Unprecedented stereoselective synthesis of catalytically active chiral Mo3CuS4 clusters

Article abstract of DOI:10.1002/chem.200500907

Cluster excision of polymeric {Mo₃S₇Cl ₄}_n phases with chiral phosphane (+)-1,2-bis[(2R,5R)-2,5- (dimethylphospholan-1-yl)]ethane ((R,R)-Me-BPE) or with its enantiomer ((S,S)-Me-BPE) yields the stereoselective formation of the trinuclear cluster complexes [Mo₃S₄{(R,R)-Me-BPE}₃Cl ₃]⁺ ([(P)-1]⁺) and [Mo₃S ₄{(S,S)-Me-BPE}₃Cl₃] ⁺ ([(M)-l] ⁺), respectively. These complexes posses an incomplete cuboidal structure with the metal atoms defining an equilateral triangle and one capping and three bridging sulfur atoms. The P and M symbols refer to the rotation of the chlorine atoms around the C₃ axis, with the capping sulphur atom pointing towards the viewer. Incorporation of copper into these trinuclear complexes affords heterodimetallic cubane-type compounds of formula [Mo ₃CuS₄-{(R,R)-Me-BPE}₃Cl₄] ⁺ ([(P)-2]⁺) or [Mo₃CuS₄{(S,S)-Me- BPE}₃Cl₄]⁺ ([(M)-2]⁺), respectively, for which the chirality of the trinuclear precursor is preserved in the final product. Cationic complexes [(P)-1]⁺, [(M)-1]⁺, [(P)-2]⁺, and [(M)-2]⁺ combine the chirality of the metal cluster framework with that of the optically active diphosphane ligands. The known racemic [Mo₃CuS₄-(dmpe)₃Cl ₄]⁺ cluster (dmpe = 1,2-bis-(dimethylphosphanyl)ethane) as well as the new enantiomerically pure Mo₃CuS₄ [(P)-2]⁺ and [(M)-2]⁺ complexes are efficient catalysts for the intramolecular cyclopropanation of 1-diazo-5-hexen-2-one (3) and for the intermolecular cyclopropanation of alkenes, such as styrene and 2-phenylpropene, with ethyl diazoacetate. In all cases, the cyclopropanation products were obtained in high yields. The diastereoselectivity in the intermolecular cyclopropanation of the alkenes and the enantioselectivity in the inter- or intramolecular processes are only moderate.

Full text of DOI:10.1002/chem.200500907

DOI: 10.1002/chem.200500907
Unprecedented Stereoselective Synthesis of Catalytically Active Chiral
Mo3CuS4 Clusters
Marta Feliz,[a] EvaGuillamón, [a] RosaLlusar,* [a] Cristian Vicent,[a] Salah-Eddine Stiriba,[b]
[b]
JuliaPØrez-Prieto,* and Mario Barberis[b]
Abstract: Cluster excision of polymeric
{Mo3S7Cl4}n phases with chiral phos-
phane (+)-1,2-bis[(2R,5R)-2,5-(dimeth-
ylphospholan-1-yl)]ethane ((R,R)-Me-
BPE) or with its enantiomer ((S,S)-Me-
BPE) yields the stereoselective forma-
tion of the trinuclear cluster complexes
copper into these trinuclear complexes
affords heterodimetallic cubane-type
compounds of formula [Mo3CuS4-
{(R,R)-Me-BPE}3Cl4]+ ([(P)-2]+) or
[Mo3CuS4{(S,S)-Me-BPE}3Cl4]+ ([(M)-
2]+), respectively, for which the chirali-
ty of the trinuclear precursor is pre-
served in the final product. Cationic
complexes [(P)-1]+, [(M)-1]+, [(P)-2]+,
and [(M)-2]+ combine the chirality of
the metal cluster framework with that
of the optically active diphosphane li-
gands. The known racemic [Mo3CuS4-
(dmpe)3Cl4]+ cluster (dmpe=1,2-bis-
(dimethylphosphanyl)ethane) as well
as the new enantiomerically pure
Mo3CuS4 [(P)-2]+ and [(M)-2]+ com-
plexes are efficient catalysts for the in-
tramolecular cyclopropanation of 1-
diazo-5-hexen-2-one (3) and for the in-
termolecular cyclopropanation of al-
kenes, such as styrene and 2-phenylpro-
pene, with ethyl diazoacetate. In all
cases, the cyclopropanation products
were obtained in high yields. The dia-
stereoselectivity in the intermolecular
cyclopropanation of the alkenes and
the enantioselectivity in the inter- or
intramolecular processes are only mod-
erate.
