Synthesis, characterization and catalytic activity of new Cr(III) complex in oxidation of primary alcohols to aldehydes

Article abstract of DOI:10.1016/j.ica.2014.05.026

New mononuclear complex of chromium(III), [Cr(bp)(N₃)(CH ₃OH)]·2CH₃OH has been synthesized where H ₂bp is N,N-bis(2-hydroxy-3,5-di-tert-butylbenzyl)-N',N'- dimethylethylene-1,2-diamine. The complex was character

Full text of DOI:10.1016/j.ica.2014.05.026

Accepted Manuscript
Synthesis, characterization and catalytic activity of new Cr(III) complex in ox-
idation of primary alcohols to aldehydes
Nader Noshiranzadeh, Rahman Bikas, Katarzyna Ślepokura, Mina Mayeli,
Tadeusz Lis
PII:
S0020-1693(14)00315-6
http://dx.doi.org/10.1016/j.ica.2014.05.026
ICA 16008
DOI:
Reference:
To appear in:
Inorganica Chimica Acta
Received Date:
Revised Date:
Accepted Date:
20 February 2014
8 May 2014
14 May 2014
Please cite this article as: N. Noshiranzadeh, R. Bikas, K. Ślepokura, M. Mayeli, T. Lis, Synthesis, characterization
and catalytic activity of new Cr(III) complex in oxidation of primary alcohols to aldehydes, Inorganica Chimica
Acta (2014), doi: http://dx.doi.org/10.1016/j.ica.2014.05.026
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Synthesis, characterization and catalytic activity of new
Cr(III) complex in oxidation of primary alcohols to
aldehydes
a,*
a
b
a
Nader Noshiranzadeh, Rahman Bikas, Katarzyna Ślepokura, Mina Mayeli, and
Tadeusz Lis
b
a
Department of Chemistry, Faculty of Science, University of Zanjan 45195-313, Zanjan,
Iran
b
Faculty of Chemistry, University of Wroclaw, Joliot-Curie 14, Wroclaw 50-383, Poland
Abstract
New mononuclear complex of chromium(III), [Cr(bp)(N
3
)(CH
3
OH)]·2CH OH
3
has been synthesized where H bp is N,N-bis(2-hydroxy-3,5-di-tert-butylbenzyl)-N',N'-
2
dimethylethylene-1,2-diamine. The complex was characterized by elemental analyses and
spectroscopic methods and X-ray diffraction analysis. Single crystal X-ray diffraction
structure analysis of the complex revealed that the chromium ion is octahedrally
2
-
coordinated where the bis(phenolate) ligand (bp ) is N
a tetradentate dinegative fashion. The catalytic potential of this complex has been tested
for the oxidation of primary alcohols using H as oxidant. The effects of various
2 2
O -bonded to the Cr(III) center in
2
O
2
parameters including molar ratio of oxidant to substrate, temperature, and solvent have
been studied. Excellent conversions have been obtained for the oxidation of benzyl
alcohols containing electron-donating groups on para-position.
Keywords: Bis(phenolate) ligands; Cr(III) complex; Catalytic oxidation; Crystal
structure; Oxidation of alcohols
1

1
. Introduction
The oxidation of alcohols is an important process in organic synthesis [1]. The
chemo-, regio-, and stereoselective oxidation of alcohols to corresponding carbonyl
compounds is one of the fundamental organic transformations from the synthetic point of
view [2]. However, the selective oxidation of primary alcoholic compounds to
corresponding aldehydes remains very difficult because in the oxidation of primary
alcohols, the main products are the corresponding carboxylic acids [3]. Many reagents
and various methods are known for selective oxidation of primary alcohols. Catalytic
oxidation of alcohols using transition metal complexes such as V [4], Cu [5], Mo, W [6],
Ru [7], Pd [8], Mn [9], etc. is one of the most important methods for obtaining carbonyl
compounds [10].
While many metal complexes catalytically convert alcohols to carbonyl
compounds, chromium compounds are particularly useful for this process [11]. So far
chromium based materials are used for oxidation of alcohols. Chromic acid [12], the
Jones reagent (chromium trioxide/H
2
SO ) [13], the Collins reagent (chromium
4
trioxide/pyridine complex) [14], pyridinium chlorochromate (PCC) [15],
poly(vinylpyridinium) chlorochromate (PVPCC) [16], and pyridinium dichromate (PDC)
[
17] are some of the more popular commercially available chromium based oxidants used
for such transformations. Nevertheless, there are few reports on catalytic oxidation of
alcohols in presence Cr(III) complexes [18]. Recently, Cr(III) complexes have been
employed as both homogenous [19] and heterogeneous [20] catalysts for epoxidation of
olefins. Also, they have been used as catalyst in selective oxidation of alcohols using
iodosylbenzene (PhIO) as the oxygen source [21]. The use of hydrogen peroxide in the
2

