Methoxycarbonylation of olefins catalyzed by palladium(II) complexes containing naphthyl(diphenyl)phosphine ligands

Article abstract of DOI:10.1002/aoc.3137

Palladium(II) complexes containing phosphine donor ligands derived from naphthyl(diphenyl)phosphine were synthesized and characterized by NMR and elemental analysis. The complexes were studied as catalyst precursors in the methoxycarbonylation reaction of several aromatic and aliphatic olefins under mild conditions. The catalysts reported high chemoselectivities (over 96%) and regioselectivities between 44% and 93% for different olefins. The best results were obtained over a styrene substrate with 97% of conversion after 6 h of reaction, with high regioselectivity (93%). Kinetic studies permitted the determination of the rate law (v-‰=-‰k [substrate] ^1.21±0.02 [catalyst]^0.94±0.11 [acid] ^0.52±0.03 [MeOH]^0.53±0.05 [CO] ^0.65±0.03) for methoxycarbonylation of styrene.

Full text of DOI:10.1002/aoc.3137

Full Paper
Received: 21 November 2013
Revised: 31 January 2014
Accepted: 10 February 2014
Published online in Wiley Online Library: 1 April 2014
(wileyonlinelibrary.com) DOI 10.1002/aoc.3137
Methoxycarbonylation of olefins catalyzed by
palladium(II) complexes containing naphthyl
(diphenyl)phosphine ligands
Santiago Zolezzia, Sergio A. Moyab, Gonzalo Valdebenitoa, Gabriel Abarcaa,
Jose Paradaa and Pedro Aguirrea*
Palladium(II) complexes containing phosphine donor ligands derived from naphthyl(diphenyl)phosphine were synthesized and
characterized by NMR and elemental analysis. The complexes were studied as catalyst precursors in the methoxycarbonylation
reaction of several aromatic and aliphatic olefins under mild conditions. The catalysts reported high chemoselectivities (over 96%)
and regioselectivities between 44% and 93% for different olefins. The best results were obtained over a styrene substrate with
97% of conversion after 6 h of reaction, with high regioselectivity (93%). Kinetic studies permitted the determination of the rate
law (v=k [substrate]1.21 0.02 [catalyst]0.94 0.11 [acid]0.52 0.03 [MeOH]0.53 0.05 [CO]0.65 0.03) for methoxycarbonylation of styrene.
Copyright © 2014 John Wiley & Sons, Ltd.
Keywords: methoxycarbonylation; olefin carbonylation; palladium catalysts; homogeneous catalysis
hydroxycarbonylation of styrene using palladium complexes. They
found that palladium hydride and palladium acyl species were
Introduction
It has been widely reported that palladium complexes catalyze
the reactions of aromatic or aliphatic olefins with CO to produce
esters or acids in the presence of alcohol or water, respectively.[1]
These products are important chemicals used in the manufacture
of several industrial products such as solvents, perfumes, drugs
and flavorings. The branched esters are of interest in the pharma-
ceutical industry because they are precursors for an important
class of non-steroidal anti-inflammatory drugs like naproxen[2]
and ibuprofen.[3,4] The most active catalysts for this reaction are
Pd(II) complexes containing phosphine ligands, and the impor-
tant issue is the selectivity towards either linear or branched
products. Methoxycarbonylation of styrene produces compounds
such as 2-phenylpropionic (methyl-2-phenylpropanoate) and
3-phenylpropionic esters. Regioselectivity is strongly dependent
on the catalytic system employed and the reaction conditions
used. In general, monocoordinated phosphorus ligands were
mainly employed to produce branched esters.[5] When palladium
(II) complexes with bidentate phosphorus ligands were used, pre-
dominantly linear esters were produced.[6,7] Some years ago, Kiss[8]
reported on the Reppe carbonylation of several substrates by
palladium–phosphine complexes. It is widely accepted that in this
type of reaction the catalytic cycle starts from the insertion of olefin
into the Pd-hydride complex or into a Pd-carboalkoxy species.[8,9]
The Pd(II)-hydride species is formed from the precursor and a
hydrogen source such as acid, water or hydrogen,[10,11] while the
Pd-carboalkoxy species is formed by the action of an alkanol on
the Pd-carbonyl species.[3,10,12,13] Recently, Fuente et al.[14] reported
on the methoxycarbonylation of ethene in an interesting study of
the mechanism of the catalytic reaction using palladium–
phosphine complexes. This mechanism suggests that Pd-hydride
and Pd-OMe are the active species in the catalytic reaction. On
the other hand the Claver group[15–17] proposed a mechanism for
present, which suggests a catalytic cycle involving palladium
hydride, palladium alkyl and palladium acyl intermediates.[18] In
our case, we have been studying the methoxycarbonylation of
styrene using palladium complexes which contain phophorus–
nitrogen ligands.[19] We found that Pd-hydride formation was
promoted by p-toluenesulfonic acid concentration, and deuterium
labeling experiments confirmed that the branch and linear esters
are products of the catalytic reaction.
