Synthesis and catalytic evaluation in the Heck reaction of deposited palladium catalysts immobilized via amide linkers and their molecular analogues

Article abstract of DOI:10.1016/j.cattod.2013.09.012

A series of deposited palladium catalysts was prepared by amidation of 3-aminopropylated silica gel with donor-functionalized acetic acids followed by treatment with palladium(II) acetate. The resulting materials containing YCH₂CONH(CH₂)₃Si groups at the surface, where Y = SMe, NMe₂, and PPh₂, as well as the corresponding catalysts generated in situ from the analogous molecular donors YCH ₂CONH(CH₂)₂Me and palladium(II) acetate were evaluated in the Heck reaction of n-butyl acrylate with bromobenzene to give n-butyl cinnamate. The heterogenized catalysts afforded consistently better yields of the coupling product than their respective molecular counterparts with the best results being achieved with the catalyst obtained from the amidoamine-functionalized support (Y = NMe₂). Additional tests revealed that the deposited catalysts serve as a source of active metal for the reaction occurring in the liquid phase and that the yield of the coupling product is controlled by the amount of the leached-out metal.

Full text of DOI:10.1016/j.cattod.2013.09.012

Catalysis Today 227 (2014) 207–214
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Synthesis and catalytic evaluation in the Heck reaction of deposited
palladium catalysts immobilized via amide linkers and their
molecular analogues
Miloslav Semlera,b, Jirˇí Cejka , Petr Steˇpnicˇka
b
a,∗
ˇ
ˇ
a Department of Inorganic Chemistry, Faculty of Science, Charles University in Prague, Hlavova 2030, 128 40 Prague, Czech Republic
b J. Heyrovsky´ Institute of Physical Chemistry, Academy of Sciences of the Czech Republic, v.v.i., Dolejsˇkova 3, 182 23 Prague, Czech Republic
a r t i c l e i n f o
a b s t r a c t
Article history:
A series of deposited palladium catalysts was prepared by amidation of 3-aminopropylated silica gel with
donor-functionalized acetic acids followed by treatment with palladium(II) acetate. The resulting mate-
rials containing YCH2CONH(CH2)3Si groups at the surface, where Y = SMe, NMe2, and PPh2, as well as
the corresponding catalysts generated in situ from the analogous molecular donors YCH2CONH(CH2)2Me
and palladium(II) acetate were evaluated in the Heck reaction of n-butyl acrylate with bromobenzene to
give n-butyl cinnamate. The heterogenized catalysts afforded consistently better yields of the coupling
product than their respective molecular counterparts with the best results being achieved with the cat-
alyst obtained from the amidoamine-functionalized support (Y = NMe2). Additional tests revealed that
the deposited catalysts serve as a source of active metal for the reaction occurring in the liquid phase and
that the yield of the coupling product is controlled by the amount of the leached-out metal.
© 2013 Elsevier B.V. All rights reserved.
Received 21 June 2013
Received in revised form
11 September 2013
Accepted 17 September 2013
Available online 12 October 2013
Keywords:
Deposited catalysts
Palladium
Amide linkers
Heck reaction
Poisoning tests
1. Introduction
salts and complexes) and “molecular” catalysts generated in situ
from a Pd precursor and an appropriate modifier (typically a ligand),
Catalysis nowadays plays a vital role in the synthesis of many
organic compounds at laboratory scale as well as in industry, where
not only fine chemicals but also large scale preparations are carried
out catalytically. Very often, high value added chemicals are pre-
pared with the aid of C C bond forming (cross-coupling) reactions
that allow for efficient “construction” of a range of simple and com-
plex molecules by selective coupling of two building blocks via the
newly formed C C bond(s). One of the prominent examples of such
processes is the Heck–Mizoroki reaction (or simply Heck reaction)
discovered in the early 1970s [1]. Heck reaction is based on the cou-
pling of olefins with organic halides (typically haloarenes) affording
substituted alkenes suitable for further synthetic transformations
[2]. The manifold industrial applications of Heck reaction, which
have been reviewed several times [3], can be exemplified by
the preparation of materials as diverse as monomer precursors
of benzocyclobutene-based resins (CycloteneTM by Dow Chemi-
cal), herbicide Prosulfuron, and the nonsteroidal anti-inflammatory
drug Naproxene.
to various heterogeneous and heterogenized catalysts. Any immo-
bilization of a palladium catalyst over a solid support is potentially
attractive for industrial, large-scale applications because such cat-
alysts can be relatively easily recovered and recycled. In addition,
the stable and efficient heterogenized catalysts appear particularly
suitable for the preparation of pharmaceutically active substances,
in the case of which the contamination with residual metals is
strictly controlled [4].
In our work, we have focused on palladium catalysts deposited
on various siliceous supports modified with N-donor groups and
their applications to the Heck coupling [5]. The results obtained
with the catalysts derived from siliceous supports such as meso-
porous molecular sieves MCM-41 [6] and SBA-15 [7] or much
cheaper and hydrolytically stable silica gel have shown that the
type (internal structure in particular) of the support affects the
overall catalytic performance of the resulting immobilized catalysts
less than the amount and the nature of the anchoring donor groups
used to modify the parent support [5]. This is rather natural because
the donor groups determine the mode of interaction between the
deposited metal and the support, thereby controlling the activity,
selectivity and stability of the catalyst, as well as a possible leaching
of the active metal from the solid support.
