Pd-catalyzed C-arylation of unsaturated compounds with pentavalent triarylantimony dicarboxylates

Article abstract of DOI:10.1016/S0022-328X(02)02179-4

Triarylantimony (V) derivatives Ar₃SbX₂ (X = Hal or acyloxy) were prepared by reaction of Ar₃Sb with equimolar amounts of a peroxide ROOH (R = t-Bu, H) in the presence of an acid or an anhydride in good to excellent yields. Ar₃Sb(O₂CR)₂ are mild and efficient C-arylation reagents of unsaturated compounds (methyl acrylate, styrene, 2-phenylpropene and acrylonitrile) under palladium catalysis at 50 °C, with PdCl₂ being the most effective catalyst. Ar₃SbHal₂ do not react under these conditions.

Full text of DOI:10.1016/S0022-328X(02)02179-4

Journal of Organometallic Chemistry 667 (2003) 176Á184
/
www.elsevier.com/locate/jorganchem
Pd-catalyzed C-arylation of unsaturated compounds with pentavalent
triarylantimony dicarboxylates
Dmitry V. Moiseev a, Aleksey V. Gushchin a,*, Andrey S. Shavirin b, Yury A. Kursky b,
Viktor A. Dodonov 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, 603600 Nizhnii Novgorod, Russia
Received 13 December 2002; received in revised form 13 December 2002; accepted 14 December 2002
Abstract
Triarylantimony(V) derivatives Ar3SbX2 (Xꢀ/Hal or acyloxy) were prepared by reaction of Ar3Sb with equimolar amounts of a
peroxide ROOH (Rꢀt-Bu, H) in the presence of an acid or an anhydride in good to excellent yields. Ar3Sb(O2CR)2 are mild and
/
efficient C-arylation reagents of unsaturated compounds (methyl acrylate, styrene, 2-phenylpropene and acrylonitrile) under
palladium catalysis at 50 8C, with PdCl2 being the most effective catalyst. Ar3SbHal2 do not react under these conditions.
# 2002 Elsevier Science B.V. All rights reserved.
Keywords: Alkenes; Antimony(V); Arylation; Cross-coupling; Palladium-catalyzed
1. Introduction
oxidant such as oxygen [7], AgOAc [8] or
(NH4)2Ce(NO3)6 [9]. In the course of our studies on
the synthesis and reactivity of organoantimony com-
pounds, we decided to prepare a series of triarylanti-
mony compounds Ar3SbX2 and to compare their
activity in the Pd-catalyzed C-arylation reaction of
unsaturated compounds.
Organoantimony compounds have been used in
organic synthesis either as reagents or as catalysts for
a number of years [1]. However, it is only in the last few
years that their application in palladium catalyzed cross-
coupling reactions has been described. In the presence of
catalytic amounts of Pd(PPh3)4 or Pd(OAc)2, pentaphe-
nylantimony Ph5Sb reacted with allyl acetate or allyl
phenyl ether to afford allylbenzene [2]. Organoantimo-
ny(V) derivatives Ar3SbX2 (XꢀCl, OAc) gave cross-
coupling products with silyloxy alkenes [3] and organo-
tin compounds [4] under palladium catalysis.
/
2. Results and discussion
Ar3Sb(OAc)2 were used in Pd(0)ÁCu(I)-catalyzed
/
2.1. Synthesis of Ar3SbX2
cross-coupling reactions with alkynylsilanes [5]. We
have recently reported that Ph3Sb(OAc)2 behaves not
only as a phenyl group donor but also as a Pd(0)
reoxidant in the Pd catalyzed C-phenylation reaction of
methyl acrylate [6]. When trivalent arylantimony com-
pounds are used, the Pd-catalyzed cross-coupling reac-
tions takes place only in the presence of an additional
The organoantimony derivatives Ar3SbX2 were ob-
tained in good yields by the one-step reaction of the
appropriate triarylantimony with an acid in the presence
of equimolar amounts of peroxide (Scheme 1) [10]:
In the synthesis of triarylantimony dicarboxylates, the
anhydride can be used instead of the carboxylic acid
(Scheme 2). However in this case, the reaction proceeded
more slowly to afford slightly reduced yields of the
diacylates.
* Corresponding author. Tel.: ꢁ
8592.
E-mail address: gushchin@mail.nnov.ru (A.V. Gushchin).