Consistently high selectivities in the hydroesterification
reaction towards branched isomers have been obtained using
complexes of Pd(II) with PPh3 and p-toluenesulfonic acid as a
promoter.[8,10–12,20,21] The absence of both compounds generates
traces of esters and Pd metal and an inactive complex of Pd(0).
It has been proposed that the role of p-toluenesulfonic acid
(p-TsOH) is to facilitate the formation of a Pd-hydride intermediate
and to reactivate the Pd(0) species by the addition of PPh3 via an
oxidative addition of the acid.
In this work we report on the synthesis and characterization of
the palladium(II) complexes containing naphthyl(diphenyl)phos-
phine ligands (Scheme 1).
The complex dichloro-bis(1-naphthyl(diphenyl)phosphine)Pd(II)
(1) was used as a catalyst precursor in the methoxycarbonylation
*
Correspondence to: Pedro Aguirre, Universidad de Chile, Facultad de Ciencias
Químicas y Farmacéuticas, Casilla 233, Santiago 1, Chile. E-mail: paguirre@ciq.
uchile.cl
a Universidad de Chile, Facultad de Ciencias Químicas y Farmacéuticas, Santiago 1,
Chile
b Universidad de Santiago de Chile, Facultad de Química y Biología, Santiago,
Chile
Appl. Organometal. Chem. 2014, 28, 364–371
Copyright © 2014 John Wiley & Sons, Ltd.

Methoxycarbonylation of olefin by palladium(II) complexes
catalyst has an induction period, which makes it very difficult to
determine the initial rate of reaction because it is not clear when
the reaction was initiated.
Material and Methods
Method of Initial Rates
One of the first steps in studying the kinetics of a chemical reac-
tion is to determine the rate law for the reaction. One method for
making this determination is to measure experimentally how the
concentration of a reactant or product varies with time, which
makes it possible to build a typical plot of the kinetics. Another
strategy for determining the rate law is to use the method of
initial rates. This method involves measuring the rate of reaction
at very short times before any significant changes occur in
concentration. The rate law for the methoxycarbonylation of olefin
reaction was determined using the method of initial rates.
Equation (1) shows the factors that influence the methoxy-
carbonylation of olefins.
Scheme 1. Palladium(II) complexes containing naphthyl(diphenyl)phos-
phine ligands.
a
b
c
d
e
v ¼ k½styreneꢀ ½COꢀ ½p ꢁ toluenesulfonic acidꢀ ½catalystꢀ ½MeOHꢀ
(1)
To determine the initial rate for each variable, the parameters are
varied one at a time while the rest remain constant. For example, if
only styrene concentration varies while all other parameters are
kept constant, equation (1) takes the following form:
a
v ¼ k′½styreneꢀ :
(2)
The natural logarithmic expression is
a
ln v ¼ ln k′ þ α ln½styreneꢀ :
(3)
The value of ln vinitial obtained at different concentrations of
styrene allows us to obtain the parameter a from a plot ln vinitial
versus ln [styrene]. The same procedure was used to obtain b, c,
d and e. The initial law was determined using the experimental
conversion in short reaction times obtained from GC analyses.
The experimental data in all cases were determined with three
replicates (n = 3) to ensure accuracy. Results are presented as the
mean SD (standard deviation) of three determinations.
Scheme 2. Products of methoxycarbonylation reactions.
reaction of various olefins under mild conditions of pressure and
temperature (see Scheme 2). This precursor showed high activity in
the methoxycarbonylation of styrene and moderate conversion for
cyclohexene, α-methylstyrene, or n-hexene. The complex (1) showed
an activity of 93% for styrene methoxycarbonylation, with high
selectivity toward the branched products. In contrast, cyclohexene,
α-methylstyrene and n-hexene showed conversion levels between
40% and 61% under the conditions of this catalytic reaction.
