Insight into the mechanism of diazocompounds transformation catalyzed by hetero cuboidal clusters [Mo3CuQ4(MeBPE)3X4]+, (Q = S, Se; X = Cl, Br): The catalytically active species

Article abstract of DOI:10.1016/j.jorganchem.2007.12.029

Two enantiomerically pure trinuclear compounds of formula (P)-[Mo₃S₄{(R,R)-Me-BPE}₃Br₃]Br and (P)-[Mo₃Se₄{(R,R)-Me-BPE}₃Cl₃]Cl, (P)-1b.Br and (P)-1c.Cl, respectively, have been synthesized in a good yield and a stereospecific manner by excision of polymeric [Mo₃Q₇X₄]_n (Q = S or Se, X = Cl or Br) phases with (R,R)-Me-BPE{1,2-bis[(2R,5R)-2,5-(dimethylphospholan-1-yl)]ethane}. They have been transformed into chiral hetereo cuboidal compounds [Mo₃S₄{(R,R)-Me-BPE}₃Br₃]PF₆, (P)-2b.PF₆, and [Mo₃Se₄{(R,R)-Me-BPE}₃Cl₃]PF₆, (P)-2c.PF₆, by reaction with copper salts. All these compounds have been characterized by ³¹P NMR, IR, UV-Vis, mass spectrometry, elemental analysis, and chiral dichroism. The catalytic potential of tetranuclear cuboidal compounds has been assessed in the paradigm intermolecular cyclopropanation reaction of styrene with ethyl diazoacetate. Results are compared with those obtained for the analogue [Mo₃S₄{(R,R)-Me-BPE}₃Cl₃]PF₆, (P)-2a.PF₆. The catalytic data demonstrate that the Se derivative (P)-2c.PF₆ is less reactive than the S analogues, but it leads to a similar product distribution as the sulfide analogue (P)-2a.PF₆. By contrast, exchange of chlorine by the bulky bromine gives rise to a catalyst which makes the carbene dimerization more competitive. These data agree with temporal breaking of one of the Cu-Q bonds to generate an active catalytic species.

Full text of DOI:10.1016/j.jorganchem.2007.12.029

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Journal of Organometallic Chemistry 693 (2008) 1723–1727
www.elsevier.com/locate/jorganchem
Note
Insight into the mechanism of diazocompounds transformation
+
catalyzed by hetero cuboidal clusters [Mo CuQ (MeBPE) X ] ,
3
4
3 4
(
Q = S, Se; X = Cl, Br): The catalytically active species
a
a,
b,
b
*
*
Eva Guillam o´ n , Rosa Llusar , Julia P e´ rez-Prieto , Salah-Eddine Stiriba
a
Departament de Qu ı´ mica F ı´ sica i Anal ı´ tica, Universitat Jaume I, Avda. Sos Baynat s/n, E-12080, Castell o´ , Spain
Instituto de Ciencia Molecula/ICmol, Universidad de Valencia, Pol ı´ gono la Coma s/n, 46980 Paterna, Valencia, Spain
b
Received 7 December 2007; received in revised form 21 December 2007; accepted 21 December 2007
Available online 8 January 2008
In memory of Professor F. Albert Cotton who passed away on February 20, 2007 and in recognition of his valuable
and enormous contributions to the chemical sciences.
Abstract
Two enantiomerically pure trinuclear compounds of formula (P)-[Mo
3 4 3 3 3 4
S {(R,R)-Me–BPE} Br ]Br and (P)-[Mo Se {(R,R)-Me–
BPE} Cl ]Cl, (P)-1b.Br and (P)-1c.Cl, respectively, have been synthesized in a good yield and a stereospecific manner by excision of poly-
3
3
meric [Mo
They have been transformed into chiral hetereo cuboidal compounds [Mo
Mo Se {(R,R)-Me–BPE} Cl ]PF , (P)-2c.PF , by reaction with copper salts. All these compounds have been characterized by
3
Q
7
X
4
]
n
(Q = S or Se, X = Cl or Br) phases with (R,R)-Me–BPE{1,2-bis[(2R,5R)-2,5-(dimethylphospholan-1-yl)]ethane}.
