Supported palladium metal as heterogeneous catalyst precursor for the methoxycarbonylation of cyclohexene

Article abstract of DOI:10.1016/j.mcat.2019.110742

The methoxycarbonylation of cyclohexene has been carried out by using Pd metal deposited on a support as heterogeneous precursors instead of the homogeneous Pd(II) complexes usually proposed in literature. The two catalytic systems (homogeneous and heterogeneous) have been compared in methanol in the presence of free triphenylphosphine and p-toluenesulfonic acid as promoter. The precursor Pd on Amberlyst IRC 50 led to the best catalytic activity which is comparable to the activity obtained by using the homogeneous Pd(II)-catalyst. The leaching of the metal was negligible and the system has been efficiently recycled at least for three times. A reaction mechanism has been also proposed and discussed.

Full text of DOI:10.1016/j.mcat.2019.110742

MolecularCatalysisxxx(xxxx)xxxx
Contents lists available at ScienceDirect
Molecular Catalysis
journal homepage: www.elsevier.com/locate/mcat
Supported palladium metal as heterogeneous catalyst precursor for the
methoxycarbonylation of cyclohexene
Andrea Vavasoria,*, Sara Bravoa, Francesco Pasinatoa, Nurbolat Kudaibergenovb,
Luca Pietrobona, Lucio Ronchina
a Department of Molecular Science and Nanosystems, Ca’ Foscari University Venice, Scientific Campus, via Torino 155, 30172 Venezia, Italy
b Department of Chemistry and Chemical Technology, Al-Farabi Kazakh National University, al-Farabi 71, 050038 Almaty, Kazakhstan
A R T I C L E I N F O
A B S T R A C T
Keywords:
The methoxycarbonylation of cyclohexene has been carried out by using Pd metal deposited on a support as
heterogeneous precursors instead of the homogeneous Pd(II) complexes usually proposed in literature. The two
catalytic systems (homogeneous and heterogeneous) have been compared in methanol in the presence of free
triphenylphosphine and p-toluenesulfonic acid as promoter. The precursor Pd on Amberlyst IRC 50 led to the
best catalytic activity which is comparable to the activity obtained by using the homogeneous Pd(II)-catalyst.
The leaching of the metal was negligible and the system has been efficiently recycled at least for three times. A
reaction mechanism has been also proposed and discussed.
Palladium catalyst
Carbonylation
Supported homogeneous catalysis
1. Introduction
promoter, the structure of the ligands, the nature of the olefins carbo-
nylated, together with the kinetic and mechanistic aspects of the re-
The alkoxycarbonylation of alkenes, catalyzed by transition-metals,
is among the most important processes in the area of homogeneous
catalysis [1–3] (reaction 1).
action [26–33]. However, one of the major drawbacks from an in-
dustrial point of view of such homogeneous process is the need to
recover the catalyst from the reaction mixture [34,35]. An obvious
solution to this separation problem could be the use of heterogeneous
catalysts, which can be readily recovered by a simple filtration step
[36–40]. Among the several approaches proposed, some interesting
results have been obtained by immobilizing the homogeneous Pd(II)-
catalysts on an insoluble support (e.g., silica, alumina [41–44], or
polymers [45–57]). However, the synthetic methods usually utilized are
complicated leading to partly unknown structures of the Pd(II) species,
which are therefore less active but also more unstable (reduction to
inactive Pd(0) or Pd metal species).
(1)
Such reaction is widely used in industry to produce a variety of
esters which found application mainly as fragrant components in per-
fumes, cosmetics, and food essences [4,5], moreover it is also used in
many organic syntheses as valuable intermediate products [1–3,6].
As compared to other syntheses of esters, the alkoxycarbonylation of
olefins has such important advantages as one-step process, mild reac-
tion conditions, and the use of accessible reagents [1–3]. Furthermore,
it is highly atom-efficient which is important for chemical industries
interested to the sustainability of the process [7]. Undoubtedly, the Pd
(II)-phosphines catalysts appear as the most promising because afford
to high activity and selectivity under relatively mild conditions
[1–3,8–19]. For instance, in the first step of the Lucite Alpha-process for
the production of methyl methacrylate, a very active Pd-diphosphine
catalyst is used to catalyze the production of methylpropionate via
methoxycarbonylation of ethene [20–25].
In the present paper the authors propose to carry out the methox-
ycarbonylation of cyclohexene by using Pd metal deposited on a sup-
port as heterogeneous catalyst precursor. Such new starting precursor
has been compared with an homogeneous ones (for instance with the
[Pd(TsO)2(PPh3)2] complex previously studied by the authors [30]) in
methanol as solvent and in the presence of phosphines (e.g. triphenyl-
phosphine, PPh3) and a Bronsted acid (e.g. p-toluenesulfonic acid,
TsOH) as a promoter [30,31]. Different heterogeneous pre-catalysts
have been readily prepared and tested. Among these the Pd on Am-
berlyst IRC 50 led to the best catalytic activity, comparable to the
homogeneous system [Pd(TsO)2(PPh3)2] [30,31]. The leaching of the
With the aim to improve the catalytic activity several authors have
studied the influence of the process parameters, the nature of the acid
⁎ Corresponding author.