A similar result has been found with the complex triflurome-
thanesulfonate [bis(1-naphthyl)diphenylphosphine]palladium(II)
(2). This precursor shows high conversion and selectivity for the
styrene methoxycarbonylation.
The catalytic behavior on styrene was studied in further detail.
Modifications of several experimental conditions were performed
in order to improve the results. To study the kinetics of the reac-
tions we used the initial rates method. Moreover, the effect of
several variables – such as CO, p-TsOH, MeOH, catalyst and sub-
strate on turnover frequency (TOF), conversion, regioselectivities
and initial rates – has also been studied.
Experimental
Materials
Diphenylphosphine chloride (PPh2Cl), 1-bromonaphthalene and
p-toluenesulfonic acid monohydrate (p-TsOH) were obtained
from Aldrich and used without previous treatment. All the sub-
strates (styrene, cyclohexene, n-hexene and α-methylstyrene)
were purified using a short neutral alumina column (Merck)
immediately prior to use. The analytical-grade solvents used
(provided by Merck) were distilled by conventional methods
and dried before use.
Physical Measurements
Micro-elemental analysis was performed in a Fison-Carlo Erba EA
1108. NMR spectra were recorded on a Bruker 350 (MHz) instru-
ment. GC analysis was carried out with a PerkinElmer 8500P
instrument equipped with flame ionization detector, using a
Carbowax 20M column and nitrogen as carrier gas. GC-MS was
On the other hand, when trying to determine the kinetic
law for other olefins such as cyclohexene, α-methylstyrene and
n-hexene, it was not possible to obtain reliable values for the rate
law, because the reactions with these olefins are slower and the
Appl. Organometal. Chem. 2014, 28, 364–371
Copyright © 2014 John Wiley & Sons, Ltd.
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S. Zolezzi et al.
performed in order to confirm the identities of the products in a
Thermo Electron Corporation Trace GC Ultra double-focusing
magnetic sector instrument (MAT 95XP).
was obtained. The AgCl was removed by filtration under nitrogen
and the solution evaporated under vacuum. The solid obtained
was recrystallized in CH2Cl2–diethyl ether at 0°C, and was recovered
by filtration and dried under vacuum. Yield 95%. Analysis: calcd (%)
for C46H34F6O6P2PdS2: C, 53.68; H, 3.33; found (%): C, 53.55; H,
Synthesis of 1-Naphthyl(diphenyl)phosphine
1
3.20. H NMR (CDCl3): 8.14 (H1, d, 8.1 Hz, 1H); 8.01 (H7, d, 8.0 Hz,
The syntheses of 1-naphthyl(diphenyl)phosphine and Pd(II)
complexes were carried out in Schlenk tubes under an inert
atmosphere (N2) using procedures similar to those previously
described for phosphorus–nitrogen complexes.[19]
1H); 7.86–7.76 (H5, H4, m, 2H); 7.63–7.52 (H2, H3, H6, m, 3H);
7.45–7.17 (PPh2, m, 10H). 13C NMR (CDCl3): 135.7 (C9, C―P); 135.1
(C11, C―P); 135.0 (o-Ph, C―H); 134.2 (m-Ph, C―H); 133.5 (C5);
132.9 (C10), 132.1 (C8, C―H); 130.8 (p-Ph, C―H); 130.3 (C6, C―H);
130.1 (C1, C―H); 129.6 (C3, C―H); 128.4 (C7, C―H); 127.6
(C2, C―H); 122.7 (CF3SO3). 31P NMR (CDCl3) 19 ppm (P1,S). IR
(KBr, cmꢁ1): 3055 (C―H); 1502 (C―H); 1482, 1437 (C―H);
693 (P―C); 1027 (―CF3); 1233 (―CF3); 1220 (S―O). UV–visible
(λ nm; CHCl3): 269, 303, 577.
Synthesis of the Ligand
1-Bromonaphthalene (1g, 2.5 mmol) was dissolved in THF (10
mL). This solution was cooled to ꢁ78°C and butylithium 1.6 M
(in hexane,1.9 mL, 3 mmol) was slowly added; the mixture was
stirred for 1 h and diphenylphosphine chloride (PPh2Cl) (0.45
mL, 2.5 mmol) was added, allowing the temperature to increase
slowly to 25°C. After 2 h the solvent was evaporated under vac-
uum and the oil obtained was dissolved in CHCl3 and precipi-
tated with diethyl ether. The solid powder obtained was dried
under vacuum and recrystallized in chloroform–diethyl ether.
