New copper(I) and silver(I) triazolato-complexes: Synthesis, reactivity and catalytic activity in olefin cyclopropanation

Article abstract of DOI:10.1016/j.jorganchem.2008.02.014

A new class of azolate ligands, deriving from the equimolar condensation of 3,5-diamino-1,2,4-triazole with salicylaldehyde (H₃L¹) and o-anisaldehyde (H₃L²) was prepared. In their anionic form, these species act as bridging moieties upon coordination to Cu(I) and Ag(I), giving rise to the formation of dinuclear complexes with the ligand in the typical N,N′-exobidentate conformation. The copper derivative [Cu(H₂L¹)(CH₃CN)]₂ (1) showed attractive reactivity in the replacement of the labile acetonitrile molecules. In particular, it was possible to isolate a dinuclear copper(I)-carbonyl complex [Cu(H₂L¹)(CO)]₂ (4), by substitution of the nitrile with carbon monoxide. Moreover, the reaction of 1 with ethyl diazoacetate (EDA) in CH₂Cl₂ afforded a mono-carbene product, as established by ¹³C NMR data. Finally, the copper derivative 1 proved to be a highly diastereoselective catalyst in olefin cyclopropanation in the presence of ethyl diazoacetate. In the case of internal alkenes a trans:cis ratio of up to 97:3 was reached. The X-ray structure of a dinuclear Ag(I) complex, namely [Ag(H₂L¹)(PPh₃)]₂ (3), obtained by reacting the polymeric [Ag(H₂L¹)]_n (2), with triphenylphosphine, is also reported.

Full text of DOI:10.1016/j.jorganchem.2008.02.014

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Journal of Organometallic Chemistry 693 (2008) 1870–1876
www.elsevier.com/locate/jorganchem
New copper(I) and silver(I) triazolato-complexes: Synthesis,
reactivity and catalytic activity in olefin cyclopropanation
G. Attilio Ardizzoia *, Stefano Brenna, Fulvio Castelli, Simona Galli *,
Chiara Marelli, Angelo Maspero
`
Dipartimento di Scienze Chimiche e Ambientali, Universita degli Studi dell’Insubria, Via Valleggio, 11, 22100 Como, Italy
Received 30 October 2007; received in revised form 14 February 2008; accepted 14 February 2008
Available online 20 February 2008
Abstract
A new class of azolate ligands, deriving from the equimolar condensation of 3,5-diamino-1,2,4-triazole with salicylaldehyde (H3L1)
and o-anisaldehyde (H3L2) was prepared. In their anionic form, these species act as bridging moieties upon coordination to Cu(I) and
Ag(I), giving rise to the formation of dinuclear complexes with the ligand in the typical N,N0-exobidentate conformation. The copper
derivative [Cu(H2L1)(CH3CN)]2 (1) showed attractive reactivity in the replacement of the labile acetonitrile molecules. In particular,
it was possible to isolate a dinuclear copper(I)-carbonyl complex [Cu(H2L1)(CO)]2 (4), by substitution of the nitrile with carbon mon-
oxide. Moreover, the reaction of 1 with ethyl diazoacetate (EDA) in CH2Cl2 afforded a mono-carbene product, as established by 13C
NMR data. Finally, the copper derivative 1 proved to be a highly diastereoselective catalyst in olefin cyclopropanation in the presence
of ethyl diazoacetate. In the case of internal alkenes a trans:cis ratio of up to 97:3 was reached. The X-ray structure of a dinuclear Ag(I)
complex, namely [Ag(H2L1)(PPh3)]2 (3), obtained by reacting the polymeric [Ag(H2L1)]n (2), with triphenylphosphine, is also reported.
Ó 2008 Elsevier B.V. All rights reserved.
Keywords: Triazole; Copper; Silver; Cyclopropanation; Imine; Homogeneous catalysis
1. Introduction
both experimental [6] and theoretical [7] studies have been
accomplished in order to elucidate the mechanism of olefin
cyclopropanation promoted by Cu-based catalysts. A large
variety of sp2-nitrogen based ligands, such as C2-symmetric
semicorrins [8], bis(oxazolines) [9], optically active bipyri-
dines [10] polypyrazolylborates [11] and diiminophosphor-
anes [12], have been used with the aim of enhancing the
selectivity. Recently, high enantioselectivities were reached
with binaphthyldiimines [13] and chiral bispidines [14].
