Synthesis, structure and oxidation of alkynes using a μ-oxo diiron complex with the ligand bis (1-(pyridin-2-ylmethyl)-benzimidazol-2-yl methyl) ether

Article abstract of DOI:10.1016/j.ica.2012.04.015

New ligand bis (1-(pyridin-2-ylmethyl)-benzimidazol-2-ylmethyl ether and its μ-oxo diferric complex has been synthesized and characterized. The dimeric [LClFe-O-FeCl₃] has been characterized crystallographically, and shows that iron atoms occupy inequivalent coordination sites. One of the Fe (III) atom is coordinated by two benzimidazole nitrogens, one ether oxygen and bridging oxide oxygen, forming the equatorial plane while one Cl^- ion and the oxygen atom of a DMF molecule occupy the axial fifth and the sixth coordination positions. The second Fe (III) is tetrahedrally coordinated by three Cl^- ions and the bridging oxide oxygen O. The bridging oxide anion is unsymmerically coordinated to the two Iron (III) atoms. Oxidation of aromatic alkynes was investigated using this complex as catalyst with small amount of tert-butyl hydroperoxide (TBHP) and Hydrogen peroxide (H ₂O₂) as an alternate source of oxygen. Isolated products were characterized by GC-Mass. Solvent, temperature, Stoichiometry and oxidant variation are studied and reaction conditions have been optimized. Dicarbonyl and α,β-acetylenic ketone are the major product and depend on the nature of the alkyne employed.

Full text of DOI:10.1016/j.ica.2012.04.015

Inorganica Chimica Acta 390 (2012) 129–134
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Note
Synthesis, structure and oxidation of alkynes using a
l-oxo diiron complex with
the ligand bis (1-(pyridin-2-ylmethyl)-benzimidazol-2-yl methyl) ether
Raghvi Khattar a, M.S. Hundal b, Pavan Mathur a,
⇑
a Department of Chemistry, University of Delhi, Delhi, India
b Guru Nanak Dev University, Amritsar, India
a r t i c l e i n f o
a b s t r a c t
Article history:
New ligand bis (1-(pyridin-2-ylmethyl)-benzimidazol-2-ylmethyl ether and its
l-oxo diferric complex
Received 22 December 2011
Received in revised form 9 April 2012
Accepted 10 April 2012
has been synthesized and characterized. The dimeric [LClFe–O–FeCl3] has been characterized crystallo-
graphically, and shows that iron atoms occupy inequivalent coordination sites. One of the Fe (III) atom
is coordinated by two benzimidazole nitrogens, one ether oxygen and bridging oxide oxygen, forming
the equatorial plane while one Clꢀ ion and the oxygen atom of a DMF molecule occupy the axial fifth
and the sixth coordination positions. The second Fe (III) is tetrahedrally coordinated by three Clꢀ ions
and the bridging oxide oxygen O. The bridging oxide anion is unsymmerically coordinated to the two Iron
(III) atoms. Oxidation of aromatic alkynes was investigated using this complex as catalyst with small
amount of tert-butyl hydroperoxide (TBHP) and Hydrogen peroxide (H2O2) as an alternate source of
oxygen. Isolated products were characterized by GC-Mass. Solvent, temperature, Stoichiometry and oxi-
Available online 20 April 2012
Keywords:
Fe (III) complex
bisbenzimidazole
Crystal structure
Alkynes
dant variation are studied and reaction conditions have been optimized. Dicarbonyl and
ketone are the major product and depend on the nature of the alkyne employed.
a,b-acetylenic
Catalyst
Ó 2012 Elsevier B.V. All rights reserved.
