A bifunctional, site-isolated metal-organic framework-based tandem catalyst

Article abstract of DOI:10.1021/ic502316v

Herein, we present the synthesis of a metal-organic framework-based tandem catalyst that contains two distinct catalytic domains. Zn(II)-based IRMOF-9-Irdcppy-NH₂ (IRMOF = isoreticular metal-organic framework) has both organocatalytic amine and organometallic Ir(I) groups that were incorporated by both pre- and postsynthetic functionalization methods. The isolated amine and Ir(I) sites of IRMOF-9-Irdcppy-NH₂ are shown to be independently catalytically active for performing a Knoevenagel condensation and allylic N-alkylation, respectively. More importantly, IRMOF-9-Irdcppy-NH₂ can act as a tandem catalyst for both of these organic transformations in a one-pot reaction, which cannot be achieved efficiently using the combined, homogeneous analogues.

Full text of DOI:10.1021/ic502316v

Article
pubs.acs.org/IC
A Bifunctional, Site-Isolated Metal−Organic Framework-Based
Tandem Catalyst
Phuong V. Dau and Seth M. Cohen*
Department of Chemistry and Biochemistry, University of California, San Diego, La Jolla, California 92093, United States
S
* Supporting Information
ABSTRACT: Herein, we present the synthesis of a metal−
organic framework-based tandem catalyst that contains two
distinct catalytic domains. Zn(II)-based IRMOF-9-Irdcppy-
NH2 (IRMOF = isoreticular metal−organic framework) has
both organocatalytic amine and organometallic Ir(I) groups
that were incorporated by both pre- and postsynthetic
functionalization methods. The isolated amine and Ir(I) sites
of IRMOF-9-Irdcppy-NH2 are shown to be independently
catalytically active for performing a Knoevenagel condensation
and allylic N-alkylation, respectively. More importantly,
IRMOF-9-Irdcppy-NH2 can act as a tandem catalyst for both
of these organic transformations in a one-pot reaction, which cannot be achieved efficiently using the combined, homogeneous
analogues.
was shown to be an effective catalyst for a tandem Meinwald
rearrangement and Knoevenagel condensation. Similarly, Cr-
MIL-101 and UiO-66 decorated with both Brønsted acids and
bases have been reported to act as tandem catalysts.26−29 These
recent reports provide examples of using MOFs as platforms to
design tandem catalysts; however, the catalytic groups used in
these studies were limited to either organocatalysts or the
SBUs. In addition, the use of SBU nodes as catalytic sites limits
the choice of MOFs, as well as the ability to tune in the desired
reactivity. It is also possible that reactivity at the SBU could lead
to MOF degradation over time.
INTRODUCTION
■
Metal−organic frameworks (MOFs) continue to be developed
as promising materials for applications such as gas storage1,2
and catalysis.3 Taking the advantage of the functional tunability
of MOFs, researchers have incorporated different types of
catalytic groups into MOFs, including organocatalysts,4,5
organometallics,6−14 transition metals,15−17 and radical spe-
cies.18 MOFs are attractive platforms for immobilizing catalysts
compared to other materials (e.g., zeolites, activated carbons,
and silica) because of their porosity,19 thermal stability, high
density of catalytic centers,3 and ordered structures.9 Despite
the great number of reports on MOF-based catalysts, there are
a limited number of MOF-based tandem catalysts. Tandem
catalysts are single systems that are comprised of more than
one active catalyst.20 The use of tandem catalysts in organic
synthesis allows the one-pot formation of products that cannot
be achieved by a single catalyst. However, the required reaction
conditions and catalyst compatibility are difficult to identify in
homogeneous systems.
The often rigid, ordered structures of MOFs make many of
them quite suitable for engineering multiple isolated catalytic
sites. Although controlling the precise relative position of
functional groups within the crystals of MOFs can be
challenging,21−23 a single MOF can be engendered with
multiple functional groups via prefunctionalization19 and
postsynthetic modification (PSM) methods.24 For example,
the Kim group has presented the use of MIL-101(Al)-NH2 as a
bifunctional, site-isolated Lewis acid−Brønsted base heteroge-
neous catalyst.25 MIL-101(Al)-NH2 contained Lewis acidic
Al(III) centers at the secondary building units (SBUs) and
Brønsted basic amines on the 2-amino-1,4-dicarboxylate (NH2-
bdc2−) organic struts within the framework. MIL-101(Al)-NH2
EXPERIMENTAL SECTION
The synthesis of all ligands and detailed characterization of MOFs can
be found in the Supporting Information.
