Rare earth metal bis(trimethylsilyl)amido complexes bearing pyrrolyl-methylamide ligand. Synthesis, structure, and catalytic activity towards guanylation of amines

Article abstract of DOI:10.1039/c0dt00246a

The N-arylaminomethyl substituted pyrrolyl ligand 2-[(2,4,6-Me ₃C₆H₂)NHCH₂](C₄H ₃NH) (1) was synthesized by reduction of 2-[(2,4,6-Me ₃C₆H₂)NCH](C₄H₃NH) using NaBH₄. Treatment of [(Me₃Si)₂N] ₃Ln(μ-Cl)Li(THF)₃ with 1 equiv. of 1 in reflux toluene for 24 h, afforded the corresponding trivalent rare earth metal amides with formula {(μ-η⁵:η¹):η¹-2-[(2,4,6- Me₃C₆H₂)NCH₂]C₄H ₃N]LnN(SiMe₃)₂}₂ (Ln = Y(2), Nd(3), Sm(4), Dy(5), Er(6)). All compounds were fully characterised by spectroscopic methods and elemental analyses. The structures of complexes 2, 4 and 6 were determined by single-crystal X-ray analyses. X-Ray analyses discovered that two rare-earth metal ions were bridged by dianion ligand with the pyrrolyl ring which coordinated to one rare earth metal in an η⁵ mode, the tethered nitrogen anion and nitrogen atom of the pyrrolyl ring coordinated to another rare earth metal in η¹ modes forming the centrosymmetric dinuclear structures. The rare earth metal complexes as catalysts for the guanylation of aromatic amines were studied. Results showed all rare earth metal complexes exhibited a high catalytic activity on the guanylation of aromatic amines. The Royal Society of Chemistry 2010.

Full text of DOI:10.1039/c0dt00246a

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Rare earth metal bis(trimethylsilyl)amido complexes bearing
pyrrolyl-methylamide ligand. Synthesis, structure, and catalytic activity
towards guanylation of amines†
Chao Liu,a Shuangliu Zhou,*a Shaowu Wang,*a,b Lijun Zhanga and Gaosheng Yanga
Received 1st April 2010, Accepted 22nd June 2010
DOI: 10.1039/c0dt00246a
The N-arylaminomethyl substituted pyrrolyl ligand 2-[(2,4,6-Me3C6H2)NHCH2](C4H3NH) (1) was
synthesized by reduction of 2-[(2,4,6-Me3C6H2)N CH](C4H3NH) using NaBH4. Treatment of
[(Me3Si)2N]3Ln(m-Cl)Li(THF)3 with 1 equiv. of 1 in reflux toluene for 24 h, afforded the corresponding
5
1
1
trivalent rare earth metal amides with formula {(m-h :h ):h -2-[(2,4,6-Me3C6H2)NCH2]-
C4H3N]LnN(SiMe3)2}2 (Ln = Y(2), Nd(3), Sm(4), Dy(5), Er(6)). All compounds were fully
characterised by spectroscopic methods and elemental analyses. The structures of complexes 2, 4 and 6
were determined by single-crystal X-ray analyses. X-Ray analyses discovered that two rare-earth metal
ions were bridged by dianion ligand with the pyrrolyl ring which coordinated to one rare earth metal in
5
an h mode, the tethered nitrogen anion and nitrogen atom of the pyrrolyl ring coordinated to another
1
rare earth metal in h modes forming the centrosymmetric dinuclear structures. The rare earth metal
complexes as catalysts for the guanylation of aromatic amines were studied. Results showed all rare
earth metal complexes exhibited a high catalytic activity on the guanylation of aromatic amines.