Typically, the Heck reactions make use of various palladium cat-
alysts ranging from defined molecular compounds (i.e., various Pd
Although a number of papers has been published on the appli-
cations of palladium catalysts deposited over siliceous supports
∗
Corresponding author. Fax: +420 221 951 253.
E-mail address: stepnic@natur.cuni.cz (P. Steˇpnicˇka).
ˇ
0920-5861/$ – see front matter © 2013 Elsevier B.V. All rights reserved.
http://dx.doi.org/10.1016/j.cattod.2013.09.012

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M. Semler et al. / Catalysis Today 227 (2014) 207–214
Scheme 3. Preparation of the molecular donors 8–10. Legend: EDC, 1-[3-
(dimethylamino)propyl]-3-ethylcarbodiimide; HOBt, 1-hydroxybenzotriazole.
Scheme 1.
in the deposited catalysts 5–7, were obtained by direct amidation
of the respective substituted acetic acids with 1-aminopropane
(Scheme 3).
modified with aminopropyl [8], mercaptopropyl [9], phosphine
[10] and carbene [11] donor groups in the Heck reactions, there
is – up to the best of our knowledge – no literature report deal-
ing with the direct comparison of catalysts possessing structurally
similar modifying groups equipped with chemically different donor
moieties. This prompted us to prepare a series of structurally anal-
ogous palladium catalysts from donor-modified, silica gel-based
supports and to compare their catalytic properties in a model
Heck reaction. To this end, we have synthesized palladium cata-
lysts from silica gel functionalized with chemically similar amide
donor pendant groups possessing different terminal donor moi-
eties (Scheme 1). In the preparation of these materials, we used the
readily accessible 3-aminopropyl modified silica gel, which was
reacted with donor-functionalized acetic acids (Me2NCH2CO2H,
Ph2PCH2CO2H, and MeSCH2CO2H) to afford the respective surface-
bound amide pendants. This approach exploiting amide functional
group as a defined linking moiety has been utilized only scarcely
in the design of deposited palladium catalysts [12]. In this contri-
bution, we report the preparation of deposited palladium catalysts
from supports bearing three different donor-amide groups at the
surface, and a comparison of their catalytic performance with sim-
ple catalysts obtained in situ by mixing a palladium source with the
respective “molecular” donor-amide ligands.
Materials 1–7 were characterized by IR spectroscopy and ele-
mental analysis. Prior to the palladation, supports 2 and 4 showed
the S/N and P/N molar ratios below unity while in the case of 3,
the amount of nitrogen was lower that the double of the amount
of nitrogen in the parent material 1. This suggests an incomplete
conversion of the 3-aminopropyl pendants into the amide ones or,
in other words, the presence of unreacted aminopropyl groups at
the supports’ surface [15]. The palladation led to incorporation of
ca. 0.5–0.6 mmol Pd per gram of the resulting solid catalyst. The
Pd/donor molar ratios were 1.06 (Pd/S) for 5 and 1.30 (Pd/P) for 7.
The Pd/N ratio determined for 6 was only 0.88 owing to the pres-
ence of two nitrogen atoms in the functional pendant (in the ideal
case).
The IR spectra of all materials were dominated by broad
intense absorptions of the siliceous support at 3000–3500
(ꢀOH), ca. 1100–1200 cm−1 (intense band due to asymmetric
Si
O
Si stretching), 800 cm−1 (symmetric Si
O
Si stretching),
and 460 cm−1 (Si
O
Si bending) [16]. Besides, the spectra of 2–4
displayed bands attributable to N H vibrations, C H valence bands
(ca. 2750–3000 cm−1) and, mainly, characteristic vibrations of the
amide moieties (amide I at 1640–1660 cm−1, and amide II at ca.
1535–1540 cm−1). The positions of the amide bands corresponded
well with those determined for the respective molecular amides
8–10 (see below). Upon palladation, however, these bands shifted
to lower wavenumbers (amide I band typically by ca. 90 cm−1),
reflecting very likely coordination of the anchored Pd species
by the donor pendant attached to the support surface. These
features are demonstrated in Fig. 1 for materials obtained from N,N-
dimethylglycine. Trends observed in the other series (i.e., 2–5–8
and 4–7–10) were similar.
The molecular amides 8–10 were characterized by NMR and
IR spectroscopy and by high-resolution mass spectrometry. The
compounds displayed all expected signals in the NMR spectra as
well as the characteristic amide bands at 1630–1650 (amide I)
and 1530–1545 cm−1 (amide II) in their IR spectra. Notably, the
energy of the amide I vibration (largely C O stretching) was found
to increase in the order 10 < 8 < 9 (P < S < N), thus following inversely
the trend of the electronegativities of the pivotal atoms in the ter-
minal group (N > S > P).
