Synthesis and NMR study of N-heterocyclic carbenes (NHC) precursors derived from troger's base

Article abstract of DOI:10.13005/ojc/290426

Since the discovery of olefin metathesis reactions, various catalysts have been developed but those based on Ruthenium and N-heterocyclic carbenes (NHC) ligands are particularly more efficient. Herein, we report a synthesis of NHC precursors derived from

Full text of DOI:10.13005/ojc/290426

ISSN: 0970-020 X
CODEN: OJCHEG
2013, Vol. 29, No. (4):
Pg. 1489-1496
ORIENTAL JOURNAL OF CHEMISTRY
An International Open Free Access, Peer Reviewed Research Journal
www.orientjchem.org
Synthesis and NMR study of N-heterocyclic
Carbenes (NHC) Precursors Derived from Troger’s Base
ERIC MUSENgIMANA and CLAvER FATAkANwA
Department of Chemistry, National University of Rwanda, Faculty of Science,
P.O. Box 117 Butare, Rwanda.
*Corresponding author E-mail: emusengimana@nur.ac.rw
http://dx.doi.org/10.13005/ojc/290426
(Received: October 28, 2013; Accepted: December 04, 2013)
ABSTRACT
Since the discovery of olefin metathesis reactions, various catalysts have been developed
but those based on Ruthenium and N-heterocyclic carbenes (NHC) ligands are particularly more
efficient. Herein, we report a synthesis of NHC precursors derived from the Tröger’s base and its
analogues which can be used in the synthesis of the new kind of metathesis catalysts. The NHC
derived from the Tröger’s base present a particular chirality that could affect stereoselectivity of
catalysis, and the form “V”of these ligands implies that the aromatic substituents point totally outside
the coordination sphere of the metal, where would be no steric hindrance unlike what happens with
the usual NHC.
key words: NHC (N-heterocyclic carbenes), Tröger’s base,
Perhalogenated adducts, thioureas adducts.
INTRODUCTION
efficient metathesis catalysts based on ruthenium
and N-heterocyclic carbenes (NHC) ligands5-10
.
Since their discovery in 1931, increasing
The NHC are stable derivatives of divalent carbon.
Since their discovery by Arduengo in 1991 11, they
are increasingly used as ligands in organometallic
chemistry. These electron-rich and sterically
hindered compounds exert a beneficial influence
on the activity of the metal complexes in which
they are incorporated 5.Because of their structural
diversity and the strength of their connections with
most metals, they lead to robust and selective active
species that can be used under mild conditions.They
have already given rise to a wide range of catalytic
systems and their development is still far from
attention is still paid to the olefination metathesis
1
reactions . These reactions correspond to the
redistribution of hydrocarbon backbone of the
molecules in which carbon-carbon double bonds
2
are rearranged . They have multiple and varied
applications in organic synthesis, in perfume industry,
in biology, in pharmaceutical chemistry, in polymers
and petrochemicals industry.Therefore, considerable
progress has been made for the development of
olefin metathesis in organic synthesis 3, 4.Numerous
studies have been devoted to the development of

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MUSENGIMANA & FATAkANwA, Orient. J. Chem., Vol. 29(4), 1489-1496 (2013)
complete 12. Among the hundreds of NHC available 6H,12H-5,11-methanodibenzo [b,f][1,5]diazocine,
at present, the most used are imidazole derivatives weresynthesizedaccordingtothemethodsdescribed
[IMes:1,3-bis(2,4,6-trimethylphenyl)-imidazol-2- in the litterature13 ,15-17. The removal of methylene
ylidene and SIMes:1,3-bis(2,4,6-trmethylphenyl)- bridge to the above Tröger’s base leading to the
imidazolin-2-ylidene] especially in many metal corresponding diazocines (2a-d): -2,8-Dimethyl-
complexes for olefin metathesis.
