Synthesis, structure and reactivity of samarium complexes supported by Schiff-base ligands

Article abstract of DOI:10.1016/j.jorganchem.2009.03.024

Three tris(salicyladiminato) samarium complexes [3, 5 - Bu₂^t - 2 - (O) C₆ H₂ CH {double bond, long} NAr^′]₃ Sm (THF)_n [Ar^′ = 4 - ClC₆ H₄ (1), 4 -

Full text of DOI:10.1016/j.jorganchem.2009.03.024

Journal of Organometallic Chemistry 694 (2009) 2409–2414
Contents lists available at ScienceDirect
Journal of Organometallic Chemistry
journal homepage: www.elsevier.com/locate/jorganchem
Synthesis, structure and reactivity of samarium complexes
supported by Schiff-base ligands
Bangyu Li a,b, Yaorong Wang a, , Yingming Yao , Yong Zhang , Qi Shen
a
a
a,*
*
a
Key Laboratory of Organic Synthesis of Jiangsu Province, College of Chemistry, Chemical Engineering and Materials Science, Dushu Lake Campus, Suzhou University,
Suzhou 215123, PR China
b
Suzhou Vocational University, Suzhou 215104, PR China
a r t i c l e i n f o
a b s t r a c t
t
2
0
0
Article history:
Three tris(salicyladiminato) samarium complexes ½3; 5-Bu -2-ðOÞC H CH@NAr ꢀ SmðTHFÞ ½Ar ¼
6
2
3
n
Received 11 December 2008
Received in revised form 10 March 2009
Accepted 16 March 2009
4-ClC
6
H
4
ð1Þ; 4-CH
3
C
6
H
4
ð2Þ; 8-C
9
H
6
NðquinolineÞ ð3Þꢀ were synthesized by the reaction of anhydrous
SmCl
3
with the sodium salts of the Schiff-bases in THF in 3:1 molar ratio. X-ray diffraction studies
revealed that the coordination geometry around samarium atom could be best described as a distorted
pentagonal bipyramidal for complexes 1 and 2 and as a distorted tricapped trigonal prism for complex
Available online 21 March 2009
3
. It was found that the coordination environment around samarium atom has significant effect on the
Keywords:
Samarium
Schiff-base
Crystal structure
catalytic activity of homoleptic Schiff-base complexes of lanthanide. The increasing order of the catalytic
activity for the ring-opening polymerization of e-caprolactone, as well as guanylation of aniline with N,N-
diisopropylcarbodiimide is 3 < 2 < 1.
Crown Copyright Ó 2009 Published by Elsevier B.V. All rights reserved.
e-Caprolactone
Polymerization
Guanylation
1
. Introduction
Only one research group concerns the chemistry of lanthanide-
Schiff-base bond [16,17], although vast of non-aqueous lanthanide
Schiff-base complexes have been reported [18–30].
In recent years the application of Schiff-base ligands in organo-
metallic chemistry of main, transition and lanthanide metals have
attracted much attention, in part because some of these complexes
were reported to have fascinating catalytic reactivity. For example,
chiral Schiff-base transition metal complexes are extensively used
in a variety of chemical transformations such as oxidation, hydrox-
ylation, aldol condensation, epoxidation and other related catalytic
processes [1–3], bis(phenoxyimine) group 4 metal complexes and
phenoxyimine Ni(II) complexes are excellent precatalysts or cata-
lysts for olefin polymerization [1,4–7]. Lanthanide complexes bear-
Recently, we have reported that bis(salicyladiminato) lantha-
i
nide chlorides [2-OC
6
H
4
CH@N(2,6- Pr
2
C H
6 3
2
)] LnCl(THF) (Ln = Yb,
Er) exhibit moderate catalytic activity for the ring-opening poly-
merization of -caprolactone ( -CL) [31], indicating that the bond
of lanthanide metal to salicyladiminato ligand is active for ring-
opening of -caprolactone. The results encouraged us to further in-
e
e
e
sight into the influence of coordination environment about the
metal coursed by Schiff-base ligands on the reactivity of lanthanide-
t
2
Schiff-base bond. Three Schiff-base ligands, ½3; 5-Bu -2ðOHÞ-C
6 2
H -
0
0
ing N
the asymmetric epoxidation of
opening polymerization of lactide and related cyclic esters [9–
1]. Chiral yttrium–salen complexes are reported to be excellent
2
O
2
tetradentate Schiff-base ligands are efficient catalysts for
CH@NAr ꢀ [Ar = 4-ClC
6 4 3 6 4 9 6
H , 4-CH C H , 8-C H N (quinoline)], were
2
t
a
,b-unsaturated ketones [8], ring-
chosen and the corresponding samarium complexes ½3; 5-Bu -
0
0
2-ðOÞC
6
H
2
CH@NAr ꢀ SmðTHFÞ ½Ar ¼ 4-ClC
6
H
4
ð1Þ; 4-CH
3
C
6
H
4
ð2Þ;
3
n
1
8-C
9
H
6
NðquinolineÞ ð3Þ] were synthesized. Preliminary results on
catalysts for enantioselective acyl transfer reactions between eno-
lesters and secondary alcohols [12], asymmetric Aldol–Tishchenko
reactions [13] and the ring-opening of epoxides mediated by
their reactivity revealed that these new homoleptic samarium com-
plexes showed moderate catalytic activity for the polymerization of
e
-CL as well as guanylation of aniline with carbodiimide. The homo-
TMSCN and TMSN
plexes can be used as efficient hydroamination of alkene catalysts
15]. In all the homogeneous catalyses these Schiff-base ligands are
3
[14]. Bis(salicyladiminato) scandium com-
leptic Schiff-base complexes of samarium can also promote cyclotri-
merization of phenyl isocyanate. Here we would like to report these
results.
