Synthesis and characterisation of new polynuclear copper(I) pyrazolate complexes and their catalytic activity in the cyclopropanation of olefins

Article abstract of DOI:10.1016/S0022-328X(03)00132-3

The reaction of [Cu(CH₃CN)₄](BF₄) with racemic pyrazole-3,5-dicarboxylic acid di-sec-butyl ester (3,5-dicarbo-sec-butoxypyrazole, Hdcsbpz) or with pyrazole-3,5-di-ter-butyl (3,5-di-ter-butylpyrazole, Hdtbpz) quantitatively yields the new [Cu(dcsbpz)]₄ and [Cu(dtbpz)]₄ complexes, respectively. Crystals of [Cu(dcsbpz)]₄ are triclinic, P1?, a =10.9748(7), b =11.8399(8), c =26.5575(17) ?, α =100.605(2), β =90.783(2), γ =105.362(2)°; [Cu(dtbpz)]₄·CH₂Cl₂ is monoclinic, P2₁/n, a =10.902(3), b =19.200(3), c =25.772(4) ?, β =93.86(2)°. Both species contain cyclic tetrameric molecules, with the heterocyclic ligands binding in the common N,N′-exo-bidentate mode; however, the shape and geometry of the inner Cu₄ moiety is remarkably different, as highlighted, for example, by the absolute values of the 1,2 and 1,3 (non-bonding) Cu?Cu interactions. These polynuclear copper(I) pyrazolate complexes catalyse the conversion of alkenes into the corresponding cyclopropane derivatives with interesting diastereomeric excesses. Aiming at the evaluation of their catalytic activities, a systematic study of the cyclopropanation reactions in the presence of ethyl diazoacetate has been performed.

Full text of DOI:10.1016/S0022-328X(03)00132-3

Journal of Organometallic Chemistry 672 (2003) 123Á129
/
www.elsevier.com/locate/jorganchem
Synthesis and characterisation of new polynuclear copper(I)
pyrazolate complexes and their catalytic activity in the
cyclopropanation of olefins
Angelo Maspero *, Stefano Brenna, Simona Galli, Andrea Penoni
Dipartimento di Scienze Chimiche, Fisiche e Matematiche, Universita` degli Studi dell’Insubria, via Valleggio 11, 22100 Como, Italy
Received 9 December 2002; received in revised form 11 February 2003; accepted 19 February 2003
Abstract
The reaction of [Cu(CH3CN)4](BF4) with racemic pyrazole-3,5-dicarboxylic acid di-sec-butyl ester (3,5-dicarbo-sec-butoxypyr-
azole, Hdcsbpz) or with pyrazole-3,5-di-ter-butyl (3,5-di-ter-butylpyrazole, Hdtbpz) quantitatively yields the new [Cu(dcsbpz)]4 and
˚
¯
[Cu(dtbpz)]4 complexes, respectively. Crystals of [Cu(dcsbpz)]4 are triclinic, P
aꢀ100.605(2), bꢀ90.783(2), gꢀ105.362(2)8; [Cu(dtbpz)]4×CH2Cl2 is monoclinic, P21/n, aꢀ
A, bꢀ93.86(2)8. Both species contain cyclic tetrameric molecules, with the heterocyclic ligands binding in the common N,N?-exo-
bidentate mode; however, the shape and geometry of the inner Cu4 moiety is remarkably different, as highlighted, for example, by
the absolute values of the 1,2 and 1,3 (non-bonding) Cu Cu interactions. These polynuclear copper(I) pyrazolate complexes
/
1; aꢀ
/
10.9748(7), bꢀ
/
11.8399(8), cꢀ
/
26.5575(17) A,
/
/
/
/
/
10.902(3), bꢀ
/
19.200(3), cꢀ
/
25.772(4)
˚
/
/
Á Á Á
/
catalyse the conversion of alkenes into the corresponding cyclopropane derivatives with interesting diastereomeric excesses. Aiming
at the evaluation of their catalytic activities, a systematic study of the cyclopropanation reactions in the presence of ethyl
diazoacetate has been performed.
# 2003 Published by Elsevier Science B.V.
Keywords: Catalysis; Cyclopropanation; Pyrazolate; Tetrameric complexes
1. Introduction
play in chemical synthesis. Indeed, cyclopropanes are
versatile intermediates that can be converted into a
variety of useful products by cleavage of the strained
three-membered ring [4]. In addition, the occurrence in
nature of molecules presenting interesting physiological
properties and containing the cyclopropane moiety [5] is
a continuous stimulus to develop new synthetic routes to
functionalised cyclopropanes.
