Synchronizing Substrate Activation Rates in Multicomponent Reactions with Metal-Organic Framework Catalysts

Article abstract of DOI:10.1002/chem.201504576

A study on the influence of the cation coordination number, number of Lewis acid centers, concurrent existence of Lewis base sites, and structure topology on the catalytic activity of six new indium MOFs, has been carried out for multicomponent reactions (MCRs). The new indium polymeric frameworks, namely [In₈(OH)₆(popha)₆(H₂O)₄]·3 H₂O (InPF-16), [In(popha)(2,2′-bipy)]·3 H₂O (InPF-17), [In₃(OH)₃(popha)₂(4,4′-bipy)]·4 H₂O (InPF-18), [In₂(popha)₂(4,4′-bipy)₂]·3 H₂O (InPF-19), [In(OH)(Hpopha)]·0.5 (1,7-phen) (InPF-20), and [In(popha)(1,10-phen)]·4 H₂O (InPF-21) (InPF=indium polymeric framework, H₃popha=5-(4-carboxy-2-nitrophenoxy)isophthalic acid, phen=phenanthroline, bipy=bipyridine), have been hydrothermally obtained by using both conventional heating (CH) and microwave (MW) procedures. These indium frameworks show efficient Lewis acid behavior for the solvent-free cyanosilylation of carbonyl compounds, the one pot Passerini 3-component (P-3CR) and the Ugi 4-component (U-4CR) reactions. In addition, InPF-17 was found to be a highly reactive, recyclable, and environmentally benign catalyst, which allows the efficient synthesis of α-aminoacyl amides. The relationship between the Lewis base/acid active site and the catalytic performance is explained by the 2D seven-coordinated indium framework of the catalyst InPF-17. This study is an attempt to highlight the main structural and synthetic factors that have to be taken into account when planning a new, effective MOF-based heterogeneous catalyst for multicomponent reactions.

Full text of DOI:10.1002/chem.201504576

DOI: 10.1002/chem.201504576
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&
Heterogeneous Catalysis |Hot Paper|
Synchronizing Substrate Activation Rates in Multicomponent
Reactions with Metal–Organic Framework Catalysts
Lina María Aguirre-Díaz, Marta Iglesias, Natalia Snejko, Enrique GutiØrrez-Puebla, and
[a]
M. ngeles Monge*
Abstract: A study on the influence of the cation coordina-
tion number, number of Lewis acid centers, concurrent exis-
tence of Lewis base sites, and structure topology on the cat-
alytic activity of six new indium MOFs, has been carried out
for multicomponent reactions (MCRs). The new indium poly-
meric frameworks, namely [In (OH) (popha) (H O) ]·3H O
dures. These indium frameworks show efficient Lewis acid
behavior for the solvent-free cyanosilylation of carbonyl
compounds, the one pot Passerini 3-component (P-3CR) and
the Ugi 4-component (U-4CR) reactions. In addition, InPF-17
was found to be a highly reactive, recyclable, and environ-
mentally benign catalyst, which allows the efficient synthesis
of a-aminoacyl amides. The relationship between the Lewis
base/acid active site and the catalytic performance is ex-
plained by the 2D seven-coordinated indium framework of
the catalyst InPF-17. This study is an attempt to highlight
the main structural and synthetic factors that have to be
taken into account when planning a new, effective MOF-
based heterogeneous catalyst for multicomponent reactions.
8
6
6
2
4
2
(
(
InPF-16), [In(popha)(2,2’-bipy)]·3H O (InPF-17), [In (OH) -
2
3
3
popha) (4,4’-bipy)]·4H O
(InPF-18),
[In (popha) (4,4’-
2 2
2
2
bipy) ]·3H O (InPF-19), [In(OH)(Hpopha)]·0.5(1,7-phen) (InPF-
2
2
2
0), and [In(popha)(1,10-phen)]·4H O (InPF-21) (InPF=
2
indium polymeric framework, H popha=5-(4-carboxy-2-ni-
3
trophenoxy)isophthalic acid, phen=phenanthroline, bipy=
bipyridine), have been hydrothermally obtained by using
both conventional heating (CH) and microwave (MW) proce-
Introduction
of the catalyst active sites when carried out in one pot, even
whilst the framework is not modified. Herein, we have studied
the influence of various structural factors over the catalytic ac-
tivity of MOFs in MCRs, while maintaining the same chemical
components.
In terms of new materials development, the last two decades
have been captivated by metal–organic frameworks (MOFs),
which facilitate the construction of a large variety of interest-
ing structures that have applications in a huge number of
[
17]
MCRs have several advantages: the isolation or purifica-
tion of intermediate products is not required, superior atom
economy, and high variability of substrates. Among numerous
types of multicomponent condensations, the Passerini and the
[
1–7]
fields. MOFs offer great potential as heterogeneous catalysts
as they can have active sites within their frameworks, both in
[
8–10]
the organic linkers and in the metal centers.
In our group,
[
18]
we have previously demonstrated that indium-based MOFs
might have high catalytic activity in several organic transfor-
mations, from simple Lewis acid catalyzed reactions, such as
cyanosilylation, acetalization, nitro group reduction, or oxida-
tion of sulfides, to more elaborate ones, such as the one-pot
Ugi reactions are highly convergent methods, which allows
for the rapid generation of organic drug-like molecule libraries
[
19]
and many different types of biologically active targets.
The Ugi four-component reaction (U-4CR) is perhaps one of
[
19–20]
the most important isocyanide-based MCRs.
It is a valuable
[
11–16]
Strecker three-component reaction (S-3CR).
method for generating a-aminoacyl amide derivatives in a very
In previous work, we showed that modulation of the ratio of
different metals in solid-solution MOFs resulted in changes to
straightforward manner by the condensation of an aldehyde,
[
18]
amine, carboxylic acid, and isocyanide in a one-pot reaction.
[
16]
their catalytic activity in a multicomponent reaction (MCR).
This demonstrated that MCRs are highly sensitive to the nature
Lewis acids are not always required for many of the reported
isocyanide-based MCRs; however, to obtain good yields and
selectivity in the U-4CR, Lewis acid catalysts do have to be
[
21–34]
used.
Recently, U-4CRs have been described by using ionic liq-
[
a] Dr. L. M. Aguirre-Díaz, Dr. M. Iglesias, Dr. N. Snejko,
Prof. E. GutiØrrez-Puebla, Prof. M. . Monge
[
35]
[28,31–32]
uids, and deep eutectic solvent–water systems.
In the
Departamento de Nuevas Arquitecturas en Química de Materiales
Instituto de Ciencia de Materiales de Madrid (ICMM-CSIC)
Sor Juana InØs de la Cruz 3, Cantoblanco 28049, Madrid (Spain)
E-mail: amonge@icmm.csic.es
case of heterogeneous catalysts, fluorite has been employed
[33]
as a mild acid catalyst under a microwave-assisted method.
The use of a novel magnetic nanocatalyst has also been de-
scribed, which resulted in a decrease of the reaction time and
Supporting information for this article is available on the WWW under
http://dx.doi.org/10.1002/chem.201504576.
[
34]
an improvement of the selectivity of the Ugi products.
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[11–16]
Based on our previous experience,
we have performed
a study of the mechanisms of the Passerini and Ugi MCRs by
using new indium MOFs, in which various structural and com-
positional variables are introduced. Thus, we have prepared six
new materials by using indium, the V-shaped tripodal ligand 5-
(
4-carboxy-2-nitrophenoxy) isophthalic acid (H popha), and in
3
some cases, the addition of different aromatic amines
Scheme 1). With this strategy, we can study the influence of
(
the cation coordination number (CN), number of Lewis acid/
base centers, concurrent existence of Lewis and/or Brønsted
sites, and structure topology on the catalytic activity of the
new MOFs, which will give us an insight into the mechanism
[36]
[37–40]
of these important reactions. The less-explored
H popha
3
linker was chosen because of its capability to coordinate to
the metal cations through three carboxylate groups in several
modes. In addition, the presence of the nitro group breaks not
only the symmetry of the molecules but also the electronic
likeness of the two aromatic rings (Scheme 1).
