Reactions of diazo compounds with alkenes catalysed by [RuCl(cod)(Cp)]: Effect of the substituents in the formation of cyclopropanation or metathesis products

Article abstract of DOI:10.1002/chem.200801211

The reaction of diazo compounds with alkenes catalysed by complex [RuCl(COd)(Cp)] (cod = 1, 5-cyclooctadiene, Cp = cyclopentadienyl) has been studied. The catalytic cycle involves in the first step the decomposition of the diazo derivative to afford the reactive [RuCl(Cp)I=C(R¹)R ²)] intermediate and a mechanism is proposed for this step based on a kinetic study of the simple coupling reaction of ethyl diazoacetate. The evolution of the Ru-carbene intermediate in the presence of alkenes depends on the nature of the substituents at both the diazo N₂=C(R ¹)R² (R¹, R² = Ph, H; Ph, CO ₂Me; Ph, Ph; C(R¹)R² = fluorene) and the olefin substrates R³(H)C= C(H)R⁴ (R³, R⁴ = CO₂Et, CO₂Et; Ph, Ph; Ph, Me; Ph, H; Me, Br; Me, CN; Ph, CN; H, CN; CN, CN). A remarkable reactivity of the complex was recorded, especially towards unstable aryldiazo compounds and electron-poor olefins. The results obtained indicate that either cyclopropanation or metathesis products can be formed: the first products are favoured by the presence of a cyano substituent at the double bond and the second ones by a phenyl.

Full text of DOI:10.1002/chem.200801211

DOI: 10.1002/chem.200801211
Reactions of Diazo Compounds with Alkenes Catalysed by [RuClACTHNUGRTNEUNG(cod)(Cp)]:
Effect of the Substituents in the Formation of Cyclopropanation or
Metathesis Products**
Marino Basato,*[a] Cristina Tubaro,[a] Andrea Biffis,[a] Marco Bonato,[a]
Gabriella Buscemi,[a] Filippo Lighezzolo,[a] Pamela Lunardi,[a] Chiara Vianini,[a]
Franco Benetollo,[b] and Alessandro Del Zotto[c]
Abstract: The reaction of diazo com-
pounds with alkenes catalysed by com-
plex [RuClACHTUNGTRENNUNG(cod)(Cp)] (cod=1,5-cyclo-
the Ru–carbene intermediate in the
presence of alkenes depends on the
nature of the substituents at both the
diazo N2=C(R1)R2 (R1, R2 =Ph, H; Ph,
CO2Me; Ph, Ph; C(R1)R2 =fluorene)
and the olefin substrates R3(H)C=
C(H)R4 (R3, R4 =CO2Et, CO2Et; Ph,
Ph; Ph, Me; Ph, H; Me, Br; Me, CN;
Ph, CN; H, CN; CN, CN). A remark-
able reactivity of the complex was re-
corded, especially towards unstable ar-
yldiazo compounds and electron-poor
olefins. The results obtained indicate
that either cyclopropanation or meta-
thesis products can be formed: the first
products are favoured by the presence
of a cyano substituent at the double
bond and the second ones by a phenyl.
octadiene, Cp=cyclopentadienyl) has
been studied. The catalytic cycle in-
volves in the first step the decomposi-
tion of the diazo derivative to afford
the reactive [RuCl(Cp){=C(R1)R2}] in-
termediate and a mechanism is pro-
posed for this step based on a kinetic
study of the simple coupling reaction
of ethyl diazoacetate. The evolution of
Keywords: coupling · cyclopropa-
nation · diazo compounds · meta-
thesis · ruthenium
Introduction
because of its thermal stability and easy preparation, but
also because of its interesting inherent reactivity. In fact, in
apolar solvents it dissociates one phosphine at moderate
temperatures to give a coordinatively unsaturated reactive
intermediate, which is capable of activating the decomposi-
tion of diazo derivatives to give selective cis coupling of the
Ruthenium cyclopentadienyl complexes are widely used cat-
[1]
À
alysts in a series of C C bond-forming reactions. In most
cases the prototype complex is [RuCl(Cp)
(PPh3)2], not only
carbene fragment,[2] cyclopropanation[3] or insertion into X
À
H (X=S, N) bonds.[4] Reactions involving diazo derivatives
(mostly N2CHSiMe3 or N2CHCO2Et) as carbene sources are
reportedly catalysed also by Ru complexes based on the
Cp* ligand or its derivatives.[5–7] In particular, many exten-
[a] Prof. M. Basato, Dr. C. Tubaro, Dr. A. Biffis, Dr. M. Bonato,
Dr. G. Buscemi, Dr. F. Lighezzolo, Dr. P. Lunardi, Dr. C. Vianini
Dipartimento di Scienze Chimiche
Universitꢀ degli Studi di Padova
via Marzolo 1, 35131 Padova (Italy)
Fax : (+39)049-827-5223
E-mail: marino.basato@unipd.it
sive reports deal with the use of [RuClACTHNUTRGENNG(U cod)ACHTUNTGERN(NUGN Cp*)] as the
catalyst for addition reactions to alkynes in the synthesis of
conjugated dienes[6] or to enynes to give alkenylbicyclo-
AHCTUNGTRENNUNG
[3.1.0]hexane derivatives.[7]
[b] Dr. F. Benetollo
ICIS—CNR, Corso Stati Uniti 4
35127 Padova (Italy)
No reports are present in the literature dealing with the
catalytic efficiency of the related cyclopentadienyl complex
[RuCl(cod)(Cp)] in this kind of reaction; this complex in
principle should exhibit a rather characteristic reactivity pat-
tern, as a consequence of the formation of the highly unsa-
turated intermediate [RuCl(Cp)] resulting from the facile
dissociation of the chelated COD ligand. The ability of
COD to be readily displaced has been exploited to easily
[c] Prof. A. Del Zotto
AHCTUNGTRENNUNG
Dipartimento di Scienze e Tecnologie Chimiche
Universitꢀ degli Studi di Udine
via Cotonificio 108, 33100 Udine (Italy)
[**] cod=1,5-cyclooctadiene, Cp=cyclopentadienyl.
Supporting information for this article is available on the WWW
under http://dx.doi.org/10.1002/chem.200801211.