oxidation of organic molecules is a major goal, both in academic and in industry. This is
related to the environmental acceptability of this oxidant, which depends mainly on the
nature of its byproduct (water) [22]. Cr(III) complexes also show considerable catalytic
activity in the presence of H
2
2
O as oxidant [23].
Considering the effect of bulky tert-butyl group as directing substituent for
selective oxidation reactions [24,25], in the present work, we report synthesis,
characterization, crystals structure and catalytic reactivity of new chromium(III) complex
of tetradentate ligand including two phenolic rings bearing bulky tert-butyl substituents at
the ortho- and para- positions relative to the phenolic oxygen (Scheme 1). This ligand
has been prepared by simple one-pot reaction from the Mannich condensation of 2,4-di-
tert-butylphenol, formaldehyde and N,N-dimethylethane-1,2-diamine. The catalytic
reactivity of this complex has been investigated in oxidation of primary alcohols in the
presence of H
2
2
O .
Scheme 1.
2
. Experimental
.1. Material and instruments
All starting chemicals were commercially available reagents and were used
2
without further purification. IR spectra were recorded in KBr discs with a Bruker FT-IR
spectrophotometer. UV-Vis solution spectra were recorded using a thermo-spectronic
1
13
Helios Alpha spectrometer. H and C NMR spectra were measured with a Bruker
Spectrospin spectrometer at 250 and 62.5 MHz, respectively. The reaction products of
oxidation were determined and analyzed by HP Agilent 6890 gas chromatograph
equipped with a HP-5 capillary column (phenyl methyl siloxane 30 µm × 320 µm × 0.25
3

µm) and gas chromatograph-mass spectrometry (Hewlett-Packard 5973 Series MS-HP
gas chromatograph with a mass-selective detector). The elemental analyses (carbon,
hydrogen and nitrogen) of compounds were obtained from Carlo ERBA Model EA 1108
analyzer. Chromium percentage of complex was measured by Varian spectrometer AA
2
20 equipment.
2
.2. Synthesis of N,N-bis(2-hydroxy-3,5-di-tert-butylbenzyl)-N',N'-dimethylethylene-1,2-
2
diamine (H bp)
For the synthesis of bis(phenolate) ligand, H
2
bp (Scheme 1a), methanol (35 mL)
was added to N,N-dimethylethane-1,2-diamine (5.40 mL, 0.05 mol) and the rapidly
stirred solution was cooled to 0 °C. Then aqueous formaldehyde solution (37wt.% in
2
H O, containing 10% methanol as stabilizer, 8 mL, 0.1 mol) was added dropwise. The
mixture was stirred for 15 minutes, then 2,4-di-tert-butylphenol (20.63 g, 0.1 mol) was
added and the mixture was refluxed for 48 h. At the end, the solution was evaporated on a
steam bath to 5 mL and cooled to room temperature. Resulting white precipitate was
separated and filtered off, washed with 20 mL of cooled methanol and re-crystallized.
Yield 80% (20.99 g). M.p. 131-133 °C. Anal. Calc. for C34
7.81; H, 10.76; N, 5.34. Found: C, 77.84; H, 10.80; N, 5.30. FT-IR (KBr, cm ): 3188 (s,
br), 2950 (m, br), 2865(m, br),1768(s), 1605(m), 1592(w), 1571(s), 1506(m), 1483(s),
H
56
N
2
O
2
(MW = 524.82): C,
-1
7
1
1
9
7
467(m), 1417(m), 1388(m), 1374(m), 1360(m), 1303(m), 1285(m), 1256(m), 1224(w),
202(w), 1160(m), 1121(m), 1105(s), 1086(w), 1057(w), 1043(s), 1024(m), 987(s),
48(m), 938(m), 923(s), 910(w), 891(w), 879(s), 824(m), 813(m), 800(w), 782(m),
1
56(m), 725(m), 681(m), 665(w), 649(m), 540(m). H NMR (250.13 MHz, CDCl
3
, 25
4

