Decarbonylation of Aromatic Aldehydes and Dehalogenation of Aryl Halides Using Maghemite-Supported Palladium Catalyst

Article abstract of DOI:10.1055/s-0036-1590892

A facile decarbonylation reaction of a variety of aromatic and heteroaromatic aldehydes using maghemite-supported palladium catalyst has been developed. The magnetic properties of catalyst facilitated an easy and efficient recovery of the catalyst from the reaction mixture using an external magnet. It was found that the catalyst could be reused up to four consecutive catalytic runs without a significant change in activity. In addition, the catalyst was also very effective in the dehalogenation of aryl halides. This is the first report on efficient utilization of directly immobilized Pd on maghemite in decarbonylation and dehalogenation reactions.

Full text of DOI:10.1055/s-0036-1590892

SYNTHESIS
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Georg Thieme Verlag Stuttgart · New York
2017, 49, A–H
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Synthesis
V. Ajdačić et al.
Paper
Decarbonylation of Aromatic Aldehydes and Dehalogenation of
Aryl Halides Using Maghemite-Supported Palladium Catalyst
Vladimir Ajdačića
Andrea Nikolića
Stefan Simića
Dragan Manojlovića
Zoran Stojanovićb
Jasmina Nikodinovic-Runicc
Igor M. Opsenica*a
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a
Faculty of Chemistry, University of Belgrade, PO Box 51, Studentski trg
6, 11158 Belgrade, Serbia
Institute of Technical Sciences, Serbian Academy of Arts and Sciences,
Knez Mihajlova 35/IV, 11000 Belgrade, Serbia
Institute of Molecular Genetics and Genetic Engineering, University of
Belgrade, Vojvode Stepe 444a, 11000 Belgrade, Serbia
igorop@chem.bg.ac.rs
1
b
c
Received: 11.07.2017
Accepted after revision: 02.08.2017
Published online: 06.09.2017
Over the past few years, magnetic supported nanocata-
lysts have attracted considerable attention because of the
ease of their preparation, high surface area to volume ratio,
efficient separation from the reaction mixture with an ex-
DOI: 10.1055/s-0036-1590892; Art ID: ss-2017-t0452-op
Abstract A facile decarbonylation reaction of a variety of aromatic and
heteroaromatic aldehydes using maghemite-supported palladium cata-
lyst has been developed. The magnetic properties of catalyst facilitated
an easy and efficient recovery of the catalyst from the reaction mixture
using an external magnet. It was found that the catalyst could be re-
used up to four consecutive catalytic runs without a significant change
in activity. In addition, the catalyst was also very effective in the dehalo-
genation of aryl halides. This is the first report on efficient utilization of
directly immobilized Pd on maghemite in decarbonylation and dehalo-
genation reactions.
10
ternal magnet, and recyclability. In addition, their chemi-
cal inertness and thermal stability enable their use as high-
ly effective catalysts in a wide range of synthetic transfor-
mations. In recent years, magnetically separable iron oxide
maghemite (γ-Fe O ) has been widely utilized as an appeal-
2
3
ing and sustainable solid support material for metal nano-
catalysts, owing to its easy production, nontoxic nature, and
economical viability. The direct immobilization of metal
nanocatalysts, which include Pd,11 Cu, Rh, Zn, and Au
12
13
14
15
Key words decarbonylation, dehalogenation, palladium catalyst, ma-
ghemite, magnetically recoverable catalyst
on the magnetic surface, without the use of an external
modifiers, has been recently reported, and the obtained
catalysts were successfully used to perform various organic
transformations. More recently, maghemite-supported
The cytochrome P450 enzymes play an important role
1
16
in the decarbonylation pathway in biological systems. The
decarbonylation of aldehydes is of great importance in syn-
thetic organic chemistry and pharmaceutical industry as
well. The transition-metal-mediated decarbonylation of al-
dehydes has been extensively investigated and established
Pd/PdO nanoparticles, have been developed and the ob-
tained catalyst was successfully used in the Heck–Mizoroki
olefination, the Suzuki reaction, and the allylic oxidation of
alkenes.
Within this study, we sought to determine if the directly
immobilized magnetically recoverable Pd-catalyst could be
efficiently utilized in the decarbonylation of aromatic alde-
hydes and in the dehalogenation of halogenoarenes.
The maghemite-supported palladium catalyst was pre-
pared by the co-precipitation method (Scheme 1) recently
reported by Rathi et al.16 and characterized by inductively
coupled plasma-quadrupole mass spectrometry (ICP-QMS)
and scanning electron microscopy (SEM).
2
as a useful synthetic transformation. The first rhodium-
mediated decarbonylation reaction was reported by Tsuji
and Ohno in 1965 using a stoichiometric amount of Wilkin-
son’s catalyst, and over the past 50 years this method has
been the most frequently employed. Efficient catalytic de-
carbonylation of aldehydes has been accomplished with
3
4
more reactive cationic Rh complexes. In addition, the de-
carbonylation of aldehydes has been successfully performed
with palladium, iridium, nickel, and ruthenium8 cata-
lysts. Recently, silica- and zirconia-supported Pd catalysts
have been developed for decarbonylation of aromatic alde-
5
6
7
1
2
) NH3(aq), 60 °C
) 100 °C, 12 h
1) PdCl2, KCl, H2O, r.t.
