Synthesis, characterization, and catalytic activity of rare earth metal amides supported by a diamido ligand with a CH2SiMe2 link

Article abstract of DOI:10.1021/ic800496d

A series of four coordinate rare earth metal amides with general formula {(CH₂SiMe₂)[2,6-ⁱPr₂C ₆H₃)N]₂}LnN(SiMe₃)₂(THF) [(Ln = Yb(2), Y (3), Dy (4), Sm (5), Nd (6)] containing a diamido ligand (CH₂SiMe₂)[(2,6-ⁱPr₂C ₆H₃)N]₂^2- with a CH ₂SiMe₂ link were synthesized in good yields via reaction of [(Me₃Si)₂N]₃Ln^III(μ-Cl)Li(THF) ₃ with the corresponding diamine (CH₂SiMe ₂)[(2,6-ⁱPr₂C₆H₃)NH] ₂ (1). All compounds were fully characterized by spectroscopic methods and elemental analyses. The structures of complexes 2, 3, 4, 5, and 6 were determined by single-crystal X-ray analyses. Investigation of the catalytic properties of the complexes indicated that all complexes exhibited a high catalytic activity on the cyclotrimerization of aromatic isocyanates, which represents the first example of cyclopentadienyl-free rare earth metal complexes exhibiting a high catalytic activity and a high selectivity on cyclotrimerization of aromatic isocyanates. The temperatures, solvents, catalyst loading, and the rare earth metal effects on the catalytic activities of the complexes were examined.

Full text of DOI:10.1021/ic800496d

Inorg. Chem. 2008, 47, 5503-5511
Synthesis, Characterization, and Catalytic Activity of Rare Earth Metal
Amides Supported by a Diamido Ligand with a CH2SiMe2 Link
Yunjun Wu,† Shaowu Wang,*,†,‡ Xiancui Zhu,† Gaosheng Yang,† Yun Wei,† Lijun Zhang,†
and Hai-bin Song§
Institute of Organic Chemistry, Anhui Key Laboratory of Functional Molecular Solids, College of
Chemistry and Materials Science, Anhui Normal UniVersity, Wuhu, Anhui 241000, P.R. China;
State Key Laboratory of Organometallic Chemistry, Shanghai Institute of Organic Chemistry,
Chinese Academy of Sciences, Shanghai 200032, P.R. China; and State Key Laboratory of
Elemento-Organic Chemistry, Nankai UniVersity, Tianjin 300071, P.R. China
Received March 19, 2008
A series of four coordinate rare earth metal amides with general formula {(CH2SiMe2)[(2,6-IPr2C6H3)N]2}LnN-
(SiMe3)2(THF) [(Ln ) Yb(2), Y (3), Dy (4), Sm (5), Nd (6)] containing a diamido ligand (CH2SiMe2)[(2,6-iPr2C6H3)N]22-
with a CH2SiMe2 link were synthesized in good yields via reaction of [(Me3Si)2N]3LnIII(µ-Cl)Li(THF)3 with the
corresponding diamine (CH2SiMe2)[(2,6-iPr2C6H3)NH]2 (1). All compounds were fully characterized by spectroscopic
methods and elemental analyses. The structures of complexes 2, 3, 4, 5, and 6 were determined by single-crystal
X-ray analyses. Investigation of the catalytic properties of the complexes indicated that all complexes exhibited a
high catalytic activity on the cyclotrimerization of aromatic isocyanates, which represents the first example of
cyclopentadienyl-free rare earth metal complexes exhibiting a high catalytic activity and a high selectivity on
cyclotrimerization of aromatic isocyanates. The temperatures, solvents, catalyst loading, and the rare earth metal
effects on the catalytic activities of the complexes were examined.
Introduction
catalysts.3 Substituted aryl-functionalized isocyanurates are
useful activators for anionic polymerization of ε-caprolactams
to nylon-6 and are known to substantially enhance the
stability of polyurethane networks and coating materials with
respect to thermal resistance, flame retardation, chemical
resistance, and film-forming characteristics.3 Different iso-
cyanate trimerization catalytic systems have been reported,
such as anions or neutral Lewis bases, organic acid salts and
tertiary amines, and some metal-based systems.3a,b Conven-
tional catalysts for cyclotrimerization of isocyanates suffer
from low activity, necessitating severe conditions, and poor
selectivity resulting in byproducts.4
From an atom-economic perspective, the reactivity of
isocyanates in the coordination sphere of various metal
centers has received some renewed interest recently.1 Such
reactions are quite attractive because they can provide a very
valuable access to various types of heterocycles as indicated
by some investigations.2 Among these investigations, much
fewer have focused on cyclotrimerization reactions of the
isocyanates, especially with rare earth metal complexes as
* To whom correspondence should be addressed. E-mail: swwang@
mail.ahnu.edu.cn.
†
Anhui Normal University.
Chinese Academy of Sciences.
Nankai University.
‡
§
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Mountford, P. Organometallics 2006, 25, 1167. (d) Dunn, S. C.;
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10.1021/ic800496d CCC: $40.75  2008 American Chemical Society
Inorganic Chemistry, Vol. 47, No. 12, 2008 5503
Published on Web 05/20/2008

Wu et al.
Scheme 1. Preparation of the Ligand 1
During the past decades, a considerable attention has been
given to the development of complexes supported by ligand
systems other than cyclopentadienyl derivatives in lanthanide
chemistry. A variety of cyclopentadienyl-free ligands have
been found to be suitable for stabilizing rare earth metal
species.5 Among these, amido ligands have attracted con-
siderable attention in recent years because the electronic
properties and steric effects of the ligands can be modified
by variation of the substituents of nitrogen atoms.6 A variety
of lanthanide complexes supported by monoamidinate ligands
have been synthesized,5a,d,g and some of them have been
found to be effective initiators for the ring-opening polym-
erization of δ-caprolactone and other polar monomers.7
However, linked diamido ligands have been relatively seldom
used in lanthanide chemistry.8,6a–g Experimental results
showed that the bridged diamido ligands significantly influ-
ence the chemical and physical properties of the resulting
organometallic complexes.5b In comparison with an un-
bridged ligand, a bridged diamido ligand will provide more
open coordination environment around the metal center,
which would be favorable for homogeneous catalysis.5g
It has been documented that isocyanate can stoichiomet-
rically insert into the rare earth metal-carbon and metal-
nitrogen bonds to produce the corresponding insertion
products.9 However, only reports on the Cp′2LnNiPr2(THF)10a
(Cp′ ) MeC5H4, Ln ) Y, Er, Yb) or Cp2LnCl/n-BuLi10b as
catalysts or catalytic system for cyclotrimerization of phenyl
isocyanate are documented. The systematic study on the
catalytic transformation of the isocyanates to isocyanurates
with cyclopentadienyl-free rare earth metal amides as
catalysts is far less explored.