°
C, TMS, ppm): δ = 1.36 (s, 18 H, CH
3
of t-Bu), 1.38 (s,18 H, CH of t-Bu), 2.30 (s, 6H,
3
CH
3
of N(CH
3
)
2
), 2.42 (t, 2 H, J = 7.0 Hz, (CH
3
)
2
N-CH
2
), 2.57 (t, 2H, J = 7.0 Hz, N-
4
4
CH
2
), 3.81 (s, 4H, Ar-CH
2
), 6.94 (d, 2H, JHH = 2.0 Hz, aryl), 7.11 (d, 2H, JHH = 2.0 Hz,
1
3
aryl), 9.16 (s, 2H, OH). C NMR (62.19 MHz, CDCl
of t-Bu), 31.4 (CH of t-Bu), 34.5 (C of t-Bu), 35.2 (C of t-Bu), 45.5 (CH
), 54.4 (CH -N), 57.8 (CH -NMe ), 121.2, 122.7 (4CH of aromatic), 128.6,
3
, 25 °C, TMS, ppm): δ = 31.2 (CH
3
3
3
of N(CH ),
3 2
)
5
1
2
4.2 (2Ar-CH
2
2
2
2
-
5
-1
-1
36.5, 141.2, 154.8 (8C of aromatic). UV-Vis (5×10 M, CH
3
OH): λmax (ε, M cm ) =
16 (33 000), 279 nm (9 100).
2
.3. Synthesis of [Cr(bp)(N
The appropriate amount of ligand H
mmol) was dissolved in CH OH in the presence of CrCl
3
)(CH
3
OH)]·2CH
bp (0.524 g, 1 mmol) and NaN
·6H O (0.532 g, 2.00 mmol).
3
OH (1)
2
3
(0.13 g, 2.00
3
3
2
The solution was gently refluxed for 6 h. After cooling, the resulting solid was filtered
off, washed with cooled absolute ethanol and dried at 100 °C. Single crystals of
[
Cr(bp)(N
0.49 g). Anal. Calc. for C37
.29%. Found: C, 62.36; H, 9.35; N, 9.79; Cr, 7.32%. FT-IR (KBr, cm ): 3419 (OH, w,
br), 2955 (CH alif., s), 2924(s), 2854(w), 2063 (N , vs), 1634(m), 1599(m), 1478(m),
470(m), 1443(m), 1435(m), 1414(w), 1386(w), 1362(m), 1297(m), 1254(w), 1237(m),
165(w), 1094(w), 1018(m), 876(m), 838(w), 758(w), 747(w), 668(w), 553(w). UV-Vis
3
)(CH
3
OH)]·2CH
3
OH were obtained by thermal gradient method. Yield 70%
(
H66CrN
5
O
5
(MW = 712.95): C, 62.33; H, 9.33; N, 9.82; Cr,
-1
7
3
1
1
-5
-1
-1
(
2.5×10 M, CH
3
OH): λmax (ε, M cm ) = 216 (35 200), 279 nm (6 300).
5