Scheme 2. Different Lewis acid catalyzed reactions: i) cyanosilylation of car-
bonyl compounds, ii) P-3CR, iii) U-4CR, and iv) Danishefsky reaction.
Figure 1. Comparison between MW and CH reaction conditions to obtain
InPF materials.
Scheme 1. The organic ligand 5-(4-carboxy-2-nitrophenoxy) isophthalic acid
(H popha) reacts with indium and nitrogenated auxiliary ligands to form
3
a series of new MOFs.
between the reaction time for each method. Under the MW
methodology, we obtained all the new materials as pure
phases in higher yields (89–97%) and much shorter reaction
times (a decrease of 97–99%) than with the CH protocol. The
purity of each sample was confirmed by using PXRD, elemental
analysis, and IR spectroscopy (see the Supporting Information).
The dynamic light scattering (DLS) analysis, performed by
using water as a solvent at 258C, showed a broad range of
particle sizes for the InPF materials (Table 1, Figure 2). Even
The differences between conventional heating (CH) and mi-
crowave(MW)-assisted hydrothermal synthesis procedures, par-
ticle size, and heterogeneous catalysis activity for each MOF
material were established. Some of them showed a catalytically
efficient evolution from the cyanosilylation reaction to the
one-pot Passerini three-component reaction (P-3CR) and the
one-pot Ugi four-component reaction (U-4CR) (Scheme 2). To
the best of our knowledge, there are no reports on the synthe-
sis of functionalized N-acylamino amides by MCRs catalyzed by
MOFs.
Table 1. Average particle size distribution for the crystalline materials ob-
tained by MW-assisted synthesis.
Material
No. particle
Particle size
distribution range [nm]
% particles in
the size range
Results and Discussion
InPF-16
InPF-17
InPF-18
InPF-19
InPF-20
InPF-21
2037
2817
2518
2982
2537
3684
355–446
389–616
148–468
355–467
295–446
389–467
78
98
68
41
74
70
With the purpose of studying the influence of the synthetic
procedure on the particle sizes and shapes and subsequently
on the catalytic activity of the InPF compounds, we performed
a study to compare conventional heating with microwave-as-
sisted hydrothermal synthesis; Figure 1 shows the differences
Chem. Eur. J. 2016, 22, 6654 – 6665
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Figure 2. SEM images of the InPF-17 material synthesized by MW (15000”
mag, left) and CH (8000” mag, right) protocols.
though several reports have suggested that materials with
well-defined particle sizes can be obtained by using MW meth-
[
41–46]
odology,
in our case, for almost all InPF materials, the
average particle size was around 400 nm, and there was
a large variation in their size distribution. The aforementioned
advantages of reduced reaction times and higher yields facili-
tate the material elaboration.
3
À
2À
Figure 3. Different coordination modes of the popha and Hpopha organ-
ic linker in InPF-16 to InPF-21 materials.
Additionally, the geometrical description of each framework,
in terms of linked nodes or SBUs (secondary building units), is
presented, which is fundamental to enable rationalization of
the corresponding MOF net topology. This study was per-
Crystal structures
The crystal structure for each compound was determined by
using single-crystal X-ray diffraction; crystals of a suitable size
were obtained through the CH hydrothermal synthesis. Details
of data collection, refinement, and crystallographic data for the
compounds InPF-16 to InPF-21 are summarized in Table 2.
[
47–49]
formed by using the TOPOS program.
InPF-16 material, with formula [In (OH) (popha) (H O) ]·
8
6
6
2
4
3H O, crystallizes in the triclinic P 1¯ space group. The asymmet-
2
3
+
ric unit consists of four crystallographically different In ions,
3
À
three molecules of the fully deprotonated popha linker, three
hydroxyl groups, and two coordinated water molecules
(Figure 4).
Structural description
The tripodal V-shaped ligand H popha possesses several differ-
3
3À
ent modes of coordination onto metal centers. Herein, six dif-
ferent coordination modes are possible for the fully deproton-
The molecules of the popha linker show three different co-
1
2
2
2
1
1
ordination modes: i) L with h -h m-h m, ii) L with h m-h -h , and
1
2
3À
2
2
2
ated popha linker and one coordination mode for the pro-
iii) L with h m- h m-h m (Figure 3). There are four crystallograph-
3
2À
tonated Hpopha species (Figure 3).
ically independent indium metal centers, all of which are in
Table 2. Main crystallographic and refinement data for compounds InPF-16 to InPF-21.
InPF-16 InPF-17 InPF-18
InPF-19
InPF-20
InPF-21
C
45
H
24In
4
N
3
O
34
C
25
H
14InN
3
O
11
C
40
H
20In
3
N
4
O
22.64
C
50
H
28In
2
N
6
O
18.30
C
20.25
H
8.5InNO10.25
27 3 10
C H14InN O
À1
M
T [K]
l [Š]
r
[gmol
]
1609.95
296
1.54178
triclinic
P1¯
647.21
296
0.71073
triclinic
P1¯
1263.30
296
1.54178
monoclinic
C2/c
17.363(1)
14.759(1)
19.890(2)
90
95.180(6)
90
5076.0(7)
4
1.653
11.4502
2444
1230.42
296
1.54178
monoclinic
P21/n
17.411(1)
18.452(1)
17.903(1)
90
101.309(5)
90
5640.1(6)
4
1.455
7.171
551.61
296
1.54178
monoclinic
P21/n
7.2776(7)
22.060(2)
15.0234(16)
90
98.687(6)
90
2384.3(4)
4
1.537
8.422
1086
655.23
293
1.54178
triclinic
P1¯
10.0013(5)
12.5596(6)
13.5491(7)
100.704(3)
105.631(3)
113.311(2)
1420.6(1)
2
crystal system
space group
a [Š]
11.2976(3)
9.9939(6)
b [Š]
c [Š]
a [8]
b [8]
g [8]
V [Š ]
Z
Dx [gcm
m [mm
F(000)
12.8826(4)
18.5044(5)
76.122(2)
88.327(2)
78.218(2)
2558.9(1)
2
2.089
15.234
1566
12.3477(8)
13.1271(8)
98.256(1)
110.786(1)
110.310(1)
1353.0(1)
2
1.589
0.938
644
3
À3
]
1.532
7.180
652.0
À1
]
2457
GOF(F2)
0.977
1.040
0.881
1.043
1.126
1.029
0
0
.0576
.1644
0.0725
0.2090
0.0823
0.2383
0.0565
0.1839
0.0816
0.3402
0.0874
0.2722
final R indexes [I>2s(I)]
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is also observed. The [InN O ] polyhedra are connected
2
5
1
2
2
3À
through the L (h -h -h ) popha organic linker to construct
4
square rings of 9.994 Š”9.916 Š dimensions that contain three
metal centers. The presence of the blocking bipyridine unit to-
gether with the square-shaped rings give rise to 2D layers,
which are perpendicular to the (001) plane, that possess an
hcb topology of a three-connected uninodal net. The supra-
molecular network was built up through two types of weak in-
teractions, which increase the dimensionality of the framework
and connect the 2D covalent layers along the a and c axes:
i) p···p from two neighboring molecules of 2,2’-bipyridine with
a distance of 3.832 Š between centroids, which display an
offset of 20.798, and ii) CÀHL···p (dD-A: 3.403 Š), which extend
the network along the (001) plane. The final 3D structure
shows a dia topology with a four-connected uninodal network
(
Figure 5).
