Supported iron catalysts for Michael addition reactions

Article abstract of DOI:10.1016/j.mcat.2017.12.029

Heterogeneous catalysts have been widely used for chemical transformations and offer easy product separation in addition to their high activity. Iron is an earth-abundant metal, but it has not been studied thoroughly as heterogeneous catalysts for organic

Full text of DOI:10.1016/j.mcat.2017.12.029

Molecular Catalysis 447 (2018) 65–71
Contents lists available at ScienceDirect
Molecular Catalysis
journal homepage: www.elsevier.com/locate/mcat
Supported iron catalysts for Michael addition reactions
Rong Yea,b,1,2, Franco F. Fauchera,b,1, Gabor A. Somorjaia,b,∗
a Department of Chemistry, Kavli Energy NanoScience Institute, University of California, Berkeley, CA 94720, United States
b Chemical Science Division, Lawrence Berkeley National Laboratory, 1 Cyclotron Road, Berkeley, CA 94720, United States
a r t i c l e i n f o
a b s t r a c t
Article history:
Heterogeneous catalysts have been widely used for chemical transformations and offer easy product
separation in addition to their high activity. Iron is an earth-abundant metal, but it has not been studied
thoroughly as heterogeneous catalysts for organic reactions. In this work, supported iron catalysts were
synthesized via loading FeCl3 onto a mesoporous silica SBA-15. These catalysts were highly active for
Michael addition reactions, a synthetic pathway for forming C C bonds that is typically achieved by
homogeneous catalysts. Our studies show that for the supported iron catalysts, larger pore sizes of the
silica resulting from the loading of iron and the oxidation state of iron being Fe(III) are essential for
the high reaction rates. Notably, the catalysts show stability against leaching, regardless the presence or
absence of a dendrimer as an additional stabilizing agent. The catalysts could be used for at least three runs
without the loss of activity. The successful Michael addition reactions of indole or 2-methylindole and
different ␣,ˇ-unsaturated ketones corroborate the synthetic scope of the catalysts. These results show
promises of using supported iron catalysts as inexpensive and effective alternatives for the formation of
Received 5 November 2017
Received in revised form
17 December 2017
Accepted 19 December 2017
Available online 4 February 2018
Keywords:
Iron
Heterogeneous
Michael addition
Dendrimer
Silica
C
C bonds.
© 2018 Elsevier B.V. All rights reserved.
1. Introduction
Iron is an inexpensive earth-abundant metal and has been an
attractive element for catalysis [11–16]. The synthesis and char-
acterization of Fe salts loaded onto mesoporous silica SBA-15 has
been explored by Kuhn et al. [17] and Tilley et al. [18], but the cat-
alytic performances of these materials have yet to be studied in
comparison to those containing dendrimers [17–19]. In this study,
the hydroxyl-terminated generation-4 polyamidoamine (PAMAM)
dendrimer, denoted as G4OH, are investigated as a potential sta-
bilizer of iron, as they are known to encapsulate and stabilize the
nanoparticles of noble metals including Pt, Pd, Au, and Rh [9,20–24].
Supported iron catalysts with or without G4OH were synthesized,
characterized, and compared in catalytic Michael addition reac-
tions. A Michael addition reaction involving indole and butenone
was used as a model reaction to test the ability of supported iron
catalysts to catalyze C C bond formation. C C bond formation
reactions remain one of the most useful but challenging chem-
ical processes for use in synthetic industries [25], among which
Michael addition reactions are an important part of the total syn-
thesis for many complex organic compounds [26]. The formation of
The large majority of catalysts consist of metals, specifically
precious metals such as Pt, Pd, Au, and Rh [1]. Many of these cata-
lysts have been synthesized in the form of heterogeneous catalysts,
which offer many benefits, including easy product separation, recy-
clability, and efficiency. These metal-containing heterogeneous
catalysts can be loaded into porous supports, such as silica [2], in
order to achieve heterogeneity. However, precious metals are vul-
nerable to leaching in organic solutions as sometimes they cannot
attach strongly to the silica framework [3–6]. Heavy metals, such as
Pt, have been shown to be toxic depending on the dose and type of
exposure, acute or chronic [7]. Aside from toxicity, metal leaching
reduces the catalytic efficacy of a catalyst over time. Dendrimers
have been used to prevent toxic metal leaching and to improve
the overall stability and recyclability of metal-containing hetero-
geneous catalysts [8–10].