2
.4. X-ray Crystallography
Data collection for X-ray structure determination was performed on a Kuma
KM4-CCD automated four-circle diffractometer with a Sapphire 2 CCD detector using
graphite monochromatized MoKα radiation (λ = 0.71073 Å) at 100(2) K (Oxford
Cryosystems cooler). Data collection, cell refinement, and data reduction and analysis
were carried out with CrysAlisCCD and CrysAlisRED, respectively [26]. Diffraction data
have been corrected for absorption effects by multi-scan [26]. The structure was solved
by direct methods using SHELXS-97 [27], and refined by a full-matrix least squares
2
technique on F with SHELXL-2013 [27]. All H atoms were found in difference Fourier
maps (except for those from disordered t-Bu group), and in the final refinement cycles
they were repositioned in their calculated positions and refined using a riding model, with
C—H = 0.95–0.99 Å and O—H = 0.84 Å, and with Uiso(H) = 1.2Ueq(CH, CH
2
) or
2
-
-
1
.5Ueq(O, CH
3
). One of the t-Bu groups of the bp ligand and N
3
anion were found to be
2
-
disordered, and were refined in two sites each, with s.o.f. = 0.757(9) and 0.243(9) for bp
-
,
and 0.579(14) and 0.421(14) for N
3
. In the refinement procedure of the disordered
regions, some geometrical restrains and constraints on the fractional coordinates and
anisotropic displacement parameters (SAME, EXYZ, EADP instructions in SHELXL-
2
013) were applied; for details see CIF file. All partially occupied atoms were refined
isotropically. The structure plots for complex 1 were prepared with DIAMOND [28]. The
crystal data and refinement parameters are presented in Table 1.
Table 1.
6

2
.5. Experimental set up for catalytic oxidation
Liquid phase catalytic oxidations of alcohols were carried out under air
(
atmospheric pressure) in a 25 mL round bottom flask equipped with a magnetic stirrer.
-3
In a typical experiment, H
2
2
O was added to a flask containing the catalyst (1.40 × 10
mmol) benzyl alcohol (1 mmol), and 1.0 mmol n-octane as internal standard in a solvent
3 mL). The course of the reaction was monitored by injection of 1 µL of reaction
(
mixture (picked from organic phase) to a gas chromatograph equipped with a capillary
column and a flame ionization detector. The oxidation products were identified by
comparing their retention times with those of authentic samples or alternatively by TLC,
1
H NMR and GC–Mass analyses. Control reactions were carried out in the absence of
catalyst, under the same conditions as the catalytic runs and indicated there was no
products in the absence of catalyst.
3
. Results and discussion
3
.1. Synthesis of ligand and Cr-complex (1)
The reaction of N,N-dimethylethane-1,2-diamine with 2,4-di-tert-butylphenol in
the presence of formaldehyde gave the desired tetradentate bis(phenolate) ligand, H
in excellent yield and purity (Scheme 1a). The formation of the ligand, H bp, has been
confirmed by NMR and infrared spectroscopy. In the IR spectrum of the ligand the bands
2
bp,
2
−
1
at 3188, 1592 and 1256 cm are due to O‒H, C=C and C‒Ophenolic stretches, respectively
[
29]. The elemental analysis is in good accordance with the proposed structure. The
2
-
Cr(III) complex of bp ligand was slowly formed by the reaction of H bp with
2
-
chromium(III) chloride in the presence of pseudohalide coligand (N
3
) in methanol
7

(
Scheme 1b). On complexation the shift of C‒Ophenolic and C‒N bands show coordination
of bp as tetradentate dianionic ligand. In the IR spectrum of
H
2
−
1
[
[
Cr(bp)(N
30], this band is observed as a new peak for the complex and is not present in the
bp
colorless) in methanol solutions are shown in Fig. S1. The bis(phenolate) ligand displays
3
)(CH
3
OH)]·2CH
3
OH (1) the strong band at 2055 cm is assigned to ν(N )
3
spectrum of the free ligand. The electronic spectra of complex 1 (green) and H
2
(
two absorption bands at 216 and 279 nm. Based on their extinction coefficients they are
assigned to π → π* and n → π* transitions, respectively. The electronic spectrum of the
complex is very similar to the spectrum of the ligand and the absorption bands are
attributed to the intraligand π → π* (216 nm) and n → π* (279 nm) transitions. A little
difference in shape of spectrum indicates the coordination of the ligand to the Cr(III) ion.
3
.2. X-ray structure of complex [Cr(bp)(N
3
)(CH
The Cr-complex of the bp ligand crystallizes as a methanol disolvate,
Cr(bp)(N )(CH OH)]·2CH OH (1). The crystal structure of 1 determined by X-ray
3 3
OH)]·2CH OH (1)
2
-
[
3
3
3
analysis is shown in Fig. 1, and selected bond lengths and bonding angles are tabulated in
Table 2. X-ray analysis of 1 reveals that this compound is a neutral mononuclear complex
of Cr(III). The coordination environment around the Cr(III) center is best described as a
distorted octahedral mer-[CrO
3
3
N ], formed by two nitrogen atoms and two oxygen atoms
provided by the bis(phenolate) ligand, one nitrogen atom from the azide co-ligand and an
oxygen atom from coordinated methanol molecule. In complex 1, two phenolate donor
atoms provided by bis(phenolate) ligand are located in a trans mode towards each other.
The N1 atom and two phenolate oxygen atoms, together with the nitrogen atom of azide
8

