Tunable catalytic activity of solid solution metal-organic frameworks in one-pot multicomponent reactions

Article abstract of DOI:10.1021/jacs.5b02313

The aim of this research is to establish how metal-organic frameworks (MOFs) composed of more than one metal in equivalent crystallographic sites (solid solution MOFs) exhibit catalytic activity, which is tunable by virtue of the metal ions ratio. New MOF

Full text of DOI:10.1021/jacs.5b02313

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Communication
Tunable catalytic activity of solid solution
MOFs in One Pot Multicomponent Reactions
Lina María Aguirre-Diaz, Felipe Gándara, Marta Iglesias, Natalia
Snejko, Enrique Gutierrez-Puebla, and M. Ángeles Monge
J. Am. Chem. Soc., Just Accepted Manuscript • Publication Date (Web): 05 Apr 2015
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Tunable catalytic activity of solid solution MOFs in One Pot
Multicomponent Reactions
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Lina María AguirreꢀDíaz, Felipe Gándara, Marta Iglesias, Natalia Snejko, Enrique GutiérrezꢀPuebla and
M. Ángeles Monge*
Departamento de Nuevas Arquitecturas en Química de Materiales ꢀ Instituto de Ciencia de Materiales de Madrid (ICMMꢀ
CSIC). Sor Juana Inés de la Cruz 3, Cantoblanco 28049, Madrid, Spain.
bedded in the MOF pores.6 Thus, there are no examples
Abstract: The aim of this research is to establish how
yet where the catalytic activity of a MOF is modified
with the introduction in the appropriate ratio of various
metal atoms in the framework. Herein we report the
synthesis and characterization of three new isostructural
metalꢀorganic frameworks (MOFs) composed of more
than one metal in equivalent crystallographic sites (solid
solution MOFs) exhibit catalytic activity, which is tunaꢀ
ble by virtue of the metal ions ratio. New MOFs with
general formula [InxGa1ꢀx(O2C2H4)0.5(hfipbb)] were
prepared by the combination of Ga and In. They are
isostructural with their monoꢀmetal counterparts, syntheꢀ
sized with Al, Ga and In. Differences in their behavior as
heterogeneous catalysts in the threeꢀcomponent, one pot
Strecker reaction illustrate the potential of solid solution
MOFs to provide the ability of addressing the various
stages involved in the reaction mechanism.
MOFs,
[Ga(OH)(hfipbb)],
[In(O2C2H4)0.5(hfipbb)]
AlPFꢀ1,
[Al(OH)(hfipbb)],
and
GaPFꢀ1,
InPFꢀ11β,
= 4,4’ꢀ
(H2hfipbb
(hexafluoroisopropylidene) bis(benzoic acid), (scheme
1), which show catalytic activity in the solvent free, one
pot Strecker reaction. These three materials showed
different behavior in this catalytic reaction affording
three different products. In case of AlPFꢀ1 the expected
αꢀaminonitrile product was obtained; however when
using GaPFꢀ1 and InPFꢀ11β, the cyanosilylation and the
imine formation products were respectively obtained.
These differences are attributed to the various possible
reaction pathways related to the reactant activation proꢀ
cess for each catalyst. Thus, in order to probe whether
the combination of both paths could reach the desired αꢀ
aminonitrile product, we have prepared solid solution
MOFs with the combinations of gallium and indium
cations. Our results demonstrate for the first time that it
is possible to control the catalytic activity of the MOFs
in a multicomponent reaction by using specifically seꢀ
lected metal ratios.
Metalꢀorganic frameworks, MOFs, are a class of crysꢀ
talline materials formed by the linkage of metal ions or
clusters (denoted secondary building units, SBUs)
through organic ligands.1 MOFs have many applications,
including gas storage or separation,2a luminescence,2b
drug delivery,2c or heterogeneous catalysis.2d Compared
to traditional heterogeneous catalysts, MOFs exhibit the
advantage of offering a wide range of different chemical
compositions, as well as topological and structural feaꢀ
tures. Thus, MOFs can be prepared with different metal
ions and in different coordination environments, suitable
to be used as catalytic active sites in organic transforꢀ
mations.3 In addition, it is possible to use different metal
elements to obtain MOFs with the same framework type
so that the properties of the materials vary depending on
the selected metal atom while keeping the same structurꢀ
al features.4 More recently, it has also been demonstrated
that different metal atoms can be incorporated within the
same MOF, occupying equivalent positions in the crysꢀ
talline framework, which we denote solid solution
MOFs.5 Despite multiꢀmetal systems offer great opporꢀ
tunities in the field of catalysis, thus far the only examꢀ
ples of multiꢀmetal MOFs as heterogeneous catalysts are
limited to materials where a second metal site is postꢀ
synthetically introduced within the framework, typically
in the form of metal complexes or as nanoparticles emꢀ
Scheme 1. The organic ligand H2hfipbb reacts with
aluminium, gallium, indium, and combination of
gallium and indium to form a series of new MOFs.