3
S
4
{(R,R)-Me–BPE} Br ]PF (P)-2b.PF and
3
3
6
,
6
,
3
1
[
P
3
4
3
3
6
6
NMR, IR, UV–Vis, mass spectrometry, elemental analysis, and chiral dichroism. The catalytic potential of tetranuclear cuboidal com-
pounds has been assessed in the paradigm intermolecular cyclopropanation reaction of styrene with ethyl diazoacetate. Results are com-
pared with those obtained for the analogue [Mo S {(R,R)-Me–BPE} Cl ]PF , (P)-2a.PF . The catalytic data demonstrate that the Se
3
4
3
3
6
6
derivative (P)-2c.PF is less reactive than the S analogues, but it leads to a similar product distribution as the sulfide analogue (P)-
6
2
6
a.PF . By contrast, exchange of chlorine by the bulky bromine gives rise to a catalyst which makes the carbene dimerization more com-
petitive. These data agree with temporal breaking of one of the Cu–Q bonds to generate an active catalytic species.
Ó 2008 Elsevier B.V. All rights reserved.
Keywords: Copper; Chalcogene; Phosphane; Chiral; Diazo ester; Cyclopropanation
1
. Introduction
els in bioinorganic issues [2]. Other important features of
their chemistry relate to the potential of species such as
0 0
Mo M S (M = Co, Ni) clusters as molecular models for
3 4
The last decade has witnessed a great interest in the
chemistry of heterodimetallic clusters with cubane-type
the active sites of heterogeneous Co/MoS or Ni/MoS
2 2
industrial catalysts [3]. In addition, [M CuQ {(dmpe) X ]
3 4 3 4
0
+
structures, M M Q (where M = Mo, W; Q = S, Se and
3
4
0
M is a transition metal) because of their numerous and sig-
nificant potential applications [1] in various fields. For
example, metal sulphur clusters are used as enzymatic mod-
cluster cations (M = Mo, W; X = Cl, Br; dmpe = 1,2-
bis(dimethylphosphine)ethane; Q = S, Se) have shown
nonlinear properties as optical limiters [4].
0
Among the many non-aqueous routes to M M Q com-
3
4
pounds, we have developed one which begins with cluster
excision from polymeric {Mo Q X } phases with diphos-
*
Corresponding authors. Tel.: +34 96 472 8086; fax: +34 96 472 8066
3
7
4 n
(
R. Llusar), tel.: +34 96 354 3050; fax: +34 96 354 3274 (J. P e´ rez-Prieto).
+
phanes [4,5]. The trinuclear [Mo Q (diphosphane) X ]
E-mail addresses: Rosa.Llusar@qfa.uji.es (R. Llusar), julia.perez@
3
4
3
3
uv.es (J. P e´ rez-Prieto).
cluster generated possesses C -symmetry, with the Mo Q
3 3 4
0
022-328X/$ - see front matter Ó 2008 Elsevier B.V. All rights reserved.