[
used as typically inert ancillary ligands to stabilize organometallic
compounds, themselves do not participate in the transformations.
2
. Experimental
*
Corresponding authors. Tel.: +86 512 65880306; fax: +86 512 65880305
Q. Shen).
E-mail address: qshen@suda.edu.cn (Q. Shen).
All manipulations were carried out under an argon atmosphere
using standard Schlenk techniques. THF, toluene and hexane were
(
0
022-328X/$ - see front matter Crown Copyright Ó 2009 Published by Elsevier B.V. All rights reserved.
doi:10.1016/j.jorganchem.2009.03.024

2
410
B. Li et al. / Journal of Organometallic Chemistry 694 (2009) 2409–2414
dried and freed of oxygen by refluxing over sodium benzophenone
ketyl and distilled under argon prior to use. -Caprolactone ( -CL)
was dried over CaH for 4 days and stored over 3 Å molecular
(m), 1026 (m), 980 (m), 887 (m), 825 (m), 794 (s), 633 (s), 555
(m), 501 (s).
e
e
2
sieves under argon after distillation. Aniline was predried and
2.4.
e-Caprolactone polymerization
distilled before use and N,N-diisopropylcarbodiimide was used
t
2
t
2
after distillation. 3; 5-Bu -2ðOHÞ-C
6
H
2
CH@Nð4-ClC
6
H
4
Þ, ½3; 5-Bu -
The procedures for the polymerization of e-CL initiated by com-
plexes 1–3 were similar, and a typical polymerization procedure is
given below. A 50 ml Schlenk flask, equipped with a magnetic stir-
ring bar, was charged with a toluene solution (3 mL) of e-CL
(0.6 mL, 5.4 mmol). To this solution was added the desired amount
of initiator in toluene by syringe at the desired temperature. After
the polymerization was carried out for a predefined time, 5 mL of
ethanol containing 2% HCl solution was added to quench the reac-
tion, and then the viscous solution was poured into a large excess
of ethanol to induce the precipitation of the polymer. The polymer
was washed with ethanol three times and dried at 30 °C under
vacuum.
t
2
-ðOHÞC
6
H
2
CH@Nð4-CH
3
C
6
H
4
Þ
[32] and 3; 5-Bu -2-ðOHÞC
6
H
2
-
2
CH@Nð8-C
9
H
6
NÞ [33] and anhydrous SmCl
3
[34] were prepared
according to the literature procedures. Metal analyses were carried
out by complexometric titration. Carbon, hydrogen and nitrogen
analyses were performed by direct combustion on a Carlo-Erba
EA-1110 instrument. The IR spectra were obtained as KBr pellets
on a Nicolet-550 FT-IR spectrometer. 1H NMR and C NMR spec-
trum were obtained on an INOVA-400 MHz apparatus. Molecular
13
n w n
weight (M ) and molecular weight distributions (M /M ) were
determined against a polystyrene standard by gel permeation
chromatography (GPC) on a PL-50 apparatus, and THF was used
as an eluent at 40 °C.
2
.5. General procedure for guanylation of aniline with
t
2
N,N-diisopropylcarbodiimide
2
.1. Preparation of ½3; 5-Bu -2-ðOÞC
6
H
2
CH@Nð4-ClC
6
H
4
Þꢀ SmðTHFÞ
3
(1)
A 30.0 mL Schlenk tube under dried argon was charged with
complex 1 (0.11 g, 0.09 mmol) and aniline (0.16 mL, 1.8 mmol).
To this mixture was added N,N-diisopropylcarbodiimide (0.28 mL,
t
2
A THF solution (20 mL) of 3; 5-Bu -2-ðOHÞC
6
H
2
CH@Nð2-ClC
6
H
4
Þ
(
(
1
2.06 g, 6.00 mmol) was added dropwise to a NaH suspension
0.17 g, 7.10 mmol) in THF at room temperature and stirred for
1
.8 mmol). The resulting mixture was stirred at 100 °C for 1 h. After
the reaction was completed, the reaction mixture was hydrolyzed
by water (3 mL), extracted with dichloromethane (310 mL), dried
over anhydrous Na
der vacuum and the final product was obtained after washing with
4 h. The mixture was then filtered. The resulting dark red solution
was added to a suspension of SmCl (0.51 g, 2.00 mmol) in THF
20 mL). The solution was stirred overnight at room temperature,
and then the precipitate was separated from the reaction mixture
by centrifugation. The solvent was removed under vacuum and the
residue was dissolved in hexane. Complex 1 was isolated as yellow
crystals at room temperature in a few days (1.82 g, 73%). Mp: 149–
3
2 4
SO , and filtered. The solvent was removed un-
(
1
hexane (0.21 g, 53%). H NMR (CDCl
.86–6.84(2H), 3.77 (2H), 3.61(2H), 1.17–1.15(12H).
CDCl ): d 150.53, 150.41, 129.45, 123.75, 121.49, 43.42, 23.56.
