Cross-coupling of polychlorobenzenes with phenylboronic acid in the presence of [Pd]-imidazolium salts as catalytic systems

Article abstract of DOI:10.1007/s11172-007-0224-8

The reactions of di-, tetra-, and hexachlorobenzenes with phenylboronic acid in the presence of [Pd]-imidazolium salt-base as catalytic systems afford cross-coupling products in moderate yields. The highest conversions are attained when imidazolium salts bearing bulky aromatic substituents are used and the reaction is carried out in the presence of alkali alkoxides containing H _α atoms. Cross-coupling is accompanied by hydrodechlorination of aromatic C-Cl bonds.

Full text of DOI:10.1007/s11172-007-0224-8

Russian Chemical Bulletin, International Edition, Vol. 56, No. 7, pp. 1467—1469, July, 2007
1467
Crossꢀcoupling of polychlorobenzenes with phenylboronic acid
in the presence of [Pd]—imidazolium salts as catalytic systems
a
a
b
a
a
aꢀ
A. S. Burukin, A. A. Vasil´ev, N. L. Merkulova, A. O. Chizhov, E. A. Mistryukov, and S. G. Zlotin
aN. D. Zelinsky Institute of Organic Chemistry,
4
7 Leninsky prosp., 119991 Moscow, Russian Federation.
Fax: +7 (495) 135 5328. Eꢀmail: zlotin@ioc.ac.ru
b
ChemBridge Corporation
1
ul. Malaya Pirogovskaya, 119435 Moscow, Russian Federation.
Fax: +7 (495) 956 4948
The reactions of diꢀ, tetraꢀ, and hexachlorobenzenes with phenylboronic acid in the presꢀ
ence of [Pd]—imidazolium salt—base as catalytic systems afford crossꢀcoupling products in
moderate yields. The highest conversions are attained when imidazolium salts bearing bulky
aromatic substituents are used and the reaction is carried out in the presence of alkali alkoxides
containing Hα atoms. Crossꢀcoupling is accompanied by hydrodechlorination of aromatic
C—Cl bonds.
Key words: crossꢀcoupling, Suzuki reaction, polychloroarenes, biaryls, imidazolium salts.
In our previous studies, we demonstrated that polyꢀ
chloroarenes can be involved into C—C crossꢀcoupling
with organozinc compounds and arylboronic acids.
These transformations open up a oneꢀstep route to funcꢀ
tionally substituted arenes and polyarylbenzenes from
readily available and inexpensive polychloroaromatic
1
1,2
Table 1. Crossꢀcoupling of PCA with PhB(OH) (1.5 mol mol–1) involving imidazolium salts (85—90 °C, 7—8 h)
2
Entry PCA
Catalytic
systemb
Solvent
Base
PCA conꢀ
version (%)
Yields of crossꢀcoupling products (mol. %)a
I
II
III
IV
1
2
3
4
5
6
7
8
9
1
1
1
1
1
2
2
2
3
3
3
3
3
3
3
4
4
I—Pd(OAc)2
I—Pd(OAc)2
I—Pd(OAc)2
II—Pd(OAc)2
I—Pd(OAc)2
I—Pd(OAc)2
I—Pd(dba)2
II—Pd(dba)2
II—Pd(OAc)2 Dioxane + MeOH KOH
II—Pd(OAc)2
Dioxane
Dioxane
Dioxane
Dioxane
Dioxane
Dioxane
Dioxane
K PO
79
~100
31
38
0
18
81
94
40
80
72
80
86
75
~100
31
38
—
4
—
—
—
—
—
—
—
—
—
—
22
—
—
—
—
—
10
—
—
—
—
—
—
—
3
4
4
K PO
3
Cs CO
2
3
K PO
3
4
K PO
3
4
KOH
4
Σ18
Σ39
1+5
3+7 c
4
Σ6
Σ34
4
t
c
Bu ONa
35+6
d
c,e
c,e
c,e
Toluene + MeOH MeOK
Σ43
Σ16
Σ60
—
Σ12
c
c
c
c
3+15
i
c
0
1
2
3
Dioxane + Pr OH
KOH
10
d
III—Pd(dba)
I—Pd(dba)2
II—Pd(dba)2
Toluene + MeOH MeOK
Toluene + MeOH MeOK
Toluene + MeOH MeOK
—
Σ28
—
2
d
c,f
c,f
c,f
Σ46
Σ48 c
d
c
a
Yields of monoꢀ (I), diꢀ (II), triꢀ (III), and tetrasubstituted products (IV) are given. According to GC/MS data; a 100% balance is
completed by unreacted PCA, in some cases, together with its hydrodechlorination product.
b
Palladium compound (6 mol.%), imidazolium salt (12 mol.%).
Mixtures of compounds with different extents of dechlorination.
c
d
Pd(dba) and imidazolium salt (each 3 mol.% ) and Bu NBr (10 mol.%).
2
4
e
Composition of the reaction mixture (the percentages of isomers for each formula are indicated in parentheses): C H Cl (6),
6
2
4
PhC H Cl (9), PhC H Cl (4 + 24), PhC H Cl (2), Ph C H (11 + 8), Ph C H Cl (2 + 10 + 12), Ph C H (8), Ph C H Cl (4).
6
4
6
3
2
6
2
3
2
6
4
2
6
3
3
6
3
3
6
2
f
Composition of the reaction mixture (%): Ph2 (3), C Cl (14), C HCl (4), PhC H Cl (3 + 7 + 4), PhC H Cl (1 + 4 + 6),
6
6
6
5
6
4
6
3
2
PhC H Cl (1 + 1 + 1 + 2), PhC HCl (3), Ph C H (1 + 8), Ph C H Cl (3 + 4 + 5), Ph C H Cl (1 + 1 + 6 + 1 + 1 + 4 + 6),
6
2
3
6
4
2
6
4
2
6
3
2
6
2
2
Ph C HCl (1 + 1 + 2 + 1).
2
6
3
Published in Russian in Izvestiya Akademii Nauk. Seriya Khimicheskaya, No. 7, pp. 1414—1416, July, 2007.
066ꢀ5285/07/5607ꢀ1467 © 2007 Springer Science+Business Media, Inc.
1

