Aerobic oxidative C?C bond cleavage of aromatic alkenes by a high valency iron-containing perovskite catalyst

Article abstract of DOI:10.1039/d1cy00245g

High valency iron-containing perovskite catalyst BaFeO_3-dcould efficiently promote the additive-free oxidative C?C bond cleavage of various aromatic alkenes to the corresponding aldehydes or ketones using O₂as the sole oxidant. This system was applicable to the gram-scale oxidation of 1,1-diphenylethylene, in which 2.71 g (75% yield) of the analytically pure ketone could be isolated.

Full text of DOI:10.1039/d1cy00245g

Showcasing research from Professor Keigo Kamata’s
laboratory, Laboratory for Materials and Structures, Tokyo
Institute of Technology, Yokohama, Japan.
As featured in:
Aerobic oxidative C=C bond cleavage of aromatic alkenes
by a high valency iron-containing perovskite catalyst
High valency iron-containing perovskite BaFeO3−δ could
efficiently promote the oxidative C=C bond cleavage of
various aromatic alkenes to carbonyl compounds using
only O , without the need for any additives. The activation of
2
C=C bond to a radical species by BaFeO3–δ is a key step
for the reaction.
See Keigo Kamata,
Michikazu Hara et al.,
Catal. Sci. Technol., 2021, 11, 2369.
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Aerobic oxidative CC bond cleavage of aromatic
alkenes by a high valency iron-containing
perovskite catalyst†
Cite this: Catal. Sci. Technol., 2021,
1, 2369
1
Received 9th February 2021,
Accepted 24th February 2021
Satomi Shibata, Keigo Kamata * and Michikazu Hara
*
DOI: 10.1039/d1cy00245g
rsc.li/catalysis
High valency iron-containing perovskite catalyst BaFeO3−δ could
efficiently promote the additive-free oxidative CC bond
cleavage of various aromatic alkenes to the corresponding
transition metals such as Cu, Ti, Mn, Co, Fe, and V have been
reported for aerobic CC bond cleavage, there is plenty of
room for improvement with respect to the activity, selectivity,
substrate scope, and need for additives (Table S1, ESI†).
aldehydes or ketones using O
was applicable to the
,1-diphenylethylene, in which 2.71
analytically pure ketone could be isolated.
2
as the sole oxidant. This system
gram-scale oxidation of
(75% yield) of the
Perovskite oxides with the general formula ABO
3
are being
1
g
actively explored for industrial applications, such as
piezoelectric,
superconducting materials.
(multi)ferroelectric,
magnetic,
and
7
,8
Moreover, perovskite oxides
The oxidative CC bond cleavage of alkenes into the
corresponding carbonyl compounds is an important reaction
in both laboratories and chemical industry because aldehydes
and ketones are useful synthetic intermediates for the
and related materials have received significant attention as
substitutes for noble metal catalysts because of their unique
stability, compositional and structural varieties, and
9,10
controllable
physicochemical
properties.
However,
1–3
production of perfumes, dyes, and pharmaceuticals.
Stoichiometric oxidants such as O , m-chloroperbenzoic acid,
catalysis over multicomponent perovskites with corner-
sharing BO octahedra has mainly been investigated for gas-
phase reactions (CO/CH and reports on
3
6
KMnO
4
, CrO
2
Cl
2
, RuO
2
, and OsO
4
are typically utilized to
10,11
4
/NO oxidation),
accomplish efficient oxidative CC bond cleavage
liquid-phase organic reactions are limited. Therefore, we have
focused on the liquid-phase catalysis of hexagonal
perovskites with unique face-sharing octahedral units based
on high valency metal species. During the course of our
2
,4
(
Scheme 1(a)), although these methods have disadvantages
such as a requirement for specific equipment due to the
instability of O and the use of excess toxic and expensive
3
reagents and/or solvents. To address these issues, research has
been conducted on catalytic oxidative CC bond cleavage
reactions based on second- or third-row transition metal salts
and complexes (Ru, W, Os, In, Pd, Mo, Re, etc.) with NaIO4,
investigation
catalysts,
on
crystalline
first-row
metal
oxide
12–17
we have successfully synthesized various
hexagonal perovskite nanoparticle catalysts for the liquid
phase selective oxidation of various organic substrates with
NaClO, KHSO
5
, tert-butyl hydroperoxide (TBHP), and H
O
2 2
as
15–17
O as the sole oxidant.
