High-valent tin(IV) porphyrins: Efficient and selective catalysts for cyclopropanation of styrene derivatives with EDA under mild conditions

Article abstract of DOI:10.1016/j.jorganchem.2013.05.046

An efficient and selective method for cyclopropanation of styrene derivatives with ethyl diazoacetate (EDA) catalyzed by tin(IV) tetraphenylporphyrinato trifluoromethanesulfonate, [SnIV(TPP)(OTf)₂], and tin(IV)tetraphenylporphyrinato tetrafluoroborate, [SnIV(TPP)(BF ₄)₂] is reported. These electron-deficient catalysts catalyzed the cyclopropanation of styrene derivatives in high yields and short reaction times under mild conditions. The reactions were highly selective and only trans-isomers were produced. Electron-rich styrenes were reacted faster than electron-poor ones. The catalysts were reused several times without loss of their catalytic activity and diastereoselectivity.

Full text of DOI:10.1016/j.jorganchem.2013.05.046

Journal of Organometallic Chemistry 741-742 (2013) 78e82
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Journal of Organometallic Chemistry
journal homepage: www.elsevier.com/locate/jorganchem
High-valent tin(IV) porphyrins: Efficient and selective catalysts for
cyclopropanation of styrene derivatives with EDA under mild
conditions
,
b
,
b
Shadab Gharaati a, Majid Moghadam b , Shahram Tangestaninejad , Valiollah Mirkhani ,
*
*
Iraj Mohammadpoor-Baltork b, Behjat Barati b, Faranak Sadegh b
a Department of Chemistry, Payame Noor University, PO Box 19395-4697, Tehran, Iran
b Department of Chemistry, Catalysis Division, University of Isfahan, Hezar Jerib, Isfahan 81746-73441, Iran
a r t i c l e i n f o
a b s t r a c t
Article history:
An efficient and selective method for cyclopropanation of styrene derivatives with ethyl diazoacetate
(EDA) catalyzed by tin(IV) tetraphenylporphyrinato trifluoromethanesulfonate, [SnIV(TPP)(OTf)2], and
tin(IV)tetraphenylporphyrinato tetrafluoroborate, [SnIV(TPP)(BF4)2] is reported. These electron-deficient
catalysts catalyzed the cyclopropanation of styrene derivatives in high yields and short reaction times
under mild conditions. The reactions were highly selective and only trans-isomers were produced.
Electron-rich styrenes were reacted faster than electron-poor ones. The catalysts were reused several
times without loss of their catalytic activity and diastereoselectivity.
Received 24 August 2012
Received in revised form
21 May 2013
Accepted 29 May 2013
Keywords:
Diazo compounds
Cyclopropanation
Olefins
Ó 2013 Elsevier B.V. All rights reserved.
Catalysis
High-valent tin(IV) porphyrin
1. Introduction
Electron-deficient metalloporphyrins have been used as mild
Lewis acid catalysts. Suda group has reported the use of chromium
Since cyclopropanes are versatile molecules with many potential
applications in organic chemistry, therefore, their preparation from
olefins is an important reaction in synthetic organic chemistry.
Frequently, cyclopropane rings can be found as biologically active
compounds and have a key role in the biosynthesis of steroids, ca-
rotenoids and retinoid [1e3]. These compounds are also useful in-
termediates in the formation of new carbonecarbon bonds.
Metal complexes are used as catalyst in the cyclopropanation of
olefins with readily available and cheap diazo compounds. This is a
simple and straight method for production of cyclopropanes [4e10].
In 1965, Nozaki et al. used copper complexes as catalyst for cyclo-
propanation of olefins with EDA [11]. Aratani et al. improved this
study by using a chiral copper complex [12e15]. Subsequently, a wide
variety of catalytic systems has been applied for cyclopropanation of
olefins but when metalloporphyrins are used as catalyst, the reaction
shows excellentactivityand selectivity [16e18]. Upto now, Co, Rh, Ru,
Os and Fe porphyrins have been used as catalyst for cyclopropanation
of olefins with diazo compounds [16,19e24].
and iron porphyrins in organic synthesis. They used Cr(tpp)Cl for
regioselective [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 stereoselective rearrangement of
epoxides to aldehydes [25e30].
Recently, we have reported the use of [SnIV(TPP)(ClO4)2], [SnIV(-
TPP)(OTf)2], [SnIV(TPP)(BF4)2], [SnIV(TNH2PP)(OTf)2] supported on
polystyrene and also [VIV(TPP)(OTf)2] in organic transformations
[31e40].
In continuation of our investigation on the reactivity of tin por-
phyrins, here, we report the application of high-valent [SnIV(-
TPP)(OTf)2] and [SnIV(TPP)(BF4)2] catalysts for efficient and selective
cyclopropanation of styrene derivatives with ethyl diazoacetate
(EDA) at room temperature (Scheme 1).
2. Experimental
All chemicals were purchased from Merck or Fluka chemical
companies. All reactions were performed under nitrogen atmo-
sphere using a glove box equipped with a M040H Dri-Train gas
* Corresponding authors. Tel.: þ98 311 7932712; fax: þ98 311 6689732.
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 2013 Elsevier B.V. All rights reserved.
http://dx.doi.org/10.1016/j.jorganchem.2013.05.046