1
468
Russ.Chem.Bull., Int.Ed., Vol. 56, No. 7, July, 2007
Burukin et al.
compounds (PCA). In the case of less nucleophilic
arylboronic acids, low reactivity of PCA required the use
of special catalytic systems comprising electronꢀenriched
Scheme 1
3
sterically hindered phosphine ligands or Nꢀheteroꢀ
4
cyclic carbene palladium complexes. The advantages of
Nꢀheterocyclic carbene complexes or their precursors
(
imidazolium salts) include air stability and ready accesꢀ
sibility.
This communication presents the results of a more
detailed study of the crossꢀcoupling of 1,2ꢀdichlorobenꢀ
zene (1), 1,4ꢀdichlorobenzene (2), 1,2,4,5ꢀtetrachloroꢀ
benzene (3), and hexachlorobenzene (4) with phenylꢀ
boronic acid in the presence of [Pd]—imidazolium salt
catalytic systems. Salts I—IV differing in the electronic
and steric properties of substituents at the heterocyclic
nitrogen atoms were used as the sources of imidazolium
ligands (Scheme 1, Table 1).
It was found that isomeric 1,2ꢀ and 1,4ꢀdichlorobenꢀ
zenes (1 and 2) (see Table 1, entries 1—4) are converted
into chlorobiphenyls in 75—100% yields in the presence
of the Pd(OAc) —I—K PO catalytic system. Tetraꢀ
2
3
4
chlorobenzene 3 is less reactive and virtually does not
1
, 5: X = H, Y = Cl; 2, 6: X = Cl, Y = H; 3, 7: X = H; 4, 8: X = Cl
react with PhB(OH) under these conditions (in the presꢀ
2
ence of this catalytic system) (see Table 1, entries 5 and 6).
However, the use of sodium tertꢀbutoxide as the base
gave a mixture of crossꢀcoupling products in 81% yield
(
entry 7). The use of the Pd(dba) —II—potassium
2
4
d
methoxide—toluene system increases the substrate conꢀ
version to 94% (entry 8); however, in this case, reductive
hydrodechlorination occurs in parallel with the crossꢀcouꢀ
pling. Hydrodechlorination also plays an important role
when KOH with methanol (entry 9) or 2ꢀpropanol
4
b,5
(
entry 10) is used. It is known
that in processes of this
type, alcohols containing Hα atoms are converted into
carbonyl compounds. The composition of reaction mixꢀ
tures prompts the conclusion that crossꢀcoupling and
hydrodechlorination proceed here at comparable rates.
The highest conversions of PCA 3 were observed in the
presence of catalytic systems containing imidazolium salts
I and II bearing bulky aryl substituents. The process carꢀ
ried out in the presence of 1,3ꢀdi(tertꢀbutyl)imidazolium
chloride (III) afforded the crossꢀcoupling product in a
yield of only 4%, together with 1,2,4ꢀtrichlorobenzene in
2
4% yield (entry 11). Systems containing Nꢀmethylꢀsubꢀ
stituted bisꢀimidazoilium derivative IV did not catalyze
this reaction.
azolium salt systems. The route and efficiency of reaction
were found to depend on the number of chlorine atoms in
the PCA molecule, the structure of the imidazolium salt
used, and the nature of the base. Under the chosen condiꢀ
tions, the process ensures high conversions of PCA but
has poor chemoꢀ and regioselectivities.
It was shown for hexachlorobenzene 4 that catalytic
systems containing imidazolium salts I and II do promote
crossꢀcoupling and dechlorination of perchloroarenes
resulting in C—C and C—H bond formation, respectively.
The PCA conversion can be as high as 80—86% (enꢀ
tries 12 and 13).
Experimental
To conclude, we studied the composition of the
dechlorination products of diꢀ, tetraꢀ, and hexachloroꢀ
GC/MS analysis was carried out on an Agilent Technologies
85973 Network instrument (EI, 70 eV) attached to an Agilent
benzenes induced by the PhB(OH) —base—[Pd]—imidꢀ
2

