D.P. Singh et al. / Journal of Molecular Catalysis A: Chemical 398 (2015) 158–163
159
regioisomers has conventionally been accomplished using 1,3-
2.3. Synthesis of [Cu (bpoh)(PPh ) ]·2CH Cl
2
3
4
2
2
dipolar cycloaddition of alkynes and organic azides under thermal
conditions, mediated by organometallic reagents, as well as under
copper or ruthenium catalysis [15–17]. However, these strate-
gies possess some drawbacks such as use of high temperatures
and regioselectivity issues. Therefore, the development of efficient,
practical, and green synthetic procedures to generate 1,4- and 1,5-
disubstituted 1,2,3-triazole modules remains a great challenge. It
is interesting to note that the use of copper catalysts in ultra-low
levels for an efficient and fast click reaction is an attractive and
emerging advance in this field [18].
The [Cu (bpoh)(PPh ) ]·2CH Cl was synthesized by react-
2
3
4
2
2
ing 50 mL solution of bis-(triphenylphosphine) copper(I) nitrate
(2 mmol, 1.30 g) in dichloromethane with 50 mL methanolic solu-
tion of ligand H bpoh (1 mmol, 0.45 g) in 2:1 (M:L) molar ratio.
2
The reaction mixture was stirred on a magnetic stirrer for 24 h
at room temperature. The product was slowly crystallized on
keeping the above solution in open atmosphere at room tem-
◦
perature. Yield (70%). Orange crystals, M.p. 195 C. Anal. Calc. for
C100H82Cl Cu N O P (1792.56): Cu, 7.09; C, 67.00; H, 4.61; N, 4.69.
4
2
6
2 4
−
1
In view of the above and as a part of our recent investigations on
the catalytic application of transition metals and their complexes
Found: Cu, 7.15; C, 67.21; H, 4.60; N, 4.73%. IR ( cm , KBr): (C N)
− −
O ) 1542 m; (C O ) 1276; (N N) 1024 w.
1572 m; (N
.4. General procedure for synthesis of 1,2,3-triazoles
C
[
19,20], we report herein the synthesis, crystal structure, and cat-
alytic activity of a Cu(I) complex for a click reaction between benzyl
halides, sodium azide, and alkynes.
2
Benzyl halide (10 mmol), sodium azide (10 mmol), alkyne
10 mmol), Cu(I) complex (0.1 mol%) and CH CN (2 mL) were added
(
3
in a 10 mL borosilicate vial. The reaction mixture was stirred at
room temperature for 3 h. After completion of the reaction, water
was added and the precipitate was filtered off. The product was
washed thoroughly with water and dried under open air. The
crude products thus obtained were purified through recrystalliza-
tion from ethanol, and characterized based upon their physical and
spectral properties.
2
. Experimental
2.1. Materials and methods
All chemicals were purchased from Sigma–Aldrich Chemicals,
USA and Merck Chemicals, India, and used without further purifi-
cation. Solvents were purified by standard methods. Analytical thin
layer chromatography (TLC) was performed on Merck Kieselgel
2.5. Physico-chemical measurements
6
0 GF254 plates (thickness 0.25 mm). Visualization was performed
with a 254 nm UV lamp and by staining in I2 chamber. All the
reactions were carried out under an open atmosphere using oven-
dried glassware. The precursor bis-(triphenylphosphine) copper(I)
nitrate was prepared by the reported procedure [21].
−3
The molar conductance of 10 M solution of the Cu(I) complex
in DMSO was measured at room temperature on a Eutech Con 510
conductivity meter. 1H and 13C NMR spectra of the compounds
were recorded in DMSO-d6 on a JEOL AL-300 FT-NMR multinu-
clear spectrometer. Infrared spectra were recorded in KBr on a
−
1
Varian 3100 FT-IR spectrophotometer in 4000–400 cm
region.
Single crystal X-ray diffraction data of the Cu(I) complex was
obtained at 295(2) K, on a Oxford Diffraction Gemini diffractome-
ter equipped with CrysAlis Pro. Using a graphite mono-chromated
Mo K␣ (ꢀ = 0.71073 Å) radiation source. The structure was solved
by direct methods (SHELXL-97) and refined against all data by full
matrix least-square on F2 using anisotropic displacement parame-
ters for all non-hydrogen atoms. All hydrogen atoms were included
in the refinement at geometrically ideal position and refined with
a riding model [22,23]. The MERCURY package and ORTEP-3 for
Windows program were used for generating structures [24,25].
2
.2. Synthesis of ligand
ꢀ ꢀ ꢀ ꢀ
(N 1E,N 2E)-N 1,N 2-bis(phenyl(pyridin-2-yl)
The
ligand,
methylene) oxalohydrazide (H bpoh) was synthesized by the
2
reported method [20], by reacting 50 mL aqueous solution of oxalic
acid dihydrazide (5 mmol, 0.59 g) with 50 mL methanolic solution
of 2-benzoylpyridine (10 mmol, 1.83 g) in 1:2 molar ratio in a
round bottom flask and reflux for 20 h. A white solid product was
obtained on cooling at room temperature. Single crystal of the
ligand H bpoh was obtained from a mixture of dichloromethane
2
and DMSO solution by slow evaporation at room temperature.
3. Results and discussion
◦
Yield (80%); M.p. 292 C. Anal. Calc. for C26H20N O (448.48):
6
2
C, 69.63; H, 4.49; N, 18.74. Found: C, 69.55; H, 4.47; N, 18.71%.
It appears from the analytical data that the reaction between bis-
−
1
IR ( cm , KBr): (NH) 3387b; (C O) 1690 s; (C N) 1582 m;
(
triphenylphosphine) copper(I) nitrate and ligand H bpoh occurs in
2
1
1
7
(N N) 994w. H NMR (DMSO-d , 300 MHz): ı = 14.08 (br s, NH, Z),
6
2:1 (M:L) molar ratio. Both >C O groups of the ligand enolize and
deprotonate during complexation and bonding occurs through two
carbonylate-O atoms. The reaction is given in Scheme 1.
13
0.28 (br s, NH, E); 8.89–7.39 (m, Ar–H) ppm. C NMR (DMSO-d6,
5 MHz): ı = 160.79 (C O); 157.48 (C N); 150.70–124.37 ppm.
Scheme 1. Synthesis of [Cu2(bpoh)(PPh3)4]·2CH2Cl2.