Use of aromatic acid anhydrides as arylation agents in the heck reaction

Article abstract of DOI:10.1023/A:1026604632062

The use of bromide or chloride additives in styrene phenylation by benzoic acid anhydride results in an increase in catalytic activity and the yield of arylation products. The best results are obtained when LiCl is used. In this case, the yield of stilben

Full text of DOI:10.1023/A:1026604632062

Kinetics and Catalysis, Vol. 41, No. 6, 2000, pp. 743–744. Translated from Kinetika i Kataliz, Vol. 41, No. 6, 2000, pp. 820–822.
Original Russian Text Copyright © 2000 by Shmidt, Smirnov.
Use of Aromatic Acid Anhydrides
as Arylation Agents in the Heck Reaction
A. F. Shmidt and V. V. Smirnov
Institute of Oil and Coal Chemical Synthesis, Irkutsk State University, Irkutsk, 664033 Russia
Received July 27, 1999
Abstract—The use of bromide or chloride additives in styrene phenylation by benzoic acid anhydride results
in an increase in catalytic activity and the yield of arylation products. The best results are obtained when LiCl
is used. In this case, the yield of stilbene increases from 14 to 85%. Kinetics and regioselectivity of the reaction
suggest that the reason for the activating effect of halides is the formation of benzoyl palladium halide com-
plexes that readily eliminate CO in the form of an acidoligand.
INTRODUCTION
(1.6 mmol). The reaction was carried out until stilbene
(the β-isomer) and 1,1-diphenylethylene (the α-isomer)
stopped being formed. Analyses were carried out using
GLC (with a HP-4890 chromatograph and 15-m columns
packed with 15% polyphenylsilicon; 100–200°C; flame-
ionization detector; and the internal standard was naphtha-
lene). Reagents were purified according to standard proce-
dures.
Recently, a method was proposed for the arylation of
alkenes by anhydrides of aromatic acids (I), which does not
require the use of bases in contrast to the Heck reaction (II).
Reaction (I) has several advantages over other methods: the
availability of reagents, the absence of bases in a reaction
medium, and the possible reuse of acid formed in the reac-
tion for anhydride synthesis. Note that the application of
aromatic acid halides (III) is known [2], but this reaction
also requires the presence of a base. That is, reaction (III)
has the same limitation as the Heck reaction (II).
DISCUSSION
We found that CO accumulated during reaction (I)
results in a substantial decrease in the rate and the
yields of arylation products. The presence of CO had a
negative effect on reactions (II) and (III) as well. In all
cases, the reason for an activity drop in the medium of
CO may be the formation of stable palladium com-
plexes PhCOPdX (complex II in the scheme):
(ArCO)2O + H2C=CHPh
Pd2+
(I)
(II)
160–190°C ArCH=CHPh + Ar(Ph)C=CH2
+ ArCOOH + CO ,
ArX + H2C=CHPh
, base ArCH=CHPh + Ar(Ph)C=CH2 + HX,
Pd2+
60–80°C
(PhCO)2O + Pd(0)
PhCOPdOCOPh
I
ArCOX + H2C=CHPh
ArCH=CHPh + Ar(Ph)C=CH2
+ HX + CO .
–CO
+X–
Pd2+, base
100°C
PhCOPdX
PhPdX
III
+CO
–PhCOO–
(III)
II
Ph
H
H
H
Ph
H
H
H
PhPdX +
=
=
Although the new arylation method has advantages
over the conventional Heck reaction (II) and reaction (III),
the catalyst activity in reaction (I) is substantially lower.
To reach acceptable yields of arylation products, it was
necessary to increase the temperature to 160–190°C [1].
The goal of this study was to elucidate the mechanism of
reaction (I) and develop a more efficient catalytic system.
PhPdX
IV
Ph
Ph
H
H
Ph
----------------
,
PdX Ph
PdX
V
H
Ph
Ph
PdX
H
=
Ph
H
+ HPdX,
EXPERIMENTAL
Ph
VI
Styrene (10 mmol) and benzoic acid anhydride
(10 mmol) were dissolved in 10 ml of N-methylpyrroli-
done. The solution was added to a flask purged with
argon, heated to a constant temperature of 140°C, and,
equipped with a magnetic stirrer. Before adding the solu-
tion, the flask contained PdCl2 (0.16 mmol) and halides
Ph
Ph
H
PdX
Ph
Ph
=
+ HPdX,
HPdX
Pd(0) + HX.
Scheme.
0023-1584/00/4106-0743$25.00 © 2000 MAIK “Nauka /Interperiodica”