Figure 4. Top: asymmetric unit of InPF-16. Bottom: polyhedral representa-
tion of the 3D structure of InPF-16 with its corresponding llj topology and
its representation of the inorganic secondary building unit.
InO -octahedral coordination environments. The environment
6
of one of the indium metallic centers (In1) is formed by two
InÀO bonds with the two hydroxyl bridge groups, one InÀO
3
À
bond with the monodentate part of the L popha linker, and
1
3
À
three InÀO bonds with the chelate popha linker (two L and
1
one L ). The environment of the second indium metallic center
3
(
In2) is formed by two InÀO bonds with the bridging hydroxyl
groups and four InÀO bonds with the chelating popha linker
two L and two L ). The third indium environment (In3) con-
3À
(
1
3
Figure 5. Top: atomic and polyhedral representation of InPF-17 structure,
which shows the asymmetric unit and a perpendicular view of the 2D layers
with the topological representation. Bottom: p···p and CÀH···p intralayer in-
teractions with the 3D supramolecular net formed and the topology repre-
sentation.
sists of two InÀO bonds with the bridging hydroxyl groups,
one InÀO bond with the monodentate part of the L linker,
2
3À
and three InÀO bonds with the chelating popha linker (one
L and two L ). The fourth indium environment (In4) exhibits
2
3
one InÀO bond with the bridging hydroxyl group, one InÀO
bond with the monodentate part of the L coordination mode,
2
3
À
two InÀO bonds with the chelating popha linker (one L and
The InPF-18 material, with formula [In (OH) (popha) (4,4’-
2
3
3
2
one L ), and two InÀO bonds with the coordinated water mole-
bipy)]·4H O, crystallizes in the monoclinic C2/c space group.
3
2
cules. An SBU is formed by four vertex-sharing octahedra (In1
to In4), which are joined through an inversion center to anoth-
er four indium centers to form eight octahedra clusters in the
The asymmetric unit consists of one and a half crystallographi-
3
+
3À
cally independent In ions, one fully deprotonated popha
linker, one and a half hydroxyl groups, and half a 4,4’-bipyri-
[
001] direction. In1 and In1’ share a face, which creates a corru-
dine molecule (Figure 6). There are two different environments
gated geometry. These clusters can be described as rods (de-
fined as a 1-periodic 3D structure with a linear axis that is de-
in the octahedral PBUs (primary building units): [InO ] and
6
[InN O ]. In the case of the fully deprotonated organic linker,
2
4
[
50]
2
2
1
termined by specifying a point on the axis and its direction)
an L (h m-h m-h ) coordination is observed. One of the PBUs,
5
that are connected through the organic units in all directions;
the result is a 3D structure with a 3-periodic bipartite 3,12-llj
topology.
À[InO ]À, is constructed from two InÀO bonds with the m-OH
6
groups, which connect In1ÀOÀIn2 and In1ÀOÀIn1, and four
InÀO bonds with the carboxylate groups. Three PBUs have
2
1
The InPF-17 material, with formula [In(popha)(2,2’-bipy)]·
h m-type coordination and only one is monodentate (h ). The
other PBU, À[InN O ]À, has two InÀN bonds with the coordi-
3
H O, crystallizes in the triclinic P 1¯ space group. The asymmet-
2
2
4
3
+
ric unit consists of one In
ion, one fully deprotonated
nated 4,4’-bipyridine, two InÀO bonds with the m-OH groups,
which connect In1ÀOÀIn2, and two InÀO bonds with the car-
3À
popha linker, and one 2,2’-bipyridine molecule. The indium
environment is made up of five InÀO bonds with the carboxyl-
2
boxylate groups, which connect In1ÀOÀIn2 with h m-type coor-
3À
ate part of the popha linker and two InÀN bonds with the
dination. Inorganic chains along the c axis are built from the
PBUs that share a vertex through the m-OH groups. The SBUs
2
,2’-bipyridine. A weak interaction between In···O6 (2.650(8) Š)
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Figure 6. Top: atomic and polyhedral representation of InPF-18 structure,
which shows the asymmetric unit and (010) view of inorganic chains.
Bottom: (001) view of the 3D network and the topological representation.
Figure 7. Top: atomic and polyhedral representation of InPF-19 structure,
which shows the asymmetric unit and its 3D framework. Bottom: two differ-
ent topological representations of InPF-19.
can be described as infinite (ÀOHÀInÀ)1 rods with carboxylate
O and bipyridine N atoms that complete the octahedral coordi-
nation around the indium centers, which results in infinite rods
3
+
In ions, both of which are placed at inversion centers, one
2À
of InO6 and InN O4 octahedra that share corners (Figure 6).
partially deprotonated Hpopha linker, and one m-OH group
2
These rods are connected in all direction through the ÀC H À (Figure 8). Both indium cations exist as À[InO ]À octahedral
10
8
6
and the ÀC NO H À linkers, which give rise to a 3D framework.
units with the following bonds: two InÀO bonds with the
1
4
3
6
The rods are assembled in a hexagonal packing arrangement
going down the (001) plane; in fact, the InPF-18 3D arrange-
ment can be described as rod-packing pillared 2D layers with
a 3,8l18 topology and a 3,10-connected binodal network
bridging hydroxyl group (In1ÀO: 2.079(8) Š and In2ÀO: 2.095
(7) Š), and four InÀO bonds with the carboxylate group (In1À
O: 2.182(9)–95(9) Š and In2ÀO: 2.129(9)–35(11) Š). The PBUs
share vertices that form infinite À[InÀOÀIn]À chains along the
[
51]
(
Figure 6).
The InPF-19 material, with formula [In (popha) (4,4’-
2
2
bipy) ]·3H O, crystallizes in the monoclinic P2 /c space group.
2
2
1
The asymmetric unit consists of two different crystallographic
3
+
3À
In ions, two fully deprotonated popha linkers, and two
,4’-bipyridine molecules (Figure 7). As a result, the formation
4
of two À[InN O ]À PBUs, which contain eight-coordinate
2
6
indium centers, is observed. They are made up of two InÀN
bonds with the 4,4’-bipyridine ligands (In1ÀN: 2.299–2.312 Š
and In2ÀO: 2.325–2.323 Š) and six InÀO bonds with the
À3
popha
linker (In1ÀO: 2.117–2.473 Š and In2-O: 2.171–
2 2 2
2
.521 Š). An L (h -h -h ) fully chelating coordination mode is
6
found for both indium metal centers. Along the c axis, the
À[InN O ]À PBUs are connected through the 4,4-bipyridine
2
6
with In1···In2 distances of 11.695(1) and 11.746(1) Š. Connec-
tions along the a and b axes are made through the popha
linker: In1···In1, In2···In2, and two In1···In2 PBUs with distances
1
5.554, 15.553, 9.693, and 9.695 Š, respectively, which gives
rise to a 3D structure. By considering the double connectivity
that is showed by the two crystallographically different 4,4-bi-
pyridine along the c axis, the topological study showed a 3D
interpenetrated (Class IIa) framework with a dmc 3,4-connect-
ed binodal network, which could also be described as the deri-
[
52]
vated fsc-3,5-Cmce-1 of a 3,5-connected binodal network.