/
7-831-233-7865; fax: ꢁ7-831-265-
/
0022-328X/02/$ - see front matter # 2002 Elsevier Science B.V. All rights reserved.
doi:10.1016/S0022-328X(02)02179-4

D.V. Moiseev et al. / Journal of Organometallic Chemistry 667 (2003) 176Á
/184
177
Fig. 1. Effect of the molar ratio 7:Ph3Sb(OAc)2 on the yields of 8a and
9a in the C-phenylation reaction with 1bꢁ0.02Pd2(dba)3 system in
CH3CN, 50 8C, 3 h.
/
Scheme 1.
initial organoantimony reagent) (Fig. 1). Concomitantly
the biphenyl 9a, resulting from a homocoupling reaction
of 1b, was formed in yields increasing from a few percent
in the reaction with ten equivalents of 7 to 18% in the
absence of the acrylate 7. Similar results were also
obtained when Pd(OAc)2 was used as the catalyst. In
Fig. 1 representing the yields of product versus the
reagent ratios, it appears that the influence of the
amount of methyl acrylate is more pronounced in the
Scheme 2.
2.2. Reaction of Ar3SbX2 with methyl acrylate
The different organoantimony(V) compounds were
then tested in the Heck-type C-arylation reaction of
methyl acrylate 7, which was used as a model unsatu-
rated substrate. Compound 7 was treated with Ar3SbX2
in the presence of catalytic amounts of various palla-
dium species to give only the trans-arylation products,
range 0Á4 molar equivalents. In fact, it can be con-
/
sidered that all the phenyl groups present in the original
organoantimony reagent can be transferred. Therefore,
a 1:3 ratio between [Sb(V)] and 7 was employed in the
subsequent investigations.
The nature of the palladium catalyst as well as the
presence of additional ligands plays a role on the yields
of methyl cinnamate 8a and of the by-product 9a (Table
1). The two palladium catalysts, PdCl2 and Li2PdCl4,
the cinnamic acid derivatives 8aÁf under mild condi-
/
tions. In some instances, besides the main product of C-
arylation, a biaryl derivative was isolated as a by-
product resulting from a competing homocoupling
reaction of the organometallic compound (Scheme 3).
In a preliminary report, we have shown that
Ph3Sb(O2CEt)2 (1b) reacts efficiently with a tenfold
molar excess of methyl acrylate 7 in the presence of 4
mol% of Pd(OAc)2 in acetonitrile at 50 8C to give the
derived methyl cinnamate [6]. However, a large excess of
the substrate 7 is not necessary for the reaction to
proceed in good to high yields. In a series of reactions,
1b was treated with various amounts of methyl acrylate
7 in acetonitrile at 50 8C in the presence of 2 mol% of
Pd2(dba)3. The yields of methyl cinnamate 8a decreased
only slowly from 83% with ten equivalents of 7 to 35%
with one equivalent of 7 (the yields being based on the
Table 1
Pd-catalyzed reaction of Ph3Sb(O2CEt)2 (1b) with methyl acrylate 7:
a
influence of the nature of the catalyst
Run
[Pd]
Yields (%)
8a
9a
1
2
PdCl2
93
83
76
71
Á
Á/
/
b
Li2PdCl4
Pd(OAc)2
Pd2(dba)3
3
6
4
8
5
Pd(PPh3)2Cl2
Á/
Á/
6
Pd(OAc)2ꢁ
Pd(dppf)Cl2
Pd2(dba)3ꢁ
/
2Ph3P
Á
9
/
Trace
1
7
8
/
2Ph3P
Á/
Á/
9
PdCl2ꢁ
PdCl2ꢁ
PdCl2ꢁ
PdCl2ꢁ
/
2Ph3As
2Ph3Sb
2Ph3As
2Ph3Sb
57
61
Trace
Trace
10
11
12
/
c
c
/
Á/
24
Á/
Á/
/
a
The reactions were performed in CH3CN at 50 8C for 6 h, under
air with ratio between 1b, 7 and [Pd] of 1:3:0.04 unless otherwise
stated.
b
3 mol% of Li2PdCl4 were used.
AcOH was used as solvent.
c
Scheme 3.

178
D.V. Moiseev et al. / Journal of Organometallic Chemistry 667 (2003) 176Á184
/
proved to be the most active as they led only to the C-
phenylated product 8a in 93 and 83%, respectively
(Table 1, entries 1 and 2). Pd(OAc)2 and Pd2(dba)3
were slightly less efficient and less selective, as the by-
Table 2
PdCl2 catalyzed reaction of Ph3SbX2 with methyl acrylate 7: influence
of the nature of the substituent X
Entry
X
Yields (%)
product 9a was also formed in 6Á8% yields (Table 1,
entries 3 and 4). The presence of additional phosphines,
Ph3P or dppf, inhibited the catalytic activity (Table 1,
/
8a
1
2
3
4
5
6
7
8
O2CH
O2CCH3
O2CC2H5
O2CCF3
O2CPh
F
130
101
96
entries 5Á8). Under these conditions, the phosphine
/
ligands bind too strongly to the palladium metallic
center to allow the exchange reaction with either the
solvent, the olefin or the arylantimony compound.
