Direct oxidative C(sp3)─H/C(sp2)─H coupling reaction using recyclable Sr-doped LaCoO3 perovskite catalyst

Article abstract of DOI:10.1002/aoc.5515

A strontium-doped lanthanum cobaltite perovskite, La_0.6Sr_0.4CoO₃, was prepared and utilized as a recyclable heterogeneous catalyst for the direct oxidative C(sp³)─H/C(sp²)─H coupling reaction between

Full text of DOI:10.1002/aoc.5515

Received: 1 October 2019
DOI: 10.1002/aoc.5515
Revised: 3 December 2019
Accepted: 2 January 2020
F U L L P A P E R
Direct oxidative C(sp3)─H/C(sp2)─H coupling reaction
using recyclable Sr-doped LaCoO3 perovskite catalyst
Khang H. Trinh | Phuong H. Tran | Thanh T. Nguyen | Son H. Doan
Minh-Vien Le | Tung T. Nguyen | Nam T.S. Phan
|
Faculty of Chemical Engineering, HCMC
University of Technology, VNU-HCM,
268 Ly Thuong Kiet, District, 10, Ho Chi
Minh City, Vietnam
A strontium-doped lanthanum cobaltite perovskite, La0.6Sr0.4CoO3, was
prepared and utilized as a recyclable heterogeneous catalyst for the direct
oxidative C(sp3)─H/C(sp2)─H coupling reaction between cyclic ethers and
alkenes or coumarins to achieve corresponding α-functionalized ethers. The α-
functionalization of cyclic thioethers or amides with alkenes or coumarins was
also achieved via this protocol. The La0.6Sr0.4CoO3 catalyst exhibited better
performance than a variety of homogeneous and heterogeneous catalysts.
Utilizing a recyclable catalyst would offer a greener option for the direct
oxidative C(sp3)─H/C(sp2)─H coupling reaction. To our best knowledge, the
C(sp3)─H/C(sp2)─H coupling between olefins and ethers to generate α-
functionalized ethers using a heterogeneous catalyst has not been previously
reported, and the α-functionalization of cyclic thioethers or amides with
alkenes or coumarins is new.
Correspondence
Tung T. Nguyen, Nam T. S. Phan, Faculty
of Chemical Engineering, HCMC
University of Technology, VNU-HCM,
268 Ly Thuong Kiet, District 10, Ho Chi
Minh City, Vietnam.
Email: tungtn@hcmut.edu.vn; ptsnam@
hcmut.edu.vn
Funding information
The Vietnam National University - Ho Chi
Minh City (VNU-HCM), Grant/Award
Number: NCM2019-20-01
K E Y W O R D S
alkenes, ethers, perovskite, coupling, heterogeneous, C─H functionalization
1 | INTRODUCTION
via α-C(sp3)─H bond functionalization of these structures
would be of considerable synthetic value.[7] Liu et al.
Metal-catalyzed organic transformations via C─H bond
functionalization have been the subject of significant
interest during the last decade, offering advantages in
terms of atom economy, step efficiency, and waste
minimization.[1–3] The functionalization of inert
C(sp3)─H bonds would be the most challenging task, as
the opportunity to utilize classical reactions is minimized
in this case.[4] Several efforts have recently been devoted
to achieving new synthetic protocols via the func-
tionalization of C(sp3)─H bonds.[5,6] α-Functionalized
ether or amine derivatives are widely present in a variety
of bioactive molecules with valuable pharmacological
and medicinal properties, and therefore transformations
previously
reported
a
CuI-catalyzed
oxidative
C(sp3)─H/C(sp2)─H coupling between olefins and ethers
to generate α-functionalized ethers.[8] Coumarins and
their derivatives are important structural motifs which
are found widely in numerous biologically active natural
products as well as functionalized organic materials.[9,10]
The modification of naturally occurring skeletons has
been extensively investigated to achieve fascinating
biological properties.[11–13] Nevertheless, reports of the
functionalization of coumarins via direct C─H bond
functionalization are very limited in the literature.[14,15]
Niu et al. previously reported a FeCl3-catalyzed oxidative
coupling transformation of coumarins to afford
corresponding α-functionalized ethers.[16] Indeed, the
field still remains to be fully explored.