2. Results and discussion
2.1. Preparation of the deposited catalysts and their molecular
analogues
The deposited, donor-amide functionalized palladium cata-
lysts were prepared as shown in Scheme 2 [13]. In the first
step, dry chromatography-grade silica gel was reacted with an
excess of (3-aminopropyl)trimethoxysilane in refluxing toluene to
afford the aminopropylated support 1. This material was in turn
reacted with the respective substituted acetic acids in the pres-
ence of peptide coupling agents [14] to give the corresponding
amide-functionalized supports 2–4. As the last step, the sup-
ports were palladated via treatment with palladium(II) acetate
in dichloromethane using 1 mmol of Pd(OAc)2 per 1 g of the
functionalized silica gel to afford catalysts 5–7. Amides 8–10, rep-
resenting molecular analogues of the functional pendants present
Scheme 2. Preparation of anchored Pd catalysts 5–7. Legend: i, (3-aminopropyl)trimethoxysilane in toluene, refluxing; ii, amidation with the appropriate acid YCH2CO2H
in the presence of peptide coupling agents (1-hydroxybenzotriazole and 1-[3-(dimethylamino)propyl]-3-ethylcarbodiimide (EDC) or the corresponding hydrochloride
(EDC·HCl)); iii, treatment with Pd(OAc)2 in dichloromethane.

M. Semler et al. / Catalysis Today 227 (2014) 207–214
209
Fig. 1. IR spectra of materials 3 and 6, and the molecular amide 9.
2.2. Catalytic evaluation
obtained with catalyst 6, whose activity increased most rapidly
upon raising the reaction temperature. The different catalytic per-
formance of the catalysts and their temperature dependences
suggest that the catalytic activity (in a particular solvent) is deter-
mined by the available donor atoms, which obviously determine
the nature and strength of the interaction between palladium and
the functionalized support, and also by an overall stability (pre-
sumably thermal and redox) of the deposited catalysts.
As for the base, we studied only the reactions performed in the
presence of sodium acetate, which is the most effective for the par-
ticular testing reaction according to our previous experience [5].
However, in this study we focused on the influence of the nature
of this salt, which is readily available in hydrated and anhydrous
forms. Thus, the reactions were performed in the presence of fused
anhydrous sodium acetate or sodium acetate trihydrate (1.5 equiv.)
with 1 mol.% Pd at 140 ◦C for 2 h using either nitrogen-flushed ves-
sels (inert conditions) or reaction tubes sealed in the air. The results
summarized in Table 1 indicate that the best yields for all catalysts
are consistently obtained in reactions carried out with the hydrated
base and with the exclusion of the air.
The catalytic properties of the supported catalysts 5–7 were
evaluated in the model Heck coupling of bromobenzene with
n-butyl acrylate to give n-butyl cinnamate (Scheme 4). The reac-
tion mixtures typically contained 1.5 equiv. of bromobenzene
(bromobenzene is the most volatile component in the reaction mix-
ture), an excess of base (sodium acetate) and the catalyst in an
amount corresponding to 1.0 mol.% of palladium with respect to n-
butyl acrylate. The initial reaction tests were aimed at finding the
best reaction conditions in terms of the reaction solvent, amount
of base and temperature. All these parameters were shown to have
a pronounced effect on the performance of the newly prepared
catalysts.
Kinetic profiles for the testing reactions performed with cata-
lysts 5–7 (1 mol.%) in two different solvents at 150 ◦C and in the
presence of anhydrous sodium acetate (1.5 equiv.) as the base are
shown in Fig. 2. In N,N-dimethylacetamide (DMA), the best results
were obtained with the S- and P-donor catalysts 5 and 7 (5: 87%
yield after 4 h, ≈100% yield after 8 h; 7: 86% yield after 4 h, 92%
yield after 8 h). Catalyst 6 containing the N-donor groups per-
formed slightly worse (59% yield after 4 h, 71% yield after 8 h). An
even more pronounced discrimination was seen in 1-octanol, in
which catalysts 5 and 6 turned practically inactive during the first
30 min (cf. the yields after 1 h/8 h; 5: 8%/12%, 6: 14%/26%) whereas
the phosphine-containing catalyst 7 maintained its catalytic activ-
ity during the whole experiment and achieved 94% yield of the
coupling products in 8 h. Reactions performed similarly in tri-n-
butylamine as the third tested solvent ensued in considerably lower
conversions (cf. conversions after 4/8 h; 5: 14%/14%, 6: 20%/17%, 7:
17%/16%), presumably due to a higher donor ability and reducing
properties of this solvent [17].
Influence of the reaction temperature was rather expected (see
Fig. 3) as the yields of the coupling product obtained with 1 mol.%
Pd catalyst after 2 h [18] increased exponentially with increasing
temperature. In terms of activity (yields), the catalysts become
more differentiated at higher temperatures. The best results were
Fig. 2. Kinetic profiles for the model reaction carried out with catalyst 5 (diamonds),
6 (triangles) and 7 (circles) performed in N,N-dimethylacetamide (filled symbols)
and 1-octanol (empty symbols). Conditions: 1.0 mmol of n-butyl acrylate, 1.5 mmol
of bromobenzene and 1.5 mmol of anhydrous sodium acetate in 5 mL of the sol-
vent; 1 mol.% Pd, reaction at 150 ◦C under nitrogen. The solid lines connecting the
experimental points in this and the following figures serve only as a guide for an
eye.