2
In particular, high valency iron-
oxidants and/or radical initiators (Scheme 1(b)); (ref. 2, 5, 6)
however, most of these reactions are homogeneous, and have
some problems in the separation and recyclability of expensive
catalysts from reaction mixtures that include co-products of the
oxidants. In contrast, the development of effective
heterogeneous catalysts based on naturally abundant and easily
available first-row transition metals with molecular oxygen (O )
2
is a strongly desired and challenging research subject.
Although heterogeneous catalyst systems based on first-row
Laboratory for Materials and Structures, Institute of Innovative Research, Tokyo
Institute of Technology, Nagatsuta-cho 4259, Midori-ku, Yokohama-city, Kanagawa,
226-8503, Japan. E-mail: kamata.k.ac@m.titech.ac.jp
†
Electronic supplementary information (ESI) available. See DOI: 10.1039/
Scheme 1 Various oxidants for the oxidative CC bond cleavage of
d1cy00245g
alkenes.
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containing BaFeO3
was found to act as an efficient
For the BaFeO -catalyzed oxidation of 1a, the O pressure
3−δ 2
−δ
heterogeneous catalyst for the aerobic oxidation of alkanes to
the corresponding alcohols and ketones, in sharp contrast to
Fe /Fe oxides. Herein, we apply the superior oxidizing
had a strong effect on the selectivity to 2a and 3a, although
the total yield remained unchanged (Fig. 2(a)). The selectivity
to 2a increased from 68% to 87% with an increase in the O2
pressure from 0.1 MPa to 1.0 MPa (Fig. S2, ESI†), which
3
+
2+
17
ability of a BaFeO3 perovskite catalyst to aerobic oxidative
−δ
CC bond cleavage. In the presence of BaFeO3−δ various
2
indicates the concentration of O is critical to the selective
types of aromatic alkenes are converted to the corresponding
CC bond cleavage of 1a to 2a. The BaFeO3 -catalyzed
−δ
carbonyl compounds using only O , without the need for any
oxidation systems could be applied to the solvent-free
2
additives. This study provides the first demonstration of an
effective and reusable perovskite oxide catalyst for the
oxidative CC bond cleavage of alkenes.‡
Perovskite oxides including BaFeO3−δ were synthesized by
the sol–gel method using aspartic acid and/or malic acid and
characterized by elemental analysis, powder X-ray diffraction
oxidative cleavage of 1a to give 2a in 29% yield (Fig. 2(a)). In
this case, the reaction rate per surface area was 1.2 × 10
−
3
−
1
−2
−4
μmol h
m
and much higher than those (2.0 × 10 –4.8 ×
−
6
−1
−2
10 μmol h m ) of previously reported catalysts (Table
S1†). The total yield could also be increased to 71% by using
tert-amyl alcohol (t-AmOH) as a solvent (Fig. 2(a)).
(
XRD), N
2
sorption, scanning electron microscopy (SEM), and
After the oxidation of 1a was completed under the
1
7
X-ray photoelectron spectroscopy (XPS) (Fig. S1, ESI†). First,
the oxidative cleavage of styrene (1a) in benzotrifluoride
(
presence of various types of perovskite oxide and simple
oxide catalysts was examined (Fig. 1). Three main products,
namely, benzaldehyde (2a), styrene oxide (3a), and benzoic
acid (4a), were formed. The reaction did not proceed in the
absence of a catalyst under the reaction conditions employed.
Among the catalysts tested, BaFeO3−δ exhibited the highest
catalytic activity and gave 2a with 68% selectivity in 34% total
conditions shown in Fig. 1, the used BaFeO3 catalyst could
−δ
be easily recovered from the reaction mixture by simple
filtration. No significant leaching of Fe and Ba species into
the filtrate was confirmed by inductively coupled plasma
atomic emission spectroscopy (ICP-AES) analysis (Fe 0.04%
and Ba 0.2% with respect to the fresh BaFeO3−δ). In addition,
catalyst precursors (Fe(OAc) , Ba(OAc) , and a mixture of
3 2
PhCF ) using O (0.1 MPa) as the sole oxidant in the
2
2
2 2
Fe(OAc) and Ba(OAc) ) were almost inactive for the oxidative
CC bond cleavage of 1a to 2a (Fig. 1), which suggests that
there was no contribution to the observed catalysis from iron
yield. Another high valency iron-containing SrFeO
3
also
efficiently catalyzed the oxidation of 1a; however, the
2
−1
intrinsic activity per surface area of SrFeO (20 m g ) was
3
2
−1
lower than that of BaFeO3−δ (11 m g ). In addition, other
Fe /Fe -containing perovskite and simple oxides such as
CaFeO2.5, LaFeO , Fe O , and Fe O were much less effective
3
+
2+
3
2
3
3 4
for the present oxidation than BaFeO3−δ. These trends were
also observed in the aerobic oxidation of adamantane with
1
7
iron-containing oxides, which indicates the high intrinsic
oxidation activity of high valency iron-containing perovskite
oxides. Other Mn-, Co-, Ni-, Cu-, and Ru-containing oxides
(
SrMnO , BaMnO , activated MnO , BaCoO , LaCoO , Co O ,
3 3 2 3 3 3 4
LaNiO
3
, NiO, CuO, and BaRuO
3
) were also inactive. In the
nanoparticles and
montmorillonite K10, which have been reported to be active
3 4
presence of commercially-available Fe O
1
8,19
for the oxidative cleavage of 1a to 2a,
no formation of 2a
was observed under the reaction conditions employed.
Fig. 2 (a) Effect of O
cleavage reaction of 1a with O
mg), 1a (1 mmol), t-AmOH (1 mL), pO
2
pressure and solvent on the CC bond
a
2
catalyzed by BaFeO3−δ
. Catalyst (25
b
2
(1.0 MPa), 363 K, 12 h. Catalyst
c
(50 mg), 1a (8.8 mmol), pO
2
(1.0 MPa), 363 K, 4 h. Catalyst (50 mg), 1a
2
(0.1–1.0 MPa), 363 K, 24 h. (b) Time course
(
1 mmol), PhCF (1 mL), pO
3
Fig. 1 Effect of catalysts on the CC bond cleavage reaction of 1a
2
for the CC bond cleavage reaction of 1a with O catalyzed by
with O
2
.
BaFeO3−δ. The reaction conditions are the same as those of Fig. 1.
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or barium species leached into the reaction solution. There
was no significant difference in the XRD patterns and XPS
spectra between the fresh and recovered catalysts, although
the XRD peaks were slightly shifted, possibly due to the
yield (fresh), selectivity (1a/2a/3a = 65%/25%/10%) at 37%
total yield (reused).
