Tetraphenylantimony carboxylates in the cascade Pd-catalyzed C-phenylation reaction of methyl acrylate in the presence of peroxide

Article abstract of DOI:10.1016/j.jorganchem.2003.11.025

Tetraphenylantimony(V) carboxylates have been used in the palladium-catalyzed C-phenylation reaction of methyl acrylate in the presence of (PhCO₂)₂ or t-BuOOH under mild conditions (50 °C). The peroxides promote a cascade participation of the organoantimony compound and result in the transfer of three phenyl groups. Organoantimony intermediates have been isolated from the reaction.

Full text of DOI:10.1016/j.jorganchem.2003.11.025

Journal of Organometallic Chemistry 689 (2004) 731–737
www.elsevier.com/locate/jorganchem
Tetraphenylantimony carboxylates in the cascade Pd-catalyzed
C-phenylation reaction of methyl acrylate in the presence of peroxide
a,
Dmitry V. Moiseev , Vera A. Morugova , Aleksey V. Gushchin ,
a
a
*
b
Andrey S. Shavirin , Yury A. Kursky , Victor A. Dodonov
b
a
a
Department of Organic Chemistry, Nizhnii Novgorod State University, 23 Gagarin Avenue, 603950 Nizhnii Novgorod, Russia
b
G.A. Razuvaev Institute of Organometallic Chemistry, Russian Academy of Sciences, GSP-445, 49 Tropinin Street, 603950 Nizhnii Novgorod, Russia
Received 20 November 2003; accepted 20 November 2003
Abstract
Tetraphenylantimony(V) carboxylates have been used in the palladium-catalyzed C-phenylation reaction of methyl acrylate in
the presence of (PhCO2)2 or t-BuOOH under mild conditions (50 °C). The peroxides promote a cascade participation of the or-
ganoantimony compound and result in the transfer of three phenyl groups. Organoantimony intermediates have been isolated from
the reaction.
Ó 2003 Elsevier B.V. All rights reserved.
Keywords: Antimony(V); Arylation; Palladium-catalyzed; Peroxide
1
. Introduction
2. Results and discussion
Organoantimony compounds have been used in or-
2.1. Ph SbX + peroxide system in the palladium-catalyzed
4
ganic synthesis either as reagents or as catalysts for a
number of years [1]. The catalysis of these reactions
using palladium has been reported [2]. We have recently
reported that triarylantimony dicarboxylates were effi-
cient reagents in the palladium-catalyzed C-arylation
reactions of unsaturated compounds with the involve-
C-phenylation reaction
The tetraphenylantimony compounds are involved in
the palladium-catalyzed phenylation reaction of methyl
acrylate to give Ph3Sb, which is inactive in a catalytic C-
phenylation [5]. Moreover, Ph3Sb can deactivate a pal-
ladium catalyst [3]. We assumed that an addition of
organic peroxide in the reaction mixture in the presence
ment of two aryl groups [3]. Triarylstibines Ar Sb can
3
also be used as reagents in the C-arylation reaction via
formation of Ar Sb(OAc) in situ in the presence of
of a carboxylic acid could convert Ph Sb into triphe-
3
3
2
peroxides [4]. Tetraphenylantimony derivatives Ph4SbX
have shown lower activities in comparison with
Ar3Sb(OAc)2. Only one phenyl group was involved in
the C-phenylation reaction [5].
The aim of the present work is to increase the effi-
ciency of tetraphenylantimony derivatives in the
C-phenylation reaction using organic peroxides.
nylantimony dicarboxylate in situ [4]. The latter is an
active phenylating agent [3,4].
We investigated the model C-phenylation reaction of
methyl acrylate 1 with tetraphenylantimony hydroxide
Ph4SbOH 2 (1:2 ¼ 4:1) in AcOH in the presence of t-
BuOOH 3 (1.2 equivalent per 2) and Li PdCl (4 mol%).
2
4
Compound 2 was selected for the following reasons. It is
one of the most accessible compounds of this type and
can easy give tetraphenylantimony acetate Ph4SbOAc 4
in AcOH solution [6,7] (Scheme 1). Peroxide 3 is the best
oxidant for antimony(III) derivatives [4]. Li2PdCl4 is the
optimum precatalyst for the C-phenylation in the pres-
ence of the peroxide [4]. Methyl acrylate 1 was taken in
*
Corresponding author. Tel.: +7-831-2337865; fax: +7-831-2658592.
E-mail address: moisdv@mail.nnov.ru (D.V. Moiseev).
0
022-328X/$ - see front matter Ó 2003 Elsevier B.V. All rights reserved.
doi:10.1016/j.jorganchem.2003.11.025

