Efficient and selective oxidation of primary and secondary alcohols using an iron(III)/phenanthroline complex: Structural studies and catalytic activity

Article abstract of DOI:10.1002/ejic.201200658

An efficient catalytic system for the oxidation of alcohols has been developed by using iron(III) catalyst [Fe(phen)₂Cl ₂]NO₃ (1) (phen = 1,10-phenanthroline) and H ₂O₂ as terminal oxidant. A series of primary and secondary alcohols were oxidized into aldehydes and ketones in good yields and excellent selectivities after a short reaction time. The mononuclear iron(III) complex [Fe(phen)₂Cl₂]NO₃ was characterized by several independent methods. The X-ray structure shows distorted octahedral geometry around the Fe^III center, which is in a high-spin state (S = 5/2) according to Moessbauer study. Copyright

Full text of DOI:10.1002/ejic.201200658

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DOI: 10.1002/ejic.201200658
Efficient and Selective Oxidation of Primary and Secondary Alcohols Using an
Iron(III)/Phenanthroline Complex: Structural Studies and Catalytic Activity
Bhaskar Biswas,*[a] Afnan Al-Hunaiti,*[b] Minna T. Räisänen,[b] Simone Ansalone,[b]
Markku Leskelä,[b] Timo Repo,*[b] Yen-Tung Chen,[c] Hui-Lien Tsai,[c] Anil D. Naik,[d]
Antoine P. Railliet,[d] Yann Garcia,[d] Rajarshi Ghosh,*[e] and Niranjan Kole*[a]
Keywords: Homogeneous catalysis / Oxidation / Iron / Alcohols / Ketones
An efficient catalytic system for the oxidation of alcohols has
been developed by using iron(III) catalyst [Fe(phen)2Cl2]NO3
(1) (phen = 1,10-phenanthroline) and H2O2 as terminal oxi-
dant. A series of primary and secondary alcohols were oxid-
ized into aldehydes and ketones in good yields and excellent
selectivities after a short reaction time. The mononuclear
iron(III) complex [Fe(phen)2Cl2]NO3 was characterized by
several independent methods. The X-ray structure shows
distorted octahedral geometry around the FeIII center, which
is in a high-spin state (S = 5/2) according to Mössbauer study.
ylation,[11d,13] and oxidation of arenes to phenols.[14] In ge-
neral, chemoselectivity is the key issue for these reactions
due to potential nonselective Fenton- or Gif-type chemis-
try.[15] Although alcohol oxidations catalyzed by iron com-
plexes have been investigated in many systems,[15d,15f,16] no
general method has been discovered so far and improve-
ments that use clean and safe oxidation procedure are still
needed. Thus a catalytic system with iron metal holds a
promising future with regards to sustainability and selective
transformations.
Polypyridine derivatives, such as 2,2Ј-bipyridine (bpy),
1,10-phenanthroline (phen), and 2,2Ј:6Ј,2ЈЈ-terpyridine
(tpy), have attracted substantial interest in recent years.[17]
1,10-Phenanthroline ligands have been extensively utilized
for the complexation of metal cations, particularly those of
the d and f blocks. For the structure–reactivity correlation
and the investigation of the mechanistic pathway, the chem-
istry of Fe–phenanthroline-catalyzed oxidations was exten-
sively studied in the nineteenth century.[18–21]
Introduction
The selective oxidation of alcohols remains an important
transformation for organic synthesis and the chemical in-
dustry.[1] Numerous catalytic systems that use transition
metals such as Co,[2] Mn,[3] Au,[4] Cu,[5] Mo,[6] Ru,[7] and
Pd[8] have been reported. However, most of these systems
suffer from high reagent load, harsh reaction conditions,
high cost, toxicity of the metal, or they form unwanted
waste. From both environmental and economic points of
view, the search for effective catalytic oxidation processes
that use clean, inexpensive terminal oxidants, such as mo-
lecular oxygen or hydrogen peroxide, is highly attractive.[9]
Iron is a cheap and less toxic metal; iron and hydrogen per-
oxide together is an ideal green combination because water
is the only byproduct formed in this transformation.[10] Re-
cently, iron has become broadly used in many oxidation
processes such as epoxidation,[11] sulfoxidation,[12] hydrox-
[a] Department of Chemistry, Raghunathpur College,
Sidho-Kanho-Birsha University,
Herein, we present a novel catalytic system for the ef-
ficient oxidation of primary and secondary aliphatic
alcohols. The system is based on a synthesized iron(III)
complex [Fe(phen)2Cl2]NO3 (1) and uses H2O2 as terminal
oxidant and aqueous solution as solvent. The synthesis,
crystal structure, and UV/Vis, IR, and Mössbauer spec-
troscopy studies of the complex are also reported.