Figure 1. One of two asymmetrical molecular structures of complex 2,
hydrogen atoms are omitted for clarity.
Scheme 2. Preparation of the Lanthanide Complexes
Synthesis and Characterization of the Rare Earth
Metal Complexes. Treatment of the diamine (CH2SiMe2)[(2,6-
iPr2C6H3)NH]2 (1) with 1 equiv of rare earth metal amides
[(Me3Si)2N]3LnIII(µ-Cl)Li(THF)3 in toluene produced the
corresponding rare earth metal complexes with general
formula {(CH2SiMe2)[(2,6-iPr2C6H3)N]2}LnN(SiMe3)2(THF)
(Ln ) Yb(2), Y(3), Dy(4), Sm(5), Nd(6)) (Scheme 2). The
complexes are sensitive to air and moisture, they are soluble
in solvents such as THF, toluene, CH2Cl2, and even n-hexane.
All complexes were fully characterized by spectroscopic
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ReV. 2002, 231, 1. (d) Piers, W. E.; Emslie, D. J. H. Coord. Chem.
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2001, 214, 91. (f) Xie, Z. Coord. Chem. ReV. 2006, 250, 259. (g)
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Chem. ReV. 2002, 102, 3031. (i) Gibson, V. C.; Spitzmesser, K. Chem.
ReV. 2003, 103, 283.
We report here the synthesis and structural characterization
of a series of novel rare earth metal amides incorporating a
dimethylsilylmethylene-linked diamido ligand. Their catalytic
activity on the cyclotrimerization of isocyanates will be for
the first time reported.
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Results and Discussion
Synthesis of the Ligand (CH2SiMe2)[(2,6-iPr2C6H3)NH]2
(1). Treatment of ClSiMe2CH2Cl with 2 equiv of (2,6-
iPr2C6H3)NHLi in THF gave (CH2SiMe2)[(2,6-iPr2C6H3)NH]2
(1) in 34% isolated yield as a white solid (Scheme 1, Figure
1). The compound was well characterized by spectroscopic
methods and elemental analyses. It is soluble in THF,
1
toluene, and nonpolar solvents such as n-hexane. H NMR
spectrum indicated that it decomposed upon exposure to air
for a few days.
5504 Inorganic Chemistry, Vol. 47, No. 12, 2008

Rare Earth Metal Amides Supported by a Diamido Ligand
Figure 2. One of two asymmetrical molecular structures of complex 3,
hydrogen atoms are omitted for clarity.
Figure 5. One of two asymmetrical molecular structures of complex 6,
hydrogen atoms are omitted for clarity.
The X-ray structure analyses revealed that the complexes
2-6 were all solvated monomeric structures crystallized in
the orthorhombic system with space group P212121; they are
isostructural and isomorphous. Each of the central metal
atoms of the above complexes is bonded with two unsym-
metrical nitrogen atoms of the chelating diamido ligand,
one nitrogen atom of the N(SiMe3)2 ligand and one oxygen
atom of THF molecule. Thus, compounds chiral at central
lanthanide metal were obtained; however, racemic com-
pounds crystallized in the same unit cell. Comparison of
the Ln-N bonds of the same molecule indicated that they
are not identical, and also the N-Ln-N, and the
N-Ln-O angles around the center metal are far from the
ideal tetrahedral angles (Table 1), so the coordination
geometry of the complexes can be described as distorted
tetrahedral.
Figure 3. One of two asymmetrical molecular structures of complex 4,
hydrogen atoms are omitted for clarity.
From Table 1, we can see that the usual consequences of
the increase of the ionic radius of the Ln3+ ion when moving
from Yb3+ to Nd3+ are clearly reflected by the average Ln-N
distances of 2.178(4) Å found in 2, 2.194(12) Å found in 3,
2.219(3) Å found in 4, 2.263(7) Å found in 5, and 2.294(5)
Å found in 6. The usual lanthanide contraction is also
reflected by the average Ln-O distances of 2.272(4) Å in
2, 2.294(11) Å in 3, 2.332(3) Å in 4, 2.400(7) Å in 5, and
2.446(5) Å in 6. From Table 1, we can also find that the
Ln-N bond distances for the metal to the chelating diamido
ligand are generally shorter than those of the metal to the
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4624. (b) Luo, Y. J.; Yao, Y. M.; Shen, Q.; Sun, J.; Weng, L. H. J.
Organomet. Chem. 2002, 662, 144. (c) Qian, C. T.; Nie, W. L.; Sun,
J. Organometallics 2000, 19, 4134. (d) Qian, C. T.; Zou, G.; Chen,
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Lou, Y. J.; Yao, Y. M.; Li, W. J.; Chen, J. L.; Zhang, Z. Q.; Zhang,
Y.; Shen, Q. J. Organomet. Chem. 2003, 679, 125. (g) Lou, Y. J.;
Yao, Y. M.; Shen, Q.; Yu, K. B.; Weng, L. H. Eur. J. Inorg. Chem.
2003, 318. (h) Chen, J. L.; Yao, Y. M.; Lou, Y. J.; Zhou, L. Y.; Zhang,
Y.; Shen, Q. J. Organomet. Chem. 2004, 689, 1019. (i) Kirillov, E.;
Toupet, L.; Lehmann, C. W.; Razavi, A.; Carpentier, J. F. Organo-
metallics 2003, 22, 4467. (j) Zhou, L. Y.; Yao, Y. M.; Zhang, Y.;
Xue, M. Q.; Chen, J. L.; Shen, Q. Eur. J. Inorg. Chem. 2004, 2167.
