Catalytic C-phenylation of methyl acrylate with tetraphenylantimony(v) halides and carboxylates

Article abstract of DOI:10.1023/A:1024883328867

Catalytic C-phenylation of methyl acrylate to methyl cinnamate with the Ph₄SbX complexes (X = F, Cl, Br, OH, OAc, O₂CEt) in the presence of the palladium compounds PdCl₂, Pd(OAc)₂, Pd₂(dba)₃, Pd(Ph₃P)₂Cl₂, and Pd(dppf)Cl₂ (dba is dibenzylideneacetone and dppf is bis(diphenylphosphinoferrocene)) was studied in organic solvents (MeCN, THF, DMF, MeOH, and AcOH). The highest yield of methyl cinnamate (73% based on the starting organometallic compound) was obtained for the Ph₄SbCl- PdCl₂ (1:0.04) system in acetonitrile.

Full text of DOI:10.1023/A:1024883328867

1376
Russian Chemical Bulletin, International Edition, Vol. 52, No. 6, pp. 1376—1379, June, 2003
Catalytic Cꢀphenylation of methyl acrylate
with tetraphenylantimony(V) halides and carboxylates
а
а
а
b
а
A. V. Gushchin,а E. V. Grunova, D. V. Moiseev, O. S. Morozov, A. S. Shavyrin, and V. A. Dodonov
ꢀ
аN. I. Lobachevsky State University of Nizhnii Novgorod,
23 prosp. Gagarina, 603950 Nizhnii Novgorod, Russian Federation.
Fax: +7 (831 2) 65 8592. Eꢀmail: gushchin@mail.nnov.ru
bG. A. Razuvaev Institute of Organometallic Chemistry, Russian Academy of Sciences,
49 ul. Tropinina, 603600 Nizhnii Novgorod, Russian Federation.
Fax: +7 (831 2) 66 1497. Eꢀmail: andrew@imoc.sinn.ru
Catalytic Cꢀphenylation of methyl acrylate to methyl cinnamate with the Ph4SbX comꢀ
plexes (X = F, Cl, Br, OH, OAc, O2CEt) in the presence of the palladium compounds PdCl2,
Pd(OAc)2, Pd2(dba)3, Pd(Ph3P)2Cl2, and Pd(dppf)Cl2 (dba is dibenzylideneacetone and dppf
is bis(diphenylphosphinoferrocene)) was studied in organic solvents (MeCN, THF, DMF,
MeOH, and AcOH). The highest yield of methyl cinnamate (73% based on the starting
organometallic compound) was obtained for the Ph4SbCl—PdCl2 (1 : 0.04) system in acetoꢀ
nitrile.
Key words: phenylation, methyl acrylate, tetraphenylantimony complexes, palladium comꢀ
pounds, Heck reaction.
Triphenylantimony is used in the Сꢀphenylation of
were obtained in the individual states, whereas tetraꢀ
phenylantimony acetate was prepared as the crystal solꢀ
vate Ph4SbOАс•AcOH. According to the published
data,6—8 this complex can have different structures deꢀ
pending on the method of synthesis: trigonalꢀbipyramidal
in which the AcOH molecule is bound by the hydrogen
bond to the acetate group at the pentacoordinated antiꢀ
mony atom6,7 and octahedral with hexacoordinated antiꢀ
mony, where the metal atom is bound to two symmetriꢀ
cally arranged acetate groups in the eightꢀmembered
cycle.8
unsaturated compounds (Heck reaction) in the presence
of equimolar amount of palladium diacetate.1—4 Unlike
triphenylantimony, triphenylantimony dicarboxylates
Ph3Sb(O2CR)2 provide phenylatation of methyl acrylate
in high yields in the presence of catalytic amounts of
palladium compounds. The organic SbV derivatives act as
both the sources of the Ph groups and the oxidants of Pd0
to PdII. Triphenylantimony dihalides have no phenylating
ability.5
It was of interest to use in these reactions triphenylꢀ
antimony(V) compounds Ph4SbX, which are accessible,
highly soluble, and stable to the air oxygen and moisture.
The involvement of all four Ph groups in the phenylation
of an organic substrate could be expected.
