Efficient and selective olefination of aldehydes with ethyl diazoacetate catalyzed by high-valent tin(IV) porphyrins

Article abstract of DOI:10.1016/j.jorganchem.2012.08.023

Tetraphenylporphyrinatotin(IV) trifluoromethanesulfonate, [Sn ^IV(TPP)(OTf)₂], and tetraphenylporphyrinatotin(IV) tetrafluoroborate, [Sn^IV(TPP)(BF₄)₂], were used as efficient catalysts for olefination of aldehydes with EDA in the presence of PPh₃. These high-valent tin porphyrins catalyzed olefination of aldehydes in high yields and short reaction times at room temperature. The reaction rate depended on the nature of substituents on aldehyde; electron poor aldehydes reacted faster than electron rich aldehydes. The olefination of aldehydes indicated that the reactions are very selective and all products are trans-isomer. Both catalysts were reused four consecutive times without loss of their catalytic activity.

Full text of DOI:10.1016/j.jorganchem.2012.08.023

Journal of Organometallic Chemistry 720 (2012) 26e29
Contents lists available at SciVerse ScienceDirect
Journal of Organometallic Chemistry
journal homepage: www.elsevier.com/locate/jorganchem
Efficient and selective olefination of aldehydes with ethyl diazoacetate catalyzed
by high-valent tin(IV) porphyrins
,
b
,
b
Shadab Gharaati a, Majid Moghadam b , Shahram Tangestaninejad , Valiollah Mirkhani ,
*
*
Iraj Mohammadpoor-Baltork b
a Department of Chemistry, Payame Noor University, P.O. Box 19395-3697, Tehran, Iran
b Department of Chemistry, Catalysis Division, University of Isfahan, Isfahan 81746-73441, Iran
a r t i c l e i n f o
a b s t r a c t
Tetraphenylporphyrinatotin(IV) trifluoromethanesulfonate, [SnIV(TPP)(OTf)2], and tetraphenylporphyr-
inatotin(IV) tetrafluoroborate, [SnIV(TPP)(BF4)2], were used as efficient catalysts for olefination of alde-
hydes with EDA in the presence of PPh3. These high-valent tin porphyrins catalyzed olefination of
aldehydes in high yields and short reaction times at room temperature. The reaction rate depended on
the nature of substituents on aldehyde; electron poor aldehydes reacted faster than electron rich alde-
hydes. The olefination of aldehydes indicated that the reactions are very selective and all products are
trans-isomer. Both catalysts were reused four consecutive times without loss of their catalytic activity.
Ó 2012 Elsevier B.V. All rights reserved.
Article history:
Received 22 June 2012
Received in revised form
12 August 2012
Accepted 22 August 2012
Keywords:
Diazo compounds
Olefination
Aldehyde
High-valent tin(IV) porphyrin
Reusable catalyst
1. Introduction
Electron-deficient metalloporphyrins have been used as mild
Lewis acids catalysts [17e19]. Suda group has reported the use of
Constructive carbonecarbon double bond of carbonyl compounds
is one of the most important reactions in organic synthesis, especially
in the areas of polymer and natural products synthesis [1,2]. Generally,
the used methods were included the Wittig reaction and its modified
reactions, the Peterson reaction, and the Julia reaction [3]. In the past
two decades a variety of organometallic compounds have been used
for this reaction and some of them was done successfully [4,5]. One of
the other procedures for olefin formation is the reaction of carbonyl
compounds with diazo compounds in the presence of a reducing agent
such as triphenylphosphine and trialkylstibines [6]. In contrast to the
tradition Wittig method, the metal-mediated syntheses are carried
out in one simple reaction. However, some drawbacks such as need
high reaction temperature especially when diazo compounds are used
to increase safety risks, using high catalyst amount, high dependence
of stereoselectivites to the nature of aldehyde and low yields. In 1998,
Fujimura reported one-pot olefination of carbonyl compounds by
a ruthenium complex as catalyst. In this system, for some aldehydes,
the yields were not particularly high [7]. Several transition metal
complexes including Mo, Re, Ru, Rh, Fe and Co, have been used as
catalysts for olefination of aldehydes with diazo compounds [8e16].
chromium and iron porphyrins in organic synthesis. They used
Cr(tpp)Cl for regioselective [3,3] rearrangement of aliphatic allyl
vinyl ethers and for Claisen rearrangement of simple aliphatic allyl
vinyl ethers, Fe(tpp)OTf for rearrangement of
a,b-epoxy ketones
into 1,2-diketones and Cr(tpp)OTf for highly regio- and stereo-
selective rearrangement of epoxides to aldehydes [20e25].
