Catalytic C-phenylation of methyl acrylate with triphenylantimony(v) dicarboxylates

Article abstract of DOI:10.1023/A:1014079428290

Triphenylantimony dicarboxylates Ph₃Sb(OAc)₂ and Ph₃Sb(O₂CEt)₂ are efficient C-phenylating agents for methyl acrylate. In the presence of the Pd(OAc)₂, Li₂PdCl₄ or Pd<

Full text of DOI:10.1023/A:1014079428290

«
A. V. Gushchin, D. V. Moiseev, and V. A. Dodonov
Russian Chemical Bulletin, International Edition, Vol. 50, No. 7, pp. 1291—1294, July, 2001
1291
Organometallic Chemistry
Catalytic C-phenylation of methyl acrylate
with triphenylantimony(V) dicarboxylates
N. I. Lobachevsky State University of Nizhnii Novgorod,
3 prosp. Gagarina, 603600 Nizhnii Novgorod, Russian Federation.
Fax: +7 (831 2) 65 8592. E-mail: guav3@uic.nnov.ru
2
Triphenylantimony dicarboxylates Ph Sb(OAc) and Ph Sb(O CEt) are efficient
3
2
3
2
2
C-phenylating agents for methyl acrylate. In the presence of the Pd(OAc) , Li PdCl or
2
2
4
Pd (dba) (CHCl ) catalysts in MeCN at 50 °C, methyl cinnamate forms in 70—150% yield
2
3
3
V
with respect to Sb . Copper(II) salts do not increase the reaction yield.
Key words: phenylation, methyl acrylate, methyl cinnamate, triphenylantimony diacetate,
triphenylantimony dipropionate, palladium compounds.
It is known that triphenylantimony is used in the
Heck reaction for the C-phenylation of unsaturated
compounds in the presence of equimolar amounts of
palladium(II) acetate.1—4 Triphenylantimony as phe-
nylating agent have advantages over aryl halides (e.g.,
PhI or PhBr), which, in most cases, require heating to
organometallic compound (OMC). In addition, propi-
onic acid (110%), SbIII propionates and biphenyl (2%)
(Table 1, entry 1) were found in the reaction products.
The reaction occurred according to the equation
II
Pd
Ph Sb(O CEt) + CH =CHCO Me
3
2
2
2
2
8
0—140 °C. A disadvantage of the triphenylantimony
II
PhCH=CHCO Me + Ph SbO CEt + EtCO H. (1)
2 2 2 2
application is a high consumption of the Pd salt,
which is reduced in the process to inactive Pd0.
This work is aimed at studying the antimony deriva-
The methyl acrylate phenylation and catalysis with
the palladium salt can be presented by the equations
tives Ph SbX (X = OAc, O CEt, Cl) as C-phenylating
agents for methyl acrylate. The chosen Sb compounds,
3
2
2
V
Ph Sb(O CEt) + Pd(OAc)2 + m L
III
0
3
2
2
unlike Sb compounds, are capable of Pd re-oxidation
II
to Pd , and this allowed palladium compounds to be
Ph2Sb(O2CEt)2(OAc) + PhPd(OAc)Lm,
(2)
(3)
used in catalytic quantities. Methyl acrylate transforms
into only one C-phenylation product, methyl cinnamate.
CH =CHCO Me + PhPd(OAc)L + (n – m) L
2
2
m
0
PhCH=CHCO Me + Pd L + AcOH,
2
n
Results and Discussion
Ph Sb(O CEt) + Pd0Ln
3
2
2
The reaction of Ph Sb(O CEt) with methyl acrylate
3
2
2
in the presence of Pd(OAc)2 in a molar ratio of
: 10 : 0.04 in MeCN at 50 °C for 1 h in air afforded
methyl cinnamate in 104% yield based on the initial
Ph SbO CEt + PhPd(O CEt)L + (n – m) L, (4)
2 2 2 m
1
where L = >C=C<, OMC of antimony.
Published in Russian in Izvestiya Akademii Nauk. Seriya Khimicheskaya, No. 7, pp. 1230—1233, July, 2001.
066-5285/01/5007-1291 $25.00 ©ꢀ2001 Plenum Publishing Corporation
1

