The salt-free diamido complexes of lanthanide supported by β-diketiminate: Synthesis, characterization, and their catalytic activity for the polymerization of acrylonitrile and ε-caprolactone

Article abstract of DOI:10.1016/j.jorganchem.2005.07.050

The synthesis and structure of the salt-free diamido complexes of lanthanide supported by β-diketiminate ligand (2,6-Me₂C ₆H₃)NC(Me)CHC(Me)N(2,6-Me₂C₆H ₃) are described. The β-diketiminate lanthanide dichloride LLnCl₂(THF)₂ (L = N,N′-bis(2,6-dimethylphenyl)-2,4- pentanediiminate) [Ln = Yb (1), Nd (2)] was prepared by the metathesis reaction of LLi with anhydrous LnCl₃ in a 1:1 molar ratio in THF at room temperature. Reactions of 1 and 2 with 2 equiv. of LiNPh₂ in THF gave the salt-free complex LLn(NPh₂)₂(THF) [Ln = Yb (3), Nd (4)] in good yield as crystalline solids. Both compounds were characterized crystallographically. The coordinated geometry around the central metal can be described as a distorted trigonal bipyramid. Complexes 3 and 4 showed good catalytic activity for the polymerization of acrylonitrile and high activity for the ring-opening polymerization of ε-caprolactone at room temperature.

Full text of DOI:10.1016/j.jorganchem.2005.07.050

Journal of Organometallic Chemistry 690 (2005) 4685–4691
www.elsevier.com/locate/jorganchem
The salt-free diamido complexes of lanthanide supported
by b-diketiminate: Synthesis, characterization, and their catalytic
activity for the polymerization of acrylonitrile and e-caprolactone
a
a
a,b,
a
Mingqiang Xue , Yingming Yao , Qi Shen
*, Yong Zhang
a
Department of Chemistry and Chemical Engineering, Suzhou University, Suzhou 215006, PR China
State Key Laboratory of Organometallic Chemistry, Shanghai Institute of Organic Chemistry, Chinese Academy of Sciences,
Shanghai 200032, PR China
b
Received 18 May 2005; received in revised form 1 July 2005; accepted 12 July 2005
Available online 22 August 2005
Abstract
The synthesis and structure of the salt-free diamido complexes of lanthanide supported by b-diketiminate ligand (2,6-
Me2C6H3)NC(Me)CHC(Me)N(2,6-Me2C6H3) are described. The b-diketiminate lanthanide dichloride LLnCl2(THF)2 (L = N,N0-
bis(2,6-dimethylphenyl)-2,4-pentanediiminate) [Ln = Yb (1), Nd (2)] was prepared by the metathesis reaction of LLi with anhydrous
LnCl3 in a 1:1 molar ratio in THF at room temperature. Reactions of 1 and 2 with 2 equiv. of LiNPh2 in THF gave the salt-free
complex LLn(NPh2)2(THF) [Ln = Yb (3), Nd (4)] in good yield as crystalline solids. Both compounds were characterized crystal-
lographically. The coordinated geometry around the central metal can be described as a distorted trigonal bipyramid. Complexes 3
and 4 showed good catalytic activity for the polymerization of acrylonitrile and high activity for the ring-opening polymerization of
e-caprolactone at room temperature.
ꢀ 2005 Elsevier B.V. All rights reserved.
Keywords: Salt-free diamido complex; b-Diketiminate ligand; Polymerization; Acrylonitrile; e-Caprolactone
1. Introduction
dergo complexation by salts [8]. ItÕs obvious that the
key to solve the problem is to choose a suitable ligand.