When less strongly binding ligands such as Ph3As and
Ph3Sb were added to the reaction system with PdCl2, the
phenylation reaction took place although with a reduced
efficiency [57 and 61%, respectively, in CH3CN (Table 1,
entries 9 and 10)]. However, the inhibiting effect of these
two ligands was strongly enhanced when AcOH, a less
donor solvent, was used. In this case, no reaction
product was detected when Ph3As was added while
only 24% of 8a were obtained in the presence of Ph3Sb
(Table 1, entries 11 and 12). Thus, PdCl2, employed
alone, appears to be the most efficient catalytic species
for this arylation reaction. It was therefore used in the
subsequent studies, for which a ratio between the
reagents [Sb]:[alkene]:PdCl2 of 1:3:0.04 was selected as
the preferred conditions.
The solvent has a determinant effect on the yield of
the products of the C-phenylation. Compared to meth-
ylene dichloride or methanol which led to the lowest
yields (43 and 51%, respectively), the more donating
solvents THF and DMF [11] afforded the highest yields
of 8a, 118 and 116%, respectively, in the reactions of 7
with 1b, but the by-product 9a was formed in significant
amounts, 18 and 15%, respectively. AcOH and espe-
cially CH3CN showed an excellent selectivity (no for-
mation of the by-product 9a under these conditions)
together with a good activity (92 and 96% yields of 8a).
Therefore, CH3CN and AcOH were considered to be the
solvents of choice for the complementary studies of the
reaction.
93
68
4
Trace
Cl
Br
Á/
The reactions were performed in CH3CN at 50 8C for 6 h, under air
with ratio between [Sb], 7 and PdCl2 of 1:3:0.04.
had little influence, 101% with the acetate and 96% with
the trifluoroacetate (Table 2, entries 2 and 4).
Concerning the aryl group, it was supposed that the
presence of electron-donating groups in the aromatic
ring would decrease the polarity of the CÁ
reduce the arylating potential of the organometallic
reagent. Indeed, in the sequence Phꢀp-tolylꢀp-anisyl,
/
M bond and
/
/
the arylating activity decreased (Table 3, entries 1, 2 and
6). The anisyl compound 6a gave 105% of the product 8f
after 12 h, compared to 186% of 8a when the pheny-
lantimony reagent 1a was employed and 163% of 8b
with the p-tolylantimony reagent 2a. After 24 h, the
yield of 8f rose only to 120%. In the methyl substituted
series of antimony reagents, the influence of the steric
hindrance can be easily observed with the most bulky
mesityl derivative being absolutely inactive: 4-
MeC6H4ꢀ
(Table 3, entries 2Á
/
3-MeC6H4ꢀ
/
2-MeC6H4ꢁ2,4,6-Me3C6H2
/
/5).
The nature of the reaction atmosphere is also an
important factor interfering with the yield of the C-
arylation products. For example, when the PdCl2
catalyzed reaction of 7 with 1a was performed in acetic
acid under an atmosphere of argon, the yield of 8a
nearly reached 100% after 12 h and did not evolve
The outcome of the reaction is also dependent upon
the structure of the organoantimony reagent Ar3SbX2,
the X substituant and the aryl group both influencing
the yield of the reaction. In our preliminary studies, we
had already noted that Ph3SbCl2 was completely
inactive in the palladium catalyzed C-phenylation reac-
tion, in contrast to Ph3Sb(OAc)2 and Ph3Sb(O2CEt)2 [6].
Under the conditions of the present study, all tripheny-
lantimony halides were again inactive in the C-phenyla-
Table 3
PdCl2 catalyzed reaction of Ar3Sb(OAc)2 with methyl acrylate 7
influence of the nature of the aryl group Ar
a
:
b
Entry
Ar
Product
Yields (%)
c
1
2
3
4
5
6
Ph
8a
8b
8c
8d
8e
8f
186
4-MeC6H4
3-MeC6H4
2-MeC6H4
2,4,6-Me3C6H2
4-MeOC6H4
163
135
79
tion reaction (Table 2, entries 6Á8) and the by-product
/
Á/
105
9a was not found in any of these reactions. On the other
hand, all triphenylantimony dicarboxylates were active
a
The reactions were performed in AcOH at 50 8C for 12 h, under
air with ratio between [Sb], 7 and PdCl2 of 1:3:0.04.
phenylating agents (Table 2, entries 1Á5). The best yield
/
b
of 8a (130%) was obtained with the least bulky formate
group (Table 2, entry 1). The strength of the acyl group
Yields of isolated products.