■
MOFs Synthesis. Synthesis of IRMOF-9. [1,1′-Biphenyl]-4,4′-
dicarboxylic acid (H2bpdc, 50 mg, 0.2 mmol) and Zn(NO3)2·6H2O
(178 mg, 0.6 mmol) were added to N,N′-dimethylformamide (DMF,
15 mL) in a scintillation vial. The mixture was sonicated at 55 °C for
∼30 min. The vial was then transferred into a preheated isotherm oven
at 120 °C for 24 h. After the sample had cooled to room temperature,
clear block crystals of IRMOF-9 were obtained. The crystals were
rinsed with DMF (3 × 10 mL), and DMF was then exchanged with
CHCl3 (3 × 15 mL). Fresh CHCl3 was replaced every day for 3 days,
and the crystals were stored in CHCl3 prior to any further
experiments.
Synthesis of IRMOF-9-dcppy. H2dcppy (50 mg, 0.2 mmol) and
Zn(NO3)2·6H2O (177 mg, 0.6 mmol) were dissolved in DMF (10
mL) with sonication in a scintillation vial. The vial was then
transferred into a preheated isotherm oven at 120 °C for 24 h. After
the sample had cooled to room temperature, clear block crystals of
Received: September 26, 2014
© XXXX American Chemical Society
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Article
IRMOF-9-dcppy were obtained. The crystals were rinsed with DMF
(3 × 10 mL), and DMF was then exchanged with CHCl3 (3 × 15 mL).
Fresh CHCl3 was replaced every day for 3 days, and the crystals were
stored in CHCl3 prior to any further experiments.
to CDCl3 (8 mL). IRMOF-9-dcppy-NH2 [∼100 mg, ∼0.13 mmol of
2−
bpdc-(NH2)2 stored in CHCl3] was removed from CHCl3 and
evacuated under vacuum for ∼30 s to remove residual solvent. The
CDCl3 solution was then transferred to the vial containing IRMOF-9-
dcppy-NH2. The reaction mixture was heated at 55 °C for 24 h in an
oven. Afterward, the mixture was cooled to room temperature and
characterized by 1H NMR, which showed ∼90% conversion of
indoline-7-carboxyaldehyde into 2-(indolin-7-ylmethylene)-
malononitrile (1). Diallyl carbonate (430 μL, 3.0 mmol) was
subsequently added to this mixture. The reaction mixture was then
heated at 55 °C for 24 h in an oven. Afterward, the mixture was cooled
to room temperature and characterized by 1H NMR, which showed no
conversion of 1 to 2-((1-allylindolin-7-yl)methylene)malononitrile (2)
(Table 1 and Figure S5 of the Supporting Information).
Synthesis of IRMOF-9-dcppy-NH2. 2,2′-diamino[1,1′-biphenyl]-
4,4′-dicarboxylic acid (H2bpdc-(NH2)2), (735 mg, 2.7 mmol), 6-(4-
carboxyphenyl)nicotinic acid (H2dcppy) (657 mg, 2.7 mmol), and
Zn(NO3)2·6H2O (3.41 g, 18 mmol) were dissolved in DMF (100 mL)
with sonication. The solution was then divided into 10 equal fractions
in 10 scintillation vials (10 mL in each vial) and transferred to a
programmable oven. These vials were heated at a rate of 2.5 °C/min
from 35 to 100 °C. The temperature was held at 100 °C for 18 h and
then decreased to 35 °C at a rate of 2.5 °C/min. Clear blocks of amber
crystals were obtained as IRMOF-9-dcppy-NH2. The crystals were
rinsed with DMF (3 × 10 mL), and DMF was then exchanged with
CHCl3 (3 × 15 mL). Fresh CHCl3 was replaced every day for 3 days,
and the crystals were stored in CHCl3 prior to any further
experiments.