(k) Zhou, S. L.; Wang, S. W.; Yang, G. S.; Li, Q. H.; Zhang, L. J.;
Yao, Z. J.; Zhou, Z. K.; Song, H. B. Organometallics 2007, 26, 3755.
(l) Zhou, S. L.; Wang, S. W.; Sheng, E. H.; Zhang, L. J.; Yu, Z. Y.;
Xi, X. B.; Chen, G. D.; Luo, W.; Li, Y. Eur. J. Inorg. Chem. 2007,
1519.
Figure 4. One of two asymmetrical molecular structures of complex 5,
hydrogen atoms are omitted for clarity.
methods and elemental analyses. The structures of all
complexes were determined by single-crystal X-ray analyses.
Molecular Structures of the Complexes. To provide full
structural information for these rare earth metal amides,
single-crystal X-ray structural investigations were carried out
for complexes 2-6 (Figures 1–5). Selected bond lengths and
angles are listed in Table 1.
Inorganic Chemistry, Vol. 47, No. 12, 2008 5505

Wu et al.
Table 1. Selected Bond Length (Å) and Bond Angle (°) of Complexes 2-6
2
3
4
5
6
Ln(1)-N(1)
2.132(4)
2.189(4)
2.217(4)
2.269(4)
2.122(4)
2.181(4)
2.224(4)
2.275(4)
2.178(4)
2.103(12)
2.193(12)
2.223(14)
2.294(11)
2.174(11)
2.222(12)
2.250(11)
2.294(11)
2.194(12)
2.294(11)
92.1(5)
122.9(4)
132.4(4)
100.6(4)
100.6(5)
102.8(4)
94.8(4)
2.177(3)
2.224(3)
2.256(3)
2.326(3)
2.160(3)
2.225(3)
2.274(4)
2.339(3)
2.219(3)
2.210(7)
2.270(6)
2.309(7)
2.392(7)
2.188(7)
2.266(6)
2.337(7)
2.407(7)
2.263(7)
2.400(7)
90.0(2)
127.6(2)
132.6(2)
98.7(3)
100.7(3)
101.1(3)
91.7(2)
2.233(5)
2.295(4)
2.354(5)
2.438(5)
2.216(5)
2.304(4)
2.359(5)
2.453(5)
2.294(5)
Ln(1)-N(2)
Ln(1)-N(3)
Ln(1)-O(1)
Ln(2)-N(4)
Ln(2)-N(5)
Ln(2)-N(6)
Ln(2)-O(2)
Ln-Nav.
Ln-Oav.
2.272(4)
2.332(3)
2.446(5)
N(2)-Ln(1)-N(1)
N(3)-Ln(1)-N(1)
N(3)-Ln(1)-N(2)
N(1)-Ln(1)-O(1)
N(2)-Ln(1)-O(1)
N(3)-Ln(1)-O(1)
N(5)-Ln(2)-N(4)
N(6)-Ln(2)-N(4)
N(6)-Ln(2)-N(5)
N(4)-Ln(2)-O(2)
N(5)-Ln(2)-O(2)
N(6)-Ln(2)-O(2)
91.64(16)
122.78(14)
132.60(15)
100.34(15)
100.47(15)
103.51(14)
94.31(15)
125.86(15)
133.54(15)
99.70(15)
98.35(15)
96.60(15)
91.26(12)
126.50(11)
132.08(12)
99.67(12)
100.53(13)
100.89(13)
92.90(11)
126.76(12)
134.11(13)
99.31(13)
98.34(12)
96.75(13)
90.34(18)
127.77(17)
132.46(17)
99.45(19)
99.99(18)
100.12(19)
91.30(18)
129.81(17)
133.86(18)
98.21(19)
97.60(17)
96.06(18)
126.7(5)
131.5(5)
101.8(5)
98.9(4)
128.7(2)
134.0(3)
99.1(3)
97.8(2)
96.2(3)
95.9(5)
N(SiMe3)2 ligand. For example, the Yb(1)-N(1) and
Yb(1)-N(2) distances are 2.132(4) Å and 2.189(4) Å in 2,
which are shorter than the Yb(1)-N(3) distance of 2.217(4)
Å. The similar results can also be found in other rare earth
complexes 3 to 6. This may be attributable to the steric effect
of different ligands. It is also found that the N(2)-Ln(1)-N(1)
angles decrease slightly as the ionic radii increase from Yb3+
to Nd3+. The other corresponding angles are also in the
similar sequence.
The average Yb-N bond distance of 2.178(4) Å in 2 is
comparable with the average Yb-N bond distance of
2.174(1) Å found in the cyclic binuclear Yb(III) complex
[{µ-2-p-(Me3SiN)2C6H4}YbCl(THF)2]2,11 but this average
Yb-N distance is shorter than that of 2.211(5) Å found in
[(Me3Si)2N]3YbIII(µ-Cl)Li(THF)3,6h 2.2376(5) Å found in the
corresponding Yb(III) complex {[o-(Me3SiN)2C6H4]Yb-
(MeC5H4)2}{Li(DME)3},12 2.290(7) Å found in the anionic
amido complex [Me2Si(NPh)2]2Yb(THF)2Li(THF)4,13 and
2.334(4) Å found in the ꢀ-diketiminate supported lanthanide
complex LYb(NPh2)2(THF) [L ) (2,6-Me2C6H3)NC(Me)-
CHC(Me)N(2,6-Me2C6H3].14 The average Sm-N bond
distance of 2.263(7) Å in complex 5 is shorter than those of
2.322(5) to 2.334(5) Å found in complex {[o-(Me3SiN)2C6H4]-
Sm(MeC5H4)2}{Li(DME)3},12 and 2.340(4) to 2.332(4) Å
found in complex {[Me2Si(NPh)2]SmC5H5}{Li(DME)3}.13
The average Nd-N bond distance of 2.294(5) Å in complex
6 is also shorter than that of 2.456 Å ꢀ-diketiminate
supported neodymium complex LNd(NPh2)2(THF) [L )
(2,6-Me2C6H3)NC(Me)CHC(Me)N(2,6-Me2C6H3].14
The N(2)-Ln(1)-N(1) angles (formed by the chelating
diamido ligand and the center metal) of 91.64(16)° in
complexes 2, 92.1(5)° in 3, 91.26(12)° in 4, 90.0(2)° in 5,
and 90.34(18)° in 6 are significantly larger than those found
in {[Me2Si(NPh)2]Yb(MeC5H4)2}{Li(DME)3}(70.17(17)°),
{[Me2Si(NPh)2]YbC5H5}{Li(DME)3}(70.0(2)°),13 [Me2Si-
(NPh)2]2Yb(THF)2Li(THF) (89.31(11)°),13 LYbCl2(THF)2
(80.2(1)°) (L ) N, N-bis(2,6-dimethylphenyl)-2,4-pentane-
diiminate),14 {[o-(Me3SiN)2C6H4]Sm(MeC5H4)2}{Li(DME)3}
(73.45(17)°),12 and {[Me2Si(NPh)2]SmC5H5}{Li(DME)3}
(67.13(15)°).13
Catalytic Activities of the Complexes. During the study
on the reactivity of the above complexes, it is found that the
above complexes can function as catalysts for the cyclotri-
merization of aromatic isocyanates to yield triaryl isocya-
nurates with a high activity and a high selectivity. To the
best of our knowledge, it represents the first application of
cyclopentadienyl-free rare earth metal complexes on catalytic
cyclotrimerization of aryl isocyanates.