E-mail address: vavasori@unive.it (A. Vavasori).
https://doi.org/10.1016/j.mcat.2019.110742
Received 5 September 2019; Received in revised form 29 November 2019; Accepted 12 December 2019
2468-8231/©2019ElsevierB.V.Allrightsreserved.
Pleasecitethisarticleas:AndreaVavasori,etal.,MolecularCatalysis,https://doi.org/10.1016/j.mcat.2019.110742

A. Vavasori, et al.
MolecularCatalysisxxx(xxxx)xxxx
metal was negligible and the catalyst has been efficiently recycle at
least for three times. A reaction mechanism has been also proposed and
discussed.
Table 2
Influence of different heterogeneous catalyst precursors containing magnetite
on the methoxycarbonylation of cyclohexene.
entry
Catalyst
Conversion
cyclohexane methyl ester
detected in solution
(mola %)
(mol %)
2. Experimental
2.1. Reagents
1
2
3
4
5
6
7
8
9
Pd/C (3 %)
83
81
92
80
69
58
55
65
77
100
100
100
8
Pd/PK, (3 %)
Pd/Amberlyst IRC 50 (3 %)
Pd/Fe3O4, (3 %)
Methanol, cyclohexene, Palladium(II) acetate, triphenylphosphine
(PPh3), p-toluenesulfonic acid monohydrate (TsOH), Amberlyst IRC 50,
Dowex 1-X8, Amberlyst 15, Cellulose MFC (Type 101), Poly(4-vi-
nylpyridine) average Mw ∼60,000, and Poly(4-vinylpyridine-co-
styrene) powder were purchased from Sigma-Aldrich; Polyketone was
synthesized from CO and ethene (supplied by SIAD Company with 're-
search grade', purity > 99.9 %) as described in literature [58].
Pd/[C + Fe3O4 5%], (3 %)
Pd/[C + Fe3O4 15%], (3 %)
Pd/[C + Fe3O4 25%], (3 %)
Pd/[PK + Fe3O4 15%], (3 %)
Pd/[Amberlyst IRC50 +
Fe3O4 15%), (3 %)
30
16
12
25
31
Run conditions: Pd/Support = 50 mg (Pd
3
%, 0.014 mmol); Pd/PPh3/
2.2. Equipments
TsOH = 1/50/60; Cyclohexene =19.74 mmol (2 mL), solvent = MeOH
(8.0 mL, 197.75 mmol); T=120 °C; t = 2 h; PCO = 50 atm.
a
The catalyst precursors were weighted on a Sartorious Micro bal-
ance (precision 0.001 mg). Gas-chromatographic (GC) analysis was
performed on a Hewlett Packard Model 7890, Series II chromatograph
fitted with a HP5, 30 m ×0.35 mm ×0.53 μm column (detector: FID;
carrier gas: N2, 0.2 ml/min; oven: 45 °C (3 min) to 250 °C at 15 °C/min).
GC/MS analyses were performed on a MS Agilent apparatus 5975C
Model, interfaced with an Agilent chromatograph 7890 A Model
equipped with a HP5 column (30 m ×0.25 mm ×0.25 μm, oven: 45 °C
(3 min) to 250 °C at 15 °C/min).
[(moles of ester detected)/(moles of cyclohexene converted)]*100.
specific surface area of each solid has measured by using the N2 fisi-
sorption-BET technique.
2.4. Synthesis of magnetic supports
The synthesis of magnetic supports was performed by deposition of
Fe3O4 nanoparticles on support surface [40] (see Table 2). In a typical
procedure, 0.115 g of Fe3O4, suspended in 5 mL of methanol, was added
under vigorous stirring to 1 g of support (carbon black or PK) suspended
in 20 mL of methanol. The mixture has refluxed for 1 h and then the
solid has separated by a permanent magnet, washed with fresh me-
thanol and dried under vacuum. The specific surface area has measured
by using the N2 fisi-sorption-BET technique.
The ICP-OES (Inductively Coupled Plasma optical emission spec-
trometry) analyses, to identification and detection of trace metals, were
performed by using the PerkinElmer ®Optima 7300 DV ICP-OES in-
strument.
The specific surface area of the powders was measured by
Micromeritics Instrument Inc. USA apparatus, ASAP 2010 model.
2.3. Synthesis of Pd-metal supported pre-catalyst
2.5. Experimental setup
The palladium metal catalyst was successfully supported on the
solid showed in Tables 1 and 2 by using a standard wet impregnation
method [59,60]. In a typical procedure, 1 g of support was added, at
room temperature and under vigorous stirring, to a solution of 65 mg of
Pd(OAc)2 (Pd(II) acetate) in 50 mL of methanol. The Pd(OAc)2 con-
centration has been eventually arranged to obtain at the end the desired
Pd loading (ca. 3 %, w/w). The suspension was refluxed for 2 h under
vigorous stirring to assure a complete reduction of Pd(II) to Pd metal.
