The first synthesis of stable palladium(II) PCP-type catalysts supported on silica - Application to the heck reaction

Article abstract of DOI:10.1016/S1381-1169(03)00158-4

An efficient method for the formation of a silica-immobilized tridentate diphosphinoaryl ligand (PCP-type) palladium(II) complex (11) is described and successfully used as a catalyst for the Heck reaction. Commercially available 5-amino-isophthalic acid dimethyl ester was converted to N-acetyl-3,5-bis(chloromethyl)aniline (4) in three steps, by reduction, acetylation, and chlorination (Scheme 1). Arbuzov reaction of 4 led to the diphosphine oxide (5). Deprotection and functional group manipulations allowed the transformation of 5 into N-[3,5-bis-(diphenyl-phosphinoylmethyl)-phenyl]-succinamic acid (7). Subsequent reduction of 7 with HSiCl₃ afforded the diphosphine (8) attached to silica by transforming compound 8 to N-{3,5-bis[(diphenyl-phosphanyl)methyl]-phenyl}-succinamic acid 2,5-dioxo-pyrrolidin-1-yl ester (9). Palladium(II) trifluoroacetate was used to form the PCP-type palladium(II) complex. This complex shows high catalytic activity in the Heck reaction for aryl iodides, and it is also active with aryl bromides. The catalyst is thermally stable and it is also stable towards oxygen and moisture. In addition, it can be recycled by simple filtration in air and reused with moderate loss of activity.

Full text of DOI:10.1016/S1381-1169(03)00158-4

Journal of Molecular Catalysis A: Chemical 201 (2003) 23–31
The first synthesis of stable palladium(II) PCP-type catalysts
supported on silica—application to the Heck reaction
Ratana Chanthateyanonth, Howard Alper∗
Centre for Catalysis Research and Innovation, Department of Chemistry, University of Ottawa,
10 Marie Curie, Ottawa, Ont., Canada K1N 6N5
Received 19 February 2003; accepted 19 February 2003
Abstract
An efficient method for the formation of a silica-immobilized tridentate diphosphinoaryl ligand (PCP-type) palladium(II)
complex(11)isdescribedandsuccessfullyusedasacatalystfortheHeckreaction. Commerciallyavailable5-amino-isophthalic
acid dimethyl ester was converted to N-acetyl-3,5-bis(chloromethyl)aniline (4) in three steps, by reduction, acetylation,
and chlorination (Scheme 1). Arbuzov reaction of 4 led to the diphosphine oxide (5). Deprotection and functional group
manipulations allowed the transformation of 5 into N-[3,5-bis-(diphenyl-phosphinoylmethyl)-phenyl]-succinamic acid (7).
Subsequent reduction of 7 with HSiCl3 afforded the diphosphine (8) attached to silica by transforming compound 8 to
N-{3,5-bis[(diphenyl-phosphanyl)methyl]-phenyl}-succinamic acid 2,5-dioxo-pyrrolidin-1-yl ester (9). Palladium(II) triflu-
oroacetate was used to form the PCP-type palladium(II) complex. This complex shows high catalytic activity in the Heck
reaction for aryl iodides, and it is also active with aryl bromides. The catalyst is thermally stable and it is also stable towards
oxygen and moisture. In addition, it can be recycled by simple filtration in air and reused with moderate loss of activity.
© 2003 Elsevier Science B.V. All rights reserved.
Keywords: PCP-type Pd(II) catalysts; Heck reaction; Silica-immobilized catalysts
1. Introduction
support can, in principle, retain the properties ob-
served for the homogeneous system and allow simple
separation from the reaction mixture.
Homogeneous catalysis is widely used in organic
chemistry as the pre-catalysts are usually commer-
cially available and well defined [1,2], and some
catalysts exhibit high selectivity and activity [3–5],
although product separation and especially catalyst
recovery can be difficult. On the other hand, heteroge-
neous catalysts can be easily separated and recycled
[6], thus making some processes more economical,
and environmentally friendly. Immobilization of the
homogeneous catalyst by means of a heterogeneous
The Heck reaction is an important method for C–C
bond formation [7,8]. However, this reaction usually
requires quite high catalyst loading (up to 10 mol%
of Pd). Recently, supported catalysts, including den-
drimers, have displayed to be very useful in organic
synthesis [9,10]. It was also shown that palladium
complexed dendrimers immobilized on silica are good
catalysts for the Heck reaction [11]. It has also been
reported that palladium complexes with pincer ligands
are excellent catalysts for the Heck reaction [5,12–14].
Compound 1 (Fig. 1), prepared by direct cyclomet-
allation, has been shown to be a highly active cata-
lyst for the Heck reaction. It is also thermally stable
∗
Corresponding author. Tel.: +1-613-562-5189;
fax: +1-613-562-5871.
E-mail address: halper@uottawa.ca (H. Alper).
1381-1169/03/$ – see front matter © 2003 Elsevier Science B.V. All rights reserved.
doi:10.1016/S1381-1169(03)00158-4

