In(III) and Sc(III) based coordination polymers derived from rigid benzimidazole-5,6-dicarboxylic acid: Synthesis, crystal structure and catalytic property

Article abstract of DOI:10.1016/j.poly.2017.10.028

Two new coordination polymers (CPs), [InCl(H₂bidc)₂(H₂O)]_n (1) and [Sc(Hbidc)(OH)(H₂O)]_n (2) (H₃bidc = benzimidazole-5,6-dicarboxylic acid) were synthesized through a solvotherma

Full text of DOI:10.1016/j.poly.2017.10.028

Polyhedron xxx (2017) xxx–xxx
Contents lists available at ScienceDirect
Polyhedron
journal homepage: www.elsevier.com/locate/poly
In(III) and Sc(III) based coordination polymers derived from rigid
benzimidazole-5,6-dicarboxylic acid: Synthesis, crystal structure and
catalytic property
Juan Chai a, Pengcheng Wang a, Jia Jia a,b, Bing Ma a, Jing Sun a, Yufang Tao a, Ping Zhang a, Li Wang a,
,
⇑
Yong Fan a,
⇑
a College of Chemistry, Jilin University, Changchun 130012, Jilin, PR China
b College of Chemistry, Baicheng Normal University, Baicheng 137000, Jilin, PR China
a r t i c l e i n f o
a b s t r a c t
Article history:
Two new coordination polymers (CPs), [InCl(H2bidc)2(H2O)]n (1) and [Sc(Hbidc)(OH)(H2O)]n (2) (H3bidc
= benzimidazole-5,6-dicarboxylic acid) were synthesized through a solvothermal approach. 1 exhibits a
1D infinite chain, which further constructs a 3D supramolecular framework via hydrogen bonds. 2 fea-
tures a 3D supramolecular framework consisting of left- and right-handed chiral layers, which contain
Received 25 July 2017
Accepted 27 October 2017
Available online xxxx
the left- and right-handed chiral spiral chains. The adjacent layers stack through
p–p stacking interac-
Keywords:
Coordination polymers
Structure
Solvothermal
Strecker reaction
Catalyst
tions between benzene and imidazole rings. 1 exhibits excellent catalytic reactivity for the Strecker reac-
tion and can be recycled four consecutive reactions with more than 95% conversion yields.
Ó 2017 Elsevier Ltd. All rights reserved.
1. Introduction
cycles without significant loss of activity [8]. However, finding a
way to give rise birth to accessible active metal centers is still a
The development of new heterogeneous Lewis acid catalysts
has become one of the main goals of green synthetic chemistry
[1]. Currently, coordination polymers (CPs) as heterogeneous cata-
lysts are receiving increasing attention [2] not only due to they
possess extensive tunability, but also for their highly regular cat-
alytic sites, which represent a unique opportunity to design CPs-
based heterogeneous catalysts [3]. Compared to conventional
homogeneous catalysts, CPs as heterogeneous catalysts have many
advantages, including separation and recovery, selectivity, higher
yield, low toxicity, and so on [4]. Generally, one promising point
for CPs-based catalysis is the presence of active metal centers, that
are coordinatively unsaturated metal centers, in the structure,
which may exhibit Lewis acidity and associated catalytic function-
ality [5]. For example, Garcia et al. reported that Fe(BTC) catalyzed
Claisen Schmidt condensation leading to chalcone in 98% yield [6].
challenge in the construction of CPs.
To obtain CPs with catalytic effective sites, various metallic
cations were tested, especially, In(III) or Sc(III). The main reason
is that some In(III) or Sc(III) usually more easily adopt a lower six
coordination number, which can provide open Lewis acid effective
sites [9] for catalysis of various organic reactions [10]. For instance,
[In(popha)(2,20-bipy)]ꢀ3H2O was found to be a highly reactive,
recyclable, Lewis acid catalyst, which allowed the efficient synthe-
sis of
a-aminoacyl amides in Ugi 4-component (U-4CR) reaction
[11]. [Sc2(C10H6S2O6)(OH)4]n as bifunctional catalysts presented
particularly good activity for the oxidation of sulfides and can be
recycled several consecutive reactions without any loss of activity
or selectivity [12].