The solid catalyst was separated by filtration (or by using a permanent
magnet when Fe3O4 was deposed), washed and dried under vacuum.
The amount of Pd-metal deposed on the support was determined
through the ICP analysis (confirmed as ca. 3 %, within 1 % of error); the
All the experiments were carried out in a stainless steel batch re-
actor of ca. 50 mL of capacity, provided with a magnetic stirrer and a
temperature control system ( 0.5 °C). Carbon monoxide was supplied
from a gas reservoir (260 mL) connected to the reactor through a
constant pressure regulator.
2.6. Experimental procedure
In a typical experiment, known quantities of the pre-catalyst, PPh3
and TsOH along with 8 mL of methanol and 2 mL of cyclohexene were
charged into the reactor. The reactor was purged twice with carbon
monoxide at room temperature with stirring, pressurized with a low CO
Table 1
Influence of different heterogeneous catalyst precursors on the methoxycarbonylation of cyclohexene.
entries
Catalyst
Specific area
Average
Conversion
TOF
Leaching of Pd
(w/w %)
(m2/g)
porous diameter
(nm)
(mol %)
[mol ester/
(molPda * h−1)]
1
2
3
4
5
6
7
[Pd(PPh3)2(TsO)2]b
Pd/Carbon (3 %)
–
–
93
83
81
82
92
91
42
646
577
563
570
649
643
292
100b
6
842
40
2
6
Pd/PKc(3 %)
20
20
6
5
Pd/Cellulose
6
Pd/Amberlyst IRC 50 (3 %)
Pd/Amberlyst 15 (3 %)
Pd/Dowex 1-X8 (3 %)
2
0.3
0.1
12
40
0.3
30
11
Run conditions: Pd/Support = 50 mg (Pd
3 %, 0.014 mmol); Pd/PPh3/TsOH = 1/50/60; Cyclohexene =19.74 mmol (2 mL), solvent = MeOH (8.0 mL,
197.75 mmol); T=120 °C; t = 2 h; PCO = 50 atm.
a
is the total Pd metal present in the support before the reaction.
homogeneous catalyst Pd/PPh3/TsOH = 1/50/60 (mol/mol/mol) [30,31].
PK = poly(1-oxo trimethylene), named polyketone [61,62].
b
c
2

A. Vavasori, et al.
MolecularCatalysisxxx(xxxx)xxxx
pressure (ca. 5 atm) and then heated up. At the working temperature
the pressure was adjusted to the desired value (typically 50 atm total
pressure) and maintained constant throughout the experiment (i.e. 2 h)
by continuously supplying the carbon monoxide from the reservoir. At
the end of each experiment the reactor was quickly cooled to room
temperature and vented. The solid was recovered by filtration, washed
and dried under vacuum. To determinate the amount of leaching it has
been measured the amount of Pd on the solid before and after the re-
action by using the ICP technique (the % of leaching has been expressed
as [[(g of Pd in the solid before reaction)-(g of Pd in the solid after
reaction)]/(g of Pd in the solid before reaction)]x100. The qualitative
and quantitative analysis of the liquid was performed by using the
GC–MS and GC technique. The conversion has been expressed as:
[(initial moles of cyclohexene – final moles of cyclohexene)/ initial
moles of cyclohexene] * 100; In all experiments the material balance
has been verify and the selectivity to ester was 100 %
Pd/Amberlyst 15 (3 %) has been used (Table 1, entries 5 and 6)
whereas it is higher when Pd/Dowex 1-X8 (3 %) is used (entry 7).
Moreover, based on our previous work [40], it has been deposited a
dosed amount of ferrimagnetic Fe3O4 (magnetite) on the surface of
some supports in order to allow an easier recovery of the catalyst by
using an external magnetic field.
Table 2 shows that the addition of Fe3O4 decreases the conversion of
cyclohexene (entries 4–9) and that it differs consistently from the
amount of cyclohexane methyl ester effectively detected in solution;
Unfortunately, at the end of the reaction all the catalysts have lost the
initial magnetic properties. By increasing the amount of Fe3O4 on the
support the cyclohexene conversion slightly change and it further de-
creases the amount of ester detected in solution (entries 4–6). As in such
experiments the material balance is not satisfied (not further by-pro-
ducts were detected), we suppose that both cyclohexene and/or its ester
could be chemisorbed on the Fe3O4 causing also the lost of its magnetic
features. This point was not further investigated because it was not in
the aim of the present work. However, on the light of such results we
decided to avoid the use of Fe3O4 and to optimize the reaction condi-
tions by using the precursor Pd/Amberlyst IRC 50, which leads to the
best result.