S. Gharaati et al. / Journal of Organometallic Chemistry 741-742 (2013) 78e82
79
Table 1
BF4
OTf
Optimization of reaction conditions in the cyclopropanation of styrene with tin
N
N
N
N
N
N
IV
Sn
IV
Sn
porphyrins.a
or
N
N
COOEt
BF4
OTf
Entry EDA
(mmol)
Solvent
[SnIV(TPP)(OTf)2]
after 20 min
[SnIV(TPP)(BF4)2]
after 30 min
R
R
N2CHCO2Et and CH2Cl2
Catalyst amount Yield Catalyst amount Yield
Scheme 1. Cyclopropanation of styrene derivatives with EDA catalyzed by [SnIV(-
(mmol)
(%)b
(mmol)
(%)b
TPP)(OTf)2] or [SnIV(TPP)(BF4)2].
1
2
3
4
5
6
7
8
9
10
1.5
CH2Cl2
CH2Cl2
CH2Cl2
CH2Cl2
CH2Cl2
CH2Cl2
CH2Cl2
n-Hexane 0.01
THF
DMSO
0.003
0.005
0.007
0.01
0.02
0.01
20
42
59
95
95
80
95
10
60
70
0.005
0.007
0.01
0.02
0.03
0.02
0.02
0.02
0.02
0.02
18
25
43
95
95
70
95
8
1.5
1.5
1.5
1.5
1
purification system. Toluene and THF were dried before use. NMR
spectra were recorded on Bruker-Avance 400 MHz spectrometer
using CDCl3 as solvent. Infrared spectra were run on a Philips
PU9716 or a Shimadzu IR-435 spectrophotometer. All GC analyses
were performed on an Agilent 6890 instrument equipped with a
flame ionization detector (FID) using a 6FT3H OV-101 column. The
GC yields were calculated by the “internal standard addition”
method and in this manner ethyl hexanoate was used as internal
standard (the same results were obtained using n-decane as in-
ternal standard). The styrene derivatives, EDA and diethyl fumarate
were identified by comparison of their retention times by known
samples. The corresponding cyclopropanes were isolated and
identified. The tetraphenylporphyrin was prepared and metallated
according to the literature [41]. The catalysts, [SnIV(TPP)(OTf)2] [34]
and [SnIV(TPP)(BF4)2] [35], were prepared as reported previously.
2
0.01
1.5
1.5
1.5
0.01
0.01
40
54
a
Reaction conditions: styrene (1 mmol), EDA, solvent (1.5 mL) and [SnIV(-
TPP)(OTf)2] or [SnIV(TPP)(BF4)2].
b
GC yield.
4). It is noteworthy that when the reaction was carried out under air,
the yield was dramatically decreased; therefore, all reactions were
performed under N2 atmosphere.
The optimized conditions, which obtained for cyclopropanation
of styrene were styrene, EDA and catalyst in a molar ratio of 100:
150: 1. Under these optimized reaction conditions, a variety of sty-
rene derivatives was reacted with EDA in the presence of electron-
deficient [SnIV(TPP)(OTf)2], and the corresponding cyclopropanes
were obtained in high yields and short reaction times (Table 2).
These results showed that the electron-poor styrenes reacted in
longer reaction times. On the other hand, electron-rich styrenes,
such as 4-methoxystyrene and 4-methylstyrene were converted to
their corresponding cyclopropanes in higher yields and shorter re-
action times. After separation of the catalyst, the E/Z ratio of cyclo-
propanes was determined by their 1H and 13C NMR spectra. In the 1H
NMR spectra of trans-cyclopropanes, the ethyl group hydrogens
appear in 4.17 and 1.28 ppm; whereas for cis-cyclopropane these
signals present at 3.88 and 0.98 ppm. Also in 13C NMR spectra, the
CH2 group of cyclopropyl ring presents at 17e20 ppm for the trans-
isomer while the same signal appears around 11 ppm for the cis-
isomer [43]. As can be seen from NMR spectra, only trans-products
