Cu and Au metal-organic frameworks bridge the gap between homogeneous and heterogeneous catalysts for alkene cyclopropanation reactions

Article abstract of DOI:10.1002/chem.201000278

The copper and gold metal-organic frameworks (MOFs) [Cu₃(BTC) ₂(H₂O)₃]_n, [Cu₃(BTC) ₂] (BTC = benzene-1,3,5-tricarboxylate), and IRMOF-3-SI-Au are active and reusable solid catalysts for the cyclopropanation of alkenes with high chemo- and diastereoselectivities. This type of material gives better results than previous solid catalysts while working together with the homogeneous catalysts. These MOFs can help to bridge the gap between homogeneous and heterogeneous catalysis.

Full text of DOI:10.1002/chem.201000278

FULL PAPER
DOI: 10.1002/chem.201000278
Cu and Au Metal–Organic Frameworks Bridge the Gap between
Homogeneous and Heterogeneous Catalysts for Alkene Cyclopropanation
Reactions
Avelino Corma,*[a] Marta Iglesias,[b] Francesc X. Llabrꢀs i Xamena,[a] and Fꢀlix Sꢁnchez[c]
Dedicated to Professor Josꢀ Barluenga on the occasion of his 70th birthday
Abstract: The copper and gold metal–organic frameworks (MOFs) [Cu
3ACHTUNGTNER(NUNG BTC)2-
A
CHTUNGTRENNUNG
are active and reusable solid catalysts for the cyclopropanation of alkenes with
high chemo- and diastereoselectivities. This type of material gives better results
than previous solid catalysts while working together with the homogeneous cata-
lysts. These MOFs can help to bridge the gap between homogeneous and hetero-
geneous catalysis.
Keywords: copper · cyclopropana-
tion · gold · heterogeneous cataly-
sis · metal–organic frameworks
Introduction
ic properties into MOFs has increased recently[4] because
both metal ions or linkers can act as catalytic centers.
Herein, we show that a copper-containing MOF [Cu3-
Metal–organic framework (MOF) materials are promising
candidates as new heterogeneous catalysts due to their high
surface area inside the pores and their tunable structure.[1]
An attractive feature of these solids is the presence of
single-site active species in an identical environment within
the crystalline matrix. Some applications of these porous
materials, such as gas separation, gas storage,[2a] and cataly-
sis,[2b–d] have already been described. Research into catalytic
applications has mainly focused on rigid MOFs with perma-
nent porosity and coordinatively unsaturated metal active
sites that are accessible to the substrate.[1d, 3] Heterogeneous
catalysis is one of the application areas in which MOFs
could play an important role. Interest in introducing catalyt-
AHCTUNGTRENNUNG
AHCTUNGTRENNUNG
base complex that lines the pore walls,[5] both give excellent
activities and selectivities for alkene cyclopropanation reac-
tions. We anticipated that if coordinative unsaturated gold
ions (i.e., open cationic gold sites) can be created in MOFs,
the resulting heterogeneous gold catalyst would emulate the
catalytic properties of homogeneous counterparts, that is,
well-defined active sites with dispersed metal ions.