The metal-assisted decomposition of diazocom-
pounds in the presence of alkenes is a highly effective
method to convert olefins into cyclopropanes [1,2];
furthermore, if suitable complexes are employed, even
diastereo- and enantio-selective cyclopropanations of
the unsaturated substrates can be successfully carried
out [3]. The development of new and efficient metal-
based catalytic systems able to induce high diastereo-
meric and/or enantiomeric excesses in the conversion of
alkenes into cyclopropanic rings is an important goal for
chemistry, because of the key role that these derivatives
The intermolecular cyclopropanation of olefins with
elevated diastereo- and enantio-selectivity and promoted
by Cu(I)- and Cu(II)-complexes containing sp2-nitrogen
based ligands, such as C2-symmetric semicorrins [6Á
bis(oxazolines) [9,10] and optically active bipyridines
[11Á13], has been widely explored. Very recently,
/8],
/
relatively high diastereomeric excesses have been also
reported using polypyrazolylborate copper(I) derivatives
[14,15].
* Corresponding author. Tel.:
312386119.
ꢁ
/
39-312386440; fax:
ꢁ/39-
E-mail address: angelo.maspero@uninsubria.it (A. Maspero).
0022-328X/03/$ - see front matter # 2003 Published by Elsevier Science B.V.
doi:10.1016/S0022-328X(03)00132-3

124
A. Maspero et al. / Journal of Organometallic Chemistry 672 (2003) 123Á129
/
Our continuous interest in the coordination chemistry
where Hpz*ꢀHdcsbpz, 1; Hdtbpz, 2.
/
of azolate ligands boosted us to investigate the synthesis
and characterisation of new copper(I) pyrazolate com-
plexes and explore their catalytic activity in the cyclo-
propanation reactions of olefins with ethyl diazoacetate
(EDA). The polynuclear copper(I) pyrazolate complexes
presented hereafter were found to catalyse the conver-
sion of alkenes into the corresponding cyclopropane
derivatives with interesting diastereomeric excesses;
therefore, in the following, we report on their synthesis,
structure and detailed quantitative aspects of their
catalytic activity and selectivity.
The synthetic method employed (Eq. (1)) has been
verified to work well for a large series of pyrazoles,
affording derivatives of general formula [Cu(3,5-R2pz)]n
(Rꢀ/H, Me, COOMe, COO-t-Bu) [16]. Actually, it is
well known that group 11 metals in the ꢁ
/
1 oxidation
state, in the absence of ancillary ligands (e.g. phosphines
or isocyanides), form neutral complexes presenting
singly bridged M(m-pz*)M units with the deprotonated
form of several pyrazoles (Hpz*). The structurally
characterised [M(pz*)]n systems (MꢀCu, Ag and Au)
/
have been found to possess a variety of molecular
arrangements (n ranging from 3 to ꢀ), with a definite
tendency of forming cyclic oligomeric species [17].
The IR spectrum of 1 recorded in the solid state shows
2. Results and discussion
only one strong carbonyl absorption at 1709 cmꢂ1
,
2.1. Synthesis
comparable to the n(CO) value found for the free ligand,
which is due to the CO stretching of the COO-s-Bu arms
and suggests the presence of two equivalent carbonyl
groups not coordinated to the copper(I) metal centres.