1. Introduction
2. Experimental
The oxidation of alkynes carrying methylene and hydroxyl moi-
eties to the corresponding carbonyl derivatives is of importance in
organic synthesis. This has been reported with transition metal
catalysts using different oxidants [1–4]. It is known that alkynes
2.1. Analysis and physical measurements
Elemental analyses of ligand and dimeric l-oxo diiron (III) com-
plex was obtained on VARIO EL III instrument from USIC, University
of Delhi, Delhi, India. Electronic spectra were recorded on a Shima-
dzu 1601 spectrometer at the Department of Chemistry, University
of Delhi, Delhi. IR spectra were recorded in the solid state as KBr
pellets on a Perkin–Elmer FTIR-2000 Spectrometer in the region
of 400–4000 cmꢀ1. GCMS spectra were recorded at Advanced
Instrumentation and Research Facility, Jawaharlal Nehru Univer-
sity, New Delhi on a GCMS-QP2010 (plus) Schimadzu instrument.
can be converted into a,b acetylenic ketones [5], dicarbonyl com-
pounds [2,6] and can undergo oxidative cleavage [7]. Earlier re-
ports on the oxidative cleavage of alkynes employed oxidants
such as ozone, potassium permanganate, ruthenium tetraoxide,
Mo and W polyoxometalates, methylrhenium trioxide, alkaline
hydrogen peroxide, [bis(trifluoroacetoxy)iodo]-benzene, and use
of these oxidants were found to have low reaction efficiencies
[8–18]. The present work was undertaken to study the oxidation
or cleavage of alkynes by iron catalyst in the presence of hydroper-
oxide. It aims to investigate if the product profile is dependent on
the catalyst or oxidant, and whether the oxidation occurs at the
C„C bond or at the adjacent methylene group. Thus the oxidation
2.2. Materials required
Bis (2-benzimidazolylmethyl) ether (DGB) was prepared as de-
scribed earlier [19]. Freshly distilled solvents were employed for all
the synthesis. All other chemicals were of AR grade.
and cleavage of alkynes has been investigated using a new
l-oxo
bridged dinuclear Fe (III) complex. It is observed that the profile
of the products depend markedly upon the solvent system, nature
of the oxidant, and reactivity of the alkynes used.
2.3. X-ray crystallographic data collection and refinement of [LClFe–
O–FeCl3].2.C3H7ON
The complex was dissolved in HPLC grade DMF, and slow evap-
oration at room temperature over a period of 48 h resulted in the
formation of golden brown hexagonal shaped crystals. X-ray data
for structure determination and refinement for the complex were
⇑
Corresponding author. Tel.: +91 1127667725x1381; fax: +91 1127666605.
E-mail address: pavanmat@yahoo.co.in (P. Mathur).
0020-1693/$ - see front matter Ó 2012 Elsevier B.V. All rights reserved.
http://dx.doi.org/10.1016/j.ica.2012.04.015

130
R. Khattar et al. / Inorganica Chimica Acta 390 (2012) 129–134
collected on a Nonius CCD using Mo K
a
(k = 0.71069). The data
at 70 °C. When turbidity appeared, 2-Picolyl chloride hydrochlo-
were corrected for Lorentz and polarization effects and absorption
corrections were applied. A total of 20857 reflections were mea-
sured out of 9153 were independent and 4379 were observed
ride (1.5 g, 9 mmol) was added and the solution was stirred for an-
other 72 h continuously at 70 °C. The solvent was stripped off on a
rotatory evaporator and the residue was treated with small
amount of distilled water to obtain a brown colored crude product.
The product was recrystallised from hot methanol and water (2:1)
.A light brownish crystalline powder was obtained that analyzed
for the composition C28N6OH24ꢁ2.5H2O, Yield (%) = 60. Anal. Calc.:
C, 66.5; N, 16.6; H, 5.7. Found: C, 66.7; N, 16.6; H, 5.8%. kmax
[I > 2
r(I)] for theta 29.19°. The structure was solved by direct
methods using SIR-97 [20] and refined by full-matrix least squares
refinement methods based on F2, using SHELX-97 [21]. All non-
hydrogen atoms were refined anisotropically. All hydrogen atoms
were fixed geometrically with their Uiso values 1.2 times of the
phenylene and methylene carbons and 1.5 times of the methyl car-
bons. All calculations were performed using WINGX [22] package.