[Mo3S4{(R,R)-Me-BPE}3Cl3]+
([(P)-
1]+) and [Mo3S4{(S,S)-Me-BPE}3Cl3]+
([(M)-1]+), respectively. These com-
plexes posses an incomplete cuboidal
structure with the metal atoms defining
an equilateral triangle and one capping
and three bridging sulfur atoms. The P
and M symbols refer to the rotation of
the chlorine atoms around the C3 axis,
with the capping sulphur atom pointing
towards the viewer. Incorporation of
Keywords: asymmetric catalysis
chirality cluster compounds
molybdenum · phosphane ligands
·
·
·
Introduction
metal) cuboidal clusters as catalysts for organic reactions is
largely unexplored; exceptions being the palladium- and
nickel-based systems that catalyze the addition of methanol
or carboxylic acids to electron-deficient alkynes[4–6] and the
Transition-metal chalcogenide clusters with cubane-type
structures, in which the metal and the chalcogen atoms
occupy adjacent vertices in a cube, have been used as simple
models for metalloenzymes and industrial hydrodesulfuriza-
tion processes.[1–3] Despite their relevance as enzymatic
models, the application of these Mo3M’S4 (M’=transition
ꢀ
Mo3RuS4 clusters that are effective for the N N bond cleav-
age of hydrazines.[7]
The development of transition-metal cluster chemistry is
closely related to the existence of rational methods for their
synthesis. In the past twenty years, several efficient ap-
proaches have evolved, namely excision from solid-state
polymers and building-block processes from lower nucleari-
ty synthons. In particular, cluster excision from polymeric
{M3Q7X4}n phases with diphosphanes has been used to pre-
pare a series of complexes of the general formula [M3Q4(di-
phosphane)3X3]+ (M=Mo, W; Q=S, Se; X =Cl, Br).[8] Such
synthetic strategies have been illustrated in the preparation
of the trinuclear [Mo3S4(dmpe)3Cl3]+ sulfido cluster
(dmpe=1,2-bis(dimethylphosphino)ethane), recently report-
ed by us.[9] The specific coordination of the diphosphane
ligand, with one phosphorus atom trans to the capping
[a]Dr. M. Feliz, E. Guillamón, Dr. R. Llusar, Dr. C. Vicent
Departament de Ci›ncies Experimentals
Universitat Jaume I, Campus de Riu Sec
PO Box 224, 12080 Castelló (Spain)
Fax : (+34)964-728-066
E-mail: llusar@exp.uji.es
[b]Dr. S.-E. Stiriba, Dr. J. PØrez-Prieto, Dr. M. Barberis
Instituto de Ciencia Molecular
Universitat de Valencia, c/Vicent AndrØs EstellØs s/n
46100 Burjasot (Spain)
Fax : (+34)963-543-949
E-mail: julia.perez@uv.es
1486
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Chem. Eur. J. 2006, 12, 1486 – 1492

FULL PAPER
sulfur atom and the other trans to the bridging sulfur atom,
results in cubane-type sulfido clusters with backbone chirali-
ty. This trinuclear complex is obtained as a racemic mixture
of the P and M enantiomers.[10] Once the chirality of one
metal center is defined, that of the other two metallic cen-
ters is equally fixed.
formation of diazo compounds, as well as preliminary stud-
ies on the catalytic performance of the chiral cubane-type
cluster in enantioselective carbene transfer reactions, in
both intra- and intermolecular processes.
These complexes react with a second metal to build up
chiral heterodimetallic cubane-type clusters of formula
[M3M’Q4(diphosphane)3X3L]+ (M’=Co, Ni, Cu, and Pd;
L=ligand coordinated to the heterometal) as racemic mix-
tures.[8] However, no studies concerning their resolution or a
strategy for their diastereoselective synthesis have been re-
ported. So far, the catalytic performance of cuboidal
Mo3CuS4 species has never been studied.
Here we report a straightforward preparation of two
enantiomerically pure cuboidal Mo3CuS4 clusters, namely
[(P)-2]+ or [(M)-2]+, based on the diastereoselective and ef-
ficient construction of their trinuclear Mo3S4 precursors,
[(P)-1]+ or [(M)-1]+, respectively, by using either (+)-1,2-
Results and Discussion
The effectiveness of copper(i) compounds for diazo transfor-
mations is well documented.[11] This fact prompted us to in-
vestigate the catalytic activity of the racemic [Mo3CuS4-
(dmpe)3Cl4]+ copper cluster in the intramolecular cyclopro-
panation of 1-diazo-5-hexen-2-one (3), as well as in the in-
termolecular cyclopropanation of alkenes with ethyl diazo-
acetate. Cuboidal complex [Mo3CuS4(dmpe)3Cl4]+ was
prepared readily as a racemic mixture from the reaction of
the [Mo3S4(dmpe)3Cl3]+ complex with CuCl or [Cu-
(CH3CN)4]PF6 in THF at room temperature, as represented
in Scheme 1.[12,13]
bis[(2R,5R)-2,5-(dimethylphospholan-1-yl)]ethane
((R,R)-
Me-BPE) or its enantiomer ((S,S)-Me-BPE). We also pres-
ent the capability of the racemic cluster of formula
[Mo3CuS4(dmpe)3Cl4]+ as an efficient catalyst for the trans-
Abstract in Spanish: La reacción de escisión de la fase poli-
mØrica {Mo3S7Cl4}n con la fosfina quiral (+)-1,2-bis-
[(2R,5R)-2,5-(dimetilfosfolan-1-il)]etano, (R,R)-Me-BPE, o
con su enantiómero, (S,S)-Me-BPE, conduce a la formación
estereoselectiva de los complejos clfflster trinucleares
[Mo3S4(R,R-Me-BPE)3Cl3]+ ([(P)-1]+) y [Mo3S4(S,S-Me-
BPE)3Cl3]+ ([(M)-1]+), respectivamente. Estos complejos
poseen una estructura de cubo incompleto, dónde los µtomos
metµlicos definen un triµngulo equilµtero, con un azufre
unido a tres µtomos de molibdeno y tres azufres puente. Los
símbolos P y M hacen referencia a la rotación de los µtomos
de cloro alrededor del eje C3, con el azufre apuntado dirigido
hacia el observador. La incorporación de cobre a estos com-
plejos trinucleares conduce a compuestos heterodimetµlicos
con estructura tipo cubano de fórmula [Mo3CuS4(R,R-Me-
Scheme 1. General synthetic procedure for [Mo3Cu(diphosphane)3Cl4]+
clusters.
