Organometallics
ARTICLE
because of their high efficiency and mild reaction conditions.
Wang et al. found that aromatic aldehydes reacted with lanthanide
amides Ln[N(SiMe ) ] (μ-Cl)Li(THF) to give amides via the
p-methylbenzaldehyde with secondary cyclic amines give higher
yields than that with linear secondary amines (Table 3, entries 8,
12, and 16), which is different from the catalytic systems reported
3
2 3
3
14
15
Cannizzaro-type disproportonation reaction. Marks et al. re-
ported that homoleptic lanthanide amides Ln[N(SiMe ) ] can
in the literatures.
3
2 3
catalyze efficiently the amidation reaction of aldehydes with
amines under mild conditions without the use of peroxide.
’
CONCLUSION
15
In summary, four heterobimetallic lanthanideꢀpotassium
Subsequently, we found that some anionic lanthanideꢀalkali
complexes stabilized by carbon-bridged bis(phenolate) ligands
have been synthesized, and their structural features are provided.
It was found that the ionic radii of lanthanide metals have a
profound effect on the structures of these complexes. These
heterobimetallic complexes are efficient catalysts for the amida-
tion reactions of aldehydes with amines under mild reaction
conditions. The new catalysts show good activity and a wide
range of substrates to produce amides in good to excellent yields
under mild reaction conditions.
metal complexes are more efficient catalysts for this reaction,
4c,d
and they have a wider range of scope for the amines. To further
explore the application of bridged bis(phenolate) lanthanide
complexes, the catalytic behavior of these heterobimetallic
lanthanideꢀpotassium complexes on the amidation reaction of
aldehydes with amines was tested.
The amidation of benzaldehyde 1a with aniline 2a was first
examined as a model reaction catalyzed by the lanthanide hetero-
bimetallic complexes 1ꢀ4, and the results are summarized in
Table 2. It can be seen that all of these heterobimetallic
lanthanideꢀpotassium complexes can catalyze this transforma-
tion to yield the amide 3aa in moderate to excellent yields at
’ ASSOCIATED CONTENT
S
Supporting Information. Crystallographic data for com-
plexes 1 to 4 in CIF format and the NMR spectra for complexes
2
5 °C with 10 mol % catalyst loading (Table 2, entries 1ꢀ4). The
b
lanthanumꢀpotassium complex 1 gave the highest yield under
the same reaction conditions, and the yield for these complexes
follows the trend Yb < Nd < La, which is consistent with the trend
of their ionic radii. For comparison, the catalytic behavior of the
1
ꢀ4 and all amidation products in PDF format. These materials
are available free of charge via the Internet at http://pubs.acs.org.
neutral ytterbium complex (MBMP)Yb(MBMPH)(THF) (5)
’ AUTHOR INFORMATION
2
16
for this reaction was also tested. It was found that the yield is
only 11% using complex 5 as the catalyst even when the loading
of the catalyst is increased to 30% (Table 2, entry 6). These
results revealed that the heterobimetallic structure plays a key
role in this reaction system. Using complex 1 as the catalyst, the
yield increases with an increase in catalyst loading (Table 2,
entries 1, 7, and 8), and the reaction with 10 mol % of complex 1
can afford a good yield (Table 2, entry 1). The reaction proceeds
smoothly at room temperature (25 °C) to give 3aa in good
isolated yield, and the yield increases slightly when the reaction
temperature increases to 65 °C (Table 2, entries 1 and 9).
The generality and scope of the amidation reaction catalyzed
by complex 1 were also investigated, and the results are listed
in Table 3. It can be seen that all of the reactions proceeded
smoothly to produce the corresponding amides in good to
excellent isolated yields. Electronic effects of the aromatic
aldehydes have a significant effect on the amidation reactions.
The aromatic aldehydes with electron-withdrawing groups at the
p-position on the phenyl ring give higher yields in comparison
with the aldehydes with electron-donating groups, which is
Corresponding Author
*Fax: (86)512-65880305. Tel: (86)512-65882806. E-mail: yaoym@
suda.edu.cn.
’
ACKNOWLEDGMENT
Financial support from the National Natural Science Founda-
tion of China (Grant 20972108), PAPD and the Qing Lan
Project is gratefully acknowledged.
’ REFERENCES
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(
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(
Table 3, entry 12). Furthermore, the amidation reactions of
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dx.doi.org/10.1021/om200283j |Organometallics 2011, 30, 3588–3595