Fe (III) complexes of a bis-benzimidazolyl diamide ligand: Spectral and Catalytic studies

Article abstract of DOI:10.1016/j.saa.2011.08.014

A new tetradentate bis benzimidaozlyl diamide ligand N,N′-Bis (benzimidazol-2-yl-methyl)-hexane-1,6-dicarboxamide (GBSA) has been synthesized and utilized to prepare new Fe(III) complexes with exogenous anionic ligand X = Cl^- and NO₃^-. Isomer shift values are in the range found for Iron in the +3 oxidation state while Quadrupole Splitting indicates large distortion from a six coordinate geometry, a finding supported by low temperature EPR work. The E_1/2 values are found to be quite cathodic indicating stability of the Iron (III) complexes. The oxidation of alcohols was investigated using [Fe(GBSA)Cl₃] as the catalyst with TBHP as an alternate source of oxygen. The respective carbonyl products have been isolated and characterized by ¹H NMR, electronic spectroscopy, mass and IR spectral studies.

Full text of DOI:10.1016/j.saa.2011.08.014

Spectrochimica Acta Part A 83 (2011) 180–186
Contents lists available at ScienceDirect
Spectrochimica Acta Part A: Molecular and
Biomolecular Spectroscopy
journal homepage: www.elsevier.com/locate/saa
Fe (III) complexes of a bis-benzimidazolyl diamide ligand:
Spectral and Catalytic studies
Gauri Ahuja, Pavan Mathur∗
Department of Chemistry, University of Delhi, Delhi 110007, India
a r t i c l e i n f o
a b s t r a c t
A new tetradentate bis benzimidaozlyl diamide ligand N,Nꢀ-Bis (benzimidazol-2-yl-methyl)-hexane-
1,6-dicarboxamide (GBSA) has been synthesized and utilized to prepare new Fe(III) complexes with
exogenous anionic ligand X = Cl− and NO3−. Isomer shift values are in the range found for Iron in the +3
oxidation state while Quadrupole Splitting indicates large distortion from a six coordinate geometry, a
finding supported by low temperature EPR work. The E1/2 values are found to be quite cathodic indicating
stability of the Iron (III) complexes. The oxidation of alcohols was investigated using [Fe(GBSA)Cl3] as the
catalyst with TBHP as an alternate source of oxygen. The respective carbonyl products have been isolated
and characterized by 1H NMR, electronic spectroscopy, mass and IR spectral studies.
Article history:
Received 23 May 2011
Received in revised form 26 July 2011
Accepted 10 August 2011
Keywords:
Benzimidazole diamide
Iron complexes
Mössbauer
© 2011 Elsevier B.V. All rights reserved.
Alcohols
Catalysis
1. Introduction
2. Experimental
The formation of ketones or aldehydes from the catalytic oxida-
tion of primary and secondary alcohols is an important reaction
in organic synthesis [1,2]. Transition metal ion catalyzed oxida-
tion of alcohols is of current interest, and various transition metal
compounds and oxidant systems have been reported [3]. Copper
(I), copper (II) salts [4,6] and Co (III) complexes [5] have been
utilized to catalyze the oxidation of alcohols with molecular oxy-
gen and H2O2. Oxidation of alcohols using H2O2 and catalytic
amounts of Fe (III) complexes has also been described [7–9]. In the
present work we report the oxidation of cinnamyl alcohol, 1-phenyl
ethanol, cyclohexanol, and 1,2,3,4-tetrahydro-1-naphthol to their
respective carbonyl products utilizing tertiary butyl hydroperox-
ide (TBHP) as an alternative source of oxygen. The oxidation of
alcohols was investigated using [Fe(GBSA)Cl3] as the catalyst. The
respective carbonyl products have been isolated and characterized
by 1HNMR, electronic spectroscopy, mass and IR spectral stud-
ies.