One strategy employed in the synthesis of cyclopropane
rings is based on the catalytic transfer of carbene fragments
from diazo compounds to olefins.[6] Transition metals from
Groups 8 to 11 have been reported to decompose diazo
compounds,[7] and the carbene unit is later transferred to a
variety of saturated or unsaturated substrates [Eq. (1)].[8]
[a] Prof. A. Corma, Dr. F. X. Llabrꢀs i Xamena
Inst. Tecnologꢁa Quꢁmica, UPV-CSIC
Universidad Politꢀcnica de Valencia
Consejo Superior de Investigaciones Cientꢁficas
Avda los Naranjos, s/n, 46022 Valencia (Spain)
Fax : (+34)963877809
E-mail: acorma@itq.upv.es
[b] Prof. M. Iglesias
Inst. Ciencia de Materiales de Madrid, CSIC
C/Sor Juana Inꢀs de la Cruz 3
Cantoblanco, 28049 Madrid (Spain)
After the first reported use of a gold-based catalyst for
the intermolecular carbene transfer from diazo com-
pounds,[9] very few other examples have been described
based on this metal.[10]
[c] Prof. F. Sꢂnchez
Instituto de Quꢁmica Orgꢂnica General, CSIC
C/Juan de la Cierva 3, 28006 Madrid (Spain)
Chem. Eur. J. 2010, 16, 9789 – 9795
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We show that [Cu
(BTC)2] and IRMOF-3-SI-Au are
for an efficient and mild catalytic cyclopropanation reaction
with ethyl diazoacetate (EDA) in the presence of [Cu3-
AHCTUNGRTEG(NNUN BTC)2]. In these initial studies, styrene was chosen as a
model substrate. In our cyclopropanation experiments, the
diazo compound was slowly added over two hours to the re-
action mixture, which contained the catalyst and olefin, with
a syringe pump. GC and GC–MS analyses of the reaction
mixtures showed that cyclopropanes (as cis/trans mixtures)
are formed as the main products of these reactions (50–
90%) together with minor amounts of coupling products.
active and selective toward the cyclopropanation of alkenes
without losing the crystalline nature of the MOF and hence
can be reused without further modification. These MOFs
are materials that can help to bridge the gap between homo-
geneous and heterogeneous catalysis.
Results and Discussion
Compounds [Cu
G
[Cu3ACTHNGUTERN(UNG BTC)2]-catalyzed transfer of a carbene unit from EDA
as heterogeneous catalysts for the cyclopropanation of al-
kenes due to the presence of well-defined, isolated, and
to styrene was initially carried out in the absence of a sol-
vent. Under these experimental conditions, the cyclopropa-
necarboxylates were obtained with low selectivity due to the
formation of relatively large amounts of dimerization prod-
ucts, together with ortho, meta, and para aromatic addition
products. The activity of the catalyst in this transformation
can be estimated on the basis of the time required for the
complete consumption of the alkene. Comparison with
other copper catalysts, such as, the homogeneous catalyst[13]
stable copper(II) and gold
cessible to the reactant.
ACHTUNGTRNE(NUNG III) active sites that are fully ac-
The structure of [Cu3ACHTUNTRGNEUNG(BTC)2] consists of a cluster of two
metal atoms that have a paddle-wheel shape and a square-
planar coordination.[11] The BTC ligand acts as a trigonal-
planar ligand that connects the diatomic metal clusters,[11b]
which defines the nanocages. The {CuBTC} structure com-
prises two types of ꢄꢄcage” and two types of ꢄꢄwindow” that
separate these cages. Large cages are interconnected by 9 ꢅ
windows with a square cross-section. The large cages are
also connected to tetrahedral-shaped pockets of approxi-
mately 6 ꢅ through triangular-shaped windows of approxi-
mately 4.6 ꢅ (Figure 1). At this point, we believe that the
À
Cu H or copper complexes supported on ultrastable Y
À
À
(USY) and MCM-41 matrices (Cu USY, Cu MCM-41),
shows that [Cu3ACTHNUTRGNEUNG(BTC)2] displays similar rates but higher se-
lectivities (Table 1).
Table 1. Catalytic results for the cyclopropanation reaction involving sty-
rene and alkyl diazoacetates.
Entry Catalyst[a]
Diazo
Conversion
t
Selectivity d.r.
Compound [%][b]
[h] [%]
[%][c]
1
2
3
4
5
6
7
8
G
G
98
3
2
98
49
71
59
55
59
68
61
62
59
74
32
60
25
74
23
57
20 100
21 100
24 100
2
48
19 100
19 100
[a] Catalyst loading: 5 mol%. [b] Selectivity towards cyclopropanes; the
remaining diazo compound was converted into coupling products.
[c] Diastereomeric selectivity: (transÀcis)/trans+cis).
