabilize a series of organolanthanide complexes [1e3]. Of these
new alternatives, nitrogen-containing ligands, such as guanidi-
reported [12e14].
Recently, we became interested in studying the synthesis and
reactivity of organolanthanide complexes supported by N-aryloxo-
functionalized b-ketoiminate ligands. In our earlier work, a series of
new lanthanide chlorides and aryloxides based on this ligand were
synthesized and it was found that the corresponding lanthanide
aryloxides are active initiators for the ring-opening polymerization
nate, amidinate [4], b-diketiminate [5] and bridged bisamide [6]
ligands have received much attention, because their electronic
of
L-lactide [15]. These results indicated that the dianionic func-
properties and steric bulkiness can be easily modified by vari-
tionalized
b
-ketoiminate ligands might have potential in the design
ation of the substituents on the nitrogen atoms.
b
-Ketoiminate
and synthesis of organolanthanide catalysts for homogeneous
catalysis. However, the catalytic activity of these lanthanide
complexes is relatively low in comparison with other organo-
lanthanide initiators, which was attributed to the formation of
stable dimeric structures via the bridging phenoxo oxygen atoms.
So we intend to introduce a bulky substituent to the ligand, and try
to synthesize monomeric organolanthaide complexes. In this
contribution, a new ferrocene-containing N-aryloxo-functionalized
ligand, as one kind of nitrogen-containing ligands, have become
among the most attractive chelating systems in main group and
transition metal coordination chemistry. These metal complexes
have been used in various applications, such as precursors for
metaleorganic chemical vapor deposition (MOCVD) for the
growth of thin films [7], and as active catalysts in homogeneous
catalysis [8e11]. However, these ligands have seldom been used
b-ketoiminate ligand FcCOCH2C(Me)N(2-HO-5-Me-C6H3) (LH2,
Fc ¼ ferrocenyl) was synthesized, and some organolanthanide
complexes stabilized by this ligand were prepared via amine
elimination reactions. It was found that the ionic radii have
a profound effect on the outcome of the reactions. Here we report
these results.
* Corresponding author. Soochow University, College of Chemistry, Chemical
Engineering & Materials Science, Dushu Lake Campus, Suzhou, 215123, PR China.
Tel.: þ86 512 65882806; fax: þ86 512 65880305.
E-mail address: yaoym@suda.edu.cn (Y.-M. Yao).
0022-328X/$ e see front matter Ó 2010 Elsevier B.V. All rights reserved.
doi:10.1016/j.jorganchem.2010.07.037

X.-Y. Gu et al. / Journal of Organometallic Chemistry 695 (2010) 2726e2731
2727
2. Experimental Section
O
HO
HO
O
O
O
OEt
H2N
N
O
The complexes described below are extremely sensitive to air
and moisture. Therefore, all manipulations were performed under
pure argon with rigorous exclusion of air and moisture using
Schlenk techniques. Solvents were dried and freed of oxygen
by refluxing over sodium/benzophenone ketyl and distilled prior
Fc
Na, THF
Fc
p-TsOH, EtOH
Fc
Scheme 1.
11.76 (s,1H, PhOH). 13C NMR (400 MHz, CDCl3, 25 ꢀC) 193.06,162.07,
149.87, 129.33, 128.75, 127.92, 125.36, 116.72, 82.12, 70.96, 69.88,
68.59, 20.41, 20.07. IR (KBr, cmꢁ1): 3411 (s), 3036 (s), 2346 (s), 1591
(s), 1528 (s), 1387 (s), 1289 (s), 1250 (s), 1196 (s), 1057 (m), 887 (m),
803 (s), 679 (m), 567 (w).
to use. Ferrocenoylacetone [16] and Ln[N(TMS)2]3(
(Ln ¼ La, Nd, Sm, Er, Yb, Y) [17] were prepared according to the
literature procedures. -Lactide was purchased from Arcos, and was
m-Cl)Li(THF)3
L
recrystallized from hot anhydrous toluene twice. The uncorrected
melting points of crystalline samples in sealed capillaries (under
argon) are reported as ranges. Lanthanide metal analyses were
performed by EDTA titration with a xylenol orange indicator and
a hexamine buffer [18]. Carbon, hydrogen and nitrogen analyses
were performed by direct combustion with a Carlo-Erba EA-1110
instrument. The IR spectra were recorded with a Nicolet-550 FT-IR
spectrometer as KBr pellets. The 1H NMR spectra were recorded in
C6D6 solution for the yttrium and lanthanum complexes and in
CDCl3 solution for the ligand with a Unity Varian-400 spectrometer.