2.7. Recycling experiments
The pre-catalyst was recovered from the reaction solution through a
simple filtration. It was thoroughly washed many time with methanol
and acetone and then dried under vacuum. The solid was weighted and
reused in the next reaction. In this case we prefer to evaluate the cat-
alytic activity in term of TOF (Turnover Frequency: moles of ester/
(moles of Pd*h)) which was calculated by considering that all the
amount of metal deposited on the surface was active in the catalysis.
This is because during the recycling operations part of the catalyst
(usually < 5 %) could be lost. The leaching in the successive reactions
was measured through the ICP analysis of the liquid phase. The next
reaction was carried out following the same procedures above de-
scribed (section 2.5).
3.2. Influence of PPh3 and TsOH on the catalytic activity and on the
leaching of palladium
The Fig. 1 shows that, in absence of PPh3 and at constant acid
concentration (for instance TsOH/Pd = 60/1), the reaction is not cat-
alyzed by Pd/Amberlyst IRC 50. However, by increasing the PPh3/Pd
molar ratio the catalyst become active and the conversion passes
through a maximum of 92 % when it is ca. 50/1.
At PPh3/Pd lower than ca. 45/1, the leaching of Pd measured was
less than 5 % of the initial metal deposited on the support. On the other
hand, at PPh3/Pd higher than 45/1 the lost of metal rapidly increases,
reaching ca. 15 % when PPh3/Pd is ca. 120/1 (conversion of ca. 50 %).
According with the studies on the homogeneous catalysis [26–33],
it is plausible that PPh3 reacts with the Pdmetal deposited on the surface
of the support forming solvable Pd(0) complexes. Such a complexes are
transformed in the active species (probably Pd(II)-H) through reaction
with the acid which increases the catalytic activity (see the Fig. 2).
However the conversion passes through a maximum because the in-
crease of free PPh3 concentration stabilizes the inactive Pd(0) species
against the active Pd(II)-H ones, causing a decrease of catalytic activity
(see the Fig. 1 and reaction mechanism).
3. Results and discussion
The methoxycarbonylation of cyclohexene (reaction 2) has been
efficiently carried out by using a heterogeneous catalyst precursor,
based on Pd metal deposited on an unsolvable support (Tables 1 and 2).
Although it was widely reported that such reaction is not catalyzed by
Pd metal [1–3,26–33], we found that by adding free PPh3 and TsOH,
similarly to the homogeneous catalytic systems [26–33], it can readily
form the active species and lead to the ester in high yield.
(2)
3.1. Influence of different supports on the catalytic activity
The Table 1 shows the activity of several Pdmetal-supported het-
erogeneous catalysts which has been compared with the activity ob-
tained by using the homogeneous [Pd(PPh3)2(TsO)2]/PPh3/TsOH (1/
50/60) system, previously studied by some of the authors [30,31].
All the pre-catalysts tested lead to good conversion regardless of
porosity and specific surface area of the support. Among these, Pdmetal
on Carbon (Pd/C), Pdmetal on polyketone (Pd/PK) and Pdmetal on cel-
lulose (Pd/cell) lead to comparable conversions (81–83 %), whereas
Pdmetal on ion exchange resins lead to different results (entries 5–7). In
particular, Pdmetal on Dowex 1-X8 leads to the worse conversion (42 %,
entry 5), whereas Pdmetal on Amberlyst IRC 50 and Pdmetal on Amberlyst
15 lead to the best conversions (92-91 %, entries 5, 6), which are almost
comparable to the conversion obtained by using the homogeneous
catalyst (93 %, entry 1).
Fig. 1. Influence of PPh3 on the catalytic activity of Pd/Amberlyst IRC 50 (3 %).
Run conditions: Pd/Amberlyst IRC 50 = 50 mg (Pd 3 % w/w); Pd/TsOH = 1/
60 mol/mol; Cyclohexene =19.74 mmol (2 mL), solvent = MeOH (8.0 mL);
T=120 °C; t = 2 h; PCO = 50 atm. TOF = moles of ester/[(moles of Pd in the
solid before reaction)*(reaction time)].
All the heterogeneous catalysts have been readily recovered at the
end of reaction by using a simple filtration apparatus. The leaching of
the metal measured was very poor when Pd/Amberlyst IRC 50 (3 %) or
3

A. Vavasori, et al.
MolecularCatalysisxxx(xxxx)xxxx
Fig. 4. Influence of catalyst recycling on the catalytic activity and on the
Fig. 2. Influence of TsOH on the catalytic activity of Pd/Amberlyst IRC 50 (3
%).
leaching of Pd.
Run conditions: Pd/Amberlyst IRC 50 = 50 mg (Pd
3
%,w/w); Pd/PPh3/
=19.74 mmol (2.0 mL),
solvent = MeOH (8.0 mL); T=120 °C; t = 2 h; PCO = 50 atm.