Scheme 4. Heck reaction of bromobenzene with n-butyl acrylate to give n-butyl
cinnamate.

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M. Semler et al. / Catalysis Today 227 (2014) 207–214
Fig. 4. Kinetic profiles for the model Heck reactions carried out in the pres-
ence of deposited catalysts 5–7 and their analogs based on the combination of
Pd(OAc)2 and ligands 8–10. Conditions: 1.0 mmol of n-butyl acrylate, 1.5 mmol of
bromobenzene, 0.75 mmol of CH3CO2Na and 0.75 mmol of CH3CO2Na·3H2O in 5 mL
of N,N-dimethylacetamide; 1 mol.% Pd, reaction at 120 ◦C under nitrogen. Catalysts
based on 8–10 were obtained by adding the respective amide ligand (20 ␮mol) and
Pd(OAc)2 (10 ␮mol) to the reaction mixture.
Fig. 3. Dependence of the yield of the coupling product upon the reaction tem-
perature. Conditions: 1.0 mmol of n-butyl acrylate, 1.5 mmol of bromobenzene and
CH3CO2Na·3H2O in 5 mL of N,N-dimethylacetamide; 1 mol.% Pd, reaction under
nitrogen for 2 h.
Table 1
The influence of the base and inert conditions on the yield of the coupling product.a
Conditions
Yield of the coupling product (%)
of 1–3 equiv. of water per one molecule of the base under identical
conditions.
Catalyst 5
Catalyst 6
Catalyst 7
Using the optimized reaction conditions (1 mol.% Pd,
AcONa + AcONa·3H2O as the base) and relatively low reaction
temperature (120 ◦C), the anchored Pd catalyst 5–7 were com-
pared with catalysts generated in situ by mixing palladium(II)
acetate with equimolar amount of the respective molecular
donors 8–10. Kinetic profiles shown in Fig. 4 clearly demonstrate
a superior performance of the immobilized catalysts, whose
activity decreased in the order 6 > 7 > 5. Although the homogenous
catalysts afforded much lower yields of the coupling product, they
maintained the same trend (9 > 10 > 8, or N > P > S in terms of the
terminal donor atoms). Consequently, the results obtained with
the least active heterogenized catalyst 5 were very similar to the
most active “molecular” catalyst 9.
Nitrogen/dry base
Nitrogen/hydrated base
Air/dry base
34
64
17
18
64
89
28
49
32
46
28
42
Air/hydrated base
a
Conditions: 1.0 mmol of n-butyl acrylate, 1.5 mmol of bromobenzene, 1.5 mmol
of CH3CO2Na or CH3CO2Na·3H2O in 5 mL of N,N-dimethylacetamide; 1 mol.% Pd,
reaction at 140 ◦C for 2 h.
Table 2
The influence of the amount of water present in the base on the yield of the coupling
product.a
Equiv. of H2O per 1 equiv of NaOAc
Yield of the coupling product (%)
Catalyst 5
Catalyst 6
Catalyst 7
The differences in the catalytic properties of material possess-
ing identical metal binding sites in free (molecular) or immobilized
form can be accounted for by the role of the chemically inert
siliceous support. The latter probably acts as a matrix, in which both
the Pd(II) species and palladium(0) particles can be dispersed and to
which they can return after leaving the catalytic cycle. Moreover,
elimination of the metal from the solid support with covalently
bound donor groups can be expected to afford metal species devoid
of any firmly bound donors (probably stabilized only by coordi-
nation of the donor solvents) and thus highly prone to oxidative
addition of the aryl halide, which is believed to open the catalytic
cycle [2]. The heterogeneous catalysts thus produce active (naked)
metal particles albeit in only a low concentration due to metal
scavenging effect of the functionalized support.
The fact that the heterogenous catalysts act as a source of active
metal particles for the reaction in the liquid phase was confirmed
by a series of poisoning tests [19]. For instance, no coupling prod-
uct was detected in the reaction mixture containing the most active
catalyst 6 when the reaction was performed in the presence of mer-
cury metal from the very beginning. Similarly, addition of mercury
or N-donor metal scavenger 12 [20], which was prepared as shown
in Scheme 5, to the reaction mixture containing the heterogeneous
catalyst after 2 h of reaction immediately stopped the reaction as
demonstrated by the kinetic profiles in Fig. 5.
0
1
1.5
2
3
9
16
17
14
12
19
24
30
19
19
9
19
18
18
16
a
Conditions: 1.0 mmol of n-butyl acrylate, 1.5 mmol of bromobenzene, mixtures
of CH3CO2Na and CH3CO2Na·3H2O in varying ratios (total amount of sodium acetate:
1.5 mmol), 5 mL of N,N-dimethylacetamide; 1 mol.% Pd, reaction at 120 ◦C under
nitrogen.
