84
P.Kr. Dutta et al. / Inorganica Chimica Acta 411 (2014) 83–89
1432 cmꢀ1
(mC
@
N stretching); ESI–MS: C14H12N2Se + H+ (289.0599).
PtSe2 + H+ (772.0858). 1H NMR (DMSO-d6, 500 MHz): d 14.86 (s,
1H NMR (DMSO-d6, 500 MHz): d 12.84 (s, 1H, NH proton), 7.90 (m,
NH proton, 1H), 8.43–6.51 (m, 8H), 2.09 (s, Me, 3H). 13C NMR
1H), 7.68 (m, 1H), 7.53–7.22 (m, 6H), 2.21 (s, 3H, Me). 13C NMR
(DMSO-d6, 125 MHz): d 146.74 (N–C–NH), 139.14, 134.37,
(DMSO-d6, 125 MHz):
d
151.30 (N–C–NH), 143.16, 134.85,
133.70, 132.79, 132.44, 131.57, 129.70, 125.85, 124.92, 123.49,
115.46, 113.70 (Ar–C), 17.53 (Se–Me). 77Se NMR (CD3CN,
95 MHz): d 326.30 ppm.
134.38, 129.85, 129.14, 128.67, 128.15, 124.80, 122.83, 121.59,
119.00, 111.36 (Ar–C), 6.71 (Se–Me). 77Se NMR (DMSO-d6,
95 MHz): d 337 ppm.
2.1.1.1. 2-(20-(Methylthio)phenyl)benzimidazole (2). Synthesis of 2
was carried out similar to that of 1 staring from 2-(methyl-
thio)benzaldehyde (480 mg, 3.45 mmol) Yield: 53% (400 mg,
1.67 mmol). 1H NMR (DMSO-d6, 500 MHz): d 12.68 (s, NH proton,
1H), 7.75 (m, 1H), 7.60 (br s, 2H), 7.48 (m, 2H), 7.31(m, 1H), 7.22
(m, 2H), 2.43 (s, Me, 3H).
2.2. X-ray crystallography
Single crystals of the compounds suitable for X-ray diffraction
were grown from acetonitrile solution by diffusing diethyl ether
vapors in a closed beaker. The crystals were carefully chosen using
a stereomicroscope supported by a rotatable polarizing stage. The
data was collected at RT on Bruker’s KAPPA APEX II CCD Duo with
2.1.1.2. 2-(20-(Methoxy)phenyl)benzimidazole (3). Synthesis of 3 was
carried out similar to that of 1 starting from 2-methoxybenzalde-
hyde (523 mg, 3.84 mmol). Yield: 51% (440 mg, 1.96 mmol). 1H
NMR (CDCl3, 500 MHz): d 10.6 (br s, 1H), 8.49 (m, 1H), 7.54 (br s,
2H), 7.30 (m, 1H), 7.20–7.12 (m, 2H), 7.03 (m, 1H), 6.49 (m, 1H),
3.95 (s, Me, 3H).
graphite monochromated Mo K
a radiation (0.71073 Å). The crys-
tals were glued to a thin glass fibre using FOMBLIN immersion
oil and mounted on the diffractometer. The intensity data were
processed using Bruker’s suite of data processing programs (SAINT),
and absorption corrections were applied using SADABS [10]. The
crystal structure was solved by direct methods using SHELXS-97
and the data was refined by full matrix least-squares refinement
on F2 with anisotropic displacement parameters for non-H atoms,
using SHELXL-97 [11]. Figures are drawn from X-seed version 2.0
[12].
2.1.2. General methodology for the preparation of complexes
A mixture of the ligand 1 (50 mg, 0.17 mmol) and Pd(C6H5CN)2-
Cl2/Pt(cod)Cl2 in 2:1 molar ratio in 10 mL dry methanol was stirred
for 3 h at reflux temperature. The reaction mixture was filtered and
to the filtrate NH4PF6 (28 mg, 0.17 mmol) was added and the prod-
uct was precipitated, filtered off and dried under vaccum.
3. Results and discussion
2.1.2.1. Palladium complex 4. Yield: 56% (93 mg, 0.096 mmol). Mp:
248 °C, dec. Anal. Calc. for C28H24F12N4P2PdSe2: C, 34.64; H, 2.49;
N, 5.77. Found: C, 34.39; H, 2.13; N, 5.61%. ESI–MS: C28H24N4-
PdSe2 + H+ (683.0055). 1H NMR (CD3CN, 500 MHz): d 12.16 (s, NH
proton, 1H), 8.32–6.69 (m, 8H), 2.18 (s, Me, 3H). 13C NMR (CD3CN,
125 MHz): d 149.01 (N–C–NH), 140.55, 135.75, 135.05, 133.82,
132.68, 131.87, 126.95, 126.01, 125.87, 123.59, 115.50, 113.93
(Ar–C), 18.60 (Se–Me). 77Se NMR (CD3CN, 95 MHz): d 263.05 ppm.
3.1. Ligand Synthesis and characterization
Several reagents [13] have been used as catalyst to prepare the
benzimidazole derivatives by the reaction of aldehyde and 1,
2-diaminobenzene. In the synthesis of 1, acetic acid was used as
catalyst [14] for the formation of 2-(20-(methylseleno)phenyl)
benzimidazole. 2-(Methylseleno)benzaldehyde was refluxed azeo-
tropically in toluene with 1,2-diaminebenzene and two drops of
acetic acid, using a Dean–Stark trap. 2-(20-(Methylseleno)phenyl)
benzimidazole was precipitated out from reaction mixture as white
compound. Thus the acetic acid catalyzed reaction afforded the
pure product simply by filtration. Similarly the oxygen and sulfur
2.1.2.2. Platinum complex 5. Yield 58% (105 mg, 0.10 mmol). Mp:
273 °C, dec. Anal. Calc. for C28H24F12N4P2PtSe2: C, 31.74; H, 2.28;
N, 5.29. Found: C, 31.53; H, 2.07; N, 4.98%. ESI–MS: C28H24N4
HN
N
NH2
Toluene, AcOHcat
24 h, reflux
O
+
E
NH2
E
Me
Me
1 E = Se (50 %)
2 E = S (53 %)
3 E = O (51 %)
Scheme 1. Synthesis of compound 1–3.
2+
2+
i. Pt(cod)Cl2
i. Pd(PhCN)2Cl2
dry methanol
reflux, 3 h
N
dry methanol
reflux, 3 h
NH
HN
NH
HN
N
H
N
N
N
N
ii. NH4PF6
58%
Pd
Pt
ii. NH4PF6
56%
Se
Se
Se
Se
Se
2(PF6)
2(PF6)
2
3
1
Scheme 2. Complexation of ligand 1 with Pd(II) and Pt(II).