White microcrystals were obtained with 75% yield. Analysis calcd
(%) for C22H17P: C, 84.80; H, 5.49; found (%): C, 84.70; H, 5.35. 1H NMR
(400 MHz, CDCl3): 8.40 (H1, dd, 7.8 Hz, 4.2 Hz, 1H); 7.89–7.84 (H4, H5,
m, 2H); 7.52–7.30 (PPh2, m, 10H); 7.03–6.99 (H2, H3, H6, H7, m, 4H).
13C NMR (CDCl3): 136.6 (C9, C―P); 136.4 (C11, C―P); 134.5 (o-Ph,
C―H); 134.2 (m-Ph, C―H); 132.2 (C5); 129.6 (C10); 129.0 (C8,
C―H); 128.8 (p-Ph, C―H); 128.7 (C6, C―H); 126.5 (C1, C―H);
126.2 (C3, C―H); 126.1 (C7, C―H); 125.8 (C2, C―H). 31P-[1H] NMR
(300 MHz, CDCl3): ꢁ21 (S). IR (KBr, cmꢁ1): 3056 (C―H); 1504
(C―H); 1479, 1433 (C―H); 776 (P―C). UV–visible (λ nm; CHCl3):
270, 303.
Methoxycarbonylation Reaction
All experiments were carried out in a stainless steel reactor
equipped with magnetic stirring, temperature control, pressure
gauge and a Pyrex glass beaker in order to prevent contamination.
In a typical experiment, the complex (32 mg, 0.04 mmol) was placed
in a pre-vacuum sealed atmosphere (N2) glass reactor together with
the substrate considered (16 mmol), p-TsOH (72 mg, 0.38 mmol)
and methanol (5 mL, 123 mmol) in 1.2-dichloroethane (DCE)
(15 mL) as solvent. The solution was introduced into the high-
pressure reactor (110 mL), which was purged three times with CO,
and then charged at the required pressure and heated at the
desired temperature. Samples of the reaction mixture were period-
ically extracted for analysis by GC and the pressure was ad-
justed if necessary. The kinetic parameters were determined
using 0.02 mmol palladium complex to obtain a low conversion
in the first hour of reaction.
Synthesis of Dichloro[bis(1-naphthyl)diphenylphosphine]
palladium(II) Complex (1)
Results and Discussion
Precursor PdCl2 (200 mg, 1.13 mmol) was dissolved in CH3CN
(20 mL) and (1-naphthyl)diphenylphosphine (705 mg, 2.26 mmol)
was added. The mixture was stirred for about 6 h under nitrogen.
A yellow solid was obtained with 80% yield. The product was
washed with diethyl ether (2 ꢂ 5 mL) and dried under vacuum.
The complex obtained showed low solubility in organic solvent.
To obtain the 13C NMR characterization, the chloro ligands of
the complex were replaced by trifluromethanesulfonate ligands.
Analysis calcd (%) for C44H34Cl2P2Pd: C, 65.89; H, 4.27; found
PdCl2 reacted with two equivalents of 1-naphthyl)diphenyl-
phosphine, generating the Pd(II) complex with high yield. The
paternal signal in 1H NMR and 31P NMR agreed well with the for-
mula proposed for the complexes.
Complexes 1 and 2 are stable in air. When they are dissolved in
1
CDCl3 or CD2Cl2, yellow solutions are obtained. H NMR and 31P
NMR spectra recorded at 5 m and after 24 h were similar,
suggesting that the complexes are stable in solution. Solutions of
the complexes prepared in solvent mixtures (methanol–toluene,
1:3 ratio) using concentrations in the range of those used in
catalysis experiments showed complete solubility, and they
were very stable.
