Catalytic activity of iron and ruthenium complexes of bis(2,3-dihydroxy benzaldehyde)pyridine diimine towards oxidation of cyclohexene, cyclohexane, THF and alcohols using O2, H2O2, t-BuOOH

Article abstract of DOI:10.14233/ajchem.2017.20168

The oxidation of primary alcohols, cyclohexene, cyclohexane and tetrahydrofuran (THF) was studied using the catalysts [Fe(L)ClH₂O] (1) and [Ru(LH₂)PPh₃Cl₂H₂O] (2) where L = bis(2,3-dihydroxy benzaldehyde)pyridine diimine in various solvents and co-oxidants. Primary aromatic alcohols gave better yields compared to aliphatic alcohols. Both catalysts oxidized cyclohexene into cyclohexene-1-ol and cyclohexene-1-one in almost 1:1 ratio with negligible epoxide formation. The conversion of cyclohexane into cyclohexanol and cyclohexanone was most effective with t-BuOOH as co-oxidant. For THF, iron complex 1 gave better results than ruthenium complex 2.

Full text of DOI:10.14233/ajchem.2017.20168

Asian Journal of Chemistry; Vol. 29, No. 1 (2017), 152-156
A
SIAN
J
OURNAL OF HEMISTRY
C
http://dx.doi.org/10.14233/ajchem.2017.20168
Catalytic Activity of Iron and Ruthenium Complexes of Bis(2,3-dihydroxy benzaldehyde)pyridine
diimine towards Oxidation of Cyclohexene, Cyclohexane, THF and Alcohols Using O2, H2O2, t-BuOOH
*
MINU GUPTA BHOWON , SABINA JHAUMEER-LAULLOO, HENRI LI KAM WAH, ANISHA MEETUN and KARISHMA MUDHOO
Department of Chemistry, Faculty of Science, University of Mauritius, Reduit, Mauritius
*Corresponding author: Tel: +230 4037502; E-mail: mbhowon@uom.ac.mu
Received: 2 July 2016;
Accepted: 19 September 2016;
Published online: 29 October 2016;
AJC-18117
The oxidation of primary alcohols, cyclohexene, cyclohexane and tetrahydrofuran (THF) was studied using the catalysts [Fe(L)ClH2O]
(1) and [Ru(LH2)PPh3Cl2H2O] (2) where L = bis(2,3-dihydroxy benzaldehyde)pyridine diimine in various solvents and co-oxidants.
Primary aromatic alcohols gave better yields compared to aliphatic alcohols. Both catalysts oxidized cyclohexene into cyclohexene-1-ol
and cyclohexene-1-one in almost 1:1 ratio with negligible epoxide formation. The conversion of cyclohexane into cyclohexanol and
cyclohexanone was most effective with t-BuOOH as co-oxidant. For THF, iron complex 1 gave better results than ruthenium complex 2.
Keywords: Catalytic, Cyclohexene, Cyclohexane, Alcohols, Co-oxidant.
spectra were recorded on a PV8700 series UV-visible spectro-
meter. The melting point of all samples was determined using
a Stuart Scientific Electric Melting point apparatus. Magnetic
susceptibility of the metal complexes was carried out on a
Sherwood Scientific magnetic balance. Carbon, hydrogen,
nitrogen and sulphur contents were obtained using a LECO
932 CHNS Mattson 1000 spectrophotometer. Gas chromato-
graphic analyses were performed with a UNICAM GC 610
series instrument on a 30 m long DB-1 column with an FID
detector.
Synthesis of [Fe(L)ClH2O] (1): To a solution of diimine
(0.5779 g, 1 mmol) in ethanol (20 mL), FeCl3·3H2O (0.261 g,
1 mmol) was added and the reaction mixture was stirred for
24 h at room temperature. The green compound was filtered,
washed with ethanol, ether and dried. m.p. > 350 °C. Yield:
62 %Anal. found: (calc.) for C; 49.8 (49.9), H; 3.1 (3.3), N; 9.2
(9.2), Cl; 8.2 (7.8). IR (KBr pellets, cm-1): 1605, 1545, 1457,
1267, 1379; magnetic moment (µeff): 5.63 BM. UV-visible
(DMSO, λmax, nm): 263 (ε = 7480 M-1cm-1), 324 (ε = 14156
M-1cm-1), 351 (ε = 2667 M-1cm-1), 609 (ε = 4372 M-1 cm-1).