The InPF-20 material, with formula [In(OH)(Hpopha)]·0.5(1,7-
Figure 8. Top: asymmetric unit representation of InPF-20. Bottom: poly-
hedral representation of InPF-20 3D framework and its corresponding cds
topology.
phen), crystallizes in the monoclinic P2 /n space group. The
1
asymmetric unit consists of two crystallographically different
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2
2
a axis; the linker with coordination mode L (h m-h m-COOH)
To evaluate the utility, stability, and capacity of these novel
indium MOF materials as heterogeneous acid catalysts, we
chose to test three different Lewis acid catalyzed organic trans-
formations: i) a two-component cyanosilylation of carbonyl
compounds, ii) the Passerini three-component reaction, and
iii) the Ugi four-component reaction (Scheme 2). The reactions
were carried out with the two MOF catalyst series: those ob-
tained by CH or MW-assisted synthesis; however, no differen-
ces between these two InPF catalyst series were found.
7
connects these chains through the two carboxylate bridging
units along the b and c axes to build a 3D covalent network,
which can be described as a 4-connected uninodal network
with a cds topology. The protonated part of the popha linker
forms an OÀH···O synthon (dH···O =2,614 Š) between adjacent
molecules of the popha linker.
The InPF-21 material, with formula [In(popha)(1,10-
phen)]·4H O, crystallizes in the triclinic P 1¯ space group. The
2
3
+
asymmetric unit consists of one In ion, one fully deprotonat-
The cyanosilylation reaction is a Lewis acid catalyzed
carbon–carbon bond formation. Over the years, many catalysts
have proved to be excellent for the cyanosilylation of alde-
hydes; nevertheless, when ketones were used as substrates,
only a few heterogeneous catalysts have shown good conver-
3À
ed popha linker, and one 1,10-phenanthroline molecule.
Indium cations form [InN O ] octa-coordinated units, which to-
2
6
2
2
2
À3
gether with the L (h -h -h ) popha linker, give rise to 2D
6
layers that are perpendicular to the (001) plane with an hcb
topology in a three-connected uninodal net. The supramolec-
ular network is constructed through two weak interactions,
which increase the dimensionality of the framework and con-
nect the 2D covalent layers along the a and c axes: i) pphen···HÀ vent.
Cphen with two neighboring 1,10-phenanthroline units at a dis-
[
53–64]
sions.
Previous studies with indium MOFs have concluded
that these materials exhibit good catalytic activity in such reac-
tions with low loadings, mild temperatures, and without sol-
[
14–16]
The cyanosilylation reactions were performed by using low
tance of 3.575 Š between the middle phenanthroline ring
centroids and the hydrogen atom of one of the carbons from
the phenanthroline, and ii) CÀHL···pL (dD-A: 3.388 Š), which
extend the network along the (001) plane. The final 3D struc-
ture shows a dia topology with a four-connected uninodal net-
work (Figure 9).
catalytic amounts (1–5 mol%), under an inert atmosphere,
without solvent, and at room temperature. The results showed
that catalysts with the six or seven-coordinated indium atoms
(InPF-16, InPF-17, InPF-18, and InPF-20) gave good yields in
short reaction times, whereas those with eight-coordinated
indium atoms showed no catalytic activity, which further
proves the important role that the Lewis acid active site on
the metallic center plays in the reactants activation. Thus, the
InPF-19 and InPF-21 materials, which do not possess available
Lewis acid sites or any other groups that are suitable to inter-
act with the substrates, were not considered as catalysts in the
subsequent studies.
The InPF-16, InPF-17, InPF-18, and InPF-20 materials pos-
sess, besides indium Lewis acid sites, Lewis base moieties, such
as bridging hydroxyl groups (m-OH) and/or noncoordinated
carbonyl groups (free C=O). This permits two-component cata-
lytic systems, which follow a mechanism that is based on the
[
65]
“
dual-activation” phenomenon in which the carbonyl com-
pound is activated by the interaction with the metal-centered
Lewis acid site, and simultaneously, the silyl group is activated
by the Lewis basic moieties (Figure 10).
Although the presence of a central oxygen atom between
the phenyl rings in the H popha organic ligand could be con-
3
sidered as a Lewis basic moiety, the presence of the nitro
group at the ortho position in one of the phenyl rings with-
draws the charge density from this central oxygen. This delo-
calizes the electron charge and decreases the basicity of this
moiety, but does not seem to show any influence on the cata-
lytic behavior of the InPF materials.
Figure 9. Top: atomic and polyhedral representation of InPF-21 structure,
which shows the asymmetric unit and a perpendicular view of a 2D layers
with hcb topology. Bottom: weak intralayer interactions with the 3D supra-
molecular net topology representation.
Catalytic activity of InPF materials
By increasing the number of active sites in the catalyst (acid
and basic moieties), we expected higher product yields over
shorter reaction times. The InPF-16 material contains eight In
clusters, m-OH moieties, and noncoordinated C=O groups (po-
tential Lewis basic sites) along its framework with an M/CO/OH
ratio of 4:3:3 as well as two easily displaceable coordinated
water molecules. Consequently, it exhibits an outstanding cata-
lytic activity by reaching 99% yield in just 10 min.
Initially, the possible accessible voids for each structure were
examined. Only the InPF-19 material, which does not possess
available Lewis acid centers, contains accessible pores (ꢀ147–
3
1
15 Š ), whereas InPF-17, InPF-18, and InPF-21 materials only
3
contain small pores (ꢀ43 Š ), and InPF-16 and InPF-20 cata-
lysts did not contain any pores. This led us to consider that the
studied MOFs represent only superficial catalytic systems.
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and the free C=O groups (M/C=O/OH ratio=3:2:3 for
InPF-18 and M/C=O ratio=1:1 for InPF-17) along its frame-
work.
After the first catalytic reaction, the InPF-20 crystalline struc-
ture was not preserved, which means that interaction between
the reactants and the catalyst affects its framework (see the
Supporting Information). Therefore, this material was not con-
sidered for subsequent studies, because the structure–activity
relationship could not be established.
Once a good catalytic behavior was demonstrated for the
InPF-16, À17 and À18 materials in the cyanosilylation transfor-
mation, the catalytic efficiency of these materials was evaluat-
ed in two multicomponent organic reactions: the Passerini (P-
3
CR) and the Ugi reactions (U-4CR).
The Passerini reaction is an isonitrile-based MCR that yields
a-acyloxy carboxamides in a one-pot synthesis from an alde-
hyde, isonitrile, and carboxylic acid. The carbonyl group is one
of the most critical reactants because of the pronounced reac-
tivity of the isonitrile carbon atom towards the electrophilic
Figure 10. Proposed mechanism for the InPF-16-catalyzed cyanosilylation of
carbonyl compounds.
2
sp carbon center; this reaction can be time consuming with
low yields if it is not carried out with a strong carboxylic acid
[
66]
The InPF-16 material, which is the superior MOF catalyst for
the cyanosilylation reaction, was also tested with the more hin-
dered, reactant-like acetophenone. Although, as expected, the
catalyst loading had to be increased for this substrate, the
yield was 67% when the reaction was carried out at with
or an unusually electrophilic carbonyl compound.
We carried out the Passerini reaction by using the one-pot
methodology, at room temperature, without any solvent, and
with 1 mol% of catalyst. InPF-16, InPF-17, and InPF-18 materi-
als demonstrated good catalytic activities (Table 3, entries 1–3).
Taking into account the dual-activation phenomena that was
manifested before by these catalysts (see above), and consider-
ing their basic and acid moieties placed along their frame-
works, we propose the following catalytic mechanism: i) Lewis
acid activation of the carbonyl compound and Lewis base acti-
vation of the OH group of the benzoic acid, ii) attack of the
oxygen of the OH group onto the isocyanide sp carbon, iii)
2
.5 mol% catalyst loading, at room temperature in only 4 h.