2.1. Materials and physical measurements
Glycine benzimidazole dihydrochloride was prepared follow-
ing the procedure reported by Cescon and Day [10]. Spectroscopic
grade solvents were used for the spectral and electrochemical stud-
ies and the rest were freshly distilled off before use. All other
chemicals were obtained from commercial sources and were used
as such. Anhydrous Iron (III) chloride and Iron (III) nitrate were
purchased from Sigma–Aldrich. Carbon, Hydrogen and Nitrogen
were estimated by using Elemental Analyzer at USIC, University of
Delhi, Delhi. IR spectra were recorded in solid state as KBr pellets
on a Perkin-Elmer FTIR-2000 spectrometer (IR stretching frequen-
cies measured to an accuracy of 1 cm−1). The electronic spectra
were recorded in HPLC grade DMF on a Shimadzu 1601 spectropho-
tometer in the region of 200–1100 nm (Errors in UV–vis wavelength
maxima are 1 and 4 nm). The 1H NMR and 13CNMR spectra of
ligand were recorded in d6-DMSO on a 400 MHz JEOL instrument at
the Department of Chemistry, University of Delhi, Delhi. ESI mass
spectra were recorded on a Waters Micromass -LCT mass spec-
trometer in chloroform. Cyclic voltammogram of the complexes
was studied on BAS CV 50 W electrochemical analyzing system
in dimethyl sulfoxide:Acetonitrile (8:3) solution at Department of
chemistry, University of Delhi, Delhi. 57Fe Mossbauer spectra were
obtained using a 57Co in Rh source, mounted on a constant acceler-
ation spectrometer, Wissel MB-550, GNDU, Amritsar. The X-band
EPR spectra were recorded on a Bruker-spectrospin with a variable
∗
Corresponding author. Tel.: +91 27667725; fax: +91 27666605.
E-mail addresses: gauriahuja84@gmail.com (G. Ahuja), pavanmat@yahoo.co.in
(P. Mathur).
1386-1425/$ – see front matter © 2011 Elsevier B.V. All rights reserved.
doi:10.1016/j.saa.2011.08.014

G. Ahuja, P. Mathur / Spectrochimica Acta Part A 83 (2011) 180–186
181
Table 1
temperature liquid nitrogen cryostat at 120 K at IIT Kanpur, India
IR spectral data of ligand for Fe (III) complexes of the ligand GBSA.
(error in g-values is 0.01). Magnetic susceptibilities of the com-
plexes were recorded on vibrating Sample Magnetometer at 298 K
in solid state at the Department of Chemistry, University of Delhi,
Delhi (error bar: 0.1 BM).
Assignments
GBSA
[Fe(GBSA)Cl3]
[Fe(GBSA)(NO3)3]
ꢁOH stretching
ꢁNH amide
ꢁNH benzimida.
ꢁCH stretching
3440
3317
3058
2923
1645
1546
1457
–
3420
3326
3037
2918
1684
1524
1460
–
3405
3341
3037
2926
1669
1524
1463
1384(s), 820(a)
747
2.2. Synthesis
ꢁC amide I
O
ꢁC
amide II
N
2.2.1. Preparation of the ligand N,Nꢀ-Bis
ꢁ
C
C N C
ꢁanions
ꢁbenzene ring
(benzimidazol-2-yl-methyl)-hexane-1,6-dicarboxamide (GBSA)
The condensation was similar to that reported earlier by Bak-
shi and Mathur [11] and Vagg and co-workers [12]. Suberic acid
(1.97 g, 0.1136 mmol) and 2-(amino methyl) benzimidazole dihy-
drochloride (5 g, 0.0227 mmol) were taken in pyridine (20 ml). The
mixture was stirred gently for 10 min, during which a white pre-
cipitate appeared. The reaction mixture was then heated slowly on
a water bath at a temperature of 40 ◦C. A solution of triphenyl phos-
phite (TPP) (7.07 ml, 22.8 mmol) was added drop wise over a period
of 15 min. The mixture was stirred simultaneously. After addition of
P(OPh3)3 was complete and the initially formed precipitate had dis-
solved, the temperature of the reaction was slowly raised to 70 ◦C.
The clear solution thus obtained was stirred for about 9–10 h at
a temperature of 70–75 ◦C on a water-bath. The resulting brown
colored solution was then washed with sodium bicarbonate till all
effervescence ceased and then washed twice with distilled water. A
yellowish white solid appeared which was washed first with water
and then acetone (Scheme 1). This was then recrystallized with
methanol and precipitated by water. The product was filtered off,
and dried and analyzed for the composition C24H28N6O2·0.5H2O,
Yield: 3 g (50.1%), m.p. 233 ◦C.
