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Transition Met Chem (2013) 38:31–36
Scheme 1 Synthesis of
ZrL2Cl2
CHO
N
H2O
reflux/1 hr
H2N
+
OH
OH
N
Cl
O
ZrCl4
N
Zr
O
Cl
2
dry CH2Cl2
OH
N
Scheme 2 Synthesis of
R2
N
R2
Cl
O
Zr
O
Cl
quinoxaline derivatives in the
presence of ZrL2Cl2 (1 mol %)
in ethanol at room temperature
N
R1
N
N
O
R1
NH2
NH2
1 mol%
+
Ethanol/ rt
O
R2
R2
which was precipitated after cooling the reaction mixture,
was filtered off and washed with cold water. The Schiff
base was purified by recrystallization from n-hexane.
reaction mixture was stirred at room temperature for an
appropriate time, as monitored by TLC (Table 1). When
the reaction was complete, the precipitate was filtered off
and washed with ethanol. The remaining product in the
filtrate was isolated from excess 1,2-diamine by plate
chromatography, eluted with n-hexane/EtOAc (10/2).
HL1; M.P: 73–75 °C; IR (KBr,): (C=N) 1,638 cm-1
;
1H NMR (250 MHz, CDCl3) dppm = 1.33 (d, 3H, J =
6.25 Hz), 2.69 (s, 1H, OH), 3.43–3.51(m, 1H), 3.66–3.72 (m,
1H), 4.04–4.11 (m, 1H), 7.40–7.74 (m, 5H, Ar), 8.3 (s, 1H,
CH=N);13CNMR(CDCl3, 63 MHz)d(ppm) = 20.6, 67.47,
68.59, 128.18, 128.62, 130.88, 135.85, 162.77; Anal. Calcd
for (C10H13NO): C, 73.6; H, 8; N, 8.6. Found: C, 73.6; H, 8.1;
N, 8.6; MS (m/e) = 163 [M]?.
1
Structural assignment of each product was based on its H
NMR, 13C NMR and MS spectra.
Results and discussion
Preparation of the complex
Characterization of the complex
Zirconium(IV) chloride (0.233 g, 1 mmol) was added to a
solution of HL (0.326 g, 2 mmol) in dry CH2Cl2 (10 ml).
The reaction mixture was stirred under N2 for 2 h at room
temperature. The precipitated product was filtered off,
washed with cold dry CH2Cl2 and then dry n-hexane. The
complex was dried under reduced pressure as a deep yel-
low powder and obtained in 80 % yield. M.P: 143 °C; IR
The Schiff base ligand HL (Scheme 1) was prepared by the
condensation of 1-amino-2-propanol with benzaldehyde in
water. Reaction of HL with ZrCl4 in CH2Cl2 gave the
expected complex, ZrL2Cl2, as a yellow powder.
Analytical and spectroscopic data for the complex are
given in the experimental section. The spectroscopic data
and elemental analyses are consistent with a monomeric
complex with a ligand:Zr ratio of 2:1. When the synthesis
was repeated using three equivalents of HL, the same
product was obtained as with two equivalents. The char-
acteristic imine band of the Schiff base (1,638 cm-1) is
shifted to higher wave number after coordination of the
azomethine nitrogen to the Zr center, appearing at
1,665 cm-1 for the complex. A sharp singlet at 8.3 ppm in
(KBr,): (C=N) 1,665 cm-1 1H NMR (400 MHz, d6-
;
DMSO) dppm = 1.17 (d, 6H, J = 6.4 Hz), 3.58–3.88 (m,
4H, CH2), 4.26 (m, 2H), 7.49–7.62 (m, 10H, Ar), 9.05(s,
2H, CH=N). 13C NMR(100.64 MHz, d6-DMSO): 21.31,
63.46, 64.16, 128.21, 129.03, 130.06, 137.07, 171.72;
Anal. Calcd for (C20H24N2O2ZrCl2): C, 49.4; H, 5; N, 5.8.
Found: C, 49.4; H, 5; N, 5.7. MS (m/e) = 484 [M?].
1
General procedure for synthesis of quinoxalines
the H NMR spectrum of the free Schiff base, assigned to
the azomethine proton is shifted downfield after complex-
ation, appearing at 9.05 ppm due to coordination of the
azomethine nitrogen. The absence of a broad singlet at
*2.75 ppm in the spectrum of the zirconium complex
The appropriate 1,2-diamine (1.2 mmol) was added to a
solution of the 1,2-dicarbonyl compound (1 mmol) and the
complex (0.0048 g, 0.01 mmol) in ethanol (1 ml). The
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