Insight into PdCl2(bipy) complex as an efficient catalyst for heck reaction and kinetic investigations in homogeneous medium

Article abstract of DOI:10.1134/S0023158413030051

PdCl₂(bipy) complex (bipy = 2,2′-bipyrydine) efficiently catalyzes the vinylation of aryl halides. The activity of this catalyst for the Heck reactionwas demonstrated for a variety of aryl halides and olefins in the presence of different organic and inorganic bases. The catalyst is stable under the reaction conditions and no degradation was observed. The kinetics of the Heck coupling of styrene with iodobenzene using the PdCl₂(bipy) complex with potassium acetate as a base was studied over a temperature range of 393-413 K in 2-nitro-2-methyl-1-propanol medium. An empirical rate model has been proposed to fit the observed data and is found to be in good agreement with experimental results. The activation energy of the reactionwas found to be 98.70 kJ/mol.

Full text of DOI:10.1134/S0023158413030051

ISSN 0023ꢀ1584, Kinetics and Catalysis, 2013, Vol. 54, No. 3, pp. 314–321. © Pleiades Publishing, Ltd., 2013.
Insight into PdCl (bipy) Complex as an Efficient Catalyst
2
for Heck Reaction and Kinetic Investigations
1
in Homogeneous Medium
S. V. Jagtap and R. M. Deshpande
a,b
a,c
a
Chemical Engineering Division, National Chemical Laboratory, Maharashtra, Pune, India
b
B.G. College, Sangvi, Pune, India
c
Dow Chemicals International Pvt. Ltd., Yerawda, Pune, India
eꢀmail: sangeetajagtap@rediffmail.com
Received May 24, 2012
Abstract—PdCl (bipy) complex (bipy = 2,2'ꢀbipyrydine) efficiently catalyzes the vinylation of aryl halides.
2
The activity of this catalyst for the Heck reactionwas demonstrated for a variety of aryl halides and olefins in
the presence of different organic and inorganic bases. The catalyst is stable under the reaction conditions and
no degradation was observed. The kinetics of the Heck coupling of styrene with iodobenzene using the
PdCl (bipy) complex with potassium acetate as a base was studied over a temperature range of 393–413 K in
2
2
ꢀnitroꢀ2ꢀmethylꢀ1ꢀpropanol medium. An empirical rate model has been proposed to fit the observed data
and is found to be in good agreement with experimental results. The activation energy of the reactionwas
found to be 98.70 kJ/mol.
DOI: 10.1134/S0023158413030051
1
ethylformamide (DMF) to give a 94% yield of prodꢀ
uct.Surprisingly, the same authors report very little or
no activity for Heck reaction using the Pd complexes
of 2,2'ꢀbioxazoline or of 2,2'ꢀbipyridine ligands. Tsai
et al. [14] have used heterogenized palladium bipyridyl
complex anchored on MCMꢀ41 as an efficient and
The Heck reaction [1, 2]
Ar
CH2
PdCl (bipy)
2
NMP
Ar
CH
ꢀ
ꢁ
+
+
Ar X
CH
Olefin
BHX
CH
Product
Ar
Aryl halide 150
°C
Base
(bipy = 2,2'ꢀbipyrydine,
recyclable heterogeneous catalyst for Heck reactions
NMP = 2ꢀnitroꢀ2ꢀmethylꢀ1ꢀpropanol)
6
with a Turn Over Number (TON) up to 10 .
nꢀButyl
bipy = 2,2'ꢀbipyrydine, NMP = 2ꢀnitroꢀ2ꢀmethylꢀ1ꢀ acrylate on reaction with pꢀbromoacetophenone was
propanol) is an important class of C–C coupling reacꢀ reported to give a 98% conversion in 16 h, but for iodoꢀ
tions [3, 4], as it is tolerant to many functional groups benzene 96 hare needed to achieve the same converꢀ
[
5]. The use of Pd–phosphine complexes for the Heck sion level. There is however no study on the Heck reacꢀ
reaction has been reported in a number of studies [6]. tion in a homogeneous medium using this Pd complex
These catalysts are known to suffer decomposition in catalyst. The Heck reaction using iminophosphine–
the course of the reaction involving the palladacycle palladium (0) complexes in NMP [15], has been
catalysts, which are reportedly more stable than the reported by Scrivanti et al. This catalyst is active only
monodentate phosphine complexes [7]. Hence, the in an inert atmosphere and is easily poisoned in the
development of stable phosphineꢀfree catalysts resistꢀ presence of oxygen.
ent to the reaction temperatures encountered in the
The kinetics of Heck reaction using Pd complexes
Heck reaction would be an important achievement. has been reported in a few studies [16–21]. In general
Compared to the phosphine modified Pd catalysts, the it has been observed that the catalyst activity has a posꢀ
Pd complexes incorporating nitrogenꢀcontaining itive dependence on olefin, aryl halide and the base.