735
744
3. Results and discussion
3.1. Electronic spectroscopy
The UV Spectral data for the ligand and the complexes were
taken in DMF and methanol depending on their solubility. The lig-
and and complexes show bands in the region 271–277 nm. These
bands are characteristics of the benzimidazole group and arise from
*
␲ to ␲ transitions. They show enhanced absorption as indicated
by their extinction coefficients. The UV bands are in general shifted
upon coordination suggesting binding of Iron (III) to the ligand
donor atom [13]. Both the complexes exhibit a broad shoulder at
349 nm. The band at 349 nm in the above complexes are predom-
inantly assigned to charge transfer transition from p␲ orbital of
*
chloride or oxygen of nitrate to half filled d␲ orbital of the FeIII
metal centre, i.e. Cl− → FeIII/NO3− → FeIII. [14]. Such a charge trans-
fer has been observed for other benzimidazole Fe (III) complexes.
The spectroscopic analysis of the ligand is as shown below:
3.2. IR spectra
Analytical data: Found (cal): C: 65.0 (65.3), H: 7.3(6.5), N:
17.8(19.0).
IR stretching bands for ligand and the complexes showing
coordination of anions are listed in Table 1. The ligand L and
its Iron (III) complexes have characteristic IR bands in the range
1645–1669 cm−1, 1524–1546 cm−1, 1457–1463 cm−1 which are
assigned to amide I (ꢁC O stretching), amide II (ꢁC N stretching) and
UV–vis [ꢀmax (nm), log ε in DMF] = 277[4.54], 271 [4.59].
2.2.2. Preparation of the complexes
2.2.2.1. [Fe(GBSA)Cl3] (1). FeCl3 (1 mmol) was dissolved in
methanol (5 ml) and added to a methanolic solution of the ligand
GBSA (1 mmol) (15 ml). The resulting brown colored solution was
stirred for 4–5 h, after which the volume was reduced to about 60%
on a water bath. The concentrated solution was kept for cooling
in a refrigerator for 1–2 h. The product obtained was washed with
small amount of acetonitrile (4–5 ml) and air dried. The product
analyzed for the composition [Fe (C24H28N6O2)Cl3]·2.5H2O
benzimidazole ring (ꢁC
C stretching) respectively. The benzene
C
N
ring gives a peak in the range 735–747 cm−1. In the complexes, shift
in amide I band, due to C O group and increase/decrease in amide
II band due to C N group [15] is indicative of the coordination of
the ligand through carbonyl oxygen in the complexes [16–18]. IR
bands due to benzimidazole NH and amide NH are shifted indicat-
ing the involvement of these groups in hydrogen bonding either
with the solvent molecules or with the exogenous anionic ligand in
the complexes. A broad band in the region 3405–3440 cm−1 in the
complexes indicates presence of water molecule or O H stretch-
ing due to H-bonding with the solvent. Characteristic stretching
frequencies for the coordinated anion are also observed: bands at
1384 cm−1 and 820 cm−1 are observed for the symmetric and anti
symmetric stretching vibration of the nitrate group in the nitrate
complexes respectively.
Yield: 80 mg (53%).
Analytical data: Found (cal): C: 44.7(45.0), H: 5.9(5.1), N:
12.6(13.1), Fe: Found (calc): 9.1 (9.2).
UV–vis [ꢀmax (nm), log ε in DMF] = 271[4.3], 277 [4.3], 349 [3.4].
2.2.2.2. [Fe(GBSA)(NO3)3] (2). Fe(NO3)3·9H2O (1 mmol) (5 ml) was
dissolved in methanol (5 ml) and added to a methanolic solution
of the ligand GBSA (1 mmol) (15 ml). The resulting brown col-
ored solution was stirred for 4–5 h, after which the volume was
reduced to about 60% on a water bath. The concentrated solu-
tion was kept for cooling in a refrigerator for 1–2 h. The product
obtained was washed with small amount of cold methanol (4–5 ml)
and dried over P2O5. The product analyzed for the composition
[Fe(C24H28N6O2)(NO3)3]·2.5H2O.
3.3. 1H-NMR and 13CNMR
The 1H NMR of the ligand GBSA in d6-DMSO shows signals for
both aliphatic and aromatic protons (Fig. 1) [19]. A singlet arises
at 12.5 ppm due to benzimidazole NH(f), The amide NH(d) proton
gives rise to a triplet at 8.86–8.84 ppm (coupled with adjacent CH2
proton (e). A symmetrical multiplet in the range of 7.46–7.43 ppm
arises due to benzimidazole ring protons (g and h). The CH2 protons
(e) give rise to a doublet at 4.79–4.77 ppm due to the coupling with
adjacent amide NH proton. The CH2 proton (c) gives a broad peak
at 2.81 ppm. The CH2 proton (b) gives a multiplet at 1.84 ppm while
Yield: 90 mg (75%).
