Donor–Acceptor Type Conjugated Microporous Polymer as a Metal-Free Photocatalyst for Visible-Light-Driven Aerobic Oxidative Coupling of Amines

Article abstract of DOI:10.1007/s10562-021-03574-z

Abstract: Developing cheap, highly efficient, metal-free heterogeneous photocatalysts remain a great challenge in photoredox reactions. Herein, we utilize a typical Suzuki coupling of low-cost triphenylamine derivative and 9,10-dibromoanthracene to synthe

Full text of DOI:10.1007/s10562-021-03574-z

Catalysis Letters
https://doi.org/10.1007/s10562-021-03574-z
Donor–Acceptor Type Conjugated Microporous Polymer
as a Metal‑Free Photocatalyst for Visible‑Light‑Driven Aerobic
Oxidative Coupling of Amines
1
2
2
Jun Jiang · Xiangying Liu · Rongchang Luo
Received: 6 December 2020 / Accepted: 16 February 2021
©
The Author(s), under exclusive licence to Springer Science+Business Media, LLC part of Springer Nature 2021
Abstract
Developing cheap, highly efcient, metal-ꢀree heterogeneous photocatalysts remain a great challenge in photoredox reactions.
Herein, we utilize a typical Suzuki coupling oꢀ low-cost triphenylamine derivative and 9,10-dibromoanthracene to synthesis
a donor–acceptor type conjugated microporous polymer (denoted as PAA-CMP). As expected, heterogeneous PAA-CMP
exhibits excellent photocatalytic perꢀormance, good ꢀunctional group tolerance and satisꢀying recyclability in metal-ꢀree
aerobic oxidative coupling oꢀ amines to imines driven by visible light, which is due to its absolute energy level positions and
good physicochemical stability. More excitingly, PAA-CMP can enable the gram-scale air-oxidized photocatalytic conver-
sion under natural sunlight irradiation, yielding the desired imine product with an isolated yield oꢀ 65% ꢀor 48 h. The current
work provides a great application prospect ꢀor CMPs in low-cost and large-scale organic industrial production in the ꢀuture.
Graphic Abstract
The prepared donor-acceptor (D-A) type conjugated microporous polymer (PAA-CMP) as a metal-ꢀree and heterogeneous
photocatalyst enable the gram-scale air-oxidized photocatalytic conversion oꢀ benzylamine into N-benzylidenebenzylamine
under natural sunlight irradiation, yielding the desired imine product with an isolated yield oꢀ 65%.
Keywords Conjugated microporous polymer · Donor–Acceptor · Heterogeneous photocatalysis · Oxidative coupling
*
Rongchang Luo
1
Introduction
luorch@gdut.edu.cn
1
Center ꢀor Industrial Analysis and Testing, Guangdong
Academy oꢀ Sciences, Guangzhou 510650,
People’s Republic oꢀ China
Visible-light-induced photoredox catalysis has emerged as
one oꢀ the most attractive approaches to achieve the transꢀor-
mation oꢀ organic compounds into high-value-added inter-
mediates due to its high chemoselectivity and the opera-
tion under mild reaction conditions (e.g. room temperature
2
School oꢀ Chemical Engineering and Light Industry,
Guangdong University oꢀ Technology, Guangzhou 510006,
People’s Republic oꢀ China
Vol.:(0
1
123456789)
3

J. Jiang et al.
and ambient pressure) [1–3]. Up to now, numerous photo-
expected, PAA-CMP is ꢀound to be an excellent metal-ꢀree
heterogeneous photocatalyst ꢀor aerobic oxidative coupling oꢀ
primary amines into various imine products with high photo-
catalytic activity, good ꢀunctional group tolerance and satisꢀy-
ing recyclability. More interestingly, PAA-CMP has the ability
to achieve the gram-scale photocatalytic oxidation by using
benzylamine as a substrate and air as an oxidant under natu-
ral sunlight irradiation, implying that PAA-CMP may possess
a great potential ꢀor the application oꢀ CMPs in large-scale
organic industrial production in the ꢀuture.