The a-diazoketone was added to a solution of the copper-
containing cluster in dichloromethane under reflux and the
mixture was stirred for 24 hours. The cyclopropanation
product, formulated as [3.1.0]pentan-2-one (4), was obtained
in a 95% yield, as shown in Table 1.[14] The UV-visible and
ESI mass spectra of the resulting solution after the complete
transformation of the diazo precursor indicated that the
Mo3CuS4 cluster remained intact. Besides, no traces of free
phosphane in the solution were detected, as confirmed by
1H and 31P{1H} NMR spectroscopic analysis. In addition, the
racemic cuboidal complex [Mo3CuS4(dmpe)3Cl4]+ was effi-
cient for cyclopropanation of styrene with ethyl diazoacetate
(ca. 80% yield; E/Z=2.4, see Table 2).
BPE)3Cl4]+ ([(P)-2]+)
y
[Mo3CuS4(S,S-Me-BPE)3Cl4]+
([(M)-2]+) donde la quiralidad del precursor trinuclear se
mantiene en el producto final. Los complejos catiónicos [(P)-
1]+, [(M)-1]+, [(P)-2]+ y [(M)-2]+ combinan la quiralidad
del esqueleto clfflster con la de los ligandos difosfina. El clffls-
ter racØmico [Mo3CuS4(dmpe)3Cl4]+ (dmpe=1,2-bis(dimetil-
fosfino)etano), así como los complejos Mo3CuS4 enantiomØ-
ricamente puros [(P)-2]+ o [(M)-2]+ son catalizadores efica-
ces para la reacción de ciclopropanación intramolecular de
1-diazo-5-hexen-2-ona (3) y para la ciclopropanación inter-
molecular de alquenos, estireno y 2-fenilpropeno, con etil dia-
zoacetato. En todos los casos los productos de ciclopropana-
ción se obtienen con rendimientos elevados. La diastereose-
lectividad en la ciclopropanación intermolecular de alquenos
y la enantioselectividad en los procesos tanto inter- como in-
tramoleculares son fflnicamente moderadas.
Table 1. Intramolecular cyclopropanation of a-diazoketone (3) catalyzed
by rac-[Mo3CuS4(dmpe)3Cl4]+ or [(P)-2]+.[a]
Catalyst
Yield of cyclopropane[c] [%]
ee [%]
rac-[Mo3CuS4(dmpe)3Cl4]+[b]
[(P)-2]+
95
84
–
25
[a]Reactions were carried out under a nitrogen atmosphere. [b] rac=rac-
emic. [c]Isolated yields.
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R. Llusar, J. PØrez-Prieto et al.
Table 2. Catalytic cyclopropanation of styrenes with ethyl diazoacetate using catalysts rac-[Mo3CuS4-
(dmpe)3Cl4]+ or [(P)-2]+.[a]
intensities, but opposite signs to
those produced by the (R,R)-
Me-BPE complex. These obser-
vations indicate that these com-
pounds are enantiomers, taking
into account that both CD spec-
tra were recorded at concentra-
tions with equal absorbance in-
tensities in the UV-visible
region. Further evidence is pro-
vided by the fact that these
compounds have the same
31P{1H} NMR spectrum, with
Alkene
Catalyst
Yield of cyclopropane[b] E/Z[c] Z isomer[d] E isomer[d]
[%]
ee [%]
ee [%]
styrene
styrene
rac-[Mo3CuS4(dmpe)3Cl4]+
[(P)-2]+
80
88
84
2.4
2.6
2.6
–
21
12
–
20
16
2-phenylpropene [(P)-2]+
[a]All reactions were carried out under a nitrogen atmosphere. [b]Isolated yields. [c]Determined by 1H
NMR spectroscopy. [d]Determined by GC analysis using a 2,3-di- O-acetyl-6-O-(tert-butyldimethylsilyl) b-
CDX column.
Furthermore, a control experiment was performed to as-
certain that the trinuclear [Mo3S4(dmpe)3Cl3]Cl compound
was catalytically inactive in the a-diazoketone transforma-
tion.