Run conditions: Pd/Amberlyst IRC 50 = 50 mg (Pd 3 %, w/w); Pd/PPh3 = 1/
50 mol/mol; Cyclohexene =19.74 mmol (2 mL), solvent = MeOH (8.0 mL);
T=120 °C; t = 2 h; PCO = 50 atm. TOF = moles of ester/[(moles of Pd in the
solid before reaction)*(reaction time)].
TsOH = 1/50/60 mol/mol/mol;
Cyclohexene
the same precursor can be used at least two times without significant
metal losses due to leaching (< 0.2 %). At the third time, however, the
catalytic activity decreases whereas the leaching increases up to 6.3 %.
According to this, the Fig. 2 shows that the catalyst is not active
without acid and linearly increases by increasing the TsOH concentra-
tion (constant PPh3 concentration, PPh3/Pd = 50/1).
3.5. On the reaction mechanism
3.3. Influence of temperature on the catalytic activity of Pd/Amberlyst IRC
50 (3 %)
The results above discussed suggest that the active species can form
in situ by reaction between PPh3, TsOH and Pd metal, similarly to what
is proposed in literature when the reaction is carried out by using the Pd
(II) homogeneous catalyst [1–3,26–33]. Consequently, we propose the
same reaction mechanism, schematized in the Fig. 5.
By increasing the temperature, the conversion passes through a
maximum at ca. 120 °C (see Fig. 3). At reaction temperatures higher
then 120 °C the conversion decreases, suggesting deactivation of the
catalyst probably due to decomposition of the active Pd(II) species to
form inactive Pd(0) complexes or Pd metal, similarly to what is re-
ported when the homogeneous catalytic system is used [30]. To note
that the leaching of metal practically does not change at different
temperatures remaining in all the tests below the 3 % w/w.
According to this, the solvable Pd-hydride species forms in situ from
Pd metal deposited on the solid surface and the free CO, PPh3 and
TsOH, present in solution, for instance following the reaction 3 and 4.
Pdmetal + (4 n)PPh3 + n CO
[Pd(CO)n (PPh3)4
]
with n=0
4
n
(3)
(4)
[Pd(CO)(PPh3)3] + TsOH
[PdH(CO)(PPh3)2]+ (TsO) + PPh3
3.4. Catalyst recycle
As the Pd(0) and/or Pd(II) complexes formed are solvable in the reac-
tion medium, it is plausible to suppose also that they determinates the
leaching observed. As a matter of fact, the Fig. 1 shows that by using a
large excess of PPh3 (PPh3/Pd higher than 50/1) the leaching increases,
but also decreases the conversion according to the fact that under such
conditions is favoured the formation of solvable, but inactive, Pd(0)
complexes. Moreover the low leaching generally measured in the ex-
periments reported in Table 1, suggests that the reaction occurs faster
The heterogeneous precursor has been recovered at the end of each
reaction and recycled (see experimental section). The Fig. 4 shows that
Fig. 3. Influence of temperature on the catalytic activity.
Run conditions: Pd/Amberlyst IRC 50 = 50 mg (Pd 3 %, w/w); Pd/PPh3/
TsOH = 1/50/60 (mol/mol/mol); Cyclohexene =19.74 mmol (2 mL),
solvent = MeOH (8.0 mL); T=120 °C; t = 2 h; PCO = 50 atm.
Fig. 5. Scheme of the proposed reaction mechanism.
4

A. Vavasori, et al.
MolecularCatalysisxxx(xxxx)xxxx
Table 3
Effect of addition of a pyridine based metal scavenger.
Experiment scavenger
(entry)
catalyst
Conversion TOF
(mol %)
92
(h−1
)
1
2
aPd/IRC 50
649
627
Pd/IRC 50 recycled from exp. 89
1
3
4
5
bPVPy
Pd/IRC 50
3
5
21
35
–
cPVPy- co-Sty Pd/IRC 50
Pd/IRC 50 recycled from exp. n.d.
3
Run conditions: Pd/Amberlyst IRC 50 (3 %) = 50 mg; Pd/PPh3/TsOH = 1/50/
60; Cyclohexene =19.74 mmol (2 mL), solvent = MeOH (8.0 mL); T=120 °C;
t = 2 h; PCO = 50 atm.
a
b
c
Pd/IRC 50 = Pd/Amberlyst IRC 50 (3 %).
PVPy = Poly(4-vinylpyridine) average Mw ∼60,000 = 150 mg.
PVPy- co-Sty = Poly(4-vinylpyridine-co-styrene) powder = 150 mg.
Fig. 6. Influence of reaction time on the catalytic activity and on the leaching of
Pd.
allow to the metal to remain inside the solid phase avoiding the
leaching. It is therefore plausible to suppose that the functional groups
of the support act as “heterogeneous” coordinating ligands (Fig. 7, path
a) and/or as cations exchanging resin between H+ and the [Pd(II)]+
cationic species which form during the catalytic cycle (Fig. 7, path b).
With the aim to test the homogeneity/heterogeneity of the catalytic
system, a metal scavenger has added to the reaction mixture [63–70].