2) NaOH, H2O, r.t.
Pd
FeSO4·7H2O
+
γ-Fe O
γ-Fe O
2
3
2
3
FeCl3·6H2O
9
hydes.
Pd
Pd
Scheme 1 Synthesis of maghemite-supported Pd catalyst16
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V. Ajdačić et al.
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SEM analysis showed that the surface area of catalyst
was well developed, with sponge-like morphology and that
the average crystallite size of the γ-Fe O was in the range
Table 1 Optimization of the Reaction Conditions for Decarbonylation
of Biphenyl-4-carboxaldehydea
2
3
O
of 1–10 μm, which was in agreement with the particle size
distribution analysis (Figure 1, A and B). SEM analysis also
showed that catalyst sample contained aggregated submi-
cronic particles. The aggregates were up to 20 μm. Laser dif-
fraction analysis showed that sample dispersed in ethanol
by means of low energy ultrasound disintegrates to two
main fractions. About 77% of sample mass make particles
with mean size of 1.2–1.3 μm with standard deviation of
Conditions
H
+
CO
H
Molecular
sieves
3a
4a
Entry Catalyst
Solvent
Temp (°C) Yield (%)b
1
2
3
4
γ-Fe
2
O
3
cyclohexane
cyclohexane
cyclohexane
toluene
130
130
130
150
150
0
78
82
76
68
Pd/γ-Fe
Pd/γ-Fe
Pd/γ-Fe
Pd/γ-Fe
2
2
2
2
O
O
O
O
3
3
3
3
(3.6 mol%)
(5.0 mol%)
(5.0 mol%)
(5.0 mol%)
0.7 μm, and the rest of mass of 23% stays in aggregates with
mean size of 14–17 μm with standard deviation of 10 μm.
The ICP-QMS analysis confirmed the presence of 5.56 wt%
Pd in the catalyst. The magnetic properties of maghemite-
supported Pd catalysts facilitates an easy and efficient re-
covery of the catalyst from the reaction mixture using an
external magnet (Figure 1, C).
5
1,4-dioxane
a
Reaction conditions: 3a (0.25 mmol), molecular sieves (100 mg), solvent
1 mL), 24 h under argon atmosphere.
Isolated yield.
(
b
ed by using 3.6 mol% of Pd/γ-Fe O in cyclohexane at 130 °C
2
3
(entry 2). Increasing the catalyst loading to 5.0 mol% was
necessary to obtain full conversion (entry 3). Regarding the
solvent, it can be changed to toluene and 1,4-dioxane, albeit
in slightly decreased yields (entries 4 and 5).
With the optimized reaction conditions in hand (Table
1, entry 3) the scope of the substrates for the decarbonyla-
tion of aromatic aldehydes catalyzed by Pd/γ-Fe O was in-
2
3
vestigated (Scheme 3).
High to excellent yields of the decarbonylated products
were obtained with different aryl aldehydes (Scheme 3, 4a–
d). Reactions in the presence of different functional groups
including nitro, cyano, and ether are successful to generate
the corresponding decarbonylated products (4e, 4g and 4h).
Ortho-substituted aryl aldehydes were also transformed
into decarbonylated products (4j and 4k) in good yields.
Furthermore, heterocyclic aldehydes produced the desired
decarbonylated products in good yields (4l–p) with the ex-
ception of benzo[b]thiophene-3-carboxaldehyde (4m).
Interestingly, no trace of the decarbonylated product
was observed for halogen substituted aryl aldehydes (4f, 4i,
and 4q), only starting compounds were identified. The
drastic changes in reactivity observed with halogen-substi-
tuted aryl aldehydes suggested that the initial oxidative ad-
dition of the C–halogen bonds to palladium is more favor-
able than the addition of the C(O)–H bond (cf. Scheme 4,
vide infra).
Figure 1 Characterization of Pd/γ-Fe O catalyst. A) SEM, B) Particle
2
3
size distribution analysis, and C) Separation of Pd/γ-Fe O catalyst from
2
3
the reaction mixture under an external magnetic field.
Initially, biphenyl-4-carboxaldehyde, prepared through
the Suzuki–Miyaura cross-coupling reaction (Scheme 2),16
was selected as a model substrate for optimization of reac-
tion conditions for decarbonylation, and the results are pre-
sented in Table 1. Reactions were performed in the pres-
ence of 3–4 Å molecular sieves, as it has been found that the
presence of molecular sieves greatly enhances the decarbo-
nylation of aldehydes.17
CHO
B(OH)2
Pd/γ-Fe2O3 (2 mol% Pd)
K2CO3, DMF/H2O, 110 °C
+
CHO
95%
Separation, recovery, and reusability are very important
properties of the catalyst from the economic, sustainability
as well as the synthetic point of view. As mentioned, the
catalyst was easily recovered from the reaction mixture us-
ing an external magnet (Figure 1, C). The catalyst was
washed with absolute ethanol and dried under vacuum
with heating at 50 °C until a complete dry mass was formed
and reused for a consecutive run under the same reaction
conditions.
