Synthesis of N-bonded enolatoruthenium(II) by oxidative addition of alkyl cyanocarboxylate to a ruthenium(0) complex

Article abstract of DOI:10.1039/a902860i

Reaction of a zero-valent ruthenium complex [Ru(cot)(cod)] 1 (cod = 1,5-cyclooctadiene; cot = 1,3,5-cyclooctatriene) with alkyl cyanoacetate in the presence of mono- and bi-dentate tertiary phosphines gave a series of hydrido(enolato)-ruthenium(n) complexes: mer-[RuH(NCCHCO₂Et)(NCCH₂CO₂Et)(PPh ₃)₃] 2; trans-[RuH(NCCHCO₂Et)(cod)-(dppe)] 3 (dppe = Ph₂PCH₂CH₂PPh₂); trans-[RuH(NCCR¹CO₂R²)(dppe)₂] (R¹ = H, R² = Et 4a: or Prⁱ 4b; R¹ = Me, R² = Et 4c) and trans-[RuH(NCCMeCO₂Et)(PMePh₂)₄] 5. The molecular structure of 3 shows that the enolato ligand co-ordinates to the ruthenium centre via the cyano group in an octahedral geometry. These hydrido-(enolato)ruthenium(II) complexes catalyse Michael and Knoeevenagel reactions under neutral and mild conditions. The Royal Society of Chemistry 1999.

Full text of DOI:10.1039/a902860i

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Synthesis of N-bonded enolatoruthenium(II) by oxidative addition
of alkyl cyanocarboxylate to a ruthenium(0) complex
Masafumi Hirano, Atsushi Takenaka, Yuji Mizuho, Makiko Hiraoka and Sanshiro Komiya*
Department of Applied Chemistry, Faculty of Technology, Tokyo University of
Agriculture and Technology, 2-24-16 Nakacho, Koganei, Tokyo 184-8588, Japan.
E-mail: komiya@cc.tuat.ac.jp; Fax: ϩ81-42-387-7500
Received 12th April 1999, Accepted 22nd July 1999
Reaction of a zero-valent ruthenium complex [Ru(cot)(cod)] 1 (cod = 1,5-cyclooctadiene; cot = 1,3,5-cyclooctatriene)
with alkyl cyanoacetate in the presence of mono- and bi-dentate tertiary phosphines gave a series of hydrido(enolato)-
ruthenium() complexes: mer-[RuH(NCCHCO2Et)(NCCH2CO2Et)(PPh3)3] 2; trans-[RuH(NCCHCO2Et)(cod)-
(dppe)] 3 (dppe = Ph2PCH2CH2PPh2); trans-[RuH(NCCR1CO2R2)(dppe)2] (R1 = H, R2 = Et 4a: or Pri 4b; R1 = Me,
R2 = Et 4c) and trans-[RuH(NCCMeCO2Et)(PMePh2)4] 5. The molecular structure of 3 shows that the enolato
ligand co-ordinates to the ruthenium centre via the cyano group in an octahedral geometry. These hydrido-
(enolato)ruthenium() complexes catalyse Michael and Knöevenagel reactions under neutral and mild conditions.
Introduction
Transition-metal enolates have attracted considerable interest in
relation to organic syntheses, since they are capable of provid-
ing regio-, chemo- and stereo-selective products under ambient
conditions.1–9 For example, Murahashi and co-workers2,6
reported that cis-[RuH2(PPh3)4] catalysed chemoselective aldol-
type and Michael reactions, where nitriles exclusively react with
electrophiles while 1,3-dicarbonyl compounds remained unre-
acted regardless of their pKa values. We have independently
isolated the zwitterionic N-bonded enolatoruthenium() com-
plex mer-[RuH(NCCHCO2R)(NCCH2CO2R)(PPh3)3] by the
reaction of cis-[RuH2(PPh3)4] or [RuH(C2H4){P(C6H4)Ph2}-
(PPh3)2] with alkyl cyanoacetate, which acts as an active key
intermediate for catalytic aldol-type and Michael reactions.3,6
Higher reactivity of the zwitterionic enolatoruthenium() com-
plex toward electrophiles such as benzaldehyde and acrylo-
nitrile than the chelating enolatoruthenium() species derived
from 1,3-dicarbonyls is found to be responsible for Murahashi’s
chemoselectivity. Thus, the structure–reactivity relationship of
the isolated enolatoruthenium complexes is considered to be
very important to create new transition metal enolate catalysts.
In this context, the supporting ligand is believed to play an
important role in controlling the structure and reactivity of the
enolato ligand. For example, addition of Ph2PCH2CH2PPh2
(dppe) to Murahashi’s catalyst enhanced its activity.2 The com-
plexes [Ru(cod)(cot)] 1 (cod = 1,5-cyclooctadiene; cot = 1,3,5-
cyclooctatriene) are known to be versatile ruthenium(0) starting
materials for preparing various complexes by simple ligand
exchange reactions.10 We report the synthesis of N-bonded eno-
latoruthenium() complexes by oxidative addition of alkyl
cyanoacetate to these ruthenium(0) complexes in the presence
of PPh3, dppe and PMePh2 under ambient conditions, along
with their catalytic Knöevenagel and Michael reactions.
Scheme 1
those of 2 prepared by the method starting from cis-
Results and discussion
Synthesis and molecular structure of N-bonded
[RuH2(PPh3)4] or [RuH(C2H4)(P(C6H4)Ph2)(PPh3)2].3,6 This
result indicates that oxidative addition of ethyl cyanoacetate
enolatoruthenium(II) complexes
to ruthenium(0) does occur to give the N-bound enolato-
Reaction of the zero-valent ruthenium complex [Ru(cod)-
(cot)] 1 with ethyl cyanoacetate and PPh3 at room temperature
produced the enolatoruthenium() complex mer-[RuH-
(NCCHCO2Et)(NCCH2CO2Et)(PPh3)3] 2 as light yellow cubes
in 45% yield (Scheme 1). All spectroscopic data are identical to
ruthenium() complex 2.
Encouraged by this result, we attempted to prepare a series
of enolatoruthenium() complexes with some tertiary phos-
phines. Reaction of 1 with ethyl cyanoacetate in the presence of
1 equivalent of dppe at room temperature resulted in the form-
J. Chem. Soc., Dalton Trans., 1999, 3209–3216
This journal is © The Royal Society of Chemistry 1999
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Table 1 Selected bond distances (Å) and angles (Њ) of [RuH(NC-
CHCO2Et)(cod)(dppe)]ؒ0.5 C6H6 3ؒ0.5 C6H6
Ru(1)–P(1)
Ru(1)–N(1)
Ru(1)–C(7)
Ru(1)–C(11)
O(1)–C(3)
C(1)–C(2)
C(4)–C(5)
C(6)–C(13)
C(8)–C(9)
2.311(1)
2.158(2)
2.259(4)
2.250(3)
1.205(4)
1.404(5)
1.466(7)
1.511(5)
1.502(5)
1.526(5)
1.519(5)
1.534(5)
Ru(1)–P(2)
Ru(1)–C(6)
Ru(1)–C(10)
N(1)–C(1)
O(2)–C(3)
C(2)–C(3)
C(6)–C(7)
C(7)–C(8)
C(8)–C(9)
C(10)–C(11)
C(12)–C(13)
2.309(1)
2.261(3)
2.256(4)
1.146(4)
1.376(4)
1.390(5)
1.390(5)
1.511(6)
1.502(5)
1.383(5)
1.513(5)
C(9)–C(10)
C(11)–C(12)
C(14)–C(15)
P(1)–Ru(1)–P(2)
P(2)–Ru(1)–N(1)
C(3)–O(2)–C(4)
C(2)–C(3)–O(1)
C(2)–C(3)–O(2)
C(7)–C(6)–C(13)
C(7)–C(8)–C(9)
C(9)–C(10)–C(11)
C(11)–C(12)–C(13)
83.42(3)
87.09(7)
120.0(3)
128.1(4)
119.8(3)
122.3(4)
115.9(3)
124.6(3)
114.7(3)
P(1)–Ru(1)–N(1)
Ru(1)–N(1)–C(1)
C(1)–C(2)–C(3)
C(2)–C(3)–O(1)
O(1)–C(3)–O(2)
C(6)–C(7)–C(8)
C(8)–C(9)–C(10)
C(10)–C(11)–C(12)
C(6)–C(13)–C(12)
84.63(7)
171.0(3)
120.3(3)
128.1(4)
112.0(3)
127.4(3)
115.8(6)
125.5(3)
117.2(3)
Fig. 2 Time–yield curves for formation of complexes 3 (᭹) and 4a (᭺)
in the reaction of 1 with ethyl cyanoacetate in the presence of dppe in
benzene-d6 at 60 ЊC.
[128.1(4)Њ] support the contribution of an oxo π-allyl structure
to the C(2)–C(3)–O(1) linkage. Although complex 2,6 the
methyl ester analogue of 23 and the related [Re(NCCHCO2-
Et)(NCCH2CO2Et)(PMe2Ph)4]4b are found to have an intra-
molecular hydrogen bond between the enolato and the
co-ordinated ester ligands, neither an intra- nor inter-molecular
hydrogen bond has been found for 3.
Consistently, the IR spectrum of compound 3 shows charac-
teristic absorption bands at 2180 and 2061 cmϪ1 assignable to
ν(CN) and ν(Ru–H), respectively. An intense band at 1610 cmϪ1
is due to ν(C᎐O) of the enolato ligand. The 1H NMR spectrum
᎐
shows a triplet at δ Ϫ10.00 (JPH = 20.2 Hz) due to the hydride
ligand coupled to two equivalent P nuclei. Two broad signals at
δ 2.3 and 3.4 are due to the aliphatic and olefinic protons of the
cod ligand. A triplet at δ 1.47, a quartet at δ 4.62 and a singlet at
δ 3.69 are assignable to the methyl, methylene and methine pro-
tons of the enolato ligand, where the methine proton has no
coupling with P nuclei. These spectroscopic data suggest that
the N-bonded enolate structure is kept in 3 in solution and the
alternative C-bonded enolate is excluded.
When the reaction of complex 1 with ethyl cyanoacetate
was performed in the presence of 2 equivalents of dppe at 55 ЊC
for 32 h a similar ruthenium enolate complex trans-[RuH-
(NCCHCO2Et)(dppe)2] 4a having two dppe ligands was
obtained. The 1H NMR spectrum shows a quintet at δ Ϫ16.27
(JPH = 18.31 Hz) which is assignable to the hydride ligand
coupled to four equivalent P nuclei. The peaks at δ 1.47(t),
4.62(q) and 3.45(s) are assignable to the methyl, methylene and
methine protons of the enolato ligand, respectively. The IR
spectrum shows characteristic bands at 2179, 1953, and 1603
cmϪ1, which are assigned as ν(CN), ν(Ru–H), and ν(CO),
respectively. Analogously to 3, the enolato ligand would also
bind to the ruthenium through the cyano group.
While complex 4a was obtained by the reaction of 1 with
only twice the amount of dppe and ethyl cyanoacetate at 55 ЊC,
3 was exclusively formed at room temperature even in the pres-
ence of an excess of dppe. The time-course curve for the reac-
tion of 1 with dppe and ethyl cyanoacetate at 60 ЊC is shown in
Fig. 2, indicating a typical successive reaction pattern via 3.
Consistently, the reaction of 3 with 1 equivalent of dppe at
50 ЊC in benzene-d6 resulted in the facile formation of 4a by re-
leasing 1,5-cod (yield: 50% for 22 h, 100% for 118 h) (Scheme 2).
Fig. 1 An ORTEP drawing of [RuH(NCCHCO2Et)(cod)(dppe)] 3.
Hydrogen atoms are omitted for clarity. Ellipsoids represent 50%
probability.
ation of yellow crystals of trans-[RuH(NCCHCO2Et)(cod)-
(dppe)] 3 in 33% yield, which was characterised by structure
analysis, IR and NMR spectroscopies, and elemental analysis.
Light yellow cubes of compound 3ؒ0.5C6H6 suitable for X-ray
crystallography were obtained from a mixture of benzene and
hexane. The ORTEP11 drawing is depicted in Fig. 1, and
selected bond distances and angles are given in Table 1.
The overall structure is best regarded as an octahedron,
where the enolato and hydrido ligands co-ordinate in the trans
configuration and the cod and the dppe ligands lie on the
equatorial plane. In accord with the structure of 2,3,6 the eno-
lato group binds to ruthenium through the cyano group. The
short N(1)–C(1) distance (1.146 Å) with almost linear Ru(1)–
N(1)–C(1) (171.0Њ) indicates that the triple bond character of
N(1)–C(1) remains intact. The relatively short C(2)–C(3) dis-
tance [1.390(5) Å], slightly long O(1)–C(3) [1.205(4) Å], and
bond angles C(1)–C(2)–C(3) [120.3(3)Њ] and O(1)–C(3)–C(2)
3210
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Stoichiometric reactions of enolatoruthenium(II) complexes with
electrophiles
To reveal the nucleophilic properties of the enolato ligand, reac-
tions with some electrophiles were performed. As we previously
reported, protonolysis of complex 2 with hydrogen chloride
in thf liberated ethyl cyanoacetate giving the dinuclear
complex [(Ph3P)2(Cl)Ru(µ-Cl)3Ru(PPh3)2(NCCH2CO2Et)].6 On
exposure of 4a and 4c to hydrogen chloride gas, ethyl cyano-
acetate and ethyl 2-cyanopropionate (53% from 4a, 64% from
4c) and molecular hydrogen (37% from 4a, 87% from 4c) were
liberated to give a known dichlororuthenium complex, trans-
[RuCl2(dppe)2].15 Complexes 3 and 5 also reacted with hydrogen
chloride gas to give ethyl cyanoacetate (46%) and ethyl 2-
cyanopropionate (38%) with generation of molecular hydrogen
in 7 and 87% yields, respectively. The fate of the ruthenium
fragment is unclear to date.
Carbon electrophiles also reacted with the enolato ligand
of complexes 3, 4a, and 4c (Table 2). The reaction of complex
4a with methyl iodide gave ethyl cyanoacetate (26%), ethyl
2-cyanopropionate (28%), and ethyl 2-cyanoisobutyrate (58%)
and the novel hydrido(iodo)ruthenium() complex trans-
[RuH(I)(dppe)2] in 70% yield. Ethyl 2-cyanopropionate is con-
sidered to be formed by the simple methylation of the enolato
ligand. In addition, dimethylation of the enolato ligand also
took place giving ethyl 2-cyanoisobutyrate.† Similarly, 3 also
reacted with methyl iodide to give ethyl cyanoacetate (16%),
ethyl 2-cyanopropionate (15%), and ethyl 2-cyanoisobutyrate
(47%). Formation of dimethylated products may be due to the
high reactivity of alkyl cyanoacetate. In fact, reactions of 4c
with methyl, ethyl and isopropyl iodides gave corresponding
ethyl α-alkylcyanopropionate and trans-[RuH(I)(dppe)2] in
almost quantitative yields. Contrary to these results, treatments
of complex 4c with neopentyl and phenyl iodides gave no reac-
tion. Such a trend for tertiary and aryl halides is general in SN2
type reactions. These data show that the enolatoruthenium()
complexes have enough nucleophilicity for C–C bond form-
ation reactions.
Scheme 2
Complex 4a was also derived by ligand exchange of 2 with 2
equivalents of dppe in benzene-d6 even at room temperature, by
releasing PPh3 and ethyl cyanoacetate (yield: 63% for 1 h, 82%
for 3 h, 82% for 14 h). However, treatment of 4a with PPh3 at
room temperature gave no reaction. These results are reflections
of the strong co-ordination ability of the dppe ligand.
More detailed information about the oxidative addition of
ethyl cyanoacetate to ruthenium(0) was obtained from the
following experiment. Treatment of complex 1 with NCCD2-
CO2Et (90% deuteriated) in the presence of 2 equivalents of
dppe at 50 ЊC in benzene-d6 resulted in the formation of trans-
[RuD(NCCDCO2Et)(dppe)2] 4a-d2, where 80% of the hydride
and the methine proton were deuteriated. The IR spectrum
shows a new band at 1329 cmϪ1 assignable to ν(Ru–D). This
fact indicates that the hydride ligand originated on the α-methyl-
ene protons of ethyl cyanoacetate, showing formal oxidative
addition of the C–H bond to ruthenium(0). Although Chaudret
and his co-workers12 reported scrambling between Ru–H and
protons of cyclo-olefins in [RuH(cod)(cot)][BF4], such a process
is negligible in our system.
The isopropyl analogue trans-[RuH(NCCHCO2Pri)(dppe)2]
4b was also obtained in a similar way (see below). When ethyl
2-cyanopropionate was employed in this reaction with dppe
or PMePh2, trans-[RuH(NCCMeCO2Et)(dppe)2] 4c and trans-
[RuH(NCCMeCO2Et)(PMePh2)4] 5 were obtained, respectively.
Of particular interest is that two sets of hydride and enolato
ligands are observed for these complexes (see Experimental
section). As a typical example, the 1H NMR spectrum of 5 has
two overlapped quintets at δ Ϫ15.32 ( JPH = 21 Hz) and Ϫ15.27
(JPH = 21 Hz) in 2:1 ratio suggesting the presence of two
hydride ligands coupled to four equivalent P nuclei. Two pairs
of ethoxycarbonyl resonances at δ 4.6–4.8(m), 1.43(t) and
1.52(t) and two methyl protons at δ 2.80(s) and 2.75(s) were
observed in 2:1 ratio at room temperature. The variable-
temperature NMR experiments showed that these two sets of
signals coalesced into a broad peak upon heating at 60 ЊC and
recovered on cooling, suggesting that these two complexes are
exchanging with each other. Compounds 4a, 4b and 4c
also have two isomers in 4:1, 4:1, and 1.5:1 ratios at 24 ЊC.
Although a facile exchange between cis and trans isomers has
been reported for [RuH2(dmpe)2]13 and [RuH(C8H6NH)-
(dmpe)2] (C8H6NH = indole),14 this process is not operating in
our system because two sets of quintet patterns for hydride
ligands were observed throughout the variable temperature
NMR experiments, showing trans configurations of both
isomers. We believe that these isomers are most likely the (E)
and (Z) conformers of the enolato ligands as shown in eqn. (1).
A similar transformation process has been observed for the
related rhenium complex cis-[Re(NCCRCO2Et)(NCCHR-
CO2Et)(PMe2Ph)4].4b
The investigation of the stoichiometric reaction of complex
4a with benzaldehyde showed that no Knöevenagel product was
formed at room temperature even after 9 d. However, a similar
treatment in the presence of methanol as proton source gave
ethyl 2-cyanocinnamate in 9.6% yield. Interestingly, when 10
equivalents of ethyl 2-cyanopropionate was added as a proton
source to both systems, the yield of ethyl 2-cyanocinnamate
increased to 55 and 48%, respectively.‡ These results show that
4a is also susceptible to nucleophilic reactions and a suitable
proton source is required to produce the Knöevenagel product.
† One of referees pointed out that the formation of ethyl 2-cyano-
isobutyrate seems to indicate facile ligand exchange reaction between
the enolate and ethyl 2-cyanopropionate. However, treatment of com-
plex 4a with ethyl 2-cyanopropionate resulted in no reaction. Although
the detailed mechanism is not clear at present, this fact suggests that the
formation of ethyl 2-cyanoisobutyrate takes place on the ruthenium
complex.
‡ Ethyl 2-cyanopropionate only acts as a proton source and does not
react with benzaldehyde at all (cf. Table 3). The most probable product
after addition of ethyl 2-cyanopropionate to this reaction mixture is
[RuH(NCCMeCO2Et)(dppe)2].
J. Chem. Soc., Dalton Trans., 1999, 3209–3216
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Table 2 Reactions of enolatoruthenium() complexes 3, 4a and 4c
intermediate to give acrylonitrile. In this case, further Michael
with organo iodides
addition took place giving a double addition product as
Murahashi and co-workers2 reported. It is also worth noting
that ethyl 2-cyanopropionate did react more smoothly with
acrylonitrile in the presence of 4c or 5, while no Knöevenagel
reaction took place with benzaldehyde in all cases. Interestingly,
Ito and co-workers16 also recently reported that alkyl 2-cyano-
propionate did not react with benzaldehyde in the presence
of a rhodium() catalyst. The reason for this selectivity is not
clear and we should wait for further detailed mechanistic
studies.
In summary, the present reaction provides a versatile method
to give catalytically active N-bonded enolatoruthenium()
complexes from the ruthenium(0) complex [Ru(cod)(cot)] 1 by
oxidative addition of the C–H bond of the alkyl cyanocarb-
oxylate.
Yield(%)
Complex RI
3
MeI
MeI
MeI
16
26
—
—
—
—
—
15
28
0
0
0
0
0
47
58
108
90
96
0
4a
4c
4c
4c
4c
4c
EtI
iPrIa
Me3CCH2I
PhIa
0
Reaction conditions: enolatoruthenium complex, 0.1 mmol; organo
iodide, 0.226–1.19 mmol; solvent, thf; room temperature. Yields were
determined by GLC. a At 50 ЊC.
Experimental
All manipulations were carried out under dry nitrogen using
standard Schlenk and vacuum line techniques unless otherwise
noted. All solvents were distilled from appropriate drying
agents prior to use. The compound triphenylphosphine was
donated by Hokko Chemical Co; 1,2-bis(diphenylphosphino)-
ethane (dppe)17 and [Ru(cod)(cot)] 118 were prepared according
to the literature methods. Acrylonitrile and methyl iodide were
dried over anhydrous magnesium sulfate and distilled under
nitrogen. Benzaldehyde, ethyl cyanoacetate, and ethyl 2-cyano-
propionate were dried with calcium chloride and distilled under
reduced pressure. Dry hydrogen chloride was generated by
the reaction of flame dried sodium chloride with concentrated
sulfuric acid under vacuum. Deuteriated solvents for use in
NMR experiments were dried with P2O5 for CDCl3 or sodium
wire for C6D6 and were vacuum-transferred from these drying
agents.
Proton NMR spectra were recorded on JEOL FX-200, LA-
300, or Bruker AM-400 spectrometers, 31P-{1H} NMR spectra
on JEOL LA-300 (121.6 MHz) or Brucker AM-400
(161.5 MHz) spectrometers with chemical shifts reported in
ppm downfield from 85% H3PO4 in D2O. The IR spectra were
obtained on a JASCO FT/IR-5M Fourier transform spectro-
meter using KBr disks. The catalytic reactions were monitored
by a Shimadzu GC-8APF gas-liquid phase chromatograph
using glass packed PEG-20M (5 mm × 4 m) or OV-1 (5 mm × 4
m) columns with flame ionisation detection (FID). The volumes
of gases generated were measured by a Toepler pump. The GLC
analyses of inorganic gases were performed with a Shimadzu
GC-3 BT gas–liquid phase chromatograph using stainless-steel
packed molecular sieves or active carbon with thermal conduct-
ivity detection (TCD). Melting points were estimated under
nitrogen with a Yazawa MP-21 capillary melting apparatus and
are uncorrected. Elemental analyses were performed by a
YANACO CHN autocorder MT-2 or Perkin-Elmer 2400 Series
II CHN analyzer. Molar electrical conductivities were meas-
ured on a TOA model CM-7B instrument.
Catalytic Knöevenagel and Michael reactions by enolato-
ruthenium(II) complexes
Since these enolatoruthenium() complexes have shown con-
siderable nucleophilicity, they were employed as catalysts for
Michael and Knöevenagel reactions of alkyl cyanocarboxylates
with acrylonitrile or benzaldehyde and the results are in Table 3.
Results of the catalytic Knöevenagel reactions are summarised
as follows: (i) dppe ligand itself has negligible activity under the
reaction conditions (entry 1); (ii) catalytic activity increased in
the order 1, 1 ϩ dppe and 2 < 3 < 4a and 4c (entries 2–7). It is
worth noting that the triphenylphosphine ligands in 2 were
easily displaced by dppe giving the catalytically more active
complex 4. The fact is in accord with the drastic improvement
of Murahashi’s aldol type reactions of nitriles catalysed by 2 by
adding a bidentate ligand such as dppe;2 (iii) Knöevenagel reac-
tion of ethyl 2-cyanopropionate with benzaldehyde did not take
place at all (entries 8–11). The results of catalytic Michael reac-
tions are as follows: (i) dppe and 1 itself also had no catalytic
activity (entries 12–14); (ii) when the concentration of 1/dppe
catalyst increased, the yield of the double Michael product
was improved (entries 15–17); (iii) complexes 2, 3 and 4c had
moderate catalytic activity (entries 18–20); (iv) catalytic
Michael reactions of ethyl 2-cyanopropionate to give acrylo-
nitrile smoothly proceeded with 4c or 5, while dppe, 1 and a
mixture of 1 and dppe showed negligible activity (entries 21–
25).
From the above results in combination with our previous
mechanistic report on Murahashi’s aldol reaction,6 a possible
mechanism for the present Knöevenagel reaction has been pro-
posed as shown in Scheme 3. First of all complex 4a is formed
from 1 via 3 or 2 in the presence of dppe ligand under ambient
conditions. The formal oxidative addition of the C–H bond of
the α-methylene proton of ethyl cyanoacetate to ruthenium(0)
takes place to give an hydrido(enolato)ruthenium() complex.
The enolato ligand in 4a is nucleophilic enough to react with
benzaldehyde to give the aldolatoruthenium() intermediate 6.
Since ethyl 2-cyanopropionate showed no reactivity, this nucleo-
philic reaction step may be sensitive to the steric properties of
the reaction centre. In the presence of an excess amount of ethyl
cyanoacetate the incoming ethyl cyanoacetate would act as a
proton source to give the product. The dehydration process
proceeds rapidly and irreversibly to produce 4a, liberating
ethyl cyanocinnamate and water. This mechanism is similar to
the one proposed for the reaction catalysed by 23,6 or [Re(NC-
CHCO2R)(NCCH2CO2R)(PMe2Ph)4],4 but the nucleophilicity
of the N-bonded enolato ligand would be much more enhanced
by the loss of hydrogen bonding between it and the co-
ordinated ester ligands.
Reactions of [Ru(cod)(cot)] 1 with ethyl cyanoacetate in the
presence of tertiary phosphine ligand
With PPh3. To a mixture of complex 1 (279.0 mg, 0.885
mmol) and PPh3 (656.0 mg, 2.50 mmol) in thf (5 cm3) was
added ethyl cyanoacetate (260 µl, 2.44 mmol) by syringe under
nitrogen. After stirring at room temperature for 45 h the result-
ing light yellow precipitate was separated by filtration.
Recrystallisation from a mixture of benzene–hexane gave
bright yellow cubes of [RuH(NCCHCO2Et)(NCCH2CO2Et)-
(PPh3)3] 2 in 45% yield (436.8 mg, 0.392 mmol). All spectro-
scopic data were identical to those of 2 derived from the alter-
native method,3,6 mp 120–121 ЊC (decomp.); νmax/cmϪ1 3000m,
2184s, 1950w, 1746s, 1600s, 1574s, 1480s, 1434s, 1328m, 1187m,
1137m, 1090w, 743s, 697vs and 519vs; δH[200 MHz, C6D6, room
Michael reactions are also considered to proceed in a similar
way involving nucleophilic reaction of an enolatoruthenium()
3212
J. Chem. Soc., Dalton Trans., 1999, 3209–3216

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Table 3 Catalytic Knöevenagel and Michael reactionsa
Active hydrogen
compound
Entry
Catalyst
(mol%)
Electrophile
Product
Yield(%)
1
2
3
4
5
6
7
dppe
1
1 ϩ dppe
2
3
4a
4c
(1.0)
(1.0)
(1.0)
(1.0)
(1.0)
(1.0)
(1.0)
0.8
29
32
29
52
76
80
8b
9b
dppe
1
1 ϩ dppe
5
(1.0)
(1.0)
(1.0)
(1.0)
No reaction
No reaction
No reaction
No reaction
10b
11
12
13
14
15
16
17
18
19
20
dppe
dppe
1
(1.0)
(4.8)
(1.0)
(1.0)
(4.4)
(5.6)
(1.0)
(1.0)
(1.0)
0.2
2.1
0
1 ϩ dppe
0
1 ϩ dppe
8.1
22
29
29
34
1 ϩ dppe
2
3
4c
21
22
23
24
25
dppe
1
1 ϩ dppe
4c
5
(1.0)
(1.0)
(1.0)
(1.3)
(1.0)
2.5
3.3
4.7
61
77
a Conditions: solvent = tetrahydrofuran; 50 ЊC; 36 h. b In C6D6.
temperature (r.t.)] Ϫ12.9 (br, 1 H), 0.83 (br t, J = 7.3, 3 H), 1.17
(br t, J = 7.3, 3 H), 2.9 (br, 2 H), 3.1 (s, 2 H), 3.76 (br q, J = 7.3,
2 H), 4.22 (br q, J = 7.3 Hz, 2 H), 6.9 (br s, 27 H) and 7.6 (br s,
18 H).
Major isomer: δH(200 MHz, C6D6, r.t.) Ϫ16.27 (qnt, JPH = 18.31,
1 H), 1.47 (t, J = 7.3, 3 H), 1.98 (br, 2 H), 2.78 (br, 2 H),
3.45 (s, 1 H), 4.62 (q, J = 7.3 Hz, 2 H), 6.85 (br, 8 H), 7.08
(br, 8 H), 7.12 (br, 8 H), 7.31 (br, 8 H) and 7.50 (br, 8 H);
δP (122.55 MHz, C6D6, 24 ЊC) 66.3 (s). Minor isomer (signals
overlapped with the major ones preventing complete charac-
terisation, only several peaks characterised.): δH(300 MHz,
C6D6, 24 ЊC) Ϫ16.36 (qnt, JPH = 19.8, 2 H), 1.38 (t, J = 7.8
Hz, 3 H), 2.56 (br, 4 H) and 3.25 (s, 1 H); δP(122.55 MHz,
C6D6, 24 ЊC) 66.0 (s).
With dppe at room temperature. Ethyl cyanoacetate (190 µl,
1.79 mmol) was added to a benzene solution (3 cm3) of com-
pound 1 (279.0 mg, 0.885 mmol) and dppe (286.6 mg, 0.978
mmol) under nitrogen. The mixture was allowed to react at
room temperature for 6 d. Addition of hexane (ca. 1 cm3) to the
mixture and slow diffusion of the hexane layer into the benzene
phase in a refrigerator resulted in the formation of light yellow
crystals of [RuH(NCCHCO2Et)(cod)(dppe)] 3 in 33% yield
(220.9 mg, 0.291 mmol), mp 166–169 ЊC (decomp.) (Found: C,
66.15; H, 6.69; N, 1.97. C39H43NO2P2Ruؒ0.5C6H6 requires C,
66.40; H, 6.10; N, 1.84%); Λ = 0.002 9 S cm2 molϪ1 (thf, 25 ЊC);
A similar treatment of complex 1 (13.4 mg, 0.0425 mmol)
with dppe (34.4 mg, 0.0863 mmol) and NCCD2CO2Et (4.8 µl,
0.044 mmol, 90% deuteriated) gave [RuD(NCCDCO2Et)-
1
(dppe)2] 4a-d2 in 76% yield (32.8 mg, 0.0324 mmol). The H
NMR spectrum shows that the hydride and the methine pro-
ton were 80% deuteriated; νmax/cmϪ1 3060m, 2174s, 1629s,
1605 (sh), 1585 (sh), 1483m, 1462s, 1434m, 1409w, 1373w,
1329w, 1133m, 1097s, 812m, 743s, 697vs, 669m, 530s, 507m
and 491m.
Ϫ1
νmax/cm 3090m, 2990m, 2180s, 2061w, 1610vs, 1420s, 1090s,
690vs and 515s (KBr, r.t.); δH(200 MHz, C D6, r.t.) Ϫ10.00
6
(t, JPH = 20.2, 1 H), 1.60 (m, 2 H), 1.47 (t, J = 7.3, 3 H), 2.0 (br, 2
H), 2.3 (br, 2 H), 3.4 (br, 2 H), 3.69 (s, 1 H), 4.4 (br, 1 H), 4.62
(q, J = 7.3, 2 H), 7.01 (br, 4 H), 7.09 (m, 4 H), 7.28 (t, J = 8.9,
4 H), 7.70 (t, J = 8.9, 4 H) and 7.93 (t, J = 8.9 Hz, 4 H).
Reaction of compound 1 with isopropyl cyanoacetate in the
presence of dppe
With dppe at 55 ЊC. To a benzene solution (4 cm3) of com-
pound 1 (166.5 mg, 0.528 mmol) and dppe (462.2 mg, 1.16
mmol) was added ethyl cyanoacetate (110 µl, 1.03 mmol) under
nitrogen. After stirring at 55 ЊC for 32 h a yellow powder was
deposited by addition of hexane. Recrystallisation of the pre-
cipitate from benzene–hexane at 0 ЊC gave yellow crystals of
[RuH(NCCHCO2Et)(dppe)2] 4a in 65% isolated yield (348.9
mg, 0.345 mmol), mp 278–280 ЊC (decomp.) (Found: C, 69.02;
A similar treatment of complex 1 (78.8 mg, 0.250 mmol) with
dppe (202.2 mg, 0.507 mmol) and isopropyl cyanoacetate (68
µl, 0.54 mmol) as mentioned above resulted in the formation of
i
[RuH(NCCHCO2 Pr)(dppe)2] 4b in 35% yield (90.1 mg, 0.088
mmol) (Found: C, 68.35; H, 6.21; N, 1.47. C58H57NO2P4Ru
requires C, 68.90; H, 6.36; N, 1.24%); νmax/cmϪ1 3100m, 2174s,
1949w, 1603vs, 1483w, 1434s, 1403s, 1139m, 1112s, 1099s,
1071m, 978m, 875m, 811m, 743s, 695vs and 527vs (KBr, r.t.).
Compound 4b is found to have two isomers, due to (E) and (Z)
isomers of the enolato ligand. The ratio of the major:minor
isomers is 4:1 at 24.0 ЊC. Major isomer: δH(300 MHz, C6D6,
24 ЊC) Ϫ16.27 (qnt, J = 18, 1 H), 1.56 (d, J = 6.6, 6 H), 1.98 (m,
4 H), 2.62 (m, 4 H), 3.42 (s, 1 H), 5.69 (sept, J = 6.6 Hz, 1 H),
6.85 (m, 12 H), 7.09 (m, 12 H), 7.29 (br, 8 H) and 7.49 (br, 8 H);
H, 5.59; N, 1.31. C57H55NO P4Ruؒ0.5C6H6 requires C, 68.63;
2
H, 5.57; N, 1.33%); Λ = 0.064 S cm2 molϪ1 (thf, at 25 ЊC); νmax
/
cmϪ1 3100m, 3000m, 2179s, 1953w, 1603vs, 1375w, 1440s, 1100s,
690vs and 530s (KBr, r.t.). Compound 4a has two isomers,
which would be due to the (E) and (Z) isomers of the enolato
ligand. The ratio of major:minor isomers is 4:1 at 24 ЊC.
J. Chem. Soc., Dalton Trans., 1999, 3209–3216
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Scheme 3
δP(121.55 MHz, C6D6, r.t.) 66.36 (s). Minor isomer (signals were
Reaction of compound 1 with ethyl 2-cyanopropionate in the
overlapped with the major ones preventing complete character-
isation, only several peaks characterised): δH(300 MHz, C6D6,
24.0 ЊC) Ϫ16.33 (qnt, J = 18, 1 H), 1.50 (d, J = 6.6, 6 H), 2.63
(m, 4 H), 3.22 (s, 1 H) and 5.84 (sept, J = 6.6 Hz); δP(121.55
MHz, C6D6, r.t.) 67.66 (s).
presence of PMePh2
Ethyl 2-cyanopropionate (120 µl, 0.953 mmol) was added into a
mixture of complex 1 (274.3 mg, 0.870 mmol) and 4 equivalents
of PPh2Me (690 µl, 3.67 mmol) in thf (5 cm3) under nitrogen.
After stirring at 55 ЊC for 30 h hexane was added to precipit-
ate a pale yellow powder. This was washed with hexane and
diethyl ether to give analytically pure [RuH(NCCMeCO2Et)-
(PMePh2)4] 5 in 93% yield (821.3 mg, 0.810 mmol), mp 154–
156 ЊC (Found: C, 69.53; H, 6.34; N, 1.43. C58H57NO2P4Ruؒ
C6H6 requires C, 69.42; H, 6.10; N, 1.27%); Λ = 0.002 2 S cm2
molϪ1; νmax/cmϪ1 3040w, 2159m, 2098w, 1968w, 1618vs, 1584w,
1479m, 1434s, 1324m,1090s, 889s, 742s, 696s, 678s and 505s.
Compound 5 also has two isomers, which would be due to (E)-
and (Z)-isomers of the enolato ligand. The ratio of these
isomers is 2/1 at r.t.. Major isomer: δH(200 MHz, C6D6, r.t.)
Ϫ15.32 (qnt., JPH = 21 Hz, 1 H), 1.43 (t, J = 7 Hz, 3 H), 1.80
(s, 12 H), 2.80 (s, 3 H), 4.6–4.8 (m, 2 H), 6.83 (br, 24 H) and
7.38 (br, 16 H). Minor isomer: δH(200 MHz, C6D6, r.t.)
Ϫ15.27 (qnt, JPH = 21, 1 H), 1.52 (t, J = 7 Hz, 3 H), 1.84 (s,
12 H), 2.75 (s, 3 H), 4.6–4.8 (m, 2 H), 6.83 (br, 24 H) and
7.38 (br, 16 H).
Reaction of compound 1 with ethyl 2-cyanopropionate in the
presence of dppe
A similar treatment of complex 1 (85.9 mg, 0.272 mmol) with
dppe (231.1 mg, 0.580 mmol) and ethyl 2-cyanopropionate
(68 µl, 0.54 mmol) as described above resulted in the forma-
tion of [RuH(NCCMeCO2Et)(dppe)2] 4c in 42% isolated yield
(117.1 mg, 0.114 mmol); mp 279–282 ЊC (Found: C, 68.53; H,
5.92; 1.34%. C58H57NO2P4Ruؒ0.5C6H6 requires C, 68.85; H,
5.68; N, 1.32%); Λ = 0.001 7 S cm2 molϪ1 (thf, 25 ЊC); νmax
/
cmϪ1 2950w, 2183s, 2087w, 1605vs, 1440s, 1410s, 1160s, 730s
and 700s. Compound 4c also has two isomers, due to (E)-
and (Z)-isomers of the enolato ligand. The ratio of
major:minor isomers is 1.5:1 at r.t.. Major isomer: δH(200
MHz, C6D6, r.t.) Ϫ16.37 (qnt, JPH = 19.6, 1 H), 1.39 (t,
J = 7.3, 3 H), 1.98 (s, 3 H), 2.58 (br, 4 H), 2.92 (br, 4 H), 4.65
(q, J = 7.3 Hz), 6.78 (br, 8 H), 7.01 (br, 8 H), 7.10 (br, 8 H),
7.31 (br, 8 H) and 7.49 (br, 8 H); δP(161.5 MHz, C6D6, r.t.)
69.89 (s). Minor isomer (signals overlapped with the major
ones preventing complete characterisation, only several peaks
characterised): δH(200 MHz, C6D6, r.t.) Ϫ16.27 (qnt, JPH = 19.6,
1 H), 1.54 (t, J = 7.3, 3 H), 2.08 (s, 3 H) and 4.69 (q, J = 7.3 Hz);
δP(161.5 MHz, C6D6, r.t.) 70.76 (s).
Time-course of the reaction of compound 1 with ethyl
cyanoacetate in the presence of dppe
Compound 1 (21.4 mg, 0.0678 mmol), dppe (53.6 mg, 0.135
mmol) and triphenylmethane as an internal standard (4.3 mg,
0.018 mmol) were dissolved in benzene-d6 (600 µl) under nitro-
gen. Ethyl cyanoacetate (14.0 µl, 0.132 mmol) was added and
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J. Chem. Soc., Dalton Trans., 1999, 3209–3216

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the mixture heated at 60 ЊC in a thermostatted oil-bath. The
yields of 3 and 4a were estimated by using the methine peak of
triphenylmethane (δ 5.43) in the H NMR spectra: 1.5 h, 3
(52%), 4a (18%); 5 h, 3 (30%), 4a (67%); 6.5 h, 3 (19%), 4a
(78%); 14 h, 3 (0%), 4a (96%).
Reactions of enolatoruthenium(II) complexes 3, 4a and 4c with
methyl iodide
1
Complex 3. Methyl iodide (74.0 µl, 1.19 mmol) was added to
compound 3 (85.8 mg, 0.119 mmol) in dry thf (ca. 2 cm3). After
stirring the reaction mixture for 46 h at room temperature, ethyl
cyanoacetate (0.0188 mmol, 16%), ethyl 2-cyanopropionate
(0.0178 mmol, 15%), ethyl 2-cyanoisobutyrate (0.0564 mmol,
47%) and 1,5-cod (0.0126 mmol, 11%) were produced.
Reaction of compound 2 with dppe
Compound 2 (17.7 mg, 1.59 mmol) was treated with 2 equiv-
alents of dppe (13.2 mg, 0.0331 mmol) in benzene-d at room
6
temperature. After reaction for 1 h 4a and ethyl cyanoacetate
were detected in 63 and 50% yields, respectively. After 3 h 2 had
completely disappeared to give 4a and ethyl cyanoacetate in
82 and 60% yields, respectively. These yields did not change for
14 h.
Complex 4a. Methyl iodide (48.0 µl, 0.771 mmol) was added
to compound 4a (77.8 mg, 0.0770 mmol) in dry thf (ca. 2 cm3).
After stirring the reaction mixture for 47 h at room temper-
ature, ethyl cyanoacetate (0.0196 mmol, 26%), ethyl 2-cyano-
propionate (0.0218 mmol, 28%) and ethyl 2-cyanoisobutyrate
(0.0443 mmol, 58%) were produced. Then, all volatile materials
were removed under vacuum to give a yellow solid, which was
washed with ether giving analytically pure trans-[RuH(I)-
(dppe)2] in 70% yield (55.1 mg, 0.0537 mmol) (Found: C, 60.02;
H, 5.01; I, 11.16. C52H49IP4Ru requires C, 60.88; H, 4.81; N,
12.37%); νmax/cmϪ1 3040w, 2068m, 1585w, 1572w, 1584m, 1432s,
1187w, 1154w, 1089s, 1066 (sh), 881m, 820s, 740s, 694vs, 648s,
529vs, 509s, 486s, 423s and 418m; δH(200 MHz, CDCl3, r.t.)
Ϫ16.23(qnt, J = 19.5 Hz, 1 H), 2.13 (br, 4 H), 2.76 (br, 4 H) and
6.94–7.26 (m, 40 H).
Reaction of compound 3 with dppe
Compound 3 (21.1 mg, 0.0293 mmol) was treated with dppe
(12.2 mg, 0.0306 mmol) in a benzene-d6 (600 µl). After reaction
at 50 ЊC for 22 h 50% of 3 was converted into 4a (yield 50%)
with liberation of 1,5-cod (50%). After 118 h 3 was completely
converted into 4a (yield 100%) with liberation of 1,5-cod
(100%).
Reaction of compound 4a with PPh3 and ethyl cyanoacetate
Compound 4a (10.9 mg, 0.0108 mmol) was treated with 3
equivalents of PPh3 (8.7 mg, 0.033 mmol) and 1 equivalent of
ethyl cyanoacetate (1.2 µl, 0.011 mmol) in benzene-d6 at room
temperature. There was no reaction.
Complex 4c. Methyl iodide (30.0 µl, 0.480 mmol) was added
to compound 4c (145.9 mg, 0.133 mmol) in thf (ca. 2 cm3).
After reaction at room temperature for 18 h ethyl 2-cyano-
isobutyrate (0.144 mmol, 108%) was produced. Hexane was
added to give a precipitate. Recrystallisation of the powder
from dichloromethane–hexane gave microcrystals, which were
characterised as [RuH(I)(dppe)2] by the following spectroscopic
data (yield: 20%, 27.8 mg, 0.0271 mmol); νmax/cmϪ1 3040w,
2067m, 1585w, 1572w, 1482m, 1432s, 1187w, 1153w, 1088s,
1073 (sh), 881m, 819s, 739s, 693vs, 648s, 529vs, 509s, 485s, and
417m; δH(200 MHz, CDCl3, r.t.) Ϫ16.23(qnt, J = 19.5 Hz, 1 H),
2.14 (br, 4 H), 2.78 (br, 4 H) and 6.95–7.26 (m, 40 H).
Protonolyses of enolatoruthenium(II) complexes 3, 4a, 4c and 5
with hydrogen chloride
Complex 3. Tetrahydrofuran (ca. 2 cm3) was introduced into
a Schlenk tube (20 cm3) containing compound 3 (58.8 mg,
0.0816 mmol) under vacuum by a trap-to-trap method. Dry
hydrogen chloride gas (28.7 cm3, 1.28 mmol) was added under
vacuum by using a mercury manometer. The reaction mixture
was stirred at room temperature for 24 h. The gas generated was
collected by using a Toepler pump and characterised by GLC,
giving molecular hydrogen (0.0056 mmol, 6.9%) and ethyl
cyanoacetate (0.038 mmol, 46%).
Reactions of enolatoruthenium(II) complex 4c with alkyl iodides
Ethyl iodide. Ethyl iodide (30.0 µl, 0.380 mmol) was added to
compound 4c (116.6 mg, 0.114 mmol) in thf (ca. 2 cm3). After
stirring for 46 h at room temperature ethyl 2-cyano-2-methyl-
butyrate (0.102 mmol, 90%) was produced.
Complex 4a. Compound 4a (103.3 mg, 0.102 mmol) was dis-
solved in 1,2-dimethoxyethane (ca. 2 cm3) in a Schlenk tube (20
cm3) under vacuum and dry hydrogen chloride gas (23.5 cm3,
0.971 mmol) introduced under vacuum. After stirring the solu-
tion at 50 ЊC for 25 h, molecular hydrogen (0.0373 mmol, 37%)
and ethyl cyanoacetate (0.0541 mmol, 53%) were detected. The
resulting precipitate was separated by filtration and washed
with hexane. After drying under vacuum a yellow powder was
obtained (153.8 mg). νmax/cmϪ1 3040m, 1585w, 1571w, 1484m,
1433vs, 1097 (br), 874w, 824m, 744m, 697vs, 527s and 520s.
Isopropyl iodide. Isopropyl iodide (60.0 µl, 0.601 mmol) was
added to compound 4c (61.6 mg, 0.0601 mmol) in thf (ca.
2 cm3). After stirring for 8 h at 50 ЊC ethyl 2-cyano-2,3-
dimethylbutyrate (0.0576 mmol, 96%) was produced. The
resulting precipitate was washed with ether and dried under
vacuum to give trans-[RuH(I)(dppe)2] in 81% yield (50.0 mg,
0.0487 mmol).
Neopentyl iodide. Neopentyl iodide (30.0 µl, 0.226 mmol) was
added to complex 4c (77.2 mg, 0.0753 mmol) in thf (ca. 2 cm
After stirring for 3 d at 30 ЊC no new products were observed by
GLC analysis. Hexane was added to give a precipitate which
was characterised as 4c (55.2 mg, 0.0542 mmol, 72%).
Complex 4c. Compound 4c (152.0 mg, 0.148 mmol) was dis-
solved in thf (ca. 2 cm3) and dry hydrogen chloride gas
(30.3 cm3, 1.35 mmol) introduced under vacuum. After 7 h at
room temperature, molecular hydrogen (0.128 mmol, 87%) and
ethyl 2-cyanopropionate (0.0902 mmol, 64%) were produced.
A yellow powder was precipitated by addition of hexane.
Recrystallisation of it from dichloromethane–hexane gave
yellow crystals. νmax/cmϪ1 3040w, 1485m, 1433vs, 1262w, 1096vs,
697vs and 527s. δH(200 MHz, CDCl3, r.t.) 2.56–2.97 (m, 8 H),
6.7–7.0 (m, 32 H), 7.5 (m, 4 H) and 8.2 (m, 4 H).
3).
Phenyl iodide. Phenyl iodide (50.0 µl, 0.450 mmol) was added
to complex 4c (159.6 mg, 0.156 mmol) in thf (ca. 2 cm3). After
stirring for 3 d at 50 ЊC no new products were observed by GLC
analysis. All volatile materials were evaporated under vacuum
and the resulting solid was washed with ether to recover 4c (93.9
mg, 0.0920 mmol, 59%).
Complex 5. Compound 5 (113.6 mg, 0.110 mmol) was dis-
solved in 1,2-dimethoxyethane (ca. 2 cm3) and dry hydrogen
chloride gas (26.8 cm3, 1.10 mmol) introduced under vacuum.
The solution turned to green from yellow within 10 min. After
reaction at 50 ЊC for 16 h molecular hydrogen (0.0961 mmol,
87%) and ethyl 2-cyanopropionate (0.0422 mmol, 38%) were
produced.
Stoichiometric reaction of compound 4a with benzaldehyde
Benzaldehyde (5.4 µl, 0.053 mmol) was added to a thf solution
(3 cm3) of complex 4a (52.2 mg, 0.0516 mmol) and bibenzyl
(11.5 mg, 0.0631 mmol) as an internal standard under nitrogen.
After stirring for 9 d at 30 ЊC no Knöevenagel products were
J. Chem. Soc., Dalton Trans., 1999, 3209–3216
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Table 4 Crystallographic data for [RuH(NCCHCO2Et)(cod)(dppe)]ؒ
0.5C6H6 3ؒ0.5C6H6
observed by GLC analysis. Then, ethyl 2-cyanopropionate (66.0
µl, 0.524 mmol) was added and the mixture was kept at 30 ЊC. A
Knöevenagel product, ethyl 2-cyanocinnamate, was detected in
30 and 55% yields after 1 h and 1 d, respectively.
Chemical formula
C42H46NO2P2Ru
759.86
Formula weight
Crystal system
Space group
a/Å
b/Å
Monoclinic
P21/c
19.055(3)
10.080(2)
19.720(4)
102.31(2)
3700(1)
Stoichiometric reaction of compound 4a with benzaldehyde in the
presence of methanol
Benzaldehyde (5.4 µl, 0.053 mmol) was added to a thf solution
(3 cm3) of complex 4a (52.7 mg, 0.0521 mmol) and bibenzyl
(11.3 mg, 0.0620 mmol) as an internal standard under nitrogen.
After stirring for 26 h at 30 ЊC no Knöevenagel product was
detected. Then, methanol (22 µl, 0.054 mmol) was added
and stirred at 30 ЊC for 9 d. A Knöevenagel product, ethyl
2-cyanocinnamate, was detected in 9.6% yield. Then, ethyl
2-cyanopropionate (66.0 µl, 0.524 mmol) was added and kept
at 30 ЊC. Ethyl 2-cyanocinnamate increased to 22 and 48% after
1 h and 1 d, respectively.
c/Å
β/Њ
V/Å3
Z
4
µ(Mo-Kα)/cmϪ1
1.511
9523
6288 (|Fo| > 3σ|Fo|)
0.0588
0.0488
No. data collected
No. observed for refinement
R
RЈ
Acknowledgements
Catalytic Michael reaction between ethyl cyanoacetate and
acrylonitrile
We are grateful to Ms. S. Kiyota for NMR measurements. This
work is financially supported by a Grant-in-Aid for Scientific
Research from the Ministry of Education, Science, Sports and
Culture, Japan and Proposal-Based New Industry Creative
Type Technology R&D Promotion Program from the New
Energy and Industrial Technology Development Organization
(NEDO) of Japan.
As a typical example, the catalytic Michael reaction with com-
plex 4a is described. Ethyl cyanoacetate (185 µl, 1.74 mmol) and
acrylonitrile (230 µl, 3.49 mmol) were added to a thf solution (2
cm3) of 4a (17.4 mg, 0.0172 mmol) under argon. The reaction
mixture was stirred at room temperature for 36 h. All volatile
materials were removed under reduced pressure and then
benzene-d6 (600 µl) and 1,4-dioxane (3.0 µl, 0.036 mmol) as
internal standard were added to the residue. The conversion of
ethyl cyanoacetate and the yield of the double Michael product
were 95 and 75%, respectively. No mono Michael product was
observed. NMR spectrum of the double Michael product
NCC(CH2CH2CN)2CO2Et: δH(200 MHz, C6D6, r.t.) 1.75 (dt,
J = 14.6, 7.2, 2 H, CH2CH2 CN), 1.96 (dt, J = 14.6, 7.2, 2 H,
CH2CH2CN), 2.26 (t, J = 7.2, 4 H, CH2CN) and 4.16 (q, J = 7.2
Hz, 2 H, OCH2). Other catalytic Michael reactions of ethyl
cyanoacetate and ethyl 2-cyanopropionate were performed
analogously and the results are summarised in Table 3.
References
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Japan.
Catalytic Knöevenagel reaction between ethyl cyanoacetate and
benzaldehyde
Ethyl cyanoacetate (170 µl, 1.60 mmol) and benzaldehyde (170
µl, 1.67 mmol) were added to a thf solution (2 cm3) of complex
4a (16.2 mg, 0.0160 mmol) under argon then stirred at room
temperature for 36 h. After removal of all volatile materials,
benzene-d6 (600 µl) and 1,4-dioxane (3.0 µl, 0.036 mmol) as
internal standard were added to the residue. The yield of the
dehydrated Knöevenagel product was 66% based on ethyl
cyanoacetate. NMR spectrum of (E)-CH(Ph)᎐C(CN)(CO Et):
᎐
2
δH(200 MHz, C6D6, r.t.) 1.00 (t, J = 7.3, 3 H, OCH2CH3), 4.02
(q, J = 7.3 Hz, 2 H, OCH2CH3), 6.95–7.71 (m, 5 H, C6H5) and
8.03 (s, 1 H, CH᎐C). Other catalytic Knöevenagel reactions
᎐
were performed analogously and the results are summarised in
Table 3.
Crystallography
Yellow crystals of compound 3 were grown from a saturated
solution of benzene–hexane. The crystallographic data were
collected at 20 ЊC on a Rigaku AFC5R diffractometer using
Mo-Kα radiation (λ = 0.710 69 Å). Using the criterion
|Fo| > 3.0σ|Fo|, 6288 out of 9523 reflections were used for calcu-
lation. The structure was solved by Patterson methods using the
R-CRYSTAN program.19 The hydrogens H(4B), H(5C), H(8A),
H(8B), H(9A), H(9B), H(12A), H(12B), H(13A), H(13B),
H(26), H(37), H(40), H(41) and H(42) were located at the ideal
positions and not refined. Others were found in the Fourier-
difference map and refined isotropically. The final R (RЈ)
value was 0.0588 (0.0488). The crystallographic data are sum-
marised in Table 4.
CCDC reference number 186/1593.
Paper 9/02860I
3216
J. Chem. Soc., Dalton Trans., 1999, 3209–3216