As is well known,
a-aminonitriles are key skeletons of some
biologically natural products such as
a-amino acids and their
Long et al. shown that Mn3[(Mn4Cl)3(BTT)8(CH3OH)10 2
]
catalyzed
derivatives [13]. Up to now, the Strecker reaction of aldimines
and trimethylsilyl cyanide (TMSCN) is the most effective method
to produce these compounds. Previously, this reaction has been
successfully catalyzed by various Lewis acid and Lewis base cata-
lysts. However, there are some problems such as in separation,
recovery and disposal of spent catalysts for the Strecker reaction
[14]. Moreover, in recent years, Strecker reaction was successfully
catalyzed by CPs that presented outstanding catalytic activity.
cyanosilylation of aromatic aldehydes and Mukaiyama-aldol reac-
tion with excellent size-selectivity effect [7]. Monge et al. prepared
a mesoporous In3O(btb)2(HCOO)(L), which was reused in up to 10
⇑
Corresponding authors.
E-mail addresses: lwang99@jlu.edu.cn (L. Wang), mrfy@jlu.edu.cn (Y. Fan).
https://doi.org/10.1016/j.poly.2017.10.028
0277-5387/Ó 2017 Elsevier Ltd. All rights reserved.
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J. Chai et al. / Polyhedron xxx (2017) xxx–xxx
Gandara et al. prepared new CPs [InxGa1ꢁx(O2C2H4)0.5(hfipbb)],
which showed how the activity of a heterogeneous catalyst can
be controlled by modulating the ratio of different metals occupying
the same crystallographic position of the framework in one-pot
Strecker reaction [15]. Ji et al. reported that Cu-CPs, featuring Lewis
acid-type catalytic sites, as very efficient and reusable catalysts,
were used for the Strecker reaction of various aldimines [16].
In the process of construction and structural tuning of CPs,
organic ligand plays a crucial role. Benzimidazole-5,6-dicarboxylic
acid (H3bidc) as a bridging ligand possesses two carboxyl groups,
which can be partial or completely deprotonated, inducing rich
coordination modes and allowing interesting structures. H3bidc
has been validated to be a proper polydentate bridging ligand for
the formation of multidimensional CPs [17]. Here, based on the H3-
bidc ligand, we prepare two new In(III)/Sc(III)-based CPs, [InCl(H2-
bidc)2(H2O)]n (1) and [Sc(Hbidc)(OH)(H2O)]n (2). 1 features infinite
1D chains and is constructed to a 3D supramolecular framework
via hydrogen bonds. 2 shows a 3D supramolecular structure, built
from left- and right-handed chiral layers along the c axis with the
washed with distilled water, and dried in air. Yield: 80% for 2
(based on Sc(NO3)ꢀ6H2O). Elemental analysis (%) for 2: Anal. Calc.
C, 38.03; H, 2.46; N, 9.86; Found: C, 37.82; H, 2.55; N, 9.72. IR
(KBr pellet, cmꢁ1) for 2 (4000–400 cmꢁ1): 3487 (s), 1793 (w),
1535 (s), 1420 (s), 1269 (m), 1171 (w), 1045 (w), 956 (m), 809
(m), 773 (w), 615(w) (Fig. S6).