Synthesis of [Ru(LH2)PPh3Cl2H2O] (2): To a solution
of bis(2,3-dihydroxy benzaldehyde)pyridine diimine LH2
(0.349 g, 1 mmol) in ethanol (20 mL), RuCl3·3H2O (0.261 g,
1 mmol) and triphenylphosphine (PPh3) (0.3934 g, 1.5 mmol)
were added and the resulting solution was refluxed for 3 h.
The black solid formed was filtered, washed with ethanol and
diethyl ether and dried. m.p. > 300 °C. Yield 68.8 %. Anal.
found: (calcd.) for Ru(LH2)PPh3Cl2H2O: C; 52.8 (53.1), N;
INTRODUCTION
The development of catalytic method for the selective
oxidation of organic substrates remains a challenge in modern
chemistry. Iron [1-4] and ruthenium [5-10] complexes of Schiff
bases have been reported to be active catalyst for oxidation
of hydrocarbons/THF/alcohols in the presence of O2, H2O2,
t-BuOOH, PhIO, NaOCl, NMO as co-oxidants. In recent times,
more environmental-friendly processes for the oxidative trans-
formation of organics have gained considerable interest. The
increased environmental concerns call for benign oxidation
including recoverable catalyst and clean oxidant such as oxygen,
hydrogen peroxide and t-butyl hydrogen-peroxide to provide
means for enhanced economics and greener processes.
In our previous work, the synthesis of bis(2,3-dihydroxy
benzaldehyde)pyridine diimine (LH2) and [Fe(L)ClH2O] (1) have
been reported [11]. In the present study, we are reporting the
synthesis of [Ru(LH2)PPh3Cl2H2O] (2) and the catalytic properties
of LH2, 1 and 2 for the oxidation of cyclohexene, cyclohexane,
THF and alcohols with regards to various solvents and terminal
oxidants such as O2, H2O2 and t-BuOOH.
EXPERIMENTAL
All chemicals were purchased from eitherAldrich or BDH
Chemicals and were used without purification. Infrared spectra
(KBr pellets) were recorded on an AVARTAR 1000 FT IR
spectrometer in the range of 4000-400 cm-1. 1H and 13C spectra
were obtained from a Bruker Spectrospin 250. UV-visible

Vol. 29, No. 1 (2017)
Catalytic Activity of Iron and Ruthenium Complexes of Bis(2,3-dihydroxy benzaldehyde)pyridine diimine 153
5.4 (5.0), H; 4.1(4.3), Cl; 8.7 (8.9). IR (KBr pellets, cm-1) 3451,
1608, 1538. 1H NMR (DMSO, δ ppm): 10.14-10.47 (s, 4H);
9.82 (s, 1H); 11.01 (s, 1H, HC=CN); 6.77-8.24 (m, 24H). UV-
visible (DMSO, λmax, nm): 257 (ε = 21604 M-1 cm-1), 325 (ε =
20112 M-1 cm-1) 478 (ε = 19074 M-1 cm-1), 628 (ε = 1697 M-1
cm-1).
Oxidation of alcohol: To a solution of the corresponding
primary alcohol (1 mmol) in dichloromethane (20 mL), O2 or
30 % H2O2 (2 mL, or t-BuOOH (1 mL) was added followed
by the complex (0.02 g). The solution was stirred for 3 h at
room temperature. The mixture was filtered, concentrated and
extracted with ether. The ether extract was concentrated and
quantified with 2,4-dinitrophenylhydrazine.
Oxidation of cyclohexene, cyclohexane and THF: The
synthesized metal complex (0.03 mmol) was dissolved in 5 mL
of CH2Cl2 or CH3CN or ethyl acetate and substrate (10 mmol)
was added to the solution together with n-octane (about 0.089 g)
as an internal standard for GC analyses. The resulting solution
was stirred using oxygen or H2O2 (1.7 mL, 15 mmol) or t-BuOOH
(1.8 mL, 10 mmol) at room temperature. The oxidation products
were monitored by GC at different time intervals (3, 24, 48
and 72 h) and were identified by comparison with authentic
samples.
terminal chlorine atoms, one triphenyl phosphine and one water
molecule while in complex 1, iron is octahedrally coordinated
with two imine nitrogens, two deprotonated oxygen atoms, one
chlorine atom and one water molecule.