Recently, b-diketiminate anion, as an isoelectronic
alternative to cyclopentadienyl ligand, has attracted
increasing attention in organometallic chemistry for
their electronic and steric properties can be easily tuned
through an appropriate choice of amine and b-diketone
used in their synthesis. The application of b-diketimi-
nate in organolanthanide chemistry has also led to the
synthesis of a variety of corresponding compounds [9–
12]. Moreover, the use of a sterically demanding b-dik-
etiminate ligand in the preparation of dialkyl scandium
compounds has made great success [13]. All these work
published encouraged us to attempt to synthesize bis-
amido complexes of lanthanide element by use of b-dik-
etiminate as an ancillary ligand. Very recently, the
synthesis of diprimary amido compound of scandium
The organolanthanide amide has been found to be
the important precatalysts in a variety of homogeneous
catalysis, including hydroamination of alkyne and al-
kene and the polymerization of polar monomers [1–5].
However, almost all of the work focused on the com-
plexes with a dianionic ancillary ligand and one amido
group. There are only a few papers dealing with the syn-
thesis of well-defined compounds of general formula
LLn[NR2]2, where L is a monoanionic ancillary ligand
[6,7]. The lack in synthesizing these targets may result
from the tendency of these types of compounds to un-
*
Corresponding author. Tel.: +86 512 6511 2513; fax: +86 512 6511
2371.
E-mail address: qshen@suda.edu.cn (Q. Shen).
0022-328X/$ - see front matter ꢀ 2005 Elsevier B.V. All rights reserved.
doi:10.1016/j.jorganchem.2005.07.050

4686
M. Xue et al. / Journal of Organometallic Chemistry 690 (2005) 4685–4691
supported by b-diketiminate was reported [14]. During
the sending of this manuscript we saw the publication
described the synthesis and molecular structure of bis-
di-trimethylsilylamido complex supported by b-diketi-
minate [15].
We have previously shown that the LYbCl2(THF)2
can be synthesized in high yield where the b-diketiminate
ligand is N,N0-bis(2,6-diisopropylphenyl)-2,4-pentane-
diiminate or N,N0-bis(2,6-dimethylphenyl)-2,4-pentane-
diiminate [16]. Here, we used the dichloride of
lanthanide with the later one as the starting material
and synthesized bisdiphenylamino complexes of Yb
and Nd. The catalytic activity of the novel compounds
synthesized was also tested. Both of the complexes
showed good activity for the polymerization of acryloni-
trile and e-caprolactone. We would like to report the
results.
complexes provided evidence of the presence of the sub-
stituents, the paramagnetic nature of these complexes
hindered full interpretation of the spectra. Definitive
formulation of the structural features of 3 and 4 was gi-
ven by single-crystal X-ray crystallography. The crystal
structural studies provided the coordination geometry of
the central metal and the connectivity of the ligand.
Complexes 3 and 4 are air- and moisture-sensitive and
have good solubility in THF and DME and moderate
solubility in toluene.
2.2. Molecular structures
The molecular structures of complexes 3 and 4 are
shown in Figs. 1 and 2, respectively. Selected bond
lengths and angles are given in Table 1. Complexes 3
and 4 are isostructural. Both of them have solvated
monomeric structure with a five-coordinate lanthanide
center ligated by two nitrogen atoms of the chelating
bidentate b-diketiminate anion, two nitrogen atoms
from two diphenylamino groups, and one oxygen atom
of the THF molecule. The coordination geometry
around the lanthanide ion for each complex can be de-
scribed as a distorted trigonal bipyramid. In each com-
plex, N(1), N(3) and N(4) form the equatorial vertices
(the sum of these bond angles is 359.6ꢁ for 3 and
359.99ꢁ for 4), another nitrogen atom [N(2)] and the
oxygen atom of the THF occupy the apical positions
[the angle of N(2)–Yb(1)–O(1), 170.0(1)ꢁ; N(2)–Nd(1)–
O(1), 174.92(4)ꢁ; see Table 1]. The structures of the
five-coordinate dichloride and dimethyl complexes sup-
ported by b-diketiminate are reported [13,17]. Thus,
the structural features of the diamido congener can be
comparable with them. The corresponding values of
175.5(3)ꢁ in dimethyl complex and 175.31(16)ꢁ in dichlo-
ride were found [13,17].