ligands although equally active have received less All these studies have been conducted with PdCl2 or
attention [8–11]. There are still few reports on the Pdꢀphosphine complexes. For the phosphineꢀfree
kinetics of Heck reactions using Pd complexes with complexes only few studies on the kinetics exist. Rosꢀ
nitrogen containing ligands [12, 13].
ner et al. [12] have investigated the kinetics of olefinaꢀ
ꢀbromobenzaldehyde with butyl acrylate using
Cabri et al. [8] have reported that Pd complexes of tion of
p
bidentate nitrogen ligand such as 1,10ꢀphenanthroline a dimeric CNꢀpalladacycle complex underthe dry
derivatives are active for Heck reactions in N,Nꢀdimꢀ conditions. They observed a firstorder dependence on
olefin concentration and a zero order dependence on
1
The article is published in the original.
aryl halide (pꢀbromobenzaldehyde) concentration.
314

INSIGHT INTO PdCl (bipy) COMPLEX AS AN EFFICIENT CATALYST
315
2
They also proposed an empirical rate model to predict
the rate observed for the dimeric palladacycle complex
with chelating nitrogen ligands [18]. Consorti and
EXPERIMENTAL
, 2,2'ꢀbipyridine, the olefins and aryl halides
2
PdCl
coworkers [13] reported a first order dependence with used were procured from “Aldrich”(USA) and used
respect to Pd catalyst and a fractional order with without any further treatment. The solvents were
respect to iodobenzene and methyl acrylate for the obtained from “Ms SDs Chemicals”(India). Bases
coupling of aryl halides with butyl acrylate and methyl and tetrabutyl ammonium bromide (TBAB) used were
acrylate using the CNꢀpalladacycle. Van Strijdonck of analytical grade, purchased from “Loba Chemiꢀ
et al. [22] reported a first order kinetics on styrene and cals” (India).
a zero order on iodobenzene concentration for
A portion of the reaction mixture was periodically
Pd(dba) catalyst (dba = dibenzylideneacetone). An
taken out from the round bottom flask and was anaꢀ
empirical rate equation was derived to fit the experiꢀ
lyzed for its contents by using a capillary gas chroꢀ
mental data.
matograph Agilent 6850 series (India) with flame ionꢀ
ization detector, on HP1 column with film thickness
We report here the results of our investigation into
the Heck reaction catalyzedby the PdCl (bipy) comꢀ
2
0
.25
μ
m
(initial temperature 80
°
C, final temperature
plex. Contrary to the reports mentioned earlier, the
250
°
C). Formation of stilbene was confirmed on GC
PdCl (bipy) complex as catalyst was very efficient for
2
by comparison with authentic standards. The identifiꢀ
cation of products of screening reaction was done
using a GC–MS Agilent 6890N series equipped with
Heck reaction in polar solvents. This catalyst is stable
and does not degrade to metallic Pd as most of the
other catalysts reportedly do, permitting the reactions
to occurat higher temperatures. This catalyst was
applied for the coupling of a variety of aryl halides and
olefins in the presence of different organic and inorꢀ
ganic bases in different solvents. Further, in order to
understand the kinetics and mechanism of this reacꢀ
tion, the effect of the process parameters on the cataꢀ
5
973N mass selective detector. Besides the confirmaꢀ
tion from GC–MS the identification was also conꢀ
firmed with authentic samples of the products—cis
ꢀ
and transꢀstilbenes. No other products except these
two were observed in the GC analysis. 1,1ꢀDiphenyl
ethylene can form as an additional product in the reacꢀ
tion, however it was not observed in this case because
its concentration was very low (below the detectable
limit).
lytic activity of the PdCl (bipy) complex was also
2
investigated for the Heck coupling of styrene with
iodobenzene in a temperature range of 393–413 K. An
empirical rate model has been proposed which was
found to fit the experimentaldata.
The conversion of the aryl halide (Ar–X) and TON
were calculated by using the following relations:
Initial amount of ArX(mole)ꢀFinal amount of Ar−X(mole)
Conversion =
× 100,
(1)
Initial amount of Ar−X(mole)
added. TBAB (1% of base) was added as a phase transꢀ
fer agent every time in case of inorganic bases. Then
Nꢀmethylꢀ2ꢀpyrrolidinone was added to make the volꢀ
ume to 10 mL. The reaction was carried out for 1 h at
Amount of product(mole)
TON =
.
(2)
Amount of catalyst(mole)
150 C.
°
Procedure for Preparation of Catalyst
In a typical preparation, 0.234 g (1.33 mmol) 2,2'ꢀ
bipyridine was added into a 50 ml round bottom flask
containing 10 ml methanol, 0.266 g (1.33 mmol)
PdCl2. The mixture was stirred at room temperature
General Procedure for Kinetic Studies
In a 25 mL two necked round bottom flask styrene,
iodobenzene, potassium acetate, TBAB (1% of base),
for 6 h. An orange yellow colored PdCl (bipy) comꢀ
2
and catalyst PdCl (bipy) were added as per the requiꢀ
2
plex precipitated, which was filtered and washed with
methanol and then dried under vacuum. Practical
yield of the complex was 0.440 g (88%). Characterizaꢀ
site concentration. Nꢀmethylꢀ2ꢀpyrrolidinone was
then added to make volume to 10 mL. The reaction
was carried out for 2 h at desired temperature in the
tion of the PdCl (bipy) complex was carried out by IR,
2
range 120–140 C (393–413K).
