Yamada et al.
catalytic cycle will be reached. On the basis of such a
hypothesis, we developed a tungsten catalyst, PWAA,
formed from H3PW12O40 and poly{[3-(acryloylamino)-
species and non-cross-linked amphiphilic polymers with
phosphine ligands and found that the complexation of 1
and 2 afforded a novel palladium-polymer catalyst,
PdAS (Pd-acrylamide-styrylphosphine). As shown in
Scheme 2,6 random copolymerization of 4-diphenyl-
styrylphosphine (4) with 12 mol equiv of N-isopropyl-
acrylamide (5) in the presence of 4 mol % AIBN gave 2
in 89% yield. The ratio of the phosphine to the amide
units in 2 was determined by 1H NMR measurements in
CDCl3 to be 1/10, and the phosphine unit was hardly
oxidized in this polymerization as shown by 31P NMR.
This ratio of the phosphine to the amide units, 1/10, was
reproducible in several experiments. The molecular
weight of 2 was wide-ranging (ca. 5000-70000) as a
result of gel-permeation chromatography relative to
polystyrene standards. Self-assembly of 1 and 2 was
investigated under conditions similar to those for the
preparation of PdCl2(PPh3)2.7 To a well-stirred solution
of 2 (3 mol equiv in phosphine) in THF was added a
solution of 1 (1 mol equiv) in H2O. The mixture was
stirred for 62 h at room temperature, and a precipitate
was formed. After water was added to the suspension,
THF was removed at 80 °C for 4 h with Dean-Stark
equipment. For removal of a trace amount of unreacted
palladium species and polymers, the suspension was
stirred at 100 °C successively in H2O, in THF, and in
H2O. After the suspension was dried in vacuo, a dark red
solid, PdAS (3), was obtained in almost quantitative yield.
It was insoluble in water and organic solvents such as
acetone, CH3OH, CH2Cl2, AcOEt, THF, and hexane.
propyldodecyldimethylammonium
nitrate]-co-(N-iso-
propylacrylamide)12} for oxidation.3a,d Since this self-
assembled catalyst exhibited great potential, we next
extended this methodology to a palladium catalyst ap-
plicable to the Suzuki-Miyaura reaction, which is the
palladium-catalyzed cross-coupling reaction of halides or
triflates with boronic acids or their esters. This reaction
is one of the most important, powerful, and versatile tools
for the synthesis of biologically active compounds and
liquid crystals.4 Although many heterogeneous catalysts,
including Pd/C, have been applied to the Suzuki-
Miyaura reaction,5 homogeneous catalytic systems still
have advantages in catalytic activity.
In this paper, we describe the development of an
assembled catalyst, PdAS, prepared from (NH4)2PdCl4 (1)
and non-cross-linked amphiphilic polymer poly[(N-iso-
propylacrylamide)-co-(4-diphenylstyrylphosphine)] (2) and
its application to the heterogeneous Suzuki-Miyaura
reaction. The coupling of aryl and alkenyl halides with
arylboronic and alkenylboronic acids was efficiently
catalyzed by 8 × 10-7 to 5 × 10-4 mol equiv of PdAS. It
should be noted that the highest turnover number (TON
() mol of product/mol of catalyst)) of PdAS reached up
to 1 250 000. To our knowledge, this is the highest TON
value by a reusable catalyst for the Suzuki-Miyaura
reaction. PdAS showed outstanding stability in any
reaction medium such as water or aqueous or anhydrous
organic solvents and was reused 10 times without loss
of activity.
To obtain information on the structure of the catalyst,
3 was characterized by gel-phase 31P NMR in CDCl3.
While a peak of 2 was observed at -2.9 ppm (ArPh2P),
two broad peaks of 3 were detected at 32.5 and 26.1 ppm,
which must be assigned to the signals of ArPh2PdO and
PdCl2(PPh2Ar)2, respectively; i.e., the phosphines in 2
coordinated with palladium to form a Pd(II) complex. In
our preliminary experiments, it was elucidated that the
complexation of 1 and poly(N-isopropylacrylamide) with-
out phospine units afforded no precipitates. Considering
these results, it could be confirmed that the phosphine
ligands of 2 cross-linked with palladium (Scheme 2).
Resu lts a n d Discu ssion
Develop m en t of a n Assem bled Ca ta lyst, P d AS. We
examined self-assembly between various palladium
(4) For reviews, see: (a) Miyaura, N.; Suzuki, A. Chem. Rev. 1995,
95, 2457-2483. (b) Suzuki, A. J . Organomet. Chem. 1999, 576, 147-
168. (c) Organometallics in Synthesis A Manual, Schlosser, M., Ed.;
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Ca t a lyt ic Act ivit y of P d AS for t h e Su zu k i-
Miya u r a Rea ction . The catalytic activity of PdAS for
the heterogeneous Suzuki-Miyaura reaction was inves-
tigated. (Table 1). Since “water” is the most safe and
easily available solvent, numerous attempts have been
made in utilizing it in organic reactions.8 While the
development of catalytic systems in water has been
confronted with many difficulties, PdAS will be a key to
developing an efficient system in water owing to its
amphiphilicity. Therefore, all the reactions in Tables 1-3
and Scheme 3 were performed in water under organic-
solvent-free conditions. The reaction of iodobenzene (6a )
(5) For recent developments and improvements for heterogeneous
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7734 J . Org. Chem., Vol. 68, No. 20, 2003