Yttrium complex 3 was employed as a catalyst for
selecting the favorable reaction conditions for the cyclotri-
merization of phenyl isocyanate. The results were listed in
Table 2. From the Table, we can see that the cyclotrimer-
ization of phenyl isocyanate could be accomplished in
solvents such as toluene, CH2Cl2, and THF in the presence
of 1-3 mol % of catalyst. It is found that the outputs of the
catalytic reaction were affected by the catalyst loading and
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R. F.; Weng, L. H. Inorg. Chem. 2005, 44, 716. (g) Zhang, C. M.;
Liu, R. T.; Zhang, J.; Chen, Z. X.; Zhou, X. Inorg. Chem. 2006, 45,
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2005, 690, 4685.
5506 Inorganic Chemistry, Vol. 47, No. 12, 2008

Rare Earth Metal Amides Supported by a Diamido Ligand
Table 2. Influence of the Conditions on the Cyclotrimerization of
Table 3. Influence of Different Rare Earth Metal Amides on the
Phenyl Isocyanate
Cyclotrimerization of Phenyl Isocyanate
entry
cat. (mol %)a
solvent
temp (°C)/time (h)
yield (%)b
entry
cat.(mol%)a
solvent
temp (°C)/time (h)
yield (%)b
1
2
3
4
5
6
7
8
3(3%)
3(2%)
3(1%)
3(1%)
3(2%)
3(1%)
3(1%)
3(3%)
3(2%)
3(1%)
3(3%)
3(2%)
3(1%)
toluene
toluene
toluene
toluene
THF
r.t./12
r.t./12
r.t./12
80/12
r.t./12
r.t./12
50/12
r.t./12
r.t./12
r.t./12
40/12
40/12
40/12
99
83
66
99
99
92
99
71
59
43
99
74
62
1
2
3
4
5
6
7
8
2(1%)
2(1%)
2(1%)
3(1%)
3(1%)
3(1%)
4(1%)
4(1%)
4(1%)
5(1%)
5(1%)
5(1%)
6(1%)
6(1%)
6(1%)
12c (1%)
12c (1%)
toluene
toluene
THF
toluene
toluene
THF
toluene
toluene
THF
toluene
toluene
THF
toluene
toluene
THF
toluene
THF
r.t./12
80/12
r.t./12
r.t./12
80/12
r.t./12
r.t./12
80/12
r.t./12
r.t./12
80/12
r.t./12
r.t./12
80/12
r.t./12
r.t./12
r.t./12
62
99
99
66
99
92
62
99
99
61
99
99
56
99
99
75
99
THF
THF
CH2Cl2
CH2Cl2
CH2Cl2
CH2Cl2
CH2Cl2
CH2Cl2
9
9
10
11
12
13
10
11
12
13
14
15
16
17
a Catalyst: yttrium complex (3), catalyst to phenyl isocyanate mole ratio.
b Isolated yield.
a Catalyst to phenyl isocyanate mole ratio. b Isolated yield. c 12:
[(Me3Si)2N]3Yb(µ-Cl)Li(THF)3.
reaction temperature when the reaction was carried out in
toluene or CH2Cl2. For example, the outputs of the reactions
decreased dramatically from 99% to 66%, and 71% to 43%
when the catalyst loading was changed from 3 mol % to 1
mol % in toluene (Table 2, entries 1-3), and in CH2Cl2
(Table 2, entries 8-10). When the reaction was carried out
at room temperature for 12 h in the presence of 1 mol %
catalyst, the conversion of phenyl isocyanate to the final
cyclotrimerization product was only 66% in toluene (Table
2, entry 3). A 99% yield of the cyclotrimerization product
was obtained when the reaction was carried out at 80 °C for
12 h, (Table 2, entry 4). It is also found that the catalytic
activity of the yttrium complex in THF was higher than that
in toluene or CH2Cl2 in the presence of the same amount of
catalyst loading (see Table 2, entries 2, 3; and entries 5, 6,
9, 10). It is notable that only the cyclotrimerization product
was isolated, and no detectable dimerization or polymeri-
zation products were observed, indicating that the complex
exhibited not only a high reactivity but also a higher
selectivity on the reaction (Figure 6). Thus, 1 mol % catalyst
loading was selected for the following study, and toluene
and THF were selected as solvents for comparison of the
catalytic activity of the catalysts.
Figure 6. Molecular structure of the compound 7, hydrogen atoms are
omitted for clarity.
To search for the generality of the above observation, and
to search for the applications of other rare earth metal amides
in this cyclotrimerization reaction, the catalytic activity and
selectivity of the above different rare earth amides on
cyclotrimerization of phenyl isocyanate were investigated.