°
NMR and the elemental analysis and was found to
match with the reported values [23].
The kinetic experiments were carried out for a
short duration, such that the conversion of liquid
phase reactant was less than 20–25% to ensure differꢀ
ential conditions. It was generally observed that in this
low conversion range, the rates of Heck reaction were
General Procedure for Screening Experiments
In a 25 mL two necked round bottom flask constant. The experiments were found to be reproducꢀ
.2 mmol of olefin, 2 mmol of aryl halide, 2.0 mmol of ible within an error of 2–4%. In each reaction, initial,
2
base, and 0.002 mmol of PdCl (bipy)catalyst were intermediate and final samples were analyzed in order
2
KINETICS AND CATALYSIS Vol. 54
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2013

316
JAGTAP, DESHPANDE
Table 1. Effect of various bases, olefins and aryl halides on activity of PdCl (bipy) catalyst in Heck reaction in homogeꢀ
2
neous medium
Entry
Olefin
Styrene
Ar
–
X
Base
Conversion, % TON Transꢀ/cisꢀstilbenes
1
2
3
4
5
6
7
8
9
Iodobenzene
TBA + TBAI
Et N
68
66
59
56
33
27
23
20
13
89
70
58
54
45
100
92
84
75
72
48
40
552
543
482
455
268
224
190
161
98
87/13
87/13
88/12
84/16
88/12
90/10
89/11
86/14
88/12
95/5
»
»
»
»
»
»
»
»
»
»
»
»
»
»
»
»
»
»
»
»
»
3
KOAc + TBAB
TBA
NaOAc + TBAB
Piperidine
NaHCO + TBAB
3
Morpholine
MgOAc + TBAB
10
11
12
13
14
15
16
17
18
19
20
21
4ꢀBromoꢀacetophenone KOAc + TBAB
733
573
477
445
370
887
754
706
594
508
401
333
4ꢀBromoꢀ1ꢀiodobenzene
4ꢀIodoanisole
»
»
»
»
»
»
»
»
»
»
»
88/12
86/14
92/8
4ꢀBromotoluene
2ꢀBromotoluene
80/20
100/0
100/0
100/0
87/13
88/12
92/8
Methylacrylate Iodobenzene
Allyl alcohol
ꢀButylacrylate
»
»
»
»
»
»
n
4ꢀVinylanisole
4ꢀMethylstyrene
4ꢀChlorostyrene
3ꢀNitrostyrene
87/13
Note: Reaction conditions: olefin (2.2 mmol) + Ar–X (2.0 mmol) + catalyst (0.002 mmol) and base (2.0 mmol) along with TBAB (0.02 mmol)
if inorganic bases used) in NMP (10 mL).Temperature 150 C, time 1 h, selectivity to stilbene 96–100%.
(
°
to check the material balance. Following this proceꢀ for the reaction, all further studies were conducted in
dure, the effect of catalyst, styrene, iodobenzene and this solvent.
KOAc concentrations on the rate of Heck reaction was
Screening of base. A detailed study on the influence
studied at 393–413 K.
of bases on the activity of PdCl (bipy) catalyst for the
2
vinylation of iodobenzene with styrene was conducted
using NMP solvent. The bases studied included aliꢀ
phatic organic bases and monovalent or divalent inorꢀ
ganic bases. TBAB was added as a phase transfer agent
RESULT AND DISCUSSION
Screening Studies
Preliminary reactions and solvents screening studꢀ (1% of base) in case of inorganic bases. The results are
ies. Since solvents are known to play a very important shown in Table 1 (Entries 1–9). Organic bases were
role in the activity and selectivity of homogeneous catꢀ found to give better activity, since they are soluble in
alysts, the activity of PdCl (bipy) catalyst for Heck the organic solvent. Inorganic bases gave relatively
2
coupling of styrene and iodobenzene was investigated lower activity [26, 27], which increases only in the
in different solvents, in the presence of PdCl (bipy) presence of a phase transfer agent like TBAB [28]. Aliꢀ
2
catalyst with KOAc base and TBAB promoter (1% of phatic bases like triethylamine (Et N) and tributyꢀ
3
KOAc) at 150
vents screened were polar solvents having a boiling ridine and morpholine, suggesting that tertiary amines
point of above 120 as it is well known that certain Pd are more reactive than secondary amines. Between
°C and a reaction time of 1 h. The solꢀ lamine (TBA) were found to be more active than pipeꢀ
°C
complexes require minimum temperatures for reacꢀ Et N and TBA, the former is more active probably
3
tion to proceed [15, 24, 25]. The highest activity was because it is sterically less hindered compared to TBA.