Analytical data: Found (cal): C:39.6(40.0), H:5.0(4.5), N:16.6(17.5),
Fe: Found (calc): 7.0 (6.6).
UV–vis [ꢀmax (nm), log ε in DMF] = 271[4.1], 277 [4.1], 349 [3.0].

182
G. Ahuja, P. Mathur / Spectrochimica Acta Part A 83 (2011) 180–186
H
C
H
O
N
O
H
C
H
N
H2 H2 H2 H2 H2 H2
H2N
HO
C
C
OH
C
C
C
C
C
C
NH2
N
H
N
H
pyridine , TPP
70o C, 9 hrs
-2H2O
e
H
d
H
d
g
e
H
g
g
O
a
H2
C
b
H2
C
c
H2
C
b
a
H
O
c
N
N
h
h
h
H2
H2
H2
C
H
N
C
C
C
C
C
N
C
H
h
N
N
H
g
H
f
f
Scheme 1. N,Nꢀ-Bis (benzimidazol-2-yl-methyl)-hexane-1,6-dicarboxamide (GBSA).
Fig. 2. 13C NMR of the ligand GBSA.
Fig. 1. 1H NMR of the ligand GBSA.
surements. The reversible one electron Fc+/Fc couple has an E1/2
of +75 mV versus Ag/AgNO3. The complexes display a reversible
redox wave assigned to Fe (III)/Fe (II) redox couple. E1/2 values for
[Fe(GBSA)Cl3] and [Fe(GBSA)(NO3)3]) are found to be −324 mV and
the central CH2 protons (a) of the central chain arise as a nultiplet
at 1.54 ppm (coupled with adjacent CH2 protons) (b).
13C spectra: Peak values, ı ppm: C atoms of the benzimidazole
ring (C7, C4): 118; C atoms of the benzimidazole ring (C5, C6): 121;
C atoms of the benzimidazole ring (C8, C9): 134; C atom of the
benzimidazole ring (C2): 152; (C1) atom of the methylene group of
benzimidazole ring: 37; C atom of the C O group: 172; C atom of
the methylene group attached to C O: 35; C atom of the methylene
group of the central chain: 25; C atom of the innermost methylene
group of the central chain: 28 (Fig. 2) [20].
10
5
3.4. Cyclic voltammetry
0
The cyclic voltammetric data of complexes are listed in (Table 2,
Figs. 3 and 4). The cyclic voltammograms were recorded in
8:3 (DMSO:Acetonitrile), containing 0.10 M TBAP as supporting
electrolyte at a platinum working electrode. A three-electrode con-
figuration composed of Pt-disk working electrode, a Pt wire counter
electrode, and an Ag/AgNO3 reference electrode was used for mea-
-5
-10
Table 2
400
200
0
-200
-400
-600
-800
Electrochemical data of Fe(III) complexes of GBSA.
Potential (mV)
Complex
Ec (mV)
Ea (mV)
E1/2 (mV)
[Fe(GBSA)Cl3]
[Fe(GBSA)(NO3)3]
−380.0
−292.0
−268.0
−178.0
−324.0
−235.0
Fig. 3. Cyclic voltammogram of [Fe(GBSA)Cl3] in DMSO:acetonitrile (8:3) at a scan
rate of 200 mV/s.

G. Ahuja, P. Mathur / Spectrochimica Acta Part A 83 (2011) 180–186
183
2000
1500
1000
500
8
6
4
2
0
-500
-1000
-1500
-2000
0
-2
-4
-6
0
500
1000
1500
2000
Field (Gauss)
400
200
0
-200
-400
-600
-800
Fig. 5. X-band EPR spectrum of [Fe(GBSA)Cl3] in DMSO at liquid nitrogen tempera-
ture.
Potential (mV)
Fig. 4. Cyclic voltammogram of [Fe(GBSA)(NO3)3] in DMSO:acetonitrile (8:3) at a
scan rate of 200 mV/s.
with transitions at low field (g ∼ 5.3 and g ∼ 7.2) while in the case
of nitrate bound complex, an additional signal at g = 3.0 was also
observed. Dowsing and Gibson [21] have shown that the absorp-
tions at 1500 G and 700 G are expected if ꢀ is almost equal to 1/3
and D is greater than 0.23 cm−1. The line at 1500 G is known to
broaden or split as ꢀ departs from 1/3. Thus, the departure of the
absorption away from geff = 4.3 is a signal for distortion from purely
rhombic to axial geometry. Since, the present series of Iron (III)
complexes show multiple signals. This is interpreted in terms of six
coordinate Fe (III) complexes undergoing departure from a purely
rhombic symmetry towards axial symmetry [22,23].