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D.V. Moiseev et al. / Journal of Organometallic Chemistry 689 (2004) 731–737
e.g. CH3CN. However Ph4SbOH is not effective in
acetonitrile where it gives mainly a homo-coupling
product, namely, biphenyl [5]. Therefore, propionate 6
was used as a phenylating agent. The reaction of 1 with
the (6 + 7) system (1:1.5) gives 5, as expected, in a 300%
yield (CH CN, 50 °C, 24 h) (Table 1, entry 8). When 7 is
3
heated in the absence of organoantimony compound
under the same conditions the phenylated product 5 is
not formed.
Scheme 1.
Thus, the tetraphenylantimony derivatives can be ef-
fective cross-coupling agents. In the presence of (PhCO2)2
they phenylate methyl acrylate under mild conditions (50
°C) to provide a transfer of three phenyl groups. It was
molar excess to 2 (4:1), one molecule of 1 per one phenyl
group of 2.
The C-phenylation reaction of 1 with the (2 + 3) sys-
tem gives methyl cinnamate 5 (Scheme 1) in a 247% yield
for 24 h (the yield being based on the initial organoan-
timony reagent, the yield of 100% corresponds to the
transfer of only one phenyl group) (Table 1, entry 1).
The yield of 5 is not changed significantly in the presence
of an excess of 3 (Table 1, entries 2 and 3). In the ab-
sence of the peroxide the product yield is only 30%
found that Ph SbOH was the preferable agent in AcOH,
4
and Ph SbO CEt in CH CN, respectively.
4
2
3
2.2. Mechanistic aspects of the organoantimony(V)
involvement in the palladium-catalyzed C-phenylation
reaction
(
Table 1, entry 5). Tetraphenylantimony propionate
To understand the mechanism of the tetraphenylan-
timony compounds participation in the investigated re-
action we isolated three key stages, within each stage
only one phenyl group is transferred. The catalytic cycle
consists of the consecutive redox reactions of the anti-
mony atom, which are caused by the presence of per-
oxide and palladium in the system.
Ph4SbO2CEt 6 being used instead of 2 shows the same
activity, the yield of 5 is 254% (Table 1, entry 4). The
high yield of 5 corresponds to the transfer of almost
three phenyl groups.
The substitution of 3 for benzoyl peroxide (PhCO2)2
7
gives rise to the yield of 5. It is 240% and 300% in the
case of 12 and 24 h duration of the reaction, respectively
Table 1, entries 6 and 7). This yield corresponds to the
(
2.2.1. Transfer of the first phenyl group
full involvement of three phenyl groups of 2. It is known
that peroxide 7 in contrast with 3 can oxidize Sb(III)
into active Sb(V) without involvement of carboxylic acid
At the first stage of the catalytic cycle tetrapheny-
lantimony carboxylate 4 reacts with the active Pd(0)
species formed on the activation stage. As a result, the
[4,8]. This allows the new system based on tetrapheny-
lantimony derivatives to be used in a neutral solvent,
phenylpalladium intermediate 8 and Ph Sb 9 are formed
3
(Eq. (1)). The intermediate 8 interacts with 1 to give the
phenylation product 5 (Eq. (2)). At this stage the yield of
5
of peroxide the yield is only 30% (Table 1, entry 5) be-
could reach a value of 100%. In reality, in the absence
Table 1
Pd-catalyzed reaction of Ph4SbOH with methyl acrylate 1 in the
cause of the inhibiting effect of Ph Sb [3].
3
presence of a peroxide: influence of the nature and the amount of the
peroxidea
Ph4SbOAc
+
Pd(0)
PhPdOAc
+
Ph3Sb
(1)
4
8
9
Entry
Peroxide
Ph SbOH:
peroxide
4
Yields of 5
b
(%)
Ph
1
2
3
t-BuOOH
t-BuOOH
t-BuOOH
t-BuOOH
–
1:1.2
1:1.5
1:2
247
257
240
254
30
+
Pd(0) HOAc
+
+
PhPdOAc
CO2Me
2
CO Me
(2)
c
4
1:1.2
–
5
d
6
(PhCO
(PhCO
(PhCO
2
2
2
)
)
)
2
2
2
1:1.5
1:1.5
1:1.5
240
300
300
7
e
8
2.2.2. Transfer of the second phenyl group
a
At the second stage the peroxide oxidizes 9 into the
active pentavalent state [3,4]. The mechanism of the
oxidation has been reported [9,10]. Ph3Sb forms either
triphenylantimony diacetate Ph3Sb(OAc)2 10 in the
AcOH solution in the presence of hydroperoxide 3 (Eq.
The reactions were performed in AcOH at 50 °C for 24 h, under air
with ratio between 1, [Sb] and Li2PdCl4 of 4:1:0.04.
b
Yields were determined by GLC, the yield of 100% corresponds to
the involvement of one phenyl group.
c
Ph4SbO2CEt was used as a phenylating agent.
Reaction duration was 12 h.
d
e
(3)) or triphenylantimony dibenzoate Ph3Sb(O2CPh)2 11
in CH3CN in the presence of benzoyl peroxide 9
Ph4SbO2CEt was used as a phenylating agent and CH3CN was
used as a solvent.