Next, we varied the amount of water in the reaction system by
introducing a mixture of anhydrous sodium acetate and sodium
acetate trihydrate in appropriate amounts (Table 2). In accordance
with previous tests, the lowest yields were uniformly achieved in
reactions with anhydrous base. In the case of catalyst 6, increasing
amount of water in the base gradually improved the yields up to
1.5 mole of water per one mole of sodium acetate represented by a
1:1 mixture of CH3CO2Na and CH3CO2Na·3H2O (N.B. This amount
corresponds to 2.25 equiv of water with respect to n-butyl acrylate
and 1.5 equiv. with respect to bromobenzene). Quite surprisingly,
any further increase in the amount of water available in the reac-
tion mixture up to 4.5 equiv. (i.e., 1.5 equiv. of CH3CO2Na·3H2O vs.
n-butyl acrylate) caused a decrease in the yield of the coupling
product. A similar but much less pronounced trend was seen also for
catalyst 5 while catalyst 7 containing phosphine functional groups
showed practically negligible variation in the yield over the range
Attempts to recycle the heterogeneous catalyst were not suc-
cessful (Table 3). Catalysts 5 and 6 recovered after the first run

M. Semler et al. / Catalysis Today 227 (2014) 207–214
211
Scheme 5. Preparation of metal scavenger 12. Legend: i, (3-chloropropyl)triethoxysilane in toluene, refluxing; ii, alkylation with N(CH2CH2NH2)3 followed by neutralization
with ammonia in ethanol/water.
results summarized in Table 2 and discussed above (the role of sol-
vate water and inert atmosphere). It appears likely that the inert
atmosphere prevents decomposition of the Pd species and possible
degradation of the donor support, thereby limiting the amount of
palladium which is not re-deposited from the liquid phase.
3. Conclusion
Amidation of 3-aminopropylated silica gel with donor-
functionalized acetic acid mediated by peptide coupling agents
proceeds smoothly to give materials modified with multidonor
amide groups (ca. 0.5–0.8 mmol of the donor pendants per 1 g
of the support). Palladation of such functionalized supports with
palladium(II) acetate affords deposited palladium catalysts that
efficiently mediate Heck coupling of n-butyl acrylate with bro-
mobenzene to afford n-butyl cinnamate. Catalytic efficiency varies
greatly with the nature of the terminal donor groups and the reac-
tion conditions. Apart from the rather expected influence of the
reaction solvent and temperature, the reaction is affected also by
the form of the base (namely by the amount of water of crystalliza-
tion in sodium acetate) and inert/non-inert conditions. Since the
catalyst poisoning and metal leaching tests suggest the catalysts
to serve as a source of active metal species, the catalytic outcome
is determined by the amount of metal available in the liquid phase
and, hence, reflects the donor ability of the functional pendants and
the solvent, chemical stability of the anchoring groups and other
factors that can affect the metal leaching (e.g., the amount of water
in the reaction mixture).
Fig. 5. Catalyst poisoning tests for 5–7. The catalytic poisons – mercury (filled
symbols) or material 12 (empty symbols) – were added after 2 h (indicated with
an arrow). Conditions: 1.0 mmol of n-butyl acrylate, 1.5 mmol of bromobenzene,
0.75 mmol of CH3CO2Na and 0.75 mmol of CH3CO2Na·3H2O in 5 mL of N,N-
dimethylacetamide; 1 mol.% Pd, reaction at 120 ◦C under nitrogen.
showed practically negligible activities whereas the phosphine
based material 7 achieved ca. 13% conversion when used for the
second time (cf. 29% in the first run). Analysis of the reaction mix-
tures revealed that yield of the coupling products increases linearly
with the amount of palladium present in the liquid phase [21].
Although the amount of metal present in the liquid phase can be
considerably higher during the reaction because the palladium con-
tent was determined in liquid phases withdrawn after cooling the
reaction mixture to room temperature, the data corroborate that
catalysts 5–7 behave as a source of active palladium species for the
catalytic process occurring in the liquid phase. Furthermore, the
data in Table 3 clearly demonstrate that the amount of leached-out
metal is much higher in reactions performed in air than in those
carried out under nitrogen, which in turn corresponds with the
4. Experimental
4.1. Materials and methods
Unless stated otherwise, the syntheses were carried out under
argon or nitrogen atmosphere using standard Schlenk techniques.
(Diphenylphosphino)acetic acid was prepared according to the lit-
erature [22]. Toluene was dried over sodium metal and freshly
distilled under argon. Dichloromethane was dried with potassium
carbonate and distilled. All other chemicals were obtained from
commercial sources (Sigma–Aldrich and Alfa-Aesar; solvents from
Lachner) and were used as received.
Table 3
Amount of Pd in the liquid phase and yields of the coupling product for reactions
mediated by fresh and recycled catalysts 5–7.a
Catalyst
Pd content in the liquid
phase [ppm]b
Yield of the coupling
product [%]
IR spectra were recorded in diffuse reflectance mode (DRIFTS)
on
a Nicolet Magna 760 FTIR spectrometer in the range
400–4000 cm−1 (64 scans, resolution 4 cm−1). The samples were
diluted with KBr prior to the measurement. NMR measurements
were performed with a Varian UNITY Inova 400 spectrometer at
25 ◦C. Chemical shifts are given relative to internal tetramethylsi-
5 under N2
6 under N2
7 under N2
5 recycled under N2
6 recycled under N2
7 recycled under N2
5 in air
6 in air
7 in air
19
36
23
2
1
5
43
92
114
15
59
29
2
2
13
–
lane (1H and 13C) or to external 85% aqueous H3PO4
0 ppm.