Our continuous interest in the coordination chemistry of
azolate ligands [15] and in the applications of the corre-
sponding coordination compounds in catalysis [16,18b]
and in material science [15b], prompted us to investigate
the synthesis and characterization of novel copper(I) and
silver(I) triazolate complexes. To this purpose, two new
ligands deriving from the condensation of 3,5-diamino-
1,2,4-triazole with salicylaldehyde and o-anisaldehyde were
prepared (respectively, H3L1 and H3L2, see Scheme 1) and
used as bridging moiety in the synthesis of binuclear Cu(I)
In the last decades, great attention has been dedicated to
the synthesis of cyclopropylic moieties [1]. Indeed, cyclo-
propanes are versatile intermediates that can be converted
into a variety of useful products by cleavage of the strained
three-membered ring [2]. In addition, the occurrence in nat-
ure of molecules presenting interesting physiological prop-
erties and containing the cyclopropane moiety [3] is a
continuous stimulus to develop new synthetic routes to
functionalized cyclopropanes.
One of the most successful methods to achieve this pur-
pose is the metal-assisted decomposition of diazo com-
pounds in the presence of alkenes [4]. Among the others,
copper complexes cover a crucial role in this field [5] and
*
Corresponding authors. Tel.: +39 031 238 6119 (G.A. Ardizzoia).
E-mail addresses: attilio.ardizzoia@uninsubria.it (G.A. Ardizzoia),
simona.galli@uninsubria.it (S. Galli).
0022-328X/$ - see front matter Ó 2008 Elsevier B.V. All rights reserved.
doi:10.1016/j.jorganchem.2008.02.014

G.A. Ardizzoia et al. / Journal of Organometallic Chemistry 693 (2008) 1870–1876
1871
Scheme 1. Synthesis of ligands: R = OH, H3L1; R = OCH3, H3L2.
and Ag(I) coordination compounds. Here we report the
synthesis and characterization of H3L1 and H3L2 and of
the resultant metal complexes, namely [Cu(H2L1)-
(CH3CN)]2, [Cu(H2L2)(CH3CN)]2 and [Ag(H2L1)]n. The
reactivity of the Cu(I) species towards CO or ethyl diazo-
acetate (EDA) and that of the Ag(I) compound towards
PPh3 is presented. The only air stable species obtained,
[Ag(H2L1)(PPh3)]2, was isolated in the form of single crys-
tals suitable for an X-ray analysis: its crystal and molecular
structures are described. Eventually, the high trans-selectiv-
ity shown by the [Cu(H2L1)(CH3CN)]2 copper(I) derivative
in the EDA-assisted cyclopropanation of olefins is
discussed.
D2O, as a further evidence of the presence of free –OH
groups. Moreover, the absence of any N–H stretching in
the infrared spectrum let us ascertain that H3L1 acts as a
mono-anionic ligand, the triazole moiety thus being the
only coordination site of the molecule. Finally, the signal
at 2.09 ppm in the 1H NMR registered in CD2Cl2 was
attributed to acetonitrile molecules bound to the metal cen-
tre. The labile acetonitrile ligands can easily be replaced, as
the reactivity of species 1 with carbon monoxide suggested
(see Section 2.4).
Unfortunately, the low stability towards oxidation
shown by 1, both in the solid state and when dissolved in
common organic solvents, did not allow us to grow single
crystals suitable for X-ray analysis. However, on the basis
of the spectral data presented above and especially by com-
parison with the analogous Ag(I) complex (see Section 2.3),
it was possible to propose a dimeric formulation to com-
plex 1, namely [Cu(H2L1)(CH3CN)]2, and to tentatively
assign a structure to this species (Fig. 1). Despite uncom-
mon among tricoordinated dinuclear compounds possess-
ing a CuN3 chromophore, the boat conformation of the
hexa-atomic [Cu–NN–Cu–NN] ring was postulated
according to our previous studies on similar Cu(I) and
Rh(I) complexes containing azolate bridging ligands [18].
2. Results and discussion
2.1. Synthesis of ligand H3L1
Treatment of 3,5-diamino-1,2,4-triazole with an excess
of salicylaldehyde at 170 °C gave a yellow compound.