doi:10.1016/j.jorganchem.2007.12.029

1724
E. Guillam o´ n et al. / Journal of Organometallic Chemistry 693 (2008) 1723–1727
0
The application of compounds containing the Mo M
3
core having one phosphorus atom from the diphosphine
ligand trans to the capping sulphur atom and the other
one trans to the bridging sulphur atom. Such stereospecific
rearrangement around the Mo S core results in structures
with backbone chirality, which has been recently exploited
for the synthesis of enantiomerically pure (P)- and (M)-
Q cuboidal cluster as catalysts for organic reactions is lar-
4
gely unexplored. Exceptions to these are the palladium-
and nickel-based systems, which catalyse the addition of
methanol or carboxylic acids to electron-deficient alkynes
and the intramolecular hydroamination of aminoalkynes,
as well as ruthenium clusters explored as effective catalysts
for the N–N cleavage of hydrazines [7]. In this context, we
3
4
[
Mo S {(R,R)-Me–BPE} Cl ]Cl salts ((R,R)-Me–BPE =
3 4 3 3
(
1
+)-1,2-bis[(2R,5R)-2,5-(dimethylphospholan-1-yl)]ethane,
a.Cl in Scheme 1) by excision of the polymeric {Mo3-
S Cl } phase with (R,R)-Me–BPE and (S,S)-Me–
have recently reported that (P)- and (M)-2a.PF are active
6
catalysts for the intramolecular and intermolecular cyclo-
propanation reactions of diazocompounds, however their
enantioselectivity was found to be low. The mechanism
7
4 n
BPE, respectively [6]. These two chiral compounds
were employed as precursors for enantiomerically pure
heterodimetallic salts of formula (P)-[Mo CuS {(R,R)-
of the diazo transformation catalysed by 2a.PF is still
3
4
6
+
Me–BPE} - Cl ]PF , (P)-2a.PF , and (M)-[Mo S {(S,S)-
not clear. Although the cluster 2a is recovered unchanged
3
4
6
6
3 4
Me–BPE} - Cl ]PF , (M)-2a.PF , as illustrated in Scheme 1.
after completion of the catalytic process, there are
reasonable doubts that it is a catalytic active species. In
fact, it is difficult to explain how the diazocompound can
coordinate to the copper without halogen or chalcogen
decoordination.
3
4
6
6
The synthetic strategy for the preparation of chiral hete-
rodimetallic compounds 2a.PF is efficient and stereospe-
6
cific, therefore, it could be extended to the synthesis of
other analogues. To obtain further insight into the role
of the cubane cluster in the transformation of diazocom-
pounds, we carried out the synthesis of the bromine and
selenium analogues of 2a, such as 2b.PF6 and 2c.PF6
(Scheme 1) and used them in the classic reaction of cyclo-
propanation of styrene with ethyl diazoacetate. The cata-
lytic results demonstrate that the presence of a bulkier
chalcogen decreases the reactivity of the catalyst, but it
leads to a similar product distribution to 2a.PF . By con-
6
trast, the exchange of the halogen by the bulky bromine
gives rise to a catalyst which makes the carbene dimeriza-
tion more competitive. In all the cases, the cyclopropanes
E/Z isomer ratio is close to 2.5/1.0 and the enantioselectiv-
ity is still low.
2. Experimental
2.1. General data
All reactions were carried out under nitrogen atmo-
sphere using standard Schlenck techniques. The polymeric
phases {Mo S X } (X = Cl, Br) [8] and the selenium ana-
3
7
4 n
logue polymeric phase {Mo Se Cl } [8b] were prepared
3
7
4 n
according to methods found in the literature. The chiral tri-
nuclear and hetero cuboidal clusters (P)-1a and (P)-2a were
prepared as described [6]. The remaining reactants were
obtained from commercial sources and used as received.
Solvents for synthesis were dried and degassed by standard
methods before use.
3
1
1
P{ H} NMR spectra were recorded on a Varian
00 MHz spectrometer, using CD Cl as a solvent and
3
2
2
are referenced to external 85% H PO . Electrospray mass
3
4
spectra were recorded on a Micromass Quattro LC
instrument using dichloromethane as solvent. Circular
dichroism measurements were recorded on a JASCO J-810
Scheme 1.

E. Guillam o´ n et al. / Journal of Organometallic Chemistry 693 (2008) 1723–1727
1725
spectropolarimeter. The sample solutions were prepared in
2.4. Preparation of (P)-[Mo Se ((R,R)-Me–
3 4
a 1 cm path length quartz cuvette and measured at 25 °C.
