Dephenylation of triphenylbismuth(v) and antimony(v) derivatives in a methyl acrylate-methanol system in the presence of copper and palladium salts

Article abstract of DOI:10.1007/s11172-006-0312-1

The influence of the central metal atom and acid residue in a molecule of organometallic compound Ph₃MX₂ (M = Bi, Sb; X = Cl, Br, OAc, O₂CEt) on the direction and yield of dephenylation products in a methyl acrylate- methanol system in the presence of Cu(OAc)₂ and Na₂PdCl₂(OAc)₂ was studied at 50 °C in acetonitrile. The main product of dephenylation of the antimony compounds is methyl cinnamate (yield 0.31-1.59 moles per mole of the starting Ph ₃SbX₂), while anisole (0.55-0.97 mol) and halobenzene (0.67-1.04 mol) are those for compounds Ph₃Bi(O₂CR) ₂ and Ph₃BiHal₂, respectively.

Full text of DOI:10.1007/s11172-006-0312-1

Russian Chemical Bulletin, International Edition, Vol. 55, No. 4, pp. 679—682, April, 2006
679
Dephenylation of triphenylbismuth(V) and antimony(V) derivatives
in a methyl acrylate—methanol system in the presence
of copper and palladium salts
A. V. Gushchin,ꢀ M. V. Korotkova, Yu. B. Malysheva, V. A. Morugova, and D. V. Moiseev
N. I. Lobachevsky Nizhnii Novgorod State University,
23 prosp. Gagarina, 603950 Nizhnii Novgorod, Russian Federation.
Fax: +7 (831 2) 65 8592. Eꢀmail: gushchin@mail.nnov.ru
The influence of the central metal atom and acid residue in a molecule of organometallic
compound Ph3MX2 (M = Bi, Sb; X = Cl, Br, OAc, O2CEt) on the direction and yield of
dephenylation products in a methyl acrylate—methanol system in the presence of Cu(OAc)2
and Na2PdCl2(OAc)2 was studied at 50 °C in acetonitrile. The main product of dephenylation
of the antimony compounds is methyl cinnamate (yield 0.31—1.59 moles per mole of the
starting Ph3SbX2), while anisole (0.55—0.97 mol) and halobenzene (0.67—1.04 mol) are those
for compounds Ph3Bi(O2CR)2 and Ph3BiHal2, respectively.
Key words: organobismuth(V) compounds, organoantimony(V) compounds, catalysis,
copper, palladium, methyl acrylate, methanol.
Organic compounds of antimony(V) and bismuth(V)
of the Ph3MX2 type are known1 to be dephenylated by
various inorganic and organic reagents due to a low enꢀ
ergy of the M—Ph bond (see Ref. 2). The majority of the
known reactions of these organometallic compounds
(OMC) with reactants containing an active hydrogen atom
proceed according to Scheme 1.
reactions of the bismuth and antimony OMC catalyzed by
copper and palladium compounds evoke special interest.
These reactions occur under mild conditions (20—50 °C)
and afford coupling products through the step of intermeꢀ
diate formation of copper and palladium σꢀphenyl deꢀ
rivatives. For instance, triphenylbismuth diacetate unꢀ
dergoes crossꢀcoupling with alcohols, phenols, and diols
in the presence of copper salts to form phenyl ethers1,3
(Scheme 2).
Scheme 1
Scheme 2
It has recently4—6 been found that Ph3Sb(OAc)2 can
be crossꢀcoupled with alkene functional derivatives in the
presence of palladium salts (Scheme 3).
Routes a and b afford nonꢀsymmetric coupling prodꢀ
ucts. Molecules of these products contain the Ph group
bonded to the functional Y group, which enters the reacꢀ
tant composition (route a), or with the X group, which is
a constituent of the starting OMC (route b). The third
route (c) includes the formation of diphenyl, and the
Ph groups can be originated from one or two OMC molꢀ
ecules. All coupling reactions are accompanied by a deꢀ
crease in the oxidation state of the central metal atom
from V to III. Numerous examples of the coupling reacꢀ
tions of the bismuth OMC involving alcohols, glycols,
phenols, ketones, ketoesters, indoles, thiols, and others
and their mechanism and stereochemical features are deꢀ
scribed in a monograph.1 In the recent time, the coupling
Scheme 3
Triphenylbismuth dicarboxylates can also undergo
similar reactions but the process is not selective in
this case.4
The present work is aimed at studying the behavior of
the antimony and bismuth Ph derivatives under the conꢀ
ditions when both Oꢀ and Cꢀphenylations of organic subꢀ
Published in Russian in Izvestiya Akademii Nauk. Seriya Khimicheskaya, No. 4, pp. 655—658, April, 2006.
1066ꢀ5285/06/5504ꢀ0679 © 2006 Springer Science+Business Media, Inc.