Purulia 723133, India
Fax: +91-3251-255235
E-mail: mr.bbiswas@rediffmail.com
Homepage: http://www.raghunathpurcollege.in/
[b] Department of Chemistry, Laboratory of Inorganic Chemistry,
University of Helsinki,
00014 Helsinki, Finland
Homepage: http://www.helsinki.fi/kemia/epaorgaaninen
[c] Department of Chemistry, National Cheng Kung University,
Tainan City, 70101, Taiwan
[d] Institute of Condensed Matter and Nanosciences (IMCN),
MOST – Inorganic Chemistry, Université Catholique de
Louvain,
Results and Discussion
1348 Louvain-la-Neuve, Belgium
[e] Department of Chemistry, The University of Burdwan,
Burdwan 713104, India
Synthesis of [Fe(phen)2Cl2]NO3 (1)
Homepage: http://www.buruniv.ac.in/EmployeeProfile.
php?emp_id=2420
Complex 1 was synthesized by adding 1,10-phenanthrol-
ine into a solution of FeCl3 in acetic acid and water (60:40
v/v). Ammonium ceric nitrate (CAN) was added into the
Supporting information for this article is available on the
WWW under http://dx.doi.org/10.1002/ejic.201200658.
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reaction mixture to maintain the FeIII oxidation state. Com- respectively, were found for the ferrous complex
pound 1 was isolated in good yield (80%) as red crystals. [Fe(phen)2Cl2][FeCl4], which indicates a high-spin (HS)
The complex is sufficiently stable in air and in the presence state.[22]
of moisture. It is soluble in almost all solvents such as meth-
anol, ethanol, dichloromethane, acetonitrile, dimethylform-
amide, and dimethyl sulfoxide. The synthetic procedure is
summarized in Scheme 1.
Figure 1. An ORTEP of [Fe(phen)2Cl2]NO3 (1) with atom-number-
ing scheme and 30% probability ellipsoids for all non-hydrogen
atoms.
Scheme 1.
Description of the Crystal Structure
Table 1. Selected bond lengths [Å] and angles [°] for 1.