UV–Vis measurements were carried out in a Shimadzu
UV-1603 instrument and the samples were prepared in a
BPE) Cl ](Cl) (1c)
3 3
This compound was prepared by an excision reaction of
the polymeric {Mo Se Cl } phase (0.300 g, 0.306 mmol)
1
-cm path length quartz cuvette, and measured at room
3
7
4 n
temperature. Column chromatography was carried out
using silica gel (60 A).
with (R,R)-Me–BPE (0.355 g, 1.374 mmol) in CH CN
3
˚
(25 mL) under reflux. After 48 h, the reaction mixture
was filtered to remove a small amount of the insoluble
impurities. The resulting filtrate was dried under vacuum,
and the solid was recrystallized from CH Cl /ether mix-
2
BPE) Br ](Br) (1b)
.2. Preparation of (P)-[Mo S ((R,R)-Me–
3 4
3
3
2
2
tures to yield 213 mg (46%) of 1c as a brown solid.
3
1
1
The molecular compound [TBA] [Mo S Br ] (0.150 g,
.102 mmol), where TBA = tetrabutylammonium was
reacted with (R,R)-Me–BPE (0.118 g, 0.457 mmol) in
P{ H} NMR (in CD Cl , 121.44 MHz) d = 54.47 (dd,
2 2
2
3
7
6
ꢀ
1
0
3P), 72.91 (dd, 3P). IR (cm , KBr): 2926 (i), 2864 (i), 953
(i), 1452 (i), 1407 (m), 1067 (m), 921 (d), 694 (m), 626 (m),
459 (d). UV–Vis (nm, CH Cl ): k(e): 442 (6761.90), 245
(55809.52 mol m cm ). ESI-MS (CH Cl , 80 V) m/z:
2 2
1485 [M ]. Anal. Calc. Mo Cl Se P C H : C, 30.94; H,
CH CN (20 mL) under refluxing conditions for 24 h. The
3
2
2
ꢀ1
3
ꢀ1
green solution was filtered to remove a small amount of
undissolved material. The filtrate was concentrated and
then ether was added to form a precipitate. The green solid
was washed with 10 mL of benzene, followed by 30 mL of a
mixture of toluene:acetone (95:5), and finally with ether to
+
3
4
4 6 18 48
5.20. Found: C, 30.30; H, 4.90%.
2.5. Preparation of (P)-[Mo CuSe ((R,R)-Me–
3
4
3
1
1
yield 0.107 g (70%) of 1b:
P{ H} NMR (CD Cl ,
BPE) Cl ]PF (2c)
3 4 6
2
2
1
21.44 MHz) d: 49.31 (dd, 3P), 62.62 (dd, 3P) (second order
0
00
0
00
ꢀ1
system AA A BB B ). IR (cm , KBr): 2926 (i), 2864 (i),
Compound
(P)-[Mo Se ((R,R)-Me–BPE) Cl ](Cl)
3 4 3 3
9
6
2
53 (i), 1452 (i), 1407 (m), 1067 (m), 921 (d), 694 (m),
(0.150 g, 0.099 mmol) 1c reacted with an excess
26 (m), 459 (d). UV–Vis (nm, CH Cl ): 632, 394, 343,
of [Cu(MeCN) ]PF (0.050 g, 0.505 mmol) and TBACl
2
2
4
6
89. ESI-MS (CH CN, 80 V): m/z (%) = 1431 (100)
(0.040 g, 0.140 mmol) in CH Cl (15 mL) for 24 h at room
2 2
temperature. The same procedure described for compound
3
+
[
M ]. Anal. Calc. Mo Br S C H P : C, 33.39; H, 5.62.
3
4 4 42 84 6
Found: C, 33.15; H, 5.41%.