Using salicylaldehyde in a fourfold excess with respect to
triazole prevented us from the formation of the mono-con-
densation product, as denoted from the presence of just the
1
imine signal at 9.45 ppm in the H NMR of the product
(Scheme 1). In the IR spectrum (nujol mull), a sharp mN–
band at 3258 cmꢀ1 and mC@N stretchings at 1609 and
2.3. Synthesis and reactivity of [Ag(H2L1)]n (2)
H
1567 cmꢀ1 were detected; the absence of any broad band
in the region between 3300 and 3500 cmꢀ1 let us assume
that the –OH groups of the H3L1 ligand were not involved
in intermolecular O–Hꢁ ꢁ ꢁN hydrogen bonds with the imine
The addition of H3L1 to a solution of AgNO3 in
CH3CN, in the presence of Et3N, afforded an orange spe-
cies, postulated as [Ag(H2L1)]n (2). The polymeric nature
of this derivative can be tentatively assumed from its
remarkable insolubility in all organic solvents and from
its reactivity, comparable to that of formerly reported pyr-
azolate and imidazolate silver(I) coordination compounds
[19]. To prove this assumption, treatment of 2 with PPh3
in CH2Cl2 was exploited and, as already observed with
the analogous [Ag(pz)]n species (pz = pyrazolate) [20],
1
nitrogen [17]. Moreover, in the H NMR, the singlet at
10.99 ppm ascribable to the –OH groups and that at
13.35 ppm due to the N–H proton of the heterocyclic ring
confirmed the lack of any O–Hꢁ ꢁ ꢁN interactions.
Noteworthy, the presence of four coordination sites
makes H3L1 a very versatile species, which could poten-
tially act even as a trianionic tetradentate (O–N–N–O)
ligand, tuning its behaviour against the hard–soft proper-
ties of the metal involved.
2.2. Synthesis of [Cu(H2L1)(CH3CN)]2 (1)
When a suspension of [Cu(CH3CN)4]BF4 in CH3CN
was treated with H3L1 in a 1:1 ratio in the presence of
Et3N, the formation of a yellow complex 1 immediately
occurred. In this species, the –OH groups of the former sal-
icylaldehyde are not involved in the coordination to the
metal, as confirmed by the resonance at about 12 ppm in
1
Fig. 1. Proposed molecular structure for complex 1.
the H NMR. This signal disappears after treatment with

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resulted into the cleavage of the polymeric chain and
formation of the binuclear [Ag(H2L1)(PPh3)]2 compound
(3), whose nature was confirmed by an X-ray analysis
(see below). The single resonance at 6.44 ppm in the
31P NMR spectrum of 3 was clearly attributed to the two
2.4. Reactivity of [Cu(H2L1)(CH3CN)]2 (1) with CO
Bubbling of CO for 4 h at room temperature through a
suspension of species 1 in CH2Cl2 resulted in the formation
of a Cu(I)-carbonyl complex derived from the substitution
of both CH3CN molecules with CO, as confirmed by the
strong and sharp stretching visible in the IR spectrum
(nujol mull) at 2105 cmꢀ1. The mCO clearly speaks for a ter-
minal CO bonded to a tri-coordinated copper centre, in
accordance with other examples reported in the literature
[18,21]. The presence of a single absorption is consistent
with the complete replacement of CH3CN by CO, giving
rise to a binuclear symmetrical complex formulated as
[Cu(H2L1)(CO)]2 (4).
A first attempt to prepare complex 4 directly from a sus-
pension of [Cu(CH3CN)4]BF4 in CH3CN, in the presence
of H3L1 and Et3N, under CO atmosphere, failed, complex
1 being the only species isolated. This could undoubtedly
be attributed to the competition between CO and CH3CN
in binding to the metal centre, the latter being favoured due
to its large excess. In contrast, when the same reaction was
carried out using a less coordinating solvent, like acetone,
instead of acetonitrile, a partial substitution took place.
Better results could eventually be obtained by conducting
the reaction in CH2Cl2, from which species 4 could be
isolated in good yields. Unfortunately, the extremely low
stability of [Cu(H2L1)(CO)]2 in solution together with the
rare affinity of Group 11 metals to carbon monoxide [22],
did not allow us to fully characterize it with an X-ray
analysis.
1
phosphines bonded to the Ag(I) centres. In the H NMR,
the presence of a broad weak signal at 12.97 ppm, disap-
pearing after treatment with D2O, was related to the pres-
ence of free –OH groups on the H2L1 moiety, this
suggesting a mono-anionic ligand coordinating in the
N,N0-exobidentate mode. Species 3 was isolated in the form
of single crystals suitable for an X-ray diffraction structural
characterization.
The crystal structure of compound 3 is composed by
dimers of [Ag(H2L1)(PPh3)]2 formula (Fig. 2) lying on a
crystallographic twofold axis, the asymmetric unit being
composed by one silver(I) ion, one H2L1 and one PPh3
ligands. Each metal centre possesses a slightly distorted
trigonal stereochemistry and is coordinated to two triazole
nitrogen atoms of two distinct H2L1 moieties and to the
phosphorous atom of one phosphine ligand. The two
H2L1 ligands, acting in the N,N0-exobidentate mode, bridge
˚
metal centres 3.72 A apart, and form dimers in which the
six-membered rings composed by the four coordinated
nitrogen atoms and the two silver(I) centres adopt a
boat-shape disposition, as already encountered in the
above mentioned Cu(I) and Rh(I) derivatives with
3,5-disubstituted pyrazolates [18]. The oxygen atoms of
the –OH groups are not involved in the coordination to
the metal centres, as expected for a metal with soft nature
like Ag(I). Nevertheless, intermolecular hydrogen bonds of
moderate strength (H–Dꢁ ꢁ ꢁA 2.63 A) are present between
2.5. Reactivity of [Cu(H2L1)(CH3CN)]2 (1) with ethyl
diazoacetate
˚
the hydroxy groups and the neighbouring iminic nitrogen
atoms.