ligand form the basal plane. The methanol oxygen atom occupies an axial position at a
distance of 2.029(3) Å. Remaining axial position in the complex is occupied by nitrogen
atom of N,N-dimethyl moiety, with the length of Cr1–N2 bond equal to 2.140(4) Å. In
complex 1 the azide ligand show asymmetric N–N distances (N3–N4/N4–N5) of
1
.207(6)/1.162(7) Å and the N3–N4–N5 angle is 177.3(12)º, which is typical shape of the
azide ligand [31]. There are some strong and directed hydrogen bonding in the crystal
lattice of the complex. Uncoordinated methanol molecules are tightly linked with the
complex molecules via both O–H···O and O–H···π contacts, as shown in Fig. S2 and
Table S1.
Fig. 1.
Table 2.
3
3
.3. Catalytic activity studies
.3.1. Oxidation of benzyl alcohol
The catalytic activity of complex 1 was tested in the oxidation of alcohols
(
Scheme 2). The catalytic oxidation of benzyl alcohol as a representative substrate with
hydrogen peroxide was studied in the presence of complex 1. Aqueous hydrogen
peroxide (30%) was selected as oxidant by considering its high selectivity, atom
economy, and environmentally benign properties. The results of control experiments
revealed that the presence of catalyst and oxidant (H
2
2
O ) is essential for the oxidation. To
achieve the maximum oxidation of alcohols the effective parameters for suitable reaction
conditions such as the oxidant concentration (moles of oxidant per moles of substrate),
solvent, and temperature of the reaction were investigated. Results of the studies are
summarized in Table 3. In all these reactions benzyl alcohol gave the benzaldehyde with
9

1
00% selectivity by catalyst and there was not any other product. The effect of oxidant
concentration on the oxidation of alcohols by complex 1 is illustrated in Fig. 2. Different
oxidant/substrate molar ratios (1:1, 2:1, 3:1 and 4:1) were considered while the ratio of
benzyl alcohol (1.0 mmol) to catalyst (1.4 µmol, 0.001 g) in 3 mL of acetonitrile was
constant. The conversion of benzyl alcohol increased with increasing the amount of
hydrogen peroxide in the reaction mixture. When H
maximum conversion of 76% was obtained at 60±1 °C. In order to find the effect of
reaction atmosphere on catalytic activity of complex, this reaction was repeated in N
2
O
2
/substrate molar ratio was 3:1, the
2
atmosphere. The result of this reaction was same with result of air atmosphere which
indicates the atmospheric oxygen has not effect on catalytic reactivity of complex 1.
In order to get the best reaction temperature, oxidation of alcohols was studied at
2
5 (room temperature), 40, 60, and 80 °C and the results are shown in Fig. 3. At room
temperature the oxidation of benzyl alcohol was very low. Increasing the reaction
temperature from 25 to 80 °C increased the conversion of benzyl alcohol and maximum
conversion was obtained as 92% after 5 hours. Fig. 4 illustrates the influence of the
solvent nature in the catalytic oxidation of benzyl alcohol. Acetonitrile, acetone, toluene,
dichloromethane, chloroform, DMSO, THF and ethyl acetate were used as solvents. It
was observed that the catalytic activity of the catalyst decreased with respect to
acetonitrile > acetone > THF > dichloromethane > chloroform > toluene > ethyl acetate >
DMSO. Overall, the reactivity of catalyst in other solvents was very much lower than in
acetonitrile.
Scheme 2.
Fig. 2.
1
0