744
SHMIDT, SMIRNOV
Styrene phenylation by benzoic anhydride
CO results in the catalytically active σ-aryl palladium
complexes (complex III) that transform via usual steps
of the Heck reaction [4] (complexes III–VI). Thus, dif-
ferent resistances of palladium benzoyl complexes con-
taining different acidoligands (complex II in the
scheme) to CO elimination can determine the catalytic
activity in reaction (I).
No.
w × 102,
mol l–1 min–1 yield, %
Stilbene
Halide added
β/αa
of run
1
2
–
NaBr
NaCl
NaI
1.0
2.4
0.7
0
14
44
6
21
23
30
–
3
This conclusion agrees with the fact that the cation
of a salt used substantially affected the catalyst activity
(see the table). The nature of the cation in water-free
N-methylpyrrolidone is very important for acidoligand
substitution. Thus, the presence of potassium and tetra-
alkylammonium cations instead of sodium cations pro-
posed in [1] was accompanied by a decrease in the
activity (see the table, rows 5, 7, and 10). By contrast,
lithium halides, which we used in reaction (I) for the
first time (rows 11–13), resulted in a substantial
increase in the reaction rate and arylation product yield.
The use of LiCl as an activator allowed us to increase
the reaction rate by a factor of 2–3 and increase the
product yield from 14 to 85%. The use of LiCl also
enables a decrease in the process temperature to 140°C.
At 100°C, the reaction occurred with rather high yields
as well (row 13).
4
0
5
6b
(NBu4)I
–
0.3
29.0
0.4
5.8
2.9
0.9
2.1
5.8
1.1
6
13
13
25
33
13
20
25
33
30
65
10
85
46
10
53
85
60
7
(NMe4)Br
–
8c
9c
10d
11
12
13e
NaI
KBr
LiBr
LiCl
LiCl
a
b
c
d
e
The ratio of stilbene to 1,1-diphenylethylene.
PhI is an arylation agent; NBu (1.3 × 10 mol) is a base.
RhCOCl is an arylation agent; NBu (1.3 × 10 mol) is a base.
–2
3
–2
3
KBr is poorly solvable in N-methylpyrrolidone.
Reaction was carried out at 100°C for 3 h.
CONCLUSION
Thus, we proposed a new catalytic system for the
arylation of alkenes by the anhydrides of aromatic acids
involving LiCl as an activator and enabling high yields
of arylation products. Kinetics and regioselectivity of
the reaction are suggestive of the effect of halides on
the catalytic activity due to the substitution of the aci-
doligand by a halide anion in the intermediate com-
plexes of the catalytic cycle. One of the reasons for the
activating effect of LiCl is the lower stability of catalyt-
ically inactive palladium benzoyl complexes formed in
the reaction.
Halide additives changed the nature of catalytically
active complexes. Thus, the regioselectivity of styrene
phenylation (the β-to-α ratio) strictly depended on the
nature of the halide anion added (see the table). The
addition of NaCl or LiCl (see the table, rows 3 and 12)
affected the regioselectivity in a similar way. About the
same β-to-α ratio was observed if benzoyl chloride was
used as an arylation agent (see the table, row 8),
because (HNBu3)Cl is formed via a noncatalytic path-
way in reaction (III) and reactive chlorine anions are
formed. Regioselectivity was independent of the choice
of bromides (see the table, rows 2, 7, and 11) with the
exception of KBr (row 10) for which the value of regi-
oselectivity was somewhat lower due to the low solu-
bility of KBr in N-methylpyrrolidone. If NBu4I was
added to reaction (I) (row 5), regioselectivity was the
same as in the conventional Heck arylation with iodo-
benzene as an arylation agent (row 6), in which case
(HNBu3)I was formed as a product, and as in the case
of arylation by benzoyl chloride with a NaI additive
(row 9). The dependence of the regioselectivity in reac-
tion (I) on halide anion points to the presence of the
step of benzoate acidoligand substitution in complex I
(see the scheme) for a halide anion. This complex is
formed by the oxidative addition of benzoic anhydride
to Pd(0) (complex II) as in [3]. Further elimination of
ACKNOWLEDGMENTS
This work was supported by the Russian Foundation
for Basic Research (project no. 99-03-32090).
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KINETICS AND CATALYSIS Vol. 41
No. 6
2000