By analogy, we could assume that also in the Cu(I)
derivative 1 the triazole moiety is the only one bonded to
the metal, the residual coordination sites being occupied
by CH3CN.
The mechanism of diazoacetates decomposition in the
presence of olefins and promoted by Cu(I) catalysts is still
under investigation, and the isolation of the postulated
Cu-carbene intermediate represents one of the main goals
in this field [23]. Consequently, considering the preliminary
information we had on the copper(I) derivatives, we inves-
tigated the reactivity of complex 1 with ethyl diazoacetate.
When a suspension of 1 in CH2Cl2 was treated with an
excess of EDA, the formation of a solution occurred and
a brown solid 5 could be isolated in good yield after addi-
tion of Et2O and pentane. The infrared spectrum (nujol
mull) of 5 showed a strong absorption at 1744 cmꢀ1, attrib-
utable to the COOEt group of EDA. The same stretching
was noted after registering the spectrum in solution
(CH2Cl2), with only a slight downfield shift (1722 cmꢀ1),
to be compared with the mCO at 1692 cmꢀ1 registered for
a solution of the starting EDA in CH2Cl2. The change of
the carbonyl frequency and the disappearing of the mNN
at 2114 cmꢀ1 could be correlated to the formation of a car-
1
bene species. The H NMR (CD2Cl2) did not provide any
useful information, this complex being fluxional even at
ꢀ90 °C. On the contrary, the 13C{1H} NMR gave satisfac-
tory information thanks to the occurrence of a broad signal
Fig. 2. Ortep representation, at a 20% probability level, of the dimeric
[Ag(H2L2)(PPh3)]2 moiety present in species 3. O–Hꢁ ꢁ ꢁN hydrogen bonds
depicted with fragmented lines.

G.A. Ardizzoia et al. / Journal of Organometallic Chemistry 693 (2008) 1870–1876
1873
at 169 ppm, attributable to the CHCOOEt group. It is
worth mentioning that the resonance at 169 ppm in
13C NMR could also derive from the insertion of the carbe-
nic fragment into the O–H bond of the ligand [24].
As a further piece of evidence for the presence of the
CHCOOEt fragment in the molecular structure of 5, we
reacted it with cyclohexene in CH2Cl2. The stoichiometric
formation of the corresponding cyclopropane esters took
place, as detected via GC–MS analysis of the crude
product. Moreover, after addition of an excess of EDA
(5/EDA ratio: 1/20), the catalytic conversion of the olefin
into the esters took place, thus suggesting the intermediate
nature of derivative 5 into the catalytic cycle.
In order to determine whether this side-reaction or the
formation of the desired carbene took place, a new ligand
bearing a –OCH3 group instead of the –OH functionality
was prepared. When 3,5-diamino-1,2,4-triazole was treated
with an excess of o-anisaldehyde in refluxing ethanol, a
yellow solid could be isolated (H3L2). The 1H NMR
revealed the occurrence of the resonance due to the iminic
proton at 9.43 ppm, together with that of the OCH3 group
at 3.88 ppm. The broad signal at 12.02 ppm, disappearing
after treatment with D2O, was attributed to the N–H pro-
ton of the triazole portion. The typical HC@N resonance
at 157.46 ppm in the 13C NMR gave a final confirmation
of the iminic nature of the ligand.
2.6. Cyclopropanation reactions
When complex 1 was suspended in dichloromethane
under inert atmosphere, in the presence of EDA, the con-
version of olefins into the corresponding cyclopropane
derivatives took place. Together with the desired products,
diethyl maleate and diethyl fumarate, deriving from EDA
self-coupling [25], were always detected. In order to mini-
mize these side-reactions, addition of a large excess of ole-
fin (namely, a Cu:EDA:olefin = 1:100:250 molar ratio) was
employed. As reported in Table 1, the yields in cyclopro-
pane products were excellent in all the runs performed.