Recently, we have reported the use of tin(IV)tetraphenylpor-
phyrinato perchlorate [26,27], tin(IV)tetraphenylporphyrinato tri-
fluoromethanesulfonate [28e32], tin(IV)tetraphenylporphyrinato
tetrafluoroborate
[33e35],
tetrakis(p-aminophenyl)porphyr-
inatotin(IV) trifluoromethanesulfonate, [SnIV(TNH2PP)(OTf)2] sup-
ported on polystyrene [36e38] and vanadium(IV)tetraphenylporp
hyrinato
trifluoromethanesulfonate
[39e42]
in
organic
transformations.
In this paper, we wish to report the application of high-valent
[SnIV(TPP)(OTf)2] and [SnIV(TPP)(BF4)2] catalysts for efficient and
selective olefination of a wide variety of aldehydes with ethyl
diazoacetate (EDA) in the presence of triphenylphosphine at room
temperature (Scheme 1).
2. Experimental
* Corresponding authors. Tel.: þ98 311 7932705, þ98 311 7932712; fax: þ98 311
6689732.
Chemicals were purchased from Merck or Fluka chemical
companies. All reactions were performed under nitrogen atmosphere
E-mail addresses: moghadamm@sci.ui.ac.ir, majidmoghadamz@yahoo.com
(M. Moghadam), stanges@sci.ui.ac.ir (S. Tangestaninejad).
0022-328X/$ e see front matter Ó 2012 Elsevier B.V. All rights reserved.
http://dx.doi.org/10.1016/j.jorganchem.2012.08.023

S. Gharaati et al. / Journal of Organometallic Chemistry 720 (2012) 26e29
27
BF4
OTf
N
N
N
N
N
N
SInV
SInV
or
N
N
BF4
OTf
CHO
Ph3P, N2CHCO2Et, Toluene
CO2Et
Scheme 1. Olefination of aldehydes with EDA catalyzed by [SnIV(TPP)(OTf)2] or [SnIV(TPP)(BF4)2].
using a glove box equipped with a M040H Dri-Train gas purification
system. Toluene and THF were dried before use. NMR spectra were
recorded on Bruker-Avance 400 MHz spectrometer in CDCl3 as
solvent. Infrared spectra were run on a Philips PU9716 or Shimadzu
IR-435 spectrophotometer. All analyses were performed on a Shi-
madzu GC-16A instrument with a flame ionization detector using
silicon DC-200 or Carbowax 20M columns and n-decane was used as
internal standard. The tetraphenylporphyrin was prepared and met-
allated according tothe literature [43]. Thecatalysts, [SnIV(TPP)(OTf)2]
[31] and [SnIV(TPP)(BF4)2] [32], were prepared as reported previously.
(q, J ¼ 7.2 Hz, 2H), 1.37 (t, J ¼ 7.2 Hz, 3H) ppm; 13C NMR (CDCl3,
100 MHz):
14.3 ppm.
d
¼ 166.0, 148.4, 141.6, 140.6, 128.6, 124.1, 122.6, 61.0,
2.2.6. (E)-Ethyl 3-(4-methoxyphenyl)acrylate (entry 6, Table 2)
1H NMR (CDCl3, 400 MHz):
d
¼ 7.64 (d, J ¼ 15.6 Hz, 1H), 7.48 (d,
J ¼ 8.7 Hz, 2H), 6.90 (d, J ¼ 8.7 Hz, 2H), 6.31 (d, J ¼ 15.6 Hz, 1H), 4.25
(q, J ¼ 7.2 Hz, 2H), 3.83 (s, 3H), 1.33 (t, J ¼ 7.2 Hz, 3H) ppm; 13C NMR
(CDCl3, 100 MHz):
114.1,61.9, 55.1, 14.3 ppm.