Structural analysis reveals that the crystal lattice of 1
consists of a mononuclear [Fe(phen)2(Cl)2]NO3 unit. An
Oak Ridge thermal ellipsoid plot (ORTEP) with an atom
numbering scheme of 1 is shown in Figure 1. Bond lengths
and angles relevant to the coordination sphere around FeIII
are listed in Table 1. The coordination polyhedron around
each FeIII is best described as a distorted octahedron with
an N4Cl2 core. The distortion from the ideal octahedral
geometry is due to the different bite angles of nitrogen
atoms of phen units and the deviation of the refined angles
(90/180°) at the metal centers (Table 1). The coordination
includes two chelated symmetrical bidentate ligated by four
N atoms along with two coordinated Cl atoms in mutual
cis orientation in 1. The angle 97.36(4)° between the two
coordinated chlorine atoms around the FeIII center as Cl2–
Bond lengths
Fe1–N1
Fe1–N2
Fe1–N2*
2.175(3)
2.132(3)
2.132(3)
Fe1–N1*
Fe1–Cl2
Fe1–Cl2*
2.175(3)
2.2683(10)
2.2683(10)
Bond angles
N1–Fe1–N2
76.72(10)
84.82(10)
90.29(10)
89.33(7)
170.63(7)
170.63(7)
97.36(4)
95.49(8)
N1–Fe1–N2*
N2–Fe1–N2*
N1*–Fe1–N2*
Cl2–Fe1–N2
Cl2–Fe1–N2*
Cl2*–Fe1–N2
Cl2*–Fe1–N1*
90.29(10)
162.50(11)
76.72(10)
95.49(7)
96.04(8)
96.04(8)
89.33(7)
N1–Fe1–N1*
N1*–Fe1–N2
Cl2–Fe1–N1
Cl2–Fe1–N1*
Cl2*–Fe1–N1
Cl2–Fe1–Cl2*
Cl2*–Fe1–N2*
Intermolecular C–H···O, intermolecular C–H···Cl hydro-
Fe1–Cl2* indicates the cisoid representation of the struc- gen bonds, and π···π interactions in 1 consolidate the inter-
ture. The Fe–N/Cl bond lengths range from 2.132(3) to locking between adjacent molecular moieties to result in 3D
2.2683(10) Å, and the difference Δ between the longest and supramolecular structures (Figure 2). The relevant non-
shortest Fe–N/Cl bonds is 0.1363 Å. Comparative values of covalent forces and the parameters are shown in Table S1
Fe–N and Fe–Cl bond lengths of 2.250(11) and 2.246(4) Å, in the Supporting Information.
Figure 2. Projection of the crystal packing showing a supramolecular network of monomeric units of 1.
2
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Efficient and Selective Oxidation of Alcohols
UV/Vis and IR Spectroscopic Studies of 1
Table 2. Oxidation of benzyl alcohol: optimization of the catalytic
system.[a]
UV/Vis spectroscopic studies of 1 were performed with a
pink methanolic solution (10–4 m). In the spectrum, initially
there are two bands that appear at 231 and 259 nm with
high absorbance values. This indicates the presence of
nǞπ* and πǞπ* transitions for the C=N chromophore
of the phen moiety coordinated to FeIII. Although FeIII is
a 3d5 system, the intense pink color of the solution is due
to charge-transfer absorption. After initial measurements,
the solution was kept for a few weeks with gradual color
changes from pink to red, and then to intense red. Simulta-
neously, a band at 508 nm with maximum absorbance (2.12)
appeared. The UV/Vis measurement was taken over a 3 h
period with an increase in the absorbance at 508 nm band
that indicates the presence of FeII in solution (Figure 3).
Entry Solvent
Oxidant 2/3[b] ratio
% Conv.[c]
1
2
MeCN
toluene
TBHP
TBHP
TBHP
O2
O2
O2
H2O2
H2O2
H2O2
H2O2
H2O2
TBHP
O2
10:1.0
10:1.2
10:1.4
10:1.6
10:3.0
10:1.0
10:1.5
10:2.8
10:0.1
10:2
88
41
60
8
13
24
65
72
98
90
60
90.1
16
3
4
alkaline water
MeCN
5
6
7
toluene
alkaline water
MeCN
8
9
10
11
12
13
MeCN/acetic acid
buffer (pH = 1)
buffer (pH = 2)
buffer (pH = 4)
buffer (pH = 1)
buffer (pH = 1)
10:2.9
2.5:10
10:1
[a] Reaction conditions: see the Exp. Section. [b] Chemoselectivity
ratio (see Scheme 2). [c] Conversion and yield were determined by
GC analysis; average of two runs.
Scheme 2.
It has recently been reported that a carefully pH-con-
trolled solution of iron-based oxidation catalyst enhances
the selectivity.[11a,11b] Similarly, when we used acidic buffer
solution (pH = 1) as a solvent, both conversion and selectiv-
ity increased to 98 and 99%, respectively (Table 2, entry 9).