Molecular weight and molecular weight distribution (PDI) were
determined against polystyrene standards by gel permeation
chromatography (GPC) on a PL 50 apparatus, and THF was used as
an eluent at a flow rate of 1.0 mL/min at 40 ꢀC.
2.2. Synthesis of [LNd{N(SiMe3)2}(THF)]2 (1)
A
THF solution (20 mL) of Nd[N(TMS)2]3(m-Cl)Li(THF)3
(1.05 mmol) was added to a THF solution (20 mL) of LH2 (0.40 g,
1.05 mmol). The mixture was stirred at room temperature for
20 min, and precipitate formed gradually. The mixture was stirred
overnight, and then the precipitate was separated from the solution
by centrifugation. The powder was dissolved with hot THF, and red
crystals were obtained from a concentrated THF solution (20 mL) at
room temperature (0.66 g, 84%). Mp: 192e194 ꢀC (dec). Anal. Calc.
for C62H90Fe2N4Nd2O6Si4: C, 49.65; H, 6.05; N, 3.73; Nd, 19.23.
Found: C, 49.27; H, 5.85; N, 4.04; Nd, 19.41. IR (KBr, cmꢁ1): 2954 (s),
1595 (s), 1496 (s), 1409 (s), 1352 (s), 1276 (s), 1126 (m),1019 (m), 934
(s), 835 (s), 762 (w), 682 (m), 626 (m), 525 (w). Crystals suitable for
an X-ray structure analysis were obtained from a concentrated THF
solution.
2.1. Synthesis of LH2
To a solution of ferrocenoylacetone (27.0 g, 0.10 mol) in absolute
ethanol (60 mL) was added 2-amino-4-methyl-phenol (12.3 g, 0.l0
mol) in absolute ethanol (30 mL) dropwise at room temperature.
After stirring in oil bath and refluxing for 2 h, the mixture was
concentrated to about 25 mL under reduced pressure. Ligand LH2
was obtained as redeyellow block crystals by filtration in the next
day (26.3 g, 70%). Mp: 190e191 ꢀC (dec). Anal. Calc. for
C21H21FeNO2: C, 67.22; H, 5.64; N, 3.73. Found: C, 67.11; H, 5.51; N,
4.12. 1H NMR (400 MHz, CDCl3, 25 ꢀC) 1.78 (s, 3H, CH3C]N), 2.26
(s, 3H, CH3 (arene)), 4.20 (s, 5H, C5H5), 4.40 (s, 2H, (H3, H4), C5H4),
4.74 (s, 2H, (H2, H5), C5H4), 5.40 (s, 1H, CH), 6.90e7.26 (m, 3H, Ar),
2.3. Synthesis of [LSm{N(SiMe3)2}(THF)]2 (2)
The synthesis of complex 2 was carried out in the same way as
that described for complex 1, but Sm[N(TMS)2]3(
(1.30 mmol) was used instead of Nd[N(TMS)2]3( -Cl)Li(THF)3. Red
microcrystals were obtained from a concentrated THF solution at
room temperature (0.78 g, 80%). Mp: 197e199 ꢀC (dec). Anal. Calc.
for C62H90Fe2N4O6Si4Sm2: C, 49.25; H, 6.00; N, 3.70; Sm, 19.89.
m-Cl)Li(THF)3
m
Table 1
Crystallographic data for complexes 1, 2, 4 and 6.