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FULL PAPER
Table 1. Kinetic data on the decomposition rate of EDA catalysed by
[RuCl
synthesise a large number of [RuCl(Cp)(L)2] complexes
(L=phosphines, amines, dienes, isocyanides); the thermody-
namics of these substitution reactions have been accurately
determined.[8] Despite its utility as a synthetic intermediate,
(cod)(Cp)] at 208C in CHCl3.[a]
ACHTUNGTRENNUNG
[a]
Run
[Ru] [m]
[EDA] [m]
rate [msÀ1
]
ACHTUNGTRENUN[NG EDA]/[Ru]
1
2
3
4
5
6
7
8
2.2ꢂ10À3
2.2ꢂ10À3
1.1ꢂ10À3
1.1ꢂ10À3
1.1ꢂ10À3
1.1ꢂ10À3
1.1ꢂ10À3
4.4ꢂ10À4
2.0ꢂ10À1
1.0ꢂ10À2
1.0ꢂ10À2
1.0ꢂ10À2
1.0ꢂ10À2[c]
1.0ꢂ10À2[d]
1.0ꢂ10À2[e]
1.0ꢂ10À2
2.7ꢂ10À5[b]
6.6ꢂ10À6[b]
3.2ꢂ10À6
2.9ꢂ10À6
1.1ꢂ10À6
8.0ꢂ10À6
1.2ꢂ10À7
1.1ꢂ10À6
100
50
10
10
10
10
10
25
the catalytic efficiency of [RuClACTHUNTGRNEUNG(cod)(Cp)] has at present
been evaluated only in the coupling of alkynes with alkenes
or allylic alcohols to produce 1,4-dienes or g,d-unsaturated
ketones, respectively.[9,10] Remarkably, the absence of methyl
substituents on the cyclopentadienyl ring leads to the predic-
tion of a different electronic and steric environment for the
metal centre and consequently a different reactivity com-
[a] The rates are determined from the ratio DACTHNUTRGNE[NUG EDA]/Dt, which is general-
(Cp*)].[11] This is confirmed for example
pared to [RuClACHTUNGTRENNUNG(cod)ACHUTNGTRENNUGN
ly constant with time. [b] Initial rate. [c] In the presence of diethyl male-
ate and diethyl fumarate, 1.0ꢂ10À1 m. [d] In the presence of (Et4N)Cl,
1.0ꢂ10À1 m. [e] In the presence of COD, 1.0ꢂ10À1 m.
in the coupling of an alkyne with an allylic alcohol: the ac-
tivity of both complexes is comparable, but the selectivity
toward the linear or branched g,d-unsaturated ketones is op-
posite.[11]
The lack of studies on the use of [RuClACHTNUTRGNEUNG(cod)(Cp)] as the
catalyst in carbene-transfer reactions utilizing diazo deri-
vates prompted us to start a systematic study on the simplest
À
C C bond-forming reactions involving carbene fragments
(coupling, cyclopropanation and metathesis). We report
here the results of an extensive synthetic and mechanistic
study on the reaction of a series of diazo derivatives with al-
kenes catalysed by [RuCl(Cp)ACTHNUTRGNEUGN(cod)]. The main goals of this
study were to gain information on the mechanism of cataly-
sis and to define how the nature of the substituents at the
diazo and at the alkene reagents directs the reaction to-
wards metathesis or cyclopropanation products. Our aim is
to establish the potential of this complex as a catalyst for cy-
clopropanations. Indeed, in recent years an increasing
number of Ru-based catalysts, besides those listed above,
have been proposed for this reaction.[12,13] Remarkably, al-
though these catalysts are usually less active than the more
popular Rh- and Cu-based catalytic systems,[14] they often
display unusual selectivities, which complement those ob-
tained with Rh or Cu complexes.
Figure 1. Dependence of the decomposition rate of EDA on the concen-
À2
*
*
tration of [RuCl
(cod)(Cp)], CHCl3, 208C. ( ): [EDA]0 =10 m; ( ):
[EDA]0 =10À2, [DEM]0 =[DEF]0 =10À1 m; (&): [EDA]0 =10À2, [COD]=
10À1 m; ( ): [EDA]0 =10À2, [(Et4N)Cl]=10À1 m; (*): [EDA]0 =2ꢂ10À1 m.
~
the concentration of the ruthenium catalyst, with a constant
TOF of 2.7ꢂ10À3 sÀ1.
Results and Discussion
Addition of diethyl maleate and diethyl fumarate, which
are the coupling products of this catalysis, decreases the rate
of EDA consumption, so that, for example, with [Ru]0 =
In the first part of this study the decomposition of ethyl
diazo acetate (EDA) catalysed by [RuCl
been investigated in detail.
(cod)(Cp)] has
1.1ꢂ10À3, [EDA]0 =10À2 and [DEM]0 =[DEF]0 =10À1
m
(DEM=diethyl maleate, DEF=diethyl fumarate) the rate
remains zero order in EDA concentration, but its value
lowers from 3.2ꢂ10À6 to 1.1ꢂ10À6 msÀ1, TOF=1.0ꢂ10À3 sÀ1.
Added COD exhibits a more marked effect and with
[COD]=10À1 m the rate reduces to approximately 1.2ꢂ
10À7 msÀ1, TOF=1.1ꢂ10À4 sÀ1. The effect of adding
[Et4N]Cl=10À1 m is somewhat surprising because the rate in-
creases by more than 160%. This effect fairly contrasts with
Mechanism of the decomposition of EDA catalysed by
[RuCl(cod)(Cp)] in CHCl3 or CDCl3: This ruthenium com-
ACHTUNGTRENNUNG
plex is a very active catalyst at room temperature. To gain
information on the mechanism of catalysis we have studied
the rate of consumption of EDA as a function of the con-
centration of the catalyst and of EDA itself (Table 1 and
Figure 1).
that observed by using [RuCl(Cp)ACHTNUTRGEN(UNG PPh3)2] complex as the
In most cases the EDA concentration decreases linearly
with time. This indicates that, for [EDA]/[Ru] molar ratios
between approximately 10 and 25, the rate of consumption
of ethyl diazoacetate DACTHNUTRGNE[NUG EDA]/Dt does not depend on its
concentration. Furthermore, as shown in Figure 1, under
these experimental conditions the rate depends linearly on
catalyst: in fact, Del Zotto suggested in the N-methylation
of amines the simultaneous dissociation of both phosphine
and chloride in methanol and this was inferred from the
slowing down effect of added chloride on the reaction
rate.[15] The opposite effect observed in our case may be at-
tributed to the higher polarity of the reaction medium in the
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1517

M. Basato et al.
presence of the ammonium salt. As a further comment on
the mechanism, the effect of increasing the initial EDA con-
centration on its rate of disappearance is rather complex, so
that, for example, maintaining constant [Ru]=2.2ꢂ10À3 m,
DACHTUNGTRENNUNG
[EDA]/Dt for [EDA]0 =2ꢂ10À1 m is no longer constant
with time (run 1) and the initial rate is about four times
higher (TOFiniz =ca. 1.2ꢂ10À2 sÀ1) than with [EDA]0 =10À2
m
(run 2).