1
(%): C, 66.01; H, 4.21. H NMR(CD2Cl2): 8.50 (H1, dd, 5.0 Hz, 8.5
Hz, 1H); 8.2 (H7, d, 9 Hz, 1H); 7.9–7.8 (H4, H5, m, 2H); 7.45–7.55
(H2, H3, m, 2H); 7.38–7.45 (PPh2, H6, m, 11H). 13C NMR (CDCl3):
135.2 (C9, C―P); 135.3 (C11, C―P); 135 (o-Ph, C―H); 134.9
(m-Ph, C―H); 134 (C5); 133.6 (C10); 132.9 (C8, C―H); 131 (p-Ph,
C―H); 130.5 (C6, C―H); 129.8 (C1, C―H); 128.9 (C3, C―H);
127.1 (C7, C―H); 126.5 (C2, C―H). 31P NMR (CDCl3) 22 ppm
(P1,S). IR (KBr, cmꢁ1): 3052 (C―H); 1505 (C―H); 1480, 1434
(C―H); 775 (P―C). UV–visible (λ nm; CHCl3): 268, 300, 572.
The 31P NMR spectra of the complexes showed a paternal
signal for phosphine ligands in trans or cis configuration. The
complexes were not crystallized with appropriate quality to obtain
X ray diffraction; however, similar compounds synthesized in the
literature suggest a trans phosphine configuration.[22,23] On the
other hand, Guang-Cun et al.[24] recently reported the synthesis of
polysubstituted furans using palladacycle catalysts containing
naphthyl(diphenyl)phosphine as ligands. This type of compound
was obtained when 1 equiv. palladium precursor reacts with 1
equiv. ligand after 24 h.[22–24] When the reaction was carried out
using 2 equiv. of the phosphine ligand, it was possible to obtain
only the complex of type PdL2Cl2 (L= naphthyl(diphenyl)phosphine
derivate ligand) and not the palladacycle complex.
Synthesis of Trifluromethanesulfonate[bis(1-naphthyl)
diphenylphosphine]palladium(II) Complex (2)
The dichloro[bis(1-naphthyl)diphenylphosphine]palladium(II) com-
plex (300 mg, 3.74 mmol) was suspended in CH2Cl2 (10 mL) and sil-
ver trifluromethanesulfonate (192 mg, 7.48 mmol) in CH2Cl2 (5 mL)
was added. The mixture was refluxed for 2 h and an orange solution
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Appl. Organometal. Chem. 2014, 28, 364–371

Methoxycarbonylation of olefin by palladium(II) complexes
Tables 1 and 2 show the catalytic activity of complexes 1 and 2
in the reaction of methoxycarbonylation of different olefins
under mild conditions of reaction. The complexes show similar
activities in all studied olefins. Both complexes show high conver-
sion in the styrene methoxycarbonylation of 93% and 97% for
complex 1 and 2 respectively in only 6 h of reaction. The other
studied olefins showed conversion between 40% and 67% with
similar behavior for both complexes.
The results indicate a high chemoselectivity towards the ester
product for all olefins considered in the study. On the other hand,
the regioselectivity (branched ester) for styrene and α-methylstyrene
was over 90%, except with hexene (>52% linear isomers).
Average values of several determinations are indicated in Fig. 1.
The graph shows the substantial difference in the catalytic
behavior observed with styrene with respect to the other alkenes.
The activity of styrene increases and a maximum conversion is
observed after around 6 h of reaction. The reaction of methoxycar-
bonylation with other olefins shows a slow conversion with a
maximum after around 24 h of reaction.
Figure 1. Methoxycarbonylation reaction of olefins catalyzed by trifluro-
methanesulfonate [bis(1-naphthyl)diphenylphosphine]palladium(II) com-
plex. Conditions of the reaction: Pd complex 0.04 mmol; substrate/
catalyst= 400; dichloroethane 15 mL; methanol 5 mL; temperature= 75°C.
Kinetic Styrene Study
The order of reaction was obtained using the initial rate method.
For example, in order to obtain the dependence on styrene, its
concentration was varied between 0.4 M and 1.7 M, keeping
constant all other parameters (concentration of p-toluenesulfonic
acid, carbon monoxide concentration, catalyst concentration and
methanol concentration). In this experiment the initial rate is a
function only of the concentration of styrene (see Table 3). The
slope of the graph, ln vinitial vs. ln [styrene], allows one to obtain
the order a for the reaction in which v =k′[styrene]a. Similar experi-
ments were performed in order to determine b, c, d and e of [CO],
[p-toluenesulfonic acid], [catalyst] and [MeOH] respectively.
Experiments were carried out to study the effects of modifica-
tions of several reaction parameters on the activity and selectivity
of both isomers formed during the methoxycarbonylation of
styrene using the trifluromethanesulfonate[bis(1-naphthyl)
diphenylphosphine]palladium(II) (complex 2).