Furthermore, the BaFeO3−δ-catalyzed system was
applicable to oxidative CC bond cleavage reactions of
formation of oxygen-deficient BaFeO3 (Fig. S3, ESI†). The
various types of alkenes with O (1.0 MPa) as the sole oxidant
−δ
2
recovered BaFeO3−δ catalyst could then be reused without a
significant change in the total yield or selectivity to each
product: selectivity (1a/2a/3a = 68%/24%/8%) at 34% total
(Table 1). Styrenes with electron-donating p-substituents
(1b–1d) were converted into the corresponding aldehydes
(2b–2d) as main products, and the formation of their
a
Table 1 CC bond cleavage reaction of various aromatic alkenes with O
2
catalyzed by BaFeO3−δ
Entry
1
Substrate
Time (h)
Product (yield (%))
24
12
6
1
1
a
2a (30)
2b (26)
4a (4)
2
b
4b (14)
b
3
1
1
1
1
c
d
e
f
2c (30)
2d (27)
2e (34)
2f (47)
4c (1)
c
4
24
24
24
96
12
4d (10)
4e (17)
4f (6)
5
6
d
7
1
1
g
2g (32)
8
9
2
2
a (30)
h
3h (4)
24
24
1
i
2a (4)
10
a (12)
1
1
j
3j (4)
1
1
2
24
24
2a (1)
k
1
1
1
l
2l (75)
e
13
30
m
2m (70)
a
b
c
Reaction conditions: catalyst (50 mg), substrate (0.5 mmol), solvent (1 mL), pO
2
(1 MPa), 363 K, 24 h. Epoxide (1% yield). Epoxide (2%
d
e
yield). 373 K. Catalyst (25 mg).
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carboxylic acids (4b and 4d) was observed in alkyl
substituent-containing styrenes (entries 2–4). Oxidative
cleavage of para-halogenated 4-fluorostyrene (1e) and
4
-chlorostyrene (1f) also proceeded to afford the
corresponding aldehydes (2e and 2f) and carboxylic acids (4e
and 4f) (entries 5 and 6). On the other hand, p-nitrostyrene
(1g) with a strong electron-withdrawing group was also
oxidized to the corresponding aldehyde, although a longer
reaction time was required (entry 7). It has been reported for
Pt@Fe O and Pd(OAc)2 systems that substrates with
2
3
electron-withdrawing substituents are less active for the
oxidative cleavage of styrene derivatives than those with
2
0,21
electron-donating
substituents.
Not
only
monosubstituted styrenes, but also disubstituted styrenes
were also oxidized to the corresponding aldehydes and
ketones. In the case of 1,2-disubstituted β-methylstyrenes,
the trans-isomer (1h) was more reactive than the cis-isomer
Fig. 3 (a) Proposed reaction pathways and (b) computational free
energy diagrams of the aerobic oxidative cleavage reaction of 1a and
−1
related reactions. Energies are shown in kJ mol
.
(1i), and the yields of 2a were 30% and 4% from 1h and 1i,
respectively (entries 8 and 9). Similar stereospecificity for
more electron-rich but sterically-hindered trans-stilbene (1j)
and cis-stilbene (1k) was observed; however, the yields of 2a
were low in comparison with 1h and 1i (entries 10 and 11). It
has also been reported that trans-isomers are more active
(2,2,6,6-tetramethylpiperidine 1-oxyl (TEMPO) or 2,6-di-tert-
butyl-p-cresol (BHT); 1 equiv. relative to 1a) from the begging
and in the middle of the reaction completely suppressed the
progress of the reaction (Fig. S6, ESI†). A similar effect of a
radical initiator and scavenger have been observed in the KSF
2
2
than
,1-Disubstited α-methylstyrene (1l) and 1,1-diphenylethylene
1m) were efficiently converted to acetophenone (2l and
benzophenone (2m) in 75% and 70% yields, respectively
entries 12 and 13). In addition, the present system was
cis-isomers
in
radical-mediated
reactions.
montmorillonite systems, for which
a
radical-type
1
9
1
(
mechanism has been proposed.
When BaFeO3 was
−δ
removed by hot filtration after 16 h, the reaction did not stop
and proceeded in a similar way to that without the filtration
step (Fig. S3, ESI†). Such phenomena were also reported for
the aerobic oxidation of sulfides with MIL-101 catalysts via a
(
applicable to the gram-scale reaction of 1m and 2.71 g of
analytically pure 2m could be isolated (eqn (1)). The present
system was not effective for the oxidative cleavage of aliphatic
alkenes (1-octene, 2-octene, and allylbenzene), and such a
limitation of scope is similar to previously reported systems
2
3
radical-chain mechanism. The reaction did not proceed at
all under an Ar atmosphere (Fig. S5(b), ESI†), which suggests
that BaFeO3−δ does not act as a stochiometric oxidant, but as
a catalyst for the present oxidation.