Changing the pH value from 1 to 2 and 4 (Table 2, entries
10 and 11) resulted in lower selectivity as the amount of
acid increased. These results are in agreement with previous
work.[24,25] A maximum in the oxidation rate is observed at
a pH that corresponds to the lowest H2O2 decomposition
rate.[26,27] Moreover, this pH range corresponds to the high-
est stability zone of the soluble FeIII(OH)+2 complex.[26,27]
By decreasing the pH (more acidic media), the concentra-
tion of stable ferric ions (Fe+3) increases at the expense of
the concentration of the Fe+2 species,[28] whereas by increas-
ing the pH (more basic media) the insoluble ferric hydrox-
ides precipitate.
Figure 3. UV/Vis spectrum of the iron compound (1Ǟ4 indicates
successive absorption bands of iron compound in methanol after
30 min interval; inset: absorption bands in the visible region).
In IR spectrum of 1, a sharp and intense band at
1384 cm–1, indicates the presence of ionic nitrate.[23] The
υ(C=N) stretching vibrations of phen bound to metal ion
are seen at 1517 (s) and 1426 (s) cm–1. All other characteris-
tic ligand vibrations are in the 1600–600 cm–1 region.
Next, we investigated the concentration effect of the oxi-
dant. Here, the hydrogen peroxide addition rate as well as
the total amount of oxidant was varied. The best results
were obtained by employing 2.0 equiv. of H2O2, which were
added to the reaction mixture within 10 min (89% conver-
Alcohol Oxidation Experiments
The synthesized catalyst was tested for alcohol oxidation sion, 75% yield).
by using benzyl alcohol as a model substrate (Table 2,
The efficiency of the catalyst was studied by using struc-
Scheme 2). We first investigated the effect of oxidants and turally diverse secondary and primary alcohols under the
then solvents. The desired benzaldehyde was only obtained optimized reaction conditions. As Table 3 shows, α,β-unsat-
in moderate to high conversion and selectivity in the pres- urated primary alcohols, such as allylic and benzylic
ence of tert-butyl hydroperoxide (TBHP) as oxidant (88, 41, alcohols, can be selectively oxidized to the corresponding
and 60%, respectively; Table 2, entries 1–3). Molecular oxy- aldehydes in excellent yields. Similarly, α,β-saturated pri-
gen showed no reactivity under the same reaction condi- mary alcohols such as 1-octanol and 1-undecanol produced
tions, whereas H2O2 demonstrated an improvement in the their corresponding aldehyde in moderate yield (52–56%;
conversion with moderate selectivity (Table 2, entries 7–9).
Table 3, entries 1–3). The capability of the catalyst to oxid-
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ize primary aliphatic alcohols into carbonyl products in Table 3. Oxidation of various alcohols into aldehydes and
ketones.[a]
very good yield is worth noting. Following the success of
oxidizing primary alcohols selectively, we tested the reac-
tion of secondary alcohols. Secondary aliphatic alcohols
were oxidized selectively to the corresponding ketones in
excellent yields (70–100%; Table 3, entries 4–9). Not only
α,β-unsaturated secondary alcohols, such as phenyl prop-
anol (95%; Table 3, entry 4) and 1-phenylethanol (96%
yield, 99% selectivity; Table 3, entry 10) were easily con-
verted but also sterically demanding secondary alcohols,
such as those in entries 6 and 7 in Table 3, were converted
to a moderate degree.
The catalyst displays an interesting regioselectivity for a
vicinal diol such as 1-phenyl-1-ethanediol. Only the second-
ary hydroxy group is oxidized, which leaves the primary
alcohol function intact (Table 3, entry 12). 2-Hydroxyace-
tophenone was observed as the main product (75%), and
only a small amount of mandelic acid (15%) was obtained.