1
292
Russ.Chem.Bull., Int.Ed., Vol. 50, No. 7, July, 2001
Gushchin et al.
Table 1. Yields of the products of C-phenylation of methyl
hand, to a more favorable structure of the transition
state of the redox stage. From this point of view, the
transfer of the phenyl and carboxylate groups from the
SbV atom to Pd through the six-membered cyclic tran-
sition state is easier than the transfer of the phenyl and
chloride groups through the four-membered transition
state (Eqs. (6) and (7)).
acrylate with the Ph SbX —PdY (1 : 0.04) system in acetoni-
3
2
2
trile at 50 °Ñ for 1 h in air
0
Entry
Ph SbX
PdY2
Yield (% per OMC)
3
2
Methyl Biphe-
cinnamate nyl
1
2
3
4
5
6
Ph Sb(O CEt)
Pd(OAc)2
Pd(OAc)2
Li PdCl4
2
104
71
64
1
85
62
2
25
15
20
2
3
2
2
Ph Sb(OAc)2
3
Ph Sb(OAc)2
3
Ph SbCl
Li PdCl4
Sb
O
Pd
O
Pd
O
3
2
2
Sb
+
(6)
Ph Sb(O CEt)
Pd (dba) (CHCl )*
3
2
2
2
2
0
3
3
O
Ph Sb(O CEt)
Pd
9
3
2
C
R
C
R
*
Dibenzylideneacetone is designated as dba.
Transmetallation occurs at the first stage to form the
phenylpalladium derivative (Eq. (2)), which arylates
methyl acrylate to methyl cinnamate. In this reaction,
the carboxylic acid and Pd0 complex are also formed
Sb
Pd
Sb
+
Pd
(7)
(
Eq. (3)). The latter enters into the redox reaction with
Cl
Cl
III
the initial Ph Sb(O CEt) , which is reduced to the Sb
compound according to Eq. (4). The Pd complex that
formed further phenylates methyl acrylate.
The general scheme of this process demonstrates a
catalytic role of palladium, which performs the catalytic
transition Pd0
3
2
2
II
It has previously4 been shown that when triphenyl-
antimony is used as a phenylating agent for methyl
acrylate the oxidation state of palladium plays a deter-
0
mining role and the Pd complexes are inactive. Unlike
PdII (Eq. (5)). The reaction ceases
this, when antimony(V) dicarboxylates are used, the
oxidation degree of palladium is not substantial, and the
yields of methyl cinnamate remain high in the presence
of both Pd0 and PdII (see Table 1, entry 5). The Pd0
complex obtained in situ by the reduction of Pd(OAc)
with triethylamine was also used (entry 6). Various Pd
salts, such as Pd(OAc) and Li PdCl , possess the same
when the organoantimony oxidant is completely con-
sumed.
SbV
SbIII
2
II
5
2
2
4
activity when Ph Sb(OAc) is used as phenylating agent
3
2
(
see Table 1, entries 2 and 3).
It should be emphasized that biphenyl is a by-
Pd0
PhPdX
(5)
product of the C-phenylation of methyl acrylate. The
yield reached 60—80% when the Ph Sb—Pd(OAc)2
3
(
1 : 1) system was used.4 The application of triphenyl-
antimony dicarboxylates decreased the yield of biphenyl
to 2—25% (see Table 1). Biphenyl is formed in the
reaction of the σ-phenyl palladium derivative with OMC
Ph
H
C
C
C C
6
,7
or without the latter according to Eqs. (8) and (9).
These stages occur much more slowly than the alterna-
Thus, triphenylantimony(V) dicarboxylates are unique
because they are simultaneously the sources of phenyl
groups for phenylation and oxidizing agents for Pd0.
When Pd(OAc)2 was used as catalyst, the yield of
methyl cinnamate decreased in the following order of
OMC: Ph Sb(O CEt) ≥ Ph Sb(OAc) >> Ph SbCl . An
insignificant difference between Sb propionate and
acetate can be explained by a lower solubility of the
latter in acetonitrile.
tive reaction with an unsaturated compound.8
PhPd(OAc)Lm + Ph Sb(OAc)2 + (n – m) L
3
0
Ph2 + Pd Ln + Ph2Sb(OAc)3
(8)
(9)
3
2
2
3
2
V
3
2
2
PhPd(OAc)Lm + (n – m) L
Ph2 + Pd0Ln + Pd(OAc)2Lm
Unlike SbV carboxylates, SbV chloride is inefficient
in C-phenylation. The yield of methyl cinnamate was
4
We have shown that the air oxygen has a substantial
1
% (see Table 1, entry 4). This is due, as we believe, to
effect on the C-phenylation of methyl acrylate with
a higher oxidation potential of triphenylantimony(V)
dicarboxylates with respect to Pd , and on the other
triphenylantimony in the presence of Pd(OAc) . In all
2
cases of using Ph Sb(OAc) and Ph Sb(O ÑEt) as
3 2 3 2 2
0