have been produced and surprisingly no cis-isomer was detected in
the presence of electron-deficient [SnIV(TPP)(OTf)2].
2.1. General procedure for the cyclopropanation of styrenes
A solution of ethyl diazoacetate (1.5 mmol) in dichloromethane
(0.5 mL) was added dropwise to a solution of styrene derivative
(1 mmol) and [SnIV(TPP)(OTf)2] (10 mg, 0.01 mmol) or
[SnIV(TPP)(BF4)2] (20 mg, 0.02 mmol) in dichloromethane (1 mL).
The reaction mixture was stirred at room temperature under ni-
trogen atmosphere. The progress of the reaction was monitored by
GC and 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
and purified by chromatography on a short column of silica gel to
afford the pure product.
3. Results and discussion
3.1. Cyclopropanation of olefins catalyzed by [SnIV(TPP)(OTf)2]
As reported in the literature [44,45], Rh, Ru, Co, Os and Fe por-
phyrins have been used as efficient and selective catalysts for
cyclopropanation of olefins. In all cases, a high trans/cis ratio has
been reported in the presence of these catalysts. The investigations
have revealed that the appropriate selection of the ligand and
metal, and the nature of the diazo compound and the olefin have
some influence on the cis/trans ratio [45]. For example, in the
cyclopropanation of styrene with EDA catalyzed by different metal
complexes of tetraphenylporphyrin, since the nature of olefin, EDA
and ligand is the same, therefore, the variation in the cis/trans ratio
can be attributed to the nature of the metal.
In order to check that GC values are completely true, some of
products were quantitatively isolated. These results were in
accordance to GC yields (Table 2).
It is important to note that no side product corresponds to
insertion of carbene into OH bond was detected in the reaction
mixture.
Initially, we investigated the effect of OTf groups on the electron
deficiency of tin(IV) porphyrin. In this manner, the cyclopropanation
of styrene with EDA was performed in the presence of 1 mol% of
[SnIV(TPP)(OTf)2] or[SnIV(TPP)Cl2] catalysts atroomtemperature. The
results showed that only 35% of the corresponding cyclopropane was
produced in the presence of [SnIV(TPP)Cl2] after 3 h, while in the
presence of [SnIV(TPP)(OTf)2], the corresponding cyclopropane was
obtained in 95% after 20 min. Then, the effect of catalyst amount, EDA
and kind of solvent in the model reaction were also investigated
(Table 1). The results showed that the highest yield of the corre-
sponding cyclopropane was obtained in the presence of 1 mol% of
[SnIV(TPP)(OTf)2] (Table 1, entry 4). Moreover, the best results were
obtained with 1.5 mmol of EDA. The excess amount of EDA was
converted to diethyl fumarate (the side product was removed in the
purification steps). The production of only fumarate ester can be
attributed to the formation of carbene dimer-tin(IV) porphyrin
complex which is blocked in a conformation favourable for the pro-
ducing of thermodynamically stable fumarate ester [42]. Under these
conditions, the highest yield of the corresponding cyclopropane was
produced. In addition, the reactionwas carried out in several solvents
and the best results were observed in dichloromethane (Table 1, entry
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