Br
3a
1
2
Scheme 2 Synthesis of biphenyl-4-carbaldehyde
Having established that palladium was necessary for ca-
talysis (Table 1, entry 1), our next task involved identifica-
tion of the optimal catalyst loading and solvent. It was
found that the decarbonylation could be smoothly promot-
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Synthesis
V. Ajdačić et al.
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O
Pd/γ-Fe2O3 (5 mol% Pd)
H
H
Cyclohexane
Ar
het-Ar
R
Ar
het-Ar
R
+
CO
Molecular sieves
130 °C, 24 h
3a–q
4a–q
H
MeO
H
4
4
a, 82%a
4b, 85%a
H
H
H
tBu
4d, 95%b
NO2
4e, 58%a (76%c)
c, 80%a
H
H
H
Br
OMe
NO2
f, 0%a
CN
4
4g, 70%b (100%d)
4h, 99%c
H
H
H
Cl
F
F
MeO
4k, 80%c
4
i, 0%b
4j, 69%c
Figure 2 A) Recycling of Pd/γ-Fe O catalyst for decarbonylation of 4-
H
2
3
tert-butylbenzaldehyde. B) Recycling of Pd/γ-Fe O catalyst for dehalo-
2
3
H
H
genation of 2-bromo-1,3,5-trimethylbenzene.
O
S
S
4
l, 74%b,e (100%d)
4m, 67%a,e
4m, 23%a,e
The dehalogenation of aryl halides represents an im-
18
portant chemical transformation in organic synthesis.
H
H
O
S
While conducting our studies on the decarbonylation of al-
dehydes, we have noticed that, under the reaction condi-
tions, the decarbonylation of the halogen-substituted aryl
aldehydes was not promoted (Scheme 3, 4f, 4i, and 4q), and
decided to further investigate the scope of the catalyst in
dehalogenation chemistry (Table 2).
4
4
n, 73%a
4o, 82%a
Br
H
S
H
F
S
p, 83%a
F
q, 0%a
4
The initial studies were conducted in propan-2-ol with
Pd/γ-Fe O as the catalyst and NaOt-Bu as the base. Several
Scheme 3 Scope of Pd/γ-Fe O -catalyzed decarbonylation of alde-
2
3
a
b
2
3
hydes. Isolated yield. GC-MS yield (naphthalene was used as an inter-
c
aryl halides were successfully dehalogenated at room tem-
perature. The catalyst system was effectively used for the
dehalogenation of sterically hindered 2-bromo-1,3,5-
trimethylbenzene and the product was obtained in nearly
quantitative yield (Table 2, entry 1). Complete conversion of
2-bromo-1,3,5-trimethylbenzene into 1,3,5-trimethylben-
zene was observed at 70 °C (entry 2). The heteroaryl bro-
mide containing thiophene moiety was also subjected to
the debromination at 70 °C to give the 2-phenylthiophene
4o in 84% yield (entry 12). Notably, using this catalytic sys-
tem, 4o was obtained in good yields either via decarbonyla-
tion or by dehalogenation starting from 5-phenylthio-
phene-2-carbaldehyde and 2-bromo-5-phenylthiophene,
respectively (Scheme 3, entry 4o and Table 2, entry 12). The
regioselective dehalogenation of some polyhalogenated
substrates was also examined. Good to high regioselectivity
nal standard). GC-MS yield (methyl benzoate was used as an internal
standard ). d Conversion based on GC-MS. e 7.5 mol% [Pd].
As summarized in Figure 2 (A), it was found that the cat-
alyst could be reused up to four consecutive catalytic runs
without a significant change in activity during the decarbo-
nylation of 4-tert-butylbenzaldehyde. The average GC-MS
yield of the product for four consecutive runs was 91%,
which clearly demonstrates the practical reusability of the
catalyst. To find out the amount of palladium leached into
the liquid we carried out ICP-QMS analysis of the filtrate re-
maining after the magnetic separation of the catalyst and it
was found that the concentration of palladium in the fil-
trate was negligible (0.64 ppm).
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V. Ajdačić et al.
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8). Besides dehalogenated products 6b–d, the products of
Table 2 Dehalogenation of Aryl Halides Catalyzed by Pd/γ-Fe O3
2
double dehalogenation 7a and 7b were also observed. How-
ever, the dehalogenation of 1-chloro-4-fluorobenzene pro-
duced fluorobenzene and benzene in nearly equal amounts.
The transition-metal-catalyzed transformation of C–F bond
represents a great challenge in organic chemistry, and the
observed defluorination could be a useful approach in the
transformation of aryl fluorides, which was confirmed with
defluorination of 4-fluorotoluene and 4-fluoroanisole (en-
tries 10 and 11). Notably, a complex reaction mixture was
observed in the case of 4-bromobenzonitrile and methyl 4-
bromo-3-methylbenzoate probably due to instability of the
cyano and ester groups under the applied reaction condi-
tions.
X
H
Pd/γ-Fe2O3 (5 mol% Pd)
NaOt-Bu (1.25 equiv), i-PrOH
Ar
Ar
R
R
het-Ar
het-Ar
5
a–h
6a–d
Entry Aryl halide
Product(s)
Temp (°C) Yield (%)
5
/6/7
1
2
3
Br
H
r.t.