24
R. Chanthateyanonth, H. Alper / Journal of Molecular Catalysis A: Chemical 201 (2003) 23–31
stopcock in an M. Braun GmbH glovebox. The sample
was then removed from the drybox, placed under high
vacuum and, without breaking vacuum, sealed off at
30 mm lengths. The tubes were then placed in zirconia
rotors that were used in the Bruker ASX-200 instru-
ment.
Fig. 1. Complex 1.
2.2. Procedure
up to 180 ◦C and not sensitive to oxygen and mois-
ture [5]. Furthermore, it was reported that when the
alkyl substituents on phosphorus were substituted for
the weakly electron-withdrawing phenyl groups, direct
cyclometallation could proceed at room temperature
[15].
In this paper, we report the successful immobiliza-
tion of a PCP-type palladium(II) complex onto silica
under mild conditions; an approach that combines the
advantages of heterogeneous and homogeneous cata-
lysts. This complex is a good catalyst for the Heck re-
action and can easily be recycled. It is also thermally
stable up to 170 ◦C and quite air stable.
2.2.1. Synthesis of N-[3,5-bis-
(diphenyl-phosphinoylmethyl)-phenyl]-
acetamide (5)
A modified literature procedure was used [18] In
a two-necked 100-ml round bottom flask, a stirred
suspension of Ph2POEt (7.4 g, 32 mmol) and com-
pound 4 (1.8 g, 8.0 mmol) in toluene (90 ml) was
refluxed for 20 h. The reaction mixture was cooled
to room temperature and the white precipitated solid
was filtered, washed with benzene, and dried in vacuo
to afford compound 5 as a white solid, which was
sufficiently pure for further synthesis. Yield: 4.4 g
(90%). 1H NMR (300.13 MHz, CD3OD) δ (ppm)
7.78–7.48 (m, 20H, ArH), 7.21 (s, 2H, ArH), 6.73
(s, 1H, ArH), 3.71 (d, J = 14 Hz, 4H, PhCH2), 2.02
2. Experimental
(s, 3H, CH3C O); 13C{1H} (75.48 MHz, CD3OD)
=
2.1. General
=
δ (ppm) 170.3 (C O), 138.9, 132.4, 132.1, 132.0,
131.2, 131.1, 131.0, 129.0, 128.9, 128.8, 128.1, 120.5,
=
All manipulations of air-sensitive materials were
carried out using standard Schlenk techniques. Sol-
vents were appropriately dried and distilled before use.
All other reagents and N-methyl-pyrrolidinone (NMP)
were obtained from commercial sources and were used
without further purification. 3,5-bis(Hydroxymethyl)
aniline (2) [16], N-acetyl-3,5-bis(hydroxymethyl)ani-
line (3) [17], and N-acetyl-3,5-bis(chloromethyl)ani-
line (4) [17] were prepared by literature proce-
dures.
(ArC), 37.1, 36.3, (PhCH2), 22.7 (CH3C O); 31P
NMR (121 MHz, CD3OD) δ (ppm) 34.7; EI MS for
C34H31NO3P2 563 (M+).
2.2.2. Synthesis of 3,5-bis-
(diphenyl-phosphinoylmethyl)-phenylamine (6)
A modified literature procedure was used [17]. To a
solution of 5 (4.2 g, 7.5 mmol) in 95% EtOH (100 ml)
was added NaOH (1.5 g, 37.5 mmol). The mixture
was refluxed for 48 h and the solution was cooled
with an ice bath, neutralized with concentrated HCl,
and the majority of the solvent was removed under
reduced pressure. The remaining residue was filtered,
washed with water, and dissolved in methanol. The
solvent was removed under reduced pressure afford-
ing the compound 6 as a yellow solid, which was
sufficiently pure for further synthesis. Yield: 3.1 g
(80%). 1H NMR (300.13 MHz, CD3OD) δ (ppm)
7.74–7.47 (m, 20H, ArH), 6.44 (s, 2H, ArH), 6.37 (s,
1H, ArH), 3.63 (d, J = 14 Hz, 4H, PhCH2); 13C{1H}
(50 MHz, CD3OD) δ (ppm) 137.3, 133.6, 133.5,
Solution NMR spectra were recorded at 20.5 ◦C,
unless otherwise indicated, on a Varian Gemini-200
(1H at 199.97 MHz and 13C{1H} at 50.28 MHz) or a
Bruker 300 NMR spectrometer (1H at 300.13 MHz,
13C{1H} at 75.48 MHz and 31P{1H} at 121.49 MHz).
The 13C and 31P CP/MAS (cross-polarization/magic
angle spinning) NMR spectra, frequency 50.32 and
81.00 MHz, respectively, were recorded on a Bruker
ASX-200 spectrometer. Solid samples were prepared
by transfer of the relevant material to a 5 mm o.d.
pyrex NMR tube and connected to a high vacuum

R. Chanthateyanonth, H. Alper / Journal of Molecular Catalysis A: Chemical 201 (2003) 23–31
25
132.6, 132.5, 132.3, 131.2, 131.1, 131.0, 130.9, 129.1,
128.9, 120.6 (ArC), 36.8, 35.9, (PhCH2); 31P NMR
(121 MHz, CD3OD) δ (ppm) 34.4; Electrospray MS
for C32H29NO2P2 522 (M + H+).
in vacuo to ca. 2 ml. Hexane was slowly added to
precipitate an off-white solid, which was filtered and
washed with hexane several times. Yield: 1.1 g (72%).
1H NMR (300.13 MHz, CD3OD) δ (ppm) 7.46–7.15
(m, 20H, ArH), 6.79 (s, 1H, ArH), 6.74 (s, 2H, ArH),
2.2.3. Synthesis of N-[3,5-bis-
3.29 (s, 4H, PhCH2), 2.79 (s, 4H, CH2C O); 13C{1H}
=
=
(diphenyl-phosphinoylmethyl)-phenyl]-succinamic
acid (7)
(75.48 MHz, CDCl3) δ (ppm) 175.0 (C O), 139.0,
138.9, 138.8, 133.5, 133.2, 128.8, 128.7, 128.4, 128.1,
=
A modified literature procedure was used [17].
To a suspension of 6 (3.1 g, 6.0 mmol) and triethy-
lamine (3.0 g, 30.0 mmol) in THF (150 ml) was added
succinic anhydride (0.7 g, 7.0 mmol). The mixture
was refluxed for 48 h, cooled, and the solvent was
removed under reduced pressure. The residue was
dissolved in ethanol (120 ml) followed by addition of
NaOH (8 M, 12 ml). The solvent was removed under
reduced pressure, yielding an off-white solid material.
This solid was washed with diethyl ether and then
added to a 6N HCl aqueous solution (30 ml). The
residue was filtered, washed with water, and then dis-
solved in methanol. The solvent was removed under
reduced pressure, affording 7 as an off-white solid,
which was sufficiently pure for subsequent reaction.
Yield: 3.0 g (80%).1H NMR (300.13 MHz, CD3OD)
δ (ppm) 7.74–7.48 (m, 20H, ArH), 7.20 (s, 2H, ArH),
6.72 (s, 1H, ArH), 3.71 (d, J = 13 Hz, 4H, PhCH2),
125.2 (ArC), 36.3, 36.1, (PhCH2), 28.1 (CH2C O);
31P NMR (121 MHz, CDCl3) δ (ppm) −9.0; Electro-
spray MS for C36H33NO3P2 590 (M + H+).
2.2.5. Synthesis of compound 10
A solution of 8 (1.0 g, 1.7 mmol) and 4-(dimethyl-
amino)pyridine (DMAP) (0.21 g, 1.7 mmol) in di-
chloromethane (20 ml) was added with 1,3-dicyclo-
hexylcarbodiimide (DCC) (0.35 g, 1.7 mmol) in
dichloromethane (1 ml) and N-hydroxysuccinimide
(0.2 g, 1.7 mmol) at 0 ◦C. The mixture was stirred
at room temperature for 18 h. The white solid was
filtered and the solvent was removed under reduced
pressure, affording compound 9 as a yellow solid.
DMAP (0.21 g, 1.7 mmol) in dichloromethane (50 ml)
and aminopropyl silica (0.5 g, 0.45 mmol) were added,
the reaction was stirred at room temperature for 1 day
and then heated at 45 ◦C for 4 days. The suspension
was filtered, washed with dichloromethane several
times, and dried in vacuo to afford 10 as a pale yel-
low solid. Yield: 0.6 g (78%). 31P CP/MAS NMR δ
(ppm) −10.5 (br s) and 31.1 (phosphine oxide); 13C
CP/MAS NMR δ (ppm) 172.1, 157.8, 140.7, 110.1,
41.5, 23.6, 10.7.
=
3.46 (m, 1H, NH). 2.65–2.50 (m, 4H, CH2C O);
13C{1H} (50 MHz, CD3OD) δ (ppm) 176.3, 172.5
=
(C O), 140.0, 133.7, 133.4, 133.1, 132.9, 132.3,
132.1, 131.7, 130.0, 129.8, 128.9, 121.4 (ArC), 38.4,
37.1, (PhCH2), 32.3, 30.1 (CH2C O); 31P NMR
=
(121 MHz, CD3OD) δ (ppm) 34.7; Electrospray MS
for C36H33NO5P2 621 (M+).
2.2.6. Synthesis of complex 11
2.2.4. Synthesis of N-{3,5-bis-
[(diphenyl-phosphanyl)-methyl]-phenyl}-
succinamic acid (8)
A suspension of compound 10 (0.6 g, 0.35 mmol),
and Pd(TFA)2 (0.06 g, 0.17 mmol) in THF (50 ml) was
stirred at room temperature for 3 days. The suspension
was filtered and washed with THF several times, dried
in vacuo to afford complex 11 as a dark yellow solid.
Yield: 0.6 g (94%). 31P CP/MAS NMR δ (ppm) 37.9
(br s) and 28.7 (phosphine oxide); 13C CP/MAS NMR
173.4, 156.9, 141.9, 130.3, 108.7, 50.6, 41.9, 33.5,
26.0, 11.2; ICP analysis mass% Pd 1.67.
A modified literature procedure was used [18]. In a
three-necked 500-ml round bottom flask, a suspension
of 7 (1.6 g, 2.6 mmol) in 1,2-dichlorobenzene (90 ml)
was refluxed at 180 ◦C until the solution became ho-
mogeneous. The reaction solution was then cooled to
140 ◦C and HSiCl3 (5 ml, 49 mmol) was added drop-
wise. The reaction mixture was then stirred at 140 ◦C
for 2 h. This solution was cooled to 0 ◦C, and an aque-
ous NaOH (4 M, 98 ml) was slowly added under vig-
orous stirring. The aqueous solution was extracted
with CH2Cl2, dried (MgSO4), and then concentrated
2.3. General procedure for the Heck reactions
A solution of bromoarene (2 mmol) or iodoarene
(12 mmol), olefin (2.4 mmol for bromoarene or

26
R. Chanthateyanonth, H. Alper / Journal of Molecular Catalysis A: Chemical 201 (2003) 23–31
Table 1
14.4 mmol for iodoarene), sodium carbonate (5 mmol
for bromoarene or 30 mmol for iodoarene), and cata-
lyst 11 (100 mg, 0.8 mol% for bromoarene or 25 mg,
0.03 mol% for iodoarene) in 10 ml of NMP for bro-
moarene, or 50 ml of NMP for iodoarene, was heated
at 140 ◦C for 24 h (bromoarene) or 6 h (iodoarene)
under nitrogen. After the reaction, the mixture was
allowed to cool, and filtered to separate the catalyst
from the liquid phase. The catalyst was washed sev-
eral times with water and diethyl ether. The aqueous
phase was extracted with diethyl ether several times
and the combined organic phase was washed with
saturated NaCl aqueous solution and water, and then
dried (MgSO4). The catalyst was dried under reduced
pressure before being recycled.
Heck reaction of iodobenzene and butyl acrylate catalyzed by 1
or 13a
Complex
Time
(h)
Yield
(%)b
TON
TOF
(mol product/ (mol product/
mol Pd)
mol Pd/h)
1
13
88
70
88
>99
108000
138000
1227
1983
a Reactions were conducted using 5 mmol iodobenzene in NMP.
b Determined by GC.
(1)
The catalytic activity of 13 was tested and compared
with complex 1 (Eq. (2) and Table 1). It was found
that the reactivity of 13 is better than 1. This could be
due to the electron-withdrawing effect of the phenyl
groups.
3. Results and discussion
3.1. Synthesis and characterization of a
silica-bound PCP-type palladium(II) complex
and catalytic properties of the immobilized
palladium(II) complex
Complex 13 [15] was synthesized from 1,3-bis-
diphenylphosphanylmethylbenzene and palladium(II)
trifluoroacetate (Pd(TFA)2) at room temperature
(Eq. (1)). Crystals suitable for X-ray analysis were
obtained for 13 (Fig. 2).
(2)
The diphosphine PCP-type ligand anchored to silica
was then prepared as shown in Scheme 1.
As mentioned previously, N-acetyl-3,5-bis(chloro-
methyl)aniline (4) was prepared in three steps (re-
duction, acetylation, and chlorination) according to
the literature, starting from commercially available
5-amino-isophthalic acid dimethyl ester [16,17]. The
diphosphine oxide compound (5) was synthesized
by Arbuzov-type reaction of 4 instead of the ana-
logue diphosphine because it is sufficiently stable for
the subsequent deprotection, and reaction with suc-
cinic anhydride provided the N-[3,5-bis-(diphenyl-
phosphinoylmethyl)-phenyl]-succinamic acid (7). Co-
mpound 7 was characterized by 1H NMR, 13C NMR,
31P{H} NMR, and X-ray crystallography (Fig. 3).
Reduction of 7 with HSiCl3 afforded the diphos-
phine compound (8), which is transformed into
N-hydroxysuccinimide ester (9). Reaction with com-
mercial aminopropyl silica gel gave the supported
ligands. CP/MAS 31P NMR was used as a tool for the
determination of the successful binding to the silica,
Fig. 2. ORTEP diagram of complex 13 (hydrogen atoms omitted
for clarity).

R. Chanthateyanonth, H. Alper / Journal of Molecular Catalysis A: Chemical 201 (2003) 23–31
27
Scheme 1.

28
R. Chanthateyanonth, H. Alper / Journal of Molecular Catalysis A: Chemical 201 (2003) 23–31
Fig. 3. ORTEP diagram of compound 4 (hydrogen atoms omitted for clarity).
as the chemical shift values are very sensitive to small
changes in the microenvironment. The CP/MAS 31P
NMR spectrum of compound 10 showed a broad sig-
nal at −10.5 ppm and a small broad signal (phosphine
oxide) at 31.1 ppm, whereas the 31P NMR solution
spectrum of compound 8 gave a signal at −9.0 ppm
(phosphine oxide at 34.7 ppm). Also the CP/MAS
13C NMR spectrum of compound 10 shows aromatic
peaks. Pd(TFA)2 was then reacted with 10 to form
the PCP-type palladium(II) complex 11. A phos-
phine/palladium ratio of 4:1 was used to avoid the for-
mation of other complexes along with the PCP-type
palladium(II) complex, such as palladium bound to
the amino groups of the aminopropyl silica gel. While
complexation of Pd(TFA)2 with 12 was completed in
6 h (rt) to form complex 13, 3 days were necessary
for the immobilized system. The 31P NMR spectra
of 11 and 13 show peak at 37.9 and at 37.2 ppm, re-
spectively (there is also a low intensity signal in the
NMR of 11, at 28.7 ppm due to phosphine oxide im-
purity). It has been reported that the chemical shifts
of the silica-bound late transition metal species which
bond with phosphine ligands are similar to those of
their molecular precursors [19]. The percentage of
palladium in 11 was determined from ICP.
with the Pd complex prior to binding with silica
(Scheme 2).
Nevertheless, due to the reactivity of the N-hydroxy-
succinimide ester, problems were encountered in the
purification of the Pd complex (14) obtained by this
route. In the previous method, the purification of the
silica-bound ligand is more facile.
The silica–PCP-type palladium(II) complex 11 was
used as a catalyst for the Heck reaction. The cou-
pling reaction of iodobenzene and butyl acrylate was
optimized by varying the temperature, base, and sol-
vent. The best conditions were similar to those re-
ported for compound 1 [5]. The reaction was carried
out at 140 ◦C, using sodium carbonate as base in NMP
(Eq. (3) and Table 2).
(3)
High turnover numbers (TON) were obtained
(3030 mol product/mol Pd), and the catalyst was recy-
cled three times with high activity. Lower reactivity
was observed when changing the substrate from butyl
acrylate to styrene (TON = 1320 mol product/mol Pd)
(Eq. (4) and Table 3). Both E/Z stilbenes were formed
in a ratio of 7:1.
The preparation of complex 11 was also attempted
by effecting cyclometallation of the phosphine ligands