2. Results and discussion
2.1. Synthesis
Complex 1 can be conveniently synthesized in high
yield by metathesis reaction of YbCl3 with b-diketimi-
nate lithium [16]. Thus, the corresponding Nd complex
can also be prepared by the same method. LLi reacted
with 1 equiv. of anhydrous NdCl3 in THF after workup
to afford the desired b-diketiminate neodymium dichlo-
ride which was identified by elemental analysis as two
THF-solvated complex LNdCl2(THF)2 (2) in 71% yield
as green crystals (Scheme 1). The IR spectrum of com-
plex 2 exhibited the strong absorptions near 1550 cmꢀ1
,
which was consistent with partial C@N double bond
character.
Complexes 1 and 2 are useful precursors for further
transformation. The metathesis reaction of 1 and 2 with
2 equiv. of LiNPh2 in THF allowed for the replacement
of chloride and the production of the one THF-solvated
diamido complex LLn(NPh2)2(THF) [Ln = Yb (3), Nd
(4)] in 72% and 80% yield, respectively (Scheme 1).
Recrystallization from concentrated toluene solution
gave 3 as blue crystals while 4 as light purple crystals.
They were characterized by elemental analyses, IR spec-
tra and NMR spectroscopy. The infrared spectra of
these complexes showed characteristic absorptions of
1
the b-diketiminate ligand. Although H NMR for both
Ar
Ln
Ar
Ar
THF
Ar
Li
THF
NPh2
N
N
N
N
N
N
2Ph NLi
2
THF
Cl
Cl
LnCl3
+
Ln
Toluene
Toluene
NPh2
THF
Ar
Ar
Ln =Yb (3), Nd (4)
Ln = Yb(1), Nd (2)
Ar =
Scheme 1.
Fig. 1. The molecular structure of complex 3.

M. Xue et al. / Journal of Organometallic Chemistry 690 (2005) 4685–4691
4687
Fig. 2. The molecular structure of complex 4.
˚
˚
The b-diketiminate ligand is symmetrically coordi-
tively] for 3 and 0.049 A [2.432(1) and 2.481(1) A, respec-
tively] for 4. The average Yb–N (b-diketiminate ligand)
nated to the center metal with the variation in Ln–N
˚
˚
˚
bond lengths of 0.028 A [2.320(4) and 2.348(4) A, respec-
distance is 2.334 A, which is also comparable to that in
the analogous complex (ArO) [(DIPPh)2nacnac]YbCl-
(THF) (2.339 A) [(DIPPh)2nacnac = N,N -bis(2,6-diiso-
Table 1
0
˚
˚
Selected bond lengths (A) and angles (ꢁ) for 3 and 4
propylphenyl)-2,4-pentanediiminate] [18]. The average
3
4
˚
Nd–N (b-diketiminate ligand) distance of 2.456 A com-
˚
Bond lengths (A)
pares well with the distance in complex 3 when the differ-
ence in ionic radii between Yb3+ and Nd3+ is considered
[19]. The bond distances of N(1)–C(2), C(2)–C(3), C(3)–
C(4) and C(4)–N(2) in both complexes lie intermediate
between the corresponding single- and double-bond dis-
tances (see Table 1), which suggest significant delocaliza-
tion with the p-system of b-diketiminate backbone
(NC3N). The quite long distances between metal center
and the carbon atoms of the backbone of the b-diketimi-