Catalyst loading of 5 mol% was necessary to obtain 99% yield
over 16 h at room temperature without any solvent (Table 3,
entry 1).
The differences in indium CNs and the presence or absence
of bridging hydroxyl groups in the structures explains the dis-
tinction in the catalytic activity between InPF-17 and InPF-18
materials. In InPF-17, the higher indium CN (seven) together
with the absence of m-OH groups makes it a slower catalyst
with moderate yields over longer reaction times (TON: 68)
compared with the more active InPF-18 catalyst (Table 3,
3
subsequent coordination onto the sp carbon of the activated
carbonyl compound, and iv) protonation of the intermediate
product and its release from the catalyst. Finally, the free inter-
mediate undergoes a 1,4-O!O acyl transfer to give the ex-
entry 2 vs. 3). The latter contains inorganic chains À[InÀOÀIn]À pected 2-cyclohexylamino-2-oxo-1-phenylethylbenzoate prod-
of six connected indium cations, bridging hydroxyl groups,
uct (Figure 11).
Table 3. Screening of indium MOFs as catalysts in different organic reactions (2, 3, and 4CR).
[
a]
Entry
Catalyst
indium CN, dimensionality)
Catalytic reaction
[
b]
[c]
[d]
(
Cyanosilylation
Benzaldehyde
Yield [%] ([h]) TON
Passerini 3CR
Ugi 4CR
Yield [%] TON
[e]
[e]
Acetophenone
Yield [%] ([h])
TON
[d]
[e]
Yield [%] ([h])
TON
1
2
3
4
5
InPF-16 (6, 3D)
InPF-17 (7, 2D)
InPF-18 (6, 3D)
InPF-20 (6, 3D)
Blank
99 (0.17)
67 (18)
85 (18)
71 (12)
28 (24)
99
68
83
87
–
99 (16)
53 (24)
80 (24)
76 (24)
–
20
11
16
15
–
89 (0.5)
86 (0.7)
83 (0.7)
66 (1.0)
50 (24)
89
86
83
66
–
traces
92
67
89
40
–
92
67
89
–
[
(
a] All reactions were tested at least 3 times by using different fresh batches of manufactured catalysts. [b] Carbonyl compound (0.001 mol), TMSCN
0.001 mol), and catalyst (1 mol% for benzaldehyde, 5 mol% for acetophenone), without solvent, N atmosphere, T=258C, t=10 min–24 h. Yields were de-
2
termined by GC-MS. [c] Benzaldehyde (0.001 mol), benzoic acid (0.001 mol), cyclohexyl isocyanide (0.001 mol), catalyst (1 mol%), without solvent, T=258C,
1
t=30 min–2 h. Yields were determined by H NMR without further purification. [d] Benzaldehyde (0.001 mol), benzoic acid (0.001 mol), aniline (0.001 mol),
cyclohexyl isocyanide (0.001 mol), and catalyst (1 mol%) in EtOH (0.5 mL), T=258C; t=2 h; The progress of the reaction was monitored by GC-MS until dis-
1
appearance of the substrates; the final solid product was analyzed by H NMR without further purification. [e] mmol substrate per mmol catalyst.
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Figure 11. Proposed mechanism for InPF-16-catalyzed Passerini reaction.
Unexpectedly, the TON value of InPF-17, which displayed
the lowest activity in the cyanosilylation reaction, was found to
be similar to those of InPF-16 and InPF-18 in the P-3CR
Figure 12. Proposal mechanism for indium-mediated U-4CR by using the 2D
InPF-17 as the catalyst.
(
Table 3, indium CN is six in the former compounds and seven
in the latter). This indicates that in MCRs the metal CN is not
the only key factor in reaching a good level of catalytic activity.
As several substrates are involved in the reaction, it seems rea-
sonable to think that synchronization in their activation is re-
quired to yield the final product with high selectivity. To prove
this point the catalysts were tested in the four-component Ugi
in the expected N-(-(cyclohexylaminocarbonyl)(phenyl)methyl)-
N-phenylbenzamide product (Figure 12).
The Lewis acid centers that are present in the InPF material
frameworks activate both the carbonyl and intermediate imine
fragments. This occurs faster with the InPF-17 catalyst than
with the InPF-18 material.
4
CR.
The increment in the reactants number, such as in the U-
CR, allows us to observe the catalytic activation processes
With the aim of proposing one of the crucial steps of the
Ugi mechanism and checking if the benzoic acid and cyclohex-
yl isocyanide coupling was possible, we carried out the Dani-
4
[
67]
that arise under InPF catalysis. The reaction was performed ac-
cording to a one-pot methodology at room temperature with
a catalyst loading of 1 mol%, and this led to good yields of
the expected products. Among various solvents that were
screened, we found ethanol to be the best choice for this reac-
tion. Usually, when this reaction was carried out without a cata-
lyst, the condensation of an aldehyde, amine, carboxylic acid,
and isocyanide is achieved through a cascade mechanism that
favors transformation of the imine and to finally obtain the a-
aminoacyl amide derivative, albeit at lower yields (Table 3,
entry 4). The proposed catalytic mechanism for the U-4CR by
using the InPF materials as catalysts also relies upon the dual-
activation phenomena, which is based on presence of both
basic and acidic moieties. The Lewis acid activation of the car-
bonyl reactant is followed by the intermediate imine formation
and its subsequent activation at the same Lewis acid site. The
OH group from the benzoic acid is activated by the Lewis
basic component of the catalyst and attacks the sp carbon of
the isocyanide derivative, which simultaneously coordinates to
shefsky reaction (Scheme 2, iv), which was performed under
exactly the same conditions that were employed for the U-4CR
(RT, ethanol, 1 mol% of InPF-17). By monitoring the reaction
by GC-MS over time, we observed that no N-formyl amide was
formed, which ruled out this species as an intermediate in the
U-4CR. In the case of the InPF-16 catalyst, the imine intermedi-
ate showed no reaction after 2 h, and only traces of the ex-
pected Ugi product were observed.
In the view of these results and based on the structural fea-
tures of the catalyst, we have tentatively established a parame-
ter 0ꢁxꢁ1 that is based on the Lewis base/acid active site
ratio, which could explain the differences in the activity for
each catalyst in the Ugi 4CR. To the best of our knowledge,
there are no other examples in the literature of MOF-catalyzed
Ugi reactions; therefore, this parameter has only been tested
in the compounds that are presented herein.
The maximum CN of indium cations is eight; therefore, we
define the number of Lewis acid sites (LA) as eight minus the
actual CN of each indium atom plus the number of coordinat-
2
the sp carbon of the activated imine. This is followed by pro-
ed water ligands (O ) (easily displaced by the reactants to gen-
L
tonation of this second intermediate and its release from the
catalyst. Finally, this intermediate undergoes a 1,4-O!N acyl
transfer known as the “mumm rearrangement”, which results
erate additional active sites): LA=Æn(8ÀCN+O ), in which n=
L
number of In cations per formula. The number of Lewis basic
sites (LB) is defined as the number of OH groups plus the non-
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coordinated carboxylate C=O groups per formula. Upon scruti-
ny of the LB/LA ratio (x) for the catalytically active materials
force in this reaction. To prove that the larger the number of
substrates, the more significant their synchronization rates
become, we tested the catalysts in the Ugi 4CR. We concluded
that the driving force was the synchronization of the sub-
strates’ activation rates, because the order of catalytic activity
went in the opposite direction to that of the two-component
cyanosilylation: InPF-16<InPF-18<InPF-17.