2
based on first-row transition metals (Table S1†).
These results indicate the BaFeO3 -catalyzed oxidation of
−δ
1a to 2a likely involves a radical mechanism where BaFeO3−δ
would activate 1a to form an active radical species such as a
benzyl radical, which has been often suggested for Fe and
Mn catalysts (Fig. 3(a)). The selectivity to 3a decreased with
(
1)
2
an increase in the O
a increased with a decrease in the selectivity to 2a; therefore,
3a would be formed by the aerobic epoxidation of 1a with 2a
2
pressure and the selectivity to 3a and
4
H2 temperature-programmed reduction (H -TPR) analysis
was conducted to compare the intrinsic oxidation ability of
2
2
4
2
as a co-reductant. At high O pressure, radical species likely
BaFeO3 to those of other iron-based perovskite oxides (Fig.
react with O2 to form peroxy intermediates followed by
−δ
S4, ESI†). The H consumption per surface area below 573 K
rearrangement to 2a (Fig. 3(a), pathway A). On the other
hand, at low O pressure radical species would attack
2
2
−
2
−2
decreased in the order of BaFeO3−δ (3.1 × 10 mmol m ) >
−
3
−2
−3
SrFeO (8.3 × 10 mmol m ) > LaFeO (1.3 × 10 mmol
hydrogen atom of 2a followed by reaction with O to form a
3
3
2
−
2
−4
−2
m ) > CaFeO (6.2 × 10 mmol m ), which is reasonable
peracid, which can promote the epoxidation of 1a to 3a with
the co-production of 4a (Fig. 3(a), pathway B). 4a is also
formed by the aerobic oxidation of 2a (Fig. 3(a), pathway C).
Density functional theory (DFT) calculations were performed
to confirm the possible reaction pathways for the formation
2
.5
given the high reactivity of BaFeO3–δ. The time course for the
oxidative cleavage of 1a to 2a with 0.1 MPa of O catalyzed by
2
BaFeO3 is shown in Fig. 2(b). The reaction proceeded with
−δ
an induction period, and only 2a was observed at the initial
stage of the reaction. The selectivity to 2a then gradually
decreased with an increase in the selectivity to 3a and 4a.
This induction period completely disappeared upon the
addition of a radical initiator (TBHP; 0.3 equiv. relative to 1a,
Fig. S5(a), ESI†), and the addition of a radical scavenger
of 2a, 3a, and 4a from 1a and O (Fig. 3(b)). The reaction of
2
1a with O
2
to form an intermediate with a four-membered
dioxyethane moiety was calculated to be endothermic by 26
−
1
kJ mol ; therefore, the pathway via this intermediate
proposed for Co, Cu, and Cr catalysts would be
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2
,25,26
thermodynamically unfavorable.
On the other hand, not
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only the CC bond cleavage oxidation of 1a with O to 2a
2
−
1
and HCHO (exothermic by −303 kJ mol ), but also the
epoxidation of 1a to 3a with peroxybenzoic acid from 2a and
−
1
O2 (exothermic by −271 kJ mol ) were thermodynamically
favourable, which is in good agreement with the proposed
reaction pathways.
In conclusion, the high valency iron-based BaFeO3
−δ
perovskite oxide could act as a heterogeneous catalyst for the
aerobic oxidative CC bond cleavage of various aromatic
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2
the sole oxidant.
This study was funded in part by JSPS KAKENHI Grant
numbers JP20J11604 and JP18H01786, JST A-STEP
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analysis with the help of K. K. S. S. and K. K. wrote the paper.
The draft was reviewed by S. S., K. K., and M. H.
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Conflicts of interest
There are no conflicts to declare.
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‡
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