complex
1$2THF
2$2THF
4$2THF
6$3THF
formula
fw
C70H106Fe2N4Nd2O8Si4
1644.13
C70H106Fe2N4O8Si4Sm2
1656.35
C70H106Fe2N4O8Si4Yb2
1701.73
C112H132Cl2Fe4La2Li4N4O15
2374.10
T(K)
223(2)
223(2)
293(2)
223(2)
crystal system
crystal size (mm)
space group
a (Å)
b (Å)
c (Å)
triclinic
triclinic
triclinic
monoclinic
0.40 ꢂ 0.20 ꢂ 0.15
P21/n
15.769(4)
22.348(6)
0.39 ꢂ 0.38 ꢂ 0.25
0.22 ꢂ 0.18 ꢂ 0.15
0.50 ꢂ 0.40 ꢂ 0.40
ꢀ
Pı
ꢀ
Pı
ꢀ
Pı
11.7480(16)
13.4189(17)
14.5079(16)
62.470(10)
74.232(13)
77.916(14)
1942.4(4)
1
1.406
1.793
846
25.35
18838
7062
6101
382
1.123
0.0578
0.1310
1.557, e0.859
11.6026(7)
13.2790(7)
14.4908(7)
117.246(8)
94.317(11)
102.320(12)
1900.35(17)
1
1.447
2.012
850
25.50
16497
7031
6170
377
1.149
0.0661
0.1488
1.589, e0.944
11.4609(3)
13.2300(2)
14.3545(2)
116.805(3)
93.870(4)
102.546(4)
1861.77(6)
1
1.518
2.988
866
25.50
15145
6881
6506
377
1.070
0.0387
0.1008
2.194, e1.286
17.340(5)
a
b
g
(deg)
(deg)
(deg)
112.279(4)
V (Å3)
5655(3)
2
1.394
1.346
2432
25.50
19581
10337
7867
Z
Dcalcd (Mg mꢁ3
)
m
(mmꢁ1
)
F(000)
qmax (deg)
collected reflns
unique reflns
obsd reflns [I > 2.0
no. of variables
GOF
s
(I)]
597
1.153
0.0839
0.1936
2.144, e1.216
R
wR
largest diff peak, hole (e.Åꢁ3
)

2728
X.-Y. Gu et al. / Journal of Organometallic Chemistry 695 (2010) 2726e2731
Scheme 2.
Found: C, 49.54; H, 6.21; N, 3.78. Sm, 19.62. IR (KBr, cmꢁ1): 2955 (s),
1590 (s),1497 (s),1400 (s),1349 (s),1270 (s),1127 (m),1021 (m), 933
(s), 850 (s), 756 (w), 680 (m), 527 (w). Crystals suitable for an X-ray
structure analysis were obtained from a concentrated THF solution.
room temperature (0.60 g, 72%). Mp: 196e198 ꢀC (dec). Anal. Calc.
for C62H90Fe2N4O6Si4Y2: C, 53.90; H, 7.78; N, 4.03; Y, 12.97. Found:
C, 54.25; H, 7.52; N, 3.86; Y, 12.52. 1H NMR (400 MHz, C6D6, 25 ꢀC):
0.15 (s, 36H, Si(CH3)3),1.33 (s, 8H, CH2 of THF),1.73 (s, 6H, CH3C]N),
2.20 (s, 6H, CH3 (arene)), 3.80 (s, 8H, CH2O of THF), 4.20e4.70 (m,
18H, Cp), 5.60 (s, 2H, CH), 7.12e7.30 (m, 6H, Ar). IR (KBr, cmꢁ1):
2952 (s),1592 (s),1488 (s),1413 (s),1336 (s),1264 (s),1120 (m),1020
(m), 931 (s), 853 (s), 759 (w), 668 (m), 522 (w).