nate ligand in these two complexes reveal that the b-dik-
etiminate ligand only acts as an N,N0-bonded chelate;
additionally, the five atoms of the ligand are virtually
coplanar with the highest deviation from the plane de-
Ln(1)–O(1)
Ln(1)–N(2)
Ln(1)–N(4)
N(1)–C(6)
N(2)–C(14)
N(3)–C(28)
N(4)–C(40)
C(2)–C(3)
C(4)–C(5)
Ln(1)–N(1)
Ln(1)–N(3)
N(1)–C(2)
N(2)–C(4)
N(3)–C(22)
N(4)–C(34)
C(1)–C(2)
C(3)–C(4)
2.396(3)
2.348(4)
2.212(3)
1.455(6)
1.457(6)
1.409(6)
1.388(5)
1.395(7)
1.519(7)
2.320(4)
2.238(3)
1.347(5)
1.325(6)
1.415(5)
1.430(5)
1.520(7)
1.409(7)
2.545(1)
2.481(1)
2.370(1)
1.436(2)
1.448(2)
1.406(2)
1.413(2)
1.399(2)
1.509(2)
2.432(1)
2.348(1)
1.335(2)
1.328(2)
1.398(2)
1.415(2)
1.510(2)
1.415(2)
˚
fined by these atoms being 0.0689 A for C(4) in 3 and
˚
0.0504 A for C(3) in 4, respectively. The central atom sits
˚
˚
0.6421 A out of this plane for Yb and 0.7621 A for Nd,
Bond angles (ꢁ)
O(1)–Ln(1)–N(1)
O(1)–Ln(1)–N(3)
N(1)–Ln(1)–N(2)
N(1)–Ln(1)–N(4)
N(2)–Ln(1)–N(4)
C(2)–N(1)–Yb(1)
C(3)–C(2)–N(1)
N(2)–C(4)–C(3)
O(1)–Ln(1)–N(2)
O(1)–Ln(1)–N(4)
N(1)–Ln(1)–N(3)
N(2)–Ln(1)–N(3)
N(3)–Ln(1)–N(4)
C(4)–N(2)–Yb(1)
C(4)–C(3)–C(2)
˚
92.5(1)
88.1(1)
80.2(1)
122.3(1)
95.2(1)
125.4(3)
125.3(4)
124.0(4)
170.0(1)
82.9(1)
115.3(1)
101.2(1)
122.0(1)
127.8(3)
130.1(4)
101.83(4)
83.56(4)
73.68(4)
117.92(4)
99.16(4)
130.9(1)
124.0(1)
123.9(1)
174.92(4)
85.00(4)
115.14(4)
96.14(4)
126.93(4)
129.9(1)
128.8(1)
which are comparable to 0.815 A for dimethyl complex
[13] and 0.694 A for dichloride [17].
˚
Ln–N(NPh2) bond distances are 2.238(3) and
˚
˚
2.212(3) A for Yb, 2.348(1) and 2.370(1) A for Nd,
respectively, which are comparable to those in lanthano-
˚
cene amide complexes: (C5Me5)2YbNPh2, 2.216(5) A
[20]; [Li(DME)3][(C5H5)2Nd(NPh2)2], 2.421(7), 2.434(7) A
˚
[21]. The Yb–N(NPh2) bond distances also compare
well with the distance found in another b-diketiminate
lanthanide amide (CH3C5H4)[(DIPPh)2nacnac]YbNPh2
˚
[2.259(6) or 2.214(6) A] [22]. The N(1)–Yb–N(2)
angle is 80.2(1)ꢁ , more acute than the corresponding
parameter in complexes [(DIPPh)2nacnac]ScCl2(THF)

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M. Xue et al. / Journal of Organometallic Chemistry 690 (2005) 4685–4691
[86.77(17)ꢁ] [17] and [(DIPPh)2nacnac]Sc(Me)2(THF)
[85.2(3)ꢁ] [13]. It is reasonable to ascribe the difference
in bond angle of complex 3 to the increased steric conges-
tion of the diphenyl amino anion.
The solvent has great effect on the polymer yields.
The solvents with ÔhighÕ dielectric constant, such as
DME and THF, give higher conversions for both com-
plexes. However, the slight difference in activity existed
in these two complexes. For complex 3, the active order
for solvent was DME > THF > toluene, while THF >
DME > toluene for complex 4 was observed.