2b was followed to obtain 0,131 g (82%) in yield of
3
1
1
compound 2c, as red solid: P{ H} NMR (CD Cl ,
2
2
ꢀ
1
2
BPE) Br ]PF (2b)
.3. Preparation of (P)-[Mo CuS ((R,R)-Me–
3
121.44 MHz) d: 56.22 (d, 3P), 69.52(d, 3P). IR (cm ,
4
KBr): 2926.89 (i), 2853 (i), 1458 (i), 1260 (m), 1070 (i),
04 (i), 796 (m), 692 (i), 466 (d), 421(d), 360 (d). UV–Vis
(nm, CH Cl ) k(e): 525 (2135.80), 467 (2216.05), 336
3
4
6
9
This cluster was prepared following a similar procedure
to that of (P)-2a [6] but dissolving [Mo S ((R,R)-Me–
2
2
+
(8574.08). ESI-EM (CH Cl , 85 V) m/z: 1514 (M ). Anal.
2 2
3
4
BPE) Br ]Br (0.080 g, 0.060 mmol) and TBABr (0.030 g,
Calc. Mo Cl CuS P F C H : C, 31.14; H, 5.24. Found:
3 4 4 7 6 42 84
3
3
0
.086 mmol) in the presence of an excess of [Cu-
C, 31.64; H, 5.41%.
(
MeCN) ]PF (0.112 g, 0.303 mmol) in 20 mL of THF
4
6
under nitrogen. After refluxing the reaction for 24 h, unre-
acted solid [Cu(MeCN) ]PF was separated by filtration
3. Results and discussion
4
6
and the desired product was precipitated by addition of
ether. The precipitated was filtered off, redisolved in
CH Cl and adsorbed in a silica gel column. The column
3.1. Synthesis of trinuclear and tetranuclear compounds
As in the case of 1a.Cl, the reaction between the chiral
phosphane (R,R)-Me–BPE and [TBA] [Mo S Br ] in
2
2
was first washed with CH Cl and then eluted with a 2 M
2
2
2
3
7
6
KPF solution in acetone, affording a red solution. The
CH CN (20 mL) led to the formation of only one out of
6
3
solution was taken to dryness, redissolved in 15 mL of
CH Cl and filtered in order to eliminate the insoluble
the four possible trinuclear complexes with formula
3
1
[Mo S ((R,R)-Me–BPE) Br ](Br). Data from P NMR
2
2
3
4
3
3
KBr and KPF inorganic salts. Remaining TBABr salt
(two doublets at 49.31 and 62.62 ppm, typical features of
6
0
00
0
00
was removed by several washing with water (4 ꢁ 15 mL).
a second order AA A BB B system) and IR spectroscopy,
mass spectrometry, and elemental analysis for this com-
pound were consistent with the structure of 1b.Br (Scheme
1). The stereochemistry of this compound was considered
as (P) by comparison of its CD spectrum with that of
(P)-1a.Cl [6]; each had a positive sign in its spectrum. On
treatment of (P)-1b.Br with [Cu(MeCN) ]PF /TBABr, the
The dichloromethane phase was dried over MgSO
4
and the resulting solution was taken to dryness to yield
3
1
1
0
1
1
3
2
.050 g (73%) of 2b as a red solid: P{ H} NMR (CD Cl ,
2 2
ꢀ1
21.44 MHz) d: 30.15 (d, 3P), 87.3 (d, 3P). IR (cm , KBr):
419 (i), 940 (i), 840 (i, P–F), 558 (i, P–F), 441 (d), 420 (d),
58 (d). UV–Vis (nm, CH Cl ): 603 (b), 441 (b), 331 (b),
2
2
4
6
+
85 (b). ESI-EM (CH Cl , 85 V) m/z: 1514 (M ). Anal.
chiral hetereo cuboidal cluster (P)-[Mo CuS ((R,R)-Me–
3 4
2
2
Calc. Mo Br CuS P F C H : C, 30.50; H, 5.13. Found:
C, 31.12; H, 5.34%.