C
C bonds under mild conditions is necessary for the commercial
production especially in the pharmaceutical industry [27,28]. Pre-
viously, Pitchumani et al. showed that Michael addition reactions
were achieved by an acidified silica under mild conditions with
high yields [29]. In this work, the characterization of supported iron
catalysts, reaction kinetics studies, metal-leaching tests, and cata-
∗
Corresponding author at: Department of Chemistry, Kavli Energy NanoScience
Institute, University of California, Berkeley, CA 94720, United States.
E-mail address: somorjai@berkeley.edu (G.A. Somorjai).
These two authors contribute equally to this work.
Present address: Department of Chemistry and Chemical Biology, Cornell Uni-
1
2
versity, Ithaca, New York 14853, United States.
https://doi.org/10.1016/j.mcat.2017.12.029
2468-8231/© 2018 Elsevier B.V. All rights reserved.

66
R. Ye et al. / Molecular Catalysis 447 (2018) 65–71
Table 1
lyst recyclability tests were carried out to understand the catalytic
properties of supported iron catalysts. Supported iron catalysts
show promises in that they are not only highly active but also stable
as they bind strongly to the silica support framework.
Loading amount of iron in catalysts.
catalyst
Fe concentration (mmol/g)a
percent loaded (%)a
Fe/G4OH/SBA-15
Fe/G4OH/SBA-15(10×)
Fe/SBA-15
Fe/SBA-15(10×)
4.49 × 10−2
1.97 × 10−1
4.54 × 10−2
2.13 × 10−1
74.9
65.7
75.7
71.0
2. Experimental
a
Approximately 10 mg of each catalyst was used in ICP-OES analyses. Samples
were prepared by digesting approximately 10 mg of a solid catalyst in a centrifuge
tube with 0.2 mL HF, 0.2 mL HNO3, and 0.6 mL HCl, and then diluted to 10 mL with
deionized water. The total amount of iron in the sample was calculated accordingly,
which was divided by that amount of iron used in the synthesis process to calculate
the loading percentage.
2.1. General information
Unless otherwise noted, all commercial materials were used as
received without purification. All glassware was dried at 100 ◦C for
8 h before use.
2.2. Chemicals
hygroscopic. The mixture was centrifuged at 4000 rpm for 5 min,
the supernatant was discarded and the resulting solid was dried
at 100 ◦C for 20 h. In addition, a version was synthesized with
the G4OH dendrimer, and the resulting catalyst was called
Fe/G4OH/SBA-15. The synthesis of Fe/G4OH/SBA-15 is similar to
that of Fe/SBA-15. First, 1 g of SBA-15, 1.5 ␮mol of G4OH den-
drimer, and 30 mL of deionized H2O were allowed to stir for three
hours at room temperature. Then the solution was centrifuged
for 5 min at 4000 rpm, and the supernatant was discarded. Next,
0.06 mmol of FeCl3 was added and allowed to mixed for 24 h at
room temperature with stirring. The mixture was centrifuged at
4000 rpm for 5 min, the supernatant was discarded and the result-
ing solid was dried at 100 ◦C for 20 h. Two other catalysts were also
synthesized using 0.6 mmol of FeCl3 without or with 15 ␮mol of
G4OH in the same way, which are denoted as Fe/SBA-15(10×) and
Fe/G4OH/SBA-15(10×), respectively.
Iron (III) chloride (≥99.99%), iron(II) sulfate heptahydrate
(≥99.0%), indole (98%), 2-methylindole (98%), butenone (99%), 2-
cyclopenten-1-one (98%), 2-cyclohexen-1-one (≥95%), 4-phenyl-
3-buten-2-one (99%), and 1,3-diphenyl-2-propenone (≥98.0%)
were purchased from Sigma-Aldrich. All PAMAM dendrimers,
G4OH, G4NH2, and G4SA were purchased from Dendritech Inc. as
water solutions. Deuterated solvents (chloroform, toluene, ben-
zene, water, methanol, and acetonitrile) were purchased from
Cambridge Isotope Laboratories, Inc.