R. Chanthateyanonth, H. Alper / Journal of Molecular Catalysis A: Chemical 201 (2003) 23–31
29
Scheme 2.
(4)
(5)
ICP analysis showed that the total palladium content
was 1.45 mass% Pd after the catalyst was used three
times (entry 10, Table 5). However, a higher loading of
catalyst (1.6×10−2 mmol Pd, 100 mg of catalyst) was
necessary and in the case of 4-bromotoluene, a lower
yield was found after the reaction was run three times
(entry 12, Table 5) (58% yield). ICP analysis showed
that there was only 0.7 mass% Pd. A control experi-
ment was carried out using a palladium–silica system
catalyst obtained by stirring Pd(TFA)2 and silica (10%
by weight of palladium to silica) in THF solution. This
system displayed poor stability as it decomposed to
Bromobenzene and several para-substituted bro-
mobenzenes were also used as substrates with methyl
or butyl acrylate. High activities and good recy-
cling properties were observed here (Eq. (5) and
Tables 4 and 5). A para-substituent on the ben-
zene ring has no significant effect on the reaction.
Chlorobenzene was found to react poorly with the
acrylate (TON = 16 mol product/mol Pd). The rate-
determining step of the reaction may involve oxidative
addition.
Table 2
Heck reaction of iodobenzene and butyl acrylate catalyzed by 11a
Table 3
Heck reaction of iodobenzene and styrene catalyzed by 11a
Run
number
Time
(h)
Yield
(%)b
TON
TOF
(mol product/ (mol product/
Run
number
Time
(h)
Yield
(%)b
TON
TOF
mol Pd)
mol Pd/h)
(mol product/ (mol product/
mol Pd)
mol Pd/h)
1
1
2
3
3
6
6
6
88
2611
3030
2958
897
505
493
>99 (90)c
84 (75)c
70
1
1
1
2
6
15
30
30
44
72
85
80
1344
1335
1320
224
89
d
d
–
–
44
c
c
–
–
a Reactions were conducted using 25 mg (3.9×10−3 mmol) of
catalyst, and 12 mmol iodobenzene in NMP.
b Determined by GC.
a Reactions were conducted using 25 mg (3.9×10−3 mmol) of
catalyst, and 12 mmol iodobenzene in NMP.
b Determined by GC.
c Isolated yield.
d Palladium loading was not measured.
c Palladium loading was not measured.

30
R. Chanthateyanonth, H. Alper / Journal of Molecular Catalysis A: Chemical 201 (2003) 23–31
Table 4
Heck reaction of bromobenzene and para-substituted bromobenzenes, and butyl or methyl acrylate catalyzed by 11a
Entry
R group
Y group
Run number
Yield (%)b
TON (mol product/mol Pd)
TOF (mol product/mol Pd/h)
1
2
3
4
5
H
C(O)On Bu
C(O)OMe
C(O)On Bu
C(O)On Bu
C(O)On Bu
1
1
1
1
1
86
95
90
>99
>99
109
120
115
127
127
4.6
5.0
4.8
5.3
>5.3
OMe
OMe
C(O)OMe
Me
a Reactions were conducted using 100 mg (1.6×10−2 mmol) of catalyst, and 2 mmol of para-substituted bromobenzenes for 24 h in NMP.
b Determined by GC or NMR.
Table 5
silica is an active catalyst for the Heck reaction. In ad-
dition, the system displays good stability and can be
recycled effectively.
Heck reaction of bromobenzene and para-substituted bromoben-
zenes, and butyl or methyl acrylate catalyzed by 11;a a recycling
study
Entry
R group
H
Y group
Run number
Yield (%)b
Acknowledgements
1
2
3
4
5
6
7
8
9
C(O)On Bu
2
3
4
5
2
3
2
3
2
3
2
3
86
79
70
79
92
94
81
83
98
94
85
58
We are grateful to NSERC for support of this re-
search, Dr. Glenn Facey for recording the CP/MAS
NMR spectra, and Dr. Victor Boyko of the National
Research Council, Canada, for ICP measurements.
OMe
C(O)OMe
C(O)On Bu
C(O)On Bu
C(O)On Bu
OMe
C(O)OMe
Me
10
11
12
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black Pd particles during a 20-h reaction and could not
be recycled without loss of activity (99% yield for the
first, 68% yield for the second, and 29% yield for the
third runs). These results clearly confirm that stable
PCP-type Pd catalysts were formed for 11 and 13 (no
visible decomposition of 11 after 3 days in solution).
Another control experiment was also carried out un-
der the same conditions, but using compound 13 plus
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