Khang H. Trinh and Phuong H. Tran contributed equally to this work.
Appl Organometal Chem. 2020;e5515.
wileyonlinelibrary.com/journal/aoc
© 2020 John Wiley & Sons, Ltd.
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https://doi.org/10.1002/aoc.5515

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TRINH ET AL.
The past few decades have witnessed extensive
research on applications of perovskites in many
fields.[17–20] Perovskites are complex metal oxides with
the general formula ABO3, in which A can be an alkali
metal, alkaline earth metal or lanthanide metal while B
represents a metallic element with a 3d, 4d or 5d
configuration.[21–23] When A is substituted by other
metals, the valence state of B is affected; therefore differ-
ent catalytic activity would be expected.[24] In the field of
catalysis, perovskites have been extensively used as het-
erogeneous catalysts for a variety of reduction–oxidation
processes.[25–29] Additionally, the acid–base catalytic
properties of perovskites have also been studied.[22]
Unmodified and modified lanthanum cobaltite perov-
skites have previously been shown to exhibit high cata-
lytic activity for CO oxidation,[24,30] NO oxidation,[31]
syngas conversion,[32,33] and hydrogen production.[34]
Nonetheless, the utilization of perovskite catalysts in the
organic synthesis field is very rare in the literature. One
example of using Sr-doped LaCoO3 perovskite catalyst
for the synthesis of triphenylpyridines has been
reported.[35]
Uses of metal oxides in organic synthesis are exten-
sively emerging. On introduction of active metals into
the framework of oxide supports using impregnating
methods, catalytic activity and thermal stability of
transition metals are improved.[36–38] Many methods that
allow for the synthesis of heterocycles from metal oxide-
catalyzed, direct C─H functionalization are known.[39,40]
Mixtures of metal oxides are also calcined to feature
synergistic effects, thus improving efficiency.[41] For
example, Glorius and co-workers reported a copper iron
oxide-catalyzed direct arylation of C─H bonds in
heteroarenes that showed both better reactivity and
more convenient separation in comparison with nano-
CuO.[42]
SCHEME 1 C(sp3)─H/C(sp2)─H coupling between olefins
and ethers or thioethers (a) and between olefins and amides (b)
2 | EXPERIMENTAL
La0.6Sr0.4CoO3 powder was synthesized using La(NO3)3,
Sr(NO3)2, and Co(NO3)2 as starting materials, following a
literature procedure.[31] The perovskite was subsequently
characterized using several common analysis methods
(Figures S1–S4). The presences of CoO3, La(OH)3, and
SrCO3 phases were confirmed using powder X-ray
diffraction (XRD) analysis (Fig. 3). The result is also in
agreement with that obtained by González-Velasco and
co-workers.[31] The results of energy-dispersive X-ray
analysis indicated the presence of lanthanum, strontium,
cobalt, and oxygen elements in the structure of the perov-
skite with a molar ratio of La:Sr:Co as 0.63:0.37:1.07
(Figure S2). Inductively coupled plasma MS results
confirmed a ratio of 0.63:0.38:1.0, which is in line with
the formula of La0.6Sr0.4CoO3.
In continuation of our interest in using metal oxides
for C─H functionalization, herein we report the applica-
tion of La0.6Sr0.4CoO3 perovskite as a recyclable heteroge-
neous
catalyst
for
the
direct
oxidative
C(sp3)─H/C(sp2)─H coupling between cyclic ethers and
alkenes or coumarins to achieve the corresponding α-
functionalized ethers (Scheme 1a). The research scope
was additionally expanded to the α-functionalization of
cyclic thioethers or amides with alkenes or coumarins
(Scheme 1b). The catalyst was recycled and reused many
times, offering a greener option for the direct oxidative
coupling than other available methods. To our best
knowledge, the C(sp3)─H/C(sp2)─H coupling between
olefins and ethers to generate α-functionalized ethers
using a heterogeneous catalyst has not been previously
reported, and the α-functionalization of cyclic thioethers
or amides with alkenes or coumarins is new.