The use of ethyl 2-phenyldiazoacetate (PhEDA) with
[Cu3ACHTUNTRGNEUNG(BTC)2] as the catalyst in the cyclopropanation reaction
Figure 1. Crystal structure of the [Cu3ACTHUNTRGNE(UGN BTC)2] MOF.
of styrene provided better results [Eq. (2) and Table 2,
entry 1]. A unique diastereoisomer (trans-Ph/COOEt) was
obtained, similar to other systems reported for this substrate
with this diazo compound.[14] The reaction times required
for complete diazo consumption are similar to those for
EDA.
activity of the catalyst may depend on 1) the availability of
significant numbers of accessible sites due to the open MOF
crystal structure, 2) the reversible coordination of organic
linkers with the metal atom, and 3) the influence of the elec-
trostatic field in the cavity by the partially charged frame-
work. It has been previously reported that the active sites in
[Cu3ACHTUNGTRENNUNG
(BTC)2] are Lewis acids[12] and IRMOF-3-SI-Au is an
excellent catalyst for domino-coupling and cyclization reac-
tions.[5] We have now explored their activity as heterogene-
ous selective catalysts in the cyclopropanation of alkenes.
Catalysis with the copper-containing MOF: Initially, we fo-
In a second series of experiments, b-methylstyrene was
cused on control experiments to optimize suitable conditions
chosen as the substrate for the cyclopropanation reaction
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Chem. Eur. J. 2010, 16, 9789 – 9795

Metal–Organic Frameworks as Catalysts for Cyclopropanation
FULL PAPER
Table 2. Cyclopropanation of alkenes with a [Cu
t[a]
3ACHTNUGTREN(UNGN BTC)2]-based catalys-
lectivity in the cyclopropanation of internal olefins. In the
case of cyclohexene or dihydropyrane, a 92:8 trans/cis ratio
was achieved. Finally, low yields of the corresponding cyclo-
propanecarboxylates were achieved with cis-cyclooctene.
This behavior could probably be ascribed to the higher
steric hindrance of the internal double bond of the olefin
with respect to the terminal double bond. As a result, in the
substitution of the labile aqua molecule, the internal olefin
coordinates in a preferred direction to the copper center.
Together with monoalkenes, dienes were employed as
substrates for the copper-catalyzed cyclopropanation reac-
tions. Indeed, 3-(1-isobutenyl)-2,2-dimethyl cyclopropane-
carboxylic acid (chrysanthemic acid) is a key intermediate
of pyrethroid insecticides,[6,15] and the conversion of DMHD
into the corresponding chrysantemate esters by means of di-
azoacetates continuously represents a fundamental target in
industrial applicable processes[16] [Eq. (3)]. Therefore, al-
kenes containing alkyl groups instead of aryl substituents
can model, to a certain extent, the behavior expected for
the corresponding diene. Very few examples of high diaster-
eoselection have been reported so far for olefins with no
aryl substituents. Consistently with the behaviour observed
for mono-olefins, when the copper-containing MOF was
used to catalyze the conversion of conjugated diolefins into
the corresponding cyclopropanes (Table 2, entries 11 and
12), the trans isomer was always the major product.
Entry
Olefin
Diazo
compound
t
Yield
[%][b]
d.r.
TON[d]
[h]
[%][c]
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
styrene
PhEDA
PhEDA
PhEDA
PhEDA
PhEDA
EDA
tBuDA
EDA
EDA
EDA
EDA
EDA
EDA
4
4
2
3
5
3
24
2
20
15
2
20
2
85
50
30
90
70
98
25
25
43
50
15
60
98
99
30
30
90
100
100
100
98
150
70
35
165
86
a-methylstyrene
b-methylstyrene
1-octene
cyclooctene
styrene
98
71
68
192
42
styrene
a-methylstyrene
a-methylstyrene
b-methylstyrene
DMHD
DMHD
1-octene
cyclohexene
cyclooctene
cyclooctene
dihydropyrane
58
48
56
80
67
100
30
120
196
196
56
100
100
67
EDA
EDA
EDA
EDA
2
2
2
24
98
71
[e]
57
60
91
198
[a] Catalyst loading: 5 mol%. [b] Yield of the cyclopropane; the remain-
ing diazo compound was converted into autocoupling products. [c] Dia-
stereomeric selectivity: (transÀcis)/trans+cis). [d] Calculated as mmol of
converted substrate/mmol of catalyst. [e] Experiments in which EDA was
completely added before starting the reaction.