observed in NMP solvent with a TON of 482. The Potassium acetate was found to have better activity
reaction was also facilitated in other polar solvents like compared to other inorganic bases. The role of TBA
N,Nꢀdimethylformamide (DMF) and N,Nꢀdimethꢀ salt is not restricted to a phase transfer catalyst [28] as
ylsulfoxide (DMSO) where TON’s of 369 and addition of a quaternary ammonium salt enhances the
2
90 respectively were obtained at a given reaction temꢀ activity even for organic bases, which are miscible with
peratures. Since NMP was found to be the best solvent the reaction solvents (Table 1, Entry 1). The Jeffrey
KINETICS AND CATALYSIS Vol. 54
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2013

INSIGHT INTO PdCl (bipy) COMPLEX AS AN EFFICIENT CATALYST
317
2
Table 2. Range of conditions studied for the kinetics of Heck reaction in NMP medium
Concentrations, kmol/m3
Reaction
T
, K (
°
C) Solvent volume, Time, min
TBAB
1% of base)
3
Catalyst
1.0–5.0)
Styrene Iodobenzene
Base
cm
(
(
×
10–4 0.11–0.44 0.10–0.40 0.10–0.40 (1.0–4.0) 10–3 393–413
×
NMP
10
120
(120–140)
effect reported earlier shows that in the presence of presence of electron withdrawing group attached to
TBAB the rates are enhanced [28]. The stereoselectivꢀ the aryl halide and an electron donating substituent on
ity of the product for all the bases—organic and inorꢀ the olefin result in higher activity.
ganic and regardless of their strength and size—was
found to be more or less the same for the iodobenzene
Kinetic Study
and styrene system. For styrene and iodobenzene sysꢀ
tem 86–90% transꢀstilbene was formed with the rest
being cisꢀstilbene, unlike that reported by Beller and
Riermeier for other Heck reactions using palladacycle
complexes [29]. In their study it was observed that the
amine changes the stereoselectivity of coupling reacꢀ
tion of aryl bromides with butyl methacrylate at 135–
The kinetics of the Heck reaction of styrene with
iodobenzene in the presence of PdCl (bipy) was invesꢀ
2
tigated. Such a study has not been reported so far and
would help elucidate the mechanism and the similariꢀ
ties with Pdꢀphosphine catalyzed system, for which
kinetics studies have been reported.
Preliminary results. Since the main objective of this
work was to investigate the kinetics, it was necessary to
first ensure the material balance and reproducibility of
1
40 C catalyzed by cyclometallated palladium comꢀ
°
plexes, via coordination to palladium during the cataꢀ
lytic cycle.
Screening of aryl halides. The activity of PdCl2 experiments. For this purpose, few experiments were
(
bipy) was assessed for the coupling of styrene with difꢀ carried out in which the amount of substrates conꢀ
ferent aryl halides. The results are presented in Table 1 sumed and the product formed were compared. A typꢀ
(
Entries 3, 10–14). Halides with strong electron withꢀ ical concentration time profile for a reaction pertains
drawing substituents showed a high activity, whereas to the Heck coupling of styrene and iodobenzene in
those with electron donating substituents were poor the presence PdCl (bipy) catalyst and KOAc as a base
2
catalysts for this reaction. This observation is in accorꢀ at 413 K. It was observed that the material balance of
dance with general trends observed for Pd complex substrates, i.e. styrene and iodobenzene, consumed
catalyzed Heck reactions [30]. For the reaction of was consistent with the amount of stilbenes formed.
4
ꢀbromoiodobenzene only the iodosubstituent underꢀ Also, in the range of conditions covered in this work,
went reaction to produce 4ꢀbromostilbene. Since only transꢀ and cisꢀstilbene was formed which was
iodoarenes are reportedly more active than the bromoꢀ confirmed by GC–MS.
derivatives, this behavior is expected. Also, no further
For the purpose of kinetic study, several experiꢀ
reaction of the 4ꢀbromostilbene was observed within ments were carried out at different styrene, iodobenꢀ
the reaction period. This was confirmed by GC–MS, zene, base and catalyst concentrations, in the temperꢀ
wherein no double Heck reaction product was ature range of 393–413 K. In each case the amount of
observed.
stilbene formed, as a function of time was observed. It
was observed that in the initial period of reaction, the
rate of reaction was almost constant. From these data
Screening of olefins. The results presented in
Table 1 (Entries 3, 15–21) show the activity of PdCl2
bipy) catalyst for the vinylation of iodobenzene with
the rates of Heck reaction (
r) were calculated as the
(
slope of plot of concentration of stilbene formed
different olefins. The olefins with strong electron
withdrawing substituents gave poor activity whereas
those with electron donating substituents were more
active. This trend is opposite to that observed for the
aryl halides. In the reported Heck reaction mechaꢀ
nism, addition of the olefin to the Pd(II) species
3
(
kmole) in m of total volume vs time (s). These were
essentially initial rates of reaction, observed under difꢀ
ferential conditions for various concentrations of aryl
halides at 393 K.