Motivated by the catalytic behavior of this racemic tetra-
nuclear cluster, we decided to investigate the stereoselective
synthesis of a closely related compound. Vahreckamp et al.
have prepared optically active organometallic clusters with
framework chirality based on the presence of four different
elements within the tetrahedron cluster unit.[15] A different
strategy to obtain enantiomerically pure transition-metal
complexes consists of their transformation into diaste-
reoisomers by the use of chiral ligands, and their subsequent
separation by means of crystallization or chromatographic
methods, which is always a time-consuming task. Indeed, the
use of chiral phosphanes in the synthesis of mononuclear
catalysts for enantioselective reactions is prevalent. In this
context, asymmetric induction of mononuclear transition-
metal complexes containing chiral phosphane ligands, such
as (R,R)-Me-BPE and its respective enantiomer (S,S)-Me-
BPE, are well known.[16,17] However, relatively few examples
concerning the preparation of chiral cluster compounds and
cluster-based catalysts with chiral phosphanes as ligands
have been reported.[18] It should also be noted that the syn-
thesis of chiral phosphane ligands containing clusters is very
promising, as the resulting compounds might combine two
sources of chirality, one arising from the chiral phosphane li-
gands (designated as R,R and S,S), and another coming
from the polynuclear cluster framework (designated as P
and M).
Scheme 2. Synthesis of chiral trinuclear clusters.
Figure 1. Circular dichroism spectra of [Mo3S4{(R,R)-Me-BPE}3Cl3]+,
([(P)-1]+, c) and [Mo3S4{(S,S)-Me-BPE}3Cl3]+ ([(M)-1]+, b) in di-
chloromethane at 258C at 1.53”10ꢀ4 m.
Reaction of the chiral diphosphane (R,R)-Me-BPE with
the polymeric {Mo3S7Cl4}n phase showed a unique efficiency
and stereoselectivity in the formation of only one out of the
four possible trinuclear [Mo3S4{(R,R)-Me-BPE}3Cl3]+ dia-
stereoisomers, [(P)-1]+, as represented in Scheme 2.
two doublets of doublets at d=53.79 (three P atoms) and
The circular dichroism (CD) spectrum of [(P)-1]+ shows
two signals at lmax =265 and 416 nm for +450 and
+136 mdeg, respectively (Figure 1). On the other hand, the
reaction of (S,S)-Me-BPE with the {Mo3S7Cl4}n phase
(Scheme 2) led to the selective formation of a unique dia-
stereoisomer [Mo3S4{(S,S)-Me-BPE}3Cl3]+ ([(M)-1]+) also
displaying two signals at lmax =265 and 413 nm with similar
64.77 ppm (three
(AA’A’’BB’B’’) system.
P
atoms), typical features for
a
The absolute configuration for [Mo3S4{(R,R)-Me-
BPE}3Cl3]+ and [Mo3S4{(S,S)-Me-BPE}3Cl3]+ were deter-
mined by X-ray crystallography as P and M, respectively.
An ORTEP representation of these two enantiomers is
given in Figure 2. Both “paddlewheel” structures were
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Chiral Mo3CuS4 Clusters
FULL PAPER
on single crystals and confirmed
by CD measurements, as previ-
ously detailed for its trinuclear
[(M)-1]+ precursor (Figure 3).
+
ꢀ
The Cu Cl distance in [(M)-2]
of 2.18 Š is similar to that
found
for
rac-[Mo3S4Cu-
(dmpe)3Cl4]+ but significantly
longer than that found in other
CuI halide complexes. The CD
spectra of [(P)-2]+ and [(M)-
2]+ are represented in Figure 4,
supporting without ambiguity
the fact that both cubanes are
enantiomers.
The same sequence in the
signs of the CD bands, as illus-
trated in Figures 1 and 4, ob-
tained either for compounds
[(P)-1]+ and [(P)-2]+ or [(M)-
1]+ and [(M)-2]+, can be con-
Figure 2. ORTEP plot of [Mo3S4{(R,R)-Me-BPE}3Cl3]PF6 ([(P)-1]PF6, left) and [Mo3S4{(S,S)-Me-BPE}3Cl3]PF6
([(M)-1]PF6, right) with the atom-numbering scheme (50% probability ellipsoids). Carbon atoms are drawn as
ꢀ
ꢀ
spheres for clarity. Selected bond lengths [Š]: [(P)-1]PF6: Mo Mo 2.8011(8), Mo(1) (m3-S(1)) 2.360(2),
ꢀ
ꢀ
ꢀ
ꢀ
ꢀ
Mo(1) (m-S(2)) 2.327(2), Mo(1) (m-S(2 A)) 2.283(2), Mo(1) P(1) 2.568(2), Mo(1) P(2) 2.641(2), Mo Cl
ꢀ
ꢀ
ꢀ
ꢀ
2.487(2); [(M)-1]PF6: Mo Mo 2.7975(9), Mo(1) (m3-S(1)) 2.362(2), Mo(1) (m-S(2)) 2.322(2), Mo(1) (m-S(2A))
ꢀ
ꢀ
ꢀ
2.282(2), Mo(1) P(1) 2.558(2), Mo(1) P(2) 2.633(2), Mo Cl 2.485(2).
solved in the noncentrosymmetric space group R3 with the
Mo3S4 core located on a three-fold axis. Deviations from the
ideal C3v symmetry are attributable to the specific arrange-
ment of the two phosphorous and one chlorine atoms in the
external sites on each Mo atom. In each case, the uniform
stereochemistry of the diphosphane ligands was observed
with no ambiguity. The refined values of the Flack parame-
ters equal zero for the two absolute structures reported, P
for [Mo3S4{(R,R)-Me-BPE}3Cl3]+ and M for [Mo3S4{(S,S)-
Me-BPE}3Cl3]+. Steric interactions upon ligand coordination
are thought to be responsible for this unprecedented stereo-
selectivity in the preparation of compounds of the Mo3S4
core type.