70
r.t.
3:97:–a
0:100:–a
19:77:4a
0:37:42a
45:48:7b
0:58:16b
0:83:0b
5a
6a
Cl
H
H
As summarized in Figure 2 (B), it was found that the cat-
alyst could be reused up to four consecutive catalytic runs
without a significant change in activity during the dehalo-
genation of sterically hindered 2-bromo-1,3,5-trimethyl-
benzene.
4
5
6
7
8
70
r.t.
70
r.t.
70
F
5
b
F
6b
H
H
7a
7a
7a
Br
H
On the basis of the above-mentioned results and rele-
vant reports in the literature,5 a possible mechanism for
this methodology is presented in Scheme 4.
h
Cl 5c
Cl 6c
H
H
O
I
H
i-PrONa
O
Ar
Ar
X
Ar
X
Ar
H
NaX
0:60:18b
H
Oxidative
addition
Migratory
extrusion
Cl 5d
Cl 6c
H
Ar
O
Ar
H
Br
H
H
CO
0:21:40a
H
9
70
70
CO
desorption
Reductive
elimination
b-H elimination
Cl 5e
Cl 6d
H
7b
Ar
H
O
CO
Ar
H
F
H
Ar
H CO
10
0:100:–a
=
γ-Fe2O3
= Pd
5f
7b
Scheme 4 Proposed mechanisms for decarbonylation and dehaloge-
nation
F
H
1
1
2
70
70
0:100:–b
0:84:–c
As previously described,16 the presence of ethanol
during the preparation of the catalyst presumably leads to
the reduction of Pd(II) to Pd(0). Oxidative addition of the
C(O)–H bond of the aldehyde to the palladium gives the
acylpalladium hydride complex, which subsequently un-
dergoes CO migration. Reductive elimination then forms
the decarbonylated product and CO desorption regenerates
the catalyst. Oxidative addition of the aryl halide to the pal-
ladium gives the arylpalladium halide intermediate. Subse-
quently, base-promoted displacement of a halide anion
generates an alkoxy-palladium species, which undergoes β-
H elimination leading to an arylpalladium hydride complex.
Finally, reductive elimination of the arene regenerates the
catalyst. The reaction mechanism involving palladium clus-
ters9c is also possible and cannot be excluded at this time.
OMe 5g
OMe 4h
Ph
Br Ph
H
1
S
S
5h
4o
a
b
c
GC-MS yields (naphthalene used as internal standard).
GC-MS yields (methyl benzoate used as internal standard).
Isolated yield.
was observed in the dehalogenation of 1-chloro-4-fluoro-
benzene, 1-bromo-4-chlorobenzene, and 1-chloro-4-iodo-
benzene, respectively (entries 3, 5, and 7) at room tempera-
ture. On the other hand, at elevated temperature the cata-
lyst system showed low regioselectivity (entries 4, 6, and
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V. Ajdačić et al.
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In conclusion, we have developed an easy and practical
decarbonylation reaction by using retrievable maghemite-
supported palladium catalyst. A number of aromatic and
heteroaromatic aldehydes were successfully decarbonylat-
ed, without using any exogenous ligand for Pd. The catalyst
was successfully recycled four times without loss of activi-
ty. In addition, the catalyst was also very effective in the de-
halogenation of aryl halides. Finally, the observed defluori-
nation could be a useful approach in the transformation of
aryl fluorides.
rated and washed thoroughly with deionized H O until the superna-
tant liquor reached neutrality. The resulting material was dried under
air at 100 °C for 12 h to give 5.38 g of maghemite.
2
16
γ-Fe O -Pd Catalyst
2
3
A solution of PdCl (349 mg) and KCl (1 g) in H O (120 mL) was stirred
2
2
for 5 min and maghemite (3 g) was added to it. The resulting mixture
was stirred at r.t. for 1 h and the suspension was adjusted to pH 12–13
by the slow addition of aq 1 M NaOH and further stirred for 24 h. The
aqueous layer was decanted with the help of an external magnet and
the ensuing material was washed with deionized H O (5 × 50 mL) un-
2
der sonication at 45 °C followed by washing with EtOH and drying un-
der reduced pressure at 60 °C for 4 h to afford 2.69 g of γ-Fe O -Pd.
2
3
The ICP-QMS analysis confirmed the presence of 5.56 wt% Pd in the
catalyst.
Dry-flash chromatography was performed on SiO (0.018–0.032 mm).