In particular it has been added a polymer containing pyridine ligand
(see Table 3) which is referred as effective scavengers for soluble Pd
complexes or salts, due to the ability of the pyridine moiety to bind Pd
species [68–70].
Run conditions: cat: Pd/Amberlyst IRC 50 = 50 mg (Pd 3 %, w/w); cat/PPh3/
pTsOH = 1/50/60 (mol/mol/mol); Cyclohexene (2.0 mL, 19.74 mmol); MeOH
=8.0 mL; T=120 °C; PCO = 50 atm.
than the diffusion of the solvable Pd(0) (or Pd(II)) species into the bulk
and that such species are somehow retained within the solid. It is
plausible therefore that the catalysis starts near the surface and, de-
pending by the relative concentration of PPh3 and TsOH (in particular
inside the pores), the solvable Pd-species readily decompose forming Pd
metal again (equilibrium 3 moves to the left), which is re-deposited on
the surface.
The Table 3 shows that the addition of such metal scavenger causes
a decrease of catalytic activity (entries 3, 4), supporting the hypothesis
that the catalysis was due to the formation of solvable Pd-species into
the pores. According to this, in the experiment in which the Pd/Am-
berlist IRC 50 has been recycled (entry 5) the ester has not detected.
According to this, the Fig. 3 shows that by increasing the tem-
perature (> 110 °C) the conversion decreases suggesting a thermal
decomposition of the catalyst with probable formation of Pdmetal
.
However, at each temperatures tested, the leaching of Pd measured was
very poor (< 0.12 %), according with the hypothesis that a re-deposi-
tion of Pdmetal on the surface of the support readily occurs. This is
further supported by the finding that the leaching is not influenced by
the reaction time (Fig. 6 shows that at 7 h it is very low, < 0.12 %) but
only by the PPh3 and TsOH concentrations (Figs. 1 and 2).
4. Conclusions
The methoxycarbonylation of cyclohexene can be efficiently carried
out in methanol by using palladium metal deposited over an unsolvable
support as catalyst precursor. Although the catalytic activity depends
on the PPh3 and TsOH concentration and on the temperature, the best
results both in terms of productivity and leaching have been obtained
by using cations exchange supports.
A further influence on the amount of leaching measured should be
due to the nature of the support In facts, the Table 1 shows that when a
cations exchange support was used the leaching was very poor (entries
5 and 6). As a matter of facts, the carboxylate groups present in the
Amberlyst IRC 50 (sulfonate in Amberlyst 15) could interact with the
cationic Pd(II) species readily formed in situ. Such interaction could
Such heterogeneous system is proposed as a more sustainable cat-
alytic pathway for the alkoxycarbonylation of olefin in comparison to
Fig. 7. Scheme of the possible interactions of the Pd(II) complexes and the functional groups of the support. Path a: coordination to the metal center; Path b: cations
exchanging.
5

A. Vavasori, et al.
MolecularCatalysisxxx(xxxx)xxxx
the homogeneous catalysis (comparable results in terms of conversion).
This is because at first the catalyst can be readily recovered from the
solution through a simple filtration with a leaching of metal < 1 %
under optimized conditions, but also because it is stable (Pd metal), it
enables to easily weight a low amount of metal (3 % of Pd metal is
dispersed into an inert solid medium) and it can be recycled efficiently
at least for three time.
[20] K. Dong, R. Sang, Wei Z, J. Liu, R. Duhren, A. Spannenberg, H. Jiao, H. Neumann,
R. Jackstell, R. Franke, M. Beller, Chem. Sci. 9 (2018) 2510–2516.
[21] R.I. Pugh, E. Drent, Adv. Synth. Catal. 344 (2002) 837–840.
[22] C. Jimenez Rodriguez, D.F. Foster, G.R. Eastham, D.J. Cole-Hamilton, Chem.
Commun. (2004) 1720–1721.
[23] G. R. Eastham, C. Jimenez, D. Cole‐Hamilton, (Ed.: LUCITE), WO/2004/014834,
2004.
[24] A. Tullo, Chem. Eng. News 87 (2009) 22–23.
[25] A.A. Kelkar, S.S. Joshi, V.V. Ranade (Eds.), Industrial Catalytic Processes for Fine
and Specialty Chemicals, Elsevier, Amsterdam, Netherland, 2016, pp. 678–679.
[26] E.G. Chepaikin, A.P. Bezruchenko, K.A. Suerbaev, K.M. Shalmagambetov, Pet.
Chem. 46 (2006) 117.
CRediT authorship contribution statement
[27] G. Cavinato, L. Toniolo, A. Vavasori, Top. Organomet. Chem. 18 (2006) 125.
[28] A. Brennfuhrer, H. Neumann, M. Beller, ChemCatChem 1 (2009) 28.
[29] O.N. Temkin, L.G. Bruk, React. Kinet. Catal. Lett. 44 (2003) 661.
