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S. Muthuramalingam et al. / Journal of Catalysis 372 (2019) 352–361
at room temperature for three days. The reaction mixture was then
extracted with CHCl3 (3 ꢀ 50 mL). The organic layer was washed
with saturated sodium hydrogen carbonate solution, evaporated,
and then dried (Na2SO4). The organic solvent was removed on a
rotary evaporator to yield the crude product as a pale-yellow oil.
The pure product was obtained by extracting the oil once again
with ethyl acetate. Yield, 1.287 g (62.4%). 1H NMR (300 MHz,
CDCl3), d, 8.4 (d, 1H, J = 4.03 Hz), 7.5 (t, 1H, J = 7.66 Hz), 7.3 (d,1H,
J = 7.78 Hz), 7.0 (t, 1H, J = 7.55 Hz), 3.7 (s, 2H), 2.7–2.6 (m, 4H),
2.6–2.5 (m, 4H), 2.2 (s, 3H), 1.7 (pentet, 2H, J = 11.77 Hz). 13C
NMR (CDCl3), d, 46.15 (CH3), 26.51, 53.62, 54.34, 56.21, 57.40,
64.75, (CH2), 121.80, 122.85, 136.27, 146.87, 159.32 ppm (ArC).
ESI-MS (m/z): [M + H]+, 206.23.
ture for 3 h. The color changed to a dark blue color. Solvent
removal under reduced pressure gave a blue colored residue which
was washed twice (10 mL each) with hexane to remove the excess
ligand. The compound was then dried under high vacuum over
fused CaCl2. Recrystallization from MeOH gave a blue colored crys-
tal suitable for X-ray crystallography analysis. Yield, 0.28 g (96%).
ESI-MS, [C12H19CuN3O4Cl]+, m/z, 368.14. Analytically calculated
elements for C12H21CuN3O9Cl2: C, 29.67; H, 4.36; N, 8.65%. Found:
C, 29.65; H, 4.37; N, 8.64%.
[Cu(L2)(H2O)ClO4]ClO4 (2): The above procedure has been fol-
lowed to synthesize 2 using ligand L2 instead of L1 in MeOH:
H2O (8:2) solution. The blue colored solid was isolated with a yield
of 0.312 g (72.4%). Slow evaporation of the mother liquor at room
temperature afforded single crystals suitable for X-ray analysis.
ESI-MS, [C13H23CuN3O5Cl]+, m/z, 399.20. Analytically calculated
elements for C13H23CuN3O9Cl2: C, 31.24; H, 4.64; N, 8.41%. Found:
C, 31.23; H, 4.63; N, 8.39%.
4.5.2. Synthesis of 4-methyl-1-[(2-(pyridine-2-yl)ethyl]-1,4-diazepane
(L2)
To a solution of 1-methylhomopiperazine (5.8 mmol, 0.662 g) in
methanol (30 mL), acetic acid (7.2 mmol, 0.432 g) and 2-
vinylpyridine (14.4 mmol, 1.514 g) were added. The reaction
mixture was then warmed to 65 °C and stirred for two days. The
mixture was cooled to room temperature, and the volatiles was
removed under reduced pressure. The remaining red-brown oil
was dissolved in H2O and carefully made basic using solid NaOH.
It was subsequently extracted three times with toluene. The
removal of toluene from the combined organic phases left the
crude product as a red oil, which was purified by repeated extrac-
tion with small amounts of hexane. The solvent was removed
under vacuum to give light yellow oil; yield, 0.62 g (40%).1H NMR
(300 MHz, CDCl3), d, 8.4 (d, 1H, J = 4.16 Hz), 7.5 (t, 1H,
J = 7.71 Hz), 7.4 (d, 1H, J = 7.76 Hz), 7.0 (t, 1H, J = 7.65 Hz), 2.9 (d,
4H, J = 1.97 Hz), 2.8 (m, 2H), 2.73 (m, 2H), 2.73 (m, 4H), 2.6 (s,
3H), 1.8 (pentet, 2H, J = 11.79 Hz). 13C NMR (CDCl3), 46.51 (CH3),
26.70, 35.89, 46.51, 49.83, 55.66, 53.81, 56.57, 57.40, 58.25,
(CH2), 121.00, 123.12, 136.27, 146.88, 160.17 ppm (Ar). ESI-MS
(m/z): [M + H]+, 220.18.
