532
K. Sada and K. Kokado
surface under the CuAAC conditions. In particular, the PCN-58 and PCN-59 modified with propargylamine having the four azide groups provided the greatest uptake
of carbon dioxide compared to that of nitrogen. The affinity for carbon dioxide could
be controlled by the modification of the amine functionality. After this approach,
Zhao and coworkers reported the amine-triazole-tagged MIL-101 byCuAAC with
a series of acetylene-containing amines from the azide-tagged MOF [38], and the
obtained modified MOF was used for CO 2 adsorption. The improved CO 2 uptake
ability increased up to 128.3 cm
3 /g at 1 atm and 273 K, and a significantly enhanced
selectivity to CO 2 over N 2 was observed. More recently, the preparation of the azidetagged NU-1000 and the subsequent click reaction with alkynes have been reported
[39], and the alkyne-tagged UiO-68 was also prepared and used for CuAAC with a
series of azides by Wang and coworkers [40]. They controlled the gas sorption by
the steric dimensions of the external substrate which affected the preference of guest
adsorption.
MOFare promising as a catalyst, but there have also been attempts to improve
the catalytic ability of the MOF by the PSM using the CuAAC. Farrusseng and
coworkers introduced both the organic base derived from N,N-diethylpropargylamine
as a catalytic site and the phenyl ring from phenylacetylene as a lipophilic site into
the framework of DMOF-NH 2 by a one-pot, two-step CuAAC (Scheme 25.4b) [41]
and used for the transesterification of aliphatic esters. The transesterification reaction
proceeded in a higher yield, when both alkynes were used for the PSM compared to
those modified by only one of the two. The improved affinity with the substrate by
introducing the lipophilic group (phenyl group) enhanced the catalytic activity. In the
cases of the bulky alcohols, the transesterification reaction did not proceed, indicating
the size selectivity of the substrate due to the pore size. More recently, Duan and
coworkers reported the preparation of the MOF with chiral 2-azidomethylpyrrolidine
by CuAAC as the asymmetric catalytic site(Scheme 25.4c) [42]. This MOF was used
for asymmetric aldol reaction between 4-nitrobenzaldehyde and cyclohexanone with
a 75% yield and 71%ee. The size selectivity of the substrates was also observed.
Furthermore, the switching of the chirality of 2-azidomethylpyrrolidine in the PSM
provided the product with the opposite chirality and the similar yield and enantioselectivity. This PSM should be used to construct the desired chiral nanopores for
asymmetric catalysis. Gao and coworkers reported the catalytic MOF derived from
UiO-67-N 3 by the CuAAC for the Knoevenagel condensation between benzaldehyde
and ethyl cyanoacetate. The triazole group formed by CuAAC acted as the crucial
active site for Knoevenagel condensation [43].
25.5 Networking and Biocongujation of MOF
by CuAAC-PSM
The open framework structures of the MOF should be useful as the template for polymerization and networking. Sada et al. reported the polymerization of organic ligands
K. Sada and K. Kokado
surface under the CuAAC conditions. In particular, the PCN-58 and PCN-59 modified with propargylamine having the four azide groups provided the greatest uptake
of carbon dioxide compared to that of nitrogen. The affinity for carbon dioxide could
be controlled by the modification of the amine functionality. After this approach,
Zhao and coworkers reported the amine-triazole-tagged MIL-101 byCuAAC with
a series of acetylene-containing amines from the azide-tagged MOF [38], and the
obtained modified MOF was used for CO 2 adsorption. The improved CO 2 uptake
ability increased up to 128.3 cm
3 /g at 1 atm and 273 K, and a significantly enhanced
selectivity to CO 2 over N 2 was observed. More recently, the preparation of the azidetagged NU-1000 and the subsequent click reaction with alkynes have been reported
[39], and the alkyne-tagged UiO-68 was also prepared and used for CuAAC with a
series of azides by Wang and coworkers [40]. They controlled the gas sorption by
the steric dimensions of the external substrate which affected the preference of guest
adsorption.
MOFare promising as a catalyst, but there have also been attempts to improve
the catalytic ability of the MOF by the PSM using the CuAAC. Farrusseng and
coworkers introduced both the organic base derived from N,N-diethylpropargylamine
as a catalytic site and the phenyl ring from phenylacetylene as a lipophilic site into
the framework of DMOF-NH 2 by a one-pot, two-step CuAAC (Scheme 25.4b) [41]
and used for the transesterification of aliphatic esters. The transesterification reaction
proceeded in a higher yield, when both alkynes were used for the PSM compared to
those modified by only one of the two. The improved affinity with the substrate by
introducing the lipophilic group (phenyl group) enhanced the catalytic activity. In the
cases of the bulky alcohols, the transesterification reaction did not proceed, indicating
the size selectivity of the substrate due to the pore size. More recently, Duan and
coworkers reported the preparation of the MOF with chiral 2-azidomethylpyrrolidine
by CuAAC as the asymmetric catalytic site(Scheme 25.4c) [42]. This MOF was used
for asymmetric aldol reaction between 4-nitrobenzaldehyde and cyclohexanone with
a 75% yield and 71%ee. The size selectivity of the substrates was also observed.
Furthermore, the switching of the chirality of 2-azidomethylpyrrolidine in the PSM
provided the product with the opposite chirality and the similar yield and enantioselectivity. This PSM should be used to construct the desired chiral nanopores for
asymmetric catalysis. Gao and coworkers reported the catalytic MOF derived from
UiO-67-N 3 by the CuAAC for the Knoevenagel condensation between benzaldehyde
and ethyl cyanoacetate. The triazole group formed by CuAAC acted as the crucial
active site for Knoevenagel condensation [43].
25.5 Networking and Biocongujation of MOF
by CuAAC-PSM
The open framework structures of the MOF should be useful as the template for polymerization and networking. Sada et al. reported the polymerization of organic ligands