Table 1. Methoxycarbonylation of olefins catalyzed by dichloro[bis
(1-naphthyl)diphenylphosphine]palladium(II)
Substrate
Selectivity
Conversion
(%)
TOF
The k of the rate law can be obtained from the point of
interception in a graph of ln vinitial vs. ln [substrate ] (see Fig. 2).
Where ln k′ = ꢁ2.93, k′ = 5.34 ꢂ 10ꢁ2 Thus, if the conditions are
k′ = k[catalyst]0.94 0.11 [acid]0.52 0.03 [MeOH]0.53 0.05 [CO] 0.65 0.03 for
[CO] = 2.0 M ; [acid] = 0.01 M; [Pd]= 0.001 M; [MeOH] = 3.1 M, the
Chemo- (%) Regio- (%)
Styrene
99
96
98
99
92a
88a
44a
93
40
61
47
62
7
α-Methylstyrene
n-Hexene
10
8
k-value can be calculated as k =135 0.6 (mol Lꢁ1 3.85
)
0.24 hꢁ1
.
Cyclohexene
100
Reaction conditions: Pd complex 0.04 mmol; substrate:catalyst
ratio = 400:1; dichloroethane 15 mL; methanol mL;
Effects of CO Pressure
5
temperature = 75°C; styrene reaction time 6 h; reaction time of
other olefins 24 h.
aBranched product.
The results of the effect of CO pressure on conversion and
regioselectivity are presented in Fig. 3(A,B). The figure shows that
regioselectivity is over 80% in the whole range of CO pressure,
but is increased with pressures over 20 bar. Above this value,
high regioselectivities between 97% and 100% were observed
for styrene between 1 h and 24 h of reaction time. Considering
Table 2. Methoxycarbonylation of olefins catalyzed by triflurome-
thanesulfonate[bis(1-naphthyl)diphenylphosphine]palladium(II)
Table 3. Determination of order a of reaction in the substrate for
methoxycarbonylation of styrene using the initial rate method
Substrate
Selectivity
Conversion
(%)
TOF
Chemo- (%) Regio- (%)
Conversion
(%)a
Initial rate Styrene
ln vinitial
ln [styrene]
Styrene
100
99
93a
90a
48a
97
47
67
51
65
8
(vinitial
)
(M)
α-Methylstyrene
n-Hexene
4.3 0.24
5.2 0.25
5.5 0.27
6.0 0.35
0.0172
0.0416
0.0715
0.1020
0.4
0.8
1.3
1.7
ꢁ4.0628459
ꢁ3.1796551
ꢁ2.6380578
ꢁ2.2827824
ꢁ0.9163
ꢁ0.2231
0.2624
100
97
11
9
Cyclohexene
100
0.5306
Reaction conditions: Pd complex 0.04 mmol; substrate:catalyst
ratio = 400:1; dichloroethane 15 mL; methanol mL;
temperature = 75°C; styrene reaction time 6 h; reaction time of
other olefins 24 h.
aBranched product.
5
Δc/Δt=vi constant = [CO], [MeOH], [p-toluenesulfonic acid], [catalyst],
amean of three experiments. Reaction time 1 h. Conversion
confirmed using internal standard method.
Appl. Organometal. Chem. 2014, 28, 364–371
Copyright © 2014 John Wiley & Sons, Ltd.
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S. Zolezzi et al.
the CO pressure/reaction time relation, it is possible to conclude
that over 50 bar the conversion does not increase significantly
after 1 h of reaction, but after 24 h the methoxycarbonylation
of styrene shows 100% conversion.
When the effect of the pressure of CO is studied (Fig. 3A,B), the
conversion is linear with increasing pressure during the first hour
of reaction. However, the conversion measured after 24 h shows
that above 50 bar the conversion decreases. Nonlinearity is
observed between conversion and the increase of pressure
above 50 bar after 24 h.
Selectivity was maintained over 97% for the branched product
(Fig. 3B). The kinetic parameter was calculated by using the
initial rate method, obtaining the following order for Pco: v = k
[CO]0.65 0.03. This result suggests that initial pressure is critical
in order to obtain high conversion, and no linear effects
were observed.
Figure 2. Relationship between ln vinitial vs. ln [substrate concentration].