Important crystal and refinement parameters are given in (Table
1). There are two DMF molecules in the molecular structure one
of which is coordinating to the metal ion. The latter showed disor-
der in terms of large thermal parameters especially for N7 and C34
and short C–N distance. The disorder could be resolved only for one
of the methyl carbons C34 which was split into two positions with
(nm), [log e]: 269 [4.12], 278 [4.14], 287 [4.13].
1H NMR (d ppm in DMSO-d6): 4.95(s, 4H), 5.60(s, 4H), 7.10–
7.17(m, 4H), 7.20–7.25 (m, 2H), 7.40–7.45 (m,4H), 7.53–7.59(m,
2H), 7.64–7.7(m, 2H), 8.40–8.45 (d,2H).
13C NMR (d ppm in DMSO-d6): 156, 151, 149,142,137,136, 123,
122,119,111,65,49.
IR(KBr pellets):3342
m(OH), 1591 m(C=N–benzim, pyr), 1080 m(C–O),
1458 (C=N–C=C–benzim), 749 m(c=c benz)
m
a total occupancy of 1.0. The rest were refined with a fixed C–N dis-
0
tance of 1.421(3) ÅA. Because of the unresolved thermal disorder in
the two solvent molecules containing four terminal methyl groups,
the cif shows three B level errors relating to the large Ueq (max)/Ueq
(min) ratios which are fully justified. A final refinement Overall the
structure refined nicely with a final refinement of 474 parameters,
with one restraint, gave R1 = 0.0512, wR2 = 0.0951 for the observed
data and R1 = 0.12187, wR2 = 0.1086 for the whole data (Table 1).
2.5. Preparation of complex
2.5.1. Preparation of [LClFe–O–FeCl3]
The ligand [L] (100 mg, 0.22 mmol) was dissolved in methanol
(10 ml). methanolic solution (5 ml) of anhydrous FeCl3
A
(35.35 mg, 0.22 mmol) was added to the ligand solution. The solu-
tion turned deep red. After 10 min’s of stirring a dark reddish-or-
ange colored product was formed which was centrifuged and
washed with small amount of cold methanol. The product obtained
was then recrystallized from a DMF: methanol (1: 2) mixture,
brown colored compound crystallized on cooling and was dried
2.4. Preparation of ligand
2.4.1. Bis (1-(pyridin-2-ylmethyl)-benzimidazol-2-yl methyl) ether [P-
DGB] [L]
A solution of Bis (2-benzimidazolylmethyl) ether (DGB) (1 g,
3.6 mmol) in DMF was stirred for 3 h with K2CO3 (1.24 g, 9 mmol)
over P2O5. The complex analyzed for the composition C28N6H24
O2Cl4 Fe2.2.C3H7ON, Yield (%) = 55.
-
Anal. Calc.: C, 46.5; H, 4.3; N,12.7. Found: C, 47.0; H, 4.1; N,
12.4%.
kmax (nm), [log
Table 1
e
] = 269[3.91], 278[3.87], 287[3.79], 312[3.65],
Crystal data and structure refinement for [LClFe–O–FeCl3].
359[3.50].