with the same copper catalyst and PhEDA as the carbene
source. Again, only one cyclopropane stereoisomer was ob-
tained. Substrates 1-octene and cyclooctene were treated
with PhEDA, and the same high diastereoselectivities were
obtained (Table 2, entries 4 and 5). The optimized protocol
was extended to other substrates to determine the scope of
the catalytic activity of [Cu3ACHTNUGTRENUNG(BTC)2] and also to study the
chemoselectivity and diastereoselectivity of the cyclopropa-
nation (Table 2). We focused on three types of olefin: styr-
enes (styrene, a-methylstyrene, b-methylstyrene), linear al-
kenes (1-octene, 1-decene), cyclic olefins (cyclohexene, cy-
clooctene, dihydropyrane), and 2,5-dimethyl-2,4-hexadiene
(DMHD) with EDA, PhEDA, and tert-butyl diazoacetate
(tBuDA) as the cyclopropanating agents (Table 2). To evalu-
ate these MOF-catalyzed reactions, the reactivity of differ-
ent styrene derivatives was studied. The presence of elec-
tron-withdrawing or -donating groups on styrene does not
affect the selectivity of the resulting cyclopropanes. Styrene
was converted almost completely into cyclopropanecarboxy-
lates in high yields (Table 2, entries 6 and 7). Substrates a-
methylstyrene and b-methylstyrene were successfully cyclo-
propanated into the corresponding products in good yields
with 60–70% diastereoselectivity. The reaction rates, charac-
terized by the turnover number (TON), were lower than
those for styrene. Interestingly, the aliphatic and cyclic ole-
fins (i.e., 1-octene, 1-decene, cyclohexene, dihydropyran,
and cis-cyclooctene) yielded the corresponding cyclopro-
panes. For terminal aliphatic alkenes (i.e., 1-octene, 1-
decene), diastereoselection occurred toward the trans cyclo-
propane. The yields were moderate for 1-decene, which was
also observed in other cases with these olefins in which the
reactivity is lower than for styrene. On the contrary, the
copper-containing MOF exhibited a remarkable diastereose-
Recycling of the copper-containing MOF: Reusability ex-
periments conducted with [Cu3ACHTNUGTRENUNG(BTC)2] demonstrated that
the copper-containing MOF is stable and no loss of either
activity or selectivity was detected for the cyclopropanation
of styrene. Table 3 shows that the conversions and yields of
the cis- and trans-cyclopropanation products derived from
styrene were maintained within three cycles. A comparison
of X-ray diffraction patterns of [Cu3ACHTNUTRGNE(UNG BTC)2] before and
after several reaction runs did not reveal any significant dif-
Table 3. Recycling experiments in the cyclopropanation of styrene with
EDA catalyzed by [Cu CHTUNGTNER(NUNG BTC)2] in CH2Cl2 at room temperature
3A
Run
Conversion
[%]
cis/trans
Selectivity
[%][a]
1
2
3
100
95
98
30:70
29:71
25:75
94
95
96
[a] Selectivity toward cyclopropanecarboxylates.
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9791

A. Corma et al.
ferences (Figure 2), so that the structural integrity of the
material is basically preserved after the catalytic use.
conversion was observed. Thus, no dissolved active species
are assumed to be present in reaction mixtures with the
copper-containing MOF [Cu3ACHTNUTRGENNUG(BTC)2] and the catalytic activ-
ity can be associated with the MOF structure.