SbV Carboxylates in C-phenylation reaction
Russ.Chem.Bull., Int.Ed., Vol. 50, No. 7, July, 2001
1293
Table 2. Influence of oxygen on the yield of phenylation
Table 3. Influence of copper salt additives on the yield
of C-phenylation products of methyl acrylate with the
products of methyl acrylate with the Ph Sb(O CEt) —Pd(OAc)
2
3
2
2
II
II
(
1 : 0.04) phenylating system in acetonitrile at 50 °C
Ph Sb(O ÑR) —Pd —Ñu (1 : 0.04 : õ) system at 50 °Ñ for
3
2
2
1
h in air
Atmosphere
Time
Yield (% per OMC)
R
PdII
ÑuII
x
Solvent
Yield*
/
h
Methyl
Biphenyl
cinnamate
Methyl Biphe-
cinnamate nyl
In the absence of air
1
80
92
92
25
6
3
2
3
1
25
5
3
9
3
9
1
3
9
1
3
9
1
3
9
Me Li PdCl
—
CuCl2
CuCl2
Li CuCl
Li CuCl
—
MeCN
64
1
0
14
19
2
6
5
1
0
2
2
4
Li PdCl
0.4 MeCN
MeCN
2
4
4
4
4
Air
104
121
135
71
114
130
115
129
153
Li PdCl
2
2
Li PdCl
0.4 MeCN
0.4 AcOH
1
2
2
4
4
Li PdCl
64
105
64
64
2
2
Air*
Et Pd(OAc)2 Cu(OAc)2 0.4 MeCN
Pd(OAc)2 Cu(OAc)2 0.4 AcOH
Pd(OAc)2 Cu(OAc)2 0.4 MeOH
Dioxygen
*
In % per OMC.
7
3
Moreover, a mild oxidation of SbIII to Sb with copper(II)
V
*
Reactions with Ph Sb(OAc) .
3 2
halides could be expected, as it is known for Ph Sb 12:
3
Ph SbOAc + 2 CuCl2
phenylating agents, dioxygen increases the yield of tar-
get methyl cinnamate, which reaches 153% with an
increase in the time of heating (Table 2). Dioxygen can
2
Ph Sb(OAc)Cl2 + 2 CuCl.
(13)
2
0
III
affect both Pd and Sb (Eqs. (10) and (11)). The free
radical scheme without changing the valences of anti-
CuCl2 additives in different amounts and Li CuCl4
did not increase (Table 3) and even decreased sharply
2
9
mony and palladium (Eq. (12)), proposed for the reac-
the yield of methyl acrylate upon C-phenylation with
tion of diphenylchlorostibine, cannot either be excluded.
the Ph Sb(OAc) —Li PdCl (1 : 0.04) system. We as-
3
2
2
4
OMC
sumed that the inhibition effect of copper halides is
explained by the reversible transformation of reactive
SbV carboxylates into nonreactive SbV halides (see
above). In this case, the addition of ÀñÎÍ should
impede this reaction. Indeed, when ÀñÎÍ was used as
solvent instead of acetonitrile, the inhibition effect was
eliminated and the yield of methyl cinnamate remained
as high as it was in the absence of copper salts.
Pd0Ln + O2
Pd L
II
[PhPdX] (10)
n–2
Pd
[
[
SbIII•Pd] + O2
SbV
[PhPdX]
(11)
(12)
HPdX•Ph SbX] + O
2
[PhPdX]
2
It is of interest that in these experiments the biphe-
nyl yield decreased with time in all cases (see Table 2).
A solvent plays a noticeable role in the C-phenylation
In this connection, we decided to replace the copper
and palladium chloro-containing compounds by acetate
of methyl acrylate. When the Ph Sb(O CÅt) —Pd(OAc)
compounds. Ph Sb(O CEt) was used as phenylating
3 2 2
3
2
2
2
0
1
(
1 : 0.04) phenylating system in acetonitrile (ε = 37.5)
is used at 50 °Ñ, the yield of methyl cinnamate was
04% for 1 h for reaction in air. The replacement of
agent. It turned out that, in this case, the copper salt
does not prevent the formation of methyl cinnamate,
whose yield in acetonitrile was 105%. The efficient
phenylation was also observed in solutions of ÀñÎÍ and
ÌåÎÍ (see Table 3).
Thus, copper salts cannot act as oxidants in methyl
acrylate C-phenylation with triphenylantimony dicarb-
oxylates. Depending on the structure and reaction con-
ditions, they either suppress the process or have no
effect on it.
1
acetonitrile by acetic acid (ε = 6.15) decreased the
product yield to 67%, and that for methanol (ε = 32.63)
decreased to 44%. Such a low yield in methanol having
a high dielectric constant can be explained by the
capability of methanol of reducing PdII to Pd . Note
that the yield of biphenyl was at most 1—2% in all cases.
0 11
In the reaction of Ph Sb(O CEt) with methyl acry-
3
2
2
late in the presence of minor amounts of palladium
compounds, only one of three phenyl groups at the Sb
atom participated in phenylation. Dioxygen facilitated
the involvement of the second Ph group but only when
the time of heating increased. Therefore, it was reason-
able to study the influence of copper salt additives,
It should specially be mentioned that the main pro-
cess, C-phenylation was slightly impeded by the side
reaction of biphenyl formation in the presented reac-
tions of triphenylantimony diacetate and especially
dipropionate with methyl acrylate in the presence of
catalytic quantities of palladium. The yield of biphenyl
was, as a rule, 1—5% (see Tables 1—3). Therefore, the
selectivity of the phenylating system is much higher
0
II
which are capable of oxidizing Pd to Pd and acting as
0
mediators of the oxygen effect on Pd (Wacker process).