2.3. Single crystal X-ray crystallography
Crystallographic data for 1 were collected on a Rigaku R-AXIS
RAPID IP diffractometer with graphite-monochromated Mo Ka
(0.71073 Å) radiation, while those of 2 were collected on a Bruker
SMART APEX-II CCD diffractometer by using graphite-monochro-
mated Mo Ka radiation (0.71073 Å) radiation at a temperature of
296(2) K. All structures were solved by direct methods and refined
by full-matrix least-squares fitting on F2 by the SHELXTL-97 crystallo-
graphic software package [18]. All non-hydrogen atoms were
refined with anisotropic displacement parameters. The hydrogen
atoms attached to C and N atoms were placed in calculated posi-
tions and refined isotropically using a riding model with an Uiso(H)
equivalent to 1.2 times of Ueq(C) or Ueq(N). The hydrogen atoms on
coordinated water molecules were located in a difference Fourier
map and included in the final refinement by use of geometrical
constraints or restraints with the O–H distances being fixed at
0.85 Å. Crystal detailed data collection and refinement of CPs 1
and 2 are summarized in Table S1.
left- and right-handed chiral spiral chains. Interactions of
p–p
stacking between benzene ring and imidazole rings make the 3D
supramolecular more stable. The heterogeneous catalytic activities
of CPs 1 and 2 for the Strecker reaction of various aldimines under
mild condition have also been investigated. 1 displays good cat-
alytic capability for heterogeneous Strecker reaction with more
than 95% conversion yields after four consecutive runs.
2. Experimental
2.4. Catalytic experiment
2.1. Materials and instrumentation
Samples of 1 and 2 were activated at 200 °C for 12 h, soaked in
CH3OH for 24 h and then heated under vacuum at 80 °C for 12 h
under vacuum before the reaction. The basic framework of 1 and
2 are retained after activation. For the experiments of catalysis,
activated catalyst (0.04 mmol), aldimine (0.14 mmol) and TMSCN
All chemicals were obtained from commercial sources and used
without further purification. Powder X-ray diffraction (PXRD) data
were obtained using SHIMADAZU XRD-6000 diffractometer with
Cu Ka radiation (k = 1.5418 Å), with a step size and count time of
0.06° and 6 s, respectively. Infrared spectra (IR) were recorded on
a Nicolet Impact 410 spectrometer between 400 and 4000 cmꢁ1
using the KBr pellet method. Thermogravimetric analysis (TGA)
was conducted on a Perkin-Elmer TGA 7 thermogravimetric ana-
lyzer with a heating rate of 10 °C minꢁ1 from room temperature
to 800 °C. Elemental analysis was conducted on a Perkin Elmer
2400 elemental analyzer. 1H NMR spectra were measured with a
Bruker Avance 400 console at a frequency of 400 MHz.
(47 ll) in CDCl3 (2.4 l) were sequentially added to a standard 20 l
vial. The reaction mixtures were stirred at room temperature.
The reactions were monitored by 1H NMR spectroscopy and the
conversion yield was determined from the ratio of the integral of
the product signal in relation to the sum of integrals of all signals
(aldimine and product).
3. Results and discussion
3.1. Structural descriptions
2.2. Synthesis
3.1.1. Structural description of [InCl(H2bidc)2(H2O)]n (1)
2.2.1. Synthesis of [InCl(H2bidc)2(H2O)]n (1)
ꢀ
1 crystallizes in a triclinic P1 space group. The asymmetric unit
A mixture of H3bidc (0.0824 g, 0.4 mmol), InCl3ꢀ4H2O (0.2 ml,
0.1 M) was added to CH3CN (4 ml), HNO3 (0.4 ml, 1 M) and H2O
(1 ml) in a 23 ml Teflon-lined autoclave and then heated under
autogenous pressure at 120 °C for 24 h, then cooled to room tem-
perature under ambient conditions. Colorless block crystals were
obtained by filtration and washed with distilled water, and dried
in air. Yield: 85% for 1 (based on InCl3ꢀ4H2O). Elemental analysis
(%) for 1: Anal. Calc. C, 37.47; H, 1.73; N, 9.71; Found: C, 37.35;
H, 1.55; N, 9.78. IR (KBr pellet, cmꢁ1) for 1 (4000–400 cmꢁ1):
3254 (s), 1594 (s), 1384 (s), 1329 (s), 1035 (m), 1235 (m), 921
(w), 847 (w), 786 (s), 639 (m), 500 (m) (Fig. S5).