Table 3
Magnetic moment values for the Iron (III) complexes of GBSA.
Complexes
Magnetic moment (BM)a
[Fe(GBSA)Cl3]
[Fe(GBSA)(NO3)3]
5.7
5.4
a
Error bar = 0.1 BM.
−235 mV respectively against reference Ag/AgNO3 electrode. Chlo-
ride complex shows cathodic potential in comparison to the nitrate
complex. Therefore the binding of chloride anion stabilizes the Fe
(III) centre whereas nitrate anion destabilizes the Fe (III) centre. The
variation in E1/2 observed supports that the anionic ligands remain
bound to Fe (III) centre in solution, an assumption which has been
confirmed from other spectral studies. The chloride complex has
a cathodic redox potential, this suggest that the Cl− anion is more
effective in reducing−the Lewis acidity of the Iron (III) centre as
compared to the NO3 anion.
3.7. Mössbauer spectroscopy
Mössbauer spectra of Fe (III) complexes were obtained using a
57Co in Rh source, mounted on a constant acceleration spectrome-
ter (Table 5, Figs. 7 and 8). The velocity scale was calibrated using
a foil of natural ␣-Fe at room temperature and all isomer shifts are
referred to centre of ␣-Fe spectrum. Experimental spectra were fit-
ted with Lorentzian lines which are allowed to vary independently
and were matched into a doublet, using a least square computer
program. Isomer shift values (ı) lie in the range of 0.24–0.44 mm/s
with respect to natural iron as is typically observed for other high
3.5. Magnetic susceptibility
Magnetic susceptibility of both the Fe (III) complexes was
determined by using Vibrating Sample Magnetometer at room tem-
perature (298 K) in solid state and is reported in (Table 3). The data
incorporates diamagnetic correction for the ligand in each com-
plex and has been estimated using Pascal constants. It is found
that the values obtained are in the range of 5.4–5.7 BM. These are
slightly lower than the spin only value of 5.9 BM/Fe3+ ion and may
be attributed to a weak-intermolecular magnetic interaction in the
solid state cannot be ruled out.
2500
2000
1500
1000
500
3.6. EPR spectroscopy
(Table 4, Figs. 5 and 6) shows X-EPR spectra of Iron (III) com-
plexes at liquid nitrogen temperature in DMSO. The present series
of Fe (III) complexes bound with chloride ion show signals at g = 4.4,
0
-500
-1000
Table 4
X-Band EPR data for Iron (III) complexes of GBSA.
0
1000
2000
Complexes
Observed EPRa g-values
Field (Gauss)
[Fe(GBSA)Cl3]
[Fe(GBSA)(NO3)3]
4.4, 5.3, 7.2
3.0, 4.4, 7.2
Fig. 6. X-band EPR spectrum of [Fe(GBSA)(NO3)3] in DMSO at liquid nitrogen tem-
a
Effective g-values.
perature.

184
G. Ahuja, P. Mathur / Spectrochimica Acta Part A 83 (2011) 180–186
Table 5
obtained was 0.32. The product obtained was characterized by,
1H NMR, mass spectroscopy and IR spectral studies. The oxida-
tion reaction was also monitored using UV–visible spectroscopy.
As the reaction proceeds, it was found that there were no major
changes in the charge transfer band of the parent Iron (III) com-
plex. This suggests that the oxidation state of Iron (III) does not
change during the course of the reaction. This further supports
the mechanism proceeding via a Hydrogen abstraction mechanism
[9a].
Mössbauer data for Iron (III) complexes of the ligand GBSA.
Complexes
Isomer shift ꢂ (mm/s)
Quadrupole splitting (ꢂEq)
[Fe(GBSA)Cl3]
[Fe(GBSA)(NO3)3]
0.26
0.44
0.35
0.82
1.02
1.00
0.98
0.96
0.94
0.92
0.90
0.88
0.86
0.84
1H NMR (CDCl3) (ppm) [Fig. 9(§)]: Signal for benzene ring pro-
tons (a, b, c and d) arise in the range of 7.39–7.54. Proton labeled
as (e) arises in the range of 6.66–6.72 and (f) proton gives a signal
in the range of 9.66–9.68.
IR (cm−1, Neat): 1678 (ꢁC O) and 749 (ꢁC C benzene).
(m/z): 133 (for the pure product). Yield (DNP derivative): 40%.