D.V. Moiseev et al. / Journal of Organometallic Chemistry 689 (2004) 731–737
733
(Eq. (4)). The triphenylantimony dicarboxylates oxidize
Pd(0) into PhPdOAc 8 (Eq. (5)), which phenylates
methyl acrylate according to Eq. (2).
2p-Tol
2
SbOAc ꢀ p-TolSbðOAcÞ þp-Tol
3
Sb
ð6Þ
2
16
17
2
.2.3. Transfer of the third phenyl group
Organoantimony(III) derivatives Ph2SbX (X ¼ OAc,
Ph
3
Sb þ t-BuOOH þ 2 AcOH
!
Ph
3
SbðOAcÞ þ t-BuOH þ H
2
O
ð3Þ
ð4Þ
ð5Þ
2
O2CPh) are involved in the third stage of the phenyla-
tion reaction. Like in the case of Ph3Sb, a peroxide
oxidizes Ph SbX to give an active antimony(V) deriva-
tive, diphenylantimony triacetate Ph2Sb(OAc)3 18 (Eq.
7) or diphenylantimony tribenzoate Ph Sb(O CPh) 19
(Eq. 8). These compounds react with Pd(0) to give the
phenylpalladium intermediate 8 (Eq. 9), which pheny-
lates the third molecule of 1 (Eq. (2)). Antimony(V) is
reduced to the phenylantimony(III) dicarboxylate.
Thus, peroxide is consumed in oxidation of both tri-
phenyl- and diphenylantimony(III) derivatives.
10
Ph Sb þ ðPhCO Þ ! Ph SbðO CPhÞ
3
2
2
3
2
2
2
1
1
Ph
3
SbðOAcÞ þ Pdð0Þ ! PhPdOAc þ Ph
2
SbOAc
12
2 2 3
2
To prove the existence of the reaction (5) we made a
special investigation of the C-arylation reaction of 1
with tris(para-tolyl)antimony diacetate p-Tol3Sb(OAc)2
1
1
3 by H NMR. This system was selected for the fol-
lowing reasons. The initial compounds as well as the
arylation products such as methyl 3-(para-tolyl)pro-
pionate 14 and bis(para-tolyl)antimony acetate 15 had
clear and easy identifiable NMR signals (Scheme 2).
D3CCOOD was used as a solvent. The reaction was
carried out under argon atmosphere.
Ph SbOAc þ t-BuOOH þ 2AcOH
2
!
Ph SbðOAcÞ þ t-BuOH þ H O
ð7Þ
ð8Þ
2
3
2
18
Ph
2
SbO
2
CPh þ ðPhCO
2
Þ2 ! Ph
2
SbðO
2
CPhÞ3
1
19
The initial H NMR spectrum of the reaction mixture
contained the resolved signals of 13 at 7.88 (d, ortho-
Ph SbX þ Pdð0Þ ! PhPdX þ PhSbX
2
3
2
protons), 7.36 (d, meta-protons), 2.39 (s, CH ), 2.06 (s,
3
X ¼ OAc; O
2
CPh
ð9Þ
OAc) ppm and 1 at 6.41, 6.16, 5.86 (d, protons at the
double bond), 3.74 (s, OMe) ppm (Fig. 1(a)). In the
second spectrum, recorded after 3 h, two new sets of
signals appeared (Fig. 1(b)). They corresponded to the
expected products 14 at 7.71 (d), 7.48 (d, ortho-protons),
Another route of Ph2SbX involvement can occur in
the presence of oxygen. Matoba et al. [2e] suggested a
radical mechanism of this process. In previous work [3]
we suggested the speculative mechanism of the oxygen
involvement via formation of a palladium hydroperox-
ide XPdOOH, which oxidized antimony(III) into
antimony(V).
7.20 (d, meta-protons), 6.48 (d), 3.79 (s, OMe), 2.35 (s,
CH ) ppm and 15 at 7.55 (d, ortho-protons), 7.24 (d,
3
meta-protons), 2.33 (s, CH ), 2.06 (s, OAc) ppm. The
3
1
4:15 ratio was 1:1. An amount of 14 corresponded to
We investigated the arylation reaction of 1 with p-
Tol3Sb(OAc)2 13 (Scheme 2) in the presence of oxygen
by H NMR. Under oxygen conditions, comparable to
an amount of consumed organoantimony compound 13.
Spectra, recorded for 12 and 24 h of the reaction du-
ration (Fig. 1(c)), confirmed that the product formation
and the consumption of 13 occurred in equivalent
amounts. However, the new signals appeared at 7.66 (d),
1
argon, products 14-17 were registered. However, in the
presence of oxygen the rate of formation of the arylation
product, 14, was observed to be greater than rate of
consumption of 13. The organoantimony(III) com-
pound p-TolSb(OAc)2 16 was the main product. It was
found that oxygen is absorbed at the rate of 0.5 mol
per 1 mol of 5. Thus, the following scheme of oxygen
involvement in the transfer of the third phenyl group
is realized (Scheme 3). The scheme could be explained
by concerted oxidation of two molecules of 12 with
an oxygen molecule in the coordination sphere of
palladium like in the homogeneous oxidation of phos-
phines with oxygen on Rh, Co, Pt catalysts [11–13]
(Scheme 4).
7.29 (d), 2.33 (s), 2.06 (s) ppm were associated with
mono(para-tolyl)antimony diacetate p-TolSb(OAc) 16
2
and signals at 7.31 (d), 7.13 (d), 2.31 (s) ppm were as-
sociated with tris(para-tolyl)antimony p-Tol3Sb 17.
These compounds are the products of the ligand ex-
change reaction of 15 according to Eq. 6. Thus, we
confirmed that triarylantimony dicarboxylates were in-
volved in the arylation according to Eq. (5). The total
catalytic process (Eqs. (1)–(3), (5)) can give 200% of
phenylation product 5 with respect to the initial
Ph SbOAc.
4
p-Tol
[Pd]
+
p-Tol SbOAc
2
p-Tol Sb(OAc)
2
+
o
3
5
0 C, argon
CO Me
CO Me
2
2
14
13
15
Scheme 2.