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The Strecker reaction is a versatile way of preparing
αꢀaminonitriles through the attack of a nitrile group to
an imine group.7 The resulting αꢀaminonitriles can be
hydrolyzed to obtain αꢀaminoacids, or used as intermeꢀ
diates in the preparation of nitrogenꢀcontaining heteroꢀ
cycles (such as imidazoles and thiadiazoles) that are
significant in organic synthesis.8 In order to perform a
highly selective and effective Strecker reaction, different
catalysts and several reaction modifications have been
studied.9 These are mainly focused on homogenous
systems, and there are only a few reports where heteroꢀ
geneous catalysts were used.10 In this threeꢀcomponent
(A3) reaction the imine group is typically prepared prior
to the addition of the nitrile group following a cascade
methodology.11 However, a one pot methodology, which
goes through the in situ imine formation by the addition
of the three reactants (scheme 2a)12 is desirable because
of the atom economy impact and its simplistic execution
cutting out several purification steps, minimizing chemiꢀ
cal waste generation, and saving time.13 Challenges are
associated to the formation of byꢀproducts, arising from
side reactions (scheme 2 bꢀd), or to the need of using
multiple catalysts.
ylene glycoxyde anions instead of the OH groups found
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in AlPFꢀ1 and GaPFꢀ1. Chains of sharing vertex octaheꢀ
dra that run along the c direction are formed. µꢀO atoms
from the OH or the ethylene glycoxyde groups occupy
the shared vertexes. In all three cases the metal coordiꢀ
nation sphere is completed with four oxygen atoms comꢀ
ing from the η2µ2ꢀη2µ2 hfipbbꢀ2 linker carboxylic groups.
The resulting rodꢀshaped inorganic SBUs17 are connectꢀ
ed through the organic linkers giving rise to a threeꢀ
dimensional framework (figure 1), which can be topoꢀ
logically simplified to a dia type network. N2 adsorption
isotherms showed no significant gas uptake by the new
materials.
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Figure 1 The structure of AlPFꢀ1, GaPFꢀ1 and InPFꢀ11β
consists of rodꢀshaped inorganic SBUs, which are linked by
the hfipbb2ꢀ anions to produce threeꢀdimensional frameꢀ
works.
MOFs constructed with pꢀblock elements as metal
centers are less common than their transition metal
counter parts despite some group 13 based MOFs14 have
already shown interesting properties in the storage of
gases15 or as catalyst.16 The new materials were prepared
under solvothermal conditions with the combination of
the corresponding metal salts and the organic linker
H2hfipbb, and their structures were determined by means
of single crystal Xꢀray diffraction. Purity of the samples
was monitored by comparison of the experimental powꢀ
der Xꢀray diffraction (PXRD) patterns with the ones
calculated from the single crystal data.
We started by testing the catalytic activity of these three
new materials in the A3 reaction between benzaldehyde,
trimethylsilyl cyanide (TMSCN), and aniline. Catalytic
amounts of the MOFs were placed in a Schlenk tube, folꢀ
lowed by the addition of the three reactants. The reactions
were performed without solvent at room temperature. The
results of the reactions are summarized in table 1. When
using AlPFꢀ1 as catalyst, the reaction evolves to the quantiꢀ
tative formation of the αꢀaminonitrile. Assuming that the
one pot Strecker reaction takes place following a mechaꢀ
nism as the one proposed in figure 2, the formation of the
αꢀaminonitrile requires the activation of both the carbonyl
and silyl groups to allow the imine formation, followed by
the cleavage of the cyano group and its attack to the imine
carbon atom.
Scheme 2. a) One pot Strecker reaction and its possi-
ble sub-products: b) imine formation, c) aniline
silanes formation and d) cyanosilylation.
