Cyclopentadienyl-free rare-earth metal amides [{(CH2SiMe 2){(2,6iPr2C6H3)N} 2}Ln{N(SiMe3)2}(THF)] as highly efficient versatile catalysts for C-C and C-N bond formation

Article abstract of DOI:10.1002/ejoc.200901015

Efficient methods have been developed for the direct synthesis of amides from aldehydes and a straightforward route to propiolamidines using cyclopentadienyl-free rare-earth metal amides [{(CH₂SiMe ₂){(2,6-iPr₂C₆H₃)N} ₂}Ln{N(SiMe₃)₂}(THF)] [Ln = Yb (1), Y (2), Dy (3), Sm (4), Nd (5)] as versatile catalysts, The results indicate that in the direct synthesis of amides from aldehydes the catalysts have the activity order 2>1～3～4～5. These methods have the advantage of easy preparation of the catalysts, low catalyst loading, high conversion of substrates to products, mild reaction conditions, and compatibility with a wide range of substrates.

Full text of DOI:10.1002/ejoc.200901015

FULL PAPER
DOI: 10.1002/ejoc.200901015
Cyclopentadienyl-Free Rare-Earth Metal Amides [{(CH2SiMe2){(2,6-
iPr2C6H3)N}2}Ln{N(SiMe3)2}(THF)] as Highly Efficient Versatile Catalysts
for C–C and C–N Bond Formation
Yunjun Wu,[a,b] Shaowu Wang,*[a,c] Lijun Zhang,[a] Gaosheng Yang,[a] Xiancui Zhu,[a]
Zhihong Zhou,[a] Hong Zhu,[a] and Shihong Wu[a]
Keywords: Lanthanides / N,O ligands / Amides / Amidines
Efficient methods have been developed for the direct synthe-
sis of amides from aldehydes and a straightforward route to
propiolamidines using cyclopentadienyl-free rare-earth
metal amides [{(CH2SiMe2){(2,6-iPr2C6H3)N}2}Ln{N(SiMe3)2}-
(THF)] [Ln = Yb (1), Y (2), Dy (3), Sm (4), Nd (5)] as versatile
catalysts. The results indicate that in the direct synthesis of
amides from aldehydes the catalysts have the activity order
2Ͼ1ϳ3ϳ4ϳ5. These methods have the advantage of easy
preparation of the catalysts, low catalyst loading, high con-
version of substrates to products, mild reaction conditions,
and compatibility with a wide range of substrates.
nide amido complexes Ln[N(SiMe3)2]3 (Ln = La, Sm, Y).[6a]
Ishihara and Yano reported the direct synthesis of N-alkyl-
carboxamides and N,N-dialkylcarboxamides by Haller–
Bauer (HB) and Cannizzaro-type reactions in the presence
of LDA (lithium N,N-diisopropylamide) as catalyst.[6b]
Abaee et al. reported a Cannizzaro reaction facilitated by
magnesium bromide–diethyl ether.[6c] Rare-earth metal
amido complexes as catalysts for the catalytic transforma-
tion of aldehydes to the corresponding amides remain to be
further explored.[7]
Propiolamidines [RN=C(CϵCRЈ)(NHR)] are important
amidine derivatives and have received considerable atten-
tion over the past decade due to their applications in bio-
logical and pharmacological systems,[8] but they can rarely
be obtained directly because of their high sensitivity to
hydrolysis due to their unique chemical and structural prop-
erties.[9] The addition of terminal alkynes to carbodiimides
could, in principle, provide a straightforward route to pro-
piolamidines. We have found that the [ethylenebis(η5-in-
denyl)][bis(trimethylsilyl)amido]lanthanide(III) complexes
{[(EBI)LnN(TMS)2]; EBI = ethylenebis(indenyl); Ln = Y,
Sm, and Yb} exhibited diverse catalytic activities on the
Introduction
The catalytic formation of C–C and C–N bonds is an
active subject in modern organic synthesis. Amides are im-
portant functional groups in polymers, natural products,