Complex 1 showed to be a highly active catalyst in the
cyclopropanation of both terminal (entries 1 and 2) and
internal olefins (entries 3 and 4). As reported in the litera-
ture, in the conversion of styrene into the corresponding
cyclopropane esters, most of the copper(I) catalysts pro-
vided the trans isomer as the main product [26], the com-
mon trans:cis ratio ranging from 50:50 to 75:25.
Increasing the size of R on N2CHCOOR enhances enantio-
control, while the diastereoselectivity is not usually affected
by steric effects, except when very bulky substituents are
used, as in the case of 2,6-di-tert-butyl-4-methyl phenyl
(BDA) diazoacetate [27]. Also species 1 confirmed this
trend, providing a 70:30 trans:cis ratio in the catalytic
cyclopropanation of styrene, as reported for other
Cu(Schiff-base) catalysts with substituted salicylaldehydes
[28]. Unfortunately, a lower trans-diastereoselectivity was
observed using a-methylstyrene as substrate (entry 2).
On the contrary, complex 1 exhibited a remarkable dia-
stereoselectivity in the cyclopropanation of internal olefins.
In the case of cyclohexene, a 92:8 exo:endo ratio was
achieved, while with 2-cyclohexen-1-one the endo isomer
was detected only in traces. This behaviour could probably
be ascribed to the higher steric hindrance of the internal
double bond of the olefin with respect to the terminal
Treatment of a suspension of [Cu(CH3CN)4]BF4 and
H3L2 in CH3CN, with Et3N, resulted in the formation of
an orange solid. On the basis of spectroscopic and analyt-
ical data it was identified as complex 6. Complex 6 revealed
to be comparable to the analogous species 1, and was for-
mulated as [Cu(H2L2)(CH3CN)]2. Specially, the resonances
at 3.84 ppm (OCH3 group) and 1.95 ppm (CH3CN mole-
1
cule) in the H NMR of 6 registered in CD2Cl2, supported
this structural assignment.
A dichloromethane suspension of [Cu(H2L2)(CH3CN)]2
treated with an excess of EDA afforded a brown solution
from which, after addition of diethylether and pentane, a
brown solid 7 could be recovered. The nature of complex
7 was conclusively established by spectroscopic data: the
infrared spectrum (nujol mull) indicated a strong absorp-
tion at about 1740 cmꢀ1, while the 13C{1H} NMR gave a
signal at 168 ppm. This could be easily attributed to the
presence of a coordinated –COOEt group, the insertion
into a –OCH3 group being in this case impossible. The
comparable reactivity with EDA of complex 6 and complex
1 strongly supported the carbenic nature of species 5. The
latter could thus be finally formulated as [Cu2(H2L1)2(CH-
COOEt)(CH3CN)], as depicted in Scheme 2. The two cop-
per centres are both tri-coordinated, one of them with a
carbenic CHCOOEt moiety on the apical position of the
hexa-atomic Cu–N–N–Cu–N–N ring. The coordination
of an acetonitrile molecule on the other metal centre was
confirmed by the 13C{1H} NMR of 5 (CD2Cl2), showing
a resonance at about 27 ppm (CH3CN).
Scheme 2. Formation of the carbene complex 5.

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G.A. Ardizzoia et al. / Journal of Organometallic Chemistry 693 (2008) 1870–1876
Table 1
Consistently with the behaviour observed for mono-ole-
fins, when complex 1 was used to catalyze the conversion of
conjugated diolefins into the corresponding cyclopropanes
(entry 5), the trans isomer was always the major product.
Indeed, on running parallel experiments (performed at
0 °C) using rhodium(II) acetate as a reference catalyst, sim-
ilar selectivities were achieved, as supported by GC–MS
analysis.
Catalytic cyclopropanation of olefins mediated by complex 1a
Entry
Olefin
Yield (%)
trans:cis ratio
1
2
3
4
5
a
Styrene
a-Methylstyrene
Cyclohexene
2-Cyclohexen-1-one
2,5-Dimethyl-2,4-hexadiene
84
92
88
85
78
70:30
55:45
92:8
97:3
62:38
Reaction conditions: CH2Cl2, RT, catalyst:EDA:olefin molar ratio
1:100:250.
3. Conclusions
one. As a result, in the substitution of the labile acetonitrile
molecule, the internal olefin coordinates in a preferred
direction to the copper.
The synthesis, characterization and reactivity of new
Cu(I) and Ag(I) complexes with triazolate ligands, namely
[Cu(H2L1)(CH3CN)]2 (1) and [Ag(H2L1)]n (2), have been
reported. Complex 1 proved to be an active catalyst in ole-
fins cyclopropanation in the presence of EDA, under very
mild conditions. Especially in the case of internal olefins,
this compound revealed remarkably high selectivities
towards the formation of the trans isomer. On the basis
of spectroscopic and analytical evidences, the intermediate
presence of a copper(I) carbene species has also been
postulated.