of 1 contains one crystallographically unique In3+ ion, two H2bidcꢁ
ligands, one coordinated H2O molecule and one terminal chlorine
atom. As shown in Fig. 1a, the In3+ ion with six coordinated envi-
2.2.2. Synthesis of [Sc(Hbidc)(OH)(H2O)]n (2)
A mixture of H3bidc (0.0206 g, 0.1 mmol), Sc(NO3)ꢀ6H2O (0.5 ml,
0.2 M) was added to H2O (9 ml), KOH (20 ll, 1 M) in a 23 ml
Teflon-lined autoclave and then heated under autogenous pressure
at 160 °C for 24 h, then cooled to room temperature under ambient
conditions. Colorless block crystals were obtained by filtration and
Fig. 1. Coordination environment of In3+ ion in 1. Symmetry mode: A = 1 ꢁ x, ꢁy,
ꢁz; B = 1 ꢁ x, ꢁy, 1 ꢁ z.
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J. Chai et al. / Polyhedron xxx (2017) xxx–xxx
3
H2bidcꢁ and one O1 atom from one coordinated H2O and one ter-
minal chlorine atom. The In–O bond lengths are in the range of
2.1379(17)–2.1971(18) Å, In–Cl is 2.4514(8) Å, the O–In–Cl bond
angles range from 85.60(5)° to 169.59(5)° and the O–In–O bond
angles range from 84.20(7)° to 175.73(6)° in 1. All of which are
comparable to those of the reported In-CPs [19].
In the structure of 1, the ligand H2bidcꢁ possesses one coordina-
tion mode I (Scheme 1). In mode I, every carboxylate group acts in
a monodentate mode linking one In3+ center. Therefore, each H2-
bidc- ligand synchronously binds to two In3+ ions to form the infi-
nite 1D chains (Fig. 2a). As shown in Table S2, there is a large
amount of hydrogen bonds: non-classical bonds (Clꢀ ꢀ ꢀH–N)
(Fig. 2b) and common bonds (O–Hꢀ ꢀ ꢀO and N–Hꢀ ꢀ ꢀO) in compound
1. The chains parallel with each other to generate a 2D layer via
non-classical hydrogen bonds Cl1ꢀ ꢀ ꢀH1–N1C and Cl1ꢀ ꢀ ꢀH3–N3I
groups (Fig. 2c). H4, H1, O3E and O4D are from benzimidazole
rings and carboxyls of different layers, respectively. N4–H4ꢀ ꢀ ꢀO3E
Scheme 1. Coordination modes of the H3bidc ligand. Cps 1 and 2 exhibit I and II
modes, respectively.
ronment exhibits approximately octahedral geometry, which is
completed by four O atoms of O2A, O5, O7 and O9B (symmetry
codes: A = 1 ꢁ x, ꢁy, ꢁz; B = 1 ꢁ x, ꢁy, 1 ꢁ z) from four individual
Fig. 2. (a) The 1D chain in 1. (b) Detailed illustration of non-classical hydrogen bonds In–Cl1Cꢀ ꢀ ꢀH1–N1 and In–Cl1Iꢀ ꢀ ꢀH3–N3 groups in 1. Symmetry mode: A = ꢁx + 1, ꢁy + 1,
ꢁz; I = x, y ꢁ 1, z. (c) 2D layer via non-classical hydrogen bonds In–Clꢀ ꢀ ꢀH–N groups. (d) View of the 3D supramolecular network along the [010] direction, the extensive
hydrogen bonds are colored black.