In
a
typical experiment,
a
mixture of
1,1-diphenylethylene (55 μl, 0.3 mmol), di-tert-butyl per-
oxide (DTBP; 220 μl, 1.2 mmol), KI (0.01 g, 0.06 mmol),
La0.6Sr0.4CoO3 catalyst, and diphenyl ether (16 μl,
0.1 mmol) as an internal standard was added into an
8 ml screw-cap pressurized vial containing 1 ml of tetra-
hydrofuran (THF). The reaction mixture was then stirred
at 120ꢀC for 20 hours. The yield of the desired product
was recorded by withdrawing samples from the reaction
mixture, dissolving in ethyl acetate (2 ml), drying over

DIRECT COUPLING REACTION UNDER PEROVSKITE CATALYSIS
3 of 10
TABLE 1 Screening of reaction conditionsa
Additive
amount
Oxidant
amount
(equiv.)
Catalyst
amount
(mol%)
Entry
1
Additive
KF
NH4Cl
KBr
NaI
KI
(mol%)
20
20
20
20
20
0
Temperature (ꢀC)
Oxidantb
DTBP
DTBP
DTBP
DTBP
DTBP
DTBP
DTBP
DTBP
DTBP
DTBP
DTBP
DTBP
DTBP
DTBP
DTBP
K2S2O8
AgNO3
Oxygen
H2O2
Yield (%)c
120
120
120
120
120
120
120
120
120
120
RT
4
4
4
4
4
4
4
4
4
4
4
4
4
4
4
4
4
4
4
4
4
4
4
4
0
1
2
3
4
4
4
4
4
4
5
5
5
5
5
5
5
5
5
5
5
5
5
5
5
5
5
5
5
5
5
5
5
5
5
5
5
5
5
0
1
3
5
7
37
0
2
3
26
60
84
0
4
5
6
KI
7
KI
10
15
20
25
20
20
20
20
20
20
20
20
20
20
20
20
20
20
20
20
20
20
20
20
20
20
20
20
39
68
84
84
0
8
KI
9
KI
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
KI
KI
KI
80
2
KI
100
120
140
120
120
120
120
120
120
120
120
120
120
120
120
120
120
120
120
120
120
120
27
84
83
1
KI
KI
KI
KI
4
KI
1
KI
1
KI
aqTBHP
dcTBHP
TBPB
2
KI
19
1
KI
KI
CHP
11
84
0
KI
DTBP
DTBP
DTBP
DTBP
DTBP
DTBP
DTBP
DTBP
DTBP
DTBP
DTBP
KI
KI
25
49
61
84
0
KI
KI
KI
KI
KI
49
65
84
85
KI
KI
KI
aReaction conditions: 1,1-diphenylethylene (0.3 mmol); THF (1 ml); under air for 20 hours.
bDTBP: di-tert-butylperoxide; aqTBHP: tert-butyl hydroperoxide in water; dcTBHP: tert-butyl hydroperoxide in decane; CHP: cumyl hydroperoxide; TBPB:
tert-butyl peroxybenzoate.
cGC yield.

4 of 10
TRINH ET AL.
anhydrous Na2SO4, filtering, and analyzing using GC
concerning the internal standard. In order to isolate the
product, ethyl acetate (3 × 15 ml) was added to the reac-
tion mixture. The ethyl acetate phase was concentrated
under reduced pressure and purified by column chroma-
tography on silica gel with hexane–ethyl acetate as elu-
KI, producing the desired product in 84% yield (entry 9).
Extending the amount of KI did not favor the transforma-
tion significantly. The temperature displayed a consider-
able impact on the coupling reaction (entries 11–15). No
product was detected if the reaction was run at room
temperature, while only 2% yield was observed for that
performed at 80ꢀC. Increasing the reaction temperature
significantly accelerated the transformation. The best
result was recorded for the reaction carried out at 120ꢀC,
affording the major product in 84% yield (entry 14).
Increasing the temperature to over 120ꢀC did not lead to
higher yield.
