Synthesis and reactivity of organolanthanoid complexes containing N and S ligands

Article abstract of DOI:10.1016/S0022-328X(01)01478-4

This paper provides a brief account of our recent researches in organolanthanoid chemistry containing N and S ligands. The first is concerned with the synthesis of organolanthanoid complexes, including anionic, supramolecular, neutral organolanthanoid amides and the organolanthanoid complexes supported by β-diketiminate, as well as organolanthanoid thiolates. The second deals with the reactivity of these organolanthanoid complexes, including the reaction with phenyl isocyanate, CS₂, and phenyl isothiocyanate, and the catalytic activity for the polymerization of polar monomers, such as methyl methacrylate, (dimethylamino) ethyl methacrylate and ε-caprolactone.

Full text of DOI:10.1016/S0022-328X(01)01478-4

Journal of Organometallic Chemistry 647 (2002) 180–189
www.elsevier.com/locate/jorganchem
Synthesis and reactivity of organolanthanoid complexes containing
N and S ligands
Qi Shen a,b,*, Yingming Yao a
a Department of Chemistry and Chemical Engineering, Suzhou Uni6ersity, Suzhou 215006, People’s Republic of China
b State Key Laboratory of Organometallic Chemistry, Shanghai Institute of Organic Chemistry, Chinese Academy of Sciences,
Shanghai 200032, People’s Republic of China
Received 22 September 2001; accepted 29 November 2001
Abstract
This paper provides a brief account of our recent researches in organolanthanoid chemistry containing N and S ligands. The
first is concerned with the synthesis of organolanthanoid complexes, including anionic, supramolecular, neutral organolanthanoid
amides and the organolanthanoid complexes supported by b-diketiminate, as well as organolanthanoid thiolates. The second deals
with the reactivity of these organolanthanoid complexes, including the reaction with phenyl isocyanate, CS2, and phenyl
isothiocyanate, and the catalytic activity for the polymerization of polar monomers, such as methyl methacrylate, (dimethy-
lamino)ethyl methacrylate and o-caprolactone. © 2002 Elsevier Science B.V. All rights reserved.
Keywords: Organolanthanoid complex; Synthesis; Reactivity; Activation small molecule; Polymerization
1. Introduction
organolanthanoid containing N and S ligand. Here, we
will present the results obtained in our laboratory.
The chemistry of organolanthanoid complexes con-
taining N and S ligand has been relatively unexplored.
Actually, the absolute bond disruption enthalpies of
2. Synthesis of organolanthanoid complexes containing
N and S ligands
LnꢀN and LnꢀS bonds are 48.2 and 73.4 kcal mol−1
,
respectively. The former lies at an intermediate between
those of LnꢀO and LnꢀC bonds, the latter is near that
of lanthanoid oxide [1]. As a result, the LnꢀN bond is
less strong than the LnꢀO bond and even comparable
to LnꢀC bonds, and the strength of LnꢀS bond might
be the same as that of LnꢀO bond. The characteristic
LnꢀN and LnꢀS bonds offers organolanthanoid amides
and organolanthanoid sulfides an opportunity to get
their reaction chemistry comparable to that of
organolanthanoid alkyl complexes and organolan-
thanoid alkoxides, respectively. Therefore, a study of
the reactivity of organolanthanoid amides and sulfides
might be interesting both for understanding the chem-
istry of LnꢀN and LnꢀS bonds and for exploring their
new reaction model. In recent years, we have focused
our attention on the synthesis and reactivity of
2.1. Synthesis of organolanthanoid amide
Anionic lanthanocene amide complexes, formulated
as [LiL][CpnLn(NR2)4−n] (n=1, 2; L=donor) are
commonly isolated from the reaction of lanthanocene
chloride with lithium amide in aprotic solvents [2]. By
using a similar method, we have synthesized the follow-
ing complexes [Li(THF)4][(t-BuC5H4)Yb(NPh2)3] [3],
[Li(DME)3][(t-BuC5H4)2Nd(NPh2)2]·1/2DME [4].
(t-BuC5H4)YbCl2
THF
+LiNPh2 “ [Li(THF)4][(t-BuC5H4)Yb(NPh2)3]
(1)
(t-BuC5H4)2NdCl
1)THF
+LiNPh22ꢀ)DꢀMꢀꢁE[Li(DME)3][t-BuC5H4)2Nd(NPh2)2]
(2)
* Corresponding author. Tel.: +86-512-5112513; fax: +86-512-
5112371.
