Synthesis, characterisation and homogeneous catalytic activity study of Mn(II) and Fe(III) ternary complexes

Article abstract of DOI:10.1016/S1381-1169(98)00072-7

The mixed ligand complexes of the type LFeACl · nH₂O and LMnA · H₂O where L is the mannich base obtained by hydrogenation of Schiff base ligands of salicylaldehyde and amino acids, and A is the bipyridyl or orthophenanthroline synthesised. These complexes were characterised by elemental analysis, spectral, magnetic, FAB mass spectral and electrochemical studies. These complexes have been used as catalysts for epoxidation of olefins like cyclohexene, cis-cyclooctene and norbornene using iodosylbenzene as the oxidant. In the epoxidation reactions using these complexes, it was found that Mn (II) complexes act as better catalysts compared to Fe (III) complexes. The mechanism of the progress of the oxidation reaction and termination of catalytic activity has been investigated by using spectral and electrochemical studies.

Full text of DOI:10.1016/S1381-1169(98)00072-7

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.
Journal of Molecular Catalysis A: Chemical 136 1998 285–291
Synthesis, characterisation and homogeneous catalytic activity
ž /
ž /
study of Mn II and Fe III ternary complexes
)
C.A. Sureshan, P.K. Bhattacharya
Department of Chemistry, Faculty of Science, M.S. UniÕersity of Baroda, Baroda-390002, India
Received 4 November 1997; accepted 9 February 1998
Abstract
The mixed ligand complexes of the type LFeAClPnH2O and LMnAPH2O where L is the mannich base obtained by
hydrogenation of Schiff base ligands of salicylaldehyde and amino acids, and A is the bipyridyl or orthophenanthroline
synthesised. These complexes were characterised by elemental analysis, spectral, magnetic, FAB mass spectral and
electrochemical studies. These complexes have been used as catalysts for epoxidation of olefins like cyclohexene,
cis-cyclooctene and norbornene using iodosylbenzene as the oxidant. In the epoxidation reactions using these complexes, it
Ž .
Ž .
was found that Mn II complexes act as better catalysts compared to Fe III complexes. The mechanism of the progress of
the oxidation reaction and termination of catalytic activity has been investigated by using spectral and electrochemical
studies. q 1998 Elsevier Science B.V. All rights reserved.
Keywords: Manganese complexes; Iron complexes; Epoxidation; Mannich base; Ternary complexes
1. Introduction
metal ion in the complex should be moderate so
that the oxo species formed is neither unstable
nor rigid. This enables the metal oxo species to
remain stable until it comes into contact with
the substrate and transfer the oxygen easily into
it, affecting its oxidation.
Currently, there is much interest in the transi-
tion metal catalysed oxidation reaction as chem-
ical model for the mono oxygenase cytochrome
w
x
P-450 1,2 . An important goal in this area of
research has been to develop catalyst systems
for mild and selective oxidations of hydrocar-
The electrochemical property of the metal
centre depends on the nature of ligand bound to
w
x
bons 3–5 .
w
x
it 6,7 . In our previous studies, mixed ligand
w x
The redox potential of the metal centre deter-
mines the ease with which the complex goes
from one oxidation state to another. In a cat-
alytic oxidation reaction, this means how easily
the formation of the catalytically active metal
oxo species takes place. Redox potential of the
complexes of ruthenium 8 , chromium, and iron
w
x
9,10 with the ligands dipicolinic acid and aro-
matic diimines with p donor sites have been
prepared and it was observed that ruthenium
complexes act as very good catalysts for the
epoxidation of olefin. With these in mind, we
have synthesised the mixed ligand complexes of
)
Ž
.
Ž .
Fe III and Mn II with one tridentate mannich
Corresponding author.
1381-1169r98r$ - see front matter q 1998 Elsevier Science B.V. All rights reserved.
Ž
.
PII: S1381-1169 98 00072-7