1
ent. The product structure was verified using GC-MS, H
NMR, and 13C NMR. To explore the possibility of catalyst
recycling, the La0.6Sr0.4CoO3 catalyst was isolated from
the reaction mixture by centrifugation, washed several
times with ethyl acetate, acetone, and diethyl ether, dried
under reduced pressure at room temperature overnight,
and reused for further catalytic runs.
Similar to other oxidative coupling reactions, an
oxidant was required for the C(sp3)─H/C(sp2)─H
3 | RESULTS AND DISCUSSION
TABLE 2 Direct oxidative C(sp3)─H/C(sp2)─H coupling
reaction between 1,1-diphenylethylene and THF utilizing various
catalystsa
The research was commenced with the direct oxidative
C(sp3)─H/C(sp2)─H coupling reaction between 1,1-
diphenylethylene and THF to produce 2-(2,2-
diphenylvinyl)tetrahydrofuran as the major product
(Table 1). Reaction conditions were studied to maximize
the yield of the coupling product. The reaction was con-
ducted at 120ꢀC under air for 20 hours, using 5 mol%
perovskite catalyst, in the presence of 20 mol% additive
and 4 equivalents of oxidant. Initially, various additives
were used (entries 1–5). In this series, KI emerged as the
best additive, affording the desired product in 84% yield
(entry 5). The reaction was considerably affected by the
amount of KI (entries 6–10). It was noted that the
reaction did not proceed in the absence of KI, with no
trace evidence of product being detected. Utilizing
10 mol% KI led to 39% yield being recorded, while 68%
yield was observed in the presence of 15 mol% KI. The
best result was achieved for the reaction using 20 mol%
Homogeneous
Entry catalyst
Heterogeneous
catalyst
Yield
(%)b
1
FeCl2
1
0
2
CuCl2
3
CuI
4
4
Cu(NO3)2
CuSO4
1
5
46
3
6
Co(NO3)2
La(NO3)2
Sr(NO3)2
7
36
54
8
9
Cu2(BPDC)2(DABCO) 37
10
11
12
13
14
15
16
17
18
19
ZIF-8A
17
10
11
8
Fe3(BTC)2(NDC)
La2O3
CoO
SrO
13
40
84
31
52
49
LaCoO3
La0.6Sr0.4CoO3
La0.2Sr0.8CoO3
La0.4Sr0.6CoO3
La0.8Sr0.2CoO3
aReaction conditions: 1,1-diphenylethylene (0.3 mmol); THF (1 ml); DTBP
(1.2 mmol); KI (20 mol%); catalyst (5 mol%); 120ꢀC; under air for 20 hours.
bGC yield.
FIGURE 1 Leaching studies showing that no additional
2-(2,2-diphenylvinyl)tetrahydrofuran was produced after catalyst
separation

DIRECT COUPLING REACTION UNDER PEROVSKITE CATALYSIS
5 of 10
coupling reaction between 1,1-diphenylethylene and
THF. We therefore tested a series of oxidants for this
reaction, including both inorganic and organic oxidants
(entries 16–24). It was noted that the reaction was mark-
edly controlled by the nature of the oxidant. Inorganic
oxidants such as K2S2O8, AgNO3, oxygen, and hydrogen
peroxide were ineffective for this transformation,
affording 2-(2,2-diphenylvinyl)tetrahydrofuran in less
than 5 % yield. tert-Butyl hydroperoxide both in water
and in decane exhibited low performance, with 2% and
19% yields being recorded, respectively. tert-Butyl per-
oxybenzoate and cumyl hydroperoxide should also not be
used for this reaction. In this oxidant series, DTBP
emerged as the best choice, and using this oxidant led to
84% yield (entry 24). The amount of DTBP was also cru-
cial (entries 25–29). No product was detected in the
absence of DTBP, verifying the essential role of the oxi-
dant in this coupling. Extending the oxidant quantity
noticeably accelerated the reaction, and the best result
was observed for the experiment utilizing 4 equivalents
of DTBP. Having these results in hand, we subsequently
investigated the influence of the amount of perovskite on
the reaction (entries 30–34). No trace of the major
product was observed in the absence of the perovskite
catalyst, while 49% yield was recorded for the reaction
using 1 mol% catalyst. Increasing the amount of the
perovskite substantially accelerated the transformation.