d
¼ 160.1, 159.6, 143.2, 127.6, 127.4, 121.9,
3. Results and discussion
2.1. General procedure for olefination of aldehydes
A mixture of aldehyde (1 mmol), [SnIV(TPP)(OTf)2] (0.01 mmol)
or [SnIV(TPP)(BF4)2] (0.02 mmol) and PPh3 (2 mmol) in toluene
(1 mL) was prepared. Then a solution of ethyl diazoacetate
(1.5 mmol mL) in toluene (0.5 mL) was added drop-wise to this
solution and stirred at room temperature for appropriate time. The
progress of the reaction was monitored by GC or TLC. After
completion of the reaction, the solvent was evaporated, n-hexane
(10 mL) was added and the catalyst was filtered. The filtrates were
concentrated under reduced pressure to afford the crude product,
which was confirmed by 1H NMR and 13C NMR spectral data.
3.1. Olefination of aldehydes with ethyl diazoacetate (EDA)
catalyzed by [SnIV(TPP)(OTf)2]
First, in order to indicate the effect of OTf groups on the electron
deficiency of tin(IV) porphyrin, the olefination of benzaldehyde
with EDA in present of PPh3 was carried out with 1 mol% of
[SnIV(TPP)(OTf)2] or [SnIV(TPP)Cl2] catalyst at room temperature.
The results showed that the amount of the corresponding olefin in
the presence of [SnIV(TPP)Cl2] was 30% after 4 h, while in the
presence of [SnIV(TPP)(OTf)2] after 1 h, the corresponding olefin
was 97%. Then, to obtain optimal reaction conditions, the amount of
catalyst and PPh3 was optimized in the olefination of benzaldehyde
(Table 1). These results showed that the highest yield of ethyl
cinnamate was produced in the presence of 1 mol% of [SnIV(-
TPP)(OTf)2] in toluene (Table 1, entry 3). Increasing the amount of
catalyst did not affect the yield but decreasing it, reduced the yield.
In the case of PPh3, when the amount of PPh3 increased from
1 mmol to 2 mmol, an increase in the yield from 56% to 97% was
observed, but with 3 mmol of PPh3, the yield dropped to 79%. It
seems that higher amounts of PPh3 can deactivate the [SnIV(-
TPP)(OTf)2]. In addition, when the same reaction was performed in
THF as solvent, the yield decreased to 44% (Table 1, entry 7). A
decrease in yield was dramatically observed when the reaction was
carried out under air; therefore, all reactions were carried out
under N2 atmosphere.
2.2. Spectral data
2.2.1. (E)-Ethyl cinnamate (entry 1, Table 2)
1H NMR (CDCl3, 400 MHz):
d
¼ 7.70 (d, J ¼ 16.0 Hz,1H), 7.53e7.51
(m, 2H), 7.39e7.36 (m, 3H), 6.45 (d, J ¼ 16.0 Hz,1H), 4.27 (q, J ¼ 7.2 Hz,
2H),1.34 (t, J ¼ 7.2 Hz, 3H) ppm;13C NMR (CDCl3,100 MHz):
¼ 166.8,
d
144.5, 137.3, 134.4, 130.1, 128.6, 118.4, 60.5, 14.5 ppm.
2.2.2. (E)-Ethyl 3-(4-chlorophenyl)acrylate (entry 2, Table 2)
1H NMR (CDCl3, 400 MHz):
d
¼ 7.64 (d, J ¼ 16.0 Hz, 1H), 7.46 (d,
J ¼ 8.7 Hz, 2H), 7.36 (d, J ¼ 8.7 Hz, 2H), 6.41 (d, J ¼ 16.0 Hz,1H), 4.27 (q,
J ¼7.2 Hz, 2H),1.34(t, J ¼7.2Hz, 3H)ppm; 13CNMR (CDCl3,100MHz):
d
¼ 160.6, 142.6, 133.6, 133.4, 128.8, 127.8, 180.8, 61.5, 14.6 ppm.