Yield determined by GLC.
c

D.V. Moiseev et al. / Journal of Organometallic Chemistry 667 (2003) 176Á
/184
179
ence and the amount of the alkene played a more
important role. For example, with a ratio of 1:3 between
1a and 7, a 100% yield of 8a was obtained after 6 h in
acetonitrile and was not improved by longer reaction
time. But with a 1:10 ratio, the yield of 8a reached 184%
after 12 h.
2.3. Reaction of Ar3SbX2 with other ethylene derivatives
Fig. 2. Effect of the reaction atmosphere on the PdCl2 catalyzed
reaction of Ph3Sb(O2CEt)2 with methyl acrylate. The reactions were
performed in AcOH at 50 8C with the ratio 1a:7:PdCl2 (1:3:0.04).
After the initial optimization studies with methyl
acrylate used as the model unsaturated substrate, the
Pd-catalyzed reactions with Ar3SbX2 reagents were
extended to the arylation of other unsaturated com-
pounds. Two monosubstituted ethylene derivatives con-
taining either an electron-withdrawing cyano group
(acrylonitrile), or an electron-donating phenyl group
(styrene) and also a disubstituted ethylene derivative, a-
methylstyrene, were selected as representative sub-
strates. Styrene 10 containing a donor phenyl group
on the double bond was the most active among the
monosubstituted ethylene derivatives (Table 4). Stilbene
10a was isolated in a 167% yield with an E:Z ratio of
80:20. Unlike 10, acrylonitrile 11 showed a lower
reactivity, as the yield of cinnamonitrile 11a was only
100%. In contrast with the stereoselectivity observed in
the arylation of methyl acrylate affording only the trans
isomer, the stereoselectivity in the case of acrylonitrile
noticeably with longer reaction times (Fig. 2). Under
these conditions, only one phenyl group is transferred
completely from the initial organometallic compound.
However, under an atmosphere of oxygen, the yield of
8a rose to nearly 200% after 12 h. This means that the
transfer of the second phenyl group from the organo-
metallic compound 1a occurs. Thus, the C-arylation
reactions with triarylantimony dicarboxylates should be
preferentially carried out either under air or under
oxygen, as they favour a considerable increase of the
efficiency of organoantimony phenylating reagents
when acetic acid is used as the solvent. By contrast,
when the C-phenylation of 7 by the PdCl2 catalyzed
reaction with 1a was performed in acetonitrile, the
nature of the atmosphere had a less remarkable influ-
Table 4
Influence of the alkene structure on the PdCl2 catalyzed reaction of Ar3Sb(OAc)2
a

180
D.V. Moiseev et al. / Journal of Organometallic Chemistry 667 (2003) 176Á184
/
considered that, in the first stage, transmetallation takes
place to yield a phenylpalladium intermediate (Eq. (1)).
This intermediate participates directly in the arylation
reaction with formation of a palladium hydride (Eq.
(2)). The palladium hydride complex is known to
decompose by reductive elimination to an acid and the
active species L2Pd(0) (Eq. (3)). Molecules of solvent,
olefins or organoantimony(III) derivatives can play the
role of ligands. Thus, the activation of the catalyst
Scheme 4.
was quite similar (E:Zꢀ83:17) to that observed with
/
styrene. In the case of a-methylstyrene 12, two isomeric
products 12a and 12b were isolated in 83 and 12% yields,
respectively (Table 4, entry 3). This fact can be explained
by the occurrence of competitive b-elimination reactions
(Scheme 4). The normal Heck product is formed via
route A and the alternative route B gives the phenyla-
involves the reactions (1)Á(3).
/
Ph3SbX2 ꢁ(L)2PdX20[Ph(L)2PdX]ꢁPh2SbX3
(1)
tion product 12b with the shifted Cꢀ
/
C double bond.
When the p-tolylantimony derivative 2a was used
instead of the phenyl derivative 1a, the analogous
products 12c and 12d were obtained in lower yields
but with the same selectivity (Table 4, entry 4).