The complex obtained has the characteristic features
of both structures. For example, the IR spectrum of
Ph4SbOАс•AcOH in Nujol or KBr pellets exhibits the
bands of stretching vibrations of the COO group bound to
the Sb atom: νas(COO) = 1560 cm–1 and νs(COO) =
1400 cm–1. In addition to these bands, the spectrum conꢀ
tains distinct absorption bands of acetic acid, which is
not bound to the metal: νas(COO) = 1730 cm–1 and
The purpose of this work is to synthesize phenylating
agents (viz., tetraphenylantimony halides and carboxyꢀ
lates) and to study their efficiency in the palladiumꢀcataꢀ
lyzed Сꢀphenylation of methyl acrylate compared to the
known reactive Ph3SbX2 compounds.
1
νs(COO) = 1270 cm–1. At the same time, the H NMR
spectrum in CDCl3 contains a singlet of the Me protons
of two identical acetate groups δ = 1.82 (s, 6 H) and a
multiplet of protons of four Ph groups δ = 7.70—7.20
(m, 20 H). Probably, when the crystalline complex is
dissolved in CDCl3, the coordination antimony polyheꢀ
dron is rearranged, and the acetate groups become identiꢀ
cal in the NMR spectrum. When the Ph4SbOАс•AcOH
adduct is stored in air, the AcOH molecule is eliminated
to form Ph4SbOАс.7
Results and Discussion
Tetraphenylantimony complexes Ph4SbX were synꢀ
thesized by neutralization of the stibonium base Ph4SbOH
with the corresponding acids. Hydrochloric acid was used
in an equimolar amount in a dilute aqueous solution.
Excess acetic and propionic acids were taken as solvents.
Tetraphenylantimony fluoride, chloride, and propionate
Published in Russian in Izvestiya Akademii Nauk. Seriya Khimicheskaya, No. 6, pp. 1302—1305, June, 2003.
1066ꢀ5285/03/5206ꢀ1376 $25.00 © 2003 Plenum Publishing Corporation

SbV derivatives in Cꢀphenylation reaction
Russ.Chem.Bull., Int.Ed., Vol. 52, No. 6, June, 2003
1377
The model reaction of Сꢀphenylation of methyl acryꢀ
late by the most accessible Ph4SbBr in the presence of
PdCl2 (molar ratio 3 : 1 : 0.04) in acetonitrile at 50 °C for
6 h was showed9 to occur via Scheme 1.
(50 °C, 6 h) in various solvents are presented below. Biꢀ
phenyl (9% based on OMC) was additionally formed in
the case of THF.
Solvent
MeCN
DMF
MeOH
THF
Yield
57
25
7
Scheme 1
6
AcOH
6
When Ph3Sb(O2CEt)2 was used as the phenylating
agent in the catalytic reaction, the ratio of activities of the
solvents was quite different: THF ≈ DMF > MeCN ≈
≈ AcOH > MeOH.10
The yield of methyl cinnamate based on the starting
organometallic compound (OMC) reaches 57% under
these conditions. The organoantimony nonvolatile resiꢀ
due contains triphenylantimony and unreacted Ph4SbBr.
The catalyst structure affects the yield of the main
product. The most often applied palladium catalysts were
used. The yields of methyl cinnamate (% based on
OMC) in the Сꢀphenylation of methyl acrylate by the
Ph4SbBr—Pd0,II (1 : 0.04) system (MeCN, 50 °C, 6 h)
are presented below (dba is dibenzylideneacetone, and
dppf is bis(diphenylphosphino)ferrocene). In the case of
Pd(OAc)2, biphenyl was additionally formed (9% based
on OMC).
The influence of the X acido ligands in the starting
Ph4SbX on the yield of the products of methyl acrylate
phenylation was studied. As can be seen from the data in
Table 1, among tetraphenylantimony halides, the yield of
methyl cinnamate is maximal in the case of tetraphenylꢀ
antimony chloride (73%) and decreases on going to broꢀ
mide and fluoride. The low yield of the phenylation prodꢀ
uct (7%) is observed along with a considerable amount of
biphenyl (32%, see Table 1) when Ph4SbOH is used. The
reactions with SbV acetate and propionate were ineffiꢀ
cient: the yield of methyl cinnamate was 21—28%. The
lower reactivity of tetraphenylantimony carboxylates comꢀ
pared to that in the case of halides was unexpected when
compared with the Ph3SbX2 derivatives. As we have shown
previously,5 triphenylantimony dicarboxylates are much
more reactive than the corresponding dihalides.
Thus, the results obtained indicate that tetraphenylꢀ
antimony(V) halides, similarly to the previously studied
triphenylantimony(V) dicarboxylates,5 can enter under
mild conditions into the palladiumꢀcatalyzed reaction of
methyl acrylate Сꢀphenylation with the yield up to 73%.