[Cu(L3)(H2O)ClO4]ClO4 (3): This complex was also prepared by
the similar reaction of Cu(ClO4)2ꢂ6H2O with ligand L3 in MeOH:
H2O (8:2) solution. Yield, 0.28 g (86%). ESI-MS, [C15H27CuN3O5Cl]+,
m/z, 427.25. Analytically calculated elements for C15H27CuN3O10
-
Cl2: C, 33.13; H, 5.00; N, 7.73%. Found: C, 33.11; H, 4.98; N, 7.71%.
4.7. Oxidation of p-nitrophenyl-b-D-glucopyranoside
The catalytic activity of the copper(II) complexes 1–3 was
assessed
using
the
oxidation
of
p-nitrophenyl-b-D-
glucopyranoside by H2O2 in water at the mild condition. Reaction
condition, the model substrate (200 mmol), a catalytic amount of
the complex (2.5 mmol, 1.25 mol %), aqueous hydrogen peroxide
(200 mmol), triethylamine (2.5 mmol) was dissolved in H2O
(3.0 mL). The mixture was stirred at 60 °C for 2 h, then the reaction
was quenched at the appropriate time by passing on silica column.
Conversion of p-nitrophenol formation was analyzed and quanti-
fied by GC/GC-MS. The blank reaction performed using identical
condition but in the absence of catalyst or H2O2.
4.5.3. Synthesis of 1-(4-methoxy-3,5-dimethylpyridin-2-yl)methyl)-4-
methyl-1,4-diazepane (L3)
4.8. Kinetic studies
A
slightly modified procedure of the previously reported
method was used to synthesize ligand. Aqueous solution (10 mL)
of NaOH (0.795 g, 20 mmol) was added dropwise to an aqueous
solution (10 mL) of 2-chloromethyl-4-methoxy-3,5-dimethylpyri
dine hydrochloride (2.22 g, 10 mmol) at 0 °C. Further addition of
1-methylhomopiperaine (1.142 g, 10 mmol) in 20 mL of water
was then added to this mixture over 15 min. The mixture was stir-
red in a loosely sealed flask at room temperature for three days.
The reaction mixture was then extracted with CHCl3 (3 ꢀ 50 mL).
The organic layer was washed with saturated sodium hydrogen
carbonate solution, evaporated, and then dried (Na2SO4). The
organic solvent was removed on a rotary evaporator to yield the
crude product as a pale-yellow oil. The pure product was obtained
by extracting the oil once again with ethyl acetate. Yield, 1.6 g
(60%). 1H NMR (300 MHz, CDCl3), 1H NMR (300 MHz, CDCl3), d,
8.20 ppm (s, 1H), 3.7 (s, 3H), 3.56 (s, 2H), 2.7–2.68 (m, 8H), 2.3
(s, 6H), 2.18 (s, 3H), 1.79 (pentet, 2H). 13C NMR (CDCl3), 164.44,
157.65, 148.56, 126.59, 125.37, 63.01, 60.21, 58.37, 56.97, 54.66,
53.88, 47.07, 27.48, 13.6, 11.3 ppm.
Kinetic experiments of the p-nitrophenol formation were stud-
ied by spectrophotometrically as time-dependent measurement at
25 °C. A solution of the stoichiometric amount of complexes 1–3
(1 ꢀ 10ꢁ4 M)
was
treated
with
p-nitrophenyl-b-D-
glucopyranoside (1 ꢀ 10ꢁ4 M), aqueous H2O2 (10 equivalent) and
pre-treated with one equivalent of Et3N in H2O at 25 °C.
Acknowledgments
We acknowledge Science and Engineering Research Board
(SERB), New Delhi and Board of Research in Nuclear Science
(BRNS), Mumbai for funding.
Appendix A. Supplementary material
Supplementary data to this article can be found online at
References
4.6. Synthesis of copper(II) complexes
Caution! During handling of the perchlorate salts of metal com-
plexes with organic ligands, care should be taken because of the
possibility of explosion.
[Cu(L1)(H2O)ClO4]ClO4 (1): To the solution of ligand (0.205 g,
1 mmol) in MeOH (8 mL) and Cu(ClO4)2ꢂ6H2O (0.37 g, 1 mmol) in
H2O (2 mL) was added dropwise under stirring at room tempera-