to produce unexpected macrocyclic structures.3b,6 Recently, Arnold
Introduction
and co-workers reported that the bis(pyrrolyimino)samarium
alkyl complexes showed excellent stereocontrol of the polymer-
ization of methyl methacrylate.7 The rare earth metal complexes
with the pyrrolide ligand have also been demonstrated to have
high catalytic activities on the ROP of e-caprolactone.8 Cui and
co-workers reported that the rare earth metal alkyl complexes
Research and development of highly active, well-defined rare
earth metallocene catalysts have stimulated the progress of
organometallic chemistry, because of their well-known versatility
in meeting the electronic and steric requirements to stabilize
a wide variety of complexes.1,2 In view of this progress, much
work has been dedicated to finding new ligand systems similar to
the Cp type ligands. Notably, nitrogen-based polydentate ligands
such as the pyrrolyl derivatives are anticipated to be alternatives
of cyclopentadienyl-based ligands in organolanthanide chemistry
owing to their p-ligation ability.3 On the other hand, they also
offer the possibility of forming s-bonds through the ring nitrogen
donor atom, providing a variety of bonding modes necessary to
accommodate diversified structures.
5
1
bearing an h or h -coordinated pyrrolide moiety exhibited high
activities toward polymerisation of isoprene and lactide.9 Hou
et al. also reported that the coordination mode of the pyrrolyl
ligands in the pyrrolyl rare earth metal aminobenzyl complexes
had significant influence on the polymerisation of styrene.10 The
5
rare earth metal aminobenzyl complexes with h -coordinated
pyrrolide showed a high catalytic activity and stereocontrol for the
1
polymerisation of styrene, however, h -coordinated pyrrolyl rare
Group 4 transition metal complexes containing pyrrolyl-
functionalized ligands have been greatly developed, which have
exhibited high activities for olefin polymerization.4 Gambarotta
and co-workers have also demonstrated that the dipyrrolide ligand
or macrocyclic tetrapyrrole polyanions could not only stabilize the
divalent lanthanide complexes but also increase the reactivity of
the metal centre such as reduction of N2 and reversible fixation
of ethylene.3g,5 In contrast, the trivalent lanthanide complexes sup-
ported by dipyrrolide or porphyrinogen ligands usually aggregated
earth metal aminobenzyl complexes had no catalytic activity. Very
recently, Cui and co-workers synthesized the ansa-ytterbium(II)
amide bearing Me2Si(Me4C5)(NC4H4) ligand, in which the Yb
5
atom is h -coordinated to both the cyclopentadienyl ring and
pyrrolyl ring, indicating pyrrolyl ligands to be alternatives of
cyclopentadienyl ligands.11 Though pyrrolyl ligands can bind to
1
5
the metal atoms in either an h or an h fashion, only a few
examples exist in which the pyrrolyl units bind to metal atoms in
both ways simultaneously.12 All the previous works on lanthanide
chemistry incorporating pyrrolyl ligands were concentrated on
the divalent complexes or trivalent alkyl complexes, the synthesis
and catalytic activity of the rare-earth metal amides incorporating
pyrrolyl units remains to be explored.
aAnhui Laboratory of Molecule-Based Materials, School of Chemistry
and Materials Science, Anhui Normal University, Wuhu, Anhui, 241000,
P. R. China. E-mail: swwang@mail.ahnu.edu.cn; Fax: +86-553-3883517;
Tel: +86-553-5910015
The catalytic addition of the N–H bond of the amines
bState Key Laboratory of Organometallic Chemistry, Shanghai Insti-
tute of Organic Chemistry, Shanghai, 200032, P. R. China. E-mail:
swwang@mail.ahnu.edu.cn
to carbodiimides (RN
C
NR) provides a direct and atom-
efficient route to the multi-substituted guanidines, which are
the important building blocks in many biologically relevant
compounds13 and also widely used as ligands for the construction
† CCDC reference numbers 770560–770562. For crystallographic data in
CIF or other electronic format see DOI: 10.1039/c0dt00246a
8994 | Dalton Trans., 2010, 39, 8994–8999
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©

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of a variety of organometallic catalysts containing early tran-
sition metals and lanthanides.14 Only the primary aliphatic
amines and cyclic secondary aliphatic amines can undergo di-
rect guanylation with carbodiimides to yield the corresponding
N,N¢,N¢¢trialkylguanidines under forcing conditions.15 Recently,
catalytic addition of N–H bond to carbodiimides has been
developed using Ti16 and V17 imido complexes, half-sandwich
yttrium alkyl,18 lithium amide,19 aluminium alkyl compound,20
and titanacarborane amide complexes.21
In our previous study, we have demonstrated that the lanthanide
amido complexes showed high catalytic activities for the guanyla-
tion of the aromatic and secondary amines.22 As our continuous
interest in developing lanthanide amido complexes as catalysts for
the atom-economical process of the addition of the E–H bonds to
the multiple bonds, we herein report that synthesis and structure
5
1
1
Fig.