Nevertheless, utilizing more than 5 mol% catalyst did not
result in higher yields.
Owing to the fact that the direct oxidative
C(sp3)─H/C(sp2)─H coupling reaction between 1,1-
diphenylethylene and THF to afford 2-(2,2-
diphenylvinyl)tetrahydrofuran proceeded in THF phase,
an important experiment that must be conducted is the
leaching test. In order to clarify if catalytically active
species were migrated to any great extent from the
solid perovskite catalyst into the liquid phase during
the transformation, a control experiment was per-
formed. The reaction was performed at 120ꢀC under air
for 20 hours, using 5 mol% perovskite catalyst, in the
presence of 20 mol% KI as the additive and 4 equiva-
lents of DTBP as the oxidant. After 4 hours reaction
time with 43% yield being noticed, the perovskite cata-
lyst was separated from the reaction mixture by centri-
fugation. The solution phase was subsequently collected
and added to a new 8 ml screw-cap pressurized vial.
The mixture was then heated at 120ꢀC under air for an
additional 16 hours. The reaction yield during this
16 hour period was monitored using GC, providing
quantitative data to confirm if the transformation using
the La0.6Sr0.4CoO3 catalyst was truly heterogeneous. It
was
noted
that
virtually
no
additional
2-(2,2-diphenylvinyl)tetrahydrofuran was detected after
the separation of the strontium-doped lanthanum
cobaltite perovskite (Figure 1). These data confirmed
that the La0.6Sr0.4CoO3-catalyzed direct oxidative cou-
pling between 1,1-diphenylethylene and THF occurred
under real heterogeneous conditions.
SCHEME 2 Radical-trapping experiment (a) and
plausible reaction mechanism (b)

6 of 10
TRINH ET AL.
To explore the advantages of using the La0.6Sr0.4CoO3
perovskite catalyst, its efficiency in the reaction between
1,1-diphenylethylene and THF was compared to that of
several homogeneous and heterogeneous catalysts
(Table 2). Initially, numerous homogeneous catalysts
were tested for this reaction (entries 1–8). FeCl2 was inac-
tive toward this reaction, with the major product being
detected in 1% yield. CuI, CuCl2, and Cu(NO3)3 also
exhibited poor performance in this transformation.
CuSO4 offered better catalytic activity, generating
2-(2,2-diphenylvinyl)tetrahydrofuran in 46% yield.
Among the three precursors utilized to prepare the
La0.6Sr0.4CoO3perovskite catalyst, Co(NO3)2 led to the
lowest catalytic efficiency, forming the desired product in
3% yield. La(NO3)3 and Sr(NO3)2 were found to be more
active than Co(NO3)2, with 36% and 54% yields being
recorded, respectively. Moving to heterogeneous cata-
lysts, MOF-based catalysts such as Cu2(BPDC)2(DABCO),
ZIF-8A, and Fe3(BTC)2(NDC) offered low activity (entries
9–11). The reaction utilizing single oxides, including
La2O3, CoO, and SrO, resulted in 11%, 8%, and 13%
yields, respectively (entries 12–14). The pristine perov-
skite, LaCoCo3, was found to be more active than three
single oxides, affording the major product in 40% yield
(entry 15). Doping the perovskite with strontium led to
higher catalytic activity, achieving 84% yield (entry 16).
Varying the ratio of lanthanum to strontium was also
attempted (entries 17–19). It was found that at a ratio of
La/Sr of 3:2 (corresponding to La0.6Sr0.4CoO3), the perov-
skite gave the best yield of product.
FIGURE 3 XRD observations of fresh (a) and reused
(b) La0.6Sr0.4CoO3 catalysts [Colour figure can be viewed at
wileyonlinelibrary.com]
could be supposed that the interaction of the
intermediate radicals with the antioxidant would cease
the reaction. In addition, MS analysis indicated the pres-
ence of 2,2,6,6-tetramethyl-1-(tetrahydrofuran-2-yloxy)
piperidine as an intermediate in the reaction mixture
(Scheme 2a). On the basis of all these results and previous
reports,[8,43–47]
a reaction pathway is proposed as
described in Scheme 2b. Initially, tert-butoxy radical
would be formed through the cleavage of DTBP with the
assistance of the perovskite catalyst. Subsequently,
tert-butoxy radical would abstract a hydrogen atom from
THF to generate the cyclic ether radical intermediate 1.