680
Russ.Chem.Bull., Int.Ed., Vol. 55, No. 4, April, 2006
Gushchin et al.
Scheme 4
strates can occur simultaneously. For this purpose, we
studied the interaction in the Ph3MX2—Cu(OAc)2—
N a 2 P d C l 2 ( O A c ) 2 — H 2 C = C H C O 2 M e — M e O H
(1 : 0.3 : 0.3 : 10 : 10) system at 50 °C in acetonitrile
for 1 h. Triphenylbismuth(V) and triphenylantimony(V)
dihalides (chloride, bromide) and dicarboxylates (acetate,
propionate) were used as phenylating agents, because the
difference in their properties in the reactions catalyzed by
palladium and copper has been observed earlier.6
Ph3Sb(OAc)2 + H2C=CHCO2Me
PhCH=CHCO2Me + Ph2SbOAc + AcOH
2 Ph2SbOAc + O2 + 2 H2C=CHCO2Me + 2 AcOH
2 PhCH=CHCO2Me + 2 PhSb(OAc)2 + 2 H2O
On going from triphenylantimony(V) dicarboxylates
to dichloride, the yield of the crossꢀcoupling product deꢀ
creases sharply but high selectivity is retained. In this
case, the yield of methyl cinnamate was 0.31 mol, and no
other products were observed (see Table 1, entry 3). We
believe that Ph3Sb(OAc)2 or Ph3Sb(OAc)Cl, which is
formed by ligand exchange between antimony(V) chloride
and copper(II) or palladium(II) acetate, acts as phenylating
agent rather than Ph3SbCl2. We have previously4,6 shown
that Ph3SbCl2 cannot phenylate methyl acrylate in the
presence of catalytic amounts of PdCl2 and Li2PdCl4 conꢀ
taining no carboxylate groups.
Thus, the antimony compounds Ph3SbX2 used unꢀ
dergo selective crossꢀcoupling reactions with methyl acryꢀ
late with catalytic participation of palladium. The role of
Cu(OAc)2 is restricted only by donating of the acetate
groups in the exchange reaction.
The bismuth compounds, unlike the antimony OMC,
afford the whole series of dephenylation products. For
Ph3Bi(O2CEt)2, the copperꢀcatalyzed Oꢀphenylation of
methanol to anisole is prevailing (Scheme 5, see Table 1,
entry 5). The reaction of triphenylbismuth dicarboxylates
occurs easily at room temperature,1,3,8—10 although simiꢀ
lar antimony compounds can react with alcohols only in
the presence of equimolar amounts of the copper salts
at 80 °C.12
When Ph3Bi(O2CEt)2 is used in the catalytic decomꢀ
position of triphenylbismuth dichloride, chlorobenzene
(0.26 mol) is formed (Scheme 6). The latter is formed in
situ due to the exchange reaction of Ph3Bi(O2CEt)2 with
Na2Pd(OAc)2Cl2.
Results and Discussion
Methyl acrylate is a convenient model compound for
Cꢀphenylation. In the presence of palladium, it is selecꢀ
tively phenylated into the transꢀposition4—7 and, at the
same time, does not react with copper salts. Methanol is
a convenient model for copperꢀcatalyzed Oꢀphenylaꢀ
tion.1,8—10 Acetonitrile is used because it is a convenient
polar solvent and simultaneously can act as an electronꢀ
donor ligand for palladium and copper ions. The reaction
was carried out in sealed ampules in the presence of air.
The dephenylation products and their yields based on the
starting OMC are given in Table 1.
The Pdꢀcatalyzed reaction of the antimony derivatives
with methyl acrylate results in selective Cꢀphenylation to
form methyl cinnamate (Scheme 4). Triphenylantimony
dicarboxylates exhibit the highest reactivity in this reꢀ
action, where the yield of methyl cinnamate reaches
1.40—1.59 moles per mole of the starting antimony OMC
(see Table 1, entries 1 and 2). We believe that one mole of
the product is formed in this process due to the deꢀ
phenylation of Ph3SbX2, which is reduced to Ph2SbX.
The latter can also react with methyl acrylate in the presꢀ
ence of air oxygen to form other 0.4—0.6 moles of methyl
cinnamate. This assumption is confirmed by the known
data6,11 on the reactions of triphenylantimony(V) diꢀ
carboxylates and diphenylantimony(III) acetate with
methyl acrylate catalyzed by the palladium salts in the
presence of air.
Table 1. Yields of the organic products of OMC dephenylation in the
Ph3MX2—Cu(OAc)2—Na2PdCl2(OAc)2—H2C=CHCO2Me—MeOH (1 : 0.3 : 0.3 : 10 : 10)
system (acetonitrile, 50 °C, reaction duration 1 h)
Entry
Ph3MX2
Yield (mole per mole of OMC)
PhCH=CHCO2Me
Ph2
MeOPh
PhHal
PhH
1
2
3
4
5
6
7
Ph3Sb(OAc)2
Ph3Sb(O2CEt)2
Ph3SbCl2
Ph3Bi(OAc)2
Ph3Bi(O2CEt)2
Ph3BiCl2
1.40
1.59
0.31
0.15
0.14
0.13
0.17
0.01
0.03
0
0.53
0.51
0.37
0.59
0
0
0
0.55
0.97
0
0
0
0
0.32
0.26
1.04
0.67
0
0
0
0.27
0.37
0.23
0.13
Ph3BiBr2
0