Also, 2-thiophenemethanol (entry 13) was smoothly oxid-
ized to the corresponding acid with high conversion and
selectivity. In general, it is considered to be a difficult sub-
strate for most oxidation systems that involve transition
metals because of their strong coordination ability with the
sulfide group. It is worth noting that the sulfide group that
is susceptible to oxidation remained here unreacted.
Next we investigated the oxidation of allylic alcohols by
testing the reactivity of cinnamyl alcohol (Table 3, entry
10). By using the standard conditions (3 mol-% of catalyst,
2.2 equiv. of H2O2, 60 min), we obtained a high conversion
(91%) but a moderate selectivity (83%) to cinnamaldehyde.
To understand the mechanism of our system, we per-
formed a concentration/time graph for the oxidation of the
benzyl alcohol (see the Supporting Information). After ad-
dition of the oxidant, the formation of benzaldehyde started
immediately. Then a linear consumption of benzyl alcohol
occurred, followed by formation of aldehyde. After 10 min
of reaction time, some degradation was observed with lower
selectivity. However, potential side products such as benzoic
acid were detected with low concentration. Next, we per-
formed additional reactions by using a radical inhibitor
[i.e., (2,2,6,6-tetramethylpiperidinyl)-N-oxyl (TEMPO)] to
exclude a radical pathway. In the presence of TEMPO
(1 equiv.), we observed a higher influence on the reactivity.
Here, benzaldehyde is obtained in 42% yield with 99%
selectivity. However, TEMPO is a well-known ligand in
iron-catalyzed oxidations.[9a,9e] Hence, we postulate that the
decrease in reactivity is due to a change in the iron complex
rather than an inactivation of radical species. In summary,
under our experimental conditions, the oxidation of
alcohols should not be induced by a Fenton free-radical
diffusion pathway.
[a] Reaction conditions: see the Exp. Section. [b] Conversion and
yield were determined by GC–MS (using decane as internal stan-
dard) and H NMR spectroscopy; average of two runs. [c] Chemo-
1
selectivity. [d] Isolated yield.
We performed ESI-MS measurements to obtain more in- peak at m/z 378.09 that corresponded to [Fe(phen)(benzyl
sights into the molecular nature of the active catalyst and alcohol)Cl] confirms the coordination of the substrate to
its precursors. The spectrum of a freshly prepared complex the complex. Although the experiment was repeated twice,
1 in acetonitrile showed in positive-ion mode a peak of m/z we could not detect H2O2 coordination. It is worth noting
486.0096 that corresponded to [Fe(phen)2Cl2]. Then, we that the oxidation of alcohols to the corresponding carb-
subjected a sample of the reaction mixture after 15 min of onyl compounds is known to take place by high-valent
reaction to ESI-MS measurements. The appearance of a metal complexes.[1a,29] Therefore, alcohol oxidation with
4
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Efficient and Selective Oxidation of Alcohols
this system could be achieved by means of high-valent iron
species. However, further studies of this mechanism are on-
going.
Experimental Section
General: All solvents and chemicals are commercially available and
were used as received or synthesized according to procedures in the
literature. Aqueous H2O2 (30%) from Sigma–Aldrich was used as
received. NMR spectra were measured with a Variant 300 spec-
trometer at 300 MHz (1H) and 75 MHz (13C). All spectra were re-
corded in CDCl3 or [D6]DMSO, and chemical shifts (δ) are re-
ported in ppm relative to tetramethylsilane referenced to the resid-
ual solvent peaks. Spectra were measured at room temperature.
High-resolution mass spectrometry experiments (ESI) were per-
formed with a time-of flight mass spectrometer equipped with an
electrospray ion source (Bruker microTOF). All analyses were car-
ried out in a positive-ion mode. The sample solutions were intro-
duced by continuous infusion with the aid of a syringe pump at a
flow rate of 180 μLmin–1. The instrument was operated at end plate
offset –500 V and capillary –4500 V. Nebulizer pressure was 0.8 bar
(N2), and the drying gas (N2) flow was 7 Lmin–1. Capillary exit
and skimmer 1 were 90 and 30 V, respectively. Sodium formate was
used for mass calibration for a calibration range of m/z 100–2000.