5,6,11,12-tetrahydrodibenzo [b, f] [1,5] diazocine,-
2,8-Dimethoxy-5,6,11,12-tetrahydrodibenzo [b, f] [1,5]
The Tröger’s base has been synthesized in diazocine, -2,8-dichloro-5,6,11,12-tetrahydrodibenzo
1887 by JuliusTröger, but its structure was elucidated [b, f] [1,5] diazocine, -5,6,11,12-tetrahydrodibenzo [b,
38 years later by Vladimir Prelog and confirmed by f] [1,5] diazocine were synthesized according to the
X-ray diffraction in 1986 13
.
methods described in the literature18.
In the last thirty years, considerable Synthesis of C6F5-adduct ofTröger’s base bearing
progress has been made for the development of the chloro, methyl and methoxy groups (3a-3c)
olefin metathesis reactions in organic synthesis3, 4,
14
In a GPC bottle, glacial acetic acid (1
and numerous studies have been devoted to the mL); 2,8-Dichloro-5,6,11,12-tetrahydrodibenzo [b, f]
development of efficient metathesis catalysts based [1,5] diazocine (1 mmol) or 2,8-Dimethyl-5,6,11,12-
on ruthenium and NHC ligands6, 14.However, no work tetrahydrodibenzo [b, f] [1,5] diazocine ( 1 mmol) or
has been reported to the synthesis of carbenes 2,8-Dimethoxy-5,6,11,12-tetrahydrodibenzo [b, f]
derived from Tröger’s base or their use as ligands [1,5] diazocine ( 1 mmol) and C6F5CHO (1.5 mmol)
in organometallic catalysis. The purpose we set for were introduced. The reaction mixture was stirred
this study was to synthesize carbene precursors at room temperature until a precipitate appears. It
(perhalogenated adducts and thioureas) derived from was filtered and washed with cold methanol (-20 °
the Tröger’s base and to investigate their conversion C). The resulting white solids were extracted with
into carbenes or into ruthenium complexes.
dichloromethane. After evaporation under reduced
pressure, the solid was analyzed by NMR.
ExPERIMENTAL
Methyl derivative (3a)
Solvents used were of technical grade and
5h, white solid, yield: 0.32 g; 76%; 1H NMR
commercial reagents were purchased from Acros, (400 MHz, CDCl3) δ 7.1-6.9 (m, 2H), 6.8-6.7 (m, 2H),
2
Sigma-Adrich, ABCR, TCI or Apollo scientific and 6.5 (s, 1H), 6.2 (s, 1H), 5.5 (s, 1H), 4.75 (d, JHH
=
used as received unless stated otherwise.THF was 16.6 Hz, 1H), 4.4 (d, 2JHH = 16.6 Hz, 1H), 4.2 (d, 2JHH
2
freshly distilled from sodium with benzophenone = 16Hz, 1H), 4.15 (d, JHH = 16.2 Hz, 1H), 2.1 (s,
under an argon atmosphere. 1H NMR was recorded 6H).
on a Bruker-300 MHz, APT, COSY, HSQC, and
HMBC were recorded on a Bruker-500 MHz
spectrometer. Chemical shifts are reported relative
Methoxy derivative (3b)
48h, white solid, yield:0.35 g;78%;1H NMR
to CDCl3 (7.26, 77.16 ppm). Spectral features were (400 MHz, CDCl3) δ 7.2-7.0 (m, 2H), 6.8-6.7 (m, 2H),
designed as follows:s = singlet, d = doublet, t = triplet, 6.47 (s, 1H), 6.33 (s, 1H), 5.65 (s, 1H), 4.85 (d, 2JHH
2
q = quartet, m = multiplet. Column chromatography = 16.7 Hz, 1H), 4.31 (d, JHH = 16.7 Hz, 1H), 4.15
was carried out on silica gel (ROCC 60, 40-63 (d, 2JHH = 17.3 Hz, 1H), 4.05 (d, 2JHH = 17.4 Hz, 1H),
¼m). TLC analyses were performed on commercial 3.70 (s, 6H).
aluminum plates bearing a 0.25 mm layer of Merck
Silica gel 60F254
.