The Pd0 complex is the active form of the catalyst accordꢀ
ing to Scheme 2.
Pd complex
PdCl2
Pd(OAc)2
Pd2(dba)3
Pd(Ph3P)2Cl2
Pd(dppf)Cl2
Yield
57
33
21
0
0
As can be seen, palladium dichloride is most efficient
in the phenylation of Ph4SbBr. The yield of methyl
cinnamate is much lower when the Pd(OAc)2 or Pd0
dibenzylideneacetone complex are used. In addition, biꢀ
phenyl, the byꢀproduct of homocoupling, was formed in
the case of Pd(OAc)2. The introduction of phosphine
ligands, such as PPh3 and bis(diphenylphosphino)ferroꢀ
cene, into the coordination sphere of palladium comꢀ
pletely stops the phenylation of an unsaturated compound
(see above). The same influence of the structure of the Pd
compounds has been found10 in the phenylation of meꢀ
thyl acrylate with the Ph3Sb(O2CEt)2 derivative.
In the first step of oxidative addition, the phenylꢀ
palladium intermediate is formed and then it perꢀ
forms phenylation of the unsaturated compound at the
C—H bond.
Table 1. Yield of methyl cinnamate in the Сꢀphenylation of
methyl acrylate by the Ph4SbX—PdCl2 (1 : 0.04) system (MeCN,
50 °C, 6 h)
It is known that polar electronꢀdonating solvents caꢀ
pable of coordinating to the Pd atom are used, as a rule, in
the Heck reaction. For example, in the reaction of
Ph4SbBr under study, the Nꢀdonating solvents DMF and
especially MeCN were most efficient. Compared to them,
Оꢀdonating THF, AcOH, and MeOH were inefficient.
The starting OMC and PdCl2 catalysts were completely
dissolved in all the solvents listed. The yields of meꢀ
thyl cinnamate (% based on OMC) in methyl acrylate
Сꢀphenylation with the Ph4SbBr—PdСl2 (1 : 0.04) system
Ph4SbX
Yield (% based on OMC)
Methyl cinnamate Ph2
Ph4SbCl
Ph4SbBr
Ph4SbF
Ph4SbOAc
Ph4SbO2CEt
Ph4SbOH
73
57
29
21
28
7
—
—
—
—
1
32

1378
Russ.Chem.Bull., Int.Ed., Vol. 52, No. 6, June, 2003
Gushchin et al.
Scheme 2
Tetraphenylchloroantimony(V) Ph4SbCl was synthesized acꢀ
cording to a previously described procedure11 from Ph4SbOH in
70% yield, m.p. 208 °C (cf. Ref. 8: m.p. 202—205; 208—210 °C).
1H NMR, δ: 7.90—7.44 (m, Ph). IR, ν/cm–1: 460 (ν(Sb—C)).
Tetraphenylfluoroantimony(V) Ph4SbF was prepared using a
known procedure12 in 76% yield, m.p. 161 °C (cf. Ref. 12: m.p.
162—163 °C).
Pd0 + Ph4SbCl
PhPdCl + Ph3Sb
PhPdCl + H2C=CHCO2Me
PhCH=CHCO2Me + Pd0 + HCl
Tetraphenylpropionatoantimony(V) Ph4SbO2CEt was syntheꢀ
sized by the dissolution of Ph4SbOH (0.7 g) in propionic acid
(2 mL) with heating on a water bath at 60 °C. The solution was
concentrated on a water bath under a reduced pressure, toluene
(2 mL) was added, and the solvent was evaporated again. The
yield of Ph4SbO2CEt was 96.5%, m.p. 120 °C (cf. Ref. 13: m.p.
The introduction of phosphine results in the formaꢀ
tion of very stable complexes, the ligand exchange beꢀ
tween palladium and antimony is violated, and the reacꢀ
tions stops (see above).
1
The substantial difference found for the influence of
the X acido ligand and the solvent on methyl acrylate
Cꢀphenylation when Ph4SbX and Ph3SbX2 are used can
be explained as follows. First, the Ph4SbX complexes,
especially halides, are ionic compounds and can dissociꢀ
ate in polar media.8 Unlike them, the Ph3SbX2 comꢀ
pounds are covalent. This should affect the rate and
mechanism of the oxidative addition step (see Scheme 2).
Second, in the case of Ph4SbX, the reaction produces
Ph3Sb. This compound, being an analog of Ph3P, is also
capable of deactivating the palladium catalyst and deꢀ
creasing the rate of phenylation in different solvents.10
Unlike this, the reaction of Ph3SbX2 affords the Ph2SbX
compounds, which do not deactivate the catalyst because
of the weak donor ability.