Reaction mechanism: Although there are experimental
studies on cyclopropanation through copper-catalyzed diazo
decomposition, theoretical studies on Cu–carbene formation
is rather scarce.[17] In mechanistic studies on copper-cata-
lyzed cyclopropanation reactions, the entire mechanism con-
sists of steps that involve the formation of a copper–carbene
moiety and the cyclopropanation reaction [Eq. (4); acac=
actetylacetone].
Figure 2. X-ray diffractograms of fresh [Cu
several runs of the reaction.
3ACHTNUGTREN(UNGN BTC)2] and this MOF after
The IR spectrum of fresh [Cu
(BTC)2] shows the charac-
ACHTUGTNRENG[NU Cu3ACHTUNGTREN(NUNG BTC)2] is a rigid MOF with a zeolites-like structure
and free coordination sites on the copper(II) ion. The free
coordination sites are oriented toward the center of one of
the larger pores.[18] The channel linings can be chemically
functionalized and the aqua ligands can be replaced by
other groups. For example, the treatment of the anhydrate
[Cu
2ACHTGNURTEN(NUNG BTC)3]n with dry pyridine (py) gave [Cu2-
AHCTUNGTRENNUNG
pattern similar to the original structure and therefore dem-
onstrates that chemical functionalization can be achieved
without a loss of structural integrity. During the cyclopropa-
nation reaction, the aqua ligands can be replaced by the car-
bene unit and one carboxylate ligand can be replaced by the
alkene, thus giving the corresponding metallacyclobutane.
The IR spectrum of the copper-containing MOF recorded
after reaction shows new bands at n˜ =1735 cmÀ1, which cor-
responds to the presence of new CO groups (Figure 3). The
spectrum also shows new bands at n˜ =2985, 2933, and
2909 cmÀ1, which can be assigned to the CH frequencies of
the diazoacetate ester of a coordinated carbene unit. This
intermediate formed by a four-centered pathway, involving
favorable interactions between the copper center and the
carbonyl group, appears to be the more facile route when
the diazo compound has carbonyl group(s).
Figure 3. IR spectra before and after the reaction with [Cu3ACTHNUTRGNEN(UG BTC)2].
1705 cmÀ1 may point to a very small amount of free carbox-
ylic groups, but the narrow and intense n(OH) band expect-
ed for an isolated benzenetricarboxylic acid is not observed,
thus confirming that the amount of uncomplexed BTC in
the solid is small.
The reusability of the material together with the fact that
the metal loading (as determined by inductively coupled
plasma atomic emission spectroscopy (ICP-AES)) remained
unchanged after the third cycle excludes the occurrence of
metal leaching from the solid to the liquid. In a control ex-
periment, the reaction was quenched after 15 min, the solid
was filtered, and the copper content of the filtrate was ana-
lyzed to confirm the heterogeneity of the reaction. Induc-
tively coupled plasma optical emission spectrometric (ICP-
OES) analysis revealed that metal leaching was negligible.
The reaction was continued with the filtrate but no further
Catalysis with the gold-containing MOF: The preparative
procedure for the synthesis of IRMOF-3-SI-Au has been re-
ported elsewhere (Figure 4).[5] We used the covalent post-
synthetic methodology to prepare MOFs with open metal
sites for potential use in catalysis. We prepared a MOF con-
taining a goldACTHUNTGRNEUNG(III)/Schiff base complex that lined the pore
walls. The XRD pattern of IRMOF-3-SI-Au corresponds to
a crystalline material with the expected structure. The ab-
sence of a diffraction peak at 2q=38.28 (AuACTHUNRTGNEUNG[111]) excludes
the occurrence of metallic gold particles of ꢀ5.0 nm.
It has recently been reported that the reaction of EDA
with styrene does not proceed in the presence of cationic
gold complexes.[10b] In fact, after four days at room tempera-
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Chem. Eur. J. 2010, 16, 9789 – 9795

Metal–Organic Frameworks as Catalysts for Cyclopropanation
FULL PAPER
are identical to the fresh cata-
lyst. The IR spectra show the
characteristic bands n
ACHTUNGTRENN(UNG C=N), n-
AHCTUNGERTG(NNUN C=C) at n˜ =1654, 1600, and
1575 cmÀ1 and the
nACHTUNGTRENNUNG(Au O)
À
band at the same position
(before and after the reaction;
i.e.,
n˜ =575 cmÀ1).