Dephenylation of SbV and BiV compounds
Russ.Chem.Bull., Int.Ed., Vol. 55, No. 4, April, 2006
681
Scheme 5
Triphenylbismuth diacetate exhibits similar reactivity
(see Table 1, entry 4).
The catalytic effect of the copper salt is observed when
Ph3BiCl2 is used, as well as in the case of Ph3SbCl2. The
reaction products contained chlorobenzene, whose yield
was 1.04 mol (see Table 1, entry 6). This process supꢀ
presses completely methanol Oꢀphenylation, which preꢀ
vails in the case of triphenylbismuth dicarboxylates. This
effect has been described previously.9 In addition to chloꢀ
robenzene, the reaction products contained diphenyl and
methyl cinnamate, whose formation is caused by catalytic
participation of palladium. When Ph3BiBr2 is used, the
reaction proceeds similarly to the case of Ph3BiCl2 (see
Table 1, entry 7).
Ph3Bi(O2CEt)2 + MeOH
MeOPh + Ph2BiO2CEt + EtCO2H
Scheme 6
Ph3BiCl2
PhCl + Ph2BiCl
Examples for the formation of halobenzenes by the
reaction of Ph3Bi(OAc)2 with Cu(OAc)2 in the presence
of calcium and ammonium halides and for the reaction of
Ph3BiCl2 with PdCl2 have been described.9,13
The bismuth(V) compounds undergo deeper depheꢀ
nylation compared to similar antimony(V) compounds.
The total amount of the Ph groups detached from bisꢀ
muth is 2.10—2.76 moles per mole of OMC (see Table 1,
entries 4—7), while that for the detachment from antiꢀ
mony is 0.31—1.65 mol (see Table 1, entries 1—3). This is
related to a lower strength of the Bi—C bond compared to
the Sb—C bond.2
In the case of Ph3Bi(O2CEt)2, two compounds inꢀ
volving palladium are formed along with anisole and chloꢀ
robenzene. For instance, methyl cinnamate, being the
product of crossꢀcoupling of Ph3Bi(O2CEt)2 with methyl
acrylate, was isolated in a yield of 0.14 mol (Scheme 7,
see Table 1, entry 5). This reaction occurs readily in the
presence of the palladium salts5 but does not occur when
they are replaced by the copper salts.
Thus, all processes studied involving the bismuth(V)
compounds are lowly selective. For copper catalysis,
bismuth(V) halides form only halobenzene, while carboxyꢀ
lates give predominantly anisole. The catalytic participaꢀ
tion of palladium is also substantial. However, the main
process in the presence of Pd is the decomposition of the
bismuth OMC to form diphenyl rather than the crossꢀ
coupling of Ph3BiX2 with methyl acrylate. This sharply
distinguishes the bismuth compounds from the antimony
compounds Ph3SbX2.
Scheme 7
Ph3Bi(O2CEt)2 + H2C=CHCO2Me
PhCH=CHCO2Me + Ph2BiO2CEt + EtCO2H
The palladiumꢀcatalyzed formation of diphenyl is more
pronounced (0.51 mol, Scheme 8, see Table 1, entry 5).
Similar mild dephenylation of compounds Ph3Bi and
Ph3BiX2 is described.14,15
Experimental
Scheme 8
Volatile reaction products were analyzed by GLC on an
LKhMꢀ80 chromatograph using a flameꢀionization detector and
helium as carrier gas. To determine the benzene content, a
column 300 cm long with 15% dinonyl phthalate on Chromaton
NꢀAWꢀDMCS at 80 °C was used. The contents of methyl
cinnamate and diphenyl were determined on a 240ꢀcm column
with 15%ꢀApieson L on Chromaton NꢀAWꢀDMCS at 220 °C.
Anisole, chlorobenzene, bromobenzene, and phenyl acetate were
determined on the same column at 130 °C.
A
Ph2
A is BiIII(V)ꢀОMС.
Benzene (0.37 mol) was also isolated along with the
mentioned coupling products. It is formed, most likely,
through the dephenylation of the bismuth OMC with acid
EtCO2H in the steps of formation of anisole and methyl
cinnamate (Scheme 9).
The syntheses of Ph3Sb(OAc)2, Ph3Sb(O2CEt)2, Ph3SbCl2,6
16,18
Ph3Bi(OAc)2, Ph3Bi(O2CEt)2, Ph3BiCl2, and Ph3BiBr2
were carried out according to known procedures; Cu(OAc)2 was
prepared from monohydrate,10 and Na2Pd(OAc)2Cl2 was obꢀ
tained from PdCl2 and NaOAc. Methanol was used as received.
Dephenylation of Ph3Bi(OAc)2. A mixture of Ph3Bi(OAc)2
(0.5 mmol), Cu(OAc)2 (0.15 mmol), Na2Pd(OAc)2Cl2
(0.15 mmol), CH2=CHCO2Me (5 mmol), MeOH (5 mmol),
and acetonitrile (4 mL) were placed in a 50ꢀmL ampule in air.
The ampule was sealed and heated for 1 h at 50 °C, and then the
liquid fraction was distilled off under reduced pressure. Acetoꢀ
nitrile (4 mL) was added to the solid residue, and H2S was
Scheme 9
PhnBiX3–n + HX
X = O2CEt; n = 1, 2, 3
PhH + Phn–1BiX4–n
This reaction is characteristic of all bismuth(III) comꢀ
pounds.16 The copper salts can accelerate this process.17