IR(cmꢀ1, KBr) = 1595
m(C=Npyr), 1108 m(C–O), 1478 m(C=N–C=C–benzim),
Identification code
SHELXL
752 m(c=c benz)
Empirical formula
Formula weight
T (K)
C34 H38 Cl4 Fe2 N8 O4
876.22
153(2)
0.71069
Monoclinic
P21/c
2.6. Oxidation of aromatic alkynes by [LClFe–O–FeCl3] using TBHP and
H2O2
k (Å)
Crystal system
Space group
Unit cell dimensions
a (Å)
b (Å)
c (Å)
11.418(5)
17.255(4)
20.463(5)
90
102.586(5)
90
2.6.1. Experimental procedure
The complex 5 mg (0.005 mmol), was dissolved in acetonitrile
(10 ml), a solution of aromatic alkyne (0.114 mmol) in acetonitrile
and 0.02 ml of oxidant (TBHP/or H2O2) were added to this. The cat-
alyst: substrate: oxidant ratio was kept as, 1:20:20. The reaction
mixture was stirred at 60 °C on a water bath for 1 h and monitored
via TLC. The reaction mixture was evaporated on a rotatory evapo-
rator to near dryness. The residue was treated with small portions
of distilled water and extracted with ethylacetate. The products
formed were analyzed using GCMS.
a
(°)
b (°)
c
(°)
V (Å3)
3935(2)
4
Z
Dcalc (Mg/m3)
Absorption coefficient
F(000)
1.479
1.057 mmꢀ1
1800
Crystal size (mm)
h (°)
Index ranges
0.19 ꢂ 0.16 ꢂ 0.16
2.99–29.19
ꢀ15 6 h 6 14, ꢀ21 6 k 6 21,
ꢀ25 6 l 6 24
20857
3. Result and discussions
Reflections collected
Independent reflections (Rint
Completeness to h = 25.00°
Absorption correction
Maximum and minimum
transmission
)
9153 (0.0422)
99.8%
Multiscan
0.853 and 0.829
3.1. Description of the crystal structure of [LClFe–O–FeCl3].2.C3H7ON
The molecular structure of the complex is comprised of two iron
atoms having inequivalent coordination sites. (Fig. 1) shows the
final structure of the dinuclear compound. Fe(1) is six coordinated
in a distorted octahedral environment by two benzimidazole nitro-
gens N(1) and N(4), ether oxygen O(1) and the bridging oxide
oxygen O(2), forming the equatorial plane. While one Clꢀ ion and
the oxygen of one of the solvent molecules, (DMF) occupies the
fifth and the sixth coordination positions. Fe (2) is tetrahedrally
Refinement method
Full-matrix least-squares on F2
9153/1/474
0.859
R1 = 0.0540, wR2 = 0.1084
R1 = 0.1314, wR2 = 0.1234
0.485 and ꢀ0.449
Data/restraints/parameters
Goodness-of-fit on (GOF) F2
Final R indices [I > 2
R indices (all data)
r(I)]
Largest difference in peak and hole
(e Åꢀ3
)

R. Khattar et al. / Inorganica Chimica Acta 390 (2012) 129–134
131
Fig. 1. Showing the final structure of
l-oxo bridged diferic complex. The uncoordinated solvent molecule and hydrogen’s have been removed. Disorder in the coordinated
solvent molecule is shown.
0
coordinated by three Clꢀ ions and the bridging oxide oxygen O(2).
0.16 ÅA out of this plane. The two pyridine rings lie on the same side
of this plane along with the coordinated solvent molecule and the
[FeCl3O]2ꢀ moiety. The two pyridine rings are almost perpendicu-
lar to each other (dihedral angle 85.9(2)°).
The Fe (1)–O(2)–Fe (2) angle is almost linear (175.24°). The O(2)–
Fe(1) and O(2)–Fe(2) distances [1.793 and 1.746 ÅA] are significantly
0
different in accordance with the unsymmetry of the molecule (Ta-
0
ble 2). Average Fe–Cl distances of Fe (2)–Cl (2.212 ÅA) are also sig-
0
nificantly shorter than Fe (1)–Cl distance (2.308 ÅA). The solvent
oxygen O(3) is strongly bonded to the metal ion Fe(1) than the
3.2. IR spectral properties and electronic spectroscopy
ethereal oxygen O(1) with respective bond lengths being 2.180
0
The free ligand L has characteristic IR bands at 1591 and
1458 cmꢀ1. These are assigned to pyridyl (mainly mC=N stretch)
and benzimidazole mC=N–C=C– stretching frequencies, respectively.