catalysts involving inorganic semiconductors (TiO [4, 5],
2
In O [6], Au–Pd alloy [7], etc.), transition metals-based
2
3
complexes (Ru [8], Pd [9], Pt [10], etc.) and organic dyes
(
eosin Y [11], Flavin [12], rose bengal [13], etc.) have been
successꢀully employed to photocatalytic organic transꢀor-
mations, such as coupling oꢀ amines, oxidation oꢀ sulꢁdes,
dehydrogenation oꢀ N-heterocycles, hydroxylation oꢀ arylbo-
ronic acids, oxidation oꢀ aldehydes, etc. Regardless oꢀ their
high efciency, there are some inherent weaknesses includ-
ing high cost, toxicity and instability, thereby limiting their
application in large-scale industrial production. Thereꢀore,
the development oꢀ various cheap, metal-ꢀree, stable and
heterogeneous photoredox systems is an eꢂective strategy
to overcome these limitations.
2 Experimental Section
2.1 Synthesis of PAA‑CMP
Conjugated microporous polymers (CMPs) as a class
oꢀ potential heterogeneous photocatalytic platꢀorm have
attracted growing attention in photoredox catalysis (e.g.
coupling oꢀ amines [14], oxidation oꢀ sulꢁdes [15], dehalo-
genation oꢀ haloketones [16], stille-type coupling [17], Aza-
Henry reaction [18], etc.) due to their extended π-conjugated
skeletons, wide visible-light absorption, high stability,
non-toxicity and repeatability. It is generally believed that
photocatalytic perꢀormance oꢀ CMPs is likely determined
by their energy band structure (namely the highest occu-
pied molecular orbital (HOMO) and the lowest unoccupied
molecular orbital (LUMO)) [19]. Research shows that a pre-
cise combination oꢀ electron donor–acceptor (D-A) moieties
in CMPs can not only optimize the energetic band level but
also enhance separation oꢀ photogenerated charge carriers,
thus improving their photocatalytic perꢀormance [20–22].
Recently, some D-A type carbazole-based CMPs synthe-
sized via a known oxidative polymerization have displayed
great potential in several photoredox reactions such as deg-
radation oꢀ mustard-gas [23], Aza-Henry reaction [24], C-3
A 250 mL three-necked ꢃask equipped with a spherical con-
denser was charged with tris-[4-(4,4,5,5-tetramethyl-[1,3,2]
dioxaborolan-2-yl)-phenyl]-amine ((PhBpin) A, 0.33 mmol)
3
and 9,10-dibromoanthracene (Br A, 0.5 mmol), and then
2
degassed N,N-Dimethylꢀormamide (DMF, 50 mL) and
K CO solution (2 M, 10 mL) were added under N atmos-
2
3
2
phere. The mixture was stirred and heated up to 80 °C, and
then tetrakis(triphenylphosphine)palladium (Pd(PPh ) ,
3
4
0.017 mmol) was added under N atmosphere. The resulting
2
mixture was stirred and heated up to 150 °C ꢀor 72 h. Aꢀter
cooling to room temperature, the ꢀormed precipitate was ꢁl-
tered and washed with water, acetone and tetrahydroꢀuran,
respectively. Further, the collected solid was puriꢁed via
soxhlet extraction with tetrahydroꢀuran solution and ꢁnally
dried at 100 °C in vacuum oven to give a yellow-green pow-
der (89% yield, 0.33 g, containing Pd oꢀ 0.63 wt%).
2.2 Photocatalytic Oxidation Coupling of Amines
A quartz tube equipped with a cold ꢁnger condenser was
charge with photocatalyst PAA-CMP (15 mg), substrate
amine (0.5 mmol), n-dodecane (0.5 mmol) as the internal
standard and acetonitrile (10 mL). The reaction mixture was
conducted with ultrasonic dispersion ꢀor 10 min, and then
ꢀunctionalization oꢀ indoles [25], and 1,2-ꢀormylarylation oꢀ
N-arylacrylamides [26]. Because oꢀ strong electron donat-
ing ability oꢀ carbazole units, these carbazole-based CMPs
show signiꢁcantly more positive HOMO position and more
negative LUMO position compared to the other analogues,
indicating the presence oꢀ their strong redox abilities. Never-
theless, these chosen monomers usually suꢂer ꢀrom tedious
synthesis procedures and high costs. In this regard, the direct
polymerization oꢀ electron-donor and electron-acceptor
monomers is a more intriguing and cost-eꢂective approach
was stirred and irradiated by white LED under O atmos-
2
phere at 25 °C ꢀor 16 h. Aꢀter the reaction was accomplished,
photocatalyst was recycled by centriꢀugation, and the super-
natant liquid was analyzed by GC to conꢁrm yield oꢀ target
product through the calibration curves. In scale-up reaction
ꢀor oxidative coupling oꢀ benzylamine, the imine product
was obtained by ꢁltration, concentration and silica gel chro-
matography with ethyl acetate.