2.3. Instruments
The catalyst loading was analyzed by Optima 7000 DV Induc-
tively coupled plasma optical emission spectroscopy (ICP-OES). The
transmission electron microscopy (TEM) images were taken with
an FEI Tecnai TEM at an accelerating voltage of 200 kV. All NMR
spectra were obtained at ambient temperature on Bruker AVB-
400 and AVQ-400 spectrometers. Centrifugation was performed
on a Thermo Scientific IEC Centra® CL2. Physisorption experiments
were recorded on Micromeritics 3Flex with Ultra-high-purity grade
N2 (Praxair, 99.999% purity). A liquid nitrogen bath was used for
the measurements at 77 K. Powder X-ray diffraction (PXRD) pat-
terns were recorded using a Rigaku Miniflex 600 (Bragg–Brentano
geometry, Cu K␣ radiation ␭ = 1.54 Å) diffractometer. X-ray pho-
toelectron spectrometric (XPS) experiments were performed on a
Perkin-Elmer PHI 5300 XPS spectrometer with a position-sensitive
detector and a hemispherical energy analyzer in an ion-pumped
chamber (evacuated to 2 × 10−9 Torr). The Mg K␣ (hv = 1253.7 eV)
X-ray source of the XPS spectrometer was operated at 350 W with
15 kV acceleration voltage.
2.6. Representative procedure for catalytic reactions
To a dry 2 mL reaction vial equipped with a stir bar, were added
0.05 mmol of butenone, 0.06 mmol of indole, 0.2 mL CDCl3, and
a catalyst. The reaction mixture was heated with stirring at the
desired temperature for 22 h. The mixture was then cooled to room
temperature, and the solid catalyst filtered using a polytetrafluo-
roethylene syringe filter. The filtrate was transferred to a NMR tube
for analysis.
3. Results and discussions
Inductively coupled plasma optical emission spectroscopy (ICP-
OES) was used to determine iron concentrations of the supported
iron catalysts, and the results are summarized in Table 1. 75.7% and
74.9% of iron used in the synthesis were found to be loaded into
Fe/SBA-15 and Fe/G4OH/SBA-15, respectively (Table 1). While the
Fe/SBA-15(10×) catalyst had 4.7% lower loading percent compared
to Fe/SBA-15, the Fe/G4OH/SBA-15(10×) catalyst had a decrease
of 9.2% in loading compared to Fe/G4OH/SBA-15. The dendrimer
decreases the loading percent of iron, which is more significant at
higher concentrations of iron.
N2 physisorption isotherms show that the addition of iron
increased the pore size of the SBA-15, which is likely due to the
restructuring of the pores during the loading process, while the
G4OH dendrimer decreased the pore size because of their steric
bulk (Fig. 1A). The physisorption isotherms for all four samples
are Type IV isotherms which are indicative of multilayer adsorp-
tion [31]. The supported iron catalysts retain their mesoporous
structure after the synthetic process, as expected. In the case of
Fe/G4OH/SBA-15(10×), the non-negligible amount of G4OH greatly
decreased the pore size, which outweighed the effect of the iron on
the SBA-15. In addition, the lower SBET of Fe/G4OH/SBA-15(10×)
shows that surface areas decrease with the addition of dendrimers
(Table 2). Similarly, the Vmicro was reduced for samples contain-
2.4. Synthesis of the support
The procedure established by Zhao et al. was followed for the
synthesis of the support SBA-15 [30]. Briefly, 8 g of Pluronic 123 was
dissolved in 60 g of deionized H2O and 240 g of 2 M HCl with stirring
at 35 ◦C for 1 h. Then, 17 g of tetraethyl orthosilicate was added and
allowed to stir for an additional 20 h. Next, the mixture was aged
at 80 ◦C for 24 h overnight without stirring. The resulting solid was
collected by filtration and washed with water and ethanol, and then
finally dried at 100 ◦C. The solid was then heated to 500 ◦C in 8 h and
held at 500 ◦C for 6 h and then allowed to cool. The resulting solid,
SBA-15, was grinded using mortar and pestle and stored before
usage.
2.5. Synthesis of catalysts
For the synthesis of the supported iron catalyst Fe/SBA-15,
approximately 0.06 mmol of FeCl3 (9.73 mg), 1 g of SBA-15, and
60 mL of H2O was mixed for 24 h at room temperature with stir-
ring. Care was taken to quickly weigh FeCl3 as it is extremely

R. Ye et al. / Molecular Catalysis 447 (2018) 65–71
67
Fig. 1. (A) N2 physisorption isotherms of solid materials at 77 K with adsorption and desorption points represented by closed and open symbols, respectively. (B) PXRD
patterns of Fe/SBA-15 and Fe/G4OH/SBA-15 catalysts. (C-F) TEM images of (C) Fe/G4OH/SBA-15, (D) SBA-15 (E) Fe/G4OH/SBA-15(10 × ), (F) Fe/SBA-15(10 × ). The scale bar is
10 nm.
