S.K. Das, et al.
MolecularCatalysis480(2020)110650
support for carrying out the C-C cross coupling reaction [30]. Alonso
et al. have described the Pd catalysed heterogeneous homocoupling of
terminal alkynes [32]. Venkatraman et al. have shown C-C coupling
reaction in homogeneous phase using Pd as catalyst in air and water
[33]. A large number of C-C homo coupling reactions are reported using
Pd as catalyst and many reactions have been performed homogeneously
[34,35]. But the major disadvantage of these reactions includes use of
toxic reagents, hazardous solvents as well as expensive metal and ligand
sources. Thus, novel approach to achieve efficient C-C coupling reaction
using inexpensive catalytic system is highly desirable. So low cost and
abundant metal like Cu, Fe, Ni, Ag based catalysts have attracted
overwhelming attention in C-C coupling reactions in the recent times
using Cu-K (λ =0.15406 nm) radiation. Diffraction patterns in the
wide angle region (10°−80°) were recorded at a rate of (2θ) = 0.4° per
min and that of small angle region (2°-10°) were recorded at a rate of
(2θ) = 0.2° per min. Ultra high resolution transmission electron mi-
croscopic (TEM) images of the COF and subsequent CuO loaded COF,
were taken by using a UHR-FEG TEM system (JEOL JEM 2100 F)
transmission electron microscope operating at 200 kV electron source.
Samples were prepared by dropping a sonicated ethanolic dilute solu-
tion of the COF TRIPTA and CuII-TRIPTA materials over a carbon coated
copper grid followed by drying under high vacuum. N2 adsorption/
desorption isotherm of both the materials were obtained froma
Autosorb-iQ surface area analyzer of Quantachrome Instruments, USA
at 77 K to calculate the Brunauer-Emmett-Teller(BET) surface area as
well as material porosity. Pore size distribution plot was obtained by
usingnon local density functional theory (NLDFT) taking N2 sorption at
77 K on carbon with slit pore model as reference. Prior to the sorption
measurement, the powder sample was Sohxlet extracted for 72 h
usinganhydrous MeOH as dispersion medium and dried itunder vacuum
at 150 °C. Prior to all the adsorption study, both the samples were de-
gassed at 423 K for 12 h under high vacuum conditions.
Thermogravimetric analysis (TGA) was performed using a Mettler
Toledo TGA/DTA 851e TA-SDT Q-600 instruments. The EPR (electron
paramagnetic resonance) spectroscopic analysis has been done for both
the freshly synthesized catalyst as well as used catalyst at room tem-
perature using a JES-FA200ESR spectrometer (JEOL). FTIR study of
boththe TRIPTA and CuII-TRIPTA were recorded from Perkin Elmer
Spectrum 100 spectrophotometer.
In this context Liu et al. reported homo coupling reactions of aryl
Grignard reagents in presence of O2 with Fe as catalyst for the forma-
tion of new C-C bond [40]. Xiao et al. have shown homo coupling re-
action proceeds smoothly over the Mg-Al oxide stabilized gold nano-
particles [41]. Sakurai et al. studied the homo coupling reaction of
arylboronic acids employing gold nanoparticles as catalyst in acidic
medium [42]. Indium was also employed for reductive homo coupling
between alkyl and aryl halides by Ranu et al. [43]. Zn containing cat-
alyst and Pd grafted Zn based MOF have been reported for C-C coupling
reaction by G. Anilkumar et al. and M. Azad et al. respectively [44,45].
Very recently Yongjun Liu et al. reported copper-catalysed C-C homo-
coupling of alkyl halides in the presence of another metal samarium
[46]. But most of the reactions are associated with inherent drawbacks
of toxicity, noneconomical, hazardous organic solvents, which are not
acceptable in the context of bulk scale synthesis following green
chemistry protocol. Among the various transition metal, 3d series metal
Cu is considered for catalyst due to its low toxic nature and higher
stability. Cheng et al. showed homogeneous catalysis of C-C homo
coupling reaction by CuCl2 [47]. Alonso et al. reported a Cu(II) cata-
lysed heterogeneous homo coupling of terminal alkyne in their different
oxidation state [32]. Yaghi et al. and Puthiaraj et al. reported homo
coupling reactions of arylboronic acids using/without using external
base where Cu based MOFs, Cu3(BTC)2 [48] and Cu(BDC) [49] are used
as catalyst.So C-C homo coupling reaction catalyzed by Cu(II) sup-
ported nanoporous materials with high surface area is very challenging.