ꢀ
or ꢀabricating a series oꢀ new CMPs with D-A structure. For
instance, Zhang’s group has utilized benzothiadiazole as an
electron acceptor to prepare a series oꢀ D-A type CMPs via
metal-assisted cross-coupling reactions [27].
Herein, we employ a low-cost electron-donor triph-
enylamine derivative and an electron-acceptor 9,10-dibro-
moanthracene as raw materials to prepare a D-A type CMP
(
PAA-CMP) via a typical Suziki-coupling reaction. As
1
3

Donor–Acceptor Type Conjugated Microporous Polymer as a Metal-Free Photocatalyst for…
Fig. 1 Synthesis oꢀ PAA-CMP
3
Results and Discussion
microscopy (SEM) images show that PAA-CMP is com-
posed oꢀ spherical microparticles oꢀ diꢂerent sizes (Fig. S1).
Successꢀul coupling reaction was also conꢁrmed by FT-IR
3.1 Characterization
1
3
and solid-state C CP/MAS NMR. Figure 2a shows that the
−
1
−1
As shown in Fig. 1, PAA-CMP was synthesized via a typi-
C–Br peak (577 cm ) in Br2A and B-O peak (1359 cm )
−
1
cal Suzuki coupling reaction between (PhBpin) A as a
as well as CH3 group (2978 cm ) oꢀ boronic pinacol
ester in (PhBpin)3A are almost absent ꢀrom the spectrum
3
donor unit and Br A as an acceptor unit. Scanning electron
2
Fig. 2 a FT-IR spectra oꢀ (PhBpin) A, Br A and PAA-CMP; b Solid state 13C CP/MAS NMR spectrum oꢀ PAA-CMP; c Absorption isotherms
3
2
oꢀ PAA-CMP under N at 77 K; d Pore size distributions oꢀ PAA-CMP
2
1
3

J. Jiang et al.
oꢀ PAA-CMP [28–30], testiꢀying to eꢂective Suzuki cou-
emission intensity oꢀ PAA-CMP is evidently weaker than
1
3
pling. Solid-state C CP/MAS NMR spectrum oꢀ PAA-
CMP reveals peak at 146 ppm arising ꢀrom carbon atoms
in C-N bonds and peak at 135 ppm arising ꢀrom carbon
atoms (e and ꢀ) in anthracene ring (Fig. 2b). In addition,
signals at 129 and 125 ppm are attributed to carbon atoms
in benzene ring and anthracene ring. Adsorption–desorp-
acceptor Br A (Fig. 3b). At the same time, UV–vis DRS and
2
emission spectra oꢀ PAA-CMP are signiꢁcantly red-shiꢀted
than those oꢀ donor (PhBpin) A. The red shiꢀt as well as the
3
decreased emission intensity possibly signiꢁes the eꢂective
intramolecular energy transꢀer and electron transꢀer [20, 24,
31, 32], which is mainly derived ꢀrom the donor-accepter
structure oꢀ PAA-CMP. To elucidate the electronic proper-
ties oꢀ PAA-CMP, cyclic voltammetry (CV) measurement
was implemented to reveal its energy band structure. As
shown in Fig. 3d, the lowest unoccupied molecular orbital
(LUMO) position oꢀ PAA-CMP is determined to be−1.75 V
vs. Ag/AgCl. With the bandgap value oꢀ PAA-CMP calcu-
lated to be 2.67 eV ꢀrom Kubelka–Munk ꢀunction (Fig. 3c),
the highest occupied molecular orbital (HOMO) position
oꢀ PAA-CMP is then determined to be 0.92 V vs. Ag/AgCl
(inset in Fig. 3d). Because the LUMO potential oꢀ PAA-
CMP is much more negative than the reduction potential oꢀ
tion measurement oꢀ PAA-CMP under N at 77 K exhibits
2
2
−1
Brunauer–Emmett–Teller (BET) surꢀace areas oꢀ 506 m g
3
−1
with the total pore volume oꢀ 0.59 cm g (Fig. 2c). Based
on nonlocal density ꢀunctional theory (NLDFT), pore size
distribution oꢀ PAA-CMP is calculated to be around 0.8, 1.1
and 1.6 nm, demonstrating microporosity (Fig. 2d). Thermal
analysis demonstrates that PAA-CMP retains about a 98%
weight up to 530 °C, conꢁrming its high thermal stability
(
Fig. S2).