Effect of p-Toluenesulfonic Acid Concentration
Fig. 4(A,B) shows the conversion and regioselectivity for different
p-toluenesulfonic acid concentrations. The study was carried out
over a range between 0.0016 M and 0.045 M p-toluenesulfonic
acid. In this range, the level conversion in the metho-
xycarbonylation of styrene reaction was enhanced when the
concentration of p-TsOH was increased. The conversion
obtained between 1 h and 24 h of reaction suggests that the acid
concentration is very important in the catalytic reaction.
However, when using over 0.045 M of acid concentration, the
conversion did not improve significantly. These results show that
the Pd-hydride species could play a key role in the first steps of
the catalytic cycle. The role of p-TsOH acid is to promote the
formation of the Pd-hydride intermediate, which has been previ-
ously reported as key to the catalytic cycle of this reaction.[25–29]
(A)
Using the Initial rate method, the rate law obtained was v = k
0.03
[p-toluenesulfonic acid]0.52
.
When conversion during the catalytic process was examined,
in all cases the conversion obtained was 100%, but when the acid
concentration was increased the maximum conversion was
obtained in a shorter reaction time, as shown in Fig. 4(B). For
example, when the acid concentration was 0.045 M, 100% conver-
sion was obtained after only 3 h of reaction, but when the acid
concentration was lower 100% conversion required a longer time
of reaction. Thus, if an acid level of 0.0016 M is used, a reaction
time of 24 h is required in order to reach 100% conversion.
(B)
Palladium Concentration
The results for the effect of the concentration of Pd(II) com-
plex on the conversion and regioselectivity are presented in
Fig. 5(A,B). Conversion in the methoxycarbonylation of styrene
was higher when the palladium concentration was increased
during the first hour of reaction. However, when the palla-
dium concentration varied between 0.5 mM (0.01 mmol) and
1.0 mM (0.02 mmol) the effect was not clear during the first
hour of reaction. On the other hand, after 6 h of reaction,
the effect of palladium concentration was very important
because significant levels of conversions were obtained with
regioselectivity towards the branched product of about 98%.
Figure 3. (A) Effect of CO pressure after 1 h and (B) after 24 h of reaction.
Reaction conditions: Pd 0.02 mmol; p-toluenesulfonic acid:catalyst ratio =
10:1; substrate:catalyst ratio = 400:1; DCE 15 mL; methanol 3.1 M.
The kinetic parameter using the initial rate method allowed
0.11
us to calculate the rate law, which was v = k [catalyst]0.94
.
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Methoxycarbonylation of olefin by palladium(II) complexes
(A)
(A)
(B)
(B)
Figure 4. (A) Effect of p-TsOH concentration after 1 h of reaction. (B)
Effect of p-TsOH concentration in the maximum conversion in styrene
methoxycarbonylation. Reaction conditions: Pd 0.02 mmol; p-
toluenesulfonic acid 0.0016–0.045 M; substrate:catalyst ratio = 400:1; DCE
15 mL; methanol 3.1 M; PCO = 50 bar.
Figure 5. Effect of catalyst concentration in methoxycarbonylation
olefin conversion and selectivity after (A) 1 h and (B) after 6 h of reaction.
Conditions of reaction: substrate:catalyst ratio = 400:1; p-toluenesulfonic
acid:catalyst ratio = 10:1; DCE 15 mL; methanol 3.1 M; PCO = 50 bar.
Effect of Styrene Concentration
Effect of Methanol Concentration
The results for the effect of styrene concentration on conversion
and regioselectivity are shown in Fig. 6(A,B). During the first
hours of reaction a linear effect between styrene concentration
and conversion was observed. For a longer time of reaction,
around 24 hours, no linear effect between styrene concentration
and conversion was observed. Over 10 mmol styrene, the conver-
sion did not improve significantly. This fact suggests that the
palladium complex decomposes during the catalytic reaction,
due probably to the fact that the high concentration of substrate
generates a large amount of product, which tends to react with
the catalyst to produce a poisoning effect, consequently decreas-
ing the conversion. However, the regioselectivity of the catalytic
process was maintained around 98% at 1 h and 95% at 24 h in
all the ranges studied (400:1 to 1700:1). The kinetic parameter
The results of the effect of methanol concentration are summa-
rized in Fig. 7(A,B). They indicate that the conversion and
regioselectivity decreased when the methanol concentration
was increased. Figure 7(A) shows the conversion and selectivity
during the first hour of reaction. When the methanol concen-
tration was increased beyond 12 M the activity decreased signif-
icantly, with low regioselectivity. The change in regioselectivity
suggests a decomposition of the active species forming Pd(0).