Table 2
Physisorption characterizations of the solid materials.
a
c
d
Catalyst
SBET (m2 g−1
)
Dpore (nm)b
VBJH (cm3 g−1
)
Vmicro (cm3 g−1
)
Fe/G4OH/SBA-15
Fe/G4OH/SBA-15(10×)
Fe/SBA-15(10×)
SBA-15
710
571
789
731
5.96
5.84
5.70
5.48
0.75
0.63
0.74
0.63
0.064
0.040
0.100
0.093
a
SBET: the BET surface area.
Dpore: average pore diameter.
BJH adsorption cumulative volumes of pores between 0.85 nm and 150.00 nm radium.
t-plot micropore volume.
b
c
d
ing the dendrimer. The size of micropores is close to the sizes of
small molecule reactants and products, so the pore size is related
to the diffusion of reactants and products; larger pores correlate
with faster reaction rates especially when bulkier reactant species
are used. On the other hand, Fe/SBA-15(10×) had a larger SBET
and Vmicro, attributable to the high amount of iron in this sam-
ple.
The powder X-ray diffraction (PXRD) patterns of Fe/SBA-15 and
Fe/G4OH/SBA-15 show only a peak for amorphous silica, but no
peak for iron species is visible (Fig. 1B), indicating that the iron
is not forming detectable nanoparticles. In addition, no particle is
observed from transmission electron microscopy (TEM) images of
the samples (Fig. 1 C-F). In fact, attempts were made to reduce Fe(III)
using strong reducing agents such as NaBH4 but these attempts did
not lead to the formation of iron nanoparticles. From these obser-
vations, either the nanoparticles are below the detection limit, i.e.,
smaller than ∼0.5 nm, or the iron is staying in the form of Fe(III)
or Fe(II) as isolated single ions. According to the negative standard
reduction potential of Fe2+/Fe relative to the standard hydrogen
electrode, the formation of Fe(0) nanoparticles is thermodynami-
cally unfavorable under our reduction conditions. Also based on the
results discussed below, the iron probably exists as isolated single
ions in the supported iron catalysts.
3.1. Michael addition and kinetics
Since nanoparticle formation was not observed, the catalytically
active species was thought to be iron ions. The Michael addition in
Fig. 2A was studied to determine the catalytic properties of sup-
ported iron catalysts. Comparing unsupported Fe(III) and Fe(II) ions,
Fe(III) is more active in the reaction than iron (II), as 3.07 ␮mol of
FeCl3 and 3.55 ␮mol of FeSO4 were found to catalyze the Michael
addition reaction to 100% and 27.0%, respectively, at 50 ◦C; no con-
version is observed without catalysts. Because the reaction can be
acid catalyzed [29], the higher activity of Fe(III) is expected because
Fe(III) is a stronger Lewis acid than Fe(II).
X-ray photoelectron spectroscopy (XPS) was utilized in an
attempt to determine the oxidation state of iron in these catalysts.
However, no iron signal was detected even for the concentrated
samples, probably because the iron has a small weight percentage
[∼1 wt% for the Fe/SBA-15(10 × )] and is distributed evenly in the

68
R. Ye et al. / Molecular Catalysis 447 (2018) 65–71
Fig. 2. (A) Schematic of the catalytic Michael addition reaction. (B) Rates of the Michael addition reaction catalyzed by iron catalysts and SBA-15. Reactions were carried out
with 0.05 mmol of butenone, 0.06 mmol of indole, 1.0 mL CDCl3 at 50 ◦C, with 10 mg Fe/SBA-15, Fe/G4OH/SBA-15, and SBA-15, and 0.449 ␮mol of FeCl3 (equimolar of Fe for
all catalysts). (C) Arrhenius Plots for the Michael addition of indole and butenone. Reactions were carried out with 0.05 mmol of butenone, 0.06 mmol of indole, 0.2 mL CDCl3
for 1.5 h with 10 mg of catalysts.
solid, which leads to a surface concentration of iron too low to be
detected by XPS.
pH of the solution resulting from the amine groups. This study
focused on the investigation of G4OH, so its effects on catalysis
could be compared to earlier works in our group that involved
G4OH dendrimers [9,32].
In addition to the identification of Fe(III) as the catalytic species,
the reaction rates with different catalysts were compared. The sup-
port SBA-15 displays very little catalytic activity, thanks to its very
small number of acid sites, but its activity is not comparable to that
of catalysts containing iron (Fig. 2B). The percent yield is approx-
imately 90% after 20 h of reaction for the three iron-containing
catalysts. Diffusion rates are not an obstacle for these catalysts.