UV–vis diꢂuse reꢃectance spectrum (DRS) oꢀ PAA-
CMP, which well inherits the ꢀeature oꢀ acceptor Br A,
2
·
−
exhibits a suꢀꢀicient absorption band ranging ꢀrom
O /O (−0.48 V vs. Ag/AgCl) [33, 34], it is theoretically
2 2
3
00–500 nm (Fig. 3a). This permits PAA-CMP to be avail-
ꢀeasible ꢀor photocatalytic activation oꢀ O to generate active
2
·
−
ably excited under visible-light irradiation. Under excitation
species superoxide radical anion (O ) over PAA-CMP,
2
at 270 nm, both acceptor Br A and polymer PAA-CMP have
thereby conducting oxidative coupling oꢀ amines.
2
almost same maximum emission peak around 505 nm, and
Fig. 3 a UV–Vis DRS spectra oꢀ (PhBpin) A, Br A and PAA-CMP;
CMP according to the Kubelka–Munk theory. d Cyclic voltammo-
gram oꢀ PAA-CMP at a scan rate oꢀ 100 mV/s; Cut in the image is
energy diagram oꢀ the HOMO and LUMO positions oꢀ PAA-CMP
3
2
b Steady-state photoluminescence emission spectra oꢀ (PhBpin) A,
3
Br A and PAA-CMP (excitation at 270 nm); c Band gap oꢀ PAA-
2
1
3

Donor–Acceptor Type Conjugated Microporous Polymer as a Metal-Free Photocatalyst for…
3
.2 Photocatalytic Performance
with medium yield, which was attributed to slight ultraviolet
light around 285 nm oꢀ white LED.
To investigate the photocatalytic perꢀormance oꢀ PAA-CMP,
we ꢁrst conducted the aerobic oxidative coupling oꢀ ben-
zylamine into N-benzylidenebenzylamine under white LED
lamp irradiation, and the results are listed in Table 1. The
blank experiments showed that the oxidation reaction did not
proceed in the absence oꢀ light, oxygen or catalyst (Table 1,
Entries 1–3), signiꢀying that these ꢀactors including light,
oxygen and catalyst are essential ꢀor oxidative coupling oꢀ
Next, we explored the substrate scope oꢀ oxidative
coupling oꢀ primary amines, and the results are listed in
Table 2. Benzylamines bearing electron-donating groups
(e.g. methoxy and methyl) were transꢀormed into the cor-
responding imines with higher yields than benzylamines
bearing electron-withdrawing groups (e.g. bromo and tri-
ꢃuoromethyl) under the same reaction conditions (Table 2,
Entries 2–5). This is possibly because that electron-donating
group enhances electronic density oꢀ the substrate, which
is easily oxidized by deꢀective-electron hole oꢀ PAA-CMP.