After that, the radical addition of the cyclic ether radical
intermediate 1 into 1,1-diphenylethylene would provide
the radical 2, followed by the direct oxidation of this
When
a
radical trapping reagent, namely
(2,2,6,6-tetramethylpiperidin-1-yl)oxyl (TEMPO), was
introduced into the reaction mixture, the cross-
dehydrogenative coupling of 1,1-diphenylethylene with
THF was totally inhibited (Scheme 2a), implying the
involvement of a radical process in this transformation. It
FIGURE 4 Fourier transform infrared spectra of fresh (a) and
reused (b) La0.6Sr0.4CoO3 catalysts [Colour figure can be viewed at
wileyonlinelibrary.com]
FIGURE 2 Catalyst recycling studies

DIRECT COUPLING REACTION UNDER PEROVSKITE CATALYSIS
7 of 10
TABLE 3 Direct oxidative C(sp3)─H/C(sp2)─H coupling reaction using La0.6Sr0.4CoO3 perovskite catalysta
Entry
Reactant 1
Reactant 2
Product
Yield (%)b
1
79
84
77
74
72
81
73
2
3
4
5
6
7
(Continues)

8 of 10
TRINH ET AL.
TABLE 3 (Continued)
Entry
Reactant 1
Reactant 2
Product
Yield (%)b
8
81
9
80
75
10
11
77
12
13
82
75
14
85
aReaction conditions: reactant 1 (0.3 mmol); reactant 2 (1 ml); DTBP (1.2 mmol); KI (20 mol%); La0.6Sr0.4CoO3 catalyst (5 mol%); 120ꢀC; under air for 20 hours.
bIsolated yield.
radical by Mn+1 and KI to release the final coupling prod-
uct 3. Meanwhile, the Mn+ species is regenerated back to
the catalytic cycle. In this catalytic cycle, M could be
cobalt sites in the La0.6Sr0.4CoO3 catalyst. The reaction
afforded 8% yield in the presence of CoO catalyst, and this
value was improved to 40% yield in the presence of
LaCoCO3 catalyst. Utilizing the strontium-doped perov-
skite, La0.6Sr0.4CoO3, as catalyst, the reaction proceeded
to 84% yield. It was previously reported that substituting
La(III) site by Sr(II) site in the LaCoCO3 perovskite would

DIRECT COUPLING REACTION UNDER PEROVSKITE CATALYSIS
9 of 10
enhance the mobility of lattice oxygen, leading to a con-
siderable improvement in the redox activity of the
perovskite.[24,48]
Some products were examined with HMBC and HSQC
analyses to clarify the isomeric structures. These results
offered a new pathway to functionalize coumarin and its
derivatives.
With these results in mind, we subsequently
investigated the possibility of catalyst recycling in the
direct
oxidative
C(sp3)─H/C(sp2)─H
coupling
reaction between 1,1-diphenylethylene and THF to pro-
duce 2-(2,2-diphenylvinyl)tetrahydrofuran. Ideally, the
La0.6Sr0.4CoO3 catalyst should be recoverable and reus-
able many times before it was ultimately deactivated
completely. To clarify this issue, the reaction was
performed at 120ꢀC under air for 20 hours, using 5 mol%
catalyst, in the presence of 20 mol% KI as the additive
and 4 equivalents of DTBP as the oxidant. Upon comple-
tion of the experiment, the La0.6Sr0.4CoO3 catalyst was
separated from the reaction mixture by centrifugation,
and thoroughly washed with ethyl acetate, acetone, and
diethyl ether to remove any residue of organic compo-
nents. After that, the perovskite was dried at room
temperature overnight under vacuum using a Schlenk
line, and reused as catalyst for the next catalytic reaction.