ð2Þ
[H(L)2PdX]0(L)2PdꢁHX
Ph3SbX2 ꢁ(L)2Pd 0[Ph(L)2PdX]ꢁPh2SbX
(3)
(4)
2.4. Possible reaction pathways
The active palladium catalytic species L2Pd(0) then
undergoes an oxidative addition step by reaction with
the initial organoantimony(V) compound to give again
the phenylpalladium intermediate (Eq. (4)). The nature
of the X group in Ar3SbX2 is important for this
Several key facts can be singled out for their
mechanistic implications: (i) only triarylantimony dicar-
boxylates participate in the arylation reaction while
dihalides are ineffective; (ii) phosphine ligands inhibit
palladium catalysis; (iii) the steric hindrance of the
aromatic rings of the organoantimony compounds leads
to a decrease in the reaction yields; (iv) the presence of
oxygen is mandatory for the transfer of a second phenyl
group from the organoantimony reagent.
The general mechanism of the Heck-type palladium
catalyzed C-arylation reaction of alkenes is now well
established [12,13]. The catalytic cycle includes four
main steps: activation of the catalyst, oxidative addition,
migratory insertion and palladium hydride elimination
[13]. In the case of the palladium catalyzed C-arylation
with Ar3SbX2, the mechanistic pathways depend on the
reaction atmosphere.
reaction. Palladium insertion along a PhÁSb bond of
/
triarylantimony dicarboxylates occurs with the partici-
pation of a carboxylic group. This favors the prelimin-
ary coordination of L2Pd(0) on the organometallic
compound and the redistribution of electrons in a five-
or a six-member cycle (Scheme 5). As a result, the
phenylpalladium intermediate is formed and the initial
antimony(V) is reduced to antimony(III), which can
serve as a ligand of the Pd atom [16,17]. Kawamura et
al. suggested a similar mechanism of AcO group
participation in the stoichiometric reaction of Pd(OAc)2
with Ph3M (MꢀP, As, Sb, Se or Te) and octene-1 [18].
/
They showed also that PdCl2 is active in these reactions
only in the presence of NaOAc additive. This mechan-
ism is not realizable for triarylantimony dihalides for
which the formation of the same cyclic transition state is
not possible. In the mild reaction conditions used in this
study, all Ph3SbHal2 showed a very low or no activity.
The presence of strongly binding ligands such as Ph3P
in the coordination sphere of the palladium metal center
induces a substantial steric hindrance both in the
2.4.1. Under inert atmosphere
Recently, Amatore and Jutand have demonstrated
that L2Pd(0) complexes are the active species in the
classical Heck reaction [14,15]. In our arylating system,
the formation of the L2Pd(0) complexes proceeds most
probably through the following steps described in Eqs.
(1)Á(4). With Pd(II) salts used as the catalyst, it can be
/
Scheme 5.

D.V. Moiseev et al. / Journal of Organometallic Chemistry 667 (2003) 176Á
/184
181
Oxygen inserts into the HÁ
/
Pd bond to give the
palladium hydroperoxide complex 14. The for-
Sb(III)Á
/
mation of such palladium hydroperoxide complexes was
suggested by Yoshimoto et al. [19] and by Bregeault et
al. [20]. Moreover, the complex [CF3COOPdOOBu-t]4
was isolated and characterized by Mimoun et al. [21]. As
hydroperoxides are able to oxidize organoantimony(III)
derivatives [10,22], the hydroperoxide 14 can undergo an
internal redox process leading to the m-oxo SbÁ
/
OÁPd
/
intermediate 15 which subsequently rearranges intramo-
lecularly to give the phenylpalladium acetate intermedi-
ate and a pentavalent phenylantimony compound 16.
The effect of oxygen appears more clearly when the
reaction is performed in AcOH. AcOH being a less
donating solvent than acetonitrile, the antimony(III)
derivative Ph2SbO2CR can remain longer in the co-
ordination sphere of the palladium atom. On the other
hand, Ph3Sb is a more strongly donating ligand of
palladium than Ph2SbOAc, so that it impedes the
coordination of oxygen with palladium and therefore
behaves as an inhibitor of the reaction. Matoba et al.
have shown that Ph2SbCl phenylates unsaturated com-
pounds in the presence of catalytic amounts of Pd(II)
salts in acetonitrile under air or an atmosphere of
oxygen [7]. But this reaction does not occur under an
inert atmosphere. They suggested a free radical mechan-
ism to explain this interaction. However, another
possible explanation for the oxygen effect can be
suggested. Oxygen could oxidize Pd(0) to Pd(II) in the
presence of an acid (Eq. (5)) [23]. Then the Pd(II) species
will accept a phenyl group from Sb(III) reagent by
transmetallation (Eq. (6)).