The results are listed in Table 3. It is found that all complexes
2, 3, 4, 5, and 6 exhibited a good to excellent catalytic activity
on the cyclotrimerization of phenyl isocyanate, and all
complexes showed a higher catalytic activity in THF than
in toluene when the reaction was carried out at room
temperature in the presence of 1 mol % catalyst. The
cyclotrimerization compounds were the only products,
indicating a high selectivity of the catalysts. The temperature
has a great influence on the conversion of reaction when the
catalytic reaction was carried out in toluene. The conversion
could be improved when the reactions were carried out at
80 °C. For comparison, the catalytic activity of complex
[(Me3Si)2N]3Yb(µ-Cl)Li(THF)3 (7) on the cyclotrimerization
of phenyl isocyanate was studied (Table 3, entries 16, 17).
Its catalytic activity on the cyclotrimerization of phenyl
isocyanate is comparable with those of all the new complexes
2 to 6. As indicated in Table 3, all the above new complexes
and [(Me3Si)2N]3Yb(µ-Cl)Li(THF)3 (12) exhibited a similar
high catalytic activity on the cyclotrimerization of isocyanate,
so complexes 2 and 3 were selected for the following study
on cyclotrimerization of different isocyanates. The results
are compiled in Table 4.
From Table 4, we can see that complexes 2 and 3 exhibited
a high catalytic activity for the cyclotrimerization of aromatic
isocyanates. The aromatic isocyanates could be phenyl
isocyanate, benzyl isocyanate, 4-isopropylbenzyl isocyanate
(Table 4, entries 1-7, Figure 7). It is strange that all the
complexes showed no catalytic activity on the cyclotrimer-
ization of the 4-nitrophenylisocyanate (Table 4, entries 8,
9), which needs to be further investigated. It is notable that
other byproducts such as dimerization products or polym-
erization products were not observed in the reactions,
indicating a high selectivity of the complexes. The structures
Inorganic Chemistry, Vol. 47, No. 12, 2008 5507

Wu et al.
Table 4. Data for the Cyclotrimerization of Different Isocyanates
entry
cat
R-
solvent
temp (°C)/time (h)
product
yield (%)a
t (°C) /time (h)
yield (%)a
99
1
2
3
4
5
6
7
8
2
3
2
3
2
3
3
2
3
2
2
3
2
2
3
2
3
phenyl
phenyl
benzyl
benzyl
4-isopropylphenyl
4-isopropylphenyl
4-isopropylphenyl
4-nitrophenyl
4-nitrophenyl
cyclohexyl
cyclohexyl
cyclohexyl
isopropyl
THF
THF
THF
THF
THF
THF
toluene
THF
THF
r.t./12
r.t./12
r.t./12
r.t./12
r.t./12
r.t./12
r.t./12
r.t./12
r.t./12
r.t./12
r.t./12
r.t./12
r.t./12
r.t./12
r.t./12
r.t./12
r.t./12
7
99
92
99
99
99
46
54
0
0
0
0
0
50/12
50/12
50/12
50/12
50/12
50/12
80/12
50/12
50/12
50/12
80/12
80/12
50/12
80/12
80/12
50/12
50/12
7
8
8
9
9
81
99
0
9
0
9
0
0
10
11
12
13
14
15
16
17
THF
10
10
10
11
11
11
0
11
26
28
15
25
24
0
toluene
toluene
THF
toluene
toluene
THF
8
0
0
0
isopropyl
isopropyl
allyl
allyl
THF
0
0
0
a Isolated yield.
isocyanate into the Ln-N(SiMe3)2 bond produced the
intermediate II. II reacted with another molecule of isocy-
anate through insertion reaction and gave intermediate III,
which further reacted with another molecule of isocyanate
to produce the final cyclotrimerization products and furnished
a catalytic cycle.
Conclusion
A series of novel lanthanide amides with general formula
{(CH2SiMe2)[(2,6-iPr2C6H3)N]2}LnN(SiMe3)2(THF) were syn-
thesized via reaction of [(Me3Si)2N]3LnIII(µ-Cl)Li(THF)3 (Ln
) Yb, Y, Dy, Sm, Nd) with the corresponding diamine
(CH2SiMe2)[(2,6-iPr2C6H3)NH]2. All complexes were fully
characterized by spectroscopic methods and elemental single-
crystal X-ray analyses. These complexes exhibited an excel-
lent catalytic activity on the cylcotrimerization of aromatic
isocyanates to yield the corresponding isocyanurates,
which represents the first example to be reported in this
field of the function of cyclopentadienyl-free rare earth
metal complexes as highly efficient selective catalysts.
These catalysts have the advantages of easy preparation
and manipulation, compatibility with different solvents,
and an excellent activity and selectivity on the cylcotri-
merization of aromatic isocyanates. These advantages of
the complexes imply the potential applications of other
cyclopentadienyl-free rare earth metal amides in this field.
Extension works on this field are now in progress in our
laboratory.
Figure 7. Molecular structure of the compound 8, hydrogen atoms and
the solvated THF molecule are omitted for clarity.
of cyclotrimerization products 7 and 8 have been determined
(Figures 6 and 7).
When we move our study on the catalytic activity of the
above complexes to the cyclotrimerization of aliphatic isocy-
anates, such as the isopropyl isocyanate, cyclohexyl isocyanate,
allyl isocyanate, it is found that all these complexes exhibited
a relatively low catalytic activity on the cyclotrimerization of
the corresponding aliphatic isocyanates. For example, no
cyclotrimerization products could be obtained when the reaction
was carried out with cyclohexyl isocyanate at room temperature
in THF or in toluene. This transformation could be achieved
but with low conversion by raising the reaction temperature
(Table 4, entries 10, 11 and 12). Similar results have been
obtained with isopropyl isocyanate (Table 4, entries 13, 14 and
15), but allyl isocyanate cannot be cyclotrimerized to the product
even at 80 °C.
On the basis of the proposed mechanism for cyclotrim-
erization of isocyanates catalyzed by zirconium compounds9h
or calcium complexes,15 the catalytic cycle is proposed as
follows (Schemes 3 and 4): Coordination of the isocyanate
to the rare earth metal led to dissociation of THF and to
formation of the intermediate I; migration insertion of the
Experimental Section
Materials and Methods. All syntheses and manipulations of
air- and moisture-sensitive materials were performed under dry
argon and oxygen-free atmosphere using standard Schlenk tech-
niques. All solvents were refluxed and distilled over sodium
benzophenone ketyl under argon prior to use unless otherwise noted.