Fig. 3. (a) Coordination environment of Sc3+ ion in 2. (b) Two different helical chains of chiral layers in 2 (hydrogen atoms are omitted for clarity). Symmetry mode: A = 3 ꢁ x,
ꢁ0.5 + y, 1.5 ꢁ z; B = 3 ꢁ x, 0.5 + y, 1.5 ꢁ z; C = 1 + x, y, z.
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J. Chai et al. / Polyhedron xxx (2017) xxx–xxx
and N1–H1ꢀ ꢀ ꢀO4D hydrogen bonds link adjacent layers to con-
struct a 3D supramolecular structure. Notably, other hydrogen
bonds of O1–H2Wꢀ ꢀ ꢀO8F, O1–H1Wꢀ ꢀ ꢀO4, N2–H2ꢀ ꢀ ꢀO6G, N2–
H2ꢀ ꢀ ꢀO1G and N3–H3ꢀ ꢀ ꢀO9H make the 3D supramolecular more
stable (Fig. 2d).
O6B and O7C from three individual Hbidc2ꢁ, two O atoms of O4
and O4A (symmetry codes: A = 3 ꢁ x, ꢁ0.5 + y, 1.5 ꢁ z; B = 3 ꢁ x,
0.5 + y, 1.5 ꢁ z; C = 1 + x, y, z) from two OHꢁ, one O5W atoms from
coordinated H2O. The Sc–O bond lengths are in the range of 2.068
(2)–2.152(2) Å, the O–Sc–O bond angles range from 85.19(10)° to
176.49(9)°, all of which are in agreement with those of the
reported Sc-CPs [20].
3.1.2. Structural description of [Sc(Hbidc)(OH)(H2O)]n (2)
In 2, the two carboxylate groups of H3bidc ligand are com-
pletely deprotonated, displaying monodentate and bis-monoden-
tate coordination mode II as shown in Scheme 1. It is worth
noting that Sc3+ ions are linked by C1, C2, C8, C9, O6, O7 of Hbidc2ꢁ
ligands to generate a left-handed helical chain (L helix) running
along the crystallographic 21 axis with a pitch of 7.6047 Å, while
2 is a 2D platelike coordination polymer. 2 crystallizes in a mon-
oclinic P21/c space group. There are one crystallographically unique
Sc3+ ion, one Hbidc2ꢁ ligands, one OHꢁ and one coordinated H2O
molecule in the asymmetric unit of 2. As shown in Fig. 3a, the
Sc3+ ion with six coordinated environment exhibits approximately
octahedral geometry, which is completed by three O atoms of O2,
Fig. 4. (a) Left chiral layer in 2. (b) Right chiral layer in 2. (c) The supramolecular 3D architecture by
interactions in 2 (hydrogen atoms are omitted for clarity).
p–p stacking interactions along the ac plane in 2. (d) p–p stacking
Table 1
Strecker reaction between N-Bn-phenylaldimine and TMSCN Catalyzed by CPs 1 and 2.
Entrya
Catalyst
Reaction time (h)
Conversion yield (%)b
1
2
3
4
5
6
1
1
1
2
2
2
0.5
5
48
0.5
5
20
59
96
10
38
86
48
a
Reaction conditions: aldimine (0.14 mmol), TMSCN (47
% Conversion calculated by 1H NMR with aldimines.
l
l), catalyst (0.04 mmol), CDCl3 (2.4 mL) at room temperature.
b
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J. Chai et al. / Polyhedron xxx (2017) xxx–xxx
5
Table 2
Strecker reaction between aldimines and TMSCN catalyzed by CP 1.