Fig. 3.
Table 3.
Fig. 4.
3
.3.2. Oxidation of various primary alcohols
In order to explore further the oxidation potential of the complex 1, oxidation of various
primary alcohols was performed under the same reaction conditions which proved to be
the best for benzyl alcohol. The effect of substituents and nature of aromatic rings on
alcohol oxidation was studied. The results are shown in Table 4 and indicate this catalytic
system led to the oxidation of different primary alcohols to corresponding aldehydes with
1
00% selectivity. It seems that efficiency of oxidation in this catalytic system is
dependent on the electronic and steric demands of the substrate. It was observed that the
presence of electron-donating (–OMe, –OH) group on the para-position of benzyl alcohol
enhanced the conversion in comparison with molecule having no substituent on the ring
(
entries 1, 2 and 3). In addition, electron-withdrawing –Cl and especially –NO groups on
2
the phenyl ring decelerated the oxidation reaction (entries 4 and 5). The influence of
steric factors in this catalytic system is also notable. The lower conversion of ortho-
substituted alcohols such as 2-Cl- and 2-NO -benzyl alcohol (entries 7 and 8) in
2
comparison with the corresponding non-hindered alcohols at similar reaction times may
be related to the steric hindrance at vicinity of the active Cr center. It is to note that the
oxidation of 2-hydroxy-benzyl alcohol is same with 4-hydroxy-benzyl alcohol (entries 2
and 6) and this may be due to formation of hydrogen bonds through phenolic O–H in
ortho position respect to the alcoholic group of the substrate and this may help to
approach the substrate near to the Cr-center.
1
1

Table 4.
3
.3.2. Possible mechanism of the catalytic reaction
It was observed that the mixed ligand complexes of Cr(III) generate Cr(V)=O
c-e
intermediate with a variety of oxidants [19 ,32]. Several studies have been reported that
the oxido-chromium(V) complexes probably are intermediates in oxidation reactions of
c-e
various organic substrates catalyzed by Cr(III) complexes [19 ,32,33]. The Cr(V)=O
species are capable intermediates for efficient oxidizing of organic substrates. The initial
solution of this catalytic system is light green in color. When H
2
2
O was added to the
solution, the color slowly changed to blue. This phenomenon expresses the interaction of
peroxido group with Cr(III) center and the presence of strong charge transfer transition in
new product. At higher temperatures this change is much faster than at room temperature.
The observed change maybe is due to the generation of oxido-chromium(V) species.
In general the total mechanism of the reaction is not fully clear. However, on the basis
of the changes in color of reaction mixture and reported mechanisms for oxidation
c-e
reactions catalyzed by Cr(III) complexes [19 ,32,33], it is predicted that the key step in
this process is the oxidation of alcohols by oxido-chromium(V) species formed in the
presence of hydrogen peroxide. The proposed catalytic pathway is shown in Scheme 3. A
similar mechanism has been reported for the catalytic oxidation of benzyl alcohol with
heterogenised Cr(III) complexes of salen ligands [34].
Scheme 3.
4
. Conclusion
A new chromium(III) complex of tetradentate bis(phenolate) ligand was synthesized
and characterized by spectroscopic and single crystal X-ray analyses. The catalytic ability
1
2