Drying gas temperature was set to 220 °C. Elemental analyses (car-
bon, hydrogen, and nitrogen) were performed with a Perkin–Elmer
2400 CHNS/O elemental analyzer. IR spectrum was recorded (KBr
discs, 4000–300 cm–1) with a Perkin–Elmer RX1 FTIR spectrome-
ter. Ground-state absorption was measured with a JASCO V-530
UV/Vis spectrophotometer. The software used for the simulations
was Bruker Daltonics Data Analysis (version 3.3) Reaction prod-
ucts were isolated and analyzed quantitatively by means of GC
(Agilent 6890 chromatograph, Agilent 19091 J-413 capillary col-
umn 0.32 mmϫ30 mϫ0.25 mm, FID detector) using decane as in-
ternal standard. Products were identified by GC–MS analyses
(Agilent 6890N equipped with Agilent 5973 mass selective
detector) and DB-innowax 19091 l-102 capillary columns
(200 mmϫ24 mϫ0.31 mm). 57Fe Mössbauer spectra were re-
corded in transmission geometry with a constant acceleration mode
conventional spectrometer equipped with a 20 mCi 57Co(Rh)
source and a Reuter Stokes proportional counter. The sample was
sealed in aluminum foil and spectra were recorded at room tem-
perature and 77 K with a liquid nitrogen cryostat Optistat DN from
Oxford instruments. The spectra were fitted with Recoil 1.05 Möss-
bauer Analysis software.[33] The isomer shift values are given with
respect to α-Fe at room temperature.
57Fe Mössbauer Spectroscopy
Mössbauer spectra of 1 were recorded at variable tem-
peratures over the temperature range 300–77 K with a rela-
tively high maximum Doppler velocity (Figure 4). Spectra
could be fitted to one singlet with isomer shift δ =
0.36(1) mms–1 at 77 K, which is typical for an iron(III) ion
in the HS state, S = 5/2. No spin-state crossover and no
ordered phase was observed over the range of investigated
temperatures and velocities. This measurement thus con-
firms the success of our synthesis without coprecipitation
of the reduced complex [Fe(phen)2Cl2] by comparison of its
hyperfine parameters at 77 K (δ = 1.02 mms–1 and ΔEQ
=
3.15 mms–1), which are typical of a ferrous material.[30] Co-
precipitation of the starting salt can also be excluded (δ =
0.53 mms–1).[31] This result is in agreement with the crystal
structure, which reveals only one iron site. It is worth noting
that the Mössbauer parameters of 1 compare well with the
isomer shift of the ferric complex [Fe(phen)2Cl2]ClO4 re-
corded at 80 K (δ = 0.39 mms–1).[32]
Synthesis: Mononuclear complex [Fe(phen)2Cl2]NO3 (1) was pre-
pared using a 1:2:1 mol ratio of iron(III) chloride, 1,10-phenan-
throline, and ammonium ceric nitrate (CAN). A typical synthesis
is described in the following: A solution of phen (0.396 g, 2 mmol)
in acetic acid/water (6:4, 5 mL) was added dropwise to a solution
of FeCl3·6H2O (0.270 g, 1 mmol) in the same solvent (10 mL) while
slowly stirring (450 rpm) the solution. Then solid CAN (550 mg,
1 mmol) was added portionwise into the pink solution and stirring
was continued for an additional 30 min. The pink solution turned
red, and the supernatant liquid was kept in air for slow evapora-
tion. After 7–10 days, complex 1 was separated out, washed with
hexane, and dried under vacuum over a silica gel dessicator. Yield
(based on metal salt): 0.2178 g (80%). C24H16Cl2FeN5O3 (1,
549.18): calcd. C 52.48, H 2.93, N 12.75; found C 52.54, H 2.99,
Figure 4. 57Fe Mössbauer spectrum of 1 at 77 K.