[(Me3Si)2N]3LnIII(µ-Cl)Li(THF)3 (Ln ) Yb, Y, Dy, Sm, and Nd)
were prepared according to literature methods.6h,m,n Elemental
analyses data were obtained on a Perkin-Elmer 2400 Series II
elemental analyzer. 1H NMR and 13C NMR spectra for analyses of
compounds were recorded on a Bruker AV-300 NMR spectrometer
(300 MHz for 1H; 75.0 MHz for 13C) in C6D6 for lanthanide
complexes and in CDCl3 for organic compounds. Chemical shifts
(15) Orzechowski, L.; Harder, S. Organometallics 2007, 26, 2144.
5508 Inorganic Chemistry, Vol. 47, No. 12, 2008

Rare Earth Metal Amides Supported by a Diamido Ligand
Table 5. Crystallographic Data for Compounds 2-8
2
3
4
5
empirical formula
formula weight
T(K)
C37H68N3OSi3Yb
828.25
C37H68N3OSi3Y
744.12
C37H68N3OSi3Dy
817.71
C37H68N3OSi3Sm
805.56
113(2)
293(2)
293(2)
294(2)
wavelength (Å)
cryst system
space group
a(Å)
0.71070
orthorhombic
P212121
11.037(8)
21.149(14)
36.69(2)
8565(10)
8
0.71073
orthorhombic
P212121
11.029(2)
21.200(4)
36.909(7)
8630(3)
8
0.71073
orthorhombic
P212121
0.71073
orthorhombic
P212121
11.2552(9)
21.0568(16)
37.425(3)
8869.8(12)
4
11.2846(14)
21.076(3)
37.567(5)
8934.8(19)
8
b(Å)
c(Å)
V(Å3)
Z
Dcalcd (g cm-3
)
1.285
1.145
1.222
1.198
µ (mm-1
F(000)
)
2.297
1.464
1.794
1.423
3448
3200
3400
3384
θ range for data collcn (deg)
reflcns collcd /unique
data/restns/params
1.47-27.93
1.10-25.02
1.46-27.60
1.08-25.02
76435/20420, [Rint ) 0.074] 51730/8384, [Rint ) 0.100] 77014/20459, [Rint ) 0.025] 46718/8674, [Rint ) 0.081]
20420/0/833
19049
1.067
0.042, 0.074
0.047, 0.076
0.840 and -0.790
8384/33/840
7571
1.102
0.086, 0.221
0.093, 0.230
3.047 and -0.729
20459/0/844
18661
1.057
0.030, 0.072
0.035, 0.074
0.574 and -1.037
8674/72/843
6640
1.028
0.041, 0.082
0.067, 0.094
0.432 and -0.686
obsd reflcns [I > 2 σ (I) ]
Goodness-of-fit F2
R1, wR2 [I > 2 σ (I) ]
R1, wR2 (all data)
largest diff peak/hole (e Å-3
)
6
7
8
empirical formula
formula weight
T(K)
C37H68N3OSi3Nd
799.45
293(2)
C25H23N3O4
429.46
293(2)
C24H21N3O3
399.44
293(2)
wavelength (Å)
cryst system
space group
a(Å)
b(Å)
c(Å)
0.71073
orthorhombic
P212121
11.3055(16)
21.110(3)
37.690(5)
90
90
90
8995(2)
4
1.178
0.71073
triclinic
P1
0.71073
monoclinic
Pn
11.4057(9)
4.5668(4)
18.9688(14)
90
90.0100(10)
90
988.04(14)
2
1.343
0.090
420
j
11.2432(17)
11.3103(17)
11.493(3)
91.117(2)
115.099(2)
119.092(2)
1108.5(4)
2
R (deg)
ꢀ(deg)
γ (deg)
V(Å3)
Z
Dcalcd (g cm-3
)
1.287
0.089
452
µ (mm-1
F(000)
)
1.262
3356
θ range for data collcn (deg)
no. of reflcns collcd/unique
data/restns/params
1.45-27.56
2.04-27.61
8412/4852, [Rint ) 0.040]
4852/0/290
2487
2.08-27.55
8049/4114, [Rint ) 0.020]
4114/2/272
3861
76032/20558, [Rint ) 0.064]
20558/0/844
14476
obsd reflcns [I > 2σ (I) ]
Goodness-of-fit F2
1.063
1.086
1.043
R1, wR2 [I > 2σ (I) ]
R1, wR2 (all data)
0.051, 0.088
0.091, 0.101
0.989 and -1.263
0.069, 0.227
0.19, 0.331
0.438 and -0.486
0.029, 0.078
0.031, 0.080
0.121 and -0.101
largest diff peak/hole (e Å-3
)
(δ) were reported in ppm. J values are reported in Hz. IR spectra
were recorded on a Shimadzu FTIR-8400s spectrometer (KBr
pellet). Mass spectra were performed on a Micromass GCT-MS
spectrometer. Melting points were determined in capillaries, and
were uncorrected.
Preparation of (CH2SiMe2)[(2,6-iPr2C6H3)NH]2 (1). To a
solution of (2,6-iPr2C6H3)NH2 (10.0 mL, 53.02 mmol) in THF (50.0
mL) was slowly added a 1.43 M n-BuLi solution (37.10 mL, 53.02
mmol) at 0 °C. The reaction mixture was stirred for 12 h at room
temperature and was then cooled to 0 °C again. To the reaction
mixture was added ClSiMe2CH2Cl (3.50 mL, 26.51 mmol) in one
portion. The reaction mixture was stirred for 12 h at 50 °C. The
solvents were pumped off under reduced pressure. The residue was
extract with n-hexane (2 × 20.0 mL), and the extractions were
combined. The solution was reduced in volume under reduced
pressure and cooled at -10 °C to give (CH2SiMe2)[(2,6-
iPr2C6H3)NH]2 (1) as white crystals (3.82 g, 34% yield). m.p.: 89
°C-91 °C. 1H NMR (CDCl3, ppm): δ 7.12-7.07 (m, 6H, aromatic
CH), 3.48 (br, 2H, CH(CH3)2), 3.16 (br, 2H, CH(CH3)2), 2.64 (br,
2H, NH), 2.48 (d, J ) 7.3, 2H, CH2), 1.25 (d, J ) 6.8, 24H, CH3),
0.30 (s, 6H, Si(CH3).13C NMR (CDCl3, ppm): δ 146.3, 142.3, 140.2,
132.4, 123.6, 123.5, 122.8, 118.5 (C6H3), 43.5 (CH2), 27.9
(CH(CH3)2), 27.5 (CH(CH3)2), 24.2 (CH3), 22.4 (CH3). IR (KBr
pellet, cm-1): ν 3356 (s), 3059 (m), 2932 (s), 2870 (s), 2801 (s),
1620 (m), 1589 (m), 1439 (s), 1381 (s), 1362 (s), 1327 (s), 1254
(s), 1196 (s), 1177 (m), 1107 (s), 1045 (s), 910 (s), 879 (m), 864
(w), 837 (m), 802 (m), 756 (m), 737 (m), 691 (m), 652 (w), 613
(w), 567 (w), 556 (w), 525 (w). HRMS (EI) m/z: calcd for
C27H44N2Si: 424.3274; Found: 424.3271. Anal. Calcd for
C27H44N2Si: C, 76.35; H, 10.44; N, 6.60. Found: C, 76.70; H, 10.16;
N, 6.49.
Scheme 3. Catalytic Cyclotrimerization of Isocyanate
Preparation of {(CH2SiMe2)[(2,6-iPr2C6H3)N]2}YbN(SiMe3)2-
(THF) (2). To a toluene (10.0 mL) solution of (CH2SiMe2)[(2,6-
iPr2C6H3)NH]2 (1) (1.35 g, 3.17 mmol) was added a toluene (50.0
mL) solution of [(Me3Si)2N]3YbIII(µ-Cl)Li(THF)3 (2.897 g, 3.17
Inorganic Chemistry, Vol. 47, No. 12, 2008 5509

Wu et al.
(0.796 g, 1.88 mmol) with [(Me3Si)2N]3SmIII(µ-Cl)Li(THF)3 (1.67
g, 1.88 mmol) in toluene. IR (KBr pellet, cm-1): ν 3059 (m), 2959
(m), 2866 (m), 2797 (m), 1937 (w), 1859 (w), 1632 (w), 1589 (w),
1443 (m), 1381 (m), 1362 (m), 1327 (m), 1254 (s), 1196 (s), 1177
(m), 1107 (m), 1045 (m), 934 (w), 912 (m), 802 (w), 737 (w), 571
(w). Anal. Calcd for C33H60N3Si3Sm (5-THF): C, 54.04; H, 8.25;
N, 5.73. Found: C, 54.33; H, 8.31; N, 5.48.
Scheme 4. Catalytic Cycle of Cyclotrimerization of Isocyanate
Preparation of {(CH2SiMe2)[(2,6-iPr2C6H3)N]2}NdN(SiMe3)2-
(THF) (6). This compound was prepared as blue crystals in 76%
yield from the reaction of (CH2SiMe2)[(2,6-iPr2C6H3)NH]2 (1)
(0.974 g, 2.30 mmol) with [(Me3Si)2N]3NdIII(µ-Cl)Li(THF)3 (2.03
g, 2.30 mmol) in toluene. IR (KBr pellet, cm-1): ν 2959 (s), 2866
(m), 2797 (m), 2361 (s), 2342 (s), 1458 (m), 1439 (s), 1254 (s),
1196 (s), 914 (s), 841 (s), 799 (s). Anal. Calcd for C33H60N3Si3Nd
(6-THF): C, 54.49; H, 8.31; N, 5.78. Found: C, 54.68; H, 8.37; N,
5.42.
X-ray Structure Determination. A suitable crystal of the
complex 2, 3, 4, 5, 6, 7, and 8 was mounted in a sealed capillary.
Diffraction was performed on a Siemens SMART CCD-area
detector diffractometer using the graphite-monochromated Mo KR
radiation (λ ) 0.71073 Å); temperature 294(2) K; ψ and ω scan
technique; SADABS effects and empirical absorption were applied
in the data corrections. All structures were solved by direct methods
(SHELXL-97), completed by subsequent difference Fourier syn-
theses, and refined by full-matrix least-squares calculations based
on F2 (SHELXL-97). Crystal data and details of the data collection
are given in Table 5. Further details are included in the Supporting
Information.
mmol) at room temperature. After the reaction mixture was stirred
at room temperature for 6 h, the mixture was then refluxed for 12 h,
the color of the solution was gradually changed from yellow to
dark red. The solvent was evaporated under reduced pressure. The
residue was extracted with n-hexane (2 × 15.0 mL). The extractions
were combined and concentrated to about 10.0 mL. The red crystals
were obtained by cooling the concentrated solution at 0 °C for
several days (2.336 g, 89% yield). IR (KBr pellet, cm-1): ν 3059
(m), 3020 (m), 2963 (s), 2866 (s), 2797 (w), 2361 (s), 2342 (s),
1624 (m), 1439 (s), 1381 (s), 1327 (s), 1254 (s), 1107 (m), 1045
(m), 968 (w), 914 (s), 841 (s), 799 (s), 737 (s). Anal. Calcd for
C33H60N3Si3Yb (2-THF): C, 52.42; H, 8.00; N, 5.56. Found: C,
52.79; H, 7.94; N, 5.23.
Preparation of {(CH2SiMe2)[(2,6-iPr2C6H3)N]2}YN(SiMe3)2-
(THF) (3). This compound was prepared as white crystals in 49%
(0.995 g) yield by treatment of (CH2SiMe2)[(2,6-iPr2C6H3)NH]2 (1)
(1.16 g, 2.73 mmol) with [(Me3Si)2N]3YIII(µ-Cl)Li(THF)3 (2.263
g, 2.73 mmol) using the procedures similar to those described above
for preparation of 2. 1H NMR (C6D6, ppm): δ 7.25-7.10 (m, 6H)
(C6H3), 4.11 (s, 4H, OC4H8), 3.78 (m, 2H, CH(CH3)2), 3.57-3.49
(m, 2H, CH(CH3)2), 3.28-3.23 (m, 2H, CH2), 3.01-2.53 (m, 4H,
OC4H8), 1.61-1.26 (s, 24H, CH3), 0.35-0.17 (s, 24H, Si(CH3)3).
13C NMR (CDCl3, ppm): δ 123.3, 122.7, 120.9, 71.8, 45.5, 27.3,
26.2, 24.5, 24.0, 23.7, 23.2, 4.0, 2.0, 0.8. IR (KBr pellet, cm-1): ν
3067 (m), 2963 (s), 2932 (s), 2870 (s), 2187 (s), 1674 (m), 1632
(m), 1497 (s), 1466 (m), 1443 (m), 1385 (m), 1362 (s), 1319 (m),
1254 (s), 1053 (s), 934 (m), 907 (m), 841 (s), 806 (s), 745 (s), 644
(w), 540 (w). Anal. Calcd for C37H68N3OSi3Y: C, 59.72; H, 9.21;
N, 5.65. Found: C, 59.77; H, 9.03; N, 5.73.
General Procedure for the Cyclotrimerization of Isocyan-
ates (816 As an Example). To a solution of THF (5 mL) in a 30.0
mL Schlenk tube under dried argon was added complex 2 (0.018
g, 0.022 mmol) and benzyl isocyanate (0.29 g, 2.2 mmol). The
resulting mixture was stirred at room temperature for 12 h. After
the reaction was completed, the reaction mixture was hydrolyzed
by water (1 mL), extracted with diethyl ether (3 × 10 mL), dried
over anhydrous Na2SO4, and filtered. After the solvent was removed
under the reduced pressure, the final products were further purified
by recrystallization from THF. Compound 8 was isolated as
1
colorless crystals (99%). White solid. Mp: 160.0-160.5 °C. H
NMR (CDCl3, ppm): δ 7.48-7.31(m, 15H, aromatic CH); 5.04(6H,
CH2). 13C NMR (CDCl3, ppm): δ 148.8, 135.4, 128.7, 128.3, 127.8,
45.9. HRMS (EI) m/z: calcd for C24H21N3O3 399.1583; Found:
399.1580.
Compound 7:3b White solid. Mp: 280.8-281.3 °C. H NMR
1
(CDCl3, ppm): δ 7.43-7.15(m, 15H, aromatic CH). 13C NMR
(CDCl3, ppm): δ 148.4, 133.3, 129.1, 128.1. HRMS (EI) m/z: calcd
for C21H15N3O3 357.1113; Found: 357.1116.
Compound 9: White solid. Mp: 287.5-288.0 °C. 1H NMR
(CDCl3, ppm): δ 7.35-7.28 (m, 12H, aromatic CH); 2.99-2.91(3H,
CH); 1.27-1.25 (d, J ) 6.9, 18H, CH3). 13C NMR (CDCl3, ppm):
δ 149.6, 130.8, 127.7, 127.0, 33.5, 23.5. HRMS (EI) m/z: calcd
for C30H33N3O3 483.2522; Found: 483.2520.
Preparation of {(CH2SiMe2)[(2,6-iPr2C6H3)N]2}DyN(SiMe3)2-
(THF) (4). This compound was prepared as colorless crystals in
81% yield following the procedure described for complex 2 from
the reaction of (CH2SiMe2)[(2,6-iPr2C6H3)NH]2 (1) (0.879 g, 2.07
mmol) with [(Me3Si)2N]3DyIII(µ-Cl) Li(THF)3 (1.87 g, 2.07 mmol).
IR (KBr pellet, cm-1): ν 2959 (s), 2866 (m), 2361 (s), 2342 (s),
1458 (m), 1439 (m), 1254 (s), 914 (s), 841 (m), 799 (m). Anal.
Calcd for C37H68N3OSi3Dy: C, 54.35; H, 8.38; N, 5.14. Found: C,
54.44; H, 8.07; N, 5.45.
Compound 10:17 White solid. Mp: 227.0-227.5 °C. H NMR
1
(CDCl3, ppm): δ 4.08–4.06 (3H, NCH), 1.95-1.04 (30H, CH2).
13C NMR (CDCl3, ppm): δ 48.8, 33.6, 25.3, 24.5. HRMS (EI) m/z:
calcd for C21H33N3O3 375.2522; Found: 375.2527.
Compound 11:18 White solid. Mp: 98.5-99.0 °C. 1H NMR
(CDCl3, ppm): δ 4.88-4.84 (3H, CH); 1.33-1.30(18H, CH3). 13
C
Preparation of {(CH2SiMe2)[(2,6-iPr2C6H3)N]2}SmN(SiMe3)2-
(THF) (5). Following the procedures described for the preparation
of complex 2, complex 5 was prepared as yellow crystals in 79%
yield from the reaction of (CH2SiMe2)[(2,6-iPr2C6H3)NH]2 (1)
(16) Richter, U. Synthesis 1975, 463.
(17) (a) Bortnick, N.; Luskin, L. S.; Hurwitz, M. D.; Rytina, A. W. J. Am.
Chem. Soc. 1956, 78, 4358. (b) Kogon, I. C. J. Am. Chem. Soc. 1956,
78, 4911.
(18) Weiss, K.; Hoffmann, K. Z. Naturforsch., Teil B 1987, 42, 769.
5510 Inorganic Chemistry, Vol. 47, No. 12, 2008

Rare Earth Metal Amides Supported by a Diamido Ligand
NMR (CDCl3, ppm): δ 148.3, 47.3, 19.2. HRMS (EI) m/z: calcd
for C12H21N3O3 255.1583; Found: 255.1579.
We are also grateful for the assistance of Prof. Baohui Du
and Jiping Hu in running the IR and NMR spectra.
Acknowledgment. This work was co-supported by the
National Natural Science Foundation of China (Grants
20672002, 20702001), the program for the NCET (Grant
NCET-04-0590), and the grant from Anhui Province, and
theAnhuiEducationDepartment(Grants2007Z016,TD200707).
Supporting Information Available: CIF file giving crystal data
for complexes 2, 3, 4, 5, 6, and compounds 7, 8. This material is
available free of charge via the Internet at http://pubs.acs.org.
IC800496D
Inorganic Chemistry, Vol. 47, No. 12, 2008 5511