1
Representative molecular structure of {(m-h :h ):h -2-
1
5
of substituted pyrrolyl lanthanide amides with h and h bonding
modes, and their catalytic activity towards guanylation of amines.
[(2,4,6-Me3C6H2)NCH2]C4H3N]LnN(SiMe3)2}2 (2). Hydrogen atoms are
omitted for clarity. The symmetry operation is x + 1, -y, z + 1.
Results and discussion
Synthesis and characterisation of the rare earth metal amides with
pyrrolyl–methylamide ligand
The reaction of [(Me3Si)2N]3Ln(m-Cl)Li(THF)3 with 1 equiv. of
2-[(2,4,6-Me3C6H2)NHCH2](C4H3NH) (1) in toluene at 100 ◦C
afforded the dinuclear rare earth metal amido complexes
5
1
1
{(m-h :h ):h -2-[(2,4,6-Me3C6H2 )NCH2 ]C4H3N]LnN(SiMe3 )2 }2
(Ln = Y (2), Nd (3), Sm (4), Dy(5), Er(6)] (Scheme 1). The com-
plexes are sensitive to air and moisture, they have good solubility
in either polar solvents or non-polar solvents. All complexes were
fully characterised by IR and elemental analyses. Complex 2 was
also characterised by 1H NMR spectra analyses. 1H NMR analyses
of complex 2 displayed that the pyrrolyl protons resonated at 6.23,
6.52, and 7.62 ppm comparable with the pyrrolyl protons of {[2-(2,
Fig.
2
Packing arrangement in the unit cell of representative
5
1
1
{(m-h :h ):h -2-[(2,4,6-Me3C6H2)NCH2]C4H3N]YN(SiMe3)2}2 (2).
5
in an h mode, the tethered nitrogen anion and nitrogen atom
of the pyrrolyl ring coordinated to another rare earth metal
in an h mode. The bridged bonding mode of this type of
i
6 - Pr2C6H3NC(H)(CH2SiMe3))C4H3N]Y(CH2SiMe3)(THF)}2,9a
1
suggesting that the pyrrolyl moiety coordinates to the yttrium
pyrrolyl ligand is different to that of the so-called contained
geometry ligand of the cyclopentadienyl type ligand in which
the dianion ligand bonds to one metal.18,23 To the best of our
knowledge, these complexes represent the first example of rare
earth metal amides incorporating the pyrrolyl ring coordinated
to the rare-earth metal center in an h and h -coordination
mode. The selected bond lengths and angles are listed in Table 1.
The bond distances between lanthanide ions and the pyrrolyl
5
1
atom in an h -fashion. The H NMR spectra of complexes 3–
6 were not informative due to lack of locking signal for the
paramagnetic property of the complexes. Therefore, the structures
of the complexes 2, 4, and 6 were determined by single-crystal
X-ray analyses.