AlPFꢀ1, GaPFꢀ1 and InPFꢀ11β are isostructural. Their
structure consists of M3+ ions in octahedral [MO6] coorꢀ
dination environment. Two of the MꢀO bonds come from
the µꢀOH group in the case of AlPFꢀ1 and GaPFꢀ1,
while in the case of InPFꢀ11β these atoms belong to
ethylene glycoxyde groups. It is worth noting that atꢀ
tempts to synthesize InPFꢀ11β under the same conditions
used for GaPFꢀ1 and AlPFꢀ1 resulted in the obtaining of
a different polymorphic compound, previously reportꢀ
ed.3b Only by using a solvent mixture of ethylene glycol
and water it was possible to obtain InPFꢀ11β. The crystal
structure of this compound reveals the presence of ethꢀ
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InGaPFꢀ1
InGaPFꢀ2
InGaPFꢀ3
GaPFꢀ1
96
64
91
96
ꢀ
ꢀ
ꢀ
ꢀ
ꢀ
ꢀ
64
91
96
ꢀ[d]
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8
1.33
0.33
0.08–8
0.17ꢀ8
1
ꢀ
ꢀ
99
ꢀ
InPFꢀ11β
[In+Ga]
AlPFꢀ1
ꢀ
99 ꢀ[d]
99
99
ꢀ
ꢀ
ꢀ
99
99
0.08
ꢀ
9
[a]benzaldehyde (1mmol), aniline (1mmol) and TMSCN
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(1mmol), 1 mol% catalyst, r.t., no solvent; [b]Isolated yield;
[c]mmol subs./mmol cat. [d]TON is calculated only when
Strecker product is obtained.
Therefore, we prepared three new MOFs with general
formula [InxGa1ꢀx(O2C4H4)0.5(hfipbb)], where x = 0.72,
0.55, and 0.28, for InGaPFꢀ1, InGaPFꢀ2, and InGaPFꢀ3,
respectively. Note that we formulate these compounds as
including ethylene glycoxyde groups instead of OH
groups, based on the absence of the typical OH vibration
band and the presence of CH2 bands in their IR spectra
(SI, S9ꢀS11). However, we cannot completely rule out
the presence of both hydroxyl and ethylene glycoxyde
anions in the structure. The metal content was deterꢀ
mined with ICP and total Xꢀray fluorescence (TXRF)
spectroscopies. The PXRD patterns of the solid solution
MOFs indicate that the three compounds maintain the
parent structure. The absence of peak splitting rules out
the possibility of having a mixture of two separate phasꢀ
es. Furthermore, a full pattern profile refinement carried
out for each one of the three compounds demonstrates
that their unit cell parameters values are ranging beꢀ
tween those of InPFꢀ11β and GaPFꢀ1 (SI, S3ꢀS5). The
mixed InGaPF compounds were subsequently used as
catalysts for the A3 Strecker reaction. InGaPFꢀ1 leads to
the product although at a very slow rate (96 h). This
indicates that the cleavage of the cyano group is still
hindered in a material with a large percentage of indium
in the framework. In the case of InGaPFꢀ2, where the
metal ratio is close to 1, the Strecker reaction becomes
much faster, reaching a 91% of conversion in 1.33 h.
Finally, InGaPFꢀ3 exhibits a rate of reaction comparable
to that of AlPFꢀ1, with a 96% of conversion to αꢀ
aminonitrile in only 0.33 h, thus indicating that the presꢀ
ence of a small amount of indium is enough to favor the
imine formation over the aldehyde cyanosilylation. The
TON values of AlPFꢀ1 and InGaPFꢀ3 are similar or
higher than the ones showed by other reported heterogeꢀ
neous catalysts under similar conditions (95 and 75 for
ref. 10c and 10d, respectively).
Figure 2. Proposed Mechanism for the M+3PF mediated A3
Strecker reaction of carbonyl compounds. Lewis acid and
base sites are proposed based on the MOFs structure.