2
Melting points were determined on a Boetius PMHK apparatus and
are not corrected. IR spectra were recorded on a Thermo-Scientific
Biphenyl-4-carbaldehyde (3a)22
1
13
Nicolet 6700 FT-IR Diamond Crystal instrument. H and C NMR
spectra were recorded on a Bruker Ultrashield Avance III spectrome-
To a stirred mixture of 4-bromobenzaldehyde (50 mg, 0.27 mmol),
ter (at 500 and 125 MHz, respectively) using CDCl as the solvent and
K
2
CO
3
(75 mg, 0.54 mmol), and phenylboronic acid (46 mg, 0.38
O (1.6 mL, 3:1, v/v) was added γ-Fe -Pd (10 mg, 2
3
TMS as an internal standard. Chemical shifts are expressed in parts
per million (ppm) on the (δ) scale. Chemical shifts were calibrated
relative to those of the solvent. GC-MS spectra of the synthesized
compounds were acquired on an Agilent Technologies 7890A appara-
tus equipped with a DB-5 MS column (30 m × 0.25 mm × 0.25 μm), a
mmol) in DMF/H
2
O
2 3
mol% Pd) under argon. The resulting mixture was stirred at 110 °C for
4 h. The solvent was removed under reduced pressure, and the resi-
due was dissolved in EtOAc. The organic phase was washed with H
and brine, dried, and concentrated under reduced pressure. The crude
product was purified by dry-flash chromatography (SiO : n-hex-
O
2
5
975C MSD and FID detector. The selected values are as follows: carri-
er gas was He (1.0 mL/min), temperature linearly increased from 40–
15 °C (10 °C/min), injection volume: 1 μL, temperature: 250 °C, tem-
perature (FID detector): 300 °C, and EI mass spectra range: m/z 40–
50. For determination of Pd concentration ICP-QMS (iCAP Q, Thermo
2
ane/EtOAc = 9:1) to afford the title compound 3a (46 mg, 95%); mp
57–61 °C .
3
IR (ATR): 3032, 2840, 2745, 1701, 1603, 1564, 1482, 1449, 1385, 1310,
5
–1
1215, 1169, 1111, 1078, 1005, 839, 766, 726, 699 cm
.
Scientific X series 2) was used. Instrument operating conditions for
determination of Pd: RF power (W) = 1548; Gas flows (L/min) = 13.9,
1
H NMR (500 MHz, CDCl ): δ = 10.06 (s, 1 H), 7.95 (d, J = 8.0 Hz, 2 H),
3
7.75 (d, J = 8.0 Hz, 2 H), 7.65–7.62 (m, 2 H), 7.50–7.46 (m, 2 H), 7.44–
1
=
.09, 0.8; Acquisition time = 3 × 50 s; Points per peak = 3; Dwell time
10 ns; Detector mode was analog/pulse; Replicates = 3. Measured
7.39 (m, 1 H).
104
105
106
108
110
isotope (normal mode): Pd, Pd, Pd, Pd, Pd. The scanning
electron microscope (SEM) images were obtained with a field emis-
sion scanning electron microscope SEM JEOL JSM-6610LV. Laser dif-
fraction on particles was measured on Malvern Mastersize 2000 de-
vice in microPrecision measuring unit. 30 mg of sample was dis-
persed in 3 mL of ethanol for 30 min. Dispersions were added in the
measuring unit until desired concentration was reached. Refractive
index used for particles was 2.94 with adsorption coefficient 1. Re-
sulting multimodal particle size distributions was then analyzed with
normalmixEM (expectation maximization) method form Mixtools
packet in R programming language. The experimental distributions
was fitted as composition of two normal distribution, which corre-
sponds to loosely aggregated and easily dispersed particles versus
hard aggregates.
Decarbonylation of Biphenyl-4-carbaldehyde to Biphenyl (4a);23
Typical Procedure for the Decarbonylation of Aldehydes
To a dry glass reaction tube purged with argon and equipped with a
magnetic stir bar were added molecular sieves (3–4 Å, 100 mg), alde-
hyde 3a (46 mg, 0.25 mmol), Pd-γ-Fe O (24 mg, 5 mol% Pd), and cy-
2 3
clohexane (1 mL) and the sealed tube was heated at 130 °C for 24 h.
The reaction mixture was decanted with the help of an external mag-
net and the catalyst was washed with CH Cl (5 × 5 mL). The crude
2 2
product was purified by dry-flash chromatography (SiO
: hexane) to
2
afford 4a (31 mg, 82%) as a white solid; mp 66–68 °C.
IR (ATR): 3154, 3113, 3064, 3037, 2928, 2856, 1960, 1887, 1823, 1752,
1
7
1
695, 1598, 1573, 1519, 1478, 1432, 1384, 1348, 1178, 1092, 1007,
–1
30, 704 cm
.
19
The syntheses of compounds 5-phenylfuran-2-carbaldehyde, 5-
H NMR (500 MHz, CDCl ): δ = 7.60–7.55 (m, 4 H), 7.45–7.40 (m, 4 H),
3
19
phenylthiophene-2-carbaldehyde, 5-(4-fluorophenyl)thiophene-2-
7.36–7.31 (m, 2 H).
1
9
carbaldehyde,
4-bromo-5-(4-fluorophenyl)thiophene-2-carbalde-
13
C NMR (125 MHz, CDCl ): δ = 141.2, 128.7, 127.2, 127.2.
20
21
3
hyde, and 5f were described previously.
GC-MS: m/z = 154.1 [M]+.