2.3. Polymerization of acrylonitrile
Several organolanthanide complexes were reported to
be able to catalyze the polymerization of acrylonitrile
including [(tert-BuCp)2NdCH3]2 [23], (ArO)2Sm [24]
[(g5:g1-C5Me4SiMe2NCMe3)Y(CH2SiMe3)(THF)] [25],
La(C5Me5)[(CH(SiMe3)2)]2(THF) [26], Ln(SAr)3(py)3
(La = Sm, Yb) [27] and Ln(OAr)3 (Ln = La, Y) [28].
However, few report concerning with the reactivity of
organolanthanide amide for the acrylonitrile polymeri-
zation was reported. In order to understand further
the chemistry of lanthanide complex containing Ln–N
bond, the catalytic activity of Yb and Nd compounds
for the acrylonitrile polymerization was examined. The
preliminary results are listed in Table 2. It can be seen
that both of Yb and Nd complexes exhibit good cata-
lytic activity. For example, the conversion reaches to
69% when the loading of catalyst is 1:400 (molar ratio
of Ln to monomer) at 0 ꢁC in DME for 3 (entry 5)
and 51% conversion can still be obtained when the load-
ing decreases to 1:1000 (entry 3). The catalytic activity is
comparable to those of Ln(SAr)3(py)3 (La = Sm, Yb)
[27] and Ln(OAr)3 (Ln = La, Y) [28] and higher than
those of [(tert-BuCp)2NdCH3]2 [23] and [(g5:g1-C5Me4-
SiMe2NCMe3)Y(CH2SiMe3)(THF)] [25]. The influence
of catalyst concentration on the polymerization has
been investigated in DME or THF at 25 ꢁC as shown
in Table 2. The data indicate that conversion depends
appreciably on catalyst concentration.
The polymerizations were carried out at 0 and 25 ꢁC,
respectively to see the effect of temperature. As shown in
Table 2, the polymerization rate increases with the
increasing temperature, while the molecular weights of
the resulting polymer were almost unaffected within
the polymerization temperature range. The microstruc-
tures of the resulting polymers were determined by 13C
NMR to be atactic.
2.4. Ring-opening polymerization of e-caprolactone
Complexes 3 and4 also showed high activity for the
ring-opening polymerization of e-caprolactone under
the mild conditions as shown in Table 3 (Scheme 2).
The monomer conversion reached to 100% for both cat-
alytic systems under the conditions of [M]/[I] = 1000
(mole ratio) at 0 ꢁC in 15 min (entries 5 and 9). Even
the catalytic loading decreases to [M]/[I] = 1500, the
polymerization still gives the conversion as high as
86% for 3 (entry 4) and 96% for 4 (entry 8). Although
there is no report on the catalytic activity of diphenyl
amido complexes of lanthanide for the ring-opening
polymerization of e-caprolactone in the literature, the
activity can be compared with the other amide com-
plexes published. It was obvious that the activity of title
complexes is slightly lower than that of bis(guandi-
nate)lanthanide diisopropylamido complexes [29] while
Table 2
Polymerization of acrylonitrile with LLn(NPh2)2(THF) [Ln = Yb (3), Nd (4)]
Entrya
Initiator
Tp (ꢁC)
Solvent
[M]/[I]
Yieldb (%)
Mg( · 10ꢀ4
)
Tacticity (%)
rr
mr
mm
31.2
1
2
3
4
5
6
7
8
9
10
11
12
a
3
25
25
25
0
DME
DME
DME
DME
DME
DME
THF
THF
PhMe
THF
400
700
1000
400
400
400
400
400
400
400
700
400
64
55
51
48
69
51
46
61
17
61
50
36
2.83
5.58
6.11
3.59
3.79
3.91
2.64
3.14
2.02
1.91
2.71
1.10
3
3
3
3c
3d
3
0
22.2
46.6
25
25
25
25
25
25
25
3e
3
26.8
26.9
28.1
25.2
45.2
41.0
43.2
42.5
27.9
32.1
28.7
32.2
4
4
THF
PhMe
4
General polymerization conditions: polymerization time 1 h, [M] = 7.5 mol/L.