Small shift upon complexation is attributed to the binding of imine
nitrogen’s to iron (III) [25,26]. The electronic spectra of ligand L and
the [LClFe–O–FeCl3] complex were recorded in HPLC grade DMF.
Three peaks in the range 265–285 nm are observed in the free li-
and 2.353 ÅA. The bond length O(1)–Fe(1) is found to be relatively
longer than the remaining bond lengths in the diiron complex. In
similarly ligated Cu(II) complexes [Cu(DGB)(Phen)][ClO4]2 and
[Cu(DGB)2(C6H2N3O7)].4C3H7NO where DGB is Bis (2-benzimidaz-
olylmethyl) ether,0 the O(1)–Cu bond length are reported to be
[2.571 and 2.583 ÅA], respect0ively [23,24]. These are even longer
than the O(1)–Fe(1) [2.353 ÅA] bond length found in the present
case.
gand and its complex and are assigned to intraligand
p
–p⁄ transi-
tion of benzimidazole and pyridyl moiety present in the ligating
system. In the diiron complex band at 359 nm is assigned as Ox-
o ? Fe (III) charge transfer bands [27].
A plane may be passed through Fe(1) and the major portion of
the ligand except the two pyridine rings. Only oxygen O1 is
Table 2
Selected bond lengths (Å) and bond angles (°).
Bond lengths (Å)
Bond angles (°)
N(1)–Fe(1)
N(4)–Fe(1)
O(1)–Fe(1)
O(2)–Fe(1)
O(3)–Fe(1)
Cl(4)–Fe(1)
Cl(1)–Fe(2)
Cl(2)–Fe(2)
Cl(3)–Fe(2)
O(2)–Fe(2)
2.074(3)
2.080(3)
2.353(2)
1.793(2)
C(1)–N(1)–Fe(1)
C(7)–N(1)–Fe(1)
C(10)–N(4)–Fe(1)
C(11)–N(4)–Fe(1)
C(8)–O(1)–Fe(1)
C(9)–O(1)–Fe(1)
Fe(2)–O(2)–Fe(1)
C(32)–O(3)–Fe(1)
O(2)–Fe(1)–N(1)
O(2)–Fe(1)–N(4)
N(1)–Fe(1)–N(4)
O(2)–Fe(1)–O(3)
N(1)–Fe(1)–O(3)
N(4)–Fe(1)–O(3)
O(2)–Fe(1)–Cl(4)
120.9(2)
133.7(2)
120.8(2)
133.4(2)
N(1)–Fe(1)–Cl(4)
N(4)–Fe(1)–Cl(4)
O(3)–Fe(1)–Cl(4)
O(2)–Fe(1)–O(1)
N(1)–Fe(1)–O(1)
N(4)–Fe(1)–O(1)
O(3)–Fe(1)–O(1)
Cl(4)–Fe(1)–O(1)
O(2)–Fe(2)–Cl(3)
O(2)–Fe(2)–Cl(2)
Cl(3)–Fe(2)–Cl(2)
O(2)–Fe(2)–Cl(1)
Cl(3)–Fe(2)–Cl(1)
Cl(2)–Fe(2)–Cl(1)
93.42(8)
91.74(8)
167.14(7)
164.02(10)
71.58(8)
71.48(9)
72.54(9)
94.59(6)
110.52(8)
113.16(9)
108.79(5)
112.36(9)
105.77(6)
105.85(6)
2.180(3)
115.33(18)
114.42(18)
175.24(15)
129.0(3)
106.52(10)
108.30(10)
142.99(10)
91.49(10)
82.67(10)
84.26(10)
101.37(8)
2.3076(14)
2.2196(16)
2.2153(12)
2.2008(12)
1.746(2)

132
R. Khattar et al. / Inorganica Chimica Acta 390 (2012) 129–134
H2
C
H2
C
N
N
b
O
a
c
N
N
c
H2C
CH2
d
b
N
N
e
h
# = Moisture.
* = DMSO
Fig. 2. 1H NMR of ligand L in DMSO-d6.