5
1
5
carbon in 2, Y–h -C(pyr ring), ranging from 2.644(4) to 2.781(4)
˚
˚
A, are comparable to those in 6 (2.638(5) to 2.763(5) A), [2-
(2-Ph2PC6H3NC(H)(CH2SiMe3 )C4H3N]2Y2(CH2SiMe3)2(THF)
9a
˚
(2.690(5) to 2.738(6) A),
and [(2-(Me2NCH2)C4H3N)-
Y(CH2SiMe3)2]2 (2.725(3) to 2.743(3) A).9b The Sm-h -C(pyr ring)
in complex 4, ranging from 2.710(4) to 2.852(4) A, are slightly
5
˚
˚
longer than those in 2 and 6, indicating effects of lanthanide
5
ionic radii. It is also noteworthy that the Ln-h -C(pyr ring)
Scheme 1 Synthesis of the rare earth metal amides with pyrrolyl–methy-
lamide ligand
5
bond lengths are close to Ln-h -C(Cp ring), suggesting that the
pyrrolyl ring can be an ideal alternative to the cyclopentadienyl
˚
X-Ray analyses revealed that complexes 2, 4 and 6 were isostruc-
tural with a centrosymmetric dinuclear structure. Representative
structure diagrams are shown in Fig. 1 and Fig. 2. Each of the
rare-earth metals adopted a distorted tetrahedral geometry, and
the two metals in each complex were bridged by the dianion
ligand with the pyrrolyl ring coordinated to one rare earth metal
ancillary ligand. The bond distance of Y(1)–N(2) (2.700(3) A) and
˚
Y(1)–N(2A) (2.392(3) A) in complex 2 is much longer than that
of Y(1)–N(1A) (2.186(3) A), well consistent with the h /h :h -
coordination mode of the pyrrolide ligand, which is comparable
to the Y–N bond distances in an h /h :h -pyrrolyl yttrium
5
1
1
˚
5
1
1
alkyl complex [(2-(Me2NCH2)C4H3N)Y(CH2SiMe3)2]2 (Y–N(1),
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◦
˚
Table 1 Selected bond lengths (A) and angles ( ) for complexes 2, 4 and
Table 2 Catalytic addition of an aniline to N,N-dicyclohexyl-
6
carbodiimidea
2a
4b
6c
Ln(1)–N(1A)
Ln(1)–N(2)
Ln(1)–N(3)
Ln(1)–N(2A)
Ln(1)–C(11)
Ln(1)–C(12)
Ln(1)–C(13)
Ln(1)–C(14)
2.186(3)
2.700(3)
2.204(3)
2.392(3)
2.781(4)
2.777(4)
2.712(4)
2.644(4)
2.229(3)
2.762(3)
2.265(3)
2.465(3)
2.847(3)
2.852(4)
2.776(4)
2.710(4)
2.164(3)
2.688(4)
2.189(4)
2.368(3)
2.763(4)
2.756(5)
2.684(5)
2.638(5)
Entry Catalyst
Catalyst loading (mol%) Solvent
Yield (%)b
1
2
3
4
5
6
7
8
4
4
4
4
4
4
4
2
3
5
6
3
2
THF
THF
95
94
87
39
89
92
90
94
92
92
93
1
0.5
2
2
2
THF
THF
n-Hexane
Toluene
Et2O
N(1A)–Ln(1)–N(3)
N(1A)–Ln(1)–N(2A)
N(3)–Ln(1)–N(2A)
113.69(13)
73.62(11)
128.82(12)
115.56(11)
71.35(10)
128.56(11)
112.43(14)
74.42(12)
127.72(15)
a The symmetry operation is x + 1, -y, z + 1. b The symmetry operation is
x + 2, -y, z + 1. c The symmetry operation is x + 1, -y, z.
2
2
THF
THF
9
10
11
2
2
THF
THF
9b
˚
˚
˚
2.735(2) A; Y–N(2A), 2.588(3) A; and Y–N(1A), 2.446(2) A).
a Conditions: aniline, 2.00 mmol; N,N-dicyclohexylcarbodiimide,
˚
The bond distances in complex 4 (Sm(1)–N(2), 2.762(3) A; Sm(1)–
N(2A), 2.465(3) A; and Sm(1)–N(1A), 2.229(3) A) are slightly
longer than those found in complex 6 (Er(1)–N(2), 2.688(4) A;
Er(1)–N(2A), 2.368(4) A; and Er(1)–N(1A), 2.164(4) A). The
2.00 mmol; time, 12 h; reaction temperature, 60 ◦C. b Isolated yield.