2.2.3. (E)-Ethyl 3-(4-bromophenyl)acrylate (entry 3, Table 2)
1H NMR (CDCl3, 400 MHz):
Table 1
d
¼ 7.63 (d, J ¼ 16.2 Hz, 1H), 7.53 (d,
Optimization of reaction conditions in the olefination of aldehyde with tin
porphyrins.a
J ¼ 8.4 Hz, 2H), 7.40 (d, J ¼ 8.4 Hz, 2H), 6.44 (d, J ¼ 16.2 Hz, 1H), 4.28
(q, J ¼ 7.2 Hz, 2H), 1.34 (t, J ¼ 7.2 Hz, 3H) ppm; 13C NMR (CDCl3,
Entry
PPh3
(mmol)
[SnIV(TPP)(OTf)2] after
60 min
[SnIV(TPP)(BF4)2] after
100 min
100 MHz):
14.35 ppm.
d
¼ 160.6, 144.1, 134.3, 131.7, 128.6, 122.4, 119.1, 61.5,
Catalyst
amount
(mmol)
Yield (%)b
Catalyst
amount
(mmol)
Yield (%)b
2.2.4. (E)-Ethyl 3-p-tolylacrylate (entry 4, Table 2)
1HNMR (CDCl3, 400 MHz):
d
¼ 7.66 (d, J ¼ 15.9 Hz, 1H), 7.42 (d,
1
2
3
4
5
6
7c
2
2
2
2
1
3
2
0.005
0.007
0.01
0.02
0.01
0.01
0.01
74
85
97
97
56
79
44
0.005
0.01
0.02
0.03
0.02
0.02
0.02
58
77
98
98
48
64
49
J ¼ 8.1 Hz, 2H), 7.18 (d, J ¼ 8.1 Hz, 2H), 6.39 (d, J ¼ 15.9 Hz, 1H), 4.25
(q, J ¼ 7.2 Hz, 2H), 2.36 (s, 3H), 1.33 (t, J ¼ 7.2 Hz, 3H) ppm; 13C NMR
(CDCl3, 100 MHz):
61.4, 21.1, 14.3 ppm.
d
¼ 166.1, 142.7, 137.7, 132.6, 129.1, 126.3, 120.4,
2.2.5. (E)-Ethyl 3-(4-nitrophenyl)acrylate (entry 5, Table 2)
1HNMR (CDCl3, 400 MHz):
¼ 8.26 (d, J ¼ 8.0 Hz, 2H), 7.72 (d,
J ¼ 18.0 Hz,1H), 7.69 (d, J ¼ 8.0 Hz, 2H), 6.57 (d, J ¼ 18.0 Hz,1H), 4.31
a
Reaction conditions: benzaldehyde (1 mmol), EDA (1.5 mmol), toluene (1.5 mL).
GC yield.
The reaction was performed in THF.
b
c
d

28
S. Gharaati et al. / Journal of Organometallic Chemistry 720 (2012) 26e29
The optimized reaction conditions, which obtained for olefina-
a Wittig reaction, the corresponding olefin is produced from ylide
and aldehyde. No olefin was produced in the absence of PPh3 or
catalyst and these are good reasons for the proposed mechanism
[2]. It is important to note that these results are in accordance with
the previously reported results in which stated that the stereo-
selectivity of the Wittig reaction depends strongly to the structure
of the ylide; unstabilized ylides give Z-alkenes while stabilized
ylides produce E-alkenes [52]. In these reactions, the produced
yield is stabilized by ester group and therefore results in E-alkenes.
tion of aldehydes, were aldehyde, EDA, PPh3 and catalyst in a molar
ratio of 100:150:200:1, using toluene as solvent. Under the opti-
mized reaction conditions, different aldehydes were converted to
their corresponding olefins in excellent yields and short reaction
times (Table 2). As can be seen, electron-rich benzaldehydes such as
4-methyl and 4-methoxy benzaldehydes require longer reaction
times. On the other hand, electron-poor benzaldehydes, such as 4-
chloro, 4-bromo and 4-nitrobenzaldehydes produced the corre-
sponding olefins in shorter times.
The E/Z ratio of olefins after their purification was determined
by their 1H NMR spectra. The chemical shift of alkenyl hydrogen
groups are present in 6.31e6.57 ppm and 7.63e7.72 ppm and the
coupling constant of about 16 Hz (18 Hz for 4-nitro derivative) in 1H
NMR spectra indicated that all products were trans-isomer [44] and
no cis isomer was engendered in the presence of electron-deficient
of tin(IV) porphyrin.