This behavior is more significant after 24 h of reaction. We have
studied the methoxycarbonylation using different organic
solvents, and in all cases the system was very sensitive to
methanol concentration. This fact was confirmed by metallic palla-
dium formation; however, using a low methanol concentration and
a short reaction time (1 h), it was possible to obtain a rate law: V = k
[methanol]0.53 0.05. This result has to be carefully analyzed, due to
the fact that the selectivity changed drastically in only 1 h of
using the initial rate method made it possible to calculate the
0.02
rate during the first hour of reaction: v = k [substrate]1.21
.
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S. Zolezzi et al.
(A)
(A)
(B)
(B)
Figure 6. Effect of styrene concentration on the methoxycarbonylation
reaction after (A) 1 h and (B) after 24 h of reaction. Reaction conditions:
Pd 0.02 mmol; p-toluenesulfonic acid:catalyst 10:1; DCE 15 mL; methanol
3.1 M; PCO = 50 bar.
Figure 7. (A) Effect of methanol concentration on conversion and
regioselectivity after 1h of reaction. (B) Effect of methanol concentration
on conversion and regioselectivity after 24 h of reaction. Reaction condi-
tions: Pd 0.02 mmol; substrate:catalyst 400:1; p-toluenesulfonic acid:cata-
lyst 10:1; DCE 15 mL; PCO = 50 bar.
reaction, which confirms the decomposition of palladium complex
when the methanol concentration increased above 3 M.
This work has sought to optimize the main variables affecting
methoxycarbonylation of olefins catalyzed by palladium(II)
complex with naphthylphosphine ligands.
the reason why the reaction should be performed at shorter
times in order to minimize this effect. Finally, the dependence
between catalyst and substrate is close to first order, although
this should be regarded with caution considering that, for high
concentrations of substrate, the catalyst tends to decompose
because the reaction product may react with palladium to form
an inactive species. The results obtained indicate that the
conversion and selectivity of the reaction increase when the
concentration of substrate and catalyst increases, obtaining prod-
ucts (esters) with improved yields and with high selectivity up to
a substrate:catalyst ratio of 400:1. On the other hand, the concentra-
tions of p-toluenesulfonic acid, carbon monoxide and methanol
must be handled with caution. The study shows that a pressure of
50 bar is optimal for the reaction. Above this value, a significant
increase is not observed in the conversion and selectivity. The
optimum concentration of acid to produce the best conversion
and selectivity to the branched esters ranges from 0.030 to
0.045 M. In addition, the acid produces a significant effect on
The reaction shows a nonlinear dependence on the acid
concentration (Fig. 4A) since, when the acid concentration is
doubled during the first hour of reaction, the conversion is
increased, but it is not proportional to the amount of acid added.
This is confirmed by the order of reaction obtained in the rate law.
Probably the excess of acid promotes the formation of a non-
catalytic species or secondary undesirable reaction, which
decreases the conversion rate achieved in the reaction. More-
over, both the CO and methanol drastically decreased the
conversion at 24 h when the pressure (50 bar) and concentration
(3 M) were increased. Under these conditions the formation of
metallic palladium was observed, together with a decrease in
the regioselectivity of the reaction, which is characteristic of the
decomposition of the palladium catalyst in the reaction. This is
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Methoxycarbonylation of olefin by palladium(II) complexes
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concentration must not exceed 3 M. Above this concentration there
is a substantial decrease in both activity and selectivity, since the
catalyst under these conditions is decomposed by the action of
methanol, drastically changing the efficiency of the reaction.
When the findings of our study are compared with those
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Palladium complexes containing naphthyl(diphenyl)phosphine
derivatives have been synthesized and characterized.
The use of a palladium complex containing naphthylphosphine
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methoxycarbonylation reaction of different olefins. The best result
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The experimental rate law for the reaction was determined
using the initial rate method:
1:21 0:02
0:94 0:11
v ¼ 135 0:6½substrateꢀ
½catalystꢀ
0:52 0:03
0:53 0:05
0:65 0:03
ꢂ½acidꢀ
½MeOHꢀ
½COꢀ
:
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Eur. J. Inorg. Chem. 2000, 647, 143.
Acknowledgment
We thank Fondecyt-Chile for financial support provided by
(Grant No. 1120149).
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Appl. Organometal. Chem. 2014, 28, 364–371
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