2.4. Synthesis of [LEr{N(SiMe3)2}(THF)]2 (3)
The synthesis of complex 3 was carried out in the same way as
that described for complex 1, but Er[N(TMS)2]3(
m-Cl)Li(THF)3
(1.22 mmol) was used instead of Nd[N(TMS)2]3( -Cl)Li(THF)3. Red
m
2.7. Synthesis of [L2La{m-Li(THF)}2(m-Cl)]2 (6)
microcrystals were obtained from a concentrated THF solution at
room temperature (0.71 g, 75%). Mp: 198e200 ꢀC (dec). Anal. Calc.
for C62H90Er2Fe2N4O6Si4: C, 48.17; H, 5.87; N, 3.62; Er, 21.64. Found:
C, 47.94; H, 5.51; N, 3.34; Er, 21.27. IR (KBr, cmꢁ1): 2950 (s), 1578 (s),
1485 (s), 1421 (s), 1362 (s), 1271 (s), 1124 (m), 1018 (m), 943 (s), 848
(s), 753 (w), 677 (m), 527 (w).
The synthesis of complex 6 was carried out in the same way as
that described for complex 1, but La[N(TMS)2]3( -Cl)Li(THF)3
(1.13 mmol) was used instead of Nd[N(TMS)2]3( -Cl)Li(THF)3. Red
m
m
microcrystals were obtained from a concentrated THF solution at
room temperature (0.38 g, 31%). Mp: 210 212 ꢀC (dec). Anal. Calc. for
C100H108Cl2Fe4La2Li4N4O12: C, 55.66; H, 5.04; N, 2.60; La, 12.88.
Found: C, 56.01; H, 5.06; N, 2.73; La, 13.13. 1H NMR (400 MHz, C6D6,
25 ꢀC): 1.38 (s, 16H, CH2 of THF), 1.70 (s, 12H, CH3C]N), 2.15 (s, 12H,
CH3 (arene)), 3.54 (s, 16H, CH2O of THF), 3.92e4.14 (m, 36H, Cp),
5.20 (s, 4H, CH), 7.06e7.20 (m, 12H, Ar). IR (KBr, cmꢁ1): 2975 (m),
1739 (s), 1548 (s), 1428 (s), 1358 (s), 1275 (s), 1208 (m), 1121 (m),
1022 (m), 922 (w), 798 (w), 669 (m), 487 (m), 437 (s). Crystals
suitable for an X-ray structure analysis were obtained from
a concentrated THF solution.
2.5. Synthesis of [LYb{N(SiMe3)2}(THF)]2 (4)
The synthesis of complex 4 was carried out in the same way as
that described for complex 1, but Yb[N(TMS)2]3(
m-Cl)Li(THF)3
(1.17 mmol) was used instead of Nd[N(TMS)2]3( -Cl)Li(THF)3. Red
m
microcrystals were obtained from a concentrated THF solution at
room temperature (0.64 g, 70%). Mp: 193e195 ꢀC (dec). Anal. Calc.
for C62H90N4O6Si4Fe2Yb2: C, 47.81; H, 5.82; N, 3.60; Yb, 22.22.
Found: C, 47.44; H, 5.41; N, 3.78; Yb, 22.40. IR (KBr, cmꢁ1): 2954 (s),
1594 (s), 1499 (s), 1412 (s), 1349 (s), 1266 (s), 1129 (m), 1017 (m), 934
(s), 840 (s), 765 (w), 665 (m), 599 (m), 521 (w). Crystals suitable for
an X-ray structure analysis were obtained from a concentrated THF
solution.
2.8. X-ray crystallography
Suitable single-crystals of complexes 1, 2, 4, and 6 were sealed in
a thin-walled glass capillary for determining the single-crystal
2.6. Synthesis of [LY{N(SiMe3)2}(THF)]2 (5)
The synthesis of complex 5 was carried out in the same way as
that described for complex 1, but Y[N(TMS)2]3(
m-Cl)Li(THF)3
(1.20 mmol) was used instead of Nd[N(TMS)2]3( -Cl)Li(THF)3. Red
m
microcrystals were obtained from a concentrated THF solution at
Fig. 1. ORTEP diagram of complex
1 showing atom-numbering scheme. Thermal
ellipsoids are drawn at the 20% probability level. Hydrogen atoms are omitted for
clarity.
Scheme 3.