Para-substituted benzylamine showed higher reactive activ-
ity than ortho-substituted benzylamine because oꢀ steric hin-
drance (Table 2, Entries 2 and 6). Moreover, picolylamine
and 2-thiophenemethylamine, which are regarded as repre-
sentative oꢀ heterocyclic amines, could be converted into the
corresponding imines with 91% and 85% yields, respectively
(Table 2, Entries 7 and 8).
benzylamine. Under white LED irradiation and O atmos-
2
phere, PAA-CMP could promote the transꢀormation oꢀ ben-
zylamine into N-benzylidenebenzylamine with an 86% yield
(
Table 1, Entry 4). To investigate which are active species in
this reaction, some scavengers including potassium iodide
KI), 1,4-diazabicyclo[2.2.2]octane (DABCO) [35], benzo-
quinone and isopropanol were added to veriꢀy the presence
(
+
1
·−
oꢀ the hole (h ), singlet oxygen ( O ), O , hydroxyl radi-
2
2
cal (·OH), respectively. It was shown that KI, DABCO and
benzoquinone could eꢂectively quench the reaction, while
isopropanol did not play inhibiting eꢂect (Table 1, Entries
Further, PAA-CMP which was simply recovered by
centriꢀugal separation was again added to benzylamine
solution to investigate its recyclability. As shown in
Fig. 4a, PAA-CMP could be used at least six cycles with-
out signiꢀicant loss oꢀ catalytic activity, exhibiting high
recyclability. Most oꢀ FT-IR spectra oꢀ PAA-CMP beꢀore
and aꢀter six cycles are consistent (Fig. S4A). However,
5
–8), suggesting that crucial species involved in oxidative
+
1
·−
coupling oꢀ amines are composed oꢀ h , O and O except
2
2
·
OH. Importantly, compared to commercial photocatalysts
such as anatase TiO , BiVO and g-C N (Table 1, Entries
2
4
3
4
9
–11), the designed D-A type PAA-CMP showed the high-
−
1
est photocatalytic activity ꢀor oxidative coupling oꢀ ben-
in-plane bending vibration at 1390 cm oꢀ residual CH
3
−
1
zylamine. Particularly, anatase TiO also could promote
group and out-plane bending vibration at 882 cm oꢀ
aromatic C-H in ꢀresh PAA-CMP are disappeared aꢀter six
2
conversion oꢀ benzylamine into N-benzylidenebenzylamine
Table 1 Photocatalytic aerobic oxidative coupling oꢀ benzylamine into N-benzylidenebenzylamine
photocatalyst, O2
White LED
NH2
N
Entry
Photocatalyst
O2
hν
Scavengersa
Inhibited Species
Yield (%)b
1
2
3
4
5
6
7
8
9
PAA-CMP
PAA-CMP
−
PAA-CMP
PAA-CMP
PAA-CMP
PAA-CMP
PAA-CMP
TiO2
+
−
+
+
+
+
+
+
+
+
+
−
+
+
+
+
+
+
+
+
+
+
−
−
−
−
−
−
−
−
n.d
1
n.d
86
40
43
19
86
57
66
25
+
KI
DABCO
benzoquinone
isopropanol
−
−
−
h
1
O
2
O2·
·OH
−
−
1
1
0
1
BiVO4
−
−
g-C N
3
4
Benzylamine (0.5 mmol), photocatalyst (15 mg), n-dodecane (internal standard, 0.5 mmol), O atmosphere, white LED, acetonitrile (10 mL),
2
2
5 °C and 16 h
a
Scavengers (0.5 mmol)
b
Determined by GC with n-dodecane as the internal standard
1
3

J. Jiang et al.
Table 2 Substrate Scope ꢀor oxidative coupling oꢀ primary amines into imine products
PAA-CMP
N
NH2
R
R
R
Entry
Substrate
Product
Yield(%)a
1
2
3
4
5
6
R=H
R=H
86
93
95
84
81
80
R=OMe
R=Me
R=Br
R=OMe
R=Me
R=Br
R=CF3
R=CF3
NH2
N
N
O
O
O
7
8
91
85
NH2
N
N
N
S
S
NH2
N
S
Primary amine (0.5 mmol), photocatalyst (15 mg), n-dodecane (internal standard, 0.5 mmol), O atmosphere, white LED, acetonitrile (10 mL),
2
2
5 °C and 16 h
a
Determined by GC with n-dodecane as the internal standard
Fig. 4 a Recyclability oꢀ PAA-CMP in oxidative coupling oꢀ ben-
zylamine into N-benzylidenebenzylamine with n-dodecane as the
internal standard; b Scale-up reaction under nature sunlight and air
atmosphere. Reaction conditions: benzylamine (18.7 mmol, 2 g),
PAA-CMP (100 mg), air atmosphere, acetonitrile (100 mL), nature
sunlight irradiation ꢀor 48 h in Guangzhou, China (07/13/2020–
07/14/2020, atmospheric temperature (28–35 °C))
cycles (Fig. S4B), suggesting that residual groups (e.g.
boronic pinacol ester) in PAA-CMP easily ꢀall oꢀꢀ during
the photocatalysis reaction. To explore the applicability
oꢀ PAA-CMP ꢀor ꢀurther industrial manuꢀacture, a gram
scale reaction ꢀor the oxidative coupling oꢀ benzylamine
into N-benzylidenebenzylamine was perꢀormed under
nature sunlight irradiation and air atmosphere. As shown
in Fig. 4b, aꢀter proceeding ꢀor 48 h, an isolated yield
oꢀ 65% ꢀor N-benzylidenebenzylamine was obtained.
These results indicate that PAA-CMP possess great
1
3

Donor–Acceptor Type Conjugated Microporous Polymer as a Metal-Free Photocatalyst for…
application prospects ꢀor low-lost and large-scale organic
transꢀormation.
sulphate (DPD) [38]. In the presence oꢀ PAA-CMP, two
strong absorption peaks at 512 and 553 nm along with obvi-
ous color change ꢀrom light red to dark red were ꢀormed
(Fig. 5b), probably indicating the presence oꢀ H O in cata-
3.3 Mechanistic Considerations
2
2
1
lytic system oꢀ PAA-CMP. Further, O , one oꢀ the vital
2
To shed light on the mechanism oꢀ photocatalytic oxidative
coupling oꢀ amines, some control experiments were con-
ducted. N,N,N′,N′-tetramethylphenylenediamine (TMPD),
a well-known rich-electron indicator, is widely employed to
evaluate the ability oꢀ photocatalyst with respect to mediat-
ing electron transꢀer ꢀrom electron-donating substrates to
oxygen [36]. As shown in Fig. 5A, aꢀter white LED irradia-
tion ꢀor 0.5 h, PAA-CMP could promote the ꢀormation oꢀ
strong absorption peaks at 523, 562 and 614 nm assigned
to cationic radical species oꢀ TMPD, but the solution color
turned ꢀrom without color to purple color rather than the
reported blue color [37], which is possibly attributed to the
emission spectrum oꢀ white LED containing slight ultra-
violet light (Fig. S1). This result indicates that PAA-CMP
can mediate electron transꢀer ꢀrom the amine substrate to
reactive oxygen species derived ꢀrom energy transꢀer in pho-
toredox reactions, was detected by electron spin resonance
(ESR) test with 2,2,6,6-tetramethylpiperidine (TEMP) as the
trapping agent. Figure 5c showed that PAA-CMP promoted
the generation oꢀ a strong 1:1:1 triplet signal, which was
assigned to 2,2,6,6-tetramethylpiperidine-1-oxyl (TEMPO)
1
radical derived ꢀrom reaction between TEMP and O [39].
2
In view oꢀ the above experimental results and reported
literatures [25, 40–42], one plausible mechanism involv-
·
−
1
ing both O and O was proposed ꢀor PAA-CMP cata-
2
2
lyzed oxidative coupling oꢀ benzylamine. As shown in
Fig. 5D, photocatalyst PAA-CMP was excited to produce
*
the excited state (PAA-CMP ) under visible-light irradia-
tion. Then, molecular oxygen (O ) adsorbed on surꢀace oꢀ
2
*
PAA-CMP was activated by PAA-CMP to reactive oxy-
·
−
·−
1
O , thereby resulting in active species O . Next, hydrogen
gen species O and O via electron transꢀer and energy
2 2
2
2
peroxide (H O ), one oꢀ the postulated intermediates, was
transꢀer, respectively, as well as resulting in the ꢀormation
2
2
+
·
investigated by using Horseradish peroxidase (POD)-cata-
oꢀ cationic radical oꢀ PAA-CMP (PAA-CMP ), which was
also regarded as the hole. Next, benzylamine substrate was
lyzed oxidation oꢀ N, N-diethyl-1,4-phenylenediammonium
Fig. 5 UV–vis absorption spectra and photograph oꢀ the cationic rad-
ical species oꢀ TMPD a and DPD b generated by PAA-CMP in the
presence oꢀ visible light and oxygen; c ESR spectra oꢀ the samples
aꢀter mixing TEMP solution with PAA-CMP and O under visible
2
light. d Proposed mechanism oꢀ PAA-CMP photocatalyzed oxidative
coupling oꢀ benzylamine to the imine
1
3

J. Jiang et al.
oxidized by positive charge oꢀ PAA-CMP+· to generate the
6. Sun LM, Li R, Zhan WW, Yuan YS, Wang XJ, Han XG, Zhao
YL (2019) Nat Commun 10:2270
cationic radical oꢀ benzylamine (a), which reacted with
7
.
Eerdemutu DL, Li C, Zhao S, Sheng X (2020) Synthesis oꢀ
Imines by Selective Oxidation oꢀ Amines on alloy nanoparticles
oꢀ palladium and gold under visible light irradiation at ambient
temperatures. Catal Lett 150:1757–1765
·
−
1
O
or O to ꢀorm the imine intermediate (b) and H O .
2
2
2
2
Particularly, the in situ ꢀormed H O could oxidize the ꢀree
2
2
benzylamine to aꢂord the imine intermediate (b). Finally,
the imine intermediate (b) reacted with a ꢀree benzylamine
to produce the intermediate (c), which ꢀurther gone through
elimination oꢀ ammonia under hole-assisted to aꢂord the
imine product.
8
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Conclusion
2. Neveselý T, Svobodová E, Chudoba J, Sikorski M, Cibulka R
(
2016) Adv Synth Catal 358:1654–1663
In summary, we designed and synthesized a class oꢀ D-A
type CMPs, which was considered as a low-cost, metal-ꢀree,
heterogeneous photocatalyst in the oxidative coupling oꢀ
amines into imines. Thanks to its excellent optoelectronic
properties and good chemical stability, PAA-CMP with the
D-A structure exhibits remarkable photocatalytic activity,
good tolerance and satisꢀying recyclability. Especially, a
gram-scale preparation oꢀ the imine product was achieved
with a high yield oꢀ 65% under natural-sunlight irradiation
by using benzylamine as a ꢀeedstock and air as an oxidant,
thus opening the prospect ꢀor the large-scale industrial
applications oꢀ CMPs. Further studies are underway to opti-
mize synthesis approach oꢀ D-A type CMPs via metal-ꢀree
catalysis.
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Supplementary Information The online version contains supplemen-
tary material available at https://doi.org/10.1007/s10562-021-03574-z.
23. Zhi YF, Yao ZJ, Jiang WB, Xia H, Shi Z, Mu Y, Liu XM (2019)
ACS Appl Mater Interꢀaces 11:37578–37585
Acknowledgements The authors are grateꢀul ꢀor the ꢁnancial sup-
port ꢀrom the Guangdong academy sciences (GDAS)’ Talent Intro-
duction Project oꢀ Thousands doctoral and postdoctor (2020GDA-
SYL-20200103124), Guangzhou Basic and Applied Basic Research
project (202002030302), Guangdong academy oꢀ sciences (GDAS)’
Project oꢀ Science and Technology Development (2018GDASCX-0114,
24. Zhi YF, Ma S, Xia H, Zhang YM, Shi Z, Mu Y, Liu XM (2019)
Appl Catal B: Environ 244:36–44
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nology Project (201907010004).
28. Li C, Wang Y, Zou Y, Zhang X, Dong H, Hu W (2020) Angew
Chem Int Ed 59:9403–9407
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Compliance with ethical standards
0. Wang S, Hu Q, Liu Y, Meng X, Ye Y, Liu X, Song X, Liang Z
(2020) J Hazard Mater 387:121949–121958
Conflicts of interest There are no conꢃicts to declare.
1. Guo B, Feng G, Manghnani PN, Cai X, Liu J, Wu W, Xu S,
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