of this complex was investigated by using the environmentally benign and clean oxidant
for oxidation of primary alcohols. The effects of various parameters including the
H
2
O
2
molar ratio of the oxidant to substrate, the temperature, and the solvent have been studied
and the optimized conditions were obtained. This complex is selective and active catalyst
for oxidation of primary alcohols to corresponding aldehydes. The presence of electron-
withdrawing and electron-donating groups on the phenyl ring of benzyl alcohol in the
reactivity of catalysts was investigated. Excellent conversions were obtained for the
oxidation of alcohols containing electron-donating groups on para-position.
Acknowledgements
We acknowledge the University of Zanjan for funding this research work.
Appendix A. Supplementary material
CCDC 963747 contains the supplementary crystallographic data for 1. This data can
be obtained free of charge from The Cambridge Crystallographic Data Centre via
www.ccdc.cam.ac.uk/data_request/cif.
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Scheme/ Figures/ Tables caption
Scheme 1. Synthesis of a) bis(phenolate) ligand, H bp, and b) complex (1)
2
Scheme 2. Catalytic Oxidation of alcohols in the presence of Cr(III) complex
Scheme 3. Proposed mechanism for catalytic oxidation of alcohols using complex 1 in
the presence of H
2
O
2
Fig. 1. The X-ray structure of the complex molecule Cr(bp)(N
3
)(CH OH) present in
3
-
[
Cr(bp)(N
3
)(CH
3
OH)]·2CH
3
OH (1). The disorder in t-Bu and N
3
, as well as the solvent
molecules are omitted for clarity. Displacement ellipsoids are drawn at the 30%
probability level. Not fully-occupied atoms are shown as spheres of arbitrary radii
Fig. 2. Effect of H
2
2
O concentration on the oxidation of benzyl alcohol by 1. Reaction
conditions: Catalyst, complex 1, 1.40 µmol (0.001 g); CH CN, 3 mL; n-octane, 1.0
3
mmol; benzyl alcohol, 1 mmol; temperature, 60±1 °C
Fig. 3. Effect of the reaction temperature on the oxidation of benzyl alcohol by 1.
Reaction conditions: Catalyst, complex 1, 1.40 µmol (0.001 g); CH CN, 3 mL; n-octane,
.0 mmol; benzyl alcohol, 1 mmol; H , 3 mmol
3
1
2
O
2
Fig. 4. Effects of the solvents on the oxidation of benzyl alcohol by 1. Reaction
conditions: Catalyst, complex 1, 1.40 µmol (0.001 g); solvent, 3 mL; n-octane, 1.0 mmol;
benzyl alcohol, 1 mmol; H
2
2
O , 3 mmol; temperature, 80±1 °C
Table 1. Crystallographic data of 1
Table 2. Selected bond lengths (Å) and angles (°) in complex 1
1
7

Table 3. Comparison the catalytic activities of catalysts 1 in the oxidation of benzyl
alcohol with hydrogen peroxide in different conditions
Table 4. Oxidation of various primary alcohols with complex 1
Scheme 1.
Scheme 2.
1
8

Scheme 3.
Fig. 1.
1
9

Fig. 2.
Fig. 3.
2
0

Fig. 4.
Table 1. Crystallographic data of 1
2
1

CCDC No.
Formula
963747
C
37
H66CrN
O
5 5
−1
r
M /g mol
712.94
Crystal size/mm
Crystal shape, color
T/K
0.35 × 0.16 × 0.09
Block, green
100(2)
Radiation
Crystal system, space group
MoKα (λ = 0.71073 Å)
Monoclinic, C2/c
31.189(9)
10.584(4)
24.920(8)
103.04(3)
8014(5)
8
a/Å
b/Å
c/Å
β/° 3
V/Å
Z
−3
Calc. density/g cm
1.182
F(000)
µ/mm
3096
0.33
−
1
Absorption correction
Empirical (multi-scan)
0.620/1.000
16987
T
min/Tmax
Measured reflections
R
int
0.115
h, k, l
Θ range
Independent reflections
Observed reflections
Data/Parameters/Restraints
−38→29, −13→9, −30→30
2.82–26.00
7678
3737
7678/447/9
a)
R1(Fobs2
)
0.085
0.207
a)
wR2(F )
GooF = S
Shift/errormax
1.00
0.000
0.62/−0.81
−
3
∆
ρmax/∆ρmin /e Å
a
2
2
c
2
2 2
o
)
R1 = ∑ Fo − Fc /∑ F ; wR2 = ∑[w(Fo − F ) ]/∑[w(F ) ] ; Detailed information on
o
the weighting scheme (w) is given in the crystallographic information file (CIF).
Table 2. Selected bond lengths (Å) and angles (°) in complex 1
Bond
Å
Angle
°
Cr1–O2
Cr1–O1
Cr1–N3
Cr1–O1M
1.939(3)
1.949(4)
2.022(5)
2.029(3)
O1–Cr1–O1M
N3–Cr1–O1M
O2–Cr1–N1
O1–Cr1–N1
86.71(14)
94.26(17)
90.02(15)
92.40(15)
2
2

