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2.3. General method for synthesis of Cu(I) complexes (1–4)
2.4. X-ray crystallography
The general method for the synthesis of complexes 1–4 has
been shown in Scheme 2. The oxadiazole compound (A–D) was dis-
solved in methanol and added 1 ml of methanolic NaOH solution
and stirred at room temperature for 30 min. Half molar quantity
of precursor complex [CuCl2(PPh3)2] dissolved in methanol was
added to the above mixture and refluxed with stirring for 3–4 h.
Then the reaction mixture was filtered and kept at room tempera-
ture for 48 h to obtain the reddish crystals of Cu(I) hydrazone
complexes.
Crystal of complex 2 was mounted on glass fibers and used for
data collection. Crystal data were collected at 295(2) K using a
Gemini
A Ultra Oxford Diffraction automatic diffractometer.
Graphite monochromated Mo-Ka radiation (k = 0.71073 Å) was
used throughout. The absorption corrections were performed by
the multi-scan method. Corrections were made for Lorentz and
polarization effects. The structures were solved by direct methods
using the program SHELXS [36]. Refinement and all further calcu-
lations were carried out using SHELXL-97 [36]. The H atoms were
included in calculated positions and treated as riding atoms using
the SHELXL default parameters. The non-hydrogen atoms were
refined anisotropically, using weighted full-matrix least squares
on F2. Atomic scattering factors were incorporated in the computer
programs.
2.3.1. Bis(salicylidene)hydrazone binuclear copper(I) complex (1)
Reddish brown; Yield: 68%. M.p.: 236 °C. UV–Vis (CH2Cl2, kmax
,
nm): 242, 284, 362, 435. FT-IR (KBr disks, cmÀ1): 1605 (C@N),
1479 (CAO), 1508 (C@C). 1H NMR (CDCl3, d): 9.83 (s, 2H, CH@N),
6.94–7.19 (m, 8H, Ar), 7.38–8.35 ppm (m, PPh3-H, 60H). 13C NMR
(DMSO-d6, d): 159.93 (C@N), 155.33 (CAO), 138.86 (Ar-C), 134.80
(Ar-C), 133.13 (Ar-C), 129.97 (Ar-C), 128.74 (Ar-C), 128.47 (Ar-C),
125.34 (Ar-C), 125.07 (Ar-C), 122.05 (Ar-C), 119.07 ppm (Ar-C).
31P NMR (CDCl3, d): À1.979 ppm (s, PPh3). Anal. [Found (Calc.)]
for C86H70N2O2P4Cu2: C, 73.14 (73.02); H, 4.87 (4.99); N, 2.11
(1.98)%.
2.5. N-alkylation
2.5.1. General procedure for the N-alkylation of amines with alcohols
0.5 mol% copper(I) catalyst was stirred with 4 mmol KOH in tol-
uene. To this mixture, 2 mmol of alcohol and 2 mmol of amine
were added at room temperature and the temperature was raised
up to 120 °C. The reaction was monitored using TLC. As soon as the
reaction was completed, the mixture was cooled to room temper-
ature and added 3 ml of distilled water. The combined mixture was
extracted with chloroform and dried by adding magnesium sul-
phate. The crude product was purified by column chromatography
(n-hexane/EtOAc) and characterized by 1H NMR spectral analyses
(S2). The 1H NMR data obtained for the catalytic products were
compared with the previous literature and found in good agree-
ment with each other [37]. The reported isolated yields are an
average of two runs.
2.3.2. Bis(5-chlorosalicylidene)hydrazone binuclear copper(I) complex
(2)
Intense Red; Yield: 82%. M.p.: 246 °C. UV–Vis (CH2Cl2, kmax
,
nm): 246, 324, 365, 436. FT-IR (KBr disks, cmÀ1): 1613 (C@N),
1427 (CAO), 1490 (C@C). 1H NMR (CDCl3, d): 9.17 (s, 2H, CH@N),
6.74–7.47 (m, 6H, Ar), 7.55–8.10 ppm (m, PPh3-H, 60H). 31P NMR
(CDCl3, d): À0.726 ppm (s, PPh3). Anal. [Found (Calc.)] for C86H68Cl2-
N2O2P4Cu2: C, 69.86 (69.63); H, 4.76 (4.62); N, 1.82 (1.89)%.