Scheme 6.
transmetallation reaction (Eq. (1)) and in the oxidative
addition process (Scheme 5). Also bulky aromatic
groups, especially ortho-substituted ones, cause a sig-
nificant steric hindrance for all reactions occuring either
in the palladium or in the antimony coordination
spheres (Eqs. (1), (2) and (4)). The mesityl derivative
5a is not reactive at all. In the case of the three isomeric
tritolylantimony derivatives 2a, 3a and 4a, the position
of the methyl group influences significantly the reaction.
Between the freely rotating p-tolyl derivative 2a and the
hindered ortho-substituted tolyl and mesityl derivatives
2a and 5a, the dihedral angles formed between the
equatorial plane (containing the antimony center and
the three ipso carbon atoms) and the plane of each
aromatic rings are expected to become more important,
making the approach of the palladium catalyst towards
the ipso carbon atoms more difficult.
It should be noted that, according to this mechanism
(Eqs. (1)Á(4)), as soon as the initial organoantimony(V)
/
Pd0 ꢁO2 ꢁ4Hꢁ0 Pd2ꢁ ꢁ2H2O
(5)
(6)
compound is totally consumed the catalytic cycle should
stop. Therefore the yield of 8a cannot be higher than
100%, and this is indeed the case when the reaction is
performed under an atmosphere of argon (Fig. 2). Thus,
the complete catalytic process of the Pd-catalyzed C-
phenylation of alkenes under argon can be represented
by the cycle shown in Scheme 6, where Pd(0) is the active
catalytic form.
Ph2SbXꢁPdX20 PhSbX2 ꢁPhPdX
This conclusion is confirmed by the greater efficiency
of oxygen in AcOH solution (Fig. 2). However, the
inhibition effect of Ph3Sb is surprising since it reacts
rather quickly with PdX2 [24], and as we [25] and others
[18] have observed that Ph3Sb can be used as phenylat-
ing agent in the presence of stoichiometric amounts of
PdCl2. Moreover, Cho et al. have observed that Ph3Sb
reacts with methyl acrylate in acetic acid in the presence
of a catalytic amount of palladium acetate and of silver
acetate acting as a reoxydant [8]. The inhibition of the
reaction described in our present work can be explained
by the insufficient oxidizing power of oxygen towards
2.4.2. Under air or an atmosphere of oxygen
In the presence of oxygen, the reaction pathway
changes (Scheme 7). Oxygen reacts with the PdÁ
complex 13, [HPdOAcÁPh2SbOAc], which is formed as
described in Scheme 6.
/Sb
/
Scheme 7.

182
D.V. Moiseev et al. / Journal of Organometallic Chemistry 667 (2003) 176Á184
/
Pd(0), when this one is relatively strongly coordinated
with Ph3Sb.
4.2. Synthesis of Ph3Sb(OAc)2 (1a) using AcOH and t-
BuOOH
Further studies are now underway to better under-
stand the various intertwined mechanistic facets of the
catalytic reaction reported in this work.
t-BuOOH (0.58 ml 97%, 5.7 mmol) was added
dropwise to a stirred cold (5Á10 8C) solution of Ph3Sb
/
(2 g, 5.7 mmol) and AcOH (0.98 ml, 17.1 mmol) in Et2O
(10 ml). The reaction mixture was kept in the dark for 24
h at room temperature. The solvent was distilled off
under reduced pressure and the solid residue was
purified by recrystallization (chloroform/hexane) to
afford 1a (2.4 g, 90%) as a white solid, m.p. 213 8C
(lit. [33] 215 8C).
Other organoantimony compounds were prepared by
the same procedure.
Triphenylantimony dipropionate (1b): m.p. 140 8C
3. Conclusion
The Heck-type Pd-catalyzed C-arylation reaction of
unsaturated compounds by triarylantimony(V) dicar-
boxylates can be easily performed at 50 8C in CH3CN
and AcOH as the best solvents, with PdCl2 (4 mol%) as
the most effective catalyst. One or two aryl groups of the
organometallic compound can participate in the C-
arylation reaction depending on the reaction conditions.
The transfer of one aryl group occurs under inert
atmosphere. Two aryl groups participate only when
the reaction is performed in air or in an atmosphere of
oxygen. In the case of ArI (as C-arylating reagents) the
(lit. [34] 139Á
Triphenylantimony diformate (1c): m.p. 160 8C (lit.
[33] 159Á160 8C).
/
140 8C).