In order to attain more insights about the possible
mechanism, a competitive experiment was performed
employing cyclohexene and 2-cyclohexen-1-one as sub-
strates. Given that 2-cyclohexen-1-one exhibits better
p-acidic properties, can be considered as a better coordi-
nating olefin to the Cu(I) centre [29]; on the contrary, the
presence of the withdrawing carbonyl group causes the
deactivation of 2-cyclohexen-1-one towards the attack of
an electrophilic carbene [1]. Monitoring (GC–MS) the for-
mation of cyclopropanes from an equimolar solution of
cyclohexene and 2-cyclohexen-1-one discloses better con-
versions of 2-cyclohexen-1-one with respect to cyclohexene
(ratio about 1/3 of cyclopropanes derived from cyclohex-
ene with respect to 2-cyclohexen-1-one). Moreover, parallel
experiments carried out employing the pure olefins, reveal a
reduction of the activity on cyclopropanation of 2-cycloh-
exen-1-one due to the presence of concurrent cyclohexene.
However, a similar effect also occurs on conversion of
cyclohexene: i.e. pure cyclohexene shows better conversion
to the corresponding cyclopropanes with respect to a 1:1
cyclohexene/2-cyclohexen-1-one mixture. Indeed, when in
mixture, cyclohexene shows a larger conversion decrement
with respect to that observed for cyclohexen-1-one (ꢀ56%
vs. ꢀ38% for cyclohexen-1-one).
4. Experimental
4.1. General procedures
All reactions were carried out under purified nitrogen
using standard Schlenk techniques. The solvents were dried
and distilled according to standard procedures prior to use.
Alkenes employed in the catalytic reactions were taken from
new bottles kept at ꢀ20 °C and their purity grade was
confirmed by GC–MS control analysis. Salicylaldehyde,
o-anisaldehyde, 3,5-diamino-1,2,4-triazole, triethylamine,
triphenylphosphine, ethyl diazoacetate and silver nitrate
(Aldrich) were used as purchased. [Cu(CH3CN)4]BF4 was
prepared as reported in the literature [32].
Infrared spectra were recorded on a Shimadzu Prestige
21 FTIR, NMR spectra were acquired on a Bruker 400
Avance instrument, elemental analyses were obtained with
a Perkin–Elmer CHN Analyser 2400 Series II. Quantitative
analyses of products were performed on a Shimadzu
GC-17A gas chromatograph with a PS225 capillary
column (25 m, 0.25 mm) equipped with a QP5000 mass
selective detector.
The mutual interference of different olefins on the cata-
lyst activity jointly to the high diastereoselectivity showed
by both substrates, seem to suggest a mechanism involving
attack of a copper carbene to a coordinated olefin, proba-
bly through an intermolecular path, rather than a mechani-
cistic pathway involving uncoordinated olefins.
A
mechanism that involves coordination of the olefin prior
to the attack of the carbene moiety is probably also respon-
sible of the high activity and diastereoselectivities showed
in the cyclopropanation of a deactivated (but better coordi-
nating) substrate as 2-cyclohexen-1-one.
4.2. Synthesis of ligand H3L1
Together with mono-alkenes, also dienes were employed
as substrates in the copper-catalyzed cyclopropanation
reactions. Indeed, 3-(1-isobutenyl)-2,2-dimethyl cyclopro-
panecarboxylic acid (chrysanthemic acid) is a key interme-
diate of pyrethroid insecticides [30] and the conversion of
2,5-dimethyl-2,4-hexadiene (DMHD) into the correspond-
ing chrysantemate esters by means of diazoacetates contin-
uously represents a fundamental target in industrial
applicable processes [31].
A suspension of 2 g (0.02 mol) of 3,5-diamino-1,2,4-tria-
zole in 9 ml (0.08 mol, d = 1.146 g/ml) of salicylaldehyde
was heated at 170 °C for 6 h. The crude product was sus-
pended in ethanol, and the resulting suspension was fil-
tered. The resulting yellow solid (H3L1) was washed with
diethylether and dried under vacuum. Yield: 60%.