2.3.3. Bis(3-methoxysalicylidene)hydrazone binuclear copper(I)
complex (3)
2.5.2. Direct N-alkylation of 2-nitropyridine with alcohol
Red; Yield: 84%. M.p.: 256 °C. UV–Vis (CH2Cl2, kmax, nm): 235,
270, 368, 421. FT-IR (KBr disks, cmÀ1): 1610 (C@N), 1454 (CAO),
1514 (C@C). 1H NMR (CDCl3, d): 9.00 (s, 2H, CH@N), 6.92–7.04
(m, 6H, Ar), 7.38–7.71 (m, PPh3-H, 60H), 3.42 ppm (s, 6H, OCH3).
13C NMR (DMSO-d6, d): 163.17 (C@N), 153.79 (CAO), 138.15 (Ar-
C), 137.17 (Ar-C), 136.46 (Ar-C), 129.63 (Ar-C), 129.23 (Ar-C),
124.49 (Ar-C), 122.96 (Ar-C), 117.85 (Ar-C), 117.30 (Ar-C),
39.76 ppm (OCH3). Anal. [Found (Calc.)] for C88H74N2O4P4Cu2: C,
71.81 (71.68); H, 4.94 (5.06); N, 1.73 (1.90)%.
To a stirred suspension of copper(I) catalyst (0.5 mol%) and KOH
(4 mmol) in toluene (5 ml), benzyl alcohol (12.0 mmol) and 2-
nitropyridine (2.0 mmol) were added at room temperature. The
temperature was then raised to 100 °C. After the completion of
the reaction (as monitored by TLC), the reaction mixture was
cooled at ambient temperature. 3 ml of distilled water was added
to the above mixture and the organic layer was extracted with CH2-
Cl2 (3 Â 10 ml). The combined organic layers were dried with mag-
nesium sulphate and concentrated. The crude product was purified
by column chromatography (n-hexane/EtOAc) and characterized
by 1H NMR spectral analyses. The reported isolated yields are an
average of two runs.
2.3.4. Bis(2-hydroxynaphthaldimene)hydrazone binuclear copper(I)
complex (4)
Brown; yield: 68%. M.p.: 262 °C. UV–Vis (CH2Cl2, kmax, nm): 244,
328, 368, 430. FT-IR (KBr disks, cmÀ1): 1620 (C@N), 1447 (CAO),
1486 (C@C). 1H NMR (CDCl3, d): 9.42 (s, 2H, CH@N), 6.78–7.14
(m, 12H, Ar), 7.31–7.65 ppm (m, PPh3-H, 60H). 13C NMR (DMSO-
d6, d): 160.68 (C@N), 158.76 (CAO), 133.23 (Ar-C), 133.04 (Ar-C),
132.85 (Ar-C), 132. 76 (Ar-C), 131.90 (Ar-C), 131.42 (Ar-C),
129.97 (Ar-C), 128.80 (Ar-C), 128.70 (Ar-C), 128.63 (Ar-C), 128.16
(Ar-C), 128.06 (Ar-C), 127.96 ppm (Ar-C). Anal. [Found (Calc.)] for
3. Result and discussion
3.1. Syntheses of new complexes
The oxadiazole compounds A–D were synthesized from a series
of reactions starting from the reaction between isoniazid and 2-
hydroxybenzaldehydes as per the literature methods. The obtained
C94H74N2O2P4Cu2: C, 74.73 (74.54); H, 4.76 (4.92); N, 1.76 (1.85)%.
N
O
Ph3P
Ph3P
O
N
HO
N
OH
N
N
N
Cu
N
NaOH/Methanol
[CuCl2(PPh3)2]
2
O
N
N
PPh3
PPh3
N
Cu
N
u
O
O
O
C
Cu
Scheme 2. Plausible mechanism for synthesis of new copper(I) complex from oxadiazole compound.