/
Triphenylantimony bis(trifluoroacetate) (1d): m.p.
109 8C (lit. [35] 109 8C).
Triphenylantimony dibenzoate (1e): m.p. 181 8C (lit.
[33] 177 8C).
Triphenylantimony difluoride (1f): m.p. 113 8C (lit.
[36] 115 8C).
Triphenylantimony dichloride (1g): m.p. 142 8C (lit.
analogous C-arylation reaction occurs at 100Á120 8C
/
with the yield of 8a 97% based on ArI [26]. The C-
arylation reaction with Ar3Sb(O2CR)2 reagents is in-
hibited by the presence of strong palladium ligands such
as Ph3P, and also by the steric hindrance in the aromatic
groups. Moreover, we have found that all triarylanti-
mony dihalides are inactive in the reaction.
[34] 139Á142 8C).
/
Triphenylantimony dibromide (1h): m.p. 218 8C (lit.
[36] 214 8C).
Tris(p-tolyl)antimony diacetate (2a): m.p. 168 8C (lit.
[4] 157Á
Tris(m-tolyl)antimony diacetate (3a): m.p. 140 8C;
1H-NMR: d 7.82Á
7.75 (m, 6H), 7.43Á7.23 (m, 6H),
2.41 (s, 9H) and 1.84 (s, 6H). Anal. Found: C, 58.5; H,
5.4. C25H27O4Sb calc.: C, 58.5; H, 5.3%.
Tris(o-tolyl)antimony diacetate (4a): m.p. 178 8C; 1H-
/
159 8C).
/
/
4. Experimental
4.1. General methods
NMR: d 8.21 (d, 3H), 7.49Á7.28 (m, 9H), 2.52 (s, 9H),
/
1.73 (s, 6H). Anal. Found: C, 58.2; H, 5.1. C25H27O4Sb
calc.: C, 58.5; H, 5.3%.
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
Trimesitylantimony diacetate (5a): m.p. 98Á101 8C;
/
1H-NMR: d 6.96 (s, 6H), 2.52 (s, 18H), 2.31 (s, 9H), 1.88
(s, 6H). Anal. Found: C, 62.5: H, 6.8. C31H39O4Sb calc.:
C, 62.3: H, 6.6%.
1
Chromaton N-AW at 220 8C. H NMR spectra were
measured on a Bruker Avance DPX-200 spectrometer
for solutions in CDCl3 with Me4Si as the internal
standard. Column chromatographies were performed
with silica gel 60 Merck.
Tris(p-anisyl)antimony diacetate (6a): m.p. 153 8C;
1H-NMR: d 7.92 (d, Jꢀ
6H), 3.83 (s, 9H), 1.81 (s, 6H). Anal. Found: C, 53.1; H,
/
9 Hz, 6H), 7.0 (d, Jꢀ9 Hz,
/
The triarylantimony compounds 1Á5 were prepared
/
5.1. C25H27O7Sb calc.: C, 53.5; H, 4.9%.
as described previously [27]. t-BuOOH was prepared by
the method of Milas and Surgenor [28]. Commercial
methyl acrylate was washed with an alkali solution until
the yellow color disappeared, then dried with Na2SO4
and distilled. Commercial styrene, a-methyl styrene and
acrylonitrile were dried with Na2SO4 and distilled. All
solvents were distilled prior to use. Li2PdCl4 [29],
Pd(OAc)2 [30], Pd2(dba)3 [31], Pd(Ph3P)2Cl2 [32] were
prepared by the reported methods, and PdCl2 or
Pd(dppf)Cl2 were commercially available.
4.3. Synthesis of Ph3Sb(OAc)2 (1a) using AcOH and
H2O2
H2O2 (1.05 ml 29.6%, 10.5 mmol) was added dropwise
over 10 min to a stirred cold (5Á10 8C) solution of
/
Ph3Sb (3.53 g, 10 mmol) and AcOH (30 mmol) in Et2O
(3 ml) and i-PrOH (20 ml). The reaction mixture was
kept in the dark for 3 h at room temperature (r.t.). The
solid was filtered and washed with i-PrOH and recrys-

D.V. Moiseev et al. / Journal of Organometallic Chemistry 667 (2003) 176Á
/184
183
talled (chloroformÁ
/
hexane) to afford 1a as white
(Z)-11a: d 7.50Á
/
7.38 (m, 5H), 7.13 (d, Jꢀ/12.3 Hz, 1H),
crystals (3.77 g, 85%).