We cautiously proposed a parameter 0ꢁxꢁ1 that was
based on the Lewis base/acid active site ratio, which explains
our results in the 4CR. The closer to 1 the x value is, the better
the catalytic behavior of the MOF. Thus, the catalyst InPF-17
(x=1) possesses equal amounts of acid and base active sites
and shows excellent catalytic activity, with the highest TON
out of all the catalysts that were studied in the 4CR. InPF-18
(x=0.8) also presents good catalytic activity with the second
highest TON value, whereas InPF-16 (x=0.6) hardly shows any
catalytic activity. As expected, InPF-19 and InPF-21 MOFs (x=
0) do not show any catalytic activity.
(
InPF-16, InPF-17, InPF-18), it was apparent that the closer the
value was to 1, the better the catalytic behavior was. This
would support the hypothesis that a synchronization of the
substrates’ activation rates was required.
Thus, InPF-17 material (x=1) owns equal amounts of Lewis
acid and base active sites and showed an excellent catalytic ac-
tivity, with the highest TON for the studied 4CR. InPF-18 mate-
rial (x=0.8) also displayed good activity, but the TON value
was the second highest, and InPF-16 (x=0.6) hardly showed
any catalytic activity. As expected, InPF-19 and InPF-21 MOFs
(
x=0) did not show any catalytic activity.
The recyclability of the best indium catalysts (InPF-16 and
InPF-17) was also tested: catalysts were recovered after centri-
fugation, washed several times with ethanol and acetone,
dried at 1308C, and reused. Even after four catalytic cycles, the
catalytic activity was maintained with only a small decrease,
which was probably due to the loss of material during the re-
covery of each catalyst (see the Supporting Information). The
crystalline structure of both materials did not suffer from any
alteration; hot filtration experiments confirmed that InPF-16
and InPF-17 are truly heterogeneous catalysts.
This study highlights that multicomponent complex reac-
tions require heterogeneous catalysts with very specific struc-
tural features, which can be delivered by MOFs though a plan-
ned synthetic strategy.
Experimental Section
Conclusions
General information
A series of 6 new indium MOFs with different chemical and
structural characteristics (indium CNs, Lewis acid active centers,
concurrent existence of Lewis bases) have been obtained.
Their structures and topological nets were determined.
The MOFs were synthesized by using CH and MW hydrother-
mal synthesis. The same pure phases we obtained with both
methods with hardly any variation of the synthetic conditions.
The particle size–catalytic behavior relationship was studied for
both MOF series, and it showed no dependence of the catalyt-
ic activity on the synthetic method. The advantages of the MW
procedure, which include reduced reaction times and higher
yields, make this the favorable method for synthesis of the ma-
terials.
All
reagents,
5-(4-carboxy-2-nitrophenoxy)isophthalic
acid
(
H popha), 1,10-phenanthroline monohydrate (1,10-phen), 1,7-phe-
3
nanthroline (1,7-phen), 4,4’-bipyridine (4,4’-bipy), 2,2’-bipyridine
2,2’-bipy), and [In(OAc) ], and solvents that were employed were
(
3
commercially available and used as received without further purifi-
cation.
Characterization methods
IR spectra were recorded from KBr pellets in the range 4000–
À1
2
50 cm on a Bruker IFS 66 V/S. Thermogravimetric and differen-
tial thermal analyses (TGA/DTA) were performed by using the Seiko
TG/DTA 320U equipment in a temperature range between 25 and
À1
À1
1
0008C in air (flow rate=100 mLmin , heating rate=108Cmin ).
Structural and topological studies of every compound al-
lowed us to propose certain catalytic mechanisms for the
tested reactions.
A PerkinElmer CNHS Analyzer 2400 was employed for the elemen-
tal analysis. Powder X-ray diffraction (PXRD) patterns were mea-
sured with a Bruker D8 diffractometer (step size=0.028, exposure
time=0.5 s per step). PXRD measurements were used to check the
purity of the obtained microcrystalline products by a comparison
of the experimental results with the simulated patterns obtained
from single-crystal X-ray diffraction data. The residues of the com-
pounds after TGA were analyzed by PXRD and compared with re-
From our catalytic studies on these six new In-MOFs we can
make the following conclusions:
For cyanosilylation reactions, in which there only are two re-
actants, the factor that drives the reaction yield is the indium
CN; therefore, the catalytic activity decreases in the following
way: InPF-16>InPF-18>InPF-17. InPF-19 and InPF-21 mate-
rials did not show any catalytic activity because both of them
possess indium CNs of 8, which means that no Lewis acid
active sites are present.
[68]
ported Inorganic Crystal Structure Database (ICSD) patterns. DLS
particle size analysis was performed by using the VASCO particle
size analyzer with a refraction index of 1.6 for the analyzed parti-
cles, by using water as the solvent (refraction index=1.33, viscosi-
ty=0.894), and by employing the statistic mode with a time limit
of 30 acquisitions at 15 seconds per acquisition.
In the three-component Passerini reaction, InPF-16, InPF-18,
InPF-17 catalysts, which all possess active sites, show a similar
level of activity. InPF17, which has the lowest catalytic activity
in the cyanosilylation reaction, displays a similar activity to the
other catalysts in the P-3CR, which suggests that synchroniza-
tion of the reactants’ activation rates would be the driving
Preparation of InPF materials
All compounds were synthesized under hydrothermal conditions,
by using conventional heating (CH) and microwave heating (MW).
The CH was performed in a conventional oven at temperatures be-
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tween 150 and 1808C. The MW-assisted synthesis was performed
in a CEM- Discover Class S n/s DC5363 apparatus by using a dynam-
ic method, during which the temperature was fixed, the power
was set to a maximum of 200 W, and the pressure reached up to
water, ethanol, and acetone to give colorless crystals of InPF-18
(0.350 g, 81%). MW synthesis: H popha (0.040 g, 0.114 mmol), 4,4’-
3
bipy (0.016 g, 0.114 mmol), In(OAc)3 (0.033 g, 0.114 mmol), and
water (2 mL) were placed in a glass vial and submitted to MW radi-
ation by using a dynamic method at 1808C with vigorous stirring
1
8 bar to allow the MW source to reach the setup temperature.
(
30 min, 200 W, 11 bar) to give the product InPF-18 (0.096 g, 96%).
[
In (OH) (popha) (H O) ]·3H O (InPF-16), CH synthesis: A mixture
8
6
6
2
4
2
À1
Elemental analysis calcd (%) for C H In N O (1312.14 gmol ): C
40
31
3
4
25
of H popha (0.089 g, 0.256 mmol) and In(OAc)3 (0.100 g,
0
less steel autoclave and heated at 1708C for 72 h. After cooling to
room temperature, the crystals that had formed were isolated by
filtration and washed with distilled water, ethanol, and acetone to
give colorless crystals of InPF-16 (0.781 g, 95%). MW synthesis: A
mixture of H popha (0.030 g, 0.085 mmol) and In(OAc)3 (0.033 g,
0
ted to MW radiation by using a dynamic method at 1708C with
vigorous stirring (30 min, 200 W, 10 bar), which led to formation of
the product InPF-16 (0.265 g, 97%). Elemental analysis calcd (%)
3
3
3
1
6.61, H 2.38, N 4.27; found: C 36.47, H 2.66, N 4.22; IR (KBr): n˜ =
.343 mmol) in water (6 mL) was transferred to a Teflon-lined stain-
610 (OÀH, coordinated), 3447 (OÀH, H O), 3076 (CÀH, aromatic)L,
2
645 and 1625 (C=O)L, 1590 (C=C, aromatic)L, 1576 (NÀO)as, 1532
(
C=N, 4,4’-bipy), 1499 and 1451 (OCO)s, 1417 (OCO)as, 1390 (CÀ
C)as, 1353 and 1307 (NÀO)s, 1271 and 1255 (CÀO)as, 1224 and
1
142 (CÀC)s, 905 and 856 doop(CÀH, 4,4’-bipy), 777, 759, and
3
À1
À1
7
16 cm doop(CÀH)L; TGA (air, 100 mLmin ): Initial weight loss
.114 mmol) in water (2 mL) was placed in a glass vial and submit-
started at <1008C, which was due to the loss of water molecules
that had been physisorbed inside the framework (total loss=
ꢀ
7%); at ꢀ2508C a loss of 3% was observed, which corresponded
À1
to loss of the hydroxyl groups in the framework; at ꢀ4508C a final
loss of 60% of the material occurred. The final residue that re-
mained at ꢀ8008C corresponded to the 30% of the material that
was converted into In O (ICSD_640179).