16
Maghemite (γ-Fe O )
2
3
Decarbonylation of 4′-Methoxybiphenyl-4-carbaldehyde to 4-Me-
thoxybiphenyl (4b)
Maghemite was prepared by the co-precipitation method. Typically,
FeSO ·7H O (6.06 g, 21.79 mmol) and FeCl ·6H O (11.75 g, 45.08
23
4
2
3
2
mmol) were dissolved in deionized H O (120 mL) under an argon at-
Following the general procedure for decarbonylation, compound 4b
2
mosphere. The resulting mixture was stirred for 15 min and heated at
(33 mg, 85%) was obtained as a white crystalline solid; mp 87–88 °C.
6
0 °C under vigorous stirring. After attaining the desired temperature,
IR (ATR): 3065, 3035, 3003, 2938, 2903, 2837, 1605, 1580, 1522, 1484,
1286, 1249, 1199, 1185, 1121, 1038, 833, 759 cm .
aq NH (30 mL, 25% NH in water) was added dropwise, a black pre-
cipitate was immediately formed, and heating was continued for 2 h
under an argon atmosphere. The precipitate was magnetically sepa-
–1
3
3
1
H NMR (500 MHz, CDCl ): δ = 7.57–7.50 (m, 4 H), 7.43–7.38 (m, 2 H),
3
7
.32–7.27 (m, 1 H), 7.00–6.95 (m, 2 H), 3.84 (s, 3 H).
©
Georg Thieme Verlag Stuttgart · New York — Synthesis 2017, 49, A–H

F
Synthesis
V. Ajdačić et al.
Paper
1
3
C NMR (125 MHz, CDCl ): δ = 159.1, 140.8, 133.8, 128.7, 128.1,
Following the general procedure for decarbonylation, compound 4k
was obtained. GC-MS yield: 80%, based on methyl benzoate as stan-
dard.
GC-MS: m/z = 126.0 [M]+.
3
1
26.7, 126.6, 114.2, 55.3.
GC-MS: m/z = 184.1 [M]+.
Decarbonylation of Anthracene-9-carbaldehyde to Anthracene
9
b
(
4c)
Following the general procedure for decarbonylation, compound 4c
34 mg, 80%) was obtained as a white crystalline solid; mp 208–212
C.
IR (ATR): 3050, 2921, 1928, 1788, 1722, 1619, 1573, 1533, 1448, 1397,
Decarbonylation of Benzo[b]furan-2-carbaldehyde to Benzo[b]fu-
ran (4l)
9b
(
°
Following the general procedure for decarbonylation, compound 4l
was obtained. GC-MS yield: 74%, based on naphthalene as standard.
GC-MS: m/z = 118.1 [M]+.
–1
1
315, 1272, 1167, 1143, 955, 881, 722 cm .
1
H NMR (500 MHz, CDCl ): δ = 8.42 (s, 2 H), 8.05–7.95 (m, 4 H), 7.50–
.45 (m, 4 H).
Decarbonylation of Benzo[b]thiophene-2-carbaldehyde to Ben-
3
9b
7
zo[b]thiophene (4m)
Following the general procedure for decarbonylation, compound 4m
26 mg, 67%) was obtained as a white crystalline powder; mp 31–33
C.
IR (ATR): 3054, 3027, 2955, 2920, 2851, 1736, 1456, 1419, 1179, 815,
13
C NMR (125 MHz, CDCl ): δ = 131.7, 128.1, 126.2, 125.3.
3
(
°
GC-MS: m/z = 178.1 [M]+.
Decarbonylation of 4-tert-Butylbenzaldehyde to tert-Butylben-
zene (4d)
–
1
24
740 cm .
1
H NMR (500 MHz, CDCl ): δ = 7.88 (d, J = 8.0 Hz, 1 H), 7.84–7.80 (m, 1
Following the general procedure for decarbonylation, compound 4d
was obtained. GC-MS yield: 95%, based on naphthalene as a standard.
GC-MS: m/z = 134.1 [M]+.
3
H), 7.43 (d, J = 5.5 Hz, 1 H), 7.37–7.30 (m, 3 H).
13C NMR (125 MHz, CDCl
23.8, 123.6, 122.5.
GC-MS: m/z = 134.0 [M]+.
): δ = 139.7, 139.6, 126.3, 124.2, 124.1,
3
1
Decarbonylation of 4-Nitrobenzaldehyde to Nitrobenzene (4e)9b
Following the general procedure for decarbonylation, compound 4e
Decarbonylation of Benzo[b]thiophene-3-carbaldehyde to Ben-
zo[b]thiophene (4m)
(25 mg, 58%) was obtained as a yellow oil (GC-MS yield 76% based on
methyl benzoate as standard).
Following the general procedure for decarbonylation, compound 4m
(7 mg, 23%) was obtained.
IR (ATR): 3076, 2925, 2858, 1065, 1524, 1477, 1348, 1315, 1173, 1107,
–1
1070, 1021, 852, 794, 705, 680 cm .
1
H NMR (500 MHz, CDCl ): δ = 8.25–8.20 (m, 2 H), 7.73–7.68 (m, 1 H),
3
Decarbonylation of 5-Phenylfuran-2-carbaldehyde to 2-Phenylfu-
7
.58–7.52 (m, 2 H).
23
ran (4n)
Following the general procedure for decarbonylation, compound 4n
29 mg, 73%) was obtained as a colorless oil.
13
C NMR (125 MHz, CDCl ): δ = 148.2, 134.5, 129.3, 123.4.
3
GC-MS: m/z = 123.0 [M]+.
(
IR (ATR): 3117, 3071, 2925, 2853, 1607, 1506, 1478, 1450, 1379, 1273,
Decarbonylation of 4-Formylbenzonitrile to Benzonitrile (4g)9b
–1
1219, 1158, 1067, 1010, 906, 885, 805, 761, 736, 693, 665 cm
.
Following the general procedure for decarbonylation, compound 4g
was obtained. GC-MS yield: 70%, based on naphthalene as standard.
GC-MS: m/z = 103.0 [M]+.
1
H NMR (500 MHz, CDCl ): δ = 7.70–7.65 (m, 2 H), 7.48–7.44 (m, 1 H),
.41–7.35 (m, 2 H), 7.27–7.22 (m, 1 H), 6.66–6.63 (m, 1 H), 6.44–6.48
3
7
(m, 1 H).
13
C NMR (125 MHz, CDCl ): δ = 154.0, 142.0, 130.9, 128.6, 127.3,
3
Decarbonylation of 3-Anisaldehyde to Anisole (4h)9b
123.8, 111.6, 104.9.
Following the general procedure for decarbonylation, compound 4h
was obtained. GC-MS yield: 99%, based on methyl benzoate as stan-
dard.
GC-MS: m/z = 108.0 [M]+.
GC-MS: m/z = 144.1 [M]+.
Decarbonylation of 5-Phenylthiophene-2-carbaldehyde to
25
2-Phenylthiophene (4o)
Following the general procedure for decarbonylation, compound 4o
35 mg, 82%) was obtained as a white crystalline solid; mp 35–36 °C.
Decarbonylation of 2-Fluoro-4-methylbenzaldehyde to 3-Fluoro-
toluene (4j)
(
IR (ATR): 3063, 2921, 2849, 1596, 1526, 1484, 1446, 1426, 1355, 1211,
[
CAS Reg. No. 352-70-5]
–1
1074, 852, 826, 755, 691 cm
.
Following the general procedure for decarbonylation, compound 4j
was obtained. GC-MS yield: 69%, based on methyl benzoate as stan-
dard.
GC-MS: m/z = 110.0 [M]+.
1
H NMR (500 MHz, CDCl ): δ = 7.63–7.59 (m, 2 H), 7.39–7.34 (m, 2 H),
.31–7.29 (m, 1 H), 7.29–7.25 (m, 2 H), 7.09–7.06 (m, 1 H).
3
7
13
C NMR (125 MHz, CDCl ): δ = 144.4, 134.4, 128.8, 128.0, 127.4,
3
1
25.9, 124.8, 123.0.
GC-MS: m/z = 160.1 [M]+.
Decarbonylation of 2-Fluoro-5-methoxybenzaldehyde to 4-Fluo-
roanisole (4k)
[
CAS Reg. No. 459-60-9]
©
Georg Thieme Verlag Stuttgart · New York — Synthesis 2017, 49, A–H

G
Synthesis
V. Ajdačić et al.
Paper
Decarbonylation of 5-(4-Fluorophenyl)thiophene-2-carbaldehyde
to 5-(4-Fluorophenyl)thiophene (4p)26
Dehalogenation of 2-Bromo-5-chlorotoluene
Following the general procedure for dehalogenation, 5e was convert-
ed into 6d and 7b. GC-MS yields of 6d and 7b were 21% and 40%, re-
spectively, based on methyl benzoate as standard.
Following the general procedure for decarbonylation, compound 4p
(
°
18 mg, 83%) was obtained as a white crystalline powder; mp 51–52
C.
IR (ATR): 3114, 3050, 2921, 2852, 2164, 2030, 2010, 1988, 1956, 1872,
+
+
6
d; GC-MS: m/z = 126.0 [M] ; 7b; GC-MS: m/z = 91.1 [M] .
1
1
1
795, 1775, 1736, 1650, 1601, 1537, 1500, 1460, 1433, 1394, 1378,
Dehalogenation of 4-Fluorotoluene
–1
299, 1264, 1232, 1160, 1098, 961, 820, 737, 697 cm
.
Following the general procedure for dehalogenation, 5f was converted
into 7b. GC-MS yield of 7b was 100% based on naphthalene as stan-
dard.
H NMR (500 MHz, CDCl ): δ = 7.60–7.55 (m, 2 H), 7.28–7.25 (m, 1 H),
3
7.24–7.21 (m, 1 H), 7.09–7.03 (m, 3 H).
13
7b: GC-MS: m/z = 91.0 [M]+.
C NMR (125 MHz, CDCl ): δ = 162.3 (d, J = 245.5 Hz), 143.3, 130.7,
3
128.0, 127.6 (d, J = 8.1 Hz), 124.7, 123.0, 115.8 (d, J = 21.8 Hz).
GC-MS: m/z = 178.1 [M]+.
Dehalogenation of 4-fluoroanisole
Following the general procedure for dehalogenation, 5g was convert-
ed into 4h. GC-MS yield of 4h was 100% based on methyl benzoate as
standard.
Recycling of γ-Fe O -Pd Catalyst for Decarbonylation of 4-tert-
Butylbenzaldehyde
2
3
4h: GC-MS: m/z = 108.0 [M]+.
Reaction conditions were as follows: 4-tert-butylbenzaldehyde (0.18
mmol), γ-Fe O -Pd (17 mg, 5 mol% Pd), molecular sieves (3–4 Å, 100
2
3
mg), cyclohexane (1 mL), 130 °C, 24 h, argon. After the completion of
the reaction, the reaction mixture was decanted with the help of an
external magnet and the residue was washed with CH Cl , absolute
Dehalogenation of 2-Bromo-5-phenylthiophene
For the dehalogenation of 2-bromo-5-phenylthiophene (5h), the typ-
ical procedure was followed. After completion of the reaction, the re-
action mixture was decanted using an external magnet and the cata-
lyst was washed with CH Cl (5 × 5 mL). The solution was washed
2
2
EtOH, and dried under vacuum with heating at 50 °C until a complete
dry mass was formed. The formed activated residue containing both
the molecular sieves as well as the γ-Fe O -Pd catalyst was used for
2
2
2
3
with H O (5 mL), brine (5 mL), dried (Na SO ), and the solvent was re-
2
2
4
the second and further reaction cycles following the general reaction
procedure.
moved under reduced pressure. Compound 4o (16 mg, 84%) was ob-
tained as a yellow crystalline powder. No further purification of the
obtained crude product was required based on NMR analysis.
Dehalogenation of 2-Bromo-1,3,5-trimethylbenzene; 1,3,5-
Trimethylbenzene (6a); Typical Procedure for the Dehalogenation
Reaction
Recycling of γ-Fe O -Pd Catalyst for the Dehalogenation of 2-Bro-
2
3
mo-1,3,5-trimethylbenzene
To a dry glass reaction tube purged with argon and equipped with a
magnetic stir bar were added 2-bromo-1,3,5-trimethylbenzene (5a;
Reaction conditions were as follows: 2-bromo-1,3,5-trimethylben-
zene (0.26 mmol), γ-Fe O -Pd (25 mg, 5 mol% Pd), NaOt-Bu (0.33
2
3
4
0 μL, 0.26 mmol), Pd-γ-Fe O (25 mg, 5 mol% Pd), NaOt-Bu (31 mg,
2 3
mmol), and i-PrOH (1 mL), 70 °C, 12 h, argon. After the completion of
the reaction, the reaction mixture was decanted with the help of an
external magnet and the catalyst was washed with CH Cl , absolute
EtOH, and dried under vacuum at 50 °C. The formed activated catalyst
was used for the second and further reaction cycles following the
general reaction procedure.
0.33 mmol), and i-PrOH (1 mL) and the sealed tube was heated at 70
°
C for 12 h. GC-MS yield of 6a: 100%, based on naphthalene as stan-
2
2
dard.
GC-MS. m/z = 120.1 [M]+.
Dehalogenation of 1-Chloro-4-fluorobenzene
Following the general procedure for dehalogenation, 5b was convert-
ed into 6b and 7a. GC-MS yields of 6b and 7a are 37% and 42%, respec-
tively, based on naphthalene as standard.
Funding Information
This research was financially supported by the Ministry of Education,
Science and Technological Development of Serbia (Grant No. 172008
+
+
6
b; GC-MS: m/z = 96.1 [M] ; 7a; GC-MS: m/z = 78.0 [M] .
and III45004).
M
n
isitry
of
E
d
u
c
oaitn
,
Secince
a
n
d
Tech
n
o
lgcai
l
D
e
v
oelp
m
e
nt
of
S
erba
i
1(
7
2
0
0
8
M) nisitry
of
E
d
u
coaitn
,
S
ecin
c
e
a
n
d
Te
c
h
n
o
lgcai
l
D
e
v
oelp
m
e
nt
of
S
erba
i
4
I
5
(0
0
4)
Dehalogenation of 1-Bromo-4-chlorobenzene
Following the general procedure for dehalogenation, 5c was convert-
ed into 6c and 7a. GC-MS yields of 6c and 7a were 58% and 16%, re-
spectively, based on methyl benzoate as standard.
Supporting Information
+
+
Supporting information for this article is available online at
https://doi.org/10.1055/s-0036-1590892.
6
c; GC-MS: m/z = 112.0 [M] ; 7a; GC-MS: m/z = 78.0 [M] .
S
u
p
p
ortioIgnfmr oaitn
S
u
p
p
o
nrtogI
i
f
rm oaitn
Dehalogenation of 1-Chloro-4-iodobenzene
Following the general procedure for dehalogenation, 5d was convert-
ed into 6c and 7a. GC-MS yields of 6c and 7a were 60% and 18%, re-
spectively, based on methyl benzoate as standard.
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+
6
c; GC-MS: m/z = 112.0 [M] ; 7a; GC-MS: m/z = 78.0 [M] .
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Georg Thieme Verlag Stuttgart · New York — Synthesis 2017, 49, A–H

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Synthesis
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Paper
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©
Georg Thieme Verlag Stuttgart · New York — Synthesis 2017, 49, A–H