Cyclometalation of IRMOF-9-dcppy-NH2 To Produce IRMOF-9-
Irdcppy-NH2. [Ir(COD)(OCH3)]2 (COD = 1,5-cyclooctadiene, 106
mg, 0.16 mmol) was dissolved in CHCl3 (4 mL) in a scintillation vial.
IRMOF-9-dcppy-NH2 (100 mg, ∼0.16 mmol of dcppy2−) was added
to the scintillation vial. The vial was then transferred to a preheated
oven at 55 °C for 24 h. After the sample had cooled to room
temperature, the crystals were rinsed with and soaked in CHCl3 (3 ×
15 mL). The rinsing procedure was repeated every day for 3 days.
Catalysis Experiments. Control: Tandem Reaction without a
Catalyst. Indoline-7-carboxyaldehyde (44 mg, 0.30 mmol), diallyl
carbonate (430 μL, 3.0 mmol), and malonitrile (198 mg, 3.0 mmol)
were added to CDCl3 (8 mL). The reaction mixture was heated at 55
°C for 24 h in an oven. Afterward, the mixture was cooled to room
temperature and characterized by 1H NMR, which showed no
conversion (Table 1 and Figure S5 of the Supporting Information).
Catalysis with IRMOF-9-Irdcppy-NH2. Indoline-7-carboxyaldehyde
(44 mg, 0.30 mmol) and malonitrile (198 mg, 3.0 mmol) were added
to CDCl3 (8 mL). IRMOF-9-Irdcppy-NH2 [∼100 mg, ∼0.13 mmol of
bpdc-(NH2)22−, ∼0.015 mmol of Ir, stored in CHCl3] was removed
from CHCl3 and evacuated under vacuum for ∼30 s to remove
residual solvent. The CDCl3 solution was then transferred to the vial
containing IRMOF-9-Irdcppy-NH2. The reaction mixture was heated
at 55 °C for 24 h in an oven. Afterward, the mixture was cooled to
room temperature and characterized by 1H NMR, which showed
∼92% conversion of indoline-7-carboxyaldehyde to 1 (Table 1).
Diallyl carbonate (430 μL, 3.0 mmol) was subsequently added to this
reaction mixture. The reaction mixture was then heated at 55 °C for 24
h in an oven. Afterward, the mixture was cooled to room temperature
1
and characterized by H NMR, which showed ∼90% conversion of 1
to 2 (Table 1).
Tandem Catalysis Using IRMOF-9-Irdcppy-NH2. Indoline-7-
carboxyaldehyde (44 mg, 0.30 mmol), diallyl carbonate (430 μL, 3.0
mmol), and malonitrile (198 mg, 3.0 mmol) were added to CDCl3 (8
mL). IRMOF-9-Irdcppy-NH2 [∼100 mg, ∼0.13 mmol of bpdc-
(NH2)22−, ∼0.015 mmol of Ir, stored in CHCl3] was removed from
CHCl3 and evacuated under vacuum for ∼30 s to remove residual
solvent. The CDCl3 solution was then transferred to the vial
containing IRMOF-9-Idcppy-NH2. The reaction mixture was heated
at 55 °C for 36 h in an oven. Afterward, the mixture was cooled to
room temperature and characterized by 1H NMR, which showed
∼95% conversion of indoline-7-carboxyaldehyde to 2 (Table 1 and
Figure S5 of the Supporting Information).
Tandem Catalysis Using a Homogeneous Catalyst. Indoline-7-
carboxyaldehyde (44 mg, 0.30 mmol), diallyl carbonate (430 μL, 3.0
mmol), and malonitrile (198 mg, 3.0 mmol) were added to CDCl3 (8
mL). Dimethyl 2,2′-diamino[1,1′-biphenyl]-4,4′-dicarboxylate (18 mg,
0.06 mmol) and [Ir(COD)(OCH3)]2 (4.5 mg, 0.007 mmol, 5 mol %
Ir) were sequentially added to the CDCl3 solution. The reaction
mixture was incubated at 55 °C for ∼5 days. Afterward, the mixture
was cooled to room temperature and characterized by 1H NMR, which
showed a ∼35% conversion of indoline-7-carboxyaldehyde to 2 (Table
1 and Figure S7 of the Supporting Information).