for C H In N O (3211.96 gmol ): C 33.65, H 1.76, N 2.62; found:
9
0
56
8
6
67
C 33.68, H 1.72, N 2.68; IR (KBr): n˜ =3636 (OÀH, coordinated), 3539
(
OÀH, coordinated H O), 3231 (OÀH, free H O), 3078 and 3088 (CÀ
2
2
2
3
H, aromatic)L, 1633 and 1613 (C=O)L, 1586 (C=C, aromatic)L, 1562
(
(
7
NÀO)as, 1458 (OCO)s, 1419 (OCO)as, 1410 (C-C)as, 1351 and 1313
[
In (popha) (4,4’-bipy) ]·3H O (InPF-19), CH synthesis: a mixture
2 2 2 2
NÀO)s, 1259 and 1229 (CÀO)as, 1143 (CÀC)s, 777, 767, and
of H popha (0.119 g, 0.343 mmol), 4,4’-bipy (0.047 g, 0.343 mmol),
and In(OAc) (0.100 g, 0.343 mmol) in a mixed solution of EtOH/
H O (11 mL, 1.2:1) was heated in a Teflon-lined stainless steel auto-
clave at 1658C for 18 h. After cooling to room temperature, crystals
were isolated by filtration and washed with distilled water, ethanol,
and acetone to give colorless crystals of InPF-19 (0.308 g, 73%).
MW synthesis: H popha (0.040 g, 0.114 mmol), 4,4’-bipy (0.016 g,
0
3
À1
12 cm doop(CÀH)L (L: linker, s: symmetric, as: asymmetric); TGA
3
À1
(
air, flow rate=100 mLmin ): initial weight loss (of ꢀ5%) started
2
at 1008C, which was due to the loss of coordinated and physisor-
bed water molecules; at ꢀ4208C a 60% loss of material had oc-
curred; the final residue that remained at ꢀ8008C corresponded
to 35% of the material that was converted into In O (ICSD_
2
3
3
6
40179).
.114 mmol), In(OAc) (0.033 g, 0.114 mmol), and water (2 mL) were
3
placed in a glass vial and submitted to MW radiation by using a dy-
namic method at 1558C with vigorous stirring (10 min, 200 W,
[
In(popha)(2,2’-bipy)]·3H O (InPF-17), CH synthesis: A mixture of
2
H popha (0.119 g, 0.343 mmol), 2,2’-bipy (0.047 g, 0.343 mmol), and
3
9
bar) to give the product InPF-19 (0.119 g, 85%). Elemental analy-
In(OAc)3 (0.100 g, 0.343 mmol) in distilled water (12 mL) was
heated in a Teflon-lined stainless steel autoclave at 1508C for 24 h.
After cooling to room temperature, the newly formed crystals were
isolated by filtration and washed with distilled water, ethanol, and
acetone to give light violet crystals of InPF-17 (0.177 g, 79%). MW
synthesis: H popha (0.040 g, 0.114 mmol), 2,2’-bipy (0.016 g,
0
placed in a glass vial and submitted to MW radiation by using a dy-
namic method at 1608C with vigorous stirring (30 min, 200 W,
À1
sis calcd (%) for C H In N O (1230.42 gmol ): C 48.80, H 2.29, N
50 28
2
6
18
6
3
1
.83; found: C 48.22, H 1.91, N 6.23; IR (KBr): 3414 (OÀH, H O),
2
243 (CÀH, aromatic, 4,4’-bipy), 3121 and 3097 (CÀH, aromatic)L,
614 and 1600 (C=O)L, 1564 (NÀO)as, 1537 (C=N, 4,4’-bipy), 1493
and 1466 (OCO)s, 1420 and 1407 (OCO)as, 1385 (CÀC)as, 1347 and
3
1
321 (NÀO)s, 1258 and 1225 (CÀO)as, 1163 and 1122 (CÀC)s, 977
.114 mmol), In(OAc) (0.033 g, 0.114 mmol), and water (2 mL) were
3
À1
and 928 doop(CÀH, 4,4’-bipy), 778, 750, and 727 cm doop(CÀH)L;
À1
TGA (air, 100 mLmin ): Initial weight loss started at ꢀ1008C,
which was due to the loss of water molecules that had been physi-
sorbed inside the framework (total loss=ꢀ5%); at ꢀ4208C the
loss of 66% of material was observed; the final residue that re-
mained at ꢀ8008C corresponded to 29% of material that had
been converted into In O (ICSD_640179).
9
9
bar), which led to formation of the product InPF-17 (0.067 g,
0%). Elemental analysis calcd (%) for C H InN O
13
2
5
22
3
À1
(
687.27 gmol ): C 43.69, H 3.22, N 6.11; found: C 43.56, H 3.10, N
5
.90; IR (KBr): n˜ =3620, 3559 (OÀH, H O), 3449 (CÀH, aromatic, 2,2’-
2
bipy), 3115 and 3083 (CÀH, aromatic)L, 1619 and 1602 (C=O)L,
2
3
1
579 (C=C, aromatic)L, 1562 (NÀO)as, 1530 (C=N, 2,2’-bipy), 1496
[In(OH)(Hpopha)]·0.5(1,7-phen) (InPF-20), CH synthesis: a mixture
and 1477 (OCO)s, 1458 and 1444 (OCO)as, 1382 n(CÀC)as, 1349
of H popha (0.119 g, 0.343 mmol), 1,7-phen (0.061 g, 0.343 mmol),
3
and 1319 (NÀO)s, 1264 and 1253 (CÀO)as, 1176 and 1164 (CÀC)s,
and In(OAc) (0.100 g, 0.343 mmol) in distilled water (10 mL) was
3
À1
9
21 and 836 doop(CÀH, 2,2’-bipy), 779, 771, and 759 cm
heated in a Teflon-lined stainless steel autoclave at 1758C for 48 h.
After cooling to room temperature, crystals were isolated by filtra-
tion and washed with distilled water, ethanol, and acetone to give
colorless crystals of InPF-20 (0.095 g, 58%). MW synthesis:
À1
doop(CÀH)L; TGA (air, 100 mLmin ): Initial weight loss started at
temperatures <1008C, which was due to the loss of water mole-
cules that had been physisorbed inside the material framework
(
ꢀ
total loss=ꢀ8%); a 70% loss of material was observed at
4308C; the final residue that remained at ꢀ8008C corresponded
to 22% of the material that had been converted into In O (ICSD_
H popha (0.040 g, 0.114 mmol), 1,7-phen (0.017 g, 0.057 mmol),
3
In(OAc)3 (0.033 g, 0.114 mmol), and water (2 mL) were placed in
a glass vial and submitted to MW radiation by using a dynamic
method at 1758C with vigorous stirring (90 min, 200 W, 9 bar) to
give the product InPF-20 (0.038 g, 70%). Elemental analysis calcd
2
3
6
40179).