Based on observations of preliminary experiments,
the kinetics of Heck reaction was investigated under
the range of conditions given in Table 2.
occurs to form a ꢀcomplex. Electron rich olefins are
π
expected to react faster than those with electron withꢀ
drawing substituents for this step, thereby enhancing
rates. It can also be seen from Table 1 (Entries 15–17) effect of catalyst concentration on the rate of Heck
Effect of catalyst concentration on activity. The
that the stereoselectivity of the aliphatic olefins shows reaction was investigated at an iodobenzene concenꢀ
3
1
00% transꢀproduct, whereas the styrene derivatives tration of 0.20 kmol/m , styrene concentration of
3
show some cisꢀproduct formation (8–12%). The 0.22 kmol/m and KOAc concentration of
results obtained in the screening studies show that the 0.20 kmol/m (with TBAB 1% of KOAc) at temperaꢀ
3
KINETICS AND CATALYSIS Vol. 54
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318
JAGTAP, DESHPANDE
iodobenzene concentration the interaction of iodoꢀ
12
benzene with catalyst species increases, thereby
increasing the rate. This step is reported to be the rateꢀ
determining step in Heck chemistry.
1
Effect of styrene concentration on activity. The
effect of styrene concentration on activity was investiꢀ
2
3
gated at iodobenzene concentration of 0.20 kmol/m
,
KOAc concentration of 0.20 kmol/m3 (with TBAB
% of KOAc) and catalyst concentration of 2.0
1
1
×
–
4
3
0 kmol/m at temperatures of 393–413K in NMP.
3
6
The results presented in Fig. 4 show a first order
dependence on styrene concentration at all the temꢀ
peratures studied. Addition of olefin to catalyst comꢀ
plex leads to formation of
in an equilibrium reaction followed by
π
ꢀcomplex (Fig. 2, step b1
)
σ
ꢀcomplex forꢀ
mation (step b2 in Fig. 2). This being an equilibrium
reaction, at higher olefin concentration a fractional
order is observed, particularly at higher temperature.
Effect of KOAc (base) concentration on activity.
The effect of base concentration on activity was invesꢀ
3
tigated at styrene concentration of 0.22 kmol/m
,
3
0
2
Catalyst]
4
10 , kmol/m
6
iodobenzene concentration of 0.20 kmol/m and catꢀ
alyst concentration of 2.0 10 kmol/m at temperaꢀ
–4
3
4
3
[
×
×
tures of 393–413 K in NMP. The TBAB added was
proportional to base concentration (1% w/w concenꢀ
tration with respect to base). The results are presented
in Fig. 5. The rate was found to increase with increase
in base concentration in the lower range of potassium
acetate concentrations. However, on further increase,
zero order dependence was observed. This trend is
expected, since the solubility of the base in NMP is
Fig. 1. Experimental and predicted rates for effect of cataꢀ
lyst concentration at temperatures 413 ( ), 403 ( ) and
93 K ( ): points—experimental data, lines—predicted
1
2
3
3
rates. Reaction conditions: concentrations of styrene,
3
iodobenzene and KOAc—0.22, 0.20 and 0.20 kmol/m ,
respectively, TBAB—1% of base, NMP—10 mL.
tures of 393–413 K in NMP. The results are preꢀ limited and once saturation is reached, no further rate
sented in Fig. 1.
enhancement is observed. In general, the quaternary
ammonium salt added serves as a phase transfer agent
to enhance the solubility. Other studies on the kinetics
of Heck reactions also show the dependence of rate on
base concentration [21, 32].
The rate was found to have a first order dependence
on the catalyst concentration. The wellꢀknown mechꢀ
anism [31] of Heck reaction is shown in Fig. 2. With
enhancement of catalyst concentration there is a comꢀ
mensurate increase in the active species. In a large
Kinetic models. From the above study the rate was
number of Pd catalyzed Heck reactions, a first order found to have a first order dependence on catalyst
tending to a zero order is reported. The partial order concentration, a first order tending towards a zero
dependence at higher catalyst concentrations has been order dependence for base concentration and a partial
attributed to the formation of inactive dimeric species. positive order dependence for styrene and iodobenꢀ
From the observed data, it appears that the formation zene concentrations where at high iodobenzene conꢀ
of such dimeric species does not occur with PdCl2 centration and empirical rate equations at 413 K a zero
(
bipy) catalyst in the range of conditions investigated. order was observed. The data were used to develop,
This leads to the observed first order dependence.
based on the observed trends. Four different forms of
rate equations were discriminated and the results are
presented in Table 3.
Effect of iodobenzene concentration on activity.
The effect of iodobenzene concentration on activity
was investigated at a styrene concentration of
0
The rate parameters k, KA, KB and KD (A, B and D
.22 kmol/m , KOAc concentration of 0.20 kmol/m3 means olefin, Ar–X and base, respectively) were evalꢀ
3
(
with TBAB 1% of KOAc) and catalyst concentration uated at 393, 403 and 413 K by fitting the observed
–4
3
of 2.0 10 kmol/m at temperatures of 393–413 K in experimental rate data to the different models using
×
NMP. The results are presented in Fig. 3. The rate was nonlinear regression analysis and an optimization rouꢀ
found to increase with a first order with respect to tine based on Marquardt’s method [33]. The values of
iodobenzene concentration at 393 K, but at higher rate parameters at different temperatures are preꢀ
temperatures, a fractional order was observed. A posiꢀ sented in Table 3. The rate equation best fitting the
tive order with respect to iodobenzene is expected data was chosen based on the values of
from the mechanism (Fig. 2, step a). With increasing defined as in equation
Φmin, which is
KINETICS AND CATALYSIS Vol. 54
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2013

INSIGHT INTO PdCl (bipy) COMPLEX AS AN EFFICIENT CATALYST
319
2
N
N
Pd
Cl
Cl
Oxidative
addition
Regeneration
of catalyst
Ar–X
Base + HX
L
L
Base
step a
II
Pd(0)
step d
I
L
L
Pd(II)
X
L
L IV
Pd(II)
Ar
step b1
H
X
III
Y
πꢀComplex
step c
step b2
Ar
L
L
Migratory
insertion
Pd(II)
Ar
Y
βꢀHydride
elimination–
dissociation
X
Y
σꢀComplex
Fig. 2. Mechanism of Heck reaction.
n
2
,
Φ
=
∑(rexp − rpre
i=1
)
(3)
14
min
where rexp is the rate observed experimentally, pre
predicted rate using nonlinear regression analysis and
is number of data points.
Besides the thermodynamic considerations
regarding equilibrium constants KA
r
is the
1
n
Φ
min
,
KB and KD also
were relied upon to choose the rate model, best repreꢀ
senting the observed kinetic data. The analysis of all
the models shows absence of negative values for the
constants, however in case of model I and model II the
2
3
7
values of rate constants
perature and hence they were not considered. Comꢀ
parison of the values of obtained for models III
k are not consistent with temꢀ
Φ
min
and IV shows that model IV gives superior fit and
hence this model is preferred. The model chosen to
best represent the kinetics observed is as follows:
k[A][B][C][D]
r =
(4)
(
1 − K [A])(1 + K [B])(1 + K [D]
)
A
B
D
0
0.1
0.2
0.3
0.4
0.5
(
here C is catalyst).
This model was found to predict the rate data
within an error of 3% (which is within the range of
Iodobezene], kmol/m3
[
±
Fig. 3. Experimental and predicted rates for effect of iodoꢀ
benzene concentration at temperatures 413 ( ), 403
) and 393 K ( ): points—experimental data, lines—preꢀ
experimental error). A comparison of the experimenꢀ
tal rates with the predicted rates using model IV at
three different temperatures, i.e. at 393, 403 and
1
(
2
3
dicted rates. Reaction conditions: concentrations of styꢀ
3
rene and KOAc—0.22 and 0.20 kmol/m , respectively,
TBAB—1% of base, concentration of catalyst—2.0
10 kmol/m , NMP—10 mL.
4
13 K, is shown in Fig. 6, which also indicates a good
×
–4
3
agreement between the experimental and predicted
KINETICS AND CATALYSIS Vol. 54
No. 3
2013

320
JAGTAP, DESHPANDE
18
12
1
1
6
2
3
9
2
3
0
0.1
0.2
0.3
0.4
0.5
[
Base], kmol/m3
0
0.1
0.2
0.3
0.4
0.5
[
Styrene], kmol/m3
Fig. 4. Experimental and predicted rates for effect of styꢀ
rene concentration at temperatures 413 ( ), 403 ( ) and
93 K ( ): points—experimental data, lines—predicted
Fig. 5. Experimental and predicted rates for effect of base
concentration at temperatures 413 ( ), 403 ( ) and 393 K
): points—experimental data, lines—predicted rates.
1
2
1
2
3
3
(3
rates. Reaction conditions: concentrations of iodobenzene
Reaction conditions: concentrations of styreneand iodoꢀ
3
3
and KOAc—0.20 kmol/m each, TBAB—1% of base,
benzene—0.22 and 0.20 kmol/m , respectively, TBAB—
–4
3
–4
3
concentration of catalyst—2.0
0 mL.
×
10 kmol/m , NMP—
1% of base, concentration of catalyst 2.0 × 10 kmol/m ,
1
NMP—10 mL.
rates. Figures 1 and 3–5 also show the comparison of plot and found to be 98.70 kJ/mol. The constants KA
,
experimental and predicted rates for the varying conꢀ KB and KD were found to be dependent on a temperaꢀ
centration of catalyst, iodobenzene, styrene and base ture. KD was found to decrease negligibly with a temꢀ
respectively at temperatures of 393–413 K. The actiꢀ perature while KA and KB showed a strong positive
vation energy (Ea) was evaluated from the Arrhenius dependence on a temperature.
Table 3. Comparison of different rate models proposed for Heck reaction in homogeneous medium
KA
KB
KD
k
,
Φ
min
12
×
Model
I
Rate equation
T
, K
R2
3
–3 –1
m kmol s
3
10
m /kmol
3
93
9.15
165
–*
–
–*
–
89.6 2.83 0.9372
0
.7
0.6
k[A] [B] [C][D]
r = ꢀꢀꢀꢀꢀꢀꢀꢀꢀꢀꢀꢀꢀꢀꢀꢀꢀꢀꢀꢀꢀ ꢀꢀ ꢀꢀꢀꢀꢀꢀꢀꢀꢀꢀꢀꢀꢀꢀꢀꢀꢀꢀ
+ K [D]
403
912
2.51 0.9735
1
D
4
13
93
9.31
–
–
21.8 7.28 0.9698
3
937
1550
17.2
–
–
–
–
–
–
3420
3120
1.41 0.9702
9.56 0.9117
k[A][B][C][D]
r = ꢀꢀꢀꢀꢀꢀꢀꢀꢀꢀꢀꢀꢀꢀꢀꢀꢀꢀꢀꢀꢀꢀꢀꢀꢀꢀꢀꢀꢀꢀꢀꢀ
II
403
1
+ K [D]
D
4
13
13.5 41.8 0.8606
70.2 1.38 0.9709
2.62
10–4
×
3
93
20.5
–
–
–
k[A][B][C][D]
r = ꢀꢀꢀꢀꢀꢀꢀꢀꢀꢀꢀꢀꢀꢀꢀꢀꢀꢀꢀꢀꢀꢀꢀꢀꢀꢀ ꢀꢀ ꢀꢀꢀꢀꢀꢀꢀꢀꢀꢀꢀꢀꢀꢀꢀꢀꢀꢀꢀꢀ ꢀꢀ
III
403
84.2
47.8
2.34
4.51
10.5 5.03 0.9412
19.9 1.29 0.9479
(
1 + K [B])(1 + K [D])
B
D
4
13
10–3 1.80 10–3
×
3
93
20.7
42.0
88.6
70.6 1.38 0.9709
67.7 8.20 0.9226
23.9 3.68 0.9850
2.63
×
k[A][B][C][D]
1 + K [A])(1 + K [B])(1 + K [D])
A B D
r = ꢀꢀꢀꢀꢀꢀꢀꢀꢀꢀꢀꢀꢀꢀꢀꢀꢀꢀꢀꢀꢀꢀꢀꢀꢀꢀ ꢀꢀ ꢀꢀꢀꢀꢀꢀꢀꢀꢀꢀꢀꢀꢀꢀꢀꢀꢀꢀꢀꢀꢀꢀꢀ ꢀꢀ ꢀꢀꢀꢀꢀꢀꢀꢀꢀꢀꢀꢀꢀꢀꢀꢀꢀꢀꢀꢀ ꢀꢀ
10–2
IV
403
13
0.636
1.31
8.52
×
(
4
6.11
*
Symbol “–” means that KA (equilibrium constant of olefins) and/or KB (equilibrium constant of Ar–X) values are not included in the
formula.
KINETICS AND CATALYSIS Vol. 54
No. 3
2013

INSIGHT INTO PdCl (bipy) COMPLEX AS AN EFFICIENT CATALYST
321
2
3
.
Handbook of Organopalladium Chemistry for Organic
Synthesis, Negishi, E., Ed., New York: Wiley, 2002.
1
6
2
8
4
0
4
5
. Zapf, A. and Beller, M., Chem. Commun., 2005, p. 431.
. Nicolaou, K.C. and Sorensen, E.J., Classics in Total
Synthesis: Targets, Strategies, Methods, Weinheim:
WileyꢀVCH, 1996.
1
6
7
. Woltermann, C., PharmaChem, 2002, vol. 1, no. 1, p. 11.
. Beletskaya, I.P. and Cheprakov, A.V., J. Organomet.
Chem., 2004, vol. 689, p. 4055.
4
4
3
13 K
03 K
93 K
8. Cabri, W., Candiani, I., Bedeschi, A., and Santi, R.,
Synlett, 1992, vol. 11, p. 871.
9
. Kawano, T., Shinomaru, T., and Ueda, I., Org. Lett.,
2002, vol. 4, no. 15, p. 2545.
10. Peris, E., Loch, J.A., Mata, J., and Crabtree, R.H.,
Chem. Commun., 2001, p. 201.