Suzuki coupling of polychlorobenzenes
Russ.Chem.Bull., Int.Ed., Vol. 56, No. 7, July, 2007
1469
Technologies 6890 chromatograph with a HPꢀ5MS capillary
column (30000×0.25 mm), injector and flame ionization deꢀ
tector temperature of 280 °C, temperature programming
monosubstituted products 5—8 were also compared with those
of authentic samples.
6
0→300 °C, 10 deg min–1, then 5 min at 300 °C, and helium as
References
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1
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of the components were then calculated. 1,2ꢀDichlorobenzene
1
2
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1) and 1,4ꢀdichlorobenzene (2) (Lancaster), 1,2,4,5ꢀtetraꢀ
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,3´ꢀ(oꢀphenylenedimethylene)bis(1ꢀmethylimidazolium) diꢀ
8
bromide (IV) were prepared by known procedures.
Crossꢀcoupling procedure. А. Palladium acetate (13 mg,
0
.06 mmol), imidazolium salt I—III (0.135 mmol) or bisꢀsalt IV
(
0.07 mmol), and K PO (431 mg, 2.03 mmol) were introduced
3
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argon. The mixture was heated at 80 °C for 1 h and cooled
to ~20 °C. Polychloroarene (1 mmol) and a solution of phenylꢀ
boronic acid (185 mg, 1.53 mmol) in dioxane (2 ml) were added.
The reaction mixture was stirred for 7 h at 95 °C, and an aliquot
sample was taken and concentrated in vacuo to remove dioxane.
The residue was dissolved in benzene, filtered through a silica
gel layer, and analyzed by GC/MS. In some experiments, other
bases were used instead of K PO (see Table 1).
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3
4
t
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simultaneously and then the reaction mixture was stirred for
7
—8 h at 95 °C.
(
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(
(
(
0.012 mmol), Bu NBr (31.2 mg, 0.041 mmol), PCA
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4
(
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9
5
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5
6
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i
МеOH or Pr OH (0.6 mL) were added under argon. Then the
reaction was carried out as described above.
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3
5
Cl isotopes, the isotope clusters corresponded to the number
7
8
. E. A. Mistryukov, Mendeleev Commun., 2006, 258.
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of chlorine atoms in the molecule) of the crossꢀcoupling prodꢀ
ucts, see: 5 and 6, PhC H Cl (188); 7, PhC H Cl (256);
6
4
6
2
3
8
, PhC Cl (324); PhC H Cl (222); PhC HCl (290); Ph C H
6 5 6 3 2 6 4 2 6 4
(
230); Ph C H Cl (264); Ph C H Cl (298); Ph C HCl (332);
2 6 3 2 6 2 2 2 6 3
Ph C Cl (366); Ph C H (306); Ph C H Cl (340); Ph C HCl
Received February 20, 2007;
in revised form April 25, 2007
2
6
4
3
6
3
3
6
2
3
6
2
(
374); Ph C Cl (408); Ph C H (382). The retention times of
3 6 3 4 6 4