The X-ray analysis performed on racemic [Mo3CuS4-
(dmpe)3Cl4]+ samples revealed that there was no significant
structural rearrangement on going from the trinuclear to the
tetranuclear complex.[12] Therefore, one would expect that
reaction of cluster [(P)-1]+ or [(M)-1]+ with CuCl would
produce the enantiomerically pure heterodimetallic cuboidal
cluster [(P)-2]+ or [(M)-2]+, respectively.
Figure 3. ORTEP plot of [Mo3CuS4{(S,S)-Me-BPE}3Cl4]CuCl2 ([(M)-
2]CuCl2) with the atom-numbering scheme (50% probability ellipsoids).
Carbon atoms are drawn as spheres for clarity. Selected bond lengths
Subsequent reaction of [(P)-1]+ or [(M)-1]+ with CuCl
proceeded in a similar way to the copper incorporation into
the dmpe-containing trinuclear complex to afford only the
heterodimetallic cubane-type cluster without changes in the
chirality of the trinuclear precursors [Eq. (1) and (2)]:
[Š]: Mo Mo 2.804(2), Mo(1) (m3-S(1)) 2.352(6), Mo(1) (m3-S(2))
ꢀ
ꢀ
ꢀ
ꢀ
ꢀ
ꢀ
2.311(5), Mo(1) (m3-S(2A)) 2.368(5), Mo(1) P(1) 2.590(5), Mo(1) P(2)
ꢀ
ꢀ
ꢀ
2.632(5), Mo(1) Cl 2.458(5), Mo(1) Cu(1) 2.843(3), Cu(1) (m3-S(2))
2.312(5), Cu(1) Cl 2.18(1).
ꢀ
sidered characteristic of the cluster asymmetry, as the chiral
diphosphane does not display electronic transitions in the
l=240–800 nm interval.
With these enantiomerically pure cubane-type clusters in
hand, we performed preliminary studies on the activity and
selectivity of the enantiomerically pure cubane [(P)-2]+
using the intramolecular cyclization of a-diazoketone 3, as
well as the intermolecular cyclopropanation of alkenes (i.e.,
styrene and 2-phenylpropene) with ethyl diazoacetate, as
model catalytic reactions (Tables 1 and 2).[14] In all cases, the
ðPÞ-½Mo3S4fðR,RÞ-Me-BPEg3Cl3Šþ þ CuCl !
ðPÞ-½Mo3CuS4fðR,RÞ-Me-BPEg3Cl4Š
ð1Þ
þ
ðMÞ-½Mo3S4fðS,SÞ-Me-BPEg3Cl3Šþ þ CuCl !
ð2Þ
þ
ðMÞ-½Mo3CuS4fðS,SÞ-Me-BPEg3Cl4Š
In the case of (M)-[Mo3CuS4{(S,S)-Me-BPE}3Cl4]+ ([(M)-2]+),
the absolute configuration was determined by X-ray analysis
Chem. Eur. J. 2006, 12, 1486 – 1492
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R. Llusar, J. PØrez-Prieto et al.
Conclusion
Enantiomerically pure cuboidal complexes, namely (P)-
[Mo3CuS4{(R,R)-Me-BPE}3Cl4]+ ([(P)-2]+)
or (M)-
[Mo3CuS4{(S,S)-Me-BPE}3Cl4]+ ([(M)-2]+) can be readily
and diastereoselectively prepared by using the right chiral
diphosphanes and the adequate polymeric {M3Q7X4}n phase.
Enantiomerically pure clusters containing chiral phosphane
ligands and catalytically active centers of the general formu-
la [M3M’Q4(diphosphane)3X3L]+ could be lead structures
for a new series of chiral catalysts. Ongoing studies are
being directed at developing more efficient cubane-type cat-
alysts by extending this strategy to other chalcogens or/and
catalytically active transition metals, as well as by using
them for other catalytic organic transformations.
Figure 4. Circular dichroism spectra of [Mo3CuS4{(R,R)-Me-BPE}3Cl4]-
CuCl2 ([(P)-2]CuCl2, c) and [Mo3CuS4{(S,S)-Me-BPE}3Cl4]CuCl2
([(M)-2]CuCl2, b) in dichloromethane (1.33”10ꢀ4 and 1.35”10ꢀ4 m, re-
spectively) at 258C.
Experimental Section
General: 31P{1H} NMR spectra were recorded on a Varian 300 MHz spec-
trometer using CD2Cl2 as the solvent and are referenced to external 85%
H3PO4. Electrospray ionization (ESI) mass spectra were recorded on a
Micromass Quattro LC instrument using dichloromethane as the solvent.