Cr1–N1
Cr1–N2
N3–N4
N4–N5
2.081(4)
2.140(4)
1.207(6)
1.162(7)
°
170.97(14)
88.23(16)
90.36(17)
84.50(14)
N3–Cr1–N1
O1M–Cr1–N1
O2–Cr1–N2
O1–Cr1–N2
N3–Cr1–N2
O1M–Cr1–N2
N1–Cr1–N2
N4–N3–Cr1
N3–N4–N5
172.98(17)
92.33(15)
95.95(15)
92.98(15)
90.52(17)
175.21(17)
82.90(16)
134.0(5)
Angle
O1–Cr1–O2
O2–Cr1–N3
O1–Cr1–N3
O2–Cr1–O1M
177.3(12)
Table 3. Comparison the catalytic activities of catalysts 1 in the oxidation of benzyl
alcohol with hydrogen peroxide in different conditions
-
1
Entry Catalyst
H
2
O
2
Solvent
Temp. Yield Selectivity
TOF(h )
a
mmol)
(°C)
(%)
1
2
3
4
5
6
7
8
9
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
2
3
4
3
3
3
3
3
3
3
3
3
3
CH
CH
CH
CH
CH
CH
CH
(CH
Toluene
CHCl
CH Cl
THF
3
CN
CN
CN
CN
CN
CN
CN
60
60
60
60
25
40
80
80
80
80
80
80
80
80
27
45
76
67
22
42
92
75
39
48
50
62
24
3
100
100
100
100
100
100
100
100
100
100
100
100
100
100
39
64
109
96
31
60
131
107
56
67
71
89
34
4
3
3
3
3
3
3
3 2
) CO
0
1
2
3
4
3
2
2
EtOAc
DMSO
Reaction conditions: catalyst, 1.40 µmol; benzyl alcohol, 1 mmol; n-octane, 1.0 mmol; solvent, 3 mL; time,
5
hours
a
Yields are based on the starting benzyl alcohol
2
3

Table 4. Oxidation of various primary alcohols with complex 1
-
1
Entry Substrate
Product
Yield (Selectivity)
TON (TOF/h )
2
4

1
98 (100)
700(140)
2
3
96 (100)
92 (100)
686 (137)
657 (131)
4
90 (100)
643 (129)
5
6
86 (100)
96 (100)
614 (123)
686 (137)
7
85 (100)
607 (121)
8
76 (100)
543 (109)
2 2
Reaction conditions: catalyst, 1.40 µmol; substrate, 1 mmol; H O , 3 mmol; n-octane, 1.0 mmol; solvent,
CH CN, 3 mL; time, 5 h, temperature, 80±1 °C
3
Graphical abstract
Synthesis, characterization and catalytic activity of new
Cr(III) complex in oxidation of primary alcohols to
aldehydes
2
5

a,34
a
b
a
Nader Noshiranzadeh,
b
and Tadeusz Lis
Rahman Bikas, Katarzyna Ślepokura, Mina Mayeli,
Graphical abstract
Synthesis, characterization and catalytic activity of new
Cr(III) complex in oxidation of primary alcohols to
aldehydes
a,34
a
b
a
Nader Noshiranzadeh,
b
and Tadeusz Lis
Rahman Bikas, Katarzyna Ślepokura, Mina Mayeli,
ꢀ
ꢀ
ꢀ
ꢀ
ꢀ
New method for oxidation of primary alcohols to corresponding aldehydes
Synthesis and structure of a new Cr(III) complex with bis(phenolate) ligand
Catalytic behavior of the Cr(III) complex in oxidation of primary alcohols
The effects of various parameters in oxidation of primary alcohols were studied
Excellent conversions were obtained for benzyl alcohols containing electron-
donating groups
2
6