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D.V. Moiseev et al. / Journal of Organometallic Chemistry 689 (2004) 731–737
8.0
7.5
7.00
6.5
6.00
5.5
5.00
4.5
4.00
3.5
3.0
2.55
2.0
1.5
(
a)
8.0
7.5
7.00
6.5
6.00
5.5
5.0
4.5
4.00
3.5
3.0
2.55
2.0
1.5
(
b)
1
Fig. 1. H NMR spectra of the reaction mixture: p-Tol3Sb(OAc)2 + 1 (1:2), PdCl2 (4 mol%), D3CCOOD, argon, 50 °C: (a) at the start of the reaction;
(b) after 3 h; (c) after 24 h.
The compound 20 in AcOH forms 18 (Eq. 10),
Ph
2
SbðOÞOAc þ 2AcOH ! Ph
2
SbðOAcÞ þ H
2
O ð10Þ
3
which acts with Pd(0) (Eq. 9). Thus, diphenylanti-
mony(V) tricarboxylates are preliminarily formed in
the both routes of transfer of the third phenyl group
at the third stage of the catalytic cycle. To prove the
The total catalytic cycle is shown on Scheme 6. The
active Pd(0) species interact with the initial tetrapheny-
lantimony compound to give phenylpalladium interme-
diate, which phenylates 1. Triphenylstibine is oxidized
by a peroxide to give antimony(V), which reacts with
Pd(0) giving PhPdX. As a result, the second molecule of
5 and antimony(III) derivative are formed. Oxygen (or
peroxide in excess) oxidizes the latter into antimony(V),
which transfers the third phenyl group to methyl acry-
Eq. 9 we used diphenylstibine acid Ph Sb(O)OH as a
2
phenylating agent. In this reaction the yield of 5 was
9
2% (50 °C, 12 h, AcOH) (Scheme 5). This fact
confirms the mechanism via diphenylantimony tri-
carboxylates. This is the final stage and the yield of 5
can reach a value of 300%.