BPE) Br ]PF , (P)-2b.PF (Scheme 1), was obtained in
3 4 6 6
3
4
4
7
6
42 84
3
1
good yield [9]. This compound was characterized by
P

1726
E. Guillam o´ n et al. / Journal of Organometallic Chemistry 693 (2008) 1723–1727
NMR (two doublets, at 30.15 and 87.3 ppm), mass spec-
trometry and elemental analysis.
The preparation of the selenium trinuclear salt,
[
Mo Se ((R,R)-Me–BPE) Cl ](Cl) was carried out in a sim-
3 4 3 3
ilar manner as the sulphur analogues. Its structure was
3
1
assigned as (P)-1c.Cl (Scheme 1) on the basis of
P
NMR (two doublet of doublets at 54.47 and 72.91), IR
and UV–Vis absorption as well as CD spectroscopy (posi-
tive sign), mass spectrometry and elemental analysis. The
hetero dimetallic cuboidal compound (P)-2c.PF was also
6
obtained in good yield by reacting (P)-1c.Cl with
Cu(MeCN) PF /KPF . Unfortunately, attempts to obtain
4
6
6
suitable crystals for X-ray diffraction analysis were unsuc-
cessful for all these compounds.
3
.2. Mechanistic studies
The intermolecular cyclopropanation reaction of styrene
with ethyl diazoacetate has been used as model reaction.
Studies have shown that the ligand structure of the metal
complex can have a strong influence on the cyclopropana-
tion yield and in the enantioselectivity of the process (when
chiral complexes are used), but examples in which the Z/E
diastereoselectivity is higher than 2.5 are exceptionally rare
[
10]. The catalytic results with (P)-2b.PF and (P)-2c.PF in
6 6
dichloromethane at reflux are shown in Table 1. The substi-
tution of chlorine in 2a.PF by bromine led to a complex
6
which produced a different product distribution in the dia-
zocompound transformation. Thus, the cyclopropane
products were obtained with a lower yield with (P)-
2
b.PF than with (P)-2a.PF (41% and 77%, respectively).
6 6
The chiral seleno cuboidal (P)-2c.PF led only to slightly
6
lower cyclopropanation yield (70%) than (P)-2a.PF , but
it proved less reactive as needed 12 h for inducing complete
diazo transformation.
6
Scheme 2. Proposed active species involved in the Cu-catalyzed cyclo-
propanation of styrene with ethyl diazoacetate.
Two hypotheses have been posed for the generation of
the active catalytic species: (a) decoordination of the halide
attached to the copper in the dimetallic cuboidal cluster 2 ,
Scheme 2) with diazoacetate ester followed by loss of nitro-
gen would lead to the copper carbenoid schematically
depicted as C (Scheme 2). An unimportant difference in
the product distribution should be expected between
2a.PF and 2b.PF , since the remaining halogen atoms
+
and (b) temporal breaking of one of Cu–Q bonds (Scheme
2
) [11].
On the one hand, in the case of decoordination of the
6
6
halide, reaction of the resulting species (structure A in
are coordinated to the molybdenum atoms, and they are
far away from the active centre. In fact, this was not the
case, and the cyclopropanation yield drastically decreased
Table 1
a
with 2b.PF6.
Catalytic results data
On the other hand, in the case of temporal breaking of
one of the Cu–Q bonds (structure B in Scheme 2) the carbe-
noid would have a structure schematically depicted as D in
Scheme 2. The metal–carbene intermediate could be less
Catalyst
1 mol %)
CH2Cl2 / reflux
COOEt
COOEt
H
Ph
(
+
COOEt
+
N2
Ph
Z
E
stable when it derives from 2b.PF than when it arises from
6
2
a.PF and 2c.PF , due to the higher steric hindrance pro-
6 6
Entry
Catalyst
Time (h)
Yield (%)
E/Z
voked by the bromo atom than the chloro atom attached to
the copper ion. In fact, the side reaction (dimerization of
the free carbene) was more competitive in the case of using
2b.PF6.