Entrya
1
Aldimine
Reaction time (h)
48
Conversion yield(%)b
97
2
48
99
3
4
48
48
95
64
5
48
98
6
7
48
48
98
97
8
9
168
168
96
77
(continued on next page)
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J. Chai et al. / Polyhedron xxx (2017) xxx–xxx
Table 2 (continued)
Entrya
10
Aldimine
Reaction time (h)
Conversion yield(%)b
75
168
11
168
50
a
Reaction conditions: aldimine (0.14 mmol), TMSCN (47
% Conversion calculated by 1H NMR with aldimines.
l
l), catalyst (0.04 mmol), CDCl3 (2.4 l) at room temperature.
b
the right-handed screw (R helix) owning the same pitch and com-
ponents as the former, as shown in Fig. 3b. The torsion angles O6–
C9–C1–C2 and O7–C8–C1–C2 are 152.9°, ꢁ72.8°, respectively. As
shown in Fig. 4a, the different helical chains with identical rotation
direction are connected to each other to form left-handed chiral
layers. In the same way, Sc3+ ions are linked to constitute another
right-handed chiral layer, as shown in Fig. 4b. Finally, the adjacent
helical layers with the opposite chirality are extended alternately
to stack in an ABAB sequence along the ac plane and the hydropho-
bic bulky benzimidazole groups project into the interlamellar
regions (Fig. 4c). The adjacent Hbidc2ꢁ ligands including one ben-
zene ring and one imidazole ring are parallel nearly. The center dis-
tances of the plane-to-plane between benzimidazole ring in the
perature PXRD patterns further indicate that the structures of CPs 1
and 2 are retained up to 250 °C and 300 °C, respectively (Figs. S7
and S8).
The IR spectra of CPs 1 and 2 show the characteristic bands of
the carboxylic groups in the usual region around 1384 and 1420
cmꢁ1 for the symmetric vibrations and at 1594 and 1535 cmꢁ1
for the asymmetric vibrations, respectively (Figs. S5 and S6). The
absence of the peak around 1700 cmꢁ1 indicates that all carboxyl
groups of organic moieties in 1 and 2 are deprotonated, which is
consistent with the result of the single-crystal X-ray analysis.
3.3. Catalytic properties
adjoining layers are 3.6824 Å, which indicate the formation of
stacking interactions as shown in Fig. 4d. As a result, the 2D layer
exists a 3D supramolecular structure. Noteworthily, the benzimi-
dazole ring involved in the stackings arrange in such a way
the nine atoms of the ring do not completely overlap those of the
other rings. This means the interaction is not ‘‘perfect face
p–
p
Strecker synthesis has long been considered one of the most
direct and viable methods for the synthesis of
a-amino acids
p–p
[22]. Strecker reaction is a Lewis acid or base catalyzed carbon–car-
bon bond formation. Over years, many compounds have been
proved to be excellent catalysts for the Strecker reaction of aldimi-
nes; nevertheless, when aldimines were used as substrates, only a
few heterogeneous catalysts showed good conversions [23]. Previ-
ous studies about CPs have postulated that certain materials exhi-
bit good catalytic activity in such reactions with low loadings, mild
temperatures [24].
The CPs 1 and 2 possess available Lewis acid catalytic centers. 1
and 2 were initially evaluated in the Strecker reaction between N-
Bn-phenylaldimine (Bn = PhCH2) and TMSCN at room temperature
(Table 1, entries 1–6). It was observed that, in contrast to 2, 1 can
catalyze the Strecker reaction with a fairly- high conversion rate.
N-Bn-aldimine proceeded smoothly in the presence of 28.6 mol%
1 in deuterochloroform (CDCl3) for 5 h, providing the correspond-
p–p
to face alignment’’ but ‘‘slipped stacking’’ [21].
3.2. Characterization
Phase purity of 1 and 2 was confirmed by PXRD measurement
and PXRD patterns of the as-synthesized samples are in agreement
with the simulated ones (Figs. S1 and S2). The difference in inten-
sity may be ascribed to the preferred orientation of the powder
samples. TGA analysis was performed on pure single crystal sam-
ple of 1 and 2 under air atmosphere with a heating rate of 10 °C
minꢁ1 in the range of 25–800 °C. 1 displays a continuous weight
loss (76.5 wt.%) in the temperature range of 290–586 °C, which
corresponds to the loss of the coordinated water molecules and H2-
bidcꢁ ligands in the framework (calc. 75.9 wt.%) (Fig. S3). The TGA
plot indicates that 2 releases its OHꢁ groups and coordinated H2O
molecules in the temperature range of 250–400 °C (calc. 12.3 wt.