Thus, Ph4SbBr and especially Ph4SbCl in the presꢀ
ence of catalytic amounts of PdCl2 can act as mild and
selective agents of Сꢀphenylation of methyl acrylate inꢀ
volving one Ph group. The structure of the acido ligand at
the Sb atom and the solvent have a strong effect on the
yield of methyl cinnamate. The character of this effect
differs from that found previously for the Ph3SbX2 comꢀ
pounds.
122 °C). H NMR, δ: 7.70—7.30 (m, 20 Н, Ph); 1.95 (q, 2 H,
CH2); 0.83 (t, 3 H, Me). IR, ν/cm–1: 1520 (ν (COO)); 1360
as
(ν (COO)); 670 (ν(Sb—O)); 470 (ν(Sb—C)).
s
Tetraphenylacetatoantimony(V) (crystal solvate with AcOH)
Ph4SbOAc•AcOH was synthesized similarly to Ph4SbO2CEt in
83% yield, m.p. 112—114 °C (cf. Refs.: m.p. 112—113 °C,8
108—110 °C 7). 1H NMR, δ: 7.70—7.30 (m, 20 Н, Ph); 1.82 (s,
6 H, Me). IR, ν/cm–1: 3200—2400 (ν(O—H)); 1730 (ν (COO));
as
1560 (ν (COO)); 1400 (ν (COO)); 1270 (ν (COO)); 670
as
s
s
(ν(Sb—O)); 460 (ν(Sb—C)). Ph4SbOAc•AcOH was stored in
air for 25 days and dried under reduced pressure to give
Ph4SbOAc, m.p. 132 °C (cf. Ref. 14: m.p. 131 °C).
Commercial compounds PdCl2, Pd(dppf)Cl2, and
Pd(Ph3P)2Cl2 were used without purification. Pd(OAc)2 was
prepared by the oxidation of palladium black with HNO3 in
AcOH for 30 h in 80% yield after recrystallization from AcOH.15
Pd2(dba)3(CHCl3) was synthesized by the reduction of Pd with
MeOH in the presence of dibenzylideneacetone16 in 66% yield.
Methyl acrylate was washed with an alkali solution until
the yellow coloration stopped, dried above Na2SO4, and disꢀ
tilled.
Reaction of Ph4SbBr with methyl acrylate and Pd(OAc)2 in
MeCN. An ampule was loaded with Ph4SbBr (0.5 mmol) and
methyl acrylate (1.5 mmol), and then a solution of Pd(OAc)2
(0.02 mmol) in acetonitrile (4 mL) was added.17 The ampule
was sealed and heated at 50 °C for 6 h. Then the ampule was
opened, and the solvent was condensed off into a trap filled with
liquid nitrogen.
Experimental
A hexane—ethyl acetate (5 : 1) eluent was added to the solid
residue, and the resulting mixture was passed through a column
with silica gel to remove inorganic products. Methyl cinnamate18
(0.17 mmol) and biphenyl (0.043 mmol) were determined in the
filtrate by GLC.
1
H NMR spectra were recorded on a Bruker Avance
DPXꢀ200 instrument in CDCl3 using Me4Si as internal stanꢀ
dard. IR spectra were obtained on a Specord Мꢀ80 spectrophoꢀ
tometer in the 4000—400 cm–1 interval in KBr pellets and in
Nujol suspension between two KBr optical windows. GLC analyꢀ
sis of volatile products was carried out on an LKhMꢀ80 chroꢀ
matograph (flameꢀionization detector, helium as carrier gas,
column 100 cm, 15% ApiesonꢀL on Chromaton NꢀAW, 220 °C).
Silica gel 60 Merck was used in column chromatography.
Tetraphenylantimony(V) Ph4SbBr was synthesized according
to a previously described procedure8 by the reaction of Ph3Sb
with PhBr in the presence of AlBr3 in 43% yield or in the presꢀ
ence of AlCl3 in 25% yield, m.p. 211 °C (cf. Ref. 8: m.p.
This work was financially supported by the Federal
Target Program "Integration of Science and Higher Eduꢀ
cation of the Russian Federation for 2002—2006" (State
Contract B 0039) and the Russian Foundation for Basic
Research (Project No. 00ꢀ03ꢀ40116).
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the treatment of a hot saturated aqueous solution of Ph4SbBr 11
with a 12% aqueous ammonia excess in 90% yield.
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in revised form December 11, 2002