X.-Y. Gu et al. / Journal of Organometallic Chemistry 695 (2010) 2726e2731
2729
Fig. 2. ORTEP diagram of complex 2 showing atom-numbering scheme. Thermal
ellipsoids are drawn at the 20% probability level. Hydrogen atoms are omitted for
clarity.
Fig. 3. ORTEP diagram of complex
4
showing atom-numbering scheme. Thermal
ellipsoids are drawn at the 20% probability level. Hydrogen atoms are omitted for
clarity.
structures. Intensity data were collected with a Rigaku Mercury
CCD area detector in
u scan mode using Mo Ka radiation
the N-aryloxo-functionalized b-ketoimine FcCOCH2C(Me)N(2-HO-
(l
¼ 0.71070 Å). The diffracted intensities were corrected for
5-Me-C6H3) (LH2, Fc ¼ ferrocenyl) in a high isolated yield, as shown
in Scheme 1, which was identified by elemental analysis and 1H
NMR spectroscopy.
Lorentz polarization effects and empirical absorption corrections.
Details of the intensity data collection and crystal data are given in
Table 1.
It was found that amine elimination reactions of lanthanide
amides with 1 equivalent of LH2 in THF is a convenient method for
the synthesis of lanthanide amides stabilized by the N-aryloxo-
The structures were solved by direct methods and refined by
full-matrix least-squares procedures based on jFj . All the non-
2
hydrogen atoms were refined anisotropically. The hydrogen atoms
in these complexes were all generated geometrically, assigned
appropriate isotropic thermal parameters, and allowed to ride on
their parent carbon atoms. All the H atoms were held stationary
and included in the structure factor calculation in the final stage of
full-matrix least-squares refinement. The structures were solved
and refined using SHELEXL-97.
functionalized
b-ketoiminate ligand. When a THF solution of Ln[N
(TMS)2]3( -Cl)Li(THF)3 was added to a suspension of LH2 in THF in
m
a 1:1 molar ratio at room temperature, the color of the solution
changed to dark-red, and precipitate formed gradually. After
workup, microcrystals of the final products [LLnN(SiMe3)2(THF)]2
[Ln ¼ Nd (1), Sm (2), Er (3), Yb (4), Y (5)] were obtained in 70e84%
isolated yields as summarized in Scheme 2.
The compositions of complexes 1e5 were established by
elemental analysis, 1H NMR spectroscopy in the case of complex 5
and molecular structure determination of complexes 1, 2, and 4. All
of these complexes are extremely sensitive to air and moisture. The
crystals turn to powder immediately when they are exposed to air.
2.9. Polymerization of
L-lactide
The procedures for the polymerization of
L
-lactide initiated by
complexes 1ꢁ5 were similar, and a typical polymerization proce-
dure is given below. A 50 mL Schlenk flask, equipped with
a magnetic stirring bar, was charged with the desired amount of
lactide and toluene. The contents of the flask were then stirred at
70 ꢀC until the
-lactide was dissolved, and then a solution of the
initiator in toluene was added to this solution by syringe. The
mixture was stirred vigorously at 70 ꢀC for the desired time, during
which time an increase in the viscosity was observed. The reaction
mixture was quenched by the addition of methanol and then
poured into methanol to precipitate the polymer, which was dried
under vacuum and weighed.
L-
Table 2
Selected bond lengths (Å) and bond angles (ꢀ) for complexes 1, 2, and 4.