(
31P), all set to
–
–
The content of C, H, N and Cl was determined by the conven-
tional combustion method. Palladium loading in solid samples was
determined by ICP-OES on an IRIS Interpid II (Thermo Electron)
instrument using axial plasma and ultrasonic CETAC nebulizer U-
5000AT+. The samples were dissolved in a mixture of concentrated
HF and HNO3 (3:2; both suprapure Merck) at 50 ◦C for 15 min,
a
Conditions: 1.0 mmol of n-butyl acrylate, 1.5 mmol of bromobenzene, 0.75 mmol
of CH3CO2Na and 0.75 mmol of CH3CO2Na·3H2O in 5 mL of N,N-dimethylacetamide;
1 mol.% Pd, reaction at 120 ◦C, reaction time 8 h.
b
The amount of palladium was determined in a sample withdrawn after cooling
the reaction mixture.

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M. Semler et al. / Catalysis Today 227 (2014) 207–214
and the solutions were diluted with redistilled water. Spectral
line at 324.240 nm was used for the measurement. The amount
of palladium in liquid samples was determined by ICP-MS for the
105Pd isotope. One milliliter of the sample was added to aqua regia
(50 mL) and the mixture was evaporated. The solid residue was
dissolved in redistilled water prior to the analysis.
vw, 1990 vw, 1870 vw, 1714 vw, 1560 w, 1438 w, 1092 s, 952 vw,
800 w, 742 vw, 692 vw, 466 s; elemental analysis (mmol g−1): C
9.94, H 16.8, N 0.76, P 0.39, Pd 0.50.
4.5. Preparation of amide 8
(Methylthio)acetic acid (0.106 g, 1.0 mmol) and EDC·HCl
(0.383 g, 2.0 mmol) were successively added to neat n-propylamine
(2.0 mL, 24 mmol). The resulting mixture was stirred at room
temperature for 2 h and then diluted with brine. The resulting mix-
ture was extracted with dichloromethane (3× 10 mL). The organic
washing were combined, dried over MgSO4 and evaporated with
silica gel. The crude pre-adsorbed product was transferred onto
a top of a chromatographic column (silica gel, ethyl acetate) and
the column was eluted with ethyl acetate. Following evaporation,
amide8 was isolatedas a yellowishoil (60 mg, 41%). 1H NMR(CDCl3,
399.95 MHz, 25 ◦C): ı 0.95 (t, 3H, 3JHH = 7.37 Hz, CH3CH2), 1.57 (m,
2H, CH3CH2), 2.13 (s, 3 H, CH3S), 3.20 (s, 2H, SCH2), 3.27 (m, 2H,
4.2. Preparation of aminopropylated silica (material 1)
Conventional chromatography-grade silica gel (Fluka,
0.063–0.2 mm; 25 g), which was dried in an oven prior to
the use (room temp. → 550 ◦C at 1 ◦C min−1
,
then at 550 ◦C
for 5 h), was suspended in dry toluene (500 mL). Neat (3-
aminopropyl)trimethoxysilane (12 mL, 74 mmol) was introduced
and the resulting mixture was heated at reflux for 25 h. After cool-
ing, the solid was filtered off, washed successively with toluene,
acetone and pentane (200 mL each), and allowed to dry in the air.
Yield: 31 g. IR DRIFTS (cm−1): 3640 w, 3070 w br, 2938 w, 2964 w,
1866 w, 1632 w, 1558 w, 1490 w, 1092 s, 950 w, 799 m, 691 w,
460 s; elemental analysis (mmol g−1): C 4.43, H 15.8, N 1.26.
1
NHCH2CH2), 6.92 (s, 1H CONH); 13C{ H} NMR (CDCl3, 100.58 MHz,
25 ◦C): ı 11.3 (NH(CH2)2CH3), 16.4 (CH3S), 22.8 (NHCH2CH2), 38.3
(SCH2), 41.4 (NHCH2), 168.2 (CONH); IR DRIFTS (cm−1): 3292 m,
3078 w, 2964 m, 2932 m, 2874 w, 1648 s, 1552 m, 1460 w, 1438
w, 1382 vw, 1315 w, 1246 vw, 1222 vw, 1160 w, 1100 w, 1074 vw,
984 vw, 954 vw, 884 vw, 786 vw, 746 vw, 688 w, 612 vw, 576 w,
472 vw; HRMS calc. for. C6H14NOS: 148.0791, found 148.0790.
4.3. Preparation of materials 2–4
1-Hydroxybenzotriazole hydrate (HOBt; 1.535 g, 10 mmol)
and (methylthio)acetic acid (0.584 g, 5.5 mmol) were dissolved
in dry dichloromethane (100 mL). The mixture was cooled in
an ice bath and treated with 1-[3-(dimethylamino)propyl]-3-
ethylcarbodiimide hydrochloride (EDC·HCl; 1.917 g, 10 mmol).