3.3. NMR spectroscopy
FeCl3 the reaction is very slow with very poor yields. This indicates
that the present metal complex is required and is indeed acting as
a catalyst. The oxidation of Diphenyl acetylene was studied in
more detail to optimize the reaction variables such as solvent, cat-
alyst: substrate: oxidant ratio, type of the oxidant, temperature
and length of reaction time.
1H NMR spectrum of the free ligand [L] (Fig. 2) shows signal at
8.4 ppm and is assigned to the H’s adjacent to the N atom of the
pyridyl group. A singlet is also observed at 5.6 and 4.95 ppm which
is assigned to the CH2 protons linked to pyridine ring and CH2 pro-
tons attached with ether O atom. Multiplets are observed in the
range 7.1–7.8 ppm and are assigned to the protons of the benz-
imidazole ring and pyridine ring [19]. 13C NMR spectrum of the li-
gand (Fig. 3) shows signals at 64 and 49 ppm assigned to
methylene carbons linked to ether O atom and to the pyridine ring.
Benzene ring and pyridine ring carbons appear in the range (111–
124 ppm) and (122–137 ppm) [28], respectively.
4.1.1. Solvent dependence
The activity of iron (III) complex was checked in different sol-
vents (acetonitrile, acetone and methanol) with tert-butylhydro-
peroxide (TBHP) as the oxidant while keeping the catalyst:
substrate: oxidant ratio as 1:20:20 (Table 3). Best conversions have
been observed in acetonirile. In this solvent% yield of the dicar-
bonyl product 1 is nearly thrice (47.6%) to that found in acetone
(14.2%). Further the products 2, ester and 3, ketone due to over oxi-
dation through oxidative cleavage or rearrangement are substan-
tially low (9 and 10%) as compared to that found in acetone
(21.6, 27.4%) as reaction medium. When the reaction is carried
out in a hydroxylic solvent like methanol the product profile is
quiet different. Besides the dicarbonyl product, formation of new
4. Reactivity of [LClFe–O–FeCl3] using TBHP and H2O2
4.1. Oxidation of aromatic alkynes
The oxidation of aromatic alkynes using tert-butylhydroperox-
ide (TBHP) and H2O2 as an oxidant in acetonitrile was studied in
the presence of the iron (III) complex. In a control experiment in
the absence of the Iron complex no product formation occurred.
While when the reaction is performed in the presence of the salt
monoketonic products
ketone 5 (13.5%) are also formed while cleavage products are nil.
The formation of the product methoxy ketone indicates partici-
pation of solvent methanol in the oxidation reaction whereas in
a hydroxy ketone 4 (10.5%) and a methoxy
a

R. Khattar et al. / Inorganica Chimica Acta 390 (2012) 129–134
133
Fig. 3. 13C NMR of ligand L in DMSO-d6.
oxidative cleavage products are found to be slightly higher 2
(13.6%) and 3 (15.7%) when compared to the reaction where ratio
of catalyst: substrate: oxidant is 1:20:20. Thus increasing the con-
centration of the oxidant has a disadvantage and does not promote
the oxidation reaction, in the desired direction.
Table 3
Product yields from the oxidation of diphenylacetylene by diiron (III) catalyst in
different solvents using tert-butyl hydroperoxide as oxidant, temperature, 60 °C.
Solvent for reaction
Acetonitrile
Products
bYield (%)
47.6
(1)
4.1.3. Temperature dependence
9.04
When the reaction temperature is increased to 100 °C the ex-
pected dicarbonyl product 1 (17.5%) yield is less than half, and
there are no cleavage products .While when the temperature is be-
low 60 °C, the% yield of all the products was proportionately low.