Conclusion
We report a convenient and efficient method for the oxi-
dation of benzylic and aliphatic primary and secondary
alcohols by using an iron-based catalyst with hydrogen per-
oxide as terminal oxidant. This methodology can also be
applied to more steric compounds like endo-fenchyl alcohol,
N 12.81. IR (KBr pellet): ν = 1384 (s), 1426 (m), 1517 (s) cm–1.
˜
menthol, or cyclopropyl(phenyl)methanol. After a short re- The complex is soluble in almost all solvents such as methanol,
ethanol, dichloromethane, acetonitrile, dimethylformamide, and di-
methyl sulfoxide.
action time (30 min up to 120 min), the desired carbonyl
compounds are obtained in moderate to very good yields
(35–98%) and excellent selectivity (80–99%). Mechanistic
investigations reveal that diffusion free radicals are not sig-
nificantly involved in the oxidation.
X-ray Crystallography: A summary of the crystallographic data and
structure refinement parameters is given in Table 4. Single crystals
(size 0.07ϫ0.09ϫ0.12 mm) of 1 were obtained by slow evapora-
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tion of the reaction mixture in an acetic acid/water solution. Red
crystals suitable for X-ray crystallographic analysis were selected
quenched by the addition of sodium sulfite (Na2SO3), and a sample
was directly taken and subjected to GC analysis.
following examination under
a microscope. Diffraction data
Isolation of 1-Phenyl-1,2-ethanediol: The crude product was puri-
fied by silica gel chromatography using a mixture of n-hexane and
ethyl acetate as eluent (gradient from 3:1 to 2:1). 1H NMR
(300 MHz, CDCl3): δ = 7.95–7.90 (m, 2 H), 7.67–7.59 (m, 1 H),
7.54–7.46 (m, 2 H), 4.89 (s, 2 H), 3.55 (br., 1 H) ppm.
250(2) K were collected with a Kappa CCD diffractometer using
Mo-Kα radiation (λ = 0.71073 Å). Systematic absence led to the
identification of space group C2/c (15). Of the 10159 unique reflec-
tions, 3335 with IϾ2σ(I) were used for structure solutions. The
structure was solved by direct methods, and the structure solution
and refinement were based on |F|2. All non-hydrogen atoms were
refined with anisotropic displacement parameters, whereas hydro-
gen atoms were placed in calculated positions when possible and
given isotropic U values 1.2 times that of the atom to which they
are bonded. At convergence the final residuals were R1 = 0.0775;
wR2 = 0.2882 with IϾ2σ(I), goodness-of-fit = 1.399. The final
differences Fourier map showed the maximum and minimum peak
heights at 2.499 and –0.505 eÅ–3 with no chemical significance. All
calculations were carried out using SHELXL-97.[34] CCDC-818508
contains the supplementary crystallographic data for this paper.
These data can be obtained free of charge from The Cambridge
Crystallographic Data Centre via www.ccdc.cam.ac.uk/data_
request/cif.
MS Studies: HR-MS (ESI-TOF) spectrum of 1 (Figure S3 in the
Supporting Information): [C24H16N4Cl2Fe], [M + H]+: m/z calcd.
486.0087; found 486.0095 (error 1.78 ppm). New species were ob-
served in the reaction mixture spectrum (Figure S4 in the Support-
ing Informaiton): [C12H8N2ClFeOC7H7], [M + H]+: m/z calcd.
378.022; found 378.0217 (error 1.36 ppm). Areas m/z 372–391 are
presented in the insets of Figures S3 and S4 in the Supporting In-
formation.
Supporting Information (see footnote on the first page of this arti-
cle): Experimental details such as general procedure for the benzyl
alcohol oxidation, time effect, catalyst amount, ESI mass spectrum
for 1 and for the reaction mixture.
Acknowledgments
Table 4. X-ray crystallographic data of [Fe(phen)2Cl2]NO3 (1).