The H-NMR spectrum of 1 registered in CD2Cl2 at
room temperature shows, beside a singlet centred at 7.3
The reaction of [Cu(CH3CN)4](BF4) with racemic
pyrazole-3,5-dicarboxylic acid di-sec-butyl ester (3,5-
dicarbo-sec-butoxypyrazole, Hdcsbpz) or with pyra-
zole-3,5-di-ter-butyl (3,5-di-ter-butylpyrazole, Hdtbpz)
in methanol and in the presence of triethylamine
(Section 4) yields quantitatively the new [Cu(dcsbpz)]4
[1] and [Cu(dtbpz)]4 [2] complexes, respectively, as
insoluble white products (Eq. (1))
1
ppm attributable to the C(4)ꢀ/H of the pyrazolate rings,
only one set of signals attributable to the aliphatic
protons of the carbo-sec-butoxy groups in the 3 and 5
positions of the pyrazolate ligand. On lowering the
temperature down to 173 K, the spectral features do not
significantly change. These observations demonstrate
that no, or little, stereochemical information of one (S
Et3N
4[Cu(CH3CN)4]BF4 ꢁ4Hpz+
ꢂCH3CN
[Cu(pz+)]4 ꢁ4(Et3NH)BF4
(1)
Table 1
Catalytic cyclopropanations by copper(I) pyrazolate complexes 1, 2 and 3

A. Maspero et al. / Journal of Organometallic Chemistry 672 (2003) 123Á
/129
125
Table 2
Synoptic table containing relevant stereochemical data for 1, 2a and 3 [18]
[Cu(dcsbpz)]4 (1)
[Cu(dtbpz)]4 (2a)
[Cu(dppz)]4 (3)
Cu1ꢀ
Cu2ꢀ
Cu3ꢀ
Cu4ꢀ
/
Cu2
Cu3
Cu4
Cu1
3.480(2)
3.400(2)
3.403(2)
3.535(2)
3.455
2.963(1)
2.989(1)
2.964(1)
2.972(1)
2.972
3.119(2)
3.131(2)
3.088(2)
/
/
/
3.132(2)
Average Cu
/
Á Á Á
/
Cu
3.118
4.366(2), 4.451(2)
Short Cu
/
Á Á Á
/
Cu diagonal(s) 4.702 (2), 5.061(2) 3.393(1)
86.22(4), 96.20(4), 85.30(4), 92.28(4) 69.73(3), 108.89(4), 69.50(3), 109,32(4) 89.19(4), 90.83(4), 88,61(4), 91.38(4)
Cu CuÁ Á Á
/
Á Á Á
/
/
/
Cu angles
Idealized Cu4 shape
Average Cuꢀ
Average NꢀCuꢀ
Parallelogram
1.870
175.2
Rhombus
1.855
171.6
Square
1.847
179.1
/
N
/
/
N
˚
Distances in A, angles in degree (e.s.d.’s in parentheses).
˚
N 1.870 and 1.855 A;
average NꢀCuꢀN 175.2 and 171.68, for 1 and 2a,
or R) residue is transferred to its partner located on the
nitrogen atoms (average Cuꢀ
/
1
opposite COOR branch. In the case of 2, the H-NMR
spectrum recorded in CD2Cl2 at room temperature
/
/
respectively). (Substituted) pyrazolates alternatively lie
on the different sides of roughly planar Cu4 moieties.
Table 2 contains a summary of chemically relevant bond
distances and angles. With reference to Fig. 1, where the
molecular structures of 1 and 2a are shown [together
with that of [Cu(dppz)]4 (3), characterised some years
exhibits only two singlets (dꢀ/5.9 and 1.4 ppm in a
1:18 ratio), clearly attributable to the C(4)ꢀ
/
H (upfield
signal) and to the equivalent aliphatic protons of the ter-
butyl residues.
Spectroscopic data for compounds 1 and 2 are
consistent with those of polynuclear copper(I) com-
plexes containing metal centres bridged by the hetero-
cycles in the common N,N?-exo-bidentate fashion. The
formulations of both complexes 1 and 2 as tetranuclear
species have been definitively settled by X-ray crystal
structure analyses.
ago [18] (Hdppzꢀ3,5-diphenylpyrazole)], one can see
/
that these species markedly differ in the shape and size
of the basic Cu4 framework: it roughly approximates an
˚
ideal rhombus in 2, with very short (B
/
3.0 A) Cu/
Á Á Á
/
Cu
interactions and a diagonal Cu/
Á Á Á
/
Cu contact of only
˚
3.393(1) A, lower that the shortest (intramolecular)
˚
intermetallic interaction found in 1 [3.400(2), A with
the Cu4 moiety arranged as a slightly bent square].
Differently, in 3, the Cu4 fragment is nearly square, and
the molecule (neglecting phenyls orientations) closely
approaches D2d symmetry.