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286
C.A. Sureshan, P.K. BhattacharyarJournal of Molecular Catalysis A: Chemical 136 1998 285–291
base ligand having s donor coordination sites
carboxylate, NH and Phenolate Oy and another
p acidic aromatic diamine 221 bipyridyl or
orthophenanthroline. These complexes were
characterised by elemental analysis, electronic
and IR spectral, FAB mass spectral, magnetic
susceptibility measurement and electrochemical
studies. These complexes were used as catalysts
for the epoxidation of the olefins like cyclohex-
ene, norbornene and cis-cyclooctene.
trode, platinum wire auxiliary electrode and
AgrAgNO3 reference electrode.
The FAB mass spectra were recorded on a
Jeol SX 102rDD 6000 mass spectrometerrData
Ž
.
system using xenon 6 KV, 10 mv as FAB gas
Ž
.
and m-Nitrobenzyl alcohol NBA as the ma-
trix.
The gas chromatographic analyses were car-
ried out on a Shimadzu G.C. 14B instrument
equipped with Oracle 3 computing integrator
using 10% SE 30 with 1% QF on chromosorb
Ž
.
column 2 M , and nitrogen as carrier gas.
2. Experimental
2.3. Synthesis of LFeAClPnH2O complexes
2.1. Materials
1 mmol of the mannich base ligand and ;2
mmol of lithium were dissolved in 50 ml
methanol, and to this was added 1 mmol of
FeCl3 in 10 ml methanol, and the reaction
mixture was stirred for about one hour. To this,
1 mmol of diimine bipyridyl or orthophenan-
throline was added. The reaction mixture was
stirred for about one hour and the solid formed
was filtered and washed with methanol and
dried in vaccuo.
Salicylaldehyde, a-alanine, l-phenylalanine
Ž
.
Ž
Sisco , orthophenanthroline, bipyridyl Quali-
.
Ž
gens FeCl3 anhydrous, MnCl2 P4H2O Sd
fine , and sodiumborohydride Spectrochem
.
Ž
.
were used, as received. The tetrabutylammoni-
Ž
.
umtetrafluoroborate Fluka used was of electro-
chemical grade. The mannich base ligands were
w
x
prepared by the method reported earlier 11 .
Iodosylbenzene was prepared by the method
w
x
reported by Lucas et al. 12 . All the substrates,
norbornene, cyclohexene, cis-cyclooctene, and
oxidation products norborneneoxide, cyclohexe-
neoxide, cyclohexene-1-ol, cyclohexene-1-one
and cis-cycloocteneoxide were obtained from
Aldrich and were used as received.
2.4. Synthesis of LMnAPH2O
1 mmol of MnCl2 P4H2O was taken in 20 ml
of 1:1 water–alcohol mixture, and to this was
added 1 mmol of diimine bipyridyl or or-
thophenanthroline in 10 ml 1:1 alcohol–water
mixture. The reaction mixture was stirred for
one hour. To this was added 1 mmol of man-
nich base ligand and 2 mmol of NaOH in 30 ml
of 1:1 alcohol–water mixture. The reaction mix-
ture was stirred for about one hour and the solid
formed was filtered, washed with 1:1 alcohol–
water mixture, and then with solvent ether and
dried in vaccuo.
2.2. Physical measurement
The elemental analyses were carried out on a
Coleman analyser model-33 and nitrogen was
estimated by Duma’s method. Manganese and
iron were estimated volumetrically. The IR
spectra were recorded on a Perkin Elmer
spectrophotometer. The UV–visible spectra
were recorded on a Shimadzu 240-UV–visible
spectrophotometer. Magnetic measurements
were carried out by using Gouy’s method. The
electrochemical unit used consists of model
174A polarographic analyser, universal pro-
grammer, x–y recorder, platinum working elec-
2.5. Oxidation of olefins
All the reactions were carried out in a schlenk
Ž
tube under dinitrogen atmosphere. Olefin 2.5
.
Ž
.
Ž
.
mmol catalyst Fe III complexes 0.01 mmol

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C.A. Sureshan, P.K. BhattacharyarJournal of Molecular Catalysis A: Chemical 136 1998 285–291
287
Table 1
Analytical and magnetic data of the complexes 1–6
3. Results and discussion
Ž
.
Elemental analyses Table 1 of the com-
plexes correspond to the expected structure. The
structure is shown in Fig. 1.
Ž
.
Complexes Analysis found calculated %
meff
Ž .
M FerMn
C
H
N
Ž . Ž . Ž . Ž .
52.01 52.3 3.9 4.3 8.6 9.2 11.9 12.2 5.7
1.
2.
3.
4.
5.
6.
Ž
.
.
.
.
.
Ž . Ž . Ž .
The IR spectra of the compounds show bands
53.9 54.7
3.9 4.3 8.3 8.7 11.2 11.6 5.6
Ž . Ž . Ž .
4.6 4.4 7.5 8.1 10.5 10.8 6.0
4.5 4.2 7.3 7.6 10.1 10.4 5.5
Ž . Ž . Ž .
5.5 5.1 7.8 8.4 10.6 11.0 5.8
at around 1640 cmy1, 1540 cmy1, and 1520
Ž
60.7 60.3
Ž
Ž . Ž . Ž .
62.8 62.1
cmy indicating coordinated carboxylate group
1
Ž
61.6 62.6
of the mannich base. The 6NH band occurs at
Ž
Ž . Ž . Ž .
64.9 64.4
4.9 4.8 7.9 8.0 10.4 10.5 5.9
around 3240 cmy indicating coordinated NH
1
group. In the complexes 1,2,5 and 6, a broad
band at 3300–3500 cmy is due to the presence
of water molecule in the lattice. Other bands
corresponding to the mannich base and the aro-
matic diimines were also seen.
The electronic spectra of all the complexes
show intraligand transition bands at 380, 270
and 250 nm. A doublet at 320, 290 nm in the
complexes containing bipyridyl and a band at
270 nm in the phenanthroline containing com-
plexes are characteristic of respective tertiary
diamines coordinated with metal ion. As ex-
1
Ž
.
dissolved in water:acetonitrile 1.3 vrv or 0.01
Ž .
mmol of Mn II complex in acetonitrile and
internal standard chlorobenzene were mixed in
the schlenk tube. The reaction mixture was
deaerated by flushing with nitrogen for 10 min.
Iodosylbenzene 0.5 mmol was added and the
reaction mixture was stirred at ambient tempera-
ture for about 5 h. 2 ml aliquots were with-
drawn from the reaction mixture and analysed
by gas chromatography using FID detector. Af-
ter the 5-h reaction time, there was no further
increase in the yield of epoxide indicating that
the reaction was complete.
Ž .
pected for Mn II complexes, d–d transition
bands are not observed in dilute solution be-
cause of their being doubly forbidden.
Fig. 1.

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C.A. Sureshan, P.K. BhattacharyarJournal of Molecular Catalysis A: Chemical 136 1998 285–291
Table 2
In the case of iron complexes the d–d band is
Electrochemical data for various complexes at 0.1 M electrolyte
concentration
observed at ;510 nm in all the complexes.
The spectrum is shown in Fig. 2.
Complexes
EP1C
EP2C
EP1a
EP2a
The magnetic susceptibility measurements at
1
2
3
4
5
6
y0.42
y0.34
y0.43
y0.48
y
y0.66
0.66
y0.79
y
Ž .
room temperature show that both Mn II and
Ž
.
Fe III complexes are high spin paramagnetic
compounds. Magnetic moment values are shown
in Table 1.
y
0.20
0.26
0.54
0.61
y
y
Ž .
The cyclic voltammetric studies of Mn II
Ž
.
Solvent for complexes 1–4 is water–Acetonitrile 1:3 vrv .
Solvent for complexes 5 and 6 is Acetonitrile.
Electrolyte, tetrabutylammoniumtetrafluroborate.
AgrAgNO3 reference electrode.
complexes were carried out in acetonitrile
medium, using tetrabutylammoniumtetrafluo-
roborate as background electrolyte. The free
ligands do not exhibit any reduction or oxida-
tion peaks in the potential region investigated.
Ž .
The Mn II complexes exhibit two peaks in the
tively. In another complex, 4, only one reduc-
Ž .
Ž
.
anodic scan corresponding to Mn II ™Mn III
tion peak is obtained at y0.48 V and this has
Ž
.
™Mn IV oxidation. The potentials have been
shown in Table 2, and cyclic voltammogram is
presented in Fig. 3a. The reaction is completely
irreversible and corresponding reduction peaks
were not obtained. The cyclic voltammetric
Ž
.
Ž .
been assigned to Fe III ™Fe II reduction. In
all cases, the electrochemical reactions are com-
pletely irreversible. Cyclic voltammogram in
case of complex 3 is shown in Fig. 4 and
potentials for all complexes are recorded in
Table 2.
Ž
.
studies of Fe III complexes were carried out in
acetonitrile–water medium. Two reduction
peaks were obtained for complexes 1–3,
Ž
.
Ž .
Ž .
assignable to Fe III ™Fe II ™Fe I , respec-
Ž
.
Ž .
Fig. 3. a Cyclic voltammogram of complex 5 in acetonitrile
Fig. 2. The electronic spectra of complex 4
after
Ž
.
Ž
.
Ž .
addition of PhIO --- in water–acetonitrile 1:3 vrv solvent
solvent. b Cyclic voltammogram of complex 5 after addition of
PhIO in acetonitrile.
mixture.

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C.A. Sureshan, P.K. BhattacharyarJournal of Molecular Catalysis A: Chemical 136 1998 285–291
289
sponds to L2 MnAX, mrzs505 to L2 MnA,
mrzs320 to L2 Mn and mrzs235 to MnA.
3.1. Catalytic reactions
The results of the oxidation of olefins with
iodosylbenzene in the presence of all the com-
plexes have been shown in Table 3. A con-
trolled experiment using cis-cyclooctene under
identical experimental conditions, but excluding
metal complexes, did not give any epoxide. For
manganese complex, acetonitrile was used as
the solvent; whereas, for the iron complex, wa-
Fig. 4. Cyclic voltammogram of complex 3 in water–acetonitrile
Ž
.
with tetrabutylammonium tetrafluroborate 0.1 M at a platinum
electrode and a scan rate 100 mV sy1
.
Ž
.
ter–acetonitrile mixture 1:3 vrv was used as
solvent for the oxidation reaction. Oxidation of
norbornene and cis-cyclooctene gave corre-
sponding epoxides selectively, whereas cyclo-
hexene gave additional oxidation products other
than cyclohexene oxide. The yield of epoxide in
the case of manganese complexes was found to
be very high as compared to iron complexes.
The turnover numbers in the case of manganese
and iron complexes were found to be 23–26 and
3–8, respectively, indicating that the reactions
are catalytic. The iron complexes show less
activity in the epoxidation reaction of the above
mentioned olefins.
The FAB mass spectra of three complexes
LFeAX.Y, L2 MnAY and L2 FeAX were
recorded. The spectrum of complex 1 is shown
in Fig. 5. In the mass spectrum of the complex
L1FeAX, peak at mrzs441 corresponds to the
parent compound L1FeAX, mrz s 405 to
L1FeA, mrzs247 to L1Fe or AFeX. For the
compounds L2 FeAX the peak at mrzs518
corresponds to parent ion, mrzs481 to L2 FeA,
mrzs325 to L2 Fe and mrzs247 to FeAX.
In case of L2 MnAX peak at mrzs523 corre-
Fig. 5. FAB mass spectrum of complex 1.