Yield: weight of polymer obtained/weight of monomer used.
Polymerization time: 3 h.
Polymerization time: 0.5 h.
Polymerization time: 2 h.
b
c
d
e

M. Xue et al. / Journal of Organometallic Chemistry 690 (2005) 4685–4691
4689
Table 3
Ring-opening polymerization of e-caprolactone initiated by LLn(NPh2)2(THF) [Ln = Yb (3), Nd (4)]
Entrya
Initiator
Tp (ꢁC)
[M] (mol/L)
[M]/[I]
Yieldb (%)
Mn( · 10ꢀ4
)
Mw/Mn
c
1
2
3
4
5
6
7
8
9
a
3
3
3
3
3
4
4d
4
4
25
25
25
25
0
25
25
25
0
0.038
0.075
1.5
1.5
1.5
1.5
1.5
1.5
1.5
500
500
95
100
100
86
100
100
100
96
12.17
10.66
11.42
10.08
9.61
15.38
11.85
9.86
1.71
1.85
1.78
1.65
1.35
1.90
1.71
1.79
1.50
1000
1500
1000
1000
1000
1500
1000
100
15.97
General polymerization conditions: in toluene, polymerization time 15 min.
Yield: weight of polymer obtained/weight of monomer used.
Measured by GPC calibrated with standard polystyrene samples.
Polymerization time: 3 min.
b
c
d
of oxygen by refluxing over Na or sodium benzophe-
none ketyl and distilled under argon prior to use. Anhy-
drous LnCl3 [31] and LLi [32] were prepared according
to the literature methods. LiNPh2 was obtained by the
reaction of HNPh2 with n-BuLi in a solution of toluene
and hexane. Acrylonitrile and e-caprolactone were dried
by stirring with CaH2 for 48 h, and then distilled under
reduced pressure. Melting points were determined in
argon-filled capillary tubes and are uncorrected. Lantha-
nide 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; quoted data are the average of at least
two independent determinations. The IR spectra were
O
O
O
O
C
Cat
CH
2
n
5
n
Scheme 2.
much higher than that of the diisopropylamido com-
plexes supported by methylcyclopentadienyl ligand
[30]. The active order of Nd > Yb was observed, which
is in agreement with that found for metallocene-based
organolanthanide catalysts [30] and guandinate ones
[29]. The polymerization systems give high molecular
weight polymers (Mn > 104) with a relatively narrow
molecular-weight distribution (Mw/Mn = 1.35–1.90).
1
recorded on a Nicolet Magna-IR 550 spectrometer. H
NMR and 13C NMR spectra were obtained in C6D6
solution for lanthanide complexes and in DMSO-d6
for polymers using a Unity Inova-400 spectrometer.
Molecular weight and molecular weight distributions
were determined against polystyrene standards by gel
permeation chromatography (GPC) at 30 ꢁC with a
Waters 1515 apparatus with three HR columns (HR-1,
HR-2, HR-4) using THF as the eluent. The triad tactic-
ities (mm, mr, and rr) of the PAN were determined from
the ratio of intensities for three methyne-carbon peaks
(26.8 ppm for mm, 27.4 ppm for mr and 27.9 ppm for
rr) in the 13C NMR spectrum [33]. The intrinsic viscosity
of polymer was determined by Ubbelodhe-type viscom-
eter in DMF at 25 ꢁC and the viscosity–average molec-
ular weights (Mg) were calculated by the following
equation [34]:
3. Conclusion
In summary, two new soluble lanthanide amides sup-
ported by b-diketiminate ligand were successfully syn-
thesized in good yield by the metathesis reaction of
b-diketiminate lanthanide dichloride with LiNPh2 in a
1:2 molar ratio, and their crystal structures were deter-
mined. The diamido complexes supported by b-diketi-
minate were found to be the novel catalysts for the
polymerization of acrylonitrile with good activity to give
atactic polyacrylonitriles and for the ring-opening poly-
merization of e-caprolactone with high catalytic activity.