Table 1. Summary of Control and Catalytic Reactions
catalytic
reaction 1
catalytic
reaction 2
tandem
a
a
a
reaction
no MOF
0
0
0
b
c
c
homogeneous catalysts
n/a
n/a
35%
b
c
IRMOF-9
0
n/a
0
b
c
IRMOF-9-dcppy
0
n/a
0
b
IRMOF-9-dcppy-NH2
90%
92%
0
0
b
IRMOF-9-Irdcppy-NH2
90%
95 4%
a
b
Conversion determined 1H NMR spectroscopy. Reaction conditions
c
are detailed in the Experimental Section. Not applicable.
Control: Tandem Reaction with IRMOF-9. Indoline-7-carboxyalde-
hyde (44 mg, 0.30 mmol), diallyl carbonate (430 μL, 3.0 mmol), and
malonitrile (198 mg, 3.0 mmol) were added to CDCl3 (8 mL).
IRMOF-9 (∼50 mg, stored in CHCl3) was removed from CHCl3 and
evacuated under vacuum for ∼30 s to remove residual solvent. The
CDCl3 solution was then transferred to the vial containing IRMOF-9.
The reaction mixture was heated at 55 °C for 24 h in an oven.
Afterward, the mixture was cooled to room temperature and
Control: Filtration. Indoline-7-carboxyaldehyde (44 mg, 0.30
mmol), diallyl carbonate (430 μL, 3.0 mmol), and malonitrile (198
mg, 3.0 mmol) were added to CDCl3 (8 mL). IRMOF-9-Irdcppy-NH2
[∼100 mg, ∼0.13 mmol of bpdc-(NH2)22−, ∼0.015 mmol of Ir, stored
in CHCl3] was removed from CHCl3 and evacuated under vacuum for
∼30 s to remove residual solvent. The CDCl3 solution was then
transferred to the vial containing IRMOF-9-Idcppy-NH2. The reaction
mixture was heated at 55 °C in an oven. After ∼8 h, the MOF was
removed from the reaction mixture via filtration. The mixture was
1
characterized by H NMR, which showed no conversion (Table 1
and Figure S5 of the Supporting Information).
Control: Knoevenagel Condensation with IRMOF-9-dcppy. Indo-
line-7-carboxyaldehyde (44 mg, 0.30 mmol) and malonitrile (198 mg,
3.0 mmol) were added to CDCl3 (8 mL). IRMOF-9-dcppy (∼50 mg,
stored in CHCl3) was removed from CHCl3 and evacuated under
vacuum for ∼30 s to remove residual solvent. The CDCl3 solution was
then transferred to the vial containing IRMOF-9-dcppy. The reaction
mixture was heated at 55 °C for 24 h in an oven. Afterward, the
1
characterized by H NMR, which showed an ∼35% conversion of
indoline-7-carboxyaldehyde to 2. The reaction mixture was incubated
1
at 55 °C for an additional 24 h in an oven. After ∼24 h, H NMR
characterization of the reaction mixture showed no further conversion
of indoline-7-carboxyaldehyde to 2 (the overall conversion remained
at ∼35%).
1
mixture was cooled to room temperature and characterized by H
NMR, which showed no conversion (Table 1 and Figure S5 of the
Supporting Information).
Catalysis with IRMOF-9-dcppy-NH2. Indoline-7-carboxyaldehyde
(44 mg, 0.30 mmol) and malonitrile (198 mg, 3.0 mmol) were added
Recyclability of IRMOF-9-Irdcppy-NH2 under Ambient Condi-
tions. After the first tandem catalytic reaction was completed (see
above), the MOF was rinsed with CDCl3 (3 × 5 mL) and soaked in
CDCl3. This rinsing procedure was repeated every day for 3 days prior
B
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Scheme 1. Synthesis of IRMOF-9, IRMOF-9-dcppy, and IRMOF-9-Irdcppy-NH2
to the next catalytic run. The second and third catalytic runs were
conducted under identical conditions as described above.