Circular dichroism measurements were recorded on a JASCO J-810 spec-
tropolarimeter. The sample solutions were prepared in a quartz cuvette
of 1 cm path length and measured at 258C. UV/Vis measurements were
carried out by using a Shimadzu UV-1603 instrument and the samples
were prepared in a quartz cuvette of 1 cm path length, and measured at
room temperature. The ee values for the cyclopropane products were
based on GC analysis with a 2,3-di-O-acetyl-6-O-(tert-butyldimethylsilyl)
b-cyclodextrin (CDX) column.
cyclopropanation products were obtained in high yields. The
diastereoselectivity in the intermolecular cyclopropanation
of the alkenes and the enantioselectivity in the inter- and in-
tramolecular processes are not very high. The lower enantio-
selectivities observed for the cyclopropanation products of
the chiral-cluster-catalyzed reactions, in comparison with
those produced by copper(i)-containing chiral N-donor li-
gands, could be due to an inherent disadvantage of the
copper-containing cuboidal cluster catalysts.[19] The forma-
tion of the presumably electrophilic copper carbene and the
preferred approach of the incoming alkene to the copper
carbene could mean a reaction can occur when there is not
enough steric hindrance between the substituents at the car-
bene and those at the chiral phosphane, the latter not being
coordinated to the copper ion.[20] At this very early point in
our studies, we can only speculate that the degree of induc-
tion could be raised by a gradual increase of the steric hin-
drance in the chiral pocket constructed by the chiral diphos-
phane in the coordination sphere of the catalytically active
copper center.
To ascertain that the integrity of the cubane clusters re-
mains after catalysis, the corresponding 31P{1H} NMR spec-
tra of [(P)-2]+, before and after its involvement in the cata-
lytic cyclopropanation of styrene with ethyl diazoacetate,
were recorded. The similarity in signal shifts and intensities,
as well as the absence of new signals, provide evidence that
the cubane structure remains intact after catalysis. It should
also be noted that a systematic UV-visible analysis of com-
pound [(P)-2]+, before and after cyclopropanation of sty-
rene, was carried out. In fact, this experiment was extremely
useful to quantify the concentration of the catalyst after the
ethyl diazoacetate transformation. UV-visible spectra moni-
tored at lmax =474 and 529 nm did not show any degradation
of the cubane complex.
All reactions were carried out under a nitrogen atmosphere using stan-
dard Schlenck techniques. The polymeric {Mo3S7Cl4}n phase and the het-
erodimetallic [Mo3CuS4(dmpe)3Cl4]+ complex were prepared according
to literature methods.[21,12] The remaining reactants were obtained from
commercial sources and used as received. Solvents for use in syntheses
were dried and degassed by standard methods before use. Chromato-
graphic work was performed by using silica gel (60 Š).
[Mo3S4{(R,R)-Me-BPE}3Cl3]Cl, [(P)-1]Cl: This compound was prepared
by an excision reaction of the polymeric {Mo3S7Cl4} phase (150 mg,
0.229 mmol) with (R,R)-Me-BPE (267 mg, 1.034 mmol) in acetonitrile
(20 mL) under reflux. After 48 h, the reaction mixture was filtered, the
solvent was removed under vacuum, and the solid was dissolved in di-
chloromethane. Addition of ether (30 mL) caused the complete precipita-
tion of a green solid (280 mg, 92%). 31P{1H} NMR (121.47 MHz, CD2Cl2,
258C): d=53.79 (dd, 3P), 64.77 ppm (dd, 3P) (AA’A’’BB’B’’ system);
UV/Vis
(CH2Cl2):
lmax
(e)=408
(5993.20),
299 nm
(12401.36 molꢀ1 m3 cmꢀ1); ESI-MS (30 V): m/z (%): 1299 (100) [M]+; ele-
mental analysis calcd (%) for Mo3S4Cl4C42H84P6: C 37.85, H 6.36; found:
C 37.81, H 6.38.
[Mo3S4{(S,S)-Me-BPE}3Cl3]Cl, [(M)-1]Cl: This complex was prepared fol-
lowing the procedure described for [(P)-1]Cl but using the enantiomeri-
cally pure (S,S)-Me-BPE phosphane. Yield: 91%; 31P{1H} NMR
(121.47 MHz, CD2Cl2, 258C): d=53.80 (dd, 3P), 64.81 ppm (dd, 3P)
(AA’A’’BB’B’’ system); UV/Vis (CH2Cl2): lmax (e)=408 (6827.60),
299 nm (14165.52 molꢀ1 m3 cmꢀ1); ESI-MS (30 V): m/z (%): 1299 (100)
[M]+; elemental analysis calcd (%) for Mo3S4Cl4C42H84: C 37.85, H 6.36;
found: C 37.84, H 6.47.