D.V. Moiseev et al. / Journal of Organometallic Chemistry 689 (2004) 731–737
735
8
.5
8.0
7.5
7.0
6.5
6.0
5.5
5.0
4.5
4.0
3.5
3.0
2.5
2.0
1.5
Fig. 1. (continued)
Ph
AcOH, [Pd]
Ph2SbOAc +
+ 0.5 O2
+
PhSb(OAc)2
CO2Me
CO2Me
- H O
2
Scheme 3.
ganoantimony compound via consecutive redox stages.
We found that (PhCO2)2 is the optimum peroxide for
this system. The reactions can be performed both in
AcOH and in CH3CN. It was established that the initial
OAc
Ph2Sb
Ph2SbOAc
Pd
OAc
O
O2
O
nL
Pd
2 Ph2Sb
+ PdLn
O
Ph2Sb
Ph SbX derivative transforms in this cascade reaction in
4
Ph2SbOAc
20
OAc
the following range: Ph SbX ! Ph Sb ! Ph SbX !
4
3
3
2
Ph SbX ! Ph SbX ! PhSbX . The final PhSbX de-
2
2
3
2
2
Scheme 4.
rivative is inactive in the C-phenylation under these
conditions. The key role of peroxides is oxidation of
inactive Ph3Sb or Ph2SbX compounds into an active
pentavalent state.
1
, [Pd]
Ph2Sb(O)OH + 2 AcOH
Ph2Sb(OAc)3
PhSb(OAc)2
-
H2O
- 5
Scheme 5.
4. Experimental
late. PhSbX2 (X ¼ OAc, O2CPh), the final product of
transformation, is not involved in the C-phenylation
reaction in these conditions. The total yield of 5 is 300%
in respect to the initial tetraphenylantimony derivative.
4.1. General methods
Gas chromatographic analyses were performed with a
LKhM-80 chromatograph using helium as the carrier
gas, column 100 cm length, 15%-Apiezon-L on the
1
3
. Conclusion
Chromaton N-AW at 220 °C. H NMR spectra were
measured on a Bruker Avance DPX-200 spectrometer
for solutions in D3CCOOD. Column chromatographies
were performed with silica gel 60 Merck.
The tetraphenylantimony compounds Ph4SbOH,
Ph4SbO2CEt and Ph2Sb(O)OH were prepared as
Thus, the addition of peroxide increases the activity
of tetraphenylantimony derivatives in the C-phenylation
reaction. The presence of the peroxide provides the in-
volvement of three phenyl groups from the initial or-

736
D.V. Moiseev et al. / Journal of Organometallic Chemistry 689 (2004) 731–737
Ph SbX
4
Pd(0)
Ph SbX2
3
5
+ HX
Ph SbX3
2
0.5 O2
PhSbX2
1
3
or 7
PhPdX
Ph SbX
2
Ph Sb
3
2 2
X = O CEt, OAc or O CPh
Scheme 6.
described [6]. The triarylantimony compounds
p-Tol3Sb(OAc)2 and Ph3Sb(OAc)2 were prepared as
described [3]. t-BuOOH was prepared by the method of
Milas and Surgenor [14]. Commercial (PhCO2)2 was
purified by recrystallization from methanol. Commercial
methyl acrylate was washed with an alkali solution until
the yellow color disappeared, then dried with Na2SO4
and distilled. All solvents were distilled prior to use.
PdCl2 was commercially available. Li2PdCl4 [15] was
prepared by the reported methods.
reaction under argon yielded 0.44 mmol of methyl
innamate.
1
4
.4. Procedure for H NMR spectroscopic study
PdCl2 (0.9 mg, 0.005 mmol) and p-Tol Sb(OAc)2
3
(64.1 mg, 0.125 mmol) were placed into NMR tube under
argon. Air-free D CCOOD (1 ml) and methyl acrylate
3
(0.034 ml, 0.375 mmol) were placed into the tube under
argon. The tube was sealed and H NMR analysis was
1
carried out. The reaction mixture was heated at 50 °C.
The H NMR spectra were recorded in 3, 12, and 24 h.
4
.2. Typical procedure for the C-phenylation reaction
1
Ph4SbOH (0.224 g, 0.5 mmol) was dissolved in AcOH
1 ml) in a 50 ml tube. A mixture of t-BuOOH (0.075 ml,
.75 mmol), Li2PdCl4 (5.2 mg, 0.02 mmol) and methyl
(
0
Acknowledgements
acrylate (0.18 ml, 2 mmol) in acetic acid (3 ml) was
added to Ph4SbOH solution. The tube was sealed and
the reaction mixture was kept at 50 °C for 24 h. The
solvent was then evaporated under reduced pressure.
The solid residue was purified from inorganic products
by elution through a short column on silica gel using a
mixture of hexane–diethyl ether (v/v, 4:1) as the eluant.
The filtrate was analyzed by GLC. Methyl cinnamate
We thank Dr. Carl Redshaw and Dr. Michael Rowan
University of East Anglia, Norwich, UK) for fruitful
(
discussions.
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