Recyclability of IRMOF-9-Irdcppy-NH2 under an Inert Atmos-
phere. The first run of the tandem catalysis was conducted under
identical conditions as described above, but under an Ar atmosphere.
After the first catalytic run was completed, the MOF was rinsed with
CDCl3 (3 × 5 mL) and soaked in CDCl3 under an Ar atmosphere.
This rinsing procedure was repeated every day for 3 days prior to the
next catalytic reaction. The second and third catalytic runs were
conducted under identical conditions as described above, but under an
Ar atmosphere.
Stability of IRMOF-9-Irdcppy-NH2 in the Presence of Malonitrile.
Pristine IRMOF-9-Irdcppy-NH2 (∼100 mg) was combined with
malonitrile (198 mg, 3.0 mmol) in CHCl3 (8 mL). The solution was
then incubated at 55 °C for 5 days in an oven. After the solution had
cooled to room temperature, the MOF was rinsed with CHCl3 (3 × 5
mL) and soaked in CHCl3 prior to PXRD analysis.
RESULTS AND DISCUSSION
■
The tandem catalysis of the Knoevenagel condensation and
allylic N-alkylation in a one-pot reaction would be predicted to
be difficult because a nucleophilic amine could act as a substrate
for alkylation via the Ir(I)phenylpyridine complex.12 However,
in a MOF, these catalytic sites can be isolated within the
framework to prevent this unproductive reaction. We utilize a
mixed-linker approach to integrate H2bpdc-(NH2)2 and
H2dcppy to produce IRMOF-9-dcppy-NH2 (Scheme 1).
IRMOF-9-dcppy-NH2 can be treated with [Ir(COD)(OCH3)]2
to obtain IRMOF-9-Irdcppy-NH2 as previously reported
(Scheme 1).23
Powder X-ray diffraction (PXRD) analysis reveals an
interpenetrated structure for IRMOF-9-dcppy-NH2, which
resembles the parent IRMOF-9 lattice (Figure 1). Furthermore,
the unit cell of IRMOF-9-dcppy-NH2 is in agreement with
IRMOF-9 (Table S1 of the Supporting Information). 1H NMR
Figure 1. PXRD analysis of simulated IRMOF-9 (black), IRMOF-9-
dcppy-NH2 (red), and IRMOF-9-Irdcppy-NH2 before (blue) and after
(green) the first catalytic run under ambient conditions.
Information). Interestingly, the synthesis of IRMOF-9-NH2
using only H2bpdc-(NH2)2 and Zn(NO3)2 was not successful
under identical solvothermal conditions.
The porosity and thermal stability of parent IRMOF-9-
dcppy-NH2 and cyclometalated IRMOF-9-Irdcppy-NH2 were
also analyzed via a N2 sorption experiment at 77 K and thermal
gravimetric analysis (TGA) (Figures S3 and S4 of the
Supporting Information). Brunauer−Emmett−Teller (BET)
surface area measurements of IRMOF-9-dcppy-NH2 and
IRMOF-9-Irdcppy-NH2 gave values of 1810
57 and 1964
34 m2/g, respectively (Table S2 of the Supporting
Information). These surface areas are similar to that of the
parent IRMOF-9 (∼1900 m2/g).30 TGA of these MOFs
revealed high thermal stability up to ∼400 °C, also comparable
to that of IRMOF-9.30
digestion of IRMOF-9-dcppy-NH2 confirms ∼57
3%
incorporation of dcppy2− and ∼43
3% incorporation of
2−
bpdc-(NH2)2 (Figure S1 of the Supporting Information).