[Mo3CuS4{(R,R)-Me-BPE}3Cl4]CuCl2, [(P)-2]CuCl2: Compound [(P)-
1]Cl (80 mg, 0.060 mmol) and an excess of CuCl (36 mg, 0.364 mmol)
were dissolved in dichloromethane (10 mL). The reaction mixture turned
red in 5 min and was stirred for 4 h at room temperature. Then, the re-
sulting solution was filtered under an inert atmosphere and evaporated
to dryness to yield the desired dark red product (76 mg, 88.5%). [a]D20
=
1490
www.chemeurj.org
ꢀ 2006 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
Chem. Eur. J. 2006, 12, 1486 – 1492

Chiral Mo3CuS4 Clusters
FULL PAPER
ꢀ8 (c=0.5 in CHCl3); 31P{1H} NMR
(121.47 MHz, CD2Cl2, 258C): d=61.36
(d, 3P), 68.40 ppm (d, 3P); UV/Vis
(CH2Cl2): lmax (e)=508 (2044), 311 nm
(11207 molꢀ1 m3 cmꢀ1); ESI-MS (30 V):
m/z (%): 1396 (100) [M]+; elemental
Table 3. Crystallographic data for [(P)-1]PF6, [(M)-1]PF6, and [(M)-2]CuCl2.
[(P)-1]PF6
[(M)-1]PF6
[(M)-2]CuCl2
empirical formula
formula weight
crystal system
C42H84Mo3P7S4Cl3F6
1442.29
trigonal
C42H84Mo3P7S4Cl3F6
1442.29
trigonal
C42H84Mo3P7S4Cl6F6Cu2
1530.75
trigonal
a [Š]15.404(2)
b [Š]15.404(2)
15.3572(4)
15.3572(4)
23.0235(13)
4702.5(3)
293(2)
14.5248(8)
14.5248(8)
25.103(3)
4586.4 (6)
293(2)
analysis
calcd
(%)
for
Mo3-
Cu2S4Cl6C42H84P6: C 32.93, H 5.54, S
8.37; found: C 32.96, H 5.56, S 8.19.
c [Š]23.058(7)
V [Š3]4738.4(18)
T [K]293(2)
[Mo3CuS4{(S,S)-Me-BPE}3Cl4]CuCl2,
[(M)-2]CuCl2: This compound was pre-
pared following the procedure de-
scribed for complex [(P)-2]CuCl2 but
using [(M)-1]Cl as the starting materi-
al. Yield: 73 mg (85%). Suitable crys-
tals for X-ray determination for com-
pound [(M)-2]CuCl2 were grown by
slow diffusion of ether into sample sol-
utions in dichloromethane. [a]2D0 =+8
(c=0.5 in CHCl3); 31P{1H} NMR
(121.47 MHz, CD2Cl2, 258C): d=61.32
(d, 3P), 68.35 ppm (d, 3P); UV/Vis
(CH2Cl2): lmax (e)=508 (2192), 311 nm
(11821 molꢀ1 m3 cmꢀ1); ESI-MS (30 V):
m/z (%): 1396 (100) [M]+; elemental
analysis calcd (%) for Mo3Cu2S4Cl6C42H84P6: C 32.93, H 5.54, S 8.37;
found: C 32.94, H 5.52, S 8.15.
space group
Z
R3
3
R3
3
R3
3
m(MoKa) [mmꢀ1]1.068
reflections collected
q range for data collection
unique reflections
goodness-of-fit on F2
R1[a]/wR2[b]
1.528
1.868
12712
11373
6545
1.76 to 29.998
5883 (Rint =0.0367)
1.063
0.0470/0.1230
0.0596/0.1310
ꢀ0.512
1.77 to 28.288
4061 (Rint =0.0532)
1.056
0.0474/0.1193
0.0657/0.1277
0.720 and ꢀ0.874
2.29 to 21.988
2519 (Rint =0.0994)
1.263
0.0710/0.1163
0.1117/0.1250
0.447 and ꢀ0.298
R1[a]/wR2[b] (all data)
residual 1 [eAꢀ3]1.570 and
[a] R1=ꢀjjFo jꢀjFc jj/ꢀFo. [b] wR2=[ꢀ[w(F2oꢀFc2)2]/ꢀ[w(Fo2)2]1/2
.
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X-ray data collection and structure refinement: Suitable crystals for X-
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ꢀ
slow diffusion of toluene into a sample solution of the PF6 salt in di-
chloromethane. Replacement of the Clꢀ anion in clusters [(P)-1]Cl and
[(M)-1]Cl were carried out by using silica gel chromatography, eluting
the product with a saturated solution of KPF6 in acetone. In the case of
complex [(M)-2]CuCl2, crystals were grown under nitrogen in a dry box.
The data collection was performed on a Bruker Smart CCD diffractome-
ter using graphite-monochromated MoKa radiation (l=0.71073 Š) in an
essentially routine manner. The diffraction frames were integrated by
using the SAINT package and corrected for absorption with
SADABS.[22,23] The crystal parameters and basic information relating to
data collection and structure refinement for the three compounds are
summarized in Table 3.
[10]Chiral molecule nomenclature: P stands for plus and M for minus as
they relate to the rotation of chlorine atoms around the C3 axis with
the capping sulfur pointing towards the viewer (see Scheme 2); for a
concise overview, see: E. L. Eliel, S. H. Wilen, Stereochemistry of
Organic Compounds, Wiley-VCH, New York, 1994, Chapter 14.