and pharmaceuticals.[1] Their value in organic, biological,
and materials chemistry mandates the development of more
efficient methods for their synthesis.[1] In general, amides
can be produced from the reaction between carboxylic acids
or their derivatives and amines.[1b,2] Rovis and Bode and
their co-workers reported amidation using N-heterocyclic
carbenes (NHCs) as catalysts.[3] We have reported an amid-
ation process for the preparation of the primary amides
using lanthanide chlorides (LnCl3) as catalysts in the reac-
tion of aromatic aldehydes with LiN(SiMe3)2 or lanthanide
amides [{(Me3Si)2N}3Ln(µ-Cl)Li(THF)3] as stoichiometric
reagents reacting with aldehydes.[4] The reactivity of lantha-
nide complexes that incorporate amido and enolate mixed
ligands towards aromatic aldehydes has been studied very
recently.[5] Seo and Marks developed a catalytic amidation
of aldehydes with amines catalyzed by homoleptic lantha-
[a] Key Laboratory of Functional Molecular Solids, Ministry of
Education, Anhui Laboratory of Molecule-Based Materials, addition of the C–H bond of terminal alkynes and the N–
H bond of amines to carbodiimides.[9b] Other precatalysts
College of Chemistry and Materials Science, Anhui Normal
University,
such as half-sandwich rare-earth metal complexes bearing
Wuhu, Anhui 241000, P.R. China
silylene-linked cyclopentadienyl-amido ligands[9a] and LiN-
Fax: +86-553-5910027
E-mail: swwang@mail.ahnu.edu.cn
[10]
(SiMe3)2
for the catalytic addition of the C–H bond of
[b] Wannan Medical College, Wuhu, Anhui 241001, P.R. China
[c] State Key Laboratory of Organometallic Chemistry, Shanghai
Institute of Organic Chemistry,
the terminal alkynes to carbodiimides have been reported.
Shen and co-workers recently found that divalent lantha-
nide complexes are active precatalysts for the addition of
the C–H bond of terminal alkynes to carbodiimides.[11]
Shanghai 200032, P.R. China
Supporting information for this article is available on the
WWW under http://dx.doi.org/10.1002/ejoc.200901015.
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Cyclopentadienyl-Free Rare-Earth Metal Amide Catalysts
However, the catalytic synthetic route to propiolamidines Table 1. Reaction of aniline with benzaldehyde catalyzed by
[{(CH2SiMe2){(2,6-iPr2C6H3)N}2}Ln{N(SiMe3)2}(THF)] [Ln
=
with cyclopentadienyl-free rare-earth metals amides as cata-
lysts remains limited.
Yb (1), Y (2), Dy (3), Sm (4), Nd (5)].[a]
We recently reported the synthesis of a series of tetraco-
ordinated rare-earth metal amides with the general formula
[{(CH2SiMe2){(2,6-iPr2C6H3)N}2}Ln{N(SiMe3)2}(THF)]
[Ln = Yb (1), Y (2), Dy (3), Sm (4), Nd (5)] (Figure 1) and
found that these complexes exhibited high catalytic activity
and selectivity in the cyclotrimerization of aromatic isocy-
anates and a high catalytic activity for the guanylation of
aromatic and heterocyclic amines.[12]
Entry
PhCHO/
PhNH2
Ln (catalyst
loading [mol-%])
Solvent Yield [%]
[b]
1
2
3
4
5
6
7
8
1:1
2:1
3:1
1:1
2:1
3:1
1:1
2:1
3:1
3:1
3:1
3:1
3:1
3:1
3:1
3:1
Nd (3)
Nd (3)
Nd (3)
Nd (3)
Nd (3)
Nd (3)
Nd (5)
Nd (5)
Nd (5)
Sm (5)
Dy (5)
Y (5)
toluene
toluene
toluene
THF
15
53
68
18
49
65
37
73
85
86
87
99
83
25
54
89
THF
THF
toluene
toluene
toluene
toluene
toluene
toluene
toluene
toluene
toluene
toluene
9
10
11
12
13
14
15
16
Yb (5)
Y (1)
Y (2)
Y (3)
[a] Room temperature, 12 h. [b] Isolated yields of amides based on
aniline.