2.2. Crystal structures
The crystal structures of 1 and 2a (2×
/
CH2Cl2) contain
discrete cyclic copper pyrazolate tetramers, with the
heterocyclic ligands binding in the common N,N?-exo-
bidentate mode and weakly interacting with the neigh-
bouring molecules through van der Waals contacts. In
2a, one crystallographically independent CH2Cl2 mole-
cule is found to be hosted in the crystal lattice. Each
copper atom is nearly linearly coordinated by two
The extreme variety of the Cu
isoelectronic systems (Table 2), reflected by the local
changes in the CuꢀN stereochemistry, may suggest that,
in 1 and 2a, markedly different interactions are present
(including, possibly, d10Ád10 contacts of the aurophilic
type). Actually, invoking subtle steric effects at work in
/
Á Á Á
/
Cu contacts in these
/
/
Fig. 1. Schakal drawing of the tetrameric [Cu(dscbpz)]4, [Cu(dtbpz)]4 and [Cu(dppz)]4 species (1, 2a and 3, left to right). Copper atoms in light grey.
Nitrogen and carbon atoms in dark grey, labelled and unlabelled, respectively. For the sake of clarity, (disordered) aliphatic residues have been
omitted in 2a.

126
A. Maspero et al. / Journal of Organometallic Chemistry 672 (2003) 123Á
/129
Chart 1. Cyclopropanation of alkenes.
the ‘squeezed’ 2a species, which contains the substitu-
ents with the largest cone angle, contrasts with the
observation of its very short intermetallic distances;
consequently, we have no explanation available for such
geometrical versatility.
trans:cis ratios (85:15) and conversion yields were
obtained.
Consistently with the behaviour observed for mono-
olefins, when compounds 1Á3 were employed to catalyse
/
the conversion of conjugated diolefins in the presence of
EDA, the trans-isomer was always favoured. Indeed, on
running parallel experiments with rhodium(II) acetate
(in the same experimental conditions but at 0 8C),
2.3. Catalysis
similar selectivities were obtained (GCÁMS evidences).
/
In order to carry out useful comparisons, along with
the two newly synthesised copper(I) derivatives 1 and 2,
the already known tetranuclear pyrazolate derivative
[Cu(dppz)]4 3, was included in the present catalytic
experiments.
3. Conclusions
The syntheses and structural characterisations of the
new homoleptic [Cu(dcsbpz)]4 and [Cu(dtbpz)]4 cop-
per(I) pyrazolate derivatives have been described. The
compounds reported have been found to possess cata-
lytic activity in the cyclopropanation reactions of
alkenes with interesting diastereoselectivities, the trans-
diastereoisomeric products being favoured in all the
examined cases. The results reported in this paper
hearten us to investigate the synthesis and characterisa-
tion of new copper(I) azolate complexes employing
chiral pyrazoles as ligands, with the aim of obtaining
new Cu(I) chiral catalysts suitable for asymmetric
homogeneous catalytic transformations.
When complexes 1Á3 were dissolved in dichloro-
/
methane under a dinitrogen atmosphere, at room
temperature, in the presence of EDA, the conversion
of olefins into the corresponding cyclopropanes deriva-
tives (Chart 1) was detected (Table 1). With the aim of
minimising EDA decomposition, a large excess of olefin
was employed (Cu:EDA:olefinꢀ1:400:1000 molar ra-
/
tio). Although diethyl maleate and diethyl fumarate
were inevitably observed, the yields in cyclopropanes
esters were good in all examined cases.
Complexes 1 and 2 were found to be active catalysts in
the cyclopropanation of styrene by EDA. The terminal
olefin was transformed into the corresponding cyclo-
propane ester by both copper(I) derivatives with good
yields and moderately high trans-diastereoselectivity
4. Experimental
(88:12ꢀtrans:cis ratio). On the contrary, only a low(er)
/
trans:cis ratio was observed in the cyclopropanation of
styrene and a-methylstyrene with compound 3. How-
ever, when the EDA:olefin molar ratio was raised (for
example, with Cu:EDA:olefin in 1:400:400 ratio), the
diastereoselectivity remarkably increased (up to a trans:-
cis ratio of 89:11 for the conversion of a-methylstyrene
into the corresponding cyclopropane ester). In styrene
cyclopropanation reactions, the trans-isomer is gener-
ally the main product [19]: the vast majority of reported
copper catalysts have provided trans:cis ratios from
All preparations and manipulations were carried out
under dinitrogen atmosphere using conventional
Schlenk techniques. Alkenes employed in catalytic
reactions were taken from new bottles kept at ꢂ
/
25 8C
and their purity grade was confirmed by GCÁ
/MS
control analysis. Solvents were purified and dried by
standard methods. Hdtbpz [20] and [Cu(dppz)]4 [18]
were prepared according to literature procedures.