Chloro derivative (3c)
5 min, white solid, yield:0.2 g, 45%, 1H NMR
Tröger ‘s base and its analogues (1a-d): (400 MHz, CDCl3) δ 7.15-6.68 (m, 8H), 5.55 (s, 1H),
-2,8-dimethyl-6H,12H-5,11-methanodibenzo[b 4.77 (d, 2JHH = 16.8 Hz, 1H), 4.23 (d, 2JHH = 16.7 Hz,
,f][1,5]diazocine, -2,8-dimethoxy-6H,12H-5,11- 1H), 4.10 (d, 2JHH = 17.4 Hz, 1H), 3.97 (d, 2JHH = 17.4
methanodibenzo[b, f][1,5]diazocine, -2,8-dichloro- Hz, 1H).
6H,12H-5,11-methanodibenzo[b,f][1,5]diazocine,

MUSENGIMANA & FATAkANwA, Orient. J. Chem., Vol. 29(4), 1489-1496 (2013)
1491
Synthesis of C6F5-adduct of the unsubstituted
Tröger’s base (3d)
were introduced. The mixture was crushed with a
glass rod and a few drops of glacial acetic acid were
added while stirring. After adding glacial acetic acid
(1 mL) a precipitate was formed. Another glacial
acetic acid (1 mL) was added, and the precipitate
obtained after filtration was washed with cold
isopropanol (-20 ° C) and then dried. The product
was obtained as a white powder.
In a GPC bottle, glacial acetic acid (1 mL);
5,6,11,12-tetrahydrodibenzo [b, f] [1,5] diazocine
(1 mmol); p-toluene sulfonic acid (2-3 g) and
C6F5CHO (1.5 mmol) were introduced.The mixture
was allowed to stir for a week at room temperature.
The reaction mixture was extracted with chloroform
(10 mL) and washed with a saturated solution of
NaHCO3 (20 mL x 3). The organic phase was dried
with MgSO4, filtered and concentrated.The orange-
brown oil obtained crystallized rapidly.These crystals
were washed with cold isopropanol and filtered.
1
Yield: 0.34g, 35%. H NMR (250 MHz,
CDCl3) δ 6.79 (s, 4H), 6.37 (s, 1H), 3.89 (m, 2H),
3.51 (m, 2H), 2.51 (s, 9H), 2.20 (s, 9H) . 13C NMR
(250 MHz, CDCl3) δ 139.07, 135.46, 130.12, 71.56,
51.04, 20.71.
1
Yield: 0.12 g, 32%, H NMR (400 MHz,
CDCl3) δ 7.25-6.78 (m, 8H), 5.70 (s, 1H), 4.92 (d,
Synthesis of chloroform adduct of 1,3-
dimesitylimidazolin-2-ylidene (6b)
2
2JHH = 16.6 Hz, 1H), 4.42 (d, JHH = 16.6 Hz, 1H),
4.19 (q, 2H).
In a GPC bottle, N, N’-ethylene-dimesityl
(2 mmol), glacial acetic acid (2 mL) and chloral (6
mmol) were introduced.After 17 h of stirring at room
temperature, there was formation of a precipitate.
The latter has been filtered on a Buchner funnel and
washed with isopropanol. The substrate has been
washed with a saturated solution of NaHCO3 (10 mL
x 3) and extracted with chloroform. The combined
organic layers were dried over MgSO4, filtrated, and
concentrated under reduced pressure. The product
was obtained as a white powder on which 1H NMR
and TGA analyses have been performed.
Synthesis of chloroform adduct ofTröger’s base
unsubstituted or bearing chloro group (4c-4d)
In a GPC bottle, chloral (2 mmol); glacial
acetic (1 mL) acid and 5,6,11,12-tetrahydrodibenzo
[b, f] [1,5] diazocine (0.5 mmol) or 2,8-Dichloro-
5,6,11,12-tetrahydrodibenzo [b, f] [1,5] diazocine
(0.5 mmol) were introduced. After 16h of stirring at
room temperature, the precipitate was formed and
filtered through a Pasteur pipette containing a cotton
wool and celite. After washing with cold methanol
(-18 ° C) the resulting solid was extracted with
dichloromethane. The latter was evaporated after
and the solid has been analyzed by NMR.
Yield:0.3g, 36%.1H NMR (250 MHz, CDCl3)
δ 6.85 (d, 4H), 5.57 (s, 1H), 3.91 (m, 2H), 3.29 (m,
2H), 2.47 (s, 6H), 2.45 (s, 6H), 2.25 (s, 6H).
Chloro derivative (4c)
Synthesis of the thiourea from Tröger’s base
(7)
1
white powder, yield: 0.02 g, 34.31%, H
NMR (400 MHz, CDCl3) δ 7.30-6.78 (m, 6H), 4.86-
4.68 (m, 3H), 4.32-4.25 (d , 2JHH = 28 Hz, 1H), 4.14-
4.07 (d, 2JHH = 28 Hz, 1H).
In a round bottom flask cooled at 0 °
C, 2,8-Dimethyl-5,6,11,12-tetrahydrodibenzo [b,
f] [1,5] diazocine (5 mmol) and Na2CO3 (0.795
g, 3.75 mmol) were introduced. In another flask
also cooled at 0 ° C, was added THF (5 mL) and
thiophosgene (6 mmol). The solution of the second
flask was added to the solution of the first flask and
stirred overnight at room temperature.TheTHF was
evaporated and the resulting solid was dissolved in
dichloromethane (50 mL). The organic phase was
washed with water (50 mL x 3), dried over MgSO4,
filtered and evaporated. The crude product was
purified by column chromatography on silica gel
with EtOAc:Petroleum Ether (8:2). The yellow solid
Hydrogenated derivative (4d)
1
yellow powder, yield: 0.1 g, 58.82%, H
NMR (400 MHz, CDCl3) δ 7.30-6.80 (m, 8H), 4.93-
4.72 (m, 3H), 4.42-4.35 (d , 2JHH = 28 Hz, 1H), 4.23-
4.16 (d, 2JHH = 28 Hz, 1H).
S y n t h e s i s o f C 6 F 5 a d d u c t o f 1 , 3 -
dimesitylimidazolin-2-ylidene (6a)
In a GPC bottle, N,N’- dimesityl-
ethanediamine (2 mmol) and C6F5CHO (3 mmol)

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obtained after concentration was analyzed by 1H and 1.5 equiv. of C6F5CHO, in glacial acetic acid. After
13C NMR.
a stirring at room temperature for various time
according to the diazocine, this formally lead to the
1
Yield: 0.65g, 46.4% H NMR (250 MHz, insertion of a carbene into the C-H bond of C6F5CHO
CDCl3) δ 7.19-6.81 (m, 6H), 6.11-6.07 (d, 3JHH = 16 (schemes 1). Interestingly, the chloro derivative 2c
Hz, 2H), 4.45-4.43 (d, 2JHH = 8 Hz, 2H), 2.18 (s, 6H), was very reactive and lead to the corresponding
13C NMR (250 MHz, CDCl3) δ 174.73, 140.05, 139.2, carbene 3c just after 5 minutes with a yield of
131.7, 130.93, 130.7, 127.05, 59.99, 21.19. )
43%. The carbenes 3a and 3b from methyl and
methoxy derivatives were isolated easily with good
yields of 76% and 78% respectively. However, the
unsubstituted derivative 2d was less reactive in the
RESULTS AND DISCUSSION
Our work started by the synthesis of starting conditions of the reaction and p-toluene sulfonic acid
materials. Firstly, Tröger’s base and its analogues (1a-d) (10 equiv.) was added (see experimental procedure).
were synthesized according to the method described in the In these last conditions, the corresponding carbene
litterature13,15,18. Thereafter, we proceeded on the removal 3d was isolated after one week with a low yield 33%;
of methylene bridge by using the method of Mahon16.This comparing to other derivatives. Several examples
lead to the corresponding diazocines (2a-d) that were used from the literature show that N-heterocyclic carbenes
in the synthesis of perhalogenated and thiourea adducts. of imidazolin-2-ylidene type can be synthesized by
heating such compounds19-20.In such reactions, there
Synthesis of perhalogenated adducts of the is a loss of C6F5 group and the formation of a free
Tröger’s base and its analogues
The diazocines (2a-d) were treated with
carbene.
O
C6F5
N
H
R
HN
CH3CO2H
R
H
+
RT
R
N
R
N
F5
1.5 equiv.
H
3a: R = Me, 5h, 76%
2a-d
3b: R = MeO, 48h, 78%
3c: R = Cl, 5 min, 43%
3d: R = H, 1 week, 33%
Scheme 1. Synthesis of C6F5-adduct of the Tröger’s base and its analogues
with these interesting carbenes in hands, other carbenes by using Cl3CHO (chloral) instead
we were secondly interested by the synthesis of of C6F5CHO (scheme 2).
CCl3
N
H
R
HN
CH3CO2H
O
R
+
Cl3C
H
16 h, RT
R
N
R
N
H
4a: R = Me, -
4 equiv.
2a-d
4b: R = MeO, -
4c: R = Cl, 18%
4d: R = H, 50%
Scheme 2. Synthesis of Cl3C-adducts of the Tröger’s base and its analogues

MUSENGIMANA & FATAkANwA, Orient. J. Chem., Vol. 29(4), 1489-1496 (2013)
1493
The results of these syntheses were
pretty random. In fact, after dissolving and mixing
all the reagents in the glacial acetic acid, we were
expecting that the products precipitate as it was the
case for the preceding synthesis ; but this was not
the case. Surprisingly, no reaction was observed for
compounds 4a and 4b after an overnight stirring at
room temperature. Impure products were isolated
containing chloral for methyl derivative 4a. For
chlorine derivative 4c and unsubstituted derivative
4d there was no appearance of a precipitate and the
reaction mixture was partitioned between chloroform
and an aqueous solution of NaHCO3. Evaporation
of the organic layers led to oils that crystallized after
one night.
with C6F5 or chloroform adducts of SIMes ligand17.
we tried to apply this method to the C6F5 adducts
of the Tröger’s base. A first test was performed
using as substrate the complex [RuCl2 (PCy3)
2
(2-phenylindenylidene)]. The Grubb’s metathesis
catalyst of first generation was refluxed in toluene
for 24 h in the presence of 3a (2 equiv.) (Scheme
3). The reaction was monitored by a 31P-NMR and
a gradual appearance of a free PCy3 was observed
in the reaction mixture.These observations seemed
auspicious, the expected reaction involving the
substitution of a phosphine ligand by analogous
carbene. However, after purification of the crude by
column chromatograph on silica gel, 1H-NMR and 13C-
NMR analyses performed on the white solid obtained
revealed that we did not isolate the expected product.
But it was a mixture of uncharacterized products.It is
therefore likely that the peak from the free phosphine
observed in 31P NMR came from the decomposition
of the starting complex, which did not withstand the
applied temperature.
Thermolysis tests of perhalogenated adducts of
Tröger’s base
It is possible to obtain various complexes
of rhodium or ruthenium bearing NHC ligands by
a conventional heating a suitable metal precursor
PCy3
Ph
C6F5
Cl
N
H
N
N
Toluene
x
Ru
+
Ph
Cl
110 ° C, 24 h
Cl
PCy3
N
Ru
Cl
PCy3
3a: 2 equiv.