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It seems clear that with AlPFꢀ1 as catalyst, these proꢀ
cesses occur with the appropriate rate to yield the final
Strecker product in a short time (Table 1, entry 7). On
the other hand, when using InPFꢀ11β as catalyst, the
formation of the imine is the main product (Table 1,
entry 5) indicating that the Lewis basic site required to
activating the silyl group and complete the addition of
the cyano group is hindered. Nevertheless, after long
reaction times (22 h), the reaction between the imine and
the cyano groups occur and the product of the Strecker
reaction was observed. GaPFꢀ1, gives only the product
of the aldehyde cyanosilylation, indicating that both the
carbonyl and the silyl groups are quickly activated and
the TMSCN is fully consumed before any imine can be
formed (Table 1, entry 4). At the view of these results,
we thought that it would be possible to control the rates
and selectivity of the different steps involved in the one
pot Strecker reaction with a combination of Ga and In
catalysts, which efficiently activate the silyl groups and
produce the imine groups, respectively. Thus, we decidꢀ
ed to start by using a physical mixture of both InPFꢀ11β
and GaPFꢀ1 catalysts. Indeed, when using equimolar
amounts of InPFꢀ11β and GaPFꢀ1 (named [In+Ga] from
now on), the αꢀaminonitrile product was quantitatively
formed (table 1, entry 6). Encouraged by these results,
we then decided to prepare solidꢀstate solution comꢀ
pounds where the two metals, In and Ga, are sharing the
same crystallographic position in the framework.
Table 1: Catalysts performance in the A3 Strecker reaction
using
benzaldehyde,
aniline
and
TMSCN.[a]
Typically, ketones are more difficult to activate than
aldehydes. Thus, there are few reports where heterogeꢀ
neous catalysts are used in Strecker reactions with keꢀ
tones, and in many cases elevated temperatures (50ꢀ60
ºC), use of solvents, and/or high catalytic loadings (4ꢀ
50mol%) are required.10 AlPFꢀ1, InPFꢀ11β and GaPFꢀ1
demonstrate excellent activity in the A3 Strecker reaction
Yield (%)[b]
Entry Catalyst
t (h)
TON[c]
a
b
c
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Angew. Chem., Int. Ed. 2006, 45, 5974. (d) Czaja, A. U.; Trukhanb,
N.; Müller, U. Chem. Soc. Rev. 2009, 38, 1284.
using acetophenone as carbonyl compound with yields
between 50ꢀ87% (Table S1). Interestingly, in all cases
the Strecker product was obtained, with the highest yield
for the cases of [In+Ga] (87%) and InGaPFꢀ3 (80%)
materials. The different results between aldehyde and
ketone based reactions presumably indicate differences
in the mechanistic pathway, possibly related to differꢀ
ences in the activation time of the carbonyl groups. Curꢀ
rent work is being carried out to find out the origin of
these differences.
1
2
3
4
5
6
7
8
(3) (a) Corma, A.; García H.; Llabrés i Xamena, F. X. Chem. Rev.
2010, 110, 4606. (b) Gándara, F.; GómezꢀLor, B.; GutiérrezꢀPuebla,
E.; Iglesias, M.; Monge, M. A.; Proserpio, D. M.; Snejko, N. Chem.
Mater. 2008, 20, 72.
(4) Gándara, F.; UribeꢀRomo, F. J.; Britt, D. K.; Furukawa, H.; Lei,
L.; Cheng, R.; Duan, X.; O'Keeffe, M.; Yaghi, O. M. Chem. Eur. J.
2012, 18, 10595.
(5) (a) Meyer, L. V.; Schönfeld, F.; MüllerꢀBuschbaum, K. Chem.
Commun. 2014, 50, 8093. (b) Okawa, H.; Sadakiyo, M.; Yamada, T.;
Maesato, M.; Ohba, M.; Kitagawa, H. J. Am. Chem. Soc. 2013, 135,
2256. (c) Wang, L. J.; Deng, H.; Furukawa, H.; Gándara, F.; Cordova,
K. E.; Peri, D.; Yaghi, O. M. Inorg. Chem. 2014, 53, 5881.
(6) (a) Katz, M. J.; Mondloch, J. E.; Totten, R. K.; Park, J. K.; Nguꢀ
yen, S. T.; Farha, O. K.; Hupp, J. T. Angew. Chem. Int. Ed. 2014, 53,
497. (b) Zhang, Z.; Chen, Y.; He, S.; Zhang, J.; Xu, X.; Yang, Y.;
Nosheen, F.; Saleem, F.; He, W.; Wang, X. Angew. Chem. Int. Ed.
2014, 53, 12517. (c) Das, M. C.; Xiang, S.; Zhang, Z.; Chen, B.
Angew. Chem. Int. Ed. 2011, 50, 10510. (d) RaseroꢀAlmansa, A. M.;
Corma, A.; Iglesias, M.; Sánchez, F. Green Chem. 2014,16, 3522.
(7) (a) Strecker. D. Ann. Chem. Pharm., 1850, 75, 27. (b) Kaur, P.;
Wever, W.; Pindi, S.; Milles, R.; Gu, P.; Shi, M.; Li, G. Green Chem.