In was noticed that under these conditions, the
La0.6Sr0.4CoO3 catalyst could be reutilized several times
without considerable loss of performance. The transfor-
mation afforded 80% yield of 2-(2,2-diphenylvinyl)tetra-
hydrofuran in the fifth run (Figure 2). Additionally, the
reused La0.6Sr0.4CoO3 catalyst was characterized using
XRD (Figure 3) and Fourier transform infrared (Figure 4)
techniques. The analysis results confirmed that the cata-
4 | CONCLUSIONS
In summary, a strontium-doped lanthanum cobaltite
perovskite, La0.6Sr0.4CoO3, was prepared and utilized as a
heterogeneous catalyst for the direct oxidative
C(sp3)─H/C(sp2)─H coupling reaction between cyclic
ethers and alkenes or coumarins to achieve
corresponding α-functionalized ethers. This protocol was
also applicable to the α-functionalization of cyclic
thioethers or amides with alkenes or coumarins. The
reaction proceeded readily in the presence of a peroxide
and an additive, and the combination of DTBP and KI
offered the best results. The La0.6Sr0.4CoO3 catalyst
exhibited better performance than that of a variety of
homogeneous and heterogeneous catalysts. The pristine
perovskite, LaCoCo3, was more active than three single
oxides, including La2O3, CoO, and SrO, while doping the
LaCoCo3 perovskite with strontium led to significantly
higher catalytic activity in the α-functionalization of
cyclic ethers, cyclic thioethers or amides with alkenes or
coumarins. The La0.6Sr0.4CoO3-catalyzed direct oxidative
coupling occurred under real heterogeneous conditions.
It was possible to recover and reutilize the La0.6Sr0.4CoO3
catalyst several times without considerable deterioration
in performance. These results would offer a greener
option for direct C(sp3)─H/C(sp2)─H coupling and would
be useful in chemical and pharmaceutical industries.
lyst
C(sp3)─H/C(sp2)─H
1,1-diphenylethylene and THF.
was
stable
in
the
direct
reaction
oxidative
between
coupling
The scope of this work was accordingly extended to
the direct oxidative C(sp3)─H/C(sp2)─H coupling
reactions of various reactants using the La0.6Sr0.4CoO3
perovskite catalyst (Table 3). In the first experiment
series, the reaction between 1,1-diphenylethylene and
several C(sp3)─H bonds was explored. Using this
ACKNOWLEDGMENT
The Vietnam National University – Ho Chi Minh City
(VNU-HCM) is acknowledged for financial support via
project no. NCM2019-20-01.
protocol,
2-(2,2-diphenylvinyl)tetrahydrofuran
was
achieved in 79% isolated yield (entry 1). Tetrahydro-
thiophene was slightly more reactive than THF, affording
2-(2,2-diphenylvinyl)tetrahydrothiophene in 84% yield
(entry 2). Similarly, tetrahydropyran (entry 3) and
1,4-dioxane (entry 4) were also reactive toward this
reaction. Interestingly, 1-methylpyrrolidin-2-one could be
ORCID
Son H. Doan https://orcid.org/0000-0002-3848-2645
Minh-Vien Le https://orcid.org/0000-0002-6651-0121
Tung T. Nguyen https://orcid.org/0000-0002-0912-9981
Nam T.S. Phan https://orcid.org/0000-0002-5928-7638
used,
forming
1-methyl-5-(2-oxo-2H-chromen-3-yl)
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pyrrolidin-2-one in 72% yield (entry 5). Dimethylfor-
mamide was more reactive, with 81% yield of the product
being recorded (entry 6). Furthermore, it was found that
coumarin could be functionalized, affording the
corresponding products in high yields (entries 7–11).
Similarly, substituted coumarins were also reactive
towards this direct oxidative coupling (entries 12–14).
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How to cite this article: Trinh KH, Tran PH,
Nguyen TT, et al. Direct oxidative C(sp3)─H/
C(sp2)─H coupling reaction using recyclable Sr-
doped LaCoO3 perovskite catalyst. Appl
Organometal Chem. 2020;e5515. https://doi.org/10.
1002/aoc.5515