[
In (OH) (popha) (4,4’-bipy)]·4H O (InPF-18), CH synthesis: a mix-
3
3
2
2
À1
ture of H popha (0.119 g, 0.343 mmol), 4,4’-bipy (0.047 g,
(%) for C H InN O (567.15 gmol ): C 44.47, H 2.13, N 4.94;
3
21 12
2
10
0
.343 mmol), and In(OAc) (0.100 g, 0.343 mmol) in distilled water
found: C 43.50, H 2.47, N 4.83; IR (KBr): 3637 (OÀH, coordinated),
3608 (OÀH)L, 3389 (CÀH, aromatic, 1,7-phen), 3232 and 3103 (CÀH,
aromatic)L, 1688, 1619, and 1598 (C=O)L, 1567 (NÀO)as, 1552 (C=
N, 1,7-phen), 1538 and 1493 (OCO)s, 1459 and 1417 (OCO)as, 1394
3
(
10 mL) was heated in a Teflon-lined stainless steel autoclave at
808C for 18 h. After cooling to room temperature, colorless crys-
tals formed were isolated by filtration and washed with distilled
1
Chem. Eur. J. 2016, 22, 6654 – 6665
www.chemeurj.org
6663
ꢀ 2016 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim

Full Paper
(
CÀC)as, 1304 (NÀO)s, 1267 and 1257 (CÀO)as, 1143 and 1111 (CÀ
was vigorously stirred at room temperature until the precipitation
of the solid product (2–3 h, monitored by H NMR and GC-MS).
À1
1
C)s, 1078 and 976 doop(CÀH, phen), 777, 759, and 707 cm
À1
doop(CÀH)L; TGA (air, 100 mLmin ): Initial weight loss started at
ꢀ
2008C, and the final residue that remained at ꢀ8008C corre-
X-ray structure determination
sponded to 31% of the material that had been converted into
In O (ICSD_640179).
2
3
The single-crystal X-ray data for compounds InPF-16 to InPF-21
[
In(popha)(1,10-phen)]·4H O (InPF-21), CH synthesis: a mixture of
were obtained on a Bruker four circle kappa-diffractometer
2
H popha (0.119 g, 0.343 mmol), 1,10-phen (0.061 g, 0.343 mmol),
equipped with a Cu INCOATED microsource, operated at 30 W
power (45 kV, 0.60 mA) to generate CuKa radiation (l=1.54178 Š),
and a Bruker VANTEC 500 area detector (microgap technology).
3
and In(OAc)3 (0.100 g, 0.343 mmol) in distilled water (8 mL) was
heated in a Teflon-lined stainless steel autoclave at 1608C for 72 h.
After cooling to room temperature, crystals were isolated by filtra-
tion and washed with distilled water, ethanol, and acetone to give
Diffraction data were collected by exploring over a hemisphere of
the reciprocal space in a combination of f and w scans to reach
yellow crystals of InPF-21 (0.220 g, 91%). MW synthesis: H popha
[69]
3
a resolution of 0.86 Š, using a Bruker APEX2 software suite (each
(
(
0.040 g, 0.114 mmol), 1,10-phen (0.034 g, 0.114 mmol), In(OAc)3
exposure of 40 s covered 18 in w). Unit cell dimensions were deter-
mined for least-squares fit of reflections with I>20s. A semi-empir-
ical absorption and scale correction based on equivalent reflection
0.033 g, 0.114 mmol), and water (2 mL) were placed in a MW glass
vial and submitted to MW radiation by using a dynamic method at
608C with vigorous stirring over 60 min at 200 W and 7 bar to
1
[70]
was carried out by using SADABS. The space-group determina-
give the product InPF-21 (0.072 g, 96%). Elemental analysis calcd
[71]
tion was carried out by using XPREP. The structures were solved
À1
(
%) for C H InN O (711.3 gmol ): C 45.59, H 3.12, N 5.91; found:
2
7
22
3
13
by direct methods. The final cycles of refinement were carried out
by full-matrix least-squares analyses with anisotropic thermal pa-
rameters of all non-hydrogen atoms. The hydrogen atoms were
fixed at their calculated positions by using distances and angle
C 45.86, H 2.86, N 5.79; IR (KBr): 3455 (OÀH, H O), 3248 (CÀH, aro-
2
matic, 1,10-phen), 3081 (CÀH, aromatic)L, 1621 and 1606 (C=O)L,
1
590 (C=C, aromatic)L, 1563 (NÀO)as, 1527 (C=N, 1,10-phen), 1496
and 1456 (OCO)s, 1432 and 1403 (OCO)as, 1383 (CÀC)as, 1348 and
[72]
constraints. All calculations were performed by using SMART and
1
311 (NÀO)s, 1263 and 1252 (CÀO)as, 1150 and 1107 (CÀC)s, 1074
[69]
[70]
APEX2 software for data collection, SAINT for data reduction,
À1
and 982 doop(CÀH, phen), 779, 748, and 724 cm doop(CÀH)L;
[71]
and SHELXTL to resolve and refine the structure details. CCDC
À1
TGA (air, 100 mLmin ): Initial weight loss started at ꢀ1008C,
1
424185 (InPF-20), 1424083 (InPF-16), 1424084 (InPF-17), 1424085
which was due to the loss of water molecules that had been physi-
sorbed inside the framework (total loss ꢀ7%), and at ꢀ4508C the
loss of 68% of material was observed. The final residue at ꢀ8008C
corresponded to 25% of the material that had been converted
into In O (ICSD_640179).
(InPF-18), 1424026 (InPF-21), and 1424055 (InPF-19) contain the
supplementary crystallographic data for this paper. These data are
provided free of charge by The Cambridge Crystallographic Data
Centre.
2
3
Acknowledgements
General procedure for the catalytic activity experiments
This work has been supported by the Spanish Ministry of Econ-
omy and Competitiveness (MINECO) projects MAT2010-17571,
MAT2013-45460-R, MAT2011-29020-C02-02, FAMA S2009/MAT-
1756, Comunidad Autónoma de Madrid, and Consolider-Ingen-
io CSD2006-2001. L.M.A.-D. acknowledges a FPI scholarship
from MINECO and Fondo Social Europeo from the European
Union.
All catalysts were previously treated at 1308C for 12 h to guarantee
the absence of adsorbed solvent molecules. The purity and crystal-
linity of the catalysts was confirmed by PXRD before and after
each catalytic reaction.
Catalytic cyanosilylation of aldehydes: Catalytic amounts of InPF-
1
6 to InPF-21 (10 mg, 1 mol%) were placed in a Schlenk tube
under nitrogen atmosphere without solvents with the correspond-
ing carbonyl compound (1 equiv); trimethylsilyl cyanide (1.5 equiv)
was then added dropwise by syringe. The mixture was stirred at
room temperature until disappearance of the aldehyde (0.08–1 h,
monitored by GC).
Keywords: heterogeneous catalysis · indium · Lewis acids ·
metal–organic frameworks · multicomponent reactions
Catalytic cyanosilylation of ketones: Catalytic amounts of InPF-16
to InPF-20 (1, 2.5, and 5 mol%) were placed in a Schlenk tube
under a nitrogen atmosphere with the corresponding ketone (1
equiv); trimethylsilyl cyanide (1.1 equiv) was then added dropwise
by syringe. The mixture was stirred and heated at room tempera-
ture until disappearance of the ketone (24–72 h, monitored by GC).
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Full Paper
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Received: November 13, 2015
Revised: January 14, 2016
1
Published online on March 24, 2016
Chem. Eur. J. 2016, 22, 6654 – 6665
www.chemeurj.org
6665
ꢀ 2016 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim