ISSN 1070-4272, Russian Journal of Applied Chemistry, 2007, Vol. 80, No. 10, pp. 1695!1698. C Pleiades Publishing, Ltd., 2007.
Original Russian Text C A.F. Shmidt, A.Al Halaiqa, V.V. Smirnov, 2007, published in Zhurnal Prikladnoi Khimii, 2007, Vol. 80, No. 10, pp. 1666 !1669.
AND INDUSTRIAL ORGANIC CHEMISTRY
Enhancement of Catalyst Performance in Heck Reaction
of Nonactivated Aryl Bromides
in the Absence of Phosphine Ligands
A. F. Shmidt, A. Al Halaiqa, and V. V. Smirnov
Irkutsk State University, Irkutsk, Russia
Irkutsk State Technical University, Irkutsk, Russia
Received March 1, 2007
Abstract-Effective procedures for raising the yield of the Heck reaction, based on the reactants (brom-
benzene, styrene), in the presence of the previously developed phosphine-free catalytic system (PdCl
NaOOCH + NaOAc) were suggested.
The catalytic arylation of alkenes with aryl halides
(I) [1, 2] has been extensively studied :
ArX + = 776 =+HX,
X = I, Br, Cl.
A special attention is paid to development of new
catalytic systems that can activate more readily avail-
able, but less reactive aryl bromides and chlorides.
Use of these catalytic systems will allow industrial ap-
plication of the Heck reaction . Insufficient cat-
alytic activity in reaction (I) is mainly due to the low
reactivity of nonactivated aryl bromides and chlorides
in the final step of the catalytic cycle, oxidative addi-
tion to Pd(0) complexes. As a result, the catalyst is
removed from the main catalytic cycle owing to
the competing Pd(0) aggregation.
The catalytic systems free of any ligands and, in
particular, of the commonly used phosphines are of
particular practical interest. Homogeneous phosphine-
free catalytic systems containing simple palladium
] and capable of activating
nonreactive aryl bromides were developed in 2003
. The reaction is accelerated with as the cata-
lyst amount decreases [8, 9]. Introduction of small
amounts of NaOOCH reducing Pd(II) to catalytically
active Pd(0) and of an excess of aryl halides prevent-
ing aggregation of Pd(0) enabled not only quantitative
arylation of an alkene , but also a larger turnover
number of the catalyst [7, 11], including reactions
with aryl chlorides . Clearly, the use of an excess
aryl halide substantially restricts the practical appli-
cability of this method. Hence we suggest simple
ways to raise the yield of the valuable product based
on aryl bromide, taken in excess, with the high
catalytic performance of the system developed in our
previous studies [10, 11] preserved.
The reactions were performed in a temperature-
controlled reaction vessel equipped with a magnetic
stirrer under aerobic conditions. The solvent was di-
methylformamide (DMF). The samples taken at regu-
lar intervals were analyzed on a HP-4890 gas3liquid
chromatograph with using a flame-ionization detector
and a 15-m HP-5 capillary column (Hewlett3Packard).
Naphthalene was used as the internal reference.
The analysis was performed under programmed heat-
ing from 100 to 250oC. The solvents and chemicals
were purified by the conventional methods. The model
reaction of styrene with bromobenzene was performed
by the previously developed procedure . PhBr
(60 mmol), styrene (10 mmol), NaOAc (11.2 mmol),
NaOOCH (1.8 mmol), and naphthalene (2 mmol, in-
ternal reference for GLC) were dissolved in DMF
(10 ml) in the reaction vessel. Then, a freshly pre-
pared solution of Pd(PhCN)
(2.5 0 10
in 25 ml
of DMF, 0.1 ml) was added. The reaction vessel was
placed in an oil bath preheated to 140oC. The reac-
tion mixture was stirred with a magnetic stirrer. After
the reaction was complete, the liquid phase was distil-