Catalytic evaluation: The oxidation of alcohols and
hydrocarbons are reported to occur using different catalysts
in the presence of different co-oxidants such as NMO, iodosyl-
benzene, H2O2, O2 and t-BuOOH [8,12-15]. The ability of
complexes 1and 2to catalyze the oxidations of primary alcohols,
cyclohexene, cylohexane and THF were systematically studied
in different solvents such as CH3CN, CH2Cl2, EtOAc in the
presence of environmental-friendly terminal oxidants such as
H2O2, O2 or t-BuOOH. The results of the different oxidation
reactions are summarized in Tables 1-4.
Primary alcohols: The primary alcohols were converted
into their corresponding aldehydes in 21-94 % yield with
turnover 9-33 (Table-1). For 1, the highest yield for oxidation
products for the alcohols was obtained with H2O2 as oxidant
while for complex 2, t-BuOOH gave better results. The product
formation using complex 1 was in the order H2O2 > t-BuOOH
> O2 while for complex 2 the order was t-BuOOH > H2O2 >
O2. Aromatic benzyl alcohols gave better yields with both
complexes compared to the aliphatic alcohols due to the fact
that the aromatic product is a non-enolisable aldehyde thus
reducing the number of possible side products [13].
RESULTS AND DISCUSSION
Bis(2,3-dihydroxy benzaldehyde)pyridine diimine (LH2)
was prepared by the reaction of 2,3-diaminopyridine and 2,3-
dihydroxy benzaldehyde in 1:2 molar ratio in ethanol. A green
solid, iron(III) complex (1) was formed by the reaction of
iron(III) chloride with LH2 in 1:1 ratio while ruthenium(IIII)
complex (2) was formed by Ru(III) chloride, LH2 and PPh3 in
the molar ratio 1:1:1.5 in ethanol.
In IR spectra of the ligand (LH2), the imine band appeared
at 1614 and 1558 cm-1, which on complexation showed a red
shift of ≈ 8-10 cm-1 indicating the coordination of the metal
ion (Ru, Fe) with imine nitrogen. The pyridine imine at 1589
cm-1 in LH2 showed no shift in the complexes indicating no
involvement in coordination of ring nitrogen with the metal.
In 1H NMR spectra of complex 2, the imine protons move
downfield at δ 9.02 and 11.01 ppm compared to δ 8.85 and
9.41 ppm in the free ligand. The phenolic OH in LH2 appeared
at δ 13.01, 12.44, 9.32, 9.27 ppm. The appearance of peaks at
10.14-10.47 ppm corresponding to 4 protons indicated no
deprotonation of hydroxyl protons in complex 2.
Both complexes exhibit well-resolved intraligand and
ligand to metal charge transfer bands in the region of 257-263
and 325 nm. In the free ligand LH2, the band at 293 and 339
nm was observed indicating a blue shift after coordination.
The metal to ligand charge transfer in the visible region was
at 609 and 478 nm for complexes 1 and 2, respectively. An
additional band at 628 nm in complex 2 was due to the d-d
charge transfer.
TABLE-1
OXIDATION OF PRIMARY ALCOHOLS
USING COMPLEXES 1 AND 2
Substrate
Co-oxidant
H2O2
Catalyst
Yield (%)
67
TON
16
25
13
15
14
32
21
28
19
18
20
33
16
20
12
13
15
12
13
19
10
9
1
2
1
2
1
2
1
2
1
2
1
2
1
2
1
2
1
2
1
2
1
2
1
2
60
56
35
63
76
94
66
82
42
87
80
68
47
55
29
66
57
57
44
43
21
39
50
Benzyl
alcohol
O2
t-BuOOH
H2O2
4-Methoxy
benzyl
alcohol
O2
t-BuOOH
H2O2
Heptan-1-
ol
O2
t-BuOOH
H2O2
Octan-1-ol
O2
9
21
t-BuOOH
TON = Turnover = No of moles of product/No of moles of catalyst.
The iron complex (1) was paramagnetic with 5 unpaired
electrons (5.363 BM) which is consistent with + 3 oxidation
state of the metal while the ruthenium complex (2) was diamag-
netic hence containing the Ru(II) acceptor center.
Based on these observations, in complex 2, ruthenium
is octahedrally coordinated with two imine nitrogens, two
Cyclohexane: The oxidation of cyclohexane gave cyclo-
hexanol and cyclohexanone as a mixture and the response
factor was determined by assuming the formation products in
a 1:1 ratio (Table-2). When complexes 1 and 2 were used with
O2 as co-oxidant, no appreciable conversion of cyclohexane

154 Bhowon et al.
Asian J. Chem.