Thus oxidation of cinnamyl alcohol gave cinnamaldehyde
a
c
-8
-6
-4
-2
0
2
4
6
8
b
e
Velocity mm/s
a
O
d
f
Fig. 7. Mössbauer spectra of [Fe(GBSA)Cl3].
c
Cinnamaldehyde
spin Iron (III) complexes [24]. The isomer shift in the present iron
complexes is indicative of iron in (+III) oxidation state. Quadrupole
splitting decreases with increase in symmetry of the central ion
atom, i.e. larger is the quadrupole splitting; larger is the distor-
tion in geometry of the central Iron atom. In the present case of
[Fe(GBSA)(NO3)3] has a much larger quadrupole splitting in com-
parison to [Fe(GBSA)Cl3] implying a larger distortion for the former
complex [25–27].
4.1.2. Oxidation of 1-phenyl ethanol
The complex [Fe(GBSA)Cl3] (0.0317 mmol) was taken in 10 ml
of methanol. To this 1-phenyl ethanol (0.476 mmol) was added
along with the oxidant TBHP (0.952 mmol). The ratio of cata-
lyst:substrate:oxidant used was 1:15:30. The reaction mixture was
stirred at 50–60 ◦C on a water bath for approximately 12 h. Peri-
odically, sample was withdrawn and TLC was developed in ethyl
acetate:hexane (15%). A spot was visualized with a spray of DNP
suggesting the formation of the corresponding carbonyl moiety
during the course of the above oxidation reaction. After about 12 h it
was worked up on a column, using hexane and ethyl acetate (1.5%).
The Rf of the product obtained was 0.42. The product obtained
was characterized by, 1H NMR, mass spectroscopy and IR spectral
studies.
4. Reactivity of [Fe(GBSA)Cl3]
4.1. Oxidation of alcohols
4.1.1. Oxidation of cinnamyl alcohol
The complex [Fe(GBSA)Cl3] (0.0317 mmol) was taken in 10 ml
of methanol. To this cinnamyl alcohol (0.476 mmol) was added
along with the oxidant TBHP (0.952 mmol). The ratio of cata-
lyst:substrate:oxidant used was 1:15:30. The reaction mixture
was stirred at 50–60 ◦C on a water bath for approximately 15 h.
Periodically, sample was withdrawn and TLC was developed in
ethyl acetate (15%):hexane. A spot was visualized with a spray
of 2,4-dinitrophenylhydrazine (DNP) suggesting the formation
of the corresponding aldehyde during the course of the above
oxidation reaction. After about 15 h it was worked up on a col-
umn, using hexane and ethyl acetate (5%). The Rf of the product
1H NMR (CDCl3) (ppm) [Fig. 10(§)]: The benzene ring protons
(a, b, c) gave signals in the range of 7.87–7.89 (t, J = 15 Hz, 2H),
7.36–7.41 (t, J = 15 Hz, 2H) and 7.46–7.51 (t, J = 15 Hz, 1H) while the
CH3 protons (d) appear at 2.52 ppm (s, 3H).
IR (cm−1, Neat): 1686 (ꢁC O) and 760 (ꢁC C benzene).
(m/z): 121 (for the pure product). Yield (DNP derivative): 37%.
1.00
0.95
0.90
-10
-5
0
5
10
Velocity (mm/s)
Fig. 8. Mössbauer spectra of [Fe(GBSA)(NO3)3].

G. Ahuja, P. Mathur / Spectrochimica Acta Part A 83 (2011) 180–186
185
Thus oxidation of 1-phenyl ethanol gave acetophenone
O
a
b
O
a
a
c
b
b
b
d
a
b
Acetophenone
Cyclohexanone
4.1.3. Oxidation of 1,2,3,4-tetrahydro-1-naphthol
The complex [Fe(GBSA)Cl3] (0.0317 mmol) was taken in 10 ml
of methanol. To this 1,2,3,4-tetrahydro-1-naphthol (0.476 mmol)
was added along with the oxidant TBHP (0.952 mmol). The ratio
of catalyst:substrate:oxidant used was 1:15:30. The reaction mix-
ture was stirred at 50–60 ◦C on a water bath for approximately
12 h. Periodically, sample was withdrawn and TLC was developed
in ethyl acetate (12%):hexane. A spot was visualized with a spray of
DNP suggesting the formation of the corresponding carbonyl moi-
ety during the course of the above oxidation reaction. After about
12 h it was worked up on a column, using hexane and ethyl acetate
(2%). The Rf of the product obtained was 0.57. The product obtained
was characterized by, 1H NMR, mass spectroscopy and IR spectral
studies.