3
): d 7.22 (2H), 6.95–6.91 (1H),
13
6
(
C NMR
3
1
51 °C (dec). Anal. Calc. for C67
3 3 4
H83Cl N O Sm: C, 64.32; H, 6.69; N,
2
.6. Reaction of complex 3 with phenyl isocyanate
3
.36; Sm, 12.02. Found: C, 63.95; H, 6.91; N, 3.16; Sm, 11.92%. IR
ꢁ1
(
KBr pellet, cm ): 2955 (s), 2909 (s), 2871 (s), 1605 (s), 1582 (s),
A mixture of PhNCO (0.35 g, 2.9 mmol), complex 3 (3.8 g,
.9 mmol) and THF (15 mL) was stirred at 40 °C for 24 h. The sol-
1
1
7
535 (s), 1481 (s), 1435 (s), 1389 (s), 1319 (s), 1258 (s), 1165 (s),
088 (m), 1026 (m), 980 (w), 926 (w), 872 (m), 833 (s), 787 (m),
25 (m), 640 (w), 602 (w), 517 (s).
2
vent was then removed by vacuum and the resulting solid was ex-
tracted with toluene. Crystallization from toluene afforded
[
2
PhNCO]
76 °C. Anal. Calc. for C25
3
ꢂ THF as light yellow crystals. Yield: 0.33 g (80%), mp
t
2
2
.2. Preparation of ½3; 5-Bu -2-ðOÞC
6
H
2
CH@Nð4-CH
3
C
6
H
4
Þꢀ SmðTHFÞ
3
H
23
N
3
O
4
: C, 69.91; H, 5.40; N, 9.78. Found:
(2)
ꢁ1
C, 69.79; H, 5.32; N, 9.81%. IR (KBr pellet, cm ): 3060 (w), 1701 (s),
1
590 (m), 1468 (s), 1445 (s), 1406 (s), 1288 (m), 1211 (m), 1146
The synthesis of complex 2 was carried out by the same way as
(
w), 1065 (s), 1025 (m), 818 (m), 745 (s), 690 (s), 579 (s).
t
that described above, but 3; 5-Bu -2-ðOHÞC
6
H
2
CH@Nð2-CH
3
C
6
H
4
Þ
2
t
2
(
1.94 g, 6.00 mmol) was used instead of 3; 5-Bu -2-ðOHÞC
6
H
2
-
2.7. X-ray structures determination
CH@Nð2-ClC
6
H
4
Þ. Yellow crystals were collected from hexane solu-
tion (1.72 g, 70%). Mp: 137–138 °C (dec). Anal. Calc. for
Suitable single-crystals of complexes 1–3 were sealed in a thin-
C
7
(
(
(
70 92 3 4
H N O Sm: C, 70.66; H, 7.79; N, 3.53; Sm, 12.64. Found: C,
walled glass capillary, and intensity data were collected on a Riga-
ku Mercury CCD equipped with a graphite-monochromotized Mo
Ka radiation (k = 0.71070 Å). Details of the intensity data collection
and crystal data are given in Table 1. The crystal structures of these
complexes were solved by direct methods using the SHELXS-97 pro-
gram and expanded by Fourier techniques. All the non-hydrogen
atoms were refined anisotropically. Hydrogen atoms were all gen-
erated geometrically (CꢁH bond lengths fixed at 0.95 Å) with as-
signed appropriate isotropic thermal parameters.
ꢁ
1
0.80; H, 7.90; N, 3.39; Sm, 12.55%. IR (KBr pellet, cm ): 2955
s), 2909 (s), 2871 (s), 1603 (s), 1589 (s), 1535 (s), 1505 (s), 1466
s), 1435 (s), 1389 (s), 1319 (s), 1250 (s), 1196 (s), 1165 (s), 1026
m), 980 (w), 926 (w), 872 (s), 833 (s), 740 (m), 679 (w), 640 (w),
5
17 (s).
t
2
2
.3. Preparation of ½3; 5-Bu -2-ðOÞC
6
H
2
CH@Nð8-C
9
H
6
NÞꢀ Sm (3)
3
The synthesis of complex 3 was carried out by the same way as
t
2
that described for complex 1, but 3; 5-Bu -2-ðOHÞC
6 2
H -
CH@Nð8-C
9
H
6
NÞ (2.16 g, 6.00 mmol) was used instead of 3;
3
. Results and discussion
t
2
5
-Bu -2-ðOHÞC
6
H
2
CH@Nð2-ClC
6
H
4
Þ. Yellow crystals were obtained
from hexane solution (2.05 g, 78%). Mp: 206–208 °C (dec). Anal.
Calc. for C72 Sm: C, 70.37; H, 6.64; N, 6.84; Sm, 12.24.
Found: C, 70.50; H, 6.70; N, 6.69; Sm, 12.15%. IR (KBr pellet,
3.1. Syntheses
81 6 3
H N O
3
Salt metathesis reaction of LnCl with alkali metal salts of
ꢁ
1
cm ): 2955 (s), 2909 (s), 2871 (s), 1613 (s), 1497 (s), 1466 (s),
427 (s), 1389 (s), 11366 (s), 1242 (s), 1157 (s), 1088 (m), 1049
Schiff-bases is a useful method for the synthesis of lanthanide
Schiff-base complexes in non-aqueous solution [18,19]. Thus, the
1

B. Li et al. / Journal of Organometallic Chemistry 694 (2009) 2409–2414
2411
Table 1
Details of the crystallographic data and refinements for complexes 1, 2 and 3.