The activation energy was 108 kJ/mol and 94 kJ/mol, based on the
Arrhenius plot (Fig. 2C) for Fe/SBA-15 and Fe/G4OH/SBA-15, respec-
tively.
In order to further study the effects of the G4OH dendrimer on
iron, hot filtration tests were performed to examine the potential
leaching of iron from Fe/SBA-15 and Fe/G4OH/SBA-15. A hot filtra-
tion was performed for a run after two hours of reaction, and the
filtrate was heated under the same condition before the filtration
till 4 h of total reaction time. The yield of such a run remains the
same after the hot filtration, but a run of 4 h without the filtration
gives a higher yield (Fig. 3A). Since free Fe(III) is catalytically active,
it is expected that if leaching does occur, the yield will increase
even after the filtration of the solid catalyst. Thus, Fig. 3A suggests
that neither Fe/SBA-15 nor Fe/G4OH/SBA-15 showed iron leaching
into the solvent, as the yield did not increase after the filtration
in either case. To further ensure the validity of the hot filtration
test, the concentrated catalysts Fe/SBA-15(10×) and Fe/G4OH/SBA-
15(10×) were also examined in the same manner (Fig. 3B) to rule
out the possibility that the concentrations of the potential leached
iron were so small that the increased yield is not detectable. A
higher concentration of iron could also increase the chance for
leaching, so the stability of the catalysts could be more rigorously
examined. Interestingly, no leaching was seen from either of the
concentrated catalysts (Fig. 3B). This is quite surprising as even
under high concentrations the iron stays attached to the silica sup-
port with or without dendrimer. Iron does not need a dendrimer
to attach to the silica framework, which could be explained by the
strong interaction between iron ions and the oxygen in the silica.
The test with the concentrated catalysts also spotlights the effects
of the dendrimer on the catalytic activity, as the yield of Fe/SBA-
15(10×) greatly exceeded that of Fe/G4OH/SBA-15(10×) (Fig. 3B),
partially because of the larger amount of iron in the same mass of
3.2. Dendrimer effects
As dendrimers could provide additional activity and stability
to the precious metal nanoparticle catalysts, to check whether the
same is true for the iron species, three different dendrimers were
mixed with FeCl3 in order to understand how iron interacts with
different dendrimers. The mixing process involved sonication of
6 ␮mol of dendrimer and 45 ␮mol of FeCl3 in 1 mL of deionized
H2O for an hour, and then aging for 24 h to allow the complexation
between the iron and the dendrimer. G4OH and succinamic acid-
terminated generation four polyamidoamine (G4SA) dendrimers
both complexed with iron as observed from the transition from
a cloudy to clear orange appearance, which occurred within three
minutes. The activity of iron was not hampered by the coordination
with these dendrimers. 10 ␮L of aged FeCl3/G4OH and FeCl3/G4SA
solutions were used to carry out the Michael addition reaction in
methanol for 1.5 h at 20 ◦C, and the yields were 17.4% and 22.5%,
respectively, comparable to free FeCl3. However, mixing FeCl3 with
the primary amine-terminated fourth-generation polyamidoamine
(G4NH2) led to a precipitation, which could be attributed to a high

R. Ye et al. / Molecular Catalysis 447 (2018) 65–71
69
Fig. 4. Solvent screening. Reactions were carried out with 0.05 mmol of butenone,
0.06 mmol of indole, 0.2 mL solvent at 20 ◦C, with 10 mg Fe/SBA-15 (0.4 mol% Fe) for
22 h.
Fe/SBA-15(10×) compared to Fe/G4OH/SBA-15(10×) (Table 1). The
steric effect of the dendrimer might further lower the turnover rate
of Fe/G4OH/SBA-15(10×).
In addition to the hot filtration test, recyclability tests were
performed on the Fe/SBA-15(10×) and Fe/G4OH/SBA-15(10×) cat-
alysts. It was initially thought that the dendrimer would offer the
advantage of recyclability based on the cases of Au, Pt, and Rh. How-
ever, both catalysts maintained 100% yield after each cycle, for at
least three cycles under the test conditions (Fig. 3C). Treatments to
reactivate the catalysts by heating them in the air at 100 or 150 ◦C
for 2 h after each cycle were performed in case of the loss of cat-
alyst activity between cycles, but catalysts after these treatments
also showed 100% conversion in each cycle.