[Cu(CH3CN)4]BF4 was prepared by following a proce-
dure analogous to that reported for the synthesis of
[Cu(CH3CN)4]PF6 [21], but using aqueous HBF4 in-
stead of HPF6. Infrared spectra were recorded on a BIO
50:50 to 75:25. Increasing the size of
R
on
N2CH2COOR generally enhances enantiocontrol; at
variance, for diastereoselectivity, only a small increase
is observed, except when very bulky substituents are
used, as in the case of 2,6-di-ter-butyl-4-methyl phenyl
(DBA) and dicyclohexylmethyl diazoacetates [9].
1
RAD FTIR 7 instrument while H-NMR spectra were
acquired on a Bruker spectrometer operating at 400
MHz. Quantitative analyses of products were performed
on a Shimadzu GC-17A instrument with a capillary
column PS255 (25 m, 0.25 mm) and coupled with a
QP5000 mass selective detector. X-ray structural deter-
minations were carried out at the Dipartimento di
Interestingly, complexes 1Á3 were also found to be
/
active catalyst in the cyclopropanation of electron-poor
olefins such as cyclohexen-1-one. In all cases, good

A. Maspero et al. / Journal of Organometallic Chemistry 672 (2003) 123Á
/129
127
Chimica Strutturale e Stereochimica Inorganica at the
University of Milan. Elemental analyses were carried
out at the Microanalytical Laboratory of the latter
University.
diffraction data showed that, in the solid, the three
diastereoisomers coexist in disordered tetragonal I41/a
crystals where hydrogen bonded tetramers are found
[22]. However, mix-Hdcsbpz and pure (S,S)-Hdcsbpz
can be distinguished by means of X-ray powder diffrac-
tion (XRPD). The unit cells obtained by a Le Bail
treatment of the XRPD spectra of the two materials are
4.1. Synthesis of pyrazole-3,5-dicarbonyl dichloride
In a 250-ml two-necked round bottom flask, 5 g (29
mmol) of pyrazole-3,5-dicarboxylic acid monohydrate
were suspended in 80 ml of thionyl chloride. The
suspension was refluxed at 120 8C for 6 h; then,
exceeding SOCl2 was removed by distillation and the
precipitation of a white solid took place. The precipitate
was suspended in hexane, the suspension filtered and the
product dried under vacuum and kept under dinitrogen
actually somewhat different (aꢀ
/
21.635(1), cꢀ
/
3
˚
˚
13.789(1) A, Vꢀ
21.603(1), cꢀ13.895(1) A, Vꢀ
[23].
/
6454(1) A for mix-Hdcsbpz; aꢀ
/
3
˚
˚
6485(1) A for (S,S)-)
/
/
4.3. [Cu(dcsbpz)]4 1
atmosphere. (Yield: 85%)*
1764 cmꢂ1, n(CO)*1
H-NMR (CD3CN) d (ppm): 8.0,
C(4)ꢀH.
/
IR: strong absorption at
To a stirred solution of [Cu(CH3CN)4](BF4) (0.252 g;
0.8 mmol) in methanol (4 ml) at room temperature and
under inert atmosphere, the nitrogen ligand Hdcsbpz
(0.223 g; 0.85 mmol) was added in one portion. After 3
min, Et3N was added dropwise. The white solid was
stirred under dinitrogen atmosphere for 2 h, then filtered
under inert atmosphere, washed with cold methanol and
/
/
4.2. Synthesis of pyrazole-3,5-dicarboxylic acid di-sec-
butyl ester (3,5-dicarbo-sec-butoxypyrazole-Hdcsbpz)
[as a mixture of meso-(R,S) and (R,R)/(S,S) forms]
dried under vacuum. (Yield: 90%)*
(330.85 g molꢂ1): Calc. C 47.19, H 5.79, N 8.47; Found:
IR
/
C13H19CuN2O4
Pyrazole-3,5-dicarbonyl dichloride (2.0 g; 10.4 mmol)
and (rac)-2-butanol (4 ml; dꢀ
0.808 g mlꢂ1; 43.6 mmol)
/
C 47.24, H 5.95, N 8.38%*
/
m.p. 166 8C (dec.)*
/
were suspended in degassed dioxane (30 ml), previously
dried with molecular sieves and passed through an
Al2O3 column. A large excess of triethylamine was
then added. The pale yellow suspension was heated at
95 8C for 8 h. The solvent was then removed under
reduced pressure and the crude solid suspended in
diethyl ether. The clear yellow solution was then
evaporated under vacuum and the oil obtained was re-
crystallised by slow addition of an aqueous solution of
CH3COONa. The suspension was eventually filtered
and the white precipitate dried under vacuum. (Yield:
(nujol): absorption at 1709 cmꢂ1. Crystals suitable for
an X-ray structure determination were obtained by slow
evaporation of a saturated pentane solution of 1.
