Polymer-incarcerated palladium with active phosphine as recoverable and reusable Pd catalyst for the amination of aryl chlorides

Article abstract of DOI:10.1055/s-2007-1000816

A new type of polymer-incarcerated (PI) Pd catalyst bearing an active phosphine ligand has been developed. This catalyst was prepared easily according to a conventional PI method (microencapsulation and cross-linking of polymer chains), and TEM images of PI Pd showed the formation of small Pd clusters dispersed on the polymer support without formation of Pd aggregates. The catalyst showed high activity in amination reactions of various aryl chlorides with amines. The reactions proceeded without addition of any external phosphine ligands, and the catalyst was recovered quantitatively by simple filtration and reused at least three times without loss of activity. Georg Thieme Verlag Stuttgart.

Full text of DOI:10.1055/s-2007-1000816

LETTER
3209
Polymer-Incarcerated Palladium with Active Phosphine as Recoverable and
Reusable Pd Catalyst for the Amination of Aryl Chlorides
Polymer
I
ncarce
a
rated
P
alla
k
dium as Rec
e
overable an
s
dReusab
h
Department of Chemistry, School of Science and Graduate School of Pharmaceutical Sciences, The University of Tokyo,
The HFRE Division, ERATO, Japan and Science Technology Agency (JST), Hongo, Bunkyo-ku, Tokyo 1130033, Japan
Fax +81(3)56840634; E-mail: shu_kobayashi@chem.s.u-tokyo.ac.jp
Received 4 October 2007
catalyst that contains more active phosphine ligand, and
Abstract: A new type of polymer-incarcerated (PI) Pd catalyst
its application to amination reactions of aryl chlorides.
bearing an active phosphine ligand has been developed. This cata-
lyst was prepared easily according to a conventional PI method (mi-
croencapsulation and cross-linking of polymer chains), and TEM
images of PI Pd showed the formation of small Pd clusters dispersed
on the polymer support without formation of Pd aggregates. The
catalyst showed high activity in amination reactions of various aryl
chlorides with amines. The reactions proceeded without addition of
any external phosphine ligands, and the catalyst was recovered
quantitatively by simple filtration and reused at least three times
without loss of activity.
Within the first generation Pd catalysis of aromatic ami-
nation reactions, triarylphosphine-based ligands8 were of-
ten employed for their easy availability and stability
towards oxidation. However, the reactions are normally
conducted at high temperatures and aryl chlorides are un-
reactive as substrates, mainly because of retardation due
to a slow oxidative addition step. Accordingly, a phosph-
inated PI Pd on diphenylphosphine basis displayed only
low activity with aryl chloride substrates; hence a more
active phosphine had to be incorporated.
Key words: heterogeneous catalysis, polymer, aminations, palladi-
um, aryl chlorides
In general bulky electron-rich phosphines were shown to
enable amination reactions of aryl chlorides under mild
conditions,9 with dialkylbiphenylphosphines being
among the most versatile due to their air stability10 and
high catalytic activity of their Pd complexes. These
ligands have been extensively studied by Buchwald’s
group, and they showed that amination of aryl chlorides
proceeded in high yields by using these ligands under
mild homogeneous conditions.9a–f
Palladium-catalyzed coupling reactions are known as one
of the most valuable tools for C–C, C–N and C–O bond
formation and have been widely used in a variety of trans-
formations in organic synthesis.1 Recently these systems
have attracted a great deal of attention from an economic
and environmental point of view and immobilization of
Pd catalysts on inorganic solid supports2 or organic
polymers3 has been widely studied. Among these, hetero-
geneous catalysts for Suzuki–Miyaura coupling4 or Heck
reaction3d,5 have been of great interest. On the other hand,
to the best of our knowledge, only limited numbers of ex-
amples of heterogeneous arylamination reactions have
been reported;6 in particular, investigation of the amina-
tion of aryl chlorides using immobilized Pd catalysts is
very limited, even though these reactions have found
widespread use in many areas of organic synthesis.
We first prepared copolymer 1, and PI Pd 2 was prepared
from Pd(OAc)2 and 1 according to a conventional PI
method (microencapsulation and cross-linking of polymer
chains) as reported previously (Scheme 1).11 ICP analysis
showed that palladium was loaded onto the polymer sup-
port nearly quantitatively (93%). In a previous report, we
have shown that immobilization of palladium onto poly-
mer supports was not successful in the absence of addi-
tives such as alkali metal salts.7d The fact that these
additives were not necessary in the present case indicates
that the phosphine moieties incorporated into the polymer
support acted as stabilizers for Pd immobilization. In ad-
dition, we believe that the phosphine moieties play a role
in the reduction of the Pd(II) salt, since some phosphines
were observed to be oxidized to the corresponding phos-
phine oxides during the preparation of the catalyst.
The PI Pd 212 thus prepared was then analyzed by trans-
mission electron microscopy (TEM). Judging from the
magnified TEM image of PI Pd 2 (Figure 1), small Pd
clusters were dispersed on the polymer support without
formation of Pd aggregates (TEM detection limit: ca. 1
nm). The formation of extremely small Pd clusters might
be due to a stabilization effect of the polymer and the
phosphine moieties.
In previous papers, we have demonstrated the polymer-in-
carcerated (PI) method for immobilization of palladium
catalysts onto polystyrene-based polymers.7 The hetero-
geneous PI palladium catalysts obtained are highly active
for hydrogenation and carbon–carbon bond-forming reac-
tions. These catalysts can be recovered quantitatively by
simple filtration and reused several times without loss of
activity. Among them, phosphinated PI Pd catalysts,
whose polymer supports contain diphenylphosphino
groups, are highly active for Suzuki–Miyaura coupling re-
actions without addition of external phosphine ligands.7c
In this paper, we report a new type of phosphinated PI Pd
SYNLETT 2007, No. 20, pp 3209–3213
x
x
.x
x
.2
0
0
7
Advanced online publication: 21.11.2007
DOI: 10.1055/s-2007-1000816; Art ID: U09507ST
© Georg Thieme Verlag Stuttgart · New York

3210
T. Inasaki et al.
LETTER
O
O
OH
4
O
Pd(OAc)2
coacervation
hexane
x
y
z
w
1) filtration
THF, reflux, 3 h
2) washing (hexane)
3) drying
cross-linking
PCy2
PI Pd 2
O
1) filtration
no solvent
1 (x:y:z:w = 65:7:6:22)
2) washing (THF)
3) drying
120 °C, 3 h
Scheme 1 Preparation of polymer incarcerated palladium (PI Pd 2) with active phosphine ligands
With the catalyst in hand we turned our attention to the in-
vestigation of its catalytic activity. First, PI Pd 2 was com-
pared with common heterogeneous catalysts or the
previously reported phosphinated PI Pd catalyst7c in the
coupling reaction of morpholine and 4-chlorotoluene
(Table 1). As shown, use of Pd/C, a commonly used het-
erogeneous palladium catalyst, did not promote the reac-
tion at all (entry 1). Addition of o-(dicyclo-
hexylphosphino)biphenyl to Pd/C as an external phos-
phine ligand resulted in the formation of trace amounts of
the desired product (entry 2). As expected, PI Pd 3 with
diphenylphosphino groups did not yield Pd catalysts with
an appropriate activity for oxidative addition to a chloro–
arene bond (entry 3). However on using PI Pd 2, we were
delighted to find that the coupling reaction proceeded in
good yield (entry 4). Thus it is noted that the PI method
gave a catalyst system that showed high catalytic activity
and low Pd leaching in the amination of an aryl chloride.
Figure 1 TEM image of PI Pd 2
Table 1 Comparison of Catalytic Activity
[Pd] (2 mol%)
NaOt-Bu
+
Cl
HN
O
N
O
toluene
100 °C, 4 h
Next, we surveyed the substrate scope of PI Pd 2-cata-
lyzed amination reactions (Table 2). Using PI Pd 2 as a
catalyst, aryl chlorides could be successfully utilized as
substrates. In the reactions using both electron-rich and
electron-deficient aryl chlorides, the corresponding aryl-
amine products were obtained in high yields. It is note-
worthy that the detected leaching values of palladium
were very low. In addition, the reactions proceeded effec-
tively using lower catalyst loadings (0.4 mol% Pd, entries
3 and 7). As for amine substrates, aromatic primary
amines, aromatic secondary amines, aliphatic primary
amines and aliphatic secondary amines were all coupled
efficiently with various aryl halides in good yields. How-
ever, in the cases of reactions of aliphatic primary amines
in toluene (entries 14 and 16), the leaching values of pal-
ladium were much higher than those with other substrates.
We supposed that this was due to a slower reductive elim-
ination reaction in the case of primary amines, which were
less bulky than secondary amines, and reasoned that the
slower the rate of the reductive elimination, the longer the
lifetime of palladium(II) species such as arylpalladium(II)
amides. It is thought that PI catalysts were able to stabilize
metal species onto their support by electronic interaction
between vacant orbitals of metal species and p-electrons
of benzene rings. However, unlike palladium(0) species,
palladium(II) species are more susceptible to ionic inter-
action of anionic species like tert-butoxide ions, rather
Entry ‘Pd’
Additive (4 mol%) Yield (%)a Leaching (%)b
1
Pd/C
–
0
0.03
Cy2P
2
Pd/C
tracec
0.23
3
4
PI Pd 3d
PI Pd 2
–
–
0
0.11
0.87
87
a Isolated yield.
b Determined by ICP analysis.
c Trace < 1%.
d PI Pd 3 was prepared from copolymer 4 by the previously reported
method.7c The loading amount of the palladium was 0.23 mmol/g.
O
O
OH
4
O
x
y
z
w
PPh2
4 (x:y:z:w = 80:4:4:12)
Synlett 2007, No. 20, 3209–3213 © Thieme Stuttgart · New York

LETTER
Polymer Incarcerated Palladium as Recoverable and Reusable Catalyst
3211
than electronic effect of benzene rings. For this reason, it the reactions were conducted by method C (Table 2), the
was assumed that palladium(II) species were leached reactions proceeded within two hours in good yields, and
from the support more easily than palladium(0) species the leaching values of palladium were greatly reduced
under typical basic conditions of arylamination reactions. compared to those observed with method B.
For the reason mentioned above, we thought that acceler- Finally, we examined the reusability of the PI Pd catalyst.
ation of the rate of the reductive elimination would sup- As shown in Table 3, the PI Pd could be recovered quan-
press the leaching of palladium. In order to examine the titatively by simple filtration and reused at least three
possibility of accelerating the catalytic cycle including the times. The catalytic activity and the reaction rate were
reductive elimination step, we selected another solvent typically unaffected and the reactions were complete
system, p-dioxane–tert-butyl alcohol, which led to en- within four hours even in the third consecutive reaction.
hanced reaction rates and conversion.9d In this way, when Furthermore, it was confirmed by ICP analysis that palla-
Table 2 Phosphinated PI Pd-Catalyzed Amination Reactionsa,12
Entry ArCl
Amine
PI Pd 2 (mol%) Methodb
Time (h)
Yield (%)c
Pd leaching (%)d
1
2
2
2
B
B
8
8
95
97
0.96
0.56
X = Br
X = Cl
X
H2N
3
0.4
A
B
B
24
77
92
89
0.84
0.12
nd
MeHN
MeHN
Cl
4
2
8
Cl
5
2
8
MeHN
HN
MeO
Cl
6
7
2
0.4
A
A
24
24
92
91
0.64
1.10
O
O
O
Cl
8
2
2
A
A
24
24
92
84
0.74
0.32
NC
Cl
HN
9
MeO
Cl
HN
OMe
10
2
B
8
73
0.19
HN
O
Cl
11
12
2
2
B
B
24
24
94
73
0.26
0.71
Cl
Cl
HN
Bu
HN
Bu
Me
HN
13
2
B
24
96
nd
Cl
Bn
14
15
2
2
B
C
8
2
92
92
9.88
2.79
H2NC6H13
Cl
Cl
16
17
2
2
B
C
8
2
97
89
8.92
1.04
H2N
a Reaction conditions: aryl halide (1.0 equiv), amine (2.0 equiv), t-BuONa (2.3 equiv).
b Method A: toluene, 100 °C. Method B: toluene, 110 °C. Method C: p-dioxane–t-BuOH (3:1), 100 °C.
c Isolated yield.
d Determined by ICP analysis; nd = not determined (<0.07%).
Synlett 2007, No. 20, 3209–3213 © Thieme Stuttgart · New York

3212
T. Inasaki et al.
LETTER
(6) (a) Parrish, C. A.; Buchwald, S. L. J. Org. Chem. 2001, 66,
3820. (b) Guinó, M.; Hii, K. K. Tetrahedron Lett. 2005, 46,
7363. (c) Leyva, A.; García, H.; Corma, A. Tetrahedron
2007, 63, 7097. (d) Nishio, R.; Sugiura, M.; Kobayashi, S.
Chem. Asian J. 2007, 2, 983. (e) To the best of our
knowledge reports on the amination of aryl chlorides using
immobilized Pd catalysts have been very limited, and in no
case, except in ref. 6d, was information relating to Pd
leaching reported. On the other hand, Lipshutz et al. reported
Ni/C catalysis for the amination: Lipshutz, B. H.; Ueda, H.
Angew. Chem. Int. Ed. 2000, 39, 4492. (f) Lipshutz, B. H.;
Tasler, S.; Chrisman, W.; Spliethoff, B.; Tesche, B. J. Org.
Chem. 2003, 68, 1177. (g) Tasler, S.; Lipshutz, B. H. J. Org.
Chem. 2003, 68, 1190.
(7) Polymer incarcerated catalysts: (a) Akiyama, R.;
Kobayashi, S. J. Am. Chem. Soc. 2003, 125, 3412.
(b) Takeuchi, M.; Akiyama, R.; Kobayashi, S. J. Am. Chem.
Soc. 2005, 127, 13096. (c) Nishio, R.; Sugiura, M.;
Kobayashi, S. Org. Lett. 2005, 7, 4831. (d) Hagio, H.;
Sugiura, M.; Kobayashi, S. Org. Lett. 2006, 8, 375.
(e) Okamoto, K.; Akiyama, R.; Yoshida, H.; Yoshida, T.;
Kobayashi, S. J. Am. Chem. Soc. 2005, 127, 2125.
(f) Kobayashi, S.; Miyamura, H.; Akiyama, R.; Ishida, T.
J. Am. Chem. Soc. 2005, 127, 9251.
dium leaching was low in each case. In addition, it was
noted that the leaching values decreased gradually in each
successive reaction, and in particular the leaching after the
third reaction approached the limit of determination
(0.07%).
Table 3 Recovery and Reuse of PI Pd 2
PI Pd 2 (2 mol%)
NaOt-Bu
+
Cl HN
O
N
O
toluene
100 oC, 4 h
Run
First
87
Second
89
Third
95
Yield (%)a
Pd leaching (%)b
a Isolated yield.
1.50
0.42
0.09
b Determined by ICP analysis.
In summary, we have developed a new type of PI Pd cat-
alyst that contains active phosphine ligands. This catalyst
showed high activity in amination reactions of various
aryl chlorides with amines. The reactions proceeded with-
out addition of any external phosphine ligands, and the
catalyst could be recovered quantitatively by simple filtra-
tion and reused at least three times without loss of activity.
We believe that this report has shown the first efficient
amination of aryl chlorides using an immobilized Pd cat-
alyst based on the PI method.
(8) (a) Wolfe, J. P.; Wagaw, S.; Marcoux, J.-F.; Buchwald, S. L.
Acc. Chem. Res. 1998, 31, 805. (b) Wolfe, J. P.; Wagaw, S.;
Buchwald, S. L. J. Am. Chem. Soc. 1996, 118, 7215.
(c) Hartwig, J. F. Acc. Chem. Res. 1998, 31, 852.
(9) (a) Old, D. W.; Wolfe, J. P.; Buchwald, S. L. J. Am. Chem.
Soc. 1998, 120, 9722. (b) Wolfe, J. P.; Buchwald, S. L.
Angew. Chem. Int. Ed. 1999, 38, 2413. (c) Wolfe, J. P.;
Tomori, H.; Sadighi, J. P.; Yin, J.; Buchwald, S. L. J. Org.
Chem. 2000, 65, 1158. (d) Ali, M. H.; Buchwald, S. L. J.
Org. Chem. 2001, 66, 2560. (e) Zim, D.; Buchwald, S. L.
Org. Lett. 2003, 5, 2413. (f) Charles, M. D.; Schultz, P.;
Buchwald, S. L. Org. Lett. 2005, 7, 3965. (g) Hamann, B.
C.; Hartwig, J. F. J. Am. Chem. Soc. 1998, 120, 7369.
(h) Stauffer, S. R.; Lee, S.; Stambuli, J. P.; Hauck, S. I.;
Hartwig, J. F. Org. Lett. 2000, 2, 1423. (i) Shen, Q.;
Shekhar, S.; Stambuli, J. P.; Hartwig, J. F. Angew. Chem. Int.
Ed. 2005, 44, 1371. (j) Shen, Q.; Hartwig, J. F. J. Am. Chem.
Soc. 2006, 128, 10028.
References and Notes
(1) (a) Tsuji, J. Palladium Reagents and Catalysts; Wiley:
Chichester, 1995. (b) Handbook of Organopalladium
Chemistry for Organic Synthesis; Negishi, E., Ed.; John
Wiley and Sons: New York, 2002. (c) Stahl, S. S. Angew.
Chem. Int. Ed. 2004, 43, 3400.
(2) (a) Yin, L. X.; Liebscher, J. Chem. Rev. 2007, 107, 133.
(b) Kwon, M. S.; Kim, N.; Park, C. M.; Lee, J. S.; Kang, K.
Y.; Park, J. Org. Lett. 2005, 7, 1077. (c) Kim, N.; Kwon, M.
S.; Park, C. M.; Park, J. Tetrahedron Lett. 2004, 45, 7057.
(d) Choudary, B. M.; Madhi, S.; Chowdari, N. S.; Kantam,
M. L.; Sreedhar, B. J. Am. Chem. Soc. 2002, 124, 14127.
(3) (a) Lin, C.-A.; Luo, F.-T. Tetrahedron Lett. 2003, 44, 7565.
(b) Luo, F.-T.; Xue, C.; Ko, S.-L.; Shao, Y.-D.; Wu, C.-J.;
Kuo, Y.-M. Tetrahedron 2005, 61, 6040. (c) Chauhan, B.
P.; Rathore, J. S.; Chauhan, M.; Krawicz, A. J. Am. Chem.
Soc. 2003, 125, 2876. (d) Biffs, A.; Zecca, M.; Basato, M.
J. Mol. Catal. A: Chem. 2001, 173, 249.
(4) (a) Tsang, C.-W.; Baharloo, B.; Riendl, D.; Yam, M.; Gates,
D. P. Angew. Chem. Int. Ed. 2004, 43, 5682. (b) Li, J.-H.;
Hu, X.-C.; Xie, Y.-X. Tetrahedron Lett. 2006, 47, 9239.
(c) He, H. S.; Yan, J. J.; Shen, R.; Zhuo, S.; Toy, P. H. Synlett
2006, 563. (d) Yamada, Y. M. A.; Takeda, K.; Takahashi,
H.; Ikegami, S. Tetrahedron Lett. 2003, 44, 2379.
(10) Barder, T. E.; Buchwald, S. L. J. Am. Chem. Soc. 2007, 129,
5096.
(11) Microencapsulated catalysts: (a) Kobayashi, S.; Nagayama,
S. J. Am. Chem. Soc. 1998, 120, 2985. (b) Nagayama, S.;
Endo, M.; Kobayashi, S. J. Org. Chem. 1998, 63, 6094.
(c) Kobayashi, S.; Endo, M.; Nagayama, S. J. Am. Chem.
Soc. 1999, 121, 11229. (d) Kobayashi, S.; Ishida, T.;
Akiyama, R. Org. Lett. 2001, 3, 2649. (e) Akiyama, R.;
Kobayashi, S. Angew. Chem. Int. Ed. 2001, 40, 3469.
(f) Akiyama, R.; Kobayashi, S. Angew. Chem. Int. Ed. 2002,
41, 2602.
(12) Preparation of Copolymer 1: Styrene (2.24 g, 21.6 mmol),
2-[(2-phenylallyloxy)methyl]oxirane (630 mg, 3.32 mmol),
tetraethyleneglycol mono-2-phenyl-2-propenyl ether (1.03
g, 3.32 mmol), dicyclohexyl-2-[4¢-(4-styrylmeth-
oxy)phenyl]phenylphosphine (2.40 g, 4.97 mmol) and 2,2¢-
azobis(isobutyronitrile) (54.4 mg, 0.332 mmol) were mixed
in CHCl3 (4.2 mL). The mixture was stirred at reflux for 27
h under argon and was then cooled to r.t. The resulting
polymer solution was poured slowly into hot deoxygenated
hexane and the precipitated polymer was collected by
filtration and washed with hexane. The polymer so obtained
was dissolved in CHCl3, and the resulting solution was
poured slowly into MeCN. The precipitated polymer was
filtered and washed with MeCN several times and dried in
(5) (a) Yamada, Y. M. A.; Tabata, H.; Takahashi, H.; Ikegami,
S. Synlett 2002, 2031. (b) Zhang, Z.; Wang, Z. J. Org.
Chem. 2006, 71, 7485. (c) Singh, G.; Bali, S.; Singh, A. K.
Polyhedron 2006, 26, 897. (d) Djakovitch, L.; Koehler, K.