1H NMR (acetone-d6, RT): 7.00 (d, 2H, Jo = 8.3 Hz),
7.03 (t, 2H, Jo = 7.6 Hz), 7.50 (t, 2H, Jo = 7.3 Hz), 7.73
(d, 2H, Jo = 7.9 Hz), 9.45 (s, 2H, HC@N), 10.99 (s, 2H,

G.A. Ardizzoia et al. / Journal of Organometallic Chemistry 693 (2008) 1870–1876
1875
OH), 13.35 (s, 1H, NH). 13C NMR (acetone-d6, RT):
117.50, 119.16 (CCH@N), 120.01, 133.96, 134.57, 155.48
(NCN), 162.02 (C–OH), 167.65 (HC@N). Anal. Calc. for
C16H13N5O2: C, 62.53; H, 4.26; N, 22.79. Found: C,
62.14; H, 4.37; N, 22.35%.
gle crystals suitable for X-ray diffraction were obtained by
slow evaporation of a saturated solution of 3 in diethyl-
ether. Anal. Calc. for C68H54Ag2N10O4P2: C, 60.37; H,
4.02; N, 10.35. Found: C, 60.18; H, 4.18; N, 10.13%.
4.7. Synthesis of [Cu(H2L1)(CO)]2 (4)
4.3. Synthesis of ligand H3L2
A suspension of 1 g (0.01 mol) of 3,5-diamino-1,2,4-tria-
zole and 5.5 g (0.04 mol) of o-anisaldehyde in 20 ml of eth-
anol was refluxed for 24 h. The light yellow solid (H3L2)
was then filtered off and washed with hot ethanol and
diethylether. Yield: 54%.
(a) A suspension of 100 mg of 1 (0.27 mmol) in 20 ml of
dichloromethane, previously degassed with CO, was
kept under CO atmosphere at room temperature for
4 h. The suspension was then filtered off and the resul-
tant yellow solid (4) was kept under N2 at ꢀ20 °C.
(b) To a suspension of 600 mg of H3L1 (1.95 mmol) in
30 ml of acetone or dichloromethane kept under
CO flow, 500 mg (1.59 mmol) of [Cu(CH3CN)4]BF4
and 300 ll (2.16 mmol) of Et3N were added. After
standing for 4 h at room temperature, the solid was
filtered off and kept under nitrogen at ꢀ20 °C.
1H NMR (DMSO-d6, RT): 3.88 (s, 6H, OCH3), 7.04 (t,
2H, J = 7.5 Hz), 7.12 (d, 2H, J = 8.4 Hz), 7.49 (dd, 2H,
Jo = 7.8 Hz, Jm = 1.3 Hz), 8.03 (dd, 2H, Jo = 7.7 Hz,
Jm = 1.4 Hz), 9.43 (s, 2H, HC@N), 12.02 (s, 2H, NH).
13C NMR (DMSO-d6, RT): 112.84, 121.59, 124.49
(CCH@N), 127.33, 134.20, 152.31 (NCN), 157.46 (HC@
N), 160.36 (C–OCH3). Anal. Calc. for C18H17N5O2: C,
64.47; H, 5.11; N, 20.88. Found: C, 64.10; H, 5.32; N,
20.47%.
Anal. Calc. for C34H24Cu2N10O6: C, 51.32; H, 3.04; N,
17.60. Found: C, 51.12; H, 3.16; N, 17.21%.
4.4. Synthesis of [Cu(H2L1)(CH3CN)]2 (1) and
[Cu(H2L2)(CH3CN)]2 (6)
4.8. Reaction of [Cu(H2L1)(CH3CN)]2 (1) with ethyl
diazoacetate (EDA)
To
a
suspension of the corresponding ligand
To a suspension of 200 mg of 1 (0.54 mmol) in 10 ml of
dichloromethane, 1.14 ml of EDA (10.85 mmol,
d = 1.085 g/ml) were added. After 1 h the suspension
turned into a brown solution. The solution was stirred at
room temperature for 4 h. The solvent was then removed
under reduced pressure and the residue was redissolved in
1 ml of diethylether. The addition of 3 ml of pentane affor-
ded a brown solid 5, kept under inert atmosphere at
ꢀ20 °C. The same procedure was carried out in reacting
[Cu(H2L2)(CH3CN)]2 (6) with EDA, allowing the recovery
(1.95 mmol) in 30 ml of CH3CN kept under nitrogen flow,
500 mg (1.59 mmol) of [Cu(CH3CN)4]BF4 and 300 ll of
Et3N (2.16 mmol, d = 0.726 g/ml) were added. The suspen-
sion was heated at 65 °C for 4 h, then filtered. The yellow 1
or orange 6 solid was washed with CH3CN. The product
was kept under nitrogen at ꢀ20 °C. Yield: 63% (1) and
57% (6). Anal. Calc. for C36H30Cu2N12O4 (1): C, 52.62;
H, 3.68; N, 20.45. Found: C, 52.32; H, 3.83; N, 20.29%.