Compound
1
2 ꢂ 0.5C
6
H
14
4
3 ꢂ C
6 14
H
Formula
Formula weight
T (K)
C
67
H
83Cl
3
3
N O
4
Sm
C
73
H
99
N
3
O
Sm
78 95 6 3
C H N O Sm
1314.95
193(2)
1251.06
173(2)
1232.90
173(2)
Crystal system
Space group
a (Å)
b (Å)
c (Å)
Triclinic
P1
Triclinic
P1
Triclinic
P1
ꢀ
ꢀ
ꢀ
12.6303(11)
16.7540(8)
17.4327(11)
62.693(5)
87.313(9)
78.957(8)
3213.6(4)
2
14.675(2)
16.238(3)
17.084(3)
99.484(2)
105.8090(10)
114.539(2)
3378.9(9)
2
13.5940(10)
15.9190(12)
18.5734(18)
78.791(7)
85.690(8)
76.002(7)
3823.9(5)
2
a
(°)
b (°)
(°)
c
3
V (Å )
Z
D
l
calc (g/cmꢁ3)
1.293
1.086
1.212
0.917
1.142
0.814
ꢁ
1
(mm
)
F(000)
Crystal size (mm)
h Range (°)
1302
1304
1382
0.38 ꢃ 0.20 ꢃ 0.16 0.40 ꢃ 0.20 ꢃ 0.15 0.30 ꢃ 0.21 ꢃ 0.15
2
50.7
50.0
50.7
Reflections
31888
32965
38374
collected
Independent
reflections
Reflections with
11713
8784
12259
10066
13936
11413
Fig. 1. Molecular structure of complex 1 drawn with 20% probability ellipsoids, the
t-butyl atoms were not shown as ellipsoids and hydrogen atoms are omitted for
clarity.
I P 2.0r(I)
Parameters refined
GOF
R
wR
746
737
806
1.089
0.0748
0.1366
1.093
0.0652
0.1263
1.123
0.0760
0.1692
homoleptic lanthanide Schiff-base complexes were synthesized by
the same method. Anhydrous SmCl reacted with three equivalents
3
of the sodium salts of the Schiff-bases formed in situ by the reac-
t
2
0
0
tion of 3; 5-Bu -2ðOHÞ-C
6
H
2
CH@NAr ½Ar ¼ 4-ClC
6 4 3 6 4
H ; 4-CH C H ;
8
-C
9
H
6
NðquinolineÞꢀ with NaH in THF, after workup, to give com-
plexes 1–3 in good isolated yields (Scheme 1).
All these complexes have good solubility in THF, toluene and
even in hexane. The compositions of these samarium species were
confirmed by elemental analysis. In the IR spectra, the bands of
ꢁ
1
stretching vibration of imine groups were observed at 1605 cm
ꢁ1
ꢁ1
for complex 1, 1603 cm for complex 2 and 1613 cm for com-
plex 3, respectively. Because of their paramagnetism, no resolvable
NMR spectrum for these samarium Schiff-base complexes was ob-
tained. The definitive molecular structures of complexes 1–3 were
provided by a single-crystal X-ray structure determination.
3.2. Description of the structures
Fig. 2. Molecular structure of complex 2 drawn with 20% probability ellipsoids, the
t-butyl atoms were not shown as ellipsoids and hydrogen atoms are omitted for
clarity.
The molecular structures of complexes 1–3 are shown in Figs.
–3, respectively, and selected bond lengths and angles are out-
1
lined in Table 2. Both complexes 1 and 2 are monomer in the solid
state and have similar molecular structure. Each samarium ion in 1
and 2 is ligated by three salicyladiminato moieties and a THF mol-
ecule. The geometry about the seven-coordinate samarium metal
center can be best described as a distorted pentagonal bipyramidal,
with two oxygen atoms (O2, O3 for complex 1 and O1, O2 for com-
plex 2) from Schiff-base ligands occupying the axial positions. The
Sm–N(Schiff-base) distances in complexes 1 and 2 range from
2.579(4) to 2.709(4) Å, which are comparable with each other
Ar'
N
But
O
Sm THF
Ar'
N
È
É
t
But
3
and also with those in N½CH
CH
NCHð2-O-3; 5-Bu C
H
Þꢀ Sm
2
2
2
6
2
3
Ar'=
Cl (1)
(a) NaH / THF
5
But
OH
(4) [2.552(5), 2.555(5) and 2.560(5) Å] [21] and (
g
-C
5
H
5
)Sm(
l
-
(b) SmCl3 / THF
CH (2)
3
OC20
H
20
N
2
O)]
2
(
l
-THF) ꢂ (THF)
2
(5) [2.55(5), 2.56(5), 2.65(5) and
But
N
2
.67(5) Å] [26] published previously. The Sm–O(Ar) bond lengths
N
Sm
vary from 2.193(4) to 2.233(3) Å, giving the average 2.214 and
2.231 Å in complexes 1 and 2, respectively. These distances are
comparable to the corresponding values observed in other lantha-
O
Ar'=
3
(3)
N
But
Scheme 1.