The Sn]C double bond is now well established, some of them
structurally characterized and the Sn]C bond length and the
environment of the respective tin atoms. An example of these tin-
carbene complexes is formed by the reaction of imidazole-2-
yiledene with SnR2Cl2 in which a square pyramidal or a trigonal
bipyramidal complex is obtained [45e48]. Another example of
these complexes is produced by the reaction of the stannylene
(R2Sn:) acting as Lewis acids, with the isocyanide (:C]NeAr),
acting as a Lewis base [49,50]. The third class of tin-carbene
complexes is cyclopropenylidene complexes of divalent tin [51].
A plausible mechanism is shown in Scheme 2. Based on this
mechanism, tin(IV) porphyrin interacts with diazo compound to
affords the tin-carbene intermediate (A) (this intermediate can be
formed according to the above mentioned explanations) and
releases the nitrogen gas. Consecutively, the intermediate (A) reacts
with PPh3 and produces intermediate (B) (ylide form) and upon
3.2. Olefination of aldehydes with ethyl diazoacetate (EDA)
catalyzed by [SnIV(TPP)(BF4)2]
Electron-deficient tin(IV) porphyrin, [SnIV(TPP)(BF4)2], was also
used as catalyst in the olefination of aldehydes with EDA in pres-
ence of PPh3. The optimized conditions, which obtained for olefi-
nation of benzaldehyde, were benzaldehyde, EDA, PPh3 and catalyst
in a molar ratio of 100:150:200:2 at room temperature (Table 1).
Under these conditions, different benzaldehydes including
electron-rich and electron-poor ones were converted to their cor-
responding olefins in excellent yields (Table 2). In the case of
[SnIV(TPP)(BF4)2], electron-poor benzaldehydes were converted to
their corresponding olefins in shorter times too.
The evaluation of the results in Table 2 indicates that [SnIV(-
TPP)(OTf)2] is more reactive than [SnIV(TPP)(BF4)2] and the higher TOFs
were observed for tin(IV) trifluoromethanesulfonate in comparison
with tin(IV) tetrafluoroborate. This can be attributed to the higher
electron deficiency of [SnIV(TPP)(OTf)2] compared to [SnIV(TPP)(BF4)2].
3.3. Catalyst reutilization
The catalyst reusability was investigated in the reaction of
benzaldehyde, EDA and PPh3 in the presence of both tin(IV)
Table 2
Olefination of aldehydes with EDA catalyzed by tin(IV) porphyrins at room temperature.a
Entry
Aldehyde
Olefin
[SnIV(TPP)(OTf)2] (1 mol%)
[SnIV(TPP)(BF4)2] (2 mol%)
Time (min)
60
Yield (%)b
TOF (hꢀ1
)
Time (min)
Yield (%)b
TOF (hꢀ1
)
1
2
97
97
100
98
29
CHO
CO2Et
Cl
50
50
97
97
116
116
70
70
97
97
42
42
Cl
Br
CHO
CHO
CO2Et
Br
3
CO2Et
Me
4
5
80
30
94
99
95
70
198
47
115
30
93
98
92
24
98
20
Me
CHO
CHO
CHO
CO2Et
CO2Et
CO2Et
O2N
MeO
O2N
MeO
6
120
140
a
Reaction conditions: aldehyde (1 mmol), EDA (1.5 mmol), PPh3 (2 mmol), toluene (1.5 mL).
GC yield.
b

S. Gharaati et al. / Journal of Organometallic Chemistry 720 (2012) 26e29
29
X
H
R
CO2Et
H
N
N
N2CHCO2Et
Ph3P=O
Sn
X
Ph3P
N
N
CO2Et
N
H
O
N
N
Ph3P=CHCO2Et
Sn
N2
R
H
N
X
(B)
(A)
X= OTf, BF4
Scheme 2. Proposed mechanism for olefination of aldehydes with EDA catalyzed by tin(IV) porphyrins.
[21] T. Takanami, R. Hirabe, M. Ueno, F. Hino, K. Suda, Chem. Lett. 25 (1996) 1031e
1032.
[22] K. Suda, K. Baba, S.-i. Nakajima, T. Takanami, Chem. Commun. (2002) 2570e
2571.
[23] K. Suda, T. Kikkawa, S.-i. Nakajima, T. Takanami, J. Am. Chem. Soc. 126 (2004)
9554e9555.
porphyrins as catalyst. At the end of each reaction, the solvent was
evaporated, n-hexane was added, the catalyst was filtered and
washed with n-hexane. The results showed that both catalysts were
reused four consecutive times without loss of their catalytic activity.