J. Am. Chem. Soc. 2001, 123, 5990.
Synlett 2007, No. 20, 3209–3213 © Thieme Stuttgart · New York

LETTER
Polymer Incarcerated Palladium as Recoverable and Reusable Catalyst
3213
vacuo to afford the desired copolymer 1 (3.67 g, 58%). The
of the residue was adjusted to 50 mL using hexane. The
solution was then divided into two halves.
molar ratio of the monomer was determined by 1H NMR
analysis {styrene–2-[(2-phenylallyloxy)methyl]oxirane–
tetraethyleneglycol mono-2-phenyl-2-propenyl ether–
dicyclohexyl-2-[4¢-(4-styrylmethoxy)phenyl]phen-
ylphosphine = 65:7:6:22}. 31P NMR (162 MHz, CDCl3): d =
–12.9, 48.5. Mw: 11520, Mn: 8470, Mw/Mn = 1.36 (GPC).
Preparation of PI Pd 2: Copolymer 1 (3.66 g) was
dissolved in THF (20 mL) and the solution was refluxed
under argon. A solution of palladium acetate (177 mg, 0.79
mmol) in THF (20 mL) was added dropwise to the polymer
solution, and the reaction mixture was refluxed under argon
for 3 h, and then cooled to r.t. Hexane (80 mL) was then
slowly added to the mixture. The mixture was left to stand at
r.t. for 1 h, and the precipitated catalyst capsules were
washed with hexane several times and dried at r.t. in vacuo.
Next, the catalyst capsules were stirred at 120 °C for 4 h
under reduced pressure to cross-link the microencapsulated
palladium. The cross-linked solid was then washed with
THF, toluene and hexane, and then dried in vacuo to give the
polymer incarcerated palladium (PI Pd 2, 3.54 g); loading
value of palladium metal: 0.19 mmol/g; the ratio of
phosphorus atoms in the polymer to palladium atoms (P/Pd):
5.71.
One portion was placed in a 50-mL test tube and the solvent
was removed by evaporation. To this mixture was added
sulfuric acid (1.0 mL), and the mixture was heated at 180 °C.
Then nitric acid (0.5 mL) was added dropwise to decompose
the organic residue. After cooling to r.t., the solution was
adjusted to 25 mL by H2O and then the amount of palladium
metal was measured by ICP analysis to determine the
leaching of palladium.
The other portion of the reaction mixture was taken, and the
solvents were removed by evaporation. The residual crude
product was purified by preparative TLC on silica gel
(hexane–EtOAc, 10:1) to afford N-(4-methylphenyl)aniline
(53.3 mg, 97%). 1H NMR (400 MHz, CDCl3): d = 2.29 (s, 3
H), 5.58 (s, 1 H), 6.87 (t, J = 7.6 Hz, 1 H), 6.99–7.02 (m, 4
H), 7.08 (d, J = 8.0 Hz, 1 H), 7.24 (dd, J = 7.6, 8.0 Hz, 2 H).
13C NMR (100 MHz, CDCl3): d = 20.7, 116.9, 118.9, 120.3,
129.3, 129.9, 130.9, 140.3, 143.9.
Typical Recycling Procedures: 4-Chlorotoluene (144.4
mg, 1.14 mmol), morpholine (197.6 mg, 2.27 mmol), PI Pd
2 (120.4 mg, 0.023 mmol, 2 mol%), and t-BuONa (250.6
mg, 2.61 mmol) were combined in toluene (3.8 mL) under
argon. The mixture was stirred for 4 h at 100 °C. After
cooling to r.t., the mixture was diluted with hexane (10 mL)
and filtered. The collected catalyst was further washed with
hexane and toluene, and then filtered. The combined organic
washing solutions were subjected to the procedures
described above for product isolation and detection of
palladium leaching. The catalyst was rinsed with H2O and
MeOH and was then dried in vacuo. The catalyst was reused
without any other purification step.
Typical Experimental Procedure for Phosphinated PI
Pd-Catalyzed Amination (Table 2, entry 2): 4-Chloro-
toluene (76.0 mg, 0.6 mmol), aniline (111.8 mg, 1.2 mmol),
PI Pd 2 (63.5 mg, 0.012 mmol, 2 mol%), and t-BuONa
(132.6 mg, 1.38 mmol) were combined in toluene (2 mL)
under argon. The mixture was stirred for 8 h at reflux. After
cooling to r.t., the mixture was diluted with hexane (6 mL),
filtered and rinsed with hexane and toluene. The combined
organic layers were concentrated in vacuo, and the volume
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