But
nide Schiff-base complexes: complex 4, 2.232(4), 2.222(4),
t
2
2.218(3) Å; fN½CH
2
CH
2
NCHð2-O-3; 5-Bu C
6
H
2
Þꢀ gNd, 2.241(6),
3

2
412
B. Li et al. / Journal of Organometallic Chemistry 694 (2009) 2409–2414
ven- and nine-coordinate Sm3+ in radii is made. However, the
Sm–N(quinoline) distances range from 2.671(5) to 2.817(5) Å, with
an average of 2.724 Å, which is slightly longer than the Sm–N(imi-
no) distances, indicating that the interaction between samarium
atom and nitrogen atom of the quinoline ring is somewhat weaker
than that between samarium atom and nitrogen atom of imino
groups.
3.3. The ring-opening polymerization of e-CL
The catalytic activity of complexes 1–3 for the ring-opening
polymerization of -CL was tested and the preliminary results
e
are shown in Table 3. It can be seen that the Schiff-base ligands
around the central metal atom have significant effect on the cata-
lytic activity of the samarium complexes. For example, the yield
reached as high as 100% at 60 °C for 35 min in the case of [M]/
[
I] = 100 (mole ratio) using complex 1 as the initiator, and 90%
yield can also be obtained when the molar ratio of [M]/[I] increased
to 300 after 140 min (Table 3, entries 1 and 7). Complex 2 showed a
somewhat lower activity than that for complex 1 (Table 3, entries
1, 3 and 9, 10). This might be attributed to the difference in elec-
tronic effect between the two ligands, and the presence of an elec-
tron-withdrawing group on the Schiff-base ligand could increase
the activity of the corresponding samarium complex. Similar re-
sults have been observed in the polymerization of propylene with
bis(phenoxyimine) titanium catalyst [5,6]. The activity of both
complexes 1 and 2 is lower than that of samarium aryloxide
complex [36], but higher than that for phenyl compound
Fig. 3. Molecular structure of complex 3 drawn with 30% probability ellipsoids, t-
butyl groups on the arene rings and hydrogen atoms are omitted for clarity.
0
0
0
2
.248(4), 2.242(6) Å [21]; [(salen )Y(
l
-Cl)(THF)]
2
(salen = N,N -
bis(3,5-di-tert-butylsalicylidene)ethylenediamine),
2.143(2),
0
2
5
.16 Å [19]; (salen )Y(C
5
Me
5
), 2.141(2), 2.148(2) Å [22]; ½3;
t
-Bu -2-ðOÞC
6
H
2
CH@Nð8-C
9
H
6
NÞꢀYbCl ðDMEÞ, 2.115(2) Å [29]
2
2
6 5 3
(C H ) Sm [37] and bis(salicyladiminato) lanthanide chlorides [2-
when corrections are made for trivalent seven-coordinate ionic
radii [35].
i
OC
the difference in central metals and ligands. In contrast, complex
is inactive under the same polymerization conditions. No activity
6 4 2 6 3 2
H CH@N(2,6- Pr C H )] LnCl(THF) (Ln = Yb, Er) [31], due to
Complex 3 has an unsolvated monomeric structure, and the
coordination sphere of the samarium center is composed of the
six nitrogen atoms and three oxygen atoms from three tridentate
Schiff-base ligands. The coordination geometry about the nine-
coordinate samarium metal center can be viewed as a distorted tri-
capped trigonal prism. The two triangular faces of the prism are
constituted by O1, O2, N1 and O3, N4, N5, while N2, N3 and N6
are in the capping positions. The three dihedral angles between
the O1O2N1 and N2N3N6 planes, the O1O2N1 and O3N4N5 planes
and the O3N4N5 and N2N3N6 planes are 12.89°, 7.63° and 5.25°,
respectively. The average Sm–N(imino) distance in complex 3 is
3
shown by complex 3 might be attributed to that three of tridentate
Schiff-base ligands with quinoline ring around the samarium atom
make the coordination sphere about the central metal much more
crowded and the coordination of an additional nitrogen atom from
quinoline to samarium makes the nine-coordinated samarium me-
tal being much more stable, which results in the difficulty in coor-
dination and insertion of
by complexes 1 and 2 have high molecular weight (M
rather narrow molecular weight distributions (M /M
.20 to 1.60). However, complexes 1 and 2 showed low initiation
efficiency (20–88%) (Table 3). Additionally, the observed molecular
e-CL to initiator. The polymers obtained
4
n
> 10 ) and
w
n
range from
1
2
.635 Å, and the average Sm–O interaction is 2.304 Å. These dis-
tances are consistent with the Sm–N and Sm–O distances in
complexes 1 and 2 if substraction of the differences between se-
weights [M
n
(obsd)] (GPC values corrected with the coefficient
Table 2
Selected bond distances (Å) and angles (°) for complexes 1, 2 and 3.