L
complex
1
2
4
Bond length
Ln(1)eO(1)
Ln(1)eO(2)
Ln(1)eO(2A)
Ln(1)eO(3)
Ln(1)eN(1)
Ln(1)eN(2)
2.271(4)
2.381(4)
2.372(4)
2.542(5)
2.515(5)
2.337(5)
2.235(4)
2.357(5)
2.328(5)
2.501(6)
2.481(6)
2.320(5)
2.158(3)
2.267(3)
2.243(3)
2.402(3)
2.384(4)
2.226(4)
Bond angle
3. Results and discussion
N(1)eLn(1)eO(2)
O(2)eLn(1)eO(2A)
O(2A)eLn(1)eO(3)
O(3)eLn(1)eN(1)
N(2)eLn(1)eO(1)
O(1)eLn(1)eN(1)
66.25(15)
67.63(16)
81.25(16)
67.09(17)
67.4(2)
81.07(18)
69.02(12)
68.28(13)
80.28(12)
Ferrocenoylacetone was prepared by the reaction of ace-
tylferrocene with ethyl acetate according to the literature method
[16]. The reaction of ferrocenoylacetone with 1 equivalent of 2-
amino-4-methyl-phenol in absolute ethanol, after workup, gave
148.44(16)
125.98(17)
74.02(15)
149.26(18)
125.62(19)
75.06(18)
149.87(13)
124.60(14)
77.62(12)

2730
X.-Y. Gu et al. / Journal of Organometallic Chemistry 695 (2010) 2726e2731
Fig. 4. ORTEP diagram of complex 6 showing atom-numbering scheme. Thermal ellipsoids are drawn at the 20% probability level. Hydrogen atoms are omitted for clarity.
All of these complexes are soluble in THF, and slightly soluble in
DME and toluene.
from one THF molecule, and one oxygen atom from another
-ketoiminate ligand. Each of the metal centers has a highly dis-
torted octahedral coordination geometry, which is similar to those
observed in -ketoiminate rare-earth metal aryloxides [15].
In complex 1, the terminal NdeO(alkoxo) bond length of 2.271
(4) Å compares well with the corresponding bond length in
b
However, reaction of LH2 with La[N(TMS)2]3(
a 1:1 molar ratio in THF at room temperature, after workup, gave
the unexpected lanthanum-lithium bimetallic cluster [L2La{ -Li
(THF)}2( -Cl)]2 (6), instead of the desired lanthanum amido
m-Cl)Li(THF)3 in
b
m
m
complex [LLaN(SiMe3)2(THF)]2 as shown in Scheme 3, which was
characterized by elemental analysis, IR spectroscopy and crystal
structure determination. The difference in the outcome of the
amine elimination reactions is supposed to reflect the difference in
the ionic radii of the lanthanide metals.
The molecular structures of complexes 1, 2, and 4 are shown in
Figs.1e3, and their selected bond lengths and bond angles are listed
in Table 2. These complexes are isomorphous, and have centro-
symmetric dimeric structures containing an Ln2O2 core. These
lanthanide amido complexes possess bridging phenoxo oxygen
atoms, which is similar to those found in the N-aryloxo-function-
neodymium
(L’
b
-ketoiminate complex [L’Nd(OAr)(THF)]2 (2.260(5) Å)
¼
OC(Me)CHC(Me)N(2eOe5eMeeC6H3), ArO
¼
Oe2,6e
But2e4eMeeC6H3) [15], but slightly smaller than that in Nd2[{OC
(But)CHC(But)N}2(CH2)3]3 (2.304(3) Å) [19]. The average NdeO(Ar)
bond length of 2.376(5) Å is comparable with the corresponding
value in [L’Nd(OAr)(THF)]2 (2.371(5) Å) [15]. The NdeN(amido)
bond length of 2.337(5) Å is comparable with those values in b-
ketoiminato samarium and erbium amido complexes when the
difference in ionic radii is considered [20]. The bond lengths of
LneO and LneN in complexes 2 and 4 are comparable with the
corresponding bond lengths in complex 1 when the difference in
ionic radii is considered.
alized
The metal centers in these complexes are six-coordinated with two
oxygen atoms and one nitrogen atom from one -ketoiminate
b-ketoiminate rare-earth metal chlorides and aryloxides [15].
The ORTEP diagram of complex 6 is shown in Fig. 4, and its
selected bond parameters are listed in Table 3. Complex 6 has
b
ligand, one nitrogen atom from the amido group, one oxygen atom
a centrosymmetric structure that consists of four b-ketoiminato
ligands, two lanthanum atoms, four lithium atoms, two chlorine
atoms and four THF molecules. The molecule can be regarded as
a dimer in which two [L2LaLi(THF)] moieties are connected by two
Table 3
Selected bond lengths (Å) and bond angles (ꢀ) for complex 6.