The
13C NMR spectra present a res-
onance due to the C-O-Au unit
at d=167 ppm. The structural
integrity of the material is basi-
cally preserved after the cata-
lytic use (Figure 5), although
XRD studies indicate a small
decrease in the crystallinity in
the reused sample (Figure 7).
The absence of the [111] peak
of metallic gold on the reused
Figure 4. The postsynthetic modification procedure used to obtain MOFs containing gold
plexes.
ACHTUNGERTN(NUNG III)/Schiff base com-
ture the corresponding cyclopropane-containing product was
not detected. However, when using our IRMOF-3-Si-Au
solid catalyst at room temperature, conversions of up to
42% were obtained for the cyclopropanation of styrene
with EDA (this MOF was also an active catalyst for the cy-
clopropantion of a variety of alkenes with EDA; Table 4).
PhEDA produced better yields in the cyclopropanation of
styrene (Table 4). It appears that gold-containing MOFs can
also be an interesting solid catalyst for cyclopropanation re-
actions, although the activity is lower than for the copper-
containing MOF.
Table 4. Cyclopropanation of alkenes with IRMOF-3-SI-Au[a]
Entry
Alkene
Diazo
compound
t
Yield
[%][b]
d.r.
TON[d]
[h]
[%][c]
1
2
2
3
4
5
styrene
styrene
b-methylstyrene
DMHD
1-octene
EDA
PhEDA
EDA
EDA
EDA
EDA
6
1
15
20
22
2
42
60
40
25
45
50
54
95
59
100
56
100
270
200
240
182
170
130
Figure 5. IR spectra of fresh IRMOF-3-SI-Au and this MOF recovered
after three runs.
cyclohexene
[a] Catalyst loading: 5 mol%. [b] Yield of cyclopropane; the remaining
diazo compound was converted into coupling products. [c] Diastereo-
meric ratio: trans/cis. [d] Calculated as mmol of converted substratem-
molÀ1 of catalyst.
Recycling of the gold-containing MOF: Table 5 and Figures
5, 6, and 7 show the results of the recycling experiments
with IRMOF-3-SI-Au. The IR and 13C magic-angle spinning
(MAS) NMR spectra of the compound after the reaction
Table 5. Recycling experiments of cyclopropanation of 1-octene with
EDA catalyzed by IRMOF-3-SI-Au in CH2Cl2 at room temperature
Run
Conversion
[%][a]
cis/trans
Selectivity
[%][b]
1
2
3
4
60
75
70
65
20:26
25:33
22:29
23:31
85
88
85
85
[a] Conversion after 24 h. [b] Selectivity toward cyclopropanecarboxy-
lates.
Figure 6. Solid-state 13C-MAS NMR spectra of fresh IRMOF-3-SI-Au
and after several runs of the reaction.
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9793