Scheme 3.Thermolysis test of C6F5- adducts of Tröger’s base with Ru complex
In parallel, another attempt was carried out
by choosing the dimer [RhCl (1,5-cyclooctadiene)]
as a binding site of carbene ligand (Scheme 4)
in the same conditions as preceding. In fact, the
rhodium complex is an air-stable ruthenium alkylidene
species which should better withstand the thermolysis
adopted to generate a carbene from the adduct 3a.
The subsequent replacement of cyclooctadiene with
carbonyl ligand, followed by the determination of
vibration frequencies n CO with infrared spectroscopy,
should also measure the electron-donor power of the
carbene derived from the Tröger’s base. However,
the NMR analysis of the crude of the reaction proved
that the starting materials were isolated unchanged;
hence no reaction.
2
C6F5
N
H
Cl
Toluene
x
+
Rh
Rh
110 ° C, 24 h
Cl
N
3a: 2 equiv.
Scheme 4:Thermolysis test of C6F5- adducts of Tröger’s base with Rh complex

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A third attempt to synthesize the free Synthesis of perhalogenated SIMes adducts and
carbene of the Tröger’s base or its dimer from the thermogravimetric analyzes
adduct 3a was carried out in a microwave reactor.
In aim to compare the stabilities of the
No metal complex was used in this experiment.The perhalogenated adducts of the Tröger’s base with
adduct 3a was simply dissolved in dry degassed those of classic N-heterocyclic carbenes, we have
toluene and the solution was heated in the microwave synthesized C6F5 and chloroform adducts of SIMes
for half an hour at 200 ° C under pressure. To verify ligand. The synthesis method used is similar to that
the presence of the carbene, few drops of CS2 followed with the Tröger’s base and its analogues,
were added to the reaction mixture. If a carbene i.e., the secondary diamine ligand 5 was stirred
was present in solution, the formation of a colored at room temperature for 17 h with 3 equiv. of
zwitterion should be observed, but it did not happen. C6F5CHO or chloral in the presence of acetic acid
1
There was no free carbene in solution. A H-NMR (Scheme 5).
spectrum recorded on the crude corresponded to
the starting materials.
CH3CO2H
O
N
X
N
NH HN
+
X
H
16 h, RT
H
6a: X = C6F5, 49%
6b: X = CCl3, 36%
5
3 equiv.
Scheme 5. Synthesis of perhalogenated SIMes adducts
Compounds 6a and 6b have been isolated as analyzes showed that the adducts of the Tröger’s
white powders with moderate yields; 49%, 36% base remain stable at least up to 200 ° C and the
respectively
exact nature of the adduct (chloroform or C6F5)
A thermogravimetric analysis of has a very little influence on the decomposition
perhalogenated adducts of the Tröger’s base, 3a, temperature. For example, compounds 3a and 3d
3d and reference compound 6b were performed. both degrade at about 220 ° C (Figure 1).In contrast,
These measures consisted of heating products compound 6b releases chloroform at a very lower
in a microbalance and record the mass loss as a temperature, around 145 ° C, which explains the
function of temperature. From a certain threshold, difference in reactivity between the two families of
adducts decompose to form free carbene and expel carbene precursors.
chloroform or the C6F5CHO. The results of these
Fig. 1:TgA adducts Tröger-Me.C6F5H (compound 3a, red curve),Tröger-H.CHCl3
(compound 3d, blue curve) and SIMes.CHCl3 (compound 6b, green curve)

MUSENGIMANA & FATAkANwA, Orient. J. Chem., Vol. 29(4), 1489-1496 (2013)
1495
Synthesis of thiourea of the Tröger’s base and
its analogues
the use of thiourea as carbene precursors. These
compounds can be obtained in one step from
compounds 3a-d previously synthesized.They were
treated overnight in THF at room temperature with
1.2 equiv.of thiophosgene in the presence of Na2CO3
(75%) to neutralize the hydrochloric acid formed
(Scheme 6).