1
2
3
a
(P)-2a.PF
(P)-2b.PF
6
5
5
12
77
41
70
2.3
2.6
2.6
6
(P)-2c.PF
6
The carbene dimerization was the side reaction. For a similar and
general setup of the catalytic cyclopropanation reaction of styrene with
ethyl diazoacetate, see Ref. [12].
All the 2.PF complexes showed low enantioselectivity,
6
which could be due to the long-distance between the Cu

E. Guillam o´ n et al. / Journal of Organometallic Chemistry 693 (2008) 1723–1727
1727
active centre and the phosphine ligand, together with an
insufficient bulkiness of the latter.
[4] M. Feliz, J. Garriga, R. Llusar, S. Uriel, M.G. Humphrey, N.T.
Lukas, M. Samoc, B. Luter-Davies, Inorg. Chem. 40 (2001)
6
132.
5] R. Llusar, S. Uriel, C. Vicent, J. Chem. Soc., Dalton Trans. (2001)
813.
6] M. Feliz, E. Guillam o´ n, R. Llusar, C. Vicent, S.-E. Stiriba, J. P e´ rez-
Prieto, M. Barberis, Chem. Eur. J. 12 (2006) 1486.
[
[
[
4
. Summary
2
Our approach to build enantiopure chiral trinuclear
7] (a) I. Takei, Y. Enta, Y. Wakebe, T. Suzuki, M. Hidai, Chem. Lett.
clusters with Mo S Cl core in a stereoselective manner,
3
4
4
3
5 (2006) 590;
as well as enantiopure chiral hetero cuboidal clusters of
the Mo CuS Cl type, has been extended to the bromine
(
b) L. Takei, K. Dohki, K. Kobayashi, T. Suzuki, M. Hidai, Inorg.
3
4
4
Chem. 44 (2005) 3768;
derivative and selenium analogues, (P)-1b.Br, (P)-1c.Cl,
P)-2b.PF , and (P)-2c.PF . The application of the cubane
(c) I. Takei, K. Suzuki, Y. Enta, K. Dohki, T. Suzuki, Y. Mizobe,
M. Hidai, Organometallics 22 (2003) 1790;
T. Murata, Y. Mizobe, H. Gao, Y. Ishii, T. Wakabayashi, F.
Nakano, T. Tanase, S. Yano, M. Hidai, I. Echizen, H. Nanikawa, S.
Motomura, J. Am. Chem. Soc. 116 (1994) 3389.
8] (a) F.A. Cotton, P.A. Kibala, M. Matuz, C.S. McCaleb, R.B.W.
Sandor, Inorg. Chem. 28 (1989) 2623;
(b) V.P. Fedin, M.N. Sokolov, A.O. Gerasko, A.V. Virovets, N.V.
Podberezskaya, V.Y. Fedorov, Inorg. Chim. Acta 81 (1991)
(
6
6
type compounds (P)-2b.PF , and (P)-2c.PF in the cyclo-
6
6
propanation reaction of styrene with ethyl diazoacetate
has been successfully used to obtain insight into the nature
of the active catalytic species. According with the experi-
mental results, we suggest temporal breaking of one of
the Cu–chalcogen bonds to generate the carbenoid
intermediate.
[
[
1
87.
+
9] We have recently demonstrated that copper incorporation in (P)-1a
affords the heterodimetallic cubane-type cluster (P)-2a . In addition,
compound 2b.PF6 shows positive sign in its CD spectrum as
+
Acknowledgement
6
compound (P)-2a.PF . For detailed and comparative studies, see
Ref. [6].
The authors gratefully acknowledge financial support
from the Ministerio de Educaci o´ n y Ciencia (MEC) of
Spain (Grant CTQ2005-09270-C02-01).
[
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