A novel and robust heterogeneous Cu catalyst using modified lignosulfonate as support for the synthesis of nitrogen-containing heterocycles

Article abstract of DOI:10.3762/BJOC.16.238

A waste biomass, sodium lignosulfonate, was treated with sodium 2-formylbenzenesulfonate, and the phenylaldehyde condensation product was then used as a robust supporting material to immobilize a copper species. The so-obtained catalyst was characterized by many physicochemical methods including FTIR, EA, FSEM, FTEM, XPS, and TG. This catalyst exhibited excellent catalytic activity in the synthesis of nitrogen-containing heterocycles such as tricyclic indoles bearing 3,4-fused seven-membered rings, 2-arylpyridines, aminonaphthalenes and 3-phenylisoquinolines. In addition, this catalyst showed to be recyclable and could be reused several times without significant loss in activity during the course of the reaction process.

Full text of DOI:10.3762/BJOC.16.238

A novel and robust heterogeneous Cu catalyst using modified
lignosulfonate as support for the synthesis of
nitrogen-containing heterocycles
Bingbing Lai1, Meng Ye1, Ping Liu2, Minghao Li1, Rongxian Bai*1 and Yanlong Gu*1,3
Full Research Paper
Open Access
Address:
Beilstein J. Org. Chem. 2020, 16, 2888–2902.
1Key Laboratory of Material Chemistry for Energy Conversion and
Storage, Ministry of Education. Hubei Key Laboratory of Material
Chemistry and Service Failure, School of Chemistry and Chemical
Engineering, Huazhong University of Science and Technology, 1037
Luoyu Road, Hongshan District, Wuhan 430074, P. R. China, 2School
of Chemistry and Chemical Engineering, the Key Laboratory for
Green Processing of Chemical Engineering of Xinjiang Bingtuan,
Shihezi University, Shihezi City, 832004, China and 3State Key
Laboratory for Oxo Synthesis and Selective Oxidation, Lanzhou
Institute of Chemical Physics, Chinese Academy of Sciences,
Lanzhou 730000, P. R. China
https://doi.org/10.3762/bjoc.16.238
Received: 28 August 2020
Accepted: 06 November 2020
Published: 26 November 2020
This article is part of the thematic issue "Green chemistry II".
Associate Editor: L. Vaccaro
© 2020 Lai et al.; licensee Beilstein-Institut.
License and terms: see end of document.
Email:
Rongxian Bai* - bairx@126.com; Yanlong Gu* - klgyl@hust.edu.cn
* Corresponding author
Keywords:
biomass; heterogeneous catalyst; immobilized copper catalyst;
lignosulfonate; nitrogen-containing heterocycles; solid acid
Abstract
A waste biomass, sodium lignosulfonate, was treated with sodium 2-formylbenzenesulfonate, and the phenylaldehyde condensa-
tion product was then used as a robust supporting material to immobilize a copper species. The so-obtained catalyst was character-
ized by many physicochemical methods including FTIR, EA, FSEM, FTEM, XPS, and TG. This catalyst exhibited excellent cata-
lytic activity in the synthesis of nitrogen-containing heterocycles such as tricyclic indoles bearing 3,4-fused seven-membered rings,
2‑arylpyridines, aminonaphthalenes and 3-phenylisoquinolines. In addition, this catalyst showed to be recyclable and could be
reused several times without significant loss in activity during the course of the reaction process.
Introduction
Heterogeneous metal catalysts have been continuously [1-4]. However, most of them often encounter the issues of poor
receiving considerable attention in the field of organic synthe- stability and metal leaching [5], especially when the substrates
sis owing to the advantages of easy separation and recycling and/or products have a powerful coordinating ability with the
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immobilized metal [6,7]. For instance, nitrogen-containing sub- process could transform the –SO3Na group left in the catalyst
strates or target products sometimes may lead to the fast deacti- after ion exchange into –SO3H, enabling the catalyst to cata-
vation of catalysts, which consequently impair the recyclability lyze the model reactions without the addition of protonic acid.
of the catalysts [8-11]. Therefore, special efforts should be paid The catalyst demonstrated impressive catalytic performance in
to enhancing the robustness of heterogeneous metal catalysts.
the synthesis of nitrogen-containing heterocycles, and there was
no deactivation even after 6 times of recycling, exhibiting en-
Sodium lignosulphonate (LS) is a waste from the paper-making hanced stability compared to that without grafting of FAS. It is
industry, containing aryl- and sodium sulfonate groups [12]. As expected that this research would shed light on the design of
a category of polyanionic material, LS can easily load metal heterogeneous metal catalysts with high activity and stability.
ions via an ion exchange process [13]. Given the desirable prop-
erty, an array of heterogeneous metal catalysts using LS as Results and Discussion
support were successfully designed and utilized to catalyze The whole preparation process of the catalyst is depicted in
some typical organic reactions in our previous work. In 2014 Figure 1. Firstly, the support was prepared through
[14], LS were used by our group, for the first time, as a solid phenol–formaldehyde condensation reaction of LS and FAS.
support of cationic catalysts. The obtained catalysts were then The FAS was chosen to embellish LS in consideration of the
successfully applied to many organic transformations, in which following reason: FAS skeleton consists of both aldehyde and
the catalysts showed not only high activity but also good recyc- sulfonic groups, so the grafting of FAS and LS can be easily
lability. However, the stability and durability of LS was very realized via phenol–formaldehyde condensation reaction, and
limited especially in polar solvents such as H2O, EtOH and at therefore equips the generated polymeric support with more
harsh conditions. In a further study of our previous work [15], a sulfonic groups. The heterogeneous Cu catalyst (LS-FAS-Cu)
LS/dicationic ionic liquid composite was prepared via an ion was finally obtained through refluxing of LS-FAS with
exchange process, and then used as catalyst support for prepar- Cu(OTf)2 in ethanol, and the loading capacity of Cu was con-
ing a heterogeneous Cu-based catalyst, the thereby obtained firmed to be 0.92 mmol/g by means of ICP. For comparison,
catalyst displayed remarkable performance in the Glaser hetero- two controlled heterogeneous catalysts, namely Resin-Cu and
coupling reaction. Combining two successful attempts, a further LS-FM-Cu were prepared using commercially available
study concerning improvement of the robustness of catalysts Amberlyst-15 and the material [13] was synthesized by conden-
and active sites when using LS as support is urgently needed. sation of formaldehyde and LS as supports, respectively (see
Supporting Information File 1, Figure S1 and Figure S2), and
In this work, we present a novel heterogeneous Cu catalyst the loading capacity of Cu was 0.45 mmol/g and 0.56 mmol/g,
using modified LS as support by a consecutive process involv- respectively.
ing the phenol–aldehyde condensation of LS with 2-formylben-
zenesulfonic acid sodium (FAS), ion exchange and acidifica- Characterization of the prepared materials
tion. Special interest is given in the application of the prepared The primary purpose of using FAS to modify LS was to
catalyst for synthesizing nitrogen-containing heterocycles. The increase the amount of –SO3Na groups in the supporting mate-
results showed that the grafting of FAS on LS provided the rial. For the verification of this assumption, elemental analysis
support with more ion exchange sites, significantly increasing was firstly conducted and the results are listed in Table S1 (see
the loading capability of the Cu species. The acidification Supporting Information File 1). From the results, it was found
Figure 1: Schematic illustration for the preparation of the catalyst in this work.
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that with introduction of the FAS moiety, LS-FAS showed a tion File 1, Figure S3), showing a high thermal stability as well
higher content of C, H and S elements compared to pristine LS, [24-26]. The above results indicated that all prepared materials
indicating the successful grafting of FAS on LS. According to could remain stable in the system when used to catalyze organic
the increment of the S element, the increment of –SO3Na reactions.
groups was 1.26 mmol/g. The chemical compositions on the
surfaces of LS, LS-FAS, LS-FAS-Cu were further character-
ized by FTIR. As shown in Figure 2, the broad and strong
absorption peak at around 3000 cm−1 was associated with the
stretching vibration of the –OH group in the skeleton of LS
[16]. The tiny peak at approximately 2900 cm−1 was assigned to
the stretching vibration of the −CH2− moiety. The character-
istic peak of the aromatic benzene ring appeared at about
1500 cm−1 [17]. The vibration bands at 1000−1200 cm−1 were
attributed to the −SO3 and O−S−O stretching of the −SO3Na (or
−SO3H) group [18,19]. Grafting of the FAS moiety changed the
peak pattern of –SO3Na in LS-FAS material, and the immobili-
zation of the Cu complex shifted the corresponding peaks to a
higher wavenumber position, implying the successful coordina-
tion of LS-FAS to the Cu complex.
Figure 3: Thermogravimetric weight loss of the obtained materials
LS-FAS and LS-FAS-Cu.
FSEM (field emission scanning electron microscopy) and
FTEM (field emission transmission electron microscopy) were
used to observe the surface morphologies of different catalysts,
and the results are presented in Figure 4. The LS-FAS-Cu cata-
lyst featured irregular and blocky morphology with uneven size
from 100 nm to 400 nm (Figure 4a–d). In addition, the
elemental mapping images clearly revealed the presence and
uniform distribution of C, Cu, O, and S in LAS-FAS-Cu.
XPS was further utilized to analyze the chemical states of the
elements on the surface of the catalyst (Figure 5). The wide
survey spectrum of LS-FAS-Cu showed that all of the essential
elements could be detected. In the high-resolution spectrum of
Figure 2: FTIR spectra of LS, LS-FAS, and LS-FAS-Cu.
C 1s, the peak at 284.9 eV was ascribed to C–C, and the peak at
286.3 eV corresponded to C–O/C–S [27,28]. The O 1s spec-
The thermal behavior of LS-FAS and LS-FAS-Cu was investi- trum clearly evidenced the presence of oxygen atoms with three
gated by TG in a temperature range of 40–800 °C (Figure 3). kinds of chemical environments: the peaks at 532.9 eV and
When the temperature was lower than 200 °C, both of them 532.2 eV were attributed to –OH and –C–O– groups, respec-
exhibited good stability with a slight drop of the curves, tively, while the peak at 533.7 eV was attributed to –SO3 [12].
possibly due to the loss of a trace amount of absorbed water In the spectrum of Cu 2p3/2, the peak at ≈936 eV was assigned
[20,21]. Two sharp weight losses were identified on the TG to Cu2+ in the spinel, accompanied by the characteristic Cu2+
curves as temperature rose. The first loss within 224–327 °C shakeup satellite peaks at 938−948 eV, while the peak at
may be caused by decomposition and elimination of the ≈933 eV suggested the presence of Cu+ and/or Cu0 species.
–SO3Na groups and the introduced small organic species in the Because Cu 2p3/2 XPS cannot differentiate between Cu+ and
materials [22], while the second loss at higher temperature of Cu0, Auger Cu LMM spectra were further recorded, and the
327–448 °C may be attributed to decomposition of the support results confirmed the presence of Cu+ at ≈570 eV, while Cu0 at
skeleton [23]. The thermal stability of referential Resin-Cu cata- 565.6 eV [29-31], meaning that Cu2+ species were partially
lyst was also investigated by TG analysis (Supporting Informa- reduced during the course of immobilization.
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Figure 4: FSEM imagine of LS-FAS-Cu in different scale label a) 1 μm, b) 200 nm; FTEM images of LS-FAS-Cu in 500 nm (c) and 100 nm (d); and
the elemental mapping of LS-FAS-Cu for C, Cu, O and S elements.
Figure 5: XPS spectra of LS-FAS-Cu in the regions of C 1s, O 1s, Cu 2p3/2 and Cu LMM (inset).
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Catalytic activity of the catalysts
ing the temperature will result in a significant loss of yields
With the catalysts in hand, we investigated their catalytic activi- (Table 1, entry 11), prolong the time could increase the yield
ty in organic reactions. Tricyclic indole alkaloids bearing 3,4- but still lower than that at 60 °C (Table 1, entry 12). Thus the
fused seven-membered rings have attracted much attention optimal conditions were confirmed to be 20 mol % of LS-FAS-
because of their interesting molecular architectures and impor- Cu (the Cu loading with reference to the substrates 1a), 60 °C
tant biological activities [32,33]. Here the three-component and 7 h. To our delight, the reaction could be easily scaled up to
reaction of 4-aminoindole (1a), 4-methylbenzaldehyde (2a) and 10 mmol without significant loss of the efficiency and selec-
diethyl acetylenedicarboxylate (3a) was performed to construct tivity (Table 1, entry 14).
the seven-membered indole ring system with the aid of the
LS-FAS-Cu catalyst, and the results are summarized in Table 1. Under the optimal conditions, the substrate scope of the model
At the beginning, the three-component reaction was conducted reaction was extended and the results were shown in Scheme 1.
without the presence of any catalyst, but no products were Aldehydes 2 with different functional groups on the benzene
formed (Table 1, entry 1). After screening different kind of sol- ring could react smoothly with compounds 1a and 3a,
vents (Table 1, entries 2–8) at 60 °C, EtOH was found to be the producing the corresponding 3,4-fused tricyclic indoles 4b–d
best one, and the target product 4a was obtained in 86% yield with yields ranging from 46% to 64%. o-Anisaldehyde, with
(Table 1, entry 8). The referential catalysts LS-FM-Cu and steric-hindrance effect, also reacted efficiently in this reaction
Resin-Cu showed inferior catalytic activity for this reaction, and gave product 4e in 55% yield. 2-Naphthaldehyde also
probably attributed to the low content of Cu species in the mate- proceeded well with 1a and 3a and the product 4f was isolated
rials (Table 1, entries 9 and 10). Further investigation revealed in 60% yield. Aldehydes with multi-substituted functional
that the reaction was also affected by the dosage of catalyst and groups also worked well in this reaction and the corresponding
the temperature. The yield was decreased significantly with the products were obtained in moderate yields (4g and 4h).
catalyst dosage decreasing (Table 1, entry 8 and 13). Decreas- It should be noted that heterocyclic aldehydes such as
Table 1: Three-component reaction of 1a, 2a, and 3a to synthesis of 4aa.
Entry
Solvent
Yield [%]b
1c
2
EtOH
AcOH
MeOH
THF
0
0
3
59
21
trace
0
4
5
DMSO
H2O
6
7
CH3NO2
EtOH
EtOH
EtOH
EtOH
EtOH
EtOH
EtOH
35
86
62
57
49
71
37
84
8
9d
10e
11f
12g
13h
14i
aReaction conditions: 1a/2a/3a = 1.5:1:1.5; 1.0 mL. bIsolated yields. cWithout the catalyst. dLS-FM-Cu was used. eResin-Cu was used. f40 °C.
g40 °C, 24 h. h10 mol % LS-FAS-Cu was used. i10 mmol scale reaction.
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Scheme 1: Substrate scope of LS-FAS-Cu catalyzed three-component reactions of 4-aminoindoles, alkynes and aldehydes.
2-bromo-4,5-methylenedioxybenzaldehyde (2i) could also Dimethyl acetylenedicarboxylate (3b), 1a and 2a could tolerate
successfully engage in this reaction and the yield of product the LS-FAS-Cu-promoted conditions as well, and gave the
4i was up to 64%. In the following investigation, the aliphatic product 4o in 65% yield. The successful attempts in the
aldehydes 2j–m were also successfully reacted, and the three-component reaction of 4-aminoindoles (1a), alkynes
products 4j–m were obtained in good to excellent yields. The and aldehydes indicate that the heterogeneous catalyst
acid-labile cyclopropanecarboxaldehyde (2n) could also LS-FAS-Cu is competent for catalyzing nitrogen-containing
participate well, and the product 4n was obtained in heterocyclic compounds without significant damage of the Cu
77% yield without damage of the cyclopropane structure. species.
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The pyridine-containing moiety, such as arylpyridines, widely In order to utilize the residual –SO3Na groups in LS-FAS-Cu
exist in natural products, pharmaceutical agents and functional after immobilization of the Cu species, LS-FAS-Cu were
materials [34-37]. Traditional methods for synthesizing pyri- further acidized by sulfuric acid solution (2 M) and denoted as
dine-containing derivatives include condensation reactions, LSA-FAS-Cu. The amount of –SO3H was determined through
cross-coupling, ring-closing, metathesis, cycloadditions, radical acid-base titration and elemental analysis, respectively
reactions and microwave-assisted reactions [38-40]. In this (Table 3). The results showed that the density of –SO3H deter-
work, we attempt to develop a greener, simpler, more efficient mined by acid-base titration was much lower than that con-
and recyclable system to synthesize arylpyridine derivatives. firmed by elemental analysis, indicating that a portion of sulfur
Initially, the reaction of acetophenone (5a) and 1,3-diamino- existed in the form of Cu complex and –SO3Na. Afterwards, the
propane (6a) was conducted with the aid of LS-FAS-Cu and catalytic activity of LSA-FAS-Cu in the model reaction was in-
TsOH·H2O in a variety of solvents at 100 °C for 24 h under an vestigated under the optimal conditions except for the absence
oxygen atmosphere (Table 2, entries 1–6). After comparing the of TsOH.H2O. Considering that the density of –SO3H in LSA-
yield, EtOH was found to be the optimal solvent, generating the FAS-Cu was a half of TsOH.H2O, so the amount of LSA-FAS-
target product 2-arylpyridine 7a in 75% yield. Other kinds of Cu should be doubled. To our delight, although the reaction
solvents were ineffective (Table 2, entries 1–5 vs entry 6). Only time was prolonged a little, LSA-FAS-Cu (Cu 40 mol %,
the addition of TsOH·H2O showed a reluctant activity in this –SO3H 0.5 equiv) could also promote the reaction smoothly and
organic transformation (Table 2, entry 7). When homogeneous generated 7a in 74% yield (Table 2, entry 11), suggesting that
Cu(OTf)2 was used, only 20% of 7a was isolated (Table 2, the acidification process enabled the catalyst to catalyze the
entry 8). The two referential catalysts LS-FM-Cu and Resin-Cu model reaction without addition of TsOH.H2O.
exhibited low catalytic efficiencies in the model reaction, only
60% and 48% of 7a were obtained, respectively (Table 2, Using LSA-FAS-Cu as catalyst, the substrate scope of the reac-
entries 9 and 10). The results indicated that the yields were also tion was subsequently investigated, and it was found that the
greatly affected by the catalyst loading and proper acid reaction could tolerate a wide range of functionalities, includ-
additives. In the same solvent, the yield decreased with the de- ing fluoro, chloro, iodo, cyclohexane and benzyloxy moieties.
creasing of the catalyst loading (Table 2, entry 6 vs entries 9 Acetophenones with an electron-donating group in the para-po-
and 10).
sition of the aromatic ring afforded the target products in better
Table 2: Optimizing the reaction condition of acetophenones and 1,3-diaminopropane to synthesis 2‑arylpyridine derivatives.a
Entry
Solvent
Yield [%]b
1
CH3CN
toluene
CH2Cl2
H2O
30
2
5
3
NR
trace
trace
75
4
5c
6
THF
EtOH
EtOH
EtOH
EtOH
EtOH
EtOH
7d
8e
9f
NR
20
60
10g
11h
48
74
aReaction conditions: 5a (0.2 mmol), 6a (0.6 mmol), solvent (1.0 mL), 0.6 equiv TsOH·H2O, O2 (1 atm), 24 h. bIsolated yield. c60 °C. dOnly 0.5 equiv
TsOH·H2O was used. eCu(OTf)2 (20 mol %) was used. fReferential catalyst LS-FM-Cu (20 mol %) was used. gReferential catalyst Resin-Cu
(20 mol %) was used. hCatalyst: LSA-FAS-Cu [Cu (40 mol %), –SO3H (0.5 equiv)], 26 h.
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(7p−t). It was noted that heterocycles-substituted ketones also
showed high reactivity in this reaction, and the corresponding
products were obtained in good yields (7u–w).
Table 3: Acid density of catalyst.
Sample
Totally S contenta SO3H densityb
(mmol/g)
(mmol/g)
In the following investigation, the LS-FAS-Cu was also found
to be an efficient catalyst for the synthesis of aminonaphthalene
derivatives (Table 5). The substituent effect of aniline was ex-
amined systematically, and the results showed that anilines
bearing electron-donating groups such as Me, OMe and t-Bu at
LSA-FAS-Cu
2.08
1.16
aDetermined by EA. bDetermined by acid−base titration.
yields than the electron-withdrawing groups (Table 4, 7b−j and the para-position could convert smoothly and give the corre-
7k–m). 3'-Methylacetophenone (5n) and 2-acetonaphthone (5o) sponding products in excellent yields (10a–c). The anilines with
could also react with 6a, and give the desired product 7n and 7o electron-withdrawing substituents such as 4-bromoaniline (9d)
in 65% and 58% yield, respectively. Some disubstituted and worked sluggishly and only a moderate yield of 10d was ob-
trisubstituted acetophenones were also examined, and most of tained. Disubstituted anilines also tolerated the catalytic system,
them could generate the desired products in moderate yields generating the product 10e in 66% yield. Naphthylamine (9f)
Table 4: Substrate scope of the ketones catalyzed by LSA-FAS-Cu.
Entry
Product
Yieldb (%)
Entry
12
Product
Yieldb (%)
1
71
39
7b
7c
7d
7m
7n
2
3
70
68
13
14
65
58
7o
7p
7q
4
63
15
68
7e
5
60
16
56
7f
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Table 4: Substrate scope of the ketones catalyzed by LSA-FAS-Cu. (continued)
6
7
82
65
17
18
64
7g
7h
7r
71
7s
8
67
19
73
7i
7t
9
63
45
40
20
21
22
76
7u
7j
7k
7l
10
11
75
7v
69
7w
aLSA-FAS-Cu [Cu (40 mol %), –SO3H (0.5 equiv). bIsolated yields.
also reacted positively with 2-(phenylethynyl)acetophenone Substituted isoquinoline derivatives are considered as an impor-
(8a) and 70% of 10f was obtained. The attempts of aliphatic tant class of N-heterocyclic compounds, showing attractive
amines were also successful, obtaining the corresponding prod- physiological, biological and pharmacological activities [41-
ucts 10g–i in good to excellent yields. It should be noted that 45]. Therefore, the feasibility of synthesizing isoquinoline de-
secondary amines such as morpholine (9j) also showed high re- rivatives using LSA-FAS-Cu as catalyst was investigated. As
activity in this reaction and 10j was obtained in 81% yield. The shown in Table 6, LS-FAS-Cu could promote 2-(phenyl-
substituent effect of 2-(phenylethynyl)acetophenone was ethynyl)benzaldehyde (11a) and urea (12a) to generate
studied subsequently, and the results showed that fluoro, chloro, 3-phenylisoquinoline (13a) in excellent yield, while the referen-
aliphatic chain and cycloolefin-substituted 2-(phenyl- tial catalysts showed inferior catalytic activity, which may be
ethynyl)acetophenone could react smoothly, generating the ascribed to the low loading capacity of Cu species (Table 6,
target products 10k–o in excellent yields. Unfortunately, aniline entry 1 vs entries 2 and 3). In addition, by increasing the
substituted with a strong electron-withdrawing group at the amount of catalyst, the yields could reach the ideal level
para-position and 2-(phenylethynyl)acetophenone substituted (Table 6, entries 4 and 5).
with an electron-donating group were reluctant to react under
this catalytic system, and no desired products were determined The recyclability of LS-FAS-Cu was investigated based on the
(10p and 10q).
three-component reaction of 4-aminoindole (1a), 4-methylben-
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zaldehyde (2a) and diethyl acetylenedicarboxylate (3a). In order ture (including the catalyst) was allowed to stir for a period of
to confirm the heterogeneity of this reaction, we investigated time firstly, and then the catalyst was isolated by hot filtration.
the Cu leaching during the reaction process. The reaction mix- The remaining liquid mixture was divided into two portions,
Table 5: LS-FAS-Cu catalyzed synthesis of aminonaphthalene derivatives.a
Entry
R1
Ph
R2
R3
Product
Yieldb (%)
1
H
4-MeC6H4
81, (65)c, (58)d
10a
10b
10c
10d
10e
2
3
4
5
Ph
Ph
Ph
Ph
H
H
H
H
4-OMeC6H4
4-t-BuC6H4
4-BrC6H4
85
79
55
66
3,4-OMeC6H3
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Table 5: LS-FAS-Cu catalyzed synthesis of aminonaphthalene derivatives.a (continued)
6
Ph
H
1-naphthalene
70
10f
7
Ph
H
Bn
61
10g
10h
10i
8
Ph
H
n-Bu
83
9
Ph
H
88
10
Ph
H
81
10j
10k
10l
11
Ph
Cl
4-MeC6H4
78
12
Ph
F
4-MeC6H4
63
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Table 5: LS-FAS-Cu catalyzed synthesis of aminonaphthalene derivatives.a (continued)
13
4-FC6H4
H
4-MeC6H4
71
10m
14
n-hexyl
H
4-MeC6H4
54
10n
15
cyclohexenyl
H
4-MeC6H4
42
10o
10p
10q
16
Ph
H
4-NO2C6H4
n.d.
17
4-OMeC6H4
H
4-MeC6H4
n.d.
aReaction conditions: 8 (0.2 mmol), 9 (0.24 mmol), DCE (1.0 mL), N2, 12 h. bIsolated yields. cLS-FM-Cu (10 mol % was used) dResin-Cu (10 mol %)
was used.
one was isolated and used to calculate the target product yield, reaction system during the reaction process. The results associ-
another one stirred for a period of time once again, and the ated with the recyclability of LS-FAS-Cu and two referential
latter did not show an increase in the yield. The Cu content in catalysts were summarized in Figure 6. After six runs of recy-
the reaction mixture after catalyst separation was confirmed to cling (Figure 6a), LS-FAS-Cu was still capable of catalyzing
be 2.78 ppm by ICP. Besides, also with the aid of ICP-MS anal- the model reaction in 70% yield, indicating that the catalyst was
ysis, we found that there was no obvious change in the Cu robust and stable under the reaction conditions and could be
content of the catalyst before and after the reaction recycled without obvious loss of catalytic activity. The slight
(0.920 mmol/g vs 0.918 mmol/g). The above results not only decreasing of yield maybe caused by the mass loss of the cata-
verified the heterogeneous property of LS-FAS-Cu catalyst, but lyst during the recovery process (mass recovery 97.5%). In
also implied that the loaded Cu species did not leach into the stark contrast, the two referential catalysts showed inferior re-
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Table 6: Synthesis of the 3-phenylisoquinoline from 11a and urea (12a).a
Entry
Catalyst
Yield [%]b
1
LS-FAS-Cu
LS-FM-Cu
Resin-Cu
LS-FM-Cu
Resin-Cu
85%, (84%)3rd cycle
2
74%
65%
81%
79%
3
4c
5c
a11a:12a = 1:1.2. bIsolated yield. c20 mol % of catalyst was used.
cyclability (Figure 6b and 6c) not only because the mass loss considering the low cost and availability of the raw materials, as
but also the low stability and capacity of the metals.
well as the facile preparation, multi-functionalities and recycla-
bility of the catalyst.
Experimental
Experimental instrumentation
The chemical composition of the samples war characterized by
Fourier transform infrared spectroscopy (FTIR, EQUINOX 55,
Bruker) in the wavenumber range of 4000–400 cm−1 and X-ray
photoelectron spectroscopy (XPS, AXIS-ULTRA DLD-600W,
SHIMADZU) at a base pressure of 2 × 10−9 Pa. Elemental
analyses (EA) were conducted using a Vario Micro cube
Elemental Analyzer (Elementar, Germany). Thermogravimetric
analyses (TGA) were performed under N2 atmosphere by
heating the materials from room temperature to 800 °C at a rate
of 10 °C·min−1. Before testing, all samples were degassed at
110 °C for 8 h under vacuum (10−5 bar) conditions. ICP-MS
data were recorded on ELAN DRC-e device. The morphologies
of samples were observed by scanning electron microscopy
(SEM, Sirion 200, Holland) equipped with an energy disper-
Figure 6: Recyclability of LS-FAS-Cu, LS-FM-Cu and Resin-Cu in the
reaction between compounds 1a, 2a and 3a.
Conclusion
A robust heterogeneous Cu catalyst was successfully prepared sive X-ray (EDX) spectroscopy and transmission electron
through immobilizing Cu on a novel and ecofriendly support- microscopy (TEM, Talos F200X), respectively. 1H and
ing material synthesized by the phenyl–aldehyde condensation 13C NMR spectra were recorded on Bruker AV-400 spectrome-
reaction of FAS and LS. This catalyst could be used for the syn- ter.
thesis of several nitrogen-containing heterocycles and exhibited
excellent catalytic activity. ICP-MS data showed that grafting Catalyst preparation procedure
of FAS on LS greatly increased the loading capability of the Cu Typically, 3.0 g of LS were dissolved in 5.0 mL of deionized
species, which was considered to be responsible for the en- water, followed by adding 0.9 g of FAS. After the addition of
hanced catalytic performance of the catalyst. This catalyst 3.0 mL of concentrated HCl (37 wt %), the solution was contin-
demonstrated a satisfying recyclability and could be reused uously stirred at 90 °C for 8 h. Subsequently, the so-obtained
several times without significant loss in activity. It is anticipat- support (denoted as LS-FAS) was filtered off, washed to be
ed that this catalyst would have a broad application prospect neutral and dried at 110 °C for 10 h.
2900

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Funding
The authors thank the National Natural Science Foundation of
China (21761132014, 21872060), the Fundamental Research
Funds for the Central Universities of China (2016YXZD033),
opening fund of Hubei Key Laboratory of Material Chemistry
and Service Failure (No. 2017MCF01K) and Natural Science
Foundation of Hubei province (No. 2019CFB219) for the finan-
cial support.
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ORCID® iDs
Bingbing Lai - https://orcid.org/0000-0002-5450-0882
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