After stirring for 30 min, modified silica gel 1 (5.0 g), which was
freshly activated by drying under vacuum at 130 ◦C for 2 h, was
added and the resultant mixture was stirred at room temperature
overnight (18 h). Then, the solid material was filtered off, washed
carefully with methanol and dichloromethane, and dried in the air.
Yield: 5.1 g. IR DRIFTS (cm−1): 3652 w, 3292 mb, 2980 vw, 2929 w,
2872 vw, 1996 vw, 1868 vw, 1648 w, 1536 w, 1442 vw, 1092 s, 958
w, 800 m, 698 w, 464 s; elemental analysis (mmol g−1): C 6.29, H
17.2, N 1.05, S 0.78.
Material 3 was prepared in exactly the same manner using N,N-
dimethylglycine (0.567 g, 5.5 mmol) for the amidation. Yield: 4.9 g.
IR DRIFTS (cm−1): 3648 w, 3306 mb, 2978 vw, 2952 vw, 2886 vw,
2832 vw, 2788 vw, 1870 vw, 1664 w, 1540 w, 1464 vw, 1092 s,
958 w, 800 m, 462 s; elemental analysis (mmol g−1): C 6.08, H
17.8, N 1.55. The phosphine-modified support 4 was prepared sim-
ilarly starting from modified silica gel 1 (2.50 g) EDC·HCl (0.958 g,
5.0 mmol), HOBt (0.768 g, 5.0 mmol), (diphenylphosphino)acetic
acid (0.672 g, 2.75 mmol) and triethylamine (0.75 mL, 5.0 mmol).
Yield: 2.6 g. IR DRIFTS (cm−1): 3640 w, 3288 m br, 3060 vw, 2938
vw, 2872 vw, 1640 w, 1534 w, 1432 vw, 1100 s, 958 w, 800 m, 736
w, 696 w, 468 s; elemental analysis (mmol g−1): C 11.3, H 23.3, N
0.73, P 0.48.
4.6. Preparation of amide 9
N,N-Dimethylglycine
(0.206 g,
2.0 mmol)
and
1-
hydroxybenztriazole hydrate (0.461 g, 2.8 mmol) were dissolved
in dry dichloromethane (10 mL). The solution was cooled in
an ice bath and treated with EDC·HCl (0.575 g, 3.0 mmol) and
triethylamine (0.75 mL, 5.0 mmol). After stirring for 30 min, neat n-
propylamine (0.50 mL, 6.0 mmol) was introduced and the mixture
was stirred at room temperature overnight (18 h). Then, anhydrous
potassium carbonate (ca. 2 g) was added and the mixture was
stirred for another 10 min and filtered. The filtrate was evaporated
with chromatographic silica gel and the preadsorbed crude prod-
uct was purified as described for 8 (silica gel; 1% triethylamine
in dichloromethane-methanol 3:1) to give amide 9 as a colorless
oil (0.103 g, 37%). 1H NMR (CDCl3, 399.95 MHz, 25 ◦C): ı 0.94 (t,
3
3H, JHH = 7.37 Hz, CH3CH2), 1.55 (m, 2H, CH3CH2), 2.30 (s, 6H,
N(CH3)2), 2.95 (s, 2H, NHCH2CO), 3.25 (m, 2H, NHCH2CH2), 7.17
1
(s, 1H, CONH); 13C{ H} NMR (CDCl3, 100.58 MHz, 25 ◦C): ı 11.4
(NH(CH2)2CH3), 22.9 (NHCH2CH2), 40.6 (NHCH2CH2CH3), 46.0
(N(CH3)2), 63.2 (CH2CO), 170.4 (CONH); IR DRIFTS (cm−1): 3308
m, 3076 w, 2964 s, 2876 m, 2824 m, 2778 m, 1664 s, 1526 s, 1458
m, 1420 vw, 1382 w, 1344 w, 1270 w, 1174 w, 1154 w, 1098 w,
1046 m, 1002 vw, 978 vw, 942 vw, 864 w, 746 vw, 678 vw, 594 w,
506 vw; HR MS calc. for C7H17N2O: 145.13354, found 145.13367.
4.4. Palladation of materials 2–4
4.7. Preparation of amide 10
A solution of palladium(II) acetate (0.448 g, 2.0 mmol) in dry
dichloromethane (10 mL) was introduced to a stirring suspension
of the respective support in the same solvent (2.0 g in 50 mL).
The resulting mixture was stirred at room temperature for 2 h
before being filtered. The solid product was washed carefully with
dichloromethane and dried in the air.