Bond lengths(Å)
La(1)eO(1)
La(1)eO(3)
La(1)eO(2)
La(1)eO(4)
Li(1)eCl(1)
Li(1)eO(4A)
Bond angles(ꢀ)
O(1)eLa(1)eO(3)
O(3)eLa(1)eO(2)
O(1)eLa(1)eO(4)
O(2)eLa(1)eO(4)
O(1)eLa(1)eN(2)
O(3)eLa(1)eN(2)
O(4)eLa(1)eN(2)
O(1)eLa(1)eN(1)
O(3)eLa(1)eN(1)
O(2)eLa(1)eN(1)
2.329(5)
2.338(6)
2.543(5)
2.549(5)
2.37(1)
La(1)eN(2)
La(1)eN(1)
La(1)eCl(1A)
La(1)eCl(1)
Li(1)eO(2)
Li(1)eO(5)
2.614(6)
2.619(6)
3.115(2)
3.116(2)
1.94(2)
Table 4
Polymerization of
L
-lactide initiated by complexes 1ꢁ5. a
Solvent Tp(oC) t(h) Yield%c Mnd(104) PDI
b
Entry Initiator [M]0/[I]0
1
2
3
4
5
6
7
8
9
1
1
1
1
2
2
3
4
5
100
200
300
400
200
300
200
100
200
Tol
Tol
Tol
Tol
Tol
Tol
Tol
Tol
Tol
70
70
70
70
70
70
70
70
70
4 h 100
4 h 100
4 h 100
6.72
5.87
7.56
1.12
3.05
1.32
2.76
2.35
1.07
1.53
1.68
1.86
1.39
1.78
1.46
1.65
1.58
1.39
1.92(1)
1.88(1)
114.2(2)
79.33(18)
78.41(17)
130.49(17)
86.59(18)
70.30(18)
63.24(19)
69.78(18)
83.84(18)
63.74(17)
N(2)eLa(1)eN(1)
O(1)eLa(1)eCl(1)
O(2)eLa(1)eCl(1)
O(4)eLa(1)eCl(1)
Cl(1A)eLa(1)eCl(1)
La(1)eCl(1)eLa(1A)
Li(1)eO(2)eLi(2A)
Li(1)eO(4A)eLi(2A)
O(4A)eLi(1)eO(2)
Li(1)eCl(1)eLi(2)
133.9(2)
89.24(16)
70.26(12)
70.76(12)
74.48(5)
105.52(5)
85.0(7)
85.7(7)
94.4(6)
151.8(5)
5 h
4 h
5 h
4 h
4 h
4 h
35
93
50
78
72
42
a
b
c
Polymerization conditions: Toluene as solvent, Vsol/V[M] ¼ 1:1.
[M]0/[I]0 ¼ [monomer]/[initiator].
Yield: weight of polymer obtained/weight of monomer used.
Measured by GPC calibrated with standard polystyrene samples.
d

X.-Y. Gu et al. / Journal of Organometallic Chemistry 695 (2010) 2726e2731
2731
(THF)LiCl moieties. The phenolate oxygen atoms and the chlorine
atoms act as bridges, and adopt m3- and m4-bridging coordination
modes, respectively. Each of the phenolate oxygen atoms is coor-
dinated to one lanthanum atom and two lithium atoms, and each of
the chlorine atoms is coordinated to two lanthanum atoms and two
lithium atoms to form a three-decker cluster. The upper and the
bottom are same, and contain the Li2O2 core. Two lithium atoms
and two oxygen atoms are coplanar with the sum of the OeLieO
bond angles of 360.1(7)ꢀ. The middle consists of two lanthanum
atoms and two chlorine atoms, which are also coplanar. The oxygen
and the neodymium amido complex showed the highest activity
among complexes 1e5.