[11] Comprehensive Asymmetric Catalysis, Vol. 2 (Eds.: A. Pfaltz, E. N.
Jacobsen, H. Yamamoto), Springer, Berlin, 1999.
[12]M. Feliz, J. M. Garriga, R. Llusar, S. Uriel, M. G. Humphrey, N. T.
Lucas, M. Samoc, B. Luther-Davies, Inorg. Chem. 2001, 40, 6132.
[13]The trinuclear [Mo 3S4(dmpe)3Cl3]+ cluster can be alternatively pre-
pared according to the literature method, see: F. A. Cotton, R.
Llusar, C. T. Eagle, J. Am. Chem. Soc. 1989, 111, 4332.
In all three compounds, the positions of the heavy atoms were deter-
mined by using direct methods and successive-difference electron-density
maps using the SHELXTL 5.10 software package.[24] Difference Fourier
maps were carried out to locate the remaining atoms. Refinement was
performed by means of the full-matrix least-squares method based on F2.
All atoms were refined anisotropically except for the fluorine atoms in
compounds [(P)-1]PF6 and [(M)-1]PF6 and carbon atoms in compound
[(M)-2]CuCl2. The positions of all hydrogen atoms were generated geo-
metrically, assigned isotropic thermal parameters, and allowed to ride on
their respective parent C atoms.
CCDC-270138 ([(P)-1]PF6), CCDC-270139 ([(M)-1]PF6), and CCDC-
270140 ([(M)-2]CuCl2) contain the supplementary crystallographic data
for this paper. These data can be obtained free of charge from the Cam-
bridge Crystallographic Data Centre via www.ccdc.cam.ac.uk/data_re-
quest/cif.
[14]For a detailed description of the catalytic cyclopropanation proce-
dure, see: M. Barberis, J. PØrez-Prieto, K. Herbst, P. Lahuerta, Orga-
nometallics 2002, 21, 1667.
[15]H. Vahrenkamp, J. Organomet. Chem. 1989, 370, 65.
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[17]A. A. Boezio, A. B. Charette, J. Am. Chem. Soc. 2003, 125, 1692.
[18]The reaction of the chiral phosphane, namely ( S)-2,2’-bis(diphenyl-
phosphino)-1,1’-binaphthyl, (S)-BINAP, with [H4Ru(CO)12]resulted
in the formation of two isomers. The isomer displaying a bridging
coordination mode of the BINAP ligand was obtained with a unique
stereoselectivity and consists of a chiral compound of the “(S)-Ru4”
core type, see: a) S. P. Tunik, T. S. Pilyugina, I. O. Koshevoy, S. I. Se-
livanov, M. Haukka, T. A. Pakkanen, Organometallics 2004, 23, 568;
b) P. Homanen, R. Persson, M. Haukka, T. A. Pakkanen, E. Nord-
lander, Organometallics 2000, 19, 5568.
Acknowledgements
We thank Generalitat Valenciana (Grants IIARCO/2004/163 and
IIARCO/2004/158) and the “Ministerio de Ciencia y Tecnología” (Grant
BQU2002-00313) for financial support of this work. The European Coop-
eration in the Field of Scientific and Technical Research (COST) Action
D24 (WG-0008-02) is also gratefully acknowledged.
Chem. Eur. J. 2006, 12, 1486 – 1492
ꢀ 2006 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
www.chemeurj.org
1491

R. Llusar, J. PØrez-Prieto et al.
[19]For more details on cyclopropanation reactions catalyzed by copper
complexes of C2- and C3-symmetric chiral N-donor ligands, see:
a) H. Fritschi, U. Leutenegger, A. Pfaltz, Helv. Chim. Acta 1988, 71,
1553; b) D. L. Christenson, C. J. Tokar, W. B. Tolman, Organometal-
lics 1995, 14, 2148.
coordinated copper(i) ion. Examples of pentacoordinated copper(i)
ions have been reported, see: H. Borzel, P. Comba, K. S. Hagen, C.
Katsichtis, H. Pritzkow, Chem. Eur. J. 2000, 6, 914.
[21]F. A. Cotton, P. A. Kibala, M. Matusz, C. S. McCaleb, R. B. W.
Sandor, Inorg. Chem. 1989, 28, 2623.
[20]A plausible mechanism for the cyclopropanation reaction catalyzed
with these copper-containing chiral cuboidal clusters could be the
[22]Bruker Analytical X-ray Systems, SAINT 6.2, Madison, WI, 2001.
[23]G. M. Sheldrick, SADABS empirical absorption program, University
of Gçttingen, Gçttingen (Germany), 1996.
ꢀ
heterolytic cleavage of the Cu S bond, caused by nucleophilic
attack of the diazo compound on the copper active center, which is
subsequently regenerated after completion of carbene transfer to
the alkene. Alternatively, the process may take place through the
formation of copper carbene without any substitution or cleavage of
[24]G. M. Sheldrick, SHELXTL 5.1, Madison, WI, 1997.
Received: July 28, 2005
ꢀ
the Cu S bond of the cuboidal clusters; this would result in a penta-
Published online: November 18, 2005
1492
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ꢀ 2006 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
Chem. Eur. J. 2006, 12, 1486 – 1492