H2
C
H2
C
H2
C
H2
C
H2C
CH2
O
C
NH
HN
C
X
O
CH2
H2C
Fe
H
N
N
N
N
H
X
1H NMR (CDCl3) (ı ppm) [Fig. 11(§)]: (a) 7.95–7.93(d, 1H,
J = 8 Hz), (b, d) 7.23–7.15 (m, 2H, J = 6 Hz), (c) 7.39–7.36 (t, 1H,
J = 12 Hz), (e) 2.58–2.55 (t, 2H, J = 6 Hz), (f) 2.08–2.02 (m, 2H, J = 6 Hz),
(g) 2.89–2.86 (t, 2H, J = 6 Hz).
X=Cl- or NO3
-
IR (cm−1, Neat) 1618 (ꢁC O) and 760 (ꢁC C benzene).
ꢀmax (nm) (CHCl3): 362,260.
(m/z): 147 (of the pure product). Yield (DNP derivative): 45%.
Proposed structure for Iron (III) complexes with the ligand N, N'–Bis
(benzimidazol-2-yl-methyl)-hexane-1,6-dicarboxamide
Thus oxidation of 1,2,3,4-Tetrahydro-1-Naphthol gave 3,4-
dihydronaphthalen-1(2H)-one.
5. Conclusion
O
a
A new bizbenzimidazole diamide tetradentate ligand has been
synthesized and utilized to prepare Iron (III) complexes. Complexes
have been characterized by cyclic voltammetry and Mossbauer
analysis. Isomer shift values are in the range found for Iron in the
+3 oxidation state while quadrupole splitting indicates large distor-
tion from a six coordinate geometry. The E1/2 values are found to be
quite cathodic indicating stability of the Iron (III) complexes. The
oxidation of alcohols was investigated using [Fe(GBSA)Cl3] as the
catalyst with TBHP as an alternate source of oxygen. The reaction
proceeds via hydrogen abstraction mechanism. The catalyst turn
over is found to be between six to eight fold.
e
f
b
c
g
d
3, 4-dihydronaphthalen-1(2H)-one
4.1.4. Oxidation of cyclohexanol
The complex [Fe(GBSA)Cl3] (0.0317 mmol) was taken in 10 ml of
methanol. To this cyclohexanol (0.476 mmol) was added along with
the oxidant tertiary butyl hydro peroxide (TBHP) (0.952 mmol). The
ratio of catalyst:substrate:oxidant used was 1:15:30. The reaction
mixture was stirred at 50–60 ◦C on a water bath for approximately
12 h. Periodically, sample was withdrawn and TLC was developed
in ethyl acetate (12%):hexane. A spot visualized with a spray of
DNP suggesting the formation of the corresponding carbonyl moi-
ety during the course of the above oxidation reaction. After about
12 h it was worked up on a column, using hexane and ethyl acetate
(1%). The Rf of the product obtained was 0.39. The product obtained
was characterized by, 1H NMR, mass spectroscopy and IR spectral
studies.
Acknowledgements
The authors gratefully acknowledge funding from CSIR Research
project No. 01(2218)/08/EMR-II and also for a special grant from
University of Delhi, Delhi.
Appendix A. Supplementary data
Supplementary data associated with this article can be found, in
the online version, at doi:10.1016/j.saa.2011.08.014.
1H NMR (CDCl3) (ı ppm) [Fig. 12 (§)]: (a) 2.13–2.10 (4H, m,
References
J = 11 Hz), (b) 1.66–1.50 (m, 6H, J = 12 Hz).
[1] T. Naota, H. Takaya, S.I. Murahashi, Chem. Rev. 98 (1998) 2599–2660.
[2] R.A. Sheldon, I.W.C.E. Arends, A. Dijksman, Catal. Today 57 (2000) 157–166.
[3] R.A. Sheldon, J.K. Kochi, Metal-catalyzed Oxidations of Organic Compounds,
Academic Press, New York, 1981.
IR (cm−1, Neat) 1648 (ꢁC O). (m/z) = 99 (pure product).
Oxidation of cyclohexanol gave cyclohexanone.

186
G. Ahuja, P. Mathur / Spectrochimica Acta Part A 83 (2011) 180–186
[4] I.E. Marko, A. Gautier, I.C. Regnaut, P.R. Giles, M. Tsukazaki, C.J. Urch, S.M. Brown,
J. Org. Chem. 63 (1998) 7576–7577.
(c) K. Visvaganesan, R. Mayilmurugan, E. Suresh, M. Palaniandavar, Inorg. Chem.