˚
˚
˚
Under the optimized reactions, complex 4 as catalyst for
the guanylation of selected aromatic amines (including amines
having electron-donating or electron-withdrawing groups) and
heterocyclic aromatic amines were studied, the results were listed in
Table 3. From Table 3, we can also see that good to excellent yields
of the products could be obtained by using the aromatic amines
either having electron-donating group such as CH3O– (Table 3,
entries 3 and 4) or having strong electron-withdrawing group such
as O2N– (Table 3, entries 5 and 6). In case of the heteroaromatic
amines, excellent yields of the products could also be isolated
(Table 3, entries 9–12) in 12 h.
˚
˚
˚
bond distances of Ln–N(3) in complex 2 (Y(1)–N(3), 2.204(3) A),
˚
complex 4 (Sm(1)–N(3), 2.265(3) A), and complex 6 (Er(1)–N(3),
˚
2.189(3) A), are compared with those in (EBI)YN(SiMe3)2 (Y(1)–
N(1), 2.243(4) A)22a and (EBI)SmN(SiMe3)2 (Sm(1)–N(1), 2.264(4)
˚
22a
˚
A). The observed variations of bond distances may result from
the combination effects of steric interactions, electronic effects and
ionic radii difference.
Catalytic addition of the aromatic amines to carbodiimides
Although catalytic addition of the N–H bond to carbodiimides
have been studied utilizing catalyst lanthanide alkyls, amides
and other metal catalysts.16–22 The lanthanide complexes with
pyrrolyl ligands as catalysts for the corresponding reaction have
not been reported. Thus, the above complexes as catalysts for
the guanylation reaction were studied. The catalytic addition of
aniline to N,N-dicyclohexylcarbodiimide were examined using the
above rare-earth metal amides with substituted pyrrolyl ligands
as catalysts, and the results are listed in Table 2. The reaction
can work well producing the guanylation product by carrying out
the reaction in THF at 60 ◦C for 6 h in the presence of 1 to
3 mol% of dinuclear complex 4 as the catalyst (Table 2, entries
1–3). The yield of the product decreased to 39% in the presence of
0.5 mol% catalyst 4 (Table 2, entry 4). Good to excellent yields of
the products can also be isolated by carrying out the reaction in
n-hexane, toluene and Et2O in the presence of 2 mol% catalyst 4
(Table 2, entries 5–7), indicating the solvent compatibility of the
catalysts. The catalytic activities of the other complexes 2, 3, 5, 6
as catalysts for the guanylation reaction were surveyed (Table 2,
entries 8–11). All complexes displayed high activities, indicating
that the rare-earth metals have little influence on the catalytic
activity of the catalysts. These results were comparable with those
obtained by using the lanthanide amides (EBI)LnN(TMS)222a and
[(Me3Si)2N]3Ln(m-Cl)Li(THF)322b as catalysts. Therefore, complex
4 was selected as the catalyst for the following guanylation of the
aromatic amines.
Conclusions
In summary, a series of dinuclear rare earth metal amido
5
1
1
complexes with substituted pyrroly ligand {(m-h :h ):h -2-[(2,4,6-
Me3C6H2)NCH2]C4H3N]LnN(SiMe3)2}2 [Ln = Y (2), Nd (3),
Sm (4), Dy(5), Er(6)] were synthesized and characterised. The
X-ray diffraction analyses of the complexes indicated that the
complexes were centrosymmetric dinuclear structure and pyrrolyl
ligands coordinated to one rare earth metal in an h mode,
the tethered nitrogen anion and nitrogen atom of the pyrrolyl
ring coordinated to another rare earth metal in h modes.