A systematic study of the catalytic activity of b-diketimi-
nate lanthanide amides in the homogeneous catalysis is
ongoing in our laboratory.
½gꢁ ¼ 2.43 ꢂ 10ꢀ2M0g.75
.
4.1. Synthesis of LNdCl2(THF)2 (2)
4. Experimental
A solution of LLi (30 mL, 3.72 mmol) in toluene–
hexane was slowly added to a suspension of NdCl3
(0.93 g, 3.72 mmol) in 40 mL THF at room temperature.
The color of the solution gradually changed to green.
All manipulations were performed under pure Ar
with rigorous exclusion of air and moisture using stan-
dard Schlenk techniques. Solvents were dried and freed

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M. Xue et al. / Journal of Organometallic Chemistry 690 (2005) 4685–4691
The reaction mixture was stirred overnight at room tem-
perature. The solvent was removed in vacuum and tolu-
ene was added to extract the product. The dissolved
portion was removed by centrifugation. The green
crystals were obtained from the concentrated toluene
solution at room temperature (1.76 g, 71%). Mp: 175–
177 ꢁC (dec). Anal. Calc. for C25H33N2Cl2O2Nd: C,
49.30; H, 5.46; N, 4.60; Nd 23.70. Found: C, 49.02; H,
5.57; N, 4.35; Nd, 23.82. IR (KBr pellet, cmꢀ1): 3137
(s), 2967 (s), 2847 (s), 2658 (w), 1597 (s), 1555 (vs),
1443 (s), 1381 (m), 1300 (s), 1200 (m), 1096 (s), 1042
(m), 968 (w), 763 (m).
0.0278 mmol) in DME (0.74 mL) at 25 ꢁC, followed by
the precipitation of yellow, atactic poly(acrylonitrile).
The polymerization was terminated after 1 h by adding
ethanol containing 5% HCl solution. The resulting poly-
mer was collected by centrifugation, washed with water
and ethanol, and then dried to constant weight in
vacuum.
4.5. Polymerization of e-caprolactone
To a toluene solution (3.8 mL) of e-caprolactone
(0.80 mL, 7.22 mmol) was added at once a toluene solu-
tion (1 mL) of complex 3 or 4 (7.22 · 10ꢀ3 mmol) with
vigorous magnetic stirring at the desired temperature.
After the polymerization was carried out for a fixed
time, the reaction mixture was quenched by ethanol con-
taining 2% HCl solution and was then poured into eth-
anol to precipitate the polymer, which was dried under
vacuum and weighted.
4.2. Synthesis of LYb(NPh2)2(THF) (3)
To a slurry of anhydrous YbCl3 (1.43 g, 5.12 mmol)
in about 40 mL THF was slowly added the solution of
LLi (20 mL, 5.12 mmol) in toluene–hexane at room tem-
perature. After YbCl3 disappeared completely, the solu-
tion of LiNPh2 (20 mL, 10.24 mmol) in THF-hexane
was added slowly. After being stirred at r.t. for 48 h,
the solvents were stripped off in vacuum and toluene
was added to extract the product. The blue supernatant
was then concentrated and cooled to ꢀ10 ꢁC to give blue
crystals (3.28 g, 72%). Mp: 135–138 ꢁC (dec). Anal.
Calc. for C49H53N4OYb: C, 66.35; H, 6.02; N, 6.32;
Yb, 19.51. Found: C, 65.93; H, 6.08; N, 6.42; Yb,
19.50. 1H NMR (C6D6, ppm): 0.3–1.93 (m, 10H),
2.10–2.33 (m, 12H), 4.87–5.02 (br, 4H), 5.36 (br, 1H),
6.89–8.40 (br, 26H). IR (KBr pellet, cmꢀ1): 3044 (m),
2920 (m), 2859 (w), 1624 (m), 1593 (s), 1555 (s), 1493
(s), 1466 (m), 1420 (w), 1312 (m), 1219 (s), 1157 (s),
1092 (w), 1026 (w), 876 (w), 748 (m).