This work was financially supported by the University Grants
Commission (UGC), New Delhi, India [MRP number F. PSW-039/
09-10(ERO), dated 08 October, 2009]. H.-L. Tsai thanks the
National Science Council of Taiwan for financial support under
grant number NSC 99-2113-M-006-003-MY3. This work was
partly funded by the Fonds National de la Recherche Scientifique
(FNRS) (grant numbers FRFC 2.4508.08, FRFC 2.4537.12, and
IISN 4.4507.10).
Empirical formula
Mr
T [K]
C24H16Cl2N5O3Fe
549.17
250(2)
0.71073
monoclinic
C2/c (15)
15.559(3)
13.588(3)
λ [Å]
Crystal system
Space group
a [Å]
b [Å]
c [Å]
12.905(3)
α [°]
β [°]
90
101.501(3)
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γ [°]
90
2673.4(9)
4
1.364
0.797
1560
0.07ϫ0.09ϫ0.12
2.01 to 28.36
–17ՅhՅ20
–18ՅkՅ15
–15ՅlՅ17
10159
3335 [R(int) = 0.0169]
99.6%
V [Å3]
Z
Dcalcd. [Mgm–3]
ε [mm–1]
F(000)
Crystal size [mm3]
θ range [°]
Index ranges
Reflections collected
Independent reflections
Completeness to θ = 28.36°
Absorption correction
Max./min. transmission
Refinement method
multiscan
0.775/0.673
full-matrix least-squares on F2
3335/0/177
Data/restraints/parameters
Goodness-of-fit on F2
Final R indices [IϾ2σ(I)]
R indices (all data)
1.399
R1 = 0.0775, wR2 = 0.2882
R1 = 0.0812, wR2 = 0.2962
Largest diff. peak/hole [eÅ–3] 2.499/–0.505
General Method for the Oxidation of Alcohols: Complex [Fe(phen)2-
Cl2]NO3 (1.5 mol-%, 0.022 mmol) was added to a 50 mL round-
bottomed flask followed by buffer solution (3 mL; HCl/KH buffer
solution pH = 1). After addition of the substrate (1.5 mmol) and
the internal standard (decane, 200 μL), the mixture was vigorously
stirred at 55 °C. The reaction started by adding the first drop of
hydrogen peroxide. The oxidant (2.2 equiv.) was added through a
syringe pump. After a time (t = 30–120 min), the reaction was
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6
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Eur. J. Inorg. Chem. 0000, 0–0

Job/Unit: I20658
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Date: 29-08-12 15:13:36
Pages: 8
Efficient and Selective Oxidation of Alcohols
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Received: June 15, 2012
Published Online: ᭿
Eur. J. Inorg. Chem. 0000, 0–0
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www.eurjic.org
7

Job/Unit: I20658
/KAP1
Date: 29-08-12 15:13:36
Pages: 8
B. Biswas, A. Al-Hunaiti, T. Repo, R. Ghosh, N. Kole et al.
FULL PAPER
Selective Alcohol Oxidation
Using
high-spin
iron(III)
complex
B. Biswas,* A. Al-Hunaiti,*
[Fe(phen)2Cl2]NO3 (1) (phen = 1,10-phen-
anthroline) and H2O2 as terminal oxidant,
a series of primary and secondary alcohols
were oxidized into aldehydes and ketones
in good yields and excellent selectivities
after a short reaction time.
M. T. Räisänen, S. Ansalone, M. Leskelä,
T. Repo,* Y.-T. Chen, H.-L. Tsai,
A. D. Naik, A. P. Railliet, Y. Garcia,
R. Ghosh,* N. Kole* ......................... 1–8
Efficient and Selective Oxidation of Pri-
mary and Secondary Alcohols Using an
Iron(III)/Phenanthroline Complex: Struc-
tural Studies and Catalytic Activity
Keywords: Homogeneous catalysis / Oxi-
dation / Iron / Alcohols / Ketones
8
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Eur. J. Inorg. Chem. 0000, 0–0