Thermolysis of perhalogenated adducts
of the Tröger’s base and its analogues was clearly
much more difficult to accomplish than expected.
Therefore, we have explored an alternative synthetic
route that should lead to the achievement of the
desired carbene. This new pathway is based on
HN
N
S
Na2CO3, 75%
THF, 16 h, RT
+
Cl2C S
N
N
H
3a
1.2 equiv.
7, 46%
Scheme 6. Synthesis of thiourea of the Tröger’s base and its analogue
Afterpurificationbycolumnchromatography
on silica gel, the product 7 was isolated as a pure
yellow solid with moderate yield of 46%. It was
analyzed by NMR.The presence of a characteristic
peak of C=S between 170 and 180 ppm in 13C NMR
spectroscopy revealed that the expected product was
formed.
with comparative thermogravimetric analysis, we
have shown that adducts pentafluorobenzene and
chloroform of the Tröger’s base are much stable
than those derived from a classic NHC. Refluxing in
toluene in the presence of a complex of Ru or Rh,
and the irradiation at 200°C in a microwave reactor
haven’t allowed the desired thermolysis. The study
of an alternative way to achieve the carbene from
Tröger’s base involving thioureas as an intermediate
key should be further investigated. A further study
should also be undertaken to investigate the
effectiveness of these new catalysts especially in
cross-coupling metathesis reactions.
CONCLUSION
The synthesis of carbenes precursors
derived from Tröger’s base is feasible. Optimization
of experimental conditions will be further investigated
to improve yields and purity of isolated products.
REFERENCES
1.
2.
3.
4.
5.
6.
7.
8.
Schuster M., Blechert S., Angew. Chem. Int.
Ed., 36: 2036 (1997).
Astruc D., Actualité chimique, 273: 3
(2004).
Chauvin Y., Angew. Chem. Int. Ed., 45: 3740
(2006).
Grubbs R.H., Angew.Chem.Int.Ed., 45:3760
(2006).
Herrmann w. A., Angew. Chem. Int. Ed., 41:
1290 (2002).
Samojlowicz C., Bienik M., Grela k., Chem.
Rev., 109: 3708 (2009).
Schrock R. R., Chem. Rev., 109: 3211
(2009).
Vougioukalakis G. C., Grubbs R. H., Chem.
Rev., 110: 1746 (2010).
P. kumar, Orient. J. Chem., 29(3): 1225-1231
(2013).
C.P. Choudhary, S.P. Sharma, C.L. Rai and
B.k. Rai, Orient. J. Chem., 29(3): 963-967
(2013).
Arduengo III A. J., Harlow R. L., kline M., J.
Am. Chem. Soc., 113: 361 (1991).
Hahn F. E., Jahnke M. C., Angew. Chem. Int.
Ed., 47: 3122 (2008).
9.
10.
11.
12.
13.
14.
15.
Sergeyev S., Helv. Chim. Acta, 92: 415
(2009).
Schrock R. R., Angew. Chem. Int. Ed., 45:
3748 (2006).
Didier D., Sergeyev S., Chimie nouvelle, 96:

1496
16.
MUSENGIMANA & FATAkANwA, Orient. J. Chem., Vol. 29(4), 1489-1496 (2013)
92 (2007).
12: 148 (2008).
DidierD.,TyllemanB., LambertN.,VandeVelde 19.
C.M.L., Blockhuys F., Collas A., Sergeyev S.,
Blum A. P., Ritter T., Grubbs R. H.,
Organometallics, 26: 2122 (2007).
Nyce G. w., Csihony S., waymouth R.
M., Hedrick J. L., Chem. Eur. J., 10: 4073
(2004).
Tetrahedron, 64: 6252 (2008).
20.
17.
18.
Irving S., Vincent L., Ly P., Craig S.w., J.Org.
Chem., 53: 98 (1988).
Mahon A. B., Craig D. C., Try A. C., Arkivoc,