3.3. Reaction optimization and synthetic scope
The reaction was carried out in six solvents in order to opti-
mize the yield and see how solvents affect the catalysts. Fe/SBA-15
performed optimally in chloroform. Toluene and benzene both
provided high yields as well. Furthermore, the catalysts provided
mediocre yields in acetonitrile, methanol, or water (Fig. 4). The par-
tial insolubility of the reactants (indole and butenone) in methanol
or water may account for the low yields in these solvents. Aside
from the solvent screening, the synthetic scope of the reaction
was also explored in CDCl3 at 50 ◦C and C6D6 at 80 ◦C (Table 3).
In these tests, the reaction time was chosen to be 23 h to com-
pare the reaction rates of various reactants at different conditions.
With higher catalysts loadings or longer reaction times, all these
reactions can reach a full conversion, demonstrating the scope of
applicability of the supported iron catalysts. Notably, among the
substitution of butenone for ␣,ˇ-unsaturated ketones tested so far,
butenone showed the highest reaction rate, presumably due to the
least steric effect it experienced as a terminal alkene. In general,
2-methylindole reacts faster than indole, attributable to the higher
nucleophilicity due to the electron donation from the methyl group.
Fig. 3. (A) and (B) Hot filtration tests of (A) Fe/SBA-15 and Fe/G4OH/SBA-15, and
(B) Fe/SBA-15(10×) and Fe/G4OH/SBA-15(10×). Reactions were carried out with
0.05 mmol of butenone, 0.06 mmol of indole, 1.0 mL CDCl3 at 50 ◦C, with 10 mg of
a catalyst. (C) Recycling tests of Fe/SBA-15(10×) and Fe/G4OH/SBA-15(10 × ). Reac-
tions were carried out with 0.20 mmol of butenone, 0.24 mmol of indole, 0.10 mmol
of CHCl2CHCl2 as the internal standard, 1.0 mL CDCl3 at 50 ◦C, with 50 mg catalysts
for 23 h. Upon the end of each 23 h cycle, the liquid was removed after centrifuga-
tion, the catalysts were dried under rotary evaporation, a new stock solution of the
solvent and reactants was added, and the next cycle started.
4. Conclusions
The Fe/SBA-15 catalyst is at least equally active compared to
its dendrimer counterpart, and almost as active as free Fe(III) in
a solution. The Fe/SBA-15 catalyst has the advantage of being a
stable catalyst, in comparison to other metal catalysts loaded in
silica, as it experiences no toxic metal leaching even without the
dendrimer, resulting in a more cost-effective application. On the

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R. Ye et al. / Molecular Catalysis 447 (2018) 65–71
Table 3
Reaction scope tests.
ketone
nucleophile
product
solvent
temperature (◦C)
yield (%)
A
B
CDCl3
CDCl3
50
50
100
100
A
A
B
B
CDCl3
C6D6
CDCl3
C6D6
50
80
50
80
33
53
51
56
A
A
B
B
CDCl3
C6D6
CDCl3
C6D6
50
80
50
80
33
66
80
87
A
A
B
B
CDCl3
C6D6
CDCl3
C6D6
50
80
50
80
17
44
42
74
A
A
B
B
CDCl3
C6D6
CDCl3
C6D6
50
80
50
80
11
41
52
73
other hand, Fe/SBA-15 also has larger pores than Fe/G4OH/SBA-15,
allowing for higher diffusion rates. The catalyst can also catalyze
the C C bond formation with several different reactants under a
variety of solvents with high yields. As a heterogeneous catalyst
consists of an earth-abundant metal and a mesoporous silica sup-
port, Fe/SBA-15 provides a promising starting point for stable and
recyclable catalysts that do not need extra stabilizers. These cata-
lysts are highly active, recyclable, cost-effective, and prove greatly
useful for synthetic reactions involving C C bond formation under
mild conditions.
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Acknowledgements
We acknowledge support from the Director, Office of Science,
Office of Basic Energy Sciences, Division of Chemical Sciences,
Geological and Biosciences of the US DOE under contract DEAC02-
05CH11231. Work at the Molecular Foundry (Proposal 4689) was
supported by the same contract. F. F. F. thanks the Summer Under-
graduate Research Fellowship program, especially the Rose Hills
Foundation for their support. We thank Prof. A. Paul Alivisatos for
the use of the TEM. We thank Mr. Brent B. Wickemeyer for his
assistance.
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