[24] T. Takanami, M. Hayashi, K. Suda, Tetrahedron Lett. 46 (2005) 2893e2896.
[25] T. Takanami, M. Hayashi, K. Iso, H. Nakamoto, K. Suda, Tetrahedron 62 (2006)
9467e9474.
4. Conclusion
[26] S. Tangestaninejad, M.H. Habibi, V. Mirkhani, M. Moghadam, J. Chem. Res. (S)
(2001) 365e367.
[27] S. Tangestaninejad, M.H. Habibi, V. Mirkhani, M. Moghadam, Synth. Commun.
32 (2002) 1337e1343.
[28] M. Moghadam, S. Tangestaninejad, V. Mirkhani, I. Mohammadpoor-Baltork,
S. Gharaati, Appl. Organomet. Chem. 23 (2009) 446e454.
[29] S. Gharaati, M. Moghadam, S. Tangestaninejad, V. Mirkhani, I. Mohammadpoor-
Baltork, F. Kosari, Inorg. Chim. Acta 363 (2010) 1995e2000.
[30] M. Moghadam, S. Tangestaninejad, V. Mirkhani, I. Mohammadpoor-Baltork,
S. Gharaati, Inorg. Chim. Acta 363 (2010) 1523e1528.
In this paper, another application of electron-deficient tin(IV)
tetraphenylporphyrinato
trifluoromethanesulfonate,
[SnIV(-
TPP)(OTf)2], and tin(IV)tetraphenylporphyrinato tetrafluoroborate,
[SnIV(TPP)(BF4)2], which are stable Sn(IV) compounds was investi-
gated. Selective olefination of different aldehydes with EDA and
PPh3 in the presence of these catalysts was carried out; the pure
trans-isomer was obtained in excellent yield and short reaction
time under mild conditions (room temperature). The both catalyst
were reused several times without loss of their catalytic activity.
[31] M. Moghadam, S. Tangestaninejad, V. Mirkhani, I. Mohammadpour-Baltork,
R. Shaibani, J. Mol. Catal. A: Chem. 219 (2004) 73e78.
[32] M. Moghadam, S. Tangestaninejad, V. Mirkhani, R. Shaibani, Tetrahedron 60
(2004) 6105e6111.
[33] M. Moghadam, S. Tangestaninejad, V. Mirkhani, I. Mohammadpoor-Baltork,
S.A. Taghavi, J. Mol. Cat A: Chem. 274 (2007) 217e223.
Acknowledgement
[34] M. Moghadam, S. Tangestaninejad, V. Mirkhani, I. Mohammadpoor-Baltork,
S.A. Taghavi, Catal. Commun. 8 (2007) 2087e2095.
We are thankful to the Center of Excellence of Chemistry of
[35] M. Moghadam, S. Tangestaninejad, V. Mirkhani, I. Mohammadpoor-Baltork,
S. Gharaati, Polyhedron 29 (2010) 212e219.
University of Isfahan (CECUI) for financial support of this work.
[36] M. Moghadam, S. Tangestaninejad, V. Mirkhani, I. Mohammadpoor-Baltork,
S. Gharaati, J. Mol. Catal. A: Chem. 337 (2011) 95e101.
References
[37] M. Moghadam, S. Tangestaninejad, V. Mirkhani, I. Mohammadpoor-Baltork,
S. Gharaati, C. R. Chim. 14 (2011) 1080e1087.
[38] S. Gharaati, M. Moghadam, S. Tangestaninejad, V. Mirkhani, I. Mohammadpoor-
Baltork, Polyhedron 35 (2012) 87e95.
[1] W. Sun, F.E. Kühn, Tetrahedron Lett. 45 (2004) 7415e7418.
[2] M.-Y. Lee, Y. Chen, X.P. Zhang, Organometallics 22 (2003) 4905e4909.
[3] P. Cao, C.-Y. Li, Y.-B. Kang, Z. Xie, X.-L. Sun, Y. Tang, J. Org. Chem. 72 (2007)
6628e6630.
[4] W. Sun, B. Yu, F.E. Kühn, Tetrahedron Lett. 47 (2006) 1993e1996.
[5] A.R. Katritzky, D. Cheng, S.A. Henderson, J. Li, J. Org. Chem. 63 (1998) 6704e6709.