682
Russ.Chem.Bull., Int.Ed., Vol. 55, No. 4, April, 2006
Gushchin et al.
purged for 1 min to bind dissolved metal compounds. The transꢀ
parent solution obtained after centrifugation and the resulting
condensate were analyzed by GLC to determine the contents of
methyl cinnamate, diphenyl, anisole, chlorobenzene, and benꢀ
zene. No phenyl acetate was found in the products. The reacꢀ
tions with other OMC were carried out similarly.
9. V. A. Dodonov, A. V. Gushchin, and T. G. Brilkina,
Zh. Obshch. Khim., 1985, 55, 2514 [J. Gen. Chem. USSR,
1985, 55 (Engl. Transl.)].
10. V. A. Dodonov, T. I. Starostina, Yu. L. Kuznetsova, and
A. V. Gushchin, Izv. Akad. Nauk, Ser. Khim., 1995, 156
[Russ. Chem. Bull., 1995, 44, 151 (Engl. Transl.)].
11. K. Matoba, S. Motofusa, C. S. Cho, K. Ohe, and S. Uemura,
J. Organomet. Chem., 1999, 574, 3.
12. A. V. Gushchin, Doct. Sci. (Chem.) Thesis, Nizhnii
Novgorod Gos. Univ., Nizhnii Novgorod, 1998, 283 pp. (in
Russian).
13. D. V. Moiseev, Yu. B. Malysheva, A. S. Shavyrin, Yu. A.
Kurskii, and A. V. Gushchin, J. Organomet. Chem., 2005,
690, 3652.
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Received January 17, 2005;
in revised form February 8, 2006