[30] A. Vavasori, L. Toniolo, G. Cavinato, J. Mol. Catal. A Chem. 191 (2003) 9–21.
[31] A. Vavasori, G. Cavinato, L. Toniolo, J. Mol. Catal. A Chem. 176 (2001) 11–18.
[32] S. Zolezzi, S.A. Moya, G. Valdebenito, G. Abarca, J. Parada, P. Aguirre, Appl.
Organomet. Chem. 28 (2014) 364–371.
Andrea Vavasori: Conceptualization, Methodology, Data curation,
Writing - original draft, Supervision, Writing - review & editing. Sara
Bravo: Methodology, Data curation. Francesco Pasinato: Data cura-
tion. Nurbolat Kudaibergenov: Writing - review & editing. Luca
Pietrobon: Data curation. Lucio Ronchin: Writing - review & editing.
[33] K. Kumar, J. Darkwa, Polyhedron 138 (2017) 249–257.
[34] P.T. Anastas, J.C. Warner, Green Chemistry: Theory and Practice, Oxford University
Press, New York, 1998.
Declaration of Competing Interest
[35] J. Hagen, Industrial Catalysis: A Practical Approach, Wiley-VCH, Weinheim,
Germany, 2006, pp. 1–14.
The authors declare that they have no known competing financial
interests or personal relationships that could have appeared to influ-
ence the work reported in this paper.
[36] M. Benaglia, Recoverable and Recyclable Catalysts, John Wiley & Sons, 2009.
[37] F.T. Hartley, Supported Metal Complexes, Dordrecht, Reidel, 1985.
[38] S. Albonetti, F. Cavani, F. Trifiro, Catal. Rev. Sci. Eng. 38 (1996) 413.
[39] A.M. Liu, K. Hidajat, S. Kawi, J. Mol. Catal. A Chem. 168 (2001) 303–306.
[40] A. Vavasori, L. Calgaro, G. Quartarone, L. Ronchin, C. Tortato, Pure Appl. Chem. 88
(2016) 445–455.
Acknowledgments
[41] J.H. Clark, D.J. Macquarrie, Chem. Commun. (1998) 853–860.
[42] Y.R. de Miguel, J. Chem. Soc., Perkin Trans. (2000) 4213–4221.
[43] C.E. Song, S.-G. Lee, Chem. Rev. 102 (2002) 3495–3524.
[44] H.P. Dijkstra, G.P.M. van Klink, G. van Koten, Acc. Chem. Res. 35 (2002) 798–810.
[45] J.W.J. Knapen, A.W. van der Made, J.C. deWilde, P.W.N.M. van Leeuwen,
P. Wijkens, D.M. Grove, G. van Koten, Nature 372 (1994) 659–663.
[46] D.E. Bergbreiter, B. Case, Y.S. Liu, J.W. Caraway, Macromolecules 31 (1998)
6053–6062.
This work was supported by the Department of Molecular Sciences
and Nanosystems of Ca’ Foscari University. The authors gratefully ac-
knowledge the support of dr. Matteo Martino for synthesis of magnetic
supports.
[47] D. Astruc, F. Chardac, Chem. Rev. 101 (2001) 2991–3024.
[48] L.Y.P. van den Broeke, E.L.V. Goetheer, A.W. Verkerk, E. de Wolf, B.-J. Deelman,
G. Van Koten, J.T.F. Keurentjes, Angew. Chem. Int. Ed. 40 (2001) 4473–4474.
[49] T.J. Dickerson, N.N. Reed, K.D. Janda, Chem. Rev. 102 (2002) 3325–3344.
[50] D.E. Bergbreiter, Chem. Rev. 102 (2002) 3345–3384.
[51] R. Van Heerbeek, P.C.J. Kamer, P.W.N.M. van Leeuwen, J.N.H. Reek, Chem. Rev.
102 (2002) 3717–3756.
References
[1] G. Kiss, Chem. Rev. 101 (2001) 3435–3456.
[2] M. Beller, Catalytic Carbonylation Reactions, Springer, Berlin, 2006.
[3] T. Kégl, L. Kollar (Ed.), Modern Carbonylation Methods, Wiley‐VCH Verlag GmbH &
Co., KGaA, 2008, pp. 161–198.
[4] K. Bauer, D. Garbe, Common Fragrance and Flavor Materials: Preparation,
Properties and Uses, VCH Verlagsgesellschaft, Weinheim, 1985.
[5] I.M. Nikitakis (Ed.), CFTA Cosmetic Ingredient Handbook, first edition, The
Cosmetic, Toiletry and Fragrance Association, Inc., Washington, DC, 1988.
[6] K. Nozaki, I. Ojima, Catalytic Asymmetric Synthesis, 2nd ed., Wiley, New York,
2000.
[52] S. Akiri, S. Ojwach, Catalysts 9 (2019) 143.
[53] B. Urbán, P. Szabó, D. Srankó, G. Sáfrán, L. Kollár, R.S. Földes, Mol. Catal. 445
(2018) 195–205.