[6] E. Ertürk, A.S. Demir, Tetrahedron 64 (2008) 7555e7560.
[7] O. Fujimura, T. Honma, Tetrahedron Lett. 39 (1998) 625e626.
[8] V.K. Aggarwal, J.R. Fulton, C.G. Sheldon, J. de Vicente, J. Am. Chem. Soc. 125
(2003) 6034e6035.
[9] A.M. Santos, C.C. Romão, F.E. Kühn, J. Am. Chem. Soc. 125 (2003) 2414e2415.
[10] X. Zhang, P. Chen, Chem. Eur. J. 9 (2003) 1852e1859.
[11] G. Cheng, G.A. Mirafzal, L.K. Woo, Organometallics 22 (2003) 1468e1474.
[12] G.A. Mirafzal, G. Cheng, L.K. Woo, J. Am. Chem. Soc. 124 (2001) 176e177.
[13] G.A. Grasa, Z. Moore, K.L. Martin, E.D. Stevens, S.P. Nolan, V. Paquet, H. Lebel,
J. Organomet. Chem. 658 (2002) 126e131.
[39] M. Moghadam, I. Mohammadpoor-Baltork, S. Tangestaninejad, V. Mirkhani,
A.R. Khosropour, S.A. Taghavi, Appl. Organometal. Chem. 25 (2011) 687e694.
[40] S.A. Taghavi, M. Moghadam, I. Mohammadpoor-Baltork, S. Tangestaninejad,
V. Mirkhani, A.R. Khosropour, C. R. Chim. 14 (2011) 1095e1102.
[41] S.A. Taghavi, M. Moghadam, I. Mohammadpoor-Baltork, S. Tangestaninejad,
V. Mirkhani, A.R. Khosropour, V. Ahmadi, Polyhedron 30 (2011) 2244e2252.
[42] S.A. Taghavi, M. Moghadam, I. Mohammadpoor-Baltork, S. Tangestaninejad,
V. Mirkhani, A.R. Khosropour, Inorg. Chim. Acta 377 (2011) 159e164.
[43] A. Adler, F.R. Long, F. Kampass, J. Inorg. Nucl. Chem. 32 (1970) 2443e2445.
[44] K.C. Nguyen, H. Weizman, J. Chem. Educ. 84 (2007) 119e121.
[45] N. Kuhn, T. Kartz, D. Bläster, R. Boese, Chem. Ber. 128 (1995) 245e250.
[46] A. Schäfer, M. Weidenbruch, W. Saak, S. Pohl, J. Chem. Soc. Chem. Commun.
(1995) 1157e1158.
[14] H. Lebel, V. Paquet, Org. Lett. 4 (2002) 1671e1674.
[47] W.A. Herrmann, C. Kocher, Angew. Chem. Int. Ed. Engl. 36 (1997) 2162e2187.
[48] F.E. Hahn, L. Wittenbecher, M. Kühn, T. Lügger, R. Fröhlich, J. Organomet.
Chem. 617e618 (2001) 629e634.
[49] C.E. Willans, Organomet. Chem. 36 (2010) 1e28.
[50] D. Bourissou, O. Guerret, F.P. GabbaÏ, G. Bertrand, Chem. Rev. 100 (2000)
39e91.
[51] C.J. Carmalt, A.H. Cowley, Adv. Inorg. Chem. 50 (2000) 1e32.
[52] F.A. Carey, R.J. Sundberg, Advanced Organic Chemistry, fourth ed., Kluwer
Academic/Plenum Publishers, 2001, p. 112.
[15] H. Lebel, V. Paquet, C. Proulx, Angew. Chem. Int. Ed. 40 (2001) 2887e2890.
[16] B.E. Ledford, E.M. Carreira, Tetrahedron Lett. 38 (1997) 8125e8128.
[17] H. Firouzabadi, A.R. Sardarian, Z. Khayat, B. Karimi, S. Tangestaninejad, Synth.
Commun. 27 (1997) 2709e2719.
[18] S. Tangestaninejad, V. Mirkhani, Synth. Commun. 29 (1999) 2079e2083.
[19] S. Tangestaninejad, V. Mirkhani, J. Chem. Res. (S) (1999) 370e371.
[20] K. Suda, M. Sashima, M. Izutsu, F. Hino, J. Chem. Soc. Chem. Commun. (1994)
949e950.