5.44 (d, Jꢀ12.3 Hz, 1H)
/
(E:Z)-a-Methylstilbene (12a) and 2,3-diphenyl-1-pro-
pene (12b) were identified by the H-NMR spectrum of
1
4.4. Synthesis of Ph3Sb(OAc)2 (1a) using (CH3CO)2O
and t-BuOOH
their mixture. (E)-12a: d 7.69Á
1H), 2.34 (s, 3H). (Z)-12a: d 7.69Á
(s, 1H), 2.25 (s, 3H). 12b: d 7.69Á7.21 (m, 10H), 5.55 (s,
1H), 5.07 (s, 1H), 3.88 (s. 2H).
/7.21 (m, 10H), 6.90 (s,
/7.21 (m, 10H), 6.52
/
t-BuOOH (0.58 ml 97%, 5.7 mmol) was added
dropwise to a stirred cold (5Á10 8C) solution of Ph3Sb
/
(E:Z)-1-para-Tolyl-2-phenyl-1-propene (12c) and 3-
para-tolyl-2-phenyl-1-propene (12d) were identified by
the 1H-NMR spectrum of their mixture. (E)-12c: d
(2 g, 5.7 mmol) and (CH3CO)2O (2.15 ml, 22.8 mmol) in
Et2O (10 ml). The reaction mixture was kept in the dark
for 90 h at r.t. The solvent was distilled off under
reduced pressure and the solid residue was purified by
7.60Á
Jꢀ1.3 Hz, 3H). (Z)-12c: d 7.60Á
1H), 2.43 (s, 3H), 2.37 (s, 3H). 12d: d 7.60Á
/
7.11 (m, 9H), 6.86 (s, 1H), 2.41 (s, 3H), 2.33 (d,
7.11 (m, 9H), 6.48 (s,
7.11 (m, 9H),
/
/
recrystallization (chloroformÁ
/
hexane) to afford 1a (1.87
/
g, 70%).
5.52 (s, 1H), 5.05 (m, 1H), 3.84 (s, 2H), 2.34 (s, 3H).
4.5. Typical procedure for the C-phenylation reaction
4.6. C-phenylation reaction under argon or oxygen
A mixture of Ph3Sb(OAc)2 (0.236 g, 0.5 mmol), PdCl2
(3.6 mg, 0.02 mmol), methyl acrylate (0.135 ml, 1.5
mmol) in acetic acid (4 ml) was placed in a 50 ml tube.
The tube was sealed and the reaction mixture was kept
at 50 8C for 12 h. The solvent was then evaporated
under reduced pressure. The solid residue was purified
from inorganic products by elution through a short
A mixture of Ph3Sb(OAc)2 (0.236 g, 0.5 mmol), PdCl2
(3.6 mg, 0.02 mmol), methyl acrylate (0.135 ml, 1.5
mmol) in acetic acid (4 ml) was placed in a 50 ml tube.
The reaction mixture was degassed by repeated freezeÁ
/
pumpÁthaw cycles and the tube was filled with argon
/
(or oxygen). The following procedure was the same as
described above.
column on silica gel using a mixture of hexaneÁdiethyl
/
ether (v/v 4:1) as the eluant. The filtrate was analyzed by
GLC. Methyl cinnamate (0.151 g) was isolated after
distillation of the solvents under reduced pressure.
In the reactions with the antimony compounds 2a, 3a,
4a and 6a, the arylated products were isolated by
column chromatography on silica gel eluting with
Acknowledgements
The spectral studies were carried out in the Analytical
Center of the G.A. Razuvaev Institute of Organome-
tallic Chemistry (Russian Academy of Sciences) with the
financial support of the Russian Foundation for Basic
Research (project no. 00-03-40116). We thank Dr. Jean-
Pierre Finet (Universite de Provence, Marseille, France)
for fruitful discussions.
hexaneÁ
the solvents afforded the arylated products.
8c 1H-NMR: d 7.67 (d, Jꢀ
16 Hz, 1H), 7.37Á
4H), 6.43 (d, Jꢀ16 Hz, 1H), 3.80 (s, 3H), 2.36 (s, 3H).
/
diethyl ether (v/v 4:1) mixture. Distillation of
/
/
7.13 (m,
/
Anal. Found: C, 74.6; H, 7.1. C11H12O2 calc.: C, 75.0;
H, 6.9%.
8d 1H-NMR: d 8.00 (d, Jꢀ
4H), 6.36 (d, Jꢀ
Anal. Found: C, 75.1; H, 7.1. C11H12O2 calc.: C, 75.0;
/
16 Hz, 1H), 7.58Á
/
7.16 (m,
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