[54] M. Mart, W. Tylus, A.M. Trzeciak, Mol. Catal. 462 (2019) 28–36.
[55] M. Sharma, M. Sharma, A. Hazarika, L. Satyanarayana, G.V. Karunakar, K.K. Bania,
Mol. Catal. 432 (2017) 210–219.
[7] D.J.C. Constable, M. Gonzalez, S.A. Morton, G. Ruiz-Mercado, H. Cabezas (Eds.),
Sustainability in the Design, Synthesis and Analysis of Chemical Engineering
Processes, Elsevier Inc., 2016, pp. 1–34.
[56] A.N. Marquard, L.E. Slaymaker, R.J. Hamers, R.H. Goldsmith, Mol. Catal. 429
(2017) 10–17.
[57] M. Nasrollahzadeh, N. Motahharifar, F. Ghorbannezhad, N.S.S. Bidgoli, T. Baran,
R.S. Varma, Mol. Catal. (2020), https://doi.org/10.1016/j.mcat.2019.110645.
[58] A. Vavasori, L. Ronchin, L. Toniolo, J. Mol. Catal. A: Chemical 363-364 (2012)
398–403.
[8] K. Kumar, J. Darkwa, Polyhedron 138 (2017) 249–257.
[9] K. Dong, X. Fang, S. Gulak, R. Franke, A. Spannenberg, H. Neumann, R. Jackstell,
M. Beller, Nature Commun. 8 (2017) 14117.
[10] Kh.A. Suerbaev, N.Zh. Kudaibergenov, A. Vavasori, Russian J. Gen. Chem. 87
(2017) 707–712.
[59] K.P. de Jong, Synthesis of Solid Catalysts, John Wiley & Sons, New York, 2009.
[60] M. Che, O. Clause, C. Marcilly, Handbook of Heterogeneous Catalysis, Wiley-VCH,
New York, 1997.
[11] J. Liu, K. Dong, R. Franke, H. Neumann, R. Jackstell, M. Beller, J. Am. Chem. Soc.
140 (2018) 10282–10288.
[61] A. Vavasori, L. Ronchin, L. Toniolo, Appl. Catal. A Gen. 449 (2012) 198–202.
[62] A. Vavasori, L. Ronchin, Polyketones: synthesis and applications, Encyclopaedia of
Polymer Science and Technology, John Wiley & Sons, Inc., 2017, pp. 1–41.
[63] J.M. Richardson, C.W. Jones, J. Catal. 251 (2007) 80.
[64] M. Weck, C.W. Jones, Inorg. Chem. 46 (2007) 1865.
[65] K. Yu, W. Sommer, J. Richardson, M. Weck, C. Jones, Adv. Synth. Catal. 347 (2005)
161.
[12] J. Liu, K. Dong, R. Franke, A. Spannenberg, H. Neumann, R. Jackstell, M. Beller,
Chem. Commun. 54 (2018) 12238–12241.
[13] H. Qi, Z. Huang, M. Wang, P. Yang, C.X. Du, S.W. Chen, Y. Li, J. Catal. 363 (2018)
63–68.
[14] S.O. Akiri, S.O. Ojwach, Inorg. Chim. Acta 489 (2019) 236–243.
[15] S. Zulu, M.G. Alam, S.O. Ojwach, M.P. Akerman, Appl. Organomet. Chem. 33
(2019) e5175.
[66] S. Klingelhöfer, W. Heitz, A. Greiner, S. Oestreich, S. Förster, M. Antonietti, J. Am.
Chem. Soc. 119 (1997) 10116.
[16] C. Jimenez Rodriguez, D.F. Foster, G.R. Eastham, D.J. Cole-Hamilton, Chem.
Commun. (2004) 1720–1721.
[67] K. Yu, W. Sommer, J.M. Richardson, M. Weck, C.W. Jones, Adv. Synth. Catal. 347
(2005) 161.
[17] K. Dong, X. Fang, S. Gülak, R. Franke, A. Spannenberg, H. Neumann, R. Jackstell,
M. Beller, Nat. Commun. 8 (2017) 14117.
[68] F.R. Hartley, Coord. Chem. Rev. 35 (1981) 143.
[18] K. Dong, R. Sang, X. Fang, R. Franke, A. Spannenberg, H. Neumann, R. Jackstell,
M. Beller, Angew. Chem. Int. Ed. 56 (2017) 5267–5271.
[19] M. Schmidt, T. Pogrzeba, L. Hohl, A. Weber, A. Kielholz, M. Kraume,
R. Schomäcker, Mol. Catal. 439 (2017) 1–8.
[69] Y. Ji, S. Jain, R.J. Davis, J. Phys. Chem. B 109 (2005) 17232.
[70] J.S. Chen, A.N. Vasiliev, A.P. Panarello, J.G. Khinast, Appl. Cat. A Gen. 325 (2007)
76–86.
6