1
2
3
Sm(1)–O(1)
Sm(1)–O(2)
Sm(1)–O(3)
Sm(1)–N(1)
Sm(1)–N(2)
Sm(1)–N(3)
Sm(1)–O(4)
2.23(5)
2.19(4)
2.22(4)
2.61(5)
2.67(5)
2.63(5)
2.52(4)
Sm(1)–O(1)
Sm(1)–O(2)
Sm(1)–O(3)
Sm(1)–N(1)
Sm(1)–N(2)
Sm(1)–N(3)
Sm(1)–O(4)
2.23(3)
2.23(3)
2.23(3)
2.71(4)
2.58(4)
2.65(4)
2.49(4)
Sm(1)–O(1)
Sm(1)–O(2)
Sm(1)–O(3)
Sm(1)–N(1)
Sm(1)–N(2)
Sm(1)–N(3)
Sm(1)–N(4)
Sm(1)–N(5)
2.32(4)
2.29(4)
2.31(4)
2.62(5)
2.68(5)
2.62(5)
2.67(5)
2.67(5)
2.82(5)
84.1(2)
71.2(2)
89.0(2)
133.6(2)
105.7(2)
120.4(2)
78.9(2)
73.1(2)
69.8(2)
Sm(1)–N(6)
O(2)–Sm(1)–O(3)
O(1)–Sm–O(4)
O(1)–Sm–N(1)
N(1)–Sm–N(3)
N(3)–Sm–N(2)
O(4)–Sm–N(2)
165.3(2)
79.9(2)
71.1(2)
79.0(2)
71.0(2)
69.9(2)
O(1)–Sm–O(2)
O(3)–Sm–N(2)
O(3)–Sm–N(3)
O(4)–Sm–N(3)
O(4)–Sm–N(1)
N(2)–Sm–N(1)
171.5(1)
82.2(1)
70.4(1)
76.4(1)
68.8(1)
70.5(1)
O(1)–Sm–O(2)
O(1)–Sm–N(1)
O(2)–Sm–N(1)
N(2)–Sm–N(3)
N(2)–Sm–N(6)
N(3)–Sm–N(6)
N(4)–Sm–N(5)
O(3)–Sm–N(4)
O(3)–Sm–N(5)

B. Li et al. / Journal of Organometallic Chemistry 694 (2009) 2409–2414
2413
Table 3
Polymerization of e
-caprolactone initiated by complexes 1, 2 and 3.a
[M]/[I]b
Temperature (°C)
Time (min)
Yield (%)
M
n
(calcd)c (ꢃ104)
M
n
(obsd)d (ꢃ104)
d
Efficiencye (%)
Entry
Init.
w n
M /M
1
2
3
4
5
6
7
8
9
1
1
1
1
1
1
1
1
2
2
2
3
100
200
200
200
300
300
300
500
100
200
500
100
60
40
60
80
60
60
60
70
60
60
70
60
35
35
35
35
35
70
140
180
35
100
26
80
87
53
82
90
98
92
74
97
0
1.1
0.6
1.8
2.0
1.8
2.8
3.1
5.6
1.0
1.7
5.5
–
2.2
3.0
2.5
3.8
2.7
3.2
3.9
7.2
2.1
3.2
6.4
–
1.60
1.20
1.39
1.40
1.37
1.37
1.37
1.85
1.40
1.24
2.18
–
50
20
72
53
67
88
79
78
48
53
86
–
1
1
1
0
1
2
35
180
35
a
b
c
Polymerization conditions: solvent, toluene; solvent/monomer = 5 v/v.
[
M]/[I] = [Monomer]/[Initiator].
M
n
(calcd) = 114 ꢃ [M]/[I] ꢃ yield (calculated for one polymer chain per samarium atom).
d
e
Measured by GPC calibrated with standard polystyrene samples and corrected by the Mark–Houwink equation [M
Initiation efficiency = M (calcd)/M (obsd).
n
(obsd) = 0.56M
n
(GPC)] [38].
n
n
0
.56) [38] are higher than the theoretical ones [M
lated for one polymer chain per samarium atom) and the value
of M (calcd)/M (obsd) could give the average number of efficient
n
(calcd)] (calcu-
Table 4
Catalytic addition of the aniline to N,N-diisopropylcarbodiimide.
n
n
Ph
Ph
N
Schiff-base ligands per samarium atom during the polymerization.
It is obvious that this average number is lower than 1. Therefore,
we can suggest that only one of the three Schiff-base ligands in
the samarium complex could initiate the ring-opening polymeriza-
NH
5 mol% [Sm]
0
C
1,3-H shift
Pr N=C=NPr + PhNH2
pri
C
pri
i
i
Pri
Pri
N
H
N
N
H
1
00 C
N
H
tion of
omers of
prepared from the oligomerization of
] molar ratio of 10 according to the literature procedures [17,36].
However, the H NMR spectra show no signal of an isopropyl group
or an Schiff-base ligand. This might be attributed to that initiation
efficiency of complex 2 is rather low and the oligomers with low
molecular weight are difficult to be obtained.
e
-CL. In order to clarify the polymerization mechanism, olig-
-CL, terminated by 2-propanol or methanol, have been
-CL with a [ -CL]/[complex
Entry
Cat.
Temperature (°C)
Time (h)
Yield (%)a
e
e
e
1
2
3
4
5
1
2
3
1
1
100
100
100
100
60
1
1
1
4
53
43
10
84
5
2
1
0.5
a
Isolated yield.
The influence of reaction conditions on the polymerization was
also examined using complex 1 as the single component initiator.
In the case of [M]/[I] = 300 (mole ratio), the yields and the molec-
ular weights of the polymers obtained increased with the increase
of the reaction time at 60 °C, whereas the molecular weight distri-
butions of the polymers remained almost unchanged (Table 3, en-
tries 5–7). The polymerization temperature also has great effect on
the catalytic activity of the samarium complexes. When the poly-
merization temperature increased from 40 to 80 °C, the yields in-
creased from 26% to 87% (Table 3, entries 2–4), and the
alyst even if the activity is rather low, and the activity depends on
the ligands.