E-mail address: qshen@suda.edu.cn (Q. Shen).
Due to the lanthanide contraction, bis(cyclopentadi-
enyl) or bis(methylcyclopentadienyl) early lanthanide
0022-328X/02/$ - see front matter © 2002 Elsevier Science B.V. All rights reserved.
PII: S0022-328X(01)01478-4

Q. Shen, Y. Yao / Journal of Organometallic Chemistry 647 (2002) 180–189
181
chloride is well known to be not stable enough to be a
precursor for the synthesis of their corresponding
derivatives [5]. We use anionic compounds, (C5H5)2-
NdCl·LiCl(THF)n and [(THF)2Li(m-Cl)2]2[(MeC5H4)-
La(THF)], as precursors, and successfully synthesized
first amide compounds with early lanthanide metals,
[Li(DME)3][(C5H4)2Nd(NPh2)2] [6] and [Li(DME)3]-
[(MeC5H4)La(NPh2)3] [7], respectively.
OAr)2]}n [9] and [(m:h5-C5Me5)Sm(OAr)(m:h5-C5Me5)-
K(THF)2]n [10].
The metathesis reaction of lanthanocene chloride
with LiNR2 takes place in aprotic solvents, such as
toluene or hexane, the corresponding neutral lan-
thanocene amide was isolated in good yields. For exam-
ple, (MeC5H4)2LnCl(THF) reacts with LiN(i-Pr)2,
LiNC5H10 (piperidine) in toluene to give the corre-
sponding amide, (MeC5H4)2LnN(i-Pr)2(THF) (Ln=Y,
Er, Yb) [11], (MeC5H4)2LnNC5H10(HNC5H10) (Ln=Y,
Er, Yb) [12].
(C5H5)2NdCl·LiCl(THF)n
1)THF
+2LiNPh22ꢀ)DꢀMꢀꢁE[Li(DME)3][(C5H5)2Nd(NPh2)2]
(3)
toluene
(MeC5H4)2LnCl+LiNR2 ꢀꢀꢀꢁ (MeC5H4)2LnNR2(L)
(MeC5H4)LaCl2·2LiCl(THF)3
1)THF
+3LiNPh22ꢀ)DꢀMꢀꢁE[Li(DME)3][(MeC5H4)La(NPh2)3] (4)
Ln=Y, Er, Yb; NR2=N(i-Pr)2, NC5H10
(6)
Even use of LiNPh2 as amido ligand, the neutral
compounds free of LiNPh2, (MeC5H4)2YbNPh2(THF),
(t-BuC5H4)2YbNPh2(THF), and (C5Me5)2YbNPh2, are
also isolated in good yield [13]. All the complexes,
except (C5Me5)2YbNPh2, are solvated.
The indenyl amido complex for lanthanide was pre-
pared by the reaction of Ln[N(i-Pr)2]3 and indene in
toluene [14].
X-ray structure determination shows that all these
complexes synthesized have an ion-pair structure
formed by lanthanide anion and lithium cation. Taking
[Li(DME)3][(MeC5H4)La(NPh2)3] as an example, its
molecular structure is shown in Fig. 1. The bond dis-
tances of LnꢀN for the above complexes range from
,
2.234(1) to 2.459(7) A.
When sodium diphenylamide, instead of lithium
diphenylamide, was used as a reagent, a self-assembly
of supramolecular lanthanide amide complexes bearing
both diphenylamido and methylcyclopentadienyl lig-
ands, [Na(THF)2(m-h5:h5-MeC5H4)2Ln(NPh2)2]n (Ln=
Sm, Er) was obtained [8].
n(MeC5H4)2LnCl(THF)
THF
+2nNaNPh2 “ [Na(THF)2(MeC5H4)2Ln(NPh2)2]n
Ln=Sm, Er
(5)
These complexes possess a polymeric structure com-
posed of units of Na(THF)2(m-h5:h5-MeC5H4)2Ln-
(NPh2)2, in which sodium is incorporated into the
complex via bridging interactions of two h5-MeC5H4
groups with lanthanide atoms (Fig. 2). The crystal
structure is similar to those of {K[(m-C5H5)2Nd(m-
Fig. 2. Molecular structure of [Na(THF)2(m-h5:h5-CH3C5H4)2-
Sm(NPh2)2]n.
Fig. 1. Molecular structure of [Li(DME)3][(MeCp)La(NPh2)3].