4.6. X-ray structural determination of 3 and 4
Suitable single crystals of complexes 3 and 4 were
each sealed in a thin-walled glass capillary, and intensity
data were collected on a Rigaku Mercury CCD
equipped with graphite-monochromated Mo Ka (k =
˚
0.71073 A) radiation. Details of the intensity data collec-
tion and crystal data are given in Table 4. The crystal
structures of these two complexes were solved by direct
Table 4
Details of the crystallographic data collection and refinement for 3 and
4
3
4
Empirical formula
Formula weight
Temperature (K)
Wavelength (A)
Crystal dimensions (mm)
Crystal system
C
887.02
193.1
49H53N4OYb
C49H53N4ONd
858.22
193.1
4.3. Synthesis of LNd(NPh2)2(THF) (4)
The synthesis of complex 4 was carried out by the
procedure for the synthesis of complex 3, but NdCl3
(1.40 g, 5.59 mmol) was used instead of YbCl3. Recrys-
tallization from toluene yielded light purple crystals of
4 (3.84 g, 80%). Mp: 122–124 ꢁC (dec). Anal. Calc. for
C49H53N4ONd: C, 68.58; H, 6.22; N, 6.54; Nd, 16.81.
Found: C, 68.11; H, 6.16; N, 6.62; Nd, 16.70. 1H
NMR (C6D6, ppm): 0.3–1.50 (br, 10H), 2.19 (br, 12H),
3.63 (br, 4H), 5.04 (br, 1H), 6.91–8.01 (br, 26H). IR
(KBr pellet, cmꢀ1): 3044 (m), 2924 (m), 1624 (m), 1593
(s), 1551 (s), 1501 (s), 1424 (m), 1308 (m), 1242 (s),
1215 (s0, 1157 (s), 1088 (w), 1026 (w), 876 (w), 748 (m)
˚
0.71070
0.60 · 0.20 · 0.20
Monoclinic
P21/n (#14)
11.4664(10)
30.515(3)
12.2354(12)
90
102.784(4)
90
4175.0(7)
4
1.411
1812.00
2.281
3.1–27.5
42105
9506 (0.053)
0.71070
0.60 · 0.55 · 0.40
Orthorhombic
Pbca (#61)
17.8023(9)
15.4081(9)
30.469(2)
90
90
90
8357.7(8)
8
1.364
Space group
˚
a (A)
˚
b (A)
˚
c (A)
a (ꢁ)
b (ꢁ)
c (ꢁ)
3
˚
V (A )
Z
Dcalc (g cmꢀ3
F(000)
)
3544.00
1.283
3.0–27.5
83834
cmꢀ1
.
l (mmꢀ1
)
h Range (ꢁ)
Reflections collected
Independent
4.4. Polymerization of acrylonitrile
9491 (0.039)
reflections (Rint
)
A typical example of polymerization is given below.
An intense orange-red solution formed as soon as
acrylonitrile (0.74 mL, 0.59 g, 11.1 mmol) was added
to a blue solution of LYb(NPh2)2(THF) (24.7 mg,
Variables
R
Rw
Goodness-of-fit on F2
550
549
0.042 [I > 2.00r(I)]
0.091 [I > 2.00r(I)]
1.002
0.047 [I > 3.00r(I)]
0.165 [I > 3.00r(I)]
1.001

M. Xue et al. / Journal of Organometallic Chemistry 690 (2005) 4685–4691
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5. Supplementary data
Crystallographic data for the structural analysis have
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12 Union Road, Cambridge CB2 1EZ, UK, fax: +44
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