(Diphenylphosphino)acetic acid (0.244 g, 1.0 mmol) and 1-
hydroxybenztriazole hydrate (0.184 g, 1.1 mmol) were dissolved
in dry dichloromethane (10 mL). The mixture was cooled in ice
and treated with neat EDC (0.20 mL, 1.1 mmol). After stirring
for another 30 min, neat n-propylamine (0.16 mL, 2.0 mmol) was
introduced and the stirring was continued at room temperature
overnight. The reaction mixture was quenched with 10% aque-
ous citric acid (10 mL). The organic layer was separated, washed
with brine and saturated aqueous NaHCO3, dried over MgSO4, and
evaporated. The residue was purified by column chromatography
(silica gel; ethyl acetate) to afford amide 10 as yellowish solid
(0.169 g, 59%). 1H NMR (CDCl3, 399.95 MHz, 25◦ C): ı 0.80 (t, 3H,
3JHH = 7.43 Hz, CH3CH2), 1.37 (m, 2H, CH3CH2), 3.02 (s, 2H, PCH2CO),
Material 5. IR DRIFTS (cm−1): 3640 w, 3222 w br, 2930 vw, 1560
w, 1425 w, 1100 s, 954 vw, 798 w, 686 vw, 460 s. Elemental analysis
(mmol g−1): C 7.19, H 16.0, N 0.90, S 0.61, Pd 0.64. Material 6. IR
DRIFTS (cm−1): 3642 w, 3246 wb, 2930 vw, 1872 vw, 1708 vw,
1570 w, 1432 w, 1330 vw, 1096 s, 956 w, 862 vw, 802 w, 682 w,
456 s. Elemental analysis (mmol g−1): C 6.89, H 17.1, N 1.41, Pd 0.62.
Material 7. IR DRIFTS (cm−1): 3648 w, 3254 w br, 3062 vw, 2930

M. Semler et al. / Catalysis Today 227 (2014) 207–214
213
3.13 (m, 2H, NHCH2), 5.61 (s, 1H, CONH), 7.32–7.37 (m, 6H, Ph),
(three vacuum/nitrogen cycles) before the solvent was introduced
to the solid components. The reaction was performed at 120 ◦C. The
respective catalytic poison (0.1 mL of mercury or 200 mg of mate-
rial 12) was added either together with the solvent (i.e., at the very
beginning) or after the reaction was allowed to proceed at 120 ◦C
for 2 h.
1
7.41–7.46 (m, 4H, Ph); 13C{ H} NMR (CDCl3, 100.58 MHz, 25 ◦C):
11.3 (NH(CH2)2CH3), 22.7 (NHCH2CH2), 37.5 (d, 1JPC = 20 Hz, PCH2),
41.5 (CH2CO), 128.7 (d, 2JPC = 7 Hz, Ph ortho-CH), 129.1 (Ph para-CH),
132.6 (d, 3JPC = 19 Hz, Ph meta-CH), 137.2 (d, 1JPC = 12 Hz, Ph Cipso),
2
1
169.1 (d, JPC = 9 Hz, CONH); 31P{ H} NMR (CDCl3, 161.90 MHz,
25 ◦C): −16.8 (s); IR DRIFTS (cm−1): 3326 m, 3070 vw, 3052 w, 3002
vw, 2962 m, 2930 w, 2874 w, 1945 vw, 1872 vw, 1802 vw, 1634 s,
1528 s, 1482 w, 1460 w, 1432 m, 1398 m, 1344 vw, 1314 w, 1276
vw, 1246 w, 1188 w, 1150 m, 1098 w, 1068 w, 1028 w, 1000 w,
956 w, 910 vw, 884 vw, 856 w, 788 w, 736 s, 692 s, 618 vw, 582 w,
502 m, 476 m, 429 w; HR MS: calc. for C17H21NOP: 286.1355, found
286.1354.
Acknowledgements
Financial support from the Czech Science Foundation (project
nos. 104/09/0561 and 13-08890S) and the Grant Agency of Charles
University in Prague (project no. 639512) is gratefully acknowl-
edged.
4.8. Preparation of metal scavenger 12
References
Silica gel for column chromatography (Fluka, particle size
0.063–0.2 mm; 100 g) was dried by heating to 550 ◦C for 8 h, cooled
under nitrogen and mixed with dry toluene (1000 mL). Neat (3-
chloropropyl)triethoxysilane (42 mL, 0.17 mol) was added to the
suspension and the resulting mixture was heated at reflux for 24 h.
After cooling to room temperature, the reaction mixture was fil-
tered and the filtrate was washed successively with toluene (1.5 L),
acetone (1.0 L), methanol (2.0 L) and, finally, with dichloromethane
(500 mL). The obtained solid was dried in the air to give chloro-
propylated silicagel 11 (95 g).
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(cm−1): 3742 w, 3660 w, 3268 w br, 2980 w, 2956 vw, 2936 vw,
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Material 11 (13.0 g), freshly dried at 130 ◦C under vacuum for 2 h,
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(10.0 mL, 67 mmol). The resulting mixture was heated at reflux for
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reactor Heidolph Synthesis I. In a typical run, n-butyl acrylate
(0.127 g, 1.0 mmol), bromobenzene (0.236 g, 1.5 mmol), sodium
acetate (1.5 mmol) and palladium catalyst (1 mol.% Pd) were mixed
in the appropriate solvent (typically N,N-dimethylacetamide;
5 mL). The reaction vessels were sealed and heated at the appropri-
ate temperature. Small aliquots were withdrawn and centrifuged
at 4000 rpm for 5 min before analyzed by gas chromatography
using an Agilent 6850 chromatograph equipped with a DB-5 col-
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20 m). Decaline or n-dodecane were used as internal standards.
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the appropriate ligand (20 ␮mol) and palladium acetate (10 ␮mol)
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214
M. Semler et al. / Catalysis Today 227 (2014) 207–214
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