80
S. Gharaati et al. / Journal of Organometallic Chemistry 741-742 (2013) 78e82
Table 2
Cyclopropanation of styrene derivatives with EDA catalyzed by tin(IV) porphyrins at room temperature.a
Entry
Styrene compound
Product
[SnIV(TPP)(OTf)2] (1 mol%)
[SnIV(TPP)(BF4)2] (2 mol%)
Time (min)
Yield (%)b,c
TOF (hꢀ1
)
Time (min)
Yield (%)b
TOF (hꢀ1
)
COOEt
1
2
20
95 (91)
285
30
95 (90)
95
COOEt
32
91 (87)
171
40
90 (87)
67
Cl
Cl
COOEt
COOEt
3
4
5
25
20
17
90
216
285
335
32
30
28
90
84
95
F
F
95 (90)
95
95 (91)
95
Me
Me
MeO
COOEt
102
MeO
Me
COOEt
6
30
90
180
35
90
77
CH3
a
Reaction conditions: olefin (1 mmol), EDA (1.5 mmol), dichloromethane (1.5 mL).
GC yield.
The yields in the parenthesis refer to isolated yield.
b
c
bipyramidal complex is obtained [46e49]. 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 [50,51]. The third class of tin-carbene com-
plexes is cyclopropenylidene complexes of divalent tin [52].
Jørgensen and coworkers have reported the use of SnCl4 for
preparation of aziridines by the reaction of imines with EDA [52].
They reported that imines bearing electron-donating substituents
coordinate better to SnCl4 compared to imines constitute electron-
withdrawing substituents. Opposite electron demands favour the
two reaction steps in the SnCl4-catalyzed aziridination reaction;
the coordination to the metal is favoured for imines having
electron-donating substituents while the addition-step of EDA
proceeds faster for imines having electron-withdrawing sub-
stituents [53].
In our work, the styrene derivatives were reacted with EDA in
the presence of [Sn(TTP)(OTf)2] as catalyst, and the products yield
as a function of time are shown in Fig.1. As can be seen, the styrenes
bearing electron-donating groups react faster than the styrenes
containing electron-withdrawing ones in the presence of
[Sn(TTP)(OTf)2] to give the corresponding cyclopropanes. The same
results were observed in the Hammett plot in Fig. 2. According to
these observations and since the addition of EDA to catalyst is more
favoured than addition of styrene, we concluded that like all met-
alloporphyrins the carbene complex is formed, and the RDS step is
the addition of styrenes to carbene complex in which the nature of
substituent affects the reaction rate.
0.4
OMe
1
0.2
Me
0.8
H
H
0.6
0
Me
F
0.4
OMe
-0.2
0.2
0
Cl
F
Cl
-0.4
0
5
10
15
20
25
30
-0.3
-0.2
-0.1
0
0.1
0.2
0.3
Time (min)
para
Fig. 1. The formation of the cyclopropanes by the reaction of styrene derivatives with
EDA in the presence of [Sn(TPP)(OTf)2] as a function of time.
Fig. 2. Hammett plot for the formation of the trans-cyclopropanes.

S. Gharaati et al. / Journal of Organometallic Chemistry 741-742 (2013) 78e82
81
Acknowledgement
We are thankful to the University of Isfahan and Payame Noor
University for financial support of this work.
Appendix A. Supplementary data
Supplementary data related to this article can be found at http://
dx.doi.org/10.1016/j.jorganchem.2013.05.046.
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In this paper, a rapid, efficient and selective method for
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diazoacetate (EDA) catalyzed by tin(IV)tetraphenylporphyrinato
trifluoromethanesulfonate, [SnIV(TPP)(OTf)2], and tin(IV)tetraphe-
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catalytic activity.

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