Figure 1. The catalysts [{(CH2SiMe2){(2,6-iPr2C6H3)N}2}Ln{N-
(SiMe3)2}(THF)] described in this paper.
As part of our continuing interest in developing rare-
earth metal amides as diverse catalysts for the catalytic for-
mation of C–C and C–N bonds in organic synthesis[4,9b,12]
we have studied the catalytic activity of the cyclopen-
tadienyl-free lanthanide amides 1–5 in the catalytic amid-
ation of aldehydes with amines and the catalytic addition
of the C–H bond of terminal alkynes to carbodiimides. We
report the results herein.
catalyst loading was fixed at 5 mol-%, the yields of the reac-
tion improved from 37 to 85% by changing the mole ratio
of aldehyde to aniline from 1:1 to 3:1 (Table 1, entries 7–9),
which indicates that the results of the reaction are signifi-
cantly influenced by the catalyst loading. Different lantha-
nide amides [{(CH2SiMe2){(2,6-iPr2C6H3)N}2}Ln{N-
(SiMe3)2}(THF)] [Ln = Yb (1), Y (2), Dy (3), Sm (4), Nd
(5)] exhibited good-to-excellent catalytic activity in the am-
idation reaction of aldehyde and aniline when the catalyst
loading was 5 mol-% and the ratio of aldehyde to aniline
was 3:1 (Table 1, entries 9–13). The complexes 1, 3, 4, and
5 exhibited similar catalytic activity with the yttrium com-
Results and Discussion
The catalytic activity of the rare-earth metal amides plex 2 showing the highest activity (Table 1, entry 12). This
[{(CH2SiMe2){(2,6-iPr2C6H3)N}2}Ln{N(SiMe3)2}(THF)] observation contrasts the results obtained with the homo-
[Ln = Yb (1), Y (2), Dy (3), Sm (4), Nd (5)] in the amid- leptic lanthanide amido catalysts Ln[N(SiMe3)2]3, in which
ation reaction of aldehydes with amines was investigated by the lanthanum complex exhibited the highest catalytic ac-
performing the reaction of aniline with benzaldehyde as a tivity,[6a] and the heterobimetallic lanthanide/sodium phen-
model reaction under various reaction conditions. The re- oxide catalytic systems, in which the samarium complex dis-
sults are given in Table 1.
played the highest activity.[7] With yttrium, the catalyst
The above results reveal that the amidation reaction of loading had a similar effect on the yields of the amides, for
benzaldehyde with aniline could work in toluene or THF at example, when the catalyst loading was changed, the yield
room temperature in the presence of the catalysts of the reaction changed greatly (Table 1, entries 12 and 14–
[{(CH2SiMe2){(2,6-iPr2C6H3)N}2}Ln{N(SiMe3)2}(THF)] 16). Thus, the optimized reaction conditions for the follow-
[Ln = Yb (1), Y (2), Dy (3), Sm (4), Nd (5)]. The results ing experiments were selected as a 3:1 mole ratio of alde-
indicate that the yields of the reaction can be improved by hyde to amine, 5 mol-% catalyst loading, toluene as solvent,
changing the mole ratio of aldehyde to aniline from 1:1 to and room temperature.
3:1. For example, the yields of the amides could be raised
The effects of the rare-earth metal and reaction time on
from 15 to 68% in toluene and 18 to 65% in THF in the the isolated yields of the amide were further investigated
presence of 3 mol-% catalyst (Table 1, entries 1–6), which under the optimized conditions. A plot of the isolated yields
indicates that solvent has little effect on the reaction, similar of amide against reaction time is shown in Figure 2 and
to observations of other amidation reactions.[6] When the shows that 1) different rare-earth metal amides
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[{(CH2SiMe2){(2,6-iPr2C6H3)N}2}Ln{N(SiMe3)2}(THF)] 3 with those of entry 5, entries 6–8 with 10, entries 17 and
[Ln = Yb (1), Y (2), Dy (3), Sm (4), Nd (5)] have different 18 with 20, and entries 21 and 22 with entry 23), which sug-
catalytic activities (complexes 1, 3, 4, and 5 exhibited sim- gests that the more electron-deficient amines disfavor the
ilar activity with the yttrium complex 2 exhibiting the high- reaction. Only 26 and 28% yields of the corresponding
est activity of the five catalysts examined and 2) the highest products were isolated when the heterocyclic amine pyrrole
conversion of the substrates to the amide could be achieved was used in the reaction (Table 2, entry 16), probably due
in 120 min. Thus, a reaction time of 2 h and complexes 2 to the low reactivity of the aromatic pyrrole ring. Note that
and 5 as catalysts were selected for the following studies for good-to-excellent results were obtained when 2-hydroxy-
comparison.
benzaldehyde was allowed to react with either electron-rich
or -deficient amines (Table 2, entries 21–23), which suggests
that the catalysts tolerate the hydroxy group and the cata-
lysts Ln[N(SiMe3)2]3[6a] and LDA[6b] systems with which the
reactions of 2-hydroxybenzaldehyde with amines were not
examined. From Table 2 we also note that the reactions cat-
alyzed by the yttrium catalyst 2 generally give higher yields
of products than those catalyzed by the neodymium catalyst
5, which further demonstrates that the yttrium complex ex-
hibits higher catalytic activity than other catalysts.
The satisfactory results obtained for the construction of
C–N bonds encouraged us to explore the use of these com-
plexes as versatile catalysts in C–C coupling reactions. The
catalytic addition of terminal alkynes to carbodiimides
could provide a straightforward route to the biologically
and pharmaceutically useful propiolamidines and as reports
on cyclopentadienyl-free rare-earth metal amido complexes
as catalysts in this type of reaction are rare we have studied
the reaction of diisopropylcarbodiimide and phenylacetyl-
ene in the presence of [{(CH2SiMe2){(2,6-iPr2C6H3)N}2}-
Ln{N(SiMe3)2}(THF)] [Ln = Yb (1), Y (2), Dy (3), Sm (4),
Nd (5)] as catalysts. The results are given in Table 3.
Figure 2. Amide yield vs. reaction time for the different catalysts
1–5.
From Table 3 we can see that the catalyst loading and
The reactions of a variety of aldehydes with different reaction temperature both have a significant effect on the
amines were evaluated under the optimized reaction condi- yields of the reaction (Table 3, entries 1–8) in either toluene
tions. The results are presented in Table 2.
or THF. For example, when the catalyst loading was in-
As shown in Table 2, a wide range of substituted alde- creased from 1 to 3 mol-%, the yields increased accordingly
hydes and amines are suitable for the reaction. The substitu- from 34 to 71% in THF (Table 3, entries 1–3) and from 36
ents on the phenyl ring could be either electron-with- to 70% in toluene (Table 3, entries 5–7). When the reaction
drawing or -donating groups, for example, CH3, CH3O, iPr, temperature was raised from room temperature to 60 °C in
HO, and Cl, and good-to-excellent yields of the products the presence of 3 mol-% catalyst, the yields of the products
can be obtained. The results indicate that the catalysts ex- increased from 71 to 89% in THF (Table 3, entries 3 and 4)
amined have advantages in comparison with those we used and from 70 to 87% in toluene (Table 3, entries 7 and 8).
in our previous work[4] and the LDA catalytic system, The reaction of phenylacetylene with N,NЈ-diisopropylcar-
which requires the transformation of the amines to the cor- bodiimide can be catalyzed by all the complexes screened
responding lithium amides.[6b] When the more sterically and the yields of the reaction were satisfactory (Table 3, en-
hindered 2,6-diisopropylaniline was employed in the reac- tries 4 and 9–12) when the reactions were carried out at
tion, the yields of the reactions were low (Table 2, entries 4, 60 °C in THF in the presence of 3 mol-% catalyst loading,
9, 14, and 19); the yields of the isolated amides were im- which indicates that the central metal of the complexes has
proved by raising the reaction temperature to 80 °C and by little influence on the activities of the catalysts. These re-
prolonging the reaction time to 12 h (Table 2, entries 4 and sults contrast those obtained in the amidation reaction of
9), which indicates that steric effects have a significant effect aldehydes in which the yttrium complex exhibited higher
on the results of the reaction. When the same amine was catalytic activity than the other complexes. Therefore cata-
treated with different aldehydes (Table 2, entries 1, 6, 11, lyst 4, 3 mol-% catalyst loading, a reaction temperature of
and 17), good-to-excellent yields of the amides were ob- 60 °C, and THF as solvent were selected as the reaction
tained, regardless of the electronic nature of the substitu- conditions for the following experiments.
ents on the aryl groups of the aldehydes. Relatively low
The results indicate that the reactions proceed smoothly
yields of amides were isolated when 4-chloroaniline, which to produce the corresponding propiolamidines regardless of
has an electron-withdrawing group on the phenyl ring, re- the electronic properties of the substituents on the phenyl
acted with benzaldehyde (compare the results of entries 1– ring of the aromatic alkynes (Table 4, entries 1–9). The sub-
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Cyclopentadienyl-Free Rare-Earth Metal Amide Catalysts
Table 2. Amidation of different aldehydes with different amines catalyzed by [{(CH2SiMe2){(2,6-iPr2C6H3)N}2}Ln{N(SiMe3)2}(THF)]
[Ln = Y (2) or Nd (5)].[a]
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S. Wang et al.
FULL PAPER
Table 2. (Continued).
[a] Reagents: 3 equiv. of aldehyde, 1 equiv. of amine, 5 mol-% catalyst, toluene. [b] Isolated yield based on amine (see ref.[8]).
Table 3. Reaction of N,NЈ-diisopropylcarbodiimide with phenyl- diisopropylcarbodiimide with terminal alkynes or substi-
acetylene catalyzed by [{(CH2SiMe2){(2,6-iPr2C6H3)N}2}Ln-
tuted phenylacetylene under the same conditions, probably
due to steric effects arising from the more bulky cyclohexyl
{N(SiMe3)2}(THF)] [Ln = Yb (1), Y (2), Dy (3), Sm (4), Nd (5)].[a]
group in the carbodiimide (Table 4, entries 1–9). The fact
that the reactions of substituted phenylacetylene with elec-
tron-withdrawing groups such as 1-ethynyl-4-bromoben-
zene and 4-chloro-1-ethynylbenzene with carbodiimides
Entry
Ln (catalyst loading [mol-%]) Solvent
T [°C] Yield [%][b]
(Table 4, entries 3–5) were somewhat easier than those of
the electron-rich substituted alkyne 4-ethynylanisole with
carbodiimides (Table 4, entries 6 and 7) is probably due to
the different acidities of the terminal alkynes, which may
favor the alkyne–amido exchange process in the catalytic
initiation step. These results indicate that the catalytic ac-
tivities of the cyclopentadienyl-free lanthanide amides in
the addition of alkynes to carbodiimides can be compared
with those of half-sandwich yttrium alkyl complexes,[9a]
lithium amide LiN(TMS)2,[10] and lanthanide(II) com-
plexes.[11] However, when an aliphatic alkyne was treated
with N,NЈ-diisopropylcarbodiimide under the same condi-
tions, a relatively low yield of the corresponding product
was isolated (Table 4, entry 10).
1
2
3
4
5
6
7
8
Sm (1)
Sm (2)
Sm (3)
Sm (3)
Sm (1)
Sm (2)
Sm (3)
Sm (3)
Yb (3)
Y (3)
THF
THF
THF
r.t.
r.t.
r.t.
60
r.t.
r.t.
r.t.
60
60
60
60
60
34
52
71
89
36
49
70
87
87
88
83
86
THF
toluene
toluene
toluene
toluene
THF
THF
THF
THF
9
10
11
12
Dy (3)
Nd (3)
[a] Reagents: 1 equiv. of phenylacetylene, 1 equiv. of N,NЈ-diisopro-
pylcarbodiimide. [b] Isolated yield.
The mechanism proposed for the amidation of aldehydes
is as follows (Scheme 1). Interaction of the amine with lan-
thanide amide gives the new amido intermediate A through
an acid–base exchange reaction.[13] Coordination of an al-
dehyde molecule to the central metal of A followed by ad-
dition of the amido group to the carbonyl group produces
stituents could be electron-donating groups such as CH3
and CH3O, or electron-withdrawing groups such as Cl and
Br. The yields of the corresponding propiolamidine ob-
tained from the reactions of N,NЈ-dicyclohexylcarbodiimide
with terminal alkynes or substituted phenylacetylene were
slightly lower than those obtained in the reactions of N,NЈ-
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Cyclopentadienyl-Free Rare-Earth Metal Amide Catalysts
Table 4. Addition of alkynes to carbodiimides catalyzed by
[{(CH2SiMe2){(2,6-iPr2C6H3)N}2}Sm{N(SiMe3)2}(THF)] (4).[a]
Entry
R1
R2
Product
Yield [%][b]
1
2
3
4
5
6
7
8
9
C6H5
C6H5
4-BrC6H4
4-BrC6H4
4-ClC6H4
4-CH3OC6H4 iPr
4-CH3OC6H4 Cy
4-CH3C6H4
4-CH3C6H4
n-C3H7
iPr
Cy
iPr
Cy
iPr
29
30
31
32
33
34
35
36
37
38
89
87
97
93
96
81
78
76
69
58
Scheme 2. Proposed mechanism for the amidation of propiol-
amides.
iPr
Cy
iPr
10
[a] Reagents: 1 equiv. of terminal alkyne, 1 equiv. of carbodiimide.
[b] Isolated yield.
Conclusions
We have developed efficient methods for the direct amid-
ation of aldehydes with amines and a straightforward route
to propiolamidines using the cyclopentadienyl-free rare-
earth metal amides [{(CH2SiMe2){(2,6-iPr2C6H3)N}2}-
Ln{N(SiMe3)2}(THF)] (Ln = Yb, Y, Dy, Sm, Nd) as versa-
tile catalysts. These methodologies have the advantage of
easy preparation of the catalysts, low catalyst loading, high
conversion of substrates to products, mild reaction condi-
tions, and compatibility with a wide range of substrates and
solvents. The results indicate that the yttrium complex is
the most efficient catalyst of the catalysts examined in the
amidation of aldehydes with amines with the Yb, Dy, Sm,
and Nd complexes displaying similar catalytic activities. Ex-
amination of the reactions of terminal alkynes with car-
bodiimides using the catalysts [{(CH2SiMe2){(2,6-
iPr2C6H3)N}2}Ln{N(SiMe3)2}(THF)] (Ln = Yb, Y, Dy,
Sm, Nd) indicates that all these complexes exhibit similar
catalytic activities. To the best of our knowledge this is the
first application of readily accessible cyclopentadienyl-free
rare-earth metal amides as catalysts in the preparation of
propiolamidines.
the intermediate B, which transfers a hydride to another
aldehyde molecule as indicated in C to give an alkoxy inter-
mediate D and the product amide. The hydride transfer pro-
cess has been proved previously by treatment of deuteriated
C6H5CDO with [{(Me3Si)2N}3Y(µ-Cl)Li(THF)3].[4] The in-
termediate D reacts with intermediate E, which is produced
by the addition of amine to aldehyde, to produce B fin-
ishing the catalytic cycle. The mechanism for the formation
of propiolamidine would be similar to the one proposed in
our previous work (Scheme 2).[9b] Interaction of the lantha-
nide amide with terminal alkyne produces the intermediate
F, which then reacts with the carbodiimide to produce the
amidinate species G by an insertion reaction.[14] G reacts
with a terminal alkyne to give the final product propiolami-
dine finishing the catalytic cycle. However, another mecha-
nism and the involvement of other intermediates in the
catalytic cycle cannot be ruled out.
Experimental Section
General Procedure for the Direct Synthesis of Amides by the Reac-
tion of Aniline with Benzaldehyde Catalyzed by [{(CH2SiMe2){(2,6-
iPr2C6H3)N}2}Nd{N(SiMe3)2}(THF)] (6 as an Example): A 30 mL
Schlenk tube under dried argon was charged with the neodymium
amide [{(CH2SiMe2){(2,6-iPr2C6H3)N}2}NdN(SiMe3)2}(THF)] (5;
0.037 g, 0.0463 mmol) and toluene (10 mL). Aniline (0.086 g,
0.926 mmol) and benzaldehyde (0.295 g, 2.778 mmol) were added
to the flask. The resulting mixture was stirred at room temperature
for 2 h and then hydrolyzed with water (1 mL) and extracted with
dichloromethane (3ϫ10 mL). The extracts were dried with anhy-
drous MgSO4 and filtered. After removing the solvent under re-
duced pressure, the final product could be isolated as white crystals
by washing the crude product with diethyl ether (10 mL) or by
recrystallization from THF; yield 0.155 g, 85%; m.p. 57–58 °C. IR
(neat): ν = 3331, 3059, 3028, 2961, 2889, 1738, 1576, 1526, 1314,
˜
1281, 1260, 1192, 868, 760, 693 cm–1. 1H NMR (CDCl3, 300 MHz):
Scheme 1. Proposed mechanism for the amidation of aldehydes.
δ = 8.46 (s, 1 H, NH), 7.93 (d, J = 7.8 Hz, 2 H), 7.50 (t, J = 6.6 Hz,
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S. Wang et al.
FULL PAPER
3 H), 7.40 (t, J = 8.1 Hz, 2 H), 7.24 (t, J = 9.6 Hz, 3 H) ppm. 13C
NMR (CDCl3, 75.4 MHz): δ = 160.1, 131.1, 128.8, 128.5, 125.6,
120.5 ppm. HRMS (EI): calcd. for C13H11NO [M]+ 197.0841;
found 197.0849.
[3] a) H. U. Vora, T. Rovis, J. Am. Chem. Soc. 2007, 129, 13796–
13797; b) J. W. Bode, S. S. Sohn, J. Am. Chem. Soc. 2007, 129,
13798–13799.
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General Procedure for the Synthesis of Propiolamidines by the Reac-
tion of N,NЈ-Diisopropylcarbodiimide with Phenylacetylene Cata-
lyzed by [{(CH2SiMe2){(2,6-iPr2C6H3)N}2}Sm{N(SiMe3)2}(THF)]
(Compound 23 as an Example): A 30 mL Schlenk tube under dried
argon was charged with the samarium amide [{(CH2SiMe2){(2,6-
iPr2C6H3)N}2}Sm{N(SiMe3)2}(THF)] (4; 0.098 g, 0.122 mmol)
and THF (10 mL). N,NЈ-Diisopropylcarbodiimide (0.317 g,
2.4 mmol) and phenylacetylene (0.248 g, 2.4 mmol) were added to
the flask and the resulting mixture was stirred at 60 °C for 12 h.
After removing the solvent under reduced pressure, the residue was
extracted with hexane and filtered to give a clean solution. The
solvent was evaporated under vacuum and the final product was
obtained as white crystals by recrystallization from n-hexane or by
silica gel column chromatography using n-hexane/ethyl acetate (1:6,
v/v) as eluent; yield 0.488 g, 89%. IR (neat): ν = 3325, 2874, 2214,
˜
1462, 1439, 1385, 1250, 1169 cm–1. 1H NMR (300 MHz, CDCl3):
δ = 1.16–1.26 (m, 12 H, CH3), 3.92–4.00 (m, 2 H, CH), 7.35–7.37
(m, 3 H, C6H5), 7.48–7.51 (m, 2 H, C6H5) ppm. 13C NMR
(75.0 MHz, CDCl3): δ = 21.6, 23.9, 24.3, 47.8, 52.5, 92.1, 118.4,
129.1, 129.2, 131.9, 132.0, 139.7, 141.6 ppm. HRMS (EI): calcd.
for C15H21N2 [M + H]+ 229.1705; found 229.1695.
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Received: September 6, 2009
Acknowledgments
This work was co-supported by the National Natural Science
Foundation of China (20672002, 20702001, 20832001) and Anhui
Province (Grant numbers TD200707, 2007Z016).
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Published Online: November 18, 2009
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