3.5. Reaction of complex 3 with phenyl isocyanate
Lanthanide complexes were reported to serve as the catalyst for
polymerization of alkyl isocyanate [48] and alkyl isocyanates are
well-known to be able to insert into Ln–C, Ln–N and Ln–S bond
to give the corresponding insertion products [49–51]. Thus, the
reaction of complex 3 with phenyl isocyanate in 1:1 molar ratio
was tried. After workup, the cyclotrimer of phenyl isocyanate
w n
molecular weight distributions (M /M ) of the resulting polymers
will be slightly broadened.
(
3
PhNCO) was isolated in 80% yield, which indicating complex 3
3.4. Guanylation of aniline with N,N-diisopropylcarbodiimide
might be an active promoter for cyclotrimerization of phenyl
isocyanate.
Recently, catalytic guanylation of amines with carbodiimides
provides a convenient approach to guanidines and has attracted
increasing attention [39–47]. Therefore, in order to further reveal
the catalytic activity of homoleptic Schiff-base complexes of lan-
thanides, we tested the catalytic activity of complexes 1–3 for
guanylation of aniline with N,N-diisopropylcarbodiimide with
4. Conclusion
Three of homoleptic Schiff-base samarium complexes with the
t
2
0
0
formula ½3; 5-Bu -2-ðOÞC
6
H
2
CH@NAr ꢀ SmðTHFÞ [Ar = 4-ClC
6 4
H
3
n
5
mol% catalyst loading (Table 4). The results showed that the reac-
(1), 4-CH C
3 6
H
4
(2), 8-C
9
H
6
N(quinoline) (3)] were prepared by
with Schiff-base salt in
tion could take place under solvent-free conditions to give the ex-
metathesis reactions of anhydrous SmCl
3
0
0
pected product (N-phenyl-N ,N -diisopropylguanidine) in 53%, 43%,
and 10% yields using the catalysts 1, 2 and 3, respectively (Table 4,
entries 1–3). The active order, 1 > 2 > 3, which agrees with that for
good yields, and structurally characterized. The Schiff-base ligands
around the central metal ion have significant effect on the catalytic
behavior of the homoleptic Schiff-base samarium complexes: com-
plexes 1 and 2 showed moderate activity for the ring-opening
e
-caprolactone polymerization, was observed. Under the same
reaction condition the reaction of amine with carbodiimine does
not occur without the presence of samarium complex. The results
indicate that homoleptic Schiff-base complexes can serve as a cat-
polymerization of e-caprolactone, as well as guanylation of aniline
with N,N-diisopropylcarbodiimide, whereas complex 3 was almost
inactive under the same reaction conditions.

2
414
B. Li et al. / Journal of Organometallic Chemistry 694 (2009) 2409–2414
[
[
[
16] W. Lin, W. Sun, Z. Shen, Chinese Chem. Lett. 18 (2007) 1133.
Acknowledgement
17] L. Zhang, X. Ni, W. Sun, Z. Shen, Chinese J. Polym. Sci. 26 (2008) 475.
18] P. Blech, C. Floriani, A. Chiesi-Villa, C. Guastini, J. Chem. Soc., Dalton Trans.
(1990) 3557.
Financial support from the National Natural Science Foundation
of China (Grant nos. 20632040 and 20771078).
[19] W.J. Evans, C.H. Fujimoto, J.W. Ziller, Chem. Commun. (1999) 311.
[
[
20] Y. Qian, J. Huang, J. Organomet. Chem. 647 (2002) 100.
21] M.W. Essig, D.W. Keogh, B.L. Scott, J.G. Watkin, Polyhedron 20 (2001) 373.
Appendix A. Supplementary material
[22] W.J. Evans, C.H. Fujimoto, J.W. Ziller, Polyhedron 21 (2002) 1683.
[
23] Y.P. Cai, H.Z. Ma, B.S. Kang, C.Y. Su, W. Zhang, J. Sun, Y.L. Xiong, J. Organomet.
Chem. 628 (2001) 99.
CCDC 670747, 670748 and 670749 contain the supplementary
crystallographic data for 1, 2 and 3. These data can be obtained free
of charge from The Cambridge Crystallographic Data Centre via
www.ccdc.cam.ac.uk/data_request/cif. Supplementary data associ-
ated with this article can be found, in the online version, at
doi:10.1016/j.jorganchem.2009.03.024.
[
24] Q. Liu, M. Ding, J. Organomet. Chem. 553 (1998) 179.
[25] D.J.H. Emslie, W.E. Piers, M. Parvez, R. McDonald, Organometallics 21 (2002)
226.
[
[
4
26] Q. Liu, M. Ding, Y. Lin, Y. Xing, Polyhedron 17 (1998) 555.
27] T. Dube, S. Gambarotta, G. Yap, Organometallics 17 (1998) 3967.
[28] O. Runte, T. Priermeier, R. Amwander, Chem. Commun. (1996) 1385.
[
[
[
29] B. Li, Y. Yao, Y. Wang, Y. Zhang, Qi. Shen, Polyhedron 27 (2008) 709.