In summary, we have successfully synthesized a series of
lanthanide metal complexes stabilized by a ferrocene-containing
dianionic N-aryloxo-functionalized
b-ketoiminate ligand, and
characterized some of their structural features by X-ray diffraction
studies. The ionic radii have a significant effect on the outcome of
the amine elimination reactions of the b-ketoimine with lanthanide
amides, and a novel lanthanum-lithium heterobimetallic cluster
stabilized by this ligand was isolated.
and nitrogen atoms of the two b-ketoiminato ligands are coordi-
nated to one lanthanum atom, which is different from those in
complexes 1, 2 and 4, and can be attributed to the large ionic radius
of the lanthanum metal ion. Each lanthanum atom is eight-coor-
dinate with four oxygen atoms and two nitrogen atoms from two
Acknowledgment
Financial support from the National Natural Science Foundation
of China (Grants 20771078, 20972108 and 20632040), the Major
Basic Research Project of the Natural Science Foundation of the
Jiangsu Higher Education Institutions (Project 07KJA15014), and
the Qing Lan Project is gratefully acknowledged.
b
-ketoiminato ligands, and two chlorine atoms to form a distorted
bicapped trigonal prism, in which the capping atoms are the
chlorine atoms. The overall coordination geometry around the
lanthanum atom is quite different from those observed in
complexes 1, 2 and 4. Each lithium atom is coordinated to two
Appendix A. Supplementary data
oxygen atoms from two b-ketoiminato ligands, one chlorine atom
and one oxygen atom from a THF molecule to form a distorted
tetrahedron.
The averageLaꢁO(alkoxo) bond length of 2.333(6) Å in complex 6
is slightly larger than the terminal LaeO(Ar) bond lengths in bridged
bis(phenolate) lanthanum complexes [ONOO]La[N(SiMe2H)2]
CCDC 773983ꢁ773986 contain the supplementary crystallo-
graphic data for complexes 1, 2, 4 and 6. These data can be obtained
free of charge via http://www.ccdc.cam.ac.uk/conts/retrieving.
html, or from the Cambridge Crystallographic Data Centre, 12
Union Road, Cambridge CB2 1EZ, UK; fax: þ44-1223-336033; or
e-mail: deposit@ccdc.cam.ac.uk.
(THF) [ONOO
[2.272(3) Å] [21], and (MBMP)La(THF)(
¼
MeOCH2CH2N{CH2e(2eOeC6H2eBut2e3,5)}2]
m-MBMP)2La(THF)2
[MBMP ¼ 2,20eCH2e(1eOeC6H2eMee4eBute6)}2] [2.286(4) Å]
[22]. The average bridging LaeO(Ar) bond length is, as expected,
somewhat larger at 2.546(5) Å, which is also apparently larger
than the bridging LaeO(Ar) bond length in (THF)La(Oe2,6e
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m
eOe2,6ePri2C6H3)2M(THF)2 (M ¼ Li, Na; 2.453(4) Å)
[23], and the bridging LneO(Ar) bond length in complexes 1, 2, and 4
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Li1eO2 and Li2AeO2 bond lengths are 1.94(2) and 1.92(1) Å,
respectively, which indicated that the phenolate group is nearly
symmetrically coordinated to two lithium atoms. The average LieO
(Ar) bond length of 1.93(1) Å is slightly shorter than those average
LieO(Ar) bond lengths reported for the bridged bis(phenolate)
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The catalytic behavior of the lanthanide amido complexes 1e5
for the ring-opening polymerization of L-lactide was examined, and
the preliminary results are summarized in Table 4. It can be seen
that these lanthanide amides can initiate the ring-opening poly-
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polymers with high molecular weights and relatively broad
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amide complexes is lower than that of the N-aryloxo-functionalized
b
-ketoiminate lanthanide aryloxides. For example, the neodymium
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70 ꢀC in 4 h [15], whereas complex 1 gave the yield of 35% in 5 h
under the same polymerization conditions (Entry 4). A possible
explanation is that the silylamide group is less nucleophilic than
aryloxo group, which caused slow initiation [26]. As in the
b
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activity decreased dramatically with the decrease of the ionic radii,