46 (2007) 10294–10306.
[5] I. Fernandez, J.R. Pedro, A.L. Rosello, R. Ruiz, I. Castro, X. Ottenwaelder, Y. Jour-
naux, Eur. J. Org. Chem. (2001) 1235–1247.
[15] K. Nakamoto, Infrared and Raman Spectra of Inorganic and Coordination Com-
pounds, fifth ed., Wiley, New York, 1997.
[6] S. Velusamy, T. Punniyamurthy, Eur. J. Org. Chem. (2003) 3913–3915.
[7] (a) S.E. Martin, A. Garrone, Tetrahedron Lett. 44 (2003) 537–549;
(b) A.G.J. Ligtenbarg, P. Oosting, G. Roelfes, R.M.L. Crios, M. Lutz, A.L. Spek, R.
Hage, B.L. Feringa, Chem. Commun. (2001) 385–386.
[16] M. Gupta, P. Mathur, R. Butcher, Inorg. Chem. 40 (2001) 878–885.
[17] S. Tehlan, M.S. Hundal, P. Mathur, Inorg. Chem. 43 (2004) 6589–6595.
[18] S.C. Mohapatra, S. Tehlan, M.S. Hundal, P. Mathur, Inorg. Chim. Acta 361 (2008)
1897–1907.
[8] U.R. Pillai, E.S. Demessie, Appl. Catal. A: Gen. 245 (2003) 103–109.
[9] (a) E.B. Hergovich, G. Speier, J. Mol. Catal. A: Chem. 230 (2005) 79–83;
(b) E.B. Hergovich, G. Speier, M. Reglier, M. Giorgi, E. Kuzmann, A. Vertes, Inorg.
Chim. Acta 357 (2004) 3689–3696;
(c) E.B. Hergovich, G. Speier, M. Reglier, M. Giorgi, E. Kuzmann, A. Vertes, Eur.
J. Inorg. Chem. (2003) 1735–1740.
[10] L.A. Cescon, A.R. Day, J. Org. Chem. 27 (1962) 581–586.
[11] R. Bakshi, P. Mathur, Inorg. Chim. Acta 363 (2010) 3477–3488.
[12] D.J. Barnes, R.L. Chapman, R.S. Vagg, E.C. Watton, J. Chem. Eng. Data 23 (1978)
349–350.
[19] F. Afreen, P. Mathur, A. Rheingold, Inorg. Chim. Acta 358 (2005) 1125–1134.
[20] R.M. Silverstein, G.C. Bassler, T.C. Morrill, Spectrometric Identification of
Organic Compounds, Wiley, 1991.
[21] R.D. Dowsing, J.F. Gibson, J. Chem. Phys. 50 (1969) 294–303.
[22] G. Batra, P. Mathur, Polyhedron 12 (21) (1993) 2635–2643.
[23] D.C. Finnen, A.A. Pinkerton, W.R. Dunham, R.H. Sands, M.O. Funk, Inorg. Chem.
30 (1999) 3960–3964.
[24] E.W. Ainscough, A.M. Brodie, J.E. Plowman, V.L. Brown, A.W. Addison, A.R.
Gainsford, Inorg. Chem. 19 (1980) 3655–3663.
[25] W.H. Armstrong, A. Spool, G.C. Papaefthymiu, R.B. Frankel, S.J. Lippard, J. Am.
Chem. Soc. 106 (1984) 3653–3667.
[13] E. Monzani, L. Quintini, A. Perotti, L. Casella, M. Gulloti, L. Randaccio, S. Geremia,
G. Nardin, P. Faleschini, G. Tabbi, Inorg. Chem. 37 (1998) 553–562.
[14] (a) T. Dhanalakshmi, M. Bhuvaneshwari, M. Palaniandavar, J. Inorg. Biochem.
100 (2006) 1527–1534;
[26] R. Herchel, Z. Sindela, Z. Travnicek, R. Zboril, J. Vanco, Dalton Trans. (2009)
9870–9880.
[27] X. Wang, S. Wang, L. Li, E.B. Sundberg, G.P. Gacho, Inorg. Chem. 42 (2003)
7799–7808.
(b) D. Mandon, A. Nopper, T. Litrol, S. Goetz, Inorg. Chem. 40 (2001) 4803–4806;