Strictly speaking, such material is a mixture of stereo-
chemically different molecules: also in this case, (S)- and
(R)-sec-butylic residues are likely to be present in a
statistical distribution, leading to a total of 28ꢀ
256
/
possible stereoisomers, which (if idealized D2d symmetry
is chosen) result in 27 different diastereoisomers (most
of them occurring as enantiomeric pairs) [24]. As later
described, this is reflected by the extreme disorder
59%)*
7.51, N 10.44; Found: C 58.21, H 7.46, N 10.45%*
101 8C*
IR: strong absorption at 1719 cmꢂ1
NMR (CD2Cl2) d (ppm): 11 (s, 1H, NꢀH), 7.33 [s,
1H, C(4)pzꢀH], 5.13 [m, 1H, CH(CH2CH3)(CH3)], 1.71
/
C13H20N2O4 (268.14 g molꢂ1): Calc. C 58.19, H
m.p.
1H-
/
affecting, in the crystals, all methylÁ/ethyl fragments of
/
*
/
the aliphatic residues.
The corresponding chiral [Cu((S,S)-dcsbpz)]4 species,
1a, has been synthesised in the same way.
/
/
[m, 2H, CH(CH2CH3)(CH3)], 1.37 [d, 3H,
CH(CH2CH3)(CH3)], 1.0 [t, 3H, CH(CH2CH3)-
(CH3)]*13
C-NMR (CD2Cl2) d (ppm): 160.0 (COOR),
/
4.4. [Cu(dtbpz)]4 2
140.8 [Cpz(3,5)], 111.0 [Cpz(4)], 74.3 [CH(CH2CH3)-
(CH3)], 29.1 [CH(CH2CH3)(CH3)], 19.6 [CH(CH2-
CH3)(CH3)], 9.8 [CH(CH2CH3)(CH3)]. It is worth
noting that the material obtained (mix-Hdcsbpz) consists
of a mixture of three diastereoisomers: the (S,S)-, the
The pyrazolate complex 2 was obtained following the
same synthetic procedure used for complex 1, but
employing 3,5-di-ter-butylpyrazole (Hdtbpz) instead of
1
(R,R)- and the meso-(R,S)-Hdcsbpz species. H-, 13C-
3,5-dicarbo-sec-butoxypyrazole
C11H19CuN2 (242.08 g molꢂ1): Calc. C 54.41, H 7.89,
N 11.54; Found: C 54.01, H 7.98, N 11.54%*m.p.
295 8C (dec.). The crystal used in the X-ray structure
determination was obtained by slow evaporation, under
dinitrogen, of a dichloromethane solution of 2 and was
shown to contain clathrated CH2Cl2.
(Yield:
94%)*
/
NMR and IR spectra of mix-Hdcsbpz were found to be
identical to those measured on pure (S,S)-Hdcsbpz
(m.p. 100 8C), obtained in a parallel synthesis with
pure (S)-sec-butanol, demonstrating the negligible in-
fluence of the absolute stereochemistry at one COOR
residue on the opposite branch. Preliminary X-ray
/

128
A. Maspero et al. / Journal of Organometallic Chemistry 672 (2003) 123Á129
/
3
˚
4.5. Procedure for copper-catalyzed cyclopropanations
3263.7(6) A , Zꢀ
g cmꢂ3, m(MoÁ
Ka)ꢀ
transmission factor 0.84, F(0 0 0)ꢀ
tions (8750 unique) measured, of which 5310 with F2oꢁ
4s(F2o) observed and used to refine 649 parameters to
wR2ꢀ0.264, R1(obs)ꢀ0.078, Gofꢀ1.066 and highest
peak in difference mapꢀ
/
2; Tꢀ
1.35 mmꢂ1, minimum relative
1376. 29753 reflec-
/
298(2) K, rcalc
ꢀ
/
1.350
/
/
To a solution of copper(I) pyrazolate complex (10ꢂ2
mmol) in dichloromethane (15 ml), at room temperature
and under inert atmosphere, EDA and olefin were
/
/
added (catalyst:EDA:olefin molar ratioꢀ
/
1:400:1000).