Anal. Calc. for C40H38Cu2N12O4 (6): C, 54.73; H, 4.36;
N, 19.15. Found: C, 54.39; H, 4.18; N, 18.93%.
of species
7
(see Section 2.5). Anal. Calc. for
C38H33Cu2N11O6 (5): C, 52.65; H, 3.84; N, 17.77. Found:
C, 52.38; H, 3.89; N, 18.04%. Anal. Calc. for
C42H41Cu2N11O6 (7): C, 54.66; H, 4.48; N, 16.69. Found:
C, 54.31; H, 4.11; N, 16.75%
4.5. Synthesis of complex [Ag(H2L1)]n (2)
To a solution of 0.5 g of AgNO3 (2.94 mmol) in 10 ml of
acetonitrile, 1.1 g of H3L1 (3.58 mmol) and 1 ml of Et3N
(7.19 mmol, d = 0.726 g/ml) were added. The suspension
was stirred at room temperature for 2 h, then the orange
solid (2) was filtered off and washed with acetonitrile.
Yield: 79%. Anal. Calc. for C16H12AgN5O2: C, 46.40; H,
2.92; N, 16.91. Found: C, 46.20; H, 2.80; N, 16.87%.
4.9. Olefins cyclopropanation
In a standard experiment, to a solution of species 1
(0.01 mmol) in dichloromethane (10 ml) at room tempera-
ture and under inert atmosphere, EDA and olefin were
added in one portion (catalyst:EDA:olefin molar ratio
1:100:250). The consumption 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:hex-
ane = 6:4). All the cyclopropanes obtained were character-
ized by 1H NMR and GC–MS. Diastereoselectivity
(trans:cis ratio) was measured by GC–MS analysis. Com-
petitive experiments were carried out in a similar manner,
employing an equimolar solution of two olefins.
4.6. Synthesis of complex [Ag(H2L1)(PPh3)]2 (3)
To a suspension of 200 mg of 2 (0.48 mmol) in 8 ml of
dichloromethane, 260 mg of PPh3 (0.99 mmol) were added.
In about 1 h the suspension turned into an orange solution.
The solution was stirred at room temperature for 4 h, the
solvent was then removed under reduced pressure, diethyl-
ether was added and the resultant yellow solid (3) was
filtered off and dried under vacuum. Yellow prismatic sin-

1876
G.A. Ardizzoia et al. / Journal of Organometallic Chemistry 693 (2008) 1870–1876
4.10. X-ray crystallography for [Ag(H2L1)(PPh3)] (3)
(c) Q. Meng, M. Li, D. Tang, W. Shen, J. Zhang, J. Mol. Struct.:
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1553.
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Asymmetry 17 (2006) 634;
C68H54Ag2N10O4P2, fw = 1352.9 g/mol. Monoclinic,
space group C2/c, a = 15.929(1), b = 21.649(2), c =
3
˚
˚
18.010(1) A, b = 100.976(2)°, V = 6103.2(7) A , Z = 4,
F(000) = 2752, q = 1.472 g cmꢀ3, l(Mo Ka) = 0.75 mmꢀ1
.
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A total of 20980 collected, 2868 observed [I > 2r(I)], and
4004 unique reflections were acquired and reduced within
the 3.2 < 2h < 45.1° sphere, by applying the x-scan mode
(Dx = 0.3°), on a Bruker AXS SMART automated diffrac-
tometer using graphite-monochromated Mo Ka radiation
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˚
(k = 0.71073 A). The data were corrected for Lorenz-polar-
ization effects and absorption [33]. The structure was
solved by direct methods [SIR-97] [34] and refined by full-
matrix least-squares on F2 (SHELX-97 [35], as implemented
in the WinGX suite of programs). All the non-hydrogen
atoms were refined anisotropically. Hydrogen atoms (but
those of the hydroxy groups) were made riding their parent
atoms with an isotropic temperature factor 1.2 times that
of their parent atoms. 396 parameters, no restraints. R1
and wR2 for the observed reflections 0.029 and 0.062,
respectively; R1 and wR2 for all the unique reflections
0.059 and 0.069, respectively. Goodness-of-fit, highest peak
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ꢀ3
˚
and deepest hole reached values of 0.945, 0.29 e A and
ꢀ0.20 e Aꢀ3, respectively.
˚
5. Supplementary material
CCDC 665289 contains the supplementary crystallo-
graphic data for 3. These data can be obtained free of
charge from The Cambridge Crystallographic Data Centre
via www.ccdc.cam.ac.uk/data_request/cif.
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Acknowledgements
We thank MUR for funding. S.G. thanks MUR for fur-
ther financial support (PRIN 2006: ‘‘Materiali ibridi metal-
lo-organici multifunzionali con leganti poliazotati”).
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