After the treatment with [Ir(COD)(OCH3)]2, PXRD analysis
of IRMOF-9-Irdcppy-NH2 shows the intact framework (Figure
1 and Figure S2 of the Supporting Information). Inductively
coupled plasma mass spectrometry (ICP-MS) unambiguously
With the desired MOF in hand, we chose to investigate the
catalytic activity of IRMOF-9-Irdcppy-NH2. Because of the
2−
different molar ratio of bpdc-(NH2)2 to Ir(I) (∼8:1) in
showed that the framework contained 2.84
0.33 wt % Ir,
IRMOF-9-Irdcppy-NH2, the control and tandem reactions were
conducted with the use of ∼5 mol % Ir catalyst and a greater
mole percentage of bpdc-(NH2)22−. The combination of
which indicated that ∼9% of the total dcppy2− ligands were
modified with Ir(I) (Figure S2 and Table S2 of the Supporting
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Scheme 2. Knoevenagel Condensation (reaction 1), Allylic N-Alkylation (reaction 2), and Tandem Catalytic Reactions
indoline-7-carboxyaldehyde and malonitrile with IRMOF-9-
dcppy-NH2 [∼40 mol % bpdc-(NH2)22−] in CDCl3 at 55 °C
yielded the corresponding Knoevenagel condensation product
1 (Scheme 2, Table 1, and Figure S5 of the Supporting
Information). As expected, no alkylated product 2 is obtained
in the presence of diallyl carbonate even after ∼1.5 day with
IRMOF-9-dcppy-NH2 as a catalyst (Scheme 2, reaction 2,
Table 1, and Figure S5 of the Supporting Information). In
addition, no condensation reaction occurs when IRMOF-9 or
IRMOF-9-dccpy is used as a catalyst (Table 1 and Figure S5 of
the Supporting Information), ruling out the possibility that the
ZnO4 SBUs or the phenylpyridine moieties of the dcppy2−
ligand are active catalytic species. Finally, these results indicate
that the secondary amine moiety of indoline-7-carboxyaldehyde
is incapable of catalyzing the Knoevenagel condensation
reaction. These reactions all indicate that the amine
functionality in IRMOF-9-dcppy-NH2 is responsible for the
Knoevenagel condensation reaction.
After the catalytic activity of IRMOF-9-dcppy-NH2 had been
confirmed, metal-loaded IRMOF-9-Irdcppy-NH2 [∼40 mol %
bpdc-(NH2)22−, ∼5 mol % Ir] was used for the tandem reaction
among indoline-7-carboxyaldehyde, malonitrile, and diallyl
carbonate (Scheme 2, tandem reaction). The final product 2
of the tandem reaction was obtained in good yield at 55 °C
after ∼1.5 day [∼95 4% (Table 1 and Figures S5 and S6 of
the Supporting Information)]. Earlier studies of MOF catalysts
have given similar results, with ∼99% conversion for the N-
alkylation of amines achieved in ∼30 h, and ∼85% conversion
for a tandem Meinwald rearrangement−Knoevenagel con-
densation in ∼96 h was reported.12,25 The heterogeneous
nature of IRMOF-9-Irdcppy-NH2 was confirmed by removal of
IRMOF-9-Irdcppy-NH2 (after ∼8 h) from the reaction mixture,
which resulted in no further progression of the catalytic
reaction, providing evidence of the heterogeneous nature of this
catalyst. ICP-MS analysis of IRMOF-9-Irdcppy-NH2 before
(2.84 wt % Ir) and after one catalytic run [2.26 wt % Ir (Table
S2 of the Supporting Information)] indicated minimal loss of
Ir.
homogeneous catalytic reaction after 5 days reveals the
disappearance of dimethyl 2,2′-diamino[1,1′-biphenyl]-4,4′-
dicarboxylate species (Figure S6 of the Supporting Informa-
tion). The disappearance and/or degradation of dimethyl 2,2′-
diamino[1,1′-biphenyl]-4,4′-dicarboxylate is likely due to
alkylation of the amine functionality (Figure S9 of the
Supporting Information).