This work also represents rare examples of the rare-earth metal
amides supported by pyrrolide species in h - and h -coordination
mode. All complexes displayed high catalytic activities for the
guanylation of aryl amines, which represent the first example
of the lanthanide amido complexes bearing pyrrolyl ligands as
catalysts for the guanylation reaction. The results indicated that
the catalysts have good compatibility for guanylation of various
aryl amines in different solvents.
5
1
5
1
Experiments
General remarks
All syntheses and manipulations of air- and moisture-sensitive
materials were performed under dry argon and oxygen-free
8996 | Dalton Trans., 2010, 39, 8994–8999
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Table 3 Catalytic addition of aromatic amines to carbodiimidesa
The compound 2-[(2,4,6-Me3C6H2)N CH](C4H3NH) (5.00 g,
23.36 mmol) in CH3OH (30 mL) solution was reduced with NaBH4
(1.76 g, 46.72 mmol) in 50 ◦C for another 5 h, then it was
hydrolyzed. The organic layer was separated and the aqueous layer
was extracted with diethyl ether (3 ¥ 20 mL). The organic fractions
were combined and dried with anhydrous MgSO4, filtered, and
evaporated to dryness. Recrystallization of crude product from
hexane gave the product 2-[(2,4,6◦-Me3C6H2)NHCH2](C4H3NH)
(1) (4.49 g, 89% yield). mp 65–66 C. dH (CDCl3, ppm) 8.34 (br,
1 H, NH), 6.85 (s, 2 H, ArH), 6.16 (s, 1 H, pyrrole H), 6.07 (s, 1
H, pyrrole H), 4.05 (s, 2 H, CH2), 2.23 (s, 9 H, CH3). dC (CDCl3,
ppm) 142.9, 132.3, 131.0, 130.6, 129.6, 117.4, 108.4, 106.0, 45.8,
20.7, 18.2. Found: C 78.59, H 8.64, N 13.04. Calcd for C14H18N2:
C 78.46, H 8.47, N 13.07%.
Entry
R
Ar–NH2
Yield (%)b
1
2
Cy
iPr
94
91
3
4
Cy
iPr
95
93
5
6
Cy
iPr
87
83
General procedures for synthesis of the rare earth metal amides
with substituted pyrrolyl ligand
7
8
Cy
iPr
91
92
To a toluene (30.0 mL) solution of [(Me3Si)2N]3Ln(m-Cl)Li(THF)3
(2.00 mmol) was added a toluene (10.0 mL) solution of ligand 1
(2.00 mmol) at room temperature. After the reaction mixture was
stirred at room temperature for 6 h, the mixture was stirred for 24 h
at 100 ◦C. The solvent was evaporated under reduced pressure. The
residue was extracted with n-hexane (20.0 mL). The extractions
were combined and concentrated to about 10.0 mL. Products
were obtained by recrystallization from the concentrated hexane
solution at 0 ◦C for several days.
9
10
Cy
iPr
88
89
11
12
Cy
iPr
93
91
a Conditions: aniline, 2.00 mmol; carbodiimide, 2.00 mmol; catalyst,
{(l-g5:g1):g1 -2-[(2,4,6-Me3C6H2)NCH2]C4H3N]YN(SiMe3)2}2
(2). Colourless crystals, 79% yield. mp 220–222 ◦C (from hex-
ane); dH (C6D6, ppm) 7.62 (s, 2 H, pyrrole H), 7.04 (s, 4 H, Ar),
6.52 (s, 2 H, pyrrole H), 6.23 (s, 2 H, pyrrole H), 4.99 (s, 4 H,
CH2), 2.46 (s, 12 H, CH3), 2.22 (s, 6 H, CH3), 0.44–0.16 (m, 36 H,
Si(CH3)3). nmax(KBr)/cm-1: 2887 m, 2855 m, 1481 s, 1435 s, 1224
m, 1198 m, 1130 w, 1063 w, 1030 s, 854 s, 793 m, 723 s, 610 w, 571
w. Found: C 51.87, H 7.18, N 8.95. Calcd for C40H68N6Si4Y2: C
52.04, H 7.42, N 9.10%.
◦
0.04 mol; THF, 5 mL; time, 12 h; reaction temperature, 60 C. b Isolated
yield.
atmosphere using standard Schlenk techniques or in a glove-
box. All solvents were refluxed and distilled over sodium
benzophenone ketyl under argon prior to use unless other-
wise noted. All amines were sublimed, recrystallized or dis-
tilled before use. N,N¢-dicyclohexylcarbodiimide and N,N¢-
diisopropylcarbodiimide were used without further purification.
[(Me3Si)2N]3Ln(m-Cl)Li(THF)3 were prepared according to lit-
erature methods.24 IR spectra were recorded on SHIMADZU
FTIR-8400S spectrometer. H NMR and 13C NMR spectra for
analyses of compounds were recorded on a Bruker AV-300 NMR
spectrometer in C6D6 for lanthanide complexes and in CDCl3 for
organic compounds.
{(l-g5:g1):g1-2-[(2,4,6-Me3C6H2)NCH2]C4H3N]NdN(SiMe3)2}2
(3). Green crystalline solid, 71% yield. mp 236–238 ◦C (from
hexane); nmax(KBr)/cm-1: 2965 m, 2914 m, 2857 w, 1626 s,
1580 m, 1418 m, 1260 m, 1206 w, 1132 m, 1094 w, 1034 s, 856 m,
791 w, 743 m, 721 w. Found: C 46.05, H 6.70, N 8.13. Calcd for
C40H68N6Si4Nd2: C 46.47, H 6.63, N 8.13%.
1
{(l-g5:g1):g1-2-[(2,4,6-Me3C6H2)NCH2]C4H3N]SmN(SiMe3)2}2
Synthesis of 2-[(2,4,6-Me3C6H2)NHCH2](C4H3NH) (1)
◦
(4). Yellow crystals, 83% yield. mp 239–241 C (from hexane);
n
max(KBr)/cm-1: 2953 m, 2854 m, 1481 s, 1433 s, 1225 s, 1193 m,
To
a
dried MeOH solution (20.0 mL) of pyrrole-2-
carboxyaldehyde (5.74 g, 60.30 mmol) were added 2,4,6-
trimethylaniline (10.0 mL, 60.30 mmol) and a catalytic amount
of formic acid (2.0 mL) under stirring. The reaction mixture
was stirred for 24 h at room temperature. Subsequently, the
white precipitate was separated by filtration and then washed
with cold methanol. Removal of the solvents afforded 2-[(2,4,6-
Me3C6H2)N CH](C4H3NH) (3.75 g, 91% yield). mp 148–149 ◦C
(from EtOH), dH (CDCl3, ppm) 7.95 (s, 1 H, NCH), 6.90 (s, 2 H,
ArH), 6.59–6.54 (m, 2 H, pyrrole H), 6.27 (s, 1 H, pyrrole H), 2.28
(s, 3 H, CH3), 2.12 (s, 6 H, CH3). dC (CDCl3, ppm) 153.8, 148.3,
133.4, 130.1, 129.0, 128.4, 124.5, 117.0, 109.9, 21.0, 18.5. Found:
C 79.33, H 7.32, N 13.27. Calcd for C14H16N2: C 79.21, H 7.60, N
13.20%.
1062 w, 1031 m, 932 s, 854 s, 793 w, 723 s, 610 w, 567 w. Found:
C 45.81, H 6.59, N 8.16. Calcd for C40H68N6Si4Sm2: C 45.93, H
6.55, N 8.03%.
{(l-g5:g1):g1-2-[(2,4,6-Me3C6H2)NCH2]C4H3N]DyN(SiMe3)2}2
(5). Colourless crystalline solid, 81% yield. mp 238–240 ◦C
(from hexane); nmax(KBr)/cm-1: 2912 m, 2855 m, 1570 w, 1481 s,
1431 m, 1225 s, 1194 m, 1130 m, 1062 w, 1031 m, 854 m,
793 m, 723 m, 610 w. Found: C 45.34, H 6.07, N 7.47. Calcd for
C40H68N6Si4Dy2: C 44.89, H 6.40, N 7.85%.
{(l-g5:g1):g1-2-[(2,4,6-Me3C6H2)NCH2]C4H3N]ErN(SiMe3)2}2
(6). Pink crystals, 75% yield. mp 241–242 ◦C (from hexane).
n
max(KBr)/cm-1: 2962 m, 2914 m, 1624 s, 1481 s, 1418 m, 1260 m,
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Table 4 Crystallographic data for complexes 2, 4 and 6
2
4
6
Empirical formula
FW
C40H68N6Si4Y2
923.18
293(2)
C40H68N6Si4Sm2
1046.06
293(2)
0.71073
Orthorhombic
Pbca
12.5437(8)
14.8642(9)
26.9042(17)
5016.3(5)
4
1.385
2.445
2120
1.51 to 26.00
36 826
C40H68N6Si4Er2
1079.88
293(2)
0.71073
Orthorhombic
Pbca
12.4386(8)
14.9104(10)
26.6642(17)
4945.3(6)
4
1.450
3.499
2168
1.53 to 27.63
40 636
T/K
˚
l/A
0.71073
Orthorhombic
Pbca
12.4503(9)
14.9010(11)
26.724(2)
4957.8(6)
4
1.237
2.458
1936
1.52 to 26.00
36 612
Crystal system
Space group
˚
a/A
˚
b/A
˚
c/A
3
˚
V/A
Z
Dc/g cm-3
m/mm-1
F(000)
q range/◦
Reflections collected
Unique reflections
4873
4922
5739
(Rint = 0.0779)
269
(Rint = 0.0313)
269
(Rint = 0.0419)
269
Parameters
Goodness of fit
R1 (I > 2s(I))
wR2 (all data)
1.023
0.0420
0.1234
0.275 and -0.312
1.317
0.0290
0.0833
0.471 and -0.324
1.237
0.0353
0.0882
0.865 and -0.459
-3
˚
Min., max. residual density/e A
1204 w, 1128 m, 1093 w, 1031 s, 858 m, 799 m, 752 m, 721 m.
Found: C 45.00, H 5.96, N 7.70. Calcd for C40H68N6Si4Er2: C
44.49, H 6.35, N 7.78%.
Acknowledgements
The support from the National Natural Science Founda-
tion (20832001, 20802001), and grants from Anhui province
(TD200707, 2007Z016) are acknowledged.
General procedure for the catalytic addition of aromatic amines to
carbodiimides
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A 30.0 mL Schlenk tube under dried argon was charged with
dinuclear rare earth metal bis(amido) complex 4 (0.05 mmol),
aromatic amines (5.0 mmol), and THF (5.0 mL), then carbodi-
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Crystal structure determinations
Suitable crystal of complexes 2, 4, and 6 was each mounted in a
sealed capillary. Diffraction was performed on a Burker SMART
CCD area detector diffractometer using graphite-monochromated
˚
Mo-Ka radiation (l = 0.71073 A). An empirical absorption cor-
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were solved by direct methods, completed by subsequent difference
Fourier syntheses, refined anisotropically for all non-hydrogen
atoms by full-matrix least-squares calculations on F2 using the
SHELXTL program package.26 See Table 4 for crystallographic
data. All hydrogen atoms were refined using a riding model. It
should be noted that disorders of the SiMe3 groups in complexes
2, 4, and 6 were observed.
8998 | Dalton Trans., 2010, 39, 8994–8999
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