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ARTICLE
DOI: 10.1039/C5CC03151F
species with the azoꢀtype ligand and the excellent stability of high thermal stability and high adsorption capacity to CO2. In
Azo-MOP-3-Ru as an efficient heterogeneous catalyst.
addition, the azoꢀtype ligands within the skeletons showed
excellent coordinating ability for Ruꢀcomplex. Efficient
methylation of amines using CO2 as C1 building block was
realized adopting the resultant AzoꢀMOPꢀRu as catalyst, thus
providing a new direction for the simultaneous adsorption,
activation and transformation of CO2 into valueꢀadded
chemicals under mild conditions.
The authors thank the National Natural Science Foundation
of China (No. 21125314, 21321063, 21402208) for the
financial support.
Table 2 Azo-MOP-N-Ruꢀcatalyzed methylation of Nꢀmethylaniline (1a)
using CO2 as a C1 building blocka
Entry
Catalyst
1a Conv.(%)b
2a yield(%)b
1
2
3
4
5
Azo-MOP-1-Ru
Azo-MOP-2-Ru
Azo-MOP-3-Ru
Azo-MOP-4-Ru
RuCl3·3H2O
98
98
100
98
92
94
99
89
64
74
a Reaction conditions: 1a 0.5 mmol, catalyst loading 4 mol% Ru based on 1a,
PPh3 0.1 mmol, organosilane PhSiH3 4 mmol, CO2 pressure 0.5 MPa, solvent
THF 2 mL, 120 oC, 24 h. b Determined by GC using dodecane as an internal
standard.
Notes and references
1 Y. Xu, S. Jin, H. Xu, A. Nagai and D. Jiang, Chem. Soc. Rev., 2013, 42
,
,
Azo-MOP-3-Ru could be applied to the reactions of various
amines with CO2 under low pressure (0.5 MPa) (Table S1, ESI).
Nꢀmethylanilines with both electronꢀdonating (Entries 2ꢀ5) and
electronꢀwithdrawing groups (Entries 6ꢀ10) could be
transformed to the corresponding N,Nꢀdimethylanilines in
excellent yields (93ꢀ99%). In addition, Nꢀmethylanilines with
substituted groups (Clꢀ or CH3ꢀ) on the ortho, metaꢀ and paraꢀ
positions of the benzene ring all converted to methylamines in
excellent yields (Entries 2ꢀ4, 8ꢀ10). Dialkylamines also showed
good reactivity (92% yield) catalyzed by Azo-MOP-3-Ru
(Entry 11). The reduction of formamide was carried out,
8012ꢀ8031.
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forming N,Nꢀdimethylaniline
(2a) solely in 99% yield
catalyzed by Azo-MOP-3-Ru under the same other conditions
(Entry 12), thus indicating the presence of the formamides
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To further gain insight into the facilitation of azoꢀ
functionalized materials to the methylation reaction of amines,
NMR technique was employed to identify the interaction of 1a
and azo functionality, by taking an azoꢀcontaining monomer
(azobenzen) instead of the insoluble AzoꢀMOPs (Figure S14,
ESI). It was found that the proton signal of NꢀH bond in 1a (Hꢀ
2) showed a slightly upfield shift from 2.76 to 2.80 ppm after
the addition of azobenzene, probably owing to the formation of
hydrogen bond between NꢀH and electronꢀgiving azo group.
Correspondingly, inductive effect caused decrease in the
electron density on the N atom of 1a, thus leading to downfield
shift of the other protons in the methyl group (Hꢀ1) and the
benzene ring (Hꢀ3 to Hꢀ5), which was further proved by the
downfield shift of the N signal in 1a from 51.32 to 52.75 ppm.
On the basis of the experimental results obtained, it can be
deduced that the AzoꢀMOPs developed herein served as
functionalized materials for efficient CO2 adsorption/activation,
showed strong coordinating ability with Ru species, activated
NꢀH containing amines through hydrogen bond formation and
thus displayed high efficiency for the methylation reaction of
amines using CO2 as a C1 building block. A possible
mechanism for the methylation of amines with captured CO2 by
AzoꢀMOPꢀ3ꢀRu was proposed as shown in Scheme S1 (ESI).
In summary, we have elaborated a novel, simple and efficient
method for the synthesis of azoꢀfunctionalized MOPs in
excellent yields (> 95%) at room temperature. The resultant
AzoꢀMOPs with BET surface areas up to 706 m2 gꢀ1 displayed
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4 | J. Name., 2012, 00, 1-3
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