The recyclability of IRMOF-9-Irdcppy-NH2 was also
investigated. Between reaction runs, the MOF was isolated by
filtration and then rinsed and soaked in CDCl3. This procedure
was repeated every day for 3 days prior to the next catalytic run
to remove substrates or products that might produce pore
blocking.12 BET area measurement of IRMOF-9-Irdcppy-NH2
after one catalytic run under ambient conditions revealed a
surface area of 1711 57 m2/g (Figure S3 of the Supporting
Information). In the second and third runs, no conversion of
reactants to final product was found after ∼1.5 days under
identical reaction conditions. As previously observed, the
decrease in catalytic activity may be due to the effects of air
on the Ir centers.12 Therefore, the tandem reaction (Scheme 2)
with IRMOF-9-Irdcppy-NH2 was explored under an Ar
atmosphere. As expected, the first catalytic run gives ∼95%
conversion of the final product at 55 °C after ∼1.5 days (Figure
2), with the second run giving ∼24% conversion of the desired
product, and the third run giving no conversion. The decreased
catalytic activity is likely due to degradation of the MOF, as
PXRD analysis showed a substantial loss of crystallinity after
the second and third runs. The PXRD of IRMOF-9-Irdcppy-
NH2 changes substantially across the course of multiple
catalytic runs, and after the third catalytic run, few reflections
remain and a predominantly amorphous pattern is observed
(Figure S10 of the Supporting Information). The decreased
crystallinity of IRMOF-9-Irdcppy-NH2 may be caused by the
mildly acidic malonitrile substrate. To test this hypothesis, a
pristine batch of IRMOF-9-Irdcppy-NH2 was incubated in a
CDCl3 solution containing malonitrile at 55 °C for 3 days.
PXRD analysis showed that after incubation, IRMOF-9-
Irdcppy-NH2 had undergone a transformation to a different
phase (Figure S10 of the Supporting Information). The phase
transformation of IRMOF-9-Irdcppy-NH2 after incubation in
malonitrile suggests that this substrate is not well-tolerated by
this MOF architecture.
The similar one-pot reaction using homogeneous catalysts
was also investigated. Using dimethyl 2,2′-diamino[1,1′-
biphenyl]-4,4′-dicarboxylate [the methyl ester form of
31,32
H2bpdc-(NH2)2] and [Ir(COD)(OCH3)]2
as catalysts,
the desired product 2 was obtained in only 35% yield at 55
°C after ∼5 days (Scheme 2 and Figures S7 and S8 of the
Supporting Information). 1H NMR characterization of the
D
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CONCLUSION
■
In conclusion, this study presents the synthesis of a site-isolated
bifunctional MOF that is capable of acting as a tandem catalyst
for both the Knoevenagel condensation and allylic N-alkylation
reactions. The bifunctional MOF represents a rare MOF-based
tandem catalyst that contains both organocatalytic and
organometallic Ir(I) centers. Even though this bifunctional
MOF is only highly active for one catalytic run, the MOF does
achieve reactivity that was not effectively achieved by the
component catalysts in a solution state. More importantly, the
study demonstrates the potential use of MOFs to engender
complex catalytic systems that are not limited to any single class
of catalytic species. Future efforts will be focused on the
development of more stable MOF-based tandem catalysts with
control of the amount of catalytic species.
ASSOCIATED CONTENT
* Supporting Information
■
S
Synthesis and characterization of ligands and MOFs and
catalysis experiments. This material is available free of charge
via the Internet at http://pubs.acs.org.
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1304.
AUTHOR INFORMATION
Corresponding Author
*E-mail: scohen@ucsd.edu. Telephone: (858) 822-5596.
■
(31) Hartwig, J. F.; Pouy, M. J. Top. Organomet. Chem. 2011, 34, 169.
(32) Liu, W.-B.; Xia, J.-B.; You, S.-L. Top. Organomet. Chem. 2012,
38, 155.
Funding
This work was supported by a grant from the Division of
Chemistry of the National Science Foundation (CHE-
1359906).
Notes
The authors declare no competing financial interest.
ACKNOWLEDGMENTS
■
We thank Dr. Y. Su [University of California, San Diego
(UCSD)] and the Molecular Mass Spectrometry Facility for
assisting with the MS experiments. We thank Dr. C. E. Moore
(UCSD) and Prof. A. L. Rheingold (UCSD) for assisting with
the single-crystal XRD experiments.
E
DOI: 10.1021/ic502316v
Inorg. Chem. XXXX, XXX, XXX−XXX