TABLE-2
actone with only t-BuOOH but in poor yield (0.7-2.2 %)
(Table-3).
CYCLOHEXANE OXIDATION USING COMPLEXES 1 AND 2
Yield (%) (TON)
Optimum
co-oxidant
Time
(h)
TABLE-3
CH3CN
CH2Cl2
EtOAc
OXIDATION OF THF USING COMPLEXES 1 AND 2
3
–
0.4 (1)
0.6 (1)
0.6 (1)
1.3 (3)
10.0 (12)
21.0 (24)
27.0 (31)
35.0 (40)
–
–
Yield (%) (TON)
Optimum Time
24
48
72
3
24
48
72
3
6.8 (16)
20.7 (47)
21.5 (49)
14.5 (17)
16.7 (19)
20.8 (24)
29.1 (33)
0.9 (2)
4.7 (11)
5.0 (12)
5.0 (12)
6.3 (7)
11.7 (10)
11.9 (14)
12.0 (14)
–
Catalyst
co-oxidant
(h)
1
2
1
t-BuOOH
t-BuOOH
H2O2
CH3CN
0.3 (1)
0.4 (0.8)
0.9 (2)
1.3 (3)
0.1 (-)
1.0 (2)
1.0 (2)
–
0.91 (2)
2.0 (5)
2.2 (5)
1.9 (4)
CH2Cl2
0.2 (1)
0.4 (1)
0.4 (1)
0.5 (1)
0.9 (2)
0.8 (7)
0.8 (2)
–
0.8 (2)
0.7 (2)
0.6 (1)
0.5 (1)
EtOAc
9.7 (22)
28.8 (65)
7.1 (16)
2.2 (5)
1.9 (4)
0.6 (1)
0.5 (1)
–
3
24
48
72
3
1
H2O2
24
48
72
3
24
48
72
1
2
t-BuOOH
t-BuOOH
24
48
72
2.1 (5)
13.2 (30)
15 (32)
–
–
–
–
1.3 (3)
1.5 (3)
1.3 (3)
1.2 (3)
0.1 (-)
0.7 (2)
–: not detected
was observed. With H2O2 as co-oxidant, complex 2 gave negli-
gible yield while complex 1 gave the yield of the products in
15 % yield after 72 h. In the presence of t-BuOOH, the % yield
of products was found in the range of 0.4-21 % for complex 1
and 12-35 % for complex 2. For the oxidation of cyclohexane,
t-BuOOH was a better co-oxidant for both catalysts and complex
2 was found to be a better catalyst than complex 1. Higher
conversion of cyclohexane was observed with catalyst 2 in
dichloromethane (Fig. 1).
Oxidation of cyclohexene: The oxidation of cyclohexene
is reported to give four products 2-cyclohexene-1-ol, 2-cyclo-
hexene-1-one, cyclohexene-oxide and cyclohexene-diol [16]
(Scheme-I).
In the present work, three products 2-cyclohexene-1-ol
(cy-ol), 2-cyclohexene-1-one (cy-one), cyclohexene-oxide (cy-
oxide) were clearly identified using gas chromatography by
comparison with the standards. The nature and relative yields
of the products formed by catalytic oxidation of cyclohexene
using complexes 1 or 2 vary considerably depending on the
catalyst, oxidant and the solvents used (Table-4).
When molecular O2, H2O2, t-BuOOH were used as co-
oxidant with iron complex, complex 1 in CH2Cl2 and CH3CN,
2-cyclohexene-1-ol was obtained in higher yield than 2-cyclo-
hexene-1-one while in EtOAc, 2-cyclohexene-1-one was the
predominant product. The product formation for O2 and H2O2
decreased in the order acetonitrile > ethyl acetate > CH2Cl2
while for t-BuOOH the order is ethyl acetate > acetonitrile >
CH2Cl2.
40
1-Acetonitrile
1-DCM
1-EtOAc
2-Acetonitrile
35
30
25
20
2-DCM
15
2-EtOAc
10
5
While using ruthenium complex 2 as catalyst in the presence
of O2 and H2O2, the formation of the cyclohexene-1-ol was
more than the cyclohexene-1-one. However, in t-BuOOH as
co-oxidant the % yield obtained for 2-cyclohexene-1-one was
higher than cyclohexene-1-ol with different solvents used. The
product formation in the presence of ruthenium complex 2
for O2 and H2O2 decreased in the order acetonitrile > CH2Cl2 >
ethyl acetate while for t-BuOOH the order was ethyl acetate >
CH2Cl2 > acetonitrile. It is reported that CH3CN suppresses
the co-ordination of t-BuOOH with substrate and compete for
0
0
0.02
0.04
Reaction time (h)
0.06
0.08
Fig. 1. Oxidation of cyclohexane using complexes 1 and 2 with t-BuOOH
Oxidation of tetrahydrofuran: The oxidation of tetra-
hydrofuran with the iron complex (1) gave no appreciable yield
of α-butyro-lactone with O2 and t-BuOOH. However, the 28.8
% yield was noted with the combination of 1/H2O2/ethyl acetate
after 24 h, which decreases considerably with time. Compared
to iron complex (1), ruthenium complex (2) gave a-butyrol-
O
OH
OH
OH
+
+
+
O
Cyclohexene
2-Cyclohexen- 2-Cyclohexene
ol 1-one
Cyclohexene
Oxide
Scheme-I: Oxidation products for cyclohexene

Vol. 29, No. 1 (2017)
Catalytic Activity of Iron and Ruthenium Complexes of Bis(2,3-dihydroxy benzaldehyde)pyridine diimine 155
TABLE-4
OXIDATION OF CYCLOHEXENE IN DIFFERENT SOLVENTS, CO-OXIDANTS USING COMPLEXES 1 AND 2
Yield (%) (TON)
Co-
oxidant
Time
(h)
Catalyst
1
CH3CN
CH2Cl2
EtOAc
Cy-ol
–
Cy-one
–
Oxide
–
Cy-ol
0.5(1)
Cy-one
0.4(1)
Oxide
–
–
0.3 (1)
0.4 (1)
0.4 (1)
0.5 (1)
1.6 (4)
Cy-ol
0.8(2)
Cy-one
2.0(5)
Oxide
–
–
3
24
48
72
3
24
48
72
3
24
48
72
3
24
48
72
3
24
48
72
3
24
48
72
4.5(10)
7.6 (17)
19.7 (44) 13.7 (31)
2.2 (6)
8.1 (22)
4.2 (10)
5.6 (13)
–
0.7 (2)
1.2 (3)
1.2 (3)
1.8 (4)
2.1 (5)
6.4 (15)
0.6 (1)
0.9 (2)
1.0 (2)
0.6 (1)
0.9 (2)
2.5 (6)
2.0 (4)
2.5 (6)
3.6 (8)
1.5 (4)
2.1 (5)
4.1 (9)
4.1 (9)
1.0 (2)
1.7 (4)
2.8 (6)
2.6 (6)
1.7 (4)
2.2 (5)
4.1 (9)
1.9 (5)
0.9 (2)
0.8 (2)
0.7 (2)
0.6 (1)
2.4 (5)
2.9 (7)
3.6 (8)
4.3 (10)
3.5 (8)
4.4 (10)
6.4 (14)
1.5 (4)
1.6 (4)
3.4 (8)
3.8 (9)
1.0 (2)
1.2 (3)
2.7 (6)
2.0 (4)
1.5 (3)
1.7 (4)
3.3 (8)
1.4 (4)
0.3 (1)
6.7 (15)
7.0 (16)
7.5 (17)
6.4 (15)
8.8 (20)
11.2 (26)
11.4 (26)
O2
O2
2.1 (5)
3.4 (8)
0.4 (1)
0.5 (1)
–
0.7 (2)
1.3 (3)
1.4 (3.1)
0.2 (0.4)
0.3 (1)
–
1.5 (4)
4.6 (13)
2
1
2
1
2
17.8 (48) 12.6 (34)
–
–
5.6 (13)
32.8 (74) 20.1 (45)
29.9 (68) 19.1 (43)
3.4 (8)
–
–
–
–
0.8 (2)
0.9 (2)
1.0 (2)
1.1 (2)
1.5 (4)
2.8 (7)
5.7 (15)
2.1 (6)
1.9 (4)
2.1 (5)
2.4 (5)
2.8 (6)
6.2 (14)
6.6 (15)
6.5 (15)
6.4 (15)
0.9 (2)
1.0 (2)
1.0 (2)
1.2 (3)
1.1 (3)
1.8 (5)
5.7 (15)
2.2 (6)
0.6 (1)
1.3 (3)
0.8 (2)
0.5 (1)
9 (21)
0.2 (0.4)
0.3 (1)
0.1 (0.3)
–
0.2 (1)
0.7 (2)
–
H2O2
H2O2
15 (30)
2.3 (6)
2.4 (6)
6.3 (17)
7.5 (20)
0.9 (2)
3.8 (9)
1.4 (3)
1.3 (3)
4.7 (10)
2.8 (6)
1.0 (2)
1.2 (1)
6.9 (16)
1.7 (5)
2.0 (5)
6.0 (16)
7.1 (19)
0.9 (2)
1.3 (3)
2.8 (6)
4.0 (9)
2.1 (5)
–
–
–
–
0.2 (10)
0.3 (1)
–
0.5 (1)
0.3 (1)
0.9 (2)
1.0 (2)
0.2 (1)
0.4 (1)
2.3 (5)
1.1 (3)
0.8 (2)
–
–
0.6 (1)
0.3 (1)
–
0.7 (1)
0.4 (1)
0.4 (1)
0.3 (1)
1.2 (3)
2.0 (5)
2.1 (5)
2.1 (5)
t-
BuOOH
–
2.1 (5)
1.4 (3)
10.5 (24) 1.2 (2.7)
10.3 (24)
12.0 (28)
8.0 (19)
10.9 (25)
t-
BuOOH
9.0 (21)
0.8 (1.8)
40
35
30
25
20
15
10
5
Ru(IV)=O moiety [5]. Inert solvent like EtOAc and chlorinated
solvent like CH2Cl2 were found to be good solvents for the
oxidation in the presence of t-BuOOH as there is less competition
between solvent and substrate molecules for coordination with
metal active site.
Fig. 2 shows the relative % yield of the different products
obtained using 1/H2O2 and 2/t-BuOOH in acetonitrile.
The oxidation of cyclohexene using ruthenium complex
2 showed the formation of 2-cyclohexene-1-ol and 2-cyclo-
hexene-1-one more compared to the epoxide formation. This
is due to the formation of Ru(IV)=O or Fe(IV)=O in the solution
which is more selective towards hydroxylation of C-H bond
rather than epoxidizing the C=C bond as reported earlier [5,9].
1-Cy-ol
1-Cy-one
1-Oxide
2-Cy-ol
2-Cy-one
2-Oxide
0
0
20
40
60
80
Reaction time (h)
Fig. 2. Oxidation of cyclohexene using 1(H2O2) and 2(t-BuOOH) in acetonitrile
Ru(IV) =O
+
+
O
Ru(II)
OH
+ Ru(IV) =O
+
+
Ru(III)OH
Ru(II)
(A)
.
OH
O
Ru(IV) =O
+
-H+
RuII
Ru(II) (B)
+
+
H
H
Scheme-II: Proposed mechanism for oxidation of cyclohexene using ruthenium complex 2

156 Bhowon et al.
Asian J. Chem.
The mechanism of formation of products may be suggested
to proceed in two ways either in heterolytic manner or radical
pathways (Scheme-II).
cyclohexene and THF in the presence of environmentally friendly
co-oxidants.
REFERENCES
The oxidation reaction for ruthenium complex 2 is believed
to proceed via Ru(IV)=O intermediate which supported by
the spectral studies. The IR spectrum of the solid mass obtained
by evaporation of reaction mixture of ruthenium complex 2
taken after 30 min exhibited a characteristic Ru(IV)oxo band
[5] at 877 cm-1 and which was not found in the IR spectrum of
the pre-cursor ruthenium complex 2. However, the other bands
in the IR remained same, which indicated no change in the
structure of ruthenium complex 2 during oxidation.
Catalyst recycling: A preliminary study of the recycling
efficiency of complexes 1 and 2 using t-BuOOH or H2O2 and
benzyl alcohol as model substrate was undertaken. The catalyst
was separated from the reaction mixture after each experiment
by filtration, washed with solvent and dried before using it in
the subsequent run. It was inferred that the catalyst could be
recycled about three times. However, there is a progressive
loss of activity accompanied by diminished yield of 5-20 %.
The IR and elemental analysis of used complexes indicated
that the complexes did not undergo major oxidative degradation
during catalysis.
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Conclusion
In summary, both catalysts 1 and 2 were successfully used
for the catalytic oxidation of primary alcohols, cyclohexane,