Herein, we have synthesized a nitrogen and phenolic−OH rich COF
material TRIPTA through solvothermal Schiff base condensation of
2,4,6-triformylphloroglucinol and 1,3,5-tris-(4-aminophenyl)triazine in
a pressure tube and further decorated its surface with CuO nano-
particles to yield an efficient heterogeneous catalyst CuII-TRIPTA
(Scheme 1). Then we have explored the catalytic activity of CuII-
TRIPTA in the C-C homo coupling reaction of aryl boronic acids for the
synthesis of biaryl derivatives.
Synthesis of COF TRIPTA
We have carried out the Schiff base condensation between TFP and
TAPT for the synthesis of this TRIPTA COF in a Pyrex sealed tube [50].
Within an oven dried clean Pyrex sealed tube we have mixed 0.4 mmol
TAPT (141.2 mg) and 0.4 mmol TFP (84 mg) in 1:1 M ratio. In that 3 mL
dioxane, 3 mL mesitylene, and 0.5 mL CH3COOH 6(N) were added.
Then the reaction mixture was sonicated for 20 min to make homo-
geneous mixture and followed by degassing three times with the freeze-
pump-thaw cycle using liquid N2 and high vacuum pump. Then the
Pyrex tube was flame sealed and allows this solvothermal reaction to
proceed for 4 days. Finally the deep orange-red coloured fine powder
material filtered off and washed with ethanol followed by THF to re-
move unreacted starting monomers. Then the guest free porous mate-
rial was obtained by Soxhlet extraction with THF: methanol (1:1) for
48 h and dried under vacuum at 150 °C for overnight. The isolated yield
of the COF material was obtained 81 wt%.
Synthesis of CuII-TRIPTA catalyst
Experimental section
To an methanolic solution of the TRIPTA (0.5 g material with 50 ml
of MeOH) 0.2(M) 25 mL of CuCl2 solution was added and allowed to stir
for overnight at room temperature in open air condition. The resultant
slurry was washed successively with water to wash out inorganic re-
sidue if any, then with acetone and ethanol. Then the resultant solid
was air dried for 2 days. Then the material was characterized thor-
oughly and after getting satisfactory characterization results its cata-
lytic activity was explored.
Chemicals
1,3,5-triformyl phloroglucinol (TFP), was synthesised from phlor-
oglucinol (Sigma-Aldrich, India). Hexamine, trifluoroacetic acid and
hydrochloric acid were obtained from Merck, India.1,3,5-tris-(4-ami-
nophenyl) triazine (TAPT), was synthesised from 4-aminobenzonitrile
and trifluoromethanesulfonic acid which were obtained from Sigma-
Aldrich, India. Anhydrous N,N-dimethylformamide, copper salts CuCl,
CuCl2 and Cu(OAc)2 and all substrate used for the catalytic study were
obtained from Spectrochem, India; all are used without further pur-
ification. All other solvents used were of analytical grade produced by
Merck, India and were distilled prior to use.
General procedure for homo coupling reaction catalyzed by CuII-
TRIPTA:
Biaryl derivatives were synthesized from phenylboronic acids in
methanol solvent. In a typical experiment 1 mmol of phenylboronic
acid was taken in 5 mL methanol and then 30 mg of CuII-TRIPTA cat-
alyst was taken into the reaction mixture. The reaction was proceeded
for 5–12 h at 60 °C temperature under air. After completion of the
coupling reaction, the reaction mixture was allowed to cool at room
temperature and water and ethyl acetate was added to it. Further using
a separating funnel organic layer was collected 4 times and dried to
Material characterizations
Powder X-ray diffraction study of both the TRIPTA and CuII-TRIPTA
COFs were done in a Bruker AXS D-8 Advanced SWAX diffractometer
2