Increasing the length of reaction time does not have any effect
on the product yield of all the products. Thus the reaction is not
facilitated by increasing the temperature or reaction time, possibly
increased thermal energy causes decay or self binding of radicals,
that are the main pathway to oxidized products.
(2)
10.0
17.5
(3)
a(1)
Acetone
(1)
(2)
(3)
14.2
21.6
27.4
4.1.4. Substrate variation
Methanol
24.1
10.5
13.5
By using the optimal condition obtained for the oxidation of Di-
phenyl acetylene, various alkynes were investigated in order to
determine the versatility of this catalytic system. The results are
summarized in (Table 4).
(1)
(4)
The nature of substrate has a profound effect on the products
formed. With the substrates phenyl propyne, phenyl butyne, phe-
nyl pentyne and TBHP as the oxidant, it is found that phenyl pro-
pyne gives a lower yield of the dicarbonyl product 6 (14.4%) in
comparison to diphenyl acetylene. Besides the cleavage product 2
(27.3%) a new product that leaves the acetylenic bond intact is also
observed 7 (29.0%). A similar kind of observation is inferred for oxi-
dation with phenyl butyne. This is the most selective oxidation
reaction found in the present series of aromatic alkynes, with a ma-
jor product 8 (42.6%). This keeps the acetylenic bond intact and
oxidation takes place preferably at the methylene group of the side
chain, very poor yield of cleavage product 2 is observed.
It is quiet intriguing that phenyl pentyne has a very low reactiv-
ity in comparison to its homologs; poor yields of product 2 and 9
are listed. It seems that the carbon chain length had a large effect
on the conversion. Remarkably oxidation of phenyl acetylene re-
sults in a cleavage product 2 (81.3%) and trace amount of monok-
etonic product 10.
(5)
a
Reaction was carried out at temperature 100 °C.
Conversions were determined using 1-Chloronapthalene as internal standard.
b
non hydroxylic solvents, like acetonitrile and acetone, formation of
dicarbonyl and cleavage products shows that these solvent’s don’t
participate in the oxidation reaction. The formation of products 2
and 5 indicate the presence of t-BuOꢀ and CH3Oꢀ radicals. This sug-
gests that the reaction proceeds via a radical pathway; the pres-
ence of product 4 also supports this mechanism (Scheme I).
4.1.2. Stoichiometry
If the reaction is carried out with the catalyst: substrate:
oxidant ratio of 1:20:100 in acetonitrile with TBHP as the oxidant,
dicarbonyl product 1 (23.7%) is formed to a lower degree. The

134
R. Khattar et al. / Inorganica Chimica Acta 390 (2012) 129–134
Table 4
Oxidation of various alkynes by diiron (III) catalyst using TBHP and H2O2 as oxidant, catalyst: substrate: oxidant ratio of 1:20:20, temperature, 60 °C.
Solvent for reaction
Products
Yield (%)
TBHP
H2O2
(1)
(2)
(3)
47.6
9.04
10.0
41.8
–
–
14.4
33.8
(6)
(2)
27.3
29.0
–
–
(7)
42.6
3.3
–
–
(8)
(2)
5.7
3.8
–
–
(9)
(2)
(2)
81.3
5.5
–
–
(10)
[4] E. Mizushima, K. Sato, T. Hayashi, M. Tanaka, Angew. Chem. Int. Ed. 41 (2002)
4563 (and references therein).
4.1.5. Nature of the oxidant
When similar reactions are performed with H2O2 as the oxidant,
% yield of products are comparatively low. Hence we find that
TBHP is a better oxidant in the present case.
[5] A.N. Ajjou, G. Ferguson, Tetrahedron Lett. 47 (2006) 3719.
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We gratefully acknowledge financial support from Council of
Scientific and Industrial Research Project No. 01 (2218)/08/EMR-
II .We also acknowledge support from University of Delhi, Delhi,
India for special grant.
Appendix A. Supplementary material
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