Table 3 Suzuki coupling of bromobenzene with phenylboronic acid
The percentage of conversions vs. time for the consecutive runs
is shown in Fig. 8. From the kinetic plot it has been observed
that efficiency of the catalyst decreases quite slowly. This slow
deactivation of the Pd-CIN-1 catalyst can be explained by the
enhanced stability of metal support due to strong interaction
between Pd and the functionalities in the network. Chan-Thaw
et al.19 observed the same behavior when they introduced nitrogen
functionalities on the surface of Pd/CTF supported material. To
get an insight on the deactivation process, we have also examined
the state of the catalysts by TEM analysis. TEM images of the
catalyst after the first run show almost similar distribution of
palladium particles as for the as-prepared catalyst, nevertheless,
very slight metallic aggregation has been observed (Fig. 9). Powder
XRD experiment of the catalyst after the first run has been
performed to investigate the crystallinity of the nanoparticles (Fig.
S6a, ESI†). The diffraction patterns show retained crystallinity
as for the as-synthesized catalyst with peaks at 40.0, 46.7, 68.3
and 82.2◦ which can be assigned to the (111), (200), and (220)
planes of face-centered cubic (fcc) structure of Pd having Fm3m
space group.55 The peak intensity is, however, considerably reduced
compared to that of the powder pattern of the as-prepared
catalyst (Fig. S3, ESI†). This can be attributed to the some
extent of disordering occurring during the course of the catalytic
reaction.
catalyzed by a variety of catalysts
Entry Catalyst (Pd, mol%) t/h Base
T/K Yield (wt%) Ref.
1
2
3
4
Pd/PE-MCM-41 (0.1) 20 K3PO4 295 61.0
CuO/Pd-3 (7.0) 10 K2CO3 353 80.0
Ca, Pd/alginate (0.4) 5.0 K2CO3 343 95.4
Pd-CIN-1 (0.6) 1.5 K2CO3 353 96.0
55
40
56
This work
5. Conclusion
We can conclude that a facile synthesis of imine-functionalized
nitrogen-rich porous organic network can be developed from
relatively cheap and industrially important building blocks by
employing an easy chemical route. With the view of possible
catalytic application, palladium has been loaded on its surface and
the resulting material showed excellent catalytic activity towards
Suzuki carbon–carbon cross coupling reaction in the absence
of any additional stabilizing ligand over a very short reaction
time. The high amount of nitrogen in the CIN-1 support makes
the Pd nanoparticles resistant to aggregation and also helps to
preserve their catalytic activity and stability during recycling.
Thus, our functional covalent porous material paves the new
strategy towards the development of organic network materials
having extensive catalytic applications.
Acknowledgements
A. B. wishes to thank DST, New Delhi for research grants. M.
K. B. and S. K. D. wish to thank CSIR, New Delhi for Senior
Research Fellowships. R. B. acknowledges CSIR’s XIth Five Year
Plan Project and DST for financial assistance.
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