A. Corma et al.
eliminate the spinning side bands, were recorded on a Bruker MSL 400
spectrometer equipped with an FT unit at 100.63 MHz; pulse width: 6 ms,
908; contact time: 2 ms; recycle delay: 5–10. The spinning frequency at
the magic angle (54844’) was 4 KHz. The olefins, EDA, and tert-butyl di-
azoacetate (tBuDA) were purchased from Aldrich. Ethyl 2-phenyldiazoa-
cetate (PhEDA) was prepared according to reported methods.[19] [Cu3-
AHCTUNGRTEG(NNNU BTC)2] (BasoliteC 300 produced by BASF; Figure 1) was supplied by
Aldrich (BET=1500–2100 m2 g). The detailed preparation and character-
ization of IRMOF-3-SI-Au has been reported previously (Figure 4).[5]
General procedure for the cyclopropanation reactions: The diazo com-
pound EDA, PhEDA, or tBuDA (11 mmol) was added to the catalyst
[Cu3ACHTNUGTRNEUNG(BTC)2]: (0.04 mmol) or IRMOF-3-SI-Au (0.0011 mmol) and olefin
(8 mmol) dissolved in dichloromethane (5 mL) either in one portion
before starting the reaction or slowly in a dropwise manner with a sy-
ringe pump over 2 h. Gas evolution was observed along with a smooth
change in color. The resulting mixture was stirred at room temperature
for 24 h. The reaction was monitored by gas chromatography on an
HP5890 II GC–MS chromatograph, cross-linked methyl silicone column
(SPB): 25 mꢆ0.2 mmꢆ0.33 mm; carrier gas: helium; P=20 p.s.i.; injector
temperature: 2308C; detector temperature: 2508C; oven program for sty-
rene: 708C (3 min), 158C minÀ1 to 2008C (5 min); retention times: EDA
3.2 min, styrene 3.82 min, n-decane 5.47 min, diethyl maleate 7.84 min, di-
ethyl fumarate 8.02 min, cis-cyclopropane 10.91 min, trans-cyclopropane
11.41 min. When the nitrogen evolution was finished, the volatiles were
removed and the extract was purified by flash chromatography with ethyl
acetate/hexane (1:9) as the eluent. For the filtration tests, an aliquot of
the reaction suspension was withdrawn at a certain conversion at the re-
action temperature, the catalyst was separated, and the supernatant was
allowed to react further in a separate vial.
Figure 7. XRD pattern of the fresh and reused IRMOF-3-SI-Au catalyst.
catalyst shows that reduction of the gold
not occur during the reaction.
ACHTUNGTREN(NGNU III) center does
Conclusion
We have described the use of MOF materials that contain
either copper or gold centers as catalysts for the cyclopropa-
nation of alkenes with diazoacetates. This example is the
first use of these materials to induce a carbene transfer reac-
tion from diazo compounds. When using ethyl 2-phenyldia-
zoacetate, the copper catalyst showed very high chemo- and
diastereoselectivities toward the trans isomer. Contrary to
previously reported results that employed cationic gold com-
plexes, the gold-containing MOF described herein is active
and selective for the cyclopropanation of styrene with EDA.
Nevertheless, its activity is lower than the copper-containing
MOF. The conventional filtration test and recycling experi-
ments demonstrate that the copper- and gold-containing
MOFs are truly heterogeneous and reusable catalysts. The
advantages of the present protocol include 1) cheap and re-
usable catalysts, 2) a simple workup and separation of the
products from the reaction system that can be achieved by
simple filtration, and 3) a highly selective catalytic system
that performs better than other solid catalysts presented
before. It appears that MOFs can establish a bridge between
homogeneous and heterogeneous catalysts for cyclopropana-
tion reactions.
Acknowledgements
The authors thank the Direcciꢇn General de Investigaciꢇn Cientꢁfica y
Tꢀcnica of Spain (Project MAT2006-14274-C02-01, MAT2006-14274-C02-
02), Consolider Ingenio 2010-MULTICAT. We also thank the PROME-
TEO Project from the Generalitat Valenciana and Fundaciꢇn Areces.
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Experimental Section
Materials and methods: All the preparations and manipulations were car-
ried out in an oxygen-free nitrogen atmosphere using conventional
Schlenk techniques. Metal contents were analyzed by atomic absorption
with
a Perkin–Elmer Analyst 300 atomic-absorption apparatus and
plasma ICP Perkin–Elmer OPTIMA 2100 DV. The IR spectra were re-
corded on
a Bruker IFS 66v/S spectrophotometer (range n˜ =4000–
200 cmÀ1) in KBr pellets. High-resolution 13C MAS or CP/MAS NMR
spectra of powdered samples, in some cases also with a Toss sequence to
9794
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Chem. Eur. J. 2010, 16, 9789 – 9795

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Received: February 2, 2010
Published online: June 11, 2010
Chem. Eur. J. 2010, 16, 9789 – 9795
ꢃ 2010 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
www.chemeurj.org
9795