182
Q. Shen, Y. Yao / Journal of Organometallic Chemistry 647 (2002) 180–189
toluene
Ln[N(i-Pr)2]3(THF)+2C9H8 ꢀꢀꢀꢁ (C9H7)2LnN(i-Pr)2
+2HN(i-Pr)2 Ln=Gd, Y, Er
(7)
Organolanthanoid derivatives bearing RCONR% moi-
ety have been reported to be synthesized by the inser-
tion of CO into the SmꢀN bond of complex
[(C5Me5)2Sm]2(N2Ph2)[15], phenyl isocyanate to the
LnꢀN bond of (MeC5H4)2LnN(i-Pr)2(THF) [11], and
the reduction coupling reaction of phenyl isocyanate
mediated by [(ArO)2Sm(THF)3](THF) [16], respectively.
This kind of complex can also be synthesized straight-
forward by metathesis of lanthanocene chloride with
corresponding alkali metal salts. Thus, (MeC5H4)2-
¸¹¹¹¹¹¹º
Fig. 3. Molecular structure of (MeC5H4)2YbOCN(CH2)4CH2.
LnCl(THF) reacts with equivalent LiOCN(CH2)4CH2
in toluene gives the complexes (MeC5H4)2-
¸¹¹¹¹º
LnOCN(CH2)4CH2 (Ln=Y, Er, Yb) [17] (Eq. (8)). The
complex is an unsolvated dimer in which ligand
¸¹¹¹¹º
OCN(CH2)4CH2 donates four electrons to the lan-
thanide ion (Fig. 3).
(8)
2.2. Synthesis organolanthanoid complex supported by
i-diketiminate
Synthesis of organolanthanoid amide with b-diketim-
inate has also been studied in our laboratory. Using
(DIPPh)2nacnac ((DIPPh)2nacnac=N,N-diisopropy-
lphenyl-2,4-pentanediimine) as an ancillary ligand, the
b-diketiminate ytterbium dichloride [(DIPPh)2nacnac]-
YbCl2(THF)2 was prepared by the metathesis reaction
of [(DIPPh)2nacnac]Li with anhydrous YbCl3 in a 1:1
Fig. 4. Molecular structure of {[(DIPPh)2nacnac]YbCl(m-
Cl)3Yb[(DIPPh)2nacnac](THF)}·1/2MePh.
molar
ratio.
Recrystallization
of
[(DIPPh)2-
nacnac]YbCl2(THF)2 from toluene gave an unexpected
complex {[(DIPPh)2nacnac]YbCl(m-Cl)3Yb[(DIPPh)2-
nacnac](THF)}·1/2MePh, which has a rare triple chlo-
ride-bridge (Fig. 4). Reaction of [(DIPPh)2nacnac]-
YbCl2(THF)2 with one equivalent of MeC5H4Na in
THF, the mixed-ligand organolanthanoid chloride
(MeC5H4)[(DIPPh)2nacnac]YbCl was isolated in high
yield. Structure analysis reveals this complex to be a
solvent-free monomeric species (Fig. 5). It is notewor-
thy that the spectator ligand, (DIPPh)2nacnac, is coor-
dinated to the metal ion in h4 fashion. Moreover,
treatment of (MeC5H4)[(DIPPh)2nacnac]YbCl with one
equivalent of LiNPh2 or LiNi-Pr2 in THF smoothly
allowed for the replacement of chloride and the produc-
Fig. 5. Molecular structure of (MeC5H4)[(DIPPh)2nacnac]YbCl.

Q. Shen, Y. Yao / Journal of Organometallic Chemistry 647 (2002) 180–189
183
sized by the reaction of lanthanide metal with ArSSAr
[19]; metathesis reaction of anhydrous LnCl3 with MSR
tion of the complexes (CH3C5H4)[(DIPPh)2nacnac]-
YbNPh2 and (CH3C5H4)[(DIPPh)2nacnac]YbNi-Pr2 in
good yields, respectively (Scheme 1). The molecular
structure of (CH3C5H4)[(DIPPh)2nacnac]YbNPh2 is
depicted in Fig. 6. This complex is a neutral unsolvated
monomer, in which the spectator ligand adopts the h2
coordinate fashion [18].
[20]; and the ligand exchange reaction of Cp%Ln with
3
HSR [21]. In order to further study the reactivity of
organolanthanoid thiolate, we use the third method to
synthesize [(MeC5H4)2LnSPh(THF)]2 (Ln=Nd, Sm) as
shown in Eq. (9) [22]. This complex is a centrosymmet-
ric binuclear molecule, with the benzenethiol ligand as
the bridging groups.
2.3. Synthesis of organolanthanoid thiolate
2(MeC5H4)3Ln+2HSPhT“HF[(MeC5H4)2LnSPh(THF)]2
Organolanthanoid thiolate complex can be synthe-
Ln=Nd, Sm
(9)
3. Reactivity of organolanthanoid complexes containing
N and S ligands
3.1. Reacti6ity of organolanthanoid amide
Organolanthanoid amides have been widely used as
precursor for synthesis of lanthanoid compounds [23].
However, their application in homogeneous catalysts
was not known until 1989. Marks and coworkers first
reported that the organolanthanoid amide is an efficient
precatalyst for hydroamination/cyclization of N-unpro-
tected aminoolefins [24]. The pioneering work indicated
that organolanthanoid amide is potential in the homo-
geneous catalysts in the formation of CꢀN bond. Dur-
ing our study on the reactivity of organolanthanoid
amide to phenyl isocyanate (PhNCO), CS2, phenyl
isothiocyanate (PhNCS), we have found that these
molecules can be activated by organolanthanoid amide,
and new CꢀN bonds are formed in these reactions.
Scheme 1.
3.1.1. Reactions with phenyl isocyanate
Organolanthanoid amides, like (MeC5H4)2LnN(i-
Pr)2(THF), (MeC5H4)2YbNC5H10(HNC5H10), and (t-
BuC5H4)2LnNC5H10(THF) (Ln=Y, Er, Yb), all
exhibit good catalytic activity for phenyl isocyanate
oligomerization. Taking (MeC5H4)2LnN(i-Pr)2(THF) as
an example, when 300 equivalents of phenyl isocyanate
was added to (MeC5H4)2LnN(i-Pr)2(THF) at 30 °C,
the reaction took place rapidly, and solid products
came down immediately. After work up, methanol in-
soluble and soluble fractions were obtained. The
methanol soluble fraction was characterized mainly to
be a trimer of PhNCO.
The active species for the reaction was studied by
stoichiometric reaction of (MeC5H4)2LnN(i-Pr)2(THF)
with PhNCO to be a complex formed from the inser-
tion of PhNCO into LnꢀN bond of (MeC5H4)2LnN(i-
Pr)2(THF), in which a new group NPhCON(i-Pr)2 as
bidentate ligand coordinated to the central metal (Eq.
(10)).
Fig. 6. Molecular structure of (MeC5H4)[(DIPPh)2nacnac]YbNPh2.

184
Q. Shen, Y. Yao / Journal of Organometallic Chemistry 647 (2002) 180–189
(10)
The molecular structure of this complex is shown in
Fig. 7. The complex
shows the catalytic activity in PhNCO polymerization
as good as the precatalyst (MeC5H4)2YN(i-Pr)2(THF)
does [11].
Fig. 7. Molecular structure of
.
3.1.2. Reactions with CS2
Activation reaction of CS2 by organolanthanoid al-
kyl complex has been known to give the corresponding
CS2 insertion product [25]. Organolanthanoid amides,
like organolanthanoid alkyl complex, can also activate
CS2 molecule. When (MeC5H4)2YNPh2(THF) is put
together with CS2 at room temperature, the color of the
solution changed to red immediately. An insertion
product of CS2 into YꢀN bond [(MeC5H4)2Y(m-
CS2)NPh2]2 is isolated in good yield, in which a new
CꢀN bond and dithiocarbamate group are formed (Eq.
(11)). X-ray crystal structure determination shows this
complex is a dimer (Fig. 8) [26].
2(MeC5H4)2YNPh2(THF)+2CS2
“[(MeC5H4)2Y(m-CS2)NPh2]2
(11)
Analog complex (MeC5H4)2YbNPh2(THF) can also
react with CS2 to give a similar complex (MeC5H4)2Yb-
(h2-CS2)NPh2 (Eq. (12)), which has a monomeric struc-
ture (Fig. 9) [26].
Fig. 8. Molecular structure of [(MeC5H4)2Y(m-CS2)NPh2]2.
Fig. 10. Molecular structure of {(MeC5H4)2Y[m-h2-SC(NPh2)NPh]}2.
Fig. 9. Molecular structure of (MeC5H4)2Yb(m-CS2)NPh2.

Q. Shen, Y. Yao / Journal of Organometallic Chemistry 647 (2002) 180–189
185
Fig. 12. Molecular structure of (MeC5H4)2Nd[h2-SC(SPh)NPh]-
(THF).
Fig. 11. Molecular structure of [(CH3C5H4)2Nd]2[m-h2-OC(SPh)-
NPh]2.
ferred to the isocyanate carbon atom in which the new
amido ligand [OC(SPh)NPh] formed is coordinated to
central metal Nd in h2-fashion (Eq. (14)) (Fig. 11).
X-ray determination shows the complex to be a dimer
[22].
(MeC5H4)2YbNPh2(THF)+CS2
“(MeC5H4)2Yb(h2-CS2)NPh2
(12)
3.1.3. Reactions with PhNCS
Organolanthanoid amide reacts with PhNCS, an
isoelectronic analog of CS2 and PhNCO, to provide a
complex with PhNC(NPh2)S moiety. In this reaction,
PhNCS inserts to LnꢀN bond, and a new CꢀN bond
(C-NPh2) is formed (Eq. (13)).
[(MeC5H4)2Nd(m-SPh)(THF)]2+2PhNCO
“[(MeC5H4)2Nd]2[m-h2-OC(SPh)NPh]2
(14)
Both [(MeC5H4)2NdSPh(THF)]2 and (MeC5H4)2-
NdOC(SPh)NPh show good catalytic activity for
oligomerization of PhNCO [29].
2(MeC5H4)2YNPh2(THF)+2PhNCS
“{(MeC5H4)2Y(m-h2-SC(NPh2)NPh]}2
(13)
3.2.2. Reaction with PhNCS
The reaction of [(MeC5H4)2NdSPh(THF)]2 with Ph-
NCS proceeds also smoothly at room temperature. An
insertion product of PhNCS into NdꢀS bond of
[(MeC5H4)2NdSPh(THF)]2 (MeC5H4)2Nd[h2-SC(SPh)-
NPh](THF) was obtained (Eq. (15)). X-ray determina-
tion shows that the new complex contains a thiocarbon-
ate derivative, i.e. the CS2N fragment of the
dihapto-coordinated ligand, formed through SPh group
linked to the isocyanate carbon atom (Fig. 12) [22].
The characterization of molecular structure indicates
the new ligand PhNC(NPh2)S donors four electrons to
the central ion. The crystal structure is shown in Fig. 10
[26].
3.2. Reacti6ity of organolanthanoid thiolate
The synthesis of organolanthanoid thiolate has been
extensively studied up to now [27]. However, the reac-
tivity of these complexes has not been well understood
[28]. Recently, we have found that organolanthanoid
thiolate [(MeC5H4)2NdSPh(THF)]2 is able to activate
small molecules, such as PhNCO and PhNCS, the new
CꢀS bond was formed in these reactions.
[(MeC5H4)2Nd(m-SPh)(THF)]2+2PhNCS
“2(MeC5H4)2Nd[h2-SC(SPh)NPh](THF)
(15)
3.3. Polymerization of polar monomers
3.2.1. Reaction with PhNCO
Organolanthanoid complexes with LnꢀC, LnꢀH
bond have been found to be the effective single compo-
nent catalysts for ethylene polymerization without
adding any cocatalyst [30]. Moreover, they can tolerate
the existence of polar group in the monomer, and
catalyze the living polymerization of alkyl methacrylate
(acrylate) to give the polymer with high molecular
weight and narrow molecular weight distribution [31].
The catalytic behavior of organolanthanoid amides in
PhNCO can be activated by organolanthanoid thio-
late [(MeC5H4)2NdSPh(THF)]2. Thus, the reaction of
[(MeC5H4)2NdSPh(THF)]2 with one equivalent of Ph-
NCO gives the product [(MeC5H4)2NdOC(SPh)NPh]2,
which shows two strong absorptions at 1597 and 1520
cm−1 assigned to bidentate CN and CO vibrations in
its IR spectrum. It is unambiguous that in this reaction
a new CꢀS bond was formed through SPh group trans-

186
Q. Shen, Y. Yao / Journal of Organometallic Chemistry 647 (2002) 180–189
Table 1
Polymerization of MMA catalyzed by organolanthanoid amides a
Entry
Catalyst
T (°C)
C (%)
Mn (×103)
Mw/Mn
1
2
(MeC5H4)2YbN(i-Pr)2(THF)
(MeC5H4)2YbN(i-Pr)2(THF)
(MeC5H4)2YbN(i-Pr)2(THF)
(MeC5H4)2YbN(i-Pr)2(THF)
(MeC5H4)2YbNC5H10(HNC5H10
(MeC5H4)2YbNPh2(THF)
(C5Me5)2YbNPh2
(t-BuC5H4)2YbNC5H10(THF)
(MeC5H4)2YN(i-Pr)2(THF)
(C9H7)2YN(i-Pr)2
40
0
0
97.1
99.9
96.2
100
100
95.0
0
268
431
–
410
125
253
–
117
148
116
50
2.10
1.79
–
1.72
1.14
1.67
–
3 b
4
−78
5
6
7
8
)
0
0
0
0
0
0
0
61.4
100
–
9
1.31
1.23
7.9
10
93.9
11 c
(R)-(neomenthyl)LaN(TMS)2
36.0 b
a Polymerization conditions: catalyst concentration, 0.2 mol% MMA; solvent, toluene; solvent/[MMA]0=10 V/V; 2 h.
b Catalyst concentration, 0.07 mol% MMA.
c 160 h.
polymerization of polar monomer was first found by
Marks and coworkers [32]. Their work shows that the
stereospecific polymerization of methyl methacrylate
(MMA) can be carried out by use of chiral organolan-
thanoid amide. We found that organolanthanoid
amides are also highly effective catalysts for the poly-
merization of polar monomers, such as MMA,
(dimethylamino)ethyl methacrylate (DMAEMA) and
o-caprolactone.
Er\Y, which is contrary to the order of the former.
The real reason of these differences is not clear yet [12].
It should be noticed that the present polymerizations
in comparable with the system with organolanthanoid
alkyl is not well-controlled, resulting in broader molec-
ular weight distribution, and greatly inflated number-
average molecular weights. This might be due to side
reactions of the electron-rich nitrogen anion with the
highly functionalized monomer [35].
3.3.1. Polymerization of MMA
3.3.2. Polymerization of DMAEMA
Table 1 summarized the typical results of MMA
polymerization catalyzed by a variety of organolan-
thanoid amides (Scheme 2) [12–14,33].
All the work on the polymerization of methacrylates
with organolanthanoid complexes published is re-
stricted to the system of unfunctionalized methacry-
lates. Recently, we have first found that
nitrogen-functionalized methacrylate, DMAEMA can
also be polymerized effectively by organolanthanoid
amide as catalyst without cocatalyst (Scheme 3) [36].
The typical results are given in Table 2.
All these complexes, except (C5Me5)2YbNPh2, show
high catalytic activity at a quite broad range of reaction
temperature from −78 to 40 °C, and give the polymer
with high molecular weight. Taking complex
(MeC5H4)2YbN(i-Pr)2(THF) as an example, the poly-
merization gives the conversion as high as 96% at 0 °C
for 2 h even though the catalyst concentration decreases
from 0.2 to 0.07 mol% MMA [33]. p Ancillary ligand
and amido groups both have an apparent effect on the
activity. The activity increases with the decrease of the
bulk of the p ligand, C5Me5Bt-BuC5H4BMeC5H4
[34]. The activity order of amido group is NPh2BNi-
Pr2BNC5H10 which is contrary to the order of their
bulk [33b]. The influence of the metal elements on
polymerization activity has also been observed. For
(diisopropylamido)-bis(methylcyclopentadienyl)lan-
thanoids, the observed increasing order, Y\Er\Yb,
is in agreement with the order of eight-coordinate ionic
radii, and is also consistent with the activity order for
organolanthanoid hydride or alkyl complexes [33b].
However, for the bis(methylcyclopentadienyl)-
(piperidino)lanthanoids, the observed order is Yb\
All the amides, except the sterically crowded complex
(C5Me5)2YbNPh2 tested have good activity. The poly-
Scheme 2.
Scheme 3.

Q. Shen, Y. Yao / Journal of Organometallic Chemistry 647 (2002) 180–189
187
Table 2
Polymerization of DMAEMA catalyzed by organolanthanoid amides a
Entry
Catalyst
[I]/[M] (%)
T (°C)
C (%)
Mn (103)
Mw/Mn
1
2
3
4
5
6
7
(MeC5H4)2YN(i-Pr)2(THF)
(MeC5H4)2ErN(i-Pr)2(THF)
(MeC5H4)2YbN(i-Pr)2(THF)
(MeC5H4)2YbNC5H10(HNC5H10
(MeC5H4)2YbNC5H10(HNC5H10
(MeC5H4)2YbNPh2(THF)
0.2
0.2
0.2
0.2
0.2
0.2
0.2
0
0
0
100
121
182
107
178
151
256
104
1.22
1.27
1.18
1.16
1.11
1.70
1.20
99.1
99.4
100
100
99.0
99.7
)
)
0
−78
0
(t-BuC5H4)2YbNPh2(THF)
0
a Polymerization conditions: solvent, toluene; solvent/monomer=10 V/V; 2 h.
3.3.3. Ring-opening polymerization of m-caprolactone
Ring-opening polymerization of lactone catalyzed by
lanthanoid complex have been reported extensively
[31b,37]. However, almost all of the catalysts are those
complexes containing LnꢀO [38], LnꢀC [39] and LnꢀH
[39] bonds, few are those containing LnꢀN bonds [40].
We have found that bis(methylcyclopentadienyl)-
lanthanide amides and related complexes are also effi-
cient catalysts for the ring-opening polymerization of
o-caprolactone (Scheme 4), Table 3 listed the main
results obtained by a variety of amides [41].
The polymers formed are generally of high molecular
weight (Mn\100 000) with narrow polydispersities
(Mw/MnB1.5). Both the central elements and the
amido group have an apparent effect on the catalytic
activity. For the central elements, the observed increas-
ing order, YbBErBY, is in agreement with the order
of eight-coordinate ionic radii; for the amido groups,
the increasing order is N(i-Pr)2BNC5H10, which is
consistent with the order of their bulk. In addition, the
chelating ligand containing organolanthanoids
Scheme 4.
Table 3
Ring-opening polymerization of o-caprolactone by organolanthanoid
amides a
Entry Catalyst
C (%) Mn (103) Mw/Mn
1
2
3
4
(MeC5H4)2YbN(i-Pr)2(THF)
26.2
–
–
(MeC5H4)2ErN(i-Pr)2(THF)
(MeC5H4)2YN(i-Pr)2(THF)
(MeC5H4)2-
66.4 117.5
84.4 180.0
1.14
1.24
1.23
96.2
79.9
YbNC5H10(HNC5H10
)
5
6
7
8
(MeC5H4)2ErNC5H10(HNC5H10
)
99.1 118.0
1.28
1.28
1.41
1.42
(MeC5H4)2YNC5H10(HNC5H10
(t-BuC5H4)2YbNC5H10(THF)
(t-BuC5H4)2ErNC5H10(THF)
)
100
123.4
133.6
139.2
100
100
a Polymerization conditions: [M]0/[I]0=500 mol/mol; solvent, tolu-
ene; solvent/[M]0=10 V/V; 20 °C; 4 h.
merization system can be carried out in a quite broad
range of reaction temperature, and gives syndiotactic
polyDMAEMA with high molecular weight and mod-
erately molecular weight distribution. p-Ligand, amido
group and central metal all have great effect on the
polymerization activity. The active order is C5Me5Bt-
BuC5H4BMeC5H4, NPh2BN(i-Pr)2BNC5H10, YbB
ErBY, which are consistent with those in MMA
polymerization systems.
It is also observed that the activity decreases with the
increase in polymerization temperature and number
molecular weights of polyDMAEMA are deviated from
the theoretic one. These results indicate that the side
reaction might also take place together with the poly-
merization reaction in the present polymerization
system.
(Ln=Yb, Er, Y) also show good catalytic activity for
the ring-opening polymerization of o-caprolactone [17].
Organolanthanoid thiolate is also effective catalyst
for the ring-opening polymerization of o-caprolactone.
For example, using [(MeC5H4)2Sm(m-SPh)(THF)]2
as catalyst, the polymerization gives the conversion
as high as 100% at 35 °C for 3 h under the
catalyst amount of 0.1 mol% [29]. In these systems,
transesterification reaction, as a side reaction, was also
observed.
4. Conclusion
The results presented in this account show that
the chemistry of organolanthanoid complexes with

188
Q. Shen, Y. Yao / Journal of Organometallic Chemistry 647 (2002) 180–189
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in lanthanoid catalysis, as ‘CꢀN’ and ‘CꢀS’
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