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C.A. Sureshan, P.K. BhattacharyarJournal of Molecular Catalysis A: Chemical 136 1998 285–291
Table 3
Olefin
The reaction can be explained in terms of
oxygen rebound mechanism as reported by
Product
Yielda % with catalyst
Ž .
w
x
1
2
3
4
5
6
Groves and McClusky 13 .
In the oxidation reaction of cyclohexene, it
was observed that the major product was cyclo-
hexene oxide in the case where manganese
complexes were used as the catalyst. However,
in the case of iron complexes, the amount of
cyclohexene oxide was found to be less and the
yield of cyclohexene-1-one was found to be
larger.
Norbornene
cis-Cyclooctene cis-cyclooctene oxide
Cyclohexene
Norbornene oxide
7
5
4
5
7
3
10 10 48 46
5
4
4
3
51 48
31 33
7 10
cyclohexene oxide
Cyclohexene-1-one
11 10 17 17
a Yield based on Iodosylbenzene charged.
Substrate: oxidant: catalyst, mole ratio 250:50:1; solvents are
H2O:CH3CN 1:3 vrv for complexes 1–4, and CH3CN for
Ž
.
complexes 5 and 6.
The termination of the reaction can be mainly
because of two reasons, the formation of m-oxo
species or the oxidative degradation of the com-
plex. Electronic spectral or electrochemical
study do not show formation of m-oxo species.
Hence, the termination may be because of the
oxidative degradation of the complex, where the
phenolic oxygen is converted to quinone form,
which gets detached from the metal leading to
the termination of the catalytic reaction. To
confirm this, IR spectrum of the solid, which
deposited after the reaction, was investigated. It
was found that the IR spectrum of the original
complex and that of the solid formed after the
reaction differ significantly. A band at 1650
To suggest the mechanism of the oxidation
reaction, the UV–visible spectra of the com-
plexes were recorded in the presence of PhIO.
After the addition of PhIO, the colour of the
solution of iron complexes changes from violet
to light reddish and in the visible spectrum, the
original d–d band in the complex reduces in
intensity and a new shoulder occurs at around
480 nm. This can be attributed to the formation
of metal oxo species.
Ž .
In the case of Mn II complexes, the colour
of the solution of the complex turns dark brown
but no new peak was observed in the visible
region. This may be because the tailing of the
charge transfer transition masks the d–d band.
The electrochemical studies were carried out
in the presence of PhIO. On addition of PhIO to
1
cmy is observed corresponding to the quinonic
CsO. This confirms the degradation of the
w
x
complexes. It was observed earlier 14 that the
mannich base complexes act as less efficient
catalysts as the phenolic –OH in the mannich
base is known to be more susceptible to oxida-
tion.
Ž .
Ž .
Ž
.
Mn II complexes 5 and 6, the Mn II ™Mn III
oxidation peak completely disappears and a new
peak occurs at around y0.61 V in the case of
complex 5, and y0.57 V in the case of complex
6. The cyclic voltammogram of complex 5 in
the presence of PhIO is shown in Fig. 3b. This
Ž
.
can be attributed to the reduction of Mn IV ™
Acknowledgements
Ž
.
Mn III . On addition of PhIO to the solution of
Ž
.
the complex, there is a formation of Mn IV s0
species which acts as an intermediate and trans-
fers oxygen to the olefin. In the case of iron
complex, the original peak corresponding to
Fe III ™Fe II reduction disappears. However,
no new peak is observed on the less negative
potential region. This may be because the reduc-
tion may be at a more positive potential not
attainable in aqueous solution.
We thank the Department of Science and
Ž
.
Technology New Delhi for the financial sup-
port on this work and the Regional Sophisti-
cated Instrumentation Centre, CDRI, Lucknow
for the FAB mass spectra. Our thanks are due to
professor A.C. Shah, Head of the Department of
Chemistry, M.S. University of Baroda for pro-
viding laboratory facilities.
Ž
.
Ž .

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291
w x
8
M.J. Upadhyay, P.K. Bhattacharya, P.A. Ganeshpure, S.
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