/
/
/
ꢂ3
˚
Both reagents were added in one portion. The reaction
mixture was kept under stirring until total disappear-
ance of the diazo-compound from solution. The con-
sumption of EDA was monitored by infrared
spectroscopy. The mixture was then worked up by
removing the solvent and the crude product was purified
by column chromatography (dichloromethane:-
/
1.10 e A
.
4.8. Crystal data for 2a
C45H78Cl2Cu4N8, Mꢀ
needle (0.30ꢃ0.08ꢃ0.03 mm), monoclinic, P21/n,
aꢀ10.902(3), bꢀ19.200(3), cꢀ
93.86(2)o, Vꢀ
5382(2) A , Zꢀ
1.303 g cmꢂ3, m(MoÁ 1.69 mmꢂ1, minimum
Ka)ꢀ
relative transmission factor 0.87, F(0 0 0)ꢀ2216. All
9417 unique reflections measured, of which 4440 with
F2oꢁ4s(F2o) observed and used to refine 532 parameters
to wR2ꢀ0.124, R1(obs)ꢀ0.070, Gofꢀ1.002 and high-
est peak in difference mapꢀ
/
1056.21 g molꢂ1, colourless
/
/
˚
/
/
/
25.772(4) A, bꢀ
/
3
˚
hexaneꢀ6:4). All the cyclopropanes obtained were
/
/
/
4; Tꢀ298(2) K, rcalc
/
ꢀ
/
characterised by 1H-NMR and GCÁ
MS. Diastereos-
/
/
/
electivities (trans:cis ratios) were measured by 1H-NMR
of the reaction bulk.
/
/
4.6. Crystallography
/
/
/
ꢂ3
˚
/
0.34 e A
.
Single crystal data for compounds 1 and 2a (2×
/
CH2Cl2) were collected at room temperature on a
Bruker AXS SMART and an Enraf Nonius CAD4
systems, respectively, equipped with graphite-mono-
5. Supplementary material
˚
0.71073 A). Inten-
chromatized MoÁ
/
Ka radiation (lꢀ
/
Crystallographic data (excluding structure factors) for
the structures reported in this paper have been deposited
with the Cambridge Crystallographic Data Centre
supplementary publication nos. CCDC 199 105 and
199 106. Copies of the data can be obtained free of
charge on application to CCDC, 12 Union Road,
sity data were corrected for Lorentz, polarization and
absorption effects (SADABS [25] for 1, c-scans [26] for
2a). The structures were solved by direct methods [27]
and refined with full-matrix least squares calculations on
F2 [28]. Anisotropic temperature factors were assigned
to all non-disordered (vide infra) atoms but hydrogens,
riding their parent atoms with a common isotropic
displacement parameter chosen as 1.2 times that of the
pertinent parent. The above mentioned racemic nature
of the starting material (sec-butylic alcohol) is reflected,
in the crystals of 1, by the high disorder affecting the
aliphatic residues of all esteric 3,5-substituents. A
thorough analysis of the geometrical models potentially
describing such complex disorder, assisted by restrained
refinements of half-occupancy methyl and ethyl resi-
dues, did not converge to any significantly stable
minimum and was therefore discarded. Thus, the model
presented above is truncated at the methylene groups
(see Fig. 1), which, together with their neighbouring
oxygen atoms, show rather large adp’s, probably due to
static disorder; nevertheless, since the inner portion of
the molecule (up to the carboxylic residues) is well
defined, the structural discussion presented remains
fully valid.
Cambridge CB21EZ, UK (Fax: ꢁ44-1223-336033; e-
/
mail: deposit@ccdc.cam.ac.uk).
Acknowledgements
We are indebted to one referee for his fruitful
suggestions. We thank the Dipartimento di Chimica
Strutturale e Stereochimica Inorganica (University of
Milan) for the generous loan of equipment. Andrea
Previtali (University of Insubria) is acknowledged for
his help in supporting our combinatorial calculations by
applying Po´lya’s theory.
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