1
1. Herrmann, W.A., Elison, M., Fischer, J., Koecher, C.,
and Artus, G.R.J., Angew. Chem. Int. Ed., 1995, vol. 34,
p. 2371.
12. Rosner, T., Le Bars, J., Pfaltz, A., and Blackmond, D.G.,
J. Am. Chem. Soc., 2001, vol. 123, no. 9, p. 1848.
0
4
rexp
8
12
10 , kmol m s–1
×
16
6
–3
13. Consorti, C.S., Flores, F.R., and Dupont, J., J. Am.
Chem. Soc., 2005, vol. 127, no. 34, p. 12054.
1
4. Tsai, F.ꢀY., Wu, C.ꢀL., Mou, C.ꢀY., Chao, M.ꢀC., Lin, H.P.,
and Liu, S.ꢀT., Tetrahedron Lett., 2004, vol. 45, p. 7503.
5. Scrivanti, A., Bertoldini, M., Matteoli, U., Beghetto, V.,
Antonaroli, S., Marini, A., and Crociani, B., J. Mol.
Catal. A: Chem., 2005, vol. 235, p. 12.
Fig. 6. Plot of
13 K.
r predicted vs. r experimental at 393, 403 and
4
1
Thus, PdCl (bipy) catalyst is found to be an active
and stable catalyst for the Heck reaction. This catalyst is
stable in polar solvents and does not decompose to metal
even at a temperature of 150°C. Detailed investigations
on the activity of PdCl (bipy) catalyst for Heck reaction
in homogeneous medium have been conducted for difꢀ
ferent solvents, olefins, aryl halides and bases. The results
show that electron withdrawing groups attached to the
aryl halide and electron donating substituents on olefin
enhance the rates. Organic bases were found to be more
2
1
1
1
1
2
6. Benhaddou, R., Czernecki, S., Ville, G., and Zegar, A.,
Organometallics, 1988, vol. 7, no. 12, p. 2435.
7. Zhao, F.ꢀG., Bhanage, B.M., Shirai, M., and Arai, M.,
Stud. Surf. Sci. Catal., 1999, vol. 122, p. 427.
8. Rosner, T., Pfaltz, A., and Blackmond, D.G., J. Am.
2
Chem. Soc., 2001, vol. 123, no. 19, p. 4621.
9. Amatore, C., Carre, E., Jutand, A., and Medjour, Y.,
Organometallics, 2002, vol. 21, no. 21, p. 4540.
0. Nilsson, P. and Wendt, O.F., J. Organomet. Chem.,
2005, vol. 690, no. 18, p. 4197.
efficient for the reaction whereas inorganic bases showed 21. Sud, A., Deshpande, R.M., and Chaudhari, R.V.,
poor activity due to solubility limitations. The kinetics of
J. Mol. Catal. A: Chem., 2007, vol. 270, p. 144.
the coupling reaction of styrene and iodobenzene in the 22. Van Strijdonck, G.F.P., Boele, M.D.K., Kamer, P.C.J.,
presence of KOAc and PdCl (bipy) catalyst has been
de Vries, J.G., and van Leeuwen, P.W.N.M., Eur. J.
Inorg. Chem., 1999, vol. 7, p. 1073.
3. McCormick, B.J., Jaynes, E.N., Jr., and Kaplan, R.I.,
Inorg. Synth., 1971, vol. 13, p. 216.
4. Miyazaki, F., Yamaguchi, K., and Shibasaki, M., Tetꢀ
rahedron Lett., 1999, vol. 40, p. 7379.
2
investigated. The rate was found to have a first order
dependence on catalyst and a partial positive order
dependence on styrene and iodobenzene concentrations.
A first order tendency towards a zero order dependence
was observed for base concentration. The trends were
found to be quite close to those observed for the Pdꢀphosꢀ
phine catalyzed reaction except for the dependence on
catalyst concentration. An empirical rate model has been
proposed to fit the observed data. The activation energy
was found to be 98.70 kJ/mol.
2
2
2
2
2
2
2
5. Albisson, D.A., Bedford, R.B., and Scully, P.N., Tetꢀ
rahedron Lett., 1998, vol. 39, p. 9793.
6. Shmidt, A.F., Khalaika, A., and Bylkova, V.G., Kinet.
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8. Jeffery, T. and Galland, J.ꢀC., Tetrahedron Lett., 1994,
vol. 35, p. 4103.
9. Beller, M. and Riermeier, T.M., Tetrahedron Lett.,
ACKNOWLEDGMENTS
S.V. Jagtap thanks University Grant Commission
of India for PhD fellowship.
1996, vol. 37, p. 6535.
30. Consorti, C.S., Zanini, M.L., Leal, S., Ebeling, G.,
and Dupont, J., Org. Lett., 2003, vol. 5, no. 7, p. 983.
3
1. Cabri, W. and Candiani, I., Acc. Chem. Res., 1995,
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KINETICS AND CATALYSIS Vol. 54
No. 3
2013