30] B. Li, Y. Yao, Y. Wang, Y. Zhang, Qi Shen, Inorg. Chem. Commun. 11 (2008) 349.
31] L. Yu, Y. Yao, Q. Shen, J. Zhang, L. Wu, L. Ye, Chinese J. Chem. 21 (2003) 442.
References
[32] V.T. Kasumov, F. Köksal, R. Kö ßs eo g˘ lu, J. Coord. Chem. 57 (2004) 591.
[
33] P.A. Cameron, V.C. Gibson, C. Redshaw, J.A. Segal, A.J.P. White, D.J. Williams, J.
Chem. Soc., Dalton Trans. (2002) 415.
[
[
1] K.C. Gupta, A.K. Sutar, Coord. Chem. Rev. 252 (2008) 1420.
2] R. Drozdzak, B. Allaert, N. Ledoux, I. Dragutan, V. Dragutan, F. Verpoort, Coord.
Chem. Rev. 249 (2005) 3055.
[34] M.D. Tayler, C.P. Carter, J. Inorg. Nucl. Chem. 24 (1962) 387.
[35] R.D. Shannon, Acta Crystallogr., Sect. A 32 (1976) 751.
[
[
[
3] L. Canali, D.C. Sherrington, Chem. Soc. Rev. 28 (1999) 85.
4] V.C. Gibson, S.K. Spitzmesser, Chem. Rev. 103 (2003) 283.
5] M. Mitani, Jun-Ichi Mohri, Y. Yoshida, J. Saito, S. Ishii, K. Tsuru, S. Matsui, R.
Furuyama, T. Nakano, H. Tanaka, Shin-ichi Kojoh, T. Matsugi, N. Kashiwa, T.
Fujita, J. Am. Chem. Soc. 124 (2002) 3327.
6] A.F. Mason, G.W. Coates, J. Am. Chem. Soc. 126 (2004) 10798.
7] A.F. Mason, G.W. Coates, J. Am. Chem. Soc. 126 (2004) 16326.
8] S.A. Schuetz, E.A. Bowman, C.M. Silvernail, V.W. Day, J.A. Belot, J. Organomet.
Chem. 690 (2005) 1011.
[36] H. Sheng, H. Zhou, H. Guo, H. Sun, Y. Yao, J. Wang, Y. Zhang, Q. Shen, J.
Organomet. Chem. 692 (2007) 1118.
[37] X. Deng, M. Yuan, C. Xiong, X. Li, J. Appl. Polym. Sci. 73 (1999) 1401.
[38] M. Save, M. Schappacher, A. Soum, Macromol. Chem. Phys. 203 (2002) 889.
[39] T.G. Ong, G.P.A. Yap, D.S. Richeson, J. Am. Chem. Soc. 125 (2003) 8100.
[40] F. Montilla, A. Pastor, A. Galindo, J. Organomet. Chem. 689 (2004) 993.
[41] W. Zhang, M. Nishiura, Z. Hou, Chem. Eur. J. 13 (2007) 4037.
[42] W. Zhang, M. Nishiura, Z. Hou, Synlett 8 (2006) 1213.
[43] H. Shen, H. Chan, Z. Xie, Organometallics 25 (2006) 5515.
[44] T.G. Ong, J.S. O’Brien, I. Korobkov, D.S. Richeson, Organometallics 25 (2006)
4728.
[
[
[
[
9] T.M. Ovitt, G.W. Coates, J. Am. Chem. Soc. 121 (1999) 4072.
[
10] S.A. Schuetz, C.M. Silvernail, C.D. Incarvito, A.L. Rheingold, J.L. Clark, V.W. Day,
J.A. Belot, Inorg. Chem. 43 (2004) 6203.
11] E. Grunova, E. Kirillov, T. Roisnel, J.-F. Carpentier, Organometallics 27 (2008) 5691.
[45] S. Zhou, S. Wang, G. Yang, Q. Li, L. Zhang, Z. Yao, Z. Zhou, H. Song,
Organometallics 26 (2007) 3755.
[
[
[
12] M.-H. Lin, T.V. RajanBabu, Org. Lett. 4 (2002) 1607.
13] C.M. Mascarenhas, S.P. Miller, P.S. White, J.P. Morken, Angew. Chem., Int. Ed. 40
[46] Q. Li, S. Wang, S. Zhou, G. Yang, X. Zhu, Y. Liu, J. Org. Chem. 72 (2007) 6763.
[47] Z. Du, W. Li, X. Zhu, F. Xu, Q. Shen, J. Org. Chem. 73 (2008) 8966.
[48] M. Deng, Y. Yao, Y. Zhou, L. Zhang, Q. Shen, Chinese J. Chem. 21 (2003) 574.
[49] W.J. Evans, K.J. Forrestal, J.W. Ziller, J. Am. Chem. Soc. 120 (1998) 9273.
[50] L. Mao, Q. Shen, M. Xue, Organometallics 16 (1997) 3711.
[51] Q. Shen, H. Li, C. Yao, Y. Yao, L. Zhang, K. Yu, Organometallics 20 (2001) 3070.
(
2001) 601.
[
[
14] B. Saha, M.-H. Lin, T.V. RajanBabu, J. Org. Chem. 72 (2007) 8648.
15] F. Lauterwasser, P.G. Hayes, S. Bräse, W.E. Piers, L.L. Schafer, Organometallics
2
3 (2004) 2234.