1
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Russ.Chem.Bull., Int.Ed., Vol. 50, No. 7, July, 2001
Gushchin et al.
than that of the earlier studied Ph Sb—Pd(OAc) sys-
This work was financially supported by the Program
"Universities of Russia" (Project No. 992839) and the
Federal Target Program "Integration" (State Contract
À 0047).
3
2
tem where the biphenyl yield was2 10—70%.
,4
Thus, we proposed a new catalytic system for the
mild and selective C-phenylation of methyl acrylate to
methyl cinnamate. The system is based on triphenyl-
antimony dicarboxylates and palladium compounds. The
organic compound of antimony(V) is both the source of
phenyl groups and oxidizing agent for conversion of
References
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II
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1
2
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Compounds Ph Sb(OAc) , Ph Sb(O CEt) , and Ph SbCl
3
2
3
2
2
3
3
2
1
were synthesized by the reaction of Ph Sb
with hydrogen
3
peroxide and the corresponding acids in a ratio of 1 : 1 : 2 in an
i
ether—Pr OH (1 : 4 v/v) mixture in 85, 78, and 94% yields,
1
4
respectively.
Li PdCl4 was prepared in ∼100% yield from
2
1
5
PdCl2 and LiCl in an aqueous medium. Pd(OAc)2 was syn-
thesized by the oxidation of palladium black with nitric acid in
AcOH for 30 h in 80% yield after recrystallization from AcOH.16
Pd (dba) (CHCl ) was prepared by the reduction of PdCl with
methanol in the presence of dibenzylideneacetone in 66%
yield. Methyl acrylate was washed with an alkali solution until
the yellow color disappeared, dried with Na SO , and distilled.
2
3
3
2
1
0
2
4
Reaction of Ph Sb(OAc) with methyl acrylate and Pd(OAc)
2
3
2
in the absence of air. Ph Sb(OAc)2 (0.50 mmol) and Pd(OAc)2
3
(
0.02 mmol) were placed into one finger of an H-like am-
pule. Anhydrous acetonitrile17 (4 mL) and methyl acrylate
5.00 mmol) were poured into another finger, the ampule was
(
degassed and sealed, the reactants were mixed, and the mixture
was heated for 1 h at 50 °Ñ. Then the ampule was open, and
the liquid was recondensed into a trap cooled with liquid
nitrogen. AcOH (0.45 mmol) was found in the condensate by
titration of an aliquot with an alkali, and methyl cinnamate
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Metody elementoorganicheskoi khimii. Sur´ma, vismut [Meth-
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(
0.001 mmol) was detected by GLC. The solid residue con-
tained the main amount of poorly volatile methyl cinnamate
and biphenyl. The residue was liberated from the palladium
compounds and antimony carboxylates by treatment with H S.
With this purpose, MeCN (6 mL) was added to the solid
14. A. V. Gushchin, Doct. Sci. (Chem.) Thesis, Nizhnii
Novgorod State Univ., N. Novgorod, 1998, 283 pp. (in
Russian).
2
residue in the ampule, the mixture was stirred, an H S flow was
2
passed through the solution, and the latter was centrifuged. A
transparent solution was separated, and acetonitrile (2 mL) was
poured to the remaining black precipitate containing palladium
and antimony sulfides. The mixture was centrifuged. Extracts
were combined, and the concentrations of methyl cinnamate
15. R. F. Heck, J. Am. Chem. Soc., 1968, 90, 5518.
16. T. A. Stephenson, S. M. Morehouse, A. R. Powell, J. P.
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Moscow, 1965, 608 (Russ. Transl.).
(
0.345 mmol) and biphenyl (0.125 mmol) were determined
by GLC.
The reactions in oxygen were conducted similarly in stan-
dard sealed 50-mL ampules without degassing of a solution.
Received January 4, 2001