2011, 3, 1288.
(8) (a) Enders, D.; Shilvock, J. P. Chem. Soc. Rev. 2000, 29, 359. (b)
Groger H. Chem. Rev. 2003, 103, 2795.
(9) (a) Ishitani, H.; Komiyama, S.; Kobayashi, S. Angew. Chem. Int.
Ed. 1998, 37, 3186. (b) Galletti, P.; Pori M.; Giacomini, D. Eur. J.
Org. Chem. 2011, 3896 and references therein.
(10) (a) Singh, A. P.; Ali, A.; Gupta, R. Dalton Trans. 2010, 39, 8135.
(b) Choi, J.; Yang, Y. Y.; Kim, H. J.; Son, S. U. Angew. Chem. Int.
Ed. 2010, 49, 7718. (c) Dekamin, M. G.; Azimoshan, M.; Ramezani,
L. Green Chem. 2013, 15, 811. (d) Rajabi, F.; Ghiassian, S.; Saidi, M.
R. Green Chem. 2010, 12, 1349.
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In conclusion, this paper shows how the activity
of a heterogeneous catalyst can be controlled by moduꢀ
lating the ratio of different metals occupying the same
crystallographic position of the framework. This reveals
a strategy to use solid solution MOFs in multicomponent
catalytic reactions.
ASSOCIATED CONTENT
Complete synthesis and characterization details and crystalꢀ
lographic information (CIF files) can be found in the supꢀ
porting information. This material is available free of
charge via the Internet at http://pubs.acs.org.
Corresponding Author
M. A. Monge. amonge@icmm.csic.es
ACKNOWLEDGMENT
This work has been supported by the Spanish Ministry of
Economy and Competitiveness (MINECO) projects
MAT2010ꢀ17571, MAT2013ꢀ45460ꢀR, MAT2011ꢀ29020ꢀ
C02ꢀ02, FAMA S2009/MATꢀ1756 Comunidad Autónoma
de Madrid, and ConsoliderꢀIngenio CSD2006ꢀ2001.
L.M.A.ꢀD. acknowledges a FPI scholarship from MINECO
and Fondo Social Europeo from the European Union. F.G.
acknowledges MINECO for funding through the “Juan de
la Cierva” program.
(11) (a) Grondal, C.; Jeanty, M.; Enders, D. Nature Chemistry 2010,
167. (b) Simón, L.; Goodman, J. M. J. Am. Chem. Soc. 2009, 131,
4070. (c) Davies, H. M. L.; Sorensen, E. J. Chem. Soc. Rev. 2009, 38,
2981.
(12) (a) Groeger, H. Chem. Rev. 2003, 103, 2795. (b) Karimi, B.;
Maleki, A. Chem. Commun. 2009, 5180. (c) Yet, L. Angew. Chem.
Int. Ed. 2001, 40, 875.
(13) (a) Trost, B. M. Science 1991, 254, 1471. (b) Newhouse, T.;
Baran, P. S.; Hoffmann, R. W. Chem. Soc. Rev. 2009, 38, 3010.
(14) Reinsch, H.; Krüger, M.; Marrot, J.; Stock, N. Inorg. Chem.
2013, 52, 1854.
(15) Gándara, F.; Furukawa, H.; Lee, S.; Yaghi, O. M.; J. Am. Chem.
Soc. 2014, 136, 5271.
(16) (a) Volkringer, C.; Loiseau, T.; Guillou, N.; Ferey, G.; Elkaim,
E.; Vimont, A. Dalton Trans. 2009, 2241. (b) AguirreꢀDíaz, L. M.;
Iglesias, M.; Snejko, N.; GutiérrezꢀPuebla, E.; Monge, M. A. Crys-
tengcomm. 2013, 15, 9562.
(17) Rosi, N. L.; Kim, J.; Eddaoudi, M.; Chen, B.; O'Keeffe, M.;
Yaghi, O. M. J. Am. Chem. Soc. 2005, 127, 1504.
REFERENCES
(1) Furukawa, H.; Cordova, K.; O'Keeffe, M.; Yaghi, O. M. Science
2013, 341, 974.
(2) (a) Morris, R. E.; Wheatley, P. S.; Angew. Chem. Int. Ed. 2008,
47, 4966. (b) Férey, G. Chem. Soc. Rev. 2008, 37, 191. (c) Horcajada,
P.; Serre, C.; ValletꢀRegı, M.; Sebban, M.; Taulelle, F.; Férey, G.
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