%), forming Sc(Hbidc), which decompose completely in the temper-
ature range of 400–490 °C (calc. 71.8 wt.%) (Fig. S4). Variable-tem-
ing
a-aminonitrile in 59% conversions (Table 1, entry 2), while 2
catalyzed only provided 38% conversions after 5 h. After 48 h, 1
and 2 achieve 96% and 86% conversions, respectively. This obvious
difference in catalytic reactivity may attribute to different metal
ions of frameworks. Compared to 2, 1 exhibits higher catalytic
reactivity for the Strecker reaction.
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J. Chai et al. / Polyhedron xxx (2017) xxx–xxx
7
Fig. 5. Reusability of 1 and 2 catalysts experiments.
To further investigate the generality of catalyst 1, we also stud-
Acknowledgments
ied the influence of different substitution groups of aldimines on
the reaction under same conditions. The experimental results
showed that the substituents have an important effect on the
Strecker reaction. The substrates containing electron-donating
groups, such as 2-bromo and 4-methoxyl, can obtain the product
in 99% and 95% after 48 h, respectively (Table 2, entries 2 and 3),
whilst, in the case of electron-drawing substrates (4-trifluo-
romethyl), conversion of the substrate was significantly sup-
pressed (64%, 48 h). In addition, we try to change the
substituents’ size, however, conversion rate was not affected
almost (Table 2, entries 5–7).
Moreover, we also studied the difference among various sizes
N-PG (PG = protected group). The experimental results showed
that, with increasing size of N-PG, conversion rate dropped dra-
matically. For example, compared to N-CH2CH2CH3-pheny-
laldimine (96%), the conversion rates of N-CH(Ph)2-
phenylaldimine and N-C(Ph)3-phenylaldimine were 75% and 50%,
respectively (Table 2, entries 10 and 11). The significant decrease
in conversion rate suggests that large substrates are less likely to
access the catalytic sites compared to small ones. The samples of
1 and 2 can be easily recovered from the reaction mixture by filter-
ing and drying.
The authors gratefully acknowledge the financial support
through the National Natural Science Foundation of China (Grant
Nos. 21171065, 21201077 and 21401005).
Appendix A. Supplementary data
CCDC 1554644–1554645 contain the supplementary crystallo-
graphic data for 1 and 2. These data can be obtained free of charge
via http://www.ccdc.cam.ac.uk/conts/retrieving.html, or from the
Cambridge Crystallographic Data Centre, 12 Union Road, Cam-
bridge CB2 1EZ, UK; fax: (+44) 1223-336-033; or e-mail:
deposit@ccdc.cam.ac.uk. Supplementary data associated with this
article can be found, in the online version, at https://doi.org/10.
1016/j.poly.2017.10.028.
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The stability and recyclability of 1 and 2 were further investi-
gated by using N-Bn-(2-bromophenyl)aldimine and N-Bn-pheny-
laldimine as substrates. As shown in Fig. 5, more than 95%
conversion of aldimine was still maintained even after four consec-
utive runs and only a slight decrease was observed in the fifth run.
For 2, the conversion has dropped to 75% in the fourth run. More-
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In summary, we reported two highly stable In-based and Sc-
based CPs 1 and 2. Such CPs catalysts exhibit rich open Lewis acid
sites, and they were then applied as efficient heterogeneous cata-
lysts for the Strecker reaction of aldimines under mild condition.
Importantly, 1 shows much higher catalytic activities to the aldi-
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With increasing size of N-PG, conversions of the aldimines were
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activity and good stability demonstrate that 1 is an efficient
heterogeneous CP catalyst for
temperature.
a-aminonitriles formation at room
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