Parallel studies on CDCl3 solutions, in which the evolu-
tion of EDA in the presence of [RuClACTHNUTRGNEUNG(cod)(Cp)] was moni-
tored by 1H NMR spectroscopy, have shown that in the
range of ruthenium concentrations studied by IR spectrosco-
py (4.4ꢂ10À4–2.2ꢂ10À3 m) and for low [EDA]/[Ru] ratios
ACHTUNGTRENNUNG(<50), the unique reaction products are diethyl maleate and
diethyl fumarate.
Scheme 1. Proposed catalytic cycle for the decomposition of ethyl diazo-
ACHUTNGRENaNUG cetate catalysed by [RuClACHTUNGTRNE(NUGN cod)(Cp)].
depend on the concentration of EDA itself. The slowdown
effect of COD, DEF and DEM, at relatively high concentra-
tions, implies that these olefins compete with EDA in the
coordinatively unsaturated intermediates I–IV, thereby low-
ering the efficiency of the catalytic cycle. Furthermore, the
effect on the rate of increasing the EDA concentration (2ꢂ
10À1 versus 10À2 m) suggests that at higher concentrations re-
action pathway b becomes important. It is possible to envis-
age a bimolecular attack on the ruthenium centre favoured
by a variation of hapticity of COD, already observed with
iridium complexes[17] and in our preliminary kinetic studies
on the substitution of COD by isocyanides in [RuCl-
To check the effect of catalyst and EDA concentrations on
the isomer distribution we have run a series of experiments
with [Ru]=2.5ꢂ10À3–5.0ꢂ10À2
5.5m. The results are as follows:
m
and [EDA]=2.5ꢂ10À3–
1) With a ratio EDA/Ru 1:1 or 1:20, DEM and DEF are
formed in an equimolar quantity corresponding to a stat-
istical distribution. The absence of any effect of catalyst
concentration on isomer distribution seems to rule out
the occurrence of a bimolecular mechanism referred to
ruthenium.[16]
2) With higher EDA/Ru ratios (10–220), the DEM/DEF
ratio (3–9) increases with increasing initial EDA concen-
tration. This can be accounted for by assuming that at
higher EDA concentrations the initially formed olefins
(DEM and DEF) can effectively compete with EDA for
coordination at the metal centre so favouring an external
attack by EDA to the coordinated carbene. This attack
affords the less sterically demanding cis isomer DEM as
fully demonstrated by Rigo and co-workers.[2]
AHCTUNGTRENNUNG
1
by H NMR spectroscopic studies at variable EDA concen-
trations. At low [EDA]/[Ru] ratios in the range of 1–10, the
conversion is fast and quantitative in a few minutes at room
temperature to give a mixture of DEM and DEF. Increasing
the [EDA]/[Ru] ratio up to 1000, the conversion of ethyl di-
azoacetate needs much longer times, because of the inhibit-
ing effect of the primary products DEM and DEF on the
rate. Furthermore, in these cases, the initially formed olefin
products undergo a thermal reaction with residual EDA to
form a cyclic product identified as 3,4,5-triethyl-4,5-dihydro-
1H-pyrazole-3,4,5-tricarboxylate
(1)
(Scheme 2
and
Figure 2).
These kinetic studies fit well with the simplified mechanism
shown in Scheme 1. At low concentrations of EDA (10À2 m)
and in the absence of added olefins, the mechanism is fairly
simple (pathway a) and implies COD dissociation from
[RuClACHTUNGTRENNUNG
(h4-cod)(Cp)] via the {h2-cod} intermediate I to give
the coordinatively doubly unsaturated [RuCl(Cp)] (II). This
undergoes successive attack by two molecules of EDA to
afford the carbene and olefin intermediates III and IV. Dis-
sociation of the olefin from IV affords the reaction products
and the intermediate II, closing the catalytic cycle. The ob-
served zero order for the rate of disappearance of EDA
may be related to the fact that the rate of formation of II,
which is the initial catalytic species in the cycle, does not
Scheme 2. Formation of compound 1.
The proposed mechanism for the formation of the di-
AHCTUNGTRENNUNG
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Reactions of Diazo Compounds with Alkenes
FULL PAPER
phenyldiazoacetate (MPDA) catalysed by [RuClACTHNUTRGENUG(N cod)(Cp)]
has been found to be fast when using MPDA alone, but be-
comes slower in the presence of EDA. In fact, in this last
case, the coupling olefin products are less sterically hindered
and compete with MPDA for the active ruthenium centre.
The formation of a highly unsaturated 14-electron species
[RuCl(Cp)] with two free coordination sites, which has been
clearly evidenced in our parallel kinetic study,[18] allows us
to foresee a marked ability to coordinate both a carbene
unit and an olefin, so leading us to evaluate the catalytic
properties of [RuCl
metathesis reactions.
ACHTUNGTRENN(UNG cod)(Cp)] in cyclopropanation and/or
Figure 2. Molecular structure of 1 with the atom nomenclature. Selected
À
À
À
bond lengths [ꢃ] and angles [8]: N1 N2 1.329(6), N1 C1 1.286(6), N2
À
À
À
À
Decomposition of diazo derivatives in the presence of an
alkene: We have chosen sets of different diazo derivatives
and alkenes and used identical reaction conditions with the
aim of understanding how the nature of the substituents and
the geometry of the alkene direct the catalytic cycle towards
the cyclopropanation or the metathesis reaction. Preliminary
catalytic tests have been performed in the decomposition of
MPDA in the presence of 1,2-disubstituted symmetric al-
kenes, like diethyl maleate, diethyl fumarate and cis- and
trans-stilbene. The choice of MPDA as the diazo compound
is based on its reduced tendency to form coupling products
compared with the previously studied EDA. We have adopt-
ed standard reaction conditions derived from literature
works (alkene (1.2 equiv), diazo compound (1 equiv),
C3 1.466(6), C1 C2 1.514(7), C2 C3 1.546(7), C1 C4 1.455(7), C2 C7
À
1.509(7), C3 C10 1.515(7); C1-N1-N2 110.0(4), N1-N2-C3 113.4(4), N2-
C3-C2 102.3, C3-C2-C1 100.7(4), C2-C1-N1 113.4(4).
To prove that the formation of 1 occurred by the pro-
posed mechanism, we have carried out the cycloaddition of
ethyl diazoacetate with DEM or DEF in a 1:1 molar ratio,
in the absence of the ruthenium catalyst and 1 was obtained
as the only product. Thus the synthesis of 1 from EDA is a
catalytic/thermal process, in which the metal catalyst pro-
motes the initial formation of the olefin, necessary for pyra-
zole formation.
The mechanistic data obtained in the first part of this
work have given important information on the characteris-
[RuClACTHNURTGNEU(GN cod)(Cp)] (0.05 equiv), 608C, controlled addition of
tics of the catalyst [RuCl
(cod)(Cp)] as follows: 1) albeit it is
diazo compound over 6 h).[5,20] The results (Table 2) are indi-
cated as the percentage conversion of the diazo derivative in
the various products; these in turn are grouped as coupling,
cyclopropanation/homologation and metathesis/2nd-cyclo-
propanation products.
These preliminary tests gave some important information.
The complex is capable of catalysing both the cyclopropana-
tion and metathesis reactions and the selectivity is strongly
dependent on olefin substituents. In fact, MPDA reacts with
diethyl fumarate or maleate to afford the cyclopropanes 2a
or 2b and the corresponding homologation compound 3, the
a 18-electron ruthenium(II) d6 complex, the dissociation of
COD is an easy process at room temperature, as already re-
ported;[8] 2) the decomposition of the diazo derivative is
always a fast process; 3) the addition of the second molecule
of diazo to give the coupling products is also a fast process;
4) the coupling reaction is not stereoselective; and 5) the re-
action products diethyl fumarate and diethyl maleate lower
the decomposition rate of EDA. The reactivity of the cata-
lytic metal centre strongly depends on the nature of the
formed olefin; for example, the decomposition of methyl
Table 2. Product distribution in the decomposition of methyl phenyldiazoacetate in presence of alkenes[a]
Diazo
Olefin
Product distribution[b]
compound
coupling
cyclopropanation/homologation
metathesis/2nd cyclopropanation
–
(8)
2a (38)
2b (34)
3
3
(17)
(19)
(36)
(27)
–
–
–
4
(39)
–
5[c]
AHCTUNGTERG(NNUN 100)
[a] For experimental conditions see the Experimental Section. [b] Yields (in parentheses) are expressed as mol% conversion of MPDA in the various products;
thermal decomposition products (methyl phenylglioxylate and methyl mandelate) complete the reaction balance. [c] The quantity of this cyclopropane of the
second cycle is comparable with the one of metathesis product.
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M. Basato et al.
latter formally deriving from an insertion of the carbene
tosylhydrazone have been reported very rarely and applica-
tions are generally limited to terminal olefins.[22] MPDA
forms with cis-stilbene mainly the diazo coupling product
and the metathesis product in low yield (Table 3, entry 3),
with a reaction outcome similar to that reported in Table 2
under slightly different conditions. The selectivity for the
metathesis/2nd-cyclopropanation product increases on
moving to cis-propenylbenzene (Table 3, entry 4). Finally,
reaction of simple styrene yields no metathesis product, but
rather alkene homologation and mainly cyclopropanation
products (Table 3, entry 5). Interestingly, the stereoselectiv-
ity in the formation of the cyclopropane ring favours the Z
product, whereas when using rhodium(II) catalysts in this
reaction almost exclusive E product formation is generally
observed.[23] Diaryl diazo derivatives, such as diphenyl diazo-
methane or 9-diazo-9H-fluorene (DAF), do not react at all
with cis-stilbene (Table 3, entries 6 and 8), whereas the
metathesis/2nd-cyclopropanation reactions occur to some
extent with cis-propenyl benzene (Table 3, entries 7 and 9).
Clearly in this last case replacement of a methyl for a
phenyl substituent on the olefin facilitates its coordination
to the metal centre, which is hindered by the Cp, Cl and
diaryl carbene ligands. This confirms once more the impor-
tance of steric factors in the formation of metallacyclo-
[12,21]
À
fragment into one of the C H bonds of the olefin.
Re-
markably, catalytic cyclopropanation of electron-poor disub-
stituted olefins, such as diethyl fumarate or maleate, appears
to be quite unprecedented in the literature; therefore, this
finding highlights the potential of our complex as a cyclo-
propanation catalyst (see also below). By contrast, with cis-
stilbene the preferred reaction is metathesis between the
carbene fragment of MPDA and the olefin, giving product
4. This process leaves on the metal centre the fragment
=CHPh, which can react with a second molecule of alkene
giving cyclopropane 5 or undergo olefin self-metathesis in a
parallel catalytic cycle. The last process has been observed,
in particular, when a large excess of cis-stilbene was used
(10-fold): the unreacted stilbene at the end of the reaction
was a mixture of cis and trans isomers in a 1:1 ratio.
This behaviour is accounted for by assuming the crucial
formation in the catalytic cycle of a metallocyclic intermedi-
ate, which, depending on the nature of the olefin substitu-
ents, can evolve to give the cyclopropanation or metathesis/
2nd-cyclopropanation products.[5,21]
Interestingly, in the reaction of MPDA with trans-stilbene
only the diazo coupling product has been isolated, thus sug-
gesting that coordination of this olefin to the metal centre is
not occurring probably because of steric hindrance.
AHCTUNGTREGbNNUN utane or, in general, in the interaction between the carbene
We performed some additional experiments aimed at
maximizing the yield in cyclopropanation and/or metathesis
and also at reducing catalyst loading. We repeated the ex-
periments with cis-stilbene by using only 1 mol% catalyst:
this causes a decrease in activity (diazo conversion 41%),
which, however, could be overcome by adding the diazoace-
tate in 22 h (diazo conversion 70%). The yield in the cou-
pling products could be lowered by using a large excess (10-
fold) of olefin. However, since the selectivity ratio between
cyclopropanation and metathesis remained unchanged upon
increasing the olefin concentration, we chose to evaluate
this parameter by using only a moderate excess (20%) of
the olefin. The diazoacetate was added very slowly, by con-
trolled addition over long reaction times (22 h), to minimize
the coupling side reaction.
To get a better insight into the effects of steric and elec-
tronic factors on the competitive cyclopropanation/metathe-
sis reactions, we have continued our study by investigating
different couples of diazo compound/olefin (Table 3). In the
first runs, 1–9, we have tried to evaluate the influence of the
substituents on the diazo compound, keeping at least one
phenyl group; in fact it has been verified that diazo deriva-
tives lacking a phenyl substituent and bearing a keto or
ester group (like for example EDA) gave complex intracta-
ble mixtures.
fragment and the external olefin. In runs 8–17 we have used
9-diazo-9H-fluorene, which gives very selective reactions,
and varied the olefin, to evaluate the contribution of the
alkene in directing the reaction. Runs 9–11 confirm that the
presence of one phenyl substituent in the alkene makes it
possible for the metathesis reaction to occur; however, this
is accompanied by the cyclopropanation reaction with trans-
propenyl benzene and styrene to give 12 and 13, respective-
ly. This difference in behaviour with respect to cis-propenyl
benzene is noteworthy and seems to indicate a high instabil-
ity for a cyclopropane bearing three substituents on one side
of the ring. Similar steric reasons can account for the lack of
reactivity of DAF with diphenyl olefins (runs 8 and 12).
Halogenated olefins are generally not reactive under these
conditions, so that, for example, in the reaction of DAF with
cis- and trans-dichloroethylene, cis-1,3-dichloropropene, 1-
chloro-3-methyl-2-butene, 1-chloro-2-methylpropene and 1-
bromo-2-methylpropene only the coupling product was ob-
served. However, in the case of the cis-1-bromopropene,
less-hindered and bearing a weaker electron withdrawing
halogen, both metathesis and cyclopropanation products
have been obtained. Remarkably, the presence of electron-
withdrawing substituents in the olefin does not preclude by
itself its reactivity towards diazo derivatives when using our
catalyst (see also above). In fact, runs 14–19 show that a
series of cyano olefins reacts very selectively with mono-
and diaryl diazo compounds to give mostly cyclization prod-
ucts, drastically minimizing also the product of diazo cou-
pling. It seems that the cyano group can very efficiently co-
ordinate to the metal centre, thereby favouring the forma-
tion of the crucial metallocyclic intermediate. Therefore, the
formation of a coordinatively highly unsaturated Ru com-
Phenyl diazomethane reacts with cis-stilbene to give as
the metathesis product trans-stilbene and a cyclopropana-
tion product (Table 3, entry 1). On the other hand, it reacts
with cis-propenyl benzene to give a very high conversion to
the cyclopropanes 6a and 6b (Table 3, entry 2). This is a re-
markable result, given that efficient cyclopropanations with
highly reactive phenyldiazomethane or its precursor phenyl
1520
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Reactions of Diazo Compounds with Alkenes
FULL PAPER
Table 3. Product distribution in the decomposition of diazocompounds in presence of olefins[a]
Run Diazo
compound
Olefin
Product distribution[b]
coupling cyclopropanation
metathesis
2nd cyclopropanation
1
2
(5)
(2)
–
(52)
5
(43)
(10)
6a
(78)
–
6b
5[c]
3
4
5
(54)
(23)
(5)
–
–
4
(25)
7
(41) 6a/6b 3.6:1[c]
8a
(13)
–
–
8b
9
(47)
(35)
6
7
(33)
(25)
–
–
–
–
10 (10) 6a/6b 3.2:1[c]
8
N
–
–
–
–
11 (52) 6a/6b 3.7:1 [c]
11 (22) 6a/6b 1:1.6[c]
14 (11)
9
10
11
12
13
14
12
13
(32)
(59)
15[c]
–
–
–
16
(35)
(56)
11 (9)
–
–
17a
–
17b (33)
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1521

M. Basato et al.
Table 3. (Continued)
Run Diazo
compound
Olefin
Product distribution[b]
coupling cyclopropanation
metathesis
–
2nd cyclopropanation
–
15
16
17
(87)
(4)
–
18
19
20
(56)[d]
(74)
–
–
–
–
(10)
(16)
18
19
–
21
G
–
–
–
–
(12)
22a
22b (46)
23
(22)
[a] For experimental conditions see the Experimental Section. [b] Yields (in parentheses) are expressed as mol% conversion of the diazo compound in
the various products; thermal decomposition products complete the reaction balance of the diazo derivatives. [c] The quantity of these cyclopropanes of
the second cycle is comparable with the one of metathesis product. [d] The remaining 40% is an unknown product, probably the other cyclopropane
isomer.
plex catalyst appears to make it
possible to prepare cyclopro-
panes from diazocompounds
and electron-poor olefins,
a
class of substrates that are
known to be very unreactive
with traditional catalytic sys-
tems. To the best of our knowl-
edge, the only hitherto reported
example of cyclopropanation of
olefins of this kind (a,b-unsatu-
rated ketones) involves the use
of sulfides as mediators.[24]
The whole of these results
are consistent with the catalytic
cycle shown in Scheme 3. The
sequence of proposed steps
leads us to classify the illustrat-
ed mechanism mostly as a stoi-
chiometric one, and not all the
metal intermediates may repre-
Scheme 3. Proposed catalytic cycle for the decomposition of diazo compounds in the presence of olefins. For
the sake of clarity the homologation products are not indicated, as well as the 1,1-disubstituted- and the trans
sent minima on the potential olefins, which are, however, discussed in the text.
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Chem. Eur. J. 2009, 15, 1516 – 1526

Reactions of Diazo Compounds with Alkenes
FULL PAPER
energy surface. The first step (ia and ib) implies the forma-
tion of the 16-electron metal–carbene intermediate A; this
is a rather easy process and its details have been fully illus-
trated in Scheme 1. The intermediate A can either react
with a second molecule of diazo compound to give the cou-
pling product (this reaction is always present to some
extent) or (ii) coordinate the olefin, to give, subsequently,
the ruthenium metallacycle B. Steric factors play a very im-
portant role in this step; in fact, with sterically hindered
diazo/olefin couples only the diazo coupling product is ob-
tained. In principle, cyclopropanation can occur also without
coordination of the olefin to the metal centre, as observed,
for example, with rhodium- and copper-metal catalysts;
however, in our case we believe that this pathway is much
less likely with an electron-rich, coordinatively unsaturated
metal centre, which should favour the formation of the met-
allacyclobutane by oxidative addition.[25] In this view, the
lack of any cyclopropanation product bearing four aryl sub-
stituents is attributed to steric hindrance, which does not
allow the formation of the metallacycle. The geometry of
the olefin also directs the reactivity, so that, for example,
MPDA does not react with trans-stilbene, whereas it gives
with the cis isomer the metathesis and 2nd-cyclopropanation
products.
The metallacycle B, depending on the nature of the vari-
ous substituents, can evolve to liberate in solution either the
cyclopropane (iii), reforming the starting 14-electron
[RuCl(Cp)] complex, or the metathesis product (iv), forming
the new 16-electron carbene complex C. A computational
analysis on a closely related system showed that the metal
precursor of the cyclopropanation way was in that case ther-
modynamically more favoured with respect to the one
giving metathesis.[7c] The prevalence of pathway iii or iv in
our system can be discussed on the basis of the stability of
the resulting products, by assuming that there are no kinetic
limitations for the evolution of intermediate B. An insight
into the factors determining the ability of intermediate B to
give both cyclopropanation and metathesis can be gained
from the products distributions shown in Tables 2 and 3:
metathesis occurs only in the presence of olefins bearing a
phenyl substituent, whereas cyclopropanation/homologation
is the only reaction observed in the presence of cyano ole-
fins. Therefore, there is a delicate thermodynamic balance
between the formation of the 16-electron carbene complex/
olefin and 14-electron complex/cyclopropane pairs. It ap-
pears that the metathesis reaction is driven in all cases by
the formation of the intermediate [RuCl(Cp)(=C(H)Ph)] C,
which is stabilized by the phenyl substituent in the
=C(H)Ph fragment, due to its ability to delocalise electron
density. This is confirmed by the reactivity exhibited by sty-
rene and propenyl benzene, which give as unique metathesis
products those resulting from the formation of C where
R3 =Ph. However, also the nature of the cyclopropane plays
an important role, so that styrene and trans-propenyl ben-
zene react with DAF to give both cyclopropanation and
metathesis products, whereas cis-propenyl benzene gives
only metathesis products. If one considers that generally the
olefin maintains its starting geometry in the cyclopropana-
tion products, these last observations can be accounted for
on purely steric bases by assuming that three hindering sub-
stituents (for example 2Ph+1Me) on the same side destabi-
lize the cyclopropane ring.
The results obtained with cyano olefins are very interest-
ing: the diazo coupling is drastically reduced and the reac-
tion is very selective towards cyclopropanation. It seems
that the cyano group can very efficiently coordinate to the
metal centre, thereby favouring the formation of the crucial
metallacyclic intermediate B; furthermore, the absence of
any phenyl substituent drains the reaction through path-
way iii.
Turning to the fate of metal intermediate C resulting from
the metathesis process, it can react with the starting olefin
to give the new metallacycle D (v). This, as a rule, liberates
the 2nd-cyclopropanation product (vi); in fact, the metathe-
sis and 2nd-cyclopropanation products are formed in almost
equivalent quantities. Alternatively, D gives the trans-olefin
isomer in a self-metathesis cycle (pathway vii)).
As a useful comment, the behaviour of [RuClACHTNUTRGNE(UNG cod)(Cp)]
as the catalyst precursor can be compared with that exhibit-
ed by the Grubbs-type catalysts. In both cases a “similar”
crucial ruthenium metallacyclo-butane (or -hexane)[26] com-
plex is proposed in the catalytic cycle.[27–29] However, this
similarity appears rather formal. In fact, the cyclopentadien-
yl intermediate is a 18-electron complex and can give either
the metathesis or cyclopropane product with corresponding
formation of a 16- or 14-electron complex. This second way
appears disfavoured in the Grubbs system, because the cy-
clopropane reductive elimination step from the metallacy-
clobutane intermediate would afford an unlikely very high-
energy 12-electron metal species.
Conclusion
ACHUTNGREN[NUG RuClCAHTUNGTRNE(NUGN cod)(Cp)], due to its possibility of generating a
double coordinative unsaturation, appears to be a very effi-
cient catalyst in the decomposition of diazo derivatives in
the presence of olefins. Both cyclopropanation and metathe-
sis reactions can occur: cyclopropanation is predominant
with cyano olefin and in the absence of phenyl substituents
on the olefin, whereas metathesis is always accompanied by
a 2nd-cyclopropanation cycle, which consumes the active
metal–carbene intermediate. The reactivity exhibited by our
complex as a cyclopropanation catalyst with unstable aryl-
diazo compounds and with electron-poor olefins appears
particularly noteworthy. We are currently engaged in better
focussing the scope of this novel catalytic system in such
challenging reactions.
Experimental Section
General comments: The reagents (Aldrich-Chemie or ABCR) were high
purity products and were generally used as received. All solvents were
Chem. Eur. J. 2009, 15, 1516 – 1526
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1523

M. Basato et al.
dried by standard procedures and distilled under nitrogen immediately
prior to use. The reaction apparatus was carefully deoxygenated, and the
reactions were performed under argon and all operations were carried
(1.2 mmol in 2 mL of dichloroethane) was added over 22 h (or 6 h for the
tests reported in Table 2) by using a syringe pump. The reaction mixture
was subsequently evaporated to dryness and analysed by NMR spectros-
copy. Reaction products were purified by column chromatography onto
silica gel 60 (eluent: n-hexane/diethylether 80:20). The reaction products
were identified by comparison of the NMR spectra with literature data
or characterized by a combination of NMR and MS techniques.
Products methyl (E)-2,3-diphenylpropenoate (4),[34] 1,2,3-triphenylcyclo-
propane (5),[35] 1-methyl-trans-2,3-diphenylcyclopropane (6a),[36] 1-
methyl-cis-2,3-diphenylcyclopropane (6b),[36a,37] (E)-methyl 2-phenylbut-
out under an inert atmosphere. Complex [RuClACTHNUTRGENUG(N cod)(Cp)] was prepared
according to a published method.[8a] The diazo derivatives phenyldiazo-
methane,[30] diphenyldiazomethane,[31] MPDA[32] and DAF[33] were synthe-
sized by literature methods. The solution 1H and 13C{1H} NMR spectra
were recorded on a Bruker Avance 300 MHz spectrometer (300.1 for 1H
and 75.5 MHz for 13C) at room temperature. The chemical shifts (d) are
reported in units of ppm relative to the residual solvent signals, with tet-
ramethylsilane as internal standard for
1H and 13C chemical shifts. GCMS
analyses were performed with
a
Varian Saturn 2100T gas chromato-
graph/mass spectrometer (injector
temperature 2408C, column Supelco
SPB 50); the temperature was pro-
grammed from 100 (1 min) to 2408C
with a gradient of 158CminÀ1
.
Synthesis of 3,4,5-triethyl-4,5-dihydro-
1H-pyrazole-3,4,5-tricarboxylate (1):
The required amounts of complex
[RuClACHTUNGTRENNUNG(cod)(Cp)] (11 mg, 0.03 mmol)
and EDA (3.2 mL, 30.0 mmol) were
placed in a Schlenk tube previously
evacuated and filled with argon. The
resulting mixture was stirred at room
temperature for 48 h and then at 408C
for 48h; after which a solid formed.
This solid was filtered and dried in
vacuum to give 1 (0.50 g, 17.5% yield)
as
(CDCl3): d=1.22–1.40 (3t, 9H;
CH2CH3), 4.15–4.38 (3q, 6H;
a
tan-coloured powder. 1H NMR
CH2CH3), 4.42 (d, 1H; CH), 4.75 (d,
1H; CH), 6.77 ppm (s, 1H; NH);
13C NMR (CDCl3): d=14.0, 14.1, 14.3
(CH2CH3), 52.2 (CH), 61.6, 62.2, 62.6
(CH2CH3), 66.2 (CH), 140.0 (CN),
162.1 168.30, 171.8 ppm (COO); FTIR
À
(KBr):
n˜ =3298
(N H),
1695,
for
1738 cmÀ1
(C=O); calcd
C12H18N2O6 (M=286.2):
C 50.32, H
6.28, N 9.78; found: C 50.64, H 6.19, N
9.53.
The same product was obtained by re-
acting a mixture of ethyl diazoacetate
(1.5 mL, 13.0 mmol) and DEM (1 mL,
6.0 mmol) (or DEF (1 mL, 6.0 mmol))
in a Schlenk tube. After stirring at
room temperature for 16 h, the result-
ing suspension was filtered, giving 1 as
a pale-yellow solid, which was washed
with n-hexane (2ꢂ2 mL) and dried
under vacuum (yield: 83% for DEM
and 73% for DEF).
2-enoate (7),[38] (1R,2S)-methyl 1,2-diphenylcyclopropanecarboxylate
(8a),[39] (1S,2S)-methyl 1,2-diphenylcyclopropanecarboxylate (8b),[39] (Z)-
methyl 2,4-diphenylbut-2-enoate (9),[39] 1,1-diphenylpropene (10),[40] 9-
methylmethylene-9H-fluorene (11),[41] trans-2-methyl-3-phenylspiro(cy-
clopropane-1,9’-[9H]fluorene) (12),[42] 2-phenylspiro(cyclopropane-1,9’-
[9H]fluorene) (13),[43] dibenzofulvene (14),[44] trans-1,2-diphenylcyclopro-
General procedure for the catalysed
decomposition of diazo derivatives: The required amount of complex (5
or 1 mol%) was placed in an NMR tube and dissolved in CDCl3 under
an inert atmosphere. The diazo compound (1.2 mmol) was added and the
reaction was followed by 1H NMR spectroscopy. Yields were calculated
by integration of NMR spectroscopic signals.
pane
(15),[45]
trans-2,3-dicyanospiro(cyclopropane-1,9’-[9H]fluorene)
General procedure for the catalysed decomposition of diazo derivatives
in the presence of alkenes: The required amounts of complex (5 mol%
for the tests reported in Table 2, or 1 mol% for the tests reported in
Table 3) and alkene (1.2 mmol) were placed in a round-bottomed flask
and dissolved in dichloroethane (3 mL) under an inert atmosphere. The
obtained solution was then heated at 608C and the diazo compound
(18),[46] 2-cyanospiro(cyclopropane-1,9’-[9H]fluorene) (19)[46] and 2,2-di-
phenylcyclopropanecarbonitrile (21)[47] have been identified by compari-
son of the NMR spectra with literature data.
AHCTUNGTERG(NNUN 2R,3S)-2,3-Diethyl-1-methyl-1-phenylcyclopropane-1,2,3-tricarboxylate
1
(2a): H NMR (CDCl3): d=1.12 (t, 6H; CH2CH3), 2.96 (s, 2H; CH), 3.65
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Reactions of Diazo Compounds with Alkenes
FULL PAPER
(s, 3H; OCH3), 4.01 (q, 4H; CH2CH3), 7.26–7.39 ppm (m, 5H; Ph);
paper. These data can be obtained free of charge from The Cambridge
Crystallographic Data Centre via www.ccdc.cam.ac.uk/data_request/cif
13C NMR (CDCl3): d=13.8 (CH2CH3), 31.8 (CH), 39.7 (C(Ph)
ACHTUNGTRENNUNG
ACHTUNGTRENNUNG(2R,3R)-2,3-Diethyl-1-methyl-1-phenylcyclopropane-1,2,3-tricarboxylate
(2b): 1H NMR (CDCl3): d=1.02 (t, 3H; CH2CH3), 1.31 (t, 3H;
CH2CH3), 3.05 (d, 1H; CH), 3.21 (d, 1H; CH), 3.65 (s, 3H; OCH3), 3.93
(q, 2H; CH2CH3), 4.22 (q, 2H; CH2CH3), 7.26–7.35 ppm (m, 5H; Ph);
13C NMR (CDCl3): d=13.8, 14.1 (CH2CH3), 31.3, 32.2 (CH), 44.7 (C(Ph)-
ACHTUNGTRENNUNG(CO2Me)), 52.9 (OCH3), 61.1, 61.6 (CH2CH3), 128.4–133.7 (Ph), 167.4,
168.7 ppm (COO).
[1] a) B. M. Trost, F. D. Toste, A. B. Pinkerton, Chem. Rev. 2001, 101,
2067; b) V. Guerchais, Eur. J. Inorg. Chem. 2002, 783; c) B. M. Trost,
Acc. Chem. Res. 2002, 35, 695.
[2] a) W. Baratta, A. Del Zotto, P. Rigo, Chem. Commun. 1997, 2163;
b) W. Baratta, A. Del Zotto, P. Rigo, Organometallics 1999, 18,
5091; c) A. Del Zotto, W. Baratta, G. Verardo, P. Rigo, Eur. J. Org.
Chem. 2000, 2795.
[3] a) W. Baratta, W. A. Herrmann, R. M. Kratzer, P. Rigo, Organome-
tallics 2000, 19, 3664; b) O. Tutusaus, S. Delfosse, A. Demonceau,
A. F. Noels, R. NfflÇez, C. ViÇas, F. Teixidor, Tetrahedron Lett. 2002,
43, 983.
[4] A. Del Zotto, W. Baratta, P. Rigo, J. Chem. Soc. Perkin Trans. 1
1999, 3079.
2,3-Diethyl-1-methyl-1-phenylprop-1-ene-1,2,3-tricarboxylate
(3):
1H NMR (CDCl3): d=1.25 (t, 3H; CH2CH3), 1.30 (t, 3H; CH2CH3), 3.29
(s, 2H; CH2), 3.79 (s, 3H; OCH3), 4.15 (q, 2H; CH2CH3), 4.26 (q, 2H;
CH2CH3), 7.26–7.48 ppm (m, 5H; Ph); 13C NMR (CDCl3): d=13.9, 14.1
(CH2CH3), 35.3 (CH2), 52.5 (OCH3), 61.0, 61.6 (CH2CH3), 127.9–134.0
(Ph), 126.9, 146.0 (C=C), 166.2, 168.5, 170.0 ppm (COO).
2-Bromo-3-methylspiro(cyclopropane-1,9’-[9H]fluorene) (16): 1H NMR
(CDCl3): d=2.30 (m, 1H; CHMe), 2.45 (d, 3H; CH3), 4.10 (d, 1H;
CHBr), 7.20–7.90 ppm (m, 8H; CH).
[5] F. Simal, A. Demonceau, A. F. Noels, D. R. T. Knowles, S. OꢄLeary,
P. M. Maitlis, O. Gusev, J. Organomet. Chem. 1998, 558, 163.
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2000, 122, 7400.
[7] a) F. Monnier, D. Castillo, S. DØrien, L. Toupet, P. H. Dixneuf,
Angew. Chem. 2003, 115, 5632; Angew. Chem. Int. Ed. 2003, 42,
5474; b) M. Eckert, F. Monnier, G. T. Shchetnikov, I. D. Titanyuk,
S. N. Osipov, L. Toupet, S. D›rien, P. H. Dixneuf, Org. Lett. 2005, 7,
3741; c) F. Monnier, C. Vovard-Le Bray, D. Castillo, V. Aubert, S.
DØrien, P. H. Dixneuf, L. Toupet, A. Ienco, C. Mealli, J. Am. Chem.
Soc. 2007, 129, 6037.
[8] a) M. O. Albers, D. J. Robinson, A. Shaver, E. Singleton, Organome-
tallics 1986, 5, 2199; b) M. O. Albers, D. J. Robinson, E. Singleton, J.
Organomet. Chem. 1986, 311, 207; c) M. E. Cucullu, L. Luo, S. P.
Nolan, P. J. Fagan, N. L. Jones, J. C. Calabrese, Organometallics
1995, 14, 289; d) J. Shen, E. D. Stevens, S. P. Nolan, Organometallics
1998, 17, 3000.
2-Cyano-3-methylspiro(cyclopropane-1,9’-[9H]fluorene) (17a): 1H NMR
(CDCl3): d=1.52 (d, 3H; CH3), 2.25 (d, 1H; CH(CN)), 2.35 (m, 1H;
CHMe), 6.90–7.60 ppm (m, 8H; CH).
2-Cyano-3-methylspiro(cyclopropane-1,9’-[9H]fluorene) (17b): 1H NMR
(CDCl3): d=1.60 (d, 3H; CH3), 2.35 (m, 1H; CHMe), 2.59 (d, 1H;
CH(CN)), 6.90–7.60 ppm (m, 8H; CH).
3-(9H-Fluoren-9-ylidene)propanenitrile (20): 1H NMR (CDCl3): d=3.78
(d, 2H; CH2), 6.50 (t, 1H; CH), 7.00–7.90 ppm (m, 8H; CH).
A
2-cyano-1-phenylcyclopropanecarboxylate
(22a):
1H NMR (CDCl3): d=1.85 (dd, 1H; CH), 1.95 (dd, 1H; CH2), 2.54 (dd,
1H; CH2), 3.82 (s, 3H; OCH3), 7.23–7.50 ppm (m, 5H; Ph); the proposed
geometry is based on the higher values of the chemical shift of the cyclo-
propane protons with respect to 22b, as observed in the cyclopropanes
8a and 8b.
A
2-cyano-1-phenylcyclopropanecarboxylate
(22b):
1H NMR (CDCl3): d=1.75 (dd, 1H; CH), 2.05 (dd, 1H; CH2), 2.30 (dd,
[9] a) B. M. Trost, A. F. Indolese, J. Am. Chem. Soc. 1993, 115, 4361;
b) B. M. Trost, K. Imi, A. F. Indolese, J. Am. Chem. Soc. 1993, 115,
8831; c) B. M. Trost, J. A. Martinez, R. J. Kulawiec, A. F. Indolese, J.
Am. Chem. Soc. 1993, 115, 10402; d) B. M. Trost, T. J. J. Müller, J.
Am. Chem. Soc. 1994, 116, 4985; e) B. M. Trost, T. J. J. Müller, J.
Martinez, J. Am. Chem. Soc. 1995, 117, 1888.
[10] Y. Yamamoto, H. Kitahara, R. Hattori, K. Itoh, Organometallics
1998, 17, 1910.
[11] For a review, see: S. DØrien, P. H. Dixneuf, J. Organomet. Chem.
2004, 689, 1382.
[12] For a review, see: G. Maas, Chem. Soc. Rev. 2004, 33, 183.
[13] a) C.-Y. Wong, W.-L- Man, C. Wang, H.-L. Kwong, W.-Y. Wong, T.-
C. Lau, Organometallics 2008, 27, 324; b) C. Bonaccorsi, F. Santoro,
S. Gischig, A. Mezzetti, Organometallics 2006, 25, 2002; c) C. Bonac-
corsi, A. Mezzetti, Organometallics 2005, 24, 4953; d) D. Huber, A.
Mezzetti, Tetrahedron: Asymmetry 2004, 15, 2193; e) D. Huber, P. G.
Anil Kumar, P. S. Pregosin, I. S. Mikhel, A. Mezzetti, Helv. Chim.
Acta 2006, 89, 1696; f) S. Buck, G. Maas, J. Organomet. Chem. 2006,
691, 2774; g) V. D. M. Hoang, P. A. N. Reddy, T.-J. Kim, Tetrahedron
Lett. 2007, 48, 8014.
1H; CH2), 3.75 (s, 3H; OCH3), 7.23–7.50 ppm (m, 5H; Ph).
Methyl 4-cyano-2-phenylbut-2-enoate (23): 1H NMR (CDCl3): d=3.08
(d, 2H; CH2), 3.78 (s, 3H; OCH3), 6.95 (t, 1H; CH), 7.20–7.40 ppm (m,
5H; Ph).
Kinetic experiments: Solutions of EDA and [RuClACTHNUGRTENUNG(cod)(Cp)] ([EDA]=
10À2–10À1 m, [Ru]=4.4ꢂ10À4–2.2ꢂ10À3 m) in CHCl3 were carefully deoxy-
genated by three freeze-thaw cycles. Aliquot portions of the reacting mix-
ture were removed, at given reaction times, through a Suba-seal rubber
stopper and immediately analysed in the 2300–1700 cmÀ1 region by using
a Perkin–Elmer 781 spectrophotometer (0.5 mm sodium chloride cells).
The reaction rate DACHTUNGTRENNUNG[EDA]/Dt was determined from the variation of the
absorbance with time of the band at 2180 cmÀ1, relative to the N–N
stretching of EDA, knowing its initial concentration. When the variation
was not linear, the initial velocity was determined.
X-ray structure determination for 3,4,5-triethyl-4,5-dihydro-1H-pyrazole-
3,4,5-tricarboxylate (1): C12H18N2O6; Mr =286.28; orthorhombic; space
group=P212121 (no. 19); a=10.504(2), b=17.737(3), c=7.875(2) ꢃ; V=
1467.2(5) ꢃ3; Z=4; 1calcd =1.296 gcmÀ3; m=0.105 mmÀ1; F
ACTHUNTRGNEU(GN 000)=608, R1
on F (wR2 on F2)=0.068 (0.149) for 1335 observed [I>2s(I)] reflections.
A prismatic crystal was lodged in a Lindemann glass capillary and cen-
tred on a four-circle Philips PW1100 diffractometer (FEBO system) with
graphite-monochromated MoKa radiation (0.71073 ꢃ), by following the
standard procedures at room temperature. All intensities were corrected
for Lorentz polarization and absorption. The structure was solved by
direct methods by using reference [48]. Refinement was carried out by
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2
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Received: June 19, 2008
Revised